SULFUR DIOXIDE-CURED EPOXY ACRYLATE FOUNDRY BINDER SYSTEM

Abstract

The present invention provides an epoxy acrylate foundry binder composition having an epoxy resin component (Part 1) and an acrylate component (Part 2) containing about 1% to less than about 6% by weight of a borate ester. The epoxy acrylate binders of the present invention are useful in making foundry cores and molds in that the addition of the borate ester increases hot strength of the binder system. Also provided is a cold-box process for making sand cores and molds using the epoxy acrylate binders cured by sulfur dioxide vapor.

Description

FIELD OF THE INVENTION

The present invention relates to improved epoxy acrylate foundry binder compositions having an epoxy resin component and an acrylate component useful in making sulfur dioxide (SO₂)-cured foundry cores and molds. More particularly, this invention relates to the use of borate esters such as trialkyl borates in the acrylate component of such foundry binder compositions to improve hot strength and thus prevent erosion-related defects.

BACKGROUND OF THE INVENTION

An important process used in the foundry industry for making metal parts is sand casting. In sand casting, disposable foundry shapes, including molds and cores, are made by shaping and curing a foundry mix. The foundry mix is a mixture of an appropriate aggregate (typically sand) and an organic or inorganic binder. The function of a binder is to bond the aggregate together to make molds and cores.

One foundry process that is commonly used for making cores and molds entails the use of sulfur dioxide (SO₂) to cure the epoxy acrylate binder system. This is a variant of the “cold-box” process in which a mixture of a peroxide, an epoxy resin, a multifunctional acrylate, and optional diluents and/or additives are mixed with an aggregate and compacted into a pattern to give the mixture a specific shape. The shaped mixture is contacted with SO₂ vapor (optionally diluted with nitrogen), by blowing the SO₂ into the pattern in which the shape is contained so that the SO₂ reacts with the peroxide to form an acid and free radicals. The acid cures the epoxy resin and the free radicals cure the multifunctional acrylate rapidly hardening the mixture to produce the core or mold which can be used immediately in a foundry core and/or mold assembly.

Although the binder composition can be added to the foundry aggregate separately, it is preferable to package the epoxy resin and free radical initiator (peroxide) as a “Part 1” and add this package to the foundry aggregate first. The ethylenically unsaturated material (acrylate) is then preferably added to the foundry aggregate as the “Part 2,” either alone or along with some of the epoxy resin before curing with SO₂ vapor.

Although SO₂-curing has been used successfully in many foundries, one of the weaknesses of SO₂-cured epoxy acrylate binder systems has been the lack of adequate erosion resistance. Erosion occurs when molten high temperature metals (such as iron or steel) contact the mold or core surfaces during the pouring process and sand is dislodged at the point of contact. Such erosion occurs because the binder does not have sufficient heat resistance, or “hot strength,” to maintain surface integrity until the pouring process is complete. The resulting loose sand may be carried into the mold cavity by the liquid metal, creating sand inclusions and weak areas in the casting. Dimensional defects may also be created on the surface of the casting caused by metal penetration into the surface of the mold or core.

To correct this problem, foundries have historically resorted to the use of refractory coatings to increase hot strength thereby improving resistance to defects caused by impingement of the high temperature metal on mold or core surfaces. For example, core and mold assemblies or parts thereof are coated with a slurry consisting of a high melting refractory oxide, a carrier, and thixotropic additives. Once dried on the mold or core surface, the coating helps prevent erosion in most cases. However, this approach is messy, adds complexity to the sand casting process, and requires expensive gas-fired, microwave, or radiant energy ovens to cure or set the coating making it cost prohibitive and inefficient. In addition, when the cores and/or molds are heated during the drying process, the strength of the organic binder-to-aggregate bond may be significantly weakened sometimes making handling of the hot cores problematic and reducing productivity due to distortion or cracking of the core or mold.

