DE2040437A1 - Process and binding agent for the production of polyurea-bound foundry moldings - Google Patents

Description

Method and binder for making polyurea bonded Foundry moldings The invention relates to that. Manufacture of foundry molded parts with Binders based on organic multifunctional isocyanates.

It is known to use quartz sand with aromatic di- and priisocyanates and solutions of phenol-formaldehyde resins, the phenol nuclei of which have methylol groups, to mix, to bring the mixtures into core boxes and in these with triethylamine-containing inert gas, such as triethylamine-containing nitrogen. The priethylamine catalyzes the reaction of the isocyanato groups with the methylol groups to form urethane groups. The resulting polyurethane binds the quartz sand to form solid molded parts that form the core boxes can be removed. A disadvantage of this way of working is the time it takes limited processability of the mixtures.

The reaction leading to the polyurethane starts when it is mixed and not only under the influence of triethylamine. Must in the foundries therefore often mixed molding compounds partly thrown away who (len, because they could no longer be completely processed before they solidified.

Another disadvantage of the known way of working is the explosion, Danger of poisoning and chemical burns when handling triethylamine and the triethylamine-containing Inert gas.

To reduce the latter dangers, but not entirely to exclude, has already been suggested, not with triethylamine-containing Inert gas, but with water vapor or water-containing aerosol and that Triethylamine or generally tertiary amines in the sand mixture to accommodate the sand mixture polyester instead of phenol-formaldehyde resins and also isocyanates should contain. By adding water under the catalytic influence of the The tertiary amines contained in the sand mixture result in polyurea and the Foundry moldings formed from the sand mixture should solidify. At tier testing However, this proposal showed that the properties of such Change the sand mixture very quickly immediately after mixing and that the intended solidification effect is too low to be moldable or even pourable To produce molded parts.

The present invention completely eliminates the above dangers by doing without tertiary amines and also eliminates the disadvantage of the above time limitation of processability. It consists in a method of manufacture of foundry molded parts by mixing molding compounds with isocyanates Binders, molding the mixed molding compounds and adding water to the Form lingen, characterized in that the molding compounds with organic multifunctional Isocyanate-containing binders mean without admixing with the isocyanates From formation of urethane groups reacting substances and without Admix mixed with tertiary amines. The water fed in reacts per mole two moles of isocyanato groups with elimination of one mole of carbon dioxide and at the same time Formation of (-NH-CO-NH-) - groups, whereby because of the multifunctionality of the isocyanates Polyureas or polyurea derivatives are created that give the moldings strength give and thus turn the bricks into solid foundry mold parts. One should now assume that the split off carbon dioxide loosens the structure of the moldings. However, this does not occur. The reaction between the water and the isocyanato groups runs relatively quickly, so that catalyzing with tertiary amines is unnecessary. If necessary, the reaction can be accelerated by warmth while treating the moldings with hot steam is particularly useful.

Products have proven to be particularly useful as organic multifunctional isocyanates proven by condensing fully aliphatic ketones with formaldehyde and Reacting the condensation products formed with aromatic di- tlnd / or Receives triisocyanates. The molar ratio of formaldehyde: ketone is at least 2 and preferably 2 to 2.6. The content of the ketone formadehyde condensation products on hydroxyl groups is determined by the known determination of the OH number. To the amount of di- or triisocyanates to be converted is measured for him. The molar ratio Isocyanate groups: 1! Hydroxyl groups is larger than i, so that the reaction products still contain at least two free isocyanato groups per molecule.

The aliphatic ketones are made with formaldehyde by known processes condensed. It is condensed in an alkaline way. Lower ones are preferred aliphatic ketones and among these butanone alone or in a mixture with acetoin. The degree of condensation is determined in a known manner the molar ratio eton: formaldehyde and influenced by the amount of water expelled. He will monitored by viscosity measurements and OH number determinations. With a given The molar ratio of ketone: formaldehyde decreases with the increasing degree of condensation from and the viscosity to. The viscosity can be increased by reacting with di- or triisocyanates continue to be increased. An expedient way of working is to use low-viscosity Ketone-formaldehyde condensation products in a first stage with diisocyanates and to react with triisocyanates in a second stage.

