JP2003096616A - Method for producing thermoplastic synthetic fiber improved in mechanical property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method causing little load of a thermoplastic synthetic fiber on the environment by which mechanical properties, particularly strength of the synthetic fiber is improved. SOLUTION: This method for producing the thermoplastic synthetic fiber comprises adding 0.3-6 wt.% carbon dioxide or nitrogen to a crystalline thermoplastic resin having >=5,000 poise melting viscosity at 290 deg.C and 20 sec<-1> and melting and mixing the resin with carbon dioxide or nitrogen and discharging the mixture under conditions satisfying the formula dP/dt>=5,000 [wherein dP/dt is a pressure release rate (kg/cm<2> .sec)] from a spinneret hole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoplastic synthetic fiber, and more particularly to a method for producing a thermoplastic synthetic fiber having improved mechanical properties, particularly strength, which has a low environmental load.

[0002]

Polyester terephthalate and other polyester fibers have well-balanced characteristics in strength, elastic modulus and dimensional stability and can be manufactured at a relatively low cost, so that they can be used not only for clothing but also for industrial applications. Widely used.

When polyester fibers are used for industrial applications, the most important characteristic is generally mechanical properties, for example, high strength, and further improvement of mechanical properties for expanding the industrial application of polyester fibers. The demand for is increasing.

A typical method for producing high-strength polyester fibers is "Handbook of Fibers" p.107 (edited by The Textile Society of Japan, Maruzen (1994)).
The method of obtaining a low orientation raw yarn with high [η] polyethylene terephthalate and subjecting it to high-strength drawing and high-temperature setting has been adopted for a long time, and an increase in [η], that is, a molecular weight is effective for increasing strength. Is generally known.

However, in melt spinning which is industrially adopted in polyester, a high molecular weight polymer has a high melt viscosity, requires a large apparatus, and has poor spinnability, resulting in spun yarn breakage, resulting in stable spinning. However, there is a problem in that yarn breakage occurs when the draw ratio is further increased.

As a method for solving this problem, a technique is known in which a plasticizer is added to high molecular weight polyester to reduce the melt viscosity (Japanese Patent Laid-Open No. 5-247436, etc.). For example, in Japanese Patent No. 3161546, by adding at least one compound selected from a biphenyl compound, a naphthalene compound, a phenyl ether compound or a mixture thereof, (1) reduction of melt viscosity-improvement of processability (2) Adoption of low spinning temperature-suppression of thermal decomposition during melting is described as an advantage. It seems that this technology can achieve high strength, but when additives are used, depending on the type, environmental pollution in the spinning process due to volatilization, equipment contamination due to bleed-out, and a large amount of components remaining in the fiber may occur. For example, there is concern about the impact on users, and also about the environmental destruction at the time of disposal. Furthermore, since the additive is basically different from polyester, it causes deterioration of the spinnability and process stability due to the precipitation of the additive during long-term operation, and the quality of the obtained product may be poor. Is also expected to have an adverse effect.

On the other hand, it has been attracting attention in recent years that a plasticizing effect is exhibited by adding carbon dioxide or the like to a polymer melt. For example T. Hobbs, AJLesser, polymer, 41,
Polyethylene terephthalate fiber is used in 6223 (2000).
C., a technique for obtaining 1.1 GPa high-strength fiber by stretching in liquid carbon dioxide and then again under dry heat of 200 ° C. is disclosed. Improvements are mentioned. However, this technique uses carbon dioxide at the time of drawing and requires pressurizing conditions, so continuous treatment of yarns is not suitable for industrialization because the equipment becomes bulky.

On the other hand, many techniques for adding carbon dioxide or the like to a molten polymer like an ordinary plasticizer are found in the field of foam molding of polyolefins, but the addition of polyester or polyamide in melt spinning is slightly special. It can only be found in Kaihei 11-172528. However, the publication does not mention the foaming behavior after discharge, which is the most problematic when adding carbon dioxide, but if the control of the foaming behavior is insufficient, the die stain becomes severe and the yarn breakage frequently occurs. There are challenges. Further, regarding the amount of addition, it is only described that "absorption and / or adsorption amount is sufficient if the amount is 0.2% by weight or more." No technical suggestions are given. Furthermore, the technique described in this publication has only the effect of reducing the viscosity and the effect of improving the elongation in high-speed spinning, and does not give any suggestion to the effect of improving the mechanical properties of the obtained fiber.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of the prior art and to provide a process for producing a thermoplastic synthetic fiber having improved mechanical properties, particularly strength, which has a low environmental load. Especially.

