JP5816487B2 - Composite resin - Google Patents

Description

  The present invention relates to a composite resin in which a filler is contained in the resin.

  Resin products are used in various parts such as automobile parts, home appliances, electronic devices, and daily necessities, and various thermosetting and thermoplastic resins have been developed and applied to actual products. It has various features such as light weight, low cost, high moldability, and excellent chemical resistance and corrosion resistance.

  In general, an inorganic filler is added to these resin products. Among them, carbon-based fillers have been widely used from the viewpoint of strength and conductivity. For the carbon-based filler, carbon black has been used for a long time, and recently, it has been well studied to use carbon fibers and especially nanocarbons such as carbon nanofibers (CNF) including carbon nanotubes (CNT). . Recently, among these, in particular, CNF has been widely used because it can impart high strength and high conductivity in composite materials with other resins (Patent Document 1).

JP 2004-143240 A

  According to the above examination, the present situation is that the metal material cannot be completely replaced in terms of strength, rigidity and toughness. Accordingly, an object of the present invention is to provide a composite resin having high strength and low volume resistivity.

  The present inventor has found that by using a combination of carbon fiber and carbon nanotube as a filler contained in the matrix resin, a synergistic effect is exhibited in the conductivity of the composition, and the present invention has been completed. I let you.

The present invention (1) includes a carbon fiber having a diameter of 1 to 50 μm,
Carbon nanofibers having a diameter of 5 to 500 nm;
A matrix resin in which the carbon fibers and the carbon nanofibers are dispersed;
Is a composite resin containing

  As a result of further intensive studies, the present inventor selected a combination of carbon nanofibers and matrix resin from those having low adhesion strength in the composite resin according to the combination of carbon fiber, carbon nanofiber and matrix resin. As a result, it was found that a synergistic effect between the carbon fiber and the carbon nanofiber was obtained and a more remarkable tensile strength was exhibited, and the present invention was completed.

That is, in the present invention (2), the carbon nanofibers and the matrix resin are:
For tensile stress values M _A in the strain of 0.05 of the matrix resin alone made from the test composite resin (A), the tensile at strain of 0.05 of the carbon nanofibers and composite resin test consisting of the matrix resin (B) the ratio of the stress value _{M B (M B / M a} ) becomes in the range of 0.9 to 1.1, a combination, a composite resin of the invention (1).

  According to the present invention (1), by combining carbon fibers and carbon nanofibers as fillers contained in the matrix resin, a synergistic effect can be obtained and a composite resin having high conductivity can be obtained. it can.

  According to the experimental data shown in FIG. 7, the synergistic effect by the combination of carbon fiber and carbon nanofiber can be confirmed. FIG. 7A is a graph showing an evaluation of conductivity in a matrix resin and carbon fiber, or a two-phase composite resin of matrix resin and carbon nanofiber. According to the result, in the two-phase composite resin, the volume resistance value of the resin using carbon nanofibers (VGCF, VGCF-S, MWNT-7) is larger than that of the resin using carbon fibers (CNF). Becomes lower.

  On the other hand, FIG.7 (b) is the graph which evaluated the electroconductivity in the three-phase type composite resin of matrix resin, carbon fiber, and carbon nanofiber. Here, in the three-phase composite resin, the total amount of carbon fibers and carbon nanofibers used is set to be the same amount as that used in the two-phase resin. According to the measurement results of the system resistance values of these three-phase composite resins, even when any carbon nanofiber is used, it shows higher conductivity than the two-phase composite resins (low). Shows volume resistance). That is, the carbon nanofiber is a single substance, and even though it can impart higher conductivity to the resin than the carbon fiber, by replacing a part of the carbon nanofiber with a carbon fiber having low conductivity, the two-phase resin material A resin material having conductivity higher than the conductivity could be obtained. That is, a combination of carbon fiber and carbon nanofiber can exhibit a synergistic effect and obtain a composite material having high conductivity.

Furthermore, according to the present invention (2), a carbon fiber, the composite resin containing the carbon nanofibers and the matrix resin, the carbon nanofibers and the matrix resin and the combination is the tensile stress value ratio (M B _{/ M A)} is, By selecting from the range of 0.9 to 1.1, a synergistic effect of the carbon fiber and the carbon nanofiber is obtained, and a more remarkable tensile strength is exhibited.

That is, as shown in Table 3, if the tensile stress value ratio _(M B / M _A) is adopted a combination of the matrix resin and the carbon nanofibers to be in the range of 0.9 to 1.1, Table 4, As shown in FIG. 3, in the tensile strength test, the three-phase composite resin shows higher strength than the two-phase composite resin. That is, from these results, in the three-phase resin material of carbon nanofibers, carbon fibers, and matrix resin, the tensile stress value ratio is set within a predetermined range in the combination of carbon nanofibers and matrix resin. Thus, it can be seen that high tensile strength can be obtained in the three-phase resin material.

