JP4866209B2 - Positive photosensitive resin composition - Google Patents

Description

The present invention has a high dissolution inhibiting effect in non-exposed areas, is highly sensitive and has excellent developability, and is excellent in coating property on a support, and is directly applied using a positive type photosensitive resin composition, a semiconductor laser, a YAG laser, or the like. The present invention relates to a positive photosensitive lithographic printing plate suitable for plate making and a plate making method using the positive photosensitive lithographic printing plate.

With the progress of computer image processing technology in recent years, a photosensitive or thermal direct plate-making system that forms a resist image directly from a digital image information with a laser beam or a thermal head, without performing output to a silver salt mask film, has attracted attention. Yes.
In particular, a laser-sensitive direct plate-making system using a high-power semiconductor laser has a high development degree, and since the semiconductor laser has a long lifetime and a small size, its realization is strongly desired.

2. Description of the Related Art Conventionally, as an image forming method using laser light sensitivity or heat sensitivity, a method of preparing a lithographic printing plate using a sublimation transfer dye is known. For example, a method of preparing a lithographic printing plate using a crosslinking reaction of a diazo compound, a method of preparing a lithographic printing plate using a decomposition reaction of nitrocellulose, and the like are known.

In recent years, a technique in which a long-wavelength light-absorbing dye is combined with a chemically amplified photoresist has been developed. For example, Patent Document 1 discloses a photosensitive material in which a specific scriberium dye is combined with a photoacid generator and a binder. ing. Furthermore, a technology (Patent Document 2) for producing a lithographic printing plate by exposing a photosensitive layer containing an infrared absorbing dye, a latent Bronsted acid, a resole resin and a novolak resin into an image with a semiconductor laser or the like, or a latent Bronsted acid A technique using a s-triazine compound instead of (Patent Document 3) is also disclosed.

These conventional methods are not practically sufficient in sensitivity and storability, and require post-exposure (heat treatment) after exposure in the plate making process, in terms of working time, equipment space, equipment cost, etc. There was a problem. In particular, since the temperature of play heat greatly affects sensitivity, printing durability, and chemical resistance, temperature control by users has been strictly demanded.

With respect to these problems, Patent Document 4 and Patent Document 5 use a positive photosensitive composition comprising a combination of a novolak resin, a cyanine dye, and a dissolution-inhibiting sulfonic acid ester, and the positive photosensitive composition. A method is disclosed in which a photosensitive layer film that is insoluble in an alkaline developer is formed, and an image is formed by changing the solubility layer by irradiation with a laser. When such a method is used, it is possible to form a highly sensitive image without requiring a post-heating step after exposure. Further, in the methods of Patent Document 4 and Patent Document 5, the greatest feature is that the alkali solubility of the photosensitive layer is increased by the heat generated by laser light irradiation, and when the alkali solubility of the photosensitive layer increases, It does not cause chemical changes. Furthermore, if an ultraviolet (UV) non-photosensitive material is used as a dissolution inhibitor or other additive, there is an advantage that the photosensitive layer becomes non-photosensitive to UV and can be operated even under a white light.

However, in the image formation method using laser light irradiation, the laser irradiation time is extremely short, so when converting light energy into heat and proceeding with a chemical change by heat, the amount of heat conversion is increased by increasing the amount of photothermal conversion material added. If an attempt is made to increase the amount of light, light is absorbed in the vicinity of the surface of the photosensitive layer, and in the inner layer, the light is attenuated and the reaction becomes extremely worse. As a result, there is a problem that the dissolution speed is attenuated toward the lower layer portion of the film, so that the dissolution time of the entire irradiated portion is not accelerated and there is a limit to increasing the sensitivity.

To solve this problem, a method of reducing the film thickness of the photosensitive layer, a method of increasing the content of the dissolution inhibitor, or a method of using a stronger dissolution inhibitor can be considered. In the method of reducing the thickness, the amount of thermal diffusion to the support or the like increases, and there is a problem that the sensitivity is lowered. Further, in the method of increasing the content of the dissolution inhibitor or the method using a stronger dissolution inhibitor, the alkali solubility of the entire photosensitive layer is lowered, so that it is necessary to increase the laser beam irradiation energy, and the exposure time is increased. In addition to causing disadvantages such as lengthening, in the inner layer, the light attenuates and the reaction becomes extremely worse, and as a result, the dissolution speed attenuates toward the lower layer of the film, and the dissolution time of the entire irradiated part Was not promoted and there was a limit to increasing sensitivity.

