JP4695499B2 - Negative type planographic printing plate - Google Patents

Description

  The present invention relates to a photosensitive lithographic printing plate. More specifically, the present invention relates to a photosensitive lithographic printing plate capable of forming an image using a scanning exposure apparatus such as a laser based on a digital signal.

  In the photosensitive composition, the molecular structure undergoes a chemical change by a photoreaction, and as a result, a physical phenomenon (physical property) changes. This chemical change by the action of light includes cross-linking, polymerization, decomposition, depolymerization, functional group conversion, etc., and there are various such as solubility, adhesiveness, refractive index, substance permeability and phase change. Such photosensitive compositions have been put into practical use in a wide range of fields such as printing plates, resists, paints, coating agents, and color filters. Furthermore, it has been utilized and developed in the field of photoresist using photoengraving technology (photolithography). Photoresists utilize changes in solubility due to photoreactions, and more precise material design is required due to high resolution requirements.

  A widely used type of lithographic printing plate has a photosensitive coating applied to an aluminum base support. In this coating film, the exposed coating film portion is cured, and the unexposed coating film portion is eluted by the development process. Such a plate is called a negative printing plate. Lithographic printing utilizes the oleophilic and hydrophilic surface properties of the pattern formed on the surface of the printing plate and the background, and when supplying ink and dampening water simultaneously to the printing plate on the printing press in lithographic printing, It utilizes the selective transfer of ink onto a pattern having an oleophilic surface. The ink transferred onto the pattern is then transferred to an intermediate body called a blanket, and further transferred to a printing paper for printing.

  Many studies have been made on a photosensitive composition that forms a relief image by utilizing the above-described change in solubility due to a photoreaction, and has been put into practical use. For example, a photosensitive composition mainly comprising a polymer having an ethylenically unsaturated bond in the side chain, a crosslinking agent, and a photopolymerization initiator is disclosed. (For example, refer to Patent Document 1.) These have photosensitivity to light having a short wavelength centered on an ultraviolet region of 400 nm or less.

  On the other hand, in recent years, with the advancement of image forming technology, a photosensitive material exhibiting high sensitivity to visible light has been demanded. For example, research on photosensitive materials and photosensitive lithographic printing plates corresponding to output machines using argon lasers, helium / neon lasers, red LEDs, and the like has been actively conducted.

  Furthermore, with the remarkable progress of semiconductor lasers, it has become possible to easily use near-infrared laser light sources of 700 to 1300 nm, and photosensitive materials and photosensitive lithographic printing plates corresponding to the laser beams have attracted attention. .

  An original for lithographic printing of an image forming method in which a polymerization initiator is decomposed by heat by infrared laser exposure to perform polymerization is disclosed. However, there is a problem that it is difficult to ensure stability such as sensitivity and long-term storage stability. For this purpose, an over layer made of polyvinyl alcohol or the like has been provided on the upper part of the photosensitive layer for the purpose of enhancing oxygen barrier properties and preventing scratches on the surface. Due to the presence of such an over layer, there is a problem of deterioration in image quality due to light scattering during laser exposure, and when developing, a pre-water washing step for removing the over layer is required prior to alkali development. In addition, there is a problem in that a process for applying an overlayer is necessary after the photosensitive layer is applied.

In order to solve the above problems, a photosensitive composition comprising a polymer having a phenyl group substituted with a vinyl group via a linking group containing a heterocyclic ring in a side chain, and a photoradical generator. It is disclosed. (For example, refer to Patent Document 3.) In this invention, since the structure of the reaction site with radicals generated by laser exposure is different from the above invention, an over layer is not required, and further, heat treatment is performed after exposure. Even without this, an image that can withstand development and printing can be obtained. However, it has problems in image quality and storability as a photosensitive material.
Japanese Examined Patent Publication No. 6-105353 Japanese Patent Laid-Open No. 2001-166459 Japanese Patent No. 3654422

  An object of the present invention is to provide a negative lithographic printing plate excellent in image quality and storage stability.

