HEAT CURED FOUNDRY BINDERS AND THEIR USE

Abstract: This invention relates to heat-curable foundry binder resins comprising: a) a nitrogen free modified furan resin, b) furfuryl acohol, c) polyvinyl acetate, and d) a tar selected from the group consisting of resorcinol pitch, bis phenol A tar, and mixtures thereof. The resins are used to prepare foundry shapes by mixing them with an aggregate and an acid curing catalyst to form a foundry mix. The resulting mix is shaped and heated at an elevated temperature to form a cured foundry shape.

Description: HEAT CURED FOUNDRY BINDERS AND THEIR USE FIELD OF THE INVENTION This invention relates to a heat cured nitrogen free foundry binder essentially free of free formaldehyde comprising (a) a nitrogen free modified furan resin, (b) furfuryl alcohol, (c) polyvinyl acetate, and preferably (d) a tar selected from the group consisting of resorcinol pitch, biεphenol A tar, and mixtures thereof. The binders are used to prepare foundry shapes by mixing them with an aggregate and latent acid curing catalyst to form a foundry mix, and shaping the resulting foundry mix. The foundry shape is heated at an elevated temperature to form a cured foundry shape. BACKGROUND OF THE INVENTION Heat cured binders based upon furan resins and furfuryl alcohol are well known. See for example U.S. Patents 4,317,763, 4,451,577, and 4,383,098 which describe heat cured foundry binders, typically cured in the presence of a latent acid curing catalyst. These binders are preferred for some applications because of their price, the availability of equipment, and the dimensional accuracy of the foundry shapes made with them. Typically heat cured binders, particularly hot-box binders, which are cured at temperatures of 100*C to 300"C in the presence of a latent acid curing catalyst, contain urea and other nitrogen containing compounds which scavenge free formaldehyde and provide extra strength to foundry shapes made with such binders. A problem with these heat curable foundry binders is that their high nitrogen content causes casting defects during metal casting processes such as pinholing and porosity. Another problem is that these binders contain free formaldehyde which is to be avoided. It is also known that the bench life of foundry mixes made with these binders is often inadequate due to the presence of the latent acid curing catalyst in the foundry mix. The bench life of the foundry mix is the time period between forming the mixture of the aggregate and binder and the time when the mixture is no longer useful for making acceptable molds and cores. A measure of mold and core acceptability is tensile strength. If a foundry mix consisting of aggregate and binder composition is used after the bench life has expired, the resulting molds and cores will have insufficient tensile strength. Since the foundry mix made with a heat curable binder contains a latent acid curing catalyst in addition to the aggregate and resin, the catalyst and resin may react prior to shaping the mix into foundry molds and cores. If this reaction occurs, it will reduce the flowability of the foundry mix and the resulting molds and cores will have reduced strength. Additionally, it will be necessary to clean the hoppers, in which the foundry mix is stored, more frequently. This is time consuming and expensive. SUMMARY OF THE INVENTION This invention relates to a heat cured nitrogen free foundry binder essentially free of free formaldehyde comprising : (a) from about 50 to about 90 parts by weight of a nitrogen free modified furan resin; (b) from about 1 to about 10 parts by weight of furfuryl alcohol; (c) from about 3 to about 20 parts by weight of polyvinyl acetate; and preferably (d) from about 3 to about 20 parts by weight of a tar selected from the group consisting of resorcinol pitch, bisphenol A tar, and mixtures thereof, wherein said parts by weight are based upon 100 parts of binder resin. Preferably from about 60 to about 85 parts by weight of nitrogen free modified furan resin, from about 10 to about 15 parts by weight of furfuryl alcohol, from about 10 to about 20 parts by weight of polyvinyl acetate, and from about 5 to about 10 parts by weight of a tar are used in the binder. Preferably a mixture of resorcinol pitch and bisphenol A tar is used. The heat cured binder is used