WO2001025331A1

WO2001025331A1 - Footwear made from a thermoplastic elastomer composition having a dull look

Info

Publication number: WO2001025331A1
Application number: PCT/EP2000/009764
Authority: WO
Inventors: Alan Michael Batt; Caroline Rita Nicole Maes; Eddy Verheyden; Philippe Vosters
Original assignee: Kraton Polymers Research B.V.
Priority date: 1999-10-06
Filing date: 2000-10-04
Publication date: 2001-04-12
Also published as: AU1133501A

Abstract

The invention relates to footwear made from a thermoplastic elastomer composition comprising (a) one or more styrenic block copolymers; (b) -optionally- one or more ingredients selected from extender oils, fillers, hardness regulators, flow improvers, flex crack resistance improvers, stabilisers, UV stabilisers, pigments, blowing agents, and anti-blocking agents; and (c) one or more metallocene-based polyolefins of ethene and from 8% to 40% by weight of an alpha-olefin comonomer having from 3 to 20 carbon atoms, having a density from 0.86 to 0.95 kg/l and a molecular weight distribution (Mw/Mn) less than 3.

Description

FOOTWEAR MADE FROM A THERMOPLASTIC ELASTOMER COMPOSITION

HAVING A DULL LOOK

Field of the invention

The invention relates to footwear made from a thermoplastic elastomer composition having a dull look. More in particular, the invention relates to footwear, such as in soles and heels. Background of the invention

Thermoplastic elastomer compositions are based on materials which behave like elastomeric rubbers at room temperature, but when heated can be processed like plastics. They are used in the manufacture of casual shoes and sport shoes. The thermoplastic elastomers (TPEs) most frequently used in the production of shoe soles are styrenic block copolymers such as poly (styrene- butadiene-styrene) or SBS copolymers (market share of about 15%) . Such compositions have advantages over natural rubber and PVC (e.g. easy and cheap to process; good low temperature crack resistance and excellent grip in wet conditions) . These ^synthetic' soles and heels are even replacing their leather counterparts in the upper class shoe range.

Shell Chemicals published a bulletin on the formulation of TPE compositions for footwear applications based on an SBS copolymer sold as "KRATON" D (KRATON is a trademark) . This bulletin, TPE 4.2.2 issued December 1994, provides a typical formulation comprising oils, styrenic resins, ethene-vinyl acetate (EVA), polyolefins, fillers, antioxidants, UV stabilisers and other ingredients in addition to the "KRATON" D TPE. This bulletin also provides general information regarding the compounding equipment and mixing schemes and conditions. A later fact sheet also available from Shell Chemicals, K0002FS-99e, "Starting Formulations for KRATON D Footwear Compounds" provides even more detailed formulations for use in e.g., general purpose solid soling, high hardness thin fashion soling, hiking/mountain boots, and sneakers/slippers.

Unfortunately, mouldings based on such TPE compositions can have a surface appearance which is less desirable in a range of sole/footwear applications. In particular, they lack the uniform ^λdull look' typical of vulcanised natural rubber. This problem may be solved by the addition of a small amount of partially crystalline syndiotactic 1, 2-polybutadiene (e.g., "RB830" sold by JSR) to the TPE composition. However, RB830 is expensive and not broadly available. It would therefore be desirable to find an alternative TPE composition for footwear applications having a uniform dull look. Moreover, the new composition should at least retain important footwear properties such as Din Abrasion. Summary of the invention

The invention provides footwear made from a thermoplastic elastomer composition comprising

(a) one or more styrenic block copolymers;

(b) -optionally- one or more ingredients selected from extender oils, fillers, hardness regulators, flow improvers, flex crack resistance improvers, stabilisers, UV stabilisers, pigments, blowing agents, and antiblocking agents; and

(c) one or more metallocene-based polyolefins of ethene and from 8% to 40% by weight of an alpha-olefin comonomer having from 3 to 20 carbon atoms, having a density from 0.86 to 0.95 kg/1 and a molecular weight distribution (Mw/Mn) less than 3. Detailed description of the invention Surprisingly, the footwear made from the TPE compositions described above have a uniform dull look, without substantial loss of other footwear properties. The components of the TPE composition will be described hereinafter in more detail. Component (a)

Styrenic block copolymers are thermoplastic elastomers having two or more distinguishable polymer blocks, of which at least one is glassy at service temperature but fluid at higher temperatures, and at least one of which is elastomeric (rubbery) at service temperature. A comprehensive review on such polymers is provided by Messrs. Legge, Holden and Schroeder, in "Thermoplastic Elastomers", published by Hanser Publishers in 1987 (ISBN 3-446-14827-2) .

