Molding material and production process

Details Molding material and production process Molding material and production process

1998-07-15

2002-09-24

Cole, Elizabeth M. (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Noninterengaged fiber-containing paper-free web or sheet...

C428S300100, C428S300700, C428S301400, C428S297400, C428S373000, C428S375000, C428S376000, C428S377000, C428S397000, C428S293400, C428S296400, C428S296700, C428S297100, C428S368000, C428S370000

Reexamination Certificate

active

06455143

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a long fiber reinforced thermoplastic resin material. In more detail, the present invention relates to a molding material which can be easily produced and contains a reinforcing fiber bundle which is well dispersed. The molded product is obtained by molding such as injection molding. This invention also relates to a production process which produces a resin composition having good flowability. The invention also relates to molded products obtained from the process.
BACKGROUND ART
Fiber reinforced composite materials containing a continuous reinforcing fiber bundle, or containing relatively long discontinuous reinforcing fibers, as reinforcing fibers in a thermoplastic resin matrix, are publicly known. These composite materials have such features as high toughness, easy recyclability and short molding cycle because of the applicability of such molding methods as injection molding and stamping, but for several reasons have not been used so widely.
The reasons are as described below. It is well known that the impregnation of a molten resin into a fiber bundle is more difficult when the melt viscosity of the resin is higher. A thermoplastic resin that has excellent mechanical properties generally has a high molecular weight and a very high melt viscosity. A fiber reinforced composite material having such a high molecular weight thermoplastic resin as the matrix is confronted with problems of low productivity, and that the production cost is very high, since it is difficult to impregnate a fiber bundle into a thermoplastic resin. On the other hand, the use of a thermoplastic resin of low molecular weight (low viscosity), to allow easy impregnation, greatly lowers the mechanical properties of the composite material.
As a method for impregnating a continuous fiber bundle into a highly viscous thermoplastic resin, for example, a process called pultrusion is used, in which a fiber bundle is immersed, opened and rubbed in a molten resin, with pressure applied to the resin for mechanical impregnation. In such a method, for impregnation into a resin having a high viscosity, say, exceeding 500 poises, the fiber bundle must be taken up at a very low speed of 10 m/min or less. Several such mechanical impregnation methods are known, but they cannot fundamentally solve the problem of impregnation and do not allow a take-up speed of higher than tens of meters per minute.
Other proposed impregnation methods include a thermoplastic resin being diluted by addition of a solvent, to lower its viscosity, for impregnation with a continuous fiber bundle, and the solvent is removed in a subsequent step. A thermoplastic resin emulsion or dispersion can be impregnated by a continuous fiber bundle, and the medium is removed. A thermoplastic resin powder can be introduced into a fiber bundle in a fluidized bed, and heated and melted to achieve impregnation. However, it can be generally judged that these methods are only capable of low productivity.
On the other hand, methods for improving the problem of impregnability by modifying the surfaces of the fibers are also proposed. It is intended to improve the wettability between the fibers and the thermoplastic resin at the time of resin impregnation by modifying the surfaces of the fibers by applying a sizing agent or coupling agent, etc.
As one of these methods, Japanese Patent Laid-Open (Kokai) No. 61-236832 discloses that a composite material having improved mechanical properties can be obtained by introducing a second thermoplastic polymer between a standard thermoplastic polymer and fibers, for improving their wettability. However, this Kokai does not state the specific amount of the second thermoplastic polymer introduced between the standard polymer and the fibers, and does not clarify the effect of promoting impregnation, though it is stated that the product's mechanical properties can be improved when a thermoplastic polymer having low wettability is impregnated. Furthermore, even though the melt viscosity of the second thermoplastic polymer is referred to in the Kokai, specific ranges of molecular weights and melt viscosities of the second thermoplastic polymer are not specified, and it cannot be known whether the material productivity can be actually improved. Moreover, though this method can improve the wettability between the fiber bundle and the matrix, it is not stated at all whether the method is intended to improve the dispersibility of the reinforcing fibers in the molded product.
It is also attempted to achieve molding by impregnation of a thermoplastic resin with a reinforcing fiber bundle and dispersion of the fibers simultaneously by molding them into a final product form. This is for increasing the productivity of the thermoplastic composite material in the entire process ranging from the material preparation to molding. When a thermoplastic molding material is molded, usually a relatively high temperature and pressure are applied. For example, in the case of injection molding, the molding material is heated in a cylinder in the plasticization step, and kneaded and pressurized by a screw. Also, in press molding, a high temperature and pressure are also applied. This provides a relatively favorable condition for impregnating a fiber bundle into a thermoplastic resin. The idea of supplying a reinforcing fiber bundle and a high molecular weight thermoplastic resin destined to be a matrix, into a molding machine for achieving impregnation, fiber dispersion and molding simultaneously, has existed for a long time as direct injection molding. According to this method, it is not necessary to produce a molded material shaped like pellets in which fibers are impregnated with a resin. In such a case it can be considered that the productivity could be greatly improved. However, actually, for example in the case of direct injection molding, impregnation and fiber dispersion are not sufficient. Alternatively, to achieve sufficient impregnation and fiber dispersion, a molding machine having a special screw form to achieve extremely high kneading must be used. So, a general purpose injection molding machine cannot be used, and furthermore, when the material is powerfully or highly kneaded, the desirable long fibers are broken into short fibers by the existing high shearing force, and the molded product cannot manifest the intended high mechanical properties. As described above, there has been no long fiber reinforced thermoplastic composition material with excellent productivity and excellent molding, and also wherein the product has high mechanical properties.
It is publicly known to modify a thermoplastic resin using various additives. The use of an aromatic modified terpene resin as an additive is stated in Japanese Patent Laid-Open (Kokai) Nos. 2-199164 and 7-11066. In these techniques, it is intended to improve the adhesiveness or paintability of polyphenylene ether or polyolefin resin, which itself has poor adhesiveness or paintability. In the case of a polyamide resin, such modification is not required so much, since the resin has high adhesiveness and paintability. However, when a polyamide resin of high molecular weight is used, or when a polyamide resin containing a large amount of a filler or flame retardant to achieve a higher elastic modulus or higher flame retardancy is used, the flowability during molding often becomes insufficient. It has not been practiced to use a resin that is similar in structure to an aromatic modified terpene resin as an additive to improve flowability during molding without greatly impairing the physical properties peculiar to a polyamide.
An object of the present invention is to provide a fiber reinforced thermoplastic resin molding material, which allows easy impregnation of a low molecular (low viscous) thermoplastic resin (high productivity) and allows high mechanical properties to be achieved when a high molecular weight thermoplastic resin is used as the matrix, and which allows a high viscous matrix to be impregnated into the fibers when the material is

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