Low emission cold curing binders for foundry industry

Abstract

The present invention primarily relates to a mixture suitable for use in a no-bake process for producing cores and molds for the foundry industry, and to a reaction mixture comprising such a mixture and an acid hardener (i.e., a catalyst acid). Furthermore, the present invention relates to a process for producing a mixture according to the invention, as well as a process for producing a mold or core. The invention also relates to a mold or core for producing metal bodies, and to a kit comprising a mixture according to the invention and certain acid hardeners. In addition, the invention relates to the use of a mixture according to the invention as a cold-curing binder and to the use of such mixtures or reaction mixtures in a no-bake process for producing metal bodies.

Description

[0001] The present invention primarily relates to a mixture suitable for use in the no-bake process for producing cores and molds for the foundry industry, and to a reaction mixture comprising such a mixture and an acid hardener (i.e., a catalyst acid). Furthermore, the present invention relates to a method for producing a mixture according to the invention, as well as a method for producing a mold or core. The invention also relates to a mold or core for producing metal bodies, and to a kit comprising a mixture according to the invention and certain acid hardeners. In addition, the invention relates to the use of a mixture according to the invention as a cold-curing binder and to the use of such mixtures or reaction mixtures in a no-bake process for producing metal bodies. Further aspects of the present invention will become apparent from the description, the exemplary embodiments, and the claims.

[0002] Most products of the iron and steel industry, as well as the non-ferrous metals industry, undergo casting processes for their initial shaping. In this process, molten materials, ferrous or non-ferrous metals, are transformed into shaped objects with specific properties. To form these castings, sometimes very complex molds must first be created to hold the molten metal. These molds are divided into expendable molds, which are destroyed after each casting, and permanent molds, which can produce a large number of castings. Expensive molds are usually made of a refractory, granular molding material that is hardened with a curable binder.

[0003] Molds are negatives; they contain the cavity to be poured, which will produce the casting. The internal contours of the future casting are formed by cores. During mold making, the cavity is formed into the molding material using a model of the casting. The internal contours are represented by cores, which are formed in a separate core box.

[0004] Both organic and inorganic binders can be used to produce molds, and these can be cured using either cold or hot processes. Cold processes are those in which curing occurs essentially at room temperature without heating the molding material mixture. Curing in these processes usually occurs through a chemical reaction, which can be triggered, for example, by passing a gaseous catalyst through the molding material mixture to be cured, or by adding a liquid catalyst to the mixture. In hot processes, the molding material mixture is heated to a sufficiently high temperature after shaping, for example, to drive off the solvent contained in the binder or to initiate a chemical reaction that cures the binder through cross-linking.

[0005] The production of the molds can proceed as follows: the molding material is first mixed with the binder, so that the granules of the refractory molding material are coated with a thin film of the binder. The resulting molding material mixture can then be placed in a suitable mold and, if necessary, compacted to achieve sufficient stability of the mold. The mold is then cured, for example, by heating it or by adding a catalyst that initiates a curing reaction. Once the mold has reached at least a certain initial strength, it can be removed from the mold.

[0006] As already mentioned, molds for the production of metal bodies are often composed of cores and molds. Different requirements are placed on the cores and molds. Molds offer a relatively large surface area to dissipate gases that are produced during casting due to the action of the hot metal. Cores, on the other hand, usually have only a very small surface area available for gas venting. If excessive gas evolution occurs, there is a risk that gas from the core will pass into the molten metal and cause casting defects.Therefore, the inner cavities are often represented by cores that have been solidified by cold-box binders, i.e., a binder based on polyurethanes, while the outer contour of the casting is represented by more cost-effective forms, such as a green sand mold, a mold bonded by a furan resin or a phenolic resin, or a steel mold.

[0007] For larger molds, organic polymers are typically used as binders for the refractory, granular molding material. Washed, classified quartz sand is frequently used as the refractory, granular molding material, but other materials such as zircon sands, chromite sands, chamotte, olivine sands, feldspar-containing sands, and andalusite sands are also employed. The resulting molding material mixture, consisting of the molding base and binder, is preferably in a free-flowing form.

[0008] Currently, organic binders such as polyurethane, furan resin, or epoxy-acrylate binders are frequently used in the production of casting molds, where the binder cures through the addition of a catalyst. Phenolic resins (acid-curing or – in the Alpha-Set process – ester-curing) are also used.

[0009] The selection of the appropriate binder depends on the shape and size of the casting, the production conditions, and the material used for the casting. For example, polyurethane binders are often used in the production of small castings manufactured in large quantities, as they enable fast cycle times and thus also series production.

[0010] Processes in which the molding material mixture is cured by heat or by the subsequent addition of a catalyst have the advantage that the processing of the molding material mixture is not subject to any particular time restrictions. The molding material mixture can initially be produced in larger quantities, which are then processed over a longer period, usually several hours. The curing of the molding material mixture only takes place after molding, with a rapid reaction being the goal. The mold can be removed directly from the mold after curing, thus enabling short cycle times. However, to achieve good mold strength, the curing of the molding material mixture must proceed uniformly within the mold. If the curing of the molding material mixture is to be achieved by the subsequent addition of a catalyst, the mold is gassed with the catalyst after molding.For this process, the gaseous catalyst is passed through the mold. The molding material mixture hardens immediately upon contact with the catalyst and can therefore be removed from the mold very quickly. As the size of the mold increases, it becomes more difficult to provide a sufficient amount of catalyst in all sections of the mold for the molding material mixture to harden. The gassing times increase, and there may still be sections in the mold that are poorly reached or not reached at all by the gaseous catalyst. Therefore, the amount of catalyst increases significantly with the size of the mold.

[0011] Similar difficulties arise with hot curing processes. Here, the mold must be heated to a sufficiently high temperature in all sections. As the size of the mold increases, the time required to heat it to a specific temperature for curing also increases. Only then can it be ensured that the mold possesses the necessary strength throughout its interior. Furthermore, the curing process becomes much more complex and expensive from an equipment perspective as the size of the mold increases.

[0012] In large-scale casting, the cores often weigh around 1000 kg or more. From a technical standpoint, such large cores are difficult or impossible to produce using gas or heat hardening processes. In these cases, cold-hardening processes are preferred.

[0013] For the production of molds for large castings, such as engine blocks for marine diesel engines or large machine parts like rotor hubs for wind turbines, so-called "no-bake binders" are typically used for the reasons mentioned above. In the "no-bake" process, the refractory molding material (e.g., sand) is often first coated with a catalyst (hardener), then the binder is added and evenly distributed over the already catalyst-coated refractory molding material by mixing. This process frequently utilizes continuous mixers. The resulting molding material mixture can then be formed into a molded part. Because the binder and catalyst are evenly distributed throughout the molding material mixture, even large molded parts cure largely uniformly.

[0014] Alternatively, in the "no-bake" process, the refractory mold base material (e.g., sand) can first be mixed with the binder, and then the hardener added. With this method, particularly when producing molds for large castings, a partially or locally excessive concentration of the hardener can lead to partial hardening or cross-linking of the binder, resulting in an inhomogeneous molding material.

[0015] Since the catalyst (hardener) is added to the molding material mixture before shaping, the curing process begins immediately after preparation. To achieve a suitable processing time for industrial applications, the components of the molding material mixture should therefore be carefully matched. For example, the reaction rate for a given quantity of binder and refractory base material can be influenced by the type and quantity of catalyst or by adding retarders. Furthermore, the processing of the molding material mixture should be carried out under very controlled conditions, as the curing rate is affected by factors such as the temperature of the mixture.

[0016] The "classic" no-bake binders are often based on furan resins and phenolic resins. They are frequently offered as systems (kits), where one component comprises a reactive furan resin or phenolic resin and the other component an acid, with the acid acting as a catalyst for the curing of the reactive resin component.

[0017] Furan and phenolic resins exhibit very good decomposition properties during casting. Under the heat of the molten metal, the furan or phenolic resin decomposes, and the mold loses its strength. Therefore, after casting, cores can be easily extracted from cavities, if necessary after prior vibration of the casting.

[0018] "Furan no-bake binders" contain reactive furan resins, which regularly include furfuryl alcohol as a key component. Furfuryl alcohol can react with itself under acidic catalysis to form a homopolymer. Furran no-bake binders are generally not produced using furfuryl alcohol alone; instead, other compounds are added to the furfuryl alcohol and polymerized into the resin. Examples of such compounds include aldehydes, such as formaldehyde or furfural; ketones, such as acetone; phenols; urea; and polyols, such as sugar alcohols or ethylene glycol. Further components can be added to the resins to influence their properties, such as their elasticity. Melamine, for example, can be added to bind any remaining free formaldehyde.

[0019] Furan no-bake binders are usually prepared by first generating precondensates of, for example, urea, formaldehyde, and furfuryl alcohol under acidic conditions. These precondensates are then diluted with furfuryl alcohol.

[0020] It is also conceivable that urea and formaldehyde can be reacted on their own. This produces so-called UF resins ("urea-formaldehyde" resins, "aminoplasts"). These are usually subsequently diluted with furfuryl alcohol. Advantages of this manufacturing method include greater flexibility / variability in the product range and lower costs, as it involves cold mixing processes. A disadvantage is that certain chemical and application-related properties cannot be achieved. Furthermore, UF resins are often cloudy, so binders produced from them are generally also cloudy and inhomogeneous. Resols can also be used to produce furan no-bake binders. Resols are produced by the polymerization of mixtures of phenol and formaldehyde. These resols are then often diluted with a large amount of furfuryl alcohol.

[0021] Furan no-bake binders are regularly cured with an acid. This acid catalyzes the cross-linking of the reactive furan resin. It is important to note that, depending on the binder type, certain amounts of acid should not be undercut, as alkaline components that may be present in the refractory base material can partially neutralize the acid.

[0022] Sulfonic acids, phosphoric acid, or sulfuric acid are frequently used as acids. In some specific cases, combinations of these are used, including with other carboxylic acids. Furthermore, certain "curing moderators" can be added to the furan no-bake binder.

[0023] Phosphoric acid is frequently used in concentrated form, i.e., at concentrations exceeding 70%, as an acid catalyst for curing. However, it is only suitable for the catalytic curing of furan resins with a relatively high urea content, as the curing of the aminoplast component in the furan no-bake binder is the primary focus. The nitrogen content of such resins is typically greater than 2.0 wt%. Sulfuric acid, being a relatively strong acid, can be added to weaker acids as a curing initiator for furan resins. However, during casting, a characteristic odor of sulfur compounds develops. Furthermore, there is a risk of sulfur absorption by the casting material, which would affect its properties.

[0024] The choice of acid catalyst for curing has a significant influence on the curing behavior of the binder, the properties of the molding compound mixture, and the resulting mold or core. The curing rate can be influenced by the quantity and strength of the acid. High acid quantities or stronger acids lead to an increase in the curing rate. If curing occurs too quickly, the working time of the molding compound mixture is drastically reduced, severely impairing its workability or even rendering it unusable. Furthermore, using excessive amounts of acid catalyst can cause the binder, such as a furan resin, to become brittle during curing, negatively impacting the strength of the mold.If too little acid catalyst is used, the resin will not fully cure (or the curing will take a very long time), resulting in lower strength of the mold.

[0025] In the production of casting molds, new sand is often used for the cores, while recycled molding material (e.g., sand) is frequently used for the molds themselves. Refractory molding materials consolidated with furan no-bake binders are very easy to recycle. Recycling is carried out either mechanically, by mechanically abrading off a layer formed from residual binder, or by thermally treating the used sand. With mechanical recycling or combined mechanical / thermal processes, recovery rates of nearly 100% can be achieved.

