EP3829798A1 - Wash composition for reducing formaldehyde emissions - Google Patents

Abstract

Described is the use of a composition containing one or more formaldehyde scavengers for producing a coating on a main part of a metal casting mold or core, said main part emitting formaldehyde when heating up, the coating forming a mold or core surface that comes into contact with a molten metal during the casting process.

Description

 HÜTTENES-ALBERTUS Chemische Werke Limited liability company

Wiesenstrasse 23, 40549 Dusseldorf

Sizing composition to reduce formaldehyde emissions

The use of certain compounds as formaldehyde scavengers is described in a coating on a base body of a mold or a core for metal casting which emits formaldehyde when heated, the coating forming a surface of the mold or core which comes into contact with a molten metal during the casting process, and the use of a composition which contains one or more of these compounds for the production of a coating on a base body of a mold or a core for metal casting which emits formaldehyde when heated, the coating forming a surface of the mold or the core which, during the casting process, is coated with a Molten metal comes into contact. Corresponding shapes and cores and their manufacture are also described. Molds and cores for metal casting are produced by molding a molding material mixture comprising a molding material (eg sand) and a binder and then curing the molded molding material mixture. Organic binders which emit formaldehyde when heated, for example polyurethanes formed by polyaddition of a phenol-formaldehyde resin with a polyisocyanate, or formaldehyde condensation resins, for example formaldehyde condensation resins from the group consisting of phenol-formaldehyde, are frequently used. dehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins. Molds are negatives, they contain the cavity to be poured, which results in the casting to be manufactured. The inner contours of a casting can be formed by cores. During the production of the mold, the cavity can be molded into the molding material by means of a model of the casting to be produced. Cores are usually formed in a core box.

Typically, in the production of molds and cores for metal casting, by molding a molding material mixture (as described above) and then curing the molded molding material mixture, a base body of the mold or core is first formed, which already has the contours of the required mold or core having. In the case of steel and iron casting in particular, a coating is usually produced on the base body thus formed, the coating forming a surface of the mold or core which comes into contact with a molten metal during the casting process. Such coatings are usually referred to as sizing. In the context of the present application, the term “shape” or “core” denotes the entirety of the base body of the shape or core and the coating arranged on this base body (size coating). This coating acts as a boundary and / or barrier layer between the base body of the core or the mold and the cast metal, and serves, among other things. for the targeted suppression of mechanisms of casting defect formation at the interface between metal and core or form or for the use of metallurgical effects. In general, coatings in foundry technology should fulfill the following functions, which are known to those skilled in the art:

 Improving the smoothness of the casting surface and / or;

 Avoidance of chemical reactions between components of the molding material mixture and the molten metal, thereby facilitating the separation between the mold / core and casting and / or

 Avoiding surface defects on the casting, e.g. Gas bubbles, penetrations, leaf ribs and / or flakes.

Ready-to-use compositions for coating the basic bodies of molds and cores are usually suspensions of fine-grained, refractory to highly refractory inorganic materials (refractories) in a carrier liquid (e.g. water, alkanols, or mixtures thereof), where further constituents can be suspended or dissolved in the carrier liquid. The size composition is suitably applied to the base body, and then the carrier liquid is removed by drying, a coating being formed on the base body. Drying usually takes place at a temperature above 40 ° C., preferably in the range from 50 ° C. to 200 ° C. At these temperatures, the base bodies of the molds or cores emit significant amounts of formaldehyde. Such emissions represent a significant workload. DE 10 2008 025 31 1 A1 discloses a casting mold for metal casting, a layer of a pollutant-absorbing material being arranged at least in sections on gas outlet surfaces of the casting mold. Gas exit surfaces are understood to mean the surfaces of the casting mold through which gaseous components can escape from the casting mold during casting. The gas exit surface can correspond to the entire outer surface of the mold. However, it is also possible for only a part of the outer surface of the casting mold to be used for dispensing gaseous components. In the case of box-bound metal casting, a box is used for the construction of the casting mold, which covers the underside and the side surfaces of the casting mold. In this case, essentially only the top of the mold is available for dispensing gaseous components. An outer surface of the casting mold is understood to mean the surfaces through which the exhaust gases generated during casting can leave the casting mold. This outer surface is visible from the outside when looking at the casting mold and does not come into contact with the liquid metal during casting. In contrast, an inner surface is understood to mean, for example, the surface of the mold cavity surrounded by the casting mold.

Materials which bind formaldehyde by chemical reactions to non-volatile reaction products are not disclosed in DE 10 2008 025 311 A1.

EP 0 012 169 A1 discloses a particle board or fiberboard which is predominantly bound with aminoplasts, characterized in that a portion of the panel, preferably the middle layer, at least partially contains a binder which does not belong to the group of aminoplasts and at the same time tolerates the introduction of formaldehyde-reactive substances in certain quantities which react with formaldehyde under the influence of moisture and / or heat or which release substances which in turn can bind formaldehyde.

The object of the present invention is to reduce the emissions of formaldehyde which arise when drying the size coating of molds or cores which release formaldehyde when heated.

