EP1148153A2

EP1148153A2 - Electroless plating process and pretreating agent used therefor

Info

Publication number: EP1148153A2
Application number: EP00307877A
Authority: EP
Inventors: Hiroshi Daishin Chemical Co. Ltd. Nagano
Original assignee: Daishin Chemical Co Ltd; Omura Toryo Co Ltd
Current assignee: Daishin Chemical Co Ltd; Omura Toryo Co Ltd
Priority date: 2000-03-27
Filing date: 2000-09-12
Publication date: 2001-10-24
Also published as: CN1315589A; KR20010089839A; JP2001271171A

Abstract

An absolutely novel electroless plating process including a step of applying a pretreating solution containing a conductive metal oxide to a material to be treated before application of a catalyst thereto, which process gives less environmental impact, which is less expensive, and which can achieve more efficient and secured reductive deposition of a metal contained in a plating solution; and a pretreating agent used therefor. In the electroless plating process, a film containing a conductive metal oxide is formed on a surface of a nonconductive material, and the resulting nonconductive material is subjected to electroless plating. The pretreating agent contains at least a conductive metal oxide, a resin, and a substance which captures and immobilizes a reduction catalyst metal.

Description

BACKGROUND OF THE INVENTION

The present invention relates to formation of a plating layer in an electroless plating process in the presence of a conductive metal oxide in addition to a metal micropowder. More specifically, the present invention relates to an electroless plating process for forming effectively a uniform plating film resorting to a synergistic effect to be brought about by a conductive metal oxide and a reduction catalyst metal such as palladium which are contained in a coating film of a pretreating agent (or solution or primer).

