Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
1998-06-18
2001-05-01
Ahmad, Nasser (Department: 1772)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S499000, C106S500000, C106S505000, C106S506000, C252S299500, C528S50200C
Reexamination Certificate
active
06224664
ABSTRACT:
TECHNICAL FIELD
The invention relates to mixtures comprising pigments which comprise oriented three-dimensionally crosslinked substances having a liquid-crystalline structure with a chiral phase, and to the use of such mixtures.
BACKGROUND ART
Pigments comprising oriented three-dimensionally crosslinked substances having a liquid-crystalline structure with a chiral phase are known, for example, from DE 42 407 43 (corresponding to U.S. Pat. No. 5,362,315). These pigments have a color which is dependent on the viewing angle and can be employed in any desired media, such as coating materials, binders or plastics, for example. This is described at length in, for example, EP 0 686 674. A broad field of application is covered by such pigments in connection with the painting of articles such as motor vehicles, for example.
As noted in EP 0 724 005, pigments prepared in accordance with DE 42 40 743 exhibit changes in color if the paint comprising said pigments is processed at different stoving temperatures. This is the case, for example, with motor vehicle finishes.
In accordance with the state of the art, motor vehicles are OEM finished at 130° C., while in the case of subsequent refinishes just 80° C. is tolerated, since constructional elements of the motor vehicle can be damaged at higher temperatures. The color differences between the original finish and the refinish, resulting from the different stoving temperatures, are disadvantageous in that they can be recognized with the naked eye.
In order to solve this problem EP 0 724 005 A2 proposes crosslinking the starting substances specified in DE 42 40 743 for preparing the pigments together with further, color-neutral compounds comprising at least two crosslinkable double bonds. The intention of this is to raise the crosslinking density of the pigments, which is said to lead to greater color stabilities in the case of application in a 130° C. and an 80° C. motor vehicle paint system.
EP 0 724 005 A2 describes pigments prepared in this way which instead of the shift in the wavelength maximum which is commonly observed with the pigments prepared in accordance with DE 42 40 743 feature a shift of just 17-24 nm when comparing room temperature drying of the refinish versus stoving temperature at 130° C. and, at a temperature differential established between 80° C. and 130° C. drying temperatures, just 10-14 nm instead of the customary 20-25 nm. Consequently, by modifying the composition as described, EP 0 724 005 has reduced the wavelength difference by half, but by no means to values of a few nm. It is only at such low wavelength differences that—depending on the spectral sensitivity of the human eye—color differences can no longer be perceived visually. The problem of the deficient color stability of the pigment-containing compositions at different application temperatures therefore continues to exist.
SUMMARY OF THE INVENTION
The invention relates to a mixture comprising a matrix, and pigments which comprise oriented three-dimensionally crosslinked substances having a liquid-crystalline structure with a chiral phase, wherein pigment and matrix are matched to one another in such a way that on application of the mixture at different temperatures to a substrate, the lowest application temperature and the highest application temperature differing by at least 10° C. and by not more than 150° C., there are no visually perceptible color differences of the pigmented paint on the substrate after drying, and where alternatively, the pigments comprising oriented three-dimensionally crosslinked substances having a liquid-crystalline structure with a chiral phase are selected such that their glass transition temperature is either not more than 10° C. higher than the lowest application temperature or is higher than the highest application temperature, or the pigments based on oriented three-dimensionally crosslinked liquid-crystalline substances with a chiral phase are selected such that in the oriented three-dimensionally crosslinked liquid-crystalline substances they comprise no substances which are not chemically fixed, or the pigments comprise said substances which are not chemically fixed only in such low concentrations in the oriented three-dimensionally crosslinked liquid-crystalline substances with a chiral phase that under application conditions only from 0 to 3% by weight, based on the overall weight of the oriented three-dimensionally crosslinked liquid-crystalline substances with a chiral phase can be dissolved out, or the matrix material is selected such that it contains no component which dissolves out substances which are not chemically bonded to the oriented three-dimensionally crosslinked liquid-crystalline substances with a chiral phase of the pigments from the oriented three-dimensionally crosslinked liquid-crystalline substances with a chiral phase, or comprises only such a small amount of such components that under application conditions only from 0 to 3% by weight, based on the overall weight of the oriented three-dimensionally crosslinked liquid-crystalline substances with a chiral phase of the pigments are dissolved out. The mixtures of the invention are particularly suitable for the coloring of substrate surfaces.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In principle, all pigments comprising oriented three-dimensionally crosslinked substances having a liquid-crystalline structure with a chiral phase are suitable for use in a mixture of the invention. Such pigments are known, for example, from DE 42 40 743 (corresponding to U.S. Pat. No. 5,362,315).
Given the use of arbitrary binders, in each case customary for the respective application, as matrix materials and at a given application temperature, the selection of the pigments which are suitable in each case for the mixture of the invention is made on the basis of the glass transition point of the respective pigments.
The glass transition point of the pigments can be determined in conventional manner in accordance with ENCYCLOPEDIA OF POLYMER SCIENCE AND ENGINEERING, Vol. 7, pp. 531-544, ed. H. F. Mark, N. M. Bikales, C. G. Overberger, G. Menges, J. I. Kroschwitz; John Wiley & Sons, Inc. 1987. It is usually defined as the inflection point or midpoint of a broad glass transition range, whose breadth for liquid-crystalline polymers is typically a few 10° C. The difference between the temperature which arises in the course of application and the glass transition point essentially determines the time constant with which the color changes on application. Depending on the desired temperature range within which color stability is required, the selection of the pigments is made such that either pigments are selected whose glass transition point is not more than 10° C. higher than the lowest temperature which arises in the course of application of the mixture, or such that pigments are selected whose glass transition point is higher than the highest temperature occurring in the course of application of the mixture.
For the purposes of the present invention the term application temperature means the stoving temperature or drying temperature of the mixture of the invention on the surface of the substrate that has been coated with the mixture.
It is common knowledge with three-dimensionally crosslinked systems that complete reaction of all functional groups which can be incorporated into the network is not always able to take place under all reaction conditions, so that a proportion of such groups is present in unincorporated form in the network. Likewise, chemical reactions generally do not proceed without the formation of byproducts, so that in some circumstances the liquid-crystalline starting material may also include groups which contain no chemically reactive, polymerizable units which hence can be incorporated into the three-dimensional network that is to be constructed.
Under certain conditions, such molecules can be dissolved out of the network by, for example, binder constituents, additives or solvents having chemical affinity for the respective type of molecule, which may b
Hanelt Eckhard
Kreuzer Franz-Heinrich
Kupfer Jurgen
Leigeber Horst
Muller-Rees Christoph
Ahmad Nasser
Brooks & Kushman P.C.
Wacker-Chemie GmbH
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