Thin film structure and method for manufacturing the same

Abstract

To easily manufacture a thin, hollow structure. [Solution] A thin film structure is provided, consisting of a water-insoluble coating 11a formed on the outer surface 15 of a model 14 made of magnesium material, which is removed by dissolving the model 14 in water.

Description

Technical Field

[0001] This invention relates to a thin film structure having a hollow portion inside and a method for manufacturing the same.

Background Art

[0002] Structures having a hollow structure are used in various applications, such as passing through the inside of the hollow structure or filling the inside of the hollow structure. The industries to which they are applied range widely, from applications such as the aerospace industry and the automotive industry to the medical field used for the human body. Structures having a hollow structure are often required to have durability while maintaining the internal hollow structure, and various manufacturing methods have been studied.

[0003] Patent Document 1 proposes a composite core composed of a combination of a metal core (A) having a melting point of 500 degrees or more and a metal core (B) having a melting point of 250 degrees or less, and a method for manufacturing a hollow resin molded product using this composite core.

[0004] Patent Document 2 discloses a method of forming a core with a water-soluble resin such as polyvinyl alcohol and using a water-insoluble resin such as nylon resin as the resin for injection molding, and removing the core by dissolving it with a medium such as water after molding.

[0005] Patent Document 3 reports that by using a magnesium alloy or an aluminum alloy for the core (water-soluble core) and manufacturing it by heat spraying or sintering, a high porosity is formed (Patent Document 3

[0011] ), and the water-soluble core rapidly dissolves from the pores.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

[0007] However, in Patent Document 1, the difference in melting points causes the metal core (B) to melt, leaving only the metal core (A). However, since it is formed using a mold, it is not possible to manufacture thin-walled structures, and its use is limited to thick structures.

[0008] Furthermore, when a water-soluble resin, such as that described in Patent Document 2, was used as the core, applying high pressure during resin injection in injection molding could cause the core to break due to insufficient strength.

[0009] The objects described in Patent Document 3 require the formation of magnesium alloys or aluminum alloys with high porosity (Patent Document 3

[0011] to

[0012] ), but there was a problem that the surface of the molded product became rough due to the irregularities formed on the surface of the core. These irregularities can cause fracture when trying to create thin structures, so it could only be applied to objects with thickness.

[0010] Therefore, the purpose of this invention is to easily manufacture a thin, hollow structure. [Means for solving the problem]

[0011] This invention is It consists of a water-insoluble coating formed on the outer surface of a model made of magnesium material. The above problem was solved by the first solution, which is a thin-film structure obtained by dissolving the aforementioned model in water and removing it.

[0012] Furthermore, this invention, The first solution, which involves a coated model in which a non-water-soluble coating is formed on the outer surface of a model made of magnesium material, enables the manufacture of a thin-film structure. The thin-film structure is obtained by removing the model from this coated model.

[0013] Furthermore, this invention, The above problem was solved by a third solution, which is a thin film structure consisting of a water-insoluble coating and having a hollow structure, with a residue made of magnesium material on the inner surface of the hollow structure.

[0014] Furthermore, this invention, The model manufacturing process for creating models made from magnesium material, A coating formation step is performed to form a water-insoluble coating on the outer surface of the aforementioned model, thereby creating a coated model. A model removal step involves immersing the coated model in an aqueous solution to dissolve and remove the model while leaving the coating intact, The above problem was solved by a fourth solution for manufacturing a thin-film structure, which includes the above.

[0015] Furthermore, in the fourth solution, this invention A fifth solution can be adopted, wherein the water-insoluble coating is a metallic material that dissolves more slowly in the aqueous solution than the magnesium material.

[0016] Furthermore, in the fourth solution, this invention A sixth solution can be adopted in which the water-insoluble coating is made of ceramics.

