NO762217L - - Google Patents

Description

Irradiation-sensitive plates.

The present invention relates to radiation-sensitive plates.

According to one feature of the invention, there is provided a radiation-sensitive plate comprising a metallic substrate having a surface coated with a radiation-sensitive layer comprising a quaternary ammonium salt of the type which will accept at least one electron upon exposure to radiation to provide a constituent capable of causing metal deposits on the substrate from an electroless plating solution in contact with this component and comprising a salt of the metal and a reducing agent.

According to another feature of the invention, there is provided a method for producing a lithographic printing plate, comprising (i) exposing a radiation-sensitive plate comprising a metal substrate with a surface coating of a radiation-sensitive layer comprising a quaternary ammonium salt of the type which will receive at least one electron by irradiation exposure to provide a component capable of causing metal deposition on the component from an electroless plating solution in contact with the component, and comprising a salt of the metal and a reducing agent, and (ii) contacting the imaged plate with the electroless plating solution comprising a metal salt and a reducing agent to thereby cause metal deposition on the irradiated areas of the layer to provide the desired lithographic plate.

The quaternary ammonium salt can be of the type described in British patent no. 1,310,812 and with the general formula

wherein R to R"*"0 are hydrogen, halogen or;11 12 ;organic substituents, R and R are, if present, halogen or organic substituents, ;Z is 0 or an integer, X~ is an anion, m =; 1 or 2, and at least one of the nitrogen atoms is quaternary. The quaternary ammonium salt is preferably a diquaternary cyclic ammonium salt, which upon addition of one electron forms Weitz radicals. Such salts are dicationic and contain nitrogen atoms in the molecule and at least two of the nitrogen atoms are quaternized and form part of the linked ring structures which are at least partially aromatic, and where the bond between the ring structures is provided by a chain with conjugated unring between the nitrogen atoms . Particularly suitable diquaternary ammonium salts for the plates according to the present invention are the bi-pyridylium salts exemplified by: ; Compounds (1) and (2) are commercially available compounds marketed under the names "PARAQUAT" and "DIQUAT" respectively. Compound (3) is N,N'-di(paracyanophenyl)-4,4'-bi-pyridyl chloride and will hereafter be denoted by CPP; Preferably, the quaternary ammonium salt is colorless or only slightly colored on exposure, and the compound formed therefrom by exposure is coloured, so that an easily visible image is formed after exposure. E.g. is the radical cation formed by the addition of one electron to the dication CPP<++>green, and the corresponding neutral molecule formed by the addition of two electrons to the dication CPP is red. The quaternary ammonium salt may comprise a single cation or it may form part of a more complex molecule, such as a dimeric cationic compound. It can be a polymeric material, where one or more of the ring structures containing quaternary nitrogen atoms are in the polymer basic structure, in end groups, in side chains or in combinations of such positions. The anions in the quaternary ammonium salts can for example be halides, perchlorates, tetrafluoroborates, silicon fluorides, methyl sulphates, bisulphates or polymeric anions such as e.g. ! polyacrylate. The presence of bromine and iodine atoms is less desirable than the presence of chlorine or fluorine atoms, because bromine and iodine act as inhibitors of the excited state of the cation. The anions must not be oxidizing or reducing agents or in any other way chemically reactive with regard to anti-ionization agents or other components used to form the layer on the substrate. The quaternary ammonium salt may be present in the radiation-sensitive layer in admixture with a film-forming polymeric binder. The binder may be such that it is inert with respect to the component formed upon exposure to the quaternary ammonium salt or it may be such that it has a stabilizing effect on the component. In this way, some of the components which are normally very active can be stabilized for a sufficient period of time to allow treatment with an electroless plating solution, although there is a time delay between their formation and such treatment. Suitable water-soluble or swellable film-forming polymers which can be used as a binder include polyvinyl alcohol, polyammonium methacrylate, gelatin, alginates and maleic anhydride copolymers, for example a kppolymer of maleic anhydride with styrene vinyl ether or ethylene. Soluble polysaccharides such as polysaccharides can also be used as a binder as well as polyvinyl pyrrolidone either alone or in a mixture with polyvinyl alcohol. Polyvinyl alcohols with varying viscosities and degrees of hydrolysis can be used, but a maximum degree of hydrolysis is preferred, as their solubility in metal salt solutions is low at room temperature. The relative weight amounts of the quaternary ammonium salt to the binder in the layer can for example be from 1:200 to 10:1. The inherent spectral sensitivity of the quaternary ammonium salts can be extended well into the visible region of the spectrum by introducing special sensitizers into the radiation-sensitive layer. Suitable spectral sensitizers are Riboflavin in the form of free base, 7-chloro-9-(N-methyl-diethyl-amino-ethyl)-isoalloxazine chloride, (hereinafter referred to as compound RD) and other very similar compounds, as well as "Arconol ., Yellow", (a dye comprising 