Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/20—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents
  • B22C1/22—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of resins or rosins
  • B22C1/2233—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of resins or rosins obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • B22C1/2273—Polyurethanes; Polyisocyanates
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/08—Processes
  • C08G18/0838—Manufacture of polymers in the presence of non-reactive compounds
  • C08G18/0842—Manufacture of polymers in the presence of non-reactive compounds in the presence of liquid diluents
  • C08G18/0847—Manufacture of polymers in the presence of non-reactive compounds in the presence of liquid diluents in the presence of solvents for the polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/08—Processes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/08—Processes
  • C08G18/0838—Manufacture of polymers in the presence of non-reactive compounds
  • C08G18/0842—Manufacture of polymers in the presence of non-reactive compounds in the presence of liquid diluents
  • C08G18/0847—Manufacture of polymers in the presence of non-reactive compounds in the presence of liquid diluents in the presence of solvents for the polymers
  • C08G18/0852—Manufacture of polymers in the presence of non-reactive compounds in the presence of liquid diluents in the presence of solvents for the polymers the solvents being organic
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/08—Processes
  • C08G18/089—Reaction retarding agents
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
  • C08G18/40—High-molecular-weight compounds
  • C08G18/54—Polycondensates of aldehydes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
  • C08G18/40—High-molecular-weight compounds
  • C08G18/54—Polycondensates of aldehydes
  • C08G18/542—Polycondensates of aldehydes with phenols
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/36—Sulfur-, selenium-, or tellurium-containing compounds
  • C08K5/41—Compounds containing sulfur bound to oxygen
  • C08K5/42—Sulfonic acids; Derivatives thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L75/00—Compositions of polyureas or polyurethanes; Compositions of derivatives of such polymers
  • C08L75/04—Polyurethanes

Definitions

• the invention relates to a polyisocyanate component for a moulding material binding agent system or a solution containing polyisocyanate for a moulding material binding agent system or a two-component binding agent system, the use of these for the production of foundry sand cores or moulds according to the cold-box method, corresponding foundry moulding materials and foundry sand cores or moulds and the preparation of these and the use of particular sulfonic acids as a means for extending the benchlife.
• binding agent systems consist of two components, a polyol (normally dissolved in a solvent) with at least two OH-groups in the molecule and a polyisocyanate (usually likewise dissolved in a solvent) with at least two NCO-groups in the molecule.
• Both components which are added separately to the moulding mixes containing a moulding matrix, preferably sand, react in the moulding mix to form a cured polyurethane binding agent, typically in the presence of catalysts, which guarantee a rapid reaction and thus a sufficiently short curing time.
• catalysts which after moulding of the moulding mix are introduced into the moulding tool as highly volatile amines with a carrier gas.
• the polyol component is usually a condensation product of (possibly substituted) phenols with aldehydes (hereinafter referred to as “phenolic resin” for short) dissolved in a solvent, having a low-to-average degree of condensation and a large number of free OH-groups in the molecule.
• phenolic resin aldehydes
• the polyol component can also be a solution of an oligomeric, dimeric or monomelic phenol body, e.g. of a terphenol, bisphenol or dihydroxybenzol.
• a large number of (generally polar) solvents are available.
• the solutions are normally set at a solid content of 40 to 95 wt. % and can further contain normal additives.
• polyisocyanates with at least two NCO-groups in the molecule can be considered as polyisocyanate components.
• aromatic polyisocyanates of which diphenylmethane-4,4′-diisocyanate, 2,2′,6,6′tetramethyldiphenylmethane-4,4′-diisocyanate, diphenyldimethylmethane-4,4′-diisocyanate and diphenyl-4,4′-diisocyanate are typical examples.
• the polyisocyanates can form the polyisocyanate component either in pure form or dissolved in an organic solvent, e.g. a mixture of aromatic hydrocarbons with a boiling point of above 150° C. In the case of a solution the concentration of the polyisocyanate is generally above 70 wt. %.
• a moulding matrix preferably a grainy moulding sand such as quarto sand, chromite sand, olivine sand, or zircon sand
• the two binding agent components wherein the proportions of the two components can be approximately in the region of 0.5 to 1.5 parts by weight of polyisocyanate component to 1 part by weight of polyol component and preferably can be dimensioned such that an almost stoichiometric ratio of the NCO-groups to the OH-groups results.
• the moulding mix is then processed to form the foundry sand cores or moulds, e.g.
• sand cores or moulds can then be removed from the moulding tool.
