NO129754B - - Google Patents

Description

Method of chemo-galvanic metallization

of plastic, as well as sensitizing solution to

use when carrying out the procedure.

It is known to equip plastic with an adhesive metal coating, whereby a thin metallic conductive layer of copper or nickel is chemically applied to the pre-treated plastic surfaces and then this is galvanically reinforced with nickel, copper, chrome, silver, gold or possibly with more of these metals.

(Comp. K. Wiebusch and co-workers, Kunststoffe _5_6 , ( 1966 ), 773). It is also known that AES plastics (grafting copolymers of acrylonitrile, butadiene and styrene) can be metallized using the so-called review process (cf. K. Heymann et al., Galvanotechnik 5_9 , ( 196 8 ), 6 52-658 , W. Metzger u.a., Galvanotechnik 5_8 ( 196 7 ), 720-72 2 ) without it simultaneously taking place

metal covering of the insulation of the electrodes which also serve as holders for the ABS parts to be metallized. Thereby, a re-stitching of the parts after the chemical metallization is superfluidized, secondly, a metal saving is achieved as the metal separation only takes place on the plastic that is to be metallized.

The review principle is consequently a chemogalvanic metallization method, where the parts to be metallized by the chemical metallization processes and the galvanic strengthening processes remain mounted on always the same holding electrode, so that all process steps are carried out without interruption in order without re-stitching the parts to be metallized, resp. without exchanging the holder electrodes.

The previously known review process includes the following steps: 1. Pickling the ABS parts in chromic sulfuric acid with a predominantly high chromic acid content (up to 300 g CrOg/1) at 50-70°C.

2. Activation in strongly acidic palladium salt solution at 55-65°C.

3. Immersion of the activated parts in a reducing solution under certain pH conditions. 4. Chemical separation of a metallic conductor layer, consisting of e.g. nickel and/or copper. 5. Galvanic reinforcement using nickel, copper, chrome, silver, gold or possibly several of these metals.

However, the hitherto known methods for review processes have some disadvantages. Their application is e.g. limited to ABS plastics only. A metallization of in and of itself metallizable polyvinyl chloride types or metallizable polypropylene types is not possible according to the known review processes.

In addition, the composition of the activation bath (2) for optimal activation of submerged parts requires that work is carried out at an elevated bath temperature, namely a narrow temperature range of 55-65°C. Thereby, palladium loss often occurs due to unwanted excretion of metallic palladium, which in practice necessitates constant monitoring of the activation bath.

The invention therefore relates to a method for chemo-galvanic metallization of plastic by pickling, sensitization and activation of the plastic surface and subsequent deposition of a metallic conductive layer and galvanic strengthening of this, the method being characterized in that the sensitization is carried out using aqueous acidic solutions of compounds of trivalent arsenic in amounts from 0.5 to 40 g per litres, preferably in the additional presence of hydrolyzable tin-IV compounds as well as possibly soluble halides or nitrates of ammonium and/or of alkali metals and/or of alkaline earth metals.

Preferred are hydrochloric acid, sulfuric acid or nitric acid solutions of the halides, sulphates, nitrates, oxychlorides, oxynitrates, carbonates and oxides of arsenic or antimony, especially arsenic III-oxide resp. As Clg in hydrochloric acid solution.

Sensitization is preferably carried out in person

of hydrolyzable tin-IV compounds acting as wetting agents, especially SnClt+, and of soluble halides or nitrates of ammonium and/or of the alkali metals (lithium, sodium or potassium) and/or the alkaline earth metals (magnesium or calcium) acting as stabilizers.

The effect of the stabilization according to the invention makes it possible to use diluted chromium sulfuric acid (5-10 g CrOg/litre, 50-65 weight percent sulfuric acid) and a reaction temperature of 50-70°C as a pickling bath.

Furthermore, the method again makes it possible to carry out the reductive sensitization step as in conventional methods, before the activation step.

As an activation bath, a diluted, aqueous, strongly acidic palladium salt solution can be used, especially dilute hydrochloric acid or sulfuric acid PdClj solution or PdSO^ solution in the pH range between 1 and 3, for example with a content of 0.2-5 g PdC^

in 5-20 ml concentrated HCl/litre.

