JPH0623860B2 - Imaging particles - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an image forming method utilizing the image forming ability of a photosensitive substance such as an electrophotographic photosensitive member and the pixel decomposition of an original by light transmitting particles. It relates to imaging particles.

Structure of Conventional Example and Problems Thereof As an image forming method using particles of this type, for example, a step of uniformly charging an electrophotographic photosensitive member, and uniformly and further electrostatically adhering light transmitting particles to the photosensitive member. Exposing the light image of the original to the photoconductor through the particles, removing particles from which the electrostatic adhesion with the photoconductor is weakened or removed from the photoconductor, and forming a particle image on the photoconductor. There is an image forming method including a step of heating particles remaining on a photoconductor and sublimating or vaporizing and transferring the sublimable or vaporizable dye contained in the particles to an image receptor.

As an image forming method in this field, for example, Japanese Patent Laid-Open No. 52-
No. 60135.

To expand the tone reproduction range with this type of image forming method,
There is a method of using particles having a wide particle size distribution. That is, since the optical path of the light that passes through the particles differs depending on the difference in particle size, the transmittance of the particles can differ. Depending on the difference in the transmittance of the particles, the intensity of light transmitted through the particles can be different, and the surface potential of the electrophotographic photoreceptor can be different. Due to this difference in surface potential, the tone reproduction range can be expanded. That is, the electrostatic adhesion force between the photosensitive member and the particles is stronger when the particle size is larger and weaker when the particle size is smaller. As a result, the particle image corresponding to the low density portion of the document (hereinafter referred to as the highlight portion) is composed of particles having a large particle diameter, and the density of the document is high (hereinafter referred to as the shadow portion).
As the number of particles becomes smaller, the proportion of particles having a smaller particle size increases in the corresponding particle image.

As described above, the tone reproduction range can be expanded even with the conventional technique, but there are the following problems.

Problem-1: In the process of removing particles from the photoconductor (hereinafter referred to as a developing process), particles having a large particle size are usually more easily removed, so that even if the particle size distribution is widened, the effect of expanding the tone reproduction range can be increased. Few.

Problem-2: Sublimation transfer or vaporization transfer of a sublimable or vaporizable dye (hereinafter simply referred to as a sublimable dye) contained in the particles by heating the particles to the image receptor (hereinafter, this step is referred to as a coloring step) , Sublimation transfer or vaporization transfer is referred to as color development), and the graininess is easily noticeable in the highlight portion of the printed image.

Problem -3: It is difficult to expand the tone reproduction range of a particle image in a printed image.

The causes of the above three problems will be described. The developing method (hereinafter referred to as developing method) includes an electrostatic developing method for removing particles by electrostatic force (electrostatic attraction), a vibration developing method for removing particles by inertial force due to vibration, and a flow of gas or liquid. There are various methods such as a fluid development method that removes particles by force, a brush development method that removes particles by frictional force and pressure from a brush, and a gravity development method that removes particles by using gravity fall. Of the development methods illustrated here,
In the vibration developing method and the gravity developing method, since the particle having a larger particle diameter has a larger mass, the inertial force and the gravity are also larger. Further, in the fluid development method and the brush development method, since the particle having a larger particle size has a larger volume, the force due to the flow, the frictional force, and the pressure are larger.

FIG. 1 shows an example of the electrostatic development system. That is, the state in which the dielectric 2 is brought into close contact with the particles on the electrophotographic photosensitive member 1 and the dielectric 2 is charged by the corona charger 3 is shown. The particles are attracted to the charged dielectric by electrostatic attraction. Here, since the particles 4 having a large particle size have a smaller distance from the dielectric 2 than the particles 5 having a small particle size, the electrostatic attractive force acting on the particles 4 is stronger.

As described above, in any of the exemplified developing methods, particles having a large particle diameter tend to be easily removed in the developing step. In other words, the larger the particle size is, the stronger the electrostatic adhesion force between the photoconductor and the particles and the force for removing the particles in the developing process.
Therefore, as described in Problem-1, it is considered that the effect of expanding the tone reproduction range is small.

