JPH0676556B2 - Carbon fiber composite polymer composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polymer composite material reinforced with carbon fiber as a filler.

(Prior Art) Composite materials such as resins reinforced with carbon fibers are being developed for applications in a wide range of fields such as sports goods, leisure goods, aerospace materials, and electromagnetic wave shielding materials.

It is expected that the applications will be further expanded in the fields where the specific strength and specific elastic modulus, which are excellent properties of carbon fiber, are utilized, and where the excellent electrical conductivity is utilized.

However, the fact that the adhesive strength with the matrix during compounding is weak and the properties of the material are not fully utilized are currently the biggest problems to be overcome in this field, and various proposals have been made to measure this improvement. ing.

As a typical method for modifying the carbon fiber, an oxidation treatment can be mentioned. As the oxidation treatment method, there are a gas-phase oxidation method, a liquid-phase oxidation method using chemicals, an electrolytic oxidation method utilizing the electric conductivity of carbon fiber, etc. In a commercial plant, the electrolytic method is most widely adopted because of its efficiency and controllability. ing.

(Problems to be Solved by the Invention) Even if any of the above-mentioned treatment methods is adopted, the excessive oxidation treatment causes deterioration of the carbon material itself, so that the treatment is naturally limited, and after the oxidation treatment, the sizing treatment or the cup treatment is performed. Even if carbon fiber treated with a ring agent and commercially available is used as a filler as it is to form a composite with a polymer material, it does not necessarily exhibit good adhesiveness with the polymer material. For example, when a polyolefin is used as the matrix, the adhesiveness is poor, and cross-section observation after tensile rupture often shows a slip-out phenomenon at the interface between the matrix and the filler, which increases the composite performance expected from the individual characteristics. Only the characteristics below are obtained. With respect to other various polymer materials that can serve as a matrix, the degree of achievement of the expected composite properties differs depending on the material, but it is difficult to say that any of them is sufficiently satisfactory.

As an index of the degree of achievement of the composite properties here, for example, regarding tensile strength, in the case of long fibers, evaluation by additivity by volume content ratio is generally used, and in the case of short fibers, it is more complicated. Yes, the Kelly-Tyson formula etc. are used.

As described above, in the conventional technique, sufficient adhesion cannot be obtained only by surface modification of the carbon fiber.Therefore, when the matrix is a polyolefin, it is also attempted to add a modified polymer as a part of the composition when forming a composite. Has been.
For example, a copolymer or a graft polymer of an olefin and an unsaturated monomer having an epoxy group and capable of radical copolymerization,
Alternatively, it is a modified polyolefin such as a copolymer or graft polymer of an olefin and an unsaturated dicarboxylic acid or its anhydride.

The combination of these materials, that is, the composite material obtained by combining the commercially available carbon fiber, which has been subjected to the sizing treatment after the oxidation treatment or the coupling agent treatment, with the modified polyolefin and the polyolefin serving as the matrix alone or with the copolymer, is compared with the case where these treatments are not applied. If this is done, the mechanical evaluation may improve, but it is lower than what can be expected from the characteristics of the material. Is big.

Other methods for modifying the surface of the carbon fiber have been proposed, such as grafting or coating of various polymers, but are not widely adopted because of the cost due to the complicated process and the effect of the treatment. I haven't arrived.

The present inventor has arrived at the present invention as a result of extensive studies for the purpose of obtaining a composite material having excellent properties by easy treatment and combination with an existing substance without deteriorating the properties of the carbon fiber. .

(Means for Solving the Problems) The present invention is a composite composition of carbon fiber (including graphite fiber) and a polymer compound, wherein (A) a compound having an epoxy group (B) a straight chain or branched A polymer compound having a carboxylic acid group or its anhydride group in the chain or a mixture of the polymer compound and a polymer compound other than the compound having an epoxy group (C) Acidic functional group on the surface It is characterized by being made of carbon fiber whose base is an alkali metal salt.

According to the present invention, without deteriorating the characteristics of the carbon fiber,
By improving the adhesiveness between the carbon fiber and the polymer material, it is possible to obtain a carbon fiber-reinforced polymer composite composition exhibiting excellent properties.

