NO782028L - ELASTOMER MIXTURE AND MANUFACTURING PROCEDURE - Google Patents

Description

Elastomer mixture and method for its production.

The present invention relates to thermoplastic elastomer mixtures of 1-olefin polymers such as e.g. polypropylene or copolymers such as e.g. polypropylene and polyethylene, and of styrene-butadiene rubber and which do not need any kind of curing or vulcanization for the development of elastomeric properties.

The aforementioned mixtures can also be partially hardened.

In the past, a small number of specific types of thermoplastic elastomers have been known and the term "thermoplastic elastomer" has usually been used for elastomers which can be easily processed and reprocessed, moulded, or the like by ordinary or conventional thermoplastic methods and which do not require vulcanization for the development of the different physical properties.

Formerly specific types of known thermoplastic elastomers are the thermoplastic urethanes, the thermoplastic polyesters such as e.g. "Hytrel" manufactured by DuPont, styrene block copolymers sold under the designation "Kraton" by Shell Oil Company and "Solprene" manufactured by Phillips Petroleum Company.

Another recent thermoplastic elastomer is a blend of polypropylene and EPDM (ethylene-propylene-non-conjugated diene monomer) as described in US Patents 3,758,743, 3,806,558 and 3,862,106. It is not surprising that mixtures of EPDM and polypropylene form a material with good mechanical properties due to the fact that EPDM contains a large number of monomer units in the basic structure identical to the units in polypropylene so that there is good miscibility between these two polymers.

Blending of an immiscible rubber with a 1-olefin polymer

like for example. polypropylene can result in a material with poor properties. Examples include polybutadiene or nitrile rubber mixed with polypropylene. It is therefore surprising that when styrene-butadiene rubber is mixed with a 1-olefin polymer such as e.g. polypropylene, a mixture with good physical properties is obtained, since styrene-butadiene rubber is so different from EPDM. That is that SBR contains an aromatic group in contrast to an almost completely aliphatic chain and furthermore it contains a large number of unsaturated groups in comparison with the usual 2 to 4 percent unsaturation in the EPDM polymer.

The latter US patent documents can thus in no way be said to have made the present invention proximate.

It is an object of the present invention to provide a thermoplastic elastomer mixture of 1-olefin polymers or copolymers with styrene-butadiene rubber, as the said mixtures may optionally be partially cured, with good physical properties without any further vulcanization, as the mixtures can be easily processed again and still retain their good physical properties.

The thermoplastic elastomer mixtures are produced by mixing the mixtures at or above the melting temperature of the aforementioned 1-olefin polymers or copolymers, and the resulting product is optionally subjected to partial curing.

In the obtained thermoplastic elastomer mixtures, both the 1-olefin polymers or copolymers and the styrene-butadiene rubber will be present in a continuous phase.

The obtained thermoplastic elastomer mixtures have extremely good resistance to ozone and ageing, good adhesion for applied varnish coats, a low brittleness point, good low-temperature impact resistance, minimal shrinkage at high temperatures and good elongation.

The invention thus relates to a thermoplastic elastomer mixture and the distinctive feature of the thermoplastic elastomer mixture according to the invention is that it comprises a mixture of a crystalline 1-olefin polymer and styrene-butadiene rubber, the 1-olefin polymer being selected from the group consisting of a homopolymer and a copolymer produced from 1-olefin monomers having from 2-20 carbon atoms, the homopolymer or copolymer having a melting point of at least 90°C, the amount of the crystalline 1-olefin polymer being from about 15 to about 48% by weight based on the total weight of the mixture, the mixture forming a thermoplastic elastomer. Additionally, the thermoplastic elastomer composition may be partially cured to have a melt flow index of at least 1.0.

The invention also relates to a method for production

of the aforementioned thermoplastic elastomer mixture, and the distinctive feature of the method according to the invention is that a mixture of a crystalline 1-olefin polymer and styrene-butadiene rubber is provided, the 1-olefin polymer being selected from the group consisting of a homopolymer and a copolymer produced from 1-olefin monomers having from 2-20 carbon atoms, the homopolymer and copolymer having a melting point of at least 90°C, the amount of the crystalline 1-olefin polymer being from about 15 to about 48% by weight based on the total weight of the/mixture , the mixture being heated to a temperature at or above the melting temperature of the crystalline 1-polymer so that a mixture which can be processed repeatedly is formed. Optionally, the method may comprise the additional step of partially curing the mixture to have a melt flow index of at least 1.0.

