1. business and industrial
2. chemicals industry
3. adhesives

Chemical Coatings
Conductive EMI/RFI Shield Coating
Market Information Manual
Presented by:
The Sherwin-Williams Company
Conductive EMI/RFI Shield Coating
Market Information Manual
Compiled by The Sherwin-Williams Company,
Chemical Coatings Division
&
Acheson Colloids Company
The Sherwin-Williams Company
Chemical Coatings Division - Marketing
101 Prospect Avenue N.W.
Cleveland, Ohio 44115
05/05
Table of Contents
Introduction…………………………………………………………………….…1
Purpose of Shielding & Trends……………………………………………....2-4
Shielding Methods & Comparisons………………………………...………5-14
Features of Conductive Shield Coatings……………………….……..…15-23
(includes application and reclamation information)
How Do You Sell EMI/RFI Shield Coatings?…………………………..……24
Generic Conductive Material Selection Information………………….…25-26
Acheson Shield Coatings & Selector Guide…………………………..…27-35
Competitive Product Cross Reference& Comparison……………….....36-37
Electrical Resistance Test Methods for EMI Coating Processes…...…38-42
UL Approval Support…………………………………………………….…….43
Frequently Asked Questions…………………………………………...…44-46
Trouble-Shooting Guide………………………………………………...…47-48
Glossary……………………………………………………………….....……..49
05/05
Introduction
This manual was compiled for the purpose of providing a hand-held
reference guide on the EMI/RFI shield coating market; a market that
represents an estimated 8 million dollars in coating sales annually.
This manual is intended to educate and provide a level of confidence in
the sales and service of EMI/RFI shield coatings. The manual is laid
out in a presentation format in an effort to keep the subject material
simple and concise as possible. Please refer to the Glossary for
abbreviation explanations.
It is our hope that after reviewing this manual you will have a better
understanding of EMI/RFI shield coatings and the EMI/RFI shield
coating marketplace.
1
05/05
What is the Purpose of Shielding?
¾ Protection of Essential Communication
¾ Allow Operation in Electrically Hostile Environment
¾ Control Interference Between Electronic Devices
¾ Data Leakage Containment
2
05/05
Areas of Use
¾ Telecom
• cellular, base station, relay stations, wireless loop, satellite dishes,
antennas
¾ Office Equipment
• computers, fire alarm systems, PDA’s, disk drives
¾ Medical
• X-ray, IV dispensing, blood counters
¾ Military
• headphones, night scopes, radio systems
3
05/05
Conductive Coating Trends
¾ Increasing use in telecommunications
• mobile phones, digital set-top boxes, & satellite dishes
¾ Best alternative for notebook computers
• thin wall housings, higher frequencies
¾ Silver paints increasingly suitable for higher
frequencies (>1 GHz)
¾ Silver plated copper blends reaching higher
conductivity levels
4
05/05
How Do You Shield?
¾ Metal
¾ Plating
¾ Vacuum Metalization
¾ Conductive paint
¾ Metal Cans
¾ Foils/Inserts
5
05/05
Technology Market Share
Cans
Inserts
Foils
Plating
Metal
Paint
Vacuum
05/05
6
Theoretical Shielding Performance
(Flat Panels)
¾ Conductive Coating - 65-85dB
¾ Electroless Plating - 85-100dB
¾ Vacuum Metalization - 85-100dB
7
05/05
Shielding Type Comparison
Attenuation (dB)
100
80
60
Silver Paint
Vacuum
Copper Paint
Electroless
40
20
10
100
Frequency (MHz)
¾ Specific enclosure
¾ Prior to humidity
8
05/05
1000
Electroless Cu/Ni Plating
¾ Pro
• Highly conductive
• Excellent shielding performance
¾ Con
•
•
•
•
Requires strict process control
Decorative paints adhere poorly
Selective plating is expensive
Disposal of plating effluents
9
05/05
Vacuum Metalization
¾ Pro
• Highly conductive
• Excellent shielding performance
¾ Con
• Requires strict process control
• Expensive special tooling and large
number of masks required
