Stock material or miscellaneous articles – Composite – Of polyamide
Reexamination Certificate
1992-09-28
2002-01-01
Weisberger, Rich (Department: 1774)
Stock material or miscellaneous articles
Composite
Of polyamide
C428S364000, C428S375000, C156S275500
Reexamination Certificate
active
06335100
ABSTRACT:
FIELD OF INVENTION
This invention relates to a structural material suited to be used in racket frame for tennis, squash, badminton or the like, pole for tent frame, pipe for structural material, buried earth pipe, block, fishing rod or the like, and a method of fabricating the same.
BACKGROUND OF INVENTION
Fiber reinforced composite materials conventionally used as structural materials for building materials or sports articles include those prepared by adding short fiber reinforced materials to a thermoplastic resin used as the matrix, or other prepared by adding long filament reinforced materials to a thermoset resin used as the matrix.
These materials, however, involve certain problems in the forming property, strength, heat resistance and fatigue characteristic, and superior fiber reinforced composite materials have been demanded.
For example, reinforced plastic poles are recently sold on market as the pole for mountaineering tent, but they have their problems as stated below, and they are presently used partly only in a field of less rugged conditions such as picnic tent.
That is, in the composition of these reinforced plastic poles, the reinforced fibers are composed of glass, carbon, or aromatic polyamide, and the matrix is made of epoxy, polyester or other thermoset resin. The most widely employed method of fabricating reinforced plastic poles is the so-called “drawing pipe” method which is to impregnate glass fibers with polyester resin, and continuously lead into the hardening bath to be hardened. In other versions, fibers are processed by filament winding (F/W) process, not limited in the axial direction, or ABS resin or other thermoplastic resins are used as the padding or covering material, but in any event the matrix of reinforced fibers is always a thermoset resin such as polyester and epoxy.
These thermoset resins are, by nature, brittle, and are easily broken when bent sharply like a tent pole. Or if the rigidity is lowered to allow a large deflection in practical usage, problems occur in the aspects of habitability or resistance to wind pressure. In particular, when several poles are joined together, stress is concentrated at joints, and most breakdowns originate in the joint. However, in the continuous drawing method, since its section is uniform, it is difficult to reinforce only the joint part integrally. Or in the case of F/W process, it is difficult to vary the complicated joint shape or outside diameter, and there are serious problems such as fluctuations of dimensional precision and performance derived from the nonuniformity of tape wrapping.
On the other hand, in the composition of fiber reinforced plastic used as the material of golf club shaft, the reinforced fibers are composed of carbon, glass, aromatic polyamide, boron or the like, and the resin matrix is made of epoxy, polyester or other thermoset resin. All of them share a main feature of lightness of weight as compared with metallic shaft, and also provide the following merits.
1) The head speed when swinging increases.
2) Even a less powerful golfer can swing easily.
Fabrication methods of this kind of shaft are roughly divided into two types as follows.
(1) Filament winding (F/W) method
A continuous filament is impregnated with resin, and is wound on a mandrel at a specified angle in the axial direction.
(2) Sheet winding method
A cloth impregnated with resin is wound on the mandrel.
In both (1) and (2), after forming on the mandrel, the material is wrapped by heat-shrink tape, and is heated in a hardening furnace.
In these methods, however, the dimensional precision when forming the material is not sufficient, and the pressure when hardening depends on the tightening force of the wrapped tape, so that the dimensional precision of product is limited. Besides, since marks of wrapping tape are left over on the product surface, it is necessary to finish the surface by buffing with centerless grinder or the like, so that part of surface fibers is shaved off. And it is also difficult to vary the complicated shape or outside diameter noncontinuously, and the degree of freedom of design is limited. Furthermore, thermoset resins of epoxy and polyester are more brittle, and may be broken when an impact is applied.
In addition, the following two types are known as the composition of fiber reinforced plastics for racket frame for ball games.
(1) Continuous fiber/resin matrix type
(2) Short fiber of chopped fiber/resin matrix type
In type (1), epoxy, polyester or phenolic thermoset resin is used as the resin matrix, and it is impregnated in continuous filament, and heated and pressurized, so that the resin is hardened and molded into a desired shape.
In type (2), the reinforced members are composed of fiber reinforced members of short discontinuous length randomly dispersed in the resin matrix, and this resin may be either thermoplastic or thermosetting. As the thermoset material, the one shown in (1) is used, and as the thermoplastic material, for example, nylon, polycarbonate, polyphenylene oxide, acetal and other so-called industrial thermoplastics are used. As the molding method, mainly injection molding is employed.
On the other hand, as the characteristics required in rackets, usually, toughness, rigidity and resilience are known. As for toughness, since the toughness of matrix resin of type (1) is inferior, expensive carbon fibers or other reinforced fibers are used usually by 60 to 70 wt. % in order to obtain a required toughness. Since this is an easy method of obtaining a required strength and desired shape, this method is employed in most existing tennis racket frames using reinforced plastics.
In the case of (2), usually, considering the moldability, in particular, fluidity at the time of injection, the molecular weight of matrix resin is kept low. The fiber content is about 30 wt. %, and the fiber length is mostly less than 1 mm (0.2 to 0.3 mm) after pelletizing and injection molding. Since the matrix resin is not high in molecular weight and the length of reinforced fibers is extremely short, improvement of mechanical strength in this composition is not expected. Therefore, if such racket strung with guts is kept in an automobile trunk, for example, and its internal temperature exceeds 80° C., it is highly possible that the frame may be deformed or broken during use.
To compensate for this defect, it is consequently necessary to increase the wall thickness of racket frame, but since the total weight increases, it is not so practical.
Recently, meanwhile, as sports are becoming popular as a pastime, consideration to sports injuries is required. For example, according to a certain polling, about one third of tennis players claimed to have “experienced pain in the elbow.” This is known as tennis elbow, and the player feels pain suddenly in the elbow of the racket holding side without any specific cause. In a racket inferior in vibration absorption property, it is said that the vibration of hitting a ball is transmitted to the elbow to damage the humerus epicondylus. In the continuous filament/resin matrix type (1) which is in the mainstream of the present racket frame materials, since the commonly used epoxy resin and polyester resin are inferior in impact absorption, it is considered that the vibration characteristic be interior.
Incidentally, as technical reports about industrial materials using nylon resins (which is similar to that used in this invention), for example, “Nylon RIM Development for Automotive Body Panels” (SAE Technical Paper Series 850157, 1985), and “Nylon 6 RIM” (American Chemical Society, 1985) are known, and also an article relating to terminal amine polyether RIM (SAE Technical Paper Series 850155, 1985), an article relating to the future of RIM in America (American Chemical Society, 1985), and an article relating to RIM monomer casting (“Plastics Technology,” May 1965 issue) are available, but nothing is mentioned about long filament reinforced products in these papers.
The present invention is devised in the light of the above background, and it is hence a primary ob
Matsuki Taketo
Matsushita Hiroomi
Niwa Kunio
Tominaga Ichiro
Yamaguchi Tetsuo
Sumitomo Rubber Industries Ltd.
Weisberger Rich
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