USE OF PARTICULATE TITANIUM DIOXIDE FOR REDUCING THE
TRANSMISSION OF NEAR-INFRARED RADIATION
FIELD OF THE INVENTION
The present invention relates to the field of polyolefins film
production. More particularly, the invention relates to the production of a film
which has a low transmission of infra-red radiation, but for which a high portion
of the visual light is passing through in a diffuse manner.
BACKGROUND OF THE INVENTION
The exposure to sunlight over longer periods of time usually has
devastating effects on most physical entities. Hence, colours of objects rapidly
fade and many materials may exhibit warping and distortion under the large
temperature fluctuations. The prolonged exposure causes deterioration of
many materials and their aesthetic aspects, usually called "ageing", typically
leading to a significantly shortened lifetime and need for replacement. Also
plants, animals and human beings are often negatively affected by a
prolonged exposure to sunlight. The shielding from sunlight has therefore
become an important feature in many circumstances.
Sunlight radiation occurs for about 45% of its energy as visible
light, in the relatively narrow visible range of wavelengths of about 380 to
about 700 nanometre (nm), but also for about 5% as ultraviolet (UV) radiation
in the range of the shorter wavelengths of 280 to 380 nm and for about 50%
as infra-red (IR) radiation in the even wider range of the longer wavelengths
from 700 nm up to about 1 mm.
To make transparent surfaces, such as glass, more energyshielding,
special plastics films have been developed, which absorb as
selectively as possible the radiation from the range, not visible to the eye, but
either the rather damaging UV range or the heat-generating IR range. The
infra-red radiation range is commonly divided into, on the one side, the nearinfrared
radiation range, N-IR or NIR or IR A&B, up to a wavelength of about
2500 nm, and the long-wavelength or far IR range, covering the range up to
50,000 nm or 50 mhi , and according to some authors even up to and including
1 mm. Because solar radiation has a major part of radiation energy with
wavelengths in the near- IR range, technological improvements have mostly
focused thereon . Hence, films have been developed which have a better infrared
absorption function, which provides a more even heat distribution and a
more pleasant interior temperature at a high incidence of light. A
disadvantage of these films is that the absorbed radiation is converted into
heat in the film . Hence, this absorption may cause local temperature
increases, which are passed on into the substrate on which the film has been
applied. With many substrates, such as glass, such local temperature
increases lead to high mechanical stress, and even may lead to glass
breakage. A second disadvantage is that the absorbed heat, although
transmitted to the interior in a more evenly manner, may still also locally cause
a considerable temperature increase, which may still be undesirable.
Hence, a high absorption of the incident solar energy does not
necessarily lead to uncomplicated solutions. To limit or avoid these
disadvantages as much as possible, films were developed with IR-reflecting
properties, especially aimed at reflection in the NIR radiation range. These
films offer a reduction of the heat absorption of a vehicle or building equipped
therewith in summer, such that cooling energy may be saved.
US 6797396 describes a birefringent dielectric multilayer film
transparent for visible light but reflecting at least 50% of light in the wavelength
region of 700-2000 nm, and made from different polymer layers and does not
contain any metals.
To make an object more resistant to sunlight exposure, solar
reflecting particulate materials may be added to the construction material of
the object, in particular when this is a polymer, or to the paint or coating with
which the object is then coated. Conventional titanium dioxide particulate
materials are known to provide high solar reflectance. These particulate
materials have a strong white colour, and with the amounts needed are not
useful when a dark coloured object is desired. Neither are these particulate
materials suitable for objects which need to be transparent to visible light, such
as transparent polymer films or clear topcoats.
WO 2009/1 361 4 1 A 1 discloses a titanium dioxide (Ti0 2)
particulate material having a large crystal size. The particulate material is
stated to absorb strongly in the UV region of the spectrum (300-400 nm) , to
scatter efficiently in the NIR region (700-2500 nm) and to show low scattering
and low absorbance in the visible region of the spectrum (400-700 nm) . The
particulate material thus shows high reflection of NIR radiation and,
simultaneously, low reflectance of visible light compared to conventional
particulate materials. The special particulate material is combined with a nonwhite
colorant within a vehicle and provides for a single coat covering that has
solar reflectivity and a non-white colour. It is therefore suitable for providing at
relatively low concentrations a high reflection of NIR radiation and diminished
reflectance of visible light compared to conventional particulate materials. The
particulate material may further be coated with a metal oxide material to
reduce its photocatalytic activity. The particulate materials are suggested for
use in a wide variety of applications including a plastic article. The particulate
materials disclosed were reported as having a mass average or mass mean
crystal size of 0.79, a mean crystal size of 0.97 microns and a mean particle
size of 0.85 microns, or a mean particle size of 0.69 microns. An uncoated
particulate material sample was added to an alkyd paint resin to record its
reflection over black, over the wavelength range of 400-2500 nm. Uncoated
particulate material was used in acrylic paint systems having various non-white
colours, of which the reflectance spectra were determined. A coated
particulate material was incorporated in an alkyd melamine formaldehyde
based paint and its weather durability was measured. Uncoated particulate
material was used in unplasticised polyvinyl chloride plaques which were
coloured with Pigment Green 17 and carbon black, of which the reflectance
spectra were measured over the wavelength range of 400-2600 nm and
integrated to obtain a result for Total Solar Reflectance. WO 2009/1 361 4 1 A 1
is concerned with and only measures the reflectance of solar radiation , also
labelled as "scattering", in particular the radiation in the NIR region of the solar
spectrum, at a secondary level also in the UV region. Neither any
transmission data nor any absorbance data are collected for any of its
products.
In agriculture, the use of polymer films, in particular polyolefin
films, has become widespread. One of the more important uses is in the
construction of low cost greenhouses, in which a more controlled atmosphere
may be established for growing agricultural crops. Another use is the
construction of low cost stables or shelters for animals, such as poultry. Such
constructions are very fast to erect, and may even be readily moveable and/or
transportable.
Especially in hot and sunny climates, it is preferred to use films
which reflect a high portion of the infra red radiation of the sunlight, primarily in
the so-called Near- Infra-Red (NIR) region from 700 nm up to 2500 nm. When
such near-infra-red radiation enters the greenhouse and hits a substrate, it
heats up the substrate. This substrate then increases its emission of heat by
convection , and also its emission of long wavelength infra-red radiation . Such
long wave infra-red radiation is readily reflected by most materials, and its
energy, once it entered the greenhouse, thus has a tendency to stay inside the
greenhouse. This phenomenon leads to an extra warming up of the
atmosphere inside the greenhouse, including increased water evaporation
from soil, animals and crops. This puts most crops and animals into a stress
situation , which is usually not favouring their growth and economic yield. A low
transmission , preferably by reflection, of the infra-red radiation, in particular of
the NIR radiation part of the sunlight is thus important for maintaining the
temperature inside the greenhouse in the more desired comfort zone for most
agricultural crops. Also with the animal shelters, it is important to keep the
temperature inside low in order to reduce the stress levels of the animals.
The use of NIR-reflecting films for preventing heat entry is
preferred far above its alternatives to reduce inside greenhouse air
temperatures, such as ventilation, evaporation, and whitening. In the hot and
sunny climates, the ambient air is already rather hot, such that ventilation has
only limited effectiveness. These climates are usually also rather arid, with
relative humidity of the ambient air dropping down to below 10% at around
noon time, and with water resources being scarce and salty. Evaporation of
water typically brings a building up of salts, which deteriorates the performance
of most cooling systems rapidly. Whitening is inexpensive, but is washed
away with rain and also reflects the useful part of the solar radiation spectrum.
There has therefore been a need for the selective reduction of
NIR transmission, while letting as much as possible of the visible light pass
through.
Indeed, for the photosynthesis reaction , and hence for plant
growth , the plants need the radiation in the so-called "Photosynthetically Active
Radiation" or "Photo Active Radiation" (PAR) part of the sunlight, which
substantially all falls within the range of the visual light, especially in the blue
and red region thereof.
