JP3133177B2 - Polyethylene naphthalate fiber excellent in heat stability and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyethylene naphthalate fiber having high strength, a high modulus of elasticity, and excellent heat stability, which is useful as an industrial material, particularly as a tire cord, and a method for producing the same.

[0002]

2. Description of the Related Art Polyethylene naphthalate fiber is expected to exhibit high strength, high modulus of elasticity and excellent thermal dimensional stability, and to outperform polyethylene terephthalate fiber in the field of industrial materials such as tire cords. ing. Regarding polyethylene terephthalate fiber, various proposals have been made to improve the thermal stability and obtain a fiber having the same thermal stability as rayon.

Some proposals have also been made on polyethylene naphthalate fibers for the purpose of improving thermal stability. For example, Japanese Patent Application Laid-Open No. Sho 62-1561212 discloses that under specific spinning and drawing conditions of spinning speed of 1,500 to 6,000 m / min, the strength is 6.5 g / de or more and the dry heat shrinkage at 180 ° C. is 3%. Hereinafter, the production of a polyethylene naphthalate fiber having a crystal melting point of 280 ° C. or more and having excellent thermal stability is described.

[0004]

However, the polyethylene naphthalate fiber described in Japanese Patent Application Laid-Open No. 62-156312 has a low strength of 6.6 g / de when the crystal melting point is as high as 285 ° C. On the contrary, strength is 7g /
When the temperature exceeds de, there is a problem that the crystal melting point is lowered to 280 to 283 ° C. In other words, strength and heat resistance cannot be compatible at a high level.

Further, the polyethylene naphthalate fiber described in Japanese Patent Application Laid-Open No. 62-156312 has a good thermal dimensional stability represented by a dry heat shrinkage,
Insufficient heat resistance to elongation of fiber under heating and load. Polyethylene naphthalate fiber is used for industrial materials,
In particular, when used as a reinforcing fiber for rubber materials such as tire cords, belts, hoses, etc., they are generally subjected to a load at elevated temperatures, so they have thermal durability against elongation at elevated temperatures and loads (ie, creep resistance). )Is required.

The present invention provides a polyethylene naphthalate fiber having high strength and excellent heat resistance, thermal dimensional stability and heat durability, which is particularly suitable as a reinforcing fiber for rubber materials such as tire cords, belts and hoses. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION The present invention provides an ethylene
Polyethylene naphthalate fiber comprising polyethylene naphthalate containing at least 90 mol% of 2,6-naphthalate units and satisfying the following (a) to (g), and having excellent thermal stability.

(A) Intrinsic viscosity [η] f ≧ 0.70 (b) Strength ≧ 7.0 g / de (c) Melting point ≧ 282 ° C. (d) Dry heat shrinkage at 180 ° C. ≦ 3.0% ( e) Creep rate at 120 ° C. ≦ 4.0% (f) 0.2 ≦ R ≦ 0.8 (g) Birefringence index (Δn) ≧ 0.31 (where R is the equatorial direction of X-ray diffraction intensity) In the distribution curve, the peak of the Bragg reflection angle 2θ = 18.7 ° and 2θ
It is the diffraction intensity ratio with the peak at = 15.6 °. )

Further, the present invention relates to a method for producing the above-mentioned polyethylene naphthalate fiber, wherein (a) ethylene-2,
Melt spinning polyethylene naphthalate containing 6-naphthalate units in an amount of 90 mol% or more and having an intrinsic viscosity of 0.75 to 1.00; (a) in the melt spinning, the length of the spinneret is reduced by straightening; Is provided with a heating cylinder having a temperature of not less than 30 cm and an atmosphere temperature of not less than the spinneret temperature and not more than 450 ° C. (c) The melt spinning is performed at a take-up speed of not less than 3,500 m / min and a spinning draft of 100 to 2,000, and birefringence is performed. To obtain an undrawn yarn having a rate of 0.22 or more; (d) winding the undrawn yarn once, or continuously feeding it to a drawing step without winding to perform at least one step of hot drawing And (e) subsequently, a fixed length or 2% between a heated roller and a non-heated roller at 200 to 250 ° C.
A method for producing a polyethylene naphthalate fiber, comprising winding after performing the following restriction shrinkage treatment.