[0026] Phenolic resins, the second major group of acid-catalyzed, no-bake binders, contain resoles as their reactive resin component; these are phenolic resins produced with a molar excess of formaldehyde. Compared to furan resins, phenolic resins exhibit lower reactivity and require strong sulfonic acids as catalysts. Phenolic resins have a relatively high viscosity, which increases further with prolonged storage. After the phenolic no-bake binder has been applied to the refractory base material, the molding compound should be processed as soon as possible to avoid deterioration of the compound's quality due to premature curing, which can lead to a reduction in the strength of the resulting molds.When using phenol no-bake binders, the flowability of the molding compound is usually lower than that of a similarly produced molding compound with a furan no-bake binder. Therefore, the molding compound must be carefully compacted during mold production to achieve high mold strength.

[0027] The production and processing of such a molding compound mixture should take place at temperatures between 15 and 35°C. At lower temperatures, the molding compound mixture is more difficult to process due to the high viscosity of the phenolic no-bake resin. At temperatures above 35°C, the processing time is reduced due to premature curing of the binder.

[0028] After casting, molding compound mixtures based on phenol no-bake binders can also be reprocessed, using either mechanical or thermal or combined mechanical / thermal methods.

[0029] As previously explained, the acid used as a catalyst in furan or phenol no-bake processes has a very significant influence on the properties of the mold. The acid must be of sufficient strength to ensure an adequate reaction rate during the curing of the mold.

[0030] The curing process should be easily controllable so that sufficiently long processing times can be set. This is particularly important when producing molds for very large castings, the construction of which requires a longer period. Furthermore, the acid must not accumulate in the regenerated material when regenerating old molding materials (i.e., materials already used to produce lost-wax molds or cores, such as old sands). If acid is introduced into the molding material mixture via the regenerated material, this shortens the processing time and leads to a reduction in the strength of the mold produced from the regenerated material.

[0031] Therefore, not every acid is suitable for use as a catalyst in no-bake processes. In practice, toluenesulfonic acid, benzenesulfonic acid, or methanesulfonic acid are frequently used, as well as, in some cases, xylenesulfonic acid or cumenesulfonic acid [2(or 4)-(isopropyl)benzenesulfonic acid], and also phosphoric acid and sulfuric acid.

[0032] As previously explained, phosphoric acid is only suitable for curing certain furan resin grades. It is not suitable for curing phenolic resins. Another disadvantage of phosphoric acid is its tendency to accumulate in the regenerated material, which complicates its reuse. Sulfuric acid, when used for casting or thermal regeneration, emits sulfur dioxide, which is corrosive, harmful to health, and unpleasant odors. See below for further disadvantages of using sulfuric acid.

[0033] For some time now, no-bake binders have been used in the production of molds and cores for large-scale and individual castings. These cold-curing systems are mostly reaction products of formaldehyde with furfuryl alcohol, phenol, and / or urea.

[0034] These well-known no-bake binding agents exhibit one or more of the following disadvantages or undesirable properties: excessively high furfuryl alcohol content, excessively high water content, excessively high formaldehyde content, excessively strong odor, excessively high ammonia content and / or excessively high total nitrogen content.

[0035] US 3,644,274 primarily relates to a no-bake process using certain mixtures of acid catalysts for curing furfuryl alcohol-formaldehyde urea resins.

[0036] US 3,216,075 describes furfuryl alcohol-formaldehyde resins used in the production of foundry cores and molds at higher temperatures, i.e., temperatures >175°C. In this application, reaction products of furfuryl alcohol and formaldehyde were initially prepared in the presence of oxalic acid. After distilling off the water, largely anhydrous, highly viscous resins were obtained, which were then diluted with furfuryl alcohol to achieve a lower viscosity.

[0037] US 3,806,491 concerns binders that can be used in the "no-bake" process. The binders used therein include products derived from the reaction of paraformaldehyde with certain ketones in an alkaline environment, as well as furfuryl alcohol and / or furan resins.

[0038] US 5,607,986 describes heat-curing binders for the production of molds and foundry cores in the "warm-box" or "hot-box" process, based on furfuryl alcohol-formaldehyde phenolic resins produced in an alkaline environment at pH values ​​in the range of 8 to 9. The binders according to US 5,607,986 further contained furfuryl alcohol and polyvinyl acetate.

[0039] US 5,491,180 describes resin binders suitable for use in the no-bake process. The binders used therein are based on 2,5-bis(hydroxymethyl)furan or methyl or ethyl ethers of 2,5-bis(hydroxymethyl)furan, containing 0.5 to 30 wt% water and regularly a high proportion of furfuryl alcohol.

[0040] EP 0 540 837 proposes low-emission, cold-curing binders based on furan resins and lignin produced using the organosolv process. The furan resins described therein contain a high proportion of monomeric furfuryl alcohol.

[0041] DE 198 56 778 describes cold resin binders which are obtained by reaction of an aldehyde component, a ketone component and a component consisting essentially of furfuryl alcohol.

[0042] EP 1 531 018 relates to no-bake foundry binder systems consisting of a furan resin and certain acid hardeners. The binder systems described therein preferably comprise 60 to 80 wt.% furfuryl alcohol.

[0043] DE 10 2008 024 727 describes certain methanesulfonic acid-containing catalyst mixtures that are used there as hardeners in the no-bake process.

[0044] US 2008 / 0207796 discloses no-bake binders which are essentially free of nitrogen and formaldehyde, based on monomeric furfuryl alcohol and "furan derivatives" or (such as 2,5-bis(hydroxymethyl)furan or 5-hydroxymethylfurfural) and / or polyester polyols.

[0045] US 4,176,114 A discloses a method for producing sand molds and cores. In this process, sand is mixed with an acid-curing resin comprising high viscosity polyfurfuryl alcohol. Curing is then achieved by contacting the mixture with gaseous sulfur dioxide in the presence of an oxidizing agent.

[0046] US 5,741,914 A discloses resin-based binder compositions comprising reaction products of furfuryl alcohol with formaldehyde. The binder compositions partially include a weak organic acid and, in some cases, only a small amount of formaldehyde.

[0047] US 6,391,942 B1 discloses furan no-bake foundry binder and its use.

[0048] Particularly in iron and steel casting, especially stainless steel casting, the lowest possible total nitrogen content is desirable, as a total nitrogen content of 4 wt% or higher in a no-bake binder can lead to casting defects. Specifically for use in steel and gray cast iron castings, a no-bake binder should have the lowest possible total nitrogen content, as surface defects, such as pinholes, can occur.

[0049] One type of pinhole is the "water-nitrogen pinhole", in which water vapor reacts with the iron companions and nitrogen-containing components to form metal oxides and nitrogen-hydrogen compounds that diffuse into the liquid metal, thus leading to micropore formation.

[0050] In large casting processes, the ammonia content in no-bake binders for large casting processes should be kept as low as possible; preferably, the use of ammonia should be avoided.

[0051] Preferably, a no-bake binding agent meets several or all of the following criteria: low viscosity, good storage stability, low-nitrogen or nitrogen-free binder, especially for high-quality steel casting, low odor, reactive, fast-curing binder for short demolding times (this eliminates the need for chemically aggressive hardeners or activators), low-sulfur or sulfur-free binder for high-quality ductile iron (this allows for a significant reduction in SO2 emissions during and after casting).

[0052] As a component of a molding compound mixture, a no-bake binder should meet several or all of the following criteria: good hardening, low binder addition required in mold or core production, low pollutant emissions during mixing, filling and compacting of the molding material mixture (the permissible OEL values ​​should regularly be significantly undercut), readily regenerable old sands are obtained. In the production of casting molds, which generally includes the relevant work steps of mixing, filling and compacting and storing the molding material, the key components formaldehyde and furfuryl alcohol must be taken into account in accordance with VDG leaflet R 304 (February 1998) ("Cold-curing molding processes with furan resin").

[0053] Compliance with occupational exposure limits (OELs) in foundries is not always easy to achieve, as it requires very complex extraction systems and filters. For example, efficient extraction of emitted pollutants is hardly feasible and practical in large-scale casting operations.

[0054] The invention was therefore based on the objective of providing a binder based on furfuryl alcohol and formaldehyde, which can be used in a no-bake process for the production of cores and molds for the foundry industry, so that a low emission of pollutants occurs during the production of molds and cores and / or during casting, in particular with regard to furfuryl alcohol and formaldehyde, and preferably also ammonia.

[0055] In a first aspect, the invention therefore relates to a mixture for use as a binder in the no-bake process, comprising (a) monomeric furfuryl alcohol, wherein the amount of monomeric furfuryl alcohol is at most 25 wt.%, (b) 40 wt.% or more of reaction products of formaldehyde, wherein the reaction products comprise (b-1) reaction products of formaldehyde with furfuryl alcohol and optionally other components, and (b-2) optionally reaction products of formaldehyde with one or more other compounds that are not furfuryl alcohol, (c) water, wherein the amount of water is at most 20 wt.%, (d) one or more organic acids having a pKa value greater than or equal to 2.5, preferably in the range of 2.75 to 6, more preferably in the range of 3 to 5, at 25°C and / or their salts, wherein the mixture has a free formaldehyde content of not more than 0.5 wt%, where the wt% values ​​are based on the total mass of the mixture.

[0056] It has now been surprisingly found that when using reaction mixtures according to the invention (as defined below), containing a mixture according to the invention, the emission of pollutants, in particular the emission of furfuryl alcohol and formaldehyde, could be drastically reduced during mixing, filling, and compacting of the molding material, without impairing the processability and other relevant properties of a no-bake binder. Thus, a multitude of desired positive properties were achieved by the mixture according to the invention. The good processability of reaction mixtures comprising mixtures according to the invention is based, among other things, on their comparatively low viscosity (see below for preferred viscosities).Other relevant properties of a no-bake binder include its influence on the curing behavior (especially depending on the water content, see below) and its influence on the stability of corresponding molds or cores upon spontaneous contact with liquid metal (especially depending on the water content, see below the notes on the bursting of molds and cores in the casting process).

[0057] The mixtures and reaction mixtures according to the invention (as defined below) can also be used particularly in the field of large casting, preferably for the production of molds and cores, in particular cores, weighing 800 kg or more, preferably 900 kg or more, and more preferably 1000 kg or more.

[0058] Refractory molding materials that have been solidified using a mixture according to the invention in the no-bake process can be very well reprocessed. This applies particularly to sand.

[0059] Furan resins are known from the prior art, but not for use in foundries. The furan resins described therein are not suitable for use in foundries as no-bake binders (i.e., not suitable for use in the no-bake process) because they exhibit one or more of the following disadvantages: excessive viscosity, excessive water content, excessive formaldehyde content, excessive ammonia content, and / or excessive total nitrogen content. Furthermore, these other furan resins known from the prior art do not regularly achieve acceptable curing profiles or sufficient strength development when used in no-bake processes.

[0060] US 2,343,972 describes resins obtained by reacting furfuryl alcohol and formaldehyde under heating in the presence of an acid such as lactic acid, formic acid, or chloroacetic acid. Specific information regarding properties important for binders in the no-bake process is lacking in US 2,343,972.

[0061] US 5,741,914 (and correspondingly US 5,849,858) describes resins as binders for the production of composite materials, obtained by reacting furfuryl alcohol with an excess of formaldehyde in the presence of an acid with a pKa value approximately greater than 4, wherein the molar ratio of furfuryl alcohol to formaldehyde is at least 1:2. Similar resins are disclosed in US 5,486,557.

