Patent Application
20160083859
1. Field of the Invention
The present invention relates to a method of surface-treating a plastic substrate and, more particularly, to a method of electroplating a plastic substrate.
This application claims the benefit of Chinese Patent Application No. CN 201410479814.8, filed Sep. 19, 2014, which is hereby incorporated by reference in its entirety into this application.
2. Description of the Related Art
Conventional electroplating for a plastic substrate is comparatively complicated and requires a large amount of energy and a long period of time. When such a plastic substrate electroplating process is performed for 3˜4 hr, plating on the surface of the plastic substrate is completed.
The color, which may be shown by the conventional plastic substrate electroplating process, is very limited and is relatively monotonous, making it impossible to satisfy current demands for beautiful goods.
Also, the conventional plastic substrate electroplating process is problematic because poisonous harmful chemicals, such as hexavalent chromium, trivalent chromium, and sulfuric acid, are contained, undesirably causing serious damage to the natural environment and the human body.
However, the use of harmful chemicals is currently inevitable in the plastic substrate electroplating process.
Among chemicals used for the conventional electroplating process, hexavalent chromium is a significantly harmful environmental pollutant, and most leading enterprises ban the use of hexavalent chromium. Furthermore, trivalent chromium is adopted to thus reduce environmental pollution, but trivalent chromium is merely less harmful compared to hexavalent chromium and is still eco-unfriendly.
Typical examples of the chromium compound may include a hexavalent chromium compound such as chromic anhydride, potassium dichromate or sodium dichromate, a trivalent chromium compound such as chromic oxide (Cr2O3), and a divalent chromium compound such as chromous oxide. The most highly toxic chromium compounds are hexavalent chromium followed by trivalent chromium.
According to studies, chromium is an element required in a small amount by mammals. Chromium compounds should not be taken in large amounts. In the case where such a chromium compound comes into direct contact with the skin of the human body, the skin suffers from excessive stimulus or even a burn.
Furthermore, the conventional electroplating process generates a large amount of polluted water, and consumes significant power and water. A fully automated cyclic production line enables the processing of a plating surface area over about 20,000 m2 per month and discharges about 2,000 tons of wastewater.
Due to the discharge of a large amount of wastewater, water resources are wasted, and the environment is seriously polluted.
Thus, there is a need for improvements or alternatives to the conventional electroplating process.
Accordingly, the present invention has been made keeping in mind the above problems including low productivity relative to the process time in conventional plastic substrate electroplating methods, and an object of the present invention is to provide a method of electroplating a plastic substrate, which may achieve metallization of the surface of a plastic substrate, may reduce the process time, may remarkably increase the production capacity, and may decrease environmental pollution and harm to the human body, and also which is improved and adapted for the surface conditions of platable plastics such as ABS, PP, etc.
In order to accomplish the above object, the present invention provides a method of electroplating a plastic substrate, comprising: (1) subjecting a plastic substrate to degreasing, hydrophilic etching, and surface coarsening, thus oxidizing and releasing a butadiene component on the surface of the plastic substrate to thereby form a spherical hole in the surface of the plastic substrate so that the surface of the plastic substrate satisfies electroless nickel plating attachment conditions; (2) subjecting the plastic substrate to neutralization to remove chromic acid from the surface thereof, and then to activation using a palladium colloid solution, so that highly active metal palladium colloid particles are effectively adsorbed to the surface of the plastic substrate to form an activated surface and to form a uniform nickel alloy by electroless nickel plating; (3) subjecting the plastic substrate to peptization to dissolve the outer layer component adsorbed to a palladium colloid nucleus so as to expose palladium, and then to electroless nickel plating, so that a deposition reaction progresses, and nickel sulfate and sodium hypophosphite in the electroless nickel plating solution react in the presence of a palladium catalyst to thus form a 0.3 μm thick electroless nickel plating layer, whereby the surface of the plastic substrate becomes conductive and thus allows for electroplating, followed by copper pyrophosphate plating, so that the electroless nickel plating layer is plated with a copper layer to enhance current-loading capacity; (4) subjecting the plastic substrate to copper electroplating using gloss copper to form a thin mold mark thereon using high brightness and superior filling capacity of the gloss copper, and then to nickel plating using gloss nickel to form a nickel plating layer thereon, so that the lower layers are protected and corrosion resistance of the product is improved; and (5) subjecting the plastic substrate to chromium electroplating or physical vapor deposition (PVD), wherein the surface of the plastic substrate undergoes PVD or undergoes chromium electroplating and then PVD.
