JPH0739107B2 - Method for producing lightweight fiber reinforced thermoplastic resin molded article - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a lightweight fiber-reinforced thermoplastic resin for producing a fiber-reinforced thermoplastic resin molded product having a density of 0.92 g / cm ³ or less by molding while expanding and expanding a fiber-reinforced thermoplastic resin sheet. The present invention relates to a method for manufacturing a resin molded product. The lightweight fiber-reinforced thermoplastic resin molded product obtained by the method of the present invention is lightweight and is useful as various industrial parts such as automobile interior / exterior materials, low-electricity parts, civil engineering and construction materials that require high rigidity. .

[0002]

2. Description of the Related Art Conventionally, as a method for producing a molded article of a fiber reinforced plastic material, a method described in JP-A-60-179234 is known. The method has a length of 7
The weight ratio of the reinforcing fiber having a high elastic modulus of ˜50 mm is 20
By heating and molding a solidified sheet of thermoplastic synthetic resin in which ˜70% is dispersed, the fiber-reinforced synthetic resin molded article is expanded by expanding the matrix into the shape of the mold by the stress applied to the fibers to make it porous. The fiber-reinforced thermoplastic resin molded product obtained by such a method is a synthetic resin sheet molded product obtained by the method of solidifying wood powder or non-woven fabric fiber with resin, which is a competitive product and is still used today. No significant improvement was observed in the strength per weight, particularly in the flexural modulus, as compared with the product.

On the other hand, in recent years, from the viewpoint of improving the fuel efficiency of automobiles, there has been a strong demand for a lighter weight and higher rigidity molding material, and the product weight per unit area can be reduced as much as possible. It is becoming an important issue. However, although a lightweight molded product can be obtained by the above technique, a molded product having high surface rigidity has not yet been obtained. As a method for producing such a light-weight sheet molded article, Japanese Patent Publication No.
No. 2283 discloses a process for producing a foamed liquid medium containing a gas dispersed in a liquid containing a surfactant in the form of very small bubbles in a bubble generator, and dispersing fibers in the foamed liquid. A paper comprising the steps of: providing a dispersion of fibers and a foamed liquid medium onto a perforated support; and extracting the liquid from the dispersion through the support to form a fibrous material web on the support. Or in a method for producing other non-woven fibrous materials, the step of predetermining the volume percentage of the gas contained in the dispersion consisting of the fibers and the foamed liquid medium, and dispersing to the dispersion on the perforated support. Monitoring the dispersion as it is being injected to ascertain the volume percentage of gas in the dispersion, and controlling the operation of the bubble generating device according to the results obtained by the monitoring to produce a foamed liquid generated within the device. Method of making a non-woven fibrous material of the paper or other fibers, characterized in that it comprises a step of adjusting the volume percentage of liquid in the body have been proposed. However, the lightweight sheet molded product obtained by such a method is not one having high surface rigidity, and further improvement in strength has been desired.

[0004]

Therefore, according to the present invention,
Strength per weight, especially surface rigidity and flexural modulus, compared to conventional synthetic resin sheet molded products obtained by solidifying resin with wood flour or non-woven fiber using fiber reinforced thermoplastic resin sheet manufactured by papermaking method. It is intended to provide a lightweight and high-rigidity molding material which is excellent in respect of the above and has been significantly reduced in weight to the extent that conventional techniques cannot achieve.

[0005]

[Means for Solving the Problems]

[Summary of the Invention] As a result of intensive studies conducted by the present inventors in view of the above problems, a fiber-reinforced thermoplastic resin sheet obtained by dispersing reinforcing fibers in a thermoplastic resin matrix is provided. A light weight fiber-reinforced thermoplastic resin molded product which is heated to a temperature equal to or higher than the melting point to reduce stress applied to the fibers, expands and expands in the thickness direction of the sheet, and then moves the sheet to a molding die for molding. In the production method of, the thermoplastic resin of the matrix has a melt flow rate of 50.
By using the crystalline polypropylene of g / 10 minutes or more, the viscosity of the thermoplastic resin at the time of heating is reduced, the elastic force of the reinforcing fibers is restored, and the fiber-reinforced thermoplastic resin sheet is expanded and expanded. Based on the finding that it is possible to obtain a lightweight and highly rigid sheet molded product with significantly reduced weight by utilizing the mechanical properties of crystalline polypropylene after solidification and the small specific gravity. The invention has been completed. That is, the method for producing a lightweight fiber-reinforced thermoplastic resin molded product according to the present invention has a length of 6 to 50 m.
30 to 30 m of reinforcing fiber in the thermoplastic resin matrix
A fiber-reinforced thermoplastic resin sheet dispersed in a proportion of 70% by weight is heated to a temperature equal to or higher than the melting point of the thermoplastic resin to reduce the stress applied to the fibers, thereby increasing the thickness of the sheet by 3 to 8 times. In the method for producing a lightweight fiber-reinforced thermoplastic resin molded product having a density of 0.92 g / cm ³ or less, which is obtained by expanding and expanding and then moving the sheet into a mold to perform compression molding, melt flow into the thermoplastic resin of the matrix It is characterized by using crystalline polypropylene having a rate of 50 g / 10 minutes or more.

