JP2013091241A - Thermal planographic printing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal planographic printing plate free from performance degradation in printability, while eliminating a printing failure to be caused by head scum.SOLUTION: This thermal planographic printing plate includes at least two image forming layers containing thermoplastic resin and a hydrophilic binder on its support. One of the image forming layers farther from the support contains barium sulfate, citric acid or malic acid.

Description

  The present invention relates to a heat-sensitive lithographic printing plate using an image-forming layer that undergoes phase conversion by heat, and relates to a heat-sensitive lithographic printing plate that does not require layer removal processing in a conventional ablation method or on-machine development method.

  In recent years, various plate making methods of planographic printing plates using various digital printers have been proposed with the development of computers and peripheral devices. For example, JP-A-6-138719 and JP-A-6-250424 disclose plate making using a dry electrophotographic laser printer, and JP-A-9-58144 discloses an on-demand ink jet printer using hot-melt ink. In addition, Japanese Patent Laid-Open No. 63-166590 discloses a method for making a plate by a thermal printer using a thermal transfer ink ribbon.

  The plate-making method using the printer as described above is largely divided from the conventional light mode type using a visible light laser and the like, and is not subject to safety light restrictions in handling. . In addition, printing plates made by these plate making methods are collectively referred to as processless printing plates because they do not require post-exposure development processing normally used in conventional optical mode types.

  However, all of the above processless printing plates form a printing plate by transferring and imparting a grease-sensitive (that is, lithographic printing ink deposition property) recorded image to the support surface provided with a water retention layer. Therefore, there were the following problems.

1) Since a layer for forming an image is hydrophilic, adhesion of toner or ink is not sufficient. For example, a transfer toner image density is insufficient, or white spots occur in a transferred image.
2) A problem that the transfer image is not sufficiently fixed, the printing durability is lowered, and a part of a small point character or a low dot image is lost.
3) A problem that a small amount of toner is irregularly transferred to a non-image portion or a thin background stain is generated due to rubbing of a thermal transfer ink ribbon.

  On the other hand, a thermosensitive lithographic printing plate in which an image-forming layer containing a thermoplastic resin or heat-meltable particles is provided on a support, and an oleophilic image portion is obtained by thermal printing with a thermal head or an infrared laser. Has also been proposed.

  For example, in Japanese Patent Application Laid-Open No. 58-199153 (Patent Document 1) or Japanese Patent Application Laid-Open No. 59-174395 (Patent Document 2), an image forming layer is directly heated by a thermal head without using a thermal transfer ribbon or the like. A heat-sensitive lithographic printing plate from which an oleophilic image area can be obtained is described. In JP 2000-190649 A (Patent Document 3) and JP 2000-301846 A (Patent Document 4), thermal lithographic printing in which an oleophilic image portion is obtained by direct heat drawing with an infrared laser or the like. The edition is listed. Each of these is a phase change type printing plate, and the part that was originally hydrophilic causes phase change and changes to hydrophobic (lipophilic). In normal lithographic printing, both water and ink are simultaneously supplied to the oleophilic image area obtained as described above, the image area accepts colored ink, and the other non-image areas are hydrophilic. In order to accept water selectively, it does not accept ink. Printing is performed by transferring the ink received on the image portion onto a printing medium such as paper.

  In particular, the direct thermal lithographic printing plates described in Patent Document 1 and Patent Document 2 are continuously drawn by the heat and pressure of the thermal head because the thermal head is directly pressed against the surface of the printing plate to perform heat drawing. During the plate making process, the hot melt material in the image forming layer adheres to the heat generating part of the thermal head, obstructs heat transfer from the thermal head, prevents good image formation, and causes poor printing. There was a problem.

  As a method for improving such a problem, for example, International Publication No. 2011/048912 (Patent Document 5) has two image forming layers and is specified for a water-soluble polymer compound in an image forming layer close to a support. It is described that by making the ratio of the above compound higher than that in the image forming layer far from the support, it is possible to improve defective printing due to head residue in addition to sufficient printability. In addition, such a document describes that printing durability and stain resistance can be improved in a well-balanced manner by using barium sulfate or zinc oxide for an image forming layer far from the support. However, depending on printing conditions, printing defects may occur due to head debris, and further improvements have been demanded.

  On the other hand, in the heat-sensitive lithographic printing plate of JP 2010-201918 (Patent Document 6), citric acid is described as a specific example of the electron-accepting compound used in the heat-sensitive recording layer, and JP 2009-073155 ( In the heat-sensitive lithographic printing plate of Patent Document 7), citric acid is described as a specific example of the water-soluble compound used in the image forming layer. JP-A-2001-051409 (Patent Document 8) describes malic acid as an example of a metal chelate compound contained in the heat-sensitive layer of a direct-drawing waterless lithographic printing plate precursor excellent in image printability, JP-A-2005-122177 (Patent Document 9) describes malic acid as an example of an organic acid contained in a contrast layer provided on an image recording layer.

JP 58-199153 A JP 59-174395 A JP 2000-190649 A Japanese Patent Laid-Open No. 2000-301846 International Publication No. 2011/048912 Pamphlet JP 2010-201918 A JP 2009-073155 A JP 2001-051409 A JP 2005-122177 A

  An object of the present invention is to provide a heat-sensitive lithographic printing plate in which printability does not deteriorate in performance and printing defects due to head residue are improved.

The above problems have been solved by the following means.
(1) The support has at least two image forming layers containing a thermoplastic resin and a hydrophilic binder, and the image forming layer far from the support contains barium sulfate and citric acid or malic acid. A heat-sensitive lithographic printing plate characterized by that.

  According to the present invention, it is possible to provide a heat-sensitive lithographic printing plate in which printability is not deteriorated and printing defects due to head residue are improved.

