JPS60221146A - Resin-coated sand for casting - Google Patents

Abstract

PURPOSE:To improve the releasability from a molded metallic mold consisting of resin-coated sand by using a binder resin compsn. prepd. by adding a small amt. of silicone oil and stearic acid (metallic salt) to an unsatd. polyester resin. CONSTITUTION:The unsatd. polyester resin is used as an essential binder and is welded to molding sand; further the silicone oil which is a mold releasing agent is added in a heated state to the main binder at 1-3wt% by the weight thereof under agitation. >=1 kinds of the mold releasing agents consisting of the stearic acid and metallic salt of the stearic acid are in succession added at >=2% thereto and the mixing and agitation are continued to form the resin-coated sand. Such coated sand has good sand removability after casting and improves the releasability from the metallic mold when used as core sand.

Description

Detailed Description of the Invention (Technical field to which the invention relates) The present invention is directed to a method of sand removal, which is used as core sand for casting low melting point metals such as aluminum, and which can be removed after casting without the need for sand baking. , relating to easily disintegrating resin-coated sand for foundry use.

(Prior art) As conventional easily disintegrating foundry resin coated sand, for example, JP-A-54-80284, JP-A-54-162622, JP-A-5
No. 5-165250, No. 55-165251, No. 65
-165252 and No. 57-11'5988, which are coated with resin compositions using unsaturated polyester/I/w resin as the main binder. In resin-coated sand coated with such a Confucian fat composition, the thermal decomposition of the resin is extremely high, so when it is used as core sand for casting low-melting point metals such as aluminum, the sand dischargeability after casting is poor. It is very good, and it is possible to remove about 100 inches of sand without performing any sand burning.

However, resin-coated sand coated with a resin composition containing an unsaturated polyester resin as the main binder,
When molding the core, there was a problem in that it was damaged when removed from the mold, resulting in poor molding yield.

(Disclosure of the Invention) This invention was made by focusing on such conventional problems, and is completely different from the conventional idea of increasing core strength. When producing resin-coated sand by the hot metal A/T method, silicone oil, preferably a small amount selected from the group consisting of dimethyl silicone oil, diphenyl silicone oil and methylphenyl silicone oil (hereinafter referred to as silicone mold release agent), is added to the binder resin. By using a binder resin composition containing at least one selected from the group consisting of stearic acid and stearic acid metal salts (hereinafter referred to as stearic acid mold release agents), resin-coated sand can be produced. The purpose of this invention is to improve the mold releasability from the molding die and solve the above problems.

When creating resin-coated sand using the hot melt method, a stearic acid-based mold release agent is added to improve the slippage between sand grains, improve sand clogging, and improve mold release from the mold. This is commonly done. This mold release mechanism is such that during heat curing, the stearic acid-based mold release agent melts, carboxylic acid or carboxylic acid metal salts are oriented to the mold surface, and the methylene skeleton of stearic acid, which has low polarity, is oriented to the mold surface. It is estimated that it is possible. When a phenolic resin, which is commonly used in the hot-melt method, is used as an inder, the stearic acid mold release agent and the phenolic resin have poor compatibility, so the stearic acid mold release agent is released from the resin during heat curing. Since it is easily oriented on the mold surface, sufficient mold releasability can be obtained. However, in the case of unsaturated polyester resin, it has ester bonds in its skeleton, so it has good compatibility with stearic acid-based mold release agents, and the stearic acid-based mold release agent is released into the resin during heat curing. If the particles are more loose than <<, they cannot be sufficiently oriented on the mold surface and sufficient mold releasability cannot be obtained. On the other hand, when producing a resin molded article, and when releasability from a mold is particularly important, a method of internally adding a silicone-based mold release agent is generally well known. In the case of resin moldings, since the resin layer is continuous, the mold release agent can migrate to the mold surface even from a relatively deep layer, so it is possible to obtain sufficient separability with a small amount added to the resin. It is.

However, in the case of resin-coated sand, the binder resin is used in a small amount, usually less than 5% by weight relative to the sand, and the resin layer is discontinuous. In this case, only a very small amount of the mold release agent contained in the resin that coats the sand grains in contact with the mold contributes to mold releasability. Therefore, in the case of resin-coated sand, when only a silicone-based mold release agent is added, the result is that there is almost no effect on mold release properties.

