PROCESS FOR THE PREPARATION OF POLYOLEFINIC PLASTO-ELASTOMERIC COMPOSITIONS BY MEANS OF DYNAMICAL VULCANIZATION

Abstract: Preparation of plasto-elastomeric compositions en­ dowed with an improved processability and consisting of a blend or mix of EPDM rubber cross-linked with a thermoplastic olefinic polymer, by means of dynamical vulcanization, using as a cross-linking agent for the rub­ ber a halogen-donor free system consisting of a phenolic non-halogenated resin and a particular oxide or metal carbonate.

Description: The present invention concerns a process for the preparation by means of dynamical vulcanization, of thermoplastic elastomeric compositions consisting of a plastomeric olefinic polymer and an elastomeric copolymer at least partly cross-linked. The preparation of compositions based on themoplastic polymers and vulcanized rubbers, according to the method of dynamical vulcanization, is quite known to the Prior Art and is described in particular in USA Patents nos. 3.758.643, 3.862.106, 3.037.954 and 3.806.558. According to such a method, the vulcanization of the elastomeric component is made to occur during the mixing or plasticization of the elastomeric component with a molten plastomeric polymer, by means of cross-linking agents which in general are of the conventional type, such as for instance: peroxides, azidic compounds, mixtures of sulphur with zinc oxide, substituted ureae, thiocarbamates, etc. If in the mix which is thus treated there is present a sufficient quantity of plastomeric polymer, the composition, at the end of the vulcanization of the elastomeric component, will maintain good processability characteristics under heat even at high percentages of vulcanized elastomer. According to a French patent no. 2.408.632, plasto-elastomeric polyolefinic compositions may be obtained through dynamical vulcanization methods using as a cross-linking agent a halogenated phenolic resin, or a not-halogenated resin however associated to halogen-donors in combination with a metal oxide (activator). According to said French patent, the mix of EPDM rubber and olefinic polymer with the phenolic resin in a proportion, with respect to the rubber, of from 5% to 20%, at a temperature sufficient for melting the olefinic polymer, is subjected to mastication after which it is additioned with the activator, thereupon carrying on the mastication at a temperature at which there occurs the cross-linking of the elastomeric component. The metal oxide, in particular zinc oxide, would in this instance favour the complete cross-linking of the elastomer, which is actually one of the objects of the process of said patent. The compositions thus obtained through the dynamical vulcanization show, however, as a feature common with all the compositions based on mixes of plastomeric polymers with cross-linked elastomers, the drawback of being so much more difficult to be processed or heat-moldable, the higher the percentage of cross-linked elastomeric component present in these compositions. Moreover, in the compositions thus obtained, the elastomeric component shows easily a dishomogenization of the cross-linking due to the difficulty of homogeneously dispersing the vulcanizing agents in the composition at the melt temperature of the plastomeric component, before their becoming active at that temperature. All these drawbacks reflect negatively on the processability properties under heat of the compositions thus obtained. It has now been found by the Applicant that with the methods of dynamical vulcanization it is possible to obtain compositions of olefinic elastomers with e.g. EPDM rubbers, endowed, with respect to the compositions of the Prior Art, with an improved processability at an equal degree of cross-linking of the rubbery component, using as a cross-linking agent a system free of halogen donors and consisting, in particular, of a non-halogenated phenolic resin and a metal component as herein after defined. More particularly, in such a cross-linking system the phenolic resin is present in a quantity of up to 10 parts by weight, but preferably comprised between 1 and 5 parts by weight on 100 parts by weight of the elastomeric component present in the composition to be prepared, while the metal compound is present in a ponderal relationship with the phenolic resin comprised between 1:1 and 5:1, but preferably comprised between 1:1 and 3:1. For the purposes of this invention as an elastomeric compound there is used a terpolymer of two α-olefinic monomers with a non-conjugated dienic monomer, this latter being present in a quantity comprised between 1% and 10% by weight on the total weight of elastomer. Examples of dienic monomers usable for the purposes are: 1,4-hexadiene; 2-methyl-1,4-pentadiene; 1,4,9-decatriene; 1,5-cyclooctadiene; 1-methyl-1,5-cyclooctadiene; 1,4-cycloheptadiene; dicyclopentadiene; ethylidene-norbornene; the substitution derivatives of said monomers. Examples of α-olefinic monomers are: ethylene; propylene; 1-butene; 1-pentene; 1-hexene; 4-methyl-1-pentene; 3-methyl-1-pentene; 3,3-dimethyl-1-butene; 3-methyl-1-hexene; 2,4,4-trimethyl-1-pentene. According to special embodiments of this invention the alpha-olefinic monomers comprising 2 to 8 carbon atoms. Amongst the terpolymers the preferred one are the ethylene-propylene-diene terpolymers containing from 25% to 