LT5997B - METHOD OF PREPARING PLASTIC SURFACE FOR THEIR CHEMICAL METALIZATION - Google Patents

Abstract

The invention is attributed to the surface preparation of plastics prior to chemical metallization and can be used in various industries where decorative or functional metal coatings on plastics are required. The object of the present invention is to provide a high quality plastics surface prior to chemical metallization at the lowest possible cost, while maintaining the stability of the etching solution without the use of carcinogenic and otherwise harmful substances to humans and the environment. The objective is achieved by the method of preparing the surface of the plastics prior to chemical metallization involving etching the plastic with an inorganic acid solution with an oxidizing agent, activating with a palladium salt solution, and treating with a reducing or accelerating solution in the proposed manner with a 0.5 to 5 g / l soluble chlorate solution. 50-80% by volume of sulfuric acid at room temperature and before the activation of the solution of palladium compounds and treatment with a reducing or accelerating solution is further treated with an alkali metal hydroxide solution; additionally add 2-20 g / l of another oxidant to the etching solution with a standard oxidation potential exceeding the chlorate ion potential.

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 the plastic with chromic acid solution followed by activation with an ionic or colloidal solution of palladium compounds and, eventually, reducing adsorbed on the plastic surface with palladium or palladium colloidal particles. solution, or acid acceleration, usually hydrochloric acid solution.

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 chemical deposition of the metal on the plastic surface. After that, the metal plating in the chemical metallization solution is already autocatalytic, i.e. the metal layer formed at the beginning catalyzes further metal deposition.

The main disadvantages of the conventional method are the carcinogenicity of the chromic acid etching solution and the frequent chemical deposition of the metal, usually nickel, on the insulated portions of the plastisol plate suspensions, which results in metal losses in further electroplating solutions.

The closest embodiment of the present invention is a method of surface preparation of plastics (see U.S. Patent Application 2005/0199587 A1) which involves etching the plastic with an acid containing 20-70 g / l potassium permanganate solution. The optimal concentration of KMnO ₄ in said solution is about 50 g / l. At concentrations below 20 g / l, the solution is ineffective and the upper limit is due to the solubility of potassium permanganate. After etching, it is activated with a palladium salt solution with an amino additive, and the plastic is then treated with a reducing agent such as borohydride, hypophosphite or hydrazine. However, this approach has its drawbacks:

- first: at high concentrations of permanganate in etching solution (about 50 g / l recommended and about 45% by volume of phosphoric acid), permanganate is rapidly degraded, especially at elevated temperatures (as noted in the specification). The recommended temperature is 100 ° F, i.e. 37 ° C. As shown by the tests performed at this temperature, the solution becomes ineffective after 4-6 hours, i.e. it does not wet the surface of the plastic and it does not cover the whole area during metallization, but the adhesion of the metal to the plastic in the exposed area is very weak. The solution often has to be adjusted with new portions of non-cheap potassium permanganate. In addition, insoluble permanganate decomposition products are formed, contaminating the metallizable surface;

- second; etching in permanganese solutions activates the surface of the plastisol hanger insulation as it is exposed to the etching reaction product manganese dioxide during etching. Manganese dioxide promotes the adsorption of palladium compounds on plastisol and, as a result, the latter tends to be metallised in chemical precipitation solutions. The formation of manganese dioxide on various surfaces is typical of permanganate etching solutions of any composition. Thus, the very important goal of metal-sparing further, in the next galvanic coating thickening, remains unsymmetrical plastisol suspension insulation.

The object of the present invention is to provide a high quality surface preparation of plastics prior to chemical metallization at the lowest possible cost, while maintaining the activity of the etching solution stable and free of carcinogenic and otherwise harmful substances for humans and the environment.

The object is achieved by a method of preparing the surface of plastics prior to chemical metallization, which comprises etching the plastic with an inorganic acid solution with an oxidant, activation with palladium salt solution and treatment with a reducing or accelerating solution, etching the plastic surface with 0.5-5 g / l soluble chlorate solution. 50-80% by volume in sulfuric acid at room temperature and further treatment with an alkali metal hydroxide solution before activation with palladium compound solution and treatment with a reducing or accelerating solution; additionally add 2-20 g / l of another oxidizing agent with a standard oxidizing potential above the chlorate potential to the etching solution.

