Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02251715 2006-10-06
UV RESISTANT PLASTIC FILM OR COATING USED FOR CLIMATE PROTECTION
The present invention refers to a UV-resistant plastic film or coating on
another carrier material
and which in particular is intended as climate protection for example to be
used in connection
with plant growing, specially in greenhouse curtains, greenhouse films and
cover material for
outdoor growing, awning etc. These films have a major problem concerning their
useful life,
since the film is exposed to sunlight and to several chemicals used in for
example plant growing.
Background to the invention
To increase the life of such films it is known to use a light stabiliser of
the kind which hindering
amines (HALS- Hindered Amines Light Stabiliser). This is described in for
example EP-A
0,214,507. These are very good stabilisers for thin films with long expected
lifetimes. They are
often combined with other types of stabilisers and also with UV-absorbents to
further increase
the life. The hindering amines are very reactive and quickly take care of the
degradation products
that are formed, and they are basic. This makes it easy for them to react with
foreign substances
which come in contact with the film and particular substances that are acidic,
e.g. sulphur-,
chlorine- and bromine-based compounds. In some greenhouses such chemicals are
extensively
used to protect the plant from various diseases and insects. When the
hindering amines react with
these chemicals their effects are lost and the film's UV-protection is knocked
out. Some
greenhouse film producers are limiting their warranties for the films life in
connection with or
exposure during longer periods of time for the following groups and
substances, insecticides,
fungicides etc., more specifically substances containing bromine, chlorine,
fluorine, iodine,
sulphur, petroleum-products and wood protecting agent containing copper.
It is also known that films and coatings obtain shorter lives when they are
exposed to so called
acid rain which may apply to awnings placed in environment with high level of
air pollution. The
producer of HALS-stabilisers market some types of stabilisers, that shall be
suitable in such
environments, so called 'acid rain resistant', but tests have shown that their
effectiveness does
not differ much from the other HALS-stabilisers.
Through JP-A-5245987 a laminated film intended for greenhouses and similar is
known. It is
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said to have high tensile strength and to be transparent and hem-resistant.
The film is made of
EVA to which an unsaturated alkoxysilane has been grafted with help of a
peroxide, whereafter
the polymer was crosslinked. At the grafting the polymer chain is opened up
with the peroxide
where the silane-group is attached, which later is crosslinked. There is no
information about any
UV-resistance of this film and in our own experiments (below), it is shown
that such silane
grafted polyolefin does not have desired UV-resistance.
Fires can start in curtain structures in greenhouses and may spread very
rapidly. A desire is
therefor to obtain flame proof material, which also must fulfil all the other
expectations such as
UV-protection, long life etc. of greenhouse curtains.
Object of the invention and its most important characteristics
The purpose with the present invention is to obtain a material suitable for
plastic film or coating
on another carrier material in greenhouse curtains, greenhouse films and cover
material for out
door greenhouse growing. As mentioned above, it may also have applications in
other products,
for example awnings and Venetian blinds, since these may too be exposed to
acidic environment.
The material shall be UV-stable and not or only in very small degree be
effected by exposure to
the chemicals they are normally exposed to in a greenhouse environment and, it
should also in
some cases be flame resistant.
This has according to the present invention been obtained by using a film or a
coating, which
wholly or partially contains a crosslinked polyolefin-silane-co-polymer.
Hereby means a
copolymer where silane groups are placed in the polyolefin chain in a
polymerisation process in
difference to a grafted polymer where the polyolefin chain is opened up for
example by a
peroxide, whereafter the silane groups are placed and crosslinked.
Crosslinking of polyolefin-silane-co-polymer is performed preferably by the
influence of water
and a silaneol condensations catalyst.
The polyolefm consists of preferably a polyethylene, for example low-density
polyethylene,
LDPE or some of its co-polymers for example EVA or EBA. The higher UV-
stability is
surprising since the material is almost an ordinary polyolefin co-polymer with
the only
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difference that the molecules are crosslinked to each other, while properties
such as crystallinity are
almost unchanged. The crosslinked polyolefin can be mixed with a non-
crosslinked polyolefin and/or
polyolefin co-polymer. The polyolefin, preferably of the group polyethylene,
can also contain one or
more other co-monomers in addition to the silane-groups. Examples of such co-
monomers are vinyl
acetate, butyl acrylate, l-butene and 1-octene.
In a multilayer film or coating shall at least one of the layers consist of
the crosslinked polyolefin-
silane-co-polymer according to the invention, but other layers may consist of
other materials, such as
heat radiation absorbing material, including EVA, EBA, PET or PA. Any of the
layers of the multiple
layer film coating can be provided with a flame protective agent as an
additive. Any of the layers of the
multiple layer film or coating can wholly or partly consist of a halogen-or
phosphorous containing
polymer.
