EP2249982B1 - Use of branched alkane diol carboxylic acid diesters in polyurethane-based foundry binders - Google Patents

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

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 bodies, so-called feeders, which act as balancing 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, 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 material and the molding mixture is brought into a mold by ramming, blowing, shooting or another method, 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 molding. The polymerization must be correspondingly slow run so that not already in the storage tanks 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 adding 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 mixed 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.

In the US 3,409,579 there is described a binder composition comprising a mixture of a resin component, a curing component and a curing 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 curing agent, the binder comprises a tertiary amine. For the production of moldings, first the phenolic resin component and the polyisocyanate component are mixed with a refractory molding material. The molding material mixture is subsequently brought into a mold and formed there to form a shaped body. To cure the molding material mixture, which is usually carried out at room temperature, the gaseous curing agent is passed through this. 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.

In the US 3,676,392 there is described a resin composition comprising a phenol resin component dissolved in organic solvents, a curing agent component, and a curing catalyst. The hardener component used is a liquid polyisocyanate comprising 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 the curing catalyst, a base having a pK _b in the range of about 7 to about 11 and used in an amount of 0.01 to 10% by weight based on the resin is used.

In the EP 0 261 775 B1 there is described 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 which contains, as solvent for the resin, an aromatic solvent in a proportion of 19% by weight, ethyl 3-ethoxypropionate in an amount of 15% by weight, "Red Oil" in an amount of 1 wt .-%, and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (TXIB) in a proportion of 5 wt .-%.

In the EP 0 695 594 A2 a polyurethane-based foundry binder is described containing a biphenyl additive. In Example 1 and Comparative Examples 2 and 3, the binder 2 wt .-% of 2, 2, 4-trimethyl-1, 3-pentanediol diisobutyrate added as a plasticizer. The solvent used is 17% by weight of aromatic solvent and 10% by weight of biphenyl which has been substituted twice or three times.

In the EP 0 766 388 A1 a polyurethane-based foundry binder is described which contains 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-1, 3-pentanediol diisobutyrate as a plasticizer. The solvents used are aromatic hydrocarbons.

In the US 4,268,425 describes a binder system for the foundry industry, which is based on polyurethanes. The binder system is accompanied by a drying oil. Example 1 describes a binder system in which the phenolic resin component contains DBE (dibasic ester) and C ₆ -C ₁₀ -dialkyl adipate as solvent. As a further component, the phenolic resin component contains 2% by weight of 2,2,4-trimethyl-1,3-pentanediol diisobutyrate. The isocyanate component contains 8.8% by weight of aromatic solvent and 6.2% by weight of petroleum ether as solvent.

In the US 4,540,724 describes a binder system based on polyurethanes, which contains a phosphorus halide as an 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.

In the WO 98/19899 there is described a binder system based on polyurethanes in which the polyisocyanate component has been modified by reaction with an aliphatic alcohol having 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.

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

In the EP 1 137 500 B1 there is described a polyurethane-based binder system in which the phenolic resin component or the polyisocyanate component comprises a fatty acid ester esterified with an alcohol having 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 percent of the hydroxymethanol groups are etherified by a primary or secondary aliphatic monoalcohol of from 1 to 10 carbon atoms. Of the Solvent content of the phenolic resin component is at most 40% by weight.

The US 4,311,631 A and the US Pat. No. 6,509,392 B1 disclose polyurethane-containing molding material mixtures for the production of moldings for the foundry industry, which make it their mission to use very low solvent amounts. Branched Alkandioldiester but do not use this. The US 2004/176491 A1 discloses the use of diesters, but not in molding compounds formable into moldings for the foundry industry containing refractories, but in polyurethane compositions, including foams, for soil consolidation for building purposes which are applied by injection of the polyurethane compositions into the soil.

The use of fatty acid esters, which are esterified with longer-chain alcohols, the smoke and smoke during casting can be significantly reduced. 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 Sindemittelelsystems 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 increase the solubility of the components of the polyurethane-based binder system 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 process, since 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.degree. 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, due to their oxygen content and their non-aromatic character, have a significantly lower tendency to smoke and smoke compared to aromatic solvents.

