Patent Application
20230340213
The present invention relates to a fiber-reinforced resin sheet containing a resin film and reinforcing fibers, a fiber-reinforced composite material made by forming the fiber-reinforced resin sheet, and a molded article made by molding the fiber-reinforced composite material.
As an exemplary fiber-reinforced resin sheet, the following one disclosed in Patent Literature 1 is known. The fiber-reinforced resin sheet (thermoplastic carbon fiber prepreg) of Patent Literature 1 contains opened carbon fibers in the shape of a sheet, and a pair of thermoplastic resin films placed on the opposite surfaces (on one surface and the other surface) of the carbon fibers. The fiber-reinforced resin sheet having the structure is produced by sandwiching the carbon fibers between the pair of resin films, and pressing and heating the same. Specifically, for the fiber-reinforced resin sheet of Patent Literature 1, there are a step of supplying carbon fibers, while being opened, through supply rollers, and a step of placing the thermoplastic resin films on the opposite surfaces of the supplied carbon fibers, and thereafter, heating the resin films by plate heaters while sandwiching the resin films by the rollers. This enables the resin films to be softened and permeate into the carbon fibers, whereby a fiber-reinforced resin sheet having the structure described above is obtainable.
Patent Literature 1 mentions that the thickness of the resin films is desirably set between 8 and 55 μm. The reason is that the volume content (Vf value) of the carbon fibers in the fiber-reinforced resin sheet can be increased to 50 to 60%, whereby a high strength is achievable.
However, in Patent Literature 1, since the resin films are respectively arranged on the opposite surfaces of the carbon fibers (the carbon fibers are sandwiched between a pair of resin films), the ratio of the resin is inevitably liable to be high. In other words, if an attempt is actually made to increase the content of the carbon fibers in Patent Literature 1 to reach 50 to 60%, there will be the need to place a great amount of carbon fibers between the pair of resin films. Therefore, even if the resin films are pressed and heated during preparation, the softened resin films are still liable to fail to sufficiently permeate the inside of the carbon fibers. When the permeation of the resin films is insufficient, a failure such as the loosening of carbon fibers after the preparation is liable to occur.
The present invention has been made in view of the circumstances described above, and an object thereof is to provide a fiber-reinforced resin sheet which has a high content of reinforcing fibers and has a reduced formation failure, thereby improving the mechanical properties of a fiber-reinforced composite material or a molded article thereof.
A fiber-reinforced resin sheet according to an aspect of the present invention, which has solved the problem described above, has a thickness of 30 μm or more and 65 μm or less, and includes a resin film which is thermoplastic; and a plurality of reinforcing fibers that are placed on the opposite surfaces of the resin film in a state of being oriented in the same direction after being opened from a bundle of reinforcing fibers, wherein the resin film has a thickness of 5 μm or more and 15 μm or less, an areal weight of the reinforcing fibers is 25 g/m2 or more and 60 g/m2 or less, and a volume content of the reinforcing fibers is 60% or more and 75% or less.
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
Preparation of Fiber-Reinforced Resin Sheet
Step S1 is a sheet preparation step of preparing the fiber-reinforced resin sheet 1 shown in
As the reinforcing fiber 3, a carbon fiber, a glass fiber, an aramid fiber, a ceramic fiber, and the like may be used. Among these, the carbon fiber is advantageous in improving the strength, the corrosion resistance and the like of the molded article. As the carbon fiber, a PAN (polyacrylonitrile)-based carbon fiber having a particularly high strength are preferably used.
As the thermoplastic resin being a material of the resin film 2, i.e., as matrix resin for the fiber-reinforced resin sheet 1, polyamide (in particular, PA6, PA9T), polyolefin, polyester, polyacetal, polyphenylene sulfide, polycarbonate, acrylic resin, an acrylnitril-butadien-styrene copolymer (ABS), polyamide-imide, polysulfone, polyphenylsulfone, polyetherimide, polyethersulfone, polyetheretherketone, polyetherketoneketone, polyimide, polyarylate, fluororesin, liquid crystal polymer, thermoplastic epoxy resin, and the like may be raised. In addition, a polymer alloy obtained by mixing two or more kinds of these thermoplastic resins may be used as the material for the resin film 2.
