Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2002-01-11
2003-12-16
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031260, C106S031340, C106S031660
Reexamination Certificate
active
06663701
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an emulsion ink for use in stencil printing, particularly to an emulsion ink containing a vegetable oil, and to a printed matter printed by the emulsion ink for stencil printing.
2. Description of the Related Art
In the stencil printing method, a stencil master is prepared by perforating a stencil sheet in accordance with a desired image, and ink is passed through a perforated portion of the stencil sheet, thereby printing on an image-receiving medium such as paper. Stencil printing is utilized for a variety of purposes because of its ease of handling and convenience.
As the ink for stencil printing, a water-in-oil (W/O) type emulsion ink is mainly used. A high-boiling point solvent such as a nondrying oil or a nonvolatile mineral oil is used for the emulsion ink for its oil phase, thus preventing so-called clogging in which the ink dries and solidifies on a printing drum of a printer and at the perforated portion of a stencil sheet, which hinders the ink from passing through the stencil sheet, when the printer is not in operation for a long period of time. On the other hand, when the ink is left in a printing drum of a printer for a long period of time, water content in the ink evaporates since the ratio of a water phase as an inner phase of the emulsion is relatively high. The ratio between an oil phase and the water phase becomes unbalanced, and ink viscosity decreases. As a result, an excessive amount of ink is transferred to printing paper when printing is restarted. Accordingly, problems occur such as increased image density and an offset phenomenon (unintentional transfer of an inked impression from printed surface of one printing paper to the reverse side of another printing paper by contact).
In order to solve these problems, Japanese Patent No. 2096338 proposes the use of a solvent having a boiling point of 180 to 270° C. Additionally, Japanese Unexamined Patent Application Publication No. 5-125320 proposes the use of a solvent that consists of 10 to 30 wt. % of a volatile solvent with an initial boiling point of 150 to 210° C. and 70 to 90 wt. % of a nonvolatile solvent. These proposals are intended to prevent changes in the ratio between a water phase and an oil phase of an emulsion ink and to prevent a decrease in ink viscosity by adding each specified amount of each solvent having the specified range of boiling point or initial boiling point, so as to allow a small amount of the solvent as an oil component to evaporate, along with evaporation of the water content in the ink.
However, even when no problems would occur in the above ink after standing not in operation at an ordinary temperature (23° C.) for one week or one month, clogging may occur due to the evaporation of a solvent when the environmental temperature rises. Also the evaporation of the solvent may damage health of printing operators and ink manufacturers.
On the other hand, ink using a vegetable oil has recently attracted attention as an environment-consciously developed printing ink. For instance, Japanese Unexamined Patent Application Publication No. 10-245516 proposes a water-in-oil type emulsion ink for stencil printing using a vegetable oil which has an iodine number of 100 or less and a congeal point (freezing point) of 0° C. or below. This ink uses a nondrying oil with an iodine number of 100 or less in order to prevent the ink from solidifying. However, when the ink is left for a long period of time, water content in the ink may evaporate and the viscosity of the ink may decrease, thereby causing excess transfer of ink and offset.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an emulsion ink which causes neither clogging nor offset after a long nonuse period of time, has shelf stability and is harmless to environment and ink handlers. Here, “a long nonuse period of time” refers to the condition under which a printer is not in operation and ink is allowed to stand in a printing drum of the printer for a long period of time. Another object of the present invention is to provide a printed matter having a desirable printing image and no offset after a long nonuse period of time.
The present inventors focused on the oxidation phenomenon of a vegetable oil and its iodine number as an index for the unsaturation degree of the vegetable oil. They found that an emulsion ink for stencil printing, which causes neither clogging nor offset after a long nonuse period of time and has shelf stability, can be provided by mixing a vegetable oil with an iodine number ranging from 110 to 150 in a specific amount or more relative to the water amount in the ink, and furthermore, by mixing an antioxidant in a specified range based on the amount of the vegetable oil mixed.
Specifically, a water-in-oil type emulsion ink for stencil printing relating to the present invention includes 20 to 50 wt. % of an oil phase and 80 to 50 wt. % of a water phase, and contains at least one kind of a vegetable oil with an iodine number ranging from 110 to 150 in the oil phase in an amount of the following formula (1) or more in wt. %, and an antioxidant in a range of 1 to 10 wt. % based on the content of the vegetable oil:
Minimum amount of vegetable oil in wt. %=amount of water in ink in wt. %×(100/iodine number)×0.09 (1)
According to the present invention, a change in ink viscosity due to water evaporation can be prevented by controlling an increase in viscosity due to the oxidation of the vegetable oil in the ink, providing an emulsion ink for stencil printing which causes no clogging or offset after a long nonuse period of time and which has shelf stability. Furthermore, the use of a vegetable oil enables one to provide an ecologically superior ink that is designed for reducing environmental damage and improving safety of printing operators and ink manufacturers.
In another aspect, the present invention provides a printed matter printed by the emulsion ink mentioned above. By utilizing the emulsion ink of the present invention, a printed matter having a desirable printing image and no offset can be produced after a long nonuse period of time.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A water-in-oil type emulsion ink for use in stencil printing (mentioned as “ink” hereinafter) relating to the present invention includes 20 to 50 wt. % of an oil phase and 80 to 50 wt. % of a water phase, and contains at least one kind of a vegetable oil with an iodine number ranging from 110 to 150 at least in the minimum amount specified by the above formula (1) relative to the water content in the ink. The semidrying or drying vegetable oil contained is oxidized after a long nonuse period of time, thereby increasing ink viscosity. Accordingly, a decrease in ink viscosity due to water evaporation from the ink can be controlled, and excess ink transfer and offset (and deterioration of such offset) after a long nonuse period of time can be prevented. Furthermore, since the ink contains the antioxidant in the specified amount based on the amount of the vegetable oil, drying solidification due to excess oxidation of the vegetable oil can also be prevented. As a result, the emulsion ink is free of clogging after a long nonuse period of time and its shelf stability is maintained.
Here, the vegetable oil is contained in an oil phase, whereas the antioxidant may be contained in any phase, such as an oil phase, a water phase, and oil and water phases. The phase in which the antioxidant is contained can be properly selected based on the kind of antioxidant and the solubility thereof in a water phase or an oil phase.
The vegetable oil with an iodine number ranging from 110 to 150 is a semidrying oil or a drying oil. Examples thereof include soybean oil, corn oil, sunflower oil, rapeseed oil, safflower oil, grape seed oil, sesame oil and the like. Each of these vegetable oils be used singly or in combination with one or more kinds thereof.
When the iodine number of the vegetable oil is 110 or above, an appropriate
Ogawa Hiroyuki
Takayama Hideaki
Goldberg Joshua B.
Klemanski Helene
Nath Gary M.
Nath & Associates PLLC
Riso Kagaku Corporation
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