50% by weight of unit of copolymerized propylene. As olefinic plastomers there may be used the polymers obtained by the polymerization of one or more mono-olefines through processes at either low or high pressure, such as for instance: polyethylene, polypropylene, poly-butene-1, poly-4-methyl-1-pentene, poly-1-hexene, poly-5-methyl-1-hexene, poly-3-methyl-1-pentene. According to special embodiments of the invention the polymers are built up from recurring units containing 2 to 8 carbon atoms. The corresponding elastomeric component/plastomeric component ratios in the compositions may vary from 20% to 60% by weight of plastomeric polymer and from 80% to 40% by weight of elastomeric polymer on the mixture of the two. Preferably one uses from 70% to 40% of elastomeric terpolymer and from 30% to 60% of plastomeric polymer on the mix. The non-halogenated resins that are part of the vulcanizing system used for the purposes of this invention, are compounds which fall under the following general formula: wherein: X₁, X₂, equal to or different from each other, are -CH₂- radicals or -CH₂-O-CH₂- radicals; R = an alkyl, aryl or alkenyl radical containing from 4 to 16 carbon atoms; n = an integer comprised between 0 and 6, extremes included. If substituent R is an alkyl group it contains preferably 4 to 8 carbon atoms. Said compounds are known to the Prior Art and may be prepared by condensation of alkylphenols with formaldehyde according to the techniques described in the literature for instance in "Kunststoffe", vol. 52 (1962), p. 19-21. Further references to such compounds and to their preparation may be found in: "Caoutchoues et plastiques", No. 599, of March 1980, page 73, and in: "Industrial and Engineering Chemistry", volume 51, No. 8, August 1959, page 937. The metal compounds which, together with the above mentioned phenolic resins, form the vulcanization system used for the purposes of this invention, are represented by the zinc oxide, calcium, magnesium and iron oxides, by titanium dioxide, by alumina, silicon dioxide and by calcium carbonate. Thus, object of the present invention is that of providing a process for the preparation of plastoelastomeric compositions, process that consists in subjecting to mastication a mixture formed of from 20% to 60% by weight of an olefinic polymer and from 80% to 40% by weight of an unsaturated elastomeric terpolymer consisting of two α-olefinic monomers and of one dienic monomer, in the presence of a crosslinking system free of halogen donators and comprising between 1 and 10 parts by weight for 100 parts b.w. of such a terpolymer of a non-halogenated phenolic resin as previously defined, and a metal compound, in a ponderal ratio, metal compound/phenolic resin, comprised between 1:1 and 5:1, chosen from amongst: the oxides of zinc, magnesium, calcium, iron and titanium, calcium carbonate, silica and alumina, at a temperature sufficient for melting said olefinic polymer, and for a dwell time sufficient for obtaining a homogeneous mixtures, and by then carrying on the mastication at a temperature at which there occurs an at least partial cross-linking of the elastomeric terpolymer. The mastication and cross-linking process may be carried out either in a closed mixer or in an extruder or again in a system consisting of a closed mixer combined with a granulator. It is also possible, however, to operate in a plurality of machines arranged in a sequence, where in a first set of machines there is achieved a thorough mixing and homogenizing of the composition, while in the successive set of machines there is carried out the cross-linking, while still carrying on the mixing or mastication. The mixing or mastication operation before cross-linking is aimed at obtaining a thorough and homogeneous mixing through of the elastomer in the molten plastomeric component with the elastomer in the form of particles in the size of one or few microns, but preferably comprised between 0.5 and 1 µm. In general, the temperature at which there occurs the cross-linking, is comprised between 170° and 250°C. The mastication time at the cross-linking temperature depends on the degree of cross-linking that one wishes to achieve in the elastomer. Preferably the quantity of cross-linked elastomer in the final composition is maintained between 30% and 90% by weight of the total quantity of elastomer present in the composition. In the mix that is subjected to mastication and cross-linking there may be present mineral fillers, carbonblack, coloured pigments, plasticizers, stabilizing agents, extension oils, and in general any other classical ingredients of the compositions based on EPDM rubbers, provided that they are not halogen-donors. By the term "halogen-donors" are meant such organic or inorganic halogenated compounds, also of the polymeric type, that are capable of yielding one or more halogen or halogenhydric acid atoms or molecules, under the above indicated cross-linking conditions. Examples of such compounds may be: metal halides, especially ferric chloride and stannous chloride, the halides of organo-stannic compounds, chlorinated paraffins, the halogenated resins and rubbers such as chlorinated or chlorosulphonated polyethylene, polychlorobutadiene, etc. The following examples are just given for more clearly illustrate the inventive idea of the invention, without, however