DE102013004663B4 - Binder system, molding material mixture containing the same, process for producing the molding material mixture, process for producing a mold part or casting core, mold part or casting core and use of the mold part or casting core thus obtainable for metal casting - Google Patents

Abstract

Binder system comprising:(A) a polyol component comprising a phenolic resin containing free OH groups,(B) an isocyanate component comprising a polyisocyanate having at least two NCO groups per molecule,(C) at least one fatty acid ester selected from esters of fatty acids or dimer fatty acids and monohydric alcohols,(D) at least one epoxidized fatty acid ester or glycidyl ether of at least dihydric non-aromatic alcohols and optionally(E) one or more further components selected from organic solvents, silanes, oils, complexing agents, plasticizers, additives for extending the sand life and internal release agents.

Description

The present invention relates to polyurethane-based binder systems for the foundry industry, in particular systems that contain epoxy compounds and fatty acid esters at the same time. The invention also relates to molding material mixtures comprising the binder system, as well as to methods for producing mold parts and cores from these molding material mixtures, a mold part or a core and the use of these mold parts and cores for metal casting.

Casting mold parts (or molds for short) form the outer wall for the casting during casting, casting cores (or cores for short) are used to form cavities within the casting. It is not absolutely necessary for the molds and cores to be made of the same materials. For example, in permanent mold casting, the external shape of the castings is created using permanent metal molds. It is also possible to combine molds and cores that consist of molding material mixtures with different compositions and/or were manufactured using different processes. When cores are mentioned below, the statements apply equally to molds that are based on the same molding material mixture and were manufactured using the same process.

The use of two-component polyurethane systems for core production has become very important in the foundry industry. One component contains a polyol with at least two OH groups per molecule, the other a polyisocyanate with at least two NCO groups per molecule. The two components are only brought into contact shortly before or during the production of molding material mixtures. The curing of the binder system is usually carried out with the help of basic catalysts. Liquid bases in particular can be added to the binder system before molding in order to cause the two components to react ( US 3,676,392 A ). Another possibility is to remove gaseous tertiary amines after molding through the molding material-binder system mixture ( US 3,409,579 A ). These two processes are known in the art as the no-bake process and the cold box process.

In US 3,676,392 A and US 3,409,579 A Phenolic resins are used as polyols, which are obtained by condensation of phenol with aldehydes, preferably formaldehyde, in the liquid phase at temperatures up to about 130°C in the presence of catalytic amounts of metal ions. In US 3,485,797 A The production of such phenolic resins is described in detail. In addition to unsubstituted phenol, substituted phenols can be used (see e.g. ( US 4,590,229 A ). In EP0177871A2 Alkoxy-modified phenolic resins are used; the alkoxylation is intended to give the binder systems increased thermal stability.

With these phenolic resin polyols, the use of solvents is necessary in order to achieve a suitable low viscosity and optimal wetting of the molding base material when mixed with the molding base material. Although the viscosity of the polyisocyanates is significantly lower than that of the phenolic resins, the isocyanate component usually also contains solvents. In general, polar solvents are suitable for phenolic resins, while non-polar solvents are better suited for polyisocyanates. In practice, mixtures of polar and non-polar solvents are therefore often used. The non-polar solvents used are usually high-boiling aromatic hydrocarbons (or mixtures thereof) with a boiling range above 150°C at normal pressure, while the polar solvents often used are high-boiling esters or ketones.

The high-boiling aromatics cause a considerable workplace burden, so that ways have been sought to replace them partially or completely with less harmful substances.

In EP0771599B2 Formulations are described in which aromatic solvents can be completely or at least largely dispensed with by using fatty acid methyl esters.

In EP1137500B9 Alkoxy-modified phenolic resins are used, which require less solvent due to their low viscosity, so that the amount of aromatic hydrocarbon solvent can also be reduced.

In EP0417600A2 For example, epoxy compounds are added to PU-based binders in order to be able to process the molding material mixtures for longer without loss of strength and to give the binders a higher thermal resistance.

In US 5,981,622 A Epoxies are added to the binders in combination with paraffin oils to increase their strength and moisture resistance.

Even though PU-based binders dominate the market and have been continuously improved since their introduction, they still have weaknesses that require further improvement. One of these weaknesses is the tendency to form certain casting defects, e.g. so-called leaf veins and mineralization.

Both casting defects can be combated according to the state of the art by adding additives to the molding material mixtures, e.g. based on organic materials such as hardwood granulate, carbohydrates, etc. or based on inorganic materials such as bauxite, glass beads, hollow glass spheres or special minerals. Examples of suitable additives are in WO98/45068 A1 , US 4,735,973 A , US 5,911,269 A , US 2002/108733 A1 and US8,122,936 B2 Another possibility is to use refractory molding materials such as chrome ore or zircon sand instead of the quartz sand that is usually used to make the core. In many cases, a complete replacement is not necessary; in most cases, a partial replacement of the quartz sand with chrome ore or zircon sand is sufficient. Applying a refractory coating, a so-called coating, to the molded parts/cores also helps to obtain flawless casting surfaces. Other foundry binders are described in DE 4327292 A1 described.