The object of the present invention is to provide a polymer having at least a phenyl group substituted with a vinyl group in a side chain on a support, a sensitizer having absorption in a wavelength region of 750 to 1100 nm, and a 10-hour half-life temperature. This was achieved by a negative lithographic printing plate having a recording layer containing an azo polymerization initiator at 70 ° C. or more and less than 200 ° C. and having no over layer.

  According to the present invention, a negative lithographic printing plate excellent in image quality and storage stability can be obtained.

  Hereinafter, the present invention will be described in detail. The binder polymer used in the present invention is a polymer having a phenyl group substituted with a vinyl group, and the phenyl group may be substituted with a substitutable group or atom, and the vinyl group is a halogen atom. , A carboxy group, a sulfo group, a nitro group, a cyano group, an amide group, an amino group, an alkyl group, an aryl group, an alkoxy group, an aryloxy group and the like. More specifically, the polymer having a phenyl group substituted with the vinyl group described above has a group represented by the following chemical formula 1 in the side chain.

In the formula, Z ₁ represents a linking group, and R ₁ , R ₂ , and R ₃ are a hydrogen atom, a halogen atom, a carboxy group, a sulfo group, a nitro group, a cyano group, an amide group, an amino group, an alkyl group, and an aryl group. A group, an alkoxy group, an aryloxy group, and the like, and these groups may be substituted with an alkyl group, an amino group, an aryl group, an alkenyl group, a carboxy group, a sulfo group, a hydroxy group, or the like. R ₄ represents a substitutable group or atom. n represents 0 to ₁ , m ₁ represents an integer of 0 to 4, and k ₁ represents an integer of ₁ to 4.

The chemical formula 1 will be described in more detail. The linking group Z ₁ preferably contains a heterocyclic ring, and other groups and atoms such as oxygen atom, sulfur atom, alkylene group, alkenylene group, arylene group, —N (R ₅ ) —, —C (O) —. O—, —C (R ₆ ) ═N—, —C (O) —, a sulfonyl group, and the following chemical formula 2 may be contained singly or in a combination of two or more. Here, R ₅ and R ₆ represent a hydrogen atom, an alkyl group, an aryl group, or the like. Furthermore, the above-described linking group may have a substituent such as an alkyl group, an aryl group, or a halogen atom.

  Examples of the heterocyclic group include pyrrole ring, pyrazole ring, imidazole ring, triazole ring, tetrazole ring, isoxazole ring, oxazole ring, oxadiazole ring, isothiazole ring, thiazole ring, thiadiazole ring, thiatriazole ring, indole ring. , Indazole ring, benzimidazole ring, benzotriazole ring, benzoxazole ring, benzthiazole ring, benzselenazole ring, benzothiadiazole ring, pyridine ring, pyridazine ring, pyrimidine ring, pyrazine ring, triazine ring, quinoline ring, quinoxaline ring, etc. A nitrogen-containing heterocyclic ring, a furan ring, a thiophene ring, and the like, and a substituent may be bonded to these heterocyclic rings. Although the example of group represented by Chemical formula 1 is shown below, it is not limited to these examples.

Among the groups represented by the above chemical formula 1, preferred ones exist. That is, it is preferable that R ₁ and R ₂ are hydrogen atoms and R ₃ is a hydrogen atom or a lower alkyl group having 4 or less carbon atoms (methyl group, ethyl group, etc.). The k ₁ is preferably 1 or 2.

  The polymer having a group as shown in the above example is preferably soluble in an alkaline aqueous solution, and therefore a polymer containing a carboxyl group-containing monomer as a copolymerization component is particularly preferable. In this case, the ratio of the group represented by Chemical Formula 1 in the copolymer composition is preferably 1% by mass or more and 95% by mass or less in the total composition of 100% by mass. If the ratio is less than this, the introduction effect may not be recognized. Further, when it is contained in an amount of 95% by mass or more, the copolymer may not be dissolved in the alkaline aqueous solution. Further, the proportion of the carboxyl group-containing monomer in the copolymer is preferably 5% by mass or more and 99% by mass or less, and the copolymer may not be dissolved in the alkaline aqueous solution at a proportion below this.

