JP7519891B2 - Thermoplastic resin film, prepreg, and prepreg laminate - Google Patents

Description

The present invention relates to a thermoplastic resin film for impregnating carbon fiber to form a prepreg, which is an intermediate material for thermoplastic carbon fiber reinforced resin, a prepreg, and a prepreg laminate using the same.

Carbon fiber reinforced resin is used in a wide range of fields, including automobiles, aircraft, and civil engineering temporary construction materials, due to its characteristics of light weight, excellent strength, and high durability. Carbon fiber reinforced resin is classified into thermosetting carbon fiber reinforced resin and thermoplastic carbon fiber reinforced resin, depending on the properties of the resin used for impregnation. Of these, thermoplastic carbon fiber reinforced resin is used particularly as a material for automobiles, due to its advantages of short molding time and recyclability by heating.

Thermoplastic carbon fiber reinforced resin is manufactured using prepreg, an intermediate material. Prepreg is obtained by opening carbon fiber tows (bundles) and impregnating the carbon fibers with thermoplastic resin, and among prepregs, those in which carbon fiber tows (bundles) are opened and aligned in one direction are called unidirectional (UD) prepregs.

However, in conventional prepregs, the thermoplastic resin has poor wettability with the sizing agent components of the carbon fibers, which causes poor adhesion between the carbon fibers and the thermoplastic resin, resulting in voids and reduced strength.

Therefore, for example, a prepreg has been proposed that is manufactured by subjecting a laminate in which carbon fibers are sandwiched between two thermoplastic resin films to a heat press (heat and pressure treatment), heat compounding, and then irradiating the laminate with an electron beam. It is described that such a configuration makes it possible to obtain a prepreg with excellent mechanical strength (see, for example, Patent Document 1).

In addition, carbon fibers for carbon fiber reinforced resin have been proposed that are electrolytically oxidized in an aqueous solution having a pH of 2 to 4 and containing an inorganic acid with a pH of 1 or less in 1 mol/L aqueous solution and an inorganic salt with a pH of 6 to 8 in 1 mol/L aqueous solution. It is described that this composition reduces the variation in the mechanical properties of the carbon fibers and the variation in the fiber surface structure, and makes it possible to uniform the adhesive strength between the carbon fibers and the resin (see, for example, Patent Document 2).

JP 2010-58286 A JP 2011-202297 A

However, the prepreg described in Patent Document 1 above had the problem that the effect could not be sustained after irradiation with electron beams, and the mechanical strength decreased over time.

Similarly, with the carbon fiber described in Patent Document 2, the electrolytic oxidation treatment was not effective for a sustained period of time, and there was a problem in that the adhesion between the carbon fiber and the resin decreased over time.

Therefore, the present invention has been made in consideration of the above problems, and aims to provide a thermoplastic resin film, a prepreg, and a prepreg laminate using the same that have high adhesion to carbon fibers and can produce a prepreg laminate with low porosity and excellent strength over a long period of time.

To achieve the above object, the thermoplastic resin film of the present invention is a thermoplastic resin film for impregnating carbon fibers to form a prepreg, and is characterized in that the ratio of hydrogen bonding components to the surface free energy is 6% or more and 35% or less.

The present invention aims to provide a thermoplastic resin film and prepreg that have high adhesion to carbon fibers, and can produce a prepreg laminate with low porosity and excellent strength over a long period of time, as well as a prepreg laminate using the same.

FIG. 2 is a schematic diagram for explaining an example of a method for producing a prepreg according to an embodiment of the present invention. FIG. 2 is a schematic diagram for explaining another example of the method for producing a prepreg according to an embodiment of the present invention.

The present invention will be described in detail below. Note that the present invention is not limited to the following embodiments, and can be modified as appropriate within the scope of the present invention.

<Thermoplastic resin film>
The thermoplastic resin film of the present invention is a resin film for forming a prepreg by placing it on one side and the other side of a sheet-like continuous carbon fiber, or by placing sheet-like continuous carbon fiber on one side and the other side of the thermoplastic resin film of the present invention and impregnating the carbon fiber by a film stacking method described later.

