WO2001044340A1

WO2001044340A1 - Polyurethane casting elastomers based on 2,5-toluylendiisocyanate

Info

Publication number: WO2001044340A1
Application number: PCT/EP2000/012158
Authority: WO
Inventors: Peter Heitkämper
Original assignee: Bayer Aktiengesellschaft
Priority date: 1999-12-15
Filing date: 2000-12-04
Publication date: 2001-06-21
Also published as: DE19960453A1; AU2003901A

Abstract

The invention relates to polyurethane casting elastomers, which are made from: a) at least one high molecular polyhydroxy compound having an average molecular weight ranging from 500 to 6000 and a functionality of at least 2, from; b) toluylendiisocyanate or a mixture of isomeric toluylendiisocyanates having a proportion of 2,5-toluylendiisocyanate equal to at least 85 %, and; c) at least one low molecular chain-lengthening and/or cross-linking agent having at least two hydroxyl groups and an average molecular weight ranging from 18 to 800, whereby constituent a) is used in quantities ranging from 35 to 96 wt. %, component b) is used in quantities ranging from 4 to 35 wt. %, and component c) is used in quantities ranging from 0.1 to 30 wt. %, each with regard to the entirety of the constituents that constitute the polymer matrix. The inventively produced polyurethane casting elastomers are used, in particular, for producing shaped parts that can be subjected to high levels of mechanical stress.

Description

Cast polyurethane elastomers based on 2,5-toluene diisocyanate

The present invention relates to polyurethane cast elastomers based on 2,5-tolylene diisocyanate, their production and their use for the production of molded parts which can withstand high mechanical loads.

Cast polyurethane elastomers (PU elastomers) have been known for a long time and have been described in numerous patent and literature publications.

An overview of PU elastomers, their properties and applications is given, for example, in the Plastics Manual, Volume 7, Polyurethane, third, revised edition 1993, published by Prof. Dr. G.W.Becker and Prof. Dr. D.Braun (Carl-Hanser-Verlag, Munich, Vienna).

For the production of polyurethane elastomers with high-quality mechanical properties, 1,5-diisocyanatonaphthalene (1,5-NDI) is preferably used as the isocyanate building block.

Since 1,5-NDI is not easy to handle due to the high melting point, there has been no shortage of attempts to replace 1,5-NDI with easier-to-handle and also less expensive diisocyanates, without the favorable properties that PU-elastomers are based on obtained from 1,5-NDI.

In this context, the German published patent applications DE-A 19 627 907, 19 628 145 and 19 628 146 are particularly worth mentioning, according to which attempts are being made to replace 1,5-NDI with other diisocyanates which are said to be suitable, compact or cellular PU To provide elastomers with a comparable favorable mechanical property profile.

According to German Offenlegungsschrift DE-A 19 627 907, mixtures of 1,4-phenylene diisocyanate and at least one are used to produce PU elatoms additional diisocyanate used. As claims 5 and 6 of this patent also teach, the addition of at least one further diisocyanate serves to liquefy comparatively high-melting 1,4-phenylene diisocyanate (melting point: 95 ° C.) and thus to make it easier to handle. However, the use of other diisocyanates, for example 4,4'-diisocyanatodiphenylmethane, considerably reduces the quality of the PU elastomers produced in this way and thus represents a serious disadvantage.

Furthermore, it is known that 1,4-phenylene diisocyanate has a very strong skin and mucous membrane irritant effect, so that the handling of this product is associated with complex protective measures.

DE-A 19 628 146 claims 3,3'-dimethoxy-4,4'-diisocyanatodiphenyl for the production of PU elastomers as isocyanate building block. This diisocyanate not only has a high melting point at 122 ° C, but also such a high boiling point that it can practically not be distilled on an industrial scale for cleaning. In addition, this diisocyanate has a comparatively low isocyanate content, which means that large proportions of this relatively expensive product have to be used to produce PU elastomers.

4,4'-diisocyanatostilbene, which is used according to DE-A 19 628 145 for the production of PU elastomers as an isocyanate building block, has an even higher melting point of 149 ° C than 1,5-NDI (melting point: 130 ° C) and is making it even more difficult to handle. In addition, the elastomers made from this diisocyanate tend to discolour extremely and are therefore for many

Applications not acceptable.