Further, the highlight portion has a low particle density and is mainly composed of particles having a large particle size as described above. For this reason, since the color-developing pixels in the highlight portion of the print image after the color-developing process are large, the graininess is conspicuous as described in Problem-2.

Furthermore, since the pixels in the highlight area are large, as can be assumed from the Murray Davis equation, the difference in the color-developed pixel area (corresponding to the halftone dot area ratio) of the printed image is small even if there is a difference in particle density. As described in point-3, the tone reproduction range of the print image becomes small.

OBJECT OF THE INVENTION The object of the present invention is to overcome the above-mentioned conventional problems,
It is an object of the present invention to provide an image forming particle which expands a tone reproduction range and improves the graininess of a printed image.

In order to achieve the above-mentioned object, the present invention is characterized in that a plurality of kinds of particles having substantially equal transmittances of particles in the visible light region and different particle diameters are mixed. Specifically, the additive amount of achromatic color or chromatic color is changed to adjust the transmittance of particles having a large particle diameter and the transmittance of particles having a small particle diameter to be substantially equal to each other. Characterize.

Description of Examples First, the action of the image forming particles of the present invention will be described in a model manner with reference to the drawings.

FIG. 2 shows that particles 7 having a large transmissivity and a small particle size 8 having the same transmittance in the visible light range are mixed on the uniformly charged photosensitive member 6 and the particles 7 are dispersed. An example of the electrostatic development system in which the dielectric 9 is brought into close contact with the particles after image exposure through the and 8 and the dielectric 9 is charged by the charger 10 (the same state as in FIG. 1). Here, since the particles 7 and 8 have almost the same transmittance, if the density of the original is the same, the charges immediately below the particles are attenuated at the same speed regardless of the particle size. Therefore, the electrostatic adhesion force between the photoconductor 6 and the particles 7 and 8 is equal regardless of the particle size. On the other hand, the particles 7 are in close contact with the dielectric 9, and the particles 8 have a gap. Therefore, the electrostatic attraction between the dielectric 9 and the particles 7 is stronger than the electrostatic attraction between the dielectric 9 and the particles 8. Therefore, at a certain document density, as shown in FIG. 3, the particles 7 having a large particle size are removed in the developing process according to the electrostatic attraction difference between the dielectric 6 and the particles, and the particles are left on the photoconductor 6. The particles 8 having a small diameter remain. That is, particles having a smaller particle size remain on the photoconductor in the highlight portion.

Since the particles 7 and the particles 8 actually have particle size distributions, the particles are sequentially removed in the developing process according to the above-mentioned principle corresponding to the difference in the document density. Therefore, the tone reproduction range of the particle image is expanded. Further, when there is a region where the particle size distributions of the particles 7 and the particles 8 overlap, particles having the same particle size but different transmittances are formed. In this case, the electrostatic attraction of the particles is the same as that of the derivative, and the particles having a high transmittance are removed due to the difference in electrostatic adhesion between the particles and the photoconductor. Therefore, the tone reproduction range is expanded even if the particle size is the same.

Although an example of the electrostatic developing system has been described with reference to FIGS. 2 and 3, the same tendency is exhibited in other examples of the electrostatic developing system and other developing systems. That is, when the image-forming particles of the present invention are used, in the portion corresponding to the same document density, there is almost no difference in the electrostatic adhesion force between the particles and the photoconductor due to the particle size, and the force for removing the particles in the developing step is The larger the particle size, the stronger. Therefore, the highlight portion is composed of particles having a small particle diameter, and the proportion of particles having a large particle diameter increases in the shadow portion.

In the above, both have described the mixing of two types of particles,
The principle is the same when three or more kinds of particles having adjusted transmittances are mixed, and the effect becomes larger as the kinds of particles mixed increase.

Further, although particles of one color have been described above, when particles of two or more colors are mixed, the particles of each color behave based on the above-mentioned principle by mixing particles having adjusted transmittances of each color.

