Machine direction oriented film for labels

Abstract

Machine direction oriented multilayer film suitable for preparing labels, comprising a core layer of a bimodal terpolymer and two outer layers comprising HDPE.

Claims

1. A machine direction oriented multilayer film suitable for labels comprising a core layer (C) and two outer layers (O-1, O-2) sandwiching the core layer, wherein (i) the core layer (C) comprises a bimodal polyethylene polymer comprising a lower molecular weight component and a higher molecular weight component, which is produced by utilizing a Ziegler-Natta catalyst, with a density between 926 kg/m.sup.3 to 950 kg/m.sup.3 according to ISO 1183, (method A), wherein the bimodal polymer contains an ethylene/1-butene/C.sub.6-C.sub.12-alpha-olefin terpolymer and 1-butene in amount of 0.1 to 3.0 mol % and C.sub.6-C.sub.12-alpha-olefin in amount of 0.2 to 4.0 mol % in relation to the bimodal polymer, and (ii) the two outer layers comprising unimodal HDPE with a density of more than 940 kg/m.sup.3 up to 970 kg/m.sup.3.

2. The multilayer film according to claim 1, wherein the film is in the form of a stretched film which is uniaxially oriented in the machine direction (MD) in a draw ratio of 1:4 to 1:12.

3. The multilayer film according to claim 1, wherein the machine direction oriented film has a final thickness of at least 25 μm up to 85 μm.

4. The multilayer film according to claim 1, wherein (A-1) the lower molecular weight component being a homopolymer of ethylene (A-2) the higher molecular weight component being the terpolymer of ethylene, 1-butene, and a C.sub.6-C.sub.12-alpha-olefin.

5. The multilayer film according to claim 1, wherein the C.sub.6-C.sub.12-alpha-olefin is selected from the group of 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene.

6. The multilayer film according to claim 4, wherein the bimodal polymer having a melt flow rate MFR.sub.2 according to ISO 1133 (190° C., 2.16 kg) of 0.01 to 6 g/10 min, a MFR.sub.5 according to ISO 1133 (190° C., 5 kg) of 0.1 to 20 g/10 min, and an overall comonomer content of 0.3 to 7% by mol, wherein the lower molecular weight component of the bimodal polymer has a melt index MFR.sub.2 according to ISO 1133 (190° C., 2.16 kg) of 50 to 3200 g/10 min, a density according to ISO 1183, (method A) of 930 to 980 kg/m3, and the amount of the lower molecular weight component in the bimodal polymer is in the range of 30 to 70 wt %.

7. The multilayer film according to claim 1, wherein the unimodal high density polyethylene of the outer layers (O-1, O-2) comprises a MFR.sub.2 according to ISO 1133 (190° C., 2.16 kg) of 0.05 to 10 g/10 min, a density according to ISO 1183, (method A) of 941-970 kg/m.sup.3, and a MWD between 2 and 20.

8. The multilayer film according to claim 1, wherein the core layer and/or the outer layers contain one or more of antioxidants, process stabilizers, polymer processing agents, pigments, UV-stabilizers, clay, talc, calcium carbonate, calcium stearate, zinc stearate, and antistatic additives in the form of a single components or as part of a masterbatch.

9. The multilayer film according to claim 8, wherein the core layer contains a pigment as part of a masterbatch.

10. The multilayer film according to claim 1, having a original thickness before being machine direction oriented of 100 to 400 μm.

11. The multilayer film according to claim 1, wherein the outer layers and core layer are all of equal thickness or alternatively each outer layer forms 10 to 35% of the total final thickness of the multilayered film and the core layer forms 30 to 80% of the total final thickness of the multilayered film.

12. A process for producing a multilayer film according to claim 1, wherein the multilayer film is first formed by a blown film coextrusion process with subsequent uniaxial orientation in machine direction.

13. The process according to claim 12, wherein the blown film coextrusion process is performed either on a 3-layer coextrusion line or on a 5- or 7-layer coextrusion line, where the central dies all extrude B-layer material to form an ABBBA or ABBBBBA type film or each of the two, respectively three outer dies extrude A-layer material to form an AABAA or AAABAAA type film or as a combination of the before described possibilities an AABBBAA type film is produced, whereby the so produced films are still ABA films as all A- respectively B-layers are identical.