DESCRIPTION OF THE RELATED ART

While plating layers can be formed by electroless plating on nonconductive plastics, ceramics, paper, glass, fibers, etc., it is necessary to apply or immobilize catalysts onto the surfaces of these nonconductive materials so as to initiate oxidation of a reducing agent contained in a plating solution.
While the sensitizing-activating method using a stannous chloride bath and a palladium chloride bath is classically known as a technique of catalyst application or immobilization treatment, the catalyst accelerator method using a stannous chloride-palladium chloride bath and a sulfuric acid (or hydrochloric acid) bath is now employed generally.
Meanwhile, there is also employed recently a method in which a material to be treated is dipped in a palladium complex solution having high adsorptivity, and the resulting material is rinsed with water, followed by deposition of palladium using a reducing agent such as dimethylamine borane. An etching step is necessary as a pretreatment to be applied prior to the catalyst application treatment step so as to secure wettability (hydrophilicity) on the surface of the material to be treated and accelerate physical adsorption of the catalyst, and chromic acid-based etching solutions are used in most cases for overall plating of plastics and the like.
A chemical etching step is very important in order to achieve microscopic roughening of the surfaces of materials to be treated, to facilitate physical capture of the catalyst metal in the catalyst application (immobilization) treatment step and to give an anchoring effect which influences adherence of the plating layers to the materials to be treated.
However, in consideration of environmental protection, electroless plating processes are recently put into practical uses, which require no etching treatment as the pretreatment described above, with increasing demands for partial or one-side plating particularly in plastic housings. In other words, there are known the enshield plus process (Enthone-OMI), the shielding process (Shipley), the SSP process (Seleco) utilizing physical adsorption of a catalyst metal by micropores after film formation, Omura Marine process (Daishin Chemical Co., Ltd.; Omura Toryo Co., Ltd.) utilizing chemical adsorption of catalyst metals by chitosan.
The above etchingless pretreating methods will be described. First, the conductive coating method involves problems in terms of cost and weight due to the great thickness of the coating film. Meanwhile, physical adsorption of catalyst metals is an unstable element in the SSP process. Although the Omura Marine process is an epoch-making technique utilizing specific chemical adsorption of catalyst metals, poor solubility in solvents and hygroscopicity of chitosan give adverse influences on coating of metal catalysts.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide an absolutely novel electroless plating process including a step of applying a pretreating solution containing a conductive metal oxide to a material to be treated before application of a catalyst thereto, which process gives less environmental impact, which is less expensive, and which can achieve more efficient and secured reductive deposition of a metal contained in a plating solution.
The objective of the present invention can be attained by the following constitution:
(1) An electroless plating process, in which a film containing a conductive metal oxide is formed on a surface of a nonconductive material; and the resulting nonconductive material is subjected to electroless plating.
(2) The electroless plating process according to (1), further including a step of applying a catalyst after formation of the film containing a conductive metal oxide.
(3) The electroless plating process according to (1) or (2), wherein the film containing a conductive metal oxide contains a resin.
(4) The electroless plating process according to any of (1) to (3), wherein the film containing a conductive metal oxide contains a substance which captures and immobilizes a reduction catalyst metal.
(5) The electroless plating process according to any of (1) to (4), wherein the film containing a conductive metal oxide contains an inorganic pigment.
(6) The electroless plating process according to any of (1) to (5), wherein the conductive metal oxide is stannic oxide.
(7) A pretreating agent for electroless plating, containing at least a conductive metal oxide, a resin, and a substance which captures and immobilizes a reduction catalyst metal.
(8) The pretreating agent according to (7), further containing an inorganic pigment.
(9) The pretreating agent according to (7) or (8), wherein the conductive metal oxide is stannic oxide.
Other embodiments and advantages of the present invention will be apparent from the following description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a method for applying a catalyst in an electroless plating process. The catalyst application, which is carried out prior to the electroless plating step, is characterized in that, before carrying out an electroless plating step, a film containing a conductive metal oxide is formed on the surface of a nonconductive material, and the film is treated with a catalyst metal salt solution, i.e., reductive deposition of the target metal ion is induced by electrons of the conductive metal oxide which is stable to acids and alkalis.
Further, in the presence of a catalyst metal such as palladium, the conductive metal oxide induces, based on its conductivity, a synergistic reducing action to enable formation of an electroless plating film speedily and uniformly on the surface of the nonconductive material compared with the prior art methods.
Meanwhile, the nonconductive material referred to in the present invention can be exemplified by plastics, ceramics, paper, glass, fibers, etc. which cannot be plated directly by electroplating.
