NO753182L - - Google Patents

Description

The invention relates to the development of photographically exposed light-sensitive photopolymer layers.

Such layers are widely used to form images on a large number of substrates and thereby produce various products such as etched monsters, printed circuits and printing plates or matrices. A particularly important application of the present invention is in the production of lithographic printing plates, although it can also be used in the production of other types of printing plates, such as letterpress plates, where the image is etched in relief, and in the production of printed circuits, integrated circuits and the like.

Printing of monsters, typography and pictorial objects on different materials, such as paper, cardboard, plastic and metal is frequently carried out using lithography. The lithographic printing method uses a special printing plate which, when moistened with water, selectively receives oleo-ink from one or more ink-coated rollers and transfers it either directly or indirectly to the paper or other material to be printed. A lithographic printing plate is alternatively known as a planographic plate or a surface plate. Print image on

a lithographic printing plate neither projects above nor goes below the level or plane of the surrounding non--bi 11 ed areas, hence the term planographic. In this way, it differs from the plates, forms and cylinders used in the other two important printing methods, namely letterpress and engraving. The printed image on the letterpress plate protrudes substantially above the supporting non-image material, and that on the engraving plate or cylinder lies below its surrounding

gende non-image surface. With the lithographic method, j

the plate to have suitable surface characteristics that make the black

able to adhere to the necessary image surfaces and not adhere to the clear non-image surfaces, and the proper choice of material components used to construct the lithographic plate is important. It is also important that the plate and the materials on it are prepared correctly, otherwise the essential oleophilic and hydrophilic properties of the image can be lost. the non-bilied areas are not achieved.

In recent years, the photographic methods used to form lithographic print images have changed. While dichromate-sensitized natural colloids (eg, albumen) were commonly used to produce what are known as surface images by exposure behind a photographic negative, two alternative systems are now commonly used for this so-called negative-working process. One of these systems used is a light-absorbing plate consisting of a diazo resin laid as a very thin layer on the surface of a metal substrate which is usually made of aluminium. In the second system, a light-absorbing plate consisting of a substrate coated with a thicker layer of a light-absorbing polymer (e.g. a cinnamic acid derivative resin) is used for the same purpose. These photosensitive polymers are negatively working, i.e. photocurable and can be defined as polymers containing a majority of groups with the structure -CH=CH-CO-. Such photopolymers are described in British patents no. 695,197; 7 94.57 2;

813,605; 838,547; 846,908; 913,764; 921,530; 949,919; 966,296;

966,297; 1,112,277; 1,117,197; 1.3H.692; 1,313,390; 1,314,689;

1,317,818; 1,338,020; 1,341,004; 1,350,351; 1,353,501;

1,363,214; 1,377,740; 1,377,747; 1,378,535 and in many other documents.

Such photopolymeric systems are produced by a method called subtractive and it is with light-sensitive plates comprising layers of such negatively working photopolymers that the present invention is about.

Light-sensitive plates based on such photopolymeric systems consist of a substrate with a surface completely coated with a layer of the light-sensitive polymer. The substrate is usually of metal which may be grained and suitably anodized to improve its properties. The polymer layer is photographically exposed to actinic light using a suitable negative. These polymer parts that are hit by the light are hardened. The image-exposed plate is selectively developed by removing unexposed and unwanted areas of the polymer from the substrate surface (i.e., the plate is "developed") and by making the underlying areas of the substrate surface adequately water-receptive, which is evident when the non-light affected areas are removed (i.e. the disc is "gummed" or "desensitized").

Poly(vinyl cinnamate) is a typical example of a photopolymer system of the type with which the present invention is concerned. This and similar light-sensitive polymers, which often include suitable sensitizers to increase their light sensitivity and also dyes, are developed by using a developer consisting of one or more suitable organic solvent liquids. The developers used are such that they dissolve the non-light-struck areas of the polymer, but not the light-struck polymer areas. Desensitization of the substrate surface exposed during development is done in the traditional way by using suitable film- or layer-forming materials to make contact and possibly react with the metal surface. Such materials are well known and can e.g. be colloidal desensitizers, gum arabic or sodium carboxymethyl cellulose or desensitizing acids such as phosphoric acid.