The resin film 2 is a member having the shape of an ultrathin sheet (film shape) having a certain thickness, and is made of the thermoplastic resin. The resin film 2 is prepared, for example, by extruding thermoplastic resin. Further, the thickness of the resin film 2 is set to 5 μm or more and 15 μm or less.
The fiber-reinforced resin sheet 1 can be produced using, for example, a sheet production apparatus 50 shown in
Specifically, the sheet production apparatus 50 includes a plurality of pairs (two pairs here) of heating rollers 51 arranged vertically, a plurality of pairs (two pairs here) of cooling rollers 522 arranged vertically below the heating rollers 51, a pair of endless belts 54 wound over the heating rollers 51 and the cooling rollers 52, a pair of draw-out rollers 55 located below the endless belts 54, and a winding bobbin 56 arranged below the draw-out rollers 55.
An opening mechanism (not illustrated) for opening and expanding the fiber bundle 3′ in a band shape is provided on both sides of the heating rollers 51 at the uppermost stage. This opening mechanism is capable of forming a large number of continuous reinforcing fibers 3 spread in a thin band shape by continuously opening the fiber bundle 3′. It is sufficient that the opening mechanism has a mechanism capable of performing the operation. Various mechanisms may be used, such as a mechanism that taps the fiber bundle to spread it, a mechanism that blows the fiber bundle to spread it, and a mechanism that applies ultrasonic waves to the fiber bundle to spread it.
In the configuration of
The heating roller 51 is a high-temperature roller heated by an electric heater, heating medium, or the like. The heating rollers 51 continuously impregnate the resin film 2 with the reinforcing fibers 3 by heating the resin film 2 and the reinforcing fibers 3 introduced onto the both surfaces of the resin film 2 while sandwiching the resin film 2 and the reinforcing fibers 3 from the opposite sides by the endless belts 54. The resin film 2 is impregnated with the reinforcing fibers 3 in a state where the reinforcing fibers 3 are oriented in the same direction (in a vertical direction in
The cooling roller 52 is a low-temperature roller cooled by cooling medium or the like. The cooling rollers 52 cool the resin film 2 impregnated with the reinforcing fibers 3 while sandwiching the resin film 2 from the opposite sides by the endless belts 54, whereby the reinforcing fibers 3 are embedded in the resin film 2. A fiber-reinforced resin sheet 1, in which the resin film 2 (matrix resin) and the reinforcing fibers 3 are integrated, is thus prepared.
The draw-out roller 55 is a roller that draws out the prepared fiber-reinforced resin sheet 1 downward while applying tension to the fiber-reinforced resin sheet 1.
The winding bobbin 56 is a core material for winding up the fiber-reinforced resin sheet 1. The bobbin 56 is rotationally driven by a drive source such as a motor, and sequentially winds up the fiber-reinforced resin sheet 1 drawn out by the draw-out rollers 55 to form the fiber-reinforced resin sheet 1 into a roll shape.
The fiber-reinforced resin sheet 1 is completed through the above-described steps. A areal weight of the reinforcing fiber 3 in the fiber-reinforced resin sheet 1, i.e., a weight of the reinforcing fibers 3 impregnated per unit area of the resin film 2 is set to 25 g/m2 or more and 60 g/m2 or less. In other words, the opening mechanism of the sheet production apparatus 50 described above supplies the reinforcing fibers 3 with a predetermined density on the both surfaces of the resin film 2 in such a manner that the areal weight of the reinforcing fibers 3 falls between 25 and 60 g/m2. Further, when needed, the target areal weight may be achieved by repeating the above-described sequence of steps (the operation of supplying the reinforcing fibers 3 onto the both surfaces of the resin film 2 to impregnate the resin film 2 with the reinforcing fibers 3) a plurality of times.
The volume content of the reinforcing fibers 3, i.e., a value (Vf value) resulting from dividing a volume occupied by the reinforcing fibers 3 by a volume of the entire fiber-reinforced resin sheet 1 is set to 60% or more and 75% or less. Specifically, the volume content of the reinforcing fibers 3 is set to 60 to 75% by impregnating the resin film 2 having a thickness of 5 to 15 μm with the reinforcing fibers 3 at the above-described areal weight (25 to 60 g/m2).
