KR100794804B1 - Method of silver plating - Google Patents

Abstract

A method of plating silver on a material is provided to improve adherence of painting process, to prevent discoloration of paint, and to simplify processes for plating without performing a chromate process. A method of plating silver without performing a chromate process includes a step(S10) of pre-treating a material to be plated, a step(S20) of a first preparation of silver plating by degreasing the pre-treated material with sodium sulfate solution, a step(S30) of applying the material to be plated, a step(S40) of second preparation of silver plating by degreasing the applied material with solution containing ammonium fluoride and sulfuric acid, and a step(S60) of plating the material with silver.

Description

Silver Plating Method {Method of Silver Plating}

1 is a process flow chart for explaining a silver plating treatment method according to an embodiment of the present invention,

Figure 2 is a photograph of the paint adhesion test results of the silver plated aluminum material according to an embodiment of the present invention.

The present invention relates to a silver plating treatment method, and more particularly, to a silver plating treatment method of a plated material which can prevent discoloration of the coating, improve paint adhesion and simplify the process without the chromate process.

Aluminum metal is well known to protect the aluminum base itself by forming a natural oxide film on the surface in air. However, the natural oxide film (Al2O3) produced in the atmosphere does not become thick except in special cases. As the use of aluminum materials is rapidly increasing with the development of the automobile industry, the aircraft industry, and the electronics industry, the development of surface treatment plating methods to improve the corrosion resistance and abrasion resistance of aluminum materials is required. It is becoming.

Therefore, in order to improve the adhesion of the paint for the case of requiring corrosion resistance or for the base of the coating, artificial anodization or chemical coating treatment is artificially performed. Chemical coating treatment is a treatment method for obtaining a chemical conversion film (Al2O3) by using a chemical reaction between a chemical solution and aluminum metal, not by an electrolytic method. In general, as the chemical conversion treatment method, an etching surface is formed on the aluminum surface after the chemical conversion treatment, and thus, a chromate method that is most suitable for coating and is easy to be used for a complicated structure is used.

Looking at the plating process of a general aluminum material, it is proceeded by the leading post-plating method, specifically, after the aluminum or aluminum alloy is processed by a die casting method, such as pre-treatment process of the coating, the coating after the chromate treatment as described above Is carried out. After the painting is completed, silver plating is performed through a silver plating pretreatment process consisting of etching, demusting (or activation). At this time, before plating silver, it is possible to improve the corrosion resistance, hardness and flexibility of the product, and to perform the base plating to enable good adhesion plating. As the base plating, zincate, zinc peeling, electroless nickel plating and silver strike plating may be sequentially performed.

In such a plating process, a process using strong chemicals is largely an etching step using caustic soda and an activation step using nitric acid and the zinc peeling step. These steps are intended to improve the adhesion of the plating and coating thereon by eroding the aluminum surface with strong alkalis and strong acids. However, the strong acid and strong alkali used herein are applied not only to the aluminum surface but also to the painted surface, which serves as a major factor in discoloring the painted color. In addition, toxic gases such as NO, NO ₂ and HF are generated to deteriorate the working environment and cause exhaust gas problems.

The present invention is to solve the problems of the prior art described above, to provide a silver plating treatment method that can prevent the discoloration of the coated product, improve the paint adhesion and simplify the process without the chromate process.

In order to solve the above technical problem, according to the present invention (a) pre-processing the material to be plated; (b) a first silver plating pretreatment step of degreasing the pretreated material to be plated using an aqueous sodium sulfate solution; (c) painting the plated material; (d) a second silver plating pretreatment step of degreasing the coated material to be coated using an aqueous solution containing ammonium fluoride and sulfuric acid; And (e) silver plating the pre-plated material to be plated with silver.

Hereinafter, the silver plating process according to the present invention with reference to the accompanying drawings will be described in detail.

1 is a process flow chart illustrating a silver plating treatment method according to an embodiment of the present invention.

As shown in Figure 1, the silver plating method of the material to be plated according to the present invention first pre-process the material to be plated. (S10)

As a material of the product which can be treated with silver plating, metal materials such as aluminum, copper, and iron may be used, and plastic materials may also be silver plated as necessary. Although the pretreatment step in the plating treatment is slightly different depending on the material of the product, a case of using a metal material, for example, an aluminum material, as in one embodiment of the present invention will be described. The pretreatment of the aluminum material may include degreasing (S11, S12), etching (S13), and activation (S14). Aluminum materials include aluminum extrusion materials and aluminum die casting materials. At this time, the degreasing process may be performed by selectively performing the solvent degreasing (S11) and ultrasonic degreasing (S12) or by performing them sequentially.

