JPH0663128B2 - Polyester fiber for reinforcing rubber structure and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polyester fiber for reinforcing a rubber structure and a method for producing the same, more specifically, high strength / high elastic modulus, dimensional stability, and fatigue resistance. The present invention relates to a polyester fiber for reinforcing a rubber structure having a significantly improved chemical resistance and a method for producing the same.

[Conventional technology]

Polyester fibers, and sometimes polyethylene terephthalate fibers, have high strength and initial elastic modulus and are excellent in various characteristics such as dimensional stability and durability. Therefore, V-belts and conveyors
It is widely used as a fiber for reinforcing rubber structures such as belts and tires. In particular, in the case of automobile tires, the amount of polyester fiber used has been increasing in recent years because such characteristics of polyester fiber match the performance required as a radial tire carcass material for passenger cars.

However, when used as a tire cord, polyester fiber is slightly inferior in fatigue resistance and chemical stability (so-called durability) in the tire when used as a tire cord, and thus polyester fiber other than passenger cars, for example, light trucks, trucks, buses, etc. The fact is that many tire cords are not used. Therefore, recently, there is a strong demand for a high-strength polyester fiber having durability close to that of a polyamide fiber and improved dimensional stability and elastic modulus. Due to this improvement, the amount used as a polyester tire cord is dramatically increased. Is expected.

Naturally, various improvement measures have been proposed for such requirements. As a method for obtaining a polyester fiber having a high strength and a high elastic modulus, a raw polymer having a relatively high degree of polymerization is annealed to form an undrawn yarn having a low degree of orientation, and this is multi-stage drawn at high magnification. Are known.

In order to improve the dimensional stability, a method of using a polyester fiber having a relatively low degree of polymerization (JP-A-53-31852, JP-A-55-122024, etc.), high speed spinning or high tension under spinning is used. A method for stretching the obtained polyester unstretched yarn having a relatively high degree of orientation (JP-A-53-58032 and JP-A-5-58032).
8-23914, etc.) has been proposed.

Further, in order to improve the chemical resistance, a method of reducing the amount of carboxyl end groups in polyester (JP-A-46-
5389, 54-132697, etc.) are known. Further, in order to improve fatigue resistance, a method (described above) for drawing a polyester undrawn yarn having a high degree of orientation obtained by high-speed spinning or spinning under high tension has been proposed.

However, although these proposals are considered to be effective in improving individual characteristics, they are sufficient to meet the above-mentioned demand for comprehensive improvement of polyester fibers for reinforcing rubber structures. It cannot be said that it gives satisfaction.

That is, the high-strength polyester fiber obtained by multi-stage drawing of a polyester undrawn yarn having a high degree of polymerization and a low degree of orientation at a high ratio has an increased heat shrinkage ratio, and therefore, the dimension proposed by the conventional method is sufficient. Fibers with stability cannot be obtained.

Further, in a method of improving dimensional stability by using a polyester fiber having a low degree of polymerization, the fiber is used for reinforcing a rubber structure,
For example, when processed into a tire cord, a drop in strength cannot be avoided and satisfactory results cannot be obtained as overall performance.

Further, in the method of improving the dimensional stability and the fatigue resistance by stretching the polyester undrawn yarn obtained by the high speed spinning or the high-strength spinning under the conventional method, the undrawn yarn is a highly oriented undrawn yarn. Because of this, it is difficult to increase the draw ratio in the industrial drawing stage, so the strength of the obtained polyester fiber becomes low, and the toughness when used as a fiber for reinforcing a rubber structure, for example, a tire cord, is also high. The value is lower than that of strong polyester fiber.

In addition, when the polyester fiber obtained by the above conventional method is viewed microstructurally, the average orientation of the fiber is low, more specifically, the orientation of the amorphous portion is low, and the relaxed structure of the entire fiber is characteristic. When the fiber is processed to reinforce a rubber structure, it shows a marked deterioration due to water or amines in the rubber, so that the so-called chemical stability tends to deteriorate.

