DE2653824A1 - DESENSITIZER FOR LITHOGRAPHIC PRINT PLATE AND METHOD OF APPLICATION - Google Patents

Description

PATENT LAWYERS

DiL E WIEGAND DIPL-ING. W. NIbVAANN DR- M. KÖHLER DIPL-ING. C. GERKHAR ¹ JT

MUNICH HAMBURG / D O O 0 Z H

TELEPHONE: 55547 «8000 M 0 N CH E N 2,

TELEGRAMS: KARPATENT L · MATH ILDENSTRASSE

TELEX: 529068 K AR P D '*

¥ 42 707/76 - Ko / Ja November 26, 1976

Fuji Photo Film Co., Ltd. Minami Ashigara-Shi, Kanagawa (Japan)

Desensitizer for lithographic printing plates and method for its use

The invention relates to an improved desensitizer for lithographic printing plates.

A lithographic printing plate is usually exposed to actinic radiation and then imagewise subjected to development treatment with a suitable solvent, * so that either the exposed areas or the unexposed areas are removed, thereby obtaining an ink-accepting image for printing.

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A printing plate made by removing the unexposed areas during development and which is an ink-receptive image corresponding to the exposed area versus a having hydrophilic support surface is referred to as negative working plate, while in the case of the positive working plate the unexposed area becomes ink-receptive after the exposed area at the Development has been removed. Both types of printing plates require the stages of exposure and development, however, depending on the requirements of the developer vary on the composition and properties of the photosensitive layer used, which usually comprises a photosensitive material, a binder, additives and the like. Different developers are known and include the aqueous photosensitive developer described in U.S. Patent No. 3,751,257 Diazo compositions, an aqueous one described in US Pat. No. 3,458,311 alkaline developer for use in developing photopolymerizable compositions, a developer of the organic solvent type containing a surfactant together with an acid corresponding to US Pat. No. 3,701,657 for use in photocurable polymer compositions.

After development with any of these developers, the developer can be removed from the surface of the printing plate removed by rinsing with water. If the developer is mainly an organic solvent, which removes the photosensitive layer by dissolving or converting it into a practically dissolved state, includes rinsing with water after development to remove the remaining developer Tendency that the photosensitive mass dissolved in the developer aggregates and deposits on the plate surface,

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Έ-ynes such deposition takes the ink to during .anschließenden pressure, so that a contamination is caused. Accordingly, when using a developer mainly containing an organic solvent, it is common practice to swell the photosensitive layer and remove it in the form of pieces of film, for which reference is mainly made to U.S. Patent 3,136,637. Such a method requires physical action in order to remove the film pieces after the layer has swelled, but has the distinct advantage that the developer is not contaminated with the mass to be removed from the carrier. Another method is already known in which an "aqueous colloid is used in place of water for rinsing in order to remove or replace the remaining developer mainly containing an organic solvent by dissolving the photosensitive layer. In this method, water is not used for Rinsing is required and it is characterized in that if the plate is wiped with a sufficient amount of a colloid solution for the soiled developer remaining on the plate and dried, the colloidal component acts as a protective rubber for the non-image areas are used under carefully controlled conditions and, if deviated from these conditions, the non-image areas show a tendency to attract the ink to cause so-called background staining 738,850 and 3,745,028 were not sufficiently effective in reducing staining during printing, and the results depend on the manufacturing conditions of the photosensitive plate used. This dependency is evidenced by the fact that occasionally a ver

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pollution occurs.

A main object of the invention is to provide an improved desensitizer for a lithographic Printing plate.

Another object of the invention is to provide an improved desensitizer that removes a developer-containing photosensitive composition can be used without the need for any water rinsing is in a method where a developer mainly containing an organic solvent and that for removing the non-image areas of the photosensitive compositions by dissolving or swelling these compositions after imagewise exposure of the photosensitive lithographic composition to active radiation.

Another object of the invention is an improved desensitizer having the favorable ability the replacement of the developer after development and at the same time the restoration and solidification of the hydrophilic ones Properties of the non-image areas.

Another object of the invention is to provide an improved developer for use in a method to prepare the developer by replacing it with the desensitizer after development, during which no deposition the photosensitive masses removed from the non-image area is caused on the image area.