For the purpose of sunlight reflection , greenhouse screens have
been developed. These screens are usually positioned against the ceilings of
permanent greenhouses, usually constructed from glass, and may be opened
and folded mechanically, usually by means of a complex system of pulleys and
electrical motors, usually in reaction to a change in the weather conditions.
The screens are typically woven and comprise strips made of metallised
materials or of metal, typically aluminium, which assure substantially full
reflection . The screens usually further comprise strips of transparent polymer
film , allowing some of the incident sunlight through for the photosynthesis
reaction. A drawback of such screens is that a part of the visible light, and
hence of the PAR radiation , is reflected.
Furthermore, greenhouses equipped with such screens
represent a significant investment to the cultivator. They are therefore
primarily affordable with the upper range of crop cultures. A much cheaper
alternative may be offered by constructing the greenhouse with an agricultural
polymer film .
DE 2544245 discloses a polymethylmethacrylate (PMMA)
glazing material for buildings and vehicles containing an interference pigment
for the screening of NIR radiation having a wavelength from 800 to 1500 nm.
The pigment has a blue-red colour and the light transmitted through the
glazing material has a yellow-green colour. When applied to greenhouses,
such glazing would have the disadvantage that portions of the visible light
which cannot be utilized by the plant are transmitted and convert into heat,
while other parts, such as the red part, which can be utilized by the plant, are
reflected.
A good agricultural film for greenhouses is characterised by a
combination of a low transmission , preferably a high reflectance, of the
radiation in the near-infra-red wavelength region with a high transmission of
the radiation in the visual wavelength region, in particular of the PAR.
US 2008/0292820 A 1 discloses, in paragraphs [0033-0034], IR
radiation absorbing particles including or made of lanthanum hexaboride, LaB6.
Lanthanum hexaboride is an effective NIR absorber, with an absorption band
centred on 900nm . The IR radiation absorbing nanoparticles may be sized
such that they do not materially impact the visible light transmission of the
polymeric binder layer. These nanoparticles may for instance have any useful
size, such as 1 to 100, 30 to 75, or 30 to 75 nm.
Although the plants need the energy of radiation in the so-called
"Photo Active Radiation" (PAR) region , most crops still suffer if they are
directly exposed to this part of the sunlight, and may even become burnt.
Plants rather prefer to receive this radiation in a diffuse manner. There has
therefore been a need for a film having high reflectance for NIR radiation,
combined with a high transmission in a diffuse manner of the radiation in the
visible region which comprises the PAR radiation.
WO 96/03029 discloses multilayer films composed of alternating
layers of polycarbonate (PC), having a refractive index n = 1.587, and
polymethylmethacrylate (PMMA) , having a refractive index n = 1.49 1,
significantly different from this of PC. The films exhibit a strong reflection of
radiation at a wavelength in one particular wavelength band, which band may
be shifted by the variation of layer thickness, number of the alternating layers
and the selection of the polymeric materials, as long as the difference in
refractive index is bigger than 0.03. Example 1 discloses a film transparent
below 700 nm and strongly reflecting in the range 7 15-755 nm. The film
contains 100 microlayers having a thickness of 100 nm (each PC layer) and
140 nm (each PMMA layer) . In Example 3, the film selectively reflects the
green light around 540 nm, yet is transparent for other radiation , including in
the NIR region . A drawback of the films proposed in WO 96/03029 is their
complexity in production and the selection of polymer materials which are
rather scarce. Another drawback of films of which the reflection of radiation is
based on interference, is that their performance depends on the angle of
incidence of the radiation , in this case the position of the sun relative to the
orientation of the film. These films therefore suffer from a relatively limited
acceptability in terms of the fields where they may be applied affordably.
WO 96/26070 discloses a three-layer polymer film , all three
layers containing an interference pigment consisting of a transparent carrier
material in the form of platelets, coated with one or more metal oxides or
transparent platelets with a refractive index of more that 1.7. Suitable carrier
materials are layered silicates, natural or synthetic mica, glass platelets and
silicon dioxide platelets, natural mica being preferred. The metal oxides used
may be tin , titanium , chromium, zirconium , cerium, iron and tungsten oxide,
and preferably titanium dioxide. The interference colour depends on the
thickness of the metal oxide layer. Preferably a pigment having a green
interference colour is used. If titanium oxide is used, a layer thickness of 120
to 160 nm will produce a green interference colour. The coated mica particles
which are used have a size of 5000 to 40000 nm. A large part of the sunlight's
short-wave infrared is reflected by the interference pigments applied. If a
green interference pigment is used, then the green part of the incident light
which is not utilized by the plant is also reflected.
US 2008/0292820 A 1 also describes a multi-layered polymer
film which has a haze value of at least 10% to further also control the sunshielding
properties by light diffusion . The reflective and transmissive
properties of the multilayer polymeric infrared reflecting film are a function of
the refractive indices of the respective layers, in the document addressed as
the microlayers. Metals may be incorporated in several successive metallic
layers in the film, and they may cooperate as a Fabry-Perot interference filter
to reflect the IR light and/or especially the so-called near-IR light. The film
further comprises a diffusing layer or surface. Exemplified is a multilayer IR
reflecting film containing 224 alternating microlayers of PET and coPMMA,
which was laminated to a Fasara San Marino or a Fasara Milano decorative
film using an optically clear adhesive. These films are even more complex
compared to the films discussed herein above. They thus suffer from the
same drawback of limited acceptability in terms of areas of application.
The drawback of these interference-based technologies is that
each application may need a film especially designed for it. One particular film
may therefore only perform well in one very specific application .
US 2008/0008832 A 1 discloses deep-tone coloured roofing
granules providing increased solar heat reflectance. A highly reflective whitepigmented
inner coating is used as a substrate to reflect additional infrared
radiation , while an outer colour coating with IR-reflective interference platelet
pigments are used to provide desirable colours. It is shown that the lightinterference
platelet pigments exhibit significantly higher solar heat reflectance
over the traditional inorganic colour pigment, e.g. iron-oxide red pigments.
US 2007/0065641 A 1 describes roofing granules with enhanced
solar reflectance, comprising a base material of crushed and sized mineral
aggregates in the form of granules and an insolubilized coating material
covering said granules comprising dark IR-reflective pigments and coarse nonpigmentary
titanium dioxide. When incorporated in roof shingles, these
granules show a higher Total Solar Reflectance (TSR) as compared to a
standard product of the same visual appearance.
JP2005330466A describes the use of 0.5 to 1.5 micrometer
diameter IR reflective particles, which may be Ti0 2, coated with a resin film
transparent to IR radiation . The film coating may contain a substantially non-
IR-absorbing pigment. However, although these products have large particle
diameters, they are not described as being made from large crystal size
titanium dioxide as in the products of the present invention. As discussed
below in more detail, the particle size and crystal size of a Ti0 2 particle are not
necessarily the same.
There therefore remains a need for a simple solution to provide
polymer films having a high reflectance for NIR radiation, combined with a high
transmission of visible radiation , whereby the radiation in the visible region of
the spectrum is transmitted in a diffused manner. A simple solution is needed
in order to penetrate a number of very cost-sensitive applications such as
greenhouses and animal shelters.
The present invention aims to obviate or at least mitigate the
above described problem and/or to provide improvements generally.
SUMMARY OF THE INVENTION
According to the invention, there is provided the use as defined
in any of the accompanying claims.
The invention therefore provides the use of a particulate
material in a polymer article for reducing the transmission of near-infrared
radiation and for allowing transmission of visible light through the article,
whereby
- the particulate material is based on crystalline titanium dioxide, i.e.
containing Ti02, in the anatase and/or the rutile crystal form,
- the particles of the particulate material are coated with an organic
and/or inorganic coating layer,
- at least 20% by weight of the particulate material particles have a
particle size of at least 400 nm and at most 1000 nm, as measured by
X-Ray disk centrifuge,
- at least 1.5% by weight and at most 40% by weight of the particles in
the particulate material have a particle size of less than 400 nm and at
least 280 nm.
