ASTM B727-83(1995)
(Practice)Standard Practice for Preparation of Plastics Materials for Electroplating (Withdrawn 2004)
Standard Practice for Preparation of Plastics Materials for Electroplating (Withdrawn 2004)
SCOPE
1.1 This practice is a guide to the surface preparation of plastic materials for decorative and functional electroplating, where the sequence of chemical treatments may include: cleaning, conditioning, etching, neutralizing, catalyzing, accelerating, and autocatalytic metal deposition. Surface preparation also includes electrodeposition of metallic strike coatings immediately after autocatalytic metal deposition. These treatments result in the deposition of thin conductive metal films on the surface of molded-plastic materials, and are described in this practice.
1.2 Once molded-plastics materials have been made conductive, they may be electroplated with a metal or combination of metals in conventional electroplating solutions. The electroplating solutions and their use are beyond the scope of this practice.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. (See Section 4.)
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:B727–83 (Reapproved 1995)
Standard Practice for
Preparation of Plastics Materials for Electroplating
This standard is issued under the fixed designation B 727; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (ε) indicates an editorial change since the last revision or reapproval.
1. Scope 3. Significance and Use
1.1 This practice is a guide to the surface preparation of 3.1 A variety of metals can be electrodeposited on plastics
plastic materials for decorative and functional electroplating, for decorative or engineering purposes. The most widely used
where the sequence of chemical treatments may include: coating consists of three layers—copper plus nickel plus
cleaning, conditioning, etching, neutralizing, catalyzing, accel- chromium—for decorative applications. However, brass, sil-
erating,andautocatalyticmetaldeposition.Surfacepreparation ver, tin, lead, cadmium, zinc, gold, other metals, and combi-
also includes electrodeposition of metallic strike coatings nations of these are used for special purposes. The key to
immediately after autocatalytic metal deposition. These treat- producing electroplated plastics of high quality lies in the care
ments result in the deposition of thin conductive metal films on taken in preparing plastics for electroplating. The information
the surface of molded-plastic materials, and are described in contained in this practice is useful in controlling processes for
this practice. the preparation of plastics for electroplating.
1.2 Once molded-plastics materials have been made con-
4. Hazards
ductive, they may be electroplated with a metal or combination
4.1 Somechemicalsolutionsareexothermicuponmixingor
of metals in conventional electroplating solutions. The electro-
in use, thereby requiring cooling and proper containment to
plating solutions and their use are beyond the scope of this
prevent injury to personnel.
practice.
4.2 For details on the proper operation and safety precau-
1.3 The values stated in SI units are to be regarded as the
tionstobefollowedbyvapordegreasing,seeASTMSTP310.
standard. The values given in parentheses are for information
only.
5. General Considerations
1.4 This standard does not purport to address all of the
5.1 Nature of Plastics Suitable for Electroplating:
safety concerns, if any, associated with its use. It is the
5.1.1 Plastics suitable for electroplating may be a combina-
responsibility of the user of this standard to establish appro-
tion of one or more polymers so formulated as to allow
priate safety and health practices and determine the applica-
selective etching of one or more constituents. The most
bility of regulatory limitations prior to use. (See Section 4.)
commonly electroplated material, acrylonitrile-butadiene-
2. Referenced Documents
styrene (ABS), is a terpolymer. During etching, soft butadiene
rubber particles dispersed in the acrylonitrile-styrene matrix
2.1 ASTM Standards:
are selectively attacked. The microscopic pockets formed by
B 532 Specification for the Appearance of Electroplated
the etching process provide sites for the physical interlocking
Plastic Surfaces
of the plastic substrate and subsequently applied metallic
B 533 Test Method for Peel Strength of Metal-Electroplated
coatings. The resultant mechanical bonding is instrumental in
Plastics
achieving metal to plastic adhesion.
B 553 Test Method for Thermal Cycling of Electroplated
5.2 Plastics Suitable for Electroplating:
Plastics
5.2.1 The plastics materials commonly used for injection
B 604 Specification for Decorative Electroplated Coatings
molded articles to be electroplated are:
of Copper Plus Nickel Plus Chromium on Plastics
5.2.1.1 Acrylonitrile-butadiene-styrene (ABS),
5.2.1.2 Polypropylene,
1 5.2.1.3 Polysulfone,
ThispracticeisunderthejurisdictionofASTMCommitteeB-8onMetallicand
5.2.1.4 Modified Polyphenylene Oxide,
Inorganic Coatings and is the direct responsibility of Subcommittee B08.02 on
Substrate Preparation.
5.2.1.5 Polycarbonate,
Current edition approved Aug. 26, 1983. Published December 1983.
Annual Book of ASTM Standards, Vol 02.05.