Although the methods of error control described above are very effective, they have one major disadvantage: All of these measures contribute significantly to increasing the cost of the process, on the one hand due to the costs of the input materials and on the other hand due to the increased technical and/or time expenditure involved in their use.

Foundries therefore want binders that make the above-mentioned complex and expensive measures unnecessary or at least significantly reduce them.

The invention was therefore based on the object of providing foundries with PU-based binder systems which lead to only minor to very minor casting defects during molded part/core production without negatively affecting the strength of the molded parts/cores.

1. (A) eine Polyolkomponente, umfassend ein freie OH-Gruppen enthaltendes Phenolharz,
2. (B) eine Isocyanatkomponente, umfassend ein Polyisocyanat mit mindestens zwei NCO-Gruppen pro Molekül,
3. (C) mindestens einen Fettsäureester ausgewählt aus Estern von Fettsäuren oder Dimerfettsäuren und einwertigen Alkoholen,
4. (D) mindestens einen epoxidierten Fettsäureester oder Glycidylether von mindestens zweiwertigen nicht-aromatischen Alkoholen und gegebenenfalls (E) ein oder mehr weitere Bestandteile ausgewählt aus organischen Lösungsmitteln, Silanen, Ölen, Komplexbildnern, Weichmachern, Additiven zur Verbesserung der Sandlebenszeit (=Verarbeitungszeit) und internen Trennmitteln

umfassen.Surprisingly, it was found that this is possible with binder systems which

1. (A) a polyol component comprising a phenolic resin containing free OH groups,
2. (B) an isocyanate component comprising a polyisocyanate having at least two NCO groups per molecule,
3. (C) at least one fatty acid ester selected from esters of fatty acids or dimer fatty acids and monohydric alcohols,
4. (D) at least one epoxidized fatty acid ester or glycidyl ether of at least dihydric non-aromatic alcohols and optionally (E) one or more further components selected from organic solvents, silanes, oils, complexing agents, plasticizers, additives to improve the sand life (= processing time) and internal release agents

include.

The fatty acid esters (C) are esters of fatty acids or dimer fatty acids and monohydric alcohols.

aufweisen,
in der R^p der von einem einwertigen Alkohol abgeleitete Rest ist und R^f der von der Fettsäure abgeleitete Rest ist.The esters are esterification products of saturated or mono- or polyunsaturated, straight-chain and/or branched fatty acids R ^f COOH or fatty acid mixtures or dimer acids thereof with monofunctional,
saturated or unsaturated, straight-chain or branched or aromatic alcohols R ^p OH, wherein the esters have the following formula

exhibit,
in which R ^p is the residue derived from a monohydric alcohol and R ^f is the residue derived from the fatty acid.

R ^f is preferably straight-chain or branched C _2-24 alkyl or straight-chain or branched C _2-24 alkenyl (wherein within the definition of R ^f an alkenyl radical has at least one CC double bond, preferably 1-6, more preferably 1-3 CC double bonds), more preferably C _6-24 alkyl or C _6-24 alkenyl (in each case straight-chain or branched), further preferably C _10-24 alkyl or C _10-24 alkenyl (in each case straight-chain or branched), most preferably C _12-24 alkyl or C _12-24 alkenyl (in each case straight-chain or branched).

Examples of unsaturated fatty acids include palmitoleic acid, oleic acid, erucic acid, linoleic acid, linolenic acid, elaeostearic acid, arachidonic acid, chupanodonic acid and docosahexaenoic acid.

Examples of saturated fatty acids include caprylic, pelargonic, capric, undecanoic, lauric, tridecanoic, myristic, pentadecanoic, palmitic, margaric, stearic, nonadecanoic, arachidic, behenic and lignoceric acid.

Dimer fatty acids and mixtures of fatty acids can also be used for esterification.

• bevorzugter C_1-10 Alkyl oder C_2-10 Alkenyl (jeweils geradkettig oder verzweigt), noch bevorzugter C_1-8 Alkyl oder C_2-8 Alkenyl (jeweils geradkettig oder verzweigt).
• Beispiele für die einwertigen Alkohole sind Methanol, Ethanol, n-Butanol, Isopropanol, n-Amylalkohol und 2- Ethylhexanol.

R ^p is preferably straight-chain or branched C _1-12 alkyl, straight-chain or branched C _2-12 alkenyl (wherein within the definition of R ^p an alkenyl radical has at least one CC double bond, preferably 1-4, more preferably 1-3 CC double bonds), C _6-10 aryl or C _7-15 aralkyl;

• more preferably C _1-10 alkyl or C _2-10 alkenyl (each straight-chain or branched), even more preferably C _1-8 alkyl or C _2-8 alkenyl (each straight-chain or branched).
• Examples of monohydric alcohols are methanol, ethanol, n-butanol, isopropanol, n-amyl alcohol and 2-ethylhexanol.