In another embodiment, the invention provides for the use of a
polymer composition containing the particulate material as defined in the use
of the particulate material according to the present invention in a concentration
from 500 ppm by weight up to 70%wt, relative to the total weight of the
composition , in the production of a polymer article for reducing the
transmission of near-infrared radiation and for allowing transmission of visible
light through the article.
In yet another embodiment, the invention provides a polymer
film composition containing the particulate material as defined in the use
according to the present invention in a concentration from 500 ppm by weight
up to 3.0%wt, relative to the total weight of the composition, preferably at least
1000 ppm, more preferably at least 1500 ppm, even more preferably at least
2000 ppm and yet more preferably at least 2500 ppm by weight, and optionally
at most 2.0%wt, preferably at most 1.0%wt, more preferably at most 8000 ppm
by weight, even more preferably at most 7000 ppm by weight, yet more
preferably at most 6000 ppm, preferably at most 5000 ppm, relative to the total
weight of the composition, in the production of a polymer film for reducing the
transmission of near-infrared radiation and for allowing transmission of visible
light through the polymer film .
We have found that the particulate material according to the
present invention is highly suitable in the production of an agricultural film or
fabric. The high amount of particles in the particulate material having a
particle size in the 400-1 000 nm range provide for a reduced transmission of
radiation in the NIR wavelength region of 700-2500 nm, preferably for a high
reflection of this NIR radiation as part of sunlight, compared to the
conventional Ti0 2-based particulate materials known from the art. The particle
size of conventional rutile Ti02 is from 250 to 400 nm, whilst conventional
anatase Ti02 has a particle size of from 200 to 400 nm. This reduced
transmission of NIR radiation brings a reduced influx of solar radiation energy
into a construction made with a polymer film comprising the particulate
material, such as a greenhouse or an animal stable or shelter, such that the
temperature of the atmosphere in the construction may be kept lower, leading
to less water evaporation , to a lower stress level of plants, crops and/or
animals which are kept underneath the polymer film or inside the construction.
We have further found that the particulate material may also be
used in a silage film, i.e. a film which is used for the outdoor storage of natural
produce such as hay and other plant cuttings for animal green feed, usually
towards an upcoming winter period, which natural produce is preferably
undergoing an anaerobic fermentation in order to increase its lactic acid
content thereby increasing the nutritional value of the natural produce. We
have found that the use of the particulate material according to the present
invention also reduces the temperature of the silage film as well as of the
enclosure defined by the silage film . We have found that this reduction in
temperature provides for better oxygen barrier properties of the film and hence
for a more effective anaerobic environment inside the enclosure promoting the
desired fermentation .
We have further found that the relatively minor amount of
particles in the particulate material having a particle size in the 280-400 nm
range provide for an increased transmission of radiation in the visible light
wavelength region of 400-700 nm, in particular in the PAR part of that region,
such as the blue and the red light region of the visible part of the spectrum.
This brings the advantage that, in comparison with the conventional Ti0 2
particulate materials known in the art, more of the part of the sunlight which is
necessary for the photosynthesis reaction is allowed to pass through the film
and reach the crops growing in the greenhouse, whereby the growth of the
crops as well as their useful yield may be enhanced. The increased
transmission of visible light is also beneficial to any animal life underneath the
film containing the particulate material. Animals inside a shelter or stable with
a film cover containing the particulate material will be more comfortable under
the increased daylight exposure, and hence experience a lower stress level, as
compared to films containing the conventional Ti0 2 particulate materials
known in the art. Also the bees inside the greenhouse, which assure the
pollination of the flowers of the crops which need to develop into the useful
products, will be able to perform better their pollination task under the
increased daylight exposure provided by a film cover containing the particulate
material, as compared to the conventional Ti0 2 particulate materials known in
the art.
We have further found that the minimum amount of particles in
the particulate material having a particle size in the 280-400 nm range also
provide for a high degree of diffusion of the transmitted visible light of the
sunlight spectrum. Particularly useful in hot and sunny climates, but also
playing to some extent in the more moderate climates, this brings the
advantage that the crops and/or animals underneath the film containing the
particulate material are also less directly exposed to the visible part of the
sunlight, such that they run a lower risk of being overheated and even burnt,
such that again their stress level is reduced.
We have further found that the particulate material in the use
according to the present invention exhibits some reduced transmission also of
radiation in the UV part of the solar spectrum, which ranges from about 200 to
about 380 nm. When used in relatively high particulate material dosing in the
film , such as with silage film , this may further improve the oxygen barrier
properties of the film, and also discourage insects and flies from getting
underneath the silage film . When used in relatively modest particulate
material dosing in the film, such as with agricultural film for greenhouse
construction , this still allows for the transmission of UV light having a
wavelength of around 340 nm, a wavelength which is not noticed by the
human eye but which is captured by the bees. This will further enhance the
comfort level of bees underneath the film containing the particulate material,
such that these insects are more comfortable and active in the performance of
their pollination task.
We have also found that the coating layer on the particulate
material particles may provide a reduced photocatalytic activity of the
particulate material towards the polymer matrix in which it is embedded.
Titanium dioxide is a strong UV adsorbent, and upon such exposure the
absorbed energy is liberated by the release of radicals. These radicals are
able to deteriorate most polymer matrices. The provision of a physical coating
layer, a sort of physical shell around the titanium dioxide, slows down the
migration of the radicals into the matrix, such as by increasing the path length
before they are able to reach the matrix, whereby the time to reach the matrix
may be significant in comparison to the half life time of the radical itself, such
that most of the radicals may have disappeared before they are able to reach
the polymer matrix.
We have further found that the coating layer may further provide
improved dispersibility of the particulate material particles, and reduced
yellowing and/or better opacity of the article containing the particulate material.
DETAILED DESCRI PTION
The present invention will be described in the following with
respect to particular embodiments and with reference to certain drawings but
the invention is not limited thereto but only by the claims. Any drawings
described are only schematic and are non-limiting. In the drawings, the size of
some of the elements may be exaggerated and not drawn on scale for
illustrative purposes. The dimensions and the relative dimensions do not
necessarily correspond to actual reductions to practice of the invention.
Furthermore, the terms first, second, third and the like in the
description and in the claims, are used for distinguishing between similar
elements and not necessarily for describing a sequential or chronological
order. The terms are interchangeable under appropriate circumstances and
the embodiments of the invention can operate in other sequences than
described or illustrated herein .
Moreover, the terms top, bottom , over, under and the like in the
description and the claims are used for descriptive purposes and not
necessarily for describing relative positions. The terms so used are
interchangeable under appropriate circumstances and the embodiments of the
invention described herein can operate in other orientations than described or
illustrated herein .
The term "comprising", used in the claims, should not be
interpreted as being restricted to the means listed thereafter; it does not
exclude other elements or steps. It needs to be interpreted as specifying the
presence of the stated features, integers, steps or components as referred to,
but does not preclude the presence or addition of one or more other features,
integers, steps or components, or groups thereof. Thus, the scope of the
expression "a device comprising means A and B" should not be limited to
devices consisting only of components A and B. It means that with respect to
the present invention, the only relevant components of the device are A and B.
Accordingly, the terms "comprising" and "including" encompass the more
restrictive terms "consisting essentially of" and "consisting of".
In the context of the present invention, a film is defined as a
material extending outwards in two dimensions and characterised by a material
thickness. In this definition , a film may also be a rigid sheet. The film may
have one or more layers. The film may have a material thickness of up to
several millimetres, such as 5 mm, but also be thinner, such as 4 mm, 3 mm,
2 mm or 1 mm. The film may have multiple layers which may be in contact
with each other, but which may also be spaced from each other, such as in a
multiple layer polycarbonate or PMMA sheet. The film may also be used as
part of a woven fabric, such as in shading screens for greenhouses.
In the context of the present invention, particle size is defined as
the diameter of the smallest sphere fully encompassing the particle.
