CS245816B1 - Thermostable isotactial polypropylene for production of fibres - Google Patents

Description

The invention relates to thermostable isotactic polypropylene prepared by stereospecific polymerization for the production of polypropylene fibers.

Polypropylene fibers are prepared by spinning isotactic polypropylene from its melt at temperatures to achieve the desired melt viscosity for a given fiber type. The polymer is melted in spinning machines and fed by pump to individual spinning sites. At the same time, a melt of color pigment concentrate is added by injection to dye the fibers in the mass.

To ensure sufficient processing stability, thermostability and light stability of the fibers, a stabilizing system is added to the basic isotactic polypropylene. For the preparation of the fibers, isotactic polypropylene prepared by direct polymerization is used, characterized by an IT index (determined according to CSN 64 0861) = 4 to 12 g / 10 min. Temperatures required to achieve the desired viscosity of the polymer result in thermo-oxidative degradation, the depth of which, in addition to the temperature level, is determined by the content and composition of the stabilizing system. In view of the stability of the fiber-forming process, it is desirable that the polymer contain as low as possible non-fibrous additives - components of the stabilizing system, while guaranteeing an optimum stabilizing effect.

Polypropylene fibers are currently made from isotactic polypropylene stabilized by a system comprising a sterically hindered phenolic antioxidant 2,6-di-tert-butyl-4-methylphenol, a thiodipropionic acid ester such as distearyl thiodipropionate DSTDP, a light stabilizer, and a calcium stearate processing additive. The total content of non-fibrous stabilizers required to guarantee a sufficient level of thermostability and processing stability reaches a level of 1.1% by weight. DSTDP with a concentration ranging from 0.4 to 0.7% by weight is a substantial part of the system. The system guarantees average processing stability, is characterized by low long-term thermostability, and the fiber light stability level expressed as the half-life of the crimped 6.7 dtex polypropylene fibers in Xenoteste at 700 to 800 hours under moderate zone conditions. The main drawbacks of the types of polypropylene used today for the production of fibers are the high content of additives and the low level of long-term thermostability expressed in the time required to disintegrate 0.5 mm foil at 140 ° C in a forced air oven.

The high content of stabilizers at high processing temperatures results in the release of a considerable amount of fumes condensing on the spinneret and causing fiber breakage and contamination of the suction line from beneath the nozzles. The high content of sulfur-containing substance - DSTDP leads to the corroding of some parts of the spinning machines.

Said drawbacks have been solved by a modified stabilization system according to the present invention.

The present invention provides thermostable isotactic polypropylene for the production of polypropylene fibers, prepared by direct polymerization and comprising

A) 2,6-di-tert-butyl-4-methylphenol,

B) distearyl thiodipropionate,

C) light stabilizer 2-hydroxy-4n-octyloxybenzophenone and

A calcium stearate, further comprising

E) 2,6-dimethyl-4-dodecane (propenylphenol), wherein the total content of the synergistic stabilizing mixture composed of components I to E) in the polypropylene is 0.50 to 1.2% by weight. the content of component A) is 0.05 to 0.20% by weight, component B) is 0.10 to 0.30% by weight, component C) is 0.20 to 0.40% by weight; % of component D) 0.05 to 0.15 wt. and component E) 0.05 to 0.30 wt.

The use of a nonvolatile, non-impeded phenolic antioxidant (E) allows, due to its synergistic effects, a significant reduction in the thiodlpropionic acid ester content and hence the total amount of the stabilizing composition while maintaining the original level of polymer processing stability as exemplified in the examples. By replacing DSTDP with an antioxidant (E), the long-term thermostability of the fibers evaluated in an oven at 140 degrees Celsius is substantially increased.

A sterically hindered phenolic antioxidant guarantees good processing stability of the polymer during spinning. This, due to the synergistic effect, is substantially increased by sterically unprotected phenol. The synergistic effect of both phenolic antioxidants is supported by the presence of a sulfur co-stabilizer and in combination with light stabilizers, for example (C) the desired light stability level of the 6.7 dtex light fibers evaluated in Xenotest min. 800 hours. The synergism of antioxidants allows the total additive concentration to be reduced by min. 0.3% by weight, in particular due to a reduction in the DSTDP content.

The preparation of the polymer for the production of fibers according to the invention can be carried out on conventional single- and double-screw spinning machines. The starting material is isotactic powdered polypropylene, characterized by an IT value of 3.5 to 15 g / 10 min, to which the desired additives in pure form, optionally in the form of concentrates in powdered polypropylene, are added. The temperatures in the extruder range from 200 to 250 ° C. The examples presented illustrate a process for preparing polypropylene with a modified stabilizing system, increased processing and long-term stability, and use in preparing polypropylene fibers.

