AQUEOUS ALKALINE BINDER COMPOSITION FOR CURING WITH CARBON DIOXIDE GAS AND USE THEREOF, A CORRESPONDING MOLDING MIXTURE FOR PRODUCING FOUNDRY MOLDS, A CORRESPONDING FOUNDRY MOLD AND A METHOD FOR PRODUCING A FOUNDRY MOLD

Abstract

The invention relates to an aqueous alkaline binder composition for curing with carbon dioxide gas, comprising a negatively charged or uncharged phenol-aldehyde resin, comprising phenol groups, which is selected from the group consisting of resoles and mixtures comprising one or more resoles and also one or more novolacs, an oxyanion selected from the group consisting of borate ions, aluminate ions, stannate ions, zirconate ions, titanate ions, and mixtures thereof, for forming a stable complex with the resole phenol-aldehyde resin, and one or more silanes in a total amount in the range from 2.5 to 10 wt %, based on the total mass of the binder composition, where the total molar to amount of the phenol groups of the phenol-aldehyde resin in the aqueous alkaline binder composition is in the range from 1 to 3 mol/kg, based on the total mass of the aqueous alkaline binder composition. The invention relates, moreover, to a corresponding use, to a molding mixture for producing a foundry mold, and also to a corresponding method for producing a foundry mold, and to a corresponding foundry mold.

Claims

1. An aqueous alkaline binder composition for curing with carbon dioxide gas, comprising a negatively charged or uncharged phenol-aldehyde resin, comprising phenol groups, which is selected from the group consisting of resoles and mixtures comprising one or more resoles and also one or more novolacs, an oxyanion, selected from the group consisting of borate ions, aluminate ions, stannate ions, zirconate ions, titanate ions, and mixtures thereof, for forming a stable complex with the resole phenol-aldehyde resin and one or more silanes in a total amount in the range from 2.5 to 10 wt %, based on the total mass of the binder composition, where the total molar amount of the phenol groups of the phenol-aldehyde resin in the aqueous alkaline binder composition is in the range from 1 to 3 mol/kg, based on the total mass of the aqueous alkaline binder composition.

2. The aqueous alkaline binder composition as claimed in claim 1, comprising one or more silanes in a total amount in the range from 3.0 to 10 wt %, preferably 3.5 to 7 wt %, more preferably 3.5 to 6 wt %, based on the total mass of the binder composition.

3. The aqueous alkaline binder composition as claimed in claim 1, where one or more or all of the silanes used are selected from the group consisting of 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane and phenyltrimethoxysilane and/or are selected from the group of epoxysilanes, and where one or more of the silanes used are preferably selected from the group consisting of 3-glycidoxypropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane.

4. The aqueous alkaline binder composition as claimed in claim 4, comprising as silanes epoxysilanes, preferably selected from the group consisting of 3-glycidoxypropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane, in a total amount in the range from 2.5 to 7 wt %, more preferably 4 to 6 wt %, based on the total mass of the binder composition.

5. The aqueous alkaline binder composition as claimed in claim 1, where the negatively charged or uncharged phenol-aldehyde resin is a negatively charged or uncharged resole-phenol-aldehyde resin, for curing with carbon dioxide gas in the phenol-resole-CO.sub.2 process.

6. The aqueous alkaline binder composition as claimed in claim 1, where the phenol-aldehyde resin possesses an average molecular weight (Mw) in the range from 750 to 1200 g/mol, preferably in the range from 750 to 1000 g/mol, more preferably in the range from 780 to 980 g/mol, and very preferably in the range from 850 to 980 g/mol, determined by means of gel permeation chromatography.

7. The aqueous alkaline binder composition as claimed in claim 1, further comprising one or more compounds selected from the group consisting of polyalkylene glycols, phenylalkylene glycol ethers, propylene glycol alkyl ethers, substituted or unsubstituted pyrrolidones, monoethylene glycol and polyethylene glycol in a total amount in the range from 1 to 40 wt %, preferably in a total amount of 1 to 15 wt %, based on the total mass of the binder composition and/or reaction products of this or these compounds.

