JPS6043821B2 - Manufacturing method of resin-coated sand for foundries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing resin-coated sand for foundries used in molding molds and cores for foundries.

When forming molds and cores, usually foundry sand grains are
Phenol resins have been extremely commonly used as coating resins in the past.

The reason for this is that resin-coated sand is obtained by molding and firing molds and cores, and the strength of the molds and cores obtained is high and the molding and firing time is short. On the other hand, when using phenolic resin-coated sand, hexamethylenetetramine is used as a hardening agent, so ammonia gas is generated when the mold and core are fired, and when used as a core for castings such as aluminum. Since it is carbonized by the heat of the phenol resin and molten metal, there is little decrease in strength, and it also has the disadvantage of poor discharge of core sand after casting. The present inventors have made extensive efforts to develop resin-coated sand for molds and cores used when casting materials such as aluminum at relatively low temperatures. We have proposed a resin composition for binding foundry sand grains that uses a base resin, has excellent discharge properties, and does not cause any irritating odor during mold and core molding, firing, and casting. The sand has a low crystallization rate and remains sticky over a long period of time. The child has poor sand clogging,
In order to impart strength to sand grains, the amount of resin used must be greater than that of phenolic resin-coated sand.

In order to improve the stickiness of the above-mentioned resin, the present inventors further conducted various studies on improving the degree of crystallinity and crystallization rate of the crystalline unsaturated polyester, and as a result, the present inventors added a crystal nucleating agent to the resin. It has been discovered that by adding it during the preparation of resin-coated sand, resin-coated sand with almost no stickiness and good sand-clogging properties can be obtained in a short time, and the present invention has been achieved.

Therefore, in the present invention, a crystal nucleating agent with an average particle size of 1 micron or less is added to the crystalline unsaturated polyester resin in the process of coating sand grains with a foundry sand binder whose main component is a crystalline unsaturated polyester resin by a hot melt method. The present invention relates to a method for producing resin-coated sand for foundries, characterized in that 1 to 6 parts by weight are added to 10 parts by weight.

In this specification, the hot melt method refers to sand grains that are heated in advance to a temperature higher than the softening point of the resin to be coated, and the resin is mixed into the heated sand and stirred.
This is a method of coating by heating and melting the resin with sand. When producing resin-coated sand for foundries by the method of the present invention,
0.1 of a crystal nucleating agent having an average particle size of 1 micron or less as a crystal nucleating agent per 100 parts by weight of the crystalline unsaturated polyester.
~3 parts by weight of the crystalline unsaturated polyester was added in advance, and in the process of using this crystalline unsaturated polyester as a foundry sand binder and coating the sand grains with it by a hot melt method, it was added again to 10 parts by weight of the crystalline unsaturated polyester. 1 to 6 parts by weight of a crystal nucleating agent is added to coat the sand grains.

In this way, the addition of the latter crystal nucleating agent improves the crystallinity and crystallization speed of the crystalline unsaturated polyester, which mainly constitutes the coating layer of the resin-coated sand, and shortens the working time of the resin-coated sand. Resin-coated sand with almost no stickiness can be obtained in a short time. The crystalline unsaturated polyester used in the present invention is a resin that shows a clear peak in X-ray diffraction, and as mentioned above, it is a solid with almost no stickiness at room temperature, preferably 250 poise or less at a softening point or higher. It is a crystalline unsaturated polyester with a viscosity of .

