EP2651581A1

EP2651581A1 - Low-emission cold-setting binder for the foundry industry

Info

Publication number: EP2651581A1
Application number: EP11808845.9A
Authority: EP
Inventors: Christian Fourberg; Gérard LADÉGOURDIE; Norbert Benz; Eckard Piech
Original assignee: Huettenes Albertus Chemische Werke GmbH
Current assignee: Huettenes Albertus Chemische Werke GmbH
Priority date: 2010-12-16
Filing date: 2011-12-16
Publication date: 2013-10-23
Anticipated expiration: 2031-12-16
Also published as: ES2816451T3; PL3495073T3; ES2746190T3; JP2014501175A; TW201235374A; EP3495073B1; EP2651581B1; TWI564317B; WO2012080454A1; EP3495073A2; US20140048740A1; CN103379971A; DE202011110617U1; CN103379971B; PL2651581T3; US9993863B2; JP5913359B2; EP3495073A3

Abstract

The present invention relates primarily to a mixture, which is suitable for use in the no-bake method 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). The present invention further relates to a method for producing a mixture according to the invention and to a method for producing a casting mold or a core. The invention further relates to a casting mold or a core for producing metal bodies and to a kit comprising a mixture according to the invention and certain acid hardeners. The invention also relates to the use of a mixture according to the invention as a cold-setting binder and to the use of such mixtures or reaction mixtures in a no-bake method for producing metal bodies.

Description

Low-emission cold-curing binder for the foundry industry

The present invention relates primarily to a mixture suitable for use in the no-bake process for the production of 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 and to a method for producing a casting mold or a core. The invention also relates to a casting mold or a 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 cold curing binder and the use of such mixtures or reaction mixtures in a no-bake process for the production of metal bodies. Further aspects of the present invention will become apparent from the description, the embodiments and the claims.

Most products of the iron and steel industry and the non-ferrous metal industry undergo casting processes for the first shaping. In this case, the melt liquefied materials, ferrous metals or non-ferrous metals are converted into shaped objects with specific workpiece properties. For the shaping of the castings must first be made in part very complicated molds for receiving the molten metal. The casting molds are divided into lost molds that are destroyed after each casting, and permanent molds, with each of which a large number of castings can be produced. The Lost forms usually consist of a refractory, granular molding material, which is solidified with the aid of a hardenable binder.

Shapes are negatives, they contain the emptying cavity, which results in the casting to be produced. The inner contours of the future casting are formed by cores. In the manufacture of the mold, the cavity is shaped into the molding material by means of a model of the casting to be manufactured. Inner contours are represented by cores formed in a separate core box.

For the production of casting molds both organic and inorganic binders can be used, the curing of which can be effected by cold or hot processes. Cold processes are processes in which the curing takes place essentially at room temperature without heating the molding material mixture. The curing is usually carried out by 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 molding material mixture. In hot processes, the molding material mixture is heated to a sufficiently high temperature after molding to drive off, for example, the solvent contained in the binder, or to initiate a chemical reaction by which the binder is cured by crosslinking.

The production of the casting molds can be carried out in such a way that the molding material is first mixed with the binder, so that the grains of the refractory molding material are coated with a thin film of the binder. The molding material mixture obtained from molding material and binder can then be introduced into a corresponding mold and optionally compacted in order to achieve a sufficient stability of the casting mold. Subsequently, the mold is cured, for example by heating it or by adding a catalyst which effects a curing reaction. If the mold has reached at least a certain initial strength, it can be removed from the mold.

As already mentioned, molds for the production of metal bodies are often composed of so-called cores and molds. Different requirements are placed on the cores and molds. In molds, a relatively large surface area is available to dissipate gases that form during casting by the action of the hot metal. In cores usually only a very small area is available, through which the gases can be derived. If there is too much gas, there is a risk that gas will pass from the core into the liquid metal and lead to the formation of casting defects. Often, therefore, the internal cavities are imaged by cores solidified by cold box binders, that is, a polyurethane based binder, while the outer contour of the casting is represented by lower cost dies, such as a Green sand mold, a form bound by a furan resin or a phenol resin, or by a steel mold.

For larger molds, organic polymers are mostly used as binders for the refractory, granular molding material. As a refractory, granular molding material often washed, classified quartz sand is used, but also other molding materials such. Zirconsande, Chromitsande, chamois, olivine sands, feldspathaltige sands and Andalusitsande. The molding material mixture obtained from mold base and binder is preferably present in a free-flowing form.

At present, for the production of molds often organic binders such. For example, polyurethane, furan resin or epoxy-acrylate used in which the curing of the binder by addition of a catalyst. Phenol resins (acid-curing or - in the Alpha-Set-process ester-curing) are also used.

The choice of suitable binder depends on the shape and size of the casting to be produced, the conditions of production and the material used for the casting. For example, in the production of small castings that are produced in large numbers, polyurethane binders are often used because they allow fast cycle times and thus also a series production.

Processes in which the curing of the molding material mixture by heat or by subsequent addition of a catalyst, have the advantage that the processing of the molding material mixture is not subject to any special time restrictions. The molding material mixture can first be produced in larger quantities, which are then processed within a longer period of time, usually several hours. The curing of the molding material mixture takes place only after molding, with a rapid reaction is sought. The mold can be removed immediately after curing from the mold so that short cycle times can be realized. However, in order to obtain a good strength of the mold, the curing of the molding material mixture must be uniform within the mold. If the curing of the molding material mixture by subsequent addition of a catalyst, the mold is gassed after molding with the catalyst. For this purpose, the gaseous catalyst is passed through the casting mold. The molding material mixture cures directly after contact with the catalyst and can therefore be removed very quickly from the mold. As the size of the mold increases, it becomes more difficult to provide an amount of catalyst sufficient to cure the molding material in all sections of the mold. The gassing times are prolonged, but can still arise sections in the mold, the very poor or not at all of the gaseous catalyst be achieved. The amount of catalyst therefore increases sharply with increasing size of the mold.

Similar difficulties occur in hot curing processes. Here, the mold must be heated in all sections to a sufficiently high temperature. As the size of the mold increases, on the one hand, the times for which the mold must be heated to a certain temperature for curing are extended. Only then can it be ensured that the casting mold also has the required strength in its interior. On the other hand, the curing with increasing size of the mold is also very expensive from the apparatus side.

In the field of large casting, the weight of the cores is often about 1000 kg or more. With methods in which the hardening with gas or by heat, such large cores are difficult or impossible to produce from a technical point of view. Here then preferably cold-curing methods are used.

In the production of molds for large castings, such as engine blocks of marine diesels or large machine parts, such as hubs of rotors for wind power plants, so-called "no-bake binders" are used for the reasons mentioned mostly "No-bake method" is the refractory mold base material (eg sand) often first with a catalyst (hardener) occupied, then added the binder and evenly distributed by mixing on the already coated with catalyst grains of the refractory molding material. In this process is often worked with so-called continuous flow mixers. The resulting molding material mixture can then be shaped into a shaped body. Since binder and catalyst are evenly distributed in the molding material mixture, the curing is largely uniform even with large moldings.

Alternatively, in the "no-bake process", the refractory base molding material (eg sand) can first be mixed with the binder and then the curing agent can be added To a high concentration of the curing agent come to a partial curing or crosslinking of the binder, whereby an inhomogeneous molding material would be obtained.

Since the catalyst (hardener) is added to the molding material mixture before molding, the curing of the molding material mixture begins immediately after its preparation. In order to achieve a suitable processing time for an industrial application, therefore, the components of the molding material mixture should be coordinated. Thus, the reaction rate for a given amount of the binder and the refractory base molding material, for example, by the nature and amount of the catalyst or by Adding delaying components influence. On the other hand, the processing of the molding material mixture should be carried out under very controlled conditions, since the rate of curing is influenced for example by the temperature of the molding material mixture.

The "classic" no-bake binders are often based on furan resins and phenolic resins. They are often offered as systems (kits) wherein one component comprises a reactive furan resin and the other component comprises an acid, which acid acts as a catalyst for the curing of the reactive resin component.

Furan and phenolic resins show very good disintegration properties during casting. Under the action of heat of the liquid metal, the furan or phenolic resin decomposes and the strength of the mold is lost. After casting, therefore, cores, possibly after prior shaking of the casting, pour out very well from cavities.

"Furan no-bake binders" contain reactive furan resins, which regularly comprise furfuryl alcohol as an essential component. Furfuryl alcohol can react with itself under acid catalysis and form a homopolymer. Furfuryl alcohol is generally not used alone for the preparation of furan no-bake binders, but further compounds are added to the furfuryl alcohol which are copolymerized into the resin. Examples of such compounds are aldehydes, such as formaldehyde or furfural, ketones, such as acetone, phenols, urea or polyols, such as sugar alcohols or ethylene glycol. The resins may be added with other components that affect the properties of the resin, such as its elasticity. Melamine can be added, for example, to bind still free formaldehyde.

Furan no-bake binders are most often prepared by first producing precondensates of, for example, urea, formaldehyde, and furfuryl alcohol under acidic conditions. These precondensates are then diluted with furfuryl alcohol.