8. The aqueous alkaline binder composition as claimed in claim 1, further comprising one or more compounds from the group consisting of C4-C20 saturated or unsaturated aliphatic carboxylic acids and alkali metal salts of said acids, in a total amount in the range from 0.1 to 5.0 wt %, preferably in a total amount of 0.5 to 3 wt %, preferably in a total amount of 0.8 to 1.5 wt %, based on the total mass of the binder composition.

9. The aqueous alkaline binder composition as claimed in claim 8, comprising one or both compounds from the group consisting of isononanoic acid and alkali metal salts of isononanoic acid, in a total amount in the range from 0.1 to 5.0 wt %, preferably in a total amount of 0.5 to 3 wt %, preferably in a total amount of 0.8 to 1.5 wt %, based on the total mass of the binder composition.

10. The aqueous alkaline binder composition as claimed in claim 1, further comprising phenoxyethanol and/or butyldiglycol and/or monoethylene glycol in a total amount in the range from 3 to 10 wt %, preferably in the range of 3-6 wt %, based on the total mass of the binder composition.

11. The aqueous alkaline binder composition as claimed in claim 1, further comprising 1,3,5-trioxacyclohexane in a total amount in the range from 0.1 to 5%, preferably in the range from 0.5 to 1.5%.

12. The aqueous alkaline binder composition as claimed in claim 1, where the pH at 20? C. is in the range from 12 to 14, preferably in a range from 13 to 14.

13. The aqueous alkaline binder composition as claimed in claim 1, where the molar amount of the phenol groups in the aqueous alkaline binder composition is in the range from 1.5 to 2.5 mol/kg, preferably in the range from 1.8 to 2.0 mol/kg, based on the total mass of the binder composition and/or the viscosity of the alkaline binder composition at 20? C. is in the range of 100-1000 mPas, preferably 150-700 mPas, more preferably 150-500 mPas, determined in accordance with DIN EN ISO 3219:1994.

14. The aqueous alkaline binder composition as claimed in claim 1, where the molar ratio of the total amount of alkali metals to phenol groups is in the range from 1.0:1 to 2.5:1, preferably in the range from 1.5:1 to 2.1:1, more preferably in the range from 1.7:1 to 1.9:1 and/or where the molar amount of the alkali metals in the aqueous alkaline binder composition is in the range from 1.0 to 7.5 mol/kg, preferably in the range from 2.0 to 6.0 mol/kg, more preferably in the range from 3.0 to 4.0 mol/kg, based on the total mass of the binder composition.

15. The aqueous alkaline binder composition as claimed in claim 1, where the molar ratio of the total amount of potassium cations to the total amount of sodium cations is in the range from 47:1 to 59:1, preferably in the range from 50:1 to 56:1, more preferably in the range from 52:1 to 55:1.

16. The aqueous alkaline binder composition as claimed in claim 1, for curing with carbon dioxide gas in the phenol-resole-CO.sub.2 process, comprising a negatively charged or uncharged phenol-aldehyde resin, comprising phenol groups, which is selected from the group consisting of resoles and mixtures comprising one or more resoles and also one or more novolacs, where the phenol-aldehyde resin possesses an average molecular weight (Mw) in the range from 750 to 1200 g/mol, preferably in the range from 800 to 1100 g/mol and more preferably in the range from 850 to 1000 g/mol, determined by means of gel permeation chromatography, an oxyanion selected from the group consisting of borate ions, aluminate ions, stannate ions, zirconate ions, titanate ions and mixtures therefore, for forming a stable complex with the negatively charged or uncharged phenol-aldehyde resin, and also one or more epoxysilanes, preferably selected from the group consisting of 3-glycidoxypropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane, in a total amount in the range from 2.5 to 10 wt %, based on the total mass of the binder composition, where the total molar amount of the phenol groups of the phenol-aldehyde resin in the aqueous alkaline binder composition is in the range from 1.8 to 2.0 mol/kg, based on the total mass of the aqueous alkaline binder composition.

17. A method of forming a foundry molding material, comprising: producing or providing an aqueous alkaline binder composition as claimed in claim 1 as a binder for the foundry molding material.