3,6-dimethyl-2-(4-dimethylaminophenyl)benzthiazolium chloride). Other sensitizers that may be used include 3,3'-diethylthiacynide iodide, proflavine, acridine orange, acriflavine, N-methylphenazinium methylsulfate, 4-cyanoquinolinium methiodide, and arythrosine. ;Chemical sensitizers that enhance the radiation sensitivity of the radiation-sensitive layer may also be present. Different sensitizers are compounds that contain active hydrogen and include alcohols, amines, phenols, carboxylic acids and sugars. Examples of such compounds are glucose, oxalic acid, p-chloro-benzoic acids, glycerol, benzenehexacarboxylic acid, triethanolamine, thiazinephenol, ethylenediaminetetraacetic acid (disodium salt), picric acid, glycine, (Ethelanin and nicotinamide adenosine dinucleotide phosphate. Preferred chemical sensitizers are substituted or unsubstituted mono- or di-aryl or 1-aryl-1-alkyl-glycolic acids or ethers, salts or other derivatives thereof. Particularly preferred sensitizers are mandelic acid, benzylic acid, p-bromo-mandelic acid, a-methoxyphenylacetic acid, p-chloro-mandelic acid, a -naphthyl glycolic acid and ammonium mandelate. ;Other materials may also be present in the layer if necessary. For example, surfactants may be added to the coating to facilitate the formation of smooth, even layers on the substrate. Other compounds, for example compounds that bind -iron (III) ions, which locally affect the properties of the electroless plating solution, can also be present in the layer. Examples of such compounds that can designated as development accelerators are ethylenediaminetetraacetic acid (diantrium salt) ammonium chloride, diammonium hydrogen citrate and silicon oxide which are sold under the trade name "Cab-o-Sil", and the latter two are particularly preferred. ;The substrate used must itself be inert with respect to the radiation-sensitive layer or must be able to be passivated so that it is inert with respect to the layer. The substrate can be made of aluminium. The preferred substrate in the case where the plate is to be used for the production of lithographic printing plates is made of very pure aluminum containing not less than 99.0% aluminum and advantageously contains from 99.3 to 99.7% aluminum. Preferably, the substrate surface which is coated with the radiation-sensitive coatings should be roughened to promote adhesion of the layer and the printed image after development. The roughening of the surface significantly affects the printer's work in maintaining the correct ink balance during printing. A roughened or grained surface can be obtained in many ways which will be known to the person skilled in the art. The treatment can be mechanical using rotating brushes or sandblasting or by ball granulation. The rough surface can also be easily obtained by etching with various chemicals that will attack the metal. However, the preferred method of graining the surface is electrochemical, which is achieved by immersing the metal in sheet form (batch process) or in roll form (continuous process) in a bath of a suitable acid or mixtures of acids and passing an alternating current between the metal and, for example a graphite electrode. If the metal is aluminium, hydrochloric acid can be used alone or in a mixture with other chemicals, such as acetic acid, or nitric acid, either alone or in a mixture with other chemicals such as acetic acid. Preferably, the substrate is given a fine-grained surface. After graining, the substrate should be cleaned to remove by-products from the graining process from the surface, which would otherwise react with the radiation-sensitive layer. The cleaning step can be carried out in a known manner by passing the granular metal through one or more baths containing various usable acids and/or alkalis. It is also advantageous for the substrate surface that this is anodized. The anodic layer, when of sufficient thickness, will prevent the radiation-sensitive layer from reacting chemically with the metal and will also significantly increase the number of copies that can be obtained from the finished printing plate for given conditions in a printing press. Anodizing can be carried out using a an-r number of electrolytes that will be known to a person skilled in the art of making lithographic printing plates from aluminum. A sulfuric acid electrolyte is preferred. ;The radiation-sensitive plate according to the present invention is produced by applying to the substrate, preferably of grained and anodised aluminium, a coating solution comprising the quaternary ammonium salt and possibly the binder and other desired additives. The amount of the quaternary ammonium salt and binder (if present) in the coating solution is not critical, and is dictated solely by the desired sensitivity and practical considerations. Satisfactory results can be obtained by using a coating solution containing 0-20 parts by weight of a water-soluble polymeric binder, 0.1-10 parts by weight of the quaternary ammonium salt and 70-99.9 parts by weight of water. The coating solution can be applied to the substrate in many ways, but dip or roller coating are the preferred methods. When using the radiation-sensitive plate according to the present invention in the production of a lithographic printing plate, the radiation-sensitive layer is image-exposed with actinic radiation, e.g. UV irradiation. The quaternary ammonium salt accepts at least one electron in the areas on which the radiation falls to produce an image which is a negative of a master. For example in the case where the quaternary ammonium salt is dicationic (the normally stable state in aqueous media) represented by Q<++>, the following reaction will take place under the influence of the irradiation: ; The image consists of the radical cation Q<+*>or the neutral molecule

