JPS58109524A - Production of sand-binding phenolic resin - Google Patents

Abstract

PURPOSE:To obtain a phenolic resin excellent in rapid curability, etc., and useful in sand binding in a shell mold process, by reacting a phenol with a formaldehyde in the presence of a specified acid catalyst and then chelating the acid catalyst. CONSTITUTION:A phenol (e.g., phenol) is reacted with a formaldehyde-yielding substance (e.g., formaldehyde) at a molar ratio of 1:0.3 in the presence of salicylic acid (below about 0.5 molar time of other acid catalysts, such as oxalic acid, can be used in combination). Then, to the resulting reaction product is added an oxide, hydroxide or weak acid salt of a metal (e.g., zinc) capable of forming a chelate with salicyclic acid (a neutralizing agent such as sodium hydroxide or ammonia can be used in combination), whereby chelation of at least 5wt% salicyclic acid and neutralization are effected. Then, the low-boiling substances are distilled out of the system by distillation to obtain a sand-binding phenolic resin.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new and useful method for producing a phenolic resin for sand coating. -1. A method for producing a novolac type phenolic resin with excellent performance such as fast curing properties, which is particularly useful for sand coating by the shell mold method, and which consists of neutralizing the system with a metal compound capable of forming . Regarding.

In recent years, there has been an increasing demand for resin-coated sand for shell molds to harden at low temperatures and within a short period of time, in other words, to be fast-curing, from the perspective of energy conservation. In response to this demand, various methods of imparting fast curing properties to sand coating resins have been studied and put into practice.

The first is produced using zinc acetate as the main catalyst.
So-called high ortho novolac resins are used for sand coating, but generally when novolac resins are thermally cured with a curing agent such as hexamylenetetramine, the higher the ortho/para bond ratio, the faster the curing. However, on the other hand, there is a tendency that the crosslinking density does not increase and the cured product itself tends to be thermally decomposed. For this reason, if molds are made with resin-coated sand obtained using such high ortho novolac resins, the molding itself is far from energy-saving, but the strength of the finished molds may be insufficient, Because the surface strength is poor, problems such as roughening of the surface of the casting are likely to occur, and coated sand obtained using such novolac resins tends to have a low fusion point, so it is difficult to use, especially in summer. had the disadvantage that it was easy to block.

Second, there is a method for preparing resin-coated sand using a random novolac resin with a wide molecular weight distribution, but in general, the fusion point of the coated sand is also high, so this method is not sufficient in itself. Although this method is preferable, it has the disadvantage that the wettability of the resin with respect to sand is reduced, making it difficult to maintain the strength of the mold after mold hardening, and the quick curing property imparted to the coated sand is also low.

Thirdly, there is a method of adding acids such as salicylic acid or benzoic acid or salts such as ammonium chloride when producing novolac resin or preparing resin-coated sand. It is generally used in combination with a random novolac resin with a high molecular weight distribution, but if the amount of acids or salts added is small, the fast curing properties imparted are also small, and vice versa. If a large amount of sulfur is added to the mold, the strength of the mold after molding decreases and the fusion point also decreases.

A fourth method is a so-called double coating method in which the sand is coated with a novolac resin and then further coated with a liquid resol resin. However, although the coated sand produced by this double coat method has excellent properties in almost all aspects, including fast curing, the process to obtain the coated sand is more complicated than in any of the above-mentioned methods. It has the disadvantage of becoming.

As described above, many methods have been proposed and implemented to obtain fast-curing resin-coated sand or to obtain resins that impart fast-curing properties to such coated sand, but none of them At present, no satisfactory method has been found, as it may require faster curing at the expense of performance, or it may involve problems in the manufacturing process or work process. .

However, as a result of intensive research in view of the current situation, the present inventors selected a specific acid catalyst, specified the molar ratio of phenols and formaldehyde supply material, and conducted the reaction. If the system is neutralized using a metal compound that can form a chelate and low-boiling substances such as water are removed from the yarn, a phenolic resin with excellent performance including quick curing can be produced. The present invention was completed based on the discovery that the process of obtaining coated sand using the resin thus produced is simpler and easier.

