Note: Descriptions are shown in the official language in which they were submitted.
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Mo-4021
LeA 29,594
A PROCESS FOR TllE
~, THERMOPLASTIC WORKING UP oF POLYURETHANES
BACKGROUND OF THE INVENTION
Thermoplastic polyurethanes (TPU) which can be worked up
e.g. by extrusion or injection molding are state of the art.
Although in the literature relating to TPUs, the NCO:OH ratios of
~i from 0.90:1 to 1.20:1 are usually broadly disclosed, the NCO:OH ratios in
( 5 specific formulations are generally not above 1.05:1. The exception is an
NCO:OH ratio of 1.08:1, which is at best used when monofunctional
reactants are chosen.
. According to the prevailing opinion, polyurethanes which can be
,, worked up (by melting) are only stable in storage if they contain no
~ 10 excess isocyanate groups but only excess hydroxyl or amino end groups;
`~ see e.g. E. Muller in Houben-Weyl, Volume XIV/2, G. Thieme Verlag,Stuttgart, 1963, pages 82 et seq. Thus, for example, it is stated on
page 85 that isocyanate groups which are capable of reacting with the
atmospheric moisture have only limited stability in storage.
~il 15 In the new edition of the same work, Georg Thieme Verlag 1987,Volume E20, page 1638, D. Dieterich states that thermoplastic
elastomers (TPE) based on polyurethanes have a linear structure, are
chemically uncrosslinked and are soluble in dimethylformamide or
tetrahydrofuran. These thermoplastic elastomers must be free from
isocyanate groups to ensure that they can be processed thermo-
plastically. Completely reacted products produced without chain
terminators contain terminal OH groups.
In the monograph, "Polyurethane Elastomers", Applied Science
st Publishers, London, 1982, Chapter 9, C. Hepburn discloses the linearity
,~: 25 of the molecules as an essential precondition for thermoplastic poly-
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urethane elastomers, and states that a partial chemical cross-linking may
be carried out in a second step after thermoplastic processing if a small
excess of NCO is used (page 252).
~: According to the teaching of German Offenlegungsschriften
5 4,030,282 and U.S. Patent 5,06~,600 (see column 2, lines 49-58),
products having higher NCO:OH ratios and/or a higher degree of
branching may be thermally shaped by deep drawing or pressing.
According to the teaching of German Patent Application 4,102,999,
thermoplastically processible synthetiG resins can be produced from
10 cross-linked isocyanate polyaddition products mixed with other
thermoplasts, but this can only be achieved with a substantial breakdown
of molecular weight, as can be seen from the examples: Putty-like mass
(Example 1), tensile strength 6 MPa-s (Example 2).
German Patent Application 4,140,733 similarly claims a process in
. 15 which polyurethane foams are worked up, optionally together with
thermoplasts. According to the teaching therein, the process claimed can
only be applied to foams of isocyanate polyaddition products which
contain isocyanate reactive compounds with an average of at least 2.5
Zerewitinoff active groups as raw materials and are not liquefied in the
20 thermoplastic shaping process.
~ DESCRIPTION OF THE INVENTION
!~¦ It has now surprisingly been found that even when there is a large
i excess of isocyanate groups, polyurethanes consisting substantially of
;~ linear components can be worked up thermoplastically via a true liquid
25 phase (melt), e.g. by injection molding, if they are subjected to a special
temperature treatment. The present invention, therefore, relates to a
process for the thermoplastic working up of polyurethanes, preferably by
injection molding, which are mainly built up of;
-
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A) one or more polydiols having average molecular weights of from
550-10,000,
~) one or more chain extending agents having molecular weights
below 500, an average functionality of about 2, and containing ~-
amino and/or hydroxyl groups as functional groups, and
C) one or more diisocyanates, -
~ wherein said components are present in quantities such that the molar
; ratio of the isocyanate groups to the Zerewitinoff-active hydrogencontaining groups of the reaction mixture is at least 1.10:1, and the
10 polyurethanes are subjected to a temperature treatment prior to
~, thermoplastic processing.
...
It is also within the scope of the present invention to heat treat the
molded articles which are formed by thermoplastically processing the
polyurethanes as described hereinabove.
As used herein, the phrase "thermoplastic processing" describes
. the processing of a TPU by, for example, extrusion with an extruder or
blow molding. Generally, temperatures of from 17û to 250C, and
~ preferably from 190 to 240C are used. There are no special
: i requirements for pressure. The preferred method of thermoplastic
20 processing is via injection molding.