Next, the material of the particles used in the present invention will be described.

The particles are generally composed of resin. As this resin, for example, a thermoplastic resin such as polyvinyl alcohol or acrylic resin, a thermosetting resin such as melamine resin or phenol resin, a styrene-butadiene copolymer, or a transparent resin such as gelatin is used.

By adding a colorant such as a dye or a pigment to the above resin, the particles selectively transmit light (color separation). As an example of the representative colorant, for red light transmission,
C. Acid dyes such as I. acid red 6,14,18,42, or C.I. I. Pigment Red 17, 48, 81
There are organic pigments such as. For green light transmission,
C. Acid dyes such as I. acid green 9, 27, 40 and 43, or gold-containing dyes such as Aizen spirone green C-GH (manufactured by Hodogaya Chemical Co., Ltd.) or C.I.
There are organic pigments such as I. Pigment Green 2 and 7. For blue light transmission, C.I. I. Solvent Blue 4
Oily dyes such as C.8, 49 or C.I. Direct dyes such as I. Direct Blue 86, C.I. I. Acid Blue 23,4
Acid dyes such as 0, 62, 83 and 120, C.I. There are organic pigments such as I. Pigment Blue 15. In addition, of course, in order to obtain other desired spectral characteristics, it can be obtained by mixing a single colorant or a plurality of types of colorants as needed.

Further, a coloring function can be imparted by adding a colored or colorless sublimable dye. As an example of a typical colored sublimable dye, cyan is C.I. I.
Basic Blue 5, C.I. I. Solvent Blue 2, C.I.
I. Disperse Blue 1 etc. The magenta color is C.I. I. Basic Violet 14, C.I. I. Tispers Violet 1 and so on. The yellow color is C.I. I. Basic Yellow 2, C.I. I. There is Disperse Yellow 2.

A colorless sublimable dye is normally colorless or light-colored, but it sublimates or vaporizes when heated, and is a sublimable substance that develops a color by reacting with a developer such as activated clay, tartaric acid, or 4,4'-diphenylpropane. Alternatively, any vaporizable color former (hereinafter referred to as a sublimable color former) may be used. Further, the sublimable color former does not normally affect the color separation function of the particles. Therefore, it is also possible to add a sublimable color former that forms a complementary color of the colorant that imparts a color separation function to the particles together with the colorant. However, when using a sublimable color former, it is needless to say that it is necessary to use the image receptor having the above-described color developer.

Typical examples of sublimable color formers are, for example, 3,7
-Bis-diethylamino-10-trichloroacetyl-
Phenoxazine, 4- (1,3,3,5-tetramethyl-indolino) methyl-7- (N-methyl-N-phenyl) amino-1 ', 3', 3 ', 5'-tetramethyl-
Spiro [2H-1-benzopyran-2,2 ′-[2 ′
H] -indole], N- (1,2-dimethyl-3-yl) methylidene-2,4-dimethoxyaniline and the like.

The image-forming particles of the present invention should be electrostatically deposited on a support having photoconductivity. For this purpose, it is desirable that at least the particle surface has conductivity. Therefore, when a non-conductive resin is used, the surface is subjected to a conductive treatment. Further, it is required that it is transparent to light even after the conductive treatment and does not affect the color separation. Copper iodide, a polymer electrolyte, or the like is applied as the conductive material. The specific resistance of the particle surface is preferably 10 ¹⁰ Ω · cm or less. Further, it is preferable to make the difference in the specific resistance value of each particle within 1 digit.

Achromatic color additives that are added to make the transmittance almost equal regardless of the particle size of the particles include titanium oxide, silicon oxide,
Examples thereof include inorganic white pigments such as barium sulfate and black pigments such as carbon black, which can be used alone or in combination.

The transmittance can also be adjusted by changing the amount of a colorant that imparts color separation to the particles.

Specific examples will be described below.

Example 1 First, a solution having the following formulation was prepared.

