Note: Descriptions are shown in the official language in which they were submitted.
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COATING COMPOSITION CAPABLE OF ABSORBING UV RADIATION
FIELD OF THE INVENTION
The present invention relates to a coating
composition that can provide protection from exposure to
ultra violet ("UV") light or UV and visible light having
wavelengths from less than 200nm and up to 500 or 550 nm.
In particular, the present invention relates to a
coating composition that can be applied to containers that
are used for storage of products that are light sensitive.
Such products include, but are not limited to, foods,
beverages, and pharmaceuticals.
BACKGROUND OF THE INVENTION
Uncoloured clear containers are known to fail to
protect light sensitive contents of the containers from
the deleterious effect of UV light or UV and visible
light.
In the prior art, only fully opaque containers
(such as metal cans and paperboard containers) and
translucent containers (such as amber coloured glass or
plastic containers) offer UV and visible light protection.
Fully opaque or deep amber coloured containers
are less attractive than clear containers in situations
where consumers wish to see and inspect the contents of
the containers.
Market research indicates that transparent blue
or green containers are particularly attractive to
consumers because they present an image of high quality.
It is commonly believed that blue or green transparent
containers provide protection from UV light or UV and
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visible light. However, in fact, such containers provide
the same low level of protection provided by uncoloured
clear containers.
A particular deleterious effect of W and visible
light on beverages such as beer or wine is the generation
of off-flavours called "lightstrike". The human nose is
particularly sensitive to such off-flavours and therefore
the use of containers with W and visible light protection
is important for such products.
One approach to the "lightstrike" problem in beer
has been the use of hops that are chemically modified so
as to remove the chemical precursor of the molecules
responsible for the off-flavours. However, these
molecules are also the chemicals that contribute to the
bitter flavour that is sought by beer drinkers. Thus, the
resulting beer is considerably less attractive to many
consumers.
Typically, beer products are packaged in amber or
green glass containers. A comparison of the W and
visible light shielding properties of amber and green
glass can be seen in Figure 1 (absorbance) and Figure 2
(transmission). Amber glass as shown in Figure 1 exhibits
significant absorbance over the whole of the W and a
significant part of the visible light spectrum, ie
generally in the wavelength region up to 500nm. On the
other hand, green glass absorbs strongly in the region
below 320nm but less well in the region between 320-500nm.
The results shown in Figures 1 and 2 are significant as it
is believed that light in these wavelengths is required
for the production of "lightstrike" flavours.
Thus, it can be seen that traditional green glass
does not prevent transmission of the damaging W and
visible light wavelengths nearly so well as amber glass,
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notwithstanding that green glass is used by many brewers
for their products and indeed has a wide consumer
acceptance.
The need to increase the W and visible light
protecting abilities of glass has been addressed in the
past by the application of organic W and visible light
absorbing materials to glass surfaces. Generally, such
materials are sacrificial and absorb W and visible light
and are thereby degraded. Such materials are both
expensive and, because of their sacrificial action, are
unsuitable for products that have long shelf lives.
It is also known that selected metal oxides can
strongly absorb in the UV and visible regions of the light
spectra. However, such metal oxides have lacked the
clarity and the transparency to be suitable for use as
additives for coatings to be applied to containers where
it is important to be able to view the contents of the
containers.
It is an object of the present invention to
provide a coating composition that is capable providing
protection from damaging wavelengths of W light or W and
visible light.
STJNIMARY OF THE INVENTION
According to the present invention there is
provided a coating composition that includes a carrier and
a pigment dispersed in the carrier, and the pigment
includes nanoparticles of a W light absorber such that
the coating composition is capable of absorbing a
significant amount of the incident UV light up to 360nm or
nanoparticles of a W and visible light absorber such that
the coating composition is apable of absorbing a
significant amount of the incident W and visible light up
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to 550nm, and the absorber includes an inorganic material.
The term "nanoparticles" is understood herein to
mean that the particles are small enough to appear
transparent with no haze in visible light.