The term "polyethylene naphthalate" as used in the present invention means that ethylene-2,6-naphthalate unit is 90 mol%.
A copolymer containing the appropriate third component at a ratio of 10 mol% or less may be used. Generally, polyethylene-2,6-naphthalate is synthesized by polymerizing naphthalene-2,6-dicarboxylic acid or a functional derivative thereof in the presence of a catalyst under appropriate reaction conditions. At this time, polyethylene-2,6-
If one or more appropriate third components are added before the completion of the polymerization of naphthalate, a copolymerized polyethylene naphthalate 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, naphthalene-2,7 -Aromatic dicarboxylic acids such as dicarboxylic acid and diphenyl dicarboxylic acid; carboxylic acids such as diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, and sodium 3,5-dicarboxybenzene sulfonate; 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 Le, p- xylylene glycol,
1,4-cyclohexanedimethanol, bisphenol A, p, p'-diphenoxysulfone-1,4-bis (β-hydroxyethoxy) benzene, 2,2-bis (p-β-hydroxyethoxyphenyl) propane, poly Oxy compounds such as alkylene glycol and p-phenylenebis (dimethylcyclohexane), or functional derivatives thereof; carboxylic acids, oxycarboxylic acids, oxy compounds and high polymerization degree compounds derived from the functional derivatives thereof; b) Compounds having one ester-forming functional group, for example, benzoic acid, benzoylbenzoic acid, benzyloxybenzoic acid, methoxypolyalkylene glycol and the like.

Further, (c) a compound having three or more ester-forming functional groups, for example, glycerin, pentaerythritol, trimethylolpropane and the like can be used as long as the polymer is substantially linear.

Needless to say, the polyester may contain additives such as a matting agent such as titanium dioxide and a stabilizer such as phosphoric acid, phosphorous acid and esters thereof.

The polyethylene naphthalate fiber of the present invention has an intrinsic viscosity [η] f of 0.70 or more.
It is preferably from 0.75 to 1.0. The intrinsic viscosity [η] f in the present invention is determined by dissolving the fiber in a mixed solvent of phenol and orthodichlorobenzene (volume ratio 6: 4),
This is a value obtained from the viscosity measured at 5 ° C.

When the intrinsic viscosity [η] f is less than 0.70, it is practically impossible to obtain a high-strength, heat-resistant, and heat-stable polyethylene naphthalate fiber aimed at by the present invention. Become. It should be noted that fibers having an intrinsic viscosity [η] f of more than 1.0 are difficult to manufacture due to frequent breakage in the spinning process.

If the strength is less than 7 g / de, when used as an industrial material, the durability is inferior, which is not preferable.
It is preferably at least 5 g / de.

In order to achieve this intensity level, the birefringence (Δn) needs to be 0.31 or more;
0.32 or more is more preferable.

Industrial materials are required to have excellent thermal properties. In general, polyethyne naphthalate fiber has better heat resistance and thermal stability than polyethene terephthalate fiber, so if its properties can be fully utilized, a far superior fiber for industrial materials will be obtained. .

As a measure of heat resistance, it can be expressed by the melting point of the crystal part present in the fiber. One of the characteristics of high-speed spinning of polyethylene naphthalate fiber is that crystals having a high melting point are obtained.
It is known from Japanese Patent Publication No. 2-5612. Spinning speed 3,
When the spinning is performed at a high speed of 500 m / min or more and the R value obtained from the equatorial pattern of the X-ray diffraction pattern is 0.2 or more, the melting point of the crystal is 282 ° C. or more, and 2
It can have a high melting point of 85 ° C. or higher. If the melting point of the crystal does not reach 282 ° C., the heat resistance will be inferior to rayon.

