JPH09276984A - Manufacture of resin coating sand - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a resin coating sand for molding a shell mold having low odor, high strength and blocking resistance without needing the setting of new equipment and apparatus. SOLUTION: In the manufacturing method of the new resin coating sand for the shell mold, phenol resin emulsion or suspension having 400-2000wt. average molecular wt. is used to a binder and further a material adding 0.1-5wt.% silane coupling agent to this emulsion or suspension, is used to the binder. To 100wt. parts of molding sand heated at 100-180 deg.C, 0.5-10wt. parts binder is added and kneaded, and volatile component is vaporized and removed to coat the resin content on the surface of the molding sand.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a resin coated sand for molding a shell mold.

2. Description of the Related Art Generally, a resin coated sand for shell mold molding is a novolac resin obtained by reacting phenol and formaldehyde under an acid catalyst, or a solid or liquid resol resin obtained at a room temperature obtained by reacting under an alkali catalyst. And a system using these in combination is 100 to 1
It is manufactured by adding it to foundry sand heated to 80 ° C., heat melting the resin, and coating the surface of the sand grains. The novolac resin is added with a solution of hexamethylenetetramine dissolved in water as a curing agent. At this time, the role of water is to uniformly disperse hexamethylenetetramine and to lower the temperature of the sand during kneading. On the other hand, the resole resin does not require hexamethylenetetramine, but water is used to cool the sand.

Novolak resins are the most common binders for molding shell molds. However, this binder requires hexamethylenetetramine as a curing agent. It is a big problem from the viewpoint of working environment that hexamethylenetetramine is thermally decomposed to generate an irritating odor of ammonia, formaldehyde, etc. in the mold making by firing using a heating die of 250 to 350 ° C. On the other hand, when a resole resin, especially a solid resole resin, is used as a binder for shell mold molding, hexamethylenetetramine is not required as a curing agent, and it is expected as a low odor binder because it can mold the mold only by thermosetting. It was However, in the case of producing resin coated sand, solid resole resin undergoes a hardening reaction due to heated molding sand to increase the molecular weight. Therefore, it is generally known that the melt viscosity becomes higher than that of the novolac resin, it becomes difficult to uniformly coat the surface of the sand grains of the foundry sand with the resin component, and the mold strength becomes low. Further, if the molecular weight of the resole resin is lowered in advance in consideration of the above reaction in order to increase the strength, there is a problem that the softening point is lowered and the blocking property of the resin and the resin coated sand during storage is increased.

In view of these problems, the present invention provides a new resin coated sand by employing a phenol resin emulsion or suspension which has not been used in the conventional binder for shell mold molding. . That is, the present invention has a weight average molecular weight of 400.
~ 2,000 phenolic resin emulsion or suspension is used as a binder, and 0.1-5% by weight of silane coupling agent is further added to this emulsion or suspension as a binder, 100-180 ° C
A new shell mold mold in which 0.5 to 10 parts by weight of a binder is added and kneaded to 100 parts by weight of the molding sand heated to 1, and volatile components are removed by evaporation to cover the molding sand surface with a resin component. It is a method for producing a resin coated sand for use. The contents of the phenol resin used here will be described later, but the obtained resin coated sand has the following features. The resin is a resol type and does not require hexamethylenetetramine as a curing agent, so that an irritating odor generated during molding is extremely low. Further, since it is a uniform dispersion liquid of a resol-type phenol resin, it has good coverage with molding sand. Therefore, even a resol type phenol resin having a high molecular weight, that is, a high viscosity does not hinder the kneading operation.
Therefore, it is possible to prepare a resin-coated sand that is less likely to cause blocking and can provide a high-strength mold with a high fusion point. Further, even when a high-strength template is required and a relatively low molecular weight resol-type phenol resin is used, the stability of the resin during storage is good because it is an emulsion or suspension. By changing the form of the resol type phenol resin to an emulsion or suspension,
It is possible to obtain a resin-coated sand having low odor, high strength, and blocking characteristics that are extremely unlikely to occur. Also, when adjusting the actual resin coated sand, since the binder is a one-liquid type, the addition amount can be accurately controlled, and various additives such as curing agents such as when using novolac resin are added. There is also an advantage that it is possible to prevent erroneous operations such as complications for this and weighing errors due to it. The phenol resin emulsion or suspension used in the present invention has a resol-type phenol resin molecular weight of 40 in terms of polystyrene equivalent weight average molecular weight.
