THERMOPLASTIC FILMS FOR PLASTICULTURE APPLICATIONS

Abstract

The present invention relates to a film for use in plasticulture that comprises at least a first layer of a thermoplastic polymer composition, said thermoplastic polymer composition comprising a linear low-density polyethylene having a melt index (MI) measured according to ASTM D1238 at a temperature of 190° C. and a load of 2.16 kg of higher than 1.0 g/10 min and at most 10.0 g/10 min, whereby the film has an RMS roughness measured by AFM according to point 4.2.2 of ISO 4287:1997 of lower than 40 nm, and/or an average roughness measured by AFM according to point 4.2.1 of ISO 4287:1997 of lower than 30 nm.

Claims

1. A film for use in plasticulture, comprising at least a first layer of a thermoplastic polymer composition, said thermoplastic polymer composition comprising a linear low-density polyethylene having a melt index measured according to ASTM D1238 at a temperature of 190° C. and a load of 2.16 kg of higher than 1.0 g/10 min and at most 10.0 g/10 min, whereby the film has an RMS roughness measured by AFM according to point 4.2.2 of ISO 4287:1997of lower than 40 nm, and/or an average roughness measured by AFM according to point 4.2.1 of ISO 4287:1997 of lower than 30 nm.

2. The film according to claim 1 in which said linear low-density polyethylene is obtained by a process for producing a copolymer of ethylene and an second α-olefin comonomer in the presence of an Advanced Ziegler-Natta catalyst, wherein the Advanced Ziegler-Natta catalyst is produced in a process comprising the steps of: (a) contacting a dehydrated support having hydroxyl groups with a magnesium compound having the general formula MgR.sup.1R.sup.2, wherein R.sup.1 and R.sup.2 are the same or different and are independently an alkyl group, alkenyl group, alkadienyl group, aryl group, alkaryl group, alkenylaryl group or alkadienylaryl group; (b) contacting the product obtained in step (a) with modifying compounds (A), (B) and (C), wherein:compound (A) is at least one of carboxylic acid, carboxylic acid ester, ketone, acyl halide, aldehyde or alcohol; compound (B) is a compound having the general formula R.sup.11.sub.f(R.sup.12O).sub.gSiX.sub.h, wherein f, g and h are each integers from 0 to 4 and the sum of f, g and h is equal to 4, Si is a silicon atom, O is an oxygen atom, X is a halide atom and R.sup.11 and R.sup.12 are the same or different and are independently an alkyl group, alkenyl group, alkadienyl group, aryl group, alkaryl group, alkenylaryl group or alkadienylaryl group, with a proviso that when h is equal to 4 then modifying compound (A) is not an alcohol; compound (C) is a compound having the general formula (R.sup.13O).sub.4M, wherein M is a titanium atom, a zirconium atom or a vanadium atom, O is an oxygen atom and R.sup.13 is an alkyl group, alkenyl group, alkadienyl group, aryl group, alkaryl group, alkenylaryl group or alkadienylaryl group; and (c) contacting the product obtained in step (b) with a titanium halide compound having the general formula TiX.sub.4, wherein Ti is a titanium atom and X is a halide atom.

3. The film according to claim 2, wherein the second α-olefin comonomer is propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, 1,3-butadiene, 1,4-pentadiene, 1,5-hexadiene or mixtures thereof.

4. The film according to claim 2, wherein said support for said Advanced Ziegler Natta catalyst is silica, alumina, magnesia, thoria, zirconia or mixtures thereof.

5. The film according to claim 2, wherein compound (A) is methyl-n-propyl ketone, ethyl acetate, n-butyl acetate, acetic acid, isobutyric acid, isobutyraldehyde, ethanoyl chloride, ethanol or sec-butanol.

6. The film according to claim 2, wherein compound (B) is tetraethoxysilane, n-propyltriethoxysilane, isobutyltrimethoxysilane, dimethyldichlorosilane, n-butyltrichlorosilane or silicon tetrachloride.

7. The film according to claim 2, wherein compound (C) is titanium tetraethoxide, titanium tetra-n-butoxide or zirconium tetra-n-butoxide.

8. The film according to claim 2, wherein TiX.sub.4 is TiCl.sub.4.

9. The file according to claim 1, wherein said thermoplastic polymer composition further comprises radiation absorbing additives, in which said absorbing additives are NIR absorbing additives and/or UV absorbing additives.

10. The film according to claim 1, wherein said thermoplastic polymer composition comprises a NIR absorbing additive or an UV absorbing additive.

11. The film according to claim 10, in which said NIR absorbing additive is an organic NIR absorbers or inorganic NIR absorbers, or combinations thereof.

