JPH09277485A - Lithographic printing plate and its image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the good durability of an printing plate having high ink repellency by a method in which the hydrophilic swelling layer of a lithographic printing plate having the hydrophilic swelling layer on a substrate is made an image receiving layer, and an ink sticking layer is formed by a thermal transfer method. SOLUTION: A direct depiction type lithographic printing plate has at least a hydrophilic swelling layer as an image receiving layer on a substrate, and an ink sticking layer is formed on the swelling layer by a thermal transfer method which transfers and forms an image using the thermal head of a usual thermal transfer printer. The printing plate which formed an image is attached to the printing cylinder of a lithographic printing machine, and ink is supplied from a contacting roller to a plate surface. A non-printing element part having the hydrophilic swelling layer on the plate surface swells by dampening water supplied from a dampening water supplying apparatus to repel ink. Besides, a printing element part formed by thermal transfer receives ink, and ink is supplied to the surface of an offset blanket plate cylinder or to the surface of a printed body to form a printed image. Pure water is used as the dampening water in printing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an image on a lithographic printing plate, which has high ink resilience without desensitizing treatment and has a wide control range of dampening water. The present invention relates to a novel lithographic printing plate in which pure water can be used and an image forming method thereof. More specifically, the present invention relates to a lithographic printing plate which is less likely to cause stains on a printed matter and has good printing durability, and an image forming method thereof.

[0002]

2. Description of the Related Art With the recent development of printing technology and progress of OA, a direct drawing type lithographic printing plate which can be easily made with an electrostatic transfer type copying machine or printer, a thermal transfer type printer, an ink jet printer or the like. Printing using is becoming widespread.

[0003] A conventional direct-drawing lithographic printing plate material is provided with an image-receiving layer containing a pigment, a water-soluble binder and a water-proofing agent as main components on a support made of paper, plastic film or the like. . In such a direct drawing type lithographic printing plate, lipophilic ink is used, and on the image receiving layer,
A method of forming a lipophilic image by a typewriter or handwriting, lipophilic by transferring the toner image formed on the electrophotographic photoreceptor to the image receiving layer of the lithographic printing plate and fixing it by heat, light, pressure, etc. There are known a method of forming an image, a method of forming a lipophilic image by thermally melting and transferring an image from an ink ribbon with a thermal transfer printer, and a method of forming a lipophilic image with an ink jet printer.

However, printing using such a printing plate requires a step of desensitizing non-image areas with an etchant to convert the image receiving layer into an ink repellent layer. When desensitization is not performed, or when desensitization is insufficient, there has been a problem that the ink repellency of the hydrophilic layer is insufficient and background stain occurs.

[0005] In order to obtain a practical level of ink resilience, it is necessary to desensitize and to use a large amount of a hydrophilic binder polymer, but the water resistance is inferior and the printing durability is lowered. Further, when the hydrophilicity is increased, the adhesiveness to an image such as a toner is deteriorated, and there is a problem that the dot in the image area is easily thinned or lost due to damage. on the other hand,
When water resistance is increased by increasing the amount of waterproofing agent added or adding a hydrophobic polymer to improve printing durability, hydrophilicity decreases and ink repulsion decreases significantly. There was a problem.

Furthermore, when an image is formed on a conventional printing plate by electrostatic transfer, the control width of dampening water is narrow in actual printing, and printing magazine, Vol. 72, No. 5, p.
As described in the above, there is a problem that stable printing cannot be performed unless an organic component such as IPA (isopropyl alcohol) is added to the fountain solution.

[0007]

Therefore, the present inventors have used high-ink repulsion without desensitizing treatment, have a wide control range of dampening water, and use pure water as dampening water. As a result of diligent study on the image forming method of the lithographic printing plate having good printing durability of the printing plate, the lithographic printing plate provided with a hydrophilic swelling layer was used to form an image by a specific method, thereby achieving a desired purpose. It has been found that can be achieved.