The present inventors have previously proposed a composition comprising a polymer of carbon fibers whose surface acidic group is an alkali metal salt, in which the polymer having an epoxy group in a straight chain or a branched chain is reduced. Patent application for a composite composition characterized by including both in part.

As a result of further study of the present invention, the present invention is further excellent in that after the reaction of the epoxy group with the portion where the acidic group on the carbon fiber surface is an alkali metal salt, and the reaction with a carboxylic acid group or its anhydride group. It is a composite composition of performance.

Regarding the properties of the composite composition, in the case of thermosetting, the adhesive strength can be evaluated by the interlaminar shear strength (ILSS), etc.
In the case of thermoplasticity, it cannot be directly evaluated by ILSS or the like, but it is clear from the improvement of the mechanical properties of the obtained composition that it is due to the improvement of adhesiveness, and this can be evaluated.

The acidic groups formed on the surface of carbon fiber are -COOH, -OH, = O,
And a lactone type compounded with these.

In order to attach these acidic groups to the surface of the carbon fiber, the carbon fiber may be subjected to treatments such as gas phase (for example, air) oxidation, electrolytic oxidation, and liquid phase oxidation.

The fact that a small amount of acidic groups are present on the surface of carbon fiber even before the oxidation treatment as a surface treatment is documented ("Carbon Fiber" edited by Sugiro Ohtani, p222, published by 1983 Modern Editor).
But it is reported. However, since few acidic groups naturally occur, the oxidation treatment is generally performed by the method described above. And preferably, an acidic group of 10 ⁻⁵ equivalent / g (CF) or more is attached (CF is an abbreviation of carbon fiber). The upper limit differs depending on the type of carbon fiber, but the treatment should be stopped to such an extent that mechanical strength does not deteriorate due to damage to the fiber. For example, in the case of PAN system, 5 × 10 ^-4 equivalent / g (CF)
It is a degree.

The carbon fibers used are all PAN type, pitch type and vapor phase growth type known carbon fibers, and these can be used regardless of heat treatment conditions such as carbonized fiber and graphitized fiber.

In order to convert the acidic groups on the surface of carbon fibers into alkali metal salts, it is sufficient to contact the carbon fibers with an alkaline substance (NaOH, KOH, etc.), which is performed in the presence of the alkaline substances. Any method such as a phase method or a method of dipping or applying carbon fiber in a liquid can be used as long as neutralization of the acidic groups on the surface can be achieved. Those treated in liquid are then washed with water and dried before use.

The present invention is a composite material of a carbon fiber and a polymer compound thus surface-treated, but a compound having an epoxy group,
It is used as a coupling agent between an alkali metal salt of an acidic group on the surface of carbon fiber and a polymer compound having a carboxylic acid group or an anhydride group thereof.

The compound having an epoxy group may be a monomer, an oligomer or a polymer, and the monomer or oligomer may be glycidyl methacrylate, styrene oxide, epichlorohydrin or the like and an oligomer obtained by a known method, and the polymer may be bisphenol A. Other epoxy resins manufactured and marketed are used (see “Epoxy Resin” edited by Hiroshi Kakiuchi (Shokodo June 1979), pages 51 to 105).

The polymer compound having a carboxylic acid group or its anhydride group in a straight chain or a branched chain has a carboxylic acid group or its anhydride group, and has a copolymerization of a radical copolymerizable unsaturated monomer and a polyolefin or the like. Examples thereof include coalesce or graft polymer.

As will be described later, the composition of the present invention is effective in a very small amount of a compound having an epoxy and a polymer compound having a carboxylic acid group. Therefore, in addition to these compounds, a polyolefin and an ethylene-vinyl acetate copolymer are used. Polymeric compounds such as In this case, for example, when polypropylene is used in combination, as a compound having a carboxylic acid group or the like, a copolymer of polypropylene and an unsaturated monomer capable of graft polymerization is suitable as a compound having a carboxylic acid group, and is commercially available, for example. There is Admer (trademark of Mitsui Petrochemical Co., Ltd.) as a product.

