NL8101419A - METHOD FOR PREPARING A THERMOPLASTIC, ELASTOMER PRODUCT. - Google Patents

Description

Process for the preparation of a thermoplastic elastomer product.

The invention relates to a process of a thermoplastic elastomer product, in which 25 - 85 parts by weight. polyolefin mixes with 75-35 parts by weight. vulcanized monoolefin copolymer rubber and optionally one or more fillers and / or other auxiliaries.

Such a method is known from Dutch patent application 7200773. According to this application, a partially vulcanized rubber is used. This application expressly warns against excessive vulcanization of the ruBBer to be used. This can be avoided by using a small amount of curing agent or by proper selection of curing conditions.

According to the invention, considerably stronger elastomeric products are obtained, moreover, a greater resistance to oil when a rubber is used, which is completely or almost completely vulcanized. Surprisingly, it has been found that a mixture with polyolefin, in which a vulcanized rubber is used as completely as possible, is nevertheless thermoplastic. remains workable.

The invention concerns a method as mentioned in the preamble, characterized in that a ruBBer is used, which is vulcanized to the percentage of extracts with cyclohexane of 23 ° C. low molecular weight constituents in the ruBBer were not attainable until it had a crosslinking density of at least 7.10 D mol per ml ruBBer, adding per 300 parts by weight. RUBBER up to 300 parts by weight. filler and lengthening oil can be used provided that so much polyolefin is used that the ratio (Wq + is at least 0.33, in which WQ is the weight of lengthening oil, - Wr is the weight of polyolefin and if the _____ Λ 8101419 9 8- St-2 - of vulcanized rubber, which is considered to contain particles larger than 50 microns, this rubber is reduced to a particle size below 50 microns before or after mixing with the polyolefin.

The crosslinking density of rubber can be determined according to Flory & Rehner, as described in J. Rubber Chem. & Techn. 30, p. 929. The Huggins solubility parameter for cyclohexane used in the calculation is according to Holly (J. Rubber. Chem. And Techn., 39, p. 1455) 0.315. The crosslinking density is half the network chain density. The solubility in cyclohexane is determined according to US Pat. No. 3,203,937 by soaking a sample in cyclohexane at 23 ° C for 48 hours, decanting the solution and drying and weighing the residue. They correct for the other ingredients by subtracting the weights of solubles such as lengthening oils and plasticizers from the initial weight and subtracting the weights of insolubles such as pigment and fillers from both the initial and final weights.

All known auxiliaries and mixtures can be used for the yulcanization, in particular the vulcanizing agents based on peroxides, azides, sulfur and sulfur compounds. Very suitable are the combinations of maleimides and. disulfides. For vulcanizing agents, see columns 3 and 4 of U.S. Patent 3,806,558.

Furthermore, fillers and many auxiliary substances can be added to these mixtures, for example carbon black, silicic acid, T1O2, pigments, clay, ZnO, stearic acid, accelerators, stabilizers, reinforcing fibers, adhesives, etc. Of particular importance is the use of extension oil (as well as soot). 30 Soot improves tensile strength and extension oil can increase oil swelling resistance and heat stability.

Amoratic, naphthenic and paraffinic extension oils are all suitable; a summary of this can be found in the aforementioned Rubber World Blue Book, pp. 145-190.

Preferably, vulcanization is carried out under conditions such that the elastomer used achieves a crosslinking density of at least 1-10 µmol / ml and contains less than 2% by weight of cyclohexane extractable components.

The result of this method according to the invention is a thermoplastic product (which can thus still be formed) with high mechanical strength; the tensile strength 2 is at least 60 kg / cm more than a corresponding mixture with unvulcanized rubber.

Suitable polyolefins for the process according to the invention are thermoplastic crystalline, high molecular substances obtained by polymerization of one or more monoolefins, either under high or low pressure. Polyethylene and polypropylene are readily available; the polyethylene is preferably used.

J5 Also vulcanizable monoolefine copolymers of two or more α-monoolefins and preferably also a diene (or other higher polyene) are suitable for practically full vulcanization in the process according to the invention. Such products are commercially available under the designations "EPM rubber" and "EPDM rubberH.

For suitable qualities, see the Rubber World Blue Book of 1975, section Materials and Compounding Ingredients for Rubber, biz. 403 and 406-410.