It is also conceivable that urea and formaldehyde are reacted alone. This produces so-called UF resins ("urea formaldehyde" resins, "aminoplasts"). These are usually subsequently diluted with furfuryl alcohol. Advantages of this manufacturing method are a higher flexibility / variability in the product range and lower costs, because it is cold mixing processes. The disadvantage is that certain chemical and performance properties can not be achieved. Furthermore, UF resins are often cloudy, so that binders usually made therefrom are also cloudy and inhomogeneous. Resoles can also be used to prepare furan no-bake binders. Resoles are prepared by polymerization of mixtures of phenol and formaldehyde. These resoles are then often diluted with a large amount of furfuryl alcohol.

Furan no-bake binders are regularly cured with an acid. This acid catalyzes the crosslinking of the reactive furan resin. It should be noted that, depending on the type of binder, certain amounts of acid should not be exceeded, since alkaline components, which may be present in the refractory base molding material, can partially neutralize the acid.

Frequently used acids are sulfonic acids, phosphoric acid or sulfuric acid. In some specific cases, combinations of these are used, inter alia, in combination with other carboxylic acids. Further, certain "curing moderators" can be added to the furan no-bake binder.

Phosphoric acid is often used as an acid catalyst for curing in concentrated form, i. H. used at concentrations greater than 70%. However, it is only suitable for the catalytic hardening of furan resins with a relatively high proportion of urea, since essentially the curing of the aminoplast moiety in the furan no-bake binder is responsive. The nitrogen content of such resins is usually more than 2.0% by weight. Sulfuric acid, as a relatively strong acid, can be added as a starter for the curing of furan resins to weaker acids. During casting, however, a smell typical of sulfur compounds develops. In addition, there is a risk that the casting material sulfur is absorbed, which affects its properties.

The selection of the acid catalyst for curing has a significant influence on the curing behavior of the binder, the properties of the molding material mixture and the casting mold or the core obtainable therefrom. Thus, the rate of curing can be influenced by the amount and the strength of the acid. High amounts of acid or stronger acids lead to an increase in the curing rate. In the case of too rapid setting, the processing time of the molding material mixture is shortened too much, so that the workability is greatly impaired or even processing is no longer possible. When using too large amounts of acid catalyst, the binder, such as a furan resin, also become brittle upon curing, which adversely affects the strength of the mold. When using too small amounts of acid catalyst, the resin is not completely cured (or the curing takes a long time), resulting in lower strength of the mold.

In the manufacture of casting molds new sand is often used for the cores, while often used for the molds reclaimed mold base material (eg sand) is used. refractory Form base materials that have been solidified with furan no-bake binders can be worked up very well again. The workup is carried out either mechanically by mechanically rubbing off a shell formed from residual binder or by thermally treating the used sand. With mechanical workup or with combined mechanical / thermal processes, return rates of up to almost 100% can be achieved.

Phenolic resins, the second large group of acid-catalyzed curable no-bake binders, contain resoles as reactive resin components, ie phenolic resins prepared with a molar excess of formaldehyde. Phenolic resins show lower reactivity compared to furan resins and require strong sulfonic acids as catalysts. Phenolic resins show a relatively high viscosity, which increases even more with prolonged storage of the resin. After the phenol no-bake binder has been applied to the refractory base molding material, the molding compound should be processed as promptly as possible so as not to suffer deterioration in the quality of the molding compound due to premature curing, resulting in deterioration of the strength of the molding compound mixture produced molds can lead. When using phenol no-bake binders, the flowability of the molding material mixture is usually worse than a comparatively produced molding material with a furan no-bake binder. In the production of the mold, the molding material mixture must therefore be carefully compacted in order to achieve a high strength of the mold can.

The preparation and processing of such a molding material mixture should take place at temperatures in the range of 15 to 35 ° C. If the temperature is too low, the molding material mixture can be processed worse because of the high viscosity of the phenol no-bake resin. At temperatures of more than 35 ° C, the processing time is shortened by premature curing of the binder.

After casting, molding mixtures based on phenol-no-bake binders can also be worked up again, in which case mechanical or thermal or combined mechanical / thermal processes can also be used.

As already explained, the acid used as catalyst in the case of furan or phenol no-bake processes has a very great influence on the properties of the casting mold. The acid must have sufficient strength to ensure a sufficient rate of reaction in the curing of the mold.

The curing should be well controllable, so that also sufficiently long processing times can be set. This is particularly important in the production of molds for very large castings, the construction requires a longer period. Furthermore, the acid must not accumulate in the regeneration during the regeneration of used materials (ie mold materials already used for the production of lost molds or cores, for example old sands). If acid is introduced into the molding material mixture via the regenerate, this shortens the processing time and leads to a deterioration in the strength of the casting mold produced from the regenerate.

Therefore, not every acid is suitable for use as a catalyst in no-bake processes. Toluenesulfonic acid, benzenesulfonic acid or else methanesulfonic acid and in some cases xylenesulfonic acid or cumene sulfonic acid [2 (or 4) - (isopropyl) -benzenesulfonic acid] are frequently used in practice to date, as well as phosphoric acid and sulfuric acid.

Phosphoric acid is, as already explained, only for the curing of certain furan resin qualities. However, phosphoric acid is not suitable for the curing of phenolic resins. As a further disadvantage, phosphoric acid tends to accumulate in the regenerate, making it difficult to reuse the regenerate. Sulfuric acid during casting and during thermal regeneration leads to the emission of sulfur dioxide, which has corrosive properties, is harmful to health and represents an odor nuisance. For further disadvantages with the use of sulfuric acid, see below.

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

These known no-bake binders have one or more of the following disadvantages or undesirable properties: too high a content of furfuryl alcohol, too high a content of water, too high a content of formaldehyde, too strong an odor, too high a content of ammonia and / or too high total content of nitrogen.

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

No. 3,216,075 describes furfuryl alcohol-formaldehyde resins which are used there for the production of foundry cores and casting molds at relatively high temperatures, ie at temperatures> 175 ° C. There were first prepared reaction products of furfuryl alcohol and formaldehyde in the presence of oxalic acid and after distilling off water largely anhydrous highly viscous resins were obtained, which were then diluted furfuryl alcohol to adjust a lower viscosity. US Pat. No. 3,806,491 relates to binders which can be used in the "no-bake" process The binders used there comprise products from the reaction of paraformaldehyde with certain ketones in a basic medium as well as furfuryl alcohol and / or furan resins.

US 5,607,986 discloses thermosetting binders for the production of molds and foundry cores in the "hot box" or "hot box" processes based on furfuryl alcohol formaldehyde phenolic resins prepared in the basic medium at pH's in the range of 8 to 9 were. The binders of US 5,607,986 also contained furfuryl alcohol and polyvinyl acetate.

No. 5,491,180 describes resin binders which are suitable for use in the no-bake method. The binders used there are based on 2,5-bis (hydroxymethyl) furan or methyl or ethyl ethers of 2,5-bis (hydroxymethyl) furan, wherein the binder 0.5 to 30 wt .-% water and regularly contain a high proportion on furfuryl alcohol.

EP 0 540 837 proposes low-emission, cold-curing binders based on furan resins and lignin from the Organosolv process. The furan resins described there contain a high proportion of monomeric furfuryl alcohol.

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.

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

DE 10 2008 024 727 describes certain methanesulfonic acid-containing catalyst mixtures which are used there as a hardener in the no-bake process.

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

US 4,176,114 A discloses a process for producing sand molds and cores. Here, sand is mixed with an acid-hardening resin comprising "high viscosity poly furfuryl alcohol." The curing then takes place by contacting the mixture with gaseous sulfur dioxide in the presence of an oxidizing agent. US 5,741,914 A discloses resin-based binder compositions comprising reaction products of furfuryl alcohol with formaldehyde. The binder compositions comprise, in part, a weak organic acid and in some cases only a small amount of formaldehyde.

US 6,391,942 B1 discloses furan no-bake foundry binders and their use.

Especially in iron and steel casting, especially in stainless steel casting, the lowest possible total nitrogen content is desirable, since in particular a total nitrogen content of 4% by weight or higher in a no-bake binder can lead to casting defects. In particular, for use in the field of cast steel and gray cast iron a no-bake binder should have the lowest possible total nitrogen content, since there surface defects, such as "pinholes" (pinholes) occur as a casting error.

One type of pinholes are the "water-nitrogen pinholes," in which water vapor reacts with the iron and nitrogen-containing components to form metal oxides and nitrogen-hydrogen compounds that diffuse into the liquid metal, resulting in micropores.

In the case of large casting processes, the ammonia content in no-bake binders for large-scale casting processes must also be kept as low as possible, and preference should be given to dispensing with the use of ammonia.

Preferably, a no-bake binder meets several or all of the following criteria:

• low viscosity

• good storage stability (storage stability)

• low-nitrogen or -free binder, especially for high-quality cast steel

• low odor

• reactive, fast-curing binder for short molding times (this makes chemically aggressive hardeners or activators unnecessary)

• Low-sulfur or -free binder for high-grade nodular cast iron (as a result of which a significant reduction in S0 ₂ emissions during and after casting is possible).

As part of a molding material mixture, a no-bake binder should fulfill several or all of the following criteria:

• good curing • low binder addition required in forming or core making

• Low pollutant emissions during mixing, filling and compression of the molding material mixture (the permissible AGW values should be significantly lower than usual)

• good regenerable old sands are obtained.

