US3567532A - Acidic conditioner for plastic materials - Google Patents

Acidic conditioner for plastic materials Download PDF

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Publication number
US3567532A
US3567532A US788954A US3567532DA US3567532A US 3567532 A US3567532 A US 3567532A US 788954 A US788954 A US 788954A US 3567532D A US3567532D A US 3567532DA US 3567532 A US3567532 A US 3567532A
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Prior art keywords
acid
acidic
bath
conditioner
plastic
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US788954A
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James L Jezl
Habet M Khelghtian
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Avisun Corp
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Avisun Corp
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/18—Pretreatment of the material to be coated
    • C23C18/20—Pretreatment of the material to be coated of organic surfaces, e.g. resins
    • C23C18/22—Roughening, e.g. by etching
    • C23C18/24—Roughening, e.g. by etching using acid aqueous solutions
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/31—Surface property or characteristic of web, sheet or block

Definitions

  • an acidic conditioning bath containing (a) a strong, liquid mineral acid, (b) a hexavalent chromium compound and (c) water, from about 0.01% to about 5% by weight of an aryl sulfonic acid or an aryl phosphonic acid is added to the aforementioned conditioning bath components.
  • the acidic conditioner is useful for chemically etching the surface of a plastic article prior to treating the article with a metallizing process. Adhesion of the deposited metal to the surface of the plastic article is improved when the plastic article is immersed in the acidic conditioning bath.
  • This invention relates to an acidic conditioning bath for conditioning or chemically etching the surface of a plastic article in order to improve the adhesion of the resulting metal plate to the surface of the plastic article. More particularly, this invention also relates to a novel conditioning bath for treating the surface of polyolefin articles.
  • the electroplating of plastic articles comprises a series of steps which include a conditioning or chemical etching of the surface of a plastic article by oxidizing in a strong acid solution followed by sensitizing the surface with an oxidizable, metallic salt that is adsorbed and later reduces the activator. The surface is then activated with a precious metal salt and thereafter electroless plating is performed followed by final plating in an electrolytic bath.
  • plastics permit greater versatility of product design and result in a more corrosion-resistant end product.
  • Metallized plastics having satisfactory bond strength between the metal and the plastic substrate improve such physical properties as fiexural modulus, impact strength and temperature deflection.
  • the acidic conditioner of the present invention comprises (a) from about 50% to by weight of a strong, liquid mineral acid such as sulfuric acid or a mixture of sulfuric acid and phosphoric acid, (b) from about 1% to 10% by weight of a hexavalent chromium compound such as an alkali metal dichromate or chromium trioxide, (c) from about 10% to 40% by weight of water and (d) from about 0.01% to about 5% by weight, and preferably about 0.1% to about 2% by weight, based on the total weight of components (a), (b) and (c) of an aryl sulfonic acid or an aryl phosphonic acid.
  • a strong, liquid mineral acid such as sulfuric acid or a mixture of sulfuric acid and phosphoric acid
  • a hexavalent chromium compound such as an alkali metal dichromate or chromium trioxide
  • c from about 10% to 40% by weight of water
  • d from about 0.01% to about 5% by
  • hexavalent chromium defines chromium in the hexavalent valence state as contained in soluble salts or oxides of such hexavalent chromium.
  • the present invention is based on the discovery that an aryl sulphonic acid or an aryl phosphonic acid in certain defined amounts and in combination with an acidic conditioning (chemical etching) bath comprising a strong, liquid mineral acid, a hexavalent chromium compound and water, when used for the conditioning of surfaces of plastic articles, produces a surface that aids in achieving enhanced adherability of metallic coatings in such processes as electroplating compared to adherability that could heretofore be obtained with conditioners based on a strong, liquid mineral acid and a hexavalent chromium compound alone.
  • an acidic conditioning (chemical etching) bath comprising a strong, liquid mineral acid, a hexavalent chromium compound and water
  • the aryl sulfonic acid may be selected from benzenemonosulfonic acid, benzenedisulfonic acids, naphthalenesulfonic acids and naphthalenedisulfonic acids.
  • the corresponding aryl trisulfonic acids may also be employed.
