EP0593593A4

EP0593593A4 - Printing blanket construction and method for reducing corrosion of printing blanket cylinders.

Info

Publication number: EP0593593A4
Application number: EP92914634A
Authority: EP
Inventors: Melvin Douglas Pinkston; John Joseph Dolan; Daniel Clyde Deitz; Michael Edward Mclean; Robert Schmid; Norbert Seitz
Original assignee: Day International Corp
Current assignee: Day International Corp
Priority date: 1991-07-05
Filing date: 1992-06-30
Publication date: 1995-03-01
Also published as: WO1993001003A1; CA2112478A1; EP0593593A1; JPH06511440A; AU2271592A

Abstract

A printing blanket construction and method for reducing corrosion of printing blanket cylinders is provided. The printing blanket (11) comprises at least one base ply (12, 13) and a surface layer (10) on one surface of the base ply wherein the opposite surface of the base ply (12) is adapted to contact the blanket cylinder. The printing blanket includes a metal or alloy having a greater negative electrochemical potential in the electromotive series than the metal comprising the surface of the blanket cylinder. The preferred metal for use may be selected from the group consisting of zinc, magnesium, cadmium or aluminum. The metal may be introduced onto the opposite surface of the base ply (12) in the form of a metal sheet, by coating, or in particle form through the use of a coating. After introduction of the metal, the opposite surface of the base ply is preferably ground to produce a smooth, nontextured surface.

Description

PRINTING BLANKET CONSTRUCTION AND METHOD FOR REDUCING CORROSION OF PRINTING BLANKET CYLINDERS

Background of the Invention The present invention relates to a printing blanket construction, and more particularly, to a printing blanket construction and method for reducing corrosion of a blanket cylinder. The type of blanket referred to herein is used primarily in offset lithographic printing, but may also find utility in other fields of printing.

In a typical lithographic printing apparatus, a rotary cylinder is covered with a printing plate which has a positive image area receptive to oil-based inks and repellent to water, and a background area where the opposite is true. The printing plate is rotated so that its surface contacts a second cylinder covered with a rubber-surfaced ink-receptive printing blanket. The ink present on the image surface of the printing plate transfers, or offsets, to the surface of the blanket. Paper or other sheet stock to be printed is then passed between the blanket-covered cylinder and a rigid back-up cylinder to transfer the image from the surface of the blanket to the paper.

Presently, most commercial printing blankets use one or more layers of woven fabrics for the base material. The working surface of the blanket which contacts the ink is typically an elastomeric layer of natural or synthetic rubber which is applied over the base layer or layers. The base layer and working surface are laminated together using suitable adhesives. During the image transferring process, it is important to position the blanket-covered cylinder and the supporting cylinder it contacts so that there is a fixed interference between the two. This assures that the blanket is compressed uniformly over the entire surface of the blanket throughout the printing run. In offset lithography as well as other printing operations, the printing plate and blanket cylinders are subject to corrosion and rust as a result of exposure to inks, water, and chemicals and solvents used to clean the machinery. To combat such problems, the blanket cylinders have sometimes been plated with chrome, nickel, or a ceramic material. These materials provide a surface that is not only corrosion resistant, but also ink repellant.

However, such nickel- and chrome-plated cylinders have not worked well in conjunction with the printing blankets comprising fabric base materials. The fountain solution of the ink, which acts as an electrolytic solution, wicks around the edges of the blanket and in the gap between ends of the blanket, spreads across the surface of the cylinder, and promotes corrosion of the metal plating. The friction due to the relative movement of the blanket and cylinder surfaces also causes a mechanical abrading of the cylinder surface. As a result, after relatively short periods of time, the protective nickel or chrome plating is removed from the cylinder surface to such an extent that the unprotected metal underneath, such as steel, is exposed. The areas on the cylinder surface where the plated metal is removed are then subject to rapid corrosion and/or oxidation. Consequently, the cylinder must be resurfaced frequently, which is an expensive and time consuming process. Several attempts have been made to reduce corrosion of the metal components used in printing operations. For example, Matsuo et al, U.S. Patent No. 4,861,396; Nishikawa et al, U.S. Patent No. 4,729,939; and Fujikura, U.S. Patent No. 4,435,230, all disclose printing plates using an aluminum alloy which resists corrosion.