FIG. 1 is a diagram showing the shape of a test piece used in a tensile test. FIG. 2 is a stress-strain diagram obtained from each tensile test of (a) two-phase composite resin and (b) three-phase composite resin. FIG. 3 is a graph summarizing the measurement results of tensile strength of (a) two-phase composite resin and (b) three-phase composite resin. FIG. 4 is a graph summarizing the measurement results of Young's modulus of (a) two-phase composite resin and (b) three-phase composite resin. FIG. 5 is an SEM photograph of fracture surfaces of two-phase composite resin (Epoxy / CF (a), Epoxy / MWNT-7 (b)) and three-phase composite resin (Epoxy / CF / MWNT-7 (c)). It is. FIG. 6 is a graph summarizing the measurement results of thermal conductivity of (a) two-phase composite resin and (b) three-phase composite resin. FIG. 7 is a graph summarizing the measurement results of volume resistivity of (a) two-phase composite resin and (b) three-phase composite resin. FIG. 8 shows the measurement results of Raman spectroscopy of each CNF.

  The composite resin of the present invention contains carbon fibers, carbon nanofibers, and a matrix resin in which the carbon fibers and the carbon nanofibers are dispersed.

In the composite resin of the present invention, and the carbon nanofibers, and the matrix resin is, for tensile stress value M _A in the strain of 0.05 of the matrix resin alone made from the test composite resin (A), the said carbon nanofibers and stress value ratio of the tensile stress values _{M B} in strain of 0.05 of the test composite resin comprising a mixture of the matrix resin _{(B) (M B / M} a) ( hereinafter, simply as "stress value ratio in the strain of 0.05" It is preferable to select a combination that falls within the range of 0.9 to 1.1. The stress value ratio at a strain of 0.05 is more preferably in the range of 0.95 to 1.05.

In the present invention, carbon nanofibers are selected by selecting a combination that reduces the adhesion strength between the matrix resin and the carbon nanofibers so that the stress value ratio (M _B / M _A ) is included in the numerical range shown above. In contrast, the three-phase composite resin of carbon fiber and matrix resin can exhibit high tensile strength, contrary to expectations.

Generally, by adding carbon nanofibers to a matrix resin, the resin and carbon nanofibers are brought into close contact with each other, and the tensile strength is increased. In a two-phase composite resin of carbon nanofibers and matrix resin, an increase in tensile stress value at a predetermined strain means that the adhesion strength between the carbon nanofibers and the matrix resin is increased. Furthermore, the value of the tensile stress value (M _B ) in the two-phase composite resin (test composite resin B) and the value of the tensile stress value (M _A ) of the matrix resin single composite resin (test composite resin A) Since the effect of increasing the tensile stress due to the addition of the carbon nanofibers to the matrix resin can be evaluated by the ratio of The adhesion strength with the fiber can be evaluated.

A method for measuring the stress value ratio at the strain of 0.05 will be described.
A test composite resin (A) composed of a matrix resin alone and a test composition (B) in which carbon nanofibers and a matrix resin are mixed are prepared according to the method for producing the composite resin of the present invention.

  Then, the test piece JIS-K7113 (1/2) shape of the shape shown in FIG. 1 is created. A desktop precision universal testing machine (Autograph AGS-J (5 kN), manufactured by Shimadzu Corporation) is used for the tensile test. Crosshead speed is 1 mm / min. The stress value at a strain of 0.05 is measured by measuring the crosshead displacement and the load history up to immediately after the breakage, and measuring the strain in the longitudinal direction of the central portion of the test piece using a strain gauge.

  In addition, since the stress value ratio is a value that reflects the adhesion strength between the carbon nanofibers and the matrix resin, by adjusting the surface properties such as the type of matrix resin, the type of carbon nanofibers, and the presence or absence of oxidation treatment, Combinations included in the above range can be selected.

  Hereinafter, each component of the composite resin of this invention is demonstrated in detail.

Carbon nanofibers The composite resin according to the present invention contains carbon nanofibers. As the carbon nanofiber, a known carbon nanofiber including a carbon nanotube can be used, and it may be a single wall or a multiwall. The diameter of the carbon nanofiber is preferably 5 to 500 nm, more preferably 8 to 300 nm, and still more preferably 9 to 200 nm. The length of the carbon nanofiber is preferably 0.1 to 100 μm, more preferably 0.1 to 50 μm, and further preferably 0.1 to 20 μm. The aspect ratio ([length] / [diameter]) of the carbon nanofan bar is preferably 10 to 3000, more preferably 15 to 1000, and still more preferably 20 to 300. By selecting a carbon nanofiber having a diameter and an aspect ratio in the above range, a synergistic effect is exhibited in the conductivity of the composite resin by combination with the carbon fiber.

  The diameter, length, and aspect ratio of the carbon nanofibers are average values measured for 100 or more structures existing within a predetermined range using an AFM (Atomic Force Microscope).

  The concentration of the carbon nanofibers in the composite resin of the present invention is preferably 0.01 to 90 wt%, more preferably 0.1 to 50 wt%, and 1 to 30 wt% of the total mass of the composite resin. Further preferred.

Carbon fiber The carbon fiber used in the present invention is not particularly limited, and any carbon fiber such as PAN (polyacrylonitrile) or pitch can be used. Of these, PAN-based carbon fibers are particularly suitable. The diameter of the carbon fiber is preferably 1 to 50 μm, more preferably 2 to 30 μm, and further preferably 3 to 20 μm. 1-100 mm is suitable for the length of carbon fiber, 1-50 mm is more suitable, and 2-10 mm is still more suitable. The aspect ratio (length / diameter) of the carbon fiber is preferably 10 to 10000, more preferably 50 to 1000, and still more preferably 100 to 700. By combining the above-mentioned nanofibers with carbon fibers having a diameter and an aspect ratio in the above range, high conductivity is exhibited.

