CZ169599A3 - Foundry binding agent - Google Patents

Abstract

The present invention discloses a foundry binder obtainable by surface modification of a) colloidal b) one or more silanes of formula (I), wherein (I) is FUSiA 4, and wherein the A 2i radicals are identical or different are hydroxyl groups or groups that can be hydrolytically removed except methoxy groups, radicals R are identical or different and these are groups that cannot be removed by hydrolysis and x is 0,1,2 or 3, wherein x> 1 in at least 50 mol% of silanes; at conditions of sol-gel process with lower stoichiometric quantities of water, based on the hydrolysis of the groups present, by the formation of a nanocomposite sol, further hydrolysis of a condensation of the nanocomposite sol, if required, before bringing the foundry sand into contact.

Description

Foundry binder

The present invention relates to a foundry binder which can be prepared by surface modification

(a) colloidal inorganic particles with

(b) one or more silanes of formula (I)

R _x -Si-A ₄ -x (I) wherein the radicals A are identical or different and are hydroxyl groups or groups which can be hydrolytically removed, except for the methoxy group, R radicals are identical or different and are groups that cannot be hydrolytically removed and x is 0, 1, 2 or 3, wherein x > 1 in at least 50 mol% of silanes;

under sol - gel process conditions with less than a stoichiometric amount of water based on the hydrolysis of the groups present, the formation of the nanocomposite sol, further hydrolysis and condensation of the nanocomposite sol, if desired, before contacting the foundry sand.

The nanocomposite sol used in the present invention is prepared by surface modification of colloidal inorganic particles (a) with one or more silanes (b), if desired also in the presence of other additives (c), under sol-gel process conditions.

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 4020916 and DE 4217432.

Examples of silanes (b) that can be used according to the present invention and radicals A that are hydrolytically removable and radicals R that are not hydrolytically removable are given herein.

• · · «0 · 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 · · •• 0 000 · ·· ·

Preferred examples of Group A radicals which are hydrolytically removable are hydrogen, halogen (F, Cl, Br and I, especially Cl and Br), alkoxy (especially C2-4-alkoxy such as ethoxy, n-propoxy, isopropoxy and butoxy), aryloxy (especially C 6-10 aryloxy such as phenoxy), alkaryloxy (e.g. benzyloxy), acyloxy (especially C 1-4 -acyloxy such as acetoxy and propyonyloxy) and alkylcarbonyl (e.g. acetyl). Similarly suitable radicals A are amino groups (e.g., mono- or dialkyl-, -aryl- and -arylalkylamino, groups having the above-mentioned alkyl, aryl and aryalkyl radicals), amide groups (e.g., benzamido) and aldoxime groups and ketoxime groups. The two or three radicals A may also together form a group that complexes the Si atom, as is the case, for example, in Si-polyol complexes derived from glycol, glycerol or pyrocatechol. Particularly preferred radicals A are C 2-4 -alkoxy groups, especially ethoxy. Methoxy groups are less suitable for the purposes of the present invention because they have too high reactivity (short process time of the nanocomposite sol).

The above hydrolyzable groups A may, if desired, carry one or more conventional substituents, for example a halogen or alkoxy group.

The radicals R which are not hydrolytically removable are preferably selected from the group consisting of alkyl (especially C 1-4 -alkyl such as methyl, ethyl, propyl and butyl), alkenyl (especially C 2-4 -alkenyl such as vinyl, 1-propenyl 2-propenyl and butenyl), alkynyl (especially C 2-4 -alkynyl such as acetylenyl and propargyl), aryl (especially C 6-10 -aryl such as phenyl and naphthyl) and the corresponding alkylaryl and arylalkyl groups. These groups may also, if desired, have one or more conventional substituents, for example, halogen, alkoxy, hydroxy, amino or epoxy groups.

The above alkyl, alkenyl and alkynyl groups include the corresponding cyclic radicals such as cyclopropyl, cyclopentyl and cyclohexyl.

Particularly preferred R radicals are substituted or unsubstituted C 1-4 -alkyl groups, especially methyl or ethyl, and substituted or unsubstituted C 6-10 -alkyl groups, especially phenyl.

- ί *

• · · 4 4 ♦ 4 »« 4 4 4 4 4 ·

9 9 9 • 4 4 • 9 9

99

It is also preferred that x in formula (I) above be 0, 1 or 2, particularly preferably x = 0 or 1. It is also preferred that x = 1 in at least 60 mol%, in particular at least 70 mol% of silanes of formula (I). In special cases, it may even be more preferred that x = 1 in more than 80 mol% or even more than 90 mol% (eg 100 mol%) of the silanes of formula (I).

