Elastomers from compositions comprising rigid thermoplastic...

Details Elastomers from compositions comprising rigid thermoplastic... Elastomers from compositions comprising rigid thermoplastic...

1999-02-08

2001-09-18

Short, Patricia A. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S066000, C525S09200D, C525S458000

Reexamination Certificate

active

06291587

ABSTRACT:

DESCRIPTION
1. Field of Invention
The present invention relates to elastomers and preferably thermoplastic elastomers (TPE's) and more specifically to thermoplastic elastomers produced from compositions comprising rubber-like materials and rigid thermoplastic polyurethane, wherein the rubber-like material phase is optionally vulcanised or optionally dynamically vulcanised.
2. Description of the Prior Art
Thermoplastic elastomers are a class of materials which combine properties of vulcanised 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
”, 2nd ed., J. E. Mark et al. eds., Academic Press, 1994.
Thermoplastic elastomers can also be produced by blending hard thermoplastic material with a rubber-like material. Examples are natural rubber-polypropylene (NR-PP) blends (TPNR's) and EPDM-PP blends, often referred to as thermoplastic olefins (TPO's). 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 vulcanising the rubber phase during the mixing process. This process is called dynamic vulcanisation 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 TPV's are based on ethylene propylene diene monomer rubber/polypropylene (EPDM/PP) dynamically vulcanized blends (see e.g. U.S. Pat. No. 3,758,643, U.S. Pat. No. 3,806,558).
Thermoplastic polyurethanes or TPU's 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 major glass transition temperatures T
g
h
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 the T
g
s
is lower than about −10° C. and the T
g
h
higher than 50° C. Blends of TPU's with other thermoplastics are well known in the art. E.g. blends of TPU with polyoxymethylene (POM), polyvinylchloride (PVC), styrene acrylonitrile (SAN) and acrylonitrile butadiene styrene (ABS) are of commercial importance.
Another type of thermoplastic polyurethane exists called rigid TPU or rTPU, which contains no or only small amounts of soft segments. These products show thermoplastic behaviour but no elastomeric behaviour and are glassy or (semi-)crystalline at ambient temperature. They usually exhibit no major glass transition temperature (T
g
) below room temperature.
U.S. Pat. No. 4,376,834 to Goldwasser et al. teaches high impact resistant rigid TPU based on an organic polyisocyanate, a chain extender and from about 2 to about 25% of an isocyanate-reactive material with a functionality of >1.9 and a molecular weight of about 500 to 20000 (soft segment). It is suggested that the material has a two-phase morphology and that the lowest T
g
occurs below room temperature, while the T
g
of the urethane glass phase occurs at approximately 100° C.
However, U.S. Pat. No. 4,567,236 (to Goldwasser) teaches virtually the same rigid TPU which has only one T
g
which is claimed to be >50° C. The rigid TPU in U.S. Pat. No. 4,567,236 is blended with materials known in the art as impact modifiers like ABS, ethylene vinyl acetate (EVA), chlorinated polyethylene (cPE), methylmethacrylate-butadiene-styrene and the like. The amount of impact modifier is said to range between 3 and 25% by weight. In the examples the amount of impact modifier used is 15 parts by weight on 85 parts by weight of rTPU.
U.S. Pat. No. 4,822,827 (to Beck et al.) teaches an improvement over the prior art rTPU's by replacing part of the chain extender composition with a cycloalkanediol. The novel rTPU's are characterised by a T
g
>125° C.
U.S. Pat. No. 5,167,899 (to Jezic) teaches the production of microfibers from rigid TPU's. An example is given of microfibers from a commercial rTPU (‘ISOPLAST’ 301, ‘ISOPLAST’ is a Trademark of DOW Chemical Co.) which composition matches this described in U.S. Pat. No. 4,822,827.
WO-A 93/02238 (to Moses et al.) teaches blends of PET and rTPU. The amount of polyol in the rTPU is limited in such a way that the T
g
remains >60° C. The rTPU used in the examples is again ‘ISOPLAST’ 301, however the T
g
is said to be 114° C.
U.S. Pat. No. 5,574,092 (to Oriani) teaches rTPU with lower melt processing temperature, by incorporating aromatic diols in the chain extender composition. The T
g
is claimed to be >50° C.
U.S. Pat. No. 5,376,723 (to Vogt et al.) discloses thermoplastic polymer blends having a Shore A hardness of about 55 to 70 comprising, in a volume percentage ratio of about 30:70 to 40:60, a PU component containing at least about 50 wt % polyisocyanate and a nitrile rubber component containing about 34 mol % acrylonitrile.
Although numerous types of thermoplastic elastomers are known, there is still a need for improved thermoplastic materials having elastomeric properties.
SUMMARY OF THE INVENTION
It has now surprisingly been found that elastomers and preferably thermoplastic elastomers with useful properties can be produced by melt blending rigid TPU not having a major T
g
of less than 60° C. and a rubber-like material having a T
g
of less than 20° C., the weight ratio of the rigid TPU and the rubber-like material being at most 85:15.
The elastomers of the invention combine some of the advantages of the conventional TPU elastomers and of the rubber-like materials used. Because of the large number of possible combinations a wide range of materials can be produced with a wide range of properties.
DETAILED DESCRIPTION OF THE INVENTION
The invention thus relates to a composition 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 T
g
of less than 20° C., wherein the weight ratio (A):(B) is at most 85:15.
The rigid thermoplastic polyurethane (rTPU) of the present invention is obtainable by reaction of diisocyanate(s) with chain extender(s) and optionally macroglycol(s) at an isocyanate index of 95 to 105, pref. 98 to 102.
Suitable thermoplastic polyurethanes may also be obtained by blending different polyurethanes in such amounts that the blend does not have a 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 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 of view of the actual polymer forming process involving the isocyanate ingredient and the isocyanate-reactive ingredients. Any isocyanate groups consumed in a preliminary ste

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