  The heat-sensitive lithographic printing plate of the present invention has an image forming layer containing a thermoplastic resin and a hydrophilic binder. When the image forming layer is heated and drawn with a thermal head, the thermoplastic resin buried in the hydrophilic binder melts at the part where heat is applied, and the hydrophobicity is obtained by elution conversion in a form that partly oozes out to the extreme surface of the layer. Appears and can accept ink during printing. The thermoplastic resin at the site where heat is not applied remains buried in the hydrophilic binder, and maintains the hydrophilicity originally possessed by the image forming layer.

  In the present invention, two image forming layers containing a thermoplastic resin and a hydrophilic binder are preferably provided adjacent to each other. The image forming layer on the side closer to one support is referred to as image forming layer (A), and the image forming layer on the side farther from the other support is referred to as image forming layer (B). The heat-sensitive lithographic printing plate of the present invention contains barium sulfate and citric acid or malic acid in the image forming layer (B). The present invention is described in detail below.

<Barium sulfate>
Barium sulfate is a precipitate produced by pulverizing barite and removing iron by washing and draining, and barium sulfate (barite powder) obtained by adding water and adding a sulfate aqueous solution to a barium chlorine solution to cause chemical precipitation. And barium sulfate. Examples of the barium sulfate produced by these methods include those commercially available from Sakai Chemical Industry Co., Ltd., Takehara Chemical Industry Co., Ltd., and Hakusui Tech Co., Ltd. Can be used in Furthermore, barium sulfate may be subjected to organic polymer treatment as a post-treatment after particle formation, and may be a hydroxide or oxide of any metal element such as Al, Si and Zr, Mg, Ca Surface treatment may be performed with a phosphate of any one of metal elements such as Sr and Ba.

  In the present invention, the image forming layer (B) is preferably the outermost layer (outermost layer), whereby excellent printability and printing defects due to head debris can be achieved at a higher level. In this case, when the average particle diameter of barium sulfate is too large, the contact area may decrease when printing is performed by directly contacting the image forming layer (B) with a thermal head. The reduction of the contact area may lead to a decrease in thermal efficiency and a decrease in printing durability. On the other hand, if the average particle size of barium sulfate is too small, the effect of improving poor printing is of course reduced, but if the contact area is excessively increased depending on the particle size of barium sulfate, peeling will occur. In some cases, the sticking resistance is lowered due to a decrease in the property. Therefore, the average particle size of barium sulfate used in the present invention is preferably in the range of 0.1 to 1.0 μm, more preferably 0.2 to 0.5 μm.

  As for the shape of barium sulfate used in the present invention, any of an indefinite shape, a plate shape, a columnar shape, a granular shape and the like can be used.

  Moreover, there exists a preferable range in content of barium sulfate which an image forming layer (B) contains, and it is preferable that it is 10-50 mass% with respect to the amount of thermoplastic resins which an image forming layer (B) contains. Thereby, it is possible to achieve both higher printing durability and improved printing defects at a higher level. Further, it is desirable that the total amount of the thermoplastic resin contained in the image forming layer (A) and the image forming layer (B) is used so as not to exceed the range of 10% by mass or less.

<Citric acid>
Citric acid is one of hydroxy acids, and both anhydride and monohydrate can be used. Citric acid is generally made by starch and sugar as the main raw material and fermented with mold, and is commercially available from Showa Kako Co., Ltd., Iwata Chemical Industry Co., Ltd., Fuso Chemical Industry Co., Ltd., etc. Can be used in the present invention.

<Malic acid>
Malic acid is one of hydroxy acids, and any of natural L-malic acid, D-malic acid, and synthetic DL-malic acid can be used. Malic acid is generally made from maleic acid and fumaric acid as raw materials and reacted with water under heat and pressure, and is commercially available from Showa Kako Co., Ltd., Fuso Chemical Industry Co., Ltd., etc. Can be used in the present invention.

  It is preferable to use citric acid or malic acid after adjusting the addition amount in a range where the pH value of the image forming layer (B) coating solution falls within 5-7.

<Hydrophilic binder>
Examples of the hydrophilic binder contained in the image forming layer (A) and the image forming layer (B) of the present invention include proteins such as gelatin and gelatin derivatives or cellulose derivatives, polysaccharides such as starch, gum arabic, dextran, and pullulan. And synthetic polymer compounds such as polyvinyl alcohol, modified polyvinyl alcohol, polyvinyl pyrrolidone, styrene / maleic acid copolymer salt, styrene / acrylic acid copolymer salt, and acrylamide polymer. These hydrophilic binders may be used alone or in combination of two or more. In the image forming layer (A), it is preferable to use gelatin and polyvinyl alcohol in combination. Particularly preferably, gelatin and polysaccharide are used in combination.

  Moreover, when using a hydrophilic binder together as mentioned above, the optimal use ratio exists in each. As an optimal use ratio, in the image forming layer (A), it is preferable to use gelatin and polyvinyl alcohol in a range of 1 to 10% by mass of polyvinyl alcohol with respect to 100% by mass of gelatin. On the other hand, in the image forming layer (B), the polysaccharide is preferably used in the range of 2 to 20% by mass with respect to 100% by mass of gelatin. The total amount of the hydrophilic binder used in the image forming layer (A) and the image forming layer (B) is preferably 0.5 to 50% by mass with respect to the total solid content of the image forming layer.

<Crosslinking agent>
The image forming layer (A) and the image forming layer (B) of the present invention preferably contain a hardening agent (waterproofing agent) depending on the type of the hydrophilic binder. As the hardener, those imparting water resistance by accelerating the crosslinking of the hydrophilic binder, such as melamine resin, epoxy resin, polyisocyanate compound, aldehyde compound, silane compound, chromium alum, and divinyl sulfone can be used. Particularly preferably, divinyl sulfone is used. The compounding amount of the hardener is preferably 0.01 to 30% by mass, more preferably 5 to 30% by mass, based on the solid content of the hydrophilic binder contained in the entire image forming layer. It is a range.

