Thermoplastic article

Abstract: Adhesive thermoplastic composition basically consisting of: 1) dynamically vulcanized thermoplastic elastomer; 2) polyethylene having a density equal to or less than 0.920 g/cm 3 ; 3) additives. The above composition is particularly useful for being firmly bound to articles made of EPM and/or EPDM vulcanized rubbers and for binding parts of vulcanized EPM and/or EPDM to each other.

Description: The present invention relates to articles consisting of at least a part of vulcanized rubber of the EPM or EPDM type and at least one thermoplastic elastomer, connected to each other so as to form a single element, with a thermoplastic composition with adhesive properties. In the production of some articles, for example curved joints used for welding two profiles of vulcanized elastomer to obtain a sealing gasket, there is the problem of applying a thermoplastic elastomeric component to a vulcanized rubber basically consisting of EPDM or EPM. It was thought that this could be possible using the known thermoplastic elastomeric blends, also called TPV, as thermoplastic elastomeric component. Thermoplastic elastomeric blends (TPV) are well-known in patent and scientific literature and are described in many reviews (see for example A.Coran in 'Thermoplastic Elastomers; a comprehensive Review", N.R. Legge, G. Holden, H.E. Schroeder eds., New York, 1987, page 130 onwards). The above TPV consist of a continuous plastic phase, generally a polyolefinic resin, in which a more or less vulcanized elastomer is dispersed, in the form of particles of 50 microns or less. As the polyolefin contained in the TPV forms the continuous phase, it could be expected that, from the point of view of adhesion, the TPV would behave similarly to the polyolefin. Patent US-A-4.537.825 underlines the fact that this behaviour does not occur when the TPV is to be bound, even without adhesives, to articles consisting of vulcanized EPDM or EPM. In particular US-A-4.537.825 specifies that it is possible to bind the TPV to vulcanized EPDM or EPM only when the content of rubber in the article to be welded is below certain values, more precisely less than 50% in volume. The problem remained of a still insufficient adhesion between the thermoplastic elastomer and the vulcanized rubber. The present invention overcomes the above drawback, allowing material to be obtained which is capable of adhering more firmly with respect to a traditional TPV, but at the same time maintaining its elasticity and aspect which are necessary for this kind of application. In accordance with this, the present invention relates to Articles comprising: i) one or more parts basically consisting of vulcanized EPDM or EPM rubber, joined in such a way as to form a single element with ii) one or more parts basically consisting of an adhesive thermoplastic composition basically consisting of: 1) a dynamically vulcanized thermoplastic elastomer (TPV) in a quantity of between i5 and 65% by weight, preferably between 25 and 45% by weight, even more preferably between 30 and 40% by weight; the above dynamically vulcanized thermoplastic elastomer consisting of a continuous phase with thermoplastic properties, mainly consisting of one or more polyolefins, in which a more or less vulcanized elastomeric phase is finely dispersed; 2) polyethylene having a density equal to or less than 0.920 g/cm 3 , in a quantity of between 85 and 35% by weight, preferably between 75 and 55% by weight, even more preferably between 70 and 60% by weight; 3) additives in a quantity of between 0 and 100, preferably between 10 and 80, even more preferably between 20 and 70, parts per 100 parts of the sum of (1) and (2). The term "additives" refers to mineral fillers, extension oils, antioxidants, processing aids, dyes, etc., substances well-known to experts in the field. Typical mineral fillers are silica, kaolin, barite, carbon black; typical processing aids are zinc oxide and stearic acid; typical antioxidants are phenols and sterically hindered amines. The extension oils can be of various kinds, for example, aromatics, naphthenes, paraffins, preferably paraffins. In a preferred embodiment, the vulcanized thermoplastic elastomer (TPV) has a content of polypropylene of between 15% and 70% by weight, preferably between 20% and 60% by weight, with respect to the total of polymers contained therein. The term polypropylene refers not only to the homopolymer deriving from the polymerization of propylene, but also copolymers of propylene having up to a maximum of 15%, preferably 10%, of other alpha-olefins. As mentioned above, vulcanized thermoplastic elastomers (TPV) are well-known in patent and scientific literature and all of them can be used as components of the adhesive thermoplastic composition of the present invention. Among the TPV known in patent literature, Santoprene (trade-name of a dynamically vulcanized thermoplastic elastomer of A.E.S. which is considered to contain polypropylene, EPDM, oil and