Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 94/22966 PCT/CA94/00192
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TITLE OF THE INVENTION
Light-modifying composition.
FIELD OF THE INVENTION
The invention relates to surface coatings
such as paints. In particular, the invention, in its
simplest form, relates to a composition comprising a
colour pigment component and a light conditioning
component characterized by being a transducing material
having the ability to absorb light and reflect at least
part of the light absorbed, thereby modifying the light
in the coating resulting from the application of the
composition. Such pigment spacing component includes
any material having the ability to partially absorb
light. Preferred are neutral grey pigments in the form
of grey powders having a minimal colour producing
effect. The pigments can be in the form of ground grey
powders such as powders taken from granite, feldspar,
quartz or limestone or in the form of spherical
metallic particles such as metallic zinc.
BACKGROUND OF THE INVENTION
The coating industry is one of considerable
importance in the industrialized world. It has
ramifications extending in various technological areas.
Hence, paints have been designed for the protection and
decoration of masonry coatings, ferrous metals, non-
ferrous metals, wood substrates and the like. Also,
paints have been designed to provide special properties
to the surface on which they are applied. Examples
include the pigmentation of anti-foulants,
electrocoatings, flame resistant and intumescent
paints, heat-resistant paints and fluorescent paints.
Pigments have also been used to prepare inks and to
colour paper goods. Other examples of use of coatings
include the pigmentation of rubbers, plastics,
cosmetics, magnetic tapes, food, textiles, adhesives
and ceramics.
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With current technology, almost any type of
coating composition prepared comprises binders,
pigments and extenders which are combined to obtain the
desired result. The most commonly used pigment is
titanium dioxide. Titanium dioxide is insoluble in all
liquids, with the exception of concentrated sulphuric
acid and hydrofluoric acid. Titanium dioxide molecules
produce a highly reflective white powder. The paint
industry has by far the most widely diversified
manufacturing requirements because each basic paint
type such as flat, semi-gloss and enamel require
different kinds and amounts of treatments using
titanium dioxide. Still, titanium dioxide is used as
a pigment by a large number of major industries such as
paints, paper, plastics, rubbers, floor coverings,
printing inks, ceramics, coated fabrics and roofing
granules. All these industries have their specific
requirements but the versatility of titanium dioxide
has allowed adaptation of its use for various purposes.
Titanium dioxide produces the effect of
whiteness on the human eye because it reflects all
wavelengths of visible light to the same degree. Under
red light, it appears red; under blue light, blue and
under green light, green. Only under illumination
containing all of the wavelengths of visible light does
titanium dioxide appear white. This property coupled
with the extremely high stability of the compound has
led to its widespread use in the coating industry.
As a general rule, shades of colour are
obtained by mixing colour pigments with black and white
pigments. At the microscopic level, the white titanium
dioxide pigments are very bright and their ref lectivity
is countered by the use of black pigments. This is
generally how colours are made. Extenders in the form
of ground powders having a particle size of usually 1
to 10 microns as well as binders which can be selected
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from a wide array of chemicals can be used to hold the
pigments together to form an applicable composition.
However, the extreme stability of titanium
dioxide, although an advantage from a technological
point of view, is a serious drawback from an
environmental point of view because any release of such
a chemical in the environment can potentially create
serious environmental hazards. The production of
titanium dioxide causes the creation of massive amounts
of highly toxic sulphur derivative by-products which
are often released in the environment.
Beyond the environmental considerations is
the fact that the use of strongly reflective pigments
such as titanium dioxide in the production of colours
can lead to problems when attempting to produce very
specific colours such as those found in nature. In
fact, the brightness of titanium dioxide makes it
almost impossible to produce something other than
colours of high reflectivity.
SUMMARY OF THE INVENTION
As embodied and broadly described herein the
invention provides a light-modifying composition
comprising a colour pigment and a grey pigment
characterized by having the ability to absorb light and
reflect at least part of the light absorbed. The grey
pigment acts to substantially evenly reduce the amount
of light flux within the composition. The term "grey
pigment", when used herein, is intended to designate
any material of a grey appearance having essentially no
chroma. A wide variety of grey pigments can be used in
the context of the present invention. The important
aspect is the fact that the grey pigment must absorb
light and reflect only a certain percentage of it.
Preferred grey pigments to be used are neutral grey but
the use of grey having between 5 and 90% reflectance
can be contemplated. Examples of grey pigments that
can be used include ground powders such as granite,
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feldspar, quartz and limestone powders. Also within
the scope of the present invention is a coating base
composition comprising a grey pigment dispersed in a
solvent, as will be discussed in detail later.
