Note: Descriptions are shown in the official language in which they were submitted.
CA 022~4231 1998-12-09
Reaction mixture and process for producing polyisocyanate
polyaddition products
The present invention relates to reaction mixtures comprising (a)
isocyanates, (b) compounds which are reactive toward isocyanates
and have a mean functionality of from 1.8 to 2.5 and a molecular
weight of from 500 to 8000 g/mol and, if desired, (c) chain
10 extenders having a molecular weight of less than 500 g/mol, (d)
catalysts and/or (e) customary auxiliaries and/or additives.
Furthermore, the invention relates to a process for producing
polyisocyanate polyaddition products by reacting (a) isocyanates
with (b) compounds which are reactive toward isocyanates and have
a mean functionality of from 1.8 to 2.5 and a molecular weight of
from 500 to 8000 g/mol and, if desired, (c) chain extenders
having a molecular weight of less than 500 g/mol, (d) catalysts
and/or (e) customary auxiliaries and/or additives, and also to
polyisocyanate polyaddition products which are obtainable by such
20 a process.
The production of polyisocyanate polyaddition products, for
example thermoplastic polyurethanes, hereinafter also abbreviated
to TPUs, is generally known.
TPUs are partially crystalline materials and belong to the class
of thermoplastic elastomers. A characteristic of polyurethane
elastomers is the segment structure of the macromolecules. Owing
to the different cohesion energy densities of the segments, in
30 the ideal case phase separation into crystalline "hard" and
amorphous "softN regions occurs. The resulting two-phase
structure determines the property profile of products which are
produced from these polyurethane systems. The soft phase is,
owing to the entropy elasticity of the long-chain soft segments,
35 responsible for the elasticity and the hard phase is responsible
for the strength, distortion resistance and heat resistance of
the polyurethane fibers. In the hard phase, the polymer chains
are fixed by means of intermolecular interactions of the hard
segments. The structure is a physical network held together
40 mainly by hydrogen bonds. Under mechanical loading, these
interactions are partly overcome, so that irreversible
restructuring of the hard segments occurs within the hard phase.
This has an adverse effect on the hysteresis behavior.
Particularly melt-spun polyurethane fibers here display large
45 working and tension losses and also high permanent extensions.
for this reason, better fixing of the rigid segments is necessary
to improve the fiber properties. Furthermore, known TPUs based on
CA 022~4231 1998-12-09
.
aromatic isocyanates have an undesirable tendency to discolor on
irradiation and storage.
It is an object of the present invention to develop a reaction
5 mixture comprising (a) isocyanates, (b) compounds which are
reactive toward isocyanates and have a mean functionality of from
1.8 to 2.5 and a molecular weight of from 500 to 8000 g/mol and,
if desired, (c) chain extenders having a molecular weight of less
than 500 g/mol, (d) catalysts and/or (e) customary auxiliaries
10 and/or additives, which mixture is suitable for producing
polyisocyanate polyaddition products by reaction of the
abovementioned components. The polyisocyanate polyaddition
products should, in particular, have an improved thermal
stability, measurable by means of the heat distortion
15 temperature, and improved hysteresis behavior after loading, and
should also be stable to light.
We have found that this object is achieved by the isocyanates (a)
20 comprising aliphatic and/or cycloaliphatic isocyanates and the
ratio of the isocyanate groups present in (a) to the
isocyanate-reactive groups present in (b) plus, if used, (c)
being from 1 : 0.98 to 1 : 0.8.
25 According to the present invention, an excess of isocyanate
groups over the groups which are reactive toward the isocyanate
groups is used in the reaction mixture. This excess can be
expressed by the molar ratio of the isocyanate-reactive groups in
the components (b) plus (c) to the isocyanate groups in the
30 component (a). According to the present invention, this ratio is
from 1 : 0.98 to 1 : 0.8, preferably from 1 : 0.95 to 1 : 0.85.