to prepare foundry shapes by mixing the binder with an aggregate and a latent acid curing catalyst to form a foundry mix. The resulting mix is shaped and heated at an elevated temperature to form a cured foundry shape. Heat is applied with warm-box or hot-box equipment, baking in an oven, or with a microwave. Unlike typical heat cured binder systems, these binder systems are free of nitrogen and essentially free of free formaldehyde. By essentially free of free formaldehyde, it is meant that the free formaldehyde content of the binder is from 0.0 to 0.05 weight percent, based upon the total weight of the foundry binder. Since the binders do not contain nitrogen, casting defects such as pinholing and porosity are not promoted. Although the tensile strengths of foundry shapes made with these binders is not significantly different than those made with nitrogen containing furan resins, it is remarkable that such strengths could be achieved without incorporating nitrogen compounds into the binder which promotes the formation of high strength urea linkages in the cured binder. The binder is cured with a latent acid curing catalyst, preferably copper tosylate at temperatures of about 100"C to 300"C. The ratios of binder components including the nitrogen free furan resin, furfuryl alcohol, resorcinol pitch, bisphenol A tar and polyvinylacetate play an important role for producing desired tensile properties. Although a bench life extender can be used in the binder, it is not necessary because the foundry mix has a bench life of up to five hours without the incorporation of a bench life extender. ENABLING DISCLOSURE AND BEST MODE The heat cured binders are based on a nitrogen free modified furan resin and furfuryl alcohol which are cured with a latent acid curing catalyst at temperatures of from about 100°C to 300"C. The furfuryl alcohol acts as a diluent and reduces the viscosity of the modified furan resin. For purposes of this disclosure, a "modified furan resin" is a furan resin which is made from furfuryl alcohol, phenol, and formaldehyde at elevated temperatures under essentially alkaline conditions at a pH of from 8.0 to 9.0, preferably 8.4 to 8.7. The weight percent of furfuryl alcohol used in making the nitrogen free modified furan resins ranges from 50 to 65 percent; the weight percent of the phenol used in making the nitrogen free modified furan resins ranges from 10 to 25 percent; and the weight percent of the formaldehyde used in making the nitrogen free modified furan resins ranges from 15 to 25 percent, where all weight percentε are based upon the total weight of the components used to make the modified furan resin. The reaction temperature used in making the nitrogen free modified furan resins ranges from 95°C to 105'C. The reaction is continued until the percentage of free formaldehyde is less than 5 weight percent, typically from 3 to 5 weight percent, and the refractive index is from 1.500 to about 1.600. The viscosity of the resin is preferably from about 200 cpε to 450 cps. The heat cured binders are made by combining the nitrogen free modified furan resin with furfuryl alcohol, polyvinyl acetate, and preferably a tar selected from the group consisting of resorcinol pitch, bisphenol A tar, and mixtureε thereof to make a heat cured binder εyεtem. Biεphenol A tar is defined aε the highly viscous product which remains on the bottom of the reaction veεεel after biεphenol A iε produced and diεtilled from the reaction veεsel. The bisphenol A tar iε a solid at room temperature and has a melting point of about 70 * C to 80 * C. Biεphenol A tar iε mostly dimers, trimerε, and polymeric biε phenol A. It may alεo contain substituted materials. Resorcinol pitch iε defined aε the highly viscous product which remains on the bottom of the reaction veεsel after reεorcinol iε produced and distilled from the reaction vessel. Resorcinol pitch is a solid at room temperature and has a melting point of about 70 ' C to 80*C. Resorcinol pitch iε moεtly dimers, trimers, and polymeric resorcinol. It may also contain substituted materials. Preferably a mixture of biεphenol A tar and reεorcinol pitch are uεed to modify the binder in an amount such that the ratio of bisphenol A tar to resorcinol pitch iε from 3:1 to 1:3, most preferably about 1:1. In general, many εaltε of a strong