A composition for producing a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated

Abstract

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

Description

[0001] “A composition for producing a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated”

[0002] BACKGROUND

[0003] What is described is the use of particular compounds as formaldehyde scavengers in a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation, and the use of a composition containing one or more of these compounds for production of a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation. Also described are corresponding molds and cores and the production thereof.

[0004] Molds and cores for metal casting are produced by shaping a molding material mixture comprising a mold base material (e.g. sand) and a binder, and then curing the shaped molding material mixture. This frequently involves using organic binders that emit formaldehyde when heated, for example polyurethanes formed by polyaddition of a phenol-formaldehyde resin with a polyisocyanate, or formaldehyde condensation resins, e.g. formaldehyde condensation resins from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, ureaformaldehyde resins, melamine-formaldehyde resins.

[0005] Molds are negatives; they contain the cavity to be cast, which results in the casting to be manufactured. The inner contours of a casting may be formed by cores. In the production of the mold, by means of a model of the casting to be manufactured, it is possible to shape the cavity into the molding material. Cores are usually shaped in a core box.

[0006] Typically, in the production of molds and cores for metal casting by shaping a molding material mixture (as described above) and then curing the shaped molding material mixture, a main body of the mold or core is first formed, which already has the contours of the required mold or the required core. Especially in the case of steel and iron casting, a coating is typically produced on the main body thus formed, the coating forming a surface of the mold or core that comes into contact with a metal melt in the casting operation. Such coatings are typically referred to as refractory coatings. In the context of the present application, the term “mold” or “core” refers in each case to the entirety of the main body of the mold or core and the coating disposed on this main body (refractory coating). This coating acts as an interface and / or barrier layer between the main body of the core or mold and the cast metal, and serves, inter alia, for controlled suppression of mechanisms of casting defect formation at the interface between metal and core / mold or for utilization of metallurgical effects. In general, refractory coatings in foundry technology should fulfil the following functions, which are known to the person skilled in the art:

[0007] - improving the smoothness of the casting surface and / or

[0008] - preventing chemical reactions between constituents of the molding material mixture and the metal melt, hence facilitating separation between mold / core and casting and / or

[0009] - preventing surface defects on the casting, for example gas bubbles, penetrations, leaf veins and / or scabs.

[0010] Ready-to-use compositions for coating of the main bodies of molds and cores are typically suspensions of fine-grain, refractory to highly refractory inorganic materials (refractories) in a carrier liquid (e.g. water, alkanols, or mixtures thereof), where further constituents may be suspended or dissolved in the carrier liquid. The refractory coating composition is applied to the main body in a suitable manner, and then the carrier liquid is removed by drying, forming a coating on the main body. The drying is typically effected at a temperature above 40° C, preferably in the range from 50° C to 200° C. At these temperatures, the main bodies of the molds or cores emit significant amounts of formaldehyde. Such emissions constitute considerable pollution of the workplace.

[0011] DE 10 2008 025 311 Al discloses a casting mold for metal casting, wherein a layer of a material that absorbs pollutants is disposed in at least sections of gas exit areas of the casting mold. Gas exit areas are understood to mean the areas of the casting mold through which gaseous components can escape from the casting mold during the casting operation. The gas exit area may correspond to the entire outer surface of the casting mold. Alternatively, it is possible that just a portion of the outer surface of the casting mold is utilized for the release of gaseous components. For instance, in the case of in-box metal casting, a box is utilized for construction of the casting mold, which covers the underside and the lateral faces of the casting mold. In that case, essentially only the top face of the casting mold is available for a release of gaseous components. An outer surface of the casting mold is understood to mean the surfaces through which offgases formed in the casting operation can leave the casting mold. This outer surface is visible when the casting mold is viewed from the outside and does not come into contact with the liquid metal in the casting operation. By contrast, an inner surface is understood to mean, for example, the surface of the mold cavity surrounded by the casting mold.

[0012] Materials that bind formaldehyde by chemical reactions to give nonvolatile reaction products are not disclosed in DE 10 2008 025 311 Al .

[0013] EP 0 012 169 Al discloses a particleboard or fibreboard bound predominantly with amino resins, characterized in that part of the area of the board, preferably the middle layer, at least partly contains a binder that is not part of the group of the amino resins and simultaneously tolerates the introduction of formaldehyde-reactive substances in particular amounts that react with formaldehyde under the action of moisture and / or heat or release substances that can in turn bind formaldehyde.

[0014] SUMMARY

[0015] It is an object of the present invention to reduce the emissions of formaldehyde that arise in the drying of the refractory coating of molds or cores that release formaldehyde when heated.

