US3245955A

US3245955A - Process for the manufacture of fibers and filaments of polyethylene terephthalate

Info

Publication number: US3245955A
Application number: US137508A
Authority: US
Inventors: Rieber Martin
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1960-09-14
Filing date: 1961-09-12
Publication date: 1966-04-12
Anticipated expiration: 1983-04-12
Also published as: BE608188A; GB986619A; NL269134A; DE1256837B; NL121430C

Description

Patented Apr. 12, 1966 3 245,955 PROCESS FOR THE MANUFACTURE OF FEBERS AND FILAMENTS F POLYETHYLENE TEREPH. THALATE Martin Richer, Kronberg, Taunus, Germany, asslgnor to Farbwerke Hoechst Aktiengeseilschatt vormals Meister Lucius & Bruning, Frankfurt am Main, Germany, a corporation of Germany No Drawing. Filed Sept. 12, 1961, Ser. No. 137,508 Claims priority, application Germany, Sept. 14, 1960, F 32,112 8 Claims. (Cl. 260-75) The object of the present invention is a process for the manufacture of fibers and filaments of polyethylene tercphthalate. It is a further object of the invention to manufacture fibers and filaments of polyethylene terephthalate which have little tendency towards pilling.

Great difficulties are encountered with textile structures containing synthetic fiber material owing to the fact that these structures, especially dress-materials, have a strong tendency towards pilling. By pilling there is understood the phenomenon that when textile structures are rubbed against one another or against another structure small conglomerations of individual fibers are forming which appear in the form of little knots on the surface and can be removed with difiiculty only. Several proposals have been made in order to remedy this evil. It has been proposed, for example, to singe and/ or to brush and to shear woven fabrics of synthetic filaments in order to reduce the pilling effect. These processes, however, involve additional expensive operations in which, moreover, the fabrics may be tendered by the heat required for singeing.

It has also been proposed to subject synthetic fibers or yarns of which woven fabrics are to be made to a chemical after-treatment in order to reduce the later pilling effect. Thus it is known, for example, to treat polyethylene terephthalate fiber yarns with aqueous solutions of hydrazine hydrate or ethylene diamine. This process has the disadvantage, however, that the yarns are frequently tendered in a considerable degree. Moreover, the fastness to light and resistance to heat of the synthetic fibers are very detrimentally affected in such operations. Attempts to reduce the later tendency towards pilling by modifying the manufacturing procedure of the synthetic fibers such, for example, as altering the stretch during the spinning procedure or the stretching ratio, have not led to satisfactory results either.

Now I have found a process for the manufacture of fibers of polyethylene terephthalate that have little tendency towards pilling which consists in adding to the polyethylene terephthalate 0.01 to of its weight of terephthalic acid, isophthalic acid, dimethylterephthalate, dimethyl isophthalate, diglycol terephthalate, diglycol isophthalate, or a mixture of these substances as a decomposing agent and working up the product obtained into filaments according to the melt extrusion process in known manner, the filaments thus obtained having a specific viscosity which is by 0.2 to 0.5 units lower than that of the original polyethylene terephthalate. The specific viscosity is determined by dissolving the polyethylene terephthalate in a mixture composed of 60 parts of phenol and 40 parts of tetrachloroethane to give a 1% solution and measuring the viscosity in a capillary viscosimeter at 25 C. Since portions of low molecular weight are contained in almost any polymer, it could not be foreseen in which way the addition of the aforementioned products would affect the properties of the polyethylene terephthalate and the filaments made thereof. It was surprising, therefore, that by adding the said substances there can be attained a very uniform decomposition of the polyethylene terephthalate in such a manner that, by adding definite proportions by weight of monomer, the specific viscosity of the polyethylene terephthalate formed can be reduced and precisely adjusted. When carrying out the process of the present invention for the manufacture of filaments having a poor tendency towards pilling, it was found that there is not obtained a mixture of the individual decomposing agents with the polyethylene terephthalate but that a chemical reaction takes place (decomposition of the chain molecules), whereby the physical properties of the filaments are modified and especially the tendency towards pilling is largely abolished.

I have found, moreover, that the amount of the decomposing agent added must be limited and exactly dosed since by the addition of too great amounts of decomposing agents to the polyethylene terephthalate prior to the spinning process the various physical data of the filaments are adversely affected; thus, for example, the tensile strength of the filaments is strongly reduced if too great a quantity of decomposing agent is applied whereby the filaments obtained become brittle.

The decomposing agent can be incorporated according to various methods:

1) After the termination of the polycondensation, i.e. after the manufacture of the polyethylene terephthalate which can take place continuously or discontinuously, the desired amount of decomposing agent is added to the molten polyethylene terephthalate. In this procedure, the melt of polyethylene terephthalate is advantageously kept under an atmosphere of nitrogen of atmospheric pressure and the decomposing agent is slowly added, with agitation. After the addition of the decomposing agent, stirring is continued for 5 to 15 minutes. By the addition of the decomposing agent and depending on the amount applied thereof, the viscosity of the melt of polyethylene terephthalate is reduced to a greater or lesser extent. The polyethylene terephthalate obtained can either be fed in the molten state directly to the spinning head, for example with the aid of a screw conveyer, and there be spun into filaments, or the melt is forced through a slot die and cooled in the air or in water. The ribbon obtained is then worked up into granules in a cutting machine. These granules can be stored and transported. From these polyethylene terephthalate granules there are obtained filaments when, after drying the granules to a water content of less than 0.04%, they are melted again and the melt is forced through a spinneret by means of spinning pumps and the filaments obtained are taken off.

