Printing – Stenciling – Stencils
Reexamination Certificate
2000-05-30
2002-05-28
Funk, Stephen R. (Department: 2854)
Printing
Stenciling
Stencils
C101S128400, C428S308400, C427S336000
Reexamination Certificate
active
06393979
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermosensitive stencil, production method thereof, a thermosensitive stencil printing master making apparatus and a thermosensitive stencil printing apparatus.
2. Discussion of Background
There is conventionally known a thermosensitive stencil which is prepared by attaching a thermoplastic resin film to a porous substrate, for example, a porous tissue paper, with an adhesive. Further, a sticking preventing layer is overlaid or. the thermoplastic resin film to prevent the thermoplastic resin film from sticking to a thermal head when perforations are made in the resin film by the application of heat thereto In practice, a porous tissue paper is made out of hemp fiber, synthetic fiber or wood fiber, which may be used in combination, and the thus prepared tissue paper and the thermoplastic resin film are laminated with an adhesive, and then a sticking preventing layer is provided on the surface of the resin film. Such a thermosensitive stencil is widely used in practice.
However, the above-mentioned conventional thermo-sensitive stencil has the following drawbacks:
(1) Since the fibers are partially superimposed in the tissue paper, the adhesive is unfavorably accumulated at the portion where the thermoplastic resin film is brought into contact with the superimposed fibers of the tissue paper. A perforation cannot be easily formed in such a port-on as mentioned above even by the application of thermal energy using the thermal head. Further, printing ink cannot smoothly permeate through the stencil at that portion. As a result, the images printed on an image-receiving medium using a printing master prepared from the above-mentioned thermosensitive stencil is lacking in evenness.
(2) The fibers themselves contained in the porous tissue paper hinder the printing ink from penetrating through the stencil, so that the printed images tend to become uneven.
(3) Because the fibers for use in the tissue paper are expensive, much spoilage is generated in the preparation of the stencil, for example, in a lamination step, and loss of tissue paper is unavoidable, the cost of the thermosensitive stencil is necessarily increased.
(4) The use of the fibers causes deforestation, and manufacture and disposal of the fibers adversely affect the environment.
To solve the above-mentioned problems, there are proposed improved thermosensitive stencils. For example, Japanese Laid-Open Patent Application No. Hei3-193445 discloses a thermosensitive stencil comprising a porous substrate comprising microfibers witha fineness of 1 denier or less. Although the above-mentioned problem (1) can be solved by this thermosensitive stencil, the problems (2) and (3) remain unsolved.
Japanese Laid-Open Patent Application No. Sho62-198459 discloses a method for producing a thermosensitive stencil by forming on a film a heat resistant resin pattern which is substantially continuous on the film by gravure printing, offset printing or flexography.
According to the above-mentioned printing technology, it is still difficult to print a pattern with a line width of 50 &mgr;m or less. Even though the formation of such a pattern can be achieved, the productivity is very poor and the cost is remarkably increased. In addition, when the line width is 30 &mgr;m or more, the heat resistant resin hinders the perforation from being clearly made, so that the printed image becomes uneven.
Furthermore, Japanese Laid-Open Patent Application No. Hei4-7198 discloses a thermosensitive stencil prepared by coating a mixture of a water-dispersed polymer and finely-divided particles of colloidal silica on the surface of a film and drying the above-mentioned mixture. Thus, a porous layer is provided on the film. From the thus prepared thermosensitive stencil, a printing master is produced, for example, using a commercially available printing master making apparatus “PRINT GOCCO” (Trademark), made by Riso Kagaku Corporation. Further, the above-mentioned application also discloses a method of printing images using such a printing master and a commercially available jet printing ink (Trademark “HG-4800 Ink”, available from EPSON HANBAI Co., Ltd.).
However, the penetrability of the printing ink through the above-mentioned porous layer becomes poor. Therefore, when a thermosensitive stencil ink for general use is employed for producing a printed image, a sufficient image density cannot be obtained in practical use. In addition, the heat insulating properties of the porous layer are insufficient, resulting in impractical perforation. To solve such problems, the jet printing ink is used instead of the thermosensitive stencil ink. However, such a jet printing ink produces blurred images, and printed ink images are easily smeared because the jet printing ink tends to spread.
Japanese Laid-Open Patent Application No. Sho54-33117 discloses a thermosensitive stencil consisting of a thermoplastic resin film. By this application, the previously mentioned conventional problems (1) to (4) can be solved because a porous substrate such as a tissue paper is not employed.
However, there occurs another problem that the stiffness of the stencil becomes low when the thickness of the thermoplastic resin film is 10 &mgr;m or less. In such a case, the transportation of the stencil in apparatus such as a printing machine causes annoyance. To solve such a problem of troublesome transportation, Japanese Patent Publication 5-70595 proposes a printing method using a printing master prepared from the above-mentioned thermosensitive stencil. To be more specific, the printing operation is carried out in such a fashion that the printing master which is not cut into pieces, but used in a continuous length is wound round the periphery of a plate cylinder of the printing machine, and rotated along with the rotation of the plate cylinder during the printing operation.
According to this printing method, however, not only the printing master, but also the units for attaching the printing master to the plate cylinder and detaching the same therefrom are caused to rotate along with the rotation of the plate cylinder in the printing operation. Therefore, the turning moment of the plate cylinder is increased and the displacement from the rotating shaft is increased. In light of the above-mentioned factors, the printing machine is required to be heavy and large in this case.
On the other hand, when the thickness of the above-mentioned thermosensitive stencil consisting of the film is 5 &mgr;m or more, the thermal sensitivity becomes so poor and the heat insulating properties are so low that perforations cannot be easily formed in the film when thermal energy is applied to the stencil by use of a thermal head.
Furthermore, the thermosensitive stencil made of a film does not have so much heat insulating properties as those of the porous layer. Accordingly, thermal energy applied by a heating means is easily escaped from the film to a platen roller. Namely, satisfactory perforation cannot be achieved due to lack of thermal energy.
Japanese Laid-Open Patent Application No. Hei8-332785 discloses a thermosensitive stencil which comprises a thermoplas-tic film and a layer made of honeycomb cells formed on one side of the thermoplastic film. Further, another thermosensitive stencil is proposed in Japanese Laid-Open Patent Application No. Hei10-24667 that comprises a thermoplastic resin film and a porous resin layer formed on one side of the thermoplastic resin film, the pores with a diameter of 5 jam or more occupying an area of 4 to 80% of the entire surface area of the porous resin layer when the pore diameter is obtained by converting the form of a pore into a true round.
One of the features of the above-mentioned thermosensitive stencils is that a porous resin layer is coated on a remarkably thin substrate having a thickness of 0.5 to 10 &mgr;m. Such a thin substrate is desirable in terms of sensitivity in making of a printing master.
However, printability of the porous resin layer thus provided on the thin f
Cooper & Dunham LLP
Funk Stephen R.
Ricoh & Company, Ltd.
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