DE102019123372B4 - Thermosetting molding material for the production of cores and molds using the sand molding process - Google Patents

Abstract

Thermosetting molding material for the production of cores and molds using the sand molding process, comprising at least
➢a two-component, phenol- and formaldehyde-free polyurethane-based binder containing a resin component as a mixture of two or more compounds which are hydrogen-active with respect to isocyanates and 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/eq 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/eq of the resin component, and a hardener component with one or more diisocyanates or polyisocyanates,
➢one or more thermally activated catalysts, the activation temperatures of which are between 50 and 180 °C, comprising Brönsted bases and/or Lewis acids that promote the polyurethane reaction, as well as their associated blocking agents, and
➢one or more refractory bulk fillers.

Description

The invention relates to a thermosetting molding material for the production of cores and molds using the sand molding process. It is a molding material made of two-component polyurethane binders, one or more thermally activated catalysts, and natural and/or ceramic sands. This molding material is characterized by its rapid curing and low emissions, as well as its suitability for warm- and hot-curing core and mold manufacturing processes.

To produce "lost" molds and cores in foundries, molding material mixtures are generally prepared by thoroughly mixing a binder with a mold base material, pouring the mixture into a pattern, and removing the molding material after the mold base 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.

Swellable clay minerals such as bentonite or aqueous alkali silicate solutions, especially modified water glasses, are used as inorganic binders. Phenolic, furan, or urea resins, as well as condensates of these with formaldehyde or their mixtures, are used as organic binders, as are phenolic resin-based two-component polyurethanes.

A wide variety of processes are used to process molding materials into "lost molds" and cores. These can generally be divided into hot-curing and cold-curing processes. These will be described and compared below, both in terms of their process parameters and the binders used. What all processes have in common is that the flowable molding material is first introduced into a mold manually or using compressed air during core shooting. The curing step, however, differs in all of the processes described.

For example, with cold-curing molding material systems, a period of 10 to 90 minutes is waited after molding, after which the molding material has cured and can be removed from the model (Pep ^Set® or no-bake process). Examples of suitable binder classes include furan resins, phenolic resins, or polyurethanes. To produce high volumes of cores, cycle times must be reduced to a few seconds to one minute, which can be achieved with cold-curing, for example, by gassing with an amine in the cold-box process.

Heat-curing processes are also used to reduce cycle times and generally differ in the temperature range or the type of heat supply.

Organic and inorganic binders are available for the various warm- and hot-curing processes. Organic binders are initially divided into hot-box and warm-box processes because the binder used results in different curing temperatures and thus different tool requirements. Both processes use a heatable core box or a heatable mold, which are relatively expensive to manufacture from metal.

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.

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

However, hot-box binders based on phenol resol resins lead to the cores adhering strongly to the mold even when release agents are used and can hardly be removed without damage, as is the case, for example, with DE 15 70 203 A emerges.

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

Disadvantages of the current hot-box and warm-box binder systems are 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. DE 15 69 023 C3 The reduction of free formaldehyde content is described as a possibility for reducing workplace exposure. Furthermore, this problem can be circumvented by a different binder system, consisting of an unsaturated polyester resin based on renewable raw materials, bisphenol A epoxy resin, and imidazole catalyst. Such a binder system is known from DE 100 31 954 A1 It is disclosed that when using 2% binder, 20 seconds to two minutes at 200 °C mold temperature are necessary for curing the molding material. Another method to circumvent phenol and formaldehyde emissions is the curing of molding materials with epoxy resins and/or epoxy novolac resins and dicyandiamide or imidazoles as latent catalysts. This is, for example, in the EP 0 423 780 A2 described. After 20 seconds to two minutes at 150 °C, the test specimens can be removed.

Another disadvantage of classic hot-box molding materials is that water released during the condensation reaction must be expelled from the molding material to prevent a reverse reaction of the binder or structural defects during casting. DE 102 56 953 A1 By using a polyurethane system, in which the addition reaction takes place with a heat-melting phenolic resin and a polyisocyanate, the molding material 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 introduction of the phenolic resin is challenging.