• Limited number of sites world wide
• Heat of application can warp thin walls
10
05/05
Conductive Coatings
¾ Pro
• Numerous applications sites world wide
• Very little seam leakage
• Low VOC coatings available
• Low cost (no need for high volume for low cost, price will go lower with
more volume)
¾ Con
•
•
•
•
Coating thickness from 0.5-1.5 mils
Slightly lower dB
Not as good abrasion resistance
Need top coat in humid area
11
05/05
Adhesion to Plastic
Aluminum
Deposition
Electroless
Coating
PC
PC/ABS
PPO/PS
ABS
12
05/05
Applied Price Comparison
Electroless
$3.75/ft2
Paint (silver)
$2.74/ft2
Paint (silver plated
copper)
$1.50/ft2
2
Vacuum Deposition $2.90/ft
13
05/05
Resistance vs Film Thickness
Electrical Resistance versus Dry Film Thickness
0.35
Indicates optimum dry film thickness
0.3
Resistance (ohms/square/mil)
0.25
0.2
SP-017
Coating
0.15
SP-029
Coating
0.1
SP-027
Coating
0.05
0
0
0.5
1
1.5
Coating Thickness (mils)
05/05
14
2
2.5
Application Equipment Costs
¾ Robot Spray Line - $250,000
¾ Plating Line - $1,000,000
¾ Aluminisation Line - $1,000,000
15
05/05
Features of the Resin Bonded
Coating Process
¾ Low cost equipment investment
¾ Easy application by robotic or automatic spray
¾ Excellent shielding performance depending on coating
formulation (silver, silver plated copper, nickel, graphite)
¾ Better contact in mating enclosure parts
¾ Excellent mechanical properties (adhesion, abrasion
resistance)
¾ Excellent environmental stability (humidity, heat, thermal
shock)
16
05/05
Thin Wall Housing
¾No
caused by heat or
chemicals when using the correct
conductive paints
17
05/05
Comprehensive Selection
¾ Nickel Coating
¾ Silver-plated Copper Coating
¾ Silver-plated Copper plus Silver Coating
¾ Silver-Nickel Blend Coating
¾ Silver Coating
18
05/05
Product Categories
¾Solvent base
•
•
•
•
Quick dry
Thin film build
Ready for Use (RFU) and concentrates
Low VOC using alcohol or acetone
¾Water-base
• Low VOC
19
05/05
Shield Coating Types
Attenuation (dB)
100
Ag
Ag/Cu
80
Ni
60
40
20
10
100
Frequency (MHz)
20
05/05
1000
Application Techniques of
Conductive Coatings
¾ Spray
• Conventional (manual)
• Conventional (automatic)
» Siphon
» Pressure fed
» Pressure fed
¾ Airless
¾ HVLP
• Factory Air
• Turbine Fed Air
¾ Brush
21
05/05
Actual Coating Coverage
¾ Conventional Spray Methods 10-30%
• Suction
• Pressure Fed
¾ High Volume Low Pressure 65-85%
• Most efficient
• Robotic systems
¾ Airless Spray Methods 70-85%
22
05/05
Reclamation
¾Sources
• Mask Washer
• Paint Booths Filters/Walls
¾Value in Metals Reclamation
• Copper, Silver-coated Copper
• Nickel
• Silver
23
05/05
How Do You Sell
EMI/RFI Shield Coatings?
It’s easy! Ask these simple questions:
1) Do you currently spray functional shield coatings?
If yes, go to #3
If no, go to #2
2) Do you ever get asked to spray functional shield
coatings?
If yes, go to #3
If no, report as “No Opportunity”
3) What type of coatings and what quantities do you use?
If necessary, for sales and technical support, contact your
regional Acheson representative for joint follow-up.
05/05
24
What Type Of Conductive Material
Do I Use?
¾ Nickel
•
•
•
•
Medium resistance material @0.9 ohms/sq.
Applied at 2.5 mils dry film thickness
Attenuation >65 dB
Oldie but still widely used (different diluent available per
substrate)
¾ Silver-Plated Copper
•
•
•
•
•
Low price
Excellent for new electronics
Applied at 1.0-1.5 mils dry film thickness
Resistance from 0.100 to @0.045 ohms/sq. @ 1mil
Attenuation of >75 dB
25
05/05
What Type Of Conductive Material
Do I Use?
¾ Silver/Nickel
•
•
•
•
•
Low price
Excellent for new electronics
Applied at 0.4 to 1.0 mils
Low resistance 0.020 ohms/sq.@ 1 mil
Attenuation 85 dB
¾ Silver
•
•
•
•
Low resistance at thin film @0.015 ohms/sq.