  The diameter, length, and aspect ratio of the carbon fibers are average values measured for 100 or more structures existing within a predetermined range using an SEM (scanning electron microscope).

  The concentration of the carbon fiber is preferably 0.01 to 90 wt%, more preferably 0.1 to 50 wt%, and even more preferably 1 to 30 wt% of the total mass of the composite resin.

  The weight ratio (CNF / CF) of carbon nanofibers (CNF) to carbon fibers (CF) is preferably 0.01 to 100, more preferably 0.05 to 20, and more preferably 0.5 to 2. Is preferred. By setting the ratio, the composite resin of the present invention exhibits particularly high conductivity (and strength).

Matrix resin The matrix resin used in the present invention is not particularly limited, and is, for example, a polymer. Polymers include epoxy resins, polyolefin resins, polyester resins, polyamide resins, polyimide resins, urethane resins, rubber resins, acrylonitrile / butadiene / styrene resins (ABS resins), acrylic resins, and fluorine resins. .

  Epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, naphthalene type epoxy resin, biphenyl type epoxy resin, glycidylamine type epoxy resin, dicyclopentadiene type epoxy resin, phenol novolac type epoxy. Resins and alicyclic epoxy resins are generally used. In addition, epoxy resins such as β-methyl epichloro type, glycidyl ether type, glycidyl ester type, polyglycol ether type, glycol ether type, and urethane-modified epoxy resin can also be used.

  A part of the epoxy resin, for example, 1 to 35 wt% (5 to 25 wt%) may be substituted with a reactive diluent having an epoxy group. Examples of the reactive diluent include n-butyl glycidyl ether, allyl glycidyl ether, 2-ethylhexyl glycidyl ether, styrene oxide, phenyl glycidyl ether, cresyl glycidyl ether, glycidyl methacrylate, vinylcyclohexene monoepoxide, and diglycidyl ether. The molecular weight of the epoxy resin is preferably 100 to 2000, more preferably 200 to 1000.

  Since the epoxy resin used for this invention can adjust the sclerosis | hardenability and hardened | cured material characteristic, it is suitable to use a hardening | curing agent. As a hardening | curing agent, an acid anhydride, an amine compound, a phenol compound etc. are mentioned, for example.

  Examples of the acid anhydride include methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylhymic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, methylcyclohexenedicarboxylic anhydride , Phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, ethylene glycol bistrimellitate, glycerol trislimitate, dodecenyl succinic anhydride, poly azelaic anhydride, poly (ethyl octadecane Acid) anhydride and the like.

  Examples of amine compounds include 2,5 (2,6) -bis (aminomethyl) bicyclo [2,2,1] heptane, isophoronediamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylaminopropyl. Examples include amine, bis (4-amino-3-methyldicyclohexyl) methane, diaminodicyclohexylmethane, bis (aminomethyl) cyclohexane, metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, diaminodiethyldiphenylmethane, and diethyltoluenediamine. Among these, 2,5 (2,6) -bis (aminomethyl) bicyclo [2,2,1] heptane, isophoronediamine and the like can be mentioned.

  Examples of the phenol compound include phenol novolac resins, cresol novolac resins, bisphenol A, bisphenol F, bisphenol AD, and derivatives such as diallylated products of these bisphenols.

  The epoxy resin can also be cured using an effect accelerator. Examples of the curing accelerator include imidazole compounds such as 2-methylimidazole and 2-ethyl-4-methylimidazole, adducts of these and epoxy resins, organophosphorus compounds such as triphenylphosphine, and tetraphenylphosphine. Examples thereof include borates such as tetraphenylborate and diazabicycloundecene (DBU). Furthermore, additives such as other fillers, pregelling agents, antifoaming agents, coupling agents, internal mold release agents, antioxidants and ultraviolet absorbers can be blended.

  Examples of other matrix resins include polyolefin resins such as polyethylene and polypropylene.

  Examples of the polyester resin include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polybutylene naphthalate (PBN).

  Examples of the polyamide-based resin include nylon 11, nylon 12, nylon 6, and nylon 66.

  Examples of the rubber-based resin include natural rubber, styrene / butadiene rubber, chloroprene rubber, and butyl rubber.

  Examples of the acrylic resin include polyacrylic acid and polyalkyl acrylate.

  Examples of the fluorine-based resin include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), and tetrafluoroethylene. / Hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer (ETFE), and ethylene / chlorotrifluoroethylene copolymer (ECTFE).

<Properties of composite resin>
The tensile strength of the composite resin is not particularly limited, but is preferably 50 MPa or more, more preferably 70 MPa or more, and further preferably 90 MPa or more. Although an upper limit is not specifically limited, For example, it is 500 Mpa or less.

  The breaking strain of the composite resin is not particularly limited, but is preferably 0.01 to 1.00, more preferably 0.02 to 0.50, and further preferably 0.04 to 0.30. 0.07 to 0.15 is particularly suitable.

  The Young's modulus of the composite resin is not particularly limited, but is preferably 2 to 50 GPa, more preferably 4 to 20 GPa, and further preferably 5 to 10 GPa.