Thus, there is a need for an SO₂-cured epoxy acrylate binder system that can provide foundry shapes with adequate hot strength during the casting process. If a way could be found to make such a binder with increased thermal stability, it would show increased hot strength properties such as increased collapsibility time in a foundry core and would represent a useful contribution to the art. Additionally, because the improved foundry shapes would be more resistant to erosion, they could be used to cast metal articles without coating the foundry shapes with refractory materials.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, there is provided a sulfur dioxide-curable binder composition comprising an epoxy resin component including at least one epoxy resin and a free radical initiator and an acrylate component including at least one acrylate and a boric acid ester. The boric acid ester is present in the binder composition in an amount of about 1% to less than about 6% by weight based on the weight of the acrylate component. In a preferred embodiment, the boric acid ester is a trialkyl borate. In a more preferred embodiment, the trialkyl borate is tri(C₂-C₈)alkyl borate.

In another embodiment, there is provided a sulfur dioxide-curable foundry mix comprising aggregate and a binder including an epoxy resin component (Part 1) and an acrylate component (Part 2). The epoxy resin component includes at least one epoxy resin and a free radical initiator, and the acrylate component includes at least one acrylate and about 1% to less than about 6% by weight of a boric acid ester, based on the weight of the acrylate component. The binder will be used at a level of from about 0.5% to about 2% based on the total weight of the foundry mix. In a preferred embodiment, the boric acid ester is a trialkyl borate. Preferred trialkyl borates include tri(C₂-C₈)alkyl borates. A particularly preferred trialkyl borate is tri-n-butyl borate.

In another embodiment, there is provided a cold-box method of making a foundry shape by preparing a foundry mix by admixing aggregate and a binder comprising an epoxy resin component including at least one epoxy resin and an effective amount of a peroxide and an acrylate component including at least one acrylate and a boric acid ester. The boric acid ester will be present in an amount of about 1% to less than about 6% by weight based on the weight of the acrylate component and the binder will be present in an amount from about 0.5% to about 2% based on the total weight of the foundry mix. The resulting foundry mix is shaped to a desired configuration to provide a shaped foundry mix. The resulting shaped foundry mix is cured with gaseous sulfur dioxide to provide a foundry shape for casting metal parts. In a preferred embodiment, the boric acid ester is a trialkyl borate. In a more preferred embodiment, the trialkyl borate is tri(C₂-C₈)alkyl borate.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, it has now been found that addition of esters of boric acid (“borate esters”) such as trialkyl borates to an epoxy acrylate binder composition provides unexpected improvements in hot strength properties in foundry cores and molds. The foundry binder system includes an epoxy resin component (Part 1) and an acrylate component (Part 2). The trialkyl borate is preferably added to the acrylate component (Part 2) of the binder.

The term “alkyl,” as used herein, refers to a monovalent saturated straight or branched chain hydrocarbon, or a monovalent saturated cyclic hydrocarbon, having the number of carbons designated (i.e. C₁-C₈ means one to eight carbons). Examples include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, n-octyl, n-decyl, n-dodecyl and cyclohexyl.

The term “aryl,” as used herein, refers to a carbocyclic aromatic system containing one or more rings (typically one, two or three rings) wherein such rings may be fused. The aromatic rings may be substituted with one or more substituents, for example, alkyl. Examples include: phenyl, naphthyl, anthracyl, o-cresyl, m-cresyl and p-cresyl.

Trialkyl and triaryl borates are organic boron compounds that are derived from boric acid, specifically esters of boric acid (“borate esters”). Preferred trialkyl borates include tri(C₂-C₈)alkyl borates. Representative useful tri(C₂-C₈)alkyl borates are triethyl borate, tri-n-propyl borate, tri-isopropyl borate, tri-n-butyl borate, tri-isobutyl borate, tri-sec-butyl borate, tri-tert-butyl borate, and tri-n-octyl borate. A particularly preferred trialkyl borate is tri-n-butyl borate (TBB). Useful triaryl borates include triphenyl borate, tri-o-cresyl borate, tri-m-cresyl borate and tri-p-cresyl borate. These and other suitable boric acid esters may be used in accordance with the present invention.

The borate esters used in the present invention must be soluble in the acrylate component (Part 2).