The reason for specifying the resin to be tested as resin-coated sand for foundries as described above is that even ordinary unsaturated polyester can become a non-tacky solid at room temperature if the molecular weight is increased, but resin-coated sand actually When producing polyester, the resin viscosity does not decrease even when the temperature exceeds the softening point, making it impossible to uniformly form a resin coating layer on the surface of the sand grains. This is because if a uniform resin coating layer is formed, the produced resin-coated sand will be sticky and cannot become dry coated sand. Raw materials for crystalline unsaturated polyesters include α,β unsaturated dibasic acids such as maleic anhydride, citraconic acid, itaconic acid, fumaric acid, mesaconic acid, and substituted products thereof. It is solid at room temperature and has crystals. Among these, in order to increase the crystallinity of the unsaturated polyester, those showing steric symmetry such as fumaric acid and mesaconic acid are particularly preferable.As saturated dibasic acids Examples include terephthalic acid, dimethyl terephthalate, adipic acid, sebacic acid, azelaic acid, isophthalic acid, endomethylenetetrahydrophthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, anthracenemaleic anhydride and their adducts, substituted Among these, in order to enhance the crystallization of unsaturated polyesters, those exhibiting steric symmetry such as terephthalic acid, dimethyl terephthalate, and adipic acid are particularly preferred.As glycols, ethylene glycol , 1,4-butanediol, diethylene glycol, triethylene glycol, 1,6-hexanediol, neopentyl glycol, hydrogenated bisphenol A1 meta-xylene glycol, and substituted products thereof. All of these are solid at room temperature and It has crystallinity or exhibits steric symmetry.Among these groups, it contains at least one kind of α,β-unsaturated dibasic acids and, if necessary, α,β-unsaturated dibasic acids. When replacing a portion of a saturated dibasic acid with a saturated dibasic acid, select a saturated dibasic acid with steric symmetry as the acid component, and select at least one type from the glycol group as a well-known acid. method, esterification, average molecular weight 1000-200
By adjusting the cooling rate, adding a crystal nucleating agent, etc., it is possible to obtain a crystalline unsaturated polyester that has no stickiness at room temperature.

The most important thing in this case is the addition of a crystal nucleating agent, and this is the factor that made it possible to achieve the object of the present invention. It is generally recognized that adding a crystal nucleating agent to a crystalline resin is extremely effective in improving the crystallization rate, and the case of crystalline unsaturated polyester is no exception. Usually, when a crystal nucleating agent is added, the rate of crystal nucleation,
Since it is possible to increase the degree of crystallinity and improve the crystallization rate of the resin, 0.1 to 10 parts by weight of the crystal nucleating agent is added to 10 parts by weight of the resin. In this case, the greater the amount of the crystal nucleating agent added, the more the crystallinity and crystallization rate can be improved, but on the other hand, the larger the amount of the crystal nucleating agent added, the higher the viscosity of the resin when melted by heating. , it has proven difficult to coat sand. Furthermore, it is preferable that the crystal nuclei be as small as possible and be present in large numbers in the resin, but especially when the resin layer is only about 10 microns thick, such as in resin-coated sand, the crystal nuclei are completely contained in the resin layer. In order for the agent to be dispersed, it is considered that the particle size of the crystal nucleating agent is preferably 1 micron or less. For this reason, crystalline unsaturated polyester for foundry sand is easy to handle at room temperature (i.e., a solid with as little stickiness as possible).
It is necessary to simultaneously satisfy the following requirements: and ease of coating during coating (that is, the viscosity when melted should be as low as possible). In the present invention, as a result of researching the amount and method of adding a crystal nucleating agent that satisfies both of these properties, we added 1.1 to 9 parts by weight in two parts to 1 part of the resin. However, this problem can be solved by adding especially the second addition during the process of coating the sand grains with the foundry sand adhesive material mainly composed of crystalline unsaturated polyester resin as described above, and it is possible to achieve good casting properties. It was possible to obtain resin-coated sand. The crystal nucleating agent used in the present invention is an inorganic oxide such as silica or alumina, and silica is particularly preferred. The present invention will be explained in detail below using Examples and Reference Examples.

Example 1 56 g of fumaric acid 1126y1 phthalic anhydride 44y1 ethylene glycol 617y1 diethylene glycol, 2
e.Pour into a four-bottle flask and use a conventional esterification condensation reaction to obtain an unsaturated polyester resin with an acid value of 25.
I got f.