14. A label comprising the multilayer structure according to claim 1.

15. The label according to claim 14, which is a pressure sensitive label, a linerless label, or a heat shrink sleeve label.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The machine direction oriented multilayer film according to the present invention comprises two outer layers and a core layer, which is sandwiched between the two outer layers, whereby the film is purely polyethylene based.

(2) Core Layer

(3) The core layer (C) comprises a bimodal ethylene/1-butene/C.sub.6-C.sub.12-alpha-olefin terpolymer.

(4) Suitable terpolymers comprise

(5) (A-1) a lower molecular weight (LMW) component of a homopolymer of ethylene and

(6) (A-2) a higher molecular weight component (HMW) of a terpolymer of ethylene, 1-butene and a C.sub.6-C.sub.12-alpha-olefin.

(7) The polyethylene component in this core layer must be bimodal, i.e. its molecular weight profile does not comprise a single peak but instead comprises the combination of two peaks (which may or may not be distinguishable) centred about different average molecular weights as a result of the fact that the polymer comprises two separately produced components.

(8) Bimodal polyethylenes are typically made in more than one reactor each having different conditions. The components are typically so different that they show more than one peak or shoulder in the diagram usually given as result of its GPC (gel permeation chromatograph) curve, where d(log(MW)) is plotted as ordinate vs log(MW), where MW is molecular weight.

(9) Thus, the bimodal polyethylene comprises a higher molecular weight component which corresponds to an ethylene terpolymer and a lower molecular weight component which corresponds to an ethylene homopolymer.

(10) Preferably the C.sub.6-C.sub.12-alpha-olefins are selected from the group of 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene.

(11) More preferably the polyethylene in the core layer is formed from an ethylene homopolymer and an ethylene butene/hexene terpolymer or ethylene butene/octene terpolymer.

(12) Such bimodal polymers may be prepared for example by two stage polymerisation or by the use of two different polymerisation catalysts in a one stage polymerisation. It is also possible to employ a dualsite catalyst. It is important to ensure that the higher and lower molecular weight components are intimately mixed prior to extrusion to form a film. This is most advantageously achieved by using a multistage process or a dual site catalyst, but could be achieved also through blending.

(13) To maximise homogeneity, particularly when a blend is employed, it is preferred that the bimodal polyethylene used in the core layer is extruded prior to being extruded to form the film of the invention. This pre-extrusion step ensures that the higher molecular weight component will be homogeneously distributed though the core layer and minimises the possibility of gel formation in the film.

(14) Preferably the bimodal polyethylene is produced in a multi-stage polymerisation using the same catalyst, e.g. a metallocene catalyst or preferably a Ziegler-Natta catalyst. Thus, two slurry reactors or two gas phase reactors could be employed. Preferably however, the bimodal polyethylene is made using a slurry polymerisation in a loop reactor followed by a gas phase polymerisation in a gas phase reactor.

(15) A loop reactor—gas phase reactor system is well known as Borealis technology, i.e. a BORSTAR® reactor system. The bimodal polyethylene in the core layer is thus preferably formed in a two stage process comprising a first slurry loop polymerisation followed by gas phase polymerisation in the presence of a Ziegler-Natta catalyst.

(16) The conditions used in such a process are well known. For slurry reactors, the reaction temperature will generally be in the range 60 to 110° C. (e.g. 85-110° C.), the reactor pressure will generally be in the range 5 to 80 bar (e.g. 50-65 bar), and the residence time will generally be in the range 0.3 to 5 hours (e.g. 0.5 to 2 hours). The diluent used will generally be an aliphatic hydrocarbon having a boiling point in the range −70 to +100° C. In such reactors, polymerisation may if desired be effected under supercritical conditions. Slurry polymerisation may also be carried out in bulk where the reaction medium is formed from the monomer being polymerised.

(17) For gas phase reactors, the reaction temperature used will generally be in the range 60 to 115° C. (e.g. 70 to 110° C.), the reactor pressure will generally be in the range 10 to 25 bar, and the residence time will generally be 1 to 8 hours. The gas used will commonly be a nonreactive gas such as nitrogen or low boiling point hydrocarbons such as propane together with monomer (e.g. ethylene).

