Patent Application
20210040637
The present invention relates to a chromium plating product having improved corrosion resistance and a method for producing the same.
Chromium plating has a silvery-white or black appearance, and therefore is used as a coating film for decoration. In the chromium plating, hexavalent chromium has been used, however, recently, the hexavalent chromium affects the environment, and therefore, the use thereof has begun to be restricted, and it has shifted to a technique using trivalent chromium.
However, trivalent chromium plating has lower corrosion resistance than hexavalent chromium plating. Therefore, a technique for improving the corrosion resistance of trivalent chromium plating has been reported. For example, Japanese Patent No. 6110049 reports a technique for enhancing the corrosion resistance in a calcium chloride environment by forming a glossy nickel plating layer, a noble potential nickel plating layer, and a trivalent chromium plating layer having at least either one of a microporous structure and a microcrack structure in this order on a substrate, and intentionally providing a potential difference within a specific range between the glossy nickel plating layer and the noble potential nickel plating layer.
However, in the trivalent chromium plating, it is necessary to intentionally provide a potential difference within a specific range, and therefore, the control of a plating solution and plating conditions is complicated, and the technique was not practical.
In view of the above, an object of the present invention is to provide a chromium plating product including a trivalent chromium plating layer as the exterior and having high corrosion resistance, and a technique that facilitates the control of a plating solution and plating conditions for obtaining the same.
The present inventors made intensive studies for achieving the above object, and as a result, they found that by providing a nickel plating layer containing titanium under a trivalent chromium plating layer, the resulting product has high corrosion resistance, and the control of a plating solution and plating conditions for obtaining the same is easy, and thus completed the present invention.
That is, the present invention is directed to a chromium plating product including a substrate, a glossy nickel plating layer formed on the substrate, a nickel plating layer containing titanium formed on the glossy nickel plating layer, and a trivalent chromium plating layer formed on the nickel plating layer containing titanium and having a microporous structure.
Further, the present invention is directed to a method for producing a chromium plating product including a step of forming a glossy nickel plating layer on a substrate, a step of forming a nickel plating layer containing titanium on the glossy nickel plating layer, and a step of forming a trivalent chromium plating layer having a microporous structure on the nickel plating layer containing titanium.
Still further, the present invention is directed to a nickel plating solution containing a powder of a titanium compound and/or titanium ions.
The chromium plating product of the present invention has high corrosion resistance, and therefore can be used for decoration of automobile components, flush metal fittings, etc.
Further, in the method for producing a chromium plating product of the present invention, only a nickel plating layer containing titanium is provided under a chromium plating layer, and the control of a plating solution and plating conditions for obtaining the same is easy, and therefore, a new facility or the like is not particularly needed.
The chromium plating product of the present invention (hereinafter referred to as “product of the present invention”) includes a substrate, a glossy nickel plating layer formed on the substrate, a nickel plating layer containing titanium formed on the glossy nickel plating layer, and a trivalent chromium plating layer formed on the nickel plating layer containing titanium and having a microporous structure.
The substrate of the product of the present invention is not particularly limited, and examples thereof include metals such as brass, iron, and stainless steel, and resins such as ABS, PC/ABS, and PP. The form of the substrate is not particularly limited, but, for example, a door handle, an emblem, or the like. The substrate may be subjected to, for example, a treatment such as etching or electroless plating.
On the substrate, a glossy nickel plating layer is formed. The thickness of the glossy nickel plating layer is not particularly limited, but it may be provided at a thickness of, for example, 1 to 25 μm, preferably 2 to 15 μm.
A nickel plating solution for forming the glossy nickel plating layer is not particularly limited, but contains, for example, a nickel compound such as nickel sulfate, nickel sulfamate, or nickel chloride, a pH buffer such as boric acid or citric acid, and an organic compound such as saccharin, allylsulfonic acid, or butynediol.
Plating may be performed using the nickel plating solution for 3 to 30 minutes under the following conditions: anode: nickel electrode, bath temperature: 40 to 60° C., and current density: 2 to 5 A/dm2.
When the substrate is a resin, a semi-glossy nickel plating layer is formed between the substrate and the glossy nickel plating layer as needed. When the semi-glossy nickel plating layer is formed, it is preferred to provide a potential difference between the semi-glossy nickel plating layer and the glossy nickel plating layer, and the potential difference is not particularly limited, but is, for example, 60 mV or more, preferably 70 to 150 mV. By providing a potential difference in this manner, corrosion in the depth direction is suppressed by the sacrificial corrosion protection of the glossy nickel plating layer having a low potential. The potential difference can be measured by an electrolytic electrometer such as an electrolytic corrosion resistance measuring device or an electrolytic plating thickness measuring device.