[0017] Furthermore, in the fourth solution, this invention A seventh solution can be adopted, wherein the water-insoluble coating is made of a water-insoluble organic material. [Effects of the Invention]

[0018] According to the present invention, thin film structures can be manufactured using a simple method. [Brief explanation of the drawing]

[0019] [Figure 1] Cross-sectional view showing an embodiment of the thin film structure according to this invention [Figure 2] Cross-sectional view showing a mold for obtaining the thin film structure shown in FIG. 1 [Figure 3] Cross-sectional view showing an example of a state in which a film is formed on the outer surface of the mold of FIG. 2 [Figure 4] Cross-sectional view showing an example of a state in which an exposed portion is formed from FIG. 3 [Figure 5] View showing an example of the situation of immersing in an aqueous solution to remove the mold [Figure 6] Photograph of a copper-plated mold during the manufacturing process shown in the examples [Figure 7] Photograph of a thin film structure made of a copper thin film obtained in the examples

Mode for Carrying Out the Invention

[0020] The thin film structure 10 according to this invention will be described together with the procedure of the manufacturing method. Hereinafter, the "manufacturing method of the thin film structure according to an embodiment of the present invention" may be referred to as "this manufacturing method". The thin film structure 10 is a structure that has a hollow structure part (hollow part 20) inside and forms an outer shape with a film.

[0021] The thin film structure 10 according to an embodiment of the present invention is composed of a water-insoluble film formed on the outer surface of a mold made of a magnesium material, and is obtained by dissolving and excluding the mold in water. However, when the mold is completely excluded, the completed thin film structure 10 is only the film 11, and it is difficult to simply recognize the characteristics by this manufacturing method. However, the thin film structure 10 having a shape that cannot be manufactured by the method of the present invention can have its shape itself as a characteristic.

[0022] Figure 1 shows a cross-sectional view of an embodiment of this thin film structure 10. The thin film structure 10 consists of a water-insoluble coating 11 and has a hollow structure portion (hollow portion 20). The coating 11 has an outer surface 12 facing outwards (the side not in contact with the hollow portion 20) and an inner surface 13 facing inwards (the side in contact with the hollow portion 20). The hollow portion 20 is connected to the outer surface 12 side via a missing portion 16.

[0023] This manufacturing method includes a model manufacturing step, a coating formation step, and a model removal step. In this manufacturing method, it is preferable to perform the model manufacturing step, the coating formation step, and the model removal step in this order. With this configuration, a thin film structure can be manufactured by a simple method. Furthermore, within the scope that does not impair the significance of the present invention, steps such as the following partial coating removal step and cleaning step may be performed before, during, or after these steps as appropriate.

[0024] [Model manufacturing process] In a model manufacturing process according to one embodiment of the present invention, a model made of magnesium material is produced. That is, in a model manufacturing process according to one embodiment of the present invention, a model 14 with the shape corresponding to the hollow portion 20 of the thin film structure 10 to be manufactured is produced. An example of the shape of the model 14 when manufacturing the thin film structure 10 of Figure 1 is shown in Figure 2. This model 14 is made of magnesium material. In this specification, "magnesium material" means a material that contains magnesium as its main component. Magnesium material includes magnesium, magnesium alloys, and materials that combine magnesium or magnesium alloys with materials other than metals and have magnesium as their main component. Here, materials other than magnesium include, for example, carbon. Note that when simply referred to as magnesium, it means magnesium with a magnesium ratio of 99% by mass or more that can be considered almost pure metal. Also, in this specification, "magnesium alloy" means "an alloy that contains magnesium as its main component." To contain magnesium as its main component or to have magnesium as its main component means that magnesium accounts for 50% or more of the total material by mass ratio or molar ratio. Materials other than metals include, for example, reinforcing materials such as resin fibers.

[0025] The method for manufacturing the model 14 from magnesium material is not particularly limited. General processing methods for magnesium alloys, such as casting, extrusion, forging, and machining, can be used. However, the advantage of using this manufacturing method is particularly evident in its ability to produce large and complex thin-film structures 10. Even large structures that cannot be manufactured with general 3D printers, or structures with intricate internal structures that are difficult to remove from molds, can be manufactured using the method of this invention. When the thin-film structure 10 has such a complex shape, for example, the rough shape of the model 14 can be formed by casting, and then the details can be shaped by drilling or filing, making it easier to manufacture a model 14 for the intricately shaped thin-film structure 10.

[0026] As the magnesium material, a decomposable magnesium alloy that dissolves rapidly in an aqueous environment (aqueous solution) is preferably used. Although it is basically possible to use it even if the dissolution rate is not sufficient, the time required in the model removal process described later becomes too long, so a certain degree of dissolution rate is necessary from the standpoint of manufacturing efficiency. A preferred decomposable magnesium alloy is one that has a dissolution rate of (mg / cm³) per day in a 2% by mass aqueous solution of sodium chloride at room temperature. 2 The concentration ( / day:mcd) is preferably 50mcd or more, more preferably 75mcd or more, even more preferably 100mcd or more, and particularly preferably 125mcd or more. A faster dissolution rate is not a particular problem. In this specification, "room temperature" refers to "15°C to 25°C".