Another object of the invention is one Desensitizer with a wide range of uses with various Printing plates made under different conditions.

As a result of extensive research into the development of desensitizers with a wide range of different! Plates manufactured under the conditions of manufacture will accomplish the various objectives listed above

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2 6 -. 3 3 2

now achieved by boric acid, nitric acid or a salt thereof or potassium borohydride or sodium borohydride be combined with an aqueous colloidal material under acidic conditions.

In a completely unexpected manner, the desensitizer obtained according to the invention was found to be complete Effective for removing dirt even on one that has been printed more than 10 months after manufacture photosensitive plate. This beneficial behavior was even more pronounced when a polyhydric alcohol was added. The desensitizer compositions have been found to be extremely beneficial the problem of the deposition of the photosensitive composition on the image area after the removal of the non-image area to solve.

It has also been found that the desensitizers according to the invention not only function as a substitute for the developer, but also have the function of a protective rubber that is largely on the Field of lithographic printing is used.

The desensitizer according to the invention consists of an aqueous solution with a pH of about 1.2 to about 7.0, the essential components of which are (i) a hydrophilic colloidal compound, (ii) a polyhydric alcohol and (iii) boric acid, nitric acid or a salt thereof, or potassium borohydride or sodium borohydride.

The hydrophilic colloid used in the context of the invention must be water-soluble and as such form a film. An important factor is the viscosity of the aqueous solution of the desensitizer composition. The suitable viscosity can be in the range from about 5 to about 120 cp at 25 ^° C. and the preferred viscosity is in the range from about 5 to about 120 cp at 25 ^° C. As this is common practice at times

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ORIGINAL

_a 26- ^ 3824

⁴ ir

for various treating agents used with lithographic printing plates is supplied as a concentrate and to be diluted before use is the viscosity range given above for the aqueous solution of the hydrophilic colloid that during use. Appropriate ones meeting such requirements hydrophilic colloids include natural products and derivatives of these, such as gum arabic, dextrin, cellulose derivatives, for example carboxymethyl cellulose, carboxyethyl cellulose, Hydroxyethyl cellulose, methyl cellulose and the like, synthetic polymeric materials such as polyvinyl alcohol and derivatives thereof, polyvinyl pyrrolidone, in aqueous Solution soluble acrylic acid copolymers, copolymers of vinyl methyl ether and maleic anhydride, copolymers of Vinyl acetate and maleic anhydride and the like .. This mate- ' rials can be used individually or in combination. The preferred materials are gum arabic, Dextrin and cellulose derivatives, preferably carboxymethyl cellulose and particularly preferably a carboxymethyl cellulose having a degree of polymerization of about 500 or less.

Suitable polyhydric alcohols that can be used include Ethylene glycol and polyethylene glycol with a degree of condensation of 2 to 500, propylene glycol, dipropylene glycol, tripropylene glycol, Sorbitol, pentaerythritol, glycerin and the like .. Suitable polyhydric alcohols that can be used are those which are water-soluble, and a preferred range for the number of hydroxyl groups is 2 to 6. These are polyvalent Alcohols can be used singly or in combination, for example a combination of polyhydric ones Alcohol that is different or that is the same but has different molecular weights.

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However, the general rules of such a combination cannot be specifically given here as the appropriate ones Combinations are dependent on the properties of the colloidal material used. The polyvalent alcohol works effectively when at a concentration of about 1 to about 30 weight percent, more preferably 5 to 20 weight percent based on the weight of the total mass. The amount of hydrophilic colloid used depends on the viscosity of the desensitizer obtained from and based on the same, the general range is about 0.5 to 20% by weight, on a dry basis.

