DE1151112B - Process for the production of polyurethane elastomers - Google Patents

Description

Process for making polyurethane elastomers The invention relates to a process for the production of polyurethane elastomers by reaction of higher molecular weight polyhydroxyl compounds and difunctional crosslinkers with an excess of diisocyanates over the total available active hydrogen atoms. In this process, partially crosslinked prepolymers with 0, 3 to 2% of free NCO groups obtained when the desired degree of crosslinking is reached by adding basic nitrogen compounds in the second stage and through Crosslinking through diisocyanates is processed further in the third stage with shaping will. The prepolymers obtained are suitable because of their plasticity, the usual treatment methods in calenders, extrusion or the like. Subject to will.

It is known to be difficult to process such prepolymers Obtain products that are bubble free when using prepolymers low viscosity is assumed, as produced by known processes can be. The purpose of the method according to the invention is therefore to address these shortcomings to fix by the fact that the prepolymers is given a plasticity, the one good processability at moderate temperatures of about 30 to 60 ° C allows. It is known that elastomers, homogeneous molded bodies or foam bodies made of linear, Polyethers or polythioethers and polyisocyanates containing urethane groups thereby to produce that first a mixture of a reacted with excess diisocyanate Polyethers with terminal hydroxyl groups with one opposite isocyanate groups Bifunctional compound brought to reaction and the reaction product after addition of a diisocyanate is deformed and cured at elevated temperature. With this one known processes, if the prepolymer still contains free isocyanate groups, stabilization can be carried out by adding a primary or secondary monoamine.

According to the invention, therefore, particularly high-quality elastomers are obtained, if to stabilize the prepolymer in the second stage as basic nitrogen compounds organic compounds with at most one nitrogen atom, the primary or secondary May be nature, and at least one hydroxyl group, in equivalent amounts with respect to the free NCO groups.

The prepolymer obtained in the first stage contains 0.3 to 2 "/ o, preferably 0.5 to 1.5% free NCO groups at the ends of all chains of the branched end product.

In the following explanation of the method according to the invention polymeric compounds with two OH groups include polyesters, polyethers, polyester amides or analogous compounds understood as they are usually used in the production used by polyurethanes and denoted by the abbreviated symbol HO-P-OH will. These are preferably polymeric compounds with a molecular weight on the order of 750 to 5000.

Under a compound that is bifunctional with respect to isocyanates understood a low molecular weight compound having two groups, which can react with isocyanate groups, such as diols, diamines or Dicarboxylic acids, which are abbreviated below with the symbol HO-B-OH. If one also designates the diisocyanates with the symbol OCN-D-NCO, the process can for the production of polyurethane elastomers according to the following scheme are represented: (M + l) [OCN-D-NCO] + M [HO-P-OH] -OCN-D OCN-D (NH-CO-O-P-O-CO-NH-D) -NCO (I) where m essentially has a value between 1 and 10, preferably between 1 and 4 has.

For the sake of simplicity, the linear polyurethane obtained according to I is referred to below with the symbol OCN-M-NCO. where n essentially has a value between 1 and 10, preferably between 1 and 4.

The branched prepolymer obtained in this way with terminal free NCO groups is to be referred to below with the symbol -E-NCO for the sake of simplicity. This End product has the molecular weight of the HO-P-OH and the specified above given coefficients m and n have a molecular weight of about 40,000, while the linear polyurethane OCN-M-NCO obtained according to I has a molecular weight of the order of magnitude 1000 to 10,000 has. This reaction is interrupted when the product has plasticity which is suitable for the usual processing methods in the rubber industry is.

However, this prepolymer is rapidly converted at room temperature check the fully networked state. In order to stabilize it, the procedure will be used according to the invention all free NCO groups that cause this conversion by terminal hydroxyl groups replaced. For this purpose, the branched prepolymer, that is obtained according to II, d. H. into the -E-NCO a polyfunctional hydroxyl compound brought in, which one group, and indeed only one group, has its ability to react is higher than the reactivity of the hydroxyl groups it contains, where this compound is applied in such an amount as the number of responsive Corresponds to groups which are equivalent to the number of free NCO groups in the -E-NCO.

This reactive group is an amino group, so that when Method according to the invention the stabilization is effected by means of an amino alcohol, the alcohols being both monohydric and dihydric or trihydric amino alcohols be considered. The amino function itself can be primary or secondary among the condition that at most one aromatic carbon is attached to the amino nitrogen is bound.

As examples of compounds for the process according to the invention are suitable are mentioned: monoethanolamine, diethanolamine, methylaminoethanol, Phenylaminoethanol or amino-2-methyl-2-propanediol-1,3.

This stabilization reaction can be represented as follows : -E-NCO + HaN-R-OH -E-NH-CO-NH-R-OH (III) The amount of amino alcohol must be molecularly equivalent the number of free NCO groups of the) -E-NCO. This amount must be strictly adhered to, since a deficit of amino alcohol results in a more or less strong crosslinking of the prepolymer while an excess affects its properties.

