Fiber-reinforced resin molded article and method of manufacturing the same

Abstract: A fiber-reinforced lightweight resin molded article with pores has a portion having a porosity lower than that of other general portions. Such a low-porosity portion serves as a rib in the resultant molded articles, to thereby enables to provide a fiber-reinforced lightweight resin molded article having excellent rigidity, bending strength, impact strength, uniformity of strength, resistance to local stress and torsion. The present invention also provides an efficient method for manufacturing the fiber-reinforced lightweight resin molded article.

Description: 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. 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 W097/29896). 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). US-A-4,374,906 discloses a fiber-reinforced lightweight resin molded article having pores which comprises a grooved portion formed in the thickness direction of the molded article. EP-A-0,755,762 discloses a method for molding a fiber-reinforced resin article, whereby the mold comprises a moveable core which can advance and retract relative to the mold cavity. 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. It is therefore the object of the invention to provide an improved method for manufacturing a fiber-reinforced lightweight resin molded article having pores, which overcomes the before mentioned disadvantages. The above mentioned objects can be solved by a method according to claim 1. Advantageous embodiments of the invention are subject matter of the dependent claims. 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 region advantageously comes to substantially serve as a rib structure. They also found that the molded article having this structure can be manufactured through a molding method in which only the regions corresponding to the movable portions are expanded by use of a movable core which can advance and retract relative to the cavity and which has a plurality of cavity molding surfaces (movable core having a plurality of movable portions). Thirdly, the present inventors found that the properties of a molded article are improved if the structure of a uniformly expanded portion is changed so that the molded article attains a kind of rib structure in which substantially no or very few pores are formed in the thickness direction between the skin layers, and that such a molded article can be manufactured through provision of a slit on the cavity side of the movable core. Fourthly, the present inventors found that if a rib-like or dispersing-type protruding portion is formed on a uniformly expanded portion, the protruding portion exhibits reinforcement effects similar to those of a rib, and, in addition, that if a fiber-containing molten resin (thermoplastic resin) is expanded, the region corresponding to the protruding portion, i.e., the portion of the protruding portion plus the region of the body thereunder, obtains a low-expanded, i.e., low-porosity dense structure as compared to other flat portions. They also found that the molded article having this structure can be manufactured through a method in which fiber-containing molten resin is injected into a specific mold cavity, and one mold is retracted toward the direction in which the mold cavity is expanded. Based on the above findings, the present inventors have accomplished the present invention. According to the present invention, there is provided a fiber-reinforced resin molded article which has excellent bending strength, rigidity, impact resistance, heat resistance, sufficient resistance to local stress and torsion, and uniformity. Also, in the method of manufacturing the same according to the present invention, reduction in the weight of a molded article can be arbitrarily regulated by use of molds having relatively simple structure, and the excellent surface quality of a molded article can be obtained, for example, the flat structure of the exterior of a highly lightweight molded article can be maintained. FIG. 1 schematically shows a first embodiment of the method of manufacturing a fiber-reinforced lightweight resin molded article of a first mode in the present invention, wherein FIG. 1(A) shows a condition immediately before expansion of the cavity of the injection mold, and FIG. 1(B) shows a condition after the expansion. FIG. 2 schematically shows the second embodiment of the method of manufacturing the fiber-reinforced lightweight resin molded article of the first mode in the present invention, wherein FIG. 2(A) shows a condition before expansion of the cavity of the injection mold, and FIG. 2(B) shows a condition after the expansion. FIG. 3 schematically shows the third embodiment of the method of manufacturing the skin-integrated, fiber-reinforced lightweight resin molded article of the first mode in the present invention, wherein FIG. 3(A) shows a condition before expansion of the cavity of the injection mold, and FIG. 3(B) shows a condition after the expansion. The present invention will next be described in detail. The present invention provides a fiber-reinforced lightweight resin molded article which has a portion having a porosity lower than that of other flat (or general) portions; more specifically, a rib or rib-like structure