In the context of the present invention, light, and in particular
visible light, is defined as a form of radiation energy, at one or more
wavelengths, which, when striking an object, may be absorbed, reflected
and/or transmitted. Generally, a combination of these three phenomena takes
place.
In the context of the present invention, concentrations are
expressed in weight units, unless otherwise specified. The term "average"
refers to the statistical mean unless otherwise specified. Average size is
referring to the "geometric volume mean size", unless stated otherwise.
Although average particle size is averaged on a weight basis,
average crystal size is given on a number basis because the analytical
techniques used provide their results on this basis, unless stated differently.
In an embodiment of the present invention, the use is further for
diffusing at least part of the photo-active radiation part of the visible light, and
preferably most of the visible light, preferably for increasing the percent haze
provided by the article, more preferably the haze being measured according to
ASTM D1003. This brings the advantage that anything which is shielded from
the sun by the polymer article according to the use of the present invention is
less exposed to the direct incidence of the visible part of the sunlight, such that
local overheating is reduced. This brings an advantage to plants and crops for
a reduced risk for local burning, to animals for a reduced risk for local
overheating, and increases the comfort level and hence reduces the stress
level of living creatures under such shield.
In an embodiment of the present invention, at least part of the
UV light spectrum, preferably the UV light perceived by bees, is transmitted by
the polymer article, preferably in a diffused manner. It has been found that the
bees need a specific spectrum of the UV light, estimated at around 340 nm, to
enhance the pollination of the plants grown in the greenhouses.
In an embodiment of the present invention, the particle size
distribution of the particulate material particles shows a major peak in the
range of 400- 1000 nm, preferably at most at 900 nm, more preferably at most
at 800 nm, even more preferably at most at 700 nm, preferably at most at
650 nm, more preferably at most at 600 nm, also preferably at least at 450 nm,
more preferably at least at 500 nm, and also preferably the particle size
distribution of the particulate material particles being unimodal and the single
peak thereof being in the specified range. This brings the advantage of further
reducing the transmission of the radiation in the NIR region of the solar
spectrum and/or further enhancing the effectiveness of the particulate material
in achieving the technical effects which are the purpose of the use according
to the present invention.
In an embodiment of the present invention, the particulate
material particles have an average particle size of at least 400 nm and up to
1200 nm, preferably more than 400 nm, more preferably at least 450 nm, even
more preferably at least 500 nm, preferably at least 600 nm, more preferably
at least 700 nm, yet more preferably at least 800 nm, and optionally at most
1100 nm, preferably at most 1000 nm, more preferably at most 900 nm, even
more preferably at most 800 nm, yet more preferably at most 700 nm,
preferably at most 650 nm, more preferably at most 600 nm and even more
preferably at most 550 nm. This brings the advantage of further reducing the
transmission of the radiation in the NIR region of the solar spectrum and/or
further enhancing the effectiveness of the particulate material in achieving the
technical effects which are the purpose of the use according to the present
invention.
In an embodiment of the present invention, at least 30% by
weight of the particulate material particles have a particle size of at least
400 nm and at most 1000 nm, preferably at least 40%, more preferably at least
50%, even more preferably at least 60%, yet more preferably at least 70%,
preferably at least 80%, more preferably at least 90% by weight of the
particulate material particles having a particle size in the specified range, and
preferably this particle size range being at most 900 nm, more preferably at
most 800 nm. This brings the advantage of further reducing the transmission
of the radiation in the NIR region of the solar spectrum and/or further
enhancing the effectiveness of the particulate material in achieving the
technical effects which are the purpose of the use according to the present
invention .
In an embodiment of the present invention , at least 60% by
weight of the particulate material particles have a particle size of at most
1000 nm, preferably at least 70%wt, more preferably at least 80%, even more
preferably at least 90% and yet more preferably at least 95% by weight of the
particulate material particles having a particle size of at most 1000 nm. This
brings the advantage of further reducing the transmission of the radiation in
the NIR region of the solar spectrum and increasing the diffusion of the visible
light which is transmitted, and/or further enhancing the effectiveness of the
particulate material in achieving the technical effects which are the purpose of
the use according to the present invention.
In an embodiment of the present invention, at least 2.0%wt by
weight of the particles have a particle size of less than 400 nm and at least
280 nm, preferably at least 3.0%wt, more preferably at least 4.0%wt, even
more preferably at least 5.0%wt, preferably at least 7.0%wt, more preferably at
least 10%wt, even more preferably at least 15%wt of the particles having a
particle size in the specified range, and optionally at most 35%wt, preferably at
most 30%wt, more preferably at most 25%wt, preferably at most 20%wt, more
preferably at most 15%wt and yet more preferably at most 10%wt of the
particles having a particle size in the specified range of 280-400 nm. This
brings the advantage of increasing the diffusion of the visible light of the solar
radiation spectrum , while maintaining a high transmission of the visible light, in
particular the PAR part thereof, which is required for the photosynthesis
reaction in plants.
In an embodiment of the present invention, the particulate
material particles, prior to their use, have been treated to selectively remove
particular size fractions, preferably to remove any particles which have a
particle size of at least 5000 nm, preferably at least 3000 nm, preferably the
particles being removed by a centrifugation treatment. This brings the
advantage that less effective particles in the particulate material are reduced
and/or avoided, such that the overall effectiveness of the particulate material in
achieving its desired technical effects is enhanced.
In an embodiment of the present invention , the titanium dioxide
has a Ti0 2 content of at least 80%wt, preferably at least 85%wt, more
preferably at least 90%wt, preferably at least 92%wt, more preferably at least
93%wt. This brings the advantage that the particulate material is more
effective in achieving its desired effects.
In an embodiment of the present invention, the polymer article
contains at most 100 ppm by weight of Fe20 3, preferably at most 80 ppm,
more preferably at most 60 ppm, even more preferably 40 ppm, yet more
preferably at most 20 ppm, preferably at most 10 ppm, more preferably at
most 5 ppm, even more preferably at most 1 ppm in order to prevent early
degradation of the polymer film .
In an embodiment of the present invention , at least 50% by
weight of the Ti0 2 crystals are in the rutile crystal form , preferably at least
60%, more preferably at least 70%, even more preferably at least 80%,
preferably at least 90%, more preferably at least 95%, even more preferably at
least 99%, yet more preferably at least 99.5% by weight. This brings the
advantage that the rutile form offers a higher refractive index, resulting in more
effective particulate material particles in achieving their desired effects. A
further advantage is that less particulate material is needed in order to achieve
a desired level of transmission hindrance to the NIR radiation, in combination
with a desired level of transmission of visible light. When optimised, this
brings the advantage that the achieved effects are stronger.
In an embodiment of the present invention , the titanium dioxide
has an average crystal size of at least 400 nm and up to 1200 nm, preferably
more than 400 nm, more preferably at least 450 nm, even more preferably at
least 500 nm, preferably at least 600 nm, more preferably at least 700 nm, yet
more preferably at least 800 nm, and optionally at most 1100 nm, preferably at
most 1000 nm, more preferably at most 900 nm, even more preferably at most
800 nm, yet more preferably at most 700 nm, preferably at most 650 nm, more
preferably at most 600 nm, even more preferably at most 550 nm The
applicants have found that this feature brings the advantage of further
reducing the transmission of the radiation in the NIR region of the solar
spectrum and increasing the diffusion of the visible light which is transmitted,
and/or further enhancing the effectiveness of the particulate material in
achieving the technical effects which are the purpose of the use according to
the present invention.
In an embodiment of the present invention , the titanium dioxide
is substantially white, preferably the particulate material having a lightness
value L* in the CIE L*a*b* colour space of greater than 80, preferably at least
85, more preferably at least 90, even more preferably at least 95, with an
absolute value of a* of less than 5 and an absolute value of b* of less than 5.
