1 Introduction
The plastic electroplating roughening process causes the plastic surface to be microscopically rough, from hydrophobic to hydrophilic, to improve the bonding between the surface and the coating. Accurately grasping the content of each component in the roughening solution is beneficial to the adjustment, maintenance and control of the coarsening bath, which is very important for the whole process of plastic plating. At present, the plastic plating production line adopts a high-chromic acid type roughening solution with high roughening speed and good effect, and its component content range is generally [1]: H2SO4330～405g/L, CrO3400～430g/L; or H2SO4600g/L, CrO3250 ~350g/L. Through analysis and experiment, the author has developed a high chromate type roughening solution analysis method. Since the establishment of the plastic electroplating production line, it has played a very good effect on the maintenance, adjustment and control of the roughening bath.
2 Analytical methods
2.1 Analysis of H2SO4 content
2.1.1 Principle of the method The Pb(NO3)2 solution added in the analysis sample reacts with CrO2-4 and SO2-4 to form PbCrO4 precipitate and PbSO4 precipitate, and the quantitative H+ is precipitated. The separated sample is titrated with NaOH standard solution. The solution was calculated to obtain the H2SO4 content in the roughened solution.
2.1.2 reagent w (Pb (NO3) 2) = 20% Pb (NO3) 2 solution, c (NaOH) = 1 mol / L NaOH standard solution, w (methyl orange) = 1% methyl orange indication Agent.
2.1.3 Analytical Procedure Take 1 mL of the roughening solution in a 250 mL beaker, and slowly add a warm (<45 °C) Pb(NO3)2 solution under continuous shaking until the supernatant clears completely disappeared and is colorless. . It was filtered through a two-layer filter paper in a 300 mL triangular beaker, and the precipitate was washed several times with warm water. The filtrate was cooled to room temperature and 1 drop of methyl orange indicator was added, and titrated with a NaOH standard solution until the solution turned from red to orange.
2.1.4 Calculate Ï(H2SO4)/(g/L)=c×V×50.6/V0-Ï(CrO3)×1.0112 where: the concentration of the substance of the c-NaOH standard solution/(mol/L); V-drip timing consumes the volume of NaOH standard solution / mL; V0 - volume of crude solution taken at the timing of titration / mL; Ï - mass concentration of CrO3 in the roughening solution / (g / L); 1.0112 - CrO3 converted to H2SO4 Conversion factor.
2.1.5 This method is compared with the traditional method (gravimetric method)
The analysis method is simple, fast and accurate, and solves the problem that the traditional method takes a long time and has high accuracy, and plays an important role in the maintenance, control and adjustment of the bath, and achieves excellent results in actual production. .
2.2 Analysis of CrO3 and Cr2O3 content The analysis method of CrO3 and Cr2O3 in the roughening solution is the same as the analysis method of CrO3 and Cr2O3 in the chromium plating solution. This analytical method is equally applicable to high sulfuric acid type roughening solution [1].
3 Conclusion
This method is practical, simple, fast and accurate. In the application process, the production is guided in time and accurately, and satisfactory results are obtained in the maintenance, adjustment and control of the roughening bath, which plays an important role in the whole process of plastic plating.
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