As a result of this excess of isocyanate groups, these isocyanate
groups form, during and possibly after the formation of the
urethane groups by reaction of (a) with (b) and, if used, (c),
35 crosslinks in the form of, for example, allophanate and/or
isocyanurate structures which lead to the improved properties of
the polyisocyanate polyaddition products. The formation of the
crosslinks can, if desired, be promoted by addition of catalysts,
e.g. alkali metal acetates or formates, which are generally known
40 for this purpose. Processing of the reaction product, i.e. the
polyisocyanate polyaddition product, to produce the desired
films, moldings, injection-molded articles, hoses, cable
sheathing and/or fibers should preferably be carried out during
and/or immediately after the formation of the urethane groups and
45 before complete reaction of the reaction mixture, since
thermoplastic processing of the polyisocyanate polyaddition
products to produce films, moldings or fibers is preferably
CA 022~4231 1998-12-09
carried out at low temperatures before and/or during the
formation of the crossllnks. Isocyanates used according to the
present invention are aliphatic and/or cycloaliphatic
isocyanates, preferably diisocyanates, particularly preferably
5 hexamethylene diisocyanate. These isocyanates according to the
present invention can, if desired, be used in combination with
customary further isocyanates, for example known aromatic
isocyanates. Preference is given to using from 50 to 100%,
particularly preferably from 75 to 100%, of the isocyanate groups
10 used as (a) in the form of aliphatic isocyanates.
The reaction of the reaction mixture of the present invention in
the process for producing polyisocyanate polyaddition products
can be carried out by known methods, for example by the one-shot
15 process or the prepolymer process, for example by reacting an
NCO-containing prepolymer which can be prepared from (a) and
parts of the components (b) and, if desired, (c) with the
remainder of (b) and, if desired, (c), on a customary belt unit,
using a known reaction extruder or equipment known for this
20 purpose. The temperature in this reaction is usually from 60 to
250~C, preferably from 60 to 180~C, particularly preferably from
70 to 120~C.
25 During and, if desired, after the formation of the polyurethane
groups by reaction of (a) with (b) and, if desired, (c), the
reaction products can be pelletized, granulated or processed by
generally known methods, for example by extrusion in known
extruders, by injection molding in customary injection molding
30 machines or by generally known spinning processes, for example by
melt spinning, to produce moldings of all types, films or, in the
case of the spinning processes, to form fibers.
Preferably, the reaction mixture is processed on extruders or
35 injection molding machines to produce films or moldings or by a
spinning process to form fibers during and, if desired, after the
formation of the urethane groups by reaction of (a) with (b) and,
if desired, (c), particularly preferably from the reaction melt
and before complete formation of allophanate and/or isocyanurate
40 crosslinks. This direct further processing of the reaction
mixture without granulation or pelletization and without
substantial or complete reaction of the reaction mixture offers
the advantage that crosslinking by formation of, for example,
allophanate and/or isocyanurate structures has occurred to only a
45 slight degree or not at all and the reaction mixture can
CA 022~4231 1998-12-09
.
therefore be processed at a desirably low temperature to form the
end products such as films, moldings or fibers.
The processing of the reaction mixture is thus preferably carried
5 out by processing the reaction mixture in a softened or molten
state on extruders or injection molding machines to form films or
moldings or by a spinning process to form fibers at from 60 to
180~C, preferably from 70 to 120~C, during the reaction of (a)
with (b) and, if desired, (c), particularly preferably from the
10 reaction melt and before complete formation of allophanate and/or
isocyanurate crosslinks.
The process product from the extruder, the injection molding
15 machine or the spinning process is preferably heated at from 20
to 120~C, preferably from 80 to 120~C, for at least two hours,
preferably from 12 to 72 hours, under otherwise customary
conditions to partially or completely form, particularly
preferably completely form, the allophanate and/or isocyanurate
20 crosslinks. This subsequent heating of the moldings, films or
fibers makes it possible to obtain the crosslinks in the
polyisocyanate polyaddition products, which crosslinks lead to
the very advantageous properties of the products in respect of
the thermostability and the hysteresis behavior after loading.
If unsaturated components (b) and/or (c), for example
cis-1,4-butenediol, are used, the moldings, films or fibers can,
after they have been produced, be treated by irradiation, for
example by irradiation with electron beams.
Examples of the components (a) to (e) are given below. In the
following, molecular weights have, unless indicated otherwise,
the unit g/mol.
35 a) Suitable organic isocyanates (a) are, according to the
present invention, aliphatic and/or cycloaliphatic and, if
desired, additionally aromatic diisocyanates. Specific
examples are: aliphatic diisocyanates such as hexamethylene
1,6-diisocyanate, 2-methylpentamethylene 1,5-diisocyanate,
2-ethylbutylene 1,4-diisocyanate or mixtures of at least two
of the C6-alkylene diisocyanates mentioned, pentamethylene
-1,5-diisocyanate and butylene 1,4-diisocyanate,
cycloaliphatic diisocyanates such as
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane
(isophorone diisocyanate), cyclohexane 1,4-diisocyanate,
1-methylcyclohexane 2,4- and 2,6-diisocyanate and also the
corresponding isomer mixtures, dicyclohexylmethane 4,4'-,
. . .
