JPS633950B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to the electroless plating of polyamides to provide a surface that is uniformly receptive to electrolessly deposited nickel and copper. The advantage of electrolessly plated non-conductive products, especially plastic products, is that in the final product the desirable properties of plastic and metal are combined, resulting in the technical and aesthetic advantages of each. Polymeric substrates are commonly plated as follows.
The surface of the plastic is pre-corroded by contacting it with an aqueous solution of at least one organic compound active to condition the surface, and then etched with a strong oxidizing acid or base to coat the surface with a noble metal catalyst. , for example with a palladium chloride solution, and then the pretreated surface is immersed in an autocatalytic electroless solution where an initial coating of a conductive metal, such as copper or nickel, is formed by chemical deposition. The metal deposit serves as a substrate for depositing a thick coating of metal thereon. Attempts to adapt conventional procedures for electroless plating of polyamides have been unsuccessful in achieving uniform, native coverage of the metal. Since the conventional electroless plating methods were found to be ineffective, an effort was initiated to find a method that would enable uniform coating of polyamide with electrolessly deposited metal. Electroless plating of polyamides, especially filled polyamides, is performed using an aqueous alkaline solution having a pH of at least about 10, preferably a solution of at least one alkali metal hydroxide (the alkali metal hydroxide content of which is about 2% by weight up to a saturated solution, preferably about 10-50% by weight) and the polyamide substrate. The alkaline solution is about 150〓
(65.6°C) to the lower of the boiling point of the solution and the softening point of the polyamide. The contact is of sufficient time to allow corrosion by the acid solution. The substrate is contacted with an acid etchant at room temperature or above. The concentration of acid is sufficient to render the polyamide surface susceptible to seeding with metal catalysts. The acid solution has the general formula (wherein each X is hydrogen, halogen or hydroxyl, provided that at least one X is halogen or hydroxyl). Contact with the acid attack is performed, followed by contacting the polyamide substrate with a metal electroless plating catalyst, which is a metal ion solution or a suspension of metal particles. Following seeding and activation of the metal catalyst by conventional means, the surface can be uniformly plated with electroless copper or nickel. Erosion is performed after rinsing impurities from the surface of the substrate with an acid or alkaline rinse solution. In carrying out the process of this invention, an alkali metal hydroxide solution is used as the modifier and preferably at a temperature of 170-200° (76.7°-93.3°C) with a contact time of about 0.5-20 minutes. used and the contact time depends on temperature and caustic concentration. No damage was detected during prolonged contact. The contact time in the aqueous acid solution is usually about 10 seconds to 15 minutes at room temperature. When a solution of acetic acid compound is used to etch the substrate, the concentration is usually from 3% by weight to saturation concentration, preferably about 5-60% by weight. In carrying out the process of the invention, the article can be treated by contacting it with an aqueous solution of an organic solvent for the polyamide, either before or after contacting the alkaline solution. Alternatively, the organic solvent can be incorporated into the alkaline solution. The solvent in the solution is generally used at a concentration of up to about 2% by weight, preferably up to about 1% by weight. Phenolic compounds such as ethylene glycol, chlorophenol, cresol and salts thereof are currently preferred. As long as the solvent is contained in its own bath or the alkali does not hydrolyze and degrade the organic solvent,
contained in its alkaline solution. The solvent is
It serves to soften the plastic against acid corrosion. Contact with the solvent solution occurs before contact with the acid etchant and, if used, with an alkaline solution. As described above, the corroded substrate is treated with an acid or base cleaning solution to remove impurities from the corrosion. According to the present invention, a method is provided that enables uniform electroless deposition of metals on polyamide substrates. In particular, the method of the invention relates to improved electroless plating of filled and unfilled polyamides such as nylon 6 and nylon 6.6. In its broadest aspect, the present invention conditions the surface of a polyamide substrate with an aqueous alkaline solution having a pH of at least about 10, rendering the polyamide substrate surface receptive to attack by acid corrosion. Alkaline compounds such as sodium metasilicate, trisodium phosphate, sodium carbonate, etc. are used alone and/or in combination with alkali metal hydroxides, although solutions of alkali hydroxides are well used. When a conditioned solution of at least alkali metal hydroxide is used, the solution has an alkali metal hydroxide content of from about 2% to a saturated solution, preferably from about 10 to 50% by weight. The alkaline conditioning solution is maintained at a temperature from 150° C. to the lower of the boiling point of the solution and the polyamide softening temperature. Contacting the polyamide substrate with the acid attack is for a sufficient period of time to render the substrate receptive to attack by the acid attack. The preferred acid solution is a solution of at least one soluble organic acid containing at least two carbon atoms, and the contact is for a sufficient time to render the polyamide substrate surface receptive to the metal surface. The metal catalyst may be a solution of functional metal ions or a dispersion of metal particles. Preferably, the organic acid is an acetic acid compound as described below. As part of the process evaluates, water rinsing with deionized water is performed between each step for better control. The substrate is a solvent for polyamide,
