JP6525154B2 - Method of manufacturing fiber reinforced cured resin - Google Patents

Description

  The present invention relates to a method of producing a fiber reinforced cured resin using recycled carbon fibers and a method of producing an article.

  BACKGROUND OF THE INVENTION Carbon fiber reinforced plastic (CFRP) is used in many products including transport forms because it can produce molded articles that are lightweight and have excellent mechanical properties. On the other hand, the disposal of a large amount of offcuts and used CFRP generated during product manufacture has become a major problem.

  Generally, in composite materials such as CFRP, it has not been effective from the viewpoint of cost and energy efficiency to separate and reuse or reuse each component. Therefore, most of the waste has been disposed of by landfilling or incineration. However, from the viewpoint of environmental protection etc., how to reuse the components of the composite material has become a major issue.

  At present, methods of recovering regenerated carbon fibers from CFRP by thermal decomposition method, chemical decomposition method, etc. have been reported.

  However, in the process of recovering regenerated carbon fibers from CFRP, the sizing agent is removed from the carbon fibers. For this reason, when CFRP is produced using regenerated carbon fibers, there is a problem that the adhesion between the regenerated carbon fibers and the resin is insufficient.

  Patent Document 1 discloses, as a method of recycling fiber reinforced plastic comprising carbon fiber and thermosetting resin, a first step of producing a harmless material by heat treating the fiber reinforced plastic and burning the thermosetting resin. And a second step of producing a recycled material while kneading the detoxifying material and the thermoplastic resin. Further, in Patent Document 1, in the second step, a sizing agent is applied or dispersed to the detoxifying agent, and then, while kneading the detoxifying agent and the thermoplastic resin, carbon fibers constituting the detoxifying agent are pulverized. It has been disclosed to produce recycled material having carbon fiber of short fiber.

JP, 2009-138143, A

  However, since carbon fibers are cut in the process of producing CFRP as a raw material of regenerated carbon fibers and in the process of recovering regenerated carbon fibers from CFRP, regenerated carbon fibers have a short fiber length and are bobbin wound. It is difficult. Therefore, it is difficult to use the roll type apparatus used in the normal sizing process, and it is difficult to uniformly apply the sizing agent to the regenerated carbon fiber, and as a result, the interface between the regenerated carbon fiber and the cured resin Adhesion can not be sufficiently improved.

  One aspect of the present invention aims at providing a fiber reinforced cured resin which is excellent in the adhesion of the interface between the regenerated carbon fiber and the cured resin, in view of the problems of the above-mentioned prior art.

One aspect of the present invention is a method of manufacturing a fiber reinforced cured resin, have a step of irradiating a microwave to the resin composite material containing recycled carbon fibers and a thermosetting resin, wherein the microwave to the volume of the recycled carbon fiber the ratio of the output of the is 0.01 W / mm ³ or more 9000 W / mm ³ or less.

  According to one aspect of the present invention, it is possible to provide a fiber reinforced cured resin which is excellent in the adhesion of the interface between the recycled carbon fiber and the cured resin.

  Next, an embodiment of the present invention will be described.

  The manufacturing method of fiber reinforced cured resin has the process of irradiating a microwave to the resin composite material containing a regenerated carbon fiber and a thermosetting resin.

  The resin composite material preferably further contains a curing agent.

  Here, when the resin composite material is irradiated with microwaves, the regenerated carbon fibers in the resin composite material are heated, and the thermosetting resin in the vicinity of the regenerated carbon fibers is cured, so the adhesion of the interface between the regenerated carbon fibers and the cured resin As a result, the mechanical properties of the fiber reinforced cured resin can be improved.

The ratio of the output of the microwave to the volume of the recycled carbon fiber is preferably 0.01~9000W / mm ^3, and more preferably a 2500~7000W / mm ^3. When the ratio of the microwave output to the volume of the regenerated carbon fiber is 0.01 W / mm ³ or more, the adhesion of the interface between the regenerated carbon fiber and the cured resin can be further improved, and is 9000 W / mm ³ or less By being present, it is possible to suppress the breakage of the recycled carbon fiber and the thermal deterioration of the thermosetting resin in the vicinity of the recycled carbon fiber.