The fiber-reinforced resin sheet 1 is made to have a thickness of 30 μm or more and 65 μm or less by setting the areal weight and the volume content of the reinforcing fibers within the respective ranges described above. The fiber-reinforced resin sheet 1 having the above thickness has a flexibility high enough to be smoothly formed into a roll shape.
Formation of Fiber-Reinforced Composite Material
After the preparation of the fiber-reinforced resin sheet 1 is completed as described above, the flow proceeds to the subsequent Step S2. Step S2 is a sheet stacking step of forming the fiber-reinforced composite material 10 by stacking the fiber-reinforced resin sheets 1 one over another. In this sheet stacking step S2, as shown in
Specifically, in the sheet stacking step S2, the fiber-reinforced resin sheet 1 (a fiber-reinforced resin sheet 1 having a long length and formed into a roll shape) prepared during the above-described sheet preparation step S1 is cut to thereby make base material sheets 1A having a proper shape and size. Thereafter, the base material sheets 1A having been cut off are stacked in the thickness direction. Here, the base material sheets 1A are stacked in such a manner that the respective fiber directions X of base material sheets 1A adjoining each other in the thickness direction are different from each other. In other words, the base material sheets 1A are stacked in such a manner that the respective fiber directions X of adjoining sheets are angularly different from one another in the plan view.
After having stacked the base material sheets 1A in the manner described above, the base material sheets 1A are heat-fused, for example by heating the base material sheets 1A while pressing them in the thickness direction. A plate-shaped fiber-reinforced composite material 10 in which the base material sheets 1A are integrally stacked is thus formed. The number of the stacked base material sheets 1A is determined in view that the fiber-reinforced composite material 10 has a thickness of roughly several millimeters.
Pressing
After the formation of the fiber-reinforced composite materials 10 is completed as described above, the flow proceeds to the subsequent Step S3. Step S3 is a press step of pressing the fiber-reinforced composite materials 10 using a heat press machine 60 shown in
Specifically, in the press step S3, as shown in
As shown in
After the placement of the fiber-reinforced composite materials 10 in the press mold is completed as described above, subsequently, the article 30 is molded by executing a main process (molding) of pressingly inserting the punch 61 into the die 62 while heating the fiber-reinforced composite materials 10. Specifically, the fiber-reinforced composite materials 10 are pressed by pressing the punch 61 downward by a press device not illustrated in a state where the insertion part 61b of the punch 61 is inserted into the recess 62a of the die 62 while heating the die 62 by the heater to thereby raise the temperature of the fiber-reinforced composite materials 10 to a predetermined degree (see
As described above, in the first embodiment of the present invention, the fiber-reinforced composite materials 10 made by stacking a plurality of fiber-reinforced resin sheets 1 (base material sheets 1A) are used as a material for producing the molded article 30, the fiber-reinforced resin sheets 1 each containing reinforcing fibers 3 at a volume content of 60 to 75%. Accordingly, the embodiment has the advantage of producing a molded article 30 having a high strength at a good moldability.
Specifically, in the first embodiment, the fiber-reinforced resin sheet 1 is prepared by placing reinforcing fibers 3 on the both surfaces of a relatively thin resin film 2 of 5 to 15 μm, and the areal weight of the reinforcing fibers 3 to the resin film 2 is set between 25 and 60 g/m2. This makes it possible to increase the volume content (Vf value) of reinforcing fibers 3 in the fiber-reinforced resin sheet 1 to 60 to 75% while preventing a formation failure of the sheet 1.
In other words, a configuration where reinforcing fibers 3 are placed on the both surfaces of the resin film 2 enables the areal weight of 25 to 60 g/m2 to be achieved over a whole without excessively increasing the placement amount of reinforcing fibers 3 on each surface (one surface or the other surface) of the resin film 2. This makes it possible to sufficiently impregnate each surface of the resin film 2 with reinforcing fibers 3 by the heating and the pressing during the preparation, and increase the bonding strength between the resin film 2 and the reinforcing fibers 3. Further, since the resin film 2 is thin in that the thickness is between 5 and 15 μm, the resin film 2 can be soften by the heating in a shorter time. This makes it possible to sufficiently place reinforcing fibers 3 inside of the resin film 2. This leads to prevention of an occurrence of a failure such as loosening of a reinforcing fiber 3 after the preparation. Additionally, under such conditions, a fiber-reinforced resin sheet 1 with a high volume content (Vf value) of 60 to 75% is realizable. As a result, the strength of a molded article made by using the fiber-reinforced resin sheets 1 (the strength of the fiber-reinforced composite material 10 and the molded article 30 made by using the same) can be sufficiently increased.
