DE102019123372A1 - Thermosetting molding material for the production of cores and molds in the sand molding process - Google Patents

Abstract

The invention relates to a thermosetting molding material for the production of cores and molds in the sand molding process. It is a molding material made from natural and / or ceramic sands and a two-component, phenolic resin-free polyurethane binder and a catalyst that can be activated by the introduction of heat. The binder is present as a two-component binder based on polyurethane, comprising ➢ a resin component as a mixture of, in terms of isocyanates, hydrogen-active compounds that 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 ➢ A hardener component consisting of one or more diisocyanates or polyisocyanates. The at least one thermally activatable Catalyst, the activation temperature of which is between 50 and 180 ° C, has Brönsted bases and / or Lewis acids that promote the polyurethane reaction, as well as their associated blocking agents. The molding material contains one or more refractory and pourable fillers in the mean grain size range of 0.1 up to 0.9 mm with 0.3 to 4.0% of the binder described, based on the basic molding material, and 0.1 to 2.5% thermally activated Kata lysators, based on the resin component of the binder.

Description

The invention relates to a thermosetting molding material for the production of cores and molds in the sand molding process. It is a molding material made from two-component polyurethane binders, one or more thermally activated catalysts and natural and / or ceramic sands. This molding material is characterized by the fact that it is shell-curing and low-emission as well as being suitable for warm and hot-curing core and mold manufacturing processes.

For the production of “lost” molds and cores in the foundry industry, molding material mixtures are generally produced by thoroughly mixing a binding agent with a molding base material, introduced into a model and, after the molding material has hardened, stripped out. After adding a core (package) and molded part halves, the casting with metallic melt takes place. Inorganic or organic binders are used to bond the basic molding material, for example quartz sand.

Swellable clay minerals such as bentonite or aqueous alkali silicate solutions, in particular modified water glasses, are used as inorganic binders. In the area of organic binders, phenolic, furan or urea resins and condensates thereof with formaldehyde or mixtures thereof are used, but also phenolic resin-based two-component polyurethanes.

A wide variety of processes are used to process molding materials into “lost forms” and cores, which can basically be divided into hot-curing and cold-curing processes. In the following, these will be described and compared with one another both with regard to their process parameters and the binders used for this purpose. What these processes have in common is that the flowable molding material is first introduced into a mold by hand or by means of compressed air during core shooting. The processing step of hardening, on the other hand, differs for all the processes described.

In the case of cold, self-curing molding material systems, a period of 10 to 90 minutes is waited after molding, after which the molding material has hardened and can be removed from the model (pep-set or no-bake process). Furan resins, phenolic resins or polyurethanes can be named as suitable binder classes for this purpose. In order to produce large numbers of cores, the cycle times have to be reduced to a few seconds to a minute, which is achieved with cold curing, for example by gassing with an amine in the cold box process.

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

Organic and inorganic binders are available for the various warm and hot-curing processes. For organic binders, a distinction is first made between hot-box and warm-box processes because, depending on the binder used, there are different curing temperatures and thus different tool requirements. In both processes, a heatable core box or a heatable model is used, which are made of metal at a relatively high cost.

In the hot box process, binders based on phenolic or furan resins are used, which harden at temperatures of up to 300 ° C. The warm box process, on the other hand, is only carried out at around 150 ° C with specially additized furan resins as a binder.

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

However, hot box binders based on phenol resole resins mean that the cores adhere strongly to the mold, even with the use of a release agent, and can hardly be removed without damage, for example from the DE 15 70 203 A emerges.

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

Disadvantages of the previous hot-box and warm-box binder systems are formaldehyde and phenol vapors or furfuryl alcohol vapors released during core production and - in the case of urea-containing phenolic resins - the release of methyl isocyanate during casting. In the DE 15 69 023 C3 the reduction of the free formaldehyde content is described as a way of lowering the workplace pollution. Furthermore, this problem can be circumvented by using 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 from DE100 31 954 A1 known, it being disclosed that when using 2% binder to harden the molding material, 20 seconds to two minutes at a mold temperature of 200 ° C. are necessary. Another method for avoiding phenol and formaldehyde emissions consists in curing molding materials with epoxy resins and / or epoxy novolak resins and dicyandiamide or imidazoles as latent catalysts. This is for example in the EP 0 423 780 A2 described. The test specimens can be removed after 20 seconds to two minutes at 150 ° C.

