Polyisocyanate polyaddition products

Details Polyisocyanate polyaddition products Polyisocyanate polyaddition products

2001-01-24

2002-12-17

Gorr, Rachel (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S109100, C521S132000, C521S131000, C521S172000, C521S176000, C521S173000, C521S175000

Reexamination Certificate

active

06495611

ABSTRACT:

The present invention relates to polyisocyanate polyaddition products comprising hydrophobic compounds plus at least one further compound selected from the group consisting of: (i) organic, cyclic compounds having a molecular weight of from 200 to 3000 g/mol, (ii) salts of metals of transition groups I, II and/or VIII, (iii) organic and/or inorganic acid anhydrides, (iv) cyclic sulfonic esters and/or sulfones, (v) lactones, lactams and/or cyclic esters and/or (vi) &agr;,&bgr;-unsaturated carboxylic acids, &agr;,&bgr;-unsaturated carboxylic acid derivatives, &agr;,&bgr;-unsaturated ketones and/or &agr;,&bgr;-unsaturated aldehydes, preferably selected from the group consisting of: (i), (iii), (iv), (v) and/or (vi), particularly preferably selected from the group consisting of (iii), (iv) and/or (vi). Furthermore, the invention relates to a process for producing these polyisocyanate polyaddition products, in particular mattresses or furniture upholstery and/or carpet backing. The invention also relates to the use of hydrophobic compounds for reducing the formation and/or the content of primary amines in polyisocyanate polyaddition products and/or for reducing the water uptake of polyisocyanate polyaddition products, in particular flexible polyurethane foams.
The production of polyisocyanate polyaddition products by reacting polyisocyanates with compounds which are reactive toward isocyanates in the presence of catalysts which accelerate the reaction of the substances which are reactive toward isocyanates with isocyanates and, if desired, blowing agents, additives and/or auxiliaries is generally known.
Like other plastics, polyisocyanate polyaddition products are subject to aging processes which generally lead to a deterioration in the use properties as time goes on. Important aging influences are, for example, hydrolysis, photooxidation and thermal oxidation which lead to rupture of bonds in the polymer chains. In the case of polyisocyanate polyaddition products, for example polyurethanes, hereinafter also referred to as PURs, especially the action of moisture and even more the combination of moisture and elevated temperature results in hydrolytic cleavage of the urethane and urea bonds.
This cleavage is not only reflected in a significant deterioration in the use properties but also leads to formation of primary aromatic amines, e.g. toluenediamine (TDA) and diaminodiphenylmethane (MDA), or primary aliphatic amines such as hexamethylenediamine or isophoronediamine.
As experiments have found, amine formation is influenced by a series of parameters. In particular, high temperatures above 80° C. in combination with high atmospheric humidity lead to hydrolytic cleavage of the urethane and urea bonds. Such conditions are of importance in some specific applications of flexible PUR foams.
A further parameter which has a significant influence on the formation of primary amines is the type and amount of catalysts used. As has been able to be shown in various experiments, the catalysts which are present in polyurethane systems and are necessary for the urethanization and blowing reaction also catalyze the hydrolytic redissociation reaction to a considerable extent. The presence of catalysts is thus a critical precondition for the hydrolysis of the urethane and urea bonds. Furthermore, it has been able to be shown that the efficiency of the hydrolysis is highly dependent on the activity and the type of catalyst, and also on whether the catalyst remains in the system or can migrate out of the material. In particular, tertiary amine catalysts having reactive functional groups such as OH and NH
2
considerably accelerate amine formation by lowering the activation energy for the cleavage reaction. The functional groups result in incorporation of the catalysts into the PUR network formed and the products produced using them have the advantage of lower odor and fogging problems since the catalysts cannot escape by diffusion after production of the PUR product. The same applies to formulations comprising polyols which have been prepared using primary or secondary amines as initiator molecules and thus have catalytically active centers. Such polyols have been increasingly used in recent times. In the case of formulations which comprise such constituents and are exposed to particularly hot and humid conditions in specific applications, the formation of primary amines as dissociation products cannot be ruled out. In contrast, in the case of foams produced using amine catalysts which contain no functional groups capable of being built into the structure, the catalysts are generally given off only a short time after manufacture or during aging of the foam. In the case of such foams, hot and humid conditions lead to significantly lower amine contents.
As compounds which reduce the aromatic amine content of flexible polyurethane foams, U.S. Pat. No. 4,211,847, GB 1 565 124 and DE-A 29 46 625 make use of sterically hindered cycloaliphatic monoisocyanates and monothioisocyanates. Owing to their steric hindrance and their lower reactivity compared to aromatic isocyanates, these isocyanates react to only a slight extent during the foaming reaction, so that free isocyanate is available for reaction with any aromatic amines present after the foaming reaction is complete. Disadvantages of these known teachings are that the compounds mentioned are relatively expensive and, especially the two last-named compounds, also participate at least partially in the urethanization reaction despite their steric hindrance and do not react only after the foaming reaction with aromatic amine formed. In addition, these isocyanates tend to migrate out of the finished foam because of their low vapor pressure and thus pose a further health hazard due to the occurrence of free isocyanate.
DE-A 42 32 420 discloses the use of &agr;,&bgr;-unsaturated ester carboxylates for producing polyurethane foams which have an improved compressive strength and elongation at break. In that document, salts of &agr;,&bgr;-unsaturated ester carboxylates are used as catalysts for the NCO/water reaction. In an aside, it is stated that the compounds are, due to the presence of olefinic double bonds adjacent to the carboxylate groups, capable of addition of amino groups which are formed during the slow aging of the foam. A disadvantage of these compounds is their catalytic action which has an adverse effect on the foaming reaction. A catalytic action of additives for reducing the amine contents of finished PUR foams is, however, not desirable since this leads, as described above, to further and accelerated formation of primary amines.
Hydrolysis inhibitors for polyurethanes containing ester groups are described in DE-A 23 31 796, FR 1 550 562 and GB 1 014 974. The increase in the hydrolysis resistance of the PUR products is usually based on an improvement in the mechanical properties after storage under hot and humid conditions. DE-A 23 31 796 describes the addition of epoxy compounds in order to avoid hydrolysis of the ester groups in PUR products. For the same purpose, FR 1 550 562 claims alkyl carbonates and GB 1 014 974 claims carbodiimides in combination with a compound containing enol groups.
DD 238 992 describes epoxidized synthetic products such as triglycerides, alkyl epoxystearates, etc., and epoxidized natural products such as soya oil as hydrolysis inhibitors for polyurethane elastomers. However, the improvement in the hydrolysis resistance (increased hardness, tensile strength and elongation at break) is restricted to polyurethane elastomers containing polyesters as polyol component. DD 298 246 claims a polyol component for producing noncellular polyurethane moldings having an improved hydrolysis resistance. The improvement in the hydrolysis resistance is achieved here by addition of fatty amines.
A similar reaction mixture is claimed in DE-A 3 443 341. The improvement in the elongation at break of possibly cellular polyurethanes is achieved here by means of a mixture of an inorganic filler, a metal salt of a fatty acid and a hydrophobiciz

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