Preferably, the light-modifying compositions
under the present inventive concept are free or
substantially free of white and black pigments,
although the presence of white or near white fillers is
not excluded. The absence of white and black pigments
allows the colour pigment to be more predominant and to
exist in a more natural light environment. Until the
present, the field of coatings has been based upon the
preparation of compositions including titanium dioxide,
binders and extenders. The light-modifying composition
of the present invention represents a departure from
previous coating technology by allowing to eliminate or
at least reduce the amount of traditional white and
black pigments in the composition. By doing so, the
required amount of colour pigment can be substantially
reduced because the pigment particles are not
overshadowed by either strongly reflecting white or
strongly absorbing black pigment particles. This is
possibly accomplished by providing a scale of light
flux which results from the use of materials which
absorb only a portion of the light in the coating film
and provides a more even light environment for the
colour pigments.
It should be appreciated, however, that the
inclusion of comparatively small amounts of white
and/or black pigments in the light modifying
composition broadly defined above is still within the
spirit of the invention.
In one of its preferred aspects, the present
invention makes use of particulate grey pigments having
a particle size of 40 ~m or less. However, any
transducing material having the ability to produce
gradual light flux reduction in a film or to convert
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light into another form of non-visible energy, such as
osmium, can be used.
In,the past, in order to prepare coatings in
a relatively economical manner, the use of white
fillers was predominant. In fact, white fillers were
the only extenders used to space pigment particles in
a coating. Unfortunately, the use of white fillers was
restricted to lighter tints available for any given
pigment.
In order to achieve darker colours, it is
often necessary to tone the composition with a black
pigment. The drawback to this approach is that the
resulting colour emitted by the composition loses
clarity and intensity as a result of an uneven loss in
light flux caused by the absorption of light by the
black pigment and by the contrast created by the white
pigment which maintains a high light contrast ratio in
the film. The only solution up to now was to add
additional costly pigment to make up for the loss in
intensity.
With the present invention, the spacing of
pigments in the darker tonal ranges is allowed without
the loss of intensity experienced with the use of black
pigments. The use of neutral grey pigments or almost
neutral grey pigments of various reflectance, generally
from 5 to 90% reflectance, but not restricted
exclusively to this range, and visually identified as
light grey, medium grey, dark grey etc., and mixtures
thereof, reduces the amount of light flux in the film
body in a more or less even fashion across the visible
spectrum. This in effect creates a more even lighting
effect in the film and by the reduction in contrast
allows the pigment particles to become brighter in the
lowering reflective grey surround.
When a neutral grey pigment or a sequence of
neutral grey pigment is used, there is no sudden loss
of flux since the grey still reflects light and the
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resulting flux density is reduced much more gradually,
allowing the colour pigment particles to give off
variable light flux. This situation cannot occur when
either black and white pigments or a black pigment and
a white filler are used because the use of mixed black
and white pigments results in an uneven distribution of
light. With the use of a grey pigment, light is
distributed more evenly in the coating and this allows
one to achieve much finer nuances in colour tinting.
The even decrease in light reflection experienced when
using grey pigments, as opposed to complete light
reflection and absorption experienced with black and
white pigments, provides a greater range of useful
light flux intensities which in turn provides a
spectrum of energies available for the colour pigment
particles. The resulting colour is viewed as more
intense since the intensity would be of those
wavelengths reflected by the colour pigments.
It should also be noted that the grey
particles can reflect light without altering
significantly the colour of the film of the composition
but only the intensity or flux of light from the film.
Still, the resulting colour composition has some grey
in its body. Without wishing to be bound by any
theory, because of the visibility of the grey pigment,
as the concentration of grey pigment particles
increases, it becomes more visually apparent that there
is grey in the composition. A more efficient grey
allows a reduction in volume of grey pigment in the
composition to achieve the same effect, thereby losing
the grey appearance of the resulting colour. Achieving
a more efficient grey can be accomplished by varying
particle size, particle shape and index of refraction
or by converting light into another form of energy. In
using the composition of the present invention, there
is observed an interaction between the light reduction
and the spacing effect of the grey pigments on the
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WO 94/22966 PCT/CA94/00192
colour pigment, thereby producing the two mechanisms
needed to achieve, colour ranges of marked freshness and
intensity. This in fact allows for colours that exist
in nature to be produced, which is not possible when
using large amounts of black and white fillers or white
pigments and white fillers.
Most preferably, the light-modifying
composition of the present invention makes use of a
binder to bind the grey and colour pigments together.