[0008]

Means for Solving the Problems That is, according to the present invention, (1) an ink inking layer is formed by a thermal transfer method using a hydrophilic swelling layer of a lithographic printing plate having at least a hydrophilic swelling layer on a substrate as an image receiving layer. An image forming method of a direct drawing type lithographic printing plate characterized by being (2) The water absorption amount of the non-image area composed of the hydrophilic swelling layer is 1 to
Characterized in that it is a 50 g / m ² (1) Lithographic printing plate image forming method according to (3) hydrophilic comprising an aqueous swellable layer non image areas initial modulus of 0.01~10kgf / mm ^{2. The} method of forming an image of a lithographic printing plate as described in (1) above, wherein (4) the hydrophilic swelling layer has a water swelling ratio of 10 to 2000%. (5) The hydrophilic swelling layer has a phase-separated structure composed of at least two phases of a hydrophilic polymer as a main component and a hydrophobic polymer as a main component. (1) A method for forming an image on a lithographic printing plate according to (1), (6) An ink inking layer by a thermal transfer method using the hydrophilic swelling layer of the lithographic printing plate having at least a hydrophilic swelling layer on a substrate as an image receiving layer. Direct drawing type lithographic printing plate characterized by forming a (7) The water absorption of the non-image areas consisting of a hydrophilic swellable layer is 1 to
Characterized in that it is a 50 g / m ² lithographic printing plate as described in (6) (8) the hydrophilic swelling layer non-image areas initial elastic modulus of 0.0
It is characterized by being 1 to 10 kgf / mm ² (6)
(9) The lithographic printing plate according to (6), wherein the water-swelling ratio of the hydrophilic swelling layer is 10 to 2000%. (10) The hydrophilic swelling layer is hydrophilic. At least two of a polymer-based phase and a hydrophobic polymer-based phase
A lithographic printing plate as described in (6), which has a phase separation structure composed of phases.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reason why a direct-drawing lithographic printing plate having a particularly excellent balance between ink repellency and printing durability can be obtained by using the image forming method of the present invention is that the hydrophilic swelling layer of the present invention has a hydrophilic swelling layer. The layer swells by containing purified water supplied as dampening water in the layer, and not only has a high dampening water holding power, but also the hydrophilic swelling layer itself has rubber elasticity due to swelling. It is presumed to be based on having properties.

The supply of dampening water by a dampening water roller, the supply of oil-based ink by an inking roller, and the transfer of ink to a blanket or paper under high pressure by an impression cylinder are repeated on the plate surface. In the printing process,
In general, the surface of the printing plate is subjected to various loads, and the printability of the plate gradually decreases, and finally the printing becomes impossible. In the printing plate of the present invention, an ink-receiving layer (image area) is formed on the hydrophilic swelling layer with an ink-receiving substance,
It is considered that the rubber swelling / cushioning property of the hydrophilic swelling layer reduces the mechanical load on the surface of the printing plate and thus the printing durability is excellent. In addition, it is presumed that it is important that the rubber elasticity of the hydrophilic swelling layer changes depending on the amount of water contained in the hydrophilic swelling layer. That is, a cycle of supplying purified water as dampening water to the printing plate surface to wet the hydrophilic swelling layer to cause oily ink to adhere to the printing plate surface, press the ink-printed surface of the printing plate onto a printing medium or blanket, and transfer the oily ink. When the dampening water is supplied and the hydrophilic swelling layer is most swollen, the rubber elasticity is large, and when the plate surface is pressed against the printing medium or the blanket and water is extruded from the hydrophilic swelling layer, the hydrophilic swelling layer is formed. Less water is contained and rubber elasticity is reduced. It is considered that the printing surface softly contacts the printing medium or the blanket in the early stage of the pressure bonding and relatively firmly in the latter half of the pressure bonding, thereby exhibiting sufficient ink inking property and at the same time, good printing durability can be obtained. In addition, since a large amount of water is contained in the hydrophilic swelling layer, the hydrophilicity is high, so that not only the desensitization treatment is not required, but also the dampening water control power is high, so that the control range of the dampening water is high. Wide and high ink repellency is exhibited.

As described above, in the conventional printing plate, the ink resilience and the printing durability are expressed as contradictory properties, whereas in the image forming method of the present invention, the ink resilience and the printing durability are compatible with each other. There are things to do.

