HK1008552B - Process for the selective or partial electrolytic metallization of surfaces of substrates made from non-conducting materials - Google Patents

Description

The invention relates to a method for selective or partial electrolytic metallization of surfaces of plastic formulations made of electrically non-conductive materials, which are attached to plastic-coated support elements for subsequent treatment.

Various methods are known for coating non-conductive surfaces: wet chemistry involves either catalysing the surfaces to be metalized first and then without current, and then, if necessary, electrolytically or directly metalizing them.

However, the first variant of the process with electricity-free metallisation proved to be unfavourable, as the process of conducting the electricity-free metallisation bath is difficult, the treatment of the waste water from this bath is time consuming and expensive and the process is long and therefore also expensive due to the low rate of precipitation of the metallisation bath.

In particular, the treatment of plastic parts, such as sanitary fittings and automotive parts, and parts used as electromagnetic shielding for electrical equipment, is a problem for the use of currentless metallization processes. The treatment of such moulds generally involves the transport of relatively large volumes of treatment solutions from one treatment bath to the next, as they have a form that allows the treatment solution to be used up when the parts are removed from the baths.

Therefore, a number of metallization processes have been developed that allow the non-conductive surfaces to be coated directly with metal without electrical metallization. However, such processes are described in particular for the metallization of the borehole walls in printed circuit boards. Direct electrolytic metallization in the drill hole metallization is much simpler than a metal coating of other plastic parts, such as plumbing fittings or with a three-dimensional contour pronounced against plates, but much easier, since smaller surfaces can be metallized.

EP 0 298 298 A2 describes a process for electrolytic metallisation of a non-conductor by coating the non-conductor surface to be metallised with a metal chalcogenide, which is formed by treating the surfaces with a palladium colloid containing tin compounds as a protective colloid and then treating them with a soluble metal chalcogenide compound, preferably a metal sulphide.

A similar process is described in US-49 19 768, which describes a process whereby the non-conductive surface is first treated with a tin-cell salt, then with a dissolved sulphide and then with a solution containing hydrochloric acid and a palladium salt, and the pre-treated surface is then electrolytically metalized.

EP 0 320 601 A2 describes a method for the metallisation of non-conductors, whereby the non-conducting surfaces are first treated with a permanganate solution, forming insoluble manganese dioxide on top of it, and then the manganese dioxide layer is converted by treatment with a solution containing chalcogen compounds, preferably sulphur compounds, after which a metal layer can be electrolytically removed.

Although the above methods allow the formation of a chalcogenide layer with a sufficiently high electrical conductivity by means of a special pre-treatment for the subsequent metallization of boreholes in circuit boards, the conductivity of such a layer is not sufficient for the metallization of large non-conductive substrates, since too large non-conductive paths must be bridged from the contact points of the power supply.

US-A-39 84 290 discloses a process whereby the borehole walls of a PCB are first treated in a solution containing the compound of a precious metal more than copper, forming a metal layer on the copper surfaces of the PCB and the non-conducting surfaces, then the metal layer is removed from the copper surfaces and the metal layer on the non-conducting surfaces and the copper surfaces is subsequently electrolytically metallized.

Another method of direct electrolytic metallisation is described in DE 33 23 476 C2. The nonmetallic articles to be metallised are first treated with a solution containing a precious metal, e.g. a palladium activator stabilized with tin compounds, and then electrolytically coated in a metallisation bath.

The printed form DE 37 41 459 C1 describes a method for the production of contact printed circuit boards by direct electrolytic metal separation on catalytically activated surfaces of the base material, whereby the surfaces are pre-treated before electrolytic metallization with a solution containing one or more nitrogen-containing organic compounds, such as polyvinylpyrrolidone, 2,2,6,6-tetramethyl-4-piperidone, pyridiniumpropyl sulfobetaine or a polymer, polyquaternary ammonium chloride.