However, in some applications such as the preparation
of cosmetics, the use of a binder is not necessary.
In one specific embodiment the grey pigments
and the colour pigments are in physical admixture,
hence the grey pigments constitute an agency to space
substantially evenly the colour pigments. In a
variant, the grey pigments and the colour pigments are
physically separated from one another. An example is
a paint system including a undercoat that contains the
grey pigments and an upper coat with the colour
pigments. Most preferably, the upper coat is a so
called "clear coat" which is non-opaque and allows at
least part of the light to reach the undercoat.
As embodied and broadly described herein, the
invention provides a light conditioning composition
comprising a grey pigments suspended in solvent, said
grey pigments having the ability to absorb light and
reflect at least part of the light absorbed, said light
modifying composition being capable of coating a
surface to form an undercoat of a layer containing
colour pigment.
As embodied and broadly described herein, the
invention also provides a light modifying composition,
said composition including:
- a first light conditioning composition
comprising grey pigments suspended in solvent, said
grey pigment having the ability to absorb light and
reflect at least part of the light absorbed; and
WO 94122966 ~ ~ ~ ~ ~ PCT/CA94100192
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- a second light conditioning composition
containing colour pigments, said second light
conditioning composition being capable of coating a
surface to form a non-opaque coloured layer, said first
light conditioning composition being capable of coating
a surface to form an undercoat for said non-opaque
coloured layer.
The present invention will be more readily
illustrated by referring to the following description.
DETAILED DESCRIPTION OF THE INVENTION
In its broadest terms, the present invention
provides a new approach to the preparation of colour
coatings. This new approach is based on the reduction
and preferably the elimination of white and black
pigments commonly used in the preparation of colour
coatings.
White and black pigments represent complete
opposites in terms of reflectivity and light
absorption. They have been used to tone colour when
attempting to reach the desired shade.
With the present invention, this approach has
been discarded and a new concept is set forth by which
white and black pigments are replaced by grey pigments
having a reflective index which is lower than the
reflective index of white pigments and higher than the
reflective index of black pigments. This range of
possible reflective indices for the grey pigments is
referred to herein as "middle reflectivity". The
middle reflectivity of the grey pigments used in the
context of the present invention eliminates the
excessive brightness caused by the standard titanium
dioxide pigments as well as the reduced number of
internal reflections caused by black pigments. In
other words, it has been demonstrated that the colours
achieved by combining white and black pigments and a
colour pigment can be enhanced when replacing the white
and black pigments with a grey pigment. For example,
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WO 94/22966 PCT/CA94100192
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when identical grey colours are prepared using either
black and white pigments Qr grey pigments, the same
addition of colour pigments gives a final coating
having very different luminosities. The initial
appearances of the grey bases are identical, but the
addition of the same quantities of colour pigments
provides much more intense colours in the base
containing the grey pigment. This, as mentioned
previously, is likely to be achieved because of a more
even distribution of the internal reflections occurring
in the coating.
The composition of the present invention
comprises a limited number of components, with the grey
pigment being the central component allowing the
achievement of the desired range of colours. When used
in the context of the present invention, the term "grey
pigment" is also intended to designate any pigment
having a middle reflectivity. Preferred materials
which can be used as grey pigments will be described in
further details but it is to be appreciated that the
light modifying. compositions of the present invention
are not restricted to this type of pigment. Similarly,
a wide variety of binders and colour pigments can be
used in the light-modifying composition of the present
invention and the present disclosure is not to be
interpreted as being limited to those colour pigments
and binders described herein.
Grey pigment
As mentioned previously, the grey pigment is
the central component of the light-modifying
composition falling within the scope of the present
invention. The grey pigment acts as a spacer for
colour pigments providing a more even light
distribution throughout the coating. In this regard,
the grey pigment material controls both value and
chroma of the resulting coating. It acts by reducing
the amount of light reflected in the coating and
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WO 94122966 PCTICA94/00192
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spacing the colour pigments. These are the
characteristic benefits encountered when using grey
pigments.
In a preferred embodiment of the present
invention, the grey pigment is either in the form of
ground carbonate, silicate, sulfate and phosphate powders
taken from materials such as granite, feldspar, quartz,
limestone (CaC03), dolomite limestone, kaolin, talc, mica
and Fuller's earth or in the form of spherical metallic
zinc powder particles. A number of parameters can be
adjusted to provide the desired reflectance in this grey
pigment. Firstly, the particle size of the ground powder
can have a substantial influence on the tone of the
coating. Particle sizes ranging from 1 to 40 micrometers
are usually preferred, with 1 to 20 micrometers being
most preferred. Also, the reflectance of the specific
grey pigments used has an influence on the final colour.