Next, the hydrophilic swelling layer will be described.

The term "hydrophilic" as used in the present invention means a property of being substantially insoluble in water and exhibiting a water swelling property, and a known hydrophilic polymer is laminated on a substrate by coating or transfer to form a known hydrophilic polymer. There is used a hydrophilic swelling layer which is cross-linked or pseudo-cross-linked by the method described above and is made water-swellable by making it insoluble in water.

The hydrophilic polymer referred to herein is a known water-soluble polymer (meaning that it is completely soluble in water), pseudo-water-soluble polymer (meaning that it is amphipathic, and macroscopically it is soluble in water). Micro means the one containing the non-dissolved part),
Refers to water-swellable polymers (meaning those that swell in water but do not dissolve). That is, it means a polymer that adsorbs or absorbs water under normal use conditions, and a polymer that dissolves in water or swells in water.

Known hydrophilic polymers can be used in the present invention, and include animal polymers, plant polymers, and synthetic polymers. For example, "Functionio
nal Monomers ”(Y. Nyquist,
Dekker), "Water-soluble polymer" (Nakamura, Kagaku Kogyo Co., Ltd.), "Comprehensive technical data collection of the latest processing and modification technology and application development of water-soluble polymer water-dispersible resin" (Business Development Center Publishing Department), The water-soluble polymers described in "Applications and Markets of New Water-Soluble Polymers" (CMC) are listed. Specific examples are shown below.

(A) Natural polymers.

Starch-acrylonitrile-based graft polymer hydrolyzate, starch-acrylic acid-based graft polymer, starch-styrene sulfonic acid-based graft polymer, starch-vinyl sulfonic acid-based graft polymer,
Starch-acrylamide graft polymer, carboxylated methyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, cellulose xanthate, cellulose-acrylonitrile graft polymer, cellulose-styrene sulfonic acid graft polymer, carboxymethyl cellulose cross-linked product, hyaluronic acid Acid, agarose, collagen, milk casein, acid casein, rennet casein, ammonia casein, potash casein, borax casein, glue, gelatin, gluten, soybean protein, alginate, ammonium alginate, potassium alginate, sodium alginate arabia gum, Tragacanth gum, Karaya gum, Guar gum, Locust bean gum, Irish moss, Large Lecithin, pectin acid, starch, carboxylated starch, agar, dextrin, mannan, etc..

(B) Synthetic polymers.

Polyvinyl alcohol, polyethylene oxide, poly (ethylene oxide-co-propylene oxide), aqueous urethane resin, water-soluble polyester, hydroxyethyl (meth) acrylate polymer, poly (vinyl methyl ether-co-maleic anhydride), Maleic anhydride type copolymer, vinylpyrrolidone type copolymer, polyethylene glycol di (meth) acrylate type crosslinked polymer, polypropylene glycol di (meth) acrylate type crosslinked polymer, poly (N-vinylcarboxylic acid amide), N -Vinylcarboxylic acid amide copolymers, etc.

The above-mentioned hydrophilic polymer may be one or two monomers or copolymer components having different substituents for the purpose of imparting flexibility or controlling hydrophilicity, within the range that does not impair the effects of the invention. It is possible to appropriately mix and use one or more species.

Specific examples of the hydrophilic polymer preferably used in the present invention are shown below, but the present invention is not limited to these examples.

(1) Maleic acid or maleic anhydride,
Maleic acid derivatives such as maleic amide or maleic imide and ethylene, propylene, butylene, isobutylene or diisobutylene having 2 to 12 carbon atoms;
A crosslinked product of a reaction product of a copolymer of a linear or branched α-olefin having 2 to 8 carbon atoms, an alkali metal compound, an alkaline earth metal compound, ammonia, and an amine.

(2) A copolymer of maleic acid or a derivative thereof with a vinyl or vinylidene compound such as styrene, vinyl acetate, methyl vinyl ether, acrylic acid ester, methacrylic acid ester or acrylonitrile, an alkali metal compound, an alkaline earth metal. Crosslinked products of compounds, ammonia and amines.

