Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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THERMOPLASTIC POLYURETHANES WITH IMPROVED MELT FLOW
BACKGROUND OF THE INVENTION
The invention relates to thermoplastic polyurethane elastomers
with improved processing behavior.
Thermoplastic polyurethane elastomers (TPU's) have long been
known. They are of technical importance because of the combination of
high-quality mechanical properties with the known advantages of
inexpensive thermoplastic processibility. A large range of variation of
mechanical properties can be achieved by the use of different chemical
components. A survey on TPU's, their properties and applications is
given e.g. in Kunststoffe 68 (1978), pages 819 to 825 and in Kautschuk,
Gummi, Kunststoffe 35 (1982), pages 568 to 584.
TPU's are built up from linear polyols, usually polyesters or
polyethers, organic diisocyanates and short-chain diols (chain extenders).
They can be prepared continuously or discontinuously. The so-called belt
process and the extruder process, as the best-known preparative
processes, are also used industrially.
For adjustment of the properties, the components can be varied
within relatively wide molar ratios. Molar ratios of polyols to chain
extenders of 1:1 to 1:12 have proven effective. By these means,
products having Shore hardness values in the range of 70 A to 75 D may
be obtained.
For improvement of the processing behavior - particularly in the
case of products for processing by extrusion - increased stability and an
controllable melt flow are of great interest. This depends on the chemical
and morphological structure of the TPU's.
The structure necessary for an improved processing behavior is
achieved in products manufactured by conventional processes only by
the use of mixtures of chain extenders, e.g. 1,4-butanediol/1,6-hexane-
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diol. As a result of this, the arrangement of the rigid segments is so
greatly distorted that not only is the melt flow improved, but
simultaneously the thermomechanical properties, e.g. tensile strength and
resistance to thermal distortion, are distinctly impaired.
Thermoplastic polyurethane elastomers with aromatic alkoxy-
glycols, e.g., 1,4-bis(2-hydroxyethoxy)benzene, as chain extenders are
distinguished by high deflection temperature, high elasticity, and low
compression set and tensile set; their processing behavior, on the other
hand, is unsatisfactory as a result essentially of a non-uniform melt flow.
DE-OS 2,817,456 describes the manufacture of thermoplastic
polyurethanes from linear polyols, organic diisocyanates and a mixture of
two glycols as chain extenders. The homogeneity and freedom from gel
of the products manufactured e.g. in an extruder are certainly pointed
out, but so also is the disadvantageous lowering of the range of softening
temperatures.
The melt flow of TPU's is often adjusted by addition of mono-
functional compounds as chain control agents which impose an upper
limit on the molecular weight of the polymer. Polymers of especially high
molecular weight cannot be prepared in this way.
The invention provides thermoplastic polyurethane elastomers that
have been obtained by reaction of
A) diisocyanates,
B) polyhydroxy compounds and/or polyamines, with
C) as chain extender, a mixture of
Cl) benzene substituted with at least two substituents selected
from the group consisting of hydroxyalkyl, hydroxyalkoxy,
aminoalkyl and aminoalkoxy moieties, and
C2) an alkanediol with 4 to 44 C atoms
wherein molar ratio C1:C2 = 60:40 to 95:5.
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The melt flow of these TPU's may be adjusted by the nature and
amount of the chain extender C2 without significant change of the
mechanical and thermal properties of the product. The addition of
monofunctional compounds as chain terminating agents is optional, but
not necessary for the adjustment of the melt flow. The products melt
homogeneously, are free from nodules and swollen matter, have improved
extrusion properties, and may be produced in reaction extruders.
Conventional catalysts that accelerate the formation of
polyurethane, for example, tertiary amines or organic metal compounds,
can be used in the preparation of the polyurethane elastomers according
to the invention. It is also possible, for limiting the molecular weight, to
use as chain terminating agents small amounts of monofunctional
compounds, preferably 0.01 to 7 equivalent %, based on the NCO
content of component A). Conventional additives, including waxes,
phenolic antioxidants and UV absorbers can likewise be used, in
amounts of 0.1 to 3 wt. %, relative to the weight of the TPU.
The substituted benzenes, C1), are preferably those having two
identical substituents, more preferably, the substituents are in the 1,4-
positions. These substituents preferably have either a terminal hydroxyl
group or a terminal amino group, contain alkyl or alkylene groups with 1 to
4 carbon atoms and may be bound to the benzene ring via oxygen
(alkoxy) or directly (alkyl). Particularly preferred compounds correspond
to the formula
X-Alk-W-Ph-W-Alk-Y
wherein
X and Y independently, denote OH or NH2,
Alk an alkylene group with 1 to 4 carbon atoms,
W a single chemical bond or an oxygen atom and
Ph the benzene ring.
