Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Forming plural articles
Patent
1999-03-22
2000-10-24
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Forming plural articles
B29B 910
Patent
active
061362514
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to a process for preparing pigment particles of defined size and shape by treating a sheetlike structure having through openings of defined shape and size with a polymerizable substance or mixture of substances in such a way that the openings are filled, removing any solvent present, polymerizing the substance or substance mixture, and isolating the resulting pigment particles from the openings.
Pigments are customarily prepared by precipitation reactions or by mechanical comminution of larger colored species. These methods of pigment preparation give rise to pigment particles differing in shape and size.
Prior German Patent Applications 19532419.6 and 19602795.0 describe processes for preparing pigments having a cholesteric liquid crystalline order structure by printing processes. This process makes it possible to obtain pigment particles of uniform shape.
To manufacture high quality pigment coatings, especially those with interference based color effects, it is advantageous to use pigment particles of defined uniform shape and size. However, obtaining a suitable thickness by printing is prohibitively complicated.
It is an object of the present invention to provide a process for preparing pigment particles of defined shape and size where the thickness is easily adjusted.
We have found that this object is achieved by the process of this invention.
Suitable sheetlike structures having through openings preferably include flexible structures such as wovens and especially nets. The sheetlike structures can be formed for example from natural or synthetic threads or metal wires, specifically from materials such as polyolefins, polyamides, polyesters or fluorinated polyolefins and wires composed of in particular stainless steel, for example.
Particularly suitable sheetlike structures are nets suitable for screen printing for example.
The mesh size determines the geometry of the pigment particles to be prepared, the size of these particles being advantageously within the range from 15 to 200 .mu.m edge length, preferably within the range from 20 to 100 .mu.m edge length.
The treatment of the sheetlike structures with the polymerizable substances can be effected for example by dipping, knife coating or saturating and squeezing off. It is also possible to apply the polymerizable mixture to a support, for example a continuously circulating smooth support film, and then transfer it to a continuously circulating netlike film. The voids in the net and the polymerizable mixture become filled [sic]. It can be advantageous in this connection to provide the sheetlike structures ahead of this treatment with agents which facilitate ready separation of the pigment particles from the substrate. Such agents include for example polyvinylpyrrolidones, vinylpyrrolidone copolymers, silicones, surface-active substances, long-chain fatty acids or esters or fluorosurfactants. The choice of sheetlike structure also determines the release agents which are most suitable for the specific substrate. The polymerizable substances can be applied as an aqueous dispersion or solution, for example.
It is advantageous to employ readily removable solvents, for example tetrahydrofuran, dioxane, butyrolactone, esters such as methyl acetate, ethyl acetate or butyl acetate, ketones such as cyclohexanone, acetone, methyl ethyl ketone or diethyl ketone or hydrocarbons such as toluene. It is also possible to use halogenated alkanes such as methylene chloride, ethylene chloride, chloroform or carbon tetrachloride.
The removal of the solvent can be effected by evaporation at room temperature or elevated temperature, if necessary under reduced pressure. The temperatures have to be chosen so that unwanted thermal polymerization does not occur.
Substances which can be converted into pigment particles are in particular dyes and liquid crystalline compounds having polymerizable groups, which become pigments on polymerization. However, it is also possible to use dyes or liquid crystalline compounds in combination with polymeriz
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K. Venkataraman, "The Chemistry of Synthetic Dyes", vol. VI, Academic Press, New York, London, 1972, pp. 213-297.
L.Shettleworth, et al., Edited by David R. Waring and Geoffrey Hallas, "The Chemistry and Application of Dyes", pp. 107-118, Plenum Press, New York, London, 1990.
Ullmann's Encyklopaedie der technischen Chemie, 4 th edition, vol. 17. p. 469.
Etzbach Karl-Heinz
Faust Tillmann
Keller Harald
Leyrer Reinhold
Schuhmacher Peter
BASF - Aktiengesellschaft
Theisen Mary Lynn
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