Composition for producing coating on body of metal cast mould or core that releases formaldehyde upon heating

Abstract

The present invention relates to a composition for producing a coating on the body of a mold or core for metal casting, the body of the mold or core releasing formaldehyde when heated, where the coating forms the surface of the mold or core in contact with a metal melt during a casting operation, where the composition comprises (a) particles of one or more refractory materials; (b) at least one ammonium salt [compound (b)] wherein the total mass of compound (b) is from 0.1% by weight to 10% by weight, based on the total mass of the particles (a) of the refractory material; (c) a carrier liquid selected from the group consisting of water, alkanol, and mixtures thereof.

Description

Background Art

[0001] Described is the use of specific compounds as formaldehyde scavengers in a coating on the body of a mold or core for metal casting that releases formaldehyde when heated, wherein the coating forms the surface of the mold or core that comes into contact with the metal melt during the casting operation, and the use of a composition containing one or more of these compounds to produce a coating on the body of a mold or core for metal casting that releases formaldehyde when heated, wherein the coating forms the surface of the mold or core that comes into contact with the metal melt during the casting operation. Also described are corresponding molds and cores and processes for their production.

[0002] Moulds and cores for metal casting are produced by shaping a moulding material mixture comprising a moulding base material (e.g. sand) and a binder and then curing the shaped moulding material mixture. This usually involves the use of organic binders which release formaldehyde when heated, such as polyurethanes formed by the polyaddition of phenol-formaldehyde resins with polyisocyanates, or formaldehyde condensation resins, such as formaldehyde condensation resins from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins.

[0003] Moulds are negative moulds; they contain the cavity to be cast, which will result in the desired casting. The inner contour of the casting can be formed by cores. In the production of the mould, the cavity is moulded in the moulding material with the aid of a model of the casting to be produced. The cores are usually moulded in a core box.

[0004] Typically, in the production of molds and cores for metal casting by molding a molding material mixture (as described above) and then solidifying the molded molding material mixture, the main body of the mold or core is first formed, which already has the contour of the desired mold or desired core. In particular, in the case of cast steel and cast iron, a coating is usually produced on the main body thus formed, which forms the surface of the mold or core in contact with the metal melt during the casting operation. Such coatings are generally referred to as refractory coatings. In the context of the present application, the term "mold" or "core" refers in each case to the entire main body of the mold or core and the coating (refractory coating) arranged on the main body. The coating acts as an interface layer and / or barrier layer between the main body of the core or mold and the cast metal, and is particularly used to controllably suppress the formation mechanism of casting defects at the interface between the metal and the core / mold or for the utilization of metallurgical effects. Typically, refractory coatings in casting technology should achieve the following functions known to those skilled in the art:

[0005] - Improve the smoothness of the casting surface, and / or

[0006] - prevent chemical reactions between components of the moulding material mixture and the metal melt, thereby facilitating separation between the mould / core and the casting, and / or

[0007] -Prevent surface defects on castings such as bubbles, pores, veins and / or scarring.

[0008] The ready-to-use composition for coating the body of the mold and core is usually a suspension of a fine-grained, refractory to highly refractory inorganic material (refractory material) in a carrier liquid (e.g., water, alkanol or a mixture thereof), in which additional components may be suspended or dissolved. The refractory coating composition is applied to the body in a suitable manner, and the carrier liquid is then removed by drying, thereby forming a coating on the body. The drying temperature is usually carried out above 40° C., preferably in the range of 50° C. to 200° C. At these temperatures, the body of the mold or core releases a large amount of formaldehyde. Such releases cause considerable pollution to the workplace.

[0009] DE 10 2008 025 311 A1 discloses a casting mold for metal casting, wherein a material layer that absorbs pollutants is arranged in at least part of the gas outlet area of ​​the casting mold. The gas outlet area should be understood as an area where gaseous components can escape from the casting mold during the casting operation. The gas outlet area can correspond to the entire outer surface of the casting mold. Alternatively, only a part of the outer surface of the casting mold can be used to release the gaseous components. For example, in the case of box-type metal casting, the casting mold is constructed using a box body, which covers the lower side and the side of the casting mold. In this case, basically only the top of the casting mold can be used for the release of gaseous components. The outer surface of the casting mold should be understood as via these surfaces, the exhaust gas formed in the casting operation can leave the casting mold. This outer surface is visible when the casting mold is observed from the outside, and does not contact with the liquid metal in the casting operation. In contrast, the inner surface should refer to, for example, the surface of the mold cavity surrounded by the casting mold.

[0010] Materials which bind formaldehyde by chemical reaction to give non-volatile reaction products are not disclosed in DE 10 2008 025 311 A1.

[0011] EP 0 012 169 A1 discloses a particleboard or fiberboard bonded predominantly with amino resins, characterised in that partial regions of the board (preferably the middle layer) at least partially contain a binder which does not belong to the amino resin class and at the same time allows the introduction of a specific amount of formaldehyde-reactive substances which react with formaldehyde under the action of moisture and / or heat or release substances which are able to bind formaldehyde. Summary of the invention

[0012] The object of the present invention is to reduce formaldehyde emissions during the drying of refractory coatings of moulds or cores which release formaldehyde when heated.

