JP2012082475A - Trivalent chromium plating method by barrel plating - Google Patents

Abstract

Provided is a novel plating method capable of forming a chromium plating film having a good appearance and excellent corrosion resistance when a chromium plating film is formed by barrel plating using a trivalent chromium plating bath. .
Chromium is characterized in that semi-bright nickel plating and bright nickel plating are sequentially performed by barrel plating, and then chromium plating is performed by barrel plating using a trivalent chromium plating bath containing a trivalent chromium compound. Plating method.
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Description

  The present invention relates to a trivalent chromium plating method by barrel plating and an article on which a trivalent chromium plating film is formed.

  Chromium plating is widely used in various fields such as decoration and industrial use. Plating is mainly performed using a chromium plating bath containing a large amount of hexavalent chromium as a chromium component.

However, since the plating bath containing hexavalent chromium (hexavalent chromium plating bath) contains chromic acid (Cr ₂ O ₃ ) at a high concentration of about 250 g / L, the oxidizing power is very high, and the barrel plating method. When the plating process is carried out in this way, since the current to the object to be plated is interrupted intermittently, the surface of the chromium plating film deposited at this time becomes non-conductive, and the formed chromium plating film has a There is a problem in that poor appearance and poor adhesion occur. For this reason, barrel plating with a hexavalent chromium plating bath is very difficult and has not been put into practical use industrially.

  In addition, when a hexavalent chromium plating bath is used, the toxicity of mist containing hexavalent chromium generated during plating is a problem, and it is toxic in consideration of the improvement of the working environment and the efficiency of wastewater treatment. A trivalent chromium plating bath using a trivalent chromium compound with a low content has become widespread (see Non-Patent Document 1 below). Such a trivalent chromium plating bath has poorer appearance and adhesion than the hexavalent chromium plating bath when the current interruption that is unavoidable by the barrel plating method occurs because the plating bath itself has low oxidation property. It is considered that the decrease in sex is difficult to occur. For this reason, by using a trivalent chromium plating bath, it is expected that chromium plating by a barrel plating method, which was impossible with a conventional hexavalent chromium plating bath, will be possible.

  However, it is known that the chromium plating film formed from the trivalent chromium plating bath is inferior in corrosion resistance compared to the chromium plating film formed from the hexavalent chromium plating bath, and in particular, the barrel plating method was applied. In some cases, it is difficult to obtain sufficient corrosion resistance in the low current density portion.

Surface technology Vol.56, No.6, 2005 302p "Development of chromium plating and environmental problems"

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is to provide a good appearance when a chromium plating film is formed by barrel plating using a trivalent chromium plating bath. It is intended to provide a novel plating method capable of forming a chromium plating film having excellent corrosion resistance.

The present inventor has intensively studied to achieve the above-described object. As a result, a semi-bright nickel plating and a bright nickel plating are sequentially performed by a barrel plating method, and then chromium plating is performed using a trivalent chromium plating bath, whereby a chromium plating film having a good gloss appearance and excellent corrosion resistance As a result, the present invention has been completed.

That is, the present invention provides the following chromium plating method and an article on which a trivalent chromium plating film is formed.
1. A chromium plating method comprising: performing semi-bright nickel plating and bright nickel plating sequentially by barrel plating, and then performing chromium plating by barrel plating using a trivalent chromium plating bath containing a trivalent chromium compound.
2. A semi-bright nickel plating bath for performing semi-bright nickel is a plating bath to which at least one component selected from the group consisting of butynediol and its derivatives is added using a Watt bath as a basic bath, and for performing bright nickel. Item 2. The chromium plating method according to Item 1, wherein the bright nickel plating bath is a plating bath to which a compound having a ═C—SO ₂ — bond is added using a Watt bath as a basic bath.
3. Item 3. The chromium plating method according to Item 1 or 2, wherein the trivalent chromium plating bath is a plating bath containing chromium sulfate as a trivalent chromium compound and not containing chloride ions.
4). Item 4. The chromium plating method according to Item 3, wherein the trivalent chromium plating bath contains 20 to 100 ppm of iron ions.
5. An article on which a chromium plating film is formed by the method according to item 1, wherein a semi-bright nickel plating film, a bright nickel plating film, and a chromium plating film formed from a trivalent chromium plating bath are sequentially laminated.

  The chromium plating method of the present invention is a method in which chromium plating is performed by barrel plating, and after performing semi-bright nickel plating and bright nickel plating sequentially, chromium plating is performed using a chromium plating bath containing a trivalent chromium compound. It is the method characterized by this.

