JP3129542B2 - Method for producing high-strength polyethylene naphthalate fiber - Google Patents

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 polyethylene naphthalate fiber having high strength, high elastic modulus and high toughness, which is particularly useful as a tire cord.

[0002]

2. Description of the Related Art Many methods have been proposed for producing high-strength, high-modulus fibers, especially for polyethylene terephthalate fibers. (For example, Japanese Patent Publication No. 41-789)
No. 2, etc.) The basic idea is that the birefringence index Δn
It is essential to obtain a low-oriented, low-oriented undrawn yarn.

[0003] A similar idea has been proposed for polyethylene naphthalate fiber. For example, Shoko 5
In Japanese Patent Application No. 0-16446, a heating cylinder having a temperature gradient is provided immediately below a spinneret, and the ambient temperature near the spun yarn is adjusted from just below the spinneret to a position where the ambient temperature becomes a secondary transition point of the polymer. A melt spinning method that controls a specific ambient temperature has been disclosed.

[0004] However, in this method, 10 g
Although high strength of / d can be achieved, there is a problem that elongation is low and toughness is low. In particular, recently, the development of so-called super fibers has been progressing, and the quality required for fibers for industrial materials has been improving, and the development of technologies for increasing the strength, elastic modulus, and toughness of polyethylene naphthalate fibers has been increasing. Coveted.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing polyethylene naphthalate fiber having high strength, high elastic modulus and high toughness, and in particular, rubber materials such as tire cords, belts and hoses. It is an object of the present invention to provide a method for producing a polyethylene naphthalate fiber suitable for a reinforcing fiber.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have controlled the cooling conditions for melt-spinning polyethylene naphthalate to obtain a specific birefringence and crystallization. It was clarified that a polyethylene naphthalate fiber having a high strength, a high elastic modulus and a high toughness can be obtained by drawing the undrawn yarn having a peak temperature and then drawing the undrawn yarn.

Thus, according to the present invention, the limiting viscosity is 0.1.
When melt-spinning polyethylene naphthalate of 65 to 1.00 at a spinning speed of 450 to 1200 m / min, (a) a length having a temperature gradient immediately below the spinneret that becomes lower as it goes downstream of the yarn. A heating cylinder having a length of 70 cm or more is installed, and at least 30 cm upstream of the heating cylinder has a spinneret temperature of 400 ° C. or less, and
Delayed cooling of the discharged yarn by setting the ambient temperature to 00 ° C or higher and 250 ° C or lower, (b) then cooling the yarn with cold air at 25 ° C or lower, (c) taking the cooled yarn with a take-up roller Then, it is taken as undrawn that simultaneously satisfies the following expressions (1) and (2). (1) Δn = 0.010 (2) Tc ≧ 205 (where Δn is the birefringence of the undrawn yarn, and Tc is (D) Crystallizing peak temperature [° C]) (d) A method for producing a polyethylene naphthalate fiber, wherein the undrawn yarn is supplied once to the drawing step after or once without winding, and is drawn entirely. Is done.

Hereinafter, the configuration of the present invention will be described in detail. Polyethylene naphthalate (hereinafter referred to as PEN) used in the present invention
Is a PEN containing 90 mol% or more of ethylene-2,6-naphthalate units, and may be a copolymer containing an appropriate third component in a proportion of 10 mol% or less. Generally PE
N is synthesized by polymerizing naphthalene-2,6-dicarboxylic acid or a functional derivative thereof under appropriate reaction conditions in the presence of a catalyst. At this time, if one or more appropriate third components are added before the completion of the polymerization of PEN, a copolymerized polyester is synthesized.

