JP4249744B2 - Polylactic acid monofilament and method for producing the same - Google Patents

Description

  The present invention is mainly composed of plant raw materials, has excellent processability, high mechanical strength, and improved durability, heat resistance, resilience, and tension retention when used as a tennis racket string. The present invention relates to a polylactic acid monofilament. The present invention also relates to a method for producing a polylactic acid monofilament.

  In recent years, from the viewpoint of protecting the natural environment, biodegradable polymers of plant materials that do not depend on petroleum as raw materials and processed products thereof have attracted attention. In particular, as an example, polylactic acid is made from plants such as corn and sugar cane, and its combustion heat is less than half that of polyethylene. It naturally hydrolyzes in soil and water, and then harmless by microorganisms. It becomes. At present, studies are being made to obtain molded articles, specifically films, sheets, fibers, and the like using polylactic acid, which have been put into practical use. Polylactic acid can be improved in strength by being stretched, but it is a hard and brittle material. There is a problem that it is not practical. This is a bigger problem when the monofilament is a thick monofilament.

  For this reason, many proposals have been made to add a soft component or a plasticizer for the purpose of imparting flexibility to polylactic acid. The inventors of the present invention have found that polylactic acid is soft under high tension and therefore has a good taste as a string for rackets. As a monofilament suitable for a string for rackets, polylactic acid is used as an aliphatic polyester other than polylactic acid. A monofilament with improved compatibility and improved heat resistance has been proposed (Japanese Patent Application Laid-Open No. 2001-40529). When this monofilament is used as a string for a racket, it has a characteristic that it has a soft feel like natural gut, but the added soft component (aliphatic polyester other than polylactic acid) hardly contributes strongly. Therefore, sufficient strength cannot be obtained and durability is not always sufficient.

  In order to improve strength and durability, the present inventors have made a monofilament made of a material in which polylactic acid is blended with a block copolymer of polylactic acid and an aliphatic polyester other than polylactic acid as a soft component having a high melting point. (Japanese Patent Laid-Open No. 2005-15970). In this monofilament, the strength was improved and the durability was improved, but it was insufficient for practical use.

  On the other hand, Japanese Patent No. 2725870 discloses a composition in which polylactic acid is blended with a block copolymer (segmented polyester elastomer) of a hard segment of polybutylene terephthalate and a soft segment of polyether glycol (claimed). Terms 30-33, column 16, lines 35-45). However, this patent publication does not disclose anything about forming a monofilament from the composition.

  Japanese Patent Application Laid-Open No. 2004-189991 discloses a resin composition containing polylactic acid, polyethylene glycol as a plasticizer, and hydrophilic silica particles (claims 1 to 3, paragraph [0044] Examples) 1).

JP 2001-40529 A JP 2005-15970 A Japanese Patent No. 2725870 JP 2004-189991 A

  In view of the above background art, it is desired to develop a polylactic acid-based monofilament excellent in durability, heat resistance, and practical performance suitable as a racket string.

  An object of the present invention is to provide a polylactic acid-based monofilament having excellent processability and sufficient mechanical strength. In particular, an object of the present invention is to provide a polylactic acid monofilament having sufficient mechanical strength when used as a racket string, and improved durability, heat resistance, resilience, and tension retention. There is to do.

  As a result of various investigations without limiting the biodegradable material as a soft component, the present inventors have blended a polyester-based elastomer at a specific ratio with respect to polylactic acid, and further introduced a cross-linked structure, thereby providing a string for rackets. It has been found that a monofilament with improved durability, heat resistance, resilience, and tension retention can be obtained.