Examples of such thermoplastic resin films include films made of polycarbonate resin, phenoxy resin, polyester resin such as polybutylene terephthalate, polyphenylene sulfide resin, polysulfone resin, polyether ether ketone resin, polyimide resin, polystyrene resin, ABS resin, etc.

Of these, it is preferable to use polycarbonate resin, phenoxy resin, polybutylene terephthalate, and polyphenylene sulfide resin, which have superior impact resistance, heat resistance, and recyclability compared to thermosetting resins, and are low cost.

The thickness of the thermoplastic resin film is preferably 10 to 100 μm, and more preferably 15 to 30 μm. If the thickness of the thermoplastic resin film is 10 μm or more, impregnation failure (occurrence of voids between carbon fibers) caused by a lack of resin components relative to the carbon fibers in the prepreg can be prevented. If the thickness of the thermoplastic resin film is 100 μm or less, a decrease in the volume fraction (Vf value) of carbon fibers caused by excess resin components in the prepreg can be prevented, and therefore a decrease in strength when made into a prepreg laminate can be prevented.

The "volume content (Vf value)" referred to here is measured in accordance with the combustion method of JIS K 7075 (Test method for fiber content and void content of carbon fiber reinforced plastics).

In addition, the thermoplastic resin film of the present invention preferably has a surface free energy of 30 mJ/ ^m2 or more and 60 mJ/ ^m2 or less. If the surface free energy is less than 30 mJ/ ^m2 , the adhesion to the carbon fiber may be significantly reduced, and a high-strength prepreg may not be produced. If the surface free energy is greater than 60 mJ/ ^m2 , blocking may occur to the extent that the thermoplastic resin film cannot be wound up, making it difficult to form the film.

This "surface free energy" can be determined using the method described in the examples below.

Here, the inventors have investigated conditions for improving the adhesion between a thermoplastic resin film and carbon fibers in a prepreg, and have found that by controlling the ratio of hydrogen bonding components to the surface free energy of the thermoplastic resin film, the compatibility between the thermoplastic resin film and the sizing agent components of the carbon fibers is improved.

More specifically, in the thermoplastic resin film of the present invention, it is important that the ratio of hydrogen bonding components to the surface free energy is 6% or more and 35% or less. If the ratio of hydrogen bonding components is 6% or more and 35% or less, the compatibility between the thermoplastic resin film and the sizing agent components of the carbon fiber is improved, and the adhesion between the thermoplastic resin film and the carbon fiber in the prepreg is improved, making it possible to reduce the void ratio in the prepreg laminate. As a result, the stress concentration occurring around the voids can be alleviated, making it possible to improve the strength of the prepreg laminate over the long term.

The term "void ratio" used here refers to the volume ratio of the portion of the prepreg laminate that is not impregnated with thermoplastic resin, measured in accordance with the combustion method of JIS K 7075 (Test method for fiber content and void ratio of carbon fiber reinforced plastics).

In addition, because the adhesion between the thermoplastic resin film and the carbon fiber is improved, fiber feathering on the surface of the prepreg and prepreg laminate is suppressed, making it possible to provide a prepreg and prepreg laminate with excellent appearance and feel.

In order to further reduce the void ratio in the prepreg laminate, the ratio of hydrogen bonding components to the surface free energy is preferably 10% or more and 30% or less.

The amount of hydrogen bonding components is preferably 3.0 mJ/m ² or more and 20 mJ/m ² or less, and more preferably 4.0 mJ/m ² or more and 18 mJ/m ² or less.

In this way, by using the thermoplastic resin film of the present invention, a prepreg laminate with low porosity and excellent strength over a long period of time can be obtained.

