WO2017075351A1

WO2017075351A1 - Polyurethane binder containing alcohol solvent

Info

Publication number: WO2017075351A1
Application number: PCT/US2016/059324
Authority: WO
Inventors: Paulo Rogerio BOLOGNESI; Alexandre Bruno Dias SOUZA; Fabiana Cordeiro VIERIA; Davi SANTOS; Michael NOCERA
Original assignee: Ask Chemicals, L.P.
Priority date: 2015-10-30
Filing date: 2016-10-28
Publication date: 2017-05-04
Also published as: JP2019502768A; BR112018008817A2; JP7189016B2; BR112018008817B1

Abstract

A binder system for a molding material mixture is useful when low emissions of aromatic solvents are required. The binder system has two components that are packaged separately, for combination at use. The first component has a polyol base resin with at least two -OH groups per molecule and an alkyl alcohol, having from two to five carbon atoms, as a solvent. The second component has a polyisocyanate with at least two - NCO groups per molecule. The alkyl alcohol may be anhydrous ethanol and the first component is substantially devoid of aromatic hydrocarbon solvents. The second component will typically consist essentially of diphenylmethane diisocyanate (MDI) with less than 0.1 % of a bench life extender. The first component may contain at least one fatty acid methyl ester and at least one dibasic ester. The binder system may be used for practicing either a "cold-box" or a "no-bake" method.

Description

POLYURETHANE BINDER CONTAINING ALCOHOL SOLVENT

Cross-reference to Related Applications

[001] This application is a non-provisional of, and makes a claim of priority to, US provisional patent application 62/248,543, filed 30 October 2015, which is incorporated by reference as if fully recited herein.

Technical Field

[002] This invention relates to a polyurethane-based binder system for use in the cold-box or no-bake process. In this system, an alcohol is used to replace, at least partially, an aromatic solvent. In particular, the alcohol selected is an alkyl alcohol with between 2 and 5 carbon atoms. Most particularly, the alcohol selected is ethanol. Also more particularly, the alcohol is used in a polyol-containing component of a two component polyurethane-based binder system.

Background

[003] When producing molds and cores, polyurethane-based binder systems are used in large amounts, in particular for mold and core production using the cold-box or polyurethane no-bake process. These systems require solvents and it is an on-going need to reduce emissions from these systems when used.

[004] In a typical polyurethane-based binder system, a two component system is provided for the user. The first component contains a polyol component that comprises a compound with at least two -OH groups per molecule. The second component is a polyisocyanate component that comprises a compound having at least two isocyanate groups per molecule. It is considered almost axiomatic that a solvent is included in at least one of the components, and in many cases, both components contain a solvent. Once the solvents are included with the respective components, they are usually packaged and sold in separate containers, only to be combined at the time of use.

[005] The specific details of the polyol and polyisocyanate components are well documented in the art, so it is not necessary to describe them in more detail here. It is, however, useful to note that when solvents are used in each component, it is particularly useful that the solvents be compatible when the components are mixed. Both the polyol and the polyisocyanate components will be used in a liquid form. Although liquid polyisocyanate can be used in undiluted form, a solid or viscous polyisocyanate can be used in the form of a solution in an organic solvent. In some instances known in the art, the solvent can account for up to 80% by weight of the polyisocyanate solution. When the polyol used in the first component is a solid or highly viscous liquid, suitable solvents will be used to adjust viscosity to allow for adequate application properties.

[006] As the prior art readily teaches, the solvent (or solvents) selected are not intended to participate in any relevant manner in the catalyzed reaction between the polyisocyanate and polyol compounds, but they may very well influence the reaction. For example, the two binder components have substantially different polarities. This limits the number of solvents that may be used. If the solvents are not compatible with both binder components, complete reaction and curing of a binder system is very unlikely. Although polar solvents of the protic and aprotic type are usually good solvents for the polyol compound, they are not very suitable for the polyisocyanate compound. Aromatic solvents in turn are compatible with polyisocyanates but are not wholly suitable for polyol resins.

