WO1993008983A1

WO1993008983A1 - Biform compressible ply

Info

Publication number: WO1993008983A1
Application number: PCT/US1992/009533
Authority: WO
Inventors: Toriran W. Flint; Joseph L. Byers
Original assignee: Reeves Brothers, Inc.
Priority date: 1991-11-08
Filing date: 1992-11-06
Publication date: 1993-05-13
Also published as: AU3066192A

Abstract

A compressible layer (5) used in forming a printing blanket (1) or a printing cushion is made to have a uniform compressibility factor over its useful life. This is accomplished by evenly dispersning both closed and open soluble cell structures in a binder to form a compound and curing the resilient compound onto substrates (2, 3). A compressible layer may also be made without a backing if a suitable amount of the compound is laid down and cured to create a flexible mat. Alternatively, compound may be laid onto a release liner, cured and then adhered to a substrate. The closed cells typically used are phenolic microspheres although other suitable structures may be substituted. They may also be formed by mechanical foaming or with decomposable materials. The open cells are created by the use of a soluble material such as salt although other suitable materials may be used. The soluble material is removed from the layer after curing by leaching out the salt or using a suitable solvent to dissolve the other soluble materials that may be used.

Description

BIFORM COMPRESSIBLE PLY

BACKGROUND OF THE INVENTION

!• Field of the Invention The field of the invention is the assembly and manufacturing of compressible layers having a primary use in printing processes as components of a printing blanket or a printing plate cushion. Printing blankets are typically mounted on a cylinder and receive an ink impression from a printing plate mounted on another cylinder. The impression from the blanket is then transferred to a permanent medium such as paper. A desirable characteristic of such blankets is that they do not deform from repeated contact with the printing plate. Likewise, printing plate cushions also should not deform.

2. Description of Related Art

Printing blankets are typically made from composites of one or more fabric layers and a printing surface with a compressible layer in between. The compressible layer acts to cushion the impact from a cylinder mounted printing plate. The construction of the compressible layer is important in determining the impression recovery characteristic of the printing blanket. Permanent deformation of the compressible layer from successive contact with a cylinder mounted printing plate results in smudged or blurred printing images because of the distortion in the printing surface overlaying the deformed compressible layer. As a conseguence it is desirable to produce printing blankets with compressible layers that are resistant to permanent deformation. In the past, compressible layers have been made with, either closed or open cell structures embedded in an elastic sheet. The presence of the cells served to resist permanent deformation that results when using a flexible sheet without cells. However, the deformation characteristics still do not remain constant over an extended period of time using either construction. The closed cell construction results in a decreasing compression factor over successive impressions while the open cell construction results in increasing compression factor over successive impressions. The desired constant compression factor is not achieved by either construction.

United State Patent No. 4,042,743, issued to Charles E. Larson, discloses a compressible offset printing blanket in which a closed cell construction is achieved using icroballoons in the elastomeric layer of the blanket. Larson also mentions that open cells are introduced into the elastomer by a process not fully understood by him. The procedure for adding the microballoons is to stir them into the elastomeric compound so as to avoid crushing any appreciable amount of the microballoons. The compound is applied to a backing, including a fabric, to form the compressible layer.

United States Patent No. 4,422,895, issued to Harao Shimura, discloses a method of making the compressible layer in a printing blanket in which open cells are formed in an elastomer that has been applied to a fabric and vulcanized. The open cells are created by placing a soluble material in the elastomer as it is being compounded and before application to the backing fabric and removing the soluble material from the vulcanized layer to form open cells by applying an effluent to the layer that dissolves the soluble material. Neither of the above methods of constructing a compressible layer has the characteristic of providing a uniform compression factor of the compressible layer in a printing blanket or printing plate cushion over an extended period in which impressions are made. Both methods exhibit a large and rapid change in compression characteristic in the early stages of use necessitating frequent press adjustments to compensate for the change.

SUMMARY OF THE INVENTION The object of the present invention is to provide a printing blanket with a uniform compression characteristic over an extended period of impressions.

Another object is to provide a cushion for a printing plate that has a uniform compression factor over an extended period of impression.

Another object is to provide a compressible layer in a composite medium with a uniform compression characteristic over an extended period of impressions.

Yet another object is to provide a compressible layer in a composite medium, without the need for a substrate, yet still having the characteristic of a uniform compression characteristic over an extended period of impressions.

