JPH09171249A - Thermosensitive image formation element and method for manufacture of printing plate by using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat sensitive image forming element usable for obtaining a printing plate which is developable by a simple method, friendly to the environment, and can be exposed by commercially usable lasers, and has high printing resistance. SOLUTION: This image forming element includes image forming layers which contain the hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder on the hydrophilic surface of a planographic base and in which the amt. of the hydrophobic thermoplastic polymer particles incorporated into the image forming layers is larger than 35wt% of the total weight of the image forming layers and compds. which are included in the image forming layers or the layers adjacent thereto and are capable of transducing light into heat. The image forming element described above is subjected to imagewise exposure. The image forming element which is obtd. in the manner described above and is subjected to the imagewise exposure is developed by using fresh water or aq. liquid and the entire part of the image forming element formed with the image obtd. in such a manner is heated to obtain the planographic printing plate.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method of making a printing plate which involves the use of a heat-sensitive imaging element and which can be developed with plain water or an aqueous liquid.

[0002]

BACKGROUND OF THE INVENTION A lithographic process is a method of printing from a specially manufactured surface that will be capable of receiving lithographic ink in some areas of the surface but not receiving the ink when wetted with water. is there. The ink receiving areas form the printed image areas and the ink-rejection areas form the background areas.

In photolithographic technology, the photographic material is made image-wise receptive to oily or greasy inks in exposed (negative-working) or unexposed areas (positive-working) on a hydrophilic background. .

In the production of common lithographic printing plates, also referred to as surface lithographic or planographic printing plates, the photosensitive composition is applied to a support which has an affinity for water or which can have such an affinity by chemical treatment. Coating. Coatings for this purpose include photopolymer layers containing diazo compounds, dichromate sensitized hydrophilic colloids and various synthetic photopolymers. In particular, diazo-sensitized 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,
The unexposed portion of the diazonium salt or diazo resin is removed.

Commercially available diazo-based printing plates most commonly use them as supports having a hydrophilic surface, since anodized and roughened aluminum offers the advantage of high print resistance. . A particular drawback of such types of printing plates is that they require specialized developers which are expensive and inconvenient for development.

EP-A 601240 discloses a diazo-based printing plate which uses as a lithographic base a polyester film provided with a cross-linked hydrophilic layer on which a photosensitive diazo layer is applied. There is. Such diazo-based printing plates can be developed by rinsing them with fresh water after image-wise exposure.

Commercially available plates using a flexible support such as paper provided with a hydrophilic layer are also available. For example, Li
thocraft 10008 FOTOPLATE ^™ is a printing plate comprising a hydrophilic layer having a diazo-based photosensitive layer provided thereon on a paper support. According to the supplier's plate instructions, lithographic printing plate precursor or image-wise exposure of the imaging element, placement of the exposed imaging element on the printing machine and L
ithocraft 10008 A plate can be produced by wiping with a development desensitizer. For the plate instructions, we are considering a method that does not use a development desensitizer. In practice, however, development desensitizers are almost always needed, since such methods very often result in poor lithographic performance.

A particular drawback of the diazo-based printing plates described above, which is usually independent of the type of lithographic base used, is that they must be shielded from light. Moreover, diazos are not sensitive enough to be exposed by commercial economical lasers.

On the other hand, methods of making printing plates involving the use of imaging elements that are heat-sensitive rather than light-sensitive are also known. For example, Research Disclosure n of January 1992
o. 33303 discloses a thermosensitive imaging element comprising a crosslinked hydrophilic layer containing a thermoplastic polymer and an infrared absorbing pigment such as carbon black on a support. Image-wise exposure to an infrared laser causes the thermoplastic polymer particles to image-wise coagulate, thereby rendering the surface of the imaging element and these parts ink-receptive without further development. The drawback of this method is that the resulting printing plate is easily damaged because some areas become ink receptive when some pressure is applied to the non-printed areas. Moreover, under critical conditions, the lithographic performance of such printing plates can be poor, and thus such printing plates have little lithographic printability.

EP 514.145 uses a heat-sensitive imaging element comprising an imaging layer comprising core-shell particles and a light-heat conversion material on a lithographic base such as anodized aluminum. It describes the method of making a printing plate. The shell of these particles is hydrophilic and makes the particles developable. The core is hydrophobic and flows out on heating. Thus, image-wise exposure with an infrared laser diode can render the imaging layer insoluble in the exposed areas. In the unexposed areas, the imaging layer can be removed with an aqueous developing agent containing ethanolamine. Then, bake the material. Although such printing plates produce high print resistance, their development is environmentally burdensome due to the use of alkanolamines.

