JPS6145554B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plate surface protective agent for lithographic printing plates, and particularly to a plate surface protective agent containing an alkali-soluble resin dispersed therein.

When making a lithographic printing plate, in the final step, a plate surface protectant (so-called gum solution) is applied to protect the non-image areas (areas that retain water and repel printing ink), which is called gumming. The process is carried out. Gumming is used not only to increase the hydrophilicity of the non-image areas of the lithographic printing plate (also called desensitization), but also to improve the period from plate making to printing, or from stopping printing midway through to starting again. To prevent the lithographic printing plate from deteriorating over time, such as when installing it on a printing machine, etc., when handling the lithographic printing plate, oil from fingers, grease, dust, etc. adhere to it, and the non-image area becomes ink receptive and becomes dirty. Similarly, when handling planographic printing plates, the purpose is to prevent scratches from occurring in non-image areas and image areas (areas that repel water and receive printing ink). This is what is done.

Among the gum liquids used for such gumming, the one with the best performance is an oil phase containing a lipophilic substance such as an organic solvent-soluble lipophilic surfactant dissolved in a petroleum fraction, and a water-soluble one. An emulsion-type gum liquid is known which consists of an aqueous phase containing dissolved dextrin. When a lithographic printing plate is gummed with this gum solution, the image area is protected by the lipophilic substance in the oil phase, while the non-image area is protected by adhesion of water-soluble dextrin in the aqueous phase. Therefore, there is little reduction in the oil sensitivity of the image area caused by the adhesion of water-soluble dextrin to the image area.

However, even if this emulsified gum solution is used, there are still disadvantages in that the oil sensitivity of image areas is still lowered and the desensitization effect on non-image areas is weak. Furthermore, when this gum liquid was used, there was also a drawback that lipophilic substances precipitated in non-image areas due to evaporation of petroleum fractions stained the non-image areas.

It is therefore an object of the present invention to provide an improved plate protectant.

Another object of the present invention is to provide a surface protective agent for lithographic printing plates that has a strong desensitizing effect on non-image areas and does not reduce the oil sensitivity of image areas.

Still another object of the present invention is to provide a surface protective agent for lithographic printing plates that does not stain non-image areas.

As a result of various studies to achieve the above objects, the present inventors discovered that the above objects can be achieved by dispersing and containing an alkali-soluble resin in an aqueous solution of a water-soluble polymer compound. This led to the invention. That is, the present invention is a plate surface protective agent for a lithographic printing plate, which is a solution containing a water-soluble resin dissolved therein, and the solution contains an alkali-soluble resin dispersed therein.

Below, regarding each component of the plate surface protectant of the present invention,
Explain in detail.

The water-soluble polymer compound used in the present invention is also called a water-soluble colloid, and any water-soluble polymer compound that can be used in gum liquids can be suitably used. Specifically, gum arabic, water-soluble cellulose ethers such as methylcellulose, ethylcellulose, carboxymethylcellulose, carboxyethylcellulose, and oxyethylcellulose, dextrins, and polyacrylic acid, its water-soluble salts (such as sodium salts), polymethacrylic acid,
Examples include water-soluble salts thereof (e.g., sodium salts), hydrolysates of copolymers of acrylic acid and vinyl acetate, and water-soluble synthetic resins such as copolymers of acrylamide and acrylic acid. can be used alone or in combination of two or more. Among these, gum arabic is particularly preferred. Additionally, the use of water-soluble cellulose ether or dextrin in an amount of about 1000 to about 20% by weight, more preferably 500 to 100% by weight based on gum arabic, can also have an effect of desensitizing the non-image areas of the lithographic printing plate. It is preferable because it does not cause a decrease in the oil sensitivity of the upper image area, which is moderate. The amount of the water-soluble polymer compound to be used can vary over a wide range, but generally it is about 3 to about 50% by weight, more preferably about 5 to about 30% by weight based on the total weight of the plate protectant of the present invention. %, most preferably 10-20% by weight.

On the other hand, the alkali-soluble resin used in the present invention has a function of preventing the oil sensitivity of the image area from decreasing when a plate surface protectant is applied to the lithographic printing plate.

In the present invention, a powdered resin with a particle size of about 10 to 100μ is mixed with a 1% by weight potassium hydroxide aqueous solution (20
℃) that dissolves 1% by weight or more in 60 minutes when contained in an alkali-soluble resin. Examples include novolak type phenolic resins such as phenol formaldehyde resin, cresol formaldehyde resin, and tert-butylphenol formaldehyde resin, so-called xylene resins in which phenol and xylene are condensed with formaldehyde, resins in which phenol and mesitylene are condensed with formaldehyde, and polyester resins. Examples include hydroxystyrene, brominated polyhydroxystyrene, Cassio resin, and partially esterified styrene-maleic anhydride copolymers. Among these, particularly preferred are:
Phenol formaldehyde resin, cresol formaldehyde resin, xylene resin, polyhydroxystyrene, brominated polyhydroxystyrene, and Casio resin, especially those with a molecular weight of about 300~
Approximately 20,000 is preferred.