<Thermoplastic resin>
The thermoplastic resin contained in the image forming layer (A) and the image forming layer (B) of the present invention is a solid organic polymer compound made of a chain polymer and exhibiting plasticity upon heating, and an aqueous dispersion Add to the image forming layer coating solution. Representative examples are synthetic rubber latex including modified products such as styrene butadiene copolymer, acrylonitrile butadiene copolymer, methyl methacrylate butadiene copolymer, styrene acrylonitrile butadiene copolymer, styrene methyl methacrylate butadiene copolymer. Styrene maleic anhydride copolymer, methyl vinyl ether maleic anhydride copolymer, polyacrylic acid copolymer, polystyrene, styrene / acrylic acid ester copolymer, polyacrylic acid ester, polymethacrylic acid ester, acrylic Aqueous dispersions such as acid ester / acrylic acid ester copolymers and low melting point polyamide resins can also be used. These thermoplastic resins can be used alone or in combination of two or more. In view of the affinity with the vehicle (binder component) of the printing ink, the thermoplastic resin is preferably a synthetic rubber latex, and particularly preferably a styrene butadiene copolymer and a modified product thereof. A preferable blending amount of the thermoplastic resin is preferably 5 to 50% by mass with respect to the solid content of all the image forming layers.

  In order to easily develop the effect of melting and fusing by heat, it is preferable to use a thermoplastic resin having a glass transition temperature of 50 to 150 ° C, more preferably 55 to 120 ° C. If the glass transition temperature is less than 50 ° C., a phase change occurs in the liquid state during the production process, and hydrophobicity is developed even in the non-image area, which may cause printing stains. When the temperature exceeds 150 ° C., the polymer is hardly melted by heat, and it may be difficult to form a strong image with a relatively small output laser or a small thermal printer.

  The content ratio of the thermoplastic resin to the hydrophilic binder in the image forming layer (A) of the present invention (the mass of the thermoplastic resin / the total mass of the hydrophilic binder) is preferably 0.1 to 50, and more preferably. Is 1-20. The content ratio of the thermoplastic resin to the hydrophilic binder (the mass of the thermoplastic resin / the total mass of the hydrophilic binder) in the image forming layer (B) is preferably 0.01 to 10, more preferably 0.8. 1-3. In addition, the content ratio of the thermoplastic resin to the hydrophilic binder in the image forming layer (A) is preferably higher than the content ratio in the image forming layer (B). Furthermore, it is more preferable that the difference between the content ratio in the image forming layer (A) and the content ratio in the image forming layer (B) is 0.5 or more. By adjusting to such a range, a heat-sensitive lithographic printing plate excellent in printing durability and stain resistance can be obtained.

<Hot-melting substance>
The image forming layer (A) and the image forming layer (B) of the present invention preferably contain a hot-melt material. Examples of the hot-melt material include at least one selected from the compounds represented by the following general formulas (1) to (4), and waxes such as carnauba wax, microcrystalline wax, paraffin wax, polyethylene wax, It is preferable to use fatty acids such as lauric acid, stearic acid, oleic acid, palmitic acid, behenic acid and montanic acid, and waxes such as esters and amides according to the purpose. Of these, organic compounds having a melting point of 50 to 150 ° C. are preferably used. If the melting point is less than 50 ° C., it will melt during the production process, which may cause soiling of the printed matter. On the other hand, when the temperature exceeds 150 ° C., it is difficult to melt by application of heat from a thermal head or the like, and the occurrence of image toughness or the expression of lipophilicity may be poor. A preferable blending amount of the heat-meltable substance in the image forming layer is preferably 1 to 50% by mass, and more preferably 10 to 30% by mass with respect to the total solid content of the image forming layer.

  The compound represented by the general formula (1) will be described below.

In the above formula, X ₁ represents —O— or —CO—O—, and R _{1 to} R ₆ each represents a hydrogen atom, an alkyl group, or an aryl group. n represents an integer of 1 to 10, and the substituents R _{1 to} R ₃ and R _{4 to} R ₆ may be bonded to each other to form an aromatic ring.

Among the compounds represented by the general formula (1), compounds in which X ₁ is —O— are preferable, and R ₁ and R ₆ are particularly a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R _{2 to} R _5. A compound in which is a hydrogen atom and n is an integer of 1 to 4 is particularly preferably used.

Examples of the compound represented by the general formula (1) include the following compounds, but the present invention is not limited thereto.
(1) 1- (1-naphthoxy) -2-phenoxyethane (2) 1- (2-naphthoxy) -4-phenoxybutane (3) 1- (2-isopropylphenoxy) -2- (2-naphthoxy) ethane (4) 1- (4-Methylphenoxy) -3- (2-naphthoxy) propane (5) 1- (2-methylphenoxy) -2- (2-naphthoxy) ethane (6) 1- (3-methylphenoxy ) -2- (2-naphthoxy) ethane (7) 1- (2-naphthoxy) -2-phenoxyethane (8) 1- (2-naphthoxy) -6-phenoxyhexane (9) 1-phenoxy-2- ( 2-phenylphenoxy) ethane (10) 1- (2-methylphenoxy) -2- (4-phenylphenoxy) ethane (11) 1,4-diphenoxybutane (12) 1,4-bis (4-methylphenyl) Noxy) butane (13) 1,2-bis (3,4-dimethylphenoxy) ethane (14) 1-phenoxy-3- (4-phenylphenoxy) propane (15) 1- (4-tert-butylphenoxy)- 2-phenoxyethane (16) 1,2-diphenoxyethane (17) 1- (4-methylphenoxy) -2-phenoxyethane (18) 1- (2,3-dimethylphenoxy) -2-phenoxyethane (19 ) 1- (3,4-dimethylphenoxy) -2-phenoxyethane (20) 1- (4-ethylphenoxy) -2-phenoxyethane (21) 1- (4-isopropylphenoxy) -2-phenoxyethane (22 ) 1,2-bis (2-methylphenoxy) ethane (23) 1- (2-methylphenoxy) -2- (4-methylphenoxy) ethane (24) 1- (4-tert-Butylphenoxy) -2- (2-methylphenoxy) ethane (25) 1,2-bis (3-methylphenoxy) ethane (26) 1- (3-methylphenoxy) -2- ( 4-methylphenoxy) ethane (27) 1- (4-ethylphenoxy) -2- (3-methylphenoxy) ethane (28) 1,2-bis (4-methylphenoxy) ethane (29) 1- (2, 3-Dimethylphenoxy) -2- (4-methylphenoxy) ethane (30) 1- (2,5-dimethylphenoxy) -2- (4-methylphenoxy) ethane (31) Phenoxyacetic acid-2-naphthyl (32) 2-Naphoxyacetic acid-4-methylphenyl (33) 2-naphthoxyacetic acid-3-methylphenyl

