JPH08156162A - Fiber reinforced resin porous molded article and manufacture of the same - Google Patents

Abstract

PURPOSE: To propose a fiber reinforced resin porous molded article having good adhesion between sheets, bending characteristics, and surface flatness and a method for manufacturing the article advantageously. CONSTITUTION: This is a porous molded article 5 which is made by expanding a laminated sheet 3 in which two or more sheet-shaped webs (a), (b) which are composed of a thermoplastic resin 1 and reinforcing fibers 2 are overlapped and heat-pressed by heating again. The fiber length of reinforcing fibers 2 contained in one laminated sheet 3 of the article 5 or the laminated sheet 3 which is positioned on the surface/back is made shorter than that of the reinforcing fibers 2 contained in the laminated sheet 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber-reinforced resin porous molded article which is useful as an automobile interior material, for example, a ceiling material or a door trim material, which is desired to be reduced in weight, and particularly to flexural strength and surface flatness. We propose an excellent fiber-reinforced thermoplastic resin porous molding and its manufacturing method.

[0002]

2. Description of the Related Art In general, a fiber reinforced resin is one in which reinforcing fibers are dispersed in a thermoplastic resin. This type of fiber reinforced resin is mainly manufactured by a papermaking method. For example, as proposed in Japanese Examined Patent Publication (Kokoku) No. 2-48423, a sheet-shaped web is obtained by making a dispersion of a thermoplastic resin and reinforcing fibers in an aqueous medium on a porous support. A dense fiber-reinforced resin sheet (consolidated sheet) can be obtained by producing the web, heating it once above the melting point of the thermoplastic resin and below the decomposition point, and then applying pressure and cooling.

Since this consolidate sheet contains reinforcing fibers that have been defibrated to a substantially single fiber state, when the fibers are heated again above the melting point of the resin and below the decomposition point, the fibers constrained by the resin will spring back. It has the property of waking up and expanding. By utilizing such a property, it is possible to form a porous body and adjust the density of the expanded product by performing expansion molding of the consolidate sheet while limiting expansion of the consolidate sheet with a pressing machine, that is, expansion molding.

The above-mentioned proposal is characterized in that the properties exhibited by such a consolidate sheet are utilized, and the consolidate sheet is reheated in a closed mold and expansion-molded while applying pressure to obtain a porous sheet. A method for obtaining a quality molded body is disclosed. In particular, in the above proposal, as a specific embodiment of this method, when the plurality of consolidate sheets are superposed and expansion-molded, an example in which the fiber content of the consolidate sheet of the outer layer is lower than the fiber content of the inner layer, On the contrary, a raised example is described.

[0005]

However, in any of the consolidate sheets according to the above proposals, when they are expansion-molded to a density of 0.3 g / cm ³ or less, the porosity in the porous molded body becomes high, and suddenly increases. Strength is reduced. In particular, there has been a problem that the bending strength, which is greatly affected by the strength of the consolidate sheet near the surface of the molded body, is significantly reduced. In addition, in a porous molded article that has been expanded and molded at a high expansion rate, the fibers may stick out on the surface of the molded article due to springback of the fiber,
There is a problem that the flatness of the surface of the molded product is lowered.

An object of the present invention is to solve the above problems, and in particular, a fiber-reinforced resin porous molded article excellent in bending properties and surface flatness, and a method capable of advantageously producing this porous molded body. Is to propose.

[0007]

[Means for Solving the Problems] As a result of intensive studies aimed at achieving the above-mentioned object, the inventors have found that when the fiber content of the fiber-reinforced resin is constant, the resin is allowed to expand freely under heating and without limitation. It has been found that the expansion coefficient at that time (hereinafter referred to as the natural expansion coefficient) changes according to the fiber length of the contained fiber and exhibits a maximum value at a certain fiber length. Furthermore, the present inventors have found that if the fiber length of the contained fibers is within the range of 6 to 30 mm, the bending strength of the expansion-molded porous molded body with an expansion coefficient of 1 to 4 will hardly change. Was conceived.