For example, ground calcium carbonate powder has a
reflectance of approximately 30% but it can be combined
with other grey powders of lower or higher reflectance to
obtain the desired colour. The reflectance can range
between 5 and 90% but the most useful materials appear to
be the neutral grey having a medium range reflectance
ranging between 30 and 80%.
The amount of grey pigment that is used in the
composition of the present invention is usually
substantial. This is the case because the middle
reflectance of the grey pigments allows for use of very
small amounts of colour pigments. In most applications,
a binder will also form part of the composition but the
percentage of binder used is relatively low.
Consequently, the percentage of grey pigment used usually
varies between 10 and 70% by weight, depending on which
application is contemplated. Preferred percentages range
between 20 and 50% by weight. However, much lower
percentages can be used if the grey pigment is in the
form of zinc powder.
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Colour pigments
Various colour pigments can be used in the
light-modifying composition of the present invention.
The colour pigment can be either inorganic or organic,
depending on the contemplated application.
In the case of inorganic pigments, oxides
such as natural or synthetic coloured iron oxides or
chromium oxides can be used. The use of chromate such
as lead chromate and chrome green pigments is also
possible. Cadmium and ferriferrocyanide pigments as
well as other inorganic colour pigments such as
ultramarine pigments, mercuric sulfide and synthetic
inorganic complexes can also be used to form the
composition of the present invention.
In the case of organic colour pigments, the
possibilities are also very wide. One can refer to the
use of nitroso, nitromonoazo, diazo and disazo
pigments. Basic dye pigments, alkali blues, peacock
blue lake, phloxine, quinacridones, lake of acid
yellow, carbazole dioxazine violet, alizarine lake, vat
pigments, phthalocyanine and tetrachloroisoindolinone
can also be used in the context of the present
invention.
Also, metallic pigments such as aluminum
flakes, copper and copper alloy flake powders, zinc
pigments and stainless steel flake pigments can be used
with the grey powder pigment described above. One can
also contemplate the use of metal protective pigments,
nacreous pigments, luminescent pigments, functional
pigments as well as food, drug and cosmetic colours.
The percentage of colour pigment used is not
a critical aspect of the invention. It can be varied
through a wide range of concentrations and is a
function of the colour which one wishes to obtain.
Preferably, the percentage of colour pigment varies
between 0.25 and 25% by weight. In situations where
very intense colours are desired, the percentage of
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colour pigment can exceed this range. Similarly, in
situations where very pale colours are desired, the
percentage of colour pigment can be less than this
range. These exceptions fall within the scope of the
present invention. Also, it would appear preferable
that the pigment used in the composition exhibits a
reflectance which is higher than the reflectance of the
grey pigment particles.
Binders
In certain applications of the composition of
the present invention, it might be necessary to use a
binder component to form an applicable composition. A
wide variety of binders such as oils, varnishes, latex
emulsions, styrene, styrene butadiene, polyvinyl
acetate, acrylic, acrylic-styrene, acrylic polyvinyl
acetate, polyurethanes and the like can be used. These
are known to the person skilled in the art. It is to
be appreciated however that binders other than those
referred to above can be efficiently employed.
The percentage of binder used in the context
of the present invention can vary from 0% to 50% by
weight. In some applications relating to the cosmetic
industry, for example, the use of a binder can
sometimes be discarded.
Additives
A wide variety of additives can be
incorporated into the composition of the present
invention to impart different properties to the final
product depending on its final use. Such additives
include dispersants, surfactants, defoamers, thickness
and the like. The choice and amount of additive is
dictated by the end use and is within the knowledge of
the person skilled in the art.
Preparation of the light-modifying composition of the
present invention
Once a pigment binder of appropriate particle
size and shape has been obtained, the composition of
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the present invention is typically prepared by first
producing a,slurry of the grey pigment, essentially to
disperse the grey pigment in the desired solvent.
Typically, the grey pigment particles are mixed with an
appropriate solvent, for example water, oils or a long
chain alcohol such as propylene glycol and ethylene
glycol, together with suitable additives required to
produce and maintain a uniform slurry such as wetting
agents, dispersants, surfactants, defoamers, thickeners
and the like, the use of which is within the knowledge
of the skilled artisan. The mixing time can vary
depending on the additives used but should be
sufficient to adequately disperse the grey pigment
particles within the slurry. A typical mixing time
using a high speed disperser varies from 10 to 30
minutes.
