Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Coatecl glass microbeads and pigment for syntheticpolymeric
material
The present invention relates to coated glass microbeads, to a
synthetic polymeric material incorporating such coated microbeads and to a
pigment for synthetic polymeric material. The invention also extends to coated
microbeads for retroreflective paint.
s It is well known to incorporate various solids into a synthetic
polymeric material for clifferent purposes. For example, glass beads can be usedas filler for modifying the mechanical properties of the filled polymer, such ~s its
flexibility or its resistance to traction, or to facilitate its application. This
incorporation is usually carried out by mixing the beads with a liquid which is
lo polymerizable or contains the polymeric material. It is also known to use coated
glass microbeads, the coating being selected so as to aclapt the surface properties
of the microbeads, such as for example their chemical bonding properties or their
surface tension properties with respect to the liquid.
Furthermore, the colouration of polymeric materials is frequently
s obtained with the aid of organic or inorganic pigments. Among the different
~pes of possible pigments, metal compounds are often used, being chosen
because of their stabili~ to heat and light and their chemical st~bility. These
pigments can be incorporated in the form of an insoluble powder consisting of
particles of metal compound which is m~xed into the material which is
polymerizable or contains the polymer, while it is in the liquid state. Certain
difficulties are encountered in distributing these particles as regularly as is
necessary. To obtain a uniform colour clearly necessitates a regular and
homogeneous distribution of the pigment particles in the material. Such
distribution is not easy to obtain, it depends notably on the viscosity
characteristics and dispersant power of the liqui~l material at the time of
incorporating the pigment. It is necessary to avoid ~gglomerating the hlsolllbleparticles and obtaining different levels of colour~tion across the m~ss of polymer.
Furthermore, since the pigments are quite expensive, it is preferable to use small
amounts.
A pre-dispersion of the pigment particles in a resin can also be c~rried
out, so as to form a "colouring concentrate", which can then be distributed in the
liquid material. However, the operation of distribution remains a difficult
operation and this pre-dispersion implies an additional manufacturing step.
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It is also common to incorporate glass beads in marking paints to
provide them with retrorefiective properties for visible light. Such paints, used
for example for road markings, can be seen easily at night because they reflect
light from the headlight~s of a vehicle back towards vehicle's driver. ~o obtain a
s retroreflection effect requires that at lea~st a part of the beads are exposed at the
surface of the paint, and that the glass cmd the paint have refractive indices
sufficiently different for the light to be reflected at the interface between these
two media. Conventionally, the glas~s beads are incorporated in aliquid materialconsisting of the fresh paint. The degree of sinking into the paint can ea~sily be
o controlled by using microbeads bearing a coating which adjusts their
characteristics of wettability by the solvent of the paint. The reflection of light at
the gla~ss-paint interface is obtained by incorporating pigment~s in the paint.
These pigments, generally formed of particles of a metal compound of high
refractive index, must again be properly distributed in the paint.
s Certain problems analogous to those described in the context of
synthetic polymeric materials can appear for retroreflective paints: the pigments
used are quite expensive and it is not always ea~sy to distribute the insoluble
particles in the paint as regularly as one would wish.
One of the objects of the present invention is to provide coated
microbeads which contribute to the colouration of the material in which they areincorporated, which facilitate good pigment distribution in the material and which
enable the quantity of pigment required to colour this material to be reduced to a
certain degree.
The present invention relates to coated glass microbeads,
characterized in that the coating comprises particles of metal compound of
refractive index greater than 2 distributed in a binding polymer and provides the
coated microbeads with a coloured external surface.
Because of their shape and size, it is generally much easier to
distribute the coated microbeads in a liquid or pa~sty material than to distribute
the very fine particles of pigment, which tend to agglomerate and are dif~lcult to
distribute regularly in such a material. Since, accor(ling to the present invention,
the external surface of the coated microbeads is coloured by the particles of metal
compound, a good distribution of the microbeads in a liquid or pasty material
leads to a good distribution of these particles in this material and preserves it
~s while this material hardens and solidifies. The colouration is therefore carried
; out more easily and more regularly in the solid material.
Moreover, it does not require any separate operation of pigment
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incorporation, and this enables the number of steps necessary to obtain a
coloured article filled with rnicrobeads to be reduced.