It is not necessary for the fatty acid and/or alcohol used for esterification to be uniform products; mixtures can also be used and, in particular, saturated fatty acids may be present in a mixture with unsaturated fatty acids. For example, the fatty acids in naturally occurring triglycerides (vegetable or animal oils) are present as mixtures, which can be used as such or can be subjected to transesterification with a monofunctional alcohol without separation.

Consequently, transesterification of vegetable oils produces mixtures of fatty acid esters whose proportions of the respective fatty acids correspond to the respective proportions in the starting oil.

The fatty acid esters (or fatty acid ester mixtures) used in the invention are either commercially available or can be produced using known processes. If the fatty acid is present as a free acid or fatty acid halide, it can be esterified using known processes. If the fatty acid is present as a triglyceride, this can either be used directly or a transesterification is carried out using conventional processes.

Suitable fatty acid esters include vegetable oils such as rapeseed oil, soybean oil, sunflower oil, linseed oil, olive oil, coconut oil, oil palm kernel oil, hemp oil, oil palm oil and tall oil, as well as esters of individual fatty acids and monohydric alcohols. Animal oils can also be used.

As component (D) at least one epoxidized fatty acid ester or glycidyl ether of at least dihydric non-aromatic alcohols is used; the polyhydric alcohol is preferably fully esterified for both options.

The epoxidized fatty acid ester (D) is the esterification product of mono- or polyunsaturated, straight-chain and/or branched fatty acids R'COOH or fatty acid mixtures whose double bond(s) were completely or partially epoxidized after the esterification, wherein the esterification was carried out with an at least divalent straight-chain or branched non-aromatic alcohol R ^z OH.

R' of the fatty acid R'COOH used is preferably straight-chain or branched C2-C24 alkenyl, more preferably C8-C24 alkenyl, more preferably C12 - C24 alkenyl and particularly preferably C18 - C24 alkenyl; within the definition of R', an alkenyl radical contains at least one C-C double bond (preferably 1-4, more preferably 1-3 C-C double bonds). Suitable fatty acids R'COOH include, for example, palmitoleic acid, oleic acid, erucic acid, linoleic acid, linolenic acid, elaeostearic acid, arachidonic acid, chupanodonic acid and docosahexaenoic acid.

The alcohol used has the formula R ^z OH, where R ^z is preferably straight-chain or branched C _1-12 alkyl or straight-chain or branched C _2-12 alkenyl (having at least one CC double bond), each substituted with at least one additional hydroxyl group (preferably 1 or 2); more preferred are C _1-10 alkyl and C _2-20 alkenyl (each straight-chain or branched and substituted with at least one additional OH group), even more preferred are C _1-8 alkyl and C _2-8 alkenyl (each straight-chain or branched and substituted with at least one additional OH group). Suitable examples of alcohol R ^z OH are ethylene glycol, glycerin, trimethylolpropane, neopentyl glycol, pentaerythritol and dipentaerythritol.

The epoxidized fatty acid esters (D) to be used according to the invention are either commercially available or can be prepared by known processes. For example, epoxidized fatty acid esters and oils can be prepared by the Prileshajev process with peroxyformic acid or by chemo-enzymatic epoxidation.

Preferred epoxidized fatty acid esters (D) are epoxidized fatty acid triglycerides, in particular epoxidized oils, since they are renewable raw materials; suitable examples are epoxidized rapeseed oil, epoxidized sunflower oil, epoxidized soybean oil, epoxidized linseed oil, epoxidized olive tree oil, epoxidized oil palm oil, epoxidized hemp oil and epoxidized tall oil.

As component (D) it is also possible to use glycidyl ethers of at least dihydric non-aromatic alcohols or mixtures of epoxidized fatty acid esters of at least dihydric non-aromatic alcohols and glycidyl ethers of at least dihydric non-aromatic alcohols.

wobei q eine ganze Zahl von mindestens 2 ist, vorzugsweise 2 - 10 und noch bevorzugter 2 - 5,
und
Z ein geradkettiger oder verzweigter, gesättigter Kohlenwasserstoffrest mit einer Valenz von q ist, wobei der Kohlenwasserstoffrest gegebenenfalls ein oder mehrere Ethersauerstoffe -O- enthält (jedoch nicht als Bindungsstelle für

Geeignete Beispiele sind: Ethylenglycol-diglycidylether, Propylenglycoldiglycidylether, Polyethylenglycol-diglycidylether, Polypropylenglycol-diglycidylether, 1,4-Butandiol-diglycidylether, Diethylenglycol-diglycidylether, Trimethylpropantriglycidylether, Glycerol-triglycidylether und Pentaerythritol-tetraglycidylether.The glycidyl ethers of polyhydric non-aromatic alcohols can be represented by the following formula:

where q is an integer of at least 2, preferably 2 - 10 and more preferably 2 - 5,
and
Z is a straight-chain or branched, saturated hydrocarbon radical with a valence of q, wherein the hydrocarbon radical optionally contains one or more ether oxygens -O- (but not as a binding site for

Suitable examples are: ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, diethylene glycol diglycidyl ether, trimethylpropane triglycidyl ether, glycerol triglycidyl ether and pentaerythritol tetraglycidyl ether.

