Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to polyethylene films and more
particularly to polyethylene greenhouse films for use in
agriculture.
One characteristic of polyethylene greenhouse film
enclosing the micro-envlronment of greenhouse space is that
the film has high transparency to the long wave infra-red
radiation energies emitted by the masses in the greenhouse
environment The black body radiation emitted by the masses
\ within the micro-environment has most of its energy within
the range of wave lengths from 5 micrometres to 68 micrometres,
with nearly 50 percent of the above energy falling in the
range below 14 micrometres. It is known~hat the atmosphere,
coincidentally, is also transparent to radiation wave lengths
of from 7 to 14 micrometres, thereby bringing the masses
within the greenhouse into direct energy exchange with the
universe when the atmosphere is clear and cloudless~ The
atmosphere absorbs and exchanges radiation of wave lengths
greater than 14 micrometres while the cloud cover effectively
absorbs and exchanges radiation over the entire range of
black body radiation.
It is well documented that any greenhouse film which
reduces the transmission of infra-red (I.R.) radiation in
the range of wave length 7 to 14 micrometres, preferably,
7 to 25 micrometres, will inevitably save energy in the form
of heat energy. If the same film also has the characteristic
of allowing the transmission of solar radiation in the photo-
synthetic active region into the greenhouse wi~ also good
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dispersion of the light, yood plant growth and yields are
obtained.
In attempts to overcome this high transparency problem
with polyethylene greenhouse film,different fillers or combin-
ations of fillers have been incorporated with the polyethyleneso as to make the film less transparent to the I.R. radiation
and thus retain, as much as possible, the energy within the
greenhouse micro-environment.
It has been found that combinations of silica and
aluminium hydroxide (as aluminium oxide trihydrate) glve
mutually additive bands of absorption to render the compositions
effective I.R. absorbers in the radiation range of 7 to 25
micrometres. This range encompasses about 75 percent of the
black body-energy emitted by the masses within a normal
greenhouse micro-environment~
United States Patent No. 4,075,784 discloses the use
in greenhouse fiim of specific alumino-silica compounds,
namely dehydrated alumino-silicates contalning 51-57~ by
weight silica, 40-46~ by weight alumina and less than 3~
impurities. Polyolefin films containing alumino~silicates
having alumina and silica proportions outside the above
ranges have been shown to be inferior in radiation retention.
Howeverr polyethylene films containing such compositions
of silica and alumina suffer from the disadvantage of not
having sufficient longevity when exposed to the elements when
used as greenhouse film. As disclosed in United States
Patent No. 4,134,875, issued January 16, 1979 to Alcudia
Empres~ Para la Industria, this deficiency has been
attributed to the presence of the fillers, specifically
silica and its related trace minerals, in the polyethylene
composition.
In accordance with the present invention it has been
found that the deficiency of short longevity of the silica
and alumin~m hydroxide combination may be overcome.
Surprisingly, we have found that a unique combination of
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stabilization additives has provided the silica and aluminium
hydroxide combination with longevity suitable for commercial
application.
It is thus an object of the present invention to provide
a polyethylene greenhouse film having commercially acceptable
long wave radiation retention and longevity.
Accordingly, the invention provides a composition
comprising at least 80~ by weight of a polyethylene base
resin having a melt index of less than 4 dg/min. and a
density of 918 - 940 kg/m3; 0.5 - 5~ by weight of silica
having a particle size in the range 1 - ~0 microns;
2 - 7~ by weight of aluminium hydroxide having a particle
size in the range 0.1 - 10 microns; an ultraviolet light
stabilizer of the polymeric sterically hindered amine (HALS)
class selected from compounds of the formulae I and II:
H H
3 > ~ 3 ~ C~HI3
(I) ~ ~ (CH2)6 - ~ ~-~---~~~~~~
N~N
1 3 1 3
1 2 I CH3
C~3 CH3 _ n
where n = 2,000 to 3,500, the melting point = 115 - 150C,
the density = 1.01 g/cm3 (20C) and the pH (at 100 g/l
water) = 8.5; and
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poly-6-morpholino-s-triazine=2,4-diyl
((2,2,6,6-tetramethyl-4-piperidyl)imino)hexamethyl
((2,2,5,6-tetramethyl-4-piperidyl)imino); having a
II softening range of 110 - 130C and volatility during
thermogravimetric analysis (heating rate 10C/minute),
and a 10% weight loss at 340C;
0.05 - 1% by weight of 2,21-oxamido bis-~ethyl 3-(3,5-di-
tert.-butyl-4-hydroxyphenyl)propionate]. and 0.1 - l.S~
by weight of 2-hydroxy-4-n-octoxy-benzophenone.
By the term polyethylene base resin is meant a base
polymer selected from polyethylene, low density polyethylene,
linear low density polyethylene, an ethylene-vinyl acetate
copolymer and mixtures thereof having a melt index of less
than 4 dg/min. when measured according to ASTM D1238
condition E and a density of 918-940 kg/m3.
The preferred polyethylene base polymer is a low density
\ ethylene/vinyl acetate copolymer ha~ing a melt index of less
than 1 dg/min.
A more preferred polyethylene base polymer is an ethylene-
vinyl acetate copolymer (polyethylene) having 4~ vinyl acetate
content, melt index of 0.58 dg/min., and density of 928 kg/m3.