(3) A crosslinked product of a reaction product of a copolymer of acrylic acid or methacrylic acid with the vinyl or vinylidene compound of the above (2), an alkali metal compound, an alkaline earth metal compound, ammonia, or an amine.

Polyoxyalkylene-based hydrophilic polymers disclosed in JP-B-58-37027, polyvinylpyrrolidone disclosed in JP-A-60-104106, and sulfonic acid groups are used as hydrophilic groups. Crosslinked products such as polystyrene sulfonic acid and acrylamidomethylpropane sulfonic acid copolymer
Polyurethane resins obtained by crosslinking a hydrophilic polymer having a hydroxyl group or an amino group with a polyisocyanate, which are disclosed in Japanese Patent No. 42416, and the like.

Next, the method of crosslinking the hydrophilic polymer will be described.

The hydrophilic swelling layer is formed on the substrate by cross-linking or pseudo-cross-linking at least one kind of the above-mentioned hydrophilic polymer as necessary and making it insoluble in water. The cross-linking is performed by a cross-linking reaction using the reactive functional group of the hydrophilic polymer.

The cross-linking reaction may be a covalent bond or an ionic bond.

Examples of the compound used in the crosslinking reaction include known polyfunctional compounds having crosslinking properties, such as polyepoxy compounds, polyisocyanate compounds, poly (meth) acrylic compounds, polymercapto compounds, polyalkoxysilyl compounds, Examples thereof include polyvalent metal salt compounds, polyamine compounds, polyaldehyde compounds, polyvinyl compounds and the like. The crosslinking reaction is carried out by adding a known catalyst to accelerate the reaction.

These hydrophilic polymers may be used alone or in combination for the purpose of maintaining the shape of the hydrophilic swelling layer and adjusting the water swelling property.
It is possible to use as a mixture of one or more kinds, and it is also possible to blend a non-hydrophilic polymer.

Further, for the purpose of improving the adhesiveness with the lower layer, it is possible to add a known silane coupling agent, isocyanate compound, catalyst or the like, or provide it as an intermediate layer.

The hydrophilic swelling layer used in the present invention preferably has a water absorption amount calculated according to the following method within a specific range.

Water absorption (g / m ² ) = W _WET −W _{DRY WDRY} : Weight in dry state (g / m ² ) W _WET : Weight after immersion in water at 25 ° C. for 10 minutes (g
/ M ² ) [Method of measuring water absorption] A non-image area of a lithographic printing plate to be measured is cut into a predetermined area and immersed in purified water at 25 ° C. After soaking for 10 minutes, the excess liquid adhering to the front and back surfaces of the hydrophilic swelling layer of the printing plate was treated with "Hize Gauze".
(Cotton cloth: manufactured by Asahi Kasei Kogyo Co., Ltd.), wiped off quickly, and the swelling weight W _WET of the printing plate was weighed. Then, the printing plate is dried in an oven at 60 ° C. for about 30 minutes, and the dry weight W _DRY is weighed.

The water absorption amount of the non-image area composed of the hydrophilic swelling layer of the present invention is 1 from the viewpoint of ink resilience and shape retention.
˜50 g / m ² , preferably 1 to 10 g / m
² , more preferably ² to 7 g / m ² .

The hydrophilic swelling layer of the present invention preferably has rubber elasticity. That is, the initial elastic modulus of the hydrophilic swelling layer calculated by the following method is preferably within a specific range.

[Measurement Method of Initial Elastic Modulus] A solution having the same composition as the portion corresponding to the non-image area of the lithographic printing plate is spread on a Teflon dish and dried at 60 ° C. for 24 hours. The obtained dried and cured film is 40 mm long using a razor blade or the like.
The test piece is cut into a rectangular test piece having a width of 1.95 mm and a thickness of about 0.2 mm.

The test piece obtained was measured at 25 ° C. before measurement.
After being left in an environment of × 50% RH for 24 hours or more to adjust the humidity, the thickness was measured with a micro gauge and the initial elastic modulus was measured under the following tensile conditions. Data processing is JIS K
It carried out according to 6301.

