DE1569012C - Process for the production of polyurethane elastomers - Google Patents

Description

Polyurethane elastomers are generally made from linear polyesters or polyethers with hydroxyl end groups and organic di- or polyisocyanates. Here z. B. the hydroxy polyester with a polyisocyanate to form an isocyanate polyester containing free isocyanate groups implemented, which is then chain extension and crosslinking with water, glycols or diamines, optionally with the addition of a further polyhydroxyl component (see German patent specification 838 826), is crosslinked to form a rubber-elastic product.

A disadvantage of the isocyanate polyesters mentioned is their limited shelf life, since those in the prepolymers contained free isocyanate groups react easily with humidity. For this it is already known, the isocyanate end groups of the isocyanate polyesters or polyethers with glycols, diamines, To block amino alcohols or monohydric basic nitrogen compounds. One obtains here stable prepolymers that can be crosslinked with excess polyisocyanate. It has, however demonstrated that the physical properties of the crosslinked elastomers made from these prepolymers are not always sufficient in practice. When using glycols to block the Isocyanate groups give elastomers with low elasticity and strength. Leave with diamines Although better elastomer properties are achieved, these prepolymers are, however, after mixing with the polyisocyanate is much more unstable and because of the more reactive amino groups they have a less favorable one Scorch behavior. Such prepolymers are in German patent specification 952 940 described. Attempts have been made to overcome the aforementioned difficulties by using amino alcohols or from mixtures of a diamine with a glycol, but one does not get in either In the case of a significant improvement in the scorch behavior. Are the remaining isocyanate groups saturated with a monovalent basic nitrogen compound, a prepolymer is obtained, which has no reactive end groups and is therefore extremely inert. This method is thus also unsuitable for practical purposes.

Except for the two-step process mentioned above

for the production of prepolymers, it is also known to use a one-step process, a mixture of a linear higher molecular weight polyhydroxyl compound and a low molecular weight chain lengthener with an organic diisocyanate (in a maximum equivalent amount to the active hydrogen atoms present) to convert to a prepolymer. With water as a chain extender you get a

Intermediate product that is vulcanized relatively little during deformation and elastomers with good physical properties Properties. Presumably, the improvement in the scorch behavior is based on the structure of the molecule in which the less active linear polyhydroxyl compound is compared to the more active chain extender is preferably attached as an end group. The reaction of water Urea bridges formed with isocyanate groups offer sufficient crosslinking possibilities, with an elastomer with good physical properties is created. The disadvantages of this method are in the difficult-to-control one-step reaction, which among other things affects the viscosity of the product is subject to great fluctuations and that it is difficult because of the use of water to use large amounts of aromatic components as chain extenders, which is essential for the achievement of certain Elastomer properties is necessary. Foaming and cracking are further difficulties and the degradation in the deformation of the elasto-. because the prepolymer is hygroscopic.

The object of the invention is therefore to overcome the aforementioned difficulties and to create an easy-to-control, reproducible process for the production of polyurethane elastomers with excellent physical properties using storage-stable prepolymers. This object is achieved by the invention.
The invention thus relates to a process for the production of polyurethane elastomers by reacting prepolymers (I) which contain no free isocyanate groups

(A) linear, higher molecular weight polyhydroxy compounds with a molecular weight of min-

'least700,

(B) aromatic diamines and

(C) aromatic diisocyanates

with (II) an excess amount of an organic polyisocyanate, which is characterized in that the prepolymers (I) used have been prepared in such a way that component (A) was used in two proportions, the first part of (A ) initially with about 1.5 to 8 equivalents (C) per equivalent (A), but at most the equivalent amount (C), based on (A) + (B), had been reacted ^{at temperatures from room temperature to 200 ° C,} and then the second part of (A) with the

retained product from (C) and the first part of (A) and with at most that of the remaining isocyanate groups in the product equivalent amount (B) had been reacted further.

