Patent Description:
Elastomeric parts are used in various applications in which two rigid parts subject to relative movement need to be connected; this may be the case for instance with ducts for fluids (for instance in the motors or other parts of vehicles), or gaskets that must be capable of retaining their function (preventing the leakage of fluids, in particular water) upon vibration of the parts between which they are positioned, as in the case of gaskets for doors of washing machines.

These parts must have a combination of properties, in particular a hardness in a given range, chemical inertness and retention of their mechanical properties in the range of operating temperatures of the intended application.

Besides, the compositions these parts are made of are thermoplastic, thus allowing the production of the parts, often with relatively complex shapes, by injection molding or similar methods.

Thermoplastic elastomer compositions with specific sets of properties are known in the art.

Patent application <CIT> discloses a composition for a gasket, including a hydrogenated styrene-based block copolymer and about <NUM> to <NUM> parts by weight of a petroleum-based softener, about <NUM> to <NUM> parts by weight of a polyolefin-based resin, about <NUM> to <NUM> parts by weight of an inorganic filler, and about <NUM> to <NUM> parts by weight of a heat-resistant polymer, wherein the parts by weight of the cited components are based on <NUM> parts by weight of the hydrogenated styrene-based block copolymer. The composition of this document is said to have good tensile strength and heat resistance.

Patent <CIT> describes thermoplastic elastomer compositions comprising <NUM> to <NUM> parts by weight of a block terpolymer including an aromatic vinyl compound and an alkene compound; <NUM> to <NUM> parts by weight of a paraffin oil; <NUM> to <NUM> parts by weight of a polyolefin resin; <NUM> to <NUM> parts by weight of an inorganic additive; and <NUM> to <NUM> parts by weight of a polyphenylene ether. The declared properties of the composition of this document are surface hardness and resistance to high temperatures.

Patent <CIT> describes A thermoplastic elastomer composition comprising (by weight) <NUM> to <NUM>% of a block terpolymer of an aromatic vinyl compound and alkene or a conjugated diene-based compound; <NUM> to <NUM>% of a paraffin oil; <NUM> to <NUM>% of a polyolefin-based resin; <NUM> to <NUM>% of an inorganic additive; and <NUM> to <NUM>% of a polyphenylene ether-based resin. Among the stated advantages of this composition are a surface hardness of <NUM> to <NUM> A (shore A) and high temperature resistance.

Finally, international patent application <CIT> describes a thermoplastic elastomer comprising (by weight): <NUM> to <NUM>% of a hydrogenated triblock copolymer; <NUM> to <NUM>% of a non-aromatic oil; <NUM> to <NUM>% of a polyolefin resin; <NUM> to <NUM>% of an inorganic filler; <NUM> to <NUM>% of a poly(phenylene ether) based resin; and <NUM> to <NUM>% of a silicone resin; optionally, the composition may further comprise between <NUM> and <NUM> parts by weight of a metal or a metal oxide per <NUM> parts by weight of the sum of the other components. The non-aromatic oil is said to be a paraffin oil, or a mixture, possibly with a naphthenic oil, including at least <NUM>% by weight, preferably at least <NUM>% by weight, of a paraffin oil; all the examples are about compositions prepared with <NUM>% paraffin oil as the non-aromatic oil. The inventors declare that these elastomers have low hardness, high strength, high surface hardness, and abrasion resistance.

Despite the declared good properties of the compositions cited above, these are still not sufficient for recent appliances, in particular those in which the elastomeric part has highly convoluted cross-sections suitable for instance for application in washing machines of reduced size. In a campaign of tests, the present inventors prepared bellows with a very compacted shape, repeating the recipes and reproducing the compositions in the prior art; when subjected to abrasion tests, the bellows so produced yielded unsatisfactory results, giving rise to breaking of the bellow before reaching <NUM>,<NUM> attrition cycles. The known compositions thus do not lend themselves to easy forming by injection molding in highly elaborated shapes; besides, the compositions of the prior art do not present the necessary resistance to wear do to rubbing of the different sections of the elastomeric part, leading to failure (formation of fractures) upon a number of cycles of vibration that is lower than the desired working life of the appliance.