Tensile speed 200 mm / min Chuck distance 20 mm Number of repetitions 4 times Measuring machine "RTM-100" (manufactured by Orientec Co., Ltd.) The initial elastic modulus of the hydrophilic swelling layer is 0.01 to 10 kgf /
It is important to be in the range of mm ² from the viewpoint of ink resilience and shape retention, and 0.01 to 5 kgf / mm
The range of ² is preferable, and the range of 0.01 to ² kgf / mm ² is more preferable. Initial elastic modulus is 0.01kgf / m
When it is less than m ^2, the shape retention of the hydrophilic swelling layer is reduced, the printing durability is poor, and the initial elastic modulus is 10 kgf / m.
When it is larger than m ² , the ink repulsion remarkably decreases.

The hydrophilic swelling layer used in the present invention preferably has a water swelling ratio calculated according to the following method within a specific range.

Water swelling rate (%) = (Θ _WET −Θ _DRY ) / Θ _DRY × 100 Θ _DRY : Thickness of the hydrophilic swelling layer consisting of non-image areas in a dry state (μm) Θ _WET : Non-swelling state Thickness (μm) of hydrophilic swelling layer consisting of image area [Method of measuring water swelling rate (A)] Cut so that a portion including a non-image area of the planographic printing plate to be measured has a cross section To make. After vacuum-drying this section at room temperature for one day and night, the thickness of the hydrophilic swelling layer at the site is observed with an optical microscope, and this is defined as _ΘDRY (μm). The observation with an optical microscope was quickly performed in an environment of 23 ° C. and 20% RH.

Further, an excess amount of water droplets was placed on the lithographic printing plate section, and the cross section was observed with an optical microscope in a state where the hydrophilic swelling layer was sufficiently swollen with water, and the thickness of the hydrophilic swelling layer at the site was read. Θ _WET (μm).

[Method of measuring water swelling ratio (B)] The non-image area of the lithographic printing plate to be measured was exposed to the atmosphere of OsO ₄ aqueous solution for 1 day to fix the hydrophilic swelling layer with OsO ₄ . An ultrathin section is prepared by cutting with a microtome so that a predetermined portion has a cross section. The thickness of the hydrophilic swelling layer at the site is observed with a transmission electron microscope (TEM) at a magnification of about 10,000 to 50,000 times, and this is defined as Θ _DRY (μm).

On the other hand, the lithographic printing plate to be measured is set to Os.
It is immersed in an O ₄ aqueous solution for 2 to 3 days to solidify / fix the hydrophilic swelling layer in a water swelling state. An ultrathin section is prepared by cutting with a microtome so that a predetermined section becomes a cross section, and this section is magnified by a transmission electron microscope (TEM) at a magnification of about 1 to 50,000 times and the thickness of the hydrophilic swelling layer at that section. Read that and Θ
_WET (μm)

The water swelling ratio of the non-image area (ink repulsion portion) formed of the hydrophilic swelling layer of the present invention is preferably 10 to 2000% from the viewpoint of ink repulsion property and shape retention, and 50 to 1700. %, And more preferably 50 to 700%. When the water swelling ratio is less than 10%, the ink resilience of the non-image portion decreases, while when the water swelling ratio of the non-image portion exceeds 2000%, the non-image portion has poor shape retention and printing. Sometimes, the non-image area is easily damaged.

The hydrophobic polymer used in the hydrophilic swelling layer of the present invention is preferably one mainly composed of an aqueous emulsion.

The aqueous emulsion referred to in the present invention means a hydrophobic polymer suspension aqueous solution in which particles comprising fine polymer particles and, if necessary, a protective layer surrounding the particles are dispersed in water.

That is, it means a self-emulsifying or forced emulsifying aqueous solution basically composed of emulsion particles composed of polymer particles as a dispersoid and a protective layer formed as necessary, and a dilute aqueous solution as a dispersion medium. Specific examples of the aqueous emulsion used in the present invention include vinyl polymer latex, conjugated diene polymer latex and aqueous or water dispersed polyurethane resin.