Other methods to reduce corrosion have included the use of a corrosion inhibitor in a fountain solution as disclosed in Bassemir et al, U.S. Patent No. 4,854,969. It has also been proposed to apply an oil containing corrosion inhibitor across the blanket cylinder prior to mounting the blanket. However, this interferes with adhering the blanket or underlying packing material to the blanket cylinder because the oil prevents effective adhesion.

Still further, Pinkston et al, U.S. Patent No. 5,006,400 assigned to the assignee of the present invention, utilizes a printing blanket having a smooth surfaced back side to reduce the abrasive effect of the blanket on the cylinder. However, none of these attempts have resulted in a complete reduction in corrosion of the blanket cylinders. Moreover, all addressed only single aspects of the causes of cylinder corrosion.

Accordingly, there is still a need in the art for a printing blanket construction and method for substantially eliminating corrosion of a blanket cylinder.

Summary of the Invention The present invention meets that need by providing a printing blanket construction and method in which a protective metal is included in one or more layers of the blanket or on the back side of the printing blanket. The protective metal in or on the blanket functions to reduce corrosion of the metal on the blanket cylinder by acting as an anode material which preferentially is sacrificed. Preferably, the blanket surface contacting the cylinder is also relatively smooth. Thus, the printing blanket of the present invention addresses both physical as well as electrochemical causes of corrosion.

It is well known that galvanic corrosion is the accelerated corrosion rate caused by the flow of electrical current to a less active metal, or cathode, which is in contact with a more active metal, or anode, via an electrically conductive solution (electrolyte) . This is due to the difference of negative electrochemical potential between the two metals. Anodic metals have a greater negative electrochemical potential in the electromotive series than cathodic metals. When two metals having a significant difference in negative electrochemical potential are coupled together via an electrolyte, the anodic metal is subjected to accelerated corrosion. As a result, the cathodic metal is protected from corrosion by the anode.

This form of cathodic protection is commonly referred to as the sacrificial-anode method, which generally includes the use of metals having a high negative electrochemical potential such as zinc, magnesium or aluminum as anodes in electrical contact with the metal to be protected. We have now applied the principle of anodic protection to the present invention wherein the protective metal used in or on the printing blanket has a greater negative electrochemical potential than the metal on the blanket cylinder. Thus, the metal in or on the printing blanket functions as a sacrificial anode to electrochemically protect the metal on the blanket cylinder from corrosion.

In accordance with one aspect of the present invention, a printing blanket construction is provided which comprises at least one base ply and a surface layer on one surface of the base ply. The opposite surface of the base ply is adapted to contact the blanket cylinder and includes a metal or metal alloy having a greater negative electrochemical potential in the electromotive series than the metal comprising the surface of the blanket cylinder. The preferred metal for use in the present invention is selected from the group consisting of zinc, magnesium, cadmium and aluminum, with aluminum being the most preferred. Although any combination of metals may be used as long as the preferred electrochemical potential is met, some metals are unsuitable for use due to their high reactivity or toxicity.

The metal is also preferably present in or on the blanket in a sufficient quantity to discharge substantially all negative ions such as chlorides or sulfates in fountain and/or wash solutions that come into contact with the blanket cylinder over the normal useful life of the blanket. The fabric of the blanket itself may be a source of negative ions which are dissolved into solution. Again, preferably the protective metal content in or on the blanket should be sufficient to discharge substantially all of that source of negative ions as well.

In one embodiment of the invention, a layer of the preferred metal is deposited on the opposite surface of the base ply which is adapted to contact the blanket cylinder surface. Preferably, the opposite surface of the base ply is ground to produce a substantially smooth, nontextured surface prior to depositing the metal on the base ply. This aids in reducing abrasive effects of the blanket cylinder surfaces. By substantially smooth and nontextured, we mean a blanket having the desired gauge (overall thickness) with a tolerance of ± 0.0005 inches. Thus, the exterior-facing surface of the base ply will not have the surface variations of greater than the designed tolerance for the blanket. In another embodiment of the invention, the base ply comprises a metal sheet of the preferred metal.