In particular, in the first embodiment, when a fiber-reinforced composite material 10 is formed from the fiber-reinforced resin sheets 1, the fiber-reinforced resin sheets 1 are stacked in such a manner that their respective fiber directions X (orientation directions of the reinforcing fibers 3) are angularly different from one another in a plan view. Therefore, the reinforcing effect of the reinforcing fibers 3 can be exerted in a plurality of different directions over the fiber-reinforced composite material 10. Consequently, the mechanical properties of the fiber-reinforced composite material 10 and the molded article 30 can be improved.
In the first embodiment, when a fiber-reinforced composite material 10 is formed from the fiber-reinforced resin sheets 1 (base material sheets 1A), the fiber-reinforced resin sheets 1 are stacked in such a manner that the respective fiber directions X of adjoining sheets are different from one another (for example, the fiber directions X vary at equal increments of 45°). However, the fiber-reinforced resin sheets 1 may be stacked in such a manner that the fiber directions X vary by each group of several sheets.
Preparation of Fiber-Reinforced Resin Sheet
Step S11 is a sheet preparation step of preparing the fiber-reinforced resin sheet 1 shown in
Preparation of Chopped Pieces
After the preparation of the fiber-reinforced resin sheet 1 is completed as described above, the flow proceeds to the subsequent Step S12. Step S12 is a chopped piece preparation step of cutting off the chopped pieces 1B shown in
First, cuts C1 extending in the longitudinal direction are formed as shown in
Next, in the subsequent section II, cuts C2 which are continuous from an end to the other end of the fiber-reinforced resin sheet 1 in the width direction are formed. The cuts C2 may be formed, for example, using a rotary cutter and the like. The cuts C2 are formed each time the fiber-reinforced resin sheet 1 is fed by a predetermined length in the longitudinal direction. Accordingly, a large number of chopped pieces 1B each having the shape of a rectangle having a shorter side with a length corresponding to a pitch of the cuts C1 and a longer side with a length corresponding to a pitch of the cuts C2 are cut off.
As described above, the fiber-reinforced resin sheet 1 is a thermoplastic resin sheet containing a large number of reinforcing fibers 3 oriented in the longitudinal direction thereof. Therefore, each chopped piece 1B cut off from the fiber-reinforced resin sheet 1 also contains a large number of reinforcing fibers 3 oriented in the longitudinal direction thereof (i.e., in a direction of the longer side thereof). Specifically, the chopped piece 1B contains a resin film 2 which is thermoplastic, and a large number of reinforcing fibers 3 placed in the resin film 2 (matrix resin) in a state of being oriented in the same direction.
The chopped piece 1B is set at a proper size in consideration of the formativeness and the like of the material in the later-described press step (S14). Specifically, the chopped piece 1B is formed in the shape of a rectangle having the shorter side with a length of 2 mm or more and 50 mm or less and the longer side with a length of 2 mm or more and 80 mm or less. As a suitable example, the chopped piece 1B is formed in the shape of a rectangle of 5×20 mm. The chopped pieces 1B have the same thickness as the thickness of the fiber-reinforced resin sheet 1, which is 30 μm or more and 65 μm or less.
Formation of Fiber-Reinforced Composite Material
After the preparation of the chopped pieces 1B is completed as described above, the flow proceeds to the subsequent Step S13. Step S13 is a chopped piece placing step of forming a fiber-reinforced composite material 20 shown in
First, as shown in
Next, the carrier sheet 21 and the chopped pieces 1B thereupon are pressed and heated using an unillustrated heating roller, whereby the carrier sheet 21 and the chopped pieces 1B are integrated with one another. Specifically, the carrier sheet 21 and the chopped piece 1B are bonded (fused) with each other, and concurrently, the accumulating chopped pieces 1B are bonded (fused) with each other by the pressing and the heating with the use of the heating roller. The bonding forms a sheet where the carrier sheet 21 and a large number of chopped pieces 1B are integrated. Further, what results from cutting the sheet into proper shape and size is obtained as the fiber-reinforced composite material 20. The thickness of the fiber-reinforced composite material 20, i.e., the total thickness of the carrier sheet 21 and the chopped pieces 1B accumulating thereupon is set at several millimeters (for example, 2 mm). In other words, the layers of the accumulating chopped pieces 1B is set at the number of layers which makes the fiber-reinforced composite material 20 have a thickness of several millimeters.