According to the method, the reaction step is to be carried out

in the order listed below:

a) Pickling in chrome sulfuric acid.

b) Sensitization with acidic, aqueous solutions of arsenic III compounds, especially arsenic, which may also contain hydrolyzable tin IV compounds as well as alkali, alkaline earth and/or ammonium halides and/or nitrates, especially ammonium chloride. c) Activation in dilute palladium salt solution, especially in hydrochloric acid or sulfuric acid palladium chloride solution. d) Chemical separation of a metallic conductor layer, of e.g. nickel and/or copper from a nickel or copper bath. e) Galvanic reinforcement using nickel, copper, chrome, silver, gold or several of these metals. Surprising finds

then no metallization of the cutlery electrodes takes place. During the overall process, the objects to be metallized remain on the holders designed as electrodes. After each review process, the holder electrodes are dipped for a short time in an oxidizing acid, e.g. chromosulfuric acid, nitric acid etc,

and they are again applicable.

This method is of particular value in the metallization of metallizable polyvinyl chloride types and in metallization processes where a conductive layer of nickel salt solutions is to be reductively deposited, the holder electrodes remaining metal-free.

As metallizable polyvinyl chloride types, copolymers of vinyl chloride with 4-20 percent by weight fumaric acid diesters and/or maleic acid diesters or copolymers of vinyl chloride with long-chain alkyl residue-containing polymerizable comonomers are used, for example, as vinyl esters preferably of long-chain carboxylic acids with the general formula Cti^ = CH - 00C - R , vinyl ethers of the formula CHj = CH-O-R, itaconic acid esters, fumaric acid esters, acrylic acid esters, methacrylic acid esters or allyl esters, preferably of long-chain carboxylic acids.

Also suitable are chlorinated polyethylenes, mixtures of chlorinated polyethylene and polyvinyl chloride, mixtures of polyethylene and chlorinated polyvinyl chloride, copolymers of vinyl chloride with ethylene as well as graft polymers of vinyl chloride on vinyl chloride copolymers, further polyolefins, such as polypropylene or poly-4-methylpentene-(1) , polyesters and the like.

However, the invention is not limited to the aforementioned plastics, but can generally be implemented with adhesive metallisable plastics such as ABS polymers, namely mixture and graft polymers of acrylonitrile, butadiene and styrene, usually with a content of 10-30% by weight acrylonitrile, 50-70% by weight styrene and 8-25% by weight of butadiene, metallisable polypropylene types, for example consisting of isotactic polypropylene with a relatively high content of an ionogenic, conductive filler such as zinc sulphide, titanium dioxide, barium sulphate etc., polysulfones, polyacetals, polyesters, polyamides and the like, as well as mixtures of these plastics with each other .

Mixtures of the aforementioned ABS types and polypropylene types with PVC, post-chlorinated PVC, chlorinated polyethylene, chlorinated polypropylene and the like are thus metallisable.

Metallizable PVC types are discussed in a Belgian patent

No. 713,290 and 718,487.

Furthermore, the object of the invention is a sensitizing solution for sensitizing plastics to be metallized, consisting of acidic solutions of compounds of trivalent arsenic or antimony.

These sensitizing solutions contain

0.5-40 g/liter, preferably 1-10 g/liter, of compounds of trivalent arsenic, calculated as AS2O2, and also 2-200 g/liter, preferably 4-30 g/liter of compounds of IV-valent tin , calculated as SnCl^, and 10 to 300 g/litre, preferably 50-150 g/litre of halides and/or nitrates of ammonium and/or of alkali metals and/or of alkaline earth metals, preferably of ammonium chloride and/or ammonium nitrate.

These sensitizing solutions are ready to use

at once, works at room temperature, remains stable, clear, colorless and free of secretions for weeks. They therefore require virtually no monitoring.

The metallized plastics produced with the help of these sensitizing solutions have an impeccably smooth surface and a good adhesion of the metal layer to the plastic surface.