EP 0 456 982 A1 describes a process for the electrolytic metallisation of a substrate, whereby the substrate surfaces are first catalyzed, for example, in a solution containing a palladium colloid solution stabilised with tin compounds, then the tin compounds are removed from the substrate surface in a known manner, the solution used for this purpose additionally containing the compound of a metal more precious than tin, and the surfaces are then electrolytically metallised.

These methods also only allow the metallization of borehole walls in conductive plates, since the conductivity of the layer formed is not sufficient to metallize even larger non-conductive surfaces.

A completely different process is described in WO 89/08375 A1 and is also used for the production of trans-contacted PCBs, but a first conductive layer is formed for subsequent electrolytic metallization from conductive polymers by first treating the non-conductive surfaces with a permanganate solution so that manganese dioxide is deposited on the treated areas, the PCB is immersed after rinsing the excess treatment solution in a solution containing a metal furomer from the monopyrrole group, pyrroles or thiophene, and the substrate is then brought into contact with an acid solution, the conductive liquid film on the monomer hole being removed to form a polymer layer which can then be electrolytically treated directly.

German Notice 39 07 789 A1 describes a process for the deposition of an electrically conductive layer on an electrically non-conductive surface, whereby an electrically conductive base layer is first produced on the surface by a currentless chemical polymerisation of at least one conductive polymer on the surface, followed by the deposition of another electrically conductive layer, such as another conductive polymer layer or a metal layer. This process can also electro-metallise substrates with larger non-conductive surfaces directly by electrolysis if the above procedure is repeated several times. However, this is not practical as it leads to extremely long periods of time.

In addition, conductive polymer layers formed on the surfaces only show a sufficiently high conductivity for a short time after their manufacture, after which they fall off quickly and large-scale metallization is not possible anyway.

EP 0 616 053 A1 describes a method for the direct metallization of non-conductive surfaces, whereby the surfaces are first treated with a cleaning/conditioning solution, then with an activator solution, such as a palladium colloid solution, stabilised with tin compounds, and then with a solution containing compounds of a metal more precious than tin, an alkali hydroxide and a complexing agent.

The known methods usually only allow direct electrolytic metallization of small surfaces, e.g. hole walls of circuit boards; the metallization of large plastic surfaces fails in most cases because of the lack of metallizability of the layers formed on the non-conductive surfaces.

For the large-scale application of direct electrolytic metallization of plastic parts which are highly structured, such as combs, or three-dimensionally formed with a significant extension into the third dimension, such as coffee pots, telephone receivers, water pipes, the workpieces must be fixed to bearings which cannot be coated during the metallisation process because this metallic layer causes production disruptions. Otherwise, the metallic layers must be removed from the bearings after the coating of the workpieces. This means an additional effort for decoating associated with the consumption of chemicals. Moreover, the productivity of the machine is reduced in this case, since the metallic layer must be removed again before the workpiece is ordered.

The present invention is therefore based on the problem of avoiding the disadvantages of the state of the art and finding a method for selective or partial electrolytic metallization of surfaces of substrates (plastic formwork) made of electrically non-conductive materials attached to plastic-coated supporting elements, e.g. supporting bearings.

The problem is solved by the method of claim 1. Preferred embodiments of the invention are given in the sub-claims.

The method of the invention comprises the following steps: (a) selection of polyvinyl chloride for the plastic coating of the support elements; (b) pretreatment of the plastic formulas with an ethanol solution containing chromium-VI-oxide; (c) subsequent treatment of the plastic formulas with a colloidal acid solution of palladium/tin compounds, avoiding prior contact of the material for the support elements with adsorption-promoting solutions; (d) treatment of the plastic formulas with a solution containing a metal compound, an alkali or erkali hydroxide, which is reducible by means of tin compounds, and an electrolytic complex for the formation of at least one metallic hydroxide in the metallic formulation of the plastic components.

The substrate surfaces may be flushed between some or all of the steps.

