JP5958360B2 - Manufacturing method of FRP sheet - Google Patents

Description

  The present invention relates to a method for producing an FRP sheet.

  It is known to produce an FRP sheet having a predetermined shape using a material (prepreg) obtained by heating and melting and integrating a fiber-reinforced thermoplastic resin composition composed of a thermoplastic resin and reinforcing fibers. Many methods for adjusting the prepreg have also been proposed. For example, in Patent Document 1, a PA6 film is arranged on both sides of a sheet of carbon fiber strands arranged in one direction, and the sandwich is sandwiched between the sheets. The laminate is heated to 230 to 260 ° C. to melt impregnate the PA6 film into the sheet. In Patent Document 2, a glass fiber strand is introduced into molten polypropylene, melt impregnated, and then a long fiber reinforced thermoplastic resin substrate obtained by pulling out from a nozzle at a required speed is cut into a short substrate. The obtained short base material is dispersed in a mold and heated and pressurized to obtain a long fiber reinforced thermoplastic resin sheet.

WO2007 / 020910 JP 2000-141502 A

  As described in Patent Document 1, a method of heating a sandwich-like laminate in which a reinforcing fiber sheet is sandwiched between thermoplastic resin films and melt-impregnating the thermoplastic resin into the gaps of the reinforcing fibers The resin flows into the gap and is produced in a sheet shape. However, in order to produce a product with a stable thickness and a uniform dispersion of the resin between the reinforcing fibers, the reinforcing fibers are pressed and restrained on the upper and lower surfaces. There is a need. Therefore, when trying to obtain a high-quality sheet, the space into which the resin flows becomes small, and the content of reinforcing fibers per unit volume becomes high. Therefore, it is inevitable that the manufacturing cost will rise. Moreover, the process which obtains the sheet-like material of the carbon fiber strand arranged in one direction, the process of making it a sandwich-like laminated body by pinching | interposing with the thermoplastic resin film on both surfaces, etc. are required.

  In the long fiber reinforced thermoplastic resin base material obtained by the method of Patent Document 2, a long reinforcing fiber is embedded in the resin with directionality, and even in a short base material cut from the long base fiber, Reinforcing fibers are embedded in the direction. Therefore, when these short base materials are put in a mold and fluidly molded, the fluidity is not sufficient, the separation of the reinforcing fibers and the resin is likely to occur, and the resulting FRP sheet tends to have a portion with extremely low physical properties.

  The present invention has been made in view of the circumstances as described above, and provides a method for producing an FRP sheet, which is easy to produce and can be produced at low cost with little variation in physical properties in the surface direction. The issue is to provide.

  In order to solve the above-mentioned problem, the present inventors have repeatedly conducted many experiments to appropriately reinforced reinforcing fibers and a thermoplastic resin, which is a matrix resin, by a conventionally known uniaxial or multiaxial screw type extrusion. Knowing that an FRP sheet that solves the above problems can be obtained by using as a substrate a strand that is a mixture of resin and reinforcing fibers extruded into a strand from the screw type extruder, Invented.

  The method for producing an FRP sheet according to the present invention includes a step of extruding a fiber reinforced thermoplastic resin composition composed of a thermoplastic resin and a reinforcing fiber as a strand using a screw type extruder, and cutting the extruded strand to a required length. And a step of placing the cut strand in the mold, and a step of heating and pressing the strand arranged in the mold to form a predetermined shape.

  In the present invention, in order to obtain a base material in which reinforcing fibers are mixed in a thermoplastic resin as a matrix resin, a screw type extruder conventionally used in the technical field of resin molding is used. Therefore, the thermoplastic resin and the reinforcing fiber can be easily and uniformly mixed, and depending on the type and physical property value of the thermoplastic resin and the reinforcing fiber, the input amount, the resin temperature in the extruder, By appropriately setting the screw rotation speed, the screw kneading length, and the like, a base material in which both are mixed as desired can be obtained as a strand. Thereby, the manufacturing cost can be reduced. Further, in the extruded strand, there are discontinuous reinforcing fibers that have been cut and defibrated as desired, making it difficult for the resin and the reinforcing fibers to be separated. Therefore, it becomes possible to obtain an FRP sheet having a desired strength with a low content of reinforcing fibers. As an example, even if the volume content of the reinforcing fibers is 10 to 50% by volume, an FRP sheet having the strength necessary for automobile parts can be obtained.

  The strand extruded from the screw type extruder is cut into a required length. The length of the strand after cutting is appropriately set according to the physical property value required for the FRP sheet to be obtained. Preferably, it is about 20-40 mm. Moreover, the diameter of the strand extruded from the extruder is also appropriately selected according to the physical property value required for the FRP sheet to be obtained. Preferably, it is about 2 to 10 mm. Preferably, the strand has an aspect ratio of 2 or more. Of course, the extruded strand may be cut to a length of 100 to 200 mm, and as will be described later, such a long strand may be arranged in the mold with directionality.