These block copolymers come in the form of linear diblocks, triblocks and multiblocks (produced with sequential polymerization techniques or difunctional coupling agents), or branched block copolymers (using multifunctional coupling agents and/or re-initiation techniques) .

The preferred block copolymers in accordance with the present invention are branched block copolymers, or a mixture of a branched block copolymer and a linear block copolymer. For instance, component (a) may be mixture of a triblock or multiblock copolymer with the diblock copolymer that has been used in the preparation of such triblock or multiblock copolymers.

The block copolymer to be used in the compound of the present invention may be prepared by any method known in the art including the well known full sequential polymerisation method, optionally in combination with re-initiation, and the coupling method, as illustrated in e.g. US Patents Nos . 3,231,635; 3,251,905; 3,390,207; 3,598,887 and 4,219,627, in European patent application Nos. 413,294, 387,671, 636,654 and International application No. 94/22931.

The or each glassy polymer block of the block copolymer is made of polymerized vinylaromatic monomer, such as styrene, in an amount of at least 80 mole% on the total monomer content of the polymer block. Styrene is the preferred vinylaromatic monomer, but other suitable vinylaromatic monomers include α-methylstyrene, p-methylstyrene, m-methylstyrene, o-methylstyrene, p-tert-butylstyrene, dimethylstyrene, and various other alkyl-substituted styrenes, alkoxy-substituted styrenes, vinylnaphthalene and vinyl xylene. These alkyl and alkoxy groups may contain from 1 to 6 carbon atoms, more preferably from 1 to 4 carbon atoms. Comonomers, if present, may be selected from (di)olefins and other compounds copolymerizable with styrene.

Preferred styrenic block copolymers are those wherein the or each elastomeric block of the block copolymer is made of polymerized conjugated diene, such as butadiene or isoprene, in an amount of at least 60 mole% on the total monomer content of the elastomeric block. Butadiene and isoprene are the preferred dienes, but other suitable conjugated dienes include dienes with from 4 to 8 carbon atoms per monomer, for example, 2-ethyl-l, 3-butadiene, 2, 3-dimethyl-l, 3-butadiene, 1, 3-butadiene,

1, 3-pentadiene, 2 , -hexadiene, 3-ethyl-l, 3-pentadiene, and mixtures thereof. These conjugated dienes may be copolymerized in either a 1,2- or 1,4-fashion, leading to a vinyl content in the range of 5-80%. Comonomers, if present, may be selected from vinylaromatic monomers and other compounds copolymerizable with the diene.

Preferred block copolymers are those that are based on styrene ("S") and butadiene ("B") or isoprene ("I") and are conventionally referred to as (SB)_nX, (SI)_nX, SB, SI, SBS and SIS, wherein "X" refers to the residue of a coupling agent, and "n" has a value of at least 2, preferably more than 2.

These styrenic block copolymers may also be fully or partially hydrogenated. Preferred hydrogenated styrenic block copolymers are those wherein only the elastomeric block is selectively hydrogenated (more than 80%, preferably more than 99% on total unsaturation) . Such hydrogenated block copolymers provide improved properties in respect of durability, sensitivity to oil and chemicals and floor marking (i.e., leaves less markings in indoor sports) .

The content of the vinyl aromatic monomer of the final block copolymer is preferably in the range of from 15 to 75% by weight, and more preferably 20 to 60% by weight, based on the total block copolymer.

