JPH0522903B2 - - Google Patents

Description

[Detailed description of the invention]

(1) Field of the Invention The present invention is useful in the field of photography. and,
A photographic element having a support and one or more hardenable hydrophilic colloid layers, including at least one emulsion layer containing radiation-sensitive silver halide grains, located on the support. Related. (2) Prior Art Black and white silver halide photography traditionally relies on developing silver to produce a visible image. While black and white photography is useful for many imaging needs, the medical radiography described below illustrates the different and sometimes competing needs directed towards silver imaging. Medical radiography often requires a relatively large area of radiation-sensitive material for a single exposure. That is, exposure in large format is common. Furthermore, the silver remaining in the photographic element for imaging will not be available for recycling in many years. Therefore, efficient use of the silver contained in radiographic elements is highly desirable.
One measure of silver usage efficiency is covering power. In this specification, covering power is the ratio of the maximum photographic density to the amount of developed silver expressed in grams of silver per 100 square centimeters (grams of silver per square decimeter).
Define it as 100 times. High covering power has been recognized as an advantageous property not only for radiographic elements but also for other black and white photographic elements. Covering power and the conditions that affect it are described in James' Theory of Photographic Processing.
4th edition, Macmillan Publishing, 1977, pp. 404, 489, 490, and
Farnell and Solman, “The Covering Power of Deposited Silver in Photography I.
Power of Photographic Silver Deposits I.
"Chemical Development)", The Journal of Photographic Science, Vol.18,
Discussed in 1970, pp. 94-101. One approach to achieving high covering power is to use relatively fine silver halide grains. This is because it is recognized that increasing particle size reduces covering power. Unfortunately, in medical radiography, the need to minimize x-ray exposure to the patient is more important than the efficient use of silver. Since silver halides become more sensitive (increased speed) as a linear function of grain size, it is not surprising that radiographic elements commonly utilize large grain sizes. Thus, although it is important to achieve high covering power, the relatively coarse silver halide emulsions that are actually used are not suitable for achieving high levels of covering power. Other techniques are therefore used to improve covering power. Large silver halide grains (typically at least 0.6 micrometers or more in average diameter) experience a reduction in covering power as a function of hardness. In order to achieve the highest covering power compatible with velocity requirements (and therefore particle size requirements), the predurality (i.e., the duramentation at the manufacturing stage) is limited to allow handling of the radiographic element. It is common in the industry to closely meet the limits required for such materials (although the risk of damage to such materials remains relatively high). Hardening to the final desired level is achieved by incorporating a hardening agent into the photographic processing composition, usually a developer. Particularly effective hardening agents for use in photographic processing compositions are dialdehydes and their bisbisulfite derivatives of the type disclosed in US Pat. No. 3,232,764. Unfortunately, hardeners must be separated from the developer composition before use. Furthermore, the presence of such hardeners places additional constraints on the selection of developer compositions. In typical medical radiographic applications, radiographic films are coated on both major sides with a relatively coarse silver halide emulsion. The emulsion layers are minimally prehardened to achieve maximum covering power. This element is more sensitive to visible light than to X-rays, and therefore imagewise exposure to X-rays fluoresces imagewise to expose the radiographic element between the pairs of phosphor plates. is typically located. The radiographic element is then photographically processed in a developer containing a hardening agent. To provide rapid access to visible images, radiographic elements are photoprocessed at temperatures above ambient (typically about 25-30°C) for less than one minute. Developing usually takes about 20 seconds. A typical photographic process of the type described above is described in US Pat. No. 3,545,971. A variety of regular and irregular grain shapes have been observed in silver halide photographic emulsions for black and white imaging applications in general and radiographic imaging applications in particular. Regular particles are often cubic or octahedral. The edges of the particles are rounded by the ripening effect, and in the presence of strong ripening agents, e.g. ammonia, the particles can even become spherical, or almost spherical slab-like, as e.g. No. 3894871 and
Zelikman and Levi, Making and Coating Photographic Emulsions
Focal Press, 1964, 223
It is written on the page. Rod-shaped and tabular grains are often observed mixed with grains of other shapes in various proportions, and the pAg (negative logarithm of the silver ion concentration) of the emulsion increases during precipitation, for example in a single jet precipitation method. This was especially true when it changed to . Tabular silver bromide grains have often been studied at large sizes that have no photographic utility. Tabular grains as defined herein are 2
A particle having two parallel or substantially parallel crystal faces, each crystal face being substantially larger than substantially any other single crystal face of the particle. The aspect ratio, ie the diameter to thickness ratio of the tabular grains, is substantially greater than 1:1. High aspect ratio tabular grain silver bromide emulsions were developed by de Cugnac and
Chateau, “Evolution of the Morphology of Silver Bromide Crystals During Physical Ripening”
Bromide Crystals During Physical
Ripening)”, Science A.
), pp. 121-125. From 1937 to 1950, Eastman Kodak Co., Ltd. manufactured Duplitized® and fully prehardened radiographic film products with No-Screen.
It was sold under the name X-Ray Code 5133. This product contained a sulfur sensitized silver bromide emulsion as a coating on both major sides of a film support. This emulsion was not spectrally sensitized as it was intended to be exposed by X-rays. The tabular grains had average aspect ratios ranging from about 5 to 7:1. The tabular grains were larger than 50% of the projected area, and the non-tabular grains were larger than 25% of the projected area. When these emulsions were replicated several times, the emulsions with the thinnest average grain thickness had an average tabular grain diameter of 2.5 μm;
The average tabular grain thickness was 0.36 μm, and the average aspect ratio was 7:1. In other replicates, the emulsion had thicker tabular grains, smaller diameters, and lower average aspect ratios. Tabular grain silver bromoiodide emulsions are known in the art, but they do not have high average aspect ratios. Tabular silver bromoiodide grains are described by Duffin, Photographic Emulsion Chemistry, Focal Press, 1966, pp. 66-72, and Trivelli.
and Smith, “The Effect of Silver Iodide Chains”
of Silver Iodide Series)”, The Photographic Journal Vol. LXXX, July 1940.
It is described on pages 285-288. Trivelli and
Smith observed that upon the introduction of iodide, both particle size and aspect ratio decreased significantly. Cutoff, “Nucleation and crystal growth rate during precipitation of silver halide emulsions.
Growth Rates During the Precipitation of
"Silver Halide Photographic Emulsions", Photographic Science and Engineering Vol. 14, No. 4, July and August 1970,
A continuous precipitation apparatus was used to prepare silver bromoiodide and silver bromide emulsions of the type prepared by the single jet precipitation method, reported on pages 248-257. A method has recently been published that is used to prepare emulsions in which the majority of the silver halide is present in the form of tabular grains. According to the teachings of U.S. Pat. No. 4,063,951:
Forms crystals with {100} cubic crystal faces and aspect ratios of 1.5 to 7:1 based on edge length.
Tabular grains have {100} square and rectangular major faces. In the reported example, the particles had an average edge length of 0.93 micrometers and an average aspect ratio of 2:1. Thus, the average grain thickness was 0.46 micrometers, indicating that thick tabular grains were formed. According to the teachings of U.S. Pat. No. 4,067,739:
A silver halide emulsion in which most of the crystals are octahedral twins forms seed crystals, increases the size of the seed crystals by Ostwald ripening in the presence of silver halide solvent, and increases the pBr (bromine ion concentration). is prepared by terminating grain growth without renucleation and Ostwald ripening while adjusting the negative logarithm. US Patent Nos. 4150994, 4184877 and 4184878 and British Patent No. 1570581 and German Published Patent No. 2905655 and
According to the teachings of No. 2,921,077, seed crystals containing at least 90 mole percent iodide were used to form silver halide grains with a flat octahedral twin structure.
Unless otherwise specified, all references to halide percentages are based on the silver present in the corresponding emulsion, grain or grain area in question. Some of the above cited references report increased covering power in emulsions and describe their usefulness in black-and-white and color photographic films. From viewing published micrographs and repeating the examples, it is clear that the average tabular grain thickness was greater than 0.4 micrometers. JP-A-142329, published on November 6, 1980, is substantially in the family of US Pat. No. 4,150,944, but does not limit the use of silver iodide as a seed particle. Thus, the patents mentioned in this paragraph are believed to teach the preparation of silver halide grain emulsions containing relatively thick tabular grains of intermediate average aspect ratio. (3) Disclosure of the Invention The object of the present invention is to provide a support and one or two emulsion layers located on the support, comprising at least one emulsion layer containing radiation-sensitive silver halide grains.
a photographic element having more than one hardenable hydrophilic colloid layer, which is sufficiently hardened to require no further hardening during photographic processing, yet achieves a high level of covering power. Our goal is to provide the following. This object, according to the invention, comprises a support and at least one particle containing radiation-sensitive silver halide grains located on the support.
a photographic element having one or more hardenable hydrophilic colloid layers, including an emulsion layer, wherein the total projected area of the silver halide grains in at least one emulsion layer is at least 50 percent has an average aspect ratio of at least 5:1 and
is populated by thin tabular grains having a thickness of less than 0.2 micrometers, and the hydrophilic colloid layer has a swelling of the hydrophilic colloid layer of 200 percent, where the percent swelling is (a) the photographic element.