[0016] In a first aspect of the invention, this object is achieved by the use of a composition comprising

[0017] - (a) particles of one or more refractories

[0018] (b) at least one ammonium salt [compound (b)] where 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 the particles (a) of the refractories,

[0019] - (c) optionally a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof, for production of a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation. Preferably, the coating does not just form the surface of the mold or core that comes into contact with a metal melt in the casting operation, but additionally extends over further regions of the mold or core. The coating preferably extends over 50% or more, further preferably over 70% or more, more preferably over 80% or more, especially preferably over 90% or more, in particular over 95% or more, of the surface of the mold or core. Most preferably, the coating extends over the entire surface of the mold or core.

[0020] DETAILED DESCRIPTION

[0021] The main body of the mold or core here is typically formed from a molding material mixture that has been bound with a binder that emits formaldehyde when heated, wherein the binder is preferably selected from the group consisting of:

[0022] - polyurethanes formed by polyaddition of a phenol-formaldehyde resin with a polyisocyanate

[0023] - formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins.

[0024] More preferably, the main body of the mold or core has been formed from a molding material mixture that has been bound with a binder that emits formaldehyde when heated, wherein the binder is selected from the group consisting of:

[0025] - polyurethanes formed by polyaddition of a phenol-formaldehyde resin with polyisocyanate

[0026] - phenol-formaldehyde resins and

[0027] - furan-formaldehyde resins.

[0028] The binder is present in cured form in the main body of the mold or core.

[0029] It has been found that, surprisingly, in the case of molds and cores that emit formaldehyde when heated, the amount of formaldehyde released to the environment in the course of drying of the refractory coating is distinctly reduced when the refractory coating is produced using the above-defined composition. It is currently assumed that the compound (b) is capable of binding formaldehyde by chemical reactions that form nonvolatile reaction products, such that less formaldehyde escapes from the core or mold into the environment. Therefore, the compound (b) is referred to here as formaldehyde scavengers.

[0030] As well as the ability to irreversibly bind a nonvolatile reaction product with formaldehyde, a number of further criteria should be noted in the selection of the compound (b). For instance, the compound (b) itself must not be volatile, and it must not break down at the temperatures at which the molds and cores are dried. The breakdown 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 ). Preference is therefore given to those compounds (b) that are solids or high-boiling liquids having low vapor pressure. In addition, compound (b) must be soluble in a sufficient amount in the carrier liquid (c).

[0031] Furthermore, the compound (b) should as far as possible not be toxic, not require any particular occupational protection and safety precautions, and be reliably available on the market under acceptable conditions.

[0032] The compound (b) is preferably a compound that is soluble in the carrier liquid (c).

[0033] Within the context of the present invention, the expression “at least one ammonium salt” is intended to denote one or more than one ammonium salt. Mixtures of ammonium salts can also be used for the purpose of the invention. In the remainder of the text, the expression “ammonium salt” is understood, for the purposes of the present invention, both in the plural and the singular form. In the context of the invention, ammonium salts are preferably ammonium slats of formula (R)4N+A‘, where R is selected from the group consisting of hydrogen, Ci-4 alkyl and phenyl and where A is an appropriate counter-ion (also called anion). Preferably, R is hydrogen. The term alkyl - alone or in combination means an alkane-derived radical containing from 1 to 4 carbon atoms, unless otherwise specified, for example CF-G alkyl defines a straight or branched alkyl radical having from F to G carbon atoms, e.g. Cl -4 alkyl defines a straight or branched alkyl radical having from 1 to 4 carbon atoms such as for example methyl, ethyl, 1 -propyl, 2-propyl, I-butyl, 2-butyl, 2-methyl-l -propyl. An alkyl group may be a straight chain alkyl or branched alkyl. Suitable anions A may be organic or inorganic.

[0034] Appropriate anions A comprise, for example, trifluoroacetate, acetate, benzenesulfonate, benzoate, bicarbonate, bitartrate, bromide, carbonate, chloride, citrate, dihydrochloride, formiate, hydrobromide, hydrochloride, methyl sulfate, nitrate, oxalate, phosphate, sulfate, and the like. Advantageously, the ammonium salt is selected from the group consisting of ammonium acetate, ammonium citrate, ammonium formiate, ammonium oxalate and ammonium chloride. Particular preference is given to ammonium chloride and ammonium citrate.