However, surprisingly, when a silicone-based mold release agent and a stearic acid-based mold release agent are used in combination in this invention, the silicone-based mold release agent reduces the compatibility between the stearic acid-based mold release agent and the unsaturated polyester. This effect makes it easier for the stearic acid-based mold release agent to align on the mold surface.
The original mold release effect can be fully exhibited. When adding a silicone-based mold release agent and a stearic acid-based mold release agent to unsaturated polyester resin, if the stearic acid-based mold release agent is added in advance, it will form a compatible solution with the resin, resulting in non-polar silicone-based mold release agents. The mold release agent wraps around the outside,
Since the silicone-based mold release agent no longer exhibits the original mold-releasing effect, the stearic acid-based silicone-based mold release agent is used.In the present invention, the silicone-based mold release agent is added to the resin by 1 to 8% oil by weight. If the amount is less than 1% by weight, the formation of an incompatible layer will not be sufficient and therefore the objective of improving mold releasability will not be achieved, while if it exceeds 8% by weight, slipping will occur between the hard particles during resin coating. This is undesirable because it becomes difficult to apply force to uniformly coat the resin on the sand surface, resulting in a decrease in mold strength after curing and poor molding yield. As shown in the examples below, the stearic acid-based mold release agent may be added in an amount of 2% by weight or more based on the resin, and the upper limit is not particularly limited, but it is generally used in an amount of 10% by weight or less. be.

The unsaturated polyester resin used in this invention is mainly composed of unsaturated dibasic acids such as fumaric acid, maleic acid, and maleic anhydride, and if necessary, contains a part of saturated dibasic acids such as phthalic anhydride. A resin obtained by a polycondensation reaction with a diol such as , ethylene f IJ col, propylene glycol, etc. can be used. On this occasion,
It is preferable to use a resin that is solid at room temperature because the I#I fat-coated sand is less likely to tack and scratch, and when the mold is filled with the sand coated by air blowing, the sand is more likely to clog.

(Examples of the Invention) Next, the present invention will be explained with reference to Examples, Comparative Examples, and Test Examples.

Examples 1-8. Comparative Examples 1 to 10 Universal mixing stirring type 5 DWM (manufactured by Shinyo Kogyo Co., Ltd.), 17
After adding 1000 g of Nikko silica sand No. 5 heated to 0'C, while stirring, add 25 g of unsaturated polyester resin Nister N +3000 (manufactured by Mitsui Toatsu Chemical Co., Ltd.) crushed to 10 mesh or less and mix and melt. , fused to the sand surface. Furthermore, with the sand temperature at 180°C, 5
g, tert-butyl peroxybenzoate 0.3
9, cyclohexanone peroxide o, s9, α-
Methacryloxypropyltrimethylsilane (A-174 manufactured by Nippon Unicar Co., Ltd.) 0.59 and a predetermined amount of the silicone-based mold release agent shown in Table 1 were mixed and stirred, and the sand temperature was raised to 70°C. At this point, a stearic acid-based mold release agent shown in Table 1 was added to obtain each resin-coated sand.

Comparative Example 11 ~] 4 Universal mixing stirring m 5 DWM (manufactured by Shinyo Kogyo Co., Ltd.), 1
Add 1000g of Nikko silica sand No. 5 heated to 70°C,
Without stirring, unsaturated polyester resin N8000 21 pulverized to 10 mesh or less and a predetermined amount of a stearic acid mold release agent shown in Table 1 were simultaneously added, mixed and melted, and fused to the surface of the sand. Furthermore, at a sand temperature of 180℃, n-
0.8 g of tert-butyl peroxybenzoate in 5 g of hexane, cyclohexanone peroxide o, a
g, α-methacryloxypropyltrimethylsilane (Japan: S-Nika Co., Ltd., A-174) 0
．． A predetermined amount of the silicone-based mold release agent shown in Table 1 and No. 59 was mixed and stirred until the sand temperature reached 70° C. or lower to obtain resin-coated sand.

Test Examples Examples 1-8. The resin-coated sand of Comparative Examples 1 to 14 was
It was subjected to bending strength measurement according to K 6910-1964. At this time, the mold for preparing the test piece was preheated to 280"C, the resin-coated sand was filled into it, and the resin-coated sand was left at ~280°C for 70 seconds to complete curing, and then the bending strength was immediately measured. In order to measure the bending strength at temperature and the mold releasability, a tapered cylindrical mold (height 15 Qu+, upper end inner diameter B-28, 4III+1 lower end inner diameter C-80, 21
111) was filled with resin-coated sand, left to harden at 210"C for 70 seconds, and then tested using a universal tensile tester manufactured by Takashi Seisakusho (
Autograph), a load was applied from the small diameter side and the load required to release the mold was measured. The obtained "pull resistance" results are also listed in Table 1.

(Effects of the Invention) As explained above, the resin-coated sand for foundries of the present invention is coated with a binder resin composition made by adding a silicone thread mold release agent and a stearic acid mold release agent to an unsaturated polyester resin. Therefore, when used as core sand, it not only improves the sand removal performance after casting, but also improves the releasability from the mold and improves the molding yield. .

Patent applicant: Nissan Motor Co., Ltd.

Claims (1)

[Claims] L Unsaturated polyester resin is used as the main binder, and silicone oil/l/1 is added to this binder resin.
- 8% by weight, and then at least 2% by weight of at least one selected from the group consisting of stearic acid and metal stearate. Resin coated sand.