CA1145997A - Lacquer emulsion and process for the manufacture of lithographic printing forms - Google Patents

Abstract

Hoe 80/K 003 Abstract of the Disclosure This invention relates to a lacquer emulsion for treating imagewise exposed lithographic printing plates, the emulsion comprising water, a high boiling monovalent alcohol which cannot at all, or to only a small degree can be mixed with water, a hydro-philic polymer which is soluble or dispersible in water, a fine-grain filler, a surfactant, and a film-forming oleophilic water-insoluble polymer which is soluble in the alcohol. The invention also relates to a process for the manufacture of lithographic printing forms em-ploying the lacquer.

Description

g7 Hoe 80/K 003 LACQUER E~ULSION AND PROCESS FOR T~E MANUFACTURE
OF LITHOGRAPHIC PRINTING FORMS
The present invention relates to a lacquer emulsion which can be used for simultaneously developing and lacquerlng exposed light-sensitive lithographic printing plates.
It is known to reinforce the image areas of exposed and developed light-sensitive lithographic printing plates by treating them with a solution of an oleophilic resin in an organic solvent, whereby their resistivity and the number of prints is increased.
Such solutions are, e.g,, described in DE-PS No. 1,180,869 and in DE-PS No. 1, 244 ,582 . In many cases , no separate develop-ing step is necessary before applying the lacquer solution. This method is cailed additive developing. It is also known to use emulsions of aqueous and organic solutions for the same purp`~se.
The application of lacquer solutions or emulsions often results in considerable disadvantages, however. Some of the resins employ0d show little adhesive strength only, or they are brittle. In the case of other emulsions it is very difficult to apply them so as to obtain a layer which is of uni~orm thickness and free from streaks. Under certain circumstances it may also occur that emulsions of this kind are irreversibly separated into an aqueous and an organic phase.
Compared with so-called subtractive developing, it is very often necessary to increase the exposure times of negative print-ing plates when a lacquer emulsion is applied, ~or, due to its content of organic solvents, the lacquer also partlally attacks hardened layers .

9~3~

Quite frequently, the dissolution capaclty is drastically reduced in the course of additive developing. Further, the commer-cial products contain considerable quantities of malodorous and/or toxic solvents whose maxumum allowable concentration values are rela tively low. ~mong these solvents are: cyclo } anone (50 ppm), cyclohexanol ~50 ppm), ethylene glycol ethyl ether acetate (100 ppm), ethylene glycol monoethyl ether (200 ppm), ethylene glycol monobutyl ether (50 ppm), and acetic acid (25 ppm).
In ad~ition, lacquers of this kind in most cases have rela-tively low flashpoints of between about 50 C and 60 C. US Pa-tent No. 4,339,530, discloses a developer emulsion for subtractive devel-oping of exposed printing plates, i.e., only the non-image areas are washed out, which emulsion contains water; a higher-boiling, prefer-ably an æ aliphatic, alcohol; a surfactant; a water-soluble or in water emulsifiable polymer; and, optionally, an acid, and a water-soluble organic solvent. m is emulsion do_s not contain a water-insoluble polymer useful for reinforcing oleophilic image æeas, nor is it suitable for lacquering printing plates.
It is, therefore, the object of the present invention to provide a laoquer emulsion for lithographic printing plates which can be used ~or simultaneously developing and lacquering litho-graphic printing plates, which is free from readily volatile, toxic, malodorous solvents, which contains a relatively small portioIl of organic solvents only, which has a high flashpoint, and which makes rapid developing possible.