Preferably, it can be treated with a dilute solution of an alkali-soluble solvent to soften the surface of the substrate to enhance corrosion. The contact with the solvent may be before or after the contact with the alkaline solution, or the solvent was included in the alkaline solution. Preferably, the substrate is contacted with the solvent after contacting with the alkaline solution. The solvent softens the surface of the substrate and enhances conditioning or corrosion. The solvent for the polyamide may be contained in a separate bath or be part of the alkaline solution as defined below. Additionally, the substrate can be contacted with acidic to basic solutions after corrosion to remove impurities present on the surface of the substrate. The method of contacting with aqueous alkaline solution prior to contacting with acid attack is essential to the method of the present invention and is the reverse of the usual method performed in electroless plating operations. Although the acceptability of electroless plating on polyamide surfaces is enhanced, the polyamide to be normally processed is a filled polyamide as used in molding operations. Typical examples of such materials are filled nylon 6, nylon 6.6, etc. The first necessary step of the invention is contacting the polyamide substrate with an aqueous alkaline solution. The preferred solution is a 3% to saturated solution, preferably a solution of at least an alkali metal hydroxide, such as sodium and/or potassium hydroxide, present in a concentration of about 10-50% by weight. The solution temperature is from about 150°C (65.6°C) to the lower of the boiling point of the solution and the softening point of the polyamide substrate, preferably 170-200°C (76.7-93.3°C).
maintained at a temperature of The contact time is approximately 0.5 to 20 minutes or more;
It has been discovered that depending on temperature and alkali concentration, however, long-term immersion does not damage the substrate. The purpose is to condition the surface of the substrate in order to make it receptive to attack by acid corrosion. After a water rinse to remove the alkaline conditioning solution, the product is subjected to an acid attack based on an organic acid having a solubility in water of about 3% or more by weight. The caustic agent comprises about 5-65% by weight, more preferably about 10-25% by weight of at least one acetic acid compound, the acetate compound having the general formula (X is independently a hydroxyl group, hydrogen or a halogen, with halogen being preferred, provided that at least one X is a halogen or a hydroxyl group in the formula). Contacting is carried out at room temperature, although elevated temperatures can also be used. The contact time ranges from about 10 seconds to 15 minutes, and is sufficient time to corrode the polyamide surface to the extent that the surface is uniformly receptive to seeding with a metal electroless plating catalyst. be. Among the acetic acid compounds that can be used, there are acetic acid trichloride, acetic acid, hydroxyacetic acid, acetic acid dichloride, acetic chloride, acetic acid fluoride, acetic acid difluoride, acetic acid trifluoride, acetic bromine, acetic acid dibromide, and the like. Trichloroacetic acid is currently preferred. Optionally, contacting the polyamide with an organic solvent can be used as part of the invention. The solvent may be carried out in a separate bath before or after alkaline conditioning solution treatment, or it may be included in the alkaline conditioning solution. The organic solvent softens the surface of the substrate to aid attack by the conditioning and/or caustic solutions. Typically, the concentration of the solvent is up to about 2% by weight, preferably up to about 1% by weight. A wide range of polyamide solvents can be used. Preferred solvents for polyamides include ethylene glycol, chlorophenol, cresol, etc. and their salts. If used as a solution in the alkaline conditioner, the solvent should not be hydrolyzed or degraded by the alkaline batch. In addition, after corrosion of the polyamide substrate, contact with an organic or inorganic based acid or alkaline solution cleans the filled and/or degraded resin surface. Such solutions are usually kept at room temperature, but elevated temperatures can be used. Solutions of acid or alkaline compounds having concentrations ranging up to about 20% by weight, preferably up to about 10% by weight can be used as modifiers. Functional acids include hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, formic acid, acetic acid, etc. For convenience, the alkaline solution used to condition the substrate can be used to minimize the number of baths. Another solution includes a solution of borax and ammonium bifluoride. Its concentration enhances the surface finish without compromising the ability of the corroded surface to receive metal catalysts. Regardless of whether a cleaning process is used, the product is rinsed with water, usually deionized water, and seeded with a metal electroless plating catalyst contained in an aqueous medium. The catalyst is based on noble or non-noble metals. Non-metallic catalysts are described in commonly assigned application USP 3,958,048. The use of noble metal catalysts contained in an aqueous medium is preferred. What is the noble metal catalyst contained in the aqueous medium?
