JP2894549B2 - Thermosensitive imaging element and method of making a printing plate therewith - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention involves the use of a heat-sensitive imaging element and relates to a method of making a printing plate that 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 areas that receive ink form the printed image areas and the ink-reject areas form the background areas.

In photolithographic techniques, photographic materials are 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 called surface lithographic or planographic printing plates, a photosensitive composition is provided on a support which has an affinity for water or which obtains such an affinity by chemical treatment. Coating. Coatings for this purpose include photopolymer layers containing diazo compounds, hydrophilic colloids sensitized with dichromates and various synthetic photopolymers. In particular, diazo-sensitized systems are widely used.

With image-wise exposure of the photosensitive layer, the exposed image areas become insoluble and the unexposed areas remain soluble. The plate is then developed using a suitable liquid,
The unexposed portion of the diazonium salt or diazo resin is removed.

[0006] Commercially available diazo-based printing plates most commonly use them as supports with hydrophilic surfaces, since anodized and roughened aluminum offers the advantage of high print resistance. . A particular disadvantage of such types of printing plates is that they require a special developer which is expensive and inconvenient for development.

[0007] EP-A 601240 discloses a diazo-based printing plate using as a lithographic base a polyester film provided with a cross-linked hydrophilic layer provided with a photosensitive diazo layer on top. I have. Such a diazo-based printing plate can be developed by rinsing it with fresh water after image-wise exposure.

[0008] Commercially available plates using a flexible support such as paper, for example, provided with a hydrophilic layer are also available. For example, Li
thocraft 10008 FOTOPLATE ^™ is a printing plate comprising a paper support and a hydrophilic layer on top of which is provided a diazo-based photosensitive layer. According to the supplier's plate instructions, the imagewise exposure of the lithographic printing plate precursor, i.e. the imaging element, the installation of the exposed imaging element on a printing machine and the L
Ithocraft 10008 Plates can be manufactured by wiping with a development desensitizer. Plate instructions also consider a method that does not use a development desensitizer. However, such methods very often result in poor lithographic performance, so in practice a development desensitizer is almost always required.

A particular disadvantage of the above-described diazo-based printing plates, which is usually independent of the type of lithographic base used, is that they must be shielded from light. In addition, diazos are of insufficient sensitivity to be exposed by commercial, economical lasers.

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

[0011] EP 514.145 uses a heat-sensitive imaging element comprising an imaging layer comprising core-shell particles and a light-to-heat conversion material on a lithographic base such as anodized aluminum. It describes a method for producing a printing plate. The shell of these particles is hydrophilic and makes the particles developable. The wick is hydrophobic and flows out on heating. Thus, with image-wise exposure using an infrared laser diode, the image forming layer can be rendered insoluble in the exposed areas. In the areas that have not been exposed, the imaging layer can be removed with an aqueous developing agent containing ethanolamine. Continue to bake the ingredients. Although such printing plates produce high print resistance, their development places a burden on the environment due to the use of alkanolamines.

[0012]

SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide a heat sensitive composition for producing printing plates which can be developed in a simple and environmentally friendly manner and which can be exposed by commercially available lasers. Is 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 a printing plate having high printing resistance.

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

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 image forming layer. The amount of the 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 adjacent layers to heat. (2) developing the image-wise exposed image-forming element thus obtained with fresh water or an aqueous liquid; and (3) developing the image-formed image-forming element obtained in this way. The present invention provides a method for producing a lithographic printing plate, comprising a step of heating.

[0016]

DETAILED DESCRIPTION OF THE INVENTION An imaging element for use in accordance with the present invention comprises, on a hydrophilic surface of a lithographic base, hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder.
The hydrophilic binder used in connection with the present invention is preferably uncrosslinked or only slightly crosslinked. The imaging element also includes a compound that can convert light to heat. The compound is preferably included in the imaging layer, but may be provided in a layer adjacent to the imaging layer.

According to one aspect of the present invention, the lithographic base can be anodized aluminum. A particularly preferred lithographic base is an electrochemically granulated 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 performed 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 present invention, the lithographic base comprises a flexible support, such as paper or plastic film, provided with a cross-linked hydrophilic layer. 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 the hydrophilic binder, hydrophilic (co) polymers such as vinyl alcohol, acrylamide, methylolacrylamide, methylolmethacrylamide,
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 at least equal to or greater than the hydrophilicity of the polyvinyl acetate hydrolyzed to at least 60% by weight, preferably to the extent of 80% by weight. high.

