CS239183B1 - A method for producing high-shrinkage copolyester fibers - Google Patents

Abstract

The subject of the invention is a method of producing high-shrinkage copolyester fibers suitable for the production of high-volume relaxation-bulking yarns, made from copolyester of terephthalic acid, isophthalic acid and ethylene glycol, whereby the shrinkage forces are increased by branching with the addition of tri- or multi-functional ester-forming compounds.

Description

The invention relates to a method of producing high-shrinkage copolyester fibers intended for relaxation bulking, which have increased relaxation forces.

In the process according to the inventions protected by Czechoslovak patents 105 653 and 117 150, relaxation-sized yarns are produced using copolyester high-shrinkage fibers, in which the basic components are terephthalic acid and ethylene glycol. The copolyesterification component is isophthalic acid. In the production of relaxation-sized yarns, yarn is prepared from shrinkable and non-shrinkable, or less shrinkable fibers. During heat treatment of such yarns, the shrinkable fibers shrink and the non-shrinkable fibers form arcs around them, thereby bulking the yarn.

It is known that the relaxation forces of isophthalic acid copolyesterified fibers can be varied by the content of the copolyesterified component, the stretching ratio and the stretching temperature. These methods have limited effect.

A substantial increase in relaxation forces is achieved according to the present invention if an additional copolyesterification component is used, namely a tri- or polyfunctional organic compound with functional groups capable of forming polyesters. Such groups are hydroxyl, phenolic, carboxyl groups. These can be free or esterified with a monohydric alcohol or ethylene glycol. These compounds branch and crosslink the copolyester. Crosslinked polyesters and copolyesters cannot be used for the production of fibers. However, if only a small amount of a polyfunctional compound is used, which causes only a small branching, the polymer remains fiber-forming. The branching of polyesters and copolyesters is known, for example, from US 2,895,946 or US 3,461,468. In these inventions, the polymers described are not used at all for the production of high-shrinkage fibers for relaxation bulking.

The essence of the invention lies in the new use of branching for the production of high-shrinkage fibers that have increased relaxation forces. Thus, they allow for increased shrinkage in yarns, which leads to increased bulkiness of the yarn.

In the production of copolyester fibers according to the invention, polyesters of terephthalic acid and ethylene glycol are copolyesterified with 4 to 15 mol % of isophthalic acid, so that terephthalic acid constitutes from 96 to 85 mol % of the acid component. In addition, 0.05 to 0.7 mol % of a polyhydric ester-forming compound is added. The process according to the invention does not require any special polyfunctional compound. Tri- or tetrafunctional compounds are sufficient. Examples of suitable trifunctional compounds are glycerin, trimethylpropane, or trimethyltrimesinate. An example of a suitable tetrafunctional compound is pontaerythritol.

The bulkiness of a yarn depends primarily on the shrinkage of the fiber that occurred during softening; a highly shrinkable fiber must overcome the resistance of the other fibers in the yarn during shrinkage. The ability to overcome resistance depends on the shrinkage forces that the fiber is able to develop. Thus, the shrinkage force affects the shrinkage during softening and thus the bulkiness of the yarn. Therefore, to achieve high bulkiness, it is necessary to have not only a fiber with sufficient shrinkage, but also a fiber that is characterized by high shrinkage forces.

The shrinkage force is defined as the force that a fiber is capable of exerting during shrinkage. When the force acting against the direction of shrinkage is zero, the fiber reaches the highest shrinkage achievable under the given conditions. When the force acting against the direction of shrinkage increases, the shrinkage decreases. The force acting against the direction of shrinkage is at the same time identical to the shrinkage force at a given shrinkage, only its direction is opposite. The force at which the fiber does not change in length is referred to as the maximum shrinkage force. When the force acting against the direction of shrinkage increases above the maximum shrinkage force, the fiber elongates.