[0012]

SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to produce a heat-sensitive printing plate which can be developed in a simple and environmentally friendly manner and which can be exposed by a commercially available laser. To provide an imaging element.

Another object of the present invention is to provide a heat-sensitive imaging element that can be used to obtain printing plates having high print resistance.

Other objects of the invention will be apparent from the description below.

The present invention comprises (1) (i) hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder on a hydrophilic surface of a lithographic base and contained in an imaging layer. The amount of hydrophobic thermoplastic polymer particles is 3% of the total weight of the image forming layer.
Image-wise exposing an imaging element comprising more than 5% by weight of an imaging layer and (ii) a compound capable of converting light contained in the imaging layer or layers adjacent thereto to heat. (2) developing the image-wise exposed image-forming element thus obtained with fresh water or an aqueous liquid, (3) and the whole image-forming imaging element thus obtained A method for producing a lithographic printing plate comprising the step of selectively heating.

[0016]

DETAILED DESCRIPTION OF THE INVENTION An imaging element for use in accordance with the invention comprises hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder on a hydrophilic surface of a lithographic base.
The hydrophilic binders used according to the invention are preferably not crosslinked or only slightly crosslinked. The imaging element also includes compounds capable of converting light into heat. This compound is preferably contained in the imaging layer, but may be provided in a layer adjacent to the imaging layer.

According to one aspect of the invention, the lithographic base can be anodized aluminum. A particularly preferred lithographic base is an electrochemically grained and anodized aluminum support. According to the present invention, an anodized aluminum support may be treated to improve the hydrophilicity of its surface. For example, the support may be silicate-treated by treating the surface of the aluminum support with a sodium silicate solution at an elevated temperature, eg, 95 ° C. Alternatively, a phosphate treatment may be applied which involves treating the aluminum oxide surface with a phosphate solution which may further contain inorganic fluoride.
Further, the aluminum oxide surface may be rinsed with a citric acid or citrate solution. This treatment may be carried out at room temperature or at a slightly elevated temperature of about 40-50 ° C. Other interesting treatments include rinsing the aluminum oxide surface with a bicarbonate solution. It is also clear that one or more of these post-treatments can be performed alone or in combination.

According to another aspect of the invention, the lithographic base comprises a flexible support provided with a cross-linked hydrophilic layer, such as paper or plastic film. Particularly suitable cross-linked hydrophilic layers are obtained from hydrophilic binders cross-linked with a cross-linking agent such as, for example, formaldehyde, glyoxal, polyisocyanate or hydrolyzed tetra-alkyl orthosilicate. The latter is particularly preferred.

As hydrophilic binders, hydrophilic (co) polymers such as vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide,
Homopolymers and copolymers of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, or maleic anhydride / vinyl methyl ether copolymer can be used. Used (co)
The hydrophilicity of the polymer or (co) polymer mixture is preferably the same as or more than that of polyvinyl acetate hydrolyzed to the extent of at least 60% by weight, preferably 80% by weight. high.

The amount of crosslinker, especially tetraalkyl orthosilicate, is preferably at least 0.2 part by weight, preferably between 0.5 and 5 parts by weight per part by weight of hydrophilic binder.
More preferably between 1.0 and 3 parts by weight.

The crosslinked hydrophilic layer in the lithographic base used according to the invention preferably also contains substances which enhance the mechanical strength and porosity of the layer. Colloidal silica can be used for this purpose. The colloidal silica used can be, for example, in the form of commercially available aqueous dispersions of colloidal silica having an average particle size of up to 40 nm, for example 20 nm. In addition, inert particles larger than colloidal silica, such as J. Colloid and Inte
Particles having an average diameter of at least 100 nm which are silica or aluminum particles or particles of titanium dioxide or other heavy metal oxides manufactured according to the Stoeber method described in rface Sci., Vol. 26, 1968, pages 62 to 69. , Can also be added. The addition of these particles gives the surface of the crosslinked hydrophilic layer a uniform rough texture consisting of irregularities of microscopic dimensions,
They act as storage places for water in the background.

The thickness of the crosslinked hydrophilic layer in the lithographic base according to the invention can vary in the range from 0.2 to 25 μm and is preferably 1 to 10 μm.

Specific examples of cross-linked hydrophilic layers suitable for use according to this aspect are EP-A601240, GB-
P-1419512, FR-P-2300354, US
-P-3971660, US-P-4284705 and EP-A 514490.