The alkali metal chlorate forms a yellow compound with sulfuric acid molecules which is capable of reacting with the surface of plastics at room temperature in the presence of a solution of normal oxidative potential in an H ₂ SO ₄ solution. As a result of this reaction, the plastic surface becomes hydrophilic and adsorbs the palladium compounds sufficiently strongly. The product of the reaction of yellow chlorate with sulfuric acid is a palladium catalyst poison. During etching, this compound penetrates the surface layers of the plastisol hanger insulation and prevents the metal from settling on the plastisol in chemical metallization solutions, but does not interfere with the process on the metallizable plastic surface.

After dissolving 1-2 g / l of sodium or potassium chloride in etching solution and further dissolving there 5-10 g / l of a strong oxidizing agent such as NaBiO3, the corrosive properties of the solution remain at room temperature for several days and allow the solution to be used without correction. If the solution contains only sodium or potassium chlorate, the corrosive properties of the solution remain significantly shorter and do not exceed 1 day.

An important feature of the proposed process compared to permanganate etching is that very high adhesion strength values of the coatings, often exceeding 1.2-1.3 kg / cm, are obtained. These values depend not only on the etching solution composition and etching time (for each etching solution composition, there is an optimum etching time for adhesion) but also on the activation solution composition. Usually, with true activation solutions, adhesion values are higher than with colloidal activation solutions.

The etching solution is obtained as follows:

Add 300 ml of deionised water with 700 ml of concentrated sulfuric acid, allowing the solution to cool. Subsequently, 2 g of potassium chlorate and 10 g of sodium perchlorate are dissolved in the solution. The solution is ready for use.

When using more than 50% by volume of water for the preparation of the solution compared to sulfuric acid, the yellow oxidizing plastic does not form a compound between the chlorate ions and the sulfuric acid molecules, so that no more than 50% by volume of water can be present.

When using less than 20% water by volume as sulfuric acid in the solution, the surface of the plastics is destroyed during etching due to the excessive concentration of sulfuric acid, and as a result the adhesion between the nickel chemical coating and the plastic is lost.

If less than 0.5 g / l of potassium chlorate is dissolved in the solution, it will take more than 15 minutes for the plastic to corrode and such concentration is unacceptable.

If more than 5 g / l of potassium chlorate is dissolved in the solution, the plastic will be etched for a minimum time, i.e. After 2-3 minutes, it becomes overstated, which results in a significantly lower adhesion strength, which is why such high chlorate concentration is also unacceptable.

Examples

Corrosion of plastic ABS (acrylic-nitrile butadiene-styrene copolymer) and PC / ABS (55% acrylic-nitrile butadiene-styrene copolymer and 45% polycarbonate) according to US patent application 2005/0199587 A1: 45% by volume in phosphoric acid containing 50 g / l KMnC> 4 at 37 ° C for 5 min (ABS plastic) or 15 min (PC / ABS plastic) or corrosive for 1-12 min at 0.5-5 g / l KCIO3 and 2-20 g / l in auxiliary oxidant 50-80% by volume in sulfuric acid at 20 ° C. After etching, the plastic is immersed for 1-2 min in a room temperature neutralization solution containing 10 g / l NaOH and further activated in true (5 min at 20 ° C) or colloidal (2 min at 35 ° C) palladium compounds (colloidal solution is D0W Chemicals Branded Solution). 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 kept for 5 min at 60 ° C in a solution containing 20 g / l sodium hypophosphite at pH 9. After activation in branded colloidal solution, the plastics are treated for 2 min in D0W Chemicals branded accelerator solution at 40 ° C. temperature. The plastics are then coated with chemical nickel in accordance with Niposit-PM technology from D0W Chemicals. The coating quality is assessed by the extent to which the plastic surface is covered or not by the plastisol insulated suspension and the adhesion strength of the coating. To assess adhesion, the Ni coating is thickened in a galvanic drive bath and the force required to tear a 1 cm wide strip of coating is measured. plastic (kg / cm). The etching time in the permanganate solution was 5 min for the ABS samples and 15 min for the PC / ABS samples. For all samples, the etching time in chlorine solution was 5 min. Preparation conditions for plastics and metallization (chemical nickel) results are shown in the table.

