PRINTING BLANKET WITH VARIABLE COMPRESSIBLE LAYER

Abstract: A printing article which includes a rotatable metal support in the form of a sleeve (13) and a compressible laminate (1) mounted upon the support. The compressible laminate (1) has upper and lower surfaces and a substantially uniform thickness and includes a printing face (9) which forms the upper surface, a fabric layer (7), a compressible layer (5) having upper and lower surfaces, and two fabric layers (2 and 3) positioned beneath the compressible layer (5). The compressible layer (5) has a relatively greater compressibility in the central region of the layer than at the outer periphery thereof. Preferably, this laminate (1) is cylindrical and is in the form of a printing blanket or printing roll. The invention also relates to methods for forming the compressible laminate.

Description: PRINTING BLANKET WITH VARIABLE COMPRESSIBLE LAYER FIELD OF THE INVENTION This invention relates to elasto eric articles for use in lithographic printing applications, and in particular to compressible cylindrical printing blankets or rollers for use in offset printing presses. BACKGROUND OF THE INVENTION In the process of offset lithographic printing, a rotary cylinder is covered with a cylindrical surface referred to as a "printing plate" which has a positive image area that is receptive to oil-based inks and repellent to water, as well as a background area that is repellent to the oil-based inks. In operation, the printing plate is rotated so that its surface contacts a second cylinder that is covered with a laminate having an ink-receptive rubber surface, which is referred to as a "printing blanket" . The ink present on the image surface of the printing plate transfers, or "offsets", to the surface of the printing blanket. Paper or other sheet stock to be printed is passed between a nip formed by the blanket-covered cylinder and a rigid back-up cylinder or another blanket covered cylinder to transfer the image from the surface of the blanket to the paper. During the steps in which the image is transferred from the printing plate to the printing blanket and subsequently from the blanket to the paper, it is important to ensure intimate contact between the two contacting surfaces. This is ordinarily achieved by positioning the blanket-covered cylinder and the supporting cylinder, or another blanket-covered cylinder for contacting the paper, so that there is a fixed interference between the two. Therefore, the rubber- surfaced printing blanket laminate is generally compressed throughout the printing run to a fixed depth, typically about 0.002 to 0.006 inches. If the printing blanket were constructed of solid rubber, it would bulge, or project radially away from the cylinder axis in the areas adjacent to the nip when subjected to high nip pressure. This is because solid rubber cannot be reduced in volume and is therefore subject to lateral flow. Bulging would, of course, tend to distort the print image as well as possibly wrinkle the paper being printed. Therefore, compressible printing blankets have been developed. To make the blanket compressible, a portion of the solid material used in forming the blanket is replaced by a gas, generally air. More specifically, layers beneath the surface of the blanket are constructed so as to contain millions of minute voids, which allow uniform compression to take place. As the voids beneath the area under pressure reduce in volume, they permit vertical compression — rather than lateral bulging — to take place at the cylinder nip. Conventional offset printing blankets generally include a multi-ply fabric base and a vulcanized elastomeric face. The threads used in forming the fabric entrain a certain amount of air and provide voids. Hence the fabric has a certain amount of compressibility. To enhance the compressibility of such blankets, however, one or more cellular compressible layers is generally buried within or attached to one of the layers or fabrics between the base and the elastomeric face of the blanket. Those skilled in the art have explored a wide variety of ways in which different open cell structures, closed cell structures, microspheres, and various combinations thereof can be used to obtain compressible layers that provide printing blankets having the desired compressibility properties. The numerous teachings of how to make compressible printing blankets include the teachings of Flint et al., U.S. Patent No. 5,364,683; Larson U.S. Patent No. 4,042,743; Shimura, U.S. Patent No. 4,422,895; Rhodarmer et al., U.S. Patent No. 3,795,568; Pinkston et al., U.S. Patent No. 4,015,046; and Burns, U.S. Patent No. 5,069,958. In order to assure uniformity of printing, it is also important that compression be maintained uniformly over the entire length of the nip between the printing blanket and the support roll. Another important consideration relates to the handling of the paper or other webs being printed. Cylindrical printing blankets constructed for use in a variety of printing processes have, for example, been produced with a concave outer surface to provide tension profiles across the width and between nips or contact points. Spreader rolls having similar concave outer surfaces are also known in the prior art for use in offset printing applications. The resultant tension profiles thus produced act to spread the web and prevent inward wrinkling. Fig. 1 shows a structure representative of a concave-surfaced prior art cylindrical printing blanket. Printing blanket 1 is constructed around a rotatable support 2 typically configured in the form of a sleeve. The outer surface of support 2 is provided with a coating of "primer" 3 which serves to bond blanket 1 to the support and to prevent wicking of materials such as