Furthermore, in the methods of Patent Document 4 and Patent Document 5, in order to improve storage stability, printing durability, and chemical resistance, particularly to improve chemical resistance and printing durability, the binder component in the photosensitive resin composition Although the molecular weight of the resin is changed to a large one, there has been a problem that the coating property to a support such as an aluminum plate is deteriorated and the alkali solubility is lowered.
Therefore, while maintaining various performances such as chemical resistance, storage stability and printing durability, it has a high dissolution inhibiting effect in non-exposed areas, is highly sensitive and has excellent developability, and photosensitivity that is excellent in coating properties on a support. There was a need for a resin composition.
Japanese Patent Laid-Open No. 6-43633 Japanese Patent Laid-Open No. 7-20629 Japanese Patent Laid-Open No. 7-271029 JP-A-10-2688512 Japanese Patent No. 3726766

In view of the above-described situation, the present invention provides a positive photosensitive resin composition, a semiconductor laser, and a YAG laser that have a high dissolution inhibiting effect in non-exposed areas, high sensitivity, excellent developability, and excellent coating properties on a support. It is an object of the present invention to provide a positive photosensitive lithographic printing plate suitable for direct plate making using the above and a plate making method using the positive photosensitive lithographic printing plate.

The present invention is a positive photosensitive resin composition containing a photosensitive resin and a dissolution inhibitor, wherein the dissolution inhibitor is a carboxylic acid-modified polyvinyl acetal and / or a sulfonic acid-modified polyvinyl acetal. It is a resin composition.
Hereinafter, the present invention will be described in detail.

As a result of intensive studies, the present inventors have used a carboxylic acid-modified polyvinyl acetal and / or a sulfonic acid-modified polyvinyl acetal as a dissolution inhibitor to be blended in a positive photosensitive resin composition. A positive-type photosensitive resin composition that has high dissolution inhibiting effect in non-exposed areas, high sensitivity, excellent developability, and excellent coating properties on a support while maintaining various properties such as printability and printing durability. As a result, the present invention has been completed.

The light-absorbing dye is not particularly limited as long as it is a compound capable of improving the solubility of an alkali-soluble resin in an alkali developer by exposure when used in combination with an alkali-soluble resin described later. A compound that can be converted into heat is preferable, and a compound having an absorption band in part or all of the wavelength range of 650 to 1300 nm is more preferable.
The light-absorbing dye efficiently absorbs light in the wavelength range of 650 to 1300 nm, while the light in the ultraviolet region hardly absorbs or is not substantially sensitive to absorption, and is included in the white lamp. Depending on such weak ultraviolet rays, a compound having no action of modifying the photosensitive composition is preferable. Examples of such light absorbing dyes include compounds represented by the following formula (1).

Further, as the light absorbing dye, a cyanine dye, a polymethine dye, a squarylium dye, a croconium dye, a pyrylium dye, and a thiopyrylium dye are preferable. Furthermore, a cyanine dye, a polymethine dye, a pyrylium dye, and a thiopyrylium dye are more preferable. Especially, when the wavelength of the light to expose is 650-900 nm, a cyanine dye and a polymethine dye are preferable, and when the wavelength of the light to be exposed is 800-1300 nm, a pyrylium dye and a thiopyrylium dye are preferable.

The minimum with preferable content with respect to the whole positive photosensitive composition of the said light absorption pigment | dye is 0.1 weight%, and a preferable upper limit is 30 weight%. A more preferred lower limit is 1% by weight, and a more preferred upper limit is 20% by weight.

The alkali-soluble resin used in the present invention is not particularly limited as long as it is a resin whose solubility in an alkali developer is improved by exposure when used in combination with the above light-absorbing dye. For example, novolak resin, resol resin, polyvinyl Examples thereof include alkali-soluble resins such as phenol resins and copolymers of acrylic acid derivatives. Of these, novolak resins and polyvinylphenol resins are preferred.

Examples of the novolak resin include phenol, m-cresol, o-cresol, p-cresol, 2,5-xylenol, 3,5-xylenol, resorcin, pyrogallol, bisphenol, bisphenol-A, trisphenol, o-ethyl. Formaldehyde, acetaldehyde, at least one aromatic hydrocarbon such as phenol, m-ethylphenol, p-ethylphenol, propylphenol, n-butylphenol, t-butylphenol, 1-naphthol and 2-naphthol in the presence of an acidic catalyst, Degenerate with at least one aldehyde or ketone selected from aldehydes such as propionaldehyde, benzaldehyde, furfural, and ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone And the like that is.
Moreover, you may use paraformaldehyde and paraaldehyde instead of the said formaldehyde and acetaldehyde, respectively.