18. A molding mixture for producing a foundry mold, comprising an aqueous alkaline binder composition as claimed in claim 1 and a foundry molding material.

19. A method for producing a foundry mold, having the following steps: producing or providing a molding mixture as claimed in claim 18, molding the molding mixture produced or provided, curing the molded molding mixture by gassing with carbon dioxide gas.

20. A foundry mold formed by a method as claimed in claim 19.

Description

EXAMPLES

[0232] The examples below are intended to illustrate the invention without limiting it.

[0233] The abbreviation pbw used in the examples denotes parts by weight (parts by mass).

Example 1

[0234] General Preparation ProtocolProduction of a Binder Composition with Variable Fraction of Silane and Variable Molecular Weight of a Resole Prepared:

[0235] A binder composition is produced as follows:

[0236] Production Step 1:

[0237] A premix is prepared by mixing [0238] 174.8 pbw of phenol and [0239] 1.72 pbw of boric acid.

[0240] Production Step 2:

[0241] Added to the premix from production step 1 are [0242] 8.4 pbw of trioxane (i.e., 1,3,5-trioxacyclohexane) and [0243] 7.7 pbw of an aqueous solution with 33 wt % of NaOH (i.e., sodium hydroxide solution 33%, aqueous).

[0244] Production Step 3:

[0245] The mixture is heated to 65? C. and [0246] 243.2 pbw of a 53% strength formaldehyde solution
are metered in over a period of 45 minutes.

[0247] Production Step 4:

[0248] The reaction mixture is heated to 80? C. and condensed at a temperature between 80 and 90? C. until the resulting mixture has a viscosity of 300 mPas at 25? C.

[0249] Production Step 5:

[0250] After having attained the desired viscosity, the reaction mixture is admixed with 76.1 pbw of an aqueous solution with 45 wt % KOH (i.e., potassium hydroxide solution, 45% strength, aqueous)

[0251] Production Step 6:

[0252] Subsequently, at a temperature of 70? C., condensation is carried out until the resole of the reaction mixture has a defined average molecular weight Mw.

[0253] Note: The average molecular weight Mw for specific examples is indicated in Table 2 below.

[0254] Production Step 7:

[0255] As soon as the defined average molecular weight has been attained, the reaction mixture is cooled to 40? C. in less than 5 minutes.

[0256] Production Step 8:

[0257] This is followed by addition of 299.1 pbw of an aqueous solution with 45 wt % of KOH, 9.5 pbw of 3,5,5-trimethylhexanoic acid, 48.1 pbw of borax (CAS number 1303-96-4), 0.072 pbw of aluminum hydroxide and 88 pbw of polyethylene glycol having an average molecular weight of 200 g/mol (CAS No.: 25322-68-3) to the reaction mixture, which is subsequently cooled to below 30? C.

[0258] Production Step 9:

[0259] After cooling to a temperature of below 30? C. has taken place, a defined amount of 3-glycidoxypropyltrimethoxysilane is added.

[0260] Note: The amount of silane used in specific examples is indicated in Table 1 below.

Example 2

[0261] Production of Binder Compositions with Different Amounts of Silane:

[0262] In accordance with the preparation protocol above (Example 1), binder compositions were produced with different amounts of silane (cf. Example 1, production step 7) and were each processed to form flexural bars as described above. After a storage time is differing in duration (see option a) under measurement method (flexural strength)) and/or after coating (see option b) under measurement method (flexural strength)), the strengths of the respective flexural bars were ascertained.

[0263] Condensation was carried out in each case up to an average molecular weight Mw for the resole of approximately 784 g/mol (cf. Example 1, production step 4).

[0264] The amounts of silane used (in wt %, based on the total mass of the binder composition) and the results of the flexural strength measurements are set out in Table 1:

TABLE-US-00001 TABLE 1 Amount of silane (3-glycidoxy- propyltrimethoxy- Flexural strengths [N/cm.sup.2] silane) [wt %] after 24 hours after 5 days after coating 0.5 160 90 230 1 180 100 250 2 190 110 250 3 200 140 280 4 210 170 300 5 220 170 290 6 200 170 300 7 190 160 290 8 180 150 290 9 170 130 290 10 140 110 290

[0265] The results of Table 1 are shown in graph form in FIGS. 1 and 2. For reasons of clarity, FIG. 2 contains a selection of the data from Table 1.