The present elastomers thus relate to uncured or partially cured mixtures of 1-olefin polymers with styrene-butadiene rubber. The 1-olefin polymer can be a monopolymer or a copolymer of different 1-olefin monomers with from 2-20 carbon atoms. Examples of suitable 1-olefin monomers include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-methylv-1-hexene, 4-ethyl-1-hexene, 6-methyl-1-heptene and such. A preferred monomer is ethylene and gives an even higher degree of propylene. In addition to the homopolymers, the 1-olefin polymer can be a copolymer made from different 1-olefin monomers. It is an important feature of the invention that only 1-olefin polymers or copolymers are used which have a melting point of 90°C or more. Thus, when different 1-olefin monomers are used to produce a copolymer, the amount of each must be adjusted so that a copolymer with a melting point of at least 90°c is produced. A preferred copolymer is prepared from a major amount of ethylene monomers and a minor amount of propylene monomers. A highly preferred copolymer is prepared from a major weight amount of propylene monomers and a minor weight amount of ethylene monomers.

The weight amount of the 1-olefin polymer in the total mixture is from about 15 to about 48%, with an amount by weight of from about 30 to about 42% being preferred. The remaining amount by weight of the mixture is thus the styrene-butadiene rubber, that is, an amount from about 85 to about 32% by weight, with an amount from about 58 to about 70% by weight being preferred.

The butadiene-styrene rubber is a random copolymer made from monomers of butadiene and styrene. The copolymer may be prepared in any usual or conventional manner known to those skilled in the art, e.g. by solution or emulsion polymerisation. Additionally, the specific type of styrene-butadiene rubber may vary. The butadiene proportion can thus e.g. be mainly 1,2-polybutadiene, i.e. as much as 90 or even 100%, or mainly.1,4-polybutadiene, i.e. as much as 90 or even 100%. The amount by weight of the butadiene can vary greatly, ranging from about 60 to about 90% by weight

based on the total copolymer is desirable, although larger or smaller amounts may be used. The number average molecular weight of the copolymer may range from about 50,000 to about 1,000,000.

Similarly, the 1-olefin polymer such as e.g. the preferred polyethylene and the still more preferred polypropylene are prepared in any usual or conventional manner as long as it is highly crystalline and has an isotactic configuration. In general, the melt flow index of the isotactic 1-olefin polymer and especially the isotactic polypropylene may be from about 0.4 to about 30 with a preferred range being from about 2 to about 12 according to AS TM No. D12'38.

An isotactic 1-olefin polymer is thus primarily used, although an amount of from 0.1 up to about 15% by weight based on the total weight of the 1-olefin polymer of a 1-olefin polymer with a low crystalline atactic configuration may be used. In a preferred embodiment, isotactic polypropylene is used together with small amounts of atactic polypropylene. Small amounts of the atactic configuration of a particular 1-olefin polymer are not only economical but also improve the flow and do not significantly reduce the various physical properties. In general, amounts greater than a total of 15% of an atactic configuration of a specific 1-olefin polymer are undesirable as the physical properties are reduced, but in some applications such a mixture may be usable and even desirable.

Regardless of the specific type of 1-olefin polymer used, the particle size is that produced by normal and conventional polymerization techniques. Generally, the particle size is greater than 1.0 microns and desirably greater than 5.0 microns, although any particle size may be used. From a practical point of view, larger particles such as sizes up to 2 mm are advantageously used, and even larger particles. Since the 1-olefin polymer is usually mixed with the styrene-butadiene rubber in a mill, large particles such as e.g. Polypropylene cubes are of course used.

It has been found that the addition of from about 2 to about 20

parts polyisobutylene per 100 parts of the mixture, surprisingly improves the texture, smoothness and surface gloss of injection molded articles and provides improved tensile elongation when added to a mixture of a 1-olefin such as polypropylene and styrene butadiene rubber.

The mixture of the 1-olefin polymer and the styrene-butadiene rubber, regardless of a partial cure, results in a thermoplastic elastomer. That is that the mixture is considered a thermoplastic elastomer in that it can be processed repeatedly and if it is partially cured it does not need further vulcanization to develop elastomeric properties. In other words, the mixture can be easily and repeatedly molded, extruded or otherwise processed as it flows at temperatures at or above the melting point of the 1-olefin polymer. In general, a partial cure is preferred in that the properties exhibit improved permanent elongation as well as a notable increase in the aging properties.

