Process for preparing polyurethane foams modified with melamine-formaldehyde precondensates.

The invention relates to a process for the production of polyurethane foams, in particular rigid polyurethane foams, by reacting organic polyisocyanates, polyols and melamine-formaldehyde precondensates and, if appropriate, chain extenders or crosslinking agents in the presence of blowing agents, catalysts and, if appropriate, auxiliaries and additives, in the form of melamine-formaldehyde Precondensates storage-stable aqueous 40 to 85% by weight resin solutions are used, which are obtained by condensation of melamine with formaldehyde in a molar ratio of 1: 1.1 to 1.75 in aqueous solution. The reaction is preferably carried out by the two-component process.

The production of polyurethane foams from polyisocyanates, polyols, optionally chain extenders, auxiliaries and additives is known from numerous patent and literature publications. For example, we would like to refer to the monographs by JH Saunders and KC Frisch, High Polymers, Volume XVI "Polyurethanes" Parts I and II (Interscience Publishers, New York) and R. Vieweg and A. Höchtlen, plastic manual, volume VII, polyurethane, Carl Hanser Verlag, Munich.

Melamine-formaldehyde precondensates are usually produced by condensing melamine with formaldehyde in various molar ratios in aqueous solution at pH values ​​greater than 7 and at elevated temperatures. The drop in pH caused by the Cannizzaro reaction of formaldehyde during the condensation is compensated for by constant addition of lye; however, it is also possible to condense in the presence of suitable buffer systems. The condensation continues; until the desired degree of condensation is reached and terminated by cooling, taking into account that the reaction still continues during the cooling.

As a measure of the degree of condensation, the dilutability of the resin solution with water is used, expressed as the amount of water that can be added to a volume unit of resin solution of ordinary concentration (ie 40 to 85%) at 20 ° C. without causing permanent turbidity.

Aqueous melamine-formaldehyde resin solutions whose condensation has been interrupted have a limited shelf life. When left standing or during storage, the condensation progresses and the viscosity increases; finally insoluble compounds separate and the resin solutions become unusable for further processing. The storage stability or shelf life of a resin solution is the period in days within which any clouding that may occur does not lead to phase separation and also does not undergo any significant changes in its properties, for example the viscosity. The storage stability is usually based on 20 ° C.

In contrast to urea-formaldehyde precondensate solutions, which can usually be stabilized well, only short-lasting melamine-formaldehyde precondensate solutions can be obtained by the known processes, the stability of the solution depending on the formaldehyde content, the degree of condensation and the pH is.

In order to improve the storage stability, it has been proposed to completely or partially etherify the melamine-formaldehyde precondensates with low-molecular alcohols or to incorporate additives into the resin solutions. For example, the addition of toluenesulfonamide in combination with alcohols (US Pat. No. 3,159,593), sucrose (DE-OS 1 420 605) or sucrose in combination with toluenesulfonamide (DE-OS 1 420 606), aliphatic nitro compounds (US Pat 3 131 157), dicyandiamide in the presence of alcohols and guanidinium salts (DE-AS 1 144 006), bis- (ß-cyano - ethyl) amine (DE-OS 2 155 104). These agents usually have to be added in relatively large amounts to achieve the desired effect and have only been tested or known for precondensation solutions that have a high proportion of formaldehyde (ie melamine-formaldehyde - molar ratios of 1 to greater than 2) .

Partly and completely etherified methylolmelamines are used as flame retardant additives for the production of polyurethane foams, according to US Pat. No. 4,139,501 and US Pat. No. 3,135,707. A disadvantage of the processes described is, inter alia, that the low molecular weight melamine derivatives can be mixed with the polyols or, if appropriate, polyisocyanates only immediately before processing.