In an alternative embodiment, the base ply comprises a smooth sheet having a layer of the preferred metal deposited or coated thereon. In another embodiment of the invention, the opposite surface of the base ply is coated with a compound which includes metal particles therein. The compound may be in the form of a paint or other liquid or semi-liquid coating. In one embodiment of the invention, the compound is an elastomer containing the metal particles therein. The opposite surface of the base ply is ground to expose the metal particles. The metal particles are selected from the preferred group consisting of zinc, magnesium, cadmium and aluminum. The compound comprises about 5-50% by weight of the metal particles and preferably comprises about 10% by weight of the metal particles. The metal particles have a diameter of up to 100 microns and preferably between about 1-50 microns.

In yet another embodiment of the invention, an intermediate layer of an elastomeric adhesive is provided between the base ply and an adjacent layer, and the base ply comprises a fabric. The intermediate layer is an elastomeric adhesive compound having metal particles comprising the preferred metal therein. The adhesive penetrates the fabric of the base ply and bonds it to an adjacent ply. The opposite surface of the base ply is then preferably ground to expose the metal particles in the adhesive to the exterior surface of the blanket. The elastomeric compound comprises about 5-50% by weight of the metal particles, and preferably comprises about 30% by weight of the metal particles. The metal particles have a diameter of up to 100 microns, and preferably between about 1-50 microns.

In an alternative embodiment of the invention, the base ply comprises a fabric including metal fibers of the preferred metal making up at least a portion of the warp or weft fibers therein.

In yet another embodiment of the invention, the base ply comprises a fabric which has been impregnated with a compound containing metal particles of the preferred metal. The compound may be in the form of a paint or other liquid or semi-liquid material which may be coated onto and impregnated into the fabric base ply. In one embodiment, the compound is an elastomer. The base ply is preferably ground to expose the metal particles on the exterior surface of the base ply. The compound comprises from about 5-50% by weight of the metal particles, and preferably about 20% by weight of the metal particles. The metal particles have a diameter of up to 100 microns and preferably between about 1-50 microns. A method for constructing a printing blanket for use on a blanket cylinder is also provided which generally comprises the steps of: providing at least one base ply with a surface layer on one surface thereof, and introducing a metal or alloy onto or into the printing blanket, preferably onto the opposite surface of the base ply or in the base ply, wherein the metal or alloy has a greater electrochemical potential in the electromotive series than the metal comprising the surface of the blanket cylinder. In the embodiment where a layer of the preferred metal is deposited on the opposite surface (i.e., exterior- facing surface) of the base ply, the method further includes the step of grinding the opposite surface of the base ply prior to depositing the metal. The base ply may be either a fabric or an elastomeric composition. The metal is then preferably introduced onto the opposite surface of the base ply by painting, spraying, vapor deposition, sputter coating, electron beam deposition, or any other suitable coating technique. In the embodiment where the opposite surface of the base ply has been coated with a compound containing metal particles, the method includes the steps of coating the opposite surface of the base ply with the compound, and then grinding the opposite surface of the base ply to expose the metal particles.

In the embodiment where there is an intermediate layer, and the intermediate layer and base play are laminated by an elastomeric adhesive compound containing metal particles, the method includes the step of grinding the opposite surface of the base ply to expose the metal particles.

In the embodiment where the base ply comprises a fabric which is impregnated with a compound containing metal particles, the method also includes the step of grinding the fabric surface to expose the metal particles. The present invention thus addresses both physical and electrochemical causes of cylinder corrosion by providing a printing blanket having both a relatively smooth, low abrasion cylinder-contacting surface as well as having a greater negative electrochemical potential than the surface of the blanket cylinder.

Accordingly, it is an object of the present invention to provide a printing blanket construction and method which substantially reduces corrosion of a blanket cylinder.

