ASTM B727-04(2020)
(Practice)Standard Practice for Preparation of Plastics Materials for Electroplating
Standard Practice for Preparation of Plastics Materials for Electroplating
SIGNIFICANCE AND USE
3.1 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. (See Section 4.)
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B727 − 04 (Reapproved 2020)
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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This practice is a guide to the surface preparation of
B532 Specification for Appearance of Electroplated Plastic
plastic materials for decorative and functional electroplating,
Surfaces
where the sequence of chemical treatments may include:
cleaning, conditioning, etching, neutralizing, catalyzing, B533 Test Method for Peel Strength of Metal Electroplated
Plastics
accelerating,andautocatalyticmetaldeposition.Surfaceprepa-
ration also includes electrodeposition of metallic strike coat- B553 Test Method for Thermal Cycling of Electroplated
Plastics (Withdrawn 1991)
ings immediately after autocatalytic metal deposition. These
treatments result in the deposition of thin conductive metal B604 Specification for Decorative Electroplated Coatings of
Copper Plus Nickel Plus Chromium on Plastics
films on the surface of molded-plastic materials, and are
described in this practice.
3. Significance and Use
1.2 Once molded-plastics materials have been made
3.1 A variety of metals can be electrodeposited on plastics
conductive, they may be electroplated with a metal or combi-
for decorative or engineering purposes. The most widely used
nation of metals in conventional electroplating solutions. The
coating consists of three layers—copper plus nickel plus
electroplating solutions and their use are beyond the scope of
chromium—for decorative applications. However, brass,
this practice.
silver, tin, lead, cadmium, zinc, gold, other metals, and
1.3 The values stated in SI units are to be regarded as the
combinationsoftheseareusedforspecialpurposes.Thekeyto
standard. The values given in parentheses are for information
producing electroplated plastics of high quality lies in the care
only.
taken in preparing plastics for electroplating. The information
contained in this practice is useful in controlling processes for
1.4 This standard does not purport to address all of the
the preparation of plastics for electroplating.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Hazards
priate safety, health, and environmental practices and deter-
4.1 Somechemicalsolutionsareexothermicuponmixingor
mine the applicability of regulatory limitations prior to use.
in use, thereby requiring cooling and proper containment to
(See Section 4.)
prevent injury to personnel.
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
4.2 For details on the proper operation and safety precau-
ization established in the Decision on Principles for the
tionstobefollowedbyvapordegreasing,seeASTMSTP310.
Development of International Standards, Guides and Recom-
5. General Considerations
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
5.1 Nature of Plastics Suitable for Electroplating:
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This practice is under the jurisdiction of ASTM Committee B08 on Metallic contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.02 on Standards volume information, refer to the standard’s Document Summary page on
Pre Treatment. the ASTM website.
Current edition approved Nov. 1, 2020. Published December 2020. Originally The last approved version of this historical standard is referenced on
approvedin1983.Lastpreviouseditionapprovedin2014asB727 – 04(2014).DOI: www.astm.org.
10.1520/B0727-04R20. 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 (2020)
5.1.1 Plastics suitable for electroplating may be a combina- 5.5 Handling of Molded Plastic Parts:
tion of one or more polymers so formulated as to allow 5.5.1 Molded-plastic parts must be kept clean and carefully
selective etching of one or more constituents. The most
handled. It is a common practice to use cotton gloves in
commonly electroplated material, acrylonitrile-butadiene- removing parts from the mold and for all subsequent handling.
styrene (ABS), is a terpolymer. During etching, soft butadiene
5.5.2 The trimming of plastic parts and the removal of flash
rubber particles dispersed in the acrylonitrile-styrene matrix and runners should be done with care to avoid introducing
are selectively attacked. The microscopic pockets formed by
surface defects. These and other mechanical finishing opera-
the etching process provide sites for the physical interlocking tions should be completed before beginning the chemical
of the plastic substrate and subsequently applied metallic
treatment of parts for electroplating. Runners are sometimes
coatings. The resultant mechanical bonding is instrumental in left intact to facilitate racking for electroplating at a later stage.
achieving metal to plastic adhesion.
