JP2006501505A - Production of lithographic printing plate precursors - Google Patents

Abstract

(I) providing a web of a lithographic support having a hydrophilic surface; (ii) coating a layer comprising a phenolic resin on the hydrophilic surface of the web; (iii) drying the layer; iv) a heating step in which the web temperature is maintained above 150 ° C. for a period of 0.1 to 60 seconds, (v) winding the coated web on a core or cutting the coated web into sheets, A process for preparing a precursor for a heat-sensitive lithographic printing plate comprising the steps of is disclosed. A short online heating step results in a significant improvement in the aging kinetics of the precursor. Stable sensitivity can be obtained in a short time after coating.

Description

  The present invention relates to a heat-sensitive lithographic printing plate precursor comprising a phenolic resin.

  Lithographic printing generally involves the use of a so-called printing master such as a printing plate installed on a cylinder of a rotary printing press. The master carries a lithographic image on its surface, applies ink to the image, and then transfers the ink from the master onto a receiving material, typically paper, to obtain a print. In normal lithographic printing, inks and aqueous fountain solutions (also called damping liquids) are oleophilic (or hydrophobic, ie ink receptive, water repellant) and hydrophilic (or oleophobic, ie water). Supplied to a lithographic image comprising receptive and ink repellent parts. In so-called dry lithographic printing, a lithographic image is composed of ink receptive and ink non-adherent (ink repellency) portions, and only ink is supplied to the master during dry lithographic printing.

  Print masters are generally obtained by image-wise exposure and processing of imaging materials called printing plate precursors. In addition to the well-known, photosensitive, so-called pre-sensitized printing plates suitable for UV contact exposure through film masks, thermosensitive printing plate precursors have become very common in the late 1990s. It was. These heat-sensitive materials offer the advantage of sunlight stability, in particular used for so-called computer-to-plate printing from a computer where the printing plate precursor is directly exposed, ie without the use of a film mask Is done. The material is exposed to heat or infrared light, and the heat generated is (physical-) chemical processes [eg ablation, polymerization, insolubilization by polymer cross-linking, heat-induced solubilization or thermoplasticity Trigger particle aggregation of polymer latex].

  Although some of these thermal steps allow printing plate manufacture without wet processing, most common heat sensitive printing plates are alkaline developers between the exposed and unexposed portions of the coating. An image is formed by the difference in solubility induced by heat in the medium. The coating generally comprises a lipophilic binder, such as a phenolic resin, whose developer solubility is reduced (negative effect) or increased (positive effect) by imagewise exposure. During processing, the difference in solubility results in the removal of non-image (non-printed) portions of the coating, thereby revealing a hydrophilic support, while the imaging (printing) portion of the coating remains on the support. Typical examples of such printing plates are described in Patent Documents 1, 2, 3, 4, 5 and 6 (see Patent Documents 1, 2, 3, 4, 5 and 6).

  The industrial production of printing plate precursors involves unwinding a coil of support material in the form of a web, typically alumina, coating one or more layers on the web, and drying the coating by blowing hot air over the web. And finally rewinding the coated web onto the core or cutting the coated web into immediate sheets which are then stacked and packaged. On an industrial scale, all these steps are performed “on-line”, ie on a moving web in a single continuous operation without any intermediate storage.

A particular problem with thermosensitive printing plate precursors comprising phenolic resins is that the coating becomes progressively more resistant to the developer, and thus during the imaging exposure period, the imaging mechanism. Their sensitivity is not stable over time because it requires more heat to be applied. In general, a high sensitivity of, for example, less than 100 mJ / cm ² is obtained immediately after coating and then gradually decreases to reach an equilibrium value of, for example, 250 mJ / cm ² . The aging period required to reach a stable sensitivity can take several months after coating. In order to shorten the aging period, US Pat. No. 6,057,075 proposes a heat treatment by leaving the material for a long period of at least 4 hours and most preferably at least 48 hours shortly after coating in an oven at 40-90 ° C. (See Patent Document 7). US Pat. No. 6,057,059 suggests that shorter time processing is possible by heating the cut sheets individually or in spaced arrangements at higher temperatures, i.e. above the glass transition temperature of the composition. (See Patent Document 8). The high temperature preferably does not exceed 150 ° C. However, even at such high temperatures, it takes a few minutes to reach a stable sensitivity, so the heat treatment methods disclosed in the prior art cannot be carried out online: webs up to eg 50 m / min For example, a 5 minute heat treatment would extend the length of the coating array by 250 m because it can pass through a modern coating array at a speed of Thus, known heat treatment methods such as those described in US Pat. Nos. 5,077,097 and 5,797 can only be performed "off-line", i.e. a stack of coils or sheets is placed in an oven and there during the required time. It can only be retained. However, offline storage must be avoided for several reasons. Apart from the additional cost and logistical significance, it is quite obvious that the coil or stack cannot be heated uniformly because the inside of the coil or stack will go through a different temperature profile than the outside. Accordingly, there is a need for a method that provides an effective heat treatment that can be performed on-line before winding a web on a coil or cutting the web into sheets.
EP 625728 European Patent No. 823327 European Patent No. 825927 EP 864420 specification EP 894622 EP 901902 specification International Publication No. 99/21715 Pamphlet US Pat. No. 6,251,559

  It is an aspect of the present invention to provide an on-line method for aging a heat sensitive printing plate material comprising a phenolic resin. This object is achieved by the method of claim 1 characterized in that the dried coating is subjected to a short heating step. According to the present invention, the long-term heat treatment disclosed in the prior art and which can only be performed off-line is up to at least 150 ° C., preferably for a period of 0.1 to 60 seconds, more preferably 1 to 30 seconds, preferably Replaced by an on-line heating step that raises the web temperature to at least 170 ° C.