[0062] DE 21 26 800 (and corresponding CA 1 200 336) describes a process for manufacturing a composite object and suitable binders for this purpose, wherein the binders are highly viscous resinous condensation products based on furan-formaldehyde, which are diluted with water.

[0063] US 3,816,375 (and correspondingly DE 23 02 629) describes partially prepolymerized furfuryl alcohol aldehyde binders, wherein the aldehyde is formaldehyde and / or furfural, which are used therein to form composites. If the material chosen for the composite is glass fiber, a prepolymerized, high-viscosity furfuryl alcohol aldehyde binder diluted with furfural is preferably used according to US 3,816,375. A similar process is disclosed in US 3,594,345 (and correspondingly DE 19 27 776).

[0064] US 2,874,148 discloses furfuryl alcohol-formaldehyde resins produced by reacting furfuryl alcohol with formaldehyde in the presence of sulfuric acid. The physical properties of the resins obtained according to US 2,874,148 depend highly on the specific reaction conditions.

[0065] Typically, a mixture according to the invention for use as a binder in the no-bake process does not include any acid having a pKa value of less than 2 at 25°C, and preferably no acid having a pKa value of less than 2.5 at 25°C. If, in exceptional cases, such acids are used, their maximum total amount is preferably less than 5% by weight, based on the total mass of the mixture. This applies to all mixtures according to the invention described below.

[0066] Typically, a mixture according to the invention for use as a binder in the no-bake process does not include refractory granular materials. If, in exceptional cases, refractory granular materials are used in the mixture, their maximum total amount is preferably less than 5% by weight, based on the total amount of the mixture. This applies to all mixtures according to the invention described below.

[0067] Typically, a mixture according to the invention is a homogeneous solution; this applies to all preferred mixtures according to the invention described below.

[0068] Preferably, a mixture according to the invention contains less than 5 wt.% monomeric furfural, preferably less than 3 wt.%, more preferably less than 1 wt.% monomeric furfural.

[0069] Preferably, the mixtures according to the invention contain less than 3 wt.% polyvinyl acetate, preferably less than 1 wt.%, more preferably they are free of polyvinyl acetate.

[0070] Preferably, a mixture according to the invention contains less than 5 wt.% monomeric furfural and less than 3 wt.% polyvinyl acetate.

[0071] Preferably, a mixture according to the invention contains less than 1 wt.% monomeric furfural and less than 1 wt.% polyvinyl acetate.

[0072] Preferably, the mixtures according to the invention comprise as part of the component (b-1) the compound 2,5-bis(hydroxymethyl)furan (BHMF), preferably in an amount of at least 2 wt.%, more preferably in an amount of 5 to 80 wt.%, particularly preferably in an amount of 10 to 70 wt.%, and especially in an amount of 20 to 60 wt.%, in each case based on the total weight of the component (b-1).

[0073] Preferably, the mixtures according to the invention comprise in component (b-1) 2,5-bis(hydroxymethyl)furan (BHMF) in an amount of at least 1 wt.%, more preferably in an amount of 5 to 40 wt.%, particularly preferably in an amount of 10 to 35 wt.%, and especially preferably in an amount of 15 to 30 wt.%, based on the total weight of a mixture according to the invention.

[0074] Preferably, a mixture according to the invention comprises monomeric furfuryl alcohol (component (a)) and 2,5-bis(hydroxymethyl)furan (BHMF) (as part of component (b-1)) in a weight ratio in the range of 3 : 1 to 1 : 3, preferably in the range of 2 : 1 to 1 : 2, further preferably in the range of 3 : 2 to 2 : 3, particularly preferably in the range of 5 : 4 to 4 : 5.

[0075] In component (b-1) of a mixture according to the invention, the proportion of "furan ring units" can be determined via the furan ring, for example via 13< C-NMR.

[0076] If nitrogen-containing components are present in component (b-2), their detection is possible via the nitrogen itself. If a phenol compound is a component in component (b-2), differentiation is also possible via the phenolic substance (e.g., determination of the residual monomer content, GC-MS analysis).

[0077] Other suitable analytical methods are 15< N-NMR and 13< C-NMR.

[0078] The proportion of furan ring units can be determined via 13C NMR. The proportion of furan ring units, calculated as furfuryl alcohol (C5H6O2), in the reaction product (b-1) of formaldehyde with furfuryl alcohol and optionally other components is preferably in the range of 60 to 96 wt.%, more preferably in the range of 70 to 95 wt.%, further preferably in the range of 75 to 90 wt.%, and particularly preferably in the range of 75 to 85 wt.%, in each case based on the total mass of component (b-1).

[0079] In component (b-2), the further compound(s) of the reaction product with formaldehyde are preferably selected from the group consisting of organic compounds that have one or more H2N groups and / or one or more HN groups, and phenolic compounds.

[0080] The particularly preferred organic compound having one or more H2N groups is urea.

[0081] The phenol compound(s) can be reacted under acidic conditions with furfuryl alcohol and formaldehyde directly or with a furfuryl alcohol / formaldehyde precondensate.

[0082] The phenolic compounds are preferably phenolic compounds with 6 to 25 carbon atoms and / or one, two, three, or four hydroxyl groups directly bonded to an aromatic ring, preferably selected from the group consisting of phenol, optionally C1-C4 alkyl mono- or disubstituted dihydroxybenzenes, trihydroxybenzenes, methylphenols, and bisphenols, and particularly preferably selected from the group consisting of phenol, o-dihydroxybenzene, m-dihydroxybenzene (resorcinol), p-dihydroxybenzene, 5-methylresorcinol, 5-ethylresorcinol, 2,5-dimethylresorcinol, 4,5-dimethylresorcinol, 1,2,3-trihydroxybenzene, 1,3,5-trihydroxybenzene, o-cresol, m-cresol, p-cresol, and bisphenol A. Phenol, resorcinol, and bisphenol A are particularly preferred.

[0083] Component (b-2) may, for example, be formaldehyde-phenol resins, which can be obtained by reacting formaldehyde and phenol and, if necessary, another component that is not furfuryl alcohol under alkaline conditions.

[0084] It is understood that a person skilled in the art can produce component (b-1) and, if present, component (b-2) of a mixture according to the invention separately and in a targeted manner. Components (b-1) and (b-2) can first be mixed together (preferably in the proportions specified as preferred) and introduced together as component (b) or, alternatively, in separate form as (b-1) and (b-2) into a mixture according to the invention.

[0085] It is further understood that the person skilled in the art can obtain or produce the components (a) to (d) of a mixture according to the invention separately. The components (a) to (d) can be mixed with one another successively or simultaneously (preferably in the proportions indicated as preferred) to obtain a mixture according to the invention.

[0086] The order in which the components (a) to (d) are added during the preparation of a mixture according to the invention is not significant. Preferably, the components (a) to (d) are mixed together at a temperature in the range of 0 to 70 °C, more preferably at a temperature in the range of 10 to 60 °C, and more preferably at a temperature in the range of 15 to 50 °C, for example at 18 to 25 °C.

[0087] For economic reasons, however, it is regularly preferred to prepare components (b-1) and (b-2) in a reaction involving furfuryl alcohol and formaldehyde in the presence of component (d), preferably in a one-pot reaction. The reaction is preferably carried out such that components (a) and (b) (i.e., component (b-1) and optionally component (b-2)) as well as components (c) and (d) of a mixture according to the invention are obtained in the desired proportions (preferably in the proportions specified as preferred). In such a case, the subsequent or separate addition of monomeric furfuryl alcohol (component (a)) is not necessary. Reference is also made to the following preparation process according to the invention.

[0088] The mixtures according to the invention contain water (component (c)). However, since water slows down the curing of the resulting molding compound mixture and is also produced during the condensation reaction in the manufacturing process, and furthermore, water is formed as a reaction product during curing, the proportion of water is preferably chosen to be low. Preferably, the proportion of water in a mixture according to the invention is less than 20 wt.%, preferably at most 15 wt.%. Preferred mixtures according to the invention contain water in an amount in the range of 5 to 15 wt.%, more preferably in an amount in the range of 7 to 14 wt.%, and particularly preferably in an amount in the range of 8 to 13 wt.%, wherein the wt. percentages are based on the total mass of the mixture according to the invention.

[0089] The comparatively low water content, compared to many prior art resin formulations, has a positive effect on the curing behavior and also means that molds or cores produced using the mixture according to the invention are less likely to crack during casting when in contact with liquid metal. With higher water contents in prior art mixtures, mold cracking is frequently observed, which can be largely avoided when using the mixtures according to the invention.

[0090] A preferred mixture according to the invention (as defined above) comprises (a) monomeric furfuryl alcohol, wherein the amount of furfuryl alcohol is at most 24.75 wt.%, preferably at most 24.60 wt.%, and / or (c) water, wherein the amount of water is at most 15 wt.%, wherein the wt. percent values ​​are based on the total mass of the mixture.

[0091] Preferably, in a mixture preferred according to the invention, the total amount of component (b) is 45 wt.% or more, preferably 50 wt.% or more, in each case based on the total mass of the mixture.

[0092] A preferred mixture according to the invention is characterized in that component (b) comprises or consists of (b-1) 40 wt.% or more, preferably 45 wt.% or more, preferably 50 wt.% or more, of reaction products of furfuryl alcohol with formaldehyde and optionally further components, preferably one or more further aldehydes, preferably glyoxal, and (b-2) reaction products of formaldehyde with one or more further compounds other than furfuryl alcohol, differing from component (b-1), wherein the amount of these further reaction products is at most 15 wt.%, preferably at most 12 wt.%, preferably at most 10 wt.%, wherein the wt. percent values ​​are based on the total mass of the mixture.

[0093] A preferred mixture according to the invention is characterized in that the mixture has a viscosity of at most 300 mPas at 20°C according to DIN 53019-1: 2008-09, preferably of at most 250 mPas, more preferably of at most 200 mPas, and more preferably of at most 150 mPas.

[0094] The viscosity is determined according to DIN 53019-1: 2008-09, i.e., according to DIN 53019-1 of September 2008, and refers to measurements at 20°C. In this text, the viscosity is given in millipascal-seconds (mPas or mPa*s). Preferably, the viscosity is determined according to DIN 53019-1 using a rotational viscometer at 20°C, for example, a Haake rotational viscometer VT 550. The viscosity values ​​determined within the scope of the present invention were measured using a cylinder (spindle) SV1 and a measuring cup (tube) SV. The rotational speed used for the viscosity measurement with the rotational viscometer was 800 rpm (revolutions / min) for a viscosity of the sample under investigation of less than 100 mPas at 20°C. Measurements were taken at a speed of 500 rpm and 20°C for a viscosity of the sample under investigation of 100 to 800 mPas.

[0095] A particularly preferred mixture according to the invention for use as a binder in the no-bake process is a mixture comprising (a) monomeric furfuryl alcohol, wherein the amount of monomeric furfuryl alcohol is at most 25 wt.%, (b) 40 wt.% or more of reaction products of formaldehyde, wherein the reaction products comprise (b-1) reaction products of formaldehyde with furfuryl alcohol and optionally other ingredients, and (b-2) optionally reaction products of formaldehyde with one or more other compounds that are not furfuryl alcohol, (c) water, wherein the amount of water is at most 15 wt.%, (d) one or more organic acids having a pKa value greater than or equal to 2.5, preferably in the range of 2.75 to 6, more preferably in the range of 3 to 5, at 25°C and / or their salts, wherein the mixture has a free formaldehyde content of not more than 0.5 wt%, where the wt% values ​​are based on the total mass of the mixture, wherein the mixture has a viscosity of at most 300 mPas at 20°C according to DIN 53019-1: 2008-09, preferably of at most 250 mPas, preferably of at most 200 mPas, further preferably of at most 150 mPas.

