JPH04168118A - Novolak type phenol resin for shell mold - Google Patents

Abstract

PURPOSE:To obtain the title resin having excellent workability, a weight-average molecular weight in a given range and a small amount of free phenol by reacting phenol and bisphenol A in a specific ratio with formaldehyde in the presence of an acidic catalyst. CONSTITUTION:100 phenol and 5-500 pts.wt. bisphenol A are blended with formaldehyde such as formalin in the presence of an acidic catalyst such as oxalic acid to give the objective resin having 1,000-2,500 weight-average molecular weight and <=1.0wt.% free phenol.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a novolac type phenolic resin for shell molds used for binding sand in shell mold casting molds.

[Prior Art] In casting by the shell mold method, a novolac type phenolic resin is generally used as a mold binder.

However, there is a problem in that unreacted, free phenol and formaldehyde vaporize during shell mold making, creating a bad odor and worsening the working environment. In addition, automotive castings, especially engine blocks and cylinder heads, use many complex cores, so if a general unmodified novolak type phenolic resin is used, the thermal expansion of the mold during pouring will be high, resulting in dimensional changes. , cracks are likely to occur. JP-A-1-135814 discloses a shell mold in which the content of a mononuclear component is less than 1% by weight and the content of a dinuclear component is less than 2% by weight, as a novolak type phenolic resin with less bad odor. There is a disclosure of a novolak type phenolic resin for use. Furthermore, as a method for producing a modified phenol resin having a small coefficient of thermal expansion, there is a disclosure of producing it by blending SR acid, which is a by-product during bisphenol purification (Japanese Patent Publication No. 56729/1983). However, this S
There is a problem in that R acid is a by-product and has a unique odor, making it difficult to easily deodorize it.

[Problem to be solved by the invention] The low-odor novolac type phenolic resin described above has a high coefficient of thermal expansion, and when the core has a thin wall thickness, the high rapid thermal expansion coefficient will affect the pouring process. There are problems such as dimensional changes and cracks.

Furthermore, the SR acid-modified novolac type phenol resin, which has a small rapid thermal expansion coefficient, has a problem in that it cannot suppress the bad odor caused by the SR acid.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a novolac type phenol resin that generates less bad odor and has a lower coefficient of rapid thermal expansion.

[Means for Solving the Problems] The novolac type phenol resin for shell molds of the present invention contains bisphenol A based on 100 parts by weight of phenol.
containing 5 to 500 parts by weight and having a weight average molecular weight of 100 when reacted with formaldehyde in the presence of an acidic catalyst.
0 to 2500 and the amount of free phenol is 1.0% or less.

The novolak phenolic resin for shell molds of the present invention is a novolak phenolic resin modified with bisphenol A. It is then used by coating foundry sand for shell molding.

This bisphenol is effective in reducing the rapid thermal expansion coefficient of novolak type phenolic resin, and phenol 10
It is blended in an amount of 5 to 500 parts by weight relative to 0 parts by weight. If the amount is less than 5 parts by weight, no effect of lowering the rapid thermal expansion coefficient will be observed, which is not preferable.

Moreover, if it exceeds 500 parts by weight, other mold properties deteriorate, which is not preferable.

As the phenol, phenol, cresol, xylenol, resorcinol, catechol, etc. can be used alone or in combination.

As formaldehyde, formalin, paraformaldehyde, trioxane, etc. can be used alone or in combination.

As the acidic catalyst, organic acids and inorganic acids that are generally used for producing novolac type phenolic resins, such as oxalic acid, hydrochloric acid, sulfuric acid, and para-toluenesulfonic acid, as well as metal salts thereof, can be used.

This novolak type phenolic resin preferably has a weight average molecular weight in the range of 1000 to 2500 in order to provide resin coated sand (hereinafter abbreviated as RC3) with a predetermined strength. The amount needs to be 1.0% or less. For this reason, it is preferable to carry out the production process of the novolak type phenolic resin by dividing the dehydration of the produced water into the following two stages, since a resin having predetermined characteristics can be easily obtained.