(18) Preferably, the lower molecular weight component is produced in a continuously operating loop reactor where ethylene is polymerised in the presence of a polymerisation catalyst as stated above and a chain transfer agent such as hydrogen. The diluent is typically an inert aliphatic hydrocarbon, preferably isobutane or propane.

(19) The higher molecular weight component can then be formed in a gas phase reactor using the same catalyst.

(20) Where the higher molecular weight component is made as a second step in a multistage polymerisation it is not possible to measure its properties directly. However, e.g. for the above described polymerisation process of the present invention, the density, MFR.sub.2 etc. of the HMW component can be calculated using Kim McAuley's equations.

(21) Thus, both density and MFR.sub.2 can be found using K. K. McAuley and J. F. McGregor: On-line Inference of Polymer Properties in an Industrial Polyethylene Reactor, AIChE Journal, June 1991, Vol. 37, No, 6, pages 825-835. The density is calculated from McAuley's equation 37, where final density and density after the first reactor is known. MFR.sub.2 is calculated from McAuley's equation 25, where final MFR.sub.2 and MFR.sub.2 after the first reactor are calculated.

(22) The bimodal terpolymer used according to the invention comprises a lower molecular weight component (LMW) of a homopolymer of ethylene and a higher molecular weight component (HMW) of a terpolymer of ethylene, 1-butene and a C.sub.6-C.sub.12-alpha-olefin.

(23) The expression “homopolymer of ethylene” used herein refers to a polyethylene that consists substantially, i. e. to at least 98% by weight, preferably at least 99% by weight, more preferably at least 99.5% by weight, most preferably at least 99.8% by weight of ethylene.

(24) As stated above the higher alpha-olefin comonomers are preferably C.sub.6-C.sub.12-alpha-olefins selected from the group of 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene.

(25) More preferably 1-hexene or 1-octene, most preferably 1-hexene is used as second comonomer beside 1-butene.

(26) Such bimodal terpolymers are known in the state of the art and are described e.g. in WO 03/066698 or WO 2008/034630 or are commercially available, such as BorShape™ FX1001 and BorShape™ FX1002 (both from Borealis AG, Vienna, Austria)

(27) The lower molecular weight component (LMW) of the ethylene homopolymer has a weight average molecular weight preferably in the range of 20 000 to 50 000 g/mol, more preferably of 25 000 to 40 000 g/mol and a melt index MFR.sub.2 in the range of 50 to 3 200 g/10 min, preferably in the range of 80 to 1 000 g/10 min and more preferably in the range of 100 to 600 g/10 min.

(28) The density of the lower molecular weight component may range from 930 to 980 kg/m.sup.3, preferably from 940 to 975 kg/m.sup.3, more preferably 960 to 972 kg/m.sup.3.

(29) The lower molecular weight component has preferably from 30 to 70 wt %, e.g. 40 to 60% by weight of the bimodal polyethylene with the higher molecular weight component forming 70 to 30 wt %, e.g. 60 to 40% by weight.

(30) The higher molecular weight component has a lower MFR.sub.2 and a lower density than the lower molecular weight component.

(31) The final bimodal terpolymer has a weight average molecular weight preferably in the range of 100 000 to 200 000 g/mol, and a Mw/Mn in the range of 5 to 20, preferably in the range of 8 to 18, more preferably in the range of 10 to 15.

(32) The density of the final terpolymer is between 926 and 950 kg/m.sup.3, preferably between 927 to 945 kg/m.sup.3, and more preferably between 930 to 940 kg/m.sup.3.

(33) Preferred terpolymers have a melt index (MI.sub.5) of 0.1 to 20 g/10 min (e.g. when measured at 190° C. and 5.0 kg, according to standard ASTM D1238), especially from 0.2 to 10 or from 0.5 to 5 g/10 min, e.g. around 2.0 g/10 min.

(34) Preferred terpolymers have a melt index (MI.sub.2) of 0.01 to 6 g/10 min (e.g. when measured at 190° C. and 2.16 kg, according to standard ASTM D1238), especially from 0.05 to 3 or from 0.1 to 2 g/10 min, e.g. around 0.5 g/10 min.

(35) The overall comonomer content in the total polymer is 0.3 to 7.0% by mol, preferably 0.6 to 4.5% by mol, more preferably 1.0 to 3.5% by mol and most preferably 1.2 to 2.3% by mol.