• initial strength a measurable strength
• the highest possible initial strength is desirable here, in order that the sand cores or moulds as far as possible can be removed from the moulding fool immediately after gasification and the tool can be freed up for another work cycle.
• phosphoryl chloride, phthaloyl chloride or chlorosilanes are added to the polyisocyanate component of the binding agent.
• DE-A-34 05 180 describes such a moulding material binding agent system containing chlorosilanes.
• Binding agent systems containing acid chlorides are known from U.S. Pat. No. 4,540,724.
• the chlorine content of the binding agent system can lead to disadvantages and health risks during the processing of the binding agent system and the subsequent metal casting, since as the binding agent system decomposes, chlorinated compounds, such as dioxins, which are a health hazard, can result.
• chlorinated compounds such as dioxins
• the substitute should be capable of fully or partially replacing the acid chlorides or chlorosilanes used to date, without adversely affecting the benchlife or the strength of the sand cores (initial strength and final strength).
• the object of the present invention is to provide a corresponding chlorine-free substitute which meets the above requirements.
• DE 2921726 discloses special emulsions containing water, an organic polyisocyanate, possibly a non-ionic, surface-active medium as an emulsifier and a sulfonic acid.
• the sulfonic acid is a sulfonic acid of the general formula R—(SO 3 H) n , in which n denotes an integer 1 or 2 and R an aromatic hydrocarbon radical with 6 to 14 carbon atoms, an aliphatic hydrocarbon radical with 10 to 18 carbon atoms, a cycloaliphatic hydrocarbon radical with 6 to 15 carbon atoms, an araliphatic hydrocarbon radical with 7 to 15 carbon atoms or an alkaramatic hydrocarbon radical with 7 to 24 carbon atoms.
• DE 2921698 A1 discloses a self-releasing, substantially anhydrous, polyisocyanate-based binding agent for the production of moulded forms consisting of
• JP 03-041116 concerns certain polyurethane resin compositions for orthopedic cast strips comprising a polyurethane prepolymer comprising a polyol and a polyisocyanate, a catalyst a stabiliser (e.g. acid chlorides such as benzoyl chloride or sulfonic acids such as methane sulfonic acid) and an ester compound polyethylene glycol.
• a stabiliser e.g. acid chlorides such as benzoyl chloride or sulfonic acids such as methane sulfonic acid
• DE 4213873 describes the use of esters that are liquid at ambient temperature as a solvent for isocyanates and/or isocyanurates, whereby the viscosity of the isocyanates and/or isocyanurates can be drastically reduced.
• DE 19542752 describes the use of vegetable oil methyl ester, preferably of rapeseed oil methyl ester, as a solvent for individual or both components of foundry moulding material binding agents with a polyurethane basis, the components of which comprise a phenolic resin containing free OH-groups and a polyisocyanate as the reaction partner.
• JP 53-128526 discloses how, for the preparation of a self-curing mould mixture, a phenolic resin containing 0.05 to 40% carboxylic and/or sulfonic acid and sand is mixed with a polyisocyanate in the presence of a basic catalyst.
• JP 62-104648 discloses how, for the preparation of a sand mould, foundry sand is kneaded with a binding agent comprising a furan resin, toluenesulfonic acid, tetraethylsilicate, methyl diisocyanate, silicon dioxide and boric acid.
• CN 102049463 discloses a method comprising the mixing of a sodium alkyl sulfonate solution with a phenolic resin, and then mixing with sand, further mixing with a polyisocyanate-ester, and the moulding of a casting mould.
• the sulfonic acids to be used according to the invention can be used to extend the benchlife of a moulding material and in so doing can replace in full or in part the known chlorosilanes or acid chlorides.
• the invention therefore also relates to (i) a polyisocyanate component for a moulding material binding agent system, and (ii) a solution containing polyisocyanate (see below).
• the invention further relates to a moulding material binding agent system for the preparation of foundry sand cores from a polyol component, containing a solution of a phenol-containing polyol, such as benzyl ether resin with ortho-ortho structures, with at least two OH-groups in the molecule, and a polyisocyanate component, as defined as above, which react with one another to form a cold-curing binding agent, e.g. for sand cores or moulding sand.
• the invention also relates to a moulding material binding agent system for the preparation of foundry sand cores from
• the invention also relates to a two-component binding agent system for the preparation of a polyurethane resin for casting (see below).