[0096] Despite a low water content of at most 15 wt.%, such a mixture according to the invention simultaneously possesses a low viscosity, which results in excellent processability of the molding material mixture in foundry operations (after mixing with the molding base). In our own investigations, the preferred mixtures according to the invention have proven particularly effective due to their good and reproducible dosing characteristics in continuous mixers. In practice, for example, with predefined screw geometries (furan cold resin plants), 35 tons of sand mixture or more are continuously mixed per hour. Good atomization of the mixture according to the invention is important here to ensure the most uniform and homogeneous distribution possible in the molding base during the short mixing time.

[0097] Furthermore, such a mixture according to the invention leads to good flowability, for example, of a freshly prepared sand mixture during mold filling. During mold filling, mold contours and undercuts should generally be well filled and compacted. Higher viscosity binders, compared to the preferred mixtures according to the invention, tend to cause the sand mixture to clump and flow poorly, resulting in surface casting defects due to poorer compaction.

[0098] A preferred mixture according to the invention is characterized in that the content of free formaldehyde is at most 0.4 wt.%, preferably at most 0.3 wt.%, preferably at most 0.2 wt.%, based on the total mass of the mixture.

[0099] Preferably, one or more organic acids with a pKa value in the range of 2.75 to 6 at 25°C, preferably in the range of 3 to 5, and / or their salts are used as component (d).

[0100] Organic acids with a pKa value in these ranges are particularly suitable condensation catalysts for the preparation of the reaction products of formaldehyde with furfuryl alcohol and optionally other components of component (b-1).

[0101] Suitable organic acids for component (d) of a mixture according to the invention include citric acid, lactic acid, benzoic acid, phthalic acid, 1-malic acid, d-tartaric acid, maleic acid, glycolic acid, glyoxylic acid, 2,4-dihydroxybenzoic acid and salicylic acid.

[0102] Preferred organic acids of component (d) are selected from the group consisting of benzoic acid, lactic acid, citric acid, phthalic acid, 2,4-dihydroxybenzoic acid, salicylic acid and their salts, since particularly good results in the sense of the present invention have been achieved with these acids, wherein particularly good results have been achieved with benzoic acid, lactic acid and citric acid respectively, and the best results have been achieved with benzoic acid.

[0103] The phase compatibility of benzoic acid in the mixture according to the invention has proven to be particularly good in our own investigations; no crystallization reaction was observed.

[0104] The use of other organic acids in component (d) is possible, but not preferred. For example, acetic acid, propionic acid, and butyric acid are intense and, in some cases, malodorous acids. Succinic acid and adipic acid, for instance, exhibit a rapid tendency to crystallize. The presence of these other organic acids in a mixture according to the invention is therefore not preferred.

[0105] Preferably, in a mixture preferred according to the invention, the total amount of component (d) is 0.5 to 8 wt.%, preferably 0.75 to 5 wt.%, particularly preferably 1 to 3 wt.%, in each case based on the total mass of the mixture.

[0106] A preferred mixture according to the invention is therefore one in which component (d) comprises an acid or a salt selected from the group consisting of benzoic acid, lactic acid, citric acid, phthalic acid, 2,4-dihydroxybenzoic acid, salicylic acid and their salts. Salicylic acid is somewhat less preferred because it negatively affects the shelf life of a mixture according to the invention in some cases, and in some cases, a comparatively low water miscibility of mixtures according to the invention prepared with salicylic acid has been found.

[0107] A preferred mixture according to the invention is one that has an ammonia content of at most 1 wt.%, preferably at most 0.5 wt.%, preferably at most 0.25 wt.%, based on the total mass of the mixture.

[0108] A preferred mixture according to the invention has a total nitrogen content of at most 4 wt.%, preferably at most 3.5 wt.%, and more preferably at most 3.0 wt.%, based on the total mass of the mixture. This applies in particular to the mixtures described above as preferred, which have a particularly low water content (in particular: at most 15 wt.%) and / or a particularly low viscosity (in particular: at 20°C a viscosity of at most 300 mPas or even lower, see above).

[0109] The total nitrogen content can be determined, for example, by elemental analysis or via the so-called Kjeldahl method (according to DIN 16916-02, point 5.6.4), with elemental analysis being preferred for determining the total nitrogen content of a mixture according to the invention.

[0110] The total nitrogen content determined within the scope of this text was determined by elemental analysis using selective CNS combustion catalysis (CNS = carbon, nitrogen, sulfur), whereby the catalytic tube combustion took place at 1140°C and foreign gases were separated (device: VARIO MAX CNS).

[0111] A preferred mixture according to the invention is a mixture whose total content of compounds with a molar mass greater than 5000 Daltons (g / mol) is at most 3 wt.%, preferably at most 1 wt.%, determined by gel permeation chromatography according to DIN 55672-1 (February 1995), wherein the weight percent values ​​refer to the total mass of the mixture.

[0112] The molar masses given below refer to molar masses determined by gel permeation chromatography (GPC) according to DIN 55672-1 (February 1995), where detection is preferably carried out with a UV detector at a wavelength of 235 nm.

[0113] In a preferred mixture according to the invention, the total content of compounds with a molar mass greater than 4000 Daltons (g / mol) is at most 3 wt.%, preferably at most 1 wt.%.

[0114] In a preferred mixture according to the invention, the total content of compounds with a molar mass greater than 3000 Daltons (g / mol) is at most 5 wt.%, preferably at most 2 wt.%.

[0115] In a preferred mixture according to the invention, component (b-1) does not comprise compounds with a molar mass greater than 5000 Daltons, more preferably not compounds with a molar mass greater than 4000 Daltons.

[0116] In a preferred mixture according to the invention, component (b-1) comprises at most 3 wt.% of compounds with a molar mass greater than 3000 Daltons.

[0117] In a preferred mixture according to the invention, component (b-1) comprises at most 5 wt.% of compounds with a molar mass greater than 2000 Daltons.

[0118] In a preferred mixture according to the invention, the molar mass mean M w (weight mean) of the component (b-1) is in the range of 200 to 600 g / mol, more preferably in the range of 225 to 500 g / mol, particularly preferably in the range of 250 to 450 g / mol, most preferably in the range of 300 to 425 g / mol.

[0119] In a preferred mixture according to the invention, the ratio of molar mass mean M w (weight mean) to molar mass mean M n (number mean) of component (b-1) is in the range of 5 : 1 to 9 : 8, more preferably in the range of 4 : 1 to 6 : 5, particularly preferably in the range of 3 : 1 to 4 : 3, and especially preferably in the range of 2 : 1 to 3 : 2.

[0120] In a preferred mixture according to the invention, the ratio of the molar mass mean Mw to the molar mass mean Mn of the two components (a) and (b-1) together is in the range of 5:1 to 9:8, more preferably in the range of 4:1 to 6:5, particularly preferably in the range of 3:1 to 4:3, and especially preferably in the range of 2:1 to 3:2.

[0121] The ratio of weight mean (molar mass mean Mw) to number mean (molar mass mean Mn) is also called polydispersity, which is often expressed as D in GPC spectra. Polydispersity is a measure of the width of a molar mass distribution. The larger D, the wider the molar mass distribution (a discrete compound has a polydispersity of 1).

[0122] In this regard, it was found that mixtures according to the invention, in which component (b-1) or the two components (a) and (b-1) together exhibit a polydispersity specified above as preferred or particularly preferred, showed particularly good results and effects in accordance with the present invention.

[0123] The mixtures according to the invention may preferably contain, for example, one or more adhesion promoters, preferably one or more silanes.

[0124] Suitable silanes include, for example, aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes and ureidosilanes, such as gamma-hydroxypropyltrimethoxysilane, gamma-aminopropyl-methyl-diethoxysilane, gamma-aminopropyltrimethoxysilane, gamma-aminopropyltriethoxysilane, 3-ureidopropyltriethoxysilane, gamma-mercaptopropyltrimethoxysilane, gamma-glycidoxypropyltrimethoxysilane, beta-(3,4-epoxycyclohexyl)trimethoxysilane, N-beta-(aminoethyl)-gamma-aminopropyltrimethoxysilane.

[0125] Gamma-Aminopropylmethyldiethoxysilane (N-Aminopropylmethyldiethoxysilane) is marketed under the trade names Silane 1100, Silane 1101, and Silane 1102 (technical grade) and AMEO T, and gamma-Aminopropyltriethoxysilane (N-Aminopropyltriethoxysilane) under Dynasilan 1505 and 1506 (technical grade). Silanes available under the trade names DAMO, DAMO-T, and Dynasilan 1411 are also suitable.

[0126] Particularly good results were achieved in the production of casting molds or cores with mixtures according to the invention containing one or more silanes, in particular one or more silanes from the group consisting of N-aminopropylmethyldiethoxysilane, N-aminoethyl-3-aminopropyltrimethoxysilane, N-aminoethyl-3-aminopropylmethyldiethoxysilane and / or N-aminopropyltriethoxysilane.

[0127] A particularly preferred mixture according to the invention therefore additionally comprises as a further component (e) one or more adhesion promoters, preferably selected from the group of silanes, preferably N-aminopropyl imethyldiethoxysilane, N-aminoethyl 3-aminopropyltrimethoxysilane, N-aminoethyl 3-aminopropylmethyldiethoxysilane and / or N-aminopropyltriethoxysilane, preferably in a total amount of up to 3 wt.%, preferably from 0.1 to 1 wt.%, wherein the wt. percent values ​​are based on the total mass of the mixture.

[0128] The mixtures according to the invention may contain further additives. For example, they may contain diols or aliphatic polyols as curing moderators, which lead to a reduction in reactivity. The proportion of these curing moderators in a mixture according to the invention should not be too high, since such curing moderators can, in unfavorable cases, lead to a reduction in the strength of the mold. The proportion of curing moderators is therefore preferably at most 10 wt.%, more preferably at most 5 wt.%, based on the total mass of the mixture.

[0129] A particularly preferred mixture according to the invention additionally comprises one or more further components selected from the group (f) organic hardening moderators, preferably selected from the group of di-, tri-, or polyols, preferably from the group of glycols with 2 to 12 carbon atoms, preferably in an amount of not more than 10 wt.%, based on the total mass of the mixture; (g) inert organic solubilizers, preferably with 1 to 6 carbon atoms, preferably selected from the group of alcohols R-OH, where R denotes a C1-C4 alkyl group, preferably ethanol, preferably in an amount of not more than 10 wt.%, based on the total mass of the mixture; (h) the reaction products of furfuryl alcohol and one or more aldehydes with 2 or more carbon atoms, preferably reaction products of furfuryl alcohol and glyoxal; (j) organic compounds having one or more H₂N groups and / or one or more HN groups, preferably urea; (k) phenolic compounds, preferably phenolic compounds with 6 to 25 carbon atoms and / or one, two,three or four hydroxyl groups directly bonded to an aromatic ring, preferably selected from the group consisting of phenol, optionally C1-C4 alkyl mono- or disubstituted dihydroxybenzenes, trihydroxybenzenes, methylphenols and bisphenols, particularly preferably selected from the group consisting of phenol, o-dihydroxybenzene, m-dihydroxybenzene, p-dihydroxybenzene, 5-methylresorcinol, 5-ethylresorcinol, 2,5-dimethylresorcinol, 4,5-dimethylresorcinol, 1,2,3-trihydroxybenzene, 1,3,5-trihydroxybenzene, o-cresol, m-cresol, p-cresol and bisphenol A, (m) benzyl alcohol, (n) aldehydes with 2 or more carbon atoms, preferably selected from the group consisting of acetaldehyde, propionaldehyde, butyraldehyde, acrolein, crotonaldehyde, benzaldehyde, salicylaldehyde, Cinnamaldehyde, glyoxal and mixtures of these aldehydes, preferably glyoxal.

