Polyurethane-forming binders

Details Polyurethane-forming binders Polyurethane-forming binders

2001-07-24

2003-08-05

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...

Reexamination Certificate

active

06602931

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
CLAIM TO PRIORITY
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a polyurethane-forming no-bake foundry binder comprising a (a) polyol component comprising (1) a polyol selected from the group consisting of polyether polyols, aminopolyols, polyester polyols, and mixtures thereof, and (2) a hydrogenfluoride of aminosilanol, (b) a polyisocyanate component, and optionally (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.
(2) Description of the Related Art
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 binder, 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. Phenolic urethane 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 phenolic urethane 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. Because the foundry mix often sits unused for extended lengths of time, the binder used to prepare the foundry mix must not adversely affect the benchlife of the foundry mix.
Among other things, the binder must have a low viscosity, be gel-free, remain stable under use conditions, and cure efficiently. 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.
Because the cores and molds are often exposed to high temperatures and humid conditions, it also desirable that the foundry binders provide cores and molds that have a high degree of humidity resistance. This is particular important for foundry applications, where the core or mold is exposed to high humidity conditions, e.g. during hot and humid weather, or where the core or mold is subjected to an aqueous core-wash or mold coating application for improved casting quality.
Phenolic urethane cold-box and no-bake foundry binders often contain a silane coupling agent and/or aqueous hydrofluoric acid to improve humidity resistance. See for example U.S. Pat. No. 6,017,978. The silane and hydrofluoric acid are typically added to the phenolic resin component of the binder.
However, the addition of the silane and free aqueous hydrofluoric acid in phenolic urethane binders often results in one or more problems. For instance, the hydrofluoric acid usually requires special handling procedures, particularly because it is known to etch vitreous materials, e.g. flow control sight tubes commonly used in pipe line systems to convey the binder from storage to its point of use. Additionally, in the case of phenolic urethane no-bake binders, the use of the silane and hydrofluoric acid retards the chemical reaction, and thus increases the worktime of the foundry mix and the striptime of the core or mold. If a longer time is required for the sand mix to set, this negatively affects productivity.
All citations referred to under this description of the “Related Art” and in the “Detailed Description of the Invention” are expressly incorporated by reference.
BRIEF SUMMARY OF THE INVENTION
This invention relates to a polyurethane-forming no-bake binder comprising:
(a) a polyol component comprising,
(1) a polyol selected from the group consisting of polyether polyols, aminopolyols, polyester polyols, and mixtures thereof,
(2) a hydrogenfluoride of aminosilanol,
(b) a polyisocyanate component, and optionally
(c) a liquid amine curing catalyst.
The compositions contain little or no free fluorinated acid and will not etch glass. Cores made with the binders have excellent humidity resistance, and this is achieved without substantial adverse effects on the reactivity of the binder, i.e. the worktime of the foundry mix and the striptime of the core from the pattern is not substantially increased, particularly when compared to the worktime and striptime increases, which result when phenolic urethane no-bake binders are used in similar formulations. This is significant because, if a longer time is required for the sand mix to set, this adversely affects productivity.
In contrast to the approaches shown in the prior art, where either HF or an aminosilane is used alone or in combination, the hydrogenfluorides of aminosilanols are the reaction product of a fluorinated acid (preferably aqueous HF) and an aminoalkoxysilane
The invention also relates to the use of the binders in foundry mixes, core-making by the no-bake process, and in the casting of ferrous and non-ferrous metals.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
Not Applicable.
DETAILED DESCRIPTION OF THE INVENTION
The detailed description and examples will illustrate specific embodiments of the invention and will enable one skilled in the art to practice the invention, including the best mode. It is contemplated that many equivalent embodiments of the invention will be operable besides those specifically disclosed.
The hydrogenfluorides of aminosilanols used in the binder have the following structural formula:
wherein:
(1) R
1
and R
2
are selected from the group consisting of H; alkyl groups, aryl groups, substituted alkyl groups, aryl groups, mixed alky-aryl groups; di- or triamino groups, amino alkyl groups, amino aryl groups, amino groups having mixed alky-aryl groups, and amino groups having substituted alkyl groups, aryl groups, mixed alky-aryl groups; aminocarbonyl groups; and alkylsilanol groups, preferably where at least one of the R
1
and R
2
groups is H and the other group is an unsubstituted alkyl group having 1-4 carbon atoms;
(2) n is a whole number from 1 to 3, preferably where n≧1;
(3) n+m=3;
(4) p is a whole number from 1 to 5, preferably 2 to 3
(5) R
a
is selected from the group consisting of alkyl groups, aryl groups, mixed alky-aryl groups, substituted alkyl groups, aryl groups, mixed alkyl-aryl groups, preferably an unsubstituted alkyl group having from 1-4 carbon atoms;
(6) x is a number and is equal to 0.1 and 3 per nitrogen atom of the aminosilanol, and is preferably from 1 to 2.5 per nitrogen atom in the aminoalkoxysilane; and
(7) Y=HF or HF complex, which results from a compound that hydrolyzes to yield HF, for instance ammonium fluoride, ammoniumbifluoride, potassium bifluoride, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluorosilicic acid, N,N-diisopropyl aminetris(hydrogenfluoride), N,N′-dimethyl-2-imidazolidone-hexakis(hydrogenfluoride), preferably HF.
The hydrogenfluorides of aminosilanols are the reaction products formed by the reaction of an aqueous solution of a fluorinated acid, either hydrofluoric acid or a fluorinated acid, which hydrolyzes to yield hydrofluoric acid, with aminoalkoxysilanes. Preferably, the fluorinated acid is hydrofluoric acid, most preferably an aqueous solution of hydrofluoric acid, containing from 10 to 90 weight percent water, preferably 30-60 weight percent water. Other fluorinated acids that can be used are ammoni

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