CS225255B1 - The polyethylene for shaped products - Google Patents

Description

The invention relates to polyethylene for moldings suitable for contact with drinking water and foodstuffs.

Various additives and fillers are added to the polyethylene to improve processing and utility properties. One frequently used additive is carbon black, which improves the processing properties of polyethylene, especially when extruding hoses used increasingly instead of metal pipelines for water supply systems. Carbon black is also an effective pigment that reliably protects products against sunlight.

Furthermore, the carbon black additive increases the conductivity of the polyethylene, thereby reducing the potential for electrostatic charges. This applies in particular to carbon blacks having a high specific surface area of the order of 1000 m / g. These carbon blacks are obtained by catalytic cracking of hydrocarbons. In some cases, they are a waste product in the production of hydrogen and are therefore cheaper compared to previously used types of carbon black and their use brings considerable economic savings. A disadvantage of this type of carbon black with a high specific surface area is its destabilizing effect on polyolefins. Carbon black contains traces of transition metals from crude oil and cracking catalyst residues that accelerate the oxidative degradation of polyolefins. The blend of polyolefins with this type of carbon black suppresses the ability of the polymer to crosslink and enhances the ability to cut polymer chains and reduce molecular weight.

225 255

225 255

Numerous attempts have been made to block this adverse effect of high surface area carbon blacks by the addition of stabilizers selected from the group of aromatic amines. A typical example is the use of p-phenylenediamine derivatives as stabilizers. However, these stabilizers cannot be used in mixtures intended to come into contact with food and drinking water.

We have now found synergistic blends of healthy stabilizers that effectively stabilize polyethylene blends containing carbon blacks with a high specific surface area and a high content of transition metals. Polyethylene blends containing these types of carbon black (containing a considerable amount of variable-valency metals) exhibit quite specific properties.

In these mixtures, the ability of the polymer to crosslink is suppressed, while the ability to cut polymer chains and reduce molecular weight is enhanced. If suitable stabilizing additives are used, the entire process of granulate production is mastered to such an extent that the resulting material exhibits optimum performance during final processing.

The present invention provides a polyethylene composition for molded articles comprising high density polyethylene, a carbon black, a stabilizer, and optionally other processing ingredients comprising 97 to 99% by weight polyethylene, 0.1 to 3% by weight carbon black with a specific surface area of 500 to 1200 m m / g ( containing from 0.1 to 1.5% by weight of ash consisting of 5 to 60 parts by weight of vanadium oxide, 11 to 32 parts by weight of nickel oxide and 1.2 to 32.5 parts by weight of iron oxide), and from 0.1 to 1% by weight % of a stabilizer mixture consisting of a carboxylic acid ester containing at least 4 aromatic nuclei and having at least one tert-butyl group in ortho position to the free phenolic hydroxyl whose carbonyl group is in X or position relative to the aromatic nuclei and a synergistic compound which is substituted triphenylphosphites or phosphonites and when the carbonyl group of the ester in the 6 position to the aromatic ring, thiopropionic or thiodipropionic acid esters, the phenolic to synergistic ratio by weight being 1: 1 to 2.5. As carboxylic acid esters containing at least 4 aromatic nuclei and having at least one tert-butyl group in ortho position to the free phenolic hydroxyl whose carbonyl group is in the 06 or position relative to the aromatic nuclei and known phenolic stabilizers such as 2,2 ^z methylene bis (4-methyl-6-tert-butylphenol) terephthalate, which contains aromatic nuclei in both the acid and ester groups, or esters of pentaerythritol such as tetrakis / methylenebis-3- / 3, ^of 5 ditercutyl-4-hydroxyphenyl propionate methane or similar ethylene glycol-; bis-3,3-tert-butyl hydroxyphenyl butyrate.

Synergic substituted triphenylphosphites and phosphonites usually contain alkylphenols, such as tris (nonylphenylphosphite) or tris (4- (1-phenyl) ethylphenyl) phosphite or tetrakis (2,4-di-tert-butyl) -4,4-bisphenylene phosphonite.

When the carbonyl group is in the aromatic ring position, propionic esters such as pentaerythritol tetrakis dodecylthiopropionate or thiodipropionic acids such as distearylthiodipropionate can be used as synergistic compounds in addition to phosphites and phosphonites.

