JP2006137082A - Platemaking method of lithographic printing plate and material of lithographic printing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a platemaking method for giving a lithographic printing plate which facilitates checking of an exposed image and excels in on-press developability and plate wear resistance, and a material of the lithographic printing plate used for it. <P>SOLUTION: In this platemaking method of the lithographic printing plate, the negative type material of the lithographic printing plate having an on-press developable thermal image forming layer on a substrate having a hydrophilic surface and being nontransparent is subjected to image exposure and then to on-press development, so as to prepare the lithographic printing plate. The absolute value of a difference between the reflection density Ds of the surface of the printing plate material before the image exposure and the reflection density Dp of the surface of a non-image part after the on-press development is 0.30-0.90. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for making a lithographic printing plate and a lithographic printing plate material used therefor, and in particular, a lithographic printing plate in which an image is formed by a computer-to-plate (CTP) method and developed on a printing machine to obtain a printing plate. The present invention relates to a plate making method and a planographic printing plate material.

  At present, in the field of printing, printing by the CTP method has been performed with the digitization of print image data. However, this printing is inexpensive and easy to handle and is equivalent to a conventional so-called PS plate. Therefore, there is a demand for a printing plate material for a CTP system having the following printability.

  In particular, in recent years, there has been a demand for a printing plate material that does not require development processing using a processing solution containing a special agent (for example, alkali, acid, solvent, etc.) and can be applied to a conventional printing machine. Phase change type printing plate material that does not require water, printing plate material that is processed with water or a substantially neutral processing liquid mainly composed of water, and development processing is performed at an initial stage of printing on a printing press. There are known printing plate materials called chemical-free type printing plate materials and processless type printing plate materials, such as printing plate materials that do not require a process.

  The above-described printing plate materials that do not require any development processing and processless type printing plate materials that are developed on a printing press perform punching necessary for attachment to the printing press after exposure, so that they are the same as conventional PS In addition, it is required to have so-called exposure visible image quality.

  In addition, the thermal laser recording method having a wavelength of near infrared to infrared is mainly used for image formation of processless type printing plate material. Separately, an ablation type, a heat fusion image layer on-machine development type, and a phase change type are known.

  On the other hand, the following printing plate materials are known as printing plate materials obtained by imparting exposure visibility to these processless type printing plate materials.

  For example, a layer containing a heat-sensitive coloring material such as a leuco dye and its developer in the image forming layer, a polymer compound having a functional group that generates sulfonic acid by heat, and a compound that changes color by the generated acid A printing plate material having a layer containing an IR-dye that can change its optical density by exposure of an imaging element (Patent Documents 1 and 2) Reference 3), a printing plate material having a hydrophilic overcoat layer that can be removed on a printing press, containing 20% by mass or more of a cyanine infrared absorbing dye whose optical density can be changed by exposure (Patent Document 4) See).

  However, since these printing plate materials contain dyes that develop, fade, or change color upon exposure, it is difficult to avoid contamination of the printing ink and fountain solution by these dyes during on-machine development. There has been a problem that the amount of damaged paper required for obtaining a normal printed matter at the time of top development may be large.

In addition, with these printing plate materials, when it is attempted to obtain sufficient exposure visibility, the printing plate material has insufficient printing durability and on-machine developability, making it difficult to achieve both printability and exposure visibility. Met.
JP 2000-225780 A Japanese Patent Laid-Open No. 2002-211150 JP-A-11-240270 JP 2002-205466 A

  An object of the present invention is to provide a plate making method for providing a lithographic printing plate which allows easy confirmation of an exposed image, excellent on-press developability and excellent printing durability, and a lithographic printing plate material used therefor.

  The object of the present invention is achieved by the following constitution.

(Claim 1)
A negative lithographic printing plate material having a heat-sensitive image-forming layer that can be developed on a printing press is image-exposed on a non-transparent substrate having a hydrophilic surface, and the lithographic printing plate material subjected to image exposure is developed on a printing press. A lithographic printing plate making method for producing a lithographic printing plate, wherein the reflection density Ds of the surface of the printing plate material before image exposure and the reflection density Dp of the surface of the non-image area after development on a printing press A method for making a lithographic printing plate, wherein the absolute value of the difference is 0.30 to 0.90.

(Claim 2)
The lithographic printing plate making method according to claim 1, wherein the relationship between the reflection density Dp and the reflection density Ds is Ds <Dp.

(Claim 3)
A lithographic printing plate material used in the lithographic printing plate making method according to claim 1 or 2.

  With the above-described configuration of the present invention, it is possible to provide a plate making method for providing a lithographic printing plate that allows easy confirmation of an exposed image, excellent on-press developability, and excellent printing durability, and a lithographic printing plate material used therefor.

  In the present invention, a negative lithographic printing plate material having a thermal image forming layer developable on a printing press is image-exposed on a non-transparent substrate having a hydrophilic surface, and the lithographic printing plate material subjected to image exposure is obtained. A method for making a lithographic printing plate by developing on a printing press to produce a lithographic printing plate, the reflection density Ds of the surface of the printing plate material before image exposure and the reflection of the surface of the non-image area after development on the printing press The absolute value of the difference from the density Dp is 0.30 to 0.90.

  In the present invention, in particular, the absolute value of the difference between the reflection density Ds of the surface of the printing plate material before image exposure and the reflection density Dp of the surface of the non-image area after development on the printing press is 0.30 to 0.90. By doing so, it is possible to provide a plate making method that provides a lithographic printing plate that allows easy confirmation of an exposed image, excellent on-press developability, and excellent printing durability.

  The reflection density according to the present invention refers to an average value of reflection density values at intervals of 20 nm from 400 nm to 700 nm as measured with an observation visual field of 2 ° and an absolute white density standard. For example, a spectral densitometer manufactured by GretagMacbeth Using Spectrolino, the reflection density at intervals of 20 nm from 400 nm to 700 nm was measured with a filter condition D65, observation field 2 °, white base: absolute white, density standard: Status-T, and the average value was calculated. It can be calculated by obtaining.

