USING THE SAME

CROSS REFERENCE TO RELATED APPLICATION This application claims priority to Chinese Patent Application No.

200910106439.1, filed on March 27, 2009, the entirety of which is hereby incorporated by reference.

FIELD OF THE INVENTION The present invention relates to surface treatment, more particularly, to a stripping solution and an electrolytic stripping method using thereof.

DESCRIPTION OF THE RELATED ART

During metal treatment processing, functional coatings, such as coatings of chromium nitride or chromium carbide, are often formed on the metal surface, having high hardness, strong corrosion resistance, high temperature oxidation resistance, and ultra-high adhesion. Because of the contamination to a surface of a workpiece or other factors, some inferior products are produced during the coating formation process, such as during physical vapor deposition process. Thus, it is always needed to strip the coating from the surface of the workpiece for re-plating. In addition, the workpiece after long-term use has been seriously injured and aged. Therefore, it also needs re- plating.

SUMMARY OF THE INVENTION In viewing thereof, the present invention is directed to solve at least one of the problems existing in the prior art. Accordingly, a stripping solution and an electrolytic stripping method may need to be provided, which will bring no damage to the substrate surface.

According to one embodiment of the invention, a stripping solution is disclosed, which may comprise a nonionic surfactant which is polyoxyethylene ether; and an acid which is not reactant with the nonionic surfactant, wherein the stripping solution has a pH value which is no less than -1.5 and no greater than 3.

According to one embodiment of the invention, an electrolytic stripping method is disclosed, which may comprise a step of electrolyzing a substrate having a coating layer on a surface thereof by using the stripping solution as described. Other variations, embodiments and features of the present disclosure will become evident from the following detailed description, drawings and claims.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION Reference will be made in detail to embodiments of the present invention. The embodiments described herein with reference to drawings are explanatory, illustrative, and used to generally understand the present invention. The embodiments shall not be construed to limit the present invention. The same or similar elements and the elements having same or similar functions are denoted by like reference numerals throughout the descriptions. In one embodiment of the present invention, the stripping solution may comprise a nonionic surfactant and an acid. The nonionic surfactant may be polyoxyethylene ether. And it should be noted that the acid does not react with the nonionic surfactant. And the stripping solution may have a pH value of no less than -1.5 and no greater than 3. In one embodiment of the present invention, the stripping solution may have a pH value ranging from about 0 to 1.

In some embodiments, the polyoxyethylene ether may be selected from at least one of fatty alcohol polyoxyethylene ether and alkyl phenol polyoxyethylene ether. The alcohol polyoxyethylene ether or the alkyl phenol polyoxyethylene ether may improve the solubilization, permeability, wetting and cleaning effects of the solution. Further, it may enhance the wettability of the metal surface, and may increase the stripping rate. Still further, it may reduce interface reaction to avoid over-erosion of the substrate metal.

In some embodiments, the fatty alcohol polyoxyethylene ether may have a general formula of RO(CH ₂ CH ₂ O) _n H, where R may be an aliphatic hydrocarbon having carbon number ranging from 5 to 50, and n may be an integer between 5 to 80. According to one embodiment of the present invention, the fatty alcohol polyoxyethylene ether may be selected at least one from a group consisting of Ci ₂ -Ci ₆ mixed fatty alcohol polyoxyethylene ether, C ₁ S fatty alcohol polyoxyethylene ether, Cio alcohol polyoxyethylene ether, and C _B alcohol polyoxyethylene ether.

In some embodiments, the alkyl phenol polyoxyethylene ether may have a general formula Of R ⁵ CeH ₄ O(CH ₂ CH ₂ O) _n H, where R' may be an alkyl having carbon number ranging from 5 to 50, and n' may be an integer ranging from 2 to 80. In one embodiment of the present invention, the alkyl phenol polyoxyethylene ether may be selected at least one from a group consisting of nonyl phenol polyoxyethylene ether, decyl phenol polyoxyethylene ether, and octyl phenol polyoxyethylene ether.