~`~ The chain extending agents preferably contain hydroxyl groups as
functional groups.
The components for synthesizing the polyurethanes to be used
according to the invention are known and are those used in the aFt~
It was surprisingly found, however, that if the polyurethane
products having the molar ratio of isocyanate groups to 7erewitinoff-
active hydrogen containing groups of at least 1.10:1 are subjected to the
required temperature treatment, the melt viscosity undergoes no further
change under subsequent temperature influences and remains virtually
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: constant over a wide range of molar ratios of isocyanate groups to
Zerewi~ino~-active hydrogen containing groups at a given temperature.
Although the products as described by D. Dieterich are no longer soluble
in solvents such as dimethylformamide, dimethylsulphoxide or tetrahydro-
5 furan, they can still be worked up very satisfactorily in injection molding
machines, i.e. they can easily be melted in spite of the high degree of
branching.
- It is particularly surprising that it is only when the solubility
described by Dieterich no longer exists that a virtually constant melt
10 viscosity is established which is independent of the molar ratio of
i
isocyanate groups to Zerewitinoff-active hydrogen containing groups
` required for the present invention. The processing conditions, e.g. in
i injection molding machines, are therefore constant over the range of
~: molar ratios of isocyanate groups to active hydrogen containing groups
15 according to the invention, and thus surprisingly independent of the
, doses or variations in doses used in the production of the polyure-
thane(urea)s.
~-' Even polyurethanes prepared on the basis of naphthylene-1,5-
diisocyanate or bis-tolylisocyanates (TODI3 can be processed surprisingly
20 easily by the process according to the invention. According to the
teaching of German Offenlegungsschrift 3,329,775, such elastomers
generally cannot be thermoplastically shaped. At best, only very soft
elastomers can be thermoplastically shaped, and only with difficulty.
The good processibility in injection molding machines of the
25 products to be used according to the invention which contain a relatively
high proportion of naphthylene-1,5-diisocyanate was, therefore, not to be
expected by one of ordinary skill in the art.
Therefore, it was surprising that even molded parts produced in
complicated molds can be obtained with very superior physical qualities
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by the process according to the invention and undergo virtually no
change in their dimensions even under prolonged exposure to elevated
temperatures.
-
The polyurethanes worked up according to the invention are
.
5 preferably waste products obtained from the production of cast
' 1 elastomers, and most preferably from Vulkollan~ production. These
,~ waste products may be molded parts which are misshapen or cuttings,
,~ etc.. Products produced by faulty dosing can only be used according to
-
. the invention if they conform to the above-mentioned criteria in their
10 composition. The products to be processed according to the invention
must, of course, be introduced into the processing maohine in a suitable
form such as, for example, granulates.
The polyurethanes to be processed according to the invention
may, however, also be produced from raw materials which are liquid
' 15 under the operating conditions such as, for example, raw materials of this
type in the form of cylindrical granulates, using known one-shot or multi-
stage processes in the presence or absence of catalyst(s). The reaction
may be carried out in solution, in which case the solvent should be ~ ~ ;
evaporated, or solvent frea, e.g. by a continuous casting process, or in a
~, 20 screw reactor analogously to German Auslegeschrift 2,302,564.
It has been found that the required temperature treatment may be
carried out in accordance with the empirical formula~
~'l t- 100
(T- 293)F
where t = the time required for the temperature treatment in
days
T= temperature in K
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F = a number of from 1 to 5, wherein 1 is selected for
. polyurethanes which are free from catalyst, and a
s number up to 5 is selected for polyurethanes which
~; contain a relatively high quantity of catalyst.
The faetor F depends on the activity of the catalyst present in the
~; polyurethane and should in principle be determined for aach type and
quantity of catalyst. It has been found in practice that it is sufficient to
half the treatment time caiculated to be required for catalyst-free systems
at a particular temperature, i.e. to assume F = 2, in order to obtain
. 10 thermoplastically processible polyurethanes. If the minimum treatment
. j,
.~ time required is thereby exceeded, this entails no disadvantages. For
. industrial production, however, it is advisable to keep the amount of
i temperature treatment as low as possible by determining the true
. numerical value of factor F by preliminary tests.
; .
. 15 The validity of Formula I was tested in the temperature range of
from 295 to 470K, i.e. from 22 to about 200C.