  The method of the present invention produces a heat sensitive printing plate precursor with stable sensitivity within a few weeks instead of months after production. Although further aging is not necessary, it is obvious that embodiments of combining a short on-line heating step according to the present invention with further off-line heat treatment are also within the scope of the present invention.

  Particular aspects of the present invention are defined in the appended claims.

  The heat-sensitive lithographic printing plate precursor of the present invention comprises a hydrophilic support and a coating comprising a phenolic resin provided thereon. The coating can consist of one or more layers, examples of which are discussed below. The phenolic resin can be present in one or more layers of the coating.

  All references herein to precursor temperature are considered to be references to the temperature of the support as well as the coating: in general, the coating is very thin in the numerical dimension of one or several micrometers, On the other hand the support has a typical thickness between 0.1 and 0.5 millimeters, so that the support, preferably a metal support, acts as a large heat sink to the coating, Regardless of whether the heating and cooling steps discussed herein are carried out by supplying heat or cooling to the coated side, back side, or both of the precursor, the temperature of the coating is equal to the temperature of the support. Equal to or very close to it. In fact, the temperature values reported here are obtained by installing a thermocouple device that can be read remotely against the back of the web as it moves through all sections of the coating facility. Recorded. In that way, an accurate temperature profile can be recorded during all stages of the method of the invention. Unless otherwise specified, all temperatures reported herein are web temperatures obtained from the thermocouple. In view of the above considerations, it will be apparent to those skilled in the art that the web temperature value is essentially equal to the temperature of the dry coating provided on the web.

  Any coating method can be used to apply one or more coating solutions to the hydrophilic surface of the support. Multilayer coatings can be applied by coating / drying each layer sequentially or by simultaneous coating of several coating solutions. Drying is generally carried out by blowing hot air over the coating, typically at a temperature of at least 70 ° C, suitably 80-150 ° C and especially 90-140 ° C. In addition, other heat sources such as infrared lamps or microwave radiation can also be used in the drying stage. The drying time can generally be 15 to 600 seconds. However, it is not necessary (and may not be possible) to remove all solvent during the drying stage. Indeed, the residual solvent content can be regarded as a further composition variable that can optimize the coating composition. Thus, the termination of the drying phase is defined herein as the moment when the coating becomes self-supporting and dries on contact.

  The heating phase starts after the end of the drying phase, preferably immediately after that. Alternatively, the precursor is first cooled between the drying and heating stages, but this is not essential. During the heating phase, the heat is maintained at a temperature above the temperature at which the coating is believed to maintain the precursor under ambient conditions (the ambient temperature is set to 20 ° C. by definition herein). So as to be supplied to the dry coating. Thus, the temperature of the precursor during the heating phase may be lower at the end of the drying phase. More preferably, the temperature of the coating during the heating phase is maintained at a value higher than the temperature of the coating at the end of the drying phase. During the online heating phase, the precursor web temperature is raised to at least 150 ° C., preferably at least 170 ° C., for 0.1 to 60 seconds, more preferably 1 to 30 seconds. The upper limit of the web temperature during the heating phase is defined by the temperature range necessary to trigger the film imaging mechanism. Thus, the upper limit depends on the specific composition of the coating, but is generally about 200 ° C, or more preferably about 250 ° C. Furthermore, heating at higher temperatures may induce irreversible chemical or physical changes in the coating that would cause the precursor to be unsuitable for image recording.

  Heating is performed, for example, by blowing hot air and / or steam onto the lithographic printing plate precursor, by irradiating the precursor with infrared light or microwaves, or by contacting the precursor with a heated roller. can do. Combinations of these methods are also suitable. The hot air and / or steam has a temperature above 150 ° C, preferably at least 170 ° C. Infrared light can irradiate the coating, the backside of the support, or both. When infrared light illuminates the coating, it has a wavelength and / or intensity that does not trigger the imaging mechanism of the coating. A heating roller that is preferably thermostatically controlled can likewise be brought into contact with the coating, the back side of the support or both, but the back side is preferred. The roller is preferably a metal roller.

  After the heating step, the precursor is preferably cooled before being wound on a core or cut into individual sheets. Alternatively, immediately after the heating step, the web can be wound on a core or cut into sheets and then allowed to cool. The preferred cooling phase is a rapid “aggressive” cooling phase, ie it reduces the coating temperature at a higher cooling rate than if the precursor is maintained under ambient conditions. In preferred embodiments, discussed further below, the cooling step is such that aggressive cooling is typically “passive” in the transition of the temperature range around the glass transition temperature of the coating as described below. It is a multiphase process that can be interrupted by the cooling phase. By “passive” cooling is meant a cooling phase in which the web is cooled at an average cooling rate that is lower than or equal to that obtained when the precursor is maintained under ambient conditions.

