JPS6232015B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resin composition for a shell mold, which is used in the shell mold casting method and is used to produce resin-coated sand grains having good disintegration properties after casting. The shell mold method using phenolic resin is currently the mainstream casting method due to its high production efficiency and good casting surface, but it is also used for castings with low pouring temperature (e.g. bronze and aluminum castings),
Also, various drawbacks have been pointed out in cores and the like. A core is used to create a hollow part in a casting.In this case, when pouring the metal, it is completely surrounded by molten metal, which creates an oxygen-free condition, and the phenolic resin carbonizes, making it strong even after casting. Retention and disintegration become a problem. This tendency is particularly noticeable in the case of casting cores with low casting temperatures, and they cannot be used as they are due to poor collapsibility. For this reason, in the case of casting cores where the pouring temperature is low, the cold box method using a furan-based liquid oven is used, and in the case of resin-coated molding sand that uses phenolic resin, it is necessary to heat the cores at 400 to 500℃ after casting. Currently, the core is sand fired for several hours to improve its collapsibility. However, the cold box method has the disadvantages of low production efficiency and the high cost of furan-based liquid resins.The latter also increases costs due to heat, so the casting industry is using shell mold resins that have good disintegration properties after casting. was strongly requested. In addition, many studies have been conducted in the past on phenolic resins for shell molds.
36-20589 uses an aromatic monocarboxylic acid as an additive to ordinary phenolic resin, but in this case, although it is effective in accelerating curing and improving shell strength, it is not effective in reducing the disintegration of the core. Nakatsuta. Furthermore, in JP-A-53-124118, aliphatic saturated dicarboxylic acids are used as additives in ordinary phenolic resins, but although this is also effective in accelerating curing and improving shell strength, it is difficult to disintegrate the core. There was no effect on Furthermore, JP-A-52-138593 discloses a technology using novolak resin using bisphenol A purification residue, but although this is effective in improving the crack resistance of the core, There was no effect on disintegration. As a result of intensive research into a new phenolic resin composition that improves these drawbacks, the present inventors found that
The purified residue of bisphenol A obtained when producing bisphenol A and phenols are used in a ratio such that the proportion of phenols in the total amount of both is 90% by weight or less, and the presence of an acidic catalyst is used. A novolac-type phenolic resin obtained by condensation with formaldehyde (hereinafter referred to as modified novolac) or a mixture of this modified novolac and a normal straight novolac obtained by condensing phenol and formaldehyde in the presence of an acidic catalyst. It has been found that by blending an aromatic carboxylic acid or its anhydride, a resin composition for shell molding that is inexpensive and has excellent disintegrability can be obtained. In this case, even if only modified novolac or a mixture of modified novolac and straight novolac is used, it is possible to obtain resin-coated molding sand with better disintegrability than when using ordinary phenolic resin, but the curing speed is It is inferior in terms of shell strength and is not suitable for practical use as it is. Furthermore, in order to accelerate the curing speed, it is known to add curing accelerators such as inorganic acids, organic acids, alkaline earth metal oxides or hydroxides, and polyhydric phenols, but the shell strength is not satisfied. The desired effect was not achieved. That is, the present invention was completed based on the discovery that addition of an aromatic carboxylic acid or its anhydride has the effect of promoting the effect and increasing the shell strength at the same time. The bisphenol A purification residue (hereinafter referred to as purification residue) used in the present invention is a residue discharged from the process of synthesizing bisphenol A from phenol and acetone and purifying the produced bisphenol A. The purification process of bisphenol A is operated to remove impurities that are produced as a by-product during the condensation reaction of phenol and acetone under an acidic catalyst, and impurities that are generated during post-processing such as catalyst removal and phenol removal. Methods include distillation, recrystallization using a solvent, and crystallization of bisphenol A and phenol adducts. In the case of purification by distillation, the distillation bottom liquid is used, in the case of solvent recrystallization, the residual liquid after recovering the solvent from the filtrate, and in the case of adduct separation method, the residual liquid after recovering the phenol from the filtrate is referred to in the present invention. Corresponds to precision residue. The composition of these purification residues varies depending on the purification conditions, but the main components are bisphenol A and its isomers, a chroman compound called chroman, other polyphenol compounds, and resinized polymer substances. To produce the modified novolak used in the process of the invention, the above-mentioned purification residue and phenols are condensed with formaldehyde in the presence of an acidic catalyst. The phenols used here include phenol, cresol, xylenol, resorcinol, or a mixture thereof, with phenol being particularly preferred. Further, formaldehyde sources such as formalin, paraformaldehyde, hexamethylenetetramine, etc. can be used. The ratio of phenols and refining residue to be used varies depending on the blending ratio with straight novolac, the manufacturing conditions of coated sand, and the type of casting, but it is based on the total amount of phenols and refining residue calculated in the resin composition. It is desirable that 10% by weight or more, preferably 20 to 80% by weight, be purified residues. Purification residue
If it is less than 10% by weight, the disintegration effect will be reduced. As the catalyst used in the above condensation reaction, acidic catalysts such as hydrochloric acid, sulfuric acid, oxalic acid, etc. are suitable, and the amount used is the same as in the case of production of ordinary phenolic resin. Alternatively, the amount is preferably in the range of 0.01 to 2 parts per 100 parts of the mixture of the purified residue and phenols. Other conditions in the condensation reaction can be determined according to the conditions for producing ordinary phenolic resins. In other words, the amount of formaldehyde used per 1 mole of phenolic component (monomer equivalent) is
The amount ranges from 0.5 to 1.5 mol, and the reaction temperature is usually 50 to 50 mol.