Among them, phenols having a mixing ratio of m-cresol: p-cresol: 2,5-xylenol: 3,5-xylenol: resorcinol in a molar ratio of 70 to 100: 0 to 30: 0 to 20: 0 to 20 or A novolak resin which is a polycondensate of phenols and aldehydes having a mixing ratio of phenol: m-cresol: p-cresol in a molar ratio of 10-100: 0-60: 0-40 is preferred.

The minimum with a preferable weight average molecular weight of the said novolak resin is 1000, and a preferable upper limit is 15000. If it is less than 1000, a sufficient coating film cannot be obtained, and if it exceeds 15000, the solubility of an unexposed portion in an alkaline developer is reduced, and a desired pattern may not be obtained. A more preferred lower limit is 1500, and a more preferred upper limit is 10,000.
In addition, the said weight average molecular weight is a numerical value measured by the gel permeation chromatography by polystyrene conversion.

Examples of the polyvinylphenol resin include o-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene, 2- (o-hydroxyphenyl) propylene, 2- (m-hydroxyphenyl) propylene, and 2- (p-hydroxy). Examples thereof include hydroxystyrenes such as phenyl) propylene alone or two or more polymers.
The hydroxystyrenes may have a substituent such as a halogen such as chlorine, bromine, iodine, fluorine or an alkyl substituent having 1 to 4 carbon atoms on the aromatic ring.

The polyvinyl phenol resin is usually obtained by polymerizing hydroxystyrenes which may have a substituent alone or in the presence of a radical polymerization initiator or a cationic polymerization initiator. Such a polyvinylphenol resin may be partially hydrogenated. Moreover, the resin which protected some OH groups of polyvinylphenols with t-butoxycarbonyl group, a pyranyl group, a furanyl group, etc. may be sufficient.
As said polyvinyl phenol resin, the polyvinyl phenol which may have a C1-C4 alkyl substituent in an aromatic ring is mentioned, Unsubstituted polyvinyl phenol is more preferable.

The minimum with a preferable weight average molecular weight of the said polyvinyl phenol resin is 1000, and a preferable upper limit is 100,000. If it is less than 1000, a sufficient coating film cannot be obtained, and if it exceeds 100,000, the solubility of an unexposed portion in an alkaline developer is reduced, and a desired pattern may not be obtained. A more preferred lower limit is 1500, and a more preferred upper limit is 50,000.

In the positive photosensitive resin composition of the present invention, a carboxylic acid-modified polyvinyl acetal and / or a sulfonic acid-modified polyvinyl acetal (hereinafter also referred to simply as a modified polyvinyl acetal) is used as a dissolution inhibitor. In the present invention, the dissolution inhibitor refers to a component for reducing the solubility of the positive photosensitive composition in an alkaline developer and reducing the dissolution rate.

The modified polyvinyl acetal is a polyvinyl acetal having a carboxylic acid group and / or a sulfonic acid group.
The minimum with preferable content of the said carboxylic acid group and / or sulfonic acid group in the said modified polyvinyl acetal is 0.5 mol%, and a preferable upper limit is 5 mol%. If it is less than 0.5 mol%, the solubility in an alkali developer is lowered, and the contrast between the photosensitive part and the non-photosensitive part may be deteriorated. If it exceeds 5 mol%, the hydrophilicity is increased. The dissolution rate with respect to the alkali developer is increased, and the dissolution inhibiting effect may be reduced.

The preferable lower limit of the acid value of the modified polyvinyl acetal is 0.05 KOHmg / g, and the preferable upper limit is 0.7 KOHmg / g. If it is less than 0.05 KOH mg / g, the solubility in an alkali developer may be lowered, and the contrast between the photosensitive part and the non-photosensitive part may deteriorate. If it exceeds 0.7 KOHmg / g, the hydrophilicity becomes high, so that the dissolution rate in an alkali developer is increased, and the dissolution inhibiting effect may be lowered.

