Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-02-14
2001-04-17
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...
C528S065000
Reexamination Certificate
active
06218479
ABSTRACT:
This invention relates to nonrigid, readily demouldable moulding compositions which comprise thermoplastic polyurethanes and which exhibit low shrinkage.
Thermoplastic polyurethane elastomers (TPUs) have long been known. They are of industrial importance on account of their combination of high-grade mechanical properties with the known advantages which result from their capacity for being processed thermoplastically and hence inexpensively. A large range of variation of mechanical properties can be achieved by the use of different chemical synthesis components. A review on TPUs, their properties and applications is given in Kunststoffe 68 (1978), 819, and in Kautschuk, Gummi, Kunststoffe 35 (1982), 568, for example.
TPUs are synthesised from linear polyols, which are mostly polyester- or polyether polyols, and from organic diisocyanates and short-chain diols (chain extenders). Catalysts can also be added in order to speed up the formation reaction. The molar ratios of the synthesis components can be varied over a relatively large range in order to adjust the properties of the products formed. Molar ratios of polyols to chain extenders ranging from 1:1 to 1:12 have proved useful, and result in products with hardnesses within the range from 80 Shore A to 75 Shore D (according to DIN 53 505).
TPUs with a Shore A hardness less than 80 can theoretically be obtained in the same manner. A disadvantage here, however, is that these products can only be handled with difficulty during the production thereof, since they are difficult to set and solidify.
TPUs with hardnesses as low as this exhibit rubber-like elastic behaviour. Therefore, the behaviour on demoulding and the dimensional stability of injection moulded parts often render these materials inadequate for processing in the injection moulding industry, on account of their shrinkage being too high.
EP-A 0 134 455 discloses that TPUs with a hardness of 60 to 80 Shore A can be obtained by the use of plasticisers comprising special phthalates and phosphates.
EP-A 0 695 786 describes the production of nonrigid TPUs based on special polyether/polyester mixtures with plasticisers comprising alkylsulphonic acid esters or benzylbutyl phthalate, with the addition of inorganic fillers.
A disadvantage of both these processes is the use of plasticisers, which makes it impossible to use these TPUs for many applications in which what is important is the purity of the TPU material or the surface quality of the processed TPU.
The object of the present invention was therefore to provide TPU moulding compositions which are nonrigid, readily deformable and thermoplastically processable, and which exhibit low shrinkage and contain no plasticisers.
It has been possible to achieve this object by means of the TPUs according to the invention.
The present invention relates to a thermoplastically processable, readily demouldable polyurethane moulding composition with low shrinkage measured in accordance with DIN 16 770 (Part 3), of lower than 2.5% and with a hardness of 65 to 85 Shore A (as determined according to DIN 53 505), consisting of a mixture of
A) 5 to 54 parts by weight of a thermoplastic polyurethane of hardness 60 Shore A to 75 Shore A (as determined according to DIN 53 505), obtainable from
1) an organic diisocyanate,
2) a polyester- and/or polyether polyol with a number average molecular weight between 500 and 5000 and
3) a chain-extending diol with a molecular weight between 60 and 400, and
B) 95-46 parts by weight of a thermoplastic polyurethane of hardness 76 Shore A to 90 Shore A (as determined according to DIN 53 505), obtainable from
1) an organic diisocyanate,
2) a polyester- and/or polyether polyol with a number average molecular weight between 500 and 5000 and
3) a chain-extending diol with a molecular weight between 60 and 400, and
4) optionally catalysts, adjuvant substances, additives, chain terminators and demoulding agents,
wherein B) is obtained continuously by a multi-stage reaction, wherein
a) one or more linear, hydroxyl-terminated polyester- and/or polyether polyols are continuously mixed, with a high level of shearing energy (sufficient to attain a good mixture of the components), with part of an organic diisocyanate in a ratio of 2.0:1 to 5.0:1,
b) the mixture produced in stage a) is continuously reacted in a reactor at temperatures >120° C. up to a conversion >90% with respect to the polyol, to form an isocyanate-terminated prepolymer,
c) the prepolymer produced in stage b) is mixed with the remainder of the organic diisocyanate (preferably the amount of the remainder is at least 2.5% of the amount of the organic diisocyanate of stage a)), wherein an NCO:OH ratio of 2.05:1 to 6.0:1 is set overall in stages a) to c) and an NCO:OH ratio of 0.9:1 to 1.1:1 is set taking into consideration all the components of stages a) to f),
d) the mixture produced in stage c) is cooled to a temperature <190° C.,
e) the mixture obtained in stage d) is continuously and intensively mixed with one or more chain-extending diols for a maximum of 5 seconds, and
f) the mixture obtained in stage e) is continuously reacted in an extruder to form the thermoplastic polyurethane.
