JPH036239B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for chrome plating the surface of a material to be plated, particularly the surface of a cylinder for gravure printing, etc., using a sergeant bath or the like, and an anode for chrome plating.

(Prior art and its problems) The chrome plating method not only provides a good appearance on the formed surface, but also provides a sufficiently hard and corrosion-resistant coating layer. , engine parts for automobiles, etc.
Widely used for plating various cylinders, tableware, cans, etc.

The chrome plating method can be roughly divided into a method using a silicate bath in which silicic acid is added to the plating bath;
There is a method of using a sergeant bath to which sulfuric acid is added, and in addition to these methods, various plating baths have been devised based on these two methods, in which additives are added or the concentration of the liquid is changed.

Because the silifying bath has a good finish and high current efficiency, it is used for plating automobile engine parts and steel plates for canning cans, which are made of tin-free steel. However, it is difficult to manage the liquid, and since the electrolytic bath contains fluoride ions, the liquid is highly corrosive and corrodes the plating apparatus itself, making maintenance difficult.

Although sergeant baths and their modified baths generally have a problem of somewhat low current efficiency, they are easy to handle and stable, so they are becoming widely used. Sargent baths and their modified baths generally use lead or lead alloys as anodes. However, anodes made of lead or lead alloys oxidize Cr ³⁺ ions generated during electrolysis.
Although it has the effect of converting to Cr ₂ O ₇ and keeping the concentration of each ion constant, the elution of lead and lead alloys from the anode is limited.
mg to several tens of mg/AH, and the eluted lead ions react with chromic acid in the solution to form lead chromate (PbCrO ₄ ).
forms and precipitates in the liquid. Therefore, not only is maintenance such as removal of the precipitates and liquid exchange time-consuming, but also there is a problem that the precipitates have an adverse effect on the chrome plating layer itself. Another disadvantage is that the electrodes have a short lifespan and must be replaced frequently.

Methods have been proposed to use ferrite or magnetite electrodes to eliminate the effects of lead, but these electrodes are themselves extremely brittle and lack mechanical strength, requiring great care when handling. Magnetite has the disadvantage that it has a relatively low electrical conductivity and cannot be used at high current densities. Also, when using this electrode, the
It has also been pointed out that the concentration of Cr ³⁺ ions increases and the current efficiency decreases.

Lead dioxide coated electrodes, which are currently used as the most suitable anodes for chrome plating, differ from the aforementioned lead electrodes in that the elution of electrode components into the plating bath is as small as 0.1 mg/AH or less, and there is almost no liquid contamination or precipitation. do not have.
However, when the lead dioxide coated electrode is used alone, the oxidizing effect on Cr ³⁺ ions is too strong, and the Cr ³⁺ concentration in the bath often becomes less than 1.5 g/min, resulting in poor plating quality.

As a noble metal-based insoluble metal electrode, a so-called dimensionally stable electrode (DSE) coated with an oxide layer containing platinum-plated titanium or a platinum group metal oxide is used. DSE has extremely high corrosion resistance and extremely high catalytic activity against oxygen generation, so it is widely used in various electrolysis applications. In the case of chrome plating, the electrode has the function of oxidizing Cr ³⁺ ions in addition to passing current, but the DSE has insufficient catalytic activity for oxidizing Cr ³⁺ ions, and
It has the disadvantage that the concentration of Cr ³⁺ ions increases.

In order to solve these problems, recently a platinum-plated titanium electrode is used as an anode, lead is immersed in a plating bath or connected to the anode, and the lead is dissolved as ions in the plating bath, and the lead ions are transferred to the titanium electrode. A method has been proposed in which the surface is modified to oxidize Cr ³⁺ ions by collecting them as lead dioxide. This method is particularly effective for plating gravure printing rolls that are frequently turned on and off, but because there is little lead dioxide deposited on the surface during anodic polarization and the adhesion of lead dioxide is relatively weak, the current supply is stopped. At times, the lead dioxide layer tends to dissolve or peel off, and its oxidizing power against chromium is weak. To improve this, it is necessary to take measures such as making the anode area larger than usual.

(Purpose of the Invention) The present invention was made to solve the above-mentioned problems, and aims to minimize contamination due to lead chromate precipitation in the plating bath and maintain an appropriate Cr ³⁺ concentration. The object of the present invention is to provide a plating method and an anode for chrome plating that can stably perform high-quality chrome plating over a long period of time.

