JP2948780B2 - Thermosensitive image forming material and method for producing lithographic printing plate using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a heat-sensitive material for producing a lithographic printing plate. The invention further relates to a method for producing a printing plate from said heat-sensitive material.

BACKGROUND OF THE INVENTION Lithographic printing is a method of printing from a specially prepared surface that does not accept ink when some areas are capable of receiving lithographic ink while others are wetted with water. The areas that receive ink form the print image area, and the areas that repel ink form the background area.

In the photolithographic art, photolithographic materials are image-wise receptive to oily or greasy inks on a hydrophilic background in exposed areas (negative action) or in unexposed areas (positive action). You.

In the production of ordinary lithographic printing plates (also referred to as surface lithographic plates or planographic printing plates), supports which have an affinity for water or which obtain such an affinity by chemical treatment are photosensitive. Coated with a thin layer of the composition. Coatings therefor include a photopolymer layer containing a diazo compound, a dichromate-sensitized hydrophilic colloid and various synthetic photopolymers. In particular, diazo sensitization systems are widely used.

Upon image-wise exposure of the photosensitive layer, the exposed image areas become insoluble and the unexposed areas remain soluble. The plate is then developed with a suitable liquid to remove the diazonium salt or diazo resin in the unexposed areas.

[0006] On the other hand, there are known methods of making printing plates that involve the use of image forming materials that are heat-sensitive rather than light-sensitive. A particular disadvantage of photosensitive imaging materials as described above for making printing plates is that they must be shielded from light. Furthermore, they have sensitivity problems in terms of storage stability, and they show low resolution. The trend toward heat-sensitive printing plate precursors is clearly visible in the market.

For example, Research Disclosure no. 333
03 (January 1992) describes a heat-sensitive image-forming material comprising a support and a crosslinked hydrophilic layer containing thermoplastic polymer particles and an infrared absorbing pigment such as carbon black. Upon image-wise exposure to an infrared laser, the thermoplastic polymer particles solidify image-wise, thereby rendering the surface of the imaging material in these areas ink-receiving without further development. The disadvantage of this method is that the printing plate obtained is easily damaged since it can become ink-receptive when a little pressure is applied to it. Furthermore, under critical conditions, the lithographic performance of such printing plates is inferior, and thus such printing plates have only a small lithographic latitude.

[0008] EP-A 514 145 describes a heat-sensitive imaging element comprising a coating comprising core-shell particles having a shell component which is soluble or swellable in an aqueous alkaline medium and a water-insoluble thermosoftening core component. I have. The red or infrared laser light imagewise directed at the imaging material at least partially fuses the selected particles to form an image, wherein the non-fused particles are selectively removed by an aqueous alkaline developer. You. Thereafter, a back coating step is performed. However, the printing durability of the printing plate thus obtained is low.

[0009] EP-A-599510 includes (i) (1)
A layer comprising a binder or a continuous phase comprising a dispersed phase comprising a water-insoluble thermosoftening component A and (2) a component B which is soluble or swellable in an aqueous medium, preferably an aqueous alkaline medium (at least one of components A and B) (I.e., containing reactive groups or precursors therefor, which can cause insolubilization of the layer at elevated temperatures and / or upon exposure to actinic radiation); and (ii)
A heat-sensitive imaging material is described which comprises a substrate which is capable of strongly absorbing radiation and transferring the energy thus obtained to the disperse phase as heat and thus causing at least partial fusion of the coating. ing. After the image-wise irradiation of the image-forming material and the development of the image-irradiated plate, the plate is heated and / or subjected to actinic radiation to render it insoluble. However, the printing durability of the printing plate thus obtained is low.

[0010] EP-A625728 includes UV and IR.
Imaging materials are described that include a layer that is photosensitive to radiation and that is either positive-working or negative-working. This layer contains a resole resin, a latent Bronsted acid and an IR absorbing material. The printing result of the lithographic printing plate obtained by irradiating the image forming material and developing is inferior.

US Pat. No. 5,340,699 describes EP-A6
Almost the same as 25728, but describes a method for obtaining a negative working IR laser recording imaging material.
The IR-sensitive layer contains a resole resin, a novolak resin, a latent Bronsted acid and an IR absorber. The printing result of a lithographic printing plate obtained by irradiating and developing the image forming material is inferior.