(36) Butene is present in an amount of 0.1 to 3.0% by mol, preferably 0.2 to 2.0% by mol, more preferably 0.3 to 1.5% by mol and most preferably 0.4 to 0.8% by mol.

(37) The C.sub.6 to C.sub.12 alpha olefin is present in an amount of 0.2 to 4.0% by mol, preferably 0.4 to 2.5% by mol, more preferably 0.7 to 2.0% by mol and most preferably 0.8 to 1.5% by mol.

(38) In addition to the bimodal terpolymer the composition may also contain antioxidants, process stabilizers, slip agents, pigments, UV-stabilizers and other additives known in the art.

(39) Examples of stabilizers are hindered phenols, hindered amines, phosphates, phosphites and phosphonites.

(40) Examples of pigments are carbon black, ultra marine blue and titanium dioxide.

(41) Examples of other additives are e. g. clay, talc, calcium carbonate, calcium stearate, zinc stearate and antistatic additives like.

(42) The additives can be added as single components or as part of a masterbatch as is known in the art.

(43) In one embodiment it is preferred to add a pigment, preferably titanium dioxide to obtain white films, providing better contrast on e.g. blue bottles. Most preferably this pigment is added as part of a masterbatch.

(44) Sandwiching Layers

(45) As identified above, the three-layer structure in accordance with the present invention comprises in addition to the core layer two layers sandwiching the core layer The layers sandwiching the core layer are layers directly contacting the core layer, preferably without any adhesive layer or surface treatment applied.

(46) The two outer layers which are sandwiching the core layer both comprise unimodal HDPE. HDPEs of use in the invention have a density of more than 940 kg/m.sup.3 and can be homopolymers or copolymers with at least one α-olefin having from 3 to 10 carbon atoms. Suitable HDPE preferably has a density within the range of about 941 kg/m.sup.3 to about 970 kg/m.sup.3. More preferably, the density is within the range of about 945 kg/m.sup.3 to about 965 kg/m.sup.3.

(47) The HDPE polymer to be employed in accordance with the present invention may be a known and e.g. commercially available, polyethylene polymer or said HDPE polymer may be prepared using any coordination catalyst, typically ZN catalysts, Cr-catalyst as well as single site catalysts (SSC).

(48) The melt flow rate (MFR) of the HDPE polymer to be employed for the outer layers in accordance with the present invention is not critical and can be varied depending on the mechanical properties desired for an end application. In one preferable embodiment MFR.sub.2 value in the range of from 0.05 to 10 g/10 min, preferably 0.1 to 7.0 g/10 min, more preferably from 0.2 to 5.0 g/10 min, yet more preferably 0.3 to 3.0 g/10 min, even more preferably 0.4 to 2.0 g/10 min an most preferably 0.5 to 1.3 g/10 min are desired.

(49) The molecular weight distribution (MWD) expressed as Mw/Mn of the HDPE polymer to be employed in accordance with the present invention can vary in a broad range. MWD is preferably in the range from 2 to 20, preferably 2.5 to 15, more preferably 3 to 10 and most preferably 3.5 to 7.

(50) HDPEs are very well known and are commercially available or can be prepared using well-documented polymerisation processes, e.g. processes described above and by adjusting the process conditions to obtain the desired density of HDPE.

(51) Thus the HDPE polymers to be employed in accordance with the present invention may be produced in principle using any polymerization method, including solution, slurry and gas phase polymerization.

(52) I. a. commercial grades of HDPEs as highly feasible materials for layer(s) of the invention, like commercial grades available from Borealis e.g. VS4470, and Reliance's commercial grades, e.g. F46003, can be mentioned as examples only, i.e. not limiting thereto.

(53) The outer layers may also contain other polymer components if necessary and may also contain minor amounts of conventional additives such as antioxidants, UV stabilisers, acid scavengers, nucleating agents, anti-blocking agents, slip agents etc as well as polymer processing agent (PPA). The additives can be added as single components or as part of a masterbatch as is known in the art.

(54) Other Layers

(55) The film of the invention may also contain further layers in addition to the main three layers defined in the invention.

(56) The optional additional layers are naturally selected so that they have no adverse effect on the inventive effect achieved with the three-layer structure according to the invention.

(57) Thus it is also possible to use the three-layer structure of the present invention for producing a 5- or even 7-layered film.