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 for sufficient mechanical Stability of the mold required amount of binder, the smoke and smoke during casting can be further reduced.

• einen feuerfesten Formgrundstoff; und
• ein Bindemittelsystem auf Polyurethanbasis, welches eine Polyisocyanatkomponente sowie eine Polyolkomponente umfasst.

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 person skilled in the art 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, it is preferred to use aromatic polyisocyanates, more preferably polymethylene-polyphenyl polyisocyanate, 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 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 be in very different proportions 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.

• Novolake sind lösliche, schmelzbare, nicht selbsthärtende und lagerstabile Oligomere mit einem Molekülgewicht im Bereich von ungefähr 500 bis 5.000 g/Mol. Sie fallen bei der Kondensation von Aldehyden und Phenolen im Molverhältnis von 1 : >1 in Gegenwart saurer Katalysatoren an. Novolake sind methylolgruppenfreie, Phenolharze, in denen die Phenylkerne über Methylenbrücken verknüpft sind. Sie können nach Zusatz von Härtungsmitteln, wie Formaldehyd spendenden Mitteln, bevorzugt Hexamethylentetramin, bei erhöhter Temperatur unter Vernetzung gehärtet werden.

The condensation reactions of phenols with aldehydes result in phenolic resins, which are subdivided into two product classes, the novolacs and resoles, depending on the proportions of the reactants, the reaction conditions and the catalysts used:

• 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 from 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 phenol resins which are particularly suitable as polyol component are referred to as "o-o" 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.

zur Herstellung der Phenolharzkomponente verwendet, wobei A, B und C unabhängig voneinander aus einem Wasserstoffatom, einem verzweigten oder unverzweigten Alkylrest, der beispielsweise 1 bis 26, vorzugsweise 1 bis 15 Kohlenstoffatome aufweisen kann, einem verzweigten oder unverzweigten Alkoxyrest, der beispielsweise 1 bis 26, vorzugsweise 1 bis 15 Kohlenstoffatome aufweisen kann, einem verzweigten oder unverzweigten Alkenoxyrest, der beispielsweise 1 bis 26, vorzugsweise 1 bis 15 Kohlenstoffatome aufweisen kann, einem Aryl- oder Alkylarylrest, wie beispielsweise Bisphenyle, ausgewählt sind.In one embodiment, phenols of general 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,

wherein 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. It is particularly preferred to use 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. The phenol and the aldehyde are reacted under substantially anhydrous conditions in the presence of a divalent metal ion at temperatures of preferably less than 130 ° C. The resulting water is distilled off. For this purpose, the reaction mixture, a suitable entraining agent may be added, 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 an alkoxy-modified phenolic resin in the one-stage or two-stage process ( EP-B-0 177 871 and EP 1 137 500 ) is also possible. In the one-step process, the phenol, the aldehyde and the alcohol are in the presence a suitable catalyst reacted. 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 comprises a portion of the carbonic acid diester of a branched alkanediol. 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 binder system does not comprise any 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. Suitable further solvents are, for example, oxygen-rich, polar, organic 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 ^a 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 available, for example, under the name "dibasic ester" (DBE) from Invista International S.à.rl, Geneva, CH. Glycol ether esters are compounds of the formula R ^c -OR ^d -OOCR ^e wherein 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 having 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 of 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.

auf, wobei, jeweils bei jedem Auftreten unabhängig voneinander bedeutet:

R¹, R⁷:

H, CH₃, C₂H₅, C₃H₇, CH₂OC(O)R³, OC(O)R³;

R², R⁴, R⁵, R⁶:

H, CH₃, C₂H₅, C₃H₇;

R³:

einen gesättigten, ungesättigten oder aroma- tischen Kohlenwasserstoffrest mit 1 bis 19 Kohlenwasserstoffatomen, bei welchem auch ein oder mehrere Wasserstoffatome durch an- dere Substituenten ersetzt sein können;

a, b, c:

eine ganze Zahl zwischen 0 und 4;

x

0, 1 oder 2; wobei:

• zumindest einer der Reste R¹, R² und R⁴ nicht Wasserstoff ist;
• wenn R¹ und R⁷ für CH₂OC (O) R³, OC (O) R³ steht, x = 0 ist; und
• die Summe a + b + c mindestens 2 be- trägt.