  The time for which the resin composite material is irradiated with the microwave is usually 10 seconds or more, preferably 5 minutes to 1 hour. The adhesion of the interface between the regenerated carbon fiber and the cured resin can be further improved by applying the microwave to the resin composite material for 5 minutes or more, and the regeneration time of the regenerated carbon fiber can be 1 hour or less. Thermal degradation of the thermosetting resin in the vicinity of the broken and regenerated carbon fibers can be suppressed.

  Alternatively, after semi-curing the resin composite material, the semi-cured resin composite material may be irradiated with microwaves.

  In addition, the resin composite material irradiated with the microwave may be further cured.

  The method for semi-curing the resin composite material and the method for curing the resin composite material irradiated with microwaves are not particularly limited, and examples thereof include a method of heating using an oven.

  The method for producing the regenerated carbon fiber, that is, the method for regenerating the carbon fiber is not particularly limited, but the carbon fiber may be formed by a thermal decomposition method, a chemical decomposition method, a super / subcritical decomposition method, an electrolytic oxidation method, a superheated steam method There is a method of treating the waste contained.

  In addition, the shape of a regenerated carbon fiber is not specifically limited, Any of a nonwoven fabric, a chop, and a milled may be sufficient.

  In addition, the regenerated carbon fiber may be coated with a sizing agent, or may be subjected to a treatment such as an organic solvent treatment or a polymer decomposition treatment.

  Furthermore, regenerated carbon fibers may be used in combination with unregenerated carbon fibers, or may be used in combination with regenerated carbon fibers regenerated by different methods.

  The thermosetting resin is not particularly limited, and epoxy resin, phenol resin, unsaturated polyester, urea resin, melamine resin, diallyl phthalate, silicon resin, vinyl ester, polyimide and the like can be mentioned, and two or more kinds may be used in combination. Good.

  The shape of the fiber reinforced cured resin is not particularly limited, and can be optionally applied according to the application.

  The fiber-reinforced curing resin can be applied to articles such as automobiles, construction structural materials, sports equipment, medical devices, housing materials of mobile devices, and the like.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by the examples.

[Preparation of recycled carbon fiber sheet]
Four sheets of carbon fiber sheet BT70-20 (manufactured by Toray Industries, Inc.) were stacked, and after impregnating the sheet with an epoxy resin by a vacuum impregnation method (VaRTM), the sheet was cured to obtain a fiber reinforced cured resin.

  The fiber reinforced cured resin was treated for 20 minutes in a superheated steam atmosphere at 700 ° C. containing 2% by volume of oxygen to obtain a regenerated carbon fiber sheet.

Example 1
Measure the weight ratio of bisphenol F type liquid epoxy resin JER 806 (made by Mitsubishi Chemical Corporation) and curing agent JER Cure ST11 (made by Mitsubishi Chemical Corporation) to be 5: 3 and mix them using a mixer, then vacuum degassing To obtain a matrix resin.

  A 35 mm long, 15 mm wide, and approximately 2 mm thick silicon sheet having a dumbbell-like No. 7 cavity defined in JIS K6251 was prepared and placed on a film. Next, the regenerated carbon fiber sheet was carefully sampled so as not to damage the single fiber, and one single fiber was fixed at the longitudinal center of the cavity so as not to be slackened. Furthermore, after pouring a matrix resin into the cavity so as to prevent air from entering, the epoxy resin was semi-cured at room temperature for 12 hours to obtain a test piece of a fiber-reinforced semi-cured resin.

The test piece of the fiber-reinforced semi-cured resin was irradiated with microwaves having a multimode frequency of 2.45 GHz for 5 minutes, and then heated in an oven at 120 ° C. for 3 hours to obtain a test piece of the fiber-reinforced cured resin. At this time, the ratio of the microwave output to the volume of the regenerated carbon fiber was 6875 W / mm ³ .

