FORMALDEHYDE SCAVENGER FOR BINDER SYSTEMS

Abstract

A description is given of a binder system, intended more particularly for use in a process from the group consisting of polyurethane cold-box processes and polyurethane no-bake processes.

Claims

1. A binder system comprising (i) a phenolic resin component comprising a) one or more phenolic resins b) a solvent where based on the total mass of the phenolic resin component (i), the concentration of the phenolic resins a) is 40% to 60% (ii) a polyisocyanate component comprising c) one or more isocyanates having at least two isocyanate groups per molecule where based on the total mass of the polyisocyanate component (ii), the concentration of the isocyanates c) is 60% to 100% (iii) a further component comprising e) one or more substances selected from the group consisting of amino acids and urea where based on the total mass of component (iii), the total concentration of the substances e) selected from the group consisting of amino acids and urea is 0.1% to 100%, where components (i), (ii) and (iii) are spatially separate from one another.

2. The binder system as claimed in claim 1, wherein the amino acids e) are selected from the group consisting of alanine, glycine, isoleucine, methionine, proline, valine, histidine, phenylalanine, tryptophan, tyrosine, asparagine, glutamine, cysteine, methionine, serine, threonine, tyrosine, lysine, arginine and histidine.

3. The binder system as claimed in claim 1, wherein, in the phenolic resin component (i) a) the phenolic resin is an ortho, ortho′-fused resole containing unetherified terminal methylol groups and/or etherified terminal methylol groups and/or b) the solvent is selected from the group consisting of dialkyl esters of C.sub.4-C.sub.6 dicarboxylic acids, saturated and unsaturated fatty acid alkyl esters, alkylene carbonates, substances from the group consisting of cashew nut shell oil, components of cashew nut shell oil and derivatives of cashew nut shell oil, liquid hydrocarbons, compounds from the group of the alkylsilanes, alkyl/alkoxysilanes, alkoxysilanes, alkylsiloxanes, alkyl/alkoxysiloxanes and alkoxysiloxanes of the formula (I) ##STR00012## where n is an integer from 0 to 20, and each R independently of the other Rs is selected from the group of the alkyl groups having one to 6 carbon atoms and alkoxy groups having one to 6 carbon atoms and mixtures thereof.

4. The binder system as claimed in claim 1, wherein the phenolic resin component (i) further comprises g) molecular formaldehyde in a concentration of less than 0.1%, and/or h) one or more β-dicarbonyl compounds and reaction products formed by reacting these β-dicarbonyl compounds with formaldehyde and/or i) monomeric compounds from the group of the phenols in a concentration of 10% or less, where the concentrations are based in each case on the total mass of the phenolic resin component (i).

5. The binder system as claimed in claim 1, wherein in the polyisocyanate component (ii) c) the isocyanates having at least two isocyanate groups per molecule are selected from the group consisting of methylenebis(phenyl isocyanates), polymethylene polyphenyl isocyanates, aliphatic isocyanates, cycloaliphatic isocyanates, isocyanates having at least two isocyanate groups and one carbodiimide group per molecule, isocyanates having at least two isocyanate groups and urethonimine group per molecule, and/or the polyisocyanate component (ii) additionally comprises d) a solvent, where the solvent is preferably selected from the group consisting of dialkyl esters of C.sub.4-C.sub.6 dicarboxylic acids, saturated and unsaturated fatty acid alkyl esters, alkylene carbonates, liquid hydrocarbons compounds from the group of the alkylsilanes, alkyl/alkoxysilanes, alkoxysilanes, alkylsiloxanes, alkyl/alkoxysiloxanes and alkoxysiloxanes of the formula (I) ##STR00013## where n is an integer from 0 to 20, and each R, independently of the other Rs, is selected from the group of the alkyl groups having one to 6 carbon atoms and the alkoxy groups having one to 6 carbon atoms and mixtures thereof and/or the polyisocyanate component (ii) additionally comprises m) one or more β-dicarbonyl compounds, where based on the total mass of the polyisocyanate component, the concentration of β-dicarbonyl compounds) is 1% to 38%.

6. A molding material mixture comprising a molding material base and also components (i), (ii) and (iii) of a binder system as claimed in claim 1.

7. The molding material mixture as claimed in claim 6, further comprising one or more reaction products of formaldehyde with one or more substances e) selected from the group consisting of amino acids and urea.

