JPH04352811A - Polyethylene naphthalate fiber and its production - Google Patents

Abstract

PURPOSE:To obtain polyethylene naphthalate fiber, having a high strength and high elastic modulus, excellent in thermal stability and creep resistance and useful for reinforcing industrial materials. CONSTITUTION:Polyethylene-2,6-naphthalate fiber, having a high strength (>=10g/de), a high elastic modulus (>=250g/de) and exhibiting thermal stability indicated by a low heat shrinkage factor (<=6% at 180 deg.C) and a low creep ratio (<=4% at 120 deg.C under 4g/de load after 15hr). As for the microstructure, the birefringence ratio is >=0.34 and the crystal melting point is >=280 deg.C. Furthermore, the density is <=1.370g/cm<3>.

Description

Description [0001] [Industrial Application Field] The present invention relates to a polyethylene naphthalate fiber having high strength and excellent thermal stability and creep resistance, and a method for producing the same, particularly for use in tire cords and belts. The present invention relates to fibers suitable for reinforcing fibers used in industrial materials such as wood, and methods for producing the same. [Prior Art] Polyethylene naphthalate (hereinafter referred to as PEN)
PEN fibers (sometimes abbreviated as Proposals have been made to use the fibers as fibers for industrial materials such as tire cords. PEN
Due to the rigidity of its molecular chains, it has a high melt viscosity and a high secondary transition point of 113°C. No particular attention was paid to other properties such as thermal stability and creep resistance. For example, in Japanese Patent Publication No. 55-1371,
By using specific stretching conditions, up to 10.3g/de
Although high strength has been achieved, the boiling water shrinkage value is 2.
It's only 3%. This boiling water shrinkage value is estimated to be about 8 to 10% when converted to a dry heat shrinkage rate at 180℃, and although it has good thermal stability compared to polyethylene terephthalate yarn, it is still
It is difficult to say that the performance of EN fibers is fully exhibited. On the other hand, an example of improved thermal stability is described where the boiling water shrinkage is 0.8% (estimated to be 4% or less at 180°C dry heat shrinkage), but the strength level is 9. 3 g/de, and considering the rigidity of the molecular chains of PEN, it cannot be said that the performance of PEN is fully demonstrated. [0004] Furthermore, JP-A-62-156312 proposes that the dry heat shrinkage rate at 180° C. be suppressed to 3% or less by increasing the spinning speed to 1,500 m/min or more. , its maximum strength remains at a low level of 8.8 g/de. [0005] When fibers are used as tire cords, the temperature of the fibers is said to rise to a high temperature of about 120°C, but when repeated elongation and compressive loads are applied at such high temperatures, Fibers elongate and deteriorate. Therefore, the creep property at elevated temperatures is an important property for fibers for industrial materials. However, P
Currently, in the literature regarding EN fibers or their manufacturing methods, there are no proposals for improving creep properties. [0006] An object of the present invention is to provide a polyethylene naphthalate fiber having high strength, high modulus of elasticity, and excellent thermal stability and creep resistance, and a method for producing the same. It is an object of the present invention to provide the fiber suitable for reinforcing belt materials and a method for producing the same. [Means for Solving the Problems] The present invention provides ethylene-2