The foundry binder of the present invention can be prepared, for example, from pure methyltriethoxysilane (MTEOS) or from a mixture of MTEOS and tetraethoxysilane (TEOS) as component (b).

Specific examples of silanes of formula (I) are compounds of the following structures:

Si (OC ₂ H ₅ ) ₄ , Si (On- or iso-C ₃ H ₇ ) ₄ , Si (OC ₄ H ₉ ) _{4 from} SiCl _{4 from} Si (OOCCH ₃ ) ₄ , CH ₃ -SiCl ₃ , CH ₃ -Si (OC ₂ H _s) 3 / C ₂ H ₅ -SíC1 _{3 15} C ₂ H ₅ Si (OC ₂ H ₅₎ 3, C3H7-S1 (OC ₂ H _{5) 3,} C ₆ H ₅ -Si- ( OC ₂ H ₅ ) 3

C ₈ H ₅ -Si (OC ₂ H ₅ ) 3, (C ₂ H ₅ O) ₃ -s-c ₃ h ₆ -ci, (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-C3H7) 3S1OH, _CH2 = CH-Si (OOCCH ₃₎ 3, CH ₂ = CH-SíC1 _{3, CH2} = CH-Si (OC2H5) 3 / HSÍCI3,

CH ₂ = CH-Si (OC ₂ H ₄ OCH ₃ ) 37 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, nC ₆ Hi ₃ -CH ₂ -CH ₂ -Si (OC ₂ H ₅₎ 3, nC ₈ Hi7 CH ₂ -CH ₂ -Si (OC ₂ H ₅ ) ₃ , (C ₂ H ₅ O) ₃ Si- (CH ₂ ) ₃ -O-CH ₂ -CH-CH ₂ .

O

These silanes can be prepared by a known method; W. Noll, Chemie und Technologie der Silikone [Chemistry and Technology of Silicones], Verlag Chemie GmbH, Weinhem / Bergstrasse, Germany (1968).

Based on components (a), (b) and (c) above, the proportion of component (b) is usually from 20 to 95 wt. %, preferably from 40 to 90 wt. % and in particular from 70 to 90 wt. %, expressed as a polysiloxane of the formula: R _x SiO (2. 0, 5-x), formed by condensation.

BB

-Ť * · · B B · · · · · · B B B B B B B B

999

AND

9 9 9

99 9

The silanes of formula (I) used in the present invention may be used wholly or partially in the form of precondensates, i.e., compounds produced by partial hydrolysis of the silane of formula (I), either alone or in admixture with other hydrolyzable compounds. Such oligomers, preferably soluble in the reaction medium, may be straight chain condensates or cyclic low molecular weight condensates (polyorganosiloxanes) with a high degree of condensation, e.g. from 2 to 100, in particular from 2 to 6.

The amount of water used for the hydrolysis and condensation of the silanes of formula (I) is preferably from 0.1 to 0.9 mol and particularly preferably from 0.25 to 0.75 mol of water per mol of hydrolyzable groups present.

Specific examples of colloidal inorganic particles (a) are salts and powders dispersible at the nano level (particle size preferably up to 300 nm, especially up to 100 nm and especially up to 50 nm), S1O2, TiO2, _ZrO2, Al2O3, Y2O3, CeO2, SnO2, ZnO, iron oxides or carbon (carbon black and graphite), especially SiO2.

The proportion of component (a), based on the content of components (a), (b) and (c), is usually from 5 to 60% by weight, preferably from 10 to 40% by weight and in particular from 10 to 20% by weight. %.

Optionally, further additives in amounts of up to 20 wt.% May be used as components (c) for preparing the nanocomposites. %, preferably up to 5 wt. %; examples are hardening catalysts such as metal salts and metal alkoxides (for example, aluminum, titanium and zirconium-derived alkoxides), organic binders such as polyvinyl acetate, starch, polyethylene glycol and acacia, pigments, dyes, flame retardants, glass forming compounds ( eg boric acid, boric acid esters, sodium methoxide, sodium acetate, aluminum sec-butoxide, etc.).

The hydrolysis and condensation is carried out under sol-gel conditions in the presence of acidic condensation catalysts (e.g. hydrochloric acid) at a pH preferably from 1 to 2 until a viscous sol is formed.

