GB2024104A

GB2024104A - Printing blanket

Info

Publication number: GB2024104A
Application number: GB7913086A
Authority: GB
Original assignee: Continental Gummi Werke AG
Current assignee: Continental AG
Priority date: 1978-04-18
Filing date: 1979-04-12
Publication date: 1980-01-09
Also published as: DE2816703A1; GB2024104B; DE2816703C2; JPS54140603A

Abstract

A printing blanket, more especially an offset printing blanket, having a cover layer 1 forming the surface of the printing blanket and made of rubber or rubber-like materials, a resiliently yielding layer 3 of rubber or rubber-like materials located below the cover layer and reinforcing members 2 being arranged between the cover layer and the resiliently yielding layer, in which the resiliently yielding layer 3 is resiliently pre-tensionable by the reinforcing members having a specific pre-tension of from 5 to 50 N/cm<2>. The pre-tension may be applied by known securing means on the cylinder. This specific pre-tension is said to provide better recovery after radial deformation of the cylinder covering. <IMAGE>

Description

SPECIFICATION Printing blanket The present invention relates to a printing blanket, more especially, however, to a printing blanket for offset printing, having a cover layer forming the surface of the printing blanket and made of rubber or rubber-like materials, a resiliently yielding, preferably microporous, layer of rubber or rubber-like materials located therebelow, and reinforcing members being arranged between the cover layer and the resiliently yielding layer.

In known printing blankets of this kind, there is generally also provided a further layer with reinforcing members which, like the aforesaid layer of reinforcing members, is preferably comprised of textile material, which serves for the adhesive securing of the aforesaid resiliently yielding layer. This layer opposing the cover layer generally has as object to absorb the forces which are required to secure the printing blanket to its associated impression cylinder. It also serves to absorb the tensional forces.

The aforesaid layer located above the microporous or resiliently yielding layer formed by the reinforcing layers in known printing blankets has predominantly as object to act as a thrust stabiiity carrier, by which the capacity is understood of distributing and absorbing locally acting forces in the direction of thrust of the printing blanket, thus to bring about stabilisation.

In known printing blankets of this kind, the reinforcing member layer located beneath the surface of the printing blanket only exerts a slight influence on the resiliently yielding, mainly microporous layer, located therebelow.

If the printing blanket is ioaded, namely by forces which extend substantially vertically to the printing blanket, then via the reinforcing member layer located above, a corresponding deformation occurs of the resilient layer located below, which in turn due to its flat coarse produces only low return forces. These return forces therefore are very slight, because the characteristic curve rises at first very flatly in order, however, to assume a progressively steeper course. Though this makes soft deflection possible, only slow and incomplete thickness recoveries occur. This leads to undesirable reconditioning by underlaying and the cylinder blanket to fail during the passage of a "creaser". The sections of the cylinder blanket not fast enough and not completely recovering due to lack of pressure are no longer able to print out fully.

The object of the present invention is to develop the aforesaid printing blankets in such a manner that, during the passage of thicker sheet sections (creasers), by increased return forces with relatively smaller spring deflections recovery occurs immediately, in order to maintain the printing quality.

According to the present invention there is provided a printing blanket, more especially an offset printing blanket, having a cover layer forming the surface of the printing blanket and made of rubber or rubber-like materials, a resiliently yielding layer of rubber or rubber-like materials located below the cover layer and reinforcing members being arranged between the cover layer and the resiliently yielding layer, in which the resiliently yielding layer is resiliently pretensionable by the reinforcing members having a specific pre-tension of from 5 to 50 N/cm2.

Preferably the pre-tension is from 1 2 to 38 N/cm2, more especially from 20 to 39 N/cm2.

Thus, the basic concept of the invention is to use the reinforcing members located above the resilient layer not only as thrust stabilisers, but at the same time as pre-tensioning elements in such a manner that the resilient layer, without any additional external influences, is already under a certain pre-tension.

The aforesaid pre-tension results in creating another favourable working point with reference to the spring characteristic and thereby -in accordance with the pre-tension force -results in relatively large return forces.

These return forces lead to a rapid, substantially complete recovery after the passage of a so-called ' "creaser".

