KR102610278B1 - Mold for sheet and plating method of the same - Google Patents

Abstract

The present invention relates to a mold for a sheet and a plating method thereof. A sheet mold plating method according to an embodiment of the present invention includes an acid treatment step of treating a sheet mold whose outer surface is made of aluminum with an acidic solution; An etching step of treating the sheet mold with an alkaline etching solution; A desmut step of removing the oxide film generated in the etching step by treating the sheet mold with an acidic solution; A substitution film forming step of forming a zinc substitution film on a sheet mold by treating it with a substitution liquid; And a chrome plating step of plating the sheet mold with chrome by treating it with a chrome plating solution containing chromic anhydride (CrO ₃ ) and sulfuric acid (H ₂ SO ₄ ).

Description

Mold for sheet and plating method thereof {Mold for sheet and plating method of the same}

The present invention relates to a sheet mold and a plating method thereof, and more specifically to a sheet mold and a plating method capable of effectively demolding a sheet from a sheet mold during the sheet molding process.

Production of products using molds is preferred due to mass production and convenience of operation. Molds can be divided into press molds, which cut and shape metal materials, and injection molds, which melt synthetic resin materials to create products of a certain shape. Injection molds are used to mold car seats.

In the case of molding a car seat using a mold, with the upper mold and lower mold in close contact, synthetic resin material for sheet molding is injected into the cavity formed between the upper mold and lower mold, and then the upper mold and lower mold are separated and The molded sheet goes through a demolding process to remove it from the mold. However, due to the physical properties of synthetic resin materials, the molded sheet does not easily fall out of the mold. Due to this problem, a release agent is first applied to the mold to facilitate demolding of the sheet prior to sheet formation. However, this process of applying the release agent is an additional task, which reduces the work efficiency of sheet molding, and the release agent, which is a chemical agent, has the problem of threatening the health of workers and causing environmental pollution.

The present invention is to provide a sheet mold and a plating method thereof that can effectively demold the sheet from the sheet mold during the sheet molding process.

According to one aspect of the present invention, an acid treatment step of treating a sheet mold whose outer surface is made of aluminum with an acidic solution; An etching step of treating the sheet mold with an alkaline etching solution; A desmut step of removing the oxide film generated in the etching step by treating the sheet mold with an acidic solution; A substitution film forming step of forming a zinc substitution film on a sheet mold by treating it with a substitution liquid; And a chrome plating step of plating the sheet mold with chrome by treating it with a chrome plating solution containing chromic anhydride (CrO ₃ ) and sulfuric acid (H ₂ SO ₄ ). A mold plating method for a sheet may be provided.

Additionally, the etching step may be performed using sodium hydroxide (NaOH) as the etching solution and 10 to 30 g/L of sodium hydroxide.

Additionally, the etching solution may contain 5 to 10 g/L of sodium gluconate.

In addition, it may further include a polishing step performed after the chrome plating step to smooth the mold for the sheet on which the chrome plating is formed.

According to another aspect of the present invention, a mold for a chrome-plated sheet can be provided by one of the above methods.

According to one embodiment of the present invention, a sheet mold and a plating method thereof that can effectively demold the sheet from the sheet mold during the sheet molding process can be provided.

1 is a block diagram showing a method of plating a mold for a sheet according to an embodiment of the present invention.
Figure 2 is a surface SEM photograph of a mold for a sheet on which plating was performed according to an embodiment of the present invention.
Figure 3 is a cross-sectional SEM photograph of a mold for a sheet on which plating was performed according to an embodiment of the present invention.
Figure 4 is a cross-sectional EDX of a mold for a sheet on which plating was performed according to an embodiment of the present invention.
Figure 5 is a block diagram showing the substitution film formation step according to another embodiment.
Figure 6 is a diagram showing a state in which primary coating peeling is performed after the primary substitution coating is formed.
Figure 7 is a diagram showing the state of the secondary substitution film formed after the primary substitution film peeling is performed using different film stripping solutions.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. However, the technical idea of the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed content will be thorough and complete and so that the spirit of the invention can be sufficiently conveyed to those skilled in the art.

In this specification, when an element is referred to as being on another element, it means that it may be formed directly on the other element or that a third element may be interposed between them. Additionally, in the drawings, the thicknesses of films and regions are exaggerated for effective explanation of technical content.