(1) Solution A SBR resin binder (hereinafter referred to as SBR): Dunbond (manufactured by Nippon Zeon Co., Ltd., hereinafter the same) ...... 100 parts by weight Silica: Snowtex ST-20 (hereinafter referred to as ST-20) ( Nissan Kagaku Co., Ltd., the same applies hereinafter .... 100 parts by weight Sublimable color former: 3,7-bis-diethylamino-10-trichloroacetyl-phenoxazine ... 1.8 parts by weight 4- (1,3,3) , 5-Tetramethyl-indolino) methyl-7- (N-methyl-N-phenyl) amino-
1 ', 3', 3 ', 5'-tetramethyl-spiro [2H
-1-Benzopyran-2,2 '-[2'H] -indole] ... 0.8 parts by weight N- (1,2-dimethyl-3-yl) methylidene-2,
4-dimethoxyaniline: 1.5 parts by weight Water: 130 parts by weight (2) Solution B The composition of solution A further includes titanium oxide (particle size 0.02 to 0.1 μm)
Add 6 parts by weight.

Solution A was obtained by dispersing a sublimable color former in water in a ball mill for about 3 hours and mixing SBR and ST-20 with this dispersion. The solution B was obtained by dispersing a sublimable color former and titanium oxide in water in a ball mill for about 5 hours, and mixing SBR and ST-20 with this dispersion.

Next, when the solutions A and B were separately granulated by a spray drying method, spherical particles having a particle size of 3 to 60 μm were obtained.

To 100 parts by weight of the particles thus obtained, 200 parts by weight of a copper iodide solution having the following formulation was separately flow-coated. Thereafter, the particles A obtained from the solution A were classified to 20 to 25 μm, and the particles B obtained from the solution B were classified to 15 to 20 μm, and the specific resistances were all about 10 ³ Ω · cm.

Copper iodide solution Copper iodide: 2 parts by weight Polyvinyl acetate: 0.2 parts by weight Acetonitrile: 100 parts by weight The transmission spectra of the two kinds of particles thus obtained were measured by a microspectrophotometer, and the results shown in Fig. 4 were obtained. Such spectra had almost equal transmittances. (Particle A is about 20μ
m, particle B is about 16 μm).

When images were formed by the image forming process described below using particles in which particles A and particles B were mixed in equal weights (called mixed particles), a print image with a tone reproduction range of about 1.4 due to difference in document density was obtained. It was Also, the number of pixels in the highlight part is about 3
It was 2 μmφ.

Image forming process: A commercially available selenium photoconductor was uniformly charged in a dark place with a corona charger to which +6 KV was applied, and the mixed particles were uniformly dispersed. Next, when the photoreceptor was lightly vibrated, the excessively adhered particles were shaken off, and the particles were electrostatically adhered to the photoreceptor in one layer. The light image of the black and white original was then exposed through the particles. When the photoreceptor was lightly shaken after the exposure, the particles whose electrostatic adhesion to the photoreceptor was weakened or removed were removed, and a positive particle image was obtained on the photoreceptor. The clay layer surface of the clay paper is brought into close contact with this particle image, and the temperature is 180 ° C to 210 ° C.
When the clay paper was peeled off, a positive image was obtained with respect to the original.

Comparative Example 1 Particle A of Example 1 was classified to 15 to 25 μm, and an image was formed by using the particles in the above-described image forming process. As a result, a print image having a tone reproduction range of about 1.1 due to a difference in document density was obtained. . Further, the pixel in the highlight portion was about 54 μmφ.

As described above, when the image forming particles of the present invention are used, the tone reproduction range is expanded from 1.1 to 1.4 and the pixel size of the highlight portion is reduced from 54 μm to 32 μm. There is an effect that a print with less property is obtained.

Next, examples in which a color image is reproduced by using the image forming particles of the present invention will be described.

Example 2 First, two kinds of red, green and blue-violet solutions were prepared according to the following formulation.