Incubate for 3 days at 38°C and 50% relative humidity, (b) measure the layer thickness, (c) immerse the photographic element in distilled water at 21°C for 3 minutes, and (d)
(measured by measuring the percentage change in layer thickness compared to the layer thickness measured in step (b))
This is achieved by a photographic element characterized in that it is hardened in an amount sufficient to reduce Photographic elements according to the invention, in one preferred form, are radiographic elements. In the radiographic elements of the present invention, the support is a substantially specular support and the hydrophilic colloid layer comprises at least one emulsion layer on each side of the support. , comprising radiation-sensitive particles containing up to 6 mole percent iodide, wherein at least 50% of the total projected area of the radiation-sensitive particles has an average aspect ratio of at least 5:1 and 0.2 micrometers. It is characterized by being dominated by thin tabular grains having a smaller thickness. The invention relates to a black and white photographic element intended for use in forming retained visible silver images having at least one relatively coarse grained silver halide emulsion layer containing a hardenable hydrophilic colloid or the like. Can be applied generally. To realize the advantages of the present invention, high aspect ratio tabular grain silver halide emulsions are used to form at least one relatively coarse grain emulsion layer. The term "thin", as it applies to silver halide emulsions, is defined as requiring that the tabular silver halide grains have a thickness of less than 0.2 micrometers. The covering power gain of the present invention is inversely proportional to the average thickness of the tabular grains of the thin tabular grain silver halide emulsion used. Typically the tabular grains have an average thickness of at least 0.03 micrometer, preferably at least 0.05 micrometer. However, even thinner tabular grains can in principle be used. For example, a thickness of 0.01 micrometers depending on the halide content. Although thin tabular grain emulsions can achieve covering power gain at low aspect ratios, to realize covering power gain as well as other advantages of tabular grain silver halide, thin tabular grain emulsions used in the practice of this invention must be Preferably, the tabular silver halide emulsions have an average aspect ratio of at least 5:1. The thin tabular grain silver halide emulsions are preferably high aspect ratio tabular grain emulsions. High aspect ratio tabular grain emulsions are those in which the thin tabular grains have an average aspect ratio greater than 8:1 and account for at least 50 percent of the total projected area of the silver halide grains. In a preferred embodiment of the invention, these thin tabular silver halide grains account for at least 70 percent and optimally at least 90 percent of the total projected area of the silver halide grains.
account for a percentage. The increase in covering power increases when tabular silver halide grains with a thickness of less than 0.2 micrometer have an average diameter of at least 0.6 micrometer,
This is particularly evident when the average diameter is optimally at least 1 micrometer. The above grain characteristics of the silver halide emulsion used in the present invention can be confirmed by methods well known to those skilled in the art. As used herein, "aspect ratio" refers to the ratio of a particle's diameter to its thickness. The "diameter" of a grain is defined as the diameter of a circle having an area equal to the projected area of the grain as viewed in a micrograph or electron micrograph of an emulsion sample. The thickness and diameter of each grain from a shaded electron micrograph of an emulsion sample can be determined to identify tabular or thin tabular grains with a thickness of less than 0.2 μm. From this, the aspect ratio of each tabular grain can be calculated and the aspect ratios of all tabular grains in the sample (meeting the criterion of thickness less than 0.3 μm) can be averaged to obtain an average aspect ratio. By this definition, the average aspect ratio is the average of the aspect ratios of the individual tabular grains. In practice, it is usually easier to obtain the average diameter and average thickness of the tabular grains and calculate the average aspect ratio as the ratio of these two averages. Depending on whether an averaged individual aspect ratio is used or an average of thickness and diameter is used to determine the average aspect ratio, the average aspect ratio obtained can be significantly are not different. The projected areas of the thin tabular silver halide grains can be summed, and the projected areas of the remaining silver halide grains in the micrograph can also be summed separately, and from the sum of these two, the projected areas of the thin tabular silver halide grains can be summed. The percentage of the total projected area of silver particles can be calculated. Reference tabular grains with a thickness of less than 0.2 μm were selected for the measurements. This is to distinguish the uniquely thin tabular grains of interest here from the thicker tabular grains, which have inferior photographic properties. When diameters are small, it is not always possible to distinguish between tabular and non-tabular grains in micrographs. Thin tabular grains for the purposes of this disclosure are silver halide grains that are less than 0.2 micrometers thick and appear tabular under 10,000x magnification. The term "projected area" is the term "projected area" commonly used in this industry.
and "projected area". For example, James and Higgins, Fundamentals of Photographic Theory,
Morgan & Morgan, New York, 15
See page. Although only one high aspect ratio tabular grain emulsion layer is required in the photographic elements of this invention, the photographic elements can have multiple such tabular emulsion layers if desired. Emulsions other than the required high aspect ratio tabular grain emulsions may take any convenient conventional form. Various conventional emulsions are described in Research Disclosure, Vol. 176,
Described in December 1978, Manuscript No. 17643, Section 1, "Emulsion Preparation and Types." Research Disclosure and Product Licensing Index by Industrial Opportunities, HomeL, Hallant, Hampshire, P09
1EF, a British publication. The silver halide emulsion layer and other layers, if present, of the photographic element, such as overcoats, interlayers, and subbing layers, can contain various hardenable colloids alone or in combination with a vehicle. The term vehicle as used herein includes both binders and peptizers. Photographic elements of this invention are precured. That is, the colloid is sufficiently crosslinked that no further hardening is required after manufacturing the photographic element. The hydrophilic colloid-containing layer is sufficiently prehardened to reduce its swelling to less than 200 percent. Although many similar swelling tests have been carried out, in order to provide specific definitions, the percentage swelling herein is referred to as Example 11 of GB 3841872.
However, it is defined as the percentage measured at an insulating temperature of 38℃ and an immersion temperature of 21℃. Specifically, the percent swelling was determined by (a) holding the photographic element at 38°C and 50°% RH for 3 days (incubation treatment), (b) measuring the layer thickness, and (c) photographing the element. Determined by immersing the element in distilled water at 21° C. for 3 minutes and (d) measuring the change in layer thickness compared to the layer measured in step (b). The percent swelling is the product of the difference between the final layer thickness and the original (after incubation) layer thickness divided by the original layer thickness times 100. Preferably, photographic elements of the invention exhibit less than 100 percent swelling. As is well known in the art, the percent swelling can be controlled by adjusting the concentration of hardener used. Precuring of photographic elements according to the present invention, instead of lacking a high aspect ratio tabular grain silver halide emulsion as described above, provides at least
It does not produce the reduction in covering power observed in commercially available prehardened photographic elements containing silver halide grains with an average diameter of 0.6 micrometers. Additionally, the prehardened photographic elements of this invention have higher covering power than comparable prehardened photographic elements containing nontabular silver halide grains of the same average diameter based on projected area. Additionally, photographic elements according to the present invention are otherwise comparable using tabular silver halide grains of greater average tabular grain thickness, either of the same average diameter or of a higher average aspect ratio. It also exhibits higher covering power than other photographic elements. Although high covering power has traditionally been achieved using smaller average silver halide grains, such grain size limits photographic sensitivity. The present invention provides for the first time a highly sensitive predural photographic element that does not suffer from a substantial reduction in covering power. The photographic elements of this invention can contain other conventional emulsion layers in addition to the required high aspect ratio tabular grain silver halide emulsions, so that the total covering power of the photographic element (as opposed to the individual emulsion layers) as)
Can vary widely. However, preferred photographic elements according to the present invention, particularly those in which all emulsion layers present contain thin tabular grains having a thickness of less than 0.2 micrometers, can be used at temperatures above ambient temperature (e.g. It exhibits a covering power of at least 80, preferably at least 100, and optimally at least 110 when developed at temperatures between 25 and 50°C. As used herein, covering power is expressed as the maximum photographic density divided by the amount of developed silver (in grams/100 square centimeters) times 100. The thin tabular grain silver halide emulsion layers and other layers of the photographic element may contain a variety of hardenable colloids, either alone or in combination as a vehicle. Suitable hydrophilic colloids include, for example, proteins, protein derivatives, cellulose derivatives (e.g. cellulose esters), gelatin (e.g. alkali-treated gelatin (cow bone or cowhide gelatin) or acid-treated gelatin (pig skin gelatin)); These include gelatin derivatives (eg, acetylated gelatin, phthalated gelatin, etc.), polysaccharides (eg, dextran), gum arabic, zein, casein, pectin, collagen derivatives, agar, arrowroot starch, albumin, and others. The emulsion layers and other layers of photographic elements, such as overcoats, interlayers, and subbing layers, may similarly be used alone or in combination with hydrophilic water-permeable colloids.