[0013] In a first aspect of the present invention, this object is achieved by using a composition comprising

[0014] - (a) particles of one or more refractory materials

[0015] (b) at least one ammonium salt [compound (b)]

[0016] wherein the total mass of compound (b) is 0.1% by weight to 10% by weight, preferably 0.1% by weight to 5% by weight, based on the total mass of particles of refractory material (a),

[0017] - (c) optionally a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof,

[0018] The composition is used to produce a coating on the body of a mold or core for metal casting, the body of the mold or core releasing formaldehyde when heated, wherein the coating forms the surface of the mold or core in contact with the metal melt during the casting operation. Preferably, the coating does not only form the surface of the mold or core in contact with the metal melt during the casting operation, but also extends to cover other areas of the mold or core. The coating preferably extends to cover 50% or more of the surface of the mold or core, further preferably 70% or more, more preferably 80% or more, particularly preferably 90% or more, especially 95% or more. Most preferably, the coating extends to cover the entire surface of the mold or core. DETAILED DESCRIPTION

[0019] The body of the mold or core here is usually formed from a molding material mixture which has been bound with a binder which releases formaldehyde when heated, wherein the binder is preferably selected from the group consisting of:

[0020] -Polyurethanes formed by the polyaddition of phenol-formaldehyde resins and polyisocyanates

[0021] - a formaldehyde condensation resin, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins.

[0022] More preferably, the body of the mold or the core has been formed from a molding material mixture which has been bound with a binder which releases formaldehyde when heated, wherein the binder is selected from the group consisting of:

[0023] -Polyurethanes formed by the polyaddition of phenol-formaldehyde resins and polyisocyanates

[0024] -phenol-formaldehyde resin and

[0025] -Furan-formaldehyde resin.

[0026] The binder is present in cured form in the body of the mold or core.

[0027] It has surprisingly been found that, in the case of molds and cores that release formaldehyde when heated, when the composition defined above is used to produce a refractory coating, the amount of formaldehyde released into the environment during the drying of the refractory coating is significantly reduced. It is currently assumed that compound (b) is able to bind formaldehyde by chemical reaction to form non-volatile reaction products, so that less formaldehyde escapes from the core or mold into the environment. Therefore, compound (b) is referred to herein as a formaldehyde scavenger.

[0028] In addition to the ability to irreversibly bind non-volatile reaction products to formaldehyde, some additional criteria should be observed when selecting compound (b). For example, compound (b) itself must not be volatile and it must not decompose at the temperature at which the mold and core are dried. The decomposition temperature must therefore be higher than the temperature at which the mold and core are dried (50° C. to 200° C., preferably 100° C. to 180° C.). Compounds (b) are therefore preferred which are solid or high-boiling liquids with a low vapor pressure. In addition, compound (b) must be soluble in sufficient amounts in the carrier liquid (c).

[0029] Furthermore, compound (b) should be as non-toxic as possible, not require any special occupational protection and safety precautions, and be reliably available on the market under acceptable conditions.

[0030] Compound (b) is preferably a compound that is soluble in the carrier liquid (c).

[0031] In the context of the present invention, the expression "at least one ammonium salt" is intended to mean one or more than one ammonium salt. Mixtures of ammonium salts can also be used for the purposes of the present invention. In the remainder of this document, for the purposes of the present invention, the expression "ammonium salt" is to be understood both in the plural and in the singular. In the context of the present invention, the ammonium salt is preferably of the formula (R)4N + A - ammonium salts, wherein R is selected from hydrogen, C 1-4The group consisting of alkyl and phenyl, and wherein A is a suitable counter ion (also referred to as anion). Preferably, R is hydrogen. The term alkyl-means, alone or in combination, a free radical derived from an alkane containing 1 to 4 carbon atoms (unless otherwise specified), such as CF-G alkyl defines a straight or branched alkyl with F to G carbon atoms, such as C1-4 alkyl defines a straight or branched alkyl with 1 to 4 carbon atoms, such as methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl. Alkyl can be a straight or branched alkyl. Suitable anion A can be organic or inorganic.

[0032] Suitable anions A include, for example, trifluoroacetate, acetate, benzenesulfonate, benzoate, bicarbonate, bitartrate, bromide, carbonate, chloride, citrate, dihydrochloride, formate, hydrobromide, hydrochloride, methylsulfate, nitrate, oxalate, phosphate, sulfate, and the like.

[0033] Advantageously, the ammonium salt is selected from the group consisting of ammonium acetate, ammonium citrate, ammonium formate, ammonium oxalate and ammonium chloride. Particularly preferred are ammonium chloride and ammonium citrate.

[0034] In the composition used according to the present invention, the total mass of compound (b) is equal to or higher than 0.1%, preferably equal to or higher than 0.5%, more preferably equal to or higher than 1.0%, based on the total mass of particles (a) of refractory material. It is further understood that the upper limit of the total mass of compound (b) is equal to or lower than 10%, preferably equal to or lower than 9%, more preferably equal to or lower than 8%, further preferably equal to or lower than 8%, further preferably equal to or lower than 7%, further preferably equal to or lower than 6%, further preferably equal to or lower than 5% by weight, based on the total mass of particles (a) of refractory material. In an embodiment of the composition of the invention, the total mass of compound (b) is 0.1% by weight to 10% by weight, preferably 0.1% by weight to 9% by weight, further preferably 0.1% by weight to 8% by weight, further preferably 0.1% by weight to 7% by weight, further 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 of the refractory material (a). In the case of a smaller amount of compound (b), no significant reduction in formaldehyde emissions will be achieved. A higher amount of compound (b) will affect the quality of the resulting coating.