No. 4,130,697 and US Pat. No. 4,176,217 describe foams with improved fire behavior from aqueous aminoplast precondensates, for example melamine-formaldehyde, preferably urea-formaldehyde and urea-melamine-formaldehyde precondensates, optionally polyols and polyisocyanates. A disadvantage of the process is that the aminoplast precondensates have to be added to the polyisocyanates at the same time as, but separately from, the acidic curing catalysts, ie Even with this method, more than two starting materials must be mixed intensively at the same time.

Compared to conventional manufacturing processes for polyurethane foams made from polyisocyanates and polyols, practical problems in accordance with the described processes involve considerable problems with the additional use of low molecular weight, wholly or partly etherified methylolmelamines or aminoplast precondensates: The aqueous melamine-formaldehyde precondensate solutions which can be used have a very limited storage stability, in particular in comparison with urea-containing aminoplast precondensates. Like any mixtures of polyol and aminoplast precondensates, the resin solutions must be freshly prepared immediately before the reaction with polyisocyanates. Because of the high reactivity of such aminoplast precondensates, the "acid" catalyst required for crosslinking cannot be incorporated into the resin solution beforehand, ie expensive multi-component foaming machines are always required for processing. Finally, the foams produced from such aminoplast precondensates have a considerable formaldehyde emission, so that they are unusable for numerous fields of application, and show a strong shrinkage, especially if no polyols were used in the production.

The object of the present invention was to develop polyurethane foams with good mechanical properties and improved flame resistance with the use of aqueous melamine-formaldehyde precondensate solutions. The polyurethane foams should be able to be produced on conventional foaming machines by the two-component process, preferably with carbon dioxide, obtained from the polyisocyanates and water, as blowing agents and without the ecologically problematic fluorohydrocarbons as far as possible. The foams obtained should also show no formaldehyde emission.

This object was surprisingly achieved by a process for the production of polyurethane foams by reacting organic polyisocyanates, polyols and melamine-formaldehyde precondensates in the presence of blowing agents and catalysts and, if appropriate, chain extenders or crosslinking agents, auxiliaries and additives, which is characterized in that that are used as melamine-formaldehyde precondensates aqueous resin solutions with a melamine-formaldehyde precondensate content of 40 to 85 wt .-%, based on the total weight, which are obtained by condensation of melamine with formaldehyde in a molar ratio of 1: 1.1 to 1.75 in aqueous solution.

It was found that aqueous 40 to 85% by weight melamine-formaldehyde precondensate solutions, which are obtained by condensation of melamine and formaldehyde in a molar ratio of 1: 1.1 to 1.75, are relatively stable in storage. It was particularly surprising that mixtures of 100 parts by weight of the aqueous melamine-formaldehyde precondensates which can be used according to the invention and 1 to 50 parts by weight of polyol and, if appropriate, chain extenders or crosslinking agents, auxiliaries and additives in the presence of basic polyurethane catalysts, in particular tertiary amines , and "acidic" curing catalysts have a storage stability at room temperature of 1 week or more, provided that the mixtures have a pH greater than 7. The polyurethane foams modified with melamine-formaldehyde precondensates can therefore advantageously be produced by the two-component process, which is used in a preferred manner. Examples of other advantages include:<ul id="ul0001" list-style="none"><li>The aqueous melamine-formaldehyde precondensate solutions can be highly concentrated, ie the solutions are still free-flowing even at a solids content of 85% by weight; carbon dioxide from water and polyisocyanate is used as the preferred blowing agent; the polyurethane foams obtained have good flame resistance and show virtually no formaldehyde emission.</li></ul>

Rigid polyurethane foams are preferably produced by the process according to the invention. However, semi-hard and soft elastic polyurethane foams can also be obtained.