[0035] In the composition for use in accordance with the 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 the particles (a) of the refractories. It is further understood that the upper limit of the total mass of compound (b) is equal to or less than 10 %, preferably equal to or less than 9%, more preferably equal to or less than 8%, further preferably equal to or less than 8%, further preferably equal to or less than 7%, further preferably equal to or less than 6% by weight, further preferably equal to or less than 5%, by weight, based on the total mass of the particles (a) of the refractories. In an embodiment of the composition of the present 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, especially preferably 0.1% by weight 5% by weight, based on the total mass of the particles (a) of the refractories. In the case of a smaller amount of compound (b), no significant decrease in formaldehyde emissions would be achieved. A higher amount of compound (b) could affect the quality of the coating produced.

[0036] In accordance with the typical understanding of the person skilled in the art (cf. DIN 51060:2000-06), “refractory” refers to masses, materials and minerals that can at least briefly withstand the thermal stress on casting or solidification of an iron melt, usually cast iron. “Highly refractory” refers to masses, materials and minerals that can briefly withstand the heat of casting of a steel melt. The temperatures that can occur in the casting of steel melts are usually higher than the temperatures that can occur in the casting of iron or cast iron melts. 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 stated otherwise, pulverulent refractories then have an average grain size (preferably measured by means of light scattering to ISO 13320:2009-10) in the range from 0.1 to 500 pm, preferably in the range from 1 to 200 pm. Suitable refractories are especially those materials that have melting points at least 200° C. above the temperature of the metal melt used in the respective case and / or do not enter into any reaction with the metal melt.

[0037] The term “refractory” (a) as used here also includes highly refractory substances. The refractories (a) are selected from those refractories that are typically used in refractory coatings, for example refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite.

[0038] The refractories (a) preferably comprise one or more refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite.

[0039] The refractories (a) more preferably comprise

[0040] - (i) one or more refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite and

[0041] - (ii) one or more refractories selected from the group of the swellable layered silicates and the zeolites.

[0042] Swellable layered silicates also act as a rheology additive (inorganic thickener). The swellable layered silicates are preferably selected from the group of the smectites, hectorites, saponites, nontronites, vermiculites and montmorillonites.

[0043] The zeolites may be natural or synthetic zeolites.

[0044] The mass ratio of the refractories (i) to the refractories (ii) is preferably in the range from 20: 1 to 5: 1, more preferably 15: 1 to 7: 1.

[0045] For example, the refractories (a) comprise

[0046] (i) one or more refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite and

[0047] - (ii) one or more refractories selected from the group of the swellable layered silicates.

[0048] For example, the refractories (a) comprise

[0049] - (i) one or more refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite and

[0050] - (ii) one or more refractories selected from the group of the zeolites.

[0051] The refractories (a) more preferably comprise

[0052] - (i) one or more refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite and

[0053] - (ii) one or more refractories selected from the group of the swellable layered silicates, and one or more refractories selected from the group of zeolites.

[0054] It has been found that, surprisingly, compositions wherein the refractories (a), as well as one or more refractories (i) as defined above, also include one or more refractories (ii) selected from the group of the swellable layered silicates and the zeolites, wherein the swellable layered silicates are preferably selected from the group of the smectites, hectorites, saponites, nontronites, vermiculites and montmorillonites, achieve a particularly significant reduction in formaldehyde emissions. This was not to be expected since all that had been described to date for some representatives of the abovementioned refractories (ii) was a function as rheology additive.

[0055] In particular cases, or under particular experimental conditions, it is even possible with a refractory coating composition containing a combination of the abovementioned refractories (i) and (ii) and no compound (b) as defined above to achieve a significant reduction in formaldehyde emissions; see the comparative examples in which a comparative refractory coating composition was used, which contains a combination of the abovementioned refractories (i) and (ii) and no compound (b) as defined above. The mass ratio of the refractories (i) to the refractories (ii) is preferably in the range from 20: 1 to 5: 1, more preferably 15: 1 to 7: 1.

[0056] What is thus described here is also the use of a composition comprising

[0057] - (a) particles of one or more refractories, where the refractories (a) comprise:

[0058] - (i) one or more refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite and

[0059] - (ii) one or more refractories selected from the group of the swellable layered silicates and the zeolites

[0060] - (c) optionally a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof, for production of a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation.

[0061] The carrier liquid (c) serves merely as vehicle for application of the substances suspended and dissolved therein to the main body of the core or mold, and is removed in the course of drying. The carrier liquid is in liquid form under standard conditions (20° C. and 1013.25 hPa) and is evaporable under standard 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.

[0062] Compositions for production of refractory coatings frequently contain further constituents such as

[0063] - (d) wetting agents,

[0064] - (e) rheology additives,

[0065] - (f) binders,

[0066] - (g) suspension aids

[0067] - (h) biocides.