Preference is given to colloidal suspensions, meaning ionic solutions or colloidal suspensions of free metals. The precious metal is
Includes gold, platinum and palladium, with palladium being preferred. A suitable ionic bath contains palladium chloride at a concentration of about 0.2 g per solution and 3 ml of concentrated hydrochloric acid. After seeding, the palladium is reduced to the free metal state by immersion in a bath of a reducing agent such as dimethylamine. Colloidal suspensions of precious metals are described in USP 3011920. Such suspensions are colloids in which the precious metal colloid is held in suspension by a protective colloid, such as a stannic acid colloid. After seeding, the colloid is stripped of its protective colloid and exposed the absorbed precious metal by immersion in an acid or alkaline promoter solution. A less preferred method involves contacting the corrosive article with a sensitive solution containing stannous chloride and then immersing it in an activating aqueous solution, such as a palladium chloride solution, where the ionic palladium is removed from the free metal at the surface of the substrate. Methods that reduce to can also be used. The suitably activated product is electrolessly plated in the usual manner. Electroless copper and nickel compositions are described in USP 3011920 and 3874072,
They are available. It consists of copper sulfate, a complexing agent for its cupric ion such as Rosier's salt, an alkali hydroxide for pH adjustment, a carbonate base as a buffer and a complexing agent for the cupric ion such as formaldehyde. Following electroless plating, the substrate is electroplated with copper, nickel, gold, silver, chrome, etc. by conventional means to provide the desired finish on the product. Adhesion was observed to increase with its aging. In the Examples and Controls below in which the product or substrate was in contact with an alkaline hydroxide solution, the bath was an approximately 35% by volume solution of sodium hydroxide held at 200°C (93.3°C). When contacted with hydrochloric acid, the solution was 28.5% by volume of concentrated hydrochloric acid in water. Trichloroacetic acid solution used (TCA solution)
was a 20% by weight aqueous solution kept at room temperature.
Seeding of the eroded substrate was done by contacting with a colloidal tin-palladium catalyst as described in USP 3011920 at an acid molar concentration of about 1.7. The catalyst was held at about 120°C (48.9°C) and the promoter at 105°C (40.6°C). The electroless copper solution used was Katuposit PM-990, manufactured and sold by Shippley Company. The electroless plating solution was prepared at room temperature. After electroless plating, the product was rinsed with deionized water, immersed in an alkaline cleaner, passed through a reverse current cleaner, an acid dip, a bright acid copper and nickel electrolyte, and finally a chrome plating solution. The plated products were cycle tested to determine adhesion under heat stress conditions. In this test, the plated product
It was held at a temperature of 180° (82.2°C) for 1 hour, then held at room temperature for 30 minutes, then cooled to -20° and held at that temperature for 1 hour. Example 1 A Metsuki grade filled nylon known as Vydeene RP-260 manufactured and sold by the Monsite Company.