A fiber made of polyethylene naphthalate containing 90 mol% or more of ,6-naphthalate units and having an intrinsic viscosity of 0.65 or more, which has high strength and excellent thermal stability and satisfies the following properties. It is. (A) Strength≧10.0g/de (B) Elastic modulus≧250g/de (C) Δn≧0.34 (D) 180°C dry heat shrinkage rate≦6% (E) 120°C creep rate≦4% ( F) Crystal melting point ≧280°C % or less of a suitable third component. Generally polyethylene-2,6-naphthalate is naphthalene-2
, 6-dicarboxylic acid or a functional derivative thereof with ethylene glycol under appropriate reaction conditions in the presence of a catalyst. At this time, an appropriate 1
If a seed or two or more types of third components are added, a copolymerized polyester is synthesized. Suitable third components include (a) a compound having two ester-forming functional groups; for example, oxalic acid;
Aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dimer acid; Alicyclic dicarboxylic acids such as cyclopropanedicarboxylic acid, cyclobutanedicarboxylic acid, and hexahydroterephthalic acid; phthalic acid, isophthalic acid, and naphthalene-2,7 - Aromatic dicarboxylic acids such as dicarboxylic acid and diphenyl dicarboxylic acid; Carboxylic acids such as diphenyl ether dicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, and sodium 3,5-dicarboxybenzenesulfonate; glycolic acid, p-oxy Oxycarboxylic acids such as benzoic acid and p-oxyethoxybenzoic acid; propylene glycol, trimethylene glycol, diethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentylene glycol, p-xylylene glycol, 1
, 4-cyclohexanedimethanol, bisphenol A
, p,p'-diphenoxysulfone-1,4-bis(β
-hydroxyethoxy)benzene, 2,2-bis(p-
oxy compounds such as β-hydroxyethoxyphenyl)propane, polyalkylene glycol, p-phenylenebis(dimethylcyclohexane); functional derivatives thereof; (b) Compounds having one ester-forming functional group, such as benzoic acid, benzyloxybenzoic acid, and methoxypolyalkylene glycol. Furthermore, (c) compounds having three or more ester-forming functional groups, such as glycerin, pentaerythritol, and trimethylolpropane, can also be used as long as the polymer is substantially linear. . Further, it goes without saying that the polyester may contain a matting agent such as titanium dioxide, and a stabilizer such as phosphoric acid, phosphorous acid, and their esters. [0011] The polyethylene naphthalate fiber of the present invention has an intrinsic viscosity of 0.65 or more, preferably 0.
．． 7 to 1.0. The intrinsic viscosity in the present invention is determined by dissolving the polymer or undrawn yarn in a mixed solvent of phenol and orthodichlorobenzene (volume ratio 6:4) at 35°C.
This is the value obtained from the viscosity measured in . Intrinsic viscosity is 0.6
If it is less than 5, high-strength, high-toughness yarn-like fibers cannot be obtained. Note that fibers with an intrinsic viscosity exceeding 1.0 tend to be defective in the spinning process, and are not desirable in practical terms. The PEN fiber of the present invention has high strength and high modulus, as well as excellent thermal stability and creep resistance, and is particularly suitable for reinforcing tire cords and belt materials. satisfies the following characteristics (a) to (g). (A) Strength≧10.0g/de (B) Elastic modulus≧250g/de (C) Δn≧0.34 (D) 180°C dry heat shrinkage rate≦6% (E) 120°C creep rate≦4% ( f) Crystal melting point≧280°C (g) Density≦1.370 g/cm3 [0013] If the strength is less than 10.0 g/de, the durability will be poor and undesirable. Strength is preferably 10.5g/de
That's all. Moreover, when the elastic modulus is less than 250 g/de,
In particular, when used as a belt material for radial tires, for example, the durability is poor. The elastic modulus is preferably 265 g/de or more. In order to exhibit such high strength and high elastic modulus, the birefringence, Δn, must be 0.3 from the viewpoint of the fiber microstructure.
