Foundry binder

Details Foundry binder Foundry binder

1999-05-03

2002-04-30

Dunn, Tom (Department: 1725)

Metal founding

Process

Shaping a forming surface

C164S528000, C523S139000

Reexamination Certificate

active

06378599

ABSTRACT:

BRIEF SUMMARY OF THE INVENTION
The invention relates to a foundry binder which is obtainable by surface modification of
a) colloidal inorganic particles with
b) one or more silanes of the general formula (I)
R
x
—Si—A
4−x
  (I)
where the radicals A are identical or different and are hydroxyl groups or groups which can be removed hydrolytically, except methoxy, the radicals R are identical or different and are groups which cannot be removed hydrolytically and x is 0, 1, 2 or 3, where x≧1 in at least 50 mol % of the silanes;
under the conditions of the sol-gel process with a sub-stoichiometric amount of water, based on the hydrolysable groups which are present, with formation of a nanocomposite sol, and further hydrolysis and condensation of the nanocomposite sol, if desired, before it is brought into contact with the foundry sand.
The nanocomposite sol employed according to the invention is prepared by surface modification of colloidal inorganic particles (a) with one or more silanes (b), if desired in the presence of other additives (c) under the conditions of the sol-gel process.
DETAILED DESCRIPTION OF THE INVENTION
Details of the sol-gel process are described in C. J. Brinker, G. W. Scherer: “Sol-Gel Science—The Physics and Chemistry of Sol-Gel-Processing”, Academic Press, Boston, San Diego, New York, Sydney (1990) and in DE 1941191, DE 3719339, DE 4020316 and DE 4217432.
Here, specific examples of the silanes (b) which can be employed according to the invention and of their radicals A which are hydrolytically removable and their radicals R which are not hydrolytically removable are given.
Preferred examples of groups A which are removable hydrolytically are hydrogen, halogen (F, Cl, Br and I, in particular Cl and Br), alkoxy (in particular C
2−4
-alkoxy, such as ethoxy, n-propoxy, isopropoxy and butoxy), aryloxy (in particular C
6−10
-aryloxy, such as phenoxy), alkaryloxy (e.g. benzyloxy), acyloxy (in particular C
1-4
-acyloxy, such as acetoxy and propionyloxy) and alkylcarbonyl (e.g. acetyl). Radicals A which are likewise suitable are amino groups (e.g. mono- or dialkyl-, -aryl- and -aralkylamino groups having the abovementioned alkyl, aryl and aralkyl radicals), amide groups (e.g. benzamido) and aldoxime or ketoxime groups. Two or three radicals A may also together form a moiety which complexes the Si atom, as for example in Si-polyol complexes derived from glycol, glycerol or pyrocatechol. Particularly preferred radicals A are C
2−4
-alkoxy groups, in particular ethoxy. Methoxy groups are less suitable for the purposes of the invention, since they have an excessively high reactivity (short processing time of the nanocomposite sol).
The abovementioned hydrolysable groups A may, if desired, carry one or more usual substituents, for example halogen or alkoxy.
The radicals R which are not hydrolytically removable are preferably selected from the group consisting of alkyl (in particular C
1−4
-alkyl, such as methyl, ethyl, propyl and butyl), alkenyl (in particular C
2−4
-alkenyl, such as vinyl, 1-propenyl, 2-propenyl and butenyl), alkynyl (in particular C
2−4
-alkynyl, such as acetylenyl and propargyl), aryl (in particular C
6−10
-aryl, such as phenyl and naphthyl) and the corresponding alkaryl and arylalkyl groups. These groups may also, if desired, have one or more usual substituents, for example halogen, alkoxy, hydroxy, amino or epoxide groups.
The abovementioned alkyl, alkenyl and alkynyl groups include the corresponding cyclic radicals, such as cyclopropyl, cyclopentyl and cyclohexyl.
Particularly preferred radicals R are substituted or unsubstituted C
1-4
-alkyl groups, in particular methyl and ethyl, and substituted or unsubstituted C
6-10
-alkyl groups, in particular phenyl.
