Modified polytrimethylene terephthalate

The present invention provides poly(trimethylene terephthalate) copolymerized with ester-forming sulfonate and a fiber thereof. The polymer of the present invention is high in melting point, small in loss of melting viscosity and has a high molecular weight. The fiber of the present invention is high in toughness, excellent in whiteness and dyeable with a cationic dye, whereby it is useful for clothing, carpets or non-woven sheets, etc.

 

What we claimed is:

1. A poly(trimethylene terephthalate) copolymer characterized in that it satisfies the following conditions (1) to (4):

(1) ester-forming sulfonate in a range from 0.5 to 5 mol % is copolymerized relative to a total dicarbonic acid component;

(2) bis (3-hydroxypropyl) ether in a range from 0.1 to 2.5 wt % is copolymerized;

(3) an intrinsic viscosity is in a range from 0.65 to 1.5 dl/g, and

(4) an amount of terminal carboxyl groups is 25 milli-equivalent per kg resin or less.

2. A poly(trimethylene terephthalate) copolymer as defined by claim 1 wherein the intrinsic viscosity is in a range from 0.85 to 1.25 dl/g.

3. A poly(trimethylene terephthalate) copolymer as defined by claim 1 wherein a b* value is in a range from -2 to 6.

4. A method for producing a poly(trimethylene terephthalate) copolymer characterized in that the method comprises the steps of: reacting lower alcohol ester of terephthalic acid, which is a main dicarboxylic acid component, with 1,3-propanediol, which is a main diol component, to form 1,3-propanediol ester of terephthalic acid and/or oligomer thereof; after completing the polycondensation reaction, once solidifying the resultant polymer; and heating the polymer in a solid state to increase an intrinsic viscosity thereof by 0.1 dl/g or more from that at a time when the polycondensation reaction has completed, and the method satisfies the following conditions (a) and (b):

(a) ester-forming sulfonate corresponding to an amount in a range from 0.5 to 5 mol % of a total dicarboxylic acid component is added at any optional stage from the initiation of reaction to the completion of the polycondensation reaction, and

(b) an amount of terminal carboxyl groups of poly(trimethylene terephthalate) copolymer is in a range from 5 to 40 milli-equivalent per kg resin before the initiation of solid-state polymerization.

5. A method for producing a poly(trimethylene terephthalate) copolymer characterized in that the method comprises the steps of: reacting terephthalic acid, which is a main dicarboxylic acid component, with 1,3-propanediol, which is a main diol component, to form 1,3-propanediol ester of terephthalic acid and/or oligomer thereof; after completing the polycondensation reaction, solidifying the resultant polymer; and heating the polymer in a solid state to increase an intrinsic viscosity thereof by 0.1 dl/g or more from that at a time when the polycondensation reaction has completed, and the method satisfies the following conditions (a) to (c):

(a) the molar ratio of 1,3-propanediol to terephthalic acid is in a range from 0.8 to 2.5,

(b) in the reaction of terephthalic acid with diol mainly composed of 1,3-propanediol, at a stage wherein a rate of reaction of terephthalic acid is in a range from 75 to 100%, an amount of ester-forming sulfonate corresponding to a range from 0.5 to 5 mol % of total dicarboxylic acid component is added, and

(c) the amount of terminal carboxyl groups of poly(trimethylene terephthalate) copolymer is in a range from 5 to 40 milli-equivalent per kg resin before the initiation of solid-state polymerization.

6. A method for producing a poly(trimethylene terephthalate) copolymer comprising the steps of: by reacting terephthalic acid, which is a main dicarboxylic acid component, with 1,3-propanediol, which is a main diol component, to form 1,3-propanediol ester of terephthalic acid and/or oligomer thereof; after completing the polycondensation reaction, characterized in that the method satisfies the following conditions (a) to (c):

(a) a molar ratio of 1,3-propanediol to terephthalic acid is in a range from 0.8 to 2.5,

(b) in the reaction of terephthalic acid with diol mainly composed of 1,3-propanediol, at a stage wherein a rate of reaction of terephthalic acid is in a range from 75 to 100%, an amount of ester-forming sulfonate corresponding to a range from 0.5 to 5 mol % of total dicarboxylic acid component is added, and

(c) an amount of terminal carboxyl groups of poly(trimethylene terephthalate) copolymer is in a range from 5 to 40 milli-equivalent per kg resin.

7. A method for producing a poly(trimethylene terephthalate) copolymer as defined by any one of claims 4 to 6, wherein an alkaline metal compound and/or an alkaline earth metal compound corresponding to an amount in a range from 1 to 100 mol % of ester-forming sulfonate is added at any optional stage from the initiation of reaction to the completion of the polycondensation reaction.

8. A poly(trimethylene terephthalate) copolymer fiber characterized in that it satisfies the following conditions (1) to (4):

(1) ester-forming sulfonate in a range from 0.5 to 5 mol % is copolymerized relative to a total dicarboxylic acid component;

(2) bis (3-hydroxypropyl) ether in a range from 0.1 to 2.5 wt % is copolymerized;

(3) an intrinsic viscosity is in a range from 0.65 to 1.5 dl/g, and

(4) an amount of terminal carboxyl groups is in a range from 5 to 40 milli-equivalent per kg fiber or less.

9. A poly(trimethylene terephthalate) copolymer fiber characterized in that ester-forming sulfonate in a range from 0.5 to 5 mol % is copolymerized relative to a total dicarboxylic acid component, and the fiber satisfies the following conditions (A) to (C):

(A) an intrinsic viscosity [.eta.] is in a range from 0.65 to 1.4 dl/g,

(B) a peak temperature of a dynamic loss tangent is in a range from 105 to 140.degree. C., and

(C) a boiling water shrinkage is in a range from 0 to 16%.

10. A poly(trimethylene terephthalate) copolymer fiber as defined by claim 9, further satisfying the following conditions (D) and (E):

(D) an elongation at break is in a range from 20 to 70%, and

(E) a toughness is 16 or more, wherein the toughness is calculated by the following equation:

Toughness=[Strength (cN/dtex)].times.[Elongation (%)].sup.1/2.

11. A poly(trimethylene terephthalate) copolymer fiber as defined by claim 10, wherein the toughness is 17.5 or more.

12. An undrawn poly(trimethylene terephthalate) copolymer fiber characterized in that it consists of poly(trimethylene terephthalate) formed by copolymerizing ester-forming sulfonate in a range from 0.5 to 5 mol % to a total dicarboxylic acid component to have an intrinsic viscosity in a range from 0.65 to 1.4 dl/g, and it has an elongation at break in a range from 150 to 600% and a crystallization peak temperature in a range from 64 to 80.degree. C.

13. A method for producing a poly(trimethylene terephthalate) copolymer fiber characterized in that an undrawn poly(trimethylene terephthalate) copolymer fiber, having an elongation at break in a range from 150 to 600% and a crystallization peak temperature in a range from 64 to 80.degree. C., is drawn at a draw ratio in a range from 30 to 99% of the maximum draw ratio, and the undrawn poly(trimethylene terephthalate) copolymer fiber consists of poly(trimethylene terephthalate) formed by copolymerizing ester-forming sulfonate in a range from 0.5 to 5 mol % to a total dicarboxylic acid component to have an intrinsic viscosity in a range from 0.65 to 1.5 dl/g.

