DK148485B - PROCEDURE FOR PREPARING PLASTIC SURFACES TO BE PROVIDED WITH AN ADJUSTABLE METAL COATING BY AIRLESS METAL COVERAGE - Google Patents

Description

in U8485

The invention relates to a method for pretreating plastic surfaces, which is of the kind set out in the preamble of claim 1.

To adjust the pH and the ratio of permanganate 5 to manganate, a buffer is used, e.g. a phosphorus or boron-containing compound, a carbonate, a bicarbonate or a pH regulator in the form of an organic or inorganic base. It is known to provide the surface of printed circuit board fabric with a coating layer obtained by treatment with alkaline permanganate solution and desiccation after the surface has been subjected to an etching process to obtain the required adhesion. strength, cf. DE Publication No. 2,239,908. Even cm alkaline pemnanganate solutions are well known - cf. U.S. Patent No. 1,141,797 - and used for cleaning or pre-treating metal surfaces, it has not been known, in the context of processes of the kind mentioned above, that the composition of the alkaline etching solution is critical to the etching result and the adhesive strength of the metal intended for etching which is applied to the substrate in a subsequent process. The following is a known reaction equation for the equilibrium setting in alkaline solution: 3Mn04 ~~ + 2H20 = Mn02 + 2Mn04 "+ 4 OH-, K = 16 and the theoretical molar ratio of manganate to permanganate 25 as a function of the pH value then the following: pH Manganate / permanganate 14 2.5 13 1.2 12 0.5 30 11 0.25

This is the starting point of the invention, the object of which is to provide a process of the kind mentioned above that can be rendered more stable by selecting a particular pH range and a specific manganate / permanganate ratio at defined temperature conditions and treatment times. while improving the desired properties with respect to the adhesive strength 5 of the metal to be applied in a subsequent process.

The stated object is achieved by a method which according to the invention is characterized by the features of claim 1.

By using solutions which fulfill the conditions set out in the characterizing part of claim 1 and proceed in the manner indicated therein, improved activation of the binding centers is achieved in the prior art.

As to the effect, the permanganate solutions are completely equivalent to the commonly known chromic acid solutions, but are not beset with the serious problems of annihilation and harmlessness of the acid and the use of very costly materials for the bath vessels, heating means, mixers, etc.

A further advantage lies in the good stability of the solution in the pH range concerned, since the hitherto commonly used, highly acidic baths are much less stable. Eg. At a solution of 2-10 g / l potassium permanganate and 600 ml / l of concentrated sulfuric acid or 500 ml of 85% phosphoric acid, a sudden and rapid, complete decomposition occurs. On the other hand, the highly alkaline permanganate solutions are very stable, but they work much more slowly and the obtained adhesive strength for the deposited metal layer on the substrate is very poor.

In the process of the invention, it is possible to use any metal salt of permanganic acid, provided that it is soluble and stable in aqueous solution up to 2 g / l. However, alkali and alkaline earth salts are preferably used, e.g.

Sodium and potassium salt.

The concentration range of permanganate solutions can be varied within wide limits, and may be between 1-2 g / l and the saturation point. However, it should be noted that the best results 5 are obtained with potassium and sodium permanganate solutions in the range of 1-60 g / l.

The rate of activation of the germs embedded in the resin surface increases with the concentration of the permanganate solution up to a concentration of 60 g / l. Above this value, no further increase in the activation rate can be observed. At concentrations lower than 10 g / l, a relatively low activation rate is obtained, which is not normally appropriate for use in production.

The pH can be adjusted by adding acids or bases, depending on the analysis result. The analysis can be carried out as follows: 1) of the solution to be examined, a sample portion is taken and cooled to room temperature; 2) the pH is measured with a suitable measuring instrument, e.g. a pH meter, 3) the adjusting solution (pH controller) is added in such a quantity that the pH value assumes the desired value, 4) a corresponding amount of adjusting solution is added to the main solution.

If the pH of the main solution, e.g. has dropped to 11.5 25 due to absorption of CO2 from the air, KOH is added dropwise to the sampled portion until the pH reaches 12.5. Then the calculated amount of KOH is added to the main solution.

The other important parameter of the present solution, namely the ratio of manganate to permanganate, is also measured by taking a sample portion and titrating it with KJ, proceeding in the same manner as in adjusting the pH value by to the sampled portion is added so much permanganate that the desired concentration is obtained, and then the calculated amount is added to the main solution.

