The document discusses various defects that can occur in adhesive coatings such as oozing, blistering, cratering, cracking, contamination, and peeling. It provides examples and descriptions for each defect type. Potential causes are outlined for many of the defects, including applying too soft an adhesive, exposure to moisture after coating, using low quality or old adhesive, applying the coating too rapidly, coating at too high a temperature, and electrostatic charges attracting dirt to the coated surface. Remedies are suggested for some defects, such as using a higher quality adhesive and allowing adequate drying time between coating and exposure to other conditions.

1. No : PCP 001 Date : 02 -01-2014
Adhesive Coating Defects
Introduction
During film formation Adhesive should transform a liquid into a closed, solid film
called coating. In order to give optimum protective and aesthetical properties the
coatings should be smooth and even without any defects. Adhesive Film defects can
ruin protective and aesthetical properties of coatings. A huge amount of time and money
is invested in preventing and resolving defects. A lot of hustle can be prevented by
using available knowledge that is simple and easy. How to resolve a defect turns out to
be logical as soon as the governing phenomena of that defect are known and understood.
A wide variety of coating defects occur and the same are discussed.
Defects , Causes and the Remedies
Adhesive Coating is a simple process
There are various methods available for the same.
In general following methods are used
Gravure
Gravure with Myer Bar
Kiss Coating
Floating Knife
Comma Coating
Or
Reverse Roll coating
We are all aware of these Coating Methods and we know how to use them to the best to
produce an Adhesive Coated Product.

2. No : PCP 001 Date : 02 -01-2014
Adhesive Oozing / Bleeding
a squeezing out of the adhesive from between layers of tape so that the sides of the roll
are very tacky.
Blistering
A small , dome like bulge in the coated film or a small recess in a coating film. Typical
blisters are caused by trapped moisture , rapid drying and the use
of improper solvents. Small to large broken or unbroken bubbles
Broken edge craters and small blister-like spots can be caused by
oil, grease or contamination on the substrate. Trapped solvents
can also show up as blisters. Blisters will occur as a result of
humidity testing on test panels, indicating moisture penetration
through the film.

3. No : PCP 001 Date : 02 -01-2014
Cratering
Is formation of bubbles (foaming) and resulting small, round concave depressions
(cratering) when bubbles break in a adhesive film, during adhesive application and
drying.
Craters are also called Pitting .Small , uniform
Indentations in coated Film .
This term refers to large blisters, sometimes deep
enough to expose the substrate, appearing like a
volcano. They are caused by oil and grease spots on
the substrate or by unwanted particles of dirt. In this
latter case, a small lump may be visible at the bottom of the crater. Fish eyes are a
special category of crater often caused by silicone
compounds, such as waxes or lubricants. Pinhole
craters are also encountered when solvent is trapped
below the film surface due to insufficient flash-off
or solvents evaporating too quickly.

4. No : PCP 001 Date : 02 -01-2014
Crawling
Crawling, also called retraction or pulling back, is a uniform de-wetting effect: the
surface energy of the solid substrate is too low to let the liquid adhesive , having a
certain surface tension, cover that substrate. The resulting effect is that the liquid
adhesive does not fully wet the substrate but it retracts and forms droplets, leaving part
of the substrate naked.
Chalking
Chalking refers to a powdery appearance and a loss of gloss. It is caused by a
disintegration of the film on a molecular level. Poor weather ability of the paint resin,
use of poorly-balanced thinning solvents and insufficient paint
agitation, can cause chalking. Formation of fine powder on the surface of the paint film
during weathering, which can cause color fading.
Cracking
Cracking in conformal coating is where a smooth surface fractures into sections with the
cracks in the coating leaving the area below exposed to potential contaminants.
Contamination
Contamination (dirt) can take many forms, particle and fibers all fall into the category of
dirt. However, in some studies of contamination, it was found that more than 50 per cent
of the dirt occurrences were caused by tiny particles. Other sources of
dirt include: Surrounding shop area

5. No : PCP 001 Date : 02 -01-2014
De Lamination
Peeling from undercoat or substrate
Delamination in adhesive coating is where the coating
lifts from the surface , leaving the area below
exposed.
Dirt Pickup: Accumulation of dirt, dust particles ,
fiber and hair , on the adhesive film; may be a major
problem
Fish Eyes
This coating defect is characterized by circular voids or
separation in the coating.
Fish-eyes can be caused by oily spots or silicone particles
and/or by air-borne droplets that are deposited on the coated
surface. This is a typical defect when adhesive is sprayed ,
or coated by pickup rollers.
Separation or pulling apart of wet film to Expose
underlying Finish or substrate. A coating defect
characterized by a small. recessed area in a coating film
with a raised area in the middle , is nothing but Fish eyes.

