JPH02289115A - Polyester fiber having high toughness and production thereof - Google Patents

Abstract

PURPOSE:To obtain the subject fiber having high strength and high toughness and suitable for industrial materials by melt-spinning polyethylene terephthalate to obtain an undrawn filament having low orientation and specific physical properties and subjecting the filament to a specific treatment. CONSTITUTION:An undrawn filament having low orientation, an intrinsic viscosity of >=0.9 and a birefringence of 0.001-0.006 is produced by the melt-spinning of polyethylene terephthalate. The undrawn filament is drawn >=3.8 times under heating and then drawn 1.07-1.35 times at 280-450 deg.C. Subsequently, the drawn yarn is passed through a hot roll of 215-280 deg.C and wound at a relaxation ratio of 1-15% to obtain the objective fiber composed mainly of ethylene terephthalate unit and having a tenacity of >=10g/d, an elongation at break of >=15%, an initial modulus M0 of <=140g/d and a ratio (M8/M0) of >=0.4 wherein M8 is modulus at a stress of 8g/d.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a polyester fiber suitable for industrial use as belt reinforcing materials, tire cords, robes, etc., and a method for producing the same. The present invention relates to high toughness polyester fibers exhibiting high toughness values and methods for producing such fibers.

[Prior art] Polyester fiber has strength comparable to nylon and initial elastic modulus comparable to rayon, and has a better balance of physical properties than other fiber materials, so it is used as an industrial material. Widely used. High-strength polyester fibers are particularly preferred for industrial materials.
In recent years, it has come to be widely used for belt reinforcing materials, tire cords, lobes, etc.

[Problems to be Solved by the Invention] As a method for producing high-strength polyester fibers, for example, Japanese Patent Publication No. 41-7891 proposes a technique using high molecular weight polyethylene terephthalate. However, this technology simply stretches high-molecular-weight polyethylene terephthalate at a high magnification, so the higher the stretching magnification and the higher the strength, the higher the strength, which is another requirement for industrial materials. It has the disadvantage that the cutting elongation is low.

On the other hand, as a technique for producing polyester fibers with high cutting elongation (that is, high toughness), for example,
24 and Japanese Patent Laid-Open No. 62-69842, etc., have been proposed. However, with the technique disclosed in Japanese Patent Publication No. 58-51524, polyester fibers with a high breaking elongation of 24.6% were obtained, but in terms of strength, only 7.8 g/d or less could be obtained. Therefore, it cannot be said that this level of strength satisfies the characteristics required for industrial materials. Also, JP-A-62-69
The technology disclosed in No. 842 attempts to obtain high elongation through relaxation heat treatment, and is a technology that appropriately controls the secondary yield point. No increase in stress is expected until the cutting elongation is reached, and a product with substantially high strength has not been obtained.

As described above, the strength and elongation at break of polyester fibers are contradictory properties, and it is desired to develop polyester fibers that simultaneously satisfy both properties.

The present invention was made to solve these technical problems, and its purpose is to provide a polyester fiber that has high strength and toughness and is optimal for use as an industrial material, and a method for producing the same. be.

[Means for Solving the Problems] The high toughness polyester fiber of the present invention that achieves the above object contains ethylene terephthalate as a main component and satisfies the following requirements (a) to (d).

(a) Strength≧to, og/d (b) Cutting elongation≧15% (C) Initial modulus (Mo)≦140g/d (d)
The ratio of the modulus (M, ) at the stress point of 8 g/d to the initial modulus (Mo) (M a / Mo) ≧ 0.4 In addition, high toughness polyester fibers such as those described above can be obtained by melt-spinning polyethylene terephthalate to obtain the ultimate Obtain a low-oriented undrawn filament with a viscosity number of 0.9 or more and a birefringence index of 0.001 to 0.006, and after stretching the filament to 3.8 times or more while heating, the filament is heated at a temperature of 280 to 450°C. 1.07~1
．． Stretched to 35 times and continued! It can be produced by rolling it through heated rolls at e2ts to 280°C with a relaxation rate of 1 to 15%.