Another disadvantage of classic hot box molding materials is that the water released during the condensation reaction has to be expelled from the molding material in order not to cause any reverse reaction of the binding agent or structural defects during casting. According to the DE 102 56 953 A1 By using a polyurethane system in which the addition reaction takes place with a phenolic resin that melts in the heat and a polyisocyanate, the molding material mixture can be cured at 250 ° C in 30 seconds without releasing excess water. With this method, however, the energy input required is very high and the introduction of the phenolic resin is demanding.

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

In the croning process, also known as the form mask process, heat curing is also used, but according to a different principle. Such a process is the subject of GB 876 493 A . The basic molding material is encased in a phenol novolak resin to which hexamethylenetetramine is also added. This free-flowing molding material is poured onto a 250 to 350 ° C warm metal plate, which represents the model, and only sets in one layer. The unbound 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 cast. However, a very high thermal input is necessary here too, and the sand has to be pretreated in a costly manner.

Furthermore, waterglass-based, inorganic binders are increasingly being used in foundries. Their molding material strengths are generally lower than those of the organic binders, but their emissions during casting are significantly lower. In addition to hardening by adding liquid esters or gassing with CO ₂ , heated tools or warm air are also common. This removes water from the molding material mixture and accelerates the hardening 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 from the DE 20 2007 019 185 U1 emerges. There were, for example, in the DE 69 533 438 T2 also described hot box variants that allow curing in 30 seconds to 2 minutes at a hot tool at 230 to 260 ° C.

Warm air has the decisive advantage that no expensive, heatable core boxes are necessary as in the hot box or warm box process, but simple plastic models can be used. The core is heated evenly by warm air. Not only is the outer shell adjacent to the core box heated, because the warm air penetrates the core evenly. In the case of a very strongly heated tool, i.e. to a temperature> 200 ° C, there is also the risk for molding materials with organic components that the organic component in contact with the tool will already burn while the interior of the core is not yet sufficient for hardening Has experienced temperature entry. A suitable device for heating air is, for example, in DE 20 2006 018 044 U1 described.

Organic binder systems are also hardened using the hot air process. Suitable binders are aqueous ammonium polyacrylates in combination with metal salts, as is also the case in US Pat U.S. 4,678,020 A is described. The binder is partially decomposed by the warm air, 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.

Generative manufacturing processes are increasingly complementing classic core manufacturing in foundries. Instead of mixing the binder and the basic molding material and putting them into a mold, sand is applied in layers in a box and a binder is applied to the desired areas. The binders are self-curing or thermosetting. The heat input takes place either after the printing is finished by transferring the box into an oven, or directly during the printing process with the help of infrared radiation. One variant is a further development of the croning process, which is included in the WO 95/32824 A1 is described and in which resin-coated sand is applied in layers and the resin is melted on at certain points with an infrared laser beam. Due to the limited production speed, such processes are mainly suitable for prototypes and therefore do not represent any competition for mass production processes such as hot box processes. The infrared light only hardens the surface layer of the molding material. The method can therefore only be used for moldings that are built up in layers.

A thermal hardening of molding materials can also be done by microwave radiation. From the DE 10 2007 027 577 A1 it is known that, particularly in the case of 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 manufacture in a special core shooter, as in the DE 11 2016 006 377 T5 is described. In the first case, the transport into 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 above-mentioned use in thermosetting processes, phenol-formaldehyde resins in particular are solidified with isocyanate-containing hardeners in the cold-box process, in which amine gassing results in an almost instantaneous hardening of the molding material with the formation of a polyurethane addition product, and this is especially true suitable for an automated core manufacturing process. The cold box process is explained in numerous publications, such as, for example U.S. 3,409,579 A , DE 2 162 137 A or the DE 1 959 023 A .

While phenolic resins use tertiary gaseous amines as catalysts in the cold box process, the same binder class is hardened with liquid, pyridine-based catalysts when used in cold, self-curing processes. The latter can also be used additively in a thermosetting process. Against this background, very little attention was paid to the blocked, thermally activated catalysts, which on the one hand enable long molding material processing times due to their chemical capping and at the same time achieve very rapid molding material hardening when exposed to heat.

