COMPOSITION CONTAINING FURFURYL SILICATES AND FURFURYL ALCOHOL

Abstract

Described are a composition comprising furfuryl silicates and furfuryl alcohol, especially for use as acid-curable binder, and processes for producing such a composition.

Claims

1. Composition comprising (A) one or more compounds of the Formula (I)
Si[OR.sup.1].sub.x[OR.sup.2].sub.y   (I), in which x is an integer selected from 1, 2, 3 and 4, y is an integer selected from 0, 1, 2 and 3, where x+y=4, each of the x structural units R.sup.1 is furfuryl, and each of the y structural units R.sup.2, independently of all other structural units R.sup.2, is selected from the group of linear and branched alkyl radicals (B) furfuryl alcohol R.sup.1—OH (C) one or more alkyl alcohols R.sup.2—OH, where R.sup.2 in each case is selected from the group of linear and branched alkyl radicals (D) one or more compounds from the group consisting of alkoxides of elements from the group consisting of B, Al, Sn, Ti and Zr and organoelement compounds of elements from the group consisting of B, Al, Sn, Ti and Zr.

2. Composition according to claim 1, comprising (B) a fraction of furfuryl alcohol in the range from 1% to 40%, (C) a total fraction of alkyl alcohols R.sup.2—OH in the range from 0.5% to 10%, (D) a total fraction of elements from the group consisting of B, Al, Sn, Ti and Zr in the range from 0.01% to 0.5%, based in each case on the total mass of the composition.

3. Composition according to claim 1, in which constituent (A) is selected from those compounds of the Formula (I) in which each of the y structural units R.sup.2, independently of all other structural units R.sup.2, is selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl and isobutyl, y is an integer selected from 1, 2 and 3, and/or (C) is selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol and isobutanol, and/or (D) is selected from the group consisting of aluminium triisopropoxide, tri-n-butyl borate, tetra-n-butyl orthotitanate, tetraisopropyl titanate, tetrakis(2-ethylhexyl) titanate and dibutyltin dilaurate.

4. Process for preparing a composition according to claim 1, where the process comprises the following step: reaction of furfuryl alcohol, with one or more compounds of the Formula (II)
Si[OR.sup.2].sub.a[OR.sup.4].sub.c   (II), in which a and c are integers selected from 0, 1, 2, 3 and 4, where one of a and c is greater than 0, where a+c=4, each of the a structural units R.sup.2, independently of all other structural units R.sup.2, is selected from the group of linear and branched alkyl radicals, each of the c structural units R.sup.4, independently of all other structural units R.sup.4, is selected from the group of structural units of the formula
—(Si[OR.sup.2].sub.d—O).sub.n—Si[OR.sup.2].sub.f   (III), in which each of the d+f structural units R.sup.2, independently of all other structural units R.sup.2, is selected from the group of linear and branched alkyl radicals, d=2, f=3, n is an integer in the range from 1 to 10, at a temperature in the range from 80° C. to 150° C, in the presence of one or more compounds from the group consisting of alkoxides of elements from the group consisting of B, Al, Sn, Ti and Zr and organoelement compounds of elements from the group consisting of B, Al, Sn, Ti and Zr.

5. Process according to claim 4, where the compound of the Formula (II) is selected from the group consisting of those compounds of the Formula (II) in which (i) R.sup.2 is selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl and isobutyl, c=0, a=4; (ii) R.sup.2 is selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl and isobutyl, a=3,c=1, R.sup.4 is selected from the group consisting of those structural units of the Formula (III) in which R.sup.2 is selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl and isobutyl, d=2, f=3, n is an integer in the range from 1 to 10.

6. Process according to claim 4, where an amount of substance of 1 mol to 5 mol of furfuryl alcohol per mole of silicon bonded in the compounds of the Fotmula (II) is used, and/or a total amount of substance of 0.001 mol to 0.05 mol of compounds from the group consisting of alkoxides of elements from the group consisting of B, Al, Sn, Ti and Zr and organoelement compounds of elements from the group consisting of B, Al, Sn, Ti and Zr per mole of silicon bonded in the compounds of the Formula (II) is used.