The simplest way to determine the shrinkage forces and the maximum shrinkage force is as follows: the individual fibers are loaded with a large weight and a selected temperature is applied to them, most often a temperature of 150 ^° C is used. A period of 5 minutes is sufficient. Then the length changes are determined. The results can be graphically represented as a relationship between the applied force and the shrinkage. From the graphic representation, the respective shrinkage force can be determined for each shrinkage. The maximum shrinkage force is subtracted from the zero change in length. It is useful to convert the shrinkage forces to a unit fineness, usually expressed in centinewtons per decitex.

Polycondensation can be carried out by all conventional methods used for the production of fiber-forming polyesters and copolyesters. Spinning and drawing can also be carried out by conventional methods known for the production of high-shrinkage fibers. High-shrinkage fibers do not settle. The main advantage of the process according to the invention is that increased relaxation forces lead to higher shrinkage and thus to higher bulkiness. The process also has other advantages. The elongation of the fibers is reduced, which improves the dimensional stability of the products. In addition, the polycondensation time is shortened, which increases the capacity of the polycondensation device and at the same time saves energy.

Example 1

46 kg of dimethyl terephthalate, 4 kg of dimethyl isophthalate and 3-6 kg of ethylene glycol were weighed into the polycondensation apparatus. 334 g of glycerin (0.4 mol %) were added. 20 g of manganese acetate was further added as a transesterification catalyst. Transesterification was carried out in the usual manner. 15 g of triphenyl phosphite was added as a stabilizer. It was matted with 230 g of titanium white. 25 g of antimony trioxide was added as a polycondensation catalyst. It was polycondensed in the usual manner, the polycondensation was completed at a limiting viscosity number of the polymer of 0.72.

The polymer was spun with a 24-hole die, polymer temperature 270 °C, spinning speed 1000 m/min. The fineness of the unstretched fiber was 420 dtex. The fiber was spun in water at 80 °C, spinning ratio 4.25. The comparison fiber was produced in the same way, but without the addition of glycerin. The fibers had the following properties:

Property

Comparison thread

Glycerin branched fiber

Limiting viscosity number dcl/g Shrinkage at 150 °C, %

Max. shrinkage force cN/dtex

0.719

24.9

0.375

0.688

28.4

0.602

Elongation, % Strength, cN/dtex 23.7 4.0 12.4 3.5 Example 2 the amount of added glycerin. The fiber was at a temperature of 75 °C on dividend ratio 4 : 0. Procedure as in the example 1 prepared The fibers had the following properties: polymer and fiber, while changed the number of Quantity Elongation, % Shrinkage, % Max. shrinkage force, glycerin mol % cN/dtex 0 29.7 24 0.239 0.3 21.5 27.7 0.373 0.7 16.5 29.5 0.427 Example 3 polyesterification components and their quantity is given in the table. The fiber was spun at a temperature of Procedure as in the example 1 prepared lote 80 °C for a dilation ratio of 4.25. Fibers other- polymer and fiber. Branching co- if the following properties: Branching modification Quantity Shrinkage Max. shrinkage component branching at 150 °C, % force, cN/dtex components mol °/o — — 23.9 0.375 trimethylolpropane 0.4 26.0 0.583 pentaerythritol 0.3 26.8 0.002 trimethyltrimesiia’1 0.4 27.1 0.596

Claims (2)

OBJECT OF THE INVENTION A process for the production of high-shrinkage copolyester fibers with enhanced relaxation forces, characterized in that the fiber-forming copolyester is spun and divided, wherein the acid component comprises terephthalic acid from 85 to 96 mol% and isophthalic acid from 4 to 15 mol%, the glycol component being and additionally polycondensated in the presence of 0.05 to 0.7 mole% of a tri, or multi-functional ester-forming compound containing hydroxyl, phenolic, or carboxyl groups, which may be free or esterified with a monohydric alcohol or ethylene glycol. 2. A process for producing high-shrinkage copolyester fibers with enhanced relaxation forces according to claim 1, wherein the three or more functional ester-forming compounds are glycerin, trimethylolpropane, trimethyltrimezinate and pentaerythritol.