Must be 4 or more. As an industrial material, high strength and high elastic modulus alone are not sufficient; thermal stability is also an essential characteristic. In particular, PEN fibers have excellent thermal stability, so if this property can be fully utilized, industrial materials far superior to conventional materials will be obtained. The dry heat shrinkage rate, which is commonly used as a measure of thermal stability, is the dimensional stability when the fiber is left at that temperature, and it is necessary that this dry heat shrinkage rate is 6% or less. If the dry heat shrinkage rate exceeds 6%, the thermal dimensional stability will be poor. Furthermore, when fibers are actually used as industrial materials, they are usually subjected to loads at elevated temperatures, and therefore resistance to elongation of the fibers under elevated temperatures and loads is important. . For this factor, 120℃,
It is suitable that the creep after 15 hours under a load of 4 g/de is 4% or less. If the creep after 15 hours at 120° C. under a load of 4 g/de exceeds 4%, the durability under a load at elevated temperatures will be poor. What must be noted here is that dry heat shrinkage and creep are usually antinomic, and if the dry heat shrinkage is low, the creep will be high. [0016] In order to achieve the above characteristics, a high degree of crystallinity is required also in terms of microstructure, and the melting point of the crystal needs to be 280°C or higher. The melting point of the crystal is 28
If it is below 0°C, the degree of crystal perfection is low, resulting in poor durability. However, if heat treatment is performed for a long time, such as for 5 minutes, in order to increase the degree of crystallinity, the degree of crystallinity will certainly improve, but since the fiber will deteriorate, the strength properties such as strength and elastic modulus will be affected. The creep characteristics at the bottom are decreasing. In the case of such long-term heat treatment, the fiber density increases, but it was also found that deterioration of strength properties and creep properties can be prevented if the fiber density is 1.370 g/cm3 or less. . [0017] Such PEN fibers are made of ethylene-2,
When melt-spinning and hot-drawing a polyethylene naphthalate resin containing 90 mol% or more of 6-naphthalate units and having an intrinsic viscosity of 0.7 or more, A heating cylinder with a temperature of 275 to 350°C is installed, (i) the spinning speed is 1,000 m/min or less and the spinning draft is 20 to 250, (g) the birefringence index of the undrawn yarn is 0.025 or less, (
c) The undrawn yarn is once wound up or directly supplied to the hot drawing process without being wound up, and the first stage drawing is performed at a draw ratio of 80% or more of the total drawing ratio, and then (c) the second drawing step is performed. Roller temperature 190~ for stretching after stage stretching
At least one stage of tension stretching is performed using a heated roller at 235°C, and (S) a fixed length or limited shrinkage of 0 to 3.0% is performed between a heated roller at a temperature of 225 to 250°C and a non-heated roller. After that, it is manufactured by winding it up. The manufacturing method of the present invention will be explained in detail below. When the polyethylene naphthalate fiber of the present invention is melt-spun from a polyethylene naphthalate resin having an intrinsic viscosity of 0.7 or more, preferably 0.8 to 1.0, after being discharged from a spinneret, the polyethylene naphthalate fiber is placed in a length of 20 to 50 cm in an atmosphere. Temperature is 275-3
It is passed through a heating tube at 50°C and cooled and solidified with cooling air. Next, after applying an oil agent, the spinning speed was increased to 1,000
The material is wound once at a spinning draft of 0 m/min or less, a spinning draft of 20 to 250, and a birefringence Δn at an unstretched stage of 0.025 or less, or directly fed to a hot stretching process without being wound. If the intrinsic viscosity of the polyethylene naphthalate resin is less than 0.7, fibers exhibiting high strength and high elastic modulus cannot be obtained. Furthermore, if the temperature of the heating tube under the nozzle is less than 275°C or the length of the heating tube is less than 20 cm, the polyethylene naphthalate resin will be viscous and the yarn will not be discharged smoothly. If yarn breakage occurs, or even if yarn breakage does not occur, fiber diameter unevenness occurs between yarns or in the yarn length direction, resulting in a decrease in yarn quality. On the other hand, if the temperature of the heating cylinder exceeds 380°C or the length of the heating cylinder exceeds 50cm, the tension of the yarn immediately after discharge is too low and the yarn sways greatly.
