CS231873B1 - Polypropylene and epdm rubber mixture - Google Patents

Description

The invention relates to a blend of polypropylene and an elastomeric ethylene propylene-diene copolymer (EPDM rubber).

Polymeric polypropylene / EPDM rubber products are often exposed to sunlight in practical applications. This is particularly true of car bumpers, as cars are often outside the covered areas all year round.

All products are required to maintain the required characteristics throughout their use to ensure proper operation. However, the original properties of the polymer blend deteriorate very rapidly due to sunlight.

Conventionally known processes for ensuring sufficient resistance of plastics and elastomers to the harmful effects of solar radiation consist, wherever the articles may be black, in the addition of about 1 to 3% by weight of carbon black.

However, the thermo-oxidative stability of the material decreases sharply with increasing concentration of carbon black in the polypropylene / EPDM rubbers mixture. If a carbon black concentration is chosen that does not reduce the thermo-oxidative stability below the carrying limit, the products have insufficient resistance to sunlight.

For example, at a carbon black concentration of 1.2% by weight, mixtures of polypropylene with EPDM rubber have only a one-year lifetime under the climatic conditions of Central Europe. As a result, besides a low carbon black concentration, it is also necessary to use special light stabilizers.

It is known that the most active substances belong to the group of tetramethylpiperidine derivatives. They are referred to as HALS. Practical tests have shown that these light stabilizers, which are very well tolerated by polypropylene, migrate from the polypropylene-EPDM rubber polymer blend to the surface of the product under the effect of light or heat, thus rendering it degraded.

Migration of light stabilizers can only be prevented by using certain combinations of thermo-oxidizing and some types of light stabilizers.

The present invention provides a blend of polypropylene and EPDM rubber containing carbon black and optionally other pigments, light and thermo-oxidizing stabilizers and lubricants containing 0.15 to 0.35% by weight of esters of 2,2,6,6-tetramethyl-4-piperidinol. 0.05 to 0.15% by weight of thiodipropionic acid ester, 0.05 to 0.15% by weight of 4-pentadecakis (propenyl) -2,6-dimethylphenol, 0.05 to 0.15% by weight of trisnonylphenylphosphite or a mixture of tri (phenylethylphenylphosphites) to 0.25% by weight of 2 / 2'-hydroxy-3'-tert-butyl-5'-methylphenyl / 5-chlorobenzotriazole or 2-hydroxy-4-octoxybenzophenone, 0.05 to 0.25% by weight of calcium stearate, 4 to 1.2% by weight of carbon black and optionally up to 1% by weight of other pigments, such as titanium dioxide.

Esters of 2,2,6,6-tetramethyl-4-piperidinol have an extremely strong protective effect against the harmful effects of sunlight. Their disadvantage is blooming on the surface of articles made of polypropylene-EPDM rubber under the influence of heat.

Since, for example, black bumpers heat up to 70 ° C in the sun during the summer months, this property of the preservative can lead to a visual deterioration of the product.

Therefore, it is necessary to choose lower concentrations of these substances and sufficient resistance to the degradation effect of the UV component of the sunlight by providing a combination of 2,2,6,6-tetramethyl-4-piperidinol ester with UV absorbers of the type 2 / 2'-hydroxy-3'- tert-butyl-5'-methylphenyl / 5-chlorobenzotriazole or 2-hydroxy-4-octoxybenzophenone.

AND

These UV absorbers do not in themselves provide the desired resistance to light, but in combination with 2,2,6,6-tetramethyl-4-piperidinol esters, the desired resistance can be achieved.

When a mixture of esters prepared by esterification of 2,2,6,6-tetramethyl-4-piperidinol with stearin is used as the light stabilizer, it is not necessary to combine it with N-absorbers of the benzophenone or benztriazole type.

In order not to bloom the components on the surface, the thermo-oxidizing components of the stabilization formulation must also be suitably selected. A mixture of 0.05 to 0.15% by weight of 4-pentadecakis / propenyl / -2,6, dimethylphenol with 0.05 to 0.10% by weight of thiodipropionic ester and 0.05 to 0.15% by weight of trisnonylphenyl phosphite complies with this condition, or mixture of tri (phenylethyl phenylphosphites).

Usually a combination of a phenolic stabilizer is used, for example pentaerythrityl tetrakis 3,5-di-tert-butyl-4-hydroxyphenylpropionate / thiodipropionic acid esters, generally in a ratio of 1: 2 to 3 at a total concentration of 0.2 to 0.3 % by weight, since this mixture shows a high protective effect against thermo-oxidative degradation.

It is known that thiodipropionic acid esters generally reduce the photostabilizing effect of 2,2,6,6-tetramethyl-4-piperidinol esters and cause them to bloom on the surface of sunscreened polypropylene-EPDM polymer blend products.