The glycidyl ethers are either commercially available or can be produced using known processes.

The total amount of fatty acid ester (C) and epoxy compound (D) in the binder system (with respect to the entire binder system of (A)+(B)+(C)+(D) and any further additives) is preferably 2 to 30 wt.%, more preferably 3 to 25 wt.% and particularly preferably 5 to 20 wt.%.

The weight proportions of epoxy compound (D) to fatty acid ester (C) are in the range from 95:5 to 5:95, preferably from 85:15 to 15:85, particularly preferably from 80:20 to 20:80.

The polyol component comprises phenol-aldehyde resins, also referred to here as phenol resins for short. All conventionally used phenol compounds are suitable for producing the phenol resins. In addition to unsubstituted phenols, substituted phenols or mixtures thereof can be used. The phenol compounds are preferably unsubstituted either in both ortho positions or in one ortho and in the para position. The remaining ring carbon atoms can be substituted. The choice of substituent is not particularly limited, provided that the substituent does not adversely affect the reaction of the phenol with the aldehyde. Examples of substituted phenols are alkyl-substituted, alkoxy-substituted, aryl-substituted and aryloxy-substituted phenols.

The above-mentioned optional substituents of the phenol preferably have 1 to 26, more preferably 1 to 15 carbon atoms and optionally one or more ether oxygen atoms. Examples of suitable substituted phenols are o-cresol, m-cresol, p-cresol, 3,5-xylenol, 3,4-xylenol, 3,4,5-trimethylphenol, 3-ethylphenol, 3,5-diethylphenol, p-butylphenol, 3,5-dibutylphenol, p-amylphenol, cyclohexylphenol, p-octylphenol, p-nonylphenol, cardanol, 3,5-dicyclohexylphenol, p-crotylphenol, p-phenylphenol, 3,5-dimethoxyphenol and p-phenoxyphenol; of these, o-cresol and cardanol are preferred.

Particularly preferred is phenol itself, as well as condensed, unsubstituted phenols, such as bisphenol A, and phenols which have more than one phenolic hydroxyl group.

zur Herstellung des Phenolharzes verwendet, wobei A, B und C unabhängig voneinander ausgewählt sind aus: Einem Wasserstoffatom, einem verzweigten oder unverzweigten Alkylrest, der vorzugsweise 1 bis 26, bevorzugter 1 bis 15 Kohlenstoffatome, aufweisen kann, einem verzweigten oder unverzweigten Alkoxyrest, der vorzugsweise 1 bis 26, bevorzugter 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 Biphenyle.In one embodiment, phenols of the general formula:

used to produce the phenolic resin, wherein A, B and C are independently selected from: a hydrogen atom, a branched or unbranched alkyl radical, which can preferably have 1 to 26, more preferably 1 to 15 carbon atoms, a branched or unbranched alkoxy radical, which can preferably have 1 to 26, more preferably 1 to 15 carbon atoms, a branched or unbranched alkenoxy radical, which can, for example, have 1 to 26, preferably 1 to 15 carbon atoms, an aryl or alkylaryl radical, such as, for example, biphenyls.

Aldehydes suitable for the production of phenolic resins include aldehydes of the formula: R-CHO where R is a hydrogen atom or a straight-chain or branched, saturated or aromatic hydrocarbon radical having preferably 1 to 8 carbon atoms. Specific examples are formaldehyde, acetaldehyde, propionaldehyde, furfurylaldehyde and benzaldehyde. Even more preferably, R has 1 to 3 carbon atoms and particularly preferably formaldehyde is used, either in its aqueous form, as paraformaldehyde, or trioxane.

In order to obtain the phenolic resins, it is preferable to use at least an equivalent number of moles of aldehyde, based on the number of moles of the phenol component.

The molar ratio of aldehyde to phenol is preferably 1.0:1 to 2.5:1, particularly preferably 1.1:1 to 2.2:1, especially preferably 1.2:1 to 2.0:1.

The phenolic resin is produced using processes known to those skilled in the art. The phenol and the aldehyde are reacted under essentially anhydrous conditions, in particular in the presence of a divalent metal ion, at temperatures of preferably less than 130°C. The water formed is distilled off. For this purpose, a suitable entraining agent can be added to the reaction mixture, for example toluene or xylene, or the distillation is carried out under reduced pressure.

The phenolic resin is chosen so that cross-linking with the polyisocyanate is possible. It goes without saying that phenolic resins that contain molecules with at least two hydroxyl groups in the molecule are necessary to create a network.