3 4
Discontinued. See 1989 Annual Book of ASTM Standards, Vol 02.05. Handbook of Vapor Degreasing, ASTM STP 310A, ASTM, 1976.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B727
5.2.1.6 Polyester, and considerations. The first is the bulk method; the second is
5.2.1.7 Nylon. called “through-racking.”
5.2.2 The preparation of these materials for electroplating 5.6.2 Bulk Method—Small parts are often processed in
generallyinvolvesthebasicstepsdescribedinthispractice,but polypropylene baskets or plastic-coated steel baskets. Some-
substantial variations may be necessary to achieve optimum what larger parts can be processed in layered baskets made of
results with plastics other than ABS. stainless steel (UNS Types S30400 or S31600), titanium, or
5.3 Molding Considerations: plastic-coated mild steel. Parts are placed as closely as possible
5.3.1 The chemical nature of plastics combined with the compatible with the need to provide for complete solution
nature of the injection molding process produces plastic parts wetting and drainage.
that are somewhat heterogeneous in composition and structure. 5.6.3 Through-Racking:
During the molding of ABS, for example, the shape, size, and 5.6.3.1 The design of racks to be used in both preparation
distribution of butadiene rubber particles may vary consider- and electroplating processes is dictated by the requirements of
ably within a part and may affect the uniformity of subsequent electroplating and the corrosive nature of the solutions.
surface etching treatments.As a result, under- and over-etching 5.6.3.2 Rack splines and hooks are generally made of
of the surface may occur, either of which can interfere with the copper or copper alloys. Rack cross bars are made of copper or
adhesion of metal coatings. The use of a properly formulated copper alloys if they are to conduct current from the splines to
etchant combined with an organic conditioner may overcome the contacts, but may be made of steel if their function is solely
problems of nonuniform etching. to strengthen and make the rack rigid. Rack contacts are
5.3.2 Although it may be possible to overcome problems of usually stainless steel, although titanium has also been used. If
nonuniform etching by suitable chemical treatments, control of spring action is necessary, phosphor bronze may be used as the
the injection molding process is critical if plastic parts are to be contact member with a short stainless steel piece for the tip.
electroplated successfully. It is essential that the resin be 5.6.3.3 The entire rack is sandblasted, primed, and coated
thoroughly dried before molding. The temperature of the mold with plastisol before use, except for the stainless steel contacts.
and all heating zones, the pressure, the total cycle time, and the During the preparation process, the rack coating may become
fill time must be controlled and monitored. Devices exist for coated with metal, but this does not usually occur because
controlling all molding parameters precisely. hexavalent chromium is absorbed in the plastisol and prevents
5.3.3 The visible defects that may arise in the molding autocatalytic metal deposition from occurring.
process are described in Specification B 532. Molded parts that 5.6.3.4 Control of immersion times in neutralizing, cata-
are obviously defective should not be processed without the lyzing, and accelerating steps is critical to prevent metal
approval of the purchaser. deposition on the rack coating.
5.3.4 Mold release agents interfere with the adhesion of 5.6.3.5 Parts are positioned on racks to optimize the thick-
metallic coatings on plastic substrates and should not be used. ness and appearance of electrodeposited coatings, and to
5.4 Process Selection: minimize solution dragout.
5.4.1 Due to the complexity and proprietary nature of 5.6.3.6 It may be necessary to use current thieves, shields,
commercially available processes for preparing plastics for or auxiliary anodes to obtain uniform metal distribution. The
electroplating, a complete process should be selected for a number of contacts is greater for plastic parts than for
specific type of plastic, and operated according to the specific comparable metal parts. For example, if the total area being
instructions of the supplier of the process. electroplated in less than 0.02 m , one contact point is usually
5.5 Handling of Molded Plastic Parts: sufficient; if the area is 0.25 to 0.60 m , 16 contact points are
5.5.1 Molded-plastic parts must be kept clean and carefully recommended.
handled. It is a common practice to use cotton gloves in 5.6.3.7 Metal deposited autocatalytically or electrolytically
removing parts from the mold and for all subsequent handling. must be chemically removed from contacts after each cycle.
5.5.2 The trimming of plastic parts and the removal of flash This is usually accomplished by using nitric acid-containing
and runners should be done with care to avoid introducing solutions, or proprietary rack strippers.
surface defects. These and other mechanical finishing opera-
tions should be completed before beginning the chemical 6. Preparation of Plastic Substrates
treatment of parts for electroplating. Runners are sometimes
6.1 Alkaline Cleaning:
left intact to facilitate racking for electroplating at a later stage.