It is thus an object of the present invention to provide a thermoplastic elastomeric composition characterized by easy formability and a high wear resistance, a process for producing the composition, as well as elastomeric parts produced with the composition.

These objects are obtained with the present invention that, in a first aspect thereof, refers to a thermoplastic elastomeric composition comprising the following components:.

The compositions of the invention may optionally comprise up to <NUM>% of one or more other additives, cumulatively referred to in the description as component (H).

In its second aspect, the invention refers to a process for the production of a composition as defined above, comprising feeding the solid components of the composition to an extruder partly through a main hopper at the beginning of the extruder and partly through one or two lateral dosing stations (side feeders), and injecting the liquid components into the extruder in one or several feeding ports between the beginning of the extruder and half its length, maintaining the temperature profile of the extruder between <NUM> and <NUM>. The composition leaving the extruder head is preferably cut into pellets with a head cutting and cooling system.

In its third aspect, the invention is about an elastomeric part produced with the composition described above.

In the description that follows, the amounts of components (A) to (G) and of optional component (H), making up the compositions of the invention, are given in terms of percent by weight (abbreviated wt%) unless specified otherwise.

In its first aspect, the present invention refers to a thermoplastic elastomeric composition that has proven particularly easy to form by injection molding and that allows to produce shaped articles with a very high resistance to abrasion wear.

The first component, (A), of the compositions of the invention, is a hydrogenated triblock copolymer.

Hydrogenated triblock copolymers useful for the aims of the invention are hydrogenated Styrene-Ethylene-Propylene-Styrene (referred to in the field with the acronym SEPS), hydrogenated Styrene-Butadiene-Styrene (SBS), hydrogenated Styrene-Isoprene-Styrene (SIS), hydrogenated Styrene-Isoprene-Butadiene-Styrene (SIBS), hydrogenated Styrene-Ethylene/Propylene block copolymer (SEP), hydrogenated Styrene-Ethylene/(Ethylene/Propylene)-Styrene (SEEPS) and, preferably, hydrogenated Styrene-Ethylene-Butadiene-Styrene (SEBS). The hydrogenated triblock copolymer must have a Melt Flow Index < <NUM> (measured according to ASTM D <NUM>, g/<NUM>, <NUM>, <NUM>) and a content of styrene between <NUM> and <NUM> wt%.

The hydrogenated triblock copolymer is present in the compositions of the invention in an amount between <NUM> and <NUM> wt%, preferably between <NUM> and <NUM> wt%, of the overall weight of the composition.

In a preferred embodiment, the hydrogenated triblock copolymer employed in the compositions of the invention has a very high molecular weight, such that a solution at <NUM> wt% of the polymer in toluene has a viscosity of at least <NUM> cP when measured at <NUM> following the procedure of standard ASTM D2196-<NUM> Method A.

The second component, (B), of the compositions of the invention, is a naphthenic oil, in an amount between <NUM> and <NUM> wt%, and preferably between <NUM>-<NUM> wt%, of the overall weight of the composition.

Naphthenic oil is a complex mixture of hydrocarbons obtained by treating a petroleum fraction with hydrogen in the presence of a catalyst. It consists of hydrocarbons having carbon numbers mostly in the range of C20 through C50, with a relatively low amount of paraffins, and is identified with <NPL>.