Φ · · _. ·

AND

-r__ · _. · · * »· Ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν ν • · ·· «·

It is preferred not to use a solvent other than the one resulting from the hydrolysis of the alkoxy groups. However, if desired, alcoholic solvents such as ethanol, other polar, protic or aprotic solvents such as tetrahydrofuran, dioxane, dimethylformamide or butyl glycol may be used, for example.

In order to achieve favorable morphology of the sol particles and sol viscosity, the resulting nanocomposite sol is preferably subjected to a special post-reaction step in which the reaction mixture is heated to a temperature of 40 to 120 ° C for a few hours to several days. Particularly preferred is storage at room temperature for one day or heating at 60-80 ° C for several hours. A nanocomposite sol having a viscosity of preferably from 5 to 500 mPas, in particular from 10 to 50 mPas, is thus obtained. Of course, the viscosity of the sol can be adjusted to appropriate values for specific applications by adding solvents or by removing reaction by-products (e.g., alcohols). The post-reaction step may preferably be associated with a reduction of the solvent content.

The nanocomposite sol and the foundry powder are combined at least after the initial hydrolysis of component (b) and in any case before the final curing. Prior to the addition of sand, the nanocomposite sol is preferably activated by adding an additional amount of water.

To produce foundry molds and cores, the nanocomposite gel is applied to the foundry molds or core sand in conventional amounts, for example in an amount of from 0.1 to 0.2 wt%. %.

If desired, conventional foundry additives such as reinforcing oils, core oils, release agents, or conventional nuclear binders may be used.

Curing may be carried out at room temperature, but heat treatment is preferred at temperatures above 50 ° C, preferably above 100 ° C, and especially at 150 ° C or above. The curing can optionally be carried out in an inert atmosphere.

By comparison with conventionally bonded cores it was found that a significantly lower amount of tail gas is emitted and that the mold can be released from the sand deposit

AND

9

9 9 9

9

9900 9 99

9 9 9 99 • · · · ·

9 99 using standard procedures. A significantly smaller amount of gas was observed during casting, which is of decisive importance in practice since this achieves a high quality surface and finer structures may be cast.

The following examples further illustrate the present invention.

The silica sol used in the following examples is an aqueous silica sol manufactured by BAYER (Levasil 300/30) having a solids content of 30 wt. % and a particle size of 7 to 10 nm. The following abbreviations are further used in the examples:

MTEOS = Methyltriethoxysian

TEOS = Tetraethoxysilane

PTEOS = Phenyltriethoxysilane

ETEOS = Ethyltriethoxysilane

Example 1

51.3 ml of MTEOS (corresponding to 60 mol%), 19.1 ml of TEOS (corresponding to 20 mol%) and 15.0 ml of PTEOS (corresponding to 20 mol%) are mixed and half of this mixture is vigorously mixed with 11.7 ml of silica sol (corresponding to 14.3 wt% silica sol) and 0.386 ml of concentrated hydrochloric acid. After 5 minutes, the second portion of the alkoxide mixture is added to the portion and the mixture is stirred for an additional 5 minutes. The resulting sol is then treated in a post-reaction step (stirring for 12 h at 60 ° C).

Approximately 2.5 ml of water is added to the sol before use to achieve a water content of 0.5 mol of water per mole of hydrolyzable group. The resulting sol is mixed with sand having a particle size of about 1 mm so that the sand represents about 84% of the total weight. The material is packed into a mold and cured at 100 ° C for 20 minutes to form a mechanically rigid molded core that does not lose shape even when exposed to 500 ° C for 1 hour.

Example 2

Using the method described in Example 1, a core sand binder is prepared from 184 ml of MTEOS, 51.4 ml of TEOS, 62.8 ml of silica sol and 1.71 ml of 37% hydrochloric acid.

The binder is ready for use after 15 minutes of post-treatment. The solids content is 327 g / l.

The dry sand of the core is mixed with the binder in an amount corresponding to a 1.5 wt% content. % solid binder. The wet material is compressed by a rammer for 30 minutes at a pressure of 100 kN and then cured at 40 ° C for 1 hour to form an inorganically bonded core that does not release any toxic gases when heated to 500 ° C and can be disintegrated by ultrasound.

Example 3

1. Preparation of a standard binder

The flask is filled with 655 g of MTEOS, 191 g of TEOS, 142 g of aqueous silica sol and immediately thereafter 9 ml of sulfuric acid (40% by weight) is added with vigorous stirring. After about 1 minute of vigorous stirring, an exothermic reaction (temperature rises to about 60 ° C) begins. In order to mature the dispersion, it is kept at room temperature overnight or is refluxed for 1 hour before its further use.