As the lithographic base flexible support in this embodiment, use is made of a plastic film such as polyester such as polyethylene terephthalate film or polyethylene naphthalate film, cellulose acetate film, polystyrene film, polycarbonate film and the like. Is particularly preferable. The plastic film support may be opaque or transparent.

It is particularly preferred to use a polyester film support provided with an adhesion improving layer. Particularly suitable adhesion improving layers for use according to the invention are EP-A6
19524, EP-A 620502 and EP-A6
Comprising a hydrophilic binder and colloidal silica as disclosed in US Pat. The amount of silica in the adhesion improving layer is 1 m ² per 200mg and 1 m ² per 750 mg. Further, the ratio of silica to hydrophilic binder is preferably greater than 1 and the surface area of the colloidal silica is preferably at least 300 m ² per gram, more preferably 500 m ² per gram.

According to the invention, an imaging layer is provided on top of the hydrophilic surface. Optionally, one or more intermediate layers may be provided between the lithographic base and the imaging layer. The imaging layer according to the present invention comprises thermoplastic polymer particles dispersed in a hydrophilic binder.

Hydrophilic binders suitable for use in the imaging layers according to the present invention are preferably those containing reactive groups such as hydroxy, amine or carboxy groups. Specific examples of hydrophilic binders are synthetic homo or copolymers,
For example, polyvinyl alcohol, dimethylhydantoin-
Formaldehyde resin, poly (meth) acrylic acid, poly (meth) acrylamide, hydroxyethyl poly (meth) acrylate, polyvinyl methyl ether, or natural binders such as gelatin, polysaccharides such as dextran,
They are pullulan, cellulose, gum arabic and alginic acid.

The hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a glass transition temperature of at least 90 ° C, more preferably at least 100 ° C.

The hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a coagulation temperature above 50 ° C and more preferably above 70 ° C. Coagulation results from the softening or melting of thermoplastic polymer particles under the influence of heat.
There is no particular upper limit on the coagulation temperature of the thermoplastic hydrophobic polymer particles, but this temperature must be well below the decomposition of the polymer particles. Preferably the coagulation temperature is at least 10 ° C below the temperature at which the decomposition of the polymer particles occurs. When the polymer particles are exposed to a temperature above the coagulation temperature, they coagulate to form hydrophobic agglomerates in the hydrophilic layer, so that in these parts the hydrophilic layer is exposed to fresh water or aqueous liquid. It becomes insoluble.

Specific examples of hydrophobic polymer particles for use in connection with the present invention include, for example, polystyrene, polyvinyl chloride, polymethylmethacrylate, polyvinylidene chloride, polyacrylonitrile, polyvinylcarbazole, and the like, or copolymers thereof. And / or a mixture.
Most preferably polymethylmethacrylate is used.

The weight average molecular weight of the polymer is 5,000 to 1,
It may be in the range of, 000,000 g / mol.

The hydrophobic particles are 0.01 μm to 50 μm,
More preferably it can have a particle size between 0.05 μm and 10 μm and most preferably between 0.05 μm and 0.5 μm.

The polymer particles are present in dispersion in the aqueous coating liquid of the imaging layer and are described in US-P-3.4.
It can be manufactured by the method disclosed in 76.937.
Another method, which is particularly suitable for producing an aqueous dispersion of thermoplastic polymer particles, is: dissolving the hydrophobic thermoplastic polymer in a water immiscible organic solvent, Dispersing in water or in an aqueous medium, and-removing the organic solvent by evaporation.

The amount of hydrophobic thermoplastic polymer particles contained in the imaging layer is preferably greater than 35 wt% and more preferably greater than 50 wt% and most preferably the total weight of the imaging layer. Is more than 65% by weight.

Suitable compounds capable of converting light to heat are preferably infrared absorbing components, provided that the absorption of the compound used is within the wavelength range of the light source used for image-wise exposure. The absorption wavelength is not particularly important. Particularly useful compounds are, for example, dyes and especially infrared dyes, carbon black, metal carbides, borides, nitrides, carbonitrides, bronze-structured oxides and oxides structurally related to the bronze family but lacking the A component. For example, WO _2.9 . It is also possible to use conductive polymer dispersions, for example conductive polymer dispersions based on polypyrrole or polyaniline.
The lithographic performance obtained, and especially the print resistance, depends on the heat sensitivity of the imaging element. In this regard, carbon black has been found to give very good and favorable results.