14. A method for producing a poly(trimethylene terephthalate) copolymer fiber characterized in that the poly(trimethylene terephthalate) is formed by copolymerizing ester-forming sulfonate in a range from 0.5 to 5 mol % to a total dicarboxylic acid component to have an intrinsic viscosity in a range from 0.65 to 1.5 dl/g, the poly(trimethylene terephthalate) is extruded from a spinneret having a surface temperature in a range from 250 to 295.degree. C. and, after being cooled and solidified, is taken up at a speed in a range from 100 to 3,000 m/min to be an undrawn yarn which is then drawn at a temperature in a range from 30 to 90.degree. C. and a draw ratio which is in a range from 30 to 99% of the maximum draw ratio, and then a drawn fiber obtained is heat-treated at a temperature from 100 to 200.degree. C.

15. A method for producing a poly(trimethylene terephthalate) copolymer fiber as defined by claim 14, wherein the polytrimethlene terephthalate is extruded from a spinneret with a heating tube having a length in a range from 20 to 500 mm and heated at a temperature in a range from 150 to 350.degree. C.

16. A method for producing a poly(trimethylene terephthalate) copolymer fiber as defined by any one of claims 13 to 15, wherein the undrawn fiber is once wound as a package and then drawn.

17. A method for producing a poly(trimethylene terephthalate) copolymer fiber as defined by any one of claims 13 to 15, wherein the undrawn fiber is not wound as a package but is continuously drawn.

18. A staple fiber obtained from the poly(trimethylene terephthalate) copolymer fiber as defined by any one of claims 8 to 10, wherein the fiber length is in a range from 3 to 300 mm and a degree of crimp is 5% or more.

19. A fiber product in which the poly(trimethylene terephthalate) copolymer fiber as defined by any one of claims 8 to 10 is partially or wholly used.

20. A fiber product in which the staple fiber as defined by claim 18 is partially or wholly used.

TECHNICAL FIELD

The present invention relates to poly(trimethylene terephthalate) copolymer (hereinafter poly(trimethylene terephthalate) is referred to as PTT), a method for producing the same, a fiber using the same and a fibrous product thereof. More specifically, it relates to PTT copolymer high in molecular weight to be a material for a PTT fiber dyeable with cationic dye, a method for producing the same, a fiber using the same and a fibrous product thereof.

Even more specifically, the invention relates to PTT copolymer capable of being produced at a high solid-state polymerization rate and having a small loss in melting viscosity, which is excellent in hue and high in molecular weight as a material for PTT fiber dyeable with cationic dye, a PTT fiber dyeable with a cationic dye excellent in processability and high in toughness, which does not shrink much during dyeing or heat-setting, and a fibrous product thereof.

BACKGROUND ART

PTT fiber obtained by melt-spinning polycondensate of terephthalic acid or lower alcohol ester of terephthalic acid and 1,3-propanediol (also referred to as trimethylene glycol) is excellent in touch of soft feeling, drapability and stretchability and is superior in low-temperature dyeability and weather resistance. These qualities have never been seen in an existing synthetic fiber such as poly(ethylene terephthalate) fiber (poly(ethylene terephthalate) is hereinafter referred to as PET) or nylon 6 fiber.

The applicant of this patent application has overcome various problems relating to the development of PTT and PTT fiber and the processing thereof, and has recently marketed a PTT fiber (trade name: Solo Fiber) for the first time in the world.

The PTT fiber could be more widely used by combining it with other fiber material or being post-treated. According to the prior art PTT fiber, however, problems relating the dyeing may occur if the mating fiber to be combined therewith or the processing technique is unsuitable. For example, as the PTT fiber is dyeable substantially solely with a disperse dye, the disperse dye is liable to migrate to the polyurethane elastomeric yarn or resin having a coarse structure to deteriorate a color fastness such as wash-fastness, sweat-fastness or dry cleaning-fastness when the PTT fiber is combined with a polyurethane elastomeric yarn or the fabric of the PTT fiber is treated with polyurethane resin.

To solve the above problems, if the PTT fiber is modified to be dyeable with cationic dye, the cationic dye is ionic-bonded with a sulfonate which is a dyeing seat introduced into PTT, whereby the above-mentioned migration of dye does not occur to result in a high color fastness. Also, there is a characteristic that the clarity of the dyed fabric becomes higher.

The present inventors have already proposed a PTT fiber dyeable with cationic dye (hereinafter referred to as a CD-PTT fiber) for the purpose of further facilitating the excellent features of the PTT fiber while solving the above-mentioned problems regarding the dyeing (WO99/09238). According to this technology, CD-PTT and a CD-PTT fiber formed thereof are provided by esterification-reacting terephthalic acid which is a dicarbonic acid component and/or lower alcohol ester of terephthalic acid, typically dimethyl terephthalate, with 1,3-propanediol which is a diol component, and adding an ester-forming metallic salt of sulfonic acid which is a dyeing seat for cationic dye. Although this technology provides the PTT dyeable with cationic dye, which has been difficult in the prior art, it is still insufficient in view of the industrial production. Also, although the CD-PTT obtained by the above-mentioned technology is excellent in whiteness, this is still unsatisfactory in a use in which whiteness or strength at a higher level is required.

On the other hand, regarding a PTT homopolymer (hereinafter referred to as a homo PTT) other than CD-PTT, Japanese Unexamined Patent Publication No. 8-311177 (Kokai) discloses a method for obtaining a PTT having a b value of 10 or less and a content of oligomer of 1 wt % or less by esterification-reacting 1,3-propanediol with a terephthalic acid component, polycondensating an esterification-reaction product thus obtained to result in a prepolymer having an intrinsic viscosity in a range from 0.7 to 0.8, and polycondensating, in a solid state, the prepolymer thus obtained at a temperature in a range from 190 to 210.degree. C. to result in an intrinsic viscosity of 0.9 or more. Also, Japanese Unexamined Patent Publication (Kokai) No. 2000-159876, disclose a polymerization technology providing a homo PTT excellent in solid-state polymerization speed and melting stability by combining a titanium catalyst with a magnesium catalyst.

However, there are neither a description nor a suggestion, in these publications, regarding the CD-PTT or the significance of the copolymerization of ester-forming metallic salt of sulfonic acid. Particularly, since the melting stability becomes worse in comparison with homo PTT, as described later, when an ester-forming metallic salt of sulfonic acid is used as a copolymerization component, the same effect would not be expected even if the technology used for the homo PTT is applied as it is to the CD-PTT. In the above publication, however, there is neither a description nor a suggestion of the solution thereto. The homo PTT described in either of these publications is unsatisfactory in whiteness. Particularly, according to Japanese Unexamined Patent Publication (Kokai) No. 2000-159876, since a magnesium catalyst is combinatorily used for the polymerization, the L value (brightness) of the polymer becomes less than 70 to result in a blackish polymer, and this technology is not applicable to a CD-PTT requiring a clear color.

Known CD-PTT fibers have problems to be solved similar to CD-PTT. That is, the known CD-PTT fibers are problematic in that 1) since they are formed of a polymer of a low molecular weight, a toughness (the toughness is a fiber stiffness usually represented by the product of a fiber strength and a square root of a fiber elongation) causes a fabric to be easily broken, and 2) as they are excessively drawn in spite of their low molecular weight, the orientation of molecules in an amorphous region is liable to relax by heat during the dyeing or heat-setting process to cause a large fiber shrinkage, which results in a harsh feeling of hand touch of a fabric, and it is difficult that the fabric develops adequately a soft feeling.