(2) It is likewise possible to add the decomposing agent to the polyethylene terephthalate in the following manner:

The melt of polyethylene terephthalate obtained after the polycondensation is formed into ribbons and these are worked up into granule-s in a cutting machine. These granules are mixed with the desired amount of the decomposing agent which should preferably be in the pulverulent or granular state. In order to warrant that the granules are intimately mixed with the decomposing agent, it is necessary to mix the composition for several hours, for example in an offset tumbling mixer. It is advantageous to add the decomposing agent to the granules prior to drying the granules and then to dry the mixture to a water content of less than 0.04% of its weight. In the drying process the pulverulent or granular decomposing agent is bonded to the granules so that in the further processing of the mixture a uniform distribution of the decomposing agent in the granules is warranted. In the further processing procedure the mixture is melted, in the course of which procedure the decomposing agent is dissolved in the melt of the polytageous to use as highly a concentrated solution as possible. This solution is added to the polyethylene terephthalate obtained after the polycondensation which, after extrusion into ribbons and comminution, is available in grandular form, while the desired amount of the decomposing agent has to be metered in carefully. The solution of the decomposing agent must be well mixed with the granular product. It is suitable for this purpose to mix the composition for several hours, for example in an offset tumbling mixer. When intimate mixing has been attained, the solvent is gradually evaporated. This can either be done by creating a vacuum or by slowly heating the composition to a temperature situated a few degrees above the boiling point of the solvent. When the solvent is evaporated, the decomposing agent deposits in a finely distributed formon the surface of the granular product. The granules thus obtained are dried to a water content'of' less than 0.04% by weight. Owing to the uniform deposition of the decomposing agent on the granular product, the uniform distribution is warranted even 'in the case of a further processing. The granules are melted while the decomposing agent is dissolved in the melt of the polyethylene terephthalate and the polyethylene terephthalate decomposes to the desired extent. The melt obtained has a lower viscosity than the melt of the original polyethylene terephthalate. With the aid of spinning pumps the melt is forced through a spinneret and shaped into filaments that can be subjected to a further treatment in known manner.

The following examples serve to illustrate the invention but they are not intended to limit it thereto:

Example 1 1 kg. of polyethylene terephthalate granules (specific viscosity: 0.85) were prepared from terephthalic acid and ethylene glycol in known manner and mixed with grams of a granular transesterification product of dimethyl terphthalate and glycol (melting point: 150 to 160 C.), then dried for two hours at 180 C. and spun at 290 C. in a melt spinning installation through a spinneret having 200 holes. After spinning the polyethylene terephthalate had a specific viscosity of 0.55. The melting point of the polyethylene terephthalate was not noticeably reduced by the spinning process (melting point: 250 C.). Then the filaments were heated and stretched in the ratio of 1:3.65, crimped, prepared, subjected to heat setting and cut. The normal polyethylene terephthalate fibers had a tensilev strength of 3.8 grams per denier and an elongation at break of while the fibers prepared according to the process of the present invention had a tensile strength of 3.4 grams per denier and an elongation at break of 23%. The yarns (No. 48 double/500 twists S/500 twists Z) which were spun from the staple fibers prepared according to this example had a considerably lower pilling efiect than normal polyethylene terephthalate yarns.

Example 2 1 kg. of granulated polyethylene terephthalate was prepared as described in Example 1 and mixed with 10 g. of dimethyl terephthalate. After drying, the mixture was spun into filaments in a melt spinning installation. The filaments. had a specific'vi cosity of 0.57 and a meltin point of about 258 C. They were stretched as described in Example 1 and processed into staple fibers. The tensile strength of normal polyethylene terephthalate fibers is 3.8 grams per denier with an elongation at break of 25 Fibers prepared according to this example had a tensile strength of 3.3 grams per denier and an elongation at break of 22%. The yarns (No. 40 double/400 twists 8/450 twists Z), which were spun from the staple fibers prepared according to this example, had an appreciably lower tendency towards pilling.

Example 3 10 grams of dimethyl terephthalate were dissolved in cc. of acetic acid ethyl ester and 1 kg. of granulated polyethylene terephthalate was added to this solution. Then the acetic ester was evaporated in vacuo, the lacquered granules were dried and processed according to the melt extrusion process intofibers as described in Example 2. The yarns obtained possessed the same properties as those obtained according to Example 2.