Additionally, in various embodiments of the present specification, terms such as first, second, and third are used to describe various components, but these components should not be limited by these terms. These terms are merely used to distinguish one component from another. Accordingly, what is referred to as a first component in one embodiment may be referred to as a second component in another embodiment. Each embodiment described and illustrated herein also includes its complementary embodiment. Additionally, in this specification, 'and/or' is used to mean including at least one of the components listed before and after.

In the specification, singular expressions include plural expressions unless the context clearly dictates otherwise. In addition, terms such as "include" or "have" are intended to designate the presence of features, numbers, steps, components, or a combination thereof described in the specification, but are not intended to indicate the presence of one or more other features, numbers, steps, or components. It should not be understood as excluding the possibility of the presence or addition of elements or combinations thereof. In addition, in this specification, “connection” is used to include both indirectly connecting a plurality of components and directly connecting them.

Additionally, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

1 is a block diagram showing a method of plating a mold for a sheet according to an embodiment of the present invention.

Referring to Figure 1, the sheet mold plating method according to an embodiment of the present invention includes a sanding step (S10), a degreasing step (S20), an acid treatment step (S30), an etching step (S40), and a dismut step (S50). ), a substitution film forming step (S60), a chrome plating step (S70), a polishing step (S80), and a surface cleaning step (S90).

A mold for a sheet in which a film will be formed through plating is provided. A mold for a seat may be used for molding a seat provided for a seat of a car or the like. The sheet mold may have an outer surface made of aluminum. Molds for sheets can be made through casting from aluminum. Sheet molds can be checked for surface defects through additional shape processing and external inspection before being provided for plating after casting.

A sanding step is performed (S10). Sanding can be performed using siliceous sand. Sanding can be performed over 4 to 6 minutes. Preferably sanding can be performed over 5 minutes. Through sanding, the adhesion of the plating film to the sheet mold can be improved.

A degreasing step is performed (S20). Degreasing may be performed over 9 to 11 minutes using a degreasing solution at 40 to 50°C. Preferably, degreasing can be performed over 10 minutes. The degreasing liquid is supplied as slightly alkaline. Degreasing can be performed by immersing the sheet mold in a degreasing liquid. Accordingly, foreign substances such as oil and dust attached to the surface of the sheet mold can be removed. After the degreasing step is performed, a post-degreasing water washing step may be performed to remove the degreasing liquid remaining in the sheet mold. After degreasing, washing can be performed with water at 20 to 30°C for 4 to 6 minutes. Preferably, washing with water after degreasing can be performed for 5 minutes.

An acid treatment step is performed (S30). The acid solution used for acid treatment may be nitric acid (HNO ₃ ). Nitric acid can be used diluted to 50-100ml/L. The purity of nitric acid provided for dilution may be 68%. The acid treatment step may be performed over 1 minute and 30 seconds to 2 minutes and 30 seconds through an acid solution at 20 to 30°C. Preferably the acid treatment step may be carried out for 2 minutes. The oxide film on the surface of the sheet mold is removed through acid treatment. After the acid treatment step is performed, a water washing step may be performed after the acid treatment to remove the acid solution remaining in the sheet mold. After acid treatment, water washing may be performed with water at 20 to 30° C. for 4 to 6 minutes. Preferably, washing with water after acid treatment can be performed for 5 minutes.

의 에칭액을 통해 1분 30초 내지 2분 30초에 걸쳐 수행될 수 있다. 바람직하게 에칭 단계는 2분동안 수행될 수 있다. 에칭액은 산화알루미늄 표면과 반응하면서, 수소가스가 발생되고 산화알루미늄(Al2O3)층이 제거될 수 있다. 에칭 단계를 통해 추후 형성될 아연 치환 피막의 밀착성이 향상될 수 있다. 에칭 단계가 수행된 후, 시트용 금형에 잔류하는 에칭액의 제거를 위해 에칭 후 수세 단계가 수행될 수 있다. 에칭 후 수세는 20 내지 30℃의 물을 통해 4분 내지 6분간 수행될 수 있다. 바람직하게 에칭 후 수세는 5분간 수행될 수 있다.An etching step is performed (S40). Etching is performed using an alkaline etchant. The etchant used for etching may be sodium hydroxide (NaOH). The etching solution can be diluted to 10-30g/L and used. Additionally, sodium gluconate (C ₆ H ₁₁ NaO ₇ ) may be added to the etching solution. Sodium gluconate can be used diluted to 5-10 g/L. Etching: 20 to 30