DISCLOSURE OF THE INVENTION

The present inventors have found the following problems by diligently studying the polymerization or spinning technology of CD-PTT.

In the melt-spinning process of CD-PTT, as metallic salts of sulfonic acid copolymerized with each other are ionically crosslinked in a melting state, the melting viscosity significantly rises. Thereby, the removal of 1,3-propanediol is inhibited at a polycondensating reaction stage to result in a problem that it is difficult to increase the degree of polymerization. In addition, as CD-PTT has a lower thermal stability in comparison with PET, poly(buthylene terephthalate) or homo PTT, which have similar structures thereto, the molecular weight thereof does not rise even if the polycondensation time is prolonged but the depolymerization occurs due to the heat decomposition before the molecular weight reaches a level necessary for forming fibers, which yellows the polymer itself, and a high-molecular weight CD-PTT is not obtainable.

The present inventors have studied a high-molecular weight CD-PTT and succeeded in obtaining a CD-PTT having a high molecular weight, not achievable through the melt-spinning method, by once preparing a low-molecular weight CD-PTT (hereinafter referred to as a prepolymer) and polymerizing the same in a solid state. As a result of specifically studying the melt-spinning characteristic, hue and solid-state polymerization characteristic, however, the following problems have been found when this technology is carried out on an industrial scale.

That is, if characteristics such as an amount of terminal carboxyl groups of the prepolymer obtained through the melt-polymerization are outside a certain range, the solid-state polymerization speed, the melting stability or hue of the high-molecular weight CD-PTT thus obtained largely deteriorates. Particularly, the amount of terminal carboxyl groups is deeply related to copolymerization ratios, catalysts, additives and conditions of polycondensating reaction. Accordingly, the present inventors have newly found that these factors must be precisely controlled to obtain the high-molecular weight CD-PTT which is the object of the present invention.

On the other hand, although the tensile strength can be increased to a relatively high level by applying a high draw ratio to melt-spun fibers formed of the low-molecular weight CD-PTT, the fiber shrinkage becomes higher because the molecules are excessively stretched for the purpose of facilitating the tensile strength. When a fabric formed of such high-shrinkage fibers is subjected to a subsequent processing such as a dyeing, the fiber largely shrinks to make the fabric harsh to the hand, which is opposite to the soft feeling of hand touch expected from a low elastic modulus of PTT.

Such a phenomenon does not occur in a PET fiber having a structure similar to PTT. This is because, as PTT has a spiral molecular structure, even if the molecule of the PTT fiber is forcibly stretched, an amorphous region thereof largely shrinks when heated so that the molecular structure returns to the original stable spiral structure, resulting in the large shrinkage of the fiber. On the contrary, a molecular structure of PET is liable to have an irreversible stretched structure. While a soft feeling of hand touch could be obtained by suitably controlling the shrinkage, the weaving or knitting density must be extremely low in such a case when the fabric is prepared, which is very difficult in design.

A first problem of the present invention is to provide a high-molecular weight PTT copolymer suitable for material of a PTT fiber dyeable with cationic dye and excellent in hue, which is produced by the solid-state polymerization at a high speed and at a small decline of melting viscosity, and a method for producing the same.

A second problem of the present invention is to provide a PTT dyeable with cationic dye high, in toughness and excellent in processability, which does not largely shrink during the dyeing or heat-setting process, and a method for producing the same.

The present inventors have specifically studied the melt-polymerization characteristic and the solid-state polymerization characteristic of CD-PTT and found that the above-mentioned problems can be solved by controlling an amount of terminal carboxyl groups at a final stage of the melt-polymerization while using an ester-forming metallic salt of sulfonic acid which prepares dyeing seats for cationic dye. Further, the present inventors have found the necessary conditions for achieving the dyeability and color fastness for cationic dye, based on which the inventive CD-PTT is obtained.

The present inventors have found that the inventive PTT fiber high in toughness, low in shrinkage during the dyeing or heat-setting process as well as being excellent in processability is obtainable by extruding CD-PTT, having a high polymerization degree in a certain range, uniformly from a spinneret having a surface temperature and an atmospheric temperature in a certain range to result in an undrawn yarn low in orientation and crystallization and good in drawability which is then drawn at a ratio in a certain range.

That is, the present invention is as follows:

1. A PTT copolymer characterized in that it satisfies the following conditions (1) to (4):

(1) ester-forming sulfonate in a range from 0.5 to 5 mol % is copolymerized relative to a total dicarbonic acid component.

(2) bis (3-hydroxypropyl) ether in a range from 0.1 to 2.5 wt % is copolymerized;

(3) an intrinsic viscosity is in a range from 0.65 to 1.5 dl/g, and

(4) an amount of terminal carboxyl groups is 25 milli-equivalent per kg resin or less.

2. A PTT copolymer as defined by the above item 1 wherein the intrinsic viscosity is in a range from 0.85 to 1.25 dl/g.

3. A PTT copolymer as defined by the above item 1 wherein a b* value is in a range from -2 to 6.

4. A method for producing a PTT copolymer characterized in that the method comprises the steps of: reacting lower alcohol ester of terephthalic acid, which is a main dicarboxylic acid component, with 1,3-propanediol, which is a main diol component, to form 1,3-propanediol ester of terephthalic acid and/or oligomer thereof; after completing the polycondensation reaction, once solidifying the resultant polymer; and heating the polymer in a solid state to increase an intrinsic viscosity thereof by 0.1 dl/g or more from that at a time when the polycondensation reaction has completed, and the method satisfies the following conditions (a) and (b):

(a) ester-forming sulfonate corresponding to an amount in a range from 0.5 to 5 mol % of a total dicarbonic acid component is added at any optional stage from the initiation of reaction to the completion of the polycondensation reaction, and

(b) an amount of terminal carboxyl groups of PTT copolymer is in a range from 5 to 40 milli-equivalent per kg resin before the initiation of solid-state polymerization.

5. A method for producing a PTT copolymer characterized in that the method comprises the steps of: reacting terephthalic acid, which is a main dicarboxylic acid component, with 1,3-propanediol, which is a main diol component, to form 1,3-propanediol ester of terephthalic acid and/or oligomer thereof; after completing the polycondensation reaction, solidifying the resultant polymer; and heating the polymer in a solid state to increase an intrinsic viscosity thereof by 0.1 dl/g or more from that at a time when the polycondensation reaction has completed, and the method satisfies the following conditions (a) to (c):

(a) the molar ratio of 1,3-propanediol to terephthalic acid is in a range from 0.8 to 2.5,

(b) in the reaction of terephthalic acid with diol mainly composed of 1,3-propanediol, at a stage wherein a rate of reaction of terephthalic acid is in a range from 75 to 100%, an amount of ester-forming sulfonate corresponding to a range from 0.5 to 5 mol % of total dicarboxylic acid component is added, and

(c) the amount of terminal carboxyl groups of PTT copolymer is in a range from 5 to 40 milli-equivalent per kg resin before the initiation of solid-state polymerization.