[0266] FIG. 1 shows flexural strengths of flexural bars produced in accordance with Example 2 with different amounts of silane, after 24 hours and after 5 days' storage, and also after coating. For each of the aforementioned storage times, and for the case where the flexural bars were coated, respectively, 10 binder compositions in each case were used with different amounts of silane (0.5 to 10 wt %) (see x-axis in FIG. 1) in order to investigate the relationship between the flexural strength and the amount of silane used. The numbers in the bars of FIG. 1 relate to the amount of silane in wt % that was used for producing the respective flexural bar (i.e., the number 0.5 in the first bar of the measurement series after 24 hours in FIG. 1 denotes that an amount of silane of 0.5 wt % was used in order to produce the flexural bar employed).

[0267] FIG. 2 shows a selection of the flexural strengths of the flexural bars produced in accordance with Example 2 with different amounts of silane (after a storage time of 24 hours or 5 days, and, respectively after coating). In FIG. 2, in contrast to FIG. 1, the amount of silane in wt % is indicated exclusively on the X-axis.

[0268] In FIG. 2 it is readily apparent that all of the mixtures comprising more than 2 wt % of 3-glycidoxypropyltrimethoxysilane exhibit higher flexural strengths in the measurements after coating and after 5 days than those mixtures for which the silane content is lower.

[0269] It is evident from FIG. 2, moreover, that in the after 24 hours column, for concentrations of 3-glycidoxypropyltrimethoxysilane in the range of 4-6 wt %, the value measured for the flexural strength is particularly high. In contrast to this, the values for the measurements after 24 hours are lower both at lower silane concentrations (<4 wt %) and at higher silane concentrations (>6 wt %).

[0270] Measurements with a mixture comprising an amount of 3-glycidoxypropyltrimethoxysilane in the range from 4 to 6 wt % are therefore linked to a number of surprising technical effects (cf. also FIGS. 1 and 2), namely [0271] a) a particularly high measurement in the after coating column (and analogously after 5 days)
and [0272] b) (additionally) a high measurement value in the column after 24 hours.

Example 3

[0273] Production of Binder Compositions with Resoles Having Different Average Molecular Weights Mw:

[0274] Binder compositions were produced with resoles having different average molecular weights Mw, and, after a variable storage time (see option a) under measurement method (flexural strength)) and/or after coating (see option b) under measurement method (flexural strength)), the respective flexural bars were investigated for their strength.

[0275] In this case, 5 wt % of 3-glycidoxypropyltrimethoxysilane was used each time, based on the total mass of the binder composition.

[0276] The results are set out in Table 2:

TABLE-US-00002 TABLE 2 Average molecular Flexural strengths [N/cm.sup.2] weight Mw of the after 15 after 1 after 24 after 5 after resole (g/mol) seconds hour hours days coating 724 80 180 110 110 110 731 100 200 160 120 160 784 110 210 210 160 350 814 110 210 200 160 330 876 130 200 200 140 320 960 130 200 200 140 320

[0277] The results of Table 2 are shown in graph form in FIG. 3.

[0278] All of the mixtures comprising resoles having a molecular weight Mw of more than 750 g/mol showed a higher or unchanged flexural strengths in comparison with those mixtures comprising phenol-aldehyde resins and/or salts thereof with a molecular weight Mw of less than 750 g/mol, in all of the measurements (flexural bars after storage for 15 seconds, for 1 hour, for 24 hours, for 5 days, and after coating). This is true especially of the initial strengths (i.e., flexural strength after 15 seconds) and of the flexural o strengths of the coated foundry molds. For molecular weights in the range from 850 to 980 g/mol (namely 876 and 960 g/mol, respectively), particularly high flexural strengths were determined for the initial strengths (i.e., flexural strength after 15 seconds).