In view of issues relating to accurate
measurement of the size of small particles, the applicant
does not wish to be limited to a definition of the term
"nanoparticles" that is based on a particular size range
of particles.
Nevertheless, preferred nanoparticles are
particles less than 100nm (0.1 microns) equivalent
spherical diameter.
More preferably, nanoparticles include no
significant concentration of particles that exceed 100nm
(as determined by Transmission Electron Microscopy) and
have effective colloidal stabilisation with no
aggregation, agglomeration or flocculation of individual
particles, both as a liquid coating composition and as a
coating of the coating composition.
More preferably, nanoparticles are particles less
than 50nm (0.05 microns) equivalent spherical diameter.
One suitable type of inorganic material of the
absorber is iron oxides.
Iron oxide-based absorbers are suited
particularly for forming coloured transparent coatings of
the coating composition.
Iron oxide-based absorbers are also suited
particularly for absorbing the W and visible region of
the light spectra.
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Another, although not the only other, suitable
type of inorganic material of the absorber is zinc oxides.
Zinc-oxide-based absorbers are suited
particularly for forming colourless transparent coatings
of the coating composition.
Zinc-oxide-based absorbers are also suited
particularly for absorbing the UV region of the light
spectra.
The pigment may include more than one type of
absorber.
Preferably the pigment further includes
nanoparticles of a pigment that provides or contributes to
the colour of the coating composition.
By way of example, the pigment may include blue
or green pigments or a combination of pigments that result
in blue or green pigments.
More preferably the pigment further includes
nanoparticles of blue or green pigments that cause the
coating composition to be a transparent blue or green
colour.
More preferably the pigment includes
nanoparticles of yellow or red iron oxide absorber
pigments and blue or green pigments that cause the coating
composition surprisingly to be a transparent blue or green
colour.
The combination of pale yellow or red iron oxide
absorber pigments and blue or green pigments creates a
coating composition having good W and visible light
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absorption characteristics whilst being a transparent blue
or green appearance - an attractive commercial
proposition.
Preferably the carrier is capable of acting as
(i) a dispersant of the pigment particles and (ii) a film
former.
Preferably the carrier is a polymeric material.
The carrier may be a composite of a number of
materials that have a range of characteristics.
For example, the materials may include materials
that have dispersant characteristics predominantly,
materials that have film-forming characteristics
predominantly, and materials that have dispersant and film
forming characteristics.
Preferably the film forming material is selected
from the group that includes polyurethanes, polyesters,
polyolefins, polyvinyls (including polyvinyl chlorides)
and polyacrylics.
According to the present invention there is also
provided a substrate having a coating of the above-
described coating composition.
The substrate may be formed from any suitable
material.
Examples of suitable materials are glass and
plastics materials.
Preferably the substrate forms a wall of a
container, such as a bottle, and the coating is on an
outer surface of the container.
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Preferably the thickness of the coating is. no
more than 100 microns.
More preferably the coating thickness is no more
than 50 microns.
The thickness of the coating is related to the
level of protection required and to the concentration of
the W light or W and visible light ("W/Vis") absorber
in the pigment in the coating composition. Specifically,
a range of different combinations of (i) the concentration
of the W/Vis absorber and (ii) the coating thickness can
provide a given level of protection.
At one extreme it is possible to have a
relatively high concentration of the W/Vis absorber and a
relatively small coating thickness and at the other
extreme it is possible to have a relatively low
concentration of the W/Vis absorber and a relatively
large coating thickness.
This is an important point because it means that
it is possible to impart desired physical attributes of
the coating, such as wear resistance, scuffing resistance,
cost and transparency by changing the concentration of the
W/Vis absorber and/or the coating thickness.
Depending on circumstances (such as the substrate
being coated, the end use of the substrate, and the
coating apparatus for applying the coating) it may be
preferable to vary the concentration of the W/Vis
absorber and the coating thickness between the above-
described two extremes to provide a given level of
protection.