  According to such a chromium plating method, a chromium plating film having a good appearance can be formed up to a portion having a low current density, even when an object having a complicated shape is to be processed. The formed chromium plating film has excellent corrosion resistance.

  Hereinafter, first, each plating bath used in the plating method of the present invention will be specifically described.

(1) Semi-bright nickel plating bath In the present invention, the nickel plating bath for forming the semi-bright nickel plating is not particularly limited, and a known semi-bright nickel plating bath can be used. Usually, a semi-bright nickel plating bath contains an additive that imparts a leveling effect called a secondary brightener to a nickel plating bath mainly composed of nickel sulfate, nickel chloride and boric acid called Watts bath. The plating bath does not contain a sulfur-containing compound called a primary brightener contained in the bright nickel plating bath.

The composition of the Watt bath is not particularly limited. For example, NiSO ₄ · 7H ₂ O is about 250 to 400 g / L, NiCl ₂ · 6H ₂ O is about 40 to 50 g / L, and boric acid is 30 to 50 g. A plating bath containing about / L is typical.

There is no limitation in particular about the kind of secondary brightener, A well-known secondary brightener can be used. Examples of such secondary brighteners include the compounds described in the following items (i) to (iv). These compounds can be used alone or in combination of two or more.
(I) Compounds having a C═O bond such as ketones, aldehydes, carboxylic acids,
(Ii) compounds having a C = C bond such as alkene carboxylic acid esters, alkene aldehydes, coumarins, derivatives thereof,
(Iii) acetylene derivatives, butynediol, its derivatives, etc.

A compound having
(Iv) compounds having a C═N bond such as azine, thiazine, dye, imidazole,
(V) ethylene cyanohydrin, etc.

A compound having

  In the present invention, it is particularly preferable to use at least one compound selected from the group consisting of butynediol and derivatives thereof as the secondary brightener. Examples of the derivatives of butynediol include butynediol ethoxylate, butynediol diethoxylate, butynediol monopropoxylate, butynediol propylene glycol mixture, and hexynediol.

  The amount of these secondary brighteners to be added is not particularly limited, and may be used within the range of commonly used amounts depending on the type of secondary brightener used. For example, with respect to at least one compound selected from the group consisting of butynediol and derivatives thereof, the added amount can be about 0.01 to 3 g / L.

(2) Bright Nickel Plating Bath As for the bright nickel plating bath for forming the bright nickel plating film, a known bright nickel plating bath can be used.

As a specific example of the bright nickel plating bath, a plating bath in which a sulfur-containing compound called a primary brightener and a secondary brightener similar to a semi-bright nickel plating bath are added to the Watt bath described above. Can be mentioned. As the primary brightener, a compound containing sulfur can be used. Specific examples include aromatic sulfonic acids such as benzenesulfonic acid, aromatic sulfonamides such as p-toluenesulfonamide, and sulfonimides such as saccharin. Examples thereof include compounds having a ═C—SO ₂ — bond. These primary brighteners can be used singly or in combination of two or more.

  Further, as the secondary brightener to be added to the bright nickel plating bath, the same compounds as the secondary brightener for the semi-bright nickel plating bath described above can be used.

  The addition amount of the primary brightener and the secondary brightener may be appropriately determined from the range usually used according to the type of the brightener used. For example, both the primary brightener and the secondary brightener are 0.01 It can be set to a range of about 3 g / L.

(3) Trivalent chromium plating bath The trivalent chromium plating solution is not particularly limited as long as it is a chromium plating bath containing a trivalent chromium compound as a chromium component. It is preferable to use a trivalent chromium plating bath that does not contain. Such a trivalent chromium plating bath includes an aqueous solution trivalent chromium compound such as chromium (III) sulfate as a chromium component, and includes sodium sulfate, potassium sulfate, ammonium sulfate and the like as a conductive salt, as a complexing agent. Aliphatic monocarboxylic acids such as formic acid and acetic acid; aliphatic dicarboxylic acids such as oxalic acid, malonic acid and succinic acid; aliphatic hydroxymonocarboxylic acids such as gluconic acid; aliphatic hydroxydicarboxylic acids such as malic acid; citric acid Examples thereof include an aliphatic hydroxytricarboxylic acid such as a plating bath containing these salts. Further, boric acid, boron oxide, sodium borate or the like may be included as a pH buffer. The concentration of each of these components is not particularly limited. For example, for a trivalent chromium compound, about 10 to 100 g / L (about 3 to 30 g / L as Cr), and for a conductive salt, about 30 to A trivalent chromium plating bath of about 300 g / L, a complexing agent of about 5 to 50 g / L, and a pH buffer of about 10 to 100 g / L can be exemplified.

