JPS6015648B2 - Manufacturing method of resin for shell mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a resin used as a binder for sand grains for shell molding.

As a binder for sand grains for shell molds, novolak-type phenolic resins, which are bound by reacting phenols and aldehydes in the presence of an acidic catalyst, or resol-type phenolic resins, which are obtained by reacting them in an alkaline catalyst, are widely used. It is used.

However, molds obtained using binders mainly composed of ordinary phenolic resins have the drawback that dimensional changes due to thermal expansion during pouring are significant and the dimensional accuracy of the product castings is reduced. This thermal expansion becomes more pronounced when sand grains with a high Si02 content are used, and may cause not only dimensional changes but also cracks in the mold. The reason is that when the sand grains are heated by the heat of the setting sun, 575
It is thought that this is caused by the fact that Si02 undergoes Q→B transformation and expands rapidly near the circle, and this is superimposed on the thermal expansion of the binder itself. In order to obtain a resin capable of suppressing this thermal expansion, formaldehyde is reacted on a mixture of Phenol 10 base and 5 to 7 bases of Pisphael A refined residue in the presence of a catalyst. A method has already been proposed (Japanese Patent Publication No. 55-9011). However, molds obtained using this modified phenolic resin are also not satisfactory in terms of rapid thermal expansion coefficient, bending strength, etc.
An object of the present invention is to provide an inexpensive method for producing a resin for shell molding, which allows a mold to be obtained with extremely low thermal elongation, particularly extremely low rapid thermal expansion coefficient.

In the method of this invention, 7 to 40 parts by weight of formaldehyde are reacted with 10 parts by weight of the created product (hereinafter referred to as "SR acid") created during the purification of Bispher/-A in the presence of an acidic or alkaline catalyst. let

SR acid is a by-product produced in the process of reacting phenol and acetone in the presence of a catalyst such as sulfuric acid or concentrated hydrochloric acid and purifying pispher/A from this reaction product.
Contains various forms of bisphenols, chroman compounds, unreacted phenols, etc. Therefore, the resin produced by reacting formaldehyde with this SR acid also contains various compounds mainly composed of various forms of phenolic resin. The phenolic resin is of the noporak type when an acidic catalyst is used, and is of the hesol type when an alkaline catalyst is used. In the case of a product based on a resol type phenolic resin, it is cured simply by heating, but in the case of a product based on a novolac type, it is necessary to add a curing agent such as hexamethylenetetramine. The mixing ratio of formaldehyde to SR acid is within the range of 7 to 40 parts by weight per 10 parts by weight of SR acid.

If the amount of formaldehyde used is less than 7 parts by weight, a large amount of the phenol component from the reaction will remain, and if it is more than 4 parts by weight, a large amount of unreacted aldehyde component will remain. The resin thus obtained is coated on sand grains, and the molds obtained using the coated sand grains according to the conventional method are almost equivalent to molds obtained using conventional shell molding resins. It has been confirmed through experiments that it has a mold strength of

Example 1 In a third flask, add 500% SR acid and 37%
After charging 161 mm of formalin and heating to 7.0 mm, adding 2.1 mm of oxalic acid, reacting at reflux temperature for 110 minutes, then adding monoethanolamine to adjust the pH of the contents to 3.0. It was adjusted to ~4.0.

Next, concentration dehydration was performed under a reduced pressure of -60 to 165 skin Hg, and when the temperature of the contents reached 180 CO, the vacuum and heating were stopped, and 16 mm of wax and 1.5 mm of aminosilane were added and dissolved. After that, it is discharged, cooled and solidified, and then melted.
8 qo of novolac type resin was obtained. Example 2 Into the separable flask, add 500 ml of SR acid and 3
Prepare 7% formalin 360°C, heat to 40°C, add 20% NaOH water soluble 20°C, and heat to 85-90°C.
The methylolation reaction was carried out for 4 minutes.

Next, the contents were cooled to 5,020 quarts, and 51 quarts of 25% ammonia water were added thereto, heated again to 70 to 75 quarts, and reacted for 80 minutes. To the obtained product, 20 parts of bisphenol S and 3 parts of aminosilane were added, and concentrated and dehydrated under a reduced pressure of 160 to 165 kg of Hg until the liquid overflow was 95 qo.
When the temperature is reached, the contents are immediately discharged and cooled to solidify.
A resol type resin having a weight average molecular weight of 1480 was obtained. This solidified resin is crushed into 6 to 20 mesh pieces, and wax 3
phr was mixed and powdered. Comparative Example 1 1. Phenol 6002, 37% in the Mitsuro flask
After 414 hours of formalin was charged and heated to 70°C, 2.1 hours of oxalic acid was added, and the mixture was reacted at reflux temperature for 150 minutes.

Next, concentration and dehydration is carried out under a reduced pressure of -60 to 165 Hg, and when the temperature of the contents reaches 160°C, the reduced pressure and heating are stopped, and after adding and dissolving wax 19, it is discharged. The mixture was cooled and solidified to obtain a novolac resin having a melting point of 6.0 and an average molecular weight of 2,490. Comparative Example 2 1. Into the separable flask, add 500 g of phenol, 8 g.
338 g of 5% paraformaldehyde and 75 g of 25% aqueous ammonia were charged, and the mixture was reacted at a temperature of 60 to 65 q0 for 120 minutes.

Concentration and dehydration was then carried out under a reduced pressure of -60 to 165 degrees Hg, and when the liquid temperature reached 100°C, the contents were immediately discharged and cooled and solidified to obtain a resol resin with a weight average molecular weight of 1730. This was crushed to 6 to 20 mesh, mixed with 3 phr of wax, and powdered. Four types of resin-coated sand grains were prepared using the resins obtained in Examples 1 and 2 and Comparative Examples 1 and 2 above, respectively.

This preparation was performed using a speed mixer (Dazhou Iron Works NSC-2).
Pour Hookah Sand 8K9 heated to 160℃ into a mold, add 160g of the resin obtained in the Examples and Comparative Examples, knead for 3 minutes, then add 120g of water to disintegrate the sand grains. After praying with a light until the water was completely dry, 8 doses of calcium stearate were added and 2 more times of praying with sand. In addition, when the novolak resin obtained in Example 1 and Comparative Example 1 is used, hexamethylene as a curing agent is added to the resin in a state dissolved in 120 g of water that is added during the process of making the lachrymal rice bran. 24 hours of tetramine was added. Table 1 shows the melting points of these resin-coated sand grains and the physical properties of molds obtained using each sand grain.

The chick landing point is based on JACT test method C-1, and the bending strength is based on JI.
SK-6910 and the rapid thermal expansion coefficient were measured based on JACT test method SM-7. Table 1 1st
From the results in the table, it is clear that the molds manufactured using the resin obtained by the method of this invention have almost the same mold strength as the molds manufactured using the conventional phenolic resin. The rapid thermal expansion coefficient has become extremely small.

Claims (1)

[Claims] 1 By-product produced during purification of bisphenol A 100
A method for producing a resin for shell molds, which comprises blending 7 to 40 parts by weight of formaldehyde and reacting the mixture in the presence of an acidic or alkaline catalyst.