CS270087B1 - Polyethylene for molded articles - Google Patents

Abstract

Polyethylene containing 0.1 to 5% by weight of carbon black with a specific surface area of 50 to 950 m2/g, treated with 0.01 to 5% by weight of sulfite pulping liquors neutralized with calcium oxide and/or alkali hydroxide, and 0.01 to 1% by weight of phenolic antioxidants is synergistically stabilized against oxidative degradation.

Description

The invention relates to polyethylene for shaped articles, also suitable for contact with drinking water and foodstuffs.

Various additives and fillers are added to polyethylene to improve processing and performance properties. One of the frequently used additives is carbon black, which improves the processing and utility properties of polyethylene, especially in the extrusion of pipes used more and more often instead of metal pipes for the construction of water mains. Soot is also a very good pigment that reliably protects products from the effects of sunlight.

In addition to carbon black, antioxidants and synergistic additives are usually used for the addition of polyethylene, which protect the polymer system against the effects of oxygen at elevated processing temperatures. Suitable stabilizers are, in particular, variously substituted arylamines, phenols, thiodipropionic acid derivatives, diaryl sulfides, dialkyl sulfides and piperidine derivatives.

In order to achieve sufficient thermo-oxidative stability of the carbon black-pigmented polyethylene, the cited substances must be used in very high concentrations, which guarantee that during granulation or processing of the granulate into the final product no harmful crosslinking of the polymer system occurs, accompanied by lowering the melt flow index and product properties.

However, the use of high concentrations of stabilizing additives brings not only positive results but also negative phenomena. They are:

1) Increased leakage of low molecular weight products of either directly used stabilizing additives or their oxidation products. These products often settle on the nozzles of extruders.

2) The formation of unpleasant odors, which are particularly undesirable in materials intended for drinking water pipes.

3) Increased stabilization costs.

For these reasons, an attempt has been made to use synergistic systems for stabilization purposes, which allow the stabilization of polyethylene at a very high level at suitably selected concentrations. Nevertheless, the concentrations of these components remain high and therefore new recipes are still being sought, which have made it possible to increase the stabilizing efficiency of the systems while eventually reducing the cost of the stabilizing system. One way is to use synergistic '* ⁴ ' additives. sorbed on carriers ·

Therefore, experiments were performed in which the individual components were first sorbed on an appropriate inorganic or organic support and in the next stage of the processing process mixed into a polymer system. The surface of the carrier used, its structure and pH are of great importance for the fixation of stabilizing additives. In this area, a number of negative results were obtained, when the monitored substances were perfectly sorbed on the surface of the support, but their functional groups were completely blocked. Such negative phenomena have been found in the sorption of piperidine derivatives, benzotrionole, arylamines on the surface of a number of inorganic fillers, such as calcium carbonate, talc, titanium dioxide and the like.

Of the carriers used, carbon black has proven to be highly effective sorbents, especially when the sorbed antioxidant contained sulfur in its molecule. It has also been shown that it is not necessary to sorb both components in two-component stabilization systems. In terms of efficiency, it has been shown that optimal results are obtained when synergistic compounds are sorbed on the surface of the carbon black, while the 2nd component - phenolic antioxidant is dosed in powder or liquid form directly into the polymer mixture.

Among the test substances, lignin sulfonates and technical products containing these functional groups, which are known as sulfite extracts, stood out in particular, but after adjusting the pH from the original acidic range to pH 6 to 8.5. Some phenols substituted in position by butyl groups have proven to be very effective in these systems as phenolic antioxidants.

CS 270 087 Bl

The subject of the invention is polyethylene for shaped articles comprising high-density or medium-density polyethylene, carbon black, stabilizers or other processing additives, characterized in that it contains 95 to 99.8 wt.%, Polyethylene, 0.1 to 10 wt.%, Carbon black specific surface area 20 to 1,100 mg / g of treated 0.01 to 5% by weight of sulphite extracts from pulp oxide and / or alkali hydroxide neutralized pulp, 0.01 to 1% by weight of phenolic antioxidants containing at least 1 tert-butyl group in the ortho position to the hydroxyl. . '.

The technology for the production of said type of polymer mixture is carried out in such a way that the carbon black with the adsorbed synergistic additive is conveyed, for example by a screw feeder, to a polymer powder stabilized by premixing with one of said phenolic antioxidants.

The mixture first comes to the mixer, then to the extruder, where the sorbed lignosulfonates with the phenolic antioxidant act synergistically at elevated temperatures. At the exit of the extruder, the polymer melt blends. The produced granulate is further used for the production of profiles, pipes, or fittings by extrusion or injection molding.

