TWO-COMPONENT BINDER SYSTEM FOR THE POLYURETHANE COLD-BOX PROCESS

Abstract

A description is given of a two-component binder system for use in the polyurethane cold box process, a mixture for curing by contacting with a tertiary amine, a method for producing a feeder, a foundry mold or a foundry core, and also feeders, foundry molds and foundry cores producible by this method, and the use of a two-component binder system of the invention or of a mixture of the invention for binding a mold raw material or a mixture of mold raw materials in the polyurethane cold box process.

Claims

1. A two-component binder system for use in the polyurethane cold box process consisting of a phenolic resin component and of a separate polyisocyanate component, where the phenolic resin component comprises an ortho-fused phenolic resole having etherified and/or unetherified terminal methylol groups, and a solvent, and optionally one or more additives and the polyisocyanate component comprises a polyisocyanate having at least two isocyanate groups per molecule and also optionally a solvent, and optionally one or more additives, the fraction of isocyanate groups in the polyisocyanate component being 90% or more, preferably 92% or more, more preferably 95% or more, very preferably 98% or more, based in each case on the total mass of the polyisocyanate component, and the stoichiometric ratio of isocyanate groups in the polyisocyanate component to hydroxyl groups in the phenolic resin component being less than 1.2, and preferably in the range from 0.5 to <1, more preferably in the range from 0.7 to 0.95, where the phenolic resin component is free from compounds from the group of the alkyl silicates and alkyl silicate oligomers, and, based on the total mass of the phenolic resin component, the fraction of aromatic hydrocarbons is less than 39.43%, preferably less than 38%, and the fraction of rapeseed oil methyl ester is less than 39.43%, preferably less than 30%.

2. The two-component binder system as claimed in claim 1, the ratio of unetherified terminal methylol groups to etherified terminal methylol groups in the ortho-fused phenolic resole being greater than 1, preferably greater than 2, more preferably greater than 4, and very preferably greater than 10, there preferably being no etherified methylol groups in the ortho-fused phenolic resole, and/or the polyisocyanate having at least two isocyanate groups per molecule being selected from the group consisting of diphenylmethane diisocyanate, polymethylene-polyphenyl isocyanates (polymeric MDI), and mixtures thereof.

3. The two-component binder system as claimed in claim 1, the solvent of the phenolic resin component comprising one or more compounds selected from the group consisting of dialkyl esters of C.sub.3-C.sub.6 dicarboxylic acids, saturated and unsaturated fatty acid alkyl esters, preferably vegetable oil alkyl esters, preferably from the group consisting of rapeseed oil methyl ester, tall oil methyl ester, tall oil butyl ester, lauric acid methyl ester, lauric acid isopropyl ester, myristic acid isopropyl ester, and myristic acid isobutyl ester, alkylene carbonates, preferably propylene carbonate, cycloalkanes, cyclic formals, aromatic hydrocarbons from the group consisting of alkyl benzenes, alkenyl benzenes, dialkyl naphthalines, and dialkenyl naphthalines, substances from the group consisting of cashew nut shell oil, components of cashew nut shell oil, and derivatives of cashew nut shell oil, preferably cardol, cardanol, and also derivatives and oligomers of these compounds.

4. The two-component binder system as claimed in claim 1, the solvent of the phenolic resin comprising: one or more compounds from the group of dialkyesters of C.sub.3-C.sub.6 dicarboxylic acids, one or more compounds from the group of the alkyl benzenes and alkenylbenzenes, and one or more compounds from the group of the saturated and of the unsaturated fatty acid alkyl esters, preferably vegetable oil alkyl esters, preferably from the group consisting of rapeseed oil methyl ester, tall oil methyl ester, tall oil butyl ester, lauric acid methyl ester, lauric acid isopropyl ester, myristic acid isopropyl ester, and myristic acid isobutyl ester.

5. The two-component binder system as claimed in claim 1, the phenolic resin component having a viscosity at 20 C. of at most 100 mPas, preferably of at most 50 mPas, determined in each case according to DIN 53019-1: 2008-09 and/or comprising less than 5%, preferably less than 1%, of monomers selected from the group consisting of monomeric unsubstituted phenol and monomeric substituted phenols, based on the total mass of the phenolic resin component.