Furthermore, the borate ester may be present in an amount from about 1% to less than about 6% by weight, based on the weight of the acrylate component (Part 2). In a preferred embodiment, the borate ester is present in an amount from about 1% to about 5% by weight, based on the weight of the acrylate component. In a more preferred embodiment, the borate ester is present in an amount from about 2% to about 4% by weight, based on the weight of the acrylate component. In a particularly preferred embodiment, the borate ester is a tri(C₂-C₈)alkyl borate. Higher use levels of certain higher carbon borate ester compounds (e.g. tri-n-octyl borate) may be required in certain applications, due to the corresponding increase in molecular weight of these compounds.

The epoxy resin component (Part 1) contains at least one epoxy resin. An epoxy resin is a resin having an epoxide group. Examples of epoxy resins include (1) diglycidyl ethers of bisphenol A, B, F, G and H, (2) epoxy novolacs, which are glycidyl ethers of phenolic-aldehyde novolacs, and (3) mixtures thereof.

Epoxy resins (1) are made by reacting epichlorohydrin with the bisphenol compound in the presence of an alkaline catalyst. By controlling the operating conditions and varying the ratio of epichlorohydrin to bisphenol compound, products of different molecular weights can be made. Epoxy resins of the type described above based on various bisphenols are available from a wide variety of commercial sources.

Examples of epoxy novolac resins (2) include epoxy cresol and epoxy phenol novolacs produced by reacting a novolac resin (usually formed by the reaction of ortho-cresol or phenol and formaldehyde) with epichlorohydrin, 4-chloro-1,2-epoxybutane, 5-bromo-1,2-epoxypentane, 6-chloro-1,3-epoxyhexane, and the like. In addition, other epoxy resins made from phenolic resins such as phenolic resoles or resitols, may be used. One useful epoxy novolac is EPON™154 (Hexion Specialty Chemicals, Inc., Houston, Tex.).

Preferred levels of epoxy resins in the epoxy resin component (Part 1) of the present invention are: Bisphenol A epoxy: 0-50% by weight, based on the weight of the epoxy resin component; Bisphenol F epoxy: 0-70% by weight, based on the weight of the epoxy resin component; and epoxy novolac: 0-25% by weight, based on the weight of the epoxy resin component.

Drying oils may be used in the epoxy resin component (Part 1). Useful drying oils are glycerides of fatty acids which contain two or more double bonds and can polymerize. Examples of some natural drying oils include soybean oil, sunflower oil, hemp oil, linseed oil, tung oil, oiticica oil and fish oils, and dehydrated castor oil, as well as the various known modifications thereof (e.g., the heat bodied, air-blown, or oxygen-blown oils such as blown linseed oil and blown soybean oil). Also, esters of ethylenically unsaturated fatty acids such as tall oil esters of polyhydric alcohols such as glycerine or pentaerythritol or monohydric alcohols such as methyl and ethyl alcohols can be employed as the drying oil. One preferred ester is butyl ester of tall oil fatty acid. If desired, mixtures of drying oils can be employed.

The epoxy resin component (Part 1) must include a free radical initiator. Preferably, the free radical initiator is a peroxide and/or hydroperoxide. Further examples include ketone peroxides, peroxy ester free radical initiators, alkyl oxides, chlorates, perchlorates, and perbenzoates. Hydroperoxides particularly preferred in the invention include t-butyl hydroperoxide, cumene hydroperoxide, paramenthane hydroperoxide, and the like. The organic peroxides may be aromatic or alkyl peroxides. Examples of useful diacyl peroxides include benzoyl peroxide, lauroyl peroxide and decanoyl peroxide. Examples of alkyl peroxides include dicumyl peroxide and di-t-butyl peroxide.