The adsorption-promoting solutions are, according to the state of the art, so-called conditioning solutions, used in particular in the manufacture of printed circuit boards. These are usually aqueous solutions containing in particular polyelectrolytes, such as polycation polymers, with a molecular weight above 10,000 g/mol. After treatment of the non-conductive surfaces with such a conditioning solution, not only the plastic surfaces to be metalized are coated with metal as desired, but also - superfluously - the outer plastic-coated supporting elements.

The method of the invention, however, does not require the metal to be removed from the supporting elements after use, since the substrates are not brought into contact with a conditioning solution. Rather, after the metallization of the substrate surfaces and the removal of the metallized substrates, the supporting elements can be immediately returned to the production cycle without further treatment and immediately replaced with other non-conductive substrates for the purpose of metallization. If metals have accumulated on the contact tips/metal tips during the metallization, these must be removed from time to time to avoid contact problems and bathroom contamination.

No additional cleaning and etching steps are required to demetalise the supporting parts away from the contact tips, which reduces waste water disposal costs, reduces the use of chemicals and increases the productivity of the metallization plant, as a given number of supporting elements allows a greater number of substrates to be treated. However, the condition is that, before the substrate is treated with the activator, it is not in any case in contact with agents which promote adsorption of the colloidal particles. In addition to the solutions known to the professional, the most important thing to be done is to avoid contaminated rinsing water, especially if circulating water is used in the factory. The discharge into this water cycle from conditioning baths of parallel production plants must be avoided, as must the introduction of agents which may act as adsorption-promoting polyelectrolytes; therefore, the parallel use of racks is not useful either for the manufacture of PCBs or for the purpose of the invention.

Another advantage of the process is that the surfaces of the substrates to be metalized can also be partially metalized by covering parts of the surfaces with a suitable material.

The method is particularly suitable for three-dimensionally structured electrically non-conductive moulds whose casing surface, which is the smallest possible surface of an object's enclosure, is significantly smaller than their surface, for example for plastic parts for sanitary, automotive or electrically shielding cases, because their disadvantage of extracting treatment solutions from the baths can often be unsatisfactory in practice.

The method according to the invention is therefore generally cheaper, less expensive and more environmentally friendly than the methods known to the state of the art.

Under the circumstances known to the practitioner, depending on the substrate to be metalized, it may be necessary to boil the substrate first in an organic solvent, such as a diethylene glycol or ethylene glycol derivative, dimethylformamide or in other polar or nonpolar solvents, before starting the process of the invention. These solvents may also be used in a mixture with water. Treatments of particular preference include additional alkalizing agents, such as alkali hydroxides or tetraalkali ammonium hydroxides. The solutions may be used at room temperature or at an elevated temperature, depending on the type of substrate to be treated.

According to the invention, in step (a) the surfaces to be metalized are pre-treated in an etching solution containing chromium (VI) oxide. This is usually a solution containing chromium acid, which may also contain sulphuric acid. Solutions containing 360 g chromium (VI) oxide and 360 g concentrated sulphuric acid in one litre of water are preferred. The solution is heated to a temperature of, for example, 60 °C for treatment. Depending on the non-metalizing substrate, the treatment time is 2 to 16 minutes.

After rinsing, chromium ((VI) compounds adhering to the substrate surfaces are reduced to chromium ((III) compounds.

After further rinse treatment, the substrate can be treated in a solution of 300 ml/l of concentrated hydrochloric acid or another mineral acid, such as concentrated sulphuric acid, in aqueous solution. This treatment is useful to avoid continuous dilution of the activator solution with which the substrate is subsequently treated by rinsing water. Since the activator contains both palladium and tin compounds, the mineral acid treatment solution may also contain these tin compounds. This partially compensates for the precipitation losses. The treatment time in this pre-treatment solution can vary widely.

The success of the method is probably due to the fact that the adsorption of palladium particles from a colloidal solution is exploited to coat the non-conductive surface with a large number of palladium particles.