[Detailed Description of the Invention] [I] Production of Fiber Reinforced Thermoplastic Resin Molded Product (1) Fiber Reinforced Thermoplastic Resin Sheet Used as a starting material in the method for producing a lightweight fiber reinforced thermoplastic resin molded product of the present invention. The fiber-reinforced thermoplastic resin sheet to be obtained is a matrix of crystalline polypropylene obtained by mixing reinforcing fibers having a length of 6 to 50 mm and crystalline polypropylene having a melt flow rate (MFR) of 50 g / 10 minutes or more. 30 to 70% by weight of reinforcing fibers
The density is 1 g / c.
m ³ or more, preferably 1.1 to 1.3 g / cm ³ sheet-like material. As such a fiber-reinforced thermoplastic resin sheet, those obtained by the following raw materials and manufacturing method are generally used.

(A) Raw Material Thermoplastic Resin The thermoplastic resin used as the matrix of the fiber-reinforced thermoplastic resin sheet includes a melt flow rate (J
It is important to use crystalline polypropylene having an IS-K7210) of 50 g / 10 min or more, preferably 55 to 200 g / 10 min. As described above, in the present invention, by using crystalline polypropylene having a high melt flow rate for the thermoplastic resin that is the matrix, it is possible to maintain good impregnation of the reinforcing fiber and the thermoplastic resin, and When the plastic resin sheet is heated above the melting point of crystalline polypropylene that is the matrix component, the expansion of the sheet can be performed uniformly. Further, crystalline polypropylene has an advantage that the heat resistance characteristics (for example, heat distortion temperature) can be remarkably improved by blending reinforcing fibers. The crystalline polypropylene used as the matrix component of the fiber-reinforced thermoplastic resin sheet of the starting material in the present invention specifically includes propylene homopolymer, propylene / ethylene random copolymer, and propylene / butene-1 random copolymer. Examples thereof include polymers, propylene-4-methylpentene-1 random copolymers, and propylene / ethylene block copolymers.

It is also possible to mix these crystalline polypropylenes with other thermoplastic resins to the extent that the object of the present invention is not significantly impaired. Examples of such other thermoplastic resin include polyolefin such as polyethylene, polyvinyl chloride, polystyrene, ABS, polyamide, polyoxymethylene, acrylic resin, polyester, polycarbonate, polyphenylene ether, polyether sulfone, polysulfone, polyether imide, Examples include polyether ether ketone, modified products and blends thereof. Further, additives, fillers, colorants, foaming agents, cross-linking agents and the like can be added depending on the purpose.

[0009] As the reinforcing fibers are dispersed in the crystalline polypropylene matrix of the fiber-reinforced thermoplastic resin sheet of the starting material in the strength fibers present invention, glass fibers, carbon fibers, inorganic fibers such as metal fibers, and plastics Fibers, synthetic fibers such as aramid fibers, and mixtures thereof can be mentioned, but glass fibers are particularly preferred. As the form of these reinforcing fibers, depending on the application, it is possible to use these monofilaments, strands, or a combination thereof, but further surface-treating these reinforcing fibers, A material impregnated with a modifier can be used. It is important to use a reinforcing fiber having a length of 6 to 50 mm, preferably 13 to 40 mm, which is used in the fiber-reinforced thermoplastic resin sheet as a starting material in the present invention. If the length of the reinforcing fiber is out of the above range, it is impossible to uniformly disperse the reinforcing fiber in the papermaking method, and further, the effect of the reinforcing fiber in the present invention, that is, the fiber-reinforced thermoplastic resin described later. When the resin sheet is heated above the melting point of the crystalline polypropylene that is the matrix, the sheet cannot be uniformly expanded, and it becomes difficult to obtain a molded article having sufficiently high rigidity. The thickness of the reinforcing fiber has a diameter of generally 3 to 100 μm ^φ , preferably 6 to
A 20 ^μmφ one is used.