The amount of crosslinking agent, in particular tetraalkyl orthosilicate, is preferably at least 0.2 parts 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 increase the mechanical strength and the porosity of the layer. Colloidal silica can be used for this purpose. The colloidal silica used can be, for example, in the form of a commercial aqueous dispersion of colloidal silica having an average particle size of up to 40 nm, for example 20 nm. In addition, inert particles larger in size than colloidal silica, such as J. Colloid and Inte
rface Sci., Vol. 26, 1968, pages 62 to 69, silica or aluminum particles or particles of titanium dioxide or other heavy metal oxides having an average diameter of at least 100 nm, which are prepared according to the Stoeber method. , Can also be added. By adding these particles, the surface of the cross-linked hydrophilic layer is given a uniform rough texture consisting of microscopic dimensional irregularities,
They act as storage for water in the background.

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

Specific examples of cross-linked hydrophilic layers suitable for use according to this embodiment are EP-A 601 240, GB-
P-1419512, FR-P-2300354, US
-P-397660, US-P-4284705 and EP-A 514490.

As the lithographic base flexible support for this embodiment, use may be made of a plastic film, for example, a polyester such as a polyethylene terephthalate film or a polyethylene naphthalate film, a cellulose acetate film, a polystyrene film, a polycarbonate film, etc. Is particularly preferred. 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 image forming layer. The imaging layer according to the present invention comprises thermoplastic polymer particles dispersed in a hydrophilic binder.

[0027] Hydrophilic binders suitable for use in the imaging layer according to the present invention are preferably those containing a reactive group, such as a hydroxy, amine or carboxy group. Specific examples of hydrophilic binders are synthetic homo or copolymers,
For example, polyvinyl alcohol, dimethylhydantoin
Formaldehyde resins, poly (meth) acrylic acid, poly (meth) acrylamide, hydroxyethyl poly (meth) acrylate, polyvinyl methyl ether, or natural binders such as gelatin, polysaccharides such as dextran,
Pullulan, cellulose, gum arabic, alginic acid.

[0028] 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.

[0029] 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 the 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 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, so that in these areas the hydrophilic layer is in fresh water or aqueous liquid. Becomes insoluble.

Specific examples of hydrophobic polymer particles for use in connection with the present invention include, for example, polystyrene, polyvinyl chloride, polymethyl methacrylate, polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole, and the like, or copolymers thereof. And / or mixtures.
Polymethyl methacrylate is most preferably used.

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

The hydrophobic particles are 0.01 μm to 50 μm,
More preferably it may 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 a dispersion in the aqueous coating solution of the imaging layer and are disclosed in US-P-3.4.
It can be produced by the method disclosed in 76.937.
Other methods particularly suitable for producing aqueous dispersions of thermoplastic polymer particles include: dissolving a hydrophobic thermoplastic polymer in a water-immiscible organic solvent; Dispersing in water or 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% by weight and more preferably greater than 50% by weight and most preferably the total weight of the imaging layer. Is greater than 65% by weight.

Suitable compounds capable of converting light into 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 those 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 according to the present invention is most preferably added to the imaging layer, but at least a portion of the light-to-heat conversion compound may be contained in a nearby layer. Such a layer can be, for example, a lithographic base cross-linked hydrophilic layer according to the second aspect of the lithographic base described above.

According to the method of the invention for producing a lithographic printing plate, an 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 heated globally to obtain the best print durability.

During image-wise exposure, compounds capable of converting light to heat absorb the light used for imagewise exposure and convert it to heat to form a heat-imageable layer in the imaging layer. Generate the pattern of As a result of this heat, the hydrophobic thermoplastic polymer particles coagulate and render the imaging layer insoluble in fresh water or aqueous liquids, but the unexposed portions remain soluble in fresh water or aqueous liquids. is there.

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

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

The image-wise exposure according to the present invention is preferably an image-wise scanning exposure involving the use of a laser or LED. It is highly preferred for the present invention to use a laser that emits in the infrared (IR) and / or near infrared, that is to say in the wavelength range from 700 to 1500 nm. Lasers that emit in the near infrared are particularly preferred for use with the present invention.

Preferred imaging devices suitable for image-wise scanning exposure according to the present invention are preferably either directly feedable to the imaging element surface via a lens or other light-guiding component or are at a remote location. 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 keep the beam output in the correct orientation relative to the imaging element surface, scan the output over the surface, and direct the laser at a location adjacent to a selected point or portion of the imaging element. Activate. The adjuster forms an accurate negative or positive image of the original in response to an input image signal corresponding to the original document and / or picture to be copied on the imaging element. The image signal is stored as a bitmap data file on a computer. Such files are stored in a raster image processor (RI
P) or other suitable means. For example, the RIP converts input data in a page-description language or as a combination of a page-description language and one or more image data files that defines all of the features required to transfer the data on the 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, the present invention, for example, EP-
A 571010, EP-A 620677 and EP-A
Particularly suitable for use in combination with the number-adjusted screening disclosed in US Pat.