The following must be stated about the starting components that can be used for the process according to the invention:<ul id="ul0002" list-style="none"><li>Examples of suitable organic polyisocyanates are aliphatic, cycloaliphatic, arylaliphatic, heterocyclic and preferably aromatic polyvalent isocyanates. Examples include: aliphatic diisocyanates such as ethylene, 1,4-tetramethylene, 1,6-hexamethylene and 1,12-dodecane diisocyanate; cycloaliphatic diisocyanates, such as cyclohexane-1,3- and 1,4-diisocyanate and any mixtures of these isomers, 1-isoeyanato-3,3,5-trimethyl-5-isoeyanatomethyl-cyclohexane, 2,4- and 2,6-hexahydrotoluylene diisocyanate and any mixtures of these isomers, 4,4'- and 2,4'-diisocyanatodicyclohexylmethane; aromatic diisocyanates such as 1,3- and 1,4-phenylene diisocyanate, 2,4- and 2,6-tolylene diisocyanate as well as any mixtures of these isomers, 2,2'-, 2,4'- and 4,4'-diphenylmethane diisocyanate and naphthalene-1,5-diisocyanate; aromatic polyisocyanates such as 4,4 ', 4 "-triphenylmethane triisocyanate, 2,4,6-triisocyanatobenzene and polyphenyl polymethylene polyisocyanates. Modified polyisocyanates can also be used, for example those described in US Pat. No. 3,492,330, polyisocyanates containing carbodiimide groups (DE-PS 10 92 007), polyisocyanates containing allophanate groups (GB-PS 994 890; BE-PS 761 626), polyisocyanates containing isocyanurate groups (DE-PS 10 22 789, DE-PS 12 22 067, DE-PS 10 27 394, DE-OS 19 29 034 and DE-OS 20 04 048), polyisocyanates containing urethane groups (BE-PS 752 26-1, US-PS 3 394 164), biuret group-containing polyisocyanates (DE-PS 11 01 394, GB-PS 889 050) and ester-group-containing polyisocyanates (GB-PS 965 474, GB-PS 10 72 956, U.S. Patent 3,567,763, German Patent 12 31 688).</li></ul>

The technically easily accessible aromatic di- and polyisocyanates such as 2,4- and 2,6-tolylene diisocyanate and any mixtures of these isomers, 2,2'-, 2,4'- and 4,4'-diphenylmethane diisocyanate are preferably used as well as any mixtures of these isomers, mixtures of 2,2'-, 2,4'-, 4,4'-diphehylmethane diisocyanates and polyphenylpolymethylene polyisocyanates (raw MDI) and mixtures of tolylene diisocyanates and raw MDI and Polyisocyanates containing urethane and isocyanurate groups. The di- and polyisocyanates mentioned can be used individually or in the form of mixtures.

Preferred linear and / or branched polyesterols and in particular polyetherols with molecular weights of 200 to 8000, preferably 800 to 5000, and in particular 1800 to 3500, are preferably used as polyols in the process according to the invention. However, other hydroxyl-containing polymers with the stated molecular weights, for example polyester amides, polyacetals and polycarbonates, in particular those made from diphenyl carbonate and 1,6-hexanediol by transesterification, are also suitable.

The polyesterols can be prepared, for example, from dicarboxylic acids, preferably aliphatic dicarboxylic acids, having 2 to 12, preferably 4 to 8, carbon atoms in the alkylene radical and polyhydric alcohols, preferably diols. Examples include aliphatic dicarboxylic acids such as glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid and preferably succinic and adipic acid, and aromatic dicarboxylic acids such as phthalic acid and terephthalic acid. Examples of dihydric and polyhydric, in particular dihydric and trihydric alcohols are: ethylene glycol, diethylene glycol, 1,2- and 1,3-propylene glycol, dipropylene glycol, decanediol-1,10, glycerin, trimethylolpropane and preferably 1,4-butanediol and 1,6-hexanediol.

The polyesterols have molecular weights from 300 to 2,800, preferably from 300 to 2,000, and hydroxyl numbers from 30 to 700, preferably from 50 to 500.

However, polyetherols which are prepared by known processes from one or more alkylene oxides having 2 to 4 carbon atoms in the alkylene radical and a starter molecule which contains 2 to 8, preferably 2 to 4, active hydrogen atoms are preferably used as polyols.

