JP2000154425A - Production of biodegradable monofilament - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method capable of producing biodegradable monofilament suitable for industrial materials such as fishnets, laver nets, ropes, fishlines or the like from polylactic acid. SOLUTION: This biodegradable monofilament is obtained by melt-spinning of polylactic acid having >=70,000 number-average molecular weight and drawing the resultant. Wherein melting and spinning are performed at (Tm+20) deg.C to (Tm+50) deg.C [Tm is the melting point of the polylactic acid ( deg.C)] within 10 min and the obtained monofilament is cooled and solidified in a liquid at (Tg-50) deg.C to (Tg+20) deg.C [Tg is the glass transition point of the polylactic acid ( deg.C)] for 2-5 s and the resultant is drawn.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a biodegradable monofilament suitable for industrial materials such as fishing nets, laver nets, ropes and fishing lines from polylactic acid.

[0002]

2. Description of the Related Art Fibers for industrial materials used for fishing, agriculture, and civil engineering are required to have excellent strength and weather resistance.
Those made of vinylon, polyolefin and the like are used. However, these fibers are not self-degrading, and when left in the wild or in the sea after use, they not only damage the landscape, but also become entangled with birds, marine life, divers, etc. There was a problem of causing a ship accident.

[0003] This problem can be solved by treating it by incineration, landfill or recovery and recycling after use. However, since such treatment requires a great deal of cost, it is actually left in the wild or in the sea. It is a fact.

Therefore, as a method of solving such a problem, use of a biodegradable material is considered, and various biodegradable fibers have been proposed. Among them, polylactic acid is a relatively inexpensive, biodegradable resin capable of producing a molded article having practical mechanical properties and heat resistance,
Various attempts have been made to convert this into a fiber (Japanese Unexamined Patent Publication No.
-60733, Japanese Patent Application No. 10-188477). However, since polylactic acid is hard and brittle and has a high crystallization rate, it has been difficult to stably produce a monofilament having excellent mechanical properties.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and makes it possible to stably produce monofilaments suitable for industrial materials such as fishing nets, laver nets, ropes and fishing lines from polylactic acid. It is a technical task to provide a method.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and found that the melting time of polylactic acid during melt spinning, the cooling and solidifying temperature of the spun yarn, and the cooling and solidifying time. By controlling, smooth melt spinning is possible,
The inventors have found that it is possible to stably produce a monofilament having good yarn quality performance, and have reached the present invention. That is, the present invention has the following configuration. (1) Melt spinning polylactic acid having a number average molecular weight of 70,000 or more,
In producing a biodegradable monofilament by stretching,
Melting and spinning at a temperature of (Tm + 20) to (Tm + 50) ° C. [Tm is the melting point of polylactic acid (° C.)] and within 10 minutes, and then (Tg−50) to (Tg + 20) A method for producing a biodegradable monofilament, comprising cooling and solidifying for 2 to 5 seconds in a liquid bath at a temperature of 0 ° C. [Tg: glass transition temperature of polylactic acid (° C.)], followed by stretching. (2) The biodegradable monofilament according to the above (1), wherein two or more stages of stretching are performed in the stretching step, and the second and subsequent stages are stretched in a gas, with the water content of the monofilament surface being 1% or less. Manufacturing method. (3) The method for producing a biodegradable monofilament according to the above (1) or (2), wherein the polylactic acid is poly-L-lactic acid having an optical purity of 95.0 to 99.5%. (4) The method for producing a biodegradable monofilament according to any one of the above (1) to (3), wherein the polylactic acid is a poly-L-lactic acid having an MFR of 25 g / 10 min or less.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The polylactic acid used in the present invention has a number average molecular weight of 7
It must be at least 10,000, preferably at least 90,000. When the number average molecular weight is less than 70,000, the flowability of the melt is poor, or the viscosity at the time of melting is low, so that the draft is cut and the spinning property is reduced, and it is impossible to perform drawing at a high draw ratio. Become.

[0008] Polylactic acid is a polymer or a copolymer containing L-lactic acid and D-lactic acid as optical isomers as main components, and among them, the optical purity is 95.0 to 99.5%, particularly 96 to 99%. Of poly-L-lactic acid. Lactic acid has an optically active carbon, and therefore has L-form and D-form optical isomers. When the ratio of the L-form component is lower than the above range, the melting temperature is lowered, and the spinning property is deteriorated, so that the fiber tends to have poor yarn quality performance. On the other hand, if this ratio is higher than the above range, workability and biodegradability tend to deteriorate.

Further, polylactic acid has a temperature of 210 ° C. and a load of 2.
MFR measured under 16kgf condition is 25g / 10min or less, especially
It is preferably 15 g / 10 min or less. If this condition is not satisfied, the ejection linear velocity becomes high, so that problems such as unevenness in the diameter of the wire and deterioration in the spinnability tend to occur.