By partial curing is meant that the styrene-butadiene rubber part of the mixture cross-links to an extent less than full curing or vulcanization. In the present invention, a partial cure is achieved when the melt flow index (ASTM No. D1238, condition "L" with the exception that the load is 45.36 kg or 100 pounds) is at least 1.0 and preferably 10.0 or more. Blends of the 1-olefin polymer and the styrene-butadiene rubber that cure beyond a partial cure and thus have a melt flow index below 1.0 result in vulcanized blends or thermoset elastomers that are clearly outside the scope of the present invention. The partial curing can be achieved by using any conventional curing compound or curing method as further explained below. Generally, good compositions according to the invention will have a melt flow index of from about 90 to about 150 with a preferred melt flow index of about 120.

It is a critical feature of the invention that the 1-olefin polymer

and the styrene-butadiene rubber are mixed together at a temperature equal to or greater than the melting point of the 1-olefin polymer. Due to variations in molecular weight and degree of crystallinity, the melting point will vary over a smaller range for the particular 1-olefin polymer. The typical polyethylene will have a melting point range of about 127°C to about 140°C

with a typical melting point of about 135°C. Melting point range

for the highly preferred polypropylene is from about 150°C

to about 175°C with a practical or typical melting point temperature of about 160°C. Temperatures within this range or preferably above this are thus necessary in the present invention. The mixing itself can take place by means of any usual or conventional mixing process and can thus easily take place on a Banbury or Brabender mill, a twin-screw extruder or the like.

When a partial cure is carried out, it is preferred to mix first

the two components and then subjected to the partial cure, although the styrene-butadiene rubber may initially be partially cured and then mixed with the 1-olefin polymer.

Another production method involves the addition of all dry ingredients to a styrene-butadiene rubber latex. When the SBR latex is coabulated using common and well-known methods, all components are intimately mixed. This mixture is then further mixed in any way, e.g. on a mill, at temperatures above the melting point temperature of the polypropylene, thereby forming the thermoplastic elastomer mixture.

If partial curing is used, the curing agent can advantageously be added together with other conventional processing aids, additives and the like before or during the mixing step. Furthermore, the partial curing can be achieved under either static or dynamic conditions. Under static conditions, the partial curing can be achieved by placing a mixture containing the curing agent in an oven and heating the mixture to a desired temperature whereby partial curing takes place, e.g. at a temperature of from about 65°C to -about 260°C for from about 5 to 30 minutes. The dynamic partial curing is achieved by working or treating the mixture containing the curing agent in an open mill, in a Banbury mixer, in an extrusion device or the like, at a temperature sufficient to cause a partial curing, e.g. from about 65°C to about 210°C for about 5 to 20 minutes. Although the dynamic curing takes place below the melting point of the 1-olefin polymer, the dynamic mixing temperature must be a

trip above the melting point of the 1-olefin polymer.

As noted, the curing agent used when partial curing is desired can be any known or conventional rubber curing agent or method known to the person skilled in the art. Variations from standard methods or compounds can of course be used. Typical types of hardeners include sulphur-containing hardeners such as e.g. sulfur itself, or sulfur donors, the various peroxides, either aromatic or aliphatic, and small irradiation doses. If a sulfur-containing curing agent is used, usually from 0.01 to 1.0 parts by weight per 100 parts mixture, the preferred range being from 0.1 to 0.2 parts. Some representative examples of sulfur-containing curing agents include sulfur, tetramethylthiourea, 2-(hexa-methyleneiminothio)-benzothiazole, sulfur dichloride, sulfur monochloride, alkylphenol disulfide, and tetramethylthiuram disulfide. A preferred curing agent is sulfur itself. Generally, it is desirable to use from 1 to 5 parts per 100 parts mixture of zinc oxide, conventional amounts of stearic acid and an accelerator to impart very good antioxidant properties to the mixture. Furthermore, this special partial curing system in combination with activated carbon provides surprisingly superior paint adhesion.' These unexpected results are particularly noteworthy for the highly preferred 1-olefin polymer of polypropylene.