6. A method for producing a PTT copolymer comprising the steps of: by reacting terephthalic acid, which is a main dicarboxylic acid component, with 1,3-propanediol, which is a main diol component, to form 1,3-propanediol ester of terephthalic acid and/or oligomer thereof; after completing the polycondensation reaction, characterized in that the method satisfies the following conditions (a) to (c):

(a) a molar ratio of 1,3-propanediol to terephthalic acid is in a range from 0.8 to 2.5,

(b) in the reaction of terephthalic acid with diol mainly composed of 1,3-propanediol, at a stage wherein a rate of reaction of terephthalic acid is in a range from 75 to 100%, an amount of ester-forming sulfonate corresponding to a range from 0.5 to 5 mol % of total dicarboxylic acid component is added, and

(c) an amount of terminal carboxyl groups of PTT copolymer is in a range from 5 to 40 milli-equivalent per kg resin.

7. A method for producing a PTT copolymer as defined by any one of the above items 4 to 6, wherein an alkaline metal compound and/or an alkaline earth metal compound corresponding to an amount in a range from 1 to 100 mol % of ester-forming sulfonate is added at any optional stage from the initiation of reaction to the completion of the polycondensation reaction.

8. A PTT copolymer fiber characterized in that it satisfies the following conditions (1) to (4):

(1) ester-forming sulfonate in a range from 0.5 to 5 mol % is copolymerized relative to a total dicarboxylic acid component.

(2) bis (3-hydroxypropyl) ether in a range from 0.1 to 2.5 wt % is copolymerized;

(3) an intrinsic viscosity is in a range from 0.65 to 1.5 dl/g, and

(4) an amount of terminal carboxyl groups is in a range from 5 to 40 milli-equivalent per kg fiber or less.

9. A PTT copolymer fiber characterized in that ester-forming sulfonate in a range from 0.5 to 5 mol % is copolymerized relative to a total dicarboxylic acid component, and the fiber satisfies the following conditions (A) to (C):

(A) an intrinsic viscosity [.eta.] is in a range from 0.65 to 1.4 dl/g,

(B) a peak temperature of a dynamic loss tangent is in a range from 105 to 140.degree. C., and

(C) a boiling water shrinkage is in a range from 0 to 16%.

10. A PTT copolymer fiber as defined by the above item 9, further satisfying the following conditions (D) and (E):

(D) an elongation at break is in a range from 20 to 70%, and

(E) a toughness is 16 or more, wherein the toughness is calculated by the following equation:

Toughness=[Strength (cN/dtex)].times.[Elongation (%)].sup.1/2.

11. A PTT copolymer fiber as defined by the above item 10, wherein the toughness is 17.5 or more.

12. An undrawn PTT copolymer fiber characterized in that it consists of PTT formed by copolymerizing ester-forming sulfonate in a range from 0.5 to 5 mol % to a total dicarboxylic acid component to have an intrinsic viscosity in a range from 0.65 to 1.4 dl/g, and it has an elongation at break in a range from 150 to 600% and a crystallization peak temperature in a range from 64 to 80.degree. C.

13. A method for producing a PTT copolymer fiber characterized in that an undrawn PTT copolymer fiber, having an elongation at break in a range from 150 to 600% and a crystallization peak temperature in a range from 64 to 80.degree. C., is drawn at a draw ratio in a range from 30 to 99% of the maximum draw ratio, and the undrawn PTT copolymer fiber consists of PTT formed by copolymerizing ester-forming sulfonate in a range from 0.5 to 5 mol % to a total dicarboxylic acid component to have an intrinsic viscosity in a range from 0.65 to 1.5 dl/g.

14. A method for producing a PTT copolymer fiber characterized in that the PTT is formed by copolymerizing ester-forming sulfonate in a range from 0.5 to 5 mol % to a total dicarboxylic acid component to have an intrinsic viscosity in a range from 0.65 to 1.5 dl/g, the PTT is extruded from a spinneret having a surface temperature in a range from 250 to 295.degree. C. and, after being cooled and solidified, is taken up at a speed in a range from 100 to 3,000 m/min to be an undrawn yarn which is then drawn at a temperature in a range from 30 to 90.degree. C. and a draw ratio which is in a range from 30 to 99% of the maximum draw ratio and, then a drawn fiber obtained is heat-treated at a temperature from 100 to 200.degree. C.

15. A method for producing a PTT copolymer fiber as defined by the above item 14, wherein the PTT is extruded from a spinneret with a heating tube having a length in a range from 20 to 500 mm and heated at a temperature in a range from 150 to 350.degree. C.

16. A method for producing a PTT copolymer fiber as defined by any one of the above items 13 to 15, wherein the undrawn fiber is once wound as a package and then drawn.

17. A method for producing a PTT copolymer fiber as defined by any one of the above items 13 to 15, wherein the undrawn fiber is not wound as a package but is continuously drawn.

18. A staple fiber obtained from the PTT copolymer fiber as defined by any one of the above items 8 to 10, wherein the fiber length is in a range from 3 to 300 mm and a degree of crimp is 5% or more.

19. A fiber product in which the PTT copolymer fiber as defined by any one of the above items 8 to 10 is partially or wholly used.

20. A fiber product in which the staple fiber as defined by the above item 18 is partially or wholly used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an unevenness curve (representing the variation of fiber weight) when a fiber passes through an USTER TESTER 3, wherein M represents a mass, t represents a time, Xi represents an instantaneous value of weight, Xave is an average value thereof, T represents a measuring time and a represents an area between Xi and Xave (a hatched portion);

FIG. 2(A) is a schematic illustration of a desired cheese-shaped package of a PTT fiber wound on a bobbin;

FIG. 2(B) is a schematic illustration of an undesired cheese-shaped package having a bulge;

FIG. 3 is a schematic illustration of one embodiment of a method for producing the inventive CD-PTT fiber (a conventional method);

FIG. 4 is a schematic illustration of one embodiment of a process for drawing an undrawn yarn once wound in a method for producing the inventive CD-PTT fiber (a conventional method); and

FIG. 5 is a schematic illustration of another embodiment of a method for producing the inventive CD-PTT fiber (a SDTU method).

In this regard, in FIGS. 3 to 5, the reference numerals denote the following:

1: a drier, 2: an extruder, 3: a bend, 4: a spin head, 5: a spin pack, 6: a spinneret, 7: a heating tube, 8: a cooling air, 9: a finishing agent applicator, 10: a first takeup roll, 11: a second takeup roll, 12: a winder (a package), 13: an undrawn yarn, 14: a first draw roll, 15: a hot plate, 16: a second draw roll, 17: a winder, 18: a first roll, 19: a second roll, 20: a free roll, 21: a winder, 21a: a spindle, and 21b: a touch roll.

DETAILED DESCRIPTION OF THE INVENTION

PTT copolymer according to the present invention is a polyester formed by copolymerizing PTT with ester-forming sulfonate in a range from 0.5 to 5 mol %. In this regard, the PTT is a polyester containing terephthalic acid as an acidic component and 1,3-propanediol as a diol component. The ester-forming sulfonate provides a dyeing seat for cationic dye, and is an indispensable copolymer component for achieving the object of the present invention. A surprising effect is obtained in that the hue becomes superior to a homo PTT by copolymerizing the ester-forming sulfonate with PTT although the reason therefor has not been identified.

