Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Polyolefin films, particularly low density polyethylene
and EVA co-polymer, are widely ussd all over the world as co~er
for protecting crops in the form of mulching, tunnels and
particularly greenhouses.
These polyolefin ilms have Serious drawbacks for
these applications and could be summarized as follows:
a) They are permeable to long wave infra-red
radiation particularly within the range of between approximately
7 and 14 microns ~.7.10 6 and 14.10 6m) which is precisely the
area of greatest transmission of the dry atmosphere. Consequently
the covers or greenhouses covered with these films loose consider-
able heat through radiation, particularly on clear nights when
the earth and the plants act as a low temperature black body
transmitter, causing the phenomenon known as thermic inversion
to occur when the termpature inside the cover or greenhouse can
be a few degrees centigrade lower than on the outsi.de producing
frosts or increasing the costs of the necessary energy when the
cover or greenhouse is heated artificially.
b) These films are poor light diffusers creating areas
of deep shadow inside the covers or greenhouses produced by the
structural support and the plants themselves.
c) These films are permeable to ultra violet radiation ~;
and therefore provide no protection from the harmful effects
o~ this form of radiation on the plants.
Reference may be had ko the following art:
1) French Patent 1,574,088 (April 16, 1968)
2) Patent of Addition to French Patent 1,574,088
(January 15, 1973).
3) Japanese Patent 7,213,853 (May 15, 1968)
4) Belgian Patent 845,925 ~.September 9, 1975)
5) Japanese Patent J.5-1074-846 (December 18, 1974)
6) Japanese Patent J.5-0088-147 (November 8, 1973)
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By this art it is known that by adding to these
polyolefin films products such as silica, alumina silicate or
aluminum hydroxiae, transmittance in the area o the spectrum
of between 7 and 14 microns is conslderably reduced as well a~
increasing the strength o light diffusion, but these products
have, among others, the following drawbacks:
a) Both silica and alumina silicates are generally
very abrasive causing serious problems of wear in the e~uipment
for preparing the composition and also in the manufacture of
the film.
; b~ The commercially known silica and aluminum silicates
have the effect of accelerating degradation of these films thus
further worsening the problem.
c) Aluminum hydroxide presents none of these problems
but it has only an absorption effect in wave lengths over 10
microns (10.10 6m) which, on a practical level, means that it
is only really effective when mixed with silica or aluminium
siIicate and thus the above problems cannot be avoided.
It is also known that ethylene and vinyl acetate co-
polymer-films (EVA co-polymeri tend to increase their absorption
in the area of the spectrum between 7 and 14 microns as the
vinyl acetate content is increased but light diffusion efects
; are very low irrespective of vinyl acetate content.
The purpose of this present invention is to solve the
earlier problems by providing a composition making up at least
80~ in weight preferably 90 to 97%-of a polyolefinj in particular
a polyethylene or ethylene and vinyl acetate co-polymer, to
which is incorporated, by the methods which will be described
later, a blend of two components, the total weight content of
which is between l to 15% b~t preferably between 3 to 10%.
These components are the following:
- A double basic sulphate having the following
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emperical formula:
(SO4)4M6111 . M21 12 (OH~
which may also contain some SO3 or H2O and wherein Ml11 is
a trivalent metal and Ml a monovalent metal.
The minerals known as aluni~e, natroalunite, jarosite,
natrojarosite etc. meet this ~ormula. Hillerbrand and Pen~ield
give the following as a constitutional formula for alunite:
OH OH
~ Al - O - s - O - Al ~
OH'" / ~ \ ~ OH
O O O
OH
10 `Al-O ~ K \ S~ o OH
O// \ / ~ O - Al
OH ~ ¦ ~ OH
~ Al - S - O - Al
OH''' - OH
These compounds have good absorption in the area of
the spectrum between approximately 7 and 10 microns (7. 10 6
10. 10 6m), they are insoluble in water, compatible with the
polyolefins and very stable in the temperature ranges used in
the preparation and manufacture of polyolefin films.
- An aluminum hydroxide Al(O~)3 normally known as
hydrated alumina and shown as A12O3 . 3H2O, which gives low
transmittance in the area of the spectrum between approximately
10 and 14 microns (10. 10 6 _ 14. 10 6m).
When this blend of product is incorporated into the
polyolefins a very low transmittance is achieved in the infra-
red spectrum between 7 and 14 microns (7. 10 6 _ 14. 10 6m),
; the range that corresponds to the maximum transmission of
the dry atmosphere.
These products should be used as finely ground powder
preferably with an average particle si~e of between 1 and 15
microns (1. 10 6 and 15. 10~6m).
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1~28;22~3
It has ~een found that blends of polyolefins containing
the above products have the following ad~antages over known
systems based on silica, alumina silicates or blends of both
with aluminium hydroxiae:
- They have no adverse eect on khe degradation
of polyethylene and EVA co-polymer ilms which
is very important for the present application wherein
the films are exposed to all types of weathers.
- They have very little abrasive mess which is also
an important factor as both the compound and the
films are manufactured in equipment normally used in
the plastics industry and such suffer severe wear
when abrasive blends are used.