On the glossy nickel plating layer, a nickel plating layer containing titanium is formed. The titanium content in the nickel plating layer containing titanium is not particularly limited, but is, for example, 0.01 to 1 mass %, preferably 0.02 to 0.5 mass %, more preferably 0.05 to 0.4 mass %. The titanium content can be measured using, for example, an analytical instrument such as EDS or a gravimetric method by film dissolution. Further, the form of titanium is also not particularly limited, and for example, titanium ions derived from a titanium salt such as titanium sulfate or titanium chloride, a powder of a titanium compound such as titanium oxide or titanium nitride, etc. are exemplified. When the powder of a titanium compound is used, the average particle diameter is 0.05 to 1.0 μm, preferably 0.1 to 0.7 μm. Among these forms of titanium, titanium oxide is preferred, titanium oxide having an average particle diameter of 0.05 to 1.0 μm is more preferred, and titanium oxide having an average particle diameter of 0.1 to 0.7 μm is particularly preferred. Here, the average particle diameter is a value measured by electron microscopic observation of the powder. Further, the state of titanium is also not particularly limited, and may be any of a rutile type, an anatase type, and a brookite type, but a rutile type is preferred from the viewpoint of stability.
The thickness of the nickel plating layer containing titanium is not particularly limited, but it may be provided at a thickness of, for example, 0.5 to 5 μm, preferably 1 to 3 μm.
A nickel plating solution for forming the nickel plating layer containing titanium is not particularly limited, but contains, for example, a nickel compound such as nickel sulfate, nickel sulfamate, or nickel chloride, a pH buffer such as boric acid or citric acid, an organic compound such as saccharin or allylsulfonic acid, a powder of a titanium compound such as titanium oxide or titanium nitride, and/or titanium ions derived from a titanium salt such as titanium sulfate or titanium chloride. As a preferred nickel plating solution, the following nickel plating solutions are exemplified.
Plating may be performed using the nickel plating solution for 1 to 5 minutes under the following conditions: anode: nickel electrode, bath temperature: 40 to 60° C., and current density: 2 to 5 A/dm2.
In the nickel plating solution, a powder of a metal oxide such as silicon oxide may be incorporated. In this case, the content is, for example, 0.1 to 3 g/L, preferably 0.2 to 2 g/L.
It is not necessary to intentionally provide a potential difference between the glossy nickel plating layer and the nickel plating layer containing titanium, however, it is preferred to provide a potential difference for further improving the corrosion resistance. The potential difference is not particularly limited, but is, for example, 1 mV or more, preferably 20 to 90 mV, more preferably 30 to 60 mV. By providing a potential difference in this manner, the sacrificial corrosion protection effect of the glossy nickel plating layer is increased. The potential difference can be measured using an electrolytic electrometer. Further, in order to provide a potential difference, for example, the concentration of a component constituting the nickel plating solution for forming the nickel plating layer containing titanium may be changed, or a known potential regulator such as chloral hydrate may be incorporated in the nickel plating solution for forming the nickel plating layer containing titanium.
On the nickel plating layer containing titanium, a trivalent chromium plating layer having a microporous structure is formed. The number of micropores is not particularly limited, but is, for example, 5,000 to 40,000/cm2, preferably 8,000 to 25,000/cm2. Here, the number of micropores is a value measured by a copper sulfate method. The thickness of the trivalent chromium plating layer having a microporous structure is not particularly limited, but it may be provided at a thickness of, for example, 0.05 to 0.5 μm, preferably 0.1 to 0.4 μm. Further, the trivalent chromium plating layer having a microporous structure is preferably black or white, and is particularly preferably black from the viewpoint of a design property.
As a trivalent chromium plating solution for forming the trivalent chromium plating layer having a microporous structure is not particularly limited, but for example, a silvery-white trivalent chromium plating solution containing a trivalent chromium compound such as a basic chromium sulfate, chromium sulfate, chromium chloride, chromium sulfamate, or chromium acetate, an aliphatic monocarboxylic acid such as formic acid, ammonium formate, or potassium formate, an aliphatic dicarboxylic acid such as succinic acid, maleic acid, malic acid, citric acid, or triammonium citrate, a complexing agent such as tartaric acid, diammonium tartrate, or sodium tartrate, a conductive salt such as a sulfate such as potassium sulfate, ammonium sulfate, or sodium sulfate, a chloride such as potassium chloride, ammonium chloride, or sodium chloride, or a sulfamate such as potassium sulfamate, ammonium sulfamate, or sodium sulfamate, a pH buffer such as boric acid, sodium borate, potassium borate, phosphoric acid, or dipotassium hydrogen phosphate, saccharin or a salt thereof such as saccharin or sodium saccharinate, and a sulfur compound such as a sulfur-containing organic compound having an allyl group such as sodium allylsulfonate, allylthiourea, ammonium 2-methylallylsulfonate, or allyl isothiocyanate, a black trivalent chromium plating solution further containing methionine, cysteine, sodium thiocyanate, or the like, etc. are exemplified. By using the silvery-white trivalent chromium plating solution, a white trivalent chromium plating layer is obtained, and by using the black trivalent chromium plating solution, a black trivalent chromium plating layer is obtained.
Plating may be performed using the trivalent chromium plating solution under the following conditions: bath temperature: 25 to 60° C., anode: carbon or iridium oxide, and cathode current density: 2 to 20 A/dm2 for 1 to 15 minutes.