Q, both of which are capable of causing metal deposition from

an electroless plating solution.

The image-exposed plate does not need to be developed immediately. Although the image degrades in the presence of moisture and oxygen, the exposed plate is sufficiently stable for handling under normal conditions, for example "step and repeat work". If, however, it is desired to save an image-exposed plate

for a longer period of time this should be stored under dry and/or oxygen-free conditions.

The image-exposed plate is developed by bringing it into contact with an electroless plating solution, for example a solution containing a sol salt and a reducing agent. Such solutions are previously known and are capable of depositing metal without an external application of an electric field.

An adherent metallic image is then deposited on the areas which

is irradiated. As soon as a trace of metal is deposited, this is able to catalyze further deposition of the same or another metal from a suitable solution. in this way, a metallic layer can be built up in the image areas. The amount of deposited metal depends on many variables such as the composition of the radiation-sensitive layer, exposure time, contact time with the electroless plating solution and its composition. For solar images, image weights of up to 25 g/m or higher can be achieved. Further treatment can be carried out if necessary to make the metallic image more oleophilic and the non-image areas more hydrophilic. The plate can be blackened and then treated in the usual way with a rubber solution for assembly in the printing press. The plate obtained can be used in a sheet feeding press to print long series of the best quality, and it can also be used to print long series on a web offset printing press. The pressure plate is also suitable for direct litho applications.

It is possible to produce radiation-sensitive plates according to the present invention which have properties such as high resolution and sharpness, and which are suitable for use in the production of lithographic printing plates with the ability to withstand the most demanding printing conditions in the same way as bimetallic lithographic printing plates.

The following examples illustrate the invention. In all cases, the quantity indicated is in parts by weight, if nothing else is stated. The amount of radiation sensitive coating mat-. according to the examples was in the order of magnitude 0.2 g/m . The solar-containing electroless plating solution used in the examples was prepared by mixing 100 ml of solution I, 25 ml of solution II and 25 ml of solution III, where the said solutions had the following composition:

Solution I

Solution II Solution III

"Synthrapol N" is a non-ionic wetting agent, and is an ethylene oxide condensate with an aliphatic alcohol.

EXAMPLE 1

The following coating solution was prepared and roll coated on an aluminum sheet which was grained in nitric acid, cleaned in phosphoric acid and finally anodized in sulfuric acid.