In the process of the present invention, in forming an electroless plating layer on the surface of such a nonconductive material, a treating solution containing a conductive metal oxide is applied over the surface of the nonconductive material to form a conductive film thereon, prior to the catalyst application step and the electroless plating step. The thus formed film accelerates deposition of the target metal ion owing to the conductivity of the conductive metal oxide in the presence of a catalyst metal such as palladium. In other words, an interface that is convenient for transference of electrons in the electroless plating step is formed on the surface of the material to be plated, and thus an electroless plating layer having excellent adherence can be formed thereon uniformly and efficiently.
The conductive metal oxide may not particularly be limited so long as it has electronic conductivity and ionic conductivity. It typically includes, for example, M₂O compounds such as Cu₂O and Ag₂O; MO compounds such as SrO, TiO, VO, MnO, FeO, CoO, NiO, CuO, ZnO, NbO, PdO, AgO, CdO and PtO; M₃O₄ compounds such as Mn₃O₄, Fe₃O₄ and Co₃O₄; M₂O₃ compounds such as Y₂O₃, Ti₂O₃, V₂O₃, Cr₂O₃, Mn₂O₃, Fe₂O₃, Ga₂O₃, Rh₂O₃, In₂O₃ and B-Al₂O₃; MO₂ compounds such as TiO₂, VO₂, CrO₂, MnO₂, RuO₂, RnO₂, NbO₂, MoO₂, SnO₂, WO₂, ReO₂, OsO₂, IrO₂ and PtO₂; M₂O₅ compounds such as V₂O₅ and Nb₂O₅; MO₃ compounds such as WO₃ and ReO₃; ABO₃ compounds such as SrTiO₃, LaTiO₃, SrZrO₃, LaVO₃, KTaO₃, LaCrO₃, SrMoO₃, AxWO₃ (x=Li, Na, K), LaMnO₃, LaFeO₃, SrFeO₃, SrRuO₃, LaCoO₃, LaRhO₃, LaNiO₃ and LaGaO₃; AB₂O₃ compounds such as MnV₃O₄, CoV₂O₄, ZnMn₂O₃, CoFe₂O₄, MnFe₂O₄, CoNi₂O₄; and A₂B₂O₅ compounds such as Ba₂Ir₂O₅.
Among others, TiO₂, SnO₂, V₂O₃, Ti₂O₃, Ga₂O₃, In₂O₃, Nb₂O₅ and VO₂ are preferred.
Further, tin oxide-based conductive metal oxides and indium oxide-based conductive metal oxides doped with antimony and the like and tin respectively so as to reduce resistance are also useful.
The conductive metal oxides may have a colloidal form or a powdery form having effectively a particle diameter in the range of 0.001 to 40 µm, preferably in the range of 0.01 to 20 µm.
The treating solution containing a conductive metal oxide desirably contains the conductive metal oxide in an amount of 5 to 70 mass %, preferably in an amount of 10 to 45 mass % in terms of the metal oxide. The effect to be brought about by adding the conductive metal oxide diminishes as the amount of the metal oxide becomes smaller than 5 mass %, making it difficult to form a conductive layer necessary for formation of a plating layer. Meanwhile, if the conductive metal oxide is added in an amount of more than 70 mass %, the effect to be brought about by the addition thereof is saturated, and adherence of the plating layer is lowered.
Referring to other components to be contained in addition to the conductive metal oxide in the conductive metal oxide-containing treating solution, a resin binder having excellent adherence to materials to be plated can be added. The resin to be added may not particularly be limited so long as it disperses well in the conductive metal oxide or is miscible therewith. Binders employable here include, for example, solvent-evaporation type (thermoplastic or thermosetting) resins such as nitrocellulose, cellulose acetate, acrylic, epoxy and phenol resins; crosslinking reaction type resins such as urethane, acrylic urethane, epoxy, polyester and epoxy polyester resins. Depending on the kind of the material to be plated, a water-soluble resin such as polyvinyl alcohols and hydroxyethyl celluloses; a hydrated resin such as of alkyd, polyester, acrylic or epoxy; and an emulsion such as of vinyl acetate resin, acrylic resin, urethane resin, silicone acrylic resin or fluororesin can be used.
Further, in addition to these resins, amino-containing polymers such as collagen, polyglutamic acids, chondroitin sulfuric acid, hyaluronic acid, chitosan, chitosan derivatives, polyethyleneimines and polyallylamines may be added singly or as a combination of two or more of them to achieve much firmer adsorption and immobilization of the reduction catalyst. Particularly chitosan and chitosan derivatives are preferred among other polymers. These compounds are usually contained, depending on the kind thereof, in an amount of 5 to 85 mass %, preferably 15 to 70 mass % in the solid content including the conductive metal oxide.
In order to ensure further adhesion with the electroless plating layer, various kinds of metal micropowders, inorganic pigments, metal oxides, carbonic salt compounds, phosphoric salt compounds, etc. are as necessary added. That is, such substances are added to achieve microscopic roughening of the surface of the film that contributes further to improvement of adherence of the plating layer, in forming an electroless plating layer, resorting to the conductivity, anchoring effect or metal ion adsorbing effect. This can be a substitute for the chemical etching step and catalyst application step in the prior art. More specifically, there may be used microparticulate powders of, for example, gold, platinum, palladium, silver, steel, nickel, graphite, nickel-plated graphite and carbon; as well as, silica, calcium silicate, iron silicate, aluminum silicate, magnesium silicate, calcium magnesium silicate, aluminum oxide, magnesium oxide, magnesium aluminate silicate, calcium aluminate silicate, barium aluminate silicate, beryllium aluminate silicate, strontium aluminate silicate, titanium oxide, calcium carbonate, barium sulfate, zinc phosphate, aluminum tertiary phosphate, aluminum secondary phosphate, aluminum primary phosphate, calcium tertiary phosphate, calcium secondary phosphate, calcium primary phosphate, cobalt phosphate, zirconyl phosphate, titanium phosphate, nickel phosphate, bismuth phosphate, magnesium tertiary phosphate, magnesium secondary phosphate, manganese secondary phosphate, manganese primary phosphate, lithium phosphate and hydroxyapatite. Among others, magnesium aluminate silicate is preferred. Such materials are usually added in an amount of 5 to 85 mass %, preferably 20 to 70 mass % in the solid content including the conductive metal oxide. If the content of such material is more than 85 wt %, the adhesion between the conductive metal oxide-containing treating agent and the material to be plated itself is lowered.
