JP2011226004A - Method for producing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To propose a method for uniformly adhering a sizing agent to carbon fiber, the agent capable of improving composite property of a composite material.SOLUTION: In a method for producing carbon fiber having the steps of adhering a sizing agent to the carbon fiber by immersing the carbon fiber in a sizing bath containing the sizing agent, and then drying the carbon fiber to adhere the sizing agent thereto, the carbon fiber, after being immersed in the sizing bath, is subjected to primary drying at a temperature of 80 to 120°C for 30 to 200 seconds, and then subjected to secondary drying at a temperature of 180 to 230°C for 30 to 200 seconds.

Description

The present invention relates to a carbon fiber production method suitable for the use of a carbon fiber reinforced composite material having excellent impact resistance and the like.

In recent years, composite materials using carbon fibers as reinforcing fibers are light and have excellent mechanical properties such as high strength, and thus are increasingly used as members of aircraft, automobiles and the like. These composite materials are molded, for example, from a prepreg, which is an intermediate product in which a reinforcing fiber is impregnated with a matrix resin, through molding and processing steps such as heating and pressing.

In order to pursue high performance in the composite of carbon fiber and matrix resin, it is essential to improve the mechanical properties such as strength and elastic modulus of the carbon fiber itself. It is expected that composite materials having higher-performance composite properties (high strength, high elasticity, high impact resistance, etc.) can be obtained by improving the properties of carbon fibers.

By the way, various sizing agents (sizing agents) are imparted to the carbon fiber in order to improve the bundling property, handling property, scratch resistance and the like of the carbon fiber bundle during prepreg and weaving of the carbon fiber. The sizing agent is also necessary for improving the composite physical properties of the composite material and stabilizing the quality and performance. For this purpose, the sizing agent must have good compatibility and adhesion to the matrix resin constituting the composite material. Adopted.

For example, in Patent Document 1, a proposal for solving the problem that the adhesive properties are inferior in the composite physical properties of a composite material using a thermosetting matrix resin such as an epoxy resin, which has not been sufficiently solved conventionally, is made. ing. Specifically, Patent Document 1 increases carbon fiber convergence, improves processability to fabrics and prepregs, and produces carbon fibers having excellent composite performance (tensile strength and interlaminar shear strength). Therefore, the epoxy resin is first applied to the carbon fiber at a mass ratio of the epoxy resin to the thermoplastic resin of 15/1 to 2/1, and after drying at 180 ° C., the thermoplastic resin is applied. A method has been proposed.

In Patent Document 2, in order to obtain a carbon fiber strand suitable for obtaining a composite material having excellent tensile strength in the fiber axis direction and excellent interlaminar shear strength that has a large influence on stress in the direction perpendicular to the fiber axis. In addition, a carbon fiber strand is proposed in which 0.3 to 5.0% by mass of a sizing agent containing a dimer acid type epoxy resin as an essential component is attached. However, these patent documents do not describe any improvement in the ring fracture strength, which is an index of the interlaminar adhesion between the fiber and the resin, among the composite performance of the composite material.

In Patent Document 3, a carbon fiber using a sizing agent containing a two-component epoxy resin composed of a low molecular weight epoxy resin and a high molecular weight epoxy resin is produced, and the tensile strength in the fiber axis direction and the fiber axis are used. It is disclosed that a composite material having excellent interlaminar fracture toughness in the vertical direction was obtained. This invention pays attention to the combination of specific resin components, but does not describe any unevenness of the sizing agent.

The present inventor tried to solve the problem because unevenness in adhesion of the sizing agent to the carbon fibers causes unevenness in the adhesiveness between the sizing agent and the matrix resin when the composite material is used. And paying attention to the change of the drying process conditions of the sizing process in the production process of carbon fiber, the adoption of simpler process conditions can uniformly adhere the sizing agent, and as a result, the composite material, In particular, it was possible to obtain a carbon fiber that contributes to an improvement in ring breaking strength.

JP 2006-188782 A JP 2004-149721 A JP-A-2005-290614

An object of the present invention is to propose a method for uniformly attaching a sizing agent to carbon fibers, which can improve the composite physical properties of a composite material.

The object of the present invention is achieved by the following invention. That is, the present invention provides a carbon fiber production method including a sizing step in which carbon fibers are immersed in a sizing bath containing a sizing agent and then dried to attach the sizing agent to the carbon fibers. The carbon fiber after being soaked in is dried at 80 to 120 ° C. for 30 to 200 seconds, followed by secondary drying at 180 to 230 ° C. for 30 to 200 seconds. It is the manufacturing method of the carbon fiber characterized. As the sizing resin, a resin mainly composed of an epoxy resin having a viscosity at 120 ° C. of 10 to 200 mPa · s is preferable. In the present invention, the sizing agent refers to a resin composition containing a sizing resin as a main component and a surfactant, a stabilizer, and other additives as subcomponents.