  The average cooling rate during the cooling phase or during the cooling phase is defined as the ratio of the temperature difference between the start and end of the cooling phase or cooling phase and the duration of the cooling phase or cooling phase.

  Aggressive cooling can be accomplished in a variety of ways, for example, by applying the precursor to one or more rollers, preferably one or more metal rollers, so that the heat of the precursor is easily transferred to one or more rollers. It can be obtained by contacting. Other cooling methods are of course possible, for example by blowing air over the precursor. However, due to the intimate contact between the cooling roller and the precursor, even if the temperature of the cooling roller is maintained at a higher value than the temperature of the outside air, the precursor is not exposed to ambient conditions, i.e. without contact with the cooling roller. The use of a metal chill roller is preferred because a temperature drop can be induced faster than would be maintained. Therefore, positive cooling can be obtained immediately after the heating step by bringing the precursor into contact with a metal cooling roller having a temperature of, for example, 50-120 ° C. For example, cooling rollers made of other materials with lower heat capacity or thermal conductivity can be used. The cooling roller can be in contact with the back side of the web or the coated side or both. It is quite obvious that the higher the temperature difference between the cooling roller and the precursor, the more rapid cooling effect is obtained. A preferred minimum value for the average cooling rate is 0.5 ° C./second, more preferably 1 ° C./second, and even more preferably 3 ° C./second.

  In some embodiments, very high average cooling rates, eg, exceeding 30 ° C./second, are avoided, as cooling can occur very rapidly, which can reduce or even eliminate the beneficial effects of the heating step. Must. The reason is therefore probably related to the high content of the amorphous state when the phenolic resin is rapidly cooled below its glass transition temperature (Tg). “Tg” as referred to herein is the glass transition temperature of the phenolic resin in the composition when it is coated, dried and heated, ie the glass transition temperature of the coating comprising the phenolic resin. . The Tg value can be easily measured by a known calorimetric method. If the coating comprises a large amount of an amorphous phenolic resin, relaxation to the more crystalline state, which inevitably occurs after days or weeks of coating, may occur during the aging period of the material. It is thought that the movement in the direction of low sensitivity that can be recognized can be explained. In order to minimize this effect, it may be beneficial to limit the average cooling rate to a maximum value of, for example, less than 30 ° C./second, more preferably less than 20 ° C./second, and most preferably less than 10 ° C./second. .

On the other hand, considering the high speed at which the web is moving through modern coating facilities, a shorter, more rapid cooling phase is preferred. The best compromise between these clearly conflicting requirements can be obtained by a three-phase cooling stage as follows:
-Cooling phase 1: rapid cooling to lower the temperature of the precursor to a value T1 higher than the Tg of the phenolic resin,
-Cooling phase 2: slow cooling to reduce the temperature of the precursor to a T2 value lower than Tg,
-Cooling phase 3: Rapid cooling again to approximately the outside temperature.

  The first rapid cooling phase may be accompanied by a very high average cooling rate, for example at least 10 ° C./second, more preferably 10-20 ° C./second or even more than 20 ° C./second. In the second cooling phase, the movement of the temperature range around Tg is carried out at a low average cooling rate, i.e. the precursor web temperature is slower than the rate in phase 1, e.g. Reduced to the range of T2. Preferred values of T1 and T2 are Tg + 20 ° C. and Tg−20 ° C., respectively, more preferably Tg + 10 ° C. and Tg−10 ° C., respectively. According to an even more preferred embodiment, phase 1 rapid cooling proceeds until the precursor temperature is just above the Tg of the phenolic resin, and then slow cooling is initiated immediately above Tg and immediately below Tg; And finally, another rapid cooling phase can be applied without inducing a significant effect on aging kinetics. As used herein, the range between “just above” and “just below” Tg is, for example, Tg + 5 ° C. to Tg−5 ° C., more preferably Tg + 2 ° C. to Tg−2 ° C.

  The average cooling rate during the second cooling phase may be higher or lower than the cooling rate corresponding to ambient conditions, i.e. without the use of cooling means such as rollers. The preferred average cooling rate in the second cooling phase is in the range of 0.1 ° C / second to 5 ° C / second, more preferably 0.2 ° C / second to 3 ° C / second, and 1 ° C / second to 2 ° C / second. The value in seconds gives excellent results. After the web temperature has thus been lowered to below Tg, in the third cooling phase, for example at least 10 ° C / second, more preferably 10-20 ° C / second or even more than 20 ° C / second Rapid cooling can be reapplied at an average cooling rate.

  Commercially available phenolic resins, such as novolacs, have a typical Tg of between 75-95 ° C, more typically between 80-90 ° C. A typical example of a preferred web temperature profile according to the present invention is shown in FIG. 1, where the Tg of the phenolic resin is 84 ° C. In FIG. 1, drying was performed using hot air having a temperature of 130 ° C., and hot air of 160 ° C. was used for the heating stage. During the first cooling phase, rapid cooling from> 150 ° C. to 100 ° C. is obtained in a few seconds, followed by a slow cooling from 100 ° C. to 70 ° C. for 16 seconds (ie 1.9 ° C./s). Followed by a rapid cooling phase that finally reached near ambient temperature in a few seconds.