6.6 is immersed in an alkaline hydroxide solution for 10 minutes,
It was then rinsed with water and soaked in TCA solution for 1 minute. The product was then rinsed in water, catalyzed, rinsed, electrolessly plated with copper, and electroplated with copper. Initial plating adhesion ranges from 1.0 to 1.5 lb/in;
The average weight was 1.3 pounds per inch. The cycle test was successful. Control 1 The method of the example was carried out in reverse, with the product soaked in TCA solution before its adhesion with the alkali hydroxide. This caused blistering of the electroless plating. Control 2 The method of Control 1 was repeated except that the TCA solution immersion time was increased to 5 minutes. The electroless metsuki caused a bulge. Control 3 Example 1 except that immersion in TCA was omitted
repeated. This also caused blistering of the electroless plating. Example 2 The procedure of Example was repeated except that after contact with the TCA solution the product was immersed in a caustic solution for 10 minutes to clean the surface. Uniform electroless and electroplated coatings were obtained. Initial adhesion is 1.5~
It ranged from 1.8 lb/in, with an average of 1.7 lb/in. The cycle test was successful. Example 3 The procedure of Example 1 was repeated, except that the immersion in the TCA solution was for 2 minutes, followed by a 1 minute immersion in the hydrochloric acid solution. The product was uniformly electroless copper plated and electroplated. The initial adhesion of the plating layer was 1.3 to 1.8 lb/in, with an average of 1.5 lb/in. The cycle test was successful. Control 4 The Vydeene product was soaked in a hydrochloric acid solution for 1 minute, rinsed, then soaked in a TCA solution for 1 minute and again in a hydrochloric acid solution for 1 minute.
Slight blistering was observed during the electroless plating operation, and severe blistering occurred during the previous electroplating reverse current cleaning operation, and the product could not be further electroplated. Control 5 Products molded from Vydeene (trade name) RP-260 were immersed in a hydrochloric acid solution for 1 minute, rinsed in a TCA solution for 1 minute, and then soaked in the caustic solution.
Soaked for 10 minutes at a reduced temperature of 160㎓ (71.1℃). A small amount of blistering was observed in the electroless plating, and large blistering occurred during reverse current cleaning. Example 4 A product molded from Vydeen (trade name) RP-260 was immersed in a caustic solution for 10 minutes, rinsed,
It was immersed for 1 minute in TCA solution and 5 minutes in cleaning solution, which was a 50% by volume solution of glacial acetic acid in water at room temperature. Its products accepted its electroless and electroplating. Initial adhesion averaged 1.2 pounds per inch. Example 5 Kapton (trade name) XPN-1030 manufactured and sold by Allied Chemical Corporation
Products molded from, filled nylon 6 are
It was soaked in a caustic solution for 10 minutes, rinsed, and then soaked in a 10% by volume solution of acetic acid dichloride for 5 minutes. Its products accepted uniform electroless and electroplating. Example 6 The procedure of Example was repeated except that the sample was immersed in dichloroacetic acid solution for 2 minutes at 120°C (48.9°C). Same results were obtained. Example 7 Articles molded from Vydeene RP-260 were immersed in 90% acetic acid at room temperature for 15 seconds after immersion in an alkaline hydroxide solution as described in Example 1. The corroded product received adhesive deposits of electroless copper and then adhesive electroplating of copper, nickel, and chrome. Example 8 The procedure of Example 1 was repeated except that the trichloroacetic acid was reduced to 10% w/v. The immersion was for 1 minute. The corroded product received uniform adhesive deposits of electroless copper, electroplating of copper, nickel and chrome. Example 9 The polyamide substrate is Kaplan (product name)
The procedure of Example 8 was repeated except for XPN-1030. The results were equally successful. Example 10 A substrate molded from Minlon (trade name) 11-C-40, nylon manufactured and sold by Dupont, was heated in a 5% w/v aqueous solution of sodium hydroxide maintained at 130°C (54.4°C). cresylic acid 2 in
% by volume solution for 5 minutes, then 10 minutes in an alkaline hydroxide solution held at 200%, and 1 minute in acetic acid trichloride 15% w/v. The corroded products accepted electroless plating of copper and electroplating of copper, nickel and chrome when catalyzed and passed the cycle test. Adhesion ranged from 2 to 3 pounds per inch. Example 11 Capron (trade name) manufactured and sold by Allied Chemical Corporation
8202F—An unfilled nylon substrate molded from Type 6 was used. The board is 200〓 and 5
Contact with caustic solution for 5 minutes, then contact with TCA solution at room temperature, then recontact with caustic solution for 5 minutes. The corroded substrate was amenable to uniform electroless and electroplating. Controls 7-9 The organic and conditioning solutions shown below failed in tests on Vydeene where contact with alkaline hydroxide solution was carried out for 5-10 minutes.