The light-to-heat conversion compound of the present invention is most preferably added to the imaging layer, although at least a portion of the light-to-heat conversion compound may be included in nearby layers. Such a layer can be, for example, a crosslinked hydrophilic layer of a lithographic base according to the second aspect of the lithographic base described above.

According to the method of the invention for producing lithographic printing plates, the imaging element according to the invention is image-wise exposed and then preferably developed by rinsing it with fresh water or an aqueous liquid. The resulting imaged imaging element is then globally heated for maximum print resistance.

During image-wise exposure, a compound capable of converting light into heat absorbs the light used for image exposure and converts it into heat, which in the image-forming layer produces a thermal image-pass. To generate the pattern. As a result of this heat, the hydrophobic thermoplastic polymer particles coagulate and render the imaging layer insoluble in fresh water or aqueous liquid, while the unexposed parts remain soluble in fresh water or aqueous liquid. is there.

After development, overall heating of the imaged imaging element will result in a substantial improvement in abrasion resistance of the printed portion during printing.

It is particularly advantageous in connection with the present invention to apply the rubber before subjecting the imaged imaging element to the overall heat treatment. This will ensure hydrophilicity in the non-printed areas, especially when anodized aluminum is used as the lithographic base. Rubbers suitable for this purpose are known and are for example Polychrome PC965 ^™ (P
Olychrome) is commercially available.

Image-wise exposure in the context of the present invention is preferably an image-wise scanning exposure involving the use of a laser or LED. It is highly preferred in the context of the present invention to use a laser which emits in the infrared (IR) and / or the near infrared, ie emits in the wavelength range 700-1500 nm. Lasers emitting in the near infrared are particularly preferred for use with the present invention.

The preferred imaging apparatus suitable for image-wise scanning exposure according to the present invention is preferably directly feedable to the imaging element surface via a lens or other ray-guiding element or at a remote location. It includes a laser output that can be transmitted from the lens to the surface of the blank imaging element using a fiber optic cable. An adjuster and associated positioning hardware keeps the light output in the correct orientation with respect to the imaging element surface, causes the output to scan over the surface, and causes the laser at a location adjacent to a selected point or portion of the imaging element. Activate. The controller responds to an input image signal corresponding to the original document and / or picture to be copied onto the imaging element to form an exact negative or positive image of that original. The image signal is stored as a bitmap data file on the computer. Such files are raster image processors (RI
P) or other suitable means. For example, a RIP is a page-written language or a combination of a page-written language and one or more image data files that defines all of the features required to transfer input data onto an imaging element, Can receive. The bitmap is configured to define the tone and screen number and angle in the case of amplification adjustment screening. However, in the present invention, for example, EP-
A 571010, EP-A 620677 and EP-
It is particularly suitable for use in combination with the number adjusted screening disclosed in A 620674.

The imaging device can be configured as a flat bed recorder or as a drum recorder and has the imaging element mounted on the inner or outer cylindrical surface of the drum.

In the preferred drum construction, the drum (and the imaging element mounted thereon) is rotated about its axis and the light beam is moved parallel to the axis of rotation, thereby circumferentially moving the imaging element. Image "grows" axially when scanned
By doing so, the required relative movement between the laser beam and the imaging element is obtained. Alternatively, moving the light rays parallel to the drum axis and increasing the angle after each pass over the imaging element causes the image on the imaging element to "grow" in the circumferential direction. In both cases, an image corresponding to the original will have been applied to the surface of the imaging element after complete scanning and development with light. In the flatbed construction, light rays are drawn over one axis of the formable element and directed along the other axis after each pass. Of course, the required relative movement between the ray and the imaging element may be caused by (in addition to) movement of the imaging element rather than movement of the ray.

Regardless of how the beam is scanned, it is generally preferred (for speed reasons) to use multiple lasers and direct their output into one writing train. After completion of each pass over or along the imaging element, the writing train is then separated by a distance determined by the number of rays emanating from the train and by the desired resolution (ie the number of image points per unit length). Be instructed.

The invention will now be illustrated by the following examples without the intention to limit the invention thereto. All parts are by weight unless otherwise indicated.

[0047]

【Example】

Example 1 Production of a lithographic base A foil was degreased by immersing a 0.2 mm thick aluminum foil in an aqueous solution containing 5 g / l sodium hydroxide at 50 ° C. and rinsed with demineralised water. The foil is then subjected to an alternating current in an aqueous solution containing 4 g / l hydrochloric acid, 4 g / l hydroboric acid and 0.5 g / l aluminum ion at a temperature of 35 ° C. and 120 ° C.
Electrochemically grained at a current density of 0A / m ^2, to form a surface topography with an average center-line roughness R _a of 0.5 [mu] m.

