EP2249982A2

EP2249982A2 - Use of branched alkane diol carboxylic acid diesters in polyurethane-based foundry binders

Info

Publication number: EP2249982A2
Application number: EP09706370A
Authority: EP
Inventors: Christian Priebe; Diether Koch
Original assignee: Ashland Suedchemie Kernfest GmbH
Current assignee: ASK Chemicals GmbH
Priority date: 2008-02-01
Filing date: 2009-01-30
Publication date: 2010-11-17
Anticipated expiration: 2029-01-30
Also published as: US8813830B2; KR20100112189A; EA201070885A1; WO2009095251A8; WO2009095251A3; CA2712656A1; EP2249982B1; DE102008007181A1; MX2010008276A; CN101932394A; EA018307B1; WO2009095251A2; PL2249982T3; ATE521436T1; US20110005702A1; ZA201004919B; UA99174C2; ES2372666T3; JP2011510818A; BRPI0906725A2

Abstract

The invention relates to a molding material mixture for production of molded products for the foundry industry, comprising at least one fire-resistant base molding material and a polyurethane-based binder system comprising a polyisocyanate component and a polyol component. According to the invention, the polyurethane-based binder system comprises a portion of a carboxylic acid diester of a branched alkane diol, said portion being at least 3 weight-%, and a portion of aromatic solvent of less than 10 weight-% of the binder system. A preferable carboxylic acid diester is 2,2,4-trimethyl-1,3-pentandiol-diisobutyrate. The molded products produced from the molding material mixture for the foundry industry are characterized by a high strength and a lower generation of fumes and smoke during pouring.

Description

Use of branched alkanediol carbonic acid diesters in polyurethane-based mold release binders

The invention relates to a molding material mixture for the production of moldings for the foundry industry, a method for producing a casting mold using the molding material mixture, a casting mold, and the use of the casting mold for metal casting.

Molds for the production of metal bodies are essentially produced in two embodiments. A first group are the so-called nuclei and forms. From these, the mold is assembled, which is essentially a negative mold of the casting to be produced, wherein cores serve to form cavities in the interior of the casting, while the molds depict the outer boundary. Often, the inner cavities are imaged by cores, while the outer contour of the casting is represented by a green sand mold or a steel mold. A second group form hollow body, so-called feeders, which act as compensation reservoir. These take up liquid metal, whereby appropriate measures are taken to ensure that the metal remains in the liquid phase longer than the metal that is in the negative mold forming mold. If the metal solidifies in the negative mold, liquid metal can flow out of the compensation reservoir to compensate for the volume contraction that occurs when the metal solidifies.

Casting molds are made of a refractory material, such as quartz sand, whose grains are connected after molding of the mold by a suitable binder to ensure sufficient mechanical strength of the mold. For the production of molds so you use a refractory molding material, which is mixed with a suitable binder. The molding material mixture obtained from molding material and binder is preferably present in a free-flowing form, so that it can be filled into a suitable mold and compacted there. The binder produces a firm cohesion between the particles of the molding base material, so that the casting mold obtains the required mechanical stability.

For the production of casting molds both organic and inorganic binders can be used, the curing of which can be effected by cold or hot processes. Cold processes are processes which are carried out essentially at room temperature without heating the molding material mixture. The curing is usually carried out by a chemical reaction, which can be triggered, for example, by passing a gaseous catalyst through the molding material mixture to be cured, or by adding a liquid catalyst to the molding material mixture. In hot processes, the molding material mixture after molding on a heated sufficiently high temperature, for example, to drive off the solvent contained in the binder, or to initiate a chemical reaction by which the binder is cured by crosslinking.

At present, for the production of casting molds, organic binders such as e.g. Polyurethane, furan resin or epoxy-acrylate binders used in which the curing of the binder is carried out by adding a catalyst. Polyurethanes based on polyurethanes are generally composed of two components, a first component containing a phenolic resin and a second component containing a polyisocyanate. These two components are mixed with the molding base stock and the molding mixture is rammed, compressed, blasted, shot or otherwise, compacted and then cured. Depending on the method in which the catalyst is introduced into the molding material mixture, a distinction is made between the "polyurethane no-bake process" and the "polyurethane cold-box process".

In the no-bake process, a liquid catalyst, generally a liquid tertiary amine, is introduced into the molding material mixture before it is shaped and cured. For the preparation of the molding material mixture phenolic resin, polyisocyanate and curing catalyst are mixed with the refractory molding material. In this case, it is possible, for example, to proceed in such a way that the molding base material is first coated with one component of the binder, and then the other component is added. The curing catalyst is added to one of the components. The ready-made molding material mixture must have a sufficiently long processing time, so that the molding material mixture can be plastically deformed for a sufficient time and processed into a shaped body. The polymerization must be correspondingly slow run so that not already in the storage containers or supply lines hardening of the molding material mixture. On the other hand, the curing should not be too slow to achieve a sufficiently high throughput in the production of molds. The processing time can be influenced, for example, by the addition of retarders, which slow down the curing of the molding material mixture. A suitable retarder is, for example, phosphorus oxychloride.

In the cold-box process, the molding material mixture is first brought into a mold without catalyst. Through the molding material mixture, a gaseous tertiary amine is then passed, which may optionally be treated with an inert carrier gas. On contact with the gaseous catalyst, the binder binds very quickly, so that a high throughput in the production of molds is achieved.

No. 3,409,579 describes a binder composition which comprises a mixture of a resin component, a curing component and a hardening agent. The resin component comprises a phenolic resin obtained by condensing a phenol and an aldehyde. The phenolic resin is dissolved in an organic solvent. The curing component comprises a liquid polyisocyanate having at least two isocyanate groups. As a hardening agent, the binder comprises a tertiary amine. For the preparation of molded articles, the phenolic resin component and the polyisocyanate component are first mixed with a refractory molding base material. The molding material mixture is subsequently brought into a mold and formed there to form a shaped body. To cure the molding mixture, which normally takes place at room temperature, the gaseous hardening agent is passed through it. Suitable curing agents are, for example, trimethylamine, dimethylethylamine, dimethylisopropylamine or triethylamine. For better Vaporizability, the tertiary amine can be heated. After curing, the mold can be removed from the mold.

US 3,676,392 describes a resin composition comprising a phenolic resin component dissolved in organic solvents, a hardener component, and a curing catalyst. The hardener component used is a liquid polyisocyanate which comprises at least two isocyanate groups. The polyisocyanate is used in an amount of 10 to 15 wt .-%, based on the weight of the resin. As Aushärtungskata ^¬ lyst is used which has a pK _b in the range of about 7 to about 11, a base, and is in an amount of 0.01 to 10 wt .-%, based on the resin used.