[0010]

Means for Solving the Problems The inventors of the present invention have made extensive studies on the addition / mixing technology and the foaming control technology in the melt spinning of carbon dioxide and nitrogen, and the improvement of the mechanical properties of the obtained fiber. Among them, the inventors have found that the drawbacks of the prior art can be solved by satisfying certain conditions such as the melt viscosity of the polymer, the addition amount of carbon dioxide or nitrogen, and the pressure release rate at the time of discharge, and the present invention has been accomplished.

That is, according to the present invention, 0.3 to 6% by weight of carbon dioxide or nitrogen is added to a crystalline thermoplastic resin having a melt viscosity of 5,000 poise or more at 290 ° C. and 20 sec ^-1 and melt-mixed. Disclosed is a method for producing a thermoplastic synthetic fiber, which comprises discharging under the conditions that satisfy the formula.

[0012]

[Equation 2]

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The requirement of the present invention is to add 0.3 to 6% by weight of carbon dioxide or nitrogen to a crystalline thermoplastic resin having a melt viscosity of 5,000 poise or more at 290 ° C. and 20 sec ⁻¹ and melt-mix it. It is to discharge from the mouth hole under the condition that the following formula is satisfied.

[0014]

[Equation 3] By carrying out melt spinning under such conditions, it is possible to produce a thermoplastic synthetic fiber having improved mechanical properties, particularly strength, with a small load on the environment. The reason for this is not fully clear, but will be described in detail below.

What is necessary to obtain a high strength fiber is to sufficiently stretch the molecular chain after spinning a high molecular weight crystalline thermoplastic resin, and it is effective to add a plasticizer to enhance the stretchability. Is a technique. Furthermore, the use of gases existing in the atmosphere, such as nitrogen and carbon dioxide, is very important in terms of reducing the load on the environment. However, it has been found that when a substance that is a gas at normal temperature and pressure, such as nitrogen and carbon dioxide, is added and mixed into the melt, there is a problem of foaming immediately after spinning, which makes it impossible to produce a yarn.

Therefore, the inventors of the present invention have conducted an analysis on the foaming behavior and found that the spunability is significantly reduced when the foam diameter itself is larger than when the number of bubbles generated by foaming is large. Therefore, as a result of studying a technique for reducing the foam diameter and a technique for suppressing foaming as the limit thereof, it was found that the problems mentioned above can be solved by increasing the pressure release rate and increasing the melt viscosity of the resin. .

Further, the stretchability of the fiber obtained by making the foam diameter as small as possible was greatly improved, and the improvement range of the mechanical properties was also large. The reason for this is not clear, but the dispersibility of nitrogen and carbon dioxide in the melt is improved,
It is presumed that the plasticizing effect was increased.

Thus, after adding nitrogen gas or carbon dioxide to the crystalline thermoplastic resin having a sufficiently large melt viscosity,
By extruding at a discharge linear velocity satisfying a specific condition, it is possible to obtain a fiber whose foaming is suppressed and whose mechanical properties are improved.

The crystalline thermoplastic resin as referred to in the present invention is not particularly limited, but it is preferable to use polyester or polyamide from the viewpoint of physical properties of fibers and production cost,
More preferably polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate,
Polyethylene naphthalate, polyhexamethylene adipamide or polycapramide, most preferably polyethylene terephthalate. Further, the crystalline thermoplastic resin in the present invention may be copolymerized with other components within a range not impairing the gist of the invention, and further, a matting agent, a flame retardant,
A small amount of additives such as a lubricant may be included.

The molecular weight of the crystalline thermoplastic resin used in the present invention is not particularly limited, but it is desirable that the molecular weight is sufficiently large in order to enhance the mechanical properties of the obtained fiber and to suppress foaming. A resin having a melt viscosity of 5,000 poise or higher at 290 ° C. and 20 sec ⁻¹ is used. It is preferable that the molecular weight, that is, the melt viscosity is high,
If it is too high, spinning and drawability will be poor.
It is preferable that the poise is not more than that.

Nitrogen or carbon dioxide is selected as the substance added to the crystalline thermoplastic resin in the present invention because it does not react with the polymer serving as the substrate and has a low environmental load. It is possible to use any of these or two at the same time, but it is preferable to use carbon dioxide from the viewpoint of the effect.