That is, in the present invention, the molar ratio of phenols (al and formaldehyde supply material fbl, +al and fb) is 1:0.3 to 1.0, and salicylic acid alone or in combination with other After the reaction is carried out in the presence of a catalyst used in combination with an acid, the reaction system is treated with an oxide, hydroxide or weak acid salt of a metal capable of forming a chelate with the above-mentioned salicylic acid, or in addition to this in a known and customary manner. To provide a method for producing a phenolic resin for sand coating, which is quick-curing and has a good balance with other properties, by neutralizing the resin in combination with an admixture, and then removing low-boiling substances from the system. It is something.

Herein, the term "phenols +a+" refers to phenol and its equivalent substances, such as phenol, cresol, resorcinol, bisphenol A, or bisphenol oligomers.

On the other hand, typical examples of the above-mentioned formaldehyde supply material include formaldehyde, various solutions of formaldehyde such as paraformaldehyde, hexamethylenetetramine, etc., or derivatives thereof.

Then, the molar ratio of both (ibl / (Jl)
) is suitably within the range of 0.3 to 1.0, and if this ratio is smaller than 0.3, formaldehyde supply material (b
When the ratio of bl becomes too small, the reaction becomes slow and the molecular weight distribution becomes too small to be used as a phenolic resin for coating foundry sand. If the amount is too large, the reaction becomes violent and there is even a risk of gelation, which is undesirable.

In addition, other typical acids that are used as acid catalysts in combination with the above-mentioned salicylic acid include inorganic acids or organic acids that are usually used as catalysts in novolak reactions, such as oxalic acid, hydrochloric acid, or sulfuric acid. These other acids are preferably used in an amount of 1/2 or less of the mole number of salicylic acid.

5- On the other hand, many metals can be used as metals that can form chelates with the above-mentioned salicylic acid, among which representative ones include zinc, cadmium, mercury, copper, silver, nickel, cobalt, iron, and manganese. , chromium, vanadium, titanium, aluminum, lead or tin, and as oxides, hydroxides or weak acid salts of these metals - for example, for zinc, zinc oxide, zinc hydroxide or Of course, it may be zinc acetate or a hydrate thereof. However, this weak acid salt is limited to those that have reactivity with the above-mentioned salicylic acid, and has a dissociation constant (pK value) such as acetate and adipic acid.
is defined as salts of acids greater than salicylic acid.

Furthermore, the neutralizing agents that can be used in combination with such chelate-forming substances include alkali metal or alkaline earth metal oxides or hydroxides such as sodium hydroxide or calcium oxide; ammonia; Examples include tertiary amines and their equivalent substances.

In the method of the present invention, the amount of each of the above-mentioned catalysts and neutralizing agents used is at least 5% by weight of the total amount of salicylic acid, regardless of the type and number of catalysts and neutralizing agents to be used. It is essential to appropriately combine these catalysts and neutralizing agents so that metal chelates are formed and neutralized, and these can be selected within any range and as long as these conditions are maintained. As long as they are used, there will be no special regulations regarding their usage.

In other words, the neutralizing agent added to form a chelate with the salicylic acid reacts with the salicylic acid and other acid catalysts used together, and the desired salicylic acid chelate is not produced. However, as mentioned above, if more than 5% of the salicylic acid is neutralized by forming a metal chelate, it may be used in combination with this salicylic acid. Regardless of the behavior of the acid catalyst, and even if some of the salicylic acid does not participate in chelation, the effects of the present invention are achieved.

If less than 5% by weight of the total amount of salicylic acid is chelated, the effect of improving performance due to chelate formation, and therefore the effect of the present invention, will be extremely reduced, which is not preferable.

Furthermore, in carrying out the method of the present invention, water is a typical low-boiling substance that should be removed from the reaction system after the completion of neutralization by chelate formation as described above; Examples include unreacted phenols, formaldehyde supply substances, and volatile catalysts.

