CARBON FIBER REINFORCED COMPOSITE AND PRODUCTION METHOD OF CARBON FIBER REINFORCED COMPOSITE

Abstract

The present invention provides a carbon-fiber-reinforced composite that can reduce the curing time and achieve high mechanical strength while reducing resin bleeding, and a method for producing a carbon-fiber-reinforced composite. Provided is a carbon-fiber-reinforced composite containing: carbon fibers, an epoxy resin, a curing agent, and a thermoplastic resin, wherein a mixture of the epoxy resin and the thermoplastic resin has a ratio of viscosity at 30 C. to viscosity at 90 C. (viscosity at 30 C./viscosity at 90 C.) of less than 100.

Claims

1. A carbon-fiber-reinforced composite comprising: carbon fibers; an epoxy resin; a curing agent; and a thermoplastic resin, wherein a mixture of the epoxy resin and the thermoplastic resin has a ratio of viscosity at 30 C. to viscosity at 90 C. (viscosity at 30 C./viscosity at 90 C.) of less than 100.

2. The carbon-fiber-reinforced composite according to claim 1, wherein the thermoplastic resin has a glass transition temperature of 60 C. or higher.

3. The carbon-fiber-reinforced composite according to claim 1, wherein the thermoplastic resin is a polyvinyl acetal resin.

4. The carbon-fiber-reinforced composite according to claim 3, wherein the polyvinyl acetal resin has structural units represented by the following formula (1): ##STR00003## wherein each R.sup.1 represents an alkyl group having a carbon number of 1 or greater, and R.sup.1s may be the same as or different from each other.

5. The carbon-fiber-reinforced composite according to claim 1, wherein the polyvinyl acetal resin has a hydroxy group content of 16.0 mol % or more and 45.0 mol % or less.

6. The carbon-fiber-reinforced composite according to claim 1, which is used as a prepreg.

7. The carbon-fiber-reinforced composite according to claim 1, wherein the epoxy resin contains a bisphenol A epoxy resin.

8. The carbon-fiber-reinforced composite according to claim 1, which contains 0.01 parts by weight or more and 40 parts by weight or less of the thermoplastic resin relative to 100 parts by weight of the epoxy resin.

9. The carbon-fiber-reinforced composite according to claim 1, which contains 0.5 parts by weight or more and 300 parts by weight or less of the epoxy resin relative to 100 parts of the carbon fibers.

10. A method for producing a carbon-fiber-reinforced composite, comprising at least the steps of: forming a resin composition containing an epoxy resin, a curing agent, and a thermoplastic resin; and forming a composite of the resin composition with carbon fibers, wherein a mixture of the epoxy resin and the thermoplastic resin has a ratio of viscosity at 30 C. to viscosity at 90 C. (viscosity at 30 C./viscosity at 90 C.) of less than 100.

Description

DESCRIPTION OF EMBODIMENTS

[0139] The present invention is more specifically described in the following with reference to, but not limited to, examples.

Example 1

(Production of Polyvinyl Acetal Resin)

[0140] An amount of 2,700 g of pure water was added to 250 g of a polyvinyl alcohol resin having an average degree of polymerization of 800 and a degree of saponification of 95.0 mol %, and stirred at 90 C. for about two hours for dissolution. This solution was cooled to 40 C., and to the solution were added 100 g of hydrochloric acid having a concentration of 35% by weight and 160 g of butyraldehyde to perform acetalization, whereby a reaction product was precipitated. Thereafter, the acetalization was completed at 40 C., followed by neutralization, washing with water, and drying by conventional methods. Thus, white powder of a polyvinyl acetal resin (polyvinyl butyral resin) was obtained.

[0141] The obtained polyvinyl acetal resin was dissolved in DMSO-d6 at a concentration of 10% by weight, and 13C-NMR was performed to measure the acetal group content (degree of acetalization), the hydroxy group content, and the acetyl group content.

(Production of Prepreg)

[0142] To 100 parts by weight of a bisphenol A epoxy resin (JER828, available from Japan Epoxy Resins Co., Ltd.) were added 6 parts by weight of a curing agent (dicyandiamide) and 10 parts by weight of the obtained polyvinyl acetal resin, and they were mixed using Process Homogenizer (available from SMT) at 15,000 rpm to prepare a resin composition.

