JPS642685B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing polyester fibers having excellent thermal dimensional stability and chemical stability as well as high strength. Polyester high-strength yarn, typified by polyester tire cord, is an organic fiber with excellent balance in terms of physical properties, and has recently come to be widely used in large quantities as an industrial fiber. Furthermore, as raw material prices for organic fibers have risen markedly in recent years, raw material costs for polyester, particularly polyethylene terephthalate, have been increasing at a lower rate than for other organic fibers such as nylon 6, so they can maintain their price advantage in the future. It is predicted that this will further expand the demand for high-strength polyester yarn. However, it is also true that depending on the application, improvements in thermal dimensional stability, chemical stability, and adhesion to reinforced materials such as rubber are required. Naturally, in response to such demands, various improvements have been proposed, including polyester fibers with relatively low intrinsic viscosity (for example, JP-A-53-31852) and highly oriented undrawn yarns ( so-called
Polyester fibers produced by drawing polyester fibers (for example, USP. 4195052) or polyester fibers subjected to electron beam irradiation (Japanese Patent Application Laid-open No. 57070/1983) have been proposed. Regarding improvement of chemical stability, proposals have been made such as a method of reducing the amount of carboxyl groups in polyester (for example, JP-A-55-116816). Furthermore, in order to improve the adhesion to rubber, there is a method of treating the yarn with a chemically active treatment agent such as an epoxy or isocyanate type during the spinning and drawing process (for example, Japanese Patent Publication No. 47-49768), or using the above-mentioned treatment agent during dip treatment. (for example, JP-A-55-
116816) has been proposed. Although each proposal seems to have achieved some results in terms of individual requests for improvement, in the recent era of technological innovation, quality improvements in the form of so-called property trade-offs are insufficient. It is becoming increasingly difficult to provide customers with sufficient satisfaction. Considering the above-mentioned prior art in this background, firstly, in the method of reducing the intrinsic viscosity and improving the dimensional stability, when the fiber is used as a tire reinforcing material, for example, a cord is formed to improve the dimensional stability. It sacrifices strength and fatigue resistance. Also
The fibers obtained by the method of US Pat. No. 4,195,032 for drawing POY also sacrifice cord toughness for improved dimensional stability when used, for example, as tire reinforcement. Furthermore, the present inventors have already filed a patent application in 1986-119614.
As disclosed in Japanese Patent Application Laid-Open No. 58-23914, this fiber has a defect in that its chemical stability is inferior to that of conventional products. This is because there are many tie molecular chains near the surface, which have a high contribution to fiber strength, and this shows a particularly remarkable tendency for deterioration caused by amines or water in rubber. According to the method of improving dimensional stability by performing three-dimensional cross-linking by electron beam irradiation or using a cross-linking agent, the toughness and fatigue resistance of the yarn are sacrificed in order to improve dimensional stability. This is simply an improvement by so-called property trade-off, where one property is improved at the expense of another property. Furthermore, methods to reduce the amount of carboxyl groups in polyester in order to improve chemical stability and methods to improve the adhesive strength of polyester fibers have improved dimensional stability as reinforcing materials for heavy vehicles that require these properties. is insufficient, and the material has not been perfected to exhibit its characteristics. In view of these points, the present inventors have already published a patent application (Japanese Patent Application No. 56-194129) that has excellent thermal dimensional stability and chemical stability, which overcomes all of the above problems, and has high strength at the same time. Polyester fibers are disclosed. That is, a drawn