Moulding material mixture of natural and / or ceramic sands with a phenol-formaldehyde resin-free binder for foundry moulding sands

Abstract

Moulding material mixture of natural and / or ceramic sands with a phenol-formaldehyde resin-free binder for foundry moulding sands, wherein the binder is either ➢as a one-component binder based on polyurethane and / or polyurea, comprising an aromatic or aliphatic oligomeric and / or polymeric isocyanate or a mixture of several aromatic and / or aliphatic oligomeric and / or polymeric isocyanates with partially delayed reactivity, and as an additive a non-functional diluent, wherein the isocyanates consist entirely or partially of pre-crosslinked reaction products, and wherein the pre-crosslinking is brought about by the reaction with di- or polyfunctional polyols with a stoichiometric deficit of hydrogen-active compounds, resulting in a residual content of free isocyanate groups in the range of 5 to 35%, and wherein the one-component binder is suitable for a multi-phase curing process using water-alcohol mixtures, or ➢ as a two-component binder based on polyurethane and / or polyurea, comprising . a component A with an average hydrogen functionality of 2.0 to 3.9, with an average equivalent weight of 450 to 900 g / eq of the reactants and with functional and / or non-functional additives that control the reactivity, non-functional admixtures that promote processability and ensure stability, wherein the reactants of component A are polyether alcohol mixtures of hydroxyl and / or mercapto groups and / or internal nitrogen-containing individual components, wherein the hydrogen-active compounds of the mixture of component A • two- to eight-functional polyether alcohols obtained by anionic or cationic ring-opening polymerization of cyclic ethers and simultaneous addition of the resulting polyether chains to OH / NH starter molecules and / or • Polythiols resulting from the esterification reaction of 3-mercaptopropionic acid with two or more alcohols or which are hydrogen-active polysulfide polymers with free SH groups, are selected and combined, and • an isocyanate-containing component B is present.

Description

[0001] The invention relates to a molding material mixture made of natural and / or ceramic sands with a phenol-formaldehyde resin-free binder for foundry molding sands. Such binders are environmentally and health-neutral due to the absence of phenol-formaldehyde resin and aromatic solvents. They are suitable for established core and mold manufacturing processes. The invention also relates to a molding material curing process.

[0002] The production of lost molds for the foundry industry, which are made from special foundry sands bonded with inorganic or organic binders and are latently stable, has been practiced for more than half a century and has been subject to continuous development in order to meet the growing demands of modern foundry technology.

[0003] The inorganic binders consist mainly of mixed silicates with a main proportion of different types of water glass, the composition of which significantly influences the curing behavior of the molding base material mixed with them.

[0004] Phenolic, furan or urea resins or mixtures thereof are predominantly used as organic binders, with catalysts being added to control the curing rate depending on the requirements of the molding process.

[0005] For cores – unlike molds – particularly stringent demands are placed on the mechanical properties of the molding materials, as these create the internal cavities of the casting. They must withstand the high thermal stresses of the molten metal that completely surrounds them during casting, yet contain as little binder as possible. This binder burns upon prolonged contact with the molten metal. The resulting gases must be removed from the mold. During this phase, casting defects can occur if the outgassing capacity of the surrounding molding material is insufficient to quickly dissipate the gases formed.

[0006] Phenol-formaldehyde resins have proven to be technically suitable for core molding. They consist of an OH-functional component A and a component B containing predominantly isocyanates. When mixed with the mold base material, these resins react with each other to form polyurethane addition products, thereby firmly bonding the sand particles for the duration of the casting process.

[0007] The phenol-formaldehyde compounds of component A, which carry at least two free hydroxyl groups, are diluted with various functionally neutral extenders and other additives that promote the polyurethane reaction and / or sand binding for the purpose of improved processability.

[0008] The B component also contains an isocyanate that is at least difunctional, predominantly of the liquid diphenylmethane diisocyanate type.

[0009] For example, WO 91 / 09908 and DE 29 23 840 A1 describe various binders based on phenolic resin-containing A components and isocyanate-containing B components as well as processes for their use.

[0010] Depending on the requirements of the foundry process, various core manufacturing processes are used when using phenol-formaldehyde resins. The cold box process is particularly widespread. This process, in which amine gassing achieves almost instantaneous curing of the mold core, is particularly suitable for automated core manufacturing. The so-called cold box process is explained in numerous publications, such as US Pat. No. 3,409,579 A, ​​DE 2,162,137 A, and DE 1,959,023 A.

[0011] The No-Bake or Pep Set ®The process, on the other hand, dispenses with the environmentally relevant amine fumigation and achieves the hardening of the binder-molding sand mixture by combining the reactive A and B components immediately before it is introduced into the mold. Depending on the nature of the planned casting, a catalyst is added in different concentrations to accelerate the hardening of the molding material mixture.

[0012] However, the use of phenol-formaldehyde resin binders is associated with numerous significant disadvantages, including the physiological workplace stress during all processing steps and the environmental hazards posed by the landfilling of contaminated used sand. These disadvantages result from the use of odorous, harmful, and toxic materials, as defined by the European Regulation on the Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH), and therefore require labeling. The harmful health effects are present in gaseous emissions during both core molding and casting, and represent a further, and above all, costly, problem when disposing of used sand.

[0013] Despite numerous efforts to reduce the harmful components in phenol-formaldehyde resin binders, as described, for example, in DE 19 529 030 A1 and DE 10 2008 055 042 A1, the fundamental hazard associated with this class of substances cannot be completely eliminated. It manifests itself in a strong, harmful, and persistent odor and hazardous substance pollution in the workplace, as well as in environmentally relevant contamination of the sand released for landfill disposal from the molding and casting processes. For example, when using phenol-formaldehyde resin binders, it is not possible to achieve the phenol index limit relevant for sand landfilling for classification in landfill class 1 according to the current Landfill Ordinance, which in turn further increases the already costly waste disposal in the foundry industry.