inorganic or organic acids, preferably organic acids, can be used as latent curing catalyεtε. ' Examples of saltε from organic acids include copper phenol sulfonate, aluminum toluene sulfonate, zinc phenol sulfonate, and preferably copper toluene sulfonate, aluminum toluene sulfonate, and phenol toluene sulfonate, and the like, most preferably copper toluene εulfonate. The amount of latent curing catalyst uεed is the amount required to result in foundry shapeε which can be handled without breaking. Generally, this amount is from 1 to 45 weight percent based upon the weight of total binder, typically from 10 to 40, preferably 15 to 35 weight percent. It will be apparent to those skilled in the art that other additives such aε release agents, solvents, etc. can be used and may be added to the binder composition, aggregate, or foundry mix. For example, where the foundry shape must show a higher degree of resistance to water, it iε preferable to uεe a εilane. In εuch caεeε the water may come from moiεture in the air or εpecial processing conditions of the foundry shapes, such as immersion in a core wash. Silanes which can be uεed can be repreεented by the following structural formula: wherein R 1 iε a hydrocarbon radical and preferably an alkyl radical of 1 to 6 carbon atomε and R iε an alkyl radical, an alkoxy-εubεtituted alkyl radical, or an alkyl-a ine- subεtituted alkyl radical in which the alkyl groups have from 1 to 6 carbon atomε. The aforesaid εilane, is employed in concentrations of 0.1% to 2%, based on the phenolic binder and hardener. Examples of some commercially available silaneε are Dow Corning Z6040; Union Carbide A-1100 (gamma aminopropyltriethoxy εilane) ; Union Carbide A-1120 (N- beta(aminoethyl)-gamma-amino-propyltrimethoxy εilane); and Union Carbide A-1160 (ureido-εilane) . Although not required, bench life extenderε may alεo be added to the binder formulation. Exa pleε of bench life extenderε include alkaline earth metal carbonateε such as magnesium carbonate, calcium carbonate, and barium carbonate, and alkaline earth metal oxides such as magnesium oxide, calcium oxide, and barium oxide, preferably calcium carbonate. The particle size of the bench life extender typically iε from about 0.5 micron to about 25 micronε, preferably from about l micron to about 10 micronε. It has been found that the uεe of the bench life extender in amounts of from 0.01 to l.o weight percent of the thermosetting reεin, preferably 0.05 to 0.5 weight percent, moεt preferably 0.05 to 0.1 weight percent, are effective. Although more bench life extender can be uεed, this is unneceεεary in most caseε and only increaεeε the cost of the binder without a significant increase in benefits, and in some cases may even decrease the bench life of the foundry mix. Since the amount of bench life extender used on the sand is a very small amount, typically from 0.001 to 0.05 weight percent based upon the. weight of the aggregate, moεt typically 0.001 to 0.01 weight percent, for most situations it is preferable to mix the alkaline earth metal carbonate with a εilicone compound to form an emulsion before adding it to the aggregate. This iε an effective way of distributing the small amount of bench life extender on the aggregate. Silicone compounds also improve the release of the foundry shapes made with the foundry mix. Silicone compounds, which can be used in the foundry mix, typically are polydimethylsiloxaneε, often trimethylεilyl terminated. Generally, they are εold commercially aε fluidε or emulsions (which contain water and a surfactant as well aε the silicone compound) . Examples of commercially available products which contain εilicone compoundε and are effective include DC 1101, DC 108, DC 24, DC 531. All of these mentioned products are emulsionε except DC 531, and all are εold by Dow Corning Corporation. Exampleε of other commercially available εilicone compounds are LE-460, AF-70 which are sold by Union Carbide and General Electric respectively. Typically the weight ratio of the bench life extender to the silicone is from 0.50 to 5.0 weight percent baεed upon the total weight of the emulsion containing the bench life extender. The aggregate uεed to prepare the foundry mixes iε that typically used in the foundry industry for such purposes or any aggregate that will work for such