yarn obtained by melt-spinning polyester containing polyethylene terephthalate as a main component, then cooling and solidifying it, and further drawing, which has the following properties: (i) an intrinsic viscosity of 0.8 or more; (ii) Diethylene glycol content based on terephthalic acid residues: 2.5 mol% or less (iii) Carboxyl group content: 30 equivalents/10 ⁶ g or less (iv) Average birefringence: 0.190 or more (v) Yarn strength: 8.5 g/d or more (vi) Single yarn The value obtained by dividing the birefringence difference between the surface and the center by the average birefringence value is 0.055 or less. Furthermore, when the drawn yarn is heat-treated at 240°C for 1 minute at a constant length, it exhibits the following characteristics. It is a polyester fiber that has excellent thermal dimensional stability and chemical stability as well as high strength. (a) Dry heat shrinkage rate 3.0% or less when free heat treated at 175℃ for 30 minutes (b) Sample length 10 inches, strain rate 0.5 inches/min, temperature
The work loss obtained by measuring the hysteresis loop at a stress between 0.6 g/d and 0.05 g/d at 150° C. is less than 2.0×10 ^-5 inch-lb/denier. As a result of intensive research on industrially useful manufacturing methods, especially spinning and drawing methods, we have developed highly oriented undrawn yarn (so-called POY) that has been cooled by relatively high-temperature cooling air and spin-draws it in two drawing zones. Stretched by method,
At that time, high-temperature heated steam is used in the first stretching zone, and a contact heating device such as a heating roll or heating plate is used in the second stretching zone, which is both economical and highly efficient in stretching operation. Established a method for producing polyester fiber. The characteristics of drawn fibers made from so-called POY, such as polyester and nylon, which exhibit an amorphous state at the solidification point during melt spinning, are low shrinkage and high modulus.However, when POY is drawn by the spin-draw method, the drawing speed is low. must be extremely high. As a result, the drawing operability is significantly reduced, and it is difficult to draw POY using the spin draw method.
As a result, from an economic standpoint, it is difficult to say that this is an excellent method. Therefore, for example, Japanese Patent Application Laid-Open No. 53-58031 only discloses a method in which a second stage of stretching is performed off-line after the first stage of stretching; It's hardly touched. Similarly, the fiber described in Japanese Patent Application No. 194129/1980 requires high-speed drawing during its production, and the conventional spin-draw method is not fully satisfactory from an industrial standpoint. Nakatsuta. For example, if two-stage stretching zones are provided and each stretching is performed using a contact heating device such as a heating roll, the operability will be extremely poor as seen in Comparative Example D in the Examples below, and the one-stage stretching zone will When heating steam stretching is carried out using only the above-mentioned materials, the consumption of heating steam becomes extremely large, as seen in Comparative Example E in the Examples described later, and both of these results cannot be said to be satisfactory from an industrial standpoint. Ta. In view of these points, the inventors of the present invention have overcome all of these problems and have excellent economic efficiency, as well as excellent thermal dimensional stability and chemical stability that can improve the operability of the drawing process, as well as high strength. We have now established a method for producing polyester fibers with The method of the present invention has an intrinsic viscosity (phenol/
Polyester (measured in a solvent of 6/4 tetrachloroethane at a temperature of 30°C, the same applies hereinafter) of 0.7 or more is melt-spun from a spinneret at a rate of 3.5 g/min or less per single hole, and then at a temperature of 50 to 80°C. The yarn tension at the solidification point is 1.5×10 ⁷ to 7.5×.
Pull out the yarn so that it is between 10 ^{and 7} dyne/ ^cm2 ,
Next, the stretching point fixing device using heated steam at a temperature of 400 to 650°C is passed between the first stress isolating device and the second stress isolating device, and the stretching ratio D (times) is determined by the following formula.