The present invention includes the following inventions.
(1) Expressed by weight ratio, polylactic acid polymer (A) 80 to 97 parts by weight, polyester elastomer (B) 3 to 15 parts by weight, and crosslinking agent (C) 0.01 to 5 parts by weight a monofilament formed of a material containing,
The polyester elastomer (B) is a monofilament that is a polyester block copolymer of a hard segment made of an aromatic-containing polyester component and a soft segment made of a polyether glycol component or an aliphatic polyester component .
(2) The monofilament according to the above (1) , wherein the melting point of the polyester elastomer (B) is 150 to 190 ° C.
(3) The crosslinking agent (C) is at least one selected from the group consisting of a peroxide crosslinking agent, a carbodiimide crosslinking agent, an epoxy crosslinking agent, and an allyl or vinyl crosslinking agent, (1) Or the monofilament as described in (2) .
(4) The monofilament according to any one of the above (1) to (3) , which has a crosslinked structure by a reaction of a crosslinking agent.
(5) A racket string comprising the monofilament according to any one of (1) to (4 ) above.
(6) A racket string in which the monofilament according to any one of (1) to (4) is used as a part of a constituent member.
(7) Expressed by weight ratio, polylactic acid polymer (A) 80 to 97 parts by weight, polyester elastomer (B) 3 to 15 parts by weight, and crosslinking agent (C) 0.01 to 5 parts by weight Melt spinning and stretching a material containing
A step of crosslinking reaction before or after melt spinning, or after stretching,
A method for producing a monofilament comprising
The polyester elastomer (B) is a method for producing a monofilament, which is a polyester block copolymer of a hard segment composed of an aromatic-containing polyester component and a soft segment composed of a polyether glycol component or an aliphatic polyester component .

  According to the present invention, it is suitable for a polylactic acid monofilament excellent in processability and sufficient mechanical strength, particularly a string for rackets, and has practically sufficient mechanical strength and improved durability. A polylactic acid monofilament having heat resistance, resilience, and tension retention is provided.

Hereinafter, the present invention will be described in detail.
The monofilament of the present invention is represented by a weight ratio of 80 to 97 parts by weight of the polylactic acid polymer (A), 3 to 15 parts by weight of the polyester elastomer (B), and 0.01 to 5 of the crosslinking agent (C). It is formed from the material containing a weight part. Each component will be described.

  The polylactic acid polymer (A) in the present invention is a polymer consisting essentially of monomer units derived from L-lactic acid and / or D-lactic acid. Here, “substantially” means that other monomer units not derived from L-lactic acid or D-lactic acid may be included as long as the effects of the present invention are not impaired. In addition, a so-called stereo complex in which poly L-lactic acid and poly D-lactic acid are mixed is also included in the polylactic acid polymer (A) in the present invention.

  The weight average molecular weight (Mw) of the polylactic acid polymer (A) is preferably in the range of 50,000 to 500,000. Below the above range, the mechanical properties and the like of the resulting monofilament tend not to be sufficiently expressed. On the other hand, if it exceeds the above range, the viscosity in the molten state becomes high, so that it tends to be inferior in workability such as difficulty in spinning into a monofilament.

  As a method for producing the polylactic acid polymer (A), any known polymerization method can be employed. The most typical one is a method of ring-opening polymerization of lactide, which is an anhydrous cyclic dimer of lactic acid (lactide method), but lactic acid may be directly subjected to condensation polymerization.

  When the polylactic acid polymer (A) is composed only of monomer units derived from L-lactic acid and / or D-lactic acid, the polymer is crystalline and has a high melting point, but L-lactic acid / D-lactic acid. Since the crystallinity and melting point can be adjusted by changing the ratio of the derived monomer units (abbreviated as L / D ratio), it is possible to control the practical characteristics according to the use of the monofilament. Further, the crystallinity and the melting point may be adjusted by copolymerizing a small amount of other hydroxycarboxylic acid or the like so as not to impair the properties of polylactic acid.

Polyester-based elastomer (B) in the present invention, soft consisting called hard segment and the block polyester der consisting of soft segment is, a hard segment consisting of Kaoru aromatic containing polyester component, polyether glycol component or an aliphatic polyester component It is a polyester block copolymer with a segment. By blending the polyester elastomer (B), the polylactic acid polymer (A) can be imparted with flexibility and modified.