[007] In the art, the common aromatic solvents include the so-called "BTX" solvents - benzene, toluene and xylene. For industrial acceptance, a given solvent needs to meet a number of criteria, including the cost of the solvent, its ecological implications and its health and safety implications. The combination of these may, in some circumstances, mandate a polyurethane based binder system in which the amount of aromatic solvents, and particularly, the BTX solvents, is reduced or eliminated to meet these criteria.

[008] It is therefore an unmet goal of the prior art to provide a polyurethane-based binder system that meets lowered limits on BTX solvents or on volatile organic carbon (VOC) emissions for use in a cold-box or no-bake process.

Summary

[009] These shortcomings of the prior art are overcome at least in part by the present invention as described in more detail below. A binder system for a molding material mixture is used when low emissions of aromatic solvents are required. The binder system has two components that are packaged separately, for combination at use. The first component has a polyol base resin with at least two -OH groups per molecule and an alkyl alcohol, having from two to five carbon atoms, as a solvent. The second component has a polyisocyanate with at least two -NCO groups per molecule. The alkyl alcohol may be anhydrous ethanol and the first component is substantially devoid of aromatic hydrocarbon solvents. The second component will typically consist essentially of diphenylmethane diisocyanate (MDI) with less than 0.1 % of a bench life extender. The first component may contain at least one fatty acid methyl ester and at least one dibasic ester. The binder system may be used for practicing either a "cold-box" or a "no-bake" method.

[0010] In some embodiments, the respective first and second components are present in a weight ratio such that the first component weighs less than the second component. More particularly, preferred embodiments will have about 48 parts by weight of the first component used with about 52 parts by weight of the second component.

[0011] In one preferred embodiment, the first component contains about 58.8% by weight of the polyol resin, 23.9% by weight of the at least one dibasic ester, and 16.9% by weight of the alkyl alcohol, with the balance being the at least one fatty acid methyl ester.

[0012] For uses as a molding material mixture, an amount of refractory mold base material is mixed with the binder system components.

[0013] Preferred refractory mold base materials will include: quartz ore sand, zirconium ore sand, chromium ore sand, olivine, chamotte, bauxite, aluminum silicate hollow spheres, glass beads, glass granules, spherical ceramic molding materials and combinations thereof.

[0014] In a molding material mixture, the binder system is present in an amount of between 0.2 to 5%, by weight, based on the weight of the refractory mold base material, preferably in the range of between 0.3 and 4% by weight, and most preferably in the range of between 0.4 and 3% by weight.

[0015] With this use of the alcohol solvent, the method of producing a mold or core for casting of a molten metal can be either a polyurethane "cold-box" method or a polyurethane "no-bake" method, depending upon how a curing agent is applied to the binder system.

Detailed Description of the Preferred Embodiments

[0016] The known method for producing cores, referred to as the "cold-box method" has attained great importance in the foundry industry. In this method, two-component polyurethane systems are used for binding a basic refractory molding material. The polyol component consists of a polyol having at least two OH groups per molecule, and the isocyanate component consists of a polyisocyanate having at least two NCO groups per molecule. The binder system is cured by conducting gaseous tertiary amines through the molding material/binder system mixture upon injection of the latter into the shaped cavity (US 3,409,579). In the no-bake process liquid amines are added to the binder system prior to molding, to bring the two components to reaction (US 3,676,392).

[0017] According to US 3,676,392 and US 3,409,579, phenolic resins are used as polyols, which are obtained by condensation of phenol with aldehydes, preferably formaldehyde, in liquid phase at temperatures up to approximately 130°C in the presence of catalytic quantities of metal ions. US 3,485,797 describes the production of such phenolic resins in detail. In addition to unsubstituted phenol, substituted phenols, preferably o-cresol and p-nonylphenol, can be used (see, e.g., US 4,590,229). As additional reaction components, according to EP 0177871 A2, phenolic resins modified with aliphatic monoalcohol groups having one to eight carbon atoms can be used. As a result of alkoxylation, the binder systems should have increased thermal stability. As a solvent for the polyol component, predominantly mixtures of high-boiling polar solvents (e.g., esters and ketones) and high-boiling aromatic hydrocarbons are used. In contrast, the polyisocyanates are preferably dissolved in high-boiling aromatic hydrocarbons.