It can be performed over 1 minute and 30 seconds to 2 minutes and 30 seconds using an etching solution. Preferably the etching step may be performed for 2 minutes. As the etchant reacts with the aluminum oxide surface, hydrogen gas is generated and the aluminum oxide (Al2O3) layer can be removed. The adhesion of the zinc-substituted film to be formed later can be improved through the etching step. After the etching step is performed, a post-etching water washing step may be performed to remove the etchant remaining in the sheet mold. After etching, water washing may be performed with water at 20 to 30° C. for 4 to 6 minutes. Preferably, water washing after etching can be performed for 5 minutes.

A dismut step is performed (S50). The dismut step is carried out with an acid solution. The acid used for dismut may be nitric acid (HNO ₃ ). Nitric acid can be used diluted to 50-100ml/L. The purity of nitric acid provided for dilution may be 68%. The dismut step may be performed for 30 seconds to 1 minute and 30 seconds in an acidic solution at 20 to 30°C. Preferably the dismut step may be performed for 1 minute. Through desmut, the oxide film that forms on the surface of the sheet mold during the etching process is removed. After the dismut step is performed, a post-dismut water washing step may be performed to remove the acid solution remaining in the sheet mold. Washing after dismuting can be performed with water at 20 to 30°C for 4 to 6 minutes. Preferably, washing with water after dismuting can be performed for 5 minutes.

A substitution film formation step is performed (S60). The substitution liquid used to form the substitution film includes sodium hydroxide (NaOH) and zinc oxide (ZnO). Fe salt may be added to the substitution solution. The Fe salt may be ferric chloride. Sodium nitrate (NaNO3) and grape acid (C4H6O6) may be added to the substitution solution. The substitution film formation can be performed over 30 to 60 seconds through a substitution solution at 20 to 30°C. When the sheet mold is immersed in the substitution liquid, oxidation and reduction reactions occur simultaneously on the surface of the sheet mold, and aluminum is replaced with Zn ²⁺ and zinc precipitates in the aluminum structure. Accordingly, a zinc-substituted film is formed on the surface of the sheet mold. After the substitution film forming step is performed, a water washing step may be performed after forming the substitution film to remove the substitution liquid remaining in the sheet mold. After forming the substitution film, washing may be performed with water at 20 to 30°C for 4 to 6 minutes. Preferably, after forming the substitution film, washing with water may be performed for 5 minutes. As the zinc substitution film is formed, a hard chrome plating film is later effectively formed on the sheet mold.

A chrome plating step is performed (S70). The chrome plating solution contains chromic anhydride (CrO ₃ ) and sulfuric acid (H ₂ SO ₄ ). Chromic anhydride is contained at a concentration of 200-300 g/L, and sulfuric acid is contained at a concentration of 1.3-2.5 g/L. Chrome plating can be performed over 2 hours 20 minutes to 2 hours 40 minutes at a current density of 10 to 80 A/dm2 in a chrome plating solution at 20 to 30°C. Preferably, chrome plating can be performed in 2 hours and 30 minutes. Accordingly, hard chrome plating is performed on the sheet mold. After the chrome plating step is performed, a water washing step may be performed after chrome plating to remove the chrome plating solution remaining in the sheet mold. Washing after chrome plating can be performed with water at 20 to 30°C for 4 to 6 minutes. Preferably, washing with water after chrome plating can be performed for 5 minutes. After chrome plating, drying takes place. Drying may be performed for 4 to 6 minutes under temperature conditions of 50 to 60°C. Drying can preferably be carried out for 5 minutes. Accordingly, moisture is removed from the sheet mold.

A polishing step is performed (S80). The polishing stage consists of rough polishing, medium polishing, and glossy polishing sequentially. Coarse polishing can be performed by polishing with an abrasive, polishing with a hand drill, or polishing with sandpaper. The polishing thickness can be performed from 190um to 210um. Preferably, the polishing thickness may be 200um. Intermediate grinding can be performed through a grinder using a slurry containing alumina particles. Polishing can be performed using chromium oxide as an abrasive. Through polishing, the hard chrome plating layer formed on the sheet mold becomes smoother, improving the release properties of the sheet.