The invention also enables the quanti~ of pigment incorporated in the
material and the colour obtained to be more easily controlled.
The 4uantities of pigment associated with the coated microbeads can
easily be adapted by moditying the proportion of pigment distribllted in the
binding polymer. It is consequently easy to adjust the colouration of the material
by a~lapting the ~luantities of coated microbea~s incorporated and the proportion
of particles in their coatin~.
o The characteristics of the coated microbeads according to the present
invention enable the quantities of pigment to be limited, and it is even possible to
use smaller quantities of pigments than are necessary when microbeads and
pigment particles are added separately.
We have discovered that such coated microbeads can be incorporated
Is in a marking p;~int and bring about an ef~ect of retroreflection of visible light.
This is quite surprising since the coated microbeads alone have a dull and opaque
- appearance. Nevertheless, these coated microbeads incorporated in the paint
produce during use a very effective retroreaective effect.
As compared with a synthetic polymeric material, where one attempts
generally to distribute a pigment as uniformly as possible in the polymeric mass, in
~- the case of retroreflective paints, it is necessary above all to obtain pigmented
particles in sufficient quantity at the microbeads-paint interfaces to permit good
retroreflection. The present invention enables these particles to be very well
placed, since they are present at the very surface of the retroreflective
microbeads. Moreover this characteristic also enables the quantity of pigment
necessary to be reduced.
Quite surprisingly, despite the high density of a metal compound in
relation to that of a binding polymer, inasmuch as the metal compo~md is in the
form of particles whose size enables the overall sphericity of the coated
.~o microbeads to be preserved, the particles of metal compoun~l distrihuted in the
binding polymer appear to cause little or no modification of the wett~bility
characteristics of the coated microbeads, by comparison with coated microbeads
which are otherwise similar but do not contain such particles. This characteristic
is particularly advantageo~ls since, provkled that the binding polymer is judiciollsly
.~s chosen, coated microbeads can he obtained which will sink more or less stron~ly
in the material in which they are incorporated. For example, coated microbeads
can be obtained which, when intro~luced into a fresh paint, float at the surface of
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the paint and will therefore be well exposed to cause retroreflection to appear.It has been found that a certain number of metal compounds can be
used to colour the external surface of the coated microbeads. Among these,
particles of zinc oxide, for example, can be used to obtain a white colour~tion,s particles of lead chromate or of caclmium sulphide to obtain a yellow colo~lration,
or again particles of chromium (III) oxide to obtain a green colouration. It is
especi~lly preferred to colour the external surface by particles of titanium dioxide.
Titatlium (Jioxide, which provides an excellent whiteness, has a refractive index of
2.9. It opacifies the~synthetic polymeric materials very well and perrnits good
IU retroreflection in marking painLs.
In the preferre~J embodiments of the invention the coating comprises a
coupling agent. Coupling agents are useful for binding organic materials to
inorganic materials. A coupling agent, by forming a bond between the glass and
the binding polymer, enables the binding polymer to be attached easily to the
glass beads and favours good adhesion of the coating t~ the glass beads. This
better cohesion facilitates storage of the coated microbeads, and their handlingand subse~uent incorporation in a synthetic p~lymeric material or in a paint
without risk of damaging them. A coupling agent can also couple the particles ofthe metal compound and the binding polymer; a coupling agent can be chosen
20 which increases the wettability of the particles of the metal compound by thebinding polymer and reinforces the adhesion between the particles and the
binding polymer.
Organometal compounds, such as silanes or organic titanates are
particularly effective as coupling agents. Such coupling agents which can be
2s quoted as examples are aminopropylsilanes, methacryloxysilanes, and
isopropyltitanates.
Preferably the coating comprises a surfactant. A surfactant enahles
the dispersion of the particles of metal compound in the material forming or
containing the binding polymer to be faci1itated: the particles are dispersed more
30 easily and more regularly. The distribution of the particles in the binding
. polymer can thus be improved.
Among the different types of surfactants, the titanates, for example,
can be used, hut a silanated sur-factant will preferably be chosen. It is possible to
select a silane which acts at the same time both as coupling agent and as
3s surfactant. The number of constituent~s present in the coating is thus reduced,
while simultaneously ensuring two different functions.
