JPS6256266B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sizing treatment for carbon fibers, and more particularly to a treatment method for improving the cohesiveness of carbon fibers. Carbon fiber has extremely high specific strength and specific elasticity, as well as excellent heat resistance, and is increasingly being used as a reinforcing fiber for composite materials. However, because of its high elasticity, it has low elongation and poor bending abrasion resistance. Therefore, during post-processing, single yarn breakage often causes yarn damage, breakage, and fuzzing, leading to a decline in product quality.
Furthermore, it is difficult to handle because it is easily charged with static electricity, and fries occur due to fluffing, which causes a deterioration of the working environment. In order to improve this problem, carbon fibers have traditionally been subjected to sizing treatment, which protects the fiber surface with a monomolecular film of a suitable resin and at the same time gives flexibility and cohesiveness, thereby suppressing fuzz caused by single fiber breakage. Improvements in processability and handling have been made. When the matrix resin is an epoxy resin, bisphenol A diglycidyl ether type epoxy resin is generally used as a sizing agent for carbon fibers, but due to its solubility in solvents, acetone, MEK, etc. It is convenient to use an organic solvent of However, although organic solvent-based sizing agents are superior in terms of uniformity of sizing agent adhesion, they are very disadvantageous from an industrial perspective in terms of safety measures and pollution prevention measures, so dispersants or surfactants are not used. However, a treatment method using a resin-water dispersion system is widely used. However, in general, it is difficult to stably and uniformly disperse epoxy resins in water due to their characteristics such as viscosity, specific gravity, and hydrophobicity, and the resin components tend to separate and settle. It is also one of the reasons why spots become larger. Generally speaking, a major factor that determines the mechanical properties of composites is the adhesion at the interface between the fibers and the matrix, but another important purpose of the sizing process is to form a monomolecular film of a suitable resin into a CF.
The purpose is to improve the mutual adhesion between the fiber and the matrix through the molecular film formed on the surface. We have arrived at the present invention as a result of intensive research into developing a sizing treatment method that improves the handling of carbon fibers, does not reduce the properties of the composite after molding, and can be treated stably in an aqueous system. That is, the present invention involves treating carbon fibers with a water emulsion of an epoxy resin composition containing a diglycidyl ether bisphenol A type epoxy resin that is solid at room temperature and having a viscosity of 10 to 10 ³ poise at 50°C. The sizing method for carbon fiber is characterized by: In the present invention, by blending a solid epoxy resin in an epoxy resin water emulsion system, sedimentation and separation of the epoxy resin is reduced, and even though the viscosity of the resin increases, the stability of the system is increased. This is probably because the hydroxyl groups in the epoxy resin contribute to the stability of the system. The epoxy resin used in the present invention is mainly composed of diglycidyl ether bisphenol A type epoxy resin, and as an epoxy resin that is solid at room temperature, it has an epoxy equivalent of about 500 or more and a melting point of 50 by the Duran mercury method. Diglycidyl ether bisphenol A-type epoxy resin that exhibits a temperature of ℃ or above. The amount of this solid epoxy resin blended is preferably such that the viscosity of the blended resin is 10 to 1000 poise at 50°C, and in most cases it is in the range of 10 to 40% of the other epoxy resins. If the viscosity of the epoxy resin composition used for sizing is less than 10 poise at 50°C, the focusing effect will be small, and if it exceeds 1000 poise, problems will arise in terms of flexibility. Note that the viscosity as used in the present invention is a value measured using a B-type viscometer on a sample at substantially 50°C. The surfactant used for emulsion of this epoxy resin composition is preferably a nonionic surfactant.
Particularly preferred are polyoxyethylene ethers,
The amount added is usually 10% to the epoxy resin composition.
