Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2002-01-16
2004-03-02
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
Reexamination Certificate
active
06699312
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to W/O emulsion ink for stencil printing, and more particularly to stencil printing W/O emulsion ink which is excellent in storage stability.
2. Description of the Related Art
The stencil printing is advantageous over other printing systems such as offset printing, gravure printing, letterpress printing and the like in that it permits to easily make prints without a skilled operator and complicated cleaning after printing is not necessary.
From the advent of the thermal stencil making system using a thermal head, image processing in the stencil printing has come to be digitized, whereby it has become feasible to easily obtain high quality printings in a short time, which makes it feasible to use the stencil printer as an information processing terminal.
Further, in the thermal stencil making system using a thermal head, perforations can be more regular in size and accordingly the amount of ink transferred to the printing paper can be more accurately controlled than in the conventional stencil making system in which infrared rays or xenon flash is employed to perforate the stencil material. Thus by using the thermal stencil making system, probability of generation of offset and/or spread of ink is reduced and the quality of printings is greatly improved.
As the stencil printing ink, W/O emulsion ink has been generally used. However, the W/O emulsion ink is disadvantageous in that coalescence of water phase particles is promoted when the ink is stored long due to its higher water phase (the inner phase of the emulsion) content relatively to the oil phase content and the water phase is separated from the oil phase. That is, the W/O emulsion ink is generally poor in storage stability.
Thus, there have been proposed various methods of improving the storage stability of the W/O emulsion ink. For example, in Japanese Unexamined Patent Publication No. 6(1994)-145577, there is disclosed that the stability of emulsion can be enhanced by the use of polyglyceryn fatty acid ester not higher than 10 in HLB. Further, in Japanese Unexamined Patent Publication No. 10(1998)-1634, there is disclosed that the stability of emulsion can be enhanced by adding acid-anhydride-containing water-soluble polymer to the water phase. Further, in Japanese Unexamined Patent Publication No. 2000-7972, there is disclosed that the stability of emulsion can be enhanced by adding to the oil phase alkyd resin or rosin-modified resin after reacting it with aluminum chelate or aluminum alcoholate.
Further, in Japanese Unexamined Patent Publication No. 6(1994)-192606, there is disclosed that the stability of emulsion can be enhanced by adding electrolyte to the water phase of the emulsion since the surface active agent density in the emulsion is increased, the particle size in the emulsion is reduced and the particle size distribution is narrowed. Further, in Japanese Unexamined Patent Publication No. 7(1995)-150091, there is disclosed that the stability of emulsion can be enhanced by adding water-soluble magnesium salt (electrolyte) to the water phase of the emulsion.
As can be understood from the description above, enhancing the stability of emulsion is very important in improving the storage stability of the emulsion ink. However, conventional emulsion inks for stencil printing are not satisfactory in all the points of view and there has been a demand for further improvement.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a W/O emulsion ink for stencil printing in which separation of phases is suppressed and which is very excellent in storage stability.
In accordance with a first aspect of the present invention, there is provided W/O emulsion ink for stencil printing characterized in that a material which reacts with oxygen dissolved in the water phase thereof and reduces the amount of oxygen dissolved in the water phase is contained in the water phase.
The material which reacts with oxygen dissolved in the water phase thereof and reduces the amount of oxygen dissolved in the water phase (will be referred to as “oxygen reducing material”, hereinbelow.) may be, for instance, an inorganic material, an organic material or a free ion.
In accordance with a second aspect of the present invention, there is provided W/o emulsion ink for stencil printing characterized in that a water-soluble and electrolytic anti-oxidant is contained in the water phase.
The “water-soluble anti-oxidant” is a water-soluble compound which prevents the W/O emulsion ink from being physically and/or chemically deteriorated by oxidization.
In accordance with a third aspect of the present invention, there is provided W/O emulsion ink for stencil printing characterized in that sulfite ions are contained in the water phase.
It is preferred that the sulfite ions be generated from sulfite and/or hydrogen sulfite contained in the water phase.
It is preferred that the sulfite or the hydrogen sulfite is an alkaline metal salt or an alkaline earth metal salt. As the alkaline metal salt, potassium salt or sodium salt is especially preferred.
It is preferred that the total amount of the sulfite and/or hydrogen sulfite is 0.01 to 5% by weight of the water phase.
In accordance with a fourth aspect of the present invention, there is provided W/O emulsion ink for stencil printing characterized in that thiosulfate is contained in the water phase.
It is preferred that the thiosulfate is an alkaline metal salt or an alkaline earth metal salt. As the alkaline metal salt, potassium salt or sodium salt is especially preferred. As the alkaline earth metal salt, magnesium salt or calcium salt is especially preferred.
It is preferred that the total amount of the thiosulfate is 0.01 to 5% by weight of the water phase.
In accordance with a fifth aspect of the present invention, there is provided W/O emulsion ink for stencil printing characterized in that at least one material selected from the group consisting of dithionous acid, pyrosulfurous acid, dithionite and pyrosulfite is contained in the water phase.
It is preferred that the dithionite or the pyrosulfite is an alkaline metal salt or an alkaline earth metal salt. As the alkaline metal salt, potassium salt or sodium salt is especially preferred.
It is preferred that the total amount of the dithionite and/or pyrosulfite is 0.01 to 5% by weight of the water phase.
It is further preferred that the total amount of electrolyte contained in the water phase be 0.1 to 5% by weight of the water phase. Sulfite, hydrogen sulfite, thiosulfate, dithionous acid, pyrosulfurous acid, dithionite and pyrosulfite are all electrolyte and “the total amount of electrolyte contained in the water phase” means the total amount of sulfite, hydrogen sulfite, thiosulfate, dithionous acid, pyrosulfurous acid, dithionite and/or pyrosulfite including other electrolyte contained in the water phase, if any.
It is preferred that the content of the oil phase be 15 to 50% by weight and the content of the water phase be 50 to 85% by weight.
Resins contained in W/O emulsion ink for stencil printing are generally added to the ink for the purpose of increasing the viscosity of the oil phase and/or enhancing the interfacial force between the oil phase and the water phase in order to improve the storage stability and printing performance of the ink. Since the resin is apt to be oriented on the interface between the oil phase and the water phase, it may be considered that oxidization of the resin by oxygen dissolved in the ink weakens the interfacial force between the oil phase and water phase, whereby the oil phase and the water phase become apt to be separated from each other.
Further when the resin and/or the oil components are oxidized, the polarity of the oil phase changes, which results in change of the required HLB of the emulsion, the compatibility of the oil phase components changes so that components which becomes unable to be dissolved in the oil phase separate out on the surface of
Hayashi Yoshihiro
Watanabe Yoshifumi
Klemanski Helene
Nixon & Peabody LLP
Riso Kagaku Corporation
Studebaker Donald R.
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