[0143] Subsequently, the obtained resin composition was impregnated into PAN carbon fibers (available from Toray Industries Inc., T700SC-12000-50C, number of filaments: 12,000, fineness: 800 tex, density: 1.8 g/cm.sup.3) by a hand lay-up method and cured by heating at 150 C. for one hour, whereby a prepreg was produced. Here, 300 parts by weight of the PAN carbon fibers were used for 100 parts by weight of the bisphenol A epoxy resin.

Examples 2 to 10 and Comparative Examples 1 to 5, 8, and 9

[0144] A polyvinyl acetal resin, a resin composition, and a prepreg were produced as in Example 1 except that a polyvinyl alcohol resin (PVA) and an aldehyde of the types and in the amounts shown in Table 1 were used, and that the resin composition was prepared in accordance with the formulation shown in Table 2.

[0145] In Examples 6 and 7 and Comparative Example 3, two different aldehydes were used.

[0146] In Examples 7 to 9 and Comparative Examples 8 and 9, a bisphenol F epoxy resin (NPEF-170, available from Nan Ya Plastics Corporation) was used instead of the bisphenol A epoxy resin (JER828, available from Japan Epoxy Resins Co., Ltd.).

[0147] In Example 10, a non-aromatic [alicyclic] epoxy resin (Celloxide 2021P, available from Daicel Corporation) was used instead of the bisphenol A epoxy resin (JER828, available from Japan Epoxy Resins Co., Ltd.)

Comparative Example 6

[0148] A resin composition and a prepreg were produced as in Example 1 except that in (Production of prepreg), 5 parts by weight of polyethersulfone (SUMIKAEXCEL 5003MPS, available from Sumitomo Chemical Co., Ltd.) was added instead of 10 parts by weight of the obtained polyvinyl acetal resin.

Comparative Example 7

[0149] A resin composition and a prepreg were produced as in Example 1 except that in (Production of prepreg), 5 parts by weight of a phenoxy resin (Phenotohto YP-50, available from Nippon Steel Chemical & Material Co., Ltd.) was added instead of 10 parts by weight of the obtained polyvinyl acetal resin.

Examples 11 to 13 and Comparative Examples 10 and 11

[0150] A resin composition and a prepreg were produced as in Example 1 except that the resin composition was prepared in accordance with the formulation (epoxy resin, curing agent, polyvinyl acetal resin, and carbon fiber) shown in Table 2.

[0151] In Comparative Example 11, a phenol novolac epoxy resin (NPPN-631, available from Nan Ya Epoxy Resin, glycidyl ether epoxy resin with functionality greater than two) was used instead of the bisphenol A epoxy resin (JER828, available from Japan Epoxy Resins Co., Ltd.).

[0152] Regarding the type of polyvinyl acetal resin, Example 1 means that the same polyvinyl acetal resin as in Example 1 was used.

(Evaluation)

[0153] The polyvinyl acetal resins (or other resins [polyethersulfone and phenoxy resin]), resin compositions, and prepregs obtained in the examples and the comparative examples were evaluated as follows. Tables 1 and 2 show the results.

(1) Measurement of Glass Transition Temperature (Tg)

[0154] The glass transition temperature of the obtained polyvinyl acetal resins (or other resins) was measured using a differential scanning calorimeter (DSC) at a temperature increase rate of 10 C./min.

(2) Rheology Evaluation (Viscosity Measurement)

[0155] The epoxy resin and the thermoplastic resin used in the production of each resin composition were mixed at the same mixing ratio as in the resin composition (for example, in Example 1, 10 parts by weight of the polyvinyl acetal resin relative to 100 parts by weight of the epoxy resin), and heated at 150 C. for dissolution, whereby a viscosity measurement sample (mixture) was produced. The viscosity of the obtained sample at 30 C. and 90 C. was measured using a rheometer (available from TA Instruments). The viscosity ratio (30 C./90 C.) was also calculated. [0156] Plate: 20-mm parallel plates [0157] Measurement temperature: 150 C. to 10 C. (temperature decrease rate: 5 C./min) [0158] Rotation rate: 100 rpm [0159] Gap: 500 m

(3) Stability Over Time

[0160] The viscosity of the viscosity measurement sample obtained in (2) Rheology evaluation (viscosity measurement) was measured in the same method as above immediately after the production of the sample.

[0161] Further, the viscosity was measured after the measurement sample was stored in a thermostatic chamber at 60 C. for three months, and the viscosity change percentage was calculated. The device and conditions for the viscosity measurement were the same as in (2) Rheology evaluation (viscosity measurement). The viscosity change percentage was calculated using the measured viscosity values at 60 C.

[0162] When the mixture of the thermoplastic resin and the epoxy resin has excellent stability over time, the carbon-fiber-reinforced composite produced using these resins can have excellent long-term storability.

