CA1271581A - Polyethylene composition and film - Google Patents

Abstract

Abstract Polyethylene Composition and Film A composition comprising a polyethylene base resin having a melt index of less than 4 dg/min. and a density of 918 - 940 kg/m3; an ultraviolet light stabilizer of the polymeric sterically hindered amine (HALS) class; silica;
aluminium hydroxide; a benzophenone and an oxamido hindered phenol. The composition is used to make film having improved infra-red characteristics for use with greenhouses.

Description

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 5~1

- 2 - C-I-l 689 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 - 1~7::L5;i3:a

- 3 ~ C-I-L 689 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

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 . ~,~, . .
~;

`:

- 4 - C-I-L 689 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

- 5 - C-I-L 689 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

- 6 - C-I-~ 689 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 5i 31

- 7 - C-I-L 689 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 , , ~

Claims (4)

CLAIMS:

1. 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 - 40 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:

(I) where n = 2,000 to 3,500, the melting point = 115 - 150°C, the density = 1.01 g/cm3 (20°C) and the pH (at 100 g/l water) = 8.5; and poly-6-morpholino-s-triazine=2,4-diyl ((2,2,6,6-tetramethyl-4-piperidyl)imino)hexamethyl ((2,2,6,6-tetramethyl-4-piperidyl)imino); having a (II) softening range of 110 - 130°C and volatility during thermogravimetric analysis (heating rate 10°C/minute), and a 10% weight loss at 340°C;
0.05 - 1% by weight of 2,21-oxamido bis-[ethyl 3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionate]; and 0.1 - 1.5% by weight of 2-hydroxy-4-n-octoxy-benzophenone.

2. A composition as claimed in Claim 1 further comprising 0.05 - 1% by weight of an antioxidant composition consisting of Tris-(2,4-di-t-butylphenyl) phosphite and octadecyl 3,5,-di-tert.-butyl-4-hydroxyhydrocinnamate in the weight ratio of 4:1.

3. A composition as claimed in Claim 2 further comprising a slip additive.

4. A film having a composition as claimed in any one of claims 1 to 3.