LT6070B - Preparation of plastic surface for chemical metallization process - Google Patents

Abstract

The invention relates to the plastic surface preparation for chemical metallization and can be used in various industries, which provide a decorative or functional metallic coatings on plastics. It aims the high-quality plastic surface preparation for chemical metallization using hot chlorate etching solution and thereby saving high adhesion values of nickel coatings with plastics. The aim is achieved by the fact that the plastic surface preparation for chemical metallization process comprises etching the surface with sulfuric acid, containing chlorate iones and an additional oxidant and following treatment with a solution containing alkali metal hydroxide, activation in palladium salt solution and treatment with reducing or accelerating solution, it added to the etching solution 0.1 to 8 g/l vanadium compound and etching performs at 20-65 oC.

Description

The invention relates to the surface preparation of plastics prior to chemical metallization and can be used in a variety of industrial applications where decorative or functional metal coatings on plastic parts are required.

The conventional method of surface preparation of plastics prior to chemical metallization, usually chemical nickelization, involves etching in a solution of chromic acid followed by activation in an ionic or colloidal solution of palladium compounds and appropriate reduction of palladium or palladium colloidal particles adsorbed on the plastic surface usually in a solution of hydrochloric acid.

Etching is required to give the surface hydrophilicity so that, at other stages of the process, it is wetted with aqueous solutions by adsorbing sufficient amounts of palladium salts and ensuring good adhesion of the metal coating to the plastic. Activation with subsequent reduction or acceleration is performed to initiate the chemical deposition of the metal on the plastic. After that, the metal plating in the chemical metallization solution is already autocatalytic, i.e. the precipitated metal from the solution catalyzes further metal deposition.

The main disadvantages of the conventional method are the carcinogenicity of the etching solution of chromic acid and the frequent chemical deposition of metal, usually nickel, on the insulated plastisol suspension parts, which results in metal losses in subsequent electroplating solutions. The closest embodiment of the present invention is a method of surface preparation of plastics (see LR Application 2012 042, filed June 5, 2012), which comprises etching plastic at room temperature in a solution of 0.5-5 g / l soluble chlorate in 50-80 vol% sulfuric acid and followed by treatment with an alkali metal hydroxide solution. The etching solution additionally contains, in addition to chlorate, another oxidizing agent whose standard oxidative potential is greater than that of chlorate ions. After treatment with an alkali metal hydroxide solution, the plastic is activated in a solution of palladium compounds, further retained in a reducing or accelerating solution, and nickelized in a chemical nickel solution. Positive features of the process are the high adhesion values of the nickel coating to the plastic and the fact that the plastisol coated plastic detailing equipment remains uncoated with the nickel coating.

The disadvantage of the method is the ability of the etching solution to absorb water vapor from the ambient air and thereby dilute it, losing its effective etching properties. The solution to this problem would be to increase the temperature of the etching solution to a level where the moisture absorption of the air is offset by evaporation of water from the solution. However, where the temperature of the etching solution is above 30 ° C, the resulting values of plastic bonding for the nickel coating are significantly lower and may even drop to zero.

The object of the present invention is to provide a high quality surface preparation of plastics prior to chemical metallization using a hot chlorinated etching solution while maintaining high values of adhesion of the nickel coating to the plastic.

The object is achieved by a method of surface preparation of plastics prior to their chemical metallization, comprising surface etching in a solution of sulfuric acid containing a chlorate ion and an additional oxidant followed by treatment in a solution containing an alkali metal hydroxide, activation in a palladium salt solution and treatment in a reducing or accelerating solution. the etching solution is introduced at 0.1-8 g / l of vanadium compound and etched at 20-65 ° C.

The incoming vanadium compound in the etching solution is involved in the etching process of the plastic both as an additional oxidizing agent on the plastic surface and as a catalyst for the oxidative action of the chlorate ions. The vanadium-containing etching solution is used at temperatures between 20-65 ° C and the resulting adhesion values on nickel-plated plastic coatings are not lower than those of the prototype. In addition, such a solution, when used at higher temperatures, may be more dilute with respect to sulfuric acid and thus cheaper and safer at work.

An important feature of the proposed process, which differs from the prototype, is the ability to more effectively etch the surfaces of plastics contaminated with soldering oils, since at high temperatures, lubricating oils are chemically degraded (oxidised) by etching solution components and no longer interfere with the etching process.