  The obtained strand is arranged in a required mold as in the conventional method, and the strand arranged in the mold is heated and pressed to obtain a FRP sheet having a predetermined shape.

  In the FRP sheet manufacturing method of the present invention, in the step of arranging the strands in the mold, the strands may be randomly arranged without directionality in the mold, and the strands are arranged with directionality in the mold. You may make it do. In the present invention, the strand is rod-shaped, and any of the above arrangement modes can be easily implemented. In the former, an FRP sheet having no directionality in physical properties can be obtained, and in the latter, an FRP sheet showing high physical properties in a desired direction can be obtained. By using a strand having a long length, it becomes easy to arrange with a directivity. In any case, as described above, since the reinforced fibers that have been cut and defibrated are discontinuously present in the strand without any directionality, during the heat and pressure molding in the mold, as described above. A high fluidity can be exhibited, and it is possible to reliably avoid a local strength reduction in the FRP sheet.

  In the method for producing an FRP sheet of the present invention, a mixed base material of a thermoplastic resin and a reinforcing fiber is formed using a conventionally known extruder for resin molding as described above. Therefore, by appropriately adjusting the conditions on the extruder side at the time of melt mixing, it becomes easy to appropriately select the optimum melt extrusion conditions for the type and combination of the thermoplastic resin to be used and the reinforcing fibers. By performing the melt extrusion test, desired conditions on the extruder side can be easily determined. Therefore, in the present invention, the thermoplastic resin and the reinforcing fiber can be appropriately selected from many types and used.

  For example, the thermoplastic resin is preferably a polyolefin resin, a polyamide resin, a polyester resin, a polycarbonate resin, a polyphenylene sulfide resin, or a polystyrene resin from the viewpoint of impregnation property, cost, and physical properties. Polyamide resins and polyester resins are preferred. As the polyolefin resin, for example, polypropylene and polyethylene are preferable. As the polyamide-based resin, for example, nylon 6.6, nylon 6, nylon 12, MXD nylon and the like are preferable. As the polyester resin, for example, polyethylene terephthalate, polybutylene terephthalate and the like are preferable. These resins may be used in admixture with additives such as colorants, modifiers and antioxidants. Further, the reinforcing fiber used in the present invention can be used alone or in combination with glass fiber, carbon fiber, aramid fiber, ceramic fiber and the like. Among these, carbon fiber is preferable from the viewpoint of weight reduction.

  In one specific embodiment of the method for producing an FRP sheet, the step of extruding as a strand includes a screw-type extruder having a screw rotation speed of 30 to 200 rpm, a screw kneading length of 100 to 450 mm, and a melting point of a resin to be used or higher. It is characterized by being performed at temperature. In this case, it is more preferable to use a fiber reinforced thermoplastic resin composition in which the thermoplastic resin is polyamide 6 and the volume content of carbon fibers that are reinforcing fibers is 20 to 30% by volume.

  Thereby, the FRP sheet excellent in bending stress, bending elastic modulus, and flow magnification is obtained. In this case, more preferably, the strand diameter is 2 to 10 mm, and the strand aspect ratio is 2 or more.

  If the screw rotation speed at the time of strand extrusion is less than 30 rpm, the production speed becomes slow and is not suitable. If it exceeds 200 rpm, the physical properties are lowered due to fiber breakage, which is not preferable. If the kneading length of the screw is less than 100 mm, fiber defibration or dispersion is insufficient, which is not preferable. If the screw kneading length exceeds 450 mm, the physical properties deteriorate due to fiber breakage, which is not preferable.

  According to the present invention, there is provided an FRP sheet manufacturing method that can be manufactured at low cost with little variation in physical properties in the surface direction while being easy to manufacture.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

[Example 1]
<Raw material> Trading card long fiber pellets, TLP1060 (manufactured by Toray Industries, Inc.) were used as fiber reinforced pellets in which bundled carbon fibers are the core and thermoplastic resin is the sheath. The amount of carbon fiber in the pellet is 30 wt% (21 Vol%), the base resin is PA6, the fiber length is 6 mm, and the diameter is 3 mm.
<Manufacturing process 1> Fiber reinforced pellets were charged from the side feed portion of the twin-screw kneading extruder. The biaxial kneading extruder was controlled so that the resin temperature in the biaxial kneading extruder was 300 ° C. and the screw rotation speed was 100 rpm. The effective screw kneading length of the twin-screw kneading extruder is 200 mm. A strand having a diameter of 1.5 mm was collected from a biaxial kneading extruder and cut into a length of 30 mm to obtain a strand.

<Manufacturing process 2> The cut strands were put into a mold, stacked randomly, and sandwiched between stainless plates and heated to 280 ° C. The material heated to 280 ° C. was put into a mold having a mold temperature of 150 ° C. and 150 mm × 150 mm, heated and pressurized to a thickness of 2 mm at a pressure of 450 kN, and then cooled for 1 minute to obtain Example Product 1. .

