MXPA06007775A - Photothermally sensitive compositions and system for ctp imaging processes - Google Patents

Abstract

Plates coated with compositions photothermally sensitive to multiple portions of the electromagnetic spectrum and useful for the preparation of lithographic printing plates, color proofing films and the like by computer to Alate imaging processes comprising a solvent, cross-linkable polymers and monomers, and energy absorbing dye/laser dye/initiator/sensitizers, where the energy absorbing dye/laser dye/initiator/sensitizers are selected from dye/initiator/sensitizers having increased sensitivities to varying portions of the electromagnetic spectrum and where the sensitivity of the imaged Alate is increased by Are-heating prior to development.

Description

PHOTOTHERMAL COMPOSITIONS AND SENSITIVE SYSTEM FOR COMPUTER IMAGE FORMATION PROCEDURES A LICENSE PLATE FIELD OF THE INVENTION The invention relates to photothermally sensitive coating compositions useful for the preparation of lithographic printing plates, color proof films and the like by computer-to-plate imaging methods.

BACKGROUND OF THE INVENTION The art of letterpress printing is based on the non-miscibility of oil and water, where the oily material or ink is preferably retained by the image area and the water or the source solution is preferably retained by the non-image area. When a suitably prepared surface is moistened with water and then an ink is applied, the toner or non-image area retains water and repels the ink, while the image area accepts the ink and repels the water. The ink on the area of the image is then transferred to the surface of a material on which the image is to be reproduced, such as paper, cloth and the like. Commonly the ink is transferred to an intermediate material called sheet, which in turn transfers the ink to the surface of the material on which the image will be reproduced. A very widely used type of lithographic printing plate has a light sensitive cover applied to an aluminum base. The cover can respond to light by having the portion that is exposed that becomes soluble, so that it is removed in the embodiment process. This plate is called positive work. Conversely, when a portion of the cover that is exposed hardens, the plate is called work in negative. In both cases the area of the image that remains is receiving the ink, or oleophilic, and the area without image or environment is receiving water, or hydrophyte. The differentiation between image and non-image areas is done in the exposure procedure, where a film is applied to the plate with a vacuum to ensure good contact. The plate is then exposed to a light source, a portion of which is composed of UV radiation. In the case that a positive plate is used, the area in the film corresponding to the image on the plate is opaque, so that the light will not affect the plate, while the area in the film corresponding to the area without image it is clear and allows the transmission of light towards the cover, which then becomes more soluble and is removed. In the case of a negative plate, the opposite is true. The area in the film that corresponds to the image area is clear, while the non-image area is opaque. The cover under the clear area of the film hardens by action of light, while the area where light does not strike is removed. The surface hardened by the light of a negative plate is therefore oleophilic and will accept the ink, while the non-image area from which the cover has been removed through the action of a developer is desensitized, and therefore It is hydrophilic. The direct digital imaging of offset printing plates has had an increasing importance in the printing industry. Advances in solid-state laser technology have made it a means for high-power diode lasers to be attractive sources of energy for plate composers, particularly lasers that emit energy in regions near the infrared (800-850 mm) . The use of controlled laser exposure obviates the need to use a film or mask when image exposures are made, thereby facilitating a masking operation of the plate. There are numerous patents of the United States relating to imaging compositions that are sensitive to infrared energy and that contain one, or a mixture of, phenolic resins and at least one ink or infrared-absorbing pigment. Positive-acting plates, based on a mixture of a novolak or resole resin or polyhydroxy-styrene resin and an IR-absorbing ink, are described in U.S. Pat. No. 6,063,544. Printing plates based on a mixture of novolak resin, a resole resin, an infrared absorbing dye or pigment and a latent Bronstead acid are described in US Pat. Us. ,372,907, 5,372,915, 5,466,577, and 5,491, 046. The exposure of these plates to infrared radiation decomposes the latent Bronstead acid to produce species that will serve for the cross-linking of resole resins and novolak, thereby hardening the mixture in the exposed areas. Subsequent heating of