SK278600B6 - Stabilized polypropylene and propylene copolymers - Google Patents

Abstract

Polypropylene and copolymers related to polypropylene with low yellow colour level and low content of grey pellets are gained, in the case a synergic mixture of phenol and phosphide stabilisers contains 10 up to 90 weight percent of phosphides being able to hydrolyse up to 7 percent and 10 up to 90 weight percent of phosphides being able to hydrolyse over 7 percent. The capability of phosphides to be hydrolysed is measured based on the contact of phosphides with air humidity.

Description

Technical field

The invention relates to stabilized propylene and its copolymers with ethylene for the production of thin-walled profiles, in particular films, oriented strips and fibers.

BACKGROUND OF THE INVENTION

In polypropylene processing, the material is subjected to short-term but intense thermal exposure and mechanical stress to the melt in a processing machine. Due to atmospheric oxygen and the trace amount of metals, which are always present in the polymer as residues of the catalytic system, thermo-oxidative degradation of the polymer matrix occurs. If the material is not stabilized appropriately, the extent of degradation can be so great that it will prevent its further use.

The polymer can be subjected to the processing conditions twice: during the primary processing of the powder into the granulate already in the production plant and then in the actual recovery of the product from the granulate - in our case e.g. by blowing and orienting the film or by passing the melt through a nozzle.

In most cases, the processor recycles the manufacturing waste so that part of the material is subjected to three or more treatments.

In particular, phenolic antioxidants, or combinations thereof with phosphorus and phosphonite compounds (QB 1526603, CS 190837, EP 184 191), are currently used to protect polypropylene from these degradation effects during processing.

Production of fibers and foils from propylene is among the most demanding in terms of processing this plastic.

The present stabilizing formulations used for this purpose show some drawbacks that cause manufacturing complications. The main phenomena are:

a) occurrence of so-called 'Gray granules', the quantity of which is related to the concentration and volatility of the phenolic component. Some granules in this case are contaminated by charred residues, which cause problems with the blowing and orientation of the film, as the material often breaks up at the point of non-homogeneity,

(b) the yellow coloring of the natural granulates, which is attributed to the metal-catalysed oxidation of the phenolic component to color products during processing.

Therefore, there is an effort to reduce the phenolic component content of the stabilizing formulation and to exploit the synergistic effect that phenolic stabilizers exhibit in combination with phosphites and phosphonites. However, when certain phosphorous-containing stabilizers are used, another undesirable phenomenon may occur:

(c) formation by establishment in a processing machine. These deposits clog the filter screen and complicate further manufacturing operations. Sediment analyzes have shown that they are products of the interaction of metal catalyst residues and calcium stearate with products of hydrolysis of organic phosphite.

%, based on the polymer matrix and optionally further processing additives, in which the phosphite stabilizer mixture comprises 10 to 90 wt. % of phosphites readily hydrolyzable and 10 to 90 wt. phosphites readily hydrolyzable.

Non-hydrolysable phosphite in the claims means phosphite which, after 60 days of storage in a Petri dish (50 mm diameter with 1 g weight in an atmosphere of 100% relative humidity at 25 ° C), does not exhibit more than 7% hydrolysis based on the original component (measured by HPLC) Easily hydrolysable phosphites are hydrolyzed to a higher degree under these conditions, a typical non-hydrolysable phosphite is, for example, tris (2,4-di-tert-butylphenyl) phosphite, and easily hydrolysable is eg bis (2,4-di-tert. butylphenyl) pentaerythritol diphosphite.

The invention is based on the use of specific features of the mechanism of action of two types of phosphites. It is known (DG Pobedimskij et al: Dev. Polym.Stab. 2, 125 (1980)) that phosphite antioxidants act multifunctionally, primarily through the following chemical reactions: non-radical decomposition of hydroperoxides, reactions with peroxy, alkoxy radicals, binding of metal traces and oxidation products of phenolic antioxidants. In particular, the latter two functions are of great importance in preventing the formation of unwanted discoloration of the polymer. An extraordinary bleaching effect is observed in the easily hydrolyzable bis (2,4-di-tert-butylphenyl) pentae diphosphite spirophosphites, which during processing gradually hydrolyzes to the corresponding phosphonate and finally to the corresponding phenol, pentaerythritol and phosphonic acid.