The percentages refer to percentage by weight. E xamples.

Preparation of sensitizing solutions suitable for the review process:

Example 1.

a) 2.5 g of arsenic III-oxide is dissolved in 20 cm 3 HC1 (conc.)

3

b) 30 g of SnCl^ are hydrolysed in 1,200 cm of water.

c) Dissolve 60 g of NH^Cl in 200 cm 3 of water.

a), b) and c) are mixed in the order b) + c) + a) and filled to 1 liter with water.

Example - 2.

a) 4 g of arsenic III-oxide is dissolved in 30 cm 3 HC1 (conc.)

bc) ) 1125 0 g g SnamCmlo4 nhiyumdnroitlyrast eroes ppi lös2e0s 0 in cm 2300 vancnm 3.water.

a), b) and c) are mixed in the order b) + c) + a) and filled to a volume of 1 liter with water.

Example 3.

a) Dissolve 15 g of arsenic III-oxide in 50 cm 3 HC1 (conc.).

b) 15 g of SnCl^ are hydrolysed in 200 cm 3 of water.

c) Dissolve 60 g of ammonium chloride and 60 g of CaC^ in 200 cm 3 of water.

After mixing in the order b) + c) + a), the solution is made up to 1 liter with water.

You get clear, colorless solutions that become free

for any excretion over several weeks.

Metallization of plastics according to the review process according to (the invention.

Example 4.

The following copolymers of vinyl chloride are used as metallizable polyvinyl chloride types:

a) 92 percent by weight VC, 8 percent by weight fumaric acid dicetyl ester or

8 weight percent maleic acid dicetyl ester,

b) 89% by weight VC, 11% by weight maleic distearyl ester

c) 92% by weight VC, 8% by weight acrylic acid stearyl ester

d) 86% by weight VC, 14% by weight lauryl vinyl ether,

e) 96% by weight VC, 4% by weight ethylene (Cl content 50.8% by weight). A press plate of the aforementioned materials with the dimensions 4.0 x 9.0 x 0.4 is 1. pickled in chrome sulfuric acid (8 g CrOg dissolved in 1 liter of 60% sulfuric acid) for 10 min. 2. After rinsing with water, the plates are immersed in an arsenic-containing sensitization bath, according to choice according to example 1, 2 or 3,

for 2-5 min.

3. After the renewed flushing with water, the plates are dipped in hydrochloric acid

or sulfuric acid palladium salt solution for 2-5 min. (e.g.

0.1 to 0.25 g PdCl2 dissolved in 10 cm<3> HC1 (conc.) and filled

to 4 liters of water).

4. After further rinsing, the plates are dipped in a chemical nickel plating bath. Within 3 min. they are completely covered

metallic nickel. The holder electrodes remain metal-free.

5. The galvanic reinforcement of the metal coating can then, by choice, be a matt gloss nickel plating known in and of itself, shiny copper plating, shiny nickel plating or pre-chroming.

According to DIN 40 802, the adhesive strength of the metal coating applied in this way to the plastic is between 6 and 8 kp.

After removing the galvanized object, the holding electrode is briefly dipped in chrome-sulphuric acid or nitric acid and is usable again.

Example 5.

The following polymers of composition are used as ABS polymers

a) 25% by weight acrylonitrile, 10% by weight butadiene and

65% by weight styrene.

b) 24% by weight acrylonitrile, 16% by weight butadiene and

60% by weight styrene.

c) 21% by weight acrylonitrile, 15% by weight butadiene and

64% by weight styrene

and is processed in the following way:

A press plate of dimensions 4.0 x 9.0 x 0.4 is stained

in chromium sulfuric acid (8 g CrOg dissolved in 1 liter of 60% sulfuric acid)

for 12 minutes. After rinsing with water, the plates are immersed in an arsenic-containing sensitization bath according to examples 1, 2 or 3 for 2-5 minutes. After repeated rinsing with water, the plates are immersed in a hydrochloric acid or equivalent sulfuric acid palladium salt solution for 2-5 minutes. (e.g. 0.1 - 0.25 g PdCl2 dissolved in 10 cm<3> HC1 (conc) and made up to 4 liters with water).