Hoe 80/K 003 ~5~

The subject of the present invention is a lacquer emulsion for the treatment of image-wise exposed lithographic printing plates, which comprises water, an organic solvent which cannot at all, or to only a small degree can be mixed with water, a hydrophilic water-soLuble or in water dispersible polymer, a fine-grain filler, a surfactant, and a film-forming oleophilic, water-insoLuble polymer.
In the emulsion according to this invention the organic solvent is a high-boiling monovalent alcohol.
The hydrophilic water-soLuble or in water dispersibLe poLy-mers may be substances which in water either dissolve to form clear, optlcally homogeneous solutions of the concentrations re-quired, or which, without the addition of dispersing agents, iorm stable disperslons when mixed with water.
Water-insoluble polymers are compounds which, without the additlon of auxiliary agents, in water can be neither dissolved nor dispersed to form stable dispersions.
Copolymers oE hydrophilic units, such as, e.g., vinyl amines or vinyl alcohol and their derivatives, and of hydrophobic units with long-chain alkyl groups, are especially suitable as the hydrophilic, in water dispersible polymers. Such copolymers reduce the surface tension of water and provide for an additional stabili~ation of the emulsion.
The hydrophilic units must be built-up such that their ~ -homopolymers are water-soluble. In addltion thereto ancl to the long-chain hydrophobic units, the polymers may include other units which themselves form water-insoluble homopolymers, but Ho~ 80/K 003 1~5~7 do not significantly reduce the surface tension, such as, e.~., units of vinyl acetate or low alkyl acrylates.
The constituent amount of hydrophilic monomers must be at least high enough to guarantee the solubility, or alternatively the dispersibility, in water mentioned above.
Vinyl amine derivatives, especially N-acylated vinyl amine derivatives with a tertiary nitrogen atom are preferably used as -the hydrophilic units.
The long-chain hydrophobic units preferably used are those which are derived from the alkyl esters of unsaturated carbonic acids having 4 to 30, preferably 6 to 20, carbon atoms in their alkyl groups, from vinyl aromatic compounds or from vinyL alkyl esters having ~L to 30, preferably 6 to 20 carbon atoms in their alkyl groups. Acrylic, methacrylic and maleic acids are the unsaturated carbonic acids which are preferably used. The con-stituent amount of hydrophobic monomer units of the copolymer in general is between 0.5 and 25 mole percent.
Versatic acid vinyl ester, isononanic acid vinyl ester, maleic acid dihexyl ester, ethyl hexyl acrylate, decyl methacryl-ate, lauryl acrylate, and 4-octyl styrene are exemplary of monomers representing suitable hydrophobic units.
In addition to the above-mentioned surface-active hydro-phLlic copolymers, homopolymers of the ~escribed hydrophilic monomers and copolymers of these monomers and of relatively low-molecular weight hydrophobic monomers, such as, e . g ., vinyl acetate, short-chain alkylacrylic acid esters and styrene also are suitable.
t ~c~c~ e ~ K

-- 'I --E~oe 80/~ 003 9~7 Other suitable water-soluble polymeric substances are , e,g,, ceLlulose ethers, such as methyl cellulose, carboxy methyl cellu-lose, hydroxy alkyl cellulose, salts and esters of alginic acid;
polyvinyl Lactams, such as poiyvinyl pyrrolidone and its copoly-mers with vinyL acetate, polyacrylic acid amide, polyvinyl acetidi-none and -water-soluble natural polymers, such a s gum arabic and dextrin s .
This polymer is either used alone, or it is mixed with another polymer, the concentrations dependmg upon their molecu-lar -weights and varying between 0. 05 and 25, preferably between 3 and 1 S percent by weight .
On one hand, the quantity employed should be sufficient to stabilize the emulsion and to render the image-free support hydrophilic, and on the other hand the viscosity of the mlxture must not be too high, or else processing will become too difficult.
Apart from -water, at least one high-boiling araliphatic alco-hol being practically immiscible with water or only to a small extent miscible with water, not malodorous and non-toxic is contained in the lacquer as a solvent , such as , e . g., l-phenyl ethanol ,