Furthermore, the method of reducing the carboxyl end groups in the polyester for the purpose of improving the chemical stability also shows no contribution to the improvement of other properties, that is, strength, elastic modulus and dimensional stability, fatigue resistance and the like. Not a thing.

[Problems to be Solved by the Invention]

In view of the state of the art as described above, the purpose of the present invention is to
It is an object of the present invention to provide a polyester fiber having a high strength and a high elastic modulus and at the same time improved dimensional stability, fatigue resistance and chemical stability, which is suitable for reinforcing a rubber structure, and a method for producing the same.

[Means for Solving the Problems]

According to the present invention, a polyester fiber mainly comprising polyethylene terephthalate units, wherein (i) intrinsic viscosity [η] is 0.65 to 1.20 (ii) terminal carboxyl concentration COOH] is 30 equivalent / 10 ⁶ g
Hereinafter, (iii) birefringence [Delta] n is 189 × 10 ^{- 3} or more, (iv) the difference between the birefringence [Delta] n (c) between the central birefringence of the surface layer portion [Delta] n (s) is 6 × 10 ^{- 3 ~13 × 10 - 3, (v} ) an initial modulus of 120~140g / d, (vi) stress - in strain curve (a) 4.5g / d stress at the strain rate of at 3.3~3.8% (b) 2-order Provided is a polyester fiber for reinforcing a rubber structure, which has a strain rate at a yield point of 7.1 to 7.8%.

According to the present invention, (a) a polyester mainly composed of polyethylene terephthalate units is spun at a take-up speed of 2000 m / min or more, and then (b) the unstretched polyester fiber obtained is rounded at a speed of 100 m / min or less. And, the relaxation rate from immediately after stretching to the winding machine is 4% or less, (i) intrinsic viscosity [η] is 0.65 to 1.20 (ii) terminal carboxyl concentration COOH] is 30 equivalent / 10 ⁶ g
Hereinafter, (iii) birefringence [Delta] n is 189 × 10 ^{- 3} or more, (iv) the difference between the birefringence [Delta] n (c) between the central birefringence of the surface layer portion [Delta] n (s) is 6 × 10 ^{- 3 ~13 × 10 - 3, (v} ) an initial modulus of 120~140g / d, (vi) stress - in strain curve (a) 4.5g / d stress at the strain rate of at 3.3~3.8% (b) 2-order Provided is a method for producing a polyester fiber for reinforcing a rubber structure, which has a strain rate at a yield point of 7.1 to 7.8%.

First, the features of the polyester fiber of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows the stress-strain curve of the polyester fiber, and the curves a and a'in the figure are the stress-strain curve of the polyester fibers of Examples 2 and 4 according to the present invention.

Further, the curve b is a comparative example 5 in which a low orientation unstretched yarn obtained by slowly spinning a raw material polymer having a high degree of polymerization is multistage stretched at a high ratio.
Is a stress-strain curve of the polyester fiber of
Is a stress-strain curve of the polyester fiber of Comparative Example 4 in which a raw material polymer having a high degree of polymerization was spun at high speed and high tension and then stretched at a relatively high speed, and curve d was obtained by spinning at high speed and high tension. 3 is a stress-strain curve of the polyester fiber of Comparative Example 2 obtained by making the relaxation rate relatively large when the undrawn polyester yarn having a relatively high degree of orientation is drawn at a low speed.

Thus, as is clear from the comparison between the curves a, a'and b, c, d, the polyester fiber of the present invention has a stress-strain curve in addition to the characteristics of (vi) (a) and (b) above. (C) Strain rate at cutting is at least 8.5%, preferably 8.5-15% (d) Stress at the secondary yield point is at least 0.6 g / d, preferably 6-9 g / d (e) Secondary yield It has the characteristics that the strain rate in the strain region higher than the point is at least 1.0%, preferably 1 to 8% at the same time, and it has a very high initial elastic modulus, and in particular the strain rate to the stress up to the second yield point is extremely small. Shows a typical shape.

On the other hand, the stress-strain curves of b, c, and d do not have the above characteristics at the same time, and the strain rate with respect to the stress up to the secondary yield point is large.

