JP2000218954A - Heat-sensitive material having improved sensitivity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-treated heat-sensitive image forming material having improved sensitivity to manufacture a lithographic printing plate having excellent printability. SOLUTION: The heat-sensitive material comprises a first image forming layer containing a hydrophilic binder, a crosslinker for the binder and dispersed hydrophobic thermoplastic polymer particles, and a heat switchable image forming layer containing a heat switchable polymer as an uppermost image forming layer on a lithographic printing support. In this case, the uppermost layer or the layer adjacent to the uppermost layer contains a compound for converting a light into a heat, and the switchable polymer contains a polymer containing an aryldiazosulphonate unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to heat-sensitive materials for making lithographic printing plates.

More specifically, the present invention relates to a processless process which provides a lithographic printing plate with high sensitivity.
s) relating to heat-sensitive materials.

[0003]

BACKGROUND OF THE INVENTION Lithographic printing is a method of printing from a specially made surface in which some areas can accept ink, while others do not.

[0004] In the field of photolithographic printing, photographic materials are image-wise oily or inky on ink repellent backgrounds in exposed areas (negative-working) or in unexposed areas (positive-working). Acceptable for greasy inks.

In the preparation of conventional lithographic printing plates, also referred to as surface lithographic printing plates or planographic printing plates, a support which has an affinity for water or which has such an affinity by chemical treatment is exposed to light. A thin layer of the composition is coated. Coatings for that purpose include photopolymer layers containing diazo compounds, dichromate-sensitized hydrophilic colloids and various synthetic photopolymers.
In particular, diazo-sensitized systems are widely used.

When such a photosensitive layer is image-wise exposed, the exposed image areas become insoluble and the unexposed areas remain soluble. The plate is then developed using a suitable solution to remove the diazonium salt or diazo resin in the unexposed areas.

[0007] On the other hand, methods are known for making printing plates that involve the use of imaging elements that are heat-sensitive rather than light-sensitive. A particular disadvantage of the photosensitive imaging element as described above for the preparation of a printing plate is that it must be shielded from daylight. Furthermore, they have the problem of unstable sensitivity with respect to storage time, and they exhibit relatively low resolution. There is a clear trend in the market towards heat-sensitive printing plate precursors.

For example, Research of January 1992
h Disclosure no. No. 33303 discloses a heat-sensitive imaging element comprising on a support a crosslinked hydrophilic layer containing thermoplastic polymer particles and an infrared absorbing pigment, for example carbon black. By image-wise exposure to an infrared laser, the thermoplastic polymer particles coagulate image-wise, thereby rendering the surface of the imaging element in these areas ink-receiving without further development. A disadvantage of this method is that the resulting printing plate is easily damaged, since it can become ink-receptive if some pressure is applied to the non-printing areas. Furthermore, under critical conditions, the lithographic performance of such printing plates can be poor, and thus such printing plates have little lithographic printing latitude.

Further, EP-A-770 494, 77
0 495, 770 496 and 770 497 are
(1) (i) an image-forming layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder on a hydrophilic surface of a lithographic base; and (ii) an image-forming layer or a layer adjacent thereto. Exposing a heat-sensitive imaging element containing a compound capable of converting light to heat to image-wise light; (2) developing the image-wise exposed element thus obtained by rinsing it with fresh water Discloses a method for making a lithographic printing plate comprising:

The above-described heat-sensitive imaging elements for making lithographic printing plates are not optimal with respect to sensitivity.

EP-A-771 645 includes: (1) imagewise exposing an imaging element having a photosensitive layer containing a photosensitive polymer containing aryldiazosulfonate units on a hydrophilic surface of a lithographic base; B) mounting the image-forming element thus obtained on a printing cylinder of a printing press and supplying an aqueous dampening solution and / or ink to the photosensitive layer while rotating the printing cylinder. Discloses a method for making a lithographic printing plate comprising the step of developing a lithographic printing plate.