[0130] Preferred organic hardening moderators of component (f) are glycols with 2 to 12 C atoms, more preferably glycols with 2 to 6 C atoms, in particular preferred is ethylene glycol, i.e. monoethylene glycol.

[0131] The amount of ethylene glycol is preferably at most 10 wt.%, preferably at most 5 wt.%, based on the total mass of the mixture according to the invention.

[0132] Preferred aldehydes forming reaction products with furfuryl alcohol according to component (h) of a mixture according to the invention are acetaldehyde, propionaldehyde, butyraldehyde, acrolein, crotonaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde, glyoxal and mixtures of these aldehydes, with glyoxal being preferred.

[0133] A preferred aldehyde with 2 or more carbon atoms of component (h) and / or component (n) of a mixture according to the invention is glyoxal, since it is not only readily available and economically advantageous, but also provides technical advantages to a mixture according to the invention. For example, even small amounts of glyoxal as component (n) as well as reaction products of furfuryl alcohol and glyoxal as component (h) have a positive influence on the reactivity of a mixture according to the invention.

[0134] If a mixture according to the invention comprises component (n), the total amount of component (n) is preferably at most 5 wt.%, preferably at most 3 wt.%, based on the total mass of the mixture.

[0135] Preferred phenolic compounds of component (k) of a mixture according to the invention are phenolic compounds with 6 to 25 C atoms and one, two, three or four hydroxyl groups directly bonded to an aromatic ring. Further preferred phenolic compounds are selected from the group consisting of phenol, optionally C1-C4 alkyl mono- or disubstituted dihydroxybenzenes, trihydroxybenzenes, methylphenols and bisphenols, particularly preferably selected from the group consisting of phenol, o-dihydroxybenzene, m-dihydroxybenzene (resorcinol), p-dihydroxybenzene, 5-methylresorcinol, 5-ethylresorcinol, 2,5-dimethylresorcinol, 4,5-dimethylresorcinol, 1,2,3-trihydroxybenzene, 1,3,5-trihydroxybenzene, o-cresol, m-cresol, p-cresol and bisphenol A (2,2-bis-(4-hydroxyphenyl)-propane), wherein phenol, resorcinol and / or bisphenol A are again particularly preferred.

[0136] Component (k) preferably comprises or consists of phenol, resorcinol and / or bisphenol A, since these free phenols in particular have shown a high affinity for reaction with formaldehyde and react rapidly with any formaldehyde that may still be present, thereby further reducing emission, especially of formaldehyde, particularly during the curing process.

[0137] Bisphenol A is particularly advantageous in this context because – presumably due to its diphenylmethane skeleton – after hardening a mixture according to the invention, as a component of a reaction mixture according to the invention, it leads to higher strength of the resulting molds and cores. Furthermore, higher thermal stability is observed, especially during the casting process, which can achieve a further positive effect with regard to emissions.

[0138] A preferred mixture according to the invention may additionally comprise benzyl alcohol as a component (m), preferably in an amount of at most 15 wt.%, based on the total mass of the mixture.

[0139] The addition of benzyl alcohol, which in a mixture according to the invention mainly serves as a solvent (m), further improves the desired properties of a mixture according to the invention.

[0140] The advantage lies, among other things, in the very good compatibility with the other components of a mixture according to the invention. Furthermore, it was found that a reduction in viscosity, i.e., also in the viscosity value, occurs, and that the storage stability of a mixture according to the invention is further improved.

[0141] When benzyl alcohol is used, compared to lower alcohols (especially 1-alkanols with 1 to 4 carbon atoms, particularly methanol, ethanol, or isopropanol), the flash point of a mixture according to the invention is increased and the odor is simultaneously reduced. Furthermore, with lower alcohols, depending on the amount used, cold curing can be undesirably delayed to a significant degree, which is only observed to a lesser extent with benzyl alcohol. A preferred mixture according to the invention has a pH value in the range of 4 to 10 at 25°C, preferably in the range of 5 to 9.5.

[0142] A mixture according to the invention preferably has a pH value in the range of 5 to 7 or in the range of 8 to 9.5 at 25°C.

[0143] The preferably set pH values ​​of a mixture according to the invention, which is usually a solution, result in excellent storage stability.

[0144] A preferred mixture according to the invention is a storage-stable mixture, preferably having a storage stability of at least 3 months at 20°C, wherein during the storage period preferably the viscosity of the mixture at 20°C, measured according to DIN 53019-1: 2008-09, increases by at most 80%, preferably by at most 70%, preferably by at most 60%, particularly preferably by at most 50%, and preferably does not exceed 300 mPas, preferably 250 mPas, more preferably 200 mPas, particularly preferably 150 mPas, and the weight fraction of component (a) decreases by at most 10%, preferably by at most 5%, based on the initial amount of monomeric furfuryl alcohol at the beginning of the storage period.

[0145] A preferred mixture according to the invention comprises or consists of: (a) monomeric furfuryl alcohol, wherein the amount of monomeric furfuryl alcohol is at most 25 wt.%, preferably at most 24.75 wt.%, (b) 40 wt.% or more of reaction products of formaldehyde, wherein the reaction products comprise (b-1) 40 wt.% or more, preferably 45 wt.% or more, of reaction products of furfuryl alcohol with formaldehyde and optionally further components, preferably one or more further aldehydes, preferably glyoxal, and (b-2) reaction products of formaldehyde with one or more further compounds other than furfuryl alcohol, differing from component (b-1), wherein the amount of these further reaction products is at most 12 wt.%, preferably at most 10 wt.%, (c) water, wherein the amount of water is at most 15 wt.%, (d) one or more organic acids having a pKa value in the range of 2.75 to 6, preferably in the range of 3 to 5, at 25°C and / or their salts,preferably in a total amount of 0.75 to 5 wt.%, (e) one or more adhesion promoters from the group of silanes, preferably N-aminopropylmethyldiethoxysilane, N-aminoethyl-3-aminopropyltrimethoxysilane, N-aminoethyl-3-aminopropylmethyldiethoxysilane and / or N-aminopropyltriethoxysilane, preferably in a total amount of up to 3 wt.%, more preferably 0.1 to 1 wt.%, (f) one or more organic curing moderators from the group of glycols with 2 to 12 carbon atoms, preferably in an amount of at most 10 wt.%, (g) one or more inert organic solubilizers selected from the group of alcohols R-OH, wherein R denotes a C1-C4 alkyl group, preferably ethanol, (h) optionally one or more reaction products of furfuryl alcohol and one or more aldehydes with 2 or more carbon atoms, preferably reaction products of furfuryl alcohol and Glyoxal, (j) optionally one or more organic compounds,(k) optionally comprising one or more H₂N groups and / or one or more HN groups, preferably urea, (k) optionally comprising one or more phenolic compounds, preferably phenolic compounds comprising 6 to 25 carbon atoms and / or one, two, three or four hydroxyl groups directly bonded to an aromatic ring, preferably selected from the group consisting of phenol, optionally C1-C4 alkyl mono- or disubstituted dihydroxybenzenes, trihydroxybenzenes, methylphenols and bisphenols, particularly preferably selected from the group consisting of phenol, o-dihydroxybenzene, m-dihydroxybenzene, p-dihydroxybenzene, 5-methylresorcinol, 5-ethylresorcinol, 2,5-dimethylresorcinol, 4,5-dimethylresorcinol, 1,2,3-trihydroxybenzene, 1,3,5-trihydroxybenzene, o-cresol, m-cresol, p-cresol and Bisphenol A, (n) optionally glyoxal, , as well as optionally free formaldehyde in an amount of no more than 0.5 wt%, where the weight percentages refer to the total mass of the mixture.

[0146] A further preferred mixture according to the invention comprises or consists of: (a) monomeric furfuryl alcohol, wherein the amount of monomeric furfuryl alcohol is at most 24.75 wt.%, preferably at most 24.60 wt.%, (b) 45 wt.% or more of reaction products of formaldehyde, wherein the reaction products comprise (b-1) 45 wt.% or more, preferably 50 wt.% or more, of reaction products of furfuryl alcohol with formaldehyde and optionally further components, preferably one or more further aldehydes, preferably glyoxal, and (b-2) reaction products of formaldehyde with one or more further compounds other than furfuryl alcohol, differing from component (b-1), wherein the amount of these further reaction products is at most 12 wt.%, preferably at most 10 wt.%, (c) water, wherein the amount of water is at most 15 wt.%, preferably in an amount of 5 to 15 wt.%, (d) one or more organic acids having a pKa value in the range of 3 to 5 at 25°C and / or their salts,preferably in an amount of 1 to 4 wt%, (e) one or more adhesion promoters from the group of silanes, preferably N-aminopropyl methyldiethoxysilane, N-aminoethyl-3-aminopropyltrimethoxysilane, N-aminoethyl-3-aminopropyl methyldiethoxysilane and / or N-aminopropyltriethoxysilane, preferably in a total amount of 0.1 to 1 wt%, (f) ethylene glycol in an amount of at most 5 wt%, preferably in an amount of 1 to 4 wt%, (g) ethanol in an amount of at most 5 wt%, preferably in an amount of 1 to 4.5 wt%, (h) optionally one or more reaction products of furfuryl alcohol and one or more aldehydes with 2 or more carbon atoms, preferably reaction products of furfuryl alcohol and glyoxal, (n) optionally glyoxal, and either component (j) or component (k) (j) one or more organic compounds containing one or more H₂ have N-groups and / or one or more HN groups, preferably urea,(k) optionally one or more phenolic compounds, preferably phenolic compounds with 6 to 25 carbon atoms and / or one, two, three or four hydroxyl groups directly bonded to an aromatic ring, preferably selected from the group consisting of phenol, optionally C1-C4 alkyl mono- or disubstituted dihydroxybenzenes, trihydroxybenzenes, methylphenols and bisphenols, particularly preferably selected from the group consisting of phenol, o-dihydroxybenzene, m-dihydroxybenzene, p-dihydroxybenzene, 5-methylresorcinol, 5-ethylresorcinol, 2,5-dimethylresorcinol, 4,5-dimethylresorcinol, 1,2,3-trihydroxybenzene, 1,3,5-trihydroxybenzene, o-cresol, m-cresol, p-cresol and bisphenol A, , as well as optionally free formaldehyde in an amount of no more than 0.5 wt%, where the weight percentages refer to the total mass of the mixture.

[0147] A particularly preferred mixture according to the invention comprises or consists of: (a) monomeric furfuryl alcohol, wherein the amount of monomeric furfuryl alcohol is at most 24.60 wt.%, (b) 45 wt.% or more of reaction products of formaldehyde, wherein the reaction products comprise (b-1) 45 wt.% or more, preferably 50 wt.% or more, of reaction products of furfuryl alcohol with formaldehyde and optionally further components, preferably one or more further aldehydes, preferably glyoxal, and (b-2) reaction products of formaldehyde with one or more further compounds other than furfuryl alcohol, differing from component (b-1), wherein the amount of these further reaction products is at most 12 wt.%, preferably at most 10 wt.%, (c) water, wherein the amount of water is at most 15 wt.%, preferably in an amount of 7 to 14 wt.%.-%, (d) one or more organic acids with a pKa value in the range of 3 to 5 at 25°C and / or their salts in an amount of 1 to 4 wt%, wherein the organic acid is selected from the group consisting of benzoic acid, lactic acid and citric acid, (e) N-aminopropyl methyldiethoxysilane and / or N-aminopropyltriethoxysilane, preferably in a total amount of 0.1 to 1 wt%, (f) ethylene glycol in an amount of not more than 5 wt%, preferably in an amount of 1 to 4 wt%, (g) ethanol in an amount of not more than 5 wt%, preferably in an amount of 1 to 4.5 wt%, (h) optionally one or more reaction products of furfuryl alcohol and one or more aldehydes with 2 or more carbon atoms, preferably reaction products of furfuryl alcohol and glyoxal, (n) optionally glyoxal, and either component (j) or component (k) (j) Urea, (k) Phenol, Resorcinol and / or Bisphenol A, and optionally free formaldehyde in an amount not exceeding 0.5 wt.-%, where the weight percentages are based on the total mass of the mixture.