[Function] The present invention is constructed as described above, but in short, polyethylene terephthalate is melt-spun to obtain a low-oriented undrawn filament exhibiting a predetermined intrinsic viscosity index and birefringence, and this filament is stretched twice. 1st after treatment
It was discovered that high toughness polyester fibers having desired properties could be produced by subjecting the fibers to a double relaxation treatment, and the present invention was completed.

The polymer used in the present invention has ethylene terephthalate as its main component, which means a polymer containing at least 90%, preferably 95%, of polyethylene terephthalate. That is, the high toughness polyester fiber according to the present invention is intended to have properties for use in tire cords, but in order to satisfy those properties, it requires a heat treatment process at a high temperature as described below. In order to prevent a decrease in the melting point due to copolymerization in this step, it is necessary to suppress the copolymerized units to at least less than 10%, preferably less than 5%. In the copolymerized unit of polyester, acid components include isophthalic acid, naphthalene dicarboxylic acid, adipic acid, oxybenzoic acid, etc., and glycol components include diethylene glycol, propylene glycol, trimellitic acid, pentaerythritol, etc. However, it is not limited to these examples. Moreover, it goes without saying that the polyester fiber according to the present invention may contain additives such as stabilizers and colorants.

Each of the requirements (a) to (a) of the polyester fiber according to the present invention
d) is satisfied, but the reason for limiting the setting value is as follows.

(a) Strength≧lO, Og/d Considering the quality level required for structural materials in the recent trend of biotechnology, the strength must be at least 10.0 g/d.

(b) Cutting elongation ≧15% In order to use polyester fiber as a structural material, its cutting elongation must be 15% or more. That is, even if the strength of the polyester fiber is 10.0 g/d or more, if the elongation at break is less than 15%, the energy absorption amount of the load cannot be said to be sufficient.

(c) Initial modulus (Mo)≦140 g/dFor fibers that produce large deformation resistance when the deformation of the structural material is small, a large work load will be applied to the fibers. However, in the high deformation region where such fibers should be effective,
Inability to secure sufficient energy absorption. For these reasons, fibers suitable for such uses must have an initial modulus (Mo: indicated by the slope of line A in FIG. 1) of stress-strain characteristics of 140 g/d or less.

The preferred range of the initial modulus M0 is 130 g/
d or less.

(d) Ratio of modulus (Mo) at 8 g/d stress point to initial modulus (Mo) (M a/Mo)≧0.
4. Fibers that can be used under high loads are best if they have a high tensile resistance even under high stress.

The polyester fiber of the present invention was tested in a tensile test (deformation rate = 1
00%win-') stress is 8g/d in the strain curve.
It has a characteristic that the modulus (Mo: slope of line B in FIG. 1) at the stress point is sufficiently high.

That is, in the polyester fiber of the present invention, the ratio of the modulus M8 at the stress point of 8 g/d to the initial modulus M0 (Ma
/Mo) of 0.4 or more can be obtained. Note that the above ratio <
A more preferable value for M 11/M O) is 0.
It is 6 or more, more preferably 0.7 or more.

Further, as for the absolute value of the modulus M♂ at the stress point of 8 g/d, if it is 40 g/d or more, the strength can be substantially set sufficiently high, but it is more preferably 50 g/d.
d or more, particularly preferably 60 g/d or more.

On the other hand, from the viewpoint of reliably achieving energy absorption when undergoing large deformation under high stress, the above modulus M
6 is preferably 50 g/d or more. Modulus M! , is less than 50 g/d, the modulus at intermediate elongation, e.g. % of elongation at break (line C in Figure 1)
(gradient), and the effect of preventing deformation is not sufficiently exerted.

By the way, for fibers with high modulus under high stress, consider the proportion of molecular chains that bear stress in the low elongation range where strain is small, and the proportion of molecules and chains that bear stress in the high elongation area where strain is large. Therefore, a structure with fewer molecular chains that bear stress in the low elongation region is suitable. From this perspective (M a/M
o) In order to obtain fibers with a high ratio, it seems that the degree of orientation on the fiber surface should be lower than the degree of orientation at the center of the fiber. Furthermore, since the degree of orientation is expressed based on the birefringence index, the above idea indicates that it is preferable that the birefringence index at the center of the fiber is larger than the birefringence index at the fiber surface.