[0018] EP 0771599 A1 and WO 00/25957 A1 describe formulations in which aromatic solvents can be entirely or at least largely replaced by using fatty acid esters.

[0019] From US 4,051 ,092, polyurethane systems are known in which epoxy resins, polyester resins or aqueous phenol formaldehyde resins are reacted with diisocyanates in the presence of a solvent such as dibutoxymethane, dipropoxymethane, diisobutoxymethane, dipentyloxymethane, dihexyloxymethane,

dicyclohexyloxymethane, n-butoxyisopropoxymethane, isobutoxybutoxymethane and isopropoxypentyloxymethane, acetaldehyde-n-propyl acetal, benzaldehyde-n-butyl acetal, acetaldehyde-n-butyl acetal, acetone-di-n-butyl ketal and acetophenone-dipropyl ketal. In the examples, the ketal butylal (l -(butoxymethoxy)butane) is used. US

4,1 16,91 6 and US 4,172,068 have a similar disclosure content.

[0020] The use of diacetals, specifically conversion products of C2 to Ce dialdehydes and C2 to C12 alcohols, in polyurethane systems is disclosed in WO 2006/09271 6 A1 . Listed as diacetals are 1 ,1 ,2,2-tetramethoxyethane, 1 ,1 ,2,2-tetraethoxyethane, 1 ,1 ,2,2- tetrapropoxyethane, 1 ,1 ,3,3-tetramethoxypropane, and 1 ,1 ,3,3-tetraethoxypropane. It was determined that the diacetals enable an extension of the processing time of the molding material mixtures. However, this has a substantially disadvantageous effect on the stability of the fresh mixtures ("shoot immediate"). The loss in stability in relation to the unmodified binder is approximately 1 5% to approximately 20%.

[0021 ] For most applications, the strength of cores and molds produced with the known polyurethane binders is high enough by far.

[0022] Nevertheless, there is great interest in increasing strength levels further in order to lower the binder content, without strength losses if at all possible, i.e., without dropping below the level that is necessary for good casting and safe handling. There are several reasons for reducing the amount of binder, e.g., to reduce the amount of gases and condensates that are produced during casting, which can result in casting defects and can pollute the environment. Moreover, a low binder content reduces the cost of regenerating the previously used, spent sand, and, not least, foundries are interested in using the smallest possible amount of binder for commercial reasons.

[0023] In terms of strength levels, it is important above all to ensure adequate initial strength levels, particularly when the cores will be assembled immediately after production in (partially) automated facilities to form complex core packages or will be placed in permanent metallic molds.

[0024] The problem addressed by the invention was therefore that of providing a polyurethane-based molding material mixture with which molded articles for the foundry industry can be produced using economically and ecologically advantageous solvents which result in lower lowered BTX and volatile organic carbon (VOC) emissions.

[0025] The object of the invention is to provide a binder for molding material mixtures, containing at least one polyol component having a polyol with at least two -OH groups per molecule and at least one isocyanate component having a polyisocyanate with at least two -NCO groups per molecule. The polyol component further comprises at least at least one alkyi alcohol, especially an alkyi alcohol with from two to five carbon atoms. Most especially, the alkyi alcohol is anhydrous ethanol.

[0026] The invention further relates to molding material mixtures which comprise basic refractory molding materials and up to 5 wt%, preferably up to 4 wt%, particularly preferably up to 3 wt% of the binder system according to the invention, referred to the weight of the basic refractory molding materials. Suitable refractory materials include quartz ore sand, zirconium ore sand, or chromium ore sand, olivine, chamotte and bauxite, for example. Synthetically produced molding materials can also be used, such as aluminum silicate hollow spheres (so-called microspheres), glass beads, glass granules, or the spherical ceramic molding materials known as "cerabeads" or

"carboaccucast". Mixtures of the above-stated refractory materials are also possible.