  The absolute value of the difference between the reflection density Ds of the surface of the printing plate material before image exposure and the reflection density Dp of the surface of the non-image portion after development on the printing press is set to 0.30 to 0.90, which will be described later. The hydrophilic surface of the substrate is colored so that the degree of coloring is adjusted, and light or heat at the time of image exposure causes a decrease in transparency and an increase in light scattering, resulting in a reflection density on the surface of the printing plate material. This is achieved by providing a layer containing a material that lowers the amount on the substrate.

〔Base material〕
The hydrophilic surface according to the present invention is a surface that can make a non-image portion from which a thermal image forming layer has been removed by development on a printing press, water-holding and printing ink repulsion when printing.

  The substrate having a hydrophilic surface according to the present invention can be obtained by a method of hydrophilizing the surface of the substrate or a method of providing a hydrophilic layer on the substrate.

  The term “opaque” according to the present invention means that the transmittance in the visible light region over the entire region from 400 nm to 700 nm is less than 1%.

  By using an opaque base material, it is possible to block the transmitted light from the back surface when visually inspecting the printing plate after image formation, and to ensure good visibility.

  As a base material which concerns on this invention, the well-known material used as a base material of a printing plate can be used.

  For example, a metal plate, a plastic film, paper treated with a polyolefin, a composite base material obtained by appropriately bonding the above materials, and the like can be given. The thickness of the base material is not particularly limited as long as it can be attached to a printing press, but a thickness of 50 to 500 μm is generally easy to handle.

  Of these substrates, metal plates are preferably used in the present invention.

  Examples of the metal plate include iron, stainless steel, and aluminum. Aluminum is particularly preferable from the relationship between specific gravity and rigidity.

  As the aluminum, those whose surface is hydrophilized are preferably used.

  The aluminum plate is usually used after degreasing with an alkali, an acid, a solvent or the like in order to remove oil used during rolling and winding existing on the surface. As the degreasing treatment, degreasing with an alkaline aqueous solution is particularly preferable. Moreover, in order to improve adhesiveness with an application layer, you may perform an easily bonding process and application | coating of an undercoat layer to an application surface.

  For example, a method of dipping in a liquid containing a coupling agent such as a silicate or a silane coupling agent or applying a liquid, followed by sufficient drying can be used. Anodizing treatment is also considered as a kind of easy adhesion treatment and can be used. Moreover, it can also use combining an anodizing process and the said immersion or application | coating process. Moreover, the aluminum base material roughened by the well-known method, what is called an aluminum grain can also be used as a base material which has a hydrophilic surface.

  As the aluminum substrate, a pure aluminum substrate or a substrate made of an aluminum alloy can be used. Various aluminum alloys can be used. For example, an alloy of a metal such as silicon, copper, manganese, magnesium, chromium, zinc, lead, bismuth, nickel, titanium, sodium, iron, and aluminum is used.

  The aluminum substrate is preferably subjected to a degreasing treatment in order to remove the rolling oil on the aluminum surface prior to the roughening treatment. As the degreasing treatment, a degreasing treatment using a solvent such as trichlene or thinner, an emulsion degreasing treatment using an emulsion such as kesilon or triethanol, or the like is used. In addition, an alkaline aqueous solution such as sodium hydroxide, potassium hydroxide, sodium carbonate, or sodium phosphate can be used for the degreasing treatment. When an alkaline aqueous solution is used for the degreasing treatment, dirt and oxide film that cannot be removed only by the degreasing treatment can be removed.

  When an alkaline aqueous solution is used for the degreasing treatment, it is preferable to perform a neutralization treatment by immersing in an acid such as phosphoric acid, nitric acid, hydrochloric acid, sulfuric acid, chromic acid, or a mixed acid thereof. When electrolytic surface roughening is performed after the neutralization treatment, it is particularly preferable to match the acid used for neutralization with the acid used for electrolytic surface roughening.

  As the roughening of the substrate, an electrolytic surface roughening treatment is carried out by a known method, but as a pretreatment, roughening by appropriately combining chemical roughening or mechanical roughening with an appropriate amount of treatment. Processing may be performed.

  Chemical roughening uses an aqueous solution of an alkali such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium phosphate as in the degreasing treatment. After the treatment, it is preferable to carry out a neutralization treatment by dipping in an acid such as phosphoric acid, nitric acid, hydrochloric acid, sulfuric acid, chromic acid, or a mixed acid thereof. When electrolytic surface roughening is performed after the neutralization treatment, it is particularly preferable to match the acid used for neutralization with the acid used for electrolytic surface roughening.

  The mechanical roughening treatment method is not particularly limited, but brush polishing and honing polishing are preferable.

  A mechanically roughened substrate is immersed in an aqueous solution of acid or alkali to remove abrasives, aluminum scraps, etc. that have digged into the surface of the substrate, or to control the pit shape. It is preferable to etch the surface. Examples of the acid include sulfuric acid, persulfuric acid, hydrofluoric acid, phosphoric acid, nitric acid, and hydrochloric acid. Examples of the base include sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium phosphate. Among these, it is preferable to use an alkaline aqueous solution.

  By using an abrasive having a particle size finer than # 400 for the mechanical surface roughening treatment, and performing an etching treatment with an alkaline aqueous solution after the mechanical surface roughening treatment, an intricate rough surface by the mechanical surface roughening treatment. The structure can be a smooth uneven surface. For this reason, even when the image forming layer of the present invention is provided, a relatively long wavelength undulation of several μm to several tens of μm can be formed without impairing the on-press developability. By adding the crystallization treatment, it is possible to obtain an aluminum substrate that has good printing performance and contributes to improved printing durability. In addition, the amount of electricity during the electrolytic surface roughening treatment can be reduced, leading to cost reduction.

  When the above is immersed in an alkaline aqueous solution, it is preferably immersed in an acid such as phosphoric acid, nitric acid, sulfuric acid, chromic acid, or a mixed acid thereof for neutralization.

  When the electrolytic surface-roughening treatment is performed after the neutralization treatment, it is particularly preferable that the acid used for neutralization is matched with the acid used for the electrolytic surface-roughening treatment.

  The electrolytic surface roughening treatment is generally a surface roughening using an alternating current in an acidic electrolyte. As the acidic electrolytic solution, those used in a general electrolytic surface roughening method can be used, but a hydrochloric acid-based or nitric acid-based electrolytic solution is preferably used, and in the present invention, a hydrochloric acid-based electrolytic solution is particularly preferable.