The resulting radiation-sensitive plate was exposed through a negative transparency in a copying pre-frame for 1.5 min. using four "Philips 300w MLU" lamps carried 600 mm above the frame. A large copy image was obtained. The exposed plate was then immersed in the sol plating solution for 3 min. at room temperature. The green image was replaced by a pale image of metallic solv, which could be polished to a glossy solv which was in conductive contact with the aluminum substrate.

EXAMPLE 2

The following coating solution was prepared and used to prepare an irradiation-sensitive plate in the same manner as in Example 1, except that the exposure time was 4 min.

The plate was exposed and developed as indicated in Example 1 except that the exposure time was 4 min., and the copy image was gray on

together as indicated in example 1.

EXAMPLE 3

The following coating solution was prepared and used for

to provide a radiation-sensitive plate in the same manner as in Example 1:

The plate was exposed as indicated in Example 1 except that the exposure time was one minute.

The green copy image on the exposed plate was replaced. with a black image of metallic sol after the plate was immersed in the sol plating solution for 3 min. at room temperature. The surface of the plate was then coated with a cotton ball dipped in a dispersion of an organic mercapto compound and a wetting agent in water to increase the initial ink receptivity of the image. After blackening and gumming in the normal way, the plate was mounted in a sheet-fed, offset, printing press and several hundred good, clean copies were printed.

EXAMPLE 4

Example 1 was repeated using the following coating solution and with an exposure time of 4 min.:

EXAMPLE 5

Example 1 was repeated using the following coating solution and with an exposure time of 10 min.:

/

"Cyanamer P26" is a copolymer of acrylamide, acrylic acid and sodium acrylate obtained from Cyanamid of Great Britain Limited.

EXAMPLE 6

The following coating solution was prepared and roll-coated onto a fine-grained and anodized aluminum sheet:

"Benzyl Viologen" is similar to "Raraquat", but where the methyl groups are replaced by benzyl groups.

The plate obtained was exposed as indicated in Example 1

for 2 min. A pale purple copy image was obtained. During treatment with the sol plating placement, sufficient sol could not be deposited to give a polishable sol image.

EXAMPLE 7

The following coating solution was prepared and coated

a fine-grained anodized aluminum substrate:

"BRU 35" is a non-ionic wetting agent and is an ethylene oxide condensate of an aliphatic alcohol.

The resulting radiation-sensitive plate was image-exposed as indicated in Example 1 for 3 min. A purple copy image was obtained.

EXAMPLE 8

Example 7 was repeated using "Diquat" instead of "Paraquat". A light blue impression was obtained.

EXAMPLE 9

Example 1 was repeated using the following coating solution and with an exposure time of 2 min.:

A shallow impression was obtained.

EXAMPLE 10.

Example 3 was repeated using the following coating solution and with an exposure time of 2 min.:

Good, clean prints of high quality were obtained.

EXAMPLE 11

Example 3 was repeated using the following coating solution and with an exposure time of 30 sec.:

Good, clean prints of high quality were obtained.

EXAMPLE 12

Example 3 was repeated using the following coating solution and with an exposure time of 15 sec.:

EXAMPLE 13

To 152 g (1.0 mol) of mandelic acid and 200 ml of methanol in a round-bottomed bottle fitted with reflux valves was added 100 ml of methanol containing approx. 10 g of anhydrous hydrogen chloride. The solution was heated under reflux on a steam bath for 5 hours and then poured into ice water in a beaker. A saturated aqueous solution of sodium bicarbonate was added until the solution was slightly alkaline. It was then extracted with 300 ml portions of

ner ether in a rinsing funnel. The ether extracts were washed with 200 ml

portion of water and dried over 50 g of anhydrous sodium sulfate. The dried ether solution was concentrated by distillation from a Claisen flask, and the residue was distilled under reduced pressure.

Mixtures containing thus obtained were prepared. methylmandelate and photoreducible quaternary ammonium salts such as "Paraquat", "Diquat" and CPP<++>. The methyl mandelate was found to be a sensitizer for photoreduction of the salts.

EXAMPLE 14

Mixtures were prepared containing a commercially available mandelic acid methyl ether and photoreducible salts such as "Paraquat", "Diquat" and CPP+,+. The ether was found to be an effective sensitizer for photoreduction of the salts.