The method of adding nitrogen or carbon dioxide to the resin is not particularly limited, and for example, nitrogen or carbon dioxide gas is introduced under pressure into the bunker of the polymer chip before melting, or the molten polymer is melted. A known method such as injecting nitrogen or carbon dioxide (regardless of gas or liquid) into the substrate is adopted. However, the method of injecting nitrogen or carbon dioxide into the polymer melted by the extruder is preferable from the viewpoint that the apparatus is not modified so much.

The amount of nitrogen or carbon dioxide added is 0.3 to 6
% By weight. If the amount added is smaller than this, the effect is not seen, and if the amount added is larger, foaming becomes more severe and the spinnability deteriorates.
The preferred addition amount is 1 to 4% by weight for carbon dioxide and 0.5 to 1% by weight for nitrogen. The addition amount in the present invention is a value obtained by the method described in the examples.

Pressure release rate (dP / dt) in the present invention
Is over 5000. When it is less than 5,000, foaming is suppressed, but large bubbles are partially generated to deteriorate the spinnability, and the plasticizing effect of nitrogen or carbon dioxide is also reduced. The pressure release rate is a value defined by the following equation, and is the rate of decrease of the die back pressure when the molten resin is discharged.

[0025]

[Equation 4] Here, in the present invention, the discharge linear velocity (v ₀ ) in the formula is calculated from the volume discharge amount and the mouth hole spec. Also △ P / l
Is calculated from the following formula using two types of spinning packs having different die hole lengths (long die and short die) and the difference in pack internal pressure at the start of discharge.

[0026]

[Equation 5] The means for fiberizing the discharged resin is not particularly limited, and the atmosphere control around the mouthpiece by the heating cylinder or the heat retention cylinder, the cooling by the fluid such as rectified air, the addition of the finishing agent are arbitrary. . However, from the viewpoint of suppressing foaming, it is desirable that the resin after discharge be cooled promptly. The cooling rate in the melt-spinning step varies depending on the yarn speed on the spinning line, and is not particularly specified as a cooling rate, but a cooling rate at which solidification is completed within 2 seconds after discharging is preferable. .

As for the take-back method, it can be taken by any method such as a roller or an air aspirator.
The spinning speed is also not particularly limited, but the spinning speed is preferably 3000 m / min or less in order to enhance the mechanical properties of the fiber.

The drawing may be carried out by a two-step method or may be carried out by direct spinning. However, in order to reduce the production cost and prevent the spun fiber from changing over time, it is taken up and then wound up. It is preferable to continuously perform stretching and heat treatment without performing the heat treatment.

The thermoplastic synthetic fibers obtained by the production method of the present invention can be used in various forms such as short fibers, long fibers and nonwoven fabrics. Further, from the viewpoint of improving mechanical properties, it can be suitably used for applications such as rubber reinforcing materials, construction civil engineering, medical hygiene, and environmental safety.

[0030]

EXAMPLES The present invention will be described specifically and in more detail with reference to the following examples. However, the present invention is not limited to the following examples. The physical property values in the examples were measured by the following methods.

A. 290 ° C., was measured at a shear rate range near 20sec ^-1 using a melt viscosity Toyo Seiki Capillograph type 1 at 20sec ^-1, was determined melt viscosity of 20sec ^-1 by approximation.

B. Amount of Nitrogen or Carbon Dioxide The amount of nitrogen or carbon dioxide discharged was measured using a Coriolis flowmeter Micro Motion Elite type manufactured by Fisher-Rosemount. The amount of resin discharged is obtained by discharging the resin added with nitrogen or carbon dioxide, receiving it in a water tank, quenching it, and air-drying it for 24 hours in the atmosphere. From the above, the amount added to the resin was calculated using the following formula.

[0033]

[Equation 6] C. Pressure release speed Die with hole diameter of 0.35mm, hole length of 20mm (long die) and
It was measured by the method described in the text using two types of caps of 0.7 mm (short die).

D. Strength / Elongation Using a Tensilon tensile tester manufactured by Orientec, the initial sample length was 200 mm and the tensile speed was 200 mm / min.