Amount ratio The amount ratio of the crystalline polypropylene and the reinforcing fiber constituting the fiber reinforced thermoplastic resin sheet in mixing is 30 to 70% by weight, preferably 35% by weight of the reinforcing fiber in the sheet.
It is compounded in a proportion of ˜60% by weight and dispersed in the crystalline polypropylene present as a matrix, and the density of the entire sheet is usually 1 g / cm ³ or more, preferably 1.1 to 1.3 g / cm ^3. Has become. In the present invention, as the thermoplastic resin component in the fiber reinforced thermoplastic resin sheet, by using crystalline polypropylene having a high melt flow rate, it is possible to maintain good impregnation of the reinforcing fiber and the thermoplastic resin. Even if the melt flow rate of the crystalline polypropylene is less than 50 g / 10 minutes and the compounding amount of the reinforcing fiber is as low as 10 to 25% by weight, the rigidity of the molded product can be increased and the strength can be maintained as high as possible. . However, as the blending amount of the reinforcing fiber becomes higher, for example, when the blending amount exceeds 40%, the impregnation of the reinforcing fiber and the thermoplastic resin becomes insufficient and the blending amount of the reinforcing fiber becomes high. However, it is difficult for the expected rigidity and strength of the molded product to be sufficiently developed.

(B) Method for producing a fiber-reinforced thermoplastic resin sheet In the method for producing a lightweight fiber-reinforced thermoplastic resin molded article of the present invention, the fiber-reinforced thermoplastic resin sheet used as a starting material is a thermoplastic material which is the above-mentioned raw material. It is produced by mixing the crystalline polypropylene of the resin and the reinforcing fiber, various methods are known for its specific production method, and the fiber-reinforced thermoplastic resin sheet used in the present invention is produced by these various production methods. The obtained product can be used, but it is particularly preferable to use a stampable sheet manufactured by a wet method using a papermaking method.

An example of manufacturing a stampable sheet by a wet method using a papermaking method will be specifically described below with reference to FIG. Production of Stampable Sheet by Wet Method (Papermaking Method) Reinforcing fiber 1 such as glass fiber having a length of 6 to 50 mm and thermoplastic resin powder 2 are continuously charged into a liquid in dispersion tank 3. In the dispersion tank 3, stirring for uniformly dispersing the reinforcing fiber 1 and the thermoplastic resin powder 2 is performed. Next, the sufficiently stirred dispersion liquid is supplied by the pump 4 into the head box 6 installed above the mesh-shaped electric belt conveyor 5. A wet box 7 is installed below the mesh-shaped electric belt conveyor 5 below the head box 6.
The internal pressure is maintained at a negative pressure, and the dispersion liquid in the head box 6 is continuously sucked and dewatered through the mesh-shaped electric belt conveyor 5, whereby the electric belt conveyor 5
A non-woven material 8 is obtained in which the reinforcing fibers 1 and the thermoplastic resin powder 2 are uniformly dispersed on the top. And this non-woven material 8
After drying in a ventilation hot-air drying oven 9, the nonwoven fabric material 8 is heated on the double-belt conveyor continuous steel press 10 to a temperature higher than the melting point of the crystalline polypropylene as a matrix, and then pressurized / cooled. By doing so, a continuous fiber-reinforced thermoplastic resin sheet 11 in which the reinforcing fibers 1 are fixed by the melted thermoplastic resin 2 is obtained. Then, the fiber-reinforced thermoplastic resin sheet is wound on a reel 14 or the like, or cut into a predetermined length by a cutter 12 to obtain a mat-shaped fiber-reinforced thermoplastic resin sheet 13. At that time, it is usual that the fiber-reinforced thermoplastic resin sheets 11 and 13 have almost no voids inside, but the fiber-reinforced thermoplastic resin sheet 1 having a low density with some voids left.
It may be 1,13.

Further, in the production of a wet stampable sheet using the above-mentioned paper-making method, the reinforcing fibers are oriented in one direction for paper-making to obtain a thermoplastic resin sheet having a directional mechanical strength. You can also In the production of the fiber-reinforced thermoplastic resin sheet, it is produced by a wet method using a papermaking method, but the reinforcing fiber and the thermoplastic resin powder are directly mixed or stirred and dispersed, and the fiber-reinforced thermoplastic resin sheet A similar fiber-reinforced thermoplastic resin sheet can be manufactured by a dry method including a laminating method for manufacturing a.

