Printing – Printing members – Rolling contact
Reexamination Certificate
1998-10-14
2001-02-06
Funk, Stephen R. (Department: 2854)
Printing
Printing members
Rolling contact
C428S909000
Reexamination Certificate
active
06182568
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a seamless cylindrical printing blanket, which is suitably used in a high-speed web offset printing press.
A printing blanket of the prior art was in the form of a plate, and was used by winding around a blanket cylinder of a printing press. With this construction, however, there arose a problem that a seam portion is formed in a printing blanket and a pressing force of a plate cylinder varies whenever the seam portion passes through a nip portion between the blanket cylinder and the plate cylinder to cause vibration and shock load, resulting in deterioration of the printing quality. Particularly, deterioration of the printing quality was remarkable at the time of high-speed printing where the blanket cylinder rotates at high speed of not less than 1,100 rpm.
Therefore, a cylindrical printing blanket having no seam in a circumferential direction has recently been suggested as a printing blanket suited for high-speed printing using a web offset printing press and the like. As shown in
FIG. 4
, such a cylindrical printing blanket
20
comprises a compressive layer
22
, which is porous and seamless, a non-expansion layer
23
and a seamless surface printing layer
25
and a cylindrical sleeve
11
to be fit over a blanket cylinder, the layers
22
,
23
and
25
being laminated in this order on the outer peripheral surface of the cylindrical sleeve
11
through seamless adhesive layers g
1
, g
2
, g
3
(see Japanese Patent Laid-Open Publication No. 5-301483), respectively.
Among the above layers, the surface printing layer is made of a volume-non-compressive (that is, non-compressive as a change in volume does not arise even if plastic deformation is applied) elastomer and absorbs ink (not shown) from a printing plate
42
at a nip portion
41
formed between a printing blanket
20
and a plate cylinder
40
(see FIG.
5
).
The compressive layer
22
is formed by applying a coating solution containing an elastomer such as rubber, drying the solution and optionally curing (or vulcanizing) in a case where the rubber is employed as the elastomer. The compressive layer
22
is volume-compressive because of its porous structure (that is, the volume is reduced by compression) and, therefore, the vibration absorbing property and pressure absorbing property are imparted to the whole printing blanket
20
, thereby to inhibit bulging in the neighborhood of the nip portion
41
and to prevent deformation of an image such as slur and double in the printing direction (i.e. circumferential direction x of blanket) of the blanket
20
.
At the time of high-speed printing; however, there arises a problem that a shear deformation is applied to the blanket
20
at the nip portion
41
and, therefore, the image is deformed in the circumferential direction x of the blanket to cause slur and double.
Therefore, for the purpose of inhibiting slur and double, the non-expansion layer
23
is provided on the compressive layer
22
. This non-expansion layer
23
is formed by spirally winding a wire
17
such as a thread in the circumferential direction x of the blanket with applying a tension. By providing such a non-expansion layer
23
, the shear deformation at the nip portion
41
of the blanket
20
can be reduced and the deformation of the printed image in the circumferential direction x of the blanket can be inhibited.
However, there is a limit in effect of inhibiting the above shear deformation by providing the non-expansion layer
23
. For example, in a high-speed printing at not less than 1,100 rpm, when the thickness of a surface printing layer
250
to be provided on the top of the non-expansion layer
23
becomes larger as shown in
FIG. 6
, it becomes impossible to obtain sufficient pressure absorbing effect due to the compressive layer
22
because the layer
250
is volume-non-compressive and the distance from the surface of the blanket
200
to the compressive layer
22
(i.e. thickness of blanket
200
) becomes larger. As a result, when the plate cylinder
40
is pressed onto the blanket
200
, bulging
43
(bulge deformation) is formed on the surface printing layer
250
.
When the bulge deformation becomes larger, the nip width also becomes larger. Therefore, the solid inking property is improved but the halftone dot becomes thick due to dot gain, resulting in deterioration of the printing reproducibility. When the thickness of the surface printing layer
250
becomes larger, it becomes impossible to obtain the effect of inhibiting the shear deformation of the blanket
200
by the non-expansion layer
23
. As a result, remarkable slur and double make it impossible to put to practical use.
On the other hand, when the surface printing layer
25
is thin as shown in
FIG. 5
, the shear deformation hardly arises and the reproducibility of the shape of the halftone dot is improved. However, since the non-expansion layer
23
is formed by winding a wire with applying a tension thereon, it contacts closely with the peripheral shape of the printing plate
42
and is not deformed and, therefore, the nip width
41
becomes smaller. At the time of high-speed printing at not less than 1,100 rpm, the time of contact between the printing plate
42
and blanket
20
becomes considerably short and transfer-of ink becomes insufficient, resulting in deterioration of the inking property of ink.
In such way, when the thickness of the surface printing layer is decreased, the halftone dot reproducibility is good and problems such as slur and double do not arise but the inking property of ink is deteriorated. On the other hand, when the thickness of the surface printing layer is increased, bulging arises and the nip width increases and, therefore, the inking property is improved but the dot gain arises to deteriorate halftone dot reproducibility. Besides, when the thickness of the surface printing layer is further increased, slur and bulging arise.
Accordingly, in order to practically satisfy both of the inking property of ink and halftone dot reproducibility, it is necessary to strictly adjust the thickness of the surface printing layer (specifically, the thickness of the surface printing layer is limited to about 0.4 mm to satisfy both the inking property and halftone dot reproducibility) and a scatter in quality of the product is liable to arise. At the time of high-speed printing at not less than 1,100 rpm, it becomes further difficult to satisfy both the inking property and halftone dot reproducibility since it is required to further reduce the thickness of the surface printing layer.
On the other hand, as shown in
FIG. 7
, in a case where a printing blanket
30
is provided with a compressive layer
32
only between a non-expansion layer
33
and a surface printing layer
35
, since it is necessary to absorb the whole pressure only by the compressive layer
32
, the thickness of the layers on the surface of the non-expansion layer
33
must be increased. In this case, the adhesion between the printing plate and the surface of the blanket
30
is improved and the solid inking property is improved. On the other hand, dot gain, slur and double do not arise at low-speed printing, however, the shear deformation arises in the circumferential direction of the blanket at high-speed printing at not less than 1,100 rpm because the thickness of the surface layers is larger than that of the non-expansion layer. Therefore, slur and double arise.
On the other hand, regarding a printing blanket disclosed in Japanese Patent Laid-Open Publication No. 6-270573, a surface printing layer is porous and fine pores are provided on the surface thereof for the purpose of inhibiting bulging. However, the above fine pores are generally formed by the extraction method using a water-soluble powder material such as salt and by the foaming method using micro-balloons, and it is difficult to obtain ultra-fine cells (pores) having a diameter of not more than 10 &mgr;m. Therefore, a lot of circular depressions having a diameter of not less than about 10 &mgr;m are formed on th
Ogita Toshikazu
Okubo Hiromasa
Sagawa Takamichi
Tomono Seiji
Birch & Stewart Kolasch & Birch, LLP
Funk Stephen R.
Sumitomo Rubber Industries Ltd.
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