1、Designation: B 727 04Standard Practice forPreparation of Plastics Materials for Electroplating1This standard is issued under the fixed designation B 727; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A
2、number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice is a guide to the surface preparation ofplastic materials for decorative and functional electroplating,where the sequenc
3、e of chemical treatments may include:cleaning, conditioning, etching, neutralizing, catalyzing, accel-erating, and autocatalytic metal deposition. Surface preparationalso includes electrodeposition of metallic strike coatingsimmediately after autocatalytic metal deposition. These treat-ments result
4、in the deposition of thin conductive metal films onthe surface of molded-plastic materials, and are described inthis practice.1.2 Once molded-plastics materials have been made con-ductive, they may be electroplated with a metal or combinationof metals in conventional electroplating solutions. The el
5、ectro-plating solutions and their use are beyond the scope of thispractice.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its
6、 use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. (See Section 4.)2. Referenced Documents2.1 ASTM Standards:2B 532 Specification for Appearance of Electroplated Pla
7、sticSurfacesB 533 Test Method for Peel Strength of Metal ElectroplatedPlasticsB 553 Test Method for Thermal Cycling of ElectroplatedPlastics3B 604 Specification for Decorative Electroplated Coatingsof Copper Plus Nickel Plus Chromium on Plastics3. Significance and Use3.1 A variety of metals can be e
8、lectrodeposited on plasticsfor decorative or engineering purposes. The most widely usedcoating consists of three layerscopper plus nickel pluschromiumfor decorative applications. However, brass, sil-ver, tin, lead, cadmium, zinc, gold, other metals, and combi-nations of these are used for special pu
9、rposes. The key toproducing electroplated plastics of high quality lies in the caretaken in preparing plastics for electroplating. The informationcontained in this practice is useful in controlling processes forthe preparation of plastics for electroplating.4. Hazards4.1 Some chemical solutions are
10、exothermic upon mixing orin use, thereby requiring cooling and proper containment toprevent injury to personnel.4.2 For details on the proper operation and safety precau-tions to be followed by vapor degreasing, see ASTM STP 310.45. General Considerations5.1 Nature of Plastics Suitable for Electropl
11、ating:5.1.1 Plastics suitable for electroplating may be a combina-tion of one or more polymers so formulated as to allowselective etching of one or more constituents. The mostcommonly electroplated material, acrylonitrile-butadiene-styrene (ABS), is a terpolymer. During etching, soft butadienerubber
12、 particles dispersed in the acrylonitrile-styrene matrixare selectively attacked. The microscopic pockets formed bythe etching process provide sites for the physical interlockingof the plastic substrate and subsequently applied metalliccoatings. The resultant mechanical bonding is instrumental inach
13、ieving metal to plastic adhesion.5.2 Plastics Suitable for Electroplating:5.2.1 The plastics materials commonly used for injectionmolded articles to be electroplated are:5.2.1.1 Acrylonitrile-butadiene-styrene (ABS),5.2.1.2 Polypropylene,5.2.1.3 Polysulfone,5.2.1.4 Modified Polyphenylene Oxide,5.2.1
14、.5 Polycarbonate,1This practice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.02 onPre Treatment.Current edition approved April 1, 2004. Published April 2004. Originallyapproved in 1983. Discontinued January 200
15、4 and reinstated in 2004 as B 72704.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.4Handbook of V
16、apor Degreasing, ASTM STP 310A, ASTM, 1976.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2.1.6 Polyester, and5.2.1.7 Nylon.5.2.2 The preparation of these materials for electroplatinggenerally involves the basic steps described in
17、 this practice, butsubstantial variations may be necessary to achieve optimumresults with plastics other than ABS.5.3 Molding Considerations:5.3.1 The chemical nature of plastics combined with thenature of the injection molding process produces plastic partsthat are somewhat heterogeneous in composi
18、tion and structure.During the molding of ABS, for example, the shape, size, anddistribution of butadiene rubber particles may vary consider-ably within a part and may affect the uniformity of subsequentsurface etching treatments. As a result, under- and over-etchingof the surface may occur, either o
19、f which can interfere with theadhesion of metal coatings. The use of a properly formulatedetchant combined with an organic conditioner may overcomeproblems of nonuniform etching.5.3.2 Although it may be possible to overcome problems ofnonuniform etching by suitable chemical treatments, control ofthe