in the interior of the molded article which contains pores therein, more specifically, a rib or rib-like structure in the thickness direction of the molded article. The present invention is directed to a fiber-reinforced lightweight resin molded article having therein pores, specifically dispersed pores, and a grooved portion in the thickness direction of the molded article, and more specifically to a fiber-reinforced lightweight resin molded article wherein a resin portion forming the grooved portion has a porosity lower than that of other flat portions. The first mode of the present invention is also directed to a method of manufacturing such a fiber-reinforced lightweight resin molded article in an efficient manner. In manufacture of the fiber-reinforced lightweight resin molded article having dispersing pores therein, a fiber-containing molten resin (thermoplastic resin) is injected or compression-injected into a mold cavity in order to fill the cavity with the resin, and then the mold cavity is expanded to the volume of a desired molded article. At this time, the molten resin is expanded to the desired volume by virtue of the springback phenomenon caused by tangled fibers contained therein. After cooling, the mold is opened, and there is obtained a fiber-reinforced lightweight resin molded article having dispersed pores therein. The manufacturing method is characterized in that a fiber-containing molten resin is injected into a mold cavity formed by a mold having a protruding portion for forming a grooved portion in the molded article, and then a movable core is retracted, while the protruding portion remains at its position, so as to expand the cavity, thereby completing the molding. In the general case where a single movable core having a simple shape, i.e., a surface shape identical with that of the entire cavity surface (in a flat shape) is used, there is obtained a fiber-reinforced lightweight resin molded article having a near-uniform expansion coefficient. Although the molded article is light, it has a larger area and volume. When the weight of the molded article is reduced further, the article may not attain sufficient strength and rigidity. In contrast, in the case in which there is used a movable core such that a gap exists between core and the side wall of a mold cavity, there is obtained a high-expansion-coefficient molded article which has a peripheral portion of 'non- or low expansion, and other non-peripheral portions, i.e., the central portion, are of uniform expansion. Since this molded article attains an unexpanded skin layer on its surface in contact with the wall of the molds under cooling, the molded article is lightweight and has high strength and rigidity. However, such a molded article having a three-layered structure composed of a skin layer/an expansion layer/a skin layer may fail to attain sufficient rigidity when its area and volume are large, and may have insufficient resistance to local stress and torsion. In order to solve these problems, the skin layers on the two surfaces are partially connected via a non- or low-expansion resin. Therefore, in the manufacturing method a fiber-containing molten thermoplastic resin is injected into a mold cavity formed by a movable core having a protruding portion for forming a grooved portion of a molded article, and then the movable core is retracted toward the direction in which the mold cavity is expanded. The shape and number of core(s) are properly determined according to the size and desired features of the molded article. The location, shape, size, number, distribution, etc. of the protruding portion(s) for forming the grooved portion are arbitrarily determined as appropriate in consideration of the shape, thickness, area, volume, degree of weight reduction, environment of use, and desired performance of the molded article. Generally, the grooved portion is provided in the reverse surface of the molded article and has a width of about 2-10 mm and a length of 10 mm or more. Preferably, the grooved portion is continuously or intermittently formed in any direction. The resin layer between the bottom surface of the grooved portion and the molded article surface at the opposite side is preferably a resin layer having substantially no or very few pores. Generally, the mold having the protruding portion for forming the grooved portion is a moving mold, and a movable core which can advance and retract therewithin and a fixed mold form a mold cavity. With this protruding portion provided in the movable core, injection of a molten resin and retraction of the movable core can be performed while the protruding portion is thrust into the cavity, and the cavity can be expanded to a predetermined volume while the protruding portion is fixed in position. Therefore, within a certain range of weight reduction, another protruding portion can be provided in the fixed mold facing the movable core. In the case in which a protruding portion is provided in the moving mold, the disposition of molds is designed such that a movable core can advance and retract within the moving mold having the protruding portion. Also, a gap may be provided in the protruding portion facing the movable core so that the gap forms a part of the mold cavity at the time of injection of a molten resin. With