DE60318600T2 - METHOD FOR PRODUCING A LITHOGRAPHIC PRESSURE PLATE - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The The present invention relates to a heat-sensitive lithographic Printing plate precursor containing a phenolic resin.

GENERAL PRIOR ART

at lithographic printing is usually used a so-called Printing master like one on a drum of a rotary printing press clamped pressure plate. The master surface carries a lithographic image and a print is obtained by first printing ink on the image applied and then Transfer the color from the master to a receiving material, usually paper becomes. In conventional lithographic printing is both ink and fountain solution water-based on the lithographic image, made of oleophilic (or hydrophobic, i.e., ink-receptive, water-repellent) And hydrophilic (or oleophobic, i.e. hydrophilic, ink-repelling) Areas constructed, appropriate. In so-called driographic The lithographic image consists of ink-receptive and ink-repellent prints (ie color repellent) Areas and will be during of driographic printing, just apply printing ink to the master.

print Master are usually by imagewise exposure and developing an image-forming apparatus called a plate precursor Materials received. Except the well-known radiation-sensitive, so-called presensitized Plates for a UV contact exposure through a film mask are suitable are in the late 90s also heat sensitive Printing plate precursors have become a very popular type of plate. Such Thermal materials have the advantage of their daylight resistance and are particularly suitable for use in the so-called computer-to-plate process (direct digital plate imaging) where the plate precursor is exposed directly, d. H. without the use of a film mask. The material comes with heat applied or exposed to infrared light and the generated thereby Heat dissolves you (physical) chemical process, such as ablation, polymerization, Insolubilization by crosslinking of a polymer, a thermal induced solubilization or coagulation of the particles of a thermoplastic polymeric latex.

Although some of these thermal processes allow for plate-making without wet development, image formation in the most popular thermal plates is accomplished by heating the plates to cause a solubility difference in alkaline developer between the heated areas and unheated areas of the coating. The coating usually contains an oleophilic binder, for. Example, a phenolic resin whose dissolution rate in the developer by the imagewise heating either limited (negative working plate) or increased (positive working plate) is. The difference in solubility causes the non-image areas (ie non-printing areas) of the coating to be removed during development, thereby exposing the hydrophilic support while leaving the image areas (ie the printing areas) of the coating intact on the substrate. Typical examples of such plates are described in e.g. B. EP-A 625 728 . EP-A 823 327 . EP-A 825 927 . EP-A 864 420 . EP-A 894,622 and EP-A 901 902 ,

The industrial production of printing plate precursors takes place step by step, being first a usually made of aluminum substrate sheet of a coil unwound and coated with one or more layers, Then the coating is dried by applying hot air over the coated web is blown, and finally the coated web wrapped again on a core or immediately cut into bows and then stacked and packaged. In industrial production all these steps are done on-line, d. H. on a running track in a single pass process without intermediate storage.

A specific problem with thermal printing plate precursors with phenolic resins is their sensitivity, which changes with time by the coating gradually becoming more resistant to the developer, which requires more heat during imagewise exposure to trigger the imaging mechanism. In general, one obtains a high sensitivity, eg. B. of less than 100 mJ / cm ² , just after coating and decreases it slowly to an equilibrium value of for example 250 mJ / cm ² . The aging time required to achieve stable sensitivity can amount to several months after the coating. To reduce this aging time is in WO 99/21715 proposed a heat treatment, wherein the material shortly after coating over a longer period, which is at least 4 hours, and most preferably at least 48 hours, in an oven with egg a temperature of 40 ° C to 90 ° C is stored. Out US 6,251,559 It is known that additional controlled improvements are achieved by controlled slow cooling after such heat treatment. In US 6,251,559 By "controlled slow cooling" is meant that the precursor loses heat more slowly than if it were cooled under ambient conditions. Such cooling can be achieved, for example, by isolating the material after its heat treatment or by storing it in an oven whose temperature is gradually decreasing. Such a cooling process takes several hours and can only be done off-line, ie a coil or stack of sheets is placed in an oven and allowed to stand in it for the necessary period of time. However, such offline storage is to be avoided for various reasons. Aside from additional costs and logistical effort, it is quite clear that a coil or stack can not be evenly cooled thereby because the inside of the coil or stack passes through a different temperature profile to the outside throughout the process. Therefore, there is a need for a method that ensures a convenient and on-line feasible cooling step before the web is wound onto a bobbin or cut into sheets.

Other solutions to the above problem can be found in EP 1 558 447 A and EP 1 551 642 A , both with the same priority date and filing date as the present patent application.

BRIEF PRESENTATION OF THE PRESENT INVENTION

task The present invention is to provide an on-line method for the Aging more sensitive to heat, a phenolic resin-containing printing plate materials. Is solved This object is achieved by the method defined in claim 1, the characterized in that the dried coating is an online cooling step is subjected. In the present invention, the long, known from the prior art and only feasible offline cooling processes replaced by an online cooling step, in which the lowering of the web temperature at one above the while storing the web Reachable under ambient conditions speed average cooling rate done, but without 30 ° C / s To exceed.

The inventive method allows the production of heat-sensitive Printing plate precursors, which after their production after a few Weeks instead of different months with stable sensitivity come up. Although there is an additional Aging not necessary, but of course includes the scope the present invention also embodiments in which a Inventive Online Cooling Step with an additional Offline-cooling step combined.

specific embodiments The present invention is described in the subclaims.

BRIEF DESCRIPTION OF THE FIGURES

1 Figure 10 shows the web temperature profile during a preferred process for making a heat-sensitive lithographic printing plate precursor of the present invention.