In the present invention, the melt spinning method comprises the steps of: melting the polylactic acid during melt spinning; cooling and solidifying the spun yarn;
If the cooling and solidification time satisfies specific conditions, a normal melt spinning method can be adopted.

First, the melting temperature of polylactic acid is (Tm + 20)
To (Tm + 50) ° C, preferably (Tm + 25) to (Tm + 45) ° C
Condition must be satisfied. When the melting temperature is less than the above range, it is difficult to completely melt the resin,
The melt viscosity becomes high, making it difficult to supply a fixed amount. On the other hand, if it exceeds the above range, the polymer is thermally decomposed to deteriorate the spinning property, which is not preferable.

The melting time of polylactic acid must be within 10 minutes, preferably 4 to 7 minutes. Here, the melting time is the time from when the polymer starts melting by heating to the time required to extrude from the nozzle hole.If this time exceeds 10 minutes, thermal decomposition of the polymer is likely to occur. Not preferred.

After melting, the spun yarn is (Tg-50)
~ (Tg + 20) ℃, preferably (Tg-30) ~ (Tg + 10) ℃
It is necessary to carry out cooling and solidification in a liquid bath of 2 to 5 seconds, preferably 2 to 3 seconds. The cooling and solidifying temperature needs to be in the above-mentioned temperature range with the glass transition temperature, which is the temperature at which the molecular chains of the polymer are frozen, as a reference temperature.
When the temperature is lower than this temperature, the resulting monofilament becomes a hard and brittle undrawn filament due to the inherent hard property of polylactic acid. It becomes possible. On the other hand, if the temperature is too high, the crystallization proceeds due to the high crystallization rate of polylactic acid, and as a result, it becomes impossible to draw the undrawn monofilament. Further, when the temperature is further increased, the monofilament is not sufficiently cooled, so that it is impossible to collect the undrawn monofilament.

Next, if the cooling and solidifying time is shorter than the above range, insufficient cooling will result, making it difficult to obtain an undrawn filament. If the cooling solidification time is longer than the above range, crystallization will proceed too much, resulting in a hard and brittle undrawn monofilament. And it becomes difficult to stretch. Although it is related to the take-off speed of the monofilament, it is necessary to increase the length of the cooling solidification and crystallization bath or the immersion length.

The liquid bath used for cooling and solidifying includes water,
Ethylene glycol, polyethylene glycol, glycerin, silicone, etc. can be used, but the liquid bath is 100 ° C or lower and does not need to be heated to high temperature, so workability is good, removal of liquid adhering to the monofilament is easy, and liquid It is most preferred to use water that has low tensile resistance to the monofilament due to viscosity.

The undrawn monofilament crystallized by cooling and solidification is optionally placed in an atmosphere at a temperature of 20 to 40 ° C.
After adjusting the crystallinity by treating for 30 to 180 seconds, the film is stretched. In this case, if the undrawn monofilament is once wound up and left at room temperature, crystallization proceeds and the degree of crystallization becomes too high, so that drawing becomes difficult. Therefore, it is preferable to carry out drawing after cooling and solidifying.

The stretching can be performed in one or two or more stages, but in order to obtain a high-strength monofilament, it is preferable to perform the stretching in two or more stages. In this case, the first-stage stretching is preferably performed in a liquid bath having high heating efficiency. This is because monofilaments generally have a large wire diameter, and it is not preferable to set a high temperature in stretching using an oven heater or the like. As the liquid, water, ethylene glycol, polyethylene glycol, glycerin, silicone and the like can be used, but water is most preferably used for the same reason as the liquid bath for cooling and solidifying.

The first-stage stretching temperature is preferably from 60 to 95 ° C. When the drawing temperature is lower than 60 ° C, the heating of the undrawn monofilament becomes insufficient, and the yarn breaks in the drawing process.On the other hand, when the drawing temperature exceeds 95 ° C, the monofilament is overheated, and a super draw phenomenon occurs, Monofilaments with molecular orientation cannot be obtained. When the liquid bath is water, it is difficult to control the temperature at 95 ° C. or higher. The first stage stretching ratio is preferably 3 times or more. If the stretching ratio is less than 3 times, it is difficult to fix the stretching point, and uneven stretching occurs, making it difficult to perform sufficient stretching.

In the case of stretching in multiple stages, a temperature of 60 to 95 ° C.
After performing the first-stage stretching at a magnification of 3 to 6 times in the above liquid, the second and subsequent stages are performed in a liquid or gas at a temperature of 100 to 250 ° C., and the total stretching ratio becomes 6.5 times or more. It is preferred that the film is stretched as follows. When the second and subsequent stretching steps are performed in a liquid, the same liquid bath as in the first stretching step can be used. If the stretching temperature after the second stage is lower than 100 ° C, the heating to the monofilament will be insufficient and the stretchability will deteriorate, and if it exceeds 250 ° C, the monofilament will melt or undergo thermal decomposition, resulting in good yarn quality. It is not preferable because a monofilament having high performance cannot be obtained and the operability is liable to deteriorate. If the total draw ratio is less than 6.5 times, it tends to be difficult to obtain a monofilament having excellent yarn quality performance. In addition, it is preferable that the stretching ratio of the second and subsequent stages is set higher than the first stage stretching ratio.