How the rubber is vulcanized is not important. Both dynamically vulcanized and statically vulcanized rubber can be used in the method according to the invention, provided that the vulcanized rubber ultimately has a particle size of at most 50 microns.

Mixing with polyolefin can be done in various ways, for example above the melting or softening point of the polyolefin. If one has a mixture in which the rubber particles are poorly dispersed or too large, it is sufficient to mill this mixture further in order to reduce the particle size to below 50 µm. Often, poor dispersion or the presence of oversized rubber particles is visible to the naked eye in a molded sheet.

This applies in Bet Special In the absence of pigments and fillers. In such a case, pulverization and reshaping results in a sheet in which aggregates of rubber particles or large particles are no longer detectable to the naked eye and the mechanical properties of which are considerably improved.

The invention is further illustrated in the example below.

100 parts by weight. EPDM rubber (a terpolymer ver-10 obtained from a 55 wt.% Ethylene, 40.6 wt.% Propylene and 4.4% diene Existing blend, and with a Mooney viscosity of 100 (ML- 8,100 ° C}} are mixed in a Brabender mixer with 5 parts zinc oxide, 1 parts stearic acid, 1.5 parts sulfur, 1.0 parts TMTD and 0.5 parts MBTS and then are pyrolized under mixing. oil temperature of 180 ° C. Mixing is continued 3 minutes after vulcanization. The vulcanized powdered rubber (containing zinc oxide, stearic acid and hardeners} is mixed in a Brabender with molten polypropylene (sg 0.902, elongation at 11%). The mixture Contains 70.8 parts of the vulcanized rubber powder and 35 parts of polypropylene The molten mass shows particles or aggregates of rubber particles which can be seen with the naked eye when pressed between cold plates. powder crushed by cold milling on a roll mill The powdered preparation 25 is used up newly mixed in the warm Brabender. Them obtains a molten mass, which is reformed / formed into a sheet. The properties of the sheet pressed at 220 ° C, which contains very few visible particles or aggregates, are listed under Preparation No. 1 in Table A. Preparation 2 is an unvulcanized comparative material. The strength of preparation J is more than 100 kg / cm greater than that of the unvulcanized preparation 2.

From the above it appears that rejected and worn-out parts of vulcanized rubber, which are usually regarded as waste or at best serve as fuel, can again be recovered by correspondingly.

according to the invention to be mixed with molten polyolefin after pulverization to a particle size below 50 microns.

TABLE A 5

Preparation No. 1 2

Vulcanized EPDM 70.8 ^

Unvulcanized EPDM - 65 10 Polypropylene 35 35 u / 2 x 10 ^ approx 14 0 2

Tensile strength, kg / cm 147.8 35.9 2 100% modulns, kg / cm 69.2 35.5 2

Young's modulus, kg / cm 701 333 15 Elongation at break,% 423 192 ^ The vulcanized EPDM beyat 65 parts. rubber.

The remainder consists of zinc oxide, stearic acid and curing agents.

The addition of fillers such as carbon black or rubber additive oil and combinations of the two additives makes it possible to prepare vulcanizates according to the invention which have essentially an unlimited range of properties. The addition of carbon black generally increases tensile strength, while addition of an extension oil usually decreases hardness and strain hardening. As indicated above, in mixtures containing large amounts of resin, sufficient lengthening oil must be used so that an effective combined amount of rubber and lengthening oil is present to obtain thermoplastic elastomeric vulcanizates.

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Claims (1)

V Λ _ '% • ...., * - 6 - Process for the preparation of a thermoplastic product, 25-85 parts by weight. polyolefin mixes with 75-15 parts by weight. vulcanized monoolefin copolymer rubber and optionally one or more fillers and / or other auxiliaries, characterized in that a rubber is used, which is vulcanized to the percentage of components extractable with cyclohexane of 23 ° C, at most 3% of the rubber or if this was not achievable due to low molecular weight constituents in the rubber, until it had a crosslinking density of at least 7.10 moles per ml of rubber, with 100 parts by weight. rubber up to 300 parts by weight. filler and lengthening oil can be used provided that so much polyololefin is used that the ratio (W + W) / VT is at least 0.33, in which orp is the weight of lengthening oil, the weight of polyolefin and if the vulcanized rubber, which is considered to contain particles larger than 50 microns, reduces this rubber before or after mixing with the polyolefin to a particle size below 50 microns. 8101419