The molar ratio isocyanato groups: hydroxyl groups in the first stage less than 1 and in the second stage chosen so large that the total molar ratio of the isocyanato groups used in both stages: Hydroxyl groups is greater than 1. The ketone-formaldehyde condensation products are with the di- resp.

Triisocyanates by simply heating or leaving them to stand normal temperature implemented. The reaction can be catalyzed in a known manner will1 e.g. B. by organic metal salts, such as those used as siccatives for drying Oils are used. Without contradicting the above waiver of tertiary Amines can cause the reaction of the ketone-formaldehyde condensation products with the isocyanates Could definitely be Yajysed by tertiary amines. After the conversion has ended the tertiary amines removed or rendered harmless. You will, for example distilled off or fixed by adsorption. The distillation can be done by blowing in Nitrogen, carbon dioxide or hydrocarbons.

Organic substances suitable for carrying out the method according to the invention polyfunctional isocyanates are not only the reaction products of the ketone-formaldehyde Condensation products with aromatic di- and / or triisocyanates, but also with other organic ones multifunctional isocyanates. The molar ratio he used isocyanato groups : Hydroxyl groups is also greater than 1 here, so that the reaction products too here still contain at least two free isocyanato groups per molecule.

Also reaction products of phenol-aldehyde condensation products containing methylol groups with organic multifunctional isocyanates, especially with aromatic di- and / or triisocyanates, with an oversupply of isocyanato groups for the presence of at least two free isocyanato groups per molecule Reaction product is provided are for carrying out the method according to the invention suitable.

Another class of for practicing the invention Organic polyfunctional isocyanates suitable for the process form the phosgenation products of condensation products of aromatic amines and aldehydes, preferably the Phosgenation products of cocondensation products from aromatic amines, phenols and aldehydes.

All organic multifunctional isocyanates mentioned here are if they are too viscous, used in the form of their solutions for mixing the molding compounds. Solvents are used that have at least a limited dissolving power for water. Aromatics, ketones, ethers, esters or mixtures are suitable Contain representatives of one or more of these substance classes.

Examples of representatives of these substance classes are benzene, alkylbenzenes, Cycohexanone, oligoglycol ether with esterified terminal hydroxyl groups.

The following examples are intended to explain the invention without limiting it to limit the examples.

1. Example 1a) Method 4 kg of dry Quanzsand, 4 g calcium stearate and 160 g of the binder described under ib) a molding compound mixed. A part of this molding compound became a immediately after mixing other part formed after three hours of storage. There were 6 bending bars in each case Shaped according to DIN 52 404 and left in the mold for treatment with steam. The shape differed from DIN 52.404 on the top with a gas feed funnel and slotted nozzles on the underside.

Steam was passed through the gas supply funnel for 2 minutes passed through the molding compound in the mold. The bending vessels were each Shaped immediately after the steam had passed through, stored for 1 hour and then tested for flexural strength according to DIN 52 404.

1b) Binder 9 moles of butanone and 1 mole of acetone were mixed with 21 moles of formaldehyde condensed until a resin with a softening temperature of approx. 600C was formed was. 350 g of a 40% strength solution of this resin in cyclohexanone were 18 g Diisocyanato-diphenylmethane for 3 hours at 80 ° C. in a reflux condenser Flask stirred.

260 g of a 20% strength solution of triisocyanato-triphenylmethane were then added in methylene chloride was added to the flask and the contents were kept for an additional 3 hours stirred at Bo ° c. Then 100 g of solvent, essentially methylene chloride, distilled from the flask and then 33 g of a C - to C - aromatics mixture and 33 g of 7 10 butyl acetate were added to the flask. The contents of the flask were now one approx. 50% solution of the reaction product and provided the binder used under la) represent.

lc) Results The mean value of the flexural strengths was at 6 bars that were formed immediately after mixing 2, 1l, 8 kp / cm2 and for the 6 rods that were molded from the molding compound stored for 3 hours was 13.2 kgf / cm.

