POLYMER FILMS

Abstract

Multi-layer polyolefin films for envelope windows, comprising at least three layers wherein the central layer comprises a propylene homopolymer; the layer of film on the outer part of the envelope, which forms the anti-reflective layer, is based on propylene copolymers in mixture with HDPE, HDPE being comprised between 40 and 50% by weight of the mixture; the inner layer in contact with the contents of the envelope is based on ethylene/propylene/butene copolymers, the film being isotropic in relation to shear strength.

Claims

1. A multi-layer polyolefin film for an envelope window, comprising at least three layers, the at least three layers including an inner layer, a central layer, and an outer layer, wherein the central layer comprises a propylene homopolymer; the outer layer comprises a layer of film on the outer part of the envelope and is based on propylene copolymers in mixture with HDPE, HDPE comprising between 40 and 50% by weight of the mixture; and the inner layer is in contact with the contents of the envelope and is based on propylene copolymers, and wherein the multi-layer polyolefin film is isotropic in relation to shear strength.

2. The multi-layer polyolefin film according to claim 1, wherein the central layer is a propylene homopolymer containing a concentration of extractables in n-hexane at 50 C. for two hours of lower than 10%.

3. The multi-layer polyolefin film according to claim 1, wherein the propylene copolymers of the outer layer are based on polypropylene with at least one other comonomer containing at least one ethylenic unsaturation, said comonomer being selected from ethylene and alpha-olefins, the ethylene and alpha-olefins being linear or branched and having 2 carbon atoms or from 4 to 12 carbon atoms, wherein the total quantity of comonomers is between 0.5 and 25% by weight of the total monomers, and wherein the HDPE of the outer layer is a matting agent and is present in a quantity of 40-50% by weight.

4. The multi-layer polyolefin film according to claim 3, wherein the comonomer is ethylene.

5. The multi-layer polyolefin film according to claim 3, wherein the comonomer comprises ethylene and an alpha-olefin, and wherein the ethylene is present in an amount of lower than 10% by weight and the alpha-olefin monomer is in an amount of between 0 and 10% by weight.

6. The multi-layer polyolefin film according to claim 1, wherein the propylene copolymers of the inner layer comprise monomers chosen from ethylene and alpha-olefins, the ethylene and alpha-olefins being linear or branched and having a variable number of carbon atoms in a chain of from 4 to 12, and wherein the quantity of ethylene and alpha-olefin comonomers is lower than 20% by weight of the total polymer.

7. The multi-layer polyolefin film according to claim 6, wherein the propylene copolymer is a propylene/ethylene/butene terpolymer and wherein the quantity of ethylene and butene is <10%.

8. The multi-layer polyolefin film according to claim 1, wherein the inner layer and outer layer further contain slip agents, anti-blocking agents, or a combination thereof, and/or the central layer further contains anti-static agents and/or polyolefin copolymers.

9. The multi-layer polyolefin film according claim 1, wherein the central layer further comprises a propylene copolymer or an ethylene copolymer, the propylene copolymer being based on polypropylene with at least one other comonomer containing at least one ethylenic unsaturation, said comonomer being selected from ethylene and alpha-olefins, the ethylene and alpha-olefins being linear or branched and having 2 carbon atoms or from 4 to 12 carbon atoms, the ethylene copolymer being with one or more linear or branched alpha-olefins with 3 to 20 carbon atoms, and wherein the central layer can optionally further comprise of other comonomers containing more than one double bond in addition to the alpha-olefin bond, conjugated or not, with 4 to 20 carbon atoms or cyclic wherein the ring has 5 or 6 carbon atoms, the total quantity of comonomers (% in moles) being between 5 and 50%, the number average molecular weight being between 300 and 25,000.

10. The multi-layer polyolefin film according to claim 9, wherein the quantity of copolymers in the central layer, in % by weight, is between 0 and 20% by weight with respect to the quantity of propylene homopolymers of the multi-layer polyolefin film or of the central layer.

11. The multi-layer polyolefin film according to claim 1, wherein the multi-layer polyolefin film is bioriented.

12. The multi-layer polyolefin film according to claim 1, wherein the thickness of the multi-layer polyolefin film is between 15 and 40 m, the central layer has a thickness of 12-38 m, and the inner layer and the outer layer each have a thickness in the range of 0.3-4 m, wherein the thickness of the inner layer and the thickness of the outer layer are the same or different from each other.

