GB2332436A - Soft thermoplastic composition. - Google Patents

Abstract

A thermoplastic polyurethane (TPU) composition comprises:- a) 3 to 200 parts of a terpolymer of styrene α-methylstyrene/acrylonitrile/C 1 -C 6 alkyl acrylate with a glass transition temperature (Tg) below 0‹C; and b) 100 parts of a thermoplastic polyurethane produced from a diisocyanate, a C 2 -C 10 diol, and a polyether and/or polyester-based polyol. The resulting blend has a Shore hardness of less than or equal to 90 and is capable of adhering to a thermoplastic substrate material. Various additives including lubricants, pigments, stabilizers, etc, can be present in the composition in addition to (a) and (b), and optionally one or more compatibilizing polymers.

Description

SOFT THERMPLASTIC COMPOSITION 2332436 The invention relates to a soft

thermoplastic polyurethane (TPU) composition and, more particularly, to a low Shore A hardness, i.e., soft, TPU composition having high abrasion resistance.

Rigid thermoplastics such as ABS, glass-filled nylon 6, and polycarbonate are used for a variety of engineering and/or structural applications such as power tool housings, luggage handles, gear shifts, automotive pedals, etc. For many of these applications, there is a need to cover over or adjoin these articles to a soft, elastomeric layer. This layer serves to provide a comfortable, ergonomic feel, reduced slippage, and increased abrasion resistance. Ideally, this combination of ffhard" and "softff materials is produced through a thermoforming operation such as coinjection molding, multi-layer extrusion, or blow molding.

U.S. Patent No. 5,154,979 is directed to a shaped article and a method for making such an article. The article consists of a base made of a first thermoplastic polymer. An attachment made of a second thermoplastic polymer is welded on top of the base. One or both of the first polymer and second polymer must contain from 5 to 75 percent by weight, based on the mixture, of an olefin homopolymer and/or copolymer. Typical examples would include an engineering thermoplastic power tool body with a handle grip made of an elastomer such as TPU, Santoprene, or the like. Unfortunately, the article disclosed in the 1979 patent provides insufficient abrasion resistance in the elastomeric portion as well as being too hard for most uses which would require an elastomeric overlay.

Until now, most thermoplastic elastomers with the required softness (5 Shore A 90) to be useful as a soft covering, including propylene and ethylene-based EPDM polymers, styrenic block teror copolymers and plasticized PVC had insufficient adhesion to the rigid thermoplastic substrate unless affixed using separate adhesives or mechanical interlocking. Unfortunately, these soft TPEs have insufficient abrasion resistance for engineering applications. Although they have the desired Shore hardness, good adhesion and abrasion resistance, plasticized TPU (TPU blended with phthalate esters, such as DOP) is unacceptable due to the tendency of the plasticizer to migrate into the thermoplastic substrate and cause stress cracking.

1 2 The present invention provides a thermoplastic polyurethane (TPU) composition comprising a bland capable of adhering to a thermoplastic substrate material, wherein the thermoplastic polyurethane blend comprises:

a) 3 to 200 parts of a terpolymer of styrene/A-methylstyrene/ acrylonitrile/C1-C6 alkyl acrylate with a glass transition temperature (Tg) below OOC; b) 100 parts of a thermoplastic polyurethane produced from a diisocyanate, a C2-Clo diol, and a polyether and/or polyesterbased polyol; and c) is 0 to 50 parts of various additives including lubricants, pigments, stabilizers, etc.

The present invention is a TPU compound having a Shore A hardness 5 90. Preferably, the Shore A hardness is less than or equal to 80 and higher than 65. The TPU compound comprises:

a) 3 to 200 parts of a terpolymer of styrene/A-methylstyrene/ acrylonitrile/C1-C6 alkyl acrylate with a glass transition temperature below CC; b) 100 parts of a thermoplastic polyurethane produced from a diisocyanate, a C2-Clo diol, and a polyether and/or polyesterbased polyol; and c) 0 to 50 parts lubricants, pigments, stabilizers, etc.

