JPH08883B2 - Phenolic resin composition for shell mold - Google Patents

Description

TECHNICAL FIELD The present invention relates to a phenol resin composition for shell molds.

[Prior Art] Resin coated sand is used in the production of shell molds. In resin coated sand, a novolac type phenol resin is generally used as a binder. As the phenol resin for the shell mold, one having a weight average molecular weight of 360 to 850 is known (JP-A-2-70717).

[Problems to be Solved by the Invention] By the way, it is preferable that the shell mold is excellent in both room temperature strength and temperature strength and has a low coefficient of thermal expansion. Therefore, various improvements have been attempted in the phenol resin composition for shell mold.

The present invention has been developed in view of this situation, and an object thereof is to provide a phenol resin composition for a shell mold, which is excellent in both room temperature strength and warm strength, and can have a low coefficient of thermal expansion. .

[Means for Solving the Problems] The present inventor has noticed that the weight average molecular weight of the phenol resin for shell mold greatly affects the characteristics of the resin coated sand. That is, when the weight average molecular weight of the phenol resin is high, the warm strength and the coefficient of thermal expansion are good, but the room temperature strength tends to be low. When the weight average molecular weight of the phenol resin is low, the room temperature strength is high, but the warm strength and the coefficient of thermal expansion tend to be poor.

In view of the above findings, the present inventors have found that a phenol resin for shell mold having good properties can be obtained by mixing a resin having a high weight average molecular weight and a resin having a low weight average molecular weight, and have completed the present invention. is there.

That is, the phenol resin composition for shell cold of the present invention comprises a first phenol resin component having a weight average molecular weight (▲ ▼) of 800 or more and 1400 or less and a second phenol resin component of a weight average molecular weight of 1500 or more and 2500 or less. And a weight ratio of (second phenol resin component / first phenol resin component) = (1/9) to (4/1) is set.

The first phenol resin component and the second phenol resin component are novolac type resins obtained by synthesizing phenols and aldehydes in the presence of an acidic catalyst. As the phenols, phenol, cresol and the like can be adopted, and as the aldehydes, formalin, paraformaldehyde and the like can be adopted. As the acidic catalyst, hydrochloric acid, sulfuric acid, phosphoric acid or the like can be adopted.

The first phenol resin component has a weight average molecular weight of 800 or more and 1400 or less, and its average molecular weight is, for example, 1000.
It can be ~ 1200. The second phenol resin component has a weight average molecular weight of 1500 or more and 2500 or less, and the average molecular weight thereof can be, for example, 2200 to 2400.

In the present invention, the value of (second phenol resin component / first phenol resin component) = (1/9) to (4/1) is set. Within the above range, the mixing ratio of the first phenol resin component and the second phenol resin component can be appropriately selected depending on the type of shell mold template required, but among them, (1/9) to (1 The value of / 1) is preferable, and the value of (1/7) to (1/2) can be used in particular.

[Function] The high molecular weight component, that is, the multimer, contained in the second resin component in a large amount improves the warm strength and maintains a low coefficient of thermal expansion, and is contained in the first resin component in a large amount. It is speculated that low-molecular components such as dimers and trimers improve the room temperature strength.

[Example] (Example 1) 100 parts by weight of phenol, 47 parts by weight of 37% formalin and 5 parts by weight of oxalic acid were added to a reaction vessel equipped with a stirrer, a heating device and a cooling tube, and the mixture was reacted under reflux for 3 hours. I went. Next, the reaction mixture is heated and dehydrated under vacuum, and the reaction mixture is heated
2 parts by weight of ethylene bis-stearic acid amide and 1 part by weight of aminotriethoxysilane are added and mixed, and cooled to solid novolak type resin A at room temperature (first
Of phenol resin) was obtained. The weight average molecular weight of this resin A was 1,100. The weight average molecular weight was measured by the GPC method.

Further, under the same conditions as in the case of obtaining the resin A, except that 60% by weight of 37% formalin and the reaction time were 4 hours, a solid novolac type resin B (second phenol resin) was obtained at room temperature.
I got The weight average molecular weight of this resin B was 1500.

Further, under the same conditions as in the case of obtaining the resin A, except that 70% by weight of 37% formalin and the reaction time were 5 hours, a solid novolac type resin C (second phenol resin) was obtained at room temperature.
I got The weight average molecular weight of this resin C was 2,400.