The volume resistance of the composite resin is not particularly limited, but is preferably 10 ⁵ Ω · cm or less, more preferably 10 ⁴ Ω · cm or less, and even more preferably 10 ¹ Ω · cm or less. Although a minimum is not specifically limited, For example, it is 10 ^<-4 > ohm * cm or more.

  The thermal conductivity of the composite resin is not particularly limited, but is preferably 0.1 to 20 W / m · K, more preferably 0.2 to 10 W / m · K, and 0.3 to 5 W / m · K. K is more preferred.

"Production method"
The composite resin of the present invention can be produced by a known method for producing a composite resin. For example, the composite resin is prepared by mixing a resin before curing, carbon nanofibers and carbon fibers to form a slurry and curing the composite. It can be produced by a method of producing a resin or a method of kneading carbon nanofibers and carbon fibers by melting the resin.

  When preparing the slurry, it is preferable to use, for example, a rotation / revolution mixer. At this time, it is preferable to prepare a composite slurry by performing a stirring process at a rotation of 500 to 1000 rpm / revolution 1000 to 3000 rpm for 1 to 60 minutes and a rotation of 30 to 120 rpm / revolution 1000 to 3000 rpm for 1 to 30 minutes. is there. By producing a slurry by such a method, high concentration carbon nanofibers and carbon fibers can be dispersed in the composite resin.

1. Test Material and Test Piece Preparation Method In this example, a two-part epoxy resin DENATOOL XNR6809 (main agent) and XNH6809 (curing agent) (manufactured by Nagase ChemteX Corporation) were used as the matrix resin. After mixing the main agent and the curing agent in a ratio of 100: 95, the epoxy resin bulk material (hereinafter referred to as “Epoxy”) is cured by heat curing at 80 ° C. for 4 hours and at 120 ° C. for 2 hours. Is obtained. Table 1 shows various properties of Epoxy.

As the reinforcing filler, carbon fiber (hereinafter simply referred to as “CF”) and carbon nanofiber (hereinafter simply referred to as “CNF”) were used. Pyrofil chopped fiber (manufactured by Mitsubishi Rayon Co., Ltd., see Table 2 for details) was used for CF. Pyrofil chopped fiber is bundled with carbon fiber by epoxy urethane sizing agent at the time of purchase. In order to remove this sizing agent and separate the carbon fiber, use an electric furnace heated at 350 ° C for 1 hour, then cooled, further immersed in acetone, and finally dried in an oven did. This treatment enabled uniform dispersion of CF into Epoxy. On the other hand, there are three types of CNF: VGCF (registered trademark) , VGCF (registered trademark) -S (Vapor Growth Carbon Fiber, manufactured by Showa Denko KK), and MWNT-7 (manufactured by Hodogaya Chemical Co., Ltd.). For details, see Table 2. The VGCF is a registered trademark, but (registered trademark) is omitted in the following description. Table 2 shows the basic physical properties of each filler. Further, when the aspect ratios (length / diameter) of these CNFs are compared, they are higher in the order of VGCF <VGCF-S <MWNT-7.

  In producing the test piece, it is necessary to produce a composite slurry of the two-component epoxy resin (Epoxy), CF, and CNF. Normally, when CNF is put into Epoxy and cured, CNF forms an aggregate, so that a uniform molded body is not produced and good physical properties cannot be obtained. In addition, it is empirically known that by hand, only about 2 to 3 wt% of CNF can be added to Epoxy at most. Therefore, in this study, by using a rotation / revolution mixer (ARE-310, Sinky Co., Ltd.), stirring is performed for 7 minutes at rotation 800 rpm / revolution 2000 rpm, and for 3 minutes at rotation 60 rpm / revolution 2200 rpm for 3 minutes. A slurry was prepared.

  Next, a test piece is obtained by heat-curing the composite slurry obtained by the above procedure. In this study, the composite slurry was poured into a mold, set in a desiccator, and then defoamed by evacuating with a rotary pump for 3 hours. It was confirmed that a molded body without voids was obtained by this treatment. The curing conditions for the composite material were primary curing at 80 ° C. for 4 hours and secondary curing at 120 ° C. for 2 hours, similar to Epoxy.

  In this study, six 2-phase composite resins composed of Epoxy / CF or Epoxy / CNF and three-phase composite resins composed of Epoxy / CF / CNF were prepared, and various material properties were evaluated. In the case of a two-phase composite resin, the weight content of CF or CNF was 10 wt% with respect to Epoxy. On the other hand, in the case of a three-phase composite resin, the weight content of each of CF and CNF was 5 wt%, and the fiber content was 10 wt% by combining the two types of fillers.

2. When a tensile test or bending test is performed on a composite material obtained by adding CNF to a CNF surface-treated thermoplastic resin, and the fracture surface is observed, the filler is pulled out from the resin without breaking. Many have been reported. This is considered to be caused by the low interfacial adhesion strength between the resin and the filler, and many studies have already been made to solve this problem. For example, by forming a film such as silicon on the CNF surface and improving wettability with resin or metal, or by introducing a functional group on the CNF surface by mixed acid treatment, the dispersibility between fibers is improved, and the matrix and A method for strengthening the chemical bond with CNF has been proposed. Furthermore, an oxidation treatment in which CNF is fired in the atmosphere has been studied. Oxidation treatment has the effect of increasing the surface area of contact with the matrix and improving the adhesion strength by intentionally introducing defects into the carbon bonds on the CNF surface and making the CNF surface properties rough.