Here, the secondary yield point is the characteristic represented by the point (A) in the stress-strain curve of FIG.
From the intersection of the tangents on the subsequent curve, a straight line indicated by an angle of θ ° is drawn on the curve, and it is determined by the intersection of this straight line and the stress-strain curve. Further, the strain rate at the time of cutting is the point of (B) in the stress-strain curve of FIG. 2, and the strain rate at 4.5 g / d stress (this is defined as the intermediate elongation) is (C). The strain rate in the strain region higher than the secondary yield point is the strain rate range represented by (B)-(A) = (D).

Furthermore, the intrinsic viscosity [η] of the unstretched polyester fiber of the present invention is in the range of 0.65 to 1.20, preferably 0.8 to 1.0.
When [η] is less than 0.65, the strength of the polyester fiber is low and it is not suitable as a fiber for reinforcing a rubber structure. Also,
When [η] is larger than 1.20, the dimensional stability as a rubber-reinforcing fiber is poor.

Terminal carboxyl group concentration of the polyester fiber of the present invention
COOH] is used to achieve the goal of improving chemical stability.
Equivalent / 10 ⁶ g or less, preferably 10 to 25 equivalent / 10 ⁶ g. When the COOH] is more than 30 equivalent / 10 ⁶ g, even if other properties are satisfied, the chemical stability to water and amines is not sufficient, which is not preferable.

The birefringence Δn of the polyester fiber of the present invention is 189 × 10 ^−
3 or more, preferably 189 × 10 ^- is a ^three range ^{- 3} to 205 × 10. Δn is 189 × 10 ^- will be left many fine structurally relaxed part because orientation is not sufficient as fibers average less than ^3, for example, 30 terminal carboxyl group concentration COOH] eq / 10
Even if it is suppressed to ⁶ g or less, the chemical resistance to water and amines is poor. Further, it is difficult to draw an undrawn yarn having a relatively high orientation to increase Δn. Therefore,
Preferably the upper limit of Δn is about 205 × 10 ^- and ^3.

Birefringence Δn of surface layer of polyester fiber of the present invention
The difference between (s) and the birefringence Δn (c) of the central portion is 6 × 10 ^{−.
1 3 ~13} × 10 ^{- 1 3.} This difference in birefringence is 13 × 10
^{A value} of more than ^-3 means that the uniformity of the polyester fiber is poor and the uniformity of the fiber for reinforcing a rubber structure is poor.

The initial modulus of the polyester fiber of the present invention is
120-140 g / to obtain fibers with the desired high elastic modulus
must be d.

In addition to the above-mentioned essential properties of the polyester fiber of the present invention, it is preferable that the elongation elastic recovery rate and work elastic recovery rate of the polyester fiber of the present invention at 3% elongation are 85% or more and 60% or more, respectively. If these recovery rates are low, the uniformity of the tire cord may be poor.

The polyester fiber according to the present invention satisfying the above-mentioned characteristics is twisted in the usual manner, further twisted in the usual manner, and then an adhesive is applied in the usual treating method to give a rubber structure-reinforcing fiber. In this case, it exhibits various excellent properties not found in conventional polyester fibers. That is, when the polyester fiber is used as a fiber for reinforcing a rubber structure, for example, an automobile tire cord, the following effects can be recognized.

(1) The tenacity holding ratio of the raw yarn at the processing stage is high, and thus the tenacity of the tire cord is high.

(2) Since the elastic modulus of the tire cord is high and the cutting elongation is properly maintained, the toughness of the cord is increased.

(3) The dimensional stability is remarkably improved, and the uniformity as a tire is improved.

(4) Fatigue resistance and chemical resistance, that is, durability is improved.

Next, the details of the relationship between the production method and production conditions of the polyester fiber according to the present invention and the performance of the obtained polyester fiber will be described.

The high-strength polyester fiber according to the present invention comprises a raw polyester mainly composed of polyethylene terephthalate units melted and discharged from a spinneret, and an unstretched system once wound at a take-up speed of 2,000 m / min or more is 100 m / min or less. It is produced by stretching at a speed.