Surface cleaning is performed (S90). Surface cleaning can be performed with water at 20 to 30°C for 1 minute and 30 seconds to 2 minutes and 30 seconds. Preferably surface cleaning may be performed for 2 minutes. Accordingly, foreign substances, abrasives, etc. on the surface of the sheet mold are removed. After surface cleaning, secondary drying is performed. Secondary drying may be performed for 4 to 6 minutes under temperature conditions of 50 to 70°C. Preferably secondary drying can be performed for 5 minutes. Accordingly, moisture is removed from the sheet mold.

Thereafter, the plated sheet mold may undergo additional product inspection prior to shipment and use. Product inspection may include visual inspection and defect inspection through a magnifying glass.

Figure 2 is a surface SEM photograph of a sheet mold on which plating was performed according to an embodiment of the present invention, and Figure 3 is a cross-sectional SEM photograph of a sheet mold on which plating was performed according to an embodiment of the present invention.

In Figures 2 and 3, each image was taken multiple times using a scanning electron microscope (SEM) at different magnifications. Referring to Figures 2 and 3, it can be seen that the chrome plating layer formed on the surface of the sheet mold has particles densely and uniformly distributed, and the chrome plating layer is formed in tight contact with the base surface of the sheet mold. .

Figure 4 is an EDX photograph of a cross section of a sheet mold on which plating was performed according to an embodiment of the present invention.

Referring to Figure 4, as a result of performing Energy Dispersive It can be seen that it was formed densely.

Chrome plating is formed on the outer surface of the sheet mold manufactured according to the sheet mold plating method according to an embodiment of the present invention. When a sheet is molded using a sheet mold, demolding is performed to separate the sheet from the sheet mold. In the process of demolding a conventional sheet from a sheet mold, the sheet sticks to the sheet mold and does not easily fall off, and therefore, if excessive force is applied to the sheet during the demolding process, damage to the sheet may occur. To prevent this phenomenon, a release agent was applied to the cavity where the sheet was formed in the sheet mold so that the sheet could easily fall off during the demolding process, and then the sheet was molded. However, such mold release agents contain ingredients that are harmful to the human body, threatening the safety of workers and causing environmental pollution. On the other hand, the sheet mold in which chrome plating was performed according to the sheet mold plating method according to an embodiment of the present invention is provided so that the sheet is in contact with the chrome plating layer, so that the sheet easily falls off from the sheet mold during the demolding process, The release agent application process can be omitted.

Figure 5 is a block diagram showing the substitution film forming step in the sheet mold plating method according to another embodiment.

The steps performed before and after the substitution film forming step are the same as the sheet mold plating method of FIG. 1.

Referring to FIG. 5, the substitution film forming step includes the first substitution film forming step (S61), the first substitution film peeling step (S62), the second substitution film forming step (S63), and the second substitution film peeling step (S64). , including a tertiary substitution film forming step (S65).

The first substitution film formation step is performed (S61). The primary substitution liquid used to form the primary substitution film includes sodium hydroxide (NaOH) and zinc oxide (ZnO). Additionally, Fe salt is added to the primary substitution solution. The Fe salt added may be ferric chloride. Sodium nitrate (NaNO3) and grape acid (C4H6O6) may be added to the substitution solution. The formation of the primary substitution film can be performed over 20 to 40 seconds using a primary substitution liquid at 20 to 30°C. Accordingly, a primary zinc substitution film is formed on the surface of the sheet mold. Additionally, when Fe salt is added, the zinc substitution film becomes an Fe alloy type, the substitution film is formed more densely, and adhesion to aluminum, which is the base material of the sheet mold, is improved. After the first substitution film forming step is performed, a water washing step may be performed after forming the first substitution film to remove the first substitution liquid remaining in the sheet mold. After forming the first substitution film, washing may be performed with water at 20 to 30°C for 4 to 6 minutes. Preferably, water washing may be performed for 5 minutes after forming the first substitution film.