The difference between the method according to the invention and the method of German patent specification 952 940, where prepolymers with free amino groups are used is that in the present process in the first reaction stage only part, preferably half, of the total polyhydroxyl compound (A) is used. In the second stage of the process according to the invention, the aromatic reacts Diamine (B) is preferred because of its higher reactivity with the isocyanate polyester of the first Stage with the formation of urea groups. Since the amount of diamine is at most the free isocyanate groups is equivalent in the isocyanate polyester also reacts (except in the borderline case where the amount on diamine (B) is equivalent to the remaining NCO groups) some of the hydroxyl groups of the newly added Polyester, so that ultimately a storage-stable prepolymer is formed in the molecule Contains ester groups, urea groups and urethane groups and does not contain free isocyanate groups, however has free hydroxyl groups.

The prepolymers have a practically linear structure and contain a sufficient amount of urea groups for the formation of networks. The analysis shows that the end groups of the prepolymers im originate essentially from the end groups of the polyhydroxyl component (A).

The term "practically linear" means that the prepolymer is sometimes only partially swollen and provides a gel-like product that is sparingly soluble in ketones or esters than other synthetic ones Elastomers with an essentially linear structure. As is well known, there is a slight deviation from the linear structure due to minor branching or incomplete crosslinking to the Rollability off.

Due to the special molecular structure, the prepolymers are within the scope of the invention prepolymers produced by the process of German patent specification 952 940 in kneadability, superior to scorch and mold flow. The scorch behavior is at the same time a measure of the storage stability of the prepolymer in a mixture with the polyisocyanate. this results from the comparison of the experiment 1-D (method of the German patent specification 952 940) with the Experiment 1-G in Table I of the invention.

In the production of the polyurethane elastomers, the prepolymers are each used with an excess implemented on polyisocyanate. A comparison of the mechanical properties of those obtained from the prepolymers elastomers produced according to the invention with those elastomers obtained from the prepolymers have been produced according to the method of German patent specification 952 940 (comparative example 1-D in Table I of the present invention) shows that the elastomers prepared according to the invention with greater Shore hardness (80 compared to 70) have a greater elongation at break (740 compared to 630). In this case, dqm comparative example 1-D even found consistently better values than the German one Patent 952,940 has.

It is also possible to select any chain extenders for the prepolymer and to add linear compounds to the end groups, which means that the processability can be changed or modified. For example, an elastomer with a low tendency to crystallize is generally desired, but the prepolymer should often have a suitable degree of crystallization to reduce its tackiness. Through the exclusive or partial use of a compound with a high tendency to crystallize as a linear component which is intended to be attached to the end groups, the processability can be significantly improved without impairing the physical properties of the end product.
The molecular weight of the component (A) must be at least 700 and may be 4,000 or more, preferably 1,000 to 2,000. Glycols, amino alcohols and other polyhydroxy compounds having a molecular weight of 5000 or less can be used in place of a part of the component (A).

The component (A) includes polyglycols or higher molecular weight polyhydroxy compounds, such as Polyester, e.g. B. that of f-caprolactone, the reaction products of aliphatic dihydric alcohols, such as ethylene glycol, propylene glycol or butylene glycol with dicarboxylic acids such as succinic acid, adipic acid, Pimelic acid or sebacic acid, polyethers, such as polyetrahydrofurans, Ethylene oxide and propylene oxide adducts, polyester amides produced by mixed condensation of aliphatic diamines such as ethylenediamine and amino alcohols, ζ. B. l-hydroxy-2-aminoethane, have been obtained with dicarboxylic acids, polythioethers, Polysulfides, formaldehyde polymers, copolymers of foramaldehyde, or mixtures of aforementioned polymers.

Dihydric alcohols, glycols or amino alcohols with lower molecular weight, which are in the mixture which can be used with component (A) are, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol or 1-hydroxy-2-aminoethane.

Examples of the aromatic diamines (B) are halogen-substituted aromatic diamines such as 2,5-dichloro - ρ - phenylenediamine, 3,3 '- dichlorobenzidine, ο - dichlorobenzidine, 4,4' - methylene - bis - (2 - chloroaniline), unsubstituted aromatic diamines, such as p-phenylenediamine, benzidine, or diamino compounds with a triazine ring, like lauroguanamine. Mixtures of these amines can also be used will.

Examples of organic diisocyanates (C) are ρ - phenylene diisocyanate, diphenylmethane - 4,4 '- diisocyanate, 1,5-naphthylene diisocyanate, 2,4-tolylene diisocyanate or mixtures of 2,4- and 2,6-tolylene diisocyanate.