Particularly suitable phenolic resins are known as "ortho-ortho" or "high-ortho" novolaks or benzyl ether resins. These are obtainable by condensation of phenols with aldehydes in a weakly acidic medium using suitable catalysts. Catalysts suitable for the production of benzyl ether resins are salts of divalent ions of metals such as Mn, Zn, Cd, Mg, Co, Ni, Fe, Pb, Ca and Ba. Zinc acetate is preferably used. The amount used is not critical. Typical amounts of metal catalyst are 0.02 to 0.3% by weight, preferably 0.02 to 0.15% by weight, based on the total amount of phenol and aldehyde.

Such resins are used, for example, in US 3,485,797 A and in EP1137500A1 described, to the disclosure of which reference is hereby made expressly both with regard to the resins themselves and with regard to their preparation.

The methylol groups of the phenolic resin can be partially etherified with a C _1-8 alkanol (preferably methanol, ethanol or n-butanol). Such etherified phenolic resins are commercially available or can be produced by known processes (see e.g. EP1137500A1 and EP0177871A2 ).

The molecular weight of the phenolic resins used is not particularly limited; all phenolic resins commonly used in the art can be used. The molecular weight is preferably up to 2000 g/mol (weight average determined by GPC using polystyrene standards).

In addition to the phenolic resins mentioned above, the polyol component of the binder system for the no-bake process can also contain other polyol compounds such as low to medium viscosity, linear or branched polyether polyols and/or polyester polyols with primary and/or secondary hydroxyl groups. Polyether polyols are obtained by known processes through the reaction of polyvalent rod molecules such as ethylene glycol, propylene glycol, glycerin, 1,4-butanediol, trimethylolpropane, pentaerythritol, sorbitol, hexanetriol, etc. or mixtures thereof with ethylene oxide and/or propylene oxide. Polyester polyols are produced by known processes in the reaction of polyalcohols or mixtures thereof with organic saturated and/or unsaturated polycarboxylic acids or mixtures thereof of the type adipic acid, sebacic acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, maleic acid and fumaric acid.

The isocyanate component of the binder system comprises an aliphatic, cycloaliphatic or aromatic polyisocyanate, preferably with 2 to 5 isocyanate groups per molecule. Depending on the desired properties, mixtures of isocyanates can also be used.

Suitable polyisocyanates include aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as 4,4'-dicyclohexylmethane diisocyanate and dimethyl-substituted derivatives thereof. Examples of suitable aromatic polyisocyanates are toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, xylylene diisocyanate and methyl-substituted derivatives of the above, and polymethylene polyphenyl isocyanates. Particularly preferred polyisocyanates are aromatic polyisocyanates, particularly preferred are polymethylene polyphenyl polyisocyanates such as technical 4,4'-diphenylmethane diisocyanate, i.e. 4,4'-diphenylmethane diisocyanate with a proportion of isomers and higher homologues.

Generally, 10-500 wt.% polyisocyanate is used based on the weight of the phenolic resin; preferably 20-300 wt.% polyisocyanate is used based on the weight of the phenolic resin.

The polyisocyanate is preferably used in an amount such that the number of isocyanate groups is from 80 to 120%, based on the number of free hydroxyl groups of the resin.
The polyol component and/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, for example, to keep the components of the binder system in a sufficiently low-viscosity state in order to achieve uniform wetting of the refractory mold base material and to maintain its flowability and to achieve good cross-linking of the binder molecules during curing.

In addition to the aromatic solvents known as solvent naphtha, oxygen-rich polar organic solvents can also be used as solvents for the phenolic resin. Suitable solvents include dicarboxylic acid esters, glycol ether esters, glycol diesters, glycol diethers, cyclic ketones, cyclic esters (lactones), cyclic carbonates or silicic acid esters or mixtures thereof.

Typical dicarboxylic acid esters which are suitable as solvents have the formula R ¹ OOC-R ² -COOR ¹ , where R ¹ is each independently an alkyl group having 1 to 12, preferably 1 to 6, carbon atoms and R ² is an alkylene group having 1 to 4 carbon atoms. Examples are dimethyl esters of carboxylic acids having 4 to 6 carbon atoms, which are available from DuPont, for example, under the name Dibasic Ester.

Typical glycol ether ester solvents are compounds of the formula R ³ -OR ⁴ -OOCR ⁵ , where R ³ represents an alkyl group having 1 to 4 carbon atoms, R ⁴ is an alkylene group having 2 to 4 carbon atoms and R ⁵ is an alkyl group having 1 to 3 carbon atoms, e.g. butyl glycol acetate; particularly preferred are glycol ether acetates.

Typical glycol diester solvents have the general formula R ³ COO-R ⁴ -OOCR ⁵ , where R ³ to R ⁵ are as defined above and the radicals are each selected independently of one another (eg propylene glycol diacetate). Glycol diacetates are preferred. Glycol diethers can be characterized by the formula R ³ -OR ⁴ -OR ₅ , where R ³ to R ⁵ are as defined above and the radicals are each selected independently of one another (eg dipropylene glycol dimethyl ether).

