KR20200120590A - Water-soluble core material and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a water-soluble core material and a method for preparing the same. According to the present invention, provided is a method for preparing a water-soluble core material, which comprises the steps of: (a) preparing a water-soluble inorganic binder; (b) preparing a mixture by mixing the water-soluble inorganic binder in an inorganic metal oxide; (c) injecting or pressing the mixture to prepare a core material; (d) preparing a sealant; and (e) coating the sealant on the surface of the core material. Accordingly, the present invention may provide a water-soluble core material prepared thereby.

Description

Water-soluble core material and manufacturing method thereof TECHNICAL FIELD

The present invention relates to a water-soluble core material and a method for manufacturing the same, and more specifically, it serves as a mold for molding a product or a core material for molding a hollow shape inside the product, and after product molding, it is easily separated from the product and It relates to a removable water-soluble core material and a method of manufacturing the same.

Among the fiber-reinforced composite parts used in the aviation, automobile, leisure and sports fields, there are many hollow structures, so in order to realize this shape, be sure to insert the core material inside and then pressurize it from the outside to form or blaze. It must be molded by pressing it from the inside to the outside using a bladder.

As described above, the water soluble core material is installed inside the mold and used to form a space in the mold that matches the shape of the water soluble core. That is, after the water-soluble core is installed inside the mold, the molten metal is injected into the mold to form a space that matches the shape of the water-soluble core.

The conventional core material did not satisfy all of the required characteristics such as heat resistance, dimensional stability, collapse and strength due to the characteristics of the material, but only partially satisfied it.

Among them, the CO ₂ type is excellent in heat resistance and strength, but the disintegration property is extremely poor, the green sand type lacks heat resistance and strength, and the resin type has a problem in heat resistance, causing problems such as seizure.

In addition, the core material produced using NaCl is used for die casting and gravity casting, but if the thickness of the core is thin or the structure is complex, the pores of the core shrink and cracks occur during casting. In particular, the core could be destroyed during pressure die casting.

In order to compensate for this, seizure was prevented by forming a coating film on the surface with a heat-resistant coating material, and collapsing properties were improved after casting by mixing and molding pitch or sawdust.

However, when the heat resistance by coating is improved, the air permeability is often lowered, and when the coating film is insufficient, there is a problem that it may be seized, and when the pitch or sawdust is mixed and molded, the amount of gas generated from the core increases rapidly.

Accordingly, there is a need to develop a core material with improved strength and improved seizure without lowering the air permeability.

In order to solve the above problems, the present invention serves as a core material so that a product with a hollow inside or a product that cannot be molded with a general mold can be molded among the fiber-reinforced plastic composite field. It is to provide a water-soluble core material that can be separated and removed from and a method for manufacturing the same.

In order to solve the above problems, a method of manufacturing a water-soluble core material according to an embodiment of the present invention includes the steps of: (a) preparing a water-soluble inorganic binder; (b) preparing a mixture by mixing the water-soluble inorganic binder with an inorganic metal oxide; (c) injecting or pressing the mixture to prepare a core material; It is possible to provide a method for manufacturing a water-soluble core material comprising the steps of (d) preparing a sealant and (e) coating the sealant on the surface of the core material.

Here, the step (a) is characterized in that a water-soluble inorganic binder is prepared by mixing two or more of monosodium phosphate, sodium tetraborate, and magnesium sulfate with water.

In addition, the step (a) is characterized in that to prepare a water-soluble inorganic binder by mixing 340 to 360 parts by weight of monobasic sodium phosphate, 18 to 28 parts by weight of sodium tetraborate, and 138 to 158 parts by weight of magnesium sulfate to 400 parts by weight of water. do.

In addition, in the step (a), the temperature of the water is 45 to 55°C, and the mixture is prepared by mixing for 8 to 12 minutes.

In addition, in step (b), when injection molding is performed in step (c), 30 to 35 parts by weight of the water-soluble inorganic binder is mixed with 100 parts by weight of the inorganic metal oxide to prepare a mixture.

In addition, the step (b) is characterized in that the mixture is prepared by mixing 10 to 15 parts by weight of the water-soluble inorganic binder to 100 parts by weight of the inorganic metal oxide when the pressure molding is performed in the step (c).

In addition, the step (c) is characterized in that the mixture is press-molded to produce a core material having a molding density of 1.8 to 2.2 g/cm ³ .