The following applies to the molar ratio of components (A), (B) and (C): At a molar ratio of [(A) + (B)] / (C) in the range 1.1 to 1.2, the prepolymer shows the best roll mill processability. If necessary, however, a molar ratio of 0.9 to 1.5 or higher can also be used. When the ratio of [(A) + (B)] / (C) is significantly higher than 1.0, the prepolymer generally has has a low viscosity and is sticky on the roller. When the ratio is much lower than 1.0, the prepolymer becomes too tough due to crosslinking and is unsuitable.

The method for the manufacture, which is not claimed here,

position of the prepolymers is carried out in two stages, the polyhydroxyl compound (A) in the two stages in a ratio of 3: 1 to 1: 3, preferably 1: 1, is used.

In the first stage of the prepolymer production, which is not claimed here, about 1.5 to 8 equivalents of component (C) are used per 1.0 equivalent of component (A), the isocyanate (C) in a maximum equivalent amount, based on (A) + (B) is used. Here the two. Components at temperatures up to 200 ⁰ C, preferably at 40 to 150 ⁰ C, mixed with one another. The response time can vary widely, e.g. B. a few minutes to several hours.

In the absence of water in component (A), the water can react with the isocyanate. The reactants must therefore be largely anhydrous. Drying can be brought about by stirring for about 2 hours at 130 to 135 ^° C. under 30 to 60 torr.

Components (A) and (C) can be reacted at atmospheric pressure. Preferably the last part of the reaction is carried out under reduced pressure to avoid formed during the reaction Remove gases.

Tertiary amines, such as N, N '- dimethylbenzylamine, N - methylmorpholine, are used as catalysts, Ν, Ν'-dimethylaniline, triethylamine or organic Tin compounds, such as tin (II) octoate, tin (IV) dibutyl bis (acetylacetonate) or tin (IV) dibutyl di (ethylhexoate).

Examples of inhibitors are inorganic acids such as hydrochloric acid, phosphoric acid, boric acid or sulfuric acid, organic .. acids such as adipic acid or succinic acid, acid chlorides such as benzoyl chloride or acetyl chloride, or Schiff bases, such as α, α'-dinitrilo-di-o-cresol.

The catalysts act in a concentration of about 0.001 to 0.5%, based on all Respondents.

When using component (C) in excess over component (A) or, if the reactivity of the component (A) is low, a part of the component (A) can by divalent Alcohols or amino alcohols of low molecular weight are replaced.

In the second stage of the prepolymer preparation process, which is not claimed here, the Reaction product of the first stage with the remainder of component (A) and with component (B) implemented, the component (B) in a maximum equivalent amount to the isocyanate groups of the Reaction product of the first stage is used. The second portion of the component (A) and the component (B) can be added either as a mixture or separately. If necessary, the Reaction product of the first stage before the reaction in the second stage, a further amount of the component (C) can be added.

The reaction conditions in the second stage are the same as those of the first. Generally runs however, the reaction in the second stage is faster and there is a rapid increase in viscosity. The mixing process must therefore be done quickly and thoroughly.

In the second stage of the prepolymer production, which is not claimed here, part of the Component (A) replaced by dihydric alcohols or amino alcohols of low molecular weight will. They improve the processability of the prepolymers obtained when the proportion of the components (B) and (C) is relatively large compared to that of component (A). In general, however, their usage is limited in the mixture, as this slightly affects the physical properties of the elastomer will.

The prepolymer obtained after the second stage is mixed with excess organic polyisocyanate cross-linked to form polyurethane elastomers. The crosslinking or vulcanization is closely related to the shaping together. The deformation processes conventional in the rubber industry can be used will. The prepolymer can be stored under conditions similar to ordinary elastomers. Processing with polyisocyanates takes place on roller mills or in an internal mixer.

