Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-09-14
2002-08-27
Sellers, Robert E. L. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S466000, C523S428000
Reexamination Certificate
active
06441060
ABSTRACT:
FIELD OF THE INVENTION
The subject invention relates to a foundry binder system which cures in the presence of a volatile amine curing catalyst comprising (a) an epoxy resin, (b) an acrylated organic polyisocyanate, (c) a reactive unsaturated acrylic monomer, acrylic polymer, or mixtures thereof, and (d) an oxidizing agent comprising a hydroperoxide. The foundry binders are used for making foundry mixes. The foundry mixes are used to make foundry shapes which 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 mix which is a mixture of sand and an organic or inorganic binder. The binder is used to strengthen the molds and cores.
The two major processes used in sand casting for making molds and cores are the (a) cold-box process and the (b) no-bake process. In the cold-box process, a gaseous curing agent is passed through a compacted shaped mix to produce a cured mold and/or core. In the no-bake process, a liquid curing catalyst is mixed with the sand and shaped into a core or and/or mold.
The major cold-box process is based upon polyurethane-forming binders. See for example U.S. Pat. Nos. 3,409,579 and 3,676,392. These systems are cured with a gaseous tertiary amine catalyst. 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 mix.
When the two components of the polyurethane-forming binder system are mixed with the sand to form a foundry mix, they may prematurely react prior to curing with the gaseous catalyst. If this reaction occurs, it will reduce the flowability of the foundry mix when it is used for making molds and cores, and the resulting molds and cores will have reduced strengths. This reduced flowability and decrease in strength with time is related to the benchlife of the foundry mix.
Sufficient benchlife of the foundry mix is important to the commercial success of these binders. Benchlife is the time interval between forming the foundry mix and the time when the foundry mix is no longer useful for making acceptable molds and cores. A measure of the usefulness of the foundry mix and the acceptability of the molds and cores prepared with the foundry mix is the tensile strength of the molds and cores. If a foundry mix is used after the benchlife has expired, the resulting molds and cores will have unacceptable tensile strengths.
Because it is not always possible to use the foundry mix immediately after mixing, it is desirable to prepare foundry mixes with an extended benchlife. When polyurethane-forming cold-box binders are used, generally a compound which improves the benchlife of the foundry mix must be added to the binder, usually to the polyisocyanate component of the binder.
Among the compounds useful for extending the benchlife of the foundry mix are organic and/or inorganic phosphorus containing compounds. Examples of organic phosphorus-containing compounds used as benchlife extenders with polyurethane-forming binder systems are disclosed in U.S. Pat. No. 4,436,881 which discloses certain organic phosphorus containing compounds such as dichloroarylphosphine, chlorodiarylphosphine, arylphosphinic dichloride, or diarylphosphinyl chloride, and U.S. Pat. No. 4,683,252 which discloses organohalophosphates such as mono-phenyldichlorophosphate.
Examples of inorganic phosphorus-containing compounds which extend the benchlife of polyurethane-forming binder systems are disclosed in U.S. Pat. No. 4,540,724 which discloses inorganic phosphorus halides such as phosphorus oxychloride, phosphorus trichloride, and phosphorus pentachloride, and U.S. Pat. No. 4,602,069 which discloses inorganic phosphorus acids such as orthophosphoric acid, phosphoric acid, hypophosphoric acid, metaphosphoric acid, pyrophosphoric acid, and poly-phosphoric acid.
As can be seen, there are numerous benchlife extenders for polyurethane-forming cold-box binders which reflects the interest in extending the benchlife of the foundry mix.
Despite the cited work, there is still a need for amine-cured binder systems with longer benchlife, particularly those which do not require expensive additives.
SUMMARY OF THE INVENTION
The invention relates to a foundry binder system which will cure in the presence of a volatile amine curing catalyst comprising:
(a) from 5 to 80 weight percent of an epoxy resin;
(b) from 10 to 80 weight percent of an acrylated organic polyisocyanate;
(c) from 5 to 75 weight percent of a reactive unsaturated acrylic monomer, acrylic polymer, and mixtures thereof; and
(d) an effective oxidizing amount of an oxidizing agent comprising a hydroperoxide,
where (a), (b), (c), and (d) are separate components or can be mixed with another component, provided (b) or (c) is not mixed with (d), and where said weight percents are based upon the total weight of (a), (b), (c), and (d). Generally, the weight percent of (a) is 5 to 50, the weight percent of (b) is 10 to 40, the weight percent of (c) is 20 to 60 and the weight percent of (d) is 1 to 30. Preferably, the weight percent of (a) is 5 to 20, the weight percent of (b) is 15 to 40, the weight percent of (c) is 20 to 55, and the weight percent of (d) is 1 to 20. More preferably, the weight percent of (a) is 5 to 25, the weight percent of (b) is 20 to 40, the weight percent of (c) is 30 to 55, and the weight percent of (d) is 5 to 15.
The foundry binders are used for making foundry mixes. The foundry mixes are used to make foundry shapes which are used to make metal castings. The use of an acrylated organic polyisocyanate in the foundry binder instead of an organic polyisocyanate which is not acrylated, improves the benchlife of foundry mixes made with the foundry binder. The foundry mixes produce cores and molds with adequate tensile strengths for commercial use. Castings, made with an assembly of cores and/or molds made with the binders, are acceptable for commercial use. Additionally, the binder does not contain any free phenol or free formaldehyde, and has zero or low volatile organic compounds (VOC).
BEST MODE AND OTHER MODES OF PRACTICING THE INVENTION
It is preferred to package and use the binders system as a two part system. Part I (epoxy component) comprises the epoxy resin, oxidizing agent, solvents, and other optional components. Part II (polyisocyanate component) comprises the (1) acrylated organic polyisocyanate, (2) a reactive unsaturated acrylic monomer, polymer, or mixtures thereof, (3) solvents, and (4) other optional components. Usually, the Part I is first mixed with sand and then the Part II is added to make a foundry mix which is shaped and cured. The weight ratio of epoxy resin to acrylated organic polyisocyanate generally is from 1:10 to 10:1, preferably from 1:5 to 5:1, most preferably from 1:3 to 3:1. The weight ratio of acrylated polyisocyanate to reactive unsaturated acrylate is generally from 1:10 to 5:1, preferably from 1:5 to 2:1.
For purposes of this disclosure, “epoxy resin” is defined as a thermosetting resin which contains one or more reactive epoxide group per molecule. Such resins have either a mixed aliphatic-aromatic or exclusively non-aromatic (i.e., aliphatic or cycloaliphatic) molecular structure. The mixed aliphatic-aromatic epoxy resins generally are prepared by the well-known reaction of a bis-(hydroxy-aromatic)alkane or a tetrakis-(hydroxy-aromatic) alkane with a halogen-substituted aliphatic epoxide in the presence of a base such as sodium hydroxide or potassium hydroxide. Examples of the halogen-substituted aliphatic epoxides include epichlorohydrin, 4-chloro-1 ,2-epoxybutane, 5-bromo-1,2-epoxypentane, 6-chloro-1,3-epoxyhexane and the like. In general, it is preferred to use a chloride substitute terminal denoting that the epoxide group is on the end of the alkyl chain.
The most widely used epoxy resins are diglycidyl ethers of bisphenol
Dammann Laurence G.
Hendershot Don Greg
Pascarella Vincent J.
Toplikar Edward Gerard
Ashland Inc.
Hedden David L.
Sellers Robert E. L.
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