EP 0 261 775 B1 describes a binder comprising a polyhydroxy component, an isocyanate component and a catalyst for the reaction between said components. The polyhydroxy component is dissolved in a liquid ester of an aliphatic alkoxycarboxylic acid. Example 6 describes a binder containing as solvent for the resin an aromatic solvent in a proportion of 19% by weight, ethyl 3-ethoxypropionate in a proportion of 15% by weight, "Red OiI" in a proportion of 1 wt .-%, and 2, 2, 4-trimethyl-l, 3-pentanediol diisobutyrate (TXIB) in a proportion of 5 wt .-%.

EP 0 695 594 A2 describes a polyurethane-based foundry binder which contains a biphenyl as an additive. In Example 1 and Comparative Examples 2 and 3, 2% by weight of 2, 2, 4-trimethyl-1,3-pentanediol diisobutyrate as plasticizer are added to the binder. The solvent used is 17% by weight of aromatic solvent and 10% by weight of biphenyl which has been substituted twice or three times. EP 0 766 388 A1 describes a polyurethane-based foundry binder which comprises an epoxy resin and preferably a paraffin oil. In Example 3 and Comparative Example 3, a binder system is used, which contains 2 wt .-% of 2, 2, 4-trimethyl-l, 3-pentanediol diisobutyrate as a plasticizer. The solvents used are aromatic hydrocarbons.

In US 4,268,425 a binder system for the foundry industry is described, which is based on polyurethanes. The binder system is accompanied by a drying oil. Example 1 describes a binder system in which the phenol resin component as solvent contains DBE (dibasic ester) and Cβ-Cio-dialkyl adipate. As a further component contains the phenolic resin component 2 wt .-% 2, 2, 4-trimethyl-l, 3-pentanediol diisobutyrate. The isocyanate component contains 8.8% by weight of aromatic solvent and 6.2% by weight of petroleum ether as solvent.

No. 4,540,724 describes a binder system based on polyurethanes which contains a phosphorus halide as essential component. Example 2 describes a binder system whose phenolic resin component contains 10% by weight of 2,2,4-trimethyl-1,3-pentanediol diisobutyrate in addition to 27% by weight of aromatic solvent. Furthermore, the phenolic resin component contains linseed oil or polymerized linseed oil. The isocyanate component also contains aromatic solvents.

WO 98/19899 describes a binder system based on polyurethanes, in which the polyisocyanate component has been modified by reaction with an aliphatic alcohol which has at least one active hydrogen atom. For the isocyanate component, aliphatic solvents can be used. In order to apply the polyhydroxy component and the isocyanate component in a thin film evenly on the grains of the molding material, the components are diluted with solvents. In order to achieve a compatibility of the components, usually aromatic solvents are used, which, however, may have a harmful effect. During casting, the binder decomposes under the action of heat of the liquid metal. When pouring therefore occurs a strong smoke smoke. The exhaust gases produced during casting must therefore be removed by a complex venting and worked up in order to comply with environmental and occupational safety regulations.

The smoke and smoke development is attributable to a considerable extent to the aromatic solvent contained in the binder. Attempts have therefore been made to develop alternative solvent systems for foundry binders which contain no aromatic solvents or which have only a small proportion of such aromatic solvents.

For example, EP 0 771 599 describes a polyurethane-based binder system which contains methyl esters of higher fatty acids as solvent. Particularly suitable is Rapeseed oil methyl ester used as the sole solvent.

EP 1 137 500 B1 describes a polyurethane-based binder system in which the phenolic resin component or the polyisocyanate component comprises a fatty acid ester which is esterified with an alcohol which has a high carbon number. Particular preference is given to using fatty acid butyl esters and fatty acid octyl or fatty acid decyl esters. The phenolic resin component comprises an alkoxy-modified phenolic resin in which less than 25 mole% of the hydroxymethanol groups are etherified by a primary or secondary aliphatic monoalcohol having from 1 to 10 carbon atoms. Of the Solvent content of the phenolic resin component is at most 40% by weight.

The use of fatty acid esters, which are esterified with long-chain alcohols, can significantly reduce the smoke and smoke during casting. Nevertheless, there is a constant search for further possibilities to further reduce emissions during casting. Among others there are two possibilities. As a first possibility, the components of the binder can be changed so that they lead to a lower smoke development. As a second possibility, the binder may be modified to have a higher bonding power, i. the proportion of the binder in the molding material mixture can be reduced.

The invention therefore an object of the invention to provide a molding material for the production of moldings for the foundry industry, which allows the use of small amounts of binder, the production of moldings, which have a sufficiently high strength, even in a technical production safely and without Damage to be handled.

This object is achieved with a molding material mixture having the features of patent claim 1. Advantageous embodiments are the subject of the dependent claims.

Surprisingly, it has been found that carboxylic acid diesters of a branched alkanediol have both a good compatibility with the polyisocyanate component and with the polyol component, so that the components of the binder system can be dissolved in a relatively small amount of solvent. In most cases, it is not necessary to add aromatic solvents to the carboxylic acid diester of a branched alkanediol in order to reduce the solubility of the components of the binder system to polyisocyanates. - -

urethane base to increase so far that on the one hand, the amount of solvent in the binder system can be kept low and on the other hand, the viscosity of the binder system or its components is lowered so far that the grains of the refractory molding material can be evenly coated with a thin layer of the binder system at low mixing times , This is very important, for example, in the no-bake method, since in this case the liquid catalyst is added to the binder system and therefore the processing time of the molding material mixture is relatively short before the binder cures.

Due to the small amount of solvent that is required in the molding material mixture according to the invention for adjusting the viscosity, a reduction of smoke and smoke during casting is already achieved. Furthermore, by the extensive or complete abandonment of aromatic solvents, the development of smoke during casting can be further reduced. Aromatic solvents are to be understood as meaning aromatic hydrocarbons, such as toluene, xylene and, in particular, high-boiling aromatic hydrocarbons having a boiling point of more than 150 ^° C. The inventors assume that the carboxylic acid diesters of branched alkanediols used in the binder system of the molding material mixture according to the invention are not useful because of their oxygen content -aromatic character compared to aromatic solvents tend significantly less smoke and smoke.

As a further advantage of the molding material mixture according to the invention, it has been found that the moldings produced and cured therefrom have a high mechanical stability. This means in a technical application that the proportion of the binder in the molding material mixture can be lowered, and yet the desired strength of the molding remains. By reducing the requirement for adequate mecha- niche stability of the mold required binder amount, the smoke and smoke during casting can be further reduced.

The invention therefore provides a molding material mixture for the production of moldings for the foundry industry, comprising at least

a refractory molding base; and a polyurethane-based binder system comprising a polyisocyanate component and a polyol component.

According to the invention, the polyurethane-based binder system comprises at least 3% by weight of a carboxylic acid diester of a branched alkanediol and less than 10% by weight of aromatic solvent, based in each case on the binder system.

