Prepreg, prepreg laminate and method for producing prepreg

Abstract

The present invention relates to a prepreg which contains an oriented liquid crystal polymer and a base that uses a continuous carbon fiber bundle as a forming material. The liquid crystal polymer is a thermotropic liquid crystal polymer and the base is included in an amount of at least 25 parts by mass but not more than 550 parts by mass per 100 parts by mass of the liquid crystal polymer.

Claims

1. A prepreg comprising an oriented liquid crystal polymer, and a base that uses a continuous carbon fiber bundle as a forming material, wherein the oriented liquid crystal polymer is impregnated into the base, and wherein a molecular chain degree of orientation of the oriented liquid crystal polymer is at least 20%.

2. The prepreg according to claim 1, wherein the liquid crystal polymer is a thermotropic liquid crystal polymer.

3. The prepreg according to claim 1, comprising the base in an amount of at least 25 parts by mass but not more than 550 parts by mass per 100 parts by mass of the liquid crystal polymer.

4. A prepreg laminate prepared by laminating a plurality of the prepreg according to claim 1.

5. A method for producing the prepreg according to claim 1, the method comprising a step of superimposing a film that uses an oriented liquid crystal polymer as a forming material, and a base that uses a continuous carbon fiber bundle as a forming material, and subsequently performing heating, thereby melt-impregnating the liquid crystal polymer into the base.

6. The prepreg according to claim 1, wherein a proportion of carbon fibers extending continuously from one end of the base to the other end of the base without a break is 50% by mass to 100% by mass with respect to a total mass of the continuous carbon fiber bundle.

Description

EXAMPLES

(1) The present invention is described below in further detail using a series of examples and a comparative example, but the present invention is not limited to these examples.

(2) <Measurement of Degree of Orientation MOR of Liquid Crystal Polymer Contained in Liquid Crystal Polymer Film>

(3) The MOR of a liquid crystal polymer film (degree of orientation in drawing direction of film/degree of orientation in direction perpendicular to drawing direction and thickness direction) was measured using a molecular orientation analyzer MOA-5012A (manufactured by Oji Scientific Instruments Co., Ltd.). An MOR value greater than 1 means the liquid crystal polymer film is oriented in the drawing direction.

(4) <Measurement of Molecular Chain Degree of Orientation of Liquid Crystal Polymer Contained in Liquid Crystal Polymer Film>

(5) A wide-angle X-ray diffraction measurement was performed by installing an imaging plate in an X-ray small-angle scattering device. The device used was a NanoSTAR (device name, manufactured by Bruker AXS GmbH). Specifics of the measurement are described below.

(6) For the X-rays, a rotating anode X-ray generator with a Cu target was used to generate X-rays at an output of 50 kV and 100 mA, and these X-rays were irradiated onto the liquid crystal polymer film. The X-rays were passed through an X-ray optical system composed of cross-coupled Goebel mirrors and three pinhole slits (wherein the hole diameters of the slits in order from the X-ray generator side were 500 μmø, 150 μmø, and 500 μmø) before contacting the liquid crystal polymer film. Upon contact with the liquid crystal polymer film, the X-rays that were scattered from the liquid crystal polymer film were detected using the imaging plate (IP), the camera length from the sample to the IP was 15 cm. The degree of vacuum inside the device was not more than 40 Pa.

(7) <Measurement of Liquid Crystal Polymer Flow Starting Temperature>

(8) Using a Flowtester CFT-500 (manufactured by Shimadzu Corporation), about 2 g of the liquid crystal polymer was packed in a cylinder fitted with a die having a nozzle with an inner diameter of 1 mm and a length of 10 mm, the liquid crystal polymer was melted by raising the temperature at a rate of 4° C./minute under a load of 9.8 MPa (100 kg/cm), the melted polymer was then extruded from the nozzle, and the temperature at which a viscosity of 4,800 Pa-s (48,000 poise) was obtained was measured.

(9) <Matrix Resins (A)>

(10) A liquid crystal polymer film (A-1) and a polyamide film (A-2) that were used as the matrix resin (A) are described below.