Brief Description of the Drawings Fig. 1 is an isometric view of a segment of the printing blanket of the present invention; Fig. 2 is a cross-sectional view of a segment of one embodiment of the printing blanket of the present invention;

Fig. 3 is a cross-sectional view illustrating another embodiment of the invention; Fig. 4 is a cross-sectional view of another embodiment of the invention;

Fig. 5 is a cross-sectional view of another embodiment of the invention;

Fig. 6 is a cross-sectional view of another embodiment of the invention; and

Fig. 7 is a cross-sectional view of another embodiment of the invention.

Detailed Description of the Preferred Embodiment The printing blanket 11 of the present invention is illustrated in Fig. l and comprises a base ply 12. The base ply is typically made up of one or a plurality of fabrics, paper, felts, elastomers, or fiber filled elastomeric reinforcements made from natural or synthetic fibers such as cotton, linen, flax, rayon, polyester, glass, metal fibers, carbon fibers, nylon, acrylic, and cellulose. As is conventional in the art, additional intermediate layers including plies of fabric such as ply 13 or layers of reinforcement materials may also be included in the blanket construction. Plies 12 and 13 may be bonded together by an elastomeric adhesive layer 20. The blanket may optionally contain a layer of compressible elastomeric material 15 under the surface layer 10, between any succeeding layers of reinforcement materials, or may be included as a reinforcement layer. Such an elastomeric material may also be used as a coating on the opposite surface of the base ply prior to the introduction of metal.

Surface layer 10, which is adapted to accept an inked image from a printing plate, is typically formed from any suitable polymeric material including both natural rubbers and synthetic compounds. Suitable rubber compounds include acrylonitrile butadiene rubber, isobutylene isoprene elastomer, polysulfide rubber, ethylene propylene diene terpolymer, natural rubber, styrene butadiene rubber, or blends of acrylonitrile-butadiene and polysulfide rubber. The surface can be talc coated-smooth molded, ground after vulcanization, or textured by any known process such as that disclosed in U.S. Patent No. 4,751,127, assigned to the assignee of the present invention. A cross-sectional view of one embodiment of the printing blanket is illustrated in Fig. 2 which shows a base ply 12 and a surface layer 10. A metal layer 14 is on the opposite surface of the base ply. The preferred metal for use in the present invention is selected from the group consisting of zinc, magnesium, cadmium and aluminum, with aluminum being the most preferred metal. Although any combination of metals may be used as long as the preferred electrochemical potential difference is met, some metals are unsuitable for use due to their high reactivity or toxicity. The metal may be introduced on the opposite surface of the base ply by painting, spraying, vapor deposition, sputter coating, electron beam deposition, or any other suitable coating technique. A coating thickness of from about 5 to 2000 angstroms may be used, with a thickness of from about 10 to 1000 angstroms being preferred. Prior to deposition of the metal on the base ply, the opposite surface of the base ply (i.e., exterior facing surface) may optionally be ground to produce a substantially smooth, nontextured surface. This can be achieved by either grinding the protruding fill thread loops from the fabric contained in the base ply or alternatively, by coating the opposite surface of the base ply with an elastomeric material which may optionally be ground to present a smooth surface as discussed in U.S. Patent No.

5,006,400, the disclosure of which is herein incorporated by reference. It is preferred that the surface of the base ply which is in contact with the blanket cylinder, be relatively smooth so that when mounted on a blanket cylinder, the nontextured surface of the base layer of the blanket contacts substantially the entire surface of the blanket cylinder. This reduces the mechanical abrasion of the cylinder surface due to relative movement between the blanket and cylinder during use. Fig. 3 illustrates an alternative embodiment in which the base ply comprises a metal sheet 16. The sheet may be made entirely of the preferred metal, or may have a coating of the metal deposited thereon. The sheet may also comprise other materials such as plastic or non-woven cloth or paper. The metal may be laminated to the surface layer by any conventional adhesion method to adhere the metal to rubber or to adhere rubber to fabric. Preferably, the minimum thickness of the metal is about 2000 angstroms. While there is no preferred maximum thickness, the thickness utilized should allow the blanket to be flexible enough for mounting on the printing blanket cylinder.