Applied at 0.3 to 1.0 mils
High shielding protection, thin film for close tolerances
Attenuation 85 dB
26
05/05
Electrodag® 456
¾ Nickel Pigment
¾ Thermosetting Acrylic Binder System
¾ Excellent Adhesion To Metal
¾ 1.000 ohms/sq/mil Typical Resistance
¾ 65 dB Shielding Performance
¾ 991 ft2/gal @ 1 mil
¾ 3.00 lbs/gal VOC
27
05/05
Electrodag® 550
¾ Nickel Pigment
¾ Acrylic Binder System
¾ Excellent Adhesion To Plastic
¾ 0.900 ohms/sq/mil Typical Resistance
¾ 60 dB Shielding Performance
¾ 422 ft2/gal @ 1 mil
¾ 5.47 lbs/gal VOC
28
05/05
Electrodag® SP-017
¾ Silver-Coated Copper Pigment
¾ Acrylic Binder System
¾ Excellent Adhesion To Plastic
¾ 0.075 ohms/sq/mil Typical Resistance
¾ 75 dB Shielding Performance
¾ 295 ft2/gal @ 1 mil
¾ 6.03 lbs/gal VOC
29
05/05
Electrodag® SP-029
¾ Silver-Coated Copper Pigment
¾ Urethane Blend Binder System
¾ Excellent Adhesion To Plastic
¾ 0.030 ohms/sq/mil Typical Resistance
¾ 75 dB Shielding Performance
¾ 168 ft2/gal @ 1 mil
¾ 6.12 lbs/gal VOC
30
05/05
Electrodag® SP-027*
¾ Silver Pigment
¾ Urethane Blend Binder System
¾ Excellent Adhesion To Plastic
¾ 0.015 ohms/sq/mil Typical Resistance
¾ 75 dB Shielding Performance
¾ 340 ft2/gal @ 1 mil
¾ 5.06 lbs/gal VOC
* Available, but not covered under distributor agreement.
31
05/05
Electrodag® SP-008A
¾ Silver-Coated Copper Pigment
¾ Acrylic Latex Binder System
¾ Excellent Adhesion To Plastic Or Metal
¾ 0.250 ohms/sq/mil Typical Resistance
¾ 75 dB Shielding Performance
¾ 450 ft2/gal @ 1 mil
¾ 2.74 lbs/gal VOC
32
05/05
Electrodag® SP-019*
¾ Silver Pigment
¾ Urethane Blend Binder System
¾ Excellent Adhesion To Plastic
¾ 0.015 ohms/sq/mil Typical Resistance
¾ 75 dB Shielding Performance
¾ 552 ft2/gal @ 1 mil
¾ 1.13 lbs/gal VOC
* Available, but not covered under distributor agreement.
33
05/05
Electrodag® 18DB70X*
¾ Silver-Nickel Pigment
¾ Acrylic Binder System
¾ Excellent Adhesion To Plastic
¾ 0.015 ohms/sq/mil Typical Resistance
¾ 75 dB Shielding Performance
¾ 320 ft2/gal @ 1 mil
¾ 0.50 lbs/gal VOC
* Available, but not covered under distributor agreement.
34
05/05
®
E le c tro d a g E M I/R F I S h ie ld in g M a te ria ls S e le c tio n G u id e
E le c tro d a g c o n d u c tiv e c o a tin g s a re d e s ig n e d to p ro te c t e n c lo s e d e le c tro n ic d e v ic e s a g a in s t ra d ia te d e le c tro m a g n e tic in te rfe re n c e a n d e le c tro s ta tic d is c h a rg e . O u r E le c tro d a g c o a tin g s
h a v e b e e n e x p e rtly fo rm u la te d u s in g v a rio u s c o n d u c tiv e p ig m e n ts to a c h ie v e o p tim a l p e rfo rm a n c e in e le c tric a lly h o s tile e n v iro n m e n ts a n d a s s is t th e d e s ig n e r to c o m p ly w ith e m is s io n s
re g u la tio n s w o rld w id e .