The amount of the organic peroxides to effect a partial cure generally varies from about 0.01 to about 0.5 parts by weight. 100 parts mixture, a preferred range being from about 0.1 to about 0.3. Here too, any peroxide compound can be used such as e.g. the aromatic diacyl peroxides, the aliphatic diacyl peroxides, dibasic acid peroxides, ketone peroxides, alkyl peroxy esters, alkyl hydroperoxides and the like. Specific examples include dicumyl peroxide, dibenzoyl peroxide, diacetyl peroxide, bis-2,4-dichlorobenzoyl peroxide, di-tert-butyl peroxide, tert -butyl cumyl peroxide and the like. Of course, the number of different peroxides is enormous and any of them may be used, the above compounds being only representative examples.

A preferred peroxide curing agent is dicumyl peroxide and 2,5-bis(tert-butylperoxy)2,5-dimethylhexane.

Of course, a plurality of peroxide curing agents, a plurality of sulfur-containing curing agents, as well as combinations of sulfur-containing and peroxide curing agents can be used as is well known to those skilled in the art. Furthermore, the amount of curing agent as stated above of course only represents the amount of the active compound.

If a hardener such as e.g. dicumyl peroxide in a solvent system, the weight of the dicumyl peroxide itself is indicated. Furthermore, the exact amount of a specific curing agent used to achieve a specific melt flow index will vary from one specific curing agent to another, depending on the general activity or effectiveness of the specific curing agents.

Another method of achieving the partial curing involves

subjecting the mixture to ionizing radiation. Ionizing rays include alpha rays, beta rays, gamma rays, electron guns, proton rays, neutron rays and X-rays. In most commercial applications, an accelerated electron gun is used. The irradiation is preferably carried out by subjecting pellets or a thin layer of the mixture to the irradiation. The irradiation can take place from one side or from both sides of the mixture. The amount of irradiation will of course vary with the thickness of the mixture. In any case, a desirable amount of irradiation is that which results in a partially cured mixture with a melt flow index above the previously indicated index number. It is a distinctive feature of the irradiation technique that the cross-linking density of the styrene-butadiene copolymers will vary with the distance from the irradiated surface. This condition can be tolerated as long as a uniform partially hardened system is produced.

However, too high a dose will result in a cross-linked system that cannot be cast or extruded and will not be reworkable. In general, the amount of irradiation will vary from about 0.1 to. about 5.0 Megarad when an electron accelerator is used and when the irradiation is admitted on only one side of the mixture and will vary from about 0.1 to about 3.0 Megarad when the irradiation is carried out on each side of

In addition to the curing agents as indicated above, other rubber components, additives, fillers, processing aids and the like may be added in conventional amounts. Specific types of additives include, in addition to accelerators, activators, colorants, antioxidant agents, flame retardants, ozone resistance compounds and various processing aids such as e.g. oil, stearic acid and the like. Examples of fillers include activated carbon, e.g. from

0.1 to preferably from about 0.6 parts to about 30 to 40 parts by weight. 100 parts mixture. Other fillers such as e.g. silica, various types of clay, calcium carbonate, talc and the like can be used in conventional amounts.

The mixtures, whether partially cured or not, generally have good physical properties and generally consist of two continuous phases. Some of the properties were completely unexpected such as e.g. low brittleness point. Other unexpected properties include minimal shrinkage at high temperatures, good low temperature impact resistance, good elongation, good paint adhesion and good resistance to ozone and aging. In general, the unexpected properties as seen in the following are generally obtained in the present compositions regardless of the exact amount of 1-olefin polymer such as e.g. polypropylene and regardless of whether the mixture is partially cured or not. However, as previously noted, partially cured mixtures provided improved permanent tensile elongation as well as improved aging properties. In general, the present thermoplastic elastomer compositions achieved an elongation at break of at least 50% and preferably at least 200%. The maximum shrinkage was less than 4% at 120°C under a load of 0.08 MPa. The mixtures did not show any ozone cracking when tested according to ASTM D518. Low temperature impact resistance at -30°C and paint peeling resistance were good as illustrated in the examples. The brittleness point of the mixtures is generally below

-20°C and preferably below -45°C.

The relationship with oz<p>n resistance was completely unexpected in that copolymers of styrene and butadiene, as is well known to those skilled in the art, exhibit poor ozone resistance. The mixtures also had very good flexibility properties and exhibited very good thermal aging properties after the addition of various heat resistance agents.

The exact combination of desired physical properties will depend on the intended applications. E.g. for outer body parts on cars, it is important that the material can withstand impact at low temperatures. When the same material is used to make a kitchen spatula, low-temperature impact resistance is irrelevant. The thermoplastic elastomer mixtures are applicable in many areas and flexible in that changes in the composition ratio between SBR and the 1-olefin polymer and especially polypropylene and changes in the mixture additives make it possible to develop a large range of desired physical properties. These changes will be obvious to the expert in the area of manufacturing plastic and rubber mixtures.

