ASTM B727-04(2009)
(Practice)Standard Practice for Preparation of Plastics Materials for Electroplating
Standard Practice for Preparation of Plastics Materials for Electroplating
SIGNIFICANCE AND USE
A variety of metals can be electrodeposited on plastics for decorative or engineering purposes. The most widely used coating consists of three layers—copper plus nickel plus chromium—for decorative applications. However, brass, silver, tin, lead, cadmium, zinc, gold, other metals, and combinations of these are used for special purposes. The key to producing electroplated plastics of high quality lies in the care taken in preparing plastics for electroplating. The information contained in this practice is useful in controlling processes for the preparation of plastics for electroplating.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: B727 − 04(Reapproved 2009)
Standard Practice for
Preparation of Plastics Materials for Electroplating
This standard is issued under the fixed designation B727; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope Plastics (Withdrawn 1991)
B604 Specification for Decorative Electroplated Coatings of
1.1 This practice is a guide to the surface preparation of
Copper Plus Nickel Plus Chromium on Plastics
plastic materials for decorative and functional electroplating,
where the sequence of chemical treatments may include:
3. Significance and Use
cleaning, conditioning, etching, neutralizing, catalyzing,
3.1 A variety of metals can be electrodeposited on plastics
accelerating,andautocatalyticmetaldeposition.Surfaceprepa-
for decorative or engineering purposes. The most widely used
ration also includes electrodeposition of metallic strike coat-
coating consists of three layers—copper plus nickel plus
ings immediately after autocatalytic metal deposition. These
chromium—for decorative applications. However, brass,
treatments result in the deposition of thin conductive metal
silver, tin, lead, cadmium, zinc, gold, other metals, and
films on the surface of molded-plastic materials, and are
combinationsoftheseareusedforspecialpurposes.Thekeyto
described in this practice.
producing electroplated plastics of high quality lies in the care
1.2 Once molded-plastics materials have been made
taken in preparing plastics for electroplating. The information
conductive, they may be electroplated with a metal or combi-
contained in this practice is useful in controlling processes for
nation of metals in conventional electroplating solutions. The
the preparation of plastics for electroplating.
electroplating solutions and their use are beyond the scope of
this practice.
4. Hazards
1.3 The values stated in SI units are to be regarded as the
4.1 Somechemicalsolutionsareexothermicuponmixingor
standard. The values given in parentheses are for information
in use, thereby requiring cooling and proper containment to
only.
prevent injury to personnel.
1.4 This standard does not purport to address all of the
4.2 For details on the proper operation and safety precau-
safety concerns, if any, associated with its use. It is the
tionstobefollowedbyvapordegreasing,seeASTMSTP310.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- 5. General Considerations
bility of regulatory limitations prior to use. (See Section 4.)
5.1 Nature of Plastics Suitable for Electroplating:
5.1.1 Plastics suitable for electroplating may be a combina-
2. Referenced Documents
tion of one or more polymers so formulated as to allow
selective etching of one or more constituents. The most
2.1 ASTM Standards:
commonly electroplated material, acrylonitrile-butadiene-
B532 Specification for Appearance of Electroplated Plastic
styrene (ABS), is a terpolymer. During etching, soft butadiene
Surfaces
rubber particles dispersed in the acrylonitrile-styrene matrix
B533 Test Method for Peel Strength of Metal Electroplated
are selectively attacked. The microscopic pockets formed by
Plastics
the etching process provide sites for the physical interlocking
B553 Test Method for Thermal Cycling of Electroplated
of the plastic substrate and subsequently applied metallic
coatings. The resultant mechanical bonding is instrumental in
achieving metal to plastic adhesion.
This practice is under the jurisdiction of ASTM Committee B08 on Metallic
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.02 on
5.2 Plastics Suitable for Electroplating:
Pre Treatment.
5.2.1 The plastics materials commonly used for injection
Current edition approved Sept. 1, 2009. Published December 2009. Originally
molded articles to be electroplated are:
approved in 1983. Discontinued January 2004 and reinstated in 2004 as B727–04.
Last previous edition approved in 2004 as B727–04. DOI: 10.1520/B0727-04R09.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM The last approved version of this historical standard is referenced on
Standards volume information, refer to the standard’s Document Summary page on www.astm.org.
the ASTM website. 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 − 04 (2009)
5.2.1.1 Acrylonitrile-butadiene-styrene (ABS), 5.6.1 Molded-plastic parts can be prepared for electroplat-
5.2.1.2 Polypropylene, ing in barrels, trays, or baskets and then transferred to racks
5.2.1.3 Polysulfone, designed specifically for electroplating, or they can be pro-
5.2.1.4 Modified Polyphenylene Oxide, cessed on racks that are used in both the preparation and
5.2.1.5 Polycarbonate, electroplating cycles. Which method of racking to use may be
5.2.1.6 Polyester, and dictated by the size of the parts, by efficiency, and other
5.2.1.7 Nylon. considerations. The first is the bulk method; the second is
5.2.2 The preparation of these materials for electroplating called “through-racking.”
generallyinvolvesthebasicstepsdescribedinthispractice,but 5.6.2 Bulk Method—Small parts are often processed in
substantial variations may be necessary to achieve optimum polypropylene baskets or plastic-coated steel baskets. Some-
results with plastics other than ABS. what larger parts can be processed in layered baskets made of
stainless steel (UNS Types S30400 or S31600), titanium, or
5.3 Molding Considerations:
plastic-coatedmildsteel.Partsareplacedascloselyaspossible
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
thecontacts,butmaybemadeofsteeliftheirfunctionissolely
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
theinjectionmoldingprocessiscriticalifplasticpartsaretobe
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 B532. Molded parts that
5.6.3.4 Control of immersion times in neutralizing, catalyz-
are obviously defective should not be processed without the
ing, and accelerating steps is critical to prevent metal deposi-
approval of the purchaser.