• the invention also relates to the use of a polyisocyanate component or a solution containing polyisocyanate, a moulding material binding agent system according to the invention or a two-component binding agent system according to the invention for the preparation of foundry sand cores according to the cold-box method.
• the invention also relates to a mixture for preparation of a core or a mould for casting, e.g. a foundry moulding material, and corresponding foundry sand cores and moulds and a method for the preparation thereof.
• a core or a mould for casting e.g. a foundry moulding material, and corresponding foundry sand cores and moulds and a method for the preparation thereof.
• the foundry moulding material can also be used as a foundry moulding sand for the preparation of casting moulds, e.g. for the no-bake method.
• the invention also relates to a polyisocyanate component for a moulding material binding agent system, containing at least one sulfonic acid in a solution of at least one polyisocyanate, containing at least two NCO-groups in the molecule, characterised in that:
• a further subject matter of the invention is a solution containing a polyisocyanate, preferably a polyisocyanate component as defined above, for a moulding material binding agent system, wherein the solution containing polyisocyanate consists of
• chlorinated compounds may, however, in individual cases, be acceptable in small quantities in the solution containing polyisocyanate according to the invention.
• Commercial grades of methylene diphenyl diisocyanate (and other polyisocyanates) in particular and their oligomers or polymers comprise certain quantities of chlorinated compounds as an impurity, due to the use of chlorinated educts during synthesis. These chlorinated compounds may be acceptable as an impurity in solutions containing polyisocyanate according to the invention.
• the (co-)solvents of component (c) can also be based on commercially available products, which apart from a (preferably chlorine-free) main ingredient also comprise certain quantities of chlorinated compounds as an impurity.
• a (preferably chlorine-free) main ingredient also comprise certain quantities of chlorinated compounds as an impurity.
• (co-)solvent (c) means that the component (c) either acts as a solvent itself, where none of the ingredients of components (a) and (b) themselves act as a solvent for the other ingredients of components (a) and (b), or acts as an additional solvent, where one or a plurality of ingredients of components (a) and (b) itself/themselves acts or act as a solvent for the other ingredients of components (a) and (b).
• Aminosilanes and aminoorganosilanes such as gamma-aminopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane, bis-(gamma-erimethoxysilylpropyl)amine, polyazamidsilane, N-beta(amincethyl)-gamma-aminopropytrimethoxysilane, N-phenyl-gamma-aminopropyltrimethoxysilane, organically modified polydimethoxysiloxsne, and triamino-functional silanes are often used as the water repellent (e).
• the solution containing polyisocyanate defined above does not comprise a resin selected from the group consisting of phenolic resins and furan resins.
• the solution containing polyisocyanate comprises no polyol that is suitable for reacting with the polyisocyanate(s) contained in the solution to form a cold-curing binding agent.
• a solution containing polyisocyanate according to the invention preferably comprises no moulding matrix, in particular no casting sand.
• the solution containing polyisocyanate according to the invention is preferably either anhydrous or contains water in a maximum quantity that is selected so that the molar ratio of NCO-groups to H 2 O is greater than 100:1, preferably greater than 1000:1.
• the polyisocyanate component according to the invention or the solution containing polyisocyanate according to the invention contains one or a plurality of sulfonic acids, wherein the one sulfonic acid or at least one of the plurality of sulfonic acids is selected from the group of sulfonic acids of the formula R—SO 2 —OH, in which R denotes an alkyl group with between 1 and 4 carbon atoms, wherein preferably the one sulfonic acid or at least one of the plurality of sulfonic acids, is methane sulfonic acid.
• the sulfonic acid can be selected from any suitable sulfonic adds.
• the sulfonic acid has the general formula R—SO 2 —OH, in which R denotes C 1-12 -alkyl, phenyl or C 1-12 -alkylphenyl, wherein an H atom in these radicals can be substituted by a hydroxyl group or amino group, which can be primary, secondary or tertiary, or R denotes NH 2 .
• the sulfonic acid can be used in pure form or as a solution in a, preferably, organic solvent.
• the sulfonic acid can be present in the form of a free acid or also partly in the form of a salt, for example an ammonium, alkaline or alkaline earth metal salt.
• the salt content, in respect of the acid groups, should preferably not exceed 30 mol %. Preferably, only the free acid is used.
• the polyisocyanate component contains 0.01 to 5 wt. %., particularly preferably 0.0025 to 2.5 wt. %., preferably 0.025 to 2.5 wt. %., in particular 0.05 to 1 wt. %, of the minimum of one sulfonic acid, in respect of the polyisocyanate component.
