EP1204703A1

EP1204703A1 - Thermoplastic vulcanizates from dynamically vulcanized tpu/apolar rubber blends

Info

Publication number: EP1204703A1
Application number: EP00947961A
Authority: EP
Inventors: Dominicus Limerkens; Gerhard Jozef Bleys
Original assignee: Huntsman International LLC
Current assignee: Huntsman International LLC
Priority date: 1999-08-09
Filing date: 2000-07-10
Publication date: 2002-05-15
Also published as: CN1368991A; AU6157300A; MXPA02000821A; JP2003506550A; HK1049178A1; AR026870A1; BR0013101A; PL353284A1; WO2001010950A1

Abstract

Dynamically vulcanized blend comprising a thermoplastic polyurethane having at least 1 major Tg of less than 60ºC and an apolar rubber.

Description

THERMOPLASTIC VULCANIZATES FROM DYNAMICALLY VULCANIZED

TPU/APOLAR RUBBER BLENDS

DESCRIPTION

Field of invention.

The present invention relates to thermoplastic vulcanizates (TPVs) and more specifically to thermoplastic vulcanizates produced from blends comprising thermoplastic polyurethane (TPU) and an apolar rubber, where the rubber phase is dynamically vulcanized.

Description of the prior art.

Thermoplastic elastomers are a class of materials which combine properties of vulcanized rubber with the processing properties of conventional thermoplastics. Examples of these materials are well known in the art. Usually they consist of block copolymers, which exhibit a multiphase microstructure. Best known examples are styrene-elastomer block copolymers like styrene-butadiene-styrene (SBS), or styrene-isoprene-styrene (SIS). Other examples are polyamide-elastomer and polyurethane-elastomer multiblock copolymers. For more examples see e.g. chapter 13 of " Science and Technology of Rubber", J.E.Mark et al. Eds.,2nd ed. Academic Press, 1994.

Thermoplastic elastomers can also be produced by blending hard thermoplastic material with a rubbery material. Examples are natural rubber/polypropylene (NR/PP) blends (TPNRs) and ethylene-propylene-diene-monomer rubber/polypropylene (EPDM/PP) blends, often referred to as thermoplastic olefins (TPOs). Many examples are given in "Thermoplastic Elastomers from Rubber-Plastic Blends", DE and BHOWMICK eds., Ellis Horwood, 1990. It is also known in the art that the properties of thermoplastic elastomers, based on rubber- plastic blends, can sometimes be improved by crosslinking or vulcanizing the rubber phase during the mixing process. This process is called dynamic vulcanization and results in a material usually referred to as a thermoplastic vulcanizate (TPV) or an elastomeric alloy (EA). TPVs have been thoroughly studied by Coran and co-workers (e.g. Rubber Chem. Technol. 53, p781, (1980), Rubber Chem.Technol. 63, p.599 (1989), Rubber Chem.Technol. 68, p351 (1995). Most commonly TPVs are based on EPDM/PP dynamically vulcanized blends (see e.g. US3758643, US3806558).

Thermoplastic elastomers based on compositions comprising (A) a rigid thermoplastic polyurethane not having a major T_g of less than 60°C and (B) a rubber-like material having a To of less than 20°C, the weight ratio (A):(B) being at most 85:15, are disclosed in the pending patent application EP98102213.0.

Thermoplastic polyurethanes or TPUs are thermoplastic elastomers consisting of soft segments and hard segments commonly produced from the reaction between macroglycols, diisocyanates and short chain diols. They exhibit elastomeric as well as thermoplastic properties and show two glass transition temperatures T_g and T_g ^s, corresponding to respectively the hard and the soft phases.

The term 'glass transition temperature^' or T_g as used herein is well understood by people skilled in the art and the concept is explained fully in chapter 2 of "Mechanical Properties of Polymers", L.E.Nielsen, Chapman & Hall, London, 1962, and can be easily established by well known methods like 'differential scanning calorimetry' (DSC). Usually T_g ^s is lower than about -10°C and T_g ^h higher than 50°C.

Blends of TPUs with other thermoplastics are well known in the art. E.g. blends of TPU with polyoxymethylene (POM), polvinylchloride (PVC), styrene acrylonitrile (SAN) and acrylonitrile butadiene styrene (ABS). are of commercial importance.

In 'Structure, Morphology and Physical Property of Dynamically Vulcanized Polyurethane/Nitrile Butadiene Rubber Blends' (Adv. Polym. Blends Alloys Technol. 4, p.1-10, 1993) Tao Tang et al. disclose dynamically vulcanized TPU/NBR blends having improved physical properties due to a synergistic effect between the TPU and NBR phase. NBR is a polar rubber; blends of TPU with apolar rubbers are not discussed.