The present thermoplastic elastomer mixtures can be used for the production of objects by pressure casting, extrusion, calendering, vacuum forming and the like, with specific objects including pipes, gaskets, toys and household items. A desired area of application is within car parts such as e.g. flexible bumpers, front panels, bumper panels and the like.

The invention will be understood more easily by reference to the following examples.

The following table identifies the different materials used in the examples.

"Profax 6523 PM" an isotactic polypropylene with a melt flow index of 4.0, manufactured by Herkules Inc.

"FRS-2006" a Firestone "hot" emulsion polymerized SBR copolymer with 23.5% bound styrene, ML/4/212 = 50

"FRS-1502" a Firestone "cold" emulsion polymerized SBR copolymer with 23.5% bound styrene, ML/4/212 =45

"Stereon 750" a Firestone solution-polymerized BD/styrene copolymer with 18 to 21%

bound styrene, ML/4/212 = 45 to 47

after oil stretching with 37.5 parts oil per 100 parts. The examples use imid-. lertid "Stereon 750" without any oil

"Stereon 700" a Firestone solution-polymerized BD/styrene copolymer with 18 to 21%

bonded styrene, ML/4/212 = 50 to 60.

"Varox" peroxide 2,5-bis(tert-butyl peroxide)-2,5-dimethyl-hexane - manufactured by Uniroyal

"Santocure NS" an accelerator, N-t-butyl-2-benzothiazole-sulfenamide manufactured by Monsanto Chemical Co.

"Afax 500 HL-1" an atactic polypropylene with a viscosity \.

pressure range of 2.5 to 5.5 Pa manufactured by Hercules, Incorporated

"Vitanex L-120" polyisobutylene manufactured by Exxon

"Agerite Superlite Butylated Bisphenol A, Manufactured by RT Solid" „ J W T u. ^, •

Vanderbilt Company

"Irganox 565" 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine manufactured by Ciba-Geigy Chemical Corporation.

EXAMPLE 1

SBR/ PP = 60/ 40 by means of Latex coagulation

v 560 g of "Profax 6523PM" polypropylene (PP) was stirred into 2 liters of water together with 0.5 ml of "Triton X-100" wetting agent. To this was added 3.03 liters of "FRS 2006 SBR" latex with 27, 7% solids content to give 840 g of SBR rubber. With vigorous onw stirring, 4 liters of methanol were added and then 10 ml of H 2 SO 4

which had been diluted with water to 150 ml. The SBR coagulated rapidly upon addition of the acid and retained essentially all of the polypropylene. The liquid was poured off and the coagulated mass was washed several times before it was again washed and converted into sheets on a washing mill. The SBR with enclosed polypropylene powder was dried for 15 hours at 75°C. The material was then mixed in a twin-screw extruder where all six heating zones were

held at between 190°C and 220°C The extrudate was cut up into pellets for injection molding. The following properties were achieved:

(Tested at room temperature at 2,000%/minute voltage increase. No cracking due to ozone aging (60 parts ozone per 100 parts at 37°C for 14 hours).

EXAMPLE II

"Stereon 750"/ PP 60/ 40

"Profax 6523 PM" in an amount of 1.2 kg was stirred into 7.2 kg of hexane cement of "Stereon 750" without oil addition having 25% solids content to give 1.8 kg of "Stereon 750" rubber. The mixture was dried on a drum drier steam-heated to about 150°C. The polypropylene was held in the sheeted rubber until the mixture was mixed in a twin screw extruder where all six heating zones were maintained at 190°C to 220°C. The extrudate was cut up into pellets for injection molding.

EXAMPLE III

" Stereo 750"/ PP - 70/ 30

The procedure was identical to Example II except that 2.1 kg of "Stereon 750" and 0.9 kg of "Profax 6523 PM" were used.

Examples II and III gave the following physical properties:

EXAMPLES IV to XIII

Dry mix

The styrene-butadiene rubber was sheeted on a two-roll mill at a temperature between 90 and 120°C. The remaining ingredients (listed in Table I) were added and milling was continued until the additives were well dispersed in the rubber. The mixture was then cut up into strips so that it could be easily fed into a twin screw extruder. The material was extruded at 200°C into a quench water bath and then cut up into small pellets which were then injection molded into briquettes (15.2 x 10.2 x 0.2 cm). The briquettes were tested for physical properties.