According to a first aspect of the invention, this object is achieved by using a composition comprising

 (a) Particles of one or more refractories

(b) one or more compounds selected from the group consisting of

 ß-dicarbonyl compounds

 di- and trihydric phenols

Phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks amino acids

 primary and secondary aminosilanes

 Melamine, benzoguanamine, urea and their derivatives

 Hydrazine and carbonohydrazide and their derivatives

 - primary and secondary amines

 Tree resins, tannins and lignins

the total mass of the compounds (b) being 0.1% by weight to 10% by weight, preferably 0.1% by weight to 5% by weight, based on the total mass of the particles (a) of the refractory materials

(c) optionally a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof,

for producing a coating on a base body of a mold or a core for metal casting which emits formaldehyde when heated, the coating forming a surface of the mold or core which comes into contact with a molten metal during the casting process. The coating preferably not only forms the surface of the mold or core that comes into contact with a molten metal during the casting process, but also extends over other areas of the mold or core. The coating preferably extends over 50% or more, more preferably over 70% or more, more preferably over 80% or more, particularly preferably over 90% or more, in particular over 95% or more of the surface of the mold or of the core. The coating very particularly preferably extends over the entire surface of the mold or core.

The base body of the mold or core is typically formed from a molding material mixture which is bound with a binder which emits formaldehyde when heated, the binder preferably being selected from the group consisting of:

 by polyaddition of a phenol-formaldehyde resin with a polyurethane formed from a polyisocyanate

 Formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins.

The base body of the mold or core is particularly preferably formed from a molding material mixture which is bonded with a binder which emits formaldehyde when heated, the binder being selected from the group consisting of

polyurethanes formed by polyaddition of a phenol-formaldehyde resin with polyisocyanate, Phenol-formaldehyde resins and

 Furan-formaldehyde resins.

The binder is present in the hardened form in the base body of the mold or core.

Surprisingly, it was found that in the case of molds and cores which emit formaldehyde when heated, the amount of formaldehyde released to the environment when the size coat was dried is significantly reduced if the composition defined above is used to produce the size coat. It is currently assumed that the compounds (b) are able to bind formaldehyde by chemical reactions in which non-volatile reaction products are formed, so that less formaldehyde escapes from the core or the form into the environment. The compounds (b) are therefore referred to here as formaldehyde scavengers.

In addition to the ability to irreversibly form a non-volatile reaction product with formaldehyde, a number of other criteria must be considered when selecting the compounds (b). Compound (b) itself must not be volatile and it must not decompose at the temperatures at which the cores and molds are dried. The decomposition temperature must therefore be higher than the temperature at which the molds and cores are dried (50 ° C. to 200 ° C., preferably 100 ° C. to 180 ° C.). Compounds (b) which are solids or high-boiling liquids with low vapor pressure are therefore preferred. Furthermore, compound (b) must be soluble in the carrier liquid (c) in a sufficient amount. In addition, the compound (b) should be as non-toxic as possible, require no special occupational safety and safety precautions, and should be reliably available on the market at acceptable conditions.

The compounds (b) are preferably selected from the group consisting of dialkyl esters of malonic acid (in particular diethyl malonate), resorcinol, pyrogallol, phloroglucinol, glycine, melamine, urea, carbonohydrazide, and tannins soluble in and in the carrier liquid (c) Carrier liquid (c) soluble lignins. Lignins, melamine, glycine and resorcinol are particularly preferred.

Phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks are also formaldehyde scavengers, but their use is generally not preferred. Phenol-formaldehyde novolaks or resorcinol-formaldehyde novolaks are preferably not used in the form of aerogels. In the composition to be used according to the invention, the total mass of the compounds (b) is 0.1% by weight to 10% by weight, preferably 0.1% by weight to 9% by weight, more preferably 0.1% by weight. % to 8% by weight, more preferably 0.1% by weight to 7% by weight, more preferably 0.1% by weight to 6% by weight, particularly preferably 0.1% by weight up to 5% by weight, based on the total mass of the particles (a) of the refractories. With a smaller amount of compounds (b), no significant reduction in formaldehyde emissions would be achieved. A higher amount of compounds (b) could affect the quality of the coating produced.

In accordance with the usual professional understanding (cf. DIN 51060: 2000-06), masses, materials and minerals are referred to as “fire-proof”, which can withstand the temperature load during casting or when a molten iron, mostly cast iron, solidifies. Masses, materials and minerals that can withstand the pouring heat of a molten steel for a short time are called "highly fire-resistant". The temperatures that can occur when casting molten steel are usually higher than the temperatures that can occur when casting molten iron or cast iron. Refractory masses, materials and minerals (refractories) and highly refractory masses, materials and minerals are known to the person skilled in the art, for example from DIN 51060: 2000-06. Unless otherwise stated, powdered refractories then have an average grain size (preferably measured by means of light scattering in accordance with ISO 13320: 2009-10) in the range from 0.1 to 500 pm, preferably in the range from 1 to 200 pm. Particularly suitable refractories are those materials which have melting points which are at least 200 ° C. above the temperature of the metal melt used in each case and / or which do not react with the metal melt.

The term “refractory (a) as used here also includes highly refractory materials.

The refractories (a) are selected from those refractories that are usually used in sizes, e.g. Refractories selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, iron oxide and bauxite.

The refractory materials (a) preferably comprise one or more refractory materials selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable sheet silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, Metakaolinite, iron oxide and bauxite. The refractory materials (a) particularly preferably comprise

 (i) one or more refractory materials selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable sheet silicates, zircon silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, iron oxide and bauxite

and

 (ii) one or more refractory materials selected from the group of the swellable layered silicates and the zeolites

Swellable layered silicates also act as a rheological additive (inorganic thickener). The swellable layered silicates are preferably selected from the group of

Smectite, hectorite, saponite, nontronite, vermiculite and montmorillonite.

The zeolites can be natural or synthetic zeolites.