In itself, a large part of the constituents of the molding material mixture according to the invention is already used in molding material mixtures for the production of casting molds, so that the knowledge of the skilled person can be used here.

Thus, all refractory materials which are customary for the production of moldings for the foundry industry can be used as the refractory molding base material per se. Examples of suitable refractory mold bases are quartz sand, zircon sand, olivine sand, aluminum silicate sand and chrome ore sand or mixtures thereof. Preferably, quartz sand is used. The refractory base molding material should have a sufficient particle size so that the molded article produced from the molding material mixture has a sufficiently high porosity to allow escape of volatile compounds during the casting process. Preferably, at least 70 wt .-%, more preferably at least 80% by weight of the refractory base molding material has a particle size ≦ 290 μm. The average particle size of the refractory base molding material should preferably be between 100 and 350 μm. The particle size can be determined, for example, by sieve analysis.

The molding material mixture according to the invention further contains a binder system based on polyurethane, for whose binder components per se can also be used on known binder systems.

The binder system initially contains a polyol component and a polyisocyanate component, in which case known components can likewise be used.

The polyisocyanate component of the binder system may comprise an aliphatic, cycloaliphatic or aromatic isocyanate. The polyisocyanate preferably contains at least 2 isocyanate groups, preferably 2 to 5 isocyanate groups per molecule. Depending on the desired properties, it is also possible to use mixtures of isocyanates. The isocyanates used can consist of mixtures of monomers, oligomers and polymers and are therefore referred to below as polyisocyanates.

The polyisocyanate component per se can be any polyisocyanate which is customary in polyurethane binders for molding mixtures for the foundry industry. Suitable polyisocyanates include aliphatic polyisocyanates, eg, hexamethylene diisocyanate, alicyclic polyisocyanates, such as 4,4'-dicyclohexylmethane diisocyanate, and dimethyl derivatives thereof. Examples of suitable aromatic polyisocyanates are toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, 1,5-naphthalene diisocyanate, xylylene diisocyanate and methyl derivatives thereof, Diphenylmethane-4,4'-diisocyanate and polymethylene-polyphenyl-polyisocyanate.

Although in principle all conventional polyisocyanates react with the phenolic resin to form a crosslinked polymer structure, preference is given to the use of aromatic polyisocyanates, more preferably polymethylene polyphenyl polyisocyanate, such as e.g. commercially available mixtures of diphenylmethane-4,4'-diisocyanate, its isomers and higher homologs.

The polyisocyanates can be used both in substance and dissolved in an inert or reactive solvent. A reactive solvent is understood to mean a solvent which has a reactive group, so that it is incorporated into the framework of the binder when the binder is set. The polyisocyanates are preferably used in dilute form, in order to be able to coat the grains of the refractory molding base material better with a thin film of the binder because of the lower viscosity of the solution.

The polyisocyanates or their solutions in organic solvents are used in sufficient concentration to effect the curing of the polyol component, usually in a range of from 10 to 500 weight percent, based on the weight of the polyol component. From 20 to 300% by weight, based on the same base, are preferably used. Liquid polyisocyanates can be used in undiluted form while solid or viscous polyisocyanates are dissolved in organic solvents. Up to 80 wt .-%, preferably up to 60 wt .-%, particularly preferably up to 40 wt .-% of the isocyanate component may consist of solvents.

Preferably, the polyisocyanate is used in an amount such that the number of isocyanate groups is 80 to 120%, based on the number of free hydroxyl groups of the polyol component. As the polyol component, all polyols used in polyurethane binders can be used per se. The polyol component contains at least 2 hydroxyl groups, which can react with the isocyanate groups of the polyisocyanate component in order to be able to achieve cross-linking of the binder during curing, and thereby better strength of the cured molding.

The polyols used are preferably phenolic resins which are obtained by condensation of phenols with aldehydes, preferably formaldehyde, in the liquid phase at temperatures up to about 180 ^° C. in the presence of catalytic amounts of metal. The processes for the preparation of such phenolic resins are known per se.

The polyol component is preferably used liquid or dissolved in organic solvents in order to allow a homogeneous distribution of the binder on the refractory base molding material. The polyol component is preferably used in anhydrous form because the reaction of the isocyanate component with water is an undesirable side reaction. Non-aqueous or anhydrous in this context means a water content of the polyol component of preferably less than 5 wt .-%, preferably less than 2 wt .-%, mean.

By "phenolic resin" is meant the reaction product of phenol, phenol derivatives, bisphenols, and higher phenol condensation products with an aldehyde. The composition of the phenolic resin depends on the specific starting materials selected, the ratio of the starting materials and the reaction conditions. For example, play the type of catalyst, the time and the reaction temperature, as well as the presence of solvents and other substances.

The phenolic resin is typically present as a mixture of different compounds and can vary in very different proportions. sen addition products, condensation products and unreacted starting compounds, such as phenols, bisphenol and / or aldehyde.

By "addition product" is meant reaction products in which an organic component substitutes at least one hydrogen on a previously unsubstituted phenol or condensation product. By "condensation product" is meant reaction products having two or more phenolic rings.

As the condensation reaction of phenols with aldehydes resulting phenolic resins which are classified depending on the proportions of the reactants, the reaction conditions and the catalysts used Kata ^¬ into two product classes, novolaks and resols:

Novolacs are soluble, meltable, non-self-curing, and shelf-stable oligomers having a molecular weight in the range of about 500 to 5,000 g / mole. They are obtained in the condensation of aldehydes and phenols in a molar ratio of 1:> 1 in the presence of acidic catalysts. Novolacs are phenol resins free of methylol groups in which the phenyl nuclei are linked via methylene bridges. They may be cured at elevated temperature with crosslinking after addition of curing agents, such as formaldehyde donating agents, preferably hexamethylenetetramine.

Resoles are mixtures of hydroxymethylphenols which are linked via methylene and methylene ether bridges and can be obtained by reaction of aldehydes and phenols in a molar ratio of 1: <1, if appropriate in the presence of a catalyst, for example a basic catalyst. They have a molecular weight M _w of <10,000 g / mol.

The phenolic resins which are particularly suitable as polyol components are known as "oo ¹ " or "high-ortho" novolaks or Benzyl ether resins known. These are obtainable by condensation of phenols with aldehydes in weakly acidic medium using suitable catalysts.

Suitable catalysts for the preparation of benzylic ether resins are salts of divalent ions of metals such as Mn, Zn, Cd, Mg, Co, Ni, Fe, Pb, Ca and Ba. Preferably, zinc acetate is used. The amount used is not critical. Typical amounts of metal catalyst are 0.02 to 0.3 wt .-%, preferably 0.02 to 0.15 wt .-%, based on the total amount of phenol and aldehyde.

