NO762006L - - Google Patents

Description

Photosensitive compositions.

The present invention generally relates to radiation-sensitive structures, more particularly to a photosensitive, single-layer film structure which is suitable for the production of water-processable printing plates and similar graphic elements.

Many different photosensitive systems are known for producing lithographic plates. Diazo compounds are often used as the photosensitive component in such systems. The diazo compounds can be processed so that they acquire several properties which enable them to be advantageously used for the production of graphic elements, e.g. they can be produced at low cost, have a long shelf life, they have good water solubility and good photosensitivity. However, the diazo compounds' receptivity to printing ink is significantly reduced by contact with water, and the durability of diazo resins is relatively low. To avoid this problem, attempts have been made to use varnish-based developers, or by coating the diazo compound with an ultraviolet-transmitting varnish or another material. This usually gives good results, but results, on the other hand, in losing the ability to easily water process the diazo compound ■ plates, and in certain cases it is desirable or necessary

you with increased exposure time. Furthermore, diazo compounds lack sufficient bonding strength to smooth surfaces and it has therefore been necessary to use granular substrates to increase the mechanical bonding of these photosensitive coatings, in order to achieve the desired long printing times.

Other known photosensitive systems use photopolymers which have both high and good receptivity to printing ink and long duration. These systems, however, usually require special solvents to develop the plates, thereby increasing the complexity of the system compared to simple water development systems, and in addition, you get unwanted waste problems.

In order to avoid the above-mentioned problems, a new photosensitive film structure has now been found which has unique and highly desirable properties.

The present invention thus relates to a single-layer film structure which includes a first phase dispersed in a matrix composed of a second phase. The first phase is a photosensitive material that changes in solubility in a selected solvent upon exposure to light. The second phase is composed of a material that is not photosensitive and not soluble in said solvent.

It has been found that such a photosensitive composition can be made selectively permeable by pictorial exposure to light. Subsequently, the film composition according to the present invention can be used for a number of purposes where selective permeability to liquids is necessary or desirable.

It is therefore an aim of the present invention to provide a photosensitive structure which can be made selectively permeable to liquids upon exposure to light.

It is also a purpose of the present invention to provide a photosensitive structure where the relative amount of the active photosensitive material is a smaller part of the mass and volume of the structure, whereby significant advantages are obtained with respect to production and costs.

It is also a purpose of the present invention to provide photosensitive film structures which can be developed with the aid of water after exposure to light, without using organic or inorganic solvents. '

It is also a purpose of the present invention to provide a photosensitive, single-layer film composition which can be used in the production of lithographic or offset printing plates.

It is also a purpose of the present invention to provide lithographic printing plates where the receptivity and durability of the image areas are relatively independent of exposure and developing agents in the medium.

It is also a purpose of the present invention to provide a unique photo-resistant material.

It is also a purpose of the present invention to provide a photosensitive film composition which has a high bond strength to a number of surfaces.

The new features of the present invention appear from the following claims. The invention as such, its purposes and advantages can, however, be most easily understood with reference to the following description and the attached drawings, where figures 1, 2 and 3 are enlarged cross-sections, each illustrating the microstructure during different stages of development, in the photosensitive system according to the present invention . However, it should be noted that these schematic sketches only serve to illustrate the structure and mechanism of the present invention and the drawings thus do not limit the invention.

The photosensitive single-layer film composition according to the present invention consists of a first phase dispersed in a matrix composed of a second phase.

The first phase is photosensitive and can change solubility with respect to a given solvent. The second phase is not photosensitive and is chosen so that it is relatively insoluble in the solvent for the first phase. Thus, when a so-called "two-phase structure" is described, this concerns the solvent used. This means that the solvent must be able to selectively act either on the exposed or unexposed photosensitive "first phase", but must be relatively passive in relation to the matrix in said "second phase". The photosensitive, single-layer film composition according to the present invention can best be described as a grid cast from an emulsion dispersion. Several microstructure designs or lattices can be formed from these emulsion dispersions, and these are each described separately, as they each have different advantages.

One of these microstructures included in the present invention is illustrated schematically in fig. 1. This lattice is cast from a dispersion consisting of coated spheres or very near spheres, and is shown as a coating on

a suitable substrate. In this system, the photosensitive first phase is thus specified as a coating on said second phase or matrix material.

The coating material that is selected must be able to wet and coat the second phase, and this coating material is soluble in the selected solvent, while said second phase is insoluble in this solvent. After actinic exposure, however, the first phase will also become insoluble. After an image-wise exposure of the photo-sensitive material and when a selected solvent is used, the unexposed areas of the grid will thus be wetted and saturated by the solvent due to said first phase still being insoluble in these areas. This thorough wetting or saturation of the lattice means that both the first and second phase material can be physically removed from the substrate by brushing, ironing or the like.