In (2), neutralization is performed using a composition composed mainly of 30 ml/L of hydrochloric acid for an immersion time of 45˜50 sec, the temperature of the electroplating solution is room temperature; and palladium colloid solution treatment is performed using a composition composed mainly of 35˜50 ppm of a palladium colloid solution and 200˜300 g/L of hydrochloric acid at 20˜30° C. for an immersion time of 2˜2.5 min, and is carried out in cyclic operation using a cotton filter or fiber filter pump. When not in use for a long period of time, the pump for cyclic operation is stopped, 5˜10 L of hydrochloric acid is added, and the amount of tin chloride is controlled to the upper limit, after which the plating bath is covered with a lid.
In (3), peptization is performed using a composition composed mainly of 100 g/L of sulfuric acid at 45˜52° C. for an immersion time of 1˜2 min, and is carried out in cyclic operation using a cotton filter or fiber core filter pump; and electroless nickel plating is performed using a composition composed mainly of 27˜31 g/L of nickel sulfate, 12˜18 g/L of sodium hypophosphite, 30˜50 g/L of sodium citrate, and 30˜40 g/L of ammonium chloride at 36˜40° C. for an immersion time of 4˜5 min, and is carried out in cyclic operation using a cotton filter or fiber filter pump. Also, in the electroless nickel plating solution, nickel ions and hypophosphite ions react directly, sodium citrate is a complexing agent of the nickel ions, and aqueous ammonia of ammonium chloride functions as a pH buffer system. Further, the concentration of the dissociated nickel ions in the electroless nickel plating solution is relatively low, and most of the nickel ions are complexed with the citrate ions and are thus present in a complex phase, and only the dissociated nickel ions may undergo a redox reaction with the hypophosphite ions in the presence of a catalyst. As the chemical reaction proceeds, the nickel ions are consumed, and the complexed nickel ions are dissociated again, so that the nickel ions are maintained at a predetermined concentration, thereby ensuring a stable reaction rate of electroless nickel. Also, copper pyrophosphate plating is performed using a copper pyrophosphate plating solution comprising 30˜36 g/L of copper pyrophosphate and 200˜240 g/L of potassium pyrophosphate under conditions of a temperature of 45˜55° C., a cathode current density of 0.5˜1.0 A/dm2, and an electroplating time of 2˜4 min, and a cotton filter is washed every week and is replaced upon washing the plating bath.
In (4), gloss copper treatment is performed using a composition composed mainly of 160˜240 g/L of copper sulfate CuSO4.5H2O, 40˜90 g/L of sulfuric acid H2SO4, 30˜120 ppm of a chloride ion Cl−, 3˜10 ml/L of a brightener A.A-MU, 0.3˜0.6 ml/L of a brightener A.A-A, and 0.3˜0.6 ml/L of a brightener A.A-B, under conditions of a plating solution temperature of 18˜35° C., a cathode current density of 1˜8 A/dm2, and an electroplating time of 7.5˜8.5 min; and gloss nickel treatment is performed using a composition composed mainly of 270˜290 g/L of nickel sulfate NiSO4.6H2O, 45˜55 g/L of nickel chloride NiCl2.6H2O, 37˜45 g/L of boric acid H3BO3, 0.3˜0.5 ml/L of a brightener TD-100, 8˜10 ml/L of a softener TD-100, and 0.5˜2.0 ml/L of a wetter TD-100, under conditions of a plating solution temperature of 50˜65° C., a cathode current density of 2˜8 A/dm2, and an electroplating time of 5˜6 min. During electroplating the plastic substrate, the copper plating and the nickel plating are performed, after which two water washings and individual ion exchange resin processes are carried out, thus recovering the copper ions and the nickel ions in the production line so as to be recycled and circulating water used for the water washing.
Also, (5) is performed in two types, one type of which is implemented in such a manner that the nickel plating is completed, and chromium plating is performed and then PVD is conducted on the chromium plating layer, and the other type of which is implemented in such a manner that the nickel plating is completed, and PVD is directly performed without chromium electroplating. In the former type, chromium plating is performed using a composition composed mainly of 140˜160 g/L of a TRI-COM M primary salt, 70˜100 ml/L of a TRI-COM CA complexing agent, 225˜275 g/L of a TRI-COM T conductive salt, and 0.5˜2.0 ml/L of a TRI-COM WA wetter, under conditions of a process temperature of 30˜38° C., a cathode current density of 8˜15 A/dm2, and an electroplating time of 2˜6 min.
According to the present invention, the treatment time of processes including coarsening, copper plating, nickel plating, etc. can be decreased, and a semi-gloss nickel plating process (a semi-gloss nickel plating layer) in a conventional electroplating process can be obviated.
