DE2126781C3 - Process for metallizing plastics - Google Patents

Description

The usual electroplating of plastics is carried out through a chemical pretreatment, which activation, immersion in a reducing agent solution, chemical and galvanic metal deposition or chemical pretreatment, sensitization, activation, chemical and galvanic metal deposition as well as a reinforcement of the metal layer by galvanic or chemical processes.

In detail, the following process steps are carried out to give plastics with a conductive To provide a base coat for an electroplated metal layer. It is necessary after each Rinse step very thoroughly.

1. Chemical treatment of the plastic surface in a solution containing chromic acid in which these changed so that optimal conditions for a germination with noble metal ions and a good one Adhesion strength of the chemically deposited metal arise.

2. Treatment in a solution to reduce GO3 ions.

3. Activating the plastic surface, mostly by immersing it in a solution of one Noble metal ion (e.g. Pd, Ag, Au) is achieved.

4. Immersion in a reducing agent solution in which the adsorbed noble metal ions become noble metal nuclei to reduce.

Can be used on surfaces that have been pretreated in this way solutions for electroless reductive metal deposition deposit a continuous metal layer. For a metal deposition on the plastic 5 surface also carries out the following pretreatment:

la) Chemical treatment as in U
2a) treatment as in 2,

3a) sensitization by immersion in an acidified solution of tin (II) chloride,
4a) Generation of precious metal nuclei as in 3.

The operation specified under 4 can then be omitted.
In process step 1, a mixture of CrO3, H ₂ SO ₄ , H ₂ O or CrO ₃ , H ₂ SO ₄ , H ₃ PO ₄ , H ₂ O is used, the composition of which depends on the type of plastic to be treated, mixtures of this type are mainly used for the pretreatment of ABS plastics, polypropylene and similar plastics

.20 substances used. The time and temperature of this Treatment are not only of the type of plastic, but also of the same type of plastic, of those of Types supplied by different manufacturers and in some cases on the manufacturing conditions and depends on the geometric shape of the processed plastic. That time and that temperature must then be determined empirically on a case-by-case basis.

The amounts of the components in the CrOs-containing

jo solutions must lie in a certain, fairly narrow concentration range. It's just deviations of a few percent by weight is permissible, otherwise it will not be used during chemical metal deposition complete coverage of the plastic surface with

Jj metal comes, or the entire coating system has insufficient adhesive strength.

Requires analytical monitoring and dosing of the chemicals consumed in the process constant control of the concentration of the various

• 10 which components and represents a complication of the Working conditions. Furthermore, such solutions have the disadvantage that they are at a certain level of Decomposition products of the plastic and trivalent chromium compounds are no longer usable. Urn the to remove used pretreatment stain, to reduce the o-valent chromium compounds, then it must be neutralized. This creates large amounts of voluminous chromium hydroxide, the removal of which puts a great strain on the detoxification systems.

All in all, this means an increased expense in terms of costs and technical equipment for the detoxification of the Chrome stains.

Processes have already become known in which the surface of plastics with sulfonating agents is treated. So recommends A. E. Sherwood in British Plastics. Vol. 37 (1964), p. 252, a method according to The polystyrene becomes antistatic by immersing it in a solution of chlorosulfonic acid in hydrocarbons Properties. The solutions of sulfur trioxide used can only be used for a short time. According to US Pat. No. 2,786,783, the surface of polyethylene is treated with Oleum, a solution of sulfur trioxide in concentrated sulfuric acid or sulfur trioxide vapor conditioned to have other resin layers on top of it to reduce water vapor permeability of polyethylene can be applied. The inventor did not recognize that under certain

Polyethylene treated with sulfur trioxide vapor for subsequent chemical electroplating may be suitable. In addition, it can be observed that the treatment of most plastics with concentrated sulfuric acid, with oleum or chlorosulphonic acid to a strong roughening and continue to Decomposition and charring of the surface lead. Such attacked surfaces are for the Covering with metal coatings is sometimes suitable, but they are because of the strongly roughened structure and mostly low adhesive strength of the applied metal layers for the purposes of electroplating not suitable

For electroplating polystyrene, according to US Pat. No. 34 72 678, the surface is provided with a Solution of sulfur trioxide in a halogenated hydrocarbon and treated with trimethyl phosphate. Here, the surface of the polystyrene is softened and thus changed so that the adhesive strength of the applied metal layers is insufficient. Also, the recommended treatment solution is little resistant. Decomposition products soon form due to the action of sulfur trioxide on the solvent, i.a. the very poisonous phosgene. Another disadvantage of this method is the fact that the The sulfur trioxide reacts with the plastic and is formed by the action of moisture in the air Sulfuric acid is deposited in the solution in small droplets that are deposited on the surface of the plastic settle and thus make an even treatment of the entire surface impossible.