And the preferable carbon fiber obtained by the manufacturing method of the carbon fiber of the said invention has the adhesion amount of a sizing agent 0.5 to 1.7 weight% with respect to carbon fiber, and is represented by the following formula The carbon fiber is characterized in that the epoxy equivalent change rate after drying is 1.2 to 2.5.
Epoxy equivalent change rate = B / A
(A represents the epoxy equivalent (equivalent / g) of the sizing agent after primary drying, and B represents the epoxy equivalent (equivalent / g) of the sizing agent after secondary drying.)

According to the production method of the present invention, it is possible to obtain a carbon fiber having a sizing agent uniformly attached, which can improve the composite physical properties of the composite material.

The present invention relates to a carbon fiber manufacturing method including a sizing step in which carbon fiber is immersed in a size bath containing a sizing agent and then dried to attach the sizing agent to the carbon fiber. The carbon fibers immersed in the substrate are primarily dried at a drying temperature of 80 to 120 ° C. for 30 to 200 seconds, and then further dried at 180 to 230 ° C. for 30 to 200 seconds.

The sizing resin that is the main component of the sizing agent used in the present invention is preferably selected according to the matrix resin used in the composite material. For example, epoxy resin, epoxy-modified polyurethane resin, polyester resin, phenol resin, polyamide A resin, a polyurethane resin, a polyimide resin, a polyvinyl alcohol resin, a polyvinyl pyrrolidone resin, a polyether sulfone resin, or the like can be used alone or in admixture of two or more. Among them, it is preferable to use an epoxy resin as a main component.

The sizing resin used in the present invention preferably has a viscosity at 120 ° C. of 10 to 200 mPa · s. When the viscosity at 120 ° C. is less than 10 mPa, the sizing agent may not sufficiently adhere to the carbon fiber, and when it exceeds 200 mPa, the sizing agent may be unevenly adhered, which is not preferable.

When the sizing agent is applied to the carbon fiber bundle, an aqueous emulsion of a resin composition containing the sizing resin as a main component or an organic solvent solution such as acetone is used. After applying a sizing agent to the carbon fiber bundle by a known method such as a roller dipping method, drying is performed. In consideration of safety to the human body, it is preferable to use an aqueous emulsion.

A surfactant can be used to make the resin composition for a sizing agent into an aqueous emulsion. Examples of such surfactants include nonionic, cationic, and anionic surfactants. From the viewpoint of solution stability when an aqueous emulsion solution is used, it is preferable to use a nonionic surfactant. . The compounding ratio of the surfactant is preferably a mass ratio (resin composition / surfactant) of 90/10 to 70/30.

The sizing agent concentration in the sizing bath is suitably 1.0 to 6.0% by weight. Exceeding 6.0% by weight is not preferable because uniform application and adhesion becomes difficult. Further, the amount of the sizing agent attached is preferably 0.5 to 1.7% by weight with respect to the carbon fiber, and if it is lower than 0.5% by weight, the handleability is impaired and fluffing is caused. When it is higher than 1.7% by weight, it is not preferable because drying cannot be sufficiently performed and operational stability is lacking.

The sizing process of the present invention involves immersing the carbon fiber in a size bath and then performing a two-stage drying process. Such a process may be performed a plurality of times until a predetermined amount of sizing agent is obtained. . Further, the process may be continuous or batch-type.

In the sizing process of the present invention, the drying treatment is performed by first drying the carbon fibers after being immersed in the size bath at a drying temperature of 80 to 120 ° C. for 30 to 200 seconds, and further at 180 to 230 ° C. for 30 to 200 seconds. This is a two-stage drying process in which secondary drying is performed. The primary drying process volatilizes and removes excess moisture of the sizing agent imparted by the aqueous emulsion, and the viscosity of the sizing resin adhering to the fiber is fluidly uniform within the fiber strand in the range of 10 to 200 mPa · s. Must adhere to. As a condition that can take this state, a drying temperature of 80 to 120 ° C. is suitable for 30 to 200 seconds, and the sizing resin that can be used at this time is a size whose viscosity at 120 ° C. is 10 to 200 mPa · s. An agent resin is suitable.

