DE1219671B - Process for the production of polyurethane foams - Google Patents

Description

Method of making polyurethane foams The invention relates to improvements in the manufacture of polyurethane foams.

It is already known, polyurethane foams by implementing a organic polyisocyanate with an organic polyhydroxyl compound and water to manufacture.

The water reacts with the polyisocyanate, creating carbon dioxide gas forms, which is included in the polymer mass, so that a cellular material arises. The density of these foam products can be adjusted by adjusting the in the Reaction mixture used water content can be varied. This is usually how it will be from a batch containing 30 / o water based on the weight of the polyhydroxyl compound obtained a foam having a density of about 0.030 to 0.03i g / cm5. Lower densities can be achieved by increasing the water content.

Although it is used for a lot of economic reasons it is advantageous to use a foam with the lowest possible density, it is sometimes desirable for the foam to have a somewhat higher density. Foam products with higher densities can be reduced by reducing the applied Water content can be produced, but the products obtained are not always completely satisfactory, especially if not more than 2.5010 water is applied. Thus, the foams obtained in this way lose a lot Often only slowly seal their surface tack and harden only slowly, d. that is, they are slow to reach their ultimate physical properties.

The U.S. patent describes the manufacture of polyurethane foams by pressing out a polyurethane polymer containing isocyanate end groups in an atmosphere containing water vapor.

In the French patent is a method of manufacture of foams made from synthetic resins are described by exposing them to high-frequency radiation get abandoned.

It has now been found that excellent polyurethane foams Can be conveniently prepared by adding an organic polyisocyanate with an organic polyhydroxyl compound and with no more than 2.5% water as a blowing agent, based on the weight of the polyhydroxyl compound, with the supply of heat implemented from the outside, with the indicator that the reaction mixture is heated by microwave heating has been supplied to the extent that the occurring in the foamed polyurethane Temperature resulting from the heat supplied by microwave heating and the Heat of reaction results, is not below 120 "C.

Since the polyurethane foaming reaction is highly exothermic, the amount of heat to be supplied to the reaction mixture depends on the final temperature to above 120 "C, in each individual case of the particular one used Approach. So it will of course be necessary to add a reaction mixture, that contains only 10 /, water, add more heat than a mixture that contains 20 /, water having. To obtain and transmit the microwaves and to absorb them known or suitable devices for use by the reaction mixture reach.

For example, the reaction mixture can be in a suitable container be introduced into a cavity resonator, which on the special frequency of the able to address the microwaves used.

A commonly used frequency is 2450 megahertz, which is the equivalent approximately a wavelength of 12.5 cm.

The surface of the foam can continue at will during the rise of the foam and / or during the subsequent curing period heated by the use of infrared radiation in a manner not claimed here will.

In the case of organic polyisocyanates and polyhydroxyl compounds, which are used in the method according to the invention are those those in connection with the production of polyurethanes according to the prior art are known.

Suitable organic polyhydroxyl compounds are, for. B. hydroxyl groups containing polyesters, polyester amides, polyethers or non-polymeric oxyalkylation products of compounds containing active hydrogen atoms.

As is known in the art, the reaction mixture can also Catalysts are incorporated, such as. B. tertiary amines or organic compounds of metals, surfactants, such as. B. Polysiloxanes, other inert blowing agents, such as B. inert volatile liquids, also fillers, fire retardants, Coloring agents and others commonly used in the manufacture of crosslinked polyurethanes Additives.

The invention is illustrated by the following example. All parts and percentages are expressed in weight: Example It became - a mass produced by rapidly mixing 400 parts of a glycerine-propylene oxide adduct- with a hydroxyl value corresponding to 56 mg KOH / g, 80 parts of an 80:20 mixture from toluene-2,4- and -2,6-diisocyanate and another mixture, the 4 parts Water, 0.4 parts of triethylenediamine, 8 parts of N, N-dimethylphenylethylamine and 4 parts of a siloxaneoxyalkylene block copolymer. While mixing was the crowd heated to 80 "C by microwaves at a frequency of 2450 megahertz. They was then poured into a mold where the foam and then heated for a further 10 minutes by infrared radiation. Within of the foam a maximum temperature of 140 "C was reached. It became an elastic Cellular product obtained with a density of 0.08 g / cm3. If the crowd doesn't was heated by microwave heating, the resulting foam collapsed or the foam shrank beyond the usual, portable limits.

Claims (1)

Claim: Process for the production of polyurethane foams, by reacting an organic polyisocyanate with an organic polyhydroxyl compound and with no more than 2.5% water as a propellant, based on the weight of the Polyhydroxylverbindung, with the supply of heat from the outside, characterized in that the reaction mixture has been supplied with heat to the extent by microwave heating is, so that the temperature occurring in the foamed polyurethane, which results from the heat supplied by microwave heating and the heat of reaction, is not below 120 "C. Documents considered: French patent specification No. 1300107; U.S. Patent No. 2,850,467; "British Plastiec", October 1963, p. 562 to 565.