While examples of the ester-forming sulfonate used in the present invention are compounds containing sulfonate groups represented by the following general formula, there is no limitation provided it is capable of being copolymerized with PTT and has a sulfonate part. For example, in place of metallic salt, organic salt may be used, such as tetraalkylphosphonium salt or tetraalkylammonium salt. However, for the purpose of obtaining PTT having a favorable hue, metallic salts represented by the following formula are preferably used. ##STR1##

wherein R.sup.1, R.sup.2 are represented by --COOH, --COOR, --OCOR, 12 --(CH.sub.2).sub.n OH, --(CH.sub.2).sub.n [O(CH.sub.2).sub.m ].sub.p OH or --CO[O(CH.sub.2).sub.n ].sub.m OH; R.sup.1, R.sup.2 may be either equal or not; R is an alkyl group containing 1 to 10 carbon atoms; n, m and p are an integer of 1 or more; M represents metal, preferably alkaline metal or alkaline earth metal; and Z is a trivalent organic group containing 1 to 30 carbon atoms, preferably a trivalent aromatic group.

Favorable ester-forming sulfonate compounds are, for example, 5-sodium sulfoisophthalate, 5-potassium sulfoisophthalate, 5-lithium sulfoisophthalate, 2-sodium sulfoterephthalate, 2-potassium sulfoterephthalate, 4-sodium sulfo-2,6-naphthalene dicarboxylate, 2-sodium sulfo-4-hydroxybenzoate, or ester derivatives thereof, such as methyl ester or dimethyl ester. Especially, these ester derivatives such as methyl ester or dimethyl ester are preferably used because the resultant polymer is excellent in whiteness and polymerization speed.

A copolymerization ratio of the ester-forming sulfonate is necessarily in a range from 0.5 to 5 mol % relative to a total number of moles of a dicarboxylic acid component forming the polyester. If the copolymerization ratio of the ester-forming sulfonate is less than 0.5 mol %, the color development is lower when dyed with cationic dye. Contrarily, if the copolymerization ratio of the ester-forming sulfonate exceeds 5 mol %, the heat durability of the polymer becomes worse not only to extremely deteriorate the polymerizability and spinnability but also to make yellow the fibers. For the purpose of improving the polymerizability and the spinnability while sufficiently maintaining the dyeability to cationic dye, the copolymerization ratio is preferably in a range from 1 to 3 mol %, more preferably from 1.2 to 2.5 mol %.

Also, bis(3-hydroxypropyl) ether (hereinafter referred to as BPE) is necessarily copolymerized with the inventive CD-PTT in a range from 0.1 to 2.5 wt % relative to a polymer mass. BPE is a chemical substance represented by the following structural formula:

HOCH.sub.2 CH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 CH.sub.2 OH

BPE is a substance formed when 1,3-propanediol, which is a raw material for CD-PTT, is dehydrated and dimerized.

When the homo PTT is polymerized by using a lower alcohol ester of terephthalic acid such as dimethyl terephthalate as a raw material, BPE of less than 0.1 wt % is usually formed, as a by-product, and copolymerized with the polymer. Also, if the polymerization is carried out by using terephthalic acid as a raw material, a proton functions as a catalyst for dimerizing 1,3-propanediol, whereby BPE of 0.3 wt % or more is copolymerized with the polymer. On the other hand, during the production of CD-PTT, the ester-forming sulfonate also functions as a catalyst for forming BPE, whereby the copolymerization ratio of BPE becomes higher than that of homo PTT if any terephthalic acid derivative is used as a raw material. While there may be an adverse effect on the melting stability, polymerization reaction and light-resistance of the polymer if an amount of BPE excessively increases, the existence of a proper amount increases the dye exhaustion ratio during the dyeing process or facilitates the alkaline weight reduction. Accordingly, the precise control of BPE amount is important in designing the polymer.

If BPE is less than 0.1 wt %, the melting point becomes high to facilitate the melting stability, but there is a problem in that the dye exhaustion for cationic dye somewhat lowers. Contrarily, if it exceeds 2.5 wt %, the melting point becomes low to deteriorate the thermal stability or the light-resistance. A favorable polymerization ratio of BPE is different in accordance with the carboxylic acid derivatives used as a raw material. When a lower alcohol ester of terephthalic acid is used, a range is preferably from 0.1 to 0.4 wt %, and when terephthalic acid is used, a range is preferably from 0.4 to 2.5 wt %. On account of a favorable balance between the thermal stability, the light-resistance and the dye exhaustion ratio of fibers, the range is preferably from 0.11 to 2.2 wt %, more preferably from 0.15 to 1.8 wt %.

Components other than the ester-forming sulfonate may be copolymerized with the inventive CD-PTT in a range not disturbing the objects of the present invention. Such copolymerized components are, for example, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,5-pentamethylene glycol, 1,6-hexamethylene glycol, heptamethylene glycol, octamethylene glycol, decamethylene glycol, dodecamethylene glycol, 1,4-cyclohexanediol, 1,3-cyclohexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, diheptanoic acid, dioctanoic acid, sebacic acid, didodecanic acid, 2-methylglutaric acid, 2-methyladipic acid, fumaric acid, maleic acid, itaconic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, isophthalic acid, poly(ethylene glycol) having a molecular weight in a range from 400 to 100000 or poly(tetraethylene glycol) having a molecular weight in a range from 400 to 100000. The copolymerization ratio is usually 10 wt % or less relative to the polymer mass although it varies in accordance with the copolymerized components.

If necessary, various additives may be copolymerized or mixed with the inventive CD-PTT, for example, a delusterant such as titanium oxide, a heat stabilizer, an antifoamer, a color controller, a fire retardant, an antioxidant, an ultraviolet absorber, an infrared absorber, a cyrstallizing nucleus, a fluorescent whitener or others. Particularly, when titanium oxide is used as a delusterant, the amount thereof is preferably in a range from 0.01 to 0.1 wt % relative to a weight of the polymer.

It is necessary that the inventive CD-PTT has an intrinsic viscosity in a range from 0.65 to 1.5 dl/g. If the intrinsic viscosity is less than 0.65 dl/g, the resultant fiber has a low strength. Contrarily, if the intrinsic viscosity exceeds 1.5 dl/g, the melting viscosity is too high to smoothly carry out weight measurement in a gear pump, whereby the spinnability becomes worse because of the erroneous extrusion of the polymer. The intrinsic viscosity is preferably in a range from 0.7 to 1.5 dl/g, more preferably from 0.85 to 1.25 dl/g for obtaining CD-PTT excellent both in strength and spinnability.

The inventive CD-PTT necessarily has an amount of terminal carboxyl groups of 25 milli-equivalent per kg resin or less, wherein the milli-equivalent per kg resin represents an amount of terminal carboxyl groups per 1 kg CD-PTT. Also, the milli-equivalent per kg fiber represents an amount of terminal carboxyl groups per 1 kg CD-PTT fiber. If the amount of terminal carboxyl group exceeds 25 milli-equivalent per kg resin, the melting stability becomes insufficient or a decline in strength is liable to occur during the treatment in a hot aqueous solution such as the dyeing process. The amount of terminal carboxyl groups is preferably in a range from 2 to 25 milli-equivalent per kg resin, more preferably from 2 to 20 milli-equivalent per kg resin, most preferably from 2 to 15 milli-equivalent per kg resin.

