EP0324004A1 - Procede de preparation de blindage emi/rfi electrolaque en plastique - Google Patents

Procede de preparation de blindage emi/rfi electrolaque en plastique

Info

Publication number
EP0324004A1
EP0324004A1 EP88906496A EP88906496A EP0324004A1 EP 0324004 A1 EP0324004 A1 EP 0324004A1 EP 88906496 A EP88906496 A EP 88906496A EP 88906496 A EP88906496 A EP 88906496A EP 0324004 A1 EP0324004 A1 EP 0324004A1
Authority
EP
European Patent Office
Prior art keywords
plastic substrate
conductive coating
substrate
electrocoated
temperature
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP88906496A
Other languages
German (de)
English (en)
Other versions
EP0324004A4 (fr
Inventor
Robert L. Coombes, Jr.
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Crown City Plating Co
Original Assignee
Crown City Plating Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Crown City Plating Co filed Critical Crown City Plating Co
Publication of EP0324004A1 publication Critical patent/EP0324004A1/fr
Publication of EP0324004A4 publication Critical patent/EP0324004A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • C25D13/20—Pretreatment

Definitions

  • This invention relates to EMI/RFI shielding in general and, more particularly, to decorative, EMI/RFI shielded electrocoated plastic components for electronic systems.
  • EMI/RFI shielding is required by many electronic systems to absorb or reflect electromagnetic and radio frequency emissions. Such shielding is generally in the form of metal enclosures around electronic assemblies or subassemblies. For aesthetic reasons, it is often desirable to paint such enclosures.
  • Electrocoating is one method which is used for applying a decorative coat of paint onto such metal enclosures.
  • a metal substrate is immersed in an electrocoating solution and an organic resin, i.e., paint, is electrolytically deposited onto the metal substrate.
  • Electrocoating solutions are typically a ⁇ ? ⁇ -ous emulsions of an electrocoating paint.
  • the paint comprises a particular resin system, such as an epoxy, acrylic, or polyester system, along with cross-linking agents, such as melamine or blocked isocyanates, and solvents, pigments, and fillers.
  • a solubilizing agent is present which combines with the resin particles to impart an electrical charge on the surface of the resin particle.
  • the solubilizing agent acts as a dispersant to disperse the particles in the water and thereby form a stable emulsion.
  • the metal substrate is immersed in the electrocoating composition, and a potential is established between the substrate and another electrode immersed in the composition.
  • the substrate may be made either anodic or cathodic to the other electrode.
  • the charged colloidal paint particles migrate toward and deposit on the metal substrate.
  • the colloidal paint particles deposit and form a nonconductive film over the surface of the substrate. Because the film is nonconductive, the plating rat slows as the film thickness builds up and, when particular thickness is achieved, no further depositio occurs at that location. Deposition continues, -however, at other locations until the same thickness is achieved. Accordingly, a uniform thickness is eventually achieve over the entire substrate. Following deposition of the electrocoating paint, the substrate is rinsed and then baked in an oven a high temperatures to cure the paint. Such curin typically .requires a temperature of at least abou 300 ⁇ F.
  • the present invention provides a process for makin plastic EMI/RFI shielded electrocoated components fo electronic systems and the like.
  • the process comprise first electrolessly plating a plastic substrate t establish a conductive surface over the substrate
  • Electroless deposition is followed by cathodicall electrocoating the plated substrate.
  • substrate is then subjected to a curing step to cure th electrocoated paint.
  • a injection-molded, three-dimensional, plastic substrat In a preferred embodiment of the invention, a injection-molded, three-dimensional, plastic substrat
  • . is processed through an electroless plating proces wherein the substrate is first mounted on a platin rack, then immersed in a chemical etchant solution, the a catalyst solution, and finally an electroless platin solution.
  • a chemical etchant solution such as copper or nickel
  • electroless platin solution conductive layer of metal, such as copper or nickel, chemically deposits over the surface of the substrate.
  • the electrolessly plated substrate is then mounte on a electrolytic plating rack such that the meta contacts of the plating rack are in electrical contac with the electrolessly plated conductive layer.
  • Th mounted substrate is then immersed in an electrocoatin solution. A current is established between th substrate and an anode immersed in the bath, an electroating paint is electrolytically deposited to uniform thickness over the entire electrolessly plate surfac .
  • the electrocoated substrate is then heated to temperature and for a time sufficient to cure th electrocoated paint without thermally deforming th plastic substrate or causing a loss of adhesion betwee the electrolessly deposited conductive layer and th substrate surface.
  • the present invention provides a process particularly applicable to the manufacture of lightweight, decorative EMI/RFI shielded, three- 5 dimensional, plastic components for electronic systems.
  • Such shielding components typically form enclosures around electronic assemblies or subassembl es- ⁇ > and -reflect and/or absorb electromagnetic and radio frequency emissions, whether generated by the electronic 0 assembly or subassembly, or by some outside source.
  • the process comprises first providing a three- dimensional plastic substrate in the desired shape.
  • the substrate is preferably formed by injection-molding and is made of a platable plastic material.
  • the plastic 5 material may be any suitable plastic which is thermally stable at the temperature at which the applied electrocoated paint is cured.
  • Preferred platable plastics include nylons, polyesters, polysul ones, and ABS-polysulfone alloys, polycarbonates and polycarbonate 0 alloys.
  • the formed platable plastic substrate is mounted on a suitable plating rack and then electrolessly plated, preferably by conventional techniques.
  • the electroless plating processes described 5 in U.S. Patent Nos. 4,335,164; 4,309,462; and 4,315,045 to Dillard, et.al. and assigned to Crown City Plating Company of El Monte, California, are preferably employed.