Typical cyclic ketones, cyclic esters and cyclic carbonates with 4 to 5 carbon atoms are also suitable (e.g. propylene carbonate). The alkyl and alkylene groups can each be branched or unbranched.

The polyol component (A) preferably contains 5-60 wt.% of one or more of the above solvents, more preferably 10-55 wt.% and particularly preferably 10-50 wt.%, preferably using aromatic solvents such as solvent naphtha.

Liquid polyisocyanates can also be used in undiluted form, while solid or viscous polyisocyanates are dissolved in organic solvents. Up to 80% by weight of the isocyanate component can consist of organic solvents. Aromatic solvents, for example, are used as solvents for the polyisocyanate. Suitable aromatic solvents include naphthalene, alkyl-substituted naphthalenes, alkyl-substituted benzenes and mixtures thereof. Particularly preferred are mixtures of aromatic solvents that have a boiling point range between 140°C and 320°C (e.g. solvent naphtha, which is a fraction of aromatic hydrocarbons with a boiling range of about 150 to 230°C):

In addition to the components already mentioned, the binder systems may contain further additives, such as silanes (e.g. according to US 3,905,934 A ), oils (e.g. according to US 4,268,425 A or EP1074568 A2 ), complexing agents (e.g. according to US 5,447,968 A ), plasticizers (e.g. dialkyl phthalates according to US 3,905,934 A ), additives to extend the processing time - also called sand life - (e.g. according to US 4,436,881 A , US 4,540,724 A , US 4,602,069 A , US 4,683,252 A , US 4,852,629 A ) and internal release agents (e.g. according to US 4,602,069 A ).

For example, silanes of the general formula (R'O) ₃ SiR can be added to the binder system. R' is a hydrocarbon radical, preferably an alkyl radical with 1-6 carbon atoms, and R is an alkyl radical, an alkoxy-substituted alkyl radical or an alkylamine-substituted amine radical with alkyl groups having 1-6 carbon atoms.
Suitable silanes include aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes and ureido silanes such as γ-hydroxypropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)trimethoxysilane and N-β-(aminoethyl)-y-aminopropyltrimethoxysilane.

Examples of commercially available silanes are Silquest Z6040 and Silquest A-187 (γ-glycidoxypropyltrimethoxysilane), Silquest A-1100 (γ-aminopropyltriethoxysilane) and Silquest A-1120 (N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane) (manufacturer Momentive Performance Materials Inc.) and Dynasilan 2201 EQ (ureidosilane) from Evonik GmbH.

The amount of silane is preferably 0 to 2 wt.% based on the binder system.

The binder system of the present invention does not contain paraffin oils as used in US 5,981,622 A be used.

The binder systems are preferably offered as two-component systems, with the polyol (optionally with solvent and/or optional additives) being one component and the polyisocyanate (optionally with solvent and/or optional additives) being the other component. Each of the components C and D can be present independently in the first or second component or in both, but they are preferably both part of the isocyanate component.

Furthermore, the invention relates to molding material mixtures which comprise refractory molding base materials and binder system according to the invention, preferably 0.2 to 5 wt.%, more preferably 0.3 to 4 wt.%, particularly preferably 0.4 to 3 wt.%, binder system based on the weight of the refractory molding base materials.

Refractory mold base materials (sometimes also referred to as aggregates) that can be used include, for example, quartz, zircon or chrome ore sand, olivine, chamotte (Al ₂ O ₃ content 10-45 wt.%) and bauxite. Synthetically produced mold base materials can also be used, such as aluminum silicate hollow spheres (so-called microspheres), glass beads, glass granulate or spherical ceramic mold base materials, which are known, for example, under the name "Cerabeads" or "Carboaccucast". Mixtures of the above-mentioned refractory mold base materials can also be used. It is preferred that refractory mold base materials contain quartz sand, and particularly preferably at least 20 wt.% (even more preferably at least 50 wt.%), based on the total amount of mold base materials. The grain size/diameter of the mold base materials that can be used in the present invention is not particularly limited; all mold base materials customary in the art can be used.
The average grain size of the molding materials is usually in the range of approx. 0.1 mm - 0.55 mm, preferably 0.2 mm - 0.45 mm and particularly preferably 0.25 - 0.4 mm.

To produce a molding material mixture, the components of the binder system are mixed with the refractory molding material, such as quartz sand.

It is possible to first mix the two components of a 2-component system as defined above with parts of the aggregate and then combine these two mixtures. It is also possible to add the components of the binder to the refractory mold base material simultaneously or one after the other (in any order). Methods for achieving a uniform mixture of the binder components and the aggregate are known to those skilled in the art. The mixture may additionally contain other conventional components, such as iron oxide, ground flax fibers, wood parts, pitch and refractory metals.

