POLYESTER FIBER

Abstract: A polyester fiber mainly comprising repeating units of ethylene terephthalate and a method of producing the same, wherein a compound represented by general formula (1), (2) or (3) is added as melt viscosity depressant. It now becomes possible to lower the melt viscosity without lowering the limiting viscosity and to facilitate the spinning of a polyester with a high melt viscosity, thus giving a high-strength fiber.

Description: The present invention relates to a melt-viscosity depressant for polyester resins and a polyester fiber having a high tenacity which can be produced easily by spinning. Polyester resins are widely used as the materials for synthetic fibers and it is believed that in order to increase the tenacity of a synthetic fiber it will suffice when the degree of polymerization of the polymers is increased. However, when the degree of polymerization of the polymer is increased, the melt viscosity thereof is increased as a matter of course to impair the workability thereof to thereby reduce the productivity. Although elevation of the melting temperature is one of the means for reducing the melt viscosity, the decomposition of the resin is accelerated at a high temperature to reduce the degree of polymerization of the polymer. Thus the object, i.e. the production of a fiber having a high degree of polymerization cannot be attained. Polyester filaments having a high degree of polymerization are used in the field of industrial high-tenacity yarns. It is demanded to further increase the tenacity thereof and, for this purpose, the melt viscosity of the resin should be reduced. When the melt viscosity of a polymer used as the material for staple fibers is reduced, the extrudability through a nozzle is improved or the mechanical power necessitated for the extrusion is reduced, thus contributing to the enhancement of the productivity. In the field of high-speed spinning recently employed in practice, the reduction in the melt viscosity of the resin is effective in increasing the extrusion rate. Although the use of a lubricant was proposed in order to solve this problem, it was found that when a lubricant such as ethylenebisstearamide, stearic acid or stearyl alcohol was incorporated into the resin, not only the melt viscosity thereof but also the degree of polymerization thereof was reduced. Meanwhile polyester fibers essentially have a poor hand and are apt to jar. Means for solving this problem include an increase in the fineness of the fibers, an alkaline weight reduction of the fibers, and a treatment of the fibers with a softener. The increase in fiber fineness is described in "Senshoku Kogyo (Dyeing industry)", Vol. 38, pages 288 to 299, by Shigenobu Kobayashi et al., the alkaline weight reduction is described in J. Soc. Dyers Colorists', Vol. 78, page 9 (1962) by I. E. Haden and in The Textile Mfr., page 293 (July, 1963) by B.C.M. Dorset, and the treatment with a softener is described in U.S. Patent No. 3,377,249. [Disclosure of the Invention] Objects of the present invention are to find out a melt-viscosity depressant capable of reducing the melt viscosity of a polyester resin without essentially reducing the degree of polymerization thereof and to facilitate the production of a polyester fiber having a high tenacity by spinning by using the melt-viscosity depressant. Compounds of formula (1) to be used in the present invention are disclosed in Japanese Patent Laid-Open Nos. 93752/1983, 2824/1982 and 18463/1987, respectively. EP 0295147B discloses a polyester yarn consisting mainly of polyethylene terephthalate for use in reinforcing rubber goods. The present invention provides a process for producing a polyester fiber which comprises adding a compound (b) of the following general formula to a polyester (a) comprising ethylene terephthalate as the main recurring unit and melt-spinning the resulting composition: wherein A 1 and A 2 each represent an alkyl group having 6 to 18 carbon atoms or an arylalkyl group, n represents 0 or 1, and X represents -S-, -SO 2 - or -O- in which R 1 and R 2 each represent H or an alkyl group having 4 or less carbon atoms. In the present invention, it is preferred that after the addition of the compound of the general formula (1) followed by melt spinning, the filaments are pre-hot-drawn at 60 to 100°C and then heat-treated at 150 to 250°C under tension. The starting polyester resin preferably has a limiting viscosity of at least 0.8 in phenol/ tetrachloroethane (60/40) at 25°C. The draw ratio is preferably at least 4. The present invention provides also a polyester fiber produced by the above-described process. The polyester fiber thus produced preferably has a tenacity of at least 61.9 mN/dtex (7 g/d). [Detailed Disclosure of the Invention] The present invention provides a melt-viscosity depressant for polyester resins which comprises a compound of the general formula (1): wherein A 1 and A 2 each represent an alkyl group having 6 to 18 carbon atoms or an arylalkyl group, n represents 0 or 1, and X represents -S-, SO 2 - or -O- in which R 1 and R 2 each represent H or an alkyl group having 4 or less carbon atoms, and a polyester fiber produced by mixing the melt-viscosity depressant