8. The molding material mixture as claimed in claim 6, wherein the molding material mixture comprises unreacted substances e) selected from the group consisting of amino acids and urea and substances e), bound in reaction products with formaldehyde, selected from the group consisting of amino acids and urea.

9. The molding material mixture as claimed in claim 6, wherein the total amount of unreacted substances e) selected from the group consisting of amino acids and urea and substances e), bound in reaction products with formaldehyde, selected from the group consisting of amino acids and urea is 0.1% to 5.0%, based on the total mass of the molding material mixture.

10. A process for producing a molding, wherein the process comprises the steps of: producing a molding material mixture by mixing a molding material base with components (i), (ii) and (iii) of a binder system as claimed in claim 1, molding the molding material mixture, curing the binder system in the molded molding material mixture, to form a molding.

11. The process as claimed in claim 10, wherein the molding material mixture is produced by metering components (i) and (ii) of the binder system such that the total concentration of components (i) and (ii) of the binder system is 0.6% to 14%, based on the total mass of the molding material mixture, and/or metering components (i) and (ii) of the binder system such that the stoichiometric ratio of isocyanate groups in the isocyanates c) to hydroxyl groups in the phenolic resins a) is in the range from 0.5 to 1.5, and/or metering component (iii) of the binder system such that the total amount of substances e) selected from the group consisting of amino acids and urea is 0.1% to 5.0%, based on the total mass of the molding material mixture.

12. The process as claimed in claim 10, wherein the concentration of the substances e) introduced into the molding material mixture with component (iii), selected from the group consisting of amino acids and urea, is set such that there is a molar excess relative to the amount of molecular formaldehyde g) introduced into the molding material mixture with the phenolic resin component (i).

13. The process as claimed in claim 10, wherein the binder system is cured in the molded molding material mixture by contacting the molded molding material mixture with a gaseous tertiary amine or with a mixture of two or more gaseous tertiary amines or with a liquid amine or with a mixture of two or more liquid amines.

14. The process as claimed in claim 10, comprising the steps of producing the molding material mixture by mixing a molding material base with components (i), (ii) and (iii) of the binder system, molding the molding material mixture, and curing the binder system in the molded molding material mixture, to give a molding, applying a coating composition comprising particles of one or more refractories, dispersed in a carrier liquid, to the molding, to form a coated molding whose surface has regions provided with the coating composition, thermally treating the coated molding at a temperature in the range from 50° to 200° C., forming an article from the group consisting of foundry molds and foundry cores, the surface of which has regions in which a coating comprising particles of one or more refractories is disposed.

15. An article from the group consisting of foundry molds and foundry cores producible by a process as claimed in claim 10 and/or comprising a molding which comprises a molding material base bound by a polyurethane formed by curing the binder system and also one or more substances e) selected from the group consisting of amino acids and urea, and/or one or more reaction products of one or more substances e) selected from the group consisting of amino acids and urea with formaldehyde.

16. The article as claimed in claim 15, wherein the surface of the article has regions in which a coating comprising particles of one or more refractories is disposed.

17. The use of e) substances selected from the group consisting of amino acids and urea for producing a binder system as claimed in claim 1.

18. The use of substances selected from the group consisting of amino acids and urea for binding the molecular formaldehyde, released from a molding under thermal loading, by forming nonvolatile reaction products, wherein the molding comprises a molding material base which is bound by a polyurethane formed by curing a binder system as claimed in claim 1.

Description

[0385] Further aspects of the present invention relate to [0386] the use of substances e) selected from the group consisting of amino acids and urea, especially glycine, for producing binder systems according to the above-described first aspect of the invention, and for producing molding material mixtures according to the above-described second aspect of the present invention [0387] the use of a binder system according to the above-described first aspect of the invention for producing articles from the group consisting of foundry molds, foundry cores and feeders, [0388] the use of a binder system according to the above-described first aspect of the invention in a process according to the above-described third aspect of the invention, where in the process of the invention the molding formed by curing the binder system in the molded molding material mixture may be subjected to further working with supply of heat, [0389] the use of a binder system according to the above-described first aspect of the invention in a process according to the above-described third aspect of the invention, where the process of the invention may comprise a further step of working, in which there is thermal treatment of the molding formed by curing the binder system in the molded molding material mixture. [0390] the use of substances selected from the group consisting of amino acids and urea for binding the molecular formaldehyde released from a molding on thermal exposure, by formation of nonvolatile reaction products, where the molding comprises a molding material base which is bound by a polyurethane formed by curing a binder system according to the first aspect of the invention as described above, preferably a molding material base bound by a cured polyurethane formed from the phenolic resin of the phenolic resin component (i) and from the polyisocyanate of the polyisocyanate component (ii) of a binder system according to the first aspect of the invention as described above. The molding material base preferably comprises a fraction of recycled foundry sand.