13. A method of making the film according to claim 1, the method comprising the following steps: coextruding a multi-layer sheet of the multi-layer polyolefin, the multi-layer sheet having a thickness between about 0.5 mm and about 4 mm; cooling the multi-layer sheet on the surface of a cooled chill roll immersed in a water bath at a temperature between 5 and 35 C.; heating the multi-layer sheet using infrared (IR) radiation units, wherein the surface of the IR units has a temperature between 100 C. and 500 C.; stretching and orienting the multi-layer sheet, thereby obtaining the multi-layer polyolefin film with a simultaneous orientation process by gripping the edges of the multi-layer sheet, the edges of the multi-layer sheet having a higher thickness than the center of the sheet, with a series of grippers and/or clamps independently guided by linear synchronous induction motors, wherein the assembly of grippers and/or clamps slides on diverging stretching tracks; the linear synchronous induction motors being powered with alternating currents whose phases and frequencies are modulated so that the grippers and/or clamps follow a pre-programmed linear speed to obtain the required stretch ratios in MD; wherein the MD stretch ratios are a function of the longitudinal linear speed profile and the TD stretch ratios are regulated by the distance (divergence) between the stretching rails; wherein the stretching frame used for the film stretching steps comprises one or more sections which are located inside an oven having a temperature between about 150 C. and 190 C.; maintaining longitudinal stretch ratios MD between 5.9 and 8 and transversal stretching ratios TD between 5.5 and 8, operating so that
|(ratio(MD)ratio(TD)|/((ratio(MD), ratio(TD))<13% wherein: ratio(MD) is the stretching ratio in MD and ratio(TD) is the stretching ratio in TD, final heat setting in TD performed using convergence of the stretching tracks in one or more sections of the stretching frame at temperatures of about 130 C.-140 C. and heat setting in MD is obtained by reducing the linear speed of the grippers.

14. A method for obtaining anti-reflective transparent windows for envelopes, postal products, or a combination thereof, the method having a percentage of application waste lower than 0.002%, the method using applicators having an application speed comprised between 1,000 and 1,300 envelopes/minute, the method comprising the use of the multi-layer polyolefin film according to claim 1.

15. Envelopes provided with anti-reflective transparent windows, wherein said windows are formed by a film according to claim 1.

Description

EXAMPLES

[0067] Tear Resistance

[0068] The determination is performed with an Elmendorf pendulum according to ASTM D 1424.

[0069] Melting Point of the Polymers

[0070] The melting point was determined using DSC.

[0071] Heat Shrinkage of the Film

[0072] The heat shrinkage of the film is determined according to standard OPMA TC 4 by heating the sample having dimensions 20 cm1 cm at 130 C. for 5 minutes in air.

[0073] The heat shrinkage in MD or TD is calculated with the following formula:

[00001]$\frac{\left(L.Math..Math.1-L.Math..Math.2\right)100}{L.Math..Math.1}$

wherein:

[0074] L1 is the length of the film prior to the heat treatment;

[0075] L2 is the length of the film after the heat treatment.

[0076] The heat shrinkage can also be indicated with the number obtained in the previous equation preceded by the negative sign ().

[0077] Extractables in n-hexane

[0078] Determined according to standard FDA 177-1520.

[0079] Melt Flow Index

[0080] The determination is performed according to ASTM D1238, at 230 C. for 10 min with a load of 2.16 kg both in MD and TD direction.

Example 1

[0081] A 3-layer film was prepared by extrusion composed as follows: [0082] inner layer corresponding to the glossy layer in contact with the contents of the envelope, with a thickness of 0.7 m, consisting of (% by weight): [0083] 95% terpolymer 03/02/04 LyondelBasell: Adsy15C30F, wherein the total quantity of C2 and C4 is less than 20% by weight; [0084] 5% slip agent masterbatch CONSTAB SAAB 6552. [0085] outer layer, corresponding to the matt layer i.e. the visible side of the envelope window having a thickness of 1.7 m, consisting of (% by weight): [0086] 98% matting agent masterbatch Ampacet Matif 400219 (matt) formed by a mixture of a 03/02/04 propylene copolymer as described for the inner layer with HDPE 40% by weight out of the mixture, [0087] 2% slip agent masterbatch CONSTAB AB6084, wherein the masterbatch polymer is a propylene homopolymer, [0088] central layer having a thickness of 20.7 m, consisting of (% by weight): [0089] 88.45% homopolymer PP LyondelBasell HP520H, [0090] 1.55% anti-static agent masterbatch Ampacet wherein the polymer is a propylene (co)polymer, [0091] 10% PP reclaim,

[0092] The total thickness of the film is 23.1 m.