this structure, the shape of the surface of the protruding portion facing the cavity is transferred to a finished molded 'article so that the influence exerted by the subsequent retraction of the movable core is eliminated, and the skin layers are formed to be firm. Likewise, the position of the protruding portion when thrust into the mold cavity and that of the movable core when thrust into the same are determined as appropriate. Generally, they are determined so as to provide an appropriate clearance between the protruding portion and the surface of the mold facing thereto. Embodiments of the present invention will next be described with reference to the drawings. FIG. 1 schematically shows a first embodiment of the method of manufacturing a fiber-reinforced lightweight resin molded article according to the present invention. FIG. 1(A) shows a condition immediately before injection of a fiber-containing molten thermoplastic resin into an injection mold and subsequent.expansion of the cavity of the injection mold. FIG. 1(B) shows a condition after expansion of the cavity of the injection mold and before opening of the injection mold, i.e., a condition upon completion of forming of a molded article. In FIG. 1(A), numeral 1 denotes a fixed mold; numeral 2 denotes a moving mold; numeral 3 denotes a movable core; numeral 4 denotes a protruding portion of the moving mold 2; numeral 5 denotes a resin passageway; numeral 6 denotes a cavity; numeral 7 denotes a gas inlet; and numeral 8 denotes a gas outlet. Upon start of the manufacture of the fiber-reinforced lightweight resin molded article of the present mode, the fixed mold 1 and the moving mold 2 having the protruding portion 4 are clamped together. The movable core 3 is advanced into the cavity 6 so as to determine a cavity volume for injection. Specifically, the movable core 3 is advanced to a position where a clearance D1 is defined in the thickness direction of a molded article as shown in FIG. 1(A). In FIG. 1(A), the tip of the protruding portion 4 is aligned with the surface of the movable core 3. However, the positional relationship between the tip and the surface may be determined as appropriate according to an expansion coefficient of a molded article and an expansion coefficient of a portion of a molded article surrounding a grooved portion formed in the molded article. Similarly, the clearance D1 and the shape or the movable core 3 may be determined as appropriate according to the shape and a degree of lightness implementation of a final molded article. A fiber-containing molten thermoplastic resin is injected from the nozzle of an unillustrated plasticator into the cavity 6 in the above initial state through the resin passageway 5. Cooling of the injected molten resin begins from a portion in contact with the mold. Before the molten resin is completely cooled and hardened, the movable core 3 is retracted as shown in FIG. 1(B). Specifically, the movable core 3 is retracted to a position corresponding to a clearance D2, i.e., to a position where the cavity volume is expanded to førm a final molded article. The retraction of the movable-core 3 effects springback of entangled fibers which are contained in the molten resin, thereby causing expansion of the molten resin into the shape of the final molded article. In other words, the thus-generated expansion force causes the molten resin to be pressed against the mold surface and to be formed accordingly. During molding, the protruding portion 4 of the moving mold 2 remains still. As a result, a grooved portion corresponding to the protruding portion 4 is formed in the molded article. After cooling, the mold is opened, and the fiber-reinforced lightweight resin molded article is taken out from the mold. According to the present embodiment, the movable core 3 is advanced into the cavity 6 in the thickness direction of the cavity 6, followed by injection of the molten resin. Then, the movable core 3 is retracted to expand the injected molten resin. Being projected into the cavity 6, the protruding portion 4 functions to cool the molten resin as do the mold surface and the surface of the movable core 3. Cooling of the molten resin, or a reduction in temperature of the molten resin, causes an increase in viscosity of the molten resin. Thus, a cooled region of the molten resin is substantially disabled or limited in its expansion as compared to the remaining region of the molten resin. As a result, the molded article includes a coarse high-expansion region H1 and a dense low-expansion region L1. Because of the presence of the protruding portion 4, the dense region L1 is formed not only along the periphery of the' molded article but also along the grooved portion of the molded article. The structure formed of the grooved portion and the surrounding dense region L1 functions like a ribbed structure, thereby yielding an effect which would be yielded by the ribbed structure. The present embodiment requires injection into the cavity 6 of a molten resin having high expansibility, which depends on a required degree of lightness implementation of a molded article. Thus, as mentioned previously, fibers contained in an injected molten resin; for example, glass fibers, preferably have a long average length. Also, in order to obtain a molded article