Packaging films with improved hot-tack performance

Abstract

The present invention is directed to hot-fill/retort packaging films having a sealant layer composition comprising a first propylene-ethylene copolymer, a second propylene-ethylene copolymer and a polyethylene. Hot-fill/retort packaging films are provided herein having a sealant layer composition that exhibits an ultimate hot tack within a range from 88 N/m to 876 H/m (0.5 lb./in to 5 lb./in) at a temperature within the range from 116° C. to 182° C. (240° F. to 360° F.).

Claims

1. A hot-fill/retort sealant film comprising: a sealant layer composition comprising: i) a first propylene-ethylene copolymer ii) a second propylene-ethylene copolymer, and iii) a polyethylene; wherein the first propylene-ethylene copolymer has a flexural modulus at 0.127 cm/min (0.05 in/min), 1% secant within a range from 124.1 N/mm.sup.2 to 689.5 N/mm.sup.2 (18,000 to 100,000 psi) as measured in accordance with ASTM D-790 test method and wherein the second propylene-ethylene copolymer is a random propylene-ethylene copolymer.

2. The hot-fill/retort sealant film according to claim 1, wherein the first propylene-ethylene copolymer is present in an amount within a range from 10% to 90% by weight relative to the total weight of the sealant layer.

3. The hot-fill/retort sealant film according to claim 1, wherein the first propylene-ethylene copolymer is present in an amount within a range from 15% to 50% by weight relative to the total weight of the sealant layer.

4. The hot-fill/retort sealant film according to claim 1, wherein the first propylene-ethylene copolymer is present in an amount within a range from 20% to 35% by weight relative to the total weight of the sealant layer.

5. The hot-fill/retort sealant film according to claim 1, wherein the second propylene-ethylene copolymer has a flexural modulus at 0.127 cm/min (0.05 in/min), 1% secant within a range from 696.4 N/mm.sup.2 to 2,068.4 N/mm.sup.2 (101,000 to 300,000 psi) as measured in accordance with ASTM D-790 test method.

6. The hot-fill/retort sealant film according to claim 1, wherein the second propylene-ethylene copolymer is present in an amount within a range from 5% to 75% by weight relative to the total weight of the sealant layer.

7. The hot-fill/retort sealant film according to claim 1, wherein the second propylene-ethylene copolymer is present in an amount within a range from 25% to 65% by weight relative to the total weight of the sealant layer.

8. The hot-fill/retort sealant film according to claim 1, wherein the polyethylene comprises a linear low density polyethylene.

9. The hot-fill/retort sealant film according to claim 1, wherein the polyethylene comprises a high density polyethylene.

10. The hot-fill/retort sealant film according to claim 1, wherein the polyethylene polymer is present in an amount within a range from 1% to 50% by weight relative to the total weight of the sealant layer.

11. The hot-fill/retort sealant film according to claim 1, wherein the polyethylene polymer is present in an amount within a range from 2.5% to 30% by weight relative to the total weight of the sealant layer.

12. The hot-fill/retort sealant film according to claim 1, wherein the polyethylene polymer is present in an amount within a range from 5% to 20% by weight relative to the total weight of the sealant layer.

13. The hot-fill/retort sealant film according to claim 1, further comprising a seal initiation temperature within a range from 127° C. to 204° C. (260° F. to 400° F.).

14. The hot-fill/retort sealant film according to claim 1, further comprising a seal strength within a range from 175 N/m to 5254 N/m (1 lb/in to 30 lb/in) when the film is heat sealed to itself at a temperature within a range from 127° C. to 204° C. (260° F. to 400° F.) under 0.28 N/mm.sup.2 (40 psi) and a dwell time of 1 second.

15. The hot-fill/retort sealant film according to claim 1, further comprising a seal strength within a range from 1751 N/m to 4378 N/m (10 lb/in to 25 lb/in) when the film is heat sealed to itself at a temperature within the range from 127° C. to 204° C. (260° F. to 400° F.) under 0.28 N/mm.sup.2 (40 psi) and a dwell time of 1 second.

16. The hot-fill/retort sealant film according to claim 1, further comprising a seal strength of within a range from 2627 N/m to 3503 N/m (15 lb/in to 20 lb/in) when the film is heat sealed to itself at a temperature within the range from 127° C. to 204° C. (260° F. to 400° F.) under 0.28 N/mm.sup.2 (40 psi) and a dwell time of 1 second.

17. The hot-fill/retort sealant film according to claim 1, further comprising an ultimate hot tack of less than 50 N/m (0.29 lb/in) at 110° C. (230° F.).

18. The hot-fill/retort sealant film according to claim 1, further comprising an ultimate hot tack within a range from 88 N/m to 876 N/m (0.5 lb/in to 5 lb/in) at a temperature within a range from 110° C. to 182° C. (230° F. to 360° F.).

19. The hot-fill/retort sealant film according to claim 1, further comprising an ultimate hot tack within a range from 105 N/m to 525 N/m (0.6 lb/in to 3 lb/in) at a temperature within a range from 110° C. to 182° C. (230° F. to 360° F.).