P ro d u ct
P ig m e n t
B in d e r
D ilu e n t*
T y p ic a l
R e s is ta n c e
o h m s /s q /m il
VOC
lb s /g a l
T h e o re tic a l
C o v e ra g e
S q ft/g a l
@ 1 m il
S h ie ld in g
P e rfo rm a n c e
(d B )
R e c o m m en d e d
S u b s tra te s
If re q uire d ,
d ilute to
u s e r’s n e e d s
1 .0 0 0
3 .0 0
991
65
M e ta l
D ilu tio n R a tio
(b y v o lu m e )
(p ro d u c t:s o lv e n t)
SOLVENT BASE
E le c tro d a g 4 5 6
N ic k e l
T h e rm o s e ttin g
A c ry lic
M A K or M E K
E le c tro d a g 5 5 0
N ic k e l
A c ry lic
S B -1 , S B -8 ,
o r S B -1 0
1 :0 .8 ra tio
0 .9 0 0
5 .4 7
422
60
P la s tic s
E le c tro d a g
S P -0 1 7
S ilv e r-c o a te d
Copper
A c ry lic
M E K , S B -1
2 :1 ra tio
0 .0 7 5
6 .0 3
295
75
P la s tic s
E le c tro d a g
S P -0 2 9
S ilv e r-c o a te d
Copper
U re th a n e
B le n d
A lc o h ol
B le n d
3 :1 ra tio
0 .0 3 0
6 .1 2
168
75
P la s tic s
E le c tro d a g
S P -0 2 7
S ilv e r
U re th a n e
B le n d
A lc o h ol
1 :1 ra tio
0 .0 1 5
5 .0 6
340
75
P la s tic s
E le c tro d a g
S P -0 0 8 A
S ilv e r-c o a te d
Copper
A c ry lic
L a te x
W a te r
R e a dy for u s e
0 .2 5 0
2 .7 4
450
75
E le c tro d a g
S P -0 2 8
S ilv e r-c o a te d
Copper
A c ry lic
W a te r
R e a dy for u s e
0 .1 0 0
3 .0 2
362
75
P la s tic
E le c tro d a g
S P -0 1 9
S ilv e r
U re th a n e
B le n d
W a te r
R e a dy for u s e
0 .0 1 5
1 .1 3
552
75
P la s tic
E le c tro d a g
1 8 D B 70 X
**V O C E X E M P T
S ilv e r
A c ry lic
A c eto n e
1 :1 ra tio
0 .0 1 5
0 .5 0
320
75
P la s tic s
LOW VOC
* S o lv e n t b le n d s m a y b e c h a n g e d fo r s p e c ific p la s tic a n d e n v iro n m e n ta l c o n ditio n s . S B -1 is fa s t d ry in g
an d is a ls o u s ed fo r to u g h to b ite in to p las tic s u rfa c e s ; S B -8 is m e d iu m d ry in g a n d c a n b e u s e d fo r
ge n e ra l p urp o s e p la s tic s ; S B -1 0 is th e s lo w e s t d ry in g a n d us e d o n s o lv e n t s e n s itiv e p la s tic s . If
blu s h in g o r d ry s p ra y o c c u r a dd u p to 5 % o f d ia c eto n e a lc o h o l o r bu ty l a lc oh o l
P la s tic o r m e ta l.
A ls o
A rc h itec tu ra l
Uses
E le c tro d a g m a te ria ls a re U L re c o g n iz e d p e r U L 7 4 6 C fo r a d h e s io n to c o m m on ly u s e d p la s tic s
fo r e n c lo s u re a p p lic a tio n s .
F o r m o re d e ta ils o n s p e c ific U L ap p ro v als c on ta c t A c h e s o n
C o llo ids C om p a n y a t 1 -8 0 0 -25 5 -1 9 0 8 .
** T h is p ro d u c t w a s fo rm u la te d u s in g m a te ria ls th a t h a v e b e e n c la s s ifie d a s e x e m p t b y th e U n ite d S ta tes E n v iro n m e n ta l P ro te c tio n A g e n c y . It is re c o m m e nd e d th a t b e fore us in g th is p rod u c t, y o u c o n ta c t y o u r
lo c a l a n d s ta te re g u la to ry a g e n c ie s fo r c on firm a tio n .
05/05
35
Competitive Product
Cross Reference
Acheson Electrodag
®
Spraylat
456 and 550
None
SP-017
Y2000
SP-008A
Z3000
SP-029
Y2000 or B3755
36
05/05
Coating Integrity
Cohesion Comparison
¾ Competitive brand
does not exhibit good
cohesive strength
¾ UL tests for adhesive
and cohesive integrity
¾ OEMs recognize
coating integrity as
critical at seams and
ground points
Electrodag
37
05/05
Brand S
Measurement of
Electrical Resistance
Forward
Measurement of electrical resistance during the processing of EMI coatings can be confusing,
especially when comparing numbers to the paint manufacturer’s method. The following
paragraphs describe current industry standards, make suggestions for proper electrical
resistance testing methods and explain the ohm/square/mil method.