EXAMPLE 15

Example 1 was repeated using the following coating solution and with an exposure time of 2 min.:

Good, clean prints of high quality were obtained.

EXAMPLE 16

Example 1 was repeated using the following coating solution and with an exposure time of 2 min.:

Good, clean prints of high quality were obtained.

EXAMPLE 17

Example 7 was repeated using the following coating solution and with an exposure time of 2 min.:

EXAMPLE 18

Example 17 was repeated using 2.0 α-naphthyl glycolic acid instead of p-chloromandelic acid. A purple imprint was obtained.

Claims (14)

1. A radiation-sensitive plate comprising a support having a surface coated with a radiation-sensitive layer comprising a quaternary ammonium salt of a type which will accept at least one electron upon exposure to radiation to provide a component capable of causing metal deposition on the component from an electroless plating solution in contact with the component, where the solution comprises a salt of the metal and a reducing agent, characterized in that the substrate is a metallic substrate. 2. Plate according to claim 1, characterized in that the quaternary ammonium salt has the general formula in which R to R are hydrogen or halogen atoms 11 12 or organic substituents, R and R , if they are present, are halogen atoms or organic substituents, Z is zero or an integer, X~ is an anion, m=1 or 2, and at least one of the nitrogen atoms is quaternary.3. Plate according to claim 1, characterized in that the quaternary ammonium salt is 4. Plate according to claims 1-3, characterized in that the quaternary ammonium salt is mixed with a polymeric binder, such as polyvinyl alcohol, polyammonium methacrylate, gelatin, an alginate, a maleic anhydride copolymer, a polysaccharide or polyvinylpyrrolidinone. 5. Board according to claim 4, characterized in that the weight ratio between salt and binder is from 1:200 to 10:1. 6. Plate according to claims 1-5, characterized in that the radiation-sensitive layer includes a spectral sensitizer such as riboflavin, 7-chloro-9-(N-methyl-diethylaminoethyl)isoalloxazine chloride, 3,6-dimethyl-2-(4-dimethylaminophenyl) )benzthiazolium chloride, 3,3'-diethylthiacyanidiodide, proflavine, acridine orange, acriflavine, N-methylphenazinium methylsulfate, 4-cyanoquinolium methiodide or erythrosine. 7. Plate according to claims 1-6, characterized in that the radiation-sensitive layer includes a chemical sensitizer. 8. Plate according to claim 7, characterized in that the chemical sensitizer is a substituted or unsubstituted mono- or diaryl- or 1-aryl- or 1-alkylglycolic acid or a salt or an ether of mandelic acid, benzylic acid, ammonium mandelate, a-nietoxyphenylacetic acid , p-chloromandelic acid, p-bromomandelic acid or oc-naphthyl glycolic acid. 9. Plate according to claims 1-8, characterized in that the radiation-sensitive layer includes (i) a surface-active agent or (ii) a development accelerator such as ammonium chloride or "rocked" silicon oxide or an iron (III) ion complex binding agent such as ethylenediamine-tetraacetic acid (disodium salt), or diammonium hydrogen citrate. 10. Plate according to claims 1-9, characterized in that the substrate is grained and anodised aluminium. 11. Plate according to claim 10, characterized in that the substrate is nitric acid-grained, sulfuric acid-anodized aluminium. 12. Plate according to claim 10, characterized in that the substrate is given a granular structure in a mixture of hydrochloric acid and acetic acid or in a mixture of nitric acid and acetic acid. 13. Method for the production of a lithographic plate according to claims 1-12, characterized in that one (i) image exposes a radiation-sensitive plate according to claims 1 - 12 and (ii) brings the exposed plate into contact with an electroless plating solution comprising a metal salt and a reducing agent to cause metal deposition on the irradiated areas of the layer to provide image areas on the lithographic printing plate. 14. Method according to claim 13, characterized in that it includes the further step of treating the image-conducting areas to make them more oleophilic and/or treating the non-image-bearing areas to make them more hydrophilic.