The preferable lower limit of the degree of acetalization of the modified polyvinyl acetal is 60 mol%, and the preferable upper limit is 80 mol%. If it is less than 60 mol%, it will be easy to dissolve in an alkali developer, so that the effect of inhibiting dissolution may be reduced and the desired shape may not be formed. If it exceeds 80 mol%, the hydrophobicity is increased, so that the solubility in an alkaline developer is lowered, and the contrast between the photosensitive part and the non-photosensitive part may be deteriorated.
In this specification, the method for calculating the degree of acetalization is a method of counting two acetalized hydroxyl groups because the acetal group of the modified polyvinyl acetal is formed by acetalization from two hydroxyl groups. Is used to calculate the mole percent of the degree of acetalization.

The preferable lower limit of the number average molecular weight of the modified polyvinyl acetal is 20,000, and the preferable upper limit is 150,000. If it is less than 20,000, it becomes easy to dissolve in an alkali developer, so that the dissolution inhibiting effect is lowered and a desired shape may not be formed. When it exceeds 150,000, the viscosity becomes too high and the coating property is lowered. A more preferable lower limit is 40,000, and a more preferable upper limit is 100,000.
In addition, the said number average molecular weight is a numerical value measured by the gel permeation chromatography by polystyrene conversion.

The minimum with preferable content with respect to the whole positive photosensitive composition of the said modified polyvinyl acetal is 3 weight%, and a preferable upper limit is 15 weight%. If the amount is less than 3% by weight, the desired shape may not be formed due to a dissolution inhibiting effect on the alkali developer. If the amount exceeds 15% by weight, the solubility in the alkali developer is lowered, and The contrast with the non-photosensitive part may deteriorate. A more preferred lower limit is 5% by weight, and a more preferred upper limit is 10% by weight.

Examples of the method for producing the modified polyvinyl acetal include a method of acetalizing carboxylic acid-modified polyvinyl alcohol and / or sulfonic acid-modified polyvinyl alcohol; carboxylic acid-modified polyvinyl alcohol and / or sulfonic acid-modified polyvinyl alcohol, and unmodified The method of acetalizing the mixture with polyvinyl alcohol is mentioned. Moreover, you may use the method of mixing what was obtained by acetalizing carboxylic acid modified polyvinyl alcohol and / or sulfonic acid modified polyvinyl alcohol, and what was obtained by acetalizing unmodified polyvinyl alcohol.

The method for acetalization is not particularly limited, and a conventionally known method such as a dissolution method, a precipitation method, and a homogeneous method can be used. For example, an aqueous solution of a modified polyvinyl alcohol, an alcohol solution, water in the presence of an acid catalyst. / Alcohol mixed solution, a method of adding various aldehydes to a dimethyl sulfoxide (DMSO) solution, and the like. It can also be produced by adding an acid catalyst and an aldehyde to an alcohol solution of polyvinyl acetate.

The aldehyde used for the acetalization is not particularly limited, and may be an aldehyde that can be acetalized, for example, an aliphatic aldehyde such as formaldehyde, acetaldehyde, butyraldehyde, and propylaldehyde, or an aromatic aldehyde such as benzaldehyde and 2-methylbenzaldehyde. Any aldehyde may be used. Of these, it is preferable to use butyraldehyde and acetaldehyde alone or to use butyraldehyde and acetaldehyde in combination.
It is more preferable to use an aldehyde having a carboxylic acid group at the terminal, such as 4-carboxybenzaldehyde.

Examples of the acid catalyst include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as acetic acid and p-toluenesulfonic acid.

As a method for producing the modified polyvinyl alcohol, for example, when polymerizing polyvinyl acetate, an ethylenic monomer having a carboxylic acid group and / or a sulfonic acid group is copolymerized to produce a modified polyvinyl acetate, Examples thereof include a method for saponifying vinyl acetate.

The solvent used in the positive photosensitive resin composition of the present invention is not particularly limited as long as it has a sufficient solubility with respect to the components used and gives good coating properties. For example, methyl cellosolve, ethyl Cellosolve solvents such as cellosolve, methyl cellosolve acetate, ethyl cellosolve acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether acetate, Propylene glycol solvents such as dipropylene glycol dimethyl ether, butyl acetate, amyl acetate, ethyl butyrate, butyl butyrate, diethyl oxalate Ester solvents such as ethyl pyruvate, ethyl-2-hydroxybutyrate, ethyl acetoacetate, methyl lactate, ethyl lactate, methyl 3-methoxypropionate, heptanol, hexanol, diacetone alcohol, furfuryl alcohol, etc. Alcohol solvents, ketone solvents such as cyclohexanone and methyl amyl ketone, highly polar solvents such as dimethylformamide, dimethylacetamide and N-methylpyrrolidone, or mixed solvents thereof and those obtained by adding aromatic hydrocarbons Can be mentioned.