' The temperature treatment is preferably carried out at
'~ temperatures above 30C, and most preferably above 50C.
Temperatures above 120C are generally not necessary.
~; ` 20 Heat treatment of the molded articles formed according to the
process of the invention may also be carried out using the empirical
formula as set forth h~reinabove. Temperatures range from a minimum
of 30C to a maximum of 120C.
The polyurethanes to be processed according to the invention may
~:; 25 contain the usual additives such as agents protecting against hydrolysis,
.... ~
antioxidants, UV stabilizers, waxes, oils, fillers, optionally in the form of
inorganic or organic fibers or platelets, pigments, dyes, antimicrobial
.
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.;~ agents and flame retardants. They may be blended or mixed with other
polymers, in particular thermoplasts, andlor contain processing
auxiliaries.
The products obtained by the process according to the present ~- :
5 invention, e.g. molded articles such as injection molded parts, are
distinguished from parts produced from conventional thermoplastic
polyurethanes by exceptionally good dimensional stability under heat and
~: exceptionally good restoring power after deformation as well as very
good dynamic properties for polyurethane thermoplasts. They also
10 combine high abrasion resistance with good resistance to oil and neutral
organic solvents.
The examples described hereinbelow further illustrate details for
the process of this invention. The invention, which is set forth in the
foregoing disclosure, is not to be limited either in spirit of scope by these
15 examples. Those skilled in the art will readily understand that known
- variations of the conditions of the following procedures can be used.
- ~: Unless otherwise noted, all temperatures are degrees celsius and all
:; parts are parts by weight.
EXAMPLES
.~ 20 Examr~le 1
100 parts by weight of a hexanediollbutanediolt2,2-dimethyl-
. propanediol polyadipate having an average molecular weight of 3300
were heated to 130C. 0.3 parts of a montan ester wax (Hoechst FE1)
and 18 parts by weight of naphthylene-1,5-diisocyanate were stirred in.
" 25 As soon as the melt was clear, stirring was continued for about 15
minutes. The reaction mixture was then heated to 150C, and 4.6 parts
by weight of butanediol were homogeneously stirred in to obtain a molar
. ratio of isocyanate groups to active hydrogen containing groups of 1.10:1
in the reaction mixture, and the reaction mixture was poured into a
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,~ polytetrafluoroethylene dish after 35 seconds. The product was
~, tempered at 100C for about 24 hours and then granulated when cold.
-, Exam~le 2
ç~ ~ The procedure was the same as described in Example 1 except
xi 5 that 4.2 parts by weight of butanediol-(1,4) were used to obtain a molar
ratio of isocyanate groups to active hydrogen containing groups of 1.20:1
` in the reaction mixture.
K .; The intrinsic melt index, i.e. IMI, in g/10 min. of the products of
i Examples 1 and 2 was determined according to DIN 53735 in a melt
: 10 index apparatus, Model HKV 2000 (Manufacturer Gotffert, Buchen,
- Odenwald, Germany) at a pressure of 2.45 bar, using a nozzle 1 mm in
diameter and 15 mm in iength at 215C after various lengths of storage
time at room temperature (see Table 1):
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::: Table 1
~ '! 15 Intrinsic melt index (IMI) at 215C after storage at 22C
Storage time iMI (9/10 min) of products from
Months Example 1 Example 2
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0 3.8
20 3 3.5 4.1
6 5.8 4.2
Exampie 3 (comparison)
A mixture of 100 parts of polybutanedioi adipate (OH number
56 mg KOH/g, acid number 0.6 mg KOHIg), 9.5 parts by weight of
25 butanediol-(1,4) and 1 part by weight of bis-diisopropylphenylcarbodi-
imide was heated to 120C.
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a) 39.4 and b) 39.7 parts by weight of 4,4'-diisocyanatodiphenyl-
methane (MDI) were stirred in for about 30 seconds and the reaction
mixture was poured into a polytetrafluoroethylene dish. It is kept at
~ 110C for 1 hour and 80C for 16 hours and granulated when cold.
:. 5 Example 4
. The procedure was the same as in Example 3 except that 42.8
parts by weight of MDI were used.
Examples 5 and 6
The procedure was the same as in Example 3 except that 46.7
~" 10 (Example 5) and 50.6 (Example ~) parts by weight of 4,4'-diisocyanato-
diphenylmethane were used.