It is from 0 to 2,000. Weight average molecular weight is 400
When it is smaller than the above range, the curing rate is slow, so that the productivity of the mold making is lowered, and the fusion temperature of the obtained resin coated is low, the risk of blocking is high, and the storage stability is lowered. On the other hand, when the weight average molecular weight is more than 2,000, the melt viscosity becomes high and the fluidity of the resin coated on the molding sand deteriorates, and the expected adhesive effect cannot be obtained. Therefore, the weight average molecular weight of the resol-type phenol resin used for the emulsion or suspension is 400
The synthesis method is not particularly limited as long as it is in the range of up to 2,000. Further, refractory particles (silica sand, alumina sand, zircon sand, chromite sand, olivine sand, mullite sand, fly ash, etc.) used as foundry sand are not particularly limited as long as they are used for molding. . The phenol resin emulsion or suspension used in the present invention is publicly known.
2-3853 "Production Method of Aqueous Emulsion of Phenolic Resin", JP-B-45-3931, JP-B-45-2
0506, JP-B-46-27256, JP-B-49-12
590, JP-B-49-49183 and JP-A-48-217.
34, JP-A-48-93691, JP-A-51-4291.
And the like. However, when a surfactant is used as an emulsifier when producing a phenol resin emulsion or suspension by these methods, the moisture resistance of a resin-coated sand using this or a mold molded with the resin-coated sand may decrease. is there. If a large amount of an emulsified colloid protective agent is used for the purpose of stabilizing the emulsion or suspension, the heat resistance and moisture resistance, which are the original characteristics of the phenol resin, may decrease, and it may be difficult to obtain a high mold strength at the same time. . Therefore, as a solution to these problems, a small amount of polyvinyl alcohol is added to the initial condensate of the resolization reaction of a phenol resin as a colloid protective agent, and then hexamethylenetetramine is added thereto.
Method 5 is useful. The phenol resin emulsion or suspension obtained by this method has excellent storage stability, and since the substantial content of phenol resin in the emulsion or suspension is higher than that obtained by other methods, the resin coated amount can be reduced with a small amount of resin. Since the sand can be adjusted and the strength of the mold using this is high, it is most suitable as a binder for molds. In preparing the phenol resin emulsion or suspension obtained by this method, gum arabic, hydroxyethyl cellulose, hydroxymethyl cellulose, casein, acrylamide or the like can be used as a colloid protective agent for the resol type phenol resin, in addition to polyvinyl alcohol. It is also possible to use a mixture of formalin and ammonia water as the emulsifier instead of hexamethylenetetramine. Further, in producing a resin coated sand using this phenol resin emulsion or suspension, it is more preferable to add 0.1 to 5 parts by weight of a silane coupling agent to the phenol resin solid content of this emulsion or suspension. Examples of the type of silane coupling agent include γ-aminopropylalkoxysilane (γ-aminopropyltriethoxysilane), glycidoxypropyltrimethoxysilane, epoxycyclohexylsilane and ethyltrimethoxysilane. The production of a resin coated sand using a phenol resin emulsion or a suspension can be carried out by a method similar to the case of a conventional resin coated sand for shell mold molding using a novolac resin or a solid resole resin. Therefore, it is not necessary to install new equipment or equipment. That is, 100 parts by weight of molding sand which has been heated to 100 to 180 ° C. in advance is put into, for example, a speed mixer, and 0.5 to 10 parts by weight of a phenol resin emulsion or suspension is added to the molding sand to start kneading. . As the kneading progresses, water in the emulsion or suspension evaporates and the sand temperature of the kneading sand decreases. When the sand temperature decreases to the fusion point of the phenol resin, the kneaded sand changes to a dry state (collapse). Therefore, 0.1 to 5 parts by weight of a lubricant such as calcium stearate or zinc stearate is added to and mixed with the foundry sand, and when the sand temperature of the kneading sand reaches 70 to 80 ° C, the sand is discharged from the mixer and the resin is removed. Get the coated sand. During the production of the resin-coated sand, additives such as red iron oxide may be added depending on the properties required of the resin-coated sand or a mold molded using the resin-coated sand. The resin-coated sand produced in this manner hardly causes blocking, and has characteristics of low odor and high strength.