(2) Heating (preforming) (a) Condition In the method for producing a lightweight fiber-reinforced thermoplastic resin molded product of the present invention, the fiber-reinforced thermoplastic resin sheet is prepared by the following molding (main molding). It is important to perform pre-molding by heating before heating. The conditions for pre-molding are heating at a temperature not lower than the melting point of the crystalline polypropylene as the matrix, preferably at a temperature of melting point + 20 ° C to melting point + 80 ° C. Is performed.

(B) Expansion Due to this heating, the fiber-reinforced thermoplastic resin sheet melts the fibers in the sheet and the crystalline polypropylene fixing the fibers to reduce the stress applied to the fibers,
3 to 10 times in the thickness direction of the fiber reinforced thermoplastic resin sheet,
It is preferably expanded 4 to 8 times to have a density of 0.92 g /
It is expanded to a value not higher than cm ³ , preferably 0.3 to 0.75 g / cm ³ . The higher the degree of expansion when heated, the higher the flexural rigidity of the finally obtained molded product. Further, in order to obtain a good lightweight fiber-reinforced thermoplastic resin molded product, after heating the fiber-reinforced thermoplastic resin sheet to a temperature equal to or higher than the melting point of the thermoplastic resin which is the matrix, and after expanding the sheet thickness as thick as possible, Molding to a predetermined plate thickness gives better molding dimensional stability. Therefore, in this preforming step, in order to expand the plate thickness as thick as possible and to increase the rigidity of the molded product and maintain the strength (for example, bending strength) as high as possible, the monofilament of the reinforcing fiber is more than the converged state. It is desirable that they are evenly stacked in a state. Therefore, the reinforcing fibers are uniformly stacked in a monofilament state, and the rigidity of the molded article is increased to maintain the strength (for example, bending strength) as high as possible. At the same time, it is necessary that the reinforcing fibers are well impregnated with each other, and at the same time, the contact points of the reinforcing fibers are expanded by being joined with a thermoplastic resin. However, if the weight ratio of the reinforcing fibers is too high, impregnation of the reinforcing fiber layer with the thermoplastic resin becomes poor, and it becomes insufficient to bond the contact points of the reinforcing fibers with the thermoplastic resin. It is desirable not to increase the weight ratio of the reinforcing fibers so much.

(3) Forming (main forming) (a) Main forming The fiber-reinforced thermoplastic resin sheet expanded and expanded in the thickness direction of the fiber-reinforced thermoplastic resin sheet by reducing the stress applied to the fiber by the heating (preforming). A plastic resin sheet is molded into a predetermined shape to produce a final molded product. Usually, except that a mold having a predetermined thickness is used so that the final molded product has a density of 0.8 g / cm ³ or less. It can be carried out in the same manner as the sheet forming method. (b) Mold In the present molding, the final molded product has a density of 0.92 g / cm or less, preferably 0.3 to 0.75 g.
By adjusting the clearance of the cavity of the mold so as to be / cm ³ , the shape is formed to be thicker than the original thermoplastic resin sheet and thinner than the expanded sheet thickness.

[II] Fiber-Reinforced Thermoplastic Resin Molded Product The fiber-reinforced thermoplastic resin sheet is preformed and then main-formed to give a density of 0.92 g / cm ^3.
The following lightweight and highly rigid fiber-reinforced thermoplastic resin molded products can be obtained. The fiber-reinforced thermoplastic resin molded product obtained by the method for producing a fiber-reinforced thermoplastic resin molded product of the present invention is thicker than the plate thickness of the fiber-reinforced thermoplastic resin sheet before heating, so that the elastic modulus as a material decreases. However, the rigidity of the molded product rather increases. This is because the rigidity of the molded product as a plate-shaped product is proportional to the elastic modulus and the cube of the plate thickness. Even if the elastic modulus as a material decreases, if the plate thickness increases It means that the rigidity of the molded product as a whole is improved, and therefore the rigidity of the molded product as a whole is increased. The lightweight and highly rigid fiber-reinforced thermoplastic resin sheet molded product (panel-shaped product) thus obtained can be expected as an interior material for automobiles as a main application. Currently, a lightweight material such as a phenolic resin-based synthetic wood board is used as an interior material for such an automobile. The lightweight and highly rigid fiber-reinforced thermoplastic resin sheet molded product obtained by the method of the present invention is used. The (panel-shaped material) can provide a material having a lower density and higher rigidity than such a lightweight material.