In the mold production, which usually includes the relevant steps mixing, filling and compacting and storage of the molding material, according to VDG leaflet R 304 (February 1998) ("Cold-curing molding process with furan resin"), among other things, the lead components formaldehyde and furfuryl be observed.

The observance of AGW values (AGW = workplace limit value) in foundries is not always easy to accomplish, since compliance with occupational exposure limits requires very expensive extraction systems and filters. For example, in the field of large casting, efficient extraction of emitted pollutants is scarcely installable and achievable.

The invention was therefore based on the object to provide a binder based on furfuryl alcohol and formaldehyde available, which can be used in a no-bake process for the production of cores and molds for the foundry industry, so that in the production of molds and cores and / or during casting a low emission of pollutants, especially with respect to furfuryl alcohol and formaldehyde and preferably also ammonia.

In a first aspect, therefore, the invention relates to a mixture for use as a binder in the no-bake method, comprising

(a) monomeric furfuryl alcohol, wherein the amount of monomeric furfuryl alcohol is at most 25% by weight,

(b) 40% by weight or more of reaction products of formaldehyde, which comprise the reaction products

(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 which is not or are not furfuryl alcohol,

(c) water, the amount of water being at most 20% by weight,

(d) one or more organic acids having a pKa of greater than or equal to 2.5, preferably in the range of 2.75 to 6, preferably in the range of 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 weight percentages are based on the total mass of the mixture.

Surprisingly, it has now been found that when using reaction mixtures according to the invention (as defined below) containing a mixture according to the invention, the pollutant emission, in particular the emission of furfuryl alcohol and formaldehyde, could be drastically reduced during mixing, filling and compression of the molding material, without thereby processability and other relevant properties of a no-bake binder. Thus, a large number of desired positive properties were achieved by the mixture according to the invention. The good processability of reaction mixtures which comprise mixtures according to the invention is based inter alia on their comparatively low viscosity (for preferred viscosities, see below). The other relevant properties of a no-bake binder include the influence on the curing behavior (in particular depending on the water content, see below) and the influence on the stability of corresponding shapes or cores in spontaneous contact with liquid metal (especially depending on the water content, see below for comments on blasting molds and cores in the casting shop).

The mixtures according to the invention and the reaction mixtures according to the invention (as defined below) can also be used in particular in the field of large-scale casting, preferably for producing molds and cores, in particular cores, having a weight of 800 kg or more, preferably 900 kg or more preferably 1000 kg or more.

Refractory mold raw materials, which were solidified using a mixture according to the invention in the no-bake method, can be worked up very well again. This is especially true for sand.

There are furan resins known in the art that do not relate to the foundry industry. The furan resins described therein are not suitable for use in the foundry industry as a no-bake binder (ie, not suitable for use in no-bake method), as these in particular had one or more of the following disadvantages: too high viscosity, too high content Water, too high content of formaldehyde, too high ammonia content and / or too high total nitrogen content. In addition, with these other furan resins known from the prior art, no acceptable curing processes and no buildup of sufficient strength are regularly achieved when used in no-bake processes.

No. 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 become. Specific details of properties that are important for binders in the no-bake process are lacking in US 2,343,972.

US Pat. No. 5,741,914 (and corresponding US Pat. No. 5,849,858) describes resins as binders for the production of composites obtained by reacting furfuryl alcohol with an excess of formaldehyde in the presence of an acid having a pKa of about greater than 4, the molar ratio of Furfuryl alcohol to formaldehyde is at least 1: 2. Similar resins are disclosed in US 5,486,557.

DE 21 26 800 (and corresponding to CA 1 200 336) describes a process for producing a composite article and binders suitable therefor, wherein the binders are highly viscous resinous condensation products based on furan-formaldehyde, which are diluted with water.

US 3,816,375 (and corresponding DE 23 02 629) discloses partially prepolymerized furfuryl alcohol aldehyde binders wherein the aldehyde is formaldehyde and / or furfural used there to form composites. When the material chosen for the composite is glass fiber, US 3,816,375 preferably uses a prepolymerized high viscosity furfuryl alcohol aldehyde binder which is diluted with furfural. The same is disclosed in US 3,594,345 (and corresponding to DE 19 27 776).

US 2,874,148 discloses furfuryl alcohol-formaldehyde resins prepared by reacting furfuryl alcohol with formaldehyde in the presence of sulfuric acid. The physical properties of the resins obtained according to US Pat. No. 2,874,148 are very dependent on the respective further reaction conditions.

Usually, a mixture according to the invention for use as binder in the no-bake method does not comprise an acid which has a pKa value of less than 2 at 25 ° C., preferably no acid which at 25 ° C. has a pKa value of less than 2 , 5. If, in exceptional cases, such acids are used, their maximum total amount is preferably less than 5 wt .-%, based on the total mass of the mixture. This applies to all mixtures according to the invention described below.

Usually, a mixture according to the invention for use as binder in the no-bake process does not comprise refractory granular substances. If refractory granular materials are used in the mixture in exceptional cases, their maximum total amount is preferably less than 5 wt .-%, based on the total amount of the mixture. This applies to all mixtures according to the invention described below. Usually, a mixture according to the invention is a homogeneous solution; This applies to all preferred mixtures according to the invention described below.

A mixture according to the invention preferably contains less than 5% by weight of monomeric furfural, preferably less than 3% by weight, more preferably less than 1% by weight of monomeric furfural.

The mixtures according to the invention preferably contain less than 3% by weight of polyvinyl acetate, preferably less than 1% by weight, more preferably they are free of polyvinyl acetate.

A mixture according to the invention preferably contains less than 5% by weight of monomeric furfural and less than 3% by weight of polyvinyl acetate.

Preferably, a blend according to the invention contains less than 1% by weight of monomeric furfural and less than 1% by weight of polyvinyl acetate.

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

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

Preferably, a blend of 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 from 2: 1 to 1: 2, more preferably in the range from 3: 2 to 2: 3, particularly preferably in the range from 5: 4 to 4: 5.

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 ³ C-NMR.

In the case that nitrogen-containing components are contained in component (b-2), their detection via the nitrogen itself is possible. In the case of phenol compound as a component in Component (b-2) is also possible to differentiate via the phenol body (for example determination of the residual monomer content, GC-MS analysis).

Further suitable analytical methods are ⁵ N-NMR and ³ C-NMR, respectively.

The proportion of "furan ring" units can be determined via ³ C-NMR The proportion of "furan ring" units, calculated as furfuryl alcohol (C5H602), in the reaction product (b-1) of formaldehyde with furfuryl alcohol and optionally other constituents preferably in the range from 60 to 96% by weight, preferably in the range from 70 to 95% by weight, more preferably in the range from 75 to 90% by weight, particularly preferably in the range from 75 to 85% by weight, in each case based on the total mass of the component (b-1).

In component (b-2), the further compound (s) of the reaction product with formaldehyde are preferably selected from the group consisting of

organic compounds having one or more H ₂ N groups and / or one or more HN groups, and

Phenolic compounds.

The particularly preferred organic compound which has one or more H ₂ N groups is urea.

For this purpose, the phenol compound (s) can be reacted under acidic conditions with furfuryl alcohol and formaldehyde directly or with a furfuryl alcohol / formaldehyde precondensate.

The phenol compounds are preferably phenol compounds having 6 to 25 C 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 C 1 -C 4 -alkyl- mono- or disubstituted dihydroxybenzenes, trihydroxybenzenes, methylphenols and bisphenols, more 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. Particularly preferred are phenol, resorcinol and bisphenol A.

Component (b-2) may be, for example, formaldehyde-phenolic resins which, when reacted with formaldehyde and phenol and optionally with another component which is not furfuryl alcohol, may be obtained under alkaline conditions. It goes without saying that the person skilled in the art can prepare component (b-1) and, if present, component (b-2) of a mixture according to the invention separately and in a targeted manner. The constituents (b-1) and (b-2) may initially (preferably in the proportions indicated as preferred) initially mixed together and together as constituent (b) or alternatively in separate form as (b)

1) and (b-2) are introduced into a mixture according to the invention.

It is further understood that the skilled artisan can separately obtain or prepare the components (a) to (d) of a mixture according to the invention. The constituents (a) to (d) can be mixed together (preferably in the proportions specified as being preferred) successively or simultaneously with each other, and thereby a mixture according to the invention can be obtained.

The order of constituents (a) to (d) in the preparation of a mixture according to the invention does not play any significant role. Preferably, the ingredients (a) to (d) are mixed together at a temperature in the range of 0 to 70 ° C, preferably at a temperature in the range of 10 to 60 ° C, more preferably at a temperature in the range of 15 to 50 ° C, for example at 18 to 25 ° C.

For economic reasons, however, it is regularly preferred to use components (b-1) and (b)

2) in a reaction by reacting furfuryl alcohol and formaldehyde in the presence of the component (d), preferably in a one-pot reaction. The reaction is preferably carried out so that the components (a) and (b) (ie component (b-1) and optionally component (b-2)) and the components (c) and (d) of a mixture according to the invention in the desired proportions (preferably in the proportions given as preferred) can be obtained. In such a case, the subsequent or separate addition of monomeric furfuryl alcohol (component (a)) is not required. For this purpose, reference is also made to the following Herste II inventive method.