From US-PS 24 00 720 is the treatment of surfaces containing an aromatic nucleus Plastic surfaces with concentrated sulfuric acid, fuming sulfuric acid, sulfur trioxide or Chlorosulfonic acid known using the liquid acid or its vapors for hydrophilization. Such a treatment enables the hydrophobic plastic surfaces to be better coated with water-soluble dyes to be colored. It is also shown that the treated surfaces with aqueous Treat solutions of easily reducible metal salts and the metal salts deposited on the surface can then reduce, whereby one z. B. obtained thin copper or silver films. It is also possible to use metals To vaporize surfaces pretreated in this way, which results in better adhesion. This procedure is particularly suitable for treating plastic glasses against tarnishing.

The object of the invention is to show a method for electroplating plastics that is based on Numerous different plastics can be used, and that a firm adhesion of galvanic or chemically applied metal layers on activated plastic surfaces. Connected to this The task is to avoid the chromic acid pickling used in practice.

This object is achieved by a method according to claim 1.

All difficulties with the ongoing analytical monitoring and regeneration of the chromic acid pickling and the difficulties in removing chromic acid pickles that have been discharged are eliminated. The pre-treatment in an atmosphere containing sulfur trioxide has the further advantage that the range of technically used plastics, which are prepared in this way for the application of a firmly adhering metal layer can be, is much more extensive than is the case with the known chromic acid pickling.

The method according to the invention can be used, for example, for the following plastics: polyethylene, Polypropylene, polyvinyl chloride, polystyrene, styrene-acrylonitrile (S AN) and acrylonitrile-butadiene-styrene (ABS).

Phenolic resin paper is also suitable as a plastic

Boards for printed circuits can also be treated with the method according to the invention, which are provided with an adhesive varnish. Also epoxy resin sheets for printed circuits made with fiberglass or cellulose material are produced as a filler, are accessible to the method according to the invention. Finally, artificial or natural elastomers, e.g. B. rubber can be used.

The method according to the present invention allows on one hand the metallization of plastics, which could not be metallized according to methods known to date and ^g: bt the possibility, in cases in which plastics were metallized by known methods, to increase the adhesion of the deposited metal layers.

The surface of the plastic changes in the electroplating process only to the extent that it is possible, with an optimally chosen sulfur trioxide concentration and treatment time, a smooth and apply a well-adhering metal coating; there are none if the procedure is applied analogously macroscopically visible changes in the surface due to abrasion or roughness. This treatment makes the previously hydrophobic surface of the plastic wettable for water.

The known ones working with sulforating agents Processes for conditioning plastic surfaces are used for the pretreatment of plastics later application of metal layers that correspond to the needs of electroplating practice, not or badly suited. It was therefore completely unexpected that a treatment with a sulfur trioxide containing gas phase the surface of many plastics for the noble metal nucleation and the makes subsequent metallization by known methods ideally suited.

The gas phase containing the chemical pretreatment of the plastics with sulfur trioxide must be used naturally contain a gas that does not react with the sulfur trioxide. Appropriate this gas will consist of air. Basically you can also use oxygen, nitrogen, carbon dioxide. Use noble gases and other gases that meet this requirement. Still contains the gas phase Water vapor, the sulfur trioxide first forms a sulfuric acid mist until all moisture bound by this reaction. Only the sulfur trioxide gas that is also viable is used for the desired treatment of the plastic surface are available. It has been shown that the The sulfuric acid mist produced by gas moisture practically does not interfere with the desired treatment.

The concentration of sulfur trioxide in the gas phase used to treat the plastic surface can in principle be between 1 mg / 1 SOj up to 100 volume percent SO ₃ . The treatment time is between 0.5 seconds and 20 minutes. The temperature of the atmosphere is of course also important for the success of the treatment. Good results have been achieved with appropriate coordination of SO3 concentration and treatment time both at -3O ⁰ C and at 130 ° C gas temperature.