The wettability and dispersion characteristics of the substrate with water as well as the capillary pressure at the interface between the lattice and the substrate are assumed to help during this "development" process and therefore provide additional system control.

Another microstructure according to the present invention is schematically illustrated in fig. 2. In this lattice system, the cavity between the spheres of said second phase is filled with a first phase of photosensitive material. The tight packing of the balls, as shown in fig. 2, results in a void volume of approx. 25%, when the balls are essentially the same size. This theoretical cavity is independent of the sphere size itself, as long as the uniformity of the spheres is maintained. As shown in the drawing, the cavity in the matrix can be filled with

a variety of photosensitive materials, such as a silver halide/

gelatin, dichromate colloids, photopolymers, diazo-colloid cysts and the like.

By using this grid system, an image-like exposure in the exposed areas will provide an effective binding of the second phase material, while unexposed areas remain water-soluble and will consequently be able to provide the desired saturation and subsequent development.

Another structure that can be used in the present invention is shown in fig. 3. In this system, said photosensitive first phase material is dispersed inside a grid or system of spheres of varying diameter.

As mentioned above, a matrix of one-dimensional spheres will have cavities of approx. 25%. By using spheres of varying diameter, this cavity is reduced, whereby smaller quantities of the first phase material can be used during the production of the photosensitive structure. This can of course be highly desirable in order to be able to reduce the costs and to be able to let the physical and chemical properties of the second phase dominate the entire photosensitive structure; properties.

The photosensitive material which can be used in the present invention includes any photosensitive compound, where an exposure to electromagnetic radiation produces a change with respect to the solubility in a given solvent. The photosensitive compound must be chosen so that it is chemically compatible with the matrix emulsion, so that a mixture produces a macroscopic two-phase lattice system. Photosensitive compounds which can be used in the present invention include aromatic diazo compounds, photosensitive dyes, azo compounds, dichromates, photopolymers and silver halide gelatin systems. Other materials that can be used as the aforementioned first phase are described, e.g. in the U.S. Patent Nos. 2,063,631 and 2,679,478 and in the book Light Sensitive Systems, by J. Kosar, published by John Wiley & Sons (1965). Particularly preferred materials which can be used in said first phase include condensation products of carbonyl compounds, such as formaldehyde or paraformaldehyde, and a diazo compound such as 4-diazo-1,1'-diphenylamine. Such condensation products are available under the trademarks Diazo No4 and Diazo No. 4L. from Fairmont Chemical Co., Newark, New Jersey.

The second phase in the photosensitive structure according to the present invention is a matrix material in which the first phase is dispersed. The matrix material is the main component of the structure and is chosen so that it matches the physical properties desired in the final product. These properties include, inter alia: durability or physical toughness, the ability to adhere to substrates, water repellency (and consequently pressure-blackening), permeability, solvent resistance, particle size, viscosity, solids content, heat-insulating properties, film- forming properties and molecular weight;

Some of the homopolymers or copolymers which in an emulsion-dispersion form which can be used for the production of the matrix structure according to the present invention include i.a. acrylic, copolymers of copolymers of acetate and. ethylene, copolymers of styrene and acrylates, polyvinyl acetates, as well as copolymers of vinyl acetate and acrylates. Each of these can be used with or without protective colloids, wetting agents, emollients or other modifying compounds.

According to a preferred embodiment of the present invention, the photosensitive film structure can be produced by casting, either as a self-supporting film or on a suitable substrate, an emulsion containing water, a suitable diazo compound, and a PVA acrylate emulsion. When dried, the resulting film will consist of a polymeric matrix where the diazo compound is applied to the PVA acrylate balls and/or fills the cavity between them. This matrix will form a water-insoluble film, while the diazophore compound only becomes water-insoluble upon exposure to light.

A very important area of application for the present invention is the production of lithographic plates for offset printing. Offset printing plates can be produced by using a hydrophilic substrate, such as silicate aluminum or the like, and a composition according to

lying invention cast or ironed on as a film on

its surface. The aforementioned copolymer matrix of vinyl acetate and a long-chain acrylate provides a flexible, non-re-emulsifiable film with high water repellency. Surprisingly, an addition of the diazo resin in the spaces between this polymeric matrix will result in thin layers of the composition being washed away from the substrate after a pictorial exposure to light. The areas of the film that have been exposed to light are not removed from the substrate during this washing or scrubbing process, while the parts of the film that have not been exposed to light can be easily removed. Furthermore, the light-exposed areas will have the desired printing ink receptivity properties and effective

tive bond, even to non-porous surfaces, such as silicified, ungrained aluminium.