The total apparent molecular weight of the block copolymer is preferably in the range from 100,000 to 500,000 g/mol, more preferably in the range from 150,000 to 400,000 g/mol. With the expression "apparent molecular weight" as used throughout the specification is meant the molecular weight of a polymer as measured with gel permeation chromatography (GPC) using polystyrene calibration standards (according to ASTM D 3536) . Suitable block copolymers include, amongst others, those sold by Shell under the trademark "KRATON". Other suppliers include Enichem ("EUROPRENE" ) ; Repsol ("CALPRENE") , Fina (" FINAPRENE" ) , DEXCO ("VECTOR"); Nippon Zeon ("QUINTAC"); Firestone ("STEREON"), Asahi ("TUFPRENE") ; Kuraray ("SEPTON") and others such as Chi- Mei; Coperbo; TSRC; LCY; and Ku ho (EUROPRENE, CALPRENE, FINAPRENE, VECTOR, QUINTAC, STEREON, TUFPRENE and SEPTON are trademarks) . Particularly suitable are "KRATON" elastomeric block copolymers sold as clear grade D1101, D1102, D1151, (all linear SBS/SB copolymers) D1155 (linear SBS), D1184, D1186 (both branched copolymers), as oil-extended grade D4123, D4270, D4271, KX224, D4272, and -for high end footwear applications such as hiking and safety boots and sports wear, hydrogenated block copolymers G1650, G1651, G1654, G1657, and RP6917. Component (c)

Suitable metallocene polyolefins and thermoplastic elastomer compositions containing the same are described in European patent application No. 712,892. The metallocene polyolefins are polyolefins produced with a metallocene catalyst such as those described in United States Patents Nos . 4,871,705, 5,322,728 and 5,272,236 which are hereby incorporated by reference. Such metallocene polyolefins are available from Dow Chemical Company under the trademark "AFFINITY" or "ENGAGE" (ethene/octene copolymers) and from Exxon Chemical Company under the trademark "EXACT" (ethene/butene copolymers) . The metallocene polyolefins have low crystallinity when ethene is copolymerised with from 8% to 40% by weight of an alpha-olefin comonomer having from 3 to 20 carbon atoms, preferably from 4 to 12 carbon atoms. Such polyolefins have a good distribution of ethene and the comonomer (as further explained in the references ) . Suitably, the metallocene polyolefins have a Melt

Flow Index in the range of 0.5 to 40 g/10 min ("MFI" at 190 °C/5 kg, determined in accordance with ISO 1133) . Preferred metallocene polyolefins have an MFI in the range of 1.0 to 30 g/10 min. The density of suitable metallocene polyolefins varies from 0.86 to 0.95 kg/1, preferably from 0.88 to 0.92 kg/1. Metallocene polyolefins having a density in the range of 0.89 to 0.90 kg/1 are preferred. Preferred metallocene polyolefins, marketed under the trademark "ENGAGE", are grades 8150 (density 0.868 kg/1; MFI 2 g/10 min); 8585 (density 0.885 kg/1; MFI 8 g/10 min); and 8440 (density 0.897 kg/1; MFI 6 g/10 min). The latter is particularly preferred.

These metallocene polyolefins may be used in amounts in which presently crystalline syndiotactic 1, 2-polybuta- diene is used. For instance, it may be used in an amount of from 5 to 35 phr of component (c) , (phr = parts by weight per 100 parts by weight of component (a) ) , preferably in an amount of from 10 to 30 phr, most preferably at around 20 phr. Components (b)

Hydrocarbon extender oils are generally known as paraffinic and/or naphthenic oils . They usually are fractions of products deriving from petroleum refining having less than about 30% by weight of aromatics, measured by clay-gel analysis, and have usually a viscosity comprised between about 100 and about 500 SSU at 37.8 °C (100 °C) . These hydrocarbon extender oils are commercially known, for instance with the trademark "CATENEX SM 925" or "PROCESS KD28", produced and sold by Shell. The amount of extender oils used in the composition of the present invention can range from 0 to 100, preferably from 5 to 30 phr. Higher amounts than 100 phr, however, may be used for some thermoplastic elastomer compositions. The extender oil may be included in the TPE, e.g., as in the oil-extended KRATON D4123, D4270, D4271, KX224, D4272 and/or VECTOR 7400D. The thermoplastic elastomer composition may comprise other components . Such components include inorganic fillers, such as clay, talc, silica, alumina, titanium dioxide, carbon black, calcium carbonate, sawdust and the like, and other pigments. The preferred fillers comprise silica, calcium carbonate and the like and mixtures thereof. The particle sizes may vary from 1 to 50 micrometers, but are usually smaller (e.g., less than 10 micrometers) . The amount of filler employed can range for each of these additional components independently from 0 to 100 phr, preferably from 5 to 50 phr.

