Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
2000-03-31
2001-12-04
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S195100, C428S409000, C428S480000, C428S913000
Reexamination Certificate
active
06326078
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a heat-sensitive sheet for stencil printing. More specifically, the invention relates to a heat-sensitive sheet for stencil printing which causes no jamming in a stencil printing apparatus during feeding and no wrinkle at the time of winding around or loaded on a printing drum, and is not elongated even when a large number of sheets of paper are printed, and thus sharp printed images can be obtained.
(For the purpose of the present invention, the words “sheets of paper” are sometimes referred to as “papers” and the words “sheet for stencil printing” are sometimes condensed to “stencil sheet” or further abbreviated to “the sheet” for brevity.)
BACKGROUND ART
Heretofore, a heat-sensitive sheet for stencil printing was not necessarily satisfactory in definition or sharpness of printed images, particularly in evenness of its solid parts. While various causes can be adduced for such circumstance, a condition ascribable to the fibers which constitute the support can be mentioned as one of the causes.
That is, a tissue paper (thin paper) which is conventionally used as the porous support in a stencil sheet and composed of natural fibers has defects as follows:
Passing of ink is liable to become uneven since diameter of the fibers is comparatively large and uneven, and cross section of the fibers is flat. Particularly, passing of ink is obstructed by the fibers located at directly under perforated portions to cause fading (or blurring) of printed letters, and
Smoothness of the surface of a film laminated on the support is deteriorated by the thick fibers, and contact of the film with a thermal head at the time of perforations is poor to often causes deficient perforations, thus, voids are formed in solid printing.
In order to improve these defects, such countermeasures have been proposed that a paper prepared by using a blend of natural (cellulosic) fibers and synthetic fibers such as polyester fibers through a wet papermaking process or a non-woven fabric is used instead of the above mentioned tissue paper composed only of natural fibers to make the fibers in the porous support fine on average or to reduce the basis weight of the paper or fabric (Laid-open Japanese Patent Publication Nos. Sho 59-2896, Sho 59-16793, and Hei 2-67197).
Definition of images is improved by thinning the diameter of fibers in the porous support or reducing the basis weight of the paper or fabric. In this case, however, there occur such problems that runnability of the sheet is lowered to cause jamming in the printing apparatuses during feeding, and that wrinkles occur on the sheet when an unperforated or perforated sheet is wound around and loaded on a printing drum, and the wrinkles degrade the quality of printing. Besides, there is a defect that the sheet is elongated (elongation at printing) or wrinkles occur on the sheet (wrinkles at printing) and thus reproducibility of a manuscript in printed papers is lowered when a number of papers are printed.
Further, in order to improve these defects, a stencil sheet having a specific tensile strength and flexural rigidity, that is, a specified tenacity and stiffness (Laid-open Japanese Patent Publication No. Hei 8-67080), and another stencil sheet having a specific wet elongation when the sheets is stretched under a certain load (Laid-open Japanese Patent Publication No. Hei 5-104875) have been proposed.
However, even when the sheet has the strength and rigidity (stiffness) described above, the effect of preventing the wrinkle occurrence when the sheet is wound around a printing drum is low, and the sheet is not thoroughly satisfied even as to the wrinkle occurrence at printing.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the problems in the prior art described above. Another object of the present invention is to provide a heat-sensitive sheet for stencil printing which sheet is excellent in runnability, occurrence of wrinkles on the sheet when the sheet is wound around a drum of a printing apparatus is efficiently prevented, elongation of the sheet is repressed and occurrence of wrinkles on the sheet can be prevented when a large number of papers are printed, and thus printed papers having a sharp images excellent in reproducibility of a manuscript can be obtained.
As a result of diligent investigations by the present inventors with the attention being focused on the mechanism by which wrinkles occur on the sheet when it is wound around a printing drum, the sheet is elongated, and wrinkles occur on the sheet at the time of printing, it has been found out that the problems described above can be solved by specifying the smoothness of the surface of porous support in the sheet and the strength of the sheet, leading to the accomplishment of the present invention.
The present invention is concerned with a heat-sensitive sheet for stencil printing comprising a laminate of a thermoplastic resin film and a porous support mainly composed of synthetic fibers which sheet has a wet tensile strength in the machine direction (longitudinal direction) of 200 gf/cm or higher, a KES bending rigidity B value in the machine direction or cross direction (lateral direction) of 0.02 g·cm
2
/cm or higher, and a PPS smoothness determined when a film is pressed against the surface of the porous support of the sheet of 0.9 &mgr;m or higher.
REFERENCES:
patent: 983868 (2000-03-01), None
patent: 985545 (2000-03-01), None
patent: 987124 (2000-03-01), None
patent: 08-067080 (1996-03-01), None
patent: 09-021092 (1997-01-01), None
patent: 10-171148 (1998-06-01), None
patent: 10-324074 (1998-12-01), None
Kinoshita Hideyuki
Watanabe Hiroshi
Yoshida Kenji
Fay Sharpe Fagan Minnich & McKee LLP
Hess Bruce H.
Nguyen Kimberly T.
Riso Kagaku Corporation
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