6. No : PCP 001 Date : 02 -01-2014
Foam
Foam can already be present in the adhesive before application starts. It can also be
introduced during the application process. Especially during Gravure or Kiss roller
coating , air can be brought into the adhesive . A coating formulator wants to develop a
adhesive that loses its foam as soon as application has finished and film formation
proceeds.
Mottle
A coated defect characterized by a ring like blotch with a
light colored area in the center of the ring. Mottle
typically occurs when metallic flake pigment is used in a
coating.
Mottling is a dull, hazy or blotchy appearance on the
surface of some vinyl films or over laminates.
Orange Peel
Orange Peel is Uneven , rough irregularities in the surface
of a coated film. Orange peel often occurs when a binder
fails to flow uniformly across an object's surface.
Uneven surface formation - much like that of the skin of
an orange - which results from poor coalescence of
atomized paint droplets. Adhesive droplets dry before
they can flow out and level smoothly together.

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An orange peel effect is generally caused by the Adhesive
viscosity that’s too high. However, poor operator
techniques, or too much adhesive coating thickness , will also produce a rough finish.
Pin holing
Pin holing is one of the most common surface issues especially
in sprayed application. This defect is characterized by pore-like
holes of about the size of a pinpoint. It frequently extends
entirely through the coating film.
Tiny deep holes exposing substrate
A small , sunken area that forms on a coating film after a bubble
ruptures. Pinholes are typically larger and less abundant across
a coating's surface than solvent pops.
Peeling
Peeling: Loss of bond due to poor adhesion. Where there is
a primer and top coat of adhesive, peeling may involve
some or all coats.

8. No : PCP 001 Date : 02 -01-2014
Wrinkling , Rough Surface
Wrinkling: A rough, crinkled adhesive surface,
which occurs when uncured adhesive forms a "skin.”
Defects Related to Substrate Surface Quality
It is well known that defects and imperfections pre-existing on the substrate surface can
be easily duplicated and magnified in the hot-dipping stage, resulting in defective
coatings.
Rough Surface
A rough substrate surface containing iron fines and slivers is prone to the development
of
outbursts in the coating. The resultant coating
is rough with numerous areas of localized
thick coatings. After being flattened in temper rolling, these areas reflect light
differently, appearing as either dark or bright spots depending on the lighting condition.
A typical sample is shown in Figure 1. Studies indicate that the density of this kind of

9. No : PCP 001 Date : 02 -01-2014
defect decreases with increasing coating weight,(4) suggesting that such a defect can be
masked by a thick coating.
The Causes
Adhesive Oozing / Bleeding
Blistering
Possible Causes:
• Applying highly plasticizer loaded or softer adhesive .
• Exposure of the Adhesive film to high temperature , humidity or moisture
shortly after adhesive is coated , especially if there was inadequate exhaust.

10. No : PCP 001 Date : 02 -01-2014
Cratering
Crawling
Possible Causes:
Use of low quality adhesive or very old adhesive.
Applying (especially rolling) paint too rapidly.
Wetting becomes more critical when the surface energy of the substrate is low and/or
when the surface tension of the liquid Adhesive is high.
A substrate having low surface energy is called
hydrophobic, implying that the surface of the substrate is
not able interacting strongly with a material brought on
top of it. Unmodified plastics, for example, are a group of
materials having low surface energy.
Even when the surface energy of the substrate is

11. No : PCP 001 Date : 02 -01-2014
relatively high, wetting may become a critical factor if highly dynamic application
processes are involved. On fast-running printing presses or roller-coater application, for
example, wetting must be very fast to obtain good results. If the substrate wetting is too
slow, uneven ink-lay, print defects or even poor ink transfer may result.
Under static conditions, the contact angle Q of a liquid drop placed on a given substrate
determines whether wetting is good or poor
Cracking
Cracking in conformal coating is where a smooth surface fractures into sections with
the cracks in the coating leaving the area below exposed to potential contaminants.
 Cure temperature too high
 Conformal coating heat cured too quickly without allowing enough time for
room temperature (RT) drying
 Film thickness too great causing coefficient of thermal expansion (CTE)
mismatch and cracks occurring in the coating
 Operating temperature too high or too low causing the conformal coating to flex
too much & crack.
Chalking
• Use of a low-grade, highly pigmented paint.
• Use of an interior paint for an outdoor application.
Contamination
Dirt Pickup:

12. No : PCP 001 Date : 02 -01-2014
Electrostatic charges develop on surfaces of film webs as they are transported through
various converting processes such as Coating, Laminating , rewinding, slitting. These
charges often cause attraction of Dirt , Dust , fibre and hair on to the web material and
defects in coating uniformity resulting in quality problems and customer dissatisfaction.
Static electricity is the cause of many problems encountered in the transporting and
converting of film webs in today’s modem machinery. As progressing technology
allows faster production speeds, static related problems are also increasing,
hampering production and affecting product quality.
Static charges are generated on the surface of the film as it unwinds from the roll and as
it contacts and separates from surfaces such as idler rolls, nip rolls and printing or
coating rolls.
Charges exist in two polarities: positive and negative. Surfaces charged to the same
polarity will repel each other. Opposite polarities will attract. A charged film of either
polarity will attract to uncharged surfaces of insulators or conductors. These occurrences
become especially evident in converting operations such as sheeting, bag making and
die-cutting where the film is no longer under the control of the mechanical structure of
the web and its transport system.
Film webs tend to develop high charges; 30 kV to 40 kV is common. The strong
electrostatic fields associated with these charges attract dust particles, fibers, bugs and
hair resulting in surface contamination. This causes obvious quality problems
in printing, coating and laminating and cleanliness problems with food, medical and
pharmaceutical packaging films.
Uneven coatings and “wicking” of adhesive are often the result of static charges.
De Lamination
Factors that influence delamination include:

13. No : PCP 001 Date : 02 -01-2014
1. Cleanliness of the surface for adhesion
2. Compatibility between the coating and the surface adhered to due to surface
energies mismatch
3. Permeability to moisture
4. Degree of coating cure
Fish Eyes
"Fish-eyes” are areas in a freshly applied surface coat that tends to thin or open up
on their own accord.
This problem is caused by the high surface tension of the adhesive applied on a
polymer surface, such as a plastic films.
Foam
Two aspects strongly dominate the formation, stabilization and release of foam. First,
foam bubbles can be stabilized by additives having a surfactant (soap) structure. This
problem is experienced most strongly in water based adhesives. The second important
aspect is the rheology of the Adhesive. Despite the viscosity being high the foam
bubbles might be able to move to the surface of the film where they can break.
However, the resulting hole possibly can not level out when the viscosity of the film is
too high,
Mottle
The plasticizers that make films soft, also make them very impressionable. So much so
that when vinyl films and overlaminates are rolled up on a roll, the films can pick the
impression of backside of the release liner.

14. No : PCP 001 Date : 02 -01-2014
Orange Peel
Adhesive might be too viscous ( high viscosity )
Or The coating nip is too tight solvent evaporation too fast
Origin and Potential Causes: Improper gun adjustment and techniques. Too little air
pressure, wide fan patterns or spraying at excessive nozzle distances causes droplets to
become too dry during their travel time to the work surface and they remain as formed
by gun nozzle. Extreme shop floor temperature. When air temperature is too high,
droplets lose more solvent and dry out before they can flow and level properly.
Improper dry.
Factors that can cause orange peel effect include:
1. The improper application of the conformal coating. This manifests in aerosol or
spray gun application where the coating is applied too far away from the substrate
and the coating is too “dry” on the surface to level out.
2. The incorrect thickness of the coating where not enough coating is deposited so
that there is insufficient conformal coating to self level.
3. The incorrect cure profile when using an accelerated curing mechanism. This could
be that the flash off zone before heat curing is inadequate or the oven profile is
incorrect.
Improper flash or recoat time between coats. If first coats of enamel are allowed to
become too dry, solvent in the paint droplets of following coats will be absorbed into the
first coat before proper flow is achieved.
Wrong solvents or reducer. Under-diluted adhesive or adhesive thinned with fast
evaporating solvents or reducers causes the atomized droplets to become too dry before
reaching the surface. Too high viscosity. Low shop floor temperature. Too little solvent
or reducer.
Materials not uniformly mixed. Many finishes are formulated with components that aid
coalescence. If these are not properly mixed, orange peel will result.

15. No : PCP 001 Date : 02 -01-2014
Substrate not treated thoroughly
Peeling
Pin holing
Pin holing is the result of trapped solvents, air or moisture.
Factors that can cause these effects include:
1. When applying the conformal coating the wet film surface can skin over,
entrapping solvents under the surface which can bubble or burst out.
2. If the coating is applied too thick or too viscous any bubbles which are created in
the process of application can become entrapped in the coating before they settle out.
3. Air entrapped under components by the coating process can be forced out during
the drying / curing process and cause bubbles.
4. Pressure pots with conformal coating inside can absorb air which can manifest as
champagne bubbles when applied.
5. Brush coating with too viscous a material or working the coating can cause
bubbles.
6. Incorrect spray equipment or pressures can cause excessive bubbles & foam.
Wrinkling , Rough Surface
Possible Causes:
• Adhesive is applied too thick.
• Adhesive coated during extremely hot weather or cool damp weather, which
causes the adhesive film to dry faster on top than on the bottom.
• Exposure of uncured adhesive to high humidity levels.
• coating of top coat of adhesive to insufficiently cured primer.
• Coating over contaminated surface (e.g., dirt or wax)

16. No : PCP 001 Date : 02 -01-2014
The Remedies
Adhesive Oozing / Bleeding
Blistering
Setting appropriate drying temp is a key to get raid of Blisters.
The drying Air temp and the velocity is critical. Adhesive coated film should never be
exposed to very high temp
in the first zone. As a
matter of fact a temp
gradient setting is essential.
The most ideal temps for
drying zone wise beginning
from First to last zone
should be set. This allows
the entire thickness of the
wet adhesive film warm up
uniformly. Thus the sudden
drying of the top layer , and
entrapment of solvent in the layer below is avoided.

