FR2510775A1 - PHOTOCONDUCTIVE COMPOSITION SENSITIVE TO AQUEOUS COMPOSITIONS - Google Patents

Abstract

THE INVENTION RELATES TO A PHOTOCONDUCTIVE COMPOSITION SENSITIVE TO AQUEOUS COMPOSITIONS. THE COMPOSITION ACCORDING TO THE INVENTION INCLUDES A MIXTURE OF: I. AT LEAST ONE INORGANIC PHOTOCONDUCTOR, II. AT LEAST ONE PHOTOCONDUCTIVE ORGANIC PIGMENT, AND III.AT LEAST ONE INSULATING RESIN SENSITIVE TO AQUEOUS COMPOSITIONS. APPLICATIONS: MANUFACTURE OF LITHOGRAPHIC PRINTING PLATES.

Description

The present invention relates to microparticles

  lithographic printing, more particularly a photoconductive insulating composition sensitive to aqueous compositions useful in the preparation of electrographic elements, these elements, a method for preparing lithographic printing plates from these electrophotographic elements and plates

  lithographic printing prepared by this method.

  Electrophotographic reproduction is based on the ability of certain normally insulating materials, whose surfaces have been electrically charged, to selectively conduct the electric charge under the effect of imagewise irradiation.

  with formation of an electrostatic latent image on this material.

  In other words, the charge is removed by conduction from above.

  face and through the portions of insulating materials that have been exposed to radiation, while areas of the surface that have not been irradiated retain their initial charges.

  electrostatic latent is an invisible pattern of electrostatic charge

  produced in a usual method of exposure, for example by means of projection through a lens or contact-pulling methods, the charge density in the various areas of the surface being a function of the intensity of irradiation in said areas during exposure The latent image thus formed can be developed (i.e., made visible) by treatment with a powder (which may or may not be colored and / or mixed with a resinous binder) which is drawn to the non-irradiated areas of the surface that have retained their charges, thus giving a strong contrast between the irradiated (non-image forming) and the nonirradiated zones (forming the image). it resists, after fixation, the compoitionaqueuse "plicated later and avoids the attack of the underlying photoconductive layer by said solution is then fixed permanently visible image on a support on which we want the image The support can be the

  initial support on which the composition was applied during the

  sition or material on which the image is transferred after development.

  Depending on the end use desired * For example, if the final product is to be a lithographic printing plate, the carrier material is a suitable material

  in lithography to which the photo composition is applied

  In exposed cases, the exposed areas are removed from the plate (stripped) after fixation of the image by means of stripping compositions, that is to say aqueous compositions. which attack the exposed photoconductive composition and either dissolve or disperse it so that it no longer adheres to the support material. The electrostatic latent image is formed on the surface of an insulating photoconductive layer carried on a support

  For example, the free surface of the photolayer

  conductive is uniformly charged in the dark, for example by applying a corona discharge, and most of the charge is retained on said surface, due to the insulating nature of the layer, in the absence of irradiation By exposure

  following the image, however, the conductivity of the layer is strong-

  increased in the irradiated areas in proportion to the inten-

  Thus, the surface charge in these areas can "leak", while the charge in non-irradiated areas is not changed. This pattern of charged and uncharged surface areas

  is the electrostatic latent image mentioned above.

  Electrophotographic materials and processes are of great importance in many areas of the graphic arts industry, including the preparation of lithographic printing plates, which have been found to be preferable to others.

  conventional processes that require additional process steps

  preparing a mask or a slide from the initial image before the exposure step This condition has among others the disadvantage of using for the slide

  a film that is expensive (especially if the film uses

  silver halide) and require additional equipment.

  for the preparation of slides in electronic

  graphics, the above step is not necessary because the image is formed on the printing plate directly from the original,

  which results in considerable savings of money and time.

  This increased interest has created a need for appropriate materials to

  making stringent requirements regarding, for example, the spectral range of use (i.e., the range of irradiation wavelengths in which the material is photoconductive), the ease of handling and the reliability in the past, these materials included elemental substances and inorganic substances such as selenium, sulfur, zinc oxide and tellurium.

  and organic substances such as anthracene and anthraquinone.

  The above substances, however, have a number of disadvantages, for example in the areas of the spectral range of use, ease of handling,

  sensitivity to light and stability.

  The foregoing disadvantages have been partly avoided with compositions comprising the substituted oxadiazoles described in U.S. Patent No. 3,189,447 or the substituted oxazoles described in U.S. Patent No. 2,257,203. which may also include insoluble resins in water, as well as photosensitizers to increase their

  sensitivity in visible regions of the spectrum.