The amount of naphthenic oil in the compositions of the invention is relatively high. Known compositions designed for similar applications as the ones of the present invention generally contain paraffinic oils as softeners. The use of a naphthenic oil as softener was foreseen in the compositions disclosed in patent application <CIT>; however, this document teaches compositions in which the softener (that may be either a naphthenic or a paraffinic oil) is present in amounts between about <NUM> to <NUM> parts by weight per <NUM> parts by weight of a hydrogenated styrene-based block copolymer, namely, a weight ratio softener:copolymer lower than <NUM>; the document also reports at the end of paragraph [<NUM>] that, when the content of the softener exceeds <NUM> parts by weight (namely, a weight ratio softener: copolymer higher than <NUM>), the composition becomes viscose due to oil bleeding, thus being readily contaminated and hardening upon ageing in operation and is thus unsuitable as material for producing gaskets. The present inventors have instead surprisingly found that with the specific compositions of the invention, in which the weight ratio softener: copolymer is between <NUM> and <NUM>, and comprising the further components specified above, said drawbacks are not observed and the articles produced with these compositions have the useful properties stated above.

Naphthenic oils useful for the aims of the invention have a kinematic viscosity according to ASTM D <NUM> in a range <NUM>-<NUM><NUM>/s, preferably between <NUM>-<NUM><NUM>/s, at <NUM>. Oils with these characteristics are commercially available and are sold for instance by Oleotecnica S. of Segrate (Milan), Italy, under the tradename NYSOL.

Component (C) of the compositions of the invention is a polyolefin resin. This component is present in the compositions of the invention in an amount between <NUM> and <NUM> wt%, preferably between <NUM>-<NUM> wt%. The polyolefin is preferably polypropylene (PP), ethylene-propylene copolymer (EP), polyethylene (PE), thermoplastic polyolefins (TPO) and mixtures thereof. The Melt Flow Index (MFI) of the polyolefin is < <NUM>/<NUM> as measured according to ISO <NUM> (<NUM>,<NUM>, <NUM>).

Component (D) of the compositions of the invention is a polyphenylene ether, of minimum purity <NUM>%, that is present in the compositions in an amount of between <NUM> and <NUM> wt%, preferably between <NUM>-<NUM> wt%. Examples of polyphenylene ether resins useful for the aims of the invention are poly(<NUM>,<NUM>-dimethyl-<NUM>,<NUM>-phenylene)ether, poly(<NUM>,<NUM>-diethyl-<NUM>,<NUM>-phenylene)ether, poly(<NUM>,<NUM>-dipropyl-<NUM>,<NUM>-phenylene)ether, poly(<NUM>-methyl-<NUM>-ethyl-<NUM>,<NUM>-phenylene)ether, poly(<NUM>-methyl-<NUM>-propyl-<NUM>,<NUM>-phenylene)ether, poly(<NUM>-ethyl-<NUM>-propyl-<NUM>,<NUM>-phenylene)ether, poly(<NUM>,<NUM>-diphenyl-<NUM>,<NUM>-phenylene)ether, copolymers of poly(<NUM>,<NUM>-dimethyl-<NUM>,<NUM>-phenylene)ether and poly(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>,<NUM>-phenylene)ether, copolymers of poly(<NUM>,<NUM>-dimethyl-<NUM>,<NUM>-phenylene)ether and poly(<NUM>,<NUM>,<NUM>-triethyl-<NUM>,<NUM>-phenylene)ether, and the like, and combinations thereof. A preferred polyphenylene ether for the aims of the invention is poly(<NUM>,<NUM>-dimethyl-<NUM>,<NUM>-phenylene)ether, having molecular formula (C<NUM>H<NUM>O)n, alone or as a copolymer with poly(<NUM>,<NUM>,<NUM>-trimethyl-<NUM>,<NUM>-phenylene)ether having formula (C<NUM>H<NUM>O)n. The polyphenylene ether resin may have a weight average molecular weight of about <NUM>,<NUM> to about <NUM>,<NUM>/mol, for example about <NUM>,<NUM> to about <NUM>,<NUM>/mol, a bulk density between <NUM> and <NUM>/dm<NUM> as measured according to ISO <NUM>, and a degree of polymerization corresponding to an intrinsic viscosity of about <NUM> to about <NUM> dL/g, as measured in chloroform as a solvent at <NUM>.