Summary of the invention.

It has now been surprisingly found that thermoplastic vulcanizates with useful properties can be produced by melt blending and dynamically vulcanizing a TPU having at least 1 major T_g of less than 60°C and an apolar rubber material.

Detailed description of the invention.

The invention therefore relates to dynamically vulcanized blends comprising a thermoplastic polyurethane having at least 1 major T_g of less than 60°C and an apolar rubber.

According to the invention, the rubber phase is dynamically vulcanized, i.e. vulcanized during the blending process. Vulcanization of the rubber phase can be achieved with compositions known to people skilled in the art, e.g. using sulphur systems, accelerated sulfur systems, peroxides, phenolics and the like. Preferably phenolic and peroxide vulcanization systems are used. An overview of the most commonly used vulcanization systems can be found in "Science and Technology of Rubber", 2nd. Ed. academic press, 1994

Melt blending and dynamic vulcanization can be achieved using classic internal or external mixers well known in the art. Alternatively blending can be achieved using extrusion, in e.g. a twin screw extruder, or a compounding single screw extruder. An overview of the practical aspects of polymer blending can be found in "Polymer Blends and Alloys", Folkes and Hope Eds,Chapman & Hall, (1993). 4

The thermoplastic polyurethane of the invention is obtained by reaction of a diisocyanate with macroglycol(s) and chain extender(s) at an isocyanate index of 95 to 105, pref. 98 to 102.

5 Suitable thermoplastic polyurethanes may also be obtained by blending different polyurethanes in such amounts that the blend has at least 1 major T_g of less than 60°C.

The term "isocyanate index" as used herein is the ratio of isocyanate-groups over isocyanate-reactive hydrogen atoms present in a formulation, given as a percentage. In ] 0 other words, the isocyanate index expresses the percentage of isocyanate actually used in a formulation with respect to the amount of isocyanate theoretically required for reacting with the amount of isocyanate-reactive hydrogen used in a formulation.

It should be observed that the isocyanate index as used herein is considered from the point 15 of view of the actual elastomer forming process involving the isocyanate ingredient and the isocyanate-reactive ingredients. Any isocyanate groups consumed in a preliminary step to produce modified polyisocyanates (including such isocyanate-derivatives referred to in the art as quasi- or semi-prepolymers) or any active hydrogens reacted with isocyanate to produce modified polyols or polyamines, are not taken into account in the calculation of 20 the isocyanate index. Only the free isocyanate groups and the free isocyanate-reactive hydrogens (including those of water, if used) present at the actual elastomer forming stage are taken into account.

The TPU can be produced in the so-called one-shot, semi-prepolymer or prepolymer 25 method, by casting, extrusion or any other process known to the person skilled in the art.

The macroglycol used has a molecular weight of between 500 and 20000 and is used in such an amount that the TPU has at least 1 major T_g of less than 60°C, usually in an amount of from 25 to 75 parts by weight on the total weight of the TPU.

J o

The amount of macroglycols as a weight percentage of the total amount of thermoplastic polyurethane is defined as the soft-block content of the thermoplastic polyurethane. 5

The macroglycols may be selected from polyesteramides, polythioethers, polycarbonates, polyacetals, polyolefins, polysiloxanes and, especially, polyesters and polyethers.

Polyether glycols which may be used include products obtained by the polymerisation of a cyclic oxide, for example ethylene oxide, propylene oxide, butylene oxide or tetrahydrofuran in the presence, where necessary, of difunctional initiators. Suitable initiator compounds contain 2 active hydrogen atoms and include water, butanediol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol and dipropylene glycol. Mixtures of initiators and/or cyclic oxides may be used.

Especially useful polyether glycols include polyoxypropylene glycols and poly(oxyethylene-oxypropylene) glycols obtained by the simultaneous or sequential addition of ethylene and propylene oxides to difunctional initiators as fully described in the prior art. Random copolymers having oxyethylene contents of up to 80%, block copolymers having oxyethylene contents of up to 25% and random/block copolymers having oxyethylene contents of up to 50%, based on the total weight of oxyalkylene units, may be mentioned, in particular those having at least part of the oxyethylene groups at the end of the polymer chain. Other particularly useful polyether glycols include polytetramethylene glycols obtained by the polymerisation of tetrahydrofuran (THF).

Polyester glycols which may be used include hydroxyl-terminated reaction prdoucts of dihydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, 1,4- butanediol, neopentyl glycol or 1 ,6-hexanediol, or mixtures of such dihydric alcohols, and dicarboxylic acids and their ester-forming derivatives, for example succinic, glutaric and adipic acids or their dimethyl esters, sebacic acid, phthalic anhydride, tetrachlorophthalic anhydride or dimethyl terephthalate or mixtures thereof.

