Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1996-10-04
2003-07-15
Pianalto, Bernard (Department: 1762)
Stock material or miscellaneous articles
Composite
Of metal
Reexamination Certificate
active
06593001
ABSTRACT:
The present invention relates to a method for perforating heat-sensitive stencil sheet, and more specifically relates to a method of perforating heat-sensitive stencil sheet by exposing it to a visible or infrared ray to make a master for stencil or screen printing, and heat-sensitive stencil sheet and a composition used in the method.
As structures of conventional heat-sensitive stencil sheet, are known a multilayer which is composed of a thermoplastic film laminated to an ink-permeable porous substrate made of Japanese paper or the like, and one layer which is composed simply of a thermoplastic film.
Methods for perforating such heat-sensitive stencil sheet to obtain a master for stencil or screen printing, include (1) a process of overlaying heat-sensitive stencil sheet on images or letters that have been formed with carbon-containing materials such as pencils and toner by hand-writing or photocopying, and then exposing them to light from flash lamps, infrared lamps or the like to cause the portions of letters or images to emit heat so that the thermoplastic film of the stencil sheet is molten and perforated at the portions contacting the images or letters, and (2) a process of melting and perforating the thermoplastic film of the stencil sheet by bringing the stencil sheet into contact with a thermal head that emits heat in dot-matrix forms so as to reproduce images in accordance with image data of electric signals into which original images or letters have been transformed.
In the above process (1), however, failure in perforation often occurs due to insufficient contact of the thermoplastic film of the stencil sheet with the original or the photocopied image portions of toner from which heat is emitted, or a problem on so-called “pin holes” also occurs which are phenomena of perforations caused in the stencil sheet at undesired portions by heat emitted from dusts on the surface of the original or toner scattered out of the image portions. In the above process (2), there often occur failure of perforation, failure of conveying and wrinkling of the stencil sheet due to unevenness of pressure exerted to press the stencil sheet to the thermal head.
It is an object of the present invention to provide a method of perforating heat-sensitive stencil sheet, which overcomes the above mentioned problems on prior art, and eliminates failure in perforation, occurance of pin-holes and wrinkling, and failure in conveying. It is another object of the present invention to provide heat-sensitive stencil sheet and a composition useful in the above method of perforating heat-sensitive stencil sheet.
According to the above objects, the present invention provides a method of perforating heat-sensitive stencil sheet particularly to make a master for screen or stencil printing, which comprises ejecting a photothermal conversion material contained in a liquid from a liquid-ejecting means to transfer it together with the liquid to heat-sensitive stencil sheet, and then exposing the heat-sensitive stencil sheet to a visible or infrared ray to perforate the heat-sensitive stencil sheet specifically at portions to which the photothermal conversion material has been transferred.
In other words, the present method is a method for making a master for screen or stencil printing, which comprises a first step of transferring a photothermal conversion material to heat-sensitive stencil sheet by ejecting a liquid which contains the photothermal conversion material, from a liquid-ejecting means to the heat-sensitive stencil sheet, and the second step of perforating the heat sensitive stencil sheet specifically at sites to which the photothermal conversion material has been transferred, by subjecting the stencil sheet to a visible or infrared ray.
The first step of the present method can be practiced, for example, by controlling a liquid-ejecting means to eject the liquid onto heat-sensitive stencil sheet while the liquid-ejecting means is moved relative to the heat-sensitive stencil sheet in accordance with image data that have previously been transformed into electric signals, and then evaporating the liquid that has been transferred to the heat sensitive stencil sheet, so that the image is reproduced on the surface of the heat sensitive stencil sheet as solid adherends mainly composed of the photothermal conversion material.
The liquid-ejecting means may be a device which comprises nozzles, slits, a porous material, or a porous film providing 10-2000 openings per inch (i.e., 10 to 2000 dpi) and connected to piezoelectric elements, heating elements, liquid-conveying pumps or the like so as to eject the liquid containing the photothermal conversion material intermittently or continuously, that is, in a form of dots or lines, in accordance with the electric signals for letters or images.
The photothermal conversion material used in the present invention is a material which can transform light energy into heat energy, and preferably is a material which efficient in photothermal conversion, such as carbon black, lampblack, silicon carbide, carbon nitride, metal powders, metal oxides, inorganic pigments, organic pigments, and organic dyes. Among them, particularly preferred are those having a high light-absorbency within a specific range of wavelength, such as phthalocyanine colorings, cyanine colorings, squalirium colorings, and polymethine colorings.
The liquid in which the photothermal conversion material is contained, may be solvents such as of aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, ketones, esters, ethers, aldehydes, carboxylic acids, amines, low molecular weight heterocyclic compounds, oxides, and water. More specific examples thereof are hexane, heptane, octane, benzene, toluene, xylene, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, ethylene glycol, diethylene glycol, propylene glycol, glycerin, acetone, methyl ethyl ketone, ethyl acetate, propyl acetate, ethyl ether, tetrahydrofuran, 1,4-dioxane, formic acid, acetic acid, propionic acid, formaldehyde, acetaldehyde, methylamine, ethylene diamine, dimethylformamide, pyridine, and ethylene oxide. These liquids may be used alone or in combination, and are preferably those which evaporate quickly after having been transferred from the liquid-ejecting means to the heat-sensitive stencil sheet. To the liquid, may be added dyes, pigments, fillers, binders, hardening agents, preservatives, wetting agents, surfactants, pH-adjusting agents, or the like, as required.
Thus, a composition for perforating heat-sensitive stencil sheet can be prepared by appropriately dispersing or mixing the above photothermal conversion material in or with the above liquid in a form readily ejectable from the liquid-ejecting means.
In the second step of the present method, when a visible or infrared ray is applied to the heat-sensitive stencil sheet to which a photothermal conversion material has been transferred, the photothermal conversion material absorbs light to emit heat. As a result, the thermoplastic film of the heat-sensitive stencil sheet is molten and perforated to obtain a master for screen or stencil printing directly from the stencil sheet itself. In this way, the present perforating method does not require stencil sheet to contact any substance such as an original or thermal head to make a master, but only requires stencil sheet itself to be exposed to a visible or infrared ray. Thus, no wrinkling occurs on stencil sheet upon making masters. The visible or infrared ray can readily be radiated using xenon lamps, flash lamps, halogen lamps, infrared heaters or the like.
The heat-sensitive stencil sheet may be stencil sheet to at least one side of which the photothermal conversion material can be transferred and which can be molten and perforated by heat emitted by the photothermal conversion material. The stencil sheet may be made of a thermoplastic film only, or may be a thermoplastic film laminated to a porous substrate.
The thermoplastic film includes a film made from polyethylene, polypropylene, polyvinyl chloride
Fitch Even Tabin & Flannery
Pianalto Bernard
Riso Kagaku Corporation
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