20、 injection molding process is critical if plastic parts are to beelectroplated successfully. It is essential that the resin bethoroughly dried before molding. The temperature of the moldand all heating zones, the pressure, the total cycle time, and thefill time must be controlled and monitored. Devi
21、ces exist forcontrolling all molding parameters precisely.5.3.3 The visible defects that may arise in the moldingprocess are described in Specification B 532. Molded parts thatare obviously defective should not be processed without theapproval of the purchaser.5.3.4 Mold release agents interfere wit
22、h the adhesion ofmetallic coatings on plastic substrates and should not be used.5.4 Process Selection:5.4.1 Due to the complexity and proprietary nature ofcommercially available processes for preparing plastics forelectroplating, a complete process should be selected for aspecific type of plastic, a
23、nd operated according to the specificinstructions of the supplier of the process.5.5 Handling of Molded Plastic Parts:5.5.1 Molded-plastic parts must be kept clean and carefullyhandled. It is a common practice to use cotton gloves inremoving parts from the mold and for all subsequent handling.5.5.2
24、The trimming of plastic parts and the removal of flashand runners should be done with care to avoid introducingsurface defects. These and other mechanical finishing opera-tions should be completed before beginning the chemicaltreatment of parts for electroplating. Runners are sometimesleft intact to
25、 facilitate racking for electroplating at a later stage.5.6 Racking:55.6.1 Molded-plastic parts can be prepared for electroplat-ing in barrels, trays, or baskets and then transferred to racksdesigned specifically for electroplating, or they can be pro-cessed on racks that are used in both the prepar
26、ation andelectroplating cycles. Which method of racking to use may bedictated by the size of the parts, by efficiency, and otherconsiderations. The first is the bulk method; the second iscalled “through-racking.”5.6.2 Bulk MethodSmall parts are often processed inpolypropylene baskets or plastic-coat
27、ed steel baskets. Some-what larger parts can be processed in layered baskets made ofstainless steel (UNS Types S30400 or S31600), titanium, orplastic-coated mild steel. Parts are placed as closely as possiblecompatible with the need to provide for complete solutionwetting and drainage.5.6.3 Through-
28、Racking:5.6.3.1 The design of racks to be used in both preparationand electroplating processes is dictated by the requirements ofelectroplating and the corrosive nature of the solutions.5.6.3.2 Rack splines and hooks are generally made ofcopper or copper alloys. Rack cross bars are made of copper or
29、copper alloys if they are to conduct current from the splines tothe contacts, but may be made of steel if their function is solelyto strengthen and make the rack rigid. Rack contacts areusually stainless steel, although titanium has also been used. Ifspring action is necessary, phosphor bronze may b
30、e used as thecontact member with a short stainless steel piece for the tip.5.6.3.3 The entire rack is sandblasted, primed, and coatedwith plastisol before use, except for the stainless steel contacts.During the preparation process, the rack coating may becomecoated with metal, but this does not usua
31、lly occur becausehexavalent chromium is absorbed in the plastisol and preventsautocatalytic metal deposition from occurring.5.6.3.4 Control of immersion times in neutralizing, cata-lyzing, and accelerating steps is critical to prevent metaldeposition on the rack coating.5.6.3.5 Parts are positioned
32、on racks to optimize the thick-ness and appearance of electrodeposited coatings, and tominimize solution dragout.5.6.3.6 It may be necessary to use current thieves, shields,or auxiliary anodes to obtain uniform metal distribution. Thenumber of contacts is greater for plastic parts than forcomparable
33、 metal parts. For example, if the total area beingelectroplated in less than 0.02 m2, one contact point is usuallysufficient; if the area is 0.25 to 0.60 m2, 16 contact points arerecommended.5.6.3.7 Metal deposited autocatalytically or electrolyticallymust be chemically removed from contacts after e
34、ach cycle.This is usually accomplished by using nitric acid-containingsolutions, or proprietary rack strippers.6. Preparation of Plastic Substrates66.1 Alkaline Cleaning:6.1.1 Cleaning in alkaline solutions is optional. If the partsare carefully handled and kept clean after molding, alkalinecleaning