Fig. 4 illustrates another embodiment of the invention wherein the opposite surface of the base ply 12 is coated with a compound containing metal particles 18. In one form, the compound is an elastomer which may comprise any of the polymeric compositions previously noted for use as surface layer 10. As is shown, the base ply has been ground to expose the metal particles. The compound comprises from about 5-50% by weight of the metal particles and preferably comprises about 10% by weight of the metal particles. The metal particles have a diameter of up to 100 microns, and preferably between about 1-50 microns.

Another embodiment of the invention is illustrated in Fig. 5 in which an intermediate layer 13 is provided between the surface layer 10 and base ply 12. Layer 13 may serve as a reinforcing layer for the blanket. The intermediate layer and the base ply comprise a fabric and are laminated together by an elastomeric adhesive compound 20 which includes metal particles 18. The adhesive may comprise any of the polymeric compositions previously noted for use as surface layer 10. As shown in Fig. 5, the adhesive compound flows into the fabric so as to be contained within the weave interstices of both the intermediate layer and base ply. The opposite surface of the base ply (i.e., exterior-facing surface) is then ground so that the metal particles within the elastomeric compound are exposed on the surface of the base ply. The elastomeric compound comprises from about 5-50% by weight of the metal particles, and preferably comprises about 30% by weight of the metal particles. The metal particles have a diameter of up to 100 microns and preferably between about 1-50 microns. Figure 6 illustrates yet another embodiment of the invention in which the base ply 12 includes metal fibers 22 within the fabric or elastomer. The opposite surface of the base ply may be ground if desired for smoothness, but this is not necessary as long as the metal fibers are sufficiently exposed to contact any fountain solution which has penetrated between the printing blanket and the cylinder. If the metal fibers are encapsulated in a non- porous material, then it may be necessary to grind the base ply to obtain sufficient exposure.

Figure 7 illustrates another embodiment of the invention wherein the base ply 12 comprises fabric which has been impregnated with a compound filled with metal particles 18. In a preferred form, the compound is an elastomer which may comprise any of the polymeric compositions previously noted for use as surface layer 10. The base ply is then ground to a relatively smooth surface to expose the metal particles. The compound comprises about 5-50% by weight of the metal particles, and from about 20% by weight of the metal particles. The metal particles have a diameter of up to 100 microns and preferably between about 1-50 microns.

Through the use of a printing blanket construction which utilizes a base ply having both a relatively smooth, nontextured surface and which contains a metal having a greater negative electrochemical potential than the surface of the blanket cylinder, the corrosion of the surface of a blanket cylinder during a printing operation is substantially reduced.

In order that the invention may be more readily understood, reference is made to the following example, which is intended to be illustrative of the invention, but is not intended to be limiting in scope. Example

To test the corrosion reducing capability of blankets made in accordance with the present invention, a number of blankets were prepared and tested in an environment designed to simulate the corrosive environments that the blankets and blanket cylinders would be subjected to in normal use. The blankets were: 5/10 - 8800 Series printing blanket manufactured by Day International, Inc. which includes a fabric base ply and a compressible intermediate layer; Sample 5/11 - the same blanket, but having the surface of the fabric base ply ground in accordance with the teachings of Pinkston et al, U.S. Patent No. 5,006,400; Sample 5/12 - the same blanket, but with an elastomeric composition coated over the fabric base ply, the elastomer containing about 10% by weight aluminum particles; and Sample 5/13 - the same blanket, but with an elastomeric composition coated over the fabric base ply. Samples 5/11, 5/12, and 5/13 all had aluminum sputter-coated onto the exterior surface of their respective base plies at a thickness of approximately 100 angstroms.

The sample blankets were mounted on a nickel- plated steel cylinder designed to simulate a printing blanket cylinder and immersed in fountain solution for thirty 24 hour cycles. Each cycle included 20 hours of immersion in the solution and a 4 hour drying period.