tion 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. 2
electroplated in less than 0.02 m , one contact point is usually
sufficient; if the area is 0.25 to 0.60 m , 16 contact points are
5.5 Handling of Molded Plastic Parts:
5.5.1 Molded-plastic parts must be kept clean and carefully recommended.
5.6.3.7 Metal deposited autocatalytically or electrolytically
handled. It is a common practice to use cotton gloves in
removing parts from the mold and for all subsequent handling. must be chemically removed from contacts after each cycle.
This is usually accomplished by using nitric acid-containing
5.5.2 The trimming of plastic parts and the removal of flash
and runners should be done with care to avoid introducing solutions, or proprietary rack strippers.
surface defects. These and other mechanical finishing opera-
6. Preparation of Plastic Substrates
tions should be completed before beginning the chemical
6.1 Alkaline Cleaning:
treatment of parts for electroplating. Runners are sometimes
6.1.1 Cleaning in alkaline solutions is optional. If the parts
left intact to facilitate racking for electroplating at a later stage.
are carefully handled and kept clean after molding, alkaline
5.6 Racking:
cleaning can usually be avoided.
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 − 04 (2009)
6.1.2 Fingerprints, grease, and other shop soil should be Concentrated solutions of chromic acid tend to oxidize buta-
removed by soaking plastic-molded parts in mild alkaline diene rubber particles in the case of ABS, selectively.
solutions that are commercially available. A suitable solution 6.3.3 Chromic/SulfuricAcidType—Thistypeofetchantmay
may contain 25 g/L of sodium carbonate and 25 g/L of contain 250 to 350 g/L of chromic acid and 200 to 250 mL/L
trisodium phosphate operated at 55 to 65°C. Parts are im- of sulfuric acid (93 mass %, density 1.83 mL/L) dissolved in
mersed in the solution for 2 to 5 min (see Note 1). water.Immersiontimesof5to10minatasolutiontemperature
of 65 6 5°C are commonly used. Several proprietary baths are
NOTE 1—Thorough rinsing after alkaline cleaning and after each of the
available.
following processing steps is essential. Multiple water rinses are recom-
6.3.4 Chromic-Sulfuric-Phosphoric Acid Type —This type
mended.
of etchant solution normally consists of 3 % by mass chromic
6.2 Conditioning:
acid, 56 % by mass sulfuric acid (density 1.83 g/mL), 10.5 %
6.2.1 Conditioning is an optional step that precedes the
by mass phosphoric acid (density 1.87 g/mL), and the balance
etching step. Conditioning can eliminate adhesion problems
water. An immersion time of about 3 min at 74 to 77°C is
associated with inadequate etching. The conditioner may be a
commonly used.
solution of chromic and sulfuric acids, or it may contain an
organic solvent. Proprietary solutions are available and should 6.4 Neutralizing (Sensitizing):
be operated according to supplier’s directions. 6.4.1 After thorough rinsing, all residual chromic acid must
6.2.2 Chromic/Sulfuric Acid Type—This type of conditioner be chemically removed from the surface of the molded-plastic
may contain 30 g/L of chromic acid and 300 mL/L of sulfuric parts. Neutralizers are used and are typically mild acid or
acid (93 mass %; density 1.83 g/mL) dissolved in water and is alkaline solutions containing complexing or reducing agents.
maintained at a temperature of 60°C 6 3°C. Parts are im- In the case of ABS, it is common to use a solution containing
mersed in the solution for 1 to 2 min. Because of the relatively a mixture of an acidsalt and a reducing agent, such as sodium
large amount of sulfuric acid in the solution, the acrylonitrile- bisulfite, to eliminate all traces of chromic acid. Typical
styrene matrix, as well as the butadiene phase, are attacked. processing conditions are 1 to 2 min immersion at 40°C.
6.2.3 Organic Solvent Type—This type of conditioner is a 6.4.2 Neutralizers may also contain ionic surfactants to
solution of an organic solvent in deionized water. The organic increase the adsorption of catalyst. The use of surfactants,
solvent may be acetone or other ketone; for example, 2,4- however, can lead to activation of the rack coating and
pentadione is sometimes used. The solution may contain 100 subsequent metal deposition on the rack. Surfactants should
to 125 mL/L of the appropriate organic solvent and is main- therefore be used with caution. Ionic surfactants are not
tained at a temperature of 40 to 45°C. Treatment is by normally used in processing ABS (see Note 4).
immersion of the plastic parts for 2.0 to 2.5 min (see Note 2
NOTE 4—Some plastics, for example, polyphenylene oxide, may
and Note 3).
require treatment in dilute solutions of ethylenediamine after neutraliza-
tion to insure adequate adsorption of the catalyst.
NOTE 2—Solutions containing volatile organic solvents require ad-
equate ventilation and must not contact metals. These materials chelate
6.5 Catalyzing (Activating):
ionic metal contaminants. Annealed polypropylene tanks are therefore
6.5.1 Small amounts of palladium are chemically deposited
used to hold this type of solution.
on the surface at this stage of processing. Palladium functions
NOTE 3—Mu
...
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