[0035] According to the common understanding of those skilled in the art (see DIN 51060:2000-06), "refractory material" refers to substances, materials and minerals that can at least temporarily withstand the thermal stresses during the casting or solidification of an iron melt (usually cast iron). "High refractory material" refers to substances, materials and minerals that can temporarily withstand the casting heat of a steel melt. The temperatures that may occur in the casting of a steel melt are generally higher than the temperatures that may occur in the casting of an iron or cast iron melt. Refractory substances, materials and minerals (refractory materials) and high refractory substances, materials and minerals are known to those skilled in the art, for example, from DIN 51060:2000-06. Unless otherwise specified, powdered refractory materials have an average particle size in the range of 0.1 to 500 μm, preferably in the range of 1 to 200 μm (preferably measured by light scattering according to ISO 13320:2009-10). Suitable refractory materials are, in particular, those which have a melting point of at least 200° C. above the temperature of the metal melt used in the respective case and / or which do not react in any way with the metal melt.

[0036] The term "refractory material" (a) as used herein also includes highly refractory substances.

[0037] The refractory material (a) is selected from those refractory materials commonly used for refractory coatings, for example, a refractory material selected from the group consisting of quartz, alumina, zirconia, aluminum silicate, non-swellable phyllosilicates, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite.

[0038] The refractory material (a) preferably comprises one or more refractory materials selected from the group consisting of quartz, alumina, zirconium oxide, aluminum silicate, non-swellable phyllosilicates, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite.

[0039] The refractory material (a) more preferably comprises

[0040] (i) one or more refractory materials selected from the group consisting of quartz, alumina, zirconium oxide, aluminum silicate, non-swellable phyllosilicate, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite

[0041] as well as

[0042] - (ii) one or more refractory materials selected from the group consisting of swellable layered silicates and zeolites.

[0043] The swellable phyllosilicate also acts as a rheological additive (inorganic thickener).The swellable phyllosilicate is preferably selected from the group of smectites, hectorites, saponites, nontronites, vermiculites and montmorillonites.

[0044] The zeolite may be a natural or synthetic zeolite.

[0045] The mass ratio of the refractory material (i) to the refractory material (ii) is preferably in the range from 20:1 to 5:1, more preferably 15:1 to 7:1.

[0046] For example, the refractory material (a) comprises

[0047] (i) one or more refractory materials selected from the group consisting of quartz, alumina, zirconium oxide, aluminum silicate, non-swellable phyllosilicate, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite

[0048] as well as

[0049] - (ii) one or more refractory materials selected from the group of swellable layered silicates.

[0050] For example, the refractory material (a) comprises

[0051] (i) one or more refractory materials selected from the group consisting of quartz, alumina, zirconium oxide, aluminum silicate, non-swellable phyllosilicate, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite

[0052] as well as

[0053] - (ii) one or more refractory materials selected from the group of zeolites.

[0054] The refractory material (a) more preferably comprises

[0055] (i) one or more refractory materials selected from the group consisting of quartz, alumina, zirconium oxide, aluminum silicate, non-swellable phyllosilicate, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite

[0056] as well as

[0057] - (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.

[0058] It has surprisingly been found that a particularly significant reduction in formaldehyde emissions is achieved in a composition wherein the refractory material (a) comprises, in addition to one or more refractory materials (i) as defined above, one or more refractory materials (ii) selected from the group of swellable phyllosilicates and zeolites, wherein the swellable phyllosilicates are preferably selected from the group of smectites, hectorites, saponites, nontronites, vermiculites and montmorillonites. This is surprising since all that has been described so far for some representatives of the above-mentioned refractory materials (ii) is that they act as rheological additives.

[0059] In certain cases or under certain experimental conditions, a significant reduction in formaldehyde emissions can even be achieved using a refractory coating composition containing a combination of the above refractory materials (i) and (ii) and not containing the compound (b) as defined above; see comparative examples in which a comparative refractory coating composition is used, the comparative refractory coating composition containing a combination of the above refractory materials (i) and (ii) and not containing the compound (b) as defined above. The mass ratio of refractory (i) to refractory (ii) is preferably in the range of 20:1 to 5:1, more preferably 15:1 to 7:1.

[0060] Thus, also described herein is a composition for use comprising

[0061] - (a) particles of one or more refractory materials, wherein the refractory material (a) comprises:

[0062] (i) one or more refractory materials selected from the group consisting of quartz, alumina, zirconium oxide, aluminum silicate, non-swellable phyllosilicate, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite

[0063] as well as

[0064] - (ii) one or more refractory materials selected from the group consisting of swellable layered silicates and zeolites

[0065] - (c) optionally a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof,

[0066] The composition is used to produce a coating on the body of a mold or core for metal casting that releases formaldehyde when heated, wherein the coating forms the surface of the mold or core that comes into contact with the metal melt during the casting operation.

[0067] The carrier liquid (c) serves only as a carrier for applying the substances suspended and dissolved therein to the body of the core or mold and is removed during the drying process. The carrier liquid is in liquid form under standard conditions (20° C. and 1013.25 hPa) and is evaporable at a temperature in the range of 50° C. to 200° C. at standard pressure (1013.25 hPa). The carrier liquid (c) is preferably selected from the group consisting of water, methanol, ethanol and isopropanol.

[0068] Compositions for producing refractory coatings usually contain additional components such as

[0069] - (d) wetting agents,

[0070] - (e) rheological additives,

[0071] - (f) a binder,

[0072] -(g) Suspension aid

[0073] - (h) Biocides.