[0068] Suitable wetting agents (d), rheology additives (e), binders (f), suspension aids (g) and biocides (h) and their function and effect are known to the person skilled in the art.

[0069] Wetting agents (d) used are preferably anionic, cationic and non-ionic surfactants. The wetting agents (d) are preferably selected from the group consisting of the group of surfactants, more preferably from alkyne diols and derivatives thereof.

[0070] Rheology additives used are, for example, organic thickeners. These are preferably selected from the group consisting of polysaccharides, proteins and cellulose ethers. It is also possible to use inorganic thickeners from the group comprising swellable clay minerals, e.g. band silicates such as palygorskites (attapulgites), and fumed silicas. The abovementioned swellable layered silicates and zeolites also act as inorganic thickeners. Such inorganic thickeners, however, are refractories and are therefore assigned to constituent (a) in respect of concentration figures.

[0071] Binders (f) used are binders that self-cure under air or dry on removal of the carrier liquid (c). Preferred binders (f) are selected from the group of the polyvinyl alcohols, polyacrylates, polyvinylacetates, co-polymers of the aforementioned polymers, natural resins, dextrins, starches and peptides.

[0072] The suspension aids (g) are preferably selected from the group consisting of salts of metals from the group consisting of alkali metals, alkaline earth metals, iron and aluminum that are soluble in the carrier liquid (c), and mixtures thereof. Compositions for use in accordance with the invention, as described above, include ready-to-use refractory coating compositions and precursors for formation of ready-to-use refractory coating compositions. Ready-to-use refractory coating compositions have a sufficiently high content of carrier liquid that they can be applied directly to the main body to form a coating. In a ready-to-use refractory coating composition, the mass of carrier liquid (c) is preferably 60% by weight to 80% by weight, based on the total mass of the composition. Precursors for production of a ready-to-use refractory coating composition do not contain any carrier liquid (c) (solid mixture) or contain a distinctly smaller amount of carrier liquid (c) compared to the ready-to-use refractory coating composition (concentrate). In the concentrates, the total mass of the carrier liquid (c) is 40% by weight to 65% by weight, preferably 40% by weight to 59% by weight, based in each case on the total mass of the composition.

[0073] A ready-to-use refractory coating composition is obtainable by suspending the solid mixture in a carrier liquid (c) (with dissolution of constituents of the solid mixture that are soluble in the carrier liquid (c)) or diluting the concentrate with a carrier liquid (c). The concentrate is typically diluted using a carrier liquid (c) having the same composition as the carrier liquid (c) of the concentrate. A ready-to-use refractory coating composition is thus producible by a process comprising the steps of

[0074] - producing or providing a solid mixture or concentrate as defined above

[0075] - adding carrier liquid (c) selected from the group consisting of water, alkanols and mixtures thereof, wherein the amount of carrier liquid (c) added is such as to result in a composition in which the total amount of the carrier liquid (c) is 60% by weight to 80% by weight, based on the total mass of the resulting composition.

[0076] The above remarks relating to suitable and preferred constituents (a)-(h) are applicable both in respect of concentrates and in respect of ready-to-use refractory coating compositions. In respect of solid mixtures, the above remarks relating to suitable and preferred refractories (a) and the above remarks relating to suitable and preferred constituents (b) and (d)-(h) are applicable, to the extent that they are solids.

[0077] A second aspect of the present invention relates to a composition for production of a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation. A composition of the invention comprises (a) particles of one or more refractories

[0078] (b) at least one ammonium salt [compound (b)] wherein 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, especially preferably 0.1% by weight to 5% by weight, based on the total mass of the particles (a) of the refractories,

[0079] - (c) a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof, where the total mass of the carrier liquid (c) is 40% by weight to 80% by weight, based on the total mass of the composition.

[0080] With regard to the selection of the refractories (a), compound (b), carrier liquids (c) and further constituents (d) and (h) as defined above, the same applies as set out above in respect of the first aspect of the invention. Preference is given to compositions wherein constituents (a)- (h) are selected from the constituents (a)-(h) identified as preferred in respect of the first aspect of the invention above.

[0081] Compositions of the invention include ready -to-use refractory coating 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) for formation of ready -to-use refractory coating compositions.

[0082] A further aspect of the present invention relates to a mold or core for metal casting. A mold or core of the invention comprises:

[0083] - a main body that emits formaldehyde when heated,

[0084] - and a coating disposed on the main body, which forms a surface of the mold or core that comes into contact with a metal melt in the casting operation, wherein the coating comprises:

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

[0086] - (b) at least one ammonium salt [compound (b)] and / or reaction products thereof with formaldehyde,

[0087] - wherein the total mass of free compound (b) and compounds bound in reaction products with formaldehyde in the coating 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, especially preferably 0.1% by weight to 5% by weight, based on the total mass of the particles (a) of the refractories.