The acrylate component (Part 2) contains at least one acrylic resin (“acrylate”). Acrylic resins include acrylate monomer, oligomer, polymer, or mixtures thereof, which contain ethylenically unsaturated bonds. Examples of such materials include a variety of mono functional, difunctional, trifunctional, tetrafunctional and pentafunctional monomeric acrylates and methacrylates. A representative listing of these monomers includes alkyl acrylates, acrylated epoxy resins, cyanoalkyl acrylates, alkyl methacrylates, cyanoalkyl methacrylates, and difunctional monomeric acrylates. Other acrylates which can be used include trimethylolpropane triacrylate, hexanediol diacrylate, pentaerythritol tetraacrylate, methacrylic acid and 2-ethylhexyl methacrylate, the first two compounds being particularly preferred. Typical reactive unsaturated acrylic polymers, which may also be used include epoxy acrylate reaction products, polyester/urethane/acrylate reaction products, acrylated urethane oligomers, polyether acrylates, polyester acrylates, and acrylated epoxy resins. In addition, phenolic urethane resins or other phenolic resins can be combined with the acrylates in the Part 2 component. A useful phenolic urethane resin is Sigma Cure 705 (HA International LLC, Westmont, Ill.). Also, optionally an effective amount of an epoxy resin may be used in the Part 2 component.

It will be apparent to those skilled in the art that other additives such as antioxidants, silanes, silicones, benchlife extenders, release agents, defoamers, wetting agents, etc. can be added to the aggregate or to the foundry mix. Useful antioxidants include butylated phenols and butylated cresols. Useful silanes include, but are not limited to, gamma-glycidoxypropyltrimethoxysilane, gamma-ureidopropyltrialkoxysilane, gamma-aminopropyltriethoxysilane, and the like. Generally the additives are added directly to either one of Part 1 or Part 2, or both, as appropriate, before admixture with aggregate. In this manner either Part 1 or Part 2, or both, can be supplied ready for use in making foundry cores and molds.

The epoxy acrylate binder system of this invention contains an epoxy resin component (Part 1) and an acrylate component (Part 2). The weight/weight ratio of the epoxy resin component (Part 1) to the acrylate component (Part 2) can range from about 3:1 to about 1:2. In a preferred embodiment, the weight/weight ratio of the epoxy resin component (Part 1) to the acrylate component (Part 2) ranges from about 2:1 to about 1:1.

Various types of aggregate and amounts of binder can be used to prepare foundry mixes by methods well known in the art. The aggregate materials commonly used in the foundry industry include silica sand, lake sand, bank sand, construction aggregate, quartz, chromite sand, zircon sand, or the like. Reclaimed sand may also be used.

Sand sold under the product designation F-5574, available from Badger Mining Corporation, Berlin, Wis., is useful in making cores and molds of the embodiments of the present invention. Likewise, sand sold under the product designation Wedron 530, available from Wedron Silica, a division of Fairmount Minerals, Wedron, Ill., is also useful. Incast 55 silica sand, available from Unimin Corp., Oregon, Ill., may also be used. Sand sold under the product designation Nugent 480, available from Nugent Sand Company, Muskegon, Mich., may also be used. As known in the art, the sand type, grain size and distribution will affect the strength development of the bound aggregate.

In ordinary sand type foundry applications, the amount of binder is generally no greater than about 5% by weight and frequently within the range of about 0.5% to about 4% by weight based upon the weight of the aggregate. It has been found that the epoxy acrylate binder made in accordance with the present invention is effective when present in an amount from about 0.5% to about 2% by weight based on the total weight of the foundry mix. It should be noted that, generally, high binder levels cause gas related defects in castings as well as result in high emission of volatile organic compounds.

The foundry mix is molded into the desired shape by ramming, blowing, or other known foundry core and mold making methods into a suitable core box or pattern. The shape is then cured by the cold-box process, using vaporous sulfur dioxide as the curing agent. The shaped article is preferably exposed to effective catalytic amounts of 100 percent vaporous sulfur dioxide, although minor amounts of a carrier gas such as nitrogen may also be used. The exposure time of the sand mix to the gas is typically from 0.5 to 3 seconds. The flow rate of the sulfur dioxide gas is dependent, of course, on the size of the shaped foundry mix as well as the amount of binder contained therein. Sufficient sulfur dioxide is passed through the shaped foundry mix to provide substantially complete reaction between the epoxy resin components and the acrylate components and to produce a cured foundry shape. The sulfur dioxide gas is injected at ambient temperature and at a pressure which can vary depending on the dimensions of the shape to be manufactured. The pressure must be sufficient for the gas to be dispersed uniformly throughout the entire bulk of the foundry shape and to escape to the outside of the mold. The cured shaped article can be purged of sulfur dioxide with an inert gas, such as nitrogen.