grease, oil, water, ink, etc. upwardly from the support into the blanket. A compressible layer 7 is thereafter formed upon the coated support by wrapping the support with one or more threads coated with an admixture comprising an elastomeric matrix 5 and a plurality of compressible open or closed cells 6. The wrapping conditions are controlled in such a manner that threads 4 sink to the lower portion of layer 7, adjacent to the coated support, whereas the remaining, i.e. , upper, portion of layer 7 is comprised solely of the elastomer/cell admixture, substantially without any threads. After layer 7 is formed, it is partially dried or cured and a second fiber layer, i.e., of reinforcing fibers 8 coated with an elastomeric matrix 9 substantially free of cells 6, is applied around the outer boundary of compressible layer 7. Subsequently, printing surface 10, for instance a solid elastomer such as a nitrile blend, is applied to the upper surface of blanket 1, atop coated reinforcing threads 8. The degree of concavity of printing surface 10 shown in Fig. 1 is exaggerated for illustrative purposes. However, it is manifest that a printing blanket or other roll surface (e.g., a spreader roll) that is concaved across its width, varies in circumference around its cross-section, and that a point at either edge of the roll will travel further during a rotation of the roll than will a point at the center of the roll. Although this concavity solves the problem of paper wrinkling which is often encountered in the printing art, it leads, on the other hand, to the formation of unequal printing pressures and nip areas across the width of the blanket which, in turn, can cause undesirable results during printing, such as substantial dot gain and decreased print contrast values. In addition, it has a negative impact on the web feed tendencies. Thus it would be desirable to have a printing blanket or similar compressible roll product (e.g., a spreader roll) that exhibits a uniform thickness across its entire width, yet which enables the provision of tension profiles across the width and between nips or contact points in order to spread the web and prevent inward wrinkling. SUMMARY OF THE INVENTION The present invention relates, in a first embodiment, to a printing article. The article comprises a rotatable support, e.g., in the form of a metal sleeve and a compressible laminate mounted upon the support. The compressible laminate has upper and lower surfaces and a substantially uniform thickness. The laminate comprises a printing face which forms the upper surface and a compressible layer, having upper and lower surfaces, positioned beneath the printing face. The depth and/or void volume of the central region of the compressible layer is greater than at the outer peripheral portions thereof. The above - described arrangement achieves improvements in printing performance and web handling since the greater the depth and/or void volume of the compressible layer, the more compressibility such a layer has. In one embodiment of the invention the upper surface of the compressible layer is more nearly adjacent the printing face in the central region of the cylindrical article than at the outer periphery thereof, while the lower surface of the compressible layer is spaced uniformly to the outer surface of the cylindrical support. Conversely, however, as described below, in an alternate embodiment the compressible layer may instead be constructed having a relatively flat upper surface and a profiled lower surface, wherein the "lower" surface is that surface extending inwardly toward the support. In the article of the invention, either the upper or the lower surface of the compressible layer may be profiled, i.e., shaped, into a variety of configurations including, but not limited to, a parabolic profile, a central step, optionally including tapered sides, a plurality of graduated steps, a diamond shape, or a center portion which is flat and end portions which radially taper toward the ends of the laminate. The difference in thickness between the highest and lowest points of the profile preferably ranges between about 0.00025-0.015 inch (0.0005-0.030 inch in outer diameter in the case of a cylindrical article) . Advantageously, in the invention described above the support is a shaft and the compressible laminate forms a roller on the shaft. Alternately the support is a printing cylinder and the compressible laminate comprises a cylindrical printing blanket mounted upon the printing cylinder. The invention also relates to the printing blanket itself. Such blankets commonly include a number of additional layers or plys, such as at least one fabric or cord ply located beneath the compressible layer and/or between the compressible layer and the elastomeric printing face. A subface formed from a high durometer, high tensile, low elongation elastomeric compound is optionally located beneath the printing face. Also, it is desirable for the printing face to have a surface profile with a roughness average of above about 0.2 and below about 2.0 microns. The compressible layer generally includes cells formed from microspheres having a diameter of between about 1 and 200 microns or from gas bubbles incorporated throughout a binder material. Alternately, open cells may be formed by one of the leaching techniques which are well-known in the art. In addition, a protective, i.e., "primer" coating of a material such as a fluorocarbon or a silicone can be provided on the fabric ply if desired to prevent absorption and wicking of fluids therethrough. Furthermore, the fabric ply can be a compressible fabric ply, if desired. The invention additionally relates to a method of producing a compressible laminate by forming a compressible laminate having upper and lower surfaces and a