[0088] A mold or core of the invention comprises a main body and a coating arranged on said main body that includes the nonvolatile constituents of the composition for use in accordance with the invention in the first aspect of the invention. With regard to the selection of the refractories (a) and compound (b) as defined above, the same applies as set out above in respect of the first aspect of the invention. Preference is given to molds and cores having a coating as defined above, wherein the refractories (a) and the compound (b) are selected from the constituents (a) and (b) identified above as being preferred for the first aspect of the invention.

[0089] This coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation. The coating preferably has a thickness in the range from 0.05 mm to 0.6 mm, more preferably 0.05 to 0.4 mm, more preferably in the range from 0.1 to 0.3 mm.

[0090] Preferably, the coating does not just form the surface of the mold or core that comes into contact with a metal melt in the casting operation, but additionally extends over further regions of the mold or core. The coating preferably extends over 50% or more, further preferably over 70% or more, more preferably over 80% or more, especially preferably over 90% or more, in particular over 95% or more, of the surface of the mold or core. Most preferably, the coating extends over the entire surface of the mold or core.

[0091] The main body of the mold or core of the invention emits formaldehyde when heated. At least a noticeable proportion of the formaldehyde emitted by the main body is bound by the compound (b) present in the coating to form nonvolatile reaction products. Therefore, the coating contains the compound (b) (especially prior to drying) and / or reaction products thereof with formaldehyde (that form during the drying). The main body of the mold or core is typically formed from a molding material mixture that has been bound with a binder that emits formaldehyde when heated. The binder is present in cured form in the main body of the mold or core. With regard to the selection of the binders, the same applies as set out above in respect of the first aspect of the invention. Preference is given to binders that are selected from the above binders identified as preferred in respect of the first aspect of the invention. The binder is more preferably selected from the group consisting of

[0092] - polyurethanes formed by polyaddition of a phenol-formaldehyde resin with polyisocyanate

[0093] - phenol-formaldehyde resins

[0094] - furan-formaldehyde resins

[0095] - urea-formaldehyde resins

[0096] - melamine-formaldehyde resins

[0097] - any combination of the above.

[0098] A fourth aspect of the present invention relates to a process for producing a mold or core of the invention for metal casting. The process comprises the steps of

[0099] - producing or providing the main body

[0100] - producing or providing a ready -to-use refractory coating composition as defined above

[0101] - applying the ready-to-use refractory coating composition to the main body and then drying, such that a coating is produced on the main body, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation.

[0102] In the process of the invention, a coating containing the nonvolatile constituents of the composition for use in accordance with the invention in the first aspect of the invention is produced on the main body of the mold or core. This coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation.

[0103] Preferably, the coating does not just form the surface of the mold or core that comes into contact with a metal melt in the casting operation, but additionally extends over further regions of the mold or core. The coating preferably extends over 50% or more, further preferably over 70% or more, more preferably over 80% or more, especially preferably over 90% or more, in particular over 95% or more, of the surface of the mold or core. Most preferably, the coating extends over the entire surface of the mold or core.

[0104] The production of the main body of the mold or core typically comprises the following steps:

[0105] - producing or providing a molding material mixture comprising one or more mold base materials and a binder that emits formaldehyde when heated,

[0106] - shaping the molding material mixture

[0107] - curing the binder in the shaped molding material mixture to form the main body of the mold or core.

[0108] Corresponding molding material mixtures, shaping methods and curing methods are known to the person skilled in the art.

[0109] The binder of the molding material mixture is preferably selected from the group consisting of

[0110] - two-component systems comprising a phenol-formaldehyde resin and a polyisocyanate to form a polyurethane

[0111] - two-component systems comprising an aqueous alkaline phenol-formaldehyde resin solution and an ester based liquid hardener formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins or any combination thereof. The binder is more preferably selected from the group consisting of

[0112] - polyurethanes formed by polyaddition of a phenol-formaldehyde resin with polyisocyanate

[0113] - phenol-formaldehyde resins

[0114] - furan-formaldehyde resins

[0115] - urea-formaldehyde resins

[0116] - melamine-formaldehyde resins

[0117] - any combination of the above.

[0118] Preference is given to a process of the invention in which the main body of the core or 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 as binder is used. The components of the binder are only contacted with one another in the course of production of the molding material mixture and form a polyurethane in the shaped molding material mixture. The binder in the shaped molding material mixture is cured by contacting the shaped molding material mixture with a gaseous tertiary amine or a mixture of two or more gaseous tertiary amines.