The organic polyisocyanates used in the vulcanization of the process according to the invention include not only the aforementioned aromatic diisocyanates, but also polyisocyanates and their Dimers and the polyisocyanate of the formula

OCN

NCO

HCH

NCO

The mixture to which excess polyisocyanate has been added is shaped and heated under pressure in a hot press after preforming, or it is heated after calendering or extrusion to produce elastomeric moldings. The compression molding can take place between 100 and 160 ^° C., preferably at 140 to 150 ^° C. The vulcanization time can be about 5 to 30 minutes and the pressing pressure 30 to 300 kg / cm ² , preferably 100 to 200 kg / cm ² . The molded body can be easily removed from the mold, but release agents such as silicone oils or waxes can also be used. About 0.05 to 1.0% of an accelerator such as lead ethylphenyldithiocarbamate can be used to shorten the vulcanization time, to prevent foaming and cracking and to facilitate removal from the mold. After removal from the mold, the physical properties of the molded body can be further improved and stabilized by ^{heating in hot air at 100 to 120 ° C. for 2 to 24 hours.}

The examples illustrate the invention. Parts are by weight unless otherwise stated.
In the examples, the following designations are used for technical polyisocyanates:

Polyisocyanate designation ₆ , isomer mixture of 80 parts
2,4- and 20 parts 2,6-Toluy-
lene diisocyanate
Dimer tolylene diisocyanate ... TDI-80
TDI dimer

example 1

An ethylene glycol adipic acid polyester with a hydroxyl number of 55 and an acid number of 2 is used dried by heating at 130 ° C for 2 hours under reduced pressure. This polyester is used to manufacture used by elastomers. Experiments 1-A to 1-F are comparative experiments according to the prior art Technology. Experiment 1-G is carried out according to the method according to the invention.

Experiment 1-A

100 parts of the polyester are mixed with 16 parts of TDI-80 and reacted at 120 ° C. for 30 minutes. The melt obtained is mixed with 8 parts of 3,3'-dichloro-4,4'-diaminodiphenylmethane added and then poured into a mold at about 100 ° C. After some Minutes, the mixture gels and after about 1 hour the molded body is removed and a further 12 hours heated in hot air to about 100 ° C. An elastomeric film is obtained.

Experiment 1-B

The gel-like material obtained in Experiment 1-A is cold-rolled and mixed with 0.5 part of piperidine. A stable, raw rubber-like prepolymer is obtained. With this prepolymer will be 6 parts of TDI dimer kneaded. This product becomes an elastomeric film at 140 ° C. for 20 minutes compression molded.

Experiment 1-C

Instead of 8 parts of 3,3'-dichloro-4,4'-diaminodiphenylmethane 4.5 parts of 1,4-butanediol are added to the melt obtained in Experiment 1-A. Man receives a tough, raw rubber-like prepolymer, which, however, does so even after the addition of additional quantities does not provide any useful elastomer of organic polyisocyanate.

Experiment 1-D

100 parts of the polyester are mixed with 12 parts of TDI-80 and 9 parts of 3,3'-dichloro-4,4'-diaminodiphenylmethane processed into a stable prepolymer that is easy to roll. In 100 parts of this product 5 parts of TDI dimer are rolled in, and immediately afterwards the product obtained is 5 minutes pressed at 130 ° C to form a tough elastomeric molding.

Experiment 1-E

From 100 parts of the polyester, 17 parts of TDI-80, 9 parts of 3,3'-dichloro-4,4'-diaminodiphenylmethane and 2.5 parts 1,4-butanediol, a prepolymer is prepared which, after incorporation of TDI dimer has a somewhat better stability than the product obtained in experiment 1-D. The product is 10 minutes pressed at 140 ° C to form an elastomeric molding with good physical properties.

Experiment 1-F

100 parts of the polyester used in Experiment 1-A are mixed with 0.9 parts of water. The Mixture is reacted with 14 parts of TDI-80 at 50 to 90 ° C. After about 15 hours you get a stable prepolymer. 100 parts of this prepolymer are kneaded with 8 parts of TDI dimers, and that The product obtained is pressed for 30 minutes at 140.degree. C. to give an elastomeric molding.

Experiment 1-G

First, 50 parts of the polyester used in Experiment 1-A are reacted with 13.5 parts of TDI-80, and then the product obtained is mixed with 50 parts of the polyester and 10 parts of 3,3'-dichloro-4,4'-diaminodiphenylmethane added and heated to 100 ° C for 2 hours. A kneadable, stable prepolymer is obtained. 100 parts of this prepolymer are kneaded with 7 parts of TDI dimers, and the product obtained is 10 minutes at 140 ° C to one tough elastomer molded body.