The applicants have found that in combination with the amount of particles
having a particle size of less than 400 nm, that this feature brings the effect of
enhanced diffusion of the visible light transmitted through the article, over the
full range of the visible light, such that the risk for local overheating on
anything shielded by the article from incident sunlight is more effectively
reduced. The CIE L*a*b* colour space describes all the colours visible to the
human eye and serves as a device-independent model to be used as a
reference. The three coordinates of CIELAB represent the lightness of the
colour (L* = 0 yields black and L* = 100 indicates diffuse white; specular white
may even be higher), which is expressed as its position between red/magenta
and green (a*, negative values indicate green while positive values indicate
magenta) and its position between yellow and blue (b*, negative values
indicate blue and positive values indicate yellow). An L* value of 80 already
indicates a light whitish colour, while a value of 95 indicates a very light colour.
A lighter colour exhibits a lower heat absorption as compared to a darker
colour. The film will therefore, thanks to this feature, absorb less heat and
thus may have a longer lifetime because the ageing process will be slowed
down.
In an embodiment of the present invention, the coating layer
represents from 0.50 to 20%wt relative to the total weight of the particulate
material particles, preferably at most 15%wt, more preferably at most 10%wt,
even more preferably at most 5%wt, yet more preferably at most 3%wt relative
to the total weight of the particulate material particles. We have found that
these levels are effective in achieving the desired effects of reduced
photocatalytic activity, as well as the other benefits associated with the coating
layer. The effectiveness of the coating layer may depend on the selection of
the material. A coating layer comprising Si0 2 may therefore be more effective
as compared to a layer comprising similar concentration of Al20 3, and hence
may be applied thinner and represent a lower weight as compared to the total
weight of the particulate material particles.
In an embodiment of the present invention, the coating layer
comprises one or more oxide materials. We have found that these materials
are particularly effective in reducing the photocatalytic activity of the particulate
material particles.
In an embodiment of the present invention, the oxide material is
an oxide and/or hydrated oxide, i.e. a hydroxide, of one or more elements
which are, referring to the Periodic Table of lUPAC dated 22 June 2007:
group 4 and 12 transition metals selected from Ti, Zr and Zn and/or
group 13 to 15 p-block elements selected from Si, Al, P and Sn
and/or
lanthanides,
preferably the material being selected from Al20 3, Si0 2, Zr0 2, Ce0 2, P20 5, and
combinations thereof, more preferably the oxide material comprising P20 5,
more preferably in combination with Al20 3 and/or Si0 2. We have found that
these compounds are particularly effective in reducing the photocatalytic
activity of the particulate material particles.
In an embodiment of the present invention, the particulate
material particles have been submitted to an organic surface treatment,
preferably with a compound selected from a polyol, an amine, an
alkanolamine, a silane and a silane derivative, such as for example
triethoxyoctylsilane, a silicone derivative, trimethylolpropane, pentaerythritol,
triethanolamine, alkyl phosphonic acid, n-octyl phosphonic acid,
trimethylolethane, and mixtures thereof. We have found that such treatment
improves the dispersibility of the particulate material particles in its surrounding
matrix.
In an embodiment of the present invention, the article is a
polymer film, preferably a polyolefin film , preferably a film based on a polymer
having ethylene as at least one monomer, more preferably a copolymer of
ethylene with at least one alfa-olefin or vinyl ester copolymer, even more
preferably a film based on a material selected from the list consisting of
polyethylene, high-density polyethylene (HDPE) , low-density polyethylene
(LDPE), linear-low-density polyethylene (LLDPE) , metallocene linear-lowdensity
polyethylene (mLLDPE) , ethylene vinyl acetate copolymer, ethylene
methyl acetate copolymer, ethylene butenyl acetate copolymer, ethylene vinyl
alcohol copolymer (EVOH), polyethylene terephthalate copolymer (PET),
polycarbonate (PC) , polymethylmethacrylate (PMMA), polypropylene (PP) and
mixtures thereof. We have found that these polymers are particularly suitable
as basis for agricultural film or sheet, consisting of one or more layers.
In an embodiment of the present invention, the polymer of the
article further comprises at least one of the additives known in the art, such as
at least one additive selected from the list consisting of a UV absorber, a near
IR absorber, a far IR absorber, a near IR reflector, a far IR reflector, a
stabilizer, an antioxidant, a processing aid, an antistatic agent, a colorant, an
inorganic salt, a pearl-luster pigment, a NIR-reflective substance, an
antifogging agent, a filler, an antiblock agent, a light stabilizer, a slip agent, a
UV blocker, a diffusing agent, and combinations thereof. It has been found
that such additives provide complementary properties to the article and/or
enhance the effects offered by the present invention.
In an embodiment of the use of the polymer composition
according the present invention , the polymer composition contains the
particulate material in a concentration from 500 ppm by weight up to 70%wt,
relative to the total weight of the composition . We have found that these levels
are effective in achieving the desired effects. Depending on the concentration
level, the level of achievement of the different effects may be further affected.
A higher concentration thereby leads to a more effective hindrance of the
transmission of the NIR radiation , as well as to a higher haze and also a higher
degree of diffusion of the transmitted visible light, while on the other hand a
lower concentration level may increase the transmission of the visible light, in
particular of the PAR part thereof. In hot and sunny climates, it will therefore
be beneficial to use according to the present invention to work with a higher
concentration of the particulate material, while in the more moderate climate a
lower particulate material concentration may readily be acceptable and even
desirable because of the higher PAR transmission and its associated benefits
to plant growth .
In an embodiment of the present invention, the polymer
composition is a masterbatch composition , preferably the masterbatch
composition being based on a polyolefin , more preferably on a polymer having
ethylene as at least one monomer, more preferably a copolymer of ethylene
with at least one alfa-olefin or vinyl ester copolymer, even more preferably on a
polymer selected from the list consisting of polyethylene, high-density
polyethylene, low-density polyethylene, linear-low-density polyethylene,
metallocene linear-low-density polyethylene (mLLDPE), ethylene vinyl acetate
copolymer, ethylene methyl acetate copolymer, ethylene butenyl acetate
copolymer, ethylene vinyl alcohol copolymer, polyethylene terephthalate
copolymer (PET) , polycarbonate (PC), polymethylmethacrylate (PMMA),
polypropylene (PP), and mixtures thereof.
In an embodiment of the present invention, the masterbatch
composition contains from 2.0%wt to 70%wt of the particulate material,
preferably at most 60%wt, more preferably at most 50%wt, even more
preferably at most 40%wt, yet more preferably at most 30%wt, preferably at
most 25%wt, more preferably at most 20%wt, even more preferably at most
15%wt and yet more preferably at most 10%wt, preferably at most 5.0w%,
more preferably at most 3.0w% of the particulate material. We have found
that these concentrations are providing a masterbatch which is very suitable
for further downstream use, such as in the production of an agricultural
polymer film or sheet, consisting of one or multiple layers.
In an embodiment of the use of the polymer film composition
according to the present invention, the polymer film composition contains the
particulate material in a concentration from 500 ppm by weight up to 3.0%wt,
relative to the total weight of the composition, preferably at least 1000 ppm,
more preferably at least 1500 ppm, even more preferably at least 2000 ppm
and yet more preferably at least 2500 ppm by weight, and optionally at most
2.0%wt, preferably at most 1.0%wt, more preferably at most 8000 ppm by
weight, even more preferably at most 7000 ppm, yet more preferably at most
6000 ppm, preferably at most 5000 ppm by weight, relative to the total weight
of the composition , in the production of a polymer film for reducing the
transmission of near-infrared radiation and for increasing the transmission of
visible light through the polymer film, preferably also for the increased diffusion
of the visible light through the polymer film. We have found that these levels
are effective in achieving the desired effects. Depending on the concentration
level, the level of achievement of the different effects may be further affected.
A higher concentration thereby leads to a more effective hindrance of the
transmission of the NIR radiation , as well as to a higher haze and also a higher
degree of diffusion of the transmitted visible light, while on the other hand a
lower concentration level may increase the transmission of the visible light, in
particular of the PAR part thereof. In hot and sunny climates, it will therefore
be beneficial to use according to the present invention to work with a higher
concentration of the particulate material, while in the more moderate climate a
lower particulate material concentration may readily be acceptable and even
desirable because of the higher PAR transmission and its associated benefits
to plant growth and animal comfort.