This was cooled to 140°C, diallyl phthalate 156
y1 Parabenzoquinone 0.33y1 Ultrafine silicic anhydride (trade name Aloesil 200, manufactured by Nippon Aloesil Co., Ltd.) was added as a crystal nucleating agent for 14y, and after thorough stirring, when the temperature reached 120°C, a part of the sample was brought to room temperature. The coating was applied to a thickness of approximately 0.2 Trm onto a 3 m thick glass plate which had been left undisturbed, and the time until the appearance of a cloudy point due to crystal precipitation in the applied coating was measured and the crystallization rate was determined. Take about 300y of the remaining sample into a beaker and keep it in a 130°C oil bath while stirring until the sample temperature is 120°C.
When the temperature reached ±1°C, the melt viscosity was measured using a Bruckfield L-type rotational viscometer.The remaining approximately 1100y sample was cooled to room temperature, solidified, and ground to -9 mesh to prepare resin-coated sand. 112.1q (
The mixture was divided into 6 pieces each containing 10 parts by weight of crystalline unsaturated polyester, 11.1 parts by weight of diallyl phthalate, and 1 part by weight of ultrafine silicic anhydride. To prepare the resin-coated sand, 4 kg of silica sand, which had been heated to 180°C in advance, was put into a speed mixer (model NSC-1, manufactured by Enshu Tekko Co., Ltd.) and stirred, and while stirring, the sample resin 112. 1y1 crosslinking agent liquid 25.3y
[A mixture of 22.3 V diallyl phthalate and 3 g of curing catalyst dicumyl peroxide (3 parts by weight per 100 parts by weight of crystalline unsaturated polyester);
The total amount of diallyl phthalate added was 33.4 parts by weight per 100 parts by weight of crystalline unsaturated polyester.]
, using the ultrafine silicic anhydride as a crystal nucleating agent 1, 2, 3, 4
, 5 and 6 y, respectively, and finally 5 y of wax (calcium stearate) was added as a lubricant.

The produced resin-coated/covered sand was subjected to a tensile test immediately after firing at 230° C. at 708° C. using a shell foundry sand high temperature tensile tester manufactured by Deitart. The above results are summarized in Table 1 and FIGS. 1 and 2. Reference examples Fumaric acid 1126f1 Phthalic anhydride 44f1 Ethylene glycol 617y1 Diethylene glycol 56f 2e
The same unsaturated polyester resin 1 as in Example 1 was prepared by charging it into a four-hole flask and carrying out an esterification condensation reaction using a conventional method.
400y was made, this resin was cooled to 140°C, diallylphthale 156y1 rosebenzoquinone 0.16y
were added, mixed thoroughly, and divided into four beakers each containing 300y of silicic acid.
Add 3.5y (also 5 parts by weight), 16.2y (also 6 parts by weight), and 21.6f (also 8 parts by weight), stir thoroughly, and when the sample reaches 120°C, take out a part. The crystal precipitation time was measured in the same manner as in Example 1, and the remaining sample was kept stirring in an oil bath at 130°C.
When the temperature reached 20°C±1°C, the viscosity was measured in the same manner as in Example 1.

After measuring the viscosity, it was cooled to room temperature, solidified and pulverized, each containing 115.1 (100 parts by weight of crystalline unsaturated polyester, 11.1 parts by weight of diallyl phthalate, 4 parts by weight of ultrafine silicic anhydride), 116.1, 117.1, 119.1
f was weighed and used as a sample for producing resin-coated sand. Using these four samples, the resin sample and 25.3q of the crosslinking agent liquid were added in this order to 4kg of sand preheated to 180°C while stirring with the speed mixer, and finally the wax 5V
was added to produce resin-coated sand.

These resin-coated sands were subjected to a tensile test at high temperature in the same manner as in Example 1. These results are summarized in Table 2 and Table 1.
- Shown in Figure 4. However, regarding sample d, the kneading time and high temperature strength were not measured because the silica sand and resin remained completely separated during the resin-coated sand operation and coating was impossible.

Comparing Example 1 and Reference Example, Tables 1 to 2 and Table 1
From Figure ~4, in the reference example (1), as the amount added increases, the crystal precipitation time becomes shorter (the resin becomes less sticky), but on the other hand, the melt viscosity increases. , it is considered unsuitable as a resin for binding sand grains.