In general, when using 0.1 to 0.5 parts of an accelerator ^ such as lead ethylphenyldithiocarbamate, reduce the pressing time when the prepolymer is reacted with the TDI dimer. You can also use the physical Properties of the elastomers after deformation by heating to 100 in air for several hours Stabilize up to 120 ° C or by aging at 20 to 30 ° C for several days to several weeks.

For comparison, Table I shows the processability of those obtained in Experiments 1-A to 1-G Pre-polymers and the physical properties of the elastomers compiled.

Table I.

Properties of the prepolymer (1-A) (l-B) (l-C) (1-D) (l-E) (1-F) (1-G) Deformation process
Manufacture of the prepoly
meren pour Press
difficult
bad
too quickly
bad Press
easy
Well
too quickly
very good Press
easy
Well
very
quickly
bad Press
easy
Well
quickly
better Press
fewer
easy
moderate
slow
very good Press
easy
very good
slow
very good Kneadability
Vulcanization
Flow in the form

209508/419

continuation

10

Properties of the elastomer (l-A) (l-B) (l-C) (l-D) (l-E) (l-F) (l-G) Shore hardness A. 75 68 very
bad 70 80 335 260 very
bad 540 360 360 380 Tensile strength (kg / cm ² ) ... 830 540 very
bad 630 720 730 740 Elongation at break (%) .... 42 38 very
bad 45 35 42 42 45 40 very
bad 68 45 40 65 Rebound resilience (%) Well bad very
bad very good very good bad very good Tear strength (kg / cm) ... Resistance to
Chemicals ...

Example 2

By changing the aromatic content in Experiment 1-G of Example 1, the hardness of the elastomers obtained can be determined change after deforming. This can be seen from Table II, which also shows the uniformity of the physical properties of the finished moldings due to the low water sensitivity of the prepolymers can be found.

Table II

attempt

(2-A)

(2 B)

(1-G) parts

(2-C)

(2-D)

1st stage
polyester
TDI-80 ..

2nd stage
polyester
Amin *) ..

(Amin + TDI-80)

(Molar ratio of active H / isocyanate)

Shore hardness A of the elastomer if 7 parts TDI dimer with 100 parts Prepolymerem are implemented ..

Influence of moisture on the product in winter
(Tokyo and Yokohama)

Influence of moisture on the product in summer
(Tokyo and Yokohama)

50
12th

50

20th

1.16

75

50 13.5

23.5

1.12 80

50 15.5

50 13 28.5

Ul 85

50 18

50 17

35

1.10

90

*) S.S'-dichloro-'M'-diaminodiphenylmethane.
(-) No influence.
(±) Influence, especially in warm weather and high humidity.

Example 3

Table III shows the effect on processability and other properties when the proportion is changed the amounts of polyester in the first and in the second reaction stage of Experiment 1-G of Example 1 are shown.

(3-A) Table III (1-G)
Parts (3-C) (3-D) attempt 30 ·
13.5 (3-B) 50
13.5 60
13.5 70
13.5 1st stage
polyester 40
13.5 TDI-80

11th attempt 2nd stage (3-A) continuation (l-G) 12th (3-D) polyester (3-B) Parts '(3-C) Amine *) Processability of the Vor 70 50 30th polymers on the roller 10 60 10 40 10 10. 10 low viscosity, very good very good, something At vulcanization according to Zu sticky something to very good too high administration of TDI dimers .. low viscosity viscosity Processability at Compression molding very good very good a little too quickly very good a little too quickly a little late very good bad reaction very good very good, * J V AAA V 'H ^ JiA V ^ * kJ
Flow Optical behavior Transfer molding something opaque something difficult half opaque transparent something transparent transparent

Example 4

Table IV shows the influence of the use of another higher molecular weight polyhydroxyl compound in Experiment 1-G of Example 1, instead of the polyester used there, on the elastomer obtained.

Experiments 4-A, 4-B and 4-C show the following changes:

4-A: 50 parts of a polypropylene ether glycol with a hydroxyl number of 57 in the first stage of the method according to the invention.