Vehicles or vehicle fillers (e.g. in the form of latexes), synthetic polymeric peptizers, carriers and/or binders such as poly(vinyl lactams), acrylamide polymers, polyvinyl alcohol and its derivatives, polyvinyl acetate. , polymers of alkyl and sulfoalkyl acrylates and methacrylates, hydrolyzed polyvinyl acetate, polyamides, polyvinylpyridine, acrylic acid polymers, maleic anhydride copolymers, polyalkylene oxides, methacrylamide copolymers, polyvinyloxazolidinones, Maleic acid copolymer, vinylamine copolymer, methacrylic acid copolymer, acryloyloxyacrylic sulfonic acid copolymer, sulfoalkylacrylamide copolymer, polyalkyleneimine copolymer, polyamine, N,N-dialkylaminoalkyl May include alkylates, vinyl imidazole copolymers, vinyl sulfide copolymers, halogenated styrene polymers, amine acrylamide polymers, and polypeptides. A layer of a photographic element containing a crosslinkable colloid (e.g., a layer containing gelatin or a gelatin derivative)
THJames “The Theory of Photo Processing”
The photographic process may be prehardened with a variety of organic and inorganic hardeners, such as those described in The Photographic Process, 4th Edition, Macmillan, 1977, pages 77-78. Prehardeners can be used alone or in admixture and in free or block form. Typical useful hardeners include formaldehyde and free dialdehydes such as succinic aldehyde and glutaraldehyde, blocked dialdehyde, alpha-diketones, active esters, sulfonate esters, active halogen compounds, s-triazines and diazines, epoxide, aziridine, two or more active vinyl groups (e.g.
an active olefin having a vinylsulfonyl group),
Block active olefin, carbodiimide, 3
- a positionally unsubstituted isoxazolium salt;
Esters of 2-alkoxy-N-carboxydi-hydroquinolines, N-carbamonyl and N-carbamoyloxypyridinium salts, multifunctional hardeners such as halogen-substituted aldehydic acids (e.g.
mucochrome and mucobromic acid), onium-substituted acrolein, and vinyl sulfones containing other hardening groups, and polymeric hardeners such as dialdehyde starch and copoly(acrolein-methacrylic acid). The use of prehardeners in mixtures is known in the art. A dura accelerator may be used. The tabular grains may be any silver halide crystal composition known to be useful for photography.
In a preferred embodiment, the present invention has observed extensive benefits using thin tabular grain silver bromoiodide emulsions. Thin tabular grain silver bromoiodide emulsions can be prepared by the following precipitation method (medium to high aspect ratio grains can be prepared simply by terminating the precipitation early). Obtaining thin grains at the beginning of precipitation as described below will result in a tabular grain emulsion with thin tabular grains): A conventional method for silver halide precipitation with an effective stirring mechanism. A dispersion medium is introduced into the reaction vessel. Typically, the dispersion medium initially introduced into the reaction vessel will be at least about 10%, preferably from 20 to 80%, based on the total weight of dispersion medium present in the silver bromoiodide emulsion at the end of grain precipitation. . The dispersion medium can be removed from the reaction vessel by ultrafiltration during silver bromide iodide particle precipitation, as described in Belgian Patent No. 886,645 and French Patent No. 2,471,620. Therefore, the volume of dispersion medium initially present in the reaction vessel is
It is recognized that the volume of silver bromoiodide emulsion present in the reaction vessel at the end of grain precipitation can be equal to or greater than this. The dispersion medium initially introduced into the reaction vessel is preferably water or a peptizer dispersed in water, optionally containing as other components one or more silver halide ripeners and/or metal dopants (for which will be detailed later). When the peptizer is initially present, it is preferably used at a concentration of 10% or higher, most preferably 20% or higher. This is a percentage based on the total peptizer present after complete precipitation of silver bromoiodide. Additional dispersion medium is added to the reaction vessel containing the silver and halide salts, which can also be introduced by separate jets. It is common practice to adjust the proportion of dispersion medium after the introduction of the salt, in particular to increase the proportion of peptizer. When forming silver bromoiodide grains, a small proportion of bromide salt, typically less than 10% by weight, is first present in the reaction vessel to adjust the bromide ion concentration of the dispersion medium at the beginning of silver bromoiodide precipitation. do. Also, the dispersion medium in the reaction vessel is initially substantially free of iodide ions. This is because the presence of iodide ions favors the formation of thick, non-tabular grains prior to the simultaneous introduction of silver and bromide salts. As used herein, "substantially free of iodide ions" in the reaction vessel means that there is not enough iodide ions present to precipitate as a separate silver iodide phase relative to bromide ions. be. Preferably, the concentration of iodide ions in the reaction vessel prior to the introduction of the silver salt is less than 0.5 mole percent of the total halide ions present. If the pBr of the dispersion medium is initially too large, the resulting tabular silver bromoiodide grains will be relatively thick, thereby reducing the aspect ratio. It is also possible to initially bring the pBr of the reaction vessel to 1.6 or lower (if a tabular grain average thickness of less than 0.2 micrometers is desired, the pBr value should be kept below 1.5). On the other hand, when pBr is too low, non-tabular silver bromoiodide grains are easily formed. Therefore, the pBr of the reaction vessel should be 0.6 or higher, preferably higher than 1.1.
The pBr used here is defined as the negative logarithm of the bromide ion concentration. PH and pAg are defined in the same way as bromine with respect to hydrogen ion concentration and silver ion concentration, respectively. During precipitation, silver, bromide, and iodide salts are added to the reaction vessel by methods well known for precipitation of silver bromoiodide particles. Typically, an aqueous solution of a soluble silver salt, such as silver nitrate, is introduced into the reaction vessel at the same time as the bromide and iodide salts are introduced. Bromide and iodide salts are also typically introduced as aqueous solutions, e.g. soluble ammonium,
one of the halide salts of alkali metals (e.g. sodium or potassium) or alkaline earth metals (e.g. magnesium or calcium);
One or more of them are introduced as an aqueous solution. The silver salt is at least initially introduced into the reaction vessel separately from the iodide salt. The iodide and bromide salts are added to the reaction vessel separately or as a mixture. The nucleation stage of particle formation begins when the silver salt is introduced into the reaction vessel. As the introduction of silver, bromide and iodide salts continues, a population of grain nuclei is formed which can act as a precipitation site for silver bromide and silver iodide. The precipitation of silver bromide and silver iodide on the grain nuclei present constitutes the growth stage of grain formation. The aspect ratio of tabular grains formed according to the present invention is less affected by iodide and bromide concentrations during the grain growth stage than during the nucleation stage. Therefore, during the simultaneous introduction of silver, bromide and iodide salts during the growth stage, the tolerance range of pBr was reduced to 0.6.
can be increased by more than , preferably about
It ranges from 0.6 to 2.2, most preferably about 0.8 to 1.5. Of course, it is possible and preferred to maintain the pBr in the reaction vessel during the introduction of the silver and halide salts at the initial limit value as mentioned before the introduction of the silver salts. This is particularly preferred when substantial grain nucleation rates are maintained throughout the introduction of silver, bromide and iodide salts, particularly in the preparation of polydisperse emulsions. Increasing the value of pBr above 2.2 during tabular grain growth increases grain thickness, which is often acceptable and results in thin tabular silver bromoiodide grains. Instead of introducing the silver, bromide, and iodide salts as aqueous solutions, the silver, bromide, and iodide salts are introduced in the form of fine silver halide grains suspended in a dispersion medium, either initially or during the growth stage. I can do it. The size of the particles is such that Ostwald ripening can be easily performed on large particle nuclei once introduced into the reaction vessel, if present. The most useful particle size depends on the particular conditions within the reaction vessel, such as temperature and the presence of solubilizers and ripening agents. Particles of silver bromide, silver iodide and/or silver bromoiodide can be introduced. (Grains of silver chlorobromide and silver chlorobromoiodide may also be used since bromide and/or iodide precipitate more easily than chloride.) Silver halide grains are preferably very fine. .
For example, an average diameter of less than 0.1 μm is preferred. Subject to the above pBr requirements, the rate and concentration of silver, bromide, and iodide salts may be in any convenient conventional manner. Silver and halide salts are preferably introduced in concentrations of 0.1 to 5 mol/mole. For example,
A wide range of customary concentrations can be envisaged, from 0.01 mol/ to saturation. A particularly preferred precipitation method shortens the precipitation time by increasing the rate at which silver and halide salts are introduced into the reaction. The rate of introduction of the silver and halide salts can be increased by increasing the rate of introduction of the dispersion medium and the silver halide salt, or by increasing the concentration of the silver halide salt in the dispersion medium to be introduced. can be increased. Particularly preferably, the rate of introduction of the silver halide salt is increased, but the rate of introduction is kept below the threshold at which new grains are nucleated, ie, preventing re-nucleation. This is US Pat. No. 3,650,757,
3672900 and 4242445 and German Published Patent No. 2107118 and European Patent Application No. 80102242 and Wey.