The following examples further illustrate the invention. They should not be construed as in any way limiting the scope of the invention.

Test Procedure

Resins were tested for hot strength as described in the examples below using the following procedure. 16.08 grams of Part 1 resin and 7.92 grams of Part 2 resin were coated on to 2000 grams of Wedron 530 sand using a Hobart mixer at speed 2 for 90 seconds. The resulting resin coated sand was used to make 1⅛″ d.×2″ ht. cylinder test specimens in a die, equipped to make three test specimens at a time. The resin-coated sand was blown into the die and cured by gassing with SO₂ for three seconds, followed by 15 seconds purge with nitrogen. The test specimens were stored in a desiccator for 2 hours prior to testing in a Dietert No. 785 Thermolab Dilatometer with the furnace equilibrated at 1800° F. A test specimen was placed in the dilatometer and subjected to a 50 psi compressive load. These conditions simulate the core behavior under the ferrostatic pressure of molten metal. The time it took for a test specimen to collapse was then measured. The time taken for the test specimen to collapse is indicative of its thermostability. Resins giving higher collapse times are thermally stable and will improve hot strength and vice versa. Six test specimens were tested in each instance and an average collapse time of those six results is reported.

In the examples below, higher collapse times indicate higher hot strength under core-making conditions. The collapse times are directly proportional to hot strength, so a shorter collapse time is indicative of poor hot strength.

EXAMPLE 1

Part 1 was prepared by mixing Bisphenol F type epoxy resin (45.6 grams), 3.6 epoxy novolac resin (25 grams), butyl ester of tall oil fatty acid (0.9 grams) and cumene hydroperoxide (28.5 grams). Part 2 was prepared by mixing Bisphenol A type epoxy resin (19.85 grams), trimethylolpropane triacrylate (45.16 grams), hexanediol diacrylate (34 grams), butylated cresol (0.09 grams) and gamma-glycidoxypropyltrimethoxysilane (0.9 grams). Parts 1 and 2 were used in the test procedure above.

EXAMPLE 2

Part 1 was prepared as in Example 1. Part 2 was prepared as in Example 1, except 2 grams of tri-n-butyl borate was substituted for 2 grams of Bisphenol A type epoxy resin. The amount of tri-n-butyl borate was 2% by weight based on the total weight of Part 2.

EXAMPLE 3

Part 1 was prepared as in Example 1. Part 2 was prepared as in Example 1, except 6 grams of tri-n-butyl borate was substituted for 6 grams of Bisphenol A type epoxy resin. The amount of tri-n-butyl borate was 6% by weight based on the total weight of Part 2.

TABLE 1
Example No. Collapse Time, sec.
1           165
2           175
3           155

Table 1 demonstrates the improvements in hot strength properties as shown by a 6% increase in collapse time using the Example 2 binder in comparison to the cylinder test specimens of Example 1, in which no borate is used. Higher collapse times indicate higher hot strength under core-making conditions. In contrast, the collapse time using the Example 3 binder decreased in comparison to the cylinder test specimens of Example 1, which indicates that the beneficial effect in this particular system resulted when tri-n-butyl borate was used in an amount less than about 6% by weight based on the total weight of Part 2.

EXAMPLE 4

Part 1 was prepared by mixing a Bisphenol A type epoxy resin (12.5 grams), Bisphenol F type epoxy resin (45.6 grams), 3.6 epoxy novolac resin (12.5 grams), butyl ester of tall oil fatty acid (0.9 grams) and cumene hydroperoxide (28.5 grams). Part 2 was prepared by mixing a phenolic urethane cold-box resin “Sigma Cure 705”—a product of HA International, Westmont, Ill. (19.85 grams), trimethylolpropane triacrylate (45.16 grams), hexanediol diacrylate (34 grams), butylated cresol (0.09 grams) and gamma-glycidoxypropyltrimethoxysilane (0.9 grams). Parts 1 and 2 were used in the test procedure above.

EXAMPLE 5

Part 1 was prepared as in Example 4. Part 2 was prepared as in Example 4, except 2 grams of tri-n-butyl borate was substituted for 2 grams of Sigma Cure 705 resin. The amount of tri-n-butyl borate was 2% by weight based on the total weight of Part 2.