Examples 1 to 4 and Comparative Example 1 Polyethylene terephthalate having a melt viscosity of 10,000 poise at 290 ° C. and 20 sec ⁻¹ was melted with a twin-screw extruder, and carbon dioxide was added from an injection port provided in the middle of the cylinder. Adjusting the metering pump speed and spinning temperature 295
℃, resin discharge rate 57.1g / min, hole diameter 0.35mm, hole length 0.7mm,
After discharging from a 48-hole mouthpiece, the rectified wind speed is 30 m / mi
Cooled with n air flow. The amount of carbon dioxide added is 0 (Comparative Example 1), 0.5 (Example 1), 2 (Example 2), 4 (Example 3), 6
(Example 4) Weight% was used. This is taken up at a speed of 1000 m / min using a roller at room temperature, and continuously 90 ° C, 140 ° C,
Two-stage drawing and heat treatment were performed using a 220 ° C. heating roller. The total draw ratio was adjusted so that the elongation of the drawn fiber would be about 12%. Table 1 shows the pressure release rate and the total draw ratio under each condition. It can be seen that the total draw ratio is improved with an increase in the amount of carbon dioxide added, and the drawability is improved.

The physical properties of the fiber thus obtained are also shown in Table 1. As can be seen from Table 1, the addition amount is 0% by weight (Comparative Example 1).
It can be seen that the addition of carbon dioxide increases the total draw ratio, and the strength increases accordingly.
However, with the addition amount of 6% by weight, a slight fluff was observed in the rolled up package, so if the addition amount is larger than this, the spinnability may deteriorate.

[0037]

[Table 1] Example 5 Polyethylene terephthalate having a melt viscosity of 24000 poise at 290 ° C. and 20 sec ⁻¹ was melted by a twin-screw extruder, carbon dioxide was added from an injection port provided in the middle of the cylinder, and the number of revolutions of the metering pump and carbon dioxide discharge. By adjusting the amounts, the resin discharge amount was 43.2 g / min and the carbon dioxide addition amount was 4% by weight. This has a hole diameter of 0.35 mm and a hole length of 0.
After discharging from a 7 mm, 48 hole mouthpiece, rectified wind speed 3
Cool with 0m / min air flow, 500m with room temperature roller
It was collected at a speed of / min. Table 2 shows the pressure release rate under these conditions. This was subjected to two-stage drawing and heat treatment at a drawing speed of 300 m / min using heating rollers of 80 ° C, 130 ° C and 220 ° C. The total draw ratio was 5.18 times when the elongation of the fiber after drawing was adjusted to about 12%, and a high strength fiber having a strength of 10.6 cN / dtex was obtained (Table 2).

Example 6 Polyethylene terephthalate having a melt viscosity of 5100 poise at 290 ° C. and 20 sec ⁻¹ was melted with a twin-screw extruder, and nitrogen was added from an injection port provided in the middle of the cylinder.
The resin discharge rate is 89.0 g / min and the nitrogen addition rate is 0.4 wt% by adjusting the metering pump rotation speed and nitrogen discharge rate.
And The pressure release rate is shown in Table 2. This has a hole diameter of 0.35 m
m, hole length 0.7 mm, after discharging from a mouthpiece with 48 holes, cooled with a rectified airflow of 30 m / min of wind speed, drawn at a speed of 3000 m / min using a room temperature roller, and continuously 90 ° C, 1
Two-stage drawing and heat treatment were performed using a heating roller at 40 ° C and 220 ° C. The total draw ratio is about 12 for the fiber after drawing.
When adjusted to be%, it becomes 2.89 times, strength 8.0 cN /
Fibers with improved dtex mechanical properties were obtained (Table 2).

[0039]

[Table 2]

[0040]

INDUSTRIAL APPLICABILITY The thermoplastic synthetic fiber obtained by the production method of the present invention has improved mechanical properties as compared with the fiber obtained by the conventional method and can be suitably used for various purposes. Furthermore, by improving the mechanical properties, stable manufacturing is possible with few process abnormalities such as single yarn breakage during yarn manufacturing. In addition, since nitrogen or carbon dioxide is used, the environmental load of substances discharged in the manufacturing process is reduced.

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Claims (4)

[Claims] 1. Melt viscosity at 290 ° C. and 20 sec ⁻¹ is 5000 poise.
Carbon dioxide or nitrogen is added to the above crystalline thermoplastic resin.
A method for producing a thermoplastic synthetic fiber, which comprises adding 3 to 6% by weight, melt-mixing, and then discharging from a mouth hole under conditions satisfying the following formula. [Equation 1] 2. The method for producing a thermoplastic synthetic fiber according to claim 1, wherein the crystalline thermoplastic resin is polyester. 3. The method for producing a thermoplastic synthetic fiber according to claim 1, wherein the discharged resin is collected at a speed of 3000 m / min or less. 4. The method for producing a thermoplastic synthetic fiber according to claim 3, wherein after the fiber is taken up, it is continuously drawn and heat treated without being once wound.