During the drying periods, the samples were dried in an oven maintained at 70°C to simulate the liquid evaporation and resulting concentration of salts on the cylinder surface which would occur during normal printing operations. The fountain solution was a 3% by volume solution of Siegwerk fount additive WV 2536 in deionized water. The fountain solution is known to be relatively corrosive. Additionally, 100 ppm of chloride ions were added to the fountain solution to exaggerate the corrosive potential of the solution. The pH of the solution was measured to be 4.22.

Corrosion was measured as a loss in the mass of the nickel-plated cylinders. The results of the tests are reported below in Table 1. As can be seen, the blankets made in accordance with the present invention (Samples 5/11, 5/12, and 5/13) reduced corrosion by about 80% over a conventional printing blanket. Under normal press operating conditions, which would be expected to be less severe than the test procedure, practically no corrosion of the nickel- plated cylinders would be expected, especially as the protective effect of the blanket would be renewed with every blanket change on the press.

TABLE 1

Having described the invention in detail and by reference to the preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

What is claimed is:

Claims

1. A printing blanket construction for reducing corrosion of a blanket cylinder comprising at least one base ply and a surface layer on one surface of said base ply, the opposite surface of said base ply adapted to contact said blanket cylinder, said printing blanket including a metal or alloy having a greater negative electrochemical potential in the electromotive series than the metal comprising the surface of said blanket cylinder.

2. The printing blanket construction of claim 1 wherein said opposite surface of said base ply is substantially smooth and nontextured.

3. The printing blanket construction of claim 1 wherein said metal is on said opposite surface of said base ply.

4. The printing blanket construction of claim 3 wherein said metal is selected from the group consisting of zinc, magnesium, cadmium and aluminum.

5. The printing blanket construction of claim 1 wherein said base ply comprises a metal sheet made from said metal.

6. The printing blanket construction of claim 5 wherein said metal is selected from the group consisting of zinc, magnesium, cadmium and aluminum.

7. The printing blanket construction of claim 1 wherein said base ply comprises a substantially smooth sheet having a layer of said metal thereon. 8. The printing blanket construction of claim 7 wherein said metal is selected from the group consisting of zinc, magnesium, cadmium and aluminum.

9. The printing blanket construction of claim 1 wherein said base ply comprises a compound having particles of said metal therein.

10. The printing blanket construction of claim 9 wherein said base ply has been ground to expose said metal particles.

11. The printing blanket construction of claim 9 wherein said metal particles are selected from the group consisting of zinc, magnesium, cadmium and aluminum.

12. The printing blanket construction of claim 9 wherein said compound is an elastomer which comprises from about 5-50% by weight of said metal particles.

13. The printing blanket construction of claim 9 wherein said compound is an elastomer which comprises about 10% by weight of said metal particles.

14. The printing blanket construction of claim 9 wherein said metal particles have a diameter up to about 100 microns.

15. The printing blanket construction of claim 1 wherein an intermediate layer of elastomeric adhesive compound is provided between said base ply and an adjacent layer, said elastomeric adhesive compound having particles of said metal therein. 16. The printing blanket construction of claim 15 wherein said base ply comprises a fabric.

17. The printing blanket construction of claim 15 wherein said opposite surface of said base ply has been ground to expose said metal particles.

18. The printing blanket construction of claim 15 wherein said metal particles are selected from the group consisting of zinc, magnesium, cadmium and aluminum.

19. The printing blanket construction of claim 15 wherein said elastomeric adhesive compound comprises from about 5-50% by weight of said metal particles.

20. The printing blanket construction of claim 15 wherein said elastomeric adhesive compound comprises about 30% by weight of said metal particles.

21. The printing blanket construction of claim 15 wherein said metal particles have a diameter of up to about 100 microns.

22. The printing blanket construction of claim 1 wherein said base ply comprises a fabric having fibers of said metal therein.

23. The printing blanket construction of claim 22 wherein said metal fibers are selected from the group consisting of zinc, magnesium, cadmium and aluminum.

