Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1999-09-27
2003-12-30
Watkins, III, William P. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S368000, C428S413000, C528S087000, C528S088000, C526S059000, C526S059000
Reexamination Certificate
active
06670006
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an epoxy resin composition for fiber reinforced plastics (abbreviated to FRP in this specification), a prepreg that is an intermediate material made up of a combination of an epoxy resin composition and reinforcing fibers, and a tubular molded article obtained by the use thereof.
This application is based on a patent application in Japan (Japanese Patent Application No. Hei 9-74794) and the contents described in that Japanese application are taken as part of this description.
BACKGROUND ART
Since epoxy resins after curing are excellent in mechanical properties, electrical properties, and adhesive properties, they are widely used in the fields, for example, of sealants for electronic materials, paints, coating materials, and adhesives. Further, epoxy resins are important as matrix resins for FRP. Particularly, when carbon fibers are used as reinforcing fibers for FRP, epoxy resins are preferably used since they are excellent in adhesion to carbon fibers. FRP molded articles made up of carbon fibers and epoxy resins are used in wide range of applications ranging from general-purpose use in fishing rods, golf club shafts, etc. to the use in airplanes.
The method for molding FRP molded articles from reinforcing fibers, such as carbon fibers, and a matrix resin, such as an epoxy resin, includes several methods. If carbon fibers are used as reinforcing fibers, a method wherein an intermediate material called a prepreg prepared by impregnating in advance the reinforcing fibers with a resin is used for the molding of an FRP molded article is most widely used. The matrix resin used in this prepreg is required to be excellent, for example, in adhesion to the reinforcing fibers and mechanical properties after the molding. Further, the prepreg is required to have suitable tack in order to make the handling good. Since epoxy resins can be made to exhibit relatively easily these properties in a well balanced manner, they are widely used as a matrix resin for prepregs.
The major application of these FRP molded articles includes tubular molded articles, such as fishing rods and golf club shafts. Such tubular molded articles are required to have, as important properties, flexural strength in the longitudinal direction and crushing strength in the diametrical direction.
In order to enhance the flexural strength of tubular molded articles in the longitudinal direction, it is already known that it is effective to arrange carbon fibers along the length. Further, in order to improve the crushing strength of tubular molded article in the diametrical direction, it is already known that it is effective to arrange carbon fibers circumferentially. However, when a tubular molded article is reinforced longitudinally and circumferentially at the same time, the tubular molded article inevitably increases in weight. An increase in weight of a tubular molded article runs counter to the recent trend wherein fishing rods and golf club shafts are made light in weight. Accordingly, there have been attempted to improve matrix resins to reduce the circumferential reinforcement of tubular molded articles. However, matrix resins that can make tubular molded articles light in weight are not now available.
The present invention aims at providing an epoxy resin composition for FRP in order to obtain tubular molded articles improved in flexural strength in the longitudinal direction and crushing strength in the diametrical direction and a prepreg made of a combination of that epoxy resin composition for FRP and reinforcing fibers.
DISCLOSURE OF THE INVENTION
The first subject matter of the present invention resides in an epoxy resin composition for FRP, characterized in that it comprises (A) a bisphenol A-type epoxy resin (hereinafter referred to as component (A)), (B) an epoxy resin having oxazolidone rings represented by (hereinafter referred to as component (B)), and (C) a curing agent (hereinafter referred to as component (C)), the component (B) is an epoxy resin having a structure represented by the following formula (1):
wherein R represents a hydrogen atom or a methyl group, and the viscosity measured by the below-described method for measuring viscosities is 100 to 5,000 poises.
Method for Measuring Viscosities
Use is made of a dynamic viscoelasticity measuring instrument, the uncured epoxy resin composition for FRP whose viscosity will be measured is filled between two disk plates 25 mm in diameter that are positioned with a space of 0.5 mm between them, one of the disk plates is rotated at a shear rate of 10 radians/sec, and the viscosity of the epoxy resin is measured under conditions in which the atmospheric temperature for the measurement is 60° C.
The second subject matter resides in an epoxy resin composition for FRP, characterized in that it comprises a component (A), a component (B), and a component (C), and (D) a thermoplastic resin that can be dissolved in a mixture of the component (A) and the component (B) (hereinafter referred to as component (D)) and has a viscosity of 100 to 5,000 poises measured by the above method.
Further, the third subject matter resides in a prepreg comprising a sheet of reinforcing fibers impregnated with the above epoxy resin composition for FRP.
Further the fourth subject matter resides in a tubular molded article having a plurality of FRP layers, characterized in that the matrix resin composition used in at least one of the FRP layers is the above epoxy resin composition for FRP.
And the fifth subject matter resides in an epoxy resin composition for FRP, characterized in that when the epoxy resin composition for FRP is molded into a tubular product, the crushing strength is 200 N or more.
In the present invention, “crushing strength” means the crushing strength, measured by the below-described method, of a tubular molded article that has an inner diameter of 10 mm, an outer diameter of 12 mm, and a volume content of fibers of 60+1% and is prepared by impregnating carbon fibers having an elastic modulus of 220 to 250 GPa with the epoxy resin composition for FRP to make unidirectional prepregs wherein the carbon fiber areal weight is 150 g/m
2
and the content of the epoxy resin for FRP is 31% by weight and laminating the unidirectional prepregs so that the directions of the fibers may be +45°/−45°/+45°/−45°/0°/0°/0°.
Method for Measuring Crushing Strength
The above-described tubular molded article is cut into a length of 10 mm to obtain a test piece. Using an indenter, a load is exerted on the test piece and the maximum load at which the test piece is broken when the indenter is moved at a rate of travel of 5 mm/min is measured and is designated as the crushing strength.
Further, the sixth subject matter resides in an epoxy resin composition for FRP, characterized in that when the epoxy resin composition for FRP is made into a unidirectional laminate, the flexural strength in a direction of 90° is 110 MPa or more.
In the present invention, “flexural strength in a direction of 90°” means the flexural strength of 90°, measured by the below-described method, of the unidirectional laminate that is prepared by impregnating carbon fibers having an elastic modulus of 220 to 250 GPa with the epoxy resin composition for FRP to make unidirectional prepregs wherein the carbon fiber areal weight is 150 g/m
2
and the content of the epoxy resin for FRP is 31% by weight and laminating fifteen unidirectional prepregs thus made (2 mm in thickness) so that the directions of the fibers may be 0 degrees.
Method for Measuring Flexural Strength in a Direction of 90°
The above-described unidirectional laminate is cut to obtain a test piece having a length of 60 mm in a direction of 90° to the direction of the fibers and a width of 10 mm. The maximum load when the test piece is broken is measured under conditions wherein the distance between the supports is 32 mm, the diameter of the tip of the indenter is 3.2 mm, and the rate of travel of the indenter is 2 mm/min and the flexural strength is calculated.
Best Mode for
Agata Akira
Gotou Kazuya
Nishimoto Yukio
Sugimori Masahiro
Taguchi Masato
Hon Sow-Fun
Mitsubishi Rayon Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Watkins III William P.
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