US Pat. No. 4,708,925 describes a positive working image forming material comprising a photosensitive composition containing an alkali-soluble novolak resin and an onium salt. The composition can optionally include an IR sensitizer. After image-wise exposing the imaging element to UV-visible- or ultimately IR radiation, followed by a development step with an aqueous alkaline liquid, a positive-working print is obtained. The printing result of a lithographic printing plate obtained by irradiating and developing the image forming material is inferior.

[0013] FR 1561957 includes a binder and a mixture of liquid or solid compounds dispersed in the binder, wherein the liquid and solid compounds are more hydrophobic than the binder and are compatible with the binder when heated. An image forming material including at least a partially formed recording layer is described.
The binder can be a compound that is insoluble or only partially soluble in water, ie a binder that contains only a limited number of solubilizing groups such as alcohols or acids. The printing result of a lithographic printing plate obtained by irradiating and developing the image forming material is inferior.

All of the above-described systems require lithographic printing plates that require post-development processing and / or have poor printing characteristics. Accordingly, there remains a need for heat-sensitive imaging materials that are easy to process and that produce lithographic printing plates with good or excellent printing characteristics.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a heat-sensitive imaging material for making lithographic printing plates with excellent printing properties in an advantageous manner.

It is another object of the present invention to provide a method for obtaining a high quality negative working lithographic printing plate using said image forming material in a convenient manner.

Further objects of the present invention will become clear from the description hereinafter.

According to the present invention, an image forming layer containing hydrophobic thermoplastic polymer particles dispersed in a water-insoluble alkali-soluble or swellable resin on a hydrophilic surface of a lithographic printing substrate, and converts light into heat. A thermosensitive image-forming material comprising a compound capable of forming a phenolic hydroxy group, wherein said compound is present in said image-forming layer or a layer adjacent thereto, wherein said alkali-swellable or soluble resin contains a phenolic hydroxy group. Provide a forming material.

According to the present invention, there is provided (a) exposing the above-mentioned image-forming material to light or heat according to an image or according to information, and (b) removing an unexposed area, thereby forming a lithographic printing plate. There is also provided a method for obtaining a lithographic printing plate comprising a step of developing the exposed image forming material with an aqueous alkaline developing solution.

Detailed Disclosure of the Invention It has been found that a lithographic printing plate having high quality, especially high printing durability, can be obtained by the method of the present invention using the image forming material as described above. More precisely, it has been found that the printing plates are of high quality and are provided in a convenient manner, which can also provide economic and environmental advantages.

In the context of the present application, the 0.1.
A compound is said to be insoluble in a solvent when less than 1 g dissolves in the solvent at 20 ° C, and a compound is said to be soluble when at least 1 g of the compound dissolves in the solvent at 20 ° C.

The image-forming material for use according to the present invention comprises a hydrophobic heat-dispersible resin dispersed in a water-insoluble alkali-soluble or swellable resin having a phenolic hydroxy group as a hydrophilic binder on a hydrophilic surface of a lithographic substrate. Contains an image forming layer containing plastic polymer particles.

In the context of the present invention, preferred hydrophilic binders for use in the imaging layer include, for example, synthetic novolak resins, such as ALNOVOL (Reichold Ho
echst and DUREZ, OxyChem), and synthetic polyvinyl phenols such as MARUK
A LYNCUR M (registered trademark of Dyna Cyanamid)
There is.

The hydrophilic binder used in connection with the present invention is preferably not crosslinked or only slightly crosslinked.

According to one embodiment of the present invention, the lithographic substrate can be anodized aluminum. A particularly preferred lithographic substrate is an electrochemically grained, anodized aluminum support. According to the invention, the anodized aluminum support may be treated to improve the hydrophilic properties of its surface. For example, an aluminum support may be silicated by treating its surface with a sodium silicate solution at an elevated temperature, eg, 95 ° C. Alternatively, a phosphate treatment can be applied that involves treating the aluminum oxide surface with a phosphate solution that may further contain inorganic fluoride. Further, the aluminum oxide surface may be washed with a citric acid or citrate solution. This treatment may be performed at room temperature or at about 30 ° C.
It can be performed at slightly elevated temperatures of ５０50 ° C. Another interesting treatment involves washing the aluminum oxide surface with a bicarbonate solution. It is further evident that one or more of these post-treatments can be performed alone or in combination.

According to another embodiment in the context of the present invention, the lithographic substrate comprises a flexible support provided with a cross-linked hydrophilic layer, for example a paper or plastic film. Particularly suitable cross-linked hydrophilic layers can be obtained from a hydrophilic binder cross-linked with a cross-linking agent such as formaldehyde, glyoxal, polyisocyanate or hydrolyzed tetra-alkyl orthosilicate. The latter is particularly preferred.