  Various waveforms such as a rectangular wave, a trapezoidal wave, and a sawtooth wave can be used as the power supply waveform used for electrolysis, and a sine wave is particularly preferable.

  Further, a divided electrolytic surface roughening treatment as disclosed in JP-A-10-869 can also be preferably used.

1-50V is preferable and, as for the voltage applied in the electrolytic surface roughening using nitric acid type electrolyte solution, 5-30V is still more preferable. The current density (peak value) is preferably from 10 to 200 A / dm ^2, more preferably 20 to 150 A / dm ^2.

Quantity of electricity by summing all the processing steps, 100~2000C / dm ^2, preferably not 200~1500C / dm ^2, more preferably a 200~1000C / dm ^2.

  The temperature is preferably 10 to 50 ° C, more preferably 15 to 45 ° C. The concentration of nitric acid is preferably 0.1 to 5% by mass.

  If necessary, nitrates, chlorides, amines, aldehydes, phosphoric acid, chromic acid, boric acid, acetic acid, oxalic acid, and the like can be added to the electrolytic solution.

  In the present invention, the electrolytically roughened substrate is etched by immersing it in an alkaline aqueous solution in order to remove surface smut or the like or to control the pit shape.

  Examples of the alkaline aqueous solution include sodium hydroxide, potassium hydroxide, sodium carbonate, sodium phosphate and the like.

  By performing the etching treatment with an alkaline aqueous solution, the printability and the background stain when the image forming layer of the present invention is provided are very good.

  After the immersion treatment with an alkaline aqueous solution, it is preferable to carry out a neutralization treatment by immersion in an acid such as phosphoric acid, nitric acid, sulfuric acid, chromic acid, or a mixed acid thereof. When the anodizing treatment is performed after the neutralizing treatment, it is particularly preferable that the acid used for the neutralization is matched with the acid used for the anodizing treatment.

  Following the roughening treatment, an anodizing treatment is performed.

There is no restriction | limiting in particular in the method of the anodizing process used by this invention, A well-known method can be used. An oxide film is formed on the substrate by anodizing. In the present invention, a method of electrolyzing with an aqueous solution containing sulfuric acid and / or phosphoric acid or the like at a concentration of 10 to 50% as an electrolytic solution at an electric current density of 1 to 10 A / dm ² is preferably used for the anodizing treatment. US Pat. No. 1,412,768 describes a method of electrolysis at a high current density in sulfuric acid, and a method of electrolysis using phosphoric acid described in US Pat. No. 3,511,661. Can be used.

  The anodized base material may be subjected to a sealing treatment as necessary. These sealing treatments can be performed using known methods such as hot water treatment, boiling water treatment, water vapor treatment, dichromate aqueous solution treatment, nitrite treatment, ammonium acetate treatment.

  In addition, the anodized base material can be appropriately subjected to a surface treatment other than the sealing treatment. Examples of the surface treatment include known treatments such as silicate treatment, phosphate treatment, various organic acid treatments, PVPA treatment, and boehmite treatment. Further, an organic acid treatment such as citric acid may be performed following the treatment with an aqueous solution containing a bicarbonate described in JP-A-8-314157 or the treatment with an aqueous solution containing a bicarbonate.

  Examples of the plastic film as the base material according to the present invention include polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polycarbonate, polysulfone, polyphenylene oxide, and cellulose esters. Therefore, an opaque base material can be obtained by coloring the base material itself or providing a colored layer.

  In addition, for the purpose of controlling the slipperiness of the back surface (for example, reducing the friction coefficient with the plate cylinder surface), a substrate provided with a back surface coating layer can also be preferably used.

(Coloring of hydrophilic surface)
The substrate having a hydrophilic surface according to the present invention preferably has a surface reflection density of 0.5 or more, more preferably 0.8 to 2.0, and particularly preferably 1.0 to 1.5. .

  The reflection density is an average value of reflection density values at intervals of 20 nm from 400 nm to 700 nm as measured with an observation visual field of 2 ° and an absolute white density standard. For example, using a spectral densitometer Spectrolino manufactured by GretagMacbeth. , Filter condition D65, observation field of view 2 °, white base: absolute white, density standard: measured by reflection density at intervals of 20 nm from 400 nm to 700 nm with values measured by Status-T, and calculated by calculating an average value can do.

  The visible light reflection density of the hydrophilic surface of the substrate can be 0.5 or more by coloring the hydrophilic surface.

  In the present invention, it is a preferred embodiment that aluminum is used as the substrate and the hydrophilic surface is colored.

  As a means for coloring the aluminum substrate, the following methods may be mentioned.

  For example, the electrolytic coloring method described in “Colored film by electrolytic method” written by Nobuyoshi Baba (Tsubaki Shoten) can be used.

  When an alternating current alumite prepared by alternating current electrolysis in a sulfuric acid bath is immersed in various metal salt aqueous solutions, the following color anodized is obtained, and this coloring can be used.

(Immersion solution: Anodized color)
Sodium tartrate / antimony: sodium orange arsenate: yellow ammonium citrate / bismuth: tan copper sulfate: cobalt cobalt acetate: cadmium black acetate: yellow gold chloride: purple lead acetate: dark iron ammonium oxalate iron: black sodium molybdate: Orange ammonium sulfate, nickel: bronze sodium selenate: reddish brown silver nitrate: gray brown ammonium chloride, stannic: yellow ammonium chloride, stannous: brown uranium acetate: brown Al-Si alloy, Al-Cr alloy, Al-Mn Alloys and the like can be colored and anodized simply by anodizing in a sulfuric acid bath, and these colored anodized are called “alloy coloring”, but these colors can also be used.

  In the alloy coloring method, the coloring does not occur or the color tone changes depending on the heat treatment status of the alloy as well as the alloy components. That is, whether the aluminum alloy is a solid solution or a eutectic affects the color development, and for example, the following colors are obtained.

(Aluminum alloy: Color)
Al-Si: black, gray Al-Cr: golden, gray Al-Mn: reddish brown Al-Mn-Cr: black, gray, yellow In addition, after making colorless anodized, coloring method to add color again The alumite coloring methods include dye coloring methods, inorganic salt immersion coloring methods, and electrolytic coloring methods, and these coloring methods can also be used. In addition, as another special coloring method, a method can be used in which a large number of mechanically fine grooves are formed on aluminum and colored by light interference.