Table

For example, No. Plastics Acid and its volume concentration in etching solution Principal oxidizing agent and its concentration in g / l The plastic was fully (+) incomplete (-) Plastisol Suspension Insulation Partially Covered (+) Not Covered (-) Inbox adhesions meanings (kg / cm) 1 ABS H3PO4, 45 KMnO ₄ , 50 + + 0.5-0.7 2 ABS H ₂ SO ₄ , 70 KCIO ₃ , 2 + - 1.0-1.3 3 * ABS H ₃ PO ₄ , 45 KMnO ₄ , 50 + + 0.2-0.3 4 * ABS H ₂ SO ₄ , 70 KCIO ₃ , 2 + - 0.8-1.0 5 PC / ABS H ₃ PO ₄ , 45 KMnO ₄ , 50 - + - 6th PC / ABS H ₂ SO ₄ , 70 KCIO ₃ , 2 + - 0.7-0.9 7 * PC / ABS H ₃ PO ₄ , 45 KMnO ₄ , 50 + + 0.1-0.3 8 * PC / ABS H ₂ SO ₄ , 70 KCIO ₃ , 2 + - 0.5-0.7 9th ABS H ₂ SO ₄ , 70 KCIO ₃ , 0.2 - - - 10th ABS H ₂ SO ₄ , 70 KCIO ₃ , 8 + - -0.1-0.3 11th PC / ABS H ₂ SO ₄ , 70 KCIO ₃ , 0.3 - - - 12th PC / ABS H ₂ SO ₄ , 70 KCIO ₃ , 10 + - -0-0.2 13th ABS H ₂ SO ₄ , 45 KCIO ₃ , 2 - - - 14th ABS H ₂ SO ₄ , 85 KCIO ₃ , 2 + - -0-0.2

* Activation in colloidal DOW solution (remaining activated in ionic activation solution)

Examples 1-4 show that in the case of permanganate etching, the plastisol suspension insulation is partially covered with chemical nickel, while in the case of chlorate etching, the plastisol insulation remains clean. In addition, both ionic activation solution and colloidal give significantly higher values of Ni coating adhesion to ABS plastic in the case of chlorate etching.

For PC / ABS plastic nickel plating (Examples 5-8), the same results are observed - in the case of chlorate etching, the plastisol suspension insulation is completely uncoated and the resulting adhesion values are significantly higher, especially when using an ionic activation solution.

In the case that the concentration of KCIO3 in the etching solution is less than 0.5 g / l, the ABS plastic is not covered with chemical nickel or not completely covered (Example 9). If the concentration of KCIO3 exceeds 5 g / l (Example 10), after 5 min. The etching ABS plastic is over-etched, so the value of chemical Ni coating adhesion is significantly lower (not enough for practical applications). Similar results at the recommended concentration range of KCIO ₃ are obtained for PC / ABS plastic metallization (Examples 11-12).

In the case of a solution containing less than 50% H ₂ SO ₄ by volume in the etching solution, the etching agent is ineffective and therefore the plastic is not coated with nickel or incompletely coated (Example 13). When the concentration of H ₂ SO _{4 is} greater than 80% by volume (Example 14), the plastic is over-etched and therefore the adhesion of the chemical nickel coating to the plastic is insufficient.

DEFINITION OF INVENTION

Claims (2)

DEFINITION OF INVENTION A method of preparing a surface of plastics prior to chemical metallization comprising etching the plastic with an inorganic acid solution with an oxidant, activating it with palladium salt solution and treating it with a reducing or accelerating solution, characterized in that the plastic surface is etched with 0.5-5 g / l soluble chlorate solution. -80% by volume in sulfuric acid at room temperature, and further treatment with an alkali metal hydroxide solution before activation with palladium compounds and treatment with reducing or accelerating solutions. 2. A process according to claim 1, characterized in that 2 to 20 g / l of another oxidizing agent is added to the etching solution which has a standard oxidation potential higher than the chlorate ion potential.