A range of ~100 parts by weight is desirable. Specific examples of polyoxyethylene ethers used in the present invention include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octyl phenol ether, and polyoxyethylene nonyl phenol. Typical examples include ether, polyoxyethylene higher alcohol ether, polyoxyethylene lauryl ether, etc., but they may be used in combination with other surfactants, and are used in combination when making the resin composition of the present invention. Epoxy resins include epoxides of hydrocarbons with a large number of unsaturations (vinylcyclohexene, dicyclopentadiene, cyclohexadiene, cyclododecatriene, butadiene, polybutadiene, divinylbenzole); polyhydric alcohols (ethylene, propylene, and butylene glycol). , polyglycol, thiodiglycol, glycerin, trimethylolpropane, pentaerythritol, sorbitol, polyvinyl alcohol, polyallyl alcohol and similar substances); polyhydric phenols (resorcinol, hydroquinone, bis-(4-hydroxyphenyl) )-methane, bis-(4-hydroxy-3-methylphenyl)-methane, bis-(4-hydroxy-3.5
-dichlorophenyl)-methane, bis-(4-hydroxy-3,5-dibromphenyl)-methane, bis-(4-hydroxy-3,5-difluorophenyl)-methane, 1,1-bis-(4-hydroxy phenyl)-ethane, 1,1-bis-
(dihydroxyphenyl)-ethane, 2,2-bis-(4-hydroxyphenyl)-propane,
2,2-bis-(4-hydroxy-3-methyl-
phenyl)-propane, 2,2-bis-(4-hydroxy-3-chlorophenyl)-propane,
3,2-bis-(4-hydroxy-3,5-dichlorophenyl)-propane, bis-(4-hydroxyphenyl)-phenylmethane, bis-(4-
hydroxyphenyl)-diphenylmethane, bis-(4-hydroxyphenyl)-4-methylphenylmethane, 1,1-bis-(4-hydroxyphenyl)-2,2,2-trichloroethane-bis-( 4-hydroxyphenyl)-(4-chlorophenyl)-methane, 1,1-bis-(4-hydroxyphenyl)-cyclohexane, bis-(4-
hydroxyphenyl)-cyclohexylmethane,
Epoxide ethers of 4,4-dihydroxydiphenyl, 2,2-dihydroxydiphenyl, 4,4-dihydroxyphenyl sulfone and their hydroxyethyl ether, phenol- or cresol-formaldehyde condensation products);
Sulfonamides and aromatic amines (N・N-diglycidylaniline, N・N′-dimethyldiglycidyl-4,4-diaminodiphenylmethane, N・
N-containing epoxides of (N・N′・N′-tetraglycidyl-4,4-diaminodiphenylmethane, N・N-diglycidylbenzenesulfonamide); and carboxylic acids having a large number of unsaturations by conventional methods or epoxides prepared from carboxylic acid esters with one unsaturation of unsaturated alcohols; glycidyl esters, obtainable by polymerization or copolymerization of glycidyl esters of unsaturated acids or other acidic compounds (cyanuric acid, Polyglycidyl ester obtained from cyclic trimethylene trisulfone (or its derivatives and other analogues).
Of course, mixtures of the aforementioned epoxide compounds can also be used. Further, if desired, auxiliary ingredients such as a softening agent and an antistatic agent may be included. The active ingredient concentration of the above sizing agent is in aqueous solution.