EXAMPLE 6

Part 1 was prepared as in Example 4. Part 2 was prepared as in Example 4, except 4 grams of tri-n-butyl borate was substituted for 4 grams of Sigma Cure 705 resin. The amount of tri-n-butyl borate was 4% by weight based on the total weight of Part 2.

TABLE 2
Example No. Collapse Time, sec.
4           154
5           186
6           181

Table 2 demonstrates the improvements in hot strength properties as shown by increased collapse times using the Example 5 and 6 binders, of 21% and 18%, respectively, in comparison to the cylinder test specimens of Example 4, in which no borate is used. Higher collapse times indicate higher hot strength under core-making conditions.

EXAMPLE 7

The resin from Example 1 and the resin from Example 5 were compared using a standard casting erosion test: “Test Casting Evaluation of Chemical Binder Systems,” Tordoff et al., AFS Transactions, 1980, Vol. 74, p. 152-153, developed by British Steel Casting Research Association, which is hereby incorporated by reference. In this test, molten iron at approximately 2580° F. was poured into a 1 inch diameter, 16 inch high sprue. The molten metal then impinges on a molded sand surface inclined at 60 degrees. The metal was poured until the bottom cavity, which holds about 60 pounds of metal, the wedge shaped section, and the sprue were filled with molten metal. The assembly was allowed to cool and the wedge shaped section was removed and the amount of erosion was measured. A casting defect due to erosion appears as a protuberance on the wedge shaped section. The area of the protuberance was measured to determine the extent of the erosion. This test was run on, in duplicate, using molds made with the resin of Example 1 and the resin from Example 5 with the following results. The sand mix used was Incast 55 silica sand, 1.2% total resin and a Part 1/Part 2 ratio of 2/1.

TABLE 3
	Metal Temp.	Erosion Area	Average Erosion
Resin System	(° F.)	(sq. in.)	(sq. in.)
Example 1-A	2584	3.52
Example 1-B	2593	3.67	3.60
Example 5-A	2593	1.28
Example 5-B	2565	0.4	0.84

This test showed that the resin system in Example 5, containing the borate compound, had 77% less erosion than the resin system in Example 1.

EXAMPLE 8

The resin system in Examples 1 and 5 were also tested in a foundry situation on a casting where erosion always occurred. Twenty four cores were made with each system, placed in molds, and then poured with molten iron at 2700° F. After cooling, the castings were removed from the molds and examined for erosion. They were rated either acceptable or scrap. Results are shown in Table 4.

	TABLE 4
	Resin System	% Acceptable	% Scrap
	Example 1	8.3	91.7
	Example 5	57	43

The improved system of Example 5 reduced erosion in the castings substantially. Furthermore, it was found that erosion on the Example 5 system could be eliminated by brushing a small area with a refractory coating, while in contrast the entire core had to be coated with the Example 1 system.

EXAMPLE 9

If a resin system were prepared by substituting triethyl borate for tri-n-butyl borate in either Example 5 or 6, it is expected that a longer collapse time would result in comparison to the cylinder test specimens of Example 4, in which no borate is used. The amount of triethyl borate would be 2-4% by weight based on the total weight of Part 2.

EXAMPLE 10

If a resin system were prepared by substituting tri-n-propyl borate for tri-n-butyl borate in either Example 5 or 6, it is expected that a longer collapse time would result in comparison to the cylinder test specimens of Example 4, in which no borate is used. The amount of tri-n-propyl borate would be 2-4% by weight based on the total weight of Part 2.

EXAMPLE 11

If a resin system were prepared by substituting triisopropyl borate for tri-n-butyl borate in either Example 5 or 6, it is expected that a longer collapse time would result in comparison to the cylinder test specimens of Example 4, in which no borate is used. The amount of triisopropyl borate would be 2-4% by weight based on the total weight of Part 2.

EXAMPLE 12

If a resin system were prepared by substituting triisobutyl borate for tri-n-butyl borate in either Example 5 or 6, it is expected that a longer collapse time would result in comparison to the cylinder test specimens of Example 4, in which no borate is used. The amount of triisobutyl borate would be 2-4% by weight based on the total weight of Part 2.