The mass ratio of the refractory (i) to the refractory (ii) is preferably in the range from 20: 1 to 5: 1, particularly preferably 15: 1 to 7: 1. For example, the refractories include (a)

 (i) one or more refractory materials selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable sheet silicates, zircon silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, iron oxide and bauxite

and

 (ii) one or more refractories selected from the group of swellable layered silicates.

For example, the refractories include (a)

 (i) one or more refractory materials selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable sheet silicates, zircon silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, iron oxide and bauxite

and

(ii) one or more refractories selected from the group of zeolites. The refractory materials (a) particularly preferably comprise

 (i) one or more refractory materials selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable sheet silicates, zircon silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, iron oxide and bauxite

and

 (ii) one or more refractory materials selected from the group of swellable layered silicates, and one or more refractory materials selected from the group of zeolites.

Surprisingly, it was found that with compositions whose refractories (a) in addition to one or more refractories (i) as defined above also one or more

Refractories (ii) selected from the group of swellable sheet silicates and zeolites, the swellable sheet silicates preferably being selected from the group of smectite, hectorite, saponite, nontronite vermiculite and montmorillonite, a particularly strong reduction in formaldehyde emissions is achieved. This was not to be expected, since of the refractory materials (ii) mentioned above, a function as a rheological additive has only been described for a few representatives.

In certain cases or under certain test conditions, it is even possible to use a size composition which is a combination of the above. Refractories (i) and (ii) contains, and no compound (b) as defined above, achieve a significant reduction in formaldehyde emissions, see the comparative examples in which a comparative size composition was used, which was a combination of the above. Refractories (i) and (ii) contains, and no compound (b) as defined above. The mass ratio of the refractory (i) to the refractory (ii) is preferably in the range from 20: 1 to 5: 1, particularly preferably 15: 1 to 7: 1. The use of a composition is thus also described here comprehensively

 (a) Particles of one or more refractories, the refractories (a) comprising:

 (i) one or more refractory materials selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable sheet silicates, zircon silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, iron oxide and bauxite

and

(ii) one or more refractory materials selected from the group of the swellable layered silicates and the zeolites (c) optionally a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof,

for producing a coating on a base body of a mold or a core for metal casting which emits formaldehyde when heated, the coating forming a surface of the mold or core which comes into contact with a molten metal during the casting process.

The carrier liquid (c) merely serves as a vehicle for applying the substances suspended and dissolved in it to the base body of the core or the mold, and is removed during drying. The carrier liquid is liquid under normal conditions (20 ° C and 1013.25 hPa) and can be evaporated under normal pressure (1013.25 hPa) at temperatures in the range from 50 ° C to 200 ° C. The carrier liquid (c) is preferably selected from the group consisting of water, methanol, ethanol and isopropanol.

Compositions for the production of size coatings often contain further constituents such as

 (d) wetting agents,

(e) rheological additives,

 (f) binders,

 (g) adjusting means

 (h) biocides.

Suitable wetting agents (d), rheological additives (e), binders (f), adjusting agents (g) and biocides (h) and their function and action are known to the person skilled in the art.

Anionic, cationic and nonionic surfactants are preferably used as wetting agents (d). The wetting agents (d) are preferably selected from the group consisting of the group of surfactants, particularly preferably alkynediols and their derivatives.

Organic thickeners, for example, are used as rheological additives. These are preferably selected from the group consisting of polysaccharides, proteins and cellulose ethers. Inorganic thickeners from the group comprising swellable clay minerals, for example band silicates such as palygorskites (attapulgites), and pyrogenic silicas can also be used. The swellable sheet silicates and zeolites mentioned above also act as inorganic thickeners. However, such inorganic thickeners are refractories and are therefore assigned to component (a) for concentration information. Binding agents which are self-hardening in air or which dry when the carrier liquid (c) is removed are used as binding agents (f). Preferred binders (f) are selected from the group of polyvinyl alcohols, polyacrylates, polyvinyl acetates, copolymers of the aforementioned polymers, natural resins, dextrins, starches and peptides. The adjusting agents (g) are preferably selected from the group consisting of salts of metals soluble in the carrier liquid (c) from the group consisting of alkali metals, alkaline earth metals, iron and aluminum, and mixtures thereof.

Compositions to be used according to the invention as described above include ready-to-use sizing compositions and precursors for the formation of ready-to-use sizing compositions. Ready-to-use sizing compositions have a sufficiently high level of carrier liquid so that they can be applied directly to the base body to form a coating. In a ready-to-use size composition, the mass of the carrier liquid (c) is preferably 60% by weight to 80% by weight, based on the total mass of the composition. Precursors for producing a ready-to-use size composition contain no carrier liquid (c) (solid mixture) or a significantly smaller amount of carrier liquid (c) (concentrate) compared to the ready-to-use size composition. The total mass of the carrier liquid (c) in the concentrates is 40% by weight to 65% by weight, preferably 40% by weight to 59% by weight, in each case based on the total mass of the composition. A ready-to-use size composition can be obtained by suspending the solid mixture in a carrier liquid (c) (in which soluble components of the solid mixture dissolve in the carrier liquid (c)) or diluting the concentrate with a carrier liquid (c). A carrier liquid (c) which has the same composition as the carrier liquid (c) of the concentrate is usually used to dilute the concentrate. A ready-to-use size composition can thus be produced by a method comprising the steps

 Manufacture or provide a solid mixture or concentrate as defined above

Add carrier liquid (c) selected from the group consisting of water, alkanols and mixtures thereof, the amount of carrier liquid (c) added being such that a composition results in which the total amount of carrier liquid (c) is 60% by weight. % to 80 wt .-%, based on the total mass of the resulting composition. The above statements regarding suitable and preferred components (a) - (h) apply both to concentrates and to ready-to-use size compositions. For solid mixtures, the above statements regarding suitable and preferred refractories (a) and the above statements regarding suitable and preferred components (b) and (d) - (h) apply, insofar as these are solids.