Spinning becomes unstable and yarn breakage is more likely to occur. Further, when the spinning speed exceeds 1,000 m/min, the Δn of the resulting undrawn yarn increases and the drawability decreases. The spinning speed is preferably 500 m/min or less. The spinning draft is defined as the ratio of the spinning take-up speed and the spinning discharge linear speed, and was determined by the following formula (1). Spinning draft = πD2 V/4W (1) (In the formula, D is the hole diameter of the spinneret, V is the spinning winding speed, and W is the volumetric output per single hole.) 250
If it exceeds Δn, not only will Δn increase, but the fiber diameter unevenness of the undrawn yarn will become large and the spinning condition will decrease, and even if the spinning condition does not decrease, the drawability will decrease. On the other hand, if the spinning draft is less than 20, the spun yarn will sway significantly and the spinning stability will be lacking. [0021] If Δn of the undrawn yarn exceeds 0.025, the drawability decreases and the high strength and high modulus fiber specified in the present invention cannot be obtained. It is preferable that Δn is 0.01 or less. The hole shape of the nozzle for discharging the yarn is not particularly limited, but the ratio of the introduction hole length (L) to the hole diameter (D), L/D
is 5 or more, particularly preferably 10 or more, since the dry heat shrinkage rate of the drawn yarn becomes low. [0022] The method of hot stretching the undrawn yarn thus obtained will now be described. The stretching of the present invention consists of at least two stages of stretching and a final stage of constant length or limited heat shrinkage. The drawing process in the present invention can be carried out either by so-called separate drawing using the undrawn yarn that has been wound up in the spinning process, or by the so-called direct drawing method in which the undrawn yarn is directly fed into the drawing process without being wound up in the spinning process. You may also use First, in the first stage stretching, the total stretching ratio is 8.
Stretching is performed at a magnification of 0% or more. If the first stage stretching ratio is less than 80% of the total stretching ratio, the achieved strength and the achieved elastic modulus will not reach the values specified in the present invention. The first stage stretching is usually 150~
Stretch using a heated supply roller at 170°C. If the stretching temperature is less than 150° C., preheating will be insufficient, resulting in excessive stretching, and the total stretching ratio will remain at a low value. On the other hand, if the roller temperature exceeds 170°C, crystallization occurs during stretching, and the total stretching ratio remains at a low value. Next, at least one stage of tension stretching is carried out using heated rollers with a roller temperature of 190 to 235° C. for stretching after the second stage of stretching. This stretching can normally be carried out as second stage stretching, but of course it may also be carried out in third stage stretching or fourth stage stretching or subsequent stages. However, when carrying out the stretching after the third stage, care should be taken to ensure that the stretching temperature is high as well as the number of stages. Normally, industrially, the above-mentioned stretching is carried out in the second stage of stretching due to constraints such as equipment costs. When carrying out the second-stage stretching, the temperature of the first-stage stretching roller is 190 to 235°C, and the stretching is carried out between the second-stage stretching roller and the second-stage stretching roller. If this temperature is less than 190°C, thermal stability will not be sufficient even if limited shrinkage is performed in the next step. On the other hand, if the temperature exceeds 235° C., the temperature is too high to withstand high drawing tension, and high-strength drawing becomes virtually impossible, making it impossible to obtain high-strength, high-modulus fibers. During this stretching, between the rollers 200 to 23
It is preferable to carry out the stretching using a heating plate at 5°C. The use of a heating plate has the effect of increasing the stretching ratio, and also has the effect of improving thermal stability because the heat setting time becomes longer. Instead of a heating plate, it is also preferable to use a heating oven or the like whose temperature is set so that the yarn temperature is substantially 200 to 235°C. As the second stage drawing roller, it is preferable to use a so-called reverse tapered roller whose roller diameter increases from the back end on the yarn entry side to the tip end on the yarn exit side. This is because the second and third stage stretching can be performed only with this second stage stretching roller. Particularly preferred is a temperature gradient type reverse taper roller in which the temperature of the reverse taper roller increases from the back side to the tip end. A stretching ratio of about 1.00 to 1.10 is possible with a reverse tapered roller. Subsequently, heat setting is performed between the stretching heating roller at the final stage of stretching and the unheated winding roller. At this time, the temperature of the drawing heating roller should be 225 to 250°C, and heat setting should be performed to a constant length or to limited shrinkage of 0 to 3.0%, preferably 2% or less. If the heating roller temperature is less than 225°C, the effect of heat setting will not be sufficient and the dry heat shrinkage rate will increase. Furthermore, when the heating roller temperature exceeds 250° C., the yarn tends to undergo thermal deterioration and its strength decreases. Furthermore, when the heat setting is on the tension side, the dry heat shrinkage rate increases. On the other hand, if the degree of shrinkage during heat setting exceeds 3.0%, the dry heat shrinkage rate will be very low, but it will be easy to elongate when loaded, and the so-called creep resistance will decrease. Dimensional stability represented by dry heat shrinkage rate and creep resistance are inherently contradictory properties, and dry heat shrinkage rate and strength properties also tend to be contradictory. For this purpose, the strength specified in the present invention is 10 g/de or more, and the elastic modulus is 2.