Treatment time, temperature and sulfur trioxide concentration in the gas depend on the type of treated plastics. On the one hand, short treatment times with a higher sulfur trioxide concentration can be achieved or higher temperature of the treatment atmosphere and, on the other hand, longer treatment times with a lower concentration of sulfur trioxide or a lower temperature to similar Results. Needless to say, according to the very different chemical structure and Reactivity of the known plastics concentration ranges for sulfur trioxide, temperature and Treatment times are selected so that a good all-round coverage with the pretreatment chemically deposited metal as well as good adhesion of the subsequently chemically or galvanically reinforced metal layer is achieved. Another advantage of the process can be said that these conditions lead to good metallization results within astonishingly wide limits for a type of plastic to lead.

For a pretreatment with the previously common chromic acid pickling, specially created stains had to be used Plastic types are used to e.g. B. with ABS types, with polypropylene and the like. A good ability to metallize and to achieve adhesive strength of the reinforced metal layers. When pretreated in sulfur trioxide containing gas phase according to the present invention, it is also possible to use plastics of these types to metallize with good success that were not created specifically for metallization. After reinforcement the metal layer this has in most cases an adhesive strength of more than 2 Kp per 2.5 cm. Amazing Adhesion strengths of over 5 Kp and higher were often measured. Almost always it can be good in itself Adhesion can be considerably increased by a heat treatment after the metallization.

The gas phase containing sulfur trioxide required according to the invention for treating the plastics can be made in different ways. You can z. B. an inert gas such as air, nitrogen, Conduct carbon dioxide or a noble gas over appropriately tempered sulfur trioxide, with over the Sulfur trioxide has a vapor pressure corresponding to the temperature. The inert gas flowing through is then loaded with an amount of sulfur trioxide corresponding to the vapor pressure. The temperature-vapor pressure curve of sulfur trioxide is known.

Another way is to evaporate sulfur trioxide by means of appropriate temperature control and the To supply steam to a suitable sealed volume of gas.

Instead of starting from pure sulfur trioxide, SCh-saturated sulfuric acid, which is _{commercially available as oleum with 65% SO 3} content, can be heated to the boiling point and the sulfur trioxide released in the process can be used according to the invention.

An atmosphere containing sulfur trioxide of a certain concentration can be produced particularly easily by introducing a solution of sulfur trioxide in iJ: · ».. 'elic acid into a closed volume of an inctpn gas and bringing it to a certain temperature. The concentration of the sulfur trioxide in the sulfuric acid and the temperature of this solution determine the vapor pressure and thus the concentration of the sulfur trioxide in the gas space.

The methods listed for producing an atmosphere containing sulfur trioxide are thus not exhausted

After treating the plastics in an atmosphere containing sulfur trioxide, the Parts rinsed and treated in precious metal solutions, such as it is also common up to now. Activation and possibly a sensitization can be done with the known solutions take place. All known solutions can be used to metallize the prepared plastic surface Use chemical deposition of copper or nickel and other metals. There is always a deposit a uniform metal layer which, even after reinforcement, has a practically interesting adhesion the plastic has

The examples represent an excerpt from the possible application of the method with regard to the applicable plastics and application conditions.

The following solutions were used:

a) to activate: dive time 1 to 2 minutes at about 20 ^° C

Solution 1:

100 mg / 1 Pd- ⁺ as palladium nitrate or palladium chloride,

20 ml / 1 sulfuric acid conc ^
Solution 2:

100 mg / 1 Pd ⁺⁺ as palladium nitrate or palladium chloride,
20 ml / 1 hydrochloric acid conc.
Solution 3:

5 g / l Pd ^{+ +} as palladium nitrate,
20 ml / 1 sulfuric acid conc.
Solution 4:

1.5 g / l silver nitrate,

5 ml / 1 ammonia conc.,

b) Sensitizing: Immersion time 1 to 2 minutes at about 2O ⁰ C

Solution 5:

20 g / l tin (ll) chloride,
20 ml / 1 hydrochloric acid conc _M

c) Reducing agent solutions: immersion time 1/2 to 1 minute at 20 ° C

Solution 6:

1 g / l N-diethylaminoborazane, pH 9

adjusted with ammonia,
Solution 7:

50 ml / 1 formaldehyde.

d) Chemical metal deposition

For chemical metal deposition on the plastic surfaces prepared according to the invention the following are mentioned:

1. Chemical nickel plating with hypophosphite

22 g / l nickel sulphate,
20 g / l sodium hypophosphite,
20 g / l sodium acetate,
pH value 5 T = 65 ° C,
Dive time 5 to i 0 minutes.

