Recording media and related methods

Abstract

A recording medium comprises an oleophilic substrate and, thereover, a topmost oleophobic layer comprising a cured polymeric silicone matrix that consists essentially of the addition-cure reaction product of a vinyl-functional polydialkylsiloxane and a silane cross-linking agent. The vinyl-functional polydialkylsiloxane has a molecular weight ranging from 30,000 to 75,000 or 110,000 to 130,000. If the molecular weight of the vinyl-functional polydialkylsiloxane is within the range of 30,000 to 75,000, the molar ratio of silane groups to vinyl groups is within the range of about 11:1 to about 25:1; and if the molecular weight of the vinyl-functional polydialkylsiloxane is within the range of 110,000 to 130,000, the molar ratio of silane groups to vinyl groups is from about 5:1 to about 27:1. The recording medium may be used as a lithographic printing plate.

Claims

1. A recording medium comprising an oleophilic substrate and, thereover, a topmost oleophobic layer comprising a cured polymeric silicone matrix that consists essentially of the addition-cure reaction product of a vinyl-functional polydialkylsiloxane and a silane cross-linking agent, and further comprising a laser-ablatable imaging layer between the substrate and the topmost layer, wherein: a) the vinyl-functional polydialkylsiloxane has a molecular weight ranging from 30,000 to 75,000 or 110,000 to 130,000; b) if the molecular weight of the vinyl-functional polydialkylsiloxane is within the range of 30,000 to 75,000, a molar ratio of silane groups in the cross-linking agent to vinyl groups in the polydialkylsiloxane is within the range of about 11:1 to about 25:1; and c) if the molecular weight of the vinyl-functional polydialkylsiloxane is within the range of 110,000 to 130,000, the molar ratio of silane groups in the cross-linking agent to vinyl groups in the polydialkylsiloxane is from about 5:1 to about 27:1 and further wherein the imaging layer (i) has a thickness no greater than 50 nm, (ii) is a thin metal/metal oxide layer and (iii) is ablatable upon exposure to a laser beam having a fluence of at least 250 mJ/cm.sup.2.

2. The recording medium of claim 1, wherein the vinyl-functional polydialkylsiloxane is vinyl-functional polydimethylsiloxane.

3. The recording medium of claim 1, wherein the vinyl-functional polydialkylsiloxane has a molecular weight ranging from 30,000 to 65,000.

4. The recording medium of claim 1, wherein the vinyl-functional polydialkylsiloxane has a molecular weight ranging from 110,000 to 130,000 and the molar ratio of silane groups in the cross-linking agent to vinyl groups in the polydialkylsiloxane is from about 20:1 to 27:1.

5. The recording medium of claim 1, wherein the silane cross-linking agent is a trimethylsiloxy-terminated polymethylhydrosiloxane.

6. The recording medium of claim 1, wherein the topmost oleophobic layer has a dry coat weight of 2 g/m.sup.2.

7. The recording medium of claim 1, wherein the substrate comprises a polyester film.

8. The recording medium of claim 1, wherein the substrate comprises a metal sheet having an oleophilic coating thereover.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing discussion will be understood more readily from the following detailed description of the invention when taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 illustrates an adhesion mechanism between a silicone layer to a metal underlying layer or substrate.

(3) FIGS. 2A-2C are enlarged sectional views of a printing member in accordance with the invention and show the results of imaging the printing member.

(4) The drawings and elements thereof may not be drawn to scale.

DETAILED DESCRIPTION

(5) 1. Lithographic Printing Members

(6) FIG. 2A illustrates a negative-working printing member 100 according to the invention that includes a substrate 102, an imaging layer 105, and a topmost layer 110. Layer 105 is sensitive to imaging (generally IR) radiation as discussed below, and imaging of the printing member 100 (by exposure to IR radiation) results in ablation of layer 105. The resulting de-anchorage of topmost layer 110 facilitates its removal by rubbing or simply as a result of contact during the print make ready process. The surface of substrate 102 exhibits a lithographic affinity opposite that of topmost layer 110. Consequently, ablation of layer 105, followed by imagewise removal of the topmost layer 110 to reveal an underlying layer or the substrate 102, results in a lithographic image. Most of the films used in the present invention are continuous, meaning that the underlying surface is completely covered with a uniform layer of the deposited material.