The inventive CD-PTT is preferably has an L value of preferably 70 or more, more preferably 80 or more because clear color development is achievable when dyed with cationic dye. Also, a b* value is preferably in a range from -5 to 8, more preferably from -2 to 6, most preferably from -1 to 5 because clear color development is achievable.

A melting point of the inventive CD-PTT is preferably 223.degree. C. or higher, more preferably 225.degree. C. or higher in view of the melting stability.

A favorable method for producing the inventive CD-PTT will be described below.

Since methods for producing the inventive CD-PTT are somewhat different in the polymerization process between when a lower alcohol of terephthalic acid is used and when terephthalic acid is used, the explanation will be carried out separately as follows:

First, a case wherein no terephthalic acid is substantially used but a lower alcohol ester of terephthalic acid is used will be explained.

The inventive CD-PTT can be produced by a method comprising the steps of: reacting a lower alcohol ester of terephthalic acid, which is a main dicarboxylic acid component, with 1,3-propanediol, which is a main diol component, to form 1,3-propanediol ester of terephthalic acid and/or oligomer thereof; after completing the polycondensation reaction, solidifying the resultant polymer; and heating the polymer in a solid state to increase an intrinsic viscosity thereof by 0.1 dl/g or more from that at a time when the polycondensation reaction has completed, and the method satisfies the following conditions (a) and (b):

(a) ester-forming sulfonate corresponding to an amount in a range from 0.5 to 5 mol % of a total dicarboxylic acid component is added at any optional stage from the initiation of reaction to the completion of the polycondensation reaction, and

(b) an amount of terminal carboxyl groups of PTT copolymer is in a range from 5 to 40 milli-equivalent per kg resin before the initiation of solid-state polymerization.

The method for producing the inventive CD-PTT includes an ester interchanging process for condensating a lower alcohol ester of terephthalic acid and 1,3-propanediol to form 1,3-propanediol ester of terephthalic acid and/or oligomer thereof, a polycondensation process for heating the resultant condensate to obtain prepolymer while removing 1,3-propanediol, and a process for polymerizing the prepolymer in a solid state.

First, the ester interchanging process will be described.

A charging ratio of 1,3-propanediol relative to a lower alcohol ester of terephthalic acid which is a raw material is preferably in a range from 0.8 to 3 as represented by a molar ratio. If the charging ratio is less than 0.8, the ester interchanging reaction does not smoothly proceed, while if it exceeds 3, the melting point becomes lower and the resultant polymer is liable to have a poor whiteness. The charging ratio is preferably in a range from 1.4 to 2.5, more preferably from 1.5 to 2.3.

To facilitate the reaction, a catalyst is preferably used, such as titanium alcoxide represented by titanium tetrabuthoxide or titanium tetraisopropoxide; metal oxide such as amorphous titanium oxide precipitate, amorphous titanium oxide/silica co-precipitate or amorphous zirconia precipitate; or metallic carbonate such as calcium acetate, manganese acetate, cobalt acetate or antimony acetate, the use of which in a range from 0.01 to 0.2 wt % relative to a total carbonate component monomer enhances a reaction speed, a whiteness and a thermal stability of the resultant polymer. Of these catalysts, titanium compounds, calcium acetate and cobalt acetate are preferable since the generation of non-melting matters formed by the reaction thereof with ester-forming sulfonate is less. It is possible to carry out the reaction while removing an alcohol such as methanol which is a by-product of the reaction, at a reaction temperature in a range approximately from 200 to 250.degree. C. A reaction time is usually in a range from 2 to 10 hours, preferably from 2 to 4 hours. The resultant reaction product contains 1,3-propanediol ester of terephthalic acid and/or oligomer thereof.

After the ester interchange reaction, the polycondensation reaction is carried out. In a polycondensation reaction carried out in a known method, titanium alcoxide represented by titanium tetrabutoxide and titanium tetraisopropoxide or a metallic oxide such as amorphous titanium oxide precipitate, amorphous titanium oxide/silica co-precipitate or amorphous zirconia precipitate in a range from 0.01 to 0.2 wt % may be added relative to a total carbonate component monomer.

To obtain the inventive CD-PTT high in solid-state polymerization speed and excellent in melting stability and hue, it is necessary that an amount of terminal carboxyl groups of prepolymer is in a range from 5 to 40 milli-equivalent per kg resin upon the completion of the polycondensation reaction. If it exceeds 40 milli-equivalent per kg resin, the solid-state polymerization speed becomes significantly slow, the melting stability is worse to lower the molecular weight and the resultant CD-PTT has a poor hue. Contrarily, if the amount of terminal carboxyl groups is less than 5 milli-equivalent per kg resin, the ester-linkable terminal carboxyl groups reduces to lower the solid-state polymerization speed. The amount of terminal carboxyl groups is preferably in a range from 5 to 35 milli-equivalent per kg resin, more preferably in a range from 10 to 32 milli-equivalent per kg resin.

For achieving such an amount of the terminal carboxyl groups of prepolymer, for example, the polycondensation reaction is carried at a polycondensation temperature in a range from 240 to 270.degree. C. for the most suitable time, usually 4 hours or less, and preferably in a range from 1 to 3 hours while estimating an amount of terminal carboxyl groups of the prepolymer. The polycondensation temperature is preferably in a range from 250 to 270.degree. C., and a degree of vacuum is in a range from 0.13 to 133 Pa. To effectively remove 1,3-propanediol in the polycondensation, it is important to increase the surface area of the polymeric product. To do so, the effective agitation is carried out by using, for example, a helical type agitator, and a charging ratio of a raw material relative to a capacity of an oven is 70% or less, preferably 60% or less. Further, the polycondensation reaction is preferably made to stop while the viscosity of the melting product increases with time at a polycondensation reaction stage. That is, it is important that the polycondensation reaction is made to stop before the melting viscosity descends. The reason is that the melting viscosity does not rise any more but rather descends even if the polymerization time is prolonged, because the thermal decomposition reaction is predominant over the polymerization reaction, whereby an amount of terminal carboxyl groups formed by the thermal decomposition reaction increases.

The ester-forming sulfonate may be added at any stage from the initiation of the ester interchange reaction to the completion of the polycondensation reaction and, in this case, is substantially copolymerized with CD-PTT. An amount to be added is in a range from 0.5 to 5 mol % relative to a total dicarboxylic acid component for the same reason described before.

The ester-forming sulfonate may be added either as a solid or by dissolving it in a suitable solvent; it is particularly preferably added while being dissolved in 1,3-propanediol in view of the ease of the addition and the accuracy of measurement. When dissolved in a solvent such as 1,3-propanediol, an amount of the solvent is preferably reduced as much as possible in view of preventing the melting point of resultant polymer from lowering. Also, the solution may be heated to facilitate the dissolution. The ester-forming sulfonate may be reacted with 1,3-propanediol at a dissolving stage. For this purpose, a known ester interchanging catalyst may be added to the ester-forming sulfonate in a range from 0.01 to 200 wt %, such as carbonate of lithium, calcium, cobalt, manganese, titanium, antimony, zinc or tin; titanium alcoxide or amorphous metallic oxide salt.