Other components to be contained in the treating solution include an organic solvent such as methanol, isopropyl alcohol, n-butanol, isobutanol, ethyl acetate, butyl acetate, methyl ethyl ketone, toluene, xylene, glycol ether, tetrahydrofuran, n-hexane, mineral terpene and glycol ether, and water. These solvents exhibit effects of improving compatibility between different kinds of resins if admixed, attacking the material to be plated to some degree and adjusting drying properties of the treating solution applied to the material to be plated. The treating solution may as necessary be incorporated with additives such as a surface controlling agent, an antiprecipitant, a dispersant, a defoaming agent and an aminosilane coupling agent, and these additives can impart appropriately leveling properties, pigment dispersibility, metal adsorbing action, hydrophilicity, etc. to the treating solution in film formation.
The conductive metal oxide-containing treating solution as described above can be applied to the surface of a material to be plated according to the conventional coating techniques, for example, spray coating, roll coating, brush coating and dipping and forms a film for immobilizing a catalyst metal thereon showing excellent adherence against the material to be plated.
After formation of such a conductive oxide film on the surface of a material to be plated, the step of capturing and immobilizing a catalyst metal as a catalyst imparting reaction and the step of electroless plating are carried out successively, and thus an electroless plating layer having excellent adherence can be formed efficiently. Further, in the present invention, the surface of the nonconductive material may partly be pretreated with a treating solution containing a conductive metal oxide to impart reductive catalysis selectively to such pretreated portions, thus achieving secured partial electroless plating.
Further, according to the present invention, electroless plating can be applied well to polyester resins such as polyethylene terephthalate; 6,6-nylon, 6-nylon, polyolefins, polycarbonates; various kinds of alloys such as PC/ABS and PC/ASA; carbon fiber or glass fiber-reinforced alloys, which have been difficult to form electroless plating layers thereon.
Referring to the catalyst application reaction, although it is possible to proceed directly to the electroless plating step after formation of the conductive metal oxide-containing film on the surface of the material to be plated, application of a reduction catalyst is preferably carried out by dipping for a short period the material to be plated, for example, in an acidic solution of a hydrochloride, nitrate or acetate of a noble metal such as Pd, Pt, Au and Ag in hydrochloric acid, nitric acid or acetic acid.
As a typical noble metal salt solution, a palladium chloride solution (0.2 to 1 g/L, hydrochloric acid 5 ml/L) as employed in the conventional method can be used.
In the case where the conductive metal oxide-containing film contains noble metal microparticles such as of Pd, Pt, Au and Ag or a salt or oxide thereof, the above catalyst application step can be omitted.
Next, the material to be plated carrying the catalyst metal in the conductive metal oxide-containing film is dipped in an electroless plating bath such as of Cu, Ni, Co, Pd or Au, or an alloy thereof, preferably of Cu or Ni, and thus an electroless plating layer having excellent adherence can be obtained continuously and efficiently based on the conductivity of the conductive metal oxide or on the interaction between the conductive metal oxide and the immobilized reduction catalyst, thus achieving desired metallization of the nonconductive material.
The metal ion concentration in the plating bath can be adjusted in a wide range. However, a too low concentration causes film formation to proceed at an extremely low speed, whereas a too high concentration causes precipitation of the metal ion or deterioration of plating films to be formed.
Thus, the metal ion concentration is preferably 0.001 to 5 mol/L, particularly preferably 0.01 to 0.5 mol/L.
While the temperature of the plating solution is not particularly limited, it is preferably 10 to 95°C. A too low temperature causes film formation to proceed at a low speed, whereas a decomposition reaction of a reducing catalyst is likely to proceed at a too high temperature.
While the pH of the plating solution is not particularly limited, it is preferably about 3 to 13. If the pH is lower then the specified range, the film formation speed is lowered, whereas if it is higher than the range, the plating solution becomes unstable to be likely to undergo autolysis. A conventional buffer can be added to the bath so as to maintain a predetermined level of pH stably. The buffer can be exemplified by potassium dihydrogenphosphate, potassium phthalate and borax.
Meanwhile, in order to improve uniformity of the film, various kinds of conventional stirring techniques can be employed. Stirring techniques employable include, for example, bubbling with air, nitrogen, oxygen, etc.; cathode lock method where a material to be plated is moved; paddling where a rod-like stirring mechanism is moved in the vicinity of a material to be plated; a method using an ultrasonic wave, particularly a superimposed ultrasonic wave formed by superimposing ultrasonic waves with different frequencies (e.g., a hybrid of three waves, 28 kHz, 45 kHz and 100 kHz); a method where the frequency is changed with lapse of time; or a method using a highfrequency ultrasonic wave having a frequency of as high as around 1 GHz.
Film formation can be achieved by charging such plating solution in a plating tank provided with a predetermined heater and a filter device and dipping a base material therein.
In addition to the ordinary dip plating processes, there can also be employed spraying where the plating solution is sprayed against a base material; and the spin coating technique where a plating solution is supplied under rotation of a base material. Particularly in these cases, the plating solutions can be recovered and recycled easily. It should be noted here that the plating solutions in these cases are preferably filtered through ca. 0.2 µm-mesh filters and the like before recycling.