(7) Each of these layers and their functions is described in detail below.

(8) a. Topmost Layer 110

(9) The topmost layer participates in printing and provides the requisite lithographic affinity difference with respect to substrate 102. In addition, the topmost layer may help to control the imaging process by modifying the heat dissipation characteristics of the printing member at the air-imaging layer interface. The topmost layer 110 remains bonded to the imaging layer and rejects ink.

(10) In accordance herewith, topmost layer 110 comprises or consists essentially of a cured polymeric silicone matrix that itself consists essentially of the addition-cure reaction product of a vinyl-functional polydialkylsiloxane and a silane cross-linking agent. The vinyl-functional polydialkylsiloxane has a molecular weight ranging from 30,000 to 75,000 or 110,000 to 130,000. If the molecular weight of the vinyl-functional polydialkylsiloxane is within the range of 30,000 to 75,000, the molar ratio of silane groups to vinyl groups is within the range of about 11:1 to about 25:1; and if the molecular weight of the vinyl-functional polydialkylsiloxane is within the range of 110,000 to 130,000, the molar ratio of silane groups to vinyl groups is from about 5:1 to about 27:1.

(11) In various embodiments, and as illustrated in the examples below, the vinyl-functional polydialkylsiloxane is vinyl-functional polydimethylsiloxane. In one implementation, the vinyl-functional polydialkylsiloxane has a molecular weight ranging from 30,000 to 65,000, while in another implementation, the vinyl-functional polydialkylsiloxane has a molecular weight ranging from 110,000 to 130,000 and the molar ratio of silane groups to vinyl groups is from about 20:1 to 27:1. The silane cross-linking agent may be, for example, a trimethylsiloxy-terminated polymethylhydrosiloxane. Layer 110 may have a dry coat weight of, for example, 2 g/m.sup.20.2 g/m.sup.2.

(12) b. Imaging Layer 105

(13) The imaging layer 105 can consist of a polymeric system that intrinsically absorbs in the near-IR region, or a polymeric coating into which near-IR-absorbing components (usually near-IR dyes and/or carbon) have been dispersed or dissolved. Alternatively, layer 105 can be a metal layer thin enough to support imaging by absorbing, rather than reflecting, IR radiation. To perform an absorptive function, a metal layer 105 should transmit as much as 70% (and at least 5%) of the IR radiation incident thereon; if transmission is insufficient, the layer will reflect radiation rather than absorbing it, while excessive transmission levels appear to be associated with insufficient absorption.

(14) Imaging layer 105 may, for example, be a thin metal layer having a high extinction coefficient in the imaging wavelength range (e.g., 600-1200 nm). In general, layer 105 is very thin (e.g., no thicker than 50 nm) so as to be ablatable upon exposure to a laser beam having a fluence of at least 250 mJ/cm.sup.2. A metal layer may be applied using physical vapor deposition methods (PVD) such as magnetron sputtering deposition, thermal evaporation, or laser vapor deposition. A preferred metal is titanium, but alternative metals include alloys of titanium, aluminum, alloys of aluminum, nickel, iron, chromium, and others exhibiting the required optical densities and adequate radiation absorption. Bilayers as described in U.S. Ser. No. 12/405,732, filed on Mar. 17, 2009 (the entire disclosure of which is hereby incorporated by reference) may also be used. Also suitable are polymeric imaging layers, e.g., nitrocellulose materials, polymers such as polyester loaded with radiation-absorptive pigments (such as carbon black), conductive polymers (such as the ICP-117 polypyrrole-based conductive material supplied by Polaroid Corp. Commercial Chemicals, Assonet, Mass., or Americhem Green #34384-C3, a proprietary polyaniline-based conductive coating supplied by Americhem, Inc., Cuyahoga Falls, Ohio), or polymers containing nigrosine in particulate or solubilized form. See, e.g., U.S. Pat. No. 5,704,291 (the entire disclosure of which is hereby incorporated by reference).