[0012] The sensitivity of such imaging elements could be improved.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a process for preparing a lithographic printing plate having excellent printability.
ss) to provide a heat-sensitive imaging material.

It is a further object of the present invention to provide a heat-sensitive imaging material for making a lithographic printing plate having an improved sensitivity of the imaging material.

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

[0016]

SUMMARY OF THE INVENTION In accordance with the present invention, a first imaging layer comprising a hydrophilic binder, a crosslinking agent for the hydrophilic binder and dispersed hydrophobic thermoplastic polymer particles, and a top imaging layer A heat switchable imaging layer comprising a heat switchable polymer as a layer is provided on the lithographic printing support, wherein the top imaging layer or a layer adjacent to the top imaging layer heats light. Wherein the thermally switchable polymer is a polymer containing an aryldiazosulfonate unit, and wherein the heat-sensitive material for preparing a lithographic printing plate is provided.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The higher sensitivity of the imaging element can be advantageously used in several ways. First,
In addition, the exposure time for image formation can be further reduced, and the output of the image forming apparatus can be increased. In the second method, it is possible to lower the output of the exposure source and prolong the life of the exposure source.

Layers which become more hydrophilic or more water-soluble under the influence of heat, or become more hydrophobic or less water-soluble, on the other hand, are called thermally switchable layers. The compound responsible for the polarity switching is called a thermally switchable compound.

The top imaging layer, which becomes more lipophilic under the influence of heat, comprises a polymer or copolymer containing aryldiazosulfonate units.

The thermally switchable polymer having aryldiazosulfonate units, also called aryldiazosulfonate resin, preferably has the formula:

[0021]

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Wherein R ⁰ , ¹ and ² each independently represent hydrogen, an alkyl group, a nitrile or a halogen such as Cl; L represents a divalent linking group; n represents 0 or 1;
A represents an aryl group, and M represents a cation], and has a corresponding aryldiazosulfonate unit.

L is preferably:-(X)_t-CONR
^Three-,-(X)_t-COO-, -X- and-(X)_t-C
A divalent linking group selected from the group consisting of O-
And t represents 0 or 1, and R ^ThreeIs hydrogen, an alkyl group or
X represents an aryl group, X represents an alkylene group, an arylene group,
Alkyleneoxy group, aryleneoxy group, alkylene
Thio group, arylenethio group, alkyleneamino group, ant
-Represents an amino group, oxygen, sulfur or an amino group.

A is preferably an unsubstituted aryl group, such as an unsubstituted phenyl group or more preferably one or more alkyl, aryl, alkoxy,
An aryloxy group or an aryl group substituted with an amino group, for example, phenyl is shown.

M preferably denotes NH ₄ ⁺ or a cation such as a metal ion, for example Al, Cu, Zn, a cation of an alkaline earth metal or an alkali metal.

The polymers having aryldiazosulfonate units are preferably obtained by radical polymerization of the corresponding monomers. Suitable monomers for use according to the invention are EP-A-339 393 and EP-A-50
7,008. Specific examples are as follows:

[0027]

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[0028]

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[0029]

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[0030]

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For example, the aryldiazosulfonate monomers as disclosed above may be homopolymerized, or other aryldiazosulfonate monomers and / or vinyl monomers such as (meth) acrylic acid or its esters, (meth) acrylamide, acrylonitrile, It can be copolymerized with vinyl acetate, vinyl chloride, vinylidene chloride, styrene, alpha-methylstyrene and the like. However, in the case of copolymers, care must be taken not to impair the water solubility of the polymer.
Preferably, the amount of aryldiazosulfonate-containing units in the copolymer associated with the present invention is between 10 mol% and 60 mol%.

According to another aspect related to the present invention, an aryldiazosulfonate-containing polymer can be prepared, for example, by reacting a polymer having an acid group or acid halide group with an amino or hydroxy substituted aryldiazosulfonate. Further details regarding this method can be found in EP-A-507008.