To achieve the above objects, both closed and open cells are used in an elastomer to form a compressible layer in a composite medium which may be used as a printing blanket or a printing plate cushion. The use of both closed and open cells in compressible layers has the effect of canceling out the divergent compression factor of layers having only one of the cell types.

The closed cells are typically microspheres, made from different materials, but nominally made of phenolic resin. The open cells are formed by embedding soluble material in an elastomer and after the curing of the compound, removing the soluble material by applying an effluent to dissolve it. Nominally a salt is used as the soluble material and water is used to leach it from the cured layer. Other soluble materials may be used if the effluent that dissolves them does not harm the cured layer.

A desirable result of uniform compression factor is achieved by using a uniform distribution of open and closed cells in the cured- layer. It is also desirable to achieve a blend of open and closed cells in which the volumes occupied by each in the cured layer is essentially equal.

BRIEF DESCRIPTION OP THE DRAWINGS Figure 1 is a representative cross section of a printing blanket.

Figure 2 is a graph illustrating the compression factor of this invention in comparison to printing blankets or printing plate cushions using either an open or closed cell compressible layer construction.

DESCRIPTION OF THE PREFERRED EMBODIMENT Making a compressible layer in a printing blanket or printing plate cushion is well known in the art. A representative printing blanket is shown in Figure 1. The printing blanket 1 is made of composite material. A process of making such printing blankets is described in United States Patent Nos. 4,042,743 issued to Charles E. Larson and 4,422,895 issued to Harao Shimura. Two fabric layers 2 and 3 are joined together by an adhesive 4 to form a substrate. It is also suitable that only one, or more than two, fabric layers be used to form the substrate. The fabric 2 and 3 may be made of a composite of cotton and polynosic rayon.

Table 1 below illustrates the specifications for a preferred fabric containing both cotton and rayon.

Table l

Yarn Composition

Warp: 181 s/2 ply Long Staple Cotton Fill: 201/singles Polynosic Rayon

Yarn Count Warp: 56/in. Fill: 56/in.

Weight

6.15 +/- 0.05 oz./sq.yd.

Gauge 0.011511 +/- 0.000511

Tensile Strength (lbs./in.)

Warp: 150 (min.) Fill: 75 (min.) Residual Stretch 2.00 % (max.)

Finish

Calendared

Other fabrics may also be used as well as other materials such as paper, rubber or plastic as the ₀ backing material to act as a substrate for the compressible printing blanket 1.

Compressible layer 5 is formed by using a binder, which may be made from a suitable resilient polymer matrix, into which microspheres and soluble 5 solid materials are evenly dispersed to form a compound. As matrix materials, elastomers are preferable with neoprene/nitrile blend being most preferred. Other ingredients may be included in the compound which are well known in the art. It is o desirable to use proportions of microspheres and solid solubles in making the compound that produce essentially equal volumes in the resulting compressible layer. Typically, the compound is applied to the fabric substrate 2 and 3 by applying thin layers in successive applications. Layers of about 0.002 inches are a suitable thickness for this application. Compressible layer 5 may be adhered to fabric 3 by an adhesive layer 6 and/or the bonding may occur by a chemical reaction in a subsequent curing process. Alternately, the compressible layer 5 may be formed by applying the compound to a release liner, curing the combination, stripping the cured compound and adhering it to the fabric 3 by use of an adhesive 6. The compound may also be applied to fabric 3 by extrusion or calendaring. A compressible layer may also be formed without a substrate if the matrix is compounded to have sufficient tensile strength and sufficiently low stretch characteristic. The compounded matrix, with both type cells, is used to form a sheet by various techniques including applying successive thin coats to form a sheet, or extruding the compound into a sheet. The resulting sheet is then cured to set the compound.

In the instance where a backing material or substrate is used, materials such as paper, rubber or plastic may be used in lieu of fabric 2 and 3.

To complete the typical printing blanket shown in Figure 1, a fabric 7 is adhered to compressible layer β by an adhesive 8. The printing surface 9, nominally a solid elastomer such as a nitrile blend, is adhered to fabric 7 by an adhesive 10. Printing surface 9 may also be calendared or extruded onto fabric 7. The resulting compressible layer 1 is cured in a conventional way.

This invention envisions that the curing will be carried out by festooning the printing blanket 1 over rollers in an oven where the curing takes place. Alternate ways of curing include roto-curing and drum curing.