(11) [Liquid crystal polymer film (A-1)]

(12) (Production of Liquid Crystal Polymer)

(13) A reactor fitted with a stirrer, a torque meter, a nitrogen gas inlet, a thermometer and a reflux condenser was charged with 1,034.99 g (5.5 mol) of 6-hydroxy-2-naphthoic acid, 378.33 g (1.75 mol) of 2,6-naphthalenedicarboxylic acid, 83.07 g (0.5 mol) of terephthalic acid, 272.52 g (2.475 mol, a 0.225 molar excess relative to the total number of moles of the 2,6-naphthalenedicarboxylic acid and the terephthalic acid) of hydroquinone and 1,226.87 g (12 mol) of acetic anhydride, and 0.17 g of 1-methylimidazole was then added as a catalyst. Subsequently, the gas inside the reactor was substituted with nitrogen gas, and with the contents undergoing constant stirring under a stream of nitrogen gas, the temperature was raised from room temperature to 145° C. over a period of 15 minutes, and the mixture was then refluxed at 145° C. for one hour. The temperature was then raised from 145° C. to 310° C. over a period of 3 hours and 30 minutes while any by-product acetic acid and unreacted acetic anhydride were removed.

(14) After holding the temperature at 310° C. for 3 hours, the contents were removed and cooled to room temperature. The thus obtained solid product was ground to a particle size of about 0.1 to 1 mm using a grinder. A solid-phase polymerization was then performed by heating the ground solid product under a nitrogen atmosphere, from room temperature to 250° C. over a period of one hour, subsequently from 250° C. to 310° C. over a period of 10 hours, and then holding the temperature at 310′C for 5 hours. The product obtained following this solid-phase polymerization was then cooled to obtain a powdered liquid crystal polymer.

(15) This liquid crystal polymer had a repeating unit (1) in which Ar.sup.1 was a 2,6-naphthylene group in an amount of 55 mol % relative to the total number of moles of all the repeating units. Further, the liquid crystal polymer had 17.5 mol % of a repeating unit (2) in which Ar.sup.2 was a 2,6-naphthylene group. Furthermore, the liquid crystal polymer had 5 mol % of a repeating unit (2) in which Ar.sup.2 was a 1,4-phenylene group. Moreover, the liquid crystal polymer also had 22.5% of a repeating unit (3) in which Ar.sup.3 was a 1,4-phenylene group and X and Y were both oxygen atoms.

(16) The flow starting temperature of the obtained liquid crystal polymer was 333° C.

(17) (Liquid Crystal Polymer Film Formation)

(18) The powdered liquid crystal polymer was granulated and pelletized using a twin-screw extruder PCM-30 (manufactured by Ikegai, Ltd.). Subsequently, the pelletized liquid crystal polymer was supplied to a single-screw extruder (screw diameter: 50 mm), melted, and extruded in a film-like form from a T-die (lip length: 300 mm, lip clearance: 1 mm, die temperature: 350° C.) and then cooled, thus obtaining a liquid crystal polymer film (A-1) having a width of 520 mm and a thickness of 25 μm.

(19) Measurement of the MOR of the obtained liquid crystal polymer film (A-1) revealed a value of 2.25, confirming orientation in the drawing direction.

(20) Measurement of the molecular chain degree of orientation for the liquid crystal polymer film (A-1) revealed a value of 17%.

(21) [Polyamide Film (A-2)]

(22) A polyamide 6 film ON-25 (manufactured by Unitika Ltd.) with a thickness of 25 μm was prepared and used as a polyamide film (A-2).

(23) [Liquid Crystal Polymer Film (A-3)]

(24) Using the same liquid crystal polymer as Example 1, but with the exception of reducing the winding speed from the single-screw extruder, the same film formation method as Example 1 was used to obtain a liquid crystal polymer film (A-3).

(25) Measurement of the MOR of the obtained liquid crystal polymer film (A-3) revealed a value of 1.35, confirming orientation in the drawing direction.

(26) In the liquid crystal polymer film (A-3), by reducing the winding speed from the extruder compared with the liquid crystal polymer film (A-1), a film of lower MOR was obtained.

(27) <Bases (B)>

(28) [Base (B-1)]

(29) A carbon fiber bundle was immersed in an acetone bath to reduce the amount of sizing agent. Following this reduction, the fiber bundle was opened using a vibrating device MH001 (manufactured by Maruhachi Corporation). The opened carbon fibers were placed in a prepreg sheet production device MH002 (manufactured by Maruhachi Corporation), and unidirectionally aligned continuous fibers spanning a width of about 240 mm were used as a base (B-1).