The mixtures according to the invention contain water (component (c)). However, since water slows down the curing of the molding material mixture obtainable therefrom and in the condensation reaction during the production and, in addition, additionally produces water as a reaction product during the 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 from 5 to 15% by weight, more preferably in an amount in the range from 7 to 14% by weight, particularly preferably in an amount in the range from 8 to 13% by weight. , wherein the percentages by weight are based on the total mass of the mixture according to the invention. The comparatively low proportion of water compared with a large number of resin formulations of the prior art, in addition to its positive influence on the curing behavior, causes molds or cores produced using the mixture according to the invention to be less easily blown in the casting operation on contact with liquid metal , At higher water contents in mixtures of the prior art, mold blisters are frequently observed, which can be largely avoided when using mixtures according to the invention.

A mixture preferred according to the invention (as defined above)

(a) monomeric furfuryl alcohol, wherein the amount of furfuryl alcohol is at most 24.75% by weight, preferably at most 24.60% by weight,

and or

(c) water, wherein the amount of water is at most 15% by weight,

wherein the weight percentages are based on the total mass of the mixture.

Preferably, in a mixture preferred according to the invention, the total amount of the constituent is

(B) 45 wt .-% or more, preferably 50 wt .-% or more, each based on the total mass of the mixture.

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 constituents, preferably one or more further aldehydes, here preferably glyoxal,

and

(b-2) reaction products of formaldehyde other than component (b-1) with one or more other compounds which is not or are not furfuryl alcohol, the amount of these further reaction products being at most 15% by weight, preferably at most 12% by weight. %, preferably at most 10% by weight,

wherein the weight percentages are based on the total mass of the mixture.

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

The viscosity is determined according to DIN 53019-1: 2008-09, i. according to DIN 53019-1 of September 2008, and refers to measurements at 20 ° C. The viscosity is given in the context of the present text in the unit millipascal seconds (as mPas or mPa * s). The viscosity is preferably determined according to DIN 53019-1 with a rotational viscometer at 20 ° C., for example using a Haake VT 550 rotational viscosimeter. The viscosity values determined in the context of the present invention were determined using a cylinder (spindle) SV1 and a measuring cup (tube). SV measured. The speed used in the measurement of the viscosity with the rotational viscometer was at a viscosity of the sample to be examined of less than 100 mPas at 20 ° C and 800 rpm (revolutions / min.); at a viscosity of the test sample of 100 to 800 mPas was measured at a speed of 500 rpm at 20 ° C.

A very particularly preferred mixture according to the invention for use as a binder in the no-bake process is a mixture comprising

(c) water, wherein the amount of water is at most 15% by weight,

(d) one or more organic acids having a pKa of greater than or equal to 2.5, preferably in the range of 2.75 to 6, preferably in the range of 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 weight percentages are based on the total mass of the mixture, wherein the mixture at 20 ° C has a viscosity of at most 300 mPas according to DIN 53019-1: 2008-09, preferably at most 250 mPas, preferably at most 200 mPas, more preferably at most 150 mPas.

Such a mixture according to the invention has, despite a low water content of at most 15 wt .-% at the same time a low viscosity, which in the foundry (after mixing with mold base) causes excellent processability of the resulting molding material mixture. In our own investigations, the preferred mixtures according to the invention have proven their worth, in particular because of their good and reproducible meterability in continuous flow mixers. In practice, for example, 35 t of sand mixture or more per hour are mixed continuously for given screw geometries (furan-resin resin plants). A good "atomization" of the mixture of the invention is important here to ensure the most uniform and homogeneous distribution in the molding material during the short mixing time.

Such a mixture according to the invention moreover leads to good flowability, e.g. a freshly prepared sand mixture during mold filling. When filling molds, mold contours and undercuts should generally be filled well and compacted. Higher viscosity binders tend to clog and poorly flow the sand mixture as compared to the preferred blends of the invention, resulting in surface casting defects due to poorer densification.

A preferred mixture according to the invention is characterized in that the content of free formaldehyde is at most 0.4% by weight, preferably at most 0.3% by weight, preferably at most 0.2% by weight, based on the total mass of the mixture ,

Preferably, component (d) used is one or more organic acids having a pKa value in the range from 2.75 to 6 at 25 ° C., preferably in the range from 3 to 5, and / or salts thereof.

Organic acids having a pKa in these ranges are particularly suitable condensation catalysts for preparing the reaction products of formaldehyde with furfuryl alcohol and optionally other constituents of component (b-1).

Citric acid, lactic acid, benzoic acid, phthalic acid, I-malic acid, d-tartaric acid, maleic acid, glycolic acid, glyoxylic acid, 2,4-dihydroxybenzoic acid and salicylic acid are suitable as organic acids of component (d) of a mixture according to the invention.

Preferred organic acids of the 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 these acids have achieved particularly good results in the context of the present invention, wherein With benzoic acid, lactic acid or citric acid particularly good results and with benzoic acid the best results were obtained. The phase compatibility of benzoic acid in the mixture according to the invention has proven to be particularly good in own investigations; no crystallization reaction was observed.

The use of other organic acids in component (d) is possible but not preferred. Thus, e.g. Acetic, propionic and butyric acids, and in some cases foul-smelling acids. For example, succinic acid and adipic acid show a rapid crystallization tendency. The presence of these other organic acids in a mixture according to the invention is therefore not preferred.

Preferably, in a mixture preferred according to the invention, the total amount of constituent (d) is from 0.5 to 8% by weight, preferably from 0.75 to 5% by weight, more preferably from 1 to 3% by weight, based in each case on the total mass of the mixture ,

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 adversely 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 was found.

A preferred mixture according to the invention is one which has a content of ammonia of at most 1% by weight, preferably of at most 0.5% by weight, preferably of at most 0.25% by weight, based on the total mass of the mixture.

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

The total content of nitrogen can be determined, for example, by elemental analysis or by the so-called Kjeldahl method (according to DIN 16916-02, point 5.6.4), the elemental analysis for determining the total nitrogen content of a mixture according to the invention being preferred. The total contents of nitrogen determined in the context of the present text were determined by means of elemental analysis by selective CNS combustion catalysis (CNS = carbon, nitrogen, sulfur), the catalytic tube combustion taking place at 1,140 ° C. and foreign gases being separated off (device: VARIO MAX CNS) ,

A preferred mixture according to the invention is a mixture whose total content of compounds having a molecular weight of greater than 5000 daltons (g / mol) is at most 3% by weight, preferably at most 1% by weight, determined by gel permeation chromatography according to DIN 55672-1 (February 1995), where the weight percentages refer to the total mass of the mixture.

The molecular weights indicated below refer to molecular weights determined by gel permeation chromatography (GPC) in accordance with DIN 55672-1 (February 1995), the detection in the present case preferably taking place with a UV detector at a wavelength of 235 nm.

In a preferred mixture according to the invention, the total content of compounds having a molecular weight of greater than 4000 daltons (g / mol) is at most 3% by weight, preferably at most 1% by weight.

In a preferred mixture according to the invention, the total content of compounds having a molecular weight of greater than 3000 daltons (g / mol) is at most 5% by weight, preferably at most 2% by weight.

In a preferred mixture according to the invention, constituent (b-1) does not comprise any compounds having a molecular weight greater than 5000 daltons, more preferably no compounds having a molecular weight greater than 4000 daltons.

In a preferred mixture according to the invention, constituent (b-1) comprises at most 3% by weight of compounds having a molecular weight of greater than 3000 daltons.

In a preferred mixture according to the invention, constituent (b-1) comprises at most 5% by weight of compounds with a molecular weight of greater than 2000 daltons.

In a preferred mixture according to the invention, the weight average molecular weight _M.sub.w (weight average) of constituent (b-1) is in the range from 200 to 600 g / mol, more preferably in the range from 225 to 500 g / mol, particularly preferably in the range from 250 to 450 g / mol, most preferably in the range of 300 to 425 g / mol. In a preferred mixture according to the invention, the ratio of weight average molecular weight M _w to number average molecular weight M _{n of} the component (b-1) is in the range from 5: 1 to 9: 8, more preferably in the range from 4: 1 to 6 : 5, more preferably in the range of 3: 1 to 4: 3, particularly preferably in the range of 2: 1 to 3: 2.

In a preferred mixture according to the invention, the ratio of molar mass average _Mw to molar mass average _{Mn of} the two constituents (a) and (b-1) together is in the range from 5: 1 to 9: 8, more preferably in the range from 4: 1 to 6 : 5, more preferably in the range of 3: 1 to 4: 3, particularly preferably in the range of 2: 1 to 3: 2.

The ratio of weight average (molecular weight average M _w ) to number average (molecular weight average M _n ) is also referred to as polydispersity, which is often given in GPC spectra with D as the ratio. Polydispersity is a measure of the width of a molecular weight distribution. The larger the D, the broader is the molecular weight distribution (a discrete compound has a polydispersity of 1).

It has been found in this regard that mixtures according to the invention in which constituent (b-1) or the two constituents (a) and (b-1) together have a polydispersity given above as being preferred or particularly preferred have particularly good results and effects in the art Sense of the present invention showed.

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

Suitable silanes are, for example, aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes and ureidosilanes, such as gamma-hydroxypropyltrimethoxysilane.gamma-aminopropylmethyldiethoxysilane, gamma-aminopropyltrimethoxysilane, gamma-aminopropyltriethoxysilane, 3-ureidopropyltriethoxysilane, gamma-mercaptopropyltrimethoxysilane, gamma-

Glycidoxypropyltrimethoxysilane, beta- (3,4-epoxycyclohexyl) trimethoxysilane, N-beta- (aminoethyl) -gamma-aminopropyltrimethoxysilane.