An inventive feature disclosed herein is the use of both closed and open cells to form a compressible layer 5. In one embodiment, both closed and open cells are dispersed into a neoprene\nitrile blend to form a compound along with other suitable ingredients well known in the art. This compound is then used in the above described steps to form a compressible layer 5 in a printing blanket. Alternately, two separate layers may be formed each with either closed or open cells and the two layers adhered together to form compressible layer 5. Multiple layers of compressible layer 5, made by either process, may be adhered together to form printing blankets and printing cushions having the desired characteristics.

In the embodiment in which both types of cells are dispersed in the same compressible layer 5, they are evenly dispersed in the compound to essentially displace equal volumes in the cured compressible layer. In the embodiment in which two separate layers are made, each containing either closed or open cell material, the respective volumes of the cells in the cured layers are proportioned to offset each type cell's compression characteristic to produce a uniform compression characteristic. In each embodiment, the goal is to have the correct proportion of each type cell to offset the divergent compression characteristic of layers made with a single type cell. Experience shows that as closed cells in a compressible layer are subjected to impressions, the layer's compression factor rapidly rises. Conversely, as open cells in a compressible layer are subjected to impressions the layer's compression factor rapidly decreases. It has been discovered that a compressible layer 5 with the correct proportion of evenly distributed cells of both types has a uniform compression characteristic, as shown in Figure 2. This result is achieved because the opposite compression characteristic of the two types of cells cancel each other out when they are combined in a compressible layer 5. Referring to Figure 2, the graph represents the change in compression factor as a function of the number of impressions. Three different compressible layer structures are represented. The plots represent layers made solely with open and closed cells and an ideal layer made according to this invention in which the layer has combined closed and open cells. Examination of Figure 2 shows that the open cell layer has a decreasing compressibility factor with increasing number of impressions and that the change is greater in the early life of the layer. Conversely, the closed cell layer has an increasing compression factor as the number of impressions increases with a greater increase in the early life of the layer. In sharp contrast is the layer made with both closed and open cells in which the compression factor is uniform from the beginning of its use to the end of its useful life. The ideal layer has the advantage that a printing or like impression process may be operated without having to adjust the pressure on the impression blanket cylinder or printing plate cushion in a printing process. The same stability of a compressible layer 5 when used as a cushioned backing in other processes allows for a uniform pressure on a backing surface.

Various forms of closed cells may be used in this invention. Microspheres are one type of closed cell. They may be made from a phenolic resin or like materials one suitable microsphere is designated as UCAR™ BJO-093 and is manufactured by Union Carbide (UCAR is a registered trademark of Union Carbide) . Other materials may be used to make microspheres, including, thermoplastics, thermosetting resins, glass, ceramics, and sintered metals. The primary characteristic of suitable microspheres is that it will not fracture under pressure.

Closed cells may also be formed in a compressible layer 5 by mechanically inducing air into a compound before it is cured, such as by aerating or stirring. Another means of creating closed cells in a compressible layer 5 is to use chemical blowing agents (the term foaming agents also is used) that are decomposable into gases as they are cured in a compound, one such class of blowing agents are the Cellogens™ which are manufactured by Uniroyal (Cellogen is a registered trademark of Uniroyal) . Cellogens are decomposable in the presence of heat, which may be applied during curing. Many other types of blowing agents are commercially available with a wide range of decomposition characteristics. Open cells may also be created in a compressible layer using different soluble materials. One suitable material used in this invention is salt, typically having an average particle size of 40 microns.

When salt is used, the cured carcass of the compressible layer 5, or assembled printing blanket, is leached by known leaching methods to remove the solid salt thereby leaving a void. The void creates the open cell. Other suitable soluble materials, including sugar, may be used to create open cells that are dissolvable by a solvent that does not harm the cured carcass of a compressible layer.

Multiple layers may be joined together as needed to create a compressible layer 5 in a printing blanket or printing plate cushion. As previously described, separate compressible layers 5 may be incorporated into such constructions. Each compressible layer may have both closed and open cells or the separate layers 5 may have distinct cell structures. In the latter instance, employing compressible layers with separate cell structures will have the same effect of offsetting each type of cell structure's compression characteristic, to produce a uniform compression characteristic for the overall printing blanket or printing plate cushion.

The description of the invention sets forth the underlying discovery that the undesirable opposite compression characteristics of closed and open cells when used in a compressible layer 5 in a compression medium 1 are compensated for by combining both types of cells in suitable proportions in the cured compound used to form the compressible layer 5. It should be understood that the invention should not be limited to the above recited embodiments and changes or modifications may be made as appropriate without departing from the spirit and scope of the invention.