(1) Red solution-1 SBR ... 100 parts by weight ST-20 ... 100 parts by weight Colorant: CI Pigment Red 5 ... 2.6 parts by weight CI Pigment Orange 21115 ... 5.3 parts by weight Anionic activator ... 1.0 parts by weight Water ... 130 parts by weight Part Sublimable color former: 3,7-bis-diethylamino-10-trichloroacetyl-phenoxazine ... 8
Parts by weight (1) Green solution-1 SBR ... 100 parts by weight ST-20 ... 100 parts by weight Colorant: CI pigment green 36 ... 5.4 parts by weight CI bat yellow 20 ... 0.8 parts by weight β-type copper phthalocyanine ... 2.2 parts by weight Activator : Anion type ... 0.3 parts by weight Nonionic type ... 0.46 parts by weight Water ... 160 parts by weight Sublimable color former: 4- (1,3,3,5-tetramethyl-indolino) methyl-7- (N-methic-N-) Funyl) amino-
1 ', 3', 3 ', 5'-tetramethyl-spiro [2H
-1-Benzopyran-2,2 '-[2'H] -indole] 2.4 parts by weight (3) Blue-violet solution-1 SBR ... 100 parts by weight ST-20 ... 100 parts by weight Colorant: CI Pigment Blue 15 ... 3 Part by weight Methyl violet lake ... 0.5 parts by weight Dioxazine violet ... 0.5 parts by weight Anionic activator ... 0.3 parts by weight Sublimable color former: N- (1,2-dimethyl-3-yl) methylidene-2,
4-dimethoxyaniline: 4.5 parts by weight Water: 160 parts by weight (4) Red solution-2 Red solution-1 contains barium sulfate (particle size 0.02 to 0.1 µ
m) Add 25 parts by weight.

(5) Green solution-2 Barium sulfate (particle size 0.02 ~ 0.1μ
m) Add 20 parts by weight.

(6) Blue-violet solution-2 Blue-violet solution-1 contains barium sulfate (particle size 0.02 to 0.1 μm)
m) Add 10 parts by weight.

The red solution-1, the green solution-1, and the blue-violet solution-1 were each dispersed with a colorant and a sublimable color former in water in a ball mill for about 3 hours, and SBR and ST-20 were added to each to separate them. Three types of solutions were obtained. The red solution-2, the green solution-2, and the bluish-purple-green solution 2 were each dispersed with a colorant, a sublimable color former, and barium sulfate in water in a ball mill for about 5 hours, and SBR and ST-20 were added to the dispersion. In addition, three separate solutions were obtained separately. When these 6 kinds of solutions were separately granulated by a spray drying method, spherical particles having a particle diameter of 3 to 60 μm were obtained. Next, as in Example-1, copper iodide was fluidly coated separately.

In this way, 2 red particles-1 obtained from the red solution-1, green particles-1 obtained from the green solution-1, and blue-violet particles-1 obtained from the blue-violet solution were obtained.
When classified to 0 to 25 μm, the specific resistance of the particles is about 10
It was ⁴ Ω · cm. Also, red particles obtained from red solution-2
2, green particles-2 obtained from green solution-2 and blue-violet particles-2 obtained from blue-violet solution-2 were classified into 15 to 20 μm,
The specific resistance of the particles was about 10 ⁴ Ω · cm.

The transmission spectra of red particle-1, green particle-1, blue violet particle-1 having a particle size of about 20 .mu.m and red particle-2, green particle-2, and blue violet particle-2 having a particle size of about 15 .mu.m are measured by a microspectrophotometer. As a result of measurement, the transmittances of the particles of each color were almost equal in the spectra shown in FIGS.

Color originals were reproduced by an image forming process described below using mixed particles obtained by mixing the six types of particles in equal weights. As a result, a print image with a tone reproduction range of 1.4 was obtained due to the difference in document density. The pixel diameter in the highlight portion was about 30 μmφ.