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Exampies are 1,4-bis(2-hydroxyethoxy)benzene, 1,3-bis(2-
hydroxyethoxy)benzene, 1,2-bis(2-hydroxyethoxy)benzene, 1,4-
bis(hydroxymethyl)benzene and 1,2 bis(hydroxymethyl)benzene.
The alkanediols C2) have 4 to 44, preferably 4 to 20, carbon
atoms. Examples include 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol,
1,10-decanediol and 1,12-dodecanediol.
The molar ratio of Cl to C2 is 60:40 to 95:5, preferably 75:25 to
90:10.
Diisocyanates include aliphatic, cycloaliphatic, araliphatic,
heterocyclic and aromatic diisocyanates. Examples are aliphatic
diisocyanates, such as hexamethylene diisocyanate, cycloaliphatic
diisocyanates, such as isophorone diisocyanate, 1,4-cyclohexane
diisocyanate, 1-methyl-2,4- and -2,6-cyclohexane diisocyanate as well as
the corresponding isomer mixtures, 4,4'-, 2,4'- and 2,2'-dicyclohexyl-
methane diisocyanate as well as the corresponding isomer mixtures and
preferably aromatic diisocyanates, such as 2,4-tolylene diisocyanate,
mixtures of 2,4- and 2,6-tolylene diisocyanate, 4,4'-, 2,4'- and 2,2'-
diphenylmethane diisocyanate, mixtures of 2,4'- and 4,4'-diphenyl-
methane diisocyanate, urethane-modified liquid 4,4'- and/or 2,4'-
diphenylmethane diisocyanates, 4,4'-diisocyanatodiphenylethane-(1,2)
and 1,5-naphthylene diisocyanate. Diisocyanates preferably used are
1,6-hexamethylene diisocyanate, dicyclohexylmethane diisocyanate,
isophorone diisocyanate, diphenylmethane diisocyanate isomer mixtures
with a 4,4'-diphenylmethane diisocyanate content of greater than 96 wt.%
and in particular 4,4'-diphenylmethane diisocyanate and 1,5-naphthylene
diisocyanate.
To the diisocyanates there may be added up to 15% of
polyisocyanates, based on the molar amount of the diisocyanate, but not
more than still allows the polymer to be processed thermoplastically.
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Examples of polyisocyanates are triphenylmethane-4,4',4"-triisocyanate
and polyphenylpolymethylene polyisocyanates.
Substantially linear polyols, polyesters, polyethers, polycarbonates
or mixtures thereof can be used as polyhydroxy compounds B).
Suitable polyether polyols can be prepared by reacting one or
more alkylene oxides with 2 to 4 carbon atoms in the alkylene group with
a starter molecule that contains two combined active hydrogen atoms.
The following, for example, may be mentioned as alkylene oxides:
ethylene oxide, 1,2-propylene oxide, epichlorohydrin and 1,2- and 2,3-
butylene oxides. Preferably, ethylene oxide, propylene oxide and
mixtures of 1,2-propylene oxide and ethylene oxide are used. The
alkylene oxides can be used individually, alternating in succession, or as
mixtures. To be considered as starter molecules are for example: water,
aminoalcohols, such as N-alkyldiethanolamines, for example N-methyl-
diethanolamine, and diols, such as ethylene glycol, 1,3-propylene glycol,
1,4-butanediol and 1,6-hexanediol. Optionally, mixtures of starter
molecules can also be used. Further suitable polyether polyols are the
hydroxyl-group-containing polymerization products of tetrahydrofuran.
The essentially linear polyether polyols preferably have a number
average molecular weight of 500 to 5000. A single polyether polyol or a
mixture of two or more such polyols may be used.
Suitable polyester polyols may be prepared for example from
dicarboxylic acids with 2 to 12 carbon atoms, preferably 4 to 6 carbon
atoms, and polyhydric alcohols. To be considered as dicarboxylic acids
are for example: aliphatic dicarboxylic acids, such as succinic acid,
glutaric acid, adipic acid, suberic acid, azelaic acid and sebacic acid, and
aromatic dicarboxylic acids, such as phthalic acid, isophthalic acid and
terephthalic acid. The dicarboxylic acids can be used individually or as
mixtures, e.g. in the form of a mixture of succinic, glutaric and adipic
acids. For the preparation of the polyesterols it can, if necessary, be
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advantageous to use, instead of the dicarboxylic acids, the corresponding
dicarboxylic acid derivatives, such as carboxylic acid diesters with 1 to 4
carbon atoms in the alcohol group, carboxylic acid anhydrides or
carboxylic acid chlorides. Examples of polyhydric alcohols are glycols
with 2 to 10, preferably 2 to 6, carbon atoms, such as ethylene glycol,
diethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-
decanediol, 2,2-dimethyl-1,3-propanediol, 1,3-propanediol and
dipropylene glycol. The polyhydric alcohols may be used singularly or as
mixtures of two or more alcohols.