The uppermost image forming layer or a layer adjacent to the uppermost image forming layer
Including compounds that can convert to heat. Suitable for converting light into heat
The compound obtained is preferably an infrared absorbing component,
Light source used for image-wise exposure of the compound to be absorbed
The absorption wavelength is not particularly important as long as it is within the above wavelength range.
Particularly useful compounds are, for example, dyes and especially infrared absorption
Dyes and pigments and especially infrared absorbing pigments.
Examples of infrared absorbing dyes are EP-A-97 203 13
1.4. An example of an infrared absorbing pigment is carbohydrate
Black, metal carbide, boride, nitride, carbonitriding
, Bronze-structured oxides and structurally bronze groups
Oxides that are linked but have no A component, such as WO _2.9It is.
Conductive polymer dispersions, such as polypyrrole or polya
It is also possible to use conductive polymer dispersions based on nilin
Wear. The compound capable of converting light into heat is preferably
Present in the imaging layer but contained in adjacent layers
You can also.

The compound capable of converting light to heat is preferably present in an amount of from 1 to 40% by weight of the total weight of the uppermost imaging layer.
More preferably, it is present in the imaging element in an amount of from 2 to 30% by weight of the total weight of the top imaging layer. The compound capable of converting light into heat is most preferably 700 nm to 1500 n.
It is present in the uppermost imaging layer in an amount that gives an optical density of at least 0.35 at a wavelength of m.

The uppermost image forming layer is preferably 0.1 to 5 g.
In an amount of / m ^2, more preferably it is applied in an amount of 0.5 to 3 g / m ^2.

According to the present invention, in order to improve sensitivity and throughput and avoid scum formation, 40 nm to 150 nm
An imaging element comprising a first imaging layer containing hydrophobic thermoplastic polymer particles having a preferred average particle size. More preferably, 40 nm to 80 n
Hydrophobic thermoplastic polymer particles having an average particle size of m are used. Further, the hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a temperature above 50 ° C.
More preferably the coagulation temperature (coagul) above 70 ° C
ation temperature). Coagulation may result from softening or melting of the thermoplastic polymer particles under the influence of heat. There is no specific upper limit for the coagulation temperature of the thermoplastic hydrophobic polymer particles, but the temperature must be well below the decomposition temperature of the polymer particles. The coagulation temperature is preferably at least 10 ° C. below the temperature at which the decomposition of the polymer particles takes place. When the polymer particles are subjected to temperatures above the coagulation temperature, they coagulate to form hydrophobic agglomerates in the hydrophilic layer, at which point the hydrophilic layer becomes hydrophobic and lipophilic.

[0037] Particular examples of hydrophobic polymer particles for use in connection with the present invention have a Tg of greater than 80 ° C. Preferably, the polymer particles are selected from the group consisting of polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole, etc., copolymers or mixtures thereof. Most preferably used are polystyrene, polymethyl methacrylate or copolymers thereof.

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

The polymer particles are present as a dispersion in the aqueous coating solution of the image forming layer and are disclosed in US Pat.
937 can be prepared. Other methods particularly suitable for the preparation of aqueous dispersions of thermoplastic polymer particles are:-dissolving a hydrophobic thermoplastic polymer in a water-immiscible organic solvent;-dissolving the solution thus obtained in water or aqueous Dispersing in a medium; removing the organic solvent by evaporation.

The amount of hydrophobic thermoplastic polymer particles contained in the image forming layer is preferably at least 10% by weight, more preferably at least 15% by weight of the total weight of the layer.
And most preferably at least 20% by weight.

Suitable hydrophilic binders for use in the first imaging layer in connection with the present invention are water-soluble (co) polymers, such as synthetic homo- or copolymers, such as polyvinyl alcohol, poly (meth) acrylic acid, Poly (meth) acrylamide, polyhydroxyethyl (meth) acrylate, polyvinyl methyl ether or natural binder,
For example, gelatin, polysaccharides such as dextran, pullulan, cellulose, gum arabic, alginic acid, inulin or chemically modified inulin.