For instance, when dimethyl 5-sodium sulfoisophthalate is used as the ester-forming sulfonate, it may be changed in 1,3-propanediol to 5-sodium sulfoisophthalate mono(1,3-propanediol), 5-sodium sulfoisophthalate bis(1,3-propanediol) or 5-sodium sulfoisophthalate monomethyl mono(1,3-propanediol), or may be hydrolyzed by a small amount of water contained in 1,3-propanediol into 5-sodium sulfoisophthalate or monomethyl ester thereof.

In the method for producing the inventive CD-PTT, to reduce the amount of terminal carboxyl groups and facilitate the thermal stability, melting stability and whiteness of the polymer, a heat stabilizer or a color inhibitor is preferably added at any stage of the polymerization, together with the application of the above-mentioned favorable amount of catalyst and reaction temperature.

As the heat stabilizer, penta-valent or trivalent phosphorus compounds or hindered phenolic antioxidants are preferable. For example, the penta- or trivalent phosphorus compounds include trimethylphosphate, triethylphosphate, tributylphosphate, triphenylphosphate, trimethylphosphite, triethylphosphite, triphenylphosphite, phosphoric acid or phosphorus acid; while the hindered phenolic antioxidants include pentaerythritol-tetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 3,9-bis(2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dime thylethyl)-2,4,8,10-tetraoxaspiro[5,5]undecan, 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzene) isophthalic acid, triethyglycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2-thio-diethylene-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], or octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

An amount to be added is preferably in a range from 0.01 to 0.5 wt % relative to CD-PTT, more preferably from 0.02 to 0.1 wt %. In this regard, even in this range, if an amount of the heat stabilizer is excessive in relation to an amount of catalyst, there may be a case wherein a speed of the polycondensation reaction or solid-state polymerization reaction is lowered, therefore, a ratio of both the amounts is preferably decided based on a suitable experiment. Such a decision of the amount ratio could be easily carried out by a person with ordinary skill in the art.

The color inhibitor includes, for example, cobalt compounds such as cobalt acetate or cobalt formate and a marketed fluorescent brightening agent, and is added to CD-PTT in a range from 0.0001 to 0.1 wt %. These additives may be added at any stage in the polymerization process.

Further, to reduce an infusible aggregate formed by the catalyst, the heat stabilizing agent and an extremely small amount of the ester-forming sulfonate metallic salt, it is preferable to add of alkaline- and/or alkaline earth-metallic salt at any stage of the polymerization, such as lithium acetate, lithium carbonate, lithium formate, sodium acetate, sodium carbonate, sodium formate, sodium hydroxide, calcium hydroxide or magnesium hydroxide. An amount to be added is preferably in a range from 1 to 100 mol %, more preferably from 1 to 20 mol % relative to the ester-forming sulfonate. The alkaline-metallic salts, particularly lithium salt and hydroxide are particularly preferably used.

If an amount of infusible aggregate is too much, there may be a problem in that a pressure in a spinning pack rises to cause yarn breakage. To avoid such a problem, it is necessary to increase the frequency of the replacement of the spinning pack, which deteriorates the productivity. These problems are avoidable by using the above-mentioned additives. While the alkaline-metallic salt may be added at any stage of the polymerization, it is preferably added at a time when the ester interchange reaction has completed, for achieving the effect, and particularly simultaneously with the addition of the ester-forming sulfonate metallic salt.

It is necessary to increase an intrinsic viscosity of the prepolymer obtained as described above through the solid-state polymerization. Particularly, it is difficult to increase the intrinsic viscosity to 0.65 or more without the solid-state polymerization. This is because, if a reaction temperature for the polycondensation is made to rise for the purpose of increasing the intrinsic viscosity, there may be a case in which the heat decomposition occurs to disturb the increase in viscosity. By the solid-state polymerization, it is possible to readily increase the intrinsic viscosity to 0.65 or more without deteriorating the melting stability and hue. The solid-state polymerization can be carried out by using chip, powder, fiber, sheet or block of the prepolymer with the existence of inert gas such as nitrogen or argon, or at a subatmospheric pressure of 1.33.times.10.sup.4 Pa or less, preferably 1.33.times.10.sup.3 Pa or less and a temperature in a range from 170 to 220.degree. C. for about 3 to 48 hours.

An advantage of the polycondensation is in that it is possible to increase the intrinsic viscosity as well as to reduce an amount of linear oligomer to 2 wt % or less, preferably to 1 wt % or less because the oligomer having the sublimating property escapes from the polymer during the solid-state polymerization. Also, as far as using the prepolymer obtained by the inventive method, the hue of CD-PTT hardly deteriorates due to the solid-state polymerization. Further, it is possible to largely reduce the amount of terminal carboxyl groups relative to the prepolymer obtained by the melting polymerization, resulting in CD-PTT excellent in melting stability and whiteness.

Next, a favorable method for the production will be described when terephthalic acid is used.

The inventive CD-PTT is produced by a method comprising the steps of: reacting terephthalic acid, which is a main dicarboxylic acid component, with 1,3-propanediol, which is a main diol component, to form 1,3-propanediol ester of terephthalic acid and/or oligomer thereof; after completing the polycondensation reaction, solidifying the resultant polymer; and heating the polymer in a solid state to increase an intrinsic viscosity thereof by 0.1 dl/g or more from that at a time when the polycondensation reaction has completed, and the method satisfies the following conditions (a) to (c):

(a) a molar ratio of 1,3-propanediol to terephthalic acid is in a range from 0.8 to 2.5,

(b) in the reaction of terephthalic acid with diol mainly composed of 1,3-propanediol, at a stage wherein a rate of reaction of terephthalic acid is in a range from 75 to 100%, an amount of ester-forming sulfonate corresponding to a range from 0.5 to 5 mol % of total dicarboxylic acid component is added, and

(c) an amount of terminal carboxyl groups of PTT copolymer is in a range from 5 to 40 milli-equivalent per kg resin before the initiation of solid-state polymerization.

The inventive method for producing CD-PTT includes the esterification reaction for condensating terephthalic acid with 1,3-propanediol to form 1,3-propanediol ester of terephthalic acid and/or oligomer thereof, the polycondensation reaction for obtaining prepolymer by heating the resultant polycondensate to remove 1,3-propanediol, and the solid-state polymerization reaction of the prepolymer.

First, the esterification reaction will be described.

It is necessary that a charging ratio of 1,3-propanediol to terephthalic acid which is a raw material is in a range from 0.8 to 2.5 in molar ratio. If the charging ratio is less than 0.8, the esterification process does not completely proceed. Contrarily, if the charging ratio is more than 2.5, the melting point becomes lower and the whiteness of the resultant polymer deteriorates. The range is preferably from 0.8 to 1.5, more preferably from 1 to 1.3.

Kinds and amounts of catalyst or conditions of the esterification reaction preferably used for facilitating the esterification reaction are the same as in the esterification reaction using a lower alcohol ester of terephthalic acid already described. In this regard, one material removed from the reaction system is water.

An amount of the ester-forming sulfonate corresponding to 0.5 to 5 mol % of a total dicarboxylic acid component is necessarily added at a stage in that a rate of reaction of terephthalic acid is in a range from 75 to 100% for obtaining the inventive CD-PTT. If the rate of reaction is less than 75%, the copolymerization ratio of BPE becomes larger to be outside the range according to the present invention. This is because, if the rate of reaction is low, an amount of protons originated from unreacted terephthalic acid increases to accelerate the formation of BPE. The addition is preferably carried out when the rate of reaction is 90% or more, most preferably when the esterification reaction has completed 95% or more. A method for adding ester-forming sulfonate is the same as when the lower alcohol ester of terephthalic acid is used.