[0027] The invention also relates to a method for producing a casting mold piece or a core. This is achieved by mixing refractory materials with the inventive binder system in a binding quantity of 0.2 to 5 wt%, preferably 0.3 to 4 wt%, particularly preferably 0.4 to 3 wt%, referred to the quantity of refractory materials, to obtain a molding mixture. This molding mixture is placed in to a mold and hardened in the pattern to obtain a self- supporting casting mold piece. The hardened molding mixture is separated from the pattern and hardened further, if necessary, to obtain a hard, solid, cured casting mold piece. At this point, molten metal may be poured into the casting mold.

[0028] Surprisingly, it has been found that the use of an alkyi alcohol, ethanol in particular, as part of the binder formulation readily delivers on the economical, ecological and practical performance criteria of the binder. As a further advantage, it has been found that the alkyi alcohol improves the low-temperature resistance of the binder component. [0029] A solution to the emission problems has apparently been found in a binder composition that uses a two-component approach to provide a polyurethane cold-box (PUCB) or a polyurethane no-bake (PUNB) binder system. In such a system, the Part I component comprises a polyol base resin, a set of suitable complements and an alky! alcohol, and the Part II component comprises a polyisocyanate accompanied by a set of suitable complements.

[0030] The phenolic resin and the polyisocyanate can be selected from the group consisting of the compounds conventionally known to be used in the cold-box process or the no-bake process, as the inventive concept is not believed to inhere in these portions of the composition.

[0031] Referring more particularly to the phenolic resin, it is generally selected from a condensation product of a phenol with an aldehyde, especially an aldehyde of the formula RCHO, where R is hydrogen or an alkyl moiety having from 1 to 8 carbon atoms. The condensation reaction is carried out in the liquid phase, typically at a temperature below 130 ^QC. A number of such phenolic resins are commercially available and will be readily known.

[0032] A preferred phenolic resin component would comprise a phenol resin of the benzyl ether type. It can be expedient in individual cases to use an alkylphenol, such as o-cresol, p-nonylphenol or p-tert-butylphenol, in the mixture, in particular with phenol, for the preparation of the phenol resin. Optionally, these resins can feature alkoxylated end groups which are obtained by capping hydroxymethylene groups with alkyl groups like methyl, ethyl, propyl and butyl groups.

[0033] As to the polymeric isocyanate, it may be preferred to use a polyisocyanate component that comprises diphenylmethane diisocyanate (MDI), although a number of commercially available polymeric isocyanates are directed for this specific market. The isocyanate component (second component) of the two-component binder system for the polyurethane cold-box or no-bake process usually comprises an aliphatic, cycloaliphatic or aromatic polyisocyanate having preferably between two and five isocyanate groups; mixtures of such polyisocyanates may also be used. Particularly suitable

polyisocyanates among the aliphatic polyisocyanates are, for example, hexamethylene diisocyanate, particularly suitable ones among the alicyclic polyisocyanates are, for example, 4,4'-dicyclohexylmethane diisocyanate and particularly suitable ones among the aromatic polyisocyanates are, for example, 2,4'- and 2,6'-toluene diisocyanate, diphenylmethane diisocyanate and their dimethyl derivatives. Further examples of suitable polyisocyanates are 1 ,5-naphthalene diisocyanate, triphenylmethane

triisocyanate, xylene diisocyanate and their methyl derivatives,

polymethylenepolyphenyl isocyanates (polymeric MDI), etc. Although all

polyisocyanates react with the phenol resin with formation of a crosslinked polymer structure, the aromatic polyisocyanates are preferred in practice. Diphenylmethane diisocyanate (MDI), triphenylmethane triisocyanate, polymethylene polyphenyl isocyanates (polymeric MDI) and mixtures thereof are particularly preferred.

[0034] The polyisocyanate is used in concentrations which are sufficient to effect curing of the phenol resin. In general, 10-500% by weight, preferably 20-300% by weight, based on the mass of (undiluted) phenol resin used, of polyisocyanate are employed. The polyisocyanate is used in liquid form; liquid polyisocyanate can be used in undiluted form, and solid or viscous polyisocyanates are used in the form of a solution in an organic solvent, it being possible for the solvent to account for up to 80% by weight of the polyisocyanate solution.