The alkali-soluble resin is preferably dispersed in the form of fine solid particles in the aqueous solution of the water-soluble polymer compound, and the particle size thereof is about 1 μm or less, more preferably 0.1 μm or less. The alkali-soluble resin is contained in an amount of about 0.02 to about 3% by weight, more preferably 0.05 to 0.5% by weight, based on the total weight of the plate surface protectant of the present invention. As the amount of alkali-soluble resin decreases below 0.02% by weight, the decrease in the oil sensitivity of the image area of the lithographic printing plate increases, while as the amount exceeds 3% by weight, the desensitization ability of the non-image area decreases. As the image quality decreases, stains occur in non-image areas.

Preferred examples of dispersing an alkali-soluble resin in an aqueous solution of a water-soluble polymer compound include (1) first dissolving the alkali-soluble resin in an aqueous alkaline solution, mixing this solution with an aqueous solution of a water-soluble polymer compound, and then adding an acid; and (2) a method in which an alkali-soluble resin is first dissolved in an alkaline aqueous solution, this solution is diluted with water, a water-soluble polymer compound is added thereto, and then an acid is added. In either case, since the PH of the plate surface protectant is used within the range of about 1 to about 7, an appropriate acid is added to adjust the PH to this range. Since the pH of the plate protection agent is neutral to acidic, the alkali-soluble resin dissolved in the aqueous alkaline solution is precipitated as fine particles, thus obtaining the plate protection agent of the present invention.

Examples of the alkaline aqueous solution used to dissolve the above-mentioned alkali-soluble resin include sodium hydroxide, potassium hydroxide, lithium hydroxide,
An aqueous solution of an alkali such as sodium silicate or potassium silicate is preferable, and its concentration is about 0.5 to about 0.5 to about the total molar amount of alkali-soluble groups (for example, hydroxyl groups in the case of a phenolic resin) of the alkali-soluble resin to be dissolved therein. A concentration that provides 5 molar equivalents is preferred. At this time, the concentration of the alkali-soluble resin dissolved in the alkaline aqueous solution is not particularly limited, but it is convenient for handling to range from about 0.1 to about 10% by weight.

Acids used to adjust pH include inorganic acids such as phosphoric acid, pyrophosphoric acid, polyphosphoric acid, monosodium phosphate, boric acid, hydrochloric acid, sulfuric acid, and nitric acid, such as succinic acid, oxalic acid, citric acid, Organic acids such as maleic acid, lactic acid, p-toluenesulfonic acid, and benzenesulfonic acid can be used, and these may be used alone or in combination of two or more. Among these, phosphoric acid and succinic acid are particularly preferred since they have the effect of desensitizing the non-image areas of the lithographic printing plate. The amount of acid used is such that the pH of the plate surface protectant of the present invention is in the range of about 1 to about 7. However, if it is desired to utilize the desensitizing effect of phosphoric acid or succinic acid, , based on the total weight of the plate protectant
Preferably, it is used in a range of 0.1 to about 10% by weight. In addition, when gum arabic is used as a water-soluble polymer compound, the pH of the plate surface protectant is approximately 1 to 1.
The acid is added to about 5, more preferably in the range of 1 to 3.

The plate surface protective agent of the present invention may further contain a wetting agent. Thereby, the plate surface protective agent of the present invention can be imparted with the property of spreading appropriately over the plate surface of the lithographic printing plate. Preferred such wetting agents are:
It is a polyhydric alcohol, and preferable specific examples include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol,
Examples include hexylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, glycerin, sorbitol, and pentaesthritol, with glycerin being particularly preferred.
The wetting agent can be used in an amount of about 0.1 to about 1% by weight, more preferably 0.1 to 0.5% by weight, based on the total weight of the plate protectant of the present invention.

Preferably, the aqueous phase further contains a water-soluble salt. As a result, when the plate surface protectant of the present invention is applied to a lithographic printing plate, the non-image area becomes more hydrophilic. Suitable water-soluble salts include alkali metal salts and ammonium salts, and those that give particularly good results include water-soluble alkali metal salts of acids such as acetic acid, molybdic acid, boric acid, nitric acid, sulfuric acid, phosphoric acid and polyphosphoric acid. Includes salts and ammonium salts. Specifically, ammonium acetate, sodium acetate, potassium acetate, sodium molybdate, potassium molybdate, sodium borate, ammonium borate, lithium nitrate, sodium nitrate, potassium nitrate, dibasic sodium phosphate, trisodium phosphate, dibasic potassium phosphate, Examples include tribasic potassium phosphate, tribasic ammonium phosphate, and sodium polyphosphate. Among the above, particularly preferred are potassium acetate, sodium borate, ammonium borate, potassium nitrate, sodium molybdate, potassium molybdate, and potassium sulfate. Such water-soluble salts can be used alone or in combination of two or more, and are about 0.01 to about 1% by weight, more preferably 0.01% by weight based on the total weight of the plate surface protectant of the present invention.
Used in the range of ~0.1% by weight.

