CS271947B1 - Binder for foundry compositions on base of phenolformaldehyde modified resol - Google Patents

Abstract

The solution relates to a binder for foundry a phenol-formaldehyde-based composition a strongly alkaline modified resol. Resole is curable by organic esters, lactones or carbonates; ldehyd-pheno1 is 1.5 to 2.5%, content sodium or potassium hydroxide 0.4 to 1.0% by weight, based on the amount % of phenol, with a dry matter content of 45 to 65% by weight. The essence of the invention is that that the binder contains 5 to 20% by weight diols, for example mono-, di-, triethylene glycol and / or mono-, di-, tripropylene glycol. The binder optionally further comprises silanes and surfactants.

Description

The present invention relates to a phenol-formaldehyde binder for potable compositions based on a strongly alkaline modified resole in aqueous solution, cold curable with organic esters, lactones and carbonates, used for the production of cores and molds.

The well-known and used COLD-BOX cold-curable systems based on phenol-formaldehyde binders alone or modified with furfuryl alcohol, catalyzed by strong inorganic acids such as sulfuric acid or organic most often sulfocyelines such as p-toluene sulfone, xylenesulfonic acid have the disadvantage of being sulfur-containing. During the thermal decomposition of the binder during the casting of liquid metal, solidification and cooling of castings, sulfur dioxide is released, which adversely affects the working atmosphere and exhalation into the atmosphere. In addition, there are adverse effects on sulfur-sensitive alloys, which prevent carbon precipitation in globular form and cause the formation of undesirable structures in the fault layers. Other processes, even using sulfur dioxide for curing as a gas phase catalyst, combining with the peroxides present in the molding material to form sulfuric acid, have similar disadvantages, in addition to the increased occupational safety risks associated with the use of peroxides and sulfur dioxide.

More modern processes use the curing of a binder at room temperature by the reaction between a strongly alkaline phenolphaldehyde resole and a carboxylic acid ester - liquid or gaseous methyl formate, characterized by molecular weights of 700 to 2,000 and 600 to 1,500, respectively, with a molar ratio of potassium hydroxide: phenol of 0.2 to 1. 2 and a molar ratio of formaldehyde: phenol of 1.2 to 2.6 t 1. The disadvantage is the relatively low strength of foundry mixtures, lower binder stability and thus changing properties over time, usually a decrease in strength over time. Also other unmodified resoles, eg with a potassium hydroxide ratio "phenol" of 0.9: 1 hardened with butylene glycol diacetate or with butyrolactone, optionally in the gas phase again with methyl formate, but catalyzed by sodium hydroxide or cured with propylene carbonate, have similar disadvantages.

An increase in strength is achieved by using a phenol-formaldehyde binder modified with a mixture of glycerin and polyethylene glycol. One of the latest methods of the COLD BOX method with gas phase curing using acetals has a disadvantage in the field of ecology, no; decompose to free formaldehyde, another disadvantage is the need to use higher temperatures than previous systems.

The binder for foundry compositions based on phenol-formaldehyde, modified, strongly alkaline resole, curable with organic esters, lactones or carbonates, where the molar ratio of formaldehyde-phenol is 1.5 to 2.5 -1 and the content of hydroxide or carbonate solves or eliminates the disadvantages of known processes. potassium and / or sodium is 0.4 to 1 based on the amount of phenol, with a dry matter content of 45 to 65% according to the invention. The essence consists in that it contains 5 to 20% by weight of diols, for example mono-, di-, triethylene glycol and / or mono-, di-, tripropylene glycol. The binder according to the invention may further comprise 0.2 to 2% by weight of a disilane such as aminopropyltriethoxysilane or cyclohexenylethyltriethoxysilane, optionally 0.1 to 1% by weight of a nonionic and / or anionic surfactant.

The advantages of the binder according to the invention are manifested by an increase in the service life and shelf life of the resole due to the high content of stabilizing hydroxyl and possibly dimethylene ether groups of lower diols, i.e. mono-, di-, triethylene glycol and / or propylene glycol. This has a positive effect on the reproducibility of the binder's properties over time. A significant effect also relates to the reduction of the viscosity of the binders and the content of low molecular weight diols, which favorably influences the handling of the binder and especially its processing into foundry compositions.

The high content of polar groups also has a positive effect on increasing the adhesion to refractory sands and thus enables higher strengths of foundry compositions to be achieved.

OS 271947 Bl

The preparation of these resoles can be carried out by conventional and known methods for the condensation of phenol and rasp formaldehyde, its aqueous solution with formalin in the presence of a strong alkali, preferably potassium hydroxide or carbonate, or their aqueous solutions. The condensation is preferably carried out while the mixture is boiling and is completed at a lower temperature, usually above 70 ° C to the desired viscosity of the mixture in the range of 25 to 300 s, measured on a 4 mm diameter Pord crucible at 20 ° C. The modification of the diol is carried out additionally in the final stage of the preparation or even by the joint reaction of the components during the condensation process. Optimal results can be obtained by the correct choice of the binder composition within the range stated in the subject matter of the invention.

To further illustrate the invention, the following example is given:

Example

Table 1 shows a comparison of the properties of the binders under Nos. 1 to 7 with the standard under the designation A, unmodified diols.

Table 1

wa> «» M «aaaaaaa» ava »* w * w« Species Binder composition one AND 1 2 3 4 5 «A.Mv« saaaa 6 7 molar ratio of formaid. : phenol / 2.0 2.0 2.0 2.0 2.5 2.0 1.6 2.0 «Rw * w a * WWW «* < «« Tnwwa »AH» ww «» a aow * ^ w «a · ——— KOH: phenol molar ratio / 0.65 0.65 0.65 0.65 0.4 X 0.65 0.9 0.8 dry matter % 53.0 54.2 54.5 55.3 50.1 53.8 61.4 57.2 viscosity with 82 45 ⁵⁰ 56 38 53 120 48 stability days 20 60 54 62 35 48 70 55 • m «a ******* * ··· · »·« ··· a. - —a - · --- —--- ---—.- ——— ——— diol species / / EG DEG TEG PG DPG TPG EG diol content % / 10 10 15 5 10 18 10 «Mia« · «· a ·« · a · «·« »*» · * aM • —a — a— ———- ——————— ———- —————— PAL % / / / / / / / 0.5

% «By weight

PAL nonionic surfactant

EG, DEG, TEG mono-, di-, triethylene glycol

PG, DPG, TPG mono-, di-, tripropylene glycol

Binders under Nos. 1 to 7, in addition to the advantages already described, lower viscosities, higher stability compared to standard A, also provide higher strengths of 10 to 100% under the same conditions.

x NaOH

Claims (3)

OBJECT OF THE INVENTION A binder for foundry compositions based on phenol-formaldehyde, a modified, strong alkaline resole curable with organic esters, lactones or carbonates, wherein the molar ratio of formaldehyde-phenol is 1.5 to 2.5: 1 and the potassium or / or sodium hydroxide or carbonate content is 0.4 to 1.0, based on the amount of phenol, with a dry matter content of 45 to 65%, characterized in that it contains 5 to 20% by weight of diols, for example mono-, di-, triethylene glycol and / or mono-, di-, tripropylene glycol. 2. A binder according to claim 1, characterized in that it contains 0.2 to 2% by weight of a silane such as aminopropyltriethoxysilane or cyclohexenylethyltriethoxysilane. 3. The binder according to claim 1, characterized in that it further comprises 0.1 to 1% by weight of a nonionic and / or anionic surfactant.