Suitable alkylene oxides are, for example. Tetrahydrofuran, 1,3-propylene oxide, 1,2- or 2,3-butylene oxide, styrene oxide and preferably ethylene oxide and 1,2-propylene oxide. L

The alkylene oxides can be used individually, alternately in succession or as mixtures. Examples of suitable starter molecules are:<ul id="ul0003" list-style="none"><li>Water, organic dicarboxylic acid, such as succinic acid, adipic acid, phthalic acid and terephthalic acid, aliphatic and aromatic, optionally N-mono-, N, N- and N, N'-dialkyl-substituted diamines having 1 to 4 carbon atoms in the alkyl radical, such as optionally mono- and dialkyl-substituted Ethylenediamine, diethylenetriamine, triethylenetetramine, 1,3-propylenediamine, 1,3- or 1,4-butylenediamine, 1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexamethylenediamine, phenylenediamines, 2,4- and 2,6-toluenediamine and 4,4'- , 2,4'- and 2,2'-diamino-diphenylmethane; Monoamines such as methylamine, ethylamine, isopropylamine, butylamine, benzylamine, aniline, the toluidines and naphthylamines. Of the compounds of the group mentioned, particularly interesting are N, N, N ', N'-tetrakis (2-hydroxyethyl) ethylenediamine, N, N, N', N'-tetrakis (2-hydroxypropyl) ethylenediamine, N , N, N ', N ", N" -pentakis (2-hydroxypropyl) ethylenetriamine, phenyldiisopropanolamine and higher alkylene oxide adducts of aniline.</li></ul>

Suitable starter molecules are also alkanolamines, such as ethanolamine, diethanolamine, N-methyl and N = ethyl_l-_diäthanola_min, N-methyl and N-ethyl-dipropanolamine and triethanolamine, hydrazine and hydrazides. Polyvalent, in particular di- and / or trihydric alcohols, such as ethylene glycol, 1,2 and 1,3 propylene glycol, diethylene glycol, dipropyl glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, glycerol, trimethylol propane and are preferably used Pentaerythritol.

Other applicable polyols are the non-reducing sugars, the non-reducing sugar derivatives and preferably their alkylene oxide adducts, in which the alkylene oxides have 2 to 4 carbon atoms. Usable non-reducing sugars and sugar derivatives are, for example, sucrose, alkyl glycosides, such as methyl glycoside and ethylene glycoside, and also glycol glycosides, such as ethylene glycol glycoside, propylene glycoside, glyceryl glycoside and 1,2,6-hexanetriol glycoside.

The polyester amides include, for example, the predominantly linear condensates obtained from polyvalent saturated and / or unsaturated carboxylic acids or their anhydrides and polyvalent saturated and / or unsaturated amino alcohols, or mixtures of polyhydric alcohols and amino alcohols and polyamines.

Examples of suitable polyacetals are the compounds which can be prepared from glycols, such as diethylene glycol, triethylene glycol, 4,4'-dioxethoxy-diphenyldimethylmethane, hexanediol and formaldehyde. Polyacetals suitable according to the invention can also be prepared by polymerizing cyclic acetals.

Suitable polycarbonates containing hydroxyl groups are those of the type known per se, for example by reacting diols such as propanediol (1,3), butanediol (1,4) and / or hexanediol (1,6), diethylene glycol, triethylene glycol , Tetraethylene glycol with diaryl carbonates, such as diphenyl carbonate or phosgene, can be produced.

The polyols can be used individually or in the form of mixtures. Mixtures of polyester and polyetherols have proven themselves, for example, the ratio of the components depending on the intended use of the rigid polyurethane foam to be produced being able to be varied within wide limits, for example in the weight ratio of polyesterol to polyetherol, from 20:80 to 80:20.