Example 1

A PET film (6 cm × 12 cm) was coated with a treating solution (Yamanaka Chemical Co., Ltd.) having a sol of amorphous colloidal stannic oxide suspended together with an acrylic ester copolymer using a bar coater No. 8, and the resulting coating layer was then subjected to forced drying at 110°C for 3 minutes. After the thus treated PET film was left to stand at 23°C × 50 % RH for 24 hours, the surface electrical resistance of the film was measured using a resistor SM-5E (Toa Electronics Ltd.), and it was found to be 8.6 × 10⁶ Ω. The thickness of the primer formed was 0.3 µm.

Next, the resulting PET film was dipped in a palladium chloride solution (PdCl₂·2H₂O: 0.2 g/L; hydrochloric acid: 5 ml/L) for one minute, rinsed with water and then subjected to electroless copper plating for 30 minutes in a plating bath having the composition as shown in Table 1. As a result, a copper plating layer having excellent luster was formed on the portion coated with the treating solution.

Component	Concentration
Copper sulfate	10 g/L
Formalin (37 %)	20 ml/L
Sodium hydroxide	10 g/L
EDTA	25 g/L
2,2'-Bipyridyl	10 mg/L
pH: 12.5 Liquid temp.: 60°C Air stirring

Example 2

After 300 g of ACRYDIC A-166 (one-component type room temperature-drying acrylic lacquer, Dainippon Ink & Chemicals, Ltd.) was introduced to a 1-liter stainless steel vessel of a batch bench sand mill (vertical), a mixing blade was set therein, and then 70 g of stannic oxide (first class grade chemical; Wako Pure Chemical Ind., Ltd.) and 2 g of Disperbyk-180 (solvent type wetting and dispersing agent, BYK-Chemie GmbH) were added thereto with stirring at a low speed, followed by stirring of the resulting mixture for 10 minutes. After the stirring, the mixing blade was replaced with dispersing discs (70 mm-diameter disc × 3). To the above mixture were added an equivalent amount of glass beads to effect dispersion of the mixture for 30 minutes at a medium speed. The glass beads were filtered off to obtain a filtrate as a pretreating stock solution. An ABS resin piece (50 mm × 150 mm × 1 mm; Ube Cycon, Ltd.) was taken as a material to be plated. After the resin piece was degreased with n-heptane, a solution obtained by diluting twice the pretreating stock solution with a mixed solvent of butyl acetate/ethyl acetate/n-butanol/toluene/ethyl cellosolve (20:25:20:20:15) was applied thereto by means of spraying and dried at 60°C for one hour. The thus treated ABS resin piece was dipped in a palladium chloride solution (PdCl₂ · 2H₂O: 0.2 g/L; hydrochloric acid: 5 ml/L) for 3 minutes, rinsed with water and then reduced with a 1% DMAB solution. Subsequently, the resulting ABS resin piece was subjected successively to plating in an electroless copper plating bath for 30 minutes and electroless nickel plating for 5 minutes using a bath composition as shown in Table 2. As a result, a uniform copper/nickel plating layer having a copper plating film thickness of 0.8 to 1.2 µm and a nickel film thickness of 0.3 to 0.8 µm was obtained.