[0148] The invention further relates to a reaction mixture comprising (i) a mixture according to the invention, preferably in one of the embodiments characterized as preferred, (ii) an acid, wherein the acid has a pKa value of less than 2 at 25°C, preferably less than 1.5, preferably less than 1.

[0149] The reaction mixture preferably has a free formaldehyde content of no more than 0.4 wt.%, where the wt. percent values ​​are based on the total mass of the reaction mixture minus the total mass of refractory granular substances in the reaction mixture.

[0150] Component (ii) is also referred to as an acid hardener. The acid hardener allows the hardening of a mixture according to the invention at low temperatures, typically at ambient temperature. The amount of component (ii) used is preferably such that hardening of the mixture according to the invention occurs even at low temperatures, typically at ambient temperature, in particular at 25°C.

[0151] Preferably, the total amount of acid used, with a pKa of less than 2 at 25°C, is such that the pH value of the resulting reaction mixture is less than 3, preferably even less than 1. The acid hardener then advantageously causes the mixture according to the invention to harden at 25°C.

[0152] Component (ii) of a reaction mixture according to the invention preferably comprises or consists of organic sulfonic acids. These may include aromatic sulfonic acids such as benzenesulfonic acid, toluenesulfonic acids, and xylenesulfonic acids. or cumenesulfonic acid [2(or 4)-(isopropyl)benzenesulfonic acid] Methanesulfonic acid and ethanesulfonic acid are also preferred. The organic sulfonic acids are readily available and exhibit a sufficiently high acid strength to achieve the desired hardening of a mixture according to the invention using the no-bake process. Within the scope of the present invention, the best results were obtained with p-toluenesulfonic acid.

[0153] A reaction mixture is preferred according to the invention, wherein the acid of component (ii) is selected from the group of organic acids, preferably organic sulfonic acids, preferably selected from the group consisting of benzenesulfonic acid, toluenesulfonic acids, xylenesulfonic acids, Cumenesulfonic acid [2(or 4)-(isopropyl)benzenesulfonic acid]and methanesulfonic acid, in particular preferably p-toluenesulfonic acid.

[0154] Preferably, the reaction mixture (i) contains no sulfuric acid or (ii) contains sulfuric acid in an amount of at most 1 wt.%, preferably at most 0.5 wt.%, wherein the wt. percent values ​​are based on the total mass of the reaction mixture less the total mass of (optionally present) refractory granular materials in the reaction mixture. Preferably, the reaction mixture contains no phosphoric acid and no hydrochloric acid; particularly preferably, the reaction mixture according to the invention contains no mineral acids at all. In the case of sulfuric acid, the acid strength is problematic in some cases. Experience has shown that binders cured solely with sulfuric acid exhibit a "spontaneously" generated polymer network with inevitably more defects. Furthermore, the material-related higher sulfur content leads to massive sulfurization of the recycled sand.Such massive sulfurization causes casting and structural defects and also smells extremely unpleasant (rotten odor). It has been shown that the sulfur from the sulfuric acid is reduced during the process to sulfur-containing compounds that remain in the molding sand.

[0155] Aromatic sulfonic acids, on the other hand, are very miscible with resins (exhibiting good phase compatibility). Compared to sulfuric acid, the curing process is more orderly, homogeneous, complete, and also more easily controlled. Furthermore, some of the organically bound sulfur evaporates from the molding material as SO₂ during the casting process. This results in less sulfurization. In terms of handling, the less corrosive nature of sulfonic acids compared to sulfuric acid is also advantageous (the service life of the tools is positively affected).

[0156] Preferably, in a reaction mixture according to the invention, acid with a pKa of less than 2 at 25°C is used in a total amount in the range of 10 to 80 wt.%, preferably 15 to 70 wt.%, more preferably 20 to 60 wt.%, particularly preferably 25 to 50 wt.%, in each case based on the total mass of formaldehyde and the components (a), (b), (c), (d), (e), (f), (g), (h), (j), (k) and (n) of the mixture according to the invention (component (i)).

[0157] Preferably, the total proportion of acid or acids with a pKa less than 2 at 25°C in a reaction mixture according to the invention is in the range of 9 to 45 wt.%, preferably 13 to 41 wt.%, more preferably 16 to 38 wt.%, particularly preferably 20 to 33 wt.%, based on the total mass of the reaction mixture according to the invention less the total mass of any refractory granular substances that may be present.

[0158] A reaction mixture is preferably, which additionally comprises (iii) one or more refractory granular materials, preferably sand, preferably in an amount of 80 wt.% or more, preferably 95 wt.% or more, based on the total weight of the reaction mixture.

[0159] If a reaction mixture according to the invention comprises, in addition to a mixture according to the invention (component (i)), an acid hardener (component (ii)) and a refractory granular material (component (iii)), a molding material mixture is present.

[0160] Preferably, reaction mixtures according to the invention do not include sulfur dioxide or do not include a peroxide (in particular methyl ethyl ketone peroxide), preferably those that do not include either sulfur dioxide or a peroxide (in particular methyl ethyl ketone peroxide).

[0161] Refractory molding materials that have been solidified using a reaction mixture according to the invention in a no-bake process can be very well reprocessed. This applies particularly to sand.

[0162] A reaction mixture according to the invention preferably comprises sand, preferably with a grain size in the range of 0.063 to 2 mm, preferably with a grain size in the range of 0.1 to 1 mm.

[0163] A reaction mixture according to the invention preferably comprises 80 wt.% or more of the component (iii), preferably 95 wt.% or more, based on the total weight of the reaction mixture (i.e. the molding material mixture).

[0164] Preferably, component (iii) comprises or consists of sand, preferably aluminum silicate sand, feldspar sand and / or quartz sand. Particularly preferably, component (iii) comprises quartz sand; more preferably, component (iii) consists of quartz sand.

[0165] The invention further relates to a method for producing a mixture according to the invention, preferably in one of the embodiments characterized as preferred or particularly preferred, comprising the following step: (S-1) Reaction of furfuryl alcohol with formaldehyde and optionally further components in the presence of one or more organic acids having a pKa value greater than or equal to 2.5, preferably in the range of 2.75 to 6, more preferably in the range of 3 to 5, at 25°C and / or their salts, wherein the molar ratio of the total amount of furfuryl alcohol used to the total amount of formaldehyde used is greater than or equal to 1, preferably in the range of 5 : 1 to 1.1 : 1, more preferably in the range of 3 : 1 to 1.25 : 1, more preferably in the range of 2 : 1 to 3 : 2.

[0166] Formaldehyde can be used both in monomeric form, for example in the form of a formalin solution, and in the form of its polymers, such as trioxane or paraformaldehyde, with the use of paraformaldehyde being preferred according to the invention.

[0167] In addition to formaldehyde, other aldehydes can also be used. Suitable aldehydes include, for example, acetaldehyde, propionaldehyde, butyraldehyde, acrolein, crotonaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde, glyoxal, and mixtures of these aldehydes.

[0168] Particularly preferred organic acids with a pKa value in the range of 3 to 5 at 25°C are selected from the group consisting of benzoic acid, lactic acid, citric acid, phthalic acid, 2,4-dihydroxybenzoic acid and salicylic acid, wherein benzoic acid, lactic acid and citric acid are further preferred, and benzoic acid is most preferred.

[0169] In step (S-1) a pH value is preferably adjusted in the range of 2.8 to 5, preferably in the range of 3.5 to 4.5, each measured at 20°C.

[0170] In a preferred method according to the invention, step (S-1) is carried out at a temperature in the range of 90 to 160°C, preferably at a temperature in the range of 100 to 150°C.

[0171] A preferred method according to the invention comprises the following further steps: (S-2) Tempering the (first) reaction mixture resulting from step (S-1) to a temperature in the range of 40 to 90 °C, preferably in the range of 50 to 80 °C, (S-3) optionally adjusting the desired pH value with an inorganic base, preferably with an alkali metal hydroxide, preferably NaOH and / or KOH, (S-4) adding one or more compounds that can react with any formaldehyde that may still be present (or(S-5) Addition of one or more compounds for reaction with any formaldehyde still present, wherein these compounds are preferably selected from the group of organic compounds with one or more H₂N and / or HN groups and / or the group of phenolic compounds, (S-6) Tempering the reaction mixture resulting from the preceding steps to a temperature in the range of 10 to 50 °C, preferably in the range of 15 to 40 °C, (S-7) Optionally adding further components, preferably one, several or all of the components (e), (f), (g), (h), (j), (k), (m) and (n) as defined above for a mixture according to the invention, preferably in one of the embodiments characterized as preferred.

[0172] In a preferred process according to the invention, the total amount of furfuryl alcohol used is at least 50 wt.%, preferably at least 55 wt.%, and preferably in the range of 60 to 75 wt.%, further preferably in the range of 62 to 72 wt.%, wherein the wt. percent values ​​are based on the total mass of the resulting mixture according to the invention.

[0173] A preferred mixture according to the invention (as defined above), preferably in one of the embodiments characterized as preferred, is a mixture producible according to a method according to the invention, preferably in one of the embodiments characterized as preferred.

[0174] The invention also relates to a method for producing a mold or core, preferably a no-bake mold or core for producing metal bodies, comprising the step of: Hardening, preferably acid-catalyzed hardening, of a mixture according to the invention, preferably in one of the embodiments characterized as preferred, or hardening of a reaction mixture according to the invention, preferably in one of the embodiments characterized as preferred, wherein the hardening preferably takes place at a temperature below 60°C, preferably in the range of 0 to 50°C, preferably in the range of 10 to 40 °C, particularly preferably in the range of 15 to 30 °C.

[0175] In a preferred embodiment for carrying out the no-bake process, the refractory molding base material according to the invention (component (iii) of a reaction mixture according to the invention) is first coated with the acid hardener (component (ii) of a reaction mixture according to the invention). Subsequently, the binder (i.e., a mixture according to the invention; component (i) of a reaction mixture according to the invention) is added and evenly distributed by mixing onto the granules of the refractory molding base material that are already coated with the catalyst. The molding material mixture can then be formed into a molded body. Since the binder and acid hardener are evenly distributed in the molding material mixture, curing occurs largely uniformly, even with large molded bodies.

[0176] In a preferred method according to the invention, hardening preferably takes place in the absence of sulfur dioxide. Preferably, a reaction mixture according to the invention is prepared for hardening a mixture according to the invention, which then hardens without further action. The descriptions of the reaction mixture according to the invention apply accordingly to the method according to the invention.

[0177] In the inventive method for producing cores and molds for the foundry industry, a preferably molding material mixture is used which is particularly suitable for the production of large casting molds and cores, wherein these casting molds and cores exhibit a reduced emission of harmful compounds during casting.

[0178] The invention also relates to a mold or core for producing metal bodies obtainable by hardening a reaction mixture according to the invention, preferably in one of the embodiments characterized as preferred.