In addition, step (d) is a step of slowly adding and dissolving polyvinyl alcohol (PVA) to water to prepare a solution; Cooling the solution and preparing a sealant by mixing ethyl alcohol with the solution may be included.

In addition, it is possible to provide a water-soluble core material manufactured by the method of manufacturing a water-soluble core material according to an embodiment of the present invention.

The water-soluble core material and its manufacturing method according to the embodiment of the present invention as described above are to prepare a water-soluble core material using an inorganic binder and a ceramic powder, and use a water-soluble sealant to prevent the resin from penetrating into the material during molding. By being manufactured by coating, it serves as a mold for molding a product or a core material for forming a hollow shape inside the product, and can be easily separated and removed from the product after product molding.

In the case of manufacturing a composite material using such a water-soluble core material, the manufacturing cost is relatively inexpensive compared to the conventional molding methods such as RIM, RTM, and Autoclave, which are commercialized in the manufacture of composite materials, so that the competitiveness of producing a prototype can be secured.

In addition, since the manufacturing and shape can be changed in various ways compared to the conventional core material and mandrel, a desired shape can be implemented, and weight reduction can be maximized.

In addition, since it is water-soluble, it is an eco-friendly material, and separate costs may not be incurred when removing the core material.

Furthermore, it is expected that the water-soluble core material manufactured according to the present invention can be usefully used in manufacturing a hollow composite product having a shape that is difficult to remove a fuel tank and an inner mandrel.

1 is a flowchart sequentially showing a method of manufacturing a water-soluble core material according to an embodiment of the present invention.
2 is a flowchart sequentially showing step S40 of FIG. 1;
3 is a graph of the average results of compressive strengths of Examples 1 to 5 and Comparative Example 1 of the present invention.
4 is a graph of the average results of compressive strengths of Examples 6 to 10 and Comparative Example 2 of the present invention.
5 is a graph showing the average results of the flexural strengths of Examples 1 to 5 and Comparative Example 1 of the present invention.
6 is a graph of the average result of the flexural strength of Examples 6 to 10 and Comparative Example 2 of the present invention.

The present invention can be modified in various ways and may have various forms, and specific embodiments will be described in detail in the text. However, this is not intended to limit the present invention to a specific form of disclosure, it is to be understood as including all changes, equivalents, or substitutes included in the spirit and scope of the present invention.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "include" or "have" are intended to designate that a combination of features, numbers, steps, components, etc. described in the specification exists, but one or more other features or numbers, It is to be understood that the presence or addition possibility of combinations of steps, components, and the like is not excluded in advance.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in this application. Does not.

Here, repeated descriptions, well-known functions that may unnecessarily obscure the subject matter of the present invention, and detailed descriptions of configurations are omitted. Embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

The present invention relates to a water-soluble core material and a method of manufacturing the same, and more specifically, to prepare a water-soluble core material using an inorganic binder and a ceramic-based powder, and coat the surface with a water-soluble sealant so that the resin does not penetrate the material during molding. The main content is a water-soluble core material that can be used as a mold for molding a product or a core material for forming a hollow shape inside the product, and a water-soluble core material that can be easily separated and removed from the product after product molding, and its manufacturing method.

Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 6.

1 is a flowchart sequentially showing a method of manufacturing a water-soluble core material according to an embodiment of the present invention, and FIG. 2 is a flowchart sequentially showing step S40 of FIG. 1.

Referring to FIG. 1, a method of manufacturing a water-soluble core material according to an embodiment of the present invention includes preparing a water-soluble inorganic binder (S10), preparing a mixture by mixing an inorganic metal oxide with a water-soluble inorganic binder (S20), and It may include injecting or pressing molding to prepare a core material (S30), producing a sealant (S40), and coating a sealant on the surface of the core material (S50).

First, the step of preparing a water-soluble inorganic binder (S10) is a step of preparing a water-soluble inorganic binder by mixing a water-soluble metal salt with water. Two or more of sodium monophosphate, sodium tetraborate, and magnesium sulfate are mixed with water to A binder can be prepared.

Here, the monobasic sodium phosphate is sodium hydrogen phosphate, the formula NaH ₂ PO ₄ ·nH ₂ O (n = 0, 1, 2), the aqueous solution (1→20) is weakly acidic, and the pH is 4.1. Dihydrated salts at 41°C or lower, monohydrated salts at 41-58°C, and anhydrous salts at 100°C can be obtained from the aqueous solution. In addition, it is easily soluble in water, but not in alcohol and ether. When heated, it becomes metaphosphate, has a slightly deliquescent property, and has a buffering function.