(Hydrophilic layer)
In the case of providing hydrophilicity, the hydrophilic layer includes a hydrophilic material, and a metal oxide is preferably used as the hydrophilic material.

  The metal oxide preferably contains metal oxide particles.

  Examples thereof include colloidal silica, alumina sol, titania sol, and other metal oxide sols.

  The form of the metal oxide particles may be spherical, needle-like, feather-like, or any other form. The average particle diameter is preferably 3 to 100 nm, and several kinds of metal oxide particles having different average particle diameters can be used in combination. The surface of the particles may be surface treated.

  The metal oxide particles can be used as a binder by utilizing the film forming property. The decrease in hydrophilicity is less than when an organic binder is used, and it is suitable for use in a hydrophilic layer.

  Among the above, colloidal silica can be preferably used in the present invention. Colloidal silica has the advantage of high film-forming properties even under relatively low temperature drying conditions, and can provide good strength.

  The colloidal silica preferably includes necklace-like colloidal silica and fine particle colloidal silica having an average particle size of 20 nm or less, and the colloidal silica preferably exhibits alkalinity as a colloidal solution.

  The hydrophilic layer that can be used in the present invention preferably contains porous metal oxide particles as a metal oxide.

  As the porous metal oxide particles, porous silica, porous aluminosilicate particles, or zeolite particles can be preferably used.

  The particle diameter of the porous inorganic particles is preferably substantially 1 μm or less, and more preferably 0.5 μm or less, when contained in the hydrophilic layer.

A silicate aqueous solution can also be used as another additive material for the hydrophilic layer. Alkali metal silicates such as silicate Na, silicate K, and silicate Li are preferred, and the SiO ₂ / M ₂ O ratio is in a range where the pH of the entire coating solution does not exceed 13 when silicate is added. It is preferable to select such that the inorganic particles are not dissolved.

  Further, an inorganic polymer or an organic-inorganic hybrid polymer using a metal alkoxide by a so-called sol-gel method can also be used. Regarding the formation of inorganic polymers or organic-inorganic hybrid polymers by the sol-gel method, for example, those described in “Application of the sol-gel method” (Sakuo Sakuo / Agne Jofusha) or in this book Known methods described in the cited documents can be used.

  The hydrophilic layer can contain a photothermal conversion agent.

  Examples of the photothermal conversion material include the following materials.

  General infrared absorbing dyes such as cyanine dyes, croconium dyes, polymethine dyes, azurenium dyes, squalium dyes, thiopyrylium dyes, naphthoquinone dyes, anthraquinone dyes, organic compounds such as phthalocyanine dyes and naphthalocyanine dyes , Azo-based, thioamide-based, dithiol-based, and indoaniline-based organometallic complexes. Specifically, JP-A-63-139191, JP-A-64-33547, JP-A-1-160683, JP-A-1-280750, JP-A-1-293342, JP-A-2-2074, Kaihei 3-26593, JP-A-3-30991, JP-A-3-34891, JP-A-3-36093, JP-A-3-36094, JP-A-3-36095, JP-A-3-42281, JP-A-3-42281 Examples thereof include compounds described in JP-A-3-97589, JP-A-3-103476, and the like. These can be used alone or in combination of two or more.

  JP-A-11-240270, JP-A-11-265062, JP-A-2000-309174, JP-A-2002-49147, JP-A-2001-162965, JP-A-2002-144750, JP-A-2001-219667. The compounds described in (1) can also be preferably used.

  When providing a hydrophilic layer, the visible light reflection density on the surface of the hydrophilic layer is preferably 0.5 or more.

(Thermal image forming layer)
The heat-sensitive image forming layer (hereinafter abbreviated as “image forming layer”) according to the present invention is a layer capable of forming an image by imagewise heating, and is a layer that can be developed on a printing press.

  There are two methods for imagewise heating: a method of heating imagewise with a direct heat source, or a method of performing image exposure with a laser or the like and heating with heat generated by exposure. In the present invention, laser light is used. A method by image exposure using is preferably used.

  “Developable on a printing press” means that the image forming layer in the non-image area can be removed by dampening water and / or printing ink in lithographic printing after exposure.

  The heated portion of the image forming layer becomes an image portion that is printing ink receptive at the time of printing, and the lithographic printing plate material according to the present invention is a negative lithographic printing plate material in which the exposed portion of image exposure becomes the image portion. is there.

  The image forming layer contains a heat-sensitive material that causes changes such as deformation, melting, and softening due to heat.

  In a preferred embodiment, the image forming layer contains a photothermal conversion agent as described above.

  Examples of the heat-sensitive material include natural or synthetic waxes, polyester, polystyrene, polyacryl, polyurethane-based resins, copolymer resins thereof, or thermally reactive materials such as blocked isocyanate.

  The heat-sensitive material is preferably a blocked isocyanate, a urethane resin, a polyester resin particle or the like in terms of printing durability, on-press developability, and the like.

  As preferable physical properties of these resins, properties such as a melting point, a softening point, and a glass transition point (Tg) are 40 ° C. or higher.

  The heat-sensitive material is preferably thermoplastic resin particles, and the average particle diameter is preferably 0.01 to 2 μm, more preferably 0.1 to 1 μm from the standpoint of on-press developability and resolution. .

  The solid content of the heat-sensitive material is preferably 50 to 95%, and the infrared absorbing dye is preferably 0.5 to 30%.

[Other materials that can be contained in the image forming layer]
The image forming layer according to the present invention preferably further contains the following materials.

  The image forming layer preferably contains a water-soluble resin or a water-dispersible resin. Examples of water-soluble resins and water-dispersible resins include oligosaccharides, polysaccharides, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyethylene glycol (PEG), polyvinyl ether, styrene-butadiene copolymers, and methyl methacrylate-butadiene copolymers. Examples thereof include resins such as conjugated diene polymer latex, acrylic polymer latex, vinyl polymer latex, polyacrylic acid, polyacrylate, polyacrylamide, and polyvinylpyrrolidone.

  Examples of the oligosaccharide include raffinose, trehalose, maltose, galactose, sucrose, and lactose, and trehalose is particularly preferable.