As the hydrophilic binder, for example, a homopolymer or copolymer of vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, or maleic anhydride / vinyl methyl ether may be used. A hydrophilic (co) polymer such as a polymer can be used. The degree of hydrophilicity of the (co) polymer or (co) polymer mixture used is at least 60
It is preferred that the degree of hydrophilicity of the polyvinyl acetate hydrolyzed up to about 80% by weight, preferably up to about 80% by weight, is equal to or higher than that.

The amount of the crosslinking agent, in particular the tetraalkyl orthosilicate, should be at least 0.2 part by weight, preferably 0.5 to 5 parts by weight, more preferably 1.0 to 5 parts by weight, per part by weight of the hydrophilic binder. Preferably it is 3 parts by weight.

The crosslinked hydrophilic layer in the lithographic substrate used according to embodiments of the present invention preferably also contains substances that increase the porosity and mechanical strength of the layer. Colloidal silica can be used for this. The colloidal silica used can be in the form of any commercially available aqueous dispersion of colloidal silica having, for example, an average particle size of 40 nm or less, for example 20 nm. In addition, inert particles larger than colloidal silica, such as J. Colloid and Interface Sc
i. Vol. 26, 1968, page 62-69, silica or alumina particles or particles of titanium dioxide or other heavy metal oxides having an average diameter of at least 100 nm, as described by Stoeber. Can be added. The incorporation of these particles gives the surface of the cross-linked hydrophilic layer a uniform rough texture consisting of microscopic hills and valleys which serve as storage for water in the background area.

The thickness of the crosslinked hydrophilic layer in the lithographic substrate according to this embodiment can vary in the range of 0.2 to 25 μm and is preferably 1 to 10 μm.

Particular examples of cross-linked hydrophilic layers suitable for use according to the invention are described in EP-A 601 240, GB-
P1419512, FR-P2300354, US-P
3971660, US-P 4,284,705 and EP-A
514490.

As a flexible support for the lithographic substrate in the context of the embodiments of the present invention, plastic films such as supported polyethylene terephthalate films, cellulose acetate films, polystyrene films,
It is particularly preferable to use a polycarbonate film or the like. The plastic film support can be opaque or transparent.

It is particularly preferred to use a polyester film support to which an adhesion improving layer has been applied. Adhesion improving layers which are particularly suitable for use according to the invention are EP-A
615524, EP-A620502 and EP-A61
9525 including a hydrophilic binder and colloidal silica. Preferably, the amount of silica in the adhesion improving layer is ^{200mg / m 2 ~750mg / m 2} . Further, the ratio of silica to hydrophilic binder is preferably greater than 1, and the surface area of the colloidal silica is at least 300
is preferably from m ² / g, at least 500 meters ² /
g is more preferable.

According to the present invention, an image forming layer is provided on a hydrophilic surface. If desired, one or more intermediate layers can be provided between the lithographic substrate and the image forming layer. The image forming layer in the context of the present invention contains thermoplastic polymer particles dispersed in a water-insoluble alkali-soluble or swellable resin having a phenolic hydroxy group as a hydrophilic binder.

The hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a solidification temperature above 35 ° C., more preferably above 50 ° C.
Solidification can result from the softening or melting of the thermoplastic polymer particles under the influence of heat. There is no particular upper limit on the solidification temperature of the thermoplastic hydrophobic polymer particles; however, the temperature should be well below the decomposition temperature of the polymer particles. Preferably, the coagulation temperature is at least 10 ° C. below the temperature at which decomposition of the polymer particles occurs. When the polymer particles are exposed to temperatures above the coagulation temperature, they coagulate to form hydrophobic agglomerates in the hydrophilic layer, thus at these parts the hydrophilic layer is exposed to tap water or aqueous liquid. Becomes insoluble.

Specific examples of hydrophobic polymers for use in connection with the present invention include, for example, polyethylene, polyvinyl chloride, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polyvinylidene chloride, polyacrylonitrile, There are polyvinyl carbazole and the like, or a copolymer thereof. Most preferably, polyethylene is used.

The weight average molecular weight of the polymer is 5,000-10
It can be in the range of 00000 g / mol.

The hydrophobic particles can have a particle size between 0.01 μm and 50 μm, more preferably between 0.05 μm and 10 μm, most preferably between 0.05 μm and 2 μm.