[0391] The above observations regarding the first aspect of the present invention are valid in respect of preferred substances e) selected from the group consisting of amino acids and urea.

[0392] The above observations regarding the first aspect of the present invention are valid in relation to preferred features and embodiments of the binder system.

[0393] The above observations regarding the third aspect of the present invention are valid in respect of preferred features, versions and variants of the process.

[0394] The invention is elucidated further hereinafter with working examples and comparative examples.

1. COMPOSITION OF THE BINDER SYSTEMS

[0395] The figures in % are based respectively on the total mass of the phenolic resin component (i), of the polyisocyanate component (ii) and/or of component (iii). The components are spatially separate from one another, meaning that they are present in separate containers.

Binder System I

[0396]

TABLE-US-00003 Phenolic resin component (i): Phenolic resin a) ortho, ortho′-fused resole with terminal methylol groups —CH.sub.2OH and also methanol-etherified terminal methylol groups —CH.sub.2OCH.sub.3, 54.5% Solvent b) mixture of dialkyl esters of C.sub.4-C.sub.6 dicarboxylic acids and rapeseed oil methyl ester- Isocyanate component (ii) Isocyanate: c) polymeric MDI, 85% Solvent d) rapeseed oil methyl ester

Binder System II

[0397]

TABLE-US-00004 Phenolic resin component (i): Phenolic resin a) ortho, ortho′-fused resole with terminal methylol groups —CH.sub.2OH and also methanol-etherified terminal methylol groups —CH.sub.2OCH.sub.3, 53.5% Solvent b) mixture of dialkyl esters of C.sub.4-C.sub.6 dicarboxylic acids and rapeseed oil methyl ester Isocyanate component (ii) Isocyanate: c) polymeric MDI, 80% Solvent d) tetraethyl silicate

Binder System III

[0398]

TABLE-US-00005 Phenolic resin component (i): Phenolic resin a) ortho, ortho′-fused resole with terminal methylol groups —CH.sub.2OH and also methanol-etherified terminal methylol groups —CH.sub.2OCH.sub.3, 52% Solvent b) mixture of dialkyl esters of C.sub.4-C.sub.6 dicarboxylic acids and aromatic hydrocarbons Isocyanate component (ii) Isocyanate: c) polymeric MDI, 81% Solvent d) C.sub.10-C.sub.13 alkylbenzene

[0399] The noninventive variant for each of the binder systems I, II and III consists of components (i) and (ii) as indicated above, with the components being spatially separate from one another, i.e., present in separate containers.

[0400] For binder system I, different inventive variants were tested, differing in the composition of component (iii), which was provided in a separate container in each case. The concentration of the glycine is based in each case on the total mass of component (iii).

TABLE-US-00006 Component (iii) variant 1 Amino acid e) glycine 100% Component (iii) variant 2 Amino acid e) glycine 25% Further constituents f) Sand H32 Component (iii) variant 3 Amino acid e) glycine 25% Further constituents f) wood flour, iron oxide,

[0401] mixed with a composition corresponding to phenolic resin component (i) of the binder system I as indicated above, with the solids fraction in component (iii) as per variant 3 being at least 80%, based on the total mass of component (iii) as per variant 3.

TABLE-US-00007 Component (iii) variant 4a Amino acid e) glycine 25% Further constituents f) starch, iron oxide Component (iii) variant 4b Amino acid e) glycine 50% Further constituents f) starch, iron oxide,

[0402] The further constituents f) of variants 3, 4a and 4b of component (iii) are customary constituents of additive mixtures for molding material mixtures. Such additives are prior art, being used, for example, to prevent casting defects. For comparison, noninventive molding material mixtures were produced, substituting for component (iii) a comparative additive 3 or 4, respectively, each containing the aforesaid further constituents of variant 3 or 4a and 4b of component (iii), but no substances from the group consisting of urea and amino acids. In comparative additive 3, the further constituents of variant 3 of component (iii) are present in the same concentration ratios relative to one another as in variant 3 of component (iii). In comparative additive 4, the further constituents of variant 4a and 4b of component (iii) are present in the same concentration ratios relative to one another as in variant 4a and 4b of component (iii).