(30) The carbon fiber roving (carbon fiber bundle) used for the base (B-1) employed the following material.

(31) Carbon fiber roving: manufactured by Toho Tenax Co., Ltd., brand name: HITS-40, fineness: 800 TEX, number of filaments: 12,000, contains adhered epoxy sizing agent, tensile strength: 4,400 MPa, tensile modulus of elasticity: 240 CPa, degree of elongation: 1.8%, density: 1.77 g/cm.sup.3

(32) [Base (B-2)]

(33) A carbon fiber bundle was immersed in an acetone bath to reduce the amount of sizing agent. Following this reduction, the fiber bundle was opened using a vibrating device MH001 (manufactured by Maruhachi Corporation). The opened carbon fibers were placed in a prepreg sheet production device MH002 (manufactured by Maruhachi Corporation), and unidirectionally aligned continuous fibers spanning a width of about 500 mm were used as a base (B-2).

(34) The carbon fiber roving (carbon fiber bundle) used for the base (B-2) employed the following material.

(35) Carbon fiber roving: manufactured by Mitsubishi Rayon Co., Ltd., brand name: TR 50S 15L fineness: 1,050 TEX, number of filaments: 15,000, contains adhered epoxy sizing agent, tensile strength: 4,900 MPa, tensile modulus of elasticity: 240 GPa, degree of elongation: 2.0%, density: 1.82 g/cm.sup.2

(36) <Prepreg Laminates>

Example 1

(37) A sheet of the liquid crystal polymer film (A-1) that had been cut to a width of about 240 mm was superimposed on each of the two surfaces of the base (B-1), and lamination was performed so that the direction of orientation of the liquid crystal polymer and the direction of alignment of the base matched. This laminate was fed continuously into the heated furnace of the prepreg sheet production device mentioned above, and by melting the liquid crystal polymer films by heating at 300° C., and melt-impregnating the base with the liquid crystal polymer, a prepreg was obtained. The basis weight of the obtained prepreg was 156 g/m.sup.2, and the thickness was 0.1 mm. Measurement of the molecular chain degree of orientation for the liquid crystal polymer contained in the prepreg using the same method as that described for the liquid crystal polymer film (A-1) yielded a result of 48%.

(38) The obtained prepreg was molded into a sheet of 140 mm×140 mm, and 26 of these sheets were laminated along the 0° direction. The resulting laminate was subjected to press molding using a hot press device (manufactured by GO-factory Co., Ltd.) under molding conditions including a press temperature of 380° C., a press pressure of 30 MPa, a press time of 2 minutes and a cooling time of 6 minutes. This process yielded a prepreg laminate of Example 1, having a size of 140 mm×140 mm×2 mm. The volume fraction of the carbon fiber bundles in the prepreg laminate of Example 1 was 49%. Further, measurement of the molecular chain degree of orientation for the liquid crystal polymer contained in the prepreg laminate using the same method as that described for the liquid crystal polymer film (A-1) yielded a result of 79%. The amounts of the liquid crystal polymer film (A-1) and the base (B-1) in the prepreg laminate of Example 1 are shown in Table 1.

Example 2

(39) With the exception of using the liquid crystal polymer film (A-3), a prepreg was obtained using the same method as Example 1. The basis weight of the obtained prepreg was 157 g/m.sup.2, and the thickness was 0.99 mm.

(40) With the exceptions of changing the press temperature to 340° C. and the press pressure to 4 MPa, a prepreg laminate of Example 2 having a thickness of 2 mm was obtained using the same method as Example 1. The volume fraction of the carbon fiber bundles in the prepreg laminate of Example 2 was 49%. The amounts of the liquid crystal polymer film (A-3) and the base (B-1) in the prepreg laminate of Example 2 are shown in Table 1.

Example 3

(41) With the exception of using the liquid crystal polymer film (A-3), a prepreg was obtained using the same method as Example 1.

(42) With the exceptions of changing the press temperature to 340° C., the press pressure to 4 MPa and the press time to 6 minutes, a prepreg laminate of Example 3 was obtained using the same method as Example 1. The amounts of the liquid crystal polymer film (A-3) and the base (B-1) in the prepreg laminate of Example 3 are shown in Table 1.

