Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Staple length fiber
Reexamination Certificate
2002-10-22
2004-09-07
Kelly, Cynthia (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Staple length fiber
C428S359000, C428S375000, C428S378000, C428S391000, C428S392000, C428S396000, C428S297400, C428S300100
Reexamination Certificate
active
06787226
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to glass chopped strands (hereinafter referred to as CS) to be used for a molded product of BMC containing an unsaturated polyester as the main component of the matrix resin, and a molded product of unsaturated polyester resin BMC employing them.
2. Discussion of Background
Glass fibers are widely used as reinforcing fibers for the production of FRP. For industrial purposes, glass fibers are used in the form of glass fiber strands having a number of glass fibers withdrawn from bushing bundled, in many cases. It is common to have a sizing agent comprising a silane coupling agent and a film-forming agent, applied thereto to prevent thread breakage or fuzzing during their handling or production process (process for production of strands) thereby to improve the operation efficiency and to improve the affinity with the resin. The glass fiber strands thus produced, are dried and used as resin-reinforcing fibers. And, a bulk molding compound (BMC) having glass fibers dispersed in a resin, obtained by uniformly kneading cut products of strands (chopped strands, hereinafter referred to simply as CS) with a resin, is commonly used as a molding material for producing FRP. This molded product of BMC is widely used for various applications, because of merits such as the strength, heat resistance, dimensional stability, etc.
Among them, particularly for a molded product to be used for a reflecting mirror of a head lamp to be mounted on e.g. automobiles, it is common to employ a thermosetting resin, since it is necessary to be durable against a high heat generated from the lamp, and to use a molded product of unsaturated polyester resin BMC employing an unsaturated polyester as the main component of the matrix resin.
As such a molded product of unsaturated polyester resin BMC, for example, JP-A-5-293823 discloses, as a molded product of BMC having high strength while maintaining excellent characteristics of a molded product prepared by the BMC molding method, a molded product of BMC wherein glass chopped strands obtained by cutting a glass strand which is obtained by bundling a group of glass filaments having a sizing agent coated on the surface, are used as a reinforcing material, wherein the number of glass filaments constituting non-fibrillated glass chopped strands is at least 0.1% based on the total number of glass filaments, and wherein the solubility in styrene of the sizing agent is preferably at most 40%, and the time for impregnation of the unsaturated polyester resin is within 10 minutes.
However, when the molded product of BMC is used for e.g. the above-mentioned reflecting mirror for lamps, a primer is coated on the surface of the molded product of BMC after molding and then metal vapor deposition is applied as a reflecting film. Therefore, after coating a primer on the surface of the molded product, leveling and heat curing are required, whereby the molded product is exposed to a high temperature of at least 100° C. Accordingly, it is required that excellent smoothness is maintained even at such a high temperature.
However, if the molded product of BMC is heated after coating the primer, it has sometimes happened that due to the temperature increase by heating, air bubbles internally present in the molded product expand and migrate to the surface of the molded product, thereby to form defects on the appearance of the surface. Namely, when air bubbles are formed at the surface of the molded product, the primer coating film is pushed up by such bubbles to form bubble-like defects, thus impairing the outer appearance and leading to a decrease in the yield in the vapor deposition process.
Such air bubbles are attributable to air contained between CS and the matrix resin, and they are believed to be formed by the following mechanism depending upon the degree of the impregnation property of the matrix resin to CS or the nature of the sizing agent to bundle CS.
Firstly, in a case where the sizing component for CS is stiff, the matrix resin will not sufficiently penetrate into the interior of CS, whereby wettability between the filaments and the matrix resin can not adequately be secured in the interior of CS. Accordingly, an air layer will be present at the interface between the filaments and the matrix resin and will form air bubbles when subjected to heat treatment.
As such a stiff sizing agent, a urethane resin may, for example, be mentioned. In a case where the matrix resin is an unsaturated polyester resin, a styrene monomer is usually employed as a typical crosslinking agent, but a urethane resin is relatively hardly soluble in this styrene monomer. Accordingly, the urethane resin tends to be stiff as a sizing agent and thus tends to include air bubbles.
Accordingly, with the molded product of BMC as disclosed in the above JP-A-5-293823, although the strength can be improved by adjusting the number of glass filaments constituting non-fibrillated glass chopped strands to be at least 0.1% and adjusting the solubility of the sizing agent in styrene to be at most 40%, there is a problem that the solubility of the sizing agent is insufficient, and accordingly, no adequate wettability is secured between the matrix resin and the filaments in the interior of CS, and inclusion of air bubbles can not be avoided.
On the other hand, if the sizing component for CS is softened in order to improve the wettability (the impregnation property) between CS and the matrix resin, CS will be unbound into monofilaments during kneading with the matrix resin. By this unbounding into monofilaments, the volume of the kneaded product expands, and air will be included among the filaments. The air thus included in the material can not completely be removed at the time of molding and will remain in the resulting molded product thereby to form bubble-like defects.
Further, with respect to a question of strength, if the wettability of CS is improved, the flexural strength will be improved, but there will be a problem that deterioration in the impact strength will be observed.
As such a soft sizing agent, a vinyl acetate resin may, for example, be mentioned. The vinyl acetate resin has a high solubility in a styrene monomer, whereby the wettability between CS and the matrix resin will be improved, but by the above-mentioned phenomenon, air bubbles are still likely to form, and the impact strength will also be deteriorated.
In view of the foregoing, in order to let the BMC molding material containing an unsaturated polyester resin as the main component of the matrix resin include no air bubbles while maintaining the mechanical strength, the sizing agent for CS is required to have a proper wettability with the matrix resin and the respective filaments in CS and have a good integrity free from the volume expansion due to unbinding into monofilaments during the kneading of BMC. However, with conventional sizing agents, it has been impossible to satisfy both requirements simultaneously.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide CS having a good integrity and a proper wettability with a matrix resin containing an unsaturated polyester as the main component, so that a molded product of an unsaturated polyester resin BMC is free from air bubbles on the surface of the molded product even at a high temperature and has a property excellent in impact strength, and a molded product of an unsaturated polyester BMC employing such CS.
In order to solve the above problems, the chopped strands of the present invention, are chopped strands having a sizing agent impregnated to glass fiber strands, to be used for a molded product of unsaturated polyester resin BMC, wherein the sizing agent comprises a urethane resin, a vinyl acetate resin and a silane coupling agent, and wherein the mass ratio of the urethane resin to the vinyl acetate resin is from 30:70 to 70:30.
Thus, the sizing agent comprises an urethane resin and a vinyl acetate resin in a prescribed ratio, whereby proper wettability can be obtain
Daicho Hisayoshi
Endou Hideki
Iizuka Manabu
Niino Yoshirou
Tanaka Hideki
Asahi Fiber Glass Company Limited
Gray J. M.
Kelly Cynthia
LandOfFree
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