The procedure for lithographic plate production described above enables the delivery of factory-coated pre-sensitized plates to the consumer and enables the consumer to quickly and economically produce printing plates. Such printing plates are capable of producing 50,000 or more satisfactory copies. When a suitable metal substrate is used, the print run obtained from a single printing plate can be as large as 400,000.

The choice of organic solvent for use in the developer is not simple because of the numerous limitations that exist.

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If a solvent is too strong, the image that consists of the light-struck polymer areas weakens. If the solvent is not strong enough, unwanted, non-light-struck polymer areas are not sufficiently removed. If the solvent further evaporates to a greater extent at room temperature, it is unsuitable and perhaps expensive to use, and if it is toxic to some extent it must be avoided. Finally, it is usually necessary to include a desensitizing acid in the *developer and therefore the solvent used should not be easily hydrolysed by the acid.

The organic solvents conventionally used to develop photopolymers all suffer from one or more of the above disadvantages. E.g. cyclohexanone is toxic and smells repulsive, especially at the higher temperature in some work rooms. Tetrahydrofurfuryl alcohol is non-toxic, but is not sufficiently strong, butyrolactone is not toxic, but hydrolyzes easily in the presence of acids, methoxybutyl acetate is toxic, has a nauseating odor and hydrolyzes in the presence of acids, 2-methoxyethyl acetate is toxic, has a repulsive odor and hydrolyzes easily in the presence of acids, and dimethylformamide is extremely toxic.

According to one aspect of the present invention there is provided

a method of preparing a photopolymeric layer that has been image-exposed, which method consists in selectively removing the non-light-affected areas of the layer by contacting the layer with a developer consisting of a lactam of the general formula:

where n is 0 or an index from 1 to 9, R is a

hydrogen atom or an alkyl, alkenyl, aralkyl, aryl or acyl radical, and each of R<1>and R", which j

IN

I may be the same or different, representing a hydrogen atom or an alkyl or aryl radical.

According to another aspect of the present invention, there is provided a developer for use in the production of a photopolymeric layer which has been image-exposed, which developer consists of a lactam of the general formula

where n, R, R' and R" have the above meanings,

and this developer further comprises an acid, a wetting agent, an inert diluent and/or a further organic liquid which is a selective solvent for the non-light-affected areas of image-exposed photopolymer.

Preferably, n has a value of from 0 to 3. Examples of γ-lactams are 2-pyrrolidinone (melting point 25°C) and the hydrate (m.p. 35°C), 1-methyl-2-pyrrolidinone, 5-methyl-2- pyrrolidinone (m.p. 41°C), 1-vinyl-2-pyrrolidinone, 1-ethyl-2-pyrrolidinone, 1-isopropyl-2-pyrrolidinone, 1-n-butyl-2-pyrrolidinone, 1-pentyl-2- pyrrolidinone, 1-phenyl-2-pyrrolidinone (m.p. 68°C), 1-(p-tolyl)-2-pyrrolidinone (m.p. 88.5°C), 1-acetyl-2-pyrrolidinone and 1,5-dimethyl- 2-pyrrolidinone. Examples of 6-lactams are 2-piperidone (m.p. 39°C), 1-methyl-2-piperidone, 3-methyl-2-piperidone (m.p. 53°C), 3-ethyl-2-piperidone (m.p. 68 °C), 3-n-propyl-2-piperidone (m.p. 59°C) and 6-n-propyl-2-piperidone (84°C). An example of a β-lactam is 6-hexano-lactam. It should be understood that when the lactam is a solid at room temperature it must be transferred to a liquid for use by heating or dilution.

