JP6788340B2 - Prepreg sheet - Google Patents

Description

The present invention relates to a prepreg sheet, which is an intermediate of a molded body made of a non-woven fabric containing carbon fibers and thermoplastic resin fibers.

Carbon fiber is generally a fiber made by carbonizing acrylic fiber or pitch (a by-product of petroleum, coal, coal tar, etc.) at a high temperature, and according to the JIS standard, the precursor of organic fiber is heat-carbonized. It is defined as a fiber in which 90% or more by mass is composed of carbon. Since carbon fibers are more dispersible and less entangled with each other than other fibers, carbon fibers are rarely used as a single material when forming a non-woven fabric, and resin fibers such as synthetic resin and carbon fibers are rarely used. It is used as a composite material in combination with.

For example, in Patent Document 1, a non-woven fabric made of carbon fibers is formed by mixing 20 to 70% by weight of carbon fibers and 30 to 80% by weight of binder fibers and burning the non-woven fabric to remove the binder fibers. How to obtain is described.

Further, as a method of improving the entanglement of the carbon fibers and the thermoplastic resin fibers to obtain a non-woven fabric, the staple-like short fibers of the carbon fibers and the thermoplastic resin fibers are mixed and made into a sheet, and then the sheets are laminated. There is known a method of entwining carbon fibers and thermoplastic resin fibers with a needle punch or the like (for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 10-314519 Japanese Unexamined Patent Publication No. 2008-081872

However, according to the method disclosed in Patent Document 1, although a non-woven fabric made of only carbon fibers can be obtained, the non-woven fabric is easily frayed due to the weak entanglement between the carbon fibers, and the carbon fibers that are broken and shortened during production are produced. It has the disadvantage of being easily dropped.

Further, the carbon fiber bundle is opened, the opened carbon fiber and the thermoplastic resin fiber are mixed and made into a sheet, and then the laminated sheet is entangled with the carbon fiber and the thermoplastic resin fiber by a needle punch or the like. When the non-woven fabric obtained by the method of making the fibers is heated and pressure-molded using the non-woven fabric to obtain a molded product, the thermoplastic resin fibers in which the fibers are entangled tend to melt and the fibers tend to be unentangled. .. Further, since the force of the carbon fibers to return to the original state before opening the fibers acts, the prepreg sheet obtained by heating and pressure molding the non-woven fabric tends to expand in the thickness direction.

Further, when a molded product is manufactured with a mold using the prepreg sheet having a tendency to expand, it becomes difficult to insert the prepreg sheet into the mold, and a desired molded product cannot be manufactured. Was causing.

The present invention has been made in consideration of the above-mentioned conventional problems, and the expansion of the thickness is suppressed even when heated during molding, enabling smooth insertion into a mold, and a desired molded product. It is intended to provide a prepreg sheet capable of obtaining.

The prepreg sheet of the present invention that has solved the above problems is a prepreg sheet that is an intermediate of a molded body made of a non-woven fabric containing carbon fibers and thermoplastic resin fibers, and is from the melting point of the thermoplastic resin fibers to the melting point +100. It is characterized in that the thickness expansion coefficient when heated at a temperature of ° C. for 90 seconds is 250% or less.

The prepreg sheet preferably has a basis weight of 100 to 1500 g / m ² and a thickness of 0.5 to 6.0 mm.

In the prepreg sheet, it is preferable that the average fiber length of the carbon fibers is 15 to 100 mm and the average fiber length of the thermoplastic resin fibers is 25 to 100 mm.

In the prepreg sheet, as the thermoplastic resin fiber, one selected from polypropylene, polyamide, polycarbonate, polyphenylene sulfide, and polyetherimide can be used.

In the prepreg sheet, it is preferable that the carbon fiber and the thermoplastic resin fiber are mixed in a mass ratio of 20/80 to 80/20.

Since the prepreg sheet of the present invention has a thickness expansion coefficient of 250% or less when heat-treated (hereinafter referred to as pre-molding treatment) performed after prepreg formation and before mold molding, a conventional prepreg sheet was used. The thermoplastic resin fibers that are entangled during heat molding, which are generated at the time, are melted, the fibers are unentangled, and the force that causes the carbon fibers to return to the original state before entanglement works, and the sheet It is possible to suppress the phenomenon that the fiber expands in the thickness direction.