[Table] Minutes)

Claims (1)

[Scope of Claims] 1 (a) A polyamide substrate for electroless plating having a pH of at least 10 and at a temperature from 150〓 (65.6°C) to the lower of the boiling point of the solution and the softening point of the polyamide surface. (b) forming a conditioned polyamide substrate for corrosion by contacting the polyamide surface with an aqueous alkaline conditioner solution maintained until for a time sufficient to render the polyamide surface susceptible to attack by an organic acid; Polyamide substrate, general formula (wherein each X may be the same or different and each X is independently hydrogen, hydroxyl or halogen, with the proviso that at least one X is halogen or hydroxyl)
corroding the prepared polyamide substrate by contacting it with an aqueous corrosive solution containing an acetate compound, the acetate compound having a solubility in water of greater than 3% by weight, and the acetate compound comprising: producing a surface of a polyamide substrate for electroless plating comprising being present in an aqueous solution thereof at a concentration sufficient to render the conditioned polyamide substrate virtually uniformly receptive to a metal electroless plating catalyst; how to. 2. The method of claim 1, wherein the polyamide substrate is cleaned by contact with an aqueous acid or base cleaning solution prior to contact with the metal catalyst. 3. The method of claim 1, wherein the polyamide substrate is contacted with a dilute aqueous solution of an organic solvent for the polyamide for a sufficient period of time to soften the surface of the polyamide substrate prior to contact with the conditioning solution. Method. 4. The method of claim 1, comprising contacting the polyamide substrate with a dilute aqueous solution of an organic solvent for polyamide for a period of time sufficient to soften the surface of the polyamide substrate after contact with the conditioning solution. 5. The method of claim 1, wherein the conditioning solution comprises an organic solvent for the polyamide. 6. The method of claim 5, wherein the polyamide substrate is cleaned by contacting with an aqueous acid or base cleaning solution prior to contact with the metal catalyst. 7. The method of claim 5, wherein the polyamide substrate is contacted with a dilute aqueous solution of an organic solvent for the polyamide for a sufficient period of time to soften the surface of the polyamide substrate prior to contact with the conditioning solution. Method. 8. The method of claim 5, comprising contacting the polyamide substrate with a dilute aqueous solution of an organic solvent for polyamide for a period of time sufficient to soften the surface of the polyamide substrate after contact with the conditioning solution. 9. The method of claim 6, wherein the conditioning solution comprises an organic solvent for the polyamide. 10. The method according to claim 9, wherein the organic solvent is an alkali-soluble organic solvent. 11. The method of claim 5, wherein the polyamide substrate is formed from filled polyamide. 12. The method of claim 5, wherein the total alkali metal hydroxide content in the conditioned solution is from 10 to 50% by weight of the solution. 13 The adjusted solution is 170~200〓(76.7~93.3
6. The method according to claim 5, wherein the temperature is maintained at a temperature of 0.degree. 14. The method of claim 5, wherein the contact time in the conditioning solution is between 0.5 and 20 minutes. 15. The method of claim 5, wherein the total acetic acid compound concentration is from 3% by weight to a saturated solution. 16. The method of claim 5, wherein the total acetic acid compound concentration is 5 to 60% by weight of the solution. 17. The method of claim 5, comprising contacting the polyamide substrate with the acetate solution for a period of 10 seconds to 15 minutes. 18. The method of claim 5, wherein the acetic acid compound is trichloroacetic acid. 19. The method of claim 5, wherein the acetic acid compound is dichloroacetic acid. 20. The method of claim 5, wherein the acetic acid compound is chloroacetic acid. 21 (a) contacting the polyamide substrate with an aqueous conditioning solution of at least one alkali metal hydroxide, the total alkali metal hydroxide concentration being from 10% by weight of the solution to a saturated solution; (b) forming a conditioned polyamide substrate by heating the substrate at a temperature of 0.5 to 20 minutes from (65.6°C) to the lower of the boiling point of the solution and the softening temperature of the polyamide surface; (b) the acetic acid; 2. The method according to claim 1, wherein the compound is at least one acetic acid compound selected from the group consisting of trichloroacetic acid, dichloroacetic acid, or hydroxyacetic acid.