Various ways of blocking amines are known from the literature. The corresponding aldimines or ketimines are obtained from the condensation of primary amines with aldehydes or ketones. The amines originally used are released again through hydrolysis.

According to the WO 2014/040922 A1 Blocked amines containing aldimine groups can be used in two-component polyurethane compositions for use as adhesives, sealants, coatings or potting compounds.
If latent amines, in particular hydrolyzable, blocked amines, are used, as in FIG WO 2009/080738 A1 mentioned, problematic emissions occur due to the so-called spin-off products. These volatile aldehydes and ketones, formed from aldimines or ketimines, sometimes cause odorous and harmful vapors.

In the U.S. 3,010,963 A Quaternary hydroxyalkyl bases of 1,4-diazabicyclo- [2.2.2] -octane or imidazole or their salts for the production of polyurethane foams have been described. In the pamphlets DE 1 928 475 A and DE 2 404 739 C2 it was disclosed that a higher processing reliability of adhesives made of polyester fiber materials and of coating compositions based on polyisocyanates and compounds with hydrogen atoms reactive toward isocyanate groups could be achieved.

Blocked amines are also used in epoxy resins. So according to the WO 2019/081581 A1 a longer storage stability of one-component epoxy resin compositions 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 reacting with carboxylic acids and in this way to obtain an easily adjustable heat-latent catalyst system. Systems of this type are used as amine catalysts with a retarding effect for the production of polyurethane foams. This can be found in the publications, among other things DE 699 21 284 T2 and DE699 26 577 T2 emerged.
In the EP1 990 387 A1 Catalysts containing tertiary amine groups are described for use in polyurethane hotmelt adhesives with which plastics containing plasticizers can be bonded.

The 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-en (DBN), as latent catalysts, which are activated at switching temperatures between 30 and 60 ° C or 80 to 150 ° C, for the production of polyisocyanate polyaddition products, polyurethane cast elastomers and for production screens, pigs, rollers, wheels, rollers, scrapers, plates, cyclones, conveyor belts, doctor blades, couplings, seals, buoys and pumps. In the WO 2012/080226 A1 similar products are made using monocarboxylic acid blocked amidines as latent catalysts for polyisocyanate polyadducts.

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

The U.S. 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 U.S. 2,800,487 A polyoxyalkylene-substituted heterocyclic amines and their ammonium salts are described as surface-active detergents.

The production and use of latent tetravalent tin catalysts is in the EP 2 274 092 B1 shown. 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 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 activated thermally, but develops its effect in conjunction with the tertiary, highly volatile amine, for example triethylamine, which is used as a catalyst according to the cold box process. This allows the consumption of the volatile amine to be reduced.

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, but at the latest during thermal decomposition during casting, and therefore represent a burden for employees and the environment.

The object on which the invention is based is to develop a system of binding agent and a suitable catalyst which is used in the molding material and which promotes hardening of the molding material with the supply of heat, which allows the molding material to be removed by moderate thermal input after the hot box or hot air. Curing processes and achieving fast cycle and stripping times that come close to those of the amine gas-curing cold box process.

Another concern of the invention is to overcome disadvantages relevant to the environment and occupational health and safety, which result from the use of molding materials containing classic organic binders, which are cured in 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 compounds (VOC), phenols, formaldehyde or hydrolytic breakdown products such as aldehydes or ketones.

The object is achieved by a thermosetting molding material having the features of claim 1, this molding material being suitable for producing cores and molds in the sand molding process. Further developments are given 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 isocyanate-active compounds with hydroxyl and / or mercapto and / or amino and / or carbamide groups with a OH, SH and NH functionality from 1.5 to 8 and equivalent weights from 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, having the polyurethane reaction promoting Bronsted bases and / or Lewis acids and their associated blocking agents, and
• • one or more refractory pourable fillers.

The two-component binder in the molding material according to the invention consists on the one hand of the resin component with isocyanate-hydrogen-active individual compounds with an average functionality of 1.8 to 4.0, as additives, preferably one or more thinners, optionally one or more additives that influence the polyurethane reaction such as catalysts or retarders and optionally homogenizing additives and, on the other hand, from the isocyanate-containing hardener component.