In addition, in the thermoplastic resin film of the present invention, the heat shrinkage rate in the direction perpendicular to the mechanical axis (longitudinal) direction (hereinafter referred to as "MD") of the film when heated for 2 minutes at a heating temperature near the melting point of the thermoplastic resin is preferably less than 7.0%, more preferably less than 5.0%, and even more preferably less than 3.0%. If the heat shrinkage rate in TD is less than 7.0%, when producing a prepreg by the film stacking method described below, no heat shrinkage (neck-in) occurs in the TD of the thermoplastic resin film, and therefore the carbon fibers can be prevented from moving to the center of the prepreg. Therefore, a prepreg with uniform properties in the plane can be realized.

The above "thermal shrinkage rate" can be determined by the method described in the examples below.

In addition, the thermoplastic resin film of the present invention may contain, in addition to the above-mentioned thermoplastic resin, an antistatic agent, a flame retardant, and a compatibilizer, as long as the properties of the thermoplastic resin film are not impaired.

As the antistatic agent, an organic antistatic agent having a hydrophilic group can be used, and examples of such antistatic agents include low molecular weight conductive monomers (surfactants) and high molecular weight conductive polymers. Examples of low molecular weight conductive monomers include nonionic, anionic, cationic, and amphoteric types, and examples of high molecular weight conductive polymers include polyethers and ion conductive polymers.

From the viewpoint of increasing the amount of hydrogen bonding components in the thermoplastic resin film, it is preferable to use a low molecular weight conductive monomer. Examples of low molecular weight conductive monomers include polyhydric alcohol fatty acid esters such as sorbitan fatty acid esters, sucrose fatty acid esters, and glycerin fatty acid esters, quaternary ammonium salts such as alkyltrimethylammonium chloride, and sulfonic acid compounds such as sodium alkanesulfonate. These antistatic agents may be used alone or in combination of two or more.

The use of an organic antistatic agent with a hydrophilic group increases the amount of hydrogen bonding components in the thermoplastic resin film, improving compatibility with the sizing agent components of the carbon fiber, which has a very high polarity, and as a result, improving adhesion between the thermoplastic resin film and the carbon fiber in the prepreg.

When an antistatic agent is used, the content of the antistatic agent in the entire thermoplastic resin film is preferably 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass, based on 100% by mass of the thermoplastic resin film, from the viewpoint of improving the hydrophilic effect of the film surface and the film moldability.

Flamme retardants that can be used include phosphorus compounds, silicon compounds, metal hydroxides, metal sulfonates, melamine compounds, and fluorine resins. More specifically, phosphorus compounds include cyclic phosphazenes and copolymerized phosphorus compounds, and metal sulfonates include potassium nonafluorobutanesulfonate. These flame retardants may be used alone or in combination of two or more.

In the present invention, the flame retardancy of the thermoplastic resin film can be improved by using such a flame retardant.

When a flame retardant is used, from the viewpoint of forming a thermoplastic resin film with a desired thickness (e.g., 20 μm), the content of the flame retardant in the entire thermoplastic resin film is preferably 5 to 30 mass %, and more preferably 7 to 20 mass %, of 100 mass % of the thermoplastic resin film.

As compatibilizers, random polymer types and graft block polymer types can be used. More specifically, examples include block copolymers of polystyrene and polycaprolactone, styrene/maleic anhydride/unsaturated derivative copolymers modified with caprolactone, ε-polycaprolactone grafted with maleic anhydride, and block copolymers of glycidyl methacrylate-styrene-acrylonitrile copolymer and polycarbonate.

In the present invention, the use of such a compatibilizer can improve the moldability of the thermoplastic resin film.

When a compatibilizer is used, from the viewpoint of forming a thermoplastic resin film with a desired thickness (e.g., 20 μm), the content of the compatibilizer relative to the entire thermoplastic resin film is preferably 0.05 to 5 mass %, and more preferably 0.1 to 1 mass %, of 100 mass % of the thermoplastic resin film.

The thermoplastic resin film of the present invention is produced, for example, by an inflation method, a T-die extrusion method, a calendar method, etc.

When manufacturing by the inflation method, molten thermoplastic resin is extruded from a ring die and formed into a continuous tube. Compressed air is fed into this tubular resin from the inside to gradually expand it into a film of a specified width, and the thermoplastic resin film of the present invention can be produced by pinching it between the nip rolls of a take-up machine and taking it up.