Component (E) is a filler and is present in the compositions in an amount between <NUM> and <NUM> wt%, preferably between <NUM> and <NUM>% by weight. The filler is employed in the form of powders with a grain size between <NUM> and <NUM>. Preferably, the filler is an inorganic material such as, for instance, talc, clay, calcium carbonate, silica, kaolin, calcined kaolin, iron oxide, glass fibers, mica, titanium dioxide, carbon black, graphite, wollastonite, or mixtures thereof; the filler is preferably talc and, more preferably, calcium carbonate.

Component (F) is a liquid silicone oil and is present in the compositions in an amount between <NUM> and <NUM> wt%, preferably between <NUM>-<NUM> wt%. This component is a liquid (thus, not a silicone gum or resin) having a viscosity between <NUM> and <NUM><NUM>/s measured according to ASTM D445.

Finally, component (G) of the compositions of the invention is one or more compounds selected among amides (comprising oleamide, erucamide and so on), silicone resins (comprising ultra-high molecular weight silicone with a molecular weight close to <NUM>,<NUM>/mol and high molecular weight silicon with a lower Mw but anyway available as a solid material) and polyurethanes (PU, TPU based on polyester and TPU based on polyether); these compounds have a synergistic effect with the liquid silicone oil imparting excellent resistance to wear to the final thermoplastic elastomer. This component (one or a mixture of the cited compounds) is present in the compositions of the invention in amounts between <NUM> and <NUM>%, preferably between <NUM> and <NUM>% by weight.

The compositions of the invention may optionally comprise up to <NUM>% of one or more other additives, cumulatively referred to in the description as component (H). This component may be one, or a mixture of, additive(s) known in the field, such as reinforcing agents, flame retardants, antimicrobial agents, UV blocking agents, hindered amine light stabilizers, antioxidants, etc..

Compared to the compositions of the prior art, the ones of the present invention have a relatively lower content of hydrogenated triblock copolymers (component (A)): this allows for higher wt% contents of the remaining components, in particular the polyphenylene ether (component (D)) and the sum of components (F) and (G). These differences in composition allow to produce parts with excellent physical and mechanical properties. In particular, these parts have Shore A hardness in the range <NUM>-<NUM> as measured according to the ISO <NUM> A (<NUM> seconds of application of force on the presser foot), a compression set, measured according to the ISO <NUM> standard, lower than <NUM>% with compression at <NUM> for <NUM> and lower than <NUM>% with compression at <NUM> for <NUM>.

In addition, the compositions of the invention show a much higher resistance to abrasion than similar compositions of the prior art: the inventors have observed that, in abrasion tests carried out as described in the experimental part, parts produced with the compositions of the invention typically resist to at least <NUM>,<NUM> abrasion cycles at <NUM>, compared less than <NUM>,<NUM> cycles of a composition of the prior art, and to at least <NUM>,<NUM> abrasion cycles at <NUM> compared to less than <NUM>,<NUM> cycles of a composition of the prior art.

In its second aspect, the invention refers to a process for producing a thermoplastic elastomeric composition described above.

The compositions described above can be produced using commercial compounders, preferably with twin-screw extruders, more preferably with co-rotating twin-screws extruders.

The high naphthenic oil/hydrogenated triblock copolymer weight ratio according to invention, at least equal to <NUM>, allows processability with twin-screw extruders even using hydrogenated block copolymers with very high viscosities, for example ones with a measured melt flow index < <NUM> at <NUM> (load <NUM>) according to the ASTM D <NUM> standard; in turn, the high viscosity of the triblock copolymer implies a high molecular weight and therefore of the ability to retain the plasticizer avoiding exudations. The silicone oil of the compositions of the invention imparts to the surface of the parts produced thereby a wet-like appearance, which is not however linked to phenomena of release of liquid components from said parts. This combination of features makes possible to obtain articles that retain their mechanical properties in time, avoiding hardening that could lead to failures of the same.