  Next, the compound represented by the general formula (2) will be described.

In the above formula, R ₇ represents an alkyl group, an aryl group, an alkylcarbonyl group, an arylcarbonyl group, an alkylsulfonyl group, or an arylsulfonyl group. The naphthalene ring in the formula may further have a substituent, and examples of preferable substituents include an alkyl group, an aryl group, a halogen group, a hydroxy group, an alkoxy group, an aryloxy group, and an alkyloxycarbonyl group. , Alkoxycarbonyl group, aryloxycarbonyl group, carbamoyl group, sulfamoyl group and the like.

Among the substituents represented by R ₇ in the general formula (2), an alkyl group having 4 to 20 carbon atoms, an aryl group having 4 to 24 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, and 7 to 20 carbon atoms. The arylcarbonyl group is more preferable. In the general formula (2), among the substituents that the naphthalene ring may further have, a halogen group, an alkyl group having 1 to 10 carbon atoms, an alkyloxycarbonyl group having 2 to 20 carbon atoms, or a 7 to 20 carbon atom. An aryloxycarbonyl group and a carbamoyl group having 2 to 25 carbon atoms are more preferable.

Examples of the compound represented by the general formula (2) include the following compounds, but the present invention is not limited thereto.
(1) 1-benzyloxynaphthalene (2) 2-benzyloxynaphthalene (3) 2-p-chlorobenzyloxynaphthalene (4) 2-p-isopropylbenzyloxynaphthalene (5) 2-dodecyloxynaphthalene (6) 2 Decanoyloxynaphthalene (7) 2-Myristoyloxynaphthalene (8) 2-p-tert-butylbenzoyloxynaphthalene (9) 2-Benzoyloxynaphthalene (10) 2-Benzyloxy-3-N- (3-dodecyl Oxypropyl) carbamoylnaphthalene (11) 2-benzyloxy-3-N-octylcarbamoylnaphthalene (12) 2-benzyloxy-3-dodecyloxycarbonylnaphthalene (13) 2-benzyloxy-3-p-tert-butylphenoxy Carbonyl naphthalene

  Next, the compound represented by the general formula (3) will be described.

In the above formula, R ₈ and R ₉ represent a hydrogen atom, a halogen group, an alkyl group having 4 or less carbon atoms, or an alkoxy group. X ₂ represents a simple bond or —O—, and n represents an integer of 1 to 4.

Examples of the compound represented by the general formula (3) include the following compounds, but the present invention is not limited thereto.
(1) dibenzyl oxalate (2) bis (p-methylbenzyl) oxalate
(3) Bisoxalate (p-chlorobenzyl)
(4) Bisoxalate (m-methylbenzyl)
(5) Bisoxalate (p-ethylbenzyl)
(6) Bisoxalate (p-methoxybenzyl)
(7) Bisoxalate (2-phenoxyethyl)
(8) Bis oxalate (2-o-chlorophenoxyethyl)
(9) Bis oxalate (2-p-chlorophenoxyethyl)
(10) Bis-oxalate (2-p-ethylphenoxyethyl)
(11) Bisoxalate (2-m-methoxyphenoxyethyl)
(12) Bisoxalate (2-p-methoxyphenoxyethyl)
(13) Bis-oxalate (4-phenoxybutyl)

  Among these exemplified compounds, preferred specific examples include dibenzyl oxalate, bis (p-methylbenzyl) oxalate, bis (p-chlorobenzyl) oxalate, bis (m-methylbenzyl) oxalate, and bisoxalate. (P-ethylbenzyl) and bis (p-methoxybenzyl) oxalate.

  The compound represented by the general formula (4) will be described below.

In the above formula, R ₁₀ , R _{10 ′} , R ₁₁ and R _{11 ′} represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, an alkoxy group, an alkylcarbonyl group, an arylcarbonyl group, an alkoxycarbonyl group or an aryloxy group. .

Examples of the compound represented by the general formula (4) include the following compounds, but the present invention is not limited thereto.
(1) 1,2-bisphenoxymethylbenzene (2) 1,3-bisphenoxymethylbenzene (3) 1,4-bis (2-methylphenoxymethyl) benzene (4) 1,4-bis (3-methyl Phenoxymethyl) benzene (5) 1,3-bis (4-methylphenoxymethyl) benzene (6) 1,3-bis (2,4-dimethylphenoxymethyl) benzene (7) 1,3-bis (2,6 -Dimethylphenoxymethyl) benzene (8) 1,4-bis (2-chlorophenoxymethyl) benzene (9) 1,2-bis (4-chlorophenoxymethyl) benzene (10) 1,3-bis (4-chloro Phenoxymethyl) benzene (11) 1,2-bis (4-octylphenoxymethyl) benzene (12) 1,3-bis (4-octylphenoxymethyl) benzene 13) 1,3-bis (4-isopropylphenyl phenoxymethyl) benzene (14) 1,4-bis (4-isopropylphenyl phenoxymethyl) benzene

  Preferred examples among these exemplary compounds include 1,2-bisphenoxymethylbenzene, 1,4-bis (2-methylphenoxymethyl) benzene, 1,4-bis (3-methylphenoxymethyl) benzene, 1,4-bis (2-chlorophenoxymethyl) benzene may be mentioned.