The coating preferably comprises a thixotropic agent. In this way the
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flow (during agitation) of the liquid material containing the particles of metalcompound is favoured, which permits the easy application of this material to theglass beads without risk of premature hardening.
Thixotropic agent~s such as ethylcellulose or organophilic clays, for
s example, can be used.
It is advantageous to use particles of the metal compound with a mean
diameter less than 1 ,um, and their diameter is preferably between 0.1 and 0.7,um.
Particles of small size enable the overall sphericity of the coated microbeads to be
well preserved. Moreover~ by comparison with particles of greater size, which
o can tend to sink in the material forming or containing the binding polymer during
their dispersion, particles of small size disperse easily and regularly. They enable
a coating of very homogeneous composition to be obtained and an approximately
uniformly coloured external surface to be provided on the coated microbeads.
On the other hand, it is preferable to avoid using particles whose size is small in
s relation to the wavelengths of visible light because they can produce a harmful
diffusing effect.
Preferably the mean diameter of the glass beads will lie between 100
~lm and 2 rnm. In general, the size of the glass beads influences the properties of
the material in which they are incorporated, and their mean diameter will be
20 chosen as a function of the type of article to be produced and of its field of use.
For example, microbeads incorporated as fillers in synthetic polymeric materials: are generally smaller than the microbeads incorporated in a retroreflective paint.
Furthermore, the size of the glass beads influences the properties of
the coated microbeads according to the present invention, and their mean
25 diameter will be chosen as a function of various criteria.
Since the specific surface area of beads of small diameter is
proportionately greater than that of glass beacls of greater diameter, weight for
weight, a proportionately greater amount of particles of metal compound will
become attached to the smaller particles when applying a coating o~ given
30 composition to a given thickness. The intensity of the colouration imparted to
the beads will depend on the amount of metal compound applied, but since the
particles of metal compound are generally fairly expensive, it is usually desire(l to
use them in amounts which are as small as possible. The mean diameter of the
glass beads may be chosen according to the desired intensity of colouration,
3s having regard to the cost of the metal compound.
The particle size distribution of the glass beads also influences the
properties of the material in which they are incorporated.
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It is preferred in general that the glass beads have a quite narrow
particle size distribution so as ea~sily to obtain a good distribution of them in the
polymeric material or paint: coated rnicrobeads well distributed in a synthetic
polymeric material enable a colouration uniformly distributed through the mass
s to be ensured and, incorporated in a marking paint, they will show a similar
de8ree of sinkage, enabling a high intensity of retroreflection to be obtained if
they are exposed at the surface of the paint.
The thickness of the coating is preferably between 0.5 and 4 ,um.
- Coatings whose thickness lies between these values are sufficiently thick to permit
o a good distribution of the particles of the metal compound in the binding
polymer. On the other hand they permit small quantities of metal compound to
be used and the size and shape of the glass beads to be preserved.
We have found that many polymers can play the part of the binding
polymer, provided that the material forming or containing this binding polymer is
presented in the form of a hardenable liquid. Thus the particles of metal
compound can be dispersed in Liquid material, the material applied to the gla~ssbeads, and coated microbeads with coloured external surface formed by
hardening the material containing the particles of metal compound.
It is especially convenient to use a thermo-setting resin. Thermo-
setting resin binder coatings tend to be more mechanically resistant than other
types of coating in view, and the coated beads are thus more able to withstand
handling prior to their incorporation into a polymeric matrix, ancl they also tend
- to be better able to withstand the temperatures to which they will be subjected
during formation or moulding of such a matrix.
2s Preferably the binding polymer is selected from silicones,
polyurethanes, polyesters, acrylic polymers or epoxy resins. These polymers meetthe condition described above: they permit a good distribution of the particles of
metal compound, harden easily, for example by polymerization with the aid of a
catalyst, by solvent evaporation or by addition of a hardening agent, and adhere.~o well to the glass.
The binding polymer can be chosen to obtain the surface tension which
it is desired to give the coated microbeads. For example a ~silicone binder enables
coated microbeads to be obtained which float in a fresh paint and after drying
produce coated microbeads which, while adhering suitably to the paint, are well
.~5 exposed to provide the retroreflection. One can al~so introduce to the paint at the
same time other coated microbeads, whose surface comprises a binding polymer
which confers different surface properties, for example if it is desired that the
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coated microbeads distribute themselves through the whole thickness of the paint.
