Plastic and nonmetallic article shaping or treating: processes – Formation of solid particulate material directly from molten... – With subsequent uniting of the particles
Reexamination Certificate
2002-02-12
2002-12-03
Weisberger, Rich (Department: 3624)
Plastic and nonmetallic article shaping or treating: processes
Formation of solid particulate material directly from molten...
With subsequent uniting of the particles
C264S005000
Reexamination Certificate
active
06488871
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fiber-reinforced resin molded article and a method of manufacturing the same, and more specifically to a lightweight resin molded article reinforced with glass fiber or like fibers, which has excellent rigidity, bending strength, impact strength, uniformity of strength, resistance to local stress and torsion, such as a fiber-reinforced resin molded article having a rib structure or a rib-like structure in the interior of the molded article. The present invention also relates to an efficient method for manufacturing the same.
2. Description of the Related Art
Conventionally, there has been known a fiber-reinforced resin molded article reinforced by addition of fibers such as glass fiber. Since the fiber-reinforced resin molded article is excellent in mechanical characteristics such as tensile strength and bending strength, and in heat resistance, it is widely used for automobile parts such as in-pane cores, bumper beams, door steps, roof-racks, rear quarter panels, and air cleaner cases, and for construction/civil engineering materials such as panels for external walls or partition walls, and cable troughs. In manufacture of these fiber-reinforced resin molded articles, there may be employed an injection molding method for injecting a fiber-containing molten resin into a cavity within molds. This injection molding method enables molding of an article having an intricate shape, as well as mass production of articles of the same shape since a predetermined molding cycle can be repeated continuously.
When the amount of the fiber added to the fiber-reinforced resin molded article manufactured through injection molding is increased in order to improve the strength and rigidity thereof, the article tends to gain weight and suffer severe warp. For the purpose of reducing the weight of the molded articles, as well as solving other problems, Japanese Patent Application Laid-Open (kokai) Nos. 7-247679, etc. disclose an expansion injection molding method in which a foaming agent is added to resin material and the material is foamed and molded into a molded article. However, in this expansion injection molding method, if a considerable amount of foaming agent is used for reducing the weight of the molded article, a sufficient expansion ratio is not easily obtained. Even if a sufficient expansion ratio is obtained, the appearance of the molded article is impaired due to foaming, large pores are easily formed within the molded article, and uniform pores are not easily formed therein. Therefore, mechanical requirements such as strength, rigidity, and impact resistance may not be sufficiently met, despite the molded article containing fiber for reinforcement.
To solve the above-mentioned problems, and to reduce the weight of molded articles while maintaining the quality of appearance and mechanical characteristics such as strength, rigidity, and impact resistance of the molded article, the following techniques have been proposed: (1) an expansion molding method in which fiber-reinforced resin pellets containing relatively long fiber are melted into molten resin and the molten resin is expanded during molding through utilization of the springback phenomenon caused by the contained fiber, to thereby obtain a lightweight molded article; (2) an expansion molding method in which a foaming agent for supplementing the expansion of resin is mixed into the fiber-reinforced resin pellets in item (1) above in order to further reduce the weight of molded articles (International Patent Publication WO97/29896). These methods sufficiently reduce the weight of molded articles without impairing the mechanical characteristics thereof, and are effective in reduction of the weight of fiber-reinforced resin molded articles.
As another method, there has been proposed (3) a method of manufacturing foamed resin molded articles in which a molten resin containing a chemical foaming agent is charged, through injection or injection compression, into the cavity of molds which comprise a movable core having a slit; the resin surface in contact with the mold is cooled and solidified without foaming; the capacity of the cavity is expanded by moving the movable core so as cause the molten resin to foam in the increased capacity of the cavity, to thereby manufacture a foamed resin molded article having a rib structure (Japanese Patent Application Laid-Open (kokai) No. 9-104043).
However, depending on the degree of weight reduction (expansion) or shape of a molded article; for example, in such a case in which the molded article has a large region or capacity, the molded article obtained through the above method (1) or (2) may have insufficient bending strength and rigidity, yet insufficient resistance to local stress, low uniformity of strength and resistance to torsion, requiring improvements. In the above method (3) using a foaming agent, expansion of the foaming agent is difficult to suppress at the time of injection. Especially, during injection molding with compressed pressure, the resin tends to foam at the time of injection due to reduction in resin pressure, resulting in silver marks on the surface of the resultant molded article. Also, at a high expansion ratio, large pores are formed within the foamed portion as shown in the Examples herein, resulting in a molded article of poor uniformity. Moreover, even if reduction of the weight is achieved, molded articles having sufficient strength are not easily obtained. Furthermore, since the foamed product comes to have closed cells, the cooling time of the resultant molded article is extended. As a result, the molding cycle is prolonged, which is a problem in productivity.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a fiber-reinforced resin molded article which has excellent bending strength, rigidity, impact strength, heat resistance, sufficient resistance to local stress and torsion, and uniformity.
Another object of the present invention is to provide a method of manufacturing such a resin molded article.
In view of the foregoing, the present inventors conducted careful studies on the overall structure—including the internal structure—of fiber-reinforced lightweight resin molded articles with dispersed pores therein and the properties thereof. As a result, they found that, in a conventional method in which a movable core is simply retracted for expansion, there is obtained a resin molded article having a non-expansion or low-expansion portion formed in the peripheral edge thereof, and near-uniform expansion occurs in other general portions such as the central portion thereof having a flat-shaped structure. They also found that if a molded article has a coarse-and-dense structure in terms of pores rather than the case in which pores are uniformly dispersed over the entirety of a molded article, and the molded article also has a unique rib-like structure by which a function of a rib is exerted between the two skin layers, the properties of the molded article are improved.
In connection with the method of forming the above-mentioned rib or rib-like structure within a resin molded article, the present inventors found firstly that if a grooved portion is provided in the thickness direction of a uniformly expanded portion, the grooved portion serves as a structure equivalent to a rib having a low porosity. They also found that the structure is attained through a method in which fiber-containing molten thermoplastic resin is injected into a cavity formed by a movable core which can advance and retract relative to the cavity of the mold and which has a protruding portion for forming a grooved portion of the molded article, and in which the movable core is subsequently retracted so as to expand the capacity of the cavity.
Secondly, they found that if a low- or non-expansion portion is formed through changing the degree of expansion relative to the uniformly expanded portion of the molded article having a substantially uniform thickness, the low- or non-expansion
Nomura Manabu
Sato Atsushi
Shima Toru
Idemitsu Petrochemical Co. Ltd.
Weisberger Rich
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