The activator is usually a mineral acid and preferably a hydrochloric acid solution of a palladium colloid. The palladium content in the solution can be adjusted to a range of about 50 mg/l to about 500 mg/l solution, especially between about 150 mg/l and 250 mg/l solution. A palladium salt is used to make the colloid. In addition, tin-cell salt is added to the solution, which is partially oxidized to tin-cell compounds by reaction of the tin-cell salt with palladium salt. The content of the solution can be adjusted to a range of about 2 g/l to about 50 g/l solution, preferably between 10 g/l and 25 g/l solution. The zinc-cell solutions are prepared in accordance with US 11-20A-36 and US 11-30A-62A-82 methods.

When using hydrochloric acid as a mineral acid, the concentration range of hydrochloric acid is between 2% and 30% by weight, preferably between 5% and 15% by weight in water. Galvanization tests have shown that the activator should be highly hydrochloric. At hydrochloric acid levels below 0.5 mol/l solution, not enough palladium is adsorbed from the activator on the surface to achieve rapid metal growth during metallisation.

After the activator treatment, the substrate is rinsed again.

The method uses the reduction capacity of tin compounds to reduce the ions to metal, preferably to metallic copper, from a metal solution containing preferably copper ions in the next treatment step, thereby separating metal, e.g. copper, between the palladium particles and removing the disruptive tin/tin IV layer.

In a special embodiment, a copper compound is used as a metal compound in this solution. However, silver, gold, palladium and other precious metals are also suitable. All compounds, especially those soluble in aqueous media, such as salts, such as copper sulphate and copper acetate, are considered copper compounds. The concentration of the metal is set in the range of 0.1 g/l to 50 g/l in aqueous solution and preferably 0.5 g/l to 15 g/l in solution.

The solution containing the metal ions is preferably alkaline. The solution contains an alkaline or earth metal hydroxide and a complex forming agent for the metal. As an alkali metal hydroxide, lithium hydroxide has proven to be particularly beneficial. However, other hydroxides, such as sodium, potassium, magnesium, calcium or barium hydroxide, are also generally suitable.

The complex-forming agent also contained in the solution is used to keep the metal dissolved in the alkaline solution, so it must have a sufficiently large complex-forming constant for the metal and be present in sufficient quantity to prevent at least the precipitation of metal hydroxides.

The operating temperature of the solution containing the metal ions can be set throughout the range, but preferably in the range 30 °C to 65 °C and in a preferred embodiment between 50 °C and 60 °C.

After treatment with the metal ion solution, the substrate is rinsed again.

The first reduction of metal ions can be supported by a further reduction step, in which the substrate is brought into contact with another solution containing reducing agents. In principle, all reducing agents are considered. However, boron/hydrogen compounds have proved to be the most advantageous.

The substrate is then rinsed again to remove any residues of the reducing agent from the substrate surface.

After this treatment, the extremely thin layer has a sufficiently high electrical conductivity for the subsequent electrolytic metallization. All the electrolytically separable metals can be directly deposited on the substrate surface pre-treated after the process without further electrical metallization. For example, copper, nickel, palladium and other precious metals are suitable for this purpose.

Such dielectric layers may also be applied to the surface of the substrate before any of the treatment steps described above to prevent metallization at that point.

As a substrate, bodies made of acrylonitrile/butadiene/styrene copolymers or their mixtures with other non-conductive materials are particularly metallized. Pre-treatment solutions containing chromium (VI) ions are not particularly susceptible to attack of substrates made of polyvinyl chloride. Therefore, when electrostatically metallizing plastics, supporting elements such as supporting racks are coated with this material to prevent their metallization during the electrolytic treatment.

The substrate is brought into contact with the treatment solutions by immersion, spraying, swallowing or injection.