Gamma-aminopropylmethyldiethoxysilane (N-aminopropylmethyldiethoxysilane) is marketed under the trade names Silan 1 100, Silane 1 101 and Silane 1 102 (technical grade) and AMEO T and gamma-aminopropyltriethoxysilane (N-aminopropyltriethoxysilane) under Dynasilan 1505 and 1506 (technical grade). Also suitable are silanes which are available under the trade names DAMO, DAMO-T and Dynasilan 141 1.

With mixtures according to the invention comprising 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 have been obtained particularly good results in the production of molds or cores, especially with N-Aminopropylmethyldiethoxysilan and / or N-aminopropyltriethoxysilane.

A particularly preferred mixture according to the invention therefore additionally comprises as further constituent

(e) one or more adhesion promoters, preferably selected 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 up to 3 wt .-%, preferably from 0.1 to 1 wt .-%, wherein the weight percentages are based on the total mass of the mixture.

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

A particularly preferred mixture according to the invention additionally comprises one or more further constituents selected from the group

(F) the organic curing moderators, preferably selected from the group of di-, tri- or polyols, preferably from the group of glycols having 2 to 12 carbon atoms, preferably in an amount of at most 10 wt .-%, based on the total mass of the mixture,

(G) the inert organic solubilizer, preferably having 1 to 6 carbon atoms, preferably selected from the group of alcohols R-OH, where R is a C1-C4 alkyl radical, preferably ethanol, preferably in an amount of at most 10 wt. %, based on the total mass of the mixture,

(h) the reaction products of furfuryl alcohol and one or more aldehydes having 2 or more carbon atoms, preferably reaction products of furfuryl alcohol and glyoxal,

(j) the organic compounds which have one or more H ₂ N groups and / or one or more HN groups, preferably urea,

(k) the phenolic compounds, preferably the phenol compounds having 6 to 25 carbon atoms and / or one, two, three or four directly attached to an aromatic ring Hydroxyl groups, preferably selected from the group consisting of phenol, optionally C 1 -C 4 -alkyl-mono- or disubstituted dihydroxybenzenes, trihydroxybenzenes, methylphenols and bisphenols, more 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) the aldehydes having 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.

Preferred organic curing moderators of component (f) are glycols having 2 to 12 carbon atoms, more preferably glycols having 2 to 6 carbon atoms, most preferably ethylene glycol, i. Monoethylene glycol.

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.

Preferred aldehydes which form 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, glyoxal in turn being preferred.

Preferred aldehyde having 2 or more carbon atoms of the component (h) and / or the component (s) of a mixture according to the invention is glyoxal, since it is not only readily available and advantageous from an economic point of view, but also brings about technical advantages of a mixture according to the invention. For example, even small quantities of glyoxal as constituent (s) but also reaction products of furfuryl alcohol and glyoxal as constituent (h) have a positive influence on the reactivity of a mixture according to the invention.

If a mixture according to the invention comprises constituent (s), the total amount of constituent (s) is preferably at most 5% by weight, preferably at most 3% by weight, based on the total mass of the mixture.

Preferred phenolic compounds of component (k) of a mixture according to the invention are phenol compounds having 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 C 1 -C 4 -alkyl-mono- or -di-substituted dihydroxybenzenes, trihydroxybenzenes, methylphenols and bisphenols, more 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), with phenol, resorcinol and / or bisphenol A again being particularly preferred.

Component (k) comprises or consists preferably of phenol, resorcinol and / or bisphenol A, since in particular these free phenols show a high affinity for reaction with formaldehyde and react rapidly with any formaldehyde still present, whereby the emission, in particular of formaldehyde, is further reduced can be, especially during the curing process.

Bisphenol A is particularly advantageous in this context, since it-presumably because of its diphenylmethane skeleton-leads to a higher strength of the resulting molds and cores after curing of a mixture according to the invention as a constituent of a reaction mixture according to the invention. In addition, a higher thermal stability is observed, in particular during the casting process, whereby a further positive effect with respect to the emission can be achieved.

A preferred mixture according to the invention may additionally comprise benzyl alcohol as constituent (m), preferably in an amount of at most 15% by weight, based on the total mass of the mixture.

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

The advantage lies inter alia in the very good compatibility with the other constituents of a mixture according to the invention. It has also been found that lowering the viscosity, i. Also the viscosity value, takes place and beyond the storage stability of a mixture according to the invention is further improved.

For this purpose, when using benzyl alcohol in comparison to lower alcohols (in particular 1-alkanols having 1 to 4 C atoms, in particular methanol, ethanol or isopropanol), the flash point of a mixture according to the invention is increased and at the same time the odor is reduced. In addition, with lower alcohols, depending on the amount used, the cold curing can be undesirably delayed significantly, which is observed only to a lesser extent in benzyl alcohol. A preferred mixture according to the invention has a pH in the range from 4 to 10 at 25 ° C., preferably in the range from 5 to 9.5.

A mixture according to the invention preferably has a pH in the range from 5 to 7 or in the range from 8 to 9.5 at 25 ° C.

The preferably adjusted pH values of a mixture according to the invention, which is usually a solution, result in excellent storage stability.

A preferred mixture according to the invention is a storage-stable mixture which preferably has a storage stability of at least 3 months at 20 ° C., preference being given during the storage period

the viscosity value of the mixture at 20 ° C., measured in accordance with DIN 53019-1: 2008-09, at most increases by 80%, preferably at most by 70%, preferably at most 60%, particularly preferably at most 50%, and preferably 300 mPas , preferably 250 mPas, more preferably 200 mPas, particularly preferably does not exceed 150 mPas, and

the proportion by weight of constituent (a) decreases by at most 10%, preferably by at most 5%, based on the starting amount of monomeric furfuryl alcohol at the beginning of the storage period.

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% by weight, preferably at most 24.75% by weight,

(b-1) 40 wt .-% or more, preferably 45 wt .-% or more, of reaction products of furfuryl alcohol with formaldehyde and optionally further constituents, preferably one or more further aldehydes, preferably glyoxal, and

(b-2) reaction products of formaldehyde other than component (b-1) with one or more other compounds which are not or are not furfuryl alcohol, the amount of these further reaction products being at most 12% by weight, preferably at most 10% by weight. -%

(c) water, wherein the amount of water is at most 15% by weight, (d) one or more organic acids having a pKa in the range of 2.75 to 6, preferably in the range of 3 to 5, at 25 ° C and / or salts thereof, 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. %, preferably from 0.1 to 1% by weight,

(f) one or more organic curing moderators from the group of glycols having 2 to 12 C atoms, preferably in an amount of at most 10% by weight,

(g) one or more inert organic solubilizers selected from the group of the alcohols R-OH, where R is a C 1 -C 4 -alkyl radical, preferably ethanol,

(h) optionally one or more reaction products of furfuryl alcohol and one or more aldehydes having 2 or more carbon atoms, preferably reaction products of furfuryl alcohol and glyoxal,

(j) optionally one or more organic compounds having one or more H ₂ N groups and / or one or more HN groups, preferably urea,

(k) optionally one or more phenol compounds, preferably phenol compounds having 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 dihydroxbenzenes, trihydroxybenzenes, methylphenols and bisphenols, more 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) optional glyoxal,

and optionally free formaldehyde in an amount of at most 0.5% by weight,

wherein the weight percentages are based on the total mass of the mixture.

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% by weight, preferably at most 24.60% by weight,

(b) 45% or more by weight of reaction products of formaldehyde, which comprise the reaction products (b-1) 45 wt .-% or more, preferably 50 wt .-% or more, of reaction products of furfuryl alcohol with formaldehyde and optionally further constituents, preferably one or more further aldehydes, preferably glyoxal, and

(c) water, wherein the amount of water is at most 15% by weight, preferably in an amount of from 5 to 15% by weight,

(d) one or more organic acids having a pKa in the range from 3 to 5 at 25 ° C. and / or salts thereof, preferably in an amount of from 1 to 4% by weight,

(E) one or more coupling agents 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 0.1 to 1 wt .-%,

(f) ethylene glycol in an amount of at most 5% by weight, preferably in an amount of from 1 to 4% by weight,

(g) ethanol in an amount of at most 5% by weight, preferably in an amount of from 1 to 4.5% by weight,

(n) optional glyoxal,

and either component (j) or component (k)

(j) one or more organic compounds which have one or more H ₂ N groups and / or one or more HN groups, preferably urea,

(k) optionally one or more phenol compounds, preferably phenol compounds having 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, more 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, and optionally free formaldehyde in an amount of at most 0.5 wt .-%, wherein the weight percentages are based on the total mass of the mixture.

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% by weight,

(b) 45% or more by weight of reaction products of formaldehyde, which comprise the reaction products

(b-1) 45 wt .-% or more, preferably 50 wt .-% or more, of reaction products of furfuryl alcohol with formaldehyde and optionally further constituents, preferably one or more further aldehydes, preferably glyoxal, and

(c) water, wherein the amount of water is at most 15% by weight, preferably in an amount of 7 to 14% by weight,

(D) one or more organic acids having a pKa in the range of 3 to 5 at 25 ° C and / or salts thereof 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-aminopropylmethyldiethoxysilane and / or N-aminopropyltriethoxysilane, preferably in a total amount of from 0.1 to 1% by weight,

(n) optional glyoxal,

and either component (j) or component (k)

(j) urea,

(k) phenol, resorcinol and / or bisphenol A, and optionally free formaldehyde in an amount of at most 0.5 wt .-%, wherein the weight percentages are based on the total mass of the mixture.

The invention further relates to a reaction mixture comprising

(i) a mixture according to the invention, preferably in one of the preferred embodiments,

(ii) an acid wherein the acid has a pKa of less than 2 at 25 ° C, preferably less than 1.5, preferably less than 1.

In this case, the reaction mixture preferably has a content of free formaldehyde of at most 0.4% by weight, the percentages by weight being based on the total mass of the reaction mixture minus the total mass of refractory granular substances in the reaction mixture.

Component (ii) is also referred to as acid hardener. The acid hardener allows the curing 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 already results at low temperatures, typically at ambient temperature, in particular at 25 ° C.

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

Component (ii) of a reaction mixture according to the invention preferably comprises or consists preferably of organic sulfonic acids. Besides aromatic sulfonic acids such as benzenesulfonic acid, toluenesulfonic acids, xylenesulfonic acids or cumene sulfonic acid [2 (or 4) - (isopropyl) -benzenesulfonic acid], also methanesulfonic acid and ethanesulfonic acid are preferred. The organic sulfonic acids are readily available and have a sufficiently high acid strength to achieve the desired curing of a mixture according to the invention in the no-bake process. In the context of the present invention, the best results were achieved with p-toluenesulfonic acid.

According to the invention, preference is given to a reaction mixture in which the acid of component (ii) is selected from the group of organic acids, preferably of organic sulfonic acids, preferably selected from the group consisting of benzenesulfonic acid, Toluenesulfonic acids, xylenesulfonic acids, cumene sulfonic acid [2 (or 4) - (isopropylbenzenesulfonic acid and methanesulfonic acid, particularly preferred is p-toluenesulfonic acid.

Preferably, the reaction mixture comprises (i) no sulfuric acid or (ii) sulfuric acid in an amount of at most 1 wt .-%, preferably at most 0.5 wt .-%, wherein the weight percentages are based on the total mass of the reaction mixture minus the total mass of ( optional) refractory granular substances in the reaction mixture. Preferably, the reaction mixture comprises no phosphoric acid and no hydrochloric acid; more preferably, the reaction mixture according to the invention comprises no mineral acids at all. In the case of sulfuric acid, the strength of the acid is in some cases problematic. According to experience, binders which are cured only with sulfuric acid show a "spontaneously" generated polymer network with inevitably more defects extremely unpleasant (foul 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 cycle.

Aromatic sulfonic acids, however, are very good resin-miscible (have a good phase compatibility). The ongoing hardening is more orderly, more homogeneous, more complete and also better controllable compared to sulfuric acid. In addition, part of the organically bound sulfur evaporates in the casting process as S0 ₂ from the molding material out. As a result, a lower desulfurization is observed. In handling, the less corrosive sulfonic acids are also positive in comparison with sulfuric acid (tool life is positively influenced).

In a reaction mixture according to the invention, preference is given to using acid having a pKa of less than 2 at 25 ° C. in a total amount of from 10 to 80% by weight, preferably from 15 to 70% by weight, preferably from 20 to 60% by weight. -%, particularly preferably from 25 to 50 wt .-%, each based on the total mass of formaldehyde and the components (a), (b), (c), (d), (e), (f), (g ), (h), (j), (k) and (n) the mixture of the invention (component (i)).

The total amount of acid or acids having a pKa of less than 2 at 25 ° C. in a reaction mixture according to the invention is preferably in the range from 9 to 45% by weight, preferably from 13 to 41% by weight, preferably from 16 to 38% by weight .-%, particularly preferably from 20 to 33 wt .-%, based on the total mass of the reaction mixture according to the invention less the total mass of any existing refractory granular materials. According to the invention, preference is given to a reaction mixture 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.

If a reaction mixture according to the invention comprises, besides a mixture according to the invention (constituent (i)), an acid hardener (constituent (ii)) and a refractory granular substance (constituent (iii)), a molding material mixture is present.

Preference is given to reaction mixtures according to the invention which do not comprise sulfur dioxide or comprise no peroxide (in particular methyl ethyl ketone peroxide), preferably those which comprise neither sulfur dioxide nor a peroxide (in particular methyl ethyl ketone peroxide).

Refractory mold raw materials, which were solidified using a reaction mixture according to the invention in the no-bake process, can be worked up very well again. This is especially true for sand.

A reaction mixture according to the invention preferably comprises sand, preferably having a particle size in the range from 0.063 to 2 mm, preferably with a particle size in the range from 0.1 to 1 mm.

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

Preferably, component (iii) comprises or consists of sand, preferably aluminum silicate sand, feldspar sand and / or quartz sand. Component (iii) particularly preferably comprises quartz sand, more preferably component (iii) consists of quartz sand.

The invention further relates to a process for the preparation of a mixture according to the invention, preferably in one of the embodiments characterized as being preferred or particularly preferred, with the following step:

(S-1) reacting furfuryl alcohol with formaldehyde and optionally further constituents in the presence of one or more organic acids having a pKa of greater than or equal to 2.5, preferably in the range of 2.75 to 6, 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, preferably in the range of 3: 1 to 1, 25: 1 , more preferably in the range of 2: 1 to 3: 2.

Formaldehyde can be used both in monomeric form, for example in the form of a formalin solution, as well as in the form of its polymers, such as trioxane or paraformaldehyde, wherein according to the invention, the use of paraformaldehyde is preferred.

In addition to formaldehyde, other aldehydes can additionally be used. Suitable aldehydes are, for example, acetaldehyde, propionaldehyde, butyraldehyde, acrolein, crotonaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde, glyoxal and mixtures of these aldehydes.

Particularly preferred organic acids having a pKa 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 more preferred, most preferred is benzoic acid.

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

In a preferred process of 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.

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) if appropriate setting the desired pH with an inorganic base, preferably with an alkali metal hydroxide, preferably NaOH and / or KOH,

(S-4) addition of one or more compounds which can react with any remaining formaldehyde (or addition of one or more compounds for reaction with optionally still present formaldehyde), these compounds are preferably selected from the group of organic compounds having a or more H ₂ N and / or HN groups and / or the group of phenolic compounds,

(S-5) 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-6) optionally adding further ingredients, 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 being preferred.

In a preferred process according to the invention, the total amount of furfuryl alcohol used is at least 50% by weight, preferably at least 55% by weight, and preferably in the range from 60 to 75% by weight, more preferably in the range from 62 to 72% by weight .-%, wherein the weight percentages are based on the total mass of the resulting mixture according to the invention.

A preferred mixture according to the invention (as defined above), preferably in one of the preferred embodiments, is a mixture preparable by a process according to the invention, preferably in one of the preferred embodiments.

The invention also relates to a method for producing a casting mold or a core, preferably a no-bake casting mold or a no-bake core for the production of metal bodies, comprising the step:

Hardening, preferably acid-catalysed curing, of a mixture according to the invention, preferably in one of the embodiments characterized as being preferred,

or

Curing a reaction mixture according to the invention, preferably in one of the embodiments characterized as being preferred,

wherein the curing is preferably carried out at a temperature below 60 ° C, preferably in the range of 0 to 50 ° C, more preferably in the range of 10 to 40 ° C, particularly preferably in the range of 15 to 30 ° C.

In a preferred embodiment for carrying out the no-bake process, the refractory molding base material according to the invention (constituent (iii) of a reaction mixture according to the invention) is first coated with the acid hardener (constituent (ii) of a reaction mixture according to the invention). Subsequently, the binder (ie a mixture according to the invention, component (i) of a reaction mixture according to the invention) is added and distributed evenly by mixing onto the already coated with the catalyst grains of the refractory molding base material. The molding material mixture can then be shaped into a shaped body. Since binder and acid hardener are evenly distributed in the molding material mixture, the curing is largely uniform even with large moldings. In a preferred process according to the invention, the curing is preferably carried out in the absence of sulfur dioxide. For curing a mixture according to the invention, a reaction mixture according to the invention is preferably prepared which then hardens without further ado. In this respect, the remarks on the reaction mixture according to the invention apply correspondingly to the process according to the invention.

In the method according to the invention for the production of 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 during casting show a reduced emission of defective compounds.

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

In a further aspect, the invention relates to the use of a mixture according to the invention, preferably in one of the embodiments marked as preferred, as cold-curing binder, preferably as a no-bake binder in the foundry, in particular in the production of metal bodies by means of a casting process, wherein the curing of Binder is preferably carried out without the use of gaseous sulfur dioxide.

In a further aspect, the invention relates to the use of a mixture according to the invention or of a reaction mixture, preferably in each case in one of the preferred embodiments, 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 curing, preferably in a no-bake process without gassing step.

The invention further relates to a kit comprising

as a first component, a mixture according to the invention, preferably in one of the preferred embodiments,

as a second component, an aqueous solution of an acid, wherein the acid has a pKa of less than 2 at 25 ° C.

The invention will be explained in more detail by way of examples. Examples

Unless otherwise indicated, all data are by weight. Abbreviations used: FA = furfuryl alcohol, Bl = evaluation index.

Table 1 below compares the chemical and physical parameters of the resins. The values given correspond to average values which are typical for the particular binder.

The non-inventive no-bake binders designated "KH-Ref1" and "KH-Ref2" are commercially available products.

Table 1

KH-Refl KH-Y KH-Ref2

(not according to the invention) (according to the invention) (not according to the invention)

Total amount of 87% by weight 67% by weight 75% by weight

inserted FA

Content of monomeric 87% by weight 24.5% by weight 63% by weight

FA

Total nitrogen content 1.05% by weight 2.85% by weight 3.5% by weight

Water content 10% by weight 1 1% by weight 10% by weight

free formaldehyde 0.15% by weight 0.15% by weight 0.06% by weight

Density at 20 ° C 1, 130 g / cm ³ 1, 185 g / cm ³ 1, 160 g / cm ³

Viscosity at 20 ° C 10 mPa * s 65 mPa * s 20 mPa * s

Appearance light brown, cloudy dark brown, clear dark brown, clear

The non-inventive no-bake binder KH-Ref2, which was also investigated for comparison purposes, had the following composition:

These ingredients of the no-bake binder KH-Ref2 were added to a reactor with stirring and the ingredients mixed for 15 minutes.

Production of cold resin TN-X:

Furfuryl alcohol (60.30% by weight), paraformaldehyde 91% (15.88% by weight), formic acid 85% (0.60% by weight), urea (12.59% by weight), Water (3.56% by weight), ethanol (4.95% by weight), ammonia 25% in water (2.12% by weight).

Throughout the process, the reactor contents are stirred. 489.9 kg of furfuryl alcohol, 63.0 kg of urea, 158.8 kg of paraformaldehyde 91%, 35.6 kg of water and 49.5 kg of ethanol are introduced into a reactor and mixed thoroughly. Subsequently, 4.8 kg of 85% strength formic acid are added and the resulting mixture is heated to 90.degree. At intervals of about 30 minutes each further 62.9 kg of urea at 90 ° C are added in portions. Subsequently, this reaction mixture is cooled a little and there are added 1 13.1 kg of furfuryl alcohol. After further cooling to 50 ° C, a pH is finally adjusted in the range of 8.1 to 8.8 by adding ammonia 25% in water. The product thus obtained is referred to herein as non-inventive mixture TN-X.

Data of cold resin TN-X: Water content: 13.5% by weight, total content of nitrogen: 6.2% by weight, content of formaldehyde: 0.1% by weight, viscosity at 20 ° C: 95 mPas.

Preparation of the no-bake binder KH-Y according to the invention:

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 solution 33% in water (0.70% by weight). Throughout the process, the reactor contents are stirred. In a reactor, 223.2 kg of furfuryl alcohol and 5.2 kg of benzoic acid are mixed thoroughly (pH value: 3.7 to 4.2) and then 123.8 kg of paraformaldehyde are added. The mixture is then heated within 30-60 minutes to 100 to 1 10 ° C and held this temperature for 60 minutes. At this temperature, two further portions of furfuryl alcohol and benzoic acid are added to the reaction mixture at intervals. Subsequently, the temperature is increased to about 135 ° C and the reaction mixture heated under reflux (duration: 3 to 5 hours, the reflux temperature drops slowly and continuously to about 125 ° C). Then, the resulting reaction mixture is cooled rapidly, added 60.7 kg of urea and cooled further. At a temperature of 60 ° C, 4.0 kg of sodium hydroxide (33% in water) are added, with a pH in the range of 5.5 to 6.0 (measured at 20 ° C) is set. After further cooling the reaction mixture to about 30 ° C 69.4 kg of water, 29.8 kg of ethanol and 19.9 kg of monoethylene glycol and 4.0 kg Dynasilan 1506 are added and mixed. Optionally, the pH of the reaction mixture is finally 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 referred to herein as the mixture according to the invention KH-Y.

Bending strength and setting behavior

The respective flexural strength values were determined in accordance with VDG leaflet P 72 (October 1999) ("Testing of cold-hardening, resin-bonded moist molded materials with hardener additive").

The production of the molding material mixture was carried out in a laboratory mixer (BOSCH). For this purpose, in each case the parts by weight of acid hardener specified in Table 2 were added to 100 parts by weight of quartz sand H32 (Quarzwerke Frechen) and mixed for 30 seconds. Subsequently, the parts by weight of binder indicated in Table 2 were added and remixed for a further 45 seconds. The resulting mixture was prepared at room temperature (18-22 ° C) and a relative humidity (RLF) of 20-55%. The sand temperature was 18 - 22 ° C.

Subsequently, the molding material mixture was introduced by hand into the Prüfriegelform and compacted with a hand plate.

Cuboid test bars measuring 220 mm x 22.36 mm x 22.36 mm, known as Georg Fischer test bars, were produced as test specimens.

To determine the hardening time, the molding material mixture in a form (cup), 80 mm in height and 80 mm in diameter, compacted with a hand plate. The surface is in particular Periods checked with a test nail. If the test nail no longer penetrates into the core surface, the curing time is given.

To determine the processing and curing time of the molding material mixture, the setting behavior was observed with the test pin in accordance with VDG P 72 using a Georg Fischer test strip.

The respective flexural strength values were determined in accordance with the above-mentioned VDG leaflet P 72. To determine the bending strengths, the test bars were placed in a Georg Fischer strength tester equipped with a three-point bending device (DISA-Industrie AG, Schaffhausen, CH) and the force was measured, which led to the breakage of the test bars.

The flexural strengths were after one hour, after two hours, after four hours and after 24 h after the preparation of the test material mixture (storage of the cores after demolding, each at room temperature 18-22 ° C, RLF 20-55%).

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

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

In the first experimental range, in each case separately 1 part by weight (corresponding to 1 wt .-%, based on the amount of sand used) no-bake binder KH-Ref2 (not according to the invention) and KH-Y (according to the invention) with 0.5 parts by weight of one 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.

In the second experimental range separately 1 part by weight (corresponding to 1 wt .-%, based on the amount of sand used) no-bake binder KH-Ref2 (not according to the invention) and KH-Y (according to the invention) 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 material mixture.

Used abbreviations:

VE = processing time in minutes

AH = curing time in minutes (100 g) DU = cure time in minutes VISC = viscosity in mPas at 20 ° C

BF1, BF2, BF4, BF24 = flexural strength after 1, 2, 4 or 24 hours (in each case in N / cm ² )

Table 2a: Setting and flexural strengths using 0.325 parts by weight of the acid hardener p-toluenesulfonic acid

Table 2b: Setting and flexural strengths using 0.26 parts by weight of the acid hardener p-toluenesulfonic acid

Emission measurements during mixing, filling, and compaction and casting results

The molding compound mixtures described in Table 3 were made into molds, and iron casting was carried out with both molds. The measured pollutant emissions during mixing, filling, and compression are shown in Table 4. The casting result was flawless in both cases. Table 3: Composition of molding material mixtures

Table 4: Results of the measurement of pollutant emissions during mixing, filling, and compression

The underlying AGW values were the occupational exposure limit values according to the Technical Rule for Hazardous Substances (TRGS) 900 January 2006 issue as of June 2010 and TRGS 402, January 2010 edition, insofar as no corresponding limit values have been published in the TRGS 900.

The valuation indices Bl AGW were determined according to TRGS 402 point 5.2. The valuation indices Bl Others were determined in accordance with TRGS 402 point 5.3. It was based on the TRGS 402 in the January 2010 issue.

Bl total = Bl AGW + Bl other. This index should not exceed the limit of 1. The mixtures according to the invention allow compliance with the limit value Bl total. Studies on storage stability

The storage stability was stored for 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 performance properties of a corresponding molding material mixture determined (as described above).

To further investigate the performance properties of a molding material mixture was first prepared. 0.5 parts by weight of a 65% strength by weight solution of p-toluenesulfonic acid in water were first added to 100 parts by weight of quartz sand H32 (Quarzwerke Frechen) and mixed for 30 seconds. Subsequently, 1 part by weight of binder KH-Y was added and remixed for a further 45 seconds. The resulting molding material mixture was prepared at room temperature (20-22 ° C) and a relative humidity (RLF) of 40-55%. The sand temperature was 20 - 22 ° C.

TABLE 5 Measurements of the storage stability of the cold resin KH-Y according to the invention

Storage period VISC VE AH 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 1 1 16 100 290 430 430

6 months 109 13 18 150 255 410 435 Table 6: Chemical and physical parameters of the no-bake binder KH-Y2 according to the invention

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

Preparation of the no-bake binder KH-Y2 according to the invention:

Furfuryl alcohol (70.18% by weight), paraformaldehyde 91% (12.03% by weight), benzoic acid (1.64% by weight), bisphenol A (2.75% by weight), urea ( 1.72% by weight), water (5.14% by weight), ethanol (3.12% by weight), monoethylene glycol (1.00% by weight), N-aminopropyltriethoxysilane (Dynasilan 1505) ( 0.40 wt%) potassium hydroxide 45% in water (2.02 wt%).

Throughout the process, the reactor contents are stirred. In a reactor, 234.0 kg of furfuryl alcohol and 5.5 kg of benzoic acid are mixed thoroughly (pH value: 3.7 to 4.2) and then 120.3 kg of paraformaldehyde are added. The mixture is then heated within 30-60 minutes to 100 - 1 10 ° C and held this temperature for 60 minutes. At this temperature, two further portions of furfuryl alcohol and benzoic acid are added to the reaction mixture at intervals. Subsequently, the temperature is increased to about 135 ° C and the reaction mixture heated under reflux (duration: 3 to 5 hours, the reflux temperature drops slowly and continuously to about 125 ° C). Then the resulting Cooled reaction mixture a little, added 27.50 kg of bisphenol A and cooled further. At a temperature of 80 ° C 20.2 kg of potassium hydroxide solution (45% in water) are added and stirred for about an additional hour. After the further cooling of the reaction mixture to about 60 ° C, 31, 2 kg of ethanol and 17.2 kg of urea are added. After further cooling of the reaction mixture to about 35 ° C are finally 51, 4 kg of water, 10.0 kg of monoethylene glycol and 4.0 kg Dynasilan 1505 added and mixed. The product thus obtained is referred to herein as the mixture according to the invention KH-Y2.

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

With this molding material mixture, the flexural strengths and the setting behavior were determined accordingly under the test conditions described above and in accordance with the above statements.

Table 6a: setting behavior and flexural strengths of the mixture according to the invention KH-Y2 using 0.325 parts by weight of the acid hardener p-toluenesulfonic acid

Binders PU AH DU BF1 BF2 BF4 BF24

KH-Y2 9 15 41 165 320 380 525

Claims

claims

1 . Mixture for use as a binder in the no-bake method, comprising

(c) water, the amount of water being at most 20% by weight,

wherein the mixture has a content of free formaldehyde of at most 0.5 wt .-%, wherein the weight percentages are based on the total mass of the mixture.

2. Mixture according to claim 1, comprising

and or

(c) water, wherein the amount of water is at most 15% by weight,

wherein the weight percentages are based on the total mass of the mixture.

3. Mixture according to claim 1 or 2, wherein the amount of the component (b) is 45 wt .-% or more, preferably 50 wt .-% or more, wherein the weight percentages refer to the total mass of the mixture.

4. Mixture according to one of the preceding claims, wherein 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 constituents, preferably one or more further aldehydes, preferably glyoxal,

wherein the weight percentages are based on the total mass of the mixture.

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

6. Mixture according to 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 weight percentages refer to the total mass of the mixture.

7. Mixture according to one of the preceding claims, wherein 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 salts thereof.

8. Mixture according to one of the preceding claims, wherein the content of ammonia is at most 1 wt .-%, preferably at most 0.5 wt .-%, preferably at most 0.25 wt .-%, wherein the percentages by weight on the total mass of Refer mixture.

9. Mixture according to one of the preceding claims, wherein the total content of nitrogen is at most 4 wt .-%, preferably at most 3.5 wt .-%, preferably at most 3.0 wt .-%, wherein the weight percent information on refer to the total mass of the mixture.

10. Mixture according to one of the preceding claims, wherein component (b-1) comprises 2,5-bis (hydroxymethyl) furan (BHMF), preferably in an amount of at least 1 wt .-%, preferably in an amount of 5 to 40 Wt .-%, based on the total weight of a mixture according to the invention.

1 1. Mixture according to one of the preceding claims, wherein the weight ratio of component (a) and 2,5-bis (hydroxymethyl) furan (BHMF) of the component (b-1) in the range from 3: 1 to 1: 3, preferably in the range from 2: 1 to 1: 2, more preferably in the range from 3: 2 to 2: 3, particularly preferably in the range from 5: 4 to 4: 5.

12. Mixture according to one of the preceding claims, wherein the total content of compounds having a molecular weight of greater than 5000 daltons (g / mol) is at most 3 wt .-%, determined by gel permeation chromatography according to DIN 55672-1 (February 1995), based on the total mass of the mixture.

13. Mixture according to one of the preceding claims, wherein the ratio of molecular weight average M _w to molecular weight average M _{n of} the component (b-1) in the range of 5: 1 to 9: 8, more preferably in the range of 4: 1 to 6: 5, more preferably in the range of 3: 1 to 4: 3, particularly preferably in the range of 2: 1 to 3: 2.

14. Mixture according to one of the preceding claims, additionally comprising as further constituent

(e) one or more adhesion promoters, preferably selected 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 up to 3% by weight, preferably from 0.1 to 1% by weight,

wherein the weight percentages refer to the total mass of the mixture.

A blend according to any one of the preceding claims additionally comprising one or more further ingredients selected from the group

(f) the organic curing moderators, preferably selected from the group of glycols having 2 to 12 C atoms, preferably in an amount of at most 10% by weight, based on the total mass of the mixture,

(g) the inert organic solubilizer, preferably selected from the group of the alcohols R-OH, where R is a C 1 -C 4 -alkyl radical, preferably ethanol,

(k) the phenolic compounds, preferably the phenol compounds having 6 to 25 carbon atoms and / or one, two, three or four directly to an aromatic ring bonded hydroxyl groups, preferably selected from the group consisting of phenol, optionally C 1 -C 4 -alkyl-mono- or disubstituted dihydroxybenzenes, trihydroxybenzenes, methylphenols and bisphenols, more 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,

16. Mixture according to one of the preceding claims, wherein the pH of the mixture at 25 ° C in the range of 4 to 10, preferably in the range of 5 to 9.5.

17. Mixture according to one of the preceding claims, wherein the mixture is a storage-stable mixture, which preferably has a storage stability of at least 3 months at 20 ° C, being preferred during the storage period

the viscosity value of the mixture at 20 ° C., measured in accordance with DIN 53019-1: 2008-09, increases by no more than 80% and preferably does not exceed 300 mPas, and

18. Reaction mixture comprising

(i) a mixture according to any one of the preceding claims,

(ii) an acid wherein the acid has a pKa of less than 2 at 25 ° C, preferably less than 1.5, preferably less than 1,

wherein the reaction mixture preferably has a content of free formaldehyde of at most 0.4 wt .-%, wherein the weight percentages are based on the total mass of the reaction mixture.

19. A reaction mixture according to claim 18, wherein the reaction mixture comprises no sulfuric acid or comprises sulfuric acid in an amount of at most 1 wt .-%, preferably in an amount of at most 0.5 wt .-%, wherein the Weight percentages are based on the total mass of the reaction mixture minus the total mass of refractory granular materials in the reaction mixture.

The reaction mixture of claim 18, 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, cumene sulfonic acid [2 (or 4) - (isopropyl) - Benzolsulfonsäurel and methanesulfonic acid, particularly preferred is p-toluenesulfonic acid.

Reaction mixture according to one of the preceding claims, additionally comprising

22. A reaction mixture according to any one of the preceding claims, not comprising sulfur dioxide or not comprising a peroxide, preferably neither comprising sulfur dioxide nor a peroxide.

Process, preferably for the preparation of a mixture according to one of claims 1 to 17, with the following step:

(S-1) reacting furfuryl alcohol with formaldehyde and optionally further constituents in the presence of one or more organic acids having a pKa of greater than or equal to 2.5 at 25 ° C and / or salts thereof, preferably one or more organic acids as defined in claim 7,

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, preferably in the range of 3: 1 to 1, 25: 1 , more preferably in the range of 2: 1 to 3: 2.

A method according to claim 23, wherein 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.

A method according to claim 23 or 24, comprising the following further steps:

(S-2) tempering the 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 with an inorganic base, preferably with an alkali metal hydroxide, (S-4) addition of one or more compounds which can react with any remaining formaldehyde, these compounds are preferably selected from the group of organic compounds having one or more H ₂ N and / or HN groups and / or Group of phenolic compounds,

(S-5) 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-6) optionally adding further ingredients, preferably one, several or all of the components (e), (f), (g), (h), (j), (k), (m) and (n) as in claims 14 and 15.

26. The method according to any one of claims 23 to 25, wherein 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 .-%, more preferably in the range of 62 to 72% by weight, the weight percentages being based on the total mass of the resulting mixture.

27. Mixture, preferably according to one of claims 1 to 17, preparable by a method according to one of claims 23 to 26.

28. A method for producing a casting mold or a core, preferably a no-bake casting mold or a no-bake core for producing metal bodies, comprising the step:

Hardening, preferably acid-catalyzed curing, of a mixture according to any one of claims 1 to 17,

or

Hardening of a reaction mixture according to any one of claims 18 to 22, wherein the curing is preferably carried out at a temperature below 60 ° C, preferably in the range of 0 to 50 ° C, preferably in the range of 10 to 40 ° C.

29. A process according to claim 28, wherein the curing is in the absence of sulfur dioxide.

30. Use of a mixture according to any one of claims 1 to 17 as cold-curing binder, preferably as a no-bake binder in the foundry, in particular in the production of metal bodies by means of a casting process, wherein the curing of the binder is preferably carried out without the use of gaseous sulfur dioxide.

31. Use of a mixture according to any one of claims 1 to 17 or a reaction mixture according to any one of claims 18 to 22 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 curing , preferably in a no-bake process without gassing step.

32. Kit comprising

as a first component, a mixture according to any one of claims 1 to 17, as a second component an aqueous solution of an acid, said acid having a pKa of less than 2 at 25 ° C.