Comparative Example 1

(43) A sheet of the polyamide film (A-2) that had been cut to a width of about 500 mm was superimposed on each of the two surfaces of the base (B-2), and lamination was performed so that the direction of orientation of the polyamide films and the direction of alignment of the base matched. This laminate was fed continuously into the heated furnace of the prepreg sheet production device mentioned above, and a prepreg was obtained by melt-impregnating the base with the polyamide.

(44) The obtained prepreg was molded into a sheet of 500 mm×500 mm, and 13 of these sheets were laminated along the 0° direction. The resulting laminate was subjected to press molding using a hot press device (manufactured by GO-factory Co., Ltd.) under molding conditions including a press temperature of 280° C., a press pressure of 30 MPa, a press time of 2 minutes and a cooling time of 6 minutes. This process yielded a prepreg laminate of Comparative Example 1, having a size of 500 mm×500 mm×2 mm. The volume fraction of the carbon fiber bundles in the prepreg laminate of Comparative Example 1 was 52%. Further, the amounts of the polyamide film (A-2) and the base (B-2) in the prepreg laminate of Comparative Example 1 are shown in Table 1.

(45) TABLE-US-00001 TABLE 1 Compar- Example Example Example ative Material 1 2 3 Example 1 Matrix Liquid 100 parts — — — resin crystal by mass (A) polymer film (A-1) Polyamide — — — 100 parts film (A-2) by mass Liquid — 100 parts 100 parts — crystal by mass by mass polymer film (A-3) Base (B-1) 124 parts 124 parts 124 parts — (B) by mass by mass by mass (B-2) — — — 170 parts by mass
<Evaluation of Mechanical Strength of Prepreg Laminates>

(46) Evaluation of the mechanical strength of the prepreg laminates from Examples 1 to 3 and Comparative Example 1 was performed by comparing the fracture energy of the prepreg laminates. Specifically, each of the prepreg laminates from Examples 1 to 3 and Comparative Example 1 was subjected to a 0° flexural test in accordance with JIS K7017, and the 0° flexural strength, the 0° flexural modulus, and the 0° flexural strain were measured. Each measurement was performed three times, with the average value being used, and the value obtained by integrating the flexural stress until the rupture point by the amount of flexural strain was recorded as the fracture energy. The results of evaluating the mechanical strength of the prepreg laminates from the examples and the comparative example are shown in Table 2. The 0° flexural test was performed under the following conditions.

(47) [Test conditions]

(48) Device: Tensilon Universal Testing Instrument, manufactured by A&D Co., Ltd.

(49) Test speed: 2 mm/minute

(50) Distance between fulcrums: 80 mm

(51) Distance between fulcrums/test piece thickness=40

(52) Test repetitions: 3

(53) Bending direction: thickness direction

(54) TABLE-US-00002 TABLE 2 Compar- Example Example Example ative 1 2 3 Example 1 Compo- Matrix (A-1) (A-3) (A-3) (A-2) sition of resin (A) prepreg Base (B) (B-1) (B-1) (B-1) (B-2) laminate Evaluation 0° flexural 1890 1407 1533 1500 of mechan- strength ical (MPa) strength at 0° flexural 109 99 105 104 prepreg modulus laminate (GPa) 0° flexural 1.82 1.53 1.62 1.58 strain (%) Fracture 8020 4529 5493 3910 energy (MPa)

(55) It was evident that the prepreg laminates of Examples 1 to 3 exhibited a much higher value for the fracture energy when compared with the prepreg laminate of Comparative Example 1 which used a conventional thermoplastic resin as the matrix. Further, as shown in Table 2, the prepreg laminate of Example 1 exhibited superior toughness to the prepreg laminate of Comparative Example 1. In this manner, it was evident that the prepreg laminate of the present invention exhibited excellent mechanical strength.

(56) The above results confirmed that the present invention is very useful.

INDUSTRIAL APPLICABILITY

(57) The present invention provides a prepreg and a prepreg laminate which have excellent mechanical strength. Further the invention also provides a method for producing the prepreg having excellent mechanical strength.

(58) Accordingly, the present invention is extremely useful industrially.