  • aryl phosphonic acids that may be used in the acidic conditioner include benzenemonophosphonic acid, benzenediphosphonic acid, naphthalenephosphonic acid and naphthalenediphosphonic acid as well as the corresponding aryl triphosphonic acids.
  • the novel conditioner of the present invention is particularly useful in preparing synthetic plastic surfaces for electroplating. Although a variety of processes have been developed for electroplating non-conductive surfaces and particularly plastics, the same general steps are usually employed and comprise conditioning (chemical etching), sensitizing, activating, electroless plating and final electrolytic plating.
  • the conditioning bath of the present invention may be applied in the etching of all plastic articles having a multiplicity of carbon to carbon bonds of which at least one carbon atom is bonded to at least one hydrogen atom.
  • Preferred plastics are synthetic polymeric materials such as the polyolefins.
  • the acidic conditioning bath of the present invention comprises (a) from about 50% to 85% by weight of a strong, liquid mineral acid such as sulfuric acid or a mixture of sulfuric acid and phosphoric acid, (b) from about 1% to 10% by weight of a hexavalent chromium compound such as an alkali metal dichromate or chromium trioxide, (c) from about 10% to 40% by weight of water, and (d) from about 0.01% to about preferably from about 0.1% to 2%, of an aryl sulfonic acid or an aryl phosphonic acid, ((1) being based on the total weight of (a) to (c).
  • a strong, liquid mineral acid such as sulfuric acid or a mixture of sulfuric acid and phosphoric acid
  • a hexavalent chromium compound such as an alkali metal dichromate or chromium trioxide
  • c from about 10% to 40% by weight of water
  • d from about 0.01% to about preferably from about 0.1% to
  • Aryl sulfonic acids that may be incorporated into the conditioning bath of this invention include aryl mononuclear sulfonic acids, aryl mononuclear phosphonic acids, naphthalene sulfonic acids, naphthalene phosphonic acids and the like.
  • Representative sulfonic acids and phosphonic acids are benzenemonosulfonic acid; (0, m, and p)-benzenedisulfonic acid; 1,3,5-benzenetrisulfonic acid; l-naphthalenesulfonic acid; Z-naphthalenesulfonic acid; 1,3-naphthalenedisulfonic acid; 1,5-naphthalenedisulfonic acid; 2,6-naphthalenedisulfonic acid; 2,7-naphthalenedisulfonic acid; and 1,3,6-naphthalenetrisulfonic acid, phenylphosphonic acid, phenylenediphosphonic acids such as p-phenylenediphosphonic acid, and naphthalenephosphonic acids such as Z-naphthylphosphonic acid.
  • the components of the acidic conditioning bath may be mixed by conventional techniques.
  • the bath may be prepared by mixing and heating at elevated temperatures such as from 60 to 100 0., preferably 80 to 90 C., the mineral acid, hexavalent chromium compound and water components and thereafter adding the aryl sulphonic acid and the aryl phosphonic acid and continuing the heating and stirring until all components are thoroughly mixed. If, as a result of heating to admix the conditioner components, the water concentration is decreased below the desirable levels indicated, such can be readily replenished.
  • the components of the conditioner described by the present invention are not limited to the specific additives described hereinabove, but may contain various additional salts such as sodium sulfate or sodium acid sulfate which have heretofore been employed in conditioners for plastic surfaces.
  • the conditioner of the present invention is useful in etching all plastic materials that have heretofore been employed as substrates for the deposition of metallic films.
  • Suitable plastic materials include vinyl aromatic polymers such as polystyrene, acrylonitrile butadiene styrene copolymers (ABS), styrene-acrylonitrile polymers, and rubber-containing polystyrenes; acrylic polymers such as poly (methyl methacrylate); cellulosic plastics such as cellulose butyrate; epoxy resins such as reaction products of bisphenol-A with epichlorohydrin; phenolic resins such as resins of phenol and formaldehyde; polyester resins such as alkyd resins or unsaturated polyester resins, as well as cross-linked polyester resins; polyurethanes; polyacetals; polyimides; polyamides; polycarbonates; polyolefins such as polypropylene and particularly solid, substantially crystalline
  • the novel conditioner of the present invention is particularly suitable for polyolefin resins, such as polypropylene, which show a surprising improvement in adherability of the metal coating to the polyolefin substrate.
  • the treatment or conditioning of plastic articles with the conditioner is generally accomplished by immersing the article to be treated in a bath of the conditioner for periods of time ranging from 1 minute or less to 60 minutes or more at an elevated bath temperature, preferably in a range of to C.
  • an elevated bath temperature preferably in a range of to C.
