Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2001-03-13
2003-09-16
Harlan, Robert D. (Department: 1713)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S378000, C427S434600, C264S143000, C264S171240
Reexamination Certificate
active
06620507
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fiber-reinforced thermoplastic resin pellets that use natural discontinuous fiber as reinforcing fiber and a manufacturing method thereof. Furthermore, the present invention relates to the automobile parts manufactured using the pellets.
2. Description of the Related Art
Recently, fiber-reinforced resin in which vegetable fibers such as wood pulp, hemp, and hemp palm are used as reinforcing fiber has been actively developed. Nowadays, awareness of waste pollution has been increasing. The reason for this will be described hereinafter. Natural fiber does not cause waste pollution even if it is used for land filling as it is an environment-friendly material. In addition, when natural fiber is burnt, it generates a great deal of combustion energy allowing high energy recovery without causing secondary pollution such as residual ash or flue gas pollution.
However, natural fiber is a discontinuous fiber differing from continuous fibers such as glass fiber, carbon fiber, metal fiber, and various synthetic fibers that have conventionally been used as reinforcing fibers for fiber reinforced-resin. Therefore, a special technique is required to manufacture molding resin pellets mixed with natural fiber that exhibit the characteristics of long fiber. For example, a continuous fiber strand is impregnated in a molten resin bath continuously and pultruded, and cooled to solidify the resin and then cut into pellets of an arbitrary length. This method is widely used to manufacture fiber-reinforced resin pellets continuously with high productivity. However, even if discontinuous natural fibers are twisted into yarns, the strength of the spun yarns is insufficient to be processed in a molten resin bath, discontinuous fiber spun yarns are often broken due to the release of discontinuous fiber in the resin bath when the spun yarns are impregnated and pultruded in the molten resin bath. This makes it difficult to continue stable operation.
For example, methods for manufacturing fiber-reinforced resin pellets using discontinuous natural fiber as a reinforcing fiber described are proposed hereinafter, but the methods have both merits and demerits.
(1) A method in which natural fiber is kneaded to mix it homogeneously in molten thermoplastic resin using a roll kneader and then the mixture is cooled to solidify, and the product is crushed to form resin pellets (J-P-A No. 108161/1982). By applying this method, molding material in which discontinuous fiber is dispersed homogeneously in matrix resin is obtained. However, the molding material has disadvantages in that the handling process, including the molding process, is difficult and quality stability of the molded product is poor due to irregularity in the size of the resin pellet.
(2) A method in which discontinuous fiber is spun to form spun yarn, spun yarn is processed to form fabrics or wovens, nonwovens, or mats, the processed product is impregnated in a molten resin bath and then cooled to solidify, and the cooled product is cut into the product of a suitable configuration and size to form resin pellets. (J-P-A Nos. 28307/1983, 7307/1991, 30916/1991, and 41280/1997). This method is suitable for applications in which the product is used for secondary molded material such as a resin-impregnated sheet, but when the product is used in the form of a pellet, the product that has been cooled and solidified is cut into pellets of a suitable configuration and size, and the cutting process requires much working and results in a low productivity. Furthermore, the cutting process is involved in a problem of much loss, and dust generated in cutting process causes pollution of the working environment.
(3) A method in which molten resin and discontinuous fiber are kneaded using a kneader or a kneading extruder and then the molten mixture is extruded, cooled, and solidified to form a rod product, afterwards, the rod product is cut into pellets of an arbitrary length (J-P-A Nos. 146945/1987, 146947/1987, and 290453/1991). This method has disadvantages in that it is difficult to feed cotton-like fiber into a kneading extruder, and the reinforcing fiber is subjected to thermal deterioration when resin is heated for melt kneading, and reinforcing fiber is subjected to mechanical damage due to the kneading force. As a result, the reinforcing effect is poor. In particular, because heat decomposition usually begins at a temperature range of 150 to 180° C. in the case of vegetable fibers such as wood pulp and linen, thermoplastic resin that does not cause such problems must be selected for composite forming depending on the fiber type and kneading time. Therefore, the freedom in selection of matrix resin is limited. Furthermore, because such resin with a low melting point is generally not strong, the application of the fiber-reinforced resin molded product is naturally limited.
(4) A method in which composite fiber strands comprising reinforcing spun yarn and thermoplastic resin fiber is formed, and the composite fiber strand is heated to melt the thermoplastic resin fiber, it is cooled and solidified, and then the solidified product is cut into pellets of a suitable length (J-P-A No. 163002/1992). To apply this method, thermoplastic resin fiber is manufactured previously or mixed yarn containing reinforcing fiber and thermoplastic resin fiber is manufactured, the manufacturing process requires a lot of work, and this method is troublesome. Furthermore, insufficient impregnation can occur causing void defects depending on the heat melting conditions for melting the thermoplastic resin fiber.
(5) A method in which a reinforcing fiber strand is impregnated with molten thermoplastic resin, cooled and solidified, and then cut into pellets of a suitable length (for example, J-P-B Nos. 37694/1988, 57407/1994 and J-P-A Nos. 178411/1989, 119807/1992). This literature disclose a case where jute (linen fiber) can be used as a reinforcing fiber, however, they mainly disclose cases where continuous fiber is used as a reinforcing fiber. This literature does not reveal any detailed problem arising when discontinuous fiber is mixed with thermoplastic resin as a reinforcing fiber to form composite material.
The inventors of the present invention are interested in a natural discontinuous fiber that has attracted much attention as a reinforcing fiber in the above-mentioned known circumstances, and have developed a technique for manufacturing discontinuous fiber reinforced thermoplastic resin pellets that solve problems of conventional resin pellets as described hereinbefore caused in the manufacturing process of molding thermoplastic resin pellets consisting of a composite material containing reinforcing fiber in thermoplastic resin. Particularly, all the problems in the continuous manufacturing process, in quality stability (homogeneous impregnation and prevention of reinforcing fiber), and in the strength characteristic of the molded product are to be solved.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide discontinuous fiber reinforced thermoplastic resin pellets that satisfy the conditions required for continuous production, quality stability of the molded material (homogeneous impregnation and deterioration prevention of reinforcing fiber), and the strength characteristics of the molded product.
It is a further object of the present invention to provide natural fiber-reinforced thermoplastic resin pellets comprising thermoplastic resin and strand comprising a plurality of spun yarns of natural fiber twisted in a range from 10 to 200 turns/m, wherein the spun yarn is No. 5 to 80 counts in diameter.
It is yet another object of the present invention to provide a method for manufacturing natural fiber-reinforced thermoplastic resin pellets comprising the steps of: an impregnating step for impregnating in a thermoplastic resin bath, a plurality of spun yarns of natural fiber being No. 5 to 80 counts in diameter, a pultruding step for pultruding the spun yarns
Asai Toshihiro
Hirano Yasuo
Kadowaki Ryosaku
Harlan Robert D.
Kabushiki Kaisha Kobe Seiko Sho
Oblon, Spivak, McClelland, Maier & Neustadt PC
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