The stretching from the second stage onward can be performed in a gas. Usually, it is performed in air, but it is also preferable to perform it in an inert gas such as nitrogen gas because thermal degradation of the monofilament can be suppressed. Further, when performing the stretching of the second stage or later in a gas, it is preferable that the stretching is performed in a state where the moisture attached to the monofilament surface is 1% or less,
When the monofilament is stretched by adhering water exceeding 1%, the obtained monofilament tends to have poor yarn properties as a result of uneven drawing or roughening of the monofilament surface.

If necessary, relaxation heat treatment may be performed after stretching by using an oven heater or the like.

Each physical property value in the present invention is obtained by the following method. (1) This is a value calculated by performing GPC measurement with a chloroform solution having a number average molecular weight of 0.4% by weight and converting to standard polystyrene. (2) Melting point (Tm) and glass transition temperature (Tg) These values were obtained by DSC measurement at a heating rate of 20 ° C / min. (3) MFR temperature was measured at 210 ° C under a load of 2.16 kgf.

[0023]

According to the present invention, unstretched monofilaments having an appropriate degree of crystallinity can be obtained by melt spinning polylactic acid and cooling and solidifying the spun monofilaments under appropriate conditions. Therefore, the stretching is performed smoothly, and a monofilament having good yarn quality can be obtained.

[0024]

Next, the present invention will be described specifically with reference to examples. The tensile strength characteristics were measured according to JIS L1013. Example 1 A poly-L-lactic acid having a number average molecular weight of 95,000 and an L-form ratio of 4% was supplied to an extruder and melted under the conditions of a temperature of 205 ° C. and a melting time of 6 minutes, and a spinneret having two nozzles having a hole diameter of 1.4 mm and two nozzles. The spun yarn was cooled and solidified in a water bath at 40 ° C. for 3 seconds, and then crystallized in air at 35 ° C. for 60 seconds. Subsequently, stretched 3.8 times in a water bath at 90 ° C,
Subsequently, the film was stretched 2.1 times in an oven heater at 170 ° C., and then subjected to a 1% relaxation heat treatment in an oven heater at 180 ° C. to obtain a monofilament. Examples 2 to 8 Under the conditions shown in Table 1, monofilaments were produced in the same manner as in Example 1. Table 1 shows the physical properties of polylactic acid used in Examples 1 to 8, production conditions, and the yarn quality of the obtained monofilament.

[0025]

[Table 1] As is clear from Table 1, the monofilaments obtained in Examples 1 to 8 had good values in both strength and elongation. Comparative Examples 1 to 5 Under the conditions shown in Table 2, monofilaments were produced in the same manner as in Example 1. Table 2 shows the physical properties, production conditions, and yarn quality of the obtained monofilaments used in Comparative Examples 1 to 5.

[0026]

[Table 2] As is clear from Table 2, in Comparative Examples 1 to 5, monofilaments could not be stably manufactured.

[0027]

According to the present invention, monofilaments suitable for industrial materials such as fishing nets, laver nets, ropes and fishing lines can be stably produced from polylactic acid resins.
And, since the monofilament obtained in the present invention has biodegradability, it is decomposed in the sea or soil after use,
It is possible to prevent environmental degradation due to waste.

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Claims (4)

[Claims] When producing a biodegradable monofilament by melt-spinning a polylactic acid having a number average molecular weight of 70,000 or more, (Tm + 20) to (Tm + 50) ° C. [Tm is the melting point of the polylactic acid ( Melting and spinning at a temperature of (° C)) and within 10 minutes, and then in a liquid bath of (Tg-50) to (Tg + 20) ° C [Tg is the glass transition temperature of polylactic acid (° C)]. A method for producing a biodegradable monofilament, comprising performing solidification by cooling for 2 to 5 seconds and stretching. 2. A multi-stage stretching of two or more stages in a stretching step,
2. The method for producing a biodegradable monofilament according to claim 1, wherein the stretching in the second and subsequent stages is performed in a gas in a state where the water content of the monofilament surface is 1% or less. 3. The method for producing a biodegradable monofilament according to claim 1, wherein the polylactic acid is poly-L-lactic acid having an optical purity of 95.0 to 99.5%. 4. A polylactic acid having an MFR of 25 g / 10 min or less.
The method for producing a biodegradable monofilament according to any one of claims 1 to 3, which is -L-lactic acid.