It is the schematic which showed an example of the manufacturing method of the prepreg sheet which concerns on embodiment of this invention, and the manufacturing method of obtaining a molded article from the prepreg sheet. It is a figure which showed an example of the prepreg sheet which concerns on embodiment of this invention, and the process until the molded article is obtained from the prepreg sheet. It is an SEM cross-sectional photograph of the prepreg sheet which concerns on embodiment of this invention. (A) shows before the pre-molding process, and (b) shows after the pre-molding process. It is a SEM cross-sectional photograph of a conventional needle punched prepreg sheet. (A) shows before the pre-molding process, and (b) shows after the pre-molding process.

Hereinafter, the prepreg sheet of the present invention will be described in detail with reference to the drawings.

As a result of various studies on the phenomenon that the sheet expands in the pre-molding process performed as a pretreatment when a molded product is obtained using the prepreg sheet, the present inventors have conducted the pre-molding process (specifically, heat). We have succeeded in obtaining a prepreg sheet having a thickness expansion coefficient of 250% or less when the plastic resin fiber is heated from the melting point to the melting point + 100 ° C. for 90 seconds). As a result, expansion in the thickness direction during molding of the sheet is suppressed, smooth insertion into the mold is possible, and a desired molded product can be obtained. The coefficient of thermal expansion does not have to satisfy 250% or less in all of the above temperature ranges, and may satisfy 250% or less in any of the above temperature ranges.

A prepreg is an intermediate material for semi-cured sheet-like molding in which carbon fibers are impregnated with a thermosetting resin or a thermoplastic resin, and is known to have stable quality when used as a molded product. ing. Recently, from the viewpoints of mass productivity, shortening of molding time, reduction of equipment cost, etc., a combination of carbon fiber and thermoplastic resin fiber has been attracting attention, and weight reduction and high performance are required. It is used for aerospace applications, automobile parts applications, sports applications, etc.

Carbon fiber is generally a fiber made by carbonizing acrylic fiber or pitch (a by-product of petroleum, coal, coal tar, etc.) at a high temperature, and according to the JIS standard, the precursor of organic fiber is heated and carbonized. It is defined as a fiber obtained by treatment and having a mass ratio of 90% or more composed of carbon. Carbon fibers using acrylic fibers are classified as PAN-based (Polyacrylonitrile), and carbon fibers using pitch are classified as pitch-based (PITCH).

As described above, carbon fibers are less dispersible and less entangled with each other than other fibers. Therefore, carbon fibers are rarely used as a single material when forming a non-woven fabric, and resins such as synthetic resins are rarely used. It is used as a composite material in which fibers and carbon fibers are combined. The carbon fiber used in the prepreg sheet of the present invention is also used as a composite material in combination with the thermoplastic resin fiber.

In the embodiment of the present invention, either PAN-based or pitch-based carbon fibers can be used, but it is more preferable to use PAN-based carbon fibers from the viewpoint of dispersibility with thermoplastic resin fibers.

The average fiber length of the carbon fibers is preferably 15 to 100 mm, more preferably 20 to 80 mm, still more preferably 30 to 70 mm. When the average fiber length is 15 mm or more, the mechanical strength when a prepreg sheet made of a non-woven fabric containing carbon fibers and thermoplastic resin fibers is molded is likely to be maintained. Further, when the average fiber length is 100 mm or less, the dispersibility of the carbon fibers and the thermoplastic resin fibers in the non-woven fabric is improved, and it becomes easy to form a uniform non-woven fabric.

The thermoplastic resin used as the resin fiber is not particularly limited as long as it is a synthetic resin that has elasticity at room temperature, is not easily deformed, and can be softened by heating and molded into a desired shape. Specifically, those selected from polypropylene, polyamide, polycarbonate, polyphenylene sulfide, and polyetherimide are preferable in consideration of productivity, material cost, and the like. Further, it is preferable to use one having an average fiber length of 25 to 100 mm, more preferably 30 to 80 mm, and even more preferably 40 to 70 mm. When the average fiber length is 25 mm or more, the mechanical strength when a prepreg sheet made of a non-woven fabric containing carbon fibers and thermoplastic resin fibers is molded is improved. Further, when the average fiber length is 100 mm or less, the dispersibility of the carbon fibers and the thermoplastic resin fibers in the non-woven fabric is improved, and it becomes easy to form a uniform non-woven fabric. Further, regarding the fineness, it is preferable to use one having a fineness of 2.2 to 22 dtex, more preferably one having a fineness of 2.2 to 20 dtex, and even more preferably one having a fineness of 2.2 to 15 dtex. When the fineness is 2.2 dtex or more, or 22 dtex or less, the dispersibility of the carbon fiber and the thermoplastic resin fiber in the non-woven fabric is improved, and it becomes easy to form a uniform non-woven fabric.