[0027] Specific examples of such decomposable magnesium alloys include magnesium alloys containing either aluminum or copper, or both (first-order magnesium alloys), and magnesium alloys containing aluminum, manganese, and nickel and / or copper (second-order magnesium alloys). Using first-order magnesium alloys and / or second-order magnesium alloys as decomposable magnesium alloys is particularly preferable in terms of decomposition performance.

[0028] The Al content of the above-mentioned first magnesium alloy is preferably 7.0% by mass or more. If the Al content is too low, the fluidity of the molten metal during casting will decrease, and the amount of Cu-Al-Mg intermetallic compounds that dissolve easily in aqueous solution will be insufficient. However, if it is 7.0% by mass or more, sufficient fluidity and an amount of Cu-Al-Mg intermetallic compounds can be ensured. On the other hand, the Al content is preferably 13.0% by mass or less. If the Al content is too high, the amount of Cu-Al-Mg intermetallic compounds will be excessive, and if it exceeds 13.0% by mass, the Cu-Al-Mg intermetallic compounds will hinder the progress of Mg dissolution, causing the dissolution rate to decrease rapidly.

[0029] The above-mentioned first magnesium alloy may contain Mn. However, the Mn content is preferably less than 0.10 mass%. This is because an increase in the Mn content leads to the inclusion of Mn in the Cu-Al-Mg intermetallic compound, which tends to become coarser. When the Cu-Al-Mg intermetallic compound becomes coarser, the dissolution rate decreases.

[0030] The Cu content of the above-mentioned first magnesium alloy is preferably 4.5% by mass or more. By adding Cu, a Cu-Al-Mg intermetallic compound with a noble potential is formed in model 14. The potential difference between α-Mg and the Cu-Al-Mg intermetallic compound promotes the depletion of α-Mg by macrocell corrosion, thereby improving the dissolution rate. In ordinary Mg alloys, the dissolution rate tends to decrease when the above-mentioned Al is present, but if the Cu content is 4.5% by mass or more, model 14 can achieve a practical dissolution rate even within the above-mentioned Al content range. In particular, a Cu content of 7.0% by mass or more is more preferable. When the Cu content is 7.0% by mass or more, the amount of Cu-Al-Mg intermetallic compound increases, and it is thought that when strain is applied to model 14, the Cu-Al-Mg intermetallic compound becomes more easily fractured, making the Cu-Al-Mg intermetallic compound phase finer and making it easier to improve the dissolution rate. On the other hand, it is preferable that the Cu content be 13.0% by mass or less. If the Cu content exceeds 13.0% by mass, coarse block-shaped Cu-Al-Mg intermetallic compounds are formed during casting, hindering the progress of Mg dissolution and reducing the effect of improving the dissolution rate through macrocell corrosion caused by the addition of Cu.

[0031] The above-mentioned first magnesium alloy may contain elements other than those listed above as unavoidable impurities. These unavoidable impurities are those that are unintentionally included due to manufacturing or raw material issues. Examples include elements such as Ag, Fe, Ca, Cd, Ga, In, Li, Mm (mischmetal), Ni, Pb, Se, Si, Ti, Y, Zn, and Zr. The amount per element is preferably less than 0.2 mass%, and more preferably less than 0.1 mass%. The lower the amount, the more uncertain factors to consider are eliminated, and it is particularly preferable that the amount is below the detection limit.

[0032] On the other hand, the second magnesium alloy preferably has an Al content of 3.9 mass% or more, and more preferably 7.0 mass% or more. Adding Al improves the strength of the model 14, but if the Al content is less than 3.9 mass%, these effects become insufficient. On the other hand, the Al content is preferably 14.0 mass% or less, and more preferably 13.0 mass% or less. If there is too much Al, the model 14 may become more prone to deformation, which may reduce its strength, and if it exceeds 14.0 mass%, it may become difficult to maintain the shape of the model 14.

[0033] The Mn content of the second magnesium alloy is preferably 0.1% by mass or more. Mn has the effect of removing some elements that are contained as impurities, and if it is too low, the dissolution rate of the alloy will deviate significantly from the value adjusted by Ni and Cu as described later, which may lead to insufficient control. On the other hand, the Mn content is preferably 0.6% by mass or less, and more preferably 0.5% by mass or less. If it is too high, a large amount of intermetallic compounds between Mn and Al, and elemental Mn will precipitate, making the alloy brittle and reducing its strength.