Among these aqueous emulsions, the hydrophobic polymer particularly preferably used in the present invention is styrene / butadiene type, acrylonitrile / butadiene type,
Latexes containing conjugated diene compounds such as methyl methacrylate / butadiene and chloroprene are mentioned.

The hydrophilic swelling layer of the present invention is laminated on the substrate by mixing the above-mentioned hydrophilic polymer and hydrophobic polymer, crosslinking or pseudo-crosslinking them if necessary, and insolubilizing them in water.

For cross-linking, it is preferable to carry out the cross-linking reaction using the reactive functional groups of the hydrophilic polymer and the hydrophobic polymer.

The crosslinking reaction may be covalent crosslinking or ionic crosslinking.

As a method for mixing the hydrophilic polymer and the hydrophobic polymer of the hydrophilic swelling layer of the present invention, a roll mixer such as a three roll mill, a kneading method using a mixer such as a kneader, a homogenizer, a ball mill, etc. The mixing is preferably carried out by a known method used for producing a paint or putty, such as a method of wet mixing and dispersing using a disperser.

As a method for forming the hydrophilic swelling layer of the present invention, since an aqueous emulsion is preferably used as the hydrophobic polymer, each component (hydrophilic polymer, hydrophobic polymer, etc.) is mixed in an aqueous solution system, A method in which a crosslinking agent is added as necessary is preferable from the viewpoint of realizing a uniform phase-separated structure and improving ink repulsion.

Therefore, it is particularly preferable to use a water-soluble polyfunctional compound as the crosslinking agent used. That is, it is preferable to use a water-soluble polyepoxy compound, polyamine compound, melamine compound, or the like.

Next, the phase separation structure in the hydrophilic swelling layer of the present invention will be described.

By adopting a phase-separated structure composed of a phase containing a hydrophilic polymer as a main component and a phase containing a hydrophobic polymer as a main component, both ink repulsion and printing durability are realized in a wide composition range. It becomes possible.

The composition ratio of the hydrophilic polymer phase and the hydrophobic polymer phase constituting the phase-separated structure is arbitrary, and (1) either one is a continuous phase and the other is a dispersed phase, (2) hydrophilic Form in which the hydrophilic and hydrophobic polymer phases have a continuous phase and a dispersed phase, respectively (3) The hydrophilic and hydrophobic polymer phases can both be freely selected from the forms in which they are continuous phases.

In the hydrophilic swelling layer used in the present invention, in addition to the above-mentioned hydrophilic polymer, hydrophobic polymer and a cross-linking agent optionally added, a known anti-aging agent usually added in a rubber composition. It is possible to add an antioxidant, an antiozonant, an ultraviolet absorber, a dye, a pigment, a plasticizer and the like.

For the purpose of improving the adhesiveness with the lower layer,
Known silane coupling agents and isocyanate compounds,
It is also possible to add a catalyst or the like or to provide an intermediate layer between the substrate and the substrate.

It is also possible to add a small amount of various additives such as dyes and pigments, pH indicators, leuco dyes, surfactants and organic acids to the hydrophilic swelling layer used in the present invention. The substrate of the lithographic printing plate used in the present invention is not limited at all, except that it needs to be flexible and can withstand the load applied during printing, which is attached to a normal lithographic printing press.

Typical examples are aluminum, copper, iron,
Examples thereof include a metal plate, a plastic film such as a polyester film and a polypropylene film, coated paper, and a rubber sheet. Further, the substrate may be a composite of the above materials.

Further, the surface of the substrate may be subjected to various surface treatments such as electrochemical treatment, acid-base treatment and corona discharge treatment for the purpose of improving plate inspection property and adhesiveness.

It is also possible to form a primer layer on these substrates by coating or the like for the purpose of improving the adhesiveness and preventing halation, to obtain substrates.

Next, the image forming method will be described.

In the present invention, the ink inking layer is formed by a thermal transfer method using the hydrophilic swelling layer of the lithographic printing plate having the hydrophilic swelling layer as an image receiving layer.