[0403] In the inventive variant of binder system II and III, respectively, component (iii) as per the above-described variant 1 was employed.

2. PRODUCTION OF TEST SPECIMENS (COLD BOX PROCESS)

[0404] Molding material mixtures comprising H32 silica sand as molding material base and also one (inventive or noninventive) variant in each case of one of the binder systems I, II and III described in section 1 were used to produce test specimens in the form of flexural bars (186 mm×22 mm×11 mm) by the cold box process.

[0405] To produce the molding material mixture, the molding material base (100 parts by mass) was charged to a mixing vessel. The phenolic resin component (i) (0.7 part by mass) and the polyisocyanate component (ii) (0.7 part by mass) of the respective binder system and, where appropriate, component (iii) (for parts by mass see tables below), or a comparative additive as described above, were then weighed out into the mixing vessel in such a way as to avoid direct mixing of the ingredients. The molding material base, phenolic resin component (i), polyisocyanate component (ii), and, where appropriate, component (iii) (for parts by mass see tables below), or comparative additive, were mixed in a bull mixer for 120 seconds at level 4 to give a molding material mixture.

[0406] The molding material mixture was molded using a Multiserw core shooting machine at a shooting pressure of 4 bar (400 kPa). To cure the binder system in the molded molding material mixture, the mixture was gassed for 10 seconds with dimethylpropyl amine (in a carrier gas stream) at a temperature in the range from 20 to 30° C. with a gassing pressure of 2 bar (200 kPa) by means of a Titronic 110 Plus gassing device.

3. MEASUREMENT OF FORMALDEHYDE EMISSIONS ON THERMAL TREATMENT

[0407] Selected test specimens without a coating based on a refractory coating were exposed to a temperature of 177° C. in a tubular oven. One minute after the test specimens had been introduced into the oven heated to 177° C., measurement of the concentration of formaldehyde in the oven air was commenced. For this purpose, air is withdrawn from the tubular oven through an LpDNPH cartridge (LpDNPH Cartridge S10 volume 3 mL from Supelco) at a volume flow rate of 1.5 L/min, using a Xact 5000 pump (from Drager) for 10 minutes. The cartridge was analyzed by HPLC according to DIN 16000-3. The results of the measurements are collated in tables 1 to 3 below.

4. MEASUREMENTS OF FLEXURAL STRENGTH

[0408] To ensure that the addition of glycine to the molding material mixture has no adverse effect on the strength of moldings produced with the binder systems I to III, flexural strengths were ascertained for the test specimens produced with different variants of the binder systems I to III, as a function of various parameters (time after the end of curing, storage time of the molding material mixture prior to molding, storage conditions of the test specimens produced, coating based on a refractory coating). Each determination was made on a separately produced test specimen. The results of the measurements are collated in tables 1 and 2 below. The terms in these tables have the following meanings:

[0409] B-1h: Test specimen dipped in refractory coating composition immediately after curing, stored at room temperature in a digester, tested after 1 hour.

[0410] B-24h: Test specimen dipped in refractory coating composition immediately after curing, stored at room temperature in a digester, tested after 24 hours.

[0411] B-72h: Test specimen dipped in refractory coating composition immediately after curing, stored at room temperature in a digester, tested after 72 hours.

[0412] D-1 h: Test specimen dipped in refractory coating composition immediately after curing, dried in the oven at 150° C. for 1 hour, tested after cooling to room temperature.

[0413] The refractory coating composition comprises in each case water as carrier liquid and particles of aluminum silicate as refractory.

[0414] F-24h: Test specimen stored immediately after curing at 100% relative humidity at room temperature for 24 hours and tested immediately on removal from storage.

[0415] F-72h: Test specimen stored immediately after curing at 100% relative humidity at room temperature for 72 hours and tested immediately on removal from storage.

5. SUMMARY OF RESULTS

[0416] In the binder systems tested, a reduction in formaldehyde emissions of around 20 to 50% was achieved, with sufficient flexural strengths, using glycine as amino acid e) in component (iii). The amount of amino acid e) added is preferably 0.1 to 3 parts by mass, more preferably 0.25 to 2 parts by mass, based on 100 parts by mass of molding material base (see table 1).