35、 can usually be avoided.6.1.2 Fingerprints, grease, and other shop soil should beremoved by soaking plastic-molded parts in mild alkalinesolutions that are commercially available. A suitable solutionmay contain 25 g/L of sodium carbonate and 25 g/L of5Standards and GuidelinesElectroplated Plastics,
36、American Society of Elec-troplated Plastics, Washington, DC, Second Edition, 1979.6Adcock, J. L., “Electroplating Plasticsan AES Illustrated Lecture,” AmericanElectroplaters Society, Inc., Winter Park, FL, 1978.B727042trisodium phosphate operated at 55 to 65C. Parts are im-mersed in the solution for
37、 2 to 5 min (see Note 1).NOTE 1Thorough rinsing after alkaline cleaning and after each of thefollowing processing steps is essential. Multiple water rinses are recom-mended.6.2 Conditioning:6.2.1 Conditioning is an optional step that precedes theetching step. Conditioning can eliminate adhesion prob
38、lemsassociated with inadequate etching. The conditioner may be asolution of chromic and sulfuric acids, or it may contain anorganic solvent. Proprietary solutions are available and shouldbe operated according to suppliers directions.6.2.2 Chromic/Sulfuric Acid TypeThis type of conditionermay contain
39、 30 g/L of chromic acid and 300 mL/L of sulfuricacid (93 mass %; density 1.83 g/mL) dissolved in water and ismaintained at a temperature of 60C 6 3C. Parts are im-mersed in the solution for 1 to 2 min. Because of the relativelylarge amount of sulfuric acid in the solution, the acrylonitrile-styrene
40、matrix, as well as the butadiene phase, are attacked.6.2.3 Organic Solvent TypeThis type of conditioner is asolution of an organic solvent in deionized water. The organicsolvent may be acetone or other ketone; for example, 2,4-pentadione is sometimes used.7The solution may contain 100to 125 mL/L of
41、the appropriate organic solvent and is main-tained at a temperature of 40 to 45C. Treatment is byimmersion of the plastic parts for 2.0 to 2.5 min (see Note 2and Note 3).NOTE 2Solutions containing volatile organic solvents require ad-equate ventilation and must not contact metals. These materials ch
42、elateionic metal contaminants. Annealed polypropylene tanks are thereforeused to hold this type of solution.NOTE 3Multiple hot water rinses are required after using the organicsolvent-type conditioner. Because organic solvents soften and swell theplastic surface, time of immersion and of transfer to
43、 rinse tanks may affectthe appearance of the final product, and should be controlled.6.3 Etching:6.3.1 Etchants are strong oxidizing solutions that micror-oughen and chemically alter the surface of molded plasticparts. The etching step is the most important step in achievingserviceable adhesion of m
44、etals to plastics. Commercially usedetchants are either chromic acid types, chromic/sulfuric acidtypes, or chromic-sulfuric-phosphoric acid types.6.3.2 Chromic Acid TypeConcentrated etchants usuallycontain greater than 850 g/L of chromic acid and as much as1200 g/L.8,9The temperature of the solution
45、 is maintained at 506 3C and treatment is by immersion for 8 to 10 min.Concentrated solutions of chromic acid tend to oxidize buta-diene rubber particles in the case of ABS, selectively.6.3.3 Chromic/Sulfuric Acid TypeThis type of etchantmay contain 250 to 350 g/L of chromic acid and 200 to 250mL/L
46、of sulfuric acid (93 mass %, density 1.83 mL/L) dis-solved in water. Immersion times of 5 to 10 min at a solutiontemperature of 65 6 5C are commonly used. Several propri-etary baths are available.6.3.4 Chromic-Sulfuric-Phosphoric Acid Type10This typeof etchant solution normally consists of 3 % by ma
47、ss chromicacid, 56 % by mass sulfuric acid (density 1.83 g/mL), 10.5 %by mass phosphoric acid (density 1.87 g/mL), and the balancewater. An immersion time of about 3 min at 74 to 77C iscommonly used.6.4 Neutralizing (Sensitizing):6.4.1 After thorough rinsing, all residual chromic acid mustbe chemica
48、lly removed from the surface of the molded-plasticparts. Neutralizers are used and are typically mild acid oralkaline solutions containing complexing or reducing agents.In the case of ABS, it is common to use a solution containinga mixture of an acidsalt and a reducing agent, such as sodiumbisulfite
49、, to eliminate all traces of chromic acid. Typicalprocessing conditions are 1 to 2 min immersion at 40C.6.4.2 Neutralizers may also contain ionic surfactants toincrease the adsorption of catalyst. The use of surfactants,however, can lead to activation of the rack coating andsubsequent metal deposition on the rack. Surfactants shouldtherefore be used with caution. Ionic surfactants are notnormally used in processing ABS (see Note 4).NOTE 4Some plastics, for example, polyphenylene oxide, may re-quire treatment in dilute solutions of ethylenediamine after neutraliz
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