A second aspect of the present invention relates to a composition for producing a coating on a base body of a mold or a core for metal casting which emits formaldehyde when heated, the coating forming a surface of the mold or core which comes into contact with a molten metal during the casting process , A composition according to the invention comprises

 (a) Particles of one or more refractories

 (b) one or more compounds selected from the group consisting of

 ß-dicarbonyl compounds

 di- and trihydric phenols

 - phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks

 amino acids

 primary and secondary aminosilanes

 Melamine, benzoguanamine, urea and their derivatives

 Hydrazine and carbonohydrazide and their derivatives

 - primary and secondary amines

 Tree resins, tannins and lignins

 wherein the total mass of the compounds (b) is 0.1% by weight to 10% by weight, preferably 0.1% by weight to 9% by weight, more preferably 0.1% by weight to 8% by weight %, more preferably 0.1% by weight to 7% by weight, more preferably 0.1% by weight to 6% by weight, particularly preferably 0.1% by weight to 5% by weight % based on the total mass of the particles (a)

Refractories

(c) a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof, the total mass of the carrier liquid (c) being 40% by weight to 80% by weight, based on the total mass of the composition. For the selection of the refractories (a), compounds (b), carrier liquids (c) and further constituents (d) to (h) as defined above, the same applies as stated above for the first aspect of the invention. Compositions are preferred whose components (a) - (h) from the above for the first aspect of the invention are selected as preferred components (a) - (h).

Compositions of the invention include ready-to-use sizing compositions (as described above in the context of the first aspect of the invention) and concentrates (as described above in the context of the first aspect of the invention) to form ready-to-use sizing compositions.

A third aspect of the present invention relates to a mold or core for metal casting. A core according to the invention or a form according to the invention comprises:

 a body that emits formaldehyde when heated,

and a coating arranged on the base body, which forms a surface of the mold or core which comes into contact with a molten metal during the casting process, the coating comprising:

 (a) Particles of one or more refractories

 (b) one or more compounds selected from the group consisting of - ß-dicarbonyl compounds

 di- and trihydric phenols

 Phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks amino acids

 primary and secondary aminosilanes

 - Melamine, benzoguanamine, urea and their derivatives

 Hydrazine and carbonohydrazide and their derivatives

 primary and secondary amines

 Tree resins, tannins and lignins

 and / or their reaction products with formaldehyde,

wherein in the coating the total mass of the free compounds (b) bound in reaction products with formaldehyde is 0.1% by weight to 10% by weight, preferably 0.1% by weight to 9% by weight, more preferably 0.1% by weight to 8% by weight, more preferably 0.1% by weight to 7% by weight, more preferably 0.1% by weight to 6% by weight, particularly preferably 0, 1% by weight to 5% by weight based on the total mass of the particles (a) of the refractories. A shape according to the invention or a core according to the invention comprises a base body and a coating arranged on this base body, which contains the non-volatile constituents of the composition to be used according to the invention according to the first aspect of the invention. For the selection of the refractories (a) and compounds (b) as defined above, the same applies as stated above for the first aspect of the invention. Preference is given to molds and cores which have a coating as defined above, the refractory materials (a) and the compounds (b) being selected from the components (a) and (b) identified as preferred for the first aspect of the invention.

This coating forms a surface of the mold or core that comes into contact with a molten metal during the casting process. The coating preferably has a thickness in the range from 0.05 mm to 0.6 mm, particularly preferably 0.05 to 0.4 mm.

Preferably, the coating not only forms the surface of the mold or core that comes into contact with a molten metal during the casting process, but also extends over other areas of the mold or core. The coating preferably extends over 50% or more, more preferably over 70% or more, more preferably over 80% or more, particularly preferably over 90% or more, in particular over 95% or more of the surface of the mold or of the core. The coating very particularly preferably extends over the entire surface of the mold or core.

The base body of the mold according to the invention or of the core according to the invention emits formaldehyde when heated. At least a noticeable proportion of the formaldehyde emitted by the base body is bound by the compounds (b) present in the coating to form non-volatile reaction products. Therefore, the coating contains the compounds (b) (especially before drying) and / or their reaction products with formaldehyde (which are formed during drying). The base body of the mold or core is typically formed from a molding material mixture which is bound with a binder which emits formaldehyde when heated. The binder is present in the hardened form in the base body of the mold or core. The same applies to the selection of the binders as stated above for the first aspect of the invention. Preferred are binders which are selected from the binders identified above as preferred for the first aspect of the invention. The binder is particularly preferably selected from the group consisting of

 polyurethanes formed by polyaddition of a phenol-formaldehyde resin with polyisocyanate,

Phenol-formaldehyde resins and Furan-formaldehyde resins.

A fourth aspect of the present invention relates to a method for producing a mold according to the invention or a core according to the invention for metal casting. The process includes the steps

- Manufacture or provide the base body

 Manufacture or provide a ready-to-use size composition as defined above

 Applying the ready-to-use size composition to the base body and then drying it so that a coating is produced on the base body, the coating forming a surface of the mold or core which comes into contact with a molten metal during the casting process.