In an embodiment of the present invention, the polymer film
composition is based on a polyolefin, more preferably on a polymer having
ethylene as at least one monomer, more preferably on a polymer selected
from the list consisting of polyethylene, high-density polyethylene, low-density
polyethylene, linear-low-density polyethylene, metallocene linear-low-density
polyethylene (mLLDPE), ethylene vinyl acetate copolymer, ethylene butenyl
acetate copolymer, ethylene vinyl alcohol copolymer, polyethylene
terephthalate copolymer, polycarbonate (PC) , polymethylmethacrylate
(PMMA) , polypropylene (PP), and mixtures thereof.
In an embodiment of the present invention, the polymer film has
at least one layer which is made from the polymer film composition.
In an embodiment, the polymer film comprising at least one
layer which is made from the polymer film composition according to the
present invention further comprises at least one of the additives known in the
art, such as at least one additive selected from the list consisting of a UV
absorber, a near IR absorber, a far IR absorber, a near IR reflector, a far IR
reflector, a stabilizer, an antioxidant, a processing aid, an antistatic agent, a
colorant, an inorganic salt, a pearl-lustre pigment, a NIR-reflective substance,
an antifogging agent, a filler, an antiblock agent, a light stabilizer, a slip agent,
a UV blocker, a diffusing agent, and combinations thereof.
In an embodiment of the present invention, the at least one
layer in the polymer film is a top layer of a multilayer film, which is further
comprising at least one extra film layer, optionally at least 2, 3, 4, 5, 6, 7, 8, 9,
10, 11, 12, 13, 14 or even 15 extra film layers. When properly installed, i.e. in
the right direction relative to the incident energy radiation , the top layer is
thereby not only shielding the underlying objects and/or animals, but also the
underlying layers of the entire film, which represents a significant advantage
with respect to the expected life time of the film, usually regardless of its
application .
In an embodiment of the present invention, the polymer film has
a transmission in the visible light region , being defined as the wavelength
region of 380-700 nm of at least 30%, preferably at least 40%, more preferably
at least 50%, preferably at least 55%, more preferably at least 60%, even
more preferably at least 65%.
In an embodiment of the present invention, the polymer film has
a transmission in the photosynthetically active part of the visible region of the
sunlight, the latter being defined as the wavelength region of 400-700 nm, of at
least 30%, preferably at least 40%, more preferably at least 50%, preferably at
least 55%, more preferably at least 60%, even more preferably at least 65%.
In an embodiment of the present invention, the polymer film has
a transmission of the near-infrared radiation in the wavelength region from
above 700 up to 2500 nm of at most 90%, preferably at most 85%, more
preferably at most 80%, even more preferably at most 75%, preferably at most
70%, more preferably at most 60%, even more preferably at most 50%, yet
more preferably at most 40%. The applicants have found that the film
according to the present invention is thus more effective in achieving its
desired effects of keeping the NIR radiation out.
In an embodiment of the present invention, the polymer film has
a haze of at least 20%, preferably at least 25%, more preferably at least 30%,
even more preferably at least 35%, preferably at least 40%, more preferably at
least 50%, even more preferably at least 60%, yet more preferably at least
70%, preferably at least 80%, more preferably at least 90%, preferably the
haze being measured according to ASTM D 1003.
In an embodiment of the use according to the present invention,
the use is for reducing the temperature inside a greenhouse and/or for
increasing the crop yield inside a greenhouse.
Processes which are suitable for preparing the titanium dioxide
based particulate material according to the present invention include, but are
not limited to, the sulphate process, the chloride process, the fluoride process,
the hydrothermal process, the aerosol process and the leaching process.
Further details for enablement of the present invention may be found in
US201 3/0048925, and the documents referred therein .
The titanium dioxide itself may comprise one or more dopants
which may be incorporated during its preparation by known processes. The
dopants may include but are not limited to calcium, magnesium , sodium,
nickel, aluminium , antimony, phosphorus, and/or cesium. The titanium dioxide
particles may be treated as known in the art with a coating agent to form
coated titanium dioxide or coated doped titanium dioxide. For example, the
first particulate material may be dispersed in water along with the coating
agent. The coating agent may be an inorganic oxide or hydrous oxide, such
as Al20 3, Si0 2, Zr0 2, P2O5, sodium silicate, aluminium chloride, etc. After
coating, the first particulate material may be washed and dried before being
ground, for example, in a fluid energy mill or micronizer, to separate particles
stuck together by the coating. At this milling stage, an organic surface
treatment, including polyols, amines, alkyl phosphonic acids and silicone
derivatives, may also be applied if desired. Further details may be found in US
2013/020971 7, and the documents referred therein.
Suitable titanium dioxide based particulate materials for the use
according to the present invention may be, but are not limited to, the Altiris®
550 and/or Altiris® 800 type grades, both produced by the company
Huntsman.
ANALYTICS
CRYSTAL SIZE
The average crystal size may preferably be determined by
transmission electron microscopy (TEM) on a rubbed out sample with image
analysis of the resulting photograph , e.g. using a Quantimet 570 Image
Analyser. This may be validated by reference to the latex NANOSPHERE™
size standard 3200 from NIST with a certified size of 199+/-6 nm.
PARTICLE SIZE
The average particle size may be preferably determined by Xray
sedimentation. To measure particle size in this context, the product is
subjected to high shear mixing, in the presence of a suitable dispersant, to
disperse the particles without comminution . The particle size distribution is
measured using a Brookhaven XDC X-ray disk centrifuge. Average particle
size, and particle size distribution, on a weight basis, may be recorded.
ASTM 1003D
The absorption and scattering behaviour of a transparent
specimen will determine how much light will pass through and how objects will
appear through the transparent product. The objective measurement of
transparency may be made using a haze meter, e.g. using a BYK Gardner
Haze-gard dual, according to the following principle: a light beam strikes the
specimen and enters an integrating sphere. The sphere's interior surface is
coated uniformly with a matte white material to allow diffusion . A detector in
the sphere measures total transmittance and transmission haze. A ring sensor
then detects the narrow angle scattering light (clarity).
TRANSM ISS ION AND REFLECTANCE
Transmission and/or reflectance may preferably be determined
by measuring the amount of transmitted light in the UV, visible and nearinfrared
region , preferably using a UV-VIS-N IR spectrophotometer, such as a
Perkin Elmer Lambda 950 equipped with a large integrated sphere PELA 1000
of 150 mm. This enables the measurement of specular, diffuse and reflectance
of materials as well as total transmission of transparent and semi-opaque
materials. The amount of transmitted light passing through a sample may be
detected with this apparatus in a wavelength range from 190 nm up to 3300
nm.
HAZE
Haze is preferably measured according to ASTM D 1003, and is
defined therein as the percentage of the light transmitted through an object
which is scattered more than 2.5 ° away from the diection of the incident
beam . Materials with haze values greater than 30% are considered diffusing.
Testing is preferably performed with a Spectrophotometer, according to
procedure B.
ANGULAR TRANSMITTANCE
Angular transmittance is preferably measured by using a
Transvision system consisting of a large integrating sphere with an internal
diameter of 1 m, a CCD array spectrometer, a Xenon light source and whereby
the system is designed according to ISO 13468. The device meets the
specifications of the measurement protocol developed by TNO and
Wageningen UR (see: Ruigrok J., 2008, "Lichtmeetprotocol
kasdekmaterialen", GLAM, TNO report 034-DTM-201 0-03385, and Swinkels,
2012, "Transvision : a light transmission measurement system for greenhouse
covering materials", Acta Hort. , 956:563-568) .
