WASH COMPOSITION FOR REDUCING FORMALDEHYDE EMISSIONS

Abstract

What is described is the use of a composition containing one or more formaldehyde scavengers 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.

Claims

1. A method of production 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) one or more compounds selected from the group consisting of β-dicarbonyl compounds di- and trihydric phenols phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks amino acids primary and secondary aminosilanes melamine, benzoguanamine, urea and derivatives thereof hydrazine and carbonohydrazide and derivatives thereof primary and secondary amines tree resins, tannins and lignins  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, wherein the composition 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.

2. The method as claimed in claim 1, wherein the compounds (b) are selected from the group consisting of dialkyl esters of malonic acid, resorcinol, pyrogallol, phloroglucinol, glycine, urea, melamine, carbonohydrazide, and tannins and lignins that are soluble in the carrier liquid (c) and/or 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/or 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.

3. The method as claimed in claim 1, wherein the binder is selected from the group consisting of: polyurethanes formed by polyaddition of a phenol-formaldehyde resin with a polyisocyanate formaldehyde condensation resins selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins.

4. The method as claimed in claim 1, wherein the composition comprises one or more further constituents selected from the group consisting of (d) wetting agents, (e) rheology additives, (f) binders, (g) suspension aids, (h) biocides.

5. The method as claimed in claim 1, wherein the composition does not contain any carrier liquid (c), or contains a carrier liquid (c), wherein the total mass of the carrier liquid (c) is 40% by weight to 65% by weight based in each case on the total mass of the composition.

6. The method as claimed in claim 1, wherein the composition contains a carrier liquid (c), wherein the total mass of the carrier liquid (c) is 60% by weight to 80% by weight, based on the total mass of the composition.

7. A process for producing a composition as defined in claim 6, comprising the steps of producing or providing a composition comprising: (a) particles of one or more refractories (b) one or more compounds selected from the group consisting of β-dicarbonyl compounds, di- and trihydric phenols, phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks, amino acids, primary and secondary aminosilanes, melamine, benzoguanamine, urea and derivatives thereof, hydrazine and carbonohydrazide and derivatives thereof, primary and secondary amines, tree resins, tannins and lignins,  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) either no carrier liquid or a carrier liquid selected from the group consisting of water, alkanols and mixtures thereof, wherein a total mass of the carrier liquid is 40% by weight to 65% by weight based on a total mass of the composition; and adding a carrier liquid 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.

8. 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) one or more compounds selected from the group consisting of β-dicarbonyl compounds di- and trihydric phenols phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks amino acids primary and secondary aminosilanes melamine, benzoguanamine, urea and derivatives thereof hydrazine and carbonohydrazide and derivatives thereof primary and secondary amines tree resins, tannins and lignins 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, 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.

9. The composition as claimed in claim 8, wherein the compounds (b) are selected from the group consisting of dialkyl esters of malonic acid, resorcinol, pyrogallol, phloroglucinol, glycine, melamine, urea, carbonohydrazide, and tannins and lignins that are soluble in the carrier liquid (c) and/or 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 (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.

10. The composition as claimed in claim 8, further comprising one or more constituents selected from the group consisting of (d) wetting agents (e) rheology additives (f) binders (g) suspension aids (h) biocides.

11. 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) one or more compounds selected from the group consisting of β-dicarbonyl compounds di- and trihydric phenols phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks amino acids primary and secondary aminosilanes melamine, benzoguanamine, urea and derivatives thereof hydrazine and carbonohydrazide and derivatives thereof primary and secondary amines tree resins, tannins and lignins 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.

12. The mold or core as claimed in claim 11, wherein the compounds (b) are selected from the group consisting of dialkyl esters of malonic acid, resorcinol, pyrogallol, phloroglucinol, glycine, melamine, urea, carbonohydrazide, tannins and lignins and/or the refractories (a) 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 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.

13. The mold or core as claimed in claim 11, wherein the binder is selected from the group consisting of: polyurethanes formed by polyaddition of a phenol-formaldehyde resin with a polyisocyanate formaldehyde condensation resins selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins.