[0014] One way to reduce the phenol-formaldehyde resin content in the binder is to partially replace it with polyether polyols or similar hydroxyl-containing compounds. For example, polyether alcohols based on polyfunctional diamines are used as a minor component, as described in US Pat. No. 4,273,700, to control reactivity in an otherwise phenolic resin-based system. EP 1 375 028 A1 describes a similar application, also in combination with glycol monoethers in the resin component. The addition of such amino polyols has a positive effect on the hardness of the molding material. On the other hand, it increases the nitrogen load in the binder. Elements such as nitrogen, sulfur, and phosphorus in the binder are known to lead to casting defects, thus negating the advantage of increased strength. The use of amine-based polyols as the main component of the resin component is therefore not recommended.The pollution caused by the remaining phenolic resin components cannot be eliminated in this way anyway. The use of only one polyether polyol in the resin component is disclosed, among other things, in WO 94 / 05447.

[0015] To adapt the processing properties of cold resin binders to the requirements of core molding, they are typically diluted with various solvents or fillers. Among other things, aromatic hydrocarbons such as Solvesso™ 100 and Solvesso™ 150 are used for this purpose. These hydrocarbons are problematic due to their harmful emissions during processing and casting.

[0016] DE 10 2008 021 980 A1 describes catalysts used in the production of polyisocyanate polyaddition products. These catalysts can be used, among other things, for the production of binders. For example, a polyurethane production process is disclosed in which Desmodur ® N3390BA, an HDI polyisocyanate, with Desmophen ® A870BA, a polyacrylate with hydroxyl groups, and a catalyst.

[0017] US 2006 / 0014917 A1 discloses a polyurethane adhesive composition comprising a high molecular weight component selected from the group consisting of polyols, polyamines, and mixtures thereof; a proton donor; and a polyisocyanate consisting of a mixture of a first isocyanate isomer and a second isocyanate isomer. The first isocyanate isomer has a higher reaction rate than the second isocyanate isomer. The first isocyanate isomer reacts with the proton donor to increase the concentration of the second isocyanate isomer as a proportion of the total unreacted isocyanate.

[0018] DE 27 59 262 A1 discloses a polyurethane-based binder system for molding material mixtures used to produce casting molds and cores. The binder system comprises a polyisocyanate with at least two NCO groups in the molecule and a polyol with at least two OH groups in the molecule, for example, a condensation resin containing OH groups, as reactants, a tertiary amine or, optionally, an organometallic compound as accelerator, and a solvent consisting of or containing esters. Esters used are those whose acid component is either an aliphatic dicarboxylic acid with six to twelve carbon atoms or a benzenepolycarboxylic acid with three or more COOH groups, and whose alcohol component is an aliphatic, cycloaliphatic, arylaliphatic, or aromatic alcohol with six to thirteen carbon atoms.

[0019] DE 10 2010 051 567 A1 describes a binder for molding material mixtures. This binder comprises (A) one or more polyol compounds having at least two hydroxyl groups per molecule, wherein at least one phenolic resin is present as the polyol compound, and (B) one or more isocyanate compounds having at least two isocyanate groups per molecule, wherein at least one isocyanate compound having at least two isocyanate groups per molecule is present as the isocyanate compound. Furthermore, the binder contains at least one urethonimine group and / or carbodiimide group per molecule.

[0020] The object underlying the invention is to avoid the disadvantages of phenol-formaldehyde resin binders and to provide a molding material mixture with a binder for foundry molding sands, in which this class of material and raw materials subject to labeling can be completely dispensed with.

[0021] The invention is achieved by a molding material mixture of natural and / or ceramic sands with a binder system having the features of claim 1. Advantageous further developments are specified in the dependent claims.

[0022] The solution to the problem of the invention consists in a molding material mixture of natural and / or ceramic sands with a phenol-formaldehyde resin-free binder for foundry molding sands, wherein the binder is either • as a one-component binder based on polyurethane and / or polyurea with contents of free isocyanate groups in the range of 5 to 35%, which is suitable for a multi-phase curing process using water-alcohol mixtures, or • as a two-component binder based on polyurethane and / or polyurea, comprising ◯ a component A with an average hydrogen functionality of 2.0 to 3.9, which corresponds to the number of reactive hydrogen atoms of hydroxyl, mercapto-amino or carboxyl groups present in the molecules, with an average equivalent weight of 450 to 900 g / eq of the reactants as well as with functional and / or non-functional additives that control the reactivity, non-functional additives that promote processability and ensure stability, wherein the reactants of component A are polyether alcohol mixtures of individual components containing hydroxyl and / or mercapto groups and / or internal nitrogen, and ◯ an isocyanate-containing component B is present.

[0023] Individual components containing internal nitrogen do not contain terminal amino groups. Component B of the two-component mixture corresponds to the isocyanate component of the two-component binder.

[0024] In this way, organic binders suitable for foundry use, odorless, easy to process, physiologically harmless and largely neutral to used sand are designed, which can not only partially but completely replace the currently used and harmful phenol-formaldehyde resin-based binders.

[0025] The invention leverages the capabilities of highly specialized polyurethane chemistry by specifically combining innovative products from this polymer sector to create novel binder components, whose effectiveness is further optimized through special additives, such as organic compounds containing heteroatoms and / or surfactants, depending on the specific core production application. The invention includes one-component and two-component systems, but in all cases they are based on the basic polyurethane reaction, in which active hydrogen atoms react with isocyanate groups to form polyurethane and / or polyurea structures.