It has high strength and high elastic modulus properties of 50g/de or more,
Furthermore, it maintains excellent dimensional stability with a dry heat shrinkage rate of 6% or less at 180℃, and exhibits excellent creep resistance with a creep rate of 4% or less after 15 hours at 120℃ under a load of 4g/de. In order to do this, it is necessary to specify the spinning method and also to narrow down the drawing method to a narrower range. [Example] The present invention will be explained in more detail with reference to Examples below. First, a method for measuring the structure and physical property values used in the present invention will be explained. Strength and elongation were measured according to JIS L 1070. Elastic Modulus The dynamic elastic modulus (E') was measured at room temperature and 10 Hz using a viscoelasticity measuring instrument "Spectrometer" manufactured by Iwamoto Seisakusho. [0031] Dry heat shrinkage rate at 180°C was measured in accordance with JIS L 1017-1963 (5, 12). Creep rate A load of 4 g/de was applied to the fiber at room temperature, the temperature was raised to 120°C, the load was held for 15 hours, the temperature was allowed to creep, the temperature was lowered to room temperature under load, and then the weight was removed. It was determined from the change in fiber length before and after the creep test. In addition, what is called the time of unloading here actually refers to the state where a small load of 0.2 g/de is applied. [0032] Crystal melting point: Using PerkinElmer's DSC-1 model, the heating rate was 1.
The endothermic peak value measured at 0° C./min was taken as the crystal melting point. Δn Determined by the retardation method using a Berek compensator (for details, see Kyoritsu Shuppan "Polymer Experimental Course, Physical Properties of Polymers II"). Density This is a value determined by density gradient tube method using carbon tetrachloride and n-heptane. Examples 1 to 6, Comparative Examples 1 to 7 Intrinsic viscosity 0.
90 polyethylene-2,6-naphthalate with 24 holes
Hole, circular spinning hole with hole diameter 0.40mm (L/D=2)
When melt spinning a polymer at a temperature of 312°C from a spinneret with a length of 40 cm, 33
After passing through a heating cylinder at 0° C., it was cooled and solidified over a length of 30 cm with cooling air at a relative humidity of 65% and a temperature of 25° C. The cooled and solidified yarn was coated with an oil using an oiling roller and then wound at 750 m/min. At this time, the draft was 60, and the intrinsic viscosity of the undrawn yarn was 0.78.
The fineness was 1,080 denier and the birefringence was 0.014. After applying 1% pretension to the undrawn yarn, the heated supply roller (FR) and the first stage drawing roller (1R
), and then the first-stage stretching roller (heating) and the heating plate (HP, 70 cm) installed immediately after were used together to perform the first-stage stretching roller and the second-stage stretching roller (magnification ratio DR1). Second stage stretching (magnification DR) between stage stretching rollers (2R)
2) was implemented. Furthermore, as a heat setting step, constant length heat setting or contraction heat setting (magnification ratio DR3) is performed between the second stage drawing roller (heated) and the unheated take-up roller (WR) at a speed of 1,500 m/min. I rolled it up. At this time, the surface temperatures of the rollers and heating plates, the draw ratio of each stage, the total draw ratio (TDR), and the drawing condition are shown in Table 1, and the characteristic values of the drawn yarn are shown in Table 2. [Table 1] [Table 2] [0038] Examples 7 to 9, Comparative Examples 8 to 10
However, spinning was carried out in the same manner as in Example 3 except that L/D = 2), the discharge amount and the spinning speed were changed as shown in Table 3.
