Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1999-10-18
2001-02-20
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031350, C106S031400, C106S031410, C106S031670, C106S031720, C106S031730
Reexamination Certificate
active
06190444
ABSTRACT:
The present invention relates to an emulsion ink for stencil printing, and more particularly it relates to an emulsion ink which is less in change of viscosity with time and can stably provide prints of high quality.
Stencil printing comprises perforating a stencil sheet to make a master and passing an ink through the perforated portions to such an article to be printed as printing paper. Since the master can be easily made, the stencil printing is utilized in a wide variety of fields.
Water-in-oil (W/O) emulsion inks are generally used for stencil printing, as disclosed in JP 61-255967 A, JP 64-14284 A, JP 4-132777 A, JP 5-117565A, JP 7-179799A and so on. However, these water-in-oil (W/O) emulsion inks suffer from the problem that their viscosity lowers with lapse of time.
In order to solve the problem, it has been proposed to use some specific surface active agents, for example, use of isostearates of polyhydric alcohols (JP 7-157701 A), use of polyglycerin fatty acid ester emulsifiers (JP 6-145577 A), use of sorbitol esters of saturated or unsaturated fatty acids of 12-24 carbon atoms (JP 6-145576 A), and use of oxyfatty acid esters of polyhydric alcohols selected from polyglycerin, sugars, and sugar alcohols (JP 3-78433 B). It is further proposed to use surface active agents having a specific HLB (JP 6-329970 A, JP 6-220383 A, and JP 6-49401 A). However, none of these proposals can secure sufficient stability of emulsion.
Another proposal is to add a water-soluble magnesium to the water phase of the water-in-oil (W/O) emulsion to improve stability with time of the emulsion (JP 7-150091 A). This method cannot still provide satisfactory stability of the emulsion.
The object of the present invention is to solve the problems in the conventional techniques and, thus, provide an emulsion ink for stencil printing which is less in change of viscosity with lapse of time and can stably provide prints of high quality.
As a result of intensive researches conducted by the inventors, it has been found that stability of emulsion in water-in-oil (W/O) emulsion inks can be markedly improved by containing a resinous component having a free carboxylic acid group, or a higher fatty acid in the oil phase, and containing a divalent or trivalent metal salt and a monovalent metal salt having alkalinity in the water phase. Thus, the present invention has been accomplished.
That is, the present invention relates to a water-in-oil (W/O) emulsion ink for stencil printing, having an oil phase and a water phase, in which the oil phase contains a resinous component having a free carboxylic acid group, or a higher fatty acid, and the water phase contains a divalent or trivalent metal salt and a monovalent metal salt having alkalinity.
According to the present invention, stability of the emulsion of the ink is markedly improved by allowing a resinous component having a free carboxylic acid group or a higher fatty acid to be present in the oil phase and allowing a divalent or trivalent metal salt and a monovalent metal salt having alkalinity to co-exist in the water phase. It is considered that this is because the free carboxylic acid of the resinous component or the higher fatty acid reacts with the divalent or trivalent metal salt in an interfacial layer of the emulsion, namely a portion at which the water phase and the oil phase contact with each other so as to produce a metallic soap, and as a result the interfacial layer becomes strong.
Although not being bound by theory, it is considered that in the ink of the present invention, first an alkali soap is produced by the reaction of the following formula (1), and then a metal soap is produced by the double decomposition reaction of the following formula (2) in which two compounds replace their components with each other to produce two new compounds.
RCOO—H+XY→RCOO—X+H−Y (1)
in which RCOO—H is a resinous component having a free carboxylic acid group, or a higher fatty acid, XY is a monovalent metal salt having alkalinity, and RCOO—X is an alkali soap.
nRCOO—X+AB→(RCOO)
n
—A+X
n
—B (2)
in which n is equal to 2 or 3, AB is a divalent or trivalent metal salt where A is a metal, and (RCOO)
n
—A is a metallic soap.
It is presumed that the metallic soap is produced in the interfacial layer of the emulsion. It is considered that since the carboxylic acid group (—COOH) in the resinous component or higher fatty acid is present in the state of being oriented to the water phase side, it becomes insoluble in water, and thus the reaction of the formula (2) immediately proceeds to produce the metallic soap, and, as a result, the stability of the emulsion is improved.
The emulsion ink for stencil printing of the present invention is prepared, for example, by gradually adding 90-10% by weight of the water phase to 10-90% by weight of the oil phase and emulsifying the mixture.
In the emulsion ink for stencil printing of the present invention, a colorant can be contained in at least one of the oil phase and the water phase. As the colorant, known pigments can be used, and examples thereof for monochromic purpose include carbon blacks such as furnace carbon black, lampblack, acetylene black and channel black, metals such as copper, iron and titanium oxide, and organic pigments such as phthalocyanine pigments, soluble azo pigments, insoluble azo pigments, and quinacridone pigments.
In the emulsion ink for stencil printing of the present invention, the oil phase basically comprises a solvent, an emulsifier, and a resinous component having a free carboxylic acid group, or a higher fatty acid.
The resinous component having a free carboxylic acid group is preferably an alkyd resin, a rosin-modified phenolic resin, a maleic acid resin or a rosin.
As the higher fatty acid, there may be used, for example, oleic acid, isostearic acid, stearic acid, palmitic acid, lauric acid, behenic acid, ricinoleic acid, hydroxyfatty acids, and tall oil fatty acids.
Amount of the resinous component or higher fatty acid is preferably 0.5-30% by weight based on the total amount of the emulsion ink. When the amount is within the above range, a sufficient amount of a metallic soap is produced in the interfacial layer of the emulsion ink, and thus stability of the emulsion can be increased.
As the solvent, a nonvolatile or volatile solvent can be used. The nonvolatile solvent includes, for example, mineral oils such as motor oil, spindle oil, machine oil and liquid paraffin, and vegetable oils such as olive oil, castor oil and salad oil. The volatile solvent includes known solvents of the type of mineral oils and vegetable oils.
The emulsifier to be added to the oil phase is used to form the water-in-oil (W/O) emulsion, and is preferably a nonionic surfactant. As examples of the surfactant, mention may be made of sorbitan higher-fatty acid esters such as sorbitan monolaurate, sorbitan monopalmitate and sorbitan sesquioleate, fatty acid glycerides such as oleic acid monoglyceride and oleic acid diglyceride, and ethylene oxide adducts of higher alcohols, alkylphenols and fatty acids.
When a colorant is contained in the water phase, the water phase of the ink may contain surfactants for dispersing the colorant or surfactants for forming the oil-in-water (O/W) emulsion. In this case, it is preferred to suitably select the emulsifiers so that the water-in-oil (W/O) emulsion is not destructed by the surfactants.
When the colorant is contained in the oil phase, it is preferred to add a resinous component to the oil phase in order to improve printability. As the resins, there may be used the above-mentioned resinous components such as alkyd resins, rosin-modified phenolic resins, maleic acid resins and rosins and, besides, phenolic resins and petroleum resins.
In the emulsion ink for stencil printing of the present invention, the water phase is basically prepared by dissolving in water the divalent or trivalent metal salt and the monovalent metal salt having alkalinity. The water phase may further contain an oil-in-water (O/W) emulsion of resin or a w
Okuda Sadanao
Yamada Hiromichi
Klemanski Helene
Pillsbury Madison & Sutro LLP
Riso Kagaku Corporation
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