The resulting composition has a Shore A hardness:5 90. The relative hardness of elastic materials such as rubber or soft plastics can be determined with an instrument called a Shore A durometer. If the indenter completely penetrates the sample, a reading of 0 is obtained, and if no penetration occurs, a reading of 100 results. The reading is dimensionless.

The materials above are combined together in a melt process, preferably using a twin-screw extruder.

Optionally, one or more UV stabilizers, one or more compatibilizers, and one or more additives selected from the group consisting of lubricants, and inhibitors, stabilizers against hydrolysis, heat stabilizers, flame retardants, dyes, pigments, inorganic and/or organic fillers and reinforcing agents may be added to the composition.

3 The TPUs usable according to the present invention can be prepared by reacting organic, preferably aromatic, diisocyanates, in particular 4,4'-diphenylmethane diisocyanate, with b) polyhydroxy compounds, preferably essentially linear polyhydroxy compounds, having molecular weights of from 500 to 8000, in particular polyalkylene glycol polyadipates having from 2 to 6 carbon atoms in the alkylene moiety and molecular weights of from 500 to 6000 or hydroxyl- containing polytetrahydrofuran having a molecular weight of from 500 to 8000, and diols as chain extenders having molecular weights of from the 60 to 400, in particular 1,4-butanediol.

in the presence of d) catalysts and optionally e) aids and/or f) additives at elevated temperatures.

Suitable organic diisocyanates for use in the manufacture of the TPUs of the invention are for example aliphatic, cycloaliphatic and preferably aromatic diisocyanates. Specific examples are:

aliphatic diisocyanates such as 1,6-hexamethylene diisocyanate, 2-methyllx5-pentamethylene diisocyanate, 2-ethyl-1, 4-butylene diisocyanate and mixtures of at least two of said aliphatic diisocyanates, cycloaliphatic diisocyanates such as isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1-methyl-2,4-cyclo- hexane diisocyanate and 1-methyl-2,6-cyclohexane diisocyanate and the corresponding isomeric mixtures, 4,41-, 2,41- or 2,21- or 2,21- dicyclohexylmethane diisocyanate and the corresponding isomeric mixtures and preferably aromatic diisocyanates such as 2,4-toluylene diisocyanate, mixtures of 2,4- and 2,6- toluylene diisocyanate, 4,41-,2,41- and 2,21-diphenylmethane diisocyanate, mixtures of 2x41- and 4x4l-diphenylmethane diisocyanate, urethane-modified liquid 4,41- and/or 2,41-diphenylmethane diisocyanates, 4,41-diisocyanato-1,2- diphenylethane, mixtures of 4,41-2,4- and 2,21-diisocyanato-1,2- diphenylethane, preferably those having a 4,41-diisocyanato-1,2-diphenylethane content of at least 95% by weight, and 1,5-naphthalene diisocyanate. Preference is given to using diphenylmethane diisocyanate isomer mixtures 1 4 having a 4,4'-diphenylmethane diisocyanate content of greater than 96% by weight and in particular essentially pure 4,41-diphenylmethane diisocyanate.

Preferred polyhydroxy compounds having molecular weights of from 500 to 8000 are polyetherols and in particular polyesterols. However, it is also possible to use other hydroxyl-containing polymers containing ether or ester groups as bridge members, for example polyacetals, such as polyoxymethylenes and in particular water-soluble formulas, e.g. polybutanediol formal and polyhexanediol formal, and polycarbonates, in particular those formed from diphenyl carbonate and 1,6-hexanediol, prepared by transesterification. The polyhydroxy compound must be at least predominantly linear, i.e., difunctional within the meaning of the isocyanate reaction. The polyhydroxy compounds mentioned may be used as individual components or in the form of mixtures.