The crosslinked hydrophilic binder in the first thermosensitive layer used in accordance with this embodiment may also be a substance which enhances the mechanical strength and porosity of the layer, such as particles of titanium dioxide or other metal oxide. It contains certain metal oxide particles having an average diameter of at least 100 nm. The introduction of these particles gives the surface of the crosslinked hydrophilic layer a uniform rough texture consisting of microscopic hills and valleys. Particularly preferred is 50 to 95% by weight of the heat-sensitive layer, more preferably 60 to 90% by weight of the heat-sensitive layer.
It is a titanium dioxide used in% by weight.

The first imaging layer also comprises a crosslinking agent such as formaldehyde, glyoxal, polyisocyanate or hydrolyzed tetra-alkyl orthosilicate. The latter is particularly preferred.

The first imaging layer preferably contains a surfactant, which can be anionic, cationic, non-ionic or amphoteric. Perfluorosurfactants are preferred. Particularly preferred are non-ionic perfluorosurfactants. The surfactants can be used alone or, preferably, in combination.

The weight of the first image forming layer is preferably from 1 to 1.
2 g / m ^2, more preferably in the range of 3~9g / m ^2.

The lithographic base of the present invention can be aluminum, for example, electrochemically and / or mechanically polished and anodized aluminum.

Further in connection with the present invention, the lithographic base can be a flexible support. As the flexible support relating to the present embodiment, a plastic film such as a substrate-based polyethylene terephthalate film, polyethylene naphthalate film, cellulose acetate film, polystyrene film, polycarbonate film, polyethylene film, polypropylene film, polyvinyl chloride film, polyether sulfone It is particularly preferred to use a film. The plastic film support can be opaque or transparent.

Further, paper or glass having a thickness of 1.2 mm or less can be used.

According to the present invention, the imaging element is image-wise exposed. During the exposure, the exposed areas are converted to hydrophobic and lipophilic areas, and the unexposed areas remain hydrophilic.

Imaging in connection with the present invention is preferably performed using an image-wise scanning exposure involving the use of a laser, more preferably an infrared or near infrared, ie, a laser operating in the wavelength range of 700 to 1500 nm. . Most preferred are laser diodes that emit in the near infrared. Exposure of the imaging element can be performed using a laser having a short pixel dwell time as well as a laser having a short pixel dwell time. Preferred are lasers having a pixel dwell time of 0.005 microseconds to 20 microseconds.

In another embodiment of the invention, the exposure of the imaging element can be performed using the imaging element already on the printing press. A computer or other source supplies graphic and textual information to the laser via leads.

The printing plate of the present invention can be used as a seamless sleeve printing plate in a printing process. This cylindrical printing plate has a diameter such that it can be slid over the printing cylinder. Further details on sleeves can be found in "GrafischNieuws" ed. Ke
esing, 15, 1995, page 4-6.

Following image-wise exposure, the image-wise exposed imaging element can be developed, preferably by washing with fresh water. The plate is then ready for printing and can be mounted on a printing press. However, in order to improve the durability, the plate is kept at 200 ° C to 30 ° C.
Baking can be performed at a temperature of 0 ° C. for 30 seconds to 5 minutes. The imaging element is subjected to an overall post-exposure to UV-radiation to cure the image and the run length of the printing plate.
angle) can be increased.

More preferably, the image-wise exposed image-forming element, optionally after wiping, is placed on the printing cylinder of a printing press with the back side of the image-forming element (the side of the support opposite the side having the photosensitive layer). Mount. According to one preferred embodiment, the printing press is then started and the dampening roller supplying the dampening liquid is lowered onto the imaging element while rotating the printing cylinder on which the imaging element is mounted, followed by the ink Lower the rollers. Generally, after about 10 revolutions of the printing cylinder, the first clean and usable print is obtained. According to another method, the ink roller and the dampening roller can be lowered simultaneously.