Polythioether glycols which may be used include products obtained by condensing thiodiglycol either alone or with other glycols, alkylene oxides or dicarboxylic acids.

Polycarbonate glycols which may be used include products obtained by reacting diols such as 1,3-propanediol, 1 ,4-butanediol, 1 ,6-hexanediol, diethylene glycol or tetraethylene glycol with diaryl carbonates, for example diphenyl carbonate, or with phosgene. Polyacetal glycols which may be used include those prepared by reacting glycols such as diethylene glycol, triethylene glycol or hexanediol with formaldehyde. Suitable polyacetals may also be prepared by polymerising cyclic acetals.

Suitable polyolefin glycols include hydroxy-terminated butadiene homo- and copolymers and suitable polysiloxane glycols include polydimethylsiloxane diols.

The chain extender can be any difunctional isocyanate-reactive species with a MW < 500 , preferably a diol or blends of different types.

Suitable chain extenders include aliphatic diols, such as ethylene glycol, 1 ,3-propanediol, 1 ,4-butanediol, 1 ,6-hexanediol, 1 ,2-propanediol, 1,3-butanediol, 2,3-butanediol, 1,3- pentanediol, 1.2-hexanediol, 3-methyl-l,5-pentanediol, diethylene glycol, dipropylene glycol and tripropylene glycol. Chain extenders with an odd-number of carbon atoms between the OH groups, and chain extenders with a branched chain stucture like 2-methyl- 1,3-propanediol, 2,2-dimethyl-2,3-propanediol, 1,3-propanediol, 1,5-pentanediol are suitable as well.

Cycloaliphatic diols like 1 ,4-cyclohexanediol, 12,-cyclohexanediol, 1,4- cyclohexanedimethanol or 1,2-cyclohexanedimethanol, and aromatic diols like hydroquinone bis(hydroxyethylether) and the like can also be used.

Organic polyisocyanates may be selected from aliphatic, cycloaliphatic and araliphatic polyisocyanates, especially diisocyanates, like hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane-l,4-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate and m- and p-tetramethylxylylene diisocyanate, and in particular aromatic polyisocyanates like tolylene diisocyanates (TDI), phenylene diisocyanates and most preferably diphenylmethane diisocyanates.

The diphenylmethane diisocyanates may consist essentially of pure 4,4 '-diphenylmethane diisocyanate or mixtures of that diisocyanate with one or more other organic polyisocyanates, especially other diphenylmethane diisocyanate isomers, for example the 2,4'-isomer optionally in conjunction with the 2,2'-isomer. The polyisocyanate component may also be an MDI-variant derived from a polyisocyanate composition containing at least 85% by weight of 4,4 '-diphenylmethane diisocyanate. MDI variants are well known in the art and, for use in accordance with the invention, perticularly include liquid products obtained by introducing carbodiimide groups into said polyisocyanate composition and/or by reating with one or more polyols.

Preferred are polyisocyanate compositions containing at least 90% by weight of 4,4'- diphenylmethane diisocyanate. Polyisocyanate compositions containing at least 95% by weight of 4,4 '-diphenylmethane diisocyanate are most preferred.

Catalysts used in the production of the TPU can be any catalysts know in the art, especially tertiary amine catalysts and metal catalysts like Sn and Bi based catalysts.

The rubbers used in the invention can be any apolar rubber commonly known in the art.

Preferred rubbers consist only of C,H,O and/or N atoms, more preferably only of C,H and O atoms and most preferably of C and H atoms only. Preferably no polar functional groups such as C≡N, -OH or -CO-O- are present. However, a small amount of polar groups may be tolerated as long as the overall polarity of the rubber is not influenced to a large extent.

Examples of suitable rubbers are (hydrogenated) butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), natural rubber (NR), butyl rubber (IIR), ethylene- propylene rubber (EPR), ethylene-propylene-diene-monomer rubber (EPDM) or other apolar rubbers considered based on polyolefins or mixtures thereof.

Preferred are (hydrogenated) diene rubbers or rubbers based on ethylene propylene blends or copolymers. More preferred are styrene butadiene rubber, isoprene rubber, natural rubber or butyl rubber, isoprene rubber being most preferred.

The amount of rubber used in the blend is at least 10 % by weight, based on the total weight of rubber and polyurethane. preferably at least 25% by weight and more preferably at least 50% by weight, based on the total weight of rubber and polyurethane.