[0018]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below. Regarding the raw materials used and the evaluation methods in these Examples and Comparative Examples, the following raw materials were used and the evaluation methods shown below were used. (1) Raw materials used Glass fibers: Chopped strands manufactured by Nippon Electric Glass Co., Ltd. were used. Crystalline polypropylene resin powder: Homopolypropylene manufactured by Mitsubishi Yuka Co., Ltd. was used. (2) Evaluation method Density: Measured by the water displacement method Bending strength: Measured by JIS-K7203 Bending elastic modulus: Measured by JIS-K7203 Surface rigidity (Eh ³ ): Product of bending elastic modulus times cube of wall thickness Indicates

[0019] Example 1 (1) after the spherical pellets prepared diameter 4 mm ^phi-woven material was frozen by immersing in liquid nitrogen, and subjected to mechanical grinding, the grinding powder by sieve until 150~1,000μm Crystalline polypropylene resin powder (melt flow rate 70
g / 10 min homopolymer) and glass fibers having a diameter of 10 μm ^φ and a length of 18 mm, and a basis weight of a composition having a glass fiber content of 40% by weight and a crystalline polypropylene resin content of 60% by weight by a papermaking method. Of 2,650 g / m ² of non-woven material was produced. (2) Production of Fiber Reinforced Thermoplastic Resin Sheet Using one piece of this nonwoven fabric material, a fiber reinforced thermoplastic resin sheet having a plate thickness of 2.26 mm (density 1.
173 g / cm ³ ) was produced. The press molding conditions are
Preheating was performed at 210 ° C. for 10 minutes with no load, and then pressure was applied at a pressure of 20 kgf / cm ² for 5 minutes, and then transferred to a cooling press set at 50 ° C. to form a fiber-reinforced thermoplastic resin sheet. (3) Preforming This fiber-reinforced thermoplastic resin sheet was placed in a far-infrared heater heating furnace and heated until the surface temperature reached 210 ° C., and the plate thickness expanded to about 10 mm. (4) Main Molding Subsequently, a spacer having a cavity thickness of 3 mm was attached to a press molding machine whose temperature was adjusted to 70 ° C., and the heat-expanded fiber-reinforced thermoplastic resin sheet was inserted to obtain a surface pressure of 10
Press molding was performed at kgf / cm ² to obtain a sheet-shaped molded product having a plate thickness of 2.91 mm. The physical properties of this sheet-shaped molded product are shown in Table 1.

Example 2 A fiber-reinforced thermoplastic resin sheet was molded by the same method as in “(1) Production of non-woven fabric material” and “(2) Production of fiber-reinforced thermoplastic resin sheet” in Example 1, and When the sheet was placed in a far infrared heater heating furnace and heated until the surface temperature reached 210 ° C., the sheet thickness expanded to about 9 mm. Subsequently, a spacer having a cavity thickness of 4 mm was attached to a press molding machine whose temperature was adjusted to 70 ° C., the heat-expanded fiber reinforced thermoplastic resin sheet was inserted, and press molding was performed at a surface pressure of 10 kgf / cm ² to obtain a plate. Thickness 3.69m
A sheet-shaped molded product of m was obtained. The physical properties of this sheet-shaped molded product are shown in Table 1.

Example 3 A fiber reinforced thermoplastic resin sheet was molded by the same method as in “(1) Production of non-woven fabric material” and “(2) Production of fiber reinforced thermoplastic resin sheet” in Example 1, and When the sheet was heated in a far infrared heater heating furnace until the surface temperature reached 210 ° C., the sheet thickness expanded to about 9 mm. Then, the cavity was adjusted to 5 in a press molding machine whose temperature was adjusted to 70 ° C.
A spacer with a thickness of mm is attached, and this heat-expanded fiber-reinforced thermoplastic resin sheet is inserted, and a surface pressure of 10 kg
Press molding was performed at f / cm ² to obtain a sheet-shaped molded product having a plate thickness of 4.76 mm. The physical properties of this sheet-shaped molded product are shown in Table 1.

Example 4 A fiber reinforced thermoplastic resin sheet was molded by the same method as in “(1) Production of nonwoven fabric material” and “(2) Production of fiber reinforced thermoplastic resin sheet” in Example 1, and When the sheet was placed in a far infrared heater heating furnace and heated until the surface temperature reached 210 ° C., the sheet thickness expanded to about 9 mm. Subsequently, a spacer having a cavity of 7.6 mm in thickness was attached to a press molding machine whose temperature was adjusted to 70 ° C., and the heat-expanded fiber-reinforced thermoplastic resin sheet was inserted,
Press-formed at a surface pressure of 10 kgf / cm ² and a plate thickness of 7.3.
A 5 mm sheet-shaped molded product was obtained. The physical properties of this sheet-shaped molded product are shown in Table 1.