the exposed plate tends to further harden the exposed coating, which becomes insoluble in the aqueous alkaline developer, while the unexposed areas remain soluble in the developer solution. In addition, the patents of E.U.A. Nos. 5,705,322 and 5,858,626 disclose laser-readable photosensitive elements based on, or in a mixture of, phenolic resin and an o-diazonaphthoquinone derivative or in the esterification product thereof with a phenolic resin and an infrared absorbing compound . The elements of the '322 patent are negative work and first require the exposure of the image, followed by exposure to the light flow before development. The elements of the '626 patent are positive work and do not require light flow before or after development. One of the problems associated with these, and with similar, systems, is that there is often insufficient integrity of the image areas that remain after the development of the printing plate to effectively perform the image representation procedure. throughout the print runs, resulting in printed images that have lower resolution and print quality than desired. The existing photosensitive aqueous coatings have comparatively much slower exposure speed and need much higher UV energy (above 10 milijoules), and therefore are not usable in modern technologies and equipment of imaging plates that use UV lasers , UV light sources and other types of lasers such as violet lasers, thermal and 830 IR. These computer-to-board (CTP) applications include different types of lasers, and therefore require photosensitive covers optimized for them and that have increased sensitivity for different wavelengths, e.g. eg, 350 nm for UV lasers, 405 nm for violet lasers, 830 or 1064 nm for IR thermal lasers, etc. The current plate-making process of conventional plates using aqueous developer chemistries is relatively simple and uses a mild alkaline aqueous developer that does not contain strong solvents or highly corrosive materials. These developer systems are environmentally friendly and user-friendly. The developer does not rust with exposure to the atmosphere, unlike other chemical developers. There have been attempts to increase the sensitivity of conventional photosensitive plates by using, for example, long preheating and / or high temperature [temperatures in excess of 121 ° C for periods in excess of 60 seconds] before development, and highly alkaline chemicals [pH of 13 or more] to develop the image. These chemical developers are highly corrosive and have a very short life, mainly due to atmospheric oxidation. These factors increase the instability of the developer to the point where expensive special processing equipment is required, which makes the whole process slow and very expensive to operate and maintain. It is also normally required that the post-processing of the plates increases the durability of the finished plate. Some thermally sensitive 830 nm IR plates are available. However, these plates suffer the dual disadvantage of producing separation residues during imaging, which must be removed from the plate with a sediment removal system in the imaging device, and / or produce toxic fumes that are released during imaging when using lasers IR of 803 nm IR. An object of this invention is to provide compositions and methods for the CTP preparation of printing plates using conventional equipment and procedures / methods of standard operation. An object of this invention is to provide compositions and methods for the CTP preparation of printing plates using the majority of conventional raw materials. An objective of this invention is to provide compositions and methods for the preparation of CTP printing plates using chemicals mild alkaline aqueous developers, and processing equipment, insurance. An object of this invention is to provide compositions and methods for the preparation of CTP printing plates using developers that do not oxidize with exposure to the atmosphere. An object of this invention is to provide compositions and methods for the preparation of CTP printing plates using a short low temperature preheating step, and the current plate processing equipment. An object of this invention is to provide compositions and methods for the CTP preparation of printing plates that do not produce toxic fumes and cover debris cut when imaging with IR lasers of 830 nm. An object of this invention is to provide compositions and methods for the CTP preparation of printing plates having a printing life of over one million impressions. An objective of this invention is to provide a photosensitive plate having increased sensitivity to match the higher speed requirements of the CTP technologies and devices for plate imaging. An objective of this invention is to provide a universal photosensitive plate that allows the plate to adjust to the requirement of Higher speed of modern CTP plate imaging technologies using variable spectrum light sources.