For example, for cold end coated containers, such
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as beer bottles it is preferred that the coating thickness
be in the range of 0.1-2 microns.
More preferably the coating thickness is 0.1-1.5
microns and more preferably 0.3-1.5 microns.
It is a surprising aspect of the invention that
smooth, W and visible light absorptive blue coatings may
be applied as cold end coatings at coating thicknesses of
0.3 to 1 microns.
According to the present invention there is also
provided a method of forming a coating composition capable
of absorbing W light up to 360nm or W and and visible
light up to 550nm, which method includes a step of wet
milling a carrier and a pigment to form a comminuted
dispersion of the pigment in the carrier, and the pigment
including nanoparticles of an absorber capable of
absorbing W light or W and visible light up to 550nm.
It is preferred particularly that the carrier
includes a dispersant in order to prevent floccs forming
during the wet milling step.
Preferred dispersants include:
(a) polycarboxylate for aqueous media; and
(b) entropic ("Solsperse") hyper-dispersants for
non-aqueous media.
Preferably the wet milling step is carried out at
a low solids content.
Preferably the solids content is 5-30 by weight.
More preferably the solids content is 15-25$ by
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_ g _
weight.
Preferably the wet milling step includes wet
stirred media milling (bead milling) in batch, continuous
passes, or continuous recirculation modes using small
beads (<0.7mm diameter) with a power input of more than
0.5kW per litre of shell volume for a prolonged period
until the required transparency is achieved.
The wet milling step may be as described in
International Application no W09717406 in the name of M J
Bos Consultants Pty. Ltd.
According to the present invention there is also
provided a method of forming a coating of a coating
composition capable of absorbing UV and visible light up
to 550nm on a substrate, which method includes the steps
of
(a) forming the coating composition as
described above; and
(b) applying the coating composition onto the
substrate to form a continuous coating on
the substrate.
The coating composition may be applied to the
substrate by any suitable means, such as spraying or
roller-coating the coating composition onto the substrate.
Preferably the method includes adding further
carrier to the coating composition formed in step (a) and
thereby diluting the coating composition to a required
pigment volume concentration prior to applying the
substrate in step (b).
Preferably the further carrier is a film forming
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material.
25-455
is 30-40~.
Preferably the pigment volume concentration is
More preferably the pigment volume concentration
Preferably the substrate is a wall of a container
and step (b) is part of a container manufacturing method.
Preferably the container is a glass container.
Glass container manufacturing, for example glass
bottle manufacturing, typically includes two stages during
which coatings may be applied to the bottle surface.
A hot end coating (HEC) is applied to glass using
chemical vapour deposition techniques immediately after
forming a glass container when the surface temperature of
the container may be 600°C or higher. The HEC is typically
a ceramic material such as tin oxide and serves both to
protect the glass surface from damage and also to provide
a substrate for the cold end coating.
A cold end coating (CEC) is applied after a glass
container has been annealed at a surface temperature of
120-180°C. The CEC consists of an organic coating that
provides the glass surface with the necessary lubricity
for high speed passage through automatic inspection and
filling lines. Some coatings also serve to protect the
glass surface from abrasion damage and to preserve the
inherent strength of the glass. Cold end coatings may be
based on silicone waxes, polyethylene, polyvinyl alcohol,
stearic acid, oleic acid, polyurethane, polyester,
polyolefins, and polyacrylics.
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The coating composition of the present invention
may be applied to a glass container in a cold end stage of
bottle manufacture.
Preferably the coating thickness is 0.1-1.5
microns.
Preferably the carrier of the cold end coating is
the carrier of the coating composition of the invention.
In a particularly preferred form of the invention
the carrier of the coating composition is a water-based
thermoplastic acrylic or polyurethane or polyester
material and the coating composition is applied to a
container surface at the CEC stage.
