Riso Kagaku Corporation

Hiromichi Yamada

Sadanao Okuda

Shoichi Ikejima

Hiroyuki Ogawa

Satoshi Nagashima

A water-in-oil (W/O) emulsion ink for stencil printing is provided which is prevented from pigment aggregation and thus excellent in ink fixability, high in printing density and less declining in printing density even after printing many sheets. The emulsion ink has a ratio by volume of the water phase to liquid components of the oil phase (i.e., volume of water phase/volume of the liquid components of oil phase) in a range of 1.0 to 3.5, preferably 1.0 to 3.0 at 23&deg; C. The liquid components of the oil phase may be composed of a resin, a solvent and a surfactant. The oil phase can contain a pigment at a ratio by volume of 0.19 or less to the total volume of the oil phase. The pigment preferably has an average particle size of 0.02 to 1.5 (&mgr;m). The water phase preferably has an average particle size of 0.1 to 1.0 (&mgr;m). The ink is suitable for containing particles of organic pigments with non-uniform shapes and a large average particle size like copper phthalocyanine blue and diaxazine violet.

Emulsion ink for stencil printing

Provided is a water-in-oil (W/O) emulsion ink for stencil printing which is less in change of viscosity with time and can give always stable prints. The emulsion ink contains a resinous component having a free carboxylic acid group or a higher fatty acid in the oil phase, and contains a divalent or trivalent metal salt and a monovalent metal salt having alkalinity in the water phase, whereby an interfacial layer of the emulsion is strengthened to stabilize the emulsion. The resinous component is preferably an alkyd resin, a rosin-modified phenolic resin, a maleic acid resin and a rosin. The monovalent metal salt or the divalent or trivalent metal salt is preferably contained in at least an amount equivalent to the free carboxylic acid of the resinous component and the higher fatty acid contained in the oil phase. The resinous component or the higher fatty acid is contained in an amount of 0.5-30% by weight based on the total amount of the emulsion ink.

There is provided a water-in-oil (W/O) emulsion ink for stencil printing having an oil phase and a water phase, the oil phase containing a reaction product of an alkyd resin or a rosin-modified resin with an aluminum chelate compound or an aluminum alcoholate. Preferably, the reaction is carried out by heating the aluminum chelate compound or aluminum alcoholate with the alkyd resin or rosin-modified resin to a temperature enough to lower the acid value of the resin to 10 or less, and the reaction is carried out in the presence of a higher fatty acid or a higher alcohol in an amount of 0.5-2.5 mols per 1 mol of on the aluminum chelate compound or aluminum alcoholate. This emulsion ink is improved in storage stability and inhibited from increase of viscosity of the ink after the ink is left, and restarting of printing after suspension of operation of the printing machine can be satisfactorily performed.

Growing community of inventors

Ibaraki-ken, Japan

Hiromichi Yamada