Example 1

99.20 wt. isotactic polypropylene powder with an IT value of 9.4 g / 10 min. 0.1 wt. 2,6-di-tert-butyl-4-methylphenol, 0.1% w / w; 2,6-dimethyl-4-dodeca (propenyl phenol, 0.2 wt.% Distearyl thiodipropionate DSTDP, 0.3 wt.% Light stabilizer 2-hydroxy-4n-octyloxybenzophenone, and 0.07 wt.% Calcium stearate. The mixture was blended for at least 3 minutes and granulated in a twin-screw extruder with 35 mm co-rotating spindles at temperatures of 230 ° C, 230 ° C, 230 ° C. The polymer had an IT value of 10.13 g / 10 min after extrusion. A foil of 0.5 mm thickness was pressed and subjected to a long-term thermostability test at 140 [deg.] C. in a forced-air drying oven.

In polypropylene containing a prior art stabilization system composed of: 0.1 wt. % 2,6-di-tert-butyl-4-methylphenol, 0.55 wt. % distearyl thiodipropionate, 0.30 wt. % Of 2-hydroxy-4n-octyloxybenzophenone and 0.15 wt. calcium stearate, and prepared in an identical manner to the first part of Example 1, a long term thermostability of 759 hours was achieved.

Example 2

A granulated polypropylene containing 0.15 wt. % 2,6- (dimethyl) di-tert-butyl-4-methylphenol, 0.20 wt. 2,6-dimethyl-4-dodeca (propenylphenol, 0.30% w / w distearyl thiodipropionate, 0.20% w / w 2-hydroxy-4n-octyloxybenzophenone, 0.15% w / w calcium stearate. value of IT = 0.32 g / 10 min From the polymer prepared in this way and with the polymer with today's stabilization system, values of degradation index ID (ČSN 643015), defined by the ratio of IT polymer after its 15 minute degradation at 280 ° C IT _deg is the original IT polymer (IT ₀ ).

ID = IT _deg / IT ₀ (2)

Value for the polymer according to the invention:

ID = 1.41.

Value for a polymer with today's stabilization system:

ID = 1.66.

The long-term thermostability evaluated as in Example 1 reached a value of 4770 hours for the polymer of the present invention as opposed to 759 hours for a polymer with today's stabilization system.

Example 3

Made of polypropylene powder with an IT value of 8.17 g / 10 min. a mixture containing 0.1 wt. % 2,6-di-tert-butyl-4-methylphenol, 0.15 wt. 2,6-dimethyl-4-dodecane (propenyl phenol, 0.15% by weight of distearyl thiodipropionate, 0.30% by weight of 2-hydroxy-4n-octyloxybenzophenone and 0.07% by weight of calcium stearate. minutes in a Henschel mixer and granulated on an extruder at 230 [deg.] C. The granulate obtained had an IT value of 10.56 g / 10 min, and a granular polymer was prepared in an identical manner with the present-day polymer stabilization system specified in Example 1.

The polymers thus prepared were used to prepare polypropylene fibers of 3.9 dtex, gray, mechanically shaped. The polymers were melted in a single screw spinner with a screw diameter of 90 mm. The following conditions were used to prepare the fibers:

Temperature of the spinning machine heating medium 316 ° C

Water temperature 290 ° C

Under these conditions, IT values of the extruded polymer, characterizing the polymer degradation depth at spinning, were determined. The values are given in the table for 4 spinning sites.

Table no. 1

IT values of extruded melt (g / 10 min)

Spinning place

3 4

Polymer according to the art.

of the invention 18.6

Polymer with today's stab.

system 40.1

The values document the higher processing stability of the polymer of the present invention. Higher stabilizing efficiency was achieved by reducing the total amount of additives by 0.40% by weight.

Light stability of the fibers thus prepared, evaluated in accelerated aging in Xenotest under moderate zone conditions:

15.6 18.4 16.3

39.9 33.0 37.3 polymer fiber according to the invention: 740 hours, polymer fiber with today's stab. system: 730 hours.

The light stability is evaluated as a decrease in fiber strength to 50 ° / o original over a given period of time.

Claims (1)

Thermostable isotactic polypropylene for the production of polypropylene fibers, prepared by direct polymerisation and containing Also 2,6-di-tert-butyl-4-methylphenol B) distearyl thiodipropionate C) light stabilizer 2-hydroxy-4n-octyloxybenzophenone and A calcium stearate, further comprising We claim: E) 2,6-dimethyl-4-dodecane (propenyl phenol), wherein the total content of the synergistic stabilizing mixture composed of components A) to E) in the polypropylene is 0.50 to 1.2% by weight, the content of component A) is 0 05 to 0.20% by weight, component BJ 0.10 to 0.30% by weight, component C) 0.20 to 0.40% by weight, component D) 0.05 to 0.15% by weight; and component Ej 0.05 to 0.30 wt.