2 is a schematic representation of an apparatus for carrying out a suitable example of the method according to the invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The heat-sensitive according to the invention lithographic printing plate precursor comprises a hydrophilic support and an attached phenolic resin-containing coating. The coating may consist of one or more layers, one of which Examples discussed below will be composed. The phenolic resin may be in one or be included in several layers of the coating.

Any reference to the temperature of the precursor is to be considered in this invention as a reference to both the temperature of the carrier and the temperature of the coating. In general, the coating is very thin, ie 1 micron or a few microns in size, the carrier, however, usually has a strength between 0.1 mm and 0.5 mm. Therefore, the support, preferably a metal support, functions as a large heat sink for the coating and the temperature of the coating is close to or very close to the support temperature, regardless of whether only the coated side of the precursor is in the heating and cooling steps discussed herein , only the back of the precursor or both sides warmed or cooled become. For recording the temperature values mentioned herein, in practice a remotely readable thermocouple device has been attached to the back of the web which measures the temperature of the web as it traverses all areas of the coater. Such a method ensures a precise recording of the temperature profile during all steps of the method according to the invention. Unless specifically stated otherwise, all temperatures mentioned herein are track temperatures read from the thermocouple. It will be apparent to those skilled in the art from the above considerations that the web temperature value is substantially equal to the temperature of the dry coating applied to the web.

To the Order one or more casting solutions the hydrophilic surface of the carrier Any coating technique can be used. In the event of a multilayer coating can either separate each layer applied sequentially and dried or can different casting solutions simultaneously be applied. Drying is usually done by that you have hot air, usually with a temperature of at least 70 ° C, preferably 80-150 ° C and especially preferably 90-140 ° C, over the Coating blows. For the Drying are other suitable heat sources in question, for. B. Infrared lamps or microwave radiation. The drying time can usually between 15 and 600 seconds. However, must but not necessarily the total amount of solvent during the drying step be removed (sometimes this is not even possible). The residual content of solvent can yes as additional Composition variable are considered by the coating composition can be optimized. Therefore, the drying step in the considered to be finished when a self-supporting and feel dry Coating is obtained.

To completed drying step, the precursor is preferably a short, additional Subjected to online heating step. Also possible is that you first the Precursor between the drying step and the heating step cooling down leaves, However, such an intermediate step is not necessary. During the additional Heating step, the dry coating is heated so that the coating temperature at a value above the temperature, which prevail during storage of the precursor under ambient conditions would, is maintained (the temperature of ambient air is present in the Invention set by definition to 20 ° C). The temperature of the precursor during of the heating step may therefore be lower than at the end of the Drying step. Particularly preferred is the coating temperature while of the heating step at one above that at the end of the drying step measured temperature of the coating lying value. In an alternative method for the heat treatment the dried coating uses a longer drying plant, which allows additional Drying air over to blow the coating once it is dry. In this embodiment The temperature of the coating during the heat treatment can be equal to the temperature be at the end of the drying step.

During the Heating step, the web temperature of the precursor is preferably to a value above the Tg value, d. H. the freezing point, of the phenolic resin increased. Under "Tg" is in the present invention, the freezing point of the phenolic resin in the applied, dried and heated composition, d. H. the freezing point of the coating containing the phenolic resin, to understand. The Tg value can be determined by the known calorimetric Measuring procedure fast be measured. In that the duration of the heat treatment is sufficiently short is, for. B. between 0.1 and 60 s, more preferably between 1 and 30 s, the heat treatment can be carried out on-line become. Preferably, the web temperature during the heating step to at least 150 ° C, preferably at least 170 ° C, elevated. The upper web temperature limit during the heating step depends on the temperature threshold, above which the imaging mechanism of the coating is triggered. This upper limit is therefore dependent on the particular composition the coating is but usually about 200 ° C or most preferably about 250 ° C. A heating to even higher Temperatures can be irreversible chemical or physical changes in the coating, which does not cause the precursor could illustrate more.

For example, the precursor is heated by blowing hot air and / or hot steam over the lithographic printing plate precursor, irradiating the precursor with infrared light or microwaves, or contacting the precursor with a heated roller. Combinations of these methods are also possible. The temperature of the hot air and / or the hot steam is preferably more than 150 ° C, more preferably at least 170 ° C. With the infrared light, either the coated side or the back of the carrier or both sides can be irradiated. If only the coating is irradiated with the infrared light, the wavelength and / or the intensity should be selected so that the imaging mechanism of the coating is not triggered. In the same way, the heated and preferably thermo statically controlled roller are brought into contact only with the coating, only with the back of the carrier or with both, but is preferred that the roller is brought into contact only with the carrier back. The roller is preferably a metal roller.

To In the heating step, the precursor is cooled before being wound on a core or to be cut into single sheets. The cooling step is a fast, "active" cooling step, d. H. a step in which the temperature of the coating is faster is lowered than taking the precursor under ambient conditions would camp. The cooling step according to the invention is defined as the step between the beginning and the end of the active cooling. In preferred embodiments described in more detail below is the cooling step a multi-stage process in which the active cooling by a "passive" cooling phase can be interrupted, usually in the transition region of the temperature interval around the Tg value. Under "passive" cooling understands a cooling step, in which the web is cooled at an average cooling rate, the maximum the achievable in storage of the precursor under ambient conditions cooling equivalent. The cooling step in the process according to the invention can therefore be a consequence of one or more active and passive cooling phases include. In such multi-phase cooling processes, the active cooling step defined as the process between the beginning of the first active cooling phase and the end of the last active cooling phase.