That is, according to the present invention, (1) a porous sheet obtained by expanding two or more sheet-like webs composed of a thermoplastic resin and reinforcing fibers by reheating the laminated sheet which is thermocompression bonded In the quality molded article, the fiber length of the reinforcing fiber contained in one laminated sheet corresponding to one of the front surface and the back surface of the porous molded article or the laminated sheet positioned on the front and back surfaces is equal to that of the other laminated sheet. The fiber-reinforced resin porous molded article is characterized in that it is made shorter than the fiber length of the reinforcing fiber contained therein. (2) In the invention described in (1) above, the reinforcing fiber contained in one laminated sheet corresponding to one of the front surface and the back surface of the porous molded article or the reinforcing sheet located on the front and back surfaces is: Desirably, the fiber length thereof is in the range of 6 to 30 mm, and the reinforcing fibers contained in the other laminated sheets are in the range of 15 to 50 mm. (3) In the invention described in (1) above, it is desirable that the reinforcing fibers are glass fibers. (4) In the method for producing a fiber-reinforced resin porous molded article from a thermoplastic resin and reinforcing fibers, at least the following (a)
~ (C) step; that is, (a) using a reinforcing resin A and B having a fiber length of A <B and a thermoplastic resin, a sheet-shaped web a containing the reinforcing fiber A, and a reinforcing fiber A step of preparing a sheet-shaped web b containing the fiber B, (b) a sheet-shaped web a as one laminated sheet corresponding to one of the front surface and the back surface of the porous molded body or the laminated sheet positioned on the front and back surfaces. A sheet-shaped web b is used as the other laminated sheet, two or more of these webs are superposed, and thermocompression-bonded in a temperature range from the melting point of the thermoplastic resin to less than the decomposition point to produce a laminated sheet. Step, (c) the laminated sheet is heated and expanded in a temperature range from the melting point of the thermoplastic resin to less than the decomposition point, and then a molding die holding a predetermined clearance adapted to the product shape under cooling. Molded in That process, a method for producing a fiber reinforced resin porous molded body characterized by undergoing. (5) In the method described in (4) above, as the reinforcing fibers A, those having a fiber length within a range of 6 to 30 mm are used, and as the reinforcing fibers B, within a range of 15 to 50 mm. Is preferred. (6) In the method described in (4) above, it is desirable to use glass fiber as the reinforcing fiber.

[0009]

The function of the present invention is to provide one reinforcing sheet contained in one of the laminated sheet corresponding to one of the front surface and the rear surface of the porous molded article composed of the laminated sheet or the laminated sheet positioned on the front and back surfaces. The length is shorter than the fiber length of the reinforcing fibers contained in the other laminated sheets. With such a structure, when the porous molded article according to the present invention is composed of a laminated sheet of two layers, one laminated sheet corresponding to one of the front surface and the back surface is laminated with three or more layers. In the case of being composed of sheets, the laminated sheets located on the front and back surfaces have a higher density (lower expansion coefficient) than other laminated sheets. As a result, the porous molded article according to the present invention has the same expansion coefficient (density) and unit weight as compared with the conventional porous molded article in which reinforcing fibers of the same form are uniformly dispersed in each laminated sheet. In, the bending strength is remarkably improved and the surface flatness is also excellent.

The structure of the fiber-reinforced resin porous molded article of the present invention will be described in detail below. The fiber-reinforced resin porous molded article of the present invention is obtained by stacking two or more sheets made of a thermoplastic resin and reinforcing fibers on top of each other.
The fiber length of the reinforcing fiber contained in one laminated sheet corresponding to one of the front surface and the rear surface of this porous molded article or the laminated sheet positioned on the front and back surfaces is the reinforcing fiber contained in the other laminated sheet. The fiber length is shorter than the fiber length.