Suitable third components include: (a) compounds having two ester-forming functional groups; for example, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid and dimer acid; cyclopropane Alicyclic dicarboxylic acids such as dicarboxylic acid, cyclobutanedicarboxylic acid, cyclobutanedicarboxylic acid and hexahydroterephthalic acid; phthalic acid, isophthalic acid, naphthalene-
Aromatic dicarboxylic acids such as 2,7-dicarboxylic acid and diphenyldicarboxylic acid; carboxylic acids such as diphenylether dicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid and sodium 3,5-dicarboxybenzenesulfonate; glycolic acid , P
Oxycarboxylic acids such as oxybenzoic acid and p-oxyethoxybenzoic acid; propylene glycol, trimethylene glycol, diethylene glycol, tetramethylene glycol, hexamethylene glycol, neopentylene glycol, p-xylylene glycol, 1,4-cyclohexane Dimethanol, bisphenol A, p,
Examples of p'-diphenoxysulfone-1,4-bis (β-hydroxyethoxy) benzene, 2,2-bis (p-β-hydroxyethoxyphenyl) propane, polyalkylene glycol, p-phenylenebis (dimethylcyclohexane) and the like An oxy compound or a functional derivative thereof; a highly polymerizable compound derived from the carboxylic acid, oxycarboxylic acid, oxy compound or a functional derivative thereof (b) a compound having one ester-forming functional group, for example, benzoic acid Acids, benzoylbenzoic acid, benzyloxybenzoic acid, methoxypolyalkylene glycol and the like.

(C) a compound having three or more ester-forming functional groups,
For example, glycerin, pentaerythritol, trimethylpropane and the like can be used within a range where the polymer is substantially linear.

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 esters thereof.

The intrinsic viscosity of the polyethylene naphthalate used in the present invention is 0.65, preferably 0.7 or more and 1.0 or less. When the intrinsic viscosity is less than 0.65, the high strength and high elastic modulus aimed at by the present invention cannot be obtained. On the other hand, when the intrinsic viscosity exceeds 1.0, spinning tends to be unstable, which is not preferable in practical use.

When melt-spinning the polyethylene naphthalate, it is necessary to install a heating cylinder immediately below the spinneret. That is, since polyethylene naphthalate has a high melt viscosity, it is necessary to increase the spinneret temperature in order to reduce the viscosity.Therefore, in order to prevent the discharged yarn from being rapidly oriented and solidified by the spinning draft, the spinneret is located just below the spinneret. This is because it is necessary to delay the cooling. Further, the length of the heating cylinder needs to be longer than that of polyethylene terephthalate or the like, and at least 70 cm or more is required.

Also, at least 30c upstream of the heating cylinder
It is necessary to maintain the atmosphere temperature of not less than m and not less than the spinneret temperature and not more than 400 ° C. As described above, in order to obtain a high-strength, high-modulus fiber, a low-orientation undrawn yarn is necessary.For this purpose, delayed cooling immediately below the die is essential, but if this temperature is lower than the spinneret temperature, Slow cooling is performed rather than delayed cooling, and the effect of reducing the birefringence is reduced. On the other hand, when the temperature exceeds 400 ° C., the yarn sway becomes large, and the spinning condition is deteriorated, for example, fusion between the single fibers occurs. If the heating length is less than 30 cm, the effect of reducing the birefringence will be small.

Further, it is necessary to set the ambient temperature of the heating cylinder so that the temperature becomes lower toward the downstream side of the yarn, and it is necessary that the lowermost temperature is 200 ° C. or more and 250 ° C. or less. By setting such a temperature gradient, the section of delayed cooling can be lengthened. When the temperature at the lowermost part of the heating cylinder is lower than 200 ° C., the crystallization peak temperature described below does not reach 205 ° C. On the other hand, when the temperature exceeds 250 ° C., the yarn sway becomes large, and the spinning condition decreases or the single fiber Fusion occurs between them.

Next, the spun yarn is cooled by blowing cold air of 25 ° C. or less, preferably 10 ° C. or less. There is no particular limitation on the blowing amount and blowing length of the cooling air, but the blowing amount is 2 to 6 Nm ³ / min, and the blowing length is 100 to 500.
mm is preferable.