2. Chemical nickel plating with hydrogen boride compounds

40 g / l crystalline nickel chloride,
20 g / l sodium acetate,
20 g / l sodium citrate,

0.2 g / l methylene-bis-naphthalenesulfonic acid, sodium salt,
2 g / l diethylaminoborane,

ifrtjg-

.1 Λ J Ui ..

2 mg / 1 lead as acetate,
pH value = 5.5 7 = 60 ° C,
Dive time 5 to 10 minutes.
3. Chemical copper plating

24 g / l copper sulphate crystalline,
110 g / l Rochelle salt,

25 g / l sodium hydroxide,
60 ml / 1 formaldehyde, 35%,
T = 20 ° C,

Dive time 10 to 15 minutes.

Between the treatment courses mentioned in the following examples, the Samples always checked thoroughly.

example 1

Flakes made of ABS plastic were in the vapor phase over 65% oleum for 1 second at room temperature treated. After activating in Solution No. 1 and immersing in Solution No. 6, the samples became chemically nickel-plated according to d 1) or d 2). The surface of the plastic was completely with a uniform, smooth nickel layer covered.

Example 2

The pre-treatment in the vapor phase led to the same result

over 23% oleum; 5 minutes at room temperature or

over 65% oleum; 2 to 60 seconds at - 28 ⁰ C gas temperature, or
of 100 percent by volume SO ₃ ; 0.5 seconds at 58 ° C gas temperature, or

of 100 percent by volume SO ₃ ; 0.5 seconds at 72 ° C gas temperature.

Example 3

Platelets made of the same plastic as in Example 1 were in a nitrogen atmosphere with sulfur trioxide in the concentration of 3 mg / l for 3 minutes. After activating in solution no.1, Immersion in Solution No. 6 and electroless nickel plating (as in Example 1) was the surface completely covered.

Example 4

The pretreatment was carried out as in Example 3; the concentration of sulfur trioxide however, it was 1 mg / l. The surface of the plastic was only about 60 to 70% with a nickel deposit covered.

Example 5

Platelets made from the same plastic as in Example 1 were given over 30% oleum in a CO2 atmosphere Room temperature 2 minutes and further treated as in Example 1 The surface of the plastic was completely covered with an even, smooth layer of nickel.

Example 6

Sheets made of ABS plastic were treated for 20 minutes at room temperature over 30% oleum, activated and chemically nickel-plated as described in Example 1. The plastic was completely nickel covered, the surface showed a slight roughness due to the unnecessarily long treatment time

Example 7

ABS platelets of different types were over Treated 30% oleum 2 minutes at room temperature and activated further as in Example 1 and chemically nickel-plated. Although they were different types of ABS from different manufacturers and one Sample is not considered suitable for electroplating, all samples were completely with a uniform

ίο smooth and bare nickel layer covered.

Example 8

ABS platelets of the same type as in Example 1 were made with over 30% oleum at room temperature different times between 30 seconds and 20 minutes and further treated as in Example 1.

Then a 30 μ thick copper layer was electrodeposited. The adhesive strength was at about the same in all samples and was 2.8 to 3.2 kgf / 2.5 cm.

Example 9

ABS platelets of the same type as in Example 1 were in the vapor phase for 2 minutes at room temperature Treated with 30% oleum. After rinsing in water, the samples were sensitized in Solution No. 5 and activated in solution no. 2 or no. 4. The electroless metal deposition took place partly in the electroless copper, jo partly in the electroless nickel bath. The plastic surfaces were completely covered with the smooth metal deposit covered.

Example 10

ABS platelets of the same type as in Example 1 were in the vapor phase for 2 minutes at room temperature treated over 30% oleum and then activated in solution # 4, immersed in solution # 7 and chemically copper-plated. The samples were completely covered with a smooth copper deposit.