20. A hot-fill/retort sealant film comprising: a sealant layer composition comprising: i) a first propylene-ethylene copolymer; ii) a second propylene-ethylene copolymer; iii) a polyethylene; and, wherein the first propylene-ethylene copolymer has a flexural modulus at 0.127 cm/min (0.05 in/min), 1% secant within a range from 124.1 N/mm.sup.2 to 689.5 N/mm.sup.2 (18,000 to 100,000 psi) as measured in accordance with ASTM D-790 test method and wherein the second propylene-ethylene copolymer is a random propylene-ethylene copolymer having a flexural modulus at 0.127 cm/min (0.05 in/min), 1% secant within a range from 696.4 N/mm.sup.2 to 2,068.4 N/mm.sup.2 (101,000 to 300,000 psi) as measured in accordance with ASTM D-790 test method.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the hot-fill/retort packaging films will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

(2) FIG. 1 illustrates a conceptual schematic of one embodiment of a film according to the present invention.

(3) FIG. 2 illustrates a chart 1 of hot tack values at various temperatures of hot-fill/retort packaging films with different sealant layer compositions.

(4) FIG. 3 illustrates a chart 2 of seal strength values at various temperatures of hot-fill/retort packaging films with different sealant layer compositions.

DETAILED DESCRIPTION OF THE INVENTION

(5) The hot-fill/retort packaging films now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

(6) Sealant Layer Compositions

(7) The sealant layer composition comprises a first propylene-ethylene copolymer, a second propylene-ethylene copolymer, and a polyethylene. The sealant layer of the hot-fill/retort packaging films is designed specifically for heat sealing to itself or another polyolefin material.

(8) In some embodiments, the first propylene-ethylene copolymer can be characterized as having a flexural modulus at 0.05 in/min (0.127 cm/min), 1% secant within a range from 2,000 psi to 100,000 psi as measured in accordance with ASTM D-790 test method. In such embodiments, the first propylene-ethylene copolymer may be present in an amount within a range from 10% to 90%, 15% to 50%, or 20% to 35% by weight relative to the total weight of the sealant layer.

(9) In some embodiments, the second propylene-ethylene copolymer can be characterized as having a flexural modulus at 0.05 in/min (0.127 cm/min), 1% secant within a range from 101,000 psi to 300,000 psi as measured in accordance with ASTM D-790 test method. In such embodiments, the second propylene-ethylene copolymer may be present in an amount within a range from 5% to 65%, 15% to 70%, or 25% to 65% by weight relative to the total weight of the sealant layer.

(10) In some embodiments, the difference between flexural moduli of the first and second propylene-ethylene copolymers can be greater than 25,000 psi, 50,000 psi, 75,000 psi, or 100,000 psi as measured at 0.05 in/min (0.127 cm/min), 1% secant in accordance with ASTM D-790 test method.

(11) The polyethylene of the sealant layer composition can be any polyethylene. In some embodiments, the polyethylene comprises a linear low density polyethylene. In other embodiments, the polyethylene comprises a high density polyethylene. In such embodiments, the polyethylene may be present in an amount within a range from 1% to 50%, 2.5% to 30%, or 5% to 20% by weight relative to the total weight of the sealant layer.

(12) The hot-fill/retort packaging films may be a monolayer or a multilayer film comprising the sealant layer composition as described herein. The sealant layer composition may be present in more than one layer of the packaging film. In some embodiments, the hot-fill/retort packaging films disclosed herein are palindromic. Palindromic films are symmetrical film structures around a central core layer and have two sealant layers.

(13) The hot-fill/retort packaging films may include any number of layers as needed depending upon the requirements of a particular packaging application. These additional layers may include, but are not limited to oxygen barrier layers, moisture barrier layers, chemical barrier layers, abuse layers, tie or adhesive layers, bulk layers, and odor and oxygen scavenging layers. The sealant layer can be combined with many different layers of materials such as, but not limited to, plastics, papers, non-woven materials, metal foils to form various packaging structures. In some embodiments, the hot-fill/retort packaging films are considered oxygen barrier films and have an oxygen transmission rate (O.sub.2TR) value of less than or equal to 155 cm.sup.3/m.sup.2/24 hours (10 cm.sup.3/100 in.sup.2/24 hours) at 1 atmosphere, 23° C. and 0% RH.