7. (canceled)

8. Reaction mixture for forming an acid-cured binder, comprising (i) a composition according to claim 1 (ii) an activator comprising a) one or more acids from the group consisting of sulfonic acids and phosphoric acid, b) optionally, one or more acids from the group of carboxylic acids, c) water, d) and, optionally, one or more compounds from the group consisting of monoethylene glycol, diethylene glycol, polyethylene glycol and 1,2-propylene glycol.

9. Reaction mixture according to claim 8, further comprising (iii) one or more refractory granular substances in an amount of 80% or more based on the total mass of the reaction mixture.

10. Process for producing an article selected from the group consisting of foundry cores, foundry moulds and feeders, comprising producing a moulding mixture comprising (i) a composition according to claim 1, (ii) an activator comprising: a) one or more acids from the group consisting of sulfonic acids and phosphoric acid, b) optionally one or more acids from the group of carboxylic acids, c) water, and d) optionally one or more compounds from the group consisting of monoethylene glycol, diethylene glycol, polyethylene glycol and 1,2-propylene glycol, (iii) one or more refractory granular substances, moulding the moulding mixture curing the composition (i) by the activator (ii).

11. Composition according to claim 2, wherein the fraction of furfuryl alcohol is in the range from 1% to 24%.

12. Composition according to claim 3, in which constituent (A) is selected from those compounds of the Formula (I) in which all structural units R.sup.2 are ethyl.

13. Process for preparing a composition according to claim 4, wherein the reaction of furfuryl alcohol takes place at a temperature in the range from 100° C. to 120° C.

14. Process according to claim 5, where the compound of the Formula (II) is selected from the group consisting of those compounds of the Foimula (II) in which (i) all structural units R.sup.2 are ethyl, c=0, a=4; (ii) all structural units R.sup.2 are ethyl, a=3, c=1, R.sup.4 is selected from the group consisting of those structural units of the Formula (III) in which all structural units R.sup.2 are ethyl, d=2, f=3, n is an integer in the range from 1 to 10.

15. Process according to claim 6, where an amount of substance of 1.53 mol to 5 mol of furfuryl alcohol per mole of silicon bonded in the compounds of the Formula (II) is used.

16. Process according to claim 6, where an amount of substance of 2.1 mol to 5 mol of furfuryl alcohol per mole of silicon bonded in the compounds of the Formula (II) is used.

17. A method of producing an article comprising: providing a composition according to claim 1 to form a moulding mixture to produce the article, wherein the article selected from the group consisting of foundry cores, foundry moulds and feeders.

18. A method of 3D printing, comprising: providing a composition according to claim 1, and printing the composition.

19. A method of construction, comprising: providing a composition according to claim 1 to form a putty or sealant; and applying the putty of sealant.

Description

EXAMPLES

[0272] 1. Production of inventive compositions by reaction of furfuryl alcohol with a compound of the Formula (II) [0273] 1.1 Tetraethyl orthosilicate as compound of the Formula (II)

[0274] Product P1

[0275] A reaction vessel equipped with reflux condenser, thermometer and stirrer is charged with 150 g of furfuryl alcohol (FA), 100 g of tetraethyl orthosilicate (TEOS) and 2 g of tetrabutyl titanate. At the start of reaction the amount of substance ratio n(FA): n(Si bound in TEOS) is 3.2:1.0. With stirring, the mixture is heated within 8 minutes to 109° C., at which point it starts to boil. The temperature is raised continuously within 45 minutes to 120° C. and a total of 48 ml of volatile constituents are distilled off. Then the heating is removed and the pressure is cautiously lowered to 700 mbar. During this procedure the temperature falls briefly to around 97° C. The pressure is then lowered further down to around 400 mbar, and at the same time the temperature is raised continuously over the course of 25 minutes to 120° C. in order to distil off further volatile constituents (around 32 ml). The product obtained has a brownish colour and is clear and translucent. The yield of non-volatile product (following the distillative removal of the volatile constituents) is around 70%, based on the total mass of furfuryl alcohol, tetraethyl orthosilicate and tetrabutyl titanate introduced.