The scale of thermal stability includes thermal dimensional stability represented by the dry heat shrinkage at 180 ° C. and thermal durability represented by the creep rate at 120 ° C. The dry heat shrinkage must be 3.0% or less, and 2.5%
The following is more preferred. When the dry heat shrinkage exceeds 3%, the thermal dimensional stability is inferior to rayon.

The creep rate at 120 ° C. indicates the resistance of the fiber to elongation under heating and load, and is an important factor when the fiber is actually used as an industrial material. In the polyethylene naphthalate fiber of the present invention, the creep rate at 120 ° C. under a load of 2.5 g / de must be 4.0% or less. If the creep rate exceeds 4.0%, the durability under temperature rise and load becomes inferior to rayon. When the R value obtained from the X-ray diffraction curve exceeds 0.8, the melting point of the crystal becomes 29
Despite being as high as 0 ° C., the creep rate exceeds 4%.

It should be noted here that the dry heat shrinkage and the creep rate are generally of the opposite nature, and that when the dry heat shrinkage is low, the creep rate increases. is there.

In order to achieve both of the above characteristics, it is necessary that the crystal has high microstructural integrity and that the melting point of the crystal be 282 ° C. or higher. in this way,
Heat resistance, thermal dimensional stability, and thermal durability influence each other, and this is the first finding of the present invention.

In order to produce such a polyethylene naphthalate fiber, polyethylene naphthalate containing at least 90 mol% of ethylene 2,6-naphthalate units and having an intrinsic viscosity of 0.75 to 1.00 is prepared by adding 3,3 500
Melt spin at a take-up speed of at least m / min.

At this time, a heating cylinder is provided immediately below the spinneret for performing delayed cooling. Polyethylene naphthalate resin has a very high melt viscosity, especially when the intrinsic viscosity is as high as 0.75 or more, so it is necessary to lower the melt viscosity by setting the spinneret temperature appropriately. Needless to say, the cooling beneath the spinneret must be delayed to prevent the discharged yarn from being rapidly oriented by the spinning draft. For this reason, the heating cylinder is indispensable, and it is more preferable that the length is long. In the study of the present inventors,
If the heating cylinder is heated to a high temperature and the length of the heating cylinder is lengthened, the discharge yarns may adhere to each other, sometimes leading to thread breakage.
It is necessary to install a heating cylinder having a length of at least 30 cm or more.

The temperature of the heating cylinder is equal to or higher than the temperature of the spinneret;
It is necessary to maintain the temperature at 0 ° C. or lower. In order to obtain a high-strength fiber under high-speed spinning, a low-orientation undrawn yarn is required. For this purpose, at least delayed cooling under a die is essential. When the temperature of the heating cylinder provided immediately below the spinneret is lower than the spinneret temperature, slow cooling is performed by heat retention rather than delayed cooling, and it becomes difficult to obtain high-strength fibers. Conversely, if the heating cylinder temperature exceeds 450 ° C, the yarn sway will increase,
In severe cases, the spinning condition deteriorates, for example, adhesion between single yarns occurs. Similarly, if the length of the heating cylinder is less than 30 cm, a sufficient delayed cooling effect cannot be obtained. It should be noted that, even within the range of temperature and length conditions of the heating cylinder specified here, if the spinning melting temperature is too high or the distance between the holes of the spinneret is inappropriate. ,
It is possible that the spinning condition may be lowered, and in some cases, the adhesion between the single yarns may occur. Therefore, it is necessary to select appropriate spinning conditions.

The spinning draft is defined as the ratio between the spinning speed (spinning speed) and the spinning discharge linear speed, and is expressed by the following equation. Spinning draft = πD ² V / 4W (where D represents the hole diameter of the die, V represents the spinning take-off speed, and W represents the volume discharge per single hole).
If it is less than the above, the tension of the spun yarn may be too small, the yarn sway may be large, and the yarn may be broken.
Conversely, if the spinning draft exceeds 2,000, thread breakage of the yarn may occur, or the spinning condition may decrease even if it does not occur.