(15) More generally, in polymeric embodiments, layer 105 can be any polymer capable of stably retaining, at the applied thickness, an IR-absorptive pigment dispersion (generally nonconductive carbon black) adequate to cause ablation of the layer in response to an imaging pulse. Layer 105 should exhibit good adhesion to the overlying layer 110, and resistance to age-related degradation may also be considered. In general, pigment loading levels are at least 25 wt %, and the coating is applied at a dry weight of at least 0.2 g/m.sup.2, or at least 0.4 g/m.sup.2, or at least 0.8 g/m.sup.2, or at least 1.0 g/m.sup.2, or in some embodiments, at least 1.5 g/m.sup.2. Representative materials include BAKELITE (phenol formaldehyde) and other phenolic resins, vinyl chloride resins, acrylic resins, and/or polyvinyl butyral. Other suitable materials include polymers formed from maleic anhydride and one or more styrenic monomers (that is, styrene and styrene derivatives having various substituents on the benzene ring), polymers formed from methyl methacrylate and one or more carboxy-containing monomers, and mixtures thereof. These polymers can comprise recurring units derived from the noted monomers as well as recurring units derived from additional, but optional, monomers (e.g., (meth)acrylates, (meth)acrylonitrile and (meth)acrylamides). The carboxy-containing recurring units can be derived, for example, from acrylic acid, methacrylic acid, itaconic acid, maleic acid, and similar monomers known in the art. Other suitable materials include polymer binders having pendant epoxy groups. Particularly useful polymers of this type have pendant epoxy groups attached to the polymer backbone through a carboxylic acid ester group such as a substituted or unsubstituted C(O)O-alkylene, C(O)O-alkylene-phenylene-, or C(O)O-phenylene group wherein the alkylene has 1 to 4 carbon atoms. Preferred ethylenically unsaturated polymerizable monomers having pendant epoxy groups useful to make these polymer binders include glycidyl acrylate, glycidyl methacrylate, 3,4-epoxycyclohexyl methacrylate, and 3,4-epoxycyclohexyl acrylate. The epoxy-containing polymers can also comprise recurring units derived from one or more ethylenically unsaturated polymerizable monomers that do not have pendant epoxy groups including but not limited to, (meth)acrylates, (meth)acrylamides, vinyl ether, vinyl esters, vinyl ketones, olefins, unsaturated imides (such as maleimide), N-vinyl pyrrolidones, N-vinyl carbazole, vinyl pyridines, (meth)acrylonitriles, and styrenic monomers. Of these, the (meth)acrylates, (meth)acrylamides, and styrenic monomers are preferred and the styrenic monomers are most preferred. For example, a styrenic monomer could be used in combination with methacrylamide, acrylonitrile, maleimide, vinyl acetate, or N-vinyl pyrrolidone.

(16) Still other useful materials include polyvinyl acetals, (meth)acrylic resins comprising carboxy groups, vinyl acetate crotonate-vinyl neodecanoate copolymer phenolic resins, maleated wood rosins, styrene-maleic anhydride co-polymers, (meth)acrylamide polymers, polymers derived from an N-substituted cyclic imide, and combinations thereof. Particularly useful materials include polyvinyl acetals, and copolymers derived from an N-substituted cyclic imide (especially N-phenylmaleimide), a (meth)acrylamide (especially methacrylamide), and a (meth)acrylic acid (especially methacrylic acid). The preferred polymeric materials of this type are copolymers that comprise from about 20 to about 75 mol % and preferably about 35 to about 60 mol % of recurring units derived from N-phenylmaleimide, N-cyclohexylmaleimide, N-benzylmaleimide, or a mixture thereof; from about 10 to about 50 mol % and preferably from about 15 to about 40 mol % of recurring units derived from acrylamide, methacrylamide, or a mixture thereof; and from about 5 to about 30 mol % and preferably about 10 to about 30 mol % of recurring units derived from methacrylic acid. Other hydrophilic monomers, such as hydroxyethyl methacrylate, may be used in place of some or all of the methacrylamide. Other alkaline-soluble monomers, such as acrylic acid, may be used in place of some or all of the methacrylic acid.

