Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-04-27
2002-05-21
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S147000, C523S148000
Reexamination Certificate
active
06391942
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to furan no-bake foundry binders comprising (a) a reactive furan resin, (b) furfuryl alcohol, and (c) a catalyst component comprising a catalytically effective amount of a Lewis acid furan catalyst. The invention also relates to foundry mixes prepared with the binder, foundry shapes prepared with the foundry mix, and metal castings prepared with the foundry shapes.
BACKGROUND OF THE INVENTION
One of the most commercially successful no-bake binders is the phenolic-urethane no-bake binder. This binder provides molds and cores with excellent strengths that are produced in a highly productive manner. Although this binder produces good cores and molds at a high speed, there is an interest in binders that have less volatile organic compounds (VOC), free phenol level, free formaldehyde, and that produce less odor and smoke during core making and castings. Furan binders have these advantages, but their cure speed is much slower than the cure speed of phenolic urethane no-bake binders. Furan binders have been modified to increase their reactivity, for instance by incorporating with urea-formaldehyde resins, phenol-formaldehyde resins, novolac resins, phenolic resole resins, and resorcinol into the binder. Nevertheless, these modified furan binders system do not provide the cure speed needed in foundries that require high productivity.
U.S. Pat. No. 5,856,375 discloses the use of BPA tar in furan no-bake binders to increase the cure speed of the furan binder. Although the cure speed of the binder is increased by the addition of the BPA tar, the tensile strength of this system does not match that of the phenolic urethane system.
Cure speed is not the only consideration in selecting a binder. Cores and molds made with the binder can have unacceptable properties that result in casting defects such as veining, penetration, and surface finish, when the cores and molds are used to make metal castings. Veining is an expansion defect that results when a mold or cores cracks under thermal stress before the casting solidifies. As a result, molten metal enters the cracks of the mold or core and a casting with “veins” or “fins” results. These veins or fins must be removed by machining for the casting to be useful. Mechanical penetration occurs when the pressure of molten metal is high enough to force it into the interstices of a mold or core surface. The result is an integral mixture of sand and metal that is quite difficult to remove in grinding room operations.
SUMMARY OF THE INVENTION
This invention relates to furan no-bake binders comprising:
(a) a reactive furan resin,
(b) furfuryl alcohol,
(c) a catalyst component comprising a catalytically effective amount of a catalyst comprising a Lewis acid.
Preferably the reactive furan resin is mixture of a conventional furan and a furan derived from the homopolymerization of binder bis-hydroxymethylfuran. Preferably, the catalyst is a mixture of a Lewis acid and a conventional furan catalyst. Preferably, the binder also contains an activator selected from the group consisting of resorcinol, resorcinol pitch, and bisphenol A tar; a bisphenol compound; a polyol; and a silane.
The binders display several advantages when compared to a conventional furan no-bake binder. Cores prepared with the binders cure much faster than those prepared with conventional furan no-bake binders. In fact, the cure speed of cores prepared by the binders of this invention is comparable to that of the phenolic urethane no-bake binder, which is used commercially to make cores where high-speed production is needed. The cure speed of cores prepared from this invention is much faster than those prepared by the conventional furan no-bake binder that do not use a Lewis acid as the catalyst or co-catalyst.
Additionally, the cores made with the binder display excellent tensile strength and excellent casting results. The cores and molds produced by this invention exhibited greater resistance to veining than those produced with furan binders that were not cured with the Lewis acid catalyst. They also exhibited better resistance to veining than cores and molds prepared with phenolic-urethane no-bake binders. The cores and molds are produced in a highly productive manner and have good core handling strength. The binders are advantageous from an environmental standpoint because they contain low VOC, low odor, zero phenol, zero solvent, no isocyanates, and produce low smoke when castings are made.
ENABLING DISCLOSURE AND BEST MODE
The furan resins used in the no-bake binders are preferably low nitrogen furan resins. The furan resins are conventional furan resins prepared by the homopolymerization of furfuryl alcohol (hereafter a conventional furan resin), or preferably furans prepared by the homopolymerization of bis-hydroxymethylfuran (hereafter a bis-hydroxymethylfuran resin), and mixtures of these resins. These resins are prepared by the homopolymerization of the monomer in the presence of heat, according to methods well-known in the art. The reaction temperature used in making the furan resins typically 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 typically from 1.400 to about 1.500. The viscosity of the resin is preferably from about 200 cps to 450 cps. The furan resins have an average degree of polymerization of 2 to 3.
Although not necessarily preferred, modified furan resins can also be used in the binder. Modified furan resins are typically made from furfuryl alcohol, urea formaldehyde, and formaldehyde at elevated temperatures under slightly alkaline conditions at a pH of from 7.0 to 8.0, preferably 7.0 to 7.2. The weight percent of furfuryl alcohol used in making the low nitrogen modified furan resins ranges from 60 to 75 percent; the weight percent of the urea formaldehyde used in making the low nitrogen modified furan resins ranges from 10 to 25 percent; and the weight percent of the formaldehyde used in making the low nitrogen modified furan resins ranges from 1 to 10 percent, where all weight percents are based upon the total weight of the components used to make the modified furan resin.
Although not necessarily preferred, urea-formaldehyde resins, phenol-formaldehyde resins, novolac resins, and phenolic resole resins may also be used in addition to the furan resin.
The furan resin is diluted with furfuryl alcohol to reduce the viscosity of the reactive furan resin.
Preferably, an activator is used in the binder. The activator promotes the polymerization of furfuryl alcohol and is selected from the group consisting of resorcinol, resorcinol pitch, and bisphenol A tar. Preferably used as the activator is resorcinol. Resorcinol pitch is defined as the highly viscous product, which remains on the bottom of the reaction vessel after resorcinol is 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 is mostly dimers, trimers, and polymeric resorcinol. It may also contain substituted materials. Bisphenol A tar is defined as the highly viscous product, which remains on the bottom of the reaction vessel after bisphenol A is produced and distilled from the reaction vessel. The bisphenol A tar is a solid at room temperature and has a melting point of about 70° C. to 80° C. Bisphenol A tar is mostly dimers, trimers, and polymeric bis phenol A. It may also contain substituted materials.
Preferably, the binder contains a bisphenol compound. The bisphenol compound used is bisphenol A, B, F, G, and H, but preferably is bisphenol A.
Preferably, the binder contains a polyol. The polyol is selected from the group consisting of polyester polyols, polyether polyols, and mixtures thereof. Aliphatic polyester polyols can be used in the binder. Aliphatic polyester polyols are well known and are prepared by reacting a dicarboxylic acid or anhydride with a glycol. They generally have an average hydr
Chang Ken K.
Hutchings David A.
Ashland Inc.
Cain Edward J.
Hedden David L.
Lee Katarzyna W.
LandOfFree
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