Claims

THE CLAIMS

We claim: 1. A resilient compressible layer for use in a composite material comprised of a matrix having a plurality of open and closed cells distributed substantially uniformly throughout in predetermined volumetric proportions so that the layer has ₀ substantially uniform compression characteristics.

2. The layer of claim 1 wherein the open and closed cells are present in essentially equal volumes.

3. The layer of claim 1 wherein the closed cells are formed from microspheres. 5 4. The layer of claim 3 wherein the microspheres are made of a material selected from the group consisting of thermoplastics, thermosetting resins, ceramics, glass and sintered metals.

5. The layer of claim 3 wherein the o microspheres are made of a phenolic resin.

6. The layer of claim I wherein the closed cells are formed from gases which are trapped within the matrix.

7. The layer of claim 1 wherein the matrix is a flexible thermoplastic or elastomeric material.

8. The layer of claim 7 wherein the matrix is a blend of neoprene and nitrile rubber.

9. A composite article comprising at least one strengthening layer and the resilient compressible layer of one of claims 1-8.

10. The article of claim 9 wherein the strengthening layer includes a fabric substrate.

11. The article of claim 10 wherein the fabric substrate includes a composite of cotton warp fibers and polynosic rayon fill fibers.

12. The article of claim 9 further comprising a surface layer for protecting the compressible layer. 13. A printing blanket comprising the composite article of claim 12, wherein the surface layer includes a printing surface. 5 14. The blanket of claim 13 wherein the surface layer is adhered to one surface of the compressible layer and the other surface of the compressible layer is adhered to the strengthening layer.

15. The blanket of claim 14 further comprising ₀ an adhesive for adhering the surface layer to the compressible layer.

16. The blanket of claim 14 further comprising an adhesive for adhering the compressible layer to the strengthening layer. 5 17. The blanket of claim 13 wherein two strengthening layers are present, each comprising a fabric substrate.

18. The blanket of claim 17 wherein the strengthening layers are adhered together. o ¹⁹« The blanket of claim 18 further comprising an adhesive for adhering the two strengthening layers together.

20. A method for producing a resilient compressible layer which comprises substantially 5 uniformly distributing a plurality of open and closed cells in predetermined volumetric proportions into a matrix to form a resilient compressible layer having substantially uniform compressible characteristics.

21. The method of claim 20 which further ₀ comprises forming the open cells in the matrix by relatively uniformly dispersing a soluble material throughout a matrix forming material; forming the matrix from the matrix forming material; and applying a solvent to the matrix to remove the soluble material therefrom and form the open cells. 22. The method of claim 21 which further comprises selecting the soluble material to be a salt or sugar compound. 23. The method of claim 21 which further comprises forming the closed cells by substantially uniformly distributing the microspheres into the matrix forming material.

24. The method of claim 23 which further comprises selecting microspheres of a thermoplastic, thermosetting resin, glass, ceramic, or sintered metal material for distribution into the matrix.

25. The method of claim 21 which further comprises forming the closed cells by substantially uniformly distributing a decomposable blowing agent into the matrix forming material and forming the matrix from the matrix forming material while decomposing the blowing agent to form the closed cells. 26. The method of claim 21 which further comprises forming the closed cells by mechanically inducing a gas into the matrix forming material before forming the matrix.

27. The method of claim 20 wherein the matrix is a flexible thermoplastic or elastomeric material and which further comprises coating said matrix onto a substrate.

28. The method of claim 27 wherein the coating step comprises successively applying a plurality of layers of the matrix to the substrate.

29. The method of claim 27 or 28 wherein the matrix is cured by heating.

30. The method of claim 20 wherein the matrix is formed by calendaring a matrix forming material of a thermoplastic or elastomeric material. 31. The method of claim 20 wherein the matrix is formed by extruding a matrix forming material of a thermoplastic or elastomeric material. 5 32. The method of claim 20 which further comprises distributing substantially equal volumes of the open and closed cells in the matrix.

33. The method of claim 21 which further comprises coating a release liner with the matrix— ₀ forming material to form the matrix; removing the matrix from the release liner; adhering the matrix to a substrate; and removing the soluble material from the matrix to form the open cells.

34. The method of claim 21 which further 5 comprises forming a sheet of matrix by curing one or more layers of the matrix-forming material containing the. soluble material and closed cells; and removing the soluble material from the matrix to form the open cells. o 35. The article of claim 9 wherein the strengthening layer is formed from a material selected from the group consisting of paper, rubber and plastic.

