Hot-curing mould material for producing cores and moulds in the sand casting process

Abstract

The invention relates to a hot-curing mould material for producing cores and moulds in the sand casting process. This mould material comprises natural and / or ceramic sands and a two-component polyurethane binder free from phenolic resin, and also a heat-activatable catalyst. Said binder takes the form of a two-component polyurethane-based binder, comprising - a two-component phenol- and formaldehyde-free polyurethane-based binder comprising a resin component in the form of a mixture of two or more compounds which are hydrogen-active in respect of isocyanates and which have hydroxyl and / or mercapto and / or amino and / or carbamide groups, with an OH, SH and NH functionality of 1.5 to 8 and equivalent weights of 9 to 2000 g / equiv. of the individual constituents and with an average H functionality of 1.8 to 4.0 and an average equivalent weight of 90 to 200 g / equiv. of the resin component, and comprising a curing component with one or more diisocyanates or polyisocyanates, - a curing component consisting of one or more diisocyanates or polyisocyanates. The at least one thermally activatable catalyst, the activation temperature of which lies between 50 and 170 °C, comprises Brønsted bases and / or Lewis acids which promote the polyurethane reaction and also their associated blocking agents. The mould material comprises one or more refractory and pourable fillers having a medium particle size range from 0.1 to 0.9 mm, and comprises 0.3 to 4.0 % of the binder described, based on the mould base material, and 0.1 to 2.5 % of thermally activatable catalyst, based on the resin component of the binder.

Description

[0001] The invention relates to a heat-curing molding material for the production of cores and molds using the sand molding process. This molding material consists of two-component polyurethane binders, one or more thermally activatable catalysts, and natural and / or ceramic sands. This molding material is characterized by its rapid curing and low emissions, and is suitable for heat-curing and hot-curing core and mold manufacturing processes.

[0002] For the production of "lost" molds and cores in foundries, molding material mixtures are generally prepared by thoroughly blending a binder with a mold base material, placed in a pattern, and demolded after the molding material has hardened. After adding a core (package) and mold halves, the casting is carried out using molten metal. Inorganic or organic binders, such as quartz sand, are used to bond the mold base material.

[0003] Inorganic binders used include swellable clay minerals such as bentonite or aqueous alkali silicate solutions, especially modified water glasses. Organic binders include phenolic, furan, or urea resins, as well as condensates thereof with formaldehyde or mixtures thereof, and also phenolic resin-based two-component polyurethanes.

[0004] Various processes are used to process molding materials into "lost molds" and cores, which can be broadly categorized as either hot-curing or cold-curing processes. These processes will be described and compared below with regard to their process parameters and the binders used. All processes share the common feature that the flowable molding material is initially introduced into a mold, either manually or using compressed air during core shooting. However, the curing step differs between the various processes described.

[0005] With cold-curing self-curing molding material systems, a period of 10 to 90 minutes is allowed after molding, after which the material has cured and can be removed from the model (Pep Set® or no-bake process). Furan resins, phenolic resins, or polyurethanes are examples of suitable binder classes for this purpose. To produce high volumes of cores, cycle times must be reduced to a few seconds to one minute, which can be achieved in cold-curing processes, for example, by gas purging with an amine in a cold-box process.

[0006] Hot curing processes are also used to reduce cycle times and generally differ in temperature range or type of heat input.

[0007] Organic and inorganic binders are available for the various warm and hot-curing processes. For organic binders, a distinction is initially made between hot-box and warm-box processes because different curing temperatures, and thus tooling requirements, result depending on the binder used. Both processes utilize a heated core box or a heated model, which are relatively expensive and made of metal.

[0008] The hot-box process uses binders based on phenolic or furan resins, which cure at temperatures up to 300 °C. The warm-box process, on the other hand, is carried out at only about 150 °C using specially added furan resins as binders.

[0009] Examples of phenol-based hot-box binders include condensates of phenol, urea, formaldehyde, and a low-molecular-weight alcohol, to which aqueous ammonium chloride solution is added as a hardener, as described, for example, in DE 15 69 023 C3. Mixtures of acidic latent hardeners and hexamethylenetetramine are also possible. Due to the masking of the hardener, the reaction only starts upon heating. The hardening agents are adducts of strong acids with weakly basic or polar substances, such as urea or polyols, or heavy metal salts of organic acids, as known, for example, from DE 37 38 902 A1. Hexamethylenetetramine acts as an additional inhibitor to further extend the processing time of the molding compound mixture. Condensation products of aromatic amines with aldehydes are also suitable as inhibitors, as described in DE 30 32 592 C2.

[0010] However, hot-box binders based on phenol-resol resins cause the cores to adhere strongly to the mold even when using release agents and can hardly be removed without damage, as can be seen, for example, in DE 15 70 203 A.

[0011] Furan resin-based hot-box systems contain dihydroxymethylated furan or the corresponding polymers, which, as is known from US 7 125 914 B2, also cure with latent acid catalysts at a temperature of 205 °C in 20 to 40 seconds.

[0012] Disadvantages of existing hot-box and warm-box binder systems include the release of formaldehyde and phenol vapors, or furfuryl alcohol vapors, during core production and—in the case of urea-containing phenolic resins—the release of methyl isocyanate during casting. German patent DE 15 69 023 C3 describes the reduction of free formaldehyde content as one way to lower workplace exposure. Furthermore, this problem can be circumvented by an alternative binder system consisting of an unsaturated polyester resin based on renewable raw materials, bisphenol A epoxy resin, and an imidazole catalyst. Such a binder system is known from German patent DE 100 31 954 A1, which discloses that when using 2% binder for molding material curing, 20 seconds to two minutes at a mold temperature of 200 °C are necessary.Another method for avoiding phenol and formaldehyde emissions involves curing molding materials with epoxy resins and / or epoxy-novolak resins and dicyandiamide or imidazoles as latent catalysts. This is described, for example, in EP 0 423 780 A2. The test specimens can be removed after 20 seconds to two minutes at 150 °C.