For the preparation of phenolic resins, all conventionally used phenols are suitable. In addition to unsubstituted phenols, substituted phenols or mixtures thereof can be used. The phenolic compounds are unsubstituted either in both ortho positions or in an ortho and in the para position to allow polymerization. The remaining ring carbon atoms may be substituted. The choice of the substituent is not particularly limited so long as the substituent does not adversely affect the polymerization of the phenol or the aldehyde. Examples of substituted phenols are alkyl-substituted phenols, alkoxy-substituted phenols and aryloxy-substituted phenols.

The abovementioned substituents have, for example, 1 to 26, preferably 1 to 15, carbon atoms. Examples of suitable phenols are o-cresol, m-cresol, p-cresol, 3, 5-xylene, 3,4-xylene, 3,4,5-trimethylphenol, 3-ethylphenol, 3, 5-diethylphenol, p-butylphenol, 3, 5-dibutylphenol, p-amylphenol, cyclohexylphenol, p-octylphenol, p-nonylphenol, 3, 5-dicyclohexylphenol, p-crotylphenol, p-phenylphenol, 3, 5-dimethoxyphenol and p-phenoxyphenol. Particularly preferred is phenol itself. Also higher condensed phenols, such as bisphenol A, are suitable. In addition, polyhydric phenols having more than one phenolic hydroxyl group are also suitable. Preferred polyhydric phenols have 2 to 4 phenolic hydroxyl groups. Specific examples of suitable polyhydric phenols are pyrocatechol, resorcinol, hydroquinone, pyrogallol, fluoroglycine, 2,5-dimethylresorcinol, 4,5-dimethylresorcinol, 5-methylresorcinol or 5-ethylresorcinol.

Mixtures of various mono- and polyhydric and / or substituted and / or condensed phenolic components can also be used for the preparation of the polyol component.

In one embodiment, phenols of general formula I:

Formula I

for the preparation of the phenolic resin component, wherein A, B and C independently of one another from a hydrogen atom, a branched or unbranched alkyl radical, which may have, for example 1 to 26, preferably 1 to 15 carbon atoms, a branched or unbranched alkoxy radical, for example 1 to 26, preferably having from 1 to 15 carbon atoms, a branched or unbranched alkenoxy radical which may, for example, have 1 to 26, preferably 1 to 15, carbon atoms, an aryl or alkylaryl radical, such as, for example, bisphenyls. Suitable aldehydes for the production of the phenolic resin component are aldehydes of the formula:

R-CHO,

where R is a hydrogen atom or a carbon atom radical having preferably 1 to 8, particularly preferably 1 to 3, carbon atoms. Specific examples are formaldehyde, acetaldehyde, propionaldehyde, furfuraldehyde and benzaldehyde. Particular preference is given to using formaldehyde, either in its aqueous form, as para-formaldehyde or trioxane.

In order to obtain the phenolic resins, an at least equivalent number of moles of aldehyde, based on the number of moles of the phenol component, should be used. The molar ratio of aldehyde to phenol is preferably 1: 1.0 to 2.5: 1, more preferably 1.1: 1 to 2.2: 1, particularly preferably 1.2: 1 to 2.0: 1.

The production of the phenolic resin component takes place by methods known to the person skilled in the art. Here, the phenol and the aldehyde is reacted under substantially anhydrous conditions in the presence of a divalent metal ion at temperatures of preferably less than 130 ⁰ C. The resulting water is distilled off. For this purpose, a suitable entraining agent may be added to the reaction mixture, for example toluene or xylene, or the distillation is carried out at reduced pressure.

For the binder of the molding material mixture according to the invention, the phenol component is reacted with an aldehyde, preferably benzyl ether resins. The reaction with a primary or secondary aliphatic alcohol to give an alkoxy-modified phenolic resin in the single-stage or two-stage process (EP-B-0 177 871 and EP 1 137 500) is likewise possible. In the one-step process, the phenol, aldehyde and alcohol are waiting for a suitable catalyst to react. In the two-stage process, an unmodified resin is first prepared, which is subsequently reacted with an alcohol. When using alkoxy-modified phenolic resins, there is no limitation on the molar ratio per se, but the alcohol component is preferably used in a molar ratio of alcohol: phenol of less than 0.25 so that less than 25% of the hydroxymethyl groups are etherified. Suitable alcohols are primary and secondary aliphatic alcohols having one hydroxy group and 1 to 10 carbon atoms. Suitable primary and secondary alcohols are, for example, methanol, ethanol, propanol, n-butanol and n-hexanol. Particularly preferred are methanol and n-butanol.

The phenolic resin is preferably selected so that crosslinking with the polyisocyanate component is possible. For the construction of a network, phenolic resins comprising molecules having at least two hydroxyl groups in the molecule are particularly suitable. The phenolic resin component or the isocyanate component of the binder system is preferably used as a solution in an organic solvent or a combination of organic solvents. Solvents may be required to keep the components of the binder in a sufficiently low viscosity state. This is u.a. required to obtain a uniform crosslinking of the refractory molding material and its flowability.

According to the invention, the polyurethane-based binder system comprises at least 3% by weight of a carboxylic acid diester of a branched alkanediol and less than 10% by weight of aromatic solvent, based in each case on the binder system. It is possible that only the polyol component or only the polyisocyanate component a proportion of the carboxylic acid diester of a branched alkanediol um- summarizes. However, it is also possible that both binder components comprise a portion of the carboxylic acid diester of a branched alkanediol. The polyurethane-based binder system preferably comprises a carboxylic acid diester content of a branched alkanediol of more than 5% by weight. According to another embodiment, the polyurethane-based binder system has a carboxylic acid diester content of more than 8% by weight of a branched alkanediol. According to another embodiment, the polyurethane-based binder system comprises less than 30% by weight of a carboxylic acid diester of a branched alkanediol, and in another embodiment less than 20% by weight of a carboxylic acid diester of a branched alkanediol. At least one of the polyol component and the polyisocyanate component preferably contains at least 3% by weight, preferably at least 5% by weight, particularly preferably at least 8% by weight, of the carboxylic acid diester of a branched alkanediol.

The solvent of the respective component can be completely formed by the carboxylic acid diester of a branched alkanediol. The proportion of aromatic solvents is preferably chosen as low as possible. The proportion of the aromatic solvent is based on the binder system less than 10 wt .-%, preferably less than 5 wt .-%, more preferably less than 3 wt .-%. Most preferably, the binding agent system does not comprise aromatic solvents. Based on the polyol component or the polyisocyanate component, at least one of these components contains less than 10 wt .-%, preferably less than 5 wt .-%, more preferably less than 3 wt .-% of aromatic solvents.