After further rinsing, the plate is immersed in a chemical nickel plating bath. Within 3 min. the surface is completely covered with metallic nickel. The electrodes remain metal-free. Further processing takes place as indicated under example 4.

According to DIN 40 802, the adhesive strength of the metal coating applied in this way amounts to 7.0 kp. Treatment of the electrodes see example 4.

Example 6.

Of ABS polymers with composition

a) 25% by weight acrylonitrile, 21% by weight butadiene and

54% by weight styrene.

b) 25% by weight acrylonitrile, 14% by weight butadiene and

61% by weight styrene.

c) 27% by weight acrylonitrile, 22% by weight butadiene and

51% by weight styrene

a press plate with dimensions 4.0 x 9.0 x 0.4 is produced and stained

in chromic sulfuric acid for 10 min. (300 g of CrO^ dissolved in 1 liter of 20% sulfuric acid). After rinsing with water, the plate is immersed in the arsenic-containing sensitizing bath (Example 1-3) for 2-5 minutes.

After repeated water rinsing, the plate is immersed in a dilute hydrochloric acid or sulfuric acid palladium salt solution for 2-5 minutes (e.g. 0.25 g - 5 g PdCl2 dissolved in 10 cm<3> HC1 (conc.)

and filled to 4 liters of water). After further rinsing, the plate is immersed in a chemical pre-coppering bath. Within 3 min.

the plate is covered with a metallic copper layer. The electrodes remain metal-free. The galvanic further treatment takes place as described in example 4.

According to DIN 40 802, the adhesive strength of the metal foil deposited on the plastic surface amounts to 6.3 kp. Treatment of the electrodes see example 4.

Example 7.

As metallizable polypropylene, an isotactic polypropylene with a filler content of 28.1% ZnS, 0.4% BaSO4 and 1.2% ZnO is used and processed as follows:

A press plate of dimensions 4.0 x 9.0 x 0.4 is stained

in chromic sulfuric acid for 10 min. (54.5 g CrO^ dissolved in 1 liter of 92% sulfuric acid). After rinsing with water, the plate is immersed in the arsenic-containing sensitizing bath (Example 1-3) for 3-5 minutes. After repeated rinsing with water, the plate is immersed in an acidic palladium salt solution for 2-5 min. (2.5 g PdCl2 dissolved in 10 cm 3 HC1 (conc.)

and filled with water to 4 litres). After further flushing

the plates are dipped in a chemical nickel-plating bath. Within 3 min. covers it completely with metallic nickel. The holder electrodes remain metal-free. The galvanic further treatment takes place according to example 4. Adhesive strengths of the metal foil applied in this way (according to DIN 40 802) of up to 7.5 kp are obtained. Treatment of the electrodes as under example 4.

In an analogous way is also an isotactic polypropylene

with a content of 1% metallisable titanium dioxide.

Claims (3)

1. Method for chemo-galvanic metallization of plastic by pickling, sensitization and activation of the plastic surface and subsequent deposition of a metallic conducting layer and galvanic strengthening of this, characterized in that the sensitization is carried out using aqueous acidic solutions of compounds of trivalent arsenic in amounts from 0.5 to 40 g per litres, preferably in the additional presence of hydrolysable tin-IV compounds as well as possibly soluble halides or nitrates of ammonium and/or of alkali metals and/or of alkaline earth metals. 2. Method according to claim 1, characterized in that the sensitization is carried out using an acidic solution of arsenic III oxide. 3. Sensitizing solution for use when carrying out the method according to claim 1, characterized in that it consists of an aqueous acidic solution of 0.5 to 40 g/litre, preferably 1 to 10 g/litre of compounds of trivalent arsenic, calculated as As2O3, 2 to 200 g/liter, preferably 4 to 30 g/liter, of compounds of IV-valent tin, calculated as SnCl^ , and 10 to 300 g/liter, preferably 50 to 100 g/liter, of halides or nitrates of' ammonium and/or of alkali metals and/or of alkaline earth metals, preferably of ammonium chloride or ammonium nitrate.