Examples of suitable organic diisocyanates 1) include aliphatic, cycloaliphatic, araliphatic, heterocyclic and aromatic diisocyanates, such as those which are described in Justus Liebigs Annalen der Chemie, 562, pages 75 to 136.
In detail, the following examples should be cited: aliphatic diisocyanates such as hexamethylene diisocyanate, cycloaliphatic diisocyanates such as isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1-methyl-2,4-cyclohexane diisocyanate and 1-methyl-2,6-cyclohexane diisocyanate, as well as the corresponding mixtures of isomers, 4,4′-dicyclohexylmethane diisocyanate, 2,4′-dicyclohexylmethane diisocyanate and 2,2′-dicyclohexylmethane diisocyanate as well as the corresponding mixtures of isomers; aromatic diisocyanates such as toluene 2,4-diisocyanate, mixtures of toluene 2,4-diisocyanate and toluene 2,6-diisocyanate, 2,4′-diphenylmethane diisocyanate and 2,2′-diphenylmethane diisocyanate, mixtures of 2,4′-diphenylmethane diisocyanate and 4,4′-diphenylmethane diisocyanate; urethane-modified, liquid 4,4′-diphenylmethane diisocyanate or 2,4′-diphenylmethane diisocyanate, 4,4′-diisocyanatodiphenylethane (1,2) and 1,5-naphthalene diiso-cyanate. The following are preferred: 1,6-hexamethylene diiso-cyanate, 1,4-cyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl-methane diiso-cyanate, mixtures of diphenylmethane diisocyanate isomers with a 4,4′-diphenylmethane diisocyanate content of more than 96% by weight; particularly 4,4′-diphenylmethane diisocyanate and 1,5-naphthalene diisocyanate. The afore-mentioned diisocyanates can be used individually or in the form of mixtures with each other. They can also be used together with up to 15 mol % (based on the total diisocyanate) of a polyisocyanate. However, the maximum amount of polyisocyanate added must be such that a product is formed which is still thermoplastically processable. Examples of polyisocyanates include triphenyl-methane 4,4′,4″-triisocyanate and polyphenyl-polymethylene polyisocyanate.
Linear, hydroxyl-terminated polyols with an average molecular weight M
n
of 500 to 5000 are preferred as component 2). Due to their method of production, these substances often contain small amounts of nonlinear compounds. Therefore, substances such as these are often also termed “substantially linear polyols”. These are also suitable. Polyester-, polyether- or polycarbonate diols or mixtures thereof are preferably used.
Suitable polyether polyols (polyether diols) can be obtained by the reaction of one or more alkylene oxides containing 2 to 4 carbon atoms in their alkylene radical with a starter molecule which contains two active hydrogen atoms. Examples of alkylene oxides include: ethylene oxide, 1,2-propylene oxide, epichlorohydrin, 1,2-butylene oxide and 2,3-butylene oxide. Ethylene oxide, propylene oxide
Brauer Wolfgang
Hoppe Hans-Georg
Winkler Jurgen
Wussow Hans-Georg
Bayer Aktiengesellschaft
Gil Joseph C.
Preis Aron
Short Patricia A.
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