Such monobasic sodium phosphate may be used in 340 to 360 parts by weight based on 400 parts by weight of water in step S10, and it is preferable to use 350 parts by weight.

This is because if the monobasic sodium phosphate is less than 340 parts by weight, the physical properties of the core material may be deteriorated, and if it exceeds 360 parts by weight, it is not dissolved in water and may be eluted.

Sodium tetraborate has the formula Na ₂ B ₄ O ₇ and is sometimes called sodium diborate (in this case, sodium tetraborate refers to Na ₂ O·4B ₂ O ₃ ), and the 10 hydrate is called borax. , Is one of the components of the buffer.

This sodium tetraborate may be used in 18 to 28 parts by weight based on 400 parts by weight of water in step S10, and it is preferable to use 23 parts by weight.

This is because when sodium tetraborate is less than 18 parts by weight, the physical properties of the core material may be deteriorated, and when it exceeds 28 parts by weight, it is not dissolved in water and may be eluted.

In addition to anhydrous salts, magnesium sulfate has many hydrous salts, and usually magnesium sulfate refers to hexahydrate, and this is called fsom salt, and natural ones are especially called saris salts (瀉利鹽). The chemical formula is MgSO ₄ , and the anhydrous salt is a white crystalline powder with a melting point of 1,185°C and a specific gravity of 2.66. It dissolves 26.9g at 0℃ and 68.3g at 100℃ in 100g of water, and slightly soluble in alcohol. The state of the hydrous salt varies depending on the temperature at which crystals are precipitated from the saturated aqueous solution.

Such magnesium sulfate may be used in 138 to 158 parts by weight based on 400 parts by weight of water in step S10, and 148 parts by weight is preferably used.

This is because if magnesium sulfate is less than 138 parts by weight, physical properties may be deteriorated, and if it exceeds 158 parts by weight, it is not dissolved in water and may be eluted.

In addition, in step S10, it is preferable to prepare a water-soluble inorganic binder by mixing monobasic sodium phosphate, sodium tetraborate, magnesium sulfate and water, that is, 350 parts by weight of monobasic sodium phosphate and 23 parts by weight of sodium tetraborate in 400 parts by weight of water. And it is more preferable to prepare a water-soluble inorganic binder by mixing 148 parts by weight of magnesium sulfate.

In addition, the temperature of the water in step S10 may be 45 to 55 ℃, it is more preferable to use water of 50 ℃. This is because monobasic sodium phosphate, sodium tetraborate, and magnesium sulfate dissolve most efficiently within the temperature range of the water.

In addition, step S10 may be mechanically stirred for 8 to 12 minutes by mixing each composition at the same mixing ratio as described above, and it is preferable to stir for 10 minutes.

At this time, if the stirring time is less than 8 minutes, the monobasic sodium phosphate, sodium tetraborate, and magnesium sulfate may not all be dissolved, and if it exceeds 12 minutes, further stirring is inefficient as it is already dissolved.

The step of preparing a mixture by mixing an inorganic metal oxide with a water-soluble inorganic binder (S20) is a step of preparing a mixture by mixing a water-soluble inorganic binder with a ceramic-based inorganic metal oxide according to a method in which the core material is formed in step S30.

Here, the inorganic metal oxide preferably includes at least one of aluminum oxide powder, magnesium oxide powder, and titanium dioxide powder, but is not limited thereto, and may further include various inorganic metal oxides.

First, when the core material is injection-molded in step S30, step S20 can prepare a mixture by mixing 30 to 35 parts by weight of a water-soluble inorganic binder with 100 parts by weight of an inorganic metal oxide, and a water-soluble inorganic binder 35 with 100 parts by weight of the inorganic metal oxide. It is more preferable to mix parts by weight.

At this time, when the content of the water-soluble inorganic binder is less than 30 parts by weight, curability may be deteriorated during molding, and when it exceeds 35 parts by weight, the water-soluble inorganic binder may be eluted during molding.

In addition, when the core material is press-molded in step S30, step S20 may prepare a mixture by mixing 10 to 15 parts by weight of a water-soluble inorganic binder with 100 parts by weight of an inorganic metal oxide, and a water-soluble inorganic binder 15 with 100 parts by weight of the inorganic metal oxide. It is more preferable to mix parts by weight.