Other components include thermoplastic polymers such as (toughened) polystyrene, polypropene, ethene-vinyl acetate and others. Polystyrene in particular is a common additive to increase the hardness, albeit at the detriment of the appearance.

Certain TPE compositions defined above are already known. For instance, European patent application No. 712,892 describes compositions comprising I) one or more block copolymers having at least two monoalkenyl arene blocks (i.e., glassy blocks) separated by a saturated conjugated diene block and II) a metallocene polyolefin having a density from 0.86 to 0.91, and a molecular weight distribution of less than 3. However, TPE compositions comprising block copolymers wherein the conjugated diene block still contains residual unsaturation are believed to be novel. Accordingly, it is a further embodiment to provide novel TPE compositions that comprise: (a) one or more styrenic block copolymers; (b) -optionally- one or more ingredients selected from extender oils, fillers, hardness regulators, flow improvers, flex crack resistance improvers, stabilisers, UV stabilisers, pigments, blowing agents, and antiblocking agents; and (c) one or more metallocene-based polyolefins of ethene and from 8% to 30% by weight of an alpha-olefin comonomer having from 3 to 20 carbon atoms, having a density from 0.86 to 0.91 and a molecular weight distribution (Mw/Mn) less than 3, with the proviso that component (a) is not a block copolymer having at least two glassy blocks separated by a saturated conjugated diene block.

The definitions of the components of this novel TPE composition is similar to those given before, with the exception of component (a) , which excludes the hydrogenated block copolymer known from European patent application No. 712,892.

The TPE compositions for footwear applications may be made by compounding the TPE with the other components, for instance using high-shear compounding equipment. On an industrial scale, this is carried out on either a batch mixer or continuous extrusion equipment . Use of co- rotating twin screw extruders have proved to be particularly suitable. Some typical mixing schemes and conditions for the various types of mixing equipment used in KRATON D compounding is disclosed in the aforementioned Bulletin TPE 4.2.2, herewith incorporated by reference. Footwear in accordance with the present invention may find use as soling material (outer, mid or in soles), as clasps (ski-boots), heel counters and toe puffs. However, the TPE composition may also be used in adhesives or other applications that require a uniform dull look. Experimental

The following compound ingredients were used in the examples : "KRATON" D-4271 branched 50 phr oil-extended block CS copolymer with 45% styrene content and MFI of 10 (ex Shell) TPS 476L hardener based on toughened polystyrene with MFI of 5 (ex BASF) "PROCESS" KD 28 paraffinic extender oil (ex Shell) "MILLICARB" 5 CaC0 filler without surface treatment (ex OMYA)

"IRGANOX" 565 antioxidant (ex Ciba-Geigy) Masterbatch sarmagum (ex Clariant) Black "ENGAGE" 8150 metallocene polyolefin with MFI of 2 (ex DuPont Dow Elastomers)

'ENGAGE" 8585 metallocene polyolefin with MFI of 8 (ex DuPont Dow Elastomers)

¹ ENGAGE" 8440 metallocene polyolefin with MFI of 6 (ex DuPont Dow Elastomers) MFI = melt flow index in g/10 min. at 190 °C/5 kg (ISO 1133)

"KRATON", "PROCESS", "MILLICARB" , "IRGANOX" and "ENGAGE" are trademarks . TPE Compositions ("compounding")

All solid ingredients, apart from the filler and hardener which were added using a separate feeder, were tumble mixed and subsequently dosed in a 40 mm, L/D = 27 co-rotating twin screw Betol extruder with gravimetric feeding devices. The oil was injected directly into the polymer melt. Extruded strands were water cooled and granulated. 8 kg was prepared of each compound. Injection moulding

