DE1907926C3 - Vulcanizable molding compounds based on polypropylene - Google Patents

Description

wherein R is a residue of an aromatic hydrocarbon or a derivative thereof and 0.05 to 5.0 percent by weight of a hydroperoxide decomposition agent, both percentages being based on based on the weight of polypropylene.

2. Process for vulcanizing the molding compositions according to claim 1, characterized in that they are heat-treated ^{at a temperature of 150 to 280 ° C.}

2P

The invention relates to novel, crosslinkable or vulcanizable molding compositions based on Polypropylene and a process for their crosslinking.

It is known that polypropylene has excellent thermal resistance and mechanical properties compared to other polyolefins. When polypropylene-i is intermolecularly crosslinked, becomes the thermal resistance further improves, and it becomes more useful for such applications which thermal resistance is required.

It is known that polyolefins, especially polyethylene, can be crosslinked with an organic peroxide. But if such an organic one Peroxide is used as a crosslinking agent for polypropylene, the polymer degradation would trigger the crosslinking reaction over, so that a break in the molecular chain would occur, with the result that a product with a lower molecular weight is obtained. This tendency is more noticeable when the Crosslinking reaction at temperatures as high as above the melting point of the polypropylene is carried out.

Therefore the merging reaction leads to polymer degradation predominate z'-u, it is necessary to use a crosslinking agent that does the crosslinking faster than the degradation reaction can occur.

It has been found that various known crosslinking agents such as in U.S. Pat 3 012016, Italian patent 568 446 and British patent 865 793 for Polypropylene, in particular isotactic polypropylene, are not sufficient in terms of crosslinking effect.

It is known the crosslinking of polypropylene by adding a quinone dioxime or a

35

40

45 esters thereof and a "dikalbadenden Verbm-SungT, for example organic **" * £ "* Ρ <% - propylene (e.g. ÖSA.-Patentscbr ^ t 3012020), or by adding a quinone dioxime or emss liters of it alone in polypropylene (e.g. B. known Tonische patent applications 18546/64 InT18 551/64). These mead are to a certain extent, insofar as the veracity is concerned. However, the resulting crosslinked product is undesirably discolored. to carry out the crosslinking of polyethylene by means of dimaleinimide in the presence of a catalytic amount of peroxide.As can be seen from this reference, with polyethylene and the addition of NN -m-phenylenedimaleinimide in the absence of dicumyl peroxide no gelation could be achieved, whereas with the addition of 0 4 g In contrast, it has now surprisingly been found that certain bis-maleimides are very useful as crosslinking agents for polypropylene Chemical resistance and the mechanical properties, it has also been found that it is particularly advantageous in the case of the molding compositions according to the invention based on polypropylene. to add a hydroperoxide decomposition agent, which serves as a stabilizer for the resulting, crosslinked polypropylene. In this way, however, the molding compositions according to the invention which contain dimaleinimides differ from those of the prior art, since they contain practically no conventional free-radical chain inhibitor and no free-radical-forming agent, namely peroxides.

It is the object of the invention. To deliver molding compounds based on polypropylene, which without The disadvantages of the above!:, conventional methods can be effectively networked, being these molding compositions contain a novel crosslinking agent and a certain stabilizer that Crosslinking reaction is not adversely affected, while acting as an anti-aging agent for the crosslinked Molding compounds based on polypropylene are used. Another object of the invention is to provide a method for the crosslinking of polypropylene

The molding compositions which can be vulcanized according to the invention and are based on polypropylene are notable characterized in that they contain 0.1 to 20 percent by weight of a bis-maleimide of the general formula

5S

60 HC-C

C-CH

wherein R is a residue of an aromatic hydrocarbon or a derivative thereof and 0.05 to

5.0 percent by weight of one ^; Hydroperoxide decomposer, both percentages being based on the weight of polypropylene.

In general, the stability of a polymer be divided into a stability at the time of processing the polymer and into one Stability of the resulting product, for example a shaped body. It is believed that the Resistance at the time of processing to oxidation and heat degradation acts while stability of the resulting product acts mainly against oxidation. It is believed, that the hydroperoxide decomposition agent prevents oxidation in the molding compounds according to the invention, during the bis-maleimide for prevention serves to reduce heat. This observation is supported by the fact that in the case of kneading the compositions according to the invention on a two-roll mill at an elevated production temperature the reduction the molecular weight and sticking to the roll surfaces as a result of the degradation occurs. The invention thus provides a polypropylene composition which can be effectively crosslinked and further Has anti-aging properties

The bis-maleimides used in the invention are represented by the following general formula:

HC-C

C-CH

N - R - N

/ \ Il

HC-C C-CH

N /

O O

wherein R is a residue of an aromatic hydrocarbon or a derivative thereof.

Preferred bis-maleimides represented by the above general formula include:

m-phenylene-bis-maleimide,

4,4'-methylene-diphenyl-bis-maleimide,

4-methyl-m-phenylene-bis-maleimide,

M'-ethylene-diphenyl-bis-maleimide,

4,4'-sulfonyldiphenyl-bis-maleimide,

2,2'-dithiodiphenyl-bis-maleimide,

4,4'-ethylene-bis-oxyphenyl-bis-maleimide or

3,3 '-Dichlor- ^' - biphenyl-bis-maleinimid as well

4,4'-vinylenediphenyl-bis-maleimide,

p-phenylene-bis-maleimide.