  The heating and cooling steps described above provide materials that are characterized by stable sensitivity after an aging period that is significantly shorter than the time period when the material is not exposed to these steps, for example after a few weeks compared to months. In addition to improved aging kinetics, the coating of the material according to the present invention also shows a significant improvement in resistance to mechanical damage. More particularly, the frictional resistance is remarkably increased by the cooling process as the range around Tg is passed more slowly.

  The method of the present invention can be carried out in a coating facility, a typical example of which is shown in FIG. The support 1 is unwound from the coil 2, then one or several layers are applied in the coating device 3, and the coating is then dried in a multi-section drying device 4-5-6-7, for example an infrared light source Or it heat-processes with the heat source 8 which is a nozzle which sprays a hot air, then cools with the roller 9, and is finally wound up on the core 13. FIG. The air nozzle 10-11-12 can be used for further cooling: the roller 9 is preferably maintained at a temperature just above the Tg of the phenolic resin so that the transition of the temperature range around the Tg is slow. And the nozzle 10 is maintained just below Tg.

  The formation of a lithographic image with the printing plate precursor of the present invention is due to the difference in solubility induced by the heat of one or more layers of the coating being processed in the developer. Specifically, the solubility of the developer in the layer comprising the phenolic resin changes with exposure. One or more further layers can contribute to the imaging process. In some embodiments, the coating can further comprise one or more layers that do not contribute to the imaging mechanism, such as a layer whose solubility in the developer does not change substantially upon exposure. One example is a protective layer that is provided on top of the coating and can be dissolved in the developer in both exposed and unexposed areas. Furthermore, the layer provided between the support and the imaging layer generally does not contribute to the imaging process.

  The solubility difference between the imaged (printed, oleophilic) and non-imaged (non-printed, hydrophilic) parts of the lithographic image is characterized by a kinetic effect rather than a thermodynamic effect, ie the non-imaged part is It is characterized by dissolving faster in the developer than the imaged part. In the most preferred embodiment, the non-imaging portion is completely dissolved in the developer before the imaging portion is attacked, so that the imaging portion is characterized by sharp edges and high ink receptivity. The time difference between the completion of the dissolution of the non-imaging part and the start of the dissolution of the imaging part is preferably longer than 10 seconds, more preferably longer than 20 seconds and most preferably longer than 60 seconds, thereby allowing a wide color development tolerance. Provides a range.

According to one embodiment, the printing plate precursor is negative working, i.e. the imaging part corresponds to the exposed part. A suitable negative working coating comprises a phenolic resin and a latent Broented acid that generates acid upon heating or IR irradiation. These acids catalyze the crosslinking of the coating and thus the curing of the exposed areas during the post-exposure heating step. Thus, the unexposed area is washed away by the developer to reveal the underlying hydrophilic substrate. For a more detailed description of such negative working printing plate precursors, see US Pat. Nos. 6,255,042 and 6,063,544 and references cited in these references. .

  According to another embodiment, the printing plate precursor is positive working. In these embodiments, one or more coatings are capable of heat-induced solubilization, i.e., they are resistant to developers, ink-receptive in the unexposed state, and hydrophilicity of the support. To the extent that the surface is revealed thereby, it becomes soluble in the developer upon exposure to heat or infrared light. Thus, after exposure and color development, the exposed part is removed from the support and defines a hydrophilic non-imaged (non-printed) part, while the non-exposed part is not removed from the support and is oleophilic imaged (printed). ) Divide the part.

  The support for the lithographic printing plate precursor has a hydrophilic surface or is provided with a hydrophilic layer. The support may be a sheet-like material such as a printing plate or a cylindrical element such as a sleeve that can slide around a printing cylinder of a printing press. The support is preferably a metal support such as aluminum or stainless steel. The support may also be a laminate comprising an alumina foil and a plastic layer, for example a polyester film.

  A particularly preferred lithographic support is an electrochemically granulated and anodized aluminum support. Aluminium granulation and anodization are well known in the art. The anodized aluminum support can be treated to improve the hydrophilicity of its surface. For example, an aluminum support can be silicated by treating its surface with a sodium silicate solution at an elevated temperature, for example 95 ° C. Alternatively, a phosphating treatment can be applied that involves treating the aluminum oxide surface with a phosphate solution that can further comprise an inorganic fluoride. Furthermore, the aluminum oxide surface can be rinsed with a citric acid or citrate solution. This treatment may be carried out at room temperature or at a slightly higher temperature of about 30-50 ° C. A further interesting treatment involves rinsing the aluminum oxide surface with a bicarbonate solution. Furthermore, the aluminum oxide surface is formed by reaction with polyvinyl phosphonic acid, polyvinyl methyl phosphonic acid, polyvinyl alcohol phosphate ester, polyvinyl sulfonic acid, polyvinyl benzene sulfonic acid, polyvinyl alcohol sulfate ester and sulfonated aliphatic aldehyde. It can be treated with an acetal of polyvinyl alcohol. Furthermore, it is clear that one or more of these post-treatments can be carried out alone or in combination. Further details of these processes are given in British Patent 1 084 070, German Patent No. 4 423 140, German Patent No. 4 417 907, European Patent No. 659 909, European Patent No. 537 633, German Patent No. No. 4,001,466, European Patent No. 292 801, European Patent No. 291 760 and US Pat. No. 4,458,005.