[0026] The present invention avoids the use of aromatic solvents and instead prefers special combinations of fillers based on renewable raw materials as well as synthetic carboxylic acid esters and organic silicon compounds.

[0027] Binders produced in this way are virtually odorless, have low vapor pressure, easy-to-process viscosity, and impart good flowability to the mold base material, optimal curing speed and dimensional stability, as well as high strength values, making them ideal for core production. During casting, the molds prove stable from pouring to cooling, but can then be easily separated from the casting. During core setting and casting, emissions are significantly lower in volatile organic compounds, aromatic hydrocarbons, and olfactory off-gassing compared to phenol-formaldehyde resin-based binders.

[0028] The two-component binders are suitable for both the No-Bake and Pep Set ® - as well as in special designs for the widely used cold box process, where the no-bake or pep set ®The process is preferred because it does not require environmentally harmful amine fumigation. The one-component systems are cured in the binder-molding sand mixture according to the invention using a process also according to the invention, in which water or water-alcohol mixtures in liquid, gaseous, or aerosolized form are passed through the binder-sand mixture. This process is based on the reaction of isocyanates with water to form polyureas, and on the reaction of the alcohols with isocyanates to form tightly cross-linked polyurethane structures, which impart a particularly strong structure to the molding sand.

[0029] According to the invention, the one-component binder comprises an aromatic or aliphatic oligomeric and / or polymeric isocyanate or a mixture of several aromatic and / or aliphatic oligomeric and / or polymeric isocyanates with partially delayed reactivity, and, as an additive, a non-functional diluent, also referred to as an extender, and optionally a catalyst. The isocyanates of the one-component binder advantageously have at least a functionality of 2.In principle, all commercially available diisocyanates are suitable for one-component systems, such as oligomeric or polymeric variants of the basic type of 2,4'- and 4,4'-diphenylmethane diisocyanate and / or oligomeric or polymeric variants of the type 2,4'- and 4,4'-dicyclohexylmethane diisocyanate and / or oligomeric or polymeric variants of naphthylene diisocyanate and / or oligomeric or polymeric derivatives of hexamethylene diisocyanate with optionally fully or partially blocked isocyanate groups and / or isophorone diisocyanate and / or its derivatives, because all of them, without exception, react with water to form polyureas, although they have large differences in terms of reactivity to active hydrogen atoms, which are structurally dependent.

[0030] For example, diphenylmethane diisocyanates or naphthylene diisocyanates generally have a higher reactivity than cycloaliphatic or aliphatic diisocyanates due to their aromatic structure, although there are still significant differences in reactivity depending on the isomer distribution. Unlike aromatic isocyanates, isocyanates with biuret or isocyanurate structures only react at higher temperatures, which can be advantageous for specific applications. Taking the reactivity of the respective isocyanate into account, customized one-component binders can be designed that can be adapted to the specific application.

[0031] Suitable isocyanates for one-component binder systems include Lupranate ® from the product range of BASF, the Desmodur ® -Types from Bayer, the Voranate ® the Dow Chemical company, the Vestanate ®from Evonik, Tolonate™ from Vencorex or Ongronate ® from BorsodChem. The above-mentioned suitable isocyanates include, in particular, Lupranat ® M70R, Lupranat ® MM103, Lupranat ® M 105, Lupranat ® MIP, Desmodur ® VLR20, Desmodur ® CD-S, Desmodur ® DN, Desmodur ® I, Desmodur ® W / 1, Vestanat ® IPDI, Vestanat ® H12MDI, Vestanat ® TMDI, Vestanat ® HT 2500 / LV, Tolonate™ HDB LV, Tolonate™ HDT LV, Ongronat ® 3800, Ongronat ® CR-30-20, Ongronat ® CR-30-40, Ongronat ® CR-30-60.

[0032] In this way, largely storage-stable one-component binder systems can be produced in a mixture with one or more non-functional diluents, such as fatty acid esters, synthetic carboxylic acid esters, sulfonic acid esters, alkyl silicates and special catalysts that promote the reaction of the isocyanate group with water, which only develop their full reactivity upon contact with gaseous, liquid or aerosolized water or water-alcohol mixtures.

[0033] Catalysts suitable for this purpose include organotin and organoaluminium compounds, but also nitrogen-containing compounds such as dimethylcyclohexylamine, N-substituted pyrrolidones, N-substituted imidazoles, triazine derivatives, diazabicyclooctane or quaternary ammonium salts in various preparations.

[0034] Suitable tin catalysts include the Kosmos ® types from Evonik, while King Industries with K-Kat ®5218 offers a suitable aluminum-containing catalyst. BASF offers Lupragen ® series offers a wide selection of catalysts with tertiary nitrogen. A quaternary ammonium salt for catalyzing the polyurethane reaction is, for example, BYK ® -ES 80.

[0035] A particular advantage of the invention has proven to be the use of the isocyanates in a pre-crosslinked form. For this purpose, the isocyanates are reacted in a stoichiometric excess with certain polyols to form prepolymers with a precisely determinable residual content of free isocyanate groups, which should be at least 5%. According to the invention, such pre-crosslinking is achieved by reaction with a stoichiometric deficit of di- or polyfunctional polyols, preferably resulting in a residual content of free isocyanate groups between 6 and 30%.

[0036] Furthermore, such prepolymers must have a processing-friendly viscosity that ensures good mixing with the molding material and is therefore a maximum of 900 mPas, but preferably 300 to 600 mPas, at 20 °C.