6. The two-component binder system as claimed in claim 1, the solvent of the polyisocyanate component comprising one or more compounds selected from the group consisting of dialkyl esters of C.sub.3-C.sub.6 dicarboxylic acids, saturated and unsaturated fatty acid alkyl esters, preferably vegetable oil alkyl esters, preferably from the group consisting of rapeseed oil methyl ester, tall oil methyl ester, tall oil butyl ester, lauric acid methyl ester, lauric acid isopropyl ester, myristic acid isopropyl ester, and myristic acid isobutyl ester, alkylene carbonates, preferably propylene carbonate, cycloalkanes, cyclic formals, aromatic hydrocarbons from the group consisting of alkyl benzenes, alkenyl benzenes, dialkyl naphthalines, and dialkenyl naphthalines.

7. The two-component binder system as claimed in claim 1, the phenolic resin component and/or the polyisocyanate component comprising as additive one or more substances selected from the group consisting of silanes, acyl chlorides, hydrofluoric acid, methanesulfonic acid phosphorus-oxygen acids additive mixture preparable by reacting a premix of (av) 1.0 to 50.0 wt % of methanesulfonic acid, (bv) one or more esters of one or more phosphorus-oxygen acids, the total amount of said esters being in the range from 5.0 to 90.0 wt %, and (cv) one or more silanes selected from the group consisting of aminosilanes, epoxysilanes, mercaptosilanes and ureidosilanes, the total amount of said silanes being in the range from 5.0 to 90.0 wt %, the fraction of water being no more than 0.1 wt %, based in each case on the total amount of constituents (av), (bv), and (cv) in the premix.

8. A mixture for curing by contacting with a tertiary amine or with a mixture of two or more tertiary amines, the mixture (a) being preparable by mixing the components of the two-component binder system as claimed in claim 1, and/or (b) comprising an ortho-fused phenolic resole having etherified and/or unetherified terminal methylol groups, a polyisocyanate having at least two isocyanate groups per molecule, a solvent and also, optionally, one or more additives, and the stoichiometric ratio of isocyanate groups in the polyisocyanate component to hydroxyl groups in the phenolic resin component being less than 1.2, and being preferably in the range from 0.5 to <1, more preferably in the range from 0.7 to 0.95, the mixture being free from compounds from the group of the alkyl silicates and alkyl silicate oligomers, and, based on the total mass of the mixture, the fraction of aromatic hydrocarbons is less than 27.6%, preferably less than 25%, and the fraction of rape seed methyl ester is less than 27.6%, preferably less than 25%.

9. The mixture as claimed in claim 8, further comprising a mold raw material or a mixture of two or more mold raw materials, the ratio of the total mass of mold raw materials to the total mass of other constituents of the mixture being in the range from 100:2 to 100:0.4, preferably from 100:1.5 to 100:0.6.

10. A method for producing an article from the group consisting of feeders, foundry molds and foundry cores, comprising the following steps: providing or producing a mold raw material or a mixture of two or more mold raw materials, mixing the mold raw material or the mixture of two or more mold raw materials with the phenolic resin component and the polyisocyanate component of a two-component binder system as claimed in claim 1, to form a molding mixture suitable for curing by contacting with a gaseous tertiary amine or with a mixture of two or more gaseous tertiary amines, the stoichiometric ratio of isocyanate groups in the polyisocyanate component to hydroxyl groups in the phenolic resin component in the molding mixture being less than 1.2, and preferably in the range from 0.5 to <1, more preferably in the range from 0.7 to 0.95 shaping the molding mixture, and contacting the shaped molding mixture with a gaseous tertiary amine or a mixture of two or more gaseous tertiary amines by the polyurethane cold box process, so that the shaped molding mixture cures to form the article from the group consisting of feeders, foundry molds and foundry cores, a total amount of gaseous tertiary amines being used which is less than 0.08 mol, preferably less than 0.05 mol, per mole of isocyanate groups.