When manufacturing a thermoplastic resin film by the inflation method, the resin is formed to a target thickness when the resin temperature at the exit of the ring die is, for example, 60°C higher than the glass transition temperature, and then the film is drawn while slowly cooling while maintaining its shape, to obtain a thermoplastic resin film with a thickness of 10 to 100 μm.

When the thermoplastic resin film of the present invention is produced by a T-die extrusion method, the cylinder temperature and die temperature of a single-screw or twin-screw extruder are set to a temperature 50°C to 150°C higher than the glass transition point of the thermoplastic resin, the thermoplastic resin is fed into the extruder, melt-kneaded at a screw rotation speed of 5 to 50 rpm, and extruded from a T-die to obtain a thermoplastic resin film having a thickness of 10 to 100 μm.

<Prepreg>
The prepreg of the present invention can be obtained by a film stacking method in which continuous carbon fibers are supplied to a fiber spreading/impregnation machine and sandwiched between the thermoplastic resin films of the present invention, or the thermoplastic resin film of the present invention is sandwiched between the continuous carbon fibers, the thermoplastic resin film is laminated onto the carbon fibers, and the carbon fibers are impregnated with the thermoplastic resin by a heat/pressure treatment.

Figure 1 is a schematic diagram for explaining an example of a method for manufacturing a prepreg according to an embodiment of the present invention.

When manufacturing the prepreg, first, the sheet-like continuous carbon fiber CS is conveyed toward the plate heater 12 by the pair of supply rollers 11 of the opening and impregnation machine 10, and thermoplastic resin films RF1, RF2 are laminated on one side and the other side of the continuous carbon fiber CS to produce a laminate consisting of the sheet-like continuous carbon fiber CS and the thermoplastic resin films RF1, RF2. Next, this laminate is conveyed in the direction of the arrow in the figure, and passed through the plate heater 12 while being sandwiched between the first roller pair 13 and the second roller pair 14, to perform a heating and pressurizing treatment. This causes the thermoplastic resin films RF1, RF2 of the laminate to soften and be impregnated into the sheet-like continuous carbon fiber CS, and the prepreg P of the present invention can be obtained.

Also, FIG. 2 is a schematic diagram for explaining another example of a method for producing a prepreg according to an embodiment of the present invention. In this case, first, the thermoplastic resin film RF is conveyed toward the plate heater 12 by the pair of supply rollers 11 of the opening and impregnation machine 10, and sheet-like continuous carbon fibers CS1, CS2 are laminated on one side and the other side of the thermoplastic resin film RF to produce a laminate consisting of the thermoplastic resin film RF and the sheet-like continuous carbon fibers CS1, CS2. Next, this laminate is conveyed in the direction of the arrow in the figure, and passed through the plate heater 12 while being sandwiched between the first roller pair 13 and the second roller pair 14, to perform a heating and pressurizing treatment. Then, the thermoplastic resin film RF of the laminate is softened and impregnated into the sheet-like continuous carbon fibers CS, and the prepreg P of the present invention can be obtained.

By using a thermoplastic resin film having the above-mentioned predetermined thickness to manufacture prepregs using a film stacking method, it becomes possible to uniformly impregnate the carbon fibers with the resin components, thereby improving the yield when manufacturing the prepregs and, as a result, making it possible to reduce the manufacturing costs of the prepregs.

When the thermoplastic resin film is impregnated into the carbon fiber by the film stacking method, the film is pre-impregnated at a temperature near the melting point of the thermoplastic resin, and then the main impregnation is performed. The thermoplastic resin film breaks at temperatures above the melting point of the thermoplastic resin, and pre-impregnation is insufficient at temperatures below that point. In addition, if thermal shrinkage (neck-in) occurs in the TD of the thermoplastic resin film near the melting point of the thermoplastic resin, the carbon fiber may move toward the center of the prepreg, resulting in in-plane variation in physical properties. For this reason, dimensional stability of the thermoplastic resin film is required. The dimensional stability of the thermoplastic resin film is evaluated, for example, by heating for 2 minutes in an oven with the inside temperature set to a heating temperature near the melting point of the thermoplastic resin, as described above, and measuring the heat shrinkage rate.