Furan resin condensates with urea can release nitrogen, which leads to gas-induced casting defects, so-called pinholes. Therefore, systems of phenol-resole resins in alkaline solution have been developed, which cure without the addition of a catalyst at 230 to 260 °C in 30 to 90 seconds. Such systems are used, for example, in WO 88/08763 A1 Another advantage is the low content of free formaldehyde, but a very hot tool is required and the binder requirement is relatively high at 2%.

The Croning process, also known as the mold shell process, also uses heat curing, but according to a different principle. Such a process is the subject of GB 876 493 A. The mold base is coated with a phenol novolak resin to which hexamethylenetetramine is also added. This free-flowing mold material is poured onto a metal plate heated to 250 to 350°C, which serves as the model, and sets in a single layer. The unbound mold 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 also requires a very high thermal input, and the sand must be extensively pretreated.

Furthermore, water glass-based, inorganic binders are increasingly being 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 gassing with _CO2, heated tools or hot air are also common. This removes water from the molding material mixture and accelerates the curing process. In practice, cycle times of two to five minutes are achieved with a hot air flow of 120 to 150 °C, as is also the case with DE 20 2007 019 185 U1 There were, for example, in the DE 69 533 438 T2 Hot-box variants are also described, which enable curing in 30 seconds to 2 minutes at a tool temperature of 230 to 260 °C.

Hot air has the decisive advantage that expensive, heatable core boxes, as with the hot-box or warm-box process, are not required; instead, simple plastic models can be used. The core is heated evenly by hot air. Not only the outer shell adjacent to the core box is heated, because the warm air penetrates the core evenly. When a tool is heated to a very high temperature, i.e., to a temperature of >200 °C, there is a risk of molding materials with organic components. There is also the risk that the organic component in contact with the tool will already burn, while the interior of the core has not yet reached a temperature sufficient for hardening. A suitable device for heating air is used, for example, in DE 20 2006 018 044 U1 described.

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

Additive manufacturing processes are increasingly complementing traditional core production in foundries. Instead of mixing binder and mold base material and pouring them into a mold, sand is applied layer by layer in a box, and a binder is applied to the desired areas. The binders are self-curing or heat-curing. Heat is applied either after printing is complete, by transferring the box to a furnace, or directly during the printing process using infrared radiation. One variant is a further development of the Croning process, which is used in the WO 95/32824 A1 In this process, resin-coated sand is applied layer by layer, and the resin is melted selectively 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. The infrared light only hardens the surface layer of the molding material. The process is therefore only suitable for molded bodies that are built up layer by layer.

Thermal curing of molding materials can also be achieved by microwave radiation. DE 10 2007 027 577 A1 It is known that, particularly with aqueous alkali silicate binders, a significant increase in the strength of the molding material can be achieved. The cores can be hardened either after production with a core shooter in a microwave oven or by direct production in a special core shooter, as described in DE 11 2016 006 377 T5 In the first case, transport to the furnace represents an additional, error-prone process step. In the second case, however, a special core shooter is required, which represents a high investment barrier in practice.

In addition to the previously described use in heat-curing processes, phenol-formaldehyde resins are particularly hardened with isocyanate-containing hardeners in the cold-box process, in which amine gassing achieves an almost instantaneous curing of the molding material with the formation of a polyurethane addition product, and which is particularly suitable for an automated core manufacturing process. The cold-box process is explained in numerous publications, such as US 3 409 579 A , DE 2 162 137 A or the DE 1 959 023 A.

While phenolic resins utilize tertiary gaseous amines as catalysts in the cold-box process, the same class of binders is cured with liquid, pyridine-based catalysts when used in cold-self-curing processes. The latter can also be used additively in a heat-curing process. Against this background, relatively little attention has been paid to blocked, thermally activated catalysts, which, on the one hand, enable long molding material processing times through their chemical capping and, at the same time, achieve very rapid molding material curing upon thermal exposure.

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. WO 2014/040922 A1 Blocked amines containing aldimine groups can be used in two-component polyurethane compositions for application as adhesives, sealants, coatings or potting compounds.

If latent amines, especially hydrolyzable, blocked amines, are used, as described in WO 2009/080738 A1 As mentioned above, problematic emissions occur due to the so-called cleavage products. These volatile aldehydes and ketones, formed from aldimines or ketimines, sometimes cause odorous and harmful vapors.