The object of the present invention is now to provide new polyurethane cast elastomers with high-quality mechanical properties based on easy-to-handle diisocyanates, in which the disadvantages mentioned are avoided. The invention therefore relates to polyurethane elastomers (PU elastomers) made from

a) at least one higher molecular weight polyhydroxy compound with an average molecular weight of 500 to 6000 and a functionality of at least

2,

b) 2,5-tolylene diisocyanate or a mixture of isomeric tolylene diisocyanates with a proportion of 2,5-tolylene diisocyanate of at least 85% and

c) at least one low molecular chain extender and / or crosslinking agent with at least two hydroxyl groups and an average molecular weight of 18 to 800,

wherein component a) in amounts of 35 to 96 wt .-%, component b) in amounts of 4 to 35 wt .-% and component c) in amounts of 0.1 to 30 wt .-%, each based on the entirety of the components making up the polymer matrix.

2,5-tolylene diisocyanate (2,5-TDI) is a known compound and is described, for example, in the publication by W. Siefken, Liebigs Annalen der Chemie, volume 562 (1949), pages 75-136 (there page 129).

2,5-TDI is usually produced by reacting 2,5-toluenediamine with phosgene. 2,5-toluenediamine is also a known compound and can be prepared, for example, by catalytic hydrogenation of 5-nitro-2-aminotoluene (see Japanese Patent 60202847).

Furthermore, 2,5-TDI can also be obtained from industrially produced tolylene diisocyanate (TDI): In general, 2,5-TDI is a component of industrial scale produced TDI, which is usually obtained as a mixture of isomers. In this mixture, the isomers 2,4- and 2,6-tolylene diisocyanate are the main components, while the proportion of 2,5-TDI is generally significantly less than 1%. The processes customary in industry, for example fractional distillation, can be used to enrich and isolate 2.5 -TDI from industrially produced TDI.

2,5-TDI has a low melting point at 38 ° C and is therefore much easier to process than 1,5-NDI.

In contrast to 1,4-phenylene diisocyanate, despite the formal chemical similarity of the two compounds, 2,5-TDI has no particular skin or mucous membrane irritant effect, so that corresponding complex protective measures are not required when dealing with 2,5-TDI.

Finally, the use of 2,5-TDI for the production of PU elastomers also has the advantage that this diisocyanate has a significantly higher isocyanate content than 1,5-NDI and accordingly it is used in smaller proportions, which results in a cost advantage.

To produce the PU elastomers according to the invention, a tolylene diisocyanate isomer mixture with a content of 2,5-TDI of at least 85%, in particular of more than 95%, can be used as the isocyanate building block. In order to produce particularly high quality PU elastomers, it can be advantageous to use pure 2,5-TDI.

Suitable higher molecular weight hydroxy compounds are in particular those with an average molecular weight of 800 to 4000, particularly preferably from 1000 to 3500. In principle, all polyhydroxy compounds which are used in polyurethane chemistry are suitable as higher molecular weight polyhydroxy compounds; in particular, polyether polyols, polyester polyols and polycarbonates having hydroxyl groups are to be considered.

The polyester, polyether and polycarbonate polyols can be used both individually and as a mixture with one another. Suitable polyester, polyether and polycarbonate polyols which can be used to construct the PU elastomers according to the invention are listed in detail, for example, in DE-A 19 627 907, page 4 and page 5.

Preferred polyester components are those which are composed of succinic acid or adipic acid and ethylene glycol, diethylene glycol, 1,4-butanediol or 1,6-hexanediol, very particularly preferably those which are composed of adipic acid and ethylene glycol.

Polyoxytetramethylene glycols are preferably used as polyether polyols.

