Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2000-04-26
2002-06-04
Short, Patricia A. (Department: 1712)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S395000, C525S411000, C525S415000
Reexamination Certificate
active
06399197
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monofilament which decomposes in the natural environment, which is excellent in heat stability and forming workability, which has high mechanical strength, particularly knot strength and longitudinal cracking resistance, and which is suitable for products typified by strings for tennis rackets.
2. Description of the Related Art
In the recent years, from the viewpoint of natural environmental protection, a biodegradable polymer and its processed product, which decompose in the natural environment, are required and studies on naturally degradable resins such as an aliphatic polyester are done actively. In particular, one of these examples, a polylactic acid, potentially has a heat of combustion not more than half of that of polyethylene, and is naturally hydrolyzed under the ground or in water and thereafter converted by microorganisms into harmless decomposed products. Studies for obtaining formed articles, specifically films, sheets, fibers and the like, using polylactic acid are being made. Polylactic acid can be improved in its strength by stretching. However, since polylactic acid is a hard and brittle material, it is poor in flexibility and usability and also in longitudinal cracking resistance and knot strength. Polylactic acid is not practical, therefore.
On the other hand, an aliphatic polyester composed of a polycondensation product from an aliphatic polyfunctional carboxylic acid and an aliphatic polyfunctional alcohol is an example of flexible, naturally degradable resins.
For example, Japanese Patent Publication (B2) No. 2851478 reports that a monofilament excellent in heat stability and mechanical properties can be obtained by using, as a biodegradable monofilament, an aliphatic polyester which has been prepared by increasing, with a coupling agent, a molecular weight of a relatively high molecular weight polyester prepolymer having a hydroxyl group on terminal of molecule which mainly contains a polyester obtained by reacting two components of a glycol and a polybasic acid (or anhydride thereof), and if necessary as a third component, at least one polyfunctional component selected from tri- or tetra-functional polyhydric alcohols, oxycarboxylic acids and polyvalent carboxylic acids (or anhydride thereof).
Japanese Laid-open Patent Publication No. 10-110332 (1998) reports that a monofilament suitable for a fishline can be obtained by melt-spinning a blend polymer containing at least one species of polyalkylene dicarboxylate having a melting point of not lower than 70° C. as a first component and at least one species selected from polylactic acid, a copolymer of polylactic acid and a poly(&bgr;-hydroxyalkanoate) as a second component in the range of (the first component)/ (the second component) weight ratio of 95/5-40/60.
However, the aliphatic polyesters obtained by these methods are flexible and low in tensile strength and exhibit great elongation, in general.. Therefore, there are problems on their practical use as monofilaments such as strings for rackets or fishlines. Moreover, since they contain much materials of relatively low melting points, they may cause problems of fusion due to frictional heat and scuffing due to rubbing, and therefore are not practical.
The strings for rackets means strings to be used for rackets for tennis, soft tennis, badminton, squash and racquetball.
Heretofore, a string for a racket has been called gut. Gut is literally made of gut of sheep or cow and has still been used by some players typified by professional players at present because of its overall playability feeling and the like. Particularly in soft tennis, whale tissue has been used in stead of gut for tennis and occupies a position similar to gut.
These have advantages in ball-hitting sounds, creep property and the like in addition to overall playability feeling, but also have disadvantages of poor water resistance, high price and the like.
For these reasons, strings made of synthetic fibers, particularly polyamide-type synthetic fibers, are now in the mainstream in the world. This is because the problems of low water resistance and high price, which are drawbacks of natural gut, can be overcome and they are excellent in durability when repeatedly used.
By the way, overall playability, durability and ease of stringing are three important properties required of strings for rackets. Lacking any one of these properties breaks their practical usability.
The overall playability, which is mainly resilience at hitting ball, includes feelings such as ball-holding feeling and soft feeling following vibration, and ball-hitting sounds. The durability includes both durability against wear in repeated use and retentiveness of tension of a string face. The ease of stringing is ease to install a string to a racket.
It has been well known that when aliphatic polyesters relating to the present invention as well as aromatic polyesters are applied for strings for rackets, good overall playability can be obtained as predicted from their tenacity-elongation curves. However, there are two problems about durability, that is, problems on the face tension retentiveness and on longitudinal cracking of filament which takes place at the time of tightening a string with a clamp or the like when the string is installed to a racket. That is, this means that there has been two problems in the important characteristics.
Thinking that overcoming these two problems can make the polyesters excellent materials as a material for strings for rackets in association with their biodegradability, the present inventors have made intensive studies and have accomplished the present invention.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a monofilament which has sufficient mechanical strength to be practically used also as a string for rackets and which is excellent in workability.
The present inventors eagerly studied in order to solve such problems, and have found that the above object can be accomplished by extruding a material prepared by blending mainly a polylactic acid type polymer and an aliphatic polyester other than polylactic acid in a predetermined proportion and drawing the extruded material.
That is, the present invention is a monofilament formed by extruding a material prepared by blending mainly a polylactic acid type polymer and an aliphatic polyester other than polylactic acid and drawing the extruded material.
Moreover, the present invention is a monofilament formed by extruding a material prepared by blending mainly a polylactic acid type polymer and an aliphatic polyesters other than polylactic acid in a blending ratio in weight of 95/5-61/39 and drawing the extruded material.
Furthermore, the present invention includes:
the monofilament wherein at least two species of the aliphatic polyesters other than polylactic acid are contained;
the monofilament wherein the aliphatic polyesters other than polylactic acid are mainly composed of an aliphatic carboxylic acid component and an aliphatic alcohol component, and/or an aliphatic hydroxycarboxylic acid component;
the monofilament wherein the polylactic acid and the aliphatic polyester other than polylactic acid have a crosslinked structure formed either in each of and/or between them;
the monofilament wherein the melting point of the aliphatic polyester other than polylactic acid is lower than that of the polylactic acid type polymer;
the monofilament wherein the drawing was conducted at temperatures not lower than the melting point of the aliphatic polyester other than polylactic acid;
the monofilament wherein the polylactic acid type polymer is oriented and the aliphatic polyester other than polylactic acid is not oriented;
the monofilament wherein the final draw ratio is 3-9 times; and
the monofilaments wherein surfaces of the aforementioned monofilaments are covered with a polymer material such as an aliphatic polyester and a polyurethane.
Furthermore, the present invention is a process for producing a monofilament comprising ext
Kanamori Takeshi
Nagano Tameyuki
Ohara Yoshiyuki
Urayama Hiroshi
Rader Fishman & Grauer
Shimadzu Corporation
Short Patricia A.
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