[0179] In another aspect, the invention relates to the use of a mixture according to the invention, preferably in one of the embodiments characterized as preferred, as a cold-curing binder, preferably as a no-bake binder in foundry work, in particular in the production of metal bodies by means of a casting process, wherein the curing of the binder preferably takes place without the use of gaseous sulfur dioxide.

[0180] In another aspect, the invention relates to the use of a mixture or reaction mixture according to the invention, preferably in one of the embodiments characterized as preferred, in a no-bake process for the production of metal bodies, preferably in a no-bake process in which no gaseous sulfur dioxide is used for hardening, preferably in a no-bake process without a gassing step.

[0181] The invention further relates to a kit comprising as a first component a mixture according to the invention, preferably in one of the embodiments characterized as preferred, as a second component an aqueous solution of an acid, wherein the acid has a pKa value of less than 2 at 25°C.

[0182] The invention will be explained in more detail below using examples. Examples

[0183] Unless otherwise stated, all specifications refer to weight. Abbreviations used: FA = furfuryl alcohol, BI = rating index.

[0184] Table 1 below compares the chemical and physical parameters of the resins. The values ​​given are average values ​​typical for the respective binder.

[0185] The non-inventive no-bake binding agents designated "KH-Ref1" and "KH-Ref2" are commercially available products. Table 1: KH-Ref1 (not according to the invention) KH-Y (according to the invention) KH-Ref2 (not according to the invention) Total amount of FA used 87% by weight 67% by weight 75% by weight Content of monomeric FA 87% by weight 24.5 wt.% 63 wt.% Total nitrogen content 1.05 wt.% 2.85 wt.% 3.5 wt.% Water content 10 wt.% 11% by weight 10 wt.% free formaldehyde 0.15 wt.% 0.15 wt.% 0.06 wt.% Density at 20°C 1.130 g / cm³< 1.185 g / cm³< 1.160 g / cm³< Dynamic viscosity at 20°C 10 mPa*s 65 mPa*s 20 mPa*s Look light brown, cloudy dark brown, clear dark brown, clear

[0186] The no-bake binding agent KH-Ref2, which was also examined here for comparison purposes and is not in accordance with the invention, had the following composition: Cold resin TN-X 56.0 wt.% Content of monomeric FA 41.3 wt.% Water 2.5 wt.% N-Aminopropylmethyldiethoxysilane 0.2 wt.%

[0187] These components of the no-bake binder KH-Ref2 were introduced into a reactor while stirring and the components were mixed for 15 minutes. Production of the cold resin TN-X:

[0188] Furfuryl alcohol (60.30 wt%), paraformaldehyde 91% (15.88 wt%), formic acid 85% (0.60 wt%), urea (12.59 wt%), water (3.56 wt%), ethanol (4.95 wt%), ammonia 25% in water (2.12 wt%).

[0189] Throughout the entire process, the reactor contents are stirred. In a reactor, 489.9 kg of furfuryl alcohol, 63.0 kg of urea, 158.8 kg of 91% paraformaldehyde, 35.6 kg of water, and 49.5 kg of ethanol are placed and thoroughly mixed. Then, 4.8 kg of 85% formic acid are added, and the resulting mixture is heated to 90 °C. At intervals of approximately 30 minutes, a further 62.9 kg of urea is added in portions at 90 °C. This reaction mixture is then cooled slightly, and 113.1 kg of furfuryl alcohol is added. After further cooling to 50 °C, the pH is adjusted to the range of 8.1 to 8.8 by adding 25% ammonia in water. The product thus obtained is referred to herein as the non-inventional mixture TN-X.

[0190] Data for the cold resin TN-X: Water content: 13.5 wt.%, Total nitrogen content: 6.2 wt.%, Formaldehyde content: 0.1 wt.%, Viscosity at 20 °C: 95 mPas. Production of the no-bake binding agent KH-Y according to the invention:

[0191] Furfuryl alcohol (66.98 wt%), Paraformaldehyde 91% (12.38 wt%), Benzoic acid (1.56 wt%), Urea (6.07 wt%), Water (6.94 wt%), Ethanol (2.98 wt%), Monoethylene glycol (1.99 wt%), N-Aminopropyltriethoxysilane (Dynasilan 1506) (0.40 wt%), Sodium hydroxide 33% in water (0.70 wt%).

[0192] Throughout the entire process, the reactor contents are stirred. In a reactor, 223.2 kg of furfuryl alcohol and 5.2 kg of benzoic acid are intensively mixed (pH: 3.7–4.2), and then 123.8 kg of paraformaldehyde are added. The mixture is then heated to 100–110°C over 30–60 minutes and this temperature is maintained for 60 minutes. At this temperature, two further portions of furfuryl alcohol and benzoic acid are added to the reaction mixture at intervals. The temperature is then increased to approximately 135°C, and the reaction mixture is heated under reflux (duration: 3–5 hours, during which the reflux temperature decreases slowly and continuously to approximately 125°C). The resulting reaction mixture is then rapidly cooled, 60.7 kg of urea is added, and further cooling is initiated. At a temperature of 60°C, 4.0 kg of sodium hydroxide solution (33% in water) is added, adjusting the pH value to the range of 5.5 - 6.0 (measured at 20°C).After further cooling of the reaction mixture to approximately 30°C, 69.4 kg of water, 29.8 kg of ethanol, 19.9 kg of monoethylene glycol, and 4.0 kg of Dynasilan 1506 are added and mixed. If necessary, the pH of the reaction mixture is adjusted to 5.5–6.5 with a maximum of 3.0 kg of sodium hydroxide solution (33% in water). The product thus obtained is hereby designated as the inventive mixture KH-Y. Flexural strength and setting behavior

[0193] The respective flexural strength values ​​were determined in accordance with VDG leaflet P 72 (October 1999) ("Testing of cold-curing, resin-bonded moist molding materials with hardener addition").

[0194] The molding compound mixture was prepared in a laboratory mixer (BOSCH). To this, 100 parts by weight of quartz sand H32 (Quarzwerke Frechen) were first mixed with the parts by weight of acid hardener specified in Table 2 for 30 seconds. Then, the parts by weight of binder specified in Table 2 were added and mixed for a further 45 seconds. The resulting mixture was prepared at room temperature (18–22°C) and a relative humidity (RH) of 20–55%. The sand temperature was 18–22°C.

[0195] The molding compound mixture was then placed into the test bar mold by hand and compacted with a hand plate.

[0196] The test specimens produced were cuboid test bars with dimensions of 220 mm x 22.36 mm x 22.36 mm, so-called Georg Fischer test bars.

[0197] To determine the curing time, the molding material mixture is compacted in a mold (cup), 80 mm high and 80 mm in diameter, using a hand plate. The surface is checked at specific intervals with a test nail. When the test nail no longer penetrates the core surface, the curing time has been reached.

[0198] To determine the processing and curing time of the molding compound mixture, the setting behavior was observed using a Georg Fischer test bar with the test pin according to VDG P 72.

[0199] The respective flexural strength values ​​were determined in accordance with the aforementioned VDG leaflet P 72. To determine the flexural strengths, the test bars were placed in a Georg Fischer strength testing device equipped with a three-point bending fixture (DISA-Industrie AG, Schaffhausen, CH) and the force that led to the failure of the test bars was measured.

[0200] The flexural strengths were measured after one hour, two hours, four hours and 24 hours after the production of the molding compound mixture to be tested (storage of the cores after demolding, each time at room temperature 18-22°C, RH 20-55%).

[0201] Test series were carried out with the no-bake binder KH-Ref2 (not according to the invention) and two test series with the no-bake binder KH-Y (according to the invention), each with two different parts by weight.

[0202] The results of the respective strength tests are summarized in Table 2 (Tables 2a and 2b) as the mean of two measurements.

[0203] In the first series of experiments, 1 part by weight (corresponding to 1 wt.%, based on the amount of sand used) of No-Bake binder KH-Ref2 (not according to the invention) and KH-Y (according to the invention) were each separately processed with 0.5 parts by weight of a 65 wt.% solution of p-toluenesulfonic acid in water (corresponding to 0.325 parts by weight of p-toluenesulfonic acid) to form a molding material mixture.

[0204] In the second series of experiments, 1 part by weight (corresponding to 1 wt.%, based on the amount of sand used) of No-Bake binder KH-Ref2 (not according to the invention) and KH-Y (according to the invention) were each separately processed with 0.4 parts by weight of a 65 wt.% solution of p-toluenesulfonic acid in water (corresponding to 0.26 parts by weight of p-toluenesulfonic acid) to form a molding compound mixture.

[0205] Abbreviations used: VE = Processing time in minutes AH = Curing time in minutes (100 g) DU = Full curing time in minutes VISC = Viscosity in mPas at 20°C BF1, BF2, BF4, BF24 = Flexural strength after 1, 2, 4 or 24 hours (values ​​in N / cm²) Table 2a Setting behavior and flexural strengths when using 0.325 parts by weight of the acid hardener p-toluenesulfonic acid binder VE UH YOU BF1 BF2 BF4 BF24 KH-Ref2 16 24 42 180 400 430 500 KH-Y 15 23 41 160 350 450 570 Table 2b Setting behavior and flexural strengths when using 0.26 parts by weight of the acid hardener p-toluenesulfonic acid binder VE UH YOU BF1 BF2 BF4 BF24 KH-Ref2 25 35 63 140 335 360 460 KH-Y 24 33 68 85 310 335 435 Emission measurements during mixing, filling, and compaction, and casting results

[0206] The molding material mixtures described in Table 3 were processed into molds, and iron and steel castings were performed using both molds. The measured pollutant emissions during mixing, filling, and compaction are shown in Table 4. The casting results were flawless in both cases. Table 3 : Composition of molding compound mixtures Molding compound mixture 1 (not according to the invention) Molding compound mixture 2 (according to the invention) No-Bake Regenerate 100 parts by weight 100 parts by weight p-Toluenesulfonic acid (65% in water) 0.3 parts by weight 0.3 parts by weight KH-Y (according to the invention) 1.0 parts by weight KH-Ref1 (not according to the invention) 1.0 parts by weight Table 4 Results of the measurement of pollutant emissions during mixing, filling, and compaction Molding compound mixture 1 (not according to the invention) Molding compound mixture 2 (according to the invention) Furfuryl alcohol 33.00 mg / m³< 10.77 mg / m³< formaldehyde 0.222 mg / m³ < 0.049 mg / m³ BI AGW 0,822 0,325 BI Other 0,628 0,160 BI Total 1,450 0,485

[0207] The underlying occupational exposure limits (OELs) were the occupational exposure limits according to the Technical Rules for Hazardous Substances (TRGS) 900, edition January 2006, status June 2010, and TRGS 402, edition January 2010, insofar as no corresponding limit values ​​are published in TRGS 900.

[0208] The BI AGW assessment indices were determined in accordance with TRGS 402, section 5.2. The BI Other assessment indices were determined in accordance with TRGS 402, section 5.3. The January 2010 edition of TRGS 402 was used as the basis for these calculations.

[0209] BI Total = BI AGW + BI Other. This index should not exceed the limit of 1.

[0210] The mixtures according to the invention allow compliance with the limit value BI total. Investigations into bearing stability

[0211] Storage stability was assessed over a period of 6 months at a constant temperature of 20-22°C and examined at monthly intervals. For this purpose, the viscosity of the cold resin KH-Y according to the invention was measured, and the application-related properties of a corresponding molding compound mixture were determined (as described above).