[0119] The ready-to-use refractory coating composition used in the process of the invention is preferably selected from the ready-to-use refractory coating compositions containing the constituents (a)-(c) that are preferred in the first aspect of the invention and optionally the constituents (d)-(h) that are preferred in the first aspect of the invention.

[0120] The ready-to-use refractory coating composition is applied to the main body typically by a process selected from the group consisting of spraying, dipping, flow coating and painting, preferably dipping, since 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 portion of the entire surface of the mold or core. The refractory coating composition applied 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 150° C.

[0121] The main body of the mold or core emits formaldehyde when drying. At least a noticeable proportion of the formaldehyde emitted by the main body is bound by the compound (b) present in the coating to form nonvolatile reaction products, such that there is a noticeable reduction in the amount of formaldehyde released to the environment in the course of drying of the mold or core.

[0122] A fifth aspect of the invention relates to the use of at least one ammonium salt (compound (b)) as formaldehyde scavenger in a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation, or in a composition for production of such a coating (ready-to-use refractory coating composition as described above in the context of the first aspect of the invention) or for production of such a composition.

[0123] Preferably, the coating does not just form the surface of the mold or core that comes into contact with a metal melt in the casting operation, but additionally extends over further regions of the mold or core. The coating preferably extends over 50% or more, further preferably over 70% or more, more preferably over 80% or more, especially preferably over 90% or more, in particular over 95% or more, of the surface of the mold or core. Most preferably, the coating extends over the entire surface of the mold or core.

[0124] A formaldehyde scavenger is understood to mean a chemical compound capable of reacting with formaldehyde to give a nonvolatile reaction product, hence reducing the emission of formaldehyde to the environment.

[0125] With regard to the selection of the compound (b) as defined above, the same applies as set out above in respect of the first aspect of the invention. Preference is given to compounds (b) that are selected from the above compound (b) identified as preferred in respect of the first aspect of the invention. In the case of use of compound (b) in the fifth aspect of the invention, it is preferable that the coating or composition for production of such a coating further comprises

[0126] - (i) one or more refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite

[0127] - (ii) optionally one or more refractories selected from the group of the swellable layered silicates and the zeolites.

[0128] With regard to the selection of the refractories (i) and (ii), the same applies as set out above in respect of the first aspect of the invention.

[0129] A sixth aspect of the invention relates to a kit for production of a mold or core for metal casting according to the third aspect of the invention as defined above. A kit of the invention comprises

[0130] - (A) a composition as described above for the first aspect of the invention, where 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,

[0131] - (B) a binder that emits formaldehyde when heated, wherein constituents (A) and (B) are separated from one another in the kit.

[0132] Within the kit of the invention, there is no possibility of contact of constituents of component (A) with constituents of component (B), for example in that component (A) on the one hand and component (B) on the other hand are each provided in a separate container, or in that component (A) on the one hand and component (B) on the other hand are each provided in a separate chamber of a container.

[0133] In the kit of the invention, the composition (A) is preferably selected from the solid mixtures and concentrates that contain the constituents (a) and (b) and optionally (c)-(h) that are preferred in the first aspect of the invention. In the kit of the invention, the binder (B) is preferably selected from the group consisting of

[0134] - two-component systems comprising a phenol-formaldehyde resin and a polyisocyanate to form a polyurethane

[0135] - two-component systems comprising an aqueous alkaline phenol-formaldehyde resin solution and an ester based liquid hardener

[0136] - formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins, melamine-formaldehyde resins, or any combination thereof.

[0137] The binder is more preferably selected from the group consisting of

[0138] - polyurethanes formed by polyaddition of a phenol-formaldehyde resin with polyisocyanate

[0139] - phenol-formaldehyde resins and

[0140] - furan-formaldehyde resins.

[0141] The invention is elucidated hereinafter by working examples.

[0142] WORKING EXAMPLES

[0143] The invention will be now described in more detail with reference to the following examples, whose purpose are merely illustrative and not intended to limit the scope of the invention. The following coating compositions are described when applied to cores, however this was for ease of testing. The coating compositions will perform the same when applied to a mold.

[0144] Measuring formaldehyde content

[0145] A coating composition, as detailed below, was applied to a core to form a coating.

[0146] Subsequently, the core was dried in a drying cabinet (Heraeus T5028 oven) at a temperature of 250°C. During drying, samples were taken at particular times from the oven air by means of a probe and the formaldehyde content therein was determined by a method according to Gasmet and Hach Lange. The method is further outlined below.