The present invention will be described below by way of examples. [Example 1] Phenol 400 g, 42% formalin 5
16 g was charged into a reaction vessel, and 25% ammonia water 73.
6 g was added and reacted at 60 ° C. for 3 hours. 1.1 × 10
^FourDegas under reduced pressure of Pa until the temperature of the reaction product rises to 70 ° C.
Concentrate water to remove the initial condensate of resol type phenolic resin.
Obtained. Weight average molecular weight of this resol type phenol resin
Was measured using a GPC device manufactured by Tosoh. polystyrene
The reduced weight average molecular weight was 650. Next to this resin
Polyvinyl chloride with a saponification degree of 88 mol% and an average degree of polymerization of 1,700
Add 108 g of 7.5% aqueous rucohol solution to homogenize
After stirring, it was cooled to room temperature. Water-in-oil type water dispersibility
A resin mixture without was obtained. 40% to this resin mixture
Add 50 g of hexamethylenetetramine aqueous solution and stir
Was. Oil-in-water type fine particle size phenolic resin aqueous emulsion
I got it. Nonvolatile of this phenol resin emulsion
When the components were measured by treatment at 105 ° C for 3 hours, it was 4
It was 7% by weight. Of this phenol resin emulsion
Add 1.0 parts by weight of silane coupling agent per solid content
It was added as a binder for mold making. Enshu Iron Works Hot Co
Using a speed mixer for the
For 100 parts by weight (8 kg) of heated flattery sand
And 4.3 weight of the phenol resin emulsion obtained above
Parts (344 g) were added. Stir after kneading for 2 minutes
Add 0.1 parts by weight of calcium phosphate to the foundry sand
After further kneading, sand was discharged and cooled to room temperature. Fusing point 1
The resin coated sand of 03 degreeC was obtained. Dama or damp
There is no generation, resin coat with normal novolac resin
It had the same appearance as the dead sand. Using a heating mold
Test piece of 10 x 10 x 60 mm at 250 ℃, 60
Molding was performed under the condition of second firing. When the bending strength was measured,
6.4 x 10⁶The value of Pa is shown. Also this resin
Ted sand in a container at 30 ℃ and 70% humidity for 1 week
No blocking occurred when left to stand. [Example 2] 400 g of phenol, 42% formalin 4
56 g was charged into a reaction vessel, and 25% ammonia water 73.
6 g was added and reacted at 60 ° C. for 3 hours. 1.1 × 10
Decompress under reduced pressure of 4 Pa until the temperature of the reaction product rises to 70 ° C.
Concentrate water to remove the initial condensate of resol type phenolic resin.
Obtained. Weight average molecular weight of this resol type phenol resin
Was measured using a GPC device manufactured by Tosoh. polystyrene
The reduced weight average molecular weight was 600. Ken to this resin
Polyvinyl acetate with a degree of conversion of 88 mol% and an average degree of polymerization of 1,700
Add 108 g of 7.5% aqueous rucol solution and stir evenly
Then, it was cooled to room temperature. 40% Hexame of Example 1
42% Formalin instead of Tylene Tetramine aqueous solution
42.8 parts by weight and 25% ammonia water 27.2 parts by weight
100 g of the above mixture was added and stirred. Similar to Example 1
A small particle size phenolic resin emulsion was obtained. Implementation
For mold making by adding silane coupling agent as in Example 1.
It was used as a binder. By the same method and conditions as in Example 1,
Fusing point of 100 ℃ using phenol resin emulsion
I got resin coated sand. No lumps or dampness
It had an appearance similar to that of Example 1. Using a heating mold
Test piece of 10 x 10 x 60 mm at 250 ℃, 60
Molding was performed under the condition of second firing. When the bending strength was measured,
5.7 x 10⁶The value of Pa is shown. Also this resin
Ted sand in a container at 30 ℃ and 70% humidity for 1 week
No blocking occurred when left to stand. [Comparative Example 1] 400 g of phenol, 42% formalin 3
04 g was charged into a reaction vessel, and 25% ammonia water was added to 18.