In another embodiment of the invention properties of the dynamically vulcanized blends of the invention are improved through the use of compatibilizing agents. In many cases the properties of TPVs can be improved through the use of compatibilizing additives, also called compatibilizers. Compounds of this kind are well known in the art and often are block copolymers or graft copolymers where the blocks consist of the polymer species which have to be compatibilized . The compatibilizers can be produced separately and added before or after blending, or can be produced in-situ during blending. The latter process is referred to as reactive compatibilization. An overview of polymer compatibilization and examples of compatibilizers for different polymer pairs are given in "Polymer Blends and Alloys", Folkes and Hope Eds., Chapman &Hall, (1993).

Compatibilizers useful in the invention can be non-reactive copolymers or non-reactive graft copolymers consisting of e.g. polyurethane - rubber graft copolymer, or a block copolymer where one block is compatible with the TPU phase and the other block with the rubber phase. The use of reactive compatibilizers, e.g. where all, or part, of the PU (or rubber) phase is modified to become reactive with the rubber (or PU ) phase, can also be contemplated. Such compatibilizers are usually added in amounts of up to 10 parts by weight, based on the total weight of the blends.

Auxiliaries and additives typical for both polyurethanes and rubber technologies may be used as well. Additives and auxiliaries can be added to both the TPU or the rubber phase separately before, during or after vulcanizing. Such auxiliaries and additives include surface-active agents for example siloxane-oxyalkylene copolymers, extender oils, flame retardants, plasticizers, organic and inorganic fillers, pigments, anti-oxidants, UV stabilizers, blowing agents, antireversion agents and internal mould release agents.

Thermally expandable microspheres containing a (cyclo)aliphatic hydrocarbon are also suitable additives in the present invention. Such microspheres are generally dry, unexpanded or partially unexpanded microspheres consisting of small spherical particles with an average diameter of typically 10 to 15 micron. The sphere is formed of a gas proof polymeric shell (consisting e.g. of acrylonitrile or PVDC), encapsulating a minute drop of a (cyclo)aliphatic hydrocarbon, e.g. liquid isobutane. When these microspheres are subjected to heat at an elevated temperature level (e.g. 150°C to 200°C.) sufficient to soften the thermoplastic shell and to volatilize the (cyclo)aliphatic hydrocarbon encapsulated therein, the resultant gas expands the shell and increases the volume of the microspheres. When expanded, the microspheres have a diameter 3.5 to 4 times their original diameter as a consequence of which their expanded volume is about 50 to 60 times greater than their initial volume in the unexpanded state. An example of such microspheres are the EXPANCEL-DU microspheres which are marketed by AKZO Nobel Industries of Sweden ('EXPANCEL' is a trademark of AKZO Nobel Industries).

The invention also relates to a process for preparing thermoplastic elastomers by melt- blending and dynamically vulcanizing blends comprising a thermoplastic polyurethane having at least 1 major T_g of less than 60°C and an apolar rubber, and to thermoplastic elastomers thus obtained.

The blends of the present invention are preferably in liquid or solid form. A particularly preferred form for the blend is granular solid.

Melt blending can take place in a separate step prior to dynamic vulcanization.

Advantage, use.

The blends of the present invention can be used to prepare thermoplastic elastomers which combine some of the advantages of classic TPU elastomers and of the rubbers used. Because of the large number of possible combinations a wide range of materials can be produced with a wide range of properties.

The resulting elastomers can be used in a number of applications like shoesoles, shoe- insoles, automotive parts (dashboards, window seals, airbag covers) or other applications like watch straps, tool grips, cable insulation, etc..

10

Examples.

In the examples the following test methods were used :

Shore A hardness : DIN 53505 Tensile strength : DIN 53504 Elongation at break : DIN53504 Young's Modulus : DIN53504 100% Modulus : DIN53504 Slip Resistance : DIN 53375

Example 1.

120g grams of isoprene rubber (Cariflex IR 310 from Shell) was blended with 80 g of P4470AT, a 70 shore A grade, poly-THF MDI based TPU available from HUNTSMAN ICI, in a HAAKE Rheomix 3000P at 180°C at 50rpm. After complete melting of the material (after about 5 minutes) 7.2 grams of 2,5-bis-(hydroxymethyl)-p-cresol from Aldrich was added. Mixing was carried on for 2 minutes at 80rpm, and for another 15 minutes at 50rpm. The material was then discharged from the mixer, cooled and shredded.

The material was extruded using the HAAKE Rheomex 252P single screw extruder, using a conventional PE screw with a 1 :3 compression ratio. Settings were : 160°C:170°C:180°C and the die temperature was 190°C. Screw speed was 50rpm. Properties were measured on the extruded material.