SUMMARY OF THE INVENTION

These disadvantages are overcome by stabilized polypropylene and its copolymers with 0.1 to 20% by weight ethylene containing 0.01 to 1% by weight. % of phenolic stabilizers and 0.01 to 1 wt. phosphite stabilizer mixtures This product mixture is a very effective synergistic stabilizer system (Schwetlick K .: Polym. Deg. Stab. 22, 357 (1988)).

It is mainly phosphoric acids and their acid esters that effectively bind trace metals.

The mildly acidic environment prevents the oxidation of phenol to the colored quinoid products. The effect of the hydrolytic products on the coloring of the polymer is therefore very positive. At higher concentrations, however, they may be responsible for the formation of these deposits. However, phosphite antioxidants that do not readily hydrolyze (e.g., tris- (2,4-di-t-butylphenol) phosphite) are also effective processing stabilizers, but do not significantly contribute to color improvement. On the other hand, they do not form deposits, as in the case of hydrolyzable phosphites.

In the invention, the specific properties of the various phosphites are utilized in combination so that the hydrolyzable phosphite is only used in an amount necessary to bleach the polymer. High process stability is then achieved by the use of a non-hydrolysable phosphite. The ratio of the two types of phosphites to each other is chosen according to the processing properties and the degree of hydrolyzability of the easily hydrolyzable phosphites. Abbreviations used: PP - polypropylene

Al-2,6-di-t-butyl-4-methylphenol

A2 - tetrakis (methyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propinate)

A3 - 2,6-dimethyl-4-oligopropylene-phenol having a number degree of oligomerization of 15 and an unreacted alkylating agent, the active substance content expressed as a concentration of bound 2,6-dimethylphenol of 6,3%

PI-tris [4 (1'-phenly) ethylphenyl] phosphite

P2 - bis [(2,4-di-t-butylphenyl) pentaerythritol] diphosphite

P3 - tris [2,4-di-t-butylphenyl] phosphite

P4 - Bis [2-tert-butyl-4- (α, dimethylbenzyl) phenyl] pentaerythrile diphosphite

Phosphonic acid P5 - (1,1'-biphenyl-4,4'-diylbis-, tetrakis (2,4-di-t-butylphenyl) ester

Table 1

Evaluation of Phosphite Hydrolyzability Phosphite% Hydrolysis Definition

Pi 78 easily hydrolyzable pz 98 easily hydrolyzable p ₃ 3 easily hydrolysable ? 4 91 easily hydrolyzable p ₅ 5 easily hydrolysable

hydrolysis measured after 60 days at lab. temperature at 100% relative humidity (phosphite charge 1 g)

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Polypropylene granulate prepared from a powdered isotactic homopolymer Mosten with an index of 1.5 g / 10 min, with a stabilization system composition of 0.25% Al, 0.02% A2, 0.08% CaST on a Japan Steel granulation line was subjected to laboratory measurements processing stability, i. j. passing through the Brabender extruder five times. After each extrusion, the flow index at 230 ° C was measured according to ČSN 64 0861.

Furthermore, the yellowness of the original granulate was measured, the A to D of which was determined by a comparative test with a control standard (where A represents the lowest degree of yellowness, D the lowest).

The occurrence of so-called "Gray granules", i.e. j. granules with a markedly changed color were randomly counted in the collected 500 g granules from the granulation line.

The results are shown in Table 2. It is clear from their values that the stabilization system used in Example 1 is sufficient to maintain processing stability, but does not fully satisfy the requirements for yellowness or gray granules.

Example 2

The PP granulate with the stabilization system composition 0.02% A2, 0.08% P2 and 0.08% CaST was prepared in-service and laboratory tested as in Example 2. The results are shown in Table 2. The measured values indicate that the stabilization the system is not sufficiently suited to ensure processing stability, but meets the yellow and gray granules requirements.

Example 3

The PP granulate containing the 0.08% P2 and 0.08% CaST stabilization system was operationally prepared and tested as in Example 1. From the results shown in Table 2 it can be seen that although the degree of yellowness achieved was excellent and the "gray granules" were not found in the product, the stabilization system is completely unsuitable for processing stability.