The positive photosensitive resin composition of the present invention has various additives such as dyes, pigments, coatability improvers, development improvers, adhesion improvers, sensitivity improvers, and oil sensitizers as long as the performance is not impaired. An agent or the like may be contained.

When the positive photosensitive resin composition of the present invention is applied to a support such as an aluminum plate, the positive photosensitive resin has high chemical resistance, storage stability, printing durability, high sensitivity and excellent developability. A sex lithographic printing plate can be obtained. Such a positive photosensitive lithographic printing plate is also one aspect of the present invention.

As a method for coating the positive photosensitive resin composition of the present invention on a support, conventionally known methods can be used. For example, spin coating, wire bar coating, dip coating, air knife coating, roll coating can be used. Blade coating, curtain coating, etc. can be used.
The coating amount varies depending on the application, but the preferred lower limit is 0.1 g / m ² (solid content), and the preferred upper limit is 10.0 g / m ² . Moreover, the preferable minimum of drying temperature is 20 degreeC, a preferable upper limit is 150 degreeC, a more preferable minimum is 30 degreeC, and a more preferable upper limit is 120 degreeC.

Examples of the support include metal plates such as aluminum, zinc, steel, and copper; metal plates plated or vapor-deposited with chromium, zinc, copper, nickel, aluminum, iron, and the like; paper, plastic film, and glass plate; resin A paper coated with a metal foil such as aluminum; a hydrophilic plastic film. Among these, an aluminum plate is preferable. As the above support, an aluminum plate that has been subjected to surface treatment such as graining treatment by electrolytic etching or brush polishing in hydrochloric acid or nitric acid solution, anodizing treatment in sulfuric acid solvent, and sealing treatment if necessary It is more preferable to use

The plate-making method of the present invention has a step of exposing the positive photosensitive lithographic printing plate of the present invention to light, and a step of developing the positive photosensitive lithographic printing plate exposed to light using an alkali developer.

In the step of exposing light to the positive photosensitive lithographic printing plate of the present invention, the light used for exposure is preferably a light such as a near infrared laser of 650 to 1300 nm, and the light source is, for example, a YAG laser, A semiconductor laser, LED, etc. are mentioned. A semiconductor laser or YAG laser having a small size and a long lifetime is particularly preferable.

The light intensity of the light source used in the above step is preferably 2.0 × 10 ⁶ mJ / s · cm ² or more, and more preferably 1.0 × 10 ⁷ mJ / s · cm ² or more. . If the light intensity is in the above range, the sensitivity characteristics of the positive planographic printing plate of the present invention are improved, and the scanning exposure time can be shortened.

In the step of developing the positive photosensitive lithographic printing plate exposed to the light beam using an alkali developer, examples of the alkali developer used include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, and metasilicic acid. Examples include aqueous solutions of alkali metal salts such as sodium, potassium metasilicate, dibasic sodium phosphate, and tribasic sodium phosphate.
A preferable lower limit of the concentration of the alkali metal salt is 0.1% by weight, and a preferable upper limit is 20% by weight.
Moreover, you may add organic solvents, such as anionic surfactant, an amphoteric surfactant, and alcohol, in the said alkali developing solution as needed.

According to the present invention, a positive photosensitive resin composition, a semiconductor laser, a YAG laser, or the like, which has a high dissolution inhibiting effect in a non-exposed portion, is highly sensitive and has excellent developability, and is excellent in coatability to a support. It is possible to provide a positive photosensitive lithographic printing plate suitable for direct plate making and a plate making method using the positive photosensitive lithographic printing plate.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
(1) Preparation of lithographic printing plate support After a 0.24 mm thick aluminum plate (material 1050, tempered H16) was degreased in a 5 wt% aqueous sodium hydroxide solution at 60 ° C for 1 minute. In an aqueous hydrochloric acid solution having a concentration of 0.5 mol / L, electrolytic etching was performed under conditions of a temperature of 25 ° C., a current density of 60 A / dm ² , and a treatment time of 30 seconds. Next, after desmutting at 60 ° C. for 10 seconds in a 5 wt% aqueous sodium hydroxide solution, in a 20 wt% sulfuric acid solution at a temperature of 20 ° C., a current density of 3 A / dm ² , and a processing time of 1 minute. Anodizing treatment was performed. Further, hot water sealing treatment was carried out with hot water at 80 ° C. for 20 seconds to produce an aluminum plate as a lithographic printing plate support.

