CA2119001A1

CA2119001A1 - Process for the thermoplastic working up of polyurethanes

Info

Publication number: CA2119001A1
Application number: CA 2119001
Authority: CA
Inventors: Hartmut Nefzger; Bernd Quiring; Walter Meckel; Werner Rasshofer; Joachim Wagner
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1993-03-18
Filing date: 1994-03-14
Publication date: 1994-09-19
Also published as: DE4308791A1; EP0615989A1; JPH06322064A

Abstract

A PROCESS FOR THE
THERMOPLASTIC PROCESSING OF POLYURETHANES
ABSTRACT OF THE DISCLOSURE
The present invention relates to a process for the thermoplastic processing of polyurethanes via the melt phase wherein said polyurethanes have a melt viscosity which is substantially independent of the molar ratio of isocyanate groups to active hydrogen containing groups. These polyurethanes comprise the reaction product of A) one or more polydiols having an average molecular weight of from 550 to 10,000, B) one or more chain extending agents having a molecular weight 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 hydrogen containing groups is at least 1.10:1, and the polyurethanes are subjected to a temperature treatment prior to thermoplastic processing.

Description

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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-s:\ksl\DB02û5 ~ - .
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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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; ~ 3 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 Mo4021 "'~

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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 Mo4021 , . . . ~ . - . .

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.
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. 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 `J
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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 ~, ~
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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~ - 9 -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 ~ Mo402 1 '`I -~ A _ , 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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r ~ 13 -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 ~ :
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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 .
~, ` 9-1 1:1 1.10 7.8 190 i 10 29.2 195 ~;:
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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15 9-4 1:1 1.02 8.9 180 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%).

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"3 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, Mo4021 ,., . . ~ . . ... . .
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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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Claims

1. A process for the thermoplastic processing of polyurethanes via the melt phase wherein said polyurethanes have a melt viscosity which is substantially independent of the molar ratio of isocyanate groups to active hydrogen containing groups, and said polyurethanes comprise the reaction product of A) one or more polydiols having an average molecular weight(s) of from 550 to 10,000, B) one or more chain extending agents having a molecular weight 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 hydrogen containing groups is at least 1.10:1, and said polyurethanes are subjected to a temperature treatment prior to said thermoplastic processing.

2. The process of Claim 1, wherein said thermoplastic processing is via injection molding.

3. The process of Claim 1, wherein said diisocyanate comprises at least 90 mol-% of naphthylene-1,5-diisocyanate.

4. The process of Claim 1, wherein the average functionality of said components A and B is from 1.95 to 2.35.

5. The process of Claim 1, wherein said chain extending agent comprises one or more dialcohols.

6. The process of Claim 1, wherein said polyurethanes to be thermoplastically processed are waste products from the production of polyurethane cast elastomers.

7. The process of Claim 1, wherein said molar ratio of said isocyanate groups to said Zerewitinoff-active hydrogen groups is at least 1.20:1.

8. The process of Claim 1, wherein said polyurethanes and/or ureas to be thermoplastically processed are stored at temperatures below 220°C until their melt viscosity remains substantially unchanged during further storage.

9. The process of Claim 1, wherein said temperature treatment is carried out over a minimum period of wherein:
t = time in days, T = temperature in °K, and F = a number of from 1 to 5, wherein 1 is selected for polyurethanes which are free from catalyst, and a number up to 5 is selected for polyurethanes which contain catalyst.

10. Molded articles produced via the process of Claim 1 which have been subjected to a heat treatment.