Special Effect Pigments
Edward Bartholomey, Kobo Products Inc , discusses the use of colour travel pigments
within the cosmetic industry
Colour travel pigments for
decorative cosmetics
pecial effect pigmenlS are used in the cosmetic industry to provide coIotx, iridescence, Ustre and glitter to a
v.ide rnnge of cosme1ic: and personal care products.
such as t:je shadoYis, fipsticks. fI'l3SC3(3S, nail enamel, hair
gels. skin lotions, shampoos and body washes. They are used
together in f()(ffiUlations with blends of inorganic and organic
pigments, as well as dyes. Their properties usually enhance
the products fOf the consumer in a variety of forms: loose (J(
pressed powder(godel), stick. gel and rlqUid.lhiS visual effect
is quite striking and apparent when products con~ these
eHect pigmentS are then applied to the e)eS, lips, nails, hair
and skirt
The colour eRects of these pigments are very dependent
upon the primary subslrate. which has specific properties,
platelet thickness. refractive index, particle size and chemical
composition. Effect pigments built upon small pMide siles
create a satin Of siI<y sheen, ...mile Iargef Size particles I\3IIe a
fT'IOfe gtitter-like appeaf3I"ICe. The intermediate size is generally
the most brilliant yade and approaches the lustre of natur3I
pearl essence, guanine, with just a touch of spal1de. The particle size ranges can be wide and the effects vary.
The special effect pigment categories are,
1. Pe¥lescent pigments 'ftiIh 0( without an absorp6on pigment
2. Interieretlce pigments with Of without an absofpOOn pigment. inckJding the next generation - ooIou" travel type.
3. Metallic pigments (silver, aluminium, copper and bronze).
Our discussion will focus upon the second category of
interference/colour tr3"IIel pigments.
S
FIg 1. Colour travel of incoming ligflt ~
reflection from • different angle of the
substr31.e of • multHayer pigmenl yield
diff~nl
colOl.lr effecls. (CoIOIJr
shih/IIoJI). The Yisufl appearance of !he
surface depends upon the geometric configurntion of Ihe light SOlHU and the
obmver relative to the surface
Inco min g light
COLOUR TRAVEl PIGMENTS
Pearls defined as having ·colour tr3ve1' are the next genera·
tion of interference multi·layered pigments (figure 1). They
generally have IT"IOf"e briniant colour and effect than stan·
dard interference pigments based on titanated mica. The
colours can shift from violet to orange or green to red, etc,
depending upon the view angle. The intensity of interfer·
ence is dependent upon the refractive Index difference
between layers and the rumber of the layers present in the
composite pigJnetIt Intensity, brilliance and traospareney usually cifferen6ate colour travel pearls from their parent. interiereoce pigments. The T10 2 ia)w and the newer Si0 2 iayers, are
designed to provide more pronounced colour upon synthetic
substrates that are more even and cleaner than natural mica.
Additional layers with different refr3ctive indices (high RI and
low Rl) increase the path of the inc:ofnWlg light and the 0Yef3II
intensity 01 the interfeftfICe coIox.
The intensity of the coIox effect is coruroled by optics and
is generally a result of a combination of reflected and transmit·
ted light Incident light is partially transmitted and partially
rellected between $UCCeSsive layers. Difference in refr3ctive
indices between the multiple layers. combined with transmitted and reflected light. leads to a colour" appearanoe thai varies
with the angle of view. 'Nhen ~t beams are split and recombined, they can undergo interference.
Thin film interference occurs when light reflected from the
two surfaces of a thin film interfere. Some wavelengths of light
are intensified, others cancelled out The light reaches the eye
of the viewer al a 0Main angle. As that angle changes, so does
the hue or interplay of colours rue to rtght interference. The
transmitIed coIox is the complemetlt of the reflected coku.
Lig ht reaches eye
In coming light
reaches eye
NATURAl ORIGINS OF EFFECTS
These interference effects originated In the natural world
and are studied in the fields of physics (optics), mineralogy,
crystallography and specialised fields of biology. Ore minerals
frequently have Iridescerll films because of a thin ia)w of alteration on the st.riaoe.. SheIs from the sea have softer and more
subdued interference coku rue to multiple·1ayer interference. Scattering and superpositioo of nlXJ"letOU$ wavelengths
soften the colour.
Mica, titanium dioxide (n02). iron oxide, silica. bismuth
oxychlofide (bismoclite) and borosilicate are naturally
Author:
Edward Bartholomey. Principat Research $cientisl, K:obo Products Inc, 3474 South Plainfo.eld, New Jersey, USA.
Tel: +1 908 757 0033; www.koboproduC\$.com
22 ppr"j - December 2014 www.coatinQsQroup.com
.e'jtJ§1'Bii'iTfl'i'e'U[$]"Q
ments with regard to precipitation. though they can also be
coated directly with metals. such as silver.
Fig 2. Good coverage at tile
substrate edge of borosilicate
glass Hake
occurring substances, present in minerals. Novel engineering of these materials, whether synthetic or natural. into
cooted platelets, allows us to simulate, optimise and commercially manufacture what occurs naturally in minerals.
plants and animals.