Growth mechanism of AgBr crystals
Mechanism of AgBr Crystals in Gelatin
Solution)”, Photographic Science
and Engineering, Vol.21, No.1, 1977
January/February 2016, page 14 onwards. By avoiding the formation of additional grain nuclei after entering the precipitation growth stage, a relatively monodisperse population of thin tabular silver bromoiodide grains can be obtained. Emulsions can be prepared with coefficients of variation of less than about 30%. (The coefficient of variation here means 100 times the standard deviation of particle diameters divided by the average particle diameter.) Of course, polydisperse emulsions with substantially high coefficients of variation can be prepared. The iodide concentration in the silver, bromoiodide emulsion used in the present invention can be controlled by introducing an iodide salt. Any conventional iodide concentration may be used. It has been recognized in the art that even very small amounts of iodide, such as as low as 0.05 mole percent, are advantageous. Unless otherwise specified, halide percentages are based on the silver present in the corresponding emulsion, grain, or grain region in question; for example, a grain consisting of silver bromoiodide with 40 mole percent iodide has 60 moles. Contains % bromide. In preferred embodiments, the emulsions used in this invention contain at least about 0.1 mole percent iodide. Silver iodide can be included in tabular silver bromoiodide grains up to the limit of its solubility in silver bromide at the grain formation temperature. In this way, the silver iodide concentration in the tabular silver bromoiodide grains can be controlled to about 40 mol % by setting the precipitation temperature to 90°C. In practice, the precipitation temperature can be lowered to near room temperature, for example to about 30°C. It is generally preferred to carry out the precipitation at a temperature of 40 to 80°C. For many photographic applications it is preferable to limit the maximum iodide concentration to about 20 mole percent.
And the optimal iodide concentration is up to about 15 mol%. Preferably, the iodide concentration in the radiocratic element is up to 6 mole percent. The relative proportions of iodide and bromide salts introduced into the reaction vessel during precipitation are maintained at a constant ratio to form a substantially uniform iodide profile within the tabular silver bromoiodide grains. or can be changed to achieve different photographic effects. Benefits in photographic speed and/or granularity shift laterally in high aspect ratio tabular grain silver bromoiodide emulsions, preferably by increasing the iodide proportion in the annular region relative to the central region of the tabular grain. Wake up. The iodide concentration in the central region of the more tabular grains ranges from 0 to 5 mole percent, and the iodide concentration in the laterally surrounding annular region is higher by at least 1 mole percent, with the iodide concentration in the silver bromide being at least 1 mole percent higher. The silver solubility can be up to preferably about 20 mole %, but suitably up to about 15 mole %. The tabular silver bromoiodide grains used in this invention have a substantially uniform or graded iodide concentration profile, the gradient of this concentration can be controlled as desired; The iodide concentration can be increased on or near the interior or surface of the silver bromoiodide grains. Although the preparation of tabular grain silver bromoiodide emulsions with high aspect ratios has been described above with respect to the preparation of neutral or non-ammoniac emulsions, the emulsions used in the present invention can be prepared by other methods. It can also be prepared with heat. In other methods, silver halide grains with high iodide concentrations are present in the reaction vessel. The silver iodide concentration in the reaction vessel is 0.05
It is preferred to reduce the maximum size silver iodide grains initially present in the reaction vessel to less than 0.05 μm. Again, thick, medium aspect ratio tabular grain bromoiodide emulsions can be prepared by simply terminating the precipitation early. Thick, medium aspect ratio, tabular grain silver bromide emulsions free of iodide can be prepared by the method detailed above, with no iodide present. Thick tabular silver bromide emulsions containing square or rectangular grains may be prepared in the following manner: Using cubic seed grains with edge lengths less than 0.15 micrometers. Maintaining the pAg of the seed grain emulsion in the range of 5.0 to 8.0 and ripening the emulsion in the substantial absence of non-halide silver ion complexing agents to produce tabular silver bromide grains with the desired aspect ratio. do. Further, other methods for producing tabular grain silver bromide emulsions with high aspect ratios that do not contain iodide will be explained in the Examples.
To illustrate other thick tabular grain silver halide emulsions that can be prepared by simply terminating the precipitation when the desired aspect ratio is achieved, the following is noted: Tabular grains of at least 50 mole percent chloride may be prepared having certain opposing crystal planes and at least one periphery parallel to the <211> crystallographic vector of one of the major surfaces.
Such tabular grain emulsions are prepared by reacting aqueous solutions of silver and chloride-containing halide salts in the presence of crystallinity-altering amounts of aminoazaindene and peptizers having thioether linkages. be able to. Tabular grain emulsions can be formed such that the silver halide grains contain silver chloride and silver bromide at least in the annular grain region and preferably in the entire region. The tabular grain regions containing silver chloride and silver bromide are prepared during the introduction of the silver, chloride, bromide, and optionally iodide salts into the reaction vessel at a molar ratio of chloride ions to bromide ions of 1.6:1 to 1.6:1. Keep it at about 260:1,
The total concentration of halide ions in the reaction vessel is 0.10.
It can be formed by keeping it at ~0.90 regulation. The molar ratio of silver chloride to silver bromide within the tabular grains can range from 1:99 to 2:3. A modifying compound can be present in the tabular grain precipitate. Such compounds can be initially present in the reaction vessel or can be added along with one or more salts by conventional methods. Metamorphizing compounds are, for example, copper, thallium, lead, bismuth, cadmium, zinc, intermediate chalcogens (i.e. sulfur, selenium, and tellurium), gold and group noble metals, which are present in the silver halide precipitate. I can do it. This is US Patent No. 1195432
No. 1951933, No. 2448060, No. 2448060, No.
No. 2628167, No. 2950972, No. 3488709, No. 3737313, No. 3772031, No. 4269927, and Research Disclosure, Vol. 134,
Described in draft No. 13452, June 1975. Research Disclosure and its predecessor publication, Product Licensing Index, are published by Industrial Opportunities, Inc.; Homeell, Havant; Pumpshire, PO9 1
EF, a British publication. Tabular grain emulsions can be internally reduction sensitized during precipitation. This is described in Moisar et al., Journal of Photographic Science, Vol. 25, 1977, paragraphs 19-27. Individual silver and halide salts are fed by gravity through the surface or through feed tubes below the surface.
Alternatively, the feed rate and the PH, pBr and/or pAg of the contents of the reaction vessel are controlled by a feeding device and added to the reaction vessel. This is US Patent No.
No. 3821002 and No. 3031304 and Claes et al., Fotographies Correspondents, Volume 102,
No. 10, 1967, page 162. In order to quickly distribute the reactants within the reaction vessel, a specially configured stirring device can be used. This is US Patent No. 2996287, US Patent No. 3342605, US Patent No.
3415650, 3785777, 4147551, 4171224, British Patent Application No. 2022431A, German Published Patent Application No. 2555364, German Publication No. 2556885, and Research Disclosure, Vol. 166, 1978. Written in February, draft No. 16662. In preparing tabular grain emulsions, the concentration of peptizer is from 0.2 to about 10% by weight, as a percentage of the total weight of the emulsion components in the reaction vessel. Preferably, the concentration of peptizer in the reaction vessel is less than about 6% by weight, based on total weight, before and during silver bromoiodide formation. The usual practice is to keep the concentration of peptizer in the reactor below about 6% by total weight before and during silver halide formation, and the concentration of the emulsion vehicle to obtain optimum coating properties. Concentrations are prepared by additional delayed additions of vehicle. The initially formed emulsion contains about 5 to 50 g of peptizer per mole of silver halide, preferably about 5 to 50 g of peptizer per mole of silver halide.
10 to 30 g can be added per mole of silver halide. The vehicle to be added has a concentration of silver chloride of 1
It can be added up to 1000g per mole. Preferably, the concentration of vehicle in the finished emulsion is greater than 50 grams per mole of silver halide. The vehicle is preferably about 30 to 70% by weight of the emulsion layer when coated and dried to form a photographic element. The grains are ripened during the preparation of the silver halide emulsion used in the present invention, and preferably the grains are ripened in a reaction vessel at least during the formation of silver bromoiodide grains. Ripening can be accelerated using known silver halide solvents. For example, the presence of excess bromide ions in the reaction vessel is known to accelerate ripening. It is therefore clear that the bromide salt solution introduced into the reaction vessel can itself promote ripening. Other ripening agents can be used, either wholly contained in the dispersion medium in the reaction vessel before adding the silver and halide salts, or one of the halide salts, silver salts or peptizers. Alternatively, two or more of them can be introduced into the reaction vessel together. Alternatively, the ripening agent can be introduced independently during the addition of the halide and silver salt. Although ammonia is a known ripening agent, it is not the preferred ripening agent for the silver bromoiodide emulsions with the highest speed-granularity relationships used in this invention. Preferred emulsions for use in this invention are non-ammoniac or neutral emulsions. Some preferred ripening agents include sulfur. Thiocyanates can be used as alkali metal salts and the like, most commonly sodium and potassium thiocyanates, and ammonium thiocyanate. Although conventional amounts of thiocyanate can be introduced, the preferred concentration is generally about 0.1 to 20 grams of thiocyanate per mole of silver halide (based on the weight of silver). Prior art teachings of using thiocyanate ripening agents are found in US Pat. No. 2,222,264, US Pat. No. 2,448,534 and US Pat. In addition, common thioether ripening agents are disclosed in U.S. Patent No. 3,271,157;
No. 3574628 and No. 3737313. It is desirable to wash thick tabular grain emulsions to remove soluble salts. Soluble salts may be removed by well known methods such as decanting, filtration, and/or cooling and leaching. This is Research Disclosure, Vol.176,
Described in December 1978, Draft No. 17643, Section. Emulsions with or without sensitizers are published in Research Disclosure, Vol. 101, September 1972;
It may be stored dry before use as described in Draft No. 10152. In the present invention, washing is particularly advantageous in that after completion of precipitation, the ripening of the tabular grains is completed and an increase in their thickness is prevented.