As a method for removing these low-boiling substances, known and commonly used methods include distillation or steam distillation under normal pressure or reduced pressure, and a method in which the reaction product is allowed to stand still for subsequent layer separation. The operating means can be applied as is.

One of the features of the method of the present invention is that the resin obtained has excellent rapid curing properties, and the second is that the resin coated with the resin thus obtained (resin-coated sand ) also has excellent fast curing properties and other properties as well, but this fast curing property is due to the involvement of the salicylic acid chelate and/or the remaining unneutralized salicylic acid. It is thought that the grant will be given in accordance with the above, but the detailed reason for this is unknown.

In addition, the salicylic acid chelate contributes to both improved mold strength and improved fusion point of resin-coated sand.

In this regard, if salicylic acid remains in a free state after producing the phenolic resin, as mentioned above, it will be the same as adding salicylic acid after preparing the resin, and the strength will also be the same as the melting point. also decreases.

However, as in the method of the present invention, -
By chelating COOH, free salicylic acid is reduced, so the melting point can be improved.

On the other hand, the following points can be considered regarding the improvement of strength.

That is, first of all, when this salicylic acid reacts with the phenolic resin chain and is incorporated into the resin during the resin formation reaction process in the method of the present invention, the salicylic acids in the resin chains form a chelate with each other. As a result, this chelate acts as a kind of crosslinking agent, and then, as a general phenomenon, during the neutralization process, the neutralized salt precipitates as crystals in the phenolic resin. However, in the method of the present invention, the salicylic acid chelate is compatible with the phenolic resin. This is because it does not have any adverse effect on the wettability of the sand.These points also explain why the coated sand using the resin obtained by the method of the present invention provides high mold strength. .

Next, the present invention will be explained in more detail with reference to Examples.

All parts and percentages hereinafter are based on weight unless otherwise specified.

Example 1 In a reaction vessel equipped with a reflux device, 755 parts of phenol and 3
487 parts of a 7% formaldehyde aqueous solution were charged, and 27 parts of salicylic acid was further added, followed by heating under reflux for 8 hours. Next, 9- After adding 34 parts of zinc acetate dihydrate to this, normal pressure distillation and reduced pressure distillation were performed sequentially to adjust the softening point of the reactant to 85°C, and 770 parts of phenol resin was gotten.

Example 2 770 parts of a phenolic resin having a softening point of 85° C. was obtained in the same manner as in Example 1, except that 10 parts of aluminum hydroxide was used instead of zinc acetate dihydrate.

Comparative Example 1 In a reaction vessel equipped with a reflux device, 755 parts of phenol and 3
80 parts of a 7% formaldehyde aqueous solution were added, and 6 parts of Schereric acid were added and reacted for 10 minutes. Then, 407 parts of a 37% formaldehyde aqueous solution was added little by little and heated under reflux for 3 hours, followed by atmospheric distillation and reduced pressure. When the softening point of the reactant was adjusted to 85° C. by successively distilling, 760 parts of phenol resin was obtained.

Comparative Example 2 In a reaction vessel equipped with a reflux device, 755 parts of phenol and 3
After adding 6 parts of oxalic acid and reacting for 10 minutes, 429 parts of 37% formaldehyde aqueous solution was added little by little and heated under reflux for 2 hours, then the same as in Comparative Example 1. 800 parts of a phenolic resin having a softening point of 85° C. was obtained by the following procedure.

10- Comparative Example 3 In a reaction vessel equipped with a reflux device, 755 parts of phenol and 3
450 parts of a 7% formaldehyde aqueous solution was added, then 3.8 parts of zinc acetate dihydrate was added and the mixture was heated under reflux for 5 hours, and then 8.5 parts of 20% sulfuric acid was added and the mixture was further heated to 10
Heating at reflux was continued for an hour. Next, 270 parts of low-boiling substances were removed by vacuum distillation, kept at 130-140°C for 2 hours, and then further vacuum distilled to lower the softening point to 8.
When the temperature was adjusted to 5°C, 720 parts of phenolic resin was obtained.

