BE600338A - - Google Patents

Description

       

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    Process for preparing photographic negatives from relief printing shapes using a developing resist,
The present invention relates to graphic arts and more particularly to photomechanical processes in the field of graphic arts. It relates more particularly still to improvements to the processes for preparing photographic negatives intended for the making of photomechanical printing plates.



   It is known to reproduce printing plates for all printing processes by photographing a proof taken from a letterpress plate or by photographing a prepared for e direct so as to obtain a negative which can be used to prepare a photomechanical photograph.

   These nega-

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 tifs generally called "line" negatives are placed in contact with a plate coated with a light sensitive emulsion. Exposure of the plate to a light source through the negative insolubilizes the exposed regions so as to form reserves for acid attack for chemical differentiation which, after appropriate treatment, gives a printing block suitable for printing processes, such as letterpress processes, gravure or offset lithography. require preparation,

   precise printing forms to obtain a satisfactory proof and precise cameras to transmit all the details of the characters to the negative.



  As the majority of all text compositions today are cast on type composition machines, it is necessary to transform that composition into a suitable negative or positive before the text can be used in a photomechanical cliché. This transparency can then be used to prepare any number of reproductions.



   A simplified and more straightforward process for obtaining a negative from an existing printing form, for making photomechanical lichés., Is to print a print directly on film coated with a photographic gelatin halide emulsion. After which, using any hydrophobic printing ink, a resist is formed which prevents the action of the processing solutions from the regions representing the printing regions of the cliché. In the case of emulsion layers of the cliché. gelatin silver halide, photographic developing agents develop silver in non-printing regions assuming, of course, that the operation is performed under normal lighting which, in fact, is

   instantly exposes the silver halide layer. By dissolving, wiping or by some other means (eg reduction of surface tension using wetting agents to allow penetration) to remove the imprint. then fixing the film? using a bath of fixa @ e phote-

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 In ordinary graphics, the silver halide which was protected by the ink during development is removed to provide transparent regions and the film effectively becomes an accurate photographic negative of the printing plate.

   The inked prints can be prepared in an ordinary proofing press as known to those skilled in the art. Cameras or darkrooms are not required in the latter process and films are normally handled under normal conditions. ordinary lighting.

   In the case of pelli-
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 cules coated with gelatin silver halide enulsion sensitive to light, the latter must be exposed to the fuze so as to force black silver except in the remainder where the printing covered by the ink prevents the 'development agent to act to reduce silver halide into silver. Ink, after
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 developing, is removed with a suitable solvent and the film is then immersed in a fixing composition which dissolves the silver halide which has not been subjected to the action of the agent.
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 development and form clear regions was a negative of the impression.

   Obviously, as light is not used in the making of 1-1i * .aage, inks or other pigmented compounds need not be. the action of the compositions of
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 traitemeyt can be used. It is also evident that a positive can be obtained by making a print resist followed by fixing, removing the ink reserve and developing.
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 In this case, the print is developed until it obtains black silver and the non-internal regions remain transparent thus forming nn. positive of material 1: oprf, n4e. It is this process of direct inking on a layer of gelatin-halozenic silver to which the present invention relates.



   Although the direct inking process on a? gelatin silver halide layer eliminates the need for e @ ploi
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 cameras and the processing of the rellzemle expo- @

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 Sized under photograD :: ia'è "! '3 black hemp conditions, the system" does have some serious drawbacks which is "! 1er". particularly evident when used in conjunction with modern printing presses. Instead of the usual .'retaillâmes images sensitized using bichro gelatin.,. At: 5e, the more recent images are made up of photopoljrm4risable layers of the type described in Belgian Patents Nos. 525,225 and 559,052.
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  Printing clichés composed of these photopolymerizable layers are easy to prepare and reproduce more faithfully! e: ¯ and the object at 1 '": 11) r11: 1st from the negative to which the picture is)') tographic" the '1t exposed (1'; e the pictures already known. The difficulties encountered in the making of Negatives by direct inking on the gelatin silver halide layers are of two types.

   Ink crushing is one of the difficulties that results in loss of fidelity and gray print regions
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 during printing of the proof and year ec.ale.7.ent 'unp tend to be a little thicker with less sharp centers than in the original. -
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 bearing paper, for example in istallatio'5 s 1'i: ï.riaerie industrial, I'at:

  aosnnere almost always contains significant amounts of down and usir.Cec. -causes the formation of discontinuous inked i.nages because Cl.'e es 7rt¯c? The ink in the air mixes with the ink on the printing press rolls and is also deposited on the surfaces. preventing satisfactory transfer of ink. When dealing with films containing images of this kind, only
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 negatives that leave q to be desired.