  Examples of the polyester segment component constituting the hard segment include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, bis (4-carboxyphenyl) methane, bis (4-carboxyphenyl) sulfone, and the like. Aromatic dicarboxylic acid or its ester, ethylene glycol, propylene glycol, tetramethylene glycol, pentamethylene glycol, 2,2-dimethyltrimethylene glycol, hexamethylene glycol, decamethylene glycol, p-xylylene glycol, cyclohexanedimethanol Aromatic-containing polyesters produced from diols such as these, or aromatic-containing copolyesters using these two or more dicarboxylic acids and / or two or more diols, etc. And the like.

  On the other hand, as the soft segment, a polymer having a molecular weight of about 400 to 6000 is preferable, and as the constituent segment component, for example, poly (ethylene oxide) glycol, poly (propylene oxide) glycol, poly (tetramethylene oxide) glycol, etc. Examples thereof include polyalkylene ether glycols and mixtures thereof, and copolymer polyether glycols obtained by copolymerizing these polyether glycol components.

  Moreover, as a soft segment component, the aliphatic polyester manufactured from C2-C12 aliphatic dicarboxylic acid and C2-C10 aliphatic glycol can be used. Examples of such aliphatic polyesters include polyethylene adipate, polytetramethylene adipate, polyethylene sebacate, polytetramethylene dodecanate, polytetramethylene azelate, polycaprolactone, and the like. Furthermore, a polyester polyether copolymer in which the above aliphatic polyester and polyether are combined can also be used.

  The proportion of the soft segment component in the polyester block copolymer is preferably 20% by weight or more and 80% by weight or less. When the proportion of the soft segment component is less than 20% by weight, the effect of imparting flexibility to the monofilament tends to be weakened. On the other hand, when the proportion of the soft segment component exceeds 80% by weight, the effect of imparting flexibility is sufficient. However, the monofilament strength tends to decrease.

  Among these, the polyester elastomer (B) having a melting point in the range of 150 ° C. to 190 ° C. is preferably used in the present invention because the difference in melting point from the polylactic acid polymer (A) is small.

  For the purpose of imparting flexibility, a relatively flexible polyester elastomer (B) having a Shore hardness (JIS D scale) of about 24 to 40 is more preferably used.

  In the present invention, a copolymer of polybutylene terephthalate and polyether glycol is particularly preferably used from the viewpoint of performance and economy.

  In the present invention, the blending ratio of the polylactic acid-based polymer (A) and the polyester-based elastomer (B) is expressed as a weight ratio, and 80 to 97 parts by weight of the polylactic acid-based polymer (A), the polyester-based elastomer (B). 3 to 15 parts by weight. When the elastomer (B) is less than 3 parts by weight, the modification effect on the polylactic acid polymer (A) is small, and when the elastomer (B) exceeds 15 parts by weight, it is in phase with the polylactic acid polymer (A). This is not preferable because the solubility becomes poor and warp cracking occurs during spinning drawing, or warp cracking tends to occur during use as a monofilament product.

  The polyester elastomer (B) has a greater modification effect on the polylactic acid polymer (A) than other polyurethane elastomers.

  In the present invention, if necessary, as the third polymer component, other resins than the polylactic acid polymer (A) and the elastomer (B) can be blended as long as the effects of the present invention are not impaired. . The third component resin is preferably a polyester resin from the viewpoint of compatibility with the main component polylactic acid polymer (A). When the third component is used, the blending amount is preferably less than 15 parts by weight in the case of 80 to 97 parts by weight of the polylactic acid polymer (A) and 3 to 15 parts by weight of the polyester elastomer (B).

  In the present invention, a cross-linking agent (C) is added to improve the compatibility between the polylactic acid polymer (A) and the polyester elastomer (B) and to improve the durability and heat resistance of the monofilament. To do. By blending the crosslinking agent (C), a crosslinked structure can be introduced into the polylactic acid polymer (A) and the polyester elastomer (B) individually and / or mutually.

  The crosslinking agent (C) is selected from a peroxide crosslinking agent, a carbodiimide crosslinking agent, an epoxy crosslinking agent, and an allyl or vinyl crosslinking agent.