[0037] Particularly suitable crosslinking polyols for the preparation of the prepolymers according to the invention are long-chain di- or trifunctional polyether alcohols with molecular weights of 2000 to 6000 g / mol, which have been prepared by alkali-catalyzed synthesis. Such polyols are, for example, Voranol ® CP 6055 from Dow Chemical, the desmophenes ® 5031 BT, 3900 and 3600Z from Bayer, the Lupranole ® 2090 and 1000 / 1 from BASF. However, it is also possible to use polyols with lower molecular weights for prepolymer formulation if the resulting viscosity can be kept below 1000 mPas at 20 °C. Such short-chain polyols include Lupranols. ®P400 and CP 260 from Dow Chemical. Impact polyols are unsuitable because the prepolymers produced with them lack sufficient stability due to their residual catalyst content.

[0038] Compared to application-oriented isocyanate selection, the use of one-component prepolymer systems offers another option for specifically optimizing the mold base / binder mixture. This approach, for example, achieves significantly higher elasticity, which is crucial for the production of some core molds.

[0039] The one-component binders are produced by intensive mixing at room temperature, excluding atmospheric humidity. Moisture ingress during production and subsequent storage must be strictly avoided, as otherwise the isocyanate contained will react prematurely. Partially pre-crosslinked one-component binders must be allowed to sit for at least 24 hours before use, but preferably three to five days after production, to allow prepolymer formation to complete. This can be monitored by determining the content of free isocyanate groups.

[0040] The core production with the one-component binder systems is carried out according to a curing process according to the invention, in which the molding material mixture of molding sand and binder is cured with liquid and / or gaseous and / or aerosolized water-alcohol mixtures or even just with water, wherein the curing takes place with water and / or water-alcohol mixtures in liquid, gaseous or aerosolized form in the temperature range from 20 to 150 °C, preferably 20 to 120 °C, and at pressures from 0.2 to 5 bar, preferably 0.5 to 2 bar.Preferably, the molding material mixture is brought into contact with water or a water-alcohol mixture in a closed system at temperatures between 20 and 120 °C, possibly under pressure, in accordance with the cold box process. The mixture is then blown dry with compressed air at a temperature between 20 and 120 °C to expel excess water or alcohol from the core. However, it is also possible to carry out the process in two steps, with the alcohol being passed through the molding material first and then the water or steam. Both variants end with a compressed air rinse. The cores produced in this way can be demolded immediately using the conventional cold box process and have very good compressive and flexural strength.This water-alcohol process has the advantage of avoiding the use of harmful, odorous, and environmentally harmful amines. Suitable alcohols include lower divalent representatives of this class of substances or amino alcohols. Examples include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, and aminoethanol.

[0041] If necessary, the molding material mixtures produced with the one-component binder systems can also be cured using the established cold-box process, i.e. by amine fumigation, but this would involve the environmental and health-related disadvantages described above.

[0042] The two-component systems provided for the molding material mixtures according to the invention preferably consist, on the one hand, of component A with individual compounds which are hydrogen-active with respect to isocyanate and have a total functionality of 2.2 to 3.9, as additive(s), preferably a functionless extender or thinner, optionally a catalyst which promotes the polyurethane reaction, optionally a stoichiometric amount of water and optionally homogenizing additives, and, on the other hand, of component B with isocyanates.

[0043] Preferably, the two-component systems intended for the molding material mixtures according to the invention use balanced combinations of various aliphatic and / or cycloaliphatic compounds that are hydrogen-active with respect to isocyanate instead of phenol-formaldehyde resins in component A. These compounds are polyols, such as polyether alcohols, polyester alcohols, polyether ester alcohols, as well as polythiols, functional polysulfide polymers, amino alcohols, polyhydric alcohols, and optionally also carboxylic acids. According to an advantageous embodiment of the invention, the percentage polyol constituents of component A result in an average equivalent weight of 450 to 900 g / eq, preferably 500 to 800 g / eq.

[0044] The functionality of these hydrogen-active compounds must be at least 2. However, for optimal crosslinking, the combination of difunctional with higher-functional compounds has proven advantageous, with the aim of achieving an optimal average functionality. According to an advantageous embodiment of the invention, the individual constituents of component A are combined such that an average H functionality of 2.2 to 3.9, preferably 2.4 to 3.7, results.

[0045] It is also advisable to incorporate the molar masses of the hydrogen-active compounds and thus their equivalent weights into the formulation of component A to achieve an optimal average equivalent weight. These hydrogen-active compounds are therefore selected and combined in such a way that their functionalities and equivalent weights form a gradient. This achieves optimal crosslinking within the polyaddition product, which is extremely beneficial for the processing properties of the mixed molding material and for the adhesive effect between the sand particles. Almost all commercially available polyether alcohols, amino alcohols, polyhydric alcohols, as well as selected polyester alcohols, polythiols, and functional polysulfide polymers are suitable as hydrogen-active components for component A, provided they have an easily processable viscosity, a low acid number, and a minimal water content.The hydrogen-active components of component A can be, for example, two- to eight-functional polyether alcohols, reactive and non-reactive polymer polyols, polyester alcohols, polyetherpolyester alcohols, polythiols, aminopolyether alcohols, di- and higher-functional alcohols, di- and higher-functional carboxylic acids and mixtures of all these individual components.Particularly suitable are difunctional to eight-functional polyether alcohols which are obtained by anionic or cationic ring-opening polymerization of cyclic ethers, such as propylene oxide, ethylene oxide, tetrahydrofuran and simultaneous addition of the resulting polyether chains to starter compounds such as ethylene glycol, 1,4-butanediol, glycerol, trimethylopropane, pentaerythritol, glucose, sucrose, sorbitol, ethylenediamine, diethylenetriamine and other H-functional starter molecules, as well as polythiols which are formed from the esterification reaction of 3-mercaptopropionic acid with dihydric and higher alcohols, as well as hydrogen-active, i.e. free SH-group-containing polysulfide polymers, which is why the hydrogen-active compounds of the mixture of component A are selected and combined according to the invention from all of these individual components.