Suitable polyetherols can be prepared from one or more alkylene oxides having from 2 to 4 carbon atoms in the alkylene moiety in a conventional manner, for example by anionic polymerization with alkali metal hydroxides, such as sodium hydroxide or potassium hydroxide, or alkali metal alcoholates, such as sodium methoxide, sodium ethoxide, potassium ethoxide or potassium isopropoxide, as catalysts and in the presence of at least one initiator molecule which contains 2 to 3, preferably 2 reactive hydrogen atoms, or by cationic polymerization with Lewis acids, such as antimony pentachloride, boron fluoride etherate, etc. or bleaching earth, as catalysts.

Preferred alkylene oxides are for example tetrahydrofuran, 1,3-propylene oxide, 1,2-butylene oxide, 2,3-butylene oxide and in particular ethylene oxide and 1,2-propylene oxide. The alkylene oxides may be used individually, alternately in succession or as mixtures. Suitable initiator molecules are for example: water, organic dicarboxylic acids, such as succinic acid, adipic acid and/or glutaric acid, alkanolamines, such as ethanolamine, N- alkylalkanolarrLines, N-alkyldialkanolamines, e.g. N-methyl- and N-ethyl- diethanolamine, and preferably dihydric alcohols which may contain ether linkages, e.g. ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, diethylene glycol, 1,5- pentanediol, 1,6-hexanediol, dipropylene glycol, 2-methyl- 1,5- pentanediol and 2-ethyl-1,4-butanediol. The initiator molecules may be used individually or as mixtures.

Pre---rence is given to using polyetherols from 1,2-propylene oxice and ethylene oxide in which more than 50%, preferably from 60 to 80%, or the OH groups are primary hydroxyl groups and where at least some of the ethylene oxide units are present as a terminal block. Such polyetherols can be obtained by, for example, polymerizing onto the initiator molecule first the 1,2-propylene oxide and then the ethylene oxide, or first the entire 1,2-propylene oxide mixed with some of the ethylene oxide and then the remainder of the ethylene oxide, or step by step first some of the ethylene oxide, then the entire 1,2-propylene oxide and then the remainder of the ethylene oxide. other preferred possibilities are the hydroxyl-containing polymerization products of tetrahydrofuran.

The essentially linear polyetherols have molecular weights of from 500 to 8000, preferably from 600 to 6000, in particular from 800 to 3500, the polyoxytetramethylene glycols preferably having molecular weights of from 500 to 2800. They can be used not only individually but also in the form of mixtures with one another.

Suitable polyesterols may be prepared for example from dicarboxylic acids of from 2 to 12, preferably from 4 to 6, carbon atoms and polyhydric alcohols. Suitable dicarboxylic acids are for example: aliphatic dicarboxylic acids, such as succinic acid, glutaric. acid, adipic acid, suberic acid, azelaic acid and sebacic acid, and aromatic dicarboxylic acids, such as phthalic. acid, isophthalic acid and terephthalic acid. The dicarboxylic acids can be used individually or as mixtures, for example in the form of a mixture of succinic acid, glutaric acid and adipic acid. To prepare the polyesterols it may be advantageous to use instead of the dicarboxylic acids the corresponding dicarboxylic acid derivatives, such as dicarboxylic monoesters or diesters having from 1 to 4 carbon atoms in the alcohol moiety, dicarboxylic anhydrides or dicarbonyl dichlorides. Examples of polyhydric alcohols are glycols of from 2 to 10, preferably from 2 to 6, carbon atoms, such as ethylene glycol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6- hexanediol, 1,10-decanediol, 2,2-dime- thylpropane-1,3-diol, 1,3-propanediol and dipropylene glycol. Depending on the properties which are desired, the polyhydric alcohols may be used alone or optionally mixed with one another.