That is, it is preferable that the difference Δn0 in the birefringence expressed as (birefringence of the fiber surface)−(birefringence of the center of the ia fiber) is less than or equal to O, and a more preferable value is the difference Δn0≦−IXIO
-3.

In this way, by suppressing the molecular chain orientation in the outer layer in the fiber cross section to be lower than the molecular chain orientation in the center,
The molecular chains in the outer layer, which have a large volume fraction, can bear stress in the high elongation range.

Fibers that have such high breaking elongation and high elastic modulus under high stress have the characteristics that when used as structural materials, the rate of increase in energy absorption is gradual and the total amount of energy absorption is large. and high safety can be obtained. Such fibers are extremely effective in ensuring safety for the human body when used, for example, in seat belts.

Next, a method for producing polyester fibers having the above characteristics will be explained.

In the present invention, first, polyethylene terephthalate is melt-spun to obtain an intrinsic viscosity of 20.9 or more and a birefringence of +0.00.
It is necessary to use low orientation undrawn filaments of 1 to 0.006.

The reason why the above-mentioned intrinsic viscosity number is set to 0.9 or more is to take into consideration the minimum strength required as an industrial material. The preferable value of the intrinsic viscosity index is 0.95 or more.

Further, the intrinsic viscosity in the present invention is a value measured at 30° C. using a mixed solvent of p-chlorophenol/tetrachloroethine (3:1).

In the present invention, as will be described later, in order to obtain high strength, it is necessary to perform the first stretching at a high temperature and at a high magnification. In this way, in order to increase the stretching ratio in the first stretching, it is necessary to suppress the molecular chain orientation in the spinning process as much as possible. From this point of view, the birefringence of undrawn filaments is 0.
It needs to be 006 or less. However, if the birefringence index of the undrawn filament is less than 0.001, stable spinning is difficult and it is not possible to obtain an undrawn yarn with few irregularities in the longitudinal direction, leading to problems such as single filament breakage in the drawing process. .

In order to obtain the fiber of the present invention, it is first necessary to carry out the first drawing at high temperature and high magnification. The temperature at this time is, for example, about 250 to 370°C. If the stretching ratio is kept low during stretching in such a temperature range, a high-strength yarn of 10.0 g/d or more cannot be obtained, so it is necessary to stretch the yarn to 3.8 times or more in a heated steam atmosphere, for example. The preferable range of the stretching ratio at this time is 5.0 times or more.

On the other hand, the second drawing is an essential step in order to obtain fibers with high toughness. In this drawing, it is necessary to carry out the drawing so that deformation occurs after the temperature of the outer layer of the yarn cross section reaches a temperature near the melting point of the polymer (while the temperature of the center has risen sufficiently). That is, it is necessary to control the heating capacity of the heater and the stretching ratio so that the stretching is performed when the temperature of the outer layer of the yarn reaches near the melting point in the temperature distribution within the cross section of the yarn. If the stretching ratio is too high, the stretching will occur before the temperature of the 6 parts in the system rises sufficiently, and although the strength can be increased, the initial elastic modulus will increase too much, making it impossible to obtain a polyester fiber with high toughness. If it is too low, the internal orientation of the yarn will not progress and a high strength yarn cannot be obtained.From this viewpoint, in the present invention, the second stretching ratio is set to 1.0.
It was set at 7 to 1.35 times. Also, from a place like this,
The stretching temperature needs to be set relatively high, and its range is from 280 to 450°C.

The reason for performing the second drawing process as described above is because we discovered that in order to obtain fibers with high toughness, it is possible to reduce the orientation of the molecular chains in the surface layer of the filament while maintaining its original strength. It is something. Although stretching has been carried out in two stages, the conventional method is to increase the stretching tension as much as possible in the second stage to achieve maximum stretching at high temperatures. It was considered desirable to be able to raise the temperature of the entire system as quickly as possible. Therefore, simply lowering the draw ratio using the conventional method will only lower the orientation of the entire system, and the strength will decrease accordingly.