  The peroxide crosslinking agent can be selected from known organic peroxides in consideration of decomposition temperature, reactivity, and the like. Typically, it can be selected from diacyl peroxides, dialkyl peroxides, peroxyesters, peroxyketals and the like.

  As the carbodiimide-based crosslinking agent, a polycarbodiimide compound having 2 or more, preferably 3 or more carbodiimide groups in the molecule is used. For example, a polycarbodiimide compound obtained by subjecting diisocyanate to a decarboxylation condensation reaction in the presence of a catalyst can be mentioned. These are commercially available, for example, as “Carbodilite” from Nisshinbo Co., Ltd.

  As the epoxy-based crosslinking agent, a compound having 2 or more, preferably 3 or more epoxy groups in the molecule is used. Preferably, a multi-epoxy compound based on a polymer type styrene acrylic or acrylic resin can be used. For example, “Alfon UG4030, UG4070” (styrene / acrylic) from Toa Gosei Co., Ltd., “Alfon XG4000, XG4010” (acrylic), “Epofriend” (epoxidized styrene elastomer) from Daicel Chemical Industries, Ltd. Etc.

  In the peroxide crosslinking agent, carbodiimide crosslinking agent, and epoxy crosslinking agent, the crosslinking reaction proceeds by heat.

  Examples of the allyl or vinyl-based crosslinking agent include compounds having 2 or more, preferably 3 or more polymerizable double bonds in the molecule. Polyfunctional allyl compounds such as triallyl isocyanurate with high thermal stability are stable even under the spinning conditions of monofilament, and can be crosslinked by irradiation with high energy rays such as ultraviolet rays or electron beams at any stage after stretching. preferable. Moreover, you may use polyfunctional acrylate compounds, such as hexanediol di (meth) acrylate, a pentaerythritol tri (meth) acrylate, and a trimethylol propane tri (meth) acrylate.

  As a crosslinking agent (C), 1 type (s) or 2 or more types can be used from the said crosslinking agent.

As a method for introducing a crosslinked structure in the present invention,
(1) A method in which pellets of a resin material subjected to a crosslinking reaction are prepared in advance before the melt spinning operation; that is, a polylactic acid polymer (A), a polyester elastomer (B), and a crosslinking agent (C). A method of mixing and melting, causing a crosslinking reaction, preparing pellets of a resin material introduced with a crosslinked structure, and performing melt spinning of monofilaments using the pellets,
(2) A method of spinning while performing a crosslinking reaction at the time of melt spinning; that is, at the time of melt spinning, a polylactic acid polymer (A), a polyester elastomer (B) and a crosslinking agent (C) are mixed and melted to cause a crosslinking reaction. While spinning,
(3) A method in which a cross-linking reaction is performed after melt spinning and stretching; that is, a material in which a polylactic acid polymer (A), a polyester elastomer (B) and a cross-linking agent (C) are mixed is substantially cross-linked. Without melt spinning and drawing, followed by a crosslinking reaction by irradiation with high energy rays such as ultraviolet rays or electron beams,
Either of these can be performed.

  Moreover, the modification method of said each method can also be performed. For example, the method (2) or (3) can be carried out by preparing a semi-crosslinked resin material pellet according to the above (1) and using the pellet.

  By such an operation, between the polylactic acid polymers (A), between the polyester elastomers (B), and / or between the polylactic acid polymer (A) and the polyester elastomer (B). A crosslinked structure is formed.

  Whether or not a cross-linked structure is introduced can be confirmed with respect to (1) and (2) above by an increase in the melt viscosity of the resin material. Further, the post-crosslinking of (3) above can be confirmed by a change in physical properties of the monofilament and a change in solvent solubility.

  In the present invention, the polylactic acid-based polymer (A) and the polyester-based elastomer (B) each independently and / or mutually have a crosslinked structure, thereby improving the compatibility of both (A) and (B). At the same time, it was found that the heat resistance and durability of the monofilament were further improved, and when the monofilament was used as a racket string, the reduction in the surface pressure of the gut after tensioning was reduced. It was found that the problem of warping of the monofilament was solved by improving the compatibility. In this way, the introduction of a cross-linked structure yields a monofilament having sufficient mechanical strength, which has practically sufficient mechanical strength even when used as a racket string, and has durability, heat resistance, and resilience. And a monofilament with greatly improved tension retention.