1. (a) Vermischen von feuerfesten Formgrundstoffen mit dem erfindungsgemäßen Bindemittelsystem (vorzugsweise 0,2 bis 5 Gew.%, bevorzugter 0,3 bis 4 Gew.%, besonders bevorzugt 0,4 bis 3 Gew.%, Bindemittelsystem bezogen auf die Menge der eingesetzten Formgrundstoffe), zum Erhalt einer Formstoffmischung (auch als Formstoffgemisch bezeichnet);
2. (b) Einbringen des in Schritt (a) erhaltenen Formstoffgemisches in ein Formwerkzeug;
3. (c) Härten des Formstoffgemischs im Formwerkzeug;
4. (d) anschließendes Trennen des gehärteten Formstoffgemischs vom Werkzeug.

The invention also relates to a method for producing a casting mold part or a casting core, comprising

1. (a) mixing refractory molding materials with the binder system according to the invention (preferably 0.2 to 5 wt.%, more preferably 0.3 to 4 wt.%, particularly preferably 0.4 to 3 wt.%, binder system based on the amount of molding materials used), to obtain a molding material mixture (also referred to as molding material mixture);
2. (b) introducing the molding material mixture obtained in step (a) into a mold;
3. (c) curing the moulding material mixture in the mould;
4. (d) subsequent separation of the hardened moulding material mixture from the tool.

To produce the molded body, the binder is first mixed with the refractory mold base material to form a molding material mixture as described above. If the molded body is to be produced using the PU no-bake process, a suitable catalyst is added to the molding material mixture. Liquid amines are preferably used for this purpose. These amines preferably have a pK _b value of 4 to 11. Examples of suitable catalysts are 4-alkylpyridines, where the alkyl group comprises 1 to 4 carbon atoms, isoquinoline, arylpyridines, such as phenylpyridine, 2-methoxypyridine, pyridazine, quinoline, n-methylimidazole, 4,4'-dipyridine, phenylpropylpyridine, 1-methylbenzimidazole, 1,4-thiazine, N,N-dimethylbenzylamine, tribenzylamine, N,N-dimethyl-1,3-propanediamine, N,N-dimethylethanolamine and triethanolamine. The catalyst can 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 preferably selected from 0.1 to 15% by weight based on the weight of the polyol component (phenolic resin plus solvent and other constituents - if present).

The molding material mixture is then introduced into a mold using conventional means and compacted there. The molding material mixture is then cured to form a molded body.

According to a further preferred embodiment, the curing takes place according to the PU cold box process. For this purpose, a gaseous catalyst is passed through the already formed molding material mixture. The usual catalysts in the field of the cold box process can be used as the catalyst, for example tertiary amines, particularly preferably dimethylethylamine, dimethyl-n-propylamine, dimethylisopropylamine, dimethyl-n-butylamine, triethylamine and trimethylamine in their gaseous form or as an aerosol.

The invention further relates to a molded body (casting mold part or casting core) as can be obtained by the method described above.

The invention further relates to the use of this molded body for metal casting, in particular iron and aluminum casting.

The invention is explained in more detail below using experimental examples without, however, being limited thereto.

Examples

To carry out all tests, so-called step cones were manufactured using the PU cold box process. The step cone is a well-known test body that can be used to investigate the thermal load during casting onto a core (see e.g. DM Gilson et al., Modern Casting, May 1995, pages 38-40 or US2011/0220316 ). The thermal stress is lowest at level 1 and highest at level 6. The number of leaf veins therefore increases from level 1 to level 6.

0.8 parts by weight of Askocure 300 EP 3901 (phenol-formaldehyde resin in aromatic solvent; resin content 50% by weight, free of fatty acid esters and epoxidized compounds) as a polyol component (ASK Chemicals GmbH) and 0.8 parts by weight of the isocyanate components listed in Table 1 were added successively to 100 parts by weight of quartz sand H 32 (Quarzwerke Frechen GmbH) and mixed intensively in a laboratory mixer (Vogel & Schemmann AG) for two minutes. The molding material mixtures were then transferred to the storage container of a core shooter (Röperwerke Gießereimaschinen GmbH) and introduced into the mold using compressed air (4 bar). The molded bodies were cured by gassing with a triethylamine-air mixture (3 ml amine, 2 bar, gassing time 30 seconds). The cured step cones were removed from the mold and stored at room temperature for 24 hours until further use.

After completion of all test specimens, one half of each step cone was coated with the water-based coating Miratec W3C (commercial product of ASK-Chemicals GmbH) and dried in the oven for 30 minutes at 150°C.

For casting, the stepped cones were placed in a corresponding outer mold and the cavity formed between the stepped cone and the outer mold was filled with 25 kg of liquid iron (1420-1430°C) within 8 seconds. After cooling, the casting was freed from adhering sand cleaned and the number of leaf veins that had formed on the individual steps was counted. The extent to which the cast surfaces had mineralization was also evaluated. Grades from 1-6 were awarded for the evaluation. The smoothed and un-smoothed sides were each examined separately.