The mass ratio of the carbon fiber to the thermoplastic resin fiber is preferably in the range of 20/80 to 80/20. When the carbon fiber content is 80% by mass or less, or when the carbon fiber content is 20% by mass or more, the thermoplastic resin fiber is sufficiently melted in the heating / pressurizing treatment after the non-woven fabric is formed, and the shape of the prepreg sheet can be easily maintained. Become.

In the embodiment of the present invention, the basis weight and thickness of the prepreg sheet are 100 to 1500 g / m ² and 0.5, respectively, in consideration of smooth processing of molded products for automobile parts applications and the like. It is preferably ~ 6.0 mm, more preferably 250 to 1200 g / m ² , 1.0 to 5.0 mm, still more preferably 500 to 1000 g / m ² , 2.0 to 4.5 mm.

Next, an example of the method for producing the prepreg sheet of the present invention and the method for obtaining a molded product from the prepreg sheet will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a schematic view showing an example of a method for producing a prepreg sheet according to an embodiment of the present invention and a method for obtaining a molded product from the prepreg sheet. FIG. 2 shows the process from opening the carbon fiber bundle to obtaining a non-woven fabric from a mixed cotton of carbon fibers and thermoplastic resin fibers and laminating them to obtain a prepreg sheet from the non-woven fabric and a molded product from the prepreg sheet. It is a chart diagram which showed an example of the process of.

In the prepreg sheet 1 of the present invention, the carbon fiber 3 obtained by opening the carbon fiber bundle 2 and the thermoplastic resin fiber 4 are mixed in a desired mass ratio (for example, 40% by mass of the carbon fiber and 60% by mass of the thermoplastic resin fiber). After the non-woven fabric 5 is obtained by laminating to form a sheet, the non-woven fabric 5 is heat-pressurized (for example, when a thermoplastic resin fiber made of polypropylene is used, the temperature is 240 ° C. for 90 seconds. It can be obtained by 1 MPa). The basis weight and thickness of the obtained prepreg sheet 1 are adjusted to desired values (for example, basis weight 250 g / m ² , thickness 0.5 to 6.0 mm). The prepreg sheet 1 is premolded (for example, when a thermoplastic resin fiber made of polypropylene is used, 240 ° C., 90 ° C.) in consideration of smooth insertion in the mold molding in the subsequent process. Seconds) is applied.

A known method can be used as a method of mixing the carbon fibers 3 obtained by opening the carbon fiber bundle 2 and the thermoplastic resin fibers 4 and then laminating them in a sheet shape. For example, a commercially available blender machine can be used for the mixed cotton, and a guarding method can be used for sheeting / laminating, and a commercially available card machine can be used.

Further, the method for heating and pressurizing the obtained nonwoven fabric 5 is not particularly limited, and a known method can be used. For example, from the viewpoint of operability and versatility, it is preferable to use the method of performing the belt press 7 in the infrared heating furnace 6, but as another method, heating by a commercially available heat-through or an oven device is also possible. .. The heating temperature is preferably from the melting point of the thermoplastic resin fiber to the melting point of + 100 ° C., more preferably from the melting point of the thermoplastic resin fiber to + 20 ° C. to the melting point of + 100 ° C., more preferably + 100 ° C., in consideration of the melting point of the thermoplastic resin fiber. The melting point of the thermoplastic resin fiber is preferably + 40 ° C. to the melting point of + 100 ° C. The heating time is preferably 30 to 300 seconds, more preferably 60 to 240 seconds, and even more preferably 60 to 180 seconds. Further, the pressing force is preferably 0.1 to 10 MPa, more preferably 0.5 to 10 MPa, still more preferably 1 to 10 MPa in consideration of the homogeneity of the carbon fiber and the thermoplastic resin fiber and the strength after the treatment. good.

The pre-molding process performed before molding the prepreg sheet 1 is performed in the infrared heating furnace 6 at a predetermined heating temperature and heating time. Specifically, the melting point of the thermoplastic resin fiber to the melting point + 100 ° C. is preferable, more preferably the melting point of the thermoplastic resin fiber + 20 ° C. to the melting point + 100 ° C., and even more preferably the melting point of the thermoplastic resin fiber + 40 ° C. to The melting point + 100 ° C. is preferable. The heating time is preferably 90 seconds.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples, and may be modified to the extent that it can be adapted to the gist of the above and the following. It is possible, and they are all within the technical scope of the invention.

