Method of electroplating plastic substrate

Abstract

Provided is a method of electroplating a plastic substrate, wherein 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 a conventional electroplating process is obviated. Also, production capacity is remarkably increased and the plating cost and use of chromium are decreased, thus lowering environmental pollution. Furthermore, the process time and the thickness of the copper and nickel plating layers are decreased, and 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. 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 3D appearance, and conventional monotonous color defects can be overcome.

What is claimed is: 
     
         1 . A method of electroplating a plastic substrate, comprising:
 (1) subjecting a plastic substrate to degreasing, hydrophilic etching, and coarsening, wherein a surface of the plastic substrate is degreased, etched and coarsened, and thus a butadiene component on the surface of the plastic substrate is oxidized and released, thereby forming 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 and activation, wherein the coarsened plastic substrate is neutralized to remove chromic acid from the surface thereof, and then activated using a palladium colloid solution, so that highly active metal palladium colloid particles are adsorbed to the surface of the plastic substrate to form an activated surface and to form a uniform nickel plating layer by electroless nickel plating;   (3) subjecting the plastic substrate to peptization, electroless nickel plating, and copper pyrophosphate plating, wherein the plastic substrate having the nickel plating layer is subjected to peptization to dissolve the outer nickel plating layer adsorbed to a palladium colloid nucleus so as to expose palladium, after which a deposition reaction proceeds and then nickel sulfate and sodium hypophosphite in an electroless nickel plating solution react in the presence of a palladium catalyst to form a 0.3 μm thick electroless nickel plating layer, so that the surface of the plastic substrate becomes conductive and thus allows for electroplating, after which the electroless nickel plating layer is plated with a copper layer using a copper pyrophosphate plating solution to enhance current-loading capacity;   (4) subjecting the plastic substrate to copper electroplating and nickel plating, wherein the plastic substrate is electroplated with copper, and then plated with nickel to form a nickel plating layer on the surface thereof, so that lower layers are protected and corrosion resistance of a product is improved; and   (5) subjecting the plastic substrate to chromium electroplating or physical vapor deposition (PVD), wherein the surface of the plastic substrate is subjected to PVD or to chromium electroplating and then PVD.   
     
     
         2 . The method of  claim 1 , wherein in (2), the neutralization is performed using a composition comprising 30 ml/L of hydrochloric acid for an immersion time of 45˜50 sec, and
 the activation is performed using a composition comprising 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, and 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 a plating bath is covered with a lid. 
 
     
     
         3 . The method of  claim 1 , wherein in (3), the peptization is performed using a composition comprising 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, the electroless nickel plating is performed using a composition comprising 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, and in the electroless nickel plating solution, a nickel ion and a hypophosphite ion directly react, sodium citrate is a complexing agent of the nickel ion, aqueous ammonia of ammonium chloride functions as a pH buffer system, the dissociated nickel ion undergoes a redox reaction with the hypophosphite ion in the presence of a catalyst, the nickel ion is consumed by a chemical reaction and the complexed nickel ion is dissociated again, so that the nickel ion is maintained at a predetermined concentration, thus ensuring a stable reaction rate of electroless nickel, and
 the copper pyrophosphate plating is performed using the 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/dm 2 , and an electroplating time of 2˜4 min, and a cotton filter is washed every week and is replaced upon washing a plating bath. 
 
     
     
         4 . The method of  claim 1 , wherein in (4), the copper electroplating is performed using a composition comprising 160˜240 g/L of copper sulfate CuSO 4 .5H 2 O, 40˜90 g/L of sulfuric acid H 2 SO 4 , and 30˜120 ppm of a chloride ion Cl − , under conditions of a plating solution temperature of 18˜35° C., a cathode current density of 1˜8 A/dm 2 , and an electroplating time of 7.5˜8.5 min,
 the nickel plating is performed using a composition comprising 270˜290 g/L of nickel sulfate NiSO 4 .6H 2 O, 45˜55 g/L of nickel chloride NiCl 2 .6H 2 O, 37˜45 g/L of boric acid H 3 BO 3 , 0.3˜0.5 ml/L of a brightener, 8˜10 ml/L of a softener, and 0.5˜2.0 ml/L of a wetter, under conditions of a plating solution temperature of 50˜65° C., a cathode current density of 2˜8 A/dm 2 , and an electroplating time of 5˜6 min, and 
 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 ion and the nickel ion in a production line so as to be recycled and circulating water used for the water washing. 
 
     
     
         5 . The method of  claim 1 , wherein (5) is performed in two types, one type of which is performed in such a manner that the nickel plating is completed, after which chromium electroplating is performed and then PVD is conducted on a chromium plating layer, and the other type of which is performed in such a manner that the nickel plating is completed, after which PVD is performed directly without chromium electroplating.