[0276] Product P2

[0277] A reaction vessel equipped with reflux condenser, thermometer and stirrer is charged with 150 g of furfuryl alcohol (FA), 100 g of tetraethyl orthosilicate (TEOS) and 3 g of tetrabutyl titanate. At the start of reaction the amount of substance ratio n(FA): n(Si bound in TEOS) was 3.2:1.0. With stirring, the mixture is heated within 2 minutes to 37° C. and the pressure is lowered to 400 mbar in order to distil off volatile constituents. The pressure is then lowered further down to around 350 mbar, and at the same time the temperature is raised continuously within 45 minutes to 110° C. in order to distil off further volatile constituents (around 76 ml). The product obtained has a brownish colour and is clear and translucent. The yield of non-volatile product (following the distillative removal of the volatile constituents) is around 76%, based on the total mass of furfuryl alcohol, tetraethyl orthosilicate and tetrabutyl titanate introduced.

[0278] Product P3

[0279] A reaction vessel equipped with reflux condenser, thermometer and stirrer is charged with 800 g of furfuryl alcohol (FA), 800 g of tetraethyl orthosilicate (TEOS) and 4 g of tetrabutyl titanate. At the start of reaction the amount of substance ratio n(FA): n(Si bound in TEOS) was 2.1:1.0. With stirring, the mixture is heated within 20 minutes to 100° C. and within a further 80 minutes continuously to 120° C. 246 g of volatile constituents are distilled off in this procedure. Then the heating is removed and the pressure is cautiously lowered to 210 mbar. During this procedure the temperature falls to around 85° C. The pressure is then held constant at 210 mbar, and at the same time the temperature is raised continuously within 60 minutes to 120° C. in order to distil off further volatile constituents. The product obtained has a brownish colour and is clear and translucent. The yield of non-volatile product (following the distillative removal of the volatile constituents) is around 76%, based on the total mass of furfuryl alcohol, tetraethyl orthosilicate and tetrabutyl titanate introduced.

[0280] 1.2 Ethyl Polysilicate as Compound of the Formula (II)

[0281] Product P4

[0282] A reaction vessel equipped with reflux condenser, thermometer and stirrer is charged with 800 g of furfuryl alcohol (FA), 800 g of ethyl polysilicate (EPS) having an arithmetic Si0.sub.2 content of 40% (obtainable as Dynasil® 40 from Evonik) and 4 g of tetrabutyl titanate. At the start of reaction the amount of substance ratio n(FA): n(Si bound in EPS) is 1.53:1.0. With stirring, the mixture is heated within 15 minutes to 103° C., at which point it starts to boil. The temperature is raised continuously within 50 minutes to 120° C. and a total of 236 g of volatile constituents are distilled off. Then the heating is removed and the pressure is cautiously lowered to 210 mbar. During this procedure the temperature falls to around 85° C. The pressure is then held constant at 210 mbar, and at the same time the temperature is raised continuously within 50 minutes to 120° C. in order to distil off further volatile constituents. The product obtained has a brownish colour and is clear and translucent. The yield of non-volatile product (following the distillative removal of the volatile constituents) is around 77%, based on the total mass of furfuryl alcohol, ethyl polysilicate and tetrabutyl titanate introduced.

[0283] Product P5

[0284] A reaction vessel equipped with reflux condenser, thermometer and stirrer is charged with 150 g of a solution of phenol-formaldehyde novolac (constituent (F) as defined above) at 30% in furfuryl alcohol, 150 g of ethyl polysilicate (EPS) having an arithmetic SiO.sub.2 content of 40% (obtainable as Dynasil® 40 from Evonik) and 3 g of dibutyltin laurate (DBTL). At the start of reaction, the amount of substance ratio n(FA): n(Si bound in EPS) is 1.53:1.0. With stirring, the mixture is heated to 127° C. within 15 minutes and continuously to 140° C. within a further 45 minutes and the temperature is subsequently held constant at 140° C. 60 ml of volatile constituents are distilled off in this procedure. The product obtained has a reddish-brown colour and is clear and translucent. The yield of non-volatile product (after the distillative removal of the volatile constituents) is around 83%, based on the total mass of phenol-formaldehyde novolac, furfuryl alcohol, ethyl polysilicate and dibutyltin laurate introduced.

[0285] 1.3 Addition of Further Constituents

[0286] Product P6

[0287] 96.1 Parts of the product P1 prepared as described above were mixed with 3.5 parts of ethanol and 0.4 part of an aminosilane (obtainable as Dynasylan 1505 from Evonik) suitable as an adhesion promoter (constituent (E) as defined above).