At this time, if the content of the water-soluble inorganic binder is less than 10 parts by weight, curability may decrease during molding, and if it exceeds 15 parts by weight, the water-soluble inorganic binder may be eluted during molding.

The step of manufacturing a core material by injecting or pressing the mixture (S30) is a step of manufacturing a core material by injecting the mixture into an injection-type molding mold and molding, or injecting it into an injection-type molding mold and pressing with a press.

When the press-molding take place in step S30, the molded density can be produced with the core material from 1.8 to 2.2g / cm ^3, the molding density is preferably made of a core material 2.0 g / cm ^3.

This is because when the molding density of the core material is less than 1.8 g/cm ³ , the shape of the specimen is not well maintained, and when it exceeds 2.2 g/cm ³ , the molding mold may be deformed due to high pressure.

In addition, step S30 may dry the prepared core material after molding.

In this case, drying may be performed first at room temperature (20±5°C) for 24 hours, followed by hot air drying at 60°C for 48 hours.

In the hot air drying after drying at room temperature as described above, it is preferable to dry the core material by dividing it into first and second steps as described above, since only the surface of the core material is dried and not the inside when hot air drying is performed immediately.

The step of preparing a sealant (S40) is a step of preparing a sealant to coat the surface of the core material, and referring to FIG. 2, a step of preparing a solution by slowly adding and dissolving polyvinyl alcohol (PVA) to water ( S41), cooling the solution (S42), and preparing a sealant by mixing ethyl alcohol with the solution (S43) may be included.

First, in step S41, polyvinyl alcohol (PVA) is slowly added and dissolved to prepare a solution. Here, polyvinyl alcohol may be dissolved in 10 to 12 parts by weight in 100 parts by weight of water, and it is preferable to dissolve in 12 parts by weight.

At this time, if the polyvinyl alcohol is dissolved in less than 10 parts by weight, the sealant function may be deteriorated, and if it is dissolved in more than 12 parts by weight, the viscosity of the sealant may increase, making it difficult to coat the core material.

In order to dissolve the polyvinyl alcohol, the water temperature is preferably 80 to 85°C, and more preferably 80°C.

Step S42 may cool the solution prepared in step S41 to room temperature. This is to prevent vaporization of ethyl alcohol to be mixed later.

In step S43, a sealant may be prepared by mixing ethyl alcohol with the solution cooled in step S42. Mixing ethyl alcohol in this way allows the sealant to dry quickly when the sealant is coated on the core material.

In step S43, 25 to 35 parts by weight of ethyl alcohol may be further added to the solution and mixed to prepare a sealant, and it is preferable to prepare a sealant by adding 30 parts by weight.

At this time, if the amount of ethyl alcohol is less than 25 parts by weight, the effect of shortening the drying time of the sealant is insignificant, and if it exceeds 35 parts by weight, it may react with PVA to cause gelation of the sealant.

In the step of coating the sealant on the surface of the core material (S50), a final water-soluble core material may be prepared by coating the sealant prepared in the step S40 on the surface of the core material prepared in the step S30.

Step S50 is a coating method, and a sealant may be coated on the surface of the core material using spraying and brushing.

Specifically, in step S50, the sealant may be coated by first applying the sealant to the surface of the core material and drying it for 3 hours or more, and then applying the sealant to drying.

A water-soluble core material according to an embodiment of the present invention can be provided through the above manufacturing method.

The water-soluble core material thus prepared has a compressive strength of 4 MPa or more, water solubility of 50 g/min·m ² or more, and a coefficient of thermal expansion of 5×10 ^-6 mm/mm·℃ or less.

As described above, the water-soluble core material and its manufacturing method according to the embodiment of the present invention prepare a water-soluble core material using an inorganic binder and ceramic powder, and make the surface water-soluble so that the resin does not penetrate the material during molding. By being manufactured by coating with a sealant, etc., it serves as a mold for molding a product or a core material for forming a hollow shape inside the product, and can be easily separated and removed from the product after product molding.

In the case of manufacturing a composite material using such a water-soluble core material, the manufacturing cost is relatively inexpensive compared to the conventional molding methods such as RIM, RTM, and Autoclave, which are commercialized in the manufacture of composite materials, so that the competitiveness of producing a prototype can be secured.