Preferably, the photosensitive layer of the image-wise exposed imaging element according to the invention is impregnated with, for example, water before mounting the imaging element on a printing press or at least before starting the printing press. Wipe with a wet cotton pad or sponge. This will remove some unexposed aryldiazosulfonate resin, but will not substantially develop the imaging element. However, it has the advantage that possible substantial contamination of the dampening system of the printing press and of the ink used is avoided.

The imaging element exposed according to the invention is preferably mounted on a printing press shortly after exposure and used for printing. However, it is possible to store the exposed imaging element in the dark for some time before using it on a printing press for printing a copy.

Suitable fountain solutions which can be used in connection with the present invention are aqueous solutions which generally have an acidic pH and comprise an alcohol such as isopropanol and silica. Dampening liquids useful in the present invention
There are no specific restrictions on the uids,
Commercially available dampening fluids, also known as taint solutions, can be used.

The invention will now be illustrated by the following examples, which are not intended to limit the invention. All parts are by weight unless otherwise specified.

[0059]

EXAMPLE 1 A first imaging layer is coated from water on a primed polyester substrate to give a heat-sensitive, cross-linked hydrophilic layer having the following composition: 3.94 g / m ² TiO. ₂ (average particle size 0.3-0.5 μm), 0.44 g / m ² polyvinyl alcohol, 2.00 g / m ² hydrolyzed tetramethyl orthosilicate and 1.49 g / m ² polystyrene latex. After coating, the layers
° C and 34% R.C. Cured in H for 7 days.

An azosulfonate layer was coated from methanol on the crosslinked first layer to give an IR-sensitive layer having the following composition: 0.072 g / m ² IR-
Dye 1 and a copolymer P20 containing 0.720 g / m ² of 20 mol% of azosulphonate 1 and 80 mol% of methyl methacrylate.

[0061]

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Synthesis of Diazosulfonate-Containing Polymer P20 Synthesis of Monomer A The azo-group-containing material must be protected from light, for example, by darkening the chamber or wrapping the flask with aluminum foil. Reagents are Fluka and Ald
, and the solvent was distilled before use. a) Preparation of three solutions 1 Dissolve 24 g of sodium sulfite and 40 g of sodium carbonate in 250 ml of water. 2 15.02 g
P. Aminoacetanilide in 100 ml of water and 3
Dilute in 6.8 ml of concentrated HCl (32%) and cool to 0-5 ° C using a cooling bath. 3 Dilute 6.8 g of sodium nitrite in 15 ml of water. Solution 3 is added dropwise to solution 2 with cooling (less than 5 ° C.), then it is stirred for 10 minutes. After filtration, the solution is mixed under vigorous stirring with solution 1
Pour quickly into. The solution is then stirred for 30 minutes. The solution may be red at the start, but after a few minutes the color turns yellow. The solid product is filtered off from the solution and used without further purification. b) Dissolve the product in 150 ml of water and add 8 g of NaO
H is then added, and the solution is heated to 50 ° C. for 1 hour before
Cool to ° C. 19.66 ml of concentrated H while still cooling
Cl (32%) is added to the solution. Then 100ml of 1
% Picric acid and about 3%
A solution of 33.6 g of sodium carbonate in 50 ml of water is poured into the mixture. Before adding methacrylic acid chloride, the temperature of the solution must be below 5 ° C. From the dropping funnel 15 ml of methacrylic acid chloride are dripped very slowly into the solution (very foaming). Mix at 0-5 ° C for 1
Time and then at room temperature must be stirred for a further hour. Then 300 ml of a saturated solution of sodium acetate are added and the solution is stored overnight in a refrigerator (about 4 ° C.). The solid product is filtered and dried at 50 ° C. under reduced pressure for 17 hours. For the removal of inorganic salts, the product is
Dissolve in MF, stir at room temperature for at least 2 hours, and filter. For the precipitation, the filtrate is poured into 2 l of diethyl ether and then filtered. Very low moisture content (2.5
%) Requires drying at 50 ° C. under vacuum for 3 days. Synthesis of polymer P20 2.11 g of monomer A are first diluted in 10 ml of water and 3.1 g of methyl methacrylate and 0.300 g of azo-bis-isobutyronitrile and 40 ml of dioxane are added. The solution must be degassed several times to remove oxygen. The solution (protected from light) is then stirred at 70 ° C. for 17 hours. The polymerization is stopped by adding a small amount of hydroquinone, the solvent is evaporated and the polymer is redissolved in 80 ml of methanol.
The solution is added dropwise to 2 l of diethyl ether and then
And dry over phosphorus pentoxide under vacuum. After drying for 3 days, a polymer having a moisture content of 2.5% is obtained.