In addition to the carboxylic acid diester of a branched alkanediol, other solvents can be used. As a further solvent all solvents can be used - -

which are conventionally used in binder systems for foundry technology. Oxygen-rich, polar, organic solvents are, for example, suitable as further solvents. Particularly suitable are dicarboxylic acid esters, glycol ether esters, glycol diesters, glycol diethers, cyclic ketones, cyclic esters or cyclic carbonates. Dicarboxylic acid esters, cyclic ketones and cyclic carbonates are preferably used. Dicarboxylic acid esters have the formula R ³ OOC-R ^b -COOR ^a , wherein the radicals R ^{a are} each independently an alkyl group having 1 to 12, preferably 1 to 6 carbon atoms and R ^{b is} an alkylene group, ie a divalent alkyl group, with 1 to 12, preferably 1 to 6 carbon atoms. R ^b may also include one or more carbon-carbon double bonds. Examples are dimethyl esters of carboxylic acids having 4 to 10 carbon atoms, which are obtainable, for example, under the name "dibasic ester" (DBE) from Invista International S.A.rl, Geneva, CH. Glycol ether esters are compounds of the formula R ^c -O-R ^d -OOCR ^e , where R ^{c is} an alkyl group having 1 to 4 carbon atoms, R ^{d is} an ethylene group, a propylene group or an oligomeric ethylene oxide or propylene oxide and R ^{e is} an alkyl group with 1 to 3 carbon atoms. Preference is given to glycol ether acetates, for example butylglycol acetate. Glycol diesters accordingly have the general formula R ^e COO-R ^d OOCR ^e , where R ^d and R ^{e are} as defined above and the radicals R ^{e are} each independently selected. Preferred are glycol diacetates such as propylene glycol diacetate. Glycol diethers can be characterized by the formula R ^c -OR ^d -OR ^c , where R ^c and R ^{d are} as defined above and the radicals R ^{c are} each independently selected. A suitable glycol diether is, for example, dipropylene glycol dimethyl ether. Cyclic ketones, cyclic esters and cyclic carbonates having 4 to 5 carbon atoms are also suitable. A suitable cyclic carbonate is, for example, propylene carbonate. The alkyl and alkylene groups may each be branched or unbranched.

The proportion of the solvent in the binder system is preferably not chosen too high, since the solvent evaporates during the production and application of the molded article produced from the molding compound and thus, for example, can lead to unpleasant odors or leads to smoke during the casting. Preferably, the proportion of the solvent in the binder system is less than 50 wt .-%, more preferably less than 40 wt .-%, more preferably less than 35 wt .-%, selected.

The dynamic viscosity of the polyol component or of the polyisocyanate component, which can be determined, for example, by the Brookfield rotary spindle method, is preferably less than 1000 mPas, more preferably less than 800 mPas and particularly preferably less than 600 mPas.

For the carboxylic acid diester of a branched alkanediol, any carboxylic acid can be used per se. The carboxylic acid may have a branched or unbranched alkyl radical. Further, the carboxylic acid may also include carbon-carbon double bonds. However, saturated carboxylic acids are preferred. The chain length of the carboxylic acid can be selected within wide limits. Preference is given to using carboxylic acids which contain 2 to 20 carbon atoms, more preferably 4 to 18 carbon atoms. Preferably, a branched carboxylic acid is used for the carboxylic acid diester of a branched alkanediol. Preference is given to using monocarboxylic acids. But it is also possible to use half esters of dicarboxylic acids.

The hydroxy groups of the alkanediol can be arranged terminal as a primary hydroxyl group or also within the carbon chain as a secondary or tertiary hydroxyl group. Under one Secondary hydroxy group is understood to mean a hydroxy group which is bonded to a carbon atom which is connected to a hydrogen atom and two carbon atoms. Accordingly, a tertiary hydroxy group is understood to mean a hydroxy group which is bonded to a carbon atom which is bonded to three further carbon atoms, and, under a primary hydroxy group, a hydroxy group which is bonded to a carbon atom which is bonded to one carbon atom and two hydrogen atoms.

Preferably, the alkanediol comprises a primary and a secondary hydroxy group.

According to a preferred embodiment, the carboxylic acid diester of a branched alkanediol has a structure of the formula I.

Formula I

on, wherein, independently of each occurrence, means:

R ¹ , R ⁷ : H, CH ₃ , C ₂ H ₅ , C ₃ H ₇ , CH ₂ OC (O) R ³ , OC (O) R ³ ;

R, R, R, R; H, CH ₃ , C ₂ H ₅ , C ₃ H ₇ ;

R ³ : a saturated, unsaturated or aromatic hydrocarbon radical having 1 to 19 hydrocarbon atoms, in which also one or more hydrogen atoms may be replaced by other substituents;

a, b, c: an integer between 0 and 4;

x 0, 1 or 2; in which :

at least one of R ¹ , R ² and R ^{4 is} not hydrogen;

when R ¹ and R ^{7 are} CH ₂ OC (O) R ³ , OC (O) R ³ , x = 0; and

the sum a + b + c is at least 2.

The carboxylic acid diester of a branched alkanediol preferably has a structure of the formula II:

Formula II

in which R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , a, b, c have the meaning given for formula I and additionally denotes:

R ¹ : H, CH ₃ , C ₂ H ₅ , C ₃ H ₇ , where R ^{1 is} not H when

R ² = R ⁴ = R ⁵ = R ⁶ = H;

R: a saturated, unsaturated or aromatic hydrocarbon radical having 1 to 19 carbon atoms, in which also one or more hydrogen atoms may be replaced by other substituents.

Preferably, either R ¹ or R ^{2 is} a methyl group or an ethyl group and the other is a hydrogen atom.

The radicals R ⁴ can be chosen independently of each other and preferably comprise 1 to 3 carbon atoms. Beiddee RReessttee RR ⁴⁴ are preferably the same and are particularly preferably a methyl group.

In another embodiment, R ⁵ and R ^{6 represent} a hydrogen atom.

R ³ and R ⁸ may be different groups. Preferably, R ³ and R ^{8 are the} same. R ³ and R ⁸ can be saturated, unsaturated or aromatic hydrocarbon radicals which comprise 1 to 19, preferably 2 to 10, particularly preferably 3 to 6, carbon atoms. One or more hydrogen atoms of the hydrocarbon group may be replaced by other substituents. Other substituents are generally understood to mean atoms or groups of atoms which are not hydrogen. Suitable other substituents are halogen atoms, in particular chlorine, a glycidyl radical, and an epoxy group. Preferably, at most 3 hydrogen atoms of the hydrocarbon radical, preferably at most 2 hydrogen atoms of the hydrocarbon radical are replaced by other substituents. Particularly preferably, no hydrogen atom of the hydrocarbon radical is replaced by another substituent.