Physical and flexural property test samples were injection moulded on a 200 KN BATTENFELD BA 200/50 CD injection moulding machine using exchangeable draw moulds. Apart from the DIN abrasion test sample, the mould cavity is film-gated over one side to give a well defined flow pattern during moulding. Testing and physical properties

Dull look was assessed on the surface of 2 mm injection moulded plates and visually ranked from very dull (best), dull, semi-shiny to shiny (worst). DIN Abrasion resistance was determined in accordance with the DIN 53516 method at 40 rpm, 10 N, 40 m. Shore A hardness was determined after 30 seconds according to the ASTM D2240 method. Resilience was determined at 45° according to the BS 903 AB method. Results and discussion

All the results are reported in Tables 1 and 2. Compositions 1 to 8 are made in accordance with the present invention, whereas compositions A to D are not.

Table 1 illustrates the suitability of metallocene polyolefins (e.g., "ENGAGE" 8440) as replacement of

RB 830. When used in the same amount, similar appearance is achieved, with a slight improvement on DIN Abrasion when using the metallocene polyolefin.

Compound D may have the best DIN Abrasion score, but it also has the worst dull look. This is the result of the presence of 20 phr hardener, instead of either metallocene polyolefin of RB 830. If the hardener is replaced by a metallocene polyolefin, then best results are achieved with "ENGAGE" 8440.

Table 1

VD = Very Dull, D = Dull, S/S = Semi Shiny, S = Shiny

Table 2

VD = Very Dull, D = Dull, S/S = Semi Shiny, S = Shiny

Claims

C L A I M S

1. Footwear made from a thermoplastic elastomer composition comprising

(a) one or more styrenic block copolymers;

(c) one or more metallocene-based polyolefins of ethene and from 8% to 40% by weight of an alpha-olefin comonomer having from 3 to 20 carbon atoms, having a density from

0.86 to 0.95 kg/1 and a molecular weight distribution (Mw/Mn) less than 3.

2. Footwear as claimed in any of the preceding claims, wherein component (a) comprises a branched block copolymer or a mixture of a branched block copolymer and a linear block copolymer.

3. Footwear as claimed in any of the preceding claims, wherein component (a) comprises an (SB)_nX, (SI)_nX, SB, SI, SBS and/or SIS block copolymer, and/or a hydrogenated version thereof.

4. Footwear as claimed in any of the preceding claims, wherein component (c) comprises a metallocene-based polyolefin of ethene and an alpha-olefin comonomer having from 4 to 12 carbon atoms.

5. Footwear as claimed in claim 4, wherein component (c) comprises a metallocene-based polyolefin the density of which varies from 0.86 to 0.95 kg/1, preferably from 0.88 to 0.92 kg/1, more preferably from 0.89 to 0.90 kg/1.

6. Footwear as claimed in claim 5, wherein component (c) comprises a metallocene-based polyolefin having a density of 0.868 kg/1 and an MFI 2 g/10 min; a density 0.885 kg/1 and an MFI 8 g/10 min; or a density of 0.897 kg/1 and an MFI of 6 g/10 min.

7. Footwear as claimed in any of the preceding claims, wherein component (c) is present in an amount of from 5 to 35 parts by weight per 100 parts by weight of component (a) (phr) , preferably in an amount of from 10 to 30 phr, most preferably at around 20 phr.

8. A thermoplastic elastomer composition comprising (a) one or more styrenic block copolymers; (b) -optionally- one or more ingredients selected from extender oils, fillers, hardness regulators, flow improvers, flex crack resistance improvers, stabilisers, UV stabilisers, pigments, blowing agents, and antiblocking agents; and (c) one or more metallocene-based polyolefins of ethene and from 8% to 30% by weight of an alpha-olefin comonomer having from 3 to 20 carbon atoms, having a density from 0.86 to 0.91 kg/1 and a molecular weight distribution (Mw/Mn) less than 3, with the proviso that component (a) is not a block copolymer having at least two glassy blocks separated by a saturated conjugated diene block.

9. A process for compounding the thermoplastic elastomer composition of claim 1 or 7, by compounding the components using high-shear compounding equipment.