2-phenyl ethanol, 3-phenyl propanol-l, 4-phenyl butanol-l, 4-phenyl butanol-2, 2-phenyl butanol-l, 2-phenoxy ethanol, ~ ;
2-benzyloxy ethanol, o-methoxy benzyl alcohol, m-methoxy benzyl alcohol, p-methoxy benzyl alcohol, benzyl alcohol or mixtures of such alcohols.
As in the case of subtractive development, the quantity of this solvent of course depends upon the lithographic printing form ~3 45gg~7 Hoe 80/K 003 to be used, and in general amounts to 4 to 20, preferal~ly to 6 to 15 percent by weight.
The lacquer emulsion contains a small amount - about 0. 02 to 1 percent by weight - of at least one surfactant which may be anionic, cationic and/or non-ionogenic.
The emulsion further contains at least one mineral, fine-grained filler, such as , e.g., talc or mineral multicomponent systems, the amount of the filler varying between 5 and 35, preferably between 1 3 and 25, percent by weight .
By adding acids, e.g., phosphoric acid, the pH value can be rendered acidic, and by adding suitable buffer salts, e . g ., sodium metasllicate , the pH value can be rendered alkaline .
The lacquer ~urther contains at least one film-formlng oleophilic polymer which has a hi~h affinity towards the image carrying layer parts and forms a continuous, mechanlcally resis-tant oleophilic film. Preference is given to modlfied and unmodi-fied epoxy resins and phenolic condensation resins, such as, e.g., resoles or novolaks or their reaction products with isocya-nates. Other resins, e.g., blocked isocyanate resins or copolymers of viDyl chloride, silicone resins or alkyd resins also may be used. Resins of these types are Icnown and are, in connect~on with lacquer emulsions, described in DE-AS No.
1,143,710, DE-AS No. 1,268,972, and in DE-AS No.
1, 194, 260~
The quantity of the oleophilic resins depends upon the nature of the resin employed. In general, it is between 2 and L5~9~ Hoe 8 0/K 0 03 8, preferably between 3 and 6, percent by weight, ~ or dyeing the lacquer emulsion, carbon black ls usually employed, but other dyed organic or inorganic pigments and sol-uble dyes also may be used. The lacquer emulslon according to the present in~ention is preferably dyed with pigment paste dis-persions in which the very finely dispersed pigment is kept in a suspended state with the aid of surfactan~s , e,g., in a mixture of water and ethylene gLycol. A great number of commercial compositions of this kind are available, The added amount oi solid pigment matter is 0,3 to 6, preferably 0,5 to 2.5, percent by weight, relative to the total emulsion.
Small quantities of other organic solvents , e . g ., of poly-valent alcohols, such as glycerol, ethylene glycol, sorbitol, pentaerythritol and poLyalkylene glycols, and of ketones, esters and aliphatic alcohols also may be added to the lacquer emulsion, if - with regard to the composition of the copying layer - such an addition seems desirable, Bearing in mind that ecological acceptability is among the desired features of the lacquer accord-ing to this invention, the added amount of these substances should be kept as low as possible, however.
The preparation of lacquer emulsions of this kind is slmple: the components are worked ~nto_a finel~ divided disper~
sion by means of, e.g., a high-speed mixer or a ball or pearl mlll. Apart from a gradual settling of the mineral fllLer due to its higher specific weight, such dispersions remain stable over a long time. Brief shaking restores good -workability of the emulsions .