As the material of the carrier sheet 21, the same thermoplastic resin as the matrix resin (i.e., the resin film 2) of the chopped pieces 1B may be basically used. However, a carrier sheet 21 of various materials may be used as long as the material is a thermoplastic resin, and a carrier sheet 21 of a material different from that of the matrix resin of the chopped pieces 1B may be also used.
Pressing
After the formation of the fiber-reinforced composite material 20 is completed as described above, the flow proceeds to the subsequent Step S14. Step S14 is a press step of pressing the fiber-reinforced composite material 20 using the heat press machine 60 shown in
As described above, in the second embodiment of the present invention, the fiber-reinforced composite material 20 containing a large number of chopped pieces 1B cutoff from the fiber-reinforced resin sheet 1 and placed one over another is used as a material for producing the molded article 30, the fiber-reinforced resin sheet 1 containing reinforcing fibers 3 at a volume content of 60 to 75%. Accordingly, this embodiment has the advantage of producing a molded article 30 having a high strength at a good moldability in the same manner as the above-described first embodiment.
In particular, in the second embodiment, a large number of chopped pieces 1B cut off into the shape of a rectangle having the shorter side with the length of 2 to 50 mm and the longer side with the length of 2 to 80 mm are prepared. The fiber-reinforced composite material 20 is formed by placing chopped pieces 1B one over another, the fiber directions of the reinforcing fibers 3 contained in the chopped piece 1B being two-dimensionally at random. This makes it possible to impart a sufficient isotropy (pseudo-isotropy) to the mechanical properties of the fiber-reinforced composite material 20. Consequently, a desirable reinforcing effect can be obtained by the reinforcing fibers 3.
In the second embodiment, the fiber-reinforced composite material 20 is formed by placing and adhering a large number of chopped pieces on a carrier sheet 21 made of a thermoplastic resin. However, the carrier sheet 21 may be omitted. In other words, it is also possible to form a composite material made solely of the chopped pieces 1B placed and adhered to one another as the fiber-reinforced composite material 20.
Next, Examples of fiber-reinforced resin sheets 1 produced according to the methods described in the first embodiment or the second embodiment (Step S1 of
Production Conditions
Here, the film material and the film preparation condition mean a material and a preparation condition of the resin film 2. The roll temperature means a temperature of the heating roller 51 of the sheet production apparatus 50. The feeding linear speed means a speed at which the reinforcing fibers 3 are fed to the resin film 2 in the sheet production apparatus 50.
One of the following materials 1 to 3 was used as a reinforcing fiber 3 in preparation of the Examples.
Materials of Reinforcing Fiber
Fiber-reinforced resin sheets 1 were produced using reinforcing fibers 3 of one of the above materials 1 to 3 and under the production conditions described above to thereby obtain Examples 1 to 8 shown in
As shown in
Here, focusing on a relationship between the resin film 2 and the areal weight of the reinforcing fibers 3, it can be generally said that the two have a relationship that the areal weight of the reinforcing fibers 3 is greater as the resin film 2 is thicker. Specifically, the areal weight in the cases (Examples 2, 3, 6) where the resin film 2 had a thickness of 10 mm was greater on average than the areal weight in the cases (Examples 1, 8) where the thickness was 5 mm, and the areal weight in the cases (Examples 4, 5, 7) where the resin film 2 had a thickness of 15 mm was greater on average than the areal weight in the cases (Examples 2, 3, 6) where the thickness was 10 mm. In this way, the areal weight of the reinforcing fiber 3 was adjusted according to the thickness of the resin film 2. Consequently, the respective volume contents of the reinforcing fibers 3 were kept within the target range (60 to 75%), and the respective thicknesses of the fiber-reinforced resin sheets 1 were also kept within the target range (30 to 65 μm).