EXAMPLE 13

If a resin system were prepared by substituting tri-sec-butyl borate for tri-n-butyl borate in either Example 5 or 6, it is expected that a longer collapse time would result in comparison to the cylinder test specimens of Example 4, in which no borate is used. The amount of tri-sec-butyl borate would be 2-4% by weight based on the total weight of Part 2.

EXAMPLE 14

If a resin system were prepared by substituting tri-tert-butyl borate for tri-n-butyl borate in either Example 5 or 6, it is expected that a longer collapse time would result in comparison to the cylinder test specimens of Example 4, in which no borate is used. The amount of tri-tert-butyl borate would be 2-4% by weight based on the total weight of Part 2.

EXAMPLE 15

If a resin system were prepared by substituting tri-n-octyl borate for tri-n-butyl borate in either Example 5 or 6, it is expected that a longer collapse time would result in comparison to the cylinder test specimens of Example 4, in which no borate is used. The amount of tri-n-octyl borate would be 2-4% by weight based on the total weight of Part 2.

EXAMPLE 16

If a resin system were prepared by using any of 1% by weight, 1.5% by weight, 5% by weight, or 5.8% by weight of tri-n-butyl borate in Example 5 (all substituting for a corresponding amount of Sigma Cure 705 resin), it is expected that a longer collapse time would result in comparison to the cylinder test specimens of Example 4, in which no borate is used. The amount of tri-n-butyl borate would be 1% by weight, 1.5% by weight, 5% by weight, and 5.8% by weight, respectively, based on the total weight of Part 2.

Although the above examples are intended to be representative of the invention, they are not intended to limit the scope of the appended claims. It will be apparent to those skilled in the art that modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.

Claims

1. A sulfur dioxide-curable binder composition comprising:

an epoxy resin component including at least one epoxy resin and a free radical initiator; and

an acrylate component including at least one acrylate and a boric acid ester, wherein the boric acid ester is present in an amount of about 1% to less than about 6% by weight based on the weight of the acrylate component.

2. The binder of claim 1 wherein the boric acid ester is a trialkyl borate.

3. The binder of claim 2 wherein the trialkyl borate is a tri(C2-C8)alkyl borate.

4. The binder of claim 3 wherein the tri(C2-C8)alkyl borate is selected from the group consisting of triethyl borate, tri-n-propyl borate, tri-isopropyl borate, tri-n-butyl borate, tri-isobutyl borate, tri-sec-butyl borate, tri-tert-butyl borate, and tri-n-octyl borate.

5. The binder of claim 1 wherein the boric acid ester is present in an amount of about 2% to about 4% by weight based on the weight of the acrylate component.

6. The binder of claim 2 wherein the trialkyl borate is present in an amount of about 2% to about 4% by weight based on the weight of the acrylate component.

7. The binder of claim 6 wherein the weight/weight ratio of the epoxy resin component to the acrylate component is from about 2:1 to about 1:1.

8. The binder of claim 1 wherein the acrylate component further includes a phenolic resin.

9. A sulfur dioxide-curable binder composition comprising:

an epoxy resin component including at least one epoxy resin and a free radical initiator; and

an acrylate component including at least one acrylate and tri-n-butyl borate, wherein tri-n-butyl borate is present in an amount of about 1% to less than about 6% by weight based on the weight of the acrylate component.

10. The binder of claim 9 wherein tri-n-butyl borate is present in an amount of about 2% to about 4% by weight based on the weight of the acrylate component.

11. The binder of claim 10 wherein the weight/weight ratio of the epoxy resin component to the acrylate component is about 2:1.

12. The binder of claim 11 wherein the epoxy resin component comprises an epoxy resin selected from the group consisting of bisphenol F, bisphenol A, epoxy novolac, and mixtures thereof.

13. The binder of claim 12 wherein the acrylate component comprises an acrylate monomer.

14. The binder of claim 13 wherein the acrylate monomer is selected from the group consisting of trimethylolpropane triacrylate, hexanediol diacrylate, and mixtures thereof.