(58) However, the three-layer structure in accordance with the present invention preferably is employed as such, without any further film material.

(59) Three-Layer Structure

(60) The three-layer structure in accordance with the present invention may be prepared by any conventional film extrusion procedure known in the art, e.g. with blown film extrusion. Preferably, the three-layer film is formed by blown film extrusion, more preferably by coextrusion processes, which in principle are known and available to the skilled person. Typical processes for preparing a three-layer structure in accordance with the present invention are extrusion processes through an angular die, followed by blowing into a tubular film by forming a bubble which is collapsed between the rollers after solidification. This film can then be slid, cut or converted, such as by using a gazette head, as desired. Conventional film production techniques may be used in this regard. Typically the core layer and the sandwiching layers are coextruded at a temperature in the range of from 160 to 240° C. and cooled by blowing gas (generally air) at a temperature of 5 to 50° C., to provide a frost line height of 1 or 2 to 8 times the diameter of the dye. The blow up ratio can be in the range of from 1 (1:1) to 4 (1:4), preferably 1.5 (1:1.5) to 3.5 (1:3.5), more preferably from 2 (1:2) to 3 (1:3).

(61) The film preparation process steps of the invention are known and may be carried out in one film line in a manner known in the art. Such film lines are commercially available, for example from Windmöller & Hölscher, Reifenhauser, Hosokawa Alpine, e.t.c.

(62) Typically the three-layer structure (ABA) is produced on a 3-layer coextrusion line, but in some embodiments it may be appreciated that the used coextruder is a 5 or 7 layer coextrusion line. In such a set up the central dies may all extrude B-layer material to form an ABBBA or ABBBBBA type film or each of the two, respectively three outer dies may extrude A-layer material to form an AABAA or AAABAAA type film or as a combination of the before described possibilities an AABBBAA type film could be produced, too. As all these A-repectively B-layers are identical, the films produced are effectively still ABA films. Preferably 5-layer coextrusion lines would be used if desired, with ABBBA being the preferred type of film structure.

(63) The multilayer film is then uniaxially oriented in the machine (or processing) direction. During the MDO, the film from the blown-film line or other film process is heated to an orientation temperature. Preferably, the temperature range for orientation can be 25K below the VICAT A-level of the outer film layer material up to the melting temperature of the outer film layer material. The heating is preferably performed utilizing multiple heating rollers.

(64) Next, the heated film is fed into a slow drawing roll with a nip roller, which has the same rolling speed as the heating rollers. The film then enters a fast drawing roll. The fast drawing roll has a speed that is 2 to 10 times faster than the slow draw roll, which effectively orients the film on a continuous basis.

(65) The oriented film then enters annealing thermal rollers, which allow stress relaxation by holding the film at an elevated temperature for a period of time.

(66) The annealing temperature is preferably within the same temperature range as used for stretching or slightly below (e.g. 10 to 20K below), with room temperature being the lower limit. Finally, the film is cooled through cooling rollers to an ambient temperature.

(67) The ratio of the film thickness before and after orientation is called “drawdown ratio.”

(68) The drawdown ratio varies depending on many factors including the desired film thickness, film properties, and multilayer film structures.

(69) Preferably, the draw-down ratio is such that the film is at or near maximum extension. Maximum extension is the draw-down film thickness at which the film cannot be drawn further without breaking. The film is said to be at maximum extension when machine direction (MD) tensile strength has a less than 100% elongation at break under ASTM D-882.

(70) The preparation process of a uniaxially oriented in MD multilayer film of the invention comprises at least the steps of forming a layered film structure and stretching the obtained multilayer film in the machine direction in a draw ratio of at least 1:4 up to 1:12, preferably 1:4.5 to 1:10 and more preferably 1:5 to 1:7.

(71) The film is stretched at least 4 times up to 12 times, its original length in the machine direction. This is stated herein as a draw ratio of at least 1:4, i.e. “1” represents the original length of the film and “4” denotes that it has been stretched to 4 times that original length.

(72) An effect of stretching (or drawing) is that the thickness of the film is similarly reduced. Thus a draw ratio of at least 1:4 preferably also means that the thickness of the film is at least four times less than the original thickness.

(73) The films of the invention have an original thickness of 100 to 400 μm before stretching, preferably 150 to 380 μm and more preferably 200 to 350 μm.