Image forming process: The panchromatic sensitized zinc oxide photoconductor was uniformly charged by a corona charger applied with −6 KV in a dark place, and the mixed particles were uniformly dispersed. Next, a polyethylene terephthalate film (hereinafter referred to as PET) having a thickness of about 75 μm was adhered to the particles, and the PET was peeled off after charging with a corona charger applied +6 KV from the back surface of the PET, and the excessively adhered particles were removed. One layer of particles electrostatically adhered onto the photoreceptor. The light image of the color original was then exposed through the particles. After the exposure, PET was again adhered to the particles, and the PET was peeled off from the back surface of the PET by charging with a corona charger applied with +6 KV. Particles with weakened or removed electrostatic adhesion to the photoreceptor adhered to PET, and a positive particle image was obtained on the photoreceptor. Next, the entire surface of the photoconductor is irradiated with white light to attenuate the electric charge remaining on the photoconductor, and then the clay layer surface of the clay paper is brought into close contact with the particles on the photoconductor, and from the back surface of the clay paper +
When the clay paper was peeled off after applying a voltage of 200 to 500 V, the particle image on the photoreceptor was transferred to the clay paper. The particles thus transferred are heated at 180 to 210 ° C. for 4 seconds,
Thereafter, the particles were cleaned to obtain a positive image on the original.

Comparative Example 2 When images were formed in the same manner as in Example 2 using particles classified to 15 to 25 μm, the tone reproduction range was 1.2 in terms of document density difference and the pixel diameter was about 52 μmφ.

As described above, when the image-forming particles of the present invention are used, the tone reproduction range is expanded from 1.2 to 1.4, and the pixel diameter of the highlight portion is reduced from 52 μm to 30 μm. There is an effect that a print with less property is obtained.

Although the above-mentioned embodiment describes the case where an achromatic color additive is added, the same effect can be obtained by increasing the amount of each colorant by 10 to 30% instead of barium sulfate in Example 2, for example.

Further, in the above embodiment, the case where two kinds of each color are mixed has been described, but the tone reproduction range expands as the kinds of particles of each color increase.

Effects of the Invention The image-forming particles of the present invention have the following effects.

(1) The tone reproduction range of the printed image can be expanded.

(2) The grain size of the print is improved because the pixel diameter forming the highlight portion of the print is small.

(3) The transmittance can be easily adjusted because it can be controlled by the transmittance of the casting film prepared by the granulation stock solution before granulation or the granulation stock solution.

(4) The tone reproduction range can be expanded by a simple method of granulating particles with adjusted transmittance separately and mixing the particles,
The graininess of the print is improved.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view for explaining an example of a conventional electrostatic developing method using image forming particles, and FIGS. 2 and 3 are electrostatic developing methods using image forming particles of the present invention. Longitudinal sectional views for explaining an example, FIG. 4, FIG. 5, FIG. 6 and FIG. 7 show transmission spectra of particles used in Examples. 6 ... Photoconductor, 7, 8 ... Image forming particles, 9 ... Dielectric material, 10 ... Corona charger.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Takashima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP 53-15140 (JP, A) JP 54-123956 (JP, A)

Claims (4)

[Claims] 1. An electrostatic device in which light-transmissive particles are dispersed in a uniform thickness on a photosensitive material that responds to light irradiation, and an optical image of an original is exposed to the photosensitive material through the light-transmissive particles. Particles used in a dynamic image forming method, which are not fixed to an image forming part, contain a sublimable or vaporizable dye, and have a particle size at which the transmittance of particles at least in the visible light region is substantially equal and different in particle size. An image-forming particle comprising a mixture of a plurality of types. 2. The image-forming particles according to claim 1, wherein the sublimable or vaporizable dye is a sublimable or vaporizable color former which reacts with a color developing material to form a color. 3. The sublimation or vaporizable color former as claimed in claim 1, wherein the light-transmissive particles are colored and selectively transmit light and contain a sublimable or vaporizable color former which forms a complementary color. Image-forming particles of. 4. The image-forming particles according to any one of claims 1 to 3, wherein the light-transmissive particles have a specific resistance of 10 ¹⁰ Ωcm or less.