[0046] Suitable polyols for the combination in the sense of this invention are again long-chain polyols such as Voranol ® CP6055 from Dow Chemical, the Desmophene ® 5031 BT, 3900 and 3600Z from Bayer, the Lupranole ® 2090 and 1000 / 1 from BASF, but also polyols with lower molecular weights, such as the Voranoles ® CP 260 and P400, the Lupranols ® 1100, 1200, 3300, 3423, 3902, the Desmophene ® 1400 BT, 1380 BT, 4051B, 21 AP25, the polyols 4640 and 4290 from Perstorp, among others. As H-functional sulfur-containing additives, the Thioplast types from Akzo Nobel and the Thiocure ® -Range from Bruno Bock has proven itself.

[0047] Suitable isocyanates for component B of the two-component binder are the aromatic, aliphatic, and cycloaliphatic isocyanates prepared by the one-component process, as well as their oligomers and polymers. The isocyanates preferably have at least a functionality of 2 and are oligomeric or polymeric variants of the basic type of 2,4'- and 4,4'-diphenylmethane diisocyanate and / or oligomeric or polymeric variants of the type of 2,4'- and 4,4'-dicyclohexylmethane diisocyanate and / or oligomeric or polymeric derivatives of hexamethylene diisocyanate with optionally fully or partially blocked isocyanate groups and / or isophorone diisocyanate and / or its derivatives.

[0048] It is also possible to crosslink the isocyanates of component B with polyols beforehand to form the prepolymer and use them in a two-component process. As already mentioned, for this purpose, the isocyanates are reacted in a stoichiometric excess with certain polyols to form prepolymers with a precisely determinable residual content of free isocyanate groups, which should be at least 5%. Such pre-crosslinking is advantageously achieved by reaction with a stoichiometric deficit of di- or polyfunctional polyols, preferably resulting in a residual content of free isocyanate groups between 5 and 35%, particularly preferably between 6 and 30%.

[0049] According to an advantageous embodiment of the invention, component B consists of mixtures of one or more isocyanates with non-functional extenders / thinners and additives ensuring processability, wherein the isocyanate content is in a balanced stoichiometric ratio to the hydrogen-active compounds of component A.

[0050] Both the one-component systems intended for the molding material mixtures according to the invention and the two-component systems intended for other molding material mixtures according to the invention are preferably supplemented and diluted with non-functional extenders or thinners that are exempt from REACH labeling to ensure good processability. Such extenders / thinners include, for example, fatty acid esters based on renewable raw materials, such as transesterification products of rapeseed oil, palm oil, soybean oil, argan oil, safflower oil, linseed oil, or jatropha oil, especially their methyl, but also ethyl, propyl, and isopropyl esters. Synthetic mono-, di-, and tricarboxylic acid esters, for example, based on benzoic acid, adipic acid, succinic acid, malonic acid, maleic acid, sebacic acid, and citric acid, are also suitable.Examples of fatty acid esters from natural oils are the rapeseed methyl ester from Glencore and other established biodiesel producers, the palm and soy methyl esters from Cremer, the Priolube™ types from Croda and RADIA. ® -Esters from Oleon.

[0051] The product ranges of Oxsoft ® - and Oxblue ® -Esters from Oxea, Softenol ® -Esters from Sasol, the dibenzoate esters from Caffaro called Freeflex and the versatile and suitable for packaging thinners such as Mesamoll ® from Lanxess and Hexamoll ® DINCH ® from BASF.

[0052] Other particularly suitable extenders / thinners are organosilicates, especially alkyl silicates and alkyl silicate oligomers, for example tetraethyl silicate, tetra-n-propyl silicate, trialkyl silicates, dialkyl silicates, and monoalkyl silicates. In addition, aromatic-free fractions from petroleum processing, such as selected tudalenes, can be used. ® from Hansen & Rosenthal, can be used individually or in mixtures with the aforementioned extenders or thinners. Sulfonic acid esters are also suitable as extenders / thinners.

[0053] Depending on the composition of the A and B components and the desired processing time in the core manufacturing process, the binders are processed with or without catalytic support. Suitable catalysts include the substance classes described under single-component binders, namely organotin and organoaluminum compounds and tertiary or quaternary nitrogen-containing substances.

[0054] Since the A and B components consist of multi-component mixtures, it has proven advantageous to use homogenizing additives to prevent possible phase separation. The homogenizing additives preferably consist of silicon- or polyacrylate-based emulsifiers and / or cationic or anionic surfactants. Suitable surfactants include anionic, amphoteric, nonionic, and cationic surfactants, as well as their specific forms, such as tertiary ammonium compounds of acrylic acid copolymers and selected polysiloxanes. Well-known commercial products include BYK. ® -P 9908, BYK ® -P 9909, Linda neutral from Linda Waschmittel GmbH or the surfactants from Impag and Julius Hoesch.

[0055] The A and B components are produced by intensively mixing the individual components at room temperature and under exclusion of moisture. When stored dry at room temperature, this results in largely storage-stable two-component systems with processing-friendly viscosities of 300 to 600 mPas / 20 °C for the A side and 300 to 500 mPas / 20 °C for the B side.

[0056] The one-component or two-component binders contained in the molding material mixture according to the invention are suitable for common natural and ceramic foundry sands, such as quartz sands of various origins, chromite sand, mollith sand, Cerabeads, and other types of molding materials. The binder content must be optimized taking into account the respective grain size spectrum and the specific sand weight and is preferably set between 1 and 2 wt.% total content or 0.5 to 1 wt.% per component for the two-component system. Other settings are also possible.