This can prevent an increase in the thickness of tabular grains and a decrease in aspect ratio. High aspect ratio tabular grain emulsions useful in this invention can have very high average aspect ratios. The average aspect ratio of tabular grains can be increased by increasing the average grain diameter. Although this produces sharpness benefits, the maximum average particle diameter is generally limited by the granularity requirements for the particular photographic application. Similarly or alternatively, the average aspect ratio of tabular grains can be increased by decreasing the average grain thickness. When silver coverage is held constant, decreasing tabular grain thickness improves granularity as a linear function of decreasing aspect ratio. The maximum average aspect ratio in the tabular grain emulsions useful in this invention is therefore a function of the maximum average grain diameter acceptable for a particular photographic application and the minimum possible tabular grain thickness that can be produced. The maximum average aspect ratio was observed to vary depending on the precipitation technique used and the composition of the tabular halide grains. Highest average aspect ratio observed in tabular grains with a photographically useful average grain diameter (500:1)
is achieved by the Ostwald ripening method of silver bromide grains,
Ratios of 100:1, 200:1 and even higher have been obtained with multiple jet precipitation methods. Although the presence of iodide reduces the maximum average aspect ratio achieved, it is possible to prepare silver bromide tabular grain emulsions with average aspect ratios of 50:1, 100:1, 200:1 or even higher. be. Average aspect ratios of 50:1 or even 100:1 can be prepared in silver chloride tabular grains optionally containing bromide and/or iodide. In all cases, the average diameter of the thin tabular grains is usually less than 10 micrometers. The invention is equally applicable to photographic elements intended to form negative or positive images. For example, it can be a type of photographic element that forms a latent image on or in it upon exposure to light and forms a negative image through photographic processing. Optionally, it can be a photographic element that directly forms a positive image in a single development step. If tabular or other imaging silver halide grains present in a photographic element are intended to form positive images directly, they may be surface fogged and used in admixture with conventional organic electron acceptors. The organic electron acceptor can be used in admixture with a spectral sensitizing dye, or can itself be a spectral sensitizing dye. When internally sensitive emulsions are used, they may be used in combination with surface fog and organic electron acceptors, but neither surface fog nor organic electron acceptors are necessary to form a direct positive image. Direct positive images may be formed by developing the internal light-sensitive emulsion in the presence of a developer or nucleating agent that may be included in the photographic element. This is Research Disclosure, Vol. 151, November 1976, No. 15162.
It is stated in the manuscript. Nucleating agents directly adsorbed to the surface of silver halide grains are preferred. Internal latent image forming high aspect ratio tabular grain emulsions containing nucleating agents are useful in the practice of this invention. In addition to the features mentioned above, the photographic elements of the invention can have conventional features. For example, the characteristics described in the following paragraph of the aforementioned Research Disclosure, Draft No. 17643. The emulsions may be chemically sensitized as described in the first paragraph of this document and/or spectrally sensitized or desensitized as described in the second paragraph. Photographic elements may contain brighteners, antifoggants, scattering or absorbing materials, coating aids, plasticizers, lubricants, and matting agents. These are Research Disclosure No. 17643 mentioned above.
It is stated in the first paragraph of the manuscript. Addition, coating and drying techniques such as those described in the second paragraph may be used. Conventional photographic supports such as those described in the first paragraph may be used. Other conventional features will be readily suggested by those skilled in the art. The invention is particularly applicable to radiographic elements. Preferred radiographic elements of the invention are photographic elements comprising at least one high or medium aspect ratio thin tabular grain emulsion, e.g., two imaging layer units formed on opposite major sides of a support. The photographic element is prepared by fully prehardening the photographic element. The intermediate support is radiation transparent to at least one, and typically both, of the imaging layer units. The two imaging layer units each contain at least one radiation-sensitive emulsion containing thin tabular silver halide grains having a medium average aspect ratio of the type described in detail above. To achieve both covering power and crossover benefits, tabular silver halide grains had spectral sensitizing dyes adsorbed on their surfaces. It is specifically proposed to use spectral sensitizing dyes with maximum absorption in the blue and minus blue (ie green and red) portions of the visible spectrum. In addition, spectral sensitizing dyes may be used to improve spectral sensitivity outside the visible spectrum for special applications. For example, infrared absorbing spectral sensitizers may be used. Thin tabular grain silver halide emulsions can be spectrally sensitized with various classes of dyes. These dyes are the polymethine dye class, which class includes cyanines, merocyanines, complex cyanines and merocyanines (i.e. trinuclear, tetranuclear and polynuclear cyanines and merocyanines), oxonol, hemioxonol, styryl, merostyryl and streptocyanin. . Cyanine-based spectral sensitizing dyes include quinolinium, pyridinium, isoquinolinium, 3H-indolium, benz[e]indolium, oxolium,
Oxazolinium, thiazolium, thiazolinium, selenazolium, selenazolium, imidazolicum, imidazolinium, benzoxazolium, benzothiazolium, benzoselenazolium, benzimidazolium, naphthooxazolium, naphthothiazolium, Made by joining two basic heterocyclic nuclei through a methine bond, such as derivatives from the quaternary salts of naphthoselenazolium, dihydronaphthothiazolium, pyrylium, and imidazopyrazinium. be. Merocyanine spectral sensitizing dye is a cyanine dye-type basic heterocyclic nucleus and an acidic nucleus bound together through a methine bond. -thiohydantoin, 4-thiohydantoin, 2-pyrazolin-5-one, 2-
Isoxazolin-5-one, indan-1,3
-dione, cyclohexane-1,3-dione,
1,3-dioxane-4,6-dione, perazoline-3,5-dione, pentane-2,4-dione, alkylsulfonylacetonitrile, malononitrile, isoquinolin-4-one and chroman-2,4-dione, etc. It is a derivative of One or more spectral sensitizing dyes can be used. Dyes are known that have sensitization maxima at wavelengths throughout the visible spectrum and have a wide variety of spectral sensitization curves. The choice of dye and relative proportions depends on the spectral range to be sensitized and the desired shape of the spectral sensitization curve. Dyes whose spectral sensitivity curves overlap are often drawn by combining curves whose sensitivity at each wavelength in the overlapping region is approximately equal to the sum of the sensitivities of the individual dyes. In this way, by using a combination of dyes having different maximum sensitivities, it is possible to obtain a spectral sensitivity curve having a maximum value between the sensitization maximums of the individual dyes. The use of a combination of spectral sensitizing dyes to supersensitize, i.e., a spectral increase that is greater in a given spectral region than would be obtained from any concentration of one dye alone or from the additive effects of the dyes. get a feeling Supersensitization is the addition of spectral sensitizing dyes and other additives, such as stabilizers and antifoggants, development accelerators, or development inhibitors, coating aids, brighteners, and antistatic agents. This can be achieved in selective combination with other agents. Compounds and reaction mechanisms that can perform supersensitization are
Gilman, “Examination of the mechanism of supersensitization (Review
of the Mechanisms of Supersensitization)”
Discussed in Photographic Science and Engineering, Vol. 18, 1974, pp. 418-430. Spectral sensitizing dyes also affect emulsions in other ways. Spectral sensitizing dyes also act as antifoggants or stabilizers, development accelerators or inhibitors, and halogen acceptors or electron acceptors. These are disclosed in US Pat. No. 2,131,038 and US Pat. No. 3,930,860. In a preferred embodiment of the invention, the tabular silver halide grains adsorb on their surfaces a spectral sensitizing dye that changes hue as a function of absorption. Conventional spectral sensitizers known to exhibit batochrome-like or hypsochrome-like increases in light absorption as a function of adsorption to the surface of silver halide grains can be used in the practice of this invention. Dyes that meet these criteria are well known in the art and are described in TH James, The Theory of the Photographic Process;
4th edition, Macmillan Publishing, 1977, Chapter 8 (especially F.
Induced color changes in cyanine and merocyanine dyes) and Chapter 9 (particularly H. Correlation of dye structure and surface aggregation) and F.
M. Hamer, "Cyanine Dyes and Related Compounds",
John Willey & Sons, 1964, Chapter (particularly F. Sensitization and Polymerization of the Second Type). merocyanine, hemicyanine,
Styryl and oxonol spectral sensitizing dyes produce H aggregation (hypsochrome displacement)
Dyes are known in the art. However, J aggregation (patochrome displacement) is unusual for these classes of dyes. Preferred spectral sensitizing dyes are cyanine dyes, which perform H or J aggregation. In a particularly preferred embodiment, the spectral sensitizing dye is a carbocyanine dye, which exhibits J aggregation. Such dyes are characterized by having two or more basic heterocyclic nuclei linked by three methine groups. Preferably, the heterocyclic nucleus includes a fused benzene ring to increase J aggregation. Preferred heterocyclic nuclei that promote J aggregation include quinolinium, benzoxazolium, benzothiazolium, benzoselenazolium, benzimidazolium, naphthoxazolium, naphthothiazolium, and naphthoselenazolium. There are quaternary salts. The inherent blue sensitivity of silver bromide or silver bromoiodide is usually based in the art on emulsion layers intended for recording exposure to blue light, but its primary absorption is in the spectral region where the emulsion has an inherent sensitivity. Significant benefits can even be obtained by using spectral sensitizers. For example, it is particularly recognized that benefits may be obtained by using blue spectral sensitizing dyes. Blue spectral sensitizing dyes useful for high aspect ratio tabular grain silver bromide and silver bromoiodide emulsions can be selected from all classes of dyes known to make spectral sensitizers. Polymethine dyes such as cyanine, merocyanine, hemicyanine, hemioxonol and merostyryl are preferred blue spectral sensitizers. Generally useful blue spectral sensitizers can be selected from among these dye classes according to their absorption characteristics or hue. However, general structural correlation functions can serve as a guide in selecting useful blue sensitizers. Generally, the shorter the methine complex, the shorter the wavelength of maximum sensitization. The nucleus also affects absorption.
