DE2603498C3 - Further development of the process for the production of crosslinked, elastic, open-cell foams containing urethane groups - Google Patents

Description

O = C

R ¹

NHR ²

40

in which R 'is a CH ₃ , NH ₂ , NHR3 or NRj' radical, where R ^{3 is} an alkyl radical having 1 to 4 carbon atoms and R ^{2 is} a water atom or an alkyl radical having 1 to 4 carbon atoms ^ or Ethylene urea or tetramethylammonium bromide or tetraethylammonium iodide is completely or partially dissolved in the aqueous solution of the crystalline cross-linking agent and this solution is dispersed in the polyether polyol.

2. The method according to claim 1, characterized in that a dispersion is used which Urea has been added.

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Foams containing urethane groups are activated by reacting polyisocyanates with Obtained polyols containing hydrogen atoms. Such foams are widely used, e.g. B. on in the field of insulation, for the production of structural elements or for upholstery purposes.

For many of these uses, open cell foam systems are desirable. Foams with closed Cells show reduced elastic behavior and tend to shrink during production.

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It is also desirable that open-cell, elastic foams can be varied as far as possible in their load-bearing capacity and hardness. A desired hardness can be given to a foam body by increasing the degree of crosslinking, by increasing the density or by increasing the polyisocyanate content of the formulation. Among these possibilities, increasing the degree of crosslinking is the most technically and economically advantageous. Both to increase the density as well as the polyisocyanate content, higher amounts of starting materials are required, which makes the production of the foams less economical. In addition, an increase in the polyisocyanate content is not advantageous, also for reasons of the resulting increased tendency towards flammability and toxicity and the hard feel of the foams.

In order to achieve higher degrees of crosslinking, according to the current state of the art, a Polyurethane foam formulation low molecular weight, polyfunctional compounds added to the active Polyols containing hydrogen atoms are soluble. The crosslinking agents can accordingly directly react after the foaming reaction has started. The possibility of the crosslinking density arbitrarily to increase, is limited in this method that, depending on the rest Constituents of the foam formulation, the crosslinking density at the point in time at which the foams their maximum height of rise and normally then the cell opening begins to be already too high to the To allow the process of cell opening to occur.

The result is foams that are highly cross-linked, but have a large proportion of closed cells or are completely closed. Such foams show reduced elasticity behavior and tend as a result due to their high level of closed cells, they cause shrinkage after manufacture.

These disadvantages are overcome according to the method of patent 25 07 161.

The subject of this patent application is a process for the production of crosslinked, elastic, open-cell foams containing urethane groups by reacting polyether polyols with a hydroxyl equivalent weight of 700 to 5000, polyisocyanates, water, catalysts, if appropriate low molecular weight compounds which are soluble in the polyether polyols and have two or more active hydrogen atoms and a molecular weight up to 750 as a crosslinking agent in an amount up to 1.5 hydroxyl equivalents, based on a hydroxyl equivalent of the polyether polyol, and optionally organic Propellants and emulsifiers or stabilizers with the additional use of crystalline, in which to foaming polyether polyol only slightly soluble or insoluble crosslinking agents at room temperature from the group sorbitol, tri- or hexamethylolmelamine, glucose, sucrose, erythritol, mixtures or hydrates of these compounds or their partial esters or ethers in an amount of 0.1 to 5.0 hydroxyl equivalents, based on a hydroxyl equivalent of the foaming polyether polyol, in the form a dispersion of these crystalline crosslinking agents in the polyether polyol.

This makes it possible to provide foams which contain urethane groups and which have a high Crosslink density and, as a result, correspondingly increased hardness values, but at the same time a

contain a small proportion of closed cells and are therefore highly elastic and after manufacture do not tend to shrink.

With increasing additions of the crosslinking agents used there, the elongation at break and tear strength increases the foams formed are somewhat reduced, but the tensile strength is increased

The compression deformation, the drop in hardness after 500,000 load changes (pressure drop), the fatigue behavior and the aging properties and the rebound resilience, on the other hand, are hardly noticeable influenced

It was found, however, that such dispersions of the crystalline crosslinkers in the polyether polyols in the Become increasingly viscous over the course of a few days and in some cases even solidify. One was therefore forced to to use these dispersions as soon as possible after their preparation.