substantially uniform thickness, comprising at least a printing face which forms the upper surface and a compressible layer positioned beneath the printing face; and forming a compressible layer which has a greater depth and/or void volume in its central region than at its outer periphery. In one embodiment, the upper surface of the compressible layer has a profile with a raised central portion spaced closer to the printing face in the central region of the laminate than at the outer periphery thereof, whereas the lower surface of the compressible layer is spaced uniformly to the outer surface of the cylindrical support, which may be a metal sleeve. Alternately, however, as noted above, the lower surface of the compressible layer may instead be profiled, while the upper surface is relatively flat. A compressible laminate comprising a compressible layer profiled upon its upper surface may be produced by several different techniques in accordance with the invention. In its most basic form, the method disclosed herein for producing such a laminate includes applying a substantially uniform thickness of the compressible layer and grinding the compressible layer to the desired profile. Alternatively, the method may include applying the compressible layer in the form of threads which carry a matrix of compressible material and varying the amount of matrix material carried by the threads to increase the deposition of the matrix material toward the central region of the laminate. The compressible layer may also be applied in the form of threads coated with a matrix of compressible material, wherein, following application of the coated threads, the drying/curing rate of the matrix material is varied across the width of the laminate prior to winding thereupon a second layer of (reinforcing) threads, to thus allow for decreasing penetration of the threads into the matrix material toward the center of the laminate. Still further, the compressible layer may be applied in the form of a matrix of compressible material, and thereafter reinforcing threads may be wound across the width of the laminate while varying the thread tension to thus allow for decreasing penetration of the threads into the matrix material in the central region of the laminate. A preferred method for forming a compressible layer with a profiled upper surface within the laminate comprises wrapping the support with threads coated with an elastomeric matrix material admixed together with a plurality of open or closed cells. During the winding, which is preferably applied in a spiral direction, the thread sinks to the bottom of the elastomeric layer, above the uppermost fabric ply or support as the case may be, to form a base portion of the compressible layer. Above this base portion there is only the cell-containing elastomeric material, i.e., without any threads. The compressible layer is then at least partially dried or cured by a process known as "pre-curing". Thereafter, the layer is wrapped with one or more reinforcing threads coated with elastomeric matrix material only, i.e., without any cells. The threads forming this second, i.e, reinforcing, winding can remain atop the upper surface of the compressible layer due to the effect of the cure. Alternatively, the coated reinforcing threads may be allowed to penetrate the compressible layer to predetermined levels by, e.g., variably decreasing the percent of full cure or altering the thread tension as discussed below. Still further, the compressible layer may be applied in the form of a matrix of compressible material, and thereafter the pressure on the compressible layer during pre-curing of the matrix material may be varied to allow for decreasing density of the compressible layer toward the center of the laminate. Similarly, the compressible layer may be applied in the form of threads which carry a matrix of compressible material, and the speed of the cylinder during the winding of the threads may be varied to increase the deposition of the matrix material toward the center of the laminate. In a further alternate embodiment of the invention the compressible material may be deposited in a substantially flat layer adapted to provide parabolic compressibility by, for example, providing the greatest amount of cell-containing media, or alternatively, the same amount of media with a greater number of compressible cells, in the central region of the layer. Still further, the layer may be formed by installing strips of varying compressibility, formed of an elastomeric material admixed with a plurality of compressible cells, with the most compressible strips being located closest to the central region of the layer, and becoming less compressible toward the outer periphery of the blanket. With the use of any of the methods described in the preceding two paragraphs, it is unnecessary to shape or "profile" either surface of the compressible layer. Rather, the variable compressibility obtained with compressible layers formed as described in the subject embodiments is instead due to the effect of the method chosen for applying the layer, including the amount and/or density of the cell-containing media applied. To produce a laminate with a compressible layer having a profiled lower surface and a substantially flat upper surface, a negative mold is first created upon the surface of a coated cylindrical support by applying thereto an elastomeric layer which is ground down or molded to achieve the profile desired for the lower portion of the compressible layer. The compressible layer is then applied upon this shaped elastomeric mold such that the lower portion of the compressible layer extends downwardly into the ground-out portion of the mold. The upper surface of the compressible layer is thereafter ground flat so as to lie substantially parallel to the outer surface of the cylindrical support. The methods described herein are also useful in applying the compressible laminate in the form of a cylinder, either as a printing blanket or a printing roller. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an enlarged sectional view through a laminated compressible printing blanket that is representative of prior art concave cylindrical blankets; Figs. 2a-2b and 4 are enlarged sectional views through laminated compressible printing blankets manufactured according to the present invention; Figs. 3a-3f are a series of schematically- represented profiles that may be exhibited by the compressible layer within a printing blanket manufactured in accordance with the present invention; and FIG. 5 is a schematic graphical representation of the interrelation between compressibility and blanket location for printing blankets constructed according to the present invention. DETAILED DESCRIPTION OF THE INVENTION In its broadest aspect, the present invention contemplates a compressible elastomeric article for use with or as a cylindrical roll assembly. For clarity in explaining the invention, the phrase "outer periphery" is used herein to refer to those portions of the article proximal or adjacent to the first and second end portions of the cylinder. The term "central region", as used herein to refer to the invention, concerns that portion of the article which is spaced inwardly from the outer periphery, i.e., toward the central region of the article. The article of the invention has an external surface which is of substantially uniform circumference across its width, and includes a compressible layer that has a depth and/or void volume which is greater in the central region of the article than it is toward the outer periphery thereof. As used herein, the term "void volume" refers to the total (uncompressed) volume of all the open and/or closed cells incorporated into the compressible layer. As noted above, the greater the depth and/or void volume of the compressible layer, the more compressibility the layer has. The compressible layer of the invention is commonly embodied in articles which are generally known and referred to as printing blankets or printing rollers. A printing blanket is generally comprised of several layers which are laminated into a single unitary structure. A description of the various layers which may be included in the present invention are described in Flint et al., U.S. Patent No. 5,364,683, the content of which is expressly incorporated herein by reference thereto. Those skilled in the art are well aware of how to make a wide variety of compressible layers, as evidenced by the teachings of Flint et al., as well as Larson, Shimura, Rhodarmer et al., Pinkston et al., and Burns, which are referred to above. The latter five patents are also expressly incorporated herein by reference to the extent necessary to understand the variations of how the compressible layer can be formed. A wide variety of printing blankets are known in general to those skilled in the art. In accordance with the present invention though, the printing blankets are constructed to have a substantially uniform thickness across their widths, despite that their compressible layers have a degree of compressibility which is greater in the central region of the blanket than at the outer periphery. This can be seen in Fig. 2a (see also FIG. 5, discussed below) . In Fig. 2a, the printing blanket 1 is formed of composite material. Two fabric layers 2 and 3 are joined together by an adhesive layer 4 to form a substrate. Compressible layer 5 is formed by using a binder, which may be made from a suitable resilient polymer matrix, into which a plurality of closed or open cells are evenly introduced to form a compressible composite. Compressible layer 5 is adhered to fabric layer 3 by adhesive layer 6. As initially formed, compressible layer 5 will generally be of uniform thickness. At this point, however, in accordance with the present invention, compressible layer 5 may be modified in thickness so that it remains thickest within the central region of blanket 1 while becoming thinner towards the outer periphery thereof. A convenient means, but not the only method, for achieving the desired thickness gradient is to grind or buff the stabilized layer to a parabolic convexity with a tool known as an o.d. grinder. Once compressible layer 5 has been modified to present thinned edges as described above, fabric layer 7 is adhered to compressible layer 5 by adhesive layer 8. The printing surface 9, for instance a solid elastomer such as a nitrile blend, is adhered to fabric layer 7 by adhesive layer 10. As taught by Flint et al., Larson, Shimura, Rhodarmer et al., Pinkston et al., and Burns, cited above, printing surface 9 is often built up directly onto the substructure. It is thus not difficult to achieve a bottom surface 11 for the printing face that corresponds to the configuration of the top surface of the compressible layer 5. Alternately, however, as noted above, the scope of the invention is sufficiently broad to encompass printing articles, e.g., blankets, as described herein wherein the lowermost surface of the compressible layer is profiled and the uppermost surface is substantially flat. In accordance with the present invention, no matter in which direction the profile faces, i.e, upwardly or downwardly, care should be taken to ensure that the top surface of the printing surface 9 is substantially flat so that it will be positioned at a substantially uniform radius from the central axis of the roll across its entire width and around its entire circumference. In other words, the exterior surface of the blanket, when mounted on a printing cylinder 13 in accordance