In the manufacturing method according to the present invention, relaxation heat treatment is finally performed, which is specifically described in the above-mentioned Japanese Patent Application Laid-open No. 62-69.
This is done in the same way as No. 842 to obtain high elongation. However, in the present invention, the desired strength is ensured by the above-mentioned two-time stretching process.

In this relaxation heat treatment, in consideration of the dimensional stability of the yarn, it is necessary to pass the yarn through heating rolls at 215 to 280°C. Further, the relaxation rate needs to be in the range of 1 to 15%. If the relaxation rate is less than 1%, troubles such as winding of the bobbin are likely to occur, and if it exceeds 15%, relaxation will progress and the strength will decrease.

Next, a method for measuring the distribution of birefringence Δn within the fiber cross section of the polyester fiber according to the present invention will be described.

<Method for measuring the distribution of birefringence Δn within the fiber cross section> The central refractive index (
n top, O, nH, O) and peripheral refractive index (n top, 0.9
, n77, 0.9) reveals the unique molecular orientation of the fibers of the invention and can be associated with the superior strength of the fibers of the invention. The distribution of the average refractive index observed from the side of the fiber can be measured by the interference fringe method obtained using a transmission quantitative interference microscope (for example, interference microscope Interfaco manufactured by Carl Zeiss Jena, East Germany). This method can be applied to fibers with a circular cross section. The refractive index of a fiber is characterized by the refractive index (n//) for polarized light vibrating parallel to the fiber and the refractive index (n on) for polarized light vibrating perpendicular to the axis perpendicular to the fiber axis. .

All the measurements described here are carried out using a xenon lamp as a light source, under polarized light, with the refractive index (n// and above n) obtained using a green light beam with an interference filter wavelength of 544n11. Below, we will explain in detail the measurement of n// and the n//, 0 and n//*'' found from above n. The fibers used are optically flat glass slides and coverslips, and the fibers are placed in an inert mounting medium with a refractive index (nE) that gives interference fringes anywhere from 0.2 to 1 wavelength. The refractive index of the mounting medium (n,
) is the value at 20° C. measured using an Atsube refractometer using green light (wavelength λ-*544 ns) as a light source. This mounting medium can be prepared, for example, from a mixed solution of liquid rough-in and α-bromnaphthalene having a refractive index of 1°48 to 1.65.

A single fiber is immersed in this mounting medium. This pattern of interference fringes is photographed, magnified 10 to 2000 times, and analyzed.

The refractive index of the fiber's encapsulant is nl, and the fiber's S.

The average refractive index between S'' is n//+ The thickness between s' and s'' is t, the wavelength λ of the used light beam, the distance between parallel interference fringes in the background (corresponding to 1λ) is Dn, and the interference fringes due to fibers. Letting the deviation of dn be the optical path difference.

If the refractive index of the sample is nl, the refractive index of the filled liquid is ns
The interference fringe pattern is evaluated using two types of <n(-nl, n3>ny-nl).

Therefore, based on [Equation 11], from the optical path difference at each position from the center of the fiber to the outer periphery, the average refractive index of the fiber at each position (n
//) can be found.

The thickness t can be calculated by assuming that the obtained fiber has a circular cross section. However, due to variations in manufacturing conditions or accidents after manufacturing, there may be cases where the cross section is not circular. In order to eliminate this inconvenience, it is appropriate to use a portion to be measured where the displacement of the interference fringes is symmetrical with the fiber axis as the axis of symmetry. When the radius of the fiber is R, the measurement ranges from 0 to 0.9R. I
By performing this at intervals of R, the average refractive index at each position can be determined. Similarly, the distribution on n can be found, so the birefringence distribution is Δn(r/R) = n // (r/R) - on n(r/R) - [11
]. Note that Δn(r/R) is preferably measured on at least three filaments, preferably 5 to 10 filaments, and used as an average value.

Hereinafter, the present invention will be explained in more detail with reference to examples, but the following examples are not intended to limit the present invention.
Any design changes for the purposes described below are included within the technical scope of the present invention.