(4) Curing Time Reduction Percentage

[0163] The curing end time of the obtained resin compositions was measured using a DSC.

[0164] Specifically, DSC measurement was performed under the conditions below. The line connecting the point at which the slope of the exothermic peak became 0 and the reaction start point was defined as the baseline. The curing reaction percentage at each time point was then calculated, where the area surrounded by the baseline and the DSC curve was taken as the heat of reaction. The time at which the curing reaction percentage reached 95% was determined as the curing end time.

[DSC Conditions]

[0165] Device: DSC (DSC 7000X) available from Hitachi High-Tech Science Corporation [0166] Measurement temperature: 20.fwdarw.160 C. (10 C./min), holding for 150 minutes [0167] Measurement atmosphere: air, 50 mL/min

[0168] The curing end time of control compositions, which were prepared by removing the thermoplastic resins from the resin compositions, was measured in the same manner. The curing time reduction percentage (%) was then calculated and evaluated in accordance with the following criteria. [0169] (Excellent): A curing time reduction percentage of 15% or higher. [0170] Good): A curing time reduction percentage of 10% or higher and lower than 15%. [0171] (Fair): A curing time reduction percentage of 5% or higher and lower than 10%. [0172] (Poor): A curing time reduction percentage of lower than 5%.

(5) Resin Composition Retention Percentage

[0173] For the obtained prepregs, the amount of resin composition remaining in the carbon fibers relative to the amount of the resin composition impregnated into the carbon fibers (resin composition retention percentage) was calculated and evaluated in accordance with the following criteria. A higher resin composition retention percentage indicates less bleeding of resin and the like from the prepreg. [0174] (Excellent): A resin composition retention percentage of 90% or higher. [0175] (Good): A resin composition retention percentage of 80% or higher and lower than 90%. [0176] (Fair): A resin composition retention percentage of 65% or higher and lower than 80%. [0177] (Poor): A resin composition retention percentage of lower than 65%.

(6) Variation in Processability

[0178] Five sheets of each of the obtained prepregs were stacked. A hole was drilled into the stack, and the opening was observed for the appearance and evaluated in accordance with the following criteria (number of samples: 10). [0179] (Excellent): No delamination occurred at all. [0180] (Good): Nine or more samples had no delamination. [0181] (Fair): Seven or eight samples had no delamination. [0182] (Poor): Six or fewer samples had no delamination.

TABLE-US-00001 TABLE 1 PVA Acetalization step Resin properties Average Degree of Aldehyde Average Degree of Hydroxy Acetyl degree of saponi- addition Thermo- degree of acetali- group group polymer- fication Aldehyde amount plastic polymer- zation content content Tg ization (mol %) type (g) resin type R.sup.1 type ization (mol %) (mol %) (mol %) ( C.) Example 1 800 95.0 Butyraldehyde 160 Polyvinyl C.sub.3H.sub.7 800 72.0 23.0 5.0 67 Example 2 300 98.0 Butyraldehyde 150 acetal resin C.sub.3H.sub.7 300 70.0 28.0 2.0 70 Example 3 400 90.0 Butyraldehyde 145 C.sub.3H.sub.7 400 67.0 23.0 10.0 65 Example 4 1000 85.0 Butyraldehyde 140 C.sub.3H.sub.7 1000 62.0 23.0 15.0 63 Example 5 400 85.0 Acetaldehyde 90 CH.sub.3 400 62.0 23.0 15.0 100 Example 6 550 80.0 Acetaldehyde 45 CH.sub.3 550 44.0 36.0 20.0 75 Butyraldehyde 20 C.sub.3H.sub.7 Example 7 300 99.0 Acetaldehyde 35 CH.sub.3 300 67.0 32.0 1.0 80 Butyraldehyde 110 C.sub.3H.sub.7 Example 8 300 98.0 Butyraldehyde 150 C.sub.3H.sub.7 300 70.0 28.0 2.0 70 Example 9 300 99.0 Butyraldehyde 135 C.sub.3H.sub.7 300 63.0 36.0 1.0 70 Example 10 300 99.0 Acetaldehyde 90 CH.sub.3 300 74.0 25.0 1.0 106 Comparative 800 93.0 Formaldehyde 83 Polyvinyl H 800 86.5 6.5 7.0 118 Example 1 acetal resin Comparative 300 99.0 Acetaldehyde 90 CH.sub.3 300 74.0 25.0 1.0 106 Example 2 Comparative 300 99.0 Acetaldehyde 30 CH.sub.3 300 67.0 32.0 1.0 75 Example 3 Butyraldehyde 110 C.sub.3H.sub.7 Comparative 300 99.0 Butyraldehyde 135 C.sub.3H.sub.7 300 63.0 36.0 1.0 70 Example 4 Comparative 300 99.0 Butyraldehyde 145 C.sub.3H.sub.7 300 69.0 30.0 1.0 68 Example 5 Comparative Polyether- 205 Example 6 sulfone Comparative Phenoxy resin 84 Example 7 Comparative 800 93.0 Formaldehyde 83 Polyvinyl H 800 86.5 6.5 7.0 118 Example 8 acetal resin Comparative 300 99.0 Acetaldehyde 90 CH.sub.3 300 74.0 25.0 1.0 106 Example 9