For example, when the reaction liquid reaches a predetermined viscosity, the pressure of the reaction system is reduced to 120 to 150 Torr and the reaction liquid reaches 120 Torr.
The first dehydration step involves heating until it reaches 0°C, and the reaction solution is heated to 1°C.
When the temperature reaches 20°C, the pressure is further lowered to 60 Torr and a second dehydration step is performed in which the reaction solution is heated until it reaches 230°C. Then, a novolac type phenolic resin having a free phenol content of 1.0% or less and a weight average molecular weight of 1000 to 2500 can be easily obtained.

After the reaction, certain additives are added and dissolved to form a resin for shell molds.

This resin and hardening agent are coated on molding sand, heated in a mold, the resin is hardened by the hardening agent, and the molding sand is bonded to form a predetermined shape.

[Operations and Effects of the Invention] The novolac type phenol resin for shell molds of the present invention contains bisphenol A in a specific proportion, has a weight average molecular weight of 1000 to 2500, and has a free phenol content of 1.0% or less. Therefore, when the mold is set to RC8, the rapid thermal expansion coefficient of the mold can be reduced. Furthermore, since the amount of free phenol is small, almost no bad odor is generated even if RC8 reaches a high temperature.

In addition, since the molecular weight is within a suitable range, it is desirable in terms of strength and has excellent properties in terms of mold forming workability. Furthermore, since the amount of gas generated at high temperatures during pouring of the casting is small, defects in the casting due to gas can be suppressed, and the number of defective castings can be reduced.

[Example] Hereinafter, this will be explained in detail using examples.

(Example 1) 1000 parts by weight of phenol, 300 parts by weight of bisphenol A, and 630 parts by weight of an aqueous formalin solution with a concentration of 37% were charged into a reaction pot equipped with stirring, heating, and cooling equipment, and heated while stirring until the reaction solution reached 80°C. When it reaches Shu I! !
After adding 6 parts by weight, the temperature is gradually raised to react at reflux temperature. After the viscosity of the reaction solution reached 76 as measured by a bubble viscometer, the reaction was continued for another 30 minutes. Next, increase the pressure inside the reaction vessel to 120~
The first dehydration step of removing produced water by heating and stirring under a reduced pressure of 15 Q Torr was carried out until the temperature of the reaction solution reached 120°C. Next, the pressure inside the reaction pot was reduced to 60 Torr or less, and the second step was carried out until the temperature of the reaction solution reached 230°C.
A dehydration step was performed and the condition was maintained for an additional 30 minutes. Next, the inside of the reaction vessel was returned to normal pressure and the temperature of the product was 16.
Cool to 0°C. When the temperature reached a predetermined temperature, 20 parts by weight of ethylene bisamide and 7 parts by weight of aminosilane were added and dissolved, and the mixture was discharged from the reaction vessel to obtain 1275 parts by weight of a solid novolac type phenol resin.

(Example 2) Solid novolac type phenol resin 1665 was produced in the same process as in Example 1, except that the composition ratio was 1000 parts by weight of phenol, 700 parts by weight of bisphenol A, 710 parts by weight of 37% formalin aqueous solution, and 8 parts by weight of oxalic acid. Parts by weight were prepared.

(Example 3) 1000 parts by weight of phenol, 1500 parts of bisphenol A
2,440 parts by weight of a solid novolac type phenol resin was prepared in the same manner as in Example 1, except that the composition ratio was 910 parts by weight, 910 parts by weight of a 37% aqueous formalin solution, and 11 parts by weight of oxalic acid.

(Example 4) A solid Noholac type phenol resin 2450 was produced in the same process as in Example 1, except that the composition ratio was 500 parts by weight of phenol, 2000 parts by weight of bisphenol A, 740 parts by weight of 37% formalin aqueous solution, and 11 parts by weight of oxalic acid. Parts by weight were prepared.

(Comparative Example 1) 1000 parts by weight of phenol, 37% formalin aqueous solution 5
60 parts by weight were placed in a reaction vessel, heated and stirred, and when the reaction solution reached 80°C, 8 parts by weight of oxalic acid was added and the temperature was gradually raised to a temperature at which the reaction solution refluxed, and the reaction was carried out at that temperature. The reaction continues until the liquid reaches a viscosity of 7 on the bubble viscometer. Next, a first dehydration step is performed in which the reaction vessel is heated and dehydrated under a reduced pressure of 120 to 150 Torr. When the temperature of the reaction solution reached 160° C., the pressure was returned to normal pressure, 15 parts by weight of ethylene bisamide and 5 parts of aminosilane were added and dissolved, and the mixture was discharged from the reaction vessel to obtain 980 parts by weight of a solid novolac type phenol resin.