5.6 Racking:
5.2 Plastics Suitable for Electroplating:
5.6.1 Molded-plastic parts can be prepared for electroplat-
5.2.1 The plastics materials commonly used for injection ing in barrels, trays, or baskets and then transferred to racks
molded articles to be electroplated are:
designed specifically for electroplating, or they can be pro-
5.2.1.1 Acrylonitrile-butadiene-styrene (ABS), cessed on racks that are used in both the preparation and
5.2.1.2 Polypropylene, electroplating cycles. Which method of racking to use may be
dictated by the size of the parts, by efficiency, and other
5.2.1.3 Polysulfone,
considerations. The first is the bulk method; the second is
5.2.1.4 Modified Polyphenylene Oxide,
called “through-racking.”
5.2.1.5 Polycarbonate,
5.6.2 Bulk Method—Small parts are often processed in
5.2.1.6 Polyester, and
polypropylene baskets or plastic-coated steel baskets. Some-
5.2.1.7 Nylon.
what larger parts can be processed in layered baskets made of
5.2.2 The preparation of these materials for electroplating
stainless steel (UNS Types S30400 or S31600), titanium, or
generallyinvolvesthebasicstepsdescribedinthispractice,but
plastic-coatedmildsteel.Partsareplacedascloselyaspossible
substantial variations may be necessary to achieve optimum
compatible with the need to provide for complete solution
results with plastics other than ABS.
wetting and drainage.
5.3 Molding Considerations:
5.6.3 Through-Racking:
5.3.1 The chemical nature of plastics combined with the
5.6.3.1 The design of racks to be used in both preparation
nature of the injection molding process produces plastic parts
and electroplating processes is dictated by the requirements of
that are somewhat heterogeneous in composition and structure.
electroplating and the corrosive nature of the solutions.
During the molding of ABS, for example, the shape, size, and
5.6.3.2 Rack splines and hooks are generally made of
distribution of butadiene rubber particles may vary consider-
copper or copper alloys. Rack cross bars are made of copper or
ably within a part and may affect the uniformity of subsequent
copper alloys if they are to conduct current from the splines to
surface etching treatments.As a result, under- and over-etching
thecontacts,butmaybemadeofsteeliftheirfunctionissolely
of the surface may occur, either of which can interfere with the
to strengthen and make the rack rigid. Rack contacts are
adhesion of metal coatings. The use of a properly formulated
usually stainless steel, although titanium has also been used. If
etchant combined with an organic conditioner may overcome
spring action is necessary, phosphor bronze may be used as the
problems of nonuniform etching.
contact member with a short stainless steel piece for the tip.
5.3.2 Although it may be possible to overcome problems of
5.6.3.3 The entire rack is sandblasted, primed, and coated
nonuniform etching by suitable chemical treatments, control of
with plastisol before use, except for the stainless steel contacts.
theinjectionmoldingprocessiscriticalifplasticpartsaretobe
During the preparation process, the rack coating may become
electroplated successfully. It is essential that the resin be
coated with metal, but this does not usually occur because
thoroughly dried before molding. The temperature of the mold
hexavalent chromium is absorbed in the plastisol and prevents
and all heating zones, the pressure, the total cycle time, and the
autocatalytic metal deposition from occurring.
fill time must be controlled and monitored. Devices exist for
5.6.3.4 Control of immersion times in neutralizing,
controlling all molding parameters precisely.
catalyzing, and accelerating steps is critical to prevent metal
5.3.3 The visible defects that may arise in the molding
deposition on the rack coating.
process are described in Specification B532. Molded parts that
5.6.3.5 Parts are positioned on racks to optimize the thick-
are obviously defective should not be processed without the
ness and appearance of electrodeposited coatings, and to
approval of the purchaser.
minimize solution dragout.
5.3.4 Mold release agents interfere with the adhesion of
5.6.3.6 It may be necessary to use current thieves, shields,
metallic coatings on plastic substrates and should not be used.
or auxiliary anodes to obtain uniform metal distribution. The
number of contacts is greater for plastic parts than for
5.4 Process Selection:
comparable metal parts. For example, if the total area being
5.4.1 Due to the complexity and proprietary nature of
commercially available processes for preparing plastics for
electroplating, a complete process should be selected for a
specific type of plastic, and operated according to the specific
Standards and Guidelines—Electroplated Plastics, American Society of Elec-
instructions of the supplier of the process. troplated Plastics, Washington, DC, Second Edition, 1979.
B727 − 04 (2020)
electroplated in less than 0.02 m , one contact point is usually 6.3.1 Etchants are strong oxidizing solutions that micror-
sufficient; if the area is 0.25 to 0.60 m , 16 contact points are oughen and chemically alter the surface of molded plastic
recommended. parts. The etching step is the most important step in achieving
5.6.3.7 Metal deposited autocatalytically or electrolytically serviceable adhesion of metals to plastics. Commercially used
must be chemically removed from contacts after each cycle. etchants are either chromic acid types, chromic/sulfuric acid
This is usually accomplished by using nitric acid-containing types, or chromic-sulfuric-phosphoric acid types.
solutions, or proprietary rack strippers. 6.3.2 Chromic Acid Type—Concentrated etchants usually
contain greater than 850 g/L of chromic acid and as much as
8,9
6. Preparation of Plastic Substrates 1200g/L. Thetemperatureofthesolutionismaintainedat50
6 3 °C and treatment is by immersion for 8 to 10 min.
6.1 Alkaline Cleaning:
Concentrated solutions of chromic acid tend to oxidize buta-
6.1.1 Cleaning in alkaline solutions is optional. If the parts
diene rubber particles in the case of ABS, selectively.
are carefully handled and kept clean after molding, alkaline
6.3.3 Chromic/SulfuricAcidType—Thistypeofetchantmay
cleaning can usually be avoided.
contain 250 to 350 g/L of chromic acid and 200 to 250 mL/L
6.1.2 Fingerprints, grease, and other shop soil should be
of sulfuric acid (93 mass %, density 1.83 mL/L) dissolved in
removed by soaking plastic-molded parts in mild alkaline
water.Immersiontimesof5to10 minatasolutiontemperature
solutions that are commercially available. A suitable solution
of65 65 °Carecommonlyused.Severalproprietarybathsare
may contain 25 g/L of sodium carbonate and 25 g/L of
available.
trisodium phosphate operated at 55 to 65 °C. Parts are im-
6.3.4 Chromic-Sulfuric-Phosphoric Acid Type —This type
mersed in the solution for 2 to 5 min (see Note 1).
of etchant solution normally consists of 3 % by mass chromic
NOTE 1—Thorough rinsing after alkaline cleaning and after each of the
acid, 56 % by mass sulfuric acid (density 1.83 g/mL), 10.5 %
following processing steps is essential. Multiple water rinses are recom-
by mass phosphoric acid (density 1.87 g/mL), and the balance
mended.
water. An immersion time of about 3 min at 74 to 77 °C is
6.2 Conditioning:
commonly used.
6.2.1 Conditioning is an optional step that precedes the
6.4 Neutralizing (Sensitizing):
etching step. Conditioning can eliminate adhesion problems
6.4.1 After thorough rinsing, all residual chromic acid must
associated with inadequate etching. The conditioner may be a
be chemically removed from the surface of the molded-plastic
solution of chromic and sulfuric acids, or it may contain an
parts. Neutralizers are used and are typically mild acid or
organic solvent. Proprietary solutions are available and should
alkaline solutions containing complexing or reducing agents.
be operated according to supplier’s directions.
In the case of ABS, it is common to use a solution containing
6.2.2 Chromic/Sulfuric Acid Type—This type of conditioner
a mixture of an acidsalt and a reducing agent, such as sodium
may contain 30 g/L of chromic acid and 300 mL/L of sulfuric
bisulfite, to eliminate all traces of chromic acid. Typical
acid (93 mass %; density 1.83 g/mL) dissolved in water and is
processing conditions are 1 to 2 min immersion at 40 °C.
maintained at a temperature of 60 °C 6 3 °C. Parts are
6.4.2 Neutralizers may also contain ionic surfactants to
immersed in the solution for 1 to 2 min. Because of the
increase the adsorption of catalyst. The use of surfactants,
relatively large amount of sulfuric acid in the solution, the
however, can lead to activation of the rack coating and
acrylonitrile-styrene matrix, as well as the butadiene phase, are
subsequent metal deposition on the rack. Surfactants should
attacked.
therefore be used with caution. Ionic surfactants are not
6.2.3 Organic Solvent Type—This type of conditioner is a
normally used in processing ABS (see Note 4).
solution of an organic solvent in deionized water. The organic
solvent may be acetone
...
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