[0288] Product P7

[0289] 73.7 Parts of the product P1 prepared as described above were mixed with 22.4 parts of a solution of bisphenol A (constituent (F) as defined above) in furfuryl alcohol (with the solution containing 4.48 parts of bisphenol A), 3.5 parts of ethanol and 0.4 part of an aminosilane (obtainable as Dynasylan 1505 from Evonik) suitable as an adhesion promoter (constituent (E) as defined above).

[0290] Product P8

[0291] 96.1 Parts of the product P2 prepared as described above were mixed with 3.5 parts of ethanol and 0.4 part of an aminosilane (obtainable as Dynasylan 1505 from Evonik) suitable as an adhesion promoter (constituent (E) as defined above).

[0292] Products P9 to P14

[0293] Further inventive products P9 to P14 were prepared by adding the amounts of further constituents as specified in Table 1 to the amount as specified in Table 1 of the product P1 prepared as described above.

TABLE-US-00001 TABLE 1 P9 P10 P11 P12 P13 P14 Furfuryl 8.80 9.30 9.30 9.30 9.30 alcohol Product P1 99.50 87.20 84.40 83.40 83.40 83.40 Bisphenol A 2.30 2.30 2.30 2.30 Ethanol 3.50 3.50 3.50 3.50 3.50 Aminosilane 0.50 0.50 0.50 0.50 0.50 0.50 Surfactant 1 1.00 Surfactant 2 1.00 Surfactant 3 1.00

[0294] 2. Non-Inventive, Comparative Products

[0295] Comparative Product C1

[0296] The non-inventive, comparative product C1, investigated for purposes of comparison, has the composition, based on its total mass, as follows (Table 2):

TABLE-US-00002 TABLE 2 Cold resin A (for composition see below) 56.0 wt % Monomeric furfuryl alcohol 41.3 wt % Water  2.5 wt % Aminosilane  0.2 wt %

[0297] Comparative product C1 was prepared by introducing the constituents identified in Table 2 into a reactor, with stirring, and carrying out mixing for 15 minutes.

[0298] To prepare the cold resin A, a reactor is charged with 489.9 kg of furfuryl alcohol, 63.0 kg of urea, 158.8 kg of 91% paraformaldehyde, 35.6 kg of water and 49.5 kg of ethanol and this initial charge is intensively mixed. Then 4.8 kg of 85% formic acid are added and the resulting mixture is heated to 90° C. At intervals of around 30 minutes in each case, a further 62.9 kg of urea are added in portions at 90° C. This reaction mixture is subsequently cooled a little and 113.1 kg of furfuryl alcohol are added. Eventually, after further cooling to 50° C., a pH in the range from 8.1 to 8.8 is established by addition of 25% ammonia in water. Throughout the process, the reactor contents are stirred. The product thus obtained is referred to here as cold resin A. The chemical and physical parameters of the cold resin A are as follows (Table 3):

TABLE-US-00003 TABLE 3 Water content 13.5 wt % (determined by Karl-Fischer titration) Total nitrogen content 6.2 wt % (determined by elemental analysis) Formaldehyde content 0.1 wt % (determined by titration by the KCN method) Viscosity at 20° C. 95 mPa*s (determined using rotary viscometer)

[0299] Comparative Product C2

[0300] The non-inventive, comparative product C2, investigated for purposes of comparison, has the composition, based on its total mass, as follows (Table 4):

TABLE-US-00004 TABLE 4 1 Furfuryl alcohol 82.38 wt % 2 Bisphenol A 13.0 wt % 3 Resorcinol 3.0 wt % 4 Formaldehyde solution 1.0 wt % 49% strength in water 5 Surfactant 0.12 wt % 6 Aminosilane 0.5 wt %

[0301] Comparative product C2 was prepared by introducing the constituents 1-4 into a reactor, with stirring, and carrying out mixing for 30 minutes. Thereafter constituents 5 and 6 are added and the resulting mixture is mixed for a further 15 minutes.

[0302] 3. Chemical Characterization

[0303] Data on the chemical composition of inventive products P1 to P5 and comparative products C1 and C2 is compiled in Table 5.