  Mixed acid treatment and oxidation treatment are considered to be essentially the same effect, but in this example, the latter oxidation treatment was adopted from the viewpoint of fewer treatment steps and excellent mass productivity. All three types of CNF were oxidized. Hereinafter, the VGCF, VGCF-S, and MWNT-7 subjected to the oxidation treatment are denoted as VGCF (H), VGCF-S (H), and MWNT-7 (H), respectively. An electric furnace is used for the oxidation treatment. In the case of VGCF, firing is performed at 690 ° C. for 2 hours, in the case of VGCF-S, 670 ° C. for 2 hours, and in the case of MWNT-7, 630 ° C. for 2 hours. I went inside. These oxidation treatment conditions are set so that the recovery rate after treatment (weight ratio of CNF before and after the oxidation treatment) is about 70%.

3. Material Property Evaluation Method In this example, as a mechanical property evaluation, a uniaxial tensile test was performed to evaluate tensile strength and Young's modulus. Further, thermal conductivity was measured as thermal characteristics, and volume resistivity was measured as electrical characteristics.

  A desktop precision universal testing machine (Autograph AGS-J (5 kN), manufactured by Shimadzu Corporation) was used for the tensile test. Crosshead speed is 1 mm / min. In addition, the crosshead displacement and the load history up to immediately after the fracture were measured, and the strain in the longitudinal direction at the center of the test piece was measured using a strain gauge. Tensile strength and Young's modulus were calculated from the obtained stress-strain diagram. The shape of the test piece was the JIS-K7113 (1/2) shape shown in FIG. Here, L is the full length, L0 is the length of the parallel portion, and t is the thickness of the test piece.

Thermal conductivity (λ [W / m · K]) was measured using a xenon flash analyzer (LFA 447 NanoFlash, NETZSCH), thermal diffusivity (α [cm ² / sec.]), And constant pressure specific heat capacity (Cp [J / g · K]) was measured. The shape of the test piece was 10 mm × 10 mm × 2 mm.

  Low resistivity meter Low Leicester (GP MCP-T610, manufactured by Mitsubishi Chemical Corporation) and High resistivity meter Hirester (UP MCP-HT450, manufactured by Mitsubishi Chemical Corporation) are used for the volume resistivity measurement test. It was. The specimen shapes were all 10 mm × 50 mm × 2 mm. Measurement was performed using a four-probe method with a low resistivity meter and a double ring probe method with a high resistivity meter.

4). Mechanical property evaluation 4.1 Stress-strain diagram of composite resin Fig. 2 shows a representative example of stress-strain diagram obtained by tensile test. Two-phase composite resin (a), three-phase composite resin (b) It shows about each of. The strain in the figure is a value (nominal strain) obtained by dividing the crosshead displacement output from the testing machine by the parallel part length (30 mm) of the test piece. FIG. 3 summarizes the tensile strengths of the two-phase composite resin and the three-phase composite resin, and FIG. 4 summarizes the measurement results of Young's modulus.

  First, looking at the stress-strain diagram of the two-phase composite resin (Epoxy / CF or CNF), in the case of Epoxy / CNF, it was confirmed that the strain continued to increase even after reaching the maximum stress, and then reached fracture. it can. On the other hand, in the case of Epoxy / CF, it can be seen that after elastic deformation as a whole, brittle fracture has occurred. From the results of the tensile strength, in the two-phase composite resin, a significant improvement due to the addition of CF and CNF cannot be confirmed. Regarding Young's modulus, VGCF, VGCF-S, MWNT-7, and CF composites have higher values in the order, and improvements of 20%, 25%, 45%, and 60% are recognized compared to Epoxy alone, respectively. It was. When comparing the results of the oxidized material and the untreated material, the tensile strength and Young's modulus of the oxidized material tend to be slightly higher.

  On the other hand, in the case of the three-phase composite resin, it can be confirmed that the tensile strength is greatly improved as compared with the result of the two-phase composite resin. In particular, the three-phase composite resin added with VGCF-S and CF. It has been found that the tensile strength of the resin is improved by about 30% as compared with Epoxy alone. In addition, with the addition of CF, the three-phase composite resin has less viscoelastic / viscoplastic behavior as a whole due to the increased rigidity of the material, and after linearly increasing strain, it leads to brittle fracture. I understand that. In addition, the Young's modulus of the three-phase composite resin is improved about twice as much as the value of Epoxy alone. However, regarding the influence of the oxidation treatment of CNF, it can be said that the oxidation rate shows a slightly lower Young's modulus.

4.2 Effect of CNF Oxidation Treatment The influence of CNF oxidation treatment will be examined in detail. When the stress-strain diagram of the two-phase composite resin in FIG. 2 is seen, with respect to Epoxy / VGCF, the result of the oxidation treatment over the entire strain shows a stress value that exceeds the result of the untreated case. . That is, it is assumed that the adhesion strength between the matrix resin and the VGCF is improved by the oxidation treatment, and as a result, the rigidity of the composite resin is improved.

  On the other hand, in almost all strain regions in which the test was performed, the stress value of the MWNT-7 composite resin exceeded that of VGCF-S regardless of the results of oxidation treatment and untreated. That is, it is considered that the MWNT-7 composite resin has a higher degree of adhesion between the fiber and the matrix resin, and it does not depend on the oxidation treatment. Further, the adhesion between VGCF-S and the matrix resin is incomplete as compared with other fibers, and no significant change in the state is caused by the oxidation treatment. From the above consideration, it can be concluded that the oxidation treatment is effective only for VGCF and is less effective for MWNT-7 and VGCF-S.