15. The binder of claim 14 wherein the acrylate component further includes a phenolic urethane resin.

16. A sulfur dioxide-curable foundry mix comprising: the binder being present in an amount from about 0.5% to about 2% based on the total weight of the foundry mix.

aggregate; and

a binder including an epoxy resin component and an acrylate component, the epoxy resin component including at least one epoxy resin and a free radical initiator, and the acrylate component including at least one acrylate and a boric acid ester, wherein the boric acid ester is present in an amount of about 1% to less than about 6% by weight based on the weight of the acrylate component; and

17. The foundry mix of claim 16 wherein the boric acid ester is a trialkyl borate.

18. The foundry mix of claim 17 wherein the trialkyl borate is a tri(C2-C8)alkyl borate.

19. The foundry mix of claim 18 wherein the tri(C2-C8)alkyl borate is selected from the group consisting of triethyl borate, tri-n-propyl borate, tri-isopropyl borate, tri-n-butyl borate, tri-isobutyl borate, tri-sec-butyl borate, tri-tert-butyl borate, and tri-n-octyl borate.

20. The foundry mix of claim 18 wherein the tri(C2-C8)alkyl borate is tri-n-butyl borate.

21. The foundry mix of claim 16 wherein the boric acid ester is present in an amount of about 2% to about 4% by weight based on the weight of the acrylate component.

22. The foundry mix of claim 20 wherein tri-n-butyl borate is present in an amount of about 2% to about 4% by weight based on the weight of the acrylate component.

23. The foundry mix of claim 22 wherein the weight/weight ratio of the epoxy resin component to the acrylate component is about 2:1.

24. The foundry mix of claim 23 wherein the epoxy resin component comprises an epoxy resin selected from the group consisting of bisphenol F, bisphenol A, epoxy novolac, and mixtures thereof.

25. The foundry mix of claim 24 wherein the acrylate component comprises an acrylate monomer.

26. The foundry mix of claim 25 wherein the acrylate monomer is selected from the group consisting of trimethylolpropane triacrylate, hexanediol diacrylate, and mixtures thereof.

27. The foundry mix of claim 16 wherein the acrylate component further includes a phenolic resin.

28. A method of making a foundry shape, comprising the steps of:

(a) preparing a foundry mix by admixing aggregate and a binder comprising an epoxy resin component including at least one epoxy resin and an effective amount of a peroxide; and an acrylate component including at least one acrylate and a boric acid ester, wherein the boric acid ester is present in an amount of about 1% to less than about 6% by weight based on the weight of the acrylate component; and wherein the binder is present in an amount from about 0.5% to about 2% based on the total weight of the foundry mix;

(b) shaping the foundry mix to a desired configuration to provide a shaped foundry mix; and

(c) curing the shaped foundry mix with gaseous sulfur dioxide to provide a foundry shape.

29. The method of claim 28 wherein the boric acid ester is a trialkyl borate.

30. The method of claim 29 wherein the trialkyl borate is a tri(C2-C8)alkyl borate.

31. The method of claim 30 wherein the tri(C2-C8)alkyl borate is selected from the group consisting of triethyl borate, tri-n-propyl borate, tri-isopropyl borate, tri-n-butyl borate, tri-isobutyl borate, tri-sec-butyl borate, tri-tert-butyl borate, and tri-n-octyl borate.

32. The method of claim 30 wherein the tri(C2-C8)alkyl borate is tri-n-butyl borate.

33. The method of claim 32 wherein tri-n-butyl borate is present in an amount of about 2% to about 4% by weight based on the weight of the acrylate component.

34. The method of claim 33 wherein the weight/weight ratio of the epoxy resin component to the acrylate component is about 2:1.

35. The method of claim 34 wherein the epoxy resin component comprises an epoxy resin selected from the group consisting of bisphenol F, bisphenol A, epoxy novolac, and mixtures thereof.

36. The method of claim 35 wherein the acrylate component comprises an acrylate monomer.

37. The method of claim 36 wherein the acrylate monomer is selected from the group consisting of trimethylolpropane triacrylate, hexanediol diacrylate, and mixtures thereof.

38. The method of claim 28 wherein the acrylate component further includes a phenolic resin.