[0093] The total hourly capacity of the three extruders is 1998 kg/h.

[0094] The production speed of the film is 250 m/min.

[0095] The film was obtained using a flat-die simultaneous biaxial Filming process, which consists of the following steps: [0096] extrusion of a three-layer sheet, [0097] cooling and tempering of the sheet, [0098] pre-heating in an IR battery, [0099] stretching in a LISIM simultaneous stretching oven, [0100] corona treatment, [0101] winding the film onto the mother roll, which is then cut into the final rolls which have the dimensions required by the application.

[0102] The details of the individual steps are reported below.

[0103] Extrusion of a Three-Layer Sheet

[0104] The inner layer was produced with a single screw extruder whose operating conditions are as follows:

[0105] capacity: 61.4 kg/h,

[0106] temperature of the screw feeding zone: 50 C.,

[0107] temperature range: 235 C.-250 C.,

[0108] temperature of the filtration and transport line of the melt to the die: 255 C.,

[0109] screw rotation speed: 9 rpm.

[0110] The outer layer was produced with a single screw extruder whose operating conditions are as follows:

[0111] capacity: 145.4 kg/h

[0112] screw feeding zone: 50 C.,

[0113] temperature range: 275 C.-285 C.,

[0114] temperature of the filtration and transport line of the melt to the die: 290 C.,

[0115] screw rotation speed: 21 rpm.

[0116] The central layer was produced with a double screw extruder equipped with a gear pump for the melt whose operating conditions are as follows:

[0117] total capacity: 2,168 kg/h,

[0118] incoming granule flow rate (excluding recycled material): 1,791 kg/h,

[0119] extruder temperature range: 240 C.-260 C.,

[0120] temperature of the melt pump: 255 C.,

[0121] temperature of the filtration and transport line of the melt: 250 C. before the

[0122] filter, 257 C. on the filter, 252 C.-237 C. after the filter,

[0123] rotation speed of the double screw extruder=145 rpm,

[0124] pump rotation speed=35 rpm.

[0125] The three independent polymer flows were superimposed in a flat die at T=250 C., so as to obtain a three-layer coextruded film.

[0126] Cooling and Tempering

[0127] After extrusion through the flat die, the three-layer film was cooled and solidified on a roller provided with a gap in which water flows at the temperature of 30 C., rotating at the linear speed of 40 m/min, and immersed in a bath in which water circulates at the temperature of 30 C. The solidified film is known as cast film.

[0128] Preheating with IR

[0129] The cast film, at the speed of 40 m/min, was heated in a battery of IR panels whose temperature range is 220-350 C.

[0130] Filming in a LISIM Simultaneous Stretching Oven.

[0131] The cast film preheated with IR was stretched in a LISIM simultaneous stretching oven, with the following process conditions:

[0132] stretch ratio in MD: 6.20.

[0133] stretch ratio in TD: 6.86.

[0134] Under these conditions value (a) equals 10.6.

[0135] Temperature profile in the preheating zone: 170 C.-173 C.-171 C.

[0136] Temperature in the biaxial stretching zone: 158 C.

[0137] Temperature profile in the annealing zone: 160 C.-166 C.-164 C.

[0138] Corona Treatment and Winding the Film onto the Mother Roll

[0139] At the oven outlet the film was subjected to a corona treatment on the matt side, so as to obtain a surface energy value of 54 dyne/cm.

[0140] It was then wound onto the mother roll.

[0141] The film obtained is an isotropic film as shown by the shear strength (tear resistance) that has substantially the same value both in the MD and the TD direction.

[0142] The tear resistance in MD is 5 cN, in TD it is 4.4 cN and their ratio is 1.14.

Example 2

[0143] A 3-layer film was prepared by extrusion composed as follows:

[0144] The inner and outer layer have the same composition as the corresponding values of the film in Example 1.

[0145] The central layer has the same film composition as the film in Example 1 but the thickness is 23.36 m.

[0146] The total thickness of the film is 25.76 m.

[0147] The total hourly capacity of the three extruders is 2,211 kg/h.

[0148] The production speed of the film is 250 m/min.

[0149] The film was obtained using a simultaneous biaxial film stretching process with a flat die, which consists of the following steps: [0150] extrusion of a three-layer sheet, [0151] cooling and tempering of the sheet, [0152] pre-heating in an IR battery, [0153] stretching in a LISIM simultaneous stretching oven, [0154] corona treatment, [0155] winding the film onto the mother roll, which is then cut into the final rolls which have the dimensions required by the application.