An essential feature of the present invention is the concomitant use of aqueous melamine-formaldehyde precondensate solutions with melamine-formaldehyde precondensate contents of 40 to 85% by weight, preferably 50 to 70% by weight, based on the total weight, which are produced by condensation of Melamine with formaldehyde in a molar ratio of 1: 1.1 to 1.75, preferably 1: 1.4 to 1.70 and especially 1: 1.5 to 1.65 in aqueous solution.

Commercial melamine and preferably aqueous, optionally stabilized formaldehyde solutions with formaldehyde contents of 30 to 40% by weight are used for this.

The condensation of the melamine-formaldehyde precondensates which can be used according to the invention is - as already explained - in aqueous solution at a temperature of 60 to 130 ° C., if appropriate under pressure, preferably at 80 to 100 ° C., and at least temporarily at a pH of greater than 8, preferably from 8 to 12 and in particular 9 to 11 (measured at room temperature and with temperature compensation) until a water dilutability of 20 ° C. of 1: 0.5 to 4 is reached. Water-dilutability in the sense of the invention means that a volume part of resin solution can be diluted at 20 ° C with 0.5 to 4 volume parts water without permanent cloudiness occurring.

To adjust the pH range, inorganic bases, such as, for example, aqueous sodium or potassium hydroxide solution, and / or organic bases, such as, for example, tertiary amines, mono-, di- and trialkanolamines, N-alkyl-, N, N-dialkylalkanolamines, N -Alkyldialkanolamine among others can be used. After the condensation has ended, the reaction times are approximately 15 to 400 minutes, the melamine-formaldehyde precondensate solutions are cooled. The solutions obtained are stable for 30 days or more at room temperature and, depending on the solids content, have viscosities at 20 ° C. of 20 cP to 5000 P, preferably 30 cP to 3000 P and in particular 30 cP to 1000 P, so that they are still relatively good Polyurethane foaming machines can be processed.

To improve the storage stability, the melamine / formaldehyde mixtures, before the start of the condensation or the melamine / formaldehyde precondensate solutions in the course of the condensation or after the condensation has ended, can optionally have stabilizing agents in amounts of at most 15% by weight, preferably from 0.1 to 3% by weight, based on the solids content of the melamine-formaldehyde precondensate solution, are incorporated. Suitable for this purpose are the stabilizers known per se, such as combinations of toluenesulfonamide with alcohols or sucrose, dicyandiamide in the presence of alcohols and guanidinium salts, lactams, caprolactams and thiourea.

The melamine-formaldehyde precondensate solutions obtained can, if appropriate, be mixed with the other starting components, auxiliaries and additives, with the exception of polyisocyanates, immediately after their preparation or only immediately before processing to give polyurethanes. The melamine-formaldehyde precondensate solutions obtained are expediently mixed with the catalysts, optionally polyols, chain extenders or crosslinking agents, inert physically active blowing agents, auxiliaries and additives, and stored as a so-called A component, immediately after the condensation. If appropriate, it can also be advantageous to carry out the condensation of melamine and formaldehyde in an aqueous medium in the presence of the polyols and the catalysts suitable for producing foam.

Mixtures of 100 parts by weight of 40 to 85% by weight melamine-formaldehyde precondensate solutions and 1 to 50 parts by weight, preferably 8 to 20 parts by weight of polyol are suitable for the production of polyurethane. However, as already mentioned, mixtures containing storage-stable, basic polyurethane and optionally acidic curing catalysts are only obtained if they have a pH greater than 7, preferably from 8 to 12.

If appropriate, it may also be expedient to use chain extenders or crosslinking agents in addition to the polyols mentioned for the production of the polyurethane foams. Such agents include polyfunctional, especially di- and trifunctional compounds with molecular weights of 17 to 600, preferably 60 to 300. For example, di- and trialkanolamines, such as diethanolamine and triethanolamine, are used. aliphatic and aromatic diamines, such as, for example, ethylenediamine, 1,4-butylenediamine, 1,6-hexamethylenediamine, 4,4'-diamino-diphenylmethane, 3,3'-dialkyl-substituted 4,4'-diaminodiphenylmethanes, 2,4- and 2, 6-toluenediamine and preferably aliphatic diols and triols having 2 to 6 carbon atoms, such as ethylene glycol, 1,4-butylene glycol, 1,6-hexamethylene glycol, glycerin and trimethylolpropane.