having a high porosity, a small amount of a foaming agent may be added to the material resin. The foaming agent complements an expansion force induced by springback phenomenon so as to bring the molten resin into close contact with the mold surface, thereby preventing the formation of sink marks. Also, after the movable core 3 starts to retract, gas having a relatively low pressure of not higher than 1 MPa may be introduced into the cavity 6 through the gas inlet 7 while the gas outlet 8 is closed. Alternatively, gas may be released from the gas outlet 8 while a gas pressure at the gas outlet 8. is maintained at a certain level. This promotes cooling of a molded article and prevents the formation of sink marks on the surface of the molded article. In contrast to isolated pores formed through use of a foaming agent for lightness implementation in a conventional method, pores formed in the fiber-reinforced lightweight resin molded article of the present invention are continuous by virtue of springback of entangled fibers which are contained in the molten resin. That is, pores are continuously formed along entangled fibers. Thus, the present invention is characterized in that gas can be introduced into a molded article while homogenizing an expanded portion of the molded article. Through introduction of gas into the molded article, the molded article can be cooled from inside as well, thus significantly shortening a molding cycle. A region of a molded article surrounding the grooved portion, which is formed in a molded article by the protruding portion 4, is of low expansion or non-expansion. In the case where gas is introduced into the cavity 6, pores are preferably formed in a molded article in a continuous manner throughout the molded article for permission of gas flow therethrough while the molded article has a low-expansion region. FIG. 2 schematically shows a second embodiment of the method of manufacturing a fiber-reinforced lightweight resin molded article according to the present invention. The second embodiment differs from the first embodiment of FIG. 1 in that when the movable core 3 is advanced, a side gap 9 is formed between the moving mold 2 and the movable core 3 and that the cavity 6 into which a molten resin is injected is defined by the mold surface, the surface of the movable core 3, and the surface of the projecting portion 4. Upon injection of a molten resin into the cavity 6, the molten resin is pressed under high pressure against the mold surface to thereby form a major outer surface of a final molded article along the mold surface, and is also subjected to cooling through the mold surface and associated solidification to some degree. Accordingly, when the movable core 3 is retracted, the outer surface, particularly the side surface, of a molded article is free of any adverse effect which would otherwise result from retracting of the movable core 3. The second embodiment imparts better appearance of the side surface to the molded article as compared to the first embodiment of FIG. 1. FIG. 3 schematically shows a third embodiment of the method of manufacturing a fiber-reinforced lightweight resin molded article according to the present invention. The third embodiment differs from the second embodiment of FIG. 2 in that a face material 10 is previously attached to the surface of the fixed mold 1 opposite the movable core 3. The third embodiment is adapted to manufacture a molded article having the face material 10 integrated therewith. Since the face material 10 is attached to the fixed mold 1, a side injection gate is employed for injection of a molten resin into the cavity 6. A molding method is substantially similar to that of the second embodiment except that the face material 10 is attached to the fixed mold 1; thus, the description thereof is omitted. Notably, in the above-described embodiments, in order to advance and retract the movable core 3, there is disposed, for example, a core-moving apparatus between the moving mold 2 and a moving-mold attachment bed. Next, the advantages and effects of the present invention will be specifically described by way of example. However, the present invention is not limited thereto. Example 1 Glass fiber-reinforced polypropylene pellets (65 parts by weight)(containing 3 wt.% maleic anhydride-polypropylene) comprising parallel-arranged glass fibers having a length of 12 mm in the amount of 60 wt.%, and polypropylene pellets (35 parts by weight) having a melt index of 30 g/10 min (MI: 230°C, under load of 2.16 kg) were dry blended, to thereby obtain molding material. An injection molding machine (clamping force: 850 t) comprising a screw having a compression ratio of 1.9 was employed in order to reduce the incidence of rupturing of the glass fibers. As shown in FIG. 2(A), while a movable core 3 having protruding portions was thrust into a cavity 6 for clamping (a clearance D1 between a fixed mold and the protruding portions of the movable core was 4 mm), the molding material was plasticized, weighed, and injected into the cavity. Two seconds after completion of charging of the molding material, the movable core 3 was retracted to the position as shown in FIG. 2(B) so that the molding material was extended, expanded, and cooled, to thereby obtain a plate-shaped (600 mm x 300 