CA 022~4231 1998-12-09
2,4'- and 2,2'-diisocyanate and also the corresponding isomer
- mixtures, 1,4- and/or 1,3-di(isocyanatomethyl)cyclohexane,
1,4- and/or 1,3-di(isocyanatoethyl)cyclohexane, aromatic
diisocyanates such as 1,3- and/or
1,4-di(isocyanatomethyl)benzene, tolylene 2,4-diisocyanate,
mixtures of tolylene 2,4- and 2,6-diisocyanate,
diphenylmethane 4,4'-, 2,4'- and/or 2,2'-diisocyanate (MDI),
mixtures of diphenylmethane 2,4'- and 4,4~-diisocyanate,
urethane-modified liquid diphenylmethane 4,4'- and/or
2,4'-diisocyanates, 1,2-di(4-isocyanatophenyl)ethane and
naphthylene l,5-diisocyanate. Preference is given to using
hexamethylene l,6-diisocyanate.
b) Suitable substances (b) which are reactive toward isocyanates
and have a mean functionality, i.e. a functionality averaged
over the component (b), of from 1.8 to 2.5, preferably from
1.9 to 2.2, particularly preferably from 1.95 to 2.1, are,
for example, polyhydroxyl compounds having molecular weights
of from 500 to 8000, preferably polyetherols and
polyesterols. However, other suitable compounds are
hydroxyl-containing polymers, for example polyacetals such as
polyoxymethylenes and especially water-insoluble formals,
e.g. polybutanediol formal and polyhexanediol formal, and
aliphatic polycarbonates, in particular those prepared from
diphenyl carbonate and 1,6-hexanediol by transesterification,
having the abovementioned molecular weights. The polyhydroxyl
compounds mentioned can be employed as individual components
or in the form of mixtures.
The mixtures for producing the TPU or TPUs have to be based
at least predominantly on bifunctional isocyanate-reactive
substances.
Further isocyanate-reactive substances (b) which can be used
are polyamines, for example amine-terminated polyethers, e.g.
the compounds known under the name Jeffamine~ (Texaco
Chemical Co.); the mean functionality of the component (b)
should be in the range according to the present invention.
Suitable polyetherols can be prepared by known methods, for
example from one or more alkylene hydroxides having from 2 to
4 carbon atoms in the alkylene radical and, if appropriate, an
initiator molecule containing two reactive hydrogen atoms in
45 bound form by anionic polymerization using alkali metal
hydroxides such as sodium or potassium hydroxide or alkali metal
alkoxides such as sodium methoxide, sodium or potassium ethoxide
CA 022~4231 1998-12-09
or potassium isopropoxide as catalysts or by cationic
polymerization using Lewis acids such as antimony pentachloride,
boron fluoride etherate, etc., or bleaching earth as catalysts.
Examples of alkylene oxides are: ethylene oxide, 1,2-propylene
5 oxide, tetrahydrofuran, 1,2- and 2,3-butylene oxide. Preference
is given to using ethylene oxide and mixtures of 1,2-propylene
oxide and ethylene oxide. The alkylene oxides can be used
individually, alternately in succession or as a mixture. Suitable
initiator molecules are, for example: water, aminoalcohols such
10 as N-alkyldialkanolamines, for example N-methyldiethanolamine,
and diols, e.g. alkanediols or dialkylene glycols having from 2
to 12 carbon atoms, preferably from 2 to 6 carbon atoms, for
example ethanediol, 1,3-propanediol, 1,4-butanediol and
1,6-hexanediol. If desired, mixtures of initiator molecules can
15 also be used. Other suitable polyetherols are the
hydroxyl-containing polymerization products of tetrahydrofuran
(polyoxytetramethylene glycols).
Preference is given to using polyetherols derived from
20 1,2-propylene oxide and ethylene oxide in which more than 50%,
preferably from 60 to 80%, of the OH groups are primary hydroxyl
groups and in which at least part of the ethylene oxide is
arranged as a terminal block, and in particular
polyoxytetramethylene glycols.