For the two-component systems according to the invention, balanced combinations of different aliphatic and / or cycloaliphatic compounds which are hydrogen-active with respect to isocyanate are preferably used in the resin component, these compounds being polyether alcohols, reactive and non-reactive polymer polyols, polycaprolactones, polyether polyester alcohols, polythiols , Aminopolyether alcohols, di- and higher-functional alcohols, amines, carbamide compounds. Two or more individual components of one or more of these substance classes are incorporated into the resin component.

In order to achieve high molding material strengths, mixtures of hydrogen-active compounds have proven to be advantageous. The selection and combination of these compounds, which are hydrogen-active with respect to isocyanate, are therefore made in such a way that their functionalities and their equivalent weights map a gradient. This achieves optimal crosslinking within the polyaddition product, which is advantageous 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 to be particularly suitable for this. 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 proportions by mass in the mixture.

According to an advantageous embodiment of the invention, the individual constituents of the resin component are selected in such a way that an average H functionality of 1.8 to 4.0, preferably 2.2 to 3.5, is present. The combination of two-functional with higher-functional compounds has proven to be advantageous for optimal crosslinking, with an optimal average functionality being sought.

Di-, tri- and tetra-functional polyether alcohols are particularly suitable as crosslinking polyols for the production of the resin component according to the invention. Such polyols are, for example Voranole ^® from Dow Chemical ^®, Desmophene ^® from Covestro ^®, Lupranole ^® from BASF ^®, Isoter ^® from Coim ^®, Puranole ^® from Jiahua ^®, Lipoxole ^® of Sasol ^®, polyglycols of Clariant ^®, polyols from Perstorp ^® . ^{Voranole ®} 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, for example, are particularly suitable 3300, 3423, 3424, 3902, the Isotere ^® 804SA, 803SA, 809SA, 840G, 860T, which Puranole R3776, F3020, G303, G305, TMP850 and the polyols 3165, 3380, 4640, 4290. The Thioplast ^® types from Akzo Nobel ^® and the Thiocure ^® range from Bruno Bock have proven useful as H-functional sulfur-containing additives. Suitable polycaprolactones are, for example Placcel ^® 205, 305 and 410 Daicel ^{®, ®} Durez Ter S S 1063-72 and 2006-120 of Sumitoma Bakelite ^® or Capa ^® 3031, 3022 and 2043 of Ingevity ^®. When NH-functional compounds can be used as polyether diamines diglycolamine Jeffamine ^® D-400 and D-230 from Huntsman ^® or even simple structures like. Polyhydric short-chain alcohols, preferably with a maximum molecular weight of 200 g / mol, are 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 single and multiple sugars such as glucose, sucrose and sorbitol are used.

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 are organotin, organobismuth, organozinc, organopotassium and organoaluminum compounds and also tertiary or quaternary nitrogen-containing substances such as dimethylcyclohexylamine, N-substituted pyrrolidones, N-substituted imidazoles, diazabicyclooctane and triazine derivatives.

Suitable metal-based catalysts are, for example, the Cosmos ^® - and DABCO ^® grades from Evonik ^®, catalysts of TIB ^®, K-Kat ^® products of King Industries ^®, the Borchi ^® Cat series of Borchers ^® and Tytane ^® from Borica. BASF offers a comprehensive selection of catalysts with tertiary nitrogen 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, the isocyanate content preferably being in a balanced stoichiometric ratio to the hydrogen-active compounds of the resin component.

Suitable isocyanates of 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 completely or partially blocked isocyanate groups and / or isophorone diisocyanate and / or its derivatives, as well as the aromatic, aliphatic and cycloaliphatic isocyanates prepared in a prepolymer process and their Oligomers and polymers. Oligomeric and polymeric derivatives of isocyanates include carbodiimides, isocyanurates, biurets, uretdiones and uretonimines. Common blocking agents for isocyanates, which can be split off again under the action of heat, are phenol, cresol, acetoacetate, diethyl malonate, ε-caprolactam and butanone oxime. The isocyanates preferably have at least functionality 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 with a residual content of free isocyanate groups between 5 and 35%, particularly preferably between 6 and 30 %, results. Furthermore, such prepolymers must have a processing-friendly viscosity which ensures thorough mixing with the basic molding 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 rotary viscometer in accordance with DIN 53019.