The polymer particles are present as a dispersion in the coating solution of the image forming layer and can be prepared by the method described in US Pat. No. 3,476,937. Particularly preferred methods for making aqueous dispersions of thermoplastic polymer particles are: (1) dissolving a hydrophobic thermoplastic polymer in an organic water immiscible solvent, and (2) dissolving the resulting solution in water or Dispersing in an aqueous medium, and (3) removing the organic solvent by evaporation.

The amount of the hydrophobic thermoplastic polymer particles contained in the image forming layer is preferably from 20% by weight to 65% by weight, more preferably from 25% by weight to 55% by weight, and most preferably from 30% by weight to 55% by weight. 45% by weight.

The imaging layer can also contain a crosslinking agent, but this is not required. Preferred crosslinking agents are, for example, melamine-formaldehyde resins, glycoluril-
It is a low molecular weight substance containing a methylol group, such as formaldehyde resin, thiourea-formaldehyde resin, guanamine-formaldehyde resin, and benzoguanamine-formaldehyde resin. Most of the melamine-formaldehyde resin and the glycoluril-formaldehyde resin are CYMEL (Dyno Cyanamid Co., Ltd.) and N
It is commercially available under the trade name of IKALAC (Sanwa Chemical Co., Ltd.).

The image forming material further contains a compound capable of converting light into heat. This compound is preferably contained in the image-forming layer, but can also be in a layer adjacent to the image-forming layer. Suitable compounds capable of converting light to heat are preferably infrared absorbing components, but the absorption wavelength is in the wavelength range of the light source used for the image-wise exposure of the compound used for absorption. As long as it is not particularly important. Particularly useful compounds include, for example, dyes, especially infrared dyes, carbon black, metal carbides, borides,
There are structurally related nitrides, carbonitrides, blond constituent oxides and A components, such as the bronze group lacking WO _2.9 . Conductive polymer dispersions such as polypyrrole or polyaniline based conductive polymer dispersions can also be used. Lithographic performance and especially the resulting printing durability are determined by the thermal sensitivity of the imaging material. In this regard, carbon black gives very good and advantageous results.

Most preferably, the light-to-heat conversion compound in the context of the present invention is added to the image-forming layer, but at least a portion of the light-to-heat conversion compound may be included in an adjacent layer. . Such a layer can be, for example, a crosslinked hydrophilic layer of a lithographic substrate according to the second embodiment of the lithographic substrate described above.

According to the method of the present invention for obtaining a printing plate, the imaging element is image-wise exposed and subsequently developed with an aqueous alkaline solution.

Imagewise exposure in the context of the present invention may be laser or L.W. E. FIG. D. Preferably, the scanning exposure according to the image includes the use of: In the context of the present invention, it emits infrared (IR) and / or near infrared, ie 7
It is highly preferred to use a laser that emits in the wavelength range from 00 to 1500 nm. Particularly preferred for use in connection with the present invention are laser diodes that emit in the near infrared.

After the image-forming material exposed according to the image is developed with an aqueous alkaline solution and dried, the resulting plate can be used as it is as a printing plate. However, an additional 40
The plate can also be baked at a temperature of from 100 ° C to 230 ° C for a period of minutes to 5 minutes. For example, the exposed and developed plate is 2
Baking can be performed at a temperature of 30 ° C. for 5 minutes, at a temperature of 150 ° C. for 10 minutes, or at a temperature of 120 ° C. for 30 minutes.

The following examples illustrate, but do not limit, the invention. All parts are by weight unless otherwise specified.

Example 1 Production of a lithographic substrate

An aluminum foil having a thickness of 0.20 mm
The foil was degreased by immersing the foil in an aqueous solution containing 5 g / l of sodium hydroxide at 0 ° C. and washed with deionized water. The foil is then subjected to alternating current in an aqueous solution containing 4 g / l hydrochloric acid, 4 g / l borohydride and 5 g / l aluminum ions at a temperature of 35 ° C. and a current density of 1200 A / m ^2. And electrochemically granulate using 0.5
A surface condition having an average center line roughness Ra of μm was formed.

After washing with deionized water, the aluminum foil was then etched with an aqueous solution containing 300 g / l of sulfuric acid at 60 ° C. for 180 seconds and washed with deionized water at 25 ° C. for 30 seconds.