11. An article from the group consisting of feeders, foundry molds and foundry cores, producible by a method as claimed in claim 10.

12. (canceled)

13. A method for binding a mold raw material or a mixture of mold raw materials in the polyurethane cold box process, comprising: utilizing a two-component binder system as claimed in claim 1 as a binding for a mold raw material or a mixture of mold raw materials in the polyurethane cold box process.

Description

[0191] The invention is elucidated further below using working examples and comparative examples.

[0192] From molding mixtures comprising a customary mixture of mold raw materials and also a two-component binder system comprising a polyisocyanate component and a phenolic resin component as described below, test specimens in the form of flexural bars are produced by the cold box process, and their initial flexural strengths are determined.

[0193] The production of the test specimens (+GF+ standard flexural strength test specimens) is carried out in accordance with VDG datasheet P73. For this purpose, the mold raw material is charged to a mixing vessel. The phenolic resin component and polyisocyanate component (ii) (amounts, see table 1) are then weighed into the mixing vessel in such a way that they do not undergo direct mixing. Thereafter, mold raw material, phenolic resin component, and polyisocyanate component are mixed in a paddle mixer (Multiserw, model RN10/P) for 2 minutes at approximately 220 revolutions/minute to form a molding mixture.

[0194] The production of test specimens takes place with a universal core shooting machine LUT, which is equipped with a Gasoman LUT/G, both from Multiserw. Immediately after its production as described above, the completed molding mixture is filled into the shooting head of the core shooting machine or initially stored for one hour in the closed container.

[0195] The parameters of the core shooting operation are as follows: shoot time: 3 seconds, delay time after shooting: 5 seconds, shooting pressure: 4 bar (400 kPa). For curing, the test specimens are gassed for 10 seconds at a gassing pressure of 2 bar (200 kPa) with dimethylpropylamine (DMPA). This is followed by flushing with air for 9 seconds at a flushing pressure of 4 bar (400 kPa). The flexural strength is measured using a Multiserw LRu-2e instrument at specific times (15 seconds, one hour, 24 hours, see table 2) after the end of flushing.

[0196] In the production of the test specimens, the following parameters were varied: [0197] solvent content and solvent composition of the phenolic resin component [0198] solvent content and solvent composition of the polyisocyanate component [0199] additives present [0200] ratio of the mass of polyisocyanate in the polyisocyanate component to the mass of resole in the phenolic resin component [0201] storage time of the molding mixture

[0202] The compositions of the two-component binder systems and molding mixtures used are listed in table 1.

[0203] The phenolic resin component comprises a resole having unetherified terminal methylol groups, i.e., terminal groups of the structure CH.sub.2OH, and a solvent comprising the following constituents

[0204] LM1 dimethyl esters of C.sub.4-C.sub.6 dicarboxylic acids

[0205] LM2 mixture of aromatic hydrocarbons

[0206] LM3 rapeseed oil methyl esters

[0207] The phenolic resin component of examples 1.1 and 1.2 comprises as additives a silane and 40% strength hydrofluoric acid (sand life extender additive). In the other examples, the phenolic resin component does not comprise any additives.

[0208] The polyisocyanate component comprises diphenylmethane diisocyanate (methylenebis(phenyl isocyanate), MDI) as polyisocyanate and also a sand life extender additive and as solvent a mixture of aromatic hydrocarbons.

[0209] The polyisocyanate component of examples 1.1, 1.2 and 1.3 comprises as sand life extender additive an additive mixture preparable by reacting a premix of the aforementioned components (av), (bv), and (cv) as described in patent application WO 2013/117256 in an amount of 1.2%, based on the total mass of the polyisocyanate component (example 1.1) or 1.4%, based on the total mass of the polyisocyanate component (examples 1.2 and 1.3). The polyisocyanate component of examples 2.1, 2.2 and 2.3 comprises as sand life extender additive phosphorus oxychloride in an amount of 0.3%, based on the total mass of the polyisocyanate component.