It is also possible to use esters of carbonic acid with the diols mentioned, in particular those having from 4 to 6 carbon atoms, such as 1, 4-butanediol and/or 1,6-hexanediol, condensation products of ihydroxycarboxylic acids, e.g. i-hydroxycaproic acid, and preferably polymerization products of lactones, for example substituted or unsubstituted i-caprolactones.

1 6 Preferred polyesterols are ethanediol polyadipates, 1,4-butanediol polyadipates, ethanediol/1,4-butanediol polyadipates, 1,6hexanediol/neopentylglycol polyadipates, 1,6-hexanediol/1,4-butanediol polyadipates and polycaprolactones.

The polyesterols have molecular weights of from 500 to 6000, preferably from 800 to 3500.

Suitable chain extenders having molecular weights of from 60 to 400, preferably from 60 to 300, are preferably aliphatic diols of from 2 to 12 carbon atoms, preferably of 2, 4 or 6 carbon atoms, e.g. ethanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol and in particular 1,4-butanediol. However, it is also possible to use diesters of terephthalic acid with glycols of from 2 to 4 carbon atoms, e.g. bisethylene glycol terephthalate, 1,4-butanediol terephthalate, and hydroxyalkylene ethers of hydroquinone, e.g. 1,4-di-(B-hydroxyethyl)hydroquinone, and also polytetramethylene glycols having molecular weights of from 162 to 378.

To set the hardness index, the formative components can be varied within relatively wide molar ratios bearing in mind that the hardness increases with an increasing level of chain extenders.

To prepare relatively soft TPUs, which are especially preferred for use in the instant invention, for example those having a Shore A hardness of less than 90, it is advantageous to use the essentially difunctional polyhydroxy compounds (b) and the diols (c) in a molar ratio of from 1:0. 1 to 1:4.5, preferably from 1:0.5 to 1:4.0, so that the resulting mixtures of (b) and (c) have a hydroxy equivalent weight of greater than 200, in particular form 239 to 450, while greater than 200, in particular form 239 to 450.

Suitable catalysts, in particular for the reaction between the NCO groups of the diisocyanates (a) and the hydroxyl groups of the formative components (b) and (c), are the customary tertiary amines, such as triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N,NIdimethylpiperazine, diazabicyclo[2.2.-2]octane and the like, in particular organic metal compounds such as titanic esters, iron compounds, tin compounds, e.g. tin diacetate, tin dioctoate, tin dilaurate or the tin dialkyl salts of aliphatic carboxylic acids such as dibutyltin diacetate, dibutyltin dilaurate and the like. The catalysts are customarily used in amounts of from 0.001 to 0.1 parts by weight per 100 1 7 parts by weight of the mixture of polyhydroxy compounds and diols.

In addition to catalysts, the formative TPU components may also contain aids and/or additives. Examples are lubricants, inhibitors, stabilizers against hydrolysis, flame retardants, dyes, pigments, inorganic and/or organic fillers and reinforcing agents.

To prepare the TPUs, the formative components, i.e., diisocyanate compound, polyhydroxy compound, and one or more chain extenders, are made to react in the presence of a catalyst and in the presence or absence of aids and/or additives in such amounts that the equivalence ratio of the diisocyanate NCO groups to the total number of hydroxyl groups of the polyhydroxy and chain extender compounds is from 0.95 to 1.10:1, preferably 0.98 to 1.08:1, in particular approximately 1.0 to 1.05:1.

The TPUs which are usable according to the present invention and which customarily contain from 8 to 20% by weight, preferably from 8 to 16% by weight, based on the total weight, of urethane groups and have a melt flow index at 190C. under 21.6 kgs of from I to 500, preferably from 1 to 200, can be prepared by the extruder technique or the belt technique by batch wise or continuous mixing of components, reacting the mixture in an extruder or on a support belt at from 60 to 250C., preferably at from 70 to 150C, and then granulating the resulting TPUs. The reactor extruder technique, such as is well known in the art is most preferred. It may be advantageous to heat the resulting TPU at from 800 to 120'C preferably at from 1000 to 1100C., for a period of from I to 24 hours before further processing.