In order to obtain the polyethylene naphthalate fiber having the physical properties specified in the present invention, it is premised that a heating cylinder is placed below the base and delayed cooling is performed as described above.
Another important requirement is that the birefringence (Δn) of the unspun yarn is 0.22 or more. Spinning speed is 50
0 m / min and a birefringence (Δn) of 0.22
When the temperature does not reach, high strength and high modulus fibers are easily obtained, but the thermal dimensional stability and heat resistance are inferior. When the spinning speed is in the so-called POY region of 2,000 to 3,000 m / min, the fiber structure has not developed in the spinning process, but a large number of microcrystal nuclei are generated and the nuclei are easily crystallized. The drawability is impaired, and only a low-strength yarn can be obtained. Rather, if the spinning speed is further increased and the fiber structure is developed during the spinning process, a high-strength yarn can be obtained. For this purpose, it is necessary to set the spinning speed to 3,500 m / min or more and the undrawn birefringence (Δn) to 0.22 or more.

The unstretched yarn thus obtained does not have sufficient crystal integrity and strength, and also has insufficient heat durability. Therefore, it is necessary to stretch at least one step. is there. The stretching temperature may be 150 ° C. or higher. Note that the drawing is performed by once winding from a spinning take-up roll and drawing by a so-called separate drawing method, or by drawing directly from a spinning take-up roll directly by a so-called straight drawing method of supplying an undrawn yarn to a drawing step. No problem. At this time, the stretching ratio needs to be set so that the R value obtained from the X-ray diffraction intensity curve is 0.2 or more and 0.8 or less. When the R value exceeds 0.8, the fiber structure is insufficiently developed, so that the creep rate increases and the heat durability deteriorates. Further, in order to reduce the R value to less than 0.2, an excessive stretching ratio is required, so that the stretching condition is deteriorated, or the stretched material has a low elongation, and the toughness is reduced. Dimensional stability decreases.

After stretching, heat setting is necessary from the viewpoint of improving thermal stability. Heat set 200-250
Using a heating roll at a constant temperature or under a limited shrinkage of 2% or less, the film is wound up. When the heat set is performed in a tension state exceeding the fixed length, that is, in a drawn state, the thermal dimensional stability of the yarn is reduced. Further, when heat setting is performed in a state where the limited shrinkage exceeds 2%, the thermal durability of the yarn becomes poor.

When the polyethylene naphthalate fiber of the present invention is used as a rubber reinforcing cord, for example, the following method can be used. That is, the drawn yarn is formed by twisting coefficient K = T · D ^1/2 (T is the number of twists per 10 cm, D
Is twisted at 990 to 2,500 to form a twisted cord, and the cord is heat-treated at 230 to 270 ° C. following the adhesive treatment. At this time, it is preferable to perform the heat treatment under the condition that the stretching does not substantially occur. The cord obtained from the polyethylene naphthalate fiber of the present invention has a high elastic modulus with a sum of an intermediate elongation at a load of 2 g / de and a dry heat shrinkage at 180 ° C. of 4.5 or less. It is extremely excellent in thermal stability. Further, the cord made of the polyethylene naphthalate fiber of the present invention has a strength of 5.8 g / de or more, and has a higher heat resistance and fatigue resistance even in a rubber structure as compared with the conventional polyethylene terephthalate cord for rubber reinforcement. The properties have been significantly improved.

Hereinafter, the present invention will be described in more detail with reference to Examples. In addition, each characteristic value in an Example and a comparative example was measured by the following method.

(1) Strength, elongation According to JIS L 1013, sample length 20c
m, and the elongation rate was 100% / min.

(2) Dry Heat Shrinkage The shrinkage at 180 ° C. for 30 minutes was determined in accordance with JIS L 1013B method (filament shrinkage).

(3) Melting point Using a THERMOFLEX TAS20 type differential calorimeter manufactured by Rigaku Corporation, a DSC curve was obtained in a nitrogen atmosphere at a sample amount of 10 mg at a heating rate of 10 ° C./min. did.

(4) Intrinsic viscosity [η] Resin or fiber was dissolved in a mixed solvent of phenol and orthodichlorobenzene (volume ratio: 6: 4) and determined from the viscosity measured at 35 ° C.

