Canadian Finishing & Coatings Manufacturing - May/June '24 - 22

INDUSTRIAL FINISHING: TESTING EQUIPMENT
Flawless
Finish
T
Troubleshooting Surface Appearance:
Orange Peel and DOI Measurement
BY SHERRI THOMPSON
he surface appearance of coatings is paramount
across numerous industries due to its significant
impact on product quality, aesthetics, and
consumer perception. Whether in automotive
finishes, architectural coatings, or consumer goods like
furniture, the surface appearance represents craftsmanship
and attention to detail. A flawless surface enhances the
product's appeal and reflects superior quality and durability.
However, even with meticulous application techniques,
surface imperfections can occur.
Two key factors play a significant role in the appearance
of surfaces-Orange Peel and Distinctness of Image (DOI).
However, to effectively troubleshoot surface appearance
issues, we must first grasp how we perceive surfaces visually.
Human perception alone is not sufficient to accurately make
appearance judgments. The sample's total appearance must
be considered to measure surface appearance accurately.
Total Appearance
Various factors contribute to orange peel, including:
VISCOSITY
Issue: Improper viscosity of the coating material can lead to
uneven flow leveling, resulting in orange peel.
Solution: Ensure the coating material is mixed correctly
and thinned according to manufacturer recommendations to
achieve the desired viscosity for optimal flow and leveling.
Total appearance refers to the overall visual impression of a surface,
considering multiple factors such as colour, gloss, texture, uniformity,
defects, and imperfections.
The evaluation of a surface entails focusing on either the
reflected image of a light source or focusing directly on the
surface itself.
When examining the reflected image of a light source,
consider its ability to form clear images, particularly its
capacity to reflect objects. This reflection quality can range
from bright to dull, often referred to as gloss. Furthermore,
phenomena like the brightening of dark areas (haze) and
fluctuations in edge sharpness or clarity (DOI) may become
apparent when observing reflections along edges. (Fig. 2)
Focusing on the surface gives additional information about
the structure size and form, seeing these structures as a wavy
pattern of light and dark areas. This waviness is often called
orange peel or flow/leveling defects. (Fig. 3)
Both evaluation methods are individually weighted and
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APPLICATION TECHNIQUE
Issue: Incorrect spraying techniques, such as spraying too
close or too far from the surface, improper gun settings, or
inconsistent spraying patterns, can cause orange peel.
Solution: Train operators on proper spraying techniques,
including maintaining consistent gun distance, angle, and
speed, to achieve uniform coating application and minimise
orange peel.
Fig. 2-3
contribute to the total appearance perception. Appearance
should be defined with objective and measurable criteria to
guarantee reliable quality assurance. The total appearance
and the visibility of structures depend on the structure size,
the observing distance, and the image-forming quality.
Understanding and Troubleshooting Orange Peel
Orange peel refers to a textured surface defect characterised
by a rippled or dimpled appearance similar to the outer peel
of an orange. It occurs due to irregularities in the coating film
during application, drying, or curing processes.
It can be seen on high-gloss surfaces as a wavy pattern
of light and dark areas. Depending on the structure's slope,
the light is reflected in various directions (Fig. 5). Only the
elements reflecting the light in the direction of our eyes are
perceived as light areas. Visibility of structures is dependent
on the observing distance. The greater the distance, the
smaller objects will appear, and less detail will be visible.
Focus on reflected image
Focus on surface
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Canadian Finishing & Coatings Manufacturing - May/June '24

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