The film or coating can also be provided with additives. Examples of such
additives are pigments,
which make it transparent to some wave lengths of the sun light, thus
producing selective sunlight
shielding. Other additives can be anti-fog agents such as glycerol stearate,
glycerol ester or other
products to avoid condensation drops. The anti-fog agent might only be added
to the outer layer. The
film or coating may also be of cellular type, where the ferment - or blow
agent, organic or inorganic, is
mixed into the plastic when the film is produced, which creates cavities which
are closed, open, or
connected, when the blow agent is developed. Other examples of additives are
mincible thermoplastics,
stabilisation agent, lubricant and flame protective agents.
Description of the invention
By the crosslinking of the polyolefin-silane-co-polymer an endless three-
dimensional molecular
structure is built up, which gives the material advantages such as:
~ higher resistance to UV-radiation;
~ higher chemical resistance;
~ higher heat resistance;
~ memory properties in the material, which results in less shrinking and a
lower tendency to form
permanent folds;
~ higher break strength;
~ better low temperature properties;
~ and combinations of the above mentioned properties.
The polymer composition in the basic chain consists of a polyolefin-co-polymer
containing
hydrolysable silane groups. Such a polymer composition is described in for
example SE-B 462 752.
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Desired flame protectiveness is obtained by adding a flame protective agent to
the plastic
film/coating, or its produced strips, which may be composed of a halogen- or
phosphorous
containing compound. These may be used without the level of UV-protection
being reduced,
which is the case, when using the so called HALS-stabilisers to obtain a
satisfying life length.
Another alternative is that the carrier material is composed of halogen- or
phosphorous
containing plastic film or strips of such a film, which are treated with a
layer of the crosslinked
polyolefin-silane-co-polymer. Suitable halogen or phosphorous containing
polymers include
PVC, PVDC, PCTFE, PVF, PVDF, FEB, PTFE or E/TFE.
The film or coating can be of a multiple layer type where at least one of the
layers contains the
cross-linked polyolefin-silane-co-polymer. In a film or coating of the
multiple layer type, a flame
protective agent can be added to any of the layers. Any of the layers can
consist wholly or partly
of a halogen- or phosphorous containing polymer.
In the experiments described below a LDPE crosslinked with a vinyl trimethoxy
silane is used.
This polymer behaves as a 'normal' low density polyethylene with respect to
extrusion
properties. This means that the polymer may be extruded to a film on a normal
extruder without
special rebuilding or additives in the form of special equipment. The
crosslinking is obtained
after extrusion in the presence of water and a catalyst. The production is
described in the
example below.
Exa'rtple 1
Production of a blown film containing a crosslinked polyethylene.
As crosslinked polymer we have used a silane crosslinked LDPE from Borealis,
LE 4421, with
addition of a catalyst in master batch form called LE 4436. LE 4421 is a
commercial copolymer
where vinyltrimethoxysilane is polymerised in the chain. We have used 5%
catalyst master
batch. The polymer and the catalyst were mixed separately just before the
extrusion, though this
can also be done with the normal mixing equipment as is usually present on the
extruder. An
advantage with the later method it that one decreases the contact time between
the polymer and
the catalyst, thereby minimizing the risk for a too early crosslinkage; which
creates gels in the
film.
The polymer and the catalyst master batch were stored protected from damp and
moisture at
about 20°C, to decrease the risk for a too early crosslinkage.
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WO 97/39058 PCT/SE97/00648
The film material with a density of 923 kg/m ' and a MFRS of 0,9 g/10 min was
run at a
temperature setting of the extruder's heat zones of 150-170 °C.-The
screw velocity was 112
rpm which gave a work force of 52 Amp, a melting pressure of 266 bar and a
melting
temperature of I78 °C.
To obtain a film with for us suitable properties, we used a blow up ratio of
1:2. The melting
temperature was kept below 180 °C to avoid problems with gel formation.
To protect the
polymer from degradation during the extrusion it was stabilised by process
stabilisers in the
form of antioxidants.
Example 2
Experiments were made to test the life at different plastic films, that were
exposed to UV-
radiation and sulphur/sulphur compounds.
The tests performed had as a goal to reflect as far as possible real
conditions in greenhouses.
The samples were first exposed to one day and one night of sulphur using a so
called sulphur
lamp, whereafter it was exposed in an Atlas Xenon Weather-ometer Ci35 A. The
conditions in
the Weather-Ometer were: 0,35 W/m ~ at 340 nm, 23 h lightl24 h. No water
spraying. The
conditions should reflect those in Florida. Samples were taken from the Weater-
Ometer at
regular intervals and were tested in a tensile tester (tensile velocity 100
mm/min) and
controlled in an FT-IR to see the carbonyl accumulation at 1718 cm
The films tested were:
70 micron LDPE + HALS
70 micron crosslinked LDPE-silane-co-polymer.