Then, 70 parts by weight of Resin A and 30 parts by weight of Resin C were melt mixed to obtain a resin composition according to Example 1. Therefore, in Example 1, the mixing ratio is (resin B / resin A) = (30/70) = (1
/2.3). The resin composition according to Example 1 had a weight average molecular weight of 1490.

Furthermore, 160 g of the resin according to Example 1, 120 g of water, 24 g of hexamine, and 8 g of calcium stearate were added to and mixed with 8 kg of fuuka sand heated to 160 ° C. in a speed mixer.
Got S). Molded using this RCS, JIS K-6
According to 910, the room temperature strength, warm strength, and coefficient of thermal expansion of the shell mold were measured. The measurement results are shown in Table 1. As shown in Table 1, room temperature strength is 60.3kg / cm ² , warm strength is 1
Both of them were high at 4.5 kg / cm ^2, and the coefficient of thermal expansion was 1.23%, which was rather low.

(Example 2) 50 parts by weight of Resin A and 50 parts by weight of Resin C were melt mixed to obtain a resin composition according to Example 2. In Example 2, the mixing ratio is (resin C / resin A) = (50/50) = (1/1). The resin composition according to Example 2 had a weight average molecular weight of 1750. Then, like the first embodiment, the RCS according to the second embodiment
Then, molding was performed using this RCS, and the RCS characteristics were investigated. First
As shown in the table, room temperature strength is 58.2kg / cm ² , warm strength is 14.6kg.
Both were high at kg / cm ^2, and the coefficient of thermal expansion was low at 1.18%.

(Example 3) 30 parts by weight of Resin A and 70 parts by weight of Resin C were melt mixed to obtain a resin composition according to Example 3. In Example 3, (resin C /
Resin A) = (70/30) = (2.3 / 1). The resin composition according to Example 3 had a weight average molecular weight of 2010. Then, as in the first embodiment
The RCS characteristics were investigated. Room temperature strength is 45.5k as shown in Table 1.
Although it was g / cm ² , the warm strength was as high as 13.5 kg / cm ² , and the fuel expansion coefficient was low at 1.15%, which was good.

(Comparative Example 1) Using the resin A obtained in Example 1, RC was used in the same manner as in Example 1.
The S characteristic was investigated. As shown in Table 1, room temperature strength is 61.2kg /
Although it is as high as cm ² , the warm strength is the lowest at 11.9 kg / cm ² ,
The coefficient of thermal expansion was 1.45%, the worst.

(Comparative Example 2) The same procedure as in Example 1 was repeated except that the resin B obtained in Example 2 was used.
The S characteristic was investigated. As shown in Table 1, room temperature strength is 55.4kg /
cm ² , warm strength is as low as 13.3 kg / cm ^2, and coefficient of thermal expansion is 1.27.
%Met.

(Comparative Example 3) RC was performed in the same manner as in Example 1 except that the resin C obtained in Example 3 was used.
The S characteristic was investigated. As shown in Table 1, the coefficient of thermal expansion is 1.12%
However, the room temperature strength was the lowest at 39.1 kg / cm ^2, and the warm strength was 12.1 kg / cm ² .

(Evaluation) According to the phenol resin compositions of Examples 1 to 3, both the contradictory room temperature strength and the warm strength of the shell mold can be improved, and the coefficient of thermal expansion can be made a good value. Recognize.

[Effect of the Invention] According to the phenol resin composition for shell molds of the present invention, it is possible to improve both contradictory properties, that is, room temperature strength and warm strength. Therefore, when applied to a shell mold, the strength of the mold can be improved, and the shell mold can be made complicated and thin.

Further, according to the phenol resin composition for shell mold of the present invention, since the warm strength can be improved as described above,
The effect of omitting the organic acid generally used for improving the warm strength can be expected.

Further, since it also contains a low molecular weight component, it is also advantageous in reducing the resinma that tends to occur when kneading a high molecular weight resin.

Claims (1)

[Claims] 1. A first having a weight average molecular weight of 800 or more and 1400 or less.
With a phenolic resin component of, and a weight average molecular weight of 1500 or more, 25
It is composed of a second phenol resin component of 00 or less, and is set to a value of (second phenol resin component / first phenol resin component) = (1/9) to (4/1) by weight ratio. A phenol resin composition for a shell mold, comprising: