NOVO-GLOSS IQ GONIOPHOTOMETER
Application Notes- Powder Coating Smoothness Scale
RHOPOINT INSTRUMENTS LTD
Novo-Gloss IQ Application Notes
 Rhopoint Instruments
Beeching Road • Bexhill-on-Sea
East Sussex, UK, TN39 3LG
Phone +44 (0) 1424214291 • Fax +44 (0) 1424 730600
Table of Contents
Powder Coating Quality............................................................ 1
Assessing Coating Reflective Qualities .................................... 1
Instrumental Assessment of Coatings ...................................... 2
Glossmeter ............................................................................... 2
Distinctness of Image ............................................................... 3
Novo-Gloss IQ Goniophotometer ............................................. 4
Haze ........................................................................................ 5
RSPEC..................................................................................... 6
BYK Micro-Wave-Scan............................................................. 6
Powder Coating Quality
A high quality finish is becoming increasingly important for powder coated products.
In the past it was best known for its durability and low environmental impact, but
with improvements in formulation and application techniques, a powder coating
finish can now match or exceed the appearance quality of liquid paints.
Achieving the highest quality finish requires skilled operators, well formulated
coatings and optimum application equipment and conditions. This is particularly
true in for powder coatings as the process can be prone to orange peel, surface
texture and haze effects. These imperfections can dramatically reduce the visual
impact of finished products and are historically difficult to measure.
Assessing Coating Reflective Qualities
To aid designers, coating manufacturers and applicators the Powder Coating
Institute has developed a comparison tool to simulate all possible finishes that are
achievable using this technology.
This visual scale comprises ten powder coated panels, which have been graded from
1- high roughness & orange peel to 10- a very smooth glossy finish.
The set is often used to grade the quality of powder coated surfaces; the operator
simply judges which the panel is closest visually to the sample.
Unsurprisingly the results achieved by this method are highly subjective and prone
to errors due to sample area, lighting conditions and coating colour.
Panels 1,5 and 10 showing the reflection of a fluorescent desk lamp. Note the decreasing amounts of orange peel.
1
Instrumental Assessment of Coatings
To avoid the errors associated with operator judgment, sample type and
measurement conditions, it is preferable to use an instrument to measure such a
crucial parameter.
Three instruments were compared to determine their suitability for measuring
textured surfaces and in particular the powder coating smoothness scale, a set of
these panels were used in the assessment.
Glossmeter
The most commonly used instrument to measure coating reflective appearance
quality is a glossmeter. Glossmeters shine light at a surface and measure the
amount of reflection at the specular angle.
The standard for gloss measurement specifies three geometries for measuring high,
medium and low gloss levels. The most commonly used geometries used in powder
coatings are 20⁰ and 60⁰.
A Rhopoint Novo-Gloss Trio was used to assess the 10 panels, the average of 10
readings for each panel is shown below.
20⁰
60⁰
85⁰
1
53.1
95.3
79.8
2
3
86.4 92.2
101.9 101.5
94.8
92
4
98.8
99.1
92
5
93.6
98.6
95.2
6
96 .8
98.3
94.3
7
94.9
96.6
93.7
8
90
95.9
90.2
9
94.5
95.8
98.8
10
93.1
98.5
99.4
Despite large differences in appearance, the gloss readings for the panels are almost
identical. This is because the glossmeter can only measure the amount of reflected
light and is not sensitive to distortions which affect appearance quality.
Differences in gloss values are only apparent on panels 1 and 2 on where the orange
peel is reflecting light outside the detection range of the instrument resulting in a
lower 20⁰ gloss value.
Applications such as powder coatings which are highly likely to be affected by
orange peel and similar effects logically require a measurement method which more
successfully quantifies texture.
2
Distinctness of Image
D.O.I is a parameter which describes the visual distortion seen in a reflection of an
object viewed in a textured surface.
To understand this concept, the reflection of a specially designed test chart has
been viewed and photographed in each of the 10 powder coating smoothness
panels.
Panel 1
Panel 2
Panel 3
Panel 4
Panel 5
Panel 6
Panel 7
Panel 8
Panel 9
Panel 10
The photographs illustrate how the very high orange peel in panel one produces an
image with poor clarity, as the orange peel reduces; the distinctness of the image
improves.
Distinctness of image is quantified instrumentally by measuring the spread of a
beam of light after it has been reflected from a surface.
Surfaces which reflect an image perfectly without any distortion have a DOI value of
100, surfaces with no image clarity have a DOI of 0.
3
Novo-Gloss IQ Goniophotometer
The new Novo-Gloss IQ instrument from Rhopoint Instruments was used to
measure the reflective qualities of the panels at 20⁰.
Unlike a glossmeter which quantifies the amount of reflected light by using a single
sensor, the IQ uses an array of 256 micro-sensors that allow it to fingerprint how the
light is reflected, producing a goniphotometric profile around the specular angle.
Connecting the instrument to a PC the user can view Goniophotometric profiles,
comparing how the light is distributed for different surfaces.
The goniophotometric profiles for panels 1,5 and 10, manipulated in MS excel to show +/- 1⁰ from specular.