Example 4

PP granules of 0.1% Al, 0.8% P3 and 0.08% CaST were prepared and laboratory tested in the same manner as in Example 1. From the results shown in Table 2, it is evident that despite the minimal "gray" granules' is the degree of yellowness insufficient and the processing stability at the serviceability limit. Flow index values do not guarantee reliability in the event of technological variations in production.

Example 5

PP granules with stabilizers of 0.1% Al, 0.02% P2, 0.06% P3 and 0.08% CaST were prepared and laboratory tested as in Example 1.

The values in Table 2 show that the stabilization system used provides very good processing stability, causes minimal yellowness and the presence of "gray granules" was not detected at all in the process sample.

Example 6

PP granules stabilized with 0.1% Al, 0.04% P2, 0.04% P3 and 0.08% CaST were manufactured and laboratory tested as in Example 1. The values shown in Table 2 show that the stabilization system used is able to provide all three endpoints.

Example 7

Granulate P stabilized with a 0.08% Al, 0.06% P3 and 0.02% P4 and 0.08% CaST stabilization system was prepared and tested in the laboratory in the same manner as in Example 1. The measurement results are shown in Table 2.

Based on these, the system used ensures excellent processing stability, high whiteness and suppresses the formation of gray granules. These excellent results as well as the measurement results in Examples 5 and 6 demonstrate a high degree of synergy when using a phenolic stabilizer with a combination of readily hydrolyzable phosphite.

Example 8

PP granulate stabilized with 0.1% Al, 0.1% A3, 0.1% PI and 0.08% CaST was prepared and laboratory tested as in Example 1. The measurement results are shown in Table 2. From the standpoint of processing stability, it was shown system as sufficient. In terms of yellowness, however, it is on the acceptability limit and the observed occurrence of "gray granules" indicates that the combination of stabilizers is completely unsuitable for this use.

Example 9

Copolymer of propylene with ethylene containing 1,8% ethylene with a flow index of 4 dg / min, containing stabilizers 0,08% Al, 0,1% A3, 0,02% PI, 0,02% P3 and 0,08% CaST was treated in the same manner as in Example 5.

The results of the laboratory tests are shown in Table 2.

In terms of processing stability and the presence of "gray granules", the recipe appears to be good, although it shows a slightly reduced degree of whiteness. 10

Example 10

A propylene-ethylene copolymer containing 16% ethylene with a flow index of 6 dg / min, containing stabilizers 0.1% Al, 0.04% P2, 0.04% P5 and 0.08% CaST was treated in the same manner as in the example.

1. The results of the laboratory tests are given in Table 2. In terms of processing stability and the appearance of 'gray granules', the formula appears to be good, although it shows a slightly reduced degree of whiteness.

Table 2

Composition of the stabilization system for the treatment of PP containing 0.08% CaST

no. [%] [dg / min] Flow index yellowness number of gray granules in 500 Al A2 A3 PI P2 P3 P4 P5 I II III IV IN 1 0.25 0.02 - - - 1.71 2.00 2.07 2.43 2.54 D 18 2 - 0.02 0.08 - - 1.81 1.95 2.21 3.27 3.56 A 1 3 - 0.08 - 1.82 2.40 3.13 3.74 9.71 A 2 4 0.1 - 0.08 1.64 1.8 2.30 2.50 2.80 C 1 5 0.1 0.02 0.06 - 1.45 1.56 1.75 1.90 2.10 A 0 6 0.1 0.04 0.04 1.42 1.58 1.71 1.84 2.03 A 0 7 0.08 - 0.06 0.02 1.41 1.55 1.7 1.99 2.0 A 0 8 0.1 0.1 0.1 - 1.80 2.15 2.59 2.82 3.10 C 20 9 0.08 0.1 0.02 - 0.02 4.0 4.08 4.35 4.60 5.05 B 3 10 0.1 - - 0.04 - - 0.04 6.0 6.13 6.17 6.65 6.90 B 1

I, II, .. V - number of passes through the extruder

Claims (1)

Stabilized polypropylene and propylene copolymers with 0.1 to 20 wt. % of ethylene containing 0.01 to 1 wt. % of phenolic stabilizers, based on the polymer matrix, and optionally further processing additives, characterized in that the phosphite stabilizer mixture is comprised of 10 to 90 wt. % of phosphites subject to hydrolysis up to 7%, and 10 to 90% by weight; phosphites or phosphonites subject to hydrolysis above 7%. 20