  Among the compounds represented by the general formulas (1) to (4), the compounds represented by the general formulas (1), (2), and (4) are preferable in that excellent printing durability can be obtained. The compounds represented by (1) and (2) are preferred, and the most preferred compound is the compound represented by the general formula (1). In addition, the above hot-melt materials may be used alone or in combination, but in the present invention, the compounds represented by the general formulas (1) to (4) and waxes are used. Each is used in combination of at least one.

  The compounds represented by the above general formulas (1) to (4) are solid substances at room temperature, but are preferably used after being subjected to a fine dispersion treatment in order to increase the reactivity with heat. As a fine dispersion treatment method, a bead mill such as a roll mill, a colloid mill, a ball mill, an attritor or a sand mill, which is a wet dispersion method generally used at the time of producing a paint, can be used. In the bead mill, ceramic beads such as zirconia, titania and alumina, metal beads such as chrome and steel, and glass beads can be used. The dispersed particle diameter is preferably from 0.1 to 1.2 μm in median diameter, particularly preferably from 0.3 to 0.8 μm. The median diameter is the particle diameter (cumulative average diameter) at which the cumulative curve becomes 50% when the total curve of one population of particles is 100%, and the particle size distribution is evaluated. As one of the parameters to be measured, it can be measured using a laser diffraction / scattering particle size distribution measuring apparatus LA920 (manufactured by Horiba, Ltd.).

  In the present invention, the content ratio of the heat-meltable substance to the hydrophilic binder in the image-forming layer (A) (the mass of the heat-meltable substance / the mass of the hydrophilic binder) has a preferable range, which is 1.0 or more. It is preferable. On the other hand, the content ratio of the heat-meltable substance to the hydrophilic binder in the image forming layer (B) (the mass of the heat-meltable substance / the mass of the hydrophilic binder) also has a preferable range, and may be 0 to 0.5. preferable. In the present invention, the content ratio of the heat-meltable substance with respect to the hydrophilic binder in the image forming layer (A) is preferably higher than the content ratio in the image forming layer (B). More preferably, it is 0.8 or more. By adjusting to such a range, a heat-sensitive lithographic printing plate excellent in printing durability and stain resistance can be obtained.

  In the heat-sensitive lithographic printing plate of the present invention, a developer or a color former (electron donating property) such as a phenol derivative or an aromatic carboxylic acid derivative used in general heat-sensitive recording paper and pressure-sensitive recording paper for ensuring visibility. Dye precursor).

<Developer>
Specific examples of the developer include 4-cumylphenol, hydroquinone monobenzyl ether, 4,4'-isopropylidenediphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4'- Dihydroxydiphenyl-2,2-butane, 4,4′-dihydroxydiphenylmethane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 2,2-bis (4-hydroxyphenyl) heptane, bis (4 -Hydroxyphenylthioethoxy) methane, 1,5-bis (4-hydroxyphenylthio) -3-oxapentane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α -Methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 1,3-bis [α-methyl-α- (4′-hydride) Xylphenyl) ethyl] benzene, 4,4'-dihydroxydiphenyl sulfide, di (4-hydroxy-3-methylphenyl) sulfine, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone 2,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone, 4-hydroxyphenyl-4'-benzyloxyphenylsulfone, 4-hydroxy-3 ', 4'-tetramethylenebiphenylsulfone, 3,4-dihydroxyphenyl-p-tolylsulfone, 4,4'-dihydroxybenzophenone, benzyl 4-hydroxybenzoate, N, N'-di-m-chlorophenylthiourea, N- (pheno Phenolic compounds such as xylethyl) -4-hydroxyphenylsulfonamide, zinc 4- [3- (p-tolylsulfonyl) propyloxy] salicylate, 4- [2- (p-methoxyphenoxy) ethyloxy] zinc salicylate, 5- [P- (2-p-methoxyphenoxyethoxy) cumyl] zinc salts of aromatic carboxylic acids such as zinc salicylate and zinc p-chlorobenzoate, and organic acidic substances such as antipyrine complexes of zinc thiocyanate The

<Coloring agent>
Specific examples of the color former (electron-donating dye precursor) include (1) 3,3′-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (Crystal Violet lactone), 3,3′-bis (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p -Dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis ( 1,2-dimethylindol-3-yl) -5-dimethylaminophthalide, 3,3-bis (1,2-dimethylindol-3-yl) -6-dimethyla Nophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -5-dimethylaminophthalide, 3- p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethylaminophthalide and the like: (2) 4,4′-bis-dimethylaminobenzhydrin benzyl ether as a diphenylmethane compound, N-halophenyl leucooramine, N-2,4,5-trichlorophenyl leucooramine, etc .: (3) As xanthene compounds, rhodamine B-anilinolactam, rhodamine Bp-nitroanilinolactam, rhodamine B -P-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3- Ethylamino-7-octylaminofluorane, 3-diethylamino-7-phenylfluorane, 3-diethylamino-7- (3,4-dichloroanilino) fluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-ethyl- Tolylamino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-phenethylfluorane, 3-diethylamino-7- (4-nitroanilino) fluorane, etc .: (4) thiazine compounds As benzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue (5) As spiro compounds, 3-methyl-spiro-dinaphthopyrans, 3-ethyl-spiro-dinaphthopyrans, 3,3'-dichloro-spiro-dinaphthopyrans, 3-benzyl-spiro-dinaphthopyrans, 3-methylnaphtho- ( 3-methoxy-benzo) -spiropyran, 3-propyl-spiro-dibenzopyran and the like. These may be used alone or in combination of two or more.