The average cooling rate while of the cooling step or while a cooling phase is defined as the ratio the temperature difference between the beginning and the end of the cooling step or the cooling phase for the duration of the cooling step or the cooling phase.

For the active Cooling Different means come into question, eg. B. one or more rollers, prefers one or more metal rolls to those with the precursor in contact is brought and / or become while the heat from the precursor takes over or take over. Of course There are other suitable cooling, z. A method, in the air over the surface the pre-stage is blown. However, the use is preferred a metal chill roll because of the close contact between chill roll and pre-stage a faster cooling the precursor triggers as if the precursor was run under ambient conditions, i. H. without Contact with a chill roll, store, and even if the temperature of the chill roll is on an above the temperature of the ambient air is maintained. For an active Cooling Thus, a method is suitable in which the precursor just after the heating step with a metal cooling roll at a temperature from Z. B. 50 ° C up to 120 ° C in touch is brought. Also suitable are chill rolls made of other materials, z. B. materials with lower heat output or thermal conductivity. The chill roll can with the back the web, the coated side of the web or both become. It's pretty obvious that with increasing temperature difference between chill roll and precursor the cooling off the faster. Preferably, the mean cooling rate at least 0.5 ° C / s, more preferably at least 1 ° C / s, At least it would be even better 3 ° C / s.

The Inventors have found that the aging behavior by limiting the average cooling rate at most 30 ° C / s, most preferably at most 20 ° C / s and most preferably at most 10 ° C / s improved can be. The reason for this probably lies in the fact that the phenolic resin on rapid cooling on a value under its Tg gets a strong amorphous state. Contains the coating a high content of phenolic resin in amorphous state, becomes the inevitable Relaxation in the days or weeks after coating the precursor convert the phenolic resin to a more crystalline state, which could explain why while the aging of the material reduces the sensitivity can occur.

• • Abkühlungsphase 1: schnelle Abkühlung, wobei die Temperatur der Vorstufe auf einen Wert T1, der über dem Tg des Phenolharzes liegt, gesenkt wird.
• • Abkühlungsphase 2: langsamere Abkühlung, wobei die Temperatur der Vorstufe auf einen Wert T2 unter dem Tg des Phenolharzes gesenkt wird.
• • Abkühlungsphase 3: erneut eine schnelle Abkühlung, um die Temperatur auf Zimmertemperatur zu bringen.

However, a shorter, faster cooling step is preferred because of the high speed at which the web passes through modern coating equipment. In the case of a prolonged cooling step, one would inevitably have to extend the coating system. The best compromise between these seemingly contradictory requirements can be achieved through a three-phase cooling step composed as follows:

• • Cooling phase 1: rapid cooling, whereby the temperature of the precursor is lowered to a value T1, which is above the Tg of the phenolic resin.
• • Cooling phase 2: slower cooling, whereby the temperature of the precursor is lowered to a value T2 below the Tg of the phenolic resin.
• • Cooling phase 3: again a rapid cooling to bring the temperature to room temperature.

The first fast cooling phase can be done at very high average cooling rate, z. B. at a speed of at least 10 ° C / s, especially preferably between 10 ° C and 20 ° C / s or even more than 20 ° C / s. In the second cooling phase finds the transition in the temperature interval around the Tg value at low mean cooling instead of, d. H. the lowering of the precursor temperature of T1 T2 occurs at a lower average cooling rate than in phase 1, z. B. at a medium speed below 10 ° C / s. Preferred values for T1 and T2 are Tg + 20 ° C or Tg - 20 ° C, especially preferably Tg + 10 ° C or Tg - 10 ° C. In a very particularly preferred embodiment takes the fast cooling off in phase 1 until the temperature of the precursor just above the Tg value of the phenolic resin comes to rest. Subsequently, will this one just over Tg value by slowly cooling down to just below lowered the Tg value, after which finally another fast Cooling phase, however, they have no significant effect on the aging behavior causes can be made. The in the present invention range between "just over" and "just below" the Tg value z. Between Tg + 5 ° C and Tg - 5 ° C, especially preferably between Tg + 2 ° C and Tg - 2 ° C.

The average cooling rate in the second cooling phase can over or below the cooling rate under ambient conditions, with no coolant such as a chill roll are used, lie. The average cooling rate in the second cooling phase is preferably between 0.1 ° C / s and 5 ° C / s, more preferably between 0.2 ° C / s and 3 ° C / s. With values between 1 ° C / s and 2 ° C / s achieved excellent results. Once the web temperature in this way can be lowered to below the Tg value, in the third cooling phase again a quick cooling be made, for. B. at a medium cooling rate of at least 10 ° C / s, more preferably between 10 ° C / s and 20 ° C / s or even more than 20 ° C / s.

Phenol resins, such as the commercially available novolak resins, generally have a Tg value between 75 ° C and 95 °, a typical Tg value is between 80 ° C and 90 ° C. A typical example of a preferred web temperature profile according to the invention is shown in FIG 1 shown in which the Tg of the phenolic resin is 84 ° C. In 1 the drying is carried out with hot air at a temperature of 130 ° C and hot air at a temperature of 160 ° C is used in the heating step. During the first cooling phase, a rapid cooling from> 150 ° C to 100 ° C takes place within a few seconds, after which a slower cooling of 100 ° C to 70 ° C within 16 s (ie at an average cooling rate of 1.9 ° C / s) and finally the web is cooled in a second rapid cooling phase in a few seconds to room temperature.