[Example] Polyethylene terephthalate having different molecular weights were melt-spun, stretched twice in succession using a superheated steam heater, and then relaxed by 8% and taken out. The manufacturing conditions and physical properties of the obtained fibers are shown in Table 1.

From Table 1, the following can be considered.

First, considering the influence of the degree of polymerization, the intrinsic viscosity is 0.8.
In condition 8 (No. 1 to 3), even if the stretching ratio was changed,
A fiber with a strength of 10.0 g/d or more and a breaking elongation of 15% could not be obtained. On the other hand, the intrinsic viscosity number is 0.94
．． 1.01.1.17 fiber (No, 4.5.8°9)
In this case, a material with a strength of 10.0 g/d or more and an elongation of 15% or more was obtained (see Fig. 1).

Next, when considering the influence of the undrawn birefringence value, under the condition that the undrawn yarn has a high orientation (No. 6.7), the birefringence value of the undrawn yarn is 10.
It was not possible to obtain a strength of 0 g/d or more (see Figure 1).

Furthermore, when considering the effect of the stretching ratio, under the conditions where the first stretching ratio is low (No, to, 11),
No fibers with a strength of 10.0 g/d or more and an elongation of 15% or more were obtained. In addition, conditions were set in which the first stretch ratio was slightly suppressed and the second stretch ratio was set high (No. 12
), no fibers with (M a/Mo) of 0.40 or more were obtained.

In addition, No. 8 (Example 3) and No. 12 (Comparative example)
The cross-sectional birefringence distribution of the fiber is as shown in Figure 2, and when compared with Table 1, the fiber with (birefringence of the fiber surface) - (birefringence of the Ia fiber center) ≦0 has a ratio ( It can be seen that M 8 /M O) has become high.

Next, polyethylene terephthalate having an intrinsic viscosity of 1.3 was melt-spun under the same spinning conditions as No. 8 (Example 3), and immediately the first temperature was 15 using a superheated steam heater.
Stretching was performed twice at 0° C. and at 270° C. for the second time. The stretching ratio at this time and the physical properties of the obtained fibers are shown in Table 2.

The stress/strain curves for each of the above fibers are also shown in FIG.

As is clear from this result, the typical stress-strain curve (line B) of the present invention has a higher modulus in the high elongation range than (No. 13 to 17).

In addition, the breaking points of No. 13 to 17 1a fibers are on the dashed dotted line in Figure 1, and are in the area where the strength is 10.0 g/d or more and the elongation is 15% (shown by the diagonal line in Figure 1). ) has not been reached.

[Effects of the Invention] The present invention is configured as described above, and the polyester fiber according to the present invention has high toughness and unprecedented high strength, and has excellent energy absorption under high stress. It is a fiber with extremely excellent impact resistance because it has the characteristic of increasing rapidly. Such fibers are particularly useful as reinforcing materials for structural members that are susceptible to large deformations.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the relationship between elongation and strength (relationship between stress and strain), and Fig. 2 shows Example 3 and Comparative Example (No. 1).

Claims (1)

[Scope of Claims] (1) The main component is ethylene terephthalate, and the following (a)
A high toughness polyester fiber characterized by satisfying the requirements of ) to (d). (a) Strength≧10.0g/d (b) Cutting elongation≧15% (c) Initial modulus (M_o)≦140g/d (d)
Ratio of modulus (M_a) at 8g/d stress point and initial modulus (M_o) (M_a/M_o) ≧0.4 (2)
The polyester fiber according to claim 1, wherein M_a≧50 g/d. (3) The polyester fiber according to claim (1) or (2), wherein (birefringence of the fiber surface) - (birefringence of the fiber center)≦0. (4) Polyethylene terephthalate is melt-spun to have an intrinsic viscosity of 0.9 or more and a birefringence of 0.001 to 0.00.
After obtaining a low orientation undrawn filament of No. 6 and drawing the filament 3.8 times or more under heating,
Stretched 1.07 to 1.35 times at a temperature of 215
A method for producing a high toughness polyester fiber, characterized in that the polyester fiber according to any one of claims (1) to (3) is obtained by winding it through a heating roll at ~280°C with a relaxation rate of 1 to 15%. .