The reaction time is 1 to 15 hours, usually 2 to 6 hours. After the condensation reaction, the catalyst is neutralized if necessary, followed by dehydration and removal of unreacted phenols to obtain a novolac-type phenolic resin (modified novolac). The modified novolak of the present invention contains bisphenol A, its isomer, and a chroman-type cyclic ether structure in its structure, so when heated in an oxygen-free condition, there are few carbonization products (fixed carbon content), and therefore, pouring It is considered that the subsequent disintegration properties are good. This modified novolac can maintain its excellent performance even when used in combination with normal straight novolac in any proportion as long as the converted purified residue ratio in the resin composition satisfies the above conditions. able to demonstrate. Therefore, there is an advantage that the usage conditions of the coated sand can be handled by adjusting the amount of straight novolac to be blended, without having to produce modified novolacs with different compositions. Examples of the aromatic carboxylic acids used in the present invention include benzoic acid, toluic acid, dimethylbenzoic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, salicylic acid, cresylic acid, naphthalenecarboxylic acid, etc. As the carboxylic anhydride, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, etc. can be used.
The amount of the aromatic carboxylic acid or its anhydride added is 0.1 to 20 parts by weight, preferably 0.5 to 15 parts by weight, per 100 parts of the modified novolac or a blend of modified novolac and straight novolac. In the present invention, the method and order of blending modified novolac, straight novolac, and aromatic carboxylic acid or its anhydride are not particularly limited, but generally there is a method of mixing them in a molten state, and They may be mixed during manufacturing. The method for producing coated sand is not limited to the hot marling method described in the examples, but can also include the semi-hot method, the cold method, and the first layer coated with the resin composition of the present invention. However, a double coating method in which the second layer is coated with a normal phenolic resin can also be applied. A more detailed explanation will be given below with reference to Examples. Note that the parts and percentages described are parts by weight and percentages by weight unless otherwise specified. Examples 1 to 4, Comparative Examples 1 to 9 Resins A and B manufactured by the method described below,
For resin compositions containing C, D and aromatic carboxylic acids and other additives, we measured the fixed carbon content, which shows values closely related to the gel time, which is a guideline for curing speed, and the disintegrability of the mold. .
Furthermore, coated sand was prepared using these resins and resin compositions, and tests on shell bending strength and collapsibility were conducted. These test results are summarized in Table-1.
As can be seen from the measured values for Examples and Comparative Examples in Table 1, the composition of the present invention has good disintegration properties,
Moreover, the addition of aromatic carboxylic acid has a remarkable effect on accelerating hardening and increasing shell strength. Compared to known curing accelerators that only accelerate the curing rate, but the shell strength is equivalent to or slightly lower than that of additives, the effect of aromatic carboxylic acids is remarkable, and the composition of the present invention is a lightweight material with good disintegrability. It can be seen that it exhibits excellent performance as a binder for alloy cores. In addition, in actual field tests, the modified novolak composition of the present invention was used to test aluminum casting cores that had poor collapsibility after casting and could not be dismantled without sand baking. It had good disintegration properties, and smooth sand removal was possible without sand baking. [Manufacturing method of phenolic resin] Resin A 200 parts of purified residue was uniformly dissolved in 800 parts of phenol and charged into a reactor equipped with a stirrer, a reflux condenser, and a thermometer, and 487% of a 37% formalin aqueous solution was added.