Advantageously, the particles of metal compound are distributed in
the binding polymer in such a way that the external surface of the coated
microbeads comprises particles of metal compound of refractive index greater
s than 2, surrounded by binding polymer. The particles of metal compound thus
distributed can provide a well coloured external surface without for all that using
large 4uantities of particles of metal compound. Moreover~ such a distribution
enables a very good bonding of the coated microbeads to the synthetic polymeric
materials or to the paints to be obtained: by comparison with coated microheads
o whose external surface would be entirely covered with particles, a surface
containing binding polymer will bond better to a synthetic polymeric material or a
paint and will enable filled articles having a high cohesion to be formed.
The bonding of the coated microbeads can be adjusted by selecting the
binding polymer as a function of the material in which the microbeads are
Is incorporated. The binding polymer will preferably be of the same nature a~ this
material, in order to favour optimum compatibility. However, a hinding polymer
different from the polymer incorporating the microbeads can be chosen. For
example, a polymer can be chosen which, while being well compatible with the
synthetic polymeric material or with the paint as the case may be, provides the
20 coated microbeads with hydrophobic properties and/or modifies the wettability characteristics of the microbeads.
Preferably the coated microbeads are hydrophobic. For this rea~son
they tend not to absorb atmospheric moisture which could otherwise cause the
agglomeration of the coated microbeads and the loss of their fluidity properties,
2s notably during the storage prior to their incorporation or during their handling.
Moreover, the accumulation of moisture at the surface of the coated microbeads
can harm the cohesion between the microbeads ancl the material in which they
are incorporated.
If it is desired to manufacture an article of low density, hollow beads
30 can be used. I-lowever, it is generally preferred to use solid beads beca~l~se of
their greater mechanical strength.
It is known that a synthetic polymeric material incorporating coated
microbeads possessing one or more of the characteristics mentioned above has
new features, and the invention conse~luently extends to a synthetic polymeric
~s material incorporating coate(i microbeads, characterized in that some at least of
the microbeads are coated gla~ss microbeads having one or more of the
characteristics described above.
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The present invention also includes a pigment for synthetic polymeric
material characterized in that it comprises coated glass microbeads whose coating
comprises particles of metal compound of refractive index greater than 2
distributed in a binding polymer and which provides the microbeads with a
s coloured external surface.
Such a pigment is very advantageous because it is generally much
easier to distribute in a liquid or pasty material than a pigment consisting of
particles of metal compound and it enables a uniforrnly coloured article to be
obtained very easily after hardening the liquid or pasty material. Moreover thiso pigment enables the quantities of particles of the metal compound to be limited
and even, in certain cases, smaller quantities of particles to be used than those
required when using a pigment in the form of particles of metal compound, while
obtaining a similar colouration.
Preferably the pigment comprises coated microbeads presenting one or
s more of the characteristics desc ibed above.
The invention extends also to rnicrobeads for retroreflective paint,
characterized in that they comprise coated gla~,s rnicrobeads whose coating
comprises particles of metal compound of refractive index greater than 2
. distributed in a binding polymer and which provides the coated microbeads with a
20 coloured external surface.
Quite surprisingly in view of their dull and opaque appearance, these
coated microbeads are very suitable for providing retroreflective properties to
paints in which they are incorporated.
Localization of the pigment particles on the surface of the
25 retroreflective microbeads also presents the additional advantage of enabling- smaller quantities of pigment than before to be used. Now, by the conventional
method, the pigment particles must be distributed as regularly as possible through
the whole of the paint so as to ensure that the glass beads incorporated afterwards
should be sufficiently in contact with them to permit retroreflection; whereas,
30 according to the present invention, the coated microbeads possess directly ontheir external surface the particles of metal compound required for
retroreflection.
The particles oE metal compound have quite a high density yet,
surprisingly, they do not appear appreciably to modify the wettability
35 characteristics oE the coated microbeads by comparison with otherwise similarcoated microbeads which do not contain these particles. The binding polymer
can consequent y be chosen as a funcoon ot ~he desireù ~inkage of the
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microbeads in the paint. This enables the production of coated microbeads
which rema~n on the surface of a paint or which sink into the latter, or again the
use of a mixture of coated microbeads of different wettabilities so as to distribute
the microbeads through the thickness of the paint.
s Preferably the rnicrobeads for retroreflective paint comprise coated
microbeads presenting one or more of the characteristics described above.