  • higher bath temperatures and longer immersion times generally result in increased adherability until a maximum is reached beyond which no additional adherability can be obtained.
  • Optimum conditions for the treatment of particular plastic surfaces are established experimentally.
  • the novel conditioner of the present invention is particularly useful in preparing plastic surfaces for electroplating. Although a variety of processes have been developed for the electroplating of non-conductive surfaces and particularly plastics, the same general steps are usually employed. Thus, the plating of plastic surfaces is generally conducted using the following steps:
  • the surface to be plated is cleaned using a mild alkaline bath to remove oils, mold-release agents, ano fingerprints.
  • the conditioned surface is sensitized with a readily oxidizable tin salt solution, such as a stannous chloride solution, which causes tin to be absorbed on the surface.
  • a readily oxidizable tin salt solution such as a stannous chloride solution
  • the surface is then activated or nucleated by treatment with an aqueous solution of a noble metal salt, such as palladium chloride, which forms a metallic film at discrete activated sites.
  • a noble metal salt such as palladium chloride
  • the surface is then subjected to electroless plating using copper, nickel, or cobalt as the metal. This is accomplished by immersing the treated surface in a solution of such metal salt containing in addition to the metal salt such as copper sulfate or nickel chloride, a reducing agent such as formaldehyde, trioxy-methylene, or the like. Sufiicient copper, nickel or cobalt is deposited on the surface of the plastic to achieve a continuous coating capable of conducting electricity.
  • the electroless deposition of metal is then followed by conventionally plating the surface with copper, nickel, and/ or chromium, or just nickel and chromium.
  • the thickness of the electroplated coating is generally within the range of 0.1 to 1.5 mil.
  • ditioner substantially improves the bond strength of the deposited metal to the surface of the plastic article.
  • two parallel cuts are made into the plated metal coating, /2" apart, an additional vertical cut is made to form a tab; one end of the resulting tab is raised sufficiently to allow gripping by a tensile testing machine; the specimen is then placed into a tensile rig and the tab is pulled vertically from the surface. The force required to pull the tab is measured as the bond strength.
  • Examples 14 are directed to the preparation of the acidic conditioning bath and Examples 11 are directed to electroplating processes.
  • Example 1 500 ml. of an acidic conditioner is prepared by combining 60% by weight of sulfuric acid (96% concentration), 5% by weight of chromium trioxide and 35% by weight of water.
  • the acid solution is heated by the exothermic reaction and then cooled to about 80 C.; thereafter 0.5 gram of m-benzenedisulfonic acid is added to the solution and the resulting mixture is thoroughly stirred and gradually heated during a 45-minute period to 8890 C. No reaction is observed with the benzenedisulfonic acid and other components of the acidic conditioning bath. During the heating, about by weight of the water in the bath is volatilized from the reaction mixture.
  • the resulting acidic conditioning bath is now ready for the treatment of plastic articles or the bath may be stored and used at a later date.
  • Example 2 Another 500 ml. solution of a similar acidic conditioning bath containing sulfuric acid, chromium trioxide and water was prepared according to Example 1 and 0.25 gram of benzenedisulfonic acid was added to the conditioning bath and thoroughly mixed with the other acidic components by the procedure described in Example 1. Again, about 10% by weight of water was volatilized from the reaction mixture. The resulting conditioner may now be used for the treatment of synthetic, polymeric articles or the bath may be stored for use at a later date.
  • Example 3 500 ml. of a conditioning bath containing the same components described in Example 1 was prepared with the exception that the amount of benzenedisulfonic acid additive added to the bath was 0.13 gram. The bath was gradually heated over a thirty-minute period to 88-90 C. and during this heating about 9% by Weight of water is volatilized from the reaction mixture. The resulting conditioner is now ready for use in the treatment of plastic surfaces.
  • Example 4 Following the procedure of Example 1, 500 ml. of an acidic conditioning composition is prepared from 60% by weight of sulfuric acid (96% concentration), 5% chromium trioxide and 35% of water. To this solution 20 grams of an additive consisting of 64% by weight of chrominum trioxide and 36% of sodium hydrogen sulfate is added and thoroughly mixed with the other components. Thereafter, 0.5 gram of benzenesulfonic acid is added and the mixture heated to about 90 C. during a 60-minute period. About 10% by weight of the water was volatilized from the reaction mixture.