12. The film according to any of the claims 1 to 11, wherein the film is made with a temperature profile of 100° C. to 300° C. and/or a die gap of 0.1 mm to 7 mm and/or a frost line height of 10 cm to 90 cm and/or a blow-up ratio of 1.2:1 to 5:1.

13. The film according to claim 10, in which said UV absorbing additive is a benzophenones, benzotriazole, salicylates, or combinations thereof.

14. The film according to claim 1 wherein the film is an agricultural film.

15. A greenhouse cover comprising a film according to claim 1.

16. The film according to claim 2, wherein compound (A) is methyl-n-propyl ketone, ethyl acetate, n-butyl acetate, acetic acid, isobutyric acid, isobutyraldehyde, ethanoyl chloride, ethanol or sec-butanol; compound (B) is tetraethoxysilane, n-propyltriethoxysilane, isobutyltrimethoxysilane, dimethyldichlorosilane, n-butyltrichlorosilane or silicon tetrachloride; and compound (C) is titanium tetraethoxide, titanium tetra-n-butoxide or zirconium tetra-n-butoxide.

17. The film according to claim 16, wherein said thermoplastic polymer composition further comprises radiation absorbing additives, in which said absorbing additives are NIR absorbing additives and/or UV absorbing additives.

18. The film according to claim 17, wherein said thermoplastic polymer composition comprises a NIR absorbing additive.

19. The film according to claim 19, in which said UV absorbing additive is a benzophenone, benzotriazole, salicylate, or combinations thereof.

20. A greenhouse cover comprising a film according to 19.

Description

EXAMPLES

[0086] The invention will now be illustrated by the following non-limiting examples.

Example 1

[0087] Step 1: Preparation of the Catalyst

[0088] 2.5 g of Sylopol 955 silica which had been dehydrated at 600° C. for 4 hours under a nitrogen flow was placed in a 40 cm.sup.3 flask. 15 cm.sup.3 of isopentane was added to slurry the silica, then 2.5 mmol of di-n-butyl magnesium was added to the flask, and the resultant mixture was stirred for 60 minutes at a temperature of 35° C. Then, 3.5 mmol of methyl n-propyl ketone was added to the flask, and the resultant mixture was stirred for 60 minutes at a temperature of 35° C. Then, 0.25 mmol of tetraethoxysilane was added to the flask and the resultant mixture was stirred for 30 minutes at a temperature of 35° C. Next, 0.25 mmol of titanium tetraethoxide was added to the flask and the resultant mixture was stirred for 30 minutes at a temperature of 35° C. Subsequently, 1.75 mmol of titanium tetrachlo ride was added to the flask and the resultant mixture was stirred for 30 minutes at a temperature of 35° C. Finally, the slurry was dried using a nitrogen purge at 70° C. for 60 minutes to field a free-flowing solid product.

[0089] Step 2: Polymerisation

[0090] The catalyst as produced in step 1 was used to produce linear low-density polyethylene in a fluidized bed gas phase polymerization reactor. The fluidized bed gas phase polymerization reactor had an internal diameter of 45 cm and was operated with a 140 cm zone height. The catalyst was fed to the reactor using a dry solid catalyst feeder to maintain a production rate of 10 kg per hour. Ethylene, 1-butene, hydrogen and nitrogen were introduced to the reactor to yield polymer with the required specifications. 5 wt % triethylaluminium (co-catalyst) solution in isopentane was continuously introduced to the reactor at a feed rate of 0.08 kg per hour. The reactor temperature was maintained at 86° C., ethylene partial pressure at 7.0 bar, total reactor pressure at 20.7 bar and superficial gas velocity at 0.42 m/s. The process ran for three consecutive days.

[0091] Step 3: Film Production

[0092] 200 ppm of Irganox 1076 (2,6-di-tert-butyl-4-(octadecanoxycarbonylethyl)phenol, CAS registry number 2082-79-3), 500 ppm of zinc stearate and 800 ppm of Weston 399 (tris(nonylphenyl) phosphite, CAS registry number 26523-78-4) were added in a Henschel mixer and mixed for 5 minutes with 25 kg of the linear low-density polyethylene produced in step 2. The mixed material was pelletized using a ZSK-30 twin-screw extruder under the following conditions: a temperature profile of 130° to 210°, screw speed of 200 rpm, screw diameter of 30 mm, screw length to diameter ratio of 26, and an output of 20 kg per hour. The obtained pellets were converted to a blown film of 25 μm thickness using a Battenfeld machine under the following conditions: a temperature profile of 190° C. to 200° C., a screw speed of 60 rpm, a screw diameter of 60 mm, screw length to diameter ratio of 27, a die gap of 2.3 mm, a frost line height of 40 cm, a blow-up ratio of 2.5:1, and an output rate of 58 kg per hour.