Next, the composition ratio of the composition of the present invention will be described.
The compound having an epoxy group is promoted for ring-opening by the alkali metal salt on the carbon fiber surface, and the ring-opened compound is bonded to the compound having a carboxylic acid group or an anhydride group through these groups. It is desirable that the amount of the compound of (4) is such that the amount of the epoxy group, the carboxylic acid group or the anhydride group therein is equal to or more than that of the alkali metal salt, but the experimental result shows that A considerable effect is recognized even with the amount of. The upper limit of the amount is not particularly limited, but can be appropriately determined by considering the properties and uses of the composition, and from the combined use of polymer compounds other than the above.

The amount of carbon fiber in the composition of the present invention can be varied within a wide range depending on the use, and a small amount is used in the range of 1-2% (weight%, the same applies hereinafter) to a large amount of about 60%.

As a method of mixing or further molding these composite compositions, when a thermoplastic resin is included in a polymer compound, carbon fibers are first treated with a compound having an epoxy group, and then a carboxylic acid group or an anhydride group thereof is added. It is common to dry-blend a polymer having a polymer with a thermoplastic resin and then pelletize or injection-mold it using a kneading extruder, or to compound it from the beginning using a dry-blending kneading extruder. .

When a thermosetting polymer is used, in addition to the method of heat-curing after dry blending, it can be heat-cured after once forming a prepreg composition of carbon fibers into a desired shape.

(Function) By converting the acidic functional group obtained by the oxidation treatment of the carbon fiber surface into an alkali metal salt, the ring-opening of the epoxy group is promoted, and the ring-opened group and the carboxylic acid group or its anhydride group are subsequently promoted. It is considered that, as a result of the chemical bonding, the composite material having the properties superior to those of the carbon fiber reinforced polymer material manufactured by the conventional method was obtained.

The carbon fiber needs to be treated with an alkali salt after the acid treatment, and even if an alkali metal salt of an organic acid is separately prepared and attached to the surface of the carbon fiber, the effect of the present invention cannot be obtained. .

(Effect) According to the present invention, without deteriorating the characteristics of the carbon fiber,
By simple treatment and combination of characteristic polymers, mechanical properties such as bending strength and bending elastic modulus can be improved as will be shown later in Examples.

(Example) (1) Reaction of carbon fiber with glycidin methacrylate Commercially available PAN-based carbon fiber (HTA-C6 manufactured by Toho Bethlon) was used at 55 ° C.
Then, the mixture was extracted with 6 Hr-acetone to remove the sizing agent (the surface state at this point is the state after the carbonization and the oxidation treatment).

After drying, add excess KOH aqueous solution (1/50 normal) and back titrate with HCl aqueous solution (1/50 normal) to quantify total acidic groups on the surface of carbon fiber. 4 × 10 ^-5 equivalent / g (CF )Met.

After removing the sizing agent, dry carbon fiber with 10 times the equivalent amount of KOH
It was immersed in an aqueous solution, treated at 80 ° C. for 4 hours and washed with water. After the completion of washing with water, vacuum drying was carried out at 100 ° C. to obtain carbon fibers whose surface acidic groups were alkali metal salts.

Next, 30 g of the above treated carbon fiber, glycidyl methacrylate
300 ml, 700 ml of nitrobenzene as a solvent, and 2 g of N-phenyl-β-naphthylamine as a radical polymerization inhibitor were placed in a separable flask and treated at 120 ° C. for 2 hours with stirring. After completion of the reaction, methanol was added to precipitate a polymer, which was separated by filtration. The polymer and carbon fiber remaining on the paper were extracted with chloroform and dried to obtain carbon fiber which was reacted with a monomer having an epoxy group.

(2) Reaction between carbon fiber and styrene oxide A method in which hydrogen gas is used as a carrier and ultrafine iron powder is dispersed in ethyl alcohol is injected into a reaction tube by the method described in JP-A-58-180615. The vapor-grown carbon fiber obtained in 1. was subjected to 48 Hr oxidation treatment under the conditions of 60% HNO ₃ and 100 ° C. After the treatment, it was washed with water until the pH reached 7.