• a solution containing polyisocyanate according to the invention preferably comprises a total quantity of sulfonic acid in the range 0.01 to 5 wt. %., in respect of the total weight of the solution.
• the weight ratio of sulfonic acid to acid chloride or chlorosilane is preferably 1:1 to 9:1, particularly preferably 1:1 to 4:1, in particular approximately 1:1.
• methane sulfonic acid is an odourless, non-oxidising, biodegradable, non-toxic, aliphatic, thermally resistant, low TOC (Total Organic Compound) and strong organic add. Furthermore, the methane sulfonic acid has an extremely low vapour pressure and is part of the natural sulphur cycle.
• the polyisocyanate component preferably contains 55 to 85 wt. %, particularly preferably 70 to 90 wt. % of the at least one polyisocyanate.
• the polyisocyanate component can also contain a solvent, preferably in a quantity of 4.99 to 44.99 wt. %, particularly preferably 9.99 to 29.99 wt. %.
• a solution containing polyisocyanate according to the invention preferably comprises a total quantity of polyisocyanate in the range 55 to 95 wt. %., in respect of the total weight of the solution.
• the total quantity of the ingredients of the polyisocyanate component or the solution according to the invention comes to 100 wt. %.
• the total quantity of polyisocyanate, sulfonic acid and solvent comes to 100 wt. %.
• the invention is applicable to all polyurethane-based binding agent systems, and can thus be used in conjunction with all normal polyol components and polyisocyanate components and also requires no changes to the preparation and processing of the moulding mixes (moulding sand mixtures).
• the optimum quantity of sulfonic acid in each case is dependent here on the nature and reactivity of the polyol component and can be determined in each individual situation through simple manual trials.
• suitable polyol components and polyisocyanate components reference may be made, by way of example, to DE-A-34 05 180.
• DE-A-10 2004 057 671, EP-A-1 057 557 554, EP-A-0 771 599 and WO 2010/060826.
• All suitable phenol-formaldehyde resins can be used, with the use of benzyl ether resins being particularly advantageous however.
• the polyisocyanate component according to the invention or the solution containing polyisocyanate according to the invention comprises one or a plurality of polyisocyanates with in each case two or more NCO-groups in the molecule, wherein the one polyisocyanate or at least one of the plurality of polyisocyanates is a methylene diphenyl diisocyanate (MDI) or an oligomer or polymer thereof.
• MDI methylene diphenyl diisocyanate
• a mixtures of 4,4′-,2,2′- and 2,4′-isomers may be involved here or individual isomers or mixtures of two of the isomers, or also oligomers or polymers of these. This means that according to the invention use may be made of
• oligomers and polymers of the methylene diphenyl diisocyanate is preferred according to the invention.
• the polyisocyanate can be selected from any suitable polyisocyanates, which contain at least NCO-groups in the molecule and with a phenol-containing polyol produce a cold-curing binding agent for casting sand.
• suitable polyisocyanates are known to a person skilled in the art.
• tetrasilicates such as tetraethyl silicate, aromatic hydrocarbons, fatty acid alkyl esters (preferably rapeseed oil methyl ester), mixtures of these and mixtures of these with alkylene carbonates such as propylene carbonate or dialkyl esters of aliphatic dicarboxylic acids, preferably dimethyl esters of adipinic acid, glutaric acid and/or succinic acid, can be considered.
• the latter dialkyl esters are for example sold under the designation DBE (Dibasic Ester). They are used as co-solvents. in order to improve the solubility, for example in tetraethyl silicate, aromatic hydrocarbons or rapeseed oil methyl esters.
• Alkylene carbonate or DBE are added to the first solvent mentioned preferably in a ratio of weight of 1:1 to 5, preferably 1:1.5 to 3, thus in a clearly low quantity.
• the subject matter of the invention is also the use of a polyisocyanate component according to the invention (as defined above) or a solution containing polyisocyanate according to the invention (as defined above) as a polyisocyanate component of a two-component binding agent system for preparation of a polyurethane resin, preferably as a polyisocyanate component of a two-component binding agent system for preparation of a polyurethane resin in the polyurethane cold-box method.