[0057] Depending on the specific formulation, the A and B components can be added in a mixing ratio of 2.5:1 to 1:2.5. However, for practical application in foundries, it has proven advantageous to formulate the binder systems so that they can be used in a mixing ratio of 1:1.

[0058] The invention relates to molding material mixtures made from natural and / or ceramic sands with the aforementioned one-component or two-component binders. Core production with the two-component systems can be carried out using the no-bake or cold-box process. This means that the two-component binders can advantageously be used equally for the no-bake and cold-box processes. While in the no-bake process, the A and B components are only combined shortly before mold filling, in the cold-box process, attention must be paid to a longer sand lifespan because, in view of the time sequences in foundry operations, both components must be present alongside each other for a certain period of time without the polyurethane reaction, which is then only triggered by the amine gassing, starting prematurely.This requirement can be met by various known reaction-retarding, acidic additives, such as phosphoric acid, phosphoryl chloride or other acid chlorides.

[0059] Further details, features and advantages of embodiments of the invention will become apparent from the following description of embodiments.

[0060] The suitability test of the binder systems intended for the molding material mixtures according to the invention was carried out in comparison with the established phenol-formaldehyde resin binders, specifically with the commercially available and widely established phenolic resin binder Pentex ® by Hüttenes Albertus, Düsseldorf. The study compared the strength values, the gaseous emissions during core production and casting with various melts, and the landfill classifications resulting from the analysis of the used sand discharged from the foundry process.

[0061] To determine flexural strength, bending bars were manufactured and measured according to VDG Data Sheets P 72 and P 73. The material for the sand analysis came from technical tests on manual core production and mechanical core shooting. The castings were pump impellers for various units of various sizes. The core breakage and burn-up sands were analyzed in accordance with the binding Landfill Ordinance (DepV, Annex 3, Table 2). Gaseous emissions were measured directly during technical core shooting and directly during casting with aluminum and gray cast iron. The emissions released during this process were recorded according to the key components of VDG Data Sheet R 305 (VDG = Association of the Foundry Industry).

[0062] For a better understanding of the invention, the application for core production in foundries is explained using the present examples in the preferred embodiments, without limiting the invention. All components of the formulations are given as percentages by weight, unless otherwise stated. The samples were cured using the cold-box, no-bake, or inventive curing process with liquid, gaseous, or aerosolized water or a water-alcohol mixture. The flexural strength was compared with the commercially available phenolic resin binder Pentex. ® (Hüttenes Albertus, Düsseldorf).

[0063] Production of test specimens with two-component binders using the no-bake method: The production and measurement of the bending bars complied with VDG Data Sheet P72. 100 parts by weight of sand were mixed with 0.5 to 1 part by weight each of component A and component B in a 1:1 ratio, along with a catalyst in the form of an organotin compound or tertiary amine in a quantity of 0.1 to 1% by weight, based on the total binder quantity, in a laboratory mixer with a planetary gear for approximately one minute. The resulting molding material mixture was poured into a molding box for bending bars measuring 22.4 x 22.4 x 172 mm each and allowed to cure. Example 1: Composition Binder 1 Component APolyol component Component BIisocyanate component Polyether polyol MG 420 15,0 % MDI oligomer 88,5 % Polyether polyol MG 450 14,0 % Fatty acid esters 11,3 % Polyether polyol MG 700 20,0 % Defoamers 0,2 % Polyether polyol MG 6000 20,0 % Dihydric alcohol 7,0 % Water 1,0 % Fatty acid esters 23,0 % Viscosity at 20 °C 470 mPas Viscosity at 20 °C 370 mPas Flexural strength with 1.6% binder and quartz sand H31: 350 N / cm 2 Example 2: Composition Binder 2 Component APolyol component Component BIisocyanate component Polyether polyol MG 200 20,0 % MDI oligomer 88,5 % Polyether polyol MG 420 15,0 % Fatty acid esters 6,3 % Polyether polyol MG 700 5,0 % Alkylsulfonic acid esters 5,0 % Polyether polyol MG 6000 25,0 % Defoamers 0,2 % Aminopolyol 11,0 % Water 0,7 % Fatty acid esters 23,3 % Viscosity at 20 °C 590 mPas Viscosity at 20 °C 500 mPas Flexural strength with 1.6% binder and quartz sand H31: 370 N / cm 2 Example 3: Composition Binder 3 Component APolyol component Component BIisocyanate component Polyether polyol MG 420 15,0 % MDI oligomer 88,5 % Polyether polyol MG 450 14,0 % Alkyl silicate 11,3 % Polyether polyol MG 700 20,0 % Defoamers 0,2 % Polyether polyol MG 6000 20,0 % Dihydric alcohol 6,3 % Water 1,0 % Polythiol 2,0 % Alkyl silicate 7,7 % Fatty acid esters 7,0 % Adipic acid esters 7,0 % Viscosity at 20 °C 440 mPas Viscosity at 20 °C 240 mPas Flexural strength with 1.6% binder and quartz sand H31: 395 N / cm 2 Example 4: Composition Binder 4 Component APolyol component Component BIisocyanate component Polyether polyol MG 420 15,0 % MDI oligomer 1 69,0 % Polyether polyol MG 450 14,0 % MDI oligomer 2 8,6 % Polyether polyol MG 700 20,0 % MDI oligomer 3 8,6 % Polyether polyol MG 6000 20,0 % Fatty acid esters 13,6 % Dihydric alcohol 7,0 % Defoamers 0,2 % Water 1,0 % Fatty acid esters 23,0 % Viscosity at 20 °C 470 mPas Viscosity at 20 °C 90 mPas Flexural strength with 1.6% binder and quartz sand H31: 450 N / cm 2 Example 5: Composition Binder 5 Component APolyol component Component BIisocyanate component Polyether polyol MG 420 15,0 % MDI oligomer 1 62,5 % Polyether polyol MG 450 14,0 % MDI oligomer 2 26,8 % Polyether polyol MG 700 20,0 % Fatty acid esters 10,5 % Polyether polyol MG 6000 20,0 % Defoamers 0,2 % Dihydric alcohol 6,3 % Water 1,0 % Polythiol 2,0 % Fatty acid esters 14,0 % Adipic acid esters 7,7 % Viscosity at 20 °C 615 mPas Viscosity at 20 °C 170 mPas Flexural strength with 1.6% binder and quartz sand H31: 330 N / cm 2 Example 6: Composition Binder 6 Component APolyol component Component BIisocyanate component Polyether polyol MG 420 15,0 % MDI oligomer 73,0 % Polyether polyol MG 450 14,0 % HDI oligomer 20,0 % Polyether polyol MG 700 20,0 % Fatty acid esters 7,0 % Polyether polyol MG 6000 20,0 % Dihydric alcohol 7,0 % Water 1,0 % Fatty acid esters 23,0 % Viscosity at 20 °C 470 mPas Viscosity at 20 °C 750 mPas Flexural strength with 1.6% binder and quartz sand H31: 320 N / cm 2