Comparative Example 1
A test piece of a fiber-reinforced cured resin was obtained in the same manner as in Example 1 except that the test piece of the fiber-reinforced semi-cured resin was not irradiated with microwaves.

  Next, the interface shear stress of the fiber reinforced cured resin was determined using a test piece of the fiber reinforced cured resin, and the adhesion of the interface between the regenerated carbon fiber and the cured resin was evaluated.

[Average diameter D of regenerated carbon fiber]
The average diameter D of the regenerated carbon fiber was measured using a scanning electron microscope S-4300 (manufactured by Hitachi High-Technologies Corporation) and found to be 6.24 μm.

[Tensile strength σ _f of regenerated carbon fiber]
The recycled carbon fiber sheet was carefully sampled so as not to damage single fibers, and one single fiber was attached to a paper frame to obtain a test piece.

  A tensile test was performed on 20 test pieces at a tensile speed of 3 μm / s using a microscope stretching stage 10073 B (manufactured by Japan High Tech Co., Ltd.).

  The distribution of tensile strength of fibers is generally considered to follow the Weibull distribution, and conversely, if the distribution of tensile strength of fibers follows the Weibull distribution, it can be judged that the test method is appropriate. The probability cumulative distribution function F (σ) that fibers with a length L break at stress σ or less is expressed by the formula when the tensile strength follows the Weibull distribution

(Wherein γ is a scale parameter, β is a shape parameter, and L ₀ is a reference length, where L = L ₀ ).
(W. Weibull, J. Appl. Mech., 9, (1951) 293). When the above equation is transformed, the equation

  Is obtained.

  Therefore, if a linear relationship is obtained when the left term of the above equation is plotted with the vertical axis (Y) and lnσ as the horizontal axis (X), it can be determined that the distribution of tensile strength of fibers follows the Weibull distribution. . Furthermore, the scale parameter γ and the shape parameter β can be obtained from the slope and the intercept of the straight line.

As a result of creating the distribution of tensile strength of the regenerated carbon fiber, it became clear that it follows the Weibull distribution. Further, when the scale parameter γ and the shape parameter β of the regenerated carbon fiber were obtained, they were 2.28 and 5.03, respectively. Furthermore, the tensile strength σ _f of the regenerated carbon fiber was 2100 MPa.

[Average fiber length of fractured recycled carbon fiber]
The fragmentation test of the test piece of the fiber reinforced cured resin was carried out using a microscope drawing stage 10073 B (manufactured by Japan High Tech Co., Ltd.). Specifically, after the test piece of the fiber reinforced cured resin was pulled at a speed of 0.1 μm / s, the operation of observing the number of breakage at every strain of 1.0% was repeated, and the number of breakage of regenerated carbon fiber was saturated At the end of the fragmentation test. At this time, using an optical microscope, the fracture of the regenerated carbon fiber in the test piece of the fiber reinforced cured resin was observed, and the fiber length of the fractured regenerated carbon fiber was measured. Next, the average value of the fiber length of the broken recycled carbon fiber was calculated.

[Interfacial shear stress τ _i of fiber reinforced cured resin]
formula

(Wherein, σ _f is the tensile strength of the regenerated carbon fiber, D is the average diameter of the regenerated carbon fiber, and L _c is the critical fiber length of the regenerated carbon fiber.)
The interfacial shear stress τ _i of the fiber reinforced cured resin was calculated by Here, the critical fiber length of the regenerated carbon fiber is the formula

(In the formula, L is an average value of the fiber length of the broken recycled carbon fiber.)
Calculated.

  Table 1 shows the evaluation results of the production conditions of the fiber reinforced cured resin and the adhesion of the interface between the recycled carbon fiber and the cured resin.

  In addition, the output in microwave irradiation means the ratio of the output of the microwave with respect to the volume of a regenerated carbon fiber.

  It is understood from Table 1 that the fiber reinforced cured resin of Example 1 is excellent in the adhesion of the interface between the recycled carbon fiber and the cured resin to the fiber reinforced cured resin of Comparative Example 1 which is not irradiated with the microwave.