Such polyetherols can be obtained by, for example, first
polymerizing the 1,2-propylene oxide onto the initiator molecule
and subsequently polymerizing on the ethylene oxide or first
30 copolymerizing all the 1,2-propylene oxide in admixture with part
of the ethylene oxide and subsequently polymerizing on the
remainder of the ethylene oxide or, stepwise, first polymerizing
part of the ethylene oxide onto the initiator molecule, then
polymerizing on all of the 1,2-propylene oxide and then
35 polymerizing on the remainder of the ethylene oxide.
The polyetherols, which are essentially linear in the case of the
TPUs, usually have molecular weights of from 500 to 8000,
preferably from 600 to 6000 and in particular from 800 to 3500.
40 They can be employed either individually or in the form of
mixtures with one another.
Suitable polyesterols can be prepared, for example, from
dicarboxylic acids having from 2 to 12 carbon atoms, preferably
45 from 4 to 8 carbon atoms, and polyhydric alcohols. Examples of
suitable dicarboxylic acids are: aliphatic dicarboxylic acids
such as succinic acid, glutaric acid, suberic acid, azelaic acid,
~ . .
CA 022~4231 1998-12-09
sebacic acid and preferably adipic 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 succinic, glutaric and adipic
5 acid mixture. Likewise, mixtures or aromatic and aliphatic
dicarboxylic acids can be used. In place of the dicarboxylic
acids, it may be advantageous to use the corresponding
dicarboxylic acid derivatives such as dicarboxylic esters having
from 1 to 4 carbon atoms in the alkohol radical, dicarboxylic
10 anhydrides or dicarboxylic acid chlorides for preparing the
polyesterols. Examples of polyhydric alcohols are alkanediols
having from 2 to 10, preferably from 2 to 6, carbon atoms, e.g.
ethanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,
1,6-hexanediol, 1,10-decanediol, 2,2-dimethylpropane-1,3-diol,
15 1,2-propanediol and dialkylene ether glycols such as diethylene
glycol and dipropylene glycol. Depending on the desired
properties, the polyhydric alcohols can be used alone or, if
desired, in mixtures with one another.
20 Also suitable are esters of carbonic acid and the diols
mentioned, in particular those having from 4 to 6 carbon atoms,
e.g. 1,4-butanediol and/or 1,6-hexanediol, condensation products
of w-hydroxycarboxylic acids, for example ~-hydroxycaproic acid,
and preferably polymerization products of lactones, for example
25 substituted or unsubstituted ~-caprolactones.
As polyesterols, preference is given to using alkanediol
polyadipates having from 2 to 6 carbon atoms in the alkylene
30 radical, e.g. ethanediol polyadipates, 1,4-butanediol
polyadipates, ethanediol-1,4-butanediol polyadipates,
1,6-hexanediol-neopentyl glycol polyadipates, polycaprolactones
and, in particular, 1,6-hexanediol-1,4-butanediol polyadipates.
35 The polyesterols usually have molecular weights (weight average)
of from 500 to 6000, preferably from 800 to 3500.
c) Preferred chain extenders (c) which usually have molecular
weights of less than 500 g/mol, preferably from 60 to
499 g/mol, particularly preferably from 60 to 300 g/mol, are
alkanediols and/or alkenediols and/or alkyne diols having
from 2 to 12 carbon atoms, preferably having 2, 3, 4 or
6 carbon atoms, e.g. ethanediol, 1,2- and/or 1,3-propanediol,
1,6-hexanediol and in particular 1,4-butanediol and/or cis-
and/or trans-1,4-butenediol, and dialkylene ether glycols
such as diethylene glycol and dipropylene glycol. However,
diesters of terephthalic acid and alkanediols having from 2
CA 022~4231 1998-12-09
to 4 carbon atoms, e.g. bis(ethanediol) terephthalate or
bis(1,4-butanediol) terephthalate, and hydroxyalkylene ethers
of hydroqulnone, e.g. 1,4-di(~-hydroxyethyl)hydroqulnone, are
also suitable.
It may also be advantageous to use small amounts, i.e. up to
15% by weight of the amount of chain extenders used, of
trifunctional compounds such as glycerol, trimethylolpropane
and/or 1,2,6-hexanetriol.
To adjust the hardness and melting point of the TPUs, the molar
ratios of the formative components (b) and (c) can be varied
within a relatively wide range. It has been found to be useful to
15 employ molar ratios of polyhydroxyl compounds (b) to chain
extenders (c) of from 1 : 1 to 1 : 12, in particular from 1 : 1.8
to 1 : 6.4, with the hardness and the melt point of the TPUs
increasing with increasing diol content.