[0210] In noninventive examples 1.1 and 2.1, the two components of the binder system were each used in a quantity and composition customary in the prior art, and so these examples serve as a reference. In the inventive examples, the solvent fraction of the polyisocyanate component is reduced compared to the reference example and the solvent fraction of the phenolic resin component is increased compared to the reference example. In all inventive examples, the stoichiometric ratio of isocyanate groups in the polyisocyanate component to hydroxyl groups in the phenolic resin component is less than 1.2, in examples 1.3 and 2.3 even less than 1.

[0211] In table 1, the definitions are as follows:

TABLE-US-00001 PBW Parts by weight MRM Mold raw material LM Solvent BM Binder (minus solvent and additives).

[0212] The results of the measurements of the flexural strength as a function of the storage time of the molding mixture prior to core production, and as a function of the time elapsed after the end of rinsing, are compiled in table 2. The flexural strength values measured at the time of 15 s after the end of rinsing are critical for the usability of cores and are referred to below as initial strengths.

TABLE-US-00002 TABLE 1 Composition of molding mixture PBW phenolic PBW Composition of resin polyisoccyanate Composition of phenolic resin Polyisoyante component/ component/ component component 100 100 Example Resole LM1 LM2 LM3 Additives MDI LM Additives PBW PBW No. [%] [%] [%] [%] [%] [%] [%] [%] MRM MRM 1.1 50.83 17.1 18.63 12.99 0.45 85 13.8 1.2 0.75 0.75 1.2 47 20 20 13 0 95 3.6 1.4 0.9 0.6 1.3 44 21 21 14 0 95 3.6 1.4 1 0.5 2.1 50.83 17.1 18.63 12.99 0.45 85 14.7 0.3 0.75 0.75 2.2 47 20 20 13 0 95 4.3 0.7 0.9 0.6 2.3 44 21 21 14 0 95 4.3 0.7 1 0.5 Composition of molding mixture Amount of substance PDW PDW PBW Amount [mol] resole/ MDI/ BM/ of substance NCO/ Amount 100 100 Mass 100 [mol] OH/ 100 of substance Example PDW PDW ratio PBW 100 PBW PBW ratio No. MRM MRM MDI/resole MRM MRM MRM NCO/OH 1.1 0.38 0.64 1.680 1.02 0.00359 0.00483 1.3451 1.2 0.40 0.57 1.439 0.97 0.00374 0.00431 1.1528 1.3 0.44 0.48 1.080 0.88 0.00416 0.00360 0.8646 2.1 0.38 0.64 1.680 1.02 0.00359 0.00483 1.3451 2.2 0.40 0.57 1.439 0.97 0.00374 0.00431 1.1528 2.3 0.44 0.48 1.080 0.88 0.00416 0.00360 0.8646

TABLE-US-00003 TABLE 2 Molding mixture Molding mixture used immediately used after one-hour storage Flexural strength [N/cm.sup.2] after Example 15 s 1 h 24 h 15 s 1 h 24 h No. after end of rinsing 1.1 217 380 480 200 395 470 1.2 230 370 435 235 365 435 1.3 245 330 425 250 370 425 2.1 220 390 480 205 385 465 2.2 240 395 455 255 410 460 2.3 250 355 430 270 375 435

[0213] In the examples with a binder system of the invention (1.2, 1.3, 2.2, 2.3) higher initial flexural strengths are obtained, despite the fact that the binder content (without solvents and additives) of the molding mixture here is lower than in the reference examples. The fact that the flexural strengths are lower, after one hour and/or after 24 h, in the case of the examples of the invention, relative to certain reference examples, is of minor significance in practice. The critical factor, in the case of partly and fully automated core fabrication operations, instead, is that the initial strengths are high, in order to prevent rupturing of the cores during handling.

[0214] Surprisingly, the molding mixtures of the invention exhibit greater shelf life than in the reference examples, irrespective of the additive used. It is evident from the fact that the flexural strengths of test specimens produced from a molding mixture of the invention stored for one hour in a closed container do not drop relative to the corresponding flexural strengths of the cores produced from the freshly mixed molding mixture of the invention.