The appropriate amount of boric acid, nitric acid or a salt thereof, or potassium borohydride or sodium borohydride depends somewhat on the type of compound, the type of hydrophilic colloid used with it, and the pH range of the solution and based on the results is generally in the range of about 0.5 to about 20% by weight, based on the Weight of the total mass. A more preferred range is 1 to 10 wt%. Suitable salts of boric acid or nitric acid are the water soluble and include the sodium, potassium, ammonium, magnesium, nickel, zinc salts and the like Salts. Specific examples of suitable salts of boric acid or nitric acid include sodium borate, sodium nitrate, Potassium borohydride, sodium borohydride, potassium nitrate, ammonium borate, ammonium nitrate, magnesium nitrate, zinc nitrate, Nickel nitrate and the like. These materials can be used singly or in combination. If two salts or more are to be used, the total amount of the salts is in the range listed above.

The desensitizer used according to the invention is preferably prepared so that it has a pH value when it is used between about 1.2 and about 7.0, and more preferably between 2 and 5. To adjust the pH value, can an inorganic or organic acid can be added.

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- 8 - ■

Suitable inorganic acids that can be used include hydrochloric acid, sulfuric acid, boric acid, nitric acid, phosphoric acid, hydrofluoric acid, hydrozirconium fluoric acid, Hydrosilicofluoric acid and the like and suitable organic acids include oxalic acid, Citric acid, tartaric acid, lactic acid, hydroxyacetic acid, Acetic acid, benzenesulfonic acid, toluenesulfonic acid, gallic acid, 2-Hydroxy-4-methoxybenzophenone-5-sulfonic acid and the like.

The addition of a surfactant, in particular an anionic or nonionic surfactant is also advantageous, but not essential.

Suitable examples of anionic surfactants include salts of long-chain aliphatic acids, salts of sulfuric acid esters of higher alcohols, salts of Phosphoric acid esters of long-chain aliphatic alcohols, sulfonic acid salts of dibasic aliphatic acid esters, Salts of aliphatic acid sulfonamides, salts of alkylarylsulfonic acids, Salts of naphthalenesulfonic acid-formaldehyde condensates and the like. Suitable examples of nonionic surfactants include polyoxyethylene alkyl ethers, Polyoxyethylene alkyl phenol ether, polyoxyethylene alkyl ester, Sorbitan alkyl esters, polyoxypropylene polyoxyethylene ethers and the like « These surfactants can be used individually or as mixtures be used. The preferred amount of these materials is less than about 10 weight percent based on that Total weight of the mass, although this limit is not particularly critical.

The desensitizer according to the invention is special suitable for lithographic plates with a negative-working photosensitive composition, in particular the following Contains photosensitive polymers, but can be used for other purposes.

Suitable photosensitive polymers include those based on one of the following photosensitive compounds: Polyesters, polyamides or polycarbonates, which are a

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repeating unit -CH = CH-C- contain, for example

a photosensitive polymer having a photosensitive group in the polymer backbone, such as in U.S. Patents 3,030,208 and 3,707,373 such as a photosensitive prepared from p-phenyl diacrylic acid and a diol Polyester, a photosensitive polymer disclosed in U.S. Patents 2,956,878 and 3,173,787, such as a of a functional glycol and a 2-propylidene malonic acid compound, such as cinnamylidene malonic acid-derived photosensitive polyester and the like, photosensitive Polymers according to US Pat. No. 2,690,966, 2,752,372 and 2,732,301, such as cinnamic acid esters of a hydroxyl group Polymers such as polyvinyl alcohol, starch, cellulose and the like., Photosensitive polymers according to U.S. Patent 3,804,628 corresponding to Japanese Patent Publication 11102/73 such as homopolymers and copolymers of cinnamic acid esters of hydroxyalkyl acrylate and the like.

Other suitable photosensitive polymers include photopolymers having repeating units with a Azide groups which are also useful and include polymers of vinylbenzoic acid azide such as those described in US Pat Japanese Patent Publication 28499/65, polymers disclosed in U.S. Patent 3,096,311, respectively GB-PS 843 541 and the like. Which change in solubility due to exposure to light, such as Polyvinyl azide benzal acetate. In addition, one can use other compositions based on a light-polymerizable material use, such as those indicated in US Pat. No. 2,760 and those which contain a polymeric binder and a diazo resin disclosed in Japanese Patent Application 36207/75.

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With regard to those in the above references suitable photosensitive compounds listed for negative-working plates that can be used according to the invention, the relevant information in the cited references are particularly included in the present description.