Here, the solvent degreasing (S11) of the aluminum material is a process for removing foreign matter, organic matters and the like adhered to the outer surface of the housings processed with aluminum alloy. If foreign matter adheres to the surface of aluminum material, it causes plating adhesion defects and a non-uniform plating layer is formed. Therefore, degreasing solvent (S11) is performed using aluminum degreasing agent to remove foreign substances or organic matter, and solvent degreasing does not touch. Ultrasonic degreasing (S12) is performed to remove the paper in the portion, ie, the bent portion of the metal base, the inside of the weld joint, and the small hole. The solvent degreasing and ultrasonic degreasing can be carried out by a conventional method used conventionally.

When solvent degreasing and / or ultrasonic degreasing are completed, an etching step (S13) is performed, which removes foreign substances or organic matters remaining after solvent degreasing or ultrasonic degreasing, and improves the adhesion strength between the material and the plating layer. will be. The etching step S13 mainly uses caustic soda, and the concentration of about 250 to 350 g / L may be performed at a temperature of 20 to 30 ° C. for about 1 to 5 minutes.

Subsequently, when the etching step S13 is completed, the activation step S14 is performed. This is to remove the black film of the metal impurity salt generated on the surface of the material after the etching process and to neutralize the alkalized material with a strong acid to improve plating adhesion. Activation step (S14) can be performed for 30 seconds to 2 minutes at a concentration of about 50 ~ 150 ml / L using nitric acid.

In the next step, the aluminum material having undergone the pretreatment step is pretreated with the first silver plating. (S20)

The first silver plating pretreatment step S20 is a process for removing the aluminum oxide film formed on the surface of the pre-plated material, for example, aluminum, and activating the surface of the aluminum material. The first silver plating pretreatment step (S20) may be performed using an aqueous sodium sulfate solution, and the aqueous sodium sulfate solution may preferably include sodium sulfate in an amount of 5 to 10% by weight. According to one embodiment of the present invention, the first silver plating pretreatment step (S20) is such that the sodium sulfate aqueous solution to a concentration of 0.5 ~ 2 mL / L, it is preferable to perform for 20-30 seconds at room temperature.

Subsequently, the first silver plated pre-plated material is coated. (S30) The coating step (S30) may use a conventional coating method such as liquid coating, preferably powder coating. Specifically, as the powder coating method, an electrostatic spray coating method may be used in which a negatively-charged powder paint under a high voltage is passed through a nozzle of a powder coating gun, sprayed onto a grounded coating object, and then heated and melted to form a film. Another powder coating may be a flow deposition method in which air is blown through the porous plate to make the powder coating fluid, and the powder coating is melted by adhering the powder coating to the workpiece using heating or static electricity.

In general, the powder coating (S30) is subjected to a pre-treatment process to clean the surface, such as chromate treatment before coating because it should not be contaminated with rust, fat, oil, etc. on the surface to be coated with powder. However, the silver plating treatment method according to the present invention does not include such chromate treatment step can improve the adhesion of the coating and plating.

The powder paint used in the powder coating is preferably a paint having alkali resistance and acid resistance that can withstand chemical reactions in the subsequent process, and in particular, one selected from the group consisting of hybrid, epoxy, polyester and polyurethane series. The above powder coating materials can be used.

In addition, the painting step (S30) may be performed at the same time silk printing. Silk printing is made of silk, nylon, edron fiber, or stainless steel, spreading out the mesh and fastening the four corners tightly to make a valve by hand or photochemical method on it to block the neck other than the necessary burn, This can be done by pouring a print ink and using a spatula, called a squeegee, to press and move the screen so that the ink passes through the mesh in the non-valve area and is printed onto a piece of paper or other printed material under the plate.

After painting and silk printing are completed, the coated material to be plated is subjected to a second silver plating pretreatment. (S40) This second silver plating pretreatment step (S40) may be performed using an aqueous solution containing ammonium fluoride and sulfuric acid, wherein the aqueous solution is 5 to 10% by weight of ammonium fluoride and 0.5 to 5% by weight of sulfuric acid. It is preferable to include. According to one embodiment of the present invention, the second silver plating pretreatment step is preferably performed for 10 to 20 seconds at a temperature of 60 ~ 70 ℃, the concentration of the aqueous solution is 2 ~ 5mL / L.

The silver plating treatment method of the present invention may further include a third silver plating pretreatment step of degreasing using an aqueous solution of sodium sulfate to remove the aluminum oxide film after the second silver plating pretreatment step S40. Here, the third silver plating pretreatment step may be performed using the same solution as the first silver plating pretreatment step and under the same treatment conditions.

The silver plating treatment method according to the present invention may further include the step of not plating the plated material subjected to silver plating pre-treatment as described above before silver plating the material to be plated. (S50)

The base plating step (S50) improves the corrosion resistance, hardness and flexibility of the product before the silver plating process, and enables a good adhesion adhesion. The base plating step is a process of silver strike plating a silver plated pretreated aluminum material, specifically, the first gating treatment, the zinc peeling, the second gating treatment, the electroless nickel plating and the silver strike plating may be sequentially performed. .