[0147] The formaldehyde content measurement method uses a Gasmet analyser which determines and quantifies the components in a gas stream at the exhaust of an oven. The fumes emitted from the oven during drying were collected in two gas wash bottles which were each filled with 50 ml of demineralized water and the concentration was measured from the total 100 ml. The maximum temperature of the gas stream was 180°C.

[0148] In the experiments carried out, each measurement lasted around 60 minutes and the measuring temperature was 150°C.

[0149] The results obtained in ppm can be converted to mg / m3, if desired, using the formula below:

[0150] Conversion of ppm to mg / m3

[0151] [mg / m3] = [ppm] * Mw * 0.0409

[0152] [mg / m3] = concentration in mg / m3

[0153] [ppm] = concentration in ppm Mw = molar mass of concerning gas in g / mol

[0154] 0.0409 = conversion factor mol air to m3

[0155] The gas concentration is then converted to gas concentration per gram sample by plotting a graph of the concentration per gram sample against time. A determination of the average gas concentration per gram sample over a desired time frame and the maximum gas concentration per gram sample can then be made.

[0156] Calculation of the total amount of emitted gas m(gas) = avg. [mg / m3g] * test time *flow / 1000 m(gas) = mass emitted gas per gram sample avg. [mg / m3g] = average concentration per gram sample test time = (min) flow = 4 L / min conversion litre to m3= 1000

[0157] After measuring the gas concentration as outlined above, the concentration of formaldehyde can be measured using a Hach Lange spectrophotometer using the equation below:

[0158] Calculation of the amount of formaldehyde

[0159] Hach Lange result (mg / 1) * V (=0.11) * 1000) / (mass sample (g) * time (min) * flow (l / min) ) = formaldehyde (mg / m3g).

[0160] Preparation of the inventive coating composition

[0161] The following section details how the coating composition according to the invention was prepared. Table 1 shows the various component parts (a to h) and their respective amounts in the inventive composition. The examples relate to the preparation of cores, although they can equally apply to the preparation of molds.

[0162] Table 1

[0163] Com. = commercial

[0164] Table 2a Table 2b

[0165] In each of the examples E3 to E9c, the layer thickness of the coating composition when applied to a core is between 225 pm and 278 pm. If lower than 225 pm then the coating comprises too much carrier liquid, e.g. water, and needs to be made more concentrated. If it is higher than 278 pm, it needs more carrier liquid. The Applicant noted that the coating prepared with ammonium chloride and ammonium citrate remained unchanged after 6 months.

[0166] Table 3 shows a comparative overview of the layer thickness and the formaldehyde concentration of the inventive compositions (E8a-E9c) and the comparative examples (E1-E7).

[0167] Table 3

[0168]

[0169] These results show that the NIL group acts as an effective formaldehyde scavenger. The Applicant has herein discovered that ammonium citrate and ammonium chloride give comparable, if not even better results in terms of reducing formaldehyde production upon burning compared to the prior art and commercial formaldehyde scavengers. E8a (ammonium citrate) and E9a (ammonium chloride) each at 3.9 wt.% produce 0.03 and 0.04 mg / m3.g formaldehyde respectively whilst examples E5 to E7, at the same wt.% of scavenger component produce between 0.04 to 0.09 mg / m3.g formaldehyde. Furthermore, the Applicant has found that when using ammonium citrate or ammonium chloride as a formaldehyde scavenger in a coating for core or mold, there are no casting defects compared to a coating using the prior art or commercial formaldehyde scavengers.

[0170] It appears that a higher concentration of ammonium citrate or ammonium chloride leads to an increase in formaldehyde removal and thus a lower concentration of formaldehyde produced.

[0171] Ammonium chloride as scavenger gives particularly interesting results, especially in terms of price. Both ammonium chloride and ammonium citrate are significantly cheaper than other currently available scavengers. Thus, to obtain the same level of formaldehyde removal, even though more ammonium chloride or ammonium citrate may be required, it is still a cheaper alternative compared to other prior art or commercial formaldehyde scavengers. More importantly, ammonium chloride and ammonium citrate are less harmful to use and thereby reduce health risks to the user. The Applicant has found that by using ammonium chloride or ammonium citrate as a formaldehyde scavenger, they can achieve comparable, if not better results to those of the prior art or commercial scavengers. Moreover, the Applicant has found that ammonium chloride and ammonium citrate provide a longer lasting coating and therefore, a longer lasting scavenger effect. Therefore, the Applicant has found alternative formaldehyde scavengers that provide significant advantages over the current state of the art. These alternative scavengers serve to reduce the concentration of formaldehyde to the lowest levels currently known, yet they are cheaper, longer lasting, as well as more user friendly.