In the method according to the invention, a coating is produced on the base body of the mold or core, which contains the non-volatile constituents of the composition to be used according to the invention in accordance with the first aspect of the invention. This coating forms a surface of the mold or core that comes into contact with a molten metal during the casting process.

Preferably, the coating not only forms the surface of the mold or core that comes into contact with a molten metal during the casting process, but also extends over other areas of the mold or core. The coating preferably extends over 50% or more, more preferably over 70% or more, more preferably over 80% or more, particularly preferably over 90% or more, in particular over 95% or more of the surface of the mold or of the core. The coating very particularly preferably extends over the entire surface of the mold or core.

The production of the base body of the mold or of the core typically comprises the following steps:

 Production or provision of a molding material mixture containing one or more basic molding materials and a binder emitting formaldehyde when heated,

 Forming the mixture of molding materials

Hardening of the binder in the molded molding material mixture, the main body of the mold or core being formed. Corresponding molding material mixtures, molding methods and curing methods are known to the person skilled in the art.

The binder of the molding material mixture is preferably selected from the group consisting of

Two-component systems comprising a phenol-formaldehyde resin and a polyisocyanate to form a polyurethane

 Formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins.

The binder is particularly preferably selected from the group consisting of

polyurethanes formed by polyaddition of a phenol-formaldehyde resin with polyisocyanate,

 Phenol-formaldehyde resins and

 Furan-formaldehyde resins.

A process according to the invention is preferred in which the base body of the core or the mold is produced by the cold box process. The cold box process is known to the person skilled in the art. In this process, a two-component system comprising a phenol-formaldehyde resin and a polyisocyanate is used as the binder. The components of the binder are only brought into contact with one another during the production of the molding material mixture and form a polyurethane in the molded molding material mixture. In the molded molding mixture, the binder is cured by contacting the molded molding mixture with a gaseous tertiary amine or a mixture of two or more gaseous tertiary amines.

The ready-to-use size composition used in the process according to the invention is preferably selected from the ready-to-use size compositions which comprise the components (a) - (c) preferred according to the first aspect of the invention and optionally the components (d) - (h ) contain.

The ready-to-use size composition is usually applied to the base body by a process selected from the group consisting of spraying, dipping, flooding and brushing, preferably dipping, because this process is particularly suitable in order to form a coating which extends over the entire Surface of the mold or core extends or at least a large part of the total surface of the mold or core. The applied size composition is dried at temperatures of 40 ° C. or more, preferably at a temperature in the range from 50 ° C. to 200 ° C., preferably from 100 ° C. to 180 ° C.

The base of the mold or core emits formaldehyde when it dries. At least a noticeable proportion of the formaldehyde emitted by the base body is bound by the compounds (b) present in the coating to form non-volatile reaction products, so that the amount of formaldehyde released to the environment when the mold or core is dried is markedly reduced.

A fifth aspect of the invention relates to the use of a compound (b) selected from the group consisting of

 ß-dicarbonyl compounds

 di- and trihydric phenols

 Phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks

 amino acids

- primary and secondary aminosilanes

 Melamine, benzoguanamine, urea and their derivatives

 Hydrazine and carbonohydrazide and their derivatives

 primary and secondary amines

 Tree resins, tannins and lignins

as a formaldehyde scavenger in a coating on a base body of a mold or a core for metal casting which emits formaldehyde when heated, the coating forming a surface of the mold or core which comes into contact with a molten metal during the casting process, or in a composition for producing a such a coating (ready-to-use size composition as described above in the context of the first aspect of the invention) or for the production of such a composition.

Preferably, the coating not only forms the surface of the mold or core that comes into contact with a molten metal during the casting process, but also extends over other areas of the mold or core. The coating preferably extends over 50% or more, more preferably over 70% or more, more preferably over 80% or more, particularly preferably over 90% or more, in particular over 95% or more of the surface of the mold or core. The coating very particularly preferably extends over the entire surface of the mold or core. A formaldehyde scavenger is understood to mean a chemical compound which is able to react with formaldehyde to form a non-volatile reaction product, and thus to reduce the formaldehyde emission to the environment.

For the selection of the compounds (b) as defined above, the same applies as stated above for the first aspect of the invention. Preferred are compounds (b) which are selected from the compounds (b) identified as preferred above for the first aspect of the invention.

When using the compounds (b) according to the fifth aspect of the invention, it is preferred that the coating or the composition for producing such a coating further comprises

(i) one or more refractories selected from the group consisting of quartz,

Aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, iron oxide and bauxite

 (ii) optionally one or more refractories selected from the group of swellable layered silicates and zeolites.

The selection of refractories (i) and (ii) is the same as that set out above for the first aspect of the invention.

A sixth aspect of the invention relates to a kit for producing a mold or a core for metal casting according to the third aspect of the invention as defined above. A kit according to the invention comprises

 (A) a composition as described above for the first aspect of the invention, wherein the composition is preferably a solid mixture as described above in the context of the first aspect of the invention or a concentrate as described above in the context of the first aspect of the invention,

(B) a binder emitting formaldehyde when heated

the components (A) and (B) in the kit being separated from one another.

Within the kit according to the invention, the contact of components of component (A) with components of component (B) is excluded, for example by providing component (A) on the one hand and component (B) on the other in a separate container, or by providing the component (A) on the one hand and component (B) on the other hand are each provided in a separate chamber of a container. In the kit according to the invention, the composition (A) is preferably selected from the solid mixtures and concentrates which contain the constituents (a) and (b) preferred according to the first aspect of the invention and optionally (c) - (h).