Example 11

High pressure polyethylene was 15 seconds at room temperature in the vapor phase over 65% Treated oleum, activated in solution no. 1, immersed in solution no. 6 and chemically nickel-plated. the The metal layer was galvanically reinforced with a copper layer of 30 μ and the adhesive strength was measured. the Values for this were over 5 kp / 2.5 cm 2 days after electroplating.

Example 12

High pressure polyethylene was treated as in Example 11, but the immersion time in the vapor phase above the oleum was 30 seconds. The adhesive strength values were 2 kp / 2.5 cm; after an additional After tempering the samples (2 hours at 60 ° C.), the adhesive strength had risen to over 5 kp / 2.5 cm.

Example 13

High pressure polyethylene was treated as in Example 11, but the oleum concentration was 30%, and the immersion time in the sulfur trioxide atmosphere was 3 to 5 minutes. The adhesive strengths achieved of the 30 μ thick copper coatings applied after chemical nickel plating lay between 3 and 5 kg / 2.5 cm.

030 247/73

Example 14

Platelets made of rigid PVC were 15 to 30 seconds at room temperature in the vapor phase over 65% Treated oleum, activated in solution no. 1, immersed in solution no. 6 and chemically nickel-plated. the The adhesive strength of the electroplated 30 μ thick Cu coating was between 4 and 5 kp / 2.5 cm.

Example 15

Flakes made from an impact-resistant PVC were placed in the for 30 seconds to 1 minute at room temperature Vapor phase over 65% oleum and further treated as in Example 14. The adhesive strength was over 5 kg / 2.5 cm.

Example 16

Polystyrene platelets were vaporized over 50% for 2 minutes at room temperature Oleum and further treated as in Example 14. The plastic surface is after chemical nickel plating smooth and completely covered with nickel.

Example 17

Platelets made of a styrene-acrylonitrile copolymer were 1 minute in the vapor phase over 50% Oleum and further treated as in Example 14. The adhesive strength of the Cu coating was 1.6 kgf / 2.5 cm and could be increased to 3.5 kp by temperature at 70 ° C.

Example 18

Polycarbonate platelets were vaporized over 65% oleum at room temperature 30 Treated seconds to 5 minutes after activation in solution # 1 and immersion in solution # 6 as well as chemical nickel plating, the surface of the samples was uniform with a nickel deposit covered.

Example 19

Epoxy resin paper boards for printed circuit boards were left in the vapor phase for 30 seconds to 5 minutes over 23% oleum and further treated as in Example 11. The adhesive strength of the metal layer was larger than 5 kg / 2.5 cm.

Example 20

Sheets made of epoxy resin reinforced with glass fiber, as are commonly used for printed circuits, are treated over 65% oleum in several samples between 5 seconds and 5 minutes at room temperature then 30 μ thick galvanically copper-plated. The adhesive strength of the metal layer increased with increasing treatment time in the sulfur trioxide gas phase from 2.5 to 4.5 kp / 2.5 cm. If the heating was continued for 1 hour at 100 ^° C. immediately after copper plating, the adhesive strength rose to over 5 kp / 2.5 cm in all samples.

Example 21

Phenolic resin paper plates for printed circuits were treated in the vapor phase over 12% oleum for 5 to 60 seconds and then activated in solution 1, dipped in solution 6 and then chemically nickel-plated. All samples were smooth and fully nickel-plated. A 30μ thick copper layer electrodeposited on top had an adhesive strength of 1.5 to 1.8 kp / 2.5 cm. The panels were rinsed after the treatment according to the invention and dried for about 30 minutes at 8O ⁰ C, then the adhesive strength was 2.4 cm to 2.6 kp / 2.5.

Example! 22nd

Phenolic resin sheets for printed circuits, provided with a layer of one for additive manufacturing Adhesive varnish common to printed circuit boards was more than 50% igerr> in the vapor phase. Oleurr. 30 seconds to 5 Minutes and further treated as in Example 1. An additionally applied 30 μ thick Cu layer had at all samples had an adhesive strength in excess of 5 kgf / 2.5 cm.