TABLE-US-00005 TABLE 5 Free Ignition Titanium furfuryl Free Free Free Water Free Nitrogen residue or tin alcohol formaldehyde resorcinol bisphenol A content ethanol fraction 1 h/900° C. content [%] [%] [%] [%] [%] [%] [%] [%] [%] P1 9.6 0.0 0.0 0.0 0.0 3.0 0.0 16.0 0.16 Ti P2 22.9 0.0 0.0 0.0 0.0 n.d. 0.0 15.0 0.22 Ti P3 7.1 0.0 0.0 0.0 0.0 1.4 0.0 26.5 0.18 Ti P4 4.7 0.0 0.0 0.0 0.0 0.8 0.0 10.0 0.05 Ti P5 13.3 0.0 0.0 0.0 0.0 n.d. 0.0 n.d 0.22 Sn C1 65.0 0.10 0.0 0.0 10.0 3.0 3.5 <0.1 0.0 C2 79.3 0.10 2.3 13.6 0.60 n.n. n.n. <0.1 0.0

[0304] In Table 5, for the invention products P1 to P5, the concentration figures for free furfuryl alcohol (constituent (B)) and ethanol (constituent (C)) are based on the total mass of the non-volatile product obtained after the distillative removal of the volatile constituents as described above in Sections 1.1 and 1.2.

[0305] The amount of titanium or tin in the products P1 to P5 was calculated on the basis of the amount of tetrabutyl titanate or dibutyltin laurate used, respectively, on the at least approximately accurate assumption that on the distillative removal of the volatile constituents virtually no tetrabutyl titanate or dibutyltin laurate is removed from the reaction system.

[0306] In the comparative products C1 and C2, all concentration figures in Table 5 are based on the total mass of the comparative product C1 or C2 prepared by mixing the constituents listed in Table 2 or Table 4, respectively, as described in Section 2 above.

[0307] In Table 5 “0.0” means that the constituent in question was not present, “n.n” denotes “not detectable” and “n.d.” denotes “not determined”, meaning that there was no analysis for the constituent in question.

[0308] The concentrations of furfuryl alcohol, resorcinol, bisphenol A and ethanol were determined by gas chromatography, the water content by Karl-Fischer titration, the free formaldehyde content by titration by the KCN method. The nitrogen fraction was determined by elemental analysis.

[0309] Relative to conventional acid-curable binders (comparative products C1 and C2), the inventive compositions (products P1 to P5) are notable for a substantially lower free furfuryl alcohol content, and they contain neither nitrogen nor free formaldehyde.

[0310] The ignition residue was determined for the inventive products P1 to P4 and the comparative products C1 and C2. For this purpose, a burner was used for oxidative preincineration of a sample, which was subsequently calcined at 900° C. in a porcelain crucible to constant mass, but for at least one hour. Because the ingredients that are volatile on calcination are mostly organic in nature, the ignition residue is a measure of the content of those constituents which on incineration form non-volatile inorganic compounds. For the compositions of the invention, the ignition residue comprises essentially silicon dioxide formed in the thermal decomposition of compounds of the Formula (I).

[0311] The inventive products P1 to P4 therefore form an ignition residue which in terms of quantity corresponds approximately to the fraction of bound silicon dioxide in the compounds of the Formula (I) present. The formation of a relatively large amount of ignition residue in the case of the inventive products P1 to P3 (produced with tetraethyl orthosilicate as compound of the Formula (II); see above) is an indication that in these products there are reaction products (compounds of the Formula (I)) formed by reaction of furfuryl alcohol with tetraethyl orthosilicate (compound of the Formula (II)). They are therefore not mere mixtures of furfuryl alcohol and tetraethyl orthosilcate, since under the conditions under which the ignition residue is determined, tetraethyl orthosilicate escapes virtually without residue.

[0312] The comparative products C1 and C2 formed a very small ignition residue, since they consist essentially of organic constituents.

[0313] For further resolution of the structure of the reaction products formed by reaction of furfuryl alcohol with tetraethyl orthosilicate, the inventive products P1 and P3 were analysed by gel permeation chromatography (GPC). In parallel to this, the non-inventive, comparative products C1 and C2 were also analysed by GPC. The chromatograms of all the products investigated are shown in FIG. 1. In this figure there are the following correspondences: [0314] Plot 1: GPC of comparative product C1 [0315] Plot 2: GPC of inventive product P1 [0316] Plot 3: GPC of inventive product P3 [0317] Plot 4: GPC of comparative product C2

[0318] Table 6 lists certain significant peaks in the chromatograms and also their assignment to particular constituents of the products analysed.