into a starting polyester resin to form a polyester resin composition and melt-spinning this composition. The number of carbon atoms in A 1 and A 2 of the compound of the formula (1) of the present invention can be freely selected in the above-described range. When the number of carbon atoms in A 1 or A 2 is less than 6, the molecular weight is so low that the resin will boil at the melting temperature to form bubbles, while when it exceeds 18, the compatibility thereof with the resin is reduced and therefore no satisfactory effect can be obtained. Examples of A 1 and A 2 include straight-chain alkyl groups such as n-hexyl, n-octyl, n-dodecyl and n-octadecyl groups; branched alkyl groups such as 2-hexyldecyl and methyl-branched octadecyl groups; and arylalkyl groups such as benzyl and 2-phenylethyl groups. The compound of the general formula (1) of the present invention can be easily produced by reacting an aromatic glycol of the formula: with an alkyl halide having 6 to 18 carbon atoms and/or an arylalkyl halide in the presence of an alkali catalyst such as NaOH or KOH. Examples of the compounds of the general formula (1) of the present invention include those given below: (hereinafter referred to as the invention compound 1 ○), (hereinafter referred to as the invention compound 2 ○), (hereinafter referred to as the invention compound 3 ○), (hereinafter referred to as the invention compound 4 ○), (hereinafter referred to as the invention compound 5 ○), (hereinafter referred to as the invention compound 6 ○), and (hereinafter referred to as the invention compound 7 ○). The polyester resin used as the starting material in the present invention preferably comprises polyethylene terephthalate as the main recurring unit and its limiting viscosity in phenol/tetrachloroethane (weight ratio: 60/40) is preferably at least 0.8 at 25°C. When the limiting viscosity of the starting polyester resin is less than 0.8, the melt viscosity of the polyester resin is not so high that the productivity is seriously reduced and no intended high tenacity can be obtained in some cases. Polyesters which are copolymers with, for example, sodium sulfoisophthalate are also usable and they are dyeable with a cationic dye. The melt-viscosity depressant of the present invention can be added to a polyester resin to form a homogeneous mixture. It scarcely fumes or colors even upon exposure to a high temperature in the melt-spinning step, namely, it has an excellent heat resistance. High-tenacity polyester fibers can be produced from the polyester resin composition containing the melt-viscosity depressant of the present invention. It is indispensable to use chips of a high polymer in the production of the high-tenacity fibers. In spinning the polymer chips, they are melted usually at 280 to 300°C. The melt viscosity of the high polymer is increased due to intertwinement of the polymer chains themselves and, therefore, elevation of the extrusion pressure and impairment of the spinnability are caused. However, when the melt-viscosity depressant of the present invention is used, the spinning pressure and the tension of the filament are reduced to make the spinning smooth. The filaments extruded through a nozzle are temporarily cooled to solidify them. The crystallization in the cooling step is not preferred when polyethylene terephthalate resin or the like is melt-spun, while the acceleration of the crystallization in the cooling step is preferred for improving the moldability when the polyester resin is injection-molded. The melt-viscosity depressant of the present invention does not cause any crystallization of the resin in the step of cooling the filaments from the spinning nozzle. The undrawn filaments thus cooled and taken up are subjected to orientation crystallization in the subsequent stretching / heat treatment step to form high-tenacity filaments. To exhibit the intended effect of the melt-viscosity depressant of the present invention, the depressant is preferably added in an amount of 0.1 to 10 parts (by weight, the same shall apply hereinafter), more preferably 0.5 to 5 parts, to 100 parts of the polyester resin. When the amount is less than 0.1 part, the effect thereof can hardly been expected, while when it exceeds 10 parts, the properties of the resin are adversely affected. The melt-viscosity depressant of the present invention may be added to the starting polyester resin in the course of the production of the resin or in a suitable step after the production thereof, or it may be mixed into resin pellets or molten resin in the spinning step. The high-tenacity fibers of the present invention are produced by homogeneously mixing the starting polyester resin with the melt-viscosity depressant of the present invention, melt-spinning the mixture, cooling the filaments, and drawing and heat-treating them. The filaments thus spun are cooled, taken up temporarily as undrawn filaments, subjected to pre-hot-drawing and then heat-treated under tension. Alternatively, the filaments are not taken up but taken off with a take-off roller and then drawn and heat-treated with a hot roller. The drawing and heat treatment can be conducted in the same manner as that of ordinary polyester fibers. A