[0074] Suitable wetting agents (d), rheological additives (e), binders (f), suspension aids (g) and biocides (h) and their functions and effects are known to the person skilled in the art.

[0075] The wetting agents (d) used are preferably anionic, cationic and nonionic surfactants. The wetting agent (d) is preferably selected from the group consisting of the group of surfactants, more preferably from the group consisting of acetylenic diols and derivatives thereof.

[0076] The rheological additives used are, for example, organic thickeners. These are preferably selected from the group consisting of polysaccharides, proteins and cellulose ethers. Inorganic thickeners can also be used, which come from the group comprising swellable clay minerals, such as banded silicates, such as palygorskite, and fumed silica. The swellable phyllosilicates and zeolites mentioned above also serve as inorganic thickeners. However, such inorganic thickeners are refractory materials and therefore belong to component (a) in terms of concentration figures.

[0077] The binder (f) used is a binder that self-cures in air or dries after removing the carrier liquid (c).Preferred binders (f) are selected from the group consisting of polyvinyl alcohol, polyacrylate, polyvinyl acetate, copolymers of the above polymers, natural resins, dextrin, starch and polypeptides.

[0078] The suspension aid (g) is preferably selected from the group consisting of metal salts soluble in the carrier liquid (c), the metal being from the group consisting of alkali metals, alkaline earth metals, iron and aluminum, and mixtures thereof.

[0079] As described above, the composition used according to the present invention comprises a ready-to-use refractory coating composition and a precursor for forming a ready-to-use refractory coating composition. The ready-to-use refractory coating composition has a sufficiently high carrier liquid content so that they can be directly applied to a body to form a coating. In the ready-to-use refractory coating composition, based on the total mass of the composition, the mass of the carrier liquid (c) is preferably 60% by weight to 80% by weight. The precursor for producing the ready-to-use refractory coating composition does not contain any carrier liquid (c) (solid mixture), or contains a significantly less amount of carrier liquid (c) (concentrate) compared with the ready-to-use refractory coating composition. In the concentrate, based on the total mass of the composition in each case, the total mass of the carrier liquid (c) is 40% by weight to 65% by weight, preferably 40% by weight to 59% by weight.

[0080] The ready-to-use refractory coating composition is obtained by suspending the solid mixture in a carrier liquid (c) (dissolving the components of the solid mixture that are soluble in the carrier liquid (c)) or diluting the concentrate with the carrier liquid (c). The concentrate is usually diluted with a carrier liquid (c) having the same composition as the carrier liquid (c) of the concentrate. Therefore, the ready-to-use refractory coating composition can be produced by a method comprising the following steps:

[0081] - producing or providing a solid mixture or concentrate as defined above

[0082] - adding a carrier liquid (c) selected from the group consisting of water, alkanols and mixtures thereof, wherein the amount of the carrier liquid (c) added is such that a composition is obtained in which the total amount of the carrier liquid (c) is from 60% by weight to 80% by weight, based on the total mass of the resulting composition.

[0083] The above discussion on suitable and preferred components (a)-(h) is applicable to both the concentrate and the ready-to-use refractory coating composition. With regard to solid mixtures, the above discussion on suitable and preferred refractory materials (a) and the above discussion on suitable and preferred components (b) and (d)-(h) are applicable insofar as they are solid.

[0084] A second aspect of the present invention relates to a composition for producing a coating on the body of a mold or core for metal casting that releases formaldehyde when heated, wherein the coating forms the surface of the mold or core that comes into contact with the metal melt during the casting operation. The composition of the present invention comprises

[0085] - (a) particles of one or more refractory materials

[0086] -(b) at least one ammonium salt [compound (b)]

[0087] wherein the total mass of the compound (b) is 0.1% by weight to 10% by weight, preferably 0.1% by weight to 9% by weight, further preferably 0.1% by weight to 8% by weight, further preferably 0.1% by weight to 7% by weight, further 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 refractory material,

[0088] - (c) a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof, wherein the total mass of the carrier liquid (c) is 40% by weight to 80% by weight based on the total mass of the composition.

[0089] With regard to the selection of refractory material (a), compound (b), carrier liquid (c) and further components (d) to (h) as defined above, the same applies as explained above in relation to the first aspect of the invention. Preference is given to compositions wherein components (a)-(h) are selected from the components (a)-(h) identified as preferred above in relation to the first aspect of the invention.

[0090] The compositions of the present invention include ready-to-use refractory coating compositions (as described above in the context of the first aspect of the present invention) and concentrates for forming ready-to-use refractory coating compositions (as described above in the context of the first aspect of the present invention).

[0091] Another aspect of the present invention relates to a mold or core for metal casting. The mold or core of the present invention comprises:

[0092] - a body that releases formaldehyde when heated,

[0093] - and a coating disposed on the body, the coating forming the surface of the mold or core that comes into contact with the metal melt during the casting operation, wherein the coating comprises:

[0094] - (a) particles of one or more refractory materials

[0095] -(b) at least one ammonium salt [compound (b)]

[0096] - and / or their reaction products with formaldehyde,

[0097] wherein the total mass of the free compounds (b) in the coating and the compounds bound to formaldehyde in the reaction product, based on the total mass of the particles of the refractory material (a), is 0.1% by weight to 10% by weight, preferably 0.1% by weight to 9% by weight, further preferably 0.1% by weight to 8% by weight, further preferably 0.1% by weight to 7% by weight, further preferably 0.1% by weight to 6% by weight, particularly preferably 0.1% by weight to 5% by weight.