In the kit according to the invention, the binder (B) is preferably selected from the group consisting of

 Two-component systems comprising a phenol-formaldehyde resin and a polyisocyanate to form a polyurethane

 Formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins.

The binder is particularly preferably selected from the group consisting of

 polyurethanes formed by polyaddition of a phenol-formaldehyde resin with polyisocyanate,

 Phenol-formaldehyde resins and

- Furan-formaldehyde resins.

The invention is explained below using exemplary embodiments.

embodiments

From a molding material mixture comprising sand H32 as the basic molding material and a two-component binder system comprising a phenol-formaldehyde resin and a polyisocyanate for the formation of a polyurethane, which are customary for core production, base bodies for brake disc cores were shaped in the usual manner by means of a core shooter, and in the usual manner Fumigation with tertiary amine hardened (cold box process). A coating is then produced on the core base bodies thus produced by applying a composition according to the invention (size composition according to the invention) or a comparison composition (comparison size composition) which does not contain any of the compounds (b) to be used according to the invention. This coating forms the surface of the core that comes into contact with the molten metal during the casting process. The cores were then dried in a drying cabinet (Memmert UFP 700). During drying, samples were taken from the oven air at certain times using a probe and their formaldehyde content was determined using an in-house method (see below for details). For comparison, cores produced in the same way without coating (un-sized comparison cores) were dried in a drying cabinet, and the amount of formaldehyde emitted was measured in the same way.

In a first series of tests, the influence of the drying temperature on the formaldehyde emissions of un-sized comparison cores was examined. The molding material mixture from which the cores for this test series were produced contained 0.8% by weight of phenol-formaldehyde resin and 0.8% by weight of polyisocyanate.

At certain times during the drying, samples were taken from the oven air and their formaldehyde content was determined. To do this, use the Xact 5000 pump over the period from the start of drying to the first measurement time (1 min) or from one measurement time to the next measurement time (5, 10, 15, 20, 25 or 30 min drying time) (Fa. Dräger) 1, 5I air is drawn from the furnace into a short-term measuring tube (Dräger) for formaldehyde (0.2 to 5ppm) and the formaldehyde concentration is determined.

The formaldehyde content (in ppm) determined at certain times during drying is shown in the following table:

This series of tests shows that the amount of formaldehyde emitted increases with increasing drying temperature (FIG. 1).

In a second series of tests, the influence of the composition of the size coating (core E1 with size composition according to the invention or core V2 with comparison size composition) on the formaldehyde emissions during drying (30 minutes at 180 ° C.) was examined. The molding material mixture from which the cores for this test series were produced contained 0.8% by weight of phenol-formaldehyde resin and 0.8% by weight of polyisocyanate, in each case based on the mass of the molding material (sand H32). The size composition according to the invention contained resorcinol as compound (b). For comparison, an unsized comparison core V1 was dried under the same conditions. The comparison size composition is as follows

The size composition according to the invention was produced by adding 3 parts by weight of resorcinol to 100 parts by weight of the comparison size.

The formaldehyde content (in ppm) determined at certain times during drying as described above is shown in the following table:

When the comparative core V 2 is dried with the coating formed from the size not according to the invention, the amount of formaldehyde emitted is already less than when the unsized comparative core V1 is dried. However, when the core E1 according to the invention is dried (with the coating formed from the size composition according to the invention), the amount of formaldehyde emitted is still significantly lower (FIG. 2).

In a third test series, the influence of the amount of resorcinol as the compound (b) to be used according to the invention on the formaldehyde emissions during the drying (30 minutes at 180 ° C.) minutes was investigated. The molding material mixture from which the cores for this test series were produced contained 1.0% by weight of phenol-formaldehyde resin and 1.0% by weight of polyisocyanate, in each case based on the mass of the basic molding material (sand H32). The cores E2 and E3 each have size coatings with different proportions of resorcinol. For comparison an unsized comparison core V3 and a comparison core V4 with a coating formed from a size not according to the invention were dried under the same conditions.

The comparison size composition is as indicated above. The size compositions according to the invention were produced by adding 0.8 parts by weight of resorcinol (core E2) or 3 parts by weight of resorcinol (core E3) to 100 parts by weight of the comparison size.

The formaldehyde content (in ppm) determined at certain times during drying as described above is shown in the following table:

When the comparison core V4 is dried with the coating formed from the size not according to the invention, the amount of formaldehyde emitted is already less than when the unfinished comparison core V3 is dried. When the cores E2 and E3 according to the invention are dried, the amount of formaldehyde emitted is significantly lower and decreases with increasing resorcinol content in the size composition according to the invention (FIG. 3). In a fourth test series, the influence of the composition of the size coating (core E4; comparative size composition, cores E5-E7, various size compositions according to the invention) on the formaldehyde emissions was observed during drying at 200 ° C. for 35 minutes. The molding material mixture from which the cores for this test series were produced contained 1% by weight of phenol-formaldehyde resin and 1% by weight of polyisocyanate, each based on the mass of the molding material (sand H32). For comparison, an unsized comparison core was dried under the same conditions.

The comparison size composition is as indicated above. The size compositions according to the invention were produced by adding 0.9 part by weight of lignin (Core E5) or 0.9 parts by weight of melamine (core E6) or 3 parts by weight of resorcinol (core E7) to 100 parts by weight of the comparison size.

The formaldehyde content (in mg / cm ³ ) determined at certain times during drying is shown in the following table:

When all of the cores E4-E7 according to the invention are dried, the amount of formaldehyde emitted is significantly less than that of the comparison core (FIG. 4).