In addition, since the manufacturing and shape can be changed in various ways compared to the conventional core material and mandrel, a desired shape can be implemented, and weight reduction can be maximized.

In addition, since it is water-soluble, it is an eco-friendly material, and separate costs may not be incurred when removing the core material.

Furthermore, it is expected that the water-soluble core material manufactured according to the present invention can be usefully used in manufacturing a hollow composite product having a shape that is difficult to remove a fuel tank and an inner mandrel.

Hereinafter, the present invention will be described in more detail by way of examples.

However, the following examples are only illustrative of the present invention, and the contents of the present invention are not limited by the following examples.

In addition, the embodiments of the present invention described below can be implemented by various substitutions, modifications, and changes within the scope of the technical spirit of the present invention, and such implementation can be implemented in the technical field to which the present invention belongs from the description of the above-described embodiment. This can be easily implemented by experts.

[ Example ]

[Example 1]

A water-soluble inorganic binder was prepared by mixing 350 parts by weight of sodium monophosphate and 23 parts by weight of sodium tetraborate in 400 parts by weight of water at 50°C, and 15 parts by weight of a water-soluble inorganic binder was mixed with 100 parts by weight of an inorganic metal oxide to prepare a mixture. , A core material having a molding density of 2.0 g/cm ³ was prepared by injecting the mixture into an injection molding mold and molding by pressure.

[Example 2]

It was prepared in the same manner as in Example 1, except that 350 parts by weight of sodium monophosphate and 148 parts by weight of magnesium sulfate were mixed with 400 parts by weight of water to prepare a water-soluble inorganic binder.

[Example 3]

It was prepared in the same manner as in Example 1, except that a water-soluble inorganic binder was prepared by mixing 148 parts by weight of magnesium sulfate and 23 parts by weight of sodium tetraborate to 400 parts by weight of water.

[Example 4]

It was prepared in the same manner as in Example 1, except that a water-soluble inorganic binder was prepared by mixing 350 parts by weight of monobasic sodium phosphate, 148 parts by weight of magnesium sulfate and 23 parts by weight of sodium tetraborate to 400 parts by weight of water.

[Example 5]

It was prepared in the same manner as in Example 1, except that the mixture was injected and molded into an injection molding mold.

[Example 6]

It was prepared in the same manner as in Example 2, except that the mixture was injected and molded into an injection molding mold.

[Example 7]

It was prepared in the same manner as in Example 3, except that the mixture was injected and molded into an injection molding mold.

[Example 8]

It was prepared in the same manner as in Example 4, except that the mixture was injected and molded into an injection molding mold.

[Comparative Example 1]

A water-soluble inorganic binder was prepared by mixing 350 parts by weight of monobasic sodium phosphate with 400 parts by weight of water at 50°C, and 15 parts by weight of a water-soluble inorganic binder was mixed with 100 parts by weight of an inorganic metal oxide to prepare a mixture, and then the mixture was added to an injection mold. Injected and press-molded to prepare a core material having a molding density of 2.0 g/cm ³ .

[Comparative Example 2]

It was prepared in the same manner as in Comparative Example 1, except that a water-soluble inorganic binder was prepared by mixing 148 parts by weight of magnesium sulfate with 400 parts by weight of water.

[Comparative Example 3]

It was prepared in the same manner as in Comparative Example 1, except that the mixture was injected and molded into an injection molding mold.

[Comparative Example 4]

It was prepared in the same manner as in Comparative Example 2, except that the mixture was injected and molded into an injection molding mold.

[ Experimental example One] Core material Compressive strength analysis

In order to compare the core materials of Examples 1 to 4 and Comparative Examples 1 and 2 and Examples 5 to 8 and Comparative Examples 3 and 4, the compressive strength was measured.

At this time, the compressive strength (MPa) was measured twice in the first and second order, and the average was derived.

The results are shown in Tables 1, 3 and 2, and 4 below.

Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Example 4 One 1.27 2.23 3.50 7.64 2.87 8.91 2 1.91 2.23 3.18 7.96 3.18 8.91 Average 1.59 2.23 3.34 7.80 3.03 8.91 Standard Deviation 0.45 0.00 0.23 0.23 0.22 0.00

Comparative Example 3 Comparative Example 4 Example 5 Example 6 Example 7 Example 8 One 1.74 2.24 5.66 7.26 2.70 13.88 2 1.58 2.05 5.30 8.22 3.01 11.97 Average 1.64 2.15 5.48 7.73 2.86 12.93 Standard Deviation 0.09 0.13 0.25 0.69 0.22 1.35

As can be seen from Tables 1 and 3, it was confirmed that the compressive strength of Examples 1 to 4 was higher than that of Comparative Examples 1 and 2, and the compressive strength of Example 4 was the highest. In addition, as can be seen from Tables 2 and 4, it was confirmed that the compressive strength of Examples 5 to 8 was higher than that of Comparative Examples 3 and 4, and the compressive strength of Example 8 was the highest.