[0098] The mold or core of the present invention comprises a main body and a coating arranged on the main body, the coating comprising the non-volatile components of the composition used according to the present invention in the first aspect of the present invention. With regard to the selection of refractory material (a) and compound (b) as defined above, the same applies as described above with respect to the first aspect of the present invention. Preferably such a mold or core has a coating as defined above, wherein refractory material (a) and compound (b) are selected from the components (a) and (b) identified as preferred above for the first aspect of the present invention.

[0099] The coating forms the surface of the mould or core which contacts the metal melt during the casting operation.The coating preferably has a thickness in the range of 0.05 to 0.6 mm, more preferably 0.05 to 0.4 mm, more preferably 0.1 to 0.3 mm.

[0100] Preferably, the coating does not only form the surface of the mold or core that is in contact with the metal melt during the casting operation, but also extends to cover other areas of the mold or core. The coating preferably extends to cover 50% or more, further preferably 70% or more, more preferably 80% or more, particularly preferably 90% or more, in particular 95% or more of the surface of the mold or core. Most preferably, the coating extends to cover the entire surface of the mold or core.

[0101] The body of the mold or core of the invention releases formaldehyde when heated. At least a significant portion of the formaldehyde released by the body is bound by the compound (b) present in the coating to form non-volatile reaction products. Thus, the coating contains compound (b) (especially before drying) and / or its reaction products with formaldehyde (which are formed during drying).

[0102] The body of the mold or core is usually formed by a molding material mixture, which has been bonded with a binder that releases formaldehyde when heated. The binder is present in the body of the mold or core in a cured form. Regarding the choice of binder, the same applies as explained above with respect to the first aspect of the present invention. Preferably such a binder is selected from the binders identified as preferred above with respect to the first aspect of the present invention. The binder is more preferably selected from the group consisting of:

[0103] -Polyurethanes formed by the polyaddition of phenol-formaldehyde resins and polyisocyanates

[0104] -Phenol-formaldehyde resin

[0105] -Furan-formaldehyde resin

[0106] -Urea-formaldehyde resin

[0107] -Melamine-formaldehyde resin

[0108] - Any combination of the above.

[0109] A fourth aspect of the present invention relates to a method for producing a mould or core of the present invention for metal casting. The method comprises the following steps:

[0110] -Production or provision entity

[0111] - producing or providing a ready-to-use refractory coating composition as defined above

[0112] - The ready-to-use refractory coating composition is applied to a body and then dried so as to produce a coating on the body, wherein the coating forms the surface of the mould or core which comes into contact with the metal melt during the casting operation.

[0113] In the method of the invention, a coating containing the non-volatile components of the composition used according to the invention in the first aspect of the invention is produced on the body of the mold or core. The coating forms the surface of the mold or core that comes into contact with the metal melt during the casting operation.

[0114] Preferably, the coating does not only form the surface of the mold or core that is in contact with the metal melt during the casting operation, but also extends to cover other areas of the mold or core. The coating preferably extends to cover 50% or more, further preferably 70% or more, more preferably 80% or more, particularly preferably 90% or more, in particular 95% or more of the surface of the mold or core. Most preferably, the coating extends to cover the entire surface of the mold or core.

[0115] The production of the main body of the mold or core generally includes the following steps:

[0116] - producing or providing a moulding material mixture comprising one or more mould base materials and a binder which releases formaldehyde when heated,

[0117] - shaping the molding material mixture

[0118] - Allowing the binder in the shaped molding material mixture to cure to form the body of the mold or core.

[0119] Corresponding molding material mixtures, molding methods and curing methods are known to those skilled in the art.

[0120] The binder of the molding material mixture is preferably selected from the group consisting of:

[0121] - Two-component system containing phenol-formaldehyde resin and polyisocyanate to form polyurethane

[0122] - Two-component system comprising an aqueous solution of an alkaline phenol-formaldehyde resin and an ester-based liquid hardener

[0123] - a formaldehyde condensation resin, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins or any combination thereof.

[0124] The binder is more preferably selected from the group consisting of:

[0125] -Polyurethanes formed by the polyaddition of phenol-formaldehyde resins and polyisocyanates

[0126] -Phenol-formaldehyde resin

[0127] -Furan-formaldehyde resin

[0128] -Urea-formaldehyde resin

[0129] -Melamine-formaldehyde resin

[0130] - Any combination of the above.

[0131] Preference is given to a method according to the invention in which the core or the main body of the mold is produced by the cold box method. The cold box method is known to the person skilled in the art. In this method, a two-component system comprising a phenol-formaldehyde resin and a polyisocyanate is used as a binder. The components of the binder come into contact with one another only during the production of the molding material mixture and form a polyurethane in the molded molding material mixture. The binder in the molded molding material mixture is cured by bringing the molded molding material mixture into contact with a gaseous tertiary amine or a mixture of two or more gaseous tertiary amines.

[0132] The ready-to-use refractory coating composition used in the method of the present invention is preferably selected from the ready-to-use refractory coating composition containing components (a)-(c) preferred in the first aspect of the present invention and optionally components (d)-(h) preferred in the first aspect of the present invention.

[0133] The ready-to-use refractory coating composition is typically applied to the body by a process selected from the group consisting of spraying, dipping, flow coating and painting, preferably dipping, as this process is particularly suitable for forming a coating that extends over the entire surface of the mold or core, or at least a large part of the entire surface of the mold or core.