(5) Wide-angle X-ray R value In the equatorial scan curve of the X-ray diffraction diagram of the fiber sample, the Bragg reflection angles 2θ = 18.7 ° and 2θ = 1
The relative diffraction intensity with 5.6 ° was designated as R, and was calculated by the following equation.

[0038]

(Equation 1)

However, Ic18.7 ゜ and Ic15.
6 ° are the Bragg reflection angles 2θ = 18.7 ° and 2 in the X-ray diffraction intensity distribution curve (equatorial direction) of the fiber, respectively.
diffraction intensity at θ = 15.6 ° (peak height of curve),
Ia18.7 ° and Ia15.6 ° are the Bragg reflection angles 2θ in the X-ray diffraction intensity distribution curve of the amorphous, respectively.
= 18.7 ° and the diffraction intensity at 2θ = 15.6 ° (the height of the peak of the curve) and was measured according to the method described in JP-B-52-5612.

(6) Birefringence (Δn) The birefringence was determined by a retardation method using a Bellec compensating center (for details, see Kyoritsu Shuppan “Lecture on Experimental Polymers, Physical Properties II of Polymers”).

(7) Creep rate (Cr) A load of 2.5 g / de was applied to the fiber at room temperature, the temperature was raised to 120 ° C., the temperature was maintained for 2 hours under the load, and after creeping, the temperature was lowered under the load. Thereafter, the weight was removed, and the creep rate was determined from the change in the fiber length before and after the creep test. Here, the term “when unloading” means a state where a small load of 0.2 g / de is applied.

(8) Heat-resistant strength retention rate The heat-resistant strength is determined by immersing a raw cord in an RFL adhesive solution, heat-treating it at 245 ° C. for 2 minutes under tension, embedding the treated cord in a vulcanization mold, 170 ° C., and a pressure of 50 kg. After accelerated vulcanization at / cm ² for 120 minutes, the treated cord was taken out and the strength was measured. The ratio of the strength of the treated cord to the strength of the raw cord was regarded as the heat resistant strength maintenance rate, and 75% or more was regarded as acceptable. In addition, the heat resistant strength retention rate of the normal polyethylene terephthalate cord was 50 to 60%.

[0043]

Examples 1 to 7 and Comparative Examples 1 to 9 A polyethylene-2,6-naphthalate chip having an intrinsic viscosity of 0.87 was prepared by adding 25 holes.
0 hole, 0.50 mm diameter circular spinning hole (L / D =
The mixture was discharged from the spinneret having step 2) at a spinneret temperature of 318 ° C., and the spinning was performed while changing the draft, the spinning speed, and the temperature and length of the heating cylinder installed immediately below the spinneret as shown in Table 1. Furthermore, a length of 45 from immediately below the heating cylinder
The yarn was cooled by blowing cooling air at 20 ° C. at a flow rate of 3.5 Nm / min over cm. Then, after applying an oil agent with an oiling roll, it was led to a take-up roll and wound up by a winder. The intrinsic viscosity of this undrawn yarn is
In the range of 0.75 to 0.77, and the birefringence (Δn)
Was as shown in Table 1. After applying 1% pretension to the obtained undrawn yarn, the first undrawn yarn is moved between a 155 ° C. heating supply roll (FR) rotating at a peripheral speed of 200 m / min and a first-stage drawing roll (1R). Step stretching (magnification DR1) is performed, and then the first-stage stretching roll heated to 200 ° C. and the second
Second-stage stretching with a two-stage stretching roll (2R) (magnification DR
2) was performed. Further, as a heat setting step, the second-stage stretching roll (2R) is heated to 220 ° C., and shrink heat setting (magnification DR3) is performed with the unheated take-up roll (WR), and then wound around a winder. I took it. First stage draw ratio (DR1)
Was set to 0.85 times the maximum stretching ratio in one-stage stretching. Magnifications DR1, DR2, DR3 were changed as shown in Table 1.

[0044]

[Table 1]

The physical properties of the obtained drawn yarn were as shown in Table 2.