mm) molded article having a thickness (D2) of 8 mm (a grooved portion: 4 mm x 6 mm x 240 mm). The molded article was cut out, and the expansion was measured, showing an expansion coefficient of 2.0 at a high-expansion portion (H1). Also, the molded article was incinerated, and the mean fiber length of the remaining fibers was measured, and found to be 7.2 mm. The inner circumferential edge, peripheral edge, and surfaces of these edges of the grooved portion were formed of a dense layer having substantially no expansion. Especially, the grooved portion has a function of a rib. Example 2 Molding was performed by use of the molding material and injection molding machine used in Example 1, and the molds as shown in FIG. 3. A face material (ten-fold foamed polypropylene/polyvinyl chloride leather: 2 mm) was applied onto the surface of a fixed mold as shown in FIG. 3(A), while a movable core was thrust; a molten resin was injected while a clearance excluding the thickness of the face material (D1) was adjusted to 2 mm; and the movable core was retracted to the position where a thickness (D2) shown in FIG. 3(B) excluding the thickness of the face material is 12 mm so that the molten resin was extended and expanded. Two seconds after the start of the retracting of the movable core, nitrogen gas was charged, through a gas pin, under pressure of 0.8 MPa for 30 seconds. After cooling, the molds were opened, and a plate-shaped (12 mm (excluding the thickness of the face material) x 600 mm x 300 mm) molded article with the face material (a grooved portion: 10 mm x 8 mm x 250 mm) was removed. The molded article was cut out, and the expansion was measured, and an expansion coefficient of about 6 was found at a high-expansion portion (H1). Also, the molded article was incinerated, and the mean fiber length of the remaining fibers was measured, and found to be 6.9 mm. The inner circumferential edge, peripheral edge, and surfaces of these edges of the grooved portion were formed of a strong layer having substantially no expansion. Especially, the grooved portion has a function of a rib.

Claims: A method of manufacturing a fiber-reinforced lightweight resin molded article having a grooved portion in the thickness direction of the molded article, whereby the method comprises the steps of injecting a fiber-containing molten thermoplastic resin into a mold cavity (6) formed within a mold (1,2,3,4) having a movable core (3) which can advance and retract relative to the mold cavity (6) and also having a protruding portion (4) for forming the grooved portion in the molded article in the thickness direction of the molded article; and retracting the movable core (3) towards the direction in which the capacity of the mold cavity (6) is expanded. The method according to Claim 1, comprising injecting the fiber-containing molten thermoplastic resin into the mold cavity (6) formed by a fixed mold (1), a movable mold (2) having the protruding portion (4) for forming the grooved portion of the molded article, and the moving core (3) capable of advancing and retracting within the moving mold. The method according to Claim 1 or 2, wherein at the time of injection a part of the mold cavity (6) is defined by a gap (D1) between the protruding portion (4) of the moving mold and the movable core (3). The method according to any one of Claims 1 through 3, wherein a gas is injected (at 5) into the interior of the fiber-reinforced lightweight resin molded article within the mold cavity (6). The method according to any one of Claims 1 through 4, wherein the fiber-containing molten thermoplastic resin is injected into the mold cavity (6) on the surface of which a face material (10) is applied in advance. The method according to any one of Claims 1 through 5, wherein the fiber-containing molten thermoplastic resin is obtained by plasticizing and melting fiber-containing thermoplastic resin pellets having a length of 2-100 mm and contains parallel-arranged fibers having the same length in an amount of 20-80 wt.% with respect to the weight of the resultant resin-fiber mixture, or obtained by plasticizing and melting a mixture of the pellets and other pellets containing the fibers so that the amount of fibers is 10-70 wt.% with respect to the weight of the entirety of the mixture. A fiber-reinforced lightweight resin molded article obtainable by a method according to any of Claims 1 through 6. The article according to claim 7 having pores, which comprises a grooved portion formed in the thickness direction of the molded article. The article according to Claim 7 or 8, wherein a resin portion forming a grooved portion has a porosity lower than that of other general portions. The article according to Claim 7, 8 or 9, wherein the fiber is glass fiber, the fiber content is 10-70 wt.% with respect to the weight of the molded article, and the mean length of the fiber is 1-20 mm, the fiber-reinforced lightweight resin molded article according to any one of Claims 7 through 10, wherein a face material (10) is integrally molded with the molded article.

Inventors: ATSUSHI SATO, MANABU NOMURA, TORU SHIMA, ATSUSHI, SATO, MANABU, NOMURA, TORU, SHIMA
Applicants: IDEMITSU PETROCHEMICAL CO, IDEMITSU PETROCHEMICAL CO., LTD.
Application year: 1998
Main classification: B29C45
IPC codes: B29C44, B29C45