Comparative Example 4 3 parts of benzoic acid was added to 100 parts of the phenol resin obtained in Comparative Example 1, and the mixture was melted and mixed uniformly to obtain a phenol resin composition.

Performance tests were conducted on the phenolic resins or phenolic resin compositions obtained in each of the Examples and Comparative Examples in the manner shown below, and the results are summarized in Table 1.

■ Adjustment of resin-coated sand.

10<1 part of silica sand, which had been heated to 140°C in advance, was placed in a mixer, and 3 parts of the phenolic resin obtained in each Example and Comparative Example or this resin composition was added separately to this. The mixture was mixed and stirred for 1 minute.

Next, add 0.45 parts of hexamethylenetetramine to 1.2 parts
1 part of water and added, mixed and stirred for 1 minute to evaporate the added water, then added 0.1 part of calcium stearate powder, mixed and stirred for 20 seconds, and then removed from the mixer. Resin coated sand with phenolic resin or phenolic resin composition on each side was obtained.

■Test method (i) Fusion point -------J A CT
(Casting Technology Promotion Association) Test method C-1 was used.

(ii) Bending strength ---IIs
According to K-6910.

(iii) Deflection ---230℃
Put the resin-coated sand into the mold and bake it for 20 seconds, take out the test piece in the next 10 seconds, set this test piece as shown in Figure 1, and then apply a 200g weight to the piece. Place it in the center and read the amount of deflection with a dial gauge. It can be said that the smaller the deflection value, the faster the coated sand hardens.

The size of the test piece is 50x150x54m, The span of deflection measurement is It is 110 dragons.

(iv) Peelback resistance - 300g of resin-coated sand is dropped from a funnel into a mold heated to 250℃, and after 60 seconds, the mold is turned over and the uncured coating and sand are removed. Exclude.

After that, invert the mold Keep it as it is, beer back phenomenon begins time (in seconds) Measure.

The display “ω” means this Origin of the beer batho phenomenon It means there wasn't.

13- Table 1 In Table 1, Comparative Example 1 uses the most standard type of resin-coated sand manufactured conventionally, and Comparative Example 2 uses a phenolic resin with a wide molecular weight distribution. What is the comparative example of high ortho-novo? For Tsukuju MM, and Comparative Example 4 exemplified a phenolic resin in which acids were added afterward, but as is clear from the results shown in the same table, the resin of Example 1 was In the case of the coated sand used in Comparative Example 1, almost all performances were superior to that in Comparative Example 1. On the other hand, in the case of the coated sand using the resin of Example 2, it was better than that in Comparative Example 1. Although the results are approximately the same as in case No. 2 in terms of speed and curing properties, the other performances are far superior to those of case No. 2.

In this regard, Comparative Example 3 also shows excellent results 14- in terms of rapid curing, but on the other hand, the strength is low and the performance is unbalanced.

In addition, in the case of Comparative Example 4, the curing speed of the resin-coated sand could be brought closer to that of the product of the present invention by appropriately selecting the acids to be added; This will have a great effect on the points and strength, and will actually cause more problems.

As described above, it is known that when the method of the present invention is followed, the coated sand produced using the resin obtained by this method has excellent fast curing properties and also has good other properties such as strength.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram showing an apparatus for carrying out a deflection test on fired resin-coated sand, and each number in the figure is as follows. t ----------One spindle 2---Test piece 3---=-Dial Gauge Patent Applicant Dainippon Ink and Chemicals Co., Ltd. 15- 1.

Claims (1)

[Claims] In the presence of an acid catalyst containing salicylic acid alone or containing salicylic acid,
(a) Phenols and (bl formaldehyde supply material), (bl/(al) molar ratio is 0.3 to 1.0
Then, by using only a metal oxide, hydroxide or weak acid salt capable of forming a chelate with the salicylic acid, or by using this chelate-forming substance and a neutralizing agent in combination, the above-mentioned It is characterized by chelating and neutralizing at least 5% by weight of the total amount of salicylic acid used as a catalyst, and then removing low-boiling substances from the system.
Method for producing phenolic resin for sand coating.