(17) Further suitable polymeric materials include resins having activated methylol and/or activated alkylated methylol groups. Such resins include, for example, resole resins and their alkylated analogs, methylol melamine resins and their alkylated analogs (e.g., melamine-formaldehyde resins), methylol glycoluril resins and alkylated analogs (e.g., glycoluril-formaldehyde resins), thiourea-formaldehyde resins, guanamine-formaldehyde resins, and benzoguanamine-formaldehyde resins. Commercially available melamine-formaldehyde resins and glycoluril-formaldehyde resins include, for example, CYMEL resins (Dyno Cyanamid) and NIKALAC resins (Sanwa Chemical). The resin having activated methylol and/or activated alkylated methylol groups is preferably a resole resin or a mixture of resole resins. Resole resins are well known to those skilled in the art. They are prepared by reaction of a phenol with an aldehyde under basic conditions using an excess of phenol. Commercially available resole resins include, for example, GP649D99 resole (Georgia Pacific).

(18) c. Substrate 102

(19) The substrate 102 provides dimensionally stable mechanical support to the printing member 100. The substrate 102 should be strong, stable, and flexible. One or more surfaces (and, in some cases, bulk components) of the substrate may be hydrophilic. The topmost surface, however, is generally oleophilic. Suitable materials include, but are not limited to, polymers, metals and paper, but generally, it is preferred to have a polymeric ink-accepting layer (e.g., applied over a metal or paper support). As used herein, the term substrate refers generically to the ink-accepting layer beneath the radiation-sensitive layer 105, although the substrate may, in fact, include multiple layers (e.g., an oleophilic film laminated to or coated on a metal support, or an oleophilic coating over a paper support).

(20) Substrate 102 desirably also exhibits high scattering with respect to imaging radiation. This allows full utilization of the radiation transmitted through overlying layers, as the scattering causes back-reflection into layer 105 and consequent increases in thermal efficiency. Polymers suitable for use in substrates according to the invention include, but are not limited to, polyesters (e.g., polyethylene terephthalate and polyethylene naphthalate), polycarbonates, polyurethane, acrylic polymers, polyamide polymers, phenolic polymers, polysulfones, polystyrene, and cellulose acetate. A preferred polymeric substrate is polyethylene terephthalate film, such as the polyester films available from DuPont-Teijin Films (Hopewell, Va.) under the trademarks MYLAR and MELINEX, for example. Also suitable are the white polyester products from DuPont-Teijin such as MELINEX 927W, 928W 329, 329S, 331.

(21) Polymeric substrates can be coated with a hard polymer transition layer to improve the mechanical strength and durability of the substrate and/or to alter the hydrophilicity or oleophilicity of the surface of the substrate. Ultraviolet or electron-beam cured acrylate coatings, for example, are suitable for this purpose. Polymeric substrates can have thicknesses ranging from about 50 m to about 500 m or more, depending on the specific printing member application. For printing members in the form of rolls, thicknesses of about 200 m are preferred. For printing members that include transition layers, polymer substrates having thicknesses of about 50 m to about 100 m are preferred.

(22) 2. Imaging and Printing

(23) An imaging apparatus suitable for use in conjunction with the present printing members includes at least one laser device that emits in the region of maximum plate responsiveness, i.e., whose .sub.max closely approximates the wavelength region where the imaging layer 105 absorbs most strongly. Specifications for lasers that emit in the near-infrared (IR) region are fully described in U.S. Pat. Nos. Re. 35,512 (the '512 patent) and 5,385,092 (the '092 patent), the entire disclosures of which are hereby incorporated by reference. Lasers emitting in other regions of the electromagnetic spectrum are well-known to those skilled in the art.