The carbon fiber strand that has been primarily dried has a sizing agent uniformly adhered to the inside of the strand, and is further subjected to secondary drying in order to maximize the composite physical properties. The secondary drying step is performed in order to impart adhesion between the sizing agent and the carbon fiber surface and to improve the adhesion with the matrix resin. In the present invention, the secondary drying is performed at 180 to 230 ° C. for 30 to 200 seconds. The carbon fiber obtained after this has an epoxy equivalent change rate of the sizing agent of 1.2 to 2.5. The epoxy equivalent change rate (B / A) of the sizing agent is determined from the ratio of the epoxy equivalent B (g / equivalent) of the sizing agent after secondary drying to the epoxy equivalent A (g / equivalent) of the sizing agent after primary drying. 1.2 to 2.5, preferably 1.2 to 2.0. When the epoxy equivalent change rate of the sizing agent is less than 1.2, the adhesion between the carbon fiber and the sizing agent is low, and good composite performance cannot be obtained. When the ratio is larger than 2.5, the adhesiveness with the matrix resin is lowered, and the composite performance is lowered. Therefore, the above range is preferable.

The carbon fiber used in the present invention is not particularly limited, but is preferably a carbon fiber having 1,000 to 50,000 filaments, and more preferably 20,000 to 30,000 filaments. In the case where the carbon fibers are bundled, for example, tow, the number of filaments per unit width is 5,000 filaments / mm or less, preferably 2,000 filaments / mm or less. If it exceeds 5,000 filaments / mm, the variation in sizing application may increase, which is not preferable.

The carbon fiber of the present invention is used as a reinforcing fiber, and a composite material can be obtained from this and a matrix resin by various known means and methods. Carbon fiber is usually used as a sheet-like reinforcing fiber material. The sheet-like material is a material in which fiber materials are arranged in a sheet shape in one direction, these are laminated in an orthogonal manner, the fiber material is formed into a fabric such as a woven or knitted fabric, and a non-woven fabric. All things, including multi-axis fabrics. As the fiber form, long fiber monofilaments or bundles of these are preferably used.

As the matrix resin, a thermosetting resin or a thermoplastic resin is used. Specific examples of thermosetting matrix resins include epoxy resins, unsaturated polyester resins, phenol resins, vinyl ester resins, cyanate ester resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, maleimide resins and cyanate ester resins. And a prepolymerized resin, bismaleimide resin, polyimide resin and polyisoimide resin having acetylene terminal, and polyimide resin having nadic acid terminal. These can also be used as one type or a mixture of two or more types. Of these, epoxy resins and vinyl ester resins excellent in heat resistance, elastic modulus, and chemical resistance are particularly preferable. These thermosetting resins may contain commonly used colorants and various additives in addition to the curing agent and the curing accelerator.

Examples of the thermoplastic resin include polypropylene, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, aromatic polyamide, aromatic polyester, aromatic polycarbonate, polyetherimide, polyarylene oxide, thermoplastic polyimide, polyamide , Polyamideimide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyacrylonitrile, polyaramid, polybenzimidazole and the like. The content of the resin composition in the composite material is 10 to 90% by weight, preferably 20 to 60% by weight, and more preferably 25 to 45% by weight.

Hereinafter, although an example explains the present invention in detail, the present invention is not limited to this. The measuring method of various physical property values in the examples is as follows.

[Resin impregnated strand strength of carbon fiber]
The resin-impregnated strand strength of the carbon fiber was measured by the method defined in JIS · R · 7608.

[Measurement of sizing agent adhesion]
About 2 g of carbon fiber bundles were dried at 105 ° C. for 30 minutes, then cooled to room temperature in a desiccator for 30 minutes and weighed (W1). Thereafter, the carbon fiber bundle was immersed in acetone to wash away the sizing agent. The washed sample was dried at 105 ° C. for 1 hour, cooled to room temperature in a desiccator for 30 minutes, and weighed (W2). And the sizing agent adhesion amount was calculated | required from following Formula.
Sizing agent adhesion amount (% by weight) = [W1 (g) −W2 (g)] / [W2 (g)] × 100

[Measurement of epoxy equivalent]
The epoxy equivalent (equivalent / g) of the sizing agent was determined by measurement according to the method described in JIS · K-7236. That is, from the epoxy equivalent (A) of the sizing agent adhering to the carbon fiber after primary drying and the epoxy equivalent (B) of the sizing agent adhering to the carbon fiber after secondary drying, Equivalent change rate (B / A) was determined.
Epoxy equivalent change rate = B / A
(A represents an epoxy equivalent (equivalent / g) after primary drying, and B represents an epoxy equivalent (equivalent / g) after secondary drying.)