[0035] Several solvents have conventionally been used in the Part I and Part II components. One is a dibasic ester, commonly a methyl ester of a dicarboxylic acid. Sigma-A!drich sells a dibasic ester of this type under the trade designation DBE, which is believed to have the structural formula CH302C(CH2)nC02CH3, where n is an integer between 2 and 4. Another solvent is kerosene, which is understood to be the generic name of a petroleum distillate cut having a boiling point in the range of 150 to 275 degrees C.

[0036] Other solvents that are useful are sold commercially as AROMATIC SOLVENT 100, AROMATIC SOLVENT 150, and AROMATIC SOLVENT 200, which are also respectively known as SOLVESSO 100, SOLVESSO 150 and SOLVESSO 200. They have the respective CAS Registry numbers 64742-95-6, 64742-95-5 and 64742-94-5. While SOLVESSO is an expired registered trademark of Exxon, the solvents are referred to by those designations even when originating from other sources. [0037] Performance additives are also included in the respective parts of the formulation. In the Part I component, an especially preferred performance additive is hydrofluoric acid (which is commonly used as a 49% aqueous solution, but it may be used in different dilution or with a different diluent). Coupling agents and additives based on fatty acids can also be used. In the Part II component, the preferred performance additives would include modified fatty oils and bench life extenders, which would include phosphoroxytrichloride (POC ), phenyl dichlorophosphate and benzyl phosphoroxy dichloride.

[0038] A recently developed binder system uses an alkyl alcohol, especially ethanol, as a solvent instead of the aromatic solvent as used conventionally. As in conventional systems, the binder is provided in two parts, with the two parts preferably being packaged separately and combined only upon use. The Part I component contains the base polyol resin, dibasic ester ("DBE"), a fatty acid alkyl ester like rapeseed methyl ester or soybean methyl ester, and ethanol. The Part II component is substantially diphenylmethane diisocyanate (MDI), although it would be common to include a small but effective amount (approximately 0.05% by weight) of a conventional bench-life extender. This formulation will immediately be notable as being devoid of the aromatic solvents benzene, toluene and xylene (generally referred to collectively as "BTX").

Therefore, a binder system having this composition would be useful in markets where BTX emissions are tightly limited, although the flash point of the system could be disadvantageous in markets where flash point limitations are in effect. However, economics of ethanol and its "green" nature may provide an advantage in selected markets.

[0039] Ethanol differs from the BTX family of solvents because it is a reactive diluent in the binder system. Other reactive diluents are used in, for illustrative purposes only, furan, epoxy, and urethane resin formulations. Some of these include, again for illustrative purposes only, triethylene glycol, resorcinol, and various mono- or di- functional glycidyl ethers. However, in conventional phenolic polyurethanes, the use of reactive diluents is uncommon and primarily for the purpose of lowering cost. A reactive solvent or diluent can polymerize during the curing process, and be dispersed within the polymer matrix. A lower amount of volatile organic compounds ("VOC") is expected because the reactive diluents participate in the reaction. Since ethanol is a mono- functional alcohol, it can react with the isocyanate in the Part II composition and terminate the polyurethane. An alcohol with a higher functionality could lengthen or cross-link the polymer.

[0040] When using solvents with reactive hydroxyl groups, it is important to consider the amount of isocyanate groups required to fully react with the total amount of polyol and solvent. Low "equivalent weight" solvents greatly increase the amount of isocyanate necessary. The formulae for equivalent weight are known in the industry and can be readily used by those of skill. An inverse of "equivalent weight" is the "equivalent", which can also be calculated for each component, again according to known equations. Most usefully, the ratio of -NCO to -OH is most commonly multiplied by 100 and expressed as an "index."