fillers) and that described in Italian patent application IT-A-MI 94/A 01790, can be mentioned. The latter basically consists of: a) polypropylene, or copolymers of propylene with other alpha-olefins, in a quantity of between 15 and 70% by weight, preferably between 20 and 60% by weight; b) from 2 to 20%, preferably from 4 to 15% by weight of polyisobutene; c) from 20 to 70% by weight, particularly from 30% to 60% by weight of elastomeric terpolymer ethylene-propylene-diene (EPDM); d) from 0 to 35% by weight, preferably from 3 to 30% by weight of elastomeric copolymer ethylene - propylene (EPM); e) from 3 to 30% by weight, preferably from 5 to 20% by weight of polybutadiene; the percentage sum of the components from (a) to (e) being equal to 100; the sum of components (c), (d) and (e) normally being vulcanized in a percentage higher than 92%. The adhesive thermoplastic composition of the present invention is presumed to consist (but there is no exact experimental evidence) of two thermoplastic elastomeric phases of which one is continuous, and a dispersed elastomeric phase consisting of particles with dimensions of less than 50 µm. The term EPDM refers to elastomeric terpolymers containing from 20 to 60% by weight, preferably between 25 and 45% by weight, of propylene, from 40 to 75% by weight of ethylene and from 2% to 11% of non-conjugated dienes, for example, 1,4-hexadiene, norbornadiene, ethylidene-norbornene, dicyclopentadiene. The term EPM refers to elastomeric copolymers ethylene - propylene having a content of propylene of between 20 and 60% by weight, preferably between 20 and 45% by weight. The polyethylene used as component (2) of the adhesive composition of the present invention must have a density of less than 0.920 g/cm 3 . It is therefore possible to use as components of the present invention all the polyethylenes belonging to the group of VLDPE (very low density polyethylene), characterized by a density of less than 0.920, and among the LLDPE (linear low density polyethylene), only those having a density of less than 0.920. On the contrary, polyethylenes of the HDPE (high density polyethylene) and LDPE (low density polyethylene) type and LLDPE with a density higher than 0.920, are not part of the composition of the present invention. A further object of the present invention relates to a process for the preparation of the adhesive thermoplastic composition as defined above, the above process comprising the following steps: a) mixing of the TPV, polyethylene and possible additives in a mixer, preferably closed, even more preferably in an extruder, at a temperature of between 170 and 250°C, preferably between 200 and 230°C, until the components have been homogenized; b) recovery of the adhesive thermoplastic composition obtained in step (a). There is no criticality in the order of addition of the components in the above process. The temperature, on the other hand is critical, in the sense that it must be within the above range, in which the plastic component, usually polypropylene, melts. The process described above comprises the use of a commercial TPV which is mixed with the polyethylene and possible additives. Alternatively, if the TPV is self-produced by dynamic vulcanization, the adhesive thermoplastic composition of the present invention can be obtained by adding the polyethylene and possible additives immediately after the vulcanization step which forms the TPV As far as the inert products are concerned, these can already be sufficiently contained in the TPV, or they can be added, partially or totally, during the homogenization phase. It is preferably however for the possible additives to be already contained, either totally or partially, preferably totally, in the starting TPV When an extruder is used, the adhesive material is granulated at the outlet from the die. If a closed mixer of the Banbury type is used, the adhesive material thus prepared is transferred to an open mixer to obtain sheets which can granulated if desired. The granules thus obtained are used to make suitably shaped articles. The composition of the present invention has adhesive properties particularly with respect to vulcanized EPDE and/or EPM rubbers. These rubbers, containing varying quantities of fillers, oil, antioxidants and other additives normally used in this field, are vulcanized in accordance with the known techniques, for example with sulphur or peroxides. Owing to its adhesive properties, the composition of the present invention is particularly suitable for firmly adhering to articles basically consisting of vulcanized EPDM and/or EPM rubbers, and for binding parts of vulcanized EPM and EPDM to each other. The articles of the present invention can be obtained with the usual transformation techniques of thermoplastic materials, in order to obtain pieces, welded to EPM or EPDM rubber, of the desired shape, properties and appearance. Examples of these techniques are compression, injection, transfer and rotational moulding. All these