In the present invention, when crosslinking is performed before the melt spinning operation or at the time of melt spinning, if the degree of crosslinking is too large, spinning and stretchability are deteriorated.
Therefore, when using a peroxide crosslinking agent, it is preferable to melt-knead addition of a crosslinking agent as a trace amount. For example, about 0.01 to 0.5 part by weight of the peroxide crosslinking agent is used for 80 to 97 parts by weight of the polylactic acid polymer (A) and 3 to 15 parts by weight of the polyester elastomer (B). It is more preferable to use about 0.1 to 0.3 parts by weight.
In the case of a carbodiimide crosslinking agent or an epoxy crosslinking agent, the crosslinking reaction is a reaction with a hydroxyl group and / or a carboxyl group at the end of the polyester, and the molecular weight of the crosslinking agent is also high. It is preferable to use about 0.05 to 5 parts by weight.

  According to the study by the present inventors, in the case of cross-linking before the melt spinning operation or at the time of melt spinning, when a proper amount of the cross-linking agent is used as described above, the use of a peroxide cross-linking agent is more preferable result. Is obtained.

  In the case of crosslinking after melt spinning drawing, the amount of allyl or vinyl crosslinking agent is 0 to 97 parts by weight of the polylactic acid polymer (A) and 3 to 15 parts by weight of the polyester elastomer (B). About 2 to 5 parts by weight is preferable. Post-crosslinking can increase the degree of cross-linking, but if the amount of cross-linking agent is excessive, or if the irradiation energy is too strong and the degree of cross-linking is excessive, the decrease in strength and elongation becomes brittle and brittle. It is necessary to select the blending amount and irradiation conditions. An allyl or vinyl crosslinking agent that is stable against heat during melt spinning is suitable for post-crosslinking by irradiation with high energy rays.

  In the monofilament of the present invention, as other components, as necessary, a filler, a lubricant, an ultraviolet absorber, an antioxidant, a stabilizer, a pigment, a colorant, an antistatic agent, a mold release agent, a plasticizer, and a fragrance. Various additives such as antibacterial agents can also be added.

  Further, in the present invention, in order to have sufficient strength and durability as a string for a racket, the molecular weight of the monofilament is important, and a high molecular weight is preferable. The preferable weight average molecular weight (Mw) of the monofilament measured by GPC method using a chloroform solvent is about 50,000 to 400,000. These can be achieved by using the materials described above to produce monofilaments under conditions with little decomposition and short melting time during melt-kneading and melt spinning. When the weight average molecular weight of the monofilament is less than the above range, the mechanical properties tend to be insufficient, and when it exceeds the above range, the viscosity in the molten state tends to be high and the spinnability tends to decrease.

  Moreover, preferable ranges for the physical properties of the monofilament are a strength of 2.5 CN / dtex or more, a knot strength of 1.3 CN / dtex or more, and an elongation of 25 to 45%. There are no particular limitations on the upper limits of strength and nodule strength. When the elongation is smaller than the above range, warp cracking and fibrillation are likely to occur, and when the elongation is larger than the above range, the elongation tends to occur, which is not preferable for strings and other applications.

  The monofilament of the present invention generally has a round cross-sectional shape, but may have a non-circular irregular cross-section such as a hollow shape having a hollow core or a polygon. Also included are monofilaments in which the two components are combined into a core sheath, sea-island shape, or the like. In the case of a composite monofilament, at least one component may be a material composition constituting the monofilament of the present invention.

  The diameter (in cross section) of the monofilament of the present invention is not particularly limited, and may be appropriately determined according to the intended use. For example, when used as a monofilament gut for a racket string application, the thickness may be about 0.6 mm to 1.50 mm.

  In addition, the monofilament of the present invention can be used as a core component or skin component of gut or in a focused state. In this case, a monofilament diameter of about 0.05 to 1.3 mm is used.