To the resulting grey pigment slurry is then
added a binder and the additives required to achieve
the desired characteristics for the final coating. At
this stage of the process, additives such as thickness,
preservatives, defoamers, buffers to maintain the
desired pH, coalescence and the like can be used.
Again, the choice of binders and additives is within
the knowledge of the person skilled in the art.
After the binder has been incorporated into
the slurry, the colour pigment is added in sufficient
amounts to yield the desired colour. The amount and
nature of the pigment can be varied depending on the
end result desired. Alternatively, the grey and colour
pigments can be dispersed together in the initial
slurry mixture once the colour pigment requirements to
achieve the desired result are known. In some
instances, it may even be advisable to fix the colour
pigments to the grey pigment particles through
preliminary mixing with the appropriate chemicals which
are within the knowledge of the skilled artisan. This
CA 02137080 2004-05-18
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can be accomplished by using a fixing process similar
to the process used for fixing dyes.
It is to be noted that the method described
above is to be viewed as a general guide for the
preparation of coloured coatings using grey pigments.
Modifications are possible depending on the end use and
fall within the scope of the invention.
Aaalication of the composition of the present invention
for the.preparation of various coatings
The composition of the present invention can
be used in numerous applications including the
preparation of masonry coatings, paints for ferrous and
non-ferrous metals, trade sales paints for wood
substrates, anti-foulants, electrocoatings, flame-
resistant and.. intumescent paints, heat-resistant
paints, fluorescent paints, joint fillers, inks, inks
for paper goods, inks for elastomers, inks for
plastics, cosmetics, markers, magnetic tapes, food
stuffs, textiles, adhesives, ceramics, artists colours,
photoconductive coatings and concrete and mortar.
Descriptions of procedures used to prepare coatings for
these different applications are described in the
Pigment handbook (Temple C. P~tton, Wiley-Interscience,
1973, Volumes 1 to 3). In most instances, the use of the
present invention involves the replacement of white and
black pigments by a grey pigment. This can involve changes
in parameters but these modifications are well within the
purview of the person skilled in the art.
Example 1
Preaaration of a green artist paint using a arey
pictment
To 740 ml of water were added 25 ml of Tamol*
731 dispersant (Rohm and 1laas), 5 ml of CF10 50%
surfactant (Triton-Rohm and Elaas), i65 ml vol. of QP40-
l0% conc. ethyl cellulose thickener (Union carbide) , 30
* Trademark
CA 02137080 2004-05-18
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ml vol. of NXZ defoamer (Diamond Shamrock) and 2.27 kg
of 325 mesh grey granite powder.
The resulting mixture was dispersed in a high
speed disperses for 15 minutes to yield a grey pigment
slurry which was then added to the letdown phase. To
the slurry were added 2.48 liters vol. of Rhoplex AC64
acrylic binder (Rohm and ttaas) , 88 ml vol. of water, 30
ml vol. of Texanol coalescent (Eastman Kodak), 13 ml of
Nopco NXZ defvamer (Diamond Shamrock), 7 ml of Proxel
to GXL preservative (ICI), 23 ml of amino-methylpropanol
buffer, 80 ml of tZP40-10% cellulose and 103 ml vol. of
ASE60-12.5% conc. of llerysol thickener (Rohm and fiaas) .
The resulting solution was mixed for approximately 20
minutes to yield approximately ~t.43 liters vol, of grey
paint having a 30% binder content and a total solids
content of about 50%. To the grey paint was added
sufficient green cobalt, pigment either in paste form or
in a paint format until the desired green colour was
obtained.
Alternatively, to a cobalt green artist paint
was added sufficient amounts of grey slurry (before the
letdown) to achieve the desired tune of green. In some
instances, it was necessary to add more acrylic
emulsion (in the form of a gloss medium) to impart the
desired flexibility and gloss ' to the resulting
composition.
In a variant, the grey pigments and the
colour pigments are applied as separate coats on the
surface to be covered, hence they are not in physical
admixture. This embodiment is particulary suitable for
modern automotive painting that uses the so-called
"clear coat" which is a layer of non-opaque material
containing colour pigments. The clear coat is applied
over a grey undercoat. The improvement provided by
this invention resides in the use of an undercoat made
of grey pigments which allows to reduce the amount of
colour pigments in the clear coat. The undercoat is
* Trademarks
WO 94122966 ~ ~ ~ PCT/CA94/00192
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prepared by dispersing the grey pigments in a solvent
(in a similar way as the base coat described earlier).
As for the clear coat it is made in a known fashion
with the exception that the amount of colour pigments
may be reduced without creating any adverse effects in
the appearance of the colour.