The Heating and cooling steps described above result Material that is significantly shorter after an aging period, as if one did not subject the material to these steps, e.g. B. after several weeks compared to several months, with a stable sensitivity. Except this improved aging behavior also causes a significant improvement in the above process resistance against mechanical damage the coating of materials according to the invention. In particular, by the above cooling process, in which the temperature transition The Tg value is slow, a significant improvement the scuff resistance achieved.

For carrying out the processes according to the invention, a coating plant for which a typical example is given in FIG 2 is used. carrier 1 is from a coil 2 unwound, then by means of a coating element 3 coated with one or more layers and then in a multistage dryer 4 - 5 - 6 - 7 dried, by heat source 8th that z. B. is an infrared light source or a Heißluftblasdüse, heated, then by roller 9 cooled and finally on core 13 wound. The air nozzles 10 - 11 - 12 can do an extra cooling. The temperature of roller 9 is preferably at a value just above the Tg of the phenolic resin and the temperature of the nozzle 10 just below the Tg value, so that the transition in the temperature interval around the Tg value is slow.

The formation of the lithographic image on the printing plate precursor of the invention is based on a thermally induced difference in solubility between one or more layers of the coating during development in the developer. In general, the exposure causes a change in the solubility of the phenol resin-containing layer in the developer. One or more additional layers may play an active role in the imaging process. In certain embodiments, the coating may further comprise one or more layers that are not important to the imaging mechanism, e.g. For example, a layer whose solubility in the developer is not significantly changed by the exposure. An example of such a layer is one attached to the coating Protective layer that can dissolve in both the exposed and unexposed areas in the developer. Also, layers attached between the support and the image-forming layers usually do not play a role in the imaging process.

Of the solubility between image areas (i.e., printing, oleophilic areas) and non-image areas (i.e., non-printing, hydrophilic areas) the lithographic image is rather by a kinetic characterized as a thermodynamic effect, d. H. the non-image areas dissolve faster in the developer than the image areas. In a very special preferred embodiment are solved first the non-image areas completely in the developer, before the developer begins to solve the image areas. Therefore, the image areas are sharp edges and a high Color attraction marked. The time difference between the end of the solution of non-image areas and the beginning of the solution the image areas is preferably longer than 10 seconds, especially preferably longer than 20 seconds, and most preferably longer than 60 seconds, which means that a further development latitude is obtained.

In one embodiment, the printing plate precursor is negative working, that is, the image areas correspond to the exposed areas. A suitable negative-working coating comprises a phenolic resin and a latent Bronsted acid which forms an acid upon heating or IR irradiation. These acids catalyze the cross-linking of the coating in a heating step subsequent to the exposure or heating step, and thus the curing of the exposed or heated areas. Accordingly, the unexposed areas may be washed away by a developer and exposed to the underlying hydrophilic substrate. For a more detailed description of such a negative-working printing plate precursor be on US Pat. No. 6,255,042 and US Pat. No. 6,063,544 as well as the references mentioned in these documents.

To another embodiment the printing plate precursor is positive working. In such embodiment can or can one or more layers of the coating by the action of Heat solubilized be, d. H. in non-heated or non-exposed Condition they are stable against the developer and color attracting, when heated or irradiated with Infrared light, however, they are made soluble in the developer so that the hydrophilic surface of the carrier to be released. After exposure and development are so the illuminated areas of the vehicle removed and form hydrophilic (non-printing) non-image areas, while the unexposed areas have not been removed from the vehicle and form an oleophilic (printing) image area.

Of the carrier The lithographic printing plate precursor has a hydrophilic surface or is provided with a hydrophilic layer. The carrier can a sheet-like material, such as a plate, or be a cylindrical Element, like a sleeve-shaped plate, which can be pushed around a printing drum of a printing press. The carrier is preferably a metal carrier, like an aluminum carrier or a carrier stainless steel. The metal carrier may also be a laminate made of an aluminum foil and a plastic layer, for. B. a polyester film exists.

A particularly preferred lithographic support is an electrochemically roughened and anodized aluminum support. The roughening and anodizing of aluminum is a process well known to those skilled in the art. The anodized aluminum support may be subjected to processing to improve the hydrophilic properties of the support surface. For example, by processing the support surface with a sodium silicate solution at elevated temperature, e.g. B. 95 ° C, silicate. Alternatively, a phosphate processing may be performed wherein the alumina surface is processed with an optional further inorganic fluoride-containing phosphate solution. Further, the alumina surface may be rinsed with a citric acid or citrate solution. This treatment can be carried out at room temperature or at a slightly elevated temperature between about 30 ° C and 50 ° C. Another interesting method is to rinse the alumina surface with a bicarbonate solution. Further, the alumina surface may be processed with polyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl alcohol, polyvinylsulfonic acid, polyvinylbenzenesulfonic acid, sulfuric acid esters of polyvinylalcohol and acetals of polyvinylalcohols formed by reaction with a sulfonated aliphatic aldehyde. Further, it is obvious that one or more of these post treatments may be performed separately or in combination. More detailed descriptions of these treatments can be found in GB-A 1 084 070 . DE-A 4 423 140 . DE-A 4 417 907 . EP-A 659 909 . EP-A 537 633 . DE-A 4 001 466 . EP-A 292 801 . EP-A 291 760 and U.S. Patent 4,458,005 ,