(Means for Solving the Problems) The present invention firstly provides a coating of at least one metal selected from metals belonging to Groups 4 and 5 of the Periodic Table on the surface of a base material on which a platinum coating is formed. Using an anode coated with an oxide having an ethyl type crystal phase, a lead component is added to the plating bath and electricity is applied to form a lead dioxide coating on the oxide coating, and the material to be plated is chrome plated. This is a chrome plating method characterized by: secondly, the surface of the base material on which the platinum coating is formed is coated with an oxide of at least one metal selected from metals belonging to Groups 4 and 5 of the periodic table; The anode for chrome plating is further formed by coating the metal oxide with a lead dioxide coating.

The present invention will be explained in detail below.

The electrode base material in the present invention is not particularly limited as long as it has corrosion resistance and conductivity during anodic polarization in a plating bath, but titanium or a titanium alloy is optimal from the viewpoint of stability and workability. The shape of the base material is preferably a perforated plate or an expanded mesh in consideration of liquid flow and gas release.

The substrate coating is then coated with platinum.

The main reaction at the anode during chrome plating is an oxygen evolution reaction, and platinum is used as the electrode component that mainly causes this reaction. Recently, electrodes coated with platinum group metal oxides (DSE) have been commonly used, but this type of electrode has an extremely catalytic effect on oxygen generation and has a low electrolytic potential. Therefore, trivalent chromium in the plating solution is not oxidized even if the electrode surface is modified with lead oxide, which will be described later. Therefore, it cannot be used as an electrode coating material in the present invention, and only platinum can be used. Note that platinum has sufficient durability as an anode in a chrome plating bath, and hardly deteriorates even after long-term operation.

The method for coating the base material with platinum is not particularly limited as long as the platinum can be firmly bonded to the base material, and conventional techniques such as electroplating and pyrolysis can be used. is particularly suitable.
To form a platinum coating by a pyrolysis method, a soluble solution containing a platinum component such as chloroplatinic acid is prepared, the solution is applied to a substrate, and then the solution is heated in air, vacuum, an inert atmosphere, etc. The material is heated to 300-700°C to form a platinum coating through thermal decomposition. In addition, in order to apply the platinum coating smoothly and uniformly to the entire surface of the base material, prevent oxidation of the base material itself, and obtain an electrode with a longer lifespan, the surface of the base material is coated in advance by thermal oxidation or thermal decomposition. A conductive oxide coating such as titanium oxide, tin oxide or (TiTa)O ₂ may be formed.

The platinum coating formed in this manner alone has insufficient ability to oxidize trivalent chromium to hexavalent chromium, and in order to increase this ability, a thin layer of lead oxide is formed on the surface. In order to form the lead oxide, first, a metal oxide layer as described below is formed on the surface of the platinum-coated electrode, and the lead ions are removed in a plating bath containing lead ions using the oxide-coated platinum electrode. oxidizes and the resulting lead dioxide is deposited. The oxide layer is a metal of Group 4 or Group 5 of the periodic table, ie, a valve metal such as titanium, zirconium, hafnium, niobium, tantalum, etc., or a metal such as tin, preferably a metal that forms an ethyl type oxide. An oxide layer is formed by a thermal decomposition method or the like. The conditions for this thermal decomposition are arbitrary; for example, a hydrochloric acid or alcohol solution containing the above metals is applied and heated at 400 to 700°C. This operation can be repeated several times to obtain an oxide layer of any desired thickness. Among these oxides, tin oxide (SnO ₂ ) is conductive by itself and can be used as is, but titanium oxide, for example, has insufficient conductivity when it is completely TiO ₂ , so it is necessary to add niobium or tantalum to it. When a small amount is dissolved in solid solution, the conductivity becomes good and an oxide coating layer of rutile type crystal can be easily obtained.

The platinum electrode on which the oxide coating layer is formed can easily form a lead oxide layer on its surface by oxidizing lead ions in the bath in a chrome plating bath, and the amount of the surface lead oxide layer is: The amount should be within a range that does not impair the electrolytic performance of platinum, preferably 0.1 to 50 g/m ² .