The following examples are intended to illustrate the invention:

Example 1:

A suitable metal frame was coated with a polyvinyl chloride based plastic (Tegumit, product of Atotech Deutschland GmbH, Berlin, Germany). After the metal contact tips of the frame, which had been first isolated by the coating process, were exposed, these tips were attached to metallizing moulds (hand towel heads) made of the plastic acrylonitrile/butadiene/styrol-ABS copolymer. The arrangement was then treated in turn in the following solutions: The parts were immersed in an aqueous solution of 360 g/l chromium (VI) oxide and 360 g/l concentrated sulphuric acid, heated to 65 °C, for annealing.After a further rinse step, the mould was briefly immersed in a bath of 300 ml of concentrated hydrochloric acid per litre of aqueous solution and then for one minute in an activator made of The solution was 300 ml of concentrated hydrochloric acid, 250 mg of palladium (used as palladium) chloride, 17 g of tin (used as tin) chloride per litre of aqueous solution. 25 g lithium hydroxide, 20 g sodium hydroxide, 4 g copper sulphate, 15 g tartaric acid per litre of aqueous solution were treated for one minute at 60 °C, probably replacing tin compounds adsorbed on the surfaces with copper.

The copper deposits were not found on the polyvinyl chloride-coated bearings. The metallic layers showed an adhesive strength of more than 1 N/mm in the DE-standard DIN test.

Example 2:

The process described in example 1 was repeated, but in step 6 with a nickel bath (Watt type) instead of the sulphuric acid copper bath, and the same result was obtained with regard to the selectivity of the process and the adhesion strength of the deposited metal layer.

Example 3:

A sample of ABS was partially coated with a polyester layer and then treated as described in example 1. The polyester layer has not been metalized.

Example 4:

A mould (phone case) which had been made in a so-called two-shot process in the injection moulding process partly of ABS-containing plastic (Cycoloy C1100 by General Electric Plastics, Rüsselsheim, Germany) and partly of a polyamide (Noryl GTX924 by General Electric Plastics) was treated as described in example 1.

Example 5:

Analogically to example 1, a frame with ABS moulds attached to it was immersed for two minutes in a solution heated to 45 °C to condition the ABS surfaces before treatment at step 3 (pre-soak) for comparison. 1 g of the polymer Luresin KNU (product of BASF, Ludwigshafen, Germany) per litre of aqueous solution After this treatment step, both the ABS and Tegumit surfaces of the frame were metallized.

Example 6:

A moulding part (car cooler grille) made of polycarbonate (Lexan BE from General Electric Plastics) was used to make the 1. at room temperature for five minutes in a solution 700 g diethylene glycol ethyl acetate per litre of boiling water and then steep in a solution at 70 °C for 6 minutes. 380 g CrO3380 g concentrated sulphuric acid20 g Cr2O30.1 g fluoride of zinc (FC 95 by 3M Corp., USA) per litre of aqueous solution for anathesis.3 After rinsing the excess ether solution, any remaining adhesive chromium (Vl) residues in a solution were removed. 40 g sodium bisulphite per litre of aqueous solution.4. The mould was then immersed in a solution at 35 °C for three minutes. 150 ml of concentrated sulphuric acid,220 mg of palladium colloid,30 g of tin (II) chloride per litre of aqueous solution activated,5. rinsed, steeped for one minute at 60 °C in a solution of After rinsing, the mould was decorated with a commercially available copper metallisation electrolyte (Cupracid HT from Atotech Deutschland GmbH). The mould was completely covered with copper after 7 minutes. The copper layer was then further treated in the same bath for 45 minutes, with a layer of 25 μm thickness being removed.

Example 7:

The test method used for the test described in Example 1 was similar to that used for ABS moulds.

The surface conductivity of the formed layer was measured before the metallization, and after the treated mould was washed and dried, a resistance measurement was carried out with two measuring electrodes pressed 1 cm apart on the surface of the treated mould.

The lateral progression of the copper layer was also determined.

A surface conductivity of about 50 pS (μS) was measured, and a metallized surface formed on the moulds, with the metallization front moving 9 cm away from the contact point of the mould within 1.5 minutes.

The conductivity in μS and the growth of the metal front in cm after 1.5 minutes (process step 6) is shown in Figure 1 as a function of the concentration of hydrochloric acid (mol/l) in the activator (process step 4).