[0034] The second magnesium alloy may contain Zn at a concentration of 1.0 mass% or less. The inclusion of Zn improves the strength of the model 14. Concentrations exceeding 1.0 mass% are undesirable because they result in insufficient ductility, making molding processes for the model 14 itself, such as extrusion and forging, difficult, and also suppressing the dissolution rate. On the other hand, the alloy does not need to contain Zn; it may be present as an unavoidable impurity.

[0035] The secondary magnesium alloy may contain either Ni and Cu, or both. By including a predetermined amount of Ni and / or Cu, the dissolution rate of the alloy in an aqueous environment (aqueous solution) can be arbitrarily adjusted. That is, by including a predetermined amount of Ni and / or Cu in the secondary magnesium alloy, the model 14 made from this secondary magnesium alloy can be quickly dissolved when it is no longer needed. However, although both Ni and Cu contribute to solubility, their influences are different.

[0036] If the second magnesium alloy contains Ni, its content should preferably be 0.01% by mass or more. Although Ni has a greater effect on the dissolution rate than Cu, if it is still less than 0.01% by mass, it becomes difficult to obtain the dissolution effect necessary for a decomposable magnesium alloy. On the other hand, it is preferable that the Ni content be 7.0% by mass or less. Even if it is included in excess, the dissolution rate of model 14 cannot be drastically improved, and the physical properties of model 14 become difficult to control. Also, too much Ni would be too burdensome in terms of cost.

[0037] If the second magnesium alloy contains Cu, its content is preferably 10.0% by mass or less. Even if it contains an excessive amount, it will not significantly improve the dissolution rate of model 14, and the physical properties of model 14 will become difficult to control.

[0038] The above-mentioned first magnesium alloy and second magnesium alloy are just examples of alloys that make up Model 14; any alloy that dissolves rapidly in an aqueous environment (aqueous solution), similar to the first and second magnesium alloys, is not particularly limited.

[0039] [Film formation process] In the coating formation process according to one embodiment of the present invention, a water-insoluble coating 11a is formed on the outer surface 15 of the model 14 to produce a coated model 10a. The coated model 10a according to one embodiment of the present invention is a model 14 made of magnesium material on which a water-insoluble coating 11a has been formed. An example of the state in which a water-insoluble coating 11a has been formed on the outer surface 15 of the model 14 shown in Figure 2 (coated model 10a) is shown in Figure 3.

[0040] As the material for the water-insoluble coating 11a, materials that dissolve more slowly in the aqueous solution than the magnesium material described above, or materials that do not dissolve in aqueous solutions at all (hereinafter collectively referred to as "water-insoluble materials") can be used. Specifically, usable materials include metal materials that dissolve more slowly in aqueous solutions than magnesium materials, ceramics, and water-insoluble organic materials.

[0041] In this specification, "metallic material" refers to a material whose main component is metal, such as alloys and pure metals. "Main component is metal" means that metal makes up 50% or more of the total material by mass or molar ratio. As a "metallic material with a slower dissolution rate in aqueous solution than magnesium," a pure metal or alloy of such pure metal that is electrically nobler than magnesium in the medium (aqueous solution) into which the coating 11a is immersed during the model removal process is suitably used. Examples of pure metals electrically nobler than magnesium in the medium (aqueous solution) into which the coating 11a is immersed during the model removal process include aluminum, zinc, iron, nickel, tin, copper, silver, and gold. When using these metallic materials as the material for the non-water-soluble coating 11a, methods for forming the coating 11a include, for example, electrodeposition or plating. This manufacturing method is particularly suitable for producing works of art that would be too costly to produce from solid materials such as silver or gold. This is because, by manufacturing with a thin-film structure 10 that has a hollow internal structure, it is possible to create works of art by using only solid materials such as silver or gold for the surface coating 11, thereby significantly reducing material costs.

[0042] The ceramics mentioned above refer to inorganic solid materials that are not metallic. Examples of ceramics include solid materials made of non-metallic elements such as silicon and diamond, and inorganic compounds such as metal oxides, metal carbides, and metal nitrides, which are compounds of metals and non-metallic elements. When using inorganic compounds as ceramics, the method used in the coating process is to coat the outer surface 15 of the model 14 with molten ceramics, as in ceramic thermal spray coating, and then cure it by reacting it with heat to form a coating 11a. When using solid materials made of non-metallic elements as ceramics, as will be described later, a liquid organic material and a solid material can be mixed and then coated onto the outer surface 15 of the model 14, and the organic material can be cured to form a coating 11a.