In some embodiments, the concentration of the polyoxyethylene ether may have a concentration ranging from about 30 to about 150 g/L. In one embodiment of the present invention, the polyoxyethylene ether may have a concentration of about 50 to 100 g/L.

In some embodiments, the acid may be at least one member selected from the group consisting of sulfuric acid, nitric acid, and hydrochloric acid. The acid amount is not limited hereto, which may just provide the stripping solution having a corresponding pH value as mentioned above. In one embodiment of the present invention, an electrolytic stripping method may comprise a step of electrolyzing a substrate having a coating layer on a surface thereof by using any stripping solution disclosed above.

In one embodiment of the present invention, the electrolytic stripping may comprise the steps of: placing the substrate serving as an anode and a cathode into the stripping solution; and stripping the substrate for about 1 to 10 minutes under a temperature of about 10 to 80 ⁰ C with a stripping voltage of about 3 to 15 V. According to an embodiment of the invention, the cathode may be a stainless steel electrode. According to an embodiment of the invention, the coating layer may include one or more selected from the group of chromium metal, chromium nitride, chromium carbide and chromium carbonitride. The coating layer may be formed by any known art, such as physical vapor deposition etc. According to an embodiment of the invention, the coating may include chromium nitride (CrN _x ), chromium carbide (CrC _x ) and chromium carbonitride (CrC _x N _y ) are formed by vacuum arc ion plating.

According to an embodiment of the invention, the substrate may be, but not limited hereto, selected from steel, steel alloy, nickel alloy, and aforementioned metal or alloy having other coatings.

The following will describe the methods for stripping hard coatings of chromium series. However, it should be noted that these examples are for illustrative only rather than limitation.

EXAMPLE 1

1. Formation of Chromium Nitride Coating

A layer of chromium nitride coating having a thickness of 2 μm is formed on a stainless steel plate with a size of 40mm ^χ 80mm ^χ lmm distributed by Rongjia

(Dongguan) Stainless Steel Material Co. , Guangdong Province, China with a Model 304 by a vacuum arc ion plating machine distributed by Zhenheng Industry Co., Ltd, Shenzhen, Guangdong Province, China with a Type of ZHC-800.

2. Preparation of Stripping Solution

50 g nonyl phenol polyoxyethylene ether (NP-40) and 100 g nitric acid with a mass ratio of 63% are added into deionized water to obtain one liter of solution. The solution has a pH value of 0.

3. Electrolytic Stripping

A stainless steel plate with the layer of chromium nitride coating is used as an anode with a stainless steel plate having a size of 60mm x 100mm x lmm as a cathode. And the stripping solution as prepared above is used as electrolyte. Then, the stainless steels are electrolyzed under a temperature of 25 ⁰ C with a stripping voltage of 5 V for 3 minutes. And then the stainless steel plate with the chromium nitride coating is taken out for washing and drying.

EXAMPLE 2 1. Formation of Chromium Nitride Coating

The formation of the chromium nitride coating is the same as that used in EXAMPLE 1.

2. Preparation of Stripping Solution

70 g isomeric Ci ₀ alcohol polyoxyethylene ether (XL-50) and 80 g nitric acid with a mass ratio of 63% are added into deionized water to obtain 1 liter of solution. The solution has a pH value of 0.1.

3. Electrolytic Stripping

A stainless steel plate with chromium nitride coating is used as an anode with a stainless steel plate having a size of 60mm ^χ 100mm x lmm as a cathode. And the stripping solution as prepared above is used as electrolyte. Then, the stainless steels are electrolyzed under a temperature of 20 ⁰ C with a stripping voltage of 4 V for 6 minutes. And then the stainless steel plate with the chromium nitride coating is taken out for washing and drying. EXAMPLE 3

1. Formation of Chromium Nitride Coating The formation of the chromium nitride coating is the same as that used in

EXAMPLE 1.

2. Preparation of Stripping Solution

100 g octyl phenol polyoxyethylene ether (OP-IO) and 50 g sulfuric acid with a mass ratio of 98% are added into deionized water to obtain 1 liter of solution. The solution has a pH value of 0.