Preferably the silica has a particle size in the range
of: 2 to 20 ~m, and is used preferably in the amount of 1 - 3%
by weight.
Preferably the aluminium hydroxide (aluminium oxide
trihydrate) has a particle size in the range of: 1.0 to 5.0 llm,
and is used preferably in the amount of 3 - 6% by weight.
Examples of a silica and an aluminium hydroxide of
use in the practice of the invention are CELITE 499*, a
product of Johns Manville, and MICRAL 932W*, a product of
Solem, respectively.
The non HALS W absorber, 2-hydroxy-4-n-octoxy-
benzophenone, has been found to enhance the light stabilizing
property of the HALS additive.
* Denotes Trade Mark
~l~7:LSBl
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The compositions according to the invention may
optionally further comprise antiblock agents, slip additives
and fillers. Antiblock and slip agents are of use to
facilitate opening of the folded film. Exampl~ of such
- 5 compounds are erucylamide slip agentsand calcium carbonate.
Optionally, the composition of the invention may further
comprise an antioxidant additive as a processing aid to
stabilize the polymer during the extrusion process carried
out during the preparation of the composition according to
the invention. A preferred antioxidant additive consists
of a 4:1 by weight mixture of -Tris(2,4-di-t-butylphenyl)
phosphite and octadecyl 3,5,-di-tert.-butyl-4-hydroxyhydro-
cinnamate. This antioxidant mixture is selected because of
its compatibility with the HALS UV stabilizing additives.
A concentration of 0.05 - 1~ by weight in the polyethylene
blend is preferred.
The amounts of the above additives for use in the
polyethylene blend may be readily determined by the skilled
man. The additives can be easily incorporated into the
polyolefin by conventional techniques well known in the
art. One recommended procedure is to use high shear equip-
ment, for example, Banbury*type internal blenders, Buss-
ko-knetter*or Werner Pfleiderer*type continuous blenders,
etc. or mill cylinders to achieve a good dispersion of the
additives with the polyolefin. Once compounded, th~
composition can be converted to agricultural film using any
known method such as calendering, casting or, preferably,
by tubular film.
The HALS stabilizer, the benzophenone and the oxamide
hindered phenol additives all melt at the processing of the
film temperature.
The invention comprises formulated polymer as herebefore
described and polymer film made therefrom.
The following example illustrates by comparison to a
composition containing no W stabilizing additives and non-
HALS W stabilizing additives, the preferred polymer
* trade mark
~ , ~
1~7~5~Y
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composition according to the invention.
EXAMPLE:
A polyethylene blend was prepared having the composition
(expressed in % w/w):
0.75 Chimassorb 944* HALS of formula I
0.38 Cyasorb W 531* 2-hydroxy -4-n-octoxy-
benzophenone
0.1 Irganox B900* combination phosphite and
phenolic antioxidants as
hereinbefore described
0.15 Naugard XL-l* oxamide phenol
1.5 Celite 499* silica
4.5 Hydral 710B* aluminium oxide trihydrate
and the balance being ethylene/vinyl acetate copolymer
(polyethylene) having 4.0% vinyl acetate content, melt
index 0.58 dg/min., and density 928 kg/m3.
* CHIMASSORB, IRGANOX, are trademarks of
Ciba Geigy.
CYASORB is a trademark of Cyanamid.
CELITE is a trademark of Johns Manville.
NAUGARD is a trademark of Uniroyal.
A masterbat~h containing the above additives was
prepared on a FCM-2*compounding machine and had the
composition:
% w/w
CHIMASSORB 944 6.22
CYASORB UV 531 3.11
IRGANOX B 900 0.78
NAUGARD XL-l 0.78
CELITE 499 11.67
HYDRAL710 B 35.0
Polyethylene copolymer balance
The masterbatch was let down with more polyethylene
and slip additive in the following ratio:
polyethylene copolymer 46.3 lbs.
slip additive masterbatch 1.65 lbs.
additive masterbatch 7.1 lbs.
and extruded into 150,um (0.006") thick film on a 2~"
20:1 Davis Standard film extrusion line.
J ' ` * trade mark
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Greenhouse films having the above thickness of 150 ~m were
exposed to accelerated weathering. After 308 MJ of UV
exposure on an EMMAQUA*unit in Arizona the film retained
> 90~ of its strength.After 3000 hours of exposure in an
Atlas Ci~65 Xenon Arc Weather-o-meter*the film retained
75% of its strength.
The films also had the characteristic of transmitting in
single layer ~ 85% of the incident light and having a
diffusion or haze of ~ 65% both measured on a Pacific
Scientific Gardner Haze metre. A photospectrograph prepared
on a Perkins-Elmer*I.R. spectrophotometre gave a graph
with substantial reduction in radiation transmittance in
the range of 7-25 ~m (micrometres). When the data is
compared to that of regular commercial greenhouse film and
the energy curve generated by the black body output it is
seen that I.R. retention films could theoretically save up
to 59-60~ of heat energy over regular films. A test using
well insulated box heated by an infra-red brooder lamp and
having a double layer of film covering only the top for
direct view of atmosphere and universe, an energy saving
of 55% was recorded. Such savings, of course, are dependent
not only on the weather surrounding the greenhouse but
especially on the type, style, and quality of the structure(s).
Th~se houses with more of non-polyethylene walls with poorer
insulation properties will be negatively affected in effecting
savings.
* trad~e ma~rk
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