CS261162B1 - Composite materials based on polyolefins and magnesium hydroxide - Google Patents

Abstract

The solution relates to composite materials based on polyolefins and magnesium hydroxide containing 40 to 70 parts by weight of magnesium hydroxide and 30 to 60 parts by weight of polyolefins. The addition of 0.5 to 10 parts by weight of partial esters of fatty acids with 12 to 22 carbon atoms with polyhydric alcohols with 3 to 10 carbon atoms or their mixtures with the said fatty acids and salts of these acids in a weight ratio of 1:10 and 10:1 increases the toughness of the composite materials while maintaining non-flammability.

Description

The invention relates to materials based on polyolefins and magnesium hydroxide, which are self-extinguishing or non-flammable and do not release toxic or corrosive fumes when exposed to heat.

For many applications, e.g. in the electrical and automotive industries, materials are required that, while maintaining easy thermoplastic processability (injection molding, extrusion, blow molding), are non-flammable or at least self-extinguishing and do not produce toxic or corrosive fumes when exposed to heat.

It is known (see JA 48-137 104, DOS 2 457 980) that a suitable filler that enables the fire safety requirement of polyolefins to be met is magnesium hydroxide, which is stable at thermoplastic processing temperatures (up to 250 °C), but when heated above 340 °C it quickly releases structural water, which suppresses combustion.

In order for polyolefins filled with magnesium hydroxide to be fully utilized in practice, especially in the electrical industry, these materials must have, in addition to non-flammability, the necessary mechanical properties, especially high toughness and the necessary thermo-oxidative stability.

It is known that the necessary condition for achieving these properties is the most perfect dispersion of the filler in the polymer matrix. It is also known that achieving good dispersion of high concentrations of mineral fillers is very difficult and that achieving this condition is particularly difficult in the case of magnesium hydroxide, which very easily forms solid aggregates.

Therefore, magnesium hydroxide particles are treated with hydrophobizing agents such as fatty acids (JA 48 137 104, DOS 2 257 980, JA 507 536, DOS 2 546 668). Another known process is the addition of calcium, magnesium or aluminum salts directly to the polymer-filler mixtures JA 55 162 691 and EP 52 868.

A disadvantage of known mixtures of polyolefins with magnesium hydroxide is the relatively low efficiency of magnesium hydroxide, which extinguishes the flame only by splitting off water. In order to achieve sufficient non-flammability of the composite material, it must contain at least 18.5% by weight of water, i.e. 60% by weight of magnesium hydroxide.

Such composite materials have very poor mechanical properties, therefore efforts are being made to combine the effect of magnesium hydroxide with other flame retardant additives such as halogen or phosphorus-containing flame retardants. It has now been possible to obtain polyolefin blends 8 with a high magnesium hydroxide content and good mechanical properties.

The subject of the invention are composite materials based on polyolefins and magnesium hydroxide, which contain 45 to 70 parts by weight of magnesium hydroxide characterized by an average particle size below 5 μm, 30 to 55 parts by weight of polyolefins and 0.5 to 10 parts by weight of partial esters of fatty acids with 12 to 22 carbon atoms with polyhydric alcohols with 3 to 10 carbon atoms or their mixtures with the said fatty acids or salts of these acids in a weight ratio of 1:10 to 10:1 of partial esters of fatty acids to fatty acids or salts thereof.

Even though it is possible to create a barrier on the surface of the filler particles by treating magnesium hydroxide with fatty acid salts, reducing their mutual adhesion, such a surface treatment is not sufficient to ensure the necessary homogeneous dispersion of the filler in the environment of non-polar polyolefins when using conventional compounding equipment, such as the KO-kneader from Buss or the twin-screw compounding extruder from Werner and Pfleiderer. Insufficient dispersion of the filler is manifested both by poorer mechanical properties of the composites and by higher flammability, especially when evaluated by the UL-94 method. It has been shown that water split off during the decomposition of the filler can only act in the immediate vicinity and only with perfect dispersion of the filler is the self-extinguishing degree V-0 achieved.

A significant reduction in flammability while simultaneously improving the toughness of polyolefins filled with magnesium hydroxide occurs when partial esters of fatty acids with 12 to 22 carbon atoms with polyhydric alcohols with 3 to 10 carbon atoms, such as glycerol monostearate or pentaerythritol distearate, are added to the mixture of polyolefins with magnesium hydroxide.

The advantages of using these additives for mixtures of polyolefins with calcium carbonate are described in AO 247 458, and for mixtures of polyolefins with talc in JA 5 738 841.

The use of these agents to improve the dispersion of magnesium hydroxide has not yet been known, in particular the possibility of using them to achieve composite materials with a very high magnesium hydroxide content and good mechanical properties has not been known.

These substances can be added to mixtures either alone or in combination with other additives, such as:

- fatty acids with 12 to 22 carbon atoms, saturated and unsaturated

- salts of fatty acids with 12 to 22 carbon atoms, both saturated and unsaturated, such as sodium stearate, calcium oleate or ammonium stearate.