1~4~ 7 ~loe ~0/K 003 Processing of the tacquer emulsion is made by soaking a sponge or cloth with the lacquer emulsion and then applying it onto a subtractively developed printing plate by rubbing. The acceptance of the lacquer by the oleophilic layer areas can be seen from a strong dyeing of these oleophilic areas. By gravi-metric tests it has been found that a layer having a weight of up to 5 g/m2 can be applied onto the layer already present.
Lacquers by means of which an additional layer of about 1 to 3 g/m2 is applied have proved to be especially suitable. It is also possible to formuLate printing plates which with this lacquer can be developed and lacquered in one step. This processing method is preferably used.
In general, the number of prints which are obtained from the printing forms prepared in this way is by 5 0 to 100 percent higher than in the case of corresponding, subtractively developed printing forms, If the lacquers are composed appropriately, the number of prints can be further increased by means of a subse-quent thermal treatment (baking).
Another advantage of the Lacquer according to the present invention is that quit~ often the quantities of light which are re-quired for developing negative-working copying layers are smaller than the light quantities which are needed in the case of a sub-tractive development of the same layers. Therefore, an increased practical light sensitivity results from the treatment proposed by this invention, The lacquer emulsions according to the present invention are preferably used for negative-working la~ers which are mainly 97 Hoe 80/K 00 composed of a diazo polycondensation product and of a water-insoluble polymeric binder. It is also possible, however, to lacquer exposed and optionally developed photopolymerizable copy-ing layers with these emulsions. Binders suitable for such layers are polymeric vinyl esters, such as, e . g., polyvinyl acetate, polyvinyl propionate, polyvinyl benzoate, polyvinyl isononanate, polyvinyl versatate, polyvinyl chloride, polyvinylidene chloride and partly saponified derivatives of these polymers; polymeric acrylic and methacrylic acid esters wherein the alcohol component may have between 1 and 20 carbon atoms; polyvinyl acetals, such as polyvinyl formal, polyvinyl butyral or polyvinyl benzal, which in addition may contain different quantities of OH and acetate groups; copolymers o~ the above mentioned substance classes, e. g., with crotonic acid, maleic acid esters and fumaric acid esters, acrylic acid and methacrylic acid; homopolymers of styrene or copolymers with the above monomers; modified and non-rnodified epoxy resins whose free epoxy groups have, e.g. been reacted with organic or inorganic acids; phenol- and cresol-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins, branched and linear polyurethane resins, and polyurethanes having terrninal isocyanate groups; copolymers of reactive monomers, such as , e.g., N-methylol acrylamide or acetoacetyl ethyl acrylate , with vinyl esters, acrylates, methacrylates and the like; alkyd resins, polyamide resins, polycarbonates and polyethylene resins, including those which have been modified with carboxyl groups.
It is known how to combine such binders into light-sensitive layers with light-sensitive substances. In general, Hoe 80/K 003 ~LS~37 these layers also contain pigments, dyes, indicators, acids, plasticizers, water-soluble polymers, surfactants, and the like.
These additives are al so known . Suitable layers are , e . g ., descrlbed in DE-OS Nos . 2,024,244; 2,034,6S4; 2,034,655;
2,039,861; 2,331,377; 2,739,774; 2,822,887; 2,834,059; and in U . S . Patent No . 3,660,097.
In general, the layer supports employed are made of one of the materials conventionally used for printing plates, such as, e.g., paper, plastic films, aluminum, copper, zinc, s~eel and similar materials. Special preference is given to alumlnum which for this purpose generally is roughened mechanically, chemically or electrochemically, and in addition may be anodically oxidized if necessary. It also may be advantageous to treat this support material with polyvinyl phosphonic acid, phosphate, silicate, hexafluorozirconate, chromate, borate, polyacrylamide, cellulose derivatives or similar materials.
In the following examples preferred embodiments of this invention are described. If not otherwise stated, quantity rela-tive numbers and percentages mean units oE weight. Parts by weight (p.b.w.~ and parts by volume (p.b.v.) are in the ratio of g to ml .
Example 1 2.4 p . b. w . of a polycondensation product of 1 mole of 3-methoxy-diphenylamine 4-diazonium chloride and 1 mole of 4,~ bis-methoxy-methyl diphenyl ether, precipitated as mesitylene sulfonate, ~L~'39';i~ Ho~ ~ 0/K 003 28.8 p.b.w. of a solution of a non-plastiEied urea resin of medium viscosity (65 percent in butanol), 0.45 p,b.w. of phosphoric acid (85 percent), and 1.2 p.b.w, of Victoria Pure Blue FGA (C.I, Basic Blue 81) were dissolved in 300 p.b,v. of ethylene glycol monomethyl ether and applied onto a layer support such that the dried layer had a weight of 0. 3 g/m . The layer support was composed of electro-chemically roughened and anodically oxi~ized aluminum having an oxide layer weight of 3 g/m2, and had been after-treated with polyvinyl phosphonic acid. A presensitized lithographic printing plate which had been prepared in this way was imagewise exposed and in one step developed and lacquered with a lacquer emulsion of the following composition:
65 0 p . b . w . of water, p.b.w. of poly~N-vinyl-N-methyl acetamide, p . b. vr . of an epoxy resin (75 percent in xylene) having an epoxy equivalent weight of 450 - 525, an epoxy value oi 0.19 -O. 22 and a softenin~ pomt of 65 - 75 (~, p . b . w . of 2-phenyl ethanol, 2 . 5 p . b . w, of phosphoric acid (85 percent), ~ ~ -220 p. b . w. of talc, and p.b.w. of a 30 percent carbon black dispersion in ethylene glycol~water ~1: 3). The carbon black dispersion contained about 1 percent of a non-ionic surfactant.