Esters of carbonic acid with the named diols, furthermore, are
suitable, especially those with 4 to 8 carbon atoms, such as 1,4-
butanediol and/or 1,8-hexanediol, condensation products of c0-hydroxy-
carboxylic acids, for example o-hydroxycaproic acid and preferably
polymerization products of lactones, for example optionally substituted co-
caprolactones.
Preferably used as polyester polyols are ethanediol-polyadipate,
1,4-butanediol-polyadipate, ethanediol-butanediol-1,4-polyadipate, 1,6-
hexanediol-neopentylglycol-polyadipate, 1,6-hexanediol-1,4-butanediol-
polyadipate and polycaprolactones.
The polyesterols have number average molecular weights of 500
to 5000.
Commercial amine-terminated polyethers, such as are known, e.g.,
under the trademark Jeffamines of Texaco Chemical Co., may be used
as polyamines B). These contain ethylene oxide, propylene oxide or
tetramethylene oxide as repeating unit and have a number average
molecular weight of 400 to 8000.
Among the preferred embodiments, a mixture of 90 to 75 mole-%
of 1, 4-bis (2-hydroxyeth oxy) benzene and 10 to 25 mole-% of one or more
members selected from the group consisting of 1,4-butanediol, 1,6-
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hexanediol, 1,8-octanediol, 1,10-decanediol and 1,12-dodecanediol may
be used as chain extender.
The alkanediols C2) may contain up to 15% (relative to the molar
amount of the chain extenders mixture C1+C 2) of a triol with a molecular
weight of up to 500. Examples are glycerol, trimethylolpropane and their
alkylene oxide adducts as well as 1,2,6-hexanetriol.
Suitable catalysts which accelerate in particular the reaction
between the NCO groups of the diisocyanates and the hydroxyl groups of
the structural components are the tertiary amines, known and
conventional according to the prior art, such as, e.g., triethylamine,
dimethylcyclohexylamine, N-methylmorpholine, N,N'-dimethylpiperazine,
2-(dimethylaminoethoxy)ethanol, diazabicyclo(2,2,2)octane and the like
as well as in particular organic metal compounds such as titanic acid
esters, iron compounds, tin compounds, e.g. tin diacetate, tin dioctoate,
tin dilaurate or the tin dialkyl salts of aliphatic carboxylic acids, such as
dibutyltin diacetate, dibutyltin dilaurate or the like. The catalysts are
usually used in quantities of 0.0005 to 0.1 parts per 100 parts of
polyhydroxy compound.
Chain terminating agents may be used in quantities of 0.01 to 7
equivalent-%, based on the NCO group content of component A).
Preferably no chain terminating agent is used.
0.1 to 3 wt.% (based on the total amount of all components) of
waxes, antioxidants and/or UV absorbers may also be used as additives.
Preferably mixtures of stabilizers are used.
Conventional antioxidants (cf. EP-A 12 343) may be used for this
purpose. Antioxidants based on stearically hindered phenols, e.g., 2,6-di-
tert-butyl-4-methylphenol and pentaerythrityltetrakis-3-(3,5-di-tert-butyl-4-
hydroxyphenyl) propionate (Irganox 1010 of the Ciba Geigy Company)
are preferred.
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In addition, auxiliary agents and/or additives may be included in
the composition of the TPU. Examples include lubricants, inhibitors,
stabilizers against hydrolysis, light, heat and discoloration, flameproofing
agents, dyes, pigments, inorganic and/or organic fillers and reinforcing
agents.
Reinforcing agents are in particular fibrous reinforcing materials,
such as, e.g., inorganic fibers, that are manufactured according to the
prior art and may also be treated with a size.
More detailed information on the aforementioned auxiliary
substances and additives may be found in the technical literature, for
example, in the monograph by J.H. Saunders and K.C. Frisch "High
Polymers", Volume XVI, Polyurethanes, Parts 1 and 2, Interscience
Publishers 1962 and 1964 respectively and in DE-A 2,901,774.
For the preparation of the TPU, the structural components,
optionally in the presence of catalysts, auxiliary substances and/or
additives, are caused to react in such proportions that the equivalent ratio
of NCO groups to the sum of the NCO-reactive groups, in particular the
OH groups, of the structural components, amounts to 0.9:1 to 1.20:1,
preferably 0.95:1 to 1.10:1.
The known mixing plants, preferably those operating with high
shearing energy, are suitable for the manufacture of TPU's. For
continuous manufacture, co-kneaders, preferably extruders, such as, e.g.,
twin-shaft extruders and Buss kneaders, as well as the mixing head/belt
process, may be mentioned.