Also, the plating process can be completed by operating the fully automated production system for 45˜55 sec in the present invention compared to 60˜80 sec in the conventional plastic electroplating process, thereby remarkably increasing the production capacity and decreasing the plating cost. Furthermore, the use of chromium is lowered, thus reducing environmental pollution.
Moreover, compared to conventional electroplating methods, the process time and the thickness of the copper and nickel plating layers are decreased. Although hardness and corrosion resistance of a conventional plating layer do not satisfy the process standards, the defects of the conventional plating process are solved by adopting a PVD process through various experiments. The electroplated surface of the plastic substrate using PVD is eco-friendly and exhibits superior heat resistance, corrosion resistance, and anti-scratching and anti-oxidation properties. Moreover, as the temperature and the gas content are adjusted in the PVD process, the resulting PVD layer can show various vivid colors having a metallic and three-dimensional (3D) appearance, and monotonous color defects in the conventional plastic electroplating process can be overcome.
As illustrated in
1) Degreasing a plastic substrate is performed to remove pollutants such as fingerprints and impurities from the surface of the plastic substrate and to carry out a swelling action on the plastic substrate.
2) Subjecting the plastic substrate to hydrophilic treatment is performed after 1). Specifically, the plastic substrate is etched.
3) Coarsening the plastic substrate is performed after 2). Specifically, the butadiene component of the surface of the plastic substrate is oxidized to thus be released, thereby forming spherical small holes in the surface of the plastic substrate, so that the surface of the plastic substrate is coarsened so as to be adapted for attaching an electroless nickel plating layer thereto. This process is regarded as important in terms of having an influence on the bonding force between the plating layer and the surface of the plastic substrate. The main composition for the coarsening process comprises chromic acid and sulfuric acid. The amounts thereof may significantly affect the quality of plating products. A coarsening solution is composed of 390˜440 g/L of chromic anhydride and 390˜420 g/L of sulfuric acid, and the temperature of the plating solution is maintained at 63˜70° C., and the immersion time is set to 3.5˜4.5 min. The amount of trivalent chromium is controlled to 10˜20 g/L, and a coarsening bath must be equipped with a trivalent chromium remover. The typical service life of the coarsening solution is three months. Since the butylene component of the plastic substrate is dissolved in a large amount, the color of the product turns to deep brown and the viscosity and specific gravity thereof are increased. Hence, half of the bath solution has to be replaced at an interval of 3˜5 months.
4) Neutralizing the plastic substrate is performed after 3). Specifically, as chromic acid is removed from the surface of the plastic substrate, chromic acid pollution that affects some subsequent processes may be decreased. The main composition for neutralization comprises 30 ml/L of hydrochloric acid. The immersion time is 45˜50 sec, and the temperature of the plating solution is room temperature.
5) Activating the plastic substrate (with a palladium colloid solution) is performed after 4). Specifically, highly active metal palladium colloid particles are easily adsorbed to the surface of the plastic substrate treated in 4), thus forming an activated surface and enabling the production of a relatively uniform nickel plating layer in an electroless nickel plating process. The main composition for the palladium colloid solution treatment comprises 35˜50 ppm of a palladium colloid solution and 200˜300 g/L of hydrochloric acid. This process is performed at 20˜30° C. for an immersion time of 2˜2.5 min, and may be carried out in cyclic operation using a cotton filter or fiber filter pump. The cotton filter is washed at an interval of three days, and is replaced with a new cotton filter every month. When not in use for a long period of time, the pump for cyclic operation is stopped. Upon stopping the system, 5˜10 L of hydrochloric acid is added depending on the volume of the bath, and the amount of tin chloride is controlled to the upper limit, after which the plating bath is covered with a lid.
6) Subjecting the plastic substrate to peptization is performed after 5). Specifically, the outer layer component adsorbed to a palladium colloid nucleus is dissolved to expose palladium, and electroless nickel plating is promoted, and thus a deposition reaction progresses. The main composition for the peptization process comprises 100 g/L of sulfuric acid. This process is conducted at 45˜52° C. for an immersion time of 1˜2 min, and is carried out in cyclic operation using a cotton filter or fiber filter pump, and the flow rate of the pump is set to at least 4 times/hr. The cotton filter is washed once a week, and is replaced with a new cotton filter every month, and the plating solution is completely replaced at an interval of 15˜20 days.