The polyester used here is 85 mol% of its repeating unit.
The above is composed of ethylene terephthalate units, and particularly polyethylene terephthalate produced from terephthalic acid or a functional derivative thereof and ethylene glycol is mainly targeted. However, a part of terephthalic acid or a functional derivative thereof which is an acid component constituting polyethylene terephthalate is contained in less than 15 mol% such as isophthalic acid, adipic acid, sebacic acid, azelaic acid,
A difunctional acid such as naphthalic acid, p-oxybenzoic acid, and 2,5-dimethylterephthalic acid, or at least one functional derivative thereof, or a part of ethylene glycol which is a glycol component. To
The copolymer may be replaced with at least one dihydric alcohol such as diethylene glycol or 1,4-butanediol in an amount of less than 15 mol%. Further, these polyesters may contain antioxidants, flame retardants, adhesion improvers, matting agents, colorants and the like.

In melt spinning for obtaining the polyester fiber of the present invention, it is desirable that the take-up speed is 2,000 m / min or more. When the take-up speed is less than 2,000 m / min, high-strength polyester yarn can be obtained, but fiber for reinforcing a rubber structure, for example, dimensional stability when used as a tire cord,
Fatigue resistance is insufficiently improved.

Further, the birefringence of the polyester undrawn yarn before drawing in the present invention 15 × 10 is ^{- 3} above, boiling water shrinkage rate of 100% or less, it is preferred breaking elongation is 250% or less. Unstretched yarn birefringence of 15 × 10 ^- less than ^3, the boiling water shrinkage 100
% And cutting elongation of more than 250%, improvement in dimensional stability and fatigue resistance cannot be said to be sufficient even if the polymerization degree of polyester is increased or decreased.

Regarding the stretching method at the time of producing the polyester fiber according to the present invention, the stretching speed is 100 m / min or less, preferably 50 m
/ Min or less, and except that the relaxation rate from immediately after stretching to the winding machine must be 4% or less,
Stretching may be carried out according to a conventional method, and it is not necessary to limit the stretching. That is, the drawing for obtaining the polyester fiber of the present invention may be carried out in one step at once or in a multi-step drawing of two or more steps. As for the heating means for stretching, the feed roller and the stretching roller may be unheated, and a hot plate, a steam jet, or the like may be adopted between the rollers, or a heating roller system may be adopted.

Further, the temperature of the heating body at this time may be 90 to 250 ° C. which is a normal stretching temperature range of the polyester fiber, but considering the stretchability of the unstretched yarn and imparting toughness and dimensional stability to the obtained polyester fiber. If so, it is desirable that the temperature is 70 ° C. to 10 ° C., which is lower than the melting point of the polyester fiber.

Further, this drawing is actually carried out in a step separated from the spinning and winding step, but the method may be a drawing step alone, or a so-called direct draw twisting method in which the twisting step is connected later is industrially possible. It becomes one of the effective means.

Here, if the stretching speed exceeds 100 m / min, it becomes difficult to stretch at a high ratio and the strength of the obtained polyester fiber becomes low.
In addition, since the stretch orientation is not performed sufficiently, the orientation (birefringence index) as the fiber average becomes low, and many microstructurally relaxed parts remain, so that water or amine used for reinforcing the rubber structure The stability to the class deteriorates. Further, when the drawing speed exceeds 100 m / min, the birefringence difference between the inside of the obtained fiber and the surface layer portion, that is, the internal strain of the fiber becomes large.

Further, when the relaxation rate from immediately after stretching to the winding machine becomes large, the elastic modulus of the obtained polyester fiber becomes low and the birefringence also becomes small. Therefore, the relaxation rate should be suppressed to 4% or less. is necessary.

Incidentally, supplementing the above characteristics in the stress-strain curve of the polyester fiber according to the present invention, in the polyester fiber having a stress at the secondary yield point lower than 6.0 g / d,
It is not suitable for the intended reinforcement because the strength is not sufficient when the fiber is used for reinforcing the rubber structure by subjecting it to a lower twist, an upper twist, and then applying an adhesive. Particularly, those having a secondary yield point of 6 to 9 g / d are preferable.