In the US 3 010 963 A Quaternary hydroxyalkyl bases of 1,4-diazabicyclo-[2.2.2]-octane or imidazole or their salts were described for the production of polyurethane foams. In the publications DE 1 928 475 A and DE 2 404 739 C2 It was revealed that this made it possible to achieve greater processing reliability for adhesives made from polyester fibre materials as well as for coating agents based on polyisocyanates and compounds containing hydrogen atoms reactive towards isocyanate groups.

Blocked amines are also used in epoxy resins. WO 2019/081581 A1 a longer storage stability of one-component epoxy resin compositions is achieved.

The 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.

A very elegant and increasingly used approach is to block tertiary amines by reaction with carboxylic acids, thus obtaining a readily adjustable heat-latent catalyst system. Such systems are used as amine catalysts with a retarding effect in the production of polyurethane foams. This is demonstrated, among other things, by the publications DE 699 21 284 T2 and DE699 26 577 T2 out.

In the EP1 990 387 A1 Catalysts containing tertiary amine groups are described for use in polyurethane hot-melt adhesives, with which the bonding of plasticizer-containing plastics can be achieved.

The WO 2011/095440 A1 describes the use of blocked tertiary amines, more specifically 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, which are activated at switching temperatures between 30 and 60 °C and 80 to 150 °C, respectively, for the production of polyisocyanate polyaddition products, polyurethane cast elastomers, as well as for the production of screens, pigs, rollers, wheels, rollers, scrapers, plates, cyclones, conveyor belts, doctor blades, couplings, seals, buoys and pumps. WO 2012/080226 A1 Similar products are produced using monocarboxylic acid blocked amidines as latent catalysts for polyisocyanate polyaddition products.

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 composite components. This is also due to the WO 2017/149031 A1 known.

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

In the US 2 800 487 A Polyoxyalkylene-substituted heterocyclic amines and their ammonium salts are described as surface-active detergents.

The production and application of latent tetravalent tin catalysts is described 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, which are complexed with an excess of mercapto compounds and thus blocked, are used in WO95/29007 A1 described.

In the DE 10 2014 110 189 A1 A cold-box binder consisting of phenolic resin, polyisocyanate, and a blocked tertiary amine or amidine as a co-catalyst is described. This co-catalyst is not thermally activated, but rather unfolds its effect in interaction with the tertiary, highly volatile amine, such as triethylamine, which is used as a catalyst in the cold-box process. This reduces the consumption of the highly volatile amine.

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

In the DE 10 2015 118 428 A1 Phenol-formaldehyde resin-free binders for foundry molding sands and molding material mixtures made from natural and/or ceramic sands containing these binders are disclosed. The binder is available either as a one-component binder based on polyurethane and/or polyurea, which is suitable for a multi-phase curing process using water-alcohol mixtures, or as a two-component binder. This two-component binder comprises 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, where 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. 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 production in cold self-curing and amine gas curing (cold box) processes.

1. a) Bilden einer Gießereimischung, wobei die Mischung ein Aggregat, ein Polyisocyanat und ein Aminopolyol umfasst, wobei das Aggregat mindestens 90 Gew.-% der Mischung umfasst,
2. b) Formen der Mischung, um eine Gießereiform zu bilden;
3. c) nach Ausbilden der Form, Aushärtenlassen der Mischung;
4. d) Bilden eines geformten Leichtmetallgusses unter Verwendung der ausgehärteten Formmischung und durch Gießen von geschmolzenem Leichtmetall in Kontakt mit der ausgehärteten Formmischung; und
5. e) Entfernen der ausgehärteten geformten Mischung von dem Leichtmetallguss.

From the US 4 370 463 A A process for casting light metals is known, which includes the following steps:

1. a) forming a foundry mixture, the mixture comprising an aggregate, a polyisocyanate and an aminopolyol, the aggregate comprising at least 90% by weight of the mixture,
2. b) shaping the mixture to form a foundry mould;
3. c) after forming the mould, allowing the mixture to harden;
4. d) forming a shaped light metal casting using the cured molding mixture and by pouring molten light metal into contact with the cured molding mixture; and
5. e) Removing the cured shaped mixture from the light metal casting.