Particularly preferred lactams are 1-methyl-2-pyrrolidinone, 1-butyl-2-pyrrolidinone, 1-cyclohexyl-2-pyrrolidinone, 2-pyrrolidinone, 1-vinyl-pyrrolidinone and ?-caprolactam. These lactams have not been found to have a particularly good solubilizing capacity on non-photosensitive surfaces

areas of the photopolymer and can therefore be used in diluted form, but does not cause unwanted swelling of the light-cured polymer. 1-Methyl-2-pyrrolidinone is particularly advantageous as it is non-toxic, has a low vapor pressure and a negligible odor. It is also stable under acidic conditions.

In the case where the developer additionally contains an acid, this can be a mineral acid, e.g. phosphoric acid, sulfuric acid or hydrochloric acid or an organic carboxylic acid, in particular a monocarboxylic acid, such as acetic acid, a hydroxycarboxylic acid, such as lactic acid and glycolic acid, or an unsaturated carboxylic acid. such as cc-pentenonic acid. The amount of acid present can be from 1-5% by volume, based on the volume of lactam used and is preferably such that the developer has a pH of from 2 to 6.

The presence of one or more wetting agents is preferred to give the developer good dispersion characteristics and to help maintain the suspension in the developer of polymer and pigment (in the case where the photopolymer layer comprises a pigment) which has been removed from the non-light affected areas. Examples of wetting agents are "Texofor FP 85 and 65 A9P" (poly-oxyethylene ether condensates from Glovers Chemicals Ltd), "Perminal BX" (sodium salt of an alkylated naphthalenesulfonic acid from ICI Ltd), "Aerosol OT" and "Tergitol MPX" (a nonylphenyl- ethylene oxide condensation product from Union Carbide).

In the case where the developer contains an inert diluent, this can e.g. be water, ethanolamine, ethylene glycol monoethyl ether (2-ethoxyethanol), ethylene glycol, diethylene glycol, diethylene glycol monoethyl ether (i.e. 2-(2-ethoxy-ethoxy)-ethanol), diacetone alcohol, isopropanol or other liquid, which when used alone, does not have any significant dissolving effect on the pictorially exposed layer.

In the event that the developer contains a further orga-- j| nic liquid which is a selective solvent for the non-light affected areas, this may be any compatible organic solvent conventionally used to develop the photopolymer. Examples of such additional organic solvents are 2-methoxyethyl acetate, γ-butyrolactone, tetrahydrofurfuryl alcohol, n-propyl alcohol and methoxybutyl acetate.

The method according to the present invention has been found to be useful for developing many photographically exposed photopolymer layers and in particular for developing layers of photopolymers containing a large number of groups with the structure -CH=CH-CO- as described in the previously mentioned documents. Specific examples of such photopolymers are photopolymerizable resin esters such as those derived from polymers containing free hydroxy groups, e.g. polyvinyl alcohol or an epoxy resin and unsaturated carboxylic acids, such as cinnamic acid.

When using the method according to the present invention in printing plate production, a photosensitive plate consisting of a layer of photopolymer laid on the surface of a substrate is exposed in a suitable manner pictorially to actinic light. The image-exposed layer is then developed by using the developer

for a sufficient time to remove the polymer from the non-light affected areas. Careful mechanical impact helps the removal. Thus, brushing is a very useful method for applying the developer to the plate. The developer has sufficient effect to be used at room temperature. However, if desired, it can be used at higher temperatures of up to 50°C. After an initial application of developer, a second application may be made followed by either a single or double application of a desensitizing material to render hydrophilic those areas of the substrate surface that were exposed when the non-light affected areas were removed. The plate is then dried and consists of a printed image formed by the light-filled areas and non-oppressive areas consisting of the exposed areas of the substrate surface.

The following non-limiting examples illustrate the invention. All parts are by weight unless otherwise stated.

EXAMPLE 1

A Super Sensalith pre-sensitized printing plate from Howson-. Algraphy, which consisted of a substrate of anodized aluminum carrying a photopolymeric layer consisting of a cinnamic acid epoxy resin was placed in contact with a "line" photographic negative and exposed to light from a carbon arc lamp for 5 minutes. It was then prepared manually by rubbing with 1-methyl-2-pyrrolidinone for 30 seconds. It was then desensitized with a solution consisting of 46 vol% water, 50 vol% gum arabic (S.G1.17), 0.9 vol% "Perminal BX", 2 vol% ammonium dihydrogen phosphate and 1.1 vol% phosphoric acid ( S.G. 1.75).

