Printing – Stenciling – Rotary machines
Reexamination Certificate
1999-09-29
2001-04-10
Hilten, John S. (Department: 2854)
Printing
Stenciling
Rotary machines
C101S120000
Reexamination Certificate
active
06213014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a stencil printer which comprises a printing drum, an internal press roller provided inside the printing drum to be brought into contact with the inner surface of the printing drum and a pinching means which is provided outside the printing drum and is pressed against the peripheral wall of the printing drum with a printing paper pinched therebetween, and more particularly to such a stencil printer in which the peripheral wall of the printing drum is prevented from being deformed inward through contact with the internal press roller.
2. Description of the Related Art
The structure of the conventional stencil printer and the drawbacks of the stencil printer will be described with reference to
FIG. 12
, hereinbelow. As shown in
FIG. 12
, the conventional stencil printer comprises a printing drum
200
having a cylindrical peripheral wall. The peripheral wall is permeable to ink and a stencil master is wound around the peripheral wall. The printing drum
200
is rotated about its longitudinal axis. Am arm
202
which is rotatable about a fixed shaft
201
is provided inside the printing drum
200
. An internal press roller
203
is mounted for rotation on the arm
202
. A doctor roller
205
is disposed near the internal press roller
203
. The doctor roller
205
forms an ink layer of a predetermined thickness on the outer surface of the internal press roller
203
. The arm
202
is rotated in synchronization with rotation of the printing drum
200
so that the internal press roller
203
presses outward the peripheral wall of the printing drum
200
. A paper pinch drum
206
is supported for rotation at a predetermined distance from the printing drum
200
. When a printing paper is supplied between the printing drum
200
and the paper pinch drum
206
, the internal press roller
203
deforms outward the peripheral wall of the printing drum
200
and the printing paper is conveyed pinched between the stencil master on the deformed part of the peripheral wall and the paper pinch drum
206
, whereby ink supplied from the internal press roller
203
to the inner surface of the peripheral wall of the printing drum
200
passes through the peripheral wall of the printing drum
200
and the stencil master and is transferred to the printing paper to form an image.
In the conventional stencil printer shown in
FIG. 12
, there has been a problem that a part of the peripheral wall of the printing drum
200
adheres to the internal press roller
203
and is deformed inward as indicated at D in FIG.
12
. This phenomenon occurs on the downstream side of the contact line between the outer surface of the internal press roller
203
and inner surface of the peripheral wall of the printing drum
200
and occurs due to the fact that a part of the inner surface of the peripheral wall of the printing drum
200
cannot be properly separated from the outer surface of the internal press roller
203
after the part passes through the contact line between the internal press roller
203
and the paper pinch drum
206
.
Accordingly, this phenomenon is more apt to occur when the peripheral wall of the printing drum
200
is deformable or when the ink has a high viscosity. This phenomenon is especially apt to occur under a low temperature where the viscosity of the ink increases. This phenomenon can occur not only in the conventional stencil printer where the peripheral wall of the printing drum
200
is flexible but also in stencil printers where the peripheral wall of the printing drum is rigid. This is because the thickness of the rigid peripheral wall of the printing drum is made as thin as possible in order to reduce the amount of ink held by the printing drum so that printing quality is improved. For example, when the peripheral wall of the printing drum is formed of a stainless steel plate which is about 0.15 mm in thickness, the aforesaid deformation of the peripheral wall can occur depending on the conditions.
The aforesaid deformation of the peripheral wall of the printing drum can cause the following problems. That is, when the peripheral wall of the printing drum is deformed, the stencil master attached on the outer surface of the peripheral wall can be stretched or displaced in the circumferential direction of the printing drum. Further when the peripheral wall is repeatedly deformed and is repeatedly subjected to stress, the peripheral wall can be broken at the part where the stress is concentrated. Further repeated deformation of the peripheral wall can finally result in plastic deformation of the peripheral wall, e.g., the peripheral wall can corrugate as seen in a cross-section parallel to the longitudinal axis of the printing drum. Further when the peripheral wall is finally moved away from the internal press roller under its resiliency, ink splashes mechanisms in the printing drum.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a stencil printer in which deformation of the peripheral wall of the printing drum can be suppressed, whereby the stencil master wound around the peripheral wall of the printing drum is stabilized, durability of the peripheral wall is increased and ink is prevented from splashing.
In accordance with the present invention, there is provided a stencil printer comprising
a printing drum which has an ink-permeable peripheral wall, around which a stencil master is wound and to the inner surface of which ink is supplied, and is rotated about its longitudinal axis,
an internal press roller which is disposed inside the printing drum and is in contact with the inner surface of the peripheral wall of the printing drum,
a pinching means which is disposed outside the printing drum and carries a printing paper with pinching the printing paper between the pinching means and the stencil master wound around the peripheral wall, and
a retainer roller which is disposed in a predetermined position near the internal press roller and the inner surface of the peripheral wall downstream of the contact line between the internal press roller and the inner surface of the peripheral wall in the direction of rotation of the printing drum.
In one embodiment of the present invention, the internal press roller is mounted on a rotatable member disposed inside the printing drum to be movable, in response to rotation of the rotatable member, between an inoperative position where it is away from the peripheral wall of the printing drum and an operative position where it presses outward the peripheral wall, the pinching means is a rotatable paper pinch drum which is disposed outside the printing drum at such a distance from the printing drum that the printing paper is pinched between the peripheral wall of the printing drum and the paper pinch drum when the internal press roller deforms outward the side, and the retainer roller is mounted for rotation on the rotatable member.
In another embodiment of the present invention, the internal press roller is mounted on a rotatable member disposed inside the printing drum to be movable, in response to rotation of the rotatable member, between an inoperative position where it is away from the peripheral wall of the printing drum and an operative position where it presses outward the peripheral wall, the pinching means is a rotatable paper pinch drum which is disposed outside the printing drum at such a distance from the printing drum that the printing paper is pinched between the peripheral wall of the printing drum and the paper pinch drum when the internal press roller deforms outward the side, and the retainer roller is mounted for rotation on a rotatable arm which is mounted for rotation on the rotatable member and is urged by an urging means toward the inner surface of the peripheral wall of the printing drum.
In still another embodiment of the present invention, the pinching means is an external press roller which is movable up and down between an operative position in which it is
Motoe Katsuro
Nakayama Koji
Grohusky Leslie J.
Hilten John S.
Nixon & Peabody LLP
Riso Kagaku Corporation
Studebaker Donald R.
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