  There is a preferred range for the molecular weight of the polymer as described above, and the weight average molecular weight is preferably in the range of 1,000 to 1,000,000, and more preferably in the range of 10,000 to 300,000.

  Examples of the polymer having a group represented by Chemical Formula 1 according to the present invention are shown below. In the formula, the number represents the mass% of each repeating unit in the copolymer total composition of 100 mass%.

  The photosensitive composition of the present invention is very suitably used for scanning exposure using near infrared to infrared light, that is, laser light having a wavelength region of 750 to 1100 nm. Cyanine, polymethine, squarylium dye, and the like can be used as the sensitizing dye used for sensitizing to the near infrared, and the following sensitizing dyes are preferably used.

The content of the sensitizing dye exemplified above is suitably about 3 to 300 mg per 1 m ^{2 of the} photosensitive composition. Preferably from 10 to 200 mg / ^{m 2.}

  As the polymerization initiator of the present invention, at least one selected from peroxides and azo compounds having a 10-hour half-life temperature of 70 ° C. or higher and lower than 200 ° C. is used. These polymerization initiators are decomposed by light or heat generated from a sensitizer that has absorbed infrared laser light, and an image is formed by generating radicals. Below this 10-hour half-life temperature, the initiator gradually decomposes over time during storage, resulting in performance degradation. Above this range, the polymerization initiator is not sufficiently decomposed by light or heat generated by laser exposure, so that a good image cannot be obtained.

Here, the half-life of the polymerization initiator means the time required for the concentration of the polymerization initiator to be ½ of the initial value. Since the decomposition reaction of the polymerization initiator at a certain temperature can be regarded as a primary reaction, the following formula:
log (a / x) = (k / 2.303) t
(In the formula, x: concentration of the initiator at time t (mol / liter), a: initial concentration of the initiator (same), k: decomposition rate constant determined by temperature, t: time)
There is a relationship represented by By plotting a against t, k at that temperature is determined. The value of k obtained is expressed by the following formula:
t1 / 2 (half life) = (ln2) / k
By substituting into, the half-life at that temperature can be obtained.

  Examples of the peroxide include t-butylperoxy 2-ethylhexanoate, m-toluoyl benzoyl peroxide, benzoyl peroxide, 1,1-bis (t-hexylperoxy) -3, 3, 5 -Trimethylcyclohexane, 1,1- (t-hexylperoxy) cyclohexane, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) ) Cyclohexane, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, 1,1-bis (t-butylperoxy) cyclododecane, t-hexylperoxyisopropyl monocarbonate, t- Butyl maleic acid, t-butylperoxy-3,5,5-trimethylhexanoate, t-butyl Peroxylaurate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylisopropyl monocarbonate, t-butylperoxy 2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2, 5-di-methyl 2,5-di (benzoylperoxy) hexane, t-butylperoxyacetate, 2,2-bis (t-butylperoxy) butane, t-butylperoxybenzoate, n-butyl4 4-bis (t-butylperoxy) valerate, di-t-butylperoxyisophthalate, α, α′bis (t-butylperoxy) diisopropylbenzene, dicumyl peroxide, 2,5-dimethyl 2,5 -Di (t-butylperoxy) hexane, t-butylcumyl peroxide, di- -Butyl peroxide, p-menthane hydroperoxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, diisopropylbenzene hydroperoxide, t-butyltrimethylsilyl peroxide, 1,1 , 3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide, t-hexyl hydroperoxide, t-butyl hydroperoxide, and the like.

  Examples of the azo polymerization initiator include 1,1′-azobis (cyclohexane-1-carbonitrile), 1-[(1-cyano-1-methylethyl) azo] formamide, 2,2′-azobis {2 -Methyl-N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, 2,2'-azobis {2-methyl-N- [2- (1-hydroxybutyl)]-propion Amide}, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) -propionamide], 2,2′-azobis [N- (2-propenyl) -2-methylpropionamide], 2 , 2'-azobis (N-butyl-2-methylpropionamide), 2,2'-azobis (N-cyclohexyl-2-methylpropionamide), 2,2'-azobis (2, , 4-trimethylpentane) and the like.