When the resulting printing plate was moistened with water and blackened with oleo black, a well-defined blackened print image became visible.

EXAMPLE 2

Example 1 was repeated except that the presensitized plate was one consisting of an anodized aluminum substrate coated with a layer of Waycoat photoresist material (Phillip A. Hunt Chemical Corporation). The Waycoat photoresist material consists of a photopolymer believed to be poly(vinyl cinnamate). One

well-defined blackened print image became visible.

EXAMPLE 3

Example 1 was repeated with equally satisfactory results by using the following developer solution:

EXAMPLE 4 4

A Super Sensalith plate (Howson-Algraphy) was automatically produced in a 7 5 cm wide Howson-Algraphy negative plate maker running at 90 cm per second. minute after exposure to a pulsating Xenon light source behind a dot-structured photographic negative. The desensitizing section of the developer was filled with a 10% aqueous solution of polyacrylamide and the developing section was filled with:

"Texofor 65A9P" is a wetting agent and is a polyoxyethylene ether condensate with the formula R.0.(C^H^O)nH, where R is a long-chain fatty group..

No difficulty was found in obtaining dense black prints from the blue image-bearing planographic plate when used on a lithographic printing press. The temperature for the solution in the developing section was 24°C.

EXAMPLE 5

Example 4 was repeated with similar success using the developer solution at 40°C. No repulsive odors were noticed in the work area. Development could be done by a faster

feed rate.

EXAMPLE 6

A photosensitive plate was produced by coating a grained and anodized aluminum foil with a photosensitive cinnamic acid-treated epoxy resin of 0.5 g per m 2. When the plate was completely dry it was exposed in contact with a line and halftone negative for 1 1/2 minutes to a mercury sol halogen lamp.

The plate was cut into 4 sections which were developed as follows:

A - developed with 1-butyl-2-pyrrolidinone at 22°C.

B - developed with 1-cyclohexyl-2-pyrrolidinone at 50°C.

C - developed with 2-pyrrolidinone at 50°C.

D - developed with 1-vinyl-2-pyrrolidinone at 22°C.

The sections were desensitized with the desensitizing solution from Example 1 and blackened while still wet with oleo black ink. In each case, a well-defined printed image was obtained.

EXAMPLE 7

This demonstrates how a suitable lactam can be diluted considerably to become economical without losing its usability.

Example 1 b]be repeated using f Saying developer. Satisfactory pressure plates were obtained in each case:

A: 9 parts 1-methyl-2-pyrrolidinone and 1 part water

B: 8 parts 1-methyl-2-pyrrolidinone and 2 parts

ethanolamine

C: 6.5 parts 1-methyl-2-pyrrolidinone and 3.5 parts

ethanolamine

D: 10 parts 1-methyl-2-pyrrolidinone and 9 parts

2-Ethoxyethanol

E: 6 parts 1-methyl-2-pyrrolidinone and 4 parts 2-(2-ethoxyethoxy)ethanol

F: 10 parts of 1-methyl-2-pyrrolidinone and 9 parts of 4-hydroxy-4-methyl-2-pentanone.

Example 1 was also repeated using the 1actamene in combination with 2-methoxyethyl acetate on the one hand and γ-butyrolactone on the other. Satisfactory results were also obtained in each case.

EXAMPLE 8

Example 4 was repeated using which induces a hot solution of 10 parts of ?-caprolactam in 9 parts of 2-ethoxyethanol: Similar results were obtained.

EXAMPLE 9

Example 1 was repeated except that an LNL lithographic plate (Kodak Limited) was used. This plate is a negative working plate and consists of a substrate coated with a photopolymer. A well-defined pressure image was obtained.