(74) After stretching, the final thickness of the uniaxially oriented films according to this invention is typically in the range 25 to 85 μm, preferably 30 to 70 μm, and more preferably 40 to 60 μm.

(75) The outer layers and core layer may all be of equal thickness or alternatively the core layer may be thicker than each outer layer. A convenient film comprises two outer layers which each form 10 to 35%, preferably 15 to 30% of the total final thickness of the 3-layered film, the core layer forming the remaining thickness, e.g. 30 to 80%, preferably 40 to 70% of the total final thickness of the 3-layered film.

(76) The three-layer structure according to the invention presents a polyethylene film which can be down-gauged by more than 20%, preferably more than 30% and even more preferred by more than 35% in comparison with a standard PE blown film made of low density polyethylene with 85 μm.

(77) Furthermore the three-layer structure according to the invention has better display properties compared to such a standard PE blown film.

(78) Compared to the machine direction oriented monolayer label film consisting of only VS4531, the three-layer structure according to the invention has the advantage of improved processability during producing the blown film and during the machine direction orientation process and better overall quality of the film. The main benefit of the multilayer film according to the invention compared to this monolayer label film is its down-gauging-ability.

(79) Compared to A/B/A co-extruded films, consisting of HDPE polymer VS4531 A-layers and Borstar® FB2230 (linear low density PE, density 923 kg/m.sup.3) B-layer, the three-layer structure according to the invention has the advantage of higher stiffness and improved punchability.

(80) The three-layer films according to the invention furthermore possess an excellent printability, higher stiffness for easy dispensing and better punchability, high conformability, very good display properties, like high gloss and low haze (for transparent films) and are additionally 100% recyclable, since they are of 100% of polyethylene.

(81) The films according to the invention are therefore i.a. highly suitable as label films and may be therefore used for label products and for labelling of items. The label products may be attached to a substrate surface such as glass or plastic bottles. Suitable label products are preferably a pressure sensitive label, a linerless label, a heat shrink sleeve label or a heat seal label, more preferably a pressure sensitive label or a heat shrink sleeve label and most preferably a pressure sensitive label.

Experimental Part

1. Methods

(82) The following methods were used to measure the properties that are defined generally above and in examples below. Unless otherwise stated, the film samples used for the measurements and definitions were prepared as described under the heading “Film Sample Preparation”.

(83) Impact resistance on film (DDI) was determined by Dart-drop (g/50%). Dart-drop was measured using ISO 7765-1, method “A”. A dart with a 38 mm diameter hemispherical head was dropped from a height of 0.66 m onto a film clamped over a hole. If the specimen failed, the weight of the dart was reduced and if it did not fail the weight was increased. At least 20 specimens were tested. The weight resulting in failure of 50% of the specimens was calculated.

(84) MFR2: ISO1133 at 190° C. at a load of 2.16 kg

(85) MFR5: ISO1133 at 190° C. at a load of 5 kg

(86) MFR21: ISO1133 at 190° C. at a load of 21.6 kg

(87) Density of the materials was measured according to ISO 1183-1(2004): method A. The test specimens were produced according to ISO 1872-2. The cooling rate of the plaques when crystallising the samples was 15 C/min. Conditioning time was 16 hours at 23° C.

(88) Tensile Tests (Modulus, Strength, Elongation at Break)

(89) Tensile modulus and tensile strength were measured in machine and transverse direction according to ISO 527-3 on film samples prepared as described under the Film Sample preparation with film thickness as given for each test in below Table 1 at a cross head speed of 1 mm/min for the modulus and 50 mm/min for the strength.

(90) Elongation at break in machine and transverse direction was determined according to ISO 527-3 on the same kind of specimens using a cross head speed of 50 mm/min.

(91) Test speed was changed after a deformation of 0.25%.

(92) Specimen type 2 acc. ISO 527-3: stripes with a width of 15 mm and length: 200 mm

(93) Thickness of the samples was 53 μm for Inventive Examples and 85 μm for the Comparative Example.

(94) Gloss was measured according to ASTM D 2457. (measured outside, lengthwise, measuring angel 20°)

(95) Haze was measured according to ASTM 1003.

(96) The following examples illustrate the present invention.