[0046]

[Table 2]

After giving 400 twists / m of Z twist to the obtained drawn yarn, two of them were combined to give 400 twists / m of S twist to obtain 1500de × 2 raw cords. The raw cord was immersed in an adhesive (RFL) solution and subjected to a tension heat treatment at 245 ° C. for 2 minutes. The properties of this cord and the heat retention strength after embedding it in rubber and vulcanizing it were measured. The results were as shown in Table 3.

[0048]

[Table 3]

In Comparative Example 9, the intrinsic viscosity of the polyethylene naphthalate chips was 0.68, and the spinneret temperature was 312 ° C. The intrinsic viscosity [η] f of this fiber is 0.
62.

As apparent from these results, the polyethylene naphthalate fiber of the present invention (Examples 1 to 7)
High strength and excellent heat resistance, thermal dimensional stability and thermal durability (creep resistance), but the spinning speed is 3500 m /
In the case of less than 1 minute (Comparative Examples 1 to 3), all of heat resistance, thermal dimensional stability and thermal durability are inferior. When the R value is 0.
When the value exceeds 8 (Comparative Example 4), the thermal durability deteriorates. On the other hand, when the value is less than 0.2 (Comparative Example 5), the toughness decreases and the thermal dimensional stability becomes poor. Further, when the length of the heating cylinder is less than 30 cm (Comparative Example 6), sufficient delayed cooling cannot be performed, and a high-strength fiber cannot be obtained. Further, when heat setting is performed in a state where the limited shrinkage exceeds 2% after stretching (Comparative Example 7), the heat durability is deteriorated. Further, in the case where high-speed spinning was performed and stretching was not performed (Comparative Example 8) and the case where the intrinsic viscosity of the fiber was less than 0.70 (Comparative Example 9), high-speed strength fibers were not obtained, and heat durability was low. It will be inferior.

[0051]

According to the present invention, it is possible to provide a polyethylene naphthalate fiber having high strength and excellent in heat resistance, thermal dimensional stability and heat durability (creep resistance). Suitable fibers can be provided as reinforcing fibers for industrial materials such as rubber and belt materials.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References Patent 2954391 (JP, B2) Japanese Patent Publication No. 52-4651 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) D01F 6/62 301-306

Claims (2)

(57) [Claims] 1. A polyethylene naphthalate having excellent thermal stability, comprising polyethylene naphthalate containing at least 90 mol% of an ethylene-2,6-naphthalate unit and satisfying the following (a) to (g): fiber. (A) Intrinsic viscosity [η] f ≧ 0.70 (b) Strength ≧ 7.0 g / de (c) Melting point ≧ 282 ° C. (d) Dry heat shrinkage at 180 ° C. ≦ 3.0% (e) 120 Creep at ≤ 4.0% (f) 0.2 ≤ R ≤ 0.8 (g) Birefringence (Δn) ≥ 0.31 (where R is the distribution curve of X-ray diffraction intensity in the equator direction) At the peak of the Bragg reflection angle 2θ = 18.7 ° and 2θ
It is the diffraction intensity ratio with the peak at = 15.6 °. ) 2. The method for producing the polyethylene naphthalate fiber according to claim 1, wherein (a) an ethylene-2,6-naphthalate unit is contained in an amount of 90 mol% or more and the intrinsic viscosity is 0.75 to 1.00. Melt-spinning polyethylene naphthalate; (a) in the melt-spinning, a length of 3
0cm or more, ambient temperature is 450 ° C or higher than spinneret temperature
(C) Take-up speed of 3,500 m / min or more, spinning draft 1
The melt-spinning is performed at 00 to 2,000 to obtain an undrawn yarn having a birefringence of 0.22 or more. (D) The undrawn yarn is wound once or continuously drawn without winding. Supplying at least one step of thermal stretching by supplying to the step; and (e) subsequently performing a fixed length or limited shrinkage treatment of 2% or less between a heated roller and a non-heated roller at 200 to 250 ° C. A method for producing a polyethylene naphthalate fiber, which is performed and then wound.