225 255

Phenolic stabilizers, in that they contain at least 4 aromatic rings in their molecule, in addition to relatively low migration rates, also exhibit the ability to partially bind,

It knows the electrons of its conjugated bonds with transition valence metals. Placing at least one target. The butyl groups in ortho position to the hydroxyl form favorable conditions for the radical cleavage of the OH bond, thereby increasing the stabilizing efficiency of this antioxidant. Placing the carbonyl group in or at the aromatic rings aids in the above-mentioned metal-T electron conjugate system interactions. The phosphites and phosphonites exemplified by their complex-forming ability enhance the passivation of transition metal metals. An analogous result 1, though a somewhat different mechanism of action occurs when a phenolic antioxidant with the C = O group in the oo position is used with thiodipropionic acid esters, in which the sulfur in these compounds effectively interacts with their free electron pairs to form a complex and passivation of transition metals .

Recently, most of the granules intended for sun-exposed molded articles have been prepared from a mixture of linear polyethylene, retort carbon black and phenolic antioxidant. However, these mixtures require complete polymer depletion of catalyst residues. Where scrubbing of polymerization catalysts is not included in linear polyethylene production technology, especially during periods when monomer polymerization is at a reduced activity and therefore at an increased catalyst concentration, those polymerization catalyst concentrations that cause polymer crosslinking, micro and macrogel formation are transferred to the final product. as a result of which the strength of the products is reduced.

Using carbon black prepared by the pyrolysis of a black oil whose ash contains high concentrations of vanadium, nickel, and iron to add such polymers, molecular weight is reduced in the preparation of granulates in the presence of phenolic antioxidant to the detriment of crosslinking, micro and macrogel formation. In the production of polymers analogous to injection types. In order to suppress this undesirable phenomenon, it is necessary to reduce the activity of these metal impurities by forming complexes or compounds which, as synergistic substances, reduce peroxide concentrations on polymer chains.

Phenolic antioxidants are not able to maintain the primary structure of the polymer chains under these circumstances, only their mixtures with the appropriate synergistic substrates will allow the polymer mixture to retain its original structure both after granulation and during processing into the final product (tubes).

In practice, the polyethylene according to the invention is prepared by feeding one of said antioxidants, optionally a mixture of a phenolic antioxidant and a powdered synergistic substance, and a liquid synergistic substance dosing pump into the powdered polymer feed device. Powdered or granulated carbon black is then metered in the other part of the line. The homogenized polymer mixture is extruded and granulated.

This stabilization can also be accomplished by dispensing one or both of the components into the polymer powder stream and storing the polymer mixture in a silo,

225 255 from where it is further transported to additive with soot and granulae.

One very effective stabilization method is to dispense one or both components in the molten state by means of an injection device. This results in an even distribution of both additives on the surface of the polymer particles and good homogeneity in the final product.

Perspective method of treatment. is the preparation of a mixture of carbon black, a phenolic antioxidant, a synergistic additive alone or in the form of a premix with the polymer, and dosing of this mixture is carried out into a stream of pure powdered polymer.

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

Powdered high-density polyethylenes produced by fluidized bed polymerization on supported catalysts were used as polymers in the examples.

Type A with a flow index of 0.05 to 0.12 g / 10 min, which was defined by gel permeation chromatography (GPC) with the following parameters: average molecular weight MZ = 920 000, weight average molecular weight Mi = 191 000, number average molecular weight MN = 5,000.

Type B with a flow index of 0.1 to 0.18 g / min defined by GPC with the following parameters: average molecular weight MZ = 1 133 000, weight average molecular weight W = 178 000, number average molecular weight MN = 16 000.

The carbon blacks defined by the following parameters were used in the examples:

6. Sample BET surface Ash content * in ₂ 0 ₅ % NiO »P ₂ o ₃ soot m ² % v pop. v pop. v pop. ΊΓ 1 910 0.65 32.1 14.3 21.6 2 778 0.29 19.1 22.1 17.7 3 805 0.36 18.0 16.1 12.2 4 510 0.31 19.8 20.4 16.1 5. 121 0.30 22.1 21.1 19.8

Phenolic antioxidants of the tetrakis (methyl n-3- (3,5-di-tert-butyl-4-hydroxyphenylpropionate)) methane (I) type have been tested as stabilizers, bis / 2,2'-methylenebis (4-methyl-6-tert-butylphenol) Ethylene glycol bis- [3,3-bls- (3 * tert-butyl-4-hydroxyphenyl) butyrate (III)], and tris (nonylphenyl) phosphite (IV) tris (4) was used as an allergic additive. - (1-phenyl) ethylphenyl / phosphite (V), pentaerythritoltetrakis (dodecylthiopropionate) (VI), tetrakis- (2,4-di-tert-butylphenyl) -4, ^# 4-biphenylylenephosphonite (VII), diatedrylthiodipropionate (VIII)