24. The printing blanket construction of claim 22 wherein said base ply has been ground to expose said metal particles. 25. The printing blanket construction of claim l wherein said base ply comprises a fabric impregnated with a compound containing particles of said metal therein.

26. The printing blanket construction of claim 25 wherein said base ply has been ground to expose said metal particles.

27. The printing blanket construction of claim 25 wherein said metal particles are selected from the group consisting of zinc, magnesium, cadmium and aluminum.

28. The printing blanket construction of claim 25 wherein said compound is an elastomer which comprises from about 5-50% by weigh of said metal particles.

29. The printing blanket construction of claim 25 wherein said compound is an elastomer which comprises about 20% by weight of said metal particles.

30. The printing blanket construction of claim 25 wherein said metal particles have a diameter of up to about 100 microns.

31. A method of constructing a printing blanket for use on a blanket cylinder comprising the steps of: providing at least one base ply with a surface layer on one surface thereof, the opposite surface of said base ply adapted to contact said blanket cylinder; and introducing a metal or alloy onto or into said printing blanket, said metal or alloy having a greater negative electrochemical potential in the electromotive series than the metal comprising the surface of said blanket cylinder. 32. The method of claim 31 wherein said metal is deposited on said opposite surface of said base ply.

33. The method of claim 32 including the step of grinding said opposite surface of said base ply to produce a substantially smooth nontextured surface prior to depositing said metal on said opposite surface of said base ply.

34. The method of claim 31 wherein said metal is selected from the group consisting of zinc, magnesium, cadmium and aluminum.

35. The method of claim 31 wherein said base ply is formed from a sheet made from said metal.

36. The method of claim 35 wherein said metal is selected from the group consisting of zinc, magnesium, cadmium and aluminum.

37. The method of claim 31 wherein said base ply is formed by coating a sheet with a layer of said metal.

38. The method of claim 37 wherein said metal is selected from the group consisting of zinc, magnesium, cadmium and aluminum.

39. The method of claim 31 wherein said opposite surface of said base ply is coated with a compound having particles of said metal therein.

40. The method of claim 39 further including the step of grinding said opposite surface of said base ply to expose said metal particles. 41. The method of claim 39 wherein said compound is an elastomer which comprises from about 5-50% by weight of said metal particles.

42. The method of claim 39 wherein said compound is an elastomer which comprises about 10% by weight of said metal particles.

43. The method of claim 39 wherein said metal particles have a diameter of up to about 100 microns.

44. The method of claim 39 wherein said metal particles are selected from the group consisting of zinc, magnesium, cadmium and aluminum.

45. The method of claim 31 wherein an intermediate layer is provided between said base ply and said surface layer.

46. The method of claim 45 wherein said intermediate layer and said base ply comprise a fabric.

47. The method of claim 45 wherein said intermediate layer is laminated to the opposite surface of said base ply by an elastomeric adhesive compound having metal particles therein to provide said metal in said base ply.

48. The method of claim 47 further including the step of grinding the opposite surface of said base ply to expose said metal particles.

49. The method of claim 47 wherein said elastomeric adhesive compound comprises from about 5-50% by weight of said metal particles. 50. The method of claim 47 wherein said elastomeric adhesive compound comprises about 30% by weight of said metal particles.

51. The method of claim 47 wherein said metal particles have a diameter of up to about 100 microns.

52. The method of claim 47 wherein said metal particles are selected from the group consisting of zinc, magnesium, cadmium and aluminum.

53. The method of claim 31 wherein said base ply comprises a fabric.

54. The method of claim 53 wherein fibers of said metal are introduced into said fabric.

55. The method of claim 54 wherein said metal fibers are selected from the group consisting of zinc, magnesium, cadmium and aluminum.

56. The method of claim 53 wherein said fabric is impregnated with a compound containing particles of said metal.

57. The method of claim 53 further including the step of grinding said fabric to expose said metal particles.

58. The method of claim 53 wherein said metal particles are selected from the group consisting of zinc, magnesium, cadmium and aluminum.