The granulate of polyurethanes from Examples 3-5 was measured
. both fresh and after 7 months' storage in a closed vessel at 22C (see
Table 2). The IMI value after 3 months storage at 22C is shown in
15 Graph I of Figure 1 vs. the molar ratio of the isocyanate groups to active ~ -
, I hydrogen groups foreach Example 3a-6.
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Table 2
Influence of storage on the viscosity of the polyurethanes
from Examples 3-6
PUR from Example
3a 3b 4 5 6
NCO OH ratio 1 00 1 02 1 10 120 1 30
Solution viscosity 3600 13300 partly insoluble
25% in dimethyl-
formamide (mPa-s)
Solution viscosity 3300 12800 slightly swelled
7 months, 22C
IMI') at 200C 26 5 7 12 5 50 120
fresh (g/10 min)
15 IMI" after storage 28 9 5 13 5 13 2 15
3 months, 22C
~ IMI') after storage 29 6 8 115 12 5 13 2
!~ 7 months, 22C
:i 1) IMI values according to DIN 53735
Tables 1 and 2 show that the products used in accordance with ~ -
the invention were not soluble in solvents such as, for example, dimethyl-
formamide but readily melt and could therefore be thermopl2stically
processed The melt viscosity of products having the same composition
but different NCO OH ratios within the range according to the present
~ 25 invention was virtuaily the same after sufficient storage (within the
`` accuracy of measurement) Molded products having tensile strengths of
from 30 to 55 mPa-s and elongations at break of from 300 to 650% were
obtained by injection molding the products from Examples 1 to 6
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, Exam~le 7
Cuttings from rolls produced from polyurethane cast elastomers
having the following composition were used:
100 parts by weight of polyethane diol adipate (OH number 56, acid
5 numberO.8)
5.5 parts by weight of butanediol-(1,4)
0.1 part by weight of trimethylolpropane
27 parts by weight of naphthylene diisocyanate
~'~ The molar ratio of isocyanate groups to active hydrogen containing
10 groups is 1.15:1.
The granulated cuttings were dried under vacuum, subjected to a
temperature treatment of 120C for 25 hours and injection molded in an
injection molding machine, Model ANKER V14 at a maximum housing
., temperature of 215C and a cycle of 30/30 sec. A silicone mold release
, . . .
15 agent was sprayed into the injection mold. Molded products having a
matt surface and the following physical data were obtained (data of cast
products having the same composition are given for comparison); see
Table 3.
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Table 3 shows that the rnolded articles obtained by injection
: molding by the process according to the invention were equal in their
; physical properties to the cast products from whose cuttings they were
~`~ produced.
5 Examp!e 8
Products having the same composition as in Examples 1 and 2
- ~ except at a molar ratio of isocyanate groups to active hydrogen groups of
`; 1.22:1 were continuously produced in a two-shaft screw extruder at a
~ .
temperature of about 220C. The granulate was stored in a drying
,' 10 cupboard for 14 days at 80C under normal pressure and the IMI was
monitored at 200C and 210C (see Table 4).
,: Table 4
Intrinsic melt index (IMI) of the product from Example 8 after storage at
. l 80C:
:~ 15Tempering time IMI (9/10 min) at
;~ days/at 80C 200C 210C ~ :
~. . ..
. 1 103
2 10
, ........................................................................ .
3 38
:~ 7 32
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9 29
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14 34
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Example 9
0.6% by weight of bis-2,6-diisopropylphenyl-carbodiimide and 0.6%
by weight of 4-methyl-2,8-di-tert.-butylphenol were incorporated in 592.3
g of dehydrated hexanediol/neo-pentylglycol polyadipate (OH number
`;~........ 5 56 mg KOH/g). 13.8 9 of isophorone diamine (IPDA) were stirred in at ~0
to 60C in 5 mlnutes. After the reaction mixture was heated to 130C,
142.2 9 of 1,5-naphthylene-diisocyanate were added and the mixture was
.; stirred for 10 minutes, the final temperature being 100C. After reheating
to 120C, the necessary quantity of chain extending agent or mixtures of
; 10 chain extending agents required for adjusting the molar ratio of
,~ isocyanate groups to active hydrogen groups (see Table 5) was added.
The mixture was intensively stirred for 60 seconds, poured out on metal
sheets and then heated at 120C for 24 hours. After granulation, the
material was worked up by the injection molding process. The molded
~- 15 products obtained were again tempered for 24 hours at 100C before
being tested for the mechanical properties shown in Table 5.