36. The blanket of claim 13 wherein the printing ₅ surface is formed of a solid elastomer.

37. The blanket of claim 36 wherein the elastomer is a nitrile blend.

0 _[received _by t_he _Internati 12 March 1993 ⁽12.03.93⁾ ; origina_l claim 2 deleted ; original claims 1, 3-19 and 35-37 amen_de_d , remaining claims unchanged (4 pages^)]

1. A printing blanket having a resilient compressible layer comprised of a matrix having a plurality of open and closed cells distributed substantially uniformly throughout, said open and said closed cells being present within said matrix in essentially equal volumetric proportions so that the layer has substantially uniform compression characteristics.

3. The printing blanket of claim l wherein the closed cells are formed from microspheres.

4. The printing blanket of claim 3 wherein the microspheres are made of a material selected from the group consisting of thermoplastics, thermosetting resins, ceramics, glass and sintered metals.

5. The printing blanket of claim 3 wherein the microspheres are made of a phenolic resin.

6. The printing blanket of claim 1 wherein the closed cells are formed from gases which are trapped within the matrix.

7. The printing blanket of claim 1 wherein the matrix is a flexible thermoplastic or elastomeric material.

8. The printing blanket of claim 7 wherein the matrix is a blend of neoprene and nitrile rubber.

9. A printing blanket accoring to one of claims 1-8 and further comprising at least one strengthening layer.

10. The printing blanket of claim 9 wherein the strengthening layer includes a fabric substrate.

11. The printing blanket of claim 10 wherein the fabric substrate includes a composite of cotton warp fibers and polynosic rayon fill fibers.

12. The printing blanket of claim 9 further comprising a surface layer for protecting the compressible layer.

13. A printing blanket according to claim 12, wherein the surface layer includes a printing surface.

14. The printing blanket of claim 13 wherein the surface layer is adhered to one surface of the compressible layer and the other surface of the compressible layer is adhered to the strengthening layer.

15. The printing blanket of claim 14 further comprising an adhesive for adhering the surface layer to the compressible layer.

16. . The printing blanket of claim 14 further comprising an adhesive for adhering the compressible layer to the strengthening layer.

17. The printing blanket of claim 13 wherein two strengthening layers are present, each comprising a fabric substrate.

18. The printing blanket of claim 17 wherein the strengthening layers are adhered together.

19. The printing blanket of claim 18 further comprising an adhesive for adhering the two strengthening layers together.

20. A method for producing a resilient compressible layer which comprises substantially uniformly distributing a plurality of open and closed cells in predetermined volumetric proportions into a matrix to form a resilient compressible layer having substantially uniform compressible characteristics.

21. The method of claim 20 which further comprises forming the open cells in the matrix by relatively uniformly dispersing a soluble material throughout a matrix forming material; forming the matrix from the matrix forming material; and applying a solvent to the matrix to remove the soluble material therefrom and form the open cells.

22. The method of claim 21 which further comprises selecting the soluble material to be a salt or sugar compound.

23. The method of claim 21 which further comprises forming the closed cells by substantially uniformly distributing the microspheres into the matrix forming material.

25. The method of claim 21 which further comprises forming the closed cells by substantially uniformly distributing a decomposable blowing agent into the matrix forming material and forming the matrix from the matrix forming material while decomposing the blowing agent to form the closed cells.

26. The method of claim 21 which further comprises forming the closed cells by mechanically inducing a gas into the matrix forming material before forming the matrix.

29. The method of claim 27 or 28 wherein the matrix is cured by heating.

30. The method of claim 20 wherein the matrix is formed by calendaring a matrix forming material of a thermoplastic or elastomeric material.

31. The method of claim 20 wherein the matrix is formed by extruding a matrix forming material of a thermoplastic or elastomeric material.

32. The method of claim 20 which further comprises distributing substantially equal volumes of the open and closed cells in the matrix.

33. The method of claim 21 which further comprises coating a release liner with the matrix— forming material to form the matrix; removing the matrix from the release liner; adhering the matrix to a substrate; and removing the soluble material from the matrix to form the open cells.

34. The method of claim 21 which further comprises forming a sheet of matrix by curing one or more layers of the matrix-forming material containing the soluble material and closed cells; and removing the soluble material from the matrix to form the open cells.

35. The printing blanket of claim 9 wherein the strengthening layer is formed from a material selected from the group consisting of paper, rubber and plastic.

36. The printing blanket of claim 13 wherein the printing surface is formed of a solid elastomer.

37. The printing blanket of claim 36 wherein the elastomer is a nitrile blend.