  Next, the results of the three-phase composite resin will be examined. As for the result of Epoxy / CF / VGCF (H), where the fiber / matrix resin interface strength is expected to be improved by oxidation treatment, the tensile strength is lower than that of Epoxy / CF / VGCF by oxidation treatment. I understand. On the other hand, as far as the results of the tensile strength of VGCF-S and MWNT-7 are observed, no significant decrease in strength due to the effect of oxidation treatment is observed. That is, from this result, it is confirmed that when CNF is oxidized to improve the adhesion at the fiber / matrix resin interface, the tensile strength of the three-phase composite resin decreases unexpectedly.

  This fact can also be explained from the results of the three-phase composite resin using VGCF-S and MWNT-7. The results of the two-phase composite resin showed higher tensile strength when MWNT-7 was used as the reinforcing filler than when VGCF-S was used, but this tendency was reversed with the three-phase composite resin. doing. That is, it can be seen that VGCF-S, which is considered to have the lowest fiber / matrix resin adhesion strength, exhibits the highest tensile strength in the three-phase composite resin and is suitable as a reinforcing filler.

  Table 4 summarizes the relationship between the tensile strength and breaking strain of the two-phase and three-phase composite resins. In the table, each composite resin is classified into a group having good adhesion at the CNF / matrix resin interface (MWNT-7, MWNT-7 (H), VGCF (H)) and a group having poor adhesion (VGCF, VGCF-S, VGCF-S (H)). In the two-phase composite resin, the MWNT-7, MWNT-7 (H), and VGCF (H) composite resins that are judged to have good adhesion to the matrix resin have higher tensile strength than other composite materials. It shows strength. On the other hand, in the three-phase composite resin, a correlation with the adhesiveness is not necessarily observed, but in the composite material determined to have a high adhesiveness, the tensile strength tends to decrease. This is due to the fact that the stress-strain diagram shows brittle behavior due to the mixed addition of CF and CNF, as shown in the stress-strain diagram of the three-phase composite resin.

  From the above results, regarding the two-phase resin, it can be determined that both the rigidity and strength of the resin can be enhanced by improving the adhesion at the CNF / matrix resin interface. On the other hand, regarding the three-phase composite resin, it is desirable that the adhesiveness between the CNF and the resin is low, and it has been confirmed that the strength of the composite resin is lowered unexpectedly when the adhesiveness is improved more than necessary.

Incidentally, the stress value the tensile in the strain of 0.05 and, for the tensile stress value _{M A} in strain of 0.05 epoxy resin (Epoxy) test composite resin made from a single piece (A), the carbon nanofibers and the matrix resin (CNF / a ratio of the tensile stress values _{M B} in strain 0.05 Epoxy) made from the test composite resin _{(B) (M B / M} a) are shown in Table 3 below. Among _these, as the weak adhesion of the CNT to M B / _{M A} are included within the scope of 0.9 to _1.1, as a strong adhesion to M B / _{M A} is greater than 1.1 of the CNT, Table 4 It was shown to.

4.3 SEM observation of fracture surface The appearance of the fracture surface after the tensile test was observed by SEM. FIG. 5 shows SEM photographs of fracture surfaces of the two-phase composite resin (Epoxy / CF (a), Epoxy / MWNT-7 (b)) and the three-phase composite resin (Epoxy / CF / MWNT-7 (c)). Show. Many fine irregularities can be confirmed on the fracture surfaces of Epoxy / MWNT-7 and Epoxy / CF / MWNT-7, but these irregularities are not seen in Epoxy / CF. That is, in the case of Epoxy / CF, the propagation of cracks generated near the interface between Epoxy and CF is not suppressed, but propagates through the matrix resin as it is, and eventually breaks. On the other hand, in the case of Epoxy / MWNT-7 and Epoxy / CF / MWNT-7, it is presumed that many irregularities were confirmed on the fracture surface by suppressing the propagation of cracks by MWNT-7. This is the same result not only with MWNT-7 but also with other CNFs. In other words, in the three-phase composite resin, it was considered that the rigidity was improved by the addition of CF, and further, the tensile strength was significantly improved by suppressing the progress of cracks by the addition of CNF.

5. Thermal characteristics and electrical characteristics evaluation 5.1 Thermal conductivity evaluation The thermal conductivity of the two-phase composite resin is shown in FIG. 6A, and the thermal conductivity of the three-phase composite resin is shown in FIG. 6B. Show. In the two-phase composite resin, it can be confirmed that the thermal conductivity is improved as compared with Epoxy alone when any filler is used. In particular, it can be confirmed that the thermal conductivity of the composite resin is greatly improved when CNF is added as compared with CF. As shown in Table 2, the thermal conductivity of CF is about 100 to 550 [W / m · K], whereas the thermal conductivity of CNF is as high as 1000 [W / m · K] or more. That is the reason.