On the other hand,
For example, in Comparative Example 1, the thickness (exceeding 15 μm) of the resin film 2 was greater than the target range although the areal weight of the reinforcing fibers 3 was within the target range. This caused a fiber shortage that the volume content of the reinforcing fibers 3 was less than the target range (60 to 75%). This means that, when a fiber-reinforced composite material is formed using this fiber-reinforced resin sheet 1, the strength of this fiber-reinforced composite material cannot be sufficiently increased.
In Comparative Example 2, the areal weight (exceeding 60 g/m2) of the reinforcing fibers 3 was greater than the target range, which caused Failure 1 causing peeling of reinforcing fibers 3. This is considered to be because the resin content of the resin film 2 was excessively small relative to the content of the reinforcing fibers 3.
In Comparative Example 3, both the thickness of the resin film 2 and the areal weight of the reinforcing fibers 3 were less than the target ranges, which resulted in both Failure 2 causing a remarkable deviation of the fiber density in the width direction and Failure 3 causing a formation failure of the resin film 2. Further, the thickness of the fiber-reinforced resin sheet 1 was out of its target range.
In Comparative Examples 4, 5, the areal weight (less than 60 g/m2) of the reinforcing fibers 3 was less than the target range, which resulted in Failure 2 causing a remarkable deviation of the fiber density in the width direction. Additionally, in Comparative Example 5, a fiber shortage that the volume content of the reinforcing fibers 3 was excessively small (less than 60%) occurred.
It can be paradoxically understood that the parameters should be kept within their respective target ranges in order to sufficiently increase the content of the reinforcing fibers 3 while securing the formability.
Next, Examples and Comparative Examples of fiber-reinforced composite materials will be described. Here, plate-shaped fiber-reinforced composite materials having a thickness of 2 mm were formed using the fiber-reinforced resin sheets 1 of Examples and Comparative Examples described above as Examples 9 to 11 and Comparative Examples 6 and 7. The respective properties are shown in
Example 9 is a fiber-reinforced composite material 10 obtained by stacking the fiber-reinforced resin sheets 1 of the above-described Example 6 in the above-described method of the first embodiment (
Example 10 is similar to Example 9 excepting that the sheet to be used as the material was the fiber-reinforced resin sheet 1 of Example 4.
Comparative Example 6 is also similar to Example 9 excepting that the sheet to be used as the material was the fiber-reinforced resin sheet 1 of Comparative Example 1.
Example 11 is a fiber-reinforced composite material 20 obtained by placing the above-described fiber-reinforced resin sheet 1 of Example 6 in the above-described method of the second embodiment (
Comparative Example 7 is similar to Example 11 excepting that the sheet to be used as the material was the fiber-reinforced resin sheet 1 of Comparative Example 1.
Example 9, Example 10, and Comparative Example 6 are fiber-reinforced composite materials 10 formed using only the respective fiber-reinforced resin sheets 1 as the material. Therefore, the respective volume contents of the reinforcing fibers 3 in the fiber-reinforced composite materials 10 coincided with those of the fiber-reinforced resin sheets 1 (Example 6, Example 4, Comparative Example 1) used as the material. On the other hand, chopped pieces 1B were prepared from the fiber-reinforced resin sheet 1 and placed on a carrier sheet 21 to form the fiber-reinforced composite materials 20 of Example 11 and Comparative Example 7. Therefore, volume contents of the reinforcing fibers 3 in the respective fiber-reinforced composite materials 20 were slightly small relative to those of the fiber-reinforced resin sheets 1 (Example 6, Comparative Example 1) which were materials prior to the formation. This is because the carrier sheet 21 increased the resin content.
A tensile test and a bending test were conducted, and tensile strength, tensile modulus, bending strength, and bending modulus were measured about the above-described Examples 9 to 11 and Comparative Examples 6, 7, respectively. The tensile test was conducted by stretching a test piece having a width of 25 mm, a length of 250 mm, and a thickness of 2 mm in a longitudinal direction thereof. The bending test was conducted by performing a so-called four-point bending test to a test piece having a width of 15 mm, a length of 100 mm, and a thickness of 2 mm. The results of the respective tests are shown in
Comparing the ones (Examples 9, 10, Comparative Example 6) formed in the method of the first embodiment (four-axis sheet stacking) to one another, Examples 9, 10 show the higher strength (tensile strength, bending strength) and modulus (tensile modulus, bending modulus) than Comparative Example 6. This is considered to be mainly because the volume contents of the reinforcing fibers 3 in Examples 9, 10 are higher than that in Comparative Example 6.