[Examples 2 to 4]
As shown in Table 1, Example Products 2, 3, and 4 were produced in the same manner as Example 1 except that the strand diameter, screw length, and screw rotation speed were changed.

[Example 5]
<Raw material> The same material as in Example 1 was used.
<Manufacturing process 1> Fiber reinforced pellets were charged from the side feed portion of the twin-screw kneading extruder. The biaxial kneading extruder was controlled so that the resin temperature in the biaxial kneading extruder was 300 ° C. and the screw rotation speed was 100 rpm. The effective screw kneading length of the twin-screw kneading extruder is 200 mm. A continuous strand having a diameter of 7.0 mm was collected from a biaxial kneading extruder and cut into a length of 150 mm.

<Manufacturing process 2> Long strands cut to a length of 150 mm were placed in a state mold arranged in the same direction, stacked, and sandwiched between stainless plates and heated to 280 ° C. The material heated to 280 ° C. was put into a mold having a mold temperature of 150 ° C. and 150 mm × 150 mm, then heated and pressurized to a thickness of 2 mm at a pressure of 450 kN, and then cooled for 1 minute to give Example Product 5.

[Examples 6 and 7]
As shown in Table 1, Example Products 6 and 7 were produced in the same manner as Example 5 except that the screw length and the screw rotation speed were changed.

[Comparative example]
[Comparative Example 1]
The raw materials used in Example 1 were put into a mold as they were, randomly stacked, and sandwiched between stainless plates and heated to 280 ° C. The material heated to 280 ° C. was put into a mold having a mold temperature of 150 ° C. and 150 mm × 150 mm, then heated and pressurized to a thickness of 2 mm at a pressure of 450 kN, and then cooled for 1 minute to obtain Comparative Example Product 1. .

[Comparative Example 2]
A comparative product 2 was prepared in the same manner as in Example 1 except that the strand diameter was 7 mm and the screw length was 1500 mm.

<Strength evaluation>
For Example Products 1 to 7 and Comparative Example Products 1 and 2, a bending test piece (100 mm × 25 mm × 2 mm) was cut out from the prepared 150 mm × 150 mm × 2 mm material, and a three-point bending test was performed according to JIS K7074. It was. The bending stress and bending elastic modulus at that time are shown in Table 1.

<Liquidity assessment>
About Example goods 1-7 and comparative example goods 1 and 2, the test piece (106mmx106mmx2mm) was cut out from the produced material of 150mmx150mmx2mm. After stacking two test pieces, the test piece was heated to 280 ° C. and pressed at a mold temperature of 150 ° C. and a load of 168 kN (7.5 MPa). (Area after pressurization / initial area) × 100 was evaluated as a flow ratio (%). The results are shown in Table 1.

[Evaluation]
Compared with the comparative example product 1, the example products 1 to 4 have a large bending stress and flexural modulus, although the volume content of the reinforcing fibers is as small as 20 Vol%. This is presumed to be the result of advancement of dispersion and defibration of the reinforcing fibers by kneading and extruding the thermoplastic resin and the reinforcing fibers using a screw type extruder.

  Further, even when compared with the comparative example product 2, the example products 1 to 4 have larger bending stress and bending elastic modulus. This is presumed to be a result of the fiber breakage occurring in Comparative Example Product 2 with a screw length as long as 1500 mm.

  In addition, the example product 1 has a smaller bending stress and bending elastic modulus and flow ratio than the example products 2 to 4, but this has a strand diameter of 1.5 mm, which is compared with others. For this reason, it is presumed that a larger shear stress was generated at the die at the exit of the extruder, and the carbon fiber was broken and shortened.

  Moreover, compared with Example goods 1-4, the value of bending stress and the bending elastic modulus of Example goods 5-7 are large. This is presumed to be the result of heating and pressurizing strands that are not random but arranged with directionality.

Claims (4)

A method of manufacturing an FRP sheet,
Extruding a fiber reinforced thermoplastic resin composition composed of a thermoplastic resin and reinforcing fibers as a strand using a screw type extruder,
Cutting the extruded strand to the required length;
The process of placing the cut strands in the mold, and
A step of heating and pressurizing the strands arranged in the mold to form a predetermined shape ,
The process of extruding as a strand is carried out at a screw rotation speed of 30 to 200 rpm of a screw type extruder, a kneading length of the screw of 100 to 450 mm, and a temperature equal to or higher than the melting point of the resin to be used. Method. 2. The method for producing an FRP sheet according to claim 1, wherein, in the step of arranging in the mold, the cut strands are randomly arranged without directionality in the mold. 2. The method for producing an FRP sheet according to claim 1, wherein, in the step of arranging in the mold, the cut strands are arranged with directionality in the mold. A thermoplastic resin is polyamide 6, any one of from the volume content of the carbon fiber is reinforced fibers claims 1, characterized by using a fiber-reinforced thermoplastic resin composition is 20~30Vol% 3 The manufacturing method of the FRP sheet | seat as described in.