Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1999-04-26
2002-01-08
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S407000, C428S212000, C523S201000
Reexamination Certificate
active
06337131
ABSTRACT:
The present invention relates to core-shell particles whose shell is filmable while the core is essentially form-stable under shell-filming conditions and whose core and shell materials differ in refractive index, to their preparation and to preparations of these particles.
This invention further relates to the use of these particles and their preparations for preparing organic effect colorants which, in a continuous matrix phase, the filmed shell material, have at least domains of regularly arrayed cores of the core-shell particles. This invention finally relates to the use of the core-shell particles of the invention or of the preparations mentioned for preparing decorative and/or protective coatings, and to the preparation of paints and inks, including printing inks, comprising the core-shell particles of the invention as latent effect colorants.
Polymeric core-shell particles have been recommended for preparing adhesives, binder systems and especially also as reinforcing materials in the production of certain groups of composite materials. Such composite materials are composed of a polymeric matrix with embedded reinforcing elements. One problem with making such materials of construction is to establish a positive bond between matrix and reinforcing materials. Such a bond is necessary if forces are to be transferred by the matrix to the reinforcing elements. The greater the difference in the mechanical properties of matrix and reinforcing materials, elasticity, hardness and deformability, the greater the likelihood of the matrix becoming detached from the reinforcing elements. This danger is to be confronted by sheathing the polymeric reinforcing particles with a second polymer material which is more similar to the matrix material and therefore able to enter a stronger bond with the matrix (Young-Sam Kim, “Synthese und Charakterisierung von mehrphasigen polymeren Latices mit Kern/Schale-Morphologie”, University of Karlsruhe thesis, Verlag Shaker Aachen, (1993), pages 2-22). It has also been recommended that the sheathing polymer be grafted onto the reinforcing polymer so as to use covalent bonds to stop the shell becoming detached from the reinforcing particles (W.-M. Billig-Peters, “Kern-Schale-Polymere mit Hilfe polymerer Azoinitiatoren”, University of Bayreuth thesis (1991)).
The specific preparation of core-shell polymers is generally effected by stepwise emulsion polymerization, a first step of preparing a latex of core particles and a second step of preparing the shell polymer, the core particles acting as “seed particles” onto whose surface the shell polymers become preferentially deposited.
The deposit can grow into a more or less symmetrical shell on the core particles, but it is also possible for irregular deposits to take place, the structures formed having a blackberrylike appearance. A good overview of the preparation of biphasic polymer particles and related phenomena, especially the formation of core-shell particles, may be found in the thesis of Katharina Landfester, “Synthese und Charakterisierung von Kern-Schale-Latices mit Elektronenmikroskopie und Festkörper-NMR”, University of Mainz (1995).
Effect colorants are colorants whose color, lightness and/or reflectivity vary with the viewing angle. They generally have a platelet-shaped structure, i.e., the thickness of the pigment particles is distinctly less than their lateral dimension.
Well known examples of effect colorants are aluminum flakes or pigments which are commercially available under the names of ®Mica, ®Iriodin or ®Paliochrom.
Metallic effect pigments, e.g., aluminum flakes, create a specular effect when viewed perpendicularly; there is no specular effect when viewed from the side. The result is therefore a light-dark effect. The same phenomenon is obtained with mica-based effect pigments.
Iriodin and Paliochrom pigments further have augmented interference effects or self-absorption. As well as the light-dark effect, they are also observed to shift somewhat in hue with the viewing angle (reference: Dr. U. Zorll, Perlglanzpigmente, Vinantz Verlag, ISBN 3-87870-429-1).
U.S. Pat. No. -4,434,010 discloses inorganic pigments which give rise to very pronounced color flops. These pigments are characterized by an extremely homogeneous construction composed of layers having different refractive indices. This construction leads to pronounced interference effects, which are utilized for color creation. However, the making of these pigments is difficult and only possible by means of complicated and costly production processes.
U.S. Pat. No. -5,364,557 discloses organic effect pigments based on cholesteric liquids. Here, an interference effect is obtained from a helical superstructure. Again, the necessary starting materials are complicated to produce and hence very costly. The pigments are produced from cholesteric liquid crystals (CLCs) by applying the cholesteric material to a carrier web in a thin layer, conducting a photochemical polymerization in the CLC phase, detaching the resulting film from the web, and grinding the detached film. As well as the costlier production of the starting materials, this process has a very serious disadvantage in that, during the production process, very great attention has to be paid to the orientation of the CLCs, since even minuscule impurities can have an adverse effect on it.
A process for coating and printing substrates by utilizing cholesteric liquid crystals is known from WO 96/02597. In this process, one or more liquid crystal compounds, of which at least one is chiral and which have one or two polymerizable groups, are applied to a substrate together with suitable comonomers—and additionally a dispersant if the mixture is applied by printing—and copolymerized.
The layers thus obtained, if they are brittle, can be detached from the substrate, comminuted and used as pigments. Furthermore, aqueous monodisperse polymer dispersions are known, for example from T. Okubu, Pro-. Polym. Sci. 18 (1993) 481-517; and W. Luck, H. Wesslau, Festschrifi for Carl Wurstier, BASF 1960, C.A.:55:14009d, which in liquid form, if necessary after purification, tend to pronounced latex crystallization and thereby lead to color effects.
A multiplicity of publications are known regarding the field of the preparation of monodisperse particles, for example EP-A-0 639 590 (preparation by precipitation polymerization), A. Rudin, J. Polymn. Sci., A:Polym. Sci. 33 (1995) 1849-1857 (monodisperse particles with core-shell structure), EP-A-0 292 261 (preparation by addition of seed particles).
EP-A-0 441 559 describes core-shell polymers having different refractive indices in the layers and their use as additives in paper coating comnpositions.
More recently, heat-controlled optical switching elements have been disclosed (SCIENCE 274 (1996), 959-960), which utilize the temperature dependence of the particle size of poly(N-isopropylacrylamide) dispersions or of the volume/temperature relationship of poly(N-isopropylacrylamide) gels. A first embodiment of these switches consists of an aqueous poly(N-isopropylacrylarnide) dispersion whose particles form a lattice-shaped arrangement and are significantly larger below the phase transition temperature than thereabove. The consequence is that the absorbance at about 530 nm increases steeply within the temperature range between 10 and 40° C. The system thus acts as an optical switch and limiter.
In a second embodiment, highly charged polystyrene particles which form a spatial lattice are embedded in a poly(N-isopropylacrylamide) hydrogel. A change in temperature will alter the volume of the hydrogel and hence the lattice spacing, of the polystyrene particles. The consequence is that the position of the absorption maximum shifts from about 700 to about 460 nm when the temperature changes from about 10 to about 40° C. This system can be used as a tunable optical filter. These materials are naturally unsuitable for use as colorants or pigments.
It is an object of the present invention to provide a material from which organic effect colorants are simple and i
Leyrer Reinhold J
Rupaner Robert
Schuhmacher Peter
BASF - Aktiengesellschaft
Le Hoa T.
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