BRIEF DESCRIPTION OF THE INVENTION A system comprising components suitable for use in plate CTP processing is described, wherein a plate substrate, preferably aluminum, is coated with a photothermally sensitive multicomponent composition, printed on a CTP plate making device, thermally treated for the cross-linking of the portions of the cover and the developed image. An optional post-heating significantly increases the functional life of the plate. The new cover compositions are usable with modern plate imaging technologies and equipment using UV lasers, UV light sources and other types of lasers, such as violet, thermal or 830 IR lasers. These computer-to-board (CTP) applications include different types of lasers and therefore require photosensitive covers optimized for them and that have increased sensitivity for different wavelengths, e.g. eg, 350 nm for UV lasers, 405 nm for violet lasers, 830/1064 nm for IR thermal lasers, 800-850 for IR lasers, etc.

The superior results derived from the use of this system depend on the selection of the components that are contained in the photothermally sensitive cover composition and the provision of a preheating step with post-imaging and pre-development conducted with specified parameters of temperature and duration. The compositions described achieve their desirable characteristics due in part to a preheating step that is provided after plaque imaging, but prior to the development of the image with an aqueous alkaline developer. In the absence of a preheating step, current technologies require significantly higher level energy to print the plate, and thus become impractical or unmanageable with computer-to-plate (CTP) lasers or UV light source applications . These and other benefits are obtained with the compositions and methods described to make the plates more photothermal sensitive and receptive to the target wavelength of the light source, by adding appropriate dye / energy absorbers having an absorption? maximum at, or close to, the corresponding wavelength of the energy source of the image formation. The speed of the composition can be intimately adjusted to the input level of the energy during image formation, by modifying the concentration of the photoinitiators to couple the required exposure rate. The specified dyes are included in the composition to increase absorption at the wavelength of energy of representation of the image. The combination of the specified dyes and other components combined with the preheating step results in a universal imaging plate, sensitive to energy sources with different wavelengths, and capable of replacing multiple types of plates each having a unique area of increased sensitivity. The process for preparing the compositions described comprises the steps of: 1. sequentially mixing the components of the photothermally sensitive composition; 2. applying the photothermally sensitive coating composition to the plate substrate; 3. optionally, apply a protective cover over the covered substrate; 4. form the image on the covered substrate; 5. thermally treat the covered substrate with the image shown; 6. develop the image; and 7. optionally post-heating the developed substrate. The described system utilizes a photothermally sensitive composition coated on a substrate and a post-imaging pre-development heating process to produce a long life printing plate sensitive to low energy imaging, and with long print life and excellent resolution.

The photothermally sensitive composition comprises a crosslinkable solvent, polymers and monomers, energy absorbing dye / laser dye / initiator / sensitizers, optional plasticizers and optional additives such as dyes or colorants. The preferable components are: 1) a solvent selected from a glycol ether. MEK, alcohol and mixtures thereof, such as EE (ethylene glycol monoethyl ether) or PM (propylene glycol methyl ether), EB (ethylene glycol monobutyl ether). Glycol ethers are preferable. 2) A high molar weight acrylate binder. 3) TLA-454 [4-4'-methylenebis (/, / V-dimethyl) benzeneamine] (initiator / sensitizer). 4) CDM-HABI [1, 1'-Bi-1 H-imidazole, 2,2, -bis (2-chlorophenyl) -4,4 \ 5,5'-tetrakis (3-methoxyphenyl)] (initiator). 5) OCL-HABI 6) BDMABP [Michler's acetone] [4,4'-bis- (dimethylamino) benzophenone] 7. A triazine such as A, D, or S [2,4,6-tris (1-aziridinyl ) -s-triazine preferable]. 8) A coloring dye such as B. Blue 007, Red 109 Sol. 9) an IR 830 dye 10) a 405 nm dye / sensitizer [coumarin 30 or preferable methane cyanine] 11) A plasticizer [preferably a mixed triethylene, dicaprate and dicaprylate ester, manufactured by PVO International] 11. A low molecular weight acrylate monomer (100-1500, preferably 200-600) 13) A multifunctional acrylate [tetra or penta] preferred functional] being preferable with TMPTA [trimethylolpropane triacrylate] When the imaging is performed using a violet laser with a target wavelength of, or close to, 405 nm, for the coumarin and the methane cyanine dyes are used which have one? max. 415 nm and 404 nm. When image formation is performed using an IR 830 thermal laser with a target wavelength of, or close to, 830 nm, IR-type IR 830 dyes are used, such as polymethine, escuarylium, pyrylium. Polyimeline dyes are preferable and an optional photoacid generator such as triazine may be added thereto. In the manufacturing process of the photothermally sensitive shell emulsions, the components are slowly added to the solvent under agitation, with the aid of a mixer, to dissolve them completely. It is preferable that the components are added in the following sequence: Solvent EE or PM, EB [glycol ethers] High-weight acrylate molar agglutinant. TLA-454 CDM-HABI OCL-HABI BDMABP [Michler's acetone] Triazine A, D, S [preferable S] Dye dye B. Blue 007, Red - 109 Sun. Dye IR 830 Dye / sensitizer 405 nm coumarin 30, coumarin 102 or cyanine methane [preferable] Plasticizer Psc Low molecular weight acrylate monomer. TMPTA or another multifunctional acrylate. The composition of each component is as follows: The components of the cover are mixed in the order listed at, or above, the ambient temperature, preferably on the scale of about 21 to 26.7 ° C, to make a solution containing from about 5 to about 50% of solids, preferably from about 25 to about 35% solids. The cover composition is covered over the plate substrate. The preferred substrate for the printing plate is aluminum, more preferably aluminum alloys of the series 1000 and 3000. Especially useful in the process are the aluminum substrates having a caliber / thickness of about 0.01 to about 0.051 cm; and a width of up to about 152.4 cms.