The polyester fiber having a strain rate at the time of cutting lower than 8.5% and a strain rate in the strain region higher than the secondary yield point lower than 1.0% has a toughness when used as a fiber for reinforcing a rubber structure, that is, a fiber. The product of the strength and the square root of elongation becomes low, and it becomes impossible to exhibit sufficient overall performance as a reinforcing fiber.

Further, in the above polyester fiber having a strain rate at a stress of 4.5 g / d of more than 3.8% and a strain rate up to the second yield point of more than 7.8%, as a result, the stretch orientation is not sufficiently performed. Therefore, the orientation as the fiber average, that is, the characteristics such as the average birefringence and the degree of orientation of the amorphous portion is lowered, and particularly the chemical resistance to water or amines in the rubber structure is deteriorated. Further, the elastic recovery rate of the fiber against repeated tension, that is, the elongation elastic recovery rate and work elastic recovery rate in the range of 0 to 9%, particularly 0 to 4%, which is generally used as a fiber for reinforcing a rubber structure. Is low, and the uniformity is poor when the tire cord is used, for example.

As described above, the high-strength polyester fiber according to the present invention, the spinning winding at 2,000 m / min or more and 100 m / min or less,
It is preferably produced by a skillful combination with drawing at a speed of 50 m / min or less, and by this method, high-stretch drawing of the highly oriented polyester undrawn yarn according to the present invention, that is, the undrawn yarn cutting elongation Of 85% or more, preferably 90% or more, can be smoothly carried out without causing troubles such as feathers and yarn breakage during drawing. And the resulting polyester fiber of the present invention, since it was smoothly drawn at a relatively low speed and a high magnification, a highly oriented drawing that is finely ordered in a microstructure proceeds, and the orientation of the inside of the fiber and the surface layer part The difference in degree (that is, the difference in birefringence) is small, and thus the fiber has high strength and high elastic modulus, and also has excellent dimensional stability, fatigue resistance, and chemical resistance.

(F) Examples The present invention will be described below with reference to Examples. The definition of the characteristics and the measuring method described in the above description and Examples are shown below.

(1) Stress-strain curve JISL 1017-19 using Shimadzu Autograph DSS-100 type
The measurement was performed according to 78 (5.4). It should be noted that the reduction of denier due to stretching such as strength, intermediate elongation, initial modulus, etc. obtained by the load-stretching curve is not normally corrected.

(2) Intrinsic viscosity [η] Orthochlorphenol 10 using an Oswald viscometer
Reduced viscosity ηsp / of solution in which 1g of sample is dissolved per 0ml
c was measured in a constant temperature water bath at 35 ° C., and [η] was calculated by the following empirical formula.

ηsp / c = [η] + K / [η] ²・ C where K: Huggins constant (0.277) C: Sample concentration 1 (g / 100 ml) (3) Terminal carboxyl group concentration COOH] POHL method: Anal.Chem ., 26, 1616 (1957).

(4) Shrinkage rate of boiling water A sample collected with a scale (1 turn: 1.125 m) was placed in boiling water for 3 times.
The treatment was carried out for 0 minutes, and the ratio (percentage) of the shrinkage length to the original yarn length was shown.

(5) Dry heat shrinkage It complied with JISL-10017 / 1978 (5.12).

(6) Birefringence [Delta] n It was measured by a retardation method using a Berek compensator with a Na-D ray as a light source and [alpha] -bromonaphthalene / olive oil as an immersion liquid using a polarizing microscope.

(7) Initial modulus The measurement was performed according to JISL-1017 / 1978 (5.7).

(8) Elongation elastic recovery rate and work elastic recovery rate at 3% elongation A tensile load is applied to the sample to elongate it by 3%, and then unloading is performed for 5 cycles. The percentage of the elongation (elastic elongation) recovered for the fifth time was expressed as a percentage, and the elongation elastic recovery ratio was obtained. Further, the work elastic recovery rate was expressed as a percentage of the ratio of the fifth elastic work to the first elongation work at this time. This measurement was performed at 20 ° C and 65% (related temperature).

For a detailed explanation, please refer to "Newly Revised Textiles" published by Tokyo Denki University.

