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
2000-11-06
2002-10-29
Cain, Edward J. (Department: 1714)
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...
C524S495000, C524S847000
Reexamination Certificate
active
06472462
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
This invention relates to a process for prebinding fiber materials by means of a pulverulent binder composition. It further relates to the use of the prebound fiber material for producing plastics moldings from fiber-reinforced unsaturated polyester resins or epoxy resins by laying up the prebound fiber material, saturating the fiber material with the unsaturated polyester resin or epoxy resin and forming the molding.
2) Background Art
High-strength sheetlike plastics parts such as, for example, automotive body parts, boat hulls and aircraft fuselages are known to be frequently produced from unsaturated polyester (UP) resins which are mechanically reinforced by means of glass, aramid or carbon fibers. The fibers are used in the form of wovens, nonwoven scrims or prebound fiber mats (=nonwovens). As part of the production process, the textile structures are draped in the molds and fully saturated with the liquid resin, and the prebinder present in the fiber mat is solubilized or dissolved by the styrene present in the UP resin. Consequently, the mats lose their intrinsic stiffness and become more readily conformable to the mold contours and at the same time the saturating of the fiber mats with the resin is speeded up.
The production process mentioned hitherto utilized thermoplastic polyester powders, especially polyester powders based on bisphenol A, as prebinders for the fiber mats. To this end, the bisphenol A polyester powders are sprinkled onto a previously laid glass web and melted during the subsequent oven trip, so that the glass fibers are bound by the molten polymer powder at their crossing points. The thusly prebound glass mats are then used for reinforcing UP resins. However, these prebinders have insufficient solubility kinetics in styrene monomers for certain applications.
A further important area of use for polymer powders is the prebinding of textile sheet materials for the purpose of shaping fiber mats before an injection resin is applied for example, for preforming prior to an RTM (=Resin Transfer Molding) process. What matters here in particular is to minimize fraying of the end-itemed fiber mat, to ensure the dimensional stability of a possibly preformed fiber mat and to avoid incompatibilities between preforming binder and injection resin.
AU-A 36659/89 describes a process for producing prebound fiber materials wherein glass fibers having two different lengths are bound with a triple combination binder comprising styrene-soluble polyester powder, polystyrene powder and polyvinyl acetate dispersion.
DE-A 2604544 describes styrene-soluble binders as unsuitable binders for consolidating fiber materials that are further processed using a thermoplastic melt. Instead, it recommends the use of hydroxyl- or carboxyl-containing polyacrylates prepared by solvent or bulk polymerization. Emulsion polymers are explicitly counseled against because the surface-active substances therein contaminate the binder and can lead to undesirable side-effects such as discoloration or thermal degradation.
EP-A 894888 discloses textile binders based on carboxyl-functional polymers which are used in combination with epoxide or isocyanate crosslinkers. Processes for producing prebound styrene-soluble fiber moldings are not discussed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a pulverulent prebinder which dissolves very rapidly in a styrenic UP resin, but which is also useful for prebinding in processes where it is the compatibility of the prebinder with the polyester resin which is the chief concern.
The present invention accordingly provides a process for prebinding fiber materials which comprises mixing a pulverulent binder composition comprising
a) a pulverulent copolymer obtainable by emulsion polymerization and subsequent drying of one or more monomers selected from the group consisting of vinyl esters, acrylic esters, methacrylic esters, vinylaromatics and vinyl chloride and 0.01 to 25% by weight, based on the total weight of the copolymer of one or more ethylenically unsaturated carboxyl-containing monomers, the copolymer having a glass transition temperature Tg or a melting point of above 35° C., and optionally,
b) at least one pulverulent compound containing at least two reactive groups capable of reaction with the carboxyl groups mentioned under a), and having a melting point of 35° C., blending with the fibrous material and spreading out the mixture, or sprinkling the pulverulent binder on the spread-out fiber material and then binding the fiber material by raising the temperature to 50° C. to 250° C.
The present invention further provides for the use of the prebound fiber materials for producing plastics moldings from fiber-reinforced unsaturated polyester resins by laying up the prebound fiber material, saturating the fiber material with the unsaturated polyester resin and forming the molding.
The present invention further provides for the use of the prebound fiber material for producing preformed sheetlike structures “preforming” and for the use of these preformed fiber materials for producing fiber-reinforced plastics moldings from liquid resins such as, for example, epoxy resins.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable copolymers are based on one or more monomers selected from the group comprising vinyl esters of unbranched or branched alkylcarboxylic acids having 1 to 15 carbon atoms, methacrylic esters and acrylic esters of alcohols having 1 to 10 carbon atoms, vinylaromatics such as styrene and vinyl chloride. Preferred vinyl esters are vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate and vinyl esters of alpha-branched monocarboxylic acids having 5 to 11 carbon atoms, for example VeoVa5® or VeoVa9® (Shell Products). VeoVa5® and VeoVa9® are the vinyl esters of 5 and 9 carbon versatic acids. Preferred methacrylic esters or acrylic esters are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate.
It is essential that the composition of the copolymers is chosen so as to produce a glass transition temperature Tg or a melting point greater than 35° C., preferably of 55° C. to 150° C. The glass transition temperature Tg and the melting point of the polymers can be determined in a conventional manner by means of differential scanning calorimetry (DSC). The Tg can also be estimated in advance by means of the Fox equation. According to Fox T.G., Bull. Am. Physics Soc. 1, 3, page 123 (1956): 1/Tg=x
1
/Tg
1
+x
2
/Tg
2
+. . . +x
n
/Tg
n
, where X
n
is the mass fraction (% by weight/100) of monomer n and Tg
n
is the glass transition temperature in degrees Kelvin of the homopolymer of monomer n. Tg values for homopolymers are recited in Polymer Handbook 2
nd
Edition, J. Wiley & Sons, New York (1975).
Preference is given to vinyl ester copolymers, styrene copolymers and acrylic ester copolymers. Particularly, preferred copolymers are vinyl acetate-ethylene, vinyl acetate-vinyl chloride, vinyl acetate-VeoVa5® and vinyl acetate-VeoVa9® copolymers which each contain 0.01 to 25% by weight of the carboxyl-containing monomer units mentioned and whose composition is chosen so as to produce the abovementioned glass transition temperatures Tg or melting points. Particular preference is also given to methyl methacrylate/butyl acrylate and styrene/butyl acrylate copolymers which each contain 0.01 to 25% by weight of the carboxyl-containing monomer units mentioned, and whose composition is chosen so as to produce the abovementioned glass transition temperatures Tg or melting points.
Suitable ethylenically unsaturated carboxyl-containing monomers are ethylenically unsaturated mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid. Carboxyl-containing comonomer units are preferably present in an amount of 0.01 to 1
Hashemzadeh Abdulmajid
Kohlhammer Klaus
Schmidt Claudia
Brooks & Kushman P.C.
Cain Edward J.
Wacker-Chemie GmbH
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