Patent Application
20050005792
The present invention relates generally to offset printing and more specifically to a printing blanket for an offset printing press.
U.S. Pat. Nos. 6,283,027 and 6,105,498, hereby incorporated by reference herein, disclose varying profile blankets, including printing blankets with concave and convex profiles. A concave blanket cylinder is also disclosed.
U.S. Pat. Nos. 5,522,315 and 5,863,367 disclose a printing blanket with a convex compressible layer to spread the web and prevent inward wrinkling. The carrier layer for the blanket is flat.
An object of the present invention is to compensate for reduced print pressure often found in the center of a blanket cylinder while still avoiding inward wrinkling.
The present invention provides a printing blanket comprising:
By having an inner convex carrier sleeve layer with a convex surface, the print pressure at the axial center of the blanket cylinder can be increased.
The convexity of the carrier sleeve layer may be provided, for example, by having the carrier sleeve layer have a uniform inner diameter and a convex outer diameter. The carrier sleeve layer itself is thus thicker in an axial middle than at the ends.
Alternately, the carrier sleeve can be of uniform thickness, and the blanket cylinder or a shim may provide the surface convexity.
The print layer may have a uniform thickness or a varying thickness. Most preferably, the outer surface of the print layer has a convex axial profile when the blanket is disposed on the blanket cylinder, although this is not necessary.
The blanket when disposed on the blanket cylinder thus preferably provides uniform axial print or nip pressure across the width of the blanket.
A compressible layer preferably is disposed between the carrier sleeve layer and the print layer. The compressible layer may be of uniform thickness, or of varying thickness.
The blanket preferably is gapless tubular blanket.
An inextensible layer, for example made of wound fibers or textile fabric, may be provided over the compressible layer and underneath the print layer.
Also provided by the present invention is an offset print unit comprising an image cylinder, a blanket cylinder having an axially convex outer surface, and a printing blanket disposed over the axially convex outer surface.
Further provided as well is an axially profiled shim for placement between a blanket cylinder and a blanket, the shim having an axially convex outer surface. Preferably, the inner surface has a uniform diameter. The shim is preferably tubular and gapless.
The blanket cylinder and blanket are most advantageous for narrow blanket cylinders with a wide axial extent, as these are most prone to bending. Thus, the blanket advantageously carries at least two images axially, and may carry at least three images in the axial direction while only one image is carried in the circumferential direction. Four axial images may be most advantageous.
The present invention will be further described with respect the following Figures., in which:
a and 1b show schematically embodiments of the convex blanket cylinder with a blanket having a uniform carrier sleeve layer with a convex surface;
a,
2
b,
2
c,
2
d,
2
e,
2
f and 2g show schematically embodiments of a blanket with a convex carrier sleeve layer;
a and 3b show schematically embodiments of the blanket cylinder, shim and blanket combination of the present invention; and
a and b show schematically a blanket-to-blanket nip for the embodiments of
Blanket 20 includes a carrier sleeve layer 22, which may be made for example of a fiberglass sleeve available commercially from Rotec GmbH & Co. KG of Ahaus-Ottenstein, Germany. Carrier sleeve layer 22 preferably is solid and rigid enough to maintain a tubular shape to permit axial placement of the blanket 20 on blanket cylinder 10, yet flexible enough to permit the expansion necessary fit the blanket 20 over the cylinder 10.
Carrier sleeve layer 22 thus has a convex outer surface 23 when located on blanket cylinder 10. A compressible layer 24 which also may be wider in an axial middle section than at the axial ends of blanket 20 is located over the outer surface 23. Compressible layer 24 may be, for example, rubber with air bubbles therein or microspheres located therein to provide compressibility.
An inextensible layer 25, for example a thread or fabric layer, may be located over compressible layer 24. Inextensible layer 25 may aid in maintaining the shape of the compressible layer 24.
A print layer 26 forms the outer layer, and may be made, for example, of solid rubber. In the embodiment of
Print surface 27 is inked by an image cylinder 5, for example a plate cylinder. Image cylinder 5 may have for example four image areas 5A, SB, 5C, 5D axially, each image area covering the circumference of image cylinder 5, a so-called one around configuration. However, image cylinder 5 could also have two (or more) images spaced circumferentially, a so-called two (or more) around configuration.
Preferably, the number of axial images is at least twice the number of circumferential images, and may be three, four or more times the number of circumferential images, as the present invention is most advantageous with small diameter, large width blankets.
The present invention is particularly advantageous for printing webs, and the printing press preferably is a lithographic web printing press.
Blanket cylinder as defined herein may include the combination of a shim and blanket cylinder body and blanket as defined herein may include the combination of a blanket body and a shim.
List of Drawing Numbers
