Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-02-16
2002-02-19
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C525S329500
Reexamination Certificate
active
06348538
ABSTRACT:
The invention relates to a method for the preparation of pigmented curable polyester molding compounds which contain an unsaturated polyester, copolymerizable monomers, a thermoplastic polymer and a color pigment.
Curable unsaturated polyester compounds such as SMC (sheet molding compound) and BMC (bulk molding compound) frequently are to be cured to form homogeneously pigmented moldings. To this end, pigments are added to the compound either in pure form or in the form of a premixture (hereinafter called ‘color paste’). Known color pastes comprise pigment particles dispersed in a suitable carrier resin. Suitable carrier resins are for instance unsaturated polyesters of low viscosity, such as described in U.S. Pat. No. 4,009,225 for instance, or a polystyrene carrier resin, functionalized with oxazoline groups, such as described in EP-A-272 127. Color pastes are used since it is extremely difficult under the usual conditions to disperse pigment particles directly in a uniform and homogeneous manner into other substances, such as for instance thermoplastic and/or thermosetting resins.
Although with the method as described in U.S. Pat. No. 4,009,225 reasonably homogeneous pigmented moldings can be obtained there is a need to further improve the uniformity of the perceived color of the molding surface. Moreover the intensity of the color and the range of possible color shades must be improved in an economically feasible way.
The aim of the present invention therefore is to provide a simple and inexpensive process for preparing homogeneously and uniformly pigmented curable molding compounds with a high color intensity and a wide range of color shades.
This objective is achieved by a process for preparing a pigmented curable molding compound comprising mixing together
A. an unsaturated polyester resin, and
B. a thermoplastic polymer, in a weight ratio A:B of 0.4 to 10, the total of A and B being 100 parts by weight (pbw),
C. 3-40 pbw of a color paste,
D. 0-450 pbw of a filler,
E. 0.2-4 pbw of a radical initiator, as well as
F. optionally further customary additives, characterized in that, the color paste C is obtained by preparing a solution of a thermoplastic polymer G in a suitable solvent H, and dissolving pigment particles in said solution.
By preparing the color paste according to the invention the dispersion of pigment particles in a molding compound containing the color paste is unexpectedly improved, and therefore also the uniformity of the perceived color.
An additional advantage of the method of the invention is that pigmented curable molding compounds of low-shrinkage (LS) and/or low-profile (LP) type can be obtained with unprecedented color homogeneity and uniformity. It is well known in the art (see for instance “Sheet Molding Compounds-Science and Technology”, Ed. Hamid G. Kia, Hanser Publ., page 69) that it is extremely difficult to provide homogeneous pigmentation for these LS and LP molding compounds, particularly in darker colors. The method according to the invention solves this problem, thereby providing molding compounds, which, when molded, produce moldings with a very smooth surface (Class A) and uniform color simultaneously.
The following remarks concern the individual components of the moulding compound according to the invention:
A. Unsaturated polyester (UP) resins are solutions of unsaturated polyesters in copolymerizable monomers, preferably in styrene. Suitable unsaturated polyesters are the usual condensation products of polybasic, in particular dibasic carboxylic acids and their esterifiable derivatives, in particular their anhydrides, which are bonded in the way of an ester with polyhydric, in particular dihydric alcohols, and which may additionally contain residues of monobasic carboxylic acids or monohydric alcohols, with at least part of the starting materials being provided with ethylenically unsaturated, copolymerizable groups. Preferred unsaturated polyesters are those on the basis of maleic anhydride and orthophthalic acid or isophthalic acid, on the one hand, and propylene glycol, ethylene glycol, diethylene glycol and/or dipropylene glycol on the other. If minor amounts of dicyclopentadiene have been incorporated in the UP resin during the condensation process, the viscosity of the resin will be lower.
B. The moulding compound contains, relative to 100 pbw of UP resin, 10 to 250 pbw, preferably 10 to 100 pbw, more preferably 20 to 80 pbw of a thermoplastic polymer. The thermoplastic polymer is added to control the polymerization shrinkage of the UP resin. Dependent on the particular shrinkage control achieved one speaks of LS-systems (linear shrinkage more than 0.05%) and of LP-systems (linear shrinkage equal to or less than 0.05%). The thermoplastic polymer B can be any thermoplastic known to be able to control the UP resin polymerization shrinkage. Suitable thermoplastics are for instance vinylaromatic polymers, such as polystyrene, polyolefinic polymers, such as polyethylene, acrylic-based polymers, such as polymethylmethacrylate, polyvinyl acetate polymers, saturated polyesters, and/or dual-thickening systems containing isocyanate prepolymers, and combinations thereof. Preferred are saturated polyesters based on adipic acid (optionally replaced up to 30 wt. % by other saturated dicarboxylic acids) on the one hand, and ethylene glycol, propylene glycol, diethylene glycol and/or dipropylene glycol (optionally replaced up to 30 wt. % by other diols) on the other. The molecular weight M
n
of the saturated polyesters is preferably between 1000 and 10,000. Up to 50%, preferably 5 to 40%, of the weight of the saturated polyester may be replaced by other thermoplastics, such as polymethylmethacrylate, polyvinylacetate and/or polystyrene. It is useful to apply component B in the form of a solution in a monomer that copolymerizes with A, e.g. styrene; it has proved to be advantageous if the viscosity of the solution at 23° C. is lower than 3000 mPa.s, preferably lower than 500 mPa.s.
C. The moulding compound comprises 3 to 40, preferably 5 to 25 pbw of color paste relative to 100 pbw of the total of UP resin and thermoplastic polymer (components A and B). The color paste according to the invention is prepared by dissolving pigment particles in a solution of a thermoplastic polymer G in a suitable solvent H. The color pigment used can be any commercially available organic and/or inorganic pigment, or a mixture of several of them. Suitable organic pigments are e.g. Phthalocyanine Blue, Perylene Red, Pyrazolone Yellow, Chromium-azo complex Red, Isoindolinone Yellow and/or Anthraquinone Red. Suitable inorganic pigments are e.g. Titanium Dioxide, Zinc Sulphide Iron (III) Oxide, Pink Red, Chromium (III) Oxide, Cobalt Blue and/or Ultramarine, as well as lead chromates, molybdates and Carbon Black. Preferred are those pigments that are not destroyed or damaged under the conditions of free radical polymerization and the usual molding conditions for thermosetting molding compounds, such as elevated temperature and pressure. Pigments being moreover resistant to the used solvent H in the color paste are particularly preferred.
D. Suitable fillers are for example customary finely pulverulent or granular inorganic fillers, such as chalk, calcium carbonate, kaolin, quartz powder, dolomite, baryte, metal powders, hydrated alumina, cement, talc, diatomaceous earth, sawdust, wood chips and the like. They are preferably present in the molding compound in amounts of 30 to 450 pbw, based on the total weight of UP resin and thermoplastic polymer (components A and B). In order to ensure flameproof properties, the resin paste preferably comprises aluminium oxide trihydrate, Al
2
O
3
.3H
2
O, as a filler.
E. The molding compound comprises 0.2 to 4, preferably 0.5 to 3 pbw of a radical initiator, preferably an organic peroxide, which decomposes into radicals, preferably in the range from 60 to 120° C., and is capable of initiating the polymerization of the UP resin.
E. Suitable further customary additives are well known to the person skilled in the art of preparing mold
Buhl Dieter
Fuerst Heinz
Schneider Harald
DSM N.V.
Mulcahy Peter D.
Pillsbury & Winthrop LLP
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