[0041] As a general rule, the Index should be within about 15% of 100. However, when these calculations are made based on a binder composition containing ethanol and a polyol resin with an equivalent weight of 1 15 g/eq, and Parts I and II in a 60/40 ratio, an Index of 58 obtains. Even with Part II being 99.95% MDI, the system lacks enough isocyanate for full reaction. If the ratio is adjusted to 48/52, the Index improves to 94, which is within the ideal range. This calculation assumes no ethanol loss from evaporation during mixing. Therefore, some further refinement of the ratio may yield improved performance.

[0042] The calculations also reveal that 1 % by weight of ethanol consumes 2.94% by weight of MDI. Thus, it must be considered that use of ethanol could require an increased amount of MDI, with the cost consequence thereof.

[0043] Ethanol, as a primary alcohol, is more reactive than diacetone alcohol (CAS Reg. Nr. 123-42-2), which has been used as a solvent in binder systems. This increased reactivity is apparent in real work time results, as well as elsewhere. The addition of bench-life extenders can solve some of the reactivity issues, but cause other issues. The binder can require additional catalyst to achieve comparable reactivity of standard systems when ethanol is used. Also, the no-bake binder system has trouble accelerating faster than a work time of 2.5 minutes, even with very strong catalysts. The mixed sand is observed to have less flowability, due to either the lower amount of total solvents, or ethanol reacting prematurely. Lastly, bench-life extenders decrease the overall strength performance of cured cores and molds.

[0044] To demonstrate the concept, several experimental formulations were devised and then used for tensile strength testing. In these examples, the polyol resin is a benzylic ether phenolic resin, CAS Reg. Nr. 9003-35-4 with a hydroxyl equivalent weight of 1 15 g/eq. The dibasic ester used is a blend of dimethyl glutarate, dimethyl succinate and dimethyl adipate. INNOVATI 170 is a commercially-available methyl ester of fatty acids of soybean oil, CAS Reg. Nr. 67784-80-9.

[0045] In the examples provided, Isocyanate Type 1 is a polymeric diphenylmethane diisocyanate with an NCO content of 31 -33%. 4-PPP is 4-(3-phenylpropyl)pyridine, CAS Reg. Nr. 2057-49-0. NMI is N-methyl imidazole, CAS Reg. Nr. 616-47-7.

References to ethanol are to anhydrous ethanol.

Composition A

[0046] A first formulation, referred to as Composition A, had the following Part I component:

[0047] The Part II component for Composition A was:

Monophenyl dichlorophosphate has the CAS Reg No 770-12-7. Composition A may be generally characterized as a binder system in which the BTX solvents have been completely replaced by ethanol in the Part I component. Such a system may have commercial application in a market where ethanol is readily available and BTX emissions are strictly limited. Such a market may be found in Brazil, as an example.

Composition B

[0048] A second formulation, referred to as Composition B, had the following Part I component:

The Part I component of Composition B modifies Part I of Composition A by replacing DBE and INNOVATI 170 solvents with aromatic hydrocarbon solvents ("BTX solvents"). Composition B also has a Part II component that is identical to Part II of Composition A.

Composition C

[0050] A third formulation, referred to as Composition C, had the following Part I component:

[0051] The Part II component for Composition C was:

Composition C is characterized as a conventional phenolic-binder system as used in the United States, and is presented as phenolic-urethane no-bake binder baseline comparison for that market. Part II has a lower percentage of Isocyanate Type I than Compositions A and B, due to the absence of ethanol in the Part I component it is used with.

Tensile strength testing

[0052] Tensile strength testing was performed on Wedron 410, 51 GFN silica sand, with a 1 .2% by weight binder level in each case.

[0053] In an initial test, shown below in Table 1 , a conventional phenolic-urethane no- bake binder formulation (Composition C) was compared to binders with ethanol- containing Parts I (Compositions A and B). Not unexpectedly, the ethanol-containing systems required more catalyst to achieve comparable work time and strip time and failed to develop tensile strength over time, due to insufficient isocyanate, as the -NCO to -OH Index was only 58, compared to the higher Index of 88 for Composition C. Note that Compositions A and B comprise a bench life extender in Part II to suppress premature reaction between ethanol and isocyanate, which led to higher catalyst demand.