[0134] The applied refractory coating composition is dried at a temperature of 40°C or higher, preferably at a temperature in the range of 50°C to 200°C, preferably 100°C to 150°C.

[0135] The body of the mold or core releases formaldehyde as it dries. At least a significant portion of the formaldehyde released by the body is bound by compound (b) present in the coating to form a non-volatile reaction product, so that the amount of formaldehyde released into the environment during the drying of the mold or core is significantly reduced.

[0136] A fifth aspect of the invention relates to the use of at least one ammonium salt (compound (b)) as a formaldehyde scavenger in a coating on the body of a mould or core for metal casting (which releases formaldehyde when heated), wherein the coating forms the surface of the mould or core which comes into contact with the metal melt during the casting operation, or in a composition for producing such a coating (such as the ready-to-use refractory coating composition described above in the context of the first aspect of the invention), or for producing such a composition.

[0137] Preferably, the coating does not only form the surface of the mold or core that is in contact with the metal melt during the casting operation, but also extends to cover other areas of the mold or core. The coating preferably extends to cover 50% or more, further preferably 70% or more, more preferably 80% or more, particularly preferably 90% or more, in particular 95% or more of the surface of the mold or core. Most preferably, the coating extends to cover the entire surface of the mold or core.

[0138] Formaldehyde scavengers are understood to mean chemical compounds which are able to react with formaldehyde to give non-volatile reaction products, thereby reducing the release of formaldehyde to the environment.

[0139] With regard to the choice of compound (b) as defined above, the same applies as explained above in relation to the first aspect of the present invention. Preferred are compounds (b) selected from the compounds (b) identified as preferred above in relation to the first aspect of the present invention.

[0140] In case compound (b) is used in the fifth aspect of the present invention, it is preferred that the coating or the composition for producing such a coating further comprises

[0141] (i) one or more refractory materials selected from the group consisting of quartz, alumina, zirconium oxide, aluminum silicate, non-swellable phyllosilicate, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite

[0142] - (ii) optionally one or more refractory materials selected from the group of swellable layered silicates and zeolites.

[0143] With regard to the selection of refractory materials (i) and (ii), the same applies as explained above in relation to the first aspect of the present invention.

[0144] A sixth aspect of the present invention relates to a kit for producing a mould or core for metal casting according to the third aspect of the present invention as defined above. The kit of the present invention comprises

[0145] - (A) a composition as described above for use in the first aspect of the present invention, wherein the composition is preferably a solid mixture as described above in the context of the first aspect of the present invention or a concentrate as described above in the context of the first aspect of the present invention,

[0146] - (B) a binder which releases formaldehyde when heated,

[0147] Therein, components (A) and (B) are separated from one another in the kit.

[0148] In the kit according to the invention, there is no possibility of contact between the components of component (A) and the components of component (B), because, for example, component (A) on the one hand and component (B) on the other hand are each provided in separate containers, or component (A) on the one hand and component (B) on the other hand are each provided in separate compartments of a container.

[0149] In the kit of parts of the present invention, composition (A) is preferably selected from solid mixtures and concentrates containing preferred components (a) and (b) and optionally (c) to (h) in the first aspect of the present invention.

[0150] In the kit of the present invention, the binder (B) is preferably selected from the group consisting of:

[0151] -Two-component system containing phenol-formaldehyde resin and polyisocyanate to form polyurethane

[0152] - A two-component system comprising an aqueous solution of an alkaline phenol-formaldehyde resin and an ester-based liquid hardener

[0153] - a formaldehyde condensation resin, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins or any combination thereof.

[0154] The binder is more preferably selected from the group consisting of:

[0155] -Polyurethanes formed by the polyaddition of phenol-formaldehyde resins and polyisocyanates

[0156] -Phenol-formaldehyde resin

[0157] -Furan-formaldehyde resin.

[0158] The invention is illustrated hereinafter by means of working examples.

[0159] Working Example

[0160] The present invention will now be described in more detail with reference to the following examples, the purpose of which is merely illustrative and not intended to limit the scope of the invention. The following coating compositions when applied to a core are described, however this is for ease of testing. The coating compositions will exhibit the same properties when applied to a mold.

[0161] Measuring formaldehyde levels

[0162] As described in detail below, the coating composition is applied to the core to form a coating.

[0163] Subsequently, the cores were dried at a temperature of 250° C. in a drying cabinet (Heraeus T5028 oven).

[0164] During the drying process, the oven air was sampled at specific times with the aid of a probe and the formaldehyde content thereof was determined by the method according to Gasmet and Hach Lange. This method is outlined in further detail below.

[0165] The formaldehyde content measurement method uses a Gasmet analyzer, which determines and quantifies the components in the gas stream at the oven exhaust. The fumes released from the oven during the drying process are collected in two scrubbing bottles each containing 50 ml of demineralized water, and the concentration is measured from a total of 100 ml. The maximum temperature of the gas stream is 180°C.

[0166] In the experiments performed, each measurement lasted approximately 60 minutes and the measurement temperature was 150°C.