The thickness of the prepreg is preferably 50 to 300 μm, more preferably 60 to 150 μm. If the thickness of the prepreg is less than 50 μm, the number of prepregs required to produce a prepreg laminate increases, which may result in a longer processing time and a decrease in productivity. In addition, since the thickness of the prepreg is small, the thickness of the thermoplastic resin film constituting the prepreg must also be small (for example, less than 10 μm), and impregnation failure may occur in the prepreg due to a shortage of resin components relative to the carbon fibers. On the other hand, if the thickness of the prepreg is greater than 300 μm, the thickness of the thermoplastic resin film constituting the prepreg must also be large (for example, greater than 100 μm), which may result in a decrease in the volume fraction (Vf value) of the carbon fibers due to excess resin components in the prepreg, and the strength of the prepreg laminate may decrease.

<Prepreg Laminate>
The prepreg laminate of the present invention is produced by stacking a plurality of prepregs in a unidirectional (UD) direction in which the fibers are aligned in one direction, and then subjecting the laminate to a heat and pressure treatment. The number of prepregs stacked can be appropriately changed based on the thickness of the prepreg laminate. For example, when the thickness of the prepreg laminate is 1.5 to 2.5 mm, 40 to 60 prepregs can be stacked.

In addition, in the prepreg laminate of the present invention, from the viewpoint of improving strength, it is preferable that the void ratio is less than 2.0%, and more preferably 1.0% or less.

Similarly, from the viewpoint of improving the strength of the prepreg laminate of the present invention, it is preferable that the volume content (Vf value) of carbon fibers in the prepreg laminate is 40 to 60%.

As described above, the prepreg laminate of the present invention has excellent strength, and the bending strength is preferably 1170 MPa or more, and more preferably 1200 MPa or more.

For example, aluminum alloys have a high flexural modulus of 70 GPa or more, but from the viewpoint of enabling replacement with metals such as aluminum, it is preferable that the flexural modulus of the prepreg laminate of the present invention is 70 GPa or more.

The term "flexural strength and flexural modulus" used here refers to the values measured in accordance with the "Bending test method for carbon fiber reinforced plastics" specified in JIS K 7074, converted to a carbon fiber volume content (Vf value) of 50%.

The present invention will be described below based on examples. Note that the present invention is not limited to these examples, and these examples can be modified or changed based on the spirit of the present invention, and are not excluded from the scope of the present invention.

The materials used in the preparation of the thermoplastic resin film are shown below.
(1) Polycarbonate resin 1 (manufactured by Sumika Polycarbonate Co., Ltd., product name: PCX-10325B, melting point: 150°C, containing sorbitan fatty acid ester-based antistatic agent)
(2) Polycarbonate resin 2 (manufactured by Sumika Polycarbonate Co., Ltd., product name: AS2010L, melting point: 150°C, containing sorbitan fatty acid ester-based antistatic agent)
(3) Polycarbonate resin 3 (manufactured by Mitsubishi Engineering Plastics Corporation, product name: NOVAREX 7022E TH, melting point: 150°C, containing sorbitan fatty acid ester-based antistatic agent)
(4) Polycarbonate resin 4 (manufactured by Sumika Polycarbonate Co., Ltd., product name: Gulliver 301-15, melting point: 150°C)
(5) Polycarbonate resin 5 (manufactured by Teijin Limited, product name: Panlite MN-4400Z, melting point: 150° C.)
(6) Polycarbonate resin 6 (manufactured by Sumika Polycarbonate Co., Ltd., product name: Gulliver 302-4, melting point: 150°C)
(7) Phenoxy resin (manufactured by Nippon Steel Chemical & Material Co., Ltd., product name: Phenototo YP-50, melting point: 95°C)
(8) Polypropylene resin (manufactured by Prime Polymer Co., Ltd., product name: F-300SP, melting point: 160°C)
(9) Polyvinyl alcohol resin (manufactured by Kuraray Co., Ltd., product name: MOWIFLEX C-500T, melting point: 200° C.)
(10) Antistatic agent 1: Sodium alkanesulfonate (manufactured by Kao Corporation, product name: Electronstripper PC-3)
(11) Polybutylene terephthalate resin (manufactured by Polyplastics Co., Ltd., product name: 700FP)
(12) Flame retardant 1: cyclic phosphazene (manufactured by Fushimi Pharmaceutical Co., Ltd., trade name: Rabitol FP110)
(13) Flame retardant 2: Polyphosphonate (manufactured by FRX Polymers, product name: Nofia HM1100)
(14) Compatibilizer 1: Block copolymer of glycidyl methacrylate-styrene-acrylonitrile copolymer and polycarbonate (manufactured by NOF Corp., product name: Modiper CL430-G)