(2) Preparation of polyvinyl butyral resin 100 g of a carboxylic acid-modified polyvinyl alcohol resin having a polymerization degree of 2000 was dissolved in 700 g of distilled water by heating and kept at 20 ° C. Then, 26 g of 70% nitric acid was added thereto, and 10 g of butyraldehyde was further added. Added. Next, it was cooled to 10 ° C. and 75 g of butyraldehyde was added. After the resin was deposited, the mixture was kept for 30 minutes, and then 93 g of nitric acid was added and the temperature was raised to 35 ° C. and kept for 3 hours. After completion of the reaction, the reaction solution was washed with distilled water for 10 hours, and sodium hydroxide was added to adjust the pH of the solution to 8. The solution was held at 50 ° C. for 6 hours and then cooled.
Next, the solution was washed with running water for 2 hours, dehydrated and dried to obtain a carboxylic acid-modified polyvinyl butyral resin. The obtained polyvinyl butyral resin had a number average molecular weight of 100,000, an acid value of 0.4 KOH mg / g, and an acetalization degree of 74 mol%.

(3) Preparation of photosensitive solution 8 g of novolak type phenolic resin as photosensitive resin, 1 g of polyvinyl butyral resin obtained as a dissolution inhibitor, 0.4 g of Karenz IR-T (manufactured by Showa Denko KK) as a light absorbing dye, and as a coloring material Victoria Pure Blue BOH (Hodogaya Chemical Co., Ltd.) 0.06 g and cyclohexanone 80 g as a solvent were mixed to obtain a photosensitive solution.

(4) Preparation of photosensitive lithographic printing plate The photosensitive solution obtained was applied to the aluminum plate prepared in (1) with a wire bar, and allowed to stand at 90 ° C. for 5 minutes in a dryer. A printed version was obtained.

(Example 2)
In Example 1 (2), a photosensitive lithographic printing plate was obtained in the same manner as in Example 1 except that a polyvinyl butyral resin was produced by the following method.
(2) Preparation of polyvinyl butyral resin 100 g of a carboxylic acid-modified polyvinyl alcohol resin having a polymerization degree of 1000 was dissolved in 700 g of distilled water by heating and kept at 20 ° C. Then, 26 g of 70% nitric acid was added thereto, and 10 g of butyraldehyde was further added. Added. Next, it was cooled to 10 ° C. and 65 g of butyraldehyde was added. After the resin was deposited, the mixture was kept for 30 minutes, and then 93 g of nitric acid was added and the temperature was raised to 35 ° C. and kept for 3 hours. After completion of the reaction, the reaction solution was washed with distilled water for 10 hours, and sodium hydroxide was added to adjust the pH of the solution to 8. The solution was held at 50 ° C. for 6 hours and then cooled.
Next, the solution was washed with distilled water for 2 hours, dehydrated and dried to obtain a carboxylic acid-modified polyvinyl acetal. The obtained polyvinyl butyral resin had a molecular weight of 40,000, an acid value of 0.4 KOH mg / g, and an acetalization degree of 65 mol%.

(Example 3)
In Example 1 (2), a photosensitive lithographic printing plate was obtained in the same manner as in Example 1 except that a polyvinyl butyral resin was produced by the following method.
(2) Preparation of polyvinyl butyral resin 100 g of a sulfonic acid-modified polyvinyl alcohol resin having a polymerization degree of 2000 was dissolved in 700 g of distilled water by heating and kept at 20 ° C., and 26 g of 70% nitric acid was added thereto, and 10 g of butyraldehyde was further added. Added. Next, it was cooled to 10 ° C. and 75 g of butyraldehyde was added. After the resin was deposited, the mixture was kept for 30 minutes, and then 93 g of nitric acid was added and the temperature was raised to 35 ° C. and kept for 3 hours. After completion of the reaction, the reaction solution was washed with distilled water for 10 hours, and sodium hydroxide was added to adjust the pH of the solution to 8. The solution was held at 50 ° C. for 6 hours and then cooled.
Next, the solution was washed with distilled water for 2 hours, dehydrated and dried to obtain a sulfonic acid-modified polyvinyl butyral resin. The obtained polyvinyl butyral resin had a molecular weight of 100,000, an acid value of 0.4 KOH mg / g, and an acetalization degree of 65 mol%.