purposeε. Generally, the aggregate will be sand which contains at least 70 percent by weight silica. Other suitable aggregate materials include zircon, alumina-silicate sand, chromite εand, and the like. Generally, the particle εize of the aggregate is such that at least 80 percent by weight of the aggregate haε an average particle εize between 40 and 150 mesh (Tyler Screen Mesh) . Although it is possible to mix the components of the binder with the aggregate in variouε sequences, it iε preferred to add the latent acid curing acid catalyεt to the aggregate and mix it with the aggregate before adding the binder. Curing is accomplished by heating the shaped foundry mix in an a convection oven, a microwave oven, or by means of another heat source. Generally, however, curing iε accompliεhed by injecting the foundry mix into a core box which has been heated to a temperature sufficient to cure the foundry mix and produce a workable foundry shape. Generally, the temperature needed to cure the foundry mix is from 135*C to 300"C, preferably from 160"C to 260*C. A workable foundry shape is one which can be handled without breaking. Generally, the dwell time of shaped foundry mix in the core box needed to produce a workable foundry shape is from 5 εecondε to 120 seconds, usually from 10 seconds to 60 εecondε. Metal caεtingε can be prepared from the workable foundry shapes by methods well known in the art. Molten ferrous or non-ferrous metals are poured into or around the workable shape. The metal is allowed to cool and solidify, and then the casting is removed from the foundry shape. The following abbreviationε are uεed in the Examples and Table I which follow: BAT = biεphenol A tar BLE = bench life extender CT = constant temperature FA = furfuryl alcohol MFR = a modified furan base resin for MFB which is the reaction product of a mixture of phenol, formaldehyde, and furfuryl alcohol under baεic conditions at a reflux temperature of 100* C, such that the ratio of formaldehyde to phenol is 3:1 and the ratio of formaldehyde to furfuryl alcohol is 0.76:1.0 MFB = CHEM-REZ 244 binder, a nitrogen free modified furan binder sold by Ashland Chemical Company which comprises MFR and FA as specified in Table I PVA = polyvinyl acetate RH = relative humidity temperature RP = resorcinol pitch EXAMPLES (All weight percentε are based upon the total charge.) Foundry mixes were prepared by mixing 4000 parts of Badger sand and 8.5 parts of a copper tosylate catalyεt for 2 minuteε. Then 50 partε of binder compoεed of the amountε specified in Table I are added and mixed for 2 minuteε. The resulting foundry mixes are forced by air blowing the mix into a standard AFS core box (dog bone shape) which was heated to a temperature of 232'C. The tensile εtrengths (in pεi) for variouε εampleε after being taken from the core box at εpecified dwell times (dwell times were 10, 20, 30, and 40 εeconds), are given in Table I. The hot tensile measurements were taken within 10 seconds after removing the εhapeε from the core box. The cold tenεileε were measured at least 1 hour after removing the shapeε from the corebox. The examples show that the foundry mixes tested had sufficient flowability and produced workable foundry shapeε under the conditionε teεted. EXAMPLES 1-6 Heat curable foundry binderε were prepared with the mixtures of MFRB, FA, polyvinyl acetate, biεphenol A tar, and resorcinol pitch. The binders were cured with a copper toluene sulfonate catalyst. Example A is the control. TABLE I Example A 1 2 3 4 5 Component AMOUNTS (pbw) MFRB 84 72 72 64 60 63 FA 16 18 18 16 15 15 PVA 0 10 0 10 10 12 BAT 0 0 0 0 5 5 RP 0 0 10 10 10 5 DWELL TIME HOT TENSILES OF CORE SAMPLES (PEI) 10 sec. 65 110 82 132 111 118 20 sec. 104 189 136 165 197 202 30 sec. 135 212 150 201 184 186 40 sec. 123 178 151 178 158 187 Although Table I shows that overall tensile εtrengthε of foundry cores prepared with the subject binders are not improved significantly when compared to the control, the subject binders are essentially free of free formaldehyde and are able to produce foundry cores without using nitrogen containing compounds to build strength. Cold tensile strengths were also measured, but are not shown in Table I because they were all found to be more than adequate for all foundry shapeε made with all the teεted binder formulationε.