Next, the cooled yarn is applied with an oil agent by a conventional method, then wound at a spinning speed of 450 to 1200 m / min, and is undrawn as simultaneously satisfying the following expressions (1) and (2). Once wound or continuously fed to the stretching step. (1) Δn ≦ 0.010 (2) Tc ≧ 205

If Δn exceeds 0.010, high-stretching cannot be performed, so that high-strength, high-modulus fibers cannot be obtained. Δn is preferably as small as possible, but is substantially 0.00
About 3 is the limit. On the other hand, when Tc is less than 205 ° C., high-stretching cannot be performed, so that high-strength, high-modulus fibers cannot be obtained. In particular, when an undrawn yarn that simultaneously satisfies the following formulas (1 ′) and (2 ′) is drawn, the tensile strength is 10 g / d or more, the tensile modulus is 270 g / d or more, and the toughness is 26 g / d%. High strength and high modulus fibers of ^1/2 or more can be obtained. (1 ′) Δn ≦ 0.008 (2 ′) Tc ≧ 208

The drawing may be carried out once by a take-up roller and then drawn by a so-called separate drawing method, or by a so-called straight drawing method in which undrawn yarn is continuously supplied from the take-up roller to a drawing step. It does not matter. The draw ratio depends on the spinning speed, but it is preferable that the draw ratio is 6.0 times or more. In order to improve the thermal dimensional stability of the fiber, it is preferable to perform heat setting in the drawing step.

[0020]

Since the present invention adopts the above-described configuration, the following operations are provided. As described above, in order to produce a high-strength, high-modulus fiber, it is indispensable to obtain a low-crystal, low-orientation undrawn yarn and draw it at a high magnification. Conventionally, the crystallinity and orientation of polyester-based undrawn fibers are generally represented by the birefringence Δn. Therefore, it is necessary to reduce the density and Δn as much as possible to obtain high strength and high elastic modulus. Was considered advantageous.

However, according to the study of the present inventors, when the spinning speed is in a so-called medium spinning speed range of 450 m / min or more, the crystallization peak temperature Tc reflects the crystal state better than the density. Turned out to be. For example, spinning speed 1
At 000 m / min, the density is 1.329 g / cm ³ and Tc is 1
At a spinning speed of 2000 m / min, the density was 1.335 g / cm ^3, which was almost unchanged at 87 ° C.
c has dropped to 158 ° C. That is, it is considered that the crystallization peak temperature Tc detects a minute difference in crystallinity even when the density is almost the same.

The heating cylinder used in the present invention and having a temperature gradient that becomes lower as it goes downstream of the yarn is also disclosed in the above-mentioned Japanese Patent Publication No. Sho 50-16446. However, the method described in this publication gradually cools the spun yarn to near the secondary transition temperature (113 ° C.), whereas in the present invention, the temperature of the lowermost part of the heating cylinder is set to 200 to 25.
The technical idea is fundamentally different in that delayed cooling is performed at 0 ° C., that is, near the crystallization peak temperature.

That is, when the temperature at the lowermost part of the heating cylinder is cooled to near the second-order transition temperature, although the effect of reducing the birefringence is certainly obtained, the crystallization is caused by the slow cooling effect rather than the delayed cooling effect. Tends to be promoted. Specifically, the crystallization peak temperature Tc does not enter the high temperature range of 205 ° C. or higher specified in the present invention, but exists on the low temperature side of 200 ° C. or lower. This suggests that crystallization, which cannot be detected by density, is appearing, and thus high-magnification stretching cannot be performed.

Hereinafter, the present invention will be described more specifically with reference to examples. The measured values in the examples were obtained by the following methods.

(1) Strong elongation Measured in accordance with JIS L 1070.

(2) Elastic Modulus The value of the dynamic elastic modulus E 'measured under the conditions of room temperature and a frequency of 10 Hz using a viscoelasticity meter "Spectrometer" manufactured by Iwamoto Seisakusho was defined as the elastic modulus.

(3) Intrinsic Viscosity The chip was dissolved in a mixed solvent of phenol and orthochlorobenzene (volume ratio: 6: 4), and was calculated by extrapolation from the relative viscosity measured at 35 ° C.