Table 1

(^*) "based on binder"

As is well-known, "work time" as used above can loosely be understood as an

expression of the time that elapses between mixing the binder components with the sand until the foundry shape being formed reaches a hardness that effectively precludes further working in the pattern. More technically, "work time" is the time elapsed for the foundry shape formed to reach a level of 60 on the Green Hardness "B" scale, using a gauge from sold by Harry W. Dietert Co., of Detroit, Ml. Details of the test are found many places, including in commonly-owned US Patent 6,602,931 . "Strip time" loosely defines the elapsed time from mixing the binder components with the sand until the formed foundry shape is able to be removed from the pattern. In the technical sense used here, the "strip time" is the time needed for the foundry shape formed to attain a level of 90 on the same Green Hardness "B" scale. The difference between strip time and work time is, therefore, an amount of dead time during which the mold being formed cannot be worked upon, but cannot yet be removed from the pattern.

[0054] Compositions C and A were tested again, using the "hotter" NMI catalyst to provide a faster work time. Composition A required a higher NMI content in a blended catalyst system to achieve the desired work time/strip time properties. The results, as shown in Table 2 below, are consistent with the Table 1 results and are not unexpected.

Table 2

[0055] As noted with regard to Table 1 , Composition A was initially tested at an Index well below the desired Index, which is between about 90 and 1 10. The latter can be obtained by adjusting the Part I to Part II ratio from 60/40 to 48/52. When this is done and the conditions of Table 1 are duplicated, the tensile strengths are again not able to match the conventional phenolic-urethane no-bake binder baseline (Composition C in Table 1 ), but the binder continues to develop strength over time.

Table 3

As noted, the binder was applied at a 1 .2% by weight in Table 1 . By increasing the binder to 1 .48% by weight and using the 48/52 ratio, Composition A was determined to have a 1 hr tensile strength of 157, with tensile strengths of 302 and 309, respectively, at 3 and 24 hrs. Thus, it is seen that Composition A (at 1 .48% binder) can approach the performance of the Composition C baseline case (at 1 .2% binder) through adjusting ratio and the amount of binder used.

VOC Testing

[0056] Volatile organic carbon ("VOC") can be measured through several different tests. The first of these is the EPA Method 24. In that test, a sample, weighing from 0.3 to 0.5 g, is dissolved in 3 ml of acetone and placed in an oven at 1 10 °C for 1 hour. The percentage of VOC is based on weight lost. The test was conducted for the Part I components of Compositions C, A and B, that is, the phenolic-urethane no-bake binder baseline and the two ethanol-containing systems. The respective %VOC were 53.9, 51 .8 and 49.8%. These results are essentially equal and not distinguishable. Although the Part II components were not actually tested according to EPA Method 24, it is believed that they would be less than 5% VOC for Compositions A and B, due to the higher isocyanate and the absence of the AROMATIC 1 00 constituent. A conventional Part II component has a VOC content according to EPA Method 24 in the range of 20% to 40%, so the ethanol-containing systems would be expected to reduce VOC content for the overall system.

[0057] The second type of VOC test is the EPA Method 24 "Reacted" test. In this test, a sample, weighing about 0.3 g, of the multi-component binder (i.e. including Part I, Part II and catalyst), is mixed in the preferred ratio and then dissolved in 3 ml of acetone. This is conditioned for 1 to 24 hours and placed in an oven at 1 10 °C for 1 hour. The percentage of VOC is based on weight lost. The baseline composition (C) had 30.2% VOC, respectively, in the EPA Method 24 "Reacted" test. When ethanol-containing Composition A was measured with a Part I/Part II ratio of 60/40, the EPA Method 24 "Reacted" was 14.4% VOC. When the same composition was measured at the more preferred 48/52 ratio, EPA Method 24 "Reacted" VOC content dropped to 7.2%, a 50% reduction and an amount that is about 20% of the baseline composition.