Various preferred embodiment~s will now be described by way of
example.
EXAMPLE 1
o Glass microbeads intended for introduction into a road marking paint
are manufactured. The glass beads are solid and have a diameter between 250
and 650 ,um.
Particles of titanium oxide of mean diameter 0.5 llm are mixed little by
little with a solution of ethyl silicate VP 2262 (from Wacker) in a proportion of
s 200 g of titanium dioxide to 100 mL of solwtion. A small amount of toluene is
added to adjust the viscosity. 40 mL of this m~xture are removed in order to treat
1 kg of glass beads. The rnixture is poured onto the glass beads. The whole is
mixed with agitation, and then dried at 80C. The ethyl silicate hardens by
hydrolysis and condensation and microbeads vvith a siliconized coa~ng are
obtained.
The coated rnicrobeads obtained have an external surface of a fairly
dull white. They are hydrophobic and the thickness of their coating is about 1
m.
The coated microbeads are incorporated in a marking paint of the
epoxy resin type, and remain well exposed in the surface. They produce a very
satisfactory retroreflection.
As a variant of this example, the whiteness of the coated microbeads
obtained is increased by adding a small quantity of cobalt stannate in the mixture
containing titanium dioxide. These coated microbeads are incorporated in a
vinyl paint.
EXAMPLE ~
Coated glass microbeads with yellow external surface, intended to
:~` colour and f~ll asynthetic polymeric material, are made.
250 g of lead chromate particles with diameters of about 0.7 ~Im are
~s slowly mixed into lOO mL of polyester resin of the Palatal P51 type (of B.A.S.F.),
:~. to which 0.5 weight % of methacryloxypropyltriethoxy- silane have been added in
advance. After homogenization, tert-butyl peroxide is added as polymerization
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catalyst. The pasty mixture obtained is dispersed by means of a fast agitator onglas~s microbeads whose diameter is between 20 and 60 llm. The whole is brought
to 140C over several minutes to harden the coating which is about 2 lum thick.
The coated microbeads formed are sieved and then incorporated in
S polypropylene at aconcentration of 40weight %. The polypropylene thLls filled
presents a yellow colour.
EXAMPLE 3
2 weight % of N-[2-(vinylbenzylamino)-ethyl]-3-aminopropyl-
trimethoxysilane are dissolved in 100 mL of toluene. Then 100 g of titanium
o dioxide particles with diameters between 0.1 ,um and 0.7 ~Im are added witha~itation. When dispersion is assured, S00 g of Plexilith 402 acrylic resin (of
Rohm) and 1 weight % of Plexilith 492 are added.
50 mL of this mixture are used to treat 1 kg oi~ beads of mean diameter
400 ,um and form coatings thereon about 3 ,um in thickness. At the end of the
s operation, a polymerization catalyst such as benzoyl peroxide is added. Thepolymerization lasts for about 30 minutes. The coated microbeads are
subsequently dned and sieved.
The whiteness of these coated rnicrobeads is evaluated by measuring
their luminance (L). The luminance value is 83 for the coated microbeads
according to the example, whereas it is 90 for titanium oxide alone and 63.4 foruntreated glass beads.
EXAMPLE 4
An epoxy resin Araldite GY260, having an initial viscosity of 12000 to
16000 mPa.s, is diluted with toluene in the proportion of S0 mL toluene to 100 gresin, so as to reduce the viscosity to between 1500 and 1600 mPa.s. Then an
organophilic clay is added to make the solution thixotropic. After
homogenization, 150 g of cadmium sulphide particles with diameters of about O.S
,um are incorporated with vigorous agitation, then 0.5 weight % of
isopropyltriisostearoyl titanate, and then a polyamine hardener.
40 g of this solution are removed to treat 1 kg of glass beads of mean
diameter about 60 l~lm. The solvent is evaporated under vac~l~lm and the resin
hardened rapidly by heating at 100C to form a coating about 1 ~Im in thickne~s~s.
The coated microbeads have a yellow external surface and can be
incorporated in a paint or in a synthetic polymeric material.
In a variant, coated microbeads of similar appearance are obtained by
usins5 a polyurethane as binding polymer.
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