Reinforcing Fiber In the present invention, the length of the fiber contained in one laminated sheet corresponding to one of the front surface and the back surface of the porous molded article or the laminated sheet positioned on the front and back surfaces has the effect of reinforcing. 6 to 30 mm in terms of excellent fluidity during molding
It is desirable to be within the range. That is, when the fiber length is less than 6 mm, the reinforcing effect is small and the fiber length is 30 mm.
This is because if it exceeds mm, the basis weight (weight per unit area) distribution becomes nonuniform and the expansion coefficient of the porous molded article becomes nonuniform. On the other hand, it is desirable that the length of the fibers contained in the sheets other than the above-mentioned laminated sheet is within the range of 15 to 50 mm, preferably 20 to 35 mm. The reason is that if the length of the fiber is less than 15 mm, the desired molded body thickness cannot be ensured due to the low expansion coefficient, and if the length of the fiber exceeds 50 mm, the basis weight distribution becomes uneven and the porous molded body is formed. This is because the expansion coefficient becomes uneven.

As described above, according to the above-mentioned structure of the porous molded article according to the present invention, the expansion coefficient of each laminated sheet is adjusted by the length of the reinforcing fiber contained in these sheets. It is possible to obtain a fiber-reinforced resin porous molded product in which voids near the surface that significantly affect the decrease in strength are suppressed.

As such reinforcing fibers, inorganic fibers such as glass fibers, carbon fibers, boron fibers and other fine metal fibers, or organic fibers such as aramid fibers, polyester fibers and polyamide fibers can be used. . In particular, it is more preferable to use glass fiber in terms of cost and property balance.

Thermoplastic Resin In the present invention, as the thermoplastic resin, a resin having a granular shape, a flake shape, a fibrous shape or the like can be used, and the resin particle diameter is preferably in the range of 50 to 2000 μm. It is desirable to use a granular resin. The reason for this is that the resin particle size is 50
If it is less than μm, troubles such as biting into the device are likely to occur during web production, while if the resin particle size exceeds 2000 μm, it is difficult to obtain a laminated sheet (consolidated sheet) in which the resin is uniformly dispersed in the fiber. Because it will be.

Examples of such a thermoplastic resin include polyolefins such as polyethylene and polypropylene, polyethylene terephthalate, polycarbonate, polyamide polyacetal, polyvinyl chloride, and copolymers and graft compounds (eg ethylene- A vinyl chloride copolymer, an ethylene-vinyl acetate copolymer, a styrene-butadiene-acrylonitrile copolymer, etc.), or a blended product of these resins can be used.

Regarding the mixing ratio of the reinforcing fiber and the thermoplastic resin,
The reinforcing fiber and the thermoplastic resin are mixed in a weight ratio (fiber /
Resin), it is desirable to be in the range of 20/80 to 70/30. The reason is that if the content of the reinforcing fiber exceeds 70 wt%, it becomes difficult to uniformly disperse the thermoplastic resin in the fiber, and the fluidity at the time of molding the product decreases. This eventually leads to a reduction in the reinforcing effect of the fibers.

Next, the method for producing the fiber-reinforced resin porous molded article according to the present invention will be described in detail. The production method according to the present invention is a laminated sheet (consolidated sheet) obtained by stacking two or more sheet-shaped webs composed of a thermoplastic resin and reinforcing fibers and thermocompressing them, and heating the laminated sheet. In the method of producing a porous molded article by expanding at a coefficient of expansion lower than a natural coefficient of expansion (expansion coefficient in a non-pressurized state), and then pressure-molding under cooling, particularly when the fiber length is A <B. A sheet-like web a containing the reinforcing fiber A and a sheet-like web b containing the reinforcing fiber B using the reinforcing fibers A and B and the thermoplastic resin having the relationship
Is used, and the sheet-shaped web a is used as one laminated sheet corresponding to one of the front surface and the back surface of the porous molded article or the laminated sheet positioned on the front and back surfaces, and the sheet-shaped web b is used as the other laminated sheet. The point is characteristic.