  • Example 5 A polypropylene plaque, 5" x 5" x 110 mil, molded from a commercially-available substantially crystalline polypropylene homopolymer having a flow rate of 3.4 and containing 0.5 by weight of a nonionic surfactant of t-octylphenoxy-polyethoxyethanol having about 10 ethoxy groups, 5.0% of titanium dioxide, 0.15% of calcium stearate, 0.2% of 2,6-ditertiarybutyl 4-methyl phenol and 0.5% of dilauryl thiodipropionate is immersed in the acidic conditioning bath described in Example 1 to C. for 5 minutes and then consecutively immersed in a stannous chloride sensitizer solution containing 30 g. per 1.
  • the resulting plaque after washing with water is then electroplated with copper for about 20 minutes at a current density of approximately 30 amps/sq. ft., resulting in a 1 mil coating of copper on the plaque.
  • the pull strength was evaluated according to the previously-described procedure and measuredabout 31 1bs./in.
  • Example 6 A polypropylene plaque containing the stabilizing and additive system described in Example 5 was electroplated according to the procedure described in Example 5 with the exception that the conditioning bath of Example 2 was used. The polypropylene plaque was immersed in the conditioning bath for 5 minutes and after electroplating the bond strength was measured as 21 lbs/in.
  • Example 7 A polypropylene plaque having the same additive system described in Example 5 was electroplated according to the procedure of Example 5 with the exception that the acidic conditioner employed was the bath described in Example 3. The plaque was immersed in the conditioning bath for a period of 5 minutes but otherwise the electroplating procedure of Example 5 is followed. Evaluation of the bond strength gave a result of 22-24 lbs./ in.
  • Example 8 A polypropylene plaque having the same additive system described in Example 5 was electroplated according to the procedure of Example 5 and immersed in the same acidic conditioner employed in Example 1, with the exception that 0.25 gram of phenylphosphonic acid was added in lieu of benzenedisulfonic acid, for a period of 15 minutes. Thereafter the plaque was electroplated by the steps described in Example 5. Evaluation of the bond strength gave a value of 8 lbs./ in.
  • Example 9 A plaque, 5" x 5" x mil, molded from a commercially-available, substantially crystalline propylene-ethylene terminal block copolymer having a flow rate of 4.0 (ASTM-1238-62T) and containing 5.0% of titanium dioxide, 0.15% of calcium stearate,-0.2% of 2,6-ditertiarybutyl 4-methyl phenol and 0.5% of dilauryl thiodipropionate was immersed in the acidic conditioning bath described in Example 1 at 85 C. for 10 minutes and then electroplated according to the procedure of Example 5. The bond strength measured about 26 lbs./ in.
  • Example 10 For purposes of comparison and understanding the benefit obtained by employing the conditioning bath of this invention, a control was run ,using the same crystalline polypropylene described in Example 9 and the same conditioning, sensitizing, activating, electroless plating and electrolytic platingidescribed in Example 5 with the exception that the acidic conditioning bath did not contain the benzenedisulfonic acid'additive but consisted of 60% sulfuric acid, 35% water and 5% chromium trioxide. The polypropylene plaque was immersed in the conditioning bath for a period of 5 minutes and following electroplating severe blistering was observed.
  • an acidic conditioning composition for the surface treatment of plastic articles wherein said acidic composition contains as essential components (a) at least one strong, liquid mineral acid selected from the group consisting af sulfuric, phosphoric, and mixtures thereof in an amount of about 50% to 85% by weight, (b) a hexavalent chromium compound in an amount of about 1% to 10% by weight, and (c) water in an amount of about 10% to 40% by weight, the improvement wherein said acidic conditioning composition additionally contains from about 0.01% to about 5 %.by weight, based on the total weight of components (a), (b) and (c), of an aryl sulfonic acid or an aryl phosphonic acid.

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  • Chemical & Material Sciences (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
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US788954A 1969-01-03 1969-01-03 Acidic conditioner for plastic materials Expired - Lifetime US3567532A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3935081A (en) * 1973-08-14 1976-01-27 Phillips Petroleum Company Density control for electroplatable polymer compositions

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3935081A (en) * 1973-08-14 1976-01-27 Phillips Petroleum Company Density control for electroplatable polymer compositions

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