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

in welcher R², R³, R⁴, R⁵, R⁶, a, b, c die bei Formel I angegebene Bedeutung aufweisen und zusätzlich bedeutet:

R¹:

H, CH₃, C₂H₅, C₃H₇, wobei R¹ nicht H ist, wenn R² = R⁴ = R⁵ = R⁶ = H;

R⁸:

einen gesättigten, ungesättigten oder aroma- tischen Kohlenwasserstoffrest mit 1 bis 19 Kohlenwasserstoffatomen, bei welchem auch ein oder mehrere Wasserstoffatome durch an- dere Substituenten ersetzt sein können.

The carboxylic acid diester of a branched alkanediol preferably has a structure of the 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 ⁸ :

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. Both radicals R ⁴ are preferably identical 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 may be saturated, unsaturated or aromatic hydrocarbon radicals comprising 1 to 19, preferably 2 to 10, more 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 precisely comprises a double bond.

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 can 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:

Particularly preferred alkanediol is 2,2,4-trimethyl-1,3-pentanediol and further preferably carboxylic acid, isobutyric acid, acetic acid, and benzoic acid.

Exemplary carboxylic diesters of a branched alkanediol are 2,2,4-trimethyl-1,3-pentanediol diacetate and 2,2,4-trimethyl-1,3-pentanediol dibenzoate.

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

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 8 to 22 carbon atoms which are 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, such as tall oil, rapeseed oil, sunflower oil, germ oil and coconut oil. Instead of natural oils and fats, it is also possible to use individual fatty acids, such as palmitic acid or oleic acid. The aliphatic alcohols used are preferably primary alcohols having 1 to 12 carbon atoms, particularly preferably 1 to 10 carbon atoms, particularly preferably 4 to 10 carbon atoms, with methanol, isopropanol and n-butanol being particularly preferred. Such fatty acid esters are for example in the EP-A-1 137 500 described. Have proven themselves in the EP-B-0 295 262 "symmetrical esters" in which both the fatty acid residue and the alcohol residue have a number of carbon atoms in the same range, preferably 6 to 13 carbon atoms.

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 .-%.

In addition to the constituents already mentioned, the binder systems may contain conventional additives, eg silanes ( EP-A-1 137 500 ), or internal release agents, for example fatty alcohols ( EP-B-0 182 809 ), drying oils ( US-A-4,268,425 ) or complexing agent ( WO 95/03903 ), or mixtures thereof.

Suitable silanes are, for example, aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes and ureidosilanes, such as γ-hydroxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) trimethoxysilane and N-β- (aminoethyl) -γ-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 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 with molding material mixtures of the prior art.

For the purposes of the invention, a cashew nut shell oil is understood to mean both the oil obtained from seed casings 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.

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 nutshell 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. Thus, test bars made from such a preferred molding compound show less sag under thermal stress than test bars made with an analogous binder, but no cashew nut shell oil was added to the binder.

The at least one component of the cashew nut shell oil and / or the at least one derivative of the cashew nut shell oil preferably forms at least a portion of the polyol component. In this embodiment, the at least one component of the cashew nut shell oil and / or the at least one derivative of the cashew nut shell oil is added during the synthesis of the polyol component so that they are incorporated into the polyol component during the synthesis. The synthesis of the polyol component is carried out in a known manner, wherein the at least one component of the cashew nut shell oil and / or the at least one derivative of cashew nut shell oil can be added to the reaction mixture already at the beginning of the synthesis or only at a later point in time of the synthesis.

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, wherein, however, in addition to the phenolic component, the cashew nut shell oil 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, and 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. The molding material mixture may additionally optionally contain other conventional ingredients such as iron oxide, milled flax fibers, wood flour granules, pitch and refractory metals.

• Bereitstellen der oben beschriebenen Formstoffmischung;
• Ausformen der Formstoffmischung zu einem Formkörper;
• Aushärten des Formkörpers durch Zugabe eines Aushärtungskatalysators.