(Manufacturing of non-woven fabric)
After 40% by mass of PAN-based carbon fiber (manufactured by Toray) having an average fiber length of 50 mm and 60% by mass of polypropylene (manufactured by Daiwabo) having an average fiber length of 51 mm and a melting point of 168 ° C. were mixed with a commercially available blender. , A non-woven fabric was produced by carding with a commercially available card machine to form a sheet and laminate the fibers. The number of samples was set to 6.

(Heating / pressurizing treatment)
The non-woven fabric obtained above was sent to a commercially available belt press machine and treated in a commercially available infrared heating furnace to obtain a prepreg sheet. The obtained prepreg sheet was used as the product of the present invention. The basis weight of the prepreg sheet was 250 g / m ² , and the thickness was 1.3 mm. The heating temperature is 240 ° C., the heating time is 90 seconds, and the pressing force is 1 MPa.

In the production of the above-mentioned non-woven fabric, a prepreg sheet obtained by the same method as the product of the present invention was used as a comparative product except that the sheet and the laminated product were fiber-entangled with a commercially available needle punch. The number of samples was set to 6.

(Pre-molding process)
The prepreg sheet obtained by the above method was treated in a commercially available infrared heating furnace. The heating temperature is 240 ° C. (melting point of polypropylene + 72 ° C.), and the heating time is 90 seconds.

(Cross-section observation before and after pre-molding process)
The cross section of the prepreg sheet obtained by the above method before and after the pre-molding treatment was observed by SEM (Scanning Electron Microscope), and the state of fiber entanglement between the carbon fiber and the thermoplastic resin fiber was examined. FIG. 3 shows the prepreg sheet of the product of the present invention, and FIG. 4 shows the prepreg sheet of the comparative product. (A) shows before the pre-molding process, and (b) shows after the pre-molding process.

From FIG. 3, it can be seen that the cross section of the prepreg sheet of the product of the present invention does not have fiber entanglement in the thickness direction regardless of before and after the pre-molding process. On the other hand, as shown in FIG. 4, the cross section of the comparative prepreg sheet has fiber entanglement in the thickness direction due to the needle punch applied before the pre-molding process, and the fiber entangled state is maintained even after the pre-molding process. You can see that.

(Measurement of apparent thickness change rate before and after pre-molding pretreatment)
For the product of the present invention and the comparative product, the apparent thickness before and after the pre-molding treatment was measured with a commercially available thickness gauge, and the apparent thickness change rate (thickness expansion coefficient) was determined. The results are shown in Table 1.

From Table 1, it can be seen that the prepreg sheet of the present invention has an average apparent thickness change rate of about 200% after the pre-molding treatment, and is suppressed to a smaller expansion than the comparative product. On the other hand, in the cross section of the comparative prepreg sheet, the apparent thickness change rate after the pre-molding treatment is about 480% on average, and it can be seen that the expansion after the pre-molding treatment cannot be suppressed.

From the above results, since the prepreg sheet of the present invention suppresses expansion in the thickness direction even when heated during molding, it enables smooth insertion of the prepreg sheet into a mold, and is used for automobiles and the like. The desired molded product can be obtained.

1 prepreg sheet 2 carbon fiber bundle 3 carbon fiber 4 thermoplastic resin fiber 5 non-woven fabric 6 infrared heating furnace 7 belt press

Claims (4)

A prepreg sheet that is an intermediate of a molded body made of a non-woven fabric containing carbon fibers and thermoplastic resin fibers.
The basis weight is 250 to 1200 g / m ² , and the thickness is 0.5 to 6.0 mm.
Ri thickness expansion coefficient der 250% or less when heated for 90 seconds at a temperature of melting point ~ melting point + 100 ° C. of the thermoplastic resin fibers,
The average fiber length of the carbon fiber prepreg sheet, wherein 30~100mm der Rukoto (except a prepreg sheet containing a thermoplastic resin which is not derived from the thermoplastic resin fibers constituting the nonwoven fabric). Prepreg sheet according to claim 1, wherein the average fiber length before the Kinetsu thermoplastic resin fibers is 25 to 100 mm. The prepreg sheet according to claim 1 or 2 , wherein the thermoplastic resin fiber is selected from polypropylene, polyamide, polycarbonate, polyphenylene sulfide, and polyetherimide. The prepreg sheet according to any one of claims 1 to 3 , wherein the carbon fiber and the thermoplastic resin fiber are mixed in a mass ratio of 20/80 to 80/20.