Alternatively, a solvent-based thermosetting
setting acrylic or polyurethane or polyester material may
be used under specialised application conditions unrelated
to cold end coating.
(a) DESCRIPTION OF DRAWINGS
The present invention is described further by
reference to the following Examples and the accompanying
drawings.
The drawings:
FIG 1 compares the W/Vis shielding properties of
clear, green and amber glass used in beer bottles,
displayed as W/Vis absorbance;
FIG 2 compares the W/Vis shielding properties of
clear, green and amber glass used in beer bottles,
displayed as W/Vis transmittance;
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FIG 3 compares the W/Vis shielding properties of
(i) a coating composition (formulation A) in accordance
with the invention as described in Example 1, (ii) clear
glass, and (iii) amber glass used in beer bottles,
displayed as W/Vis absorbance;
FIG 4 compares the UV/Vis absorbance of the
composition used in Figure 3 against the W/Vis absorbance
of comanercial glass products;
FIGS 5 and 6 compares the W/Vis absorbance of a
1 microns film of coating composition (formulation B) in
accordance with the invention as described in Example 1
and commercial glass products;
FIG 7 compares the W/Vis absorbance of a 0.5
microns film of coating composition (formulation RH503) in
accordance with the invention as described in Example 4
and amber glass;
FIG 8 compares the W/Vis absorbance of a 0.6
microns film of coating composition (formulation RH502,
RH504, RH505 blend) in accordance with the invention as
described in Example 4 and amber glass; and
FIG 9 compares the W/Vis absorbance of a film of
a Zn0-based coating composition in accordance with the
invention as described in Example 5 and a control coating.
EXAMPLES
EXAMPLE 1. Formulations A and B - in accordance with
the invention.
Formulation A - based on a thermosetting acrylic carrier.
On a solid/solid basis, the coating composition
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included:
12~ Fe00H (TOY-Pigment Yellow 42) pigment
1.3~ Fez03 (TOR-Pigment Red 101) pigment
0.5$ Blue 5203 pigment (Pigment Blue 15:3)
20 parts per hundred of pigment of solsperse 3000
(a hyperdispersant)
40 parts thermosetting acrylic solution
"TOY" is an iron oxide yellow pigment supplied
commercially by Johnson Matthey under the product name
Trans Oxide Yellow AC0500.
"TOR" is an iron oxide supplied by Johnson
Matthey under the product name Trans Oxide Red AC1000.
Formulation B - based on a polyethylene emulsion as a
carrier.
The coating composition was similar to
formulation A, with the exception that it was (i) aqueous,
(ii) included 20 parts per hundred of pigment of Orotan
731 (a polycarboxylic dispersant) pre-prepared as the
ammonium salt as a replacement for the solsperse 3000; and
(iii) included a commercially available polyethylene
emulsion product (used as a cold end coating in glass
bottle manufacture and sold under the trade name DURACOTE)
as a replacement for the acrylic resin of formulation A.
Physical characteristics of formulations A and B.
The applicant found that nanoparticles of iron
oxide pigment in formulations A and B did not flocculate
and the coating compositions were a green colour.
The colour of the coating compositions was
virtually indistinguishable from the traditional green
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glass used for beer bottles.
Performance of formulation A
The extent to which formulation A, the coating
composition based on the thermosetting acrylic carrier,
could absorb W and visible light was evaluated by forming
a thin coating of 2 microns of the composition on a glass
plate and comparing the W/Vis absorbance with that of an
untreated glass plate and a comanercially available amber
glass product used for beer bottles. The results are
shown in Figure 3.
It can be seen from Figure 3 that the coated
glass had significantly improved absorbance compared with
the untreated glass and provided similar protection to the
known amber glass product.
The formulation used above was applied as a
coating on a green bottle. As has already been observed,
the W absorbance of green bottles falls short of the
standard desired by food producers and brewers. The
effect of coating the green bottle with the formulation is
shown in Figure 4.