If chain extenders or crosslinking agents are used, they are used in amounts of 1 to 60, preferably 10 to 30, per 100 parts by weight of polyol.

To accelerate the reaction between the polyols, water and, if appropriate, chain extenders or crosslinking agents and the organic polyisocyanates, the reaction mixture or preferably the A component is mixed with conventional polyurethane catalysts in an amount of 0.5 to 15 parts by weight, preferably 3 up to 10 parts by weight per 100 parts by weight of the aqueous melamine-formaldehyde precondensate solution. Basic polyurethane catalysts are preferably used, for example tertiary amines, such as dimethylbenzylamine, dicyclohexylmethylamine, dimethylcyclohexylamine, N, N, N ', N'-tetramethyl-diamino-ethyl ether, bis- (dimethylaminopropyl) urea, N-methyl or N- Ethylmorpholine, dimethylpiperazine, pyridine, 1,2-dimethylimidazole, 1-azobicyclo- (3,3,0) octane, dimethylaminoethanol, N, N ', N "-Tris- (dialkylaminoalkyl) hexahydro-triazines, for example N, N ', N "-Tris- (dimethylaminopropyl) -s-hexahydrotriazine and in particular triethylene diamine and triethanolamine. However, metal salts such as iron (II) chloride, zinc chloride, lead octoate and preferably tin salts such as tin dioctoate are also suitable. Tin diethylhexoate and dibutyltin dilaurate, which are usually used when the two-component process is not used.

In addition to the polyurethane catalysts, it has also proven to be advantageous to use “acidic” curing catalysts for the production of the polyurethane foams, so that this process variant is preferably used. Examples of acidic curing catalysts which are used in amounts of 0.5 to 5 parts by weight, preferably 1 to 3 parts by weight, per 100 parts by weight of melamine-formaldehyde precondensate solution are: inorganic acids such as hydrochloric, sulfuric and especially phosphoric acid, organic carboxylic acids such as formic acid, oxalic acid, trichloroacetic acid, sulfonic acids such as amidosulfonic acid and p-toluenesulfonic acid, Lewis acids such as boron trifluoride, phosphorus trichloride and phosphorus oxychloride, organic carboxylic acid chlorides and so-called benzoyl chloride, such as benzoyl chloride latent hardeners such as the salts of ammonia, organic amines or magnesium of the abovementioned acids and their esters. Water is preferably used as blowing agent, which is incorporated in a large excess with the aqueous melamine-formaldehyde precondensate solution in the reaction mixture and partially reacts with the polyisocyanates to form carbon dioxide.

In a mixture with water, physically active blowing agents can also be used. Liquids which are inert to the organic polyisocyanates and boiling points below 100 ° C., preferably below 50, are suitable^OC, especially between -50⁰C and 30 ° C at atmospheric pressure, so that they evaporate under the influence of the exothermic polyaddition and polycondensation reaction. Examples of such preferably usable liquids are hydrocarbons such as pentane, n- and isobutane and propane, ethers such as dimethyl ether and diethyl ether, ketones such as acetone and methyl ethyl ketone, ethyl acetate and preferably halogenated hydrocarbons such as methylene chloride, trichlorofluoromethane, dichlorodifluoromethane, Dichloromonofluoromethane, dichlorotetrafluoroethane and 1,1,2-trichloro-1,2,2-trifluoroethane. Mixtures of these low-boiling liquids with one another and / or with other substituted or unsubstituted hydrocarbons can also be used.