Example 8

Example 7 was repeated and the samples were examined according to different parameters. The growth of the metal front on the substrate surface was measured starting from the cathode. The results are given in the following tables and graphically illustrated in the figures. Table 1 shows the spread of the metal front from two samples to a metallization time of 2.5 minutes at a galvanising voltage of 0.6 volts. Table 2 shows the calculated growth rate (cm/min) from a large number of samples metallized at different galvanisation stresses at different times since the beginning of the metallization.Other It is noteworthy that the maximum growth rate is reached about 2 min after the start of coating and then remains almost constant. Table 3 and Figure 2 show that the growth rate depends on the bath temperature during the treatment as described in step c) in claim 1 and step 5 in examples 1 and 8. With residence times in this bath (Cu-LINK) of 1 to 10 min at 27°C, 45°C, 60°C, different metallization times in the electrolytic copper bath are obtained for the samples used, 15 x 6 cm.The result is a correspondingly long metallization time. On the other hand, it is apparent that between about 45°C and 60°C bath temperature and the same residence time there is little difference in coating time and thus in the average growth rate. Tabelle 1

Zeit [min]	Probe 1	Weg [cm] Probe 2	Mittelwert
0	0	0	0
½	<0,5	0,7	~0,5
1	2,8	2,5	2,7
1½	6,5	7,5	7,0
2	8,5	10	9,3
2½	12,5	10	11,3

Tabelle 2

Zeit [min]	Galvanisierspannung [V]
	0,45	0,60	0,80	1,00
0	0	0	0	0
½	0,4	2.2	2,5	0,8
1	2,6	2,8	4,3	7,7
1½	2,0	3,8	5,5	9,0
2	2,4	3,9	5,7	9,5
2½	2,6	4,2	5,1
3	2,6	3,8
3½	3,4	3,8
4	3,0
4½	3,0
5	3,0

Tabelle 3

Zeit [min]	Temperatur [°C]
	27	45	60
1		10,0	9,0
3		8,0	10,0
5		6,0	5,5
7	6,0	5,2	5,5
10	5,0	4,0	3,2

Claims (7)

1. Method of selectively electrolytically metallising moulded plastics material parts from electrically non-conductive materials, which are secured, for the following treatment, on retaining elements which are coated with plastics material and are not to be metallised, including the method steps:

   a) selecting polyvinyl chloride for coating the retaining elements with plastics material;

   b) pretreating the moulded plastics material parts by means of an etching solution containing chromium (VI) oxide;

   c) subsequently treating the moulded plastics material parts with a colloidal acidic solution of palladium/tin compounds, so as to avoid prior contact between the material for the retaining elements and adsorption-promoting solutions;

   d) treating the moulded plastics material parts with a solution, containing a soluble metal compound, which is reducible by means of tin (II) compounds, an alkaline-metal or alkaline-earth metal hydroxide and a complex former for the metal in a quantity which prevents at least the precipitation of metal hydroxides; and

   e) electrolytically metallising the moulded plastics material parts.
2. Method according to claim 1, characterised in that the moulded plastics material parts are partially metallised when, prior to the method being accomplished, parts of the surfaces of the moulded plastics material parts are covered with a material selected from the group consisting of polyvinyl chloride, polyester or polyamide.
3. Method according to one of the preceding claims, characterised in that the moulded plastics material parts are rinsed between some or all of the method steps.
4. Method according to one of the preceding claims, characterised by a copper compound as the soluble metal compound.
5. Method according to one of the preceding claims, characterised by lithium hydroxide as the alkali hydroxide.
6. Method according to one of the preceding claims, characterised by tartaric acid and/or tartrate as the complex former.
7. Method according to one of the preceding claims, characterised in that moulded plastics material parts of materials formed from acrylonitrile/ butadiene/styrene copolymers or their mixtures with other non-conductive materials or formed from polycarbonate are metallised.