7) Subjecting the plastic substrate to electroless nickel plating is performed after 6). Specifically, nickel sulfate and sodium hypophosphite in the electroless nickel plating solution react in the presence of a palladium catalyst, thus forming an electroless nickel plating layer. As the surface of the plastic substrate may become conductive, it is possible to perform a typical electroplating process thereon. The main composition for the electroless nickel plating process comprises 27˜31 g/L of nickel sulfate, 12˜18 g/L of sodium hypophosphite, 30˜50 g/L of sodium citrate, and 30˜40 g/L of ammonium chloride. This process is conducted at 36˜40° C. for an immersion time of 4˜5 min, and is carried out in cyclic operation using a cotton filter or fiber filter pump. The cotton filter is washed once a day, and is replaced with a new cotton filter every week. The direct reaction components in the electroless nickel plating solution are nickel ions and hypophosphite ions, and sodium citrate is a complexing agent of the nickel ions, and aqueous ammonia of ammonium chloride functions as a pH buffer system. The concentration of the dissociated nickel ions in the electroless nickel plating solution is relatively low, and most of the nickel ions are complexed with the citrate ions and are thus present in a complex phase, and only the dissociated nickel ions may undergo a redox reaction with the hypophosphite ions in the presence of a catalyst. As the chemical reaction proceeds, the nickel ions are consumed, and the complexed nickel ions are dissociated again, so that the nickel ions are maintained at a predetermined concentration, thereby ensuring a stable reaction rate of electroless nickel. If the ratio of individual components is unbalanced, electroless nickel may be decomposed, and also a chemical reaction may occur while forming the catalytic reaction center due to the bath solution and the other impurities contained in the bath, in addition to the chemical reaction of the surface of the part to be plated. Hence, the rotational rate of the pump for cyclic operation is maintained, and the amounts of the components, operating conditions, and periodic bath washing are strictly controlled, thereby maintaining the preferable reaction rate. When the amount of sodium hypophosphite that is a chemical reaction byproduct is high, the chemical reaction is suppressed and thus plating omission may take place. Accordingly, the solution is cleanly maintained, and side reactions and self-reaction are decreased as much as possible, so that the amount of sodium hypophosphite is not increased, thus prolonging the service life of the solution. To this end, the bath has to be cautiously handled upon washing, and the inside of the bath is neither damaged nor roughly handled. Furthermore, the portion (especially the edge or the angled portion) of the bath and the filter pump are checked in terms of whether there is deposited nickel. If there is deposited nickel, it must be removed.
8) Subjecting the plastic substrate to copper pyrophosphate plating is performed after 7). Specifically, the electroless nickel plating layer obtained in 7) is as thin as 0.3 μm, and may be further plated with a copper layer to enhance current-loading capacity so that the subsequent processes are made easy. A copper pyrophosphate plating solution for the copper pyrophosphate plating process is composed mainly of 30˜36 g/L of copper pyrophosphate and 200˜240 g/L of potassium pyrophosphate. This electroplating process is performed at 45˜55° C. for 2˜4 min under a cathode current density of 0.5˜1.0 A/dm2. The cotton filter is washed every week, and is replaced when the plating bath is washed.
9) Subjecting the plastic substrate to copper plating (with gloss copper) is performed after 8). Specifically, gloss copper enables the formation of a thin mold mark on the surface of the plastic substrate using high brightness and superior filling capacity thereof, and may decrease inner stress of the plating layer. The main composition for the gloss copper plating process includes a gloss copper mixture available from DEYUANBAO Chemical, comprising 160˜240 g/L of copper sulfate CuSO4.5H2O, 40˜90 g/L of sulfuric acid H2SO4, 30˜120 ppm of a chloride ion Cl−, 3˜10 ml/L of a brightener A.A-MU, 0.3˜0.6 ml/L of a brightener A.A-A, and 0.3˜0.6 ml/L of a brightener A.A-B. The temperature of the plating solution is 18˜35° C., the cathode current density is 1˜8 A/dm2, and the electroplating time is 7.5˜8.5 min.
10) Subjecting the plastic substrate to nickel plating (with gloss nickel) is performed after 9). Specifically, nickel plating is conducted on the surface of the plastic substrate so that the lower layers are protected and corrosion resistance of the product may be improved. The main composition for the gloss nickel plating process includes a nickel mixture available from TUODONG Science and Technology, comprising 270˜290 g/L of nickel sulfate NiSO4.6H2O, 45˜55 g/L of nickel chloride NiCl2.6H2O, 37˜45 g/L of boric acid H3BO3, 0.3˜0.5 ml/L of a brightener TD-100, 8˜10 ml/L of a softener TD-100, and 0.5˜2.0 ml/L of a wetter TD-100. The temperature of the plating solution is 50˜65° C., and the cathode current density is 2˜8 A/dm2, and the electroplating time is 5˜6 min. In the process of electroplating the plastic substrate according to the present invention, copper plating and nickel plating are performed, followed by two water washings and individual ion exchange resin processes, thus recovering the copper ions and the nickel ions in the production line so as to be recycled and circulating water used for the water washing.