The amount of physically active blowing agents required in addition to water can be determined in a simple manner depending on the desired foam density and is approximately 5 to 40 parts by weight, preferably 10 to 30 parts by weight per 100 parts by weight of melamine-formaldehyde. Pre-condensate solution. It may be appropriate to mix the organic polyisocyanate with L the physically active blowing agent and thereby reduce the viscosity of the B component.

Auxiliaries and additives can also be incorporated into the reaction mixture. Examples include stabilizers, hydrolysis protection agents, pore regulators, fungistatic and bacteriostatic substances, dyes, pigments, fillers, surface-active substances, plasticizers and flame retardants.

For example, surface-active substances are considered which serve to support the homogenization of the starting materials and, if appropriate, are also suitable for regulating the cell structure of the foams. Siloxane-oxyalkylene copolymers and other organopolysiloxanes, oxyethylated alkylphenols, oxyethylated fatty alcohols, paraffin oils, castor oil or Ricinoleic acid esters and Turkish red oil, which are used in amounts of 0.2 to 8, preferably 0.5 to 5 parts by weight per 100 parts by weight of melamine-formaldehyde precondensation solution.

It may also be advantageous to include a plasticizer in the reaction mixture so that the tendency towards brittleness in the products is reduced. Conventional plasticizers can be used, but it is particularly expedient to use agents which contain phosphorus and / or halogen atoms and thereby additionally increase the flame resistance of the polyurethane plastics. Such agents include tricresyl phosphate, tris-2-chloroethyl phosphate, tris-chloropropyl phosphate and tris-2,3-dibromopropyl phosphate.

In addition to the melamine-formaldehyde condensates and halogen-substituted phosphates already mentioned, inorganic flame retardants, such as antimony trioxide, arsenic oxide, ammonium phosphate and calcium sulfate, can also be used to flame retard the polyurethane foams.

In general, it has proven to be advantageous to use 5 to 50 parts by weight, preferably 5 to 25 parts by weight, of the flame retardants mentioned for every 100 parts by weight of melamine-formaldehyde precondensate solution.

The polyurethane foams can be produced using the one shot process. For this purpose, the organic polyisocyanates and polyols, melamine-formaldehyde precondensates, water and optionally chain extenders or crosslinking agents in the presence of the catalysts at temperatures of 5 to 40 ° C., preferably 18 to 25⁰C reacted in such proportions that 0.2 to 35, preferably 5 to 15 and in particular approximately one reactive hydrogen atom (s) bonded to OH, NH per NCO groups₂-, NH =, SH-, COOH- or CONH₂Groups of the polyols, melamine-formaldehyde precondensate and optionally chain extenders or crosslinking agents are present and the molar ratio of equivalents of water to equivalents of NCO groups is 135 to 0.9, preferably 20 to 5: 1 and in particular 15 to 5: 1.

When using a mixing chamber with several inlet nozzles, the starting materials, auxiliaries and additives can be added individually and mixed intensively in the mixing chamber. If a certain increase in viscosity, which may occur when mixing the melamine-formaldehyde precondensate solution with the polyols, does not adversely affect the processing, it has proven expedient to work according to the two-component process and the polyols, aqueous Melamine-formaldehyde precondensate solutions, polyurethane catalysts, acidic curing catalysts and optionally chain extenders or crosslinking agents, physically active blowing agents, To combine auxiliaries and additives in the A component and to use the organic polyisocyanates as the B component, if appropriate in a mixture with physically active blowing agents, auxiliaries and additives.

It is advantageous here that the A and B components can be transported in a space-saving manner and stored for a limited time and only have to be mixed intensively before the polyurethane foams are produced.

Polyurethane foam molded parts produced by this process variant show practically no or only slight shrinkage.