[0013] Another disadvantage of conventional hot-box molding compounds is that water released during the condensation reaction must be driven out of the compound to prevent a reverse reaction of the binder or structural defects during casting. According to DE 102 56 953 A1, by using a polyurethane system in which the addition reaction occurs with a heat-melting phenolic resin and a polyisocyanate, the molding compound mixture can be cured at 250 °C in 30 seconds without releasing excess water. However, this method requires a very high energy input, and the incorporation of the phenolic resin is challenging.

[0014] Furan resin condensates containing urea can release nitrogen, leading to gas-induced casting defects known as pinholes. Therefore, systems of phenol-resol resins in alkaline solution have been developed that cure without a catalyst at 230 to 260 °C in 30 to 90 seconds. Such systems are described, for example, in WO 88 / 08763 A1. A further advantage is the low content of free formaldehyde; however, a very hot mold is required, and the binder requirement is relatively high at 2%.

[0015] The Croning process, also known as the mold masking process, also utilizes heat curing, but according to a different principle. Such a process is the subject of GB 876 493 A. The mold base material is coated with a phenol-novolac resin to which hexamethylenetetramine is added. This free-flowing molding material is poured onto a metal plate heated to 250 to 350°C, which represents the model, and hardens there in only one layer. The unbonded molding material can be reused. Due to the excellent flowability of the "dry" sand, thin cross-sections and fine contours can be reproduced particularly well in the casting. However, this process also requires a very high thermal input, and the sand must undergo extensive pretreatment.

[0016] Water glass-based, inorganic binders are increasingly used in foundries. Their molding material strengths are generally lower than those of organic binders, but their emissions during casting are significantly lower. In addition to curing by adding liquid esters or CO₂ gassing, heated molds or hot air are also common. This removes water from the molding material mixture and accelerates curing. In practice, cycle times of two to five minutes are achieved with a hot air flow of 120 to 150 °C, as also described in DE 20 2007 019 185 U1. Hot-box variants have also been described, such as in DE 69 533 438 T2, which enable curing in 30 seconds to 2 minutes with a mold heated to 230 to 260 °C.

[0017] Warm air has the decisive advantage that no expensive, heated core boxes, as used in hot-box or warm-box processes, are necessary; instead, simple plastic models can be used. Warm air heats the core evenly. It doesn't just heat the outer shell in contact with the core box, because the warm air penetrates the core uniformly. With a very hot mold, i.e., a temperature >200 °C, there is also a risk for molding materials containing organic components that the organic component in contact with the mold will burn off before the interior of the core has reached a temperature sufficient for hardening. A suitable device for heating air is described, for example, in DE 20 2006 018 044 U1.

[0018] Organic binder systems are also cured using the hot air method. Suitable binders are aqueous ammonium polyacrylates in combination with metal salts, as described in US 4,678,020 A. The hot air partially decomposes the binder, releasing ammonia and forming water-insoluble metal polyacrylates that bind the molding material. In addition to the hot air at 100 to 150 °C, the core mold was heated to the same temperature.

[0019] Additive manufacturing processes are increasingly complementing traditional core production in foundries. Instead of mixing binder and mold base material and placing it in a mold, sand is applied layer by layer in a box, and a binder is applied at the desired locations. The binders are either self-curing or heat-curing. Heat is applied either after printing is complete, by transferring the box to an oven, or directly during the printing process using infrared radiation. One variant is a further development of the Croning process, described in WO 95 / 32824 A1, in which resin-coated sand is applied layer by layer, and the resin is selectively melted with an infrared laser beam. Due to their limited production speed, such processes are primarily suitable for prototypes and therefore do not compete with series production methods such as hot-box processes.Infrared light only hardens the surface layer of the molding material. Therefore, this process is only suitable for molded parts that are built up layer by layer.

[0020] Thermal hardening of molding materials can also be achieved using microwave radiation. DE 10 2007 027 577 A1 discloses that this method can significantly increase the strength of molding materials, particularly with aqueous alkali silicate binders. The cores can be hardened either in a microwave oven after production using a core shooting machine or directly in a dedicated core shooting machine, as described in DE 11 2016 006 377 T5. In the first case, transporting the cores to the oven represents an additional, error-prone process step. In the second case, however, a dedicated core shooting machine is required, which poses a significant investment barrier for practical application.

[0021] In addition to the previously described use in heat-curing processes, phenol-formaldehyde resins with isocyanate-containing hardeners are particularly well-suited for cold-box curing. This process, involving amine gassing, achieves an almost instantaneous curing of the molding material, forming a polyurethane addition product. It is especially well-suited for automated core manufacturing processes. The cold-box process is described in numerous publications, such as US 3,409,579 A, ​​DE 2,162,137 A, and DE 1,959,023 A.

[0022] German patent application DE 10 2015 118 428 A1 discloses phenol-formaldehyde resin-free binders for foundry molding sands and molding material mixtures made from natural and / or ceramic sands. The binder is either a one-component polyurethane- and / or polyurea-based binder suitable for a multi-phase curing process using water-alcohol mixtures, or a two-component binder. This two-component binder comprises a component A with an average hydrogen functionality of 2.0 to 3.9 and an average equivalent weight of 450 to 900 g / val of the reactants, wherein the reactants of component A are polyether alcohol mixtures of hydroxyl and / or mercapto groups and / or individual components containing internal nitrogen, and an isocyanate-containing component B.The binders are environmentally and health-neutral due to the absence of phenol-formaldehyde resin and aromatic solvents. They are suitable for core and mold making using both cold self-curing (Pep Set®) and amine gas-curing (Cold-Box) processes.