TABLE-US-00006 TABLE 6 Mp Peak (molar mass in Peak contained g/mol at the Assigned structure; No. in plot peak apex) presumed structural unit labelled with (*) 1 1-4 99.3 Furfuryl alcohol (molar mass 98.1 g/mol) 2 4 145 Resorcinol (molar mass 1110.111 g/mol) 3 1-4 155.3 4 4 214.8 Bisphenol A (molar mass 228.286 g/mol) 5 2, 3 (shoulder) 268.0 [00002] 5.1 2, 3 313.3-313.8 [00003] 5.2 2, 3 347.7-351.0 [00004] 5.3 2, 3 384.4-388.4 [00005] 6 2, 3 588-598 7 2, 3 776 8 3 945 9 3 1100 none [00006]

[0319] All GPC plots contain a peak assignable to the monomeric furfuryl alcohol, since all the products analysed contain monomeric furfuryl alcohol. Plot 4 has GPC peaks which can be assigned to resorcinol and bisphenol A, respectively, since comparative product C2 contains these constituents. Only plots 2 and 3 (inventive products P1 and P3) have peaks which can be assigned to the mixed furfuryl/ethyl esters (having 1, 2 or 3 furfuryl radicals) of orthosilicic acid or to the furfuryl tetrasilicate (compounds of the Formula (I)), respectively. A peak assignable to tetraethyl orthosilicate (molar mass 208.327 g/mol) is not evident in plot 2, despite the fact that product P1 was prepared by reacting tetraethyl orthosilicate with furfuryl alcohol. This is a further indication that furfuryl alcohol has undergone reaction with tetraethyl orthosilicate (compound of the Formula (II)) to give compounds of the Formula (I).

[0320] 4. Physical Characterization

[0321] Certain physical parameters of the inventive products P1-P5 and of the comparative products C1 and C2 are compiled in Table 7.

TABLE-US-00007 TABLE 7 Viscosity Surface @ 20° C. tension acc. Density (Rotary to Wilhelmy @ 20° C. Refractive experiment) @ 25° C. [g/cm.sup.3] index n.sup.D.sub.20 [mPa*s] [mN/m] P1 1.182 1.487 11 35.4 P3 1.231 1.479 42 n.d. P4 1.133 1.465 9 n.d. P5 n.d. n.d. 940 n.d. C1 1.160 1.485 20 n.d. C2 1.137 1.501 12 40.5 In Table 7, “n.d.” denotes “not determined”, meaning that there was no measurement of the parameter in question.

[0322] In spite of their substantially lower fraction of monomeric furfuryl alcohol, the inventive products P1, P3 and P4 have a viscosity situated within the same order of magnitude as that of comparative products C1 and C2, and they are therefore suitable for use as binders in the no-bake process. The product P5 is suitable for use as a binder in the warm-box or hot-box process.

[0323] With regard to the other parameters, the inventive products are not significantly different from the comparative products.

[0324] 5. Application as Acid-Curable Binder in the No-Bake Process

[0325] Test specimens in the form of bending bars were produced from moulding mixtures comprising silica sand H32 (obtainable from Quarzwerke GmbH, D-50207 Frechen) as mould raw material, the comparative product C1 or one of the inventive products P6 to P8 as acid-curable binder, and the activator S1 or S2. The activators S1 and S2 used respectively for curing had the composition specified in Table 8 (based on 100 parts by weight of activator each).

TABLE-US-00008 TABLE 8 para-Toluene- Sulfuric Monoethylene Activator sulfonic acid acid glycol Water S1 65.0 1.0 0 34.0 S2 48.2 0.8 23.0 28.0

[0326] The compositions of the individual moulding mixtures can be seen from Table 9. Curing took place in the no-bake process. Determinations were made of the working properties of the moulding mixtures and also of the flexural strength of the resulting test specimens, at various points in time after curing (performance investigation). The results of the performance investigation are compiled in Table 9. In that table, the pbw figures correspond to the parts by weight of sand, binder and activator in the respective moulding mixture.