In the US 6 348 121 B1 describes a polyol/polyisocyanate binder system comprising an isocyanate component and a catalyzing component, which components form a thermosetting composition when mixed and heated above a threshold temperature.

The object underlying the invention is to develop a system used in the molding material consisting of a binder and a suitable catalyst which promotes the curing of the molding material under the application of heat, which system allows the molding material to be cured by moderate thermal input according to the warm box or warm air process and thereby achieves fast cycle and demolding times which are close to those of the amine gas-curing cold box process.

A further aim of the invention is to overcome environmental and occupational safety-related disadvantages that arise from the use of conventional molding materials containing organic binders that are cured using the warm/hot box and/or warm/hot air process. In particular, this concerns the avoidance of the release of emission-relevant substances such as volatile organic compounds (VOCs), phenols, formaldehyde, or hydrolytic decomposition products such as aldehydes or ketones.

This object is achieved by a thermosetting molding material having the features of claim 1, which molding material is suitable for producing cores and molds using the sand molding process. Further developments are specified in the claims dependent on claim 1.

• • ein zweikomponentiges, phenol- und formaldehydfreies Bindemittel auf Polyurethan-Basis, enthaltend eine Harz-Komponente als Gemisch von zwei oder mehreren in Bezug auf Isocyanate wasserstoffaktiven Verbindungen mit Hydroxyl- und/oder Mercapto- und/oder Amino- und/oder Carbamidgruppen mit einer OH-, SH- und NH-Funktionalität von 1,5 bis 8 und Äquivalentgewichten von 9 bis 2000 g/val der Einzelbestandteile und eine Härter-Komponente mit einem oder mehreren Diisocyanaten oder Polyisocyanaten.
• • einen oder mehrere thermisch aktivierbare Katalysatoren, deren Aktivierungstemperaturen zwischen 50 und 180 °C liegen, aufweisend die Polyurethan-Reaktion fördernde Brönsted-Basen und/oder Lewis-Säuren sowie ihre zugehörigen Blockierungsmittel, und
• • einen oder mehrere feuerfeste schüttfähige Füllstoffe.

The thermosetting molding material according to the invention comprises at least

• • a two-component, phenol- and formaldehyde-free binder based on polyurethane, containing a resin component as a mixture of two or more compounds which are hydrogen-active with respect to isocyanates and 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/eq of the individual components and a hardener component with one or more diisocyanates or polyisocyanates.
• • one or more thermally activatable catalysts, the activation temperatures of which are between 50 and 180 °C, comprising Brönsted bases and/or Lewis acids which promote the polyurethane reaction, as well as their associated blocking agents, and
• • one or more fire-resistant, pourable fillers.

The two-component binder in the molding material according to the invention consists, on the one hand, of the resin component with individual compounds which are hydrogen-active with respect to isocyanate and have an average functionality of 1.8 to 4.0, as additive(s), preferably 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.

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 preferably used in the resin component. These compounds are polyether alcohols, reactive and non-reactive polymer polyols, polycaprolactones, polyetherpolyester alcohols, polythiols, aminopolyether alcohols, difunctional 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.

Mixtures of hydrogen-active compounds have proven advantageous for achieving high molding material strengths. These compounds, which are hydrogen-active with respect to isocyanate, are 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 beneficial for the processing properties of the molding material mixed with it and for the adhesive effect between the sand particles. Resin components with an average equivalent weight of 90 to 200 g/eq, based on the hydrogen-active constituents, have proven 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.

According to the invention, the individual constituents 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 present. For optimal crosslinking, the combination of difunctional with higher-functional compounds has proven advantageous, with the aim of achieving an optimal average functionality.