Example 1
<Preparation of Thermoplastic Resin Film>
First, the cylinder temperature and die temperature of the single screw extruder were set to 240 to 280°C, and the above-mentioned polycarbonate resin was fed into the extruder, melt-kneaded at a screw rotation speed of 5 to 50 rpm, and extruded from a T-die to obtain a thermoplastic resin film having a thickness of 20 μm.

<Calculation of the ratio of hydrogen bond components to surface free energy>
The surface free energy on the surface of the obtained thermoplastic resin film was calculated by measuring the contact angles of various liquid droplets (measurement temperature: 25° C.) and using the values thus measured according to the OWRK theory (Owens-Wendt-Rable-Kaelble).

More specifically, a droplet of diiodomethane was used as the "dispersion component" and a droplet of pure water was used as the "hydrogen bond component (= polar component)". Using a fully automatic contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name: DM-901), the contact angles of diiodomethane and pure water were measured in accordance with JIS R 3257 under conditions of a temperature of 25°C and a relative humidity of 50%. From these, the surface free energies of the dispersion component and the hydrogen bond component (polar component) were calculated, and the surface free energy [mJ/m ² ] on the surface of the thermoplastic resin film was calculated from the sum of the calculated surface free energies using the calculation formula of the OWRK theory, and the ratio [%] of the hydrogen bond component to the surface free energy was calculated. Each surface energy was calculated using surface free energy analysis software (manufactured by Kyowa Interface Science Co., Ltd., product name: FAMAS). The above results are shown in Table 1.

<Calculation of heat shrinkage rate>
Both ends of a thermoplastic resin film of 50 mm (TD) x 100 mm (MD) in the MD were fixed on a SUS plate of 0.3 mm thickness with aluminum tape along the TD, and the film was placed in an oven (manufactured by Espec Corp., model: PHH-201M), and the film was maintained for 2 minutes at a damper opening of 50% and a heating temperature (170°C) near the melting point. The length (mm) of the most shrunk part in the TD of the resin film was then measured, and the shrinkage rate in the TD was calculated from the ratio to 50 mm. The above calculation was performed 10 times, and the average value was taken as the heat shrinkage rate of this example. The results are shown in Table 1.

<Preparation of prepreg>
Next, the obtained resin film and carbon fiber tow (manufactured by Toray Industries, Inc., product name: T700SC-1200 0 ) were supplied to the opening and impregnation machine 10 shown in FIG. 2 , and the polycarbonate resin film was sandwiched between the continuous carbon fibers. Heat and pressure treatment was performed at a temperature of 250° C. and a rate of 10 m/min, thereby obtaining a prepreg having a width of 220 mm and a thickness of 85 μm.

<Preparation of prepreg laminate>
Next, 48 pieces of the prepreg were cut to the size of a press die (200 mm square), and stacked so that the carbon fibers were aligned in the same direction. This laminate was then placed in a press die and subjected to a heat press treatment at a temperature of 260° C. and a pressure of 5 MPa for 15 minutes to produce a prepreg laminate with a thickness of 1.9 mm.

