Printing blanket

Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Woven fabric – Including strand which is of specific structural definition

Reexamination Certificate

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Details

C428S909000

Reexamination Certificate

active

06207597

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sheet-shaped printing blanket which is used for winding around a blanket cylinder of an offset printing press.
2. Description of the Prior Art
The printing blanket generally has a structure wherein a surface printing layer made of an elastomer such as rubber is laminated on at least one base fabric.
To cope with an increase in speed of printing presses and an improvement in quality of printed images, there has recently been popularized a so-called air-type printing blanket having a porous compressible layer made of an elastomer such as rubber, for instance, which is interposed between the above base fabric and surface printing layer.
The above air-type printing blanket is lower in compressive stress in a nip deformed portion produced by being pressed against a plate cylinder, as compared with a conventional printing blanket having no compressible layer (normally referred to as a solid-type printing blanket) and is also lower in a fluctuation in compressive stress with respect to the change in amount of distortion at the above nip deformed portion. Therefore, the air-type blanket is generally high in impact absorbability.
Accordingly, the air-type blanket is superior in preventing impact produced by the feeding gears of the printing press or impact produced at the time when the joint of the blanket wound around the blanket cylinder passes through the pressed portion against the plate cylinder, for example, from affecting printing precision.
The solid-type printing blanket causes a so-called bulge by stress concentrations on the surface printing layer in the nip deformed portion, which might result in inferior printing such as out of register due to expansion in the circumferential direction, inferior paper feeding, double, or deformation of a dot pattern (particularly, dot gain).
On the other hand, the air-type printing blanket also has the effect of preventing the above-mentioned inferior printing because the compressible layer has the function of lowering stress concentrations on the surface printing layer, thereby inhibiting expansion of the surface printing layer in the circumferential direction.
The examples include a compressible layer having a closed cell structure in which voids are independent of each other, which is formed by (a) foaming matrix rubber constituting the compressible layer by an expanding agent which is decomposed by heating to emit gas, or (b) blending a hollow microsphere with matrix rubber, for example, and a compressible layer having an open cell structure in which voids connect with each other, which is formed by (c) a so-called leaching method for dispersing particles such as common salt particles, extractable by a solvent (water in the case of the common salt particles) which does not affect rubber, in matrix rubber, vulcanizing the matrix rubber, and then extracting the particles.
In order to form the compressible layer, however, a lot of complicated steps are required even in the printing blanket having either one of the structures as described above and, furthermore, the size of the cell structure is liable to vary. Therefore, the air-type printing blanket is lower in productivity than the solid-type printing blanket.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel printing blanket which is superior in productivity because it has a simpler structure than that of an air-type printing blanket, and has excellent compression properties similar to those of the air-type printing blanket.
To accomplish such an object, a sheet-shaped printing blanket according to the present invention comprises substantially a surface printing layer and at least one base fabrics, at least one of the base fabric being composed of a hollow fiber in whole or in part.
The description “comprises substantially a surface printing layer and a base fabric” means that the printing blanket according to the present invention has a structure similar to that of a conventional solid-type printing blanket containing no compressible layer. For example, it is not intended to eliminate use of an auxiliary component such as adhesive containing a vulcanizable rubber (so-called vulcanizable adhesive) for bonding the base fabric and surface printing layer or bonding base fabrics when two or more base fabrics are laminated each other.
In the printing blanket according to the present invention, a cavity in the hollow fiber constituting a part or the whole of the base fabric functions similarly to the voids in the conventional compressible layer, whereby the compressible layer can be omitted.
Therefore, the printing blanket according to the present invention is superior in productivity because it has a laminated structure which is simpler than that of an air-type printing blanket and is substantially the same as that of a solid-type printing blanket, and has excellent compression properties similar to those of the air-type printing blanket.
On the basis of the same thought as that of the present invention, that is, the thought of improving the structure of the base fabric while omitting the compressible layer to obtain compression properties similar to those of the air-type printing blanket, for example, Japanese Examined Patent Publication No. 55519/1987 discloses a printing blanket using, as a base fabric, a three-dimensional woven fabric woven by using warp and weft yarns and a vertical yarn extending directly in the orientation direction of both these yarns.
However, the above-mentioned printing blanket is superior in compression properties in the initial stage of use as is apparent from the results of the examples and comparative examples mentioned later, but is insufficient in durability as compared with that of the present invention. Therefore, it causes a problem that so-called setting arises because flex deformation of the vertical yarn is remained as permanent set when printing is continuously performed, resulting in large fluctuation (deterioration) of compression properties.
Claim 1 of Japanese Laid-Open Patent Publication No. 297877/1994 discloses a printing blanket using, as a base fabric, those produced by laminating a mixed or twist yarn made of a high-tension fiber, obtained by cutting a high-tension chemical fiber into pieces of 10 to 30 cm in length, and an arbitrary short fiber of about 5 cm or less in length.
However, such a base fabric is produced without considering that a function of the compressible layer is imparted to the base fabric. Therefore, a printing blanket using such a base fabric is superior in durability in repeat use as is apparent from the results of the examples and comparative examples mentioned later, but good compression properties similar to those of the printing blanket of the present invention can not be obtained even in the initial stage of use.
Claim 2 of Japanese Laid-Open Patent Publication No. 297877/1994 discloses to improve compression properties of a printing blanket by using the above-mentioned base fabric in combination with the above-mentioned three-dimensional woven fabric. In this case, the structure is complicated and the durability of the printing blanket becomes insufficient similar to those described in the above-mentioned publications, resulting in large fluctuation (deterioration) of compression properties at the time of continuous printing.
Regarding the hollow fiber used in the present invention, since the cavity itself functions similar to the voids in the conventional compressible layer as mentioned above, there can be used, as a base fabric containing said hollow fiber, those which are easily produced and have a simple construction, for example, textile having a simple weave design such as plain weave, nonwoven fabric or the like.
On the other hand, the three-dimensional woven fabric used in both publications mentioned above must be produced by using an exclusive special weaving machine and the productivity is low.
Therefore, even in case of the construction disclosed in any publication, it is impossible

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