The jinkate treatment is another term called zinc substitution precipitation plating, and is performed before silver strike plating is applied to the surface of the silver plated aluminum material. Aluminum is an active metal and its surface is always covered with an oxide film, which makes it difficult to directly plate on aluminum. Generally, substitution is performed on other metals, and plating is performed on the substituted and deposited metal film. Aluminum is easily substituted and precipitated in a solution containing a metal salt, so that the zinc coating is performed to improve adhesion. The gating process can be easily carried out by those skilled in the art.

In the present invention, it is preferable that the gating process is carried out in two steps. After the first zincate treatment, the secondary zincate treatment is performed to maintain a uniform plating state. Zinc stripping is a pretreatment step in which zinc formed on the surface of an aluminum material is removed by immersion in nitric acid solution. Subsequently, the secondary zincate treatment is carried out in the same manner as the primary zincate treatment, thereby maintaining a uniform zinc plating state and giving good adhesion. The surface of the exfoliated aluminum material remains alloy substitution component, and may act as a nucleus of the substitution reaction during the second gating process. Therefore, when the aluminum material is deposited in the secondary quenching solution, a substitution reaction is formed in which the amount of the substitution metal is applied to the entire surface in an instant.

After the secondary zincating process is completed, electroless nickel plating is performed. Silver plating reacts with external oxygen over time and is easily oxidized or discolored. Therefore, electroless nickel is widely used as a base plating. Since the electroless plating layer is made of an amorphous alloy, growth of crystal grains does not occur even if the thickness is large, and a uniform surface is obtained, and thus, corrosion resistance and abrasion resistance are obtained. Electroless nickel plating is chemical plating or self-catalyst plating which does not receive electric energy from the outside. Generally, the most commonly used plating agents include copper and nickel-phosphorus-nickel-boron alloys. Compared to electroplating, the plating layer has a dense and uniform thickness, and there is an advantage that it can be applied to various substrates such as plastics or organics as well as conductors.

When electroless nickel plating is completed, silver strike plating is performed. The silver strike plating is to obtain excellent adhesion between the silver plating and the electroless nickel plating layer during the silver plating process, and is performed using an alkali type deposition electroplating method. Specifically, after the aluminum material is deposited under the conditions of a temperature of 15 to 30 ° C., a concentration of 1 to 2 g / L of silver cyanide, and a current density of 1 to 2 A / dm ² , silver strike plating may be performed by applying a high voltage momentarily. .

The plated material thus treated is silver plated in the next step. (S60)

Silver is a metal having excellent thermal conductivity, electrical conductivity, and resistivity. Although silver has a disadvantage of being expensive compared to general materials, silver can improve the RF characteristic signal by plating silver on an aluminum surface having excellent workability and conductivity. According to one embodiment of the invention, the silver plating step (S60) is a temperature of 15 ~ 30 ℃, silver cyanide concentration 10 ~ 40 g / L, potassium cyanide concentration 80 ~ 150 g / L and current density 0.2 ~ 0.3 A / dm ² It is preferable to apply a low voltage and to advance silver plating gradually on condition of.

The silver plating treatment method according to the present invention may further include a discoloration prevention treatment step to prevent discoloration of the plating layer after the silver plating step (S60). After silver plating is completed, silver is easily oxidized and discolored when exposed to air, so it is treated with a discoloration inhibitor to prevent discoloration.

The silver plating treatment method according to the present invention treated as described above is applicable to any device that requires silver plating and painting, in particular can be usefully applied to the TMA device.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are for illustrative purposes only and are not intended to limit the present invention.

Example

The die cast aluminum material was ultrasonically degreased for 5 minutes using a caustic soda solution. Subsequently, in a 300 g / L caustic soda solution, the solution was etched at 20 ° C. for 3 minutes and activated for 1 minute with 100 ml / L nitric acid.

The aluminum material was converted into an aluminum pretreatment agent 'AL-104' (Youngin Plachem) stock solution concentration 1 ml / L

It was degreased at room temperature for 20 seconds.

The finished aluminum material was made of aluminum pretreatment agent 'AL-103' (Youngin Plachem) stock solution concentration 3ml / L, degreased at 60 ° C. for 15 seconds, and once again the stock solution concentration was used using 'AL-104'. It degreased at 1 ml / L for 20 second at normal temperature.

The aluminum plated pre-treatment of aluminum was zinc-substituted at room temperature for 30 seconds using a zinc solution consisting of caustic soda 500g / L, rossel salt 10g / L, zinc oxide 100g / L, and 100ml / L nitric acid solution. The mixture was treated for 2 minutes, peeled off, and then zinc-substituted twice. A silver strike plate was applied thereto by applying a voltage of 3.5 V for 5 seconds at room temperature using a mixed solution of 80 g / L potassium cyanide and 1 g / L silver cyanide.