Suitable isocyanates for the binder of the molding material of the invention include Lupranate ^® from the product range of BASF ^® company, Desmodur ^® grades by the company 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 above-mentioned suitable isocyanates particular Lupranat ^® M include 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, that is to say resin and hardener, are preferably supplemented by thinners with the aim of good processability. Such thinners are, for example, fatty acid esters based on renewable raw materials, such as transesterification products from vegetable oils, especially their methyl, ethyl, propyl, isopropyl, butyl and isobutyl esters. 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-functional terminal polyethers are also suitable.

Examples of fatty acid esters from natural oils are the rapeseed methyl ester from Glencore or other established biodiesel manufacturers, the palm and soy methyl esters from Cremer, the Priolube ^® types from Croda ^® , the DUB ^® products from Stearinerie Dubois ^® , and the RADIA ^® - esters of Oleon ^{®. The product ranges of Oxsoft ®} and Oxblue ^® esters from Oxea ^® , Softenol ^® esters from Sasol ^® , Jayflex ^® products from Exxon ^® , the dibenzoate esters labeled Freeflex ^® from Caffaro ^® or represent the possible uses of synthetic carboxylic acid esters Plasticizers from BASF ^® , such as Hexamoll ^® DINCH or Plastomoll ^®, are available. Suitable organosilicates, in particular alkyl silicates and Alkylsilikatoligomere are, for example, tetraethyl silicate, tetra-n-propyl silicate, as well as mono-, di- and Trialkylsilikate the company Wacker ^®, Evonik ^® and Dow Corning ^®.

In order to accelerate the polyurethane reaction of resin and hardener, thermally activatable amine catalysts and / or metal-based catalysts are used according to the invention for curing the molding material in a heated core box according to the warm box process or in the unheated core box by introducing hot air. These are presented as part of the resin component in this and / or added to the molding material as an individual component. The thermally activated catalyst releases the catalytically active species at temperatures from 50 to 180 ° C. The polyurethane reaction of the two-component binder initiated as a result ensures immediate hardening of the molding material and enables the hardened molding material to be removed 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 the usual catalysts, when using thermolabile catalysts, the processing time at room temperature remains largely unaffected.

The thermally activated catalysts have, as catalytically active, thermally releasable tertiary amines, for example 1,8-diazabicyclo [5.4.0] undec-7-en (DBU), 1,4-diazabicyclo [2.2.2] octane (DABCO), bis ( 2-dimethylaminoethyl) ether, imidazole, piperazine, guanidine or morpholine derivatives. Possible acids for blocking are 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 acid anhydrides such as phthalic anhydride, maleic anhydride or succinic anhydride.

Choline and its derivatives, for example, are suitable as quaternary ammonium salts which release tertiary amines when exposed to heat. Furthermore, reaction products from cyclic carboxylic acid anhydrides and diamines such as N, N-dimethylethylenediamine can also be used.

Typical latent catalysts are for example blocked amine and amidine catalysts of the manufacturer Evonik ^® as Polycat ^® SA 1/10, SA 2 LE, SA 4 and SA-8, Dabco ^® KTM 60, Tosoh ^® example TOYOCAT ^® DB 2, DB 30 , DB 31, DB 40, DB 41, DB 42, DB 60, DB 70, Huntsman ^®, for example Accelerator DY 9577, and Nitroil ^®, for example, 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 180 ° C can also be used.

Intensive mixing of the individual components for the resin or hardener component of the binder at room temperature and with the exclusion of moisture gives the respective components with easy-to-use 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 has 50 to 100%, preferably 70 to 90%, hydrogen-active compounds and the hardener component of the binder 50 to 100%, preferably 80 to 95%, polyisocyanates.

The two-component binders described 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 commonly referred to as basic mold 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 special sands. The preferred mean 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 spectrum and the specific sand weight, and is preferably between 0.3 and 4.0%, based on the mold base material, and 0.1 to 2.5% thermally activated Catalyst, based on the resin component, adjusted. The invention is not limited to these settings and amounts.

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

The resin and hardener components of the binder can be added in a mixing ratio of 2.5: 1 to 1: 2.5, depending on the respective recipe. For practical use in foundries, however, it has proven to be useful to formulate the binder systems in such a way that they can be used in a mixing ratio of 1: 1, based on the mass.