A first substitution film peeling step is performed (S62). The primary film stripping solution is provided as a mixture of nitric acid (HNO ₃ ) and hydrofluoric acid (HF). The primary film stripping solution may be provided by mixing nitric acid and hydrofluoric acid in a molar ratio of 3 to 1. The primary film peeling solution can be diluted to 50 to 100 ml/L. The first substitution film peeling step may be performed for 30 seconds to 1 minute using a primary film stripping solution at 20 to 30°C. Preferably, the first substitution film peeling step may be performed for 40 seconds. Through peeling of the primary substitution film, a portion of the primary substitution film formed on the surface of the sheet mold is removed. Additionally, in the area of the primary substitution coating that contacts the base material of the sheet mold, the substitution coating and aluminum react to form some alloy. After the first substitution film peeling step is performed, a water washing step may be performed after the first substitution film peeling to remove the film peeling liquid remaining in the sheet mold. After peeling off the first substitution film, washing may be performed with water at 20 to 30°C for 4 to 6 minutes. Preferably, washing with water may be performed for 5 minutes after peeling off the first substitution film.

A secondary substitution film formation step is performed (S63). The secondary substitution liquid used to form the secondary substitution film includes sodium hydroxide (NaOH) and zinc oxide (ZnO). Fe salt may be added to the secondary displacement solution. The Fe salt may be ferric chloride. Sodium nitrate (NaNO3) and grape acid (C4H6O6) may be added to the secondary substitution solution. Secondary displacement film formation may be performed over 30 to 60 seconds using a secondary displacement liquid at 20 to 30°C. Accordingly, a secondary zinc substitution film is formed on the surface of the sheet mold on the outside of the primary zinc substitution film that partially remains after peeling. In addition, during this process, the zinc substitution coating becomes more dense, and its adhesion to aluminum, which is the base material of the sheet mold, improves, thereby reducing the risk of the substitution coating peeling off the aluminum. After the secondary substitution film forming step is performed, a water washing step may be performed after forming the secondary substitution film to remove the secondary substitution liquid remaining in the sheet mold. After forming the secondary substitution film, washing may be performed with water at 20 to 30°C for 4 to 6 minutes. Preferably, water washing may be performed for 5 minutes after forming the secondary substitution film.

A secondary substitution film peeling step is performed (S64). The secondary film stripping solution is provided as nitric acid (HNO ₃ ). The secondary film stripping solution can be diluted to 50-100ml/L. The secondary substitution film peeling step may be performed over 30 seconds to 1 minute using a secondary film stripping solution at 20 to 30°C. Preferably, the secondary substitution film peeling step may be performed for 40 seconds. A portion of the secondary substitution film formed on the surface of the sheet mold is removed through secondary substitution film peeling. After the secondary substitution film peeling step is performed, a water washing step may be performed after the secondary substitution film peeling to remove the film peeling liquid remaining in the sheet mold. After peeling off the secondary substitution film, washing may be performed with water at 20 to 30°C for 4 to 6 minutes. Preferably, water washing may be performed for 5 minutes after peeling off the secondary substitution film.

A third substitution film formation step is performed (S65). The tertiary substitution liquid used to form the tertiary substitution film includes sodium hydroxide (NaOH) and zinc oxide (ZnO). Fe salt may be added to the substitution solution. The Fe salt may be ferric chloride. Sodium nitrate (NaNO3) and grape acid (C4H6O6) may be added to the substitution solution. The formation of the tertiary displacement film can be performed over 30 to 60 seconds using a secondary displacement liquid at 20 to 30°C. Accordingly, a tertiary zinc-substituted film is formed on the surface of the sheet mold on the outside of the secondary zinc-substituted film that partially remains after peeling. In addition, during this process, the zinc substitution coating becomes more dense, and its adhesion to aluminum, which is the base material of the sheet mold, improves, thereby reducing the risk of the substitution coating peeling off the aluminum. After the tertiary substitution film forming step is performed, a water washing step may be performed after forming the tertiary substitution film to remove the tertiary substitution liquid remaining in the sheet mold. After forming the tertiary substitution film, washing may be performed with water at 20 to 30°C for 4 to 6 minutes. Preferably, water washing may be performed for 5 minutes after forming the secondary substitution film.

Figure 6 is a diagram showing a state in which primary coating peeling is performed after the primary substitution coating is formed.