<Calculation of void ratio and fiber volume content (Vf)>
Next, the void content and fiber volume content (Vf) of the obtained prepreg laminate were calculated in accordance with the combustion method of JIS K 7075 (Test method for fiber content and void content of carbon fiber reinforced plastics).

More specifically, the mass of the prepreg laminate, which was the measurement sample, was measured using an electric furnace and an electronic balance, and then it was heated from room temperature in a crucible under a nitrogen atmosphere at a heating rate of 20°C/min. When it reached 550°C, it was incinerated for 10 minutes to convert the resin content in the sample to ashed material.

Since carbon fiber does not decompose when heated in a nitrogen atmosphere, the weight at 550°C was used as the carbon fiber weight, and the volume of the carbon fiber was calculated by multiplying this by the specific gravity. The weight of the ashed resin was used as the resin weight, and the volume of the resin was calculated by multiplying this by the specific gravity of the resin.

Then, the fiber volume content (Vf) [%] was calculated using formula (3) in JIS K 7075, and the void ratio [%] was calculated using formula (4) in JIS K 7075. The results are shown in Table 1.

<Measurement of bending strength and bending modulus>
Next, in accordance with JIS K 7074 (bending test method for carbon fiber reinforced plastics), the bending strength and bending modulus of the obtained prepreg laminate were calculated by a four-point bending method.

More specifically, samples were cut from the obtained prepreg laminate to a width of 15 mm and a length of 100 mm, and four-point bending measurements were performed using a tensile tester (Shimadzu Corporation, product name: Autograph 5000) equipped with a four-point bending jig under conditions of a crosshead speed of 5.0 mm/min, a support span of 81 mm, an indenter span of 27 mm, a support diameter of 4 mm, and an indenter diameter of 10 mm, to measure the bending strength [MPa] and bending modulus [GPa].

The measured four-point bending strength [MPa] and four-point bending modulus [GPa] were then divided by the volume content of carbon fiber (Vf value) and multiplied by 50% to calculate the four-point bending strength [MPa] and four-point bending modulus [GPa] converted to Vf50%. The results are shown in Table 1.

(Examples 2 to 6, 8 to 9, Comparative Examples 1 to 2)
Thermoplastic resin films, prepregs, and prepreg laminates having the thicknesses shown in Tables 1 and 2 were produced in the same manner as in Example 1 described above, except that the materials forming the thermoplastic resin films were changed to the materials shown in Tables 1 and 2.

In Example 5, 100 parts by mass of polycarbonate resin and 1.5 parts by mass of antistatic agent were mixed in a blender, and the molten resin extruded into strands using a twin-screw extruder was cooled and pelletized using a pelletizer. Thereafter, a thermoplastic resin film, prepreg, and prepreg laminate having the thicknesses shown in Table 1 were produced in the same manner as in Example 1 above.

In Example 8, 4 parts by mass of flame retardant 1, 10 parts by mass of flame retardant 2, and 1 part by mass of compatibilizer 1 were added to 100 parts by mass of polycarbonate resin, and the mixture was mixed in a blender. The molten resin was extruded into a strand shape using a twin-screw extruder, cooled, and pelletized using a pelletizer. Then, in the same manner as in Example 1 described above, a thermoplastic resin film, prepreg, and prepreg laminate having the thicknesses shown in Table 1 were produced.

(Example 7)
The material for forming the thermoplastic resin film was changed to the material shown in Table 1, and a thermoplastic resin film was formed by the inflation method. More specifically, the molten phenoxy resin was formed into a film of the target thickness when the resin temperature at the outlet of the ring die was 200°C, and extruded from the ring die to form a continuous tube. Compressed air was fed into this tubular resin from the inside to gradually expand it to a film of a predetermined width, and the film was taken up by nipping it between the nip rolls of a take-up machine to obtain a thermoplastic resin film of a thickness of 20 μm. Thereafter, a prepreg and a prepreg laminate were produced in the same manner as in Example 1 described above.