<Photothermal conversion material>
Furthermore, in the present invention, a photothermal conversion substance can be blended in the image forming layer. By using a photothermal conversion substance, writing with active light such as an infrared laser as well as a thermal head is possible. As an example of the photothermal conversion substance, a material that efficiently absorbs light and converts it into heat is preferable. Depending on the light source used, for example, when a semiconductor laser emitting near infrared light is used as the light source, Near-infrared light absorbers having an absorption band outside are preferable, for example, organic materials such as carbon black, cyanine dyes, polymethine dyes, azurenium dyes, squalium dyes, thiopyrylium dyes, naphthoquinone dyes, anthraquinone dyes Examples thereof include metal compounds such as compounds, phthalocyanine-based, azo-based, and thioamide-based organometallic complexes, iron powder, graphite powder, iron oxide powder, lead oxide, silver oxide, chromium oxide, iron sulfide, and chromium sulfide.

  In addition, preservatives, surfactants, antifoaming agents, leveling agents, pH adjusting agents, other coating aids, and the like may be added to the image forming layer (A) and the image forming layer (B) of the present invention as necessary. Can be added.

The image-forming layer of the heat-sensitive lithographic printing plate of the present invention has a dry solid content of 0.5 to 30 g / m ² from the viewpoints of printing durability of image areas, water resistance of non-image areas and mechanical strength. It is preferable. In addition, as a method for coating the image forming layer (A) and the image forming layer (B) in the present invention, the image forming layer (A) on the side close to the support is applied, and then the image forming layer (B). There are a method of sequentially applying and stacking layers, a method of simultaneously applying multiple layers by a slide hopper method, and either method may be used.

  In the heat-sensitive lithographic printing plate of the present invention, an undercoat layer comprising titanium dioxide, a binder resin, and a crosslinking agent is preferably provided between the support and the image forming layer. As a result, there is no change in the plate pressure due to contamination due to plate pressure changes during printing, specifically, slight undulations on the blanket roller of the printing press, without degrading image quality and printing durability. It is possible to improve the printing stain that occurs and develops at the extreme tip and bottom edge of the printing paper surface.

<Titanium dioxide>
The titanium dioxide contained in the undercoat layer may be either a rutile type or an anatase type, and the production method is not limited to either the sulfuric acid method or the chlorine method. You may use them individually or in mixture. Furthermore, from the viewpoint of dispersion stability and other functionality, it is possible to selectively use those subjected to various surface treatments. As the surface treatment composition, alumina, silica, zinc oxide, zirconia and the like are common. Examples of commercially available titanium dioxide include SR-1, R-650, R-5N, R-7E, R-3L, A-110, and A-190 from Sakai Chemical Industry Co., Ltd. ) From Taipei R-580, R-930, A-100, A-220, CR-58, Titanium Industry Co., Ltd., Kronos KR-310, KR-380, KA-10, KA -20, Teica Co., Ltd., and Titanics JR-301, JR-600A, JR-800, and JR-701, DuPont Co., Ltd., Taipure R-900, and R-931.

The average particle diameter of titanium dioxide used for the undercoat layer is preferably smaller than the average dry film thickness of the undercoat layer. In general, titanium dioxide is present in the form of secondary particles, tertiary particles, etc., in which some primary particles are aggregated. The average particle size of the titanium dioxide is, for example, titanium dioxide in a dispersion medium to which a dispersant such as polycarboxylic acid, fatty acid amine, sulfonic acid amide, ε-caprolactone, hydrostearic acid, polyesteramine is added. Is dispersed using a media mill such as a ball mill, a bead mill, or a sand grinder, a pressure disperser such as a high pressure homogenizer or an ultra high pressure homogenizer, an ultrasonic disperser, and a thin film swirl disperser. It is preferable to adjust appropriately. A preferable average particle size used in the titanium dioxide layer is preferably 0.1 to 1.5 μm, particularly preferably 0.2 to 1.0 μm. The average particle diameter in the present invention can be measured as a number median diameter using a laser scattering particle size distribution meter (for example, LA920 manufactured by Horiba, Ltd.). On the other hand, the dry solid content of the undercoat layer is preferably in the range of 0.5 to 20 g / m ² .

  The content of titanium dioxide used in the undercoat layer can be set in a wide range, but it is preferably used at 200 to 1000% by mass with respect to 100 parts by mass of the binder resin solid content contained in the undercoat layer. More preferably, it is 400-600 mass%. When the content of titanium dioxide is low, the concealing property may be reduced. When used in excess, the stability of the coating liquid may be reduced or the bulk density may increase due to irregular aggregation. As a result, the surface roughness may increase and the image quality may deteriorate.

<Binder resin>
As the binder resin contained in the undercoat layer, for example, gelatin such as lime-processed gelatin, acid-processed gelatin, and enzyme-processed gelatin, water-soluble polymers such as polysaccharides, polyvinyl alcohol, and polyvinylpyrrolidone can be used. It is preferable to use it.

<Crosslinking agent>
As the crosslinking agent contained in the undercoat layer, for example, melamine resin, epoxy resin, polyisocyanate compound, aldehyde compound, silane compound, chromium alum, divinyl sulfone, and the like can be preferably used. Is preferred. The blending amount of the crosslinking agent is preferably 1 to 30% by mass, more preferably 2 to 15% by mass, based on the solid content of the binder.

<Support>
A water-resistant support is used as the support used in the heat-sensitive lithographic printing plate of the present invention, but a water-resistant support such as a plastic film, resin-coated paper, and water-resistant paper can be preferably used. Specifically, plastic films such as polyolefins such as polyethylene and polypropylene, polyethersulfone, polyester, poly (meth) acrylate, polycarbonate, polyamide, and polyvinyl chloride, and resin-coated paper with these plastics laminated or coated on the surface, melamine Paper that has been made water resistant by a wet paper strength agent such as formaldehyde resin, urea formaldehyde resin, or epoxidized polyamide resin can be suitably used.