Conclusion
Point-to-point resistance results are dependant on many factors including size, shape,
geometry of the part, distance between the points, film thickness and type of substrate. For
this reason, suppliers typically supply ohms/square/mil levels for their coatings as this data is
obtained under controlled test conditions. Because the profile of the part to be coated will be
different for each OEM, it is impossible to be able to state what the point-to-point resistance
will be for any given part. The industry instead provides ohm/square/mil data so that end
users can compare products for electrical resistivity properties.
The customer is urged to use Versatronic® probes in a meter capable of reading 0.001ohm.
This enables point-to-point readings over long distances and at 1 cm spacing for tight space
checks (side walls, etc.) and in the ohm/square/mil method described below.
It is essential that coaters monitor film thickness, degree of cure and conductivity on a daily
basis to ensure optimum coating performance and control costs.
05/05
38
Measurement of
Electrical Resistance
Current Industry Standards
There are two methods for measuring electrical resistivity: point-to-point, which is used for
QC purposes and ohms/square/mil which should be used for comparing one product to
another.
The most common and easiest resistance measurement is point-to-point testing performed by
simply touching ohmmeter probes to the painted surface. Locations of the probes are agreed
upon between the OEM and coater. Drawbacks of this method, which affect resistance
values, include uncontrolled normal force (pressure applied), sharpness of the probes and
oxidation of the probes. While point-to-point is a good and necessary practice, it should be
accompanied by film thickness and ohm/square/mil monitoring.
05/05
39
Electrical Resistance Test Method for
Sprayed Electronic Coatings
4-PROBE ELECTRICAL RESISTANCE TEST
METHOD FOR SPECIAL JIG
SCOPE:
To determine the dry film electrical resistivity of conductive coatings.
EQUIPMENT:
1. Ohmmeter with low resistance capability that can accept four leads.
2. Special compression contact jig for measuring the electrical resistivity of a 1” X 3” area of coated surface.
METHOD:
1. A product to be tested for electrical resistance should be applied to a suitable substrate (most commonly
a glass plate or GE Lexan panel) measuring 3” in width and a minimum 4” in. length. The coating needs to
be properly cured before testing. If the coating is applied onto a glass panel this same panel can be used to
measure dry film thickness after resistivity has been recorded. If the coating is applied onto plastic, a glass
slide (typically a 1” X 3” microscope slide) needs to be fixed onto the back of the panel, partially exposed, in
the area where resistivity will be measured (see diagram #1)
NOTE:Identification of application method, cure, dilution ratio, if any, and recommended film
thickness can be found on the Product Data Sheet.
2. Product application for this test can be by spray or drawdown technique, as specified on the Product Data
Sheet. If drawdown technique is used, it must be performed on glass substrate to accurately measure dry
film thickness.
05/05
40
Electrical Resistance Test Method for
Sprayed Electronic Coatings
3. A one-inch wide section should be scribed into the cured coating. This can be done using a 1” X 3”
standard microscope slide. Be certain that the scribe goes completely through the coating.
4. The electrical resistance of the coating can then be tested using the special jig and the ohmmeter. The
ohmmeter must accept four leads to eliminate lead resistance failures. Ensure the leads from the inner
probes are wired to the source input on the ohmmeter and the outer probes are wired to the sense input of
the ohmmeter. Before performing actual resistance measurements, check the electrical resistance
specifications of the product being tested and set the ohmmeter at an appropriate scale.
5. Once the meter has been properly adjusted, insert the coated test panel into the special jig ensuring the
scribed area is lined up with the contacts. There is a red painted area on the jig for this purpose.
6. Obtain and record the electrical resistance reading from the ohmmeter.
7. Measure the thickness of the coated glass slide using a micrometer. The measurement must be done in
an area where the electrical resistance was made (see diagram #1). Remove the coating using a razor
blade (in the same area the initial thickness measurement was made) and determine the thickness of the
glass slide with the micrometer. Subtracting the thickness of the glass slide from the thickness of the glass
slide and coating will give the thickness of the coating.