techniques are in fact suitable for the contact and adhesion of the adhesive thermoplastic composition with the vulcanized EPDM or EPM. The articles of the present invention therefore comprise, for example, shaped articles of EPM and/or EPDM rubber welded together with joint elements consisting of the adhesive thermoplastic composition of the present invention. For example it is useful to remember sealing gaskets for car's wind-screens consisting of elements in vulcanized EPM or EPDM rubber welded to each other by curvilinear joint elements basically consisting of the adhesive thermoplastic composition of the present invention. The method used so far for the production of this type of gasket comprises the extrusion and subsequent vulcanization of a linear profile consisting of a composition containing EPDM. The profile was then cut and the pieces were welded in suitable moulds, in which the two pieces were then brought together, and a mixture in suitable EP(D) M was injected into the mould and then vulcanized. The process of the prior art has a first disadvantage due to the long operating times and a second one due to the production of many non-recyclable waste products, owing to the necessity of trimming to eliminate the flashes. According to the process of the present invention, the above articles are prepared by applying, by means of moulding, the adhesive thermoplastic material of the present invention to the profile of vulcanized rubber of the EPDM and/or EPM type. The process of the present invention has numerous advantages, among which the elimination of the vulcanization step and recycling of the material. The following examples provide a better understanding of the present invention. EXAMPLES The adhesion to EPDM of the thermoplastic composition of the present invention is evaluated by means of ultimate tensile strength tests on C type samples (ASTM D-412) of an average thickness of 2.5 mm., taken from plates with dimensions (13.6 x 6.8 cm) obtained by welding the adhesive thermoplastic material of the present invention in an injection press to a sheet of vulcanized EPDM, having dimensions of 6.8 x 6.8 cm and a thickness of 2.5 mm. The C type samples have, in the centre, the joining point between the vulcanized elastomeric phase and the adhesive composition of the present invention. The samples were stretched according to regulation ASTM D 412 relating to the ultimate tensile strength measurement. EXAMPLES 1-7 Table 1 shows the compositions and adhesion values of some thermoplastic compositions consisting of TPV and polyethylene (formulations 2 to 7) and TPV alone (formulation 1). Formulations 2 to 5 are a part of the present invention, whereas formulations 1, 6 and 7 should be considered comparative examples. The thermoplastic elastomeric materials of formulations 2 to 7 were obtained by mixing 50% by weight of Santoprene 73 and 50% by weight of different types of PE. In example 2 the polyethylene Clearflex MQFO, a polyethylene of the VLDPE type, is used, characterized by a density equal to 0.895 g/cm 3 , a melt flow index at 190°C of 13 g/10 min. and a melting point of 111°C. In example 3 the polyethylene Clearflex MQBO of the VLDPE type, is used, characterized by a density equal to 0.911 g/cm 3 , a melt flow index at 190°C of 13 and melting point of 116°C. In example 4, the PE used is Clearflex CHDO, a PE of the VLDPE type (density = 0.900, melt flow index = 2, melting point = 115°C). In example 5, Flexirene MS20 is used, a PE of the LLDPE type, with a density equal to 0.918, melt flow index = 26, melting point = 116°C. In comparative example 6, Eraclene MP90 is used, a PE of the HDPE type, having a density of 0.960 and melt flow index = 7. In comparative example 7, Riblene FC20 is used, a PE of the LDPE type, with a density equal to 0.922, a melt flow index = 0.27 and a melting point of 113°C. In all the formulations a composition is used in EPDM normally used for compact profiles and vulcanized with sulphur. This composition consists of 24% by weight of an EPDM (having a propylene content of between 25 and 30% and an ENB content (ethylidene norbornene) of between 3.5 and 5%), 22% by weight of oil, 39% of carbon black and 15% of mineral fillers, processing aids and vulcanizing agents. TEST 1C 2 3 4 5 6C 7C Santoprene 73 100 50 50 50 50 50 50 Clearfl. MQFO --- 50 --- --- --- --- --- Clearfl. MQBO --- --- 50 --- --- --- --- Clearfl. CHDO --- --- --- 50 --- --- --- Flexir. MS20 --- --- --- --- 50 --- --- Eraclene MP90 --- --- --- --- --- 50 --- Riblene FC 20 --- --- --- --- --- --- 50 Adhesion (MPa) 0.7 2.3 3.6 2.3 3.8 0.5 1.6 As can be clearly seen from the data of examples 2 to 5, the adhesive power of the compositions of the present invention increases considerably with respect to TPV alone (comparative example 1C). Compared to the compositions of the present invention, mixtures of TPV and Polyethylenes of the HDPE and LDPE type have much lower adhesive properties. EXAMPLES 8-12 Table 2 shows the compositions and adhesion