  The addition amount of a polymerization initiator is 0.1-50 mass parts with respect to a photosensitive composition total 100 mass parts, Preferably it is 0.2-15 mass parts. If it is less than this range, the sensitivity will be low, and if it is too much, the film properties of the polymerized layer will deteriorate.

  The photosensitive composition of the present invention preferably contains a polyfunctional polymerizable monomer or oligomer polymerizable compound having two or more polymerizable double bonds in the molecule. The molecular weight of the polymerizable compound is 10,000 or less, preferably 5000 or less. Examples of the compound include compounds having two or more polymerizable double bonds such as an acryloyl group, a methacryloyl group, and a phenyl group substituted with a vinyl group.

  Examples of the compound having an acryloyl group or a methacryloyl group as a polymerizable double bond include 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, and neopentyl glycol di (meth) acrylate. , Tetraethylene glycol di (meth) acrylate, trisacryloyloxyethyl isocyanurate, tripropylene glycol di (meth) acrylate, ethylene glycol glycerol tri (meth) acrylate, glycerol epoxy tri (meth) acrylate, trimethylolpropane tri (meth) Acrylate, trimethylolethane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipe Data pentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, pyrogallol triacrylate.

  When a polymerizable compound having two or more phenyl groups substituted with vinyl groups in the molecule is used, crosslinking is effectively performed by recombination of styryl radicals generated by the generated radicals. A negative photosensitive material which is not required can be produced. A compound having a phenyl group substituted with a vinyl group as a polymerizable double bond is typically represented by the following general formula.

In the formula, Z ₂ represents a linking group, R ₂₁ and R ₂₂ are a hydrogen atom, a halogen atom, a carboxy group, a sulfo group, a nitro group, a cyano group, an amide group, an amino group, an alkyl group having 1 to 4 carbon atoms, An alkoxy group having 1 to 4 carbon atoms or the like is represented. R ₂₃ is a hydrogen atom, halogen atom, carboxy group, sulfo group, nitro group, cyano group, amide group, amino group, alkyl group, aryl group, alkoxy group, aryloxy group, etc., and these groups are It may be substituted with an alkyl group, amino group, aryl group, alkenyl group, carboxy group, sulfo group, hydroxy group or the like. R ₂₄ represents a substitutable group or atom. m2 represents an integer of 0 to 4, and k2 represents an integer of 2 or more. When m3 is 2 or more, R ₂₄ may be the same or different.

The above general formula will be described in more detail. As the linking group for Z ₂ , an oxygen atom, a sulfur atom, an alkylene group, an alkenylene group, an arylene group, —N (R ₂₅ ) —, —C (O) —O—, —C (R ₂₆ ) ═N—, Examples include —C (O) —, a sulfonyl group, a heterocyclic group, or a group in which two or more are combined. Here, R ₂₅ and R ₂₆ represent a hydrogen atom, an alkyl group, an aryl group, or the like. Furthermore, the above-described linking group may have a substituent such as an alkyl group, an aryl group, or a halogen atom.

  Examples of the heterocyclic group include pyrrole ring, pyrazole ring, imidazole ring, triazole ring, tetrazole ring, isoxazole ring, oxazole ring, oxadiazole ring, isothiazole ring, thiazole ring, thiadiazole ring, thiatriazole ring, indole ring. , Indazole ring, benzimidazole ring, benzotriazole ring, benzoxazole ring, benzthiazole ring, benzselenazole ring, benzothiadiazole ring, pyridine ring, pyridazine ring, pyrimidine ring, pyrazine ring, triazine ring, quinoline ring, quinoxaline ring, etc. A nitrogen-containing heterocyclic ring, a furan ring, a thiophene ring and the like, and a substituent may be bonded to these.

Among the compounds represented by the above general formula, there are preferable compounds. That is, R ₂₁ and R ₂₂ are hydrogen atoms, R ₂₃ is a hydrogen atom or a lower alkyl group having 4 or less carbon atoms (methyl group, ethyl group, etc.), and k3 is preferably a compound having 2-10. Although a specific example is shown below, it is not limited to these examples.