Adding a fusion ring to the nucleus tends to lengthen the absorption wavelength. Substitutes can also change absorption properties. Spectral sensitizing dyes useful for sensitizing silver halide emulsions are available from Research Disclosure,
Vol. 176, December 1978, No. 17643, Section 1. Conventional amounts of dyes can be used to spectrally sensitize emulsion layers containing nontabular or thick tabular silver halide grains. To fully realize the benefits of this invention, it is preferred to adsorb an optimum amount of spectral sensitizing dye to the grain surfaces of thin tabular grain emulsions. That is, in an amount sufficient to achieve at least 60% of the maximum photographic sensitivity obtainable from the particles under possible exposure conditions. The amount of dye used can vary with the particular dye or combination of dyes and the aspect ratio and size of the particles. As is known in the photographic industry, optimal spectral sensitization is achieved by coating surface-sensitive silver halide grains with a single layer of organic dye ranging from about 25 to 100% or more of the total available surface area. can get. For example, West et al., ``The Adsorption of Sensitizing Dyes in Photographic Elements''
Photographic Emulsions)”, Journal of Physical Chemistry, Vol. 56, p. 1065,
1952 page, Spence et al., Physical and Colloid Chemistry, Vol. 56, No. 6, 1948 6
May, pp. 1090-1103 and U.S. Pat. No. 3,979,213. The optimal dye concentration level is Mees,
``Theory of the photographic processing''
Photographic Process), 1942, Macmillan Publishing, pp. 1067-1069. Spectral sensitization can be carried out at any stage of emulsion preparation heretofore known to be useful.
It is a common practice in the art to perform chemical sensitization, followed by spectral sensitization. However, in particular, spectral sensitization selectively
It can be done simultaneously with chemical sensitization, it can be done completely before chemical sensitization, and it can even begin before completing halide grain silver precipitation. These are US Pat. No. 3,638,960 and US Pat.
No. 4,225,666. US Patent No. 4225666
According to the teachings of this issue, it is also possible to introduce a spectral sensitizing dye into an emulsion by allowing a portion of the spectral sensitizing dye to be present before chemical sensitization and introducing the remaining portion after chemical sensitization. be. Unlike US Pat. No. 4,225,666, spectral sensitizing dyes can be added to the emulsion after 80% of the silver halide has been precipitated. Sensitization can be enhanced by pAg modulation, which involves changing pAg to complete one or more cycles during chemical and/or spectral sensitization.
A specific example of pAg regulation is given in Research Disclosure, Vol. 181, May 1979, article No. 18155. In a preferred embodiment, a spectral sensitizer can be added to the emulsion used in the invention prior to chemical sensitization. Similar results can be obtained in some cases by introducing other adsorbable substances, such as finishing modifiers, into the emulsion prior to chemical sensitization. Regardless of the prior introduction of adsorbable substances, it is preferred to use thiocyanate during chemical sensitization in a concentration of about 2.times.10.sup. ^-3 to 2 mol %, based on silver. This is taught in US Pat. No. 2,642,361. Other ripening agents can be used during chemical sensitization. A further third approach, which can be carried out in combination with or separately from one or two of the above approaches, is to adjust the concentration of silver and/or halide salts present during or immediately before chemical sensitization. It is preferable to do so. Soluble silver salts such as silver acetate, silver trifluoroacetate, and silver nitrate can be added, as well as silver salts that can precipitate on the particle surface, such as silver thiocyanate, silver phosphate, silver carbonate, and the like. Fine grains of silver halide (ie silver bromide, silver iodide and/or silver chloride) can be added to the surfaces of the tabular grains to enable Ostwald ripening. For example, Lippmann emulsions can be introduced during chemical sensitization. Additionally, chemical sensitization of spectrally sensitized thin grain emulsions can be carried out at one or more discrete sites on the tabular grains. It is believed that by preferentially adsorbing a spectral sensitizing dye to the crystal faces forming the major faces of the tabular grains, chemical sensitization can be selectively caused on different crystal surfaces of the tabular grains. It is being Preferred chemical sensitizers that yield the highest sensitivity-granularity relationships are gold and sulfur sensitizers, gold and selenium sensitizers, and gold, sulfur and selenium sensitizers. Thus, in a preferred embodiment of the invention, thin tabular grain silver bromide or most preferably silver bromoiodide emulsions contain intermediate chalcogens such as sulfur and/or selenium (which are not detectable) and gold (which is detectable). ). Although emulsions usually contain detectable levels of thiocyanate, the concentration of cyanate in the final emulsion is greatly reduced by known emulsion cleaning methods. In various preferred embodiments described above, the tabular silver bromide or silver bromoiodide grains have on their surfaces other silver salts such as silver thiocyanate or other silver halides containing different halogens (such as silver chloride or silver bromide). etc., but other silver salts can also be present below detectable levels. Although it is not necessary for the emulsions used in this invention to realize all of their benefits, it is preferred that the emulsions be suitably chemically and spectrally sensitized in normal preparative practice. That is, it is preferred to have a sensitivity of at least 60% of the maximum logarithmic sensitivity obtainable from the particles in the spectral region of sensitization under possible conditions of use and processing. Here the logarithmic sensitivity is
Refers to the quantity expressed as 100 (1-logE), in the formula,
E is the exposure measured in meters candle seconds at a density that is 0.1 greater than fog. Once the silver halide grains of the emulsion have been characterized,
From further product analysis and performance evaluation, it is possible to determine whether the product's emulsion layers are practically optimally chemically and spectrally sensitized with respect to comparable commercial products from other manufacturers. In addition to the features specifically mentioned above, the radiographic element of the invention may include additional features customary for radiographic elements. Examples of this type of feature are, for example, Research Disclosure, Vol. 184,
Disclosed in Draft No. 18431, August 1979. For example, the emulsions may contain stabilizers, antifoggants, and anti-twist agents, as described in paragraphs A-K. As described in the first paragraph, the radiographic element may include an antistatic agent and/or an antistatic layer. As described in the first paragraph, the radiographic element may include an overcoat layer. As disclosed in Article No. 18431, paragraph 1, the crossover benefits of the present invention can be further improved by conventional crossover exposure control techniques. Preferred are radiographic elements comprising at least one thin tabular grain emulsion layer in each of two imaging units formed on opposite major faces of a support capable of substantially specular transmission of imagewise radiation.
Medical radiographic elements are usually tinted blue. Blue dyes are generally added directly to the molten polyester prior to extrusion and must be thermally stable. Preferred bluish dyes are anthraquinone dyes. The spectral sensitizing dye is preferably such that, in its adsorbed state, the adsorption peak shifts, usually in the H or J band, to the range of the spectrum corresponding to the wavelength of the electromagnetic radiation with which the photographic element is imagewise exposed. The electromagnetic radiation for imagewise exposure is typically emitted from the sulfur of the intensifying screen. Separate intensifying screens expose each of the two imaging units located on either side of the support. Intensifier screens emit light in the ultraviolet, blue, green, or red ranges, which vary depending on the specific phosphorus added. In a particularly preferred form of the invention, the spectral sensitizing dye is a carbocyanine dye, which exhibits J-band absorption when adsorbed to tabular grains. This spectral region corresponds to the peak emission by the intensifying screen and is usually in the green region of the spectrum. Although the intensifier screen can itself form part of the radiographic element, it is usually a separate element that is used repeatedly in sequential exposures of the radiographic element. Intensifying screens are well known in the radiographic industry.
Conventional intensifier screens and their components are disclosed in the aforementioned Research Disclosure Vol. 18431, paragraph 1 and in U.S. Pat. No. 3,737,313. Photographic elements, and for preferred applications radiographic elements, are photographically processed to produce visible silver images with alkaline aqueous developers and, when developers are included in the photographic element, alkaline activated aqueous solutions.
Development that provides the highest covering power is preferred. “Theory of Photographic Processing” by James, supra, 404,
As pointed out by Farnell and Solmen, pp. 405, 489, 490, and also supra, the highest covering power is obtained by developing the silver in the most filamentary manner. Direct development or chemical development is preferred because it yields relatively high covering power compared to physical development. When using silver halide grains that mainly form a surface latent image, it is preferable to use a developer containing a small amount of a silver halide solvent, that is, a surface developer. It has been found that covering power is increased by developing for a short period of time, ie, at a relatively high speed. Exposure and development of photographic elements of the invention for less than 1 minute and preferably less than 30 seconds to form a visible silver image increases covering power, whereas developing for 8 minutes substantially reduces covering power. , has little to do with the aspect ratio of the particles. It is preferred to use relatively strong developers to achieve rapid development. A preferred developer is hydroquinone used alone or preferably in admixture with a secondary developer such as pyrazolidone, especially 3-pyrazolidone, and an aminophenol such as p-methylaminophenol sulfate. Research Disclosure, No.