The resulting heat sensitive material was applied to a Creo 3244 Trendset operating at drum speeds of 40, 62, 80 and 112 rpm and a laser power of 11 watts.
Imaged at 2400 dpi on ter ^™ .

After image formation, K + E 80 was used as the ink.
The plate was mounted on an AB Dick ^™ press using 0 ^™ and water containing 2% Name ^™ as the dampening solution. Subsequently, the printing press was started by rotating the printing cylinder on which the heat-sensitive material was mounted. The dampening roller of the printing press is then lowered onto the imaging element to supply the dampening fluid to the heat-sensitive material,
After 10 rotations of the printing cylinder, the ink roller was lowered to supply ink. After a further 25 revolutions, a clean print was obtained with no ink absorption in the non-image areas. 80
At rpm, i.e. 242 mJ / cm < ² >, acceptable ink absorption in the IR-imaged area was observed.

Comparative Example 1 This comparative example corresponds to Example 1, but describes the results of a heat-sensitive material without azosulfonate on top.

The first layer was coated in the same manner as in Example 1.

On top of the crosslinked first layer a top layer having the following composition was coated from methanol: 0.07
2 g / m ² of IR-dye 1.

The resulting heat-sensitive material was image-formed and printed as in Example 1. 40 rpm, ie 48
At 5 mJ / m ² acceptable ink absorption in the IR-imaged area was observed.

COMPARATIVE EXAMPLE 2 This comparative example corresponds to Example 1 but without a first layer, ie without a layer containing hydrophobic thermoplastic polymer particles in the cross-linked hydrophilic binder. Describe the results.

The first imaging layer is coated from water on a primed polyester substrate to give a crosslinked hydrophilic layer having the following composition: 3.94 g / m ² TiO ₂
(Average particle size 0.3-0.5 μm), 0.44 g / m ² polyvinyl alcohol, 2.00 g / m ² hydrolyzed tetramethyl orthosilicate. After coating, the layer was brought to 57 ° C and 34% Cured in H for 7 days.

The azosulfonate layer was coated from methanol on the crosslinked first layer to give an IR-sensitive layer having the following composition: 0.072 g / m ² IR-
Dye 1 and a copolymer P20 containing 0.720 g / m ² of 20% by weight of azosulfonate 1 and 80% by weight of methyl methacrylate.

The resulting heat-sensitive material was image-formed and printed as in Example 1. 60 rpm, ie, 31
At 3 mJ / cm ² acceptable ink absorption in the IR-imaged area was observed.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Giyoan Vermeersch Belgium 2640 Malt Cell Septes Trat 27 Agfa-Gevert Na Mrose Hoennenjapp

Claims (1)

[Claims] Claims: 1. A first image forming layer comprising a hydrophilic binder, a crosslinking agent for the hydrophilic binder and dispersed hydrophobic thermoplastic polymer particles, and a thermally switchable top image forming layer. A heat switchable imaging layer comprising a polymer is provided on a lithographic printing support, wherein the top imaging layer or a layer adjacent to the top imaging layer comprises a compound capable of converting light to heat. A heat-sensitive material for preparing a lithographic printing plate, wherein the thermally switchable polymer is a polymer containing an aryldiazosulfonate unit.