with the present invention, should be substantially cylindrical. Blanket 1 illustrated in Fig. 2b is similar in many respects to the blanket shown in Fig. 2a and thus like numbers are used in describing like features. It comprises fabric layers 2 and 3 joined together by adhesive 4 to form a substrate. Compressible layer 5, formed as described above, is adhered to the fabric with adhesive layer 6 and fabric layer 7 is installed thereover, held in place by adhesive 10. Blanket 1 in Fig. 2b further comprises, however, sleeve 13 providing support for the laminate, upon which the blanket is mounted. Sleeve 13 is preferably constructed of metal, e . g. , steel. Alternatively, however, sleeve 13 may be formed from a variety of other materials including, but not limited to, plastics, phenolic resins, fabrics and heavy papers such as cardboard. Primer layer 12 prevents corrosion of sleeve 13 (when the sleeve is made of metal) as well as adsorption and wicking of fluids such as inks, water, oils and solvents, upwardly into blanket 1 from sleeve 13. Furthermore, blanket l of Fig. 2b additionally comprises a subface 11 formed from a high durometer, high tensile, low elongation elastomeric compound. Subface 11 is provided to enhance the physical properties of fabric ply 7 and thereby to enhance the stability of printing face 9, thus resulting in improved print quality and durability. Subface 11 also serves to improve the resistance of printing face 9 to cutting while blanket 1 is in use. Blanket 1 in Fig. 2b is thus less susceptible to the consequent swelling and delamination which may otherwise occur when liquids such as inks, oils and solvents enter through cuts in the printing face. While blankets manufactured according to the invention will often be formed with a parabolic convexity due to the ease of achieving that profile, a variety of alternative grinding profiles, shown in FIG. 3, are contemplated as being within the scope of the present invention. The degree of convexity of compressible layer 5 as shown in Figs. 2a, 2b and 3a-f is exaggerated for illustrative purposes. Fig. 3 illustrates a parabolic profile (Fig. 3a) , a large central step profile (Fig. 3b) , a profile consisting of graduated small steps (Fig. 3c) , a diamond-shaped profile (Fig. 3d) , a profile in which the ends have been radially ground (Fig. 3e) , and a profile which has a center step and tapered sides (Fig. 3f) . The invention should not be viewed as being limited to these specific profiles, however. As noted above, one method for forming the desired profile in a compressible layer incorporated into the laminate of the invention is by grinding, e.g., with an o.d. grinder. Compressible layer profiles in accordance with the present invention may, however, also be formed by means other than grinding a pre-formed conventional layer. Particularly in the case of cylindrical printing blankets, the following procedures have been found useful in achieving suitable profiles. For instance, the size of thread/dip tank exit hole may be varied from small to large to small across the width of the article during the winding of the threads used in forming the compressible layer to allow for increasing deposition of the compressible matrix toward the center of the width, i.e., in the central region. Alternatively, one may variably dry or cure the compressible matrix from less to more to less dry or cured across the width prior to winding of the reinforcing layer to allow for decreasing penetration of the reinforcing threads, i.e., the second winding, applied after the compressible matrix is at least partially dried or cured, into the compressible matrix toward the center of the width. One may also vary the reinforcing thread tension from high to low to high across the width to allow for decreasing penetration of the reinforcing threads into the compressible matrix toward the center of the width. Still further, one may variably pressurize the compressible layer from high to low to high across the width during stabilization or pre-curing to allow for decreasing density toward the center of the width. Alternately, one may variably pressurize the completed composite from high to low to high across the width during curing to allow for decreasing density toward the central region of the width and provide a flat profile to the upper surface. Or instead, one may vary the traverse speed and/or the surface speed of the substrate/cylinder from fast to slow to fast during the winding of the compressible layer to allow for the increased deposition of the compressible matrix toward the central region of the width. The method of varying the compressibility of the compressible layer is not critical, so long as it results in a compressible layer that is less compressible towards its peripheral ends and more compressible towards its central region. It is unnecessary to profile, i.e., shape, either the upper or the lower surface of a compressible layer constructed according to any of the methods set forth in either of the two preceding paragraphs, however, since the variable compressibility obtained with these embodiments is attributable not to the shape of the compressible layer, but rather to the method(s) of applying the various components which form the layer. Turning to Fig. 4 there is illustrated a further embodiment of the invention comprising a cylindrical printing blanket 1 produced as follows. A layer 12 of primer is applied to the outer surface of sleeve 13. This primer layer prevents wicking of liquids from sleeve 13 upwardly into blanket 1. It also improves the bond to layer 5. When sleeve 13 is formed of metal, layer 12 may additionally contain well known additives for preventing corrosion of the metal upon contact with materials commonly encountered in the printing