The high efficiency of the additive of partial esters of fatty acids with polyhydric alcohols can be explained by the fact that the two free -OH groups of the partial ester form solid complexes with the transition metal compounds present, which are always present in trace concentrations in magnesium hydroxide. This suppresses the thermo-oxidative degradation of polyolefins, in which these compounds are used as catalysts.

Magnesium hydroxide for the composites according to the present invention is characterized by a particle size below 5 µm, polyolefins can be polyethylene and its copolymers with higher olefins, polypropylene and mixtures thereof. The composites can further contain pigments, stabilizers and other processing additives. The production of composite materials according to the present invention is carried out by conventional compounding methods.

The invention will be illustrated by the following examples. The parts and percentages in the examples are by weight.

Example

Composite materials containing 38% polypropylene (homopolymer characterized by a melt flow index of 2.8 g/10 min) were prepared in a Brabender Plasticorder at a temperature of 200 °C.

58% magnesium hydroxide (characterized by a specific surface area of 9 m2/g) and 2% stearin and 2% glycerol monostearate.

The test specimens were prepared by pressing at 230 °C. The material has the following properties:

Melt flow index: 6.9 g/10 min.

Average burning time in UL-94 test: 4.2 s

Flammability rating: V-0

Example 2

The procedure is the same as in Example 1, but instead of glycerol monostearate, pentaerythritol distearate was used. The material has the following properties:

Melt flow index: 4.4 g/10 min

Average burning time: 10.5 s

Flammability rating: V-l

Example 3

A mixture containing 38% polypropylene (homopolymer characterized by a melt flow index of 2.8 g/10 min), 58% magnesium hydroxide (characterized by a specific surface area of 9 m/g, 2% stearin and 2% glycerol monostearate) was prepared on a Buss MDK 46 KO kneader at a temperature of 200 °C. The test specimens were prepared by injection molding at 230 °C. The following properties were determined:

Melt flow index: 5.2 g/10 min Modulus of elasticity: 4.5 GPa — 2

Notch toughness: 4.0 kJ.m Oxygen number: 29 Flammability rating: V-l

Example 4 to 6 (ČSN 64 0614) (ČSN 64 0612) (ČSN 64 0756) (UL-94 test) •

Composite materials containing 55% polypropylene and 45% magnesium hydroxide, characterized by a specific surface area of 23.6 m/g, were prepared in a Brabender Plasticorder at 200 °C. The stability of the composites was evaluated by measuring the induction period until the onset of oxidation at 180 °C and by monitoring the color of the composite at the onset of decomposition.

Example 4 5 6 Filler coating 0.5% HSt + 1.0 » CaSt Induction period 78 min 0.5% VAT + 1.0% VAT 1% VAT 132 112 min min Explanations: Induction period (See D. Ryšavý: Chemical Industry 16, 675 /1966/)

HSt: stearic acid

GMSt: glycerol monostearate CaSt: calcium stearate

Color purple cream cream

A composite material containing 40% high-pressure polyethylene (Bralen RB 03-23, characterized by a melt flow index of

0.35 g/10 min and 60% magnesium hydroxide (characterized by a specific surface area of 8 m/g), which was treated with a layer of 1.0% stearic acid and 2.0% glycerol monostearate. Test specimens prepared by pressing at 200 °C, the material had the following properties:

Melt flow index: 0.02 g/10 min Oxygen number: 29.0

Notch toughness at -20 °C: 3.4 kJ.m

Example

A composite material containing 2% Mg(OH) _2, characterized by a specific surface area of 9 m/g, 2% calcium stearate and 0.2% sorbitan monolaurate, and 35.88% polypropylene with a flow index of 2.89/10 min was prepared in a Brabender Plasticorder at a temperature of 200 °C.

Test specimens prepared by pressing at 230 °C. The material has the following properties:

Melt flow index: 4.6 g/10 min Oxygen number: 31 Flammability rating: V-0

Example 9

A composite material containing % polypropylene (copolymer characterized by a flow index of 5.1 g/10 min), 57 % magnesium hydroxide (characterized by a specific surface area of 10 m ), 2 % stearin and 1 % l-(l,3,5-trimethylolbenzene) monobehenate was prepared in a Brabender Plasticorder at a temperature of 200 °C.

Test specimens prepared by pressing at 230 °C, the material had the following properties:

Melt flow index: 9.2 g/10 min

Elasticity model: 3.5 GPa

Flammability rating: V-l

Claims (1)

SUBJECT OF THE INVENTION Composite materials based on polyolefins and magnesium hydroxide, characterized in that they contain: 40 to 70 parts by weight of magnesium hydroxide, characterized by an average particle size below 5 µm - 30 to 60 parts by weight of polyolefins - 0.5 to 10 parts by weight of partial esters of fatty acids of 12 to 22 carbon atoms with polyhydric alcohols of 3 to 10 carbon atoms or mixtures thereof with said fatty acids or salts of these acids in a weight ratio of 1:10 to 10: 1 of partial esters of fatty acids to fatty acids or their salts.