It can be seen from Figure 4 that the coating
provided generally superior protection against W light in
the harmful wavelengths between 350nm and 500nm.
Performance of formulation B
The W/Vis absorbance of a 1 micron coating of
formulation B, the composition based on a polyethylene
emulsion, was measured and compared with that of a
standard amber bottle. The results are shown in Figure 5.
The absorbance of the coating on the quartz slide
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was comparable to that of the amber bottle. However, the
results should be considered in the context that a quartz
slide has no absorbance in the wavelengths measured and
that the film thickness was only 1 micron.
The W/Vis absorbance of formulation B was also
compared with that of a green glass beer bottle as shown
in Figure 6. The W/Vis protection offered by the coating
formulation was very similar to, or better than, amber
glass.
EXAMPLE 2
The transparent coating formulations in
accordance with the invention tested in this example
contained 5-100nm diameter nanoparticles of iron oxide and
other pigments dispersed in carriers having dispersant and
film-forming characteristics.
Milling procedure.
The coating formulations were formed in
accordance with the following standardized procedure.
A 1 litre stainless steel vessel of 100mm
internal diameter was fitted with a water jacket for
cooling. A rotor shaft carrying 4 plain, 6mm thickness,
90mm diameter, circular discs made of ultra high molecular
weight polyethylene were placed in the vessel. The net
volume of the mill was 850 ml. This net volume was
charged to 85~ with 0.268kg of 0.4 to 0.7mm diameter
partially stabilized zirconia beads (47~ voidage). A lid
was bolted and sealed to the top of the mill with the
rotor shaft passing through a hole and stirrer guide in
the lid. 400m1 of each of the mill base formulations set
out below were charged to the mill. The actual weight of
the additions was determined according to density. For
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example, for a mill base formulation of density 2.2 kg/1,
the amount of mill base added was 0.88kg. The rotor was
driven at a rate such that the peripheral speed of the
discs was 10 m/s, ie 2100rpm for the 90mm diameter discs.
Milling of each of the formulations, with ambient
temperature water passing through the cooling jacket, was
continued for at least two hours.
The above-described nano-milling is very
intensive by comparison with mere dispersive milling of
pigments for paint and inks. In terms of intensity,
measured as litres of mill base per litre of bulk beads
per hour, the milling produced 0.3 litres or less compared
to 9 litres or more produced in conventional milling, with
beads of several mm diameter, of pigments for ink and
paint.
It was by means of this intensive milling that
the coating formulations were able to achieve the clarity
and the protective absorption of light that is reported
below.
Formulations
As indicated above, the transparent coating
formulations contained 5-100nm diameter nanoparticles of
iron oxide and other pigments dispersed in carriers having
dispersant and film-forming characteristics.
Colloidal stabilisation of the 5-100nm diameter
nanoparticles and the correspondingly high surface areas
(1000-50 square metres per millilitre) of the
nanoparticles were necessary both:
(a) throughout the milling to prevent re-
aggregation of particles and flocculation;
and
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(b) on blending with resins and dilution to
coating to prevent flocculation and loss of
protective absorbance.
At the same time, in addition to having
dispersant characteristics, the carrier was also required
to be film forming and mechanically and pasteurisation
resistance.
The dispersants used in the formulations were:
(a) polycarboxylate dispersants for aqueous
media, including a proportion of
polyacrylic acid as an ammonium salt; and
(b) entropic ("Solsperse") hyperdispersants for
non-aqueous media.
The coating formulations were low in viscosity, 5
to lOcP, and had negligible rheological yield value, ie
they were Newtonian.
The coating formulations had the following
compositions and characteristics.
Formulation 1 - blue-green light protective cold-end
coating additive - 12$ Fe203 PR101 - 8~ PY124 - 3~ CuPc-
PB15:3 aq - l8pph Joncryl 61HV- lOp Dispex A40. Milled
for 2.25 hr. Strong pure bottle green - clear.