14. The mold or core as claimed in claim 11, wherein the coating has a thickness in the range from 0.05 mm to 0.6 mm.

15. A process for producing a mold or core for metal casting as claimed in claim 11, comprising the steps of producing or providing the main body producing or providing a composition applying the 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, wherein the composition comprises: (a) particles of one or more refractories (b) one or more compounds selected from the group consisting of β-dicarbonyl compounds, di- and trihydric phenols, phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks, amino acids, primary and secondary aminosilanes, melamine, benzoguanamine, urea and derivatives thereof, hydrazine and carbonohydrazide and derivatives thereof, primary and secondary amines, tree resins, tannins and lignins,  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, wherein a total mass of the carrier liquid is 60% by weight to 80% by weight based on a total mass of the composition.

16. The process as claimed in claim 15, wherein the producing of the main body of the mold or core comprises the following steps: producing or providing a molding material mixture comprising one or more mold base materials and a binder that emits formaldehyde when heated, shaping the molding material mixture curing the binder in the shaped molding material mixture to form the main body of the mold or core.

17. The process as claimed in claim 16, wherein the binder is selected from the group consisting of two-component systems comprising a phenol-formaldehyde resin and a polyisocyanate to form a polyurethane formaldehyde condensation resins selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins.

18. The process as claimed in claim 17, wherein the binder is a two-component system comprising a phenol-formaldehyde resin and a polyisocyanate to form a polyurethane and 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.

19. The process as claimed in claim 15, wherein the composition is applied to the main body by a process selected from the group consisting of spraying, dipping, flow coating and painting.

20. The process as claimed in claim 15, wherein the drying is effected at a temperature in the range from 50° C. to 200° C.

21-22. (canceled)

23. A kit for producing a mold or core for metal casting as defined in claim 11, wherein the kit comprises (A) a composition comprising, (a) particles of one or more refractories (b) one or more compounds selected from the group consisting of β-dicarbonyl compounds di- and trihydric phenols phenol-formaldehyde novolaks and resorcinol-formaldehyde novolaks amino acids primary and secondary aminosilanes melamine, benzoguanamine, urea and derivatives thereof hydrazine and carbonohydrazide and derivatives thereof primary and secondary amines tree resins, tannins and lignins  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, (B) a binder that emits formaldehyde when heated, wherein constituents (A) and (B) are separated from one another in the kit.

24. The kit as claimed in claim 23, wherein the binder is selected from the group consisting of two-component systems comprising a phenol-formaldehyde resin and a polyisocyanate to form a polyurethane formaldehyde condensation resins, preferably selected from the group consisting of phenol-formaldehyde resins, furan-formaldehyde resins, urea-formaldehyde resins and melamine-formaldehyde resins.

Description

WORKING EXAMPLES

[0186] A molding material mixture comprising H32 sand as mold base material and a two-component binder system customary for core production, comprising a phenol-formaldehyde resin and a polyisocyanate for formation of a polyurethane, was used in the customary manner, by means of a core shooting machine, to shape main bodies for brake disk cores, and these were cured in the customary manner by sparging with tertiary amine (cold box process). Subsequently, a coating is produced on the main core bodies thus produced by applying an inventive composition (inventive refractory coating composition) or a comparative composition (comparative refractory coating composition) that does not contain any of the compounds (b) for use in accordance with the invention. This coating forms the surface of the core that comes into contact with the metal melt in the casting operation. Subsequently, the cores were dried in a drying cabinet (Memmert UFP 700). During the drying, at particular times, samples were taken from the oven air by means of a probe and the formaldehyde content therein was determined by an in-house method (see below for details). For comparison, cores produced in the same way without coating (comparative cores with no refractory coating) were dried in the drying cabinet, and the amount of formaldehyde emitted was measured in the same way.

[0187] In a first test series, the effect of drying temperature on the emissions of formaldehyde from comparative cores without refractory coating was examined. The molding material mixture used to produce the cores for this test series contained 0.8% by weight of phenol-formaldehyde resin and 0.8% by weight of polyisocyanate.