The first stage of stretching is performed within the range shown in (1), and 0.70Y≦D≦0.90Y...(1) [However, in formula (1), Y is the value shown in the following formula (2). be. Y=6.834×10 ⁻⁴ ×B ² −0.0874×B+4.816 (2) In formula (2), B represents the average birefringence of the spun yarn×10 ⁻³ . The average birefringence value is in the range 15×10 ⁻³ to 70×10 ⁻³ . ] Subsequently, stretching is performed between the second stress isolation device and the third stress isolation device at a temperature of 180°C or higher up to the melting point, and at a stretching ratio of 1.05 to 1.20, and then immediately or the fourth stress isolation device is applied. This is a method for producing polyester fibers having excellent thermal dimensional stability and chemical stability as well as high strength, which is characterized by relaxing the fibers using a separating device and then winding them up. Since the polyester in the present invention is mainly intended to be supplied as a high-strength fiber for industrial use, it is necessary that at least 95 mol% or more of the repeating structural unit is ethylene terephthalate and that the intrinsic viscosity of the polyester is 0.7 or more. . If the intrinsic viscosity is less than 0.7, high-strength polyester fibers cannot be obtained and are not suitable for use as industrial high-strength fibers. Next, when the polyester used in the present invention is spun from a spinneret, it is necessary to spin the polyester at a rate of 3.5 g/min or less per single hole. If the discharge rate exceeds 3.5 g/min, the difference in birefringence between the inner and outer layers of each filament of the spun yarn becomes large, and the effect of using high-temperature cooling air, which will be described later, is poor, and the birefringence of the resulting drawn yarn increases. is also a low value. As a result, low-shrinkage fibers with high strength for industrial use cannot be obtained, and therefore, when producing high-strength polyester fibers suitable as rubber reinforcing materials for automobile tires, etc., they are not suitable for the purpose of use as rubber reinforcing materials. It disappears. In the present invention, the polyester is extruded through the spinneret, and the polyester is extruded immediately or after the yarn has passed through the heat-insulating cylinder without using a so-called heating cylinder, and then the polyester is extruded using relatively high-temperature cooling air having a temperature of 50 to 80°C, preferably. is cooled to the yarn solidification point by high-temperature cooling air having a temperature of 60 to 80°C.
By doing so, the temperature difference between the inner and outer layers of the filament at the solidification point is significantly reduced, and as a result, the difference in the degree of molecular chain orientation of the spun yarn between the inner and outer layers of the filament is significantly reduced. For example, change the cooling air temperature from 20℃ to 50℃
By changing to , the birefringence difference between the center and surface of the single filament of the spun yarn is significantly reduced from 15% to 5%. In this case, if the cooling air temperature is lower than 35° C., the strength suitable for the purpose of the present invention cannot be obtained, and the operability will also deteriorate. Furthermore, when the temperature of the cooling air exceeds 80°C, utility costs increase and at the same time the distance from the nozzle to the solidification point becomes extremely long, resulting in poor operability and making it difficult to put it into practical use industrially. Furthermore, since the yarn tension at the solidification point determines the birefringence value of the spun yarn, the yarn tension at the solidification point is important in the present invention. After the yarn is solidified, the yarn tension increases monotonically mainly due to the tension caused by air friction.
Since it has nothing to do with the orientation of the molecular chains of the yarn, controlling the tension at the solidification point is a technical point when the birefringence of the spun yarn is important as in the present invention. The main factors that determine the solidification point tension are the single hole discharge rate, the distance from the nozzle to the point where the cooling air hits the yarn, and the spinning speed, so various spinning conditions must be adjusted to provide the necessary solidification point tension. Conceivable. In the present invention, from 1.5×10 ⁷ dyne/cm ² to 7.5×
¹⁰⁷ dyne/ ^cm2 , preferably between 2.0× ¹⁰⁷ dyne/ ^cm2 and 6.5×
Make it between 10 ⁷ dynecm ² . The value of solidification point tension 1.5×10 ⁷ to 7.5×10 ⁷ dyne/cm ² is
This corresponds to a birefringence value of 15×10 ⁻³ to 70×10 ⁻³ of the spun yarn. In such cases, the yarn tension at the solidification point is set to 1.5.
If it is less than ×10 ⁷ dyne/cm ² , it will not be possible to obtain a polyester fiber having low shrinkage, which is the most important effect of the present invention. Furthermore, if the yarn tension at the solidification point exceeds 7.5×10 ⁷ dyne/cm ² , it is recognized that the spun yarn has already been crystallized (determined by wide-angle X-ray diffraction); has extremely high birefringence within the filament, resulting in a polyester fiber with low fiber strength after stretching. In order to obtain a high-strength yarn with excellent thermal dimensional stability and chemical stability, it is necessary to provide a two-stage drawing zone and draw it by a spin draw method. It is possible to reduce the production cost and obtain high-quality fibers with excellent economic efficiency. As a result of extensive research into such two-stage stretching, the present inventors found that the first-stage stretching was carried out at a temperature of 400 to 650.