• a further subject matter of the present invention is a two-component binding agent system for preparation of a polyurethane resin for casting, consisting of
• Phenol-formaldehyde resins are synthetic resins, which are obtained by condensation of phenols with formaldehyde and if necessary by derivatisation of the resultant condensates. Phenol-formaldehyde resins are normally, depending on the proportions of the educts (phenol component and formaldehyde), the reaction conditions and the catalysts used, split into two product classes, the novolacs (phenol novolacs) and resoles:
• novolacs are soluble, fusible, non-self-curing and stable when stored oligomers with molecular weights in the range of approximately 500 to 5000 g/mol. They are produced by condensing formaldehyde and a phenol component in a molar ratio of approximately 1:1.25 to 2 in the presence of acid catalysts. Novolacs are generally free of methylol groups, and their aromatic rings are linked by methylene bridges. Novolacs can be cured by reactive cross-linkers (curing agents) (e.g.
• Resoles are mixtures of hydroxymethyl phenols, linked by methylene and methylene ether bridges. They are prepared by an alkaline catalysed condensation reaction with molar excess of the aldehyde. Once a certain degree of polymerisation has been reached here the condensation is interrupted. Resoles are self-curing through their reactive methylol groups. Depending on the degree of condensation resoles are liquid and as such have different viscosities and are as a rule soluble in water and alcohol. Resoles can be converted into highly cross-linked structures (resites) under the effect of heat. For particular areas of application it is sometimes desirable for resoles to have a certain solubility in organic solvents. In order to achieve this solubility, resoles are then normally subjected to modification reactions, such as for example, condensation at higher temperature with unsaturated compounds (such as for example vegetable oils), esterification or etherification with mono- or polyfunctional alcohols.
• modification reactions such as for example, condensation at higher temperature with unsaturated compounds
• a particular class of phenol formaldehyde resins are benzyl ether resins.
• Benzyl ether resins are the products of condensation of a phenol component and formaldehyde, obtained under the catalytic influence of bivalent metal ions, see U.S. Pat. No. 3,485,797.
• Benzyl ether resins are particularly suitable as a resin component for casting binding agents for use in the cold-box method (see U.S. Pat. No. 3,676,392 and U.S. Pat. No. 3,409,579).
• Benzyl ether resins are liquid up to a certain degree of condensation. Benzyl ether resins are as a rule incompatible with wafer, but compatible with alcohols and other organic solvents.
• benzyl ether resins have phenol bodies which are linked by both methylene groups —CH 2 — and by ether groups —CH 2 —O—CH 2 —, wherein the linking of two bodies takes place predominantly in the ortho-ortho position, in benzyl ether resins there is a high content of hydroxymethyl groups (—CH 2 OH) and phenolic hydroxyl groups (—OH).
• benzyl ether resins have predominantly o,o-structures (ortho-ortho-structures) and accordingly have a linear molecular structure, makes them highly reactive to cross-linkers (see again U.S. Pat. No. 3,485,797).
• Preferred benzyl ether resins are described in EP-B-1 057 554.
• Compounds that are preferably used according to the invention are described there in paragraphs [0004] to [10006], wherein particular reference may be made to Formulas I and II given there.
• the phenol-formaldehyde resins are preferably used as a polyol component and can be termed a phenol-containing polyol.
• the viscosity of she polyol component is in particular 130 to 140 mPa s at 20° C.
• the polyol component can have a solvent, for example in a quantity of 30 to 50 wt. %. Suitable solvents are aromatic and aliphatic hydrocarbons, esters, ketones, alkyl silicates, fatty acid esters and similar solvents.
• solvent contents can be considerably reduced.
• the subject matter of the present invention is also the use of a polyisocyanate component according to the invention as defined above or a solution containing polyisocyanate according to the invention as defined above or a two-component binding agent system as defined above
• a further subject matter of the invention is a mixture for the preparation of a core or a mould for casting, comprising
• Such mixtures comprising a (I) moulding matrix, wherein the moulding matrix preferably is a moulding sand, and (ii) a binding agent system (in particular the two components of a two-component binding agent system) are in connection with the present invention also referred to as (foundry) moulding materials, moulding mixes or moulding sand mixtures.
• a binding agent system in particular the two components of a two-component binding agent system
• sand for example quartz sand, or another suitable moulding matrix
• sand for example quartz sand, or another suitable moulding matrix
• mixing preferably takes place at room temperature using normal mixing equipment.
• the foundry moulding materials obtained in this way can be used in any suitable method for the preparation of foundry sand cores or moulds.
• the foundry sand cores or moulds are produced according to the cold-box method.
• the cold-box method is one of the most important polyurethane gasification methods. The designation is that used by the VDG and has also been introduced into the German casting industry to designate this method. On this point reference may be made to U.S. Pat. No. 3,409,579.