Photo processing techniques of the type described in the first paragraph of the 17643 manuscript may be utilized. Particularly preferred is a roller-feeding treatment of the radiographic element. Although the photographic elements of this invention are prehardened, conventional developers containing prehardeners may be used without any loss of covering power. Since the photographic elements of this invention are usually well prehardened, it is of course preferable to completely remove the hardening agent from the photographic processing solution. After development, the photographic element may optionally be fixed by conventional techniques to remove residual silver halide. (4) Embodiments The present invention can be further understood by referring to the following examples. In each example, the contents of the reaction vessel were vigorously stirred during all introductions of silver and halide salts. Further, in each example, the term "percentage" means % by weight unless otherwise specified, and the term "M" means molar concentration unless otherwise specified. All solutions are aqueous unless otherwise specified. Examples 1-15 For the purpose of comparing covering power as a function of tabular grain aspect ratio, three tabular grain silver bromide emulsions according to the invention and one low aspect ratio tabular grain bromoiodide emulsion were compared. A silver emulsion was prepared. The tabular grains are shown in Table 1 below.

Table: Emulsions A, B, and C of Examples are high aspect ratio tabular grain emulsions and are within the preferred limits of application of this patent. Some tabular grains less than 0.6 μm in diameter were included when calculating average tabular grain diameter and projected area percentage in the emulsions of these and following examples, but no exclusions are specifically noted. Except at times, tabular grains with insufficiently small diameters were present to clearly change the reported numbers. The average grain diameter was compared to the average grain thickness to determine the typical average aspect ratio of the grains of the control emulsion. Although not measured, the projected area attributable to the few tabular grains in the control emulsion that meet the critical values of less than 0.3 micrometers in thickness and at least 0.6 micrometers in diameter exceeds the total projected area of the total grain population in the control emulsion. Evaluation was made by visually observing a very small amount, if any, of the projected image area. Each emulsion was chemically sensitized with sulfur and gold;
with the sodium salt of anhydrous 5,5'-dichloro-9-ethyl-3,3'-di(3-sulfopropyl)-oxacarbocyanine (600 mg per mole of silver) and potassium iodide (400 mg per mole of silver). The green spectrum part was sensitized. The emulsion was then hardened in separate samples. Three samples of each emulsion were mixed with the hardener bis(vinylsulfonylmethyl)ether (BVSME) at 0.5, 1.5, and 4.5 weight percent, respectively, based on the weight of gelatin. Three samples of each emulsion contained 0.24, 0.75, and 2.5% by weight, respectively, based on the weight of gelatin.
The hardening agent formaldehyde (HCHO) was mixed in. Three samples of each emulsion were mixed with the hardening agent mucochloric acid (MA) at 0.24, 0.75, and 2.5% by weight, based on the weight of gelatin, respectively. Each sample was applied identically to a separate poly(ethylene terephthalate) transparent film support immediately after hardening.
Each emulsion sample was coated at 2.15 g silver/m ² and 2.87 g gelatin/m ² . 0.88g gelatin/ ^m2 for each sample
I applied the top coat. Seven days after coating, the swelling percentage of the emulsion coated sample that had not been photographically processed was measured. 38℃ for 3 days,
Incubation was performed at 50 percent relative humidity. The emulsion layer thickness was first measured and then each sample was immersed in distilled water at 21°C for 3 minutes. Then, changes in the thickness of the emulsion layer were measured. Only a small portion of each sample was required to perform the swelling measurement procedure described above. The remainder of each sample was exposed to maximum photographic density and photographically processed in a conventional commercially available radiographic element photographic processor, Kodak RP X-Omat film processor M6A-N. The development time was 21 seconds at 35°C. Instead of using a standard developer containing glutaraldehyde as a prehardener in this photoprocessor, a similar developer of the type disclosed in Example 1 of U.S. Pat. A developing solution completely free of pre-hardening agent was used. Covering power of each sample, maximum photographic density in grams/ ^100cm2
It was measured by dividing by the unit of developed silver. The covering power of each emulsion with each hardener was determined by plotting the covering power against the swelling percentage for three samples hardened to different degrees with the same hardener (unless otherwise specified). ) measured at 199 percent swelling.
The results are listed in Table 2 below.

Table 2 shows that at the same level of hardening, photographic elements of the invention prepared with high aspect ratio tabular grain emulsions exhibit high covering power, and covering power is higher than that of higher aspect ratio tabular silver bromide emulsions. It can be seen that there is an increase in Table 3 is similar to that listed in Table 2, but (unless otherwise noted) measurements were taken at 99% swelling.

Table: Since mucochloroic acid is a weak hardening agent, the concentrations employed were insufficient to reduce the percentage swelling below 100 percent. Therefore, the covering power at that swelling amount cannot be reported. It is thought that at higher concentrations, mucochloroic acid could have reduced the swelling to less than 100%.

[Table] When the results shown in Tables 2 and 3 are organized as shown in Table 4, the photographic elements of the present invention:
It can be seen that as a function of increased hardness there is a significant resistance to covering power loss. Examples 16-19 Control emulsions with the same grain characteristics as the control emulsions in Table 1 were sensitized with sulfur and gold and 600 mg/Ag mole of anhydrous 5,5'-dichloro-9-ethyl-3,3'- The green spectral portion was sensitized with the sodium salt of di(3-sulfopropyl)oxacarbocyanine and 400 mg of potassium iodide per mole of Ag. The emulsion was then divided into six portions and different amounts of bis(vinylsulfonylmethyl)ether (BVSME) were added as shown in Table 3. The amount of BVSME was expressed as weight percent based on the weight of gelatin in the emulsion. Emulsion D, a thin tabular grain emulsion, was prepared similarly to Emulsion A, but with an average aspect ratio of 8.3:1 near the end of the preparation. The tabular grains had a diameter of 1.66 μm and a thickness of 0.20 μm.
These tabular grains accounted for more than 80% of the projected area of the entire grain. Emulsion D was similarly sensitized with sulfur and gold, and Ag
600 mg per mole of anhydrous 5,5'-dichloro-9-ethyl-3,3'-di(3-sulfopropyl)oxacarbocyanine sodium salt and 400 mg per mole of Ag.
The green spectral portion was sensitized with mg potassium iodide. Emulsion D was divided into four parts and BVSME hardener was added to each part. The amount of hardener added was varied as shown in Table 5. Upon addition of the hardener, both the control emulsion and emulsion D were coated separately on the same polyethylene terephthalate transparent film support under the same conditions. The coating rate was 2.15 g Ag/m ² and 2.87 g gelatin/m ² . 7 days after coating (3
The temperature was maintained at 38°C and RH 50% for several days), and the swelling percentage was measured. The thickness of the emulsion layer was first measured and then each sample was immersed in distilled water at 21°C for 3 minutes. Then, changes in the thickness of the emulsion layer were measured. It was sufficient to use only a small amount of each sample for the above-mentioned swelling percentage measurements. The remainder of each sample was exposed to maximum density and processed in a commercially available radiographic element photographic processor (Kodak RP X-Omat Film Processor-M6A-N). Develop at 35℃
It lasted 21 seconds. A developer of the type described in Example 1 of Barnes et al. US Pat. No. 3,545,971 was used. The % swelling and covering power results obtained using different portions of each sample are shown in Table 5.

【table】

[Table] From the above results, it can be seen that the highest level of swelling for both the control emulsion and emulsion D is essentially the same when experimental precision is taken into account. The covering power at 100% swelling was measured by interpolation. The covering power and % loss of covering power at the same % swelling of each sample were measured. The results are shown in Table 6.

TABLE From Table 6, it can be seen that the % covering power loss of the control emulsion is approximately an order of magnitude greater than that of Emulsion D. This demonstrates that the photographic elements of this invention exhibit unexpectedly excellent covering power retention with increased hardness. The following experiments describe details of the preparations in the above examples but do not form part of the present invention. A Example 1 Solution A, 17.5 liters of a 1.5% bone gelatin aqueous solution containing 0.14 molar potassium bromide, was heated at 55°C.
and pBr0.85, solution B-1 i.e. 1.15
Molar potassium bromide aqueous solution and solution C-1
That is, a 1.00 molar silver nitrate aqueous solution was added over a period of 8 minutes by the multiple diet method, consuming 1.05% of the total silver nitrate used. Addition of these solutions B-1 and C-1 was stopped after the initial 8 minutes. Solutions B-2, a 2.29 molar aqueous solution of potassium bromide, and C-2, a 2.0 molar aqueous solution of silver nitrate, were then added to the reaction vessel at pBr 0.85 and 55 DEG C. by multiple diet method. At this time, the rate of addition was accelerated to 4.2 times the initial rate, and solution C-2 was consumed in approximately 20 minutes, consuming 14.1% of the total silver nitrate used. Addition of solution B-2 was stopped. Solution C-3, an aqueous solution of 2.0 molar silver nitrate, was added to the reaction vessel over a period of about 12.3 minutes to reach a pBr of 2.39 at a temperature of 55°C, and the total amount of silver nitrate used was
Consumed 10.4%. Stir this emulsion for 15 minutes and
The pBr was maintained at 2.39 at °C. Solution C-3 and solution B-3, i.e., a 2.0 molar potassium bromide aqueous solution, were added to the reaction vessel at a constant rate for about 88 minutes by the multiple-feed method, consuming 74.5% of the total silver nitrate used; Temperature 55 during this time
The pBr was kept at 2.39 at °C. Addition of solutions B-3 and C-3 was stopped. A total of 41.1 moles of silver were used to prepare this emulsion. Finally, the solution was cooled to 35°C and
Coagulation cleaning was performed as described in No. 2614929. B Example 2 Solution A, a 1.5% bone gelatin aqueous solution containing 0.14 molar potassium bromide, was stirred at pBr 0.85 at 55°C and the flow rate was kept constant for 8 minutes using the multiple diet method. 3.22% of the total was consumed, solution B-1 or potassium bromide 1.15 molar aqueous solution and solution C-1 or silver nitrate.