1 part and 10 parts of oxalic acid were added and heated while stirring. Reflux begins at about 98℃, but after the start of reflux
The reaction was carried out at 95-100°C for 120 minutes. After the reaction is complete,
Softening point is 96.0℃ after dehydration and removal of unreacted phenol.
1010 parts of resin were obtained. Resin B 914 parts of a resin with a softening point of 100.5°C was obtained using the same procedure as in the manufacturing method of Resin A, except that 500 parts of phenol, 500 parts of purified residue, and 386 parts of 37% formalin aqueous solution were charged. Resin C 1010 parts of a resin with a softening point of 105.5° C. was obtained using the same procedure as in the production method of Resin A, except that 300 parts of phenol, 700 parts of purified residue, and 300 parts of 37% formalin aqueous solution were charged. Resin D Phenol 1000 parts, 37% formalin aqueous solution 692
1 part and 4.5 parts of 20% hydrochloric acid were charged into a reactor equipped with a stirrer, a reflux condenser, and a thermometer, and heated while stirring. Reflux started at about 97°C, and the reaction was continued under reflux for an additional 60 minutes after the start of reflux. After the reaction is complete,
Softening point is 100 by dehydration and removal of unreacted phenol.
1050 parts of straight novolac at 100°C were obtained. [Blending of curing accelerator] Immediately before discharging the resins A, B, and C from the reactor, a predetermined amount of curing accelerator was added and mixed uniformly to prepare Examples 1 to 4, Comparative Examples 1, 3, and The resin composition used in 5 was obtained. [Production of coated sand] Quickly add 4000g of silica sand preheated to 190℃ into a small laboratory mixer. 110 g of coarsely crushed novolac was added, mixed for 60 seconds, and then 70 g of a 15% aqueous solution of hexamethylenetetramine was added. The fluidity of the sand improves in about 5 minutes, so 4 g of calcium stearate is added, mixed for 30 seconds, and then the sand is discharged. [Disintegration test and measurement of shell bending strength] 50g of the above coated sand was filled into a cylindrical mold with a diameter of 28mm and a height of 70mm preheated to 450°C.
Cure for 3 minutes at ℃. After removing the test piece from the mold, the test piece was embedded in calcined granular coke and air was shut off according to JISK-2425 creosote oil, processed tar, tar pitch, and pavement tar test method for determining fixed carbon content. , at 600℃
Bake for 30 minutes. After cooling to room temperature, the test piece was taken out and vibrated for 30 seconds using an oscillating sieve shaker.
Weigh the portion remaining on the sieve as the undisintegrated portion. The disintegration rate is determined by the following formula. Collapse rate (%) = (weight of original test piece) - (weight of uncollapsed part) / (weight of original test piece) x 100 Room temperature shell bending strength is 250℃ according to JISK-6910
A test piece of 10 x 10 x 60 mm was made and measured. The subsequent comparison of the normal temperature shell bending strength was performed using the highest measured value of each shell bending strength. Examples 4 and 5 A mixed resin of modified novolac and straight novolac of the present invention was prepared using the above-mentioned resins C and D, and a composition to which aromatic carboxylic acid or its anhydride was added was similarly tested. Table 2 shows the results.
It was shown to. As can be seen from Table 2, the resin composition of the present invention has good disintegration properties, and the addition of aromatic carboxylic acid or its anhydride has a remarkable effect on accelerating curing and increasing shell strength. Also, the ratio of purified residue in the mixed resin is approximately 50%.
However, this composition is the same as that of Example 1, and the disintegration properties are also almost the same.

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Claims (1)

[Scope of Claims] 1. The purified residue of bisphenol A obtained during the production of bisphenol A and phenols are used in such a ratio that the proportion of phenols in the total amount of both is 90% by weight or less. A resin composition for a shell mold, which is prepared by blending an aromatic carboxylic acid or its anhydride with a novolac type phenolic resin obtained by condensing formaldehyde with formaldehyde in the presence of an acidic catalyst. 2. In the presence of an acidic catalyst, the purified residue of bisphenol A obtained during the production of bisphenol A and phenols are used in a ratio such that the proportion of phenols in the total amount of both is 90% by weight or less. A novolac-type phenolic resin obtained by condensing phenol with formaldehyde and a normal straight novolac resin obtained by condensing phenol and formaldehyde in the presence of an acidic catalyst are mixed, and an aromatic carboxylic acid or its anhydride is further blended. Resin composition for shell mold.