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

The foil is then placed in an aqueous solution containing 200 g / l sulfuric acid at a temperature of 45 ° C., a voltage of about 10 V and 150 A.
Solution / at a current density of m ² over the anodic oxidation for about 300 seconds to form an anodic oxidation film of Al ₂ O ₃ of 3 g / m ^2, then washed with demineralized water, containing sodium bicarbonate 20 g / l At 40 ° C. for 30 seconds, then rinsed with demineralized water at 20 ° C. for 120 seconds and dried.

The lithographic base obtained was immersed in an aqueous solution containing 5% by weight of citric acid at 50 ° C. for 60 seconds, rinsed with demineralized water and dried.

Preparation of the imaging element (material) The following coating composition was prepared and applied to the above lithographic base in an amount of 30 g / m ² (wet coating amount).
An imaging element according to the present invention was prepared by coating at 50 ° C. and drying it at 35 ° C.

Preparation of coating composition 12.5 g of a 10% dispersion of polymethylmethacrylate (particle diameter 90 nm) stabilized with Hostapal ^™ B (1% based on polymer) in deionized water, with stirring. 5.8
15% dispersion of 3 g carbon black in water, 57.9
2 g of water and 25 g of a 2% solution of 98% hydrolyzed polyvinyl acetate were added successively.

Production of Printing Plates and Printed Copies Therewith The above imaging elements were subjected to image-wise scanning exposure using an infrared laser diode emitting at 830 nm.
The scanning speed was 1 m / sec, the spot size was 10 μm and 120 mW on the plate surface. The imaging element is then filled with water to a Hydroprint ^™ water treatment system (Agfa-Gev
aert NV).

The obtained printing plate was then treated with Heide equipped with K + E125 ink and Rotamatic ^™ as fountain solution.
Installed on a lberg GTO46 ^™ offset printing machine. 3000 copies were obtained with no ink receptivity in the non-image areas. After that, printing was no longer possible due to damage to the image areas.

Example 2 A printing plate was prepared as described in Example 1 except that the plate was heated at 200 ° C for 2 minutes after development. Next, when printing was performed under the same conditions as in Example 1, 15,000 copies were printed without observing any damage to the image portion, and no damage was observed even after these 15,000 copies.

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Claims (9)

[Claims] 1. (1) (i) a hydrophobic polymer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder on a hydrophilic surface of a lithographic base, the hydrophobic being contained in an imaging layer. Of the thermosetting thermoplastic polymer particles is 35% by weight based on the total weight of the image forming layer.
Image-wise exposing an imaging element comprising more imaging layers and (ii) a compound capable of converting light contained in the imaging layer or layers adjacent thereto to heat, 2) developing the image-wise exposed imaging element thus obtained with fresh water or an aqueous liquid, (3) and heating the imaged imaging element thus obtained totally A method of manufacturing a lithographic printing plate comprising the step of: 2. The compound capable of converting light into heat is selected from the group consisting of infrared absorbing dyes, carbon black, metal borides, metal carbides, metal nitrides, metal carbonitrides and conductive polymer particles. The method of claim 1 selected. 3. The method of claim 1 wherein said lithographic base is anodized aluminum or comprises a flexible support having thereon a crosslinked hydrophilic layer. 4. The thermoplastic polymer particles are at least 35.
A method according to any of claims 1 to 3 having a coagulation temperature of ° C. 5. The group in which the hydrophilic binder in the image-forming layer comprises polyvinyl alcohol, poly (meth) acrylic acid, poly (meth) acrylamide, hydroxyethyl poly (meth) acrylate, polyvinyl methyl ether, and a polysaccharide. The method according to any one of claims 1 to 4, selected from 6. The group of said hydrophobic thermoplastic polymer particles consisting of polyethylene, polystyrene, methyl poly (meth) acrylate, polyvinyl chloride, ethyl poly (meth) acrylate, polyvinylidene chloride, polyacrylonitrile and polyvinylcarbazole. The method according to any one of claims 1 to 5, selected from 7. The method of claim 1, wherein the image-wise exposure is a scanning exposure. 8. The method according to claim 7, wherein the scanning exposure is performed by a single laser or a plurality of lasers. 9. The method of claim 1 wherein the imaged imaging element is treated with rubber prior to global heating.