The plate surface protective agent of the present invention can contain a surfactant. This surfactant has the function of stabilizing the dispersion of the soluble resin contained in the plate surface protectant of the present invention. Various kinds of surfactants can be used, such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. nonionic active surfactants such as glycerin fatty acid esters, such as fatty acid salts, alkyl sulfates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, dialkyl sulfosuccinate ester salts, alkyl phosphate ester salts, naphthalene sulfonic acid Formalin condensates, anionic surfactants such as polyoxyethylene alkyl sulfate salts, cationic surfactants such as alkylamine salts, quaternary ammonium salts, polyoxyethylene alkylamine salts, and betaines such as alkylbetaines. Examples include amphoteric surfactants typified by active surfactants. The surfactant is about 0.001 to about 0.1 based on the total weight of the plate surface protectant of the present invention.
It can be used in a range of 0.005 to 0.015% by weight, more preferably 0.005 to 0.015% by weight.

The plate surface protective agent of the present invention can be used for various lithographic printing plates, but in particular, a photosensitive lithographic printing plate (preliminarily imparted with photosensitivity) having an aluminum plate as a support and a photosensitive layer thereon is used. In the print version
It's called the PS version. ) can be suitably used for lithographic printing plates obtained by imagewise exposure and development. A preferable example of such a PS board is a photosensitive PS board made of a mixture of a diazo resin (a salt of a condensate of p-diazodiphenylamine and formaldehyde) and silica as described in British Patent No. 1350521, for example. layer on an aluminum plate,
A photosensitive layer made of a mixture of a diazo resin and a polymer having hydroxyethyl methacrylate units or hydroxyethyl acrylate units as a main repeating unit as described in British Patent Nos. 1460978 and 1505739 is made of aluminum. Negative type PS like those installed on a board
and a positive-working PS plate in which a photosensitive layer made of a mixture of an o-quinone diazide photosensitive material and a novolac type phenol resin is provided on an aluminum plate as described in Japanese Patent Application Laid-Open No. 50-125806. Further, PS plates in which a photosensitive layer of a photocrosslinkable photopolymer is provided on an aluminum plate as specifically shown in US Pat. No. 3,860,426, and each of US Pat. No. 4,072,528 and US Pat. No. 4,072,527 PS in which a photosensitive layer of a photopolymerizable photopolymer composition as described in the specification is provided on an aluminum plate
Also preferred are PS plates in which a photosensitive layer made of a mixture of azide and a water-soluble polymer is provided on an aluminum plate, as described in British Patent Nos. 1,235,281 and 1,495,861.

Next, an example of the use of the plate surface protective agent of the present invention when a PS plate is used will be described.

First, the PS plate is imaged exposed and then developed to create a lithographic printing plate. After washing the lithographic printing plate with water and squeezing out the water on the plate surface, a drop of the plate surface protectant of the present invention is poured onto the plate surface and rubbed with a sponge so as to coat the entire surface of the plate.

This completes the gumming of the lithographic printing plate. The plate surface protective agent of the present invention is applied onto the lithographic printing plate in a dry weight range of about 0.1 to about 1.5 g/m ² . As the coating weight decreases below 0.1 g/m ² , the prevention of scratches that are likely to occur when handling the lithographic printing plate becomes insufficient, while coating weights above 1.5 g/m ² do not provide any benefit. On the contrary, it takes a long time to remove the plate surface protective agent by washing with water before starting printing, and the amount of water used increases.

When starting printing, the plate surface protectant on the lithographic printing plate is removed by washing with water, and then printing is started according to the normal procedure.

The plate protection agent of the present invention has various functions as a plate protection agent, such as desensitizing non-image areas without reducing the oil sensitivity of the image areas of the lithographic printing plate. It is surprising that such excellent effects could be achieved simply by dispersing and containing an alkali-soluble resin in the form of solid fine particles, rather than using an emulsion-type agent like conventional plate surface protectants.

Hereinafter, the present invention will be explained in detail based on examples. In the examples, % refers to % by weight.

The lithographic printing plates used in each example were obtained as follows.

A grained 2S aluminum plate was immersed in a 2% sodium hydroxide aqueous solution kept at 40°C for 1 minute to corrode a portion of the surface. After washing with water, it was immersed in a sulfuric acid-chromic acid mixture for about 1 minute to expose the surface of pure aluminum. It was immersed in 20% sulfuric acid kept at 30°C, anodized for 2 minutes at a DC voltage of 1.5V and a current density of 3A/dm ² , then washed with water and dried. Next, add a photosensitive solution with the following composition to a dry weight of 2 g/m ²
The coating was carried out continuously using a roll coater so that the coating was evenly coated.