The base plated aluminum material is coated with a plating solution of 130 g / L potassium cyanide, 35 g / L silver cyanide, 0.3 g / L curing agent, and 0.1 g / L polishing agent at a temperature of 0.2 A / dec at room temperature for 15 minutes. Silver plated. The silver plated aluminum material was treated with Taniban 7.14 ml / L at 20 ° C. for 40 seconds to prevent discoloration.

In order to test the coating adhesion of the silver plated aluminum material according to the present invention, the surface of the aluminum material on which the coating layer was formed was lined horizontally and vertically at intervals of 1 mm to form a square shape, and then attached and detached using an adhesive tape. It was. As a result, as shown in FIG. 2, the coating layer was not separated, and it was found that the adhesion between coating and plating was excellent. In addition, discoloration of the coating color did not appear upon plating after coating.

Thus, according to the silver plating process of this invention, the adhesiveness between coating and plating is excellent, and discoloration prevention of coating is possible. In addition, the cost is reduced by omitting the conventional chromate step, and the plating and silk printing can be carried out at the same time, the silver plating process is possible, so that the required time can be significantly shortened compared to the existing process.

As described above, the silver plating treatment method of the aluminum material according to the present invention not only prevents discoloration of the coating and improves the coating adhesion through the silver plating pretreatment process, but also enables coating and silk printing at the same time without a chromate process during coating. Can be simplified.

Claims (19)

(a) pretreating the material to be plated; (b) a first silver plating pretreatment step of degreasing the pretreated material to be plated using an aqueous sodium sulfate solution; (c) painting the plated material; (d) a second silver plating pretreatment step of degreasing the coated material to be coated using an aqueous solution containing ammonium fluoride and sulfuric acid; And (e) silver plating the silver plated preplated material; Silver plating processing method comprising a. The method of claim 1, wherein the plated material is selected from the group consisting of aluminum, copper, and iron. The method of claim 1, wherein (a) the pretreatment step comprises degreasing, etching, and activating steps. The method of claim 3, wherein the degreasing is performed by selecting at least one of solvent degreasing and ultrasonic degreasing. The method of claim 1, wherein (b) the first silver plating pretreatment step is performed using an aqueous solution containing 5 to 10% by weight of sodium sulfate. The silver plating method of claim 1, wherein (b) the first silver plating pretreatment step is performed at room temperature for 20-30 seconds at a concentration of 0.5-2 mL / L aqueous sodium sulfate solution. The silver plating method according to claim 1, wherein the coating step (c) uses an electrical method of spraying the powder coating material through a nozzle of the powder coating gun and spraying the grounded workpiece. The method of claim 1, wherein the coating step (c) uses air immersion to blow the air through the porous plate to make the powder coating flow, and to attach the powder coating to the coating by heating or static electricity. Silver plating processing method. The method of claim 1, wherein the coating step (c) is characterized in that the silk printing is performed at the same time. The method of claim 1, wherein (d) the second silver plating pretreatment step is performed using an aqueous solution containing 5 to 10% by weight of ammonium fluoride and 0.5 to 5% by weight of sulfuric acid. The silver plating according to claim 1, wherein (d) the second silver plating pretreatment step is performed at a temperature of 60 to 70 ° C. for 10 to 20 seconds at a concentration of 2 to 5 ml / L of the aqueous solution containing ammonium fluoride and sulfuric acid. Treatment method. The silver plating method according to claim 1, further comprising (d) a third silver plating pretreatment step of degreasing using an aqueous sodium sulfate solution to remove the aluminum oxide film after the second silver plating pretreatment step. The method of claim 12, wherein the third silver plating pretreatment step is performed under the same conditions as the first silver plating pretreatment step. The method of claim 1, further comprising the step of (e) plating the material to be plated before the silver plating step. 15. The method of claim 14, wherein the base plating step is performed by sequentially performing the first gating, zinc peeling, second gating, electroless nickel plating and silver strike plating. The method of claim 15, wherein the silver strike plating is performed under a condition of a temperature of 15 to 30 ° C., a concentration of silver cyanide of 1 to 2 g / L, and a current density of 1 to 2 A / dm ² . The method of claim 1, wherein the (e) silver plating step is carried out under the conditions of temperature 15 ~ 30 ℃, silver cyanide concentration 10 ~ 40 g / L, potassium cyanide concentration 80 ~ 150 g / L and current density 0.2 ~ 0.3 A / dm ² Silver plating process performed. The silver plating method according to claim 1, further comprising a discoloration preventing treatment step to prevent discoloration of the plating layer after the silver plating step. A plated product manufactured according to the silver plating treatment method of any one of claims 1 to 18.

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