In Figure 6, (a) shows a state in which a primary substitution film was formed on each of different aluminum materials, and (b) shows a state in which film peeling was performed using nitric acid as a film stripping solution after the primary substitution film was formed. In c), after the primary substitution film is formed, film peeling is performed using a mixture of nitric acid and hydrofluoric acid as a film stripping solution. Nitric acid and hydrofluoric acid were mixed in a molar ratio of 3 to 1. Referring to this, although there is a difference in degree depending on the aluminum material, when the substitution film is peeled using a mixture of nitric acid and hydrofluoric acid as the film stripping solution, rather than when peeling the substitution film using nitric acid as the film stripping solution. , it can be seen that more film peeling occurs, and the surface roughness is greater.

Figure 7 is a diagram showing the state of the secondary substitution film formed after the primary substitution film peeling is performed using different film stripping solutions.

In Figure 7, (a) shows a state in which a secondary substituted film was formed after performing substitution film peeling using nitric acid as a film stripping solution, and (b) shows a state in which a substitution film was peeled using a mixture of nitric acid and hydrofluoric acid as a film stripping solution. After performing the process, a secondary substitution film is formed. Referring to this, in both cases, it can be seen that when the secondary substitution film is formed, the particles are smaller and more uniformly distributed than when the primary substitution film is formed. This appears to be because the particles remaining on the surface after the substitution film peeling is performed contribute to the growth of the secondary substitution film. Additionally, the primary substituted coating and the secondary substituted coating can be tightly coupled to each other by an anchor effect. On the other hand, when comparing the secondary films, the case where film peeling was performed using nitric acid as a film stripping solution prior to the formation of the secondary substituted film was compared to the case where film peeling was performed using a mixture of nitric acid and hydrofluoric acid as a film stripping solution. It can be seen that the surface is smoother. This is believed to be due to the fact that more film peeling occurred when substitution film peeling was performed using a mixture of nitric acid and hydrofluoric acid as the film stripping solution, resulting in greater surface roughness.

Considering these characteristics, in the substitution film forming step according to another embodiment of the present invention, the first film peeling is performed with a mixture of nitric acid and hydrofluoric acid, and the second film peeling is performed with nitric acid, so that a third substitution film is formed. do. As the secondary substitution film is formed after peeling the primary film with a mixture of nitric acid and hydrofluoric acid, the particle state of the secondary substitution film is such that a sufficient anchor effect can occur between the secondary substitution film and the tertiary substitution film. It becomes a state. And the secondary film peeling is performed with nitric acid, so that a more uniform and smooth tertiary substitution film can be formed.

On the other hand, when the secondary substitution coating is formed after peeling the primary substitution coating with nitric acid, the particle state of the secondary substitution coating becomes inadequate to have a sufficient anchor effect with the tertiary substitution coating. Additionally, when the secondary film is peeled using a mixture of nitric acid and hydrofluoric acid, the roughness of the tertiary film increases.

Above, the present invention has been described in detail using preferred embodiments, but the scope of the present invention is not limited to the specific embodiments and should be interpreted in accordance with the appended claims. Additionally, those skilled in the art should understand that many modifications and variations are possible without departing from the scope of the present invention.

Claims (5)

An acid treatment step of treating a sheet mold whose outer surface is made of aluminum with an acidic solution;
An etching step of treating the sheet mold with an alkaline etching solution;
A dismut step of removing the oxide film generated in the etching step by treating the sheet mold in a nitric acid solution diluted to 50 to 100 ml/L at a temperature of 20 to 30°C for 30 seconds to 1 minute and 30 seconds;
The sheet mold for which the desmut step has been completed is immersed in a substitution solution at 20 to 30° C. containing sodium hydroxide, zinc oxide, ferric chloride, sodium nitrate, and grape acid for 30 to 60 seconds to form the sheet mold. A substitution film forming step of forming a zinc substitution film; and
A method of plating a mold for a sheet including a chrome plating step of plating a mold for a sheet with chrome by treating it with a chrome plating solution containing chromic anhydride (CrO3) and sulfuric acid (H2SO4). According to paragraph 1,
A method of plating a mold for a sheet in which the etching step is performed using sodium hydroxide (NaOH) as the etching solution and 10 to 30 g/L of sodium hydroxide. According to paragraph 2,
A mold plating method for a sheet wherein the etching solution contains 5 to 10 g/L of sodium gluconate. According to paragraph 1,
A method of plating a mold for a sheet further comprising a polishing step performed after the chrome plating step to smooth the mold for a sheet on which the chrome plating is formed. A mold for a sheet chrome plated by the method of any one of claims 1 to 4.