[0417] As far as the reduction in formaldehyde emissions is concerned, it makes no substantial difference whether the amino acid e) has been added in pure form (variant 1), or as part of a mixture with a molding material base (variant 2), or as part of a mixture with constituents of typical additive mixtures for molding material mixtures (variants 3, 4a, 4b), see table 3. The addition of the amino acid e) as part of a mixture with one or more further constituents f), which are present in any case in the desired molding material mixture (e.g., the respective molding material base, or the respective phenolic resin component), or which are typically added to the desired molding material mixture (e.g., additive mixtures for preventing casting defects), has practical advantages, as the addition and metering of the amino acid e) is facilitated.

6. FURTHER EXAMPLES

[0418] In-house investigations showed that other amino acids, particularly from the group consisting of glutamine, alanine, valine and serine, and also urea, have a similar effect in the reduction of formaldehyde emissions.

TABLE-US-00008 TABLE 1 Test results for binder system I without component (iii) and, respectively, with component (iii) as per variant 1 Glycine concentration in molding 0 0.1 0.5 1.0 2.0 3.0 material mixture [parts by mass] Concentration of formaldehyde 6.0 4.6 4.0 3.6 3.1 3.3 [mg/m.sup.3] in oven air after 10 minutes Reduction [%] in formaldehyde — 23 33 40 48 45 concentration relative to noninventive variant without glycine Flexural strengths [N/cm.sup.2] no storage of molding material mixture prior to molding 15 s after end of curing 210 200 200 200 190 190 1 h after end of curing 350 360 350 350 350 330 24 h after end of curing 410 410 400 400 390 380 1 h storage of molding material mixture prior to molding 15 s after end of curing 200 200 190 190 190 190 1 h after end of curing 350 350 330 340 330 320 24 h after end of curing 400 390 380 380 370 360 2 h storage of molding material mixture prior to molding 15 s after end of curing 190 190 190 190 190 180 1 h after end of curing 340 340 320 320 330 310 24 h after end of curing 390 370 370 360 360 340 Test specimens with coating based on a refractory coating B- 1 h 330 330 310 290 280 260 B - 24 h 430 440 420 420 400 350 D - 1 h 530 540 520 490 510 490 Storage at 100% humidity F - 24 h 360 350 340 320 290 270

TABLE-US-00009 TABLE 2 Test results for binder systems I (different test specimens from table 1), II and III without component (iii) and, respectively, with component (iii) as per variant 1 Binder system I II III Glycine concentration in 0 1.0 0 1.0 0 1.0 molding material mixture [parts by mass] Concentration of 6.0 3.6 6.5 4.9 6.0 2.9 formaldehyde [mg/m.sup.3] in oven air after 10 minutes Reduction [%] in — 40 — 25 — 38 formaldehyde concentration relative to noninventive variant without glycine Flexural strengths [N/cm.sup.2] no storage of molding material mixture prior to molding 15 s after end of curing 210 200 270 270 250 240 1 h after end of curing 350 350 410 390 460 440 24 h after end of curing 410 400 450 420 520 490 1 h storage of molding material mixture prior to molding 15 s after end of curing 200 190 270 260 240 240 1 h after end of curing 350 340 410 380 470 450 24 h after end of curing 400 380 460 440 510 500 2 h storage of molding material mixture prior to molding 15 s after end of curing 190 190 260 240 240 240 1 h after end of curing 340 320 380 370 450 450 24 h after end of curing 390 360 420 410 490 470 Test specimens with coating based on a refractory coating B - 1 h 330 290 290 270 410 370 B - 24 h 430 420 440 430 480 460 D - 1 h 530 490 510 540 610 570 Storage at 100% humidity F - 24 h 360 320 380 350 430 390

TABLE-US-00010 TABLE 3 Formaldehyde emissions of test specimens produced with binder system I, with different variants of component (iii) Amount of Glycine Formaldehyde Component component (iii) concentration concentration (iii) or or comparative in molding [mg/m.sup.3] in comparative additive used material mixture oven air additive [parts by mass] [parts by mass] after 10 minutes — — 0 6.0 Variant 1 0.5 0.5 4.0 Variant 2 2 0.5 4.2 Variant 3 2 0.5 3.9 Comparative 2 0 6.1 additive 3 Variant 4a 1 0.25 4.9 Variant 4b 1 0.5 4.4 Comparative 1 0 additive 4