  By adding a water-soluble iron compound to the trivalent chromium plating bath, the throwing power in the low current density region is improved. Examples of such water-soluble iron compounds include iron sulfate, iron chloride, iron nitrate, ammonium iron citrate, and iron iron sulfate. About the addition amount of an iron compound, it is preferable to set it as about 20-100 ppm as iron ion concentration in a trivalent chromium plating bath, and it is more preferable to set it as about 30-70 ppm.

Furthermore, in the trivalent chromium plating bath, a compound having an SO ₂ group or an SO ₃ group may be added as a brightening agent, or a known mist inhibitor may be added as necessary.

Barrel Plating Method In the plating method of the present invention, first, semi-bright nickel plating and bright nickel plating are sequentially performed using the above-described semi-bright nickel plating bath and bright nickel plating bath by the barrel plating method.

  Prior to performing semi-bright nickel, conventional pretreatment such as degreasing and acid activity may be performed on the object to be plated in accordance with a conventional method.

  There is no particular limitation on the type of the object to be plated. Basically, plating can be performed without any limitation as long as it is a conductive material. For example, a copper alloy such as steel, brass, and stainless steel can be plated by performing appropriate pretreatment according to a conventional method.

  The barrel plating apparatus to be used is not particularly limited, and a known barrel plating apparatus can be used.

  As for the conditions of semi-bright nickel plating, for example, a plating temperature of about 40 to 60 ° C. and a pH of about 4.0 to 4.5 may be used, and barrel plating may be performed at a voltage of about 5 to 8 V for about 60 to 180 minutes. In this case, it is preferable to set the condition that a semi-bright nickel plating film having a minimum film thickness of about 2 to 3 μm is formed even in a low current density portion where the film thickness is the thinnest. The upper limit of the thickness of the semi-bright nickel plating film is not particularly limited, but is usually about 5 μm.

  As for the conditions for bright nickel plating, for example, barrel plating may be performed at a voltage of about 5 to 8 V for about 30 to 60 minutes with a bath temperature of about 40 to 60 ° C. and a pH of about 3.8 to 5.0. In this case, it is preferable that the low nickel film with a minimum film thickness of about 0.5 μm or more is formed even in the low current density portion where the film thickness is the thinnest. The upper limit of the thickness of the bright nickel plating film is not particularly limited, but is usually about 3 μm.

  After the semi-bright nickel plating and the bright nickel plating are sequentially performed by the above-described method, a trivalent chromium plating film is formed by a barrel plating method using a trivalent chromium plating bath. The conditions of the 3 chrome plating are not particularly limited. For example, the pH of the trivalent chromium plating bath is about 3 to 4, the liquid temperature is about 40 to 50 ° C., and the plating is performed for about 15 to 30 minutes at a voltage of about 5 to 10 V. The film thickness of the chromium plating film to be formed is preferably about 0.05 μm or more, and is usually in the range of about 0.1 to 0.2 μm.

  According to the present invention, when a chromium plating film is formed by barrel plating using a trivalent chromium plating bath, a chromium plating film having a good gloss appearance and excellent corrosion resistance can be formed.

Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
Use a mild steel screw (length: about 1.5cm) as the object to be plated, and after performing degreasing, electrolytic degreasing, and acid activity in the usual way, add 200g to a mini barrel (capacity: 200ml) made by Yamamoto Kakin I put it in.

  Next, the barrel containing the object to be plated was immersed in a semi-bright nickel plating bath containing nickel sulfate 300 g / L, nickel chloride 45 g / L, boric acid 45 g / L, and hexynediol 0.05 g / L. Then, barrel plating is performed for 60 minutes by constant-voltage electrolysis under conditions of bath temperature 50 ° C., pH 4.2, bath voltage 8V (average current 5-7A) (barrel rotation speed is 5 rpm, the same applies hereinafter), semi-glossy A nickel plating film was formed. The film thickness of the formed semi-bright nickel plating film was about 5 μm on average.

  Next, the barrel after semi-bright nickel treatment is placed in a bright nickel plating bath containing nickel sulfate 280 g / L, nickel chloride 40 g / L, boric acid 40 g / L, saccharin 2 g / L and butynediol 0.05 g / L. Immersion was performed, and barrel plating was performed for 40 minutes by constant-voltage electrolysis under conditions of a bath temperature of 50 ° C., a pH of 4.2, and a bath voltage of 8 V (average current of about 5 to 7 A) to form a bright nickel plating film. The thickness of the formed bright nickel plating film was about 3 μm on average.