  The addition amount of the above-described polymerizable compound is preferably included in the range of 0.01 to 10 parts by mass with respect to 1 part by mass of the binder resin, and further included in the range of 0.05 to 1 part by mass. It is particularly preferred that

  As a polymerization accelerator, a polymerization accelerator represented by amine, thiol, disulfide, or the like, a chain transfer catalyst, or the like can be added. Specific examples include, for example, amines such as N-phenylglycine, triethanolamine, N, N-diethylaniline, thiols described in US Pat. No. 4,414,312 and JP-A No. 64-13144, Disulfides described in JP-A-2-29161, thiones described in U.S. Pat. No. 3,558,322 and JP-A-64-17048, and o-acylthiohydroxa described in JP-A-2-291560. And mate and N-alkoxypyridinethiones. The addition amount of the polymerization accelerator is preferably 0.1 to 5% by mass of the total solid content of the polymerization layer. If it is less than this range, the effect cannot be expected. On the other hand, if the amount is too large, the film quality of the polymerized layer tends to deteriorate.

  In the photosensitive composition of the present invention, other components may be preferably added for various purposes in addition to the components described above. In particular, it is preferable to add various polymerization inhibitors for the purpose of preventing thermal polymerization or thermal crosslinking of styryl groups and improving long-term storage stability. As the polymerization inhibitor in this case, compounds having various phenolic hydroxyl groups such as hydroquinones, catechols, naphthols, and cresols, quinone compounds, and the like are preferably used, and hydroquinone is particularly preferably used. In this case, the polymerization inhibitor is preferably added in an amount of 0.1 to 10 parts by mass with respect to 100 parts by mass of the polymer.

  In addition, as an element constituting the photosensitive composition, various fine dyes and pigments are added for the purpose of enhancing the visibility of the image, and inorganic fine particles or organic fine particles are added for the purpose of preventing blocking of the photosensitive composition. The addition is also preferably performed.

  Regarding the thickness of the photosensitive layer itself when used as a lithographic printing plate material, it is preferably formed on the support with a dry thickness in the range of 0.5 to 10 microns, and more preferably in the range of 1 to 5 microns. Is extremely preferable in order to greatly improve printing durability. The photosensitive layer is prepared by mixing a solution containing the above three elements, and is coated on a support and dried using various known coating methods. As the support, for example, a film or polyethylene-coated paper may be used, but a more preferable support is an aluminum plate that is polished and has an anodized film.

  In order to use a material having a photosensitive layer formed on a support as described above as a printing plate, an alkaline developer is obtained by subjecting the exposed part to exposure or laser scanning exposure and crosslinking the exposed part. Therefore, pattern formation is performed by eluting unexposed portions with an alkaline developer described later.

  The alkaline developer is not particularly limited as long as it is a solution that dissolves the binder according to the present invention, but preferably sodium hydroxide, potassium hydroxide, sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, An aqueous developer containing an alkaline compound such as monoethanolamine, diethanolamine, triethanolamine, triethylammonium hydroxide, etc., can selectively dissolve the unexposed areas and expose the lower support surface. preferable. Furthermore, it is also preferable to add various alcohols such as ethanol, propanol, isopropanol, ethylene glycol, diethylene glycol, triethylene glycol, glycerin and benzyl alcohol to the alkaline developer. After developing with such an alkaline developer, normal gumming is preferably performed using gum arabic or the like.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples as well as the effects.

Using a grained anodized aluminum plate having a thickness of 0.24 mm, a photosensitive coating solution represented by the following formulation is applied on the plate so that the dry thickness is 2.0 microns. And drying for 6 minutes in a 75 ° C. dryer. A sample immediately after production and after storage for 1 month at 40 ° C. was used as a sample.
<Photosensitive coating solution>
Polymer (P-1) 12 parts by weight polymerization initiator 1 part by weight polymerizable compound (C-5) 3 parts by weight sensitizing dye (S-1) 0.5 parts by weight dioxane 70 parts by weight cyclohexane 20 parts by weight

Various kinds of photosensitive materials of Reference Examples were prepared by changing the type of the polymerization initiator in the photosensitive coating solution as shown in Table 1.