environment, e.g., inks, water, solvents and even the lower surface of the blanket itself. Compressible layer 5 may thereafter be formed by wrapping coated sleeve 13, preferably in a spiral configuration, with one or more threads 14 coated with an admixture of an elastomeric matrix and a plurality of closed or open compressible cells. Due, at least in part, to the tension applied during the wrapping operation and/or the comparatively greater density of the coated threads vis a vis that of the compressible material alone, the threads 14 applied in the initial winding sink to the lowermost portion of compressible layer 5, forming a base portion for layer 5, the threads of which are substantially surrounded by the elastomeric matrix 15 mixed with cells 16. The upper portion of compressible layer 5 thus remains substantially free of threads 14, containing only the elastomeric matrix 15 mixed with cells 16. If desired, an additional quantity of the matrix/cell admixture may be applied to the surface of layer 5 once the winding of threads 14 is completed. Thereafter, the thus-formed compressible material may be at least partially cured, i.e., "pre-cured", in a manner well-known in the art to set the various components of layer 5 in place. Layer 5 may be provided with, for example, any of the profiles illustrated in Fig. 3 but the invention is not limited only to those profiles. Further, as would be well understood by one of ordinary skill in the art, the varying compressibility of layer 5 may be produced by any of the methods described above, e.g., by grinding, by varying the amount of cells applied to the threads used to wind the central region, etc. Moreover, it is additionally understood that in any of the embodiments discussed above layer 5 can terminate or be omitted prior to the outer peripheries of the blanket, instead of being present at those locations with a lesser depth or thickness than in the central region. Subsequently, following the formation of profiled compressible layer 5, a reinforcing layer 7 is applied thereto by applying a second winding of one or more threads around the compressible layer. Threads 17 used in forming this reinforcing layer (also referred to herein as reinforcing threads) are preferably wound in a spiral direction around layer 5, optionally in a direction opposite that chosen for winding threads 14, and are coated with elastomeric matrix material 18. No compressible cells are admixed therein. Due to the pre- curing of compressible material 15, reinforcing threads 17 are prevented from sinking down into layer 5. They thus remain atop layer 5, forming an upper fabric ply upon the compressible layer, bound thereto by the adhesive properties of the compressible material. Following the application of reinforcing layer 7, subface 11 and printing face 9 are applied to complete the construction of blanket 1 shown in Fig. 4. Alternately, as noted above it may be desirable for some applications to produce a compressible layer profiled upon its lower surface and relatively flat, i.e., substantially parallel with the outer surface of supporting sleeve 13, upon its upper surface. In order to produce such a compressible layer the cylindrical support is first coated with primer, followed by a layer of elastomer, e.g., rubber. The elastomer layer is ground down, e.g., with an o.d. grinder, or molded to form a negative mold corresponding to the desired profile for the compressible layer. The compressible layer is thereafter formed, e.g., by winding threads coated with a mixture of elastomer material and compressible cells, or alternately by any of the other methods described above, and then cured. After curing, the uppermost surface of the compressible layer is ground until it is substantially flat, that is, parallel to the outer surface of support sleeve 13. FIG. 5 provides a compressibility profile of compressible layers with varying compressibility produced according to the invention. The subject graph compares the force necessary to achieve compressibility (measured in pounds per square inch) versus the location within the compressible layer wherein the measurement is taken, e.g., the end (peripheral portion) or the middle (central region) . As one of ordinary skill in the field would readily understand from reviewing FIG 5, a greater pressure must be applied at the outer periphery of the compressible layer in comparison to that which must be applied in the central region of the layer in order to obtain comparable compression. This further validates the principle that the greater the depth and/or the void volume of the compressible layer, the more compressibility it has. In addition to printing blankets, the principles of the present invention may be applied also to other similar printing and paper aking machine components such as impression blankets, plate cushions, spreader rollers and support and calendaring rollers. In these designs, the present invention provides a compressible cylindrical roll assembly that comprises a metal shaft which is covered by a compressible laminate that has an external surface, for instance an elastomeric printing face, that is of substantially uniform circumference across its width. This compressible laminate includes a compressible layer which has an upper surface the circumference of which is greater in the center of the roll than it is toward both ends of the roll. Thus, the entire roll, rather than a printing blanket, is configured to include the desired compressible layer of the invention. Although the preferred embodiments of the invention have been specifically described, it is contemplated that changes may be made without departing from the scope or spirit of the invention, and it is desired that the invention be limited only by the appended claims.

