Sleeves, their preparation, and use

Details Sleeves, their preparation, and use Sleeves, their preparation, and use

2000-08-14

2001-08-07

Yoon, Tae H. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C523S139000, C523S140000, C523S141000

Reexamination Certificate

active

06271284

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 organic polyisocyanate, (c) a reactive unsaturated acrylic monomer or polymer, and (d) an oxidizing agent. 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 old-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 bench life. When polyurethane-forming cold-box binders are used, generally a compound which improves the bench life of the foundry mix must be added to the binder, usually the polyisocyanate component of the binder.
Among the compounds useful to extend the bench life 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 monophenyldichlorophosphate.
Examples of inorganic phosphorus-containing compounds which extend the bench life 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 polyphosphoric acid.
Carboxylic acids, such as citric acid, are also used to extend the benchlife of polyurethane-forming foundry binders. See U.S. Pat. No. 4,760,101.
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.
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 5 to 80 weight percent of an organic polyisocyanate;
(c) from 5 to 75 weight percent of a reactive unsaturated acrylic monomer or polymer; and
(d) from 2 to 45 weight percent of an oxidizing agent, 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). Preferably, the weight percent of (a) is 20 to 40, the weight percent of (b) is 20 to 40, the weight percent of (c) is 15 to 40, 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 foundry binder systems described herein have considerably longer benchlife than the previously cited phenolic urethane binders. 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). The binders are not photochemically reactive and the used sand is reclaimable.
BEST MODE AND OTHER MODES OF PRACTICING THE INVENTION
The subject binder must contain an epoxy resin. The weight ratio of epoxy resin to organic polyisocyanate generally is from 1:10 to 10:1, preferably from 1:5 to 5:1, most preferably from 1:2 to 2:1.
For purposes of this disclosure, “epoxy resin” is defined as a thermosetting resin which contains more than one 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, for example, 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 A. These are made by reaction of epichlorohydrin with bisphenol A in the presence of an alkaline catalyst. By controlling the operating conditions and varying the ratio epichlorohydrin to bisphenol A, products of different molecular weight can be made. Other epoxy resins include (a) the diglycidyl ethers of other bisphenol compounds such as bisphenol B, F, G, and H, (b) epoxy resins produced by reacting a novolac resin with a halogen-substituted aliphatic epoxide such as epichlorohydrin, 4-chloro-1,2-epoxybutane, 5-bromo-1,2-epoxypentane, 6-chloro-1,3-epoxyhexane and the like, (c) epoxidized polybutadiene resins, and (d) epoxidized drying oils.
Particularly preferred are epoxy resins with a weight per epoxy group of 175 to 200. Although the viscosities of the epoxy resins are high, usually greater than 5,000 cps at 25° C., the epoxy component viscosity is reduced to a workable level when the epoxy resin is mixed with the oxidizing agent. Useful epoxy resins are disclosed

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