Example 5 (1) Manufacture of non-woven fabric material A crystalline polypropylene resin polymer powder classified to 150 to 1,000 μm (melt flow rate 70 g /
10 minutes homopolymer), diameter 10 μm ^φ , length 13
mm glass fiber and a glass fiber content of 50% by weight and a crystalline polypropylene resin content of 5 by a papermaking method.
A non-woven fabric material having a compositional weight of 0 wt% and a basis weight of 1,810 g / m ² was produced. (2) Production of Fiber Reinforced Thermoplastic Resin Sheet Using one piece of this nonwoven fabric material, a fiber reinforced thermoplastic resin sheet (density 1.2) having a plate thickness of 1.5 mm was formed by press molding.
1 g / cm ³ ) was produced. The conditions for press molding include preheating at 220 ° C. and no load for 5 minutes, and then at a pressure of 10
It was pressurized at kgf / cm ² for 5 minutes and then transferred to a cooling press set at 80 ° C. to form a fiber reinforced thermoplastic resin sheet. (3) Preforming This fiber-reinforced thermoplastic resin sheet was placed in a far-infrared heater heating furnace and heated until the surface temperature reached 205 ° C., and the sheet thickness expanded to about 10 mm. (4) Main molding Subsequently, a spacer having a cavity thickness of 4.5 mm was attached to a press molding machine whose temperature was adjusted to 50 ° C., the heat-expanded fiber-reinforced thermoplastic resin sheet was inserted, and the surface pressure was 5 kgf / cm ^2. Was press-molded with to obtain a sheet-shaped molded product having a plate thickness of 4.22 mm. The physical properties of this sheet-shaped molded product are shown in Table 1.
Shown in.

[0024] Example 6 (1) after the angular pellets prepared diameter 3 mm ^phi-woven material was frozen by immersing in liquid nitrogen, and subjected to mechanical grinding, 150～1,300Myuemu the pulverized powder by sieve Crystalline polypropylene resin powder (melt flow rate 75
g / 10 min homopolymer) and glass fiber having a diameter of 10 μm ^φ and a length of 25 mm, and a basis weight of a composition having a glass fiber content of 40% by weight and a crystalline polypropylene resin content of 60% by weight by a papermaking method. Produced a non-woven material of 1,345 g / m ² . (2) Production of Fiber Reinforced Thermoplastic Resin Sheet Using these two nonwoven fabric materials, a fiber reinforced thermoplastic resin sheet having a plate thickness of 2.25 mm (density 1.
196 g / cm ³ ) was produced. The press molding conditions are
Preheating was carried out at 200 ° C. for 5 minutes with no load, then, pressure was applied at a pressure of 40 kgf / cm ² for 5 minutes, and then transferred to a cooling press set at 60 ° C. to form a fiber reinforced thermoplastic resin sheet. (3) Preforming This fiber-reinforced thermoplastic resin sheet was placed in a far-infrared heater heating furnace and heated until the surface temperature reached 215 ° C., and the sheet thickness expanded to about 15 mm. (4) Main molding Subsequently, a spacer having a cavity thickness of 5.2 mm was attached to a press molding machine whose temperature was adjusted to 90 ° C., the heat-expanded fiber-reinforced thermoplastic resin sheet was inserted, and the surface pressure was 5 kgf / cm ^2. Was press-molded to obtain a sheet-shaped molded product having a plate thickness of 5.03 mm. The physical properties of this sheet-shaped molded product are shown in Table 1.
Shown in.

Example 7 (1) Production of non-woven fabric material A crystalline polypropylene resin powder classified to 100 to 1,000 μm (melt flow rate 100 g / 1
0 minute homopolymer), diameter 10 μm ^φ , length 13 m
glass fiber content of 60% by weight and polypropylene resin content of 40% by weight by a papermaking method using m glass fiber
A non-woven fabric material having a basis weight of 1,480 g / m ² was produced. (2) Production of Fiber Reinforced Thermoplastic Resin Sheet Using these two nonwoven fabric materials, a fiber reinforced thermoplastic resin sheet having a plate thickness of 2.37 mm (density 1.
250 g / cm ³ ) was produced. The press molding conditions are
Preheating was carried out at 220 ° C. for 7 minutes with no load, then, pressure was applied for 5 minutes at a pressure of 40 kgf / cm ² , and then transferred to a cooling press set at 100 ° C. to form a fiber-reinforced thermoplastic resin sheet. (3) Preforming This fiber-reinforced thermoplastic resin sheet was placed in a far-infrared heater heating furnace and heated until the surface temperature reached 200 ° C., and the sheet thickness expanded to about 17 mm. (4) Main molding Subsequently, a spacer having a thickness of 3.5 mm is attached to a press molding machine whose temperature is adjusted to 90 ° C., the heat-expanded fiber-reinforced thermoplastic resin sheet is inserted, and the surface pressure is 5 kgf / cm ^2. Was press-molded to obtain a sheet-shaped molded product having a plate thickness of 3.38 mm. The physical properties of this sheet-shaped molded product are shown in Table 1.
Shown in.