This effect is also assisted by the inherent tension in the reinforcing members above the resilient layer which is necessary to produce the pre-tension. Also the weft threads of the reinforcing members are preferably tensioned thereby contribute towards substantially accelerating the recovery of the printing blanket.

The present invention will be further illustrated, by way of example, with reference to the accompanying drawing, in which the single figure shows a cross-section through an offset printing blanket mounted on an impression cylinder, only a circumferential section of this printing blanket being shown.

For reasons of better illustration the wall thickness of the printing blanket is shown substantially larger and thicker; means, known per se, may be used for retaining the printing blanket at both its ends or to connect same to the impression cylinder.

The printing blanket in accordance with a preferred embodiment is comprised of four layers 1 to 4 which are adhesively interconnected by vulcanisation or the like. The external cover layer 1 participating in the printing operation is preferably comprised of elastomeric polymers, such as Nitrile, Butyl, EPDM, Polysulfide, NBR, polyurethane or chloroprene or mixtures of these said elastomers in a single layer or a multilayered arrangement in a thickness range of from 0.15 to 0.6 mm and a hardness range of from 40 to 70 Shore A. Below the cover layer 1, there is preferably two plies 2 of complete fabric with weft and warp threads, produced from cotton, regenerated cellulose or synthetic materials. These plies have relatively high strength values of 2400 to 4000 N/5 cm according to DIN.The elongation values are also comparatively low, and amount to about 0.2 to 1.3% residual elongation in the tension region of the printing blanket (between 500 and 1000 N/5 cm width). This low residual elongation may be attained by the use of materials of low elongation or by prior treatment, e.g. stretching out of the natural shape and fixing of the stretched fabric plies. The rubberised plies 2 are adjoined by a compressible, resiliently yielding layer 3 of rubber or rubber-like materials for which the materials mentioned in connection with the cover layer 1 may be used. The layer 3 is a microcellular elastomeric layer having a wall thickness of 0.2 to 0.6 mm and an average return force of 20 to 80 N/cm2 at 1/10 impression each.

The layer 3 is adhesively located on one of possibly several fabric plies 4 which have higher elongation values compared with the plies 2. These elongation values may amount to 5 to 20%. A supporting function is not attributed to the fabric ply 4. Its object essentially is only to cover the layer 3 and to act as abutment on the impression cylinder.

The relatively low elongation plies 2 are tensioned by securing means not shown in detail in accordance with the arrows 5, whereby the resilient layer 3 is radially compressed and herewith is given a pre-tension of from 20 to 30 N/cm2.

This pre-tension still permits a resilient deflection with radial forces to be produced.

The return forces, however, subject to the said pre-tension are so considerable that when any thicker sheet sections (creasers) impact the cover layer then immediate return occurs and thus the printing quality is not endangered.

Claims

1. A printing blanket more especially an offset printing blanket, having a cover layer forming the surface of the printing blanket and made of rubber or rubber-like materials, a resiliently yielding layer of rubber or rubberlike materials located below the cover layer and reinforcing members being arranged between the cover layer and the resiliently yielding layer, in which the resiliently yielding layer is resiliently pre-tensionable by the reinforcing members having a specific pre-tension of from 5 to 50 N/cm2.

2. A printing blanket as claimed in claim 1, in which the pre-tension is from 1 2 to 38 N/cm2.

3. A printing blanket as claimed in claim 2, in which the pre-tension is from 20 to 30 N/cm2.

4. A printing blanket as claimed in claim 1, 2 or 3, in which the reinforcing members in the tension region of the printing blanket (between from 500 to 1000 N/5 cm width) have a residual elongation of from 0.2 to 1.3%.

5. A printing blanket as claimed in claim 4, in which the reinforcing members together have strength values of from 2400 to 4000 N/5 cm according to DIN.

6. A printing blanket as claimed in any preceding claim, in which a fabric ply or plies facing the impression cylinder and acting as an underlay for the resilient layer has a substantially greater resilient elongation than the reinforcing members arranged between the cover layer and the resiliently yielding layer.

7. A printing blanket as claimed in claim 6, in which the elongation value of the fabric ply or plies is from 5 to 20%.

8. A printing blanket as claimed in any preceding claim in which the resiliently yielding layer is microporous.

9. A printing blanket, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.