~ 11 -Hoe 8O~K 00 This practically odorless lacquer could be processed rapidly, whereby completely covered, deep-black solid areas were obta ined, whereas not even the finest screened areas were smudged, nor were visible layer remainders left.
For comparison, a printlng plate which had been prepared and exposed in the same way was developed with a solution of:
2 p . b . w . of benzyl alcohol, O. 3 p.b. w. of sodium metasilicate 9 H20, and p . b . w. oE sodium lauryl sulfate in 96. 7 p.b.w. of water.
In ordsr to obtain the same number of fully hardened steps on a step wedge which had besn copied simultaneously, the exposurs time had to be increased by about 40 percent compared with the first test.
In a lithographic press the number of prints obtalned from the additively developed printing form was ~0 percent higher than the number of prints obtained from the subtractively developed printing form.
Example 2 After imagewise exposure the lithographic printing plate described in Example 1 was treated with a lacquer emulsion of the following composition:
4 8 p . b . w . of water, 4 . 5 p . b . w. of the epoxy resin described in Example 1, p . b. w . of gum arabic, p . b . w . of 2-phenoxy ethanol, p, b, w . of benzyl alcohol, i;997 Hoe 80/K 003 4 . 7 p . b . w . of ethylene glycol, 0 . 2 p . b. w, of phosphoric acid (85 percent), 4.75 p.b.w. of the carbon black dispersion described in Example 1, and 17 . 5 p . b . w . of a mineral three-component composition of mlca, chlorite, and quartz having an apparent density of 470 g/l and a grain size distribution of 99 percent below 1 5~m .
Here, also, it was possLble to reduce the exposure time compared with subtractive developing as described in Example l;
the number of prints obtained could be increased by about 50 percent .
Example 3 After imagewise laser exposure (10 mJ/cm2), the presen-sitized lithographic printing plate described in Example 1 was treated with a lacquer of the following composition:
74 2 p . b . w . of water, 12 8 p, b . w . of gu m arabic, 2054. 6 p.b.w. of a cresol-formaldehyde novoLak having a softening point of 105 ~ 12 0 C, 170 p~,b.w. of 2-phenoxy ethanol,

3 p . b. w. of phosphoric acid (85 percent), 198 p.b.w. of the filler described m Example 2, 72 p,b.w. of ethylene glycol, and 72 p. b. w. of the pigment dispersl~n described in Example 1.