According to a further embodiment, the carrier may also be a flexible carrier, which with The flexible support is, for example, paper, a plastic film, a thin aluminum support or a laminate of these materials Preferred examples of plastic films are a film of polyethylene terephthalate, polyethylene naphthalate, Cellulose acetate, polystyrene, polycarbonate, etc. The plastic film backing may be opaque or translucent The primer layer is preferably a crosslinked hydrophilic layer obtained from a hydrophilic binder crosslinked with a curing agent such as formaldehyde, glyoxal, polyisocyanate or hydrolyzed tetraalkylorthosilicate Suitable hydrophilic primer layers for use in the present invention are disclosed in U.S. Patent Nos. 4,305,359 EP-A 601 240 . GB-P 1 419 512 . FR-P 2 300 354 . U.S. Pat. No. 3,971,660 and U.S. Patent 4,284,705 ,

The Phenol resin is preferably a binder with acid groups, their pKa is less than 13. This ensures that that it is soluble or at least swellable in aqueous alkaline Developers is. Conveniently, the binder is a polymer or polycondensate with free phenolic hydroxyl groups, such as by reaction of phenol, resorcinol, a cresol, a xylenol or a trimethylphenol with aldehydes, in particular formaldehyde, or ketones are obtained. The polymers can additionally Contain units of other monomers without acid groups. As such Units are vinylaromatics, methyl (meth) acrylate, phenyl (meth) acrylate, Benzyl (meth) acrylate, methacrylamide or acrylonitrile. In a preferred embodiment the phenolic resin is a novolac, resol or polyvinyl phenol. The Novolac is preferably a cresol / formaldehyde novolak or a Cresol / xylenol / formaldehyde novolac, the amount of novolac expediently at least 50% by weight, preferably at least 80% by weight, in each case based on the total weight of all binders. The amount Phenol resin is suitably between 40 and 99.8% by weight, preferably between 70 and 99.4% by weight particularly preferably between 80 and 99 wt .-%, each based on the total weight of non-volatile Components of the coating.

The solution behavior of the phenolic resin in the developer may be due to optional solubility regulating substances be fine adjusted. In addition there are development accelerators and development inhibitors in question. These ingredients can be the the phenol resin-containing layer and / or one or more be added to other layers of the coating.

Development accelerators are compounds which promote the solution because they can increase the rate of dissolution of the phenolic resin. By way of example, cyclic acid anhydrides, phenols or organic acids can be used to enhance the developability in aqueous media. Examples of cyclic acid anhydrides include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 3,6-endoxy-4-tetrahydrophthalic anhydride, tetrachlorophthalic anhydride, maleic anhydride, chloromaleic anhydride, α-phenyl maleic anhydride, succinic anhydride, and pyromellitic anhydride as described in US Pat US Pat. No. 4,115,128 , Examples of the phenols 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'-tetramethyltriphenylmethane and the like. Examples of the organic acids include sulfonic acids, sulfinic acids, alkylsulfuric acids, phosphonic acids, phosphates and carboxylic acids, as described, for example, in US Pat JP-A 60-88,942 and JP-A 2-96755 , Typical examples of these organic acids include p-toluenesulfonic acid, dodecylbenzenesulfonic acid, p-toluenesulfinic acid, ethylsulfuric acid, phenylphosphonic acid, phenylphosphinic acid, phenylphosphate, diphenylphosphate, 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. The amount of cyclic acid anhydride, phenol or organic acid in the coating is preferably between 0.05% and 20% by weight.

In a preferred embodiment contains the coating also developer resistance agent, also as a development inhibitor denotes, d. H. one or more ingredients, the or the the release the non-exposed areas during to delay development can or can. The solution-inhibiting Effect is preferably mitigated by the heating, so that the solution the exposed areas is not delayed and thereby a large difference in solution between exposed and non-exposed areas. Such developer resistance agents can a layer containing phenolic resin or another layer of the material are added.

The in for example EP-A 823 327 and WO 97/39894 described compounds act as dissolution inhibitors (dissolution inhibitors) as a result of their interaction, for. By forming a hydrogen bond with the alkali-soluble binder (s) in the coating. Inhibitors of this type contain in the Rule a hydrogen bond forming group, such as nitrogen atoms, onium groups, carbonyl groups (-CO groups), sulfinyl groups (-SO groups) or sulfonyl groups (-SO ₂ groups), and a high hydrophobic portion, such as one or more aromatic rings.

Other suitable inhibitors enhance resistance to the developer by retarding the penetration of the aqueous alkaline developer into the phenol resin-containing layer. Such compounds may be included in the phenolic resin-containing layer itself as described in, for example, US Pat. B. EP-A 950 518 , or in an on this layer development barrier layer, as described in, for. B. EP-A 864 420 . EP-A 950 517 . WO 99/21725 and WO 01/45958 , In the positive working embodiment, the barrier layer preferably contains a polymeric material which is insoluble in the developer or impermeable to the developer, e.g. As acrylic (co) polymers, polystyrene, styrene-acrylic copolymers, polyesters, polyamides, polyureas, polyurethanes, nitrocelluloses and epoxy resins and silicones. In this embodiment, the solubility of the barrier layer in the developer or the penetrability of the developer in the barrier layer can be increased by heating or exposure to infrared light.