It is assumed that the image-wise light exposure results in a selective permeability to the given solvent. When you e.g. has a diazo-PVA-acrylate matrix composition, exposure to light will cause the diazo compound to become insoluble in the parts of the film that have been exposed to light, so that the entire film in these areas becomes impermeable to water. The diazo compound will, on the other hand, in the parts of the film that are not exposed to light, remain water-soluble, whereby a water-permeable PVA/acrylate matrix is obtained. This permeability to water creates high internal tensions which cause the film to split off or simply cause the binding ability to fail. The photosensitive film composition according to the present invention is thus made selectively permeable to water by exposure from a slide.

When a photosensitive structure of the type described here is used on a hydrophilic substrate in the production of lithographic printing plates, the parts of the composition which are not exposed to light can be easily removed during the water development step. When this water-insoluble matrix can be removed from the substrate, it is assumed that this is partly due to the water affecting the interphase between the matrix and the substrate, as mentioned above, and the water can reach this interphase due to the fact that the unexposed parts of the film are permeable to water. As the PVA-acrylate copolymer matrix is hydrophobic (and oleophilic), photo-sensitive film compositions according to the present invention will

nelse be ideally suited for use during lithographic offset printing processes. As the said matrix materials are not light sensitive and are not affected by light exposure and the development itself, they can thus be chosen so that you get opti-

paint properties with respect to printing ink receptivity, durability, and binding properties in the resulting plates. If e.g. great durability is desirable, then a simple heating of the developed plate will result in the balls fusing together, and this gives a far better durability.

By also making a suitable choice of the matrix material, its thickness and a suitable choice of substrate, it is possible to create both hydrophobic and hydrophilic properties in the film composition, which are relatively independent of those found in the substrate. After an image-like exposure, the photosensitive phase of the film will in such cases retain its solubility in the unexposed areas, so that a porous surface can be obtained by leaching with a selected solvent. By developing the film without scrubbing or brushing, the matrix material will essentially

lig retain their structural uniformity over the entire substrate. The unexposed, porous parts can then be mechanically wetted

with water, while the exposed areas are non-porous and consequently have hydrophobic properties. This difference in "wettability" of the film's surface is very well suited for lithographic printing and enables the manufacturer to select any inexpensive substrate material that may be suitable.

The applicability of the photosensitive single-layer film structures according to the present invention has been described above with regard to the production of lithographic offset printing plates. It is understood, however, that the invention is not limited to this one area. The photosensitive film substructures according to the present invention can be used for other purposes, where selective permeability to a given liquid or solvent is desired. Thus, according to the present invention, photosensitive structures can be cast as a self-supporting film and afterwards exposed to a slide and developed without destroying the structure of the matrix. In this way, a structure will be achieved which is selectively permeable to certain liquids.

Such a structure can be used for a number of purposes such as applying patterns or images to an underlying surface by means of printing ink or the like, which is capable of penetrating the structure.

.The present photosensitive structure can of course also be used for numerous photoresistant purposes. The matrix material must of course be selected and adapted to the appropriate environment. One can thus easily find special emulsion/dispersion systems that provide resistance to acids or bases or with a necessary and desirable dielectric constant. As soon as you have found a suitable system you can

a compatible photosensitive phase is added, and the desired structure is achieved.

It should be obvious that the photosensitive structure according to the present invention will be easier to develop if you have a higher concentration of the first phase. On the other hand, it is desirable to keep the concentration of the first phase to a minimum in certain cases, because the second phase material provides improved durability, binding properties and printing properties, which form an important part of the present invention. The relative amounts between the first and second phase will therefore depend on the properties desired in a given photosensitive structure. As an example, however, one can mention that the diazo material used in example III can vary in amounts from 0.03

to 10% by weight, without particularly affecting the final product.

The thickness of the photosensitive film also affects the development of the structure, as the solvent must penetrate a greater distance to reach the substrate when using thicker films. It has generally been found that good results are obtained when using photosensitive films whose thickness varies from 0.5 to 25 microns.

However, the particle size in the matrix material and

the type of lattice structure used affects the thickness limits that can be used for a given purpose.