It has now been found that this disadvantage can be avoided by further training of the method of patent 25 07 161 such a dispersion of the crystalline crosslinking agent in the Polyether polyol used, which has been prepared by 0.5 to 50 wt .-%, based on the Amount of water in the foaming kit, a compound of the general formula

The inventive method is the

Cream time shortened by which one understands the time which elapses until the reaction approach as a result of the the beginning of COa formation has a creamy appearance

Preferred among the aforementioned compounds are the more hydrophilic substances, i.e. those which are in Water are more soluble than in the organic components of the reaction mixture to be foamed. The use of urea is particularly preferred.

The invention is explained in more detail by the following example:

A mixture consisting of

R ¹

O =

NHR ²

in which R ^{1 represents} a CH ₃ , NH ₂ , NHR ³ or NRr radical, where R ^{3 is} an alkyl radical with 1 to 4 carbon atoms and R ^{2 is} a hydrogen atom or an alkyl radical with 1 to 4 carbon atoms, or ethylene urea or tetramethylammonium bromide or tetraethylammonium iodide completely or partially dissolves in the aqueous solution of the crystalline crosslinking agent and this solution is dispersed in the polyether polyol.

The compounds of the general groups dissolved in the dispersion in the process according to the invention formula

O = C

R ¹

NHR ²

Ethylene urea, tetramethylammonium bromide or tetraethylammonium iodide degrade water associates.

This also has the effect that the reaction of the isocyanate groups with the water in the Foaming approach is included, is selectively accelerated, so that the propellant gas in an early Stage of the urethane formation reaction is available and the water as quantitatively as possible with the Isocyanate groups reacts. In addition, this counteracts the observation that the crystalline Polyols bind parts of the water contained in the foaming and the foaming reaction only are available with a delay.

100, OG parts by weight

1.96 parts by weight
2.00 parts by weight
1.00 part by weight
0.40 parts by weight
6.00 parts by weight

1.00 part by weight
10.00 parts by weight

a glycerol-started P-clyoxyalkylene triol, which is made up of 84% by weight of propylene oxide and 16% by weight of ethylene oxide, and has an OH number of 35,
Water,
Glycerine,
Triethylenediamine,
Dimethylethanolamine,
a dispersion of 25% by weight sorbitol and 7% by weight urea in a glycerol-started polyoxyalkylene triol, which is made up of 84% by weight of propylene oxide and 16% by weight of ethylene oxide, and an OH number of 35 having, the dispersion containing 14 wt .-% water

a polyether-polysiloxane block copolymer
Trichlorofluoromethane

is with 51.5 parts by weight of a mixture of 65 parts by weight of 2,4- / 2,6-tolylene diisocyanate (isomer ratio 80:20) and 35 parts by weight of crude diphenylmethane diisocyanate in an open box brought to reaction. The result is an open-cell, non-shrinking foam with a height of 28.5 cm. The cream time is 10 seconds, the rise time 105 seconds.

A reaction mixture which has the aforesaid composition but differs in

so that the sorbitol dispersion does not contain urea, also results in an open-cell, non-shrinking one Foam. However, it only reaches a height of 27 cm and the cream time is 15 seconds Climbing time 135 seconds.

The technical progress achieved with the present invention is further enhanced by it proves that the urea-containing dispersion of sorbitol in polyether polyol still after several weeks, During the entire observation period, it remained uniformly fluid, while the urea-free Preparation initially becomes increasingly viscous within three days. The crystalline portion of the The dispersion is finally so coarse that the polyether polyol preparation solidifies after a week.

Claims (1)

Patent claims: 1. Further training of the process for the production of cross-linked, elastic, open-celled Foams containing urethane groups by reacting polyether polyols with a Hydroxyl equivalent weight of 700 to 5000, polyisocyanates, water, optionally in the polyether polyols soluble low molecular weight compounds with two or more active hydrogen atoms and a molecular weight up to 750 as a crosslinking agent in an amount up to 1.5 Hydroxyl equivalent, based on a hydroxyl equivalent of the polyether polyol, and optionally organic blowing agents and emulsifiers or stabilizers with additional use more crystalline, in the polyether polyol to be foamed at room temperature only slightly soluble or insoluble crosslinking agents from the group Sorbitol, tri- or hexamethylolmelamine, glucose, sucrose, erythritol, mixtures or hydrates of these Compounds or their partial esters or ethers in an amount of 0.1 to 5.0 hydroxyl equivalents, based on a hydroxyl equivalent of the foaming polyether polyol, in In the form of a dispersion of these crystalline crosslinking agents in the polyether polyol according to the patent 25 07 161, characterized in that such a dispersion of the crystalline crosslinking agents in the polyether polyol is used, which has been prepared by adding 0.5 to 50% by weight, based on the amount of water in the foaming approach, a compound of the general formula