The solid components are partly introduced into a main loading hopper at the beginning of the extruder and partly through one or two lateral dosing stations (side feeders), while the liquid components are injected into the extruder in one or several feeding ports between the beginning of the extruder and half its length.

The loading of the components takes place through the use of gravimetric dosers of single components or pre-weighed mixtures of the same; it would also be possible to use volumetric dosers if these are precisely synchronized; gravimetric dosers are preferred due to the ease of maintaining the desired weight ratio among the different components.

The temperature profile of the extruder is variable depending on the specific composition; generally, this temperature is between <NUM> and <NUM>.

The composition leaving the extruder head is then preferably cut into small pellets with the classic head cutting and cooling system.

In its third aspect, the invention is about manufactured articles obtained with the compositions described above. These compositions have proven particularly suitable for forming parts with complex and convoluted shapes by injection molding. Elastomeric parts that can be produced with the compositions of the invention are bellows and, particularly, gaskets for washing machine doors.

The invention will be further described by the examples that follow.

In the experiments, the following instruments and materials were employed:.

This example is about the production of three compositions of the invention and, for comparison, of two compositions according to the prior art. In the following, the three compositions according to the invention are indicated respectively as I1, I2 and I3, while the compositions of the prior art are indicated as C1 and C2; these latter are according to <CIT> and <CIT>, respectively.

The components indicated in Table <NUM> below were compounded in a twin-screws extruder in the reported weight percent amounts:.

In composition I3, component A is of the preferred kind, namely, with high MW giving rise to a solution at <NUM> wt% in toluene with a viscosity ≥ <NUM> cP when measured at <NUM> according to standard ASTM D2196-<NUM> Method A.

Composition C2 is not reported as such in <CIT>: it has been produced using the minimum amount of component A allowed by this prior art document, and using a <NUM>:<NUM> mixture of paraffin oil and naphthenic oil as softener; these characteristics have been chosen to obtain a composition as close as possible, remaining within the limits of said document, to the compositions of the present invention, in order to highlight the different and advantageous results obtained by the latter.

For the production of the compositions of the invention, the components SEBS, EP, antioxidants, UHMW silicone + oleamide and PPE were dosed in the main hopper of the extruder; CaCO<NUM> was added through lateral doser in the middle of the extruder; naphthenic oil was dosed with an injector at the beginning of the extruder; silicone was dosed with a second injector at the beginning of the extruder. Extruder temperatures are in the range <NUM>-<NUM>, speed at <NUM> rpm, output <NUM>/h.

For the production of the compositions of the prior art, the components were added following exactly the same process described above, in order to have comparable results.

This example is about the measure of abrasion resistance of the compositions of the invention and of the prior art.

The tests were carried out with an apparatus assembled in the laboratories of the applicant, schematically illustrated in <FIG>. In brief, the apparatus, <NUM>, comprises a roller <NUM> with a circular cross section and diameter <NUM>, onto which is wound a first specimen <NUM> of a composition under test completely covering the circular surface of the roller. The apparatus further comprises two clamps, <NUM> and <NUM>', for mounting a second specimen, <NUM>, of the composition under test, in the form of a tape; specimen <NUM> is kept taut against specimen <NUM> by a constant force due to a metallic part <NUM> of weight <NUM> attached to the lower clamp <NUM>'; the angle formed by the two sections of specimen <NUM> at the two opposite sides of roller <NUM> is of <NUM>°. The test is performed by rotating the roller <NUM>, and thus specimen <NUM>, at <NUM> rpm, and counting the number of cycles before break of specimen <NUM> by means of a counter <NUM>. A first series of test was carried out at <NUM> +/-<NUM>; a second series of test was carried out at <NUM> +/-<NUM> by positioning apparatus <NUM> into a climatic chamber.

The compositions obtained in Example <NUM> (both of the invention and of the prior art) were used to produce tapes of thickness <NUM>; specimens <NUM> in the tests had a width of <NUM> and were <NUM> ± <NUM> long.