In the method of the present invention, an electrode base material on which a lead dioxide coating is not formed on the surface is used, a plating solution containing a lead component is used during chrome plating on the base material, and the lead dioxide is coated on the surface of the base material at the start of plating. It is efficient to form a coating. However, the anode for chrome plating according to the present invention can also be manufactured by a method other than the above method, such as by plating lead dioxide in a separate plating bath on the base material before coating with lead dioxide, or by applying a suspension at a temperature below 200°C. A lead dioxide coating can also be formed by a coating heating method in which the lead dioxide is heated and fixed.

In the method of the present invention and the anode for chrome plating according to the present invention, an oxide layer of metal such as tin is formed between the platinum-coated base material and the lead dioxide coating on the surface.
The adhesion of the lead dioxide coating to the base material is improved, which not only extends the life of the electrode, but also prevents the precipitation of lead chromate, which improves work efficiency by several degrees.

(Examples) The present invention will be explained in more detail based on Examples below, but the present invention is not limited to these Examples.

Example 1 Made of JIS 1st grade titanium, length 50mm, width 50mm and thickness
A 1.5 mm expanded mesh was used as a base material, and the surface was roughened by sandblasting, then degreased and pickled in a 20% boiling hydrochloric acid aqueous solution. A platinum coating was formed on the surface of the base material by the thermal decomposition method described below. In other words, as a coating solution, chloroplatinic acid (25 g as metal) is dissolved in a solution made by mixing isopropyl alcohol and 10% hydrochloric acid aqueous solution at a ratio of 1:1 (volume ratio), and the mixed solution is applied to the surface of the substrate with a brush. After drying at room temperature, it was fired for 10 minutes in a Matsufuru furnace with air flowing through it at 530° C. This operation was repeated 20 times to obtain a platinum-coated substrate with 10 g/m ² of platinum attached to titanium.

Next, a tin oxide (SnO ₂ ) coating was formed on the platinum coating by a thermal decomposition method according to the method described below.
The coating solution is made by dissolving tin chloride in aluminum alcohol, heating it for 3 hours with a reflux condenser to remove chlorine ions, and then adding a few drops of deionized water to convert some of the tin component into hydroxide. I made it so that it would be done. This coating solution was spray-coated onto the platinum-coated substrate, dried at 150°C, and then baked at 500°C for 10 minutes. This operation was repeated four times to form a coating of about 2 g-Sn/m ² . Observation with a powder X-ray diffractometer revealed that the crystal phase of the tin oxide was rutile type.

For comparison, a sample electrode without tin oxide coating was prepared using the same manufacturing method.

Both electrodes are anodes, and a copper piece of the same shape, 50 mm long, 50 mm wide, and 1.5 mm thick, is used as the cathode.
The surface of the copper piece was then chromed at 15 A/dm ² for 3 continuous hours using a sergeant bath chroming solution to which basic lead carbonate was added so that the concentration before electrolysis was 1 g-Pb/.

In plating using the electrode of this example, the current efficiency is 16
%, the Cr ³⁺ concentration after plating was 6 g/, whereas when plating with the comparison electrode, the current efficiency was
The Cr ³⁺ concentration after plating decreased to 14% and decreased to 10g/
It was found that it did not have sufficient oxidation ability for Cr ³⁺ .

Example 2 A 10% hydrochloric acid aqueous solution containing titanium chloride and tantalum chloride was applied as a coating liquid to the surface of a titanium base material prepared in the same manner as in Example 1 so that the atomic ratio of titanium and tantalum was 20:80. After drying, it was baked at 550°C for 10 minutes to form a titanium-tantalum oxide solid solution base layer on the surface. Do this operation 4
The total metal content was 1 g/m ² by repeating the test several times. Observation with a powder X-ray diffractometer revealed that the crystalline phase of the oxide phase was rutile type.

This surface was coated with approximately 10 g/m ² of platinum in the same manner as in Example 1, and further coated with a rutile-type oxide solid solution having a metal content of 1.0 g/m ² made of titanium-tantalum as described above. Coatings were formed under similar conditions.

For comparison, an electrode was prepared in the same manner except that the titanium-tantalum surface oxide solid solution coating was not formed.