The chain extenders and crosslinking agents known from polyurethane chemistry, the average molecular weight of which is preferably 18 to 400, in particular 60 to 300, and which are derived, for example, from alkanediols, dialkylene glycols and Polyoxyalkylene glycols (chain extenders) and trihydric or tetravalent alcohols and oligomeric polyoxyalkylene polyols with a functionality of 3 to 6 (crosslinking agent). In this connection, reference is again made to DE-A 19 627 907, page 5 and page 6. Particularly preferred chain extenders and crosslinking agents (c) are: ethylene glycol, diethylene glycol, 1, 4-butanediol, 1,6-hexanediol, hydroquinone bis (2-hydroxyethyl) ether, l, l, l-tris (hydroxymethyl) -n-propane or water. Of course, the chain extenders and crosslinking agents can be used both individually and in a mixture with one another, with both the use of the various chain extenders and crosslinking agents and the use of the above-mentioned higher molecular weight polyhydroxy compounds depending on the desired mechanical properties of the PU elastomers to be produced.

The PU elastomers according to the invention based on 2,5-TDI can be obtained both as compact elastomers and in cellular form.

To adjust the mechanical properties, for example the hardness in the case of the PU elastomers, the structural components a) to c) can be varied in wide quantitative ratios, the hardness of the functional chain lengthening and at least trifunctional crosslinking agents in the PU elastomer increasing. Depending on the desired hardness, the required amounts of the structural components can be determined experimentally in a simple manner. For the production of compact PU elastomers, it is preferred to use the structural component a) in amounts of 35 to 96% by weight, in particular 55 to 91% by weight, the structural component b) in amounts of 4 to 35% by weight, in particular 8 to 25% by weight and component c) in amounts of

0.5 to 30% by weight, in particular 1 to 20% by weight, in each case based on the totality of the components which form the polymer matrix.

For the production of cellular PU elastomers, the amount of component a) is 50 to 96% by weight, preferably 55 to 91% by weight, the amount of

Component b) 4 to 35% by weight, preferably 8 to 25% by weight, and the amount of component c) 0.1 to 15% by weight, preferably 0.2 to 10% by weight, in each case based to the entirety of the components that make up the polymer matrix.

Of course, the PU elastomers according to the invention can also be used in the

Polyurethane chemistry usual additives are incorporated. May be mentioned for example, surface-active substances, fillers, flame retardants, nucleating agents, oxidation retarders, stabilizers, lubricants and mold release agents, dyes and pigments, and also in the case of cellular PU elastomers, foam stabilizers and cell regulators. In this connection, reference is made to DE-A 19 627 907, pages 8 and 9.

The PU elastomers are preferably produced by the so-called prepolymerization process by using 2,5-TDI or a 2,5-rich TDI isomer mixture in the form of a prepolymer having isocyanate groups. This prepolymer can be produced, for example, by reacting

2,5-TDI or the 2,5-TDI-rich TDI isomer mixture with at least one higher molecular weight polyhydroxy compound a) or a mixture of a) and at least one chain extender and / or at least one crosslinking agent c) or by stepwise reaction of 2.5 -TDI or the 2,5-TDI-rich TDI isomer mixture with at least one higher molecular weight polyhydroxy compound a) and then with at least one chain extender and / or crosslinking agent.

The procedure is preferably such that the polyol components mentioned are reacted with 2,5-TDI or the 2,5-TDI-rich TDI isomer mixture to give a prepolymer which has an isocyanate content of 1 to 24%, preferably 2 to 12%, in particular 2 to 9%. The isocyanate-terminated prepolymer obtained in this way is reacted with component c) in a quantity ratio such that a characteristic number of 0.9 to 1.3, preferably 0.95 to 1.2, particularly preferably 1.0 to 1,2 results.

It may be helpful for the preparation of the prepolymer as well as for the reaction of the prepolymer with the chain extender and / or crosslinking agent mentioned. Add catalysts. In principle, all catalysts known in polyurethane chemistry, for example organic metal compounds, preferably organic tin compounds, such as tin (II) salts of organic carboxylic acids, for example dibutyltin diacetate, are suitable as catalysts for the preparation of both the prepolymers and the finished PU elastomers. Dibutyltin dilaurate, dibutyltin maleate and dioctyltin diacetate. The organic metal compounds are used alone or in combination with strongly basic amines, such as amidines, tertiary amines, tetraalkylenediamines, alkanolamine compounds. In this connection, reference is again made to DE-A 19 627 907, page 7.

If catalysts are used in the production of the PU elastomers according to the invention, the amount of catalyst is usually 0.001 to 3% by weight, preferably 0.001 to 1% by weight, based on the structural components a) + b).