  According to another embodiment, the support can also be a flexible support provided with a hydrophilic layer, hereinafter referred to as the “base layer”. The flexible support is, for example, paper, plastic film, thin aluminum or a laminate thereof. Preferred examples of the plastic film are polyethylene terephthalate film, polyethylene naphthalate film, cellulose acetate film, polystyrene film, polycarbonate film, and the like. The plastic film support may be opaque or transparent. The base layer is preferably a cross-linked hydrophilic layer obtained from a hydrophilic binder cross-linked with a curing agent such as formaldehyde, glyoxal, polyisocyanate or hydrolyzed tetra-alkylorthosilicate. Specific examples of hydrophilic base layers suitable for use in accordance with the present invention are European Patent No. 601 240, British Patent No. 1 419 512, French Patent No. 2 300 354, US Pat. No. 3,971,660 and US Pat. No. 4 284 705.

  The phenolic resin is preferably a binder with an acidic group having a pKa of less than 13 to ensure that it is soluble or at least swellable in an aqueous alkaline developer. The binder is advantageously a polymer or polycondensate having a hydroxyl group of a free phenol, such as obtained, for example, by reacting phenol, resorcinol, cresol, xylenol or trimethylphenol with an aldehyde, in particular formaldehyde or ketone. The polymer may further comprise units of other monomers that do not have acidic units. These units include vinyl aromatics, methyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, methacrylamide or acrylonitrile. In a preferred embodiment, the phenolic resin is novolak, resole or polyvinylphenol. The novolak is preferably cresol / formaldehyde or cresol / xylenol / formaldehyde novolak, wherein the amount of novolak is advantageously at least 50% by weight, preferably at least 80% by weight, based on the total weight of all the binders, respectively. is there. The amount of phenolic resin is advantageously 40 to 99.8% by weight, preferably 70 to 99.4% by weight, particularly preferably 80 to 99% by weight, each based on the total weight of the non-volatile components of the coating. .

  The dissolution kinetics of the phenol resin in the developer can be finely adjusted with an optional solubility adjusting component. More particularly, color development accelerators and color development inhibitors can be used. These components can be added to the layer comprising the phenolic resin and / or one or more other coatings.

  Development accelerators are compounds that act as dissolution promoters because they can increase the dissolution rate of the phenolic resin. In order to improve the aqueous color development, for example, a cyclic acid anhydride, a phenol or an organic acid can be used. Examples of cyclic acid anhydrides include phthalic acid anhydride, tetrahydrophthalic acid anhydride, hexahydrophthalic acid anhydride, as described in US Pat. No. 4,115,128, 3,6- Includes endoxy-4-tetrahydro-phthalic anhydride, tetrachlorophthalic anhydride, maleic anhydride, chloromaleic anhydride, alpha-phenylmaleic anhydride, succinic anhydride and pyromellitic anhydride . Examples of phenol include bisphenol A, p-nitrophenol, p-ethoxyphenol, 2,4,4′-trihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 4-hydroxybenzophenone, 4,4 ′, 4 "-trihydroxytriphenylmethane and 4,4 ', 3", 4 "-tetrahydroxy-3,5,3'.5'-tetramethyltriphenyl-methane etc. are included. Examples of organic acids Examples include sulfonic acid, sulfinic acid, alkylsulfuric acid, phosphonic acid, phosphate and carboxylic acid as described in JP-A-60-88,942 and JP-A-02-96,755. Specific examples of the organic acid include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, p-toluenesulfinic acid, and ethyl sulfate. Phenylphosphonic acid, phenylphosphinic acid, phenyl phosphate, diphenyl phosphate, benzoic acid, isophthalic acid, adipic acid, p-toluic acid, 3,4-dimethoxybenzoic acid, 3,4,5-trimethoxybenzoic acid, 3,4,5-trimethoxycinnamic acid, phthalic acid, terephthalic acid, 4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid, n-undecanoic acid and ascorbic acid are included. The amount of cyclic acid anhydride, phenol or organic acid to be added is preferably in the range of 0.05 to 20% by weight.

  In a preferred embodiment, the coating also includes a color resisting means, also called a color development inhibitor, i.e. one or more components that can delay dissolution of the unexposed parts during processing. The dissolution inhibiting effect is preferably attenuated by heating so that dissolution of the exposed portion is not delayed, thereby providing a large solubility difference between the exposed and unexposed portions. Such developer resistance means can be added to a layer comprising phenolic resin or to another layer of material.

For example, the compounds described in EP 823 327 and WO 97/39894 are used as dissolution inhibitors by interaction with one or more alkali-soluble binders in the coating, for example by hydrogen bridge formation. work. Such inhibitors typically include a nitrogen atom, an onium group, a hydrogen bridge-forming group such as a carbonyl (—CO—), a sulfinyl (—SO—) or sulfonyl (—SO ₂ —) group and one or more. It comprises a large hydrophobic portion such as an aromatic nucleus.

  Other suitable inhibitors improve the resistance of the developer because they retard the penetration of the aqueous alkaline developer into the layer comprising the phenolic resin. These compounds can be incorporated in the layer itself as described, for example, in EP 950 518, or in, for example, EP 864 420, 950 517, WO 99/21725 and 01 / It can be present in the developer barrier layer on top of the layer as described in pamphlet No. 45958. In a positive working embodiment, the barrier layer is preferably a polymeric material that is insoluble in the developer or impervious to the developer, such as acrylic (co) polymer, polystyrene, styrene-acrylic copolymer, polyester, polyamide, Comprising polyurea, polyurethane, nitrocellulose material, epoxy resin and silicone. In this embodiment, the solubility of the barrier layer in the developer or the transparency of the barrier layer by the developer can be increased by exposure to heat or infrared light.