Claims: CLAIMS We claim: 1. A heat cured foundry binder compriεing in admixture: (a) from about 50 to about 90 partε by weight of a nitrogen free modified furan reεin; (b) from about 1 to about 25 partε by weight of furfuryl alcohol; (c) from about 3 to about 20 partε by weight of polyvinyl acetate; and (d) an effective free formaldehyde reducing amount of a tar εelected from the group conεiεting of reεorcinol pitch, bisphenol A tar, and mixtures thereof, wherein εaid partε by weight are baεed upon 100 partε of binder reεin. 2. The foundry binder of claim 1 wherein the tar is present in the amount of 3 to 20 parts by weight. 3. The foundry binder of claim 1 where the tar iε resorcinol pitch. 4. The binder of claim 3 where a mixture of bisphenol A pitch and resorcinol pitch is uεed in a weight ratio of 3:1 to 1:3. 5. A foundry mix compriεing in admixture: (a) a foundry aggregate; (b) from about 50 to about 90 partε by weight of a nitrogen free modified furan resin; (c) from about 1 to about 25 parts by weight of furfuryl alcohol; (d) from about 3 to about 20 parts by weight of polyvinyl acetate; and (e) an effective free formaldehyde reducing amount of a tar selected from the group conεiεting of reεorcinol pitch, biεphenol A tar, and mixtureε thereof, wherein εaid partε by weight are based upon 100 partε of binder reεin. 6. The foundry mix of claim 5 wherein the tar iε in an amount of from 3 to 20 parts by weight. 7. The foundry mix of claim 6 wherein the tar is resorcinol pitch. 8. The foundry mix of claim 6 wherein a mixture of bisphenol A pitch and resorcinol pitch is used in a weight ratio of 3:1 to 1:3. 9. A process for preparing a foundry shape comprising: (1) mixing a foundry aggregate with a bonding amount of up to about 10 percent by weight, based upon the weight of the aggregate, of a binder composition comprising: (2) a heat curable foundry binder comprising: (a) from about 50 to about 90 parts by weight of a nitrogen free modified furan resin; (b) from about 1 to about 25 parts by weight of furfuryl alcohol; (c) from about 3 to about 20 parts by weight of polyvinyl acetate; and (d) an effective free formaldehyde reducing amount of a tar selected from the group consisting of reεorcinol pitch, biεphenol A tar, and mixtureε thereof, wherein εaid partε by weight are baεed upon 100 partε of binder reεin; and (3) an acid catalyεt; B. shaping the foundry mix of A into a foundry εhape; C. contacting the foundry shape of B with a source of heat at a temperature sufficient to cure said mix; and D. allowing the foundry shape to harden into a workable foundry shape. 10. The procesε of claim 9 wherein the tar iε present in an amount of 3 to 20 partε by weight. 11. The proceεε of claim 10 wherein the tar iε reεorcinol pitch. 12. The foundry mix of claim 11 wherein a mixture of bisphenol A pitch and resorcinol pitch iε uεed in a weight ratio of 3:1 to 1:3. 13. A foundry εhape prepared in accordance with claim 9. 14. A foundry shape prepared in accordance with claim 12. 15. A method for preparing a metal casting comprising: (a) fabricating a εhape in accordance with claim 9; (b) pouring εaid low melting metal while in the liquid state into and around εaid shape; (c) allowing εaid low melting metal to cool and solidify; and (d) then separating the molded article. 16. A method for preparing a metal casting compriεing: (a) fabricating a εhape in accordance with claim 12; (b) pouring εaid low melting metal while in the liquid state into and around εaid εhape; (c) allowing εaid low melting metal to cool and εolidify; and (d) then εeparating the molded article. 17. A metal casting prepared in accordance with claim 15. 18. A metal casting prepared in accordance with claim 16.

Inventors: HAUGSE A LEONARD, KIM YOUNG D, HAUGSE, A., LEONARD, KIM, YOUNG, D.
Applicants: ASHLAND OIL INC, ASHLAND OIL, INC.
Application year: 1995
Main classification: B22C1
IPC codes: B22C1, C08L31, C08L61, C08L95