The number of cycles required to break the specimens at the two test temperatures are reported in Table <NUM> below:.

The specimens produced with the compositions of the invention resist to a number of abrasion cycles more than ten times higher than the specimen of the prior art at <NUM>, and at least three times (and up to more than ten times) higher than the specimens of the prior art at <NUM>. Particularly remarkable are the results obtained with parts produced with composition I3, that, at both test temperatures, resist to abrasion for a number of cycles well above ten times the number of cycles reached before breaking by the specimens of the prior art.

Composition I1 produced as described in Example <NUM> was used for preparing specimens for stress-strain measures directed to determining the elongation at break of specimens having shape according to standard KSM <NUM>.

Three different production runs, referred to below as R1, R2 and R3, were carried out with the composition of the invention as described in Example <NUM>. With each produced composition, three specimens were produced by injection molding, indicated below as R#a, R#b and R#c.

Each specimen was tested for elongation at break with tests according to KSM <NUM> standards; the measures were carried out at <NUM>. The results obtained in the tests are reported in the Tables <NUM> and <NUM> below, reporting respectively the absolute values obtained in the tests and a statistical analysis of the same.

<FIG> reports graphically the trend of stress-strain behavior of three tested specimens, one for each of preparation runs R1, R2 and R3; the curve for only one specimen for preparation run is shown in the figure for representation clarity, since the three curves for the specimens of each preparation were very close. In particular, in <FIG> are presented the stress-strain curves obtained with specimen R1c (lower curve, dotted), with specimen R2c (middle curve, solid) and with specimen R3b (upper curve, dashed).

Similar results have been obtained with compositions I2 and I3 which, produced in a great number of production runs, displayed values of elongation at break between <NUM> and <NUM>% and ultimate loads between <NUM> and <NUM> Mpa at <NUM>.

Similar tests carried out at <NUM> on specimens prepared with compositions I1, I2 and I3 resulted in values of elongation at break between <NUM> and <NUM>%.

Particularly interesting is the behavior of the compositions of the invention compared to those of prior art regarding the trend of elongation at break at different temperatures: the compositions of both considered prior art documents show a decrease of the value of elongation at break with increasing temperature: see, in this regard, Table <NUM> in <CIT>, and Table <NUM> in <CIT>, the relevant data of which are reproduced below:.

This behavior of the compositions of the prior art has been confirmed by the present inventors that, in tests carried out on specimens produced with compositions C1 and C2, have measured values of elongation at break at <NUM> of <NUM>% for a specimen produced with composition C1, and of <NUM>% for a specimen produced with composition C2.

To the contrary, the compositions of the invention display values of elongation at break that increase when increasing the temperature.

An increase in elongation at break with increasing temperature, as displayed by articles produced with the compositions of the present invention (and contrary to the behavior of the compositions of the prior art) is useful where a product made with these compositions must stretch, bend or in any case be stressed in elongation by working at high temperatures, as it happens for instance with bellows of a washing machine working at <NUM> or a washer-dryer that works at temperatures as high as <NUM>.

Claim 1:
A thermoplastic elastomeric composition comprising:
(A) between <NUM> and <NUM>% by weight of a styrene hydrogenated triblock copolymer having a Melt Flow Index < <NUM> measured according to ASTM D <NUM> and a wt% of styrene between <NUM> and <NUM>;
(B) between <NUM> and <NUM>% by weight of a naphthenic oil;
(C) between <NUM> and <NUM>% by weight of a polyolefin resin having a Melt Flow Index ≤ <NUM>/<NUM> measured according to ISO <NUM>;
(D) between <NUM> and <NUM>% by weight of a polyphenylene ether;
(E) between <NUM> and <NUM>% by weight of a filler;
(F) between <NUM> and <NUM>% by weight of a liquid silicone oil having a viscosity between <NUM> and <NUM><NUM>/s measured according to ASTM D445;
(G) between <NUM> and <NUM>% by weight of one or more components selected among amides, silicone resins and polyurethanes.