Below are the results obtained. They are based on tensile strength
measurements.
Table 1. Time to 50% relative stretching
1 2
A 1400 h > 1500 h
B 470 h > 1500 h
RECTIFIED SHEET (RULE 91 )
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In experiment A the film samples were exposed only to the Weather-Ometer. In
experiment B
the samples were first exposed 24 h to a sulphur lamp and thereafter to the
Weather- Ometer.
As seen from experiments, the crosslinked film is very UV-stable
irrespectively of whether it
was exposed to sulphur or not. The uncrosslinked polymer had a good UV-
stability when it was
not exposed to sulphur, but after exposure the film's UV-stability decreased
exponentially. If one
wishes to increase the life of the crosslinked polymer it is of course
possible to add a HALS-
stabiliser to it. The stabiliser's effect at acidic environments may however
be questioned.
Example 3
The experiment was performed to compare the life of plastic films of HDPE
silane grafted
HDPE and ethene/vinylsilane-co-polymer which has been exposed to UV-radiation
The films were exposed in an Atlas Xenon Weather-Ometer Ci35A under the
conditions: 0,35
W/m2 at 340 nm, 23 h light/24 h. No water spraying. A simple mechanical test
was performed
continuously during the time the samples were ageing by taking them out and
bending them. As
long as this could be performed without the film sample broke or fell into
pieces, the ageing
continued. The time it took until the sample was broke or became fragile, is
given in Table 2.
The films tested were:
A. 50 micron HDPE
B. 50 micron HDPE + HALS
C. 50 micron silane grafted HDPE
D. 50 micron silane grafted HDPE + HALS
E. 70 micron ethylene/vinylsilane co-polymer
F. 50 micron ethylene/vinylsilane co-polymer + HALS
G. 50 micron 50/50 (ethylene/vinylsilane co-polymer + HpPE)
H. 50 micron 50/50 (ethylene/vinylsilane co-polymer + HDPE) + HALS
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Below are the results obtained.
Table 2. Time until the samples became fragile.
A B C D E F G H
1000h 1450h 1300h 1300h >SOOOh >SOOOh >2000h >2000h
As seen surprisingly good results were obtained with the ethylene/vinyl co-
polymer compared to
the silane grafted polyethylene.
The material according to the invention can as already mentioned be in the
form of a film or in
the form of a coating on another carrier material. The thickness is preferably
<~500 micron. With
films we refer to both continuous films and small film strips, which can be
used in greenhouse
curtains. The film or coating can be of multiple layer type where at least one
of the layers is
composed of crosslinked polyolefin-silane-co-polymer according to the
invention, while other
layers may be of other material, for example heat absorbing material. Example
of such materials
are the polyethylene-co-polymers EVA, EBA, PET or PA. Any of the layers of the
multiple layer
film or coating can have a flame protective agent as an additive. In another
embodiment of the
invention, any of the layers of the multiple layer or coating wholly or partly
consists of a
halogen-or phosphorous containing compound.
The film or coating can be pigmented to obtain selective screening of the
sunlight to affect plant
growth. With this we mean it is transparent only to some wave lengths of the
sunlight. Examples
of such pigments are interference pigments as described in WO 95/05727. Also
addition of UV-
absorbents is a possibility, particularly of benzophenone or benzotriazole
type. It may also
contain so called anti-fog agents to avoid condensation droplets. The anti-fog
agent may be
added to only the surface layer of the film.
The film or coating may also be a so called cell type, with which we mean a
plastic film where a
ferment- or bubble component, organic or inorganic, is mixed into the plastic
when the film is
produced, which creates cavities or bubbles, closed, open, or connected, when
the bubbling
component is broken down.
An example of how the film can be used is as foldable climate protection
curtains or awnings of
that kind which comprises with each other connected strips. The strips can be
either plaited
together or with each other and/or connected through a system of yarn threads,
for example
through a knitting or weaving process. One example of such a climate
protection curtain is
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WO 97139058 PCT/SE97/00648
described in EP 0 109 951. The strips shall here at least partly contain the
UV-resistant plastic
film according to this invention.
Another example on the use of the invention is as foldable water proof climate
protection
curtains or awnings of the kind that comprises of with each other connected
strips, yarn treads
or a combination of strips and yarn treads, where the curtain on at least one
side has a water
proof layer wholly or partially composed of the UV-resistant plastic film
according to the
invention.
At least a part of the strips in the climate curtain or awning can be light
permeable. The strips
may have an additive of a flame protective agent.
The invention is of course not limited to the described examples, but several
modifications are
possible within the scope of claims.
RECTIFIED SHEET (RULE 91 )