Diisocyanates were crosslinked, starting from the prepolymer which was stabilized with ethanolamine or with piperidine. The percentages of the two stabilizers correspond to equimolecular amounts. The theoretically required amounts of ethanolamine or piperidine for perfect stabilization according to the above statements are 0.9 and 1.20 / o, respectively. % Elasticity losses breaking strength elongation Stabilization through (0) (1) (2) (3) (4) I 0, 6 200 15 3, 4 550 II 0, 7 200 13 3, 8 520 III 0.9 190 14 4.2 580 IV Ethanolamine 1, 0 170 17 3, 5 590 Ia piperidine ....................... 0.8 140 22 2.5 630 IIa 1, 0 155 21 2, 7 610 IIIa piperidine ....................... 1.2 155 25 2.6 595 IV a 1, 4 120 27 2 725 (0) Percentage calculated on the amount of prepolymers.

(1) Young's modulus at 150% (g / mm2).

(2) Hysteresis losses at 20 ° C.

(3) Breaking strength (kg / mm2).

(4) elongation (o / o).

The table shows that the most beneficial amount of ethanolamine is the Reason of the free NCO groups theoretically calculated corresponds. It surrenders also that the elastomer with ethanolamine with respect to the modulus of elasticity, the Losses and, in particular, breaking strength are superior to rubber with piperidine is.

With the sample III, which is stabilized with 0.9 ethanolamine, was a heating measurement was carried out in the Goodrich flexometer under the following conditions : Load 7 kg / cm2, path 6, 2 mm, number of vibrations 1560 per minute, test temperature 38 ° C.

The test showed a temperature increase of 26 ° C with a continuous Deformation of 1, 9, which is comparable to that under the same conditions measured heating and fatigue values of a vulcanized natural rubber. In the case of the elastomer stabilized with piperidine, on the other hand, the measurement in the flexometer cannot be performed under the same conditions. The samples heated up and were destroyed before the end of the experiment.

Working examples II, III and IV Working examples II, III and IV were carried out in the same way as embodiment I, wherein however, the ethanolamine was replaced: in embodiment II by 1.550 / o Diethanolamine, in embodiment III by 1, 1% N-methylethanolamine and in embodiment IV by 2% N-phenylethanolamine.

The "vulcanization" of these prepolymers, including the prepolymer according to Example I was carried out with the introduction of 3 parts of magnesia, 8 parts Dimethyl 3, 3'-diphenylmethane diisocyanate 4, 4 'and 0.1 part cobalt naphthenate 100 parts prepolymer.

The table below shows the properties of the vulcanizates: Hysteresis fracture Elastomer elasticity elongation loss of strength the end Experiment No. The values are under the same conditions determined as in the previous table 1 197, 5 14, 5 4, 3 555 II 207, 6 18, 7 4, 3 515 III 180, 5 17, 5 2, 6 545 IV 153, 5 17 3, 4 660 Example V 1000 parts of a polyadipate of 3 parts of ethylene glycol and 1 part of propylene glycol with an OH number of 81.4 and an acid number of 0.7 were mixed with 320 parts of dimethyl-3,3 at 90 ° C. and for a period of 60 minutes '-biphenylene-di-isocyanate-4, 4' reacted in the presence of 0.1 part of iron chloride and 10 parts of magnesia. Then 5 parts of adipic acid and 25 parts of butanediol-1. 4 added. After good homogenization, the mixture was poured into a trough and heated to 120 ° C. for 3 to 5 hours.

The urethane elastomer thus obtained was made by adding 0.9% ethanolamine stabilized. After the mass on a cylinder mixer at 50 ° C 90 parts of dimethyl-3, 3'-diphenylmethane-di-isocyanate-4, 4 'and 20 parts of magnesia, calculated. on 1000 parts of the starting polyester had been added, the mixture became 60 minutes heated to 134 ° C under a pressure of 15 kg / cm2.

A urethane elastomer having the following properties was obtained : Modulus of elasticity at 250% (g / mm2) 355 rebound elasticity at 60 ° C. 90, 3 breaking strength (kg / mm2) .. 4, 8 elongation at break (° / 0) ..... 600 The one for stabilization of the -E-NCO required amount of amino alcohol can be determined by a chemical determination of the free NCO groups of the prepolymer; but it can also be determined by a simple and straightforward method based on the property of the amino alcohol is based to degrade the prepolymer -E-NCO if it is in excess is present and, if it is used in insufficient quantity, its plasticity to diminish.

The experiment consists in that in the presence of a catalyst, for example Cobalt naphthenate, in small samples of the prepolymer of 20 g known amounts of ethanolamine are introduced, which are dimensioned so that they theoretically according to the starting formula Include approximately calculated amount. After the samples are up for 1/4 hour 120 ° C, shows the sample, the plasticity of which has not changed, the amount of ethanolamine needed to properly stabilize the prepolymer necessary is. It has been shown that this amount corresponds to the amount calculated on the basis of the determination of the isocyanate groups in the mass.