  As polysaccharides, starches, celluloses, polyuronic acids, pullulans and the like can be used, but cellulose derivatives such as methyl cellulose salts, carboxymethyl cellulose salts, hydroxyethyl cellulose salts are particularly preferable, and sodium salts and ammonium salts of carboxymethyl cellulose are preferable. More preferred.

  The polyacrylic acid, polyacrylic acid, polyacrylate (Na salt, etc.), and polyacrylamide preferably have a molecular weight of 3,000 to 5,000,000, and more preferably 5,000 to 1,000,000.

  Water-soluble resins and water-dispersible resins may be added to improve background stains and heat resistance after storage of printing plate materials over time, and on-press developability. Since the durability of the part may be lowered, the addition amount is preferably the minimum necessary, usually in the range of 50% by mass or less, more preferably in the range of 30% or less.

  The image forming layer can contain a water-soluble surfactant. Surfactants such as Si, F, and acetylene glycol can be used.

  Further, it may contain an acid (phosphoric acid, acetic acid, etc.) or an alkali (sodium hydroxide, silicate, phosphate, etc.) for pH adjustment.

The amount per image forming layer, a 0.01 to 10 g / m ^2, preferably from 0.1 to 3 g / m ^2, more preferably from 0.2 to 2 g / m ^2.

  As a preferable embodiment of the printing plate material of the present invention, an image forming layer is provided on an aluminum substrate whose surface has been hydrophilized, or a hydrophilic layer provided on the substrate, and the image forming layer or the same. A printing plate material containing a photothermal conversion agent in any of the constituent layers on the substrate other than the above.

(Material that reduces reflection density)
In the present invention, it is preferable to provide a layer containing a material that causes a decrease in transparency and an increase in light scattering properties due to light or heat at the time of image exposure on the substrate, and reduces the reflection density of the surface of the printing plate material, This layer is preferably the image forming layer or an adjacent layer thereof. In particular, the image forming layer preferably contains the above material.

  In the present invention, for example, the reflection density of the surface of the printing plate material before image exposure is adjusted by adjusting the degree of coloring of the surface of the hydrophilic layer of the substrate described above and the amount of the material that lowers the reflection density. By setting the absolute value of the difference between Ds and the reflection density Dp of the surface of the non-image portion after development on the printing press to be 0.30 to 0.90, the exposed portion and the unexposed portion of the printing plate material, The image can be easily discriminated.

  In the present invention, an embodiment in which the hydrophilic surface of the base material is colored as described above is particularly preferable, and a case where Ds <Dp is preferable.

  Examples of the material for reducing the reflection density include the following.

(Metal oxide)
The metal oxide preferably contains metal oxide particles.

  Examples thereof include colloidal silica, alumina sol, titania sol, and other metal oxide sols.

  The form of the metal oxide particles may be spherical, needle-like, feather-like, or any other form. The average particle size is preferably 3 to 2000 nm, and several types of metal oxide particles having different average particle sizes can be used in combination. The surface of the particles may be surface treated.

  In addition, it is preferable that porous metal oxide particles are included as the metal oxide. As the porous metal oxide particles, porous silica, porous aluminosilicate particles, or zeolite particles described later can be preferably used.

(Porous silica porous silica or porous aluminosilicate particles)
The porous silica particles are generally produced by a wet method or a dry method. In the wet method, it can be obtained by drying and pulverizing a gel obtained by neutralizing an aqueous silicate solution, or by pulverizing a precipitate deposited after neutralization. In the dry method, silicon tetrachloride is burned together with hydrogen and oxygen to obtain silica. These particles can be controlled in porosity and particle size by adjusting the production conditions.
(Zeolite particles)
Zeolite is a crystalline aluminosilicate and is a porous body having regular three-dimensional network voids having a pore diameter of 0.3 to 1 nm.

  The particle diameter of the porous inorganic particles is preferably substantially 1 μm or less, and more preferably 0.5 μm or less.

  Further, in the visible image imparting layer of the printing plate material of the present invention, layered mineral particles are preferably used as a metal oxide.

  The layered mineral particles include kaolinite, halloysite, talc, smectite (montmorillonite, beidellite, hectorite, saponite, etc.), vermiculite, mica (mica), chlorite, and hydrotalcite, layered polysilicate ( Kanemite, macatite, ialite, magadiite, kenyaite, etc.). Among them, it is considered that the higher the charge density of the unit layer (unit layer), the higher the polarity and the higher the hydrophilicity. The charge density is preferably 0.25 or more, more preferably 0.6 or more. Examples of the layered mineral having such a charge density include smectite (charge density 0.25 to 0.6; negative charge), vermiculite (charge density 0.6 to 0.9; negative charge) and the like. In particular, synthetic fluoromica is preferable because it can be obtained with stable quality such as particle size. Among the synthetic fluorine mica, those that are swellable are preferable, and those that are free swell are more preferable.

  Also, intercalation compounds of the above-mentioned layered mineral particles (pillar crystals, etc.), those subjected to ion exchange treatment, and those subjected to surface treatment (silane coupling treatment, compounding treatment with organic binder, etc.) Can be used.

  As the size of the layered mineral particles, the average particle size (maximum particle length) is 20 μm or less in the state of being contained in the layer (including the case of undergoing the swelling process and dispersion peeling process). Preferably, the aspect ratio (maximum particle length / particle thickness) is 20 or more, the average particle size is 5 μm or less, the average aspect ratio is more preferably 50 or more, and the average particle size Is more preferably 1 μm or less and the average aspect ratio is 50 or more. When the particle size is in the above range, the continuity and flexibility in the planar direction, which are the characteristics of the thin layered particles, are imparted to the coating film, and it is difficult for cracks to occur, and a tough coating film can be obtained in a dry state. Moreover, in the coating liquid containing many particulate matters, sedimentation of particulate matter can be suppressed by the thickening effect of the layered clay mineral.

  When the layered mineral particles are included, the content is preferably 1 to 90% by mass of the entire layer, more preferably 4 to 80% by mass, and particularly preferably 4 to 50% by mass. .

  In particular, swellable synthetic fluorinated mica and smectite are preferable because they are effective even when added in a small amount. The layered mineral particles may be added as a powder to the coating solution, but in order to obtain a good degree of dispersion even with a simple preparation method (no need for a dispersion step such as media dispersion), the layered mineral particles are used alone. It is preferable that the gel swollen in water is prepared and then added to the coating solution.

  Further, an inorganic polymer or an organic-inorganic hybrid polymer using a metal alkoxide by a so-called sol-gel method can also be used. The formation of an inorganic polymer or an organic-inorganic hybrid polymer by the sol-gel method is described in, for example, “Application of the sol-gel method” (Sakuo Sakuo / Published by Agne Jofusha) or cited in this book. Known methods described in the published literature can be used.

  In the present invention, the reflection density of the region where heat or light is applied in an imagewise manner decreases because a rapid temperature change occurs in a short time due to laser light or the like. It is presumed that the microscopic cracks are generated or the incident light of the observation light source is scattered because the gas is included in the layer, and as a result, the density of the printing plate material surface is lowered.

  The layer containing the material that lowers the reflection density is provided on the image forming layer side of the substrate, but it may be provided as a separate layer from the image forming layer, but from the viewpoint of reducing the number of coating steps and improving photothermal conversion efficiency. Also, it is a preferred embodiment that it is also used as an image forming layer.

  As a material for reducing the reflection density, layered mineral particles such as montmorillonite described above are added at a ratio of about 5 to 50% of the total solid content of the layer. These are swollen by mixing with water to form a solution-like state. For example, polyester emulsion as a heat-sensitive material, water-soluble infrared absorbing dye and mixing in an aqueous solvent to form an image It can contain in the coating liquid for layers.

  In addition, if the heat-sensitive material used in the image forming layer is a material that causes a change in the reflection density of the exposed portion with respect to the reflection density of the unexposed portion under the condition that the heat-sensitive material itself is exposed by infrared laser light or the like, It can also be used as a material for reducing the reflection density.

The amount with the layer containing the material to reduce the reflection density is preferably 0.1 to 3 g / m ^2, more preferably 0.2 to 1.5 g / m ^2.

Preferably 0.01g / m ² ~5.00g / m ² as the amount with a material to reduce the reflection density, particularly preferably ^{0.05g / m 2 ~1.00g / m 2} .

  When the image forming layer contains a material that lowers the reflection density, drying after coating the image forming layer coating liquid on the substrate having a hydrophilic surface is performed at 20 ° C. to 200 ° C. for about 10 seconds to 30 minutes. It is preferred to do so. At that time, it is necessary to adjust the temperature and time so that the heat-sensitive material is softened and melted by heat so that it cannot be removed by washing with water and does not adhere to the hydrophilic surface.

  In order to easily confirm the exposure image, it is necessary to increase the material that reduces the reflection density per unit area. That is, it is necessary to increase the thickness of the layer containing the material that lowers the reflection density or increase the content ratio.

  However, when the thickness is increased, more energy is required for the image-forming layer to bind to the hydrophilic surface, and when the content ratio is increased, the resistance to binding to the hydrophilic surface due to heat decreases. It tends to cause deterioration in printability. In addition, there is a concern that an image forming layer component mixed in ink or fountain solution in a printing press or a material that lowers the reflection density lowers the saturation of the ink or changes the color of the printing paper.

  In the present invention, the absolute value of the difference between the reflection density of the surface of the printing plate material before image formation and the reflection density of the area where the image forming layer after printing is removed is controlled within a certain range. It was found that the energy required for image formation can be reduced while providing a visible image, and a sufficient number of printable sheets (press life) can be secured.

  A preferable range is such that the absolute value of the difference between the reflection density Ds of the surface of the printing plate material before image formation and the reflection density Dp of the area where the image forming layer after printing is removed is 0.30 to 0.90.

  A protective layer may be provided as an upper layer of the image forming layer. As a material used for the protective layer, a water-soluble resin or a water-dispersible resin can be preferably used.

Further, hydrophilic overcoat layers described in JP-A No. 2002-019318 and JP-A No. 2002-086948 can also be preferably used. The amount per the protective layer is 0.01 to 10 g / m ^2, preferably from 0.1 to 3 g / m ^2, more preferably from 0.2 to 2 g / m ^2.

(Image forming method)
In the plate-making method of the present invention, image development is performed after image exposure. Laser light is preferably used for image exposure, and it is particularly preferable to perform image formation by exposure with a thermal laser.

  For example, scanning exposure using a laser that emits light in the infrared and / or near infrared region, that is, emits light in the wavelength range of 700 to 1500 nm is preferable.

  A gas laser may be used as the laser, but it is particularly preferable to use a semiconductor laser that emits light in the near infrared region.

  As an apparatus suitable for scanning exposure, any apparatus may be used as long as it can form an image on the surface of the printing plate material in accordance with an image signal from a computer using this semiconductor laser.

  In general, (1) a printing plate material held by a flat plate holding mechanism is exposed two-dimensionally using one or a plurality of laser beams to expose the entire surface of the printing plate material. ) The printing plate material held along the cylindrical surface inside the fixed cylindrical holding mechanism is used in the circumferential direction of the cylinder (main scanning direction) using one or more laser beams from inside the cylinder. A method in which the entire surface of the printing plate material is exposed by moving in a direction perpendicular to the circumferential direction (sub-scanning direction) while scanning, and (3) printing held on the surface of a cylindrical drum that rotates about an axis as a rotating body The plate material is printed by moving in the direction perpendicular to the circumferential direction (sub-scanning direction) while scanning in the circumferential direction (main scanning direction) by rotating the drum using one or multiple laser beams from the outside of the cylinder. A method that exposes the entire plate material That. In particular, in an apparatus that performs exposure on a printing apparatus, the exposure method (3) is used.

[On-press development method]
The removal of the unexposed part of the image forming layer on the printing machine can be performed by contacting a watering roller or an ink roller while rotating the plate cylinder. The various sequences can be performed.

In that case, the water amount may be adjusted by increasing or decreasing the amount of dampening water required for printing, and the water amount adjustment may be divided into multiple stages or steplessly. You may change it to.
(1) As a sequence for starting printing, a watering roller is brought into contact with the plate cylinder to make one to several dozen rotations, then an ink roller is brought into contact with the plate cylinder to make one to several dozen rotations, and then Start printing.
(2) As a sequence for starting printing, an ink roller is contacted to rotate the plate cylinder 1 to several tens of turns, then a watering roller is contacted to rotate the plate cylinder 1 to tens of rotations, Start printing.
(3) As a sequence for starting printing, the watering roller and the ink roller are brought into contact with each other substantially simultaneously to rotate the plate cylinder 1 to several tens of times, and then printing is started.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In the examples, “parts” represents “parts by mass” unless otherwise specified.