To produce compact, solid PU elastomers, components a) to c) are reacted in the absence of moisture and physical or chemical blowing agents. If cellular PU elastomers are to be produced, the reaction of the structural components mentioned is carried out in the presence of a blowing agent. For example, water or low-boiling liquids which evaporate under the influence of the exothermic polyaddition reaction and advantageously have a boiling point under normal pressure in the range from -40 to 120 ° C, or gases as physically active blowing agents or chemically acting blowing agents can be used as blowing agents. Of course, the low-boiling liquids can be used in combination with water as a blowing agent. Liquids of the above-mentioned type and gases suitable as blowing agents are all known blowing agents known for the production of cellular polyurethane moldings, for example low-boiling alkanes, ethers, alcohols and the known halogenated, preferably fluorinated alkanes, and also gases such as nitrogen, carbon dioxide and noble gases. Blowing agents suitable for the production of cellular PU elastomers are listed in detail, for example, in DE-A 19 627 907, page 8.

As mentioned, the production of the compact or cellular PU elastomers can preferably be carried out according to the prepolymerization process. Of course, it is also possible for the PU elastomers to be produced by other customary process techniques for polyurethanes. For details on the production of compact or cellular PU elastomers, reference is again made to DE-A 19 627 907, pages 9 and 10.

The compact PU elastomers according to the invention have a density without filler of 1.0 to 1.4 g / cm, preferably 1.1 to 1.3 g / cm, products containing filler usually having a density greater than 1.2 g / cm. The cellular PU elastomers have a density of 0.2 to 1.1 g / cm ³ , preferably 0.35 to 0.80 g / cm ³ .

The PU elastomers according to the invention are used for the production of molded bodies which can withstand high mechanical loads, for example for mechanical engineering and the transport sector. The cellular PU elastomers are particularly suitable for the manufacture of damping and spring elements.

Examples

General implementation:

A polyester made of adipic acid and ethylene glycol (OH number 56 mg KOH / g; acid number 0.9 mg KOH / g) was placed in a flat ground glass cup, dewatered at 120 ° C. and 20 mbar for 30 minutes and then cooled to 110 ° C. , 2,5-tolylene diisocyanate (2,5-TDI) or (for the comparative example) 2,4-tolylene diisocyanate (2,4-TDI) was then added with stirring. For the reaction, the mixture was heated to 120 ° C. and stirred at 180 mbar for 15 minutes at 120 ° C., then for 30 minutes at 130 ° C. The mixture was then cooled to 110 ° C., 1, 4-butanediol was added to extend the chain and the mixture was stirred at 110 to 120 ° C. and 20 mbar for 2 minutes. The product was then poured into a test specimen mold preheated to 120 ° C. and annealed at 120 ° C. for 24 hours. After removal from the mold, the test specimen was annealed at 120 ° C. for a further 24 hours and then measured.

The values are summarized in the table below, which also contains the values of the comparative test.

Result: The mechanical properties of the cast elastomer according to the invention based on 2,5-tolylene diisocyanate are significantly better than those of the comparative product based on 2,4-tolylene diisocyanate.

Claims

claims

1. Polyurethane cast elastomers made from

a) at least one higher molecular weight polyhydroxy compound with an average molecular weight of 500 to 6000 and a functionality of at least 2,

wherein component a) in amounts of 35 to 96 wt .-%, component b) in amounts of 4 to 35 wt .-% and component c) in amounts of 0.1 to 30 wt .-%, each based on all of the components making up the polymer matrix.

2. A process for the production of cast polyurethane elastomers according to claim 1, characterized in that the higher molecular weight polyhydroxy compounds a) optionally with part of the low molecular chain extenders and / or crosslinking agents c) initially with 2.5-

Toluene diisocyanate b) or the 2,5-tolylene diisocyanate-rich tolylene diisocyanate isomer mixture is converted to an isocyanate-terminated prepolymer by the prepolymerization process and then this prepolymer is reacted with the remaining chain extension and / or crosslinking agent and / or higher molecular weight polyhydroxy compounds. / 44340

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3. Use of polyurethane cast elastomers according to claim 1 for the production of mechanically highly resilient molded articles.