The device measures angular and hemispherical transmittance,
as well as spectral haze (1.5 ° ) in the range of 350-2000 nm for clear and
diffuse samples. The angle of incidence is the angle between a beam incident
on a surface and the line perpendicular to the surface at the point of incidence,
called the normal. The direct transmittance for x ° is defined as the
transmittance of light with an angle of incidence x , measured in degrees
according to a degree system having 360 degrees for a full circle.
EXAMPLES
Masterbatches according to the present invention (1MB 1 and 2)
as well as comparative masterbatches (CMB 1 and 2), all of which the
compositions are shown in Table 1, were produced using a twin screw extruder
of the type ZSK26, obtained from Coperion, equipped with 14 consecutive
temperature zones.
As base resin a ground low-density polyethylene (LDPE)
general purpose polymer material was used having a melt index or melt flow
index of 2 1 g/1 0 min , measured according to ASTM D 1238 and ISO 1133 at
190°C with the standard weight of 2.16 kg, and forwhich the internal code was
lco N2105- 1000. In the CMB 1, Iriodin® SHR 9870 was used as an
interference pigment, as supplied by Merck. This pigment is widely used as an
NIR blocker. CMB 2 comprises a conventional pigmentary rutile Ti02 grade,
Tipure R 103-07, supplied by DuPont de Nemours, which is typically used for
outdoor applications.
Altiris® types 550 and 800 were respectively added to the
invention masterbatches IMB1 and IMB2. These are Ti02 grades, supplied by
the company Huntsman , which are especially designed for NIR blocking
purposes with a selective particle size distribution. The Altiris® type Ti02
grades contain more than 93.0 %wt Ti02, with more than 99.0 %wt thereof in
the rutile crystal form. The Ti02 particles are coated with a material which is
based on oxides of Aluminium and/or Silicium , and have not been subjected to
a carbon treatment. Altiris® grades of the types 550 and 800 have a published
particle size ranging from 0.04-2.28 mhi and 0.04-2.837 mhi respectively, as
measured by laser diffraction spectrometry (LDS) (BT-2003, Dandong better
size Instruments, Ltd.). The dispersant used was sodium henamephosphate.
The refractive index of the Ti02 particles and the surrounding medium were
2.81 and 1.333, respectively. The measured median particle size is 0.36 mhi
for the Altiris® 550 and 0.41 mhi for the Altiris® 800 grade (J . Song, 201 4) .
The twin-screw extruder of the type ZSK 26 was operated at an
output of 20 kg/hr and at a speed of 400 rpm. The following temperature set
points were used for the compounding of the different masterbatches: T zones
2 till 9 = 180°C and T zone 10 till 14 = 170°C.
Table 1
Escorene FL 00209, obtainable from the company Exxon Mobil
Chemical, is an ethylene vinyl actetate (EVA) grade containing 9% vinyl
acetate (VA). Escorene FL 00209 was dry blended with concentrations
ranging from 0.2% to 1.0% of the comparative masterbatches CMB 1 and 2
and with the working masterbatches 1MB 1 and 2, and each of the blends was
subsequently fed into a blown film extrusion line of the Macchi 55 type, using a
die with a diameter of 180 mm, a throughput of 75 kg/hr, and a blow-up ratio
(BUR) of about 1.84, in order to produce a set of EVA-based blown monofilms
of about 150 mhi thickness.
Figure 1 shows the total visible light transmission T, in the full
range from 400 to 700 nm, as a function of the concentration C of the additive
in the films, expressed in wt%, shown as the abscis. On Figure 1, the label A
represents a blank sample containing Escorene only, without any additive,
hence at 0%, label B designates the CMB 1, containing Iriodin® SHR 9870,
label C represents the 1MB 2 containing Altiris® 800, label D represents the
1MB 1 containing Altiris® 550, and label E designates the CMB 2 containing
Tipure R 103-07.
The influence on the total light transmission in the PAR area of
an increasing additive concentration in CMB 1 is relatively limited, whereas
adding a general purpose Ti02 grade, such as in the CMB 2, results in a
significant decrease in total light transmission at increasing concentrations.
In comparison to the currently known NIR technology, which is
represented by the CMB 1 samples, the samples with the Altiris® grades show
a lower visible light transmission. However, in comparison to the samples
containing the conventional pigmentary rutile Ί 0 2 represented by the CMB2
samples, in the samples containing the Altiris® grades show a much better
total visible light transmission , which is beneficial for plant growth in
greenhouses. The commercially acceptable total visible light transmission in
greenhouses, which is usually more than 70%, is reached with an addition
level of up to about 0.6% Altiris® 550 and 800 in the final film , while not more
than 0.2% of the conventional pigmentary rutile Ti02 of the R 103 type could
be added before reaching this same limit of acceptable total visible light
transmission .
The average total visible light transmission as shown in Figure 1
is a first indication on the total visible light which is eventually reaching the
plants. It is however also important to have an idea of the influence of the
incident light angle on the total light transmission of the film, as the angle of
light originating from the sun varies with the hour of the day.
A significant drawback of the currently used NIR technology
(represented by CMB 1) is that the total light transmission is depending on the
incident light angle.
Figure 2 shows the angular transmittance (AT) in percentage,
as a function of the angle of light incidence A, expressed in degrees (360 ° for
a full circle, 0° being perpendicular light incidence) , measured for three 150
mhi EVA-based films: label A: with no additive, label B' : 2.4% of Iriodin SHR
9870 added, and label D' : 0.4% of Altiris® 550 added. The sample with label
B' thus represents the conventional NIR technology. The sample with label D'
represents a working example of the present invention. The concentrations for
the samples B' and D' were chosen such that the total visible light transmission
in the direction perpendicular to the film (= incident angle 0° ) was the same for
both samples and within the commercially acceptable range.
In particular at the higher incident angles A above 50 ° , the
angular light transmittance of the Iriodin® SHR 9870 containing sample B'
reduces significantly as compared to the Altiris® 550 grade containing sample
D'. This experiment shows that the Altiris® type grades offer a beneficial effect
when used in a greenhouse structure, because it will result in a higher total
transmission of the light over the full day.
In warmer climates NIR blockers are commonly used, and it is in
those climates not only important to have a high total visible light transmission,
but also to obtain a higher diffuse part of this light transmittance. The diffuse
light typically brings positive effects on crop growth , whereas an excessively
high intensity of direct light may lead to plant damage because of local
overexposure, as explained herein before.
In Figure 3 the percentage DT(%) of diffuse light, expressed
relative to the total transmitted visible light, is shown for a 150 mhi EVA film as
a function of the concentration C, expressed in wt%, of additive in the final film.
Similar to Figure 1, the labels A, B, C, D and E stand respectively for the
blank experiment, the CMB 1 containing Iriodin® SHR 9870, the 1MB 2
containing the Altiris® 800 grade, the 1MB 1 containing the Altiris® 550 grade,
and the CMB 2 containing the Tipure R 103-07.
The conventional NIR blocker, represented by CMB 1,
demonstrated only a minor effect in diffusing the transmitted light. The Altiris®
grades shown as C and D offer the advantage of providing a film having a high
total light transmission combined with at the same time a high degree of
diffusing the transmitted light, as compared to the conventional pigmentary
rutile Ti02 of the R 103 type, shown as E, of which Figure 1 has shown that the
total visible light transmission is significantly lower. At the higher
concentrations, i.e. more than 0.8% in a 150 mhi film , the portion of diffused
light may become higher for the Altiris® grades than for the conventional Ti02,
and this is again in combination with a significantly higher total light
transmission for the Altiris® grades.
To show the difference in NIR transmission between the
currently offered NIR blocking technology and the Altiris® 550 grade, a UVVIS-
NIR spectrum is shown in Figure 4 for different additive levels. The total
light transmission of a 150 mhi EVA film is shown as a function of the
wavelength l expressed in nanometers. The label A stands for the blank
150 mhi film sample, labels B 1, B2 and B3 respectively represent the 0.2 wt%,
0.4 wt% and 0.6 wt% Iriodin® SRH 9870 samples for the conventional NIR
blocking technology, labels D 1, D2 and D3 respectively represent the 0.2 wt%,
0.4 wt% and 0.6 wt% Altiris® samples, and labels E 1 , E2 and E3 respectively
represent the 0.2 wt%, 0.4 wt% and 0.6 wt% Tipure R 103 samples.