The photosensitive structures according to the present invention also have far better light sensitivity compared to previously known systems. Thus, photosensitive printing plates as described here can be "activated"

at an actinic exposure that is from 3-5 times faster than for ordinary diazo plates. This improved photosensitivity provides further advantages. As the development efficiency is significantly affected by the wettability and permeability of the film surface, a short actinic exposure will only affect the surface or near the surface, and this will give an efficient selective penetration and development. Such a short exposure can also be advantageous in cases where heat is subsequently used after development, as the print ink receptivity and durability of the finished structure are not affected by the exposure in such cases.

The following examples illustrate the present invention.

EXAMPLE I

100 ml of Rhoplex AC-388 (an acrylic emulsion liquid available from Rohm&Haas, Philadelphia, Pa.), 10 ml of water and 2 g of Diazo 4L were mixed for approx. 5 minutes.

This mixture was then added to a roller coater and applied

a brushed grained aluminum substrate so that a dry film with a thickness of approx. 5 microns. Air drying occurred within 2 minutes. The sensitized plate was placed in vacuum contact with a film negative and exposed for 15 seconds from a 2 KW Xenon lamp. After exposure, the plate was developed with ordinary tap water and coated with rubber. The plate was then placed in an offset press where normal solutions and printing inks were used. One could achieve up to 80,000

high quality copies with minimal image degradation.

EXAMPLE II

100 ml of Elvace 1875 (a water-based acetate/ethylene copolymer emulsion available from DuPont, Wilmington,

Delaware) 5 ml of water and 1 g of Diazo (a photosensitive material available from Graf-Com Co., Easton, Maryland) were mixed for approx. 2 minutes in a regular blender. The mixture was then spread over a brushed, grained aluminum substrate and dried to a film thickness of approx. 2 microns. Air drying took place within 1 minute. The sensitized plate was then placed in vacuum contact with a film negative and exposed for approx. 30 seconds from a 2 Kw Xenon lamp. After the exposure, the plate was developed with ordinary water and coated with rubber in the usual way. The plate was then mounted in an offset press (e.g. 1250 Adressograph/Multigraph) and the printing was done using a normal alkaline solution and a normal printing ink. Several thousand copies were produced.

EXAMPLE III

100 ml of Gelva TS 100 (a water-based polyvinyl acetate/long chain acrylate copolymer emulsion available from Monsanto Corp., Newport Beach, Cal.) 10 ml of water, and 4 g of Diazo 4L were mixed. The mixture was applied to an ungrained, silicified aluminum plate and dried to a thick-. emperor of approx. 5 microns. Air drying occurred within 2 minutes. The sensitized plate was then placed in vacuum contact with a film negative and exposed for 5 seconds to a 3 KW mercury vapor lamp. After exposure, the plate was developed with plain water. After development, the plate was placed in an offset press and printing took place using common materials. Six thousand high-quality copies were produced, without the image apparently being worn.

EXAMPLE IV

100 ml of Gelva TS 30 and 100 ml of Gelva S 52 (both aqueous polyvinyl acetate emulsions available from Monsanto Corp., Newport Beach, Cal.) and 2 g of Diazo were mixed for approx. 2 minutes. The mixture was applied to a brushed, grained aluminum plate and dried to a film thickness of approx. 10 microns. Two sensitized plates prepared as above were then placed

in vacuum contact with a film negative and.exposed for 60 seconds using a 3 Kw Xenonl,amp. After exposure, the plates were developed with ordinary water and then coated with rubber.

A plate was then placed in a convection oven that was set on

about. 120°C for 2 minutes. Comparison between the two plates showed that far better durability and better printing ink receptivity was achieved on the heated plate. However, both discs provide high-quality copies. About. 50,000 copies were obtained with the unheated plate, while over 200,000 copies were obtained with the heated plate.

EXAMPLE V

100 ml Gelva TS 100, 50 ml water and lg Diazo 4L were mixed for approx. 1 minute. The mixture was then applied to a tellurium-coated mylar substrate and dried to a film thickness of approx. 2 microns. Air drying occurred within 1 minute. The sensitized plate was then placed in vacuum contact with a film negative and exposed for 10 seconds using a 3KW mercury vapor lamp. After exposure, the plate was developed in an aqueous solution of NaOCL and NaOH without brushing or washing. inspection of the plate shows that the tellurium had been etched by the solution in the unexposed areas while the film coating on the plate was intact. Thus, no removal was obtained, but rather a selective permeability.