The hydrocarbon radicals R ³ and R ⁸ may also be an unsaturated hydrocarbon residue, said 1 to 4, preferably 1 to 3, particularly preferably holds exactly one double bond environmentally. The groups R ³ and R ⁸ particularly preferably represent a saturated, aliphatic hydrocarbon radical having 1 to 19, preferably 2 to 10, particularly preferably 2 to 5, hydrocarbon atoms. The saturated hydrocarbon radical may be straight-chain or branched, with branched hydrocarbon radicals being preferred. R ³ and R ⁸ are preferably an iso-butyl group.

The indices a, b and c can, independently of one another, assume the values 0, 1, 2, 3 and 4, the sum a + b + c being at least 2. More preferably, the value for the indices a and c is at least 1. The sum of a + b + c is preferably less than 10, preferably less than 8.

The alkanediol may have a large structural variation. Exemplary alkanediols are shown below:

CH. CH, CH.

H. 3C-CI-CH 2 -ClH-CH 3, HO-CH; 2CIH-CH-CH 2; CiH-C.3H ₇ 7 HO-CH; 2CIH-CI -C ₉ 2H5.

OH OH OH CH OH CH-

HO-CH-CH-CH-CH-CH-CH-OH HO-CH-CH-CH-CH-CH-CH-CH-CH-C ₄ H ₉

CH ₃ OH CH ₃

CH,

HO-CHr

CH ₃

Particularly preferred as alkanediol is 2, 2, 4-trimethyl-l, 3-pentanediol and further preferably used as carboxylic acid isobutyric acid, acetic acid, and benzoic acid. Exemplary carboxylic acid diesters of a branched alkanediol are 2, 2, 4-trimethyl-l, 3-pentanediol diacetate and 2,2,4-trimethyl-1, 3-pentanediol dibenzoate.

Particular preference is given to using 2,2,5,4-trimethyl-1,3-pentanediol diisobutyrate as the carboxylic acid diester of a branched alkanediol in the novel molding material mixture.

According to a preferred embodiment, the polyurethane-based binder system contains at least a portion of a fatty acid ester as solvent. Suitable fatty acids preferably contain from 8 to 22 carbon atoms which have been esterified with an aliphatic alcohol. The fatty acids may be present as a homogeneous compound or as a mixture of different fatty acids. Preferably, fatty acids of natural origin are used, e.g. Tall oil, rapeseed oil, sunflower oil, germ oil and coconut oil. Instead of natural oils and fats, individual fatty acids, e.g. Palmitic acid or oleic acid, are used. As aliphatic alcohols are preferably primary alcohols having 1 to 12 carbon atoms, particularly preferably 1 to 10 Kohlenstoffatoraen, more preferably 4 to 10 carbon atoms used, with methanol, isopropanol and n-butanol being particularly preferred. Such fatty acid esters are described for example in EP-A-I 137 500. The "symmetrical esters" described in EP-B-0 295 262, in which both the fatty acid radical and the alcohol radical have a number of carbon atoms in the same range, preferably from 6 to 13 carbon atoms, have also proved useful.

The proportion of the at least one fatty acid ester in the polyurethane-based binder system is preferably less than 50% by weight, more preferably less than 40% by weight, particularly preferably less than 35% by weight. According to one embodiment, the proportion of the at least one fatty acid ester on the binder system more than 3 wt .-%, preferably more than 5 wt .-%, particularly preferably more than 8 wt .-%.

The proportion of the binder system in the molding material mixture, based on the weight of the refractory molding material, preferably between 0.5 and 10 wt .-%, preferably selected between 0.6 and 7 wt .-%.

Besides the components already mentioned, the binder systems may contain conventional additives, e.g. Silanes (EP-A-I 137 500), or internal release agents, e.g. Fatty alcohols (EP-B-0 182 809), drying oils (US-A-4, 268, 425) or complexing agents (WO 95/03903), or mixtures thereof.

Suitable silanes are, for example, aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes and ureidosilanes, such as γ-hydroxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, 3-ureido-propyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-glycidyloxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) trimethoxysilane and N-β- (aminoethyl) -Y-aminopropyltrimethoxysilane.

According to one embodiment, the molding material mixture according to the invention may comprise a binder system which comprises a proportion of cassava nut shell oil, at least one component of the cassava nut shell oil and / or at least one derivative of the cashew nut shell oil. By adding cashew nut shell oil or derivatives of cashew nut shell oil to the binder, moldings for the foundry industry can be obtained which have high thermal stability. As a further advantage, the content of monomers which are still contained in the polyol component, in particular phenol and formaldehyde, can be significantly reduced. In the processing of the molding material mixture and in particular during the casting process, therefore, relatively small amounts of monomers are liberated in comparison to molding mixtures of the prior art. For the purposes of the invention, cashew nut shell oil is understood as meaning both the oil obtained from seed casks of the cashew tree, which comprises about 90% anacardic acid and about 10% cardol, and the technical cashew nut shell oil which is obtained from the natural product by heat treatment acidic environment, and contains as main ingredients Cardanol and Cardol.

n = 0,2, 4, 6 n = 0,2,4,6

Cardanol Cardol

Suitable components of the binder are the cashew nut shell oil itself, in particular the technical cashew nut shell oil, as well as the components obtained therefrom, in particular Cardol and Cardanol, and mixtures thereof and their oligomers, such as those remaining in the bottoms during the distillation of cashew nut shell oil. These compounds can also be used in technical quality. The mixture of essentially cardanol and cardol, which is also known as cashew nutshell liquid (CNSL), formed during the distillation of cashew nut shell oil is preferably used. The double bonds of cardanol and cardol contained in the side chain may be partially or fully reacted with hydroxyl groups, epoxide groups, halogens, acid anhydrides, diclyclopentadiene or hydrogen. These groups can in turn be reacted with nucleophiles. In polyvalent cashew nut shell oil derivatives, the phenolic OH groups can also be completely or partially derivatized, for example by addition of ethylene oxide or propylene oxide units. These derivatives of cashew nut shell oil can also be used according to the invention in the molding material mixture.

The cashew nut shell oil or the compounds derived therefrom may be present as a separate component in the binder. These components act as a reactive solvent, which reacts with the curing of the binder in the resulting crosslinked polymer. In this embodiment of the molding material mixture according to the invention in particular a high stability of the molded body is achieved at elevated temperature. To show test bars that are made of such a preferred molding material mixture, under thermal stress is less than deflection test bars, which have been prepared with an analog binder, but the Bindemit ^¬ tel no cashew nutshell oil had been added.