  • the nylon substrate is first 0 preconditioned by immersion in an aqueous alkali metal hydroxide solution having a pH of at least about 10 and a temperature of about 150 ⁇ F, and preferably about 185°F.
  • the substrate is then etched by immersion in a solution containing an organic acid, preferably tri- 5 chloroacetic acid.
  • the substrate is seeded with a metal electroless plating catalyst, suc as that described in U.S. Patent No. 3,011,920 to C.R. Shipley, Jr. If required, the substrate is then • immersed in an activating solution to activate the catalyst, and then immersed in an electroless plating solution wherein metal, preferably copper or nickel, deposits onto the catalyzed surface of the substrate.
  • the polyester substrate is optionally first contacted with a detergent rinse, followed by immersion in a hydrolyzer solution containing, for example, 350 grams per liter of chromic acid and 140 millimeters per liter of sulfuric acid, and maintained at a temperature of about 100°F to about 185°F.
  • the polyester substrate is then conditioned by contact with an alkaline conditioner having a pH of at least 8 and maintained a a temperature of at least 135°F.
  • the substrate is then contacted with " an aqueous acid fluoride etch having a pH less than abou 5 and a fluoride concentration of at least about 1 mole per liter.
  • the fluoride etch is preferably maintained at a temperature from about 125°F to about 150 ⁇ F.
  • the etched polyester substrate is then catalyzed and electrolessly plated generally as described above.
  • an electroless plating process as described in U.S. Patent No. 4,125,649 to Donovan et al., assigned to Crown City Plating Company, is preferably employed.
  • the substrate is first contacted with a chromic acid/sulfuric acid hydrolyzer solution as described above, followed by immersion in a pre-etch conditioner containing chlorinated compounds, such as dichloropropanol.
  • the conditioner is maintained at a temperature of from about
  • the substrate is then immersed in
  • an etchant preferably a chromic acid etchant as described in U.S. Patent No. 3,668,130 to Kadison et al., assigned to Crown City Plating Company.
  • the substrate " is rinsed, immersed in an " " alkaline cleanser, and then catalyzed and electrolessly plated as described above.
  • ABS acrylonitrile butadiene styrene
  • polycarbonates such as acrylonitrile butadiene styrene (ABS) and polycarbonates.
  • ABS acrylonitrile butadiene styrene
  • Such plastics are electrolessly plated, for example, according to the processes described in U.S. Patent Nos. 3,668,130 to
  • Re-racking the substrate onto a plating rack is generally not preferred because of the added handling of the substrate which increases the rejection rate due to accidental marring, fingerprints, and the like. Also, the increased labor and the need for an additiona plating rack increases the cost of processing.
  • points of contact between the first plating rack and th substrate are in recesses which entrap air when immerse in the various treating solutions, including th electroless plating solution. Such recesses do not ge electrolessly plated. Without re-racking, the meta contacts of the rack would not be in electrical contac with the conductive electroless plate which deposit over other areas of the substrate. Such electrica contact is required in the electrocoating step.
  • re-racking may simply b desirable.
  • many electroless plating rack are uncoated and therefore plate during the electroles plating process.
  • Such racks are coated during th electrocoating process. This, of course, waste electrocoating material and makes the racks difficult to strip.
  • a coated plating rack is used, i.e. one coated with * a nonconductive material except for the contacts, metal often- ' deposits on the coating material during the electroless plating process. If the deposited metal is in electrical communication with the metal contacts of the rack, the deposited metal will be electrocoated. Again, this wastes electrocoating material and makes the racks difficult to strip.
  • the electrolessly plated substrate is suitably racked, it is then immersed in an electrocoating solution.
  • a voltage is established between the substrate and one or more electrodes also immersed in the solution. The voltage is sufficient to cause the deposition of charged organic resin components onto the substrate.
  • the electrocoated substrate is removed, rinsed with water and dried, preferably with an air gun.
  • the electrocoated substrate is then subjected to a curing step, preferably baking at a temperature and for a time sufficient to cure the electrocoated paint, yet insufficient to warp the plastic substrate or cause any loss of adhes ⁇ on- between, the substrate " ''and - the -electrolessly deposited metal layer, or between the metal layer and the electrocoated layer.
  • a curing step preferably baking at a temperature and for a time sufficient to cure the electrocoated paint, yet insufficient to warp the plastic substrate or cause any loss of adhes ⁇ on- between, the substrate " ''and - the -electrolessly deposited metal layer, or between the metal layer and the electrocoated layer.
  • a curing step preferably baking at a temperature and for a time sufficient to cure the electrocoated paint, yet insufficient to warp the plastic substrate or cause any loss of adhes ⁇ on- between, the substrate " ''and - the -electrolessly deposited metal layer, or between the metal
  • the electrocoating solution may be based on any suitable system, including acrylic, polyester, epoxy, and urethane systems. Currently, it is preferred to use an epoxy-based system as curing temperatures, for epoxy-based systems tend to be lower than for of other systems.
  • the presently preferred electrocoating solution is manufactured by PPG Industries under the trade name PowerCron R 650.
  • Such an electrocoating solution is an epoxy-based solution which requires a curing temperature of about 250°F.
  • cathodic electrocoating solutions avoid electrolytic dissolution of the electrolessly deposited metal on the surface of the substrate. That is, if an anodic electrocoating solution is used when a voltage is established to make the substrate anodic, electrolessly deposited metal on the surface of the substrate will dissolve as the charged electrocoating particles deposit. Because the electroless layer is thin, such metal dissolution could cause a loss of conductivity which, in turn, could prevent an adequate buildup in the thickness of the electrocoated paint and possibly prevent deposition of the electrocoating paint entirely.