(Comparative Example 1)
In Example 1 (2), a photosensitive lithographic printing plate was obtained in the same manner as in Example 1 except that a polyvinyl butyral resin was produced by the following method.
(2) Preparation of polyvinyl butyral resin Unmodified polyvinyl acetal was obtained in the same manner as in Example 1 except that an unmodified polyvinyl alcohol resin having a polymerization degree of 200 was used. The obtained polyvinyl butyral resin had a molecular weight of 10,000, an acid value of 0.009 KOH mg / g, and an acetalization degree of 74 mol%.

(Comparative Example 2)
In Example 1 (2), a photosensitive lithographic printing plate was obtained in the same manner as in Example 1 except that a polyvinyl butyral resin was produced by the following method.
(2) Preparation of polyvinyl butyral resin 100 g of unmodified polyvinyl alcohol resin having a polymerization degree of 2000 was dissolved in 700 g of distilled water by heating, and then kept at 20 ° C., to which 26 g of 70% nitric acid was added, and further 10 g of butyraldehyde was added. did. Next, it was cooled to 10 ° C. and 50 g of butyraldehyde was added. After the resin was deposited, the mixture was kept for 30 minutes, and then 93 g of nitric acid was added and the temperature was raised to 35 ° C. and kept for 3 hours. After completion of the reaction, the reaction solution was washed with distilled water for 10 hours, and sodium hydroxide was added to adjust the pH of the solution to 8. The solution was held at 50 ° C. for 6 hours and then cooled.
Next, the solution was washed with running water for 2 hours, dehydrated and dried to obtain a polyvinyl butyral resin. The obtained polyvinyl butyral resin had a molecular weight of 100,000, an acid value of 0.009 KOH mg / g, and an acetalization degree of 60 mol%.

(Comparative Example 3)
A photosensitive lithographic printing plate was obtained in the same manner as in Example 1 except that 1 g of ethyl p-toluenesulfonate was used as the dissolution inhibitor in Example 1 (2).

(Evaluation)
The photosensitive solutions and photosensitive lithographic printing plates obtained in the examples and comparative examples were evaluated by the following methods. The results are shown in Table 1.

(1) A coatable photosensitive solution was applied on the aluminum plate produced in (1) of Example 1 with a bar coater, dried at 80 ° C. for 3 minutes by a blow dryer, and then 1 at 50 ° C. The surface condition was evaluated after standing for a while.
○: There is no unevenness on the front surface and it is smooth ×: There is unevenness on the front surface

(2) About the contrast photosensitive lithographic printing plate, the roughness of the boundary between the photosensitive part and the non-photosensitive part was evaluated with a microscope.
○: The boundary is clear ×: Undissolved material remains and the boundary is not clear

(3) Dissolution rate The photosensitive lithographic printing plate was immersed in an alkali developer, and the time (A) until the photosensitive layer was completely dissolved was measured. In the above formulation examples, the dissolution inhibition effect was evaluated by calculating the ratio (= A / B) when the dissolution time when the inhibitor was not added was taken as (B).

According to the present invention, a positive photosensitive resin composition, a semiconductor laser, a YAG laser, or the like, which has a high dissolution inhibiting effect in a non-exposed portion, is highly sensitive and has excellent developability, and is excellent in coatability to a support. It is possible to provide a positive photosensitive lithographic printing plate suitable for direct plate making and a plate making method using the positive photosensitive lithographic printing plate.

Claims (3)

Light absorbing dye, a positive photosensitive resin composition containing an alkali-soluble resin and a dissolution inhibitor, the dissolution inhibitor, Ri Oh carboxylic acid-modified polyvinyl acetal and / or sulfonic acid-modified polyvinyl acetal, wherein the carboxylic An acid-modified polyvinyl acetal and / or a sulfonic acid-modified polyvinyl acetal has a positive photosensitive resin composition having an acid value of 0.05 to 0.7 KOH mg / g . The positive photosensitive lithographic printing plate characterized by being coated with a positive photosensitive resin composition according to claim 1 Symbol mounting to a support. Exposing the light to the positive photosensitive lithographic printing plate according to claim 2 ;
A plate making method comprising a step of developing a positive photosensitive lithographic printing plate exposed to light with an alkali developer.