The range of 0.1 to 10 wt% is preferred, and the range of 0.5 to 5 wt% is particularly preferred. In addition, the concentration of these treated aqueous solutions is such that the amount of sizing agent attached to the carbon fiber is 0.1
It is preferable to set it within a range of ~10 wt%, and it is preferable to change it as appropriate depending on the tension applied to the carbon fiber, the squeezing conditions after impregnation, etc. After the sizing treatment, the carbon fibers that have passed through the squeezing rollers are dried for a predetermined time using hot air or an infrared heater to remove moisture. Although systems using liquid epoxy resin alone as a sizing agent have some effect in imparting flexibility, they have problems with the cohesiveness of carbon fiber bundles due to their low viscosity at room temperature. . The treatment system according to the present invention exhibits better flexibility and convergence than a system using a liquid epoxy resin alone at room temperature, and has vastly improved handling properties. It has excellent composite properties, particularly in that the ILSS decreases at high temperatures, but this is probably due to the increased hydroxyl group concentration caused by the blended solid epoxy resin, which inhibits interaction with the functional groups that are thought to exist on the surface of the carbon fiber. It is thought that this is because the wettability between the carbon fiber and the matrix resin has greatly improved as a result. The carbon fibers referred to in the present invention are obtained by heat-treating organic fibers in an oxidizing atmosphere to make them flame resistant and then heat-treating them in a non-oxidizing atmosphere at high temperatures, or by heat-treating pith as a raw material. ~
It consists of a fiber bundle made up of about 500,000 to 200,000 single fibers with a diameter of about 15μ. This will be explained in detail below using examples. Example 1 Solid epoxy resin (Epicoat manufactured by Yuka Ciel Co., Ltd.
1001) and 10 g of liquid epoxy resin (Epicoat 828 manufactured by the same company) were heated and mixed at about 90℃, and heated to about 200℃ at 50℃.
A poise resin composition was obtained. An emulsion was prepared by adding 5 g of a nonionic active surfactant (Emulgen 903, manufactured by Kao Atlas Co., Ltd.) and dispersing it in 2 parts of water. This emulsion remained stable with no resin precipitation observed even after being left at room temperature for about 5 hours. Squeezing conditions were adjusted so that about 1 g of the above emulsion solution adhered to each 1 g of carbon fibers, and after sizing treatment, hot air at about 110° C. was blown to remove water and dry. The sizing treatment effect of the treatment system was evaluated by the following method. Hang the carbon fibers on a chrome-plated bar with a diameter of 5 mm so that the inner angle is 90°, and add 50 mg/kg to the tow.
The convergence was evaluated by reciprocating at a rate of 50 times/minute while applying a load of d so that the rubbing length was approximately 100 mm. The resulting treatment system showed good focusing properties. 100g of Epicoat 828 (trademark manufactured by Ciel Chemical Co., Ltd.) was applied to the carbon fibers sized as described above.
A resin composition consisting of 90 g of methylnadic anhydride and 2 g of benzyldimethylamine was uniformly impregnated using a drum winder type impregnation device to prepare a prepreg that was aligned in one direction. The obtained prepreg was cut to a length of 250 mm and a width of 250 mm, laminated, and cured and molded under a pressure of 5 kg/cm ² at 90° C. for 2 hours and then at 150° C. for 4 hours to obtain a composite with a thickness of 2 mm. The ILSS of the resulting composite was measured according to ASTM D-2344. The ILSS at room temperature was 8.3Kg/mm ² and the value at 100°C was 4.7Kg/mm ² . The results are shown in Experiment No. 2 in Table 1. In the above sizing method, Epicoat is used instead of Epicoat 1001 as a solid epoxy resin.
Table 1 shows examples using 1004 and 1007 (trademarks manufactured by Ciel Chemical Co., Ltd.). Evaluations were also carried out by varying the amount of solid epoxy resin blended. The sizing treatment according to the present invention greatly improved composite properties.

[Table] Comparative Example 1 As a comparative example, the convergence and composite properties of Example 1 were evaluated for the case where the sizing treatment was performed using Epicote 828 (trademark manufactured by Ciel Chemical Co., Ltd.) alone without adding solid epoxy. Table of results-1
Shown in conjunction with The effect of adding solid epoxy resin is clearly visible. Furthermore, the stability of the emulsion system at room temperature in this case was about 2 hours.

Claims (1)

[Claims] 1 Add solid diglycidyl ether bisphenol A type epoxy resin at room temperature,
A method for sizing carbon fibers, comprising treating carbon fibers with a water emulsion of an epoxy resin composition having a viscosity of 10 to 10 ³ poise at °C.