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, acryline, 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 were added 1,770.6 g of phenol, 984.3 g of paraformaldehyde (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 ° C. At this temperature was distilled until reaching a refractive index (25 ° C) of about 1.5940. The distillation was then continued under reduced pressure until the mixture had a refractive index (25 ° C) of about 1.6000. 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) Not according to the invention inventively A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 phenolic resin 67.5 67.5 67.5 67.5 67.5 67.5 67.5 67.5 67.5 67.5 67.5 Rapsölfettsäuremethylester 32 16 isopropyl 32 16 2-ethylhexyl 2-ethylhexanoate 32 16 Tetraethyl orthosilicate 32 16 DBE 32 16 2,2,4-trimethyl-1,3-pentanediol diisobutyrate 32 16 16 16 16 16 silane 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

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) Not according to the invention inventively B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 Polymer tech. 4,4'-MDI 80 80 80 80 80 80 80 80 80 80 80 Rapsölfettsäuremethylester 20 10 isopropyl 20 10 2-ethylhexyl 2-ethylhexanoate 20 10 tetraethylorthosilicate 20 10 DBE 20 10 2,2,4-trimethyl-1,3-pentanediol diisobutyrate 20 10 10 10 10 10

Example 3: Production 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 material 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.

• unmittelbar nach ihrer Herstellung
• nach 24 h Lagerung bei Raumtemperatur
• nach 24 h Lagerung bei 98 % relativer Luftfeuchtigkeit.

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 portion of the test bars was dried after storage for 30 minutes at room temperature, at 150 ° C for 30 minutes. 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 Not according to the invention inventively Component 1 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 Component 2 B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 Strengths N / cm ² Immediately 145 110 115 150 110 175 180 200 175 160 135 24 hours 460 415 410 440 440 490 500 495 470 455 440 24 hours at 98% rel. Humidity te 300 310 315 305 215 335 350 365 345 315 245 Water-based (wet) 320 295 310 315 270 325 325 330 320 310 295 Water-based (dried) 470 455 455 480 480 510 535 530 525 500 490

Test bars, 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-1,3-pentanediol diisobutyrate is used as the solvent. However, high strengths are also obtained if the solvent contains fatty acid esters which have an average polarity, or else strongly polar esters and also dibasic esters or tetraethyl orthosilicate.

Example 4: Influence of the proportion of 2,2,4-trimethyl-1,3-pentanediol diisobutyrate in the solvent

The influence of further solvents was tested on the example of isopropyl laurate, which was used in various proportions in addition to 2,2,9-trimethyl-1,3-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) A2 A12 A8 A13 A6 phenolic resin 67.5 67.5 67.5 67.5 67.5 isopropyl 32 22.4 16 9.6 2,2,4-trimethyl-1,3-pentanediol diisobutyrate 9, 6 16 22.4 32 silane 0.5 0.5 0.5 0.5 0.5 B2 B12 B8 B13 B6 Polymer tech. 4,4 '- MDI 80 80 80 80 80 isopropyl 20 14 10 6 2,2,4-trimethyl-1,3-pentanediol diisobutyrate 6 10 14 20

Strength test:

Test bars were produced and their strength tested analogously to Example 3. The results are summarized in Table 6. Table 6: Strength tests using mixed solvents Component 1 A2 A12 A8 A13 A6 Component 2 B2 B12 B8 B13 B6 Strengths N / cm ² Immediately 110 190 200 200 175 24 hours 415 450 495 485 490 24 hours at 98% rel. humidity 310 360 365 340 335 Water-based (wet) 295 310 330 335 325 Water-based (dried) 455 500 530 490 510

Results:

Even a small proportion of 2,2,4-trimethyl-1,3-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 mixed 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. Table 7: Composition of the polyol component (% by weight) A14 A15 A16 A17 A18 A19 phenolic resin 67.5 67.5 67.5 67.5 67.5 67.5 isopropyl 19.8 11 2.2 19.8 11 2.2 DBE 10 10 10 tetraethylorthosilicate 10 10 10 2,2,4-trimethyl-1,3-pentanediol diisobutyrate 2.2 11 19.8 2.2 11 19, 8 silane 0.5 0.5 0.5 0.5 0.5 0.5 B14 B15 B16 B17 B18 B19 phenolic resin 80 80 80 80 80 80 isopropyl 9 5 1 9 5 1 DBE 10 10 10 tetraethylorthosilicate 10 10 10 2,2,4-trimethyl-1,3-pentanediol diisobutyrate 1 5 9 1 5 9