(9) Surface layer portion / internal difference of Δn Using an interference microscope, white light 550 μm was used as a light source, methylene iodide and α-bromonaphthalene / olive oil were used as immersion liquids, and Δn (s) of the surface layer portion of the sample single fiber was used. The inside (center) of Δn (c) was measured and the difference (Δn
(S) -Δn (c)) was calculated.

(10) Strong retention rate Calculated as follows.

Treated cord tenacity retention rate (%) = [treated cord tenacity / (raw yarn tenacity x 2)] x 100 (11) toughness Calculated by the following.

(12) Intermediate elongation In the case of the drawn yarn, the elongation at 4.5 g / d stress is shown, and in the case of the treated cord, the elongation at 4.5 kg stress is shown.

(13) Dimensional stability The parameters of intermediate elongation, dry shrinkage at 160 ° C and dimensional stability were used.

(14) Tube life Based on JISL 1017/1978 (13Z1A method), the time until tube breakage is shown.

(15) Heat-resistant strength retention rate After heat treatment was applied at 180 ° C for 1 hour with the treated cord embedded in rubber, the cord was taken out of the rubber and the strength ratio before and after heat treatment was measured to prevent it from reacting with water and amines. The chemical stability parameter was used.

Heat-resistant strength retention rate (%) = (process code strength after heat treatment / process code strength) x 10
0 Examples 1 to 9 Intrinsic viscosity [η] = 0.97, terminal carboxyl group concentration COO
H] = 18 (equivalents / 10 ⁶ g) of polyethylene terephthalate chips were melted by a screw extruder and spun. The polymer temperature at this time was 297 ° C, and the spinneret had a hole diameter of 0.35 m.
A m-hole having 250 holes was used.

The spun yarn discharged from the spinneret was passed through a heating cylinder with a length of 40 cm and an internal surface temperature of 200 ° C.
It is cooled and solidified by blowing cooling air with a relative humidity of 0%, and then oiled with an oiling roller.
It was wound through a take-up roll having a rotating peripheral speed of 00 to 4000 m / min and then wound.

Then, the obtained undrawn yarn is subjected to 10 to 10 by a horizontal drawing machine including a take-up roller, a feed roller, a hot plate, a drawing roller, a relaxing roller, and a winding machine.
Stretching at a winding speed of 0 m / min, limiting shrinkage (relaxation),
Various drawn yarns of 1000 (D) / 250 (f) were prepared.

The above-mentioned working conditions according to the present invention and the physical properties of the undrawn yarn are shown in Examples No. 1 to 9 of Table 1, and the physical properties of the drawn yarn are shown in Examples No. 1 to 9 of Table 2. The stress-strain curves of the drawn yarns obtained in Examples Nos. 2 and 4 are shown by curves a and a'in FIG. 1, respectively.

Here, the stretching speed under the stretching conditions in Table 1 indicates the rotational peripheral speed of the stretching roller described above, and the stretching ratio indicates the rotational peripheral speed of the take-up roller and the stretching roller described above.
The relaxation rate is a deceleration ratio of the winding machine with respect to the stretching roller, which is expressed as a percentage. The stretching temperature indicates the surface temperature of the hot plate described above, and in the present embodiment, the heating of the rollers is not performed. Further, the stretched state refers to the result of objective judgment based on the occurrence of feathers and yarn breakage during stretching and the observation of feathers of the stretched yarn.

Comparative Examples 1 and 2 Using the same undrawn yarn and the same drawing device as those used in Examples 2 to 4 or 7 to 9 above, a drawing speed of 18 m
/ Min, stretching ratio 2.237, relaxation rate 6% and 8%, respectively. Regarding the stretching temperature, the hot plate was set at 220 ° C. and the stretching roller was set at 210 ° C., so that relaxation could be performed without any problem. (By heating the drawing roller, a relaxation operation of 4% or more is possible.) The above comparative execution conditions and undrawn yarn properties are shown in Comparative Examples 1 and 2 of Table 1, and the drawn yarn properties are shown in Table 1. Comparative Example 1
And 2 are shown.