TABLE-US-00002 TABLE 2 Resin composition (parts by weight) Thermoplastic resin Epoxy resin Polyvinyl acetal resin Evaluation (mixture) Addition Curing Addition Other Carbon Viscosity (Pa .Math. s) Type amount agent Type amount resins fiber 30 C. 90 C. Example 1 Bisphenol A 100 6 Example 1 10 300 45.2 1.8 Example 2 epoxy resin 100 6 Example 2 10 300 85.4 0.9 Example 3 100 6 Example 3 5 300 39.8 1.6 Example 4 100 6 Example 4 20 300 46.3 1.4 Example 5 100 6 Example 5 10 300 87.2 2.0 Example 6 100 6 Example 6 5 300 51.1 1.8 Example 7 Bisphenol F 100 6 Example 7 10 300 40.5 6.7 Example 8 epoxy resin 100 6 Example 8 10 300 11.8 0.2 Example 9 100 6 Example 9 10 300 34.3 0.4 Example 10 Non-aromatic 100 6 Example 10 10 300 12.3 0.4 epoxy resin Example 11 Bisphenol A 100 6 Example 1 1 300 3.1 0.3 Example 12 epoxy resin 100 6 Example 5 5 300 18.1 0.4 Example 13 100 6 Example 5 30 300 5642.5 119.0 Comparative Bisphenol A 100 6 Comparative 10 300 1229.2 4.7 Example 1 epoxy resin Example 1 Comparative 100 6 Comparative 3 300 878.5 2.2 Example 2 Example 2 Comparative 100 6 Comparative 10 300 135.0 1.2 Example 3 Example 3 Comparative 100 6 Comparative 10 300 78.0 0.6 Example 4 Example 4 Comparative 100 6 Comparative 5 300 129.8 1.1 Example 5 Example 5 Comparative 100 6 5 300 71.9 0.5 Example 6 Comparative 100 6 5 300 399.8 1.5 Example 7 Comparative Bisphenol F 100 6 Comparative 10 300 666.7 2.5 Example 8 epoxy resin Example 8 Comparative 100 6 Comparative 5 300 370.9 1.2 Example 9 Example 9 Comparative 100 6 Comparative 45 350 19682.1 138.3 Example 10 Example 9 Comparative Phenol novolac 100 6 Comparative 10 300 23240.0 6.1 Example 11 epoxy resin Example 9 Evaluation (mixture) Stability Evaluation over time Resin Viscosity Viscosity Curing time composition ratio change reduction retention (30 C./ percentage percentage percentage Variation in 90 C.) (%) (%) (%) processability Example 1 25.1 132 Example 2 94.9 117 Example 3 24.9 109 Example 4 33.1 126 Example 5 43.6 113 Example 6 28.4 108 Example 7 6.0 133 Example 8 59.0 138 Example 9 85.8 146 Example 10 30.8 111 Example 11 10.3 102 Example 12 45.3 104 Example 13 47.4 289 Comparative 261.5 254 x x x Example 1 Comparative 399.3 277 x Example 2 Comparative 112.5 213 x Example 3 Comparative 125.8 200 Example 4 Comparative 118.0 181 Example 5 Comparative 143.8 172 x x Example 6 Comparative 266.5 241 x Example 7 Comparative 266.7 268 x x x Example 8 Comparative 309.1 250 x Example 9 Comparative 142.3 462 x Example 10 Comparative 3809.8 365 x x Example 11

INDUSTRIAL APPLICABILITY

[0183] The present invention can provide a carbon-fiber-reinforced composite that can reduce the curing time and achieve high mechanical strength while reducing resin bleeding, and a method for producing a carbon-fiber-reinforced composite.