The desensitizer according to the invention can also be used with positive working lithographic plates. Photosensitive materials useful for positive type plates are, for example, the sulfonic acid esters or sulfonic acid amides of o-quinonediazide such as naphthoquinone-1,2-diazide-4- (or -5 ^ sulfonic acid ester of a polyhydroxyphenyl resin prepared by condensing acetone with pyrogallol, naphthoquinone -1,2-diazide-4 (or -5 ^ sulfonic acid ester according to US-PS 3,635,709, naphthoquinone-1,2-diazide-4 (or -5) -sulfonic acid ester of a cresol-formaldehyde resin according to US-PS 3 046 120 and 3 188 210, naphthoquinone-1,2-diazid-4 (or ^ -sulphonic acid amides of polymerized amines, for example HpN (C ^ gHy ₀

^ 18 ^ 37 ^s tsprechend ^ he Japanese Patent Application reproduced 96575/73 / Other useful POS include those containing a heteropolyacid or an isopolyacid of metals of the groups Va and VIa of the periodic table and a Diazoharζ, as described in US-PS 3,211,533 and those as disclosed in Japanese Patent Publication 23684/68, which comprise a diazo resin and a half ester derived from a polymer material of a hydroxyl group and phthalic anhydride, and the like.

Suitable support materials for such photosensitive compositions include aluminum, aluminum alloys, tin, magnesium _/ chromium and the like, and the surface of these substrates can be treated using any of the following surface treatments: a sodium silicate treatment according to US Pat.

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speaking of Japanese Patent Publication 22063/61, a polyvinylbenzenesulfonic acid treatment according to Japanese Patent Publication 23982/64, a polyacrylic acid treatment corresponding to Japanese Patent Publication 706/59, corresponding to a phosphate glass treatment GB-PS S82 856 and the like. Furthermore, a marble grain, brush grain corresponding to the Japanese Patent Application 33911/73, U.S. Patent 3,550,320, and the like. and an electrolytic grain according to Japanese Patent Publication No. 27481/71 also for surface treatment can be used. These methods can be used individually or in combination, or they can additionally combined with an anodic oxidation treatment.

Suitable anodizing processes or anodic oxidizing processes include a direct current electrolytic process in aqueous sulfuric acid solution disclosed in Japanese Patent Publication 27481/71, a phosphoric acid electrolyzing process corresponding to US Pat. No. 3,511,661. and electrolysis in sulfuric acid solution with immersion treatment in a phosphoric acid bath according to DT-OS 2 404 657.

The desensitizer according to the invention is used in the following way: After the photosensitive lithographic Printing plate exposed to active radiation and developed with an organic solvent type developer the desensitizer is spread over the developed plate, which is still damp from the developer, for example, using cotton wool or a sponge, and gently rubbed, thereby removing the developer on the surface of the plate is removed and replaced by the desensitizer and at the same time the components of the desensitizer to restore the hydrophilicity of the plate and to protect the plate surface the attack by the printing ink on the background during printing, so that it is free of dirt or sludge

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- reproductions can be obtained.

Suitable developers which can be used in the context of the invention are aqueous alkali solutions which are well known as developing solutions for positive-working photosensitive layers. Examples of suitable alkaline aqueous solutions include aqueous solutions of an inorganic alkali such as sodium hydroxide, potassium hydroxide, sodium silicate, potassium silicate, sodium tertiary phosphate, potassium tertiary phosphate, sodium carbonate, potassium carbonate, an aqueous solution of an organic base such as ethanolamine and the like Materials. Furthermore, an organic solvent, a
surface-active agent and the like. If desired, this
can be added, that is, when the wettability and the penetrability of the developing solution due to a coated on the positive-working photosensitive layer
organic material layer compared to the speed of the same in the case of using the developing solution
is low directly on the positive working photosensitive layer, it is preferred to add an organic solvent such as n-propyl alcohol or a surface active agent such as sodium lauryl sulfate.

After the desensitizer replacement is complete, the plate can be rinsed with water as described above, or the plate can be rinsed with a piece of one
wiped off with a soft cloth and left to dry. In the latter case, the treatment level can be shortened
since the desensitizer also acts as a protective rubber, the coating of which is inevitably carried out in the final stage of plate-making.