EXAMPLE VI

50 ml of Gelva TS 100, 50 ml of water and 2 g of Diazo were mixed for approx. 2 minutes. The mixture was then applied to a grained, non-silicate coated aluminum substrate and dried to a film thickness of approx. 2 microns. Air drying occurred within 2 minutes. The sensitized plate was then placed in vacuum contact with a film negative and exposed for 30 seconds using a 2 KW Xenon lamp. After exposure, the plate was developed by running water over the plate. No brushing or ironing was used and the coating remained intact. The plate was then tested for different wetting and using different printing inks by wetting with a common solution and applying printing ink using

of a cotton ball. Selective images of the printing ink were obtained and this confirms the fact that the unexposed areas have been made water-wettable due to leaching of diazophor-

the bond and this gives a porosity.

EXAMPLE VII

50 ml of TS 30 and 50 ml of TS9 8 (both polyvinyl acetate water-based emulsions from Monsanto Corp., Newport Beach, Cal.) and 2 g of Diazo 4L were mixed for approx. 2 minutes.

The mixture was then applied to both a fine and a slightly coarser grained aluminum sheet. The films were dried in air for approx. 3 minutes to a thickness of approx. 8 microns. The sensitized plates were then placed in vacuum contact with a film negative and exposed for 90 seconds using a 3 KW Xenon lamp. After the exposure, the plates were developed using ordinary water and gentle washing and then rubber coated. Both plates were heat-treated at 120°C for 2 minutes and then placed on a conventional lithographic press. Even after printing 150,000 copies, no wear of the image could be observed on any of the plates.

It is understood that one can easily carry out various changes and modifications of the invention without thereby abandoning the intention of the invention. Thus, one can easily perform many variations of the lattice structures described above without thereby abandoning the invention as such. Also, passive film materials as a third phase can be added to improve storage time to provide better color or to provide special photo, magnetic or electrical properties.

Claims (18)

1. Photosensitive, single-layer film structure, characterized by consisting of a first phase material dispersed with another phase matrix material, where said first phase is a photosensitive material whose solubility with respect to a given solvent changes upon exposure to electromagnetic radiation, and where said other phase is a material which is essentially insoluble in said solvent. 2. Photosensitive, structure according to claim 1, characterized in that said first phase is selected from the group consisting of diazo compounds, photopolymers, light-sensitive dyes, azo compounds, dichromates and silver halide gelatin cisterns. 3. Photosensitive structure according to claim 1, . characterized in that the first phase is a condensation product of a carbonyl compound and a diazo compound. 4. Photosensitive structure according to claim 1, characterized in that said first phase is a condensation ion product of a carbonyl compound and 4-diazol-1,1'-diphenylamine. 5. Photosensitive structure according to claim 1, characterized in that said second phase is cast from a polymeric emulsion dispersion. 6. Photosensitive structure according to claim 5, characterized in that the polymeric material in said emulsion-dispersion is selected from the group consisting of polyacrylic compounds, copolymers of acetate and ethylene, copolymers of styrene and acrylate <p> olivinyl acetates and copolymers of vinyl acetate and acrylates. 7. Photosensitive structure according to claim 1, characterized in that said first phase is a water-soluble diazo compound which is made water-insoluble by actinic exposure and where said second phase is cast from a water-based polymeric emulsion dispersion. 8. Photosensitive structure according to claim 7, characterized in that said second phase is cast from an acrylic emulsion dispersion. 9. Photosensitive structure according to claim 7, characterized in that said second phase is cast from an acetate/ethylene copolymer emulsion dispersion. 10. Photosensitive structure according to claim 7, characterized in that said second phase is cast from a polyvinyl acetate/long-chain acrylic copolymer emulsion dispersion. 11. Photosensitive structure according to claim 7, characterized in that said second phase is cast from a polyvinyl acetate emulsion dispersion. 12. Photosensitive printing plate, characterized by consisting of a substrate which is coated on at least one side with a photosensitive, single-layer film structure according to claim 1. 13. Water-developable printing plate, characterized by consisting of a substrate which is coated on at least one side with a photosensitive, single-layer film composition according to claim 7. 14. Printing plate according to claim 13, characterized in that the plate is heated after actinic exposure and water hardening to produce a fused matrix material. which shed said second phase. 15. Printing plate according to claim 13, characterized in that said photosensitive structure has a thickness varying from 0.5 to 25 microns. 16.. Photosensitive lithographic printing plate, characterized by consisting of a photosensitive film structure according to claim 1, on a substrate layer, and where said second phase of the matrix material essentially retains its structure on the entire substrate, and where said film structure after pictorial actinic exposure has a selective water wettability in relation to this exposure. 17. Photoresist, characterized by consisting of a substrate layer which is coated on at least one side with a photosensitive single-layer film structure according to claim 1. 18. Water-developable photoresist, characterized by consisting of a substrate layer which is coated on at least one surface with a photosensitive, single-layer film structure according to claim 7.