(24) Suitable imaging configurations are also set forth in detail in the '512 and '092 patents. Briefly, laser output can be provided directly to the plate surface via lenses or other beam-guiding components, or transmitted to the surface of a blank printing plate from a remotely sited laser using a fiber-optic cable. A controller and associated positioning hardware maintain the beam output at a precise orientation with respect to the plate surface, scan the output over the surface, and activate the laser at positions adjacent selected points or areas of the plate. The controller responds to incoming image signals corresponding to the original document or picture being copied onto the plate to produce a precise negative or positive image of that original. The image signals are stored as a bitmap data file on a computer. Such files may be generated by a raster image processor (RIP) or other suitable means. For example, a RIP can accept input data in page-description language, which defines all of the features required to be transferred onto the printing plate, or as a combination of page-description language and one or more image data files. The bitmaps are constructed to define the hue of the color as well as screen frequencies and angles.

(25) Other imaging systems, such as those involving light valving and similar arrangements, can also be employed; see, e.g., U.S. Pat. Nos. 4,577,932; 5,517,359; 5,802,034; and 5,861,992, the entire disclosures of which are hereby incorporated by reference. Moreover, it should also be noted that image spots may be applied in an adjacent or in an overlapping fashion.

(26) The imaging apparatus can operate on its own, functioning solely as a platemaker, or can be incorporated directly into a lithographic printing press. In the latter case, printing may commence immediately after application of the image to a blank plate, thereby reducing press set-up time considerably. The imaging apparatus can be configured as a flatbed recorder or as a drum recorder, with the lithographic plate blank mounted to the interior or exterior cylindrical surface of the drum. Obviously, the exterior drum design is more appropriate to use in situ, on a lithographic press, in which case the print cylinder itself constitutes the drum component of the recorder or plotter.

(27) In the drum configuration, the requisite relative motion between the laser beam and the plate is achieved by rotating the drum (and the plate mounted thereon) about its axis and moving the beam parallel to the rotation axis, thereby scanning the plate circumferentially so the image grows in the axial direction. Alternatively, the beam can move parallel to the drum axis and, after each pass across the plate, increment angularly so that the image on the plate grows circumferentially. In both cases, after a complete scan by the beam, an image corresponding (positively or negatively) to the original document or picture will have been applied to the surface of the plate.

(28) In the flatbed configuration, the beam is drawn across either axis of the plate, and is indexed along the other axis after each pass. Of course, the requisite relative motion between the beam and the plate may be produced by movement of the plate rather than (or in addition to) movement of the beam. Examples of useful imaging devices include models of the TRENDSETTER imagesetters (available from Eastman Kodak Company) that utilize laser diodes emitting near-IR radiation at a wavelength of about 830 nm. Other suitable exposure units include the CRESCENT 42T Platesetter (operating at a wavelength of 1064 nm, available from Gerber Scientific, Chicago, Ill.) and the SCREEN PLATERITE 4300 series or 8600 series plate-setter (available from Screen, Chicago, Ill.).

(29) Regardless of the manner in which the beam is scanned, in an array-type system for on-press applications it is generally preferable to employ a plurality of lasers and guide their outputs to a single writing array. The writing array is then indexed, after completion of each pass across or along the plate, a distance determined by the number of beams emanating from the array, and by the desired resolution (i.e., the number of image points per unit length). Off-press applications, which can be designed to accommodate very rapid scanning (e.g., through use of high-speed motors, mirrors, etc.) and thereby utilize high laser pulse rates, can frequently utilize a single laser as an imaging source.

(30) FIGS. 2A-2C show the consequences of imaging the printing member 100. As illustrated in FIG. 2B, the exposed area of the layer 105 absorbs the imaging pulse and converts it to heat. The heat builds up until the layer 105 ablates, i.e., undergoes either rapid phase transformation (e.g., vaporization) or catastrophic thermal overload. This process is mainly attributed to the contribution of an explosive mechanism generated in the image areas of the plate by exposure to laser radiation.

(31) After imaging, the topmost layer 110 is degraded and/or de-anchored in the areas that received imaging radiation. The exposed areas that contain ablation debris are either purged of the debris prior to printing or during print make ready. In some embodiments, the printing member can be used on press immediately after being imaged without the need for a post-imaging processing step. More typically, however, the de-anchored overlying layer and the central layer are removed (at least partially) by a post-imaging cleaning processe.g., rubbing of the plate with or without a cleaning liquidto reveal the third layer (typically an oleophilic polymer, such as polyester). In a preferred embodiment, the printing member is cleaned with a cleaning liquid that is aqueous in nature and free of organic solvent. For example, the cleaning liquid may consist essentially of water, e.g., plain tap water, and may be warmed to a temperature of 32-50 C. The cleaning liquid may be applied manually, using a cloth and/or brush, or mechanically using commercial plate-cleaning equipment. For example, many platemakers contain internal rotary scrub rollers that clean the plate following imaging.