  • the electrolessly plated substrate may be electrolytically plated prior to electrocoating.
  • Such an additional step in the process may be desirable in certain cases.
  • the electrolytic deposition of metal over the electroless layer would allow the overall thickness of the metal to buildup sufficiently to avoid any problems created by the use of an anodic electrocoating solution.
  • the electrolytically deposited metal may be any suitable metal or combination of metals. Copper or a layer of copper followed by a layer of nickel is presently pref rred.
  • a clear electrocoated paint over a decoratively plated plastic substrate.
  • a decorative plate typically comprises one or more layers of electrolytically deposited metal over the electrolessly deposited layer.
  • the final electrolytic layer e.g. gold, brass, chrome, etc. , imparts the desired appearance to the part, and the underlying layers, if used, impart desired physical properties, such as corrosion resistance, smoothness or leveling, ductility, and the like.
  • While the presently preferred method of curing is by baking at a suitable temperature, it is also understood that other methods may be used. The suitability of other methods depend upon many factors, including-ithe -particular-*"electrocoating--solution -used, the size and shape of the substrate, and the availability of equipment. For example, ultraviolet light, electron beam, or microwave curing may be suitable in some applications. If a polyurethane system, involving the reaction of a polyol and an isocyanate is used, curing may be accomplished by contact of the electrocoated substrate with a gaseous tertiary-amine catalyst, as described, for example, in U.S. Patent Nos.
  • Electrocoated plastic substrates offer numerous advantages over conventional electrocated metal substrates. Plastic substrates are much lighter, and the material tends to be less expensive than corresponding metal substrates. Moreover, complex shapes are often easier to produce by injection-molding than by conventional casting or other metal fabrication techniques. Because electroless processes involve chemical deposition rather than electrolytic deposition, complex shapes typically do not create problems with respect to coverage of the electrolessly deposited metal. That is, metal deposition over all areas of the substrate in contact with the electroless plating solution occurs whether those areas are high- current density or low-current density areas. This enables electrocoating over the entire surface of the substrate plated in the electroless process. Moreover, the deposited electroless layer provides sufficient conductivity so that the electrocoated substrates can be used as EMI/RFI shielding, if so desired.
  • the process of first applying a conductive electroless layer followed by a nonconductive electrocoated layer may be repeated, if desired, one or more times to yield a laminate or sandwich effect.
  • the substrate was rinsed and immersed in an etch solution containing about 15% trichloracetic acid at ambient temperature.
  • the substrate was then rinsed and immersed in the second sodium hydroxide solution containing 150g/l sodium hydroxide and maintained at 150"F for about 1 minute.
  • the article was then immersed in an acid solution containing 4% fluoboric acid at about 125DF for about 1 minute.
  • the substrate was then catalyzed by immersion for about 60 seconds in a colloidal palladium catalyst manufactured by The Shipley Company under the trade name Cataposit PM 958.
  • the catalyst solution was maintained at about 120 ⁇ F.
  • the substrate was then immersed in an acid accelerator to expose the palladium metal.
  • the accelerator contained 4% fluoboric acid ..and .was maintained at about 120"F.
  • Contact time was for about 120 seconds.
  • the substrate then was electrolessly plated by immersion in a nickel electroless plating solution sold by The Shipley Company under the trade name Niposit PM 980. Immersion time was about 420 seconds, and the temperature of the solution was about 80*F.
  • the substrate was then rinsed and dried.
  • the substrate was removed from the electroless plating rack and mounted on an electrolytic plating rack.
  • the substrate was then cleaned by immersion in an alkaline soak cleaner.
  • the cleaned substrate was then .electrolytically plated with copper for twenty minutes at about 2 volts.
  • the plated substrate was then rinsed and dried.
  • the electrolytically plated substrate was then racked onto a steel non-coated rack and immersed in a cathodic acrylic electrocoating solution sold under the trade name PowerCron s 650 by PPG Industries.
  • the electrocoating solution was maintained at a temperature of 76" to 78°F, and a voltage was established of 75 to 100 volts. Electrocoating continued for one minute.
  • the electrocoated part was then rinsed, blown dry wit an air gun, and baked for twenty minutes at 250"F to cure the electrocoated paint.
  • EXAMPLE 2 A hub cap made of Capron 8260 resin, a mineral filled nylon manufactured and sold by Allied Corp., wa electrolessly plated by the process described in Exampl 1.
  • the electrolessly plated substrate was then racke onto a steel non-coated rack and immersed in the sam electrocoating solution as described in Example 1, i.e., a cathodic acrylic electrocoating solution sold unde the trade name PowerCron 650 by PPG Industries.
  • the electrocoating solution was maintained at a temperature of about 80" A F, and a voltage was established of 125 volts for 30 seconds and was then increased to 150 volts for an additional 15 seconds.
  • the electrocoated part was then rinsed, blown dry with an air gun, and baked for twenty minutes at 270° A F to " cure the electrocoated paint.
  • the electrolyti ⁇ ally plated substrate was then racked onto a steel non-coated rack and immersed in a cathodic acrylic electrocoating solution sold under the trade name PowerCron 650 by PPG Industries.
  • the electrocoating solution was maintained at a temperature of about 85DF, and a voltage was established of about 150 volts. Electrocoating continued for one minute.
  • the electrocoated part was then rinsed, blown dry with an air gun, and baked for twenty minutes at 270DF to cure the electrocoated paint.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemically Coating (AREA)