Subsequently, it was stretched at the same stretching temperature as in Example 3. Table 3 shows the spinning and stretching conditions at this time. Note that the intrinsic viscosity of all undrawn yarns was 0.78. Table 4 shows the characteristic values of the obtained drawn yarn. Example 10 Spinning and drawing were carried out in the same manner as in Example 7 except that the L/D of the spinneret was changed to 10. The spinning and drawing conditions at this time are shown in Table 3, and the characteristic values of the obtained drawn yarn are shown in Table 4. Example 11 DR2=1.16, 2R is a reverse taper roller (thread entry side temperature 225°C, thread exit side temperature 233°C), 1.03
Spinning and stretching were carried out in the same manner as in Example 3, except that the stretching was doubled. The spinning and drawing conditions at this time are shown in Table 3, and the characteristic values of the obtained drawn yarn are shown in Table 4. [Table 3] [Table 4] [Effects of the Invention] According to the present invention, polyethylene naphthalate having high strength, high modulus of elasticity, and excellent thermal stability and creep resistance is produced. In particular, fibers suitable as reinforcing fibers for industrial materials such as tire cords and belt materials can be provided.

Claims

[Claims] Claim 1: A fiber made of polyethylene naphthalate containing 90 mol% or more of ethylene-2,6-naphthalate units and having an intrinsic viscosity of 0.65 or more, which is highly strong and thermally stable and satisfies the following properties: Polyethylene naphthalate fiber with excellent properties. (A) Strength≧10.0g/de (B) Elastic modulus≧250g/de (C) Δn≧0.34 (D) 180°C dry heat shrinkage rate≦6% (E) 120°C creep rate≦4% ( f) Crystal melting point ≧280℃ (g) Density≦1.370g/cm3 [Claim 2] When producing polyethylene naphthalate fiber by a melt spinning-hot drawing method from polyethylene naphthalate containing 90 mol% or more of ethylene-2,6-naphthalate units and having an intrinsic viscosity of 0.7 or more, ( h) Directly below the spinneret, length 20~50cm, ambient temperature 275~
A heating cylinder of 350°C was installed, and (i) the spinning speed was 1,000.
m/min or less, taken up at a spinning draft of 20 to 250, (
h) The birefringence index of the undrawn yarn is set to 0.025 or less; (c) The undrawn yarn is wound once or directly supplied to a hot drawing process without being wound up, and the drawing ratio is 80% or more of the total drawing ratio. After performing the first stage stretching at a magnification of
At least one stage of tension stretching is performed using a heated roller at 235°C, and (S) a fixed length or limited shrinkage of 0 to 3.0% is performed between a heated roller at a temperature of 225 to 250°C and a non-heated roller. 2. The method for producing polyethylene naphthalate fiber according to claim 1, wherein the polyethylene naphthalate fiber is wound up after performing the above steps. 3. The method for producing polyethylene naphthalate fiber according to claim 2, wherein the ratio L/D of the introduction hole length (L) to the hole diameter (D) of the spinneret used during melt spinning is 5 or more. [Claim 4] The spinning speed is 500 m/min or less,
The method for producing polyethylene naphthalate fiber according to claim 2 or 3, wherein the undrawn yarn has a birefringence index of 0.01 or less. 5. The method for producing polyethylene naphthalate fiber according to any one of claims 2 to 4, wherein at least one stage of the tension stretching step after the second stage stretching is carried out by winding the yarn around an inverted tapered roller.