Printing – Rolling contact machines – Rotary
Patent
1993-01-19
1994-12-20
Eickholt, Eugene H.
Printing
Rolling contact machines
Rotary
101375, 101376, 355212, B41F 1310
Patent
active
053737881
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a printing apparatus with a printing roller provided with a profile which comprises raised and lowered parts in circumferential direction, a printing belt provided at one side with a complementary profile, and an opposite roller which together with the printing roller determines a nip through which the printing belt runs, in such a way that its profile side interacts with the printing roller, and its printing side interacts with the opposite roller.
Such a printing apparatus is known from Dutch Application 8700431. In the case of this known printing apparatus the printing belt is made of a flexible, rubber-like material on which printing plates containing the printing image are placed. The flexible belt is provided with teeth running in the crosswise direction which interact with complementary teeth provided on the printing roller. The purpose of these interacting teeth is to position the printing plates correctly with the web of paper to be printed, which must also be guided through the nip between printing roller and impression roller.
This known printing apparatus has various disadvantages. The first disadvantage is that the flexible printing belt has a varying flexural rigidity, viewed in its lengthwise direction. At the position of the teeth the printing belt is thicker and therefore more rigid than at the places between the teeth. This means that the printing plates do not run in an accurate circular shape around the printing roller and through the nip, but at the position of the teeth are more flattened than at the places between the teeth. This leads to imperfections in the image printed on the web of paper.
A further disadvantage of this known printing belt arises from the fact that it is made of relatively flexible material. As a result of the undercut, in other words the distance over which the impression roller presses in the printing belt, a certain displacement of the flexible material occurs at the position where it is pressed in. This displacement manifests itself in a widening of the pressed-in material, which leads to the image on the printing plates also being widened. A point in the image to be printed, for example, acquires greater dimensions as a result, which adversely affects the printing obtained on the paper web.
SUMMARY OF THE INVENTION
The object of the invention is to provide a printing apparatus of the above-mentioned type which does not have these disadvantages. This is achieved in that the printing belt is composed of an interlocked strip of plate material which is flexible as regards bending and is rigid as regards deformations in its plane, on one side of which a profiling of another material is provided. The printing belt according to the invention has a printing surface which consists entirely of the plate material suitable for offset printing. This means that deformation of the image in the plane of said plate material is virtually out of the question. Contrasting with the known apparatuses, in which the images to be printed were on separate plates which were interconnected by a flexible printing belt, the correct relative positions of the images can be ensured in this way.
It is also no longer possible for point widening to occur as a result of the undercut, as in the case of the known printing apparatus described above.
As a result of the profiling present on one side of the printing belt, it can be accurately positioned relative to the paper web to be printed. In view of the constant flexural rigidity of the plate material in the lengthwise direction of the strip, it can be guided around the printing roller with a constant radius of curvature. No flattening or sharper curves occur as in the case of the known apparatus.
This uniform curvature, arising from a uniform flexural rigidity in the lengthwise direction of the printing belt, can be beneficially influenced further by carrying out the profiling in a more flexible material than the plate material. According to the invention, this is achieved in that
REFERENCES:
patent: 2066179 (1936-12-01), Keller
patent: 2901540 (1959-08-01), Canepa
patent: 4178094 (1979-12-01), Silverberg
patent: 4462676 (1984-07-01), Shimura et al.
patent: 4480935 (1984-11-01), Kurihara et al.
patent: 4758486 (1988-07-01), Yamazaki et al.
Drukband Holland B.V.
Eickholt Eugene H.
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