Example 23

A soft rubber sheet was treated for between 5 and 60 seconds over 65% strength oil and then activated in solution 3 for 5 minutes, post-treated in solution 6 for 1 minute and chemically nickel-plated in bath d) 2 for 5 minutes. The metal layer was then galvanically reinforced with 30 μ copper. Immediately after the treatment, 2.5 to 3.5 kp / 2.5 cm was measured as the adhesive strength, depending on the pretreatment time. ^{If the specimens were heated to 80 °} C. for a further 2 hours after copper plating, the adhesion was so great that the metal coating did not come off, but rather the rubber was torn.

To the progress of the pretreatment according to the present invention compared to the usual pretreatment With chromic acid mixtures to show, some characteristic plastics were known after Process pretreated and compared with the corresponding results of Examples 1 to 23.

The following stains were used for pretreatment. These stains are in those of K. Wiebusch (Galvanotechnik, 59, p. 640 ff., 1968) recommended areas.

Stain A 410 g chromic acid,
700 ml water,
200 ml sulfuric acid 1.84,
Temperature: 60 ⁰ C,
Treatment time: 10 minutes.

Pickle B 600 g sulfuric acid 1.84,
200 g phosphoric acid, 85%,
270 g water,

10 g chromic acid,
Temperature: 6O ⁰ C,
Treatment time: 10 minutes.

Stain C 30 g chromic acid,
200 g water,
1500 g sulfuric acid 1.84,
Temperature: 20 ° C,
Treatment time: 10 minutes.

The plastics pretreated in one of the above-mentioned stains were (with intermediate rinsing between the individual baths) activated in solution a) 3, immersed in solution c) 6 and in solution d) 2 The plastic surface was also nickel-plated

1 1

12th

a nickel layer was covered, then in an acidic copper bath was about 30 μ thick Copper layer deposited on it and the adhesive strength of the coating determined in accordance with DIN 40 802.

Table I.

In Table I the result of the treatment in

electroless nickel bath marked by the symbol. It means:

I = no nickel deposition, II = surface only partially nickel-plated, III = completely nickel-plated.

plastic Result of the treatment
in an electroless nickel bath stain B stain C Adhesion strength in Kp
according to DIN 40 802 A. Stain B Stain C When treating it.
of the present invention 2.8 ... 3.2 Stain A II IU stain • 2.1 - 1.7 ... 1.9 Example of adhesive strength
No. in Kp / 2.5 mm > 5 SECTION III III I. 1.9 .. .0.8
• 2.4 *) 0.7 ... 1.0
2.0 ... 2.4 *) - 8th 4 ... 5 High pressure poly
ethylene IH I. I. 0.6 ..
2.2 .. - - 12th > 5 Rigid PVC I. I. I. - - - 14th 1.6 (3.5) *) PVC impact resistant I. I. I. - - - 15th > 5 Styrene acrylonitrile
Polymer I. III III - 1.0 ... 1.4 0.5 ... 0.9 17th 2.4 ... 2.6 Epoxy resin paper III I. I. 1.5 - - 19th 2.5 ... 3.5 (5) *) Phenolic resin paper I. I. II - - - 21 Soft rubber I. - 23

') After tempering for 2 hours at 70 ^° C.

Claims (4)

Patent claims: 1. Process for metallizing plastics, in which the plastic surface with gaseous Sulfur trioxide pretreated in such a way that there is no macroscopically visible change in the surface results, and the so pretreated plastic surface by treating with a metal salt solution and Reduction of the metal salts deposited on the plastic surface activated, characterized in that that the sulfur trioxide is applied in the gas phase for 0.5 seconds to 20 minutes and then after the activation - by precious metal salt solution with subsequent reduction with a reducing agent solution or by an acidified tin (II) chloride solution followed by treatment with a noble metal salt solution - an electroless metal deposition takes place, possibly with a subsequent galvanic or chemical reinforcement of the metal layer. 2. The method according to claim 1, characterized in that a gas phase is used which the Contains sulfur trioxide in concentrations of 10 mg SO3 / I up to the concentration that corresponds to the Corresponds to the vapor pressure of SO3 above 65% oleum at room temperature. 3. The method according to any one of claims 1 or 2, characterized in that a gas phase is used which contains an inert gas in addition to sulfur trioxide. 4. The method according to claim 3, characterized in that that air, nitrogen, a noble gas and / or carbon dioxide is used as the inert gas.