The thermal transfer in the present invention refers to a method of transferring and forming an image by using a thermal head on the plate surface of a lithographic printing plate having a hydrophilic swelling layer by an ordinary thermal transfer printer. Specifically, a thermosensitive sheet coated with a binder in which a color former, a color developer, and a sensitizer are dispersed on a substrate (a sheet for forming a color / image by directly mixing the color developer and the color developer by heat). , An ink ribbon that holds a thin layer of solid ink (the ink that is selectively heated by the thermal head changes from a solid to a highly viscous liquid, and the adhesive force between the recording surface and the ink ribbon base material becomes the adhesive force. Lithographic printing plate with hydrophilic swelling layer as ink repulsion layer, such as overcoming transfer and image formation), ink ribbon holding thermal diffusion / sublimation dye (only coloring material is transferred without binder), etc. Again,
A method in which heating is performed from the rear surface while pressing with a platen roller or the like with a thermal head, and ink is received only in the heated portion to form an image can be mentioned. The thermal head has heating resistors formed on a line at equal intervals,
Image formation / recording is performed by using Joule heat generated by the heating resistor. The resolution of the thermal transfer method is often about 8 to 16 dots / mm, but is not limited to this. Further, an area gradation method or a density gradation method can be used for forming a halftone image.

Next, a printing method using the planographic printing plate of the invention will be described.

A known lithographic printing machine is used for the lithographic printing of the present invention. That is, sheet-fed and rotary printing machines of the offset and direct printing type are used.

After forming an image on the lithographic printing plate of the present invention by electrostatic transfer or heat transfer, these are mounted on the plate cylinder of a lithographic printing machine, and ink is supplied to the plate surface from an inking roller in contact therewith.

The non-image area having the hydrophilic swelling layer on the plate surface swells with the dampening water supplied from the dampening water supply device and repels the ink. On the other hand, the image area formed by electrostatic transfer or thermal transfer receives the ink and supplies the ink to the surface of the offset blanket cylinder or the surface of the printing medium to form a printed image.

The fountain solution used in printing a lithographic printing plate having a hydrophilic swelling layer drawn by the image forming method of the present invention may be an etchant used in ordinary lithographic printing. It is possible, but pure water without any additives can be used.

[0072]

The present invention will be described in more detail with reference to the following examples.

Example 1 A polyethylene terephthalate film having a thickness of 0.15 mm was coated with the following composition using acrylamide-n-butyl methacrylate copolymer (weight composition ratio 40/60) as a hydrophilic polymer. After that, 150 ℃ x 60
It was heat-treated for a minute to apply a hydrophilic swelling layer having a thickness of 3 g / m ² .

<Hydrophilic swelling layer composition (parts by weight)> (1) Hydrophilic polymer 28 parts by weight (2) Tetraethylene glycol diglycidyl ether 5 parts by weight (3) Aqueous latex “JSR0596” 65 parts by weight [carboxy-modified styrene -Butadiene copolymer latex: made by Japan Synthetic Rubber] (4) 2-Aminopropyltrimethoxysilane 2 parts by weight (5) Purified water 900 parts by weight The obtained hydrophilic swelling layer is swollen in water and then dyed with OsO _4. , TEM (transmission electron microscope) observation. As a result of observation, it was confirmed that the hydrophilic swelling layer had a phase-separated structure composed of a phase containing a hydrophilic polymer as a main component and a phase containing a hydrophobic polymer as a main component.

Next, a thermal transfer printer (RUPOJW95
JV: manufactured by Toshiba Corp.) to make a printing plate by forming an image area on the hydrophilic swelling layer.

This printing plate was mounted on a sheet-fed offset printing machine "Sprint 25: manufactured by Komori Corporation", and then printing was carried out using fine paper while supplying commercially available purified water as fountain solution. At the time of printing 10,000 sheets,
Ink resilience and ink receptivity were evaluated as indicators of printing durability. The ink repellency was evaluated by visually observing the degree of dirt on the white background. For the ink receptivity, the shape of the halftone dots on the plate surface was observed with an optical microscope, and the maximum and minimum halftone dot diameters of each halftone dot were measured to determine the width of the distribution.

The water absorption amount, the initial elastic modulus and the water swelling ratio of the hydrophilic swelling layer were measured according to the methods described above. The results are shown in Table 1.