Formulation 2 - amber light protective coating additive -
18~ Fe203 PR101 - 4~ PY124 1.5~ CuPc-PB15:3 aq - l8pph
Joncryl 61HV - lOpph Dispex A40. Milled for 2 hr. Dark
amber - clear. The colour changes intensity less with
variation in film thickness on spraying.
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Formulation 3 - blue-green light protective cold-end
coating additive - 12~ Fe203 PR101 - 2.3~ PY124 - 8.8~
CuPc-PB15:3 aq. Milled for 2 hr. Strong blue green -
very clear. The colour is more blue-green than
formulation 1.
Formulation 4 - increased level of Fez03 PR101for more
protection at lower thickness - 09F(506) 18$ Fe203-PR101 -
4$ PY124 1.5~aCuPc-PB15:3 aq. - l8pph Joncry 161HV - 10 pph
Dispex. Milled for 1.75hr. Gold-Brown - very clear.
Formulation 5 - 04F(500) 12~ Fe203 - 8$ PY124 - 3$ CuPc aq.
- 18p Joncryl 61HV - lOpph Dispex. Milled for 5 hr.
Strong blue green - clear.
Formulation 6 - 10~ Fe203 - 12~ Pigment Green - 36 1~ CuPc
aq. - 18p Joncryl 61HV - l0pph Dispex. Milled for 3 hr.
Bright green - clear. Pigment Green 36 yields a purer
green than combinations of blue and yellow 03J(475).
Formulation 7 - 10$ Fe203 - 14~ PG36 aq. - l8pph Joncryl
61HV - lOpph Dispex. Milled for 2 hr. Bright yellow-green
- clear. Pigment Green 36 yields a purer green than
combinations of Blue and Yellow 03J(474).
Formulation 8 - (468) 10.3 Fe203 - 13.7$ PG36 aq. - 18p
Joncryl 61HV - lOpph Dispex. Milled for 2 hr. Yellow
green - clear.
Light absorbance evaluation of formulations 1 to 8
The light absorbance of coating formulations 1 to
8 was tested. The test procedure and the results are
discussed below.
~ Clear dispersions of the formulations produced by
the milling procedure were diluted to 35~ pigment
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volume concentration with resins, as is
appropriate, such as polyethylene aqueous
emulsion for cold-end coating or aqueous or
solvent borne acrylic or solvent borne
polyurethane resin.
~ The diluted formulations were applied to glass or
clear plastic to form coatings of about 1 microns
film thickness, sometimes as thin as 0.5 or 0.3
microns, yet providing the protection exceeding
that of amber glass and film properties required.
~ Absorbance of W and visible (Blue) light by the
coatings was measured on a Varian Cary Model 1E
W-Visible Spectrometer and exceeded 2 (99~) up
to 450nm and exceeded 1 (90~) up to 500nm for the
coatings of the formulations. In other words,
the absorbance exceeded the absorbance of amber
glass typically used for beer bottles.
~ Haze of 0.5 to 1 microns thick coatings of the
formulations was less than 15$ as measured on the
Cary Spectrophotometer.
~ Film thickness was measured on a Taylor Hobson
Talysurf 10 Surface Profile Analyser
~ Pasteurisation resistance was tested by immersion
in water at 65-70°C for one hour. The results
were satisfactory.
~ Scuff resistance and lubricity of the coatings
with bottle to bottle contact were also assessed.
The results were satisfactory.
EXAMPLE 3
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The following coating formulation components were
added to a stirred vessel in the parts by weight indicated
below to form a mill base:
BASF Sico FR1363 PY124 0.78 parts
BASF Heliogen Blue D7072 PB15:3 0.309 parts
Johnson Matthey AC1000 PR101 1.200 parts
Rhodia Joncryl 61HD 35~ 0.589 parts
Ciba Dispex A40 40~ 0.343 parts
Water 6.78 parts
Total lOparts
The mill base was milled, firstly pass by pass,
then by recirculation from a well-stirred vessel to a 1.2
litre Drais Double Chamber Process Head Mill.