Preferred examples of the latter type of inhibitors include water repellent polymers such as polymers comprising siloxane and / or perfluoroalkyl units. In a typical embodiment, the precursor between 0.5~25mg / ^{m 2,} preferably between 0.5-15 / ^{m 2,} and most preferably an appropriate amount of between 0.5 to 10 mg / ^{m 2} It comprises a barrier layer containing a water repellent polymer. Larger or smaller amounts are suitable depending on the hydrophobicity / oleophobicity of the compound. When the water-repellent polymer is also ink repellant, for example in the case of polysiloxanes, greater than 25 mg / m ² may result in weak ink acceptance of the unexposed portions. On the other hand, less than 0.5 mg / m ² may lead to unsatisfactory color development resistance. The polysiloxane can be a linear, cyclic or complex cross-linked polymer or copolymer. The term polysiloxane compound is intended to include any compound in which R and R ′ contain two or more siloxane groups —Si (R, R ′) — O—, optionally substituted with alkyl or aryl groups. Preferred siloxanes are phenylalkyl siloxanes and dialkyl siloxanes. (Co) The number of siloxane groups in the polymer is at least 2, preferably at least 10, more preferably at least 20. It may be less than 100, preferably less than 60. In another embodiment, the water repellent polymer is a block-copolymer or graft-copolymer of poly (alkylene oxide) and a polymer comprising siloxane and / or perfluoroalkyl units. Suitable copolymers comprise about 15-25 siloxane units and 50-70 alkylene oxide groups. Preferred examples include phenylmethyl siloxanes and / or dimethyl siloxanes such as Tego Glide 410, Tego Wet 265, Tego Protect 5001 or Silikophen P50 / X and ethylene oxide and / or propylene oxide, all commercially available from Tego Chemie, Essen, Germany. Copolymers comprising are included. Such copolymers, when coated, tend to place themselves at the interface between the coating and air due to their bifunctional structure, so that even when applied as a component in the same solution as the phenolic resin, Acts as a surfactant that forms the top layer. These surfactants simultaneously serve as spreading agents that improve the coverage. Alternatively, the water repellent polymer can be applied in a second solution coated on a layer comprising a phenolic resin. In that embodiment, it may be advantageous to use a solvent in the second coating solution that cannot dissolve the components present in the first layer so that a significantly rich water repellent phase is obtained on top of the material. Absent.

  The coating preferably also includes a compound that absorbs infrared light and converts the absorbed energy into heat. The IR absorbing compound can be present in the same layer as the phenolic resin, in any of the barrier layers discussed above, or in any other layer. According to a highly preferred embodiment, the dye or pigment is concentrated in or near the barrier layer, for example in an intermediate layer between the lipophilic layer and the barrier layer. According to that embodiment, said intermediate layer comprises a higher amount of IR absorbing compound than the amount of IR absorbing compound in the lipophilic layer or barrier layer. The concentration of IR absorbing compound in the coating is generally between 0.25 and 10.0% by weight, more preferably between 0.5 and 7.5% by weight. Preferred IR absorbing compounds are dyes such as cyanonin and melocyanin dyes or pigments such as carbon black. Examples of suitable IR absorbers are described, for example, in European Patent Nos. 823327, 978376, 1029667, 1053868, 1093934, WO 97/39894 and 00/29214. Are listed. Preferred compounds are the following cyanonin dyes:

It is.

  In order to protect the surface of the coating from mechanical damage, in particular, a protective layer may optionally be applied. The protective layer generally comprises at least one water soluble polymer binder such as polyvinyl alcohol, polyvinyl pyrrolidone, partially hydrolyzed polyvinyl acetate, gelatin, hydrocarbons or hydroxyethyl cellulose, if necessary Can be produced in any known manner, such as from aqueous solutions or dispersions, which can contain small amounts, ie less than 5% by weight of organic solvent, based on the total weight of the coating solvent for the protective layer. . The thickness of the protective layer can suitably be any amount, advantageously up to 5.0 μm, preferably 0.1 to 3.0 μm, particularly preferably 0.15 to 1.0 μm.

  The coating and, more specifically, the layer or layers comprising a phenolic resin, may optionally further comprise further components. Preferred components are, for example, polymers containing further binders, in particular sulfonamide and phthalimide groups, in order to improve the printing plate run length and chemical resistance. Examples of such polymers are those described in EP 933682, 894622 and WO 99/63407. In addition, colorants such as dyes or pigments that impart a visible color to the coating and remain in the coating in the unexposed areas can be added so that a visible image is formed after exposure and processing. Typical examples of such contrast dyes are amino-substituted tri- or diarylmethane dyes such as crystal violet, methyl violet, victoria pure blue, flex sobrau 630, basonyl brou 640, auramine and malachite green. .