Preferred examples of inhibitors of the latter type include water-repellent polymers such as a polymer having siloxane units and / or perfluoroalkyl units. In a typical embodiment, the precursor comprises a barrier layer comprising a water repellent polymer in a suitable amount between 0.5 and 25 mg / m ² , preferably between 0.5 and 15 mg / m ^2, and most preferably between 0.5 and 10 contains mg / m ² . Depending on the hydrophobic / oleophobic degree of the compound, higher or lower amounts are also suitable. Is the water-repellent polymer also color repellent, z. Example, when using polysiloxanes, the use of amounts exceeding 25 mg / m ² can lead to a weak color attraction of the unexposed areas. On the other hand, an amount less than 0.5 mg / m ² may result in unsatisfactory developer resistance. The polysiloxane may be a linear, cyclic or complex crosslinked polymer or copolymer. The term "polysiloxane compound" includes any compound containing more than one siloxane group -Si (R, R ') - O- in which R and R' represent an optionally substituted alkyl or aryl group Preferred siloxanes are phenylalkylsiloxanes and dialkylsiloxanes. The number of siloxane groups in the (co) polymer is at least 2, preferably at least 10, more preferably at least 20. It can be below 100, preferably below 60. In another embodiment, the water-repellent polymer is a block copolymer or graft copolymer of a poly (alkylene oxide) and A suitable copolymer contains about 15 to 25 siloxane units and 50 to 70 alkylene oxide groups Preferred examples include copolymers with phenylmethylsiloxane and / or dimethylsiloxane and ethylene oxide and / or propylene oxide such as Tego Glide 410, Tego Wet 265, Tego Protect 5001 or Silikophen P50 / X, all by Tego Chemie, Essen, German land, be distributed. As a result of its bifunctional structure, such a copolymer acts as a surfactant during coating, tending to position itself at the interface between the coating and the air to form a separate topcoat even as an ingredient of the same coating solution as the phenolic resin is applied. At the same time, such surfactants act as spreading agents, which improves the coating quality. However, the water repellent polymer may also be applied from a second solution to the phenol resin-containing layer. In this embodiment, it may be advantageous to use in the second coating solution a solvent which is incapable of dissolving the ingredients contained in the first layer, whereby a highly concentrated water-repellent phase is obtained on the material.

The coating preferably also contains a compound that absorbs infrared light and converts the absorbed energy into heat. The infrared absorbing compound may be embedded in the same layer as the phenolic resin, in the optional barrier layer discussed above, or in another optional layer. In a most preferred embodiment, the dye or pigment is concentrated in or near the barrier layer, e.g. In an intermediate layer between the oleophilic layer and the barrier layer. According to this embodiment, the amount of the IR-absorbing compound in the intermediate layer is above the amount of the IR-absorbing compound in the oleophilic layer or in the barrier layer. The ratio of the IR-absorbing compound in the coating is generally between 0.25 wt .-% and 10.0 wt .-%, more preferably between 0.5 wt .-% and 7.5 wt .-%. Preferred infrared absorbing compounds are dyes such as cyanine dyes and merocyanine dyes, or pigments such as carbon black. Examples of suitable IR absorbers are described in, for. B. EP-A 823 327 . EP-A 978,376 . EP-A 1 029 667 . EP-A 1 053 868 . EP-A 1 093 934 . WO 97/39894 and WO 00/29214 , A preferred compound is the cyanine dye according to the following formula:

Optional Furthermore, a protective layer can be attached to the surface of the Protect coating especially against mechanical damage. The protective layer contains in the Usually at least one water-soluble polymeric binder, such as polyvinyl alcohol, polyvinylpyrrolidone, partially hydrolyzed polyvinyl acetates, gelatin, carbohydrates or hydroxyethyl cellulose, and may be any known Technique can be made, such as from an aqueous solution or dispersion, if necessary small amounts of organic solvents may contain, d. H. Amounts below 5 wt .-%, based on the total weight the for the protective layer used coating solvents. The strength of Protective layer can be chosen arbitrarily be, is expediently to 5.0 μm and is preferably between 0.1 .mu.m and 3.0 .mu.m, more preferably between 0.15 μm and 1.0 μm.

Optionally, the coating, and in particular the phenolic resin-containing layer (s), may further contain additional ingredients. For example, z. As additional binders, especially sulfonamide-containing and phthalimide-containing polymers, through which the shelf life and chemical resistance of the plate can be improved. Examples of such polymers are those in EP-A 933,682 . EP-A 894,622 and WO 99/63407 described polymers. It is also possible to add colorants, such as dyes or pigments, which give the coating a visible color. Such colorants remain in the unexposed areas of the coating and ensure that a visible image is obtained after exposure and development. Typical examples of such contrasting dyes are the amino-substituted tri- or diarylmethane dyes, e.g. Crystal Violet, Methyl Violet, Victoria Pure Blue, Flexo Blue 630, Basonyl Blue 640, Auramine and Malachite Green.

to Production of the lithographic printing plate precursor may be any known technique are applied. By way of example, the above ingredients in a solvent mixture that is not irreversible reacts with the ingredients and preferably to the intended Coating process, the layer thickness, the composition of the Layer as well as the drying conditions is tuned to be solved. To suitable solvents counting Ketones, such as methyl ethyl ketone (butanone), and chlorinated hydrocarbons, such as trichlorethylene or 1,1,1-trichloroethane, alcohols, such as methanol, Ethanol or propanol, ethers, such as tetrahydrofuran, glycol monoalkyl ethers, such as ethylene glycol monoalkyl ethers, e.g. 2-methoxy-1-propanol, or propylene glycol monoalkyl ether and esters, such as butyl acetate or propylene glycol monoalkyl ether acetate. It can also be used a mixture, which for special purposes additionally solvents like Acetonitrile, dioxane, dimethylacetamide, dimethyl sulfoxide or water may contain.