Disadvantages of the 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 in particular is a considerable process disadvantage. The corresponding equipment must be equipped with 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 does not have these disadvantages. It enables the mold material to harden quickly, for example for core production, without having to use gaseous amines as in the cold box process.

The invention takes up the innovative technology of chemically disguised 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 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 any volatile components.

The binders and the molding materials themselves have advantageous processing properties such as odorlessness, low vapor pressure, low viscosity, good flowability, adjustable curing speed and high flexural strengths. The cores and molds produced with the molding materials described have a low tendency to flaws and good disintegration under casting conditions. During casting, the emissions of volatile organic compounds such as aromatic hydrocarbons and formaldehyde are significantly reduced compared to phenol-formaldehyde resin and furan resin-based binders.

Due to these advantages and the very short curing times achieved through the introduction of heat, the molding materials according to the invention therefore make an important contribution to a low-emission and highly productive foundry.

Further details, features and advantages of embodiments of the invention emerge from the following description of exemplary embodiments.

The test conditions are based on the VDG leaflet P71. For the production of molding material mixtures of the following binder examples, quartz sand H31 with 1.6% binder, 0.8% each of which is resin and hardener, and amounts of thermally activatable amounts shown in Table 1 were used Catalysts, based on the amount of resin, used. These molding material mixtures were stirred in a laboratory mixer for 60 to 120 seconds, then shot with a PLS test body shooting machine at 4 bar shooting pressure into the heatable PBH core box from GF DISA AG and hardened with the introduction of heat through the core box or by introducing heated air. The associated molding material strengths of the test specimens obtained in this way with the dimensions 22.4 x 22.4 x 175 mm were determined as a function of time using the LRu-2e universal strength tester from Multiserw.

The compositions of the binders used are shown below. All percentages [%] in this document are always to be understood as percentages by weight, unless a different definition is made in the explanatory text.

Example 1: Composition of binder 1 Resin polyol component Hardener isocyanate component 430 MW polyether polyol 15.5% MDI oligomer 88.5% Polyether polyol MW 520 17.5% Fatty acid esters 11.5% 860 MW polyether polyol 24.0% 2920 MW polyether polyol 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 of binder 2 Resin polyol component Hardener isocyanate component 430 MW polyether polyol 15.5% MDI oligomer 88.5% Polyether polyol MW 520 17.5% Fatty acid esters 11.5% 860 MW polyether polyol 24.0% 2920 MW polyether polyol 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 of binder 3 Resin polyol component Hardener isocyanate component 430 MW polyether polyol 15.5% MDI oligomer 88.5% Polyether polyol MW 520 17.5% Fatty acid esters 11.5% 860 MW polyether polyol 24.0% 2920 MW polyether polyol 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 of binder 4 Resin polyol component Hardener isocyanate component Polycaprolactone MG 400 65.0% MDI oligomer 85.0% 420 MW polyether polyol 15.0% Fatty acid esters 15.0% 440 MW polyether polyol 5.0% Polyether polyol, MW 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 of binder 5 Resin polyol component Hardener isocyanate component 420 MW polyether polyol 15.0% MDI oligomer 71.0% 430 MW polyether polyol 15.0% HDI biuret 20.0% Polyether polyol MW 500 21.0% Fatty acid esters 9.0% Polyether polyol, MW 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 of binder 6 Resin polyol component Hardener isocyanate component Polyether polyol MW 200 18.0% MDI oligomer 82.0% Polyether polyol MW 3500 10.0% Polyether polyol, MW 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 MW 200 16.0% MDI oligomer 82.0% Polyether polyol MW 3500 5.0% Polyether polyol, MW 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

Table 1 below shows the test results with the exemplary embodiments described and comparative examples V1 and V2 not according to the invention.

From the data it can be seen that a thermally activated catalyst is absolutely necessary in order to obtain short curing times. After the test specimens have cooled down completely (1-hour value), the final strength (24-hour value) is almost reached in most cases.

Comparative examples C1 and C2 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 the comparative binder 2 are not heat-curable. Presumably, additives in the binder inhibit a reaction of the thermolatent catalyst.