(4) Birefringence Δn The birefringence was determined by a retardation method using a Bellek compensator. (For details, see Kyoritsu Shuppan's “Experimental Course on Polymer Experiments, Physical Properties of Polymers II”)

(5) Crystallization peak temperature Tc Using a THERMOFLEX TAS20 type differential calorimeter manufactured by Rigaku Denki, a DSC curve was obtained at a temperature rising rate of 10 ° C./min in a nitrogen atmosphere with a sample amount of 10 mg. The position was defined as the crystallization peak temperature Tc.

[0030]

EXAMPLES 1-4, COMPARATIVE EXAMPLES 1-5 A polyethylene-2,6-naphthalate chip having an intrinsic viscosity of 0.85 was filled with 25 holes.
0, a polymer temperature of 315 ° C. and a spinning speed of 500 from a spinneret having a circular spinning hole (L / D = 2) having a hole diameter of 0.4 mm.
Melt spinning was performed at m / min to obtain an undrawn yarn of 10500 de / 250 fill. At this time, a cylindrical heating cylinder having a length of 30 cm was connected in three stages immediately below the base, and each was set to various temperatures. HS1, HS2, H
Name it S3. In some cases, the heating cylinder is two-stage (HS1
And HS2, total length of 60 cm) or 1 step (HS1, 30
cm length). Further, a cooling air at 20 ° C. was blown over the length of 45 cm at a rate of 3.5 Nm 3 / minute directly below the heating cylinder to cool the yarn. Next, after applying an oil agent with an oiling roller, it was guided to a take-up roller and wound up by a winder.

After applying 1% pretension to the undrawn yarn, the first drawing is carried out between the heating supply roller at 155 ° C. and the first drawing roller, and then the first drawing roller and the second drawing The second stage stretching was performed 1.06 times with the stage stretching roller. Further, as a heat setting step, shrinkage heat setting was performed at a relaxation rate of 2% between the second-stage stretching roller and the unheated winding roller, and winding was performed at 200 m / min.
Table 1 shows the temperature of the heating tube, the drawing conditions, and the physical properties of the undrawn yarn and the drawn yarn.

[0032]

[Table 1]

[0033]

Examples 5 and 6 and Comparative Example 6 The same procedures as in Example 1 were carried out except that spinning was carried out with the following conditions changed. First, in Example 5, stretching was performed by the direct stretching method. In Comparative Example 6, the cooling air temperature under the heating cylinder was 30 ° C.
And Further, in Example 6, the cooling air temperature under the heating cylinder was set to 10 ° C. Table 2 shows the results.

[0034]

[Table 2]

[0035]

Examples 7 and 8 and Comparative Example 7 The same procedure as in Example 1 was carried out except that the spinning speed was changed as shown in Table 3. Table 3 shows the results.

[0036]

[Table 3]

[0037]

According to the present invention, polyethylene-2,6-naphthalate fiber having high strength, high elastic modulus and high toughness, particularly suitable for reinforcing tire cords and belt materials, can be produced.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-352811 (JP, A) JP-A-50-5819 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D01F 6/62

Claims (2)

(57) [Claims] (1) When melt-spinning polyethylene naphthalate having an intrinsic viscosity of 0.65 to 1.00 at a spinning speed of 450 to 1200 m / min, (a) immediately downstream of a yarn immediately below a spinneret. A heating cylinder having a temperature gradient of 70 cm or more having a temperature gradient that becomes lower as the temperature rises, at least 30 cm on the upstream side of the heating cylinder is at a spinneret temperature or more and 400 ° C or less, and the lowermost part of the heating cylinder is 200 ° C or more and 250 ° C or less. (B) Then, cool the yarn with cold air of 25 ° C or less, and (c) take up the cooled yarn with a take-up roller. (1) Δn ≦ 0.010 (2) Tc ≧ 205 (where Δn is the birefringence index of the undrawn yarn and Tc is the crystallization peak) Temperature (° C)) (d) The undrawn yarn was once wound Or method for producing polyethylene naphthalate fibers, which comprises supplying to the drawing step without winding total draw. 2. A fiber having a tensile strength of 10 g / d or more, a tensile modulus of elasticity of 270 g / d or more and a toughness of 2
The method for producing polyethylene naphthalate fiber according to claim 1, wherein the amount is 6 g / d% ^1/2 or more.