(32) Printing with the printing member includes disposing ink on at least a portion of the printing member, preferably the oleophilic exposed areas. The ink is transferred in the imagewise lithographic pattern (created as described above) to a recording medium such as paper. The inking and transferring steps may be repeated a desired number of times, e.g., the approximately 5,000 to approximately 50,000 times in a low to medium printing run.

EXAMPLES

Examples 1-3 and C1

(33) These examples describe negative-working waterless printing plates that include a highly crosslinked silicone layer disposed above a thin titanium imaging layer that is itself disposed on a polyester substrate. A preferred substrate is a 175 m white polyester film sold by DuPont-Teijin Films (Hopewell, Va.) under the name MELINEX 927W.

(34) The imaging layer of the printing member is a thin titanium layer disposed on the polymer substrate by DC magnetron sputtering of a titanium target using ultrahigh purity argon as the sputtering gas. Prior to the metal deposition, the sputtering chamber is evacuated to base pressures below 310.sup.5 Torr and back-filled with argon up to a pressure of 5 mTorr. The sputtering process yields a layer of mixed metal/metal oxide composition with total thickness of 25 nm which, upon exposure to air, reacts with water molecules yielding a surface rich in hydroxyl functional groups. The latter act as the bonding sites for the adhesion of the polymer top-silicone layer of the plate structure.

(35) The silicone layers used in the present invention may have a highly crosslinked network structure produced via the addition or hydrosilylation reaction between the vinyl groups (SiVi) of vinyl-terminated functional silicones and the silicon hydride groups of trimethylsiloxy-terminated poly(hydrogen methylsiloxane) crosslinker, in the presence of a Pt catalyst complex and an inhibitor.

(36) The vinyl polymers employed in the following examples have a nominal chemical formula of [CH.sub.2CHSi(CH.sub.3).sub.2O[{Si(CH.sub.3).sub.2O}.sub.nSi(CH.sub.3).sub.2CHCH.sub.2] with an average degree of polymerization, n, between 840 and 1580 and molecular weight ranging from 62,000 to 117,000 g/mol. The below table details the properties of a series of vinyl-terminated polydimethylsiloxanes (PDMS) manufactured by Gelest Inc. (Morrisville, Pa.) used in the ensuing examples. A higher-molecular-weight example is also included for comparative purposes.

(37) TABLE-US-00001 Product Molecular Weight Viscosity Density Weight % name (g/mol) (cps) (g/l) Vinyl DMS-V41 62,700 10,000 0.97 0.08-0.12 DMS-V42 72,000 20,000 0.98 0.07-0.09 DMS-V46 117,000 60,000 0.98 0.04-0.06 DMS-V52 155,000 165,000 0.98 0.03-0.04

(38) Silicone formulations of the following composition, by weight, were prepared with each of the vinyl-functional PDMS examples listed in the previous table.

(39) TABLE-US-00002 Component Parts Vinyl Silicone 12.40 DC Syl Off 7367 Crosslinker 0.53 CPC 072 Pt Catalyst 0.17 Heptane 86.9

(40) The DC SYL OFF 7367 is a trimethylsiloxy-terminated poly(hydrogen methylsiloxane) crosslinker manufactured by Dow Corning Silicones (Midland, Mich.) which is supplied as a 100% solids solution containing about 30% 1-ethynylcyclohexane [CHCHCH(CH.sub.2).sub.5], which functions as catalyst inhibitor. This crosslinker has a nominal formula of [(CH.sub.3).sub.3SiO{SiH(CH.sub.3)O}.sub.mSi(CH.sub.3).sub.3] with degree of polymerization, m, between 30 to 32, and average molecular weight of about 2000 g/mol.