Buffer substances, such as phosphates, borates, carbonates or bicarbonates, also serve to achieve the desired pH during the setting of the correct manganate / permanganate ratio. Particularly preferred buffers are potassium phosphate or monobasic potassium phosphate or dibasic potassium phosphate, potassium pyrophosphate or potassium polyphosphate or the corresponding sodium salts. Also suitable have been found the salts of boric acid such as potassium borate, potassium diborate, metaborate, orthoborate and the corresponding sodium salts.

Of course, the quantities needed to set the correct pH value also depend on the desired pH value. When working with dissolved salts, a significant simplification is obtained if the same number of grams of the buffer or the salts used for pH adjustment as the permanganate amount is used. In this case, from 2 to 60 g / l of alkali phosphate, carbonate, mono- or dibasic phosphate or peroxydiphosphate or one of the borates already mentioned may be used.

If necessary, a common wetting agent, such as e.g. fluorocarbon.

The time and temperature of the activation step will vary and generally the process is accelerated at higher temperatures. The treatment time varies from 30 seconds to 2 hours, the temperature can be between 20 ° C and 100 ° C, with the best results usually being obtained at temperatures between 40 and 70 ° C and treatment times between 2 and 20 minutes. The surfaces to be treated can be brought into contact with the solution in various ways, e.g. by immersion, or spraying or similar commonly known methods.

The articles to be treated either consist in their entirety of an artificial resin or resin mixture, or they have only a coating of such material.

The plastic surfaces are preferably pretreated in such a way that they are at least for a time polarized and wettable.

This can be accomplished by spraying or dipping in a liquid such as dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, ketones or halogenated hydrocarbons or mixtures thereof.

For certain substrates, e.g. an acrylonitrile-butadiene-styrene resin, it is advisable to have a pretreatment consisting of dipping e.g. in a strong solution of sulfuric acid, nitric acid, phosphoric acid, toluene sulfonic acid or a strong amine. With such treatment, excellent bonds can be obtained without blistering. Surprisingly, such benefits are not obtained with this substrate when strong solutions of hydrochloric acid or sodium hydroxide are used instead.

It will be clear to those skilled in the art of powerless metal deposition that if the surface is not itself active for the deposition of metal by powerless wood, e.g. if no catalyst such as copper oxide is present in the resin body, after pretreatment according to the invention to promote activation of bonding points, it will be necessary to insert a 25 step to render the activated surface catalytic for uptake of deposited metal before contact with the powerless metal deposition bath. Many well-known methods for making the surface catalytic exist. Among these, there are incremental processes such as immersing the body first in a solution of stannous ions and then in an acidic solution of precious metal such as palladium or platinum ions. On the other hand, a single bath may also be used for such purposes as the colloidal palladium and tin ions dispersions disclosed in U.S. Patent No. 3,011,920, or preferably the 6 U8485 soluble complexes of precious metals, stannous ions and anions. , disclosed in U.S. Patent No. 3,672,938.

The resin body thus activated (and, if necessary, catalyzed) is then metallized by powerless deposition, e.g. a nickel layer is deposited from a conventional acidic nickel hypophosphite bath at a moderately elevated temperature such as 50-60 ° C, or from an alkaline nickel bath at about 20 to 35 ° C, as known in the art. Instead of nickel, copper can be applied by current-free pathway from a conventional copper deposition bath, which, in addition to a copper reducing agent, contains a complexing agent and other conventional ingredients. A suitable copper deposition bath consists e.g. of: CuSO ^ -5 ^ 0.30 g / l; Rochelle salt, 150 g / l; wetting agent 1 ml; sodium cyanide, 30 mg / l; formaldehyde (37%), 15 ml / l; sodium hydroxide in a 15 to give pH 13. Other suitable streamless metal deposition baths are disclosed in U.S. Patents Nos. 3,445,350, 3,437,507, 3,433,828 and 3,625,758, and gold, silver and cobalt, and others. Powerless outlets are known to those skilled in the art.

Although not imperative, it is a preferred practice, after treatment with the present invention, to promote activation of the binding sites with another agent to "neutralize" the permanganate prior to catalysis and powerless metal deposition. This agent appears to remove excess permanganate from the resin surface and prevents pre-25. thinning and other possible effects due to residual strong oxidizing agent on the following steps and baths in the process. Stannous ions such as those derived from an acidic stannous chloride bath may be used as neutralizing agents. Also suitable are bisulfitions, hydroxylamine, sugar or indeed any commonly known water-soluble compound which can be oxidized by permanganate. All that is needed to achieve the desired neutralizing effect is to immerse the permanganate-treated substrate in an aqueous solution of the neutralizing agent at a concentration of e.g. 2 to 35 100 g / l for a short time and then rinse thoroughly with water before performing the next step. This optional step is illustrated in the examples.