The visible light region (V) and the near-infrared light region (IR)
are also indicated on Figure 4. At equal additive concentration, the
conventional Iriodin® SHR 9870 pigment (B) is showing a much higher NIR
transmission as compared to the conventional Ti02 (E) and also to the Altiris®
grade (D). The Iriodin® SHR 9870 pigment (B) thus has a lower NIR blocking
effect than the two alternatives shown (D and E), at equal concentrations.
Remarkable is also that the shape of the curves for the Altiris grade (D) are
significantly different from those for the conventional pigmentary Ti02 (E).
The Altiris® 550 grade, as compared to conventional pigmentary Ti02 (R1 03),
combines a significantly higher transmission in the visible light region for about
equal NIR transmission levels.
From the spectra in Figure 4, the average total transmission of
respectively the visible light (400-700 nm) and the NIR radiation (700-2300
nm) ranges were calculated, always relative to the intensity of the solar
spectrum at the corresponding wavelength. The resulting average relative
percentages of transmission of the visible light and the NIR parts of the solar
spectrum are summarized in Table 2.
Table 2
Table 2 shows that it is clear that at equal concentrations of
additive, the conventional Ti02 is able to provide about equal NIR blocking but
at the same time results in a much lower total visible light transmission which
will have a negative effect on crop growth. Compared to the currently used
NIR technology (Iriodin® SHR 9870), the Altiris® 550 type grade requires a
much lower addition rate in order to reach an equal NIR blocking and at the
same time offers in addition a higher light diffusion.
Having now fully described this invention, it will be appreciated
by those skilled in the art that the invention can be performed within a wide
range of parameters within what is claimed, without departing from the scope
of the invention, as defined by the claims.

CLAIMS
1. The use of a particulate material in a polymer article for
reducing the transmission of near-infrared radiation and for allowing
transmission of visible light through the article, whereby
- the particulate material is based on crystalline titanium dioxide, i.e.
containing Ti0 2, in the anatase and/or the rutile crystal form ,
the particles of the particulate material are coated with an organic
and/or inorganic coating layer,
at least 20% by weight of the particulate material particles have a
particle size of at least 400 nm and at most 1000 nm,
at least 1.5% by weight and at most 40% by weight of the particles
in the particulate material have a particle size of less than 400 nm
and at least 280 nm.
2. The use according to claim 1 for diffusing at least part of
the photo-active radiation part of the visible light.
3. The use according to claim 1 or 2 for transmitting at
least part of the UV light spectrum .
4. The use according to any one of the preceding claims
wherein the particle size distribution of the particulate material particles shows
a major peak in the range of 400-1 000 nm, and preferably the particle size
distribution of the particulate material particles being unimodal and the single
peak thereof being in the specified range.
5. The use according to any one of the preceding claims
wherein the particulate material particles have an average particle size of at
least 400 nm and up to 1200 nm.
6. The use according to any one of the preceding claims
wherein at least 30% by weight of the particulate material particles have a
particle size of at least 400 nm and at most 1000 nm.
7. The use according to any one of the preceding claims
wherein at least 60% by weight of the particulate material particles have a
particle size of at most 1000 nm.
8. The use according to any one of the preceding claims
wherein at least 2.0%wt by weight of the particles have a particle size of less
than 400 nm and at least 280 nm.
9. The use according to any one of the preceding claims
wherein, prior to the use, the particulate material particles have been treated to
selectively remove particular size fractions.
10. The use according to any one of the preceding claims
wherein the titanium dioxide has a Ti02 content of at least 80%wt.
11. The use according to any of one of the preceding claims
wherein the polymer article contains at most 100 ppm of Fe20 3.
12. The use according to any one of the preceding claims
wherein at least 50% by weight of the Ti0 2 crystals are in the rutile crystal
form.
13. The use according to any one of the preceding claims
wherein the titanium dioxide has an average crystal size of at least 400 nm
and up to 1200 nm.
14. The use according to any one of the preceding claims
wherein the titanium dioxide is substantially white, preferably the particulate
material having a lightness value L* in the CIE L*a*b* colour space of greater
than 80, with an absolute value of a* of less than 5 and an absolute value of b*
of less than 5.
15. The use according to any one of the preceding claims
wherein the coating layer represents from 0.50 to 20%wt relative to the total
weight of the particulate material particles.
16. The use according to any one of the preceding claims
wherein the coating layer comprises one or more oxide materials.
17. The use according to the preceding claim wherein the
oxide material is an oxide and/or hydrated oxide, i.e. a hydroxide, of one or
more elements which are, referring to the Periodic Table of lUPAC dated 22
June 2007:
group 4 and 12 transition metals selected from Ti, Zr and Zn and/or
group 13 to 15 p-block elements selected from Si, Al, P and Sn,
and
lanthanides.
18. The use according to any one of the preceding claims
wherein the particulate material particles have been submitted to an organic
surface treatment.
19. The use according to any one of the preceding claims
wherein the article is a polymer film.
20. The use according to any one of the preceding claims
wherein the polymer of the article further comprises at least one of the
additives known in the art.
2 1. The use of a polymer composition containing the
particulate material as defined in the use according to any one of the
preceding claims in a concentration from 500 ppm by weight up to 70%wt,
relative to the total weight of the composition, in the production of a polymer
article for reducing the transmission of near-infrared radiation and for
increasing the transmission of visible light through the article.
22. The use according to the preceding claim wherein the
polymer composition is a masterbatch composition.
23. The use according to the preceding claim wherein the
masterbatch composition contains from 2.0%wt to 70%wt of the particulate
material.
24. The use of a polymer film composition containing the
particulate material as defined in the use according to any one of the
preceding claims in a concentration from 500 ppm by weight up to 3.0%wt,
relative to the total weight of the composition, in the production of a polymer
film for reducing the transmission of near-infrared radiation and for increasing
the transmission of visible light through the polymer film.
25. The use according to the preceding claim wherein the
polymer film composition is based on a polymer selected from the list
consisting of polyethylene, high-density polyethylene, low-density polyethylene,
linear-low-density polyethylene, metallocene linear-low-density polyethylene,
ethylene vinyl acetate copolymer, ethylene butenyl acetate copolymer,
ethylene vinyl alcohol copolymer, polyethylene terephthalate copolymer,
polycarbonate, polymethylmethacrylate, polypropylene, and mixtures thereof.
26. The use according to any one of claims 24-25 wherein
the polymer film has at least one layer which is made from the polymer film
composition.
27. The use according to claim 26 wherein the at least one
layer further comprises at least one of the additives selected from the list
consisting of a UV absorber, a near IR absorber, a far IR absorber, a near IR
reflector, a far IR reflector, a stabilizer, an antioxidant, a processing aid, an
antistatic agent, a colorant, an inorganic salt, a pearl-lustre pigment, a NIRreflective
substance, an antifogging agent, a filler, an antiblock agent, a light
stabilizer, a slip agent, a UV blocker, a diffusing agent, and combinations
thereof.
28. The use according to the preceding claim wherein the at
least one layer is a top layer of a multilayer film.
29. The use according to any one of claims 24-28, wherein
the polymer film has a transmission in the visible light region of the sunlight, of
at least 30%.
30. The use according to any one of claims 24-29, wherein
the polymer film has a transmission in the photosynthetically active part of the
visible region of the sunlight, of at least 30%.
3 1. The use according to any one of claims 24-30 wherein
the polymer film has a transmission of the near-infrared radiation in the
wavelength region from above 700 up to 2500 nm of at most 90%.
32. The use according to any one of claims 24-31 wherein
the polymer film has a haze of at least 20%.
33. The use according to any one of the preceding claims
for reducing the temperature inside a greenhouse and/or for increasing the
crop yield inside a greenhouse.