17. No : PCP 001 Date : 02 -01-2014
Cratering
• Use high quality adhesive which will allow good flow and appearance
• coat an appropriate primer before using such Adhesive over the surface.
Crawling
Crawling can be prevented in a number of ways. A pre-condition that has to be met in
order to obtain complete wetting is that the substrate is clean. In some cases the
substrate must be modified in such a way that the surface energy of the substrate is
raised, i.e. the substrate is changed from hydrophobic to hydrophilic. Substrate treatment
is often applied to plastics prior to coating.
Improved Wetting
There are two ways to improve wetting characteristics:
 Raising the surface energy of the substrate through cleaning - removal of oils
and/or other contaminants - or through surface treatment (corona pre-treatment,
flaming, acid or caustic wash).
 Lowering the surface tension of the coating by using additives made
specifically for this purpose.
Corona treatment helps to a great extent in improving the wettability of the substrate.
Another approach being most often used to prevent crawling is lowering the surface
tension of the liquid adhesive by adding wetting agent. However, the use of wetting
agents can worsen key properties of the system, like hardness, recoat ability and foam
sensitivity.

18. No : PCP 001 Date : 02 -01-2014
Cracking
It is possible to minimise conformal coating cracking effects by
 Lowering the initial cure temperature
 Allowing an initial drying time at room temperature before exposure to elevated
temperature
 Reducing the coating thickness to avoid CTE mismatch issues
 Select a coating with a wider temperature range performance.
 Select a more flexible coating
Contamination
Dirt Pickup:
NEUTRALIZING CHARGES ON THE FILM WEB
If static charges on the film web can be controlled to a low level, most electrostatic
related problems can be eliminated. A neutral material will have no electric field so
induction charging, particle attraction and most ESD events will not occur.
Unlike conductors, charges on insulative materials cannot be neutralized by simply
grounding. Methods such as modifying the surface of the material to give it some degree
of conductivity or the use of air ionization must be employed.
Humidity
Raising relative humidity is sometimes used to increase surface conductivity of some
normally insulate materials in an effort to reduce static charging.

19. No : PCP 001 Date : 02 -01-2014
Ionization
The use of air ionizers is the most common, cost effective method of controlling static
charges on the film web. Ionizers emit vast quantities of both negative and positive
charged gas molecules called air ions. The ions are made available to the charged web
where the electric field attracts the necessary ions of opposite polarity to its surface, thus
balancing the charge on the web.
The most common ionizers used in film transport systems are static bars and ionized air
blowers. They may be electrically operated, passive, or may use radioactive materials as
the ion generation source.

20. No : PCP 001 Date : 02 -01-2014
De Lamination
Fish Eyes
Reduction of the surface tension is required to avoid fish-eyes. This can be achieved
thanks to surface modifying agents such as surfactants.
Incorporation of surfactants in the formulation will help you to improve the coating
appearance.
Foam
The prevention of foam in films can be arranged in a number of ways. At first, the use
of surfactants should be minimized. Secondly, introduction of air in the adhesive during
production, handling and application should be prevented as much as possible. Finally,
the rheology of the system should be such that the air that was introduced can escape in
a short period of time during the first stage of film formation. Be aware that the use of
defoamer, being an approach that cannot always be prevented, increases the risk of

21. No : PCP 001 Date : 02 -01-2014
cratering , as well as reduction in Peel adhesion values. However addition of around 0.5
to 1.0 % of Defoam / Anti Foam is generally followed .
Mottle
Orange Peel
Adjust the Adhesive viscosity or the nip replace the solvent
Peeling
Pin holing
Surface modifying additives, especially surfactants, will reduce the surface tension, and
help entrapped bubbles to move to the surface.
The use of surfactants in adhesive formulation will avoid pinholes to appear on the dry
paint film.
Wrinkling , Rough Surface
• Scrape or sand substrate to remove wrinkled coating. If using a primer, allow it to
dry completely before applying top coat. Recoat , (avoiding
temperature/humidity extremes) .
Dear Members ,
I have made an attempt to highlight the issue’s related to coating defects in general.
Please feel to write to me for any specific problem you might be facing . It’s a promise
from my side to guide you , in terms of selection of a suitable additive or a process.