The end user can perform the imagewise exposure of the lithographic printing plate precursor either directly by heating, e.g. B. by means of a thermal head, or indirectly with infrared light, preferably near infrared light. The infrared light is preferably converted to heat by an infrared-absorbing compound as discussed above. The heat-sensitive lithographic printing plate precursor of the present invention is preferably insensitive to visible light, that is, exposure to visible light does not significantly affect the rate of dissolution of the coating in the developer. Most preferably, the coating is insensitive to ambient daylight, ie visible light (400-750 nm) and near ultraviolet light (300-400 nm), at a light intensity and exposure time corresponding to those used under normal operating conditions Handling no darkroom required. By "insensitive" to daylight is meant that exposure to ambient daylight does not cause a noticeable change in dissolution rate of the coating in the developer. In a preferred daylight resistant embodiment, the coating does not contain radiation sensitive components such as diazide, quinone diazide, diazo or diazonium compounds, photoacids, photoinitiators, sensitizers, etc., which are described in Son absorb near ultraviolet light and / or visible light contained therein, thereby changing the solubility of the coating in the exposed areas.

The printing plate precursor according to the invention can by means of z. B. an LED or a laser can be exposed to infrared light. Very particularly preferred for the exposure is a near infrared light having a wavelength between about 750 and about 1500 nm emitting laser, such as a semiconductor laser diode, a Nd: YAG laser or a Nd: YLF laser. The laser power required depends on the sensitivity of the imaging layer, the pixel dwell time of the laser beam as determined by the beamwidth (a typical value at 1 / e ² maximum intensity is between 10 and 25 microns for modern platesetters), scanning speed and resolution of the opacity (ie the number of addressable pixels per unit length, often expressed in dots per inch or dpi / typical values are between 1,000 and 4,000 dpi).

It are two types more common Laser imager, d. H. an inner drum plate setter (ITD platesetter) and an outer drum plate setter (XTD) plate-. ITD plate-setters for thermal plates usually by very high scanning speeds up to 500 m / s and sometimes need a laser power of several watts. XTD platesetter for thermal plates operate at a lower scanning speed, e.g. B. between 0.1 m / s and 10 m / s, and a typical laser power between about 200 mW and about 1 W.

The known platesetters are suitable for use as off-press gelators, which offers the advantage of reducing press downtime. XTD platesetter configurations are also suitable for on-press exposure, which has the advantage of immediate registration of the plate into a multi-color press. More detailed technical information on on-press-gelators are z. In US 5,174,205 and US 5,163,368 described.

In the development step, the non-image areas of the coating are removed by immersion in a conventional aqueous alkaline developer, optionally in combination with mechanical wiping, e.g. B. by means of a brush roller. During development any possible water-soluble protective layer is also removed. To avoid damaging the (possible) toner layer of the substrate, preferred are silicate-based developers having a silica to alkali metal oxide ratio of at least 1. Preferred alkali metal oxides include Na ₂ O and K ₂ O and mixtures thereof.

In addition to alkali metal silicates, the developer, as well known to those skilled in the art, may further contain other ingredients such as buffering agents, chelating agents, defoaming agents, small amounts of organic solvents, corrosion inhibitors, dyes, surfactants and / or hydrotropes. The development is preferably carried out at a temperature between 20 ° C and 40 ° C in a conventional, known to those skilled in developing machines. Suitable solutions for the regeneration are alkali metal silicate solutions having an alkali metal content between 0.6 and 2.0 mol / l. These solutions may have the same silica / alkali metal oxide ratio as the developer (but usually lower) and optionally contain other ingredients. The required quantities of regenerated material are to be matched to the processing equipment used, the daily board throughput, the image areas, etc., and are generally between 1 and 50 ml per square meter of recording material. The addition can be controlled, for example, by measuring the conductivity as described in EP-A 0 556 690 ,

The printing plate precursor of the invention may then be post-treated, if necessary, as known to those skilled in the art, with a suitable correcting agent or preservative. To increase the resistance of the finished printing plate and thus to increase the achievable print run, the layer can be briefly heated to high temperatures ("burn-in"). This baking step increases the resistance of the printing plate to washout agents, correction agents and UV-curable inks. Such a thermal aftertreatment is described inter alia in DE-A 14 47 963 and GB-A 1 154 749 ,

Except the mentioned above Aftertreatment may also further the development of the printing plate precursor a rinsing step, a drying step and / or a gumming step.

The printing plate thus obtained is suitable for conventional, so-called wet offset printing, in which printing ink and fountain solution are applied to the plate. In another suitable printing method so-called single-fluid printing ink is used without fountain solution. Single-fluid printing inks which are suitable for use in the process according to the invention are described in US Pat US 4,045,232 . US 4,981,517 and US 6,140,392 , In a most preferred embodiment, the single-fluid ink contains an ink phase, also referred to as hydrophobic or oleophilic phase, and a polyol phase, as be wrote in WO 00/32705 ,

EXAMPLES

The following composition is applied in a wet layer thickness of 26 μm and at a speed of 16 m / min. on a conventional, roughened and anodized aluminum carrier web applied: - Methoxypropanol (Dowanol PM ^™ ) 410.80 g - Methyl ethyl ketone 266.03 g - tetrahydrofuran 209.20 g 40.4% by weight solution (Alnovol SPN 452 ^™ ) of Novolac in Dowanol PM ^™ 103.25 g 3,4,5-trimethoxycinnamic acid 5.34 g Dye IR-1 (see formula above) 2.10 g - Basonyl Blue 640 ^TM (contrasting dye) 0.53 g TEGO Glide 265 ^™ (10% strength by weight solution of a surfactant Polyalkylene oxide and polysiloxane) 0.85 g TEGO Glide 410 ^™ (10% strength by weight solution of a surfactant Polyalkylene oxide and polysiloxane) 2.12 g

The Coating is at 135 ° C dried air and then an optional heating step and a cooling step subjected. In the heating step, air with the in Table 1 temperature for 1.2 s on the coating. In Examples 1 and 2, the hot air nozzles are turned off. Right after will the back the web with a metal chill roll brought into contact with the temperature given in Table 1. A chill roll with a temperature of 57 ° C lowers the temperature of the heated coating very quickly (> 30 ° C / s) to a value below Tg. When using a chill roll with a temperature of 75 ° C The temperature interval around the Tg value is bridged at much lower mean cooling rate.