  Moreover, when using a monofilament as a racket string as it is, the twist (torsion) of 30-200 times / m can be provided as needed. By imparting twist, the stretchability to the racket, the feel especially softness, and the spin property are improved.

  Further, by using the monofilament of the present invention as a constituent component of the string for the racket, a core yarn, a leather yarn, or a concentrated yarn can be used to obtain a softer feel.

The manufacturing method of the monofilament of this invention is demonstrated.
The monofilament of the present invention is represented by a weight ratio of 80 to 97 parts by weight of the polylactic acid polymer (A), 3 to 15 parts by weight of the polyester elastomer (B), and 0.01 to 5 of the crosslinking agent (C). It can be produced by a method comprising a step of melt spinning and stretching a material containing parts by weight, and a step of crosslinking reaction before or during melt spinning, or after stretching.

  The mixing method and mixing apparatus of the polylactic acid polymer (A) and the polyester elastomer (B) are not particularly limited, but a method and apparatus capable of continuous treatment are industrially advantageous and preferable. For example, two or more types of pellets (A) and (B) and the crosslinking agent (C) may be mixed at a predetermined ratio, and directly put into a hopper of an extruder, melted, and immediately molded into a monofilament. . Moreover, after melt-mixing these components, they may be once pelletized and then melt-molded into monofilaments as necessary. Similarly, the polylactic acid-based polymer (A) and the polyester-based elastomer (B) are separately melted by an extruder or the like, and these and the cross-linking agent (C) are mixed at a predetermined ratio by a static mixer and / or a mechanical stirring device. Then, it may be immediately formed into a monofilament or once pelletized. You may combine mixing by mechanical stirring, such as an extruder, and a static mixer.

  In order to mix uniformly, the method of pelletizing once is more preferable, but in the case of the melt mixing method, it is necessary to substantially prevent degradation and deterioration of the polymer, and mixing within a short time at the lowest possible temperature. Is preferred. The melt extrusion temperature is appropriately selected in consideration of the melting point and mixing ratio of the resin used, but is usually in the range of 180 to 250 ° C.

  The molten polymer material is extruded from the nozzle holes and then cooled as usual. Water is generally used for cooling, but other solvents may be used. The temperature of water is usually 30 to 70 ° C. After the polymer material is cooled, it is guided to the first roll to obtain an undrawn yarn. Usually, the stretching process is continued. However, the film can be stretched after being wound up as an unstretched yarn.

  Stretching can be performed wet or dry. Here, wet means includes hot water, steam, and liquid bath stretching such as glycerin and polyethylene glycol. Drying refers to stretching with hot air, an infrared heater, a hot plate, a hot roll, or the like. Stretching can be performed at a multistage stretching twice or more as required. As a standard process, wet-dry heat or wet-heat-wet heat stretching is performed in two to three stages, but is not limited to this, and can be selected and combined as appropriate. Further, a constant length or relaxation heat treatment can be performed after stretching or in an intermediate stage. Although it does not specifically limit as extending | stretching temperature, 70-170 degreeC is preferable. The total draw ratio is preferably about 3 to 9 times. When the draw ratio is increased, the strength is increased, but there is a problem that warp cracking (fibrillation) tends to occur. It is particularly preferable to set the conditions such that the draw ratio is 4 to 7 times, and the cut elongation is 25% to 45%, particularly preferably 30 to 40%.

  When the crosslinking treatment is performed after stretching, the crosslinking can be performed using a high energy source such as an ultraviolet ray or an electron beam. In this case, by changing the irradiation conditions, it is possible to control such as changing the crosslinking density or causing crosslinking only in the monofilament surface layer portion. Irrespective of the present invention, when a monofilament is irradiated with an electron beam or the like without using a crosslinking agent, polylactic acid is preceded by decomposition, leading to a decrease in strength and a decrease in elongation. When an appropriate cross-linking agent as described above according to the present invention is used, it is presumed that the cross-linking reaction takes place over decomposition over low energy.