[0026]

[Table 1]

[0027] Comparative Example 1 (1) After a round pellet manufacturing diameter 4 mm ^phi-woven material was frozen by immersing in liquid nitrogen, and subjected to mechanical grinding, 150～1,000Myuemu the pulverized powder by sieve Crystalline polypropylene resin powder (melt flow rate 25
g / 10 min homopolymer) and glass fiber having a diameter of 10 μm ^φ and a length of 13 mm, and a basis weight of a composition having a glass fiber content of 40% by weight and a crystalline polypropylene resin content of 60% by weight by a papermaking method. Produced a non-woven material of 1,370 g / m ² . (2) Production of Fiber Reinforced Thermoplastic Resin Sheet Using one piece of this nonwoven fabric material, a fiber reinforced thermoplastic resin sheet having a plate thickness of 1.15 mm (density 1.
188 g / cm ³ ) was produced. The press molding conditions are
Preheating was carried out at 210 ° C. for 5 minutes with no load, then, pressure was applied at a pressure of 20 kgf / cm ² for 5 minutes, and then transferred to a cooling press set at 110 ° C. to form a fiber-reinforced thermoplastic resin sheet. (3) Preforming This fiber-reinforced thermoplastic resin sheet was placed in a far-infrared heater heating furnace and heated until the surface temperature reached 210 ° C, and the sheet thickness expanded to about 9 mm. (4) Main molding Subsequently, a spacer having a cavity thickness of 1.5 mm was attached to a press molding machine whose temperature was adjusted to 70 ° C., the heat-expanded fiber reinforced thermoplastic resin sheet was inserted, and the surface pressure was 5 kgf / cm ^2. Was press-molded to obtain a sheet-shaped molded product having a plate thickness of 1.37 mm. Table 2 shows the physical properties of this sheet-shaped molded product.
Shown in.

Comparative Example 2 A fiber reinforced thermoplastic resin sheet was formed by the same method as in “(1) Production of non-woven fabric material” and “(2) Production of fiber reinforced thermoplastic resin sheet” of Comparative Example 1. When the sheet was placed in a far infrared heater heating furnace and heated until the surface temperature reached 210 ° C., the sheet thickness expanded to about 9 mm. Subsequently, a spacer having a cavity thickness of 2 mm was attached to a press molding machine whose temperature was adjusted to 70 ° C., the heat-expanded fiber-reinforced thermoplastic resin sheet was inserted, and press molding was performed at a surface pressure of 10 kgf / cm ² to obtain a plate. Thickness 1.91m
A sheet-shaped molded product of m was obtained. Table 2 shows the physical properties of this sheet-shaped molded product.

Comparative Example 3 A fiber-reinforced thermoplastic resin sheet was molded by the same method as in “(1) Production of non-woven fabric material” and “(2) Production of fiber-reinforced thermoplastic resin sheet” of Comparative Example 1. When the sheet was placed in a far infrared heater heating furnace and heated until the surface temperature reached 210 ° C., the sheet thickness expanded to about 9 mm. Subsequently, a spacer having a cavity thickness of 2.5 mm was attached to a press molding machine whose temperature was adjusted to 70 ° C., and the heat-expanded fiber-reinforced thermoplastic resin sheet was inserted,
Press formed with a surface pressure of 10 kgf / cm ² , and a plate thickness of 2.1.
A 1 mm sheet-shaped molded product was obtained. Table 2 shows the physical properties of this sheet-shaped molded product.

Comparative Example 4 A fiber-reinforced thermoplastic resin sheet was molded by the same method as in “(1) Production of non-woven fabric material” and “(2) Production of fiber-reinforced thermoplastic resin sheet” of Comparative Example 1. When the sheet was placed in a far infrared heater heating furnace and heated until the surface temperature reached 210 ° C., the sheet thickness expanded to about 9 mm. Subsequently, a spacer having a cavity thickness of 2.5 mm was attached to a press molding machine whose temperature was adjusted to 70 ° C., and the heat-expanded fiber-reinforced thermoplastic resin sheet was inserted,
Press-formed at a surface pressure of 10 kgf / cm ² and a plate thickness of 3.9
An 8 mm sheet-shaped molded product was obtained. Table 2 shows the physical properties of this sheet-shaped molded product.