  When comparing the thermal conductivity of the three-phase composite resin and the two-phase composite resin, the effect of improving the thermal conductivity of the three-phase composite resin is low, and the thermal conductivity of the two-phase composite resin is improved by about 50%. It can be confirmed that only the effect is obtained. Generally, in a resin matrix composite material, the thermal conductivity tends to increase as the CNF content increases. The two-phase composite resin produced this time has a CNF content of 10 wt%, whereas the three-phase composite resin has a low setting of 5 wt%. That is, it was considered that the three-phase composite resin had a lower thermal conductivity than the two-phase composite resin because the content of CNF having a high thermal conductivity was small. From the above, in order to improve the thermal conductivity of the three-phase composite resin, it has been determined that it is effective to increase the CNF content as much as possible with respect to the CF content.

  Next, the effect of improving the thermal conductivity due to the difference in CNF will be compared. When VGCF is used in the two-phase composite resin, the thermal conductivity improvement effect is about 4.6 times that of Epoxy alone, whereas in the case of VGCF-S and MWNT-7, Epoxy alone is used. On the other hand, it shows a large improvement effect of about 6 times. Here, Fujiwara et al. Conducted a theoretical prediction based on EMA (Effective Medium Application) regarding the thermal conductivity of the polypropylene / CNF composite material, and the length (aspect ratio) of CNF on the thermal conductivity of the composite material. Investigating the effects (Osamu Fujiwara, Kazuaki Enomoto, Akiyuki Yasuhara, Junya Murakami, Junichi Teraki, Naoto Otake, “Thermal conductivity of resin-based carbon nanofiber composites”, Journal of Precision Engineering, Vol. 72, No. 1 (2006), pp. 95-99.). As a result, it is concluded that an increase in the aspect ratio of CNF is the most effective for improving the thermal conductivity, and that the effect of forming a heat conduction path by contact between fillers is small. This is considered to be because CNF having a larger aspect ratio can suppress scattering of phonons (lattice vibrations) responsible for heat conduction. That is, among the three types of CNFs used this time, the thermal conductivity of Epoxy / VGCF-S and Epoxy / MWNT-7 is higher because the aspect ratio of VGCF-S and MWNT-7 is larger than that of VGCF. It was thought.

When CNF subjected to oxidation treatment was added, it was confirmed that both the two-phase composite resin and the three-phase composite resin had a decrease compared to the thermal conductivity of the untreated product. This is presumably because phonon scattering occurred due to the introduction of functional groups and defects in the sp ² bond of carbon by the oxidation treatment. Therefore, the Raman spectroscopic analysis will be conducted and discussed in detail in “5.3 Discussion” in the following section.

5.2 Volume resistivity evaluation The volume resistivity of the two-phase composite resin is shown in FIG. 7 (a), and the volume resistivity of the three-phase composite resin is shown in FIG. 7 (b). In addition, the upper limit of the measurable area of the Hirester used this time is 9.99 × 10 ¹³ [Ω · cm], and the volume resistivity of Epoxy alone is out of the measurement range (1 × 10 ¹⁴ [Ω · cm] or more). Therefore, it is shown as 1 × 10 ¹⁴ [Ω · cm] as a reference value.

When a conductive filler such as CNF or CF is added to the matrix resin, the conductivity of the composite material exhibits percolation behavior, and the volume resistivity decreases rapidly after exceeding a certain percolation threshold, and thereafter Has been reported to decrease almost linearly. In addition, when a high aspect ratio filler such as carbon nanotube is added, the percolation threshold is generally shown at a content rate of several percent. Since the volume resistivity of the composite material measured this time is as small as 1 × 10 ³ [Ω · cm] or less in both the two-phase composite resin and the three-phase composite resin, a filler exceeding the percolation threshold was added. It is judged that

  Since Epoxy, which is a matrix resin, is electrically insulating, in order for the composite material to have conductivity, it is necessary to form a conductive network by contact between the additive fillers. The denser the conductive network, the better the electrical conductivity of the composite material. In the case of a two-phase composite resin, the volume resistivity varies depending on the type of CNF to be added. When VGCF-S and MWNT-7 are added, a decrease in volume resistivity is confirmed as compared with VGCF. This is because the fiber diameter of VGCF-S and MWNT-7 is small compared to VGCF, so that a large number of fibers can be contained in the composite material, and because the fibers are long compared to VGCF, It was thought that this was because a dense conductive network was formed by increasing the number of contact portions. The reason why the volume resistivity of Epoxy / CF is higher than that of Epoxy / CNF is considered to be that the volume resistivity of CF is about 15 to 20 times larger than CNF.

  Next, when the volume resistivity of the two-phase composite resin and that of the three-phase composite resin were compared, the volume resistivity of the three-phase composite resin was low and high electrical conductivity was exhibited. In a three-phase system, CF having an aspect ratio of about 600 is considered to be the main conduction path, but CNF is responsible for coupling the conduction paths of individual CFs, resulting in high electrical conductivity. It is thought that sex was achieved.

  When CNF subjected to oxidation treatment was used, the volume resistivity was higher than that of untreated CNF regardless of the two-phase composite resin and the three-phase composite resin. This will be described in detail in the “5.3 Considerations” section below, together with the results of thermal conductivity. In addition, in each said test result, Table 5 shows a list of values (average values) shown in the graph.