830nm laser diode mounting the external drum system platesetter, using PT-R4000 manufactured by Dainippon Screen Mfg. Co., drum rotation speed 1000rpm resolution 2400 dpi, under the conditions of the laser irradiation energy 100 mJ / cm ^2, the sample prepared 50 % Flat screen exposure. After the exposure, development was performed with a developer using an automatic developing machine PD-1310 for PS plate manufactured by Dainippon Screen Mfg. Co., Ltd. as an automatic developing machine. A developer having the following composition was used.
<Developer>
Potassium hydroxide 20g
Potassium silicate 20g
Perex NBL 60g
1L of water

  About the lithographic printing plate produced as mentioned above, the sharpness of the edge part of a halftone dot was observed and the image quality was evaluated according to the following evaluation criteria. The results are shown in Table 1.

○: A uniform halftone image is formed with sharp edges.
X: Unevenness is seen in the edge portion of the image and a non-uniform network image is formed.

  Evaluation similar to Example 1 was performed by replacing the polymerization initiator of Example 1 with that of Table 2. The results are summarized in Table 2.

(Comparative Example 1)
Using a grained anodized aluminum plate having a thickness of 0.24 mm, a photosensitive coating solution represented by the following formulation is applied on the plate so that the dry thickness is 2.0 microns. And drying for 6 minutes in a 75 ° C. dryer. A sample immediately after production and after storage for 1 month at 40 ° C. was used as a sample.
<Photosensitive coating solution>
Polymer (P-1) 12 parts by weight polymerization initiator 1 part by weight polymerizable compound (C-5) 3 parts by weight sensitizing dye (S-1) 0.5 parts by weight dioxane 70 parts by weight cyclohexane 20 parts by weight

  Various types of photosensitive materials were prepared by changing the type of the polymerization initiator in the photosensitive coating solution as shown in Table 3.

830nm laser diode mounting the external drum system platesetter, using PT-R4000 manufactured by Dainippon Screen Mfg. Co., drum rotation speed 1000rpm resolution 2400 dpi, under the conditions of the laser irradiation energy 100 mJ / cm ^2, the sample prepared 50 % Flat screen exposure. After the exposure, development was performed with a developer using an automatic developing machine PD-1310 for PS plate manufactured by Dainippon Screen Mfg. Co., Ltd. as an automatic developing machine. A developer having the following composition was used.
<Developer>
Potassium hydroxide 20g
Potassium silicate 20g
Perex NBL 60g
1L of water

  About the lithographic printing plate produced as mentioned above, the sharpness of the edge part of a halftone dot was observed and the image quality was evaluated according to the following evaluation criteria. The results are shown in Table 3.

○: A uniform halftone image is formed with sharp edges.
X: Unevenness is seen in the edge portion of the image and a non-uniform network image is formed.

(Comparative Example 2)
The same evaluation as in Comparative Example 1 was performed by replacing the polymerization initiator in Comparative Example 1 with that in Table 4. The results are summarized in Table 4.

  As is clear from the results of Tables 1 to 4, a lithographic plate having high image quality and excellent storage stability by using a peroxide or azo polymerization initiator having a 10-hour half-life temperature of 70 ° C. or more and less than 200 ° C. A printing plate is obtained.

  As an application example of the present invention, use as a printing plate for lithographic printing can be mentioned. Since it is excellent in storability, it is easy to handle and has good image quality, so it can be used for many printed materials.

Claims (1)

A polymer having at least a phenyl group substituted with a vinyl group in a side chain on a support, a sensitizer having absorption in a wavelength region of 750 to 1100 nm, and a 10-hour half-life temperature of 70 ° C. or more and less than 200 ° C. A negative lithographic printing plate having a recording layer containing an azo polymerization initiator and having no overlayer.