  Furthermore, by covering the surface of the monofilament with a polymer material, improvement in durability as a gut can be expected. Although it does not specifically limit as a polymeric material to coat | cover, It is preferable to coat | cover with resin, such as a polyester type, a polyamide type, and a polyurethane type.

  As mentioned above, the monofilament of the present invention has been described focusing on the racket string application. However, the monofilament of the present invention can be used for various purposes such as monofilament alone, twisted yarn, braided string, sewing thread, string for electric use, bird-proofing, anti-animal thread, mowing, brush, fishing line, etc. Can also be used.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

In the examples and comparative examples, the following raw materials were used.
<Polylactic acid polymer (A1)>
Poly L-lactic acid "Toyota Eco Plastic U'z B1" manufactured by Toyota Motor Corporation
Mw = 200,000, glass transition temperature 60 ° C., melting point 175 ° C.
<Polyester elastomer (B1)>
"Hotrel 3078" manufactured by Toray DuPont, melting point 172 ° C
<Peroxide crosslinking agent (C1)>
“Kayahexa AD40C” (2,5-dimethyl-2,5-di (t-butylperoxy) hexane) manufactured by Kayaku Akzo
<Epoxy-based crosslinking agent (C2)>
“Alfon UG4070” manufactured by Toagosei (epoxy-modified styrene acrylic resin)
<Carbodiimide type crosslinking agent (C3)>
Nisshinbo "Carbodilite LA-1"
<Allyl crosslinking agent (C4)>
Nippon Kasei Triallyl Isocyanurate (TAIC)
<Flexible component for comparison with aliphatic polyester (B2)>
Polylactic acid-aliphatic polyester copolymer (Dainippon Ink "Plamate PD-150")

[Examples 1 to 3]
After the polylactic acid (A1) and the polyester-based elastomer (B1) were each vacuum dried, as shown in Table 1, (A1), (B1) and a predetermined crosslinking agent were mixed in a weight mixing ratio (A1) / (B1). /(C1)=92/8/0.2 (Example 1), (A1) / (B1) / (C2) = 92/8 / 1.0 (Example 2), (A1) / (B1) /(C3)=92/8/1.0 (Example 3) and mixed with a V-type blender. This was continuously supplied to a 30 mm same-direction twin-screw extruder kneader set at 210 ° C., melt-extruded, made into a strand and pelletized to prepare a spinning raw material.

  After the obtained raw material is dried, it is supplied to a single-screw melt extruder set at a temperature of 210 ° C., extruded from a circular nozzle with a diameter of 3 mm, and taken up by a first roller, and cooled to 50 ° C. just below the nozzle. It led to the water tank and cooled, and the unstretched monofilament was obtained.

  Continuously, it was led to a first stretching tank of hot water set at 93 ° C., and further stretched with a second roller at a take-up speed ratio of 4.2 times. Subsequently, the monofilament was guided to a hot water second stretching tank set at 98 ° C., and further stretched with a third roller at a take-up speed ratio of 1.5 times (final draw ratio of 6.3 times). Furthermore, it heat-fixed in 98 degreeC hot water (same speed), and wound up with the winder.

  Table 1 shows the physical property evaluation results of the obtained monofilament. Strength (N), strength (CN / Dtex), nodule strength (N) and elongation (%) were measured according to JIS L1013. That is, using a tensile tester, measurement was performed under the conditions of a yarn length of 250 mm and a tensile speed of 300 mm / min.

  Further, durability and heat resistance were evaluated using the obtained monofilament as a gut as follows. The evaluation results are also shown in Table 1.

(Durability test)
A silicone oil was applied to the monofilament to obtain a gut. The obtained gut was stretched on a tennis racket with a tension of 40 pounds, and a hard tennis ball was allowed to collide with the tennis racket (ball speed 100 km / hr), and the number of collisions of the ball until the string was cut was measured. The number of collisions was evaluated as durability.