[Preparation of substrate]
[Preparation of substrate 1]
An aluminum plate (material 1050, tempered H16) having a thickness of 0.24 mm was immersed in a 1% by mass sodium hydroxide aqueous solution at 50 ° C., dissolved so that the dissolved amount became 2 g / m ² , and washed with water. Then, it was immersed in 0.1 mass% hydrochloric acid aqueous solution at 25 ° C. for 30 seconds, neutralized, and then washed with water.

Next, this aluminum plate was subjected to an electrolytic surface roughening treatment with an electrolytic solution containing hydrochloric acid 10 g / L and aluminum 0.5 g / L using a sine wave alternating current and a peak current density of 50 A / dm ^2. It was.

The distance between the electrode and the sample surface at this time was 10 mm. Perform electrolytic graining treatment is divided into 12 times, and the quantity of electricity used in one treatment (at a positive polarity) as the 40C / dm ^2, treatment quantity of electricity 480C / dm ² in total (at a positive polarity). In addition, a rest period of 5 seconds was provided between each surface roughening treatment.

After electrolytic surface roughening, it is immersed in a 1% by weight sodium hydroxide aqueous solution kept at 50 ° C. and etched so that the amount of dissolution including the smut of the roughened surface becomes 1.2 g / m ^2. Then, it was washed with water, then immersed in a 10% aqueous sulfuric acid solution maintained at 25 ° C. for 10 seconds, neutralized, and then washed with water. Next, anodization was performed in a 20% sulfuric acid aqueous solution so that the amount of electricity was 150 C / dm ² under a constant voltage condition of 20 V, followed by washing with water.

  Next, after squeezing the surface water after washing with water, it was immersed in a 1% by mass sodium dihydrogen phosphate aqueous solution maintained at 70 ° C. for 30 seconds, washed with water, and then dried at 80 ° C. for 5 minutes to obtain a substrate. Obtained.

  Ra of this base material was 460 nm (measured 40 times using RST Plus manufactured by WYKO).

[Coloring of substrate]
Electrolytic coloring method is used for the base material, anodized film is applied to 10 μm, and metal fine particles are deposited in the pores during anodization by treating for 2 minutes with an AC constant voltage method in an electrolytic solution containing metal ions. I let you.

  In order to make the surface black, stannous sulfate was used and coloring was performed under the following electrolytic conditions.

Electrolytic solution: stannous sulfate 10 g / L, sulfuric acid 10 g / L, catechol 5 g / L
Soft start with treatment temperature of 28 ° C., voltage of 15 V, rise for 15 seconds The reflection density on the surface of the aluminum substrate after coloring was in the range of 1.75 to 1.85.

  Density measurement was performed using a spectral densitometer Spectrolino manufactured by GretagMacbeth, and the reflection density of black (K) was measured with the values measured under filter condition D65, observation field of view 2 °, white base: absolute white, density standard: Status-T. did.

  Subsequently, carboxymethyl cellulose 1150 (manufactured by Daicel Chemical Industries, Ltd.) was made into an aqueous solution with a solid content concentration of 0.1% by mass, immersed in a bath maintained at 75 ° C. for 30 seconds with stirring, washed with water and dried. As a result, a substrate 1 was obtained.

[Preparation of lithographic printing plate materials]
[Printing plate materials 1-8]
After sufficiently stirring and mixing the materials having the following composition, the concentration was appropriately adjusted by dilution with pure water and filtered to obtain a coating solution for the image forming layer (1) having a solid content of 2.5% by mass.

  Next, the coating liquid of the image forming layer (1) is adjusted on the substrate 1 by using a wire bar, and the amount of the coating liquid after drying is adjusted so that the reflection density Ds before the printing process becomes as shown in Table 2. It was applied and dried at a temperature of 50 ° C. for 3 minutes.

  Next, an aging treatment at 40 ° C. for 24 hours was performed to obtain printing plate materials 1 to 8. A mass part ratio represents the mass ratio in solid content after drying.

Coating liquid composition of image forming layer (1) Thermosensitive material: Block type urethane prepolymer aqueous dispersion (Mitsui Takeda Chemical Co., Ltd., Takenate WB-700 solid content 44% by mass)
155 parts Water-soluble resin: aqueous solution of sodium polyacrylate, Aqualic DL522 (manufactured by Nippon Shokubai Co., Ltd.), solid content 10% by mass 40 parts Infrared absorbing dye: 1% by mass aqueous solution of ADS830WS (manufactured by American DyeSource) 800 parts Layered mineral Particle: 5% aqueous solution of hydrophilic smectite SWN manufactured by Coop Chemical Co., Ltd.
400 parts [printing plate materials 9 to 16]
Printing plate materials 9 to 16 were produced in the same manner except that the base material 1 used in the printing plate materials 1 to 8 was changed to the following base material 2.

Base material 2
An aluminum plate (material 1050, tempered H16) having a thickness of 0.24 mm was immersed in a 1% by mass sodium hydroxide aqueous solution at 50 ° C., dissolved so that the dissolved amount became 2 g / m ² , and washed with water. Then, it was immersed in 0.1 mass% hydrochloric acid aqueous solution at 25 ° C. for 30 seconds, neutralized, and then washed with water.

Next, this aluminum plate was subjected to an electrolytic surface roughening treatment with an electrolytic solution containing hydrochloric acid 10 g / L and aluminum 0.5 g / L using a sine wave alternating current and a peak current density of 50 A / dm ^2. It was. The distance between the electrode and the sample surface at this time was 10 mm.

Perform electrolytic graining treatment is divided into 12 times, and the quantity of electricity used in one treatment (at a positive polarity) as the 40C / dm ^2, treatment quantity of electricity 480C / dm ² in total (at a positive polarity). In addition, a rest period of 5 seconds was provided between each surface roughening treatment.