Subsequently, the materials are exposed at different energy density values on a Creo Trendsetter 3244 (830 nm). The exposed plates are at a speed of 0.84 m / min. developed using Agfa Ozasol EP26 developer at 25 ° C in an Agfa Autolith PN85 processor and finally gummed with Agfa Ozasol RC795. The IR sensitivity is defined as the minimum energy density setting needed to achieve 50% light absorption in areas exposed to 50% area coverage (@ 200 lpi), with the measurement on the developed plate occurs at the maximum wavelength of the dye. Sensitivity is measured on fresh material as well as on material aged under ambient conditions during the number of days indicated in Table 1. Table 1 example Temperature of hot air (° C) Temperature of cooling roll (° C) Sensitivity (mJ / cm ² ) after aging 0 days 5 days 10 days 15 days 25 days 1 (see) - 57 - 26 60 80 107 2 (required) - 75 - 103 110 133 130 3 (required) 170 75 93 160 187 208 205

From the data in Table 1 it can be seen that the materials cooled according to the invention reach a stable sensitivity from 25 days after their coating, while the sensitivity of the comparative material in Example 1 was still variable even after 25 days and only two months after coating on a Stabilized value of 165 mJ / cm ² .

• * AG: Abkühlgeschwindigkeit

The improved aging behavior can also be detected by subjecting the materials treated according to the method of the invention to an offline heat treatment. Produced Examples 4, 5 and 6 are obtained by applying and drying the same composition in the same way as described for the previous examples. Subsequently, the dried materials are subjected to a heat treatment step in which air at a temperature of 135 ° C is blown onto the dry coating by means of an additional dryer. Between this heat treatment and where the web reaches the chill roll, the web cools down under ambient conditions so that the web has a temperature of 118 ° C just prior to reaching the chill roll. Then follows a first rapid cooling with a metal roller with a constant temperature given in Table 2. The contact between the material and the cooling roll takes 2.41 s. Once the web has been conveyed past the metal chill roll, air at a temperature of 50 ° C. is immediately blown onto the coating in a second, slower cooling phase for 32 s. Table 2 Ex. Cooling with metal roller (2.41 s) Cooling with air heated to 50 ° C (32 s) Temp. Of the chill roll (° C) Bahntemp. just after the chill roll (° C) average AG * with the cooling roller (° C / s) Bahntemp. just after cooling with air (° C) average AG * when cooled with air (° C / s) 4 65 66 22 51 0.47 5 75 76 18 57 0.59 6 85 86 14 63 0.72

• * AG: cooling rate

Sensitivity is measured on fresh material as well as material that has undergone 7 days off-line artificial aging at the temperature indicated in Table 3. From the data in Table 3 it can be seen that the slower, ie cooled with a chill roll with higher temperature, cooled materials with a more stable aging behavior. Example 6 is cooled in the temperature interval around the Tg value at a very low cooling rate and gives the best aging behavior, as can be seen from the small effect of the additional off-line heat treatment. Table 3 example 0 days 7 days at 20 ° C 7 days at 25 ° C 7 days at 30 ° C 4 17 159 210 222 5 87 167 200 226 6 101 210 220 233

Claims (7)

A marked by the following steps Process for the preparation of a heat-sensitive lithographic Printing plate precursor: (i) providing a web of lithographic carrier with a hydrophilic surface, (Ii) Application of a coating containing a phenolic resin on the hydrophilic Web surface (Iii) Drying the coating by heating the coated web, (Iv) an active cooling step, in which the web temperature at an average cooling rate, the higher is as when the web is stored under ambient conditions, however Does not exceed 30 ° C / s, lowered will, and (v) winding the precursor to a core or cutting the precursor in bow. Method according to claim 1, characterized in that that the average cooling rate not more than 20 ° C / s is. Method according to claim 1, characterized in that that the average cooling rate not more than 10 ° C / s is. Method according to one of the preceding claims, characterized characterized in that the web temperature at the beginning of the cooling step above the Freezing point Tg of the phenol resin-containing coating is and the web temperature during of the cooling step at a medium cooling rate below 10 ° C / s from T1 to T2, with either T1 Tg + 20 ° C and T2 Tg - 20 ° C or T1 Tg + 10 ° C and T2 Tg - 10 ° C. Method according to claim 4, characterized in that that the web temperature during of the cooling step - in a first phase at a mean cooling rate of at least 10 ° C / s T1 is lowered and - in a second phase at a mean cooling rate below 10 ° C / s of T1 is lowered to T2. Method according to claim 4, characterized in that that the web temperature during of the cooling step - in a first phase at a mean cooling rate of at least 10 ° C / s T1 is lowered, - in a second phase at a mean cooling rate below 10 ° C / s of T1 is lowered to T2 and - in a third phase at a mean cooling rate of at least 10 ° C / s of T2 is lowered to room temperature. Method according to claim 4, 5 or 6, characterized that cooling off from T1 to T2 at an average cooling rate below 5 ° C / s.