[0023] From DE 693 31 286 T2, a cold-curing foundry mixture is known, comprising a foundry aggregate containing less than 0.2 wt% moisture, where the weight is based on the total weight of the foundry aggregate. Furthermore, the cold-curing foundry mixture comprises a binder, which includes a polyether polyol component having a functionality greater than 2.0, a hydroxyl number of about 200 to about 600, and a viscosity of about 100 cP to about 1000 cP at 25 °C, and an organic polyisocyanate component, wherein the polyether polyol component and the polyisocyanate component are compatible with each other. Finally, the cold-curing foundry mixture comprises about 0.75 wt% to about 2.25 wt%, based on the total weight of the polyether polyol, of a liquid tertiary amine catalyst in the mixture.

[0024] While phenolic resins in cold-box curing processes utilize tertiary gaseous amines as catalysts, the same class of binders is cured using liquid, pyridine-based catalysts in cold self-curing processes. The latter can also be used additively in hot-curing processes. Against this background, relatively little attention has been paid to blocked, thermally activated catalysts, which, on the one hand, enable long processing times for the molding material due to their chemical encapsulation and, on the other hand, achieve very rapid curing of the molding material upon thermal exposure.

[0025] Various methods for blocking amines are known from the literature. For example, the condensation of primary amines with aldehydes or ketones yields the corresponding aldimines or ketimines. Hydrolysis releases the originally used amines again. According to WO 2014 / 040922 A1, blocked amines containing aldimine groups can be used in two-component polyurethane compositions for applications as adhesives, sealants, coatings, or potting compounds.

[0026] When latent amines, especially hydrolyzable or blocked amines, are used, problematic emissions can occur due to the so-called release products, as mentioned in WO 2009 / 080738 A1. These volatile aldehydes and ketones, formed from aldimines or ketimines, sometimes cause odorous and harmful fumes.

[0027] US Patent 3,010,963 A describes quaternary hydroxyalkyl bases of 1,4-diazabicyclo-[2.2.2]octane or imidazole, or their salts, for the production of polyurethane foams. German Patent Applications DE 1,928,475 A and DE 2,404,739 C2 disclosed that this resulted in improved processing reliability of adhesives for polyester fiber materials, as well as of coatings based on polyisocyanates and compounds with hydrogen atoms reactive towards isocyanate groups.

[0028] Blocked amines are also used in epoxy resins. According to WO 2019 / 081581 A1, this achieves longer storage stability for single-component epoxy resin compositions.

[0029] EP 2 864 435 B1 describes the use of ketimines, enamines, oxazolidines, aldimines and / or imidazolidines as blocked amine catalysts for moisture-curing polymer compositions based on a trialkylsilane-terminated sulfur-containing polymer, which can be used as sealants for sealing an opening.

[0030] A very elegant and increasingly used approach involves blocking tertiary amines by reacting them with carboxylic acids, thereby obtaining a well-tuned, heat-latent catalyst system. Such systems, known as amine catalysts with retarding properties, are used in the production of polyurethane foams. This is described, among other sources, in German patent applications DE 699 21 284 T2 and DE 699 26 577 T2.

[0031] EP1 990 387 A1 describes catalysts containing tertiary amine groups for use in polyurethane hot melt adhesives, which can be used to bond plasticizer-containing plastics.

[0032] WO 2011 / 095440 A1 describes the use of blocked tertiary amines, more precisely 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo[2.2.2]octane (DABCO) and / or 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), as latent catalysts that are activated at switching temperatures between 30 and 60 °C and 80 and 150 °C respectively, for the production of polyisocyanate polyaddition products, polyurethane casting elastomers, and for the production of sieves, pigs, rollers, wheels, cylinders, scrapers, plates, cyclones, conveyor belts, squeegees, couplings, seals, buoys and pumps. In WO 2012 / 080226 A1, similar products are prepared using monocarboxylic acid-blocked amidines as latent catalysts for polyisocyanate polyaddition products.

[0033] Thermolatent catalysts based on tertiary amines, which become catalytically active in the range of 50 to 120 °C, can be used in so-called sheet molding compounds for the production of fiber-reinforced composite components. This is also known from WO 2017 / 149031 A1, among other sources.

[0034] US 2 891 025 A describes quaternary imidazolium salts that serve as polymerizable starting materials which, in the form of homo- and co-polymer products, are used as plastics, coatings, adhesives, laminations, casting resins or fiber-forming materials.

[0035] US 2 800 487 A describes polyoxyalkylene-substituted heterocyclic amines and their ammonium salts as surfactant detergents.

[0036] The production and application of latent tetravalent tin catalysts is shown in EP 2 274 092 B1. They represent an alternative to toxic mercury catalysts and are mainly used for the production of foams. For coatings, tin or bismuth catalysts that are complexed with an excess of mercapto compounds and thus blocked are described in WO95 / 29007 A1.

[0037] German patent DE 102014 110 189 A1 describes a cold-box binder consisting of phenolic resin, polyisocyanate, and a blocked tertiary amine or amidine as a co-catalyst. This co-catalyst is not thermally activated but exerts its effect in conjunction with the volatile tertiary amine, for example, triethylamine, which is used as a catalyst in the cold-box process. This reduces the consumption of the volatile amine.

[0038] The organic binders described above consist largely of phenolic resins or furfuryl alcohols. Their monomers are mostly toxic and / or carcinogenic and are released during processing, or at the latest during thermal decomposition during casting, thus posing a risk to employees and the environment.

[0039] The object of the invention is to develop a system used in the molding material consisting of a binder and a suitable catalyst that promotes the curing of the molding material under heat input, which makes it possible to cure the molding material by moderate thermal input according to the warm-box or warm-air process and thereby achieve fast cycle and demolding times that are close to those of the amine gas-curing cold-box process.

[0040] A further aim of the invention is to overcome environmental and occupational safety disadvantages arising from the use of molding compounds containing conventional organic binders, which are cured using warm / hot box and / or warm / hot air processes. This particularly concerns the prevention of the release of emission-relevant substances such as volatile organic compounds (VOCs), phenols, formaldehyde, or hydrolytic degradation products such as aldehydes or ketones.