Component	Concentration
Nickel sulfate	20 g/L
Sodium hypophosphite	15 g/L
Citric acid	5 g/L
Sodium acetate	3 g/L
Glycine	2 g/L
Lactic acid	3 g/L
Thiourea	5 ppm
Lead nitrate	3 ppm
pH: 6.0 Liquid temp.: 55 to 60°C

Example 3

After 300 g of DIANAL LR-248 (one-component type room temperature-drying acrylic lacquer, Mitsubishi Rayon Company Limited), and 50 g of a mixed solvent of butyl acetate/PGM (2:1) were introduced to a 1-liter stainless steel vessel of a batch bench sand mill (vertical), a mixing blade was set therein, and then 65 g of stannic oxide (first class grade chemical; Wako Pure Chemical Ind., Ltd.), 5 g of mica coated with diindium trioxide doped with antimony (Catalysts & Chemicals Industries Co., Ltd.), 20 g of FLOWNON SH-290 (solvent type antiprecipitant for coatings, Kyoeisha Chemical Co., Ltd.), and 4 g of Disperbyk-108 (BYK-Chemie GmbH), were added thereto with stirring at a low speed, followed by stirring of the resulting mixture for 10 minutes. After the stirring, the mixing blade was replaced with dispersing discs (70 mm-diameter disc × 3). To the above mixture were added an equivalent amount of glass beads to effect dispersion of the mixture for 30 minutes at a medium speed.
The glass beads were filtered off, and the filtrate mixture was obtained as a pretreating stock solution. An ABS resin piece (50 mm × 150 mm × 1 mm; Ube Cycon, Ltd.) was taken as a material to be plated. After the resin piece was degreased with n-heptane, a solution obtained by diluting twice the pretreating stock solution with a mixed solvent of butyl acetate/ethyl acetate/n-butanol/toluene/ethyl cellosolve (20:25:20:20:15) was applied thereto by means of spraying and dried at 60°C for one hour.
After treatment of the surface of the thus treated ABS resin piece with an alkali, the resin piece was dipped in a palladium chloride solution (PdCl₂·2H₂O: 0.2 g/L; hydrochloric acid: 5 ml/L) for 3 minutes, rinsed with water and then reduced with a 1% DMAB solution. Subsequently, the resulting ABS resin piece was subjected successively to plating for 45 minutes in an electroless copper plating bath as shown in Table 1 and electroless nickel plating for 5 minutes using a bath composition as shown in Table 2. As a result, a uniform copper/nickel plating layer having a copper plating film thickness of 0.7 to 1.5 µm and a nickel film thickness of 0.3 to 0.8 µm was obtained.

Example 4

To a 2-liter stainless steel vessel were introduced 550 g of acrylic copolymer (Toray Industries, Inc.), 120 g of stannic oxide (Yamanaka Chemical Co., Ltd.), 8 g of titanium oxide RD-1 (Kemira Pigments Oy), 50 g of magnesium aluminate metasilicate (Tomita Pharmaceutical Co., Ltd.) and 10 g of BYK-410 (BYK-Chemie GmbH), and the resulting mixture was stirred for 5 minutes. After the stirring, dispersing discs (100 mm-diameter disc × 4) were attached to a batch bench sand mill (vertical), and 850 g of glass beads for dispersing white paints were introduced thereto to effect dispersion of the resulting mixture for 30 minutes at a medium speed. The glass beads were filtered off, and to the filtrate mixture was added the residual liquid in the stainless steel vessel washed with 70 g of butyl acetate/PGM (2:1) to provide a pretreating stock solution. Resin pieces of an ABS resin (TM-20, Mitsubishi Rayon Company Limited), PC (FIN-5000R, Mitsubishi Engineering Plastics Corporation), PC/ABS (T-3011, Teijin Chemicals Ltd.), PC/GF 10 % (SP-7602, General Electric Japan, Ltd.), Nylon 6 (PAMXD6, Mitsubishi Engineering Plastics Corporation) were taken as materials to be plated. After each resin piece was degreased with n-heptane, a solution obtained by adding 0.5 part of an epoxy curing agent DENACOL EX-850 (Nagase Chemicals Ltd.) to 100 parts of the pretreating stock solution and diluting twice the resulting mixture with a mixed solvent of butyl acetate/ethyl acetate/isobutanol/toluene/PGMAC (25:25:25:10:15) was applied thereto by means of spraying and dried at 60°C for one hour.
After treatment of the surface of the thus treated resin piece with an alkali, the resin piece was dipped in a palladium chloride solution (PdCl₂·2H₂O: 0.2 g/L; hydrochloric acid: 5 ml/L) at 30°C for 3 minutes, rinsed with water and then reduced with a 1% DMAB solution. Subsequently, the resulting resin piece was subjected successively to plating for 30 minutes in an electroless copper plating bath as shown in Table 1 and electroless nickel plating for 5 minutes using a bath composition as shown in Table 2. As a result, a uniform copper/nickel plating layer having a copper plating film thickness of 0.8 to 1.2 µm and a nickel film thickness of 0.3 to 0.8 µm was obtained. The thus obtained copper/nickel plating layer was evaluated by subjecting it to high-temperature shelf test, heat cycle test, humidity resistance test and salt spray exposure test. The results are as shown in Tables 3 to 22. Here, methods of evaluation are as shown below.

