Compositions: coating or plastic – Coating or plastic compositions – Marking
Patent
1998-10-27
2000-05-23
Klemanski, Helene
Compositions: coating or plastic
Coating or plastic compositions
Marking
10628714, C09D 1102
Patent
active
060661992
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an emulsion ink whose consumption level is substantially constant with temperature. The ink is particularly useful on digital and stencil duplicators, but may also be useful in other printing applications, e.g. letterpress and silk-screen printing.
BACKGROUND OF THE INVENTION
Inks for use on digital duplicators and stencil duplicators are generally based on water-in-oil emulsions, although the use of non-emulsion inks is also known. Examples of conventional water-in-oil emulsion inks are disclosed in U.S. Pat. No. 5,378,739.
JP-A-6,128,516 discloses a water-in-oil emulsion ink for use in a stencil printing method and which has improved set-off properties. The ink includes a thermosetting or a hot-melting component in the oil phase and a siliccone oil in the aqueous and/or oil phase in an amount of 1 to 20% w/w based on the total ink. In the inks exemplified the amount of silicone oil in the oil phase is at most 21.6% w/w.
A disadvantage with such inks is that their consumption level is dependent upon temperature, and consequently they give varying print quality depending on the temperature of the operating environment. Aspects of print quality which relate to ink consumption, and therefore ink temperature, include print density, set-off and solid area infill.
EP-A-0,661,356 discloses a water-in-oil emulsion ink said to have improved temperature dependence. The ink contains a water-insoluble colouring agent in the aqueous phase thereby avoiding the need for a resinous dispersing agent in the oil phase. While a degree of temperature independence is achieved, this is only significant at the lower end of the normal operating range, and not over the whole range.
SUMMARY OF THE INVENTION
According to the present invention, an ink comprises a water-in-oil emulsion consisting of an aqueous phase and an oil phase, and a colouring agent, wherein the oil phase is a continuous phase and comprises at least 25% w/w of a silicone oil, and an emulsifier.
Provided that the silicone oil is present in sufficient concentration, the ink consumption in a digital or stencil duplicator, at least, is largely independent of temperature over the normal operating range, eg. around 10-35.degree. C.
DESCRIPTION OF THE INVENTION
The silicone oil used in the present invention is incapable of forming an emulsion in the absence of a suitable emulsifier. Any suitable emulsifier may be used, but preferably the emulsifier is a silicone-based emulsifier as better miscibility with the silicone oil and better emulsion stability can be achieved with an emulsifier of this type.
In its simplest form, the oil phase comprises only emulsifier and silicone oil. In this case, the Emulsifier is preferably soluble in the silicone oil, but this is not essential as simple water-in-silicone emulsions can be achieved with emulsifiers that are insoluble in the silicone oil; see for instance "A Guide to Formulating Water-in Silicone Emulsions with Dow Corning 3225C Formulation Aid", Dow Corning 1995. Examples of emulsifiers that are soluble in silicone oils are disclosed in U.S. Pat. No. 5,132,047, and comprise alkyl siloxane polymers modified by a polyether group, or other substituent, attached to one of the terminal silicon atoms thereof.
It may be desirable to include a third component in the oil phase, to alter the properties of the ink according to the printing application, or to increase the miscibility of the emulsifier with the silicone oil. In this case, it is essential that the silicone oil at least is soluble in the third component, so as to form a substantially continuous oil phase. Preferably, the emulsifier is also soluble in the third component.
Examples of emulsifiers that are immiscible with the silicone oil, either totally, or as a result of the proportions of these components in the oil phase, and with which it may be desirable to use a third component as described above, include alkyl siloxane polymers having polyether side chains, of the general formula: ##STR1## in which R i
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Adams John Christopher
Stotereau Peter James
G R Advanced Materials Ltd.
Klemanski Helene
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