(2) For this reason, the kneading time to uniformly coat the sand grains becomes longer, and the time during which the resin, crosslinking agent, curing catalyst, etc. are kept at high temperatures is longer, and some of them may decompose and volatilize, resulting in lower high-temperature tensile strength of resin-coated sand. is low overall. On the other hand, in Example 1, which is an example of the present invention, (1) Most of the added amount of the crystal nucleating agent is added when the resin is melted and completely uniformly coated, so there is no influence of the resin, and the crystal nucleating agent is As the amount added increases, crystallization becomes faster and the kneading time becomes shorter.

(2) Therefore, the high-temperature tensile strength of the resin-coated sand is stably high in the range of 8 parts by weight from 2 parts by weight of the crystal nucleating agent.

As described above, the example of the present invention in which a crystal nucleating agent is added during the preparation of resin-coated sand is an extremely effective method for shortening the kneading time (improving the crystallization rate) and preventing an increase in the viscosity of the resin. Recognize.

Example 2 1137V of fumaric acid, 29y of adipic acid, 617y of ethylene glycol, and 56y of diethylene glycol were charged into a 2E four-bottle flask, and an unsaturated polyester resin 1400y with an acid value of 28 was obtained by an esterification condensation reaction using a conventional method.

This was cooled to 140℃ and Hydrokino 0.33f1
Diallyl phthalate 156f1 Ultrafine particle silicic anhydride 28
y was added and thoroughly mixed with stirring, about 300 y was taken into a beaker, and the crystallization time and melt viscosity were determined in the same manner as in Example 1. The remaining sample was cooled and solidified as it was, pulverized to -9 mesh, divided into 6 pieces each weighing 113.1 g, and used to prepare resin-coated sand. To prepare the resin-coated sand, 4 kg of silica sand, which had been heated to 180°C in advance, was put into the speed mixer and stirred, and the sample resin was 113.1 da, and the crosslinking agent liquid was 25.3 f11.
As a crystal nucleating agent, the ultrafine silicic anhydride is used as 1, 2, 3, 4,
5 and 6 Da were added, respectively, and finally 5 Y of calcium stearate was added as a lubricant. The evaluation was performed by measuring the manufacturing time described above and using a tensile test at high temperature. The results obtained are shown in Table 3, FIGS. 5 and 6. As can be seen from Table 3, Figures 4 and 5, the addition of a crystal nucleating agent during the production process of resin-coated sand increases the crystallization rate by adding it to the resin itself, which increases the viscosity and makes it suitable for casting. It was confirmed that this is an extremely effective method to solve the problem of unavailability.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the influence of the amount of nucleating agent on kneading time, Figure 2 is a diagram showing the influence of the amount of nucleating agent on high temperature strength, and Figure 3 is a diagram showing the influence of the amount of nucleating agent on high temperature strength.
The figure is a diagram showing the influence of the amount of crystal nucleating agent added on crystal precipitation, Figure 4 is a diagram showing the influence of the amount of crystal nucleating agent added on viscosity,
FIG. 5 is a diagram showing the relationship between the total amount of crystal nucleating agent and kneading time in Example 2, and FIG. 6 is a diagram showing the relationship between the total amount of crystal nucleating agent and high temperature strength in Example 2.

Claims (1)

[Claims] 1. In the process of coating sand grains with a foundry sand binder containing a crystalline unsaturated polyester resin as a main component by a hot melt method, a crystal nucleating agent is added to 100 parts by weight of the crystalline unsaturated polyester resin. A method for producing resin-coated sand for foundries, characterized in that 1 to 6 parts by weight are added. 2 Foundry sand caking material is crystalline unsaturated polyester resin 10
The method for producing resin-coated sand for foundries according to claim 1, which contains a crystal nucleating agent in an amount of 0.1 to 3 parts by weight per 0 parts by weight. 3. The method for producing resin-coated sand for foundries according to claim 1 or 2, in which silica having an average particle size of 1 micron or less is used as a crystal nucleating agent. 4. The crystalline unsaturated polyester resin is fixed at room temperature by the addition of 2 parts by weight or less of the silica,
4. The method for producing resin-coated sand for foundries according to claim 3, which is non-adhesive and exhibits a viscosity of 250 poise or less above the softening point.