   An i.nprierie photograph exhibited from such a negative shows broken lines and imperfect characters and also imitations and solids.
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 It is obvious, for this reason, that the prints made from negatives soiled with down and
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 dust do not reproduce faithful copies and ar -aī ^ the eye of the original.

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   The invention aims to provide: an improved process for making negatives for photomechanical printing; a process which allows a simple and safe preparation of high quality negatives from relief printing shapes; a method which avoids the drawbacks of the known methods associated with particles of fluff and dust; a process which eliminates the unwanted effects of ink crushing.



   These objects are achieved in the present invention which comprises a process for preparing high quality negatives from a raised printing form, for example a line, halftone or line and halftone plate combined or a letterpress form, according to which one covers the surface in relief in the form of a light layer of a hydrophobic development resist, one draws a first print of the surface of the emulsion on a transparent flexible film covered with a layer of photographic emulsion sensitive to light, this relief surface of the shape is cleaned to eliminate the development reserve that may remain,

   the relief surface is covered again with a light layer of the developing resist and a second print is made on the film in exact repeating with the first, the emulsion layer is developed in the regions not covered with the resist. development, then the developing resist and the photographic emulsion layer below this resist are removed from the film.



   High quality negatives can be obtained by this process to take advantage of the novel polymeric printing plates noted above. The invention is a novel inking process which will be described in detail later. In this process, the cliché or the typographic form to be reproduced in the usual proofing press is first lightly inked, then a proof is printed on a film coated with an emulsion.

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 photo printing by applying an impression thin enough to minimize the tendency to smear the ink to a minimum. The printing plate is then wiped or washed to remove the layer of ink which remains.

   The cliché is then slightly re-inked and a second impression is made on the film in exact registration with the first. The intermediate phase of washing the cliché and second inking is used to move the location of the defects caused by dust and down on the printing form so that in two or more inks there is obtained a continuous film of ink reproducing the printing surface and serving as a developing resist on the gelatin silver halide layer of the film. It is thus possible to obtain a good quality conversion of inverted regions of large dimensions and solids as well as texts and halftone.

   Any type of gelatin silver halide emulsion can be used, including high contrast negative materials and direct positive films. The latter films are particularly suitable because they are sensitive to prolonged handling in the environment. the proofing workshop.

   Chemical blackening agents, such as sodium sulfide, can be used instead of developing agents, eliminating the need for light exposure. Normal room lighting is suitable, but high intensity fluorescent lamps and mercury lamps should not be used during the proof printing operation, especially in the case of high speed emulsions or -1 $ direct positive emulsions due to the development process independent photolytic silver format.



   The type of ink used is generally a matter of personal choice, any hydrophobic ink which can be satisfactorily transferred from the printing form to the gelatin silver halide coated film to form a developing resist may be suitable. Numerous lithographic inks are commercially available. An ink

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 Suitable can also be prepared by melting together 10 parts petroleum jelly (petroleum jelly), 1/2 part amorphous silica and 1/3 part carbon black.

   The inks do not necessarily have to be used as a stock of processing solution and can include photographic desensitizers which act directly on the emulsion to prevent the development of image regions. Resists can also be prepared without the inclusion of a pigment or desensitizer, for example by melting together one part beeswax and one part petroleum jelly.



   The processing solutions, i.e., alkaline photographic developing agerts and acidic photographic fixing agents, may be of the conventional type and are selected for maximum effectiveness with the particular silver gelatin halide emulsion chosen.



   The invention is illustrated in the following examples, EXAMPLE I.



   A good quality printer form is stuck in a proof press capable of printing with exact registration.



    After: =: Normal preparation and test prints, a positive transparent photographic film is attached directly to the cylinder of the proof plate. A thin layer of ercre is then printed on the emulsion side of the film. The printing form is then wiped with an ink solvent applied sparingly to a down-free cloth and the form is inked again. A second thin application of esc ink printed in exact registration on the first print.

   The film element is then placed emulsion side up in a cuvette containing a developing agent of the following composition:

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Water 1 liter
Sodium sulphite (anhydrous) 120.0 g
Paraformaldehyde 30.0 g
Potassium metabisulphite 150.0 g
Boric acid, crystals 30.0 g
Hydroquinone 90.0 g
Potassium bromide 6.0 g
Water to make 2 liters The cuvette is shaken for about 45 seconds to develop the film uniformly and obtain a maximum density of at least 3.5. The film is then placed in a cuvette containing an acid stopping bath composed of 5% acetic acid and stirred for about 5 seconds.

   After this treatment, a cotton swab moistened with a 50-50 mixture of ethyl alcohol and hyposulphite fixing bath is used to remove the ink. Care is taken to remove all ink by inverting the ink. tampon and rubbing again. The film is then placed in a cuvette containing a fixing bath of the following composition:
Water (15 C) 600.0 cm3
Sodium hyposulfite (anhydrous) 15.0 g
Sodium sulphite (anhydrous) 18.0 g
Potassium alum 20.0 g
Glacial acetic acid 12.0 g
Water to make 1.0 liter
The film is stirred in this bath for about 1 minute or until the area which has been covered with ink is cleaned. The film is then washed and dried by the usual methods. The resulting negative is an excellent reproduction of the original printing form.

   The negative is placed on a photopolymerizable printing element prepared as described in Example IV of Belles Patents Nos. 559,052 and 580,820.



  The element and negative are placed in an empty frame and

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 exposed for 12 seconds to 0.27 watts of actnic radiation per cm2 using a high pressure 1800 watt mercury arc lamp. After exposure, the unexposed regions of the element are removed by jet washing for 8 minutes using a 0.08N aqueous solution of sodium hydroxide. A clear polymerized relief printing plate is obtained, the raised regions corresponding to the transparent regions and to the reliefs or printing regions of the original cliché. The resulting plate, used in a conventional printing press, gives good quality reproductions comparable to those obtained from the original plate.

   There are no pinholes or other defects in the text, the halftone or the solid regions of the image, defects however frequent when the inking is carried out in a single pass. Of course, coarse surface defects, such as craters, nicks or other imperfections in the printing surface are reproduced. During the preparation of the negative, a control negative is prepared under the same conditions, except that only one normally inked impression is made on the proof press. The other conditions are the same. A photopolymerized printing plate obtained from the processed negative prints characters that are larger and have more jagged edges than those of the original.

   This defect corresponds to the crushing of the ink and also produces prints in which the solid parts and characters are unbroken where the ink could not be satisfactorily transferred to the film due to the presence of particles of fluff and dust in the ink and on the plate.



  EXAMPLE II.



   Example I is repeated using, instead of the direct positive film, a high contrast gelatin-chlorobrone silver film. After inking as described in Example I, the film element is placed, side

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 emulsion upwards, in a cuvette containing a developing agent of the following composition:
Water 500 cm3 Methyl-p-aminophenol 3.0 g
Sodium sulphite (anhydrous) 45.0 g
Hydroquinone 12.0 g
Sodium carbonate (anhydrous) 67.5 g
Potassium bromide 1.9 g
Water to make 2.0 liters
The cuvette is stirred for about 20 seconds to develop the film evenly and achieve a maximum density of at least 3.5.

   Processing of the film is then continued as described in Example I, including ink removal, fixing, washing, drying and exposure. The raised polymerized printing cliché has characteristics similar to those of an exposed cliché? through the negative formed using the direct positive transparent film.



   An important aspect of the invention is that any film coated with a gelatin silver halide emulsion can be used in the process. For example, high contrast films suitable for graphic arts can be employed. As noted above, when using high speed and / or very sensitive films, attenuated light is desirable to reduce the possibility of photolytic silver formation which would occur in the layer in the regions ultimately covered. of enere when drawing a proof. During the fixing operation, after the ink has been removed, this spontaneous forged silver would remain and could not be removed by the fixing solution.

   This, of course, would not achieve a clear image without the flaws of the negative on the click '-.' of photopoly @ risable i @ ri @ erie. The layer of enulsiop intended to receive @ ir

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 1-lir., Ink pressure does not necessarily have to be t = f "-crr.e. on a transparent film. A translucent support; <-" j *: be used and may have auxiliary layers in. folds of the esiulsion layer to obtain translucency. The emulsion bowl itself may contain d4'rst + t agents; '5 <;;!' ..! 12.:1 has a matte surface which can help prevent ink crushing.



  This matte surface also helps to allow air e..r; sr.ë to escape in order to ensure rapid contact ext == the n4çzif and the cliché 'when printing is performed dar-e es 2;!. S
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 empty.
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  Any raised surface, cut - ;;:,: Co; ' or planographic can be used co = -ie forre '..¯ = :. e: -. o-r receive the print. For example, co ,, ipos: Lti5ns of earzeters (Linotype and Intertype), individual characters t: and
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 Foundry), photogravures and electrotypes, and ci -! -
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 lithographic keys can be used. L.rc ??! '; j -t be executed from clichés in zinc, copper, <- =% 1 "m, ragn4sit ,, <, steel, nickel, chrome, brass, metal Torir ca = zc;% = 4s
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 printing, plastic, etc.
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  Many variations can be made on the negatives of the new process of the invention. ¯¯¯ = ¯, # printing clichés upside down or upside down: - ': - r ?, r obtained by exposing the plate photopo1.7;, C.é :: - i:! :: :: ", - ¯¯ ¯; r ie on the emulsion side or through the side without eoilsicr of re12i ==; Ie
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 negative processed.
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  When you want to make c1ic?:; Rf e-fe -.:::- '? for example, the inked film can be processed 4 '= ce <== bzz fixing, then after washing and eliinziian. of the ink, 47 :: '? ment of the emulsion which was covered by 1' c ==, I. = c case, the regions reco, intoxicated by the ink dee.:. ± 'iz.-é, =, t we get a transparent positive. By imre5ic d ', -j = -é appropriate from this film, we paint = -eWr ¯ -:, ¯ :: -:' A whose print regions scr L ec c7x 4: --- lcr

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 raised non-printing regions.



   The film backing for the emulsion layers used in the new process can be any suitable transparent plastic material. For example, cellulose carriers, such as cellulose acetate, cellulose triacetate, mixed esters of cellulose, etc. can be used. Polymerized vinyl compounds, for example copolymerized vinyl acetate and vinyl chloride, polystyrene and polymerized acrylates can also be mentioned. An important aspect which determines the choice of the appropriate medium is the stability of dimensions due to the need for exact registration of the inking operation and of the printing operation.

   The film formed from the product of polyesterification of a dicarboxylic acid and a dihydric alcohol prepared according to Belgian Patent No. 538,815 and the patents cited therein may be suitable. Other suitable carriers are the polyethylene terephthalate / isophthalates of UK patent 766,290 and Canadian patent 562,672 and those obtainable by condensing terephthalic acid and dimethyl terephthalate with propylene glycol, diethylene glycol, tetramethylene glycol or cyclohexane 1,4-dimethanol (hexahydro-p-xylene alcohol). The above polyester films are particularly suitable because they have stable dimensions.



   Of course, the double inking process can also be applied to non-photographic but chemically sensitized films which, upon contact with a suitable reagent, form transparent images which can be used to expose the printing plates described herein. -above.



   The main advantage of the new process of the invention is that it avoids the loss of fine details and the pre-exercise of small spots due to incomplete inking, an inherent defect.

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 to known methods.



    CLAIMS. l.- Process for preparing high quality photographic negatives from a raised printing form, characterized in that the relief surface of this form is covered with a light layer of a hydrophobic developing resist, takes a first print on the emulsion surface of a transparent, flexible film, covered with a layer of photographic emulsion sensitive to light, the relief surface of the form is cleaned to remove the remainder of the development reserve, the raised surface is covered with a second light layer of the developing resist and a second print is made on the film in exact registration with the first print, the emulsion layer is developed in the regions not covered with the developing resist ;

   then the film is freed from this resist and from the underlying photographic emulsion layer.


    

Claims (1)

2. - Method according to claim 1, characterized in that the developing reserve is a hydrophobic ink. 3. - Method according to claim 1, characterized in that the photographic film is a high contrast gelatin-silver chlorobromide film. 4. A method according to claim 1, characterized in that the light-sensitive photographic emulsion is a direct positive emulsion. 5.- A method of preparing high quality photographic negatives upright from a raised printing form, characterized in that the raised surface of this form is covered with a light layer of hydrophobic development resist, a first print is taken on the emulsion surface of a flexible transparent film coated with a layer of light-sensitive photographic emulsion, the relief surface of the form is cleaned to remove the remainder of the <Desc / Clms Page number 14> development reserve, the raised surface is covered again with a light layer of development reserve and a second proof is printed on the film in exact registration with the first, the emulsion is removed from the film in the regions not covered by the developing resist, the developing resist is removed from the film and the photographic emulsion is developed on the film previously coated with the developing resist. 6. - Method according to claim 4, characterized in that the developing reserve is a hydrophobic ink. 7. A method according to claim 4, characterized in that the photographic film is a high contrast gelatin-silver chlorobromide film.