DE1190912B - Process to reduce the shrinkage capacity and to stabilize the force-elongation behavior of drawn threads, tapes or films made of low-pressure polyethylene - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

D 06 c

German class: 8 b - 33

Number: 1190 912

File number: F19206 VII a / 8 b

Filing date: December 31, 1955

Opening day: April 15, 1965

As experience shows, drawn threads, fibers or the fabrics made from them are as well Ribbons and films made of low-pressure polyolefins, especially low-pressure polyethylene, on the other hand When exposed to heat below its melting point, it is geometrically and mechanically unstable. So when they are warmed above room temperature, they retire to one of the temperature, manufacturing conditions and raw material-dependent amount together, a process that is commonly referred to as shrinkage and is theoretically made up of the tendency to reverse the stretching can explain. The amount of shrinkage, in the following only referred to as shrinkage, is also essentially retained when the structure is off Low pressure polyethylene has returned to room temperature. Simultaneously with this geometric The mechanical properties have changed even after exposure to heat, z. B. the force-elongation behavior changed. The tear strength decreases, the elongation at break increases, and the higher the temperature of the heat, the more so. This becomes the use value of structures made of low-pressure polyethylene, even if they are only used occasionally, e.g. B. for a boil wash, are brought to a higher temperature, significantly impaired.

Low-pressure polyethylene is to be understood as meaning a polyethylene which, in the unstretched, pure state, has a density higher than 0.930 g / cm ³ (see Chemical Week, June 4, 1955, p. 58) and has so far only been produced by the known low-pressure processes can be. According to the current state of knowledge, it owes its properties, which are significantly different from high-pressure polyethylene, primarily to less branching of the molecular chains.

The present invention relates to a process for reducing the shrinkage capacity and for stabilizing the force-elongation behavior of drawn threads, tapes or films made of low-pressure polyethylene, which is characterized in that these structures undergo a heat treatment at temperatures between 80 and 135 ° C , in particular between 100 and 125 ° C., with simultaneous shrinkage up to a maximum of 5%. After such a heat treatment, the tensile strength of the structure remains practically unchanged, and the elongation at break may increase slightly. On the other hand, the shrinkage of the structure that occurs when the heat is applied later in use is compared with the un-procedures for reducing the shrinkage capacity and for stabilizing the force-elongation behavior of drawn threads,
Ribbons or foils made from low-pressure polyethylene

Applicant:

Farbwerke Hoechst Aktiengesellschaft

formerly Master Lucius & Brüning, Frankfurt / M.

Named as inventor:

Dr. Karlheinz Riggert, Hofheim (Taunus);

Dr. Felix Schmieder,

Frankfurt / M.-Unterliederbach

treated structures, considerably reduced and thus an important functional property improved.

The USA. Patent 2325 060 can be seen that a heat treatment of threads High pressure polyethylene, as opposed to the major improvements made to structures can be obtained from low-pressure polyethylene by using the method according to the invention, neither in the still relaxed state leads to a satisfactory shrinkage resistance, and that only a two-stage heat treatment ensures the desired result, which consists in that one subjects the threads to a heat treatment in the first stage without any possibility of shrinkage and in the second stage, a heat treatment is carried out with complete relaxation.

The older method according to German Auslegeschrift 1111339 deals with hot stretching of low-pressure polyethylene structures. The inventive concept is based on such raw structures Procedure.

In contrast to these methods, the subject matter of the invention is treatment of already stretched threads, tapes or films made of low-pressure polyethylene, which is how already mentioned, by its higher molecular weight, by a higher degree of its crystallinity and its higher density due to less branching of its macromolecules of high pressure polyethylene differs. While threads from the latter after a heat treatment in ge or

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relaxed form only have insufficient shrinkage resistance and only through a two-stage Heat treatment, d. H. first in the relaxed state and then in the relaxed state, a decrease experience their shrinkage, is already stretched by the process according to the invention Threads, tapes or films made of low-pressure polyethylene are made in a single operation Exposed to temperatures between 80 and 135 ° C and shrunk to a maximum of 5% will.

To carry out the method according to the invention, the structures can be clamped in a frame that allows a certain amount of shrinkage. So-called shrink reels, too adjustable shrinkage allow can be used. Two-dimensional stretched films must be anchored in the longitudinal and transverse direction accordingly. Finally, the treatment can also be continuous take place with the help of two godets running at different peripheral speeds, Over which the thread or the tape, with the interposition of a heating zone, is guided.

Treatment temperature and duration depend on the requirements in the individual case. As a rule, the longer the dwell time and the higher the temperature, the stronger the effects; H. more shrink-proof structures are obtained. Strands and coils with thick windings will become useful Treated for a longer period of time at a correspondingly lower temperature to ensure even heating to get, with z. B. treatment temperatures of 125 ° C and below are used can be. In the case of continuous treatment churning out, on the other hand, generally only If it takes seconds or fractions of a second, the temperature gets as high as possible go, with temperatures up to 135 ° C can be used.

In the novel process treated monofilament yarns have a boil-off shrinkage on which is at a soaking temperature of 120 ° C and a contact time of 10 minutes, 1.7%, and at a contact time of 30 minutes only 1.2%, and that with an unchanged tear strength and elongation at break.

example

A monofilament drawn thread with a diameter of 345 μ made of low-pressure polyethylene, one

Solution viscosity number ^ ~ - - 2.8 (measured on a

Solution in tetrahydronaphthalene, concentration 5 g / l, ίο at a temperature of 120 ° C) has a Tear strength of 4.5 g / den, an elongation at break of 28% and a boiling shrinkage (5 minutes free shrink in boiling water) of 13.2%. This thread is wound into a strand and in attached to a suitable frame so that it can shrink by 5%. It will be for 10 minutes exposed to heat treatment in air at 120 ° C. After that are tear strength and elongation at break unchanged. In contrast, the boiling shrinkage decreased from 13.2 to 1.7%. One performs the same Heat treatment for 30 minutes, then also tear strength and elongation at break are then unchanged, while the boiling shrinkage has decreased from 13.2 to 1.2%.

Claims (1)

Claim: Process for reducing the shrinkage capacity and for stabilizing the force-elongation behavior of stretched threads, tapes or films made of low-pressure polyethylene, characterized in that these structures undergo a heat treatment at temperatures between 80 and 135 ° C, in particular between 100 and 125 ° C, with simultaneous shrinkage up to a maximum of 5% will. Considered publications:
German Patent Nos. 822 240, 733 643;
German patent application B 15519 VII / 8b (published on 12.3.1953); Journal: Melliand Textile Reports, 1953, p. 261; 1951, pp. 215 to 221;
Journal: Deutsche Färberzeitung, 1952, p. 7. 509 539/151 4.65 © Bundesdruckerei Berlin