  Any known method can be used for the preparation of lithographic printing plate precursors. For example, the aforementioned components do not react irreversibly with those components and are preferably dissolved in a solvent mixture adapted to the intended coating method, layer thickness, layer composition and drying conditions. Can do. Suitable solvents include ketones (eg methyl ethyl ketone (butanone)) as well as chlorinated hydrocarbons (eg trichloroethylene or 1,1,1-trichloroethane), alcohols (eg methanol, ethanol or propanol), ethers (eg tetrahydrofuran), glycol- Monoalkyl ethers (eg ethylene glycol monoalkyl ether), such as 2-methoxy-1-propanol, or propylene glycol monoalkyl ethers and esters (eg butyl acetate or propylene glycol monoalkyl ether acetate) are included. Furthermore, it is also possible to use mixtures which can additionally contain solvents such as acetonitrile, dioxane, dimethylacetamide, dimethyl sulfoxide or water for special purposes.

  The end consumer can, for example, expose the lithographic printing plate precursor imagewise either directly with heat by a thermal head or indirectly by infrared light, preferably by near infrared light. Infrared light is preferably converted to heat by an IR light absorbing compound as described above. The precursors of the heat-sensitive lithographic printing plate of the present invention are preferably not sensitive to visible light, ie exposure to visible light does not induce a substantial effect on the dissolution rate of the coating in the developer. Most preferably, the coating is external sunlight, i.e. visible light (400-750 nm) and at an intensity and exposure time corresponding to normal working conditions, so that the material can be processed without the need for a safe light environment. Not sensitive to near UV light (300-400 nm). “Non-photosensitive” to sunlight shall mean that exposure to ambient sunlight does not induce a substantial change in the dissolution rate of the coating in the developer. In a preferred sun-stable embodiment, the coating absorbs near UV and / or visible light present during sunlight or office lighting, thereby changing the solubility of the coating on the exposed portion, (quinone) diazide or diano It does not contain photosensitive components such as (nium) compounds, photoacids, photoreaction initiators, photosensitizers and the like.

The printing plate precursor of the present invention can be exposed to infrared light by, for example, LEDs or lasers. Most preferably, the light beam used for exposure is a laser emitting near infrared light having a wavelength in the range of about 750 to about 1500 nm, such as a semiconductor laser diode, Nd: YAG or Nd: YLF laser. The required laser power is the pixel residence time of the laser beam determined by the sensitivity of the image recording layer, the spot diameter (typical values for modern plate-setters at 1 / e ² of maximum intensity: 10-25 μm), Depending on the exposure device scan speed and resolution (ie, the number of addressable pixels per linear distance unit, often expressed in dots per inch or dpi; typical values: 1000-4000 dpi).

  Two types of laser exposure devices are commonly used: an internal drum (ITD) and an external drum (XTD) plate-setter. ITD plate-setters for thermal printing plates are typically characterized by very high scan speeds of 500 m / sec and may require several watts of laser power. XTD plate-setters for thermal printing plates with typical laser powers of about 200 mW to about 1 W operate at lower scan speeds, for example 0.1-10 m / sec.

  Known plate-setters can be used as offset printing exposure devices that offer the advantage of reduced press down-time. The XTD plate-setter configuration can also be used for on-set printing exposure, which gives the advantage of immediate registration in multicolor printing. More technical details of on-press exposure apparatus are described in, for example, US Pat. Nos. 5,174,205 and 5,163,368.

In the developing stage, the non-imaged part of the coating is removed by immersion in a conventional aqueous alkaline developer that can be combined with mechanical friction, for example with a rotating brush. During the development, any water-soluble protective layer present is also removed. To ensure that the alumina layer (if present) of the substrate is not damaged, a silicate substrate developer having a ratio of at least one silicon dioxide to alkali metal oxide is preferred. Preferred alkali metal oxides include Na ₂ O and K ₂ O and mixtures thereof. In addition to the alkali metal silicate, the developer may optionally be a buffer material, complexing agent, bubble suppressant, small amount of organic solvent, corrosion inhibitor, dye, surfactant and / or hydrophobic well known in the art. Additional components such as agents can be included. The development is preferably carried out at a temperature of 20-40 ° C. in an automated processing unit customary in the art. For regeneration, an alkali metal silicate solution containing 0.6 to 2.0 mol / l of alkali metal can be appropriately used. These solutions can have the same silica / alkali metal oxide ratio as the developer (but generally lower) and can optionally contain further additives. The required amount of reclaimed material must be adapted to the developing device used, daily printing plate throughput, imaging area, etc., and is generally 1-50 ml per square meter of recording material. The addition can be adjusted, for example, by measuring the conductivity as described in EP 0 556 690.

  The printing plate precursor according to the present invention can be post-treated with a suitable corrective or preservative known in the art, if necessary. In order to increase the resistance of the finished printing plate and thereby extend the travel of the printed material, the layer can be heated to a high temperature for a short time [baking]. As a result, the resistance of the printing plate to cleaning agents, modifiers and UV-curable printing inks is also increased. Such thermal after-treatment is described inter alia in DE 14 47 963 and GB 1 154 749.

  In addition to the post-treatment, the processing of the printing plate precursor can also comprise a rinsing step, a drying step and / or a gumming step.