[0064] Comparative example according to the prior art to a two-component system, which is not part of the invention: For comparison, the phenol-formaldehyde-based cold resin Pentex ® analogous test specimens were prepared. The bending bars were, as indicated, each filled with 0.8 parts by weight of component A in the form of Pentex ® Resin 8243 and the isocyanate-containing component B in the form of the activator GH-E4 from Hüttenes-Albertus, i.e., in a mixing ratio of 1:1, as well as 0.15% 4-(3-phenylpropyl)pyridine as catalyst (Catalyst 1251), based on the binder quantity, were prepared, and the cured flexural bars were tested for their strength. With 1.6% binder and quartz sand H31, the flexural strength was 380 N / cm. 2 .

[0065] The following table shows the bending strengths of the bending rods for selected systems compared with Pentex ®at a 1.6% binder content using quartz sand H31. The values ​​were measured at various intervals after the production of the bending bars. Comparison of flexural strengths: Time / h Flexural strength in N / cm 2 Pentex ® Binder 1 Binder 2 Binder 3 1 70 60 150 50 2 110 140 215 220 4 150 230 300 270 24 380 350 370 395

[0066] Production of test specimens with two-component binders using the cold box method: In order to be able to use the two-component binders intended for the molding material mixtures according to the invention in the cold box process, the sand service life must be adjusted, which is achieved by adding reaction retarders to component B. The molding material mixture with the reaction-retarded component B is first prepared analogously to the no-bake process and then transferred in batches after a storage time of 1, 3, and 5 hours to the flexible rod shooting box according to VDG Data Sheet P73, where it is gassed with triethylamine according to process A and then purged with air. Example 7: Composition Binder 7 Component APolyol component Component BIisocyanate component Polyether polyol MG 420 15,0 % MDI oligomer 88,5 % Polyether polyol MG 450 14,0 % Fatty acid esters 10,5 % Polyether polyol MG 700 20,0 % retarder 0,8 % Polyether polyol MG 6000 20,0 % Defoamers 0,2 % Dihydric alcohol 7,0 % Water 1,0 % Fatty acid esters 23,0 % Viscosity at 20 °C 470 mPas Viscosity at 20 °C 170 mPas Flexural strength with 1.6% binder and quartz sand H32: 320 N / cm 2

[0067] Production of test specimens with one-component binders and water-alcohol curing: 1.6 parts by weight of Binder 8 or 9 were intensively mixed with 100 parts by weight of sand and 1% of a 33% solution of diazabicyclooctane in dipropylene glycol as a catalyst, based on the binder quantity, for 1 minute. The flexible rod locking box according to VDG Data Sheet P73 was again used to produce the flexible bars. Instead of amine gassing as in the classic cold-box process, a mist of water, 1,4-butanediol, and compressed air was introduced via the gas supply device for 2 minutes and then blown dry with compressed air for 2 minutes. The flexible bars were removed and tested for their flexural strength. The system is also cold-box capable, meaning the sand-binder mixture can be stored for 2 hours and only then gassed with the mist of water, 1,4-butanediol, and compressed air without significantly reducing the flexural strength. Example 8: Composition Binder 8 MDI oligomer 62,6 % Polyether polyol, MG 2000 5,0 % Polyether polyol, MG 6000 10,0 % Fatty acid esters 22,2 % Defoamers 0,2 % Viscosity at 20 °C 510 mPas Flexural strength with 1.6% binder and quartz sand H31: 605 N / cm 2 Example 9: Composition Binder 9 MDI oligomer 80 % Polyether polyol, MG 2000 10,0 % Polyether polyol, MG 6000 10,0 % Viscosity at 20 °C 655 mPas Flexural strength with 1.6% binder and quartz sand H31: 400 N / cm 2 List of abbreviations used in the tables (without chemical symbols) H31-H35 Halterner quartz sand varieties (grain size ranges) HDI Hexamethylene diisocyanate MDI Diphenylmethane diisocyanate MG Molecular weight in [g / mol]