[0167] If necessary, the results obtained in ppm can be converted to mg / m using the following formula: 3 :

[0168] ppm to mg / m 3 Conversion

[0169] [mg / m 3 ]=[ppm]*Mw*0.0409

[0170] [mg / m 3 ] = concentration in mg / m3

[0171] [ppm] = concentration in ppm Mw = molar mass of the relevant gas in g / mol

[0172] 0.0409 = mol air to m 3 Conversion factor

[0173] The gas concentration is then converted to gas concentration per gram of sample by plotting a graph of the concentration per gram of sample versus time. The average gas concentration per gram of sample and the maximum gas concentration per gram of sample over the desired time range can then be determined.

[0174] Calculation of the total amount of released gas

[0175] m(gas) = ​​average [mg / m 3 g]*test time*flow rate / 1000

[0176] m(gas) = ​​mass of gas released per gram of sample

[0177] Average [mg / m 3 g] = average concentration per gram of sample

[0178] Test time = (min)

[0179] Flow rate = 4L / min

[0180] Rise to m 3 Conversion of = 1000

[0181] After measuring the gas concentration as outlined above, the concentration of formaldehyde can be measured using a Hach Lange spectrophotometer using the following equation:

[0182] Calculation of the amount of formaldehyde

[0183] Hach Lange result (mg / l)*V(=0.1l)*1000) / (sample mass (g)*time (min)*flow rate (l / min))=formaldehyde (mg / m 3 g).

[0184] Preparation of the coating composition of the present invention

[0185] The following section details how to prepare the coating composition according to the present invention. Table 1 shows the various components (a to h) in the composition of the present invention and their respective amounts. These examples relate to the preparation of cores, although they can also be applied to the preparation of molds.

[0186] Table 1

[0187]

[0188] Com.=Commercial

[0189] Table 2a

[0190]

[0191]

[0192] Table 2b

[0193]

[0194] In each of Examples E3 to E9c, the layer thickness of the coating composition when applied to the core is between 225 μm and 278 μm. If it is below 225 μm, the coating contains too much carrier liquid (e.g., water) and needs to be made more concentrated. If it is above 278 μm, it needs more carrier liquid. The applicant noted that the coatings prepared with ammonium chloride and ammonium citrate remained unchanged after 6 months.

[0195] Table 3 shows a comparative overview of the layer thicknesses and formaldehyde concentrations of compositions according to the invention (E8a-E9c) and comparative examples (E1-E7).

[0196] Table 3

[0197]

[0198]

[0199] These results show that the NH2 group acts as an effective formaldehyde scavenger. Applicants herein have found that ammonium citrate and ammonium chloride give comparable, if not better, results in reducing formaldehyde generation during heating compared to prior art and commercial formaldehyde scavengers. E8a (ammonium citrate) and E9a (ammonium chloride) each produced 0.03 and 0.04 mg / m3, respectively, at 3.9 wt.%. 3 .g of formaldehyde, while Examples E5 to E7 produced between 0.04 and 0.09 mg / m at the same wt.% of scavenger component. 3 In addition, applicants have found that when ammonium citrate or ammonium chloride is used as a formaldehyde scavenger in a coating for cores or molds, there are no casting defects compared to coatings using prior art or commercial formaldehyde scavengers.

[0200] The results show that higher concentrations of ammonium citrate or ammonium chloride lead to increased formaldehyde removal and therefore lower concentrations of formaldehyde produced.

[0201] Ammonium chloride as a scavenger gives particularly interesting results, especially in terms of price. Both ammonium chloride and ammonium citrate are much cheaper than other currently available scavengers. Therefore, even though more ammonium chloride or ammonium citrate may be required to obtain the same level of formaldehyde removal, ammonium chloride or ammonium citrate is still a cheaper alternative compared to other prior art or commercial formaldehyde scavengers. More importantly, ammonium chloride and ammonium citrate are less hazardous to use and thus reduce health risks to users.

[0202] Applicants have discovered that by using ammonium chloride or ammonium citrate as formaldehyde scavengers, comparable, if not better, results than prior art or commercial scavengers can be achieved. In addition, Applicants have discovered that ammonium chloride and ammonium citrate provide longer lasting coatings, and therefore provide longer lasting scavenger effects. Thus, Applicants have discovered alternative formaldehyde scavengers that provide significant advantages over the current prior art. These alternative scavengers serve to reduce formaldehyde concentrations to the lowest levels currently known, and they are less expensive, more durable, and more user friendly.

[0203] The present invention describes and illustrates, by way of example, the use of specific compounds as formaldehyde scavengers in a coating on the body of a mold or core for metal casting, the body of which releases formaldehyde when heated, wherein the coating forms the surface of the mold or core that contacts the metal melt during the casting operation, and describes and illustrates the use of a composition containing one or more of these compounds for producing a coating on the body of a mold or core for metal casting, the body of which releases formaldehyde when heated, wherein the coating forms the surface of the mold or core that contacts the metal melt during the casting operation. Corresponding molds and cores and their production are also described.

Claims

1. A composition for producing a coating on the body of a mold or core for metal casting, the body of the mold or core releasing formaldehyde when heated, wherein the coating forms the surface of the mold or core that comes into contact with the metal melt during the casting operation, wherein the composition comprises: (a) particles of one or more refractory materials (b) at least one ammonium salt [compound (b)] wherein the total mass of compound (b) is 0.1% by weight to 10% by weight based on the total mass of particles (a) of the refractory material, (c) optionally a carrier liquid selected from the group consisting of water, alkanols, and mixtures thereof.

2. A composition according to claim 1, wherein The total mass of the carrier liquid (c) is 40% by weight to 80% by weight of the composition, based on the total mass of the composition.