(Comparative Example 2) 1000 parts by weight of phenol, 37% formalin aqueous solution 5
60 parts by weight and 8 parts by weight of oxalic acid, but in the same manner as in Example 1, 960 parts by weight of a solid novolac type phenol resin was obtained.

(Comparative Example 3) 240 parts by weight of phenol, 960 parts by weight of SR acid (a by-product produced during the purification of bisphenol A), and 514 parts by weight of a 37% formalin aqueous solution were charged into a reaction vessel and heated and stirred to reach 70°C. Add 4 parts by weight of 100% sulfur and react for 150 minutes at reflux temperature, then 120 to 150 parts by weight
Perform heating dehydration under reduced pressure of
34 parts by weight of salicylic acid and 6 parts by weight of aminosilane were added and dissolved and discharged from the reaction vessel to obtain 1200 parts of solid novolac type phenol resin.

(Evaluation Results) The melting point, weight average molecular weight, and amount of free phenol were measured for each novolac type phenol resin produced in Examples 1 to 3 and Comparative Examples 1 to 3. The results are shown in Table 1.

Further, RC3 was formed by coating Zuka sand with 2% by weight of each resin, and the room temperature strength, warm strength, and rapid thermal expansion coefficient were measured, and the results are shown in Table 1.

In addition, the weight average molecular weight and the amount of free phenol were measured by high performance liquid chromatography. Room temperature strength is JAC
It was measured using a T-designated bending tester, and the warm strength was measured using a small bending tester MOLDELSC-200D. Rapid thermal expansion coefficient was measured based on JACT test method 5M-7.

Furthermore, the gas when 1 g of each of the above RC3 was decomposed at 300°C was collected and diluted 30 times, 100 times, 300 times, 1000 times, and 3000 times according to the three-point comparative odor bag method. Six testers sniffed the diluted gas and statistically calculated the odor concentration from the highest dilution ratio at which the odor was felt. The results are shown in Table 1.

In the examples, the melting point of the resin is 65° C. or higher, which is higher than that of the comparative example, the weight average molecular weight is 1200 to 1500, and the amount of free phenol is 1.0% or less, which is within the scope of the present invention. In a method in which the second dehydration step with a -5 ratio inversion of 1.3 is not performed, the amount of free phenol is 1.0% or more, resulting in a high odor concentration.

When produced in the same process as in Example without containing bisphenol A of Comparative Example 2, the amount of free phenol is 1.0% or less, but the melting point is slightly low and the rapid heat engraving rate is high. That is, unless bisphenol A is included, the rapid heat engraving rate cannot be reduced. Comparative Example 3 contains SR acid, so the rapid heat engraving rate is small, but the odor concentration is high.In other words, this SR acid is a byproduct of the bisphenol production reaction, so it contains various impurities and is not used in the second dehydration step. Even if free phenol is removed by increasing the degree of vacuum, the odor will not decrease. Comparative example 1
If it does not contain bisphenol A and has a large amount of free phenol, the rapid heat engraving rate cannot be lowered. In the one-stage dehydration process of Comparative Example 1.3, it is difficult to keep the amount of phenol released below a predetermined value. If the same steps as in Examples are used as in Comparative Example 2, the weight average molecular weight and amount of free phenol can be set to predetermined values, but since bisphenol A is not included, the resin properties are not improved.

Therefore, the bisphenol A modified resin of the present invention has a low odor concentration, a low rapid heat engraving rate, and can maintain a predetermined strength.

Patent applicant: Aisin Kako Co., Ltd. Same Toyota Motor Corporation

Claims (1)

[Claims] Contains 5 to 500 parts by weight of bisphenol A per 100 parts by weight of phenol, and has a weight average molecular weight of 1000 to 1000 when reacted with formaldehyde in the presence of an acidic catalyst.
A novolac type phenolic resin for shell molds, characterized in that the amount of free phenol is 1.0% or less at a temperature of 2500%.