[0041] The problem is solved by a heat-curing molding material with the features of claim 1, wherein this molding material is suitable for the production of cores and molds using the sand molding process. Further developments are specified in the dependent claims of claim 1.

[0042] The thermosetting molding material according to the invention comprises at least A two-component, phenol- and formaldehyde-free polyurethane-based binder, comprising a resin component as a mixture of two or more hydrogen-active compounds with respect to isocyanates, having hydroxyl and / or mercapto and / or amino and / or carbamide groups, with an OH, SH and NH functionality of 1.5 to 8 and equivalent weights of 9 to 2000 g / val of the individual components and an average H functionality of 1.8 to 4.0 and an average equivalent weight of 90 to 200 g / val of the resin component, and a hardener component comprising one or more diisocyanates or polyisocyanates, one or more thermally activatable catalysts with activation temperatures between 50 and 170 °C, and containing Brønsted bases and / or Lewis acids promoting the polyurethane reaction, as well as their associated blocking agents.wherein the thermally activatable catalyst(s) are adducts of tertiary amines and organic acids (blocking agent) or quaternary ammonium salts, and the catalytically active tertiary amine is intended for release by thermal input between 90 and 170 °C, and one or more refractory bulk fillers.

[0043] The two-component binder in the molding material according to the invention consists, on the one hand, of the resin component with hydrogen-active individual compounds with respect to isocyanate of average functionality of 1.8 to 4.0, preferably as an additive(s) one or more diluents, optionally one or more additives influencing the polyurethane reaction such as catalysts or retarders and optionally homogenizing additives, and, on the other hand, of the isocyanate-containing hardener component.

[0044] Preferably, for the two-component systems according to the invention, balanced combinations of various aliphatic and / or cycloaliphatic compounds that are hydrogen-active with respect to isocyanate are used in the resin component. These compounds are polyether alcohols, reactive and non-reactive polymer polyols, polycaprolactones, polyether polyester alcohols, polythiols, aminopolyether alcohols, di- and higher-functional alcohols, amines, and carbamide compounds. Two or more individual components of one or more of these substance classes are incorporated into the resin component.

[0045] To achieve high molding compound strengths, mixtures of hydrogen-active compounds have proven advantageous. The selection and combination of these isocyanate-hydrogen-active compounds is therefore carried out in such a way that their functionalities and equivalent weights form a gradient. This results in optimal crosslinking within the polyaddition product, which is beneficial for the processing properties of the molding compound and for the adhesive effect between the sand particles. Resin components with an average equivalent weight of 90 to 200 g / val, based on the hydrogen-active components, have proven particularly suitable for this purpose. This average equivalent weight is calculated from the percentage content of OH and / or SH and / or NH groups of the individual components, taking into account their mass fractions in the mixture.

[0046] According to the invention, the individual components of the resin component are selected such that an average H-functionality of 1.8 to 4.0, preferably 2.2 to 3.5, is achieved. For optimal crosslinking, the combination of bifunctional and higher-functional compounds has proven advantageous, with the aim of achieving optimal average functionality.

[0047] Particularly suitable as crosslinking polyols for the production of the resin component according to the invention are di-, tri-, and tetra-functional polyether alcohols. Examples of such polyols are Voranols® from Dow Chemical®, Desmophene® from Covestro®, Lupranols® from BASF®, Isoters® from Coim®, Puranols® from Jiahua®, Lipoxols® from Sasol®, polyglycols from Clariant®, and polyols from Perstorp®. Particularly suitable are, for example, the Voranols ®< CP 260, CP 6055 and P400, the Desmophene ®< 1262 BD, 1300 BT, 1380 BT, 4051B, 5031 BT, 21 AP25, the Lupranols ®< 1000 / 1, 1100, 1200, 2070, 2090, 3300, 3423, 3424, 3902, the Isotere ®< 804SA, 803SA, 809SA, 840G, 860T, the Puranols R3776, F3020, G303, G305, TMP850 and the Polyols 3165, 3380, 4640, 4290. H-functional sulfur-containing additives have proven effective in the Thioplast ®< types from Akzo Nobel ®< and the Thiocure ®< range from Bruno Bock.Suitable polycaprolactones include, for example, Placcel® 205, 305 and 410 from Daicel®, Durez® Ter S 1063-72 and S 2006-120 from Sumitoma Bakelite®, or Capa® 3031, 3022 and 2043 from Ingevity®. As NH-functional compounds, polyetherdiamines such as Jeffamine® D-400 and D-230 from Huntsman®, or even simple structures like diglycolamine, can be used. Polyhydric short-chain alcohols, preferably with a maximum molecular weight of 200 g / mol, include diols such as ethylene glycol, 1,3-propanediol, 2-butyl-2-ethylpropanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,4-butanediol, diethylene glycol, 1,5-pentanediol, 2,2,4-trimethylpentane-1,3-diol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 1,6-hexanediol and 2-ethylhexane-1,3-diol, triols such as glycerol, trimethylolpropane, triethanolamine, tetrols such as pentaerythritol or di(trimethylolpropane) as well as monosaccharides and polysaccharides such as glucose, sucrose and sorbitol.

[0048] According to an advantageous embodiment of the invention, the hardener component consists of mixtures of one or more isocyanates with thinners and additives ensuring processability, wherein the isocyanate content is preferably in a balanced stoichiometric ratio to the hydrogen-active compounds of the resin component.

[0049] Suitable isocyanates for the hardener component of the molding compound according to the invention include oligomeric or polymeric derivatives 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 wholly or partially blocked isocyanate groups and / or isophorone diisocyanate and / or its derivatives, as well as aromatic, aliphatic, and cycloaliphatic isocyanates prepared in a prepolymer process and their oligomers and polymers. Oligomeric and polymeric derivatives of isocyanates include, among others, carbodiimides, isocyanurates, biuretes, uretdiones, and uretonimines. Common blocking agents for isocyanates that can be cleaved again under the influence of heat are phenol, cresol, acetoacetic ester, diethyl malonate, ε-caprolactam and butanone oxime.Preferably, the isocyanates have at least functionality 2 and are liquid at room temperature.

[0050] The aforementioned prepolymers are produced by pre-crosslinking a stoichiometric deficit of di- or multifunctional polyols with suitable aliphatic and / or aromatic and / or cycloaliphatic isocyanates, preferably resulting in a residual content of free isocyanate groups between 5 and 35%, particularly preferably between 6 and 30%. Furthermore, such prepolymers must have a process-friendly viscosity that ensures good mixing with the base material and is therefore a maximum of 900 mPas, but preferably 300 to 600 mPas, at 20 °C. All viscosities specified in connection with the present invention were determined using a rotational viscometer according to DIN 53019.

[0051] Suitable isocyanates for binders of the molding compound according to the invention include, among others, Lupranate® from the product range of BASF®, Desmodur® types from Covestro®, Voranate® and Isonate® from Dow Chemical®, Vestanate® from Evonik®, the Suprasec® series from Huntsman®, Tolonate® from Vencorex®, Polurene® and Hydrorene® from Sapici®, and Ongronate® from Wanhua®. The suitable isocyanates mentioned above include, in particular, Lupranat ®< M 70 R, Lupranat MM ®< 103, Lupranat M ®< 105, Lupranat ®< MIP, Lupranat ®< M 10 R, Lupranat ®< M 20 S, Desmodur ®< 44 V 70 L, Desmodur ®< 44 V 20 L, Desmodur ®< CD-S, Desmodur ®< DN, Desmodur ®< I, Desmodur ®< W / 1, Vestanat ®< IPDI, Vestanat ®< H12MDI, Vestanat ®< TMDI, Vestanat ®< HT 2500 / LV, Suprasec ®< 2030, Suprasec ®< 2085, Tolonate ®< HDB LV, Tolonate ®< HDT LV, Ongronat ®< 3800, Ongronat ®< CR-30-20, Ongronat ®< CR-30-40, Ongronat ®< CR-30-60.

[0052] The binder components of the molding compounds according to the invention, i.e., resin and hardener, are preferably supplemented with thinners to ensure good processability. Such thinners are, for example, fatty acid esters based on renewable raw materials, such as transesterification products of vegetable oils, especially their methyl, ethyl, propyl, isopropyl, butyl, and isobutyl esters. Also suitable are synthetic mono-, di-, and tricarboxylic acid esters, organosilicates, sulfonic acid esters, and / or largely aromatic-free fractions from petroleum refining, phosphoric acid esters, cyclic and non-cyclic carbonates, and / or non-hydroxy-terminal polyethers.

[0053] Examples of fatty acid esters from natural oils include rapeseed methyl ester from Glencore or other established biodiesel producers, palm and soy methyl esters from Cremer, the Priolube® types from Croda®, the DUB® products from Stearinerie Dubois®, and the RADIA® esters from Oleon®. For applications of synthetic carboxylic acid esters, the product ranges of Oxsoft® and Oxblue® esters from Oxea®, Softenol® esters from Sasol®, the Jayflex® products from Exxon®, the Freeflex® dibenzoate esters from Caffaro®, or plasticizers from BASF®, such as Hexamoll® DINCH or Plastomoll®, are available. Suitable organosilicates, especially alkyl silicates and alkyl silicate oligomers, include, for example, tetraethyl silicate, tetra-n-propyl silicate, as well as mono-, di- and trialkyl silicates from Wacker ®< , Evonik ®< and Dow Corning ®< .

[0054] To accelerate the polyurethane reaction of resin and hardener, thermally activatable amine catalysts and / or metal-based catalysts are used to cure the molding material in a heated core box using the warm-box process or in an unheated core box by introducing warm air. These are introduced as part of the resin component and / or added to the molding material as a separate component. The thermally activatable catalyst releases the catalytically active species at temperatures of 50 to 170 °C. The resulting polyurethane reaction of the two-component binder ensures immediate curing of the molding material and allows for the immediate removal of the cured material from the core box. The reaction rate is many times higher than with other common polyurethane catalysts or without any catalyst at all.In contrast to conventional catalysts, the processing open time at room temperature remains largely unaffected when using thermolabile catalysts.

[0055] Thermally activatable catalysts include, for example, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-diazabicyclo[2.2.2]octane (DABCO), bis(2-dimethylaminoethyl) ether, imidazole, piperazine, guanidine, or morpholine derivatives, which are catalytically active and thermally releasable. Possible blocking acids include monocarboxylic acids such as formic acid, dichloroacetic acid, trifluoroacetic acid, or 2-ethylhexanoic acid; dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, cortic acid; and hydroxycarboxylic acids such as citric acid or salicylic acid. Complex thermally releasable catalysts are mostly adducts of tertiary amines with short-chain diols such as ethylene glycol and carboxylic anhydrides such as phthalic anhydride, maleic anhydride or succinic anhydride.

[0056] Suitable examples of quaternary ammonium salts that release tertiary amines upon heating include choline and its derivatives. Furthermore, reaction products of cyclic carboxylic anhydrides and diamines such as N,N-dimethylethylenediamine can also be used.

[0057] Typical latent catalysts include, for example, blocked amine and amidine catalysts from manufacturers such as Evonik® (e.g., Polycat® SA 1 / 10, SA 2 LE, SA 4 and SA-8), Dabco® KTM 60, Tosoh® (e.g., Toyocat® DB 2, DB 30, DB 31, DB 40, DB 41, DB 42, DB 60, DB 70), Huntsman® (e.g., Accelerator DY 9577), and Nitroil® (e.g., PC Cat Q8, PC Cat Q7-2, PC Cat NP93, PC Cat DBU TA). Examples of metal-based latent catalysts are offered by the Thorcat® series from Thor Especialidades®. However, all other latent catalysts from polyurethane chemistry with a so-called switching temperature of 50 °C to 170 °C that fall under the subject matter of the claim can also be used.

[0058] Intensive mixing of the individual components of the resin or hardener of the binder at room temperature and in the absence of moisture yields the respective components with process-friendly viscosities of 200 to 600 mPas at 20 °C for the resin component and 200 to 500 mPas at 20 °C for the hardener component. The resin component of the binder contains 50 to 100%, preferably 70 to 90%, hydrogen-active compounds, and the hardener component of the binder contains 50 to 100%, preferably 80 to 95%, polyisocyanates.

[0059] The described two-component binders, in combination with refractory and free-flowing fillers, are suitable for producing the molding material according to the invention. These natural and ceramic foundry sands are also commonly referred to as molding base materials. They include quartz sands of various origins and grain shapes, chromite sand, zircon sand, olivine sand, R-sand, magnesia, alkali and alkaline earth halides, aluminum silicates such as J-sand and Kerphalite®, synthetic sands such as Cerabeads®, chamotte, M-sand, Alodur®, bauxite sand, silicon carbide, expanded and foamed glasses, fly ash, and other specialty sands. The preferred average grain size is between 0.1 and 0.9 mm.The binder and catalyst content in the molding compound must be optimized taking into account the respective particle size distribution and the specific weight of the sand, and is preferably adjusted to between 0.3 and 4.0%, based on the base molding compound, and 0.1 to 2.5% of thermally activatable catalyst, based on the resin component. The invention is not limited to these settings and quantities.

[0060] The heat-curing molding compound can be produced in a batch or continuous mixer from one or more refractory bulk fillers comprising 95.9 to 99.6%, a binder comprising 0.3 to 4.0%, and one or more thermally activatable catalysts comprising 0.002 to 0.1%.

[0061] The resin and hardener components of the binder can be incorporated in a mixing ratio of 2.5:1 to 1:2.5, depending on the specific formulation. However, for practical application in foundry operations, it has proven advantageous to formulate the binder systems so that they can be used in a 1:1 mixing ratio, based on mass.

[0062] Disadvantages of previous hot-box and warm-box binder systems, such as the release of formaldehyde and phenol or furfuryl alcohol vapors during core production or disruptive water released through a condensation reaction, are avoided when using the molding compound mixture according to the invention.

[0063] In the cold-box process, the use of toxic amine gas is a significant disadvantage. The corresponding equipment requires complex ventilation systems. As a reaction promoter, the amine gas does not react with the molding material and therefore must be continuously removed from the process by an amine scrubber. The present invention avoids these disadvantages. It enables rapid molding material curing, for example, for core production, without the need to use gaseous amines as in the cold-box process.

[0064] The invention utilizes the innovative technology of chemically encapsulated and thermally releasable catalysts. These are used for the thermally induced curing of polyurethane and / or polyurea binders in the molding compound.

[0065] The present invention does not include any harmful aromatic solvents. Instead, fatty acid esters based on renewable raw materials, synthetic carboxylic acid esters, aliphatic carbonates and / or organic silicon compounds are used, which preferably do not contain volatile components.

[0066] The binders and the molding materials themselves exhibit advantageous processing properties such as odorlessness, low vapor pressure, low viscosity, good flowability, adjustable curing rate, and high flexural strength. Cores and molds produced with these materials show low defect susceptibility and good disintegration under casting conditions. Furthermore, emissions of volatile organic compounds, such as aromatic hydrocarbons and formaldehyde, are significantly reduced during casting compared to phenol-formaldehyde resin and furan resin-based binders.

[0067] Due to these advantages and the very short curing times achieved through heat input, the molding materials according to the invention therefore represent an important contribution to a low-emission and highly productive foundry.

[0068] Further details, features and advantages of embodiments of the invention will become apparent from the following description of exemplary embodiments.

[0069] The test conditions were based on VDG Data Sheet P71. To produce the molding compound mixtures of the following binder examples, quartz sand H31 with 1.6% binder (of which 0.8% each was resin and hardener) and the amounts of thermally activatable catalysts (based on the resin quantity) listed in Table 1 were used. These molding compound mixtures were stirred in a laboratory mixer for 60 to 120 seconds, then shot into the heated core box PBH from GF DISA AG using a PLS test specimen firing machine at a firing pressure of 4 bar. The samples were then hardened by heat input from the core box or by introducing heated air. The corresponding molding compound strengths of the resulting test specimens, measuring 22.4 x 22.4 x 175 mm, were determined over time using the LRu-2e universal strength testing apparatus from Multiserw.

[0070] The following describes the composition of the binders used. All percentages [%] in this document are always to be understood as weight percent, unless a different definition is given in the explanatory text. Example 1:

[0071] Composition Binder 1 Resin polyol component Hardener isocyanate component Polyether polyol MG 430 15,5 % MDI oligomer 88,5 % Polyether polyol MG 520 17,5 % Fatty acid esters 11,5 % Polyether polyol MG 860 24,0 % Polyether polyol MG 2920 10,0 % Dihydric alcohol 5,5 % Water 1,0 % Fatty acid esters 26,5 % PC CAT DBU TA 0 - 1,0 % Dabco T-120 0,0075 % Viscosity at 20 °C 180 mPas Viscosity at 20 °C 310 mPas Example 2:

[0072] Composition Binder 2 Resin polyol component Hardener isocyanate component Polyether polyol MG 430 15,5 % MDI oligomer 88,5 % Polyether polyol MG 520 17,5 % Fatty acid esters 11,5 % Polyether polyol MG 860 24,0 % Polyether polyol MG 2920 10,0 % Dihydric alcohol 5,5 % Water 1,0 % Fatty acid esters 26,5 % PC CAT Q8 0,75 % Dabco T-120 0,0075 % Viscosity at 20 °C 180 mPas Viscosity at 20 °C 310 mPas Example 3:

[0073] Composition Binder 3 Resin polyol component Hardener isocyanate component Polyether polyol MG 430 15,5 % MDI oligomer 88,5 % Polyether polyol MG 520 17,5 % Fatty acid esters 11,5 % Polyether polyol MG 860 24,0 % Polyether polyol MG 2920 10,0 % Dihydric alcohol 5,5 % Water 1,0 % Fatty acid esters 26,5 % PC CAT Q7-2 0,75 % Dabco T-120 0,0075 % Viscosity at 20 °C 180 mPas Viscosity at 20 °C 310 mPas Example 4:

[0074] Composition Binder 4 Resin polyol component Hardener isocyanate component Polycaprolactone MG 400 65,0 % MDI oligomer 85,0 % Polyether polyol MG 420 15,0 % Fatty acid esters 15,0 % Polyether polyol MG 440 5,0 % Polyether polyol MG 6000 5,0 % Water 1,0 % Fatty acid esters 6,0 % PC CAT DBU TA 0,5 % Viscosity at 20 °C 450 mPas Viscosity at 20 °C 260 mPas Example 5:

[0075] Composition Binder 5 Resin polyol component Hardener isocyanate component Polyether polyol MG 420 15,0 % MDI oligomer 71,0 % Polyether polyol MG 430 15,0 % HDI-Biuret 20,0 % Polyether polyol MG 500 21,0 % Fatty acid esters 9,0 % Polyether polyol MG 6000 20,0 % Dihydric alcohol 7,0 % Water 1,0 % Fatty acid esters 21,0 % PC CAT DBU TA 0,5 - 0,75 % Dabco T-120 0,0075 % Viscosity at 20 °C 550 mPas Viscosity at 20 °C 650 mPas Example 6:

[0076] Composition Binder 6 Resin polyol component Hardener isocyanate component Polyether polyol MG 200 18,0 % MDI oligomer 82,0 % Polyether polyol MG 3500 10,0 % Polyether polyol MG 6000 10,0 % Polycaprolactone Mg 250 5,0 % Ethyl silicate 8,0 % Polycaprolactone MG 530 33,0 % Dihydric alcohol 7,0 % Dihydric alcohol 2,5 % Water 0,5 % Fatty acid esters 20,0 % Propylene carbonate 4,0 % PC CAT DBU TA 0,75 % Viscosity at 20 °C 320 mPas Viscosity at 20 °C 340 mPas Example 7:

[0077] Composition Binder 7 Resin polyol component Hardener isocyanate component Polyether polyol MG 200 16,0 % MDI oligomer 82,0 % Polyether polyol MG 3500 5,0 % Polyether polyol MG 6000 10,0 % Polycaprolactone MG 550 35,0 % Ethyl silicate 8,0 % Polycaprolactone MG 1560 10,0 % Dihydric alcohol 7,0 % Dihydric alcohol 2,5 % Water 0,5 % Fatty acid esters 20,0 % Propylene carbonate 4,0 % PC CAT DBU TA 0,75 % Viscosity at 20 °C 800 mPas Viscosity at 20 °C 340 mPas Comparative example 1 (not according to the invention):

[0078] Composition: Phenolic resin binder, Pep Set® Resin polyol component Hardener isocyanate component Modified phenolic resin ~75 % MDI oligomer ~85 % phenol ~8 % Solvent Naphtha 180-210 ~15 % formaldehyde <0,4 % Solvent Naphtha 180-210 ~15 % PC CAT DBU TA 0 - 0,5 % Viscosity at 20 °C 300 mPas Viscosity at 20 °C 60 mPas Comparative example 2 (not according to the invention):

[0079] Composition: Phenolic resin binder, cold box Resin polyol component Hardener isocyanate component Phenolic resin ~65 % MDI oligomer ~80 % phenol ~7,5 % Propylene carbonate ~20 % Methanol <0,3 % Glycoxylic acid ~0,2 % Hydrogen fluoride ~0,1 % Aromatic hydrocarbons ~25 % Dibasic esters ~5 % PC CAT DBU TA 0 - 0,5% Viscosity at 20 °C 150 mPas Viscosity at 20 °C 40 mPas

[0080] The following Table 1 presents the test results with the described embodiments and non-inventive comparative examples V1 and V2.

[0081] The data indicate that a thermally activated catalyst is absolutely necessary to achieve short curing times. In most cases, the final strength (24-hour value) is almost reached after the test specimens have completely cooled (1-hour value).

[0082] The comparative examples V1 and V2 show that the method according to the invention is not suitable for phenol-formaldehyde resin-based binders. The Pep Set® binder V1 requires significantly longer curing times than the variants according to the invention. Comparative binder 2 is a classic cold-box binder. The molding materials with comparative binder 2 are not heat-curable. Presumably, additives in the binder inhibit a reaction of the thermolatent catalyst. Table 1 Nr. Proceedings Category quantity [%] T [°C] Time [s] Heat resistance [N / cm²< ] Cold strength for 1 hour [N / cm²< ] Cold strength 24 hrs. [N / cm²< ] 1 WB 0,5 90 180 35 425 575 1 WB 0 110 240 50 420 475 1 WB 0,25 110 120 50 355 425 1 WB 0,5 110 90 45 300 545 1 WB 0,75 110 60 80 450 475 1 WB 1,0 110 45 60 430 515 1 WB 0,5 130 75 45 440 495 1 WB 0,5 150 60 60 425 475 1 WB 0,5 170 45 55 440 495 1* WL 0 110 300 - - - 1 WL 0,5 110 150 95 405 505 1 WL 1,0 110 90 85 450 465 2 WB 0,75 110 90 40 285 380 3 WB 0,75 110 90 40 270 385 4 WB 0,5 110 90 70 380 440 5 WB 0,5 110 120 45 280 335 6 WB 0,75 110 90 55 405 410 7 WB 0,75 110 60 40 275 290 V1 WB 0 110 240 45 470 560 V1 WB 0,5 110 180 35 445 515 V2* WB 0 110 240 - - - V2* WB 0,5 110 240 - - - * no hardening List of abbreviations used in the tables (excluding chemical symbols)