4-B: 25 parts of diethylene glycol adipic acid polyester and 25 parts of ethylene glycol adipic acid poly

table

ester in the first stage and 50 parts of a polyester from 30 parts of propylene glycol, 70 parts of ethylene glycol and adipic acid in the second stage, each polyester having a hydroxyl number of 54 to 58 and a Has an acid number of 2 or less.

4-C: 50 parts of a polyester made from 50 parts of 1,4-butanediol and 50 parts of ethylene glycol and adipic acid in the first stage and 25 parts of a polyether Tetrahydrofuran and propylene oxide in the second stage (hydroxyl number of the polyester 54, the polyether 110).

IV

Properties of prepolymers Viscosity changed insignificantly, sticky handle, tendency to ver
slightly less hardening due to crystallization
Viscosity practically unchanged, processability on the roller very good
Well. Practically no hardening due to crystallization
Low viscosity, sticky on the roller
Slightly lower, processability practically unchanged
Practically the same as the prepolymer of Run 1-G
Considerably less than the prepolymer from Experiment 1-G; research
does not take longer to deform, but it can be done with an accelerator
be deformed (4-B) (4-C) (1-G) 4-A (4-A) 75
330
600
40
55
(-) 85
290
540
46
60
considerably better
as 1-G
(-) 80
380
740
42
65
(++) 4-B 75
280
560
38
45
a little better
as 1-G
(±) 4-C Reactivity of the prepolymers 4-A 4-B 4-C Physical Properties
of elastomers Shore hardness A
Tensile strength (kg / cm ² )
Elongation at break (%)
Rebound resilience (%)
Tear strength (kg / cm)
Resistance to chemicals.
Hardening through crystallization.

(±) Does not crystallize at room temperature, gradually crystallizes at -5 to +5 ⁰ C. (+ +) Crystallizes rapidly at room temperature.
(-) Not crystallizable.

Example 5

Experiment 5-A

50 parts of the polyester used in Example 1 are heated ^{to 100 °} C. with 19 parts of diphenylmethane-4,4'-diisocyanate for 30 minutes. The mixture is reacted with 11 parts of lauroguanamine and 50 parts of said polyester. This prepolymer, 8 parts of diphenylmethane-4,4'-diisocyanate are kneaded, and the product is pressed for 16 hours at 14O ⁰ C for an elastomeric film having the following properties:

Shore hardness A 80

Tensile strength (kg / cm ² ) 375

Elongation at break (%) 910

This film has a particularly high crease resistance.

Experiment 5-B

When using 16 parts of 1,5-naphthylene diisocyanate instead of the TD1-80 and 9.5 parts of o-dichlorobenzidine used in Experiment 1-G of Example 1 instead of 3,3'-dichloro-4,4'-diaminodiphenylmethane, a prepolymer with a somewhat too high one becomes Preserved viscosity. By replacing half of the 1,5-naphthylene diisocyanate used by 6.8 parts TDI and when using 10 parts of a mixture of 80% o-dichlorobenzidine and 20% 3,3'-dichloro-4,4'-diaminodiphenylmethane Instead of 9.5 parts of dichlorobenzidine, a prepolymer with a favorable viscosity is obtained. There can also be 9 parts of the Mixture of 20% benzidine and 80% 3,3'-dichloro-4,4'-diaminodiphenylmethane can be used. Out Films produced with these prepolymer according to Experiment 1-G have an improved tear resistance. So far, such combinations of diisocyanates and diamines have been used because of their overly high reactivity considered difficult to deform; however, they can by the method according to the invention can be deformed well.

Claims (1)

Claim: Process for the production of polyurethane elastomers by reacting no free Prepolymers (I) containing isocyanate groups (A) linear, higher molecular weight polyhydroxy compounds with a molecular weight of at least 700, (B) aromatic diamines and (C) aromatic diisocyanates with (II) an excess amount of an organic polyisocyanate, characterized in that the prepolymers (I) used have been prepared in such a way that component (A) was used in two portions, the first part of (A) initially with about 1.5 to 8 equivalents (C) per equivalent (A), but at most the equivalent amount (C), based on (A) + (B), ^{had been reacted at temperatures from room temperature to 200 °} C., and then the second part of (A) had been reacted further with the product obtained from (C) and the first part of (A) and with at most the amount (B) equivalent to the remaining isocyanate groups in the product.