If the concentration of thiodipropionic acid esters does not exceed 0.1% by weight, their negative effect on photostability will not be shown. A more serious problem is the issue of blooming. of thiodipropionic acid esters on the surface of the products.

This phenomenon can be prevented if, on the one hand, a concentration of 0.1% by weight is not exceeded, and in particular if 4-pentadecakis / propenyl / -2,6-dimethylphenol is used as the phenolic components of the stabilization system, which is characterized by extremely high polymer compatibility and suppresses the tendency for blooming of thiodipropionic acid esters.

However, in order to ensure a sufficiently high stabilizing efficiency in polymer processing, the stabilizing system must be supplemented with a phosphite stabilizer with trisnonylphenyl phosphite or a mixture of tri (phenylethylphenylphosphites).

Another component of the stabilizing combination is calcium stearate, which neutralizes the acid components resulting from the decomposition of the polymerization catalysts and serves simultaneously as a lubricant to facilitate processing.

Carbon black imparts the desired black color to the products and to some extent protects the polymer blend from the harmful effects of sunlight. The size of the carbon black can favorably influence the resistance of the composition to the destructive effect of light, as shown in the table.

It is therefore advantageous to use a small particle diameter carbon black. Titanium dioxide, in combination with carbon black and possibly also with other color pigments, makes it possible to achieve the desired gray-black tint.

Mixtures can be prepared as follows:

Polypropylene and weighed amounts of powder additives except carbon black are metered into the powder concentrate mixer. loss.

From there the concentrate is dosed simultaneously with the screw mixer into which it is also fed

The mixture is mixed and transferred to containers with a concenestabilized powdered polymer into two pumps dispensing liquid stabilizing ingredients.

This intensive mixer homogenizes all the components of the blend and melts the blend by applying shear and heat to the melt flowing through the overflow into a single screw extruder on which the polymer is granulated.

In another apparatus, the stream of stabilized polypropylene granulate is mixed with the stream of EPDM concentrate and carbon black and granulated on an extruder.

The following examples show the properties of the individual ingredients and combinations thereof. Parts and% in the examples are by weight unless otherwise indicated.

He did

3

To 30 parts of polypropylene powder was added 100 cm 3 of acetone, 4 cm 1% 4-pentadecakis (propenyl) -3,5-dimethylphenol acetone solution, 4 cm 1% acetone solution of tri (phenylethylphenylphosphite), 4 cm ³ 1% acetone solution of distearyl thiodipropionate and 0.48 g of carbon black with a particle diameter of 95 .mu.m. The suspension was stirred until the acetone was evaporated.

The dry mixture was transferred to a Brabender plastograph kneading chamber to which 10 parts of EPDM concentrate were simultaneously added. The kneading chamber was heated to 200 ° C. After five minutes the kneading was discontinued and the contents of the kneading chamber were transferred to a press in which a 0.5 mm thick film was pressed at 250 ° C.

Strips of 40 mm x 10 mm were cut from this film and placed in Xenotest 450 to monitor the accelerated weathering process and in an oven heated to 70 ° C to observe heat-induced efflorescence.

The evaluation results are shown in Table 1.

Examples 2 to 17

Mixtures Nos. 2 to 17 were prepared in the same manner as Mixture No. 1. Acetone-soluble stabilizers were added as one percent solutions. Ca stearate was added as a one percent acetone suspension.

Carbon black and titanium dioxide were added in appropriate parts numbers directly to the acetone slurry of polypropylene powder. The amount of additives was added to 30 parts of polypropylene powder so that in the resulting polymer blend thirty parts of polypropylene with ten parts of EPDM concentrate was desired (in Tab. 1 stated / concentration of impurities.

. The evaluation results are shown in Table 1.

Claims (3)

1. The carbon black itself, used at a concentration of 1.2%, without the addition of light stabilizers, does not sufficiently protect the polymer (mixture 1 and 2). 2. The presence of a 0.25% DSTDP (distearyl thiodipropionate) thermo-oxidizing stabilizer will produce undesirable efflorescence on the surface of the products (mixtures 3 and 11). At the same time, the efficiency of the light stabilizer (mixture 11) is significantly reduced compared to mixture 7). Thus, the composition of the thermo-oxidizing mixture greatly affects the durability and of the products. The presence of 0.1% DSTDP does not have a negative effect (see mixtures 4-10 and 12-17). 3. Light stabilizers effectively protect the polymer blend (blends 4 to 17), but only the types and combinations of light stabilizers proposed by us meet all the requirements for the blend in terms of both durability and surface quality of products / blends 7 to 10 and 12 to 17 /. The use of a small particle diameter carbon black results in an increase in stability (mixture 8 compared to 7 and mixture 13 compared to mixture 12). Also, the presence of titanium dioxide positively contributes to the light resistance of the polymer blend (blend 10 as compared to blend 8).