  These compositions, however, have the disadvantages of poor resolution and sensitivity to the "pre-exposure" effect.

  and colts high substances.

  "Sensitivity to the pre-exposure effect" relates to the property of certain insulating photoconductive materials whose ability to be charged as well as photoco; iductivity after

  irradiation are temporarily reduced by radiation exposure.

  before electrostatic charging These reduced capacities are

  come to their normal values after the elements have been stored in the dark for a certain period of time. The need for this "dark storage" is disadvantageous either with regard to an increase in "dead time" or because it requires a

additional inventory.

  In addition, the elements comprising the compositions

  photoconductors above may be stripped only by

  Currently, the environmental impact of all industrial processes and materials is examined with great care, this factor may be a limitation

  extreme of the use of these compositions and constitutes a stimulus

  to greater research efforts to produce

  which can be stripped by means of aqueous compositions.

  The present invention overcomes the disadvantages mentioned above by providing a low cost composition which has good spectral sensitivity, good speed, good separating power, is not subject to the pre-exposure effect and can be

  stripped by aqueous compositions.

  An object of the invention is to propose a photoconductive insulating composition having a good spectral sensitivity, a

  good speed and good separating power, which is soluble or

  persable in aqueous compositions.

  Another object of the invention is to propose a

  electrophotographic film with good spectral sensitivity, good speed, good separating power and, after exposure

  following the image and fix, can be stripped by means of composi-

aqueous solutions.

  According to another of its objects, the invention also proposes a low-cost lithographic printing plate having a good separating power. These and other objects of the invention will be partly discussed and will appear partly in the reading.

  of the detailed description of the preferred embodiment.

  According to the invention, the applicant has discovered that it is possible to prepare a photoconductive composition having a good spectral sensitivity, a good speed, a good separating power and which is soluble or dispersible in the aqueous compositions by mixing an inorganic photoconductor, a pigment photoconductive organism and at least one insulating resin which is soluble or

  dispersible in aqueous compositions.

  According to the invention, therefore, a photoconductive composition which is sensitive to aqueous compositions, comprising a mixture of at least one inorganic photoconductor and at least one photoconductive organic pigment, is proposed; and

  III at least one insulating resin sensitive to com: posi-

aqueous solutions.

  Inorganic photoconductors useful according to the invention are any of those known in the art,

  including zinc oxide, titanium dioxide and the like.

  A preferred inorganic photocanductor is zinc oxide.

  The organic photoconductive pigments which can be used according to the invention are known in the art and

  include pigments of the anthraquinone class, pre-

  For example, the Red for Color Index Pigment 168 (for example, the one sold under the name "Monolite Red 2 Y" by the ICI Co Company) and the Orange for the CI Pigment 43 (for example, the one sold as "Indofast" by Hermon Chemical Co., and orange

  GR "Hostaperm" from Hoechst Co).

  The resins sensitive to aqueous compositions (defined as being either soluble or dispersible in the aqueous composition) useful according to the invention are known in the art and include phenol-formaldehyde resins, resins and resins.

  phenoxy, epoxy resins and homo and copolymers include

  containing residues of "vinyl" alcohol (which exists only in polymers), hydroxyalkyl acrylates or methacrylates, vinyl acetate, acrylic monomers, N-vinylpyrrolidone-2, vinylsulfonic acid, , styrene sulfonic acid, acrylamide and its derivatives, maleic anhydride, vinyl ethers, etc. The preferred resins are phenoxy resins (for example the phenoxy resin P Kh11 sold under the name "Bakelite" by Union Carbide Corp) and

  homo or copolymers of polyvinyl acetate.

  The aqueous stripping compositions may be any of those known in the art for

  strip resins sensitive to aqueous compositions, preferably

  alkaline aqueous solutions with a pH greater than 10.

  The use of the above compositions is however limited because of their relatively low speed. According to another embodiment of the invention, it has been found that the speed of the above compositions can be increased by the addition of photosensitizer dyes The photosensitizers which can be used according to the invention include triarylmethane dyes such as Methyl Violet, xanthene dyes such as rhodamines (eg Rhodamine B) and phthalein

  (eg Rose Bengal), and analogues and mixtures thereof.

  A preferred photosensitizer is Rose Bengal.