Similar results were obtained with the addition of glycine as compound (b).

In another test series, the influence of glycine as a formaldehyde scavenger on the formaldehyde emissions during drying (30 minutes at 180 ° C) was examined. For this purpose, test specimens (cores for the manufacture of brake disks) were produced in a conventional manner from a molding material mixture containing 1% by weight of phenol-formaldehyde resin and 1% by weight of polyisocyanate, based in each case on the mass of the basic molding material (sand H32) which have been cured in the usual way by gassing with a tertiary amine (cold box process). These test specimens were provided with a size coating by immersion (test specimen E8 with the size composition according to the invention or test specimen V5 with the comparison size composition). The comparison size composition is as indicated above. A size composition according to the invention was produced by adding 1 part by weight of glycine to 100 parts by weight of the comparison size.

The test specimen provided with the size coating was placed in a preheated drying oven from Elpo (internal temperature 170 ° C.). The during the drying period of The amount of exhaust air discharged from the drying chamber of the furnace in 10 minutes is 267 m ³ . The measurement of the formaldehyde concentration in the furnace air started one minute after the test specimen was placed in the furnace and the furnace door was closed. A rod probe was inserted into the exhaust pipe of the drying oven for sampling. With the help of a Dräger Xact 5000 pump, the air was drawn out of the drying chamber with a volume flow of 1.5 L / min during the drying period of 10 minutes, and the sample volume drawn via LpDNPH cartridges (LpDNPH Cartridge S10 from Supelco). The analysis is carried out using HPLC analogous to DIN 16000-3.

When drying the test specimen E8 according to the invention (with the coating formed from the size composition according to the invention), the concentration of formaldehyde in the exhaust air from the furnace is reduced by more than a third compared to the comparison test specimen V5 with the coating formed from the size according to the invention.

Claims

claims

1. Use of a composition comprising

 (a) Particles of one or more refractories

 (b) one or more compounds selected from the group consisting of β-dicarbonyl compounds

 di- and trihydric phenols

 Phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks amino acids

 primary and secondary aminosilanes

 Melamine, benzoguanamine, urea and their derivatives

 Hydrazine and carbonohydrazide and their derivatives primary and secondary amines

 Tree resins, tannins and lignins

 the total mass of the compounds (b) being 0.1% by weight to 10% by weight, based on the total mass of the particles (a) of the refractory materials

(c) optionally a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof,

 for producing a coating on a base body of a mold or a core for metal casting which emits formaldehyde when heated, the coating forming a surface of the mold or core which comes into contact with a molten metal during the casting process.

2. Use according to claim 1, wherein

 the compounds (b) are selected from the group consisting of dialkyl esters of malonic acid, resorcinol, pyrogallol, phloroglucine, glycine, urea, melamine, carbonohydrazide, tannins and lignins soluble in the carrier liquid (c)

 and or

 the refractories (a) include:

(i) one or more refractories selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, not swellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, iron oxide and bauxite

 and

 (ii) one or more refractory materials selected from the group of the swellable layered silicates and the zeolites

 and or

 the carrier liquid (c) is selected from the group consisting of water, methanol, ethanol and isopropanol.

3. Use according to claim 1 or 2, wherein

 the base body of the mold or core is formed from a molding material mixture which is bound with a binder emitting formaldehyde when heated, the binder preferably being selected from the group consisting of: by polyaddition of a phenol-formaldehyde resin with a polyisocyanate formed polyurethanes

 Formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins.

4. Use according to one of claims 1 to 3, wherein the composition contains one or more further constituents selected from the group consisting of

 (d) wetting agents,

 (e) rheological additives,

 (f) binders,

 (g) adjusting means

 (h) biocides.

5. Use according to one of claims 1 to 5, wherein the composition contains no carrier liquid (c),

or contains a carrier liquid (c), the total mass of the carrier liquid (c) being 40% by weight to 65% by weight, preferably 40% by weight to 59% by weight, in each case based on the total mass of the composition.

6. Use according to one of claims 1 to 4, wherein the composition contains a carrier liquid (c), wherein the total mass of the carrier liquid (c) 60

% To 80% by weight, based on the total mass of the composition.

7. A method of making a composition as defined in claim 6 comprising the steps

 - Making or providing a composition as defined in claim 5

 Add carrier liquid (c) selected from the group consisting of water, alkanols and mixtures thereof, the amount of carrier liquid (c) added being such that a composition results in which the total amount of carrier liquid (c) is 60% by weight. -% to 80 wt .-%, based on the total mass of the resulting composition.

8. Composition for the production of a coating on a base body of a mold or a core for metal casting which emits formaldehyde when heated, the coating forming a surface of the mold or the core which, when

Casting process comes into contact with a molten metal, the composition comprising

 (a) Particles of one or more refractories

 (b) one or more compounds selected from the group consisting of - ß-dicarbonyl compounds

 di- and trihydric phenols

 Phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks amino acids

 primary and secondary aminosilanes

Melamine, benzoguanamine, urea and their derivatives Hydrazine and carbonohydrazide and their derivatives

 primary and secondary amines

 Tree resins, tannins and lignins

 the total mass of the compounds (b) being 0.1% by weight to 10% by weight, based on the total mass of the particles (a) of the refractory materials

 (c) a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof, the total mass of the carrier liquid (c) being 40% by weight to 80% by weight, based on the total mass of the composition.