[0327] The workability time was determined in accordance with the P 72 information sheet “Binder testing—testing of cold-curing, synthetic resin-bonded, moist moulding materials with addition of curing agent” from the VDG (German Foundrypersons Association) using an acid-resistant steel test rod having a diameter of around 6 mm and a weight of 12 g, this bar having conical tapering at one end and carrying, at the tip of the cone, a hemisphere with a diameter of 2 mm. The test is repeated on the test specimen at intervals of 30 s in each case until the tip of the testing pin, placed cautiously onto the test specimen, no longer leaves any deeper impression in the core than that corresponding to its radius (around 1 mm). The time which elapses (in min) between the addition of resin and the point in time at which the tip of the test pin, placed cautiously onto the test specimen, no longer leaves any deeper impression in the core than that corresponding to its radius is the workability time of the test mixture. The cure time is determined in a similar way to the determination of the workability time, with the test rod being weighted with an additional weight of 100 g.

TABLE-US-00009 TABLE 9 Room temperature: 21° C. Relative Sand temperature: humidity: PERFORMANCE INVESTIGATION 21° C. 45% Binder Activator pbw Flexural strengths in N/cm.sup.2 at Experi- pbw per per 100 pbw Workability Cure different times after curing ment 100 pbw of time in time in 1 2 4 24 No. sand H 32 Sand H 32 minutes minutes hour hours hours hours 1 C1 S1 13 19 195 390 435 475 1.00 0.50 2 C1 S1 35 45 65 190 215 305 1.00 0.25 3 C1 S2 42 58 0 30 180 365 1.00 0.50 4 C1 S2 55 70 0 10 50 250 1.00 0.25 5 P6 S2 6 8 110 170 200 260 1.00 0.25 6 P7 S2 7 11 160 210 255 315 1.00 0.25 7 P7 S1 1:1 in 12 18 95 175 215 260 1.00 ethanol 0.25 (incl. ethanol) 8 P8 S2 8 12 95 220 235 255 1.00 0.25

[0328] The moulding mixtures with the inventive products P6 to P8 as binder have significantly shorter cure times, for a given quantity and composition of activator, than those with the comparative product C1 as binder (comparison of experiments 4, 5, 6 and 8). The high reactivity of the binder compositions of the invention makes it possible to lessen the amount of activator used in the moulding mixtures of the invention and to use activators with a lower acid content and/or with less-corrosive acids (e.g. p-toluenesulfonic acid instead of sulfuric acid) while nevertheless obtaining test specimens of acceptable strength. If necessary, the workability time of the moulding mixture can be extended by dilution of the activator (see experiment 7).

[0329] Following performance investigation, test specimens (bending bars) produced from moulding mixtures comprising silica sand H32 (obtainable by Quarzwerke GmbH, D-50207 Frechen) as mould raw material with the comparative product C1 or with the inventive product P7 as binder and with the activators S1 or S2 were subjected to pyrolysis at 900° C. The pyrolysis gases were analysed for the concentration (in mg/kg of moulding mixture) of certain emissions-relevant lead components. The compositions of the corresponding moulding mixtures, the results of the performance investigation of the test specimens, and the concentrations of certain emissions-relevant lead components in the pyrolysis gas from pyrolysis of the test specimen are listed in Table 10.

[0330] In moulding mixtures with the inventive product P7 as binder, as a result of the silicon fraction present therein, the amount of carbon introduced by the binder is reduced for the same binder composition as in the moulding mixture with the comparative product C1 as binder, and so a smaller amount of organic emissions are released on the burning of the binder.

[0331] The emissions of benzene and toluene reduce significantly if instead of the activator S1, the activator S2, which has a lower para-toluenesulfonic acid content, is used. With the activator S2, however, test specimens having acceptable strengths are obtained only from moulding mixtures with the binder of the invention. When using the binder of the invention, accordingly, it is possible to achieve a reduction in the emissions of benzene and toluene because of the ability to use activators with a lower level of para-toluenesulfonic acid without detractions from the flexural strength of the mouldings.