8. The electrical resistance is expressed in units of ohms per square inch at a thickness of 0.001 inch (one
mil). This is possible since the compression contacts on the electrical resistance jigs are one inch apart
41
05/05
Electrical Resistance Test Method for
Sprayed Electronic Coatings
9. To calculate the electrical resistance, multiply the obtained electrical resistance by the film thickness of
the coating. This will give an electrical resistance value normalized to a thickness of 0.001 inch.
Diagram #1
Area where
resistivity
will be
measured
Glass
Slide
Back
(Uncoated)
Front
(Coated)
42
05/05
Tape
UL Approval Support
For a current list of UL approved companies, contact
Chemical Coatings Marketing in Cleveland
43
05/05
Frequently Asked Questions
Q) How much diluent can I use to make the coating go farther? Does it matter which solvent I use to
dilute the product with?
A) Dilutions in excess of the recommended amounts can help with such things as blushing, dry spray, and
laying down lower film builds. However, there is a fine line as to the amount that can be added before
performance properties such as resistance and cohesion are affected. If additional diluent is necessary to
enhance application properties I would recommend no more than four additional ounces per gallon for
concentrated products and no more than six additional ounces per gallon for ready-for-use products. Except
to compensate for blushing or dry spray, I would always recommend the products be diluted and applied per
the directions on the Product Data Sheet.
The diluent used must be compatible with the other ingredients in the formulation to avoid plugging of the
gun, poor wetting of the coating, poor adhesion, high resistivity, and other possible problems. Follow the
Product Data Sheet to determine the proper diluent. If the proper diluent is not available contact either
Technical or the assigned Application Specialist for advice on a suitable replacement.
Q) What type of equipment do I need to apply these coatings?
A) Because of their metal conductive pigment, EMI shielding coatings do not stay in suspension for very long
(anywhere from 2 minutes to 20 minutes before settling). Recommended application equipment includes a
sealed pressure pot with agitation, a pump to move material to the gun and back to the tank, and pressure
regulators to control fluid and atomization levels. With the material under constant agitation in the pressure
pot and constantly recirculated from the pot to the gun and back, settling out of the pigment can be
eliminated. We recommend the use of a HVLP type spray gun because of the high transfer efficiency it has
over conventional spray guns. Also, we recommend just enough agitation in the pressure pot to keep the
material moving. Avoid creating a vortex that can bring excessive air into the product, interfering with proper
application and film thickness, especially with water-based coatings.
05/05
44
Frequently Asked Questions
Q) Are there special storage requirements with these coatings?
A) Yes. Water-based coatings should not be stored in freezing temperatures (below 32F). Freezing waterbased coatings will change the properties of the resin and the material may be unusable. Solvent-based
coatings should be stored below 90F. Storing solvent-based coatings above 90F will shorten the shelf life of
the material.
Q) When I open a new container do I need to use all of the material or can I repackage the product
for later use?
A) Coatings containing silver-coated copper as the conductive pigment should only be opened once or twice
before the product is used up. The repeated exposure of these coatings to fresh air results in rapid oxidation
of the copper in the product, resulting in poor resistivity. Other pigmented coatings can be reopened several
times with minimal effect on the product. However, excessive headspace should be avoided to prevent
solvent loss.
Q) Is there a preferred method of mixing these products before application?
A) Use of a paint shaker is preferred over blade mixers for two reasons. One, with a paint shaker the
container does not need to be opened and exposed to the atmosphere, preventing evaporation of any
volatiles, maintaining solids content. Two, there is less likelihood of excess amounts of air getting mixed into
the material. Trapped air can interfere with the proper application and performance properties of the
coatings, especially the waterborne materials.
05/05
45
Frequently Asked Questions
Q) How can I tell if the coating is thoroughly cured?
A) The best method of testing cure is to measure resistivity of the coating. While recording time and
temperature, measure resistance point to point at specified locations. Resistance readings will significantly
decrease as the coating cures. This decrease will end when the coating is cured. The temperature and time
should be recorded for future reference as to proper cure conditions.
Note: Established cure conditions are dependent upon dried film thickness. If the film thickness
increases or decreases, the time and temperature necessary for proper cure will have to be
reestablished.
Q) Can EMI shielding coatings be topcoated?
A) Yes. The resin systems used in these coatings are easily adhered to by most decorative and protective
coatings. However, there will be an increase in resistivity when conductive coatings are topcoated that will
need to be compensated for.