Then, in the same manner as in Example 1 described above, the ratio of hydrogen bond components to the surface free energy, the heat shrinkage rate, the porosity, and the fiber volume content (Vf) were calculated, and the bending strength and bending modulus were measured. The results are shown in Tables 1 and 2.

(Comparative Example 3)
Except for changing the material for forming the thermoplastic resin film to the material shown in Table 2, a thermoplastic resin film having the thickness shown in Table 2 was produced in the same manner as in Example 1 described above, and the ratio of hydrogen bonding components to the surface free energy was calculated.

The polyvinyl alcohol resin film of Comparative Example 3 was prone to blocking and difficult to wind, so prepregs could not be produced using the film stacking method described above. Therefore, calculations of heat shrinkage, void ratio, and fiber volume content (Vf), and measurements of bending strength and bending modulus were not performed.

As shown in Table 1, in the thermoplastic resin films of Examples 1 to 9, the ratio of hydrogen bonding components to the surface free energy is 6% or more and 35% or less, so it is clear that it is possible to obtain a prepreg laminate with improved adhesion between the thermoplastic resin and the carbon fiber, low porosity, and excellent strength over the long term.

On the other hand, as shown in Table 2, in the thermoplastic resin films of Comparative Examples 1 and 2, the ratio of hydrogen bonding components to the surface free energy is less than 6%, so the porosity of the prepreg laminate is high and the strength is inferior to that of Examples 1 to 7. In particular, in the polypropylene resin film of Comparative Example 2, the ratio of hydrogen bonding components to the surface free energy is very low, so the porosity of the prepreg laminate is very high and the strength is significantly reduced.

As described above, the present invention is suitable for a thermoplastic resin film for impregnating carbon fibers to form a prepreg, a prepreg, and a prepreg laminate using the same.

REFERENCE SIGNS LIST 10 Fiber opening and impregnation machine 11 Supply roller pair 12 Plate heater 13 First roller pair 14 Second roller pair CS, CS1, CS2 Carbon fiber P Prepreg RF, RF1, RF2 Thermoplastic resin film

Claims (8)

A thermoplastic resin film for impregnating carbon fibers having a sizing agent to form a prepreg,
The sizing agent is an epoxy resin,
The thermoplastic resin film contains a polycarbonate resin,
The amount of hydrogen bonding components in the thermoplastic resin film is 4.0 mJ/m2 ^or more and 18 mJ/m2 ^or less,
A thermoplastic resin film, characterized in that the ratio of hydrogen bonding components to the surface free energy is 6% or more and 35% or less. The thermoplastic resin film according to claim 1, characterized in that both ends in the MD of the thermoplastic resin film of 50 mm (TD) x 100 mm (MD) are fixed along the TD with aluminum tape to a 0.3 mm thick SUS plate, placed in an oven, and maintained at 170°C for 2 minutes with the damper open to 50%, after which the length (mm) of the most shrunken part in the TD of the resin film is measured, and the heat shrinkage rate in TD calculated as the ratio to 50 mm is less than 7.0%. 3. The thermoplastic resin film according to claim 1, wherein the thermoplastic resin film contains the polycarbonate resin and an antistatic agent. 3. The thermoplastic resin film according to claim 1, wherein the thermoplastic resin film contains the polycarbonate resin and a flame retardant. A prepreg characterized in that the carbon fibers are impregnated with the thermoplastic resin film described in any one of claims 1 to 4. A prepreg laminate comprising the prepreg according to claim 5. The prepreg laminate according to claim 6, characterized in that the prepreg laminate has a four-point bending strength calculated at Vf50% of 1301.1 MPa or more and 1412.4 MPa or less. A method for producing the thermoplastic resin film according to claim 1 or 2, comprising the steps of:
A step of setting a cylinder temperature and a die temperature of a single screw extruder to 240 to 280° C. and supplying the polycarbonate resin to the single screw extruder;
a step of melt-kneading the mixture at a screw rotation speed of 5 to 50 rpm and extruding the mixture through a T-die to obtain the thermoplastic resin film;
A method for producing a thermoplastic resin film, comprising:

Images