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Table fi
MVI values of the granulates obtained according to
Example 9
.~ Example Butanediol~ NCO/OH MVI')
hexanediol molarValue Temp.
(mol/mol) ratiog/10 ()
min
.
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` 9-1 1:1 1.10 7.8 190
i 10 29.2 195
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9-2 1:1 1.16 16.6 190
~, 9-3 1:0 1.10 1.8 200
:27.0 235
Comparison ~xample:
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9-5 1:1 1.06 3.9 185
15.7 190
1) Melt Volume index according to DIN 53735
~' Example 10
20 Preparation of Isocyanate Prepolymer:
24 parts of 1,5-naphthylene diisocyanate were added at 130C in a glass
beaker with stirrer to 6~ 2/3 parts of a hexanediol/neopentyl glycol/pQly-
adipate (OH number 56 mg KOH/g) which had previously bsen
dehydrated and to which Hoechstwachs-C (0.6% by weight), bis-2,6-
25 diisopropylphenyl carbodiimide (0.6% by weight) and 4-methyl-2,6-di-tert.-
butylphenol (0.1% by weight) had previously been added. The 1,5-
` j naphthylenediisocyanate dissolved in about 15 minutes. Heating was
adjusted to 90C, whereby the temperature of the reaction mixture fell to
: ~ this value within about 2 hours. The isocyanate value was found to be
30 7.3% (theory 7.4%).
Mo4021
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2.333 parts of isophoronediamine was stirred into 33 1/3 parts of a
' hexanedioi/neopentyl glycol polyadipate at about 60C. This mixture was
then added to the isocyanate prepolymer described hereinabove which
was at a temperature of 80-90C: (and had in the meantime been
5 transferred to a tin can). The mixture thus obtained was then again
stirred at this temperature for about 5 minutes to ensure complete mixing.
~; The viscosity remained substantially constant during this time and the
mixture became cloudy. The reaction mixture was then heated to 120C
and the quantity of chain lengthening agent (mixture) required for
10 adjusting the index was added. The reaction mixture, now containing all
the components, was in~ensively stirred for about a further 50 seconds,
. during which a slight exothermic reaction was observed (about 5-10C).
.. At the end of this time, the mixture was stili fluid for a short time and was
poured out on metal sheets coated with Teflon film. The white,
15 absolutely homogeneous product thus obtained was then heated in a
circulating air drying cupboard at 120C for 24 hours, granulated and
worked up by injection molding and analyzed, see Table 7: ~:
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Example 11
. The product from Example 7 was produced in a two-shaft screw
extruder at temperatures of from 160 to 220C by the prepolymer
process wherein an isocyanate semi-prepolymer was first prepared from
5 half the polyester and all the naphthylene diisocyanate, using various
NCO:OH molar ratios.
The melting leaving the reactor was chilled in water at about 15C,
dried ur,der vacuum at 80C for 48 hours and tempered. The following
~ intrinsic melt indices (IMI, determined in g/10 minutes~ was determined at
- 10 220C and 2.45 bar for different NCO:OH molar ratios. This is shown in
Table 8 and Graph ll in Figure 1.
Table 8
I NCO:OH _ IMI at 220C
",
.. ~ 1.01 18
1.05 14
i 1.09 30
~j 1.13 38
1.18 35
Examele 12
The procedure used was the same as described in Example 11
except that a mixture of 5.1 parts by weight of butanediol-(1,4) and 0.75
parts by weight of hexanediol-(1,6) was used as the chain extending
agent instead of the mixture of butanediol and trimethylolpropane. In
~ .~
addition, 25 ppm of titanium tetra-butylate, based on the weight of the
polyester, was used as a catalyst. The products after being cooled in air,
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were tempered in a vacuum at 80C for 16 hours. The following intrinsic
melt indices were then determined, see Table 9 and Graph lll in
Figure 1.
'.' 1
~ ~ Table 9
.
~; 5 NCO:OH _ IMI at 218C
1.02 3
1.07 19
:., 1.12 16
1.2 17
As may be seen from Table 9, a factor F of about 3 is sbtained for
catalysis with 25 ppm ~based on the weight of the polyester) of titanium
tetrabutylate.
~;! Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood that such
` I 15 detail is solely for that purpose and that variations can be made therein
,t`, by those skilled in the art without departing from the spirit and scope of
~i the invention except as it may be limited by the claims.
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