  Then, 40% chromium sulfate (III) 35g / L (3.5g / L as Cr), oxalic acid dihydrate 8.5g / L, boric acid 60g / L, sodium sulfate 200g / L, and saccharin 3g / L In addition, using a trivalent chromium plating bath containing 50 ppm of iron (III) sulfate as the Fe amount, the barrel after the bright nickel treatment was immersed in the trivalent chromium plating bath, bath temperature 40 ° C., pH 3 Barrel plating was performed for 30 minutes by constant voltage electrolysis under the conditions of .5 and a bath voltage of 8 V to form a trivalent chromium plating film. The film thickness of the formed trivalent chromium plating film was about 0.1 μm on average.

Example 2
Example, except using a plating bath containing nickel sulfate 300 g / L, nickel chloride 40 g / L, boric acid 40 g / L, saccharin 2 g / L, and butynediol ethoxylate 0.05 g / L as a bright nickel plating bath In the same manner as in Example 1, after semi-bright nickel plating and bright nickel plating, trivalent chromium plating was performed.

Comparative Example 1
In the method described in Example 1, a trivalent chromium plating film was formed in the same manner as in Example 1 except that the plating time for bright nickel plating was set to 1 hour without performing semi-bright nickel plating. .

Comparative Example 2
Instead of the semi-bright nickel plating bath used in Example 1, a Watt bath (nickel sulfate: 240 g / L, nickel chloride: 45 g / L, boric acid: 30 g / L pH = 4.5) not containing a brightener was used. Bright nickel plating and trivalent chromium plating are performed in the same manner as in Example 1 except that barrel plating is performed for 3 hours by constant-voltage electrolysis under conditions of a bath temperature of 45 ° C. and a bath voltage of 8 V (average current of about 5 to 7 A). went.

Comparative Example 3
In place of the semi-bright nickel plating bath used in Example 1, a nickel sulfamate bath not containing a brightener (nickel sulfamate: 320 g / L, nickel bromide: 10 g / L, boric acid: 30 g / L, pH = 3.5), the same as in Example 1, except that barrel plating is performed for 3 hours by constant-voltage electrolysis under conditions of a bath temperature of 45 ° C. and a bath voltage of 8 V (average current of about 5 to 7 A). Trivalent chromium plating was performed.

  About each trivalent chromium plating film obtained by the above method, the film appearance and corrosion resistance were evaluated by the following methods. The results are shown in Table 1 below.

* Appearance of the film The appearance of the film is visually observed. The case where the whole has a good gloss is indicated by a circle, and the case where a matte part is present is indicated by a mark.

* Corrosion resistance Corrosion resistance test was conducted on five samples by the salt spray test according to JIS Z2371, and the time until rust was generated was measured.

  As is clear from the above results, in Example 1 and Example 2, after performing the semi-bright nickel plating and the bright nickel plating, by performing trivalent chromium plating, it has a good gloss appearance. In addition, a trivalent chromium plating film excellent in corrosion resistance could be formed by a barrel plating method.

  On the other hand, as shown in Comparative Example 1, when only the bright nickel plating film was formed as the base of the trivalent chromium plating film, the formed trivalent chromium plating film had a glossy appearance. The corrosion resistance was inferior.

  In addition, as shown in Comparative Examples 2 and 3, even when two nickel plating films are formed, when bright nickel plating is performed after matte nickel plating, a good gloss appearance is obtained. It was difficult to form a trivalent chromium plating film and the corrosion resistance was poor.

Claims (5)

A chromium plating method comprising: performing semi-bright nickel plating and bright nickel plating sequentially by barrel plating, and then performing chromium plating by barrel plating using a trivalent chromium plating bath containing a trivalent chromium compound. A semi-bright nickel plating bath for performing semi-bright nickel is a plating bath to which at least one component selected from the group consisting of butynediol and its derivatives is added using a Watt bath as a basic bath, and for performing bright nickel. The chromium plating method according to claim 1, wherein the bright nickel plating bath is a plating bath to which a compound having a ═C—SO ₂ — bond is added using a Watt bath as a basic bath. The chromium plating method according to claim 1 or 2, wherein the trivalent chromium plating bath is a plating bath containing chromium sulfate as a trivalent chromium compound and not containing chloride ions. The chromium plating method according to claim 3, wherein the trivalent chromium plating bath contains 20 to 100 ppm of iron ions. The article in which a chromium plating film is formed by the method according to claim 1, wherein a semi-bright nickel plating film, a bright nickel plating film, and a chromium plating film formed from a trivalent chromium plating bath are sequentially laminated.