6.1.1 Cleaning in alkaline solutions is optional. If the parts
5.6 Racking:
are carefully handled and kept clean after molding, alkaline
5.6.1 Molded-plastic parts can be prepared for electroplat-
cleaning can usually be avoided.
ing in barrels, trays, or baskets and then transferred to racks
6.1.2 Fingerprints, grease, and other shop soil should be
designed specifically for electroplating, or they can be pro-
removed by soaking plastic-molded parts in mild alkaline
cessed on racks that are used in both the preparation and
solutions that are commercially available. A suitable solution
electroplating cycles. Which method of racking to use may be
may contain 25 g/L of sodium carbonate and 25 g/L of
dictated by the size of the parts, by efficiency, and other
5 6
Standards and Guidelines—Electroplated Plastics, American Society of Elec- Adcock, J. L., “Electroplating Plastics—anAES Illustrated Lecture,”American
troplated Plastics, Washington, DC, Second Edition, 1979. Electroplaters’ Society, Inc., Winter Park, FL, 1978.
B727
trisodium phosphate operated at 55 to 65°C. Parts are im- temperature of 656 5°C are commonly used. Several propri-
mersed in the solution for 2 to 5 min (see Note 1). etary baths are available.
6.3.4 Chromic-Sulfuric-Phosphoric Acid Type —This type
NOTE 1—Thorough rinsing after alkaline cleaning and after each of the
of etchant solution normally consists of 3 % by mass chromic
following processing steps is essential. Multiple water rinses are recom-
acid, 56 % by mass sulfuric acid (density 1.83 g/mL), 10.5 %
mended.
by mass phosphoric acid (density 1.87 g/mL), and the balance
6.2 Conditioning:
water. An immersion time of about 3 min at 74 to 77°C is
6.2.1 Conditioning is an optional step that precedes the
commonly used.
etching step. Conditioning can eliminate adhesion problems
6.4 Neutralizing (Sensitizing):
associated with inadequate etching. The conditioner may be a
6.4.1 After thorough rinsing, all residual chromic acid must
solution of chromic and sulfuric acids, or it may contain an
be chemically removed from the surface of the molded-plastic
organic solvent. Proprietary solutions are available and should
parts. Neutralizers are used and are typically mild acid or
be operated according to supplier’s directions.
alkaline solutions containing complexing or reducing agents.
6.2.2 Chromic/SulfuricAcid Type—This type of conditioner
In the case of ABS, it is common to use a solution containing
may contain 30 g/L of chromic acid and 300 mL/L of sulfuric
a mixture of an acidsalt and a reducing agent, such as sodium
acid (93 mass %; density 1.83 g/mL) dissolved in water and is
bisulfite, to eliminate all traces of chromic acid. Typical
maintainedatatemperatureof60°C63°C.Partsareimmersed
processing conditions are 1 to 2 min immersion at 40°C.
in the solution for 1 to 2 min. Because of the relatively large
6.4.2 Neutralizers may also contain ionic surfactants to
amountofsulfuricacidinthesolution,theacrylonitrile-styrene
increase the adsorption of catalyst. The use of surfactants,
matrix, as well as the butadiene phase, are attacked.
however, can lead to activation of the rack coating and
6.2.3 Organic Solvent Type—This type of conditioner is a
subsequent metal deposition on the rack. Surfactants should
solution of an organic solvent in deionized water. The organic
therefore be used with caution. Ionic surfactants are not
solvent may be acetone or other ketone; for example, 2,4-
normally used in processing ABS (see Note 4).
pentadione is sometimes used. The solution may contain 100
to 125 mL/L of the appropriate organic solvent and is main-
NOTE 4—Some plastics, for example, polyphenylene oxide, may re-
tained at a temperature of 40 to 45°C. Treatment is by
quire treatment in dilute solutions of ethylenediamine after neutralization
immersion of the plastic parts for 2.0 to 2.5 min (see Note 2 to insure adequate adsorption of the catalyst.
and Note 3).
6.5 Catalyzing (Activating):
NOTE 2—Solutions containing volatile organic solvents require ad-
6.5.1 Small amounts of palladium are chemically deposited
equate ventilation and must not contact metals. These materials chelate
on the surface at this stage of processing. Palladium functions
ionic metal contaminants. Annealed polypropylene tanks are therefore
as a catalyst for autocatalytic deposition of copper or nickel to
used to hold this type of solution.
follow. Palladium is deposited either by the older, two-step
NOTE 3—Multiple hot water rinses are required after using the organic
procedure or by the more reliable one-step procedure.
solvent-type conditioner. Because organic solvents soften and swell the
6.5.2 Two-Step Procedure—The molded-plastic parts are
plastic surface, time of immersion and of transfer to rinse tanks may affect
first immersed in a solution of stannous chloride, 6 to 10 g/L,
the appearance of the final product, and should be controlled.
operated at pH 1.8 to 2.4 (pH adjusted with hydrochloric acid),
6.3 Etching:
and at 20 to 25°C for 1 to 3 min. The parts are then rinsed
6.3.1 Etchants are
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