The one or more acrylate based rubbers of the composition generally comprise a terpolymer. An example of an illustrative com- mercially available material is Goodyear Chemicals' Sunigume.

one or more UV stabilizers may be used as additives which will preferentially absorb and dissipate energy by relieving excited molecules of excess energy and releasing it as heat. In general, the stabilizers preferred for use herein will be effective in the range of from 300 to 360 nm. An example of suitable UV and heat stabilizers are derivatives of o-hydroxybenzophenone, o-hydroxyphenyl salicylates, 2-(ohydroxyphenyl)-benzotriazoles, and hindered phenols.

I Sunigum@ is a registered trademark of Goodyear Chemical 8 It has been found that the particular TiV stabilizer compositions of the claimed invention surprisingly confer heat stability without the dulling and yellowing found in many prior art TJv-stabilized compositions.

Also suitable for use herein as UV stabilizers are hindered amine light stabilizers. Preferred UV stabilizers are those having active ingredients which are sterically hindered benzotriazol type stabilizers. It will be appreciated that many UV stabilizers are concentrates containing other materials in addition to the active ingredient. Particularly preferred active ingredients for use as TJV stabilizers are 2-(2-hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole, 1, 6-hexanediylbis(3-benzotriazolN-yl)-4-hydroxy-5-tertbutyl) phenyl propionate, and mixtures thereof.

In particular, the most preferred one or more UV stabilizers for use in the instant invention will be stabilizer concentrates containing the aforementioned most preferred active ingredients.

Such stabilizer concentrates will preferably further contain thermoplastic polyurethanes (TPU) and 1,3,5-triglycidyl-isocyanurate. Such UV stabilizer concentrates are discussed in DE 4211335 A, the disclosure of which is herein incorporated by reference. The most preferred UV stabilizer concentrates will contain approximately 40 to 80 weight percent of thermoplastic polyurethanes, 10 to 30 weight percent 1, 3,5-triglycidyl-isocyanurate and 10 to 30 weight percent 2-(2-hydroxy-3,5di-tertamyl-phenyl)-2H-benzotriazole, 1,6-he-xanediYlbis(3-benzotriazolNyl)-4-hydroxy-5-tert-butyl) phenyl propionate, and mixtures thereof.

In addition, the thermoplastic polyurethane compositions of the invention may further optionally contain one or more compatibilizing polymers. Such compatibilizing polymers are generally comprised of copolymers formed from styrene, alpha-methylstyrene, acrylonitrile, methacrylonitrile, butadiene, acrylate, and mixtures thereof. Preferred compatibilizers are poly(styrene-acrylonitrile) and ABS. Especially preferred is poly(styrene-acrylonitrile).

Finally, the thermoplastic polyurethane compositions of the invention may further optionally contain additives selected from the group consisting of lubricants, inhibitors, stabilizers against hydrolysis, flame retardants, dyes, pigments, inorganic and/or organic fillers and reinforcing agents. Particularly preferred additives are dyes and pigments. Titanium dioxide is a commonly used pigment. Of course, those skilled in the art will 1 9 appreciate that the incorporation of such dyes and pigments depends upon the desired appearance of the end use application.

With respect to the foregoing components of the thermoplastic polyurethane compositions of the invention, such compositions will preferably contain from 50 to 100% of one or more thermoplastic polyurethanes, from greater than 10 to 49% of one or more acrylate based rubbers, and from 0.1 to 5.0% of active ingredients of one or more UV stabilizers, as based on the total combined weight of the components.

More preferably, the thermoplastic polyurethane compositions of the invention will contain from 60 to 80% of one or more thermoplastic polyurethanes, from greater than 20 to 40% of one or more acrylate based rubbers, and from 1.0 to 4.0% of active ingredient of one or more UV stabilizers, as based on the total combined weight of the components.