Preferably, the at least one component of the cashew nutshell oil and / or at least one derivative of the cashew nut shell oil ^¬ at least a portion of the polyol component is formed. In the ser ^¬ embodiment, the at least one component of the cashew nutshell oil and / or at least one derivative of the cashew nutshell oil during the synthesis of the polyol component is added so that they are incorporated in the polyol component during the synthesis. The synthesis of the polyol is conducted in known manner, wherein the at least one Kom ^¬ component of cashew nutshell oil and / or at least one derivative of the cashew nutshell oil may be added at the beginning of the synthesis or at a later stage of the synthesis the reaction mixture.

More preferably, the polyol component is formed by condensation of a phenolic component and an oxo component, wherein the cashew nut shell oil containing at least one component of the cashew nut shell oil and / or the at least one derivative of the cashew nut shell oil Cashew nut shell oil forms at least a portion of the phenolic component.

The synthesis of the polyol component is carried out in the manner described above for the preparation of the phenolic resin, but in addition to the phenol component, the cashew nut shell or the at least one component of cashew nut shell oil or the at least one derivative of cashew nut shell oil is added as a further component. As phenol component, the phenols described above, as the oxo component, the above-described aldehydes can be used.

The proportion of the cashew nut shell oil, the at least one component of the cashew nut shell oil and / or the at least one derivative of the cashew nut shell oil in the phenolic component is preferably from 0.5 to 20% by weight, more preferably from 0.75 to 15% by weight, particularly preferably 1 to 10 wt .-%.

The cashew nut shell oil, its components or derivatives may be added to the reaction mixture at any time during the synthesis. Preferably, the addition takes place already at the beginning of the synthesis.

Cashew nut shell oil, cashew nut shell components and cashew nut oil derivatives may also be added to the isocyanate component, where they may also react with a portion of the isocyanate groups.

For the preparation of the molding material mixture, the components of the binder system can first be combined and then added to the refractory molding material. However, it is also possible to add the components of the binder simultaneously or sequentially to the refractory base molding material. To obtain a uniform mixture of the components of the molding material mixture, conventional methods can be used. Form- In addition, the composition may optionally contain other conventional ingredients such as iron oxide, milled flax fibers, wood flour granules, pitch, and refractory metals.

As a further subject matter, the invention relates to a process for producing a shaped body, comprising the steps:

Providing the molding compound mixture described above; Molding the molding material mixture into a shaped body;

Curing the molding by adding a curing catalyst.

For the production of the molded article, the binder is first mixed with the refractory molding base material to form a molding material mixture as described above. If the molding is to be produced by the PU-No-Bake process, a suitable catalyst can also already be added to the molding material mixture. For this purpose, liquid amines are preferably added to the molding material mixture. These amines preferably have a pK _b value of 4 to 11. Examples of suitable catalysts are 4-alkylpyridines, wherein the alkyl group comprises 1 to 4 carbon atoms, isoquinoline, arylpyridines, such as phenylpyridine, pyridine, acrylin, 2-methoxypyridine, pyridazine, 3-chloropyridine, quinoline, n-methylimidazole, 4, 4 ' -Dipyridine, phenylpropylpyridine, 1-methylbenzimidazole, 1,4-thiazine, N, N-dimethylbenzylamine, triethylamine, tribenzylamine, N, N-dimethyl-1,3-propanediamine, N, N-dimethylethanolamine, and triethanolamine. The catalyst may optionally be diluted with an inert solvent, for example 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, or a fatty acid ester. The amount of catalyst added is selected in the range of 0.1 to 15% by weight, based on the weight of the polyol component. The molding material mixture is then introduced by conventional means into a mold and compacted there. The molding material mixture is then cured to a shaped body. When curing, the shaped body should preferably retain its outer shape.

According to a further preferred embodiment, the curing takes place according to the PU cold box method. For this purpose, a gaseous catalyst is passed through the molded molding material mixture. As catalyst, the usual catalysts in the field of cold-box process can be used. Particular preference is given to using amines as catalysts, in particular preferably dimethylethylamine, dimethyl-n-propylamine, dimethylisopropylamine, dimethyl-n-butylamine, triethylamine and trimethylamine in their gaseous form or as aerosol.

The molded article produced by the process may per se have any shape customary in the field of foundry. In a preferred embodiment, the shaped body is in the form of foundry molds or cores.

Furthermore, the invention relates to a shaped body, as can be obtained by the method described above. This is characterized by a high mechanical stability and by a low quality development during metal casting.

Furthermore, the invention relates to the use of this molding for metal casting, in particular iron and cast aluminum.

The invention will be explained in more detail below with reference to preferred embodiments.

Example 1: Synthesis of the phenolic resin

In a reaction vessel equipped with reflux condenser, thermometer and stirrer, 1,770.6 g of phenol, 984.3 g of paraform aldehyde (91%), 1.5 g of zinc acetate dihydrate and 279.6 g of n-butanol submitted. With stirring, the temperature of the mixture was raised to 105 to 150 ° C and the mixture kept at this temperature until a refractive index (25 ° C) of about 1.5590 was reached. Thereafter, the condenser was replaced by a distillation bridge and the temperature increased within one hour to 124 to 126 ⁰ C. At this temperature was distilled until reaching a refractive index (25 ⁰ C) of about 1.5940. The distillation was then continued under reduced pressure until the mixture had a refractive index of about 1.6000 ⁽⁰ C 25). The yield is 78%.

Example 2: Preparation of the binders

Polyol component (binder component 1):

With the phenolic resin obtained in Example 1, the polyol components shown in Table 1 were prepared.

TABLE 1 Composition of the polyol components (binder component 1) (% by weight)

Isocyanate component (binder component 2):

From polymeric technical 4,4'-MDI, the polyisocyanate components shown in Table 2 were prepared.

Table 2: Composition of the polyisocyanate component (binder component 2) (% by weight)

Example 3; Hers-division of test specimens

To 100 parts by weight of quartz sand H32 (Quarzwerke Frechen), in each case 0.8 part by weight of the phenolic resin solutions given in Table 1 and the polyisocyanate component given in Table 2 are added and mixed intensively in a laboratory mixer (Vogel and Schemmann AG, Hahn, DE). After the mixture had been mixed for 2 minutes, the molding mixtures were transferred to the storage bunker of a core shooter (Röperwerke, Gießereimaschinen GmbH, Viersen, DE) and introduced into the mold by means of compressed air (4 bar). The moldings were cured by gassing with 1 ml of triethylamine (2 sec, 2 bar pressure, then 10 sec. Rinsing with air).

Cuboid test bars measuring 220 mm x 22.36 mm x 22.36 mm, known as Georg Fischer test bars, were produced as test specimens. To determine the flexural strengths, the test bars were placed in a Georg Fischer strength tester equipped with a three-point bending device (DISA-Industrie AG, Schaffhausen, CH) and the force was measured, which resulted in the breakage of the test bars.

The flexural strengths were measured according to the following scheme:

immediately after their production

after 24 h storage at room temperature after 24 h storage at 98% relative humidity.