The desensitizer according to the invention can be used as a protective rubber in the final stage of plate making
or as a rubber to prevent plate contamination,
if printing is interrupted for any reason,

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2BB3824

for example, interruption of the operating device, can be used. The desensitizer according to the invention has an improved effect of preventing plate fouling because of the hydrophilic nature of the Plate surface reinforced better than a common aqueous gum arabic solution. In summary, serves the desensitizer according to the invention not only as an improved one Rubber solution for lithographic printing, but also as a removal agent for mainly a soiled developer comprising an organic solvent after development.

The present invention is explained below with specific reference to the examples, without the invention being limited thereto. Unless otherwise specified, all parts, percentages, Ratios and the like. Based on weight.

example 1

A 2S aluminum plate mechanically constructed in accordance with the method described in Japanese Patent Application 33911/73 corresponding to U.S. Patent Application Serial No. A method as described by August 30, 1972 284,851 had been grained was partially etched on the surface by immersion for one minute in an aqueous 2% sodium hydroxide solution at 4O ⁰ C. After rinsing the plate with water, the plate was then immersed in nitric acid (70% by weight) for one minute to expose the pure aluminum surface. Then, the plate was subjected to anodic oxidation treatment in an aqueous 20% sulfuric acid solution using a current of 15 volts direct current at a current density of 3 A / dm for 2 minutes. After rinsing with water, the plate was in

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ORIGINAL INSPECTED

- K-

immersed a 10% aqueous solution of phosphoric acid for 30 sec. at 5O ⁰ C, washed again with water, then in a 2% solution of sodium silicate (product JIS-3) immersed in 7CPC for 2 minutes, rinsed with water and by heating (60 ° C) dried. After the aluminum plate was cooled to room temperature (about 20-30 ⁰ C), a sub-coating mixture of the following composition was coated on the plate using a roll coating device:

Each polyvinylpyrrolidone (K-90, product

from the Baden aniline and soda factory) 2.5 g

Methyl alcohol 1000 ml

The coated plate was dried at 10CPC for 2 minutes and then coated with the following photosensitive composition.

Polyester (condensation product of p-phenylene diethoxy acrylate and 1,4-ß-hydroxyethoxycyclohexane, molar ratio 1: 1) 115 g

Tert-Butylphenolharz (PR-5O53O, product of Sumitomo Durez Co., melting point 62-72 ⁰ C,

: 1.85 - 2.10, 10 g / 100 ml ethyl alcohol 5 g

2-benzoylmethylene-i-methyl-ß-naphthothiazoline 5.7 g

Diheptyl phthalate 48 g

4.4 ^t -thio-bis (3-methyl-6-tert-butylphenol) 2.5 g

Phthalocyanine blue (Color Index No. CI.

Pigment Blue No. 15) 25 g

Monochlorobenzene 1880 g

Ethylene dichloride. 1221 g

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Drying takes place at 100 ^° C. for 2 minutes. The coating weight was 1.2 grams on a dry basis. The plate thus prepared was brought into contact with a transparent optically negative original film in a vacuum printing frame, through which exposure was carried out using a light source for PS plates available from Fuji Photo Film Co., Ltd. under the name "Fuji Film PS Light ", which was equipped with the Toshiba metal halide lamp MU-2000-0L with a capacity of 3 KW, was carried out for seconds at a distance of 1 meter between the plate and the light source.

A sufficient amount of a 90% aqueous lactic acid solution was then applied to the photosensitive The surface of the plate was poured, spread over the entire surface with a piece of cotton wool and then became rub the surface gently for 30 seconds until the photosensitive coating of the unexposed area was completely removed. The developer remaining on the surface after development was squeezed off and then a desensitizer of the following composition was applied at an amount of 100 ml / m over the surface spread out with a piece of cotton wool:

Gum arabic (solution with 70 Be) 900 g glycerine 100 g

Phosphoric acid (85% aqueous solution) 20 g benzyl alcohol 10 g

Noigen ET-120 (product of Daiichi Kogyo Seiyaku Co., nonyl ether from Polyoxyethylene) 2 g

Sodium borate 50 g

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After the surface has been rubbed lightly,

the contaminated desensitizer was absorbed in a piece of cotton wool and removed from the surface. Again an appropriate amount (100 ml / m) of the fresh desensitizer was applied over the entire surface of the plate spread and then wiped with a soft cloth, and the plate was then dried at room temperature.