Example 2
Measure the weight ratio of bisphenol F type liquid epoxy resin JER 806 (made by Mitsubishi Chemical Corporation) and curing agent JER Cure ST11 (made by Mitsubishi Chemical Corporation) to be 5: 3 and mix them using a mixer, then vacuum degassing To obtain a matrix resin.

  Four regenerated carbon fiber sheets were stacked, and the matrix resin was impregnated into the sheet by VaRTM, and then the epoxy resin was semi-cured at room temperature for 12 hours to obtain a fiber-reinforced semi-cured resin.

The fiber-reinforced semi-cured resin was irradiated with microwaves having a multimode frequency of 2.45 GHz for 20 minutes to obtain a fiber-reinforced cured resin. At this time, the ratio of microwave output to carbon fiber volume was set to 0.04 W / mm ³ so that the temperature of the test piece of the fiber reinforced semi-cured resin would be 120 ° C. Here, the temperature of the test piece of fiber reinforced semi-hardened resin was measured using a radiation thermometer and an infrared sensor.

Comparative Example 2
A fiber-reinforced cured resin was obtained in the same manner as Example 2, except that the fiber-reinforced semi-cured resin was not irradiated with microwaves.

Comparative Example 3
A fiber-reinforced cured resin was obtained in the same manner as in Example 2, except that the fiber-reinforced semi-cured resin was heated for 3 hours in an oven at 120 ° C., instead of irradiating the fiber-reinforced semi-cured resin with microwaves.

  Next, the flexural modulus and the flexural strength of the fiber reinforced cured resin were measured.

[Flexural modulus and flexural strength of fiber reinforced cured resin]
The fiber reinforced cured resin was molded to a width of 15 mm, a length of 60 mm, and a thickness of 1 mm to obtain a test piece of the fiber reinforced cured resin.

  Using a precision universal testing machine AG-IS (manufactured by Shimadzu Corporation), a three-point bending test of the test piece of the fiber reinforced cured resin was conducted to measure the flexural modulus and the flexural strength of the fiber reinforced cured resin. At this time, the crosshead speed was 5 mm / min.

  Table 2 shows the measurement conditions of the fiber reinforced cured resin, the measurement results of the flexural modulus and the flexural strength.

  In addition, the output in microwave irradiation means the ratio of the output of the microwave to the volume of a regenerated carbon fiber.

  Table 2 shows that the fiber reinforced cured resin of Example 2 is excellent in flexural modulus and flexural strength.

  On the other hand, since the fiber reinforced cured resin of Comparative Example 2 is not irradiated with the microwave, the bending strength is low.

  Moreover, since the fiber reinforced cured resin of Comparative Example 3 is heated in an oven instead of being irradiated with microwaves, the bending strength is low.

In addition, since it originates in the preform structure which made continuous fiber the woven fabric, the bending elastic modulus of fiber reinforced cured resin hardly changes even if a heating condition changes.

Claims (5)

Have a step of irradiating a microwave to the resin composite material containing recycled carbon fibers and a thermosetting resin,
Method for producing a fiber reinforced cured resin, wherein the ratio of the output of the microwave to the volume of the recycled carbon fiber is not more than 0.01 W / mm ³ or more 9000 W / mm ^3. The method further includes the step of semi-curing the resin composite material,
Method for producing a fiber-reinforced curable resin according to claim 1, characterized by irradiating the microwave to the semi-cured resin composite material. The method of producing a fiber reinforced cured resin according to claim 1 or 2 , further comprising the step of curing the resin composite material irradiated with the microwave. The said thermosetting resin is an epoxy resin, a phenol resin, unsaturated polyester, a urea resin, a melamine resin, a diallyl phthalate, a silicone resin, a vinyl ester, or a polyimide, The any one of the Claims 1 thru | or 3 characterized by the above-mentioned. The manufacturing method of the fiber reinforced cured resin as described in. A method for producing an article, comprising the step of producing a fiber-reinforced cured resin using the method for producing a fiber-reinforced cured resin according to any one of claims 1 to 4 .