2. Example 2a) Method 4 kg of dry quartz sand, 8 g bentonite activated with Na ions and 160 g of the binder described under 2b) a molding compound mixed. Part of this molding compound was immediately after Mix, another part formed after three hours of storage. There were each 6 bending bars shaped according to DIN 52 404 and left lying immediately after shaping formed on the base and removing the mold halves. The still soft bending vessels were placed on the surface with this in a chamber for 1 hour, in the approx. 25 ° C and approx.

98 X relative humidity prevailed. After that were the bending bars fixed. They were stored outside the chamber for 1 hour and then according to DIN 52 404 tested for flexural strength.

2b) Binder 9 moles of butanone and 1 mole of methyl isobutyl ketone were condensed with 25 moles of formaldehyde until a resin with a softening temperature of approx. 100 ° C was created.

This resin was exactly as under ib) with diisocyanatodiphenylmethane and triisocyanato-tripenylmethane reacted, but at the beginning 20 g of cobalt abietate were used put in the flask and the heating time from 2 times 3 hours to 2 times 1.5 Hours reduced.

2c) Results The mean value of the flexural strength was for the 6 Bars molded immediately after mixing were 16.3 kgf / cm² and for the 6 rods that were molded from the molding compound that had been stored for 3 hours, 15.8 kg / cm².

2. Example 3a) Procedure as 1a).

3b) Binder 200 g phenol, 180 g 38 96% aqueous formaldehyde solution and 100 g of 5% sodium hydroxide aqueous solution were refluxed for 1 hour cooked. It was then neutralized with oxalic acid and refluxed within 65 g of aniline were added dropwise over a period of 30 minutes and reflux temperature for a further 3 hours held. After the aqueous phase had been separated off, it was heated up to 1350C completely dehydrated and unreacted aniline driven off.

The brown resin was a 20% solution in a mixture of cyclohexanone, Benzene, chlorobenzene and o-dichlorobenzene are phosgenated. One freed from the solvent The sample of the phosgenation product had a chlorine content of approx.

2.5 X on. When the phobgenation was complete, there was so much solvent evaporated until a 70% solution resulted was that then with cyclohexanone to 50, was diluted.

3c) Results The mean value of the flexural strengths was 6 bars molded immediately after mixing, 19.5 kgf / cm² and for the 6 rods that were molded from the molding compound that had been stored for 3 hours, 23.8 kgf / cm².

Claims (5)

Claims 1.) Process for the production of foundry molded parts by mixing of molding compounds with binders containing isocyanates, forms of the mixed Molding compound and supplying water to the moldings, characterized in that the molding compositions with binders containing organic polyfunctional isocyanates without admixing with the isocyanates reacting with the formation of urethane groups Substances and without adding tertiary amines. 2.) Binder for performing the method according to claim 1, characterized characterized in that there are reaction products of a) condensation products of aliphatic Ketones and formaldehyde in a molar ratio of formaldehyde: ketone of at least two with b) organic having at least two isocyanato groups per molecule Contains isocyanates, but not the one offered under b) for the reaction converted amount of isocyanato groups greater than that under a) for the reaction offered amount of hydroxyl groups. 3.) Binder for performing the method according to claim 1, characterized characterized in that there are reaction products of a) condensation products containing methylol groups from phenols and aldehydes with b) organic, at least two isocyanato groups per molecule containing isocyanates contains, whereby the under b) Amount of isocyanato groups offered for implementation but not converted is greater than the amount of methylol groups offered for the implementation under a). 4.) Binder for performing the method according to claim l, characterized characterized in that there are phosgenation products of condensation products from aromatic Contains amines and aldehydes. 5.) Binder for performing the method according to claim 1, characterized characterized in that there are phosgenation products of cocondensation products from phenols, contains aromatic amines and aldehydes.