Table 1 No. Procedure Cat. - amount [%] 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 3rd WB 0.75 110 90 40 270 385 4th WB 0.5 110 90 70 380 440 5 WB 0.5 110 120 45 280 335 6th WB 0.75 110 90 55 405 410 7th 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 reference symbols

DBU DABCO

Diazabicyclo [2.2.2] octane 1,8-diazabicyclo [5.4.0] undec-7-en

H31

Halterner type of quartz sand (grain size range)

HDI

Hexamethylene diisocyanate

MDI

Diphenylmethane diisocyanate

MG

Molecular weight in [g / mol]

WB

Warm box

WL

Warm air

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

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Claims (15)

Thermosetting molding material for the production of cores and molds by sand molding, at least comprising ➢ a two-component, phenol- and formaldehyde-free binder based on polyurethane, containing a resin component as a mixture of two or more isocyanate-active compounds with hydroxyl and / or mercapto and / or amino and / or carbamide groups with a OH, SH and NH functionality from 1.5 to 8 and equivalent weights from 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, having the polyurethane reaction promoting Bronsted bases and / or Lewis acids and their associated blocking agents, and ➢ one or more refractory pourable fillers. Thermosetting molding material after Claim 1 , characterized in that the two-component binder on the one hand a resin component with isocyanate-hydrogen-active individual compounds with an average functionality of 1.8 to 4.0, as additives one or more diluents, optionally one or more catalysts that influence the polymerization or Retarder and, on the other hand, a hardener component containing one or more isocyanates which have at least functionality 2, and one or more thinners as an additive. Thermosetting molding material after 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, including polyether alcohols, reactive and non-reactive polymer polyols, polycaprolactones, polyether polyester alcohols, polythiols, aminopolyether alcohols, di- and higher-functionality alcohols, amines and carbamide compounds . Thermosetting molding material according to one of the Claims 1 to 3rd , characterized in that the resin component of the binder, based on the hydrogen-active constituents, has an average equivalent weight of 90 to 200 g / eq. Thermosetting molding material according to one of the Claims 1 to 4th , characterized in that the individual constituents of the resin component are combined in such a way that an average H functionality of 1.8 to 4.0, preferably 2.2 to 3.5, results. Thermosetting molding material according to one of the Claims 1 to 5 , 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 completely or partially blocked isocyanate groups and / or isophorone diisocyanate and / or its derivatives. Thermosetting molding material according to one of the Claims 1 to 6th , 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 molding material according to one of the Claims 1 to 7th , characterized in that the resin component of the binder has 50 to 100% hydrogen-active compounds and the hardener component of the binder has 50 to 100% polyisocyanates. Thermosetting molding material according to one of the Claims 1 to 8th , characterized in that the thermally activatable catalyst or catalysts are adducts of tertiary amines and organic acids (blocking agent) or quaternary ammonium salts and the catalytically active tertiary amine for release by thermal input between 50 and 180 ° C, preferably between 80 and 150 ° C , particularly preferably between 100 and 130 ° C, is provided. Thermosetting molding material according to one of the Claims 1 and 9 , characterized in that one or more thermally activatable catalysts, individual components, are premixed into the molding material and / or into the resin component. Thermosetting molding material according to one of the Claims 1 to 10 , characterized in that the thermally activatable catalyst or catalysts contain catalytically active amine bases which can be released thermally in situ and which promote the hardening of the molding material. Thermosetting molding material according to one of the Claims 1 to 11 , characterized in that the resin and hardener components of the binder have one or more thinners, 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 petroleum processing, phosphoric acid esters, cyclic and non-cyclic carbonates and non-hydroxy-functional terminal polyethers. Thermosetting molding material according to one of the Claims 1 to 12th , 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 as well as an average grain size of 0.1 to 0.9 mm. Thermosetting molding material according to one of the Claims 1 to 13th , comprising one or more refractory pourable fillers from 95.9 to 99.6%, a binder from 0.3 to 4.0% and one or more thermally activated catalysts from 0.002 to 0.1%. Use of a thermosetting molding material according to one of the Claims 1 to 14th for use in the warm box process or in the warm air process, curing between 50 and 180 ° C, preferably between 80 and 150 ° C, particularly preferably between 100 and 130 ° C.