11) Subjecting the plastic substrate to chromium plating or PVD is performed after 10). Specifically, in the present process, the surface of the substrate treated in 10) may be subjected to PVD so as to obtain higher hardness, corrosion resistance, and anti-oxidation properties. Alternatively, the surface of the substrate treated in 10) may be subjected to chromium plating (to prevent oxidation of the nickel layer and to enhance hardness and corrosion resistance), and then to PVD. More specifically, one of the two types as above is performed in such a manner that the previous process 10 (the nickel plating process) is completed, after which chromium plating is implemented and then PVD is performed on the chromium plating layer. The other type is performed in such a manner that the previous process 10 (the nickel plating process) is completed, after which PVD is implemented directly without chromium plating.
In particular, the main composition for the chromium plating process includes a plating mixture available from MENGXIANG, comprising 140˜160 g/L of a TRI-COM M primary salt, 70˜100 ml/L of a TRI-COM CA complexing agent, 225˜275 g/L of a TRI-COM T conductive salt, and 0.5˜2.0 ml/L of a TRI-COM WA wetter. The process temperature is 30˜38° C., the cathode current density is 8˜15 A/dm2, and the electroplating time is 2˜6 min. The trivalent chromium plating process is performed instead of hexavalent chromium plating techniques that cause serious pollution, thus exhibiting high environmental protection performance, and yielding a plating layer with a bright color and high gloss. The resulting product may operate at very low metal concentration, thereby lowering the chromium metal wastewater processing costs.
The material used in the final PVD process may be selected from among eco-friendly metal materials, such as a zirconium metal material, a titanium metal material, a chromium metal material, and a tin metal material, depending on the market demand. The PVD process enables a predetermined color to be imparted to the PVD layer to thus satisfy the market demand, by adjusting the amounts of argon and nitrogen in a PVD chamber, and the process temperature and time. The reason why the PVD process is adopted is that the metal used therefor, such as titanium or zirconium, is eco-friendly and is thus harmless to the human body and manifests comparatively high corrosion resistance, anti-oxidation properties, heat resistance, and anti-scratching properties (PVD may be selected from among medium frequency ion deposition, multi-arc magnetron deposition, and magnetron medium frequency deposition). In the present process, the nickel plating layer or the chromium plating layer may be subjected to a kind of PVD for stripe processing, thus improving the outer appearance of the product.
Even when new methods are created by combining any one step of the embodiments with the technical solution of the invention on the basis of the above embodiments by the technicians in the art, they are incorporated in the scope of the present invention by the present applicant. In order to simplify the description of the present application, other exemplary methods of these steps are not listed.
The method of electroplating the plastic substrate according to the present invention is advantageous as follows. First, the treatment time of processes including coarsening, copper plating, nickel plating, etc. is decreased, and a semi-gloss nickel plating process (a semi-gloss nickel plating layer) in the conventional electroplating process is obviated.
Second, the plating process may be completed by operating the fully automated production system for 45˜55 sec in the present invention compared to 60˜80 sec in the conventional plastic electroplating process, thereby remarkably increasing the production capacity and reducing the plating cost. Furthermore, the use of chromium is decreased, thus lowering the environmental pollution. Third, compared to conventional electroplating methods, the process time and the thickness of the copper and nickel plating layers are decreased. Although hardness and corrosion resistance of a conventional plating layer do not satisfy the process standards, the defects of the conventional plating process are solved by adopting the PVD process through various experiments. Moreover, the electroplated surface of the plastic substrate by PVD is eco-friendly and exhibits superior heat resistance, corrosion resistance, and anti-scratching and anti-oxidation properties. Furthermore, as the temperature and the gas content are adjusted in the PVD process, the resulting PVD layer may show various vivid colors having a metallic and 3D appearance, and monotonous color defects in the conventional plastic electroplating process may be overcome.
The technical solution and the technical effects according to the present embodiments are different from the conventional techniques in terms of the following: metallization of the surface of the plastic substrate may be achieved, thus reducing the process time necessary for the conventional process, drastically increasing the production capacity, and decreasing the environmental pollution and harm to the human body. Hence, the present process is adapted for the surface conditions of platable plastics, such as ABS, PP, etc.
Although the preferred embodiments of the present invention regarding the method and the system structure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
The present invention is not limited to the above method, and all embodiments that implement the object of the present invention using the structure and the method similar to the present invention are incorporated in the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201410479814.8 | Sep 2014 | CN | national |