The product of the present invention has sufficient corrosion resistance, and therefore, a chromate treatment that is generally performed for enhancing corrosion resistance may not be performed on the trivalent chromium plating layer having a microporous structure, however, it is preferred to perform a chromate treatment for further improving the corrosion resistance.
Preferred embodiments of the product of the present invention are shown in
The product of the present invention obtained in this manner is subjected to evaluation according to JIS H 8502, and has corrosion resistance showing a rating number (R.N.) of 9 or more.
Therefore, the product of the present invention is favorable for decoration of automobile components, flush metal fittings, etc.
Hereinafter, the present invention will be described in detail by showing Examples, however, the present invention is by no means limited to these Examples.
Preparation of Plating Solution:
After the components shown in the following Table 1 were mixed, the pH was adjusted to 4.5 with nickel carbonate or sulfuric acid, whereby a plating solution (hereinafter referred to as “MP nickel plating solution”) for forming a nickel plating layer containing titanium (hereinafter referred to as “MP nickel plating layer”) was prepared.
Production of Chromium Plating Product:
A test piece (size: 1 dm2) of an ABS resin was subjected to etching, catalyst application, chemical nickel plating, and copper plating treatments. Subsequently, in order to form a semi-glossy nickel plating layer, plating was performed so that the film thickness was 3 μm using the following plating solution under the following conditions: anode: nickel electrode, bath temperature: 55° C., current density: 3 A/dm2, and plating time: 5 minutes.
Subsequently, in order to form a glossy nickel plating layer thereon, plating was performed so that the film thickness was 3 μm using the following plating solution under the following conditions: anode: nickel electrode, bath temperature: 50° C., current density: 3 A/dm2, and plating time: minutes. Incidentally, a potential difference (electrolytic corrosion resistance measuring device) between the semi-glossy nickel and the glossy nickel was 100 mV or more.
Subsequently, in order to form an MP nickel plating layer thereon, plating was performed so that the film thickness was 1.2 μm using the MP nickel plating solution described in Example 1 or Comparative Examples 1 to 2 under the following conditions: anode: nickel electrode, bath temperature: 50° C., current density: 3 A/dm2, and plating time: 2 minutes. Incidentally, a potential difference between the glossy nickel and the MP nickel was 9 mV.
Finally, in order to form a trivalent chromium plating layer thereon, plating was performed so that the film thickness was 0.25 μm using the following plating solution under the following conditions: anode: carbon electrode, bath temperature: 40° C., current density: 10 A/dm2, and plating time: 3 minutes to obtain a chromium plating product having a black appearance. Incidentally, the number of micropores (copper sulfate method) in the trivalent chromium plating layer was about 10,000 to 20,000 in each case.
With respect to the thus obtained chromium plating products, the following CASS test was performed. The results are shown in Table 2.
The test was performed according to JIS H 8502. A test piece after the CASS test for 48 hours was evaluated based on the total corrosion rate, which was shown as a rating number (R.N.).
The titanium content in the nickel plating layer containing titanium of the chromium plating product was analyzed by EDS. The results are also shown in Table 2.
From the results of the CASS test, it was found that by incorporating titanium oxide in the MP nickel plating layer, corrosion resistance is improved without intentionally providing a large potential difference between the glossy nickel and the MP nickel and further even without performing a chromate treatment after trivalent chromium plating.
Preparation of Plating Solution:
After the components shown in the following Table 3 were mixed, the pH was adjusted to 4.5 with nickel carbonate or sulfuric acid, whereby an MP nickel plating solution was prepared.
Production of Chromium Plating Product:
A chromium plating product was produced in the same manner as in Example 2 except that the MP nickel plating solution prepared in Examples 3 to 7 was used. The number of micropores in the trivalent chromium plating layer, the potential difference between the glossy nickel plating layer and the MP nickel plating layer, the results of the CASS test, and the results of measurement of the titanium content in each chromium plating product are shown in Table 4.
From the above results, in Examples 3 to 5 and 7, corrosion resistance was favorable as they were even without intentionally adjusting the potential difference. In Example 6, by intentionally adjusting the potential difference to 40 mV, the corrosion resistance was further improved.
Production of Chromium Plating Product:
A chromium plating product was produced in the same manner as in Example 2 except that the following white trivalent chromium plating solution was used.
From the above results, even in the case of white trivalent chromium plating using a chloride, corrosion resistance can be favorable.
Production of Chromium Plating Product:
A chromium plating product was produced in the same manner as in Example 2 except that the following white trivalent chromium plating solution was used.
From the above results, even in the case of white trivalent chromium plating using a sulfate, corrosion resistance can be favorable.
Production of Chromium Plating Product:
A chromium plating product was produced in the same manner as in Example 2 except that a brass plate (size: 1 dm2) was used as the test piece and semi-glossy nickel plating was not performed.
From the above results, even in the case where semi-glossy nickel plating was not performed for the metal material, the corrosion resistance of the trivalent chromium plating product can be favorable.
The chromium plating product of the present invention has high corrosion resistance, and therefore can be used for, for example, automobile components, flush metal fittings, etc.