After electrolytic surface roughening, it is immersed in a 1% by weight sodium hydroxide aqueous solution kept at 50 ° C. and etched so that the amount of dissolution including the smut of the roughened surface becomes 1.2 g / m ^2. Then, it was washed with water, then immersed in a 10% aqueous sulfuric acid solution maintained at 25 ° C. for 10 seconds, neutralized, and then washed with water.

Next, anodization was performed in a 20% sulfuric acid aqueous solution so that the amount of electricity was 150 C / dm ² under a constant voltage condition of 20 V, followed by washing with water.

  Next, after squeezing the surface water after washing with water, it was immersed in a 1% by mass sodium dihydrogen phosphate aqueous solution maintained at 70 ° C. for 30 seconds, washed with water, and then dried at 80 ° C. for 5 minutes to obtain a substrate. Obtained. Ra of this base material was 460 nm (measured 40 times using RST Plus manufactured by WYKO).

  A material having the following composition was sufficiently stirred and mixed using a homogenizer, and then filtered to prepare a coating solution for the hydrophilic layer (1) having a solid content of 15% by mass.

The coating liquid for the hydrophilic layer (1) is applied onto the undercoat surface A of the base material using a wire bar so that the applied amount after drying is 1.5 g / m ^2, and at 100 ° C. for 3 minutes. Dried. Next, an aging treatment at 60 ° C. for 72 hours was performed to obtain a substrate 2.

  Hydrophilic layer coating solution composition (numbers in the table represent parts by mass)

[Image formation by infrared laser exposure]
The printing plate material was wound around the exposure drum and fixed. A laser beam having a wavelength of 830 nm and a spot diameter of about 18 μm was used for exposure, and the exposure energy was 400 mJ / cm ² , and an image was formed with 2400 dpi (dpi represents the number of dots per 2.54 cm) and 175 lines. The exposed image includes a solid image and a 1 to 99% halftone dot image.

  Table 2 shows the reflection density of the surface of the printing plate material in the unexposed area and the reflection density of the non-image area after on-press development in the exposed area. The concentration was measured by the same method as that for the substrate 1.

[Printing method]
Printing machine: DAIYA1F-1 manufactured by Mitsubishi Heavy Industries, Ltd., coated paper, dampening water: 2% by mass of Astro Mark 3 (manufactured by Nikken Chemical Research Co., Ltd.), ink (TK High Unity Red, manufactured by Toyo Ink Co., Ltd.) And printed.

  The printing plate material was attached to the plate cylinder as it was after exposure, and printed using the same printing sequence as the PS plate. The density of the solid image portion of the printed material was adjusted to 1.4 (density measurement conditions are the same as described above).

(On-press developability)
[Color]
Each printing plate material is printed unprinted for 20 plates on a printing machine, and 100 sheets are printed on the printing machine. After the image forming layer components are transferred to the printing machine, the exposed plate of the same type is attached and printing is started. to the solid portion of the 200 th printed material L ^* a ^* b ^* values measured using a GretagMacbeth Co. spectrodensitometer Spectrolino a solid portion was printed under the same conditions in the PS plate L ^* a ^* b ^* The color difference (ΔE) with the value was compared and used as one of on-press developability indicators.

  After printing of each printing plate material, the printing machine was cleaned and replaced with new printing ink and fountain solution.

[Number of waste paper]
For each printing plate material, the number of sheets printed from the start of printing was determined for completion of on-press development.

  The on-machine development end index is that the non-image area is not smudged on the printed material, the density of the solid image area is 1.6 or more (measured in the M mode using Macbeth RD918), and 95% The halftone dot image is open. The number of damaged paper sheets until satisfactory printing was obtained was determined and used as one of on-press developability indicators.

(Evaluation of visibility)
The printing plate material for image formation by infrared laser exposure was observed under the light source of a standard light source device, Proflight (for reflection) LD50-440 model, manufactured by Gretag Macbeth Co., Ltd., and an image of a halftone dot step portion was observed.

  At that time, the possibility of discriminating the gradation difference between steps with different halftone dots% was compared and evaluated according to the following rank.

(Rank)
5: Step difference in which halftone dot difference% is 5% can be visually discriminated in all areas from halftone dot 1% to 99%. 4: Halftone difference% in halftone dot in area 5% to 95%. Can visually discriminate the difference of 5% step 3: In the area of 10% to 90% of the halftone dot, the step difference of 20% of the gradation difference of the halftone dot can be visually discriminated 2: 0% of the halftone dot (unexposed) Part) and 50% and 100% (solid exposure part) step difference can be visually discriminated. 1: The difference between halftone dot 0% (unexposed part) and 100% (solid exposure part) step can be visually discriminated. Printability)
For each printing plate material, in printing from printing to 40,000 sheets, it is determined what number of prints a 50% halftone dot portion has a faint portion where no minute ink adheres when visually observed with a 20-fold loupe. Observation was made and this number was used as an index of printing durability.

  The results are shown in Tables 2 and 3.

  From Tables 2 and 3, it can be seen that the plate making method of the present invention provides a lithographic printing plate having excellent visible image properties after exposure, good on-press developability, and excellent printing durability.

(Printing plate materials 17-22)
In the same manner except that the processing time for coloring the base material of the printing plate material 4 was reduced from 2 minutes and the reflection density of the base material was adjusted so that the reflection density after printing was as shown in Table 4. Image formation by infrared laser exposure was performed and the visual image quality was compared.

  From the results of Table 4, the plate making method of the present invention is excellent in visible image quality after exposure, and particularly excellent when the reflection density of the surface of the non-image area after development on a printing press is 1.5 or more. I understand.

Claims (3)

A negative lithographic printing plate material having a heat-sensitive image-forming layer that can be developed on a printing press is image-exposed on a non-transparent substrate having a hydrophilic surface, and the lithographic printing plate material subjected to image exposure is developed on a printing press. A lithographic printing plate making method for producing a lithographic printing plate, wherein the reflection density Ds of the surface of the printing plate material before image exposure and the reflection density Dp of the surface of the non-image area after development on a printing press A method for making a lithographic printing plate, wherein the absolute value of the difference is 0.30 to 0.90. The lithographic printing plate making method according to claim 1, wherein the relationship between the reflection density Dp and the reflection density Ds is Ds <Dp. A lithographic printing plate material used in the lithographic printing plate making method according to claim 1 or 2.