Di-, tri-, and tetrafunctional polyether alcohols are particularly suitable as crosslinking polyols for producing the resin component according to the invention. Examples of such polyols include ^Voranole® from Dow ^Chemical® , ^Desmophene® from ^Covestro® , ^Lupranole® from ^BASF® , ^Isoter® from ^Coim® , ^Puranole® from ^Jiahua® , ^Lipoxole® from ^Sasol® , polyglycols from ^Clariant® , and polyols from ^Perstorp® . Particularly suitable are, for example, the Voranoles ^® CP 260, CP 6055 and P400, the Desmophene ^® 1262 BD, 1300 BT, 1380 BT, 4051B, 5031 BT, 21 AP25, the Lupranole ^® 1000/1, 1100, 1200, 2070, 2090, 3300, 3423, 3424, 3902, the Isotere ^® 804SA, 803SA, 809SA, 840G, 860T, the Puranoles R3776, F3020, G303, G305, TMP850 and the Polyols 3165, 3380, 4640, 4290. The Thioplast ^® grades from Akzo Nobel ^® and the Thiocure ^® range from Bruno Bock have proven effective as H-functional sulfur-containing additives. Suitable polycaprolactones include 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 ^® . NH-functional compounds that can be used include polyetherdiamines such as Jeffamine ^® D-400 and D-230 from Huntsman ^® or simple structures such as diglycolamine. 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 simple and multiple sugars such as glucose, sucrose and sorbitol are used as polyhydric short-chain alcohols, preferably with a maximum molecular weight of 200 g/mol. Depending on the composition of the resin and hardener components and the desired processing time in the core and mold manufacturing process, the binders are processed with or without additional catalytic support. Suitable catalysts include organotin, organobismuth, organozinc, organopotassium, and organoaluminum compounds, as well as tertiary or quaternary nitrogen-containing substances such as dimethylcyclohexylamine, N-substituted pyrrolidones, N-substituted imidazoles, diazabicyclooctane, and triazine derivatives.

Suitable metal-based catalysts include the Kosmos ^® and DABCO ^® types from Evonik ^® , catalysts from TIB ^® , K-Kat ^® products from King Industries ^® , the Borchi ^® Kat series from Borchers ^® and Tytane ^® from Borica. A comprehensive selection of catalysts with tertiary nitrogen is available. BASF with the Lupragen ^® series, Lanxess ^® with Addocat ^® types and Huntsmann ^® with the Jeffcat ^® series.

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.

Suitable isocyanates for the hardener component of the molding material according to the invention are 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 fully 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, as well as their oligomers and polymers. Oligomeric and polymeric derivatives of isocyanates include carbodiimides, isocyanurates, biurets, uretdiones, and uretonimines. Common blocking agents for isocyanates that can be cleaved under heat are phenol, cresol, acetoacetic ester, diethyl malonate, ε-caprolactam, and butanone oxime. The isocyanates preferably have at least a functionality of 2 and are liquid at room temperature.

The aforementioned prepolymers are prepared by pre-crosslinking a stoichiometric deficit of di- or polyfunctional 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 processing-friendly viscosity that ensures good mixing with the molding base material and is therefore a maximum of 900 mPas, but preferably 300 to 600 mPas, at 20°C. All viscosities stated in connection with the present invention were determined using a rotational viscometer in accordance with DIN 53019.

Suitable isocyanates for binders of the molding material according to the invention include ^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® or ^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.

The binder components of the molding materials according to the invention, i.e., resin and hardener, are preferably supplemented with thinners to ensure good processability. Such thinners include, 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 processing, phosphoric acid esters, cyclic and non-cyclic carbonates, and/or non-hydroxy-functionally terminated polyethers.

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

To accelerate the polyurethane reaction of resin and hardener, thermally activated 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 using warm air. These are introduced as part of the resin component and/or added to the molding material as individual components. The thermally activated catalyst releases the catalytically active species at temperatures between 50 and 180 °C. The resulting polyurethane reaction of the two-component binder ensures immediate curing of the molding material and enables the cured molding material to be removed directly from the core box. The reaction rate is many times higher than with other common polyurethane catalysts or without a catalyst at all. In contrast to common catalysts, the processing open time at room temperature remains largely unaffected when thermolabile catalysts are used.

The thermally activated catalysts contain catalytically active, thermally releasable tertiary amines such as 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. 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, suberic acid; and hydroxycarboxylic acids such as citric acid or salicylic acid. Complex thermally releasable catalysts are usually adducts of tertiary amines with short-chain diols such as ethylene glycol and carboxylic anhydrides such as phthalic anhydride, maleic anhydride or succinic anhydride.

Suitable quaternary ammonium salts that release tertiary amines upon exposure to heat include choline and its derivatives. Reaction products of cyclic carboxylic acid anhydrides and diamines, such as N,N-dimethylethylenediamine, can also be used.