Example 1

In a Papenmeier mixer, a mixture of 97.2 parts of polyethylene type A was mixed,

2.5 parts of carbon black prepared by pyrolysis of mazut number 2, 0.1 parts of antioxidant I and 0.2 parts of synergistic additive IV. The mixture was homogenized in the melt and extruded in duplicate

225 «55

Werner Pfleiderer screw extruder, granulated and prepared from the granulate by extrusion of a 25 mm outside diameter tube. The tubes were subjected to pressure tests at 80 ° C. The average tube burst time was 420 h.

Example 2

In a Papenmeier mixer, a mixture of 98.7 parts of polyethylene type A, a part of carbon black # 1 prepared by mazut pyrolysis and 0.1 wt. The mixture was melt homogenized and extruded with a Werner-Pfleiderer twin screw extruder, granulated and prepared from the granulate by extrusion of a 25 mm outside diameter tube. The tubes were subjected to pressure tests at 80 ° C. The average time to rupture of the tube was 485 h.

Example 3

In a Papenmeier mixer, a mixture of 98.7 parts of polyethylene type B, a part of soot No. 4 prepared by a black oil pyrolysis was mixed, and 0.1 parts of phenolic antioxidant II and 0.2 parts of synergistic additive VI were used as a stabilizer system. The mixture was homogenized in the melt and extruded with a Werner-Pfleiderer twin screw extruder, homogenized and prepared from the granulate by extrusion of a 25 mm outside diameter tube. The tubes were subjected to pressure tests at 80 ° C. The average time to rupture of the tube was 515 h.

Example 4

In a Papenmeier mixer, a mixture of 97.2 wt. parts of polyethylene A,

2.5 wt. 5 parts, 0.1 parts of phenolic antioxidant I and 0.2 parts of synergistic additive IV. The mixture was homogenized in the melt and extruded with a Werner-Pfleiderer twin screw extruder, granulated and prepared from the granulate by extrusion of a 25 mm outside diameter tube. The tubes were subjected to pressure tests at 80 ° C. The average time to rupture of the tube was 216 h.

Example 5

In a Papenmeier mixer, a mixture of 98.7 parts of polyethylene type A, part of carbon black # 2, 0.1 parts of antioxidant I, and 0.2 parts of synergistic additive VII was mixed. The mixture was homogenized in the melt and extruded with a Werner Pfleiderer twin screw extruder, granulated and prepared from the granules by extrusion of a 25 mm outside diameter tube. The tubes were subjected to pressure tests at 80 ° C. The average time to rupture of the tube was 512 h.

225 255

Example 6

In a Papanmeier mixer, a mixture of 98.7 parts of polyethylene type B, a part of soot No. 4 prepared by mazut pyrolysis was blended, and 0.1 parts of antioxidant II and 0.2 parts of synergistic additive VIII were used as a stabilizer. The mixture was homogenized in the melt and extruded with a Werner-Pfleiderer twin screw extruder, granulated and prepared from the granulate by extrusion of a 25 mm outside diameter tube. The tubes were subjected to pressure tests at 80 ° C. The average time to rupture of the tube was 515 h.

Claims (1)

OBJECT OF THE INVENTION Polyethylene for moldings containing high density polyethylene, carbon black, stabilizers and optionally other processing ingredients, characterized in that it contains 97 to 99% by weight polyethylene, 0.5 to 3% by weight carbon black with a specific surface area of 505 to 1200 m / g containing 0, 1 to 1.5% by weight of ash containing 5 to 60 parts by weight of vanadium pentoxide, 11 to 32 parts by weight of nickel oxide and 1.2 to 32.5 parts by weight of iron oxide and 0.1 to 1% by weight of a stabilizer mixture consisting of an ester a carboxylic acid having at least 4 aromatic nuclei and having at least one tert-butyl group ortho to the free phenolic hydroxyl group whose carbonyl group is at or relative to the aromatic nuclei and the synergistic compound being substituted triphenylphosphites or phosphonites; wherein the carbonyl ester group is vap an aromatic nucleus, thiopropionic acid or thiodipropionic acid esters, the weight ratio of phenolic to synergetic being 1: 1 to 2.5.