IL3L~ 7 Hoe 80/K 003 This lacquer emulslon could be processed ~rery easlly, even by unskilled persons, as its oleophilic phase was extremel~ well ac-cepted by the image areas o~ the printing plate. The number o~ prints ob-tained from a printing form which had been prepared in this wa~ was at least three times as high as the number o~ prints obtained in the case of subtractive development.
When heating the printing form which had been lacquered as proposed by this invention for 6 minutes to 230 C, the num-ber of prints obtained was more than 5 times higher, whereas in the case of a subtractively developed printing plate the nu~nber of prints could not be noticeably increased by heating the plate.
Example 4 1.15 p.b.w. of the diazo condensation product described in Example 1, 3 . 45 p b . w ~ of a polyurethane binder having a softening point of about 110 C which had been prepared by reacting 0.125 mole of a triisocyanate of 1 mole of trimethyloL
propane and 3 moles oE tolylene diiso-cyanate with 0.3~6 mole of hexane diol-1, 6, 0 . 4 p . b . w . of Victoria Pure Blue, 0. 04 p.b w. of metanil yellow (C.I. 13 ,065), and 0 . 1 p . b . w . of phosphoric acid (85 percent), were dissolved in 100 p.b.v. of ethylene glycol monomethyl ether and applied onto the layer support described in Example 1, such that the weight of the dried layer was 0. 6 g/m . After ~-~.4~ii99~ Hoe 80/K 003 imagewise exposure, the lacquer described in Example 3 was applied. Similar results were obtained.
Exam~le 5 A solution of l . 4 p. b. w. of a copolymer of methyl methacrylate and methacrylic acid having an acid number of 105, l . 4 p . b. w . of trimethylol ethane triacrylate, 0 . 4 p . b . w . of l, 6-dihydroxy ethoxy hexane, and 0. 05 p.b.w. of benz-(a)-acridine in 13 p . b . w . of ethylene glycol monoethyl ether, was filtered and applied onto electrolytically roughened and anodically oxidized aluminum (3 g of oxide per m2) in such a quantity that, after drying, a layer weight of 5 g/m2 was obtain ed .
The plate was Lmagewise exposed and developed with a solution of 3 p.b.w. of sodium metasilicate, 0 . 05 p . b . w . of strontium chloride, 0 . 03 p . b. w. of sodium lauryl sulfate, 2 p.b.w. of a copolymer of N-vinyl-N-methyl acetamide and octyl acrylate (91 : 9), and 3 p . b . w . of 2-phenoxy ethanol in 10 0 p . b . w . of water .
Thereafter the plate was treated with the lacquer de~ `
scribed in Example 3, in order to obtain a higher number of prints .

~ .

1~4599'7 Hoe 80/K 003 It will be obvious to those skilled in the art that many modifications may be made within the scope of the present inven-tion without departing from the spirit thereof, and the invention includes all such modifications.

Claims (10)

Hoe 80/K 003 WHAT IS CLAIMED IS:

1. A lacquer emulsion for treating imagewise exposed lithogra-phic printing plates, said emulsion comprising water, a high boiling mono-valent alcohol which cannot at all or to only a small degree can be mixed with water, a hydrophilic polymer which is soluble or dispersible in water, a fine-grain filler, a surfactant, and a film-forming oleophilic water-insoluble polymer which is soluble in the alcohol.

2. A lacquer emulsion as claimed in claim 1 which contains about 4 - 20 percent by weight of the high-boiling monovalent alcohol.

3. A lacquer emulsion as claimed in claim 1 which contains about 0.05 - 25 percent by weight of the polymer which is sol-uble in water or dispersible in water.

4. A lacquer emulsion as claimed in claim 1 which contains about 0.02 - 1 percent by weight of the surfactant.

5. A lacquer emulsion as claimed in claim 1 which contains about 2 - 8 percent by weight of the water-insoluble polymer.

6. A lacquer emulsion as claimed in claim 1 which contains about 10 - 30 percent by weight of the filler.

7. A lacquer emulsion as claimed in claim 1 which addi-tionally contains a color pigment or a dye.

8. A lacquer emulsion as claimed in claim 1 which addi-tionally contains a polyvalent aliphatic alcohol.

Hoe 80/K 003

9. A process for the manufacture of lithographic printing forms, comprising treating a lithographic printing plate, which has been imagewise exposed and developed, with a lacquer emul-sion as claimed in claim 1.

10. A process for the manufacture of lithographic printing forms, which comprises simultaneously developing and lacquering an imagewise exposed lithographic printing plate with a lacquer emulsion as claimed in claim 1.