The following examples illustrate the invention. The% given in the examples are by weight.

Polymers used:

A High density polyethylene powdered flow index 0.15 g / 10 min.

B Medium density polyethylene in powder form flow index 0.16 g / 10 min.

Additives used:

1. tetrakis (methylene-3 (3 ', 5', - ditert-butyl-4-hydroxyphenyl propionate) methane

2. 4,4'-thio bis (6-tert-butyl-3-methyl phenol)

3. 2,6-ditert-butyl-4-methylphenel

4. glycerol monostearate

5. Stearyl-terminated polydimethylsiloxane

6. sulphite extract from pulp production treated with calcium oxide and sodium hydroxide to pH 6,9 '

7. tris nonyl phenyl phosphite

8. distearylthio dipropionate. 9. phenyl Q-naphthylamine

Fillers used:

I. Sterling R carbon black with a specific surface area of 25 m 2 / g, treated with 0,2% by mass, of sulphite extracts neutralized with calcium oxide and sodium hydroxide to pH 7,1 2

II. Ketjenblack E carbon black with a specific surface area of 1,100 m 2 / g, treated with 1.2% by weight, sulphite extracts neutralized with calcium oxide and sodium hydroxide to pH 7.6 2

III. Nigros carbon black with a specific surface area of 115 m 2 / g, treated with 1.5% by weight, sulphite extracts neutralized with calcium oxide and sodium hydroxide to pH 7,5 * IV. ISAF carbon black with a specific surface area of 115 m ² / g without sorbed additives

V.o ISAF carbon black with a specific surface area of 115 m 2 / g, treated with 1.5% by weight, sulphite extracts, without further neutralization

VI. micronized limestone with a particle size <20 / u, surface area 3 m / g, treated with neutralized sulphite extracts

VII. micronized talc - particle size 40 40yU, surface area 4 m / g, treated with neutralized sulphite extracts of

VIII. silica with a specific surface area of 280 m 2 / g, treated with neutralized sulphite extracts.

Examples 1 to 16

Mixtures were prepared from the respective polyethylene powders, additives and fillers, which were homogenized with a Brabender extruder and granulated. Films 0.5 mm thick were extruded from the granules, of which a part weighing 0.2 mm was used to measure thermooxidative stability at 180 ° C in a pure oxygen environment. Measured values in

CS 270 087 81 reduction periods represent the time in minutes required for the measurable oxygen uptake by the sample to occur. The results of the experiments are shown in Table 1 below.

Table 1

Example Polymer Additives Soot / Filler Induction period 180 (min) 1 AND 0.1% AI 2.5% III. 580 2 8 0.1% A2 2.5% III. 630 3 AND 0.1% A2, 0.1% A4 2.5% III. 5Θ0 4 AND 0.3% A2, 0.1% A4 2.5% III. 2 B00 5 AND 0.05% A2, 0.08% A4 2.5% III. 565 6 B 0.05% A3, 0.01% A5 2.5% III. 540 ^r 7 B 0.1% A7, 0.1% · A5 2.5% III. 90 8 AND 0.1% A8 2.5% III. 55 v 9 AND 0.1% A9 2.5% III. 115 ' 10 AND 0.1% A2 2.5% I. 818 11 AND 0.1% A2 2.5% II. 605 12 AND 0.1% A2, 1.5% Á6 2.5% IV. 76 13 AND 0.1% A2 2.5% V. 44 14 AND 0.1% A2 2.5% VI. 45 15 AND 0.1% A2 2.5% VII. 55 · 16 AND 0.1% A2 2.5% VIII. 48

The results shown in Table 1 show that carbon blacks with sorbed sulfite extracts in combination with phenolic antioxidants containing at least 1 tert-butyl group in the ortho position to the hydroxyl show an excellent stabilizing effect in polyethylene.

Claims (1)

Polyethylene for shaped articles, containing high-density or medium-density polyethylene, carbon black, stabilizers or other processing additives, characterized in that it contains 90 to 99.8% by weight of polyethylene, 0.1 to 10% by weight, carbon black of a specific surface area of 20 to 1 100 m 2 / g, treated with 0.01 to 5% by weight, of sulphite extracts from the production of pulp neutralized with calcium oxide or alkali hydroxide, and 0.01 to 1% by weight, phenolic-. antioxidants containing at least 1 tertiary butyl group in the ortho position to the hydroxyl. .