Another objective of this invention is to include a
W radiation filter in the proportion of 0,05 to 2% but
preferably of 0,1 to 0,6%. By partially absorbing the UV
radiation, these films inhibit the adverse effect of this
radiation on the plants, increasing crop growth. Among the
products that absorb UV radiation are included the benzophenone
family and the benzotriazoles.
As well as those additives which are the object of this
invention, others with known effect can be incorporated such as
anti-oxidants, W stabilizers, humectants, anti-static agents,
etc.
All of these addi~ives may readily be incorporated
i}ltO the polyolefins by any of the known systems of compound
manufacture although it is recommended to employ high shear
equipment, Banbury ~ type internal blenders, Buss-ko-knetter
or Werner Pfleiderer ~ type continuous blenders etc., or mill
` 30 cylinders in order to achie~e a good dispersion of the mineral
products. Once the composition has been prepared, the
agricultural film may be manufactured by any o the known
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1~28ZZ8
methods such as calendering, casting or tubular film, this
latter procedure being preferable.
Polyole~in films manufactured with the composition
described herein have, amonyst othexs, ~he ~ollowing advankage~:
- They are quite opaque to radiation in the spectrum
range of from between 7 and 14 microns (7. 10 6 and
14. 10 6m) which act to provide reduction in heat
loss in the greenhouse or cover and consequently
lessens the risk of frost.
- They are relatively opaque to W radiation which acts
to considera~ly reduces the adverse effect on plants.
- They are excellent light diffusers, reducing the
shadow inside the greenhouse caused by the structural
support and by the plants themselves.
- They are highly transparent to the radiation of
visible light and short wave infra-red which is
fundamental in order to get the greenhouse effect.
- Their mechanical strength is practically equivalent
to that of the films normally used for this
application made of polyolefins without ~illers.
- As it starts from a composition that can be considered
non-abrasive, the manufacture of the films by
traditional methods presents no problem.
For all the above reasons, the films for agricultural
uses describedLn this invention have the pxoperty as has been
demonstrated in a number of expariments using them, of
- increasing the early development of plants and crop growth
in comparison to polyolefin films without illers and this
results in a considerable increase in productivity.
The following examples are an illustration of this:
; Example No. 1
A series of compositions based on low density
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polyethylene having a melt flow index o 0,3 gr/10 min. and
containing variable quantities of alunite and aluminium
hydroxide such that the total o both was always 5% were
placed in mill cylinders. ~nploying ilms of a 0,150 I~m
thickness manufactured by the tubular process, measurements
were taken o visible light transmission, percentage of
transmittance in the area of the spectrum between 1450 and 730
cm l (approximately between 7 and 14 microns~, percentage of
transmission of the energy emitted by the black body at 10C
in the area of the spectrum between 1450 and 730 cm l, this
latter corresponding to that of the transparency of the dry
atmosphere and between 1500 and 400 cm 1 which is more than
90~ of the total energy emitted by the ~lack body. Finally,
the light dispersion was also measured as a percentage of
light transmitted and dispersed at an angle over 8 above the
impinging ray. The results are shown in Table l. As a
reference, a sample having no iller additives and another
sample containing 5% silica were also prepared.
Example No. 2
To measure the abrasive effect of compositions of
various formulations containing 80% polyethylene and 20%
different mineral illers, the films were extruded in an
` extruder with a special part attached to ~he end of the screw.
The abrasive effect was determined on the basis of weight
loss in the metallic attachment during an extrusion cycle of
500 hours. The results are as follows:
Sample Wei~ht loss in 500 hr cycle
20% silica
Celite ~ - 499 0,026 gr.
10% of (OE)3Al. 10% alunite 0,010 gr.
20% TiO2 rutile type ~control) 0,010 gr.
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Example No. 3
To measure the effect of various mineral illers on
the aging of polyolefin films, various films having a thiakness
of 0,150 mm based on LDP~ with a melt ~low index of 0,3 gr/10
min. containing 5% mineral filler and no UV stabilizer were
prepared. They were exposed to natural aging in the sun under
identical conditions. Degradation of the films was determined
by the number of hours re~uired to achieve a 0,2% level of
carbonyl groups. The results are shown in Table 2 which clearly
demonstrate the superiority o additives used in this invention
against the various types of silica and aluminium silicate.
Example No. 4
To determine the effect on plants, three agronomically
identical greenhouses were set up having a surface of approxi-
mately 500 m2. The greenhouses were covered with natural
polyethylene films without fillers (Greenhouse 1) polyethylene
with 0,4~ of a W light absorber of the benzophenone type
(Greenhouse 2) and finally a film demonstrating this invention
containing 3% alunite, 2~ (,OH)3Al and 0,4~ UV absorber
(Greenhouse 3). Temperatures, early developmen~ and production
of various types of plants and profitability of the greenhouses
were recorded. The results are shown in Table 3.
-~ The average minimum temperatures were approximately 2C
higher in Greenhouse 3 than in No. 1 and No. 2 and the
; mechanical strength of the films was in all cases sufficiently
good to withstand winds of up to 100 Km/hour.
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