Comparative Example 3 Using an undrawn yarn under exactly the same conditions as the undrawn yarn used in Examples 2 to 4 or 7 to 9 above, drawing was performed at a drawing speed of 1,500 m / min. At this time, the stretching device includes a take-up roller, a feed roller, a stretching roller, a relaxing roller,
Using a vertical stretching device consisting of a winding machine and a winder, the feed roller temperature is 130 ° C, the stretching roller temperature is 230 ° C, and the stretching ratio is
2.152, relax rate was 2%.

The above-mentioned 2.152 was the limit for the draw ratio, and the relaxation rate was 2% or less, it was impossible to collect.

Comparative Example 4 Using the same undrawn yarn and the same drawing device as those used in Examples 2 to 4 or 7 to 9 above, the drawing speed was 150 m / min, the drawing temperature was 220 ° C. and the relaxation rate was 2%. I went.

The draw ratio of 2.152 above was the limit, and above this range, feathers and yarn breakage occurred frequently.

First, the above-mentioned execution conditions and physical properties of undrawn yarn of Comparative Examples 3 and 4
The physical properties of the drawn yarns thus obtained are shown in Comparative Examples 3 and 4 in the table and in Comparative Examples 3 and 4 in Table 2.

Comparative Example 5 Using the same chips as those used in Examples 1 to 9 above, melting and spinning were carried out in a screw extruder. The polymer temperature at this time was 293 ° C., and the spinneret used had a hole diameter of 0.35 mm and a hole number of 192 holes.

The spun yarn discharged from this spinneret was passed through a heating cylinder with a length of 40 cm and an internal surface temperature of 300 ° C, and then blown with cooling air having a temperature of 20 ° C and a relative humidity of 80%. After cooling and solidifying, an oiling agent was applied by an oiling roller and the oil was guided to a take-up roller, and immediately stretched without winding.

The stretching conditions at this time are: take-up roller 475 m / min, feed roller 480 m / min, first stretching roller 1983 m / min, second
The stretching roller was 2887 m / min, the relaxing roller was 2800 m / min, and the roller temperature was 100 ° C. for the feed roller, 130 ° C. for the first stretching roller, 230 ° C. for the second stretching roller, and 180 ° C. for the relaxing roller.

After this, the drawn yarn is immediately wound up 1000 (D) / 192
The drawn yarn of (f) was used.

The above comparative execution conditions and unstretched yarn properties are shown in Comparative Example 5 in Table 1, and the stretched yarn properties are shown in Comparative Example 5 in Table 2.

Comparative Example 6 A polyethylene terephthalate chip having [η] = 0.67 and COOH] = 19 (equivalent / 10 ⁶ g) was melted by a screw extruder and spun. Polymer temperature at this time is 291 ℃,
The spinneret used was 0.35 mm and had 384 holes.

The spun yarn discharged from the spinneret was passed through a heat-retaining cylinder having a length of 15 cm and an internal surface temperature of 110 ° C., and then cooled and solidified by blowing cooling air having a temperature of 20 ° C. and a relative humidity of 80%,
Then, an oiling agent was applied by an oiling roller and the oil was guided to a take-up roller, and immediately stretched without winding.

The drawing conditions at this time were: take-up roller 620 m / min, feed roller 626 m / min (110 ° C), first drawing roller 2400 m / min.
Min (130 ° C.), second stretching roller 3600 m / min (240 ° C.), relax roller 3500 m / min (230 ° C.). After this,
Immediately wind the drawn yarn 1000 (D) / 384 (f)
Of the drawn yarn.

The above comparative actual spinning conditions and unstretched yarn properties are shown in Comparative Example 6 in Table 1, and the stretched yarn properties are shown in Comparative Example 6 in Table 2.

The stress-strain curves of the drawn yarns obtained in Comparative Examples 5, 4 and 2 are shown by curves b, c and d in FIG. 1, respectively.