3. A composition according to claim 1 or claim 2, wherein: The at least one ammonium salt has the formula (R)4N + A - ammonium salts, wherein R is selected from hydrogen, C 1-4 The invention relates to a group consisting of an alkyl group and a phenyl group, and wherein A is an anion selected from the group consisting of trifluoroacetate, acetate, benzenesulfonate, benzoate, bicarbonate, bitartrate, bromide, carbonate, chloride, citrate, dihydrochloride, formate, hydrobromide, hydrochlorate, methylsulfate, nitrate, oxalate, phosphate and sulfate.

4. A composition according to any one of claims 1 to 3, wherein The refractory material (a) comprises: (i) one or more refractory materials selected from the group consisting of quartz, alumina, zirconium oxide, aluminum silicate, non-swellable phyllosilicate, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite, and (ii) one or more refractory materials selected from the group of swellable layered silicates and zeolites, and / or the carrier liquid (c) is selected from the group consisting of water, methanol, ethanol and isopropanol and mixtures thereof.

5. A mold or core for metal casting, the mold or core comprising a body that releases formaldehyde when heated and a coating disposed on the body, the coating forming a surface of the mold or core that contacts a metal melt during a casting operation, wherein the coating comprises: (a) particles of one or more refractory materials (b) at least one ammonium salt [compound (b)] and / or their reaction products with formaldehyde, The total mass of the free compound (b) in the coating and the compound (b) combined with formaldehyde in the reaction product is 0.1 to 10% by weight, based on the total mass of the particles (a) in the refractory material.

6. A mold or core for metal casting according to claim 5, wherein: The at least one ammonium salt has the formula (R)4N + A - ammonium salts, wherein R is selected from hydrogen, C 1-4 The invention relates to a group consisting of an alkyl group and a phenyl group, and wherein A is an anion selected from the group consisting of trifluoroacetate, acetate, benzenesulfonate, benzoate, bicarbonate, bitartrate, bromide, carbonate, chloride, citrate, dihydrochloride, formate, hydrobromide, hydrochlorate, methylsulfate, nitrate, oxalate, phosphate and sulfate.

7. A mold or core for metal casting according to claim 5 or claim 6, wherein: The refractory material (a) comprises: (i) one or more refractory materials selected from the group consisting of quartz, alumina, zirconium oxide, aluminum silicate, non-swellable phyllosilicate, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite, and (ii) One or more refractory materials selected from the group consisting of swellable layered silicates and zeolites.

8. A mold or core for metal casting according to any one of claims 5 to 7, wherein: The body of the mold or core has been formed from a molding material mixture which has been bound with at least one binder which releases formaldehyde when heated, the binder being selected from the group consisting of: - polyurethanes formed by the polyaddition of phenol-formaldehyde resins with polyisocyanates, and - a formaldehyde condensation resin selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins or any combination thereof.

9. A mold or core for metal casting according to any one of claims 5 to 8, wherein: The thickness of the coating is in the range of 0.05 mm to 0.6 mm.

10. A method of producing a coating on the body of a mold and core for metal casting, the method comprising: A composition is applied to the body of the mold or core for metal casting, the composition comprising: (a) particles of one or more refractory materials (b) at least one ammonium salt [compound (b)] wherein the total mass of compound (b) is 0.1% by weight to 10% by weight based on the total mass of particles (a) of the refractory material, (c) optionally a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof, wherein the mold or core releases formaldehyde when heated, and The coating forms the surface of the mold or core that comes into contact with the metal melt during the casting operation.

11. The method according to claim 10, wherein: The at least one ammonium salt has the formula (R)4N + A - ammonium salts, wherein R is selected from hydrogen, C 1-4 The invention relates to a group consisting of an alkyl group and a phenyl group, and wherein A is an anion selected from the group consisting of trifluoroacetate, acetate, benzenesulfonate, benzoate, bicarbonate, bitartrate, bromide, carbonate, chloride, citrate, dihydrochloride, formate, hydrobromide, hydrochlorate, methylsulfate, nitrate, oxalate, phosphate and sulfate.

12. The method according to claim 10 or claim 11, wherein: The refractory material (a) comprises: (i) one or more refractory materials selected from the group consisting of quartz, alumina, zirconium oxide, aluminum silicate, non-swellable phyllosilicate, zirconium silicate, olivine, talc, mica, graphite, coke, feldspar, diatomaceous earth, kaolin, calcined kaolin, metakaolin, iron oxide and bauxite, and (ii) one or more refractory materials selected from the group of swellable layered silicates and zeolites, and / or the carrier liquid (c) is selected from the group consisting of water, methanol, ethanol and isopropanol.

13. The method according to any one of claims 10 to 12, wherein: The total mass of the carrier liquid (c) is from 40% by weight to 80% by weight, based in each case on the total mass of the composition.

14. The method according to any one of claims 10 to 13, wherein: The body of the mold or core has been formed from a molding material mixture which has been bound with at least one binder which releases formaldehyde when heated, the binder being selected from the group consisting of: - polyurethanes formed by the polyaddition of phenol-formaldehyde resins with polyisocyanates, and - a condensation resin selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins.

15. Use of at least one ammonium salt (compound (b)) as formaldehyde scavenger in a coating on the body of a mold or core for metal casting which releases formaldehyde when heated, or in a composition for producing such a coating, or in a composition for producing such a coating, wherein the coating forms the surface of the mold or core which comes into contact with the metal melt during the casting operation.

Images