9. The composition of claim 8, wherein

 the compounds (b) are selected from the group consisting of dialkyl esters of malonic acid, resorcinol, pyrogallol, phloroglucinol, glycine, melamine, urea, carbonohydrazide, tannins and lignins soluble in the carrier liquid (c)

 and or

 the refractories (a) include:

 (i) one or more refractory materials selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable sheet silicates, zircon silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, Iron oxide and bauxite

 (ii) one or more refractory materials selected from the group of the swellable layered silicates and the zeolites

 and or

 - The carrier liquid (c) is selected from the group consisting of water, methanol, ethanol and isopropanol and mixtures thereof.

10. The composition of claim 8 or 9, further comprising one or more ingredients selected from the group consisting of

 (d) wetting agent

(e) rheological additives (f) binder

 (g) adjusting means

 (h) biocides.

11. Mold or core for metal casting, comprising

 a base body which emits formaldehyde when heated,

 and a coating arranged on the base body, which forms a surface of the mold or core which comes into contact with a molten metal during the casting process, the coating comprising:

 (a) Particles of one or more refractories

 (b) one or more compounds selected from the group consisting of

 ß-dicarbonyl compounds

 di- and trihydric phenols

 Phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks - amino acids

 primary and secondary aminosilanes

 Melamine, benzoguanamine, urea and their derivatives

 Hydrazine and carbonohydrazide and their derivatives primary and secondary amines

 - tree resins, tannins and lignins

 and / or their reaction products with formaldehyde, the total mass of free compounds (b) bound in reaction products with formaldehyde in the coating being 0.1% by weight to 10% by weight, based on the total mass of the particles (a) refractory materials.

12. The mold or core of claim 11, wherein

the compounds (b) are selected from the group consisting of dialkyl esters of malonic acid, resorcinol, pyrogallol, phloroglucinol, glycine, melamine, urea, carbonohydrazide, tannins and lignins and or

 the refractories (a) include:

 (i) one or more refractory materials selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable sheet silicates, zircon silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, iron oxide and bauxite

 and

 (ii) one or more refractory materials selected from the group of the swellable layered silicates and the zeolites.

13. Form or core according to claim 11 or 12, wherein

 the base body of the mold or core is formed from a molding material mixture which is bound with a binder which emits formaldehyde when heated, the binder preferably being selected from the group consisting of: by polyaddition of a phenol-formaldehyde resin with a polyisocyanate nat formed polyurethanes

 Formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins.

14. Mold or core according to one of claims 11 to 1, wherein the coating has a thickness in the range of 0.05 mm to 0.6 mm.

15. A method for producing a mold or a core for the metal casting according to one of claims 11 to 14, comprising the steps

 Manufacture or provide the base body

 - Making or providing a composition as defined in claim 6

Applications of the composition as defined in claim 6 onto the base body and subsequent drying so that a coating is produced on the base body, the coating forming a surface of the mold or core which comes into contact with a molten metal during the casting process.

16. The method according to claim 15, wherein the production of the base body of the mold or of the core comprises the following steps:

 Production or provision of a molding material mixture containing one or more basic molding materials and a binder emitting formaldehyde when heated,

 Forming the mixture of molding materials

 Hardening of the binder in the molded molding material mixture, the main body of the mold or core being formed.

17. The method of claim 16, wherein the binder is selected from the group consisting of

 Two-component systems comprising a phenol-formaldehyde resin and a polyisocyanate to form a polyurethane

 Formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins

18. The method of claim 17, wherein

 the binder is a two-component system comprising a phenol-formaldehyde resin and a polyisocyanate to form a polyurethane, and in the molded molding mixture the binder is obtained by contacting the molded molding mixture with a gaseous tertiary amine or a mixture of two or more gaseous tertiary amines is cured.

19. The method according to any one of claims 15 to 18, wherein the composition as defined in claim 6 is applied to the base body by a method selected from the group consisting of spraying, dipping, flooding and brushing, preferably dipping.

20. The method according to any one of claims 15 to 19, wherein the drying is carried out at a temperature in the range from 50 ° C to 200 ° C, preferably from 100 ° C to 180 ° C.

21. Use of a compound (b) selected from the group consisting of β-dicarbonyl compounds

 di- and trihydric phenols

 Phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks - amino acids

 primary and secondary aminosilanes

 Melamine, benzoguanamine, urea and their derivatives

 Hydrazine and carbonohydrazide and their derivatives

 primary and secondary amines

 - tree resins, tannins and lignins

 as a formaldehyde scavenger in a coating on a base body of a mold or a core for metal casting which emits formaldehyde when heated, the coating forming a surface of the mold or core which comes into contact with a molten metal during the casting process

 or in a composition for making such a coating or for making such a composition.

22. Use according to claim 21, wherein the coating or composition for making such a coating further comprises

 (i) one or more refractory materials selected from the group consisting of quartz, aluminum oxide, zirconium dioxide, aluminum silicates, non-swellable sheet silicates, zircon silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolines, calcined kaolines, metakaolinite, iron oxide and bauxite

 (ii) optionally one or more refractories selected from the group of swellable layered silicates and zeolites.

23. Kit for producing a mold or a core for metal casting as defined in any one of claims 11 to 14

the kit includes (A) a composition as defined in any one of claims 1 to 6, preferably a composition according to claim 5

 (B) a binder emitting formaldehyde when heated

 the components (A) and (B) in the kit being separated from one another.

24. The kit of claim 23, wherein the binder is selected from the group consisting of

 Two-component systems comprising a phenol-formaldehyde resin and a polyisocyanate to form a polyurethane

 Formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins.