Vinylidene fluoride resin monofilament and process for producing the same

Abstract

A monofilament obtained by smelt-spinning and stretching of a vinylidene fluoride resin is subjected to a high-temperature relaxation treatment for an extremely short period of 0.05-0.5 sec. within a high-temperature heating oil bath at a temperature of 140-175° C., thereby producing a vinylidene fluoride resin monofilament, which comprises a vinylidene fluoride resin having an inherent viscosity of at least 1.40 dl / g, and has a knot strength (JIS L1013) of at least 600 MPa and excellent anti-twist property represented by a twist index of at least 0.90 when measured after the monofilament being subjected to application for 1 minute of a tensile load equal to approximately 50% of a maximum tensile load (JIS K7113), removal of the load, and standing for 3 hours.

Description

TECNHNICAL FIELD [0001] The present invention relates to a vinylidene fluoride resin monofilament (monofilament of vinylidene fluoride resin) which has a high strength, is flexible and is less liable to twist and is therefore particularly suitable for use as a fishing line, and a process for production thereof. BACKGROUND ART [0002] Vinylidene fluoride resin monofilament is excellent in various properties, such as tenacity, impact resistance, tensile force-transmitting property (sensitivity or fish signal detectability) and weatherability, and moreover has a high specific gravity (=1.79) leading to easiness of sinking in water, a refractive index (=ca. 1.42) close to the refractive index (=1.33) of water leading to difficulty for noticeability by seeing and almost no hygroscopicity allowing the preservation of these properties for a long period of time. These properties are regarded as most suitable properties for fishing lines including a line in a narrower sense and a leader, part...

AI Technical Summary

Benefits of technology

[0011] Accordingly, a principal object of the present invention is to provide a vinylidene fluoride resin monofilament having mechanical strengths represented by a high knot strength and excellent anti-twist property in combination, and a process for production thereof.

[0012] According to studies of the present inventors, it has been discovered that even a highly stretched monofilament of vinylidene fluoride resin of a high polymerization degree as represented by a high inherent viscosity can be improved in anti-twist property while retaining a high knot strength by subjecting it to an extremely short period of relaxation heat treatment with a high-temperature medium of a high heat-conductivity.

[0014] Further, the process for producing a vinylidene fluoride resin monofilament of the present invention is characterized by comprising: subjecting a vinylidene fluoride resin monofilament after melt-spinning and stretching to a high-temperature relaxation treatment for an extremely short period of 0.05-0.5 sec. within a high-temperature heating oil bath at a temperature of 140-175° C.

[0019] In the present invention, a vinylidene fluoride resin having a high molecular weight represented by an inherent viscosity (referring to a logarithmic viscosity at 30° C. of a solution of 4 g of resin in 1 liter of N, N-dimethylformamide; hereinafter sometimes denoted by “ηinh”) of at least 1.40 dl / g, is used. Such a high-molecular weight vinylidene fluoride resin is particularly effectively used because it can easily provide a monofilament having a high knot strength through an appropriate high orientation treatment while having a liability of developing a high twistability, but an excellent anti-twist property can be imparted while retaining the high knot strength according to the present invention. The upper limit of the inherent viscosity should desirably be within a range capable of retaining adaptability to melt-spinning and stretching that are ordinarily be adopted for providing high-strength monofilament.

[0023] According to a preferred embodiment, the PVDF monofilament of the present invention has a core-sheath laminar structure comprising a core and a sheath each comprising PVDF, particularly a laminar structure comprising a core of PVDF having a higher ηinh and a sheath of PVDF having a lower ηinh. As mentioned before, PVDF of a high ηinh is generally liable to provide a difficulty in melt-spinning and high-ratio stretching, but the above-mentioned core-sheath structure allows the melt-spinning and high-ratio stretching even by using such a core of high ηinh PVDF, thus allowing the formation of a PVDF monofilament having a high effective ηinh. Herein, the effective ηinh is obtained as a weighted average based on the weights of ηinh of the core PVDF and ηinh of the sheath but can be conveniently determined by way of measuring a logarithmic viscosity of a solution at 30° C. of a monofilament having such a core-sheath structure at a concentration of 4 g / liter in N, N-dimethylformamide.

[0030] The final stretching ratio through the stretching process is not particularly restricted but may preferably be at least 5 times, more preferably at least 5.9 times, further preferably 6 times or higher. This provides an enhanced orientation of molecular chains of the vinylidene fluoride resin suitable for obtaining the PVDF monofilament of the present invention having a knot strength of at least 600 MPa and a twist index of at least 0.90 after 3 hours of standing.

Problems solved by technology

1.42) close to the refractive index (=1.33) of water leading to difficulty for noticeability by seeing and almost no hygroscopicity allowing the preservation of these properties for a long period of time.

A vinylidene fluoride resin, however, has a high crystallinity and a high elastic modulus by its nature resulting in a rigid monofilament, and the hardness is further enhanced at such a higher molecular weight and a higher orientation to result in severe twisting, which gives rise to a difficulty in handling.

For this reason, there has not been actually obtained a vinylidene fluoride resin monofilament sufficiently satisfying high knot strength and low twistability in combination.

However, it is yet difficult to regard these proposals as satisfactory.

The production process (5) is accompanied with a problem that a noticeable lowering of strength is caused if excessive relaxation heat-treatment is applied.

Further, the method (6) of adding a large amount of plasticizer is accompanied with problems that the strength is noticeably lowered and the added plasticizer is liable to bleed out to provide a filament surface with a white powdery appearance.

The method (7) of simply using a copolymer provides a simply soft filament but fails to provide a monofilament having a high knot strength in combination therewith.