According to a further process variant, the polyols are first completely or partially reacted with the polyisocyanates to form prepolymers containing isocyanate groups, which are then used as the B component. It has proven to be advantageous here, from at least 50% by weight, preferably more than 90% by weight, of the polyols isocyanate groups used_-to produce prepolymers containing. The remaining amount of polyols can either be mixed directly in the mixing head with the other starting components, auxiliaries and additives or, as described above, the polyols can be physically mixed with the aqueous melamine-formaldehyde precondensate solutions, polyurethane catalysts, acidic curing catalysts and optionally chain extenders or crosslinking agents acting blowing agents, auxiliaries and additives are combined to form the A component.

The isocyanate group-containing prepolymers are prepared by conventional methods from the above-mentioned polyols and preferably aromatic polyisocyanates and have NCO contents of 3 to 35, preferably 12 to 28.

The polyurethane foams produced by the process according to the invention have densities of 10 to 300 kg / m³, preferably 30 to 50 kg / m³ and are characterized by low water absorption, low shrinkage, low thermal conductivity and practically no formaldehyde emission.

The products are preferably used as insulation material.

The parts mentioned in the examples relate to the weight.

Preparation of the aqueous melamine-formaldehyde precondensate solutions.

Examples la to lc

la) 2388 g of 40% formaldehyde solution, 2432 g of melamine and 1942 g of water were mixed in a reaction vessel and mixed with 12.9 ml of potassium hydroxide solution (c = 1.8 mol / 1) and 12 ml of diethylethanolamine. The mixture is then heated to 96 ° C., during which the reaction mixture goes into solution. The condensation was continued at 96 ° C for 140 min and then cooled to 20 ° C.

The pH of the solution was 10.1, the formaldehyde-melamine molar ratio 1.65, the viscosity 35 cP / 20 ° C, the solids content 50%, the water dilutability 1: 2 and the storage stability at 20 ° C for 35 days .

Ib) To produce a 75% resin solution, 500 g of water were distilled off from 1500 g of the solution described in Example la under reduced pressure.

1c) To prepare an 80% resin solution, 600 g of water were distilled off from 1600 g of the solution described in Example la under reduced pressure.

ld) To prepare a 70% resin solution, 400 g of water are distilled off from 1400 g of the solution described in Example la under reduced pressure.

Example 2.

Analogously to the information from Example la, 2388 g of 40% formaldehyde solution, 2585 g of melamine, 2095 g of water and 12.0 ml of potassium hydroxide solution (c = 1.8 mol / 1) and 10 ml of diethylethanolamine were mixed and condensed. The pH of the solution was 10.1, the formaldehyde-melamine molar ratio 1.55, the viscosity 31 cP, the solids content 50.3%, the water dilutability 1: 2 and the storage stability for 40 days at 20 ° C.

Resin solutions with a higher solids content can in turn be obtained by distilling off water under reduced pressure.

Manufacture of polyurethane foams

Examples 3 to 9

To produce the polyurethane foams, the A and B components, which have room temperature, are mixed intensively at room temperature for 20 seconds and left to foam in an open mold.

The starting materials and amounts used as well as the measured starting, climbing, tack-free times, densities and fire behavior are summarized in Table I.

In the table, the molar ratio of formaldehyde:<ul id="ul0004" list-style="none"><li>Melamine abbreviated F: M.<img file="EP0040720A2_D0001.tif" /><img file="EP0040720A2_D0002.tif" /></li></ul>

Examples 10 ad

To prepare the prepolymers containing isocyanate groups, the organic polyisocyanates and polyols are mixed with stirring at room temperature and the polyaddition is then completed in 3.5 hours at 70.degree.

The starting components and amounts used and the NCO contents of the prepolymers obtained are summarized in Table II<tables id="tabl0001" num="0001"><img file="EP0040720A2_D0003.tif" /></tables>

Examples 11-14

The polyurethane foams are produced analogously to the information in Examples 3-9.

The starting components and amounts used as well as the measured start, climb and tack free time, the density and the fire behavior according to ASTM D 635-77 are summarized in Table III.<tables id="tabl0002" num="0002"><img file="EP0040720A2_D0004.tif" /></tables>