  In a preferred embodiment, the photoconductive composition comprises from about 3 to about 25 percent by weight of the photoconductive composition.

  inorganic conductor, about 4 to 30% by weight of photo pigment

  organic conductor and about 20 to 80% by weight of the resin sensitive to aqueous compositions, all these percentages being

  based on the weight of the dried coating.

  In a particularly preferred embodiment, the composition further comprises about 0.5 to 5% of the total weight of the dried coating with sensitizing dyes.

  In addition, if desired, the photo composition

  The conductive agent may contain other additives selected from other resins, i.e., resins which are insensitive to aqueous compositions, reactive diluents which are irradiated to resins sensitive to aqueous compositions, or "other resins, plasticizers, fillers, dyes, thermal and / or photolytic polymerization initiators,

  thermal polymerization inhibitors, etc., and mixtures thereof.

  Other useful resins according to the invention can be represented by polystyrene, ABS terpolymers, ethylene-propylene rubbers, etc. Reactive diluents may be any of those known in the art, such as vinyl acetate, styrene, alkyl acrylates and methacrylates, maleic anhydride, and the like. According to the invention, there is also provided an electrophotographic element comprising an electroconductive support, on at least a part of the surface of which any one of

  photoconductive compositions of the invention described above.

  The electricity carrier may include any of those known in the art, including metal foils, glass plates, paper sheets or fabrics, or plastic sheets or fabrics,

  especially those made of electroconductive resins.

  The substrates, depending on the desired end use of the elements, may be opaque, translucent or transparent. If an absorbent support such as paper is used, it is desirable that it be pretreated to avoid the absorption of the coating solution. The pretreatment may be carried out, for example, by adsorption of methylcellulose or polyvinyl alcohol using solutions

  aqueous or polyamides with hydroalcoholic solutions.

  The photoconductive compositions may be applied to the support by any means known in the art, for example projection, meniscus, reverse coating by wire wound on a rod, printing coating, vortex coating from solutions in the art. suitable solvents or melt coating with the compositions

undissolved photoconductors.

  The present invention also relates to a method for producing lithographic printing plates which comprises the following steps: electrostatically charging the free surface of the photoconductive layers of any of the above elements, prepared according to the invention, the carrier conductor comprising a material suitable for lithography; The surface charged to

  radiation, the charge being discharged into the exposed areas proportionately

  tionally to the intensity of the radiation, to give an electrostatic latent image; III develops said latent image to give a visible image; IV is fixed said visible image; and the exposed photoconductive composition is removed by treatment with a suitable aqueous composition to produce

the desired printing plate.

  If desired, steps I through IV can be repeated several times before proceeding to step V, using different masks to superimpose several images in the final plate, although the coatings are by themselves insensitive radiation, the application to them of a positive or negative electrostatic charge, for example by means of a

  corona discharge, makes them sensitive to radiation.

  The electrostatic latent image is formed on the irradiation-charged element thereof according to the image. The radiation may be selected throughout the electromagnetic spectrum, including visible light, UV or IR radiation, and electron beams. favorite are in the UV regions and

visible light of the spectrum.

  The development of the latent electrostatic image can be carried out by any means known in the art, including the treatment of the imagewise exposed element with liquid or dry toners or developers, such as filled resins. by a dye and carbon black or-the colored resin

  described in U.S. Patent No. 3,189,447.

  The developed (visible) image is then made permanent (i.e., fixed), for example by heating in the presence or absence of solvent vapors or by steam treatment.

and / or the pressure.

  The image element thus fixed is then transformed into the desired lithographic printing plate by treatment with a suitable aqueous composition, preferably an aqueous alkali solution preferably having a fold greater than 10, to eliminate the

  photoconductive composition which is soluble or dispersible in the

  Aqueous compositions that have been exposed If desired, the composition

  aqueous solution may also contain organic solvents to facilitate

  the wetting of the resinous components of the photo-

  conductive, which facilitates the removal of the exposed composition

of the support.

  The following examples illustrate the invention without

however, limit its scope.

EXAMPLE 1

  A mixture comprising 10.0 g of Red 2 Y "Monolite", 8.0 g of ZnO, 0.1 g of Rose Bengal, 50 ml of 2-methoxyethanol sold under the name "Methyl Cellosolve" is milled for 16 hours ( MC) and 100 ml of methyl ethyl ketone (MEK) in a ball mill (using "borundum" beads). A solution comprising 40.0 g of a carboxylated vinyl acetate terpolymer is then added to the above mixture. manufactured by National Starch and Chemical Corp., Bridgewater, NJ, under the name "Resyn 28-2930", ml of MC and 100 ml of m EC Gold then grinds the resulting mixture for a further 3 h. above, by means of a rod on which is wound a wire n 18, on a sheet of aluminum 12 gauge, 36.83 cm x 55.88 cm, which first

  was seeded with pumice and anodized.

  result using a hot air blower 4 and then

  heated at 100 C for 1/2 h to obtain the

desired photographic.

  The free insulating surface of the above element is then electrostatically charged by means of a corona discharge, imagewise exposed by means of a visible light argon laser (Muirhead Company, Inc.). The resulting plate is then stripped to remove the exposed (non-imagewise) portions of the coating by means of an aqueous alkaline solution. Stripping The stripped plate is then glued by conventional means and used on an "ATF Chief" press to produce

121,000 acceptable impressions.

EXAMPLE 2

  Example 1 is repeated except that 5.0 g of "esyn 28-2930" is replaced by 0 g of phenoxy resin PKHHII "Bakelite", the red "Monolite" with 10.0 g of Orange GR ". Hostaperm "and we only use

  4.0 g of Zn O contains similar results.

  It is understood that the invention is not limited to

  preferred embodiments described above as illustrative

  and that those skilled in the art may make various modifications and changes thereto without departing from the scope and spirit of the invention.

Claims (11)

R E V E N D I C A T IO N S   A photoconductive composition sensitive to aqueous compositions, characterized in that it comprises a mixture of at least one inorganic photoconductor, II at least one photoconductive organic pigment, and   III at least one insulating resin sensitive to aqueous solutions.   Photoconductive composition according to claim 1,   characterized in that it further comprises a sensitizing dye tor.   Photoconductive composition according to claim 2, characterized in that said sensitizing dye is selected from   triarylmethane dyes and xanthene dyes.   4 Photoconductive composition according to claim 3, characterized in that said sensitizing dye is Rose Bengal. Photoconductive composition according to claim 1 or 2, characterized in that it further comprises at least one additive chosen from dyes, other resins, reactive diluents, plasticizers, fillers, thermal and / or photolytic polymerization initiators, thermal polymerization inhibitors and analogs.   Photoconductive composition according to claim 1 or 2, characterized in that said organic photoconductor is chosen   among ZnO, TiO 2 and the like.   7 photoconductive composition according to claim 6 characterized in that said photoconductor is Zn O. 8 photoconductive composition according to claim 1 or 2, characterized in that said photoconductive organic pigment is an anthraquinone pigment.   9 photoconductive composition according to claim 8, characterized in that said pigment is selected from the red for   Pigment C 168, Orange for Pigment C 43 and the like.   Photoconductive composition according to claim 1 or 2, characterized in that said resin is chosen from phenol-formaldehyde resins, phenoxy resins, epoxy resins and homo and copolymers comprising residues of vinyl alcohol, acrylates or methacrylates of hydroxyalkyls, vinyl acetate, acrylic monomers, Nvinylpyrrolidone-2, vinylsulfonic acid, styrenesulfonic acid, acrylamide and its derivatives, maleic anhydride, vinyl ethers and the like. 11 Photoconductive composition according to claim 2, characterized in that said inorganic photoconductor is Zn O, the organic photoconductor is Pigment Red I 168   or orange for Pigment C I 43, the resin is a copolymer containing   carboxylated polyvinyl acetate and the sensitizer is the Rose Bengal.   Electrophotographic element characterized in that it comprises a conductive base material on at least one face   a photoconductive composition sensitive to aqueous compositions comprising   At least one inorganic photoconductor,   II at least one photoconductive organic pigment, and   III at least one insulating resin sensitive to aqueous conditions.   Element according to claim 12, characterized in that   said composition further comprises a sensitizing dye.   14 Process for making lithographic printing plates   graphic, characterized in that it comprises the following steps: electrostatically charging the free surface of the photoconductive layers of an element prepared according to claim 12 or 13, the conductive support comprising a suitable material in lithography; The surface charged with radiation is exposed according to the image, the charge being discharged into the exposed areas in proportion to the intensity of the radiation, to give an electrostatic latent image; III develops said latent image to give a visible image; IV is fixed said visible image; and the exposed photoconductive composition is removed by treatment with a suitable aqueous composition to produce the desired printing plate.   Process according to Claim 14, characterized in that steps I to IV are repeated 1 to 6 times, the image being   different in each of the steps II.   16 Lithographic printing plate according to the claim.   dication 14, characterized in that said base material is selected from aluminum and its alloys} sheets of plastic material   lined with metal foil, and the like.