During the final networking in the third stage of the procedure using the groups by which the free NCO groups are replaced, d. H. of the hydroxyl groups, which come from the amino alcohol as a stabilizer, that stabilized Prepolymers finally "vulcanized" by introducing a polyisocyanate, preferably an aromatic diisocyanate, and heating to a temperature from 130 to 150 ° C under pressure.

In this way, a “vulcanized” urethane rubber is obtained with excellent properties, especially with regard to rebound resilience and the breaking strength.

This "vulcanization" can, if desired, be further promoted by basic inorganic or organic compounds, for example magnesia or by metal compounds such as salts or organometallic compounds of the Iron or cobalt, which act as catalysts in the "vulcanization reaction" works.

The polyurethane elastomers obtained in this way differ advantageously from the known elastomers in which primary or secondary monoamines were used for stabilization. Comparative measurements of an elastomer stabilized according to the invention with ethanolamine with such known elastomers are compiled in the table below: Elastic-hysteresis-fracture-fracture- modulus of elasticity losses strength elongation at 20 * C (g / mm) (kg / mm) ("/.) Ethanolain ... 207 17 4, 5 498 Piperidine ...... 160 27 2, 85 560 N-butylamine .. 202 26 3, 32 535 EXAMPLE I 19.5 parts of butanediol were added to 1000 parts of a polyadipate of a mixture of 3 parts of ethylene and 1 part of propylene glycol with an OH number of 83.5, an acid number of 0.5 and a water content of 0.1% and added 5 parts of adipic acid. After adding 320 parts of dimethyl-3,3'-biphenylene-di-isocyanate-4, 4 'and 10 parts of magnesia at 90 ° C with subsequent 3 to 5 hours of heating at 120 ° C, a prepolymer was obtained which at Temperatures of 40 to 70 ° C in the rolling mill could be processed well, but this had the disadvantage that it crosslinked slowly at room temperature.

The stabilization was achieved that in the mass a such amount of ethanolamine was introduced, the equivalent of the amount in the Isocyanate groups present in prepolymers prevented its change on storage cause.

In the exemplary embodiment, the determination had shown that 0.6% NCO groups were contained in the non-stabilized prepolymer, and the required The amount of ethanolamine was 0.9% in accordance with that after the aforementioned direct method calculated amount.

The stability of the prepolymer treated in this way results from the following viscosity measurements according to Mooney. At first- Plasticity after the expiration of plasticity after Mooney 1 month 2 months 3 months Stabilized .... 20 20 25 25 Not stabilized 20 40 crosslinked For comparison, stabilization was also carried out by means of piperidine, which was used in an amount of 1.2% equivalent to the ethanolamine. The prepolymer showed excellent stability, but the physical properties of the elastomer after "vulcanization" are less good than those of an elastomer that has been "vulcanized" with ethanolamine.

The following comparison table shows the properties of the »Vulcanizates «Obtained with the same crosslinking formula, per 100 parts of the Initial polyester were used: 3 parts of magnesia, 8 parts of dimethyl-3, 3'-diphenylmethane-di-isocyanate-4, 4 'and 1 part cobalt naphthenate.

The use of cobalt naphthenate as a catalyst in the isocyanate reaction proved necessary as in his absence it was impossible to get out of with Piperidine stabilized mass, a correspondingly malleable and crosslinkable prepolymer to obtain. However, this does not apply to the prepolymer stabilized with ethanolamine the same thing, since without the use of this catalyst it will vulcanize perfectly «Left.

The heating was carried out at 134 ° C for 60 minutes and under a pressure of 15 kg / cm2.

In the table below are the properties of the elastomers indicated by means of

Claims (2)

PATENT CLAIMS: 1. Process for the production of polyurethane elastomers by a) reaction of higher molecular weight polyhydroxyl compounds and difunctional ones Crosslinkers with an excess of diisocyanates over the total available active hydrogen atoms to partially crosslinked prepolymers with 0.3 to 2% free NCO groups in the first Stage, b) stabilization of the degree of crosslinking at the desired point in time by addition of basic nitrogen compounds in the second stage and c) crosslinking through Diisocyanates in the third stage with shaping, characterized in that as basic nitrogen compounds in the second stage organically niche connections with at most one nitrogen atom, which can be primary or secondary in nature, and at least one hydroxyl group in equivalent amounts with respect to the free NCO groups are used. 2. The method according to claim 1, characterized in that as compounds with at most one nitrogen atom, which can be primary or secondary, and at least a hydroxyl group monoethanolamine, diethanolamine, methylaminoethanol, phenylaminoethanol or amino-2-methyl-2-propanediol-1,3 is used. Publications considered: German Patent No. 838,652; German Auslegeschrift No. 1 028 772; U.S. Patent No. 2,760,953.