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 Component 1 A14 A15 A16 A17 A18 A19 Component 2 B14 B15 B16 B17 B18 B19 Strengths N / cm ² Immediately 210 190 195 170 200 210 24 hours 490 495 485 485 480 495 24 hours at 98% rel. humidity 340 330 345 300 305 305 Water-based (wet) 305 295 305 260 275 275 Water-based (dried) 510 520 520 475 470 455

Result:

If, in addition to 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, fatty acid esters and strongly polar solvents are used in the binder system, an increase in the strength of the test bars is likewise observed.

Example 6: Investigation of smoke development

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 ° C in the oven. After taking the test bars, 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 Component 1 A2 A8 A6 A15 Component 2 B2 B8 B6 B15 rating 10 8th 5 4

By using 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, the smoke development can be reduced.

Claims (17)

1. A moulding material mixture for the production of casting moulds for the foundry industry, comprising at least:

   - a fire-resistant base moulding material; and

   - a polyurethane-based binder system comprising a polyisocyanate component and a polyol component,

   characterized in that the polyurethane-based binder system includes a carboxylic acid diester of a branched alkane diol in a proportion of at least 3% by weight and an aromatic solvent in a proportion of less than 10% by weight, relative to the binder system in each case.
2. The moulding material mixture according to claim 1, characterized in that carboxylic acid diester of a branched alkane diol is present in the binder system in a proportion greater than 5% by weight.
3. The moulding material mixture according to claim 1 or 2, characterized in that the carboxylic acid diester of a branched alkane diol has a structure of the formula

   

   wherein, each independent from each other and wherever they occur mean:

   R¹, R⁷: H, CH₃, C₂H₅, C₃H₇, CH₂OC(O)R³, OC(O)R³;

   R², R⁴, R⁵, R⁶: H, CH₃, C₂H₅, C₃H₇;

   R³: 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; wherein:

   - at least one of the radicals R¹, R² and R⁴ is not hydrogen;

   - if R¹ and R⁷ represent CH₂OC(O)R³, OC(O)R³, x = 0; and

   - the sum of a + b + c is at least 2.
4. The moulding material mixture according to any one of the preceding claims, characterized in that the branched carboxylic acid diester of a branched alkane diol is 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate.
5. The moulding material mixture according to claims 1 to 4, characterized in that the polyurethane-based binder system comprises at least one fatty acid ester.
6. The moulding material mixture according to claim 4, characterized in that the portion of the at least one fatty acid ester in the polyurethane-based binder system is selected to be less than 90% by weight.
7. The moulding 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. The moulding material mixture according to any one of the preceding claims, characterized in that the polyol component is formed by condensing a phenolic component and an oxo-component.
9. The moulding material mixture according to claim 8, characterized in that the oxo-component is formed by an aldehyde.
10. The moulding material mixture according to any one of the preceding claims, characterized in that the polyol component is formed by a benzyl ether resin.
11. The moulding material mixture according to any one of the preceding claims, characterized in that the isocyanate component is an aliphatic, aromatic or heterocyclic isocyanate having at least two isocyanate groups per molecule, or oligomers or polymers thereof.
12. The moulding material mixture according to any one of the preceding claims, characterized in that the binder system is present in a proportion of 0.5 to 10% by weight relative to the weight of the fire-resistant base moulding material.
13. A method for producing a casting mould for the foundry industry, characterized by the following steps:

    - Providing a moulding material mixture as described in any of claims 1 to 12;

    - Forming the moulding material mixture to produce a casting mould;

    - Curing the casting mould by adding a curing catalyst.
14. The method according to claim 13, characterized that the curing catalyst is added in gaseous form.
15. The method according to one of claims 13 or 14, characterized that curing is carried out essentially at room temperature.
16. A casting mould for the foundry industry, obtained by a method according to one of claims 13 to 15.
17. Use of a casting mould according to claim 16 for casting metal.