Typical latent catalysts include blocked amine and amidine catalysts from ^Evonik® such as ^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 the ^Thorcat® series from Thor ^{Especialidades®} . However, all other latent catalysts from polyurethane chemistry with a so-called switching temperature of 50 °C to 180 °C can also be used.

By intensively mixing the individual components of the resin or hardener component of the binder at room temperature and under exclusion of moisture, the respective components are obtained with processing-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.

The described two-component binders in combination with refractory and pourable fillers are suitable for producing the molding material according to the invention. These natural and ceramic foundry sands are also commonly referred to as mold 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 foam glass, 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 material must be optimized taking into account the respective grain size spectrum and the specific sand weight and is preferably set between 0.3 and 4.0%, based on the molding base material, and 0.1 to 2.5% of thermally activated catalyst, based on the resin component. The invention is not limited to these settings and amounts.

The thermosetting molding material can be produced from one or more refractory pourable fillers at 95.9 to 99.6%, a binder at 0.3 to 4.0% and one or more thermally activated catalysts at 0.002 to 0.1% in a batch or continuous mixer.

Depending on the specific formulation, the resin and hardener components of the binder can be mixed in a 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 ratio of 1:1, based on the mass.

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

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

The invention utilizes the innovative technology of chemically capped and thermally releasable catalysts. These are used for the thermally induced curing of polyurethane and/or polyurea binders in the molding material.

Furthermore, the present invention does not contain 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 any volatile components.

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. The cores and molds produced with the described molding materials exhibit 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.

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

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

The test conditions are based on VDG Data Sheet P71. To produce the molding material mixtures for the following binder examples, quartz sand H31 with 1.6% binder, of which 0.8% each is resin and hardener, and the amounts of thermally activated catalysts based on the resin quantity shown in Table 1 were used. These molding material mixtures were stirred in a laboratory mixer for 60 to 120 seconds. They were then shot into the heatable PBH core box from GF DISA AG using a PLS test specimen shooting machine at 4 bar shooting pressure. The test specimens were cured by applying heat through the core box or by introducing heated air. The corresponding molding material 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.

The compositions of the binders used are shown below. All percentages [%] in this document are to be understood as weight percent, unless otherwise defined in the explanatory text. Example 1: 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: 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: 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: 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: 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: 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: 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): 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): 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% Glyoxylic acid ~0.2% Hydrogen fluoride ~0.1% Aromatic KW ~25% Dibasic esters -5% PC CAT DBU TA 0 - 0.5% Viscosity at 20 °C 150 mPas Viscosity at 20 °C 40 mPas

The following Table 1 shows the test results with the described embodiments and non-inventive comparative examples V1 and V2.

The data demonstrate that a thermally activated catalyst is essential to achieve short curing times. After complete cooling of the test specimens (1-hour value), the final strength (24-hour value) is almost reached in most cases.

Comparative Examples C1 and C2 demonstrate that the inventive method is not suitable for phenol-formaldehyde resin-based binders. The Pep ^Set® binder C1 requires significantly longer curing times than the inventive variants. Comparative Binder 2 is a classic cold-box binder. The molding materials containing Comparative Binder 2 are not heat-curable. Presumably, additives in the binder inhibit the reaction of the thermolatent catalyst. Table 1 No. Proceedings Cat. quantity [%] T [°C] Time [s] Hot strength [N/cm ² ] Cold strength 1 hour [N/cm ² ] Cold strength 24 hours [N/cm ² ] 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 curing

DABCO

Diazabicyclo[2.2.2]octan

DBU

1,8-Diazabicyclo[5.4.0]undec-7-en

H31

Halterner Quarzsandsorte (Korngrößenbereich)

HDI

Hexamethylendiisocyanat

MDI

Diphenylmethandiisocyanat

MG

Molekulargewicht in [g/mol]

WB

Warm-Box

WL

Warmluft

List of abbreviations used in the tables (without chemical symbols)

DABCO

Diazabicyclo[2.2.2]octane

DBU

1,8-Diazabicyclo[5.4.0]undec-7-ene

H31

Halterner quartz sand variety (grain size range)

