Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-12-22
2004-05-04
Shosho, Callie (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S405000, C524S556000, C524S801000
Reexamination Certificate
active
06730716
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to emulsion ink for stencil printing, and more particularly to stencil printing emulsion ink free from an emulsifier which forms a liquid crystal structure between the oil phase and the water phase.
2. Description of the Related Art
The stencil printing is a method of printing in which paper and the like is printed by transferring ink from one side of a stencil to the other side. Stencil printing ink has been improved from various viewpoints such as working properties including handling properties, printing properties and the like or film properties such as workability, drying characteristics, color, film strength, resistances to various factors and the like.
Various stencil printing emulsion inks which are improved in their storage stability have been proposed. For instance, in Japanese Unexamined Patent Publication No. 6(1994)-49401, there is disclosed an emulsion ink in which the HLB (hydrophilic-lipophilic balance) is set to 3 to 5.5 and the water phase is thickened. In Japanese Unexamined Patent Publication No. 6(1994)-145576, there is disclosed an emulsion ink in which the oil phase contains therein 0.5 to 5.0% of sorbitol fatty ester which is 12 to 24 in number of carbon atoms and is not larger than 7 in HLB. In Japanese Unexamined Patent Publication No. 6(1994)-220383, there is disclosed an emulsion ink in which the oil phase contains therein two kinds of emulsifiers, one being 0.1 to 3.0 in HLB and the other being 5.0 to 15.0 in HLB. In Japanese Unexamined Patent Publication No. 6(1994)-329970, there is disclosed an emulsion ink containing therein sorbitan fatty ester or glycerin-fatty acid ester which is 1.5 to 3.0 in HLB. Further, in Japanese Unexamined Patent Publication No. 7(1995)-150091, there is disclosed an emulsion ink in which the oil phase contains therein nonionic emulsifier not larger than 10 in HLB and water-soluble magnesium salt.
In the conventional emulsion ink, a nonionic emulsifier is employed as a means for improving the storage stability, and those in which ability of polyglycerol fatty-ester to form liquid crystal is utilized are prevailing.
Generally the emulsifier is adsorbed by an interface of an oil phase and a water phase under the balance of the hydrophilic nature and the lipophilic nature (hydrophobic nature) and greatly reduces the free energy (or surface tension) of the interface, thereby facilitating formation of emulsion. Though the majority of the emulsifiers forms emulsion adsorbed by the interface in monomolecular film, the polyglycerol fatty-ester is adsorbed by the interface in ploymolecular film, that is, in the case of the polyglycerol fatty-ester, a plurality of polyglycerol fatty-ester films are formed around a water phase of a W/O emulsion ink (or an oil phase in the case of an O/W emulsion ink) and a so-called liquid crystal structure is formed. It is conceived that this is the reason why highly stable emulsion ink is obtained by polyglycerol fatty-ester.
However, emulsion ink the storage stability of which is improved by formation of a liquid crystal structure involves a problem that penetration of the ink into the printed paper is slow since its water content is less apt to be evaporated due to the liquid crystal structure. Since printed papers are generally superposed one on another immediately after printing, slow penetration of the ink into the printed paper, which normally results in a long drying time, can involve offset (ink on the surface of one printed paper is transferred to the back side of another printed paper) and/or blocking (printed papers are bonded by ink on their surfaces).
Penetration of the emulsion ink into paper is mainly governed by the viscosity of the ink, the surface tension of the water phase, and separation of the water phase from the oil phase when the ink is transferred to the paper. Accordingly, in order to improve penetration of the emulsion ink into paper, the viscosity of the ink should be low, the surface tension of the water phase should be low and separation of the water phase from the oil phase should be rapid. However, when the emulsion ink forms a liquid crystal structure, the viscosity of the ink becomes high, the surface tension of the water phase is increased by superposed films and separation of the water phase from the oil phase is slowed, whereby penetration of the emulsion ink into paper becomes very slow. That is, the emulsion ink which is improved with its storage stability by use of an emulsifier which forms a liquid crystal structure between the oil phase and the water phase cannot be rapid in penetration into paper. To the contrast, when the ability of the emulsion ink to form liquid crystal is weakened in order to improve penetration into paper, storage stability is deteriorated. That is, it has been difficult to make emulsion ink which is excellent in both storage stability and penetration into paper by use of the known emulsifiers.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide emulsion ink which is excellent in storage stability, penetration into paper and coloring material fixing performance.
The emulsion ink in accordance with the present invention comprises an oil phase component, a water phase component and alkyl-modified carboxyvinyl polymer and/or carboxyvinyl polymer.
The emulsion ink of this invention may contain alkyl-modified carboxyvinyl polymer or carboxyvinyl polymer alone or may contain both alkyl-modified carboxyvinyl polymer and carboxyvinyl polymer in combination.
Carboxyvinyl polymer is normally an acid high polymer of polymerized acrylic acids. The carboxyvinyl polymer may be a carboxyvinyl polymer salt. The alkyl-modified carboxyvinyl polymer is a polymer which is provided with the emulsifying ability by converting part of hydrophilic groups of the aforesaid carboxyvinyl polymer into hydrophobic groups. The alkyl-modified carboxyvinyl polymer or the carboxyvinyl polymer may be selected from those which are commercially available, but those which are small in change with time of viscosity and highly stable are preferred.
The alkyl-modified carboxyvinyl polymer and the carboxyvinyl polymer themselves normally lean toward acidity, whereas the stencil printing emulsion ink is generally kept neutral. Accordingly, the stencil printing emulsion ink of the present invention, it is preferred that the acidity of the alkyl-modified carboxyvinyl polymer and/or the carboxyvinyl polymer be neutralized. As a neutralization agent, an alkali such as borax, sodium hydroxide, potassium hydroxide, or ammonia may be used. From the viewpoint of fixation of the ink, borax is preferred. Borax is a water-containing borate mineral having composition represented by Na
2
B
4
O
7
·10H
2
O.
It is preferred that borax is contained in 0.001 to 2% by weight of the total weight of the ink, more preferably in 0.05 to 1.0% by weight, and most preferably in 0.01 to 0.5% by weight.
The content of the alkyl-modified carboxylvinyl polymer and/or the carboxyvinyl polymer is preferably 0.01 to 1% by weight, more preferably 0.01 to 0.6% by weight, and most preferably 0.2 to 0.4% by weight of the total weight of the ink irrespective of the kind of the alkyl-modified carboxyvinyl polymer and/or the carboxyvinyl polymer, or whether only one of the alkyl-modified carboxyvinyl polymer and the carboxyvinyl polymer is used or both the alkyl-modified carboxyvinyl polymer and the carboxyvinyl polymer are used in combination.
It is preferred that the ink is in the form of a W/O emulsion in which the content of the oil phase is preferably 20 to 40% by weight, more preferably 25 to 38% by weight, and most preferably 30 to 36% by weight of the total weight of the ink and the content of the water phase is preferably 60 to 80% by weight, more preferably 62 to 75% by weight, and most preferably 64 to 70% by weight of the total weight of the ink.
The emulsion ink of the present invention is excellent in storage stability, penetration into pa
Nixon & Peabody LLP
Riso Kagaku Corporation
Shosho Callie
Studebaker Donald R.
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