In this state, the total amount of acidic groups on the surface determined by the same method as in Example 1 was 5 × 10 ⁻⁴ equivalent / g (CF).

Subsequent to washing with water, dip in 10 times the equivalent amount of KOH aqueous solution and
After Hr treatment, it was washed with water.

After the completion of washing with water, vacuum drying was carried out at 100 ° C. to obtain carbon fibers whose surface acidic groups were alkali metal salts.

Next, the above treated carbon fiber 30g, styrene oxide 250m
750 ml of nitrobenzene as a solvent was placed in a separable flask and treated at 110 ° C. for 3 hours while stirring. After completion of the reaction, methanol was added to precipitate a polymer, which was separated by filtration. The polymer remaining on the paper and the carbon fiber were extracted with chloroform and dried to obtain a carbon fiber reacted with a monomer having an epoxy group.

(3) Carboxylic acid-modified polypropylene Polypropylene (Trade name: Syo aroma, Brand name: MA51
0) 100g, maleic anhydride (Tokyo Kasei) 75g, benzoyl peroxide (Tokyo Kasei) 0.75g xylene 1.6l as a solvent
The mixture was put in and reacted at 120 ° C. for 2.5 hours. After completion of the reaction, acetone was added to precipitate the polymer, and then the unreacted monomer was washed out by re-dissolving and re-precipitating to obtain a modified polypropylene containing a carboxylic acid anhydride group.

The graft amount was calibrated by infrared absorption spectrum. The graft amount was 0.4% by weight.

(4) Comparative carbon fiber A commercially available carbon fiber (HTA-C6 manufactured by Toho Bethlon) was used as it was. This fiber has been subjected to oxidation treatment and sizing agent addition by the manufacturer.

(5) Comparative carbon fiber The carbon fiber described above was subjected to the sizing agent removal treatment by acetone extraction shown in Example 1. That is, it corresponds to a surface state obtained by subjecting the carbon fiber to only the oxidation treatment.

(6) Comparative carbon fiber A carbon fiber obtained by subjecting the carbon fiber of the above (5) to a treatment in which the surface acidic group is changed to an alkali metal salt by the same method as in (1).

(7) Comparative carbon fiber The vapor-grown carbon fiber shown in (2) that has been subjected to oxidation treatment.

(8) Comparative carbon fiber In the same procedure as in (2), the vapor-grown carbon fiber was subjected to a treatment in which the acidic group on the surface was changed to an alkali metal salt.

(9) Comparative carbon fiber Carbon fiber as produced in the gas phase by the method of (2).

(10) Preparation of Composite Material and Its Properties Each of the above-mentioned carbon fibers, modified polypropylene having a carboxylic acid anhydride group, and polypropylene (trade name; Sialoallomer brand: MA510) are blended in the ratio shown in Table 1 by Labo Plastomill. (Toyo Seiki Seisakusho: Model 28-125, roller mixer model R-60) was used for kneading. As the carbon fiber, a PAN-based fiber having a length of about 6 mm was used, but after kneading, the average was 300 μm. Also, fine carbon fibers were used for the vapor phase method.

Kneading conditions Temperature 170 ° C. time Resin kneading 5 minutes Carbon fiber feeding 〃 Kneading 〃 After cooling the obtained kneaded material, it was cut into an average size of 2 to 4 mm cubic and molded at 220 ° C. using a hot plate press. A test piece was punched out from a flat plate into a predetermined size and subjected to bending strength, bending elastic modulus, tensile strength, and Izod impact test.

The results are summarized in Table 1.

The characteristics of the composite obtained by combining both PAN-based carbon fiber and vapor-grown carbon fiber by this method are 1
It became clear that it was significantly improved compared to the case where one was lacking.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C08K 9/02 KCN 7242-4J C08L 23/12 LCS 7107-4J

Claims (1)

[Claims] 1. A compound having (A) an epoxy group, (B) a polymer compound having a carboxylic acid group or an anhydride group thereof in a straight chain or a branched chain, or a compound other than the polymer compound and an epoxy group-containing compound. Mixture with other polymer compound (C) A carbon fiber composite polymer composition comprising carbon fibers having an alkali metal salt as an acidic functional group on the surface.