values of some thermoplastic elastomeric materials. Formulations 9 to 11 form part of the present invention, whereas formulations 8 and 12 should be considered comparative examples. The TPV indicated in example 8 (comparative) belongs to those described in Italian patent application IT-A-Ml 94/A 01790. This TPV was obtained by the dynamic vulcanization of a composition consisting of 100 parts of EPDM, 50 parts of polypropylene, 10 parts of polybutadiene, 10 parts of polyisobutene, 3.5 parts of peroxide, 70 parts of extension oil, 50 parts of filler, 1 part of vulcanization coagent, 16 parts of processing aids. The polypropylene used in this TPV is a homopolymer having a fluidity degree (230°C and 216 N - ASTM D 1238/L) equal to 0.3 dg/g, specific weight of 0.9 g/cm 3 and a melting point of 160°C. The EPDM of this TPV has a content of propylene equal to 28% by weight, of ethylene of 68% and ethylidene-norbomene of 4%; the Mooney viscosity (1+4)125 is 43; the content of paraffinic oil is 40%. The butadienic rubber of the TPV has a Mooney viscosity ML(1+4)100 equal to 43 and a content of microstructure cis > 98%. The type of polyisobutene has an intrinsic viscosity of 3.7 dl/g in diisobutene and a specific weight of 0.92 g/cm 3 . The adhesive thermoplastic material of example 9-11 was obtained by mixing various percentages (see table 2) of the TPV described above and polyethylene. The percentages were calculated with the sum of the polymers contained in the adhesive TPV equal to 100 and the other additives are not considered. TEST 8C 9 10 11 12C TPV 100 62 35.5 15 --- Clearfl. MQBO --- 38 64.5 85 100 EPDM 1 1.6 3.2 5.5 6.2 6.5 EPDM 2 2.4 3.4 4.9 5.4 5.6 EPDM 3 1.4 2.7 4.2 5.7 4.6 EPDM 4 1.0 1.9 2.5 4.8 5.0 EPDM 5 1.5 2.7 4.2 4.9 4.9 EPDM1 indicates a composition of EPDM vulcanized with sulphur. The composition consists of 52% by weight of an EPDM (percentage of polypropylene of between 25 and 30% and ENB of between 3.5 and 5%), 14% by weight of oil, 29% of carbon black and 5% of processing aids and vulcanizing agents. EPDM2 indicates a composition of EPDM vulcanized with sulphur, consisting of 22% by weight of an EPDM (content of polypropylene of between 25 and 30% and ENB of between 3.5 and 5% by weight), 35% of oil, 41% of carbon black and 2% of processing aids and vulcanizing agents. EPDM3 indicates a composition of EPDM vulcanized with sulphur, consisting of 26% by weight of an EPDM (content of polypropylene of between 25 and 30% and ENB of between 3.5 and 5% by weight), 26% of oil, 36% of carbon black, 9% of mineral fillers and 3% of processing aids and vulcanizing agents. EPDM4 indicates a composition of EPDM usually used for compact profiles vulcanized with sulphur. The composition consists of 24% by weight of EPDM (content of polypropylene of between 25 and 30% and ENB of between 3.5 and 5% by weight), 22% of oil, 39% of carbon black and 15% of mineral fillers, processing aids and vulcanizing agents. EPDM5 indicates a composition of EPDM used for the production of compact clear shaped articles vulcanized with sulphur. The composition consists of 24% by weight of EPDM (content of polypropylene of between 30 and 35% and ENB of between 9 and 10% by weight), 13% of oil, 55% of mineral fillers and 8% of processing aids and vulcanizing agents. Compositions EPDM1 and EPDM2 correspond to the formulations A and F of example 1 of US-A-4.537.825. In fact in EPDM1 the content of EPDM is 65% by volume, whereas in EPDM2 the content of EPDM is 30% by volume, as described in US-A-4.537.825. From the data of table 2, in particular from the tests carried out on EPDM1, it can be clearly seen that the adhesive composition of the present invention proves to be efficient even when the content in volume % of EPDM is higher than 50%. It should be noted that US-A-4.537.825 specified that good adhesions could be obtained only on compositions containing an EPDM % of less than 50% by volume. The data of table 2 show how the adhesive properties increase with an increase in the quantity of polyethylene. Table 3 on the other hand indicates the other characterizations carried out on the same formulations as table 2. TEST 8C 9 10 11 12C Yield stress D638 (MPa) -- -- 4.8 6.1 7.9 Breaking stress D638 (MPa) 5.2 6.1 6.2 8.3 9.8 Elong. to break D638 (%) 220 235 435 680 740 Tens. Set D412 (%) 12 18 28 34 50 Vicat 1 kg 50°C/h D1525 (°C) 61.5 54.0 58.5 67.0 75.0 Shore A / after 5" D2240 70 80 84 90 90 Comparing the data of table 2 with those of table 3, it can be seen how the best balance between adhesive and elastomeric properties is obtained with formulation 10, corresponding to a weight ratio between the TPV (comprising the fillers) and polyethylene of 1/1. As the TPV used has a content of additives of 48% with respect to the total composition of TPV, the sum of the polymers contained in the adhesive TPV being 100, the percentage of additives contained in the formulations varies as follows: test 8c, 82%; test 9, 53%; test 10, 29%; test 11, 12%; test 12c, 0%.