[0212] To further investigate the application-related properties, a molding compound mixture was first prepared. To 100 parts by weight of quartz sand H32 (Quarzwerke Frechen), 0.5 parts by weight of a 65 wt% solution of p-toluenesulfonic acid in water were added and mixed for 30 seconds. Subsequently, 1 part by weight of binder KH-Y was added and mixed for a further 45 seconds. The resulting molding compound mixture was prepared at room temperature (20–22°C) and a relative humidity (RH) of 40–55%. The sand temperature was 20–22°C. Table 5 : Measurements on the storage stability of the cold resin KH-Y according to the invention Storage period VISC VE UH BF1 BF2 BF4 BF24 0 months 52 15 22 105 345 435 460 1 month 60 10 14 210 420 540 495 2 months 67 12 16 140 325 460 550 3 months 69 14 19 125 295 490 500 4 months 71 13 18 120 380 480 520 5 months 99 11 16 100 290 430 430 6 months 109 13 18 150 255 410 435 Table 6 : chemical and physical parameters of the no-bake binding agent KH-Y2 according to the invention KH-Y2 (according to the invention) Total amount of FA used 70.18 wt.% Content of monomeric FA 24.1 wt.% Total nitrogen content 0.75 wt.% Water content 10.5 wt.% free formaldehyde 0.2 wt.% Density at 20°C 1.185 g / cm³< Dynamic viscosity at 20°C 70 mPa*s Look dark brown, clear

[0213] The KH-Y2 mixture according to the invention has a very low total nitrogen content, which is why this no-bake binder according to the invention is particularly suitable for iron and steel casting, especially for stainless steel casting. Production of the no-bake binding agent KH-Y2 according to the invention:

[0214] Furfuryl alcohol (70.18 wt%), Paraformaldehyde 91% (12.03 wt%), Benzoic acid (1.64 wt%), Bisphenol A (2.75 wt%), Urea (1.72 wt%), Water (5.14 wt%), Ethanol (3.12 wt%), Monoethylene glycol (1.00 wt%), N-Aminopropyltriethoxysilane (Dynasilan 1505) (0.40 wt%), Potassium hydroxide 45% in water (2.02 wt%).

[0215] Throughout the entire process, the reactor contents are stirred. In a reactor, 234.0 kg of furfuryl alcohol and 5.5 kg of benzoic acid are intensively mixed (pH: 3.7–4.2), and then 120.3 kg of paraformaldehyde are added. The mixture is then heated to 100–110°C over 30–60 minutes and this temperature is maintained for 60 minutes. At this temperature, two further portions of furfuryl alcohol and benzoic acid are added to the reaction mixture at intervals. The temperature is then increased to approximately 135°C, and the reaction mixture is heated under reflux (duration: 3 to 5 hours, during which the reflux temperature decreases slowly and continuously to approximately 125°C). The resulting reaction mixture is then cooled slightly, 27.50 kg of bisphenol A is added, and further cooling is permitted. At a temperature of 80°C, 20.2 kg of potassium hydroxide (45% in water) are added and stirred for about another hour.After further cooling of the reaction mixture to approximately 60 °C, 31.2 kg of ethanol and 17.2 kg of urea are added. After further cooling of the reaction mixture to approximately 35 °C, 51.4 kg of water, 10.0 kg of monoethylene glycol, and 4.0 kg of Dynasilan 1505 are finally added and mixed. The product thus obtained is hereby designated as the mixture KH-Y2 according to the invention.

[0216] Analogous to the first test series mentioned above, 1 part by weight (corresponding to 1 wt.%, based on the amount of sand used) of the inventive no-bake binder KH-Y2 was processed with 0.5 parts by weight of a 65 wt.% solution of p-toluenesulfonic acid in water (corresponding to 0.325 parts by weight of p-toluenesulfonic acid) to form a molding material mixture.

[0217] The flexural strength and setting behavior were determined using this molding material mixture under the test conditions described above and in accordance with the above explanations. Table 6a : Setting behavior and flexural strength of the inventive mixture KH-Y2 when using 0.325 parts by weight of the acid hardener p-toluenesulfonic acid binder VE UH YOU BF1 BF2 BF4 BF24 KH-Y2 9 15 41 165 320 380 525

Claims

1. Mixture for use as binder in the no-bake process, comprising (a) monomeric furfuryl alcohol, wherein the amount of monomeric furfuryl alcohol is at most 25 wt.%, (b) 40 wt.% or more of reaction products of formaldehyde, wherein the reaction products comprise (b-1) reaction products of formaldehyde with furfuryl alcohol and optionally other constituents, and (b-2) optionally reaction products of formaldehyde with one or a plurality of other compounds, which is not or are not furfuryl alcohol, (c) water, wherein the amount of water is at most 20 wt.%, (d) one or a plurality of organic acids with a pKa value greater than or equal to 2.5, preferably in the range from 2.75 to 6, preferably in the range from 3 to 5, at 25°C and / or salts thereof, wherein the mixture has a content of free formaldehyde of at most 0.5 wt.%, wherein the percentages by weight are relative to the total weight of the mixture.

2. Mixture according to any one of the preceding claims, wherein constituent (b) comprises or consists of (b-1) 40 wt.% or more, preferably 45 wt.% or more, preferably 50 wt.% or more, of reaction products of furfuryl alcohol with formaldehyde and optionally further constituents, preferably one or a plurality of further aldehydes, preferably glyoxal, (b-2) reaction products of formaldehyde with one or a plurality of other compounds, which is not or are not furfuryl alcohol, said reaction products being different from constituent (b-1), wherein the amount of these further reaction products is at most 15 wt.%, preferably at most 12 wt.%, preferably at most 10 wt.%, wherein the percentages by weight are relative to the total weight of the mixture.

3. Mixture according to any one of the preceding claims, wherein the mixture has a viscosity at 20°C of max. 300 mPas according to DIN 53019-1: 2008-09, preferably of max. 250 mPas, preferably of max. 200 mPas, more preferably of max. 150 mPas.

4. Mixture according to any one of the preceding claims, wherein the content of free formaldehyde is at most 0.4 wt.%, preferably at most 0.3 wt.%, wherein the percentages by weight are relative to the total weight of the mixture.

5. Mixture according to any one of the preceding claims, wherein constituent (d) comprises an acid or a salt selected from the group consisting of benzoic acid, lactic acid, citric acid, phthalic acid, 2,4-dihydroxybenzoic acid, salicylic acid and salts thereof.

6. Mixture according to any one of the preceding claims, wherein constituent (b-1) comprises 2,5-bis(hydroxymethyl)furan (BHMF), preferably in an amount of at least 1 wt.%, preferably in an amount from 5 to 40 wt.%, relative to the total weight of a mixture according to the invention.

7. Mixture according to any one of the preceding claims, wherein the total content of compounds with a molecular weight above 5000 dalton (g / mol) is at most 3 wt.%, determined by gel permeation chromatography according to DIN 55672-1 (February 1995), relative to the total weight of the mixture.

8. Mixture according to any one of the preceding claims, wherein the ratio of average molecular weight Mw to average molecular weight Mn of constituent (b-1) is in the range from 5 : 1 to 9 : 8, more preferably in the range from 4 : 1 to 6 : 5, particularly preferably in the range from 3 : 1 to 4 : 3, quite particularly preferably in the range from 2 : 1 to 3 : 2.

9. Mixture according to any one of the preceding claims, additionally comprising one or a plurality of further constituents, selected from the group of (f) organic curing moderators, preferably selected from the group of glycols with 2 to 12 carbon atoms, preferably in an amount of max. 10 wt.%, relative to the total weight of the mixture, (g) inert organic solubilisers, preferably selected from the group of alcohols R-OH, wherein R denotes a C1-C4 alkyl residue, preferably ethanol, (h) reaction products of furfuryl alcohol and one or a plurality of aldehydes with 2 or more carbon atoms, preferably reaction products of furfuryl alcohol and glyoxal, (j) organic compounds that have one or a plurality of H2N groups and / or one or a plurality of HN groups, preferably urea, (k) phenolic compounds, preferably the phenolic compounds with 6 to 25 carbon atoms and / or one, two, three or four hydroxyl groups bound directly to an aromatic ring, preferably selected from the group consisting of phenol, optionally C1-C4-alkyl-mono- or -disubstituted dihydroxybenzenes, trihydroxybenzenes, methylphenols and bisphenols, particularly preferably selected from the group consisting of phenol, o-dihydroxybenzene, m-dihydroxybenzene, p-dihydroxybenzene, 5-methylresorcinol, 5-ethylresorcinol, 2,5-dimethylresorcinol, 4,5-dimethylresorcinol, 1,2,3-trihydroxybenzene, 1,3,5-trihydroxybenzene, o-cresol, m-cresol, p-cresol and bisphenol A, (m) benzyl alcohol, (n) aldehydes with 2 or more carbon atoms, preferably selected from the group consisting of acetaldehyde, propionaldehyde, butyraldehyde, acrolein, crotonaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde, glyoxal and mixtures of these aldehydes, preferably glyoxal.

10. Reaction mixture, comprising (i) a mixture according to any one of the preceding claims, (ii) an acid, wherein the acid has a pKa value of less than 2 at 25°C, preferably of less than 1.5, preferably of less than 1, optionally additionally comprising (iii) one or a plurality of refractory granular materials, preferably sand, preferably in an amount of 80 wt.% or more, preferably 95 wt.% or more, relative to the total weight of the reaction mixture.

11. Reaction mixture according to claim 10, wherein the reaction mixture comprises no sulphuric acid or comprises sulphuric acid in an amount of max. 1 wt.%, preferably in an amount of at most 0.5 wt.%, wherein the percentages by weight are relative to the total weight of the reaction mixture minus the total weight of refractory granular materials in the reaction mixture and / or wherein the acid of component (ii) is selected from the group of organic acids, preferably the organic sulphonic acids, preferably selected from the group consisting of benzenesulphonic acid, toluenesulphonic acids, xylenesulphonic acids, cumenesulphonic acid, and methanesulphonic acid, p-toluenesulphonic acid being quite particularly preferred.

12. Method for preparing a mixture according to any one of claims 1 to 9, with the following step: (S-1) reaction of furfuryl alcohol with formaldehyde and optionally further constituents in the presence of one or a plurality of organic acids with a pKa value greater than or equal to 2.5 at 25°C and / or salts thereof, preferably one or a plurality of organic acids as defined in claim 7, wherein step (S-1) preferably takes place at a temperature in the range from 90 to 160°C, preferably at a temperature in the range from 100 to 150°C. wherein the molar ratio of the total amount of furfuryl alcohol used to the total amount of formaldehyde used is greater than or equal to 1, preferably in the range from 5 : 1 to 1.1 : 1, preferably in the range from 3 : 1 to 1.25 : 1, more preferably in the range from 2 : 1 to 3 : 2.

13. Method of producing a mould or a core, preferably a no-bake mould or a no-bake core for producing metal objects, comprising the step: - curing, preferably acid-catalysed curing, of a mixture according to any one of claims 1 to 9, or - curing of a reaction mixture according to either of claims 10 and 11, wherein curing preferably takes place at a temperature below 60°C, preferably in the range from 0 to 50°C, preferably in the range from 10 to 40°C.

14. Use of a mixture according to any one of claims 1 to 9 as cold-setting binder, preferably as no-bake binder in foundry practice, in particular in the production of metal objects by a casting process, wherein the curing of the binder preferably takes place without the use of gaseous sulphur dioxide.

15. Kit, comprising - as a first component, a mixture according to any one of claims 1 to 9, - as a second component, an aqueous solution of an acid, wherein the acid has a pKa value below 2 at 25°C.