7 148Λ85

It has been found that superior bonds are obtained if the metallizing bath is formulated in a known manner such that the deposition of metal by a powerless path occurs slowly. In one embodiment, the deposit is started with a slow bath, whereupon the article is moved to a fast powerless bath. This minimizes the decline in speed at this key production stage.

Example 1.

The following example illustrates the use of an activation bath in which the pH and permanganate / manganate ratio are controlled by a strong base.

An epoxy glass laminate with a surface coating of a resin-rich epoxyphenol resin nitrile rubber is metallized by the following procedure: a) the surface is cleaned and rinsed with water; b) the blank is immersed for 2 minutes at ca. 60 g C with gentle stirring in a solution containing KMnO 4 40 g KOH (45% aqueous solution) to pH 12.5 water (up to) 1000 ml, 20 c) the substance is rinsed in still (non-running) water, - d) neutralize for 5 minutes at 20-25 ° C in a solution containing hydroxylamine · HCl 50 g wife. HCl (37% aqueous solution) 20 ml water (up to) 1000 ml, e) immerse the blank for 2 minutes at 20-25 ° C in water containing 300 ml / l 37% hydrochloric acid, ) rinse the blank with running water at 20-25 ° C, 30 g) immerse the blank for 10 minutes in a sensitization solution containing: 8 148485 palladium chloride 1 g stannous chloride 60 g wife. HCl (37% aqueous solution) 100 ml water (up to) 1000 ml, in the form of a palladium chloride-stannous chloride complex, U.S. Patent No. 3,672,938; (h) rinsing with water; the blank at 55¾ in a powerless copper deposition bath, according to U.S. Patent No. 3,672,986, Example 7, ca. 50 hours for powerless deposition of a ductile copper coating of approx. 0.25 mm, and j) rinse with water and air dryer.

The metallized layer is tested for adhesion by measuring the peel strength by standard procedures. High peel strengths of more than 1.8 kg / cm and up to 2.3 kg / cm are obtained with an average of about 1.9 kg / cm for 6 samples.

Example 2.

The procedure of Example 1 is repeated, however, using a cast plate of "Cycolac" EP 3530, an insulating substrate or base material consisting of a butadiene-acrylonitrile-styrene graft copolymer containing small amounts of stabilizers, plasticizers and pigments, pretreatment dipping in 80% by weight aqueous sulfuric acid at 23 ° C for 3 to 10 minutes. The immersion in the activating solution at pH 12.5 lasts for 10 minutes at 23 ° C. Excellent bond strengths and metallized layers without blisters are obtained.

The following examples illustrate baths in which the permanganate / manganate ratio and pH are controlled with buffer compounds.

Example 3.

A cast plate of a butadiene-acrylonitrile-styrene grafting polymer ("Cycolac" EP 3530) is metallized by the following procedures: a) the surface is cleaned for 5 minutes at 70 ° C in water containing 50 g / ml 1 trisodium phosphate, b) rinse with water, 5 c) immerse the blank for 5 minutes at approx. 20-25 ° C with gentle stirring in a solution containing methyl ketone 200 ml nonionic wetting agent (Triton X-100, Rohm & Haas Co.) 1 ml 10 water (up to) 1000 ml d) promoting activation of the binding points by immersing for 10 minutes at 70 ° C in a solution consisting of formulation # 3 (see the following table), 15 e) rinsing in still (non-running water, f) neutralizing (optionally) for 5 minutes minutes at 20-25 ° C in a solution containing: stannous chloride dihydrate 30 g of hydrochloric acid (37%) 330 ml of water (up to) 1000 ml.

Sensitization and metallization are performed by the procedure of Example 1, steps e) to j).

The metallized plate is tested for adhesion by measuring the peel strength by standard procedures. A high peel value of from 1.46 to 1.80 kg / cm (the width of the strip of metal strip) is obtained.

Example 4

The procedure of Example 3 is repeated, instead of using the bath in step d), a solution consisting of: Formulation # 4 (see table below).