(1) High-temperature shelf test

After each test piece was stored at 85 ± 2°C for 14 days using a dry heat sterilizer SH-62 (Yamato Scientific Co., Ltd.), electrical resistance and adhesion of the plating layer were evaluated. Electrical resistance was measured across two points taken on a diagonal of the test piece using a digital multimeter TR-6847 (ADVANTEST CORPORATION). Adhesion was tested by means of cross cut test at intervals of 1 mm using a cutter guide (The same shall apply hereinafter).

(2) Heat cycle test

After each test piece was subjected three times to the cycle of 85°C ± 2°C for 1 hour → 23°C ± 2°C for 1 hour → 29°C ± 2°C for 1 hour → 23°C ± 2°C for 1 hour using a small thermo-hygrostat SH-240 (Tabi Espec Corp.), electrical resistance, adhesion of the plating layer were evaluated. A 30-minute interval was taken after each temperature treatment.

(3) Humidity resistance test

After each test piece was stored under the conditions of 35°C ± 2°C and 90 ± 5 % RH for 14 days using a thermo-hygrostat PR-1ST (Tabi Espec Corp.), electrical resistance and adhesion of the plating layer were evaluated.

(4) Salt spray exposure test

After 5 % salt water was sprayed against each test piece at 35°C for 48 hours using a nozzle type salt spray exposure tester (Toyo Seiki Seisakusho Ltd.), the resulting test piece was left to stand for 24 hours, and electrical resistance and adhesion of the plating film were evaluated.
Test plate: Mitsubishi Rayon Company Limited., ABS TM-20, HB type

Degreasing: Done (wiped with heptane); single-side plated

(1) High-temperature shelf test
High-temperature shelf test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.162	0.178	100/100	100/100
II	0.152	0.153	100/100	100/100
III	0.150	0.164	100/100	100/100

(2) Heat cycle test
Heat cycle test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.168	0.165	100/100	100/100
II	0.162	0.178	100/100	100/100
III	0.168	0.176	100/100	100/100

(3) Humidity resistance test
Humidity resistance test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.163	0.155	100/100	100/100
II	0.156	0.155	100/100	100/100
III	0.161	0.175	100/100	100/100

(4) Salt spray exposure test
Salt spray exposure test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.170	0.225	100/100	100/100
II	0.161	0.200	100/100	100/100
III	0.169	0.205	100/100	100/100

Test plate: Mitsubishi Engineering Plastics Corporation, PC FIN-5000R, V0 type

Degreasing: Done (wiped with heptane); single-side plated

(1) High-temperature shelf test
High-temperature shelf test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.181	0.220	100/100	100/100
II	0.173	0.178	100/100	100/100
III	0.171	0.183	100/100	100/100

(2) Heat cycle test
Heat cycle test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.170	0.173	100/100	100/100
II	0.170	0.180	100/100	100/100
III	0.164	0.160	100/100	100/100

(3) Humidity resistance test
Humidity resistance test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.168	0.188	100/100	100/100
II	0.173	0.202	100/100	100/100
III	0.180	0.183	100/100	100/100

(4) Salt spray exposure test
Salt spray exposure test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.160	0.189	100/100	100/100
II	0.149	0.205	100/100	100/100
III	0.161	0.305	100/100	100/100

Test plate: Teijin Chemicals Ltd., PC/ABS T-3011, HB type

Degreasing: Done (wiped with heptane); single-side plated

(1) High-temperature shelf test
High-temperature shelf test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.228	0.254	100/100	100/100
II	0.255	0.255	100/100	100/100
III	0.238	0.259	100/100	100/100