[Measurement of ring breaking strength]
For evaluation of composite physical properties, epoxy resin (epoxy resin manufactured by Japan Epoxy Resin Co., Ltd., EP827) and amine-based curing agent (manufactured by Huntsman Corporation, Jeffermin T403) were mixed at a ratio of 100: 40 as matrix resin. Using the composition, ring fracture strength was determined according to the method described in JIS · K-7037. The ring breaking strength is desirably 4000 MPa or more.

[Examples 1 to 3] and [Comparative Examples 1 to 6]
Acrylic fibers were made flame resistant and carbonized by a conventional method to obtain a carbon fiber bundle (24,000 filaments, 1600 Tex, tensile strength 5100 MPa, tensile modulus 242 GPa) to which no sizing agent was applied. The carbon fiber bundle not provided with the sizing agent was immersed in a sizing solution bath and then dried under the drying conditions described in Table 1. The sizing solution contains 30% of an epoxy resin (epoxy resin EP828 manufactured by Japan Epoxy Resin Co., Ltd .: epoxy resin EP1001 = 1: 1.2 manufactured by Japan Epoxy Resin Co., Ltd., viscosity at 120 ° C .: 150 mPa · s) as a main component. The aqueous emulsion was diluted to a concentration of 3.0% by weight. The sizing agent adhesion amount, strand strength, fluff quality, and ring breaking strength of the obtained carbon fiber strands were evaluated, and the results are shown in Table 1.

As can be seen from Table 1, Examples 1 to 3 showed good composite physical properties. On the other hand, in Comparative Example 1, since the secondary drying temperature was as low as 150 ° C., the epoxy equivalent after the secondary drying was low and the epoxy equivalent change rate was not sufficient, so that sufficient composite physical properties could not be obtained. In Comparative Example 2, since the secondary drying temperature was too high at 250 ° C., the epoxy equivalent after the secondary drying was high and the epoxy equivalent change rate was too large, so that sufficient composite physical properties could not be obtained. In Comparative Example 3, since the primary drying temperature was too low at 50 ° C., the primary drying was not sufficiently performed, and the target carbon fiber could not be obtained. In Comparative Example 4, since the primary drying temperature was too high at 220 ° C., the sizing agent adhered unevenly, and sufficient composite physical properties could not be obtained. In Comparative Example 5, the adhesion amount of the sizing agent was too low at 0.3% by weight, so that the adhesion between the fiber and the resin was not sufficient, and sufficient composite physical properties could not be obtained. In Comparative Example 6, an attempt was made to produce carbon fibers having a sizing agent deposition amount of 3.0% by weight. However, since the amount of sizing agent attached was too high, the process became unstable and the target carbon fiber could not be obtained.

[Example 4]
Carbon fibers were obtained in the same manner as in Example 1 except that the epoxy resin component as the main component of the sizing agent was (EP828 / EP1001 = 1: 1.3, viscosity at 120 ° C .: 200 mPa · s). The obtained carbon fiber ring has the breaking strength shown in Table 2.

[Comparative Example 7]
Carbon fibers were obtained in the same manner as in Example 1 except that the epoxy resin component as the main component of the sizing agent was (EP828 / EP1001 = 1: 1.5, viscosity at 120 ° C .: 250 mPa · s). The obtained carbon fiber ring has the breaking strength shown in Table 2. In Example 4, good composite physical properties could be obtained, but in Comparative Example 7, the resin viscosity of the sizing agent used was too high, so that sufficient composite physical properties could not be obtained.

Claims (3)

In the carbon fiber manufacturing method including a sizing step in which carbon fiber is immersed in a size bath containing a sizing agent and then dried to attach the sizing agent to the carbon fiber, carbon after being immersed in the size bath as the sizing step The carbon fiber is characterized by adopting a two-stage drying process in which the fiber is primarily dried at a drying temperature of 80 to 120 ° C. for 30 to 200 seconds and then secondarily dried at 180 to 230 ° C. for 30 to 200 seconds. Production method. 2. The method for producing carbon fiber according to claim 1, wherein the sizing agent comprises an epoxy resin having a viscosity at 120 ° C. of 10 to 200 mPa · s as a sizing resin as a main component. A carbon fiber obtained by the method for producing carbon fiber according to claim 1 or 2, wherein the adhesion amount of the sizing agent is 0.5 to 1.7% by weight with respect to the carbon fiber, and is represented by the following formula: A carbon fiber, wherein the epoxy equivalent change rate of the sizing agent after secondary drying is 1.2 to 2.5.
Epoxy equivalent change rate = B / A
(A represents the epoxy equivalent (equivalent / g) of the sizing agent after primary drying, and B represents the epoxy equivalent (equivalent / g) of the sizing agent after secondary drying.)