5.3 Discussion From the measurement results of thermal conductivity and volume resistivity, it was confirmed that the effect of improving the thermal characteristics and electrical characteristics of oxidized CNF was lower than that of untreated CNF. Therefore, in this section, in order to clarify the influence of the oxidation treatment of CNF, Raman spectra of untreated CNF and oxidized CNF were measured and compared with each other. FIG. 8 shows the results of Raman spectroscopic measurement of each CNF. The vertical axis represents the intensity of scattered light, and the horizontal axis represents the Raman shift. In any case of CNF, D-band is observed in the vicinity of Raman shift 1350 [cm ⁻¹ ], and G-band is observed in the vicinity of 1580 [cm ⁻¹ ]. Here, D-band is a peak due to a point defect or a crystal edge defect, while G-band is a peak commonly seen in graphite materials. Moreover, about CNF which performed the oxidation process, it can confirm that D-band peak intensity | strength is increasing with respect to an untreated product. Here, the R value is generally used as an evaluation standard for the defect amount of CNT and CNF. The R value is a value determined by the ratio (R = ID / IG) of the D-band peak intensity (ID) and G-band peak intensity (IG) in the Raman spectrum. Means that there are few lattice defects. Table 6 shows the R value of each CNF, and it can be seen that in all CNFs, the oxidized product has a higher R value than the untreated product.

The VGCF, VGCF-S, and MWNT-7 used this time are all classified into multi-walled carbon nanotubes, and have a multi-layer structure composed of coaxial tubular graphene cylinders. Since the carbon atom constituting the six-membered ring is an sp ² bond, the heat conductivity and electric conductivity are essentially excellent. However, it is considered that defects or oxygen atoms are introduced into the crystal by the oxidation treatment, and as a result, sp ² bonds between carbon atoms are locally broken. This appears to be a cause of deterioration in thermal conductivity and electrical conductivity of the oxidized CNF composite material as well as appearing in a change in the R value in the Raman spectrum.

  In this example, a three-phase composite resin was produced using epoxy resin (Epoxy), which is a typical thermosetting resin, as a matrix and PAN-based carbon fibers (CF) and carbon nanofibers (CNF) as reinforcing fillers. The mechanical properties, thermal properties, and electrical properties were evaluated and examined. In addition, three types of CNFs were oxidized to improve the adhesion strength at the fiber / matrix resin interface. The results obtained in this study are shown below.

(1) Regarding Epoxy / CF and Epoxy / CNF · two-phase composite resin, an increase in Young's modulus of about 10 to 30% was observed, but no significant increase in tensile strength was observed. In the case of a three-phase composite resin of Epoxy / CF / CNF, a high improvement effect was obtained in both Young's modulus and tensile strength due to the synergistic effect of CF and CNF.
(2) It was found that the fiber / resin adhesion of the VGCF-added composite material was improved by the oxidation treatment of the CNF fiber. The MWNT-7-added composite material was considered to have high fiber / resin adhesion regardless of the presence or absence of oxidation treatment, and no change in mechanical properties due to oxidation treatment was observed. Regarding the VGCF-S-added composite material, the adhesion between the fibers / resins was low, and the adhesion could not be improved even after the oxidation treatment.
(3) In the case of a two-phase composite resin, good characteristics can be obtained for both Young's modulus and tensile strength by using CNF having excellent adhesion to the matrix resin. On the other hand, in the case of a three-phase composite resin, it has been found that higher strength characteristics can be obtained by using CNF having weak adhesion to the matrix resin. That is, in this study, it was considered that the oxidation treatment of CNF is effective only for the two-phase composite resin. This is because the brittle behavior is exhibited by adding CF in the three-phase composite resin.
(4) In the two-phase composite resin, when CNF was added, significant improvement in thermal conductivity and volume resistivity was observed. In particular, the higher the aspect ratio of CNF, the greater the improvement in thermal conductivity and electrical conductivity was confirmed. On the other hand, in the case of the three-phase composite resin, the thermal conductivity was lowered but the electrical conductivity was improved as compared with the two-phase composite resin. In order to further improve the thermal conductivity, it was judged that it is effective to reduce the CF addition amount and increase the CNF addition amount as much as possible.
(5) As a result of analyzing the oxidized CNF and the untreated CNF by Raman spectroscopy, the oxidized product was inferior in purity to the untreated product. That is, it is presumed that defects or oxygen atoms are introduced into the crystal of the oxidation-treated product, and the sp ² bond between carbon atoms is locally broken. This is considered to be the reason why the thermal conductivity and electrical conductivity of the composite resin using the oxidized CNF are deteriorated as compared with the case of the untreated product.

Claims (2)

A carbon fiber having a diameter of 1 to 50 μm;
Carbon nanofibers having a diameter of 5 to 500 nm;
A matrix resin in which the carbon fibers and the carbon nanofibers are dispersed;
A composite resin containing
The carbon nanofibers and the matrix resin are
For tensile stress values M _A in the strain of 0.05 of the matrix resin alone made from the test composite resin (A), the tensile at strain of 0.05 of the carbon nanofibers and composite resin test consisting of the matrix resin (B) the ratio of the stress value _{M B (M B / M a} ) becomes in the range of 0.9 to 1.1, a combination,
A composite resin in which the carbon nanofiber is an oxidation treatment material of VGCF (registered trademark), VGCF (registered trademark) -S, or VGCF (registered trademark) -S , and the matrix resin is an epoxy resin.   The composite resin according to claim 1, wherein the strain at break is 0.07 to 0.15.