Claims: THE CLAIMS What is claimed is: 1. A printing article comprising a rotatable support in the form of a sleeve and a compressible laminate mounted upon the support, the compressible laminate having upper and lower surfaces and a substantially uniform thickness and comprising a printing face which forms the upper surface and a compressible layer having upper and lower surfaces positioned beneath the printing face wherein a central region of said compressible layer has a relatively greater compressibility than the peripheral portions thereof. 2. The article of claim 1 wherein the upper surface of the compressible layer is spaced closer to the printing face in the central region of the layer than at the peripheral portions thereof. 3. The article of claim 2 wherein the upper surface of the compressible layer has a parabolic profile. 4. The article of claim 2 wherein the upper surface of the compressible layer has a central step. 5. The article of claim 4 wherein the central step has tapered sides. 6. The article of claim 2 wherein the upper surface of the compressible layer has a profile which includes a plurality of graduated steps. 7. The article of claim 2 wherein the upper surface of the compressible layer has a diamond-shaped profile. 8. The article of claim 2 wherein the upper surface of the compressible layer has a central portion which is flat and peripheral portions which radially taper toward the outer periphery of the laminate. 9. The article of claim 2 wherein the support is a shaft and the compressible laminate forms a roller on the shaft. 10. The article of claim 2 wherein the support is a printing cylinder and the compressible laminate comprises a printing blanket. 11. The article of claim 10 wherein the printing blanket is cylindrical. 12. The article of claim 10 wherein the printing blanket further comprises at least one fabric ply located beneath the compressible layer. 13. The article of claim 12 which further comprises a protective coating on said fabric ply to prevent absorption and wicking of fluids therethrough. 14. The article of claim 13 wherein said protective coating comprises a fluorocarbon or a silicone material. 15. The article of claim 12 wherein the fabric ply is a compressible fabric ply. 16. The article of claim 10 wherein the printing blanket further comprises at least one fabric ply located between the compressible layer and the printing face. 17. The article of claim 10 wherein the printing blanket further comprises a subface formed from an elastomeric compound, said subface located beneath said printing face. 18. The article of claim 10 wherein the printing face has a surface profile with a roughness average of above about 0.2 microns and below about 2.0 microns. 19. The article of claim 10 wherein the compressible layer includes cells formed from microspheres having a diameter of between about 1 and 200 microns. 20. The article of claim 10 wherein the compressible layer includes cells formed from gas bubbles incorporated throughout a binder material. 21. The article of claim 10 wherein said support is formed from a material selected from the group consisting of a metal, plastic, phenolic resin, fabric and cardboard. 22. A printing blanket having upper and lower surfaces and a substantially uniform thickness and comprising a printing face which forms an upper surface and a compressible layer having upper and lower surfaces positioned beneath the printing face wherein a central region of said compressible layer has a relatively greater compressibility than peripheral portions thereof. 23. The blanket of claim 22 wherein the upper surface of the compressible layer is spaced closer to the printing face in the central region of the layer than at the outer periphery thereof. 24. The blanket of claim 23 wherein the upper surface of the compressible layer has a parabolic profile. 25. The blanket of claim 23 wherein the upper surface of the compressible layer has a central step. 26. The article of claim 25 wherein the central step has tapered sides. 27. The blanket of claim 23 wherein the upper surface of the compressible layer has a profile which includes a plurality of small graduated steps. 28. The blanket of claim 23 wherein the upper surface of the compressible layer has a diamond-shaped profile. 29. The blanket of claim 23 wherein the upper surface of the compressible layer has a central region which is substantially flat and outer peripheral portions which radially taper toward the outer periphery of the blanket. 30. The blanket of claim 23 wherein the printing blanket further comprises at least one fabric ply located beneath the compressible layer. 31. The blanket of claim 23 wherein the printing blanket further comprises at least one fabric ply located between the compressible layer and the printing face. 32. The blanket of claim 23 wherein the printing blanket further comprises a subface formed from an elastomeric compound, said subface located beneath said printing face. 33. The blanket of claim 23 wherein the printing face has a surface profile with a roughness average of above about 0.2 microns and below about 2.0 microns. 34. The blanket of claim 23 wherein the compressible layer includes cells formed from microspheres having a diameter of between about 1 and 200 microns. 35. The blanket of claim 23 wherein the compressible layer includes cells formed from gas bubbles trapped within a binder material. 36. The blanket of claim 30 which further comprises a protective coating on said fabric ply to prevent absorption and wicking of fluids therethrough. 37. The blanket of claim 36 wherein said protective coating comprises a fluorocarbon or a silicone material. 38. The blanket of claim 30 wherein the fabric ply is a compressible fabric ply. 39. The blanket of claim 22 in the form of a cylindrical tube and further comprising a rotatable support in the form of a sleeve having an outer surface upon which is mounted said printing blanket. 40. The blanket of claim 39 wherein said support is formed from a material selected from the group consisting of a metal, plastic, phenolic resin, fabric and cardboard. 41. A method of forming a compressible laminate for use on a printing article which includes a rotatable support in the form of a cylinder, which method comprises forming a compressible laminate having upper and lower surfaces and a substantially uniform thickness from at least a printing face which forms the upper surface and a compressible layer having upper and lower surfaces positioned beneath the printing face; and forming a central region of said compressible layer having a relatively greater compressibility than the outer peripheral portions thereof. 