  The printing plate thus obtained can be used for ordinary so-called wet offset printing in which ink and aqueous wetting liquid are supplied to the printing plate. Another suitable printing method uses a so-called single-fluid ink that does not use a wetting liquid. Single fluid inks suitable for use in the method of the present invention are described in US Pat. Nos. 4,045,232, 4,981,517 and 6,140,392. In the most preferred embodiment, the single fluid ink comprises an ink phase, also called a hydrophobic or lipophilic phase, and a polyol phase as described in WO 00/32705.

The following composition was coated on a normal granular anodized alumina support web at a wet film thickness of 26 μm and a speed of 16 m / min:
-Methoxypropanol (Dowanol PM ^™ ) 410.80 g
-266.03 g of methyl ethyl ketone
-Tetrahydrofuran 209.20 g
-Novolak 40.4 wt% solution in Dowanol PM ^™ (Alnovol SPN 452 ^™ ) 103.25 g
-3,4,5-trimethoxycinnamic acid 5.34 g
-Dye IR-1 (the above formula) 2.10 g
-Basonylblau 640 ^™ (contrast dye) 0.53 g
-TEGO Glide 265 ^TM (polyalkylene oxide /
0.85 g of 10% by weight polysiloxane surfactant)
-TEGO Glide 410 ^TM (polyalkylene oxide /
(10 wt% solution of polysiloxane surfactant) 2.12 g.

  The coating was dried with air having a temperature of 135 ° C. and then subjected to heating and cooling steps. During the heating phase, air having the temperature shown in Table 1 was blown over the coating for 1.2 seconds. In the control example 1, the hot air nozzle was switched off. Immediately thereafter, the back side of the web was brought into contact with a metal cooling roller having the temperature shown in Table 1. The temperature of the heated coating drops very rapidly (> 30 ° C./sec) to a value below Tg with a 57 ° C. cooling roller. The temperature range around Tg is passed through the 75 ° C. cooling roller at a much slower rate.

  The material was then imaged on a Creo Trendsetter 3244 (830 nm) with various energy density settings. The exposed version was processed at 25 ° C. in an Agfa Automatic PN85 processor operating at a speed of 0.84 m / min using an Agfa Ozasol EP26 developer, and finally glued with Agfa Ozasol RC795. IR-sensitivity is the minimum energy density required to obtain 50% light absorption, measured on the developer plate at the maximum wavelength of the dye, in the exposed part with a dot area of 50% screen (@ 200 lpi) Defined. Sensitivity was measured for fresh material and material aged under ambient conditions for days as shown in Table 1.

The data in Table 1 shows that the material heated according to the present invention reached a stable sensitivity from 15 days after coating, while the sensitivity of the control material of Example 1 still fluctuated after 25 days, 165 mJ after about 2 months of coating. It shows that it has been found to stabilize at / cm ² .

  The samples of Examples 4 and 5 were coated, dried and cooled as discussed above for Examples 1 and 2, respectively, except that in Example 5, the coatings were exposed to IR radiation (two units). 12 kW lamp) The hot air heat treatment in Example 2 was replaced, which caused the web temperature to rise to 150 ° C. for 2.8 seconds. The web temperature at the same time in Comparative Example 4 (IR lamp was turned off) was 60 ° C. Table 2 shows that Example 5 exhibits significantly improved aging kinetics compared to Example 4.

Figure 2 shows a web temperature profile during a preferred process for producing a heat sensitive lithographic printing plate precursor according to the present invention. Figure 2 shows a schematic representation of an apparatus for carrying out a suitable example of the method of the invention.

Claims (10)

(I) providing a web of a lithographic support having a hydrophilic surface;
(Ii) applying a coating comprising a phenolic resin on the hydrophilic surface of the web;
(Iii) drying the coating;
(Iv) a heating stage in which the web temperature is maintained above 150 ° C. for a period of 0.1 to 60 seconds;
(V) winding the precursor on the core or cutting the precursor into sheets;
A process for preparing a thermosensitive lithographic printing plate precursor comprising the steps of:   The method of claim 1, wherein the web temperature is maintained above 170 ° C for a period of 1 to 30 seconds during the heating phase.   3. A method according to claim 1 or 2, wherein the heating step is performed by blowing hot air or steam over the precursor.   A method according to claim 1 or 2, wherein the heating step is carried out by exposing the precursor to infrared or microwave radiation.   A method according to any preceding claim, further comprising a cooling step between steps (iv) and (v).   6. The method of claim 5, wherein during the cooling phase, the precursor web temperature is reduced at an average cooling rate that is faster than the rate at which the precursor would be maintained under ambient conditions.   The method of claim 6, wherein the average cooling rate is at least 0.5 ° C./second.   During the cooling phase, the web temperature is reduced from T1 to T2 with an average cooling rate lower than 10 ° C./second, where T1 is higher than Tg, T2 is lower than Tg, and Tg is a glass of a coating comprising a phenolic resin. The method according to any one of claims 5 to 7, which is a transition temperature. During the cooling phase, the web temperature-in the first phase at T1 with an average cooling rate of at least 10 ° C / sec,
In the second phase from T1 to T2 with an average cooling rate lower than 10 ° C./s,
-In the third phase, from T2 to approximately ambient temperature with an average cooling rate of at least 10 ° C / sec,
9. A method according to any one of claims 8 to be reduced.   The method according to claim 8 or 9, wherein T1 is Tg + 20 ° C and T2 is Tg-20 ° C.

Images