The resulting material had a shore A hardness of 52, a tensile strength of 2.9 MPa, and an elongation at break of 440%.

Example 2.

A TPV was produced as in example 1, but the TPU used was now P4485AT which is a 85 shore A grade, poly-THF - MDI based TPU available from HUNTSMAN ICI. The resulting material had a shore A hardness of 55, a tensile strength of 3.3MPa and an elongation at break of 490 %

Example 3.

TPVs were produced as in example 2, but the curative used is 2,5-bis-(hydroxymethyl)-p- cresol ('Purum' grade, available from Aldrich). The curative was used in different levels (phi : parts per 100 parts rubber). Some mechanical properties of the resulting TPVs are given in Table 1.

Table 1

Example 4.

TPVs were produced as in example 2, but the TPU/rubber weight ratio is now 50/50, the curative used is Trigonox ©145-45 (peroxide curative obtainable from Akzo Nobel) and the blending temperature was varied as indicated in Table 2. The extruded material was compression moulded into 2 mm thick plaques. The applied force was 200kN for 2 minutes, after which the plaque was cooled between water-cooled plates. Some mechanical properties of the resulting TPVs are listed in Table 2. Table 2

Example 5.

TPVs were produced as in example 2, but the curative used is Trigonox® 145-45, kept constant at a concentration of 4 phr, kneader temperature was set at 205°C, and the amount of rubber was varied as indicated in Table 3. The extruded material was compression moulded as in example 4. Some mechanical properties of the resulting materials are listed in Table 3.

Table 3

Example 6.

A TPV was produced as in example 2, but the rubber used was now EPDM (Keltan® 4903 from DSM; ethylene content about 48%), and the TPU used was P4472 DB, a polyester- polyol based TPU with a Shore A hardness of around 72D, available from Huntsman ICI. The curative used was dicumyl peroxide in a concentration of 3 phr. Some mechanical properties of the resulting TPV are listed in Table 4.

Table 4.

Claims

14CLAIMS.

1. Dynamically vulcanized blend comprising a thermoplastic polyurethane having at least 1 major T_g of less than 60°C and an apolar rubber.

2. Blend according to claim 1 wherein the rubber is selected from the group consisting of diene rubbers, hydrogenated diene rubbers or rubbers based on ethylene propylene blends or copolymers.

3. Blend according to claim 2 wherein the rubber is selected from the group consisting of styrene butadiene rubber, isoprene rubber, natural rubber, butyl rubber or EPDM.

4. Blend according to claim 3 wherein the rubber is isoprene rubber or EPDM.

5. Blend according to anyone of the preceding claims wherein the amount of apolar rubber is at least 10% by weight, based on the total weight of the blend.

6. Blend according to claim 5 wherein the amount of apolar rubber is at least 25% by weight, based on the total weight of the blend.

7. Blend according to claim 6 wherein the amount of apolar rubber is at least 50% by weight, based on the total weight of the blend.

8. Blend according to any one of the preceding claims wherein the thermoplastic polyurethane is based on diphenylmethane diisocyanate.

9. Blend according to claim 8 wherein the diphenylmethane diisocyanate comprises at least 90% by weight of 4,4'-diphenylmethane diisocyanate.

10. Blend according to any one of the preceding claims wherein the thermoplastic polyurethane is based on a polyether polyol or a polyester polyol, or a mixture thereof.

1 1. Blend according to claim 10 wherein the polyether polyol is a polytetramethylene polyol.

12. Blend according to any one of the preceding claims wherein the soft-block content of the thermoplastic polyurethane is from 25 to 75 parts by weight, based on the total weight of the thermoplastic polyurethane.

13. Blend according to any one of the preceding claims which contains a compatibihser.

14. Blend according to claim 13 wherein said compatibihser is a reactive compatibihser.

15. Blend according to any one of the preceding claims wherein the vulcanizing system is selected from the group consisting of systems comprising, phenolics or peroxides.

16. Process for preparing thermoplastic elastomers by melt-blending and dynamically vulcanizing blends according to any one of the preceding claims comprising a thermoplastic polyurethane having at least 1 major T_g of less than 60°C, and an apolar rubber.

17. Thermoplastic elastomers obtained by the process according to claim 16.

18. Blends as defined in any one of claims 1-15 which is in solid or liquid form.

19. Blends according to claim 18 which is a granular solid.

20. Use of blends as defined in any one of the claims 1-15 or 18-19 for making thermoplastic elastomers wherein the thermoplastic polyurethane having at least 1 major T_g of less than 60°C, and the apolar rubber are mixed and dynamically vulcanized prior to or during the thermoplastic elastomer production.