Examples

Corrosion of plastic ABS (acrylic-nitrile-butadiene-styrene copolymer) and PC / ABS (55% acrylic-nitrile-butadiene-styrene copolymer and 45% polycarbonate) corrodes for 5 min in 120 g / l KCIO3 and 10 g / l KJO4 containing oxidant 30-70% by volume in sulfuric acid at 20 ° C, 40 ° C and 65 ° C or corrosive solution of the same formulation under the same conditions but with addition of 0.1 to 10 g / l soluble vanadium compound. Soak the plastics for 2 minutes after etching. to room temperature neutralization solution containing 10 g / l NaOH and further activated in real (5 min at 20 ° C) solution of palladium compounds. The stock solution has a concentration of 0.1 g / l PdCl ₂ and a pH of 2.7. After activation in true Pd solution, the plastics are retained for 5 min at 60 ° C and 20 g / l sodium hypophosphite, pH 9. The plastics are then coated with chemical nickel according to Dipw Chemicals NipositPM. The coating quality is evaluated by the adhesion strength of the coating to the plastic. To assess adhesion, the Ni coating layer is thickened in a galvanic immersion bath and the force required to tear a 1 cm wide coating strip from the plastic (kg / cm) is measured. Preparation conditions of plastics for metallization and results of metallization (chemical nickel plating) are shown in the Table.

Examples 1 and 2 show that etching solution containing no vanadium compounds can only be used for etching ABS at room temperature. At higher temperatures of the etching solution, for example 40 oC, the adhesion of ABS Ni coatings is close to zero. In the case of etching solution containing vanadium compound (Examples 3 and 4), the Ni coating adhesion to ABS by etching in higher temperature solution is not less than in the absence of vanadium solution in solution and at room temperature etching. Examples 5, 6 and 7 show that the same patterns in the presence or absence of etching solution in vanadium compound also occur in the etching of PC / ABS plastic. The data of Examples 8, 9, 10 and 11 show that the sulfuric acid concentration in the etching solution can be reduced to 30% by volume when etched at 65 ° C. However, reducing sulfuric acid concentration to less than 30% by volume is not worthwhile, since the adhesion of Ni coating to plastics, even at 30% by volume, is noticeably lower. Examples 12 and 13 show that reducing the concentration of vanadium compound in etching solution by more than 0.1 g / l or increasing it by more than 8 g / l is not appropriate because of significantly lower Ni coating adhesion values.

For all 13 examples, the plastic samples were fully coated with Ni and the Ni coating did not form on the plastisol parts of the equipment.

Table

For example, No. Plastics Concentration of H ₂ SO ₄ in etching solution,% vol Concentration of KCIO ₃ in etching solution,% vol Etching temperatures, ° C Vanadium compound and its concentration in etching solution, g / l Inbox adhesions meanings, kg / cm 1 ABS 66 2 20th - 1.0-1.3

2 ABS 66 2 40 - 0-0.1 3 ABS 66 2 40 V ₂ O ₅ , 0.5 1.1-1.3 4 ABS 66 2 65 V ₂ O ₅ , 0.5 1.3-1.4 5 PC / ABS 66 2 20th - 0.7-0.9 6th PC / ABS 66 2 65 - 0-0.1 7th PC / ABS 66 2 65 V ₂ O ₅ , 0.5 0.9-1.1 8th ABS 40 10th 65 NaVO ₃ , 1.0 1.0-1.2 9th PC / ABS 40 10th 65 NaVO ₃ , 1.0 0.7-0.9 10th ABS 30th 10th 65 NaVO ₃ , 1.0 0.5-0.7 11th PC / ABS 30th 10th 65 NaVO ₃ , 1.0 0.3-0.5 12th ABS 66 2 65 V ₂ O ₅ , 0.1 1.0-1.3 13th ABS 66 2 65 V ₂ O ₅ , 8.0 0.8-1.0

Claims (1)

DEFINITION OF INVENTION A method of preparing a surface of plastics prior to chemical metallization comprising etching the surface in a solution of sulfuric acid containing a chlorate ion and auxiliary oxidant, followed by treatment in a solution containing an alkali metal hydroxide, activation in a palladium salt solution and treatment in a reducing or accelerating solution. adds 0.1-8 g / l of vanadium compound and etching at 2065 ° C.