The instrument calculates GLOSS, HAZE, RSPEC and DISTINCTNESS OF IMAGE using
the angular tolerances specified in relevant international standards for these
measurements. The values shown are the average of 10 readings.
The instrument is operated with a single button push, all values are displayed on a
single screen.
4
Gloss20⁰
Log Hze
RSpec
DOI
1
46.0
488.2
9.6
31.3
2
3
91.4 102.6
104.0
2.2
20.6 32.8
44.4 60.2
4
98.8
0.0
41.4
74.2
5
96.5
0.0
54.3
89.1
6
99.2
0.0
61.5
92.8
7
97.0
0.0
70.3
96.9
8
93.5
0.0
71.9
98.1
9
94.7
0.0
79.0
98.9
10
92.4
0.0
79.9
99.5
The DOI perfectly shows the reduction in orange peel from panels 1 to 10, whilst
gloss values can be seen to equate to those measured using a conventional
instrument.
The DOI of the panels increases as the amount of texture reduces (orange peel).
Haze
Haze is a phenomenon where micro structures on the surface of the coating cause
reflected light to be slightly diffused around the specular angle.
Surfaces with haze exhibit a milky finish or a halo effect around the reflection of a
strong light source.
The effect of surface haze can be viewed on the reflected test panel pictures 1 and
2, the edges of these charts are blurred and slightly enlarged compared to the
panels without measured haze.
Powder coating is especially prone to haze effects; this can be due to stoving
problems, raw material incompatibilities or additive migration.
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RSPEC
RSPEC is the peak gloss value at the specular angle; surfaces with high DOI have a
sharper goniophotometric curve and hence have a higher RSPEC value.
BYK Micro-Wave-Scan
The BYK wave scan is used extensively to measure surface texture on automotive
finishes. A smaller version of this instrument the micro-wave-scan is used to assess
curved surfaces and small parts.
Its mode of operation is different to that of glossmeters and the Novo-Gloss IQ, the
instrument is rolled across the surface to be tested and a laser is employed to
measure the topography.
The information obtained is mathematically manipulated to provide a number of
indices that are used to assess quality and diagnose faults in paint application.
The instrument also produces DOI values, and these were used to assess the finish
of the PCI powder coat smoothness panels.
1
Du
Wa
Wb
Wc
Wd
LW
SW
OP
DOI
BOI
out
of
range
2
25.5
38.1
69.6
96.2
75
104
84.9
25
71.9
49.8
3
12.5
32.3
60.8
81.8
67.8
86.9
76.9
25
79.1
64.1
4
13.6
27.6
43.3
56.8
53.3
54
44
25
84.1
74.1
5
7.2
14.3
24.4
43.2
45.3
38.6
22.3
25
90.5
87.1
6
5.2
9.7
16.9
30.8
41.4
28.2
14.5
25.7
93
91.9
7
3.1
11.8
22.4
16.4
30.9
14.6
18.8
43
92.4
90.9
8
7.1
12.6
19.9
14.8
32.5
13.6
15.5
40.1
91.6
89.4
9
6.1
14.5
19.7
12.3
16.1
6
14.4
62.3
91.8
89.6
10
5.8
16.1
27.3
8.5
11
3.2
21.9
71.2
90.8
87.6
Data obtained for the PCI set using a BYK micro gloss (average of 5 readings). The instrument could not measure panel one.
6
A chart showing two DOI indices calculated for the PCI set using the BYK micro-wave scan. BOI is BYK DOI.
The data provided by the instrument is more detailed than that provided by the
Novo-Gloss IQ and may contain information on the size and frequency of the
structures that are the causing orange peel effects.
The DOI indices used in the Micro-Wave-Scan do not show the improvement in
surface finish after panel 6 in the PCI scale.
Samples with a high degree of orange peel such as panel one cannot be measured
with this instrument.
Conclusions
Many coating technologies can be affected by surface texturing caused by poor
formulation, application technique, and substrate quality or application conditions.
Visual assessment of these defects is subjective and prone to error introduced by
lighting conditions and the size, colour and orientation of the surface being
measured.
The tradition glossmeter is not able to measure orange peel and other types of
surface texture.
The DOI values obtained by the BYK micro-wave-scan do not alone describe the
orange peel affects seen on a PCI powder coating scale and it cannot measure the
most textured surfaces.
7
More detailed data about the size and frequency of textures is available from the
wavescan but the complexity of interpreting such information and costs of
ownership may limit the instruments use to research and the automotive industry.
The Rhopoint IQ is backwards compatible with measurements taken using a
traditional glossmeter.
It also measures DOI which perfectly described the orange peel effects viewed on
the PCI powder coating smoothness panels.
The instrument can measure samples of any size and the measurements are
independent of colour.
The Haze information detailed by the instrument is extremely useful in the powder
coating industry as well as most other coating applications.
The instrument is simple to use and the data easy to understand and set
specifications around.
The cost of this instrument makes it suitable as QA or Research tool.
Tony Burrows
Rhopoint Instruments Ltd
Oct 2009
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