Abstract

Procédé d'électrolaquage de substrats en plastique consistant à monter le substrat en plastique sur un montage porte-pièce et ensuite à galvaniser le substrat sans courant. Ensuite on monte le substrat galvanisé sans courant sur un second montage porte-pièce et on l'immerge dans une solution d'électroplaquage cathodique dans laquelle une couche de peinture non conductrice se dépose sur le substrat. Puis on durcit la couche de peinture non conductrice par cuisson à une température suffisante pour durcir la couche, mais insuffisante pour provoquer une déformation du substrat.
EP19880906496 1987-06-29 1988-06-29 Procede de preparation de blindage emi/rfi electrolaque en plastique. Withdrawn EP0324004A4 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US6793687A 1987-06-29 1987-06-29
US67936 1998-04-28

Publications (2)

Publication Number Publication Date
EP0324004A1 true EP0324004A1 (fr) 1989-07-19
EP0324004A4 EP0324004A4 (fr) 1989-12-13

Family

ID=22079389

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19880906496 Withdrawn EP0324004A4 (fr) 1987-06-29 1988-06-29 Procede de preparation de blindage emi/rfi electrolaque en plastique.

Country Status (2)

Country Link
EP (1) EP0324004A4 (fr)
WO (1) WO1989000075A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0416338A (ja) * 1990-05-09 1992-01-21 C Uyemura & Co Ltd 電磁波シールド層の形成方法

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3558290A (en) * 1968-04-02 1971-01-26 Union Carbide Corp Plated plastic printing plates
US4368222A (en) * 1981-06-05 1983-01-11 Ashland Oil, Inc. Vapor permeation curable coatings for surface-porous substrates
JPS6289898A (ja) * 1985-10-15 1987-04-24 C-Ren Kk 繊維布帛の加工方法

Also Published As

Publication number Publication date
EP0324004A4 (fr) 1989-12-13
WO1989000075A1 (fr) 1989-01-12

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