Table I also gives several properties of the mixtures. All tests are in accordance with the ASTM standard with the exception of the paint adhesion test and the cold impact test, which will therefore be described in detail in the following.

Paint adhesion test

Before painting, a test briquette was first washed with a mild alkaline solution and then cleaned in water. After drying, the briquette was sprayed with "Seibert Oxidermo" primer and quickly dried for at least two minutes. A top coat of "Durethane 100" was then applied and cured for 40 minutes at 120°C. The paint-scratch resistance was assessed by scratching the painted surface with the edge of a coin. For surfaces that showed excellent paint adhesion, the paint could not be scraped cleanly from the substrate. When adhesion was poor, the paint could be easily peeled off with only gentle pressure applied to the coin.

Cold shock test

The cold impact test used was that required by General Motors for flexible thermoplastic elastomer parts to be approved. For this test, the ends of a ground test piece (7.62 x 15.2 x 0.3 cm) were inserted into grooves cut in a base plate 7.62 cm apart. The test sample was then allowed to acclimate at -30°C for at least 4 hours. Then, the dom-like test piece was struck on top by means of a hemispherical drop body (5 cm diameter, 27 kg) dropped from a height of 32.2 cm. To pass this test, the sample must not be crushed or cracked. In addition to the properties given in Table I, it is noted that no samples showed any ozone cracking when tested according to ASTM D518 and showed less than 5% shrinkage when tested for 30 minutes at 120°C under a load of 0, 08 MPa.

To illustrate the clear reworkability of the compositions, the compositions of Example VIII were re-extruded three times prior to injection molding. Substantially identical tensile properties were obtained compared to the mixture that had only been extruded once and then injection molded.

Claims (28)