The TPU according to the invention may be manufactured in a
twin-shaft extruder e.g. by making the prepolymer in the first section of
the extruder and adding the polyol and chain extender in the second
section. Alternatively, the components of the prepolymer may be mixed
outside the extruder in a mixing head or nozzle, and the prepolymer
reaction then carried out in the first section and the afore-mentioned
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stages in the second section of the extruder. Moreover, the whole
prepolymer stage may also be carried out before the extruder. The
prepolymer prepared is then fed into the extruder together with the polyol
and the chain extender .
In another embodiment, a prepolymer is prepared from polyol and
diisocyanate in a tank, and the chain extension mixture added to the
prepolymer. The mixture is then agitated at 210 to 240 C until the
reaction is completed.
According to the invention, chain extender mixtures are used in
which the distance between the functional hydroxyl groups of the diol C2)
which react with isocyanate groups is geared to the corresponding
distance in substituted benzene C1). Easier flowing thermoplastic
polyurethanes are obtained if the chain lengths of the diol and the
benzene derivative do not "match" , i.e., if the diol chain is either too
short or too long. Through a correct choice, therefore, high-molecular
TPU with good melt flow can be prepared without a chain control agent.
The thermoplastic polyurethanes according to the invention have a
melt flow that is adjustable via the chain length of the diol C2). Thus, for
example with 1,4-bis(2-hydroxyethoxy)benzene as chain-extender Cl)
and 1,6-hexane-diol or 1,12-dodecanediol as co-chain-extender C2),
lower-melting products are obtained, while with 1,8-octanediol somewhat
less readily melting products are obtained.
The thermoplastic polyurethanes according to the invention have
excellent mechanical properties. The values of strain at break are
always above 450% and, in most cases exceed 600%. The plastic strain
after stretching of the sample to 200% is very low and independent of the
co-chain extender used. For applications in which strips or films are
extended, this is a particularly important property, since the molded
article returns almost to its original dimensions.
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The thermoplastic polyurethanes according to the invention have
as principal advantage a very high heat deflection temperature,
measured as softening point in the thermomechanical analysis (TMA).
The heat deflection temperature is retained even with optimized melt
flow.
The thermoplastically processible polyurethanes according to the
invention may be used to prepare injection molded articles, fibre and
coating compound, but particularly as extrudate. In the case of extruded
products, such as, for example, films, the thermoplastic polyurethane
according to the invention results in an improved melt flow with
essentially the same other properties.
In the following examples the results of melt volume index (MVI)
measurements are reported as a function of temperature and are a
measure of the melt flow according to the invention. The heat deflection
temperature of the samples was determined by thermomechanical
analysis (TMA; intersection of tangents method).
The invention is further illustrated but is intended to be limited by
the following examples in which all parts and percentages are by weight
unless otherwise specified.
EXAMPLES
Preparation: Prepolymer Process
The polyether polytetrahydrofuran (molecular weight-number
average about 2000) is provided in a flat-flange flask with stirrer and
reflux condenser and dehydrated at 120 C and 14 mbar for 1 hour. Then
dibutyltin dilaurate as catalyst and bis-(4-isocyanatophenyl)methane
(MDI) are added and the mixture is stirred at 120 C. After about 1 hour,
the particular calculated content of free NCO groups is reached.
Ethylenebis(stearylamide) and ionol (2,6-di-tert.-butyl-4-methylphenol) are
dissolved in the melt and the corresponding amount of chain extender is
added. After brief homogenization (ca. 1 min), the reaction mixture is
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poured out into Teflon pans and post-annealed for about 12 hours at 100 C.
Table 1 gives details.
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~-- Le A 30 783 - 12 -
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N
C U) Q a)
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Q. I I I I
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a~
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~ cII 0 Co
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Cn Cfl u) m 0 0
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CV d' ~ ~ N
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a
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C/) Q. ~ 00 00 00 ~
C
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C r
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0
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H
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Clear dependence of the melt flow on length of the carbon chain
of the chain extender C2) is observed in the examples. At the same time
it is observed that the tensile strength reaches a maximum when the co-
chain-extender C2) is optimally adapted to the chain extender Cl). The
strain at break, plastic strain and - particularly remarkable and surprising -
the resistance to thermal distortion, measured as softening point in the
thermomechanical analysis (TMA) behave largely independently of the
adaptation of the chain extender Cl) and C2). Precisely, the
combination of high resistance to thermal distortion and low plastic strain
with the possibility of adjustment of the melt flow distinguishes the
thermoplastic polyurethane according to the invention.
Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood that such
detail is solely for that purpose and that variations can be made therein
by those skilled in the art without departing from the spirit and scope of
the invention except as it may be limited by the claims.