[0188] During the drying, at particular times, samples were taken from the oven air and the formaldehyde content therein was determined. For this purpose, over the period from commencement of drying to the first measurement time (1 min) and from one measurement time to the next measurement time in each case (drying time 5, 10, 15, 20, 25 and 30 min), by means of a pump Xact 5000 (Dräger), 1.5 l of air was drawn by means of a probe from the oven into a fast detector tube (Drager) for formaldehyde (0.2 to 5 ppm), and the formaldehyde concentration was ascertained.

[0189] The The formaldehyde content (in ppm) ascertained at particular times during the drying is reported in the following table:

TABLE-US-00001 Formaldehyde content [ppm] after x [min] Oven temperature 1 5 10 15 20 25 30 [° C.] min min min min min min min 180° C. 1.5 2.5 3.0 5.0 5.0 4.0 3.0 150° C. 0.0 1.0 1.0 1.0 1.0 1.5 1.5 100° C. 0.0 0.0 0.5 0.5 0.5 0.5 0.5

[0190] This test series shows that the amount of formaldehyde emitted rises with increasing drying temperature (FIG. 1).

[0191] In a second test series, the influence of the composition of the refractory coating (core El with inventive refractory coating composition and core V2 with comparative refractory coating composition) on formaldehyde emissions during drying (30 minutes at 180° C.) was examined. The molding material mixture used to produce the cores for this test series contained 0.8% by weight of phenol-formaldehyde resin and 0.8% by weight of polyisocyanate, based in each case on the mass of the mold base material (H32 sand). The inventive refractory coating composition contained resorcinol as compound (b). For comparison, a comparative core V1 without refractory coating was dried under the same conditions.

[0192] The comparative refractory coating composition is as follows:

TABLE-US-00002 Proportion Constituent [% by wt.] Refractories (i) 30.8 in total (aluminum silicates (nonswellable), graphite and iron oxide) Refractories (ii) 3.7 (swellable smectite-containing layered silicates) Carrier liquid (c) 64 Wetting agents (d), binders (f), suspension aids (g) 1.5 in total and biocides (h)

[0193] The inventive refractory coating composition was produced by adding 3 parts by weight of resorcinol to 100 parts by weight of the comparative refractory coating.

[0194] The formaldehyde content (in ppm) ascertained as described above at particular times during the drying is reported in the following table:

TABLE-US-00003 Formaldehyde content [ppm] after x [min] Test 1 min 5 min 10 min 15 min 20 min 25 min 30 min V1 2.5 5.0 6.0 5.0 4.0 4.0 4.0 V2 0.5 1.5 3.0 3.0 3.0 3.0 2.0 E1 0.5 1.0 1.0 0.5 0.5 0.5 0.2

[0195] On drying of the comparative core V2 with the coating formed from the noninventive refractory coating, the amount of formaldehyde emitted is already lower than on drying of the comparative core V1 without refractory coating. On drying of the inventive core El (with the coating formed from the inventive refractory coating composition), however, the amount of formaldehyde emitted is much lower again (FIG. 2).

[0196] In a third test series, the influence of the amount of resorcinol as compound (b) for use in accordance with the invention on formaldehyde emissions during drying (30 minutes at 180° C.) minutes was examined. The molding material mixture used to produce the cores for this test series contained 1.0% by weight of phenol-formaldehyde resin and 1.0% by weight of polyisocyanate, based in each case on the mass of the mold base material (H32 sand). The cores E2 and E3 each have refractory coatings with different proportions of resorcinol. By way of comparison, a comparative core V3 having no refractory coating and a comparative core V4 with a coating formed from a noninventive refractory coating were dried under the same conditions.

[0197] The comparative refractory coating composition is as specified above. The inventive refractory coating compositions were produced by adding 0.8 part by weight of resorcinol (core E2) or 3 parts by weight of resorcinol (core E3) to 100 parts by weight in each case of the comparative refractory coatings.