Next, a plate making method using the heat-sensitive lithographic printing plate of the present invention described above will be described. The heat-sensitive lithographic printing plate of the present invention can be suitably used when making a plate using a thermal head. As such an apparatus, a line printer using a thick film or thin film line head, a serial printer using a thin film serial head, or the like can be used. The recording energy density is preferably 10 to 100 mJ / mm ² , and the head image recording density is preferably 300 dpi or more in order to obtain a relatively high quality output image.

  EXAMPLES Hereinafter, although this invention is demonstrated using an Example, this invention is not limited by this description. In the following description, “%” and “part” represent a mass ratio unless otherwise specified.

Example 1
On one side of a polyethylene resin-coated paper having a thickness of about 180 μm that has been laminated on both sides, slide an undercoat layer coating solution of the following composition, and an image forming layer a-1 and an image forming layer b-1 coating solution. By the hopper coating method, three layers were simultaneously applied from the support side so that the undercoat layer, the image forming layer a-1, and the image forming layer b-1 (uppermost layer) were in this order. At that time, the wet coating weight, the undercoat layer coating solution 17 g / ^{m 2,} the image forming layer a-1 coating liquid 33 g / ^{m 2,} the image forming layer b-1 coating liquid to 12 g / ^{m 2} Set and went.

<Preparation of titanium dioxide slurry>
Titanium dioxide (SR-1, manufactured by Sakai Chemical Industry Co., Ltd., rutile type, alumina treatment) 4.0 parts Acrylic acid copolymerized metal salt 10% aqueous solution 0.2 parts Water to make 11 parts in total, using a homomixer A high-speed fine dispersion treatment for 30 minutes was performed.

<Undercoat layer coating solution>
Gelatin (cow bone, alkali treatment) 0.82 parts Titanium dioxide slurry 11.0 parts Dioctyl sodium sulfosuccinate 5% aqueous solution 0.06 parts Divinyl sulfone 5% aqueous solution 2.0 parts The total amount was made 17 parts with water. A part of the undercoat layer coating solution was sampled, diluted, and the average particle diameter of titanium dioxide was measured using a laser scattering type particle size distribution meter (LA920 manufactured by Horiba, Ltd.). there were.

<Preparation of developer mixed slurry>
As the developer mixed slurry, one prepared in advance by the following preparation method was used.
Material a: 1,2-bis (3-methylphenoxy) ethane
(KS-232 manufactured by Sanko Co., Ltd.)
Material b: 4-hydroxy-4'-isopropoxydiphenyl sulfone
(Nihon Soda Co., Ltd. D-8)
Material c: Anionic styrenic resin 15% aqueous solution
(Polymarlon 1318 manufactured by Arakawa Chemical Industries, Ltd.)

  After mixing 1 part each of material a and material b in water with 0.7 parts of the above material c added under constant stirring, the average particle diameter is reduced using zirconia beads in a small dyno mill (bead mill). A fine dispersion treatment was performed until the particle size became 0.6 μm to obtain a developer mixed slurry. In addition, it prepared so that solid content concentration in the sum total of the material a, the material b, and the material c might be about 35%.

<Image forming layer a-1 coating solution>
Gelatin (cow bone, alkali treated) 0.78 parts Polyvinyl alcohol (PVA-505 manufactured by Kuraray Co., Ltd.) 0.07 parts Latex of carboxyl-modified styrene-butadiene copolymer 2.8 parts (Rack manufactured by DIC Corporation) Star 7132C, 45% slurry, Tg = 60 ° C.)
Developer mixed slurry 8.4 parts 3-dibutylamino-6-methyl-7-anilinofluorane 30% slurry
0.7 parts dioctyl sodium sulfosuccinate 5% aqueous solution 0.4 parts divinyl sulfone 5% aqueous solution 2.0 parts The total amount was 33 parts with water.

<Preparation of barium sulfate slurry>
1.0 parts of barium sulfate (B-35 manufactured by Sakai Chemical Industry Co., Ltd., average particle size = 0.3 μm)
Acrylic acid copolymerized metal salt 10% aqueous solution 0.7 part The total amount was 10 parts with water, and high-speed fine dispersion treatment was performed for 30 minutes using a homomixer.

<Image forming layer b-1 coating solution>
Gelatin (cow bone, alkali-treated) 0.29 part Citric acid 0.005 part Pullulan (Pullulan manufactured by Hayashibara Corporation) 0.02 part Latex of carboxyl-modified styrene-butadiene copolymer 0.6 part (DIC ( Co., Ltd. Rack Star 7132C, 45% slurry, Tg = 60 ° C.)
3-dibutylamino-6-methyl-7-anilinofluorane 30% slurry
0.3 part 5% aqueous solution of dioctyl sodium sulfosuccinate 0.2 part 30% slurry of montanate ester wax 0.3 part (Hydrin J-537 manufactured by Chukyo Yushi Co., Ltd.)
Barium sulfate slurry 1.0 part Divinyl sulfone 5% aqueous solution 0.7 part The total amount was 12 parts with water. At this time, the pH of the b-1 coating solution was 6.4.

  After three layers were simultaneously applied at the moisture application amount, the coating film was immediately gelled with cold air of 1 to 3 ° C., and then dried with hot air set at 30 ° C. After drying, a thermosensitive lithographic printing plate of Example 1 was obtained by heating for 7 days using a constant temperature and humidity chamber adjusted to a temperature of 40 ° C./humidity of 40%.

The thermal lithographic printing plate produced as described above was subjected to image output (recording energy density 70 to 100 mJ / mm ² ) using a thermal digital printer for CTP (Thermal Digiplater TDP-459: 1200 dpi / 120 lpi manufactured by Mitsubishi Paper Industries). The electric capacity was 330 W), and a printing plate was prepared.