It is most preferable to carry out the stretching at a stretching ratio shown by the formula (1) using heated steam at ℃, and furthermore, the second stage stretching is carried out at a temperature of 180°C or higher up to the melting point and at a stretching ratio of 1.05 to 1.20. I discovered that. The spun yarn is drawn at a temperature of 400 to 650 in the first stage.
Heated with steam at ℃. The temperature of the heated steam at this time is important in obtaining high-strength yarn;
If the temperature is below .degree. C., the amount of steam used will increase to achieve sufficient stretching, and if the temperature is extremely low, it will no longer be possible to stretch to the first-stage stretching ratio required by the present invention. In addition, the heating steam temperature is 650
If the temperature exceeds .degree. C., the yarn will melt, making it impossible to achieve the object of the present invention.
Here, the previous formula (1) shows the optimal range of the first stage stretching ratio.
Several kinds of spun yarns (POY) with birefringence in the range of 15 × 10 ^-3 to 75 × 10 ^-3 were supplied at a speed of 100 m/min, and the surface temperature of the supply roller was set to [90 + (IV - 0.6) × 4.5 -
POY×280〕-5℃ (However, IV is the intrinsic viscosity,
POY represents the average birefringence of POY. ), hot plate temperature 230℃, take-up roller temperature
Stretching is carried out using a stretching machine set at 140°C, and the break stretch ratio is measured by increasing the rotation of the take-up roller. From the thus determined break stretch ratio Y and the birefringence value of the spun yarn, the secondary It was obtained by performing regression analysis and deriving equation (2), using equation (2) as a guide. When such a stretching distribution is applied, the amount of heated steam used per weight of the fiber product is minimized in the first stage stretching, and operability is improved. Next, second-stage stretching is performed, and the stretching temperature in this case is 180°C or higher to the melting point, preferably 200°C to the melting point.
It is necessary that the temperature be in the range of 240°C; if this temperature is less than 180°C, stretching becomes impossible and yarn breakage occurs frequently. Furthermore, if this temperature exceeds the melting point, the threads will be fused and cannot be drawn. Furthermore, the stretching ratio in the second stage stretching is 1.05~
It is necessary to carry out the stretching within a range of 1.20, and in this case, if the stretching ratio is less than 1.05, sufficient strength will not be obtained, and therefore a high-strength yarn will not be obtained. Furthermore, if the stretching ratio exceeds 1.20 times, the maximum stretching ratio will be exceeded and yarn breakage will occur frequently. In addition, it is preferable that the take-off speed after stretching is 5500 m/min or less, and if the take-off speed exceeds 5500 m/min, the stretching speed becomes too high, and as a result,
The drawn yarn breaks frequently, making operation difficult. Next, the present invention will be explained based on examples. Example 1 Polyethylene terephthalate having an intrinsic viscosity of 1.0, a diethylene glycol content of 1.0 mol%, and a carboxyl group content of 10 equivalents/10 ⁶ g was spun and drawn under the conditions shown in Table 1. A, B, and C show the experimental results of the present invention, and D, E, F, and G show the experimental results of the comparative example. All of A, B, and C are effective methods from an industrial standpoint, whereas Comparative Example D, in which heated rolls were used for the first drawing and no heated steam was used, caused the drawn yarn to break. The production rate was extremely high, making it difficult to carry out industrial production. Comparative Example E is a case in which heated steam is used for the first-stage stretching and no second-stage stretching is performed, but in this case, the amount of heated steam used is extremely large, and the utility cost is extremely high, making industrial production difficult. That's not the right way to do it. Furthermore, the single hole discharge rate during spinning exceeds 3.5 g/min, and the final winding speed is 5500 m/min.
In Comparative Example F, in which the drawing speed exceeded 10 minutes, the drawing speed was too high, and therefore the drawing yarn breakage rate was extremely high, which had a negative effect on the operability. In order to make the final winding speed 5500 m/min or less, the birefringence value of the spun yarn sent to the first godet roller must be set to a high value while keeping the spinning speed as low as possible. Therefore, the intrinsic viscosity of the discharged polymer is 0.7 or more, and the discharge temperature is 280 to 325.
