JP4338640B2 - Production of lithographic printing plate precursors - Google Patents

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 involves rewinding the coated web onto the core or cutting the coated web into immediate sheets that 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 applying more heat to trigger. 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). Patent Document 8 discloses that controlled slow cooling after heat treatment provides further improvements (see Patent Document 8). According to the latter document (Patent Document 8), “controlled slow cooling” means that heat is lost from the precursor more slowly than it is cooled under ambient conditions. Examples of such cooling methods include insulating the material after heat treatment, or leaving the material in an oven that gradually cools to a lower temperature. Such a cooling process lasts several hours and can only be performed "offline", i.e. a coil or sheet stack is placed in an oven and left there for the required time. However, offline storage must be avoided for several reasons. Apart from the additional costs and logistical implications, it is quite obvious that the coil or stack cannot be cooled 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 cooling step that can be performed on-line prior to 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 an on-line cooling step. In accordance with the present invention, the long cooling process disclosed in the prior art and that can only be performed off-line is higher than the rate at which the web will be maintained under ambient conditions, but above 30 ° C./sec. It is replaced by an on-line cooling stage where the web temperature is reduced with no average cooling rate.

  The method of the present invention produces a thermosensitive printing plate precursor with stable sensitivity within weeks instead of months after production. Although further aging is not necessary, it is obvious that embodiments in which an on-line cooling step according to the present invention is combined with a further off-line cooling step 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.

  After completion of the drying stage, the precursor is subjected to a further heating stage, preferably a short on-line. Alternatively, the precursor can be cooled first between the drying and heating stages, but this is not essential. During the optional heating phase, the temperature of the coating is maintained at a value higher than that at which the precursor would be maintained under ambient conditions (the ambient temperature is set herein to 20 ° C. by definition). As such, heat is supplied to the dried coating. Thus, the temperature of the precursor during the heating phase can be lower than the temperature 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 coating temperature at the end of the drying phase. Alternatively, the dried coating can be heat treated by extending the length of the drying apparatus so that additional dry air is blown over the coating after it has been dried. In that embodiment, the coating temperature during the heat treatment period can be the same as the temperature at the end of the drying phase.

  During the online heating phase, the precursor web temperature is preferably raised above the glass transition temperature Tg of the phenolic resin. “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. The heat treatment is sufficiently short so that it can be performed on-line, for example 0.1 to 60 seconds, more preferably 1 to 30 seconds. The web temperature is preferably raised to at least 150 ° C, preferably at least 170 ° C during the heating phase. 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 preferably has a temperature above 150 ° C, more 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 heated roller, preferably thermostatically controlled, can likewise be contacted 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 cooled before being wound on a core or cut into individual sheets. The cooling phase is a rapid “aggressive” cooling phase, that is, it lowers the coating temperature at a higher cooling rate than if the precursor is maintained under ambient conditions. Thus, the cooling phase referred to herein is defined as the phase between the start and end of active cooling. In the preferred embodiment discussed further below, the cooling phase is a multiphase process in which active cooling can be interrupted by a “passive” cooling phase, typically in the transition of the temperature range around Tg. It is. 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. Thus, the cooling stage in the method of the present invention can be a series of one or more active and passive cooling phases. In such a multiphase cooling process, the active cooling phase is defined as the process between the start of the first active cooling phase and the end of the last active cooling phase.

  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 a faster cooling effect is obtained when the temperature difference between the cooling roller and the precursor is high. A preferred minimum value of average cooling rate is 0.5 ° C./second, more preferably 1 ° C./second, and even more preferably 3 ° C./second.

  Improved aging kinetics can be obtained by limiting the average cooling rate to a value not exceeding 30 ° C./second, more preferably not exceeding 20 ° C./second, and most preferably not exceeding 10 ° C./second. It was determined by the inventor that this can be done. The reason is therefore probably related to the high content of the amorphous state when the phenolic resin is rapidly cooled below its Tg. If the coating comprises a large amount of a phenolic resin in the amorphous state, 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 movement in the direction of lower sensitivity that can be recognized can be explained.

On the other hand, considering the high speed at which the web is moving through modern coating facilities, the duration of the cooling phase would otherwise extend the length of the coating array, so that A more rapid cooling step 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 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 produces an acid upon heating or IR radiation. 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, the one or more coatings are capable of heat-induced solubilization, i.e., they are resistant to developers, are ink-receptive in the unexposed state, and are hydrophilic on the support. The surface becomes soluble in the developer upon exposure to heat or infrared light to the extent that it appears. 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 by reacting, for example, 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, in the case of polysiloxanes, for example, greater than 25 mg / m ² may result in weak ink acceptance in the unexposed areas. 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 such as ethylene glycol monoalkyl ethers such as 2-methoxy-1-propanol, or propylene glycol monoalkyl ethers and esters such as 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 provides 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 (although generally lower) and can optionally contain additional additives as well. 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 optional 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 Examples 1 and 2, 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 is reduced very rapidly (> 30 ° C./sec) to a value below Tg by a 57 ° C. cooling roller. The temperature range around Tg is passed at a much slower average cooling rate by the 75 ° C. cooling roller.

  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 cooled according to the present invention achieves stable sensitivity after 15 days of coating, while the sensitivity of the control material of Example 1 still fluctuates after 25 days, after about 2 months of coating. It shows that it was found to stabilize at 165 mJ / cm ² .

  Improved aging kinetics can also be demonstrated by subjecting the material to an off-line heat treatment after applying the method of the present invention. Examples 4, 5 and 6 were obtained by coating the same composition and drying according to a method similar to that discussed in the previous examples. The dried material was then subjected to a heat treatment by using a further drying apparatus that blows air at 135 ° C. over the dried coating. Between the latter heat treatment and the cooling roller, the web was cooled under ambient conditions such that the web temperature just before the cooling roller was 118 ° C. Initial rapid cooling was obtained with a metal roller whose temperature was maintained at the value given in Table 2. Contact between the material and the cooling roller lasted 2.41 seconds. Immediately after passing through the metal cooling roller, the second slow cooling phase was allowed to pass by blowing air at 50 ° C. over the coating for 32 seconds.

  The sensitivity of fresh material and material artificially aged off-line for 7 days at the temperatures given in Table 3 was measured. The data in Table 3 shows that materials that cool more slowly, i.e., that are cooled by higher chill roller temperatures, have more stable aging kinetics. Example 6 is cooled to the near Tg region at a very slow cooling rate and gives the best aging kinetics since there is little impact from further off-line heat treatment.

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 (2)

(I) providing a web of 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 by supplying heat to the coated web;
(Iv) an aggressive cooling phase in which the web temperature is reduced at an average cooling rate that is higher than the rate at which the web would be maintained under ambient conditions but not higher than 30 ° C./second;
(V) winding the precursor on the core or cutting the precursor into sheets,
A manufacturing method of the heat-sensitive lithographic printing plate precursor comprising the steps,
At the beginning of the cooling phase, the web temperature is higher than the glass transition temperature, Tg, of the coating comprising the phenolic resin, and during the cooling phase, the web temperature is
-In the first phase, at a T1 higher than Tg with an average cooling rate of at least 10 ° C / sec,
In the second phase, from T1 with an average cooling rate lower than 10 ° C./s, to T2 lower than Tg,
A method characterized by that. During the cooling phase, the web temperature is-in the first phase at T1 with an average cooling rate of at least 10 ° C / s
The second phase is reduced from T1 to T2 with an average cooling rate lower than 10 ° C./s, and the third phase is reduced from T2 to approximately ambient temperature with an average cooling rate of at least 10 ° C./s. The method according to 1 .

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