Claims

[1] Moulding material mixture of natural and / or ceramic sands with a phenol-formaldehyde resin-free binder for foundry moulding sands, where the binder is either ➢as a one-component binder based on polyurethane and / or polyurea, comprising an aromatic or aliphatic oligomeric and / or polymeric isocyanate or a mixture of several aromatic and / or aliphatic oligomeric and / or polymeric isocyanates with partially delayed reactivity, and as an additive a non-functional diluent, wherein the isocyanates consist entirely or partially of pre-crosslinked reaction products, and wherein the pre-crosslinking is brought about by the reaction with di- or polyfunctional polyols with a stoichiometric deficit of hydrogen-active compounds, resulting in a residual content of free isocyanate groups in the range of 5 to 35%, and wherein the one-component binder is suitable for a multi-phase curing process using water-alcohol mixtures, or ➢ as a two-component binder based on polyurethane and / or polyurea, comprising . a component A with an average hydrogen functionality of 2.0 to 3.9, with an average equivalent weight of 450 to 900 g / eq of the reactants and with functional and / or non-functional additives that control the reactivity, non-functional admixtures that promote processability and ensure stability, wherein the reactants of component A are polyether alcohol mixtures of hydroxyl and / or mercapto groups and / or internal nitrogen-containing individual components, wherein the hydrogen-active compounds of the mixture of component A • two- to eight-functional polyether alcohols obtained by anionic or cationic ring-opening polymerization of cyclic ethers and simultaneous addition of the resulting polyether chains to OH / NH starter molecules and / or • Polythiols resulting from the esterification reaction of 3-mercaptopropionic acid with two or more alcohols or which are hydrogen-active polysulfide polymers with free SH groups, are selected and combined, and • an isocyanate-containing component B is present. [2] Moulding material mixture according to claim 1, characterized by that the isocyanates have at least functionality 2 and are oligomeric or polymeric variants of the basic type of 2,4'- and 4,4'-diphenylmethane diisocyanate and / or oligomeric or polymeric variants of the type of 2,4'- and 4,4'-dicyclohexylmethane diisocyanate and / or oligomeric or polymeric derivatives of hexamethylene diisocyanate with optionally fully or partially blocked isocyanate groups and / or isophorone diisocyanate and / or derivatives thereof. [3] Moulding material mixture according to claim 1 or 2, characterized by that the pre-crosslinking results in a residual content of free isocyanate groups between 6 and 30%. [4] Moulding material mixture according to claim 1, characterized bythat the two-component systems consist, on the one hand, of component A with individual compounds which are hydrogen-active with respect to isocyanate and have a total functionality of 2.2 to 3.9, as additive / additives preferably a functionless diluent, optionally a catalyst which promotes the polyurethane reaction, optionally a stoichiometric amount of water and optionally homogenisation additives and, on the other hand, of a component B with isocyanates, wherein the isocyanates have at least a functionality of 2 and are oligomeric or polymeric variants of the basic type of 2,4'- and 4,4'-diphenylmethane diisocyanate and / or oligomeric or polymeric variants of the type of 2,4'- and 4,4'-dicyclohexylmethane diisocyanate and / or oligomeric or polymeric derivatives of hexamethylene diisocyanate with optionally fully or partially blocked isocyanate groups and / or isophorone diisocyanate and / or derivatives thereof. [5] Moulding material mixture according to claim 4, characterized by that the isocyanates of component B consist completely or partially of pre-crosslinked reaction products with a stoichiometric deficit of hydrogen-active compounds, wherein the pre-crosslinking is brought about by the reaction with di- or polyfunctional polyols and a residual content of free isocyanate groups between 5 and 35%, preferably between 6 and 30%, results. [6] Moulding material mixture according to claim 4 or 5, characterized by that other hydrogen-active components of component A are reactive and non-reactive polymer polyols, polyester alcohols, polyether polyester alcohols, aminopolyether alcohols, di- and higher functional alcohols, di- and higher functional carboxylic acids and mixtures of all these individual components. [7] Moulding material mixture according to one of claims 4 to 6, characterized by that the percentage polyol constituents of component A result in an average equivalent weight of 500 to 800 g / eq. [8] Moulding material mixture according to one of claims 4 to 7, characterized by that the individual components of component A are combined in such a way that an average H functionality of 2.2 to 3.9, preferably 2.4 to 3.7, results. [9] Moulding material mixture according to one of claims 4 to 8 characterized by that component B consists of mixtures of one or more isocyanates with non-functional extenders / thinners and additives ensuring processability, the isocyanate content being in a balanced stoichiometric ratio to the hydrogen-active compounds of component A. [10] Moulding material mixture according to one of claims 1 to 9, characterized bythat the non-functional extenders / thinners are fatty acid esters based on renewable raw materials, synthetic mono-, di- and tricarboxylic acid esters, organosilicates, sulfonic acid esters and / or largely aromatic-free fractions from petroleum processing and that the additives for homogenisation consist of emulsifiers based on silicon or polyacrylate and / or cationic or anionic surfactants. [11] Moulding material mixture according to one of claims 1 to 10, characterized by that the binder content is set between 1 and 2 wt.% with respect to the specific sand weight. [12] Molding material curing process using a molding material mixture according to one of claims 1 to 3, in which the curing of the molding material mixture with water and / or water-alcohol mixtures in liquid, gaseous or aerosolized form takes place in the temperature range from 20 to 150 °C and at pressures from 0.2 to 5 bar. [13] Moulding material curing process according to claim 12, characterized by that ethylene glycol and / or 1,2-propanediol and / or 1,3-propanediol and / or 1,4-butanediol and / or 2,3-butanediol and / or monoethanolamine is / are used as the alcohol component / alcohol components. [14] Use of a molding material mixture according to one of claims 1 and 4 to 11 in a no-bake process or a cold-box process.