42. The method of claim 41 which further comprises forming the upper surface of said compressible layer to have a profile with a raised central region spaced closer to the printing face than the peripheral portions of said layer. 43. The method of claim 42 which further comprises applying a substantially uniform thickness of the compressible layer and grinding the compressible layer to a desired profile. 44. The method of claim 42 which further comprises applying the compressible layer in the form of threads carrying a matrix of compressible material, and varying the amount of matrix material carried by the threads to increase the deposition of the matrix material toward the central region of the laminate. 45. The method of claim 42 which further comprises applying the compressible layer in the form of a first layer of threads carrying a matrix of compressible material, and varying the rate at which the matrix material is set across the width of the laminate prior to winding a second layer of reinforcing threads thereover to thus allow for decreasing penetration of said first threads into the matrix material toward the central region of the laminate. 46. The method of claim 42 which further comprises applying the compressible layer in the form of a matrix of compressible material, and thereafter winding reinforcing threads across the width of the laminate while varying the winding tension to thus allow for decreasing penetration of the reinforcing threads into the matrix material toward the central region of the laminate. 47. The method of claim 42 which further comprises applying the compressible layer in the form of a matrix of compressible material, and thereafter varying the pressure on the compressible layer during pre-curing of the matrix material to allow for decreasing density of the compressible layer toward the central region of the laminate. 48. The method of claim 42 which further comprises applying the compressible layer in the form of threads carrying a matrix of compressible material, and varying the speed of the cylinder during the winding of the threads to increase the deposition of the matrix material toward the central region of the laminate. 49. The method of claim 42 which further comprises applying the compressible layer in the form of an elastomeric material admixed with a plurality of compressible cells, and applying a relatively greater amount of cell-containing medium in a central region of the compressible layer in relation to an amount which is applied at the outer periphery thereof. 50. The method of claim 42 which further comprises applying the compressible layer in the form of an elastomeric material admixed with a plurality of compressible cells, and mixing a relatively greater amount of said cells into the elastomeric material applied in the central region of the compressible layer in relation to the amount which is applied at the outer periphery thereof. 51. The method of claim 42 which further comprises applying said compressible layer in the form of a series of compressible strips of varying compressibility, wherein the strips having the relatively greatest degree of compressibility are positioned in the central region of said compressible layer. 52. The method of claim 42 which further comprises applying the compressible laminate in the form of a cylinder. 53. The method of claim 42 which further comprises applying the compressible laminate in the form of a printing blanket. 54. The method of claim 42 which further comprises applying the compressible laminate in the form of a printing roller. 55. A method of forming a cylindrical printing blanket which comprises: providing a rotatable support member having an outer surface thereon; applying to at least a portion of said outer surface of said support member a coating material adapted for preventing corrosion of and promoting adhesion to said support; winding around said coated support a first thread layer coated with an admixture of an elastomeric material and a plurality of compressible cells, wherein, during said winding, said thread sinks downwardly into said admixture adjacent said coated support member; at least partially curing said elastomeric material to form a compressible layer upon said support; winding around an outer surface of said compressible layer a second, reinforcing thread layer wherein said threads are coated with an elastomeric material substantially free of said compressible cells and wherein the depth to which said second layer sinks into said elastomeric material is controlled during said second winding step; and forming a printing face upon an upper surface of said fabric ply. 56. The method of claim 55 wherein said first and said second thread layers are applied by winding them in a substantially spiral direction. 57. The method of claim 56 wherein said first and said second thread layers are wound in opposing spirals. 58. The method of claim 55 which further comprises producing a parabolic profile upon the upper surface of the compressible layer. 59. The method of claim 55 which further comprises forming said compressible layer with a central step upon its upper surface. 60. The method of claim 59 which further comprises tapering the sides of said central step. 61. The method of claim 55 which further comprises forming said compressible layer with a profile including a plurality of graduated steps. 62. The method of claim 55 which further comprises providing the upper surface of said compressible layer with a diamond-shaped profile. 63. The method of claim 54 wherein the compressible layer is formed with a substantially flat central region and outer peripheral portions which radially taper toward the peripheral portions of the layer. 64. The method of claim 55 which further comprises interposing a subface between said fabric ply and said printing face, said subface formed from an elastomeric compound. 65. The method of claim 55 which further comprises providing said printing face with a surface profile having a roughness average above about 0.2 microns and below about 2.0 microns.

Inventors: BEHNKE RICHARD L, BRIDGES VERNON O, BYERS JOSEPH L, FLINT W TORIRAN, BEHNKE, RICHARD, L., BRIDGES, VERNON, O., BYERS, JOSEPH, L., FLINT, W., TORIRAN
Applicants: BEHNKE RICHARD L, BRIDGES VERNON O, BYERS JOSEPH L, FLINT W TORIRAN, REEVES BROS INC, BEHNKE, RICHARD, L., BRIDGES, VERNON, O., BYERS, JOSEPH, L., FLINT, W., TORIRAN, REEVES BROTHERS, INC.
Application year: 1995
Main classification: B41N10
IPC codes: B41N10