If the thermoplastic polyurethane composition of the invention also comprises a compatibilizing polymer, such polymer should be present in an amount of from 1 to 10% as based on the total weight of the combined components. More preferably, the thermoplastic polyurethane composition comprising a compatibilizing polymer will contain less than 5% of the polymer, and most prefe- rably, will comprise from 2 to 4% of compatibilizing polymer. It will be appreciated that additives will be present in amounts dependent upon the desired end properties of the composition.

It will be appreciated that in the instant invention, thethermo- plastic polyurethane composition is a blend wherein the predominant matrix is comprised of thermoplastic polyurethane. Dispersed in said matrix are particles of one or more acrylate based rubbers. if present, compatibilizing polymer will serve as the interface between said acrylate based rubber particles and the TPU matrix. Also interspersed within the matrix TPU will be UV stabilizers.

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Claims (14)

1. A thermoplastic polyurethane composition comprising:

   a) 3 to 200 parts of a terpolymer of styrene/Amethylstyrene/acrylonitrile/C1-C6 alkyl acrylate with a glass transition temperature (Tg) below O'C; and b) 100 parts of a thermoplastic polyurethane produced from a diisocyanate, a C2-Clo diol, and a polyether and/or polyester-based polyol; wherein the thermoplastic polyurethane blend has a Shore a hardness of less than or equal to 90.
2. 2.

   The thermoplastic polyurethane composition of claim 1, further comprising one or more compatibilizing polymers.
3. 3. The thermoplastic polyurethane composition of claim 1, wherein the thermoplastic polyurethane composition is prepared using polyhydroxy compounds selected from the group consisting of polyetherols and polyesterols.
4. 4. The thermoplastic polyurethane composition of claim 3, wherein the thermoplastic polyurethane composition is prepared using polyetherols.
5. The thermoplastic polyurethane composition of claim 1, wherein the thermoplastic polyurethane composition is prepared using aromatic isocyanates.
6. The thermoplastic polyurethane composition of claim 1, wherein the thermoplastic polyurethane composition is prepared using diphenyImethane diisocyanate.
7. 7. The thermoplastic polyurethane composition of claim 1, wherein the acrylate terpolymer has a Tg less than 0 degrees C.
8. 8. The thermoplastic polyurethane composition of claim 7, wherein the acrylate terpolymer has from 40 to 85% C1-6 alkyl acrylate.
9. 9. The thermoplastic polyurethane composition of claim 1, further comprising a UV stabilizer comprised of one or more materials having an active ingredient selected from the group consisting of benzotriazole type stabilizers and hindered phenol type stabilizers.
10. 10. The thermoplastic polyurethane composition of claim 9, wherein the UV stabilizer comprises an active ingredient which is selected from the group consisting of 2-(2-hydroxy-3,5-di-tert-amyl-phenyl)-2H- benzotriazole 1,6-hexanediylbis(3-benzotriazol-N-yl)-4-hydroxy-5- tertbutyl) phenyl propionate and mixtures thereof.
11. 11. The thermoplastic polyurethane composition of claim 2 wherein the composition comprises from 1 to 10% of a compatibilizing polymer, as based on the total weight of components in the thermoplastic polyurethane composition.
12. 12. The thermoplastic polyurethane composition of claim 11 wherein the composition comprises less than 5% of a compatibilizing polymer, as based on the total weight of components in the thermoplastic polyurethane composition.
13. 13. The thermoplastic polyurethane composition of claim 12 wherein the composition comprises from 2 to 4% of a compatibilizing polymer, as based on the total weight of components in the thermoplastic polyurethane composition.
14. 14. The thermoplastic polyurethane composition of claim 2 wherein the compatibilizing polymer is an acrylonitrile/styrene copolymer.

    is. A thermoplastic polyurethane composition as claimed in claim 1 and substantially as hereinbefore described.