[0172] What is herein described and illustrated by the above examples, is the use of particular compounds as formaldehyde scavengers in a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation, and the use of a composition containing one or more of these compounds for production of a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation. Also described are corresponding molds and cores and the production thereof.

Claims

CLAIMS1. A composition for producing a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation, wherein the composition comprises:(a) particles of one or more refractories(b) at least one ammonium salt [compound (b)] where the total mass of compounds (b) is 0.1% by weight to 10% by weight, based on the total mass of the particles (a) of the refractories,(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, 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 is an ammonium salt of formula (R)4N+A‘, wherein R is selected from the group consisting of hydrogen, Ci-4 alkyl, and phenyl and wherein A is an anion selected from the group consisting of trifluoroacetate, acetate, benzenesulfonate, benzoate, bicarbonate, bitartrate, bromide, carbonate, chloride, citrate, dihydrochloride, formiate, hydrobromide, hydrochloride, methyl sulfate, nitrate, oxalate, phosphate and sulfate. .

4. A composition according to any one of claims 1 to 3, wherein the refractories (a) comprise:(i) one or more refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite, and(ii) one or more refractories 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.

5. A mold or core for metal casting, comprising a main body that emits formaldehyde when heated, and a coating disposed on the main body, which forms a surface of the mold or core that comes into contact with a metal melt in the casting operation, wherein the coating comprises:(a) particles of one or more refractories(b) at least one ammonium salt [compound (b)] and / or reaction products thereof with formaldehyde, wherein the total mass of the free compounds (b) and of those bound in reaction products with formaldehyde in the coating is 0.1% to 10% by weight, based on the total mass of the particles (a) in the refractories.

6. A mold or core for metal casting according to claim 5, wherein the at least one ammonium salt is an ammonium salt of formula (R)4N+A‘, wherein R is selected from the group consisting of hydrogen, Ci-4 alkyl, and phenyl and wherein A is an anion selected from the group consisting of trifluoroacetate, acetate, benzenesulfonate, benzoate, bicarbonate, bitartrate, bromide, carbonate, chloride, citrate, dihydrochloride, formiate, hydrobromide, hydrochloride, methyl sulfate, nitrate, oxalate, phosphate and sulfate.

7. A mold or core for metal casting according to claim 5 or claim 6, wherein the refractories (a) comprise:(i) one or more refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite, and(ii) one or more refractories selected from the group of the swellable layered silicates and the zeolites.

8. A mold or core for metal casting according to any one of claims 5 to 7, wherein the main body of the mold or core has been formed from a molding material mixture that has been bound with at least one binder that emits formaldehyde when heated, the binder being selected from the group consisting of: polyurethanes formed by polyaddition of a phenol-formaldehyde resin with a polyisocyanate, and formaldehyde condensation resins selected from the group consisting of phenolformaldehyde 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 coating has a thickness in the range from 0.05 mm to 0.6 mm.

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

11. The method according to claim 10, wherein the at least one ammonium salt is an ammonium salt of formula (R)4N+A‘, wherein R is selected from the group consisting of hydrogen, Ci-4 alkyl, and phenyl and wherein A is an anion selected from the group consisting of trifluoroacetate, acetate, benzenesulfonate, benzoate, bicarbonate, bitartrate, bromide, carbonate, chloride, citrate, dihydrochloride, formiate, hydrobromide, hydrochloride, methyl sulfate, nitrate, oxalate, phosphate and sulfate.

12. The method according to claim 10 or claim 11, wherein the refractories (a) comprise:(i) one or more refractories selected from the group consisting of quartz, alumina, zirconia, aluminum silicates, nonswellable layered silicates, zirconium silicates, olivine, talc, mica, graphite, coke, feldspar, diatomite, kaolins, calcined kaolins, metakaolinite, iron oxide and bauxite and(ii) one or more refractories 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.

13. The method according to any one of claims 10 to 12, wherein the total mass of the carrier liquid (c) is 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 main body of the mold or core has been formed from a molding material mixture that has been bound with at least one binder that emits formaldehyde when heated, the binder being selected from the group consisting of: polyurethanes formed by polyaddition of a phenol-formaldehyde resin with a polyisocyanate, and condensation resins selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins.

5. A use of at least one ammonium salt (compound (b)) as formaldehyde scavenger in a coating on a main body of a mold or core for metal casting that emits formaldehyde when heated, wherein the coating forms a surface of the mold or core that comes into contact with a metal melt in the casting operation, or in a composition for production of such a coating or for production of such a composition.

Images