[ Experimental example 2] Core material Flexural strength analysis

In order to compare the core materials of Examples 1 to 4 and Comparative Examples 1 and 2 and Examples 5 to 8 and Comparative Examples 3 and 4, the flexural strength was measured.

At this time, the flexural strength (MPa) was measured twice in the first and second order in the case of pressure molding, and three times in the first, second, and third order in the case of injection molding, and the average was derived.

The results are shown in Tables 3, 5 and 4, and 6 below.

At this time,-means the intensity value is too low to measure.

1 in comparison Comparative Example 2 Example 1 Example 2 Example 3 Example 4 One 4.19 - 5.27 10.15 5.54 15.96 2 4.58 3.69 5.27 8.74 5.60 14.51 Average 4.39 3.69 5.27 9.45 5.57 15.24 Standard Deviation 0.28 0.00 1.00 0.04 1.03

Comparative Example 3 Comparative Example 4 Example 5 Example 6 Example 7 Example 8 One 2.06 3.52 6.02 9.39 7.51 11.87 2 1.86 3.84 6.20 7.91 7.77 11.87 3 1.80 3.73 5.93 7.77 7.77 12.27 Average 1.91 3.70 6.05 8.36 7.68 12.00 Standard Deviation 0.14 0.16 0.14 0.90 0.15 0.23

As can be seen from Table 3 and FIG. 5, it was confirmed that the flexural strength of Examples 1 to 4 was higher than that of Comparative Examples 1 and 2, and the flexural strength of Example 4 was the highest. In addition, as can be seen from Tables 4 and 6, it was confirmed that the flexural strength of Examples 5 to 8 was higher than that of Comparative Examples 3 and 4, and that the flexural strength of Example 8 was the highest. Therefore, It is believed that the water-soluble core material of the present invention has excellent compressive strength and flexural strength, and thus the strength is improved.

Above, a specific part of the content of the present invention has been described in detail, and for those of ordinary skill in the art, this specific technology is only a preferred embodiment, and the scope of the present invention is not limited thereby It will be obvious. Therefore, it will be said that the practical scope of the present invention is defined by the appended claims and their equivalents.

Claims (4)

(a) preparing a water-soluble inorganic binder;
(b) preparing a mixture by mixing the water-soluble inorganic binder with an inorganic metal oxide;
(c) injecting or pressing the mixture to prepare a core material;
(d) preparing a sealant and
(e) coating the sealant on the surface of the core material,
The step (a),
A water-soluble inorganic binder was prepared by mixing 340 to 360 parts by weight of monobasic sodium phosphate, 18 to 28 parts by weight of sodium tetraborate and 138 to 158 parts by weight of magnesium sulfate to 400 parts by weight of water,
The step (a),
The temperature of the water is 45 to 55 ℃, prepared by mixing for 8 to 12 minutes,
The step (c),
Dry the prepared core material, but first dry at room temperature and then secondarily dry with hot air drying at 60°C,
The step (c),
The mixture is press-molded to prepare a core material having a molding density of 1.8 to 2.2 g/cm ³ ,
The step (d),
Preparing a solution by slowly adding and dissolving polyvinyl alcohol (PVA) to water;
Cooling the solution and
Comprising the step of preparing a sealant by mixing ethyl alcohol with the solution Method for producing a water-soluble core material.
The method of claim 1,
The step (b),
When the injection molding is performed in the step (c), 30 to 35 parts by weight of the water-soluble inorganic binder is mixed with 100 parts by weight of the inorganic metal oxide to prepare a mixture.
The method of claim 1,
The step (b),
The method for producing a water-soluble core material, characterized in that when performing pressure molding in step (c), a mixture is prepared by mixing 10 to 15 parts by weight of the water-soluble inorganic binder to 100 parts by weight of the inorganic metal oxide.
A water-soluble core material manufactured by the manufacturing method of any one of claims 1 to 3.

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