Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
2001-11-08
2002-06-25
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S367000, C428S413000, C523S466000, C523S468000, C528S120000, C528S122000, C528S124000, C528S407000, C528S418000, C528S421000
Reexamination Certificate
active
06410127
ABSTRACT:
TECHNICAL FIELD
The present invention relates to epoxy resin compositions. More particularly it relates to an epoxy resin composition for a fiber-reinforced composite material which has a low viscosity and can be easily handled for impregnating reinforcing fibers, and the resulting fiber-reinforced composite materials obtained after the composition is cured has excellent heat resistance and mechanical properties including compressive strength, and to the fiber-reinforced composite materials obtained therefrom.
BACKGROUND ART
As fiber-reinforced composite materials comprising reinforcing fibers and matrix resins are lightweight and have excellent mechanical properties, they have been widely used in various fields including aerospace, sports and general industrial fields.
A thermosetting resin is predominantly employed for the matrix resin of the fiber-reinforced composite. Among them, an epoxy resin having excellent heat resistance, high elastic modulus and good chemical resistance, as well as a little curing shrinkage is most commonly employed.
For producing fiber-reinforced composite materials, various methods, such as prepreg method, hand lay-up method, filament winding method, pull-trusion method, and RTM (resin transfer molding) method have been employed.
Among them, the RTM method, in which a preform comprising reinforcing fibers is placed in a mold, and a resin is poured thereinto to impregnate the preform and cured to produce a molded product, has a great advantage that a large component having a complicated shape can be molded in a short time.
The resin for use in RTM method needs to have a low viscosity to facilitate the impregnation of the preform. If the viscosity of the resin is high, a longer time is required for injection, which may result in a low productivity or provide unimpregnated portions of the obtained fiber-reinforced composite materials. In the RTM method, the viscosity of the resin can also be lowered by raising the temperature of the resin, however, in the case of molding a large component, the entire mold must be heated, therefore it is greatly disadvantageous from the viewpoint of the facility and the required energy. Furthermore, the curing of the resin may be progressed by the heat during the injection process, which may result in an increase of the viscosity of the resin. Therefore, a resin requiring no heating and having a sufficiently low viscosity around the room temperature has been strongly desired.
As the thermosetting resin for use in the RTM method, epoxy resins are often employed. In addition to that, thermosetting resins for use in the RTM method include unsaturated polyester resins, vinyl ester resins, and phenol resins etc. Many of these unsaturated polyester resins, vinyl ester resins and phenol resins have low viscosities around the room temperature, therefore show good injection workability around the room temperature, however, epoxy resins are desirable to provide fiber-reinforced composite materials having excellent heat resistance and mechanical properties and to reduce the polymerization shrinkage during the curing reaction.
Unfortunately all the epoxy resins are either those having good heat resistance or mechanical properties of the resulting fiber-reinforced composite materials, but poor injection workability around the room temperature due to its high viscosity, or those having good injection workability due to its low viscosity at the room temperature but insufficient heat resistance or mechanical properties of the resulting fiber-reinforced composite materials, therefore when good heat resistance and mechanical properties are required for the molded product, the epoxy resins must be heated and employed in the RTM method. In the publication of Japanese Patent Laid-Open Hei 6-329763, an epoxy resin composition comprising an epoxy resin and diethyl toluene diamine as a curing agent has been disclosed, however there are problems that this composition still has a high viscosity and poor injection workability around the room temperature and the obtained fiber-reinforced composite materials have some parts which have some unimpregnated parts with the resin, therefore the desired mechanical properties are not attained.
DISCLOSURE OF INVENTION
The epoxy resin compositions according to the present invention have the following construction in order to solve the above-mentioned problems. Accordingly an epoxy resin composition comprising an aromatic epoxy resin having at least di-functionality, an aromatic amine compound and/or an alicyclic amine compound, wherein 5 minutes after the main agent comprising the epoxy resin and the curing agent comprising the aromatic amine compound and/or the alicyclic amine compound are mixed at 25° C., the composition shows a viscosity at 25° C. in a range of from 1 to 1500 mPa sec, and Tc, tc, and Tg satisfy the following equation.
Tg≧Tc+
20−
k
×(
Tc−
90) (1)
k=0 when 60≦Tc<90
k=0.35 when 90≦Tc≦200
Tc: highest temperature (°C.) during the curing process (60≦Tc≦200)
tc: retention time (min) at the highest temperature (1≦tc≦120)
Tg: glass transition point of the epoxy resin composition after a lapse of tc (min) at Tc (°C.).
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have found that an epoxy resin composition in which an aromatic epoxy resin having at least di-functionality, and an aromatic amine compound and/or an alicyclic amine compound are blended (hereinafter simply referred to as an epoxy resin composition) can provide a greatly improved resin injection workability around a room temperature, i.e. around 25° C. in the present invention, and greatly improved impregnation of reinforcing fibers with the resin, and that the resulting fiber-reinforced composite materials have both high heat resistance and good mechanical properties, and completed the present invention.
The epoxy resin composition according to the present invention comprises an aromatic epoxy resin having at least di-functionality. Here, the term “functionality” as used in di-functionality means an epoxy group. Also in the present invention, the term “epoxy resin” is used to refer to the monomer or oligomer as well, which are not yet polymerized or cured. The term “epoxy resin composition” means a composition in which the elements which are required for the polymerization or curing reaction are mixed, and the term “cured epoxy resin” (or “cured resin”, or “cured product” or “cured product of an epoxy resin composition”) refers to a product obtained after the polymerization or curing reaction is carried out. The term “aromatic epoxy resin” means an epoxy resin having an aromatic ring in one molecule. The aromatic epoxy resin having at least di-functionality is blended in order to impart excellent heat resistance and mechanical properties to the fiber-reinforced composite materials (hereinafter simply abbreviated as composite materials) as it reacts with a curing agent to form a crosslinked structure.
It is necessary that the epoxy resin composition has a sufficiently low viscosity around the room temperature in order to improve the impregnation of the reinforcing fibers. But a too low viscosity becomes a cause of providing unimpregnated portions and voids in the obtained molded products. From the viewpoint of good injection workability, impregnating properties, and improved mixing of the main agent and the curing agent, the viscosity of the main agent and that of the curing agent at 25° C. shall be respectively within the range of from 1 to 3000 mPa sec, preferably from 1 to 2000 mPa sec, more preferably from 1 to 1000 mPa sec.
According to the present invention, when the viscosity of the main agent at 25° C. is within the range of from 2000 to 3000 mPa sec, the viscosity of the curing agent at 25° C. is preferably within the range of from 1 to 500 mPa sec. When the viscosity of the main agent at 25° C. is within the range of from 1000 to 2000 mPa sec, the viscosity of the curing agent at 25° C. is preferably within the range of from 1 to 1000
Kamae Toshiya
Kouchi Shinji
Noda Shunsaku
Oosedo Hiroki
Sawaoka Ryuji
Aylward D.
Dawson Robert
Morrison & Foerster / LLP
Toray Industries Inc.
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