Laminated sheet (consolidated sheet) The laminated sheet (consolidated sheet) may be produced by any method, but it is particularly preferable to produce it by a papermaking method. For example, a granular thermoplastic resin and a reinforcing fiber are dispersed in a surfactant aqueous solution containing microbubbles, and the dispersion is made on a porous support to form the thermoplastic resin and the reinforcing fiber. A sheet-shaped web is prepared, and two or more webs are superposed and heated and pressed to produce a laminated sheet. In the production method of the present invention, in order to suppress the expansion of the surface layer and enhance the reinforcing effect, it is used for one laminated sheet corresponding to one of the front surface and the back surface of the porous molded article or the laminated sheet positioned on the front and back surfaces. As the reinforcing fibers contained in the sheet-like web, those having a fiber length within the range of 6 to 30 mm are used, and as the reinforcing fibers contained in the sheet-like web used for other laminated sheets, within the range of 15 to 50 mm. It is desirable to use the one. The laminated sheet thus obtained has a basis weight of 200 to 8000 g / m ² , and preferably 500 to 30.
Adjusted to be 00g / m ² .

Here, the heating temperature of the web can be appropriately selected within a temperature range from the melting point of the thermoplastic resin constituting the web to the decomposition point. For example, when polypropylene is used as the thermoplastic resin, it is heated to 170 to 230 ° C, preferably 190 to 210 ° C because the melting point of this polypropylene is about 170 ° C and the decomposition point is about 230 ° C. Further, the pressing force of the web is 3 to 3 in order to obtain a dense consolidate sheet without causing damage to the reinforcing fibers.
It is desirable to set it within the range of 500 kgf / cm ² .

Expansion of Consolidated Sheet The laminated sheet (consolidated sheet) obtained as described above is once expanded by reheating at an expansion rate not higher than the natural expansion rate (expansion rate in the unpressurized state). After that, it is subjected to pressure molding using a mold, so-called expansion molding. As the conditions of this expansion molding, the conditions of heating and pressurization in the production of the consolidate sheet are applied as they are. The porous molded body thus obtained is adjusted to a desired thickness by the height of the spacer of the mold to be pressed, the mold clamping height of the press, and the like. In order to make the molded body a porous sheet, the expansion rate of the consolidate sheet is 1.1 to 8.0, and preferably 1.5 to 6.0.

The porous molded body obtained by the manufacturing method as described above for the final molded body is a laminated sheet corresponding to one of the front surface and the back surface of the porous molded body or the laminated sheets positioned on the front and back surfaces. The fiber length of the reinforcing fibers contained in the sheet is shorter than the fiber length of the reinforcing fibers contained in the other laminated sheets. With such a structure, when the porous molded article according to the present invention is composed of a laminated sheet of two layers, one laminated sheet corresponding to one of the front surface and the back surface is laminated with three or more layers. In the case of being composed of sheets, the laminated sheets located on the front and back surfaces have a higher density (lower expansion coefficient) than other laminated sheets. As a result, the porous molded article according to the present invention has the same expansion coefficient (density) and unit weight as compared with the conventional porous molded article in which reinforcing fibers of the same form are uniformly dispersed in each laminated sheet. In, the bending strength is remarkably improved and the surface flatness is also excellent.

[0022]

Embodiment An embodiment will be described below with reference to FIG.
In this embodiment, the thermoplastic resin 1 is MFR6.
5, polypropylene with an average particle size of 500 μm was used. As the reinforcing fibers 2, glass fibers having an average fiber length shown in Table 1 were used for the inner layer laminated sheet 3 and the outer layer laminated sheet 3, respectively. The glass fiber 2 had a fiber diameter of 10 μm, and the mixing ratio of the thermoplastic resin 1 to the glass fiber 2 was 1: 1.

First, the thermoplastic resin 1 and the glass fiber 2 of A in the table were dispersed in a surfactant containing fine bubbles and paper-making to obtain a web a having a basis weight of 500 g / m ² . Similarly, using a glass fiber of B in the table, a web having a basis weight of 1000 g / m ² b
I got Next, these webs were laminated in three layers so as to have an a / b / a structure, preheated at 210 ° C, and then the preheated webs were placed between cooling plates at 25 ° C. It was pressed at a pressure of 5 kgf / cm ² to obtain a dense laminated sheet (consolidated sheet) 3. Then, the laminated sheet (consolidated sheet) 3 is preheated again at 210 ° C., then compressed at 3 kgf / cm ² in the mold 4, and then expanded between the spacers of 6.5 mm to have a thickness of 6.2 mm. ， Density 0.
A porous molded body 5 having a basis weight of 24 g / cm ³ and a basis weight of 2000 g / cm ² was obtained.

