Polyurethane-forming binders

Details Polyurethane-forming binders Polyurethane-forming binders

2001-07-24

2003-10-14

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, C523S143000, C523S147000

Reexamination Certificate

active

06632856

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) polyether polyol component comprising (1) a polyether polyol, (2) hydrofluoric acid, and (3) an aminoalkoxysilane, (b) a polyisocyanate component, (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. Although this patent covers the use of silanes in general, the examples utilize a ureido silane, which is preferred. The silane and hydrofluoric acid are typically added to the phenolic resin component of the binder.
However, a disadvantage of adding the silane and free aqueous hydrofluoric acid to phenolic urethane no-bake binders, is that the addition 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 polyether polyol component comprising,
(1) a polyether polyol,
(2) a fluorinated acid, and
(3) an aminoalkoxysilane,
(b) a polyisocyanate component, and
(c) a liquid amine curing catalyst.
Cores and molds 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 or mold from the pattern is not substantially increased. Thus, the use of these binders have an advantage not found when phenolic urethane having similar formulations are used as no-bake binders, since the worktime of foundry mixes made with phenolic urethane binders typically increases and the striptime also increases, when hydrofluoric acid and a silane are added to the binder. This improvement is significant because, if a longer time is required for the sand mix to set, this adversely affects productivity. These advantages are obtained without sacrificing other properties such as casting quality.
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 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 these specifically disclosed.
The aminoalkoxysilanes used in the binder composition typically have the following general formula:
wherein:
(1) R
1
and R
2
are selected from the group consisting of H; alkyl groups, aryl groups, mixed alky-aryl groups, substituted alkyl groups, 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; and alkoxysilane groups, where R
1
and R
2
can be the same or different and 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, and
(5) R
a
and R
b
are selected from the group consisting of alkyl groups, aryl groups, mixed alky-aryl groups, substituted alkyl groups, aryl groups, preferably an unsubstituted alkyl group having from 1-carbon atoms, and can be identical or different.
This structure does not include ureido silanes, which do not work effectively for purposes of this invention.
Specific examples of aminoalkoxysilanes include 3-aminopropyldimethyl-methoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyl-triethoxysilane, 3-aminopropylmethyl-dimethoxysilane 3-aminopropylmethyl-diethoxysilane, N-(n-butyl)-3-aminopropyl-trimethoxysilane, N-aminoethyl-3-aminopropylmethyl-dimethoxysilane, 3-ureidopropyltrimethoxysilane, 3-ureido-propyltriethoxysilane, N-phenyl-3-aminopropyl-trimethoxysilane, N-[(N′-2-aminoethyl)-2-aminoethyl)]-3-aminopropyltrimethoxysilane and bis (3-trimethoxy-silylpropyl) amine. Preferably used as the aminoalkoxysilanes are aminoalkoxysilanes where 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; 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.
The polyether polyol component comprises a polyether polyol. The polyether polyols, which are used in the polyurethane-forming foundry binders are liquid polyether polyols or blends of liquid polyether polyols typically having

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