It is also preferable that x in the above formula (I) is 0, 1 or 2, particularly preferably 0 or 1. It is also preferable if x=1 in at least 60 mol %, in particular at least 70 mol %, of the silanes of the formula (I). In particular cases, it may be even more favourable if x=1 in more than 80 mol %, or even more than 90 mol % (e.g. 100 mol %), of the silanes of the formula (I).
The foundry binder according to the present invention may be prepared, for example, from pure methyl-triethoxysilane (MTEOS) or from mixtures of MTEOS and tetraethoxysilane (TEOS), as component (b).
Concrete examples of silanes of the general formula (I) are compounds of the following formulae:
Si(OC
2
H
5
)
4
, Si(O-n- or iso-C
3
H
7
)
4
, Si(OC
4
H
9
)
4
, SiCl
4
, Si(OOCCH
3
)
4
, CH
3
—SiCl
3
, CH
3
—Si(OC
2
H
5
)
3
, C
2
H
5
—SiCl
3
, C
2
H
5
—Si(OC
2
H
5
)
3
, C
3
H
7
—(OC
2
H
5
)
3
, C
6
H
5
—Si—(OC
2
H
5
)
3
, C
6
H
5
—Si(OC
2
H
5
)
3
(C
2
H
5
O)
3
—Si—C
3
H
6
—Cl, (CH
3
)
2
SiCl
2
, (CH
3
)
2
Si(OC
2
H
5
)
2
(CH
3
)
2
Si(OH)
2
, (C
6
H
5
)
2
SiCl
2
, (C
6
H
5
)
2
Si(OC
2
H
5
)
2
, (C
6
H
5
)
2
Si(OC
2
H
5
)
2
, (iso-C
3
H
7
)
3
SiOH, CH
2
═CH—Si(OOCCH
3
)
3
, CH
2
═CH—SiCl
3
, CH
2
═CH—Si(OC
2
H
5
)
3
, HSiCl
3
, CH
2
═CH—Si(OC
2
H
4
OCH
3
)
3
, CH
2
═CH—CH
2
—Si(OC
2
H
5
)
3
, CH
2
═CH—CH
2
—Si(OOCCH
3
)
3
, CH
2
═C(CH
3
) COO—C
3
H
7
—Si—(OC
2
H
5
)
3
, CH
2
═C(CH
3
)—COO—C
3
H
7
—Si(OC
2
H
5
)
3
, n-C
6
H
13
—CH
2
—CH
2
—Si(OC
2
H
5
)
3
, n-C
8
H
17
—CH
2
—CH
2
—Si(OC
2
H
5
)
3
,
These silanes can be prepared by known methods; cf. W. Noll, “Chemie und Technologie der Silicone” [Chemistry and Technology of the Silicones], Verlag Chemie GmbH, Weinheim/Bergstra&bgr;e, Germany (1968).
Based on the abovementioned components (a), (b) and (c), the proportion of component (b) is usually from 20 to 95% by weight, preferably from 40 to 90% by weight, and particularly preferably from 70 to 90% by weight, expressed as polysiloxane of the formula: R
x
SiO
(2−0.5x)
which is formed in the condensation.
The silanes of the general formula (I) used according to the invention may be employed wholly or partially in the form of precondensates, i.e. compounds produced by partial hydrolysis of the silanes of the formula (I), either alone or in a mixture with other hydrolysable compounds. Such oligomers, preferably soluble in the reaction medium, may be straight-chain or cyclic low-molecular-weight partial condensates (polyorgano-siloxanes) having a degree of condensation of e.g. from about 2 to 100, in particular from about 2 to 6.
The amount of water employed for hydrolysis and condensation of the silanes of the formula (I) is preferably from 0.1 to 0.9 mol, and particularly preferably from 0.25 to 0.75 mol, of water per mole of the hydrolysable groups which are present. Particularly good results are often achieved with from 0.35 to 0.45 mol of water per mole of the hydrolysable groups which are present.
Specific examples of colloidal inorganic particles (a) are sols and powders dispersible at the nano level (particle size preferably up to 300 nm, in particular up to 100 nm and particularly preferably up to 50 nm) of SiO
2
, TiO
2
, ZrO
2
, Al
2
O
3
, Y
2
O
3
, CeO
2
, SnO
2
, ZnO, iron oxides or carbon (carbon black and graphite), in particular of SiO
2
.
The proportion of component (a), based on the components (a), (b) and (c), is usually from 5 to 60% by weight, preferably from 10 to 40% by weight, and particularly preferably from 10 to 20% by weight.
For preparing the nanocomposite, other additives in amounts of up to 20% by weight, preferably up to 10% by weight, and in particular up to 5% by weight, may be employed as optional components (c); examples are curing catalysts, such as metal salts and metal alkoxides (e.g. aluminium alkoxides, titanium alkoxides or zirconium alkoxides), organic binders, such as polyvinyl alcohol, polyvinyl acetate, starch, polyethylene glycol and gum arabic, pigments, dyes, flame retardants, compounds of glass-forming elements (e.g. boric acid, boric acid esters, sodium methoxide, potassium acetate, aluminium sec-butoxide, etc).
The hydrolysis and condensation is carried out under sol-gel conditions in the presence of acid condensation catalysts (e.g. hydrochloric a

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