(Heat resistance test)
The gut was stretched on a tennis racket with a tension of 40 pounds and left at room temperature for 24 hours. The racket after standing was heat-treated in an atmosphere of 70 ° C. for 16 hours. After the heat treatment, the racket was taken out and the surface pressure was measured, and the holding ratio with respect to the surface pressure before the heat treatment was determined.
(Retention ratio) = [(surface pressure after heat treatment) / (surface pressure before heat treatment)] × 100
Retention rate 50% or more: ○
Retention rate 25% or more and less than 50%:
Retention rate less than 25%: ×
Judged by.

[Comparative Example 1]
Example 1 except that aliphatic polyester (B2) was used instead of polyester elastomer (B1) and the weight mixing ratio (A1) / (B2) / (C1) = 92/8 / 0.2 was used. Monofilaments were produced under the same conditions. The evaluation results of the obtained monofilament are shown in Table 1. The monofilament of Comparative Example 1 was more transparent than the monofilaments of Examples 1-3.

[Comparative Example 2]
A monofilament was produced by the same operation as in Example 1 except that no crosslinking agent was added. The evaluation results of the obtained monofilament are shown in Table 1.

  From Table 1, the monofilaments of Examples 1 to 3 are more durable than the monofilament of Comparative Example 1 using a polylactic acid-aliphatic polyester copolymer and the monofilament of Comparative Example 2 in which no crosslinking agent was added. It is clear that the heat resistance has improved significantly. Among Examples 1 to 3, Example 1 using a peroxide crosslinking agent gave the best results.

[Example 4]
After the polylactic acid (A1) and the polyester-based elastomer (B1) were each vacuum dried, as shown in Table 1, (A1), (B1) and the crosslinking agent triallyl cyanurate (C4) were mixed in a weight mixing ratio (A1 ) / (B1) / (C4) = 92/8 / 1.0. This was continuously supplied to a 30 mm same-direction twin-screw extruder kneader set at 210 ° C., melt-extruded, made into a strand and pelletized to prepare a spinning raw material.

  Using the obtained raw material, a monofilament was produced under the same conditions as in Example 1. The evaluation results of the obtained uncrosslinked monofilament are shown in Table 1. In this uncrosslinked state, the heat resistance was poor.

  Next, the uncrosslinked monofilament was crosslinked by irradiation with an electron beam. The electron beam irradiation conditions were two ways of 15 kGy and 30 kGy. The evaluation results are shown in Table 1. Cross-linking improved the heat resistance of the monofilament.

Claims (7)

A material containing 80 to 97 parts by weight of a polylactic acid polymer (A), 3 to 15 parts by weight of a polyester elastomer (B), and 0.01 to 5 parts by weight of a crosslinking agent (C), expressed by weight ratio. a monofilament formed of,
The polyester elastomer (B) is a monofilament that is a polyester block copolymer of a hard segment made of an aromatic-containing polyester component and a soft segment made of a polyether glycol component or an aliphatic polyester component . The melting point of the polyester-based elastomer (B) is 150 to 190 ° C., the monofilament of claim 1. Crosslinking agent (C) is a peroxide crosslinking agent, a carbodiimide crosslinking agents, epoxy crosslinking agents, and is at least one selected from the group consisting of allyl or vinyl-based crosslinking agent, according to claim 1 or 2 Monofilament. The monofilament according to any one of claims 1 to 3 , which has a crosslinked structure by a reaction of a crosslinking agent. The string for rackets which consists of a monofilament of any one of Claims 1-4 . The string for rackets in which the monofilament of any one of Claims 1-4 is used as a part of structural member. A material containing 80 to 97 parts by weight of a polylactic acid polymer (A), 3 to 15 parts by weight of a polyester elastomer (B), and 0.01 to 5 parts by weight of a crosslinking agent (C), expressed by weight ratio. A step of melt spinning and stretching,
A step of crosslinking reaction before or after melt spinning, or after stretching,
A method for producing a monofilament comprising
The polyester elastomer (B) is a method for producing a monofilament, which is a polyester block copolymer of a hard segment composed of an aromatic-containing polyester component and a soft segment composed of a polyether glycol component or an aliphatic polyester component .