1. Thermoplastic elastomer compound, characterized by the fact that it includes ; a mixture of a crystalline 1-olefin polymer and styrene-butadiene rubber, the 1-olefin polymer being selected from the group consisting of a homopolymer and a copolymer prepared from 1-olefin monomers having from 2-20 carbon atoms, the homopolymer or copolymer having a melting point of at least 90 °C, the amount of the crystalline 1-olefin polymer being from about 15 to about 48% by weight based on the total weight of the composition, the butadiene-styrene rubber having been partially cured if desired. 2. Thermoplastic elastomer mixture as stated in claim 1, characterized in that the crystalline 1-olefin polymer contains up to about 15% by weight of a low crystalline configuration. 3. Thermoplastic elastomer mixture as stated in claim 1, characterized in that the 1-olefin polymer is selected from the group consisting of a homopolymer of polyethylene and a copolymer made from a main weight amount of ethylene monomers and a smaller weight amount of propylene monomers. 4. Thermoplastic elastomer mixture as stated in claim 1, characterized in that the 1-olefin polymer is selected from the group consisting of a polypropylene homopolymer and a copolymer produced from a main weight amount of propylene monomers and a smaller weight amount of ethylene monomers, the propylene homopolymer containing up to about 15% by weight of an atactic polypropylene. 5. Thermoplastic elastomer mixture as stated in claim 4, characterized in that the amount of crystalline polypropylene in the mixture is from about 30 to about 42% by weight. 6. Thermoplastic elastomer mixture as stated in claim 4, characterized in that it comprises from about 2 to about 20 parts by weight of polyisobutylene per 100 parts of the mixture. 7. Thermoplastic elastomer mixture as stated in claim 1, characterized in that the styrene-butadiene rubber is partially cured and has a melt flow index of at least 1.0. 8. Thermoplastic elastomer mixture as stated in claim 7, characterized in that the crystalline 1-olefin polymer contains up to about 15% by weight of a low crystalline configuration. 9. Thermoplastic elastomer mixture as stated in claim 7, characterized in that the 1-olefin polymer is selected from the group consisting of a homopolymer of polyethylene and a copolymer produced by a main weight amount. ethylene monomers and a smaller amount by weight of propylene monomers. 10. Thermoplastic elastomer mixture as set forth in claim 7, characterized in that the 1-olefin polymer is selected from the group consisting of a polypropylene homopolymer and a copolymer produced from a main weight amount of propylene monomers and a smaller weight amount of ethylene monomers, the propylene homopolymer containing up to approximately 15 wt% of an atactic pp polypropylene. 11. Thermoplastic elastomer mixture as stated in claim 10, characterized in that the amount of crystalline polypropylene in the mixture is from about 30 to about 42% by weight. 12. Thermoplastic elastomer mixture as stated in claim 11, characterized in that the partial curing is carried out by means of a compound selected from the group consisting of a sulfur-containing curing agent and an organic peroxide curing agent, the amount of the sulfur-containing curing agent being from about 0.01 to approximately 1.0 parts by weight per 100 parts by weight of the mixture and wherein the amount of the organic peroxide curing agent is from about 0.01 to about 0.5 parts by weight per 100 parts by weight mixture. 13. Thermoplastic elastomer mixture as stated in claim 12, characterized in that said curing agent is a sulfur-containing curing agent and comprises from about 1 to about 5 parts by weight per 100 parts by weight of the mixture of zinc oxide. 14. Thermoplastic elastomer mixture as stated in claim 10, characterized in that it comprises from about 2 to about 20 parts by weight of polyisobutylene per 100 parts by weight of the mixture. 15. Method for producing the thermoplastic elastomer mixture specified in claim 1, characterized by the following steps: a mixture of a crystalline 1-olefin polymer and styrene-butadiene rubber is prepared, the 1-olefin polymer being selected from the group consisting of a homopolymer and a copolymer prepared from 1-olefin monomers with from 2 to 20 carbon atoms, the homopolymer and the copolymer having a melting point of at least 90°C, the amount of the crystalline 1-olefin polymer is from about 15 to about 48% by weight based on the total weight of the mixture, and the mixture is heated at a temperature at or above the melting point of the crystalline 1-olefin polymer so that a reworkable mixture is formed, after which the resulting mixture is subjected to partial curing if desired. 16. Method as stated in claim 15, characterized in that the crystalline 1-olefin polymer contains up to about 15% by weight of a low crystalline configuration. 17. Method as stated in claim 15, characterized in that the 1-olefin polymer is selected from the group consisting of a homopolymer of polyethylene and a copolymer produced from a main weight amount of ethylene monomers and a smaller weight amount of propylene monomers. 18. Method as set forth in claim 15, characterized in that the 1-olefin polymer is selected from the group consisting of a polypropylene homopolymer and a copolymer produced from a main weight amount of propylene monomers and a smaller weight amount of ethylene monomers, the propylene homopolymer containing up to approximately 15% by weight of an atactic polypropylene. 19. Method as stated in claim 18, characterized in that the amount of crystalline polypropylene in the mixture is from about 30 to about 42% by weight. 20. Method as stated in claim 18, characterized in that approximately 2 to approximately 20 parts by weight of polyisobutylene are used per 100 parts by weight of the mixture. 21. Method as stated in claim 15, characterized in that the obtained mixture is partially hardened to have a melt flow index higher than 1.0 so that the mixture can still be processed again. 22. Method as stated in claim 21, characterized in that the crystalline 1-olefin polymer contains up to about 15 percent by weight of a low crystalline configuration. 23. Method as set forth in claim 21, characterized in that the 1-olefin polymer is selected from the group consisting of a homopolymer of polyethylene and a copolymer produced with a main weight amount of ethylene monomers and a smaller weight amount of propylene monomers. 24. Method as set forth in claim 21, characterized in that the 1-olefin polymer is selected from the group consisting of a polypropylene homopolymer and a copolymer produced from a main weight amount of propylene monomers and a smaller weight amount of ethylene monomers, the propylene homopolymer containing up to approximately 15% by weight of a atactic polypropylene. 25. Method as stated in claim 24, characterized in that the amount of crystalline polypropylene in the mixture is from about 30 to about 42% by weight. 26. Method as set forth in claim 25, characterized in that the partial curing is carried out using a compound selected from the group consisting of a sulfur-containing curing agent and an organic peroxide curing agent, the amount of sulfur-containing curing agent being from about 0.1 to about 1, 0 part by weight per 100 parts by weight of the mixture and wherein the amount of the organic peroxide curing agent is from about 0.01 to about 0.5 parts by weight per 100 parts by weight of the mixture. 27. Method as stated in claim 26, characterized in that the hardener is a sulfur-containing hardener and comprises from about 1 to about 5 parts by weight of zinc oxide per 100 parts by weight mixture. 28. Method as stated in claim 27, characterized in that about 2 to about 20 parts by weight of polyisobutylene are used per 100 parts by weight mixture.