Environmentally Conscious Pretreatment Process for Plating on PPS Resins
Authors: Nomura Taro , Tashiro Katsuhiko , Umeda Yasushi , Honma Hideo , Takai Osamu 
Published: February 2020

<Introduction>
Polyphenylene sulfide (PPS) is a heat-resistance material partially crystalline polymer with a simple chemical construction. The PPS has a high melting point of about 280°C, outstanding chemical resistance and non-combustibility established by an industry flammability test without any flame retardant chemical. Furthermore, the PPS is widely used in the replacement of high-functional insulation and various metals from their properties. When the PPS is plated, surface roughening is treated with a mixed solution of Nitric acid and hydrofluoric acid conventionally. However, the solution is difficult in waste water treatment. So the correspondence to these problems is demanded.
Therefore we reported a formation technology of the plating film superior in adhesion strength for pretreatment of the insulation resin until now. In this study, we applied the atmospheric UV irradiation method for PPS resins and investigated the plating process.
<Experimental>
PPS substrates was annealed at 80 °C for 1 h in order to relax the internal stress. The substrate was irradiated using ultraviolet (UV) irradiation equipment (KOL1-300S, KOTO Electric Co., LTD) in the atmosphere. After the atmospheric UV irradiation, the substrate was plated about 0.3 μm metal film by electroless NiP plating bath. After electroless NiP plating and after electrolytic copper plating bath, samples were heated at 80 °C for 1 h in order to improve adhesion.
The condition of the deposited NiP film after electroless plating was visually observed. Wettability testing of the substrate after atmospheric UV irradiation and proceeding alkaline treatment was performed by water contact angle.
Adhesion strength of the plated film to the substrate after electrolytic plating was measured by 90° peel test according to the JIS H 8630-2006 procedure with a pull speed of 50 mm min-1. Adhesion strength was measured on an Orient Precision Machine Factory Strike Log Rough E2-L05. The measurement involved peeling the plated film from the substrate at three different locations for which the average was calculated.
Surface morphologies of the untreated substrate, the substrate after atmospheric UV irradiation were observed by scanning probe microscope (SPM) using the atomic force microscopy (AFM) mode. The surface roughness (Ra) of the samples was measured over a 10 μm2 area. Similarly, surface morphologies of the substrate after atmospheric UV irradiation and proceeding alkaline treatment was observed by scanning electron microscope (SEM).
Fourier transform infrared spectroscopy (FT-IR) of the substrate before and after atmospheric UV irradiation was performed using the attenuated total reflection (ATR) method. Therefore, the similar samples was confirmed the change of functional groups on the substrate before and after atmospheric UV irradiation by X-ray photoelectron spectroscopy (XPS). For samples prepared for FT-IR analysis and XPS analysis, atmospheric UV irradiation time was 5 min, 10 min, and 30 min.
<Results and Discussion>
The high-quality electroless NiP plating was visually confirmed on the PPS resin surface by surface modification using atmospheric UV irradiation. Adhesion strength of about 0.8 kN m-1 was obtained for the treatment. Similarly, as a result of having measured the water contact angle, it was decreased with 31.2° for the treatment of 20 min whereas the untreated substrate was 79.4°. It is thought that a hydrophilicity of the PPS resin surface improved by atmospheric UV irradiation. The change in substrate morphology and surface roughness using atmospheric UV irradiation was observed by SPM. The Ra of untreated PPS and PPS after atmospheric UV irradiation were almost no change, a smoothness of the substrate had been kept. Furthermore after the atmospheric UV irradiation, the dimples was formed on the modified surface. The dimples is considered that the elastomers component in PPS resins was eluted. Subsequently, we confirmed the increase in the adsorption of O-H, C=O and C-O groups increasing the UV irradiation time by FT-IR spectroscopy. In addition, as a result of analyzed by XPS, C-C and C-S bonds were confirmed in the untreated substrate, subsequently by UV irradiation we confirmed that C-C bonding peak decreased and the detection of C-O and COO bonding peaks due to the hydrophilic increased.
<Summary>
From the above results, the plating on PPS resins was possible to applying the atmospheric UV irradiation method that is environmentally friendly. Furthermore, a smoothness of the substrate had been kept with superior to adhesion strength.
Acknowledgement: This study was aided by “MEXT-supported Program for the Strategic Research Foundation at Private Universities”.