[0043] The above-mentioned water-insoluble organic materials refer to organic materials that do not swell or dissolve in an aqueous environment, or swell or dissolve to a negligible degree, and can maintain the shape of a thin film. Specifically, water-insoluble organic materials include thermoplastic resins such as polyethylene, polypropylene, polyamide, polystyrene, and ABS (acrylonitrile butadiene styrene) resin, thermosetting resins such as polyester, epoxy resin, melamine resin, and urea resin, and rubbers such as butadiene rubber, silicone rubber, and styrene butadiene rubber. When using these water-insoluble organic materials as the material for the water-insoluble coating 11a, a method used to form the coating 11a is to coat it onto the outer surface of the model 14 in a molten or pre-cured state, and then cure it by cooling or heating to form the coating 11a.

[0044] Furthermore, as the water-insoluble material, two or more materials selected from the group consisting of metal materials that dissolve more slowly in aqueous solutions than magnesium materials, ceramics, and water-insoluble organic materials may be used as a mixture. For example, the coating 11a can also be formed by kneading fine powder of metal material or ceramics with resin and then solidifying it. In any case, the coating 11a can be finished as a thin film unless it is removed in the next model removal step.

[0045] The preferred thickness of the coating 11a varies depending on the material used. When the material of the water-insoluble coating 11a is a metallic material that dissolves more slowly in aqueous solution than magnesium, the thickness of the coating 11a is preferably 2 μm or more, and more preferably 10 μm or more. Depending on the type of metal, if it is too thin, it becomes difficult to maintain the shape after removing the model 14, so a certain thickness is necessary to ensure strength. On the other hand, since it is difficult to plate with a thickness exceeding 100 μm, the thickness of the coating 11a is realistically 100 μm or less, preferably 60 μm or less, more preferably 55 μm or less, and even more preferably 50 μm or less.

[0046] If the coating 11a is made of ceramics and / or a water-insoluble organic material, it is preferable that the thickness of the coating 11a be 20 μm or more, and more preferably 50 μm or more, because it becomes difficult to maintain the shape if the thickness of the coating 11a is less than 20 μm. If the coating 11a is made of a water-insoluble organic material, it is even more preferable that the thickness of the coating 11a be 100 μm or more. On the other hand, if the thickness of the coating 11a exceeds 500 μm, in the partial coating removal step described below, when forming the missing portion 16 in the coating 11a using polishing and / or drilling, the coating 11a may peel off and deform due to insufficient adhesion of the coating 11a. Therefore, it is preferable that the thickness be 500 μm or less, and more preferably 350 μm or less.

[0047] In the example shown in the figure, the coating 11a is a single-layer structure made of one type of material, but it may also be a laminated structure made of the same type or multiple types of materials.

[0048] In the above coating formation process, (i) when the coated model 10a is immersed in the medium (aqueous solution), a coating 11a having missing parts 16 may be formed so that a part of the outer surface 15 of the model 14 is exposed as an exposed part 17, or (ii) the coating 11a may be formed so as to cover the entire outer surface 15 of the model 14.

[0049] In the coating formation process, if the coating 11a forms a missing portion 16 as described in (i) above, one method for forming the missing portion 16 in the coating 11a is to avoid painting or thermal spraying that portion from the beginning. Alternatively, the area that will become the exposed portion 17 may be masked with masking tape before painting or thermal spraying, and then the masking tape may be removed.

[0050] [Formation of exposed areas and partial removal of coating] In the coating formation step, if a coating 11a is formed to cover the entire outer surface 15 of the model 14 as described in (ii) above, a partial coating removal step is performed afterward to remove a portion of the coating 11a to form an exposed portion 17. In other words, this manufacturing method may include a partial coating removal step, and it is preferable that the partial coating removal step be performed after the coating formation step. With this configuration, even if a coating 11a is formed to cover the entire outer surface 15 of the model 14 in the coating formation step, a portion of the outer surface 15 of the model 14 can be exposed to the medium (aqueous solution) into which the coated model 10a in Figure 3 is immersed in the subsequent model removal step. If this manufacturing method includes a partial coating removal step, it is preferable that the partial coating removal step be included between the coating formation step and the model removal step in order to smoothly carry out the subsequent model removal step. Figure 4 shows an example of a situation where a portion of the coating 11a is removed from the coated model 10a in Figure 3 as a missing portion 16, and the exposed portion 17 of model 14 is provided on the coated model 10a.