The imaging device can be configured as a flatbed recorder or as a drum recorder and has imaging elements mounted on the inside or outside cylindrical surface of the drum.

In a preferred drum configuration, 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 causing the imaging element to move circumferentially. When scanned, the image "grows" in the axial direction
By doing so, the required relative movement between the laser beam and the imaging element is obtained. Alternatively, moving the light beam 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, after complete scanning and development by the light beam, an image corresponding to the original will have been applied to the surface of the imaging element. In a flat-bed configuration, light rays are drawn across one axis of the buildable element and are directed along the other axis after each pass. Of course, the necessary relative movement between the light beam and the imaging element may be caused by (in addition to) the movement of the imaging element rather than the movement of the light beam.

Regardless of how the light beam is scanned, it is generally preferred (for speed reasons) to use multiple lasers and to direct their output to a single writing column. After completion of each pass over or along the imaging element, the writing column is then moved by a distance determined by the number of rays emanating from the column 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, which are not intended to limit the invention thereto. All parts are by weight unless otherwise indicated.

[0047]

【Example】

Example 1 Preparation of a lithographic base The foil was degreased by dipping 0.2 mm thick aluminum foil in an aqueous solution containing 5 g / l of sodium hydroxide at 50 ° C. and rinsed with demineralized water. The foil is then heated using 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 demineralized 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 rinsed with demineralized water at 25 ° C. for 30 seconds.

The foil was then placed in an aqueous solution containing 200 g / l of 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 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 invention was prepared by coating at 35 ° C. and drying it at 35 ° C.

Preparation of Coating Composition To 11.25 g of a 10% dispersion of polymethyl methacrylate (particle diameter 90 nm) stabilized with Hostapal ^™ B (1% based on polymer) in deionized water, with stirring. , 5.8
3 g of a 15% dispersion of 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 the printing plate and the printed copy using it The image-forming element described above was subjected to an 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 by a Hydroprint ^™ water processor (Agfa-Gev
aert NV).

The printing plate obtained was then subjected to a Heide equipped with K + E125 ink and Rotamatic ^™ as fountain solution.
lberg Installed on GTO46 ^TM offset printing press. 3000 copies were obtained without ink receptivity in the non-image areas. Printing was no longer possible due to damage to the image area.

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

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI G03F 7/30 G03F 7/30 7/40 501 7/40 501 (56) References JP-A-7-306528 (JP, A) JP-A-9-120164 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03F 7/004 505 B41C 1/055 501 G03F 7/00 503 G03F 7/033 G03F 7/20 505 G03F 7/30 G03F 7/40 501

Claims (9)

(57) [Claims] (1) (i) comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder on a hydrophilic surface of a lithographic base, wherein the hydrophobic thermoplastic polymer particles are contained in an image forming layer. 35% by weight of the total weight of the image forming layer
Exposing the imaging element comprising more imaging layers and (ii) a compound capable of converting light contained in said or adjacent layers to heat, image-wise; 2) developing the image-wise exposed imaging element thus obtained using fresh water or an aqueous liquid, and (3) heating the imaged imaging element thus obtained entirely A method for producing a lithographic printing plate comprising the steps 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, which is selected. 3. The method of claim 1 wherein said lithographic base is anodized aluminum or comprises a flexible support having a hydrophilic layer crosslinked thereon. 4. The method of claim 1, wherein said thermoplastic polymer particles have at least 35 particles.
The method according to any of the preceding claims, having a coagulation temperature of ° C. 5. The group wherein 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 polysaccharide. A method according to any of the preceding claims, selected from: 6. The group of hydrophobic thermoplastic polymer particles comprising polyethylene, polystyrene, poly (methyl meth) acrylate, polyvinyl chloride, ethyl poly (meth) acrylate, polyvinylidene chloride, polyacrylonitrile and polyvinyl carbazole. The method according to any one of claims 1 to 5, wherein the method is selected from: 7. The method of claim 1, wherein said imagewise exposure is a scanning exposure. 8. The method according to claim 7, wherein said scanning exposure is performed by a single laser or a plurality of lasers. 9. The method of claim 1 wherein said imaged imaging element is treated with rubber prior to global heating.