Pigmentos de Efecto –
Características y problemática
Universidad de Alicante, 5 de julio de 2006
Dpto. Interuniversitario de Óptica
Werner Rudolf Cramer
info@wrcramer.de
Manipulation of light
• The sun - our main light source - sends rays
in all directions. Under 1% of them reach our
blue planet.
• Some rays pass the atmosphere and are
visible for us.
• Altogether, these rays create a white
impression in our eye and brain.
• If their are manipulated, they create colors.
• The kind of manipulation can be different:
absorption and scattering, reflection and
refraction
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Different Pigments
• Manipulation and impact of light rays by:
- absorbing pigments (pigmentum = color):
- aluminum pigments,
- and interference pigments.
• These pigments are used as stand-alones or
in mixtures with others.
• Interference pigments are very common in
the industrial and automotive industries.
• Interference pigments may be classified by
their structure or the method employed for
their manufacture.
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Absorbing pigments
Scattering in all directions: same color
100
R [%]
80
Yellow
60
40
20
0
400 nm
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500 nm
600 nm
700 nm
4
Aluminium pigments
Reflection in favored directions:
Angle of incident = angle of reflection
160
Aluminum
L*
120
80
40
0
15
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20
25
45
70
[°]
5
Interference pigments
Selective reflection/interference:
assigned wavelengths are preferred
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Interference pigments
Playing with the undercoat:
Combination of reflection colors and
transmission colors.
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Interference pigments: overview
• Iriodin/Afflair Merck
natural mica coated with high refractive metal oxides
like TiO2 or Fe2O3.
• Xirallic Merck
Al2O3-platelets coated with high refractive metal
oxides.
• Colorstream Merck
SiO2-platelets coated with high refractive metal
oxides.
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Interference pigments: overview
• Variocrom BASF
Optical Variable Pigments (OVP)
chemical vapor deposition
• ChromaFlair Flex Products
5-layers with opaque reflector, dielectrical and semitransparent layers.
• SpectraFlair Flex Products
microstructure surface and opaque reflector layer.
• Helicone Wacker Chemie
Liquid Crystals Polymers (LCP)
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Reflection and transmission
reflection
15
a*
10
TiO2
5
mica
0
15
-5
Iriodin Pearlred
-10
20
25
30
35
40
45
50
55
60
65
aspecular [°]/45° illumination
Iriodin Pearlgreen 9235
-15
-20
-25
-30
transmission
Interference of white light leads to a reflection color
and a complementary transmission color.
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Ray tracing at mica pigment
normal
I0
illumination
mica
R
1
2
reflection
D
a
δ = n(AB + BC) − AD
C
A
TiO2-layer
R
d
β
δ = 2d n 2 − sin 2 α
B
Δ = 2d n 2 − s i n 2 α +
λ
2
transmission
Resulting color depends upon
• thickness of TiO2-layer,
• refractive index,
• angle of illumination.
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Impact of angle of illumination
The method of application can influence the color impression:
Top: basecoat system with two spraying layers
Below: Same system with additional effect layer
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Impact of refractive index
400
R [%]
9215/9505
9215: 25°/140°
9215: 75°/90°
300
9505: 25°/140°
9505: 75°/90°
Δ = 2d n 2 − sin 2 α +
200
100
0
400 nm
500 nm
600 nm
wavelength [λ]
700 nm
Deposition of materials with different indices of refraction on
same platelets leads to different colors.
Coating materials: 9215 titanium oxide, 9505 iron oxide
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λ
2
Impact of thickness
Color shift with increasing thickness
R [%]
λ
Δ = 2d n − s i n α +
2
2
350
2
300
9205
250
9215
200
9219
150
9235
100
9225
50
0
330nm
430nm
530nm
630nm
wavelength [λ]
The resulting color (reflection) shifts to longer wavelength with
increasing thickness of the layer.
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Impact of angle of illumination
600
Color shift with flatter angle of illumination
R [%]
500
400
Δ = 2d n 2 − sin 2 α +
300
200
25°/140° 70°/95°
100
0
400nm
500nm
600nm
700nm
wavelength [λ]
The resulting color (reflection) shifts to shorter wavelength if
the angle of illumination becomes flatter.
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λ
2
Characterizating the pigments
9215 interference
35
9235 interference
9215 aspecular
350
30
R [%]
9235 aspecular
25°/140°
25
300
20
250
25°/140°
45°/120°
75°/90°
15
200
10
150
5
100
25°/140°
0
-50
-40
-30
-20
-10
0
10
-a*
20
30
40
50
50
-5
-10
-b*
0
400 nm
Iriodin 9235
500 nm
600 nm
700 nm
-15
Interference pigments are characterized by the „interference line“ and
the „aspecular line“:
Interference line: varied illumination angle, constant aspecular angle
Aspecular line: constant illumination angle, varied aspecular angles
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Observing the interference
To watch the interference
shift you have to move the
panel parallel up and down.
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Mixing behavior
Subtractive mixing:
Absorbing pigments
Additive mixing:
Interference pigments
Absorbing pigments: Yellow + Blue = Green
Interference pigments: Yellow + Blue = White
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Mixing behavior
100
100
Subtractive mixing of
Red and Blue 1:1
R [%]
Subtractive mixing of
Yellow and Blue 1:1
R [%]
80
80
60
60
40
40
20
20
0
400 nm
0
500 nm
600 nm
wavelength λ
700 nm
150
R [%]
400 nm
500 nm
600 nm
wavelength λ
700 nm
wavelength λ
700 nm
200
Additive mixing of
Red and Blue 1:1
R [%]
Additive mixing of
Yellow and Blue 1:1
150
100
100
50
50
0
400 nm
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0
500 nm
600 nm
wavelength λ
700 nm
400 nm
500 nm
600 nm
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Two components of colors
Color system
Interference pigments
Absorption pigments
illumination 75°
illumination 45°
illumination 25°
20°
30°
aspecular
<180°
Mixtures of interference pigments and absorbing
pigments lead to different „fields of interest“.
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Two components of colors
30
40
a* - data
a*
b* - data
b*
30
20
20
10
10
0
15
20
25
30
35
40
45
50
60
65
aspecular [°]/45° illumination
-10
-20
55
0
15
20
25
30
35
40
45
50
-10
Xirallic T60-24 SW Stellar Green
-20
Iriodin Pearlgreen 9235
-30
-30
55
60
65
aspecular [°]/45° illumination
Xirallic Galaxy Blue SW
Iriodin Pearlblue 9225
-40
-40
-50
-50
-60
Transparent pigments on white background: Color
change at aspecular angles between 20° and 30°.
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Conclusions
• Interference pigments ensure for selctive
reflection of the white light (interference).
• Their resulting colors depend on influences
like:
- angle of illumination,
- angle of observing,
- aspecular angle (difference between
specular angle and oberserving angle),
- method of application etc.
• In color systems, their influence on the
color is up to 25° aspecular.
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El fin. Muchas gracias!
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