Both electrodes were immersed together with a lead piece in a chromic acid solution containing chromium trioxide at a concentration of 250 g/g and sulfuric acid at a concentration of 1 g/d, and anodic polarization was performed at 15 A/dm ² for 30 minutes. Analysis of the lead concentration in the liquid at this time
The amount of lead dioxide attached to each sample electrode was 14 g/m ² for the electrode of this example, and 12 g/m ² for the comparative electrode.

Furthermore, both electrodes were immersed in the above chromic acid solution at a temperature of 50°C.
The mixture was held for 30 minutes while stirring the liquid. In the comparative electrode, most of the lead was eluted, whereas in the electrode of this example, 5 g/m ² of lead oxide remained.

From the above, electrodes with a titanium-tantalum solid solution oxide surface layer are more likely to form lead dioxide on the surface during anodic polarization than electrodes without such a surface layer, and are also strongly attached and difficult to dissolve. I understand.

Example 3 A JIS Type 1 titanium plate having a thickness of 1 mm was pretreated in the same manner as in Example 1, and a base layer was formed in the same manner as in Example 2. A 5% aqueous solution of hydrochloric acid containing 50 g of chloroplatinic acid was used as the plating liquid, and the current density was 1 A/dm ² at room temperature.
Platinum plating was performed to a thickness of 0.5 μm. This surface was coated with 2 g/m ² of tin dioxide in the same manner as in Example 1.

This was used as an anode, and a plating solution was added to a chromic acid solution containing chromium trioxide at a concentration of 250 g/g and sulfuric acid at a concentration of 1 g/g, and pure lead was suspended in a plating tank as a lead source to make the lead ion concentration 45 ppm. Chrome plating was applied to the surface of the copper piece. 50℃ while circulating the liquid
After continuous electrolysis at 15A/ ^dm2 for 4000 hours,
The decrease in platinum content is almost zero, with 25g/ ^m2 on the surface.
of lead was firmly attached as lead dioxide. On the other hand, when commercially available platinum-plated titanium (platinum thickness 1 μm) was used, the platinum content decreased by about 10% under the same conditions, and the amount of lead on the surface was 17 g/m ² , which was smaller than that in this example. Nakatsuta.

(Effects of the Invention) In the method of the present invention, when performing chrome plating, metals belonging to Groups 4 and 5 of the periodic table, such as tin, are applied to a specific plating electrode, that is, the surface of a base material coated with platinum. Using an anode coated with an oxide of at least one selected metal, and applying electricity while adding a lead component to the plating bath, the surface of the base material coated with the tin oxide etc. is coated with lead dioxide. While forming, the material to be plated is plated.

A lead dioxide coating is formed on the anode by simply dissolving a small amount of lead in the plating bath during plating, and the anode remains stable for a long period of time even under plating conditions that are frequently turned on and off, such as in gravure roll plating. It becomes possible to perform plating operations. Therefore, by using the anode according to the method of the present invention in place of the conventional lead alloy anode, which tends to have a short lifespan, not only the lifespan of the anode can be extended, but also the precipitation of lead chromate in the liquid can be almost eliminated, making maintenance easier. This makes plating easier and allows you to continue plating for a long time without stopping the operation.

Further, the chrome plating anode according to the present invention can similarly perform chrome plating stably for a long period of time, and hardly causes precipitation.

Claims (1)

[Claims] 1. Using an anode in which the surface of a base material coated with platinum is coated with an oxide of at least one metal selected from metals belonging to Groups 4 and 5 of the periodic table, A chrome plating method characterized in that a lead component is added to a plating bath while electricity is applied to form a lead dioxide coating on the oxide coating, and the material to be plated is chrome plated. 2. The chrome plating method according to claim 1, wherein the plating bath is a plating bath that does not contain fluorine. 3 The surface of the material on which the platinum coating has been formed is coated with an oxide of at least one metal selected from metals belonging to Groups 4 and 5 of the periodic table, and further a lead dioxide coating is applied on the metal oxide. A coated anode for chrome plating. 4. The anode for chrome plating according to claim 3, wherein the metal oxide has a rutile crystal phase. 5. The chrome plating method according to claim 3 or 4, wherein the metal oxide is a tin oxide. 6. The chrome plating method according to claim 3 or 4, wherein the metal oxide is a titanium oxide and/or a tantalum oxide. 7. The chrome plating method according to any one of claims 3 to 6, wherein the coating thickness of the metal oxide is 1 μm or less.