3. Electrolytic Stripping

A stainless steel plate with chromium nitride coating is used as an anode with a stainless steel plate having a size of 60mm ^χ 100mm x lmm as a cathode. And the stripping solution as prepared above is used as electrolyte. Then, the stainless steels are electrolyzed under a temperature of 30 ⁰ C with a stripping voltage of 6 V for 2 minutes. And then the stainless steel plate with the chromium nitride coating is taken out for washing and drying.

EXAMPLE 4

1. Formation of Chromium Nitride Coating The formation of the chromium nitride coating is the same as that used in

EXAMPLE 1.

2. Preparation of Stripping Solution

100 g Ci ₂ -Ci6 mixed fatty alcohol polyoxyethylene ether (AEO-7) and 20 g sulfuric acid with a mass ratio of 98% are added into deionized water to obtain one liter of solution. The solution has a pH value of 0.4.

3. Electrolytic stripping A stainless steel plate with chromium nitride coating is used as an anode with a stainless steel plate having a size of 60mm ^χ 100mm x lmm as a cathode. And the stripping solution as prepared above is used as electrolyte. Then, the stainless steels are electrolyzed under a temperature of 15 ⁰ C with a stripping voltage of 10 V for 2 minutes. And then the stainless steel plate with the chromium nitride coating is taken out for washing and drying.

EXAMPLE 5

1. Formation of Chromium Carbide Coating

A layer of chromium carbide coating having a thickness of 2.5 μm is formed on a stainless steel plate with a size of 40mm ^χ 80mm ^χ lmm distributed by Rongjia

(Dongguan) Stainless Steel Material Co. , Guangdong Province, China with a Model

304 by a vacuum arc ion plating machine distributed by Zhenheng Industry Co., Ltd,

Shenzhen, Guangdong Province, China with a Type of ZHC-800.

2. Preparation of Stripping Solution 7O g nonyl phenol poly oxy ethylene ether (NP-10) and 5O g nitric acid with a mass ratio of 63% are added into deionized water to obtain one liter of solution. The solution has a pH value of 0.3.

3. Electrolytic Stripping

A stainless steel plate with the layer of chromium carbide coating is used as an anode with a stainless steel plate having a size of 60mm x 100mm x lmm as a cathode. And the stripping solution as prepared above is used as electrolyte. Then, the stainless steels are electrolyzed under a temperature of 28 ⁰ C with a stripping voltage of 15 V for 4 minutes. And then the stainless steel plate with the chromium nitride coating is taken out for washing and drying. COMPARATIVE EXAMPLE 1

1. Formation of Chromium Nitride Coating A layer of chromium nitride coating having a thickness of 2 μm is formed on a stainless steel plate with a size of 40mm x 80mm x lmm distributed by Guirong

(Dongguan) Stainless Steel Material Co. , Guangdong Province, China with a Model

304 by a vacuum arc ion plating machine distributed by Zhenheng Industry Co., Ltd, Shenzhen, Guangdong Province, China with a Type of ZHC-800.

2. Preparation of Stripping Solution

1O g nonyl phenol polyoxyethylene ether (NP -40) and 0.1 g nitric acid with a mass ratio of 63% are added into deionized water to obtain one liter of solution. The solution has a pH value of 3.1. 3. Electrolytic Stripping

A stainless steel plate with the layer of chromium nitride coating is used as an anode with a stainless steel plate having a size of 60mm x 100mm x lmm as a cathode. And the stripping solution as prepared above is used as electrolyte. Then, the stainless steels are electrolyzed under a temperature of 25 ⁰ C with a stripping voltage of 5 V for 5 minutes. And then the stainless steel plate with the chromium nitride coating is taken out for washing and drying.

Through visual observation, the hard coatings of Chromium series in the samples of EXAMPLES 1-5 are stripped clearly without damage to the substrate surface, while that of COMPARATIVE EXAMPLE 1 is stripped partially with residues which are distributed non-uniformly.

Although the present disclosure has been described in detail with reference to several embodiments, additional variations and modifications exist within the scope and spirit as described and defined in the following claims.