[0198] The formaldehyde content (in ppm) ascertained as described above at particular times during the drying is reported in the following table:

TABLE-US-00004 Formaldehyde content [ppm] after x [min] Test 1 min 5 min 10 min 15 min 20 min 25 min 30 min V3 1.0 5.0 5.0 5.0 7.0 7.0 7.0 V4 0.5 2.5 3.0 3.0 3.0 3.0 2.0 E2 0 0.0 0.2 0.5 1.0 1.5 1.0 E3 0 0.0 0.0 0.2 0.5 0.5 0.5

[0199] On drying of the comparative core V4 with the coating formed from the noninventive refractory coating, the amount of formaldehyde emitted is already lower than on drying of the comparative core V3 without refractory coating. On drying of the inventive cores E2 and E3, the amount of formaldehyde emitted is much lower, and falls with increasing resorcinol content of the inventive refractory coating composition (FIG. 3).

[0200] In a fourth test series, the influence of the composition of the refractory coating (core E4; comparative refractory coating composition, cores E5-E7; various inventive refractory coating compositions) on formaldehyde emissions during drying at 200° C. was monitored over the course of 35 minutes. The molding material mixture used to produce the cores for this test series contained 1% by weight of phenol-formaldehyde resin and 1% by weight of polyisocyanate, based in each case on the mass of the mold base material (H32 sand). For comparison, a comparative core without refractory coating was dried under the same conditions.

[0201] The comparative refractory coating composition is as specified above. The inventive refractory coating compositions were produced by adding 0.9 part by weight of lignin (core E5) or 0.9 part by weight of melamine (core E6) or 3 parts by weight of resorcinol (core E7) to 100 parts by weight in each case of the comparative refractory coatings.

[0202] The formaldehyde content (in mg/cm.sup.3) ascertained at particular times during the drying is reported in the following table:

TABLE-US-00005 Formaldehyde emission in [mg/m.sup.3] Time [min] V E4 E5 E6 E7 5 3.06 0.94 0.31 0.36 0.33 10 5.42 1.10 0.10 0.59 0.63 15 5.60 1.25 0.09 0.66 0.74 20 4.81 1.48 0.07 0.98 0.86 25 4.66 1.65 0.04 1.21 0.96 30 4.77 2.90 0.08 1.50 1.13 35 4.54 1.96 0.08 1.70 1.25

[0203] On drying of all inventive cores E4-E7, the amount of formaldehyde emitted is much lower than in the case of the comparative core (FIG. 4).

[0204] Similar results were obtained with addition of glycine as compound (b).

[0205] In a further test series, the influence of glycine as formaldehyde scavenger on formaldehyde emissions during drying (30 minutes at 180° C.) was examined. For this purpose, in a customary manner, a molding material mixture containing 1% by weight of phenol-formaldehyde resin and 1% by weight of polyisocyanate, based in each case on the mass of the mold base material (H32 sand), was used to produce test specimens (cores for brake disk production) with a core shooting machine, which were cured in the customary manner by sparging with a tertiary amine (cold box process). These test specimens were provided with a refractory coating by dipping (test specimens E8 with inventive refractory coating composition or test specimens V5 with comparative refractory coating composition). The comparative refractory coating composition is as specified above. An inventive refractory coating composition was produced by adding 1 part by weight of glycine to 100 parts by weight of the comparative refractory coatings.

[0206] The test specimens provided with the refractory coating were introduced into a preheated drying oven from Elpo (internal temperature 170° C.). The air output volume removed from the drying chamber of the oven during the drying time of 10 minutes is 267 m.sup.3. The measurement of the formaldehyde concentration in the oven air began one minute after the test specimen had been introduced into the oven and the oven door had been closed. For sampling, a bar probe was introduced into the offgas tube of the drying oven. With the aid of a Dräger Xact 5000 pump, during the drying time of 10 minutes, the air was drawn out of the drying chamber at a volume flow rate of 1.5 l/min, and the sample volume drawn was guided through LpDNPH cartridges (LpDNPH Cartridge S10 from Supelco). Analysis was effected by means of HPLC analogously to DIN 16000-3.

TABLE-US-00006 mg formaldehyde/m.sup.3 output air Test in 10 minutes of drying time V5 0.82 100% E8 0.51  62%

[0207] On drying of the inventive test specimen E8 (with the coating formed from the inventive refractory coating composition), the concentration of formaldehyde in the output air from the oven is reduced by more than one third compared to the comparative test specimen V5 with the coating formed from the noninventive refractory coating.