The DCP mill may be fitted with a 0.25mm aperture
bead separation screen, but was operated without a bed
separation screen, and charged with 3.7kg of 0.4 to 0.7mm
diameter partially stabilised zirconia beads.
The rotor speed was at maximum rate and a pumping
rate, using a progressing cavity of 5 to 151/min was
maintained for 16 hours. At this point the mill base was
clearly transparent.
The resultant coating composition was tested as a
cold end coating by mixing 2 parts of the mill base and 1
part of DIC Duracote 20~ polyethylene coating emulsion in
an homogeniser.
The resultant coating composition was sprayed
onto hot glass panels and hot glass bottles from a 130°C
oven to a dry film thickness of 1.0 micron as measured by
a Talysurf Surface Profile Analyser.
"Absorbance" of the film on glass was measured on
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a Cary Model 1E W-Visible Spectrophotometer in
transmission mode and compared with the "absorbance" of
amber glass.
Absorbance of the coating composition exceeded
the absorbance of amber glass.
Absorbance of both the coating composition and
amber glass exceeded the value of 1.0 (10~ transmission at
500nm) and exceeded 2.0 (1~ transmission) at less that
470nm down to 200nm in the W region.
EXAMPLE 4
Experimental work was carried out on 4 other iron
oxide-based formulations RH502, RH503, RH504, and RH505 in
accordance with the invention.
The composition of the formulations is set out below:
Formulation RH503 - 18~ Fez03 PR101 - 4~ PY124 1.5~ CuPc,
aq - l8pph Joncryl 61 - lOpph Dispex A40.
Formulations RH502, Rh504, and RH505 - 18~ Fe203 PR101 - 4~
PY124 1.5$ CuPc, aq - l8pph Joncryl 61 - lOpph Dispex A40.
Formulation RH503 was prepared by milling in the
1 litre stainless steel mill described in Example 2 to
produce a transparent coating formulation. The milling
time was 6 hours. A coating of the formulation was formed
and tested in accordance with the procedure described in
Example 2. The coating thickness was 0.5 microns. Figure
7 illustrates the performance of the coating.
Formulations RH502, RH504 and RH505 were prepared
by milling in a glass container in a shaker mill to
produce transparent coating formulations. The milling
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time was 48 hours. A coating of a blend of the
formulations was formed and tested in accordance with the
procedure described in Example 2. The coating thickness
was 0.6 microns. Figure 8 illustrates the performance of
the coating.
As can be seen from Figures 7 and 8 the
formulations achieved absorbances at or above 1.5 at a
wavelength of 500nm and had better absorbance than the
amber glass standard over the wavelength range of
interest.
EXAMPLE 5
Experimental work was carried out on a zinc
oxide-based coating formulation in accordance with the
invention.
The formulation was prepared by adding 35~ 20nm
Zn0(s) to 15 pph (based on solids) of Avecia Solsperse
24000 GR dispersant and 202gms propylene glycol monomethyl
ether acetate, alpha-isomer (PGMA) carrier. This
formulation was milled for 46 hours to produce a
transparent coating formulation. The resultant liquid was
very clear, with no evidence of flocculation. The coating
formulation was added to a polyurethane to give the
equivalent of 5~, 7.5~, 10~ and 15~ dispersions of Zn0 and
the dispersions were used to form coatings. The results
of the W absorption characteristics of the coatings are
given in Figure 9.
It can be seen from Figure 9 that the Zn0 coating
formulation had significantly better absorbance than the
control coating formulation in the range of 300-400nm,
with absorbance increasing with Zn0 concentration.
The invention has been described by way of
CA 02444705 2003-10-20
WO 02/085992 PCT/AU02/00490
- 23 -
example. The examples are not, however, to be taken as
limiting the scope of the invention in any way.
Modifications and variations of the invention
such as would be apparent to a skilled addressee are
deemed to be within the scope of the invention.