HDI

Hexamethylene diisocyanate

MDI

Diphenylmethane diisocyanate

MG

Molecular weight in [g/mol]

WB

Warm box

WL

warm air

Claims (14)

Thermosetting molding material for the production of cores and molds using the sand molding process, comprising at least ➢a two-component, phenol- and formaldehyde-free polyurethane-based binder containing a resin component as a mixture of two or more compounds that are hydrogen-active with respect to isocyanates and contain 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/eq 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/eq of the resin component, and a hardener component containing one or more diisocyanates or polyisocyanates, ➢one or more thermally activatable catalysts, whose activation temperatures are between 50 and 180°C, having polyurethane reaction-promoting components Brønsted bases and/or Lewis acids and their associated blocking agents, and ➢one or more refractory, pourable fillers. Thermosetting molding material according to Claim 1 , characterized in that the two-component binder comprises, on the one hand, a resin component with individual compounds which are hydrogen-active with respect to isocyanate and have an average functionality of 1.8 to 4.0, as additive(s) one or more thinners, optionally one or more catalysts or retarders which influence the polymerization and, on the other hand, a hardener component containing one or more isocyanates which have at least a functionality of 2, and, as additive, one or more thinners. Thermosetting molding material according to Claim 1 or 2 , characterized in that the hydrogen-active constituents of the resin component of the binder are selected from one or more substance classes, comprising polyether alcohols, reactive and non-reactive polymer polyols, polycaprolactones, polyether polyester alcohols, polythiols, aminopolyether alcohols, difunctional and higher alcohols, amines and carbamide compounds. Thermosetting moulding material according to one of the Claims 1 until 3 , characterized in that the individual components of the resin component are combined in such a way that an average H functionality of 2.2 to 3.5 results. Thermosetting moulding material according to one of the Claims 1 until 4 , characterized in that the isocyanates of the hardener component are oligomeric or polymeric derivatives of the basic type of 2,4'- and 4,4'-diphenylmethane diisocyanate and/or oligomeric or polymeric derivatives 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. Thermosetting moulding material according to one of the Claims 1 until 5 , characterized in that the hardener component consists of one or more isocyanates with thinners and additives ensuring processability, the isocyanate content being in a balanced stoichiometric ratio to the hydrogen-active compounds of the resin component. Thermosetting moulding material according to one of the Claims 1 until 6 , characterized in that the resin component of the binder contains 50 to 100% hydrogen-active compounds and the hardener component of the binder contains 50 to 100% polyisocyanates. Thermosetting moulding material according to one of the Claims 1 until 7 , characterized in that 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 introduction in the range of 70 °C and 170 °C, preferably between 100 and 130 °C. Thermosetting moulding material according to one of the Claims 1 and 8 , characterized in that one or more thermally activatable catalysts are premixed as individual components to the molding material and/or into the resin component. Thermosetting moulding material according to one of the Claims 1 until 9 , characterized in that the thermally activatable catalyst(s) contain catalytically active amine bases which can be released thermally in situ and promote the curing of the molding material. Thermosetting moulding material according to one of the Claims 1 until 10 , characterized in that the resin and hardener components of the binder comprise one or more diluents, these being selected from the substance classes fatty acid esters based on renewable raw materials, synthetic mono-, di- and tricarboxylic acid esters, organosilicates, sulfonic acid esters, largely aromatic-free fractions from petroleum processing, phosphoric acid esters, cyclic and non-cyclic carbonates and non-hydroxy-functionally terminal polyethers. Thermosetting moulding material according to one of the Claims 1 until 11 , characterized in that the filler or fillers is/are selected from quartz sand, chromite, 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 and silicon carbide, expanded and foam glass, fly ash and other special sands and has/have an average grain size of 0.1 to 0.9 mm. Thermosetting moulding material according to one of the Claims 1 until 12 , comprising one or more refractory pourable fillers at 95.9 to 99.6%, a binder at 0.3 to 4.0% and one or more thermally activatable catalysts at 0.002 to 0.1%. Use of a thermosetting moulding material according to one of the Claims 1 until 13 for use in the warm box process or the hot air process, curing in the range from 90 °C to 170 °C, preferably between 100 and 130 °C.