After the esterification reaction has completed, the polycondensation reaction and the solid-state polymerization are carried out, conditions and additives of which are the same as in the polycondensation reaction when the lower alcohol ester of terephthalic acid is used as already described.

A high-molecular weight CD-PTT thus obtained is spun into a fiber by a known spinning method, which fiber is dyeable with cationic dye and is very excellent in color development and clarity in comparison with a known CD-PTT fiber, because the raw material polymer is good in whiteness. Particularly, by adopting the following spinning method, a fiber which is an object of the present invention high in toughness and excellent in processability, and not excessively shrinking during the treatment, is obtainable.

That is, the favorable inventive CD-PTT fiber is a fiber wherein ester-forming sulfonate in a range from 0.5 to 5 mol % is copolymerized relative to a total dicarboxylic acid component, and the fiber satisfies the following conditions (A) to (C):

(A) an intrinsic viscosity [.eta.] is in a range from 0.65 to 1.4 dl/g,

(B) a peak temperature of a dynamic loss tangent is in a range from 105 to 140.degree. C., and

(C) a boiling water shrinkage is in a range from 0 to 16%.

It is necessary that the inventive CD-PTT fiber has an intrinsic viscosity in a range from 0.65 to 1.4 dl/g. A high-toughness fiber is obtainable when the intrinsic viscosity is within this range. If the intrinsic viscosity is less than 0.65 dl/g, a satisfactory toughness is not achievable because the degree of polymerization is too low. Contrarily, if the intrinsic viscosity exceeds 1.4 dl/g, the melting viscosity becomes excessively high during the spinning process, whereby a melt fracture or others may occur to be an uneven fiber poor in toughness. Also, even if the spinning conditions are regulated, it is difficult to release a molecular stress, resulting in a high boiling water shrinkage. The intrinsic viscosity of fiber is preferably in a range from 0.68 to 1.3 dl/g, particularly preferably from 0.7 to 1.2 dl/g.

It is necessary that the peak temperature of the dynamic loss tangent (herein after referred to as Tmax) of the inventive CD-PTT fiber is in a range from 105 to 140.degree. C. Tmax is a value obtained by the measurement of dynamic viscoelasticity and corresponds to the denseness in an amorphous portion of the molecule. The larger the value, the denser the structure of the amorphous portion. If Tmax is less than 105.degree. C., there may be a case in which the denseness of the amorphous portion is low to worsen the orientation of molecule in the axial direction of fiber, whereby a toughness of the fiber becomes inferior and a fabric formed of such fibers is liable to break. Contrarily, if it exceeds 140.degree. C., the denseness in the amorphous portion of the molecule becomes too high for the cationic dye to migrate into the fiber, whereby it is difficult to provide a deep color dyed product. In order to improve both the toughness and the color development of the dyed product, Tmax is particularly preferably in a range from 110 to 120.degree. C.

It is necessary that the boiling water shrinkage (hereinafter referred to as BWS) of the inventive CD-PTT is in a range from 0 to 16%. Since the molecule is in an excessively stressed state if the BWS exceeds 16%, the resultant fabric is largely shrunk during a subsequent processing such as a dyeing process to have a hard touch which is contradictory to a soft touch inherent in the PTT fiber. Contrarily, if the BWS is less than 0%, that is, when the fiber extends in boiling water, there may be a case wherein a fabric free from wrinkles is not obtainable even though it is heat-treated. BWS is preferably in a range from 3 to 15%, more preferably from 5 to 14%.

The elongation at break of the inventive CD-PTT fiber is preferably in a range from 20 to 70%. To improve the fiber toughness and prevent fluff or yarn breakage from occurring during the drawing or subsequent processing process, the elongation at break is preferably 20% or more. To improve the fiber toughness so that the uniform drawing is possible to obtain fibers small in size irregularity, the elongation at break is preferably 70% or less. The elongation at break is more preferably in a range from 25 to 65%, furthermore preferably from 30 to 60%, particularly preferably from 35 to 55%.

The toughness of the inventive CD-PTT fiber is preferably 16 or more. The toughness is calculated by the following equation:

Toughness=[Strength (cN/dtex)].times.[Elongation (%)].sup.1/2

If the toughness is 16 or more, the resultant fabric is difficult to tear. The upper limit of the toughness is not be restricted, but a higher value is better. To make the best use of the effect of high molecular weight of the inventive CD-PTT and sufficiently exhibit the durability and stiffness of the resultant fiber product, the toughness is preferably 17.5 or more, more preferably 18 or more, most preferably 19 or more.

The tensile strength of the inventive CD-PTT fiber is preferably 2.2 cN/dtex or more. Since the strength is excessive low if this value is less than 2.2 cN/dtex, it is necessary to increase the elongation when the toughness is to be increased, which is liable to cause a so-called "irreversible shaping" in which a portion of the fabric to which a force has been applied upon the formation of the fabric remains deformed. The tensile strength is more preferably 2.4 cN/dtex or more, furthermore preferably 2.6 cN/dtex, particularly preferably 2.8 cN/dtex or more.

The elastic recovery at 20% elongation of the inventive CD-PTT fiber is preferably 60% or more for the purpose of achieving the excellent stretchability inherent to PTT., more preferably 65% or more, particularly preferably 70% or more.

The density of the inventive CD-PTT fiber is preferably 1.330 g/cm.sup.3 or more. The density is an index representing the crystallinity of the fiber. The higher the density, the higher the crystallinity of the fiber. To enhance the crystallinity and exhibit the excellent stretchability inherent to PTT, as well as to sufficiently fix the molecule by the crystallization so that BWS is within a preferable range defined by the present invention, the density is 1.330 g/cm.sup.3 or more. On the other hand, since the crystalline density of PTT is 1.431 g/cm.sup.3 (see, Material, Vol. 35, No. 396, page 1067, published in 1986), it is thought that the upper limit of the density of the copolymerized CD-PTT cannot exceed this value. The density is more preferably 1.335 g/cm.sup.3 or more, furthermore preferably 1.340 g/cm.sup.3 or more.

The U % of the inventive CD-PTT fiber is preferably in a range from 0 to 3%. When the fiber passes through an USTER TESTER 3 at a constant speed, a curve of the unevenness of the fiber size (the variation of fiber weight) illustrated in FIG. 1 is obtained. The U % is obtainable based on this result in accordance with the following equation (1). The U % is preferably 2% or less, more preferably 1.5% or less on account of suppressing fluff or yarn breakage during the subsequent processing and minimizing the irregularity in mechanical properties and the uneven dyeing.

U %=[a/(Xave.times.T)].times.100 (1)

wherein, in FIG. 1, Xave is an average value, a is an area between an instantaneous value (Xi) of a weight and Xave (a hatched portion) and T is a measurement time.

The hue of the inventive CD-PTT fiber is preferably in a range from -30 to 5 as represented by a YI value (yellowness) and in a range from 50 to 150 as represented by a WI value (whiteness). If the hue is within this range, it is possible to easily obtain a dyed fabric of a desired color excellent in color development when the fabric is dyed with a light color. To obtain the hue within such a range, it is important that the whiteness of the polymer satisfies the b* valu