After the development, a sharp point image with no fringes was obtained on the plate and the one obtained thereby Plate was mounted on a printing device and used for printing. The results were prints with good reproductions of the original with no contamination (ink contamination) at the non-image areas and dot destruction (Pointing out) on the dark areas (or shadow areas).

Comparative example 1

3 sheets of the photosensitive lithographic plate prepared in the same manner as in Example 1 were thermostatically held at 100 ^° C. for 30 minutes and allowed to cool to room temperature, whereupon they were exposed in the same manner as in Example 1 using the same light source and were developed. The first plate, designated Plate A, was treated with the desensitizer of Example 1 under the same conditions as above. The second plate B was treated with a desensitizer similar to that of Example 1, except that the desensitizer did not contain sodium borate. The third plate C was treated with an aqueous gum arabic solution of 7 ⁰ Be. ¹ Although all plates have a similar appearance after development and desensitization

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2 R ^ "ΐ Π

They exhibited completely different behavior when printing 2000 reproductions were subjected. On plate C, there was an ink deposit on the background areas between 200 and 500 prints took place and the spots grew until clear between 1000 and 2000 prints were detectable. In the case of plate B, there was a slight tendency to stain the background between 1000 and 2000 reproductions observed while on plate A desensitized with the desensitizer from Example 1 there was no pollution at all.

Examples 2 to 16

Lithographic photosensitive bodies prepared according to the procedures and conditions of Example 1 Plates were prepared under the same conditions as in Example 1 and with a developer of the following Composition developed:

4-butyrolactone 1000 ml

Glycerin 100 ml

Phosphoric acid (85/6 aqueous solution) 25 ml

Zonyl A (product of E.I. Du Pont de Nemours & Co., the following chemical Formula:

) 10 g of pure water 100 ml

D _a nn was desensitized each of the plates with one of the listed in the following table desensitizers.

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ORIGINAL INSPECTED

For each desensitizer 2 plates were made, one of which was used for printing immediately after desensitization, while the others for printing after a week of storage thereafter used to desensitization. No background pollution was observed on all plates during the pressing of 200 reproductions, all the same whether the plate was used for printing immediately after desensitization or after one week of storage,

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Desensitizer approach used Component Belspiel no.

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Hydrophilic colloid component

Gum arabic (aqueous solution 900g900g 900g- 900g 900g 900g 900g .-- - - - - - -

of 7 ⁰ Be ')

Cellogen 7A * 1 ------- 30g 30g 30g 30g 30g - _dj> ^

Cream dextrin * 2 --------- - - - 90g 90g 90g ~ ^ ~

M ore value alcohol component

ι ^! Ethylenr; lykoI -100 ------- - - - - - - N>

O 'polyethylene glycol 1000 80 τ. - 80 80 80 - - - -, cn

(Molecular weight 1000) "^ ¹

Q. Polyethylene glycol 4000 60 60 100 60 60 - - - 100 60 60 60 60.S £

"Ζ, ο (molecular weight 4000) '£ ·

j- "CD \ S r ~,

- °° Boric acid / nitric acid or salts thereof, borohydride component - '

ZN) Boric acid T3 - ⁷ ZB - - - - 20 20 20 - 20 20

^ °° Sodium borate - - - 15, 25 25 - -

■ rn Q magnesium nitrite - - 15- 25- - - - 15 - - - 15 25

£ ■} ^ ₀ nitric acid _ · | 5 --_-_-_ - - - - - -

ffl _ *

O - ~ j Not an essential component

Pure water 100 -. - - - - 900 900 900 900 900 900 900 900

Phosphoric acid (85% aqueous solution) 20 20 20 20 20 - 20 20 25 20 20 20

Oxalic acid _-__- 20--20- - - - - -

Citric acid - - -6.5- - 15-

Noigen ET-120 * 3 -53- 33-3- 3 - - 3 3 3 '