Example 4 30 grams of diglycol terephthalate were dissolved in Example 5 200 kg. of polyethylene terephthalate were prepared in a vessel (capacity: 500 kg.) by transesterification from dimethyl terephthalate and ethylene glycol and subsequent condensation, as usual. As soon as the condensation mass had attained a specific viscosity of 0.85, 1 kg. of diglycol terephthalate (preliminary condensate) was charged to the condensation vessel in small portions without vacuum, under an atmosphere of nitrogen, while agitation was continued for 15 minutes at 280 C. Then the molten contents of the vessel were discharbed and the melt granulated in the usual manner. The granules had a specific viscosity of 0.6. The polyethylene terephthalate filaments prepared therefrom in a melt spinning installation were processed into staple fibers as described in Example 1. The filaments had a tensile strength of 3.5 grams per denier. From the staple fibers there was obtained a yarn (No. 48 double/500 twists S/500 twists Z) which had a very low tendency towards pilling.

I claim:

1. A process for manufacturing polyethylene terephthalate fibrous structures having improved wearing prop erties which comprises admixing polyethylene terephthalate having a specific viscosity of about 0.8 to about 0.9 with 0.1 to 5% by weight, calculated on the weight of said polyethylene terephthalate, of a decomposing agent selected from the group consisting of dimethyl terephthalate, dimethyl isophthalate, diglycol terephthalate and diglycol isophthalate, reacting said mixture to decompose said polyethylene terephthalate to a specific viscosity of about 0.5 to about 0.6, and spinning said mixture to form said fibrous structures, said specific viscosity being determined by measuring the viscosity of a 1% solution of said polyethylene terephthalate in a mixture of 60 parts phenol and 40 parts tetrachloretha'ne in a capillary viscosimeter at 25 C.

2. A process as defined in claim 1 wherein said fibrous structures are multifilamcnts.

3. A process as defined in claim 1 wherein said fibrous structures are monofilaments.

4. A process as defined in claim 1 wherein said polyethylene terephthalate is in molten form and said decomposing agent is admixed therewith.

5. A process as defined in claim 1 wherein said polyethylene terephthalate is dried after admixture of said decomposing agent and prior to spinning.

6. A process as defined in claim 1 wherein said polyethylene terephthalate is in granular form and said step of admixing said polyethylene terephthalate and said decomposing agent, prior to reacting them, comprises dissolving said decomposing agent in a solvent selected from the group consisting of methylene chloride, dioxane, acetic acid ethyl ester and ethanol, applying the solution of said decomposing agent and said solvent to said polyethylene terephthalate granules, evaporating said solvent from said granules, and drying said granules.

7. A process as defined in claim 1 wherein said mixture of polyethylene terephthalate and decomposing agent is reacted at a temperature in the range of about 270 to 290 C. and continuously stirred for about 5 to 15 minutes.

8. In a process for manufacturing fibrous structures of polyethylene terephthalate, the step of improving the wearing properties of said fibrous structures which comprises admixing with polyethylene terephthalate having a specific viscosity of about 0.8 to about 0.9, 0.1 to 5% by weight, calculated on the weight of said polyethylene terephthalate, of a decomposing agent selected- References Cited by the Examiner UNITED STATES PATENTS 2,799,664 7/1957 2,897,042 7/ 1959* Heiks 8130.1 2,938,811 5/1960 Hermes 117102 3,014,011 12/1961 Zoetbrood 260 3,070,575 12/1962 Cramer 26047 FOREIGN PATENTS 728,550 4/1955 Great Britain.

WILLIAM H. SHORT, Primary Examiner. LOUISE P. QUAST, Examiner.

Drewitt 260-75

Claims

1. A PROCESS FOR MANUFACTURING POLYETHYLENE TEREPHTHALATE FIBROUS STRUCTURES HAVING IMPROVED WEARING PROPERTIES WHICH COMPRISES ADMIXING POLYETHYLENE TEREPHTHALATE HAVING A SPECIFIC VISCOSITY OF ABOUT 0.8 TO ABOUT 0.9 WITH 0.1 TO 5% BY WEIGHT, CALCULATED ON THE WEIGHT OF SAID POLYETHYLENE TEREPHTHALATE, OF A DECOMPOSING AGENT SELECTED FROM THE GROUP CONSISTING OF DIMETHYL TEREPHTHALATE, DIMETHYL ISOPHTHALATE, DIGLYCOL TEREPHTHALATE AND DIGLYCOL ISOPHTHALATE, REACTING SAID MIXTURE TO DECOMPOSE SAID POLYETHYLENE TEREPHTHALATE TO A SPECIFIC VISCOSITY OF ABOUT 0.5 TO ABOUT 0.6, AND SPINNING SAID MIXTURE TO FORM SAID FIBROUS STRUCTURES, SAID SPECIFIC VISCOSITY BEING DETERMINED BY MEASURING THE VISCOSITY OF A 1% SOLUTION OF SAID POLYETHYLENE TEREPHTHALATE IN A MIXTURE OF 60 PARTS PHENOL AND 40 PARTS TETRACHLORETHANE IN A CAPILLARY VISCOSIMETER AT 25*C.