[0051] In this partial coating removal process, the method for forming the missing portion 16 in the coating 11a is not particularly limited, as long as an exposed portion 17 is formed by physically removing a part of the coating 11a to expose the outer surface 15 of the model 14. Specifically, methods such as a scraping process in which a part of the coating 11a is scraped off with a file or sandpaper, a drilling process in which a hole is made in a part of the coating 11a with a drill or puncher, and a melting removal process in which a part of the coating 11a is melted off and removed if the coating 11a is a thermoplastic resin can be used. Furthermore, the area to be removed is an area that may be omitted in the thin film structure 10 that is to be ultimately manufactured.

[0052] [Model removal process] In the model removal process according to one embodiment of the present invention, the coated model 10a is immersed in an aqueous solution to dissolve and remove the model 14 while leaving the coating intact. Specifically, in the model removal process, by immersing the coated model 10a in an aqueous solution, the aqueous solution penetrates into the inside of the coated model 10a through the missing parts 16 formed in the coating 11a. As a result, the exposed parts 17 of the model 14, which is made of magnesium material, come into contact with the aqueous solution, and the model 14 gradually dissolves from the exposed parts 17. As a result, the coating 11a that covered the outer surface 15 of the model 14 remains while maintaining its shape (resulting in the coating 11). An example of the situation when the coated model 10a is immersed in an aqueous solution S is shown in Figure 5. Hydrogen gas H escapes from the missing parts 16 formed in the coating 11a, and a precipitate of magnesium hydroxide is discharged. Therefore, it is preferable that the coating 11a has a cutout for releasing hydrogen gas H and a cutout for releasing magnesium hydroxide, and it is preferable that it has a plurality of cutouts 16. In other words, it is preferable that the model 14 has a plurality of exposed parts 17. With this configuration, as the magnesium material of the model 14 dissolves and penetrates through the gaps between the plurality of cutouts 16, these cutouts 16 can each play a role as a place where the aqueous solution S mainly penetrates into the inside of the coated model 10a and precipitates escape, and a place where hydrogen gas H mainly escapes from the coating 11a. This allows the model 14 to be quickly dissolved in the aqueous solution S.

[0053] Here, the aqueous solution S is a solution mainly containing water (i.e., pure water) that can dissolve the above-mentioned magnesium material. The aqueous solution S preferably contains an electrolyte as a solute. From the viewpoint of availability and safety, the electrolyte is preferably sodium chloride, sodium bicarbonate, and / or potassium chloride. Also from the viewpoint of availability and safety, the aqueous solution S is preferably seawater. Furthermore, from the viewpoint of availability, cost, and solute safety, the aqueous solution S is more preferably a sodium bicarbonate aqueous solution or seawater. If the aqueous solution S is an aqueous solution containing an electrolyte such as a sodium chloride aqueous solution, the dissolution of the magnesium material proceeds more easily, which is preferable. If the aqueous solution S is a sodium chloride aqueous solution, it is preferable that the concentration is 0.05% by mass or more, as this clearly improves the dissolution rate compared to water. Also, from the viewpoint of promoting the dissolution of the magnesium material, the conductivity of the aqueous solution S at 25°C is preferably 1.0 mS / cm or more.

[0054] If the aqueous solution S is acidic, the dissolution of the magnesium material can be accelerated, but if it is strongly basic, the magnesium material cannot be dissolved and the model 14 cannot be removed. Also, if it is strongly acidic, the coating 11a may be damaged in some cases. The aqueous solution S is preferably acidic or neutral, and more preferably neutral. For this reason, the pH of the aqueous solution S is preferably between 1 and 9, and more preferably between 5 and 9.

[0055] In the model removal process, the immersion time of the coated model 10a in the aqueous solution S should be adjusted as appropriate depending on the size and shape of the model 14, the temperature and pH of the aqueous solution, etc. If the coating 11a is made of a metal material, immersion for too long may remove the coating 11a as well, so it is best to remove the model from the aqueous solution S when the model 14 has been removed and the coating 11a remains. The aqueous solution S used in the model removal process may be unheated, or if the dissolution is to be accelerated, the aqueous solution S may be heated to a temperature that does not boil.