Aluminum substrates that have been mechanically or electrochemically granulated and anodized and sealed with PVPA alkali silicate, work well in the process. Aluminum substrates that have been post-sealed in anodized with PVPA are especially preferable. The aluminum substrates that have been anodized and sealed show a marked improvement in the adhesion of the photothermally sensitive layer. Also, without the post-anodizing and sealing, the plate environment (the non-image area) is prone to sensitivity when put on the press and shelf life of the product is not good. The photothermally sensitive coating is applied to the substrate in an amount sufficient to provide a cover weight of from about 1 to about 90 mg / dm2, preferably from about 10 to about 30 mg / dm2. After covering the substrate it is dried at a temperature in the range of about 65.6 to about 121 ° C, preferably at a temperature in the range of about 76.7 to about 93.3 ° C, for a sufficient period to dry the cover , typically from about 15 seconds up to about 3 minutes, preferably from about 45 up to about 90 seconds. To prevent the degradation of the roof, it is desirable to cover it with a dust jacket / protective oxygen barrier. A suitable top cover comprises the following components: Water Vinyl 107 and / or 203 Polyvinylpyrrolidone / vinyl acetate S-630 Ethyl celusolve Triton X-100 Alcohol 3A. The composition of the top cover remains the same for each type of photothermally sensitive layer, and comprises about 70 to about 95% water, preferably about 80 to 90% water, to which is added: 1) vinyl 107 or 203 or a mixture thereof, preferably in equal amounts, to comprise from about 0.5 to about 30% by weight of the solution, preferably from about 10 to about 20%, and 2) the other components above listed, each in an amount from about 0.1 to about 10% by weight, preferably from about 1 to about 2% by weight. The protective top cover is produced by adding slowly, under constant agitation with a mixer, vinyl or a mixture of vinyls and PVP-VA, in water to completely dissolve the polymers. The mixture is then concentrated by heat for a period of about 1 to about 3 hours, preferably about 2 hours, at a temperature in the range of about 37.78 ° C to about 93.33 ° C, preferably in the range from about 82.22 ° C to about 98.89 ° C.

The solution is allowed to cool to below 32.22 ° C.

Then alcohol and X-100 wetting agent are added and mixed in the solution. The concentration of the solution is adjusted to contain from about 1 to about 30% solids, preferably from about 10 to about 15% solids. The protective top cover is applied to the substrate in an amount sufficient to provide a cover weight of from about 1 to about 50 mg / dm2. After covering the substrate, it is dried at a temperature in the range of about 10 to about 121 ° C, preferably at a temperature in the range of 37.78 ° C to about 93.33 ° C., for a sufficient period to dry the cover, typically from about 5 seconds to about 2 minutes, preferably from about 20 to about 60 seconds. To the appropriate type of CTP plate depending on the wavelength of the light source, the image is represented in an image forming device such as one of plate composition, in the conventional manner for these devices. In a critical step, the plate with the image is then preheated to a temperature on the scale of about 60 to about 121 ° C, preferably on the scale of about 82.22 to 110 ° C for a period of about 5 to about 120 seconds, preferably from about 10 to about 30 seconds.

After cooling to room temperature, the plate is developed with aqueous alkaline developer. The aqueous alkaline developer is comprised primarily of water and an alkali compound. Alkali hydroxide or alkali carbonates (most preferably sodium) are preferred at concentrations within the range of about 1.0 to about 1.5%. At a pH of 12-13 the developer is corrosive and prone to oxidation. However, at a pH of 11.5 or lower the developer does not oxidize. The image on the plate produced by the described process has very good resolution and a long press life for high quality commercial printing applications. To further increase press life, the plate can be post-housed at a temperature in the range of about 176.67 to about 287.78 ° C, preferably at a temperature in the range from 232.22 to about 279.44 ° C, during a period of about 15 to about 5000 seconds; preferably from about 60 to about 90 seconds, to significantly harden the image, thereby providing increased press resistance and chemical resistance to allow for extensive press life.

