Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-23
2001-09-11
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...
C523S142000, C523S139000
Reexamination Certificate
active
06288139
ABSTRACT:
TECHNICAL FIELD
This invention relates to polyurethane-forming foundry binder systems comprising a phenolic resin component and a polyisocyanate component, where the polyisocyanate component contains an ortho ester. The invention also relates to foundry mixes prepared from the binder and an aggregate, as well as foundry shapes prepared by the no-bake and cold-box processes. The foundry shapes are used to make metal castings.
BACKGROUND OF THE INVENTION
One of the major processes used in the foundry industry for making metal parts is sand casting. In sand casting, disposable foundry shapes (usually characterized as molds and cores) are made by shaping and curing a foundry binder system that is a mixture of sand and an organic or inorganic binder. The binder is used to strengthen the molds and cores.
Two of the major processes used in sand casting for making molds and cores are the no-bake process and the cold-box process. In the no-bake process, a liquid curing agent is mixed with an aggregate and shaped to produce a cured mold and/or core. In the cold-box process, a gaseous curing agent is passed through a compacted shaped mix to produce a cured mold and/or core. Polyurethane-forming binders, cured with a gaseous tertiary amine catalyst, are often used in the cold-box process to hold shaped foundry aggregate together as a mold or core. See for example U.S. Pat. No. 3,409,579. The polyurethane-forming binder system usually consists of a phenolic resin component and polyisocyanate component which are mixed with sand prior to compacting and curing to form a foundry binder system.
Among other things, the binder must have a low viscosity, be gel-free, remain stable under use conditions, and cure efficiently. The foundry binder system made by mixing sand with the binder must have adequate benchlife or the mix will not shape and cure properly. The cores and molds made with the binders must have adequate tensile strengths under normal and humid conditions, and release effectively from the pattern. Binders which meet all of these requirements are not easy to develop.
Ortho esters are known in the prior art to stabilize organic isocyanates. U.S. Pat. No. 3,535,359 (Chadwick) discloses that certain ortho-esters are capable of stabilizing a polyisocyanate against several different kinds of degradation, for instance moisture, and viscosity increases, even when only small amounts of ortho esters are used. The stabilized isocyanates are useful in the preparation of polyurethane foam, nonporous plastics including polyurethane castings such as gear wheels and the like, and coating compositions. Chadwick does not disclose the use of such polyisocyanates in foundry binders, foundry mixes, or the preparation of foundry shapes and metal castings.
SUMMARY OF THE INVENTION
This present invention relates to a foundry binder system curable with a catalytically effective amount of an amine curing catalyst comprising:
A. a phenolic resin component; and
B. a polyisocyanate component comprising in admixture:
(1) an organic polyisocyanate;
(2) at least 5 weight percent of a non reactive organic solvent based upon the weight of (1); and
(3) an effective amount of an ortho ester.
The foundry binder systems are preferably used to make molds and cores, preferably by the cold-box process which involves curing the molds and cores with a gaseous tertiary amine. The cured molds and cores are used to cast ferrous and non ferrous metal parts.
When added to a polyisocyanate component that contains a non reactive organic solvent, the ortho ester improves the tensile strength of foundry shapes, particularly in solvent systems that contain some moisture, and cases where the foundry shapes are coated with an aqueous coating. Improved tensile strengths are also observed for foundry shapes prepared with a foundry mixes that set unused for extended periods of time. Polyisocyanate components containing the ortho ester have lower turbidity, which indicates that it is more stable or homogeneous. As a result the polyisocyanate component will not be subjected to settling of particulate matter, and will be easier to pump.
BEST MODE AND OTHER MODES OF THE INVENTION INCLUDING
The phenolic resole resin is preferably prepared by reacting an excess of aldehyde with a phenol in the presence of either an alkaline catalyst or a metal catalyst. The phenolic resins are preferably substantially free of water and are organic solvent soluble. The preferred phenolic resins used in the subject binder compositions are well known in the art, and are specifically described in U.S. Pat. No. 3,485,797 which is hereby incorporated by reference. These resins, known as benzylic ether phenolic resole resins are the reaction products of an aldehyde with a phenol. They contain a preponderance of bridges joining the phenolic nuclei of the polymer which are ortho-ortho benzylic ether bridges. They are prepared by reacting an aldehyde and a phenol in a mole ratio of aldehyde to phenol of at least 1:1 in the presence of a metal ion catalyst, preferably a divalent metal ion such as zinc, lead, manganese, copper, tin, magnesium, cobalt, calcium, and barium.
The phenols use to prepare the phenolic resole resins include any one or more of the phenols which have heretofore been employed in the formation of phenolic resins and which are not substituted at either the two ortho-positions or at one ortho-position and the para-position. These unsubstituted positions are necessary for the polymerization reaction. Any of the remaining carbon atoms of the phenol ring can be substituted. The nature of the substituent can vary widely and it is only necessary that the substituent not interfere in the polymerization of the aldehyde with the phenol at the ortho-position and/or para-position. Substituted phenols employed in the formation of the phenolic resins include alkyl-substituted phenols, aryl-substituted phenols, cyclo-alkyl-substituted phenols, aryloxy-substituted phenols, and halogen-substituted phenols, the foregoing substituents containing from 1 to 26 carbon atoms and preferably from 1 to 12 carbon atoms.
Specific examples of suitable phenols include phenol, 2,6-xylenol, o-cresol, p-cresol, 3,5-xylenol, 3,4-xylenol, 2,3,4-trimethyl phenol, 3-ethyl phenol, 3,5-diethyl phenol, p-butyl phenol, 3,5-dibutyl phenol, p-amyl phenol, p-cyclohexyl phenol, p-octyl phenol, 3,5-dicyclohexyl phenol, p-phenyl phenol, p-crotyl phenol, 3,5-dimethoxy phenol, 3,4,5-trimethoxy phenol, p-ethoxy phenol, p-butoxy phenol, 3-methyl-4-methoxy phenol, and p-phenoxy phenol. multiple ring phenols such as bisphenol A are also suitable.
The aldehyde used to react with the phenol has the formula RCHO wherein R is a hydrogen or hydrocarbon radical of 1 to 8 carbon atoms. The aldehydes reacted with the phenol can include any of the aldehydes heretofore employed in the formation of phenolic resins such as formaldehyde, acetaldehyde, propionaldehyde, furfuraldehyde, and benzaldehyde. The most preferred aldehyde is formaldehyde.
The phenolic resin used must be liquid or organic solvent-soluble. The phenolic resin component of the binder composition is generally employed as a solution in an organic solvent. The amount of solvent used should be sufficient to result in a binder composition permitting uniform coating thereof on the aggregate and uniform reaction of the mixture. The specific solvent concentration for the phenolic resins will vary depending on the type of phenolic resins employed and its molecular weight. In general, the solvent concentration will be in the range of up to 80% by weight of the resin solution and preferably in the range of 20% to 80%.
The polyisocyanate component of the binder typically comprises a polyisocyanate and organic solvent. The polyisocyanate has a functionality of two or more, preferably 2 to 5. It may be aliphatic, cycloaliphatic, aromatic, or a hybrid polyisocyanate. Mixtures of such polyisocyanates may be used. Also, it is contemplated that capped polyisocyanates, prepolymers of polyisocyanates, and quasi prepolymers of polyisocyanates can be used. Optional ingr
Ashland Inc.
Cain Edward J.
Hedden David L.
Wyrozebski-Lee Katarzyna
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