20 d) Suitable catalysts which, in particular, accelerate the
reaction of the NCO groups of the diisocyanates (a) with the
hydroxyl groups of the formative components (b) and (c) are
the customary catalysts known from the prior art, for example
tertiary amines such as triethylamine,
dimethylcyclohexylamine, N-methylmorpholine,
N,N'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol,
diazabicyclo[2.2.2]octane and the like and also, in
particular, organic metal compounds such as titanate esters,
iron compounds such as iron(III) acetylacetonate, tin
compounds such as tin diacetate, tin dioctoate, tin dilaurate
or the dialkyltin salts of aliphatic carboxylic acids such as
dibutyltin diacetate, dibutyltin dilaurate or the like. The
catalysts are usually used in amounts of from 0.002 to
0.1 part per 100 parts of polyhydroxyl compound (b).
e) Apart from catalysts, customary auxiliaries and/or additives
(e) can also be added to the formative components (a) to (c).
Examples which may be mentioned are surface-active
substances, fillers, flame retardants, nucleating agents,
oxidation inhibitors, stabilizers, lubricants and mold
release agents, dyes and pigments, inhibitors, stabilizers
against hydrolysis, light, heat or discoloration, inorganic
and/or organic fillers, reinforcing materials and
plasticizers.
CA 022~423l 1998-l2-09
More detailed information on the abovementioned auxiliaries and
additives may be found in the specialist literature.
The process of the present invention is illustrated by the
5 following examples.
Example 1 (Ratio NCO:OH = 1.1:1):
10 100 g (0.051 mol) of polytetrahydrofuran having a molecular
weight of 2000 and a hydroxyl number of 57.3 mgKOH/g were placed
in a Teflon vessel and heated to T=100~C. While stirring
vigorously, the following were added at 10 minute intervals,
8.99 g (0.102 mol) cis-1,4-butenediol, 28.3 g (0.1683 mol) of
15 hexamethylene diisocyanate (HDI) and 3 mg of dibutyltindiacetate
as catalyst. About 5 minutes after addition of the catalyst, the
viscosity of the reaction mixture increased greatly as a result
of the increase in molecular weight. To complete the reaction,
stirring was continued for another 20 minutes at 100~C.
The polyurethane melt which still contains free NCO groups due to
the excess of HDI was immediately afterward, without granulation,
used as spinning polymer for the melt spinning process.
25 The spinning process was carried out using a piston-type spinning
unit. The spinning temperature was 80~C and the residence time was
30 minutes. The fiber obtained was not sticky and could be wound
without problems. After storage for two days at room temperature,
the fiber was heated at 100~C for 24 hours, giving a significant
30 property improvement.
The polyisocyanate polyaddition products produced by this method
were no longer soluble in DMA/DMF and accordingly contained
35 allophanate and/or isocyanurate crosslinks; they displayed
significantly improved fiber properties.
Comparative Examples 2-4:
40 Polyurethane fibers were produced as described in Example 1,
except that the molar ratio of polytetrahydrofuran: butenediol:
HDI was 1:1.5:2.5 (Example 2), 1:2:3 (Example 3) or 1:3:4
(Example 4).
~5 The fiber properties of the TPU fibers are shown in the following
table:
CA 022~4231 1998-12-09
.
Table 1:
Example 1 2 3 4
NCO/OH 1.1:1 1:1 1:1 1:1
~ rell)insoluble 1.35 1.34 1.37
Permanent 35 110 95 120
extension
1st cycle [%]
Permanent 45 130 115 140
extension
5th cycle [%]
Tenacity 7.0 3.0 3.4 3.2
[cN/tex]
Extension at700 1100 800 800
break
[%]
Tension loss0.115 0.24 0.24 0.22
bw5
HDT [~C] 125 80 90 95
20 1) 0.5 % strength by weight of solution in DMA, ~: viscosity
The fiber properties were determined in accordance with DIN
53835.
Compared to conventional melt-spun TPU fibers, the
allophanate-crosslinked TPU fiber of the present invention
displays significantly improved fiber properties.
The covalent crosslinking of the hard segments by means of
30 allophanate links made it possible to achieve a significant
improvement in the hysteresis behavior (lower permanent extension
and tension loss), a doubling of the tenacity and an increased
HDT.