Claims: Articles comprising: i) one or more parts basically consisting of vulcanized EPDM or EPM rubber, joined in such a way as to form a single element with ii) one or more parts basically consisting of an adhesives thermoplastic composition basically consisting of: 1) a dynamically vulcanized thermoplastic elastomer (TPV) in a quantity of between 15 and 65% by weight; the above dynamically vulcanized thermoplastic elastomer consisting of a continuous phase with thermoplastic properties, mainly consisting of one or more polyolefins, in which a more or less vulcanized elastomeric phase is finely dispersed; 2) polyethylene having a density equal to or less than 0.920 g/cm 3 , in a quantity of between 85 and 35% by weight; the sum of (1) and (2) being equal to 100: 3) additives in a quantity of between 0 and 100 parts per 100 parts of the sum of (1) and (2). Articles according to claim 1, characterized in that in the component ii) the vulcanized thermoplastic elastomer (1) is present in a quantity of between 25 and 45% by weight, the polyethylene (2) in a quantity of between 75 and 55% by weight, the additives (3) in a quantity of between 10 and 80 parts per 100 parts of the sum of (1) and (2). Articles according to claim 2, characterized in that the vulcanized thermoplastic elastomer (1) is present in a quantity of between 30 and 40% by weight, the polyethylene (2) in a quantity of between 70 and 60% by weight, the additives (3) in a quantity of between 20 and 70 parts per 100 parts of the sum of (1) and (2). Articles according to claim 1, characterized in that the vulcanized thermoplastic elastomer (1), the sum of the polymers contained therein being 100, has a content of polypropylene of between 15% and 70% by weight. Articles according to claim 4, characterized in that the vulcanized thermoplastic elastomer (1) has a content of polypropylene of between 20% and 60% by weight. Articles according to claim 1, characterized in that the thermoplastic elastomer (1) is obtained by the dynamic vulcanization of a polymeric composition basically consisting of: a) polypropylene, or copolymers of propylene with other alpha-olefins, in a quantity of between 15 and 70% by weight, preferably between 20 and 60% by weight; b) from 2 to 20%, preferably from 4 to 15% by weight of polyisobutene; c) from 20 to 70% by weight, particularly from 30% to 60% by weight of elastomeric terpolymer ethylene-propylene-diene (EPDM); d) from 0 to 35% by weight, preferably from 3 to 30% by weight of elastomeric copolymer ethylene-propylene (EPM); e) from 3 to 30% by weight, preferably from 5 to 20% by weight of polybutadiene; the percentage total of the components from (a) to (e) being equal to 100; the sum of components (c), (d) and (e) normally being vulcanized in a percentage higher than 92%. Articles according to claim 1, comprising: i) one part basically consisting of vulcanized EPDM or EPM rubber, joined in such a way as to form a single element with ii) one part basically consisting of the adhesive thermoplastic composition. Articles according to claim 1, comprising: i) two parts basically consisting of vulcanized EPDM or EPM rubber, joined to each other in such a way as to form a single element, by means of ii) one part basically consisting of the adhesive thermoplastic composition. Process for the preparation of articles according to claim 1 which comprises the welding of one or more parts of vulcanized EPM and/or EPDM rubber to the adhesive thermoplastic composition defined in claim 1, the above welding being carried out using moulding techniques selected from compression, injection, transfer and rotational moulding.

Inventors: CIACCIA VITTORIO, LONGO EUGENIO, PIANCASTELLI PATRIZIA, CIACCIA, VITTORIO, LONGO, EUGENIO, PIANCASTELLI, PATRIZIA
Applicants: POLIMERI EUROPA SPA, POLIMERI EUROPA S.P.A.
Application year: 1996
Main classification: C08L23
IPC codes: C09J123, C08L23, C08J5, C09J201