Example A (Comparative)

[0093] A sample of a commercially available LLDPE grade was used. This grade is produced using a conventional Ziegler-Natta catalyst, using 1-butene as comonomer. Pellets of the LLDPE material were converted to a blown film of 25 μm thickness using a Battenfeld machine under the following conditions: a temperature profile of 190° C. to 200° C., a screw speed of 60 rpm, a screw diameter of 60 mm, screw length to diameter ratio of 27, a die gap of 2.3 mm, a frost line height of 40 cm, a blow-up ratio of 2.5:1, and an output rate of 58 kg per hour.

[0094] The properties of the LLDPE materials and films produced as described above are presented in table 1 below.

[0095] Samples of materials from examples 1 and A were subjected to topography imaging by AFM. A method for topography imaging by AFM is for example described in Atomic Force Microscopy, V. Bellitto (ed), InTech, 2012, p. 147-174. The resulting images are presented in FIG. 1 (example 1) and FIG. 2 (example A).

TABLE-US-00001 TABLE 1 Example A Test method Example 1 (comparative) Density (kg/m.sup.3) ASTM D-792 918 921 Melt Index 2.16 kg/ ASTM D-1238 1.94 1.89 190° C. (g/10 min) Melt Index 21.6 kg/ ASTM D-1238 56.8 45.8 190° C. (g/10 min) Melt Flow Rate ASTM D-1238 29.4 24.2 Mn (g/mole) ASTM D-6474 99 27179 28903 Mw (g/mole) ASTM D-6474 99 113715 115343 MWD (g/mole) ASTM D-6474 99 4.18 3.99 Mz (g/mole) ASTM D-6474 99 351880 327421 Mz + 1 (g/mole) ASTM D-6474 99 788744 735037 1% Secant modulus ASTM D-882 167.1/191.7 166.2/169.6 MD/TD (MPa) Tear resistance ASTM D-1922  4.8/16.3  5.2/15.4 MD/TD (g/mic) Tensile strength ASTM D-882  9.9/10.2  9.8/10.6 at yield MD/TD (MPa) Tensile strength ASTM D-882 33.3/28.1 36.0/31.7 at break MD/TD (MPa) Tensile elongation ASTM D-882 53.8/14.1 65.7/13.8 at yield MD/TD (%) Tensile elongation ASTM D-882 645/830 690/856 at break MD/TD (%) Clarity (%) ASTM D-1746 97 98.7 95.9 Haze (%) ASTM D-1003 7.96 20.87 RMS roughness ISO 4287 1997 12.0 45.0 5 μm (nm) Average roughness ISO 4287 1997 6.5 34.4 5 μm (nm)

[0096] ASTM D-792 relates to a standard test method for density and specific gravity (relative density) of plastics by displacement.

[0097] ASTM D-1238 relates to a standard test method for melt flow rates of thermoplastics by extrusion plastometer.

[0098] ASTM D-6474 99 relates to a standard test method for determining molecular weight distribution and molecular weight averages of polyolefins by high temperature gel permeation chromatography.

[0099] ASTM D-882 relates to a standard test method for tensile properties of thin plastic sheeting.

[0100] ASTM D-1922 relates to a standard test method for propagation tear resistance of plastic film and thin sheeting by pendulum method

[0101] ASTM D-1746 97 relates to a standard test method for transparency of plastic sheeting.

[0102] ASTM D-1003 relates to a standard test method for haze and luminous transmittance of transparent plastics

[0103] ISO 4287:1997 relates to geometrical product specifications- Surface texture: Profile method. The data regarding RMS roughness and average roughness given in Table 1 as well as the images FIG. 1 and FIG. 2 were obtained in tapping mode by AFM using A Bruker Dimension Edge AFM. Measurements were done on the primary profile with the Bruker Nanoscope V6.14 software. One dimensional bow removal was applied prior to measurements. Scan rate was 1 Hz with 256 data points per line. Image size 5 μm by 5 μm. An OTESPA-R3 silicon probe with the following characteristics was used: cantilever thickness 3.7 μm, cantilever length 160 μm, cantilever width 40 μm; spring constant (k): 26 N/m; resonance frequency (f.sub.0): 300 kHz. For RMS roughness and/or average roughness measurements sampling length was 5 μm.

[0104] The AFM topographic images, obtained in tapping mode, as presented in FIG. 1 (relating to example 1) and FIG. 2 (relating to comparative example A) show that the surface structure of the material of example 1 is clearly different from the surface structure of the material according to comparative example A, in that the image of the material of comparative example A shows for example a globular morphology having significantly larger globules than is the case for the image of the material of example 1.