Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-03-28
2003-06-03
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S146000, C428S220000, C428S537500, C101S128210, C101S127000
Reexamination Certificate
active
06572951
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing sheet.
Further, the present invention relates to a printing sheet particularly suitable for stencil printing on which ink can be very well fixed in at high ink density, no setoff appears after printing, and a high image quality print without uneven printing can be obtained.
2. Description of the Related Art
A printing sheet on which ink can be very well fixed in at high ink density, ink is very well fixed, no setoff appears after printing, and a high image quality print without uneven printing can be obtained is in need for offset printing, gravure printing, letterpress printing, stencil printing, or the like.
Stencil printing is a generally known printing system represented by mimeograph printing and screen printing in which ink is transferred through a plate consisting of an image area, i.e., perforations through which ink can pass, and a non-image area, i.e., a membrane through which ink cannot pass, onto a printing sheet.
Today, in widely used stencil printing, a plate is made by an area corresponding to an image area of a film being directly melted by heat using a thermal head or the like to perforate and make dots on a stencil sheet which is generally made of a thermoplastic resin film. Printing is carried out through the perforation image thus formed in the perforated area. Namely, ink ejected from an ink supplying part mounted inside of the plate equipped on a plate cylinder is exuded through the perforations and transferred onto the surface of a printing sheet such as paper. Further, it is desirable that the printing be basically maintenance-free, that no washing be required after printing, and that the perforations do not become clogged with dried ink when ink is left for long periods till the next printing so that a good printed material can be obtained from the start of the next printing under various conditions.
Accordingly, printing inks for stencil printing having high stability, which are different from process inks used for ordinary printing, such as oil-based inks in which a coloring agent such as a pigment is dispersed in a vehicle such as mineral oil, and water-in-oil emulsion inks in which water is added to a vehicle, which is highly liquid and is not hardened by oxidation, light reaction or the like, have been invented and various improvements have been carried out (for example, Japanese Patent Publication No. S44-2165, Japanese Patent Publication No. S52-7370, Japanese Patent Application Laid-open No. H4-372671, Japanese Patent Application Laid-open H5-62628, and Japanese Patent Application Laid-open No. H5-117564). These inks can be left on a printing plate for a long period of time in a consistently stable state and are considered to be favorable for maintenance-free printing.
In stencil printing using heat-sensitive perforations, digitized plates can be easily made owing to the development of electronic equipment and peripheral devices. Further, a system applicable to a so-called computer-to-plate system, in which an image of a printing material can be made on a computer screen and the printing plate information can be transferred directly to a printing machine, is available, and at the same time, printing at a higher speed (120 sheets/minute) and at a higher resolution (600 dpi) is now possible. Thus, stencil printing is attracting attention once more because of its easy operation, low cost, and the like.
As mentioned above, the printing principle of stencil printing is entirely different from that of other printing systems, such as letterpress printing, gravure printing, and offset printing and thus, the quantity of ink to be transferred onto a printing sheet in stencil printing is much greater as compared to these other printing systems. Since conventional printing paper has poor ink absorbability, it causes problems when used as a printing sheet in stencil printing; namely, wet ink left unabsorbed on the printing layer of the paper after printing is transferred on the reverse side of the next printing material, namely, a phenomenon called setoff occurs, and the ink soils other printed materials, operators, working environment, or the like during handling of the printed materials. These are the problems to be primarily solved with the recent development of high-speed printers.
Japanese Patent Application Laid-open No. H4-183762 and Japanese Patent Application Laid-open H7-179799 propose improvement of ink fixing ability by controlling the diameter of an ink emulsion particle to 1-20 &mgr;m, and the diameter of a coloring agent particle in an ink emulsion to less than 0.4 &mgr;m. Further, Japanese patent Application Laid-open H8-73795 provides an ink having excellent permeability into a printing layer by controlling the average particle diameter and the specific surface area of a pigment used as a coloring agent. However, improvement of ink quality alone cannot solve all the problems so that studies in terms of the printing sheet have become urgent.
The size and shape of dots in stencil printing become uneven, for example, depending on the accuracy of perforation in plate making, control of the quantity of ink transfer during printing, and ink blur along fine voids on the printing layer as ink is absorbed through diffusion and permeation into the printing layer of the printing sheet. The lack of dot uniformity results in poor detail and quality of the printed material as compared to ordinary offset-printed material so that an improvement in quality is needed. On the other hand, unlike conventional mimeograph printing, stencil printing has shifted to tone expression by dots with the digitization of printing plates, wherein feathering can be expected to a certain extent when dot information perforated on a printing plate is transferred onto a printing sheet upon printing. Accordingly, white spots or other imperfections appear on the solid printed area if ink diffusion is not sufficient.
Conventionally, papers such as wood free paper and mechanical paper for plain paper copy (PPC paper) are generally used as stencil printing sheet because of their easy availability and low cost. There has been no sheet specific for stencil printing.
In order to prevent setoff after printing and further to improve print quality, various stencil printing sheets have been proposed. Japanese Patent Application Laid-open No. H5-331796 proposes a stencil printing paper which has an ink fixing layer consisting of diatomaceous earth as a pigment and a binder; Japanese Patent Application Laid-open No. H6-171201 proposes a stencil printing paper which has an ink absorbing layer consisting of a pigment having an oil absorbability of more than 45 ml/100 g and less than 120 ml/100 g and a binder; Japanese Patent Application Laid-open No. H9-250100 proposes a stencil printing paper which has an ink absorbing layer consisting of a pigment having an oil absorbability of more than 150 ml/100 g and a specific surface area of more than 200 cm
2
/g and a binder; Japanese Patent Application Laid-open No. H10-292292 proposes a stencil printing paper which has an ink absorbing layer consisting of an amorphous silica pigment having an oil absorbability of more than 150 m/100 g and an average particle diameter of 3-15 &mgr;m and a binder; and Japanese Patent Application Laid-open No. H11-99607 proposes a stencil printing sheet which has an ink receiving layer consisting of a resin-containing porous membrane having an average air hole diameter of 0.5-30 &mgr;m and a density of 0.1-0.8 g/cm
3
.
However, all of these proposed papers have an ink receiving layer spread on a supporting sheet, and excessive ink absorbability suppresses dot diffusion too much instead of having an significant effect on preventing setoff and produces white spots on solid printed areas or dark areas to easily cause poor print quality.
Furthermore, Japanese Patent Application Laid-open No. S63-309700 shows that PPC paper can be modified to be fit for stencil printing at an air permeability of less than 15 seconds, an apparen
Chatani Akinobu
Hasegawa Makoto
Kumazawa Noriko
Nakanishi Nobuo
Ono Ryuta
Knobbe Martens Olson & Bear LLP
Nippon Paper Industries Co. Ltd.
Watkins III William P.
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