(2) Heat cycle test
Heat cycle test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.254	0.255	100/100	100/100
II	0.248	0.255	100/100	100/100
III	0.227	0.256	100/100	100/100

(3) Humidity resistance test
Humidity resistance test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.222	0.242	100/100	100/100
II	0.228	0.243	100/100	100/100
III	0.220	0.235	100/100	100/100

(4) Salt spray exposure test
Salt spray exposure test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.247	0.293	100/100	100/100
II	0.248	0.613	100/100	100/100
III	0.245	0.345	100/100	100/100

Test plate: General Electric Japan, Ltd., PC/GF 10%, SP-7602, V0 type

Degreasing: Done (wiped with heptane); single-side plated

(1) High-temperature shelf test
High-temperature shelf test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.301	0.332	100/100	100/100
II	0.293	0.317	100/100	100/100
III	0.295	0.309	100/100	100/100

(2) Heat cycle test
Heat cycle test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.305	0.308	100/100	100/100
II	0.304	0.300	100/100	100/100
III	0.300	0.290	100/100	100/100

(3) Humidity resistance test
Humidity resistance test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.299	0.328	100/100	100/100
II	0.295	0.306	100/100	100/100
III	0.301	0.299	100/100	100/100

(4) Salt spray exposure test
Salt spray exposure test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.278	0.317	100/100	100/100
II	0.306	0.373	100/100	100/100
III	0.294	0.314	100/100	100/100

Test plate: Mitsubishi Engineering Plastics Corporation, PAMXD 6, HB type

Degreasing: Done (wiped with heptane); single-side plated

(1) High-temperature shelf test
High-temperature shelf test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.173	0.185	100/100	100/100
II	0.126	0.138	100/100	100/100
III	0.170	0.186	100/100	100/100

(2) Heat cycle test
Heat cycle test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.151	0.158	100/100	100/100
II	0.164	0.161	100/100	100/100
III	0.175	0.178	100/100	100/100

(3) Humidity resistance test
Humidity resistance test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.173	0.183	100/100	100/100
II	0.169	0.183	100/100	100/100
III	0.126	0.161	100/100	100/100

(4) Salt spray exposure test
Salt spray exposure test
No.	Electrical resistance (Ω)	Adhesion
	Before test	After test	Before test	After test
I	0.184	0.213	100/100	100/100
II	0.174	0.168	100/100	100/100
III	0.175	0.290	100/100	100/100

As is clear from Tables 3 to 22, the copper/nickel plating layers obtained each showed substantially no gain in the electrical resistance values in various environmental tests, and no secondary adhesion occurred.
As has been described heretofore, the present invention can provide an absolutely novel electroless plating process including a step of applying a pretreating solution containing a conductive metal oxide to a material to be treated before application of a catalyst thereto, which process gives less environmental impact, which is less expensive, and which can achieve more efficient and secured reductive deposition of a metal contained in a plating solution.
While some embodiments and examples of the present invention are described above, the present invention is not limited to the above description, and various changes and modifications can be made without departing from the spirit and scope of the present invention.

Claims

An electroless plating process, which comprises:

forming a film containing a conductive metal oxide on a surface of a nonconductive material; and

subjecting the resulting nonconductive material to electroless plating.
The electroless plating process according to Claim 1, further comprising a step of applying a catalyst after formation of the film containing a conductive metal oxide.
The electroless plating process according to Claim 1 or 2, wherein the film containing a conductive metal oxide contains a resin.
The electroless plating process according to any of Claims 1 to 3, wherein the film containing a conductive metal oxide contains a substance which captures and immobilizes a reduction catalyst metal.
The electroless plating process according to any of Claims 1 to 4, wherein the film containing a conductive metal oxide contains an inorganic pigment.
The electroless plating process according to any of Claims 1 to 5, wherein the conductive metal oxide is stannic oxide.
A pretreating agent for electroless plating, comprising at least a conductive metal oxide, a resin, and a substance which captures and immobilizes a reduction catalyst metal.
The pretreating agent according to Claim 7, further comprising an inorganic pigment.
The pretreating agent according to Claim 7 or 8, wherein the conductive metal oxide is stannic oxide.