Subsequently, in an aqueous solution containing 200 g / l of sulfuric acid, at a temperature of 45 ° C., a voltage of about 10 V and a voltage of 15
The foil was anodized at a current density of 0 A / m ² for about 300 seconds to form an anodized film of 3.00 g / m ² Al ₂ O ₃ , then washed with deionized water and 20 g / l
After treatment with a solution containing sodium bicarbonate at 40 ° C. for 30 seconds, followed by a wash with ionic water at 20 ° C. for 120 seconds,
Dried.

Next, the granulated and anodized lithographic substrate is
Dipped for 60 seconds in an aqueous solution containing 5% by weight of citric acid, washed with deionized water and dried at 40 ° C.

Preparation of the image-forming material The image-forming material according to the present invention forms the following coating composition,
It was coated on the lithographic substrate described above in an amount of 30 g / m ² (wet) and dried at 35 ° C.

Preparation of the coating composition 0.48 g of MARUKA LYNCUR MH-2
(Homopolymer of polyvinylphenol from Maruzen Co.) was added 14.32 g of a 1% by weight NaOH solution in water. To 6.17 g of the above and tolerated solution, 29.3
Polymethylmethacrylate stabilized with 3 g of water, polyethylene oxide surfactant Hostapal B (1% by weight based on polymer) in deionized water (particle diameter 90 nm)
2.50 g of a 20% by weight dispersion of
2.00 g of a 5% by weight dispersion and a solution of the wetting agent in water.
4 ml were added.

Production of Printing Plate and Production of Original Copy The image forming material as described above was subjected to a scanning NdYLE infrared laser emitting at 1.05 μm (scanning speed 4).
m / s and 8 m / s, spot size 15 μm, and power at the plate was changed from 120 mW to 540 mW).

After image formation, the plate was treated with a Fuji PS-plate developer DP-5 (alkaline aqueous developer) to remove non-exposed areas to produce a negative working lithographic printing plate.

The resulting lithographic printing plate could be used for printing on a conventional offset printing press using commonly used inks and fountain solutions. Excellent copy and high print durability were obtained.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Joan Vermeersch Septestart, Mortseel, Belgium 27 Inside Agfa Geverth na Mroseze Bennoutchap (56) References JP-A-9-239942 (JP, A) JP-A-9-244228 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B41N 1/14

Claims (10)

(57) [Claims] An image forming layer containing hydrophobic thermoplastic polymer particles dispersed in a water-insoluble alkali-soluble or swellable resin on a hydrophilic surface of a lithographic substrate, and a compound capable of converting light into heat. A heat-sensitive image forming material, wherein the compound is present in the image forming layer or a layer adjacent thereto, wherein the alkali swellable or soluble resin contains a phenolic hydroxy group. Heat-sensitive image forming material. 2. The heat-sensitive image forming material according to claim 1, wherein the water-insoluble alkali-swellable or soluble resin containing a phenolic hydroxy group is a novolak resin or a polyvinylphenol resin. 3. The heat-sensitive image-forming material according to claim 1, wherein the thermoplastic polymer particles have a solidification temperature of at least 35 ° C. 4. The method according to claim 1, wherein the thermoplastic polymer particles are polyethylene, polystyrene, polymethyl (meth) acrylate,
The heat-sensitive image according to any one of claims 1 to 3, wherein the heat-sensitive image is selected from the group consisting of polyethyl (meth) acrylate, polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole, and a copolymer thereof. Forming material. 5. The compound capable of converting light into heat is selected from the group consisting of an infrared absorbing dye, carbon black, a metal boride, a metal carbide, a metal nitride, a metal carbonitride, and a conductive polymer dispersion. The heat-sensitive image-forming material according to any one of claims 1 to 4, wherein 6. The heat-sensitive substrate according to claim 1, wherein the lithographic substrate comprises anodized aluminum or a flexible support having a hydrophilic layer cross-linked thereon. Image forming material. 7. The heat-sensitive image forming material according to claim 1, wherein the image forming layer contains a crosslinking agent. 8. The image forming layer according to claim 1, wherein the compound capable of converting light into heat is present in the image forming layer.
The heat-sensitive image-forming material according to any one of the above. 9. An image forming material according to claim 1, wherein the image forming material is exposed to light or heat according to an image or information, and (b) an aqueous alkaline developing solution for removing unexposed areas. Developing the exposed image-forming material, thereby forming a lithographic printing plate. 10. The method for producing a lithographic printing plate according to claim 9, wherein the exposed and developed image forming material is baked at a temperature of 100 ° C. to 230 ° C. for 40 minutes to 5 minutes.