A 1.0 molar aqueous solution was added. Addition of solution B-1 and solution C-1 was stopped after the first 8 minutes. Solution B-2, a 3.95 molar aqueous solution of potassium bromide, and solution C-2, a 2.0 molar aqueous solution of silver nitrate, were mixed at pBr 0.85 and 55°C.
The solution C-2 was added at an accelerated rate of 4.2 times, and in about 20 minutes, 28.2% of the total silver nitrate used was consumed and all of the solution C-2 was added. Addition of solution B-2 was stopped. Solution C-3, a 2.0 molar silver nitrate aqueous solution, was added at a constant flow rate for about 2.5 minutes to give a solution of pBr2.43,
The temperature was 55°C and 4.18% of the total silver nitrate used was consumed. This emulsion was stirred at 55°C for 15 minutes. Solution C-3 and solution B-3, a 2.0 molar aqueous solution of potassium bromide, were then added at pBr2.43 at 55°C for 31.1 minutes while accelerating the flow rate so that the final flow rate was 1.4 times the initial value, and the silver nitrate used was 64.4% of the total
consumed. Addition of solution B-3 and solution C-3 was discontinued. An emulsion was prepared using 29.5 moles of silver nitrate. Finally, the emulsion was cooled to 35°C and a coagulation wash was performed as described in Example 1. C Example 3 Solution A, a 1.5% bone gelatin aqueous solution containing 0.14 molar potassium bromide, pBr 0.85 and 4.76% of the total silver nitrate used was added at 55°C by the double diet method with stirring at a constant flow rate for 8 minutes. was consumed, and Solution B-1, an aqueous solution containing 1.15 molar potassium bromide, and Solution C-1, a 1.0 molar aqueous solution of silver nitrate, were added. After the first 8 minutes, solution B-
1 and solution C-1 were stopped. Then solution B-2, a 2.29 molar aqueous solution of potassium bromide, and solution C-2, a 2.0 molar solution of silver nitrate.
pBr0.85,
At 55 DEG C., solution C-2 was added at an accelerated rate of 4.2 times the initial amount, and solution C-2 was consumed in about 20 minutes, consuming 59.5% of the total amount of silver nitrate used. Addition of solution B-2 was stopped. Solution B-1 and solution B-2 were added to the surface of solution A at three locations in the above addition. Solution C-3, a 2.0 molar aqueous solution of silver nitrate, was added to the reaction vessel at a constant flow rate over about 10 minutes;
At pBr2.85 and 55°C, 35.7% of the total silver nitrate used was consumed. A total of 23.5 moles of silver nitrate was used to prepare this emulsion. Finally, the emulsion was cooled to 35°C and coagulation washed as described in Example 1. D. Control Emulsion This emulsion was prepared as described in US Pat. No. 4,184,877. In a 5% solution of bone gelatin in water 17.5 at 65 °C
4.7M ammonium iodide solution and 4.7M silver nitrate solution at a constant flow rate for 3 minutes to a pI of 2.1.
(consuming about 22% of the silver nitrate used in seed grain preparation) with stirring in a multiple diet method. Then, the flow rates of both solutions were adjusted to such a rate that about 78% of the total amount of silver nitrate used for seed particle preparation was consumed in 15 minutes. Then the ammonium iodide solution feed was stopped and the silver nitrate solution was continued to be added to bring the pI to 5.0. A total of about 56 moles of silver nitrate was used in the seed particle preparation. The emulsion was cooled to 30°C. It was used as a seed grain (emulsion (grain size 0.24 μm)) for further precipitation as described below. 15.0% of the 5% gelatin solution containing 4.1 mol of the AgI emulsion prepared above was heated to 65°C. 4.7M ammonium bromide solution and 4.7M silver nitrate solution
It was added at an equal constant flow rate for 7.1 minutes while maintaining a pBr of 4.7 (consuming 40.2% of the total silver nitrate used for precipitation into seed particles). Then only the ammonium bromide solution was added until the pBr was about 0.9 and then stopped. Then 2.7 g of 11.7 M ammonium hydroxide solution was added and the emulsion was held for 10 minutes. The pH was adjusted to 5.0 with sulfuric acid, and a double diet of ammonium bromide solution and silver nitrate solution was introduced again to maintain pBr of approximately 0.9, reducing the amount to 56.8% of the total consumed silver nitrate.
was taken as the consumption speed. The pBr was then adjusted to 3.3 and the emulsion was cooled to 30°C. A total of about 87 moles of silver nitrate was used. The emulsion was coagulation washed as described in Example 1. E Emulsions A, B, C of Examples prepared as above
5 potassium tetrachloraurate per mole of Ag
mg, sodium thiocyanate 150 mg per mole of Ag,
and optimally chemically sensitized at 70°C using 10 mg of sodium thiosulfate per mole of Ag. The control emulsion was optimally chemically sensitized at 70°C using 0.6 mg of potassium gold tetrachloride per mole of Ag and 4.2 mg of sodium thiosulfate per mole of Ag according to the teachings of US Pat. No. 4,184,877. (5) Effects and Benefits of the Invention The photographic elements of the present invention are sufficiently prehardened to require no additional hardening during photographic processing, yet still achieve high levels of covering power. High covering power images are obtained by imagewise exposure of photographic elements, especially radiographic elements, such as those mentioned above.
Formed by developing a visible image in less than 1 minute. The present invention allows for black and white photographic elements that are fully prehardened and are intended to form visible images that require no additional hardening during photographic processing, yet still achieve high levels of covering power. The present invention provides relatively high-sensitivity, high-covering-power photographs that can be rapidly processed without the risk of damage caused by incomplete dura or without the need to use hardening agent-containing photographic processing baths. It fulfills a long-standing need in the industry for elements, particularly radiographic elements. Photographic elements of the present invention for use in radiography have sufficiently reduced crossover that, taking into account other photographic characteristics, there is less sharpness loss attributable to crossover. To be more specific,
Photographic elements of the invention for use in radiography include:
At selected silver coverages (based on weight of silver per unit area of emulsion layer) and comparable sensitivities, it has at least one silver halide emulsion layer that allows less crossover of exposing radiation. The emulsions used in this invention and the photographic elements of this invention have significant benefits in sharpness and speed-granularity relationships that are independent of crossover. These improvements are realized regardless of the halide content of the tabular silver halide grains. Compared to conventional tabular grain emulsions, the silver bromoiodide emulsions of the present invention have the highest sensitivity ever achieved with silver bromoiodide emulsions.
The sensitivity-granularity relationship is generally improved compared to the granularity relationship. When using a blue spectral sensitizer,
The blue sensitivity of silver bromide and silver bromoiodide emulsions is greatly increased compared to their original blue sensitivity.

Claims (1)

[Scope of Claims] 1. A support and at least one radiation-sensitive silver halide grain located on the support.
a photographic element having one or more hardenable hydrophilic colloid layers, including an emulsion layer, wherein the total projected area of the silver halide grains in at least one emulsion layer is at least 50 percent has an average aspect ratio of at least 5:1 and
is populated by thin tabular grains having a thickness of less than 0.2 micrometers, and the hydrophilic colloid layer has a swelling of the hydrophilic colloid layer of 200 percent, where the percent swelling is (a) the photographic element.
Incubate for 3 days at 38°C and 50% relative humidity, (b) measure layer thickness, (c) immerse the photographic element in distilled water at 21°C for 3 minutes, and (d)
(measured by measuring the percentage change in layer thickness compared to the layer thickness measured in step (b))
A photographic element characterized in that it is hardened in an amount sufficient to reduce 2. the photographic element is a radiographic element;
and in the radiographic element the support is a substantially specular support and the hydrophilic colloid layer comprising at least one emulsion layer on each side of the support comprises 6 containing radiation-sensitive particles containing up to mol% iodide;
characterized in that at least 50% of the total projected area of the radiation-sensitive grains is occupied by thin tabular grains having an average aspect ratio of at least 5:1 and a thickness of less than 0.2 micrometers. A photographic element according to claim 1, wherein: