Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1998-07-24
1999-08-24
Green, Anthony
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
106498, 106499, 106506, C09B 6742, C09B 6702, C09K 1900, C09K 1952
Patent
active
059420308
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for preparing pigments by applying a polymerizable mixture to a surface, orienting the liquid crystals present in the mixture, polymerizing the mixture, detaching the polymer film from the surface and comminuting the polymer film to form pigment particles, wherein the polymerizable mixture comprises:
a.sub.1) at least one chiral liquid-crystalline polymerizable monomer or
a.sub.2) at least one achiral liquid-crystalline polymerizable monomer and a chiral compound, and additionally
b) a polymeric binder and/or monomeric compounds which are converted by polymerization into a polymeric binder and/or a dispersion auxiliary.
The present invention additionally relates to pigments obtainable by this process, to coating compositions comprising these pigments, to the use of the pigments in emulsion paints and other surface coatings, to the use of the coating compositions comprising the pigments for coating commodity articles, especially vehicles, and to vehicles coated with these coating compositions.
Pigments having a cholesteric liquid-crystalline structure are of interest as special-effect pigments whose perceived color depends on the viewing angle. The perceived color arises through interference effects in a helical superstructure which is an essential feature of the cholesteric liquid-crystalline phase.
Pigments whose color depends on the viewing angle, which consist of oriented three-dimensionally crosslinked substances of liquid-crystalline structure with a chiral phase, and if desired of further dyes and pigments, are known from EP-B1-0 601 483. However, the brightness of color of these pigments is not fully satisfactory.
Prior German Patent Application 19 532 419.6 describes a process for the surface coating of substrates, in which the coating composition comprises liquid-crystalline polymerizable monomers, with or without chiral compounds which induce a cholesteric structure, and, in addition, a polymeric binder and/or monomeric compounds which can be converted into the polymeric binder by polymerization, or a dispersion auxiliary. These polymeric binders and dispersion auxiliaries facilitate the orientation of the liquid-crystalline compounds and enable spontaneous orientation to form the cholesteric liquid-crystalline phase merely by means of the coating operation.
It is an object of the present invention to discover a process for preparing pigments whose color depends on the viewing angle and which are particularly bright in color.
We have found that this object is achieved by the pigment preparation process described at the outset.
The novel process starts from a polymerizable mixture. Polymerizable in this context means that the monomers present in the mixture can be converted into polymers by various upbuilding reactions, for example chain addition polymerization, stepwise addition polymerization or condensation polymerization.
The polymerizable mixture is first of all applied to a surface, preferably a film or a rotatable roller. It is preferably applied in a thin coat with a thickness of between 1 and 100 .mu.. This coat thickness defines the maximum thickness of the pigments in the subsequent grinding process and also facilitates the grinding of the coat into plateletlike pigments. These plateletlike pigments are able to arrange themselves uniformly in thin coating films to give a uniform perceived color.
Liquid crystals with twisted cholesteric phases develop their optical properties only when the individual molecules are aligned in a helical superstructure. The formation of this superstructure occurs to some extent spontaneously, while in some cases the orientation has to be induced by the action of external forces.
Following application, therefore, the liquid-crystalline compounds are oriented in the coat. This is achieved most simply by means of the shear forces which act during application. However, orientation can also be effected by other known methods, such as knife coating, alignment layers or, for some liquid-crystalline systems, by means of el
REFERENCES:
patent: 5362315 (1994-11-01), Muller-Rees et al.
patent: 5683622 (1997-11-01), Kratzschmar et al.
Gomez Juan Antonio Gonzalez
Schneider Norbert
Schuhmacher Peter
Siemensmeyer Karl
BASF - Aktiengesellschaft
Green Anthony
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