(41) The CPC 072 is a 1,3 diethyenyl-1,1,3,3-tetramethyldisiloxane Pt complex catalyst manufactured by Umicore Precious Metals (South Plainfield, N.J.) which is supplied as a 3% xylene solution. The formulation solvent, heptane, is supplied by Houghton Chemicals (Allston, Mass.).

(42) Silicone formulations were prepared by mixing of catalyst and vinyl PDMS in heptane, followed by addition of a heptane solution of the crosslinker. The formulations were applied to the metalized substrate with a wire-round rod, then dried and cured at 138 C. for one minute to produce uniform silicone coatings of 1.1 g/m.sup.2.

(43) The printing members of these examples were evaluated by two different methods to obtain information on the effect of the changes in silicone formulation on plate durability. First, plates were tested in the laboratory by assessing adhesion and solvent resistance with methyl ethyl ketone (MEK). A MEK resistance test is performed on pieces of the plate examples having lengths of about 20 cm by applying, in a reciprocating mode, MEK double-rubs using a five-pound load. The cycle is repeated to the point of visual evidence failure, i.e., marring of the surface or loss of silicone adhesion.

(44) These plate examples were also imaged and run on-press to determine their press durability. The plates were imaged on a Presstek DIMENSION 425 plate setter at a power of 300 mJ/cm.sup.2 and manually cleaned to remove the loosened silicone debris left on the plate after imaging. The cleaning involves a two-step procedure: first, a dry rubbing the surface with a dry cotton towel, and second, wet rubbing with a cotton towel saturated with isopropanol.

(45) The press durability of the printing members was evaluated on a GTO Heidelberg press using black ink (Aqualess Ultra Black MZ waterless ink, Toyo Ink America LLC, Addison, Ill.) and uncoated stock (Williamsburg Plus Offset Smooth, 60 lb white, item number: 05327, International Paper, Memphis, Tenn.). The plates were run until signs of background wear were observed on the printing sheets. The number of print sheets at which background wear starts to appear is reported as the press durability of these printing members under the described printing conditions.

(46) The following table shows the results of the laboratory and press evaluation of different printing plate examples.

(47) TABLE-US-00003 Vi-PDMS Molecular MEK Press Example Weight (g/mol) SiH:SiVi Rubs Durability Example 1 62,700 13.3:1 15-20-25 5000 to 6000 Example 2 72,000 15.2:1 20-25-30 5000 to 6000 Example 3 117,000 24.7:1 15-20-25 5000 to 6000 Example C1 155,000 32.8:1 5-10 3000

(48) Both the MEK solvent resistance and press testing demonstrate that printing members made with vinyl-functional PDMS resins of molecular weight from 62,700 to 117,000 g/mol and having high SiH:SiVi ratios between 13:1 and 25:1 display at least twice the durability of the comparative example made with a high-molecular-weight vinyl silicone.

Examples 4-6 and C2

(49) Printing members similar to those described in Examples 1-3 were made with a thicker silicone top layers to create more durable printing members. In these examples, the same formulations were applied to the metalized substrate with a wire-round rod, then dried and cured at 138 C. for one minute to produce coatings of 2.0 g/m.sup.2.

(50) The printing members were imaged, cleaned, and tested as described in Examples 1-3. The performance of these examples is summarized in the following table:

(51) TABLE-US-00004 Vi-PDMS Molecular Formulation MEK Press Example weight (g/mol) SiH:SiVi Rubs Durability Example 4 62,700 13.3:1 30-35 12,000 to 14,000 Example 5 72,000 15.2:1 30-35 13,000 to 15,000 Example 6 117,000 24.7:1 30-35 15,000 to 16,000 Example C2 155,000 32.8:1 10-15 8000

(52) Consistent with the results obtained in the previous examples, the results show that printing members made with the intermediate-molecular-weight silicone resin exhibit improved durability, which is at least twice that of the comparative Example C2 made with the same silicone layer thickness. Furthermore, doubling the coating weight leads to at least a two-fold increase in durability compared to the above examples made with the 1.1 g/m.sup.2 silicone layer.