EXAMPLE 10

The front of an unused sheet of photo-etched zinc (S.D. Syndi-

cate Ltd.) was cleaned and coated with a layer of KPR (Kodak Limited). KPR consists of a photopolymer believed to be poly-(vinyl cinnamate). After drying, the resulting lysomfin-

expose the plate to actinic light while in contact with a contrast line negative for several minutes. The plate was then developed using 1-methyl-2-pyrrolidinone and dried. The image remaining on the foil after development was used as a resist material while the plate was etched with an etchant containing nitric acid to produce a relief-image letterpress printing plate.

EXAMPLE 11

A smooth piece of copper clad resin laminated board used in the manufacture of printed circuits was coated with Waycoat f.autoresistor material (Philip A. Hunt Chemical Corporation).

The resulting light-absorbing plate was exposed behind a photographic negative reproduction of an electronic circuit and pro-

called with a solution containing 10 parts of 1-methyl-'2-pyrrolidi-

non and 8 parts isopropyl alcohol (diluent). A cleanly developed well-defined etched resist image was obtained.

Claims (11)

1.. Procedure for developing a pictorial ex- poned layer of a photopolymer such as a photopolymerizable resin ester, e.g. poly(vinyl cinnamate) or cinnamic acid-treated epoxy resin, which method comprises selective removal of the non-light-affected areas of the layer by bringing the layer into contact with an organic liquid solvent alternatively mixed with an acid such as phosphoric acid and optionally mixed with a wetting agent, characterized by that a lactam with the general formula is used as organic liquid solvent where n is 0 or an index from 1 to 9, R is H, a hydrogen atom or an alkyl, alkenyl, aralkyl, aryl or acyl radical, and each of R' and R"", which may be the same or different, represents a hydrogen atom or an alkyl or aryl radical. 2. Process according to claim 1, characterized in that the lactam is 1-methyl-2-pyrrolidinone. 3. Process according to claim 1, characterized in that the lactam is 1-butyl-2-pyrrolidinone, 1-cyclohexyl-2-pyrrolidinone, 2-pyrrolidinone, 1-vinyl-2-pyrrolidinone or £-caprolactam. 4. Process according to any of the preceding claims 1-3, characterized in that the lactam is in a mixture with an inert diluent such as water, ethanolamine or 2-ethoxyethanol. 5. Method according to any of the preceding claims 1-4, characterized in that the lactam is in admixture with a further organic liquid, such as tetrahydrofurfuryl alcohol, 2-methoxyethyl acetate or γ-butyrolactone, which is a selective solvent for the non-light-affected areas. 6. Developer for use in the production of a photopolymer layer by the method according to claim 1, character e- characterized in that it consists of (i) a lactam of the general formula: where n is 0 or an index from 1 to 9, R is a hydrogen atom or an alkyl, alkenyl, aralkyl, aryl or acyl radical and each of R' and R", which may be the same or different, denotes a hydrogen atom or an alkyl or aryl radical, and (ii) an acid, a wetting agent, an inert diluent and/or an additional organic liquid which is a selective solvent for non-opaque areas of image-exposed photopolymer. 7. Inducer according to claim 6, characterized in that the lactam is 1-methyl-2-pyrrolidinone. 8. Developer according to claim 6, characterized in that the lactam is 1-butyl-2-pyrrolidinone, 1-cyclohexyl-2-pyrrolidinone, 2-pyrrolidinone or £-caprolactam. 9. Developer according to claim 6, 7 or 8, characterized in that the acid is a mineral acid, such as phosphoric acid or hydrochloric acid or an organic carboxylic acid, such as acetic acid, lactic acid, glycolic acid or α-pentenonic acid. 10. Induces according to any of claims 6-9, characterized in that the diluent is water, ethanolamine or 2-ethoxyethanol. 11. Developers according to any one of claims 6 to 10, characterized in that the further organic liquid is tetrahydrofurfuryl alcohol, 2-methoxyethyl acetate or Y-butyrola^-ton-^