[0156] The details of the individual steps are reported below.

[0157] Extrusion of a Three-Layer Sheet

[0158] The inner layer was produced with a single screw extruder whose operating conditions are as follows:

[0159] capacity: 61.4 kg/h,

[0160] temperature of the screw feeding zone: 50 C.,

[0161] temperature range: 235 C.-250 C.,

[0162] temperature of the filtration and transport line of the melt to the die: 255 C.,

[0163] screw rotation speed: 9 rpm.

[0164] The outer layer was produced with a single screw extruder whose operating conditions are as follows:

[0165] capacity: 145.4 kg/h

[0166] screw feeding zone: 50 C.,

[0167] temperature range: 275 C.-285 C.,

[0168] temperature of the filtration and transport line of the melt to the die: 290 C.,

[0169] screw rotation speed: 22 rpm.

[0170] The central layer was produced with a double screw extruder equipped with a gear pump for the melt whose operating conditions are:

[0171] total capacity: 2,211 kg/h,

[0172] incoming granule flow rate: 2,004 kg/h,

[0173] extruder temperature range: 240 C.-260 C.,

[0174] temperature of the melt pump: 255 C.,

[0175] temperature of the filtration and transport line of the melt:

[0176] 250 C. before the filter, 257 C. on the filter, 252 C.-237 C. after the filter,

[0177] double screw rotation speed: 163 rpm,

[0178] pump rotation speed: 39 rpm.

[0179] The three independent polymer flows were superimposed in a flat die at T=250 C., so as to obtain a three-layer coextruded film.

[0180] Cooling and tempering

[0181] After extrusion through the flat die, the three-layer film was cooled and solidified on a roller provided with a gap in which water flows at the temperature of 30 C., rotating at the linear speed of 40 m/min, and immersed in a bath in which water circulates at the temperature of 30 C.

[0182] Preheating with IR

[0183] The film at the speed of 40 m/min was heated in a battery of IR panels whose temperature range is 240-370 C.

[0184] Filming in a LISIM Simultaneous Stretching Oven

[0185] The cast preheated with IR was coated in a LISIM simultaneous stretching oven, with the following process conditions:

[0186] stretch ratio in MD: 6.20.

[0187] stretch ratio in TD: 6.86.

[0188] Under these conditions value (a) is 10.6.

[0189] Temperature profile in the preheating zone: 173 C.-176 C.-174 C.

[0190] Temperature set of the biaxial stretching zone: 159 C.

[0191] Temperature profile of the annealing zone: 161 C.-167 C.-165 C.

[0192] Corona Treatment and Winding Onto the Mother Roll

[0193] At the oven outlet the film was subjected to a corona treatment on the outer layer, so as to obtain a surface energy value of 54 dyne/cm.

[0194] The film was then wound onto the mother roll.

[0195] The film is isotropic as shown by the shear strength that has substantially the same value both in the MD and the TD direction.

[0196] The tear resistance in MD is 5.7 cN, in TD it is 5.3 cN and their ratio is 1.08.

Example 3

Comparative

[0197] Example 1 was repeated but the film has a thickness of 35 micron and was prepared using a sequential stretching machine with a stretching ratio in MD of 5.0 and in TD of 7.5.

[0198] Under these conditions value (a) is 40%.

[0199] The film obtained is not an isotropic film as shown by the shear strength that has a lower value in the MD direction than in the TD direction.

[0200] The tear resistance in MD is 10 cN, in TD it is 6.6 cN and their ratio is 1.52 which indicates that the film is not isotropic in relation to tear resistance.

Example 4

Application

[0201] The rolls used have a width of 120 mm and were cut during application to a length of 120 mm.

[0202] The film of Example 1 was used on a Winker-Dunnebier AG 102 RE machine which produces windows for envelopes in which the visible part of the window has the dimensions 10045 mm and the window has total dimensions 12065 mm, the matt side being fixed to the envelopes using Eukalin 6415 EF glue sold by Henkel. The machine produces 1300 envelopes/minute. In 24 hours two envelopes were rejected.

Example 5

Application

[0203] Example 4 Application was repeated but using the film of Example 2. The results are substantially equal to those obtained in Example 4 Application.

Example 5

Comparative Application

[0204] Example 4 Application is repeated but using the film of Example 3 Comparative. The results showed a clearly higher level of waste, equal to 135 envelopes in 24 hours.