The results can be found in Table 2. Tab. 1 Composition of the isocyanate components not according to the invention according to the invention A B C D E F G H I J polym. MDI ¹⁾ 80 80 80 80 80 80 80 80 80 80 epox. soybean oil ²⁾ 20 10 10 10 epoxy linseed oil ³⁾ 10 Rapeseed oil methyl ester ⁴⁾ 20 10 10 10 Isopropyl laurate ⁵⁾ 20 10 Tall oil butyl ester ⁶⁾ 20 10 THE 331 ⁷⁾ 20 10 1) available from Bayer (MDI = diphenylmethane diisocyanate) 2) available from Hobum; epoxy oxygen approx. 6.5% 3) available from BASF; epoxy oxygen approx. 9% 4) available from Agravis; iodine number 120; free of epoxy oxygen 5) available from BASF; free of epoxy oxygen 6) available from Arizona Chemicals; iodine number 80; free of epoxy oxygen 7) available from Dow Chemicals, bisphenol A epoxy resin, MW < 700 g/mol

Table 2 shows that step cones bonded with the binder systems according to the invention produce better cast surfaces than step cones produced with binder systems that do not contain the combination of epoxy compounds and fatty acid esters according to the invention. This statement applies regardless of whether the test specimens were coated or not.

The strength of the cores produced in the examples according to the invention is comparable to the strength of the cores of the comparative examples.

Claims (20)

Binder system comprising: (A) a polyol component comprising a phenolic resin containing free OH groups, (B) an isocyanate component comprising a polyisocyanate with at least two NCO groups per molecule, (C) at least one fatty acid ester selected from esters of fatty acids or dimer fatty acids and monohydric alcohols (D) at least one epoxidized fatty acid ester or glycidyl ether of at least dihydric non-aromatic alcohols and optionally (E) one or more further components selected from organic solvents, silanes, oils, complexing agents, plasticizers, additives for extending the sand life and internal release agents. Binder system according to Claim 1 , which is a 2-component system in which (A) forms the first component and (B) the second component, the optional components (E), if present, belong to the first and/or second component and each of components C and D is independently present in the first or second component or in both, preferably C and D are both components of the isocyanate component. Binder system according to one of the Claims 1 or 2 , wherein the total amount of (C) + (D) is 2 to 30 wt.% based on the total binder system. Binder system according to one of the Claims 1 until 3 , where the ratio (D) : (C) is from 95 : 5 to 5 : 95. Binder system according to one of the Claims 1 until 4 wherein the epoxy ester compound (D) comprises at least one epoxidized fatty acid triglyceride. Binder system according to one of the Claim 1 until 5 , where (C) are esters of fatty acids with monohydric alcohols. Binder system according to one of the Claims 1 until 6 , wherein (C) is a mixture of esters derived from an oil selected from rapeseed oil, soybean oil, sunflower oil, linseed oil, olive oil, coconut oil, oil palm kernel oil, oil palm oil, hemp oil and tall oil, which has been subjected to transesterification with a saturated monohydric C _1-12 alcohol. Binder system according to one of the Claims 1 until 6 , wherein the fatty acid ester (C) is derived from a monohydric C _1-12 alcohol or a mixture thereof and a saturated or unsaturated, straight-chain or branched C _8-24 fatty acid or a mixture thereof. Binder system according to one of the Claims 1 until 8th , wherein (D) is an epoxidized oil selected from epoxidized rapeseed oil, epoxidized sunflower oil, epoxidized soybean oil, epoxidized linseed oil, epoxidized olive tree oil, epoxidized oil palm oil, epoxidized hemp oil and epoxidized tall oil. Binder system according to one of the Claims 1 until 9 , where the phenolic resin is partially etherified with a C _1-8 alkanol. Moulding material mixture comprising a binder system as in any of the Claims 1 until 10 defined and at least one refractory molding material. Moulding material mixture according to Claim 11 , wherein the amount of the binder system is 0.2 to 5 wt.%, based on the weight of the refractory molding material. Moulding material mixture according to Claim 11 or 12 , whereby the refractory molding material comprises quartz sand. Moulding material mixture according to one of the Claims 11 until 13 , further containing an amine catalyst. Process for producing a moulding material mixture as in one of the Claims 11 until 14 defined, comprising the addition of the substances as defined in any of the Claims 1 until 10 defined components of the binder system and, if necessary, an amine catalyst to form the refractory molding base material. Process for producing a moulding material mixture according to Claim 15 , whereby the binder system is a 2-component system according to Claim 2 and the two components are added to the refractory molding base simultaneously or in any order, and wherein the amine catalyst, if added, is added as a component of the first component. A method for producing a casting mold part or casting core, comprising (a) introducing a molding material mixture according to one of the Claims 11 until 14 into a mold, (b) curing the molding material mixture in the mold, and (c) subsequently separating the cured molding material mixture from the mold to obtain a molded part or a mold core. Procedure according to Claim 17 , wherein the molding material mixture introduced into the mold does not contain an amine catalyst and the curing in step (b) is achieved by passing a gaseous amine catalyst through the molded molding material mixture. Casting part or casting core available according to the process of Claim 17 or 18 . Use of the mould part or the core according to Claim 19 for metal casting.