The stabilizers used in the invention are Hydroperoxide decomposition agents] The hydroperoxide decomposition agents are sulfur or phosphorus compounds.

Preferred hydroperoxide decomposing agents include: Too-difatty acid dialkyl esters, such as dauryl thio-dipropionate or distearyl thio dipropionate; Salts of dithiocarbamic acid, such as zinc-dimethyldithio-. carbaniate, lead diethyl thhiocarbamate or sodium ίο methyldithiocarbamate, thiazoles, such as mercaptobenzothiazole, Dibenzthiazoyl disulfide or zinc mercapto-benzothiazole; or phosphites and thiophosphites, such as trinonylphenyl phosphite, triphenyl phosphite, Tribenzyl-phosphite or Trilauryltrithio-phosphite

IS phit thio-bis-phenols, which are not only hydroperoxide-decomposing Effectiveness, but also have a radical chain inhibitor effect, are used as stabilizers excluded for the mass according to the invention.

The polypropylene to be used in the invention is not based on a homopolymer of propylene limited, but may also be modified with a small amount of a monomer copolymerizable with propylene such as ethylene and the like, or can be a mixture of these with a small one

Amount of any other polymer;

for example polyethylene, ethylene-propylene-rubber

chuk and the like

The molding compositions according to the invention based on polypropylene are capable of crosslinking

Heating to a temperature of ISO to 280 ° C

be subjected to that sufficient to produce the desired

To cause crosslinking reaction.

The crosslinking agent and the hydroperoxide decomposition agent can with the polymer in are mixed in a known manner, for example on a two-roll mixing mill, in a Banbury mixer or a screw press.

If desired, the crosslinkable composition according to the invention can further contain conventional additives, for example Pigment filler, lubricant, antistatic agent, or flame retardant additives.

The invention is explained in more detail with reference to the following examples, the gel percentage of the crosslinked polypropylene was calculated as follows: Approximately 0.5 g of a sample of the crosslinked Polymer was produced in a from a metal sieve with 0.074 mm internal width (200 mesh) Filled container which took 3 hours at

so 150 ° C was immersed in tetralin. Then became the insoluble polymer dried in vacuo and weighed. The gel percentage was after calculated using the following equation:

Gel percentage% =

Weight of the insoluble part of the sample

Weight of the sample before immersion

example 1

100 parts by weight of a powdery !, isotactic polypropylene with a melt index of 1.0 and a density of 0.9U 2.0 parts by weight m-phenylene-bis-maleimide (as a crosslinking agent) and 0.2 parts by weight of dilauryl thiodipropionate were mixed in a Henschel mixer and then after transfer to a two-roll mixer maintained at 180 ° C Kneaded for 10 minutes. After kneading, the homogeneous mixture became in the form of a about 2 mm thick skin removed. The pelt was made into pellet form with a cutting machine convicted. The composition in pellet form was

de placed in a mold with internal dimensions of 50 150 χ 1 mm and ^{pressed together and cured for 10 minutes under a pressure of 200 kg / cm 2} in a ^{hydraulic 100 t press heated to 20O 0} C. After curing, the pressure was released and the sample was taken out and cooled. The gel percentage of the sample thus guessed was 44.0%.

When the procedure of Example 1 is repeated in the same way with the exception that 0.2 parts by weight of 1,13-tris- (2 ^ methyl-4-hydroxy-5-tert-butylphenylHnitane, which was a radical chain inhibitor, as a stabilizer in place of the dilauryl thiodipropionate was added, the gel percentage of the obtained sample was 0%.

Examples 2 to 5
and Comparative Examples 1 to 4

In these examples, the comparative results of the effects are different compared to Example 1 different hydroperoxide decomposing agents together with the effects of various radical chain inhibitors shown

. When the procedure of Example 1 was repeated in the same manner except that 0.2 part by weight any hydroperoxide decomposer or free radical inhibitor was added the gel percentage of the samples obtained as indicated in the table. From the table is the effect the invention can be seen beyond doubt.

Example! 2 According to the invention 4th 5 1 Comparative experiment 3 4th 100 3 100 100 100 2 100 100 Isotactic polypropylene 2 100 2 2 2 100 2 2 m-phenylene-bis-maleimide 2 2 Hydroperoxide decomposer 0.2 Trinonylphenyl phosphite Trilauryl trithiophosphite 0.2 0.2 Dibenzothiazole disulfide 0.2 Zinc dimethyldithiocarbamate ... R. radical chain inhibitor 0.2 3,5-di-tert-butylhydroxytoluene .. Phenyl - /? - naphthylamine 0.2 4,4-thiobis- (6-tert-butyl- 0.2 3-methylphenol) n-octadecyl- / 3- (4'-hydroxy-3 ', 5'-di- 0.2 tert-butylphenyl) propionate .. 44.5 59.2 38.8 small amount 0 0 Gel percentage 41.3 0

Claims (1)

Patent claims: 1. Vulcanizable molding compositions based on polypropylene, characterized in that they contain 0.1 to 20 percent by weight of a bis-maleimide of the general form! IO