Mum·LAYERED PiGMENTS - MICA
The most commonly recognised interference pigment in
this category is Ti0 2·coated natural mica. This pearlescent
material for cosmetics dates back to 1967. Ti0 2 is precipitated on to the natural mica platelet as a thin film and
interference colours result when a certain thickness of the
coating is achieved. As the thickness of the coating is
titrated and increases (60·160nm) on both sides of the
substrate. the interference colour changes gold to red and
then blue to green. Average particle Sizes generally range
from 10· 60IJm (figure 2).
Colour travel pigments build upon interferellGe pigment
technology and may also contain iron oxides or other colours
in tandem with the relatively thick Ti0 2 coating on the substrate and in combination with other novel layers.
MULTI-LAYERED PlGMENTS -
Comparison - Substrates of
colour travel pigments
Substrates:
SYNTHEnC SUBSTRATES
More recent materials introduced to the cosmetic industry are
based upon borosilicate glass or synthetic mk:a. The borosili·
cate, whiCh is a planar platelet, consists of silicon dioJCide and
oxides ofboran. calcium. sodium or aluminium, etc. Pigments,
based upon borosilk:ate, are smoother and exhibit a higher
cJewee of transparency, while the substrate is also thicker.
They differ from the natural mica·based pigments in that the
composition can be controlled. Because of the controlled
geometry of the pigment. coatings can have bener coverage
(figure 2) and provide a multi·coIoured sparkle effect. The
process for the Ti0 2 coating is similar to the mica·based pig.
Platelet thickness (nm),
Particle size range (jJm)
Natural mica pigments 300·600nm
Refractive index
(substrate)
1.58
2·'4~m
Borosmcate pigments 1000·1 200nm
1.50 - 1.58
00. All 0). B20 1•
Si02, NaO
1.55 -1 .62
!<M&AfSil 0'0 Fl
1.76
All 0]
20·'50~m
Synthetic
300nm :
Auorphlogopitt
Aluminium oxide
30·120~m
300·500nm:
Primary
Chemical
Composition
(substrate)
IW I(Si]AI01O> (OH)1
1.77
5·40~m
Silicon d'oxide
SO·400nm or up
to 1000nm
5·150~m
1.42-1.47
Si01
Because the glass substrate is smooth and planar there is
less scanering than with natural mica and greater colour depth
and gloss may be achieved. The smoother the surface, the
greater the intensity of the lustre. Moonshine glass flake pig.
ments are commercial examples.
Synthetic mica or Huorophlogopite is more similar to mk:a
but offers greater brilliance since the manufacturing condi·
tions can be controlled.
The series of Kobopearl Perpetual pigments is an example
in the mar1retplace.
Silicon dioxide can also be utilised as a thin film or coating
on to the substrate providing additional vibrancy of colour
since it has a low refractive index. The Si0 2 can encapsulate
the substrate and protect it while providing a better surlace
for the Ti0 2 1ayer. Bener lustre is achieved as the difference
in the refractive indices between akemate layers, such as the
TiOzlayer and the next layer, Si0 2 , becomes larger. 5102 can
also be used in the same manner as a coating layer for
borosilicate or alumina and other substrates. The stratum
corneum upon which the pear1s may be applied. depending
upon the product form, has a refractive index of about 1.50·
1.55 closer to the borosilicate.
Silica flakes are synthetic and manufactured to a much thin·
ner platelet than the above· mentioned piwnents. They have a
lower refractive index than mica and, therefore, lead to a high·
er degree of interference effects. Most silica·based pigments
use the rutile crystalline form ofTi0 2 for coatings.
Colour travel pigments based upon alumina have a
sparkling effect and lustre. Alumina has a higher refractive
index than the other substrates and is. therefore. whiter.
Pigments using polymer technology consisting of poIysilox·
ane liquid crystals are more transparent but also show colour
flop The aspect ratio, which is expressed as the ratio of the
·partlcle major diameter/average thickness·, is very useful in
describing the overall dimension of colour travel pigments.
FORMULATION
Colour travel pigments may be used in concentrations as low
as 0.10% and up to 50% or greater in cosmetic fonnula·
tions. They are very versatile and can be used in many different mediums, such as pressed or loose powders, suspensions. emulsions and anhydrous vehicles. In suspensions,
which is generally a more transparent medium. such as nail
enamels or clear gels, smaller amounts of the pigments may
be used, such as 0.10·10.00%. In the USA, there is a limit
on the size of mica·based pigments for cosmetics used in
the eye area. This size limit is currently 'S149jJm (100% of
the panicles through a 100 mesh screen).
Generally, colcor travel pigments will perfonn much
bener in transparent liquid media or in powders where
transparent fillers are selected as the base. One must be
careful formulating since too high a level of opaque pigment
in the product will diminish the special effects. In more
opaque mediums or in those applications intended to cre·
ate a more dramatic effect, the concentration should be
hig1ler, such as in pressed powders. these pigments can be
used up to 50% or more. AVOid mixing complementary
interference pigments to avoid cancelling out the intensity
of their colour effect (eg red and green).
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