Furthermore, the resistance of the test pieces to water-based finishes was tested. For this purpose, the test bars were 10 min. immersed after its preparation for 3 seconds in a water sizing MIRATEC ^® DC 3 (ASK-Chemicals GmbH, Hilden, DE), and then stored for 30 min at room temperature. A portion of the size-coated test bar was subjected to the strength test after storage for 30 minutes at room temperature. Another part of the test bars was after 30 minutes of storage at room temperature, dried at 150 ⁰ C for 30 min. After cooling to room temperature, these test bars were also tested for their strength.

The results of the strength test are summarized in Table 3. Table 3: Strength tests

Test bars, which have been prepared using a binder system containing 2, 2, 4-trimethyl-1,3-pentanediol diisobutyrate, show higher strength. Higher strengths are obtained when only 2, 2, 4-trimethyl-l, 3-pentanediol diisobutyrate is used as the solvent. However, high strengths are also obtained when the solvent contains fatty acid esters which have an average polarity, or else strongly polar esters and also dibasic esters or tetraethylorthosilicate.

Example 4 Influence of the proportion of 2, 2, 4-Tr-i ™ <= 1-ethyl-l, 3-pentanediol diisobutyrate in the solvent

The influence of other solvents was tested on the example of isopropyl laurate, which was used in various proportions in addition to 2, 2, 4-trimethyl-l, 3-pentanediol diisobutyrate. The composition of the polyol component used for the preparation of the test bars is summarized in Table 4. The Composition of the polyisocyanate component is summarized in Table 5.

Table 4: Composition of the polyol component (% by weight)

Table 5: Composition of the polyisocyanate component (% by weight)

Strength test:

Test bars were produced and their strength tested analogously to Example 3. The results are summarized in Table 6. - 9 -

Table 6: Strength tests using mixed solvents

Results:

Even a small proportion of 2, 2, 4-trimethyl-l, 3-pentanediol diisobutyrate in addition to the fatty acid ester causes an increase in the strength of the test bars.

Example 5: Use of 2, 2,4-trimethyl-1,3-pentanediol diisobutyrate in view with: different polar solvents

Georg Fischer test bars were prepared analogously to Example 1. The composition of the polyol component is shown in Table

7 and the composition of the polyisocyanate component in Table

8 indicated. Table 7: Composition of the polyol component (% by weight)

Table 8: Composition of polyisocyanate component (% by weight)

Strength test:

The strength of the test bars was determined analogously to Example 3. The results of the strength test are summarized in Table 9. Table 9: Strength test

Result :

Be used in the binder system in addition to 2, 2, 4-trimethyl-l, 3-pentanediol diisobutyrate fatty acid esters and highly polar solvents, an increase in the strength of the test bars is also observed.

Example 6: Investigation of Quaimontwicklung

Test bars were prepared analogously to Example 3 using the binders indicated in Table 10. The test bars were 1 min. long stored at 650 ⁰ C in the oven. After taking the test blank, the development of the smoke was determined against a dark background and rated subjectively with grades 10 (very strong) to 1 (barely perceptible). The result is summarized in Table 10. Table 10: Evaluation of smoke development

By using 2, 2, 4-trimethyl-l, 3-pentanediol diisobutyrate the smoke development can be reduced.

Claims

claims

1. molding material mixture for the production of moldings for the foundry industry, comprising at least

a refractory molding base; and a polyurethane-based binder system which comprises a polyisocyanate component and a polyol component, characterized in that the polyurethane-based binder system contains at least 3% by weight of a carboxylic acid diester of a branched alkanediol and an amount of aromatic solvent, based in each case on the binder system, less than 10% by weight.

2. Molding material mixture according to claim 1, characterized in that the proportion of the carbonic acid diester of a branched alkanediol on the binder system is greater than 5 wt .-%.

3. Molding material mixture according to claim 1 or 2, characterized in that the carboxylic acid diester of a branched alkanediol has a structure of the formula

wherein, independently of each occurrence, each means: - AA -

R ¹ , R ⁷ H, CH ₃ , C ₂ H ₅ , C ₃ H ₇ , CH ₂ OC (O) R ³ , OC (O) R ³ ;

R ² , R ⁴ , R ⁵ , R ⁶ : H, CH ₃ , C ₂ H ₅ , C ₃ H ₇ ,;

R ³ : a saturated, unsaturated or aromatic hydrocarbon radical having 1 to 19 hydrocarbon atoms, wherein also one or more hydrogen atoms may be replaced by other substituents;

a, b, c: an integer between 0 and 4;

x 0, 1 or 2; in which:

at least one of R ¹ , R ² and R ^{4 is} not hydrogen;

when R ¹ and R ^{7 are} CH ₂ OC (O) R ³ , OC (O) R ³ , x = 0; and

the sum a + b + c is at least 2.

4. Molding material mixture according to one of the preceding claims, characterized in that the carboxylic acid diester of a branched alkanediol is 2, 2, 4-trimethyl-l, 3-pentanediol diisobutyrate.

5. Molding material mixture according to one of claims 1 to A _1, characterized in that the binder system based on polyurethane comprises at least one fatty acid ester.

6. molding material mixture according to claim A _1, characterized in that the proportion of at least one fatty acid ester on - -

Polyurethane based binder system less than 90 wt .-% is selected.

7. Molding material mixture according to claim 5 or 6, characterized in that the fatty acid ester is a methyl ester, a butyl ester and / or an isopropyl ester.

8. Molding material mixture according to one of the preceding claims, characterized in that the polyol component is formed by condensation of a phenolic component and an oxo component.

9. molding material mixture according to claim 8, characterized in that the oxo component is formed by an aldehyde.

10. Molding material mixture according to one of the preceding claims, characterized in that the polyol component is formed by a benzyl ether resin.

11. Molding material mixture according to one of the preceding claims, characterized in that the isocyanate component is an aliphatic, aromatic or heterocyclic Isocyana- nat with at least two isocyanate groups per molecule or its oligomers or polymers.

12. Molding material mixture according to one of the preceding claims, characterized in that the binder system in a proportion of 0.5 to 10 wt .-%, based on the weight of the refractory molding base material, is included.

13. A process for producing a molded article for the foundry industry, characterized by the steps of:

Providing a molding material mixture according to any one of claims 1 to 12; Molding the molding material mixture into a shaped body;

Curing the molding by adding a curing catalyst.

14. The method according to claim 13, characterized in that the hardening catalyst is added in gaseous form.

15. The method according to any one of claims 13 or 14, characterized in that the curing is carried out substantially at room temperature.

16. Moldings for the foundry industry, obtained by a method according to any one of claims 13 to 15.

17. Use of a shaped body according to claim 16 for the mettell casting.