05/05
46
Troubleshooting
- Coating Appearance P rob lem
C ause
S olution
C oating blisters
d uring cure
1) C oating applied too
heavy
2) C oating applied too
w et
3) Insufficient flash tim e
before oven cure
T o avoid blisters, it is m ost im portant to apply the m aterial so as to avoid too
heavy and/or too w et of a film . If the coating is applied too heavy or w et, blisters
m ay be avoided by increasing flash tim e.
C oating cracks
after cure
S olvent attack on the
substrate
1) C hange application technique to apply the coating drier by increasing the
atom ization air and/or decreasing the volum e of m aterial.
2) A dd a sm all am ount of either D iacetone A lcohol, B utyl C ellosolve or S B -10
solvent (<4 ounces/gal).
3) R ecom m end a less aggressive coating, either w ater or alcohol based to be
sued on solvent sensitive substrates.
4) A pply a thin coat, flash, then apply norm al layers. The thin coat w ill act as a
barrier upon flashing, protecting the substrate.
C oating is
rou gh like
sandp ap er
D ry spray
1) C hange gun settings to increase feed and/or decrease atom ization air
2) C hange application technique by decreasing gun distance from part and/or
slow ing gun speed
3) A dd sm all am ount (<4ounces/gal) of slow solvent (B utyl C ellosolve or
D iacetone A lcohol)
G rit in product from
previously opened
container
S train product through 40-60 m esh filter.
B lushing
B lushing occurs w hen coatings containing fast solvents are applied in high
hum idity conditions. To m inim ize blushing, add a sm all am ount of either B utyl
C ellosolve or D iacetone A lcohol (< 4ounces/gal).
C oating has
w hite surface
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47
Troubleshooting
- Performance Properties Problem
Resistance
readings are
higher than they
should be.
Coating exhibits
poor cohesion in
tape test.
Coating exhibits
poor adhesion in
cross-hatch tape
test
05/05
Cause
Solution
1) Insufficient film build
Be sure the coater has a method of measuring dried film thickness. Recommend
using a glass microscope slide attached somewhere on the part that can be
removed and film thickness then measured with a micrometer after the coating is
cured. If the dried film thickness is less than recommended, check the container for
undispersed solids. If the material was mixed uniformly, adjust gun settings to
achieve proper film build.
2) Insufficient Cure
If the degree of cure is suspect, place a coated part into any available oven at the
recommended cure time and temperature. Once the coating has properly cured,
retest for resistance.
3) Product is past
shelf-life.
Check the lot number to determine if product has exceeded shelf-life.
1) Poor application
technique
If the coating was applied too wet, cohesive failure can result due to settling of the
pigment onto the substrate, leaving a resin rich-layer on top. This results in poor
pigment-to-binder ratio on the bottom, where cohesive failure will occur.
If the coating was applied too dry, the atomized droplets were not able to flow
together and are easily pulled apart. Dry spray will also be evidenced by a rough,
sandpaper-like surface.
2) Older generation
EMI coating.
Some older EMI coatings were formulated with low resistivity as the main criteria.
To accomplish this, pigment to binder ratios were increased, trading cohesion for
resistance. (Example: SP-010) If cohesion is an issue with a new project with EMI
coatings, check with technical for recommended coatings that excel in this area.
Contaminated surface
or inappropriate
substrate/coating
combination
The substrate needs to be free of any dirt, oils and mold release compounds before
coatings will adhere. There is a UL listing available for our coatings and the
substrates on which they are approved.
48
Glossary
ABS
Ag
Cu
dB - Decibel
Acrylonite Butadiene Styrene Plastic*
Silver
Copper
A numerical expression of the relative differences in power
levels of electrical signals equal to ten times the common logarithm of the
ratio of the two signal powers. Used in electronic, radio.
Electromagnetic Interference
One billion hertz
The international unit of frequency, equal to one cycle per second
One million hertz
Nickel
Unit of electrical resistance
Polycarbonate Plastic*
Polyphenoleneoxide Plastic*
Polystyrene Plastic
Radio frequency interference
Shielding plastics
EMI
Ghz - Gigahertz
hertz
Mhz - Megahertz
Ni
Ohms
PC
PPO
PS
RFI
SP
*Reference Sherwin-Williams’ Plastic Selector Guide, Dyment #2004538
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49