Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-03-03
2001-09-18
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S139000, C523S143000, C523S147000, C164S047000
Reexamination Certificate
active
06291550
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a solventless polyurethane no-bake foundry binder system comprising, as individual components (a) a polyol component comprising a polyether polyol, glycol, and an aromatic polyester polyol, (b) an organic polyisocyanate component, and (c) a liquid tertiary amine catalyst component. Foundry mixes are prepared by mixing the binder system with a foundry aggregate by a no-bake process. The resulting foundry shapes are used to cast metal parts from ferrous and non-ferrous metals.
BACKGROUND OF THE INVENTION
In the foundry industry, one of the processes used 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.
One of the processes used in sand casting for making molds and cores is the no-bake process. In this process, a foundry aggregate, binder, and liquid curing catalyst are mixed and compacted to produce a cured mold and/or core. In the no-bake process, it is important to formulate a foundry mix which will provide sufficient worktime to allow shaping. Worktime is the time between when mixing begins and when the mixture can no longer be effectively shaped to fill a mold or core.
A binder commonly used in the no-bake process is a polyurethane binder derived by curing a polyurethane-forming binder with a liquid tertiary amine catalyst. Such polyurethane-forming binders used in the no-bake process, have proven satisfactory for casting such metals as iron or steel which are normally cast at temperatures exceeding about 1370° C. They are also useful in the casting of light-weight metals, such as aluminum, which have melting points of less than 815° C. The phenolic resin component typically contains small amounts of free formaldehyde and free phenol which are undesirable. Both the phenolic resin component and the polyisocyanate components generally contain a substantial amount of organic solvent which can be obnoxious to smell and smoke during the mixing and the pouroff stages in the workplace.
U.S. Pat. No. 5,689, 613 discloses polyurethane-forming foundry binders which use ester-based aromatic polyols as the polyol component of the binder. These binders are do not have any free formaldehyde or free phenol. However, they are too viscous to use without a solvent.
U.S. Pat. No. 5,688,857 discloses a polyurethane-forming cold-box binder which is solvent free and does not contain any free formaldehyde or free phenol. Although satisfactory for cold-box applications, this binder is not satisfactory for no-bake applications because early tensile strengths of cores and molds prepared with this binder were not sufficient. Consequently, there is an interest in improving the early tensile strengths for no-bake applications to allow the cores and molds to be more readily stripped from the pattern, and thus improve higher productivity.
SUMMARY OF THE INVENTION
This invention relates to a solventless polyurethane no-bake foundry binder system comprising:
(1) a polyol component comprising
(a) a polyether polyol,
(b) a glycol component, and
(c) an aromatic polyester polyol component,
(2) an organic polyisocyanate component, and
(3) a liquid tertiary amine catalyst component.
Foundry mixes are prepared by mixing the binder with a foundry aggregate by a no-bake process. The resulting foundry shapes are used to cast metal parts from ferrous and non-ferrous metals. The binders do not contain free formaldehyde or free phenol, or solvents. The binder has low viscosity for easy pumping, low odor, and low smoke at pouroff. The early tensile strengths of cores and molds prepared with the binders are improved by the addition of the aromatic ester to the polyol component. The sand shakes out from the castings effectively and the surface finish of the casting is good.
BEST MODE AND OTHER MODES
The polyether polyols which are used in the polyurethane no-bake foundry binder are liquid polyether polyols generally having hydroxyl a number of from about 200 to about 1,000, more preferably from 300 to 800, and most preferably from 300 to 600 milligrams of KOH based upon one gram of polyether polyol. The viscosity of the polyether polyol is from 100 to 1,000 centipoise, preferably from 200 to 700 centipoise, most preferably 300 to 500 centipoise. The hydroxyl groups of the polyether polyols are preferably primary and/or secondary hydroxyl groups.
The polyether polyols are prepared by reacting an alkylene oxide with a polyhydric alcohol in the presence of an appropriate catalyst such as sodium methoxide according to methods well known in the art. Representative examples of alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, amylene oxide, styrene oxide, or mixture thereof. The polyhydric alcohols typically used to prepare the polyether polyols generally have a functionality greater than 2.0, preferably from 2.5 to 5.0, most preferably from 2.5 to 4.5. Examples include ethylene glycol, diethylene glycol, propylene glycol, trimethylol propane, and glycerin.
The amount of the polyether polyol in the polyol component is generally from 10 to 50 weight percent, preferably from 20 to 40 weight percent, based upon the polyol component.
The glycols used in the polyol component are preferably monomeric glycols having an average functionality of 2 to 4, hydroxyl numbers from 500 to 2,000, more preferably from 700 to 1,200, and viscosities less than 200 centipoise at 25° C. preferably less than 100 centipoise at 25° C. Examples of such monomeric polyols include ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propane diol, 1,4-butanediol, dipropylene glycol, tripropylene glycol, glycerin, tetraethylene glycol, and mixture thereof.
The amount of glycol the polyol component is generally from in the polyol component is generally from 10 to 50 weight percent, preferably from 20 to 40 weight percent, based upon the polyol component.
The aromatic polyester polyols used in the polyol component are liquid polyester polyols, or a blend of liquid aromatic polyester polyols, generally having a hydroxyl number from about 500 to 2,000, preferably from 700 to 1200, and most preferably from 250 to 600; a functionality equal to or greater than 2.0, preferably from 2 to 4; and a viscosity of 500 to 50,000 centipoise at 25° C., preferably 1,000 to 35,000, and most preferably 2,000 to 25,000 centipoise. They are typically prepared by ester interchange of aromatic ester and alcohols or glycols by an acidic catalyst. The amount of the aromatic polyester polyol in the polyol component is from 2 to 50 weight percent, preferably from 10 to 35 weight percent, most preferably from 10 to 25 weight percent based upon the polyol component. Examples of aromatic esters used to prepare the aromatic polyesters include phthalic anhydride and polyethylene terephthalate. Examples of alcohols used to prepare the aromatic polyesters are ethylene glycol, diethylene glycol, triethylene glycol, 1,3, propane diol, 1,4 butane diol, dipropylene glycol, tripropylene glycol, tetraethylene glycol, glycerin, and mixtures thereof. Examples of commercial available aromatic polyester polyols are STEPANPOL polyols manufactured by Stepan Company, TERATE polyol manufactured by Hoechst-Celanese, THANOL aromatic polyol manufactured by Eastman Chemical, and TEROL polyols manufactured by Oxide Inc. The weight ratio of glycol to polyether polyol in the polyol component is preferably from 1:1 to 1:1.5, most preferably from 1:1 to 1:1.2. The weight ratio of aromatic polyester to polyether polyol in the polyol component is preferably from 1.5:1.0 to 0.5:1.0, most preferably from 1.1:1.0 to 0.9:1.0.
Although not preferred, minor amounts of phenolic resin and/or amine-based polyols polyol can be added to the polyol component. By minor amounts, it is meant that less than 15 weight percent, preferably less than 5 weight percent, said weight percent based upon the weight of the polyol component. If a phenolic resin is added to the polyether
Chang Ken K.
Chen Chia-Hung
Ashland Inc.
Chol Ling-Siu
Hedden David L.
Wu David W.
LandOfFree
Solventless polyurethane no-brake foundry binder does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Solventless polyurethane no-brake foundry binder, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Solventless polyurethane no-brake foundry binder will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2478126