[0056] Depending on the application of the thin film structure 10, the model 14 may not completely dissolve, and some residue of magnesium material may remain on the inner surface 13 of the coating on the hollow structure side of the coating 11. In other words, the thin film structure according to one embodiment of the present invention consists of a water-insoluble coating and has a hollow structure, and has a residue of magnesium material on the inner surface of the hollow structure (inner surface of the thin film). In this case, since it is not necessary to strictly adjust the timing of withdrawal from the aqueous solution S in this manufacturing method, the thin film structure 10 becomes easier to manufacture.

[0057] The thin-film structure 10 according to this invention provides a structure made of a thin coating 11 that is difficult to manufacture by general casting, processing, welding, etc.

[0058] [Washing process] In the model removal process according to one embodiment of the present invention, a precipitate of magnesium hydroxide formed by the reaction of the magnesium material with an aqueous solution may remain in a part of the obtained thin film structure. In other words, the thin film structure according to one embodiment of the present invention may be a thin film structure consisting of a water-insoluble coating, having a hollow structure, and having a residue containing magnesium hydroxide on the inner surface of the hollow structure. Combined with the above, the thin film structure according to one embodiment of the present invention may be a thin film structure consisting of a water-insoluble coating, having a hollow structure, and having a residue containing magnesium material and / or magnesium hydroxide on the inner surface of the hollow structure.

[0059] Therefore, in this manufacturing method, a cleaning step may be performed to clean the thin film structure after the model removal step. From the viewpoint of strictly reducing the percentage of residue consisting of magnesium hydroxide remaining on the inner surface of the thin film structure, it is preferable to use a solvent that dissolves magnesium hydroxide but does not dissolve the film as the cleaning solution in the cleaning step. On the other hand, if some residue consisting of magnesium hydroxide may remain on the inner surface of the thin film structure, the solvent (cleaning solution) used in the cleaning step is not particularly limited as long as it is a solvent that does not dissolve the film, and pure water is an example. [Examples]

[0060] An example of actually manufacturing a thin film structure according to this invention is shown. A 1 cm cube model was manufactured using a magnesium alloy consisting of 11% by mass of Al, 10% by mass of Cu, less than 0.1% by mass of unavoidable impurities in total, and the remainder being Mg (dissolution rate of 150 mcd per day in a 2% by mass sodium chloride aqueous solution at room temperature) (model manufacturing process).

[0061] The entire surface of this model was plated with 50 μm thick copper by electroplating (coating formation process). A photograph of the plated model is shown in Figure 6. Next, the top and bottom surfaces of the plated cube were polished with sandpaper to remove the copper layer and expose the magnesium alloy layer. In other words, the top and bottom surfaces were made exposed. The model with the exposed layers was immersed in a 2 mass% NaCl aqueous solution (electrical conductivity at 25°C: 33.0 mS / cm) and left to stand at room temperature for 3 days until the magnesium alloy dissolved, at which point it was removed (model removal process). A photograph of the resulting thin-film structure made of a rectangular prismatic copper thin film is shown in Figure 7. [Explanation of Symbols]

[0062] 10 Thin film structure 11 Coating 11a Coating 12 Outer surface of coating 13 Inner surface of coating 14 Model 15 Outer surface 16 Missing parts 17 Exposed part 20 Hollow part H Hydrogen gas S Aqueous solution

Claims

1. It consists of a water-insoluble coating formed on the outer surface of a model made of magnesium material. A thin film structure obtained by dissolving and removing the aforementioned model.

2. A coated model in which a water-insoluble coating is formed on the outer surface of a model made of magnesium material.

3. It consists of a water-insoluble coating and has a hollow structure. A thin film structure having a residue made of magnesium material on the inner surface of the hollow structure.

4. The model manufacturing process for creating models made from magnesium material, A coating formation step is performed to form a water-insoluble coating on the outer surface of the aforementioned model, thereby creating a coated model. A model removal step involves immersing the coated model in an aqueous solution to dissolve and remove the model while leaving the coating intact, A method for manufacturing a thin film structure, including [the specified element].

5. The method for manufacturing a thin film structure according to claim 4, wherein the water-insoluble coating is a metallic material that dissolves more slowly in the aqueous solution than the magnesium material.

6. The method for manufacturing a thin film structure according to claim 4, wherein the water-insoluble coating is a ceramic.

7. The method for manufacturing a thin film structure according to claim 4, wherein the water-insoluble coating is made of a water-insoluble organic material.

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