in any way limiting its indicated scope. Example 1 Operating in a closed mixer, there were prepared plasto-elastomeric compositions, using the following components in the quantities indicated on Table 1: EPDM elastomer, consisting of 28% b.w. of propylene, 67.2% by weight of ethylene and 4.8 b.w. of ethylidene-norbornene, said elastomer having a density = 0.87 g/ml, a Mooney (ML 121°C) viscosity = 28, and extended with 30% by weight of paraffin oil. polypropylene; phenol-formaldehyde resin of the resolic type, of the formula: zinc oxide. The polymeric compounds were fed all together into the mixer and, after a short period of mixing, the mixture was additioned with phenolic resin and then with zinc oxide. The mixing operation was continued until achieving the melting of the polypropylene (i.e. at about 165°C) and was then carried on until attaining cross-linking temperature, that is until obtaining the cross-linking of the elastomer at the desired degree. The temperature attained-in the cross-linking stage was comprised between 180° and 200°C. The composition was then discharged from the mixer and subjected to the following determinations: % of cross-linked EPDM, by means of solubility tests in xylol at 125°C; processability by measuring the head pressure in extrusion tests in an extruder. In those tests the extruder was of the TR 1S type and operated at a temperature of 230°C, with a spinneret of 2 mm diameter and a screw ratio L/D = 20, and with an output rate of 6.8 g/minute. tension set at 75%, measured at 100°C, according to ASTM D-412 rules, on a test piece punched out from an injection molded ASTM specimen. On Table 1 have been recorded, besides the quantities of the products used in the mixing, also the characteristics of the compositions obtained. Exmple 2 It was operated as in example 1, except that as an elastomer there was used an EPDM elastomer containing 29% by weight of propylene, 67.5% by weight of ethylene and 3.5% by weight of ethylidenenorbornene, showing a density equal to: 0.8 g/ml, a Mooney viscosity (ML 121°C) = 65, and not extended with oils. On Table 2 there have been recorded the quantities of the products used in the mixing as well as the characteristics of the compositions obtained. Example 3 Using a closed mixer there were prepared plasto-elastomeric compositions using the following polymeric components and phenolic resins, in the quantities indicated on Table 3. EPDM elastomer of example 1, expanded with 30% by weight of paraffin oil; polypropylene similar to that of example 1; polyethylene having a density = 0.960 g/ml; not halogenated phenolic resin, similar to the one of example 1; bromided phenolic resin of the formula: The operational conditions were similar to those indicated in example 1. On Table 3 have been recorded the products used in the mixing, their quantity as well as the characteristics of the compositions obtained, determined according to the procedures described in example 1, when not otherwise indicated.

Claims: 1. Process for the preparation of plasto-elastomeric compositions, consisting in subjecting to mastication a mix consisting of 20% to 60% by weight of an olefinic polymer, and from 80% to 40% by weight of an unsaturated elastomeric terpolymer consisting of two α-olefinic monomers and of a dienic monomer, in the presence of a cross-linking system free of halogen donors and comprising: (a) up to 10 parts by weight, for 100 parts by weight of said terpolymer, of a non-halogenated phenolic resin of the following general formula: wherein: X₁, X₂, equal to or different from each other, are -CH₂ or -CH₂-O-CH₂- radicals; R = alkyl, aryl or alkenyl radical, containing from 4 to 16 carbon atoms; n = an integer comprised between 0 and 6, extremes excluded; and (b) a metal compound chosen from amongst zinc oxide, magnesium oxide, iron oxide, titanium dioxide, calcium oxide, aluminia, silica and calcium carbonate, in a ponderal ratio with the phenolic ratio with the phenolic resin comprised between 1:1 and 5:1; at a temperature sufficient for melting said olefinic polymer and for a duration sufficient for obtaining a homogeneous mixture, and by then continuing with the mastication at a temperature at which there will occur at least a partial cross-linking of the elastomeric terpolymer. 2. Process according to claim 1, characterized in that said mixture contains from 70% to 40% by weight of elastomeric terpolymer and from 30% to 60% by weight of olefinic polymer. 3. Process according to claims 1 or 2, characterized in that the elastomeric terpolymer is an ethylene/propylene/diene terpolymer containing from 25% to 50% by weight of copolymerized propylene units. 4. Process according to any of claims 1 to 3, characterized in that the phenolic resin is used in a quantity comprised between 1 and 5 parts by weight per 100 parts by weight of elastomeric terpolymer. 5. Process according to any of claims 1 to 4, characterized in that the ponderal ratio between the metal compound and the phenolic resin is comprised between 1:1 and 3:1. 6. Plasto-elastomeric compositions obtainable according to the process of any of claims 1 to 5.

Inventors: DANESI, SERGIO, FORTI, SERGIO, MANICA, MICHELE
Applicants: MONTEDISON S.P.A.
Application year: 1981
Main classification: C08L23
IPC codes: C08L21, C08K3, C08L7, C08L61, C08L23, C08L57, C08L101