Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Reexamination Certificate
1996-05-31
2002-07-09
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
C264S165000, C528S044000, C528S060000, C528S061000, C528S065000, C528S076000, C528S080000, C528S085000
Reexamination Certificate
active
06417312
ABSTRACT:
The present invention relates to thermoplastic polyurethane elastomers, to a process for the production thereof and to the use thereof.
Thermoplastic polyurethanes (TPU) are of significance because they have good elastomeric properties and may readily be melt processed. A very wide range of mechanical properties may be obtained by appropriate selection of the components. A review of TPU, their properties and applications may be found, for example, in
Kunststoffe
68 (1978), pp. 819-825
, Kautschuk, Gummi, Kunststoffe
35 (1982), pp. 569-584 and G. Becker, D. Braun
Kunststoff-Handbuch
, volume 7
, Polyurethane
, Munich, Vienna, Carl Hanser Verlag 1983. A review of production processes may be found in
Plastverarbeiter
40 (1989).
TPU are mainly synthesized from linear polyols, such as polyester or polyether polyols, organic diisocyanates and short-chain, mainly difunctional alcohols (chain extenders). They may be produced continuously or discontinuously. The best known production processes are the belt process and the extruder process.
In the belt process, the starting materials are metered into a mixing head and vigorously mixed together in a very short period of time while they are still at a low viscosity. The reaction composition is then discharged onto a circulating steel or plastic belt on which the mixture reacts and solidifies with the addition of heat (GB-PS 1,057,018; DE-OS 3,224,324).
In the extruder process, the starting materials are together metered into a screw reactor, where they undergo polyaddition and are then converted into uniform pellets (U.S. Pat. No. 3,642,964; DE-PS 2,302,564; DE-PS 2,549,371; DE-OS 3,230,009; EP-OS 0,031,142).
The advantage of the belt process resides in the short mixing time for the starting materials and the subsequent shear-free and thus undisrupted reaction. The resultant polyurethanes exhibit very good phase segregation and are particularly suitable for films. The disadvantage of the belt process resides in the costly working up processes for the primary polymer sheets or strands obtained using this process. These do not have a uniform polymer structure and must subsequently be comminuted into homogeneous pellets and re-extruded.
In contrast, the extruder process is simple and low in cost, but the starting materials are not mixed until they reach the extruder under conditions in which polyaddition occurs. As a consequence, there are elevated concentrations of one component in certain areas of the extruder and unwanted and uncontrollable secondary reactions occur. Moreover, the polyurethanes are exposed to elevated shear forces throughout the period of production. As a result, the phase segregation which occurs during polyaddition is severely disrupted and the resultant polyurethanes are only poorly suited to certain purposes, for example film production.
It is proposed in EP-A 0,554,718 and EP-A 0,554,719 to improve the extruder process by bringing the starting materials together in a nozzle and mixing them before they enter the extruder. Here too, the majority of the polyaddition reaction proceeds in the extruder, such that the TPU are exposed to severe shear forces during production and are thus damaged.
There is thus still considerable interest in TPU with improved properties and in processes which avoid the stated disadvantages in such a manner that polyurethanes may be produced in a controlled manner and with purposefully selected properties.
It has now been found that TPU having improved properties may be obtained in a process where the isocyanate is first mixed with the isocyanate-reactive component in a first static mixer to form a substantially unreacted reaction mixture and complete the reaction later in a second static mixer.
By means of this process, homogeneous TPU with greatly improved properties compared with those of known processes are obtained. This was not expected.
The present invention provides a process for the production of thermoplastic polyurethane elastomers which comprises
(a) introducing and homogeneously mixing (A), (B) and optional (C) in a first static mixer at a shear rate of 500 to 50000 s
−1
and at a temperature of 50 to 250° C., to form a substantially unreacted mixture and
(b) reacting said substantially unreacted mixture in a second static mixer operating at a shear rate of 1 to 100 s
−1
and a temperature of 50 to 250° C., to form a thermoplastic polyurethane elastomer, wherein (A) denotes one or more isocyanates, and where (B) denotes a mixture of (B1) and (B2) where B1 is 0 to 85 equivalent-% (relative to the isocyanate groups in (A)) of one or more compounds having an average of 1.8 to 3.0 Zerewitinoff active hydrogen atoms and a number average molecular weight of 400 to 10000, and where B2 is 15 to 100 equivalent-% (relative to the isocyanate groups in (A)) of one or more chain extenders having an average of 1.8 to 3.0 Zerewitinoff active hydrogen atoms and a molecular weight of 62 to 400, and where (C) is a positive amount up to 20% (relative to the weight of said thermoplastic polyurethane elastomer) of auxiliary additives.
The present invention furthermore provides the thermoplastic polyurethane elastomers obtained in this manner.
The present invention also provides the use of the thermoplastic polyurethane elastomers for the production of moldings (for example by casting, compression molding, injection molding), such as sheets, containers, equipment components, casings, rollers, gears, machinery and vehicle components, rolls, elastic coatings, blown and flat films, sheathing, tubes, catheters, seals, profiles, bearing bushes, threads, filaments and fibers.
Isocyanates (A) which may be used are aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates or any mixture of these polyisocyanates (c.f. Houben-Weyl,
Methoden der Organischen Chemie
, volume E 20
, Makromolekulare Stoffe
, Georg Thieme Verlag, Stuttgart, New York 1978, pages 1587-1593). Examples are ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, 1,3-cyclobutane diisocyanate, 1,3- and 1,4-cyclohexane diisocyanate together with any desired mixtures of these isomers, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane, 2,4- and 2,6-hexahydrotolylene diisocyanate together with any desired mixtures of these isomers, hexahydro-1,3- and/or -1,4-phenylene diisocyanate, perhydro-2,4′- and/or -4,4′-diphenylmethane diisocyanate, norbornene diisocyanates (for example U.S. Pat. No. 3,492,330), 1,3- and 1,4-phenylene diisocyanate, 2,4- and 2,6-tolylene diisocyanate together with any mixture of these isomers, 2,4′- and/or -4,4′-diphenyl methane diisocyanate.
Aromatic diisocyanates are preferred, in particular optionally alkyl-substituted tolylene and diphenylmethane diisocyanates, aliphatic diisocyanates, in particular hexamethylene diisocyanate and cycloaliphatic diisocyanates such as 1-isocyanato-3,3,5-trimethyl-5-isocyanato methylcyclohexane, perhydro-2,4′- and/or -4,4′-diphenylmethane diisocyanates.
Isocyanates having a functionality greater than 2.0 to 3.0 may optionally also be used, such as 4,4′,4″-triphenylmethane triisocyanate, polyphenyl/polymethylene polyisocyanates (for example obtained by aniline/formalde-hyde condensation and subsequent phosgenation), together with the distillation residues which contain isocyanate groups which result during industrial isocyanate production, optionally in one or more of the above-stated polyisocyanates. However, care must be taken in this case to ensure that an average functionality of two is not exceeded if the polyurethanes are to be melt processed. It may be necessary to compensate for reactants with high functionality by using additional reactants with a functionality lower than two.
Monofunctional isocyanates suitable for this purpose are, for example, stearyl isocyanate, cyclohexyl isocyanate and phenyl isocyanate.
Zerewitinoff active compounds B1 are compounds having an average of 1.8 to 3.0 Zerewitinoff active hydrogen atoms
Kirchmeyer Stephan
Liesenfelder Ulrich
Müller Hanns-Peter
Ullrich Martin
Bayer Aktiengesellschaft
Gil Joseph C.
Preis Aron
Sergent Rabon
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