5 g was added and reacted at 60 ° C. for 1.5 hours. 40%
27.5 g of xamethylenetetramine aqueous solution was added,
And reacted for 1 hour. 40% hexamethylene after completion of reaction
Add 62.5 g of an aqueous tetramine solution and add 9.3 x 10^Four
4:00 until the reaction temperature rises to 90 ° C under reduced pressure of Pa
During concentration, a solid resol type phenol resin was obtained. this
The weight average molecular weight of the solid resol resin is measured in the same manner as in the example.
did. The polystyrene equivalent weight average molecular weight was 560.
Was. As in the example, a speed mixer for hot coating
100 weight of flattery sand that was heated to 140 ℃
To 2 parts by weight of this solid resol resin crushed product
did. After kneading for 2 minutes, cast calcium stearate
Add 0.1 parts by weight to sand and further knead, then remove sand
And cooled to room temperature. Resinous resin with a wet fusion point of 85 ° C
I got the ted sand. 10 × 10 × 6 using a heating mold
A 0 mm test piece is baked at 250 ° C. for 60 seconds.
Molded. The bending strength was measured to be 2.5 x 10⁶
The value of Pa is shown. Also, this resin coated sand
If left in a container at 30 ° C and 70% humidity for 1 week,
It was blocking as it was. [Comparative Example 2] The amount of 42% formalin added was 609 g.
Except that the reaction was the same as in Comparative Example 1 except that
A knoll resin was obtained. The polystyrene equivalent weight average molecular weight is
It was 930. Same as in Comparative Example 1
I got a hand. This resin coated sand is wet
However, the fusion point was 90 ° C.
A test piece of 10 × 10 × 60 mm is heated using a heating die.
Molding was performed under the conditions of firing at 250 ° C. for 60 seconds. Measures bending strength
When set, 3.4 × 10⁶The value of Pa is shown. Also
Use this resin coated sand at a temperature of 30 ° C and a humidity of 70%.
If you leave it in the container for 1 week, it will collapse when it is broken by hand.
I was rocking. [Comparative Example 3] The amount of 42% formalin added was 912 g.
Except that the reaction was the same as in Comparative Example 1 except that
A knoll resin was obtained. The polystyrene equivalent weight average molecular weight is
It was 1,100. Same as Comparative Example 1
I got Dosando. This resin coated sand is wet
There is some lumps, but the fusion point is 87 ° C.
Was. 10 x 10 x 60 mm test pie using a heating mold
The mold was molded under the conditions of firing at 250 ° C. for 60 seconds. Bending strength
Was measured to be 2.0 x 10⁶The value of Pa is shown.
In addition, this resin coated sand is 30 ℃, 70% humidity
If you leave it in the container for 1 week, it will collapse when you unravel it by hand.
I was blocking.

[Table 1] (Note) RCS in the table is an abbreviation for resin coated sand.

According to the present invention, the following effects can be obtained by using the phenol resin emulsion or suspension. (1) A resin coated sand having low odor is obtained. (2) It is possible to manufacture a resin coated sand that can obtain a high strength mold. (3) A resin coated sand having a difficult blocking property can be obtained. (4) When manufacturing the resin coated sand, it is not necessary to install new equipment or devices.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomoyo Muraishi 700 Sukuodarishou, Takasaki City, Gunma Prefecture Inside Gunei Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. A phenol / formaldehyde resin (hereinafter referred to as phenol resin) emulsion or suspension having a weight average molecular weight of 400 to 2,000 is used as a binder.
Add 0.1 to this emulsion or suspension.
-5% by weight of a silane coupling agent was used as a binder, and 0.5 to 10 parts by weight of a binder was added to 100 parts by weight of molding sand heated to 100 to 180 ° C to obtain a casting. A method for producing a resin coated sand obtained by coating a sand surface.