As is clear from the above Examples 1 to 9 and Comparative Examples 1 to 6, the drawn yarn of the present invention has an elongation (intermediate elongation) at 4.5 g / d stress and an elongation at the second yield point. Low, high degree of orientation Initial modulus, birefringence Δ despite undrawn yarn
The values of n, extension elastic recovery rate, work elastic recovery rate are high, and the difference in birefringence between the surface layer portion and the inside is relatively small, which is a very characteristic characteristic.

Examples 1 ′ to 9 ′ and Comparative Examples 1 ′ to 6 ′ The drawn yarns obtained in the above Examples and Comparative Examples were twisted with a twisting machine to make a lower twist in the Z direction of 490 T / m and an upper twist in the S direction of 490 T / m.
After making it into a raw cord and then applying an adhesive mainly composed of resorcin / formalin / rubber latex to this raw cord, dry heat at 160 ° C for 90 seconds at a constant length, dry heat at 240 ° C for 120 seconds under tension , 240 ℃ dry heat, 40 in relaxed state
A heat treatment was performed for 2 seconds to obtain a treatment code. The tension rate and the relaxation rate depend on the physical properties of the drawn yarn.
The elongation at 4.5 kg stress was set to 4.5%.

The treated cord made of the drawn yarn according to the present invention has a high strength utilization factor, high strength, high elastic modulus, high toughness, and is remarkably comprehensive in improvement of dimensional stability, fatigue resistance, and chemical stability. It can be seen that also has extremely excellent performance.

[Brief description of drawings]

FIG. 1 is a stress-strain curve of a drawn polyethylene terephthalate yarn, curves a (Example 2) and a ′ (Example 4) are stress-strain curves of the polyester fiber according to the present invention, and curve b (comparison). Examples 5), c (Comparative Example 4) and d (Comparative Example 2) are stress-strain curves of polyester fibers according to the prior art. Further, in FIG. 1, (a) shows the range when the initial modulus in the present invention is converted to 1% elongation, and (b) shows the strain rate range at the time of 4.5 g / d stress in the present invention. , (C) show the strain rate range at the secondary yield point in the present invention. FIG. 2 shows the definition of each part of the stress-strain curve. (A): Second yield point, (B): Strain rate (elongation) at cutting, (C): Strain rate at 4.5 g / d stress (intermediate elongation), (D): Second yield point The strain rate in the higher strain region.

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Claims (2)

[Claims] 1. A polyester fiber mainly composed of polyethylene terephthalate units, wherein (i) intrinsic viscosity [η] is 0.65 to 1.20 (ii) terminal carboxyl concentration COOH] is 30 equivalents / 10 ⁶ g.
Hereinafter, (iii) birefringence [Delta] n is 189 × 10 ^{- 3} or more, (iv) the difference between the birefringence [Delta] n (c) between the central birefringence of the surface layer portion [Delta] n (s) is 6 × 10 ^{- 3 ~13 × 10 - 3, (v} ) an initial modulus of 120~140g / d, (vi) stress - in strain curve (a) 4.5g / d stress at the strain rate of at 3.3~3.8% (b) 2-order A polyester fiber for reinforcing a rubber structure, which has a strain rate at a yield point of 7.1 to 7.8%. (A) Polyester mainly composed of polyethylene terephthalate units is spun at a drawing speed of 2000 m / min or more, and (b) the obtained unstretched polyester fiber is stretched at a speed of 100 m / min or less and immediately after stretching. (I) intrinsic viscosity [η] is 0.65 to 1.20 (ii) terminal carboxyl concentration COOH] is 30 equivalents / 10 ⁶ g, with a relaxation rate of from 4 to less than 4%.
Hereinafter, (iii) birefringence [Delta] n is 189 × 10 ^{- 3} or more, (iv) the difference between the birefringence [Delta] n (c) between the central birefringence of the surface layer portion [Delta] n (s) is 6 × 10 ^{- 3 ~13 × 10 - 3, (v} ) an initial modulus of 120~140g / d, (vi) stress - in strain curve (a) 4.5g / d stress at the strain rate of at 3.3~3.8% (b) 2-order A method for producing a polyester fiber for reinforcing a rubber structure, which comprises producing a polyester fiber having a strain rate at a yield point of 7.1 to 7.8%.