<Head residue improvement>
For evaluation of head residue improvement, the first plate and the 100th plate are made with only halftone dots, and the others are made up of 98 patterns made up of halftone dots and letters. The first plate and the 100th plate are visually checked. The following criteria were used for determination. The results are shown in Table 1.
○: No difference in image quality between the 1st and 100th plates ×: Difference in image quality between the 1st and 100th plates

<Print durability>
As for printing durability, an image for printing evaluation was made under the above-mentioned plate making conditions, and a printing test was conducted using this as a printing sample. The printing machine uses HAMADA H234C (offset printing machine manufactured by Hamada Printing Machinery Co., Ltd.), the printing ink is ECO Diamond Excel (Mitsubishi Paper Co., Ltd.), and the dampening liquid is TDP-DL1 (Mitsubishi Paper Co., Ltd.). ) Moisturizing liquid) A 10% aqueous solution was used, and printing was started after wiping the plate surface with a 25% aqueous solution of TDP-HL (an etching liquid manufactured by Mitsubishi Paper Industries Co., Ltd.) all over the printing plate. For printing durability evaluation, the printing paper surface at the start and the printing paper surface at the time of printing 5,000 sheets were compared, and the attenuation ratio of 20% halftone dot and 50% halftone dot was observed with a 25 times loupe. The evaluation criteria were used. The results are shown in Table 1.
○: Almost no change in both 20% and 50% halftone dots ○ △: Almost no change in the 50% halftone dot portions, but attenuation can be confirmed in the 20% halftone dot portions △: Both the 20% and 50% halftone dot portions △: Attenuation of 50% or more is observed at 20% halftone dot part X: Attenuation of 90% or more is observed at 20% halftone dot part

<Blank dirt>
With respect to the blemishes, a printing evaluation image was made under the plate making conditions, and a printing test was conducted using this image as a printing sample. RYOBI660 (offset printing machine manufactured by Ryobi Co., Ltd.) is used as the printing machine, the printing ink is FusionG black N (manufactured by DIC Corporation), and the dampening liquid is Ecology II (Fuji Film Co., Ltd. humidifying liquid). Printing was started after using a 5% aqueous solution and wiping the plate surface with a 10% aqueous solution of TDP-HL (Mitsubishi Paper Co., Ltd. etching solution) before starting printing. As a blank stain evaluation, the blanket stain level at the end of 1,000 sheets from the start of printing was determined using the following evaluation criteria. The results are shown in Table 1.
◎: No dirt is generated ○: Slightly dirty ○ △: Lightly dirty △: Slightly dirty ×: Very dirty

(Example 2)
The heat-sensitive lithographic printing plate of Example 2 was prepared in the same manner as in Example 1 except that 0.0035 parts of DL-malic acid was added instead of citric acid in the image forming layer b-1 coating solution of Example 1. Obtained. The pH of the b-1 coating solution was 6.6. Evaluation was performed in the same manner as in Example 1 using the obtained thermosensitive lithographic printing plate. The results are shown in Table 1.

(Comparative Example 1)
A heat-sensitive lithographic printing plate of Comparative Example 1 was obtained in the same manner as in Example 1 except that 0.024 part of 3N sulfuric acid was added instead of citric acid in the image forming layer b-1 coating solution of Example 1. . The pH of the b-1 coating solution was 6.4. Evaluation was performed in the same manner as in Example 1 using the obtained thermosensitive lithographic printing plate. The results are shown in Table 1.

(Comparative Example 2)
A heat-sensitive lithographic printing plate of Comparative Example 2 was obtained in the same manner as in Example 1 except that the citric acid of the image forming layer b-1 coating solution of Example 1 was changed to succinic acid-1Na. The pH of the b-1 coating solution was 6.5. Evaluation was performed in the same manner as in Example 1 using the obtained thermosensitive lithographic printing plate. The results are shown in Table 1.

(Comparative Example 3)
A heat-sensitive lithographic printing plate of Comparative Example 3 was obtained in the same manner as in Example 1 except that the citric acid of the image forming layer b-1 coating solution of Example 1 was not added. The pH of the b-1 coating solution was 7.7. Evaluation was performed in the same manner as in Example 1 using the obtained thermosensitive lithographic printing plate. The results are shown in Table 1.

(Comparative Example 4)
A heat-sensitive lithographic printing plate of Comparative Example 4 was obtained in the same manner as in Example 1 except that the barium sulfate slurry of the image forming layer b-1 coating liquid of Example 1 was not added. The pH of the b-1 coating solution was 5.9. Evaluation was performed in the same manner as in Example 1 using the obtained thermosensitive lithographic printing plate. The results are shown in Table 1.

(Comparative Example 5)
A heat-sensitive lithographic printing plate of Comparative Example 5 was obtained in the same manner as in Example 1 except that the citric acid and barium sulfate slurry of the image forming layer b-1 coating solution of Example 1 was not added. The pH of the b-1 coating solution was 7.7. Evaluation was performed in the same manner as in Example 1 using the obtained thermosensitive lithographic printing plate. The results are shown in Table 1.

(Comparative Example 6)
The image forming layer a-1 coating solution of Example 1 was not used, and the same procedure as in Example 1 was performed except that two layers were simultaneously applied with the undercoat layer coating solution and the image forming layer b-1 coating solution. A heat-sensitive lithographic printing plate of Comparative Example 6 was obtained. Evaluation was performed in the same manner as in Example 1 using the obtained thermosensitive lithographic printing plate. The results are shown in Table 1.

  As can be seen from the results shown in Table 1, it can be seen that a heat-sensitive lithographic printing plate having no deterioration in printability and improved printing defects due to the head residue is obtained according to the present invention.

Claims (1)

  It has at least two image forming layers containing a thermoplastic resin and a hydrophilic binder on a support, and the image forming layer far from the support contains barium sulfate and citric acid or malic acid. A heat-sensitive lithographic printing plate.