Highly bonded metal layers are obtained after powerless deposition.

10 148485

Example 5

The procedure of Example 3 is repeated, instead of using the bath in step d), a solution consisting of: Formulation No. 5 (see table below).

Highly bonded metal layers are obtained after powerless deposition.

Table

Aktiverinqsbade

Formulation No. 34 5 10 KMn04, g 40 40 40 kh2po4, g K2HPO4, g 30 K3PO4, g 40 K2CO3, g 40 15 k3bo3, g

Water bp to 1000 1000 1000 pH 11.6 12.5 11.0 * - Sufficient KOH has been added to reach pH 12.5.

A variety of activation solutions containing 40 g / l potassium-20 permanganate and 30 g / l K 2 HPO 4 are prepared and adjusted to various pH values in the range of 11 to 13.0.

Activated surfaces are prepared according to the general procedure of Example 1, however, using an activation bath temperature of 70 ° C and a dip for 15 minutes.

The neutralization bath contains 50 g / l hydroxylamine hydrochloride and 20 ml / l 37% hydrochloric acid.

After metallization, the peel strengths are determined; the data obtained are shown graphically in FIG. 1. The upper curve shows the data from activation of one type of resin layer; the lower curve 30 shows the data from activation of another type of resin layer, namely an epoxyphenol resin nitrile rubber adhesive.

These data show that high bond strengths are ensured and a particularly preferred maximum is achieved at between 12 and 12.5 on the pH scale.

Similarly, the effect of the temperature on the peel strength was determined by preparing an activation bath containing 40 g / l potassium permanganate, 30 g / l K 2 HPO 4 and adjusted to a pH of 12.5 with potassium hydroxide. . The general procedure of Example 1 was used with a activation time of 15 minutes and the temperature of the activation bath varied over the range from 60 to 80 ° C. The data obtained are shown in graphical form in FIG. 2. The upper curve shows data from activation of one type of resin layer; the lower curve shows data from activation of another type of resin layer. Similarly, the effect of the permanganate concentration on the peel strength was determined by preparing an activation bath containing 30 g / l of K 2 HPO range from 20 to 50 g / l. These baths 20 were used according to the procedure of Example 1 with an activation time of 15 minutes and the temperature of the activation bath was maintained at 70 ° C. The data obtained are shown in graphical form in FIG. 3. The upper curve represents data from activation of one type of resin layer; the lower curve represents data from activation of another type of resin layer, namely, an epoxy-phenol-resin-nitrile rubber adhesive.

Instead of the copper bath, other powerless baths containing Group IB and VIII metals, e.g. the nickel baths described in Brenner, Metal Finishing, November 30, 1954, pages 68-76, or the gold baths disclosed in U.S. Patent No. 2,976,181. Also cobalt, silver and other baths well known to those skilled in the art can be used.

In the activation solutions, instead of water alone, as

Claims (4)

148485 t of solvent is used a mixture of water and other non-oxidizable solvents such as acetic acid. Instead of potassium permanganate, sodium and lithium permanganate can be used. Instead of e.g. potassium carbonate or potassium hydroxide, sodium and lithium hydroxides can be used. In certain embodiments, dimethylformamide, methyl chloride, dimethyl sulfoxide, and N-methyl-2-pyrrolidone can be used in place of methyl ethyl ketone (Example 3, step c). A process for pre-treating plastic surfaces to which an adhesive metal layer is to be applied by electroless metal deposition, by means of buffered redox systems based on permanganic acid in aqueous solution, characterized in that the surface activation solutions containing permanganate and manganese in a molar ratio of up to to 1.2 and having a pH between 11 and 13 are contacted with the plastic surfaces in a temperature range between 20 and 100 ° C, preferably between 40 and 70 ° C for a period of from 30 seconds to 120 minutes, preferably from 2 to 20 minutes, after which the plastic surfaces are rinsed and then, if desired, treated with a neutralization solution. Process according to claim 1, characterized in that the pH of the surface activation solution is kept at 12.5. Process according to claim 1 or 2, characterized in that the ratio of permanganate to manganese ions in the surface activation solution as well as its pH is adjusted by continuous or semi-continuous addition of a pH-regulating substance. Process according to claim 1, 2 or 3, characterized in that the ratio of permanganate to manganese ions in the surface activation solution as well as its pH is adjusted in a manner known per se by the addition of buffers, preferably using phosphates as buffers. , carbonates, borates and mixtures thereof.