preferred preheating temperature in the drawing step is 60 to 100°C and a preferred heat treatment temperature is 150 to 250°C. To obtain high-tenacity fibers, the draw ratio is desirably at least 4. The polyester resin according to the present invention is preferably one comprising polyethylene terephthalate as the main recurring unit. It may also be a polyester resin partially copolymerized with, for example, polyethylene glycol, POE(2) bisphenol A, sodium sulfoisophthalate or 1,4-butanediol. The polyester fibers dyeable with a cationic dve according to the present invention are those produced from a polyester resin partially copolymerized with sodium sulfoisophthalate or the like as a constituent. The following Examples will further illustrate the present invention, which by no means limit the invention. Example 1 Each compound listed Table 1 was added to polyethylene terephthalate resin and melt-mixed in an extruder. The resulting strands were cooled with water and cut to form samples. The melt flow index of the resin composition was determined in terms of the amount of a molten resin extruded through an orifice having a diameter of 2.095 mm and a length of 8 mm at a temperature of 275°C by application of a load of 2160 g in 10 min. The higher the melt flow index, the lower the melt viscosity. After the determination of the melt flow index, the sample was dissolved in a solution of phenol/tetrachloroethane (60/40) to determine the limiting viscosity [η] at 25°C. When the value of [η] of the sample is equal to that of an additive-free polyethylene terephthalate resin, the resin may be deemed to be essentially free from a reduction in the degree of polymerization. The results are given in Table 1. Compound Amount (weight % based on resin) Melt flow index (cm 3 /10 min) [η] (dℓ/g) not added (comparative) - 12.1 0.771 invention compound 1 ○ 3 23.1 0.770 invention compound 1 ○ 5 38.2 0.768 invention compound 2 ○ 5 35.7 0.771 invention compound 3 ○ 5 38.4 0.768 invention compound 4 ○ 5 34.1 0.767 invention compound 5 ○ 5 37.1 0.772 invention compound 6 ○ 5 36.2 0.770 invention compound 7 ○ 5 35.9 0.766 <Results> The compounds of the present invention are capable of reducing the melt viscosity without essentially reducing the limiting viscosity and facilitate the spinning of polyesters having a high melt viscosity. Example 2 100 parts by weight of polyethylene terephthalate resin having a limiting viscosity of 1.2 was dryblended with 5 parts by weight of the invention compound 1 ○. The blend was placed in an extruder-type melt-spinning machine and extruded at a rate of 3 g/m through a spinning nozzle having a diameter of 0.5 mm while keeping the temperature of the spinning section at 290°C. The filaments thus formed were taken up at a rate of 1000 m/min at a distance of 2.5 m beneath the nozzle. The undrawn filaments thus taken up were drawn 5-fold in an oil bath at 80°C and then heat-treated at 170°C for 30 min while keeping the filament length constant. In the spinning step, the pressure in the nozzle was 6.4 MPa (65 kgf/cm 2 ), the limiting viscosity of the undrawn filament was 0.98, and the tenacity of the drawn filament was 84.0 mN/dtex (9.5 g/d). Comparative Example 1 The same experiment as that of Example 2 was repeated without addition of the invention compound 1 ○. In the spinning step, the pressure in the nozzle was 9.8 MPa (100 kgf/cm 2 ), the limiting viscosity of the undrawn filament was 0.97, and the tenacity of the drawn filament was 85.7 mN/dtex (9.7 g/d). Example 3 The same experiment as that of Example 2 was repeated except that the invention compound 2 ○ was used. In the spinning step, the pressure in the nozzle was 5.9 MPa (60 kgf/cm 2 ), the limiting viscosity of the undrawn filament was 0.98, and the tenacity of the drawn filament was 83.0 mN/dtex (9.4 g/d).

Claims: A process for producing a polyester fibre characterised by adding a compound of the following general formula (1) to a polyester (a) comprising ethylene terephthalate as the main recurring unit and melt-spinning the resulting composition: wherein A 1 and A 2 each represent an alkyl group having 6 to 18 carbon atoms, n represents 0 or 1, and X represents -S-, -SO 2 - or -O- in which R 1 and R 2 each represent H or an alkyl group having 4 or less carbon atoms. A process according to Claim 1, wherein, after the addition of the compound of the general formula (1) followed by the melt spinning, the fibres are pre-hot-drawn at 60 to 100°C and then heat-treated at 150 to 250°C under tension. A process according to Claim 1, wherein the starting polyester resin has a limiting viscosity of at least 0.8 in phenol/tetrachloroethane (60/40) at 25°C. A process according to Claim 2, wherein the draw ratio is at least 4. Process according to Claim 1, wherein A 1 and A 2 each represent an alkyl group having 18 carbon atoms or n-octyl or n-dodecyl.

Inventors: ISHII YASUO, SUZUE SHIGETOSHI, SUZUKI NOBUYUKI, TANAKA TSUTOMU, ISHII, YASUO, SUZUE, SHIGETOSHI, SUZUKI, NOBUYUKI, TANAKA, TSUTOMU, SUZUKI, NOBUYUKI 3-1, FUNATSUCHO 1-CHOME, TANAKA, TSUTOMU 2-1, FUJIMIDAI 6-CHOME
Applicants: KAO CORP, KAO CORPORATION
Application year: 1990
Main classification: D01F6
IPC codes: C08K5, D01F6, D01F1