Acetone - naphthoquinone of pyrogallol resin -
1,2-diazide(2)-5-sulfonic acid ester (synthesis method is described in US Pat. No. 3,635,709, Example 1)
5g PR-50530 (tertiary manufactured by Sumitomo Julias Co., Ltd.)
butylphenol-formaldehyde resin)
0.5g Hytanol #3110 (cresol-formaldehyde resin manufactured by Hitachi Chemical Co., Ltd.) 5g Methyl ethyl ketone 50g Cyclohexanone 40g The plate was dried for 2 minutes at 100℃.
It has the performance of a PS version, and its performance was satisfactory even after one year of use when stored in a cool and dark place. The photosensitive lithographic printing plate made in this way was placed in a vacuum printing frame and exposed to Fuji Film from a distance of 1 m through a transparent positive film.
PS light (Toshiba metal halide lamp MU2000−
2-OL type 3KW light source, Fuji Photo Film
Exposure was carried out for 30 seconds using a camera (sold by Co., Ltd.). Subsequently, development was performed with an aqueous sodium silicate solution having a pH of about 13 to obtain a lithographic printing plate.

Example 1 After dissolving 2.1 g of potassium hydroxide in 65.2 g of ion-exchanged water, 2.8 g of cresol formaldehyde resin with a number average molecular weight of about 400 was added and dissolved at room temperature, followed by dilution by adding 539.7 g of ion-exchanged water. . After adding and dissolving 157.2 g of cream dextrin, 179.7 g of a 28% gum arabic aqueous solution was added.
After thorough stirring, 0.7 g of Amogen K (trade name: alkyl betaine-based amphoteric surfactant, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added, followed by 52.6 g of 85% phosphoric acid. By adding phosphoric acid, the color changed from brown and transparent to milky brown and opaque. 25℃ of this plate protectant
The pH was 1.55, the specific gravity was 1.10, and the viscosity was 12.5 centipoise.

This was applied onto a planographic printing plate that had been washed with water using a sponge. The coating amount after drying was 0.4 g/m ² .

For comparison, a plate protectant was prepared by removing the cresol formaldehyde resin from the above plate protectant, and the above was coated onto a plate under the same conditions.

30 pieces of each plate coated with a plate protectant.
After being left in a room at 30°C for 3 days, printing was performed using an automatic proofing machine, and the ink was completely transferred to the paper on 4 plates coated with a plate protectant containing cresol formaldehyde resin, resulting in excellent prints.
However, when using a plate coated with a plate protectant to which no cresol-formaldehyde resin was added, which was used as a comparison, the ink was not completely transferred to the paper even after printing 10 sheets, and excellent printed matter could not be obtained. It should be noted that there was no staining with either of the two plate surface protectants, and they had sufficient desensitizing effect on non-image areas. As described above, the plate surface protectant to which cresol formaldehyde resin was added prevented a decrease in the oil sensitivity of the image area, and also had a sufficient effect of desensitizing the non-image area.

Example 2 Phetol formaldehyde resin was used in place of the cresol formaldehyde resin used as the plate surface protectant used in Example 1.

Example 3 Polybrominated parahydroxystyrene having a molecular weight of about 10,000 was used in place of the cresol formaldehyde resin used as a plate surface protectant in Example 1.

Example 4 Oak resin was used in place of the cresol formaldehyde resin used in Example 1 as a plate surface protectant.

Example 5 Potassium hydroxide, plate surface protectant used in Example 1
1.5g of sodium hydroxide was used instead of 2.1g.

Example 6 Potassium hydroxide, plate surface protectant used in Example 1
5.3g of sodium metasilicate was used instead of 2.1g.

Example 7 In place of the 52.6 g of phosphoric acid used in Example 1 as a plate surface protectant, half of it (26.3 g) and half of it (13.2 g) were used.

The results of Examples 2 to 7 were exactly the same as Example 1.

Example 8 The same plate protectant as in Example 1 was obtained by reducing the 2.8 g of the cresol formaldehyde resin used in Example 1 to 1.4 g, which was half that amount, and 5.6 g, which was doubled, and 2.1 g of potassium hydroxide to 1.1 g and 4.2 g, respectively. Therefore, I used Matsutaku in the same way. As a result, as in Example 1, it was possible to obtain excellent printed matter in which the ink was completely transferred to the paper by printing four sheets each using a proof printing machine.

Claims (1)

[Claims] 1. A plate surface protective agent for a lithographic printing plate, which is a solution containing a water-soluble resin dissolved therein, the solution containing an alkali-soluble resin dispersed therein.