• an amine gassing agent such as for example dimethyl isopropylamine serves as an acceleration catalyst, which considerably accelerates the addition of polyisocyanate to a phenolic resin, e.g. benzyl ether resin.
• Resins used in the cold-box method are as a rule anhydrous here, since water would react prematurely with the polyisocyanate.
• the process normally involves the foundry sand containing the binding agent system according to the invention (core sand) initially being fired into core boxes. Then using an amine-air or amine-nitrogen mixture in gas or aerosol form, it is gasified.
• the amines involved are generally triethyl-, dimethylethyl-, dimethyl-n-propyl- or dimethylisopropylamine, which are in each case blown into the core boxes at a pressure of 2 to 6 bar.
• the residual gases are normally driven out of the core with heated scavenging air, nitrogen or CO 2 gas and can be disposed of in an acid scrubber, charged with diluted sulphuric acid or phosphoric acid.
• the binding agent system according to the invention depending on the amine, cures at temperatures of preferably 20 to 100° C., particularly preferably 45 to 80° C.
• the curing normally takes place at the respective ambient temperature normally prevailing in the foundry, that is to say generally at a temperature in the range 15 to 50° C., in particular at a temperature in the range 15 to 40° C. Therefore the binding agent is referred to as a cold-curing binding agent for moulding sand.
• the cold-box method has extensive applications, in particular in metal casting and for example in engine castings.
• the moulding materials according to the invention can also be used as moulding sand for the preparation of sand moulds for casting, e.g. in the non-bake method.
• the moulding materials/moulding sands after casting are to the greatest possible extent chlorine-free, so that corrosion of the cast parts is avoided and the used sand cores or moulds can be re-used as used sand.
• the used sand is heat and/or mechanically treated. Both of these treatment methods result in insignificant or no burdening with chemicals that are damaging to health. This re-employment of previously used sand cores or treatment of used sand is ever possible with systems containing bentonite or basic systems.
• the cooler was then switched to atmospheric distillation and the temperature increased within one hour to 125 to 126° C., until a refractive index of approximately 1.593 was reached.
• the yield was 82 to 83% of the raw materials used.
• the phenolic resin was used for the preparation of test specimens according to the cold-box method.
• PW Phenol resin precondensate from Example 1
• PW Aromatic hydrocarbons with a boiling point of 165 to 180° C.
• PW DBE Dibasic Ester
• PW Diphenylmethane diisocyanate 12.4 PW Aromatic hydrocarbons with a boiling point of 165 to 180° C. 2 PW Rapeseed oil methyl ester (RME) 0.2 PW Methane sulfonic acid 0.4 PW Water repellent
• the polyisocyanate solution for comparison BB7 corresponds to solution BB3, with the difference that instead of methane sulfonic acid phosphoryl chloride is used to extend the benchlife.
• the mixing time was in each case 60 seconds.
• test specimens (+GF+bar) were fired, which were than gasified for 10 seconds at a gasification pressure of 4 bar with dimethylisopropylamine and then flushed with air for 10 seconds.
• the sand quantify per test specimen was 3 kg
• the sand temperature and the ambient temperature were approximately 25° C.
• the relative humidity (RH) was approximately 39%.
• the flexural strengths of the test specimens obtained in this way were determined according to the GF method. In the preparation of the test as specimens and the testing of the flexural strengths the specifications of VDG leaflet P 73 of February 1996 were applied.
• Table 1 provides a comparison of the strength values of six cores according to the invention and a conventional core (in N/cm 2 ).
• the mixing time was in each case 60 seconds.
• test specimens (+GF+bar) were fired, which were than gasified for 10 seconds at a gasification pressure of 4 bar with dimethylisopropylamine and then flushed with air for 10 seconds.
• the sand quantity per test specimen was 3 kg
• the sand temperature and the ambient temperature were approximately 25° C.
• the relative humidity (RH) was approximately 39%.
• the flexural strengths of the test specimens obtained in this way were determined according to the GF method. In the preparation of the test specimens and the testing of the flexural strengths the specifications of VDG leaflet P 73 of February 1996 were applied.
• Table 2 provides a comparison of the strength values of seven cores according to the invention and a conventional core (in N/cm 2 ).
• the substantial difference between the conventional core and the cores according to the invention is that in their preparation and also during casting the latter no longer produce any noticeable burden on the workplace. Behaviour during casting has been confirmed by is sample castings performed under laboratory conditions.

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