The porous molded body 5 thus obtained
Was prepared in accordance with JIS K 7055, and then subjected to a 3-point bending test. The results are shown in Table 1 together with the observation results of the surface properties. As is clear from the results shown in this table,
The porous molded article 5 according to the present invention is significantly improved in bending strength and excellent in surface flatness at the same expansion coefficient (density) and basis weight, as compared with Comparative Examples not conforming to the present invention. It was confirmed.

[0025]

[Table 1]

[0026]

As described above, according to the present invention, it is possible to obtain a fiber-reinforced thermoplastic resin porous molded article which is excellent in bending strength and surface flatness. Moreover, it is possible to obtain a porous molded body having a low density even with the same bending strength. As a result, the porous molded article of the present invention can be advantageously applied to automobile interior materials, such as ceiling materials and door trim materials, for which weight reduction is desired.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram showing an embodiment of the present invention.

[Explanation of symbols]

 1 Thermoplastic Resin 2 Reinforcing Fiber (Glass Fiber) 3 Laminated Sheet (Consolidated Sheet) 4 Mold 5 Porous Molded Body a, b Web

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Claims (6)

[Claims] 1. A porous molded article obtained by expanding two layers of sheet-shaped webs composed of a thermoplastic resin and reinforcing fibers by reheating and stacking two or more sheet-like webs, which are thermocompression-bonded to each other. The fiber length of the reinforcing fiber contained in one laminated sheet corresponding to one of the front surface and the back surface of the molded article or the laminated sheet positioned on the front and back surfaces, and the fiber length of the reinforcing fiber contained in the other laminated sheet. A fiber-reinforced resin porous molded product characterized by being made shorter than the length. 2. The reinforcing fiber contained in one laminated sheet corresponding to one of the front surface and the back surface of the porous molded body or the laminated sheet positioned on the front and back surfaces has a fiber length of 6 or less.
The fiber-reinforced resin porous material according to claim 1, wherein the reinforcing fiber contained in the other laminated sheet has a fiber length within a range of 15 to 50 mm. Molded body. 3. The fiber-reinforced resin porous molded article according to claim 1, wherein the reinforcing fiber is glass fiber. 4. A method for producing a fiber-reinforced resin porous molded article from a thermoplastic resin and a reinforcing fiber, which comprises at least the following steps (a) to (c); that is, (a) the fiber length is A <B.
A step of preparing a sheet-shaped web a containing the reinforcing fiber A and a sheet-shaped web b containing the reinforcing fiber B by using the reinforcing fibers A and B and the thermoplastic resin having the relationship of
(b) using a sheet-shaped web a as one laminated sheet corresponding to one of the front surface and the back surface of the porous molded body or a laminated sheet positioned on the front and back surfaces, and using a sheet-shaped web b as the other laminated sheet, A step of producing a laminated sheet by stacking two or more of these webs and thermocompressing them in a temperature range from the melting point of the thermoplastic resin to the decomposition point, (c) the laminated sheet of the thermoplastic resin A fiber characterized by undergoing a step of expanding by heating in a temperature range of not less than the melting point and less than the decomposition point, and then molding in a molding die while maintaining a predetermined clearance suitable for a product shape under cooling. A method for producing a reinforced resin porous molded body. 5. The reinforcing fiber A has a fiber length of 6 to 6.
Using a fiber within the range of 30 mm as the reinforcing fiber B, 15 to
A device having a diameter within a range of 50 mm is used.
The manufacturing method described in. 6. The manufacturing method according to claim 4, wherein glass fibers are used as the reinforcing fibers.