[0083] DABCO Diazabicyclo[2.2.2]octane DBU 1,8-Diazabicyclo[5.4.0]undec-7-ene H31 Haltern quartz sand variety (grain size range) HDI Hexamethylene diisocyanate MDI Diphenylmethane diisocyanate MGM Molecular weight in [g / mol] WBW Warm-Box WL Warm air

Claims

1. A hot-curing mould material for producing cores and moulds in the sand casting method, at least comprising ➢ a two-component binding agent free from phenol and formaldehyde based on polyurethane, containing a resin component as a mixture of two or more compounds which are hydrogen-active with regard to isocyanate with hydroxyl and / or mercapto and / or amino and / or carbamide groups with an OH-, SH- and NH-functionality of 1.5 to 8 and equivalent weights of 9 to 2000 g / val of the individual parts and an average H-functionality of 1.8 to 4.0 and an average equivalent weight of 90 to 200 g / val of the resin component and a hardener component with one or more diisocyanates or polyisocyanates, ➢ one or more thermally activatable catalysts, whose activation temperatures are between 50 and 170°C, having Brönsted bases and / or Lewis acids promoting the polyurethane reaction, as well as their associated blocking agents, wherein the one or more thermally activatable catalysts are adducts of tertiary amines and organic acids (blocking agents) or quaternary ammonium salts and the catalytically active tertiary amine is provided for release through thermal input between 90 and 170°C, and ➢ one or more refractory pourable fillers.

2. The hot-curing mould material according to claim 1, characterised in that the two-component binding agent comprises, on the one hand, a resin component with individual compounds which are hydrogen-active with regard to isocyanate with the average functionality of 1.8 to 4.0, one or more diluents as an additive / additives, optionally one or more catalysts or retardants influencing polymerisation and, on the other hand, a hardener component, containing one or more isocyanates which possess at least functionality of 2, as well as one or more diluents as an additive.

3. The hot-curing mould material according to claim 1 or 2, characterised in that the hydrogen-active parts of the resin component of the binding agent are selected from one or more substance classes comprising polyether alcohols, reactive and non-reactive polymer polyols, polycaprolactones, polyether polyester alcohols, polythiols, aminopolyether alcohols, two- or higher functional alcohols, amines and carbamide compounds.

4. The hot-curing mould material according to any one of claims 1 to 3, characterised in that the individual parts of the resin component are combined so that an average H-functionality of 2.2 to 3.5 results.

5. The hot-curing mould material according to any one of claims 1 to 4, characterised in that the isocyanates of the hardener component are oligomeric or polymeric derivatives of the basic type of the 2,4'- and 4,4'-diphenylmethane diisocyanate and / or oligomeric or polymeric derivatives of the type of the 2,4'- and 4,4'-dicyclohexylmethane diisocyanate and / or oligomeric or polymeric derivatives of the hexamethylene diisocyanate with optionally fully or partially blocked isocyanate groups and / or isophorone diisocyanate and / or derivatives thereof.

6. The hot-curing mould material according to any one of claims 1 to 5, characterised in that the hardener component consists of one or more isocyanates with diluents as well as additives guaranteeing processability, wherein the isocyanate proportion is in the balanced stochiometric relation to the hydrogen-active compounds of the resin component.

7. The hot-curing mould material according to any one of claims 1 to 6, characterised in that the resin component of the binding agent has 50 to 100% hydrogen-active compounds and the hardener component of the binding agent has 50 to 100% polyisocyanates.

8. The hot-curing mould material according to any one of claims 1 to 7, characterised in that the catalytically active tertiary amine is provided for release through thermal input between 100 and 130°C.

9. The hot-curing mould material according to any one of claims 1 to 8, characterised in that one or more individual components of thermally activatable catalysts are pre-mixed into the mould material and / or into the resin component.

10. The hot-curing mould material according to any one of claims 1 to 9, characterised in that the one or more thermally activatable catalysts include thermally in situ releasable, catalytically effective amine bases promoting curing of the mould material.

11. The hot-curing mould material according to any one of claims 1 to 10, characterised in that the resin and the hardener component of the binding agent has one or more diluents, wherein these are selected from the substance classes of fatty acid esters based on renewable raw materials, synthetic mono-, di- and tricarboxylic acid esters, organosilicates, sulfonic acid esters, fractions from crude oil processing largely free from aromatics, phosphoric acid esters, cyclic and noncyclic carbonates and non-hydroxy-functionally terminal polyethers.

12. The hot-curing mould material according to any one of claims 1 to 11, characterised in that the filler or the fillers is / are selected from quartz sand, chromite, zirconium sand, olivine sand, R-sand, magnesia, alkaline and earth alkaline halogenides, aluminium silicates such as J-sand and kerphalites, synthetic sands such as cerabeads, chamotte, M-sand, alodur, bauxite sand and silicon carbide, expanded and foam glasses, fly ash and other special sands as well as has / have a medium grain size of 0.1 to 0.9 mm.

13. The hot-curing mould material according to any one of claims 1 to 12, comprising 95.9 to 99.6% of one or more refractory pourable fillers, 0.3 to 0.4% of a binding agent as well as 0.002 to 0.1% of one or more thermally activatable catalysts.

14. Use of a hot-curing mould material according to any one of claims 1 to 13 for employment in the hot box method or in the hot air method, curing between 90 and 170°C, preferably between 100 and 130°C.