Examples 7 and C3-C5

(53) Silicone formulations of the following composition, by weight, were made with the vinyl-functional PDMS formulations described above. These examples contain about half the concentration of the crosslinker used in Examples 1-3.

(54) TABLE-US-00005 Component Parts Vinyl Silicone 12.40 DC Syl Off 7367 Crosslinker 0.27 CPC 072 Pt Catalyst 0.17 Heptane 87.16

(55) The formulations were applied to the metalized substrate with a wire-round rod, then dried and cured at 138 C. for one minute to produce coatings of about 1.1 g/m.sup.2.

(56) TABLE-US-00006 Vi-PDMS Molecular Formulation MEK Example weight (g/mol) SiH:SiVi Rubs Example C3 62,700 6.6:1 5-10 Example C4 72,000 7.6:1 5-10 Example 7 117,000 12.4:1 15-20 Example C5 155,000 16.4:1 5-10

(57) The reduction of the crosslinker concentration leads to considerable loss of solvent resistance by the printing members of Examples C3 and C4 made with the lower-molecular-weight resins (compared to Examples 1 and 2). The change may be attributed to the reduction of crosslinker molecules available for crosslinking and bonding to the metal surface. Note that these two formulations have a much lower SiH:SiVi ratio than that used in the earlier examples.

(58) The decrease in crosslinker density has slight or no effect on the solvent resistance of Example 7 (compared to Example 3) made with the higher-molecular-weight resin. The formulation of Example 7 has a relatively high (>10:1) SiH:SiVi ratio, which appears sufficient to achieve formation of a highly crosslinked silicone network and provide adhesion to the metal substrate.

Examples 8 and C6-C8

(59) Silicone formulations of the following composition, by weight, were prepared with each of the vinyl-functional PDMS formulations described above. These examples contain one-fourth the concentration of the crosslinker used in Examples 1-3.

(60) TABLE-US-00007 Component Parts Vinyl Silicone 12.40 DC Syl Off 7367 Crosslinker 0.13 CPC 072 Pt Catalyst 0.17 Heptane 87.30 Vi-PDMS Molecular Formulation MEK Example weight (g/mol) SiH:SiVi Rubs Example C6 62,700 3.3:1 0-5 Example C7 72,000 3.8:1 0-5 Example 8 117,000 6.2:1 15-20 Example C8 155,000 8.2:1 10-15

(61) Comparative Examples C6 and C7 present very low solvent resistance. This is consistent with the observations made regarding Examples C3 and C4, and shows that further reduction of SiH:SiVi ratio to values lower than six causes complete loss of the MEK resistance of these silicone coatings. An important observation is that Example 8, made with the 117,000 g/mol vinyl PDMS, still displays good solvent resistance. Note that Example 8 has relatively high (>6:1) SiH:SiVi ratio.

Examples C9-C12

(62) Silicone formulations of the following composition, by weight, are prepared with each of the vinyl-functional PDMS described above. These examples contain twice the concentration of the crosslinker used of Examples 1-3.

(63) TABLE-US-00008 Component Parts Vinyl Silicone 12.40 DC Syl Off 7367 Crosslinker 1.07 CPC 072 Pt Catalyst 0.17 Heptane 86.36

(64) The formulations were applied to the metalized substrate with a wire-round rod, then dried and cured at 138 C. for one minute to produce coatings of 1.1 g/m.sup.2.

(65) TABLE-US-00009 Vi-PDMS Molecular Formulation MEK Example weight (g/mol SiH:SiVi Rubs Example C9 62,700 26.5:1 0-5 Example C10 72,000 30.4:1 0-5 Example C11 117,000 49.4:1 0-5 Example C12 155,000 65.5:1 0-5

(66) These comparative examples show that an excess of crosslinking molecules causes complete loss of the solvent resistance of the printing members made with the intermediate-molecular-weight PDMS resins. The formulations of these four examples would lead to the formation of silicone coatings with large amounts of loose residual crosslinker.

(67) It will be seen that the foregoing techniques provide a basis for improved lithographic printing and superior plate constructions. The terms and expressions employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. Instead, it is recognized that various modifications are possible within the scope of the invention claimed.