TABLE-US-00010 TABLE 10 Composition of the moulding mixture Binder pbw per 100 pbw of sand H 32 C1 C1 P7 P7 1 1 1 1 Activator pbw per 100 pbw of sand H 32 S1 S2 S1 S2 0.5 0.5 0.5 0.5 Performance investigation Room temperature ° C. 22.5 22.6 22.7 22.7 Sand temperature ° C. 21.3 21.3 21.3 21.3 Relative humidity % 26 26 26 51 Workability time min 15 68 3 7 Cure time 100 g min 23 115 4 13 Flexural strength after 1 h N/cm.sup.2 110 0 170 90 Flexural strength after 2 h N/cm.sup.2 230 0 230 200 Flexural strength after 4 h N/cm.sup.2 260 40 250 250 Flexural strength after 24 h N/cm.sup.2 220 210 220 265 Emissions on pyrolysis Benzene mg/kg 204.5 76.5 177.5 85 Toluene mg/kg 11 1.5 6 1.5 o/m/p-Xylene mg/kg 1 2 1 1 Mesityl oxide mg/kg 2.9 1.9 0.3 0.6 Styrene mg/kg 3.5 3.85 1.95 1.65 Isophorone mg/kg 6.85 5 2.65 1.95 N-Methylaniline mg/kg 2.95 0.65 0.2 0.2 Naphthalene mg/kg 20.35 19.75 11.45 8.95 p-Toluidine mg/kg 0 0.8 0 0 o-Cresol mg/kg 2.3 2.25 1.5 0.4 Phenol mg/kg 0.25 0.55 0.25 0.6 m-Cresol mg/kg 0 0 0.3 0 3,5-Dimethylphenol mg/kg 1.6 0.85 0 0 3-Methyl-1H-Indanole mg/kg 0 0 0 0

[0332] 6. Further Performance Investigations

[0333] The purpose of further performance investigations is to gain fundamental knowledge regarding the suitability of moulding mixtures with the binder of the invention for the production of mouldings by 3D printing (as used for example in rapid prototyping). Here, in contrast to the performance investigations described in Section 5, the mould raw material used was of a substantially finer grade (sand GS 14), as required for 3D printing. Moreover, certain of the moulding mixtures investigated contained binders of the invention with addition of surfactants (constituent (H)). The binders for moulding mixtures to be processed by 3D printing are commonly admixed with surfactants in order to set a suitable surface tension.

[0334] Test specimens in the form of bending bars were produced from moulding mixtures comprising in each case 100 parts by weight of sand GS 14 (obtainable from Strobel Quarzsand GmbH Freihung) as mould raw material, one part by weight of a binder selected from the group consisting of the comparative products C1 and C2 and the inventive products P9 to P14 and 0.3 part by weight of an activator from the group of activators S1 to S4. The activators S1 to S4 used for curing had the composition specified in Table 11 (based on 100 parts by weight of activator in each case).

TABLE-US-00011 TABLE 11 para- Toluenesulfonic Sulfuric Monoethylene- Activator acid acid glycol Water S1 65.0 1.0 0 34.0 S2 48.2 0.8 23.0 28.0 S3 63.0 3.0 0 34.0 S4 57.9 0.9 7.0 34.2

[0335] The compositions of the individual moulding mixtures can be seen from Table 12. Curing took place in the no-bake process. Determinations were made of the working properties of the moulding mixtures and also of the flexural strength of the resulting test specimens, at various points in time after curing (performance investigation). The results of the performance investigation are compiled in Table 12. In that table, the pbw figures correspond to the parts by weight of sand, binder and activator in the respective moulding mixture.

TABLE-US-00012 TABLE 12 Room temperature: 21° C. Relative Sand temperature: humidity: PERFORMANCE INVESTIGATION 21° C. 43% Workability Cure Flexural strengths in N/cm.sup.2 at time in time in different times after curing No. Binder Activator minutes minutes 1 hour 2 hours 4 hours 24 hours 1 P9  S2 7 11 70 160 170 180 2 P10 S2 8 12 60 155 180 180 3 P11 S2 8 12 90 185 205 195 4 P12 S2 8 13 75 140 205 190 5 P13 S2 9 13 90 150 180 185 6 P14 S2 9 13 70 165 185 175 7 P9  S4 6 10 70 85 100 100 8 P10 S4 5 9 160 170 196 195 9 P11 S4 6 10 110 165 170 180 10 P12 S4 6 9 140 165 180 190 11 P13 S4 7 11 130 205 205 190 12 P14 S4 7 10 130 185 190 160 13 C1 S1 7 10 135 190 150 185 14 C2 S3 7 10 165 220 200 210

[0336] The workability times and cure times of the majority of moulding mixtures 1-12 with inventive binders are relatively short because of the high reactivity of the inventive binders, despite the fact that the acid content of the activators used in the moulding mixtures 1-12 is lower than the acid content in the moulding mixtures 13 and 14 with the non-inventive binders.