2. Examples

(97) The following materials have been used: Core layer: as bimodal terpolymer Grade BorShape™ FX1002 (Borealis Polyolefine AG-Vienna, Austria) was used. FX1002 is a bimodal Ziegler Natta produced terpolymer (C.sub.2/C.sub.4/C.sub.6) with MFR.sub.5 of 2.0 g/10 min, density of 937 kg/m.sup.3. In Inventive Example 1 15 wt % of Polywhite® NG 8600 H1 provided by A. Schulman (white masterbatch containing 60% TiO.sub.2 (Rutil-Type) in polyethylene) was added to the terpolymer. Outer layers: as unimodal HDPE grade VS4470 (Borealis Polyolefine AG-Vienna, Austria) was used. VS4470 is a unimodal Ziegler Natta produced high density polyethylene with MFR.sub.2 of 0.65 g/10 min and density of 947 kg/m.sup.3 In addition as polymer processing agent Polybatch® AMF 705 HF provided by A. Schulman was added. Comparative Example: Himod™ FT7324 (Borealis Polyolefine AG-Vienna, Austria) was used. FT7324 is a tubular, low density polyethylene grade with MFR.sub.2 of 4.0 g/10 min and density of 932 kg/m.sup.3

(98) The following film structures have been prepared:

(99) (xx %, like 25%, mean the percentage of the thickness of the three layer structure of each separate layer form, relative to the final thickness)

Comparative Example 1

(100) MONOLAYER FILM with film thickness of 85 μm

(101) FT7324 was converted into a monolayer film with a thickness of 85 μm on 200 mm die with 1.5 mm die gap. The film was produced by a low stalk technique with a blow-up ratio (BUR) of 1:3. This film is not machine-direction oriented and it is representative of the incumbent film used in high tensile strength, thin film applications for label films. The film properties are listed in Table 1

Inventive Example 1: Final Film Thickness 53 μm

(102) Outer layer (O-1): 20%: 98 wt % VS4470+2 wt % Polybatch® AMF 705 HF

(103) Core layer (C): 60%: 85 wt % bimodal terpolymer FX1002+15 wt % Polywhite® NG 8600 H1

(104) Outer layer (O-2): 20%: 98 wt % VS4470+2 wt % Polybatch® AMF 705 HF

Inventive Example 2: Final Film Thickness 53 μm

(105) Outer layer (O-1): 20%: 98 wt % VS4470+2 wt % Polybatch® AMF 705 HF

(106) Core layer (C): 60%: 100 wt % bimodal terpolymer FX1002

(107) Outer layer (O-2): 20%: 98 wt % VS4470+2 wt % Polybatch® AMF 705 HF

(108) Film Sample Preparation

(109) Inventive Film Samples were produced by coextrusion on a commercially available 3-layer coextrusion blown film line with die diameter 500 mm, frost line height 3DD, at a blow up ratio (BUR) 1:2.4 and die gap 2.25 mm, with internal bubble cooling.

(110) The extruder comprised three extruders in parallel (70/105/70)

(111) Extruder temp setting: 210° C. to form 3-layered film with a relative layer thickness distribution of 20:60:20 relative to the final thickness

(112) Take off speed was 7.5 m/min and the roll width was 1900 mm.

(113) The machine direction orientation was performed on a commercially available MDO unit. The unit consists of preheating, drawing, annealing, and cooling sections, with each set at specific temperatures to optimize the performance of the unit and produce films with the desired properties. The heating was at 105° C., the stretching was done at 125° C., cooling and annealing was done at 110° down to 40° C.

(114) Inlet speed was 7.5 m/min, outlet speed was then 45 m/min. Drawdown ratio (DDR) was around 1:6.1.

(115) TABLE-US-00001 TABLE 1 Comparative Method Unit Example 1 Example 2 Example DDR 1:6.151 DDR 1:6.138 — 53 μm 53 μm 85 μm white transparent transparent Tensile MPa 1243 1263 310 Modulus MD Tensile MPa 1259 1306 360 Modulus TD Tensile MPa 186 193 19 Strength MD Tensile MPa 28.8 29.4 14.9 Strength TD Elongation at % 43 48 120 break MD Elongation at % 330 488 229 break TD DDI g/μm 1.2 1.2 1.9 Haze % 103.0 4.4 9.8 Gloss % 71 110 100