DE2511165B2 - PROCESS FOR THE STABILIZATION OF CORE AND MOLDING SAND BINDERS BASED ON RESIN - Google Patents

Description

It is known that synthetic resins based on phenol-formaldehyde are used as binders for foundry molds and cores, Urea-formaldehyde, meiamin-formaldehyde and furfuryl alcohol-formaldehyde. These Synthetic resin systems or mixtures thereof can be used together with sand and mineral acids and / or mixed with organic acids, are used for the production of so-called cold-hardening sand mixtures. So was z. B. the use of organic sulfonic acids (CH-PS 4 49 857 and CH-PS 5 02 860) and halogenated carboxylic acids (US-PS 33 12 650) as curing agents for the resins at room temperature described.

From the DT-AS 12 42 358 and the DT-AS 12 52 853 is also known, the properties of such synthetic resins by adding small amounts Organosilicon compounds, so-called silanes, with the general formula (I) to improve considerably

R—

OR '

OR '

(D

40

Here, R 'represents a hydrocarbon or, preferably, an alkyl group having 1-6 carbon atoms represents, while R is an alkyl group with 2-6 carbon atoms, which with different functional Groups such as amino, aminoethylamino, chloro, mercapto, epoxy, vinyl or other terminal groups is substituted, means.

The mode of action of these silanes consists in a greatly improved adhesive strength of the binder film on the quartz grain, resulting in an increase in strength compared to the untreated synthetic resin

Table I.

expresses. It occurs with a suitable choice of the appropriate Silane types appear in both thermally curing and cold-curing binder systems.

By using these binders mixed with silane, the cold curing process manufactured cores and molds achieved an increase in strength of a high degree, whereby the proportion of binder in the molding compound by up to 50% compared to the corresponding unsilanized resins Type can be reduced without loss of strength, which undoubtedly increases the economy

The effect of this beneficial, strength-increasing effect through the addition of silane could be applied to cold-curing Phenolic resins made with alkaline or alkaline earth catalysts are well transferred.

A disadvantage was found that the strength initially achieved only over a period of was constant for a few days. With increasing storage time of the silanized phenolic resin occurs a further decrease in strength, which - if the mixing ratios remain the same - is no longer justifiable is.

Table I below shows the drop in strengths of a silanized, commercially available phenolic resin (Molar ratio phenol / formaldehyde 1: 1.2), the one not according to the invention, at room temperature the resin hardening acid was added, depending on the storage time, tested on a Mixture consisting of

100 parts by weight quartz sand H 31,
0.4 part by weight of 60% strength aqueous p-toluenesulfonic acid

re,
1.2 parts by weight of phenolic resin.

Storage time (resin)

(Days)
immediately 1

10

20th

30th

Flexural strength ob (N / cm ² )

430

390

290 250

230

200

190

170

It is also known that phenol-formaldehyde 65 is phenol-formaldehyde resins, the one

Resins if, under certain conditions, they contain a high percentage of benzyl ether groups,

are condensed, the addition of silane with only a small amount to the catalysts with which those are preferred

Decrease in strength can be stabilized. Resin types (phenolic resins substituted in the ortho position)

25 Ll 165

ze) are produced, include mainly organic heavy metal salts, such as. B. lead naphthenate, zinc naphthenate, Manganese acetate and others such as B. are described in the following publications:

NL-PS67 03 782; NL-PS 67 10 574; GB-PS 12 72 972; U.S. Patent 3,4 09,579; DT-AS 17 20 222; DT-AS 15 83 521.

There are several disadvantages to using this type of resin. Process engineering occurs during manufacture Difficulties arise. The relatively high content of free formaldehyde leads to stronger Odor nuisance during processing. Due to the high viscosity, a homogeneous mixing in is possible in the Foundry sand not guaranteed. In addition, the delayed setting behavior leaves an economical one Use in the cycle times required by a call-hardening system is not permitted.

Surprisingly, it has been found that also with alkaline and alkaline earth catalysts produced phenol-formaldehyde resins receive the silane additive in its strength-increasing effect can be, these phenol-formaldehyde resins, of course, small amounts known per se Modifying agents such as cresols, natural resin, urea and the like may contain.

This stabilizing effect is achieved when the finished resin is carboxylic acids and / or salts of Carboxylic acids with weak bases can be added.

In addition, these alkaline or alkaline earth catalyzed phenol-formaldehyde resins stand out

Table II

thanks to a very low free formaldehyde content and a viscosity range that can be adjusted to meet requirements the end. Furthermore, the setting behavior corresponds to the requirements placed on cold-curing systems.

example 1

A commercially available phenol-formaldehyde resin, MoI-Veräknis 1: 1 ^ 2 phenol / formaldehyde, in the presence made of sodium or barium hydroxide was examined as follows:

5 kg of Halterner Sand H 31 were mixed with 60 g of this resin and 20 g of an aqueous 60% solution of p-toluene / sulfonic acid and shaped into + GF + bending test bars in the + GF + test rod form. After shaping, the bars were stored at room temperature for 24 hours and then measured for flexural strength with the usual + GF + strength tester. Flexural strengths of 100-120 N / cm ^{2 were} obtained.

Example 2

0.2% of an organosilicon compound (e.g. y-aminopropyltriethoxysilane) mixed in cold.

The processing and testing are carried out in the same way as in Example 1. In addition, the testing was carried out according to different storage times of the silanized resin repeated. From the following table 11 are the The flexural strengths found as a function of the resin storage time can be seen.

Storage time (resin)

(Days)

immediately 1

10

20th

30th

Flexural strength ob (N / cm ² )

430

390

250

230

200

190

170

Example 3

Samples of the phenol-formaldehyde resin according to Example 1 were provided with various additives. It were z. B. each

2% salicylic acid (additive A)
2% aluminum acetate (additive B)

Table St.

2% zinc acetate (additive C)

2% ammonium acetate (additive D)

mixed in cold. Then 0.2% γ-aminopropyltriethoxysilane was added.

The processing and testing of the individual resin samples was carried out analogously to Example 2. From the Table III below shows the flexural strengths found as a function of the resin storage time.

Storage time resin Flexural strengths (N / cm *) + Add. B. + Add. C + Add. D (Days) without addition + Add. A 440 430 460 1 390 460 420 410 450 4th 290 460 420 400 440 7th 250 450 400 390 440 10 230 450 390 380 430 15th 200 440 380 ' 370 430 20th 190 440 380 370 420 170 430 '

Claims (3)

Patent claims: 1. Process for stabilizing the strength values of silanized, alkaline or alkaline earth Condensation agents of cold-curing phenol-formaldehyde resins for foundry purposes, characterized in that the resin contains carboxylic acids and Axi & r salts of Carboxylic acids with weak bases can be added in an amount of 0.1 to 10%. 2. Method to stabilize the strength! values of silanized cold-curing products made with alkaline or alkaline earth condensation agents Phenol-formaldehyde resins for foundry purposes according to Claim 1, characterized in that acetic acid and / or salicylic acid are added to the resin as stabilizers. 3. Process for stabilizing the strength values of silanized, alkaline or alkaline earth Cold-curing phenol-formaldehyde resins produced with condensation agents for foundry purposes according to claim 1 and 2, characterized in that the resin contains the salts of aluminum, Zinc, manganese and ammonium are added to the acids mentioned in claim 2.