[0058] The third type of VOC test that is considered relevant by one or more regulatory authorities is the OCMA test (Ohio Cast Metals Association). In this test, weight loss is measured for a mixed bowl of sand and binder over 24 hours. Because of the ability to vary the binder amount, the results can be reported as either pounds of VOC per ton of mixed sand or pounds of VOC per pound of binder. When baseline Composition C was tested, using a 55/45 ratio and 1 .25% by weight BOB of 4-PPP, the pounds of VOC per ton of sand was measured at 1 .03 after 12 hours and at 1 .41 after 24 hours, which translates to 0.050 and 0.069 pounds of VOC per pound of binder, respectively. It was noted that the majority of weight loss in the ethanol-containing Composition A occurred during mixing, which is not unexpected.

[0059] Among the alcohols with low molecular weights, ethanol may be uniquely situated for this application. Methanol has a lower flashpoint and higher toxicity. It also is less likely to be available from a renewable "green" source. Propanol, in either of its isomers, and the higher molecular weight alcohols, are not typically available through fermentation of renewable resources, although all have higher flash points than ethanol.

Claims

CLAIMS What is claimed is:

Claim 1. A binder system for a molding material mixture, comprising:

a first component, having a polyol base resin with at least two -OH groups per molecule and an alkyl alcohol, having from two to five carbon atoms, as a solvent; and a second component, having a polyisocyanate with at least two -NCO groups per molecule;

wherein the respective components are packaged separately and combined upon use.

Claim 2. The polyurethane binder precursor of claim 1 , wherein:

the alkyl alcohol is anhydrous ethanol.

Claim 3. The binder system of claim 1 or claim 2, wherein at least the first component is substantially devoid of aromatic hydrocarbon solvents.

Claim 4. The binder system of claim 1 or claim 2, wherein:

the respective first and second components are present in a weight ratio such that the first component weighs less than the second component.

Claim 5. The binder system of claim 1 or claim 2, wherein:

the second component consists essentially of diphenylmethane diisocyanate (MDI) with less than 0.1 % of a bench life extender.

Claim 6, The binder system of claim 1 or claim 2, wherein:

the first component comprises, in addition to the polyol base resin and the alkyl alcohol, at least one fatty acid methyl ester and at least one dibasic ester.

Clam 7. The binder system of claim 6, wherein: the first component contains about 56.

8% by weight of the polyol resin, 23.9% by weight of the at least one dibasic ester, and 16.9% by weight of the alkyl alcohol, with the balance being the at least one fatty acid methyl ester.

Claim 8, The binder system of claim 1 or claim 2, wherein:

the first and second components are packaged such that about 48 parts by weight of the first component is used with about 52 parts by weight of the second component.

Claim 9. A molding material mixture, comprising:

a refractory mold base material; and

a binder system according to any one of claims 1 through 8.

Claim 10, The molding material mixture of claim 9, wherein:

the refractory mold base material is selected from the group consisting of: quartz ore sand, zirconium ore sand, chromium ore sand, olivine, chamotte, bauxite, aluminum silicate hollow spheres, glass beads, glass granules, spherical ceramic molding materials and combinations thereof.

Claim 11. The molding material mixture of claim 9 or claim 10, wherein:

the binder system is present in an amount of between 0.2 to 5%, by weight, based on the weight of the refractory mold base material, preferably in the range of between 0.3 and 4% by weight, and most preferably in the range of between 0.4 and 3% by weight.

Claim 12. A method for producing a mold or core for casting of a molten metal, comprising the steps of:

providing an organic binder system and a refractory molding material, the organic binder system provided as two components that are not combined until the time of use; mixing the two components of the organic binder system with the refractory molding material to provide a shapeable foundry mix;

forming the shapeable foundry mix into a mold or core; and

curing the mold or core formed.

Claim 13. The method of claim 12, wherein:

the method is a polyurethane "cold-box" method and the curing step is achieved by conducting gaseous tertiary amines through the formed mold or core.

Claim 14. The method of claim 12, wherein:

the method is a polyurethane "no-bake" method in which the curing step is achieved by adding tertiary amines in a liquid phase to the two components and the refractory molding material.