2. Preparation of Standard Binder B

The flask is filled with 621 g of MTEOS, 181 g of TEOS and 185 g of aqueous silica sol (Levasil 50/50; 50% solids SiO2 content, manufactured by BAYER), and immediately thereafter 10.3 ml of acid is added under vigorous stirring. sulfuric acid (40 wt%). After about 1 minute of vigorous stirring, an exothermic reaction (temperature rises to about 60 ° C) begins. To mature, the dispersion is kept at room temperature overnight or refluxed for 1 hour before use.

• •• ftft ί · ft · ft · ft · ft ·

.. /.

Ftft ftft ftft

3. Preparation of standard binder C

The flask is filled with 463 g of MTEOS, 180 g of TEOS and 180 g of dimethyldiethoxysilane, 5 then 267 g of aqueous silica sol is added and the resulting mixture is immediately added with vigorous stirring 6.06. ml. HCl (37% by weight). After about 1 minute of vigorous stirring, an exothermic reaction begins (temperature rises to about 60 ° C). The dispersion can be used directly after cooling to room temperature.

4. Production of sand core for casting

Standard binder A (10 kg, solids content: 34 wt%) is concentrated in a rotary evaporator to a solids content of 60 wt%. %. To 1 kg of said concentrated binder dispersion 90 ml of water is added dropwise with vigorous stirring and the mixture is vigorously stirred for 10 minutes. 200 g of said mixture is vigorously mixed with 10 kg of core sand in a vibratory mixer for 3 minutes, and then the mixture is transferred to a container of a core firing machine commonly used in the foundry industry.

By means of said core-firing machine, the molds are shot according to the hot-box process at a mold temperature of 200 ° C, a pressure of 6.5 bar and an interval of 1.5 s. After 60 s the resulting sand cores are sufficiently cured to detach from the mold. The cores are cast in gray cast iron and brass.

Claims (9)

Patent claims 1. Foundry binder which can be prepared by surface modification of 5 a) colloidal inorganic particles with a (b) one or more strong formula (I) R _x -Si-A ₄ -x (I) wherein the radicals A are identical or different and are hydroxyl groups or groups which can be hydrolytically removed, except for the methoxy group, The radicals R are identical or different and are groups which cannot be removed hydrolytically and x is 0, 1, 2 or 3, wherein x> 1 in at least 50 mol% of the silanes; Foundry binder according to claim 1, characterized in that the surface modification has been carried out in the presence of an acid condensation catalyst at a pH of from 1 to 2. Foundry binder according to claims 1 and 2, characterized in that the nanocomposite sol has been subjected to post-reaction treatment at temperatures from room temperature to 120 ° C. Foundry binder according to any one of claims 1 to 3, characterized in that the 20 colloidal inorganic particles (a) are selected from the group consisting of salts and dispersible powders with nanosize S1O2, TiO2, ZrO2, Al2O3, Y2O3, CeO2, SnC2, ZnO. , iron oxides or carbon. A foundry binder according to any one of claims 1 to 4, characterized in that: Other additives (c), such as curing catalysts, organic binders and / or glass-forming compound compounds, have been used to prepare the nanocomposite sol. A foundry binder according to any one of claims 1 to 5, characterized in that from 5 to 60 wt.% Is used for the preparation of the nanocomposite sol. %, preferably from 10 30 to 40 homt. and in particular from 10 to 20 wt. % of component (a). Foundry binder according to any one of claims 1 to 6, characterized in that from 20 to 95% by weight of nanocomposite sol is used. %, preferably from · · · · · · · «« -Po - • · · ·· 40 to 90 wt. % and in particular from 70 to 90 wt. % of component (b), expressed as polysiloxane of the formula: R _x SiO (2-o.5-x), A foundry binder according to any one of claims 5 to 7, characterized in that no more than 20% by weight of nanocomposite sol is used. %, preferably no more than 10 wt. % and in particular not more than 5 wt. % of other additives (c). Foundry binder according to any one of claims 1 to 8, characterized in that the surface modification has been carried out using from 0.1 to 0.9 mol, preferably from 10 0.25 to 0.75 mol of water per mol of hydrolyzable groups present. A process for producing foundry molds and cores characterized by the use of a foundry binder in a step with any one of claims 1 to 9.