℃, the discharge amount per single hole must be 3.5 g/min or less. Comparative Example G shows the results obtained by the usual spin-draw method, and in this case, the tension at the solidification point is low, and the resulting yarn has a high dry heat shrinkage rate.

【table】

[Table] Example 2 In Example 1, A and C (fibers according to the present invention) obtained under the conditions shown in Table 1 and G (normal high-strength polyester fiber as a comparative example) were used as a tire cord. I compared the characteristics. Each fiber is made into a double thread cord with a twist count of 40 x 40 (T/10 cm), and each cord is deep-treated with a resorcinol-formalin-latex treatment solution containing Vulcabond E (formerly known as Pexcel; a product of ICI) (processing temperature
240℃). The dip cord characteristics of the three types of cords thus obtained were compared. The results are shown in Table-2.

【table】

[Table] As is clear from Table 2, the fibers obtained by the method of the present invention have the same strength and chemical stability as the high-strength polyester fibers produced by the prior art, and have significantly improved thermal dimensional stability. It can be seen that there has been a significant improvement. Through these experiments, it was recognized that the present invention has great significance in that such useful fibers can be produced at a relatively low cost. Example 3 Polyethylene terephthalate having an intrinsic viscosity of 1.0, a diethylene glycol content of 1.0 mol %, and a carboxyl group content of 10 equivalents/10 ⁶ g was spun and drawn under the conditions shown in Table 3. The experimental results under each condition are shown in H to M in Table 3. H is an example in which the single-hole discharge rate exceeds 3.5 g/min. In this case, the birefringence difference between the filament surface and center of the spun yarn becomes large, and the high-temperature quenching wind (active high-temperature cooling wind) The effect is low, resulting in a low birefringence value of the drawn yarn and therefore low shrinkage polyester fibers with high strength cannot be obtained. J is when the solidification point tension is slightly lower than 1.5×10 ⁷ dyne/cm ² , I is when the solidification point tension is extremely lower than 1.5×10 ⁷ dyne/cm ² , and both have a large dry heat shrinkage rate. Therefore, low shrinkage polyester fibers cannot be obtained. K is an example in which the solidification point tension exceeds 7.5×10 ⁷ dyne/cm ² , and in this case, the spun yarn is already crystallized according to wide-angle X-ray diffraction measurements, and the The birefringence within the filament of the yarn has become extremely large, resulting in frequent breakage of the drawn yarn.
The strength after stretching is extremely low. L is an example when the quench air temperature is 50°C, M is an example when the quench air temperature is 30°C, and L, which satisfies the method of the present invention, has a slightly higher yarn breakage rate,
On the other hand, it can be seen that in the case of M, the strength is low and the yarn breakage rate is extremely high, which does not achieve the purpose of the present invention.

【table】

【table】

Claims (1)

[Claims] 1. A polyester whose main repeating unit is ethylene terephthalate and which has an intrinsic viscosity of 0.7 or more (measured in a phenol/tetrachloroethane 6/4 solvent at a temperature of 30°C) is discharged per single hole from a spinneret. Melt-spun at a rate of 3.5g/min or less, then at a temperature of 50~
The yarn was cooled with cooling air at 80°C and pulled out so that the yarn tension at the solidification point was between 1.5×10 ⁷ and 7.5×10 ⁷ dyne/cm ² .
The first stage of stretching is performed by passing through a stretching point fixing device using heated steam at a temperature of 400 to 650°C between the stress isolation device and the stretching ratio D (times) within the range shown by the following formula (1). 0.70Y≦D≦0.90Y...(1) [However, in formula (1), Y is the value shown by the following formula (2). Y=6.834×10 ⁻⁴ ×B ² −0.0874×B+4.816 (2) Formula (2) B indicates the average birefringence of the spun yarn×10 ³ . The average birefringence value is in the range 15×10 ⁻³ to 70×10 ⁻³ . ]Subsequently, the second stress isolation device and the third
It is stretched between stress isolation devices at a temperature of 180°C or higher up to the melting point and at a stretching ratio of 1.05 to 1.20, and then immediately or after relaxing using the fourth stress isolation device, it is rolled up. A method for producing a polyester fiber having excellent thermal dimensional stability and chemical stability as well as high strength.