[0031]

[Table 2]

Comparative Example 5 Table 3 shows the physical properties of a wood-based polypropylene sheet commercially available as an interior material for automobiles.

Comparative Example 6 Table 3 shows the physical property values of a phenolic resin-based synthetic wooden board which is commercially available as an automobile interior material.

Comparative Example 7 Crystallinity was obtained by using the hot flow stamping molding method (a method of injecting a resin from an injection molding machine into a mold installed on a press molding machine, and then closing the mold for molding). A door trim molded product containing polypropylene resin containing 40% by weight of talc was molded. Table 3 shows the physical properties of the molded product.

[0035]

[Table 3]

Comparative Example 8 Physical properties of a molded article of the fiber reinforced plastic material described in JP-A-60-179234 are shown in Tables 4 and 5.

[0037]

[Table 4]

[0038]

[Table 5]

From these Examples and Comparative Examples, the plate-shaped expansion-molded articles of the fiber-reinforced thermoplastic resin sheet according to the method of the present invention obtained by the Examples are the same as those of the fiber-reinforced thermoplastic resin sheets obtained by the Comparative Examples. In order to clearly prove that the molded product is lightweight and highly rigid as compared with the plate-shaped expansion molded product, the correlation between the density and the bending elastic modulus of the molded product in these Examples and Comparative Examples is shown in FIG. As shown in FIG. 2, the lines (block points 1 to 8) according to the correlation between the density and the bending elastic modulus of the plate-shaped expansion-molded product of the fiber-reinforced thermoplastic resin sheet of the present invention are the comparative examples 1 to 4. And the lines according to Comparative Examples 5 to 7 (block points 14 to 17) and the lines according to Comparative Example 8 and (plot points 18 to 26) have substantially the same flexural modulus. It has been shown that the density in the case is lower. That is, it has been proved that a plate-shaped molded product having the same shape can be a lighter molded product.

[0040]

The fiber-reinforced thermoplastic resin molded product obtained by the method for producing a lightweight fiber-reinforced thermoplastic resin molded product of the present invention has a higher density than that of a conventional phenol resin-based synthetic wood board, which is an interior material for automobiles. It is a low- and light-weight, high-rigidity fiber-reinforced thermoplastic resin sheet-shaped molded product (panel-shaped product), and is therefore suitable as an interior material for automobiles.

[0041]

[Brief description of drawings]

FIG. 1 is a concept of a process for producing a stampable sheet by a wet method using a papermaking method for a fiber-reinforced thermoplastic resin sheet used in a method for producing a lightweight fiber-reinforced thermoplastic resin molded article in an example of the present invention. It is a figure.

FIG. 2 is a diagram showing a correlation between the density and the flexural modulus of a molded product in Examples of the present invention and Comparative Examples.

[Explanation of symbols]

 1 Fiber for Reinforcement 2 Thermoplastic Resin Powder 3 Dispersion Tank 4 Pump 5 Mesh Electric Belt Conveyor 6 Head Box 7 Wet Box 8 Nonwoven Material 9 Hot Air Drying Furnace 10 Double Belt Conveyor Type Continuous Steel Press 11 Fiber Reinforced Thermoplastic Resin Sheet 12 Cutter 13 Matte Fiber Reinforced Thermoplastic Resin Sheet 14 Reel

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Satoshi Tokai-shi, Aichi Prefecture 5-3 Shinkai Nippon Steel Co., Ltd. Nagoya Steel Works (72) Inventor Takao Kimura Toho-cho, Yokkaichi-shi, Mie No. 1 Mitsubishi Petrochemical Co., Ltd. Yokkaichi Research Institute

Claims (1)

[Claims] 1. A fiber-reinforced thermoplastic resin sheet obtained by dispersing reinforcing fibers having a length of 6 to 50 mm in a thermoplastic resin matrix in a proportion of 30 to 70% by weight is heated to a temperature not lower than the melting point of the thermoplastic resin. Then, by reducing the stress applied to the fibers, the sheet is expanded and expanded 3 to 8 times in the thickness direction of the sheet, and then the sheet is moved to a mold and compression-molded so that the density is 0.92 g / cm ³ or less. In the method for producing a lightweight fiber-reinforced thermoplastic resin molded article, a lightweight fiber-reinforced thermoplastic resin molded article characterized in that crystalline polypropylene having a melt flow rate of 50 g / 10 min or more is used as the thermoplastic resin of the matrix. Production method.