Monogenic Υ-100 * 4 '3--3-_ 3- 3- - - - -'

Aerosol OS 5 ---------- 33 ---

Benzyl alcohol 20 - - - 12 12 - 20 - - - - - -

£ H; ■ 1.9 3.2 1.7 6.9 1.7 3.5 5.1 2.1 1.6 2; o '4.5 3.0 1.6 1.3 1.4

Cellogen 7A: carboxymethyl cellulose, viscosity from 10 to

20 ep at 25 ^° C. of an aqueous solution with 2% by weight,

Product of the Daiichi Kogyo Seiyaku Co.

Cream dextrin:

50% aqueous solution with a viscosity of 430 cp, product of Matsutani Kagaku Co.

Noigen ET-120:

Polyoxyethylene nonyl ether, product of Daiichi Kogyo Seiyaku Co.

Monogenic Y-100:

Sodium Lauryl Sulphate, product of Daiichi Kogyo Seiyaku Co.

Aerosol OS:

Sodium isopropylnaphthalene sulfonate, product of American Cyanamide Co.

The invention has been preferred by way of above Embodiments, without being limited thereto, described.

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Claims (12)

Claims 1 + ' Desensitizer for lithographic printing plates, consisting of an aqueous solution with a pH value between about 1.2 and about 7.0 containing (1) a hydrophilic colloid, (2) a polyhydric alcohol and (3) at least one of the following compounds: boric acid, nitric acid, salts of these acids, potassium borohydride and sodium borohydride. 2. desensitizer of claim 1, characterized in that the aqueous solution has a viscosity in the range of about 5 cp at 25 ⁰ C to about the 500th 3. Desensitizer according to claim 1 or 2, characterized in that that the hydrophilic colloid made from gum arabic, dextrin, a cellulose derivative, polyvinyl alcohol or a derivative thereof, polyvinylpyrrolidone, an acrylic acid copolymer soluble in aqueous solution, a Copolymers of vinyl methyl ether and maleic anhydride or a copolymer of vinyl acetate and maleic anhydride consists. 4. Desensitizer according to claim 1 to 3, characterized in that that the polyhydric alcohol from ethylene glycol, a polyethylene glycol with a degree of condensation of 2 to 500, propylene glycol, dipropylene glycol, tripropylene glycol, sorbitol, pentaerythritol or glycerin. 709823/071 7 5. Desensitizer according to claim 1 to 4, characterized in that that the compound (3) of boric acid or a water-soluble salt thereof, nitric acid or a water-soluble salt thereof. 6. Desensitizer according to claim 5, characterized in that the water-soluble salt consists of a sodium, Potassium, ammonium, magnesium, nickel or zinc salt. 7. Desensitizer according to claim 6, characterized in that the salt of sodium borate, sodium nitrate, Potassium nitrate, ammonium borate, ammonium nitrate, magnesium nitrate, zinc nitrate or nickel nitrate. 8. Desensitizer according to claim 1 to 7, characterized in that that the polyhydric alcohol in an amount of about 1 to about 30 weight percent, based on weight of the total mass, and the compound (3) in an amount of about 0.5 to about 20% by weight, based on the weight of the entire mass. 9. Desensitizer according to claim 1 to 8, characterized in that that the pH is between 2 and 5. 10. Desensitizer according to claim 1 to 9, characterized in that that the desensitizer contains a surfactant and this in an amount of Less than 10% by weight, based on the total weight of the mass, is present. 709823/0717 ^ ₃ - 2653324 11. A method for desensitizing a negative-working lithographic printing plate, characterized in that that the desensitizer according to claim 1 to 10 on the exposed and developed surface the plate is applied. 12. The method according to claim 11, characterized in that a negative working lithographic printing plate is used, which is one or more of the following materials (a) as a photosensitive compound light-sensitive polyester, polyamide or polycarbonate, which has recurring units of the formula -CH = CH-C-, or (b) a photosensitive polymer having repeating units containing an azide group. 709823/0717 ORIGINAL INSPECTED