Similarly, comparing the ones (Example 11, Comparative Example 7) formed in the method of the second embodiment (chopped piece accumulation) to one another. Example 11 shows the higher strengths and moduli than Comparative Example 7. This is also considered to be mainly attributable to a difference in the volume contents of the reinforcing fibers 3 from each other.
From the above, it can be understood that the fiber-reinforced composite materials formed using the fiber-reinforced resin sheets of Examples have more excellent mechanical properties than the fiber-reinforced composite materials formed using the liber-reinforced resin sheets of Comparative Examples.
The inventions included in the embodiments described above are summarized hereinafter.
A fiber-reinforced resin sheet according to an aspect of the present invention is a fiber-reinforced resin sheet having a thickness of 30 μm or more and 65 μm or less, and contains a resin film which is thermoplastic, and a plurality of reinforcing fibers that are placed on the opposite surfaces of the resin film in a state of being oriented in the same direction after being opened from a bundle of reinforcing fibers, wherein the resin film has a thickness of 5 μm or more and 15 μm or less, an areal weight of the reinforcing fibers is 25 g/m2 or more and 60 g/m2 or less, and a volume content of the reinforcing fibers is 60% or more and 75% or less.
In this configuration, reinforcing fibers are placed on both surfaces of a relatively thin resin film of 5 to 15 μm to prepare the fiber-reinforced resin sheet, and further, the areal weight of the reinforcing fibers to the resin film is set between 25 and 60 g/m2. This makes it possible to increase the volume content of the reinforcing fibers in the fiber-reinforced resin sheet to 60 to 75% while preventing a formation failure of the sheet.
In other words, a configuration where reinforcing fibers are placed on the both surfaces of the resin film enables the achievement of the areal weight of 25 to 60 g/m2 over a whole without excessively increasing the placement amount of reinforcing fibers on each surface (one surface or the other surface) of the resin film. This makes it possible to sufficiently impregnate each surface of the resin film with reinforcing fibers by the heating and the pressing during the preparation, and increase the bonding strength between the resin film and the reinforcing fibers. Further, since the resin film is thin in that the thickness is from 5 to 15 μm, the resin film can be softened by the heating in a shorter time. This makes it possible to sufficiently place reinforcing fibers inside of the resin film. This leads to prevention of an occurrence of a failure such as loosening of a reinforcing fiber after the preparation. Additionally, under such conditions, a fiber-reinforced resin sheet with a high volume content of 60 to 75% is realizable. As a result, the strength of a molded article made by using the fiber-reinforced resin sheets can be sufficiently increased.
A fiber-reinforced composite material according to another aspect of the present invention is a fiber-reinforced composite material including the above-described fiber-reinforced resin sheets stacked in a thickness direction, wherein the fiber-reinforced resin sheets are stacked in such a manner that their respective fiber directions that are orientation directions of the reinforcing fibers are angularly different from one another in a plan view.
In this configuration, the reinforcing effect of the reinforcing fibers can be exerted in a plurality of different directions over the fiber-reinforced composite material. Consequently, the mechanical properties of the fiber-reinforced composite material can be improved.
A fiber-reinforced composite material according to a still another aspect of the present invention is a fiber-reinforced composite material including a plurality of chopped pieces that are cut off from the above-described fiber-reinforced resin sheet and are stacked in a thickness direction, wherein the chopped pieces have the shape of a rectangle having a shorter side with a length of 2 mm or more and 50 mm or less and a longer side with a length of 2 mm or more and 80 mm or less, and are stacked in such a manner that their respective fiber directions that are orientation directions of the reinforcing fibers are two-dimensionally at random (Claim 3).
This configuration makes it possible to impart a sufficient isotropy (pseudo-isotropy) to the mechanical properties of the fiber-reinforced composite material. Consequently, a desirable reinforcing effect can be obtained by the reinforcing fibers.
A molded article according to a still another aspect of the present invention is a molded article made by molding the above-described fiber-reinforced composite material.
In this configuration, the strength of a molded article can be sufficiently increased.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-218665 | Dec 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/043554 | 11/29/2021 | WO |