Example 2 A printing plate was prepared in the same manner as in Example 1 except that double-end blocked isocyanate polyoxyethylene # 30000 was selected as the hydrophilic polymer and the following hydrophilic swelling layer composition was used. And evaluated.

<Hydrophilic swelling layer composition (parts by weight)> (1) Hydrophilic polymer 100 parts by weight (2) Tetraethylene glycol diglycidyl ether 20 parts by weight (3) 2-Aminopropyltrimethoxysilane 2 parts by weight (4 ) Purified water 900 parts by weight The results are shown in Table 1.

[0080]

[Table 1] It can be seen from Table 1 that as the number of printed sheets increases, the halftone dots, which are the image areas, are damaged and the halftone dot diameter gradually decreases. Regarding the shape of the halftone dots, as a result of the printing durability test (10,000 sheets), the halftone dots in the image areas of Examples 1 and 2 were circular.

[0081]

Example 3 The lithographic printing plate used in Example 1 and a normal PS
A plate (FNS; manufactured by Fuji Photo Film Co., Ltd.) exposed to light and developed to form a printing plate was mounted on the same plate cylinder, and printing was performed while supplying commercially available purified water as fountain solution.

When the supply amount of the dampening water was increased from the standard state, the ink density in the image area of the PS plate was extremely lowered, and so-called "water loss" caused defective ink replenishment.
On the other hand, in the planographic printing plate used in Example 1, the degree of inking failure was slight.

When the feed amount of dampening water was reduced from the standard state, ink stains were generated on the entire surface of the PS plate. On the other hand, with the planographic printing plate used in Example 1, good printed matter was obtained. Table 2 shows the evaluation results.

[0084]

[Table 2]

[0085]

INDUSTRIAL APPLICABILITY In the present invention, when an ink inking layer is formed on a lithographic printing plate having a hydrophilic swelling layer by a thermal transfer method, it has a high ink resilience without desensitizing treatment, and a fountain solution. It is possible to obtain a direct drawing type printing plate which has a wide control range and is capable of using pure water as dampening water and which has excellent printing durability.

Claims (10)

[Claims] 1. A direct drawing type lithographic printing plate comprising a lithographic printing plate having at least a hydrophilic swelling layer on a substrate and forming an ink inking layer by a thermal transfer method using the hydrophilic swelling layer as an image receiving layer. Image forming method. 2. The method for forming an image on a lithographic printing plate according to claim 1, wherein the water absorption amount of the non-image area composed of the hydrophilic swelling layer is 1 to 50 g / m ² . 3. The method of forming an image on a lithographic printing plate according to claim 1, wherein the non-image area formed of the hydrophilic swelling layer has an initial elastic modulus of 0.01 to 10 kgf / mm ² . 4. The water swelling ratio of the hydrophilic swelling layer is 10 to 200.
The image forming method for a lithographic printing plate according to claim 1, wherein the image forming method is 0%. 5. The hydrophilic swelling layer has a phase-separated structure composed of at least two phases, a phase containing a hydrophilic polymer as a main component and a phase containing a hydrophobic polymer as a main component. 1. The method for forming an image on a lithographic printing plate as described in 1. 6. A direct drawing type lithographic printing plate comprising a lithographic printing plate having at least a hydrophilic swelling layer on a substrate and forming an ink inking layer by a thermal transfer method using the hydrophilic swelling layer as an image receiving layer. . 7. The lithographic printing plate as claimed in claim 6, wherein the non-image area composed of the hydrophilic swelling layer has a water absorption of 1 to 50 g / m ² . 8. The lithographic printing plate as claimed in claim 6, wherein the non-image area of the hydrophilic swelling layer has an initial elastic modulus of 0.01 to 10 kgf / mm ² . 9. The water-swelling rate of the hydrophilic swelling layer is 10 to 200.
It is 0%, The planographic printing plate of Claim 6 characterized by the above-mentioned. 10. The hydrophilic swelling layer has a phase-separated structure composed of at least two phases, a phase containing a hydrophilic polymer as a main component and a phase containing a hydrophobic polymer as a main component. The planographic printing plate described in 6.