Claims (13)

NOVELTY OF THE INVENTION CLAIMS

1. - Cover compositions photothermally sensitive to multiple portions of the electromagnetic spectrum and useful for the preparation of lithographic printing plates, color test films and the like by computer-to-plate imaging methods, comprising a solvent, polymers and linkable monomers cross-linked, energy absorbing dye / laser dye / initiator / sensitizers, optional plasticizers and optional additives, where the energy absorbing dye / laser dye / initiator / sensitizers are selected from dye / initiator / sensitizers that have increased sensitivities to the variant portions of the electromagnetic spectrum.

2. The cover composition according to claim 1, further characterized in that the sensitivity of the cover composition with the image shown is increased by heat treatment before development. 3.- Photothermally sensitive cover compositions, useful for the preparation of lithographic printing plates, color test films and the like by computer-to-plate imaging methods, comprising a solvent, crosslinkable polymers and monomers, energy absorbing dye / dye laser / initiator / sensitizers, optional plasticizers and optional additives, where the solvent is selected from the group consisting of glycol ether, MEK, alcohol and mixtures thereof, the crosslinkable polymer is a high molecular weight acrylate, the monomer is a low molecular weight acrylate monomer, the energy absorbing dye / laser dye / initiator / sensitizers are selected from [4,4'-methylenebis (/ V, / V-dimethyl) benzeneamine], [1, 1'-Bi-1 H-imidazole, 2,2'-bis (2-chlorophenylH ^ '.d.d'-tetrakis-methoxyphenyl)], OCH-HABI, [4,4'-bis- (dimethylamino) benzophenone ], a triazine, an IR 830 dye, a multifunctional acrylate [tetra or penta functional preferable], a dye / sensitizer of 405 nm, and mixtures thereof. 4. The composition according to claim 3, further characterized in that the solvent is glycol ether, the dye is Blue 007 or Red-109 Sol., The 405 nm dye / sensitizer is coumarin 30 or methane cyanine, the Low molecular weight acrylate monomer has a molecular weight of 100-1500 daltons, and the multifunctional acrylate is tetra or penta functional. 5. The composition according to claim 3, further characterized in that the solvent is selected from ethylene glycol monoethyl ether, propylene glycol methyl ether, ethylene glycol monobutyl ether and mixtures thereof, the triazine is 2,4,6- tris (1-aziridinyl) -s-triazine, the 405 nm dye / sensitizer is coumerin 30 or methane cyanine, the low molecular weight acrylate monomer has a weight molecular weight of 200-600 daltons, and the multifunctional acrylate is trimethylolpropane triacrylate. 6. A method for making photothermally sensitive cover compositions useful for the preparation of lithographic printing plates, color proof films and the like by computer-to-plate imaging methods, comprising: 1) sequentially mixing the components of the photothermally sensitive composition; 2) applying the photothermally sensitive coating composition to the plate substrate; 3) optionally, apply a protective cover over the covered substrate; 4) represent the image on the covered substrate; 5) heat treating the covered substrate with the image shown; and 6) develop the image. 7. The method according to claim 6, further characterized in that the thermal treatment step is conducted at a temperature in the range from 60 to about 121 ° C for a period of about 5 to about 120 seconds. 8. The method according to claim 6, further characterized in that the thermal treatment step is conducted at a temperature in the range of about 82.22 to about 110 ° C for a period of about 10 to about 30 seconds. . 9. The method according to claim 4, further characterized in that the substrate developed is post-homed to a temperature on the scale of about 176.67 to about 287.78 ° C for a period of about 15 to about 5000 seconds. 10. The method according to claim 4, further characterized in that the substrate developed is post-home at a temperature in the range of about 232.22 to about 279.44 ° C for a period of about 60 to about 90 seconds. . 11. A lithographic plate comprising the photothermally sensitive cover of claim 1 on a substrate wherein the cover is present in an amount sufficient to provide a cover weight of from about 1 to about 90 mg / dm2. 12. A lithographic plate comprising a substrate, the photothermally sensitive cover of claim 1 wherein the cover is present in an amount sufficient to provide a cover weight of from about 1 to about 90 mg / dm2, and a cover top comprising water, vinyl 107 or 203, polyvinylpyrrolidone / vinyl acetate S-630, ethyl cellosolve, Triton X-100, and alcohol 3A. 1

3. The lithographic plate according to claim 12, further characterized in that the upper cover comprises about 70 to about 95% water, vinyl 107 or 230 or a mixture thereof in an amount of about 0.5 to about of 30% by weight of the solution, and the other specified components, each in an amount of about 0.1 to about 10% by weight.