(14) The hot-fill/retort packaging films can be fabricated by several different conventional methods known in the art including but not limited to blown film coextrusion, slot cast coextrusion, extrusion lamination, extrusion coating and combinations thereof. In some embodiments, the hot-fill/retort packaging film can be produced using a coextrusion blown film line. In this method, the line can be equipped with multiple extruders (for multilayer hot-fill/retort packaging films) which feed into a multi-manifold circular die head through which the film layers can be forced and formed into a cylindrical multilayer film bubble. The bubble can be quenched, then collapsed and formed into a multilayer film. Films produced using blown film processes are known in the art and have been described, for example, in The Encyclopedia of Chemical Technology, Kirk-Othmer, 3rd ed., John Wiley & Sons, New York, 1981, Vol. 16, pp. 416-417 and Vol. 18, pp. 191-192, the disclosures of which are incorporated herein by reference. Typically, the resins and any additives forming one or more film layers can be introduced to an extruder where the resins were melt-plastified by heating and then transferred to an extrusion (or coextrusion) die for formation into the bubble or tube. If desired, resins can be blended or mechanically mixed by well-known methods using commercially available equipment including tumblers, mixers or blenders, and well-known additives such as processing aids, slip agents, anti-blocking agents, pigments and mixtures thereof may be incorporated into the resin by blending prior to extrusion. The extruder and die temperatures will generally depend upon the particular resin(s) containing mixtures being processed, and suitable temperature ranges for commercially available resins are generally known in the art or are provided in technical bulletins made available by resin manufacturers. The specific conditions for operation of any specific extrusion equipment can be readily determined by one skilled in the art. After formation, the bubble can be cooled, collapsed or separated into two films, slit, and wound around a roller for further processing.

(15) Once the hot-fill/retort packaging film is wound around a roller, it can be further converted into a package or package component including, but not limited to liners, bags, pillow pouches, stand-up pouches, quad pouches, zipped pouches, over-wraps, lidding films, thermoformed trays, vacuum packages, vacuum skin packaging, horizontal form-fill-seal packages, and especially vertical form-fill-seal packages.

WORKING EXAMPLES

(16) The following examples are intended to be representative of specific embodiments of hot-fill/retort packaging films and are not intended to be limiting to the scope of the invention.

(17) FIG. 1 illustrates one embodiment of a hot-fill/retort packaging film having a palindromic structure of thirteen layers. In this drawing, hot-fill/retort packaging film 10 comprises in the following order, a first sealant layer 101, a tie layer 201, a first barrier layer 301, a second barrier layer 302, a third barrier layer 303, a second tie layer 202, a core layer 400, a third tie layer 203, a fourth barrier layer 304, a fifth barrier layer 305, a sixth barrier layer 306, a fourth tie layer 204, and a second sealant layer 102. This embodiment can be produced using a blown film process by co-extruding a seven-layer film having sealant layer 101, tie layer 201, first barrier layer 301, second barrier layer 302, third barrier layer 303, second tie layer 202, and core layer 400, then collapsing the blown bubble onto itself to form a thirteen layer palindromic film.

(18) In the following examples, each film had a thirteen layer construction as depicted in FIG. 1 and were produced from a seven layer collapsed blown film as described above. The total thickness of the films were each approximately of 127μ (micron) (5 mil). Detail descriptions of a non-limiting exemplary first polypropylene-ethylene copolymer, PP-PE.sub.1, second first polypropylene-ethylene copolymer, PP-PE.sub.2, first polyethylene, PE.sub.1 and second polyethylene, PE.sub.2 are provided below following the Comparative Examples description.

Example 1

(19) Example 1 (Ex-1) had a structure and layer compositions as described below and as illustrated in FIG. 1. 1.sup.st Sealant Layer 101: 61 wt.-% of PP-PE.sub.2, 28 wt.-% of PP-PE.sub.1, and 10 wt.-% of PE.sub.2, and 1.0 wt.-% of processing additives. 1.sup.st Tie Layer 201: 100 wt.-% of a maleic anhydride grafted polypropylene having a density of 0.920 g/cm.sup.3 and a melt index of 3.5 dg/min (2.16 kg @ 230° C.)-AMPLIFY® TY XUS 69109.00 (The Dow Chemical Company, Midland, Mich.). 1.sup.st Barrier Layer 301: 80 Wt.-% of a nylon 6 having a melting temperature of 220° C. and a density of 1.13 g/cm.sup.3-Ultramid® B36 01 (BASF Corporation, Wyandotte, Mich.) and 20 wt.-% of a nylon 6/66 having a melting temperature of 192-194° C. and a density of 1.12 g/cm.sup.3-Ultramid® C40 L 01 (BASF Corporation, Wyandotte, Mich.). 2.sup.nd Barrier Layer 302: 100 wt.-% of an ethylene vinyl alcohol copolymer having a melting temperature of 188° C. and a density of 1.19 g/cm.sup.3-Soarnol™ RB7405B (Soarus LLC, Arlington Heights, Ill.). 3.sup.rd Barrier Layer 303: Same as 1st Barrier Layer 301. 2.sup.nd Tie Layer 202: 80 wt.-% of a linear low density polyethylene having a melting temperature of 119° C. and a density of 1.0 g/cm.sup.3-DOWLEX™ 2045G (The Dow Chemical Company, Midland, Mich.) and 20 wt.-% of am maleic anhydride modified linear low density polyethylene having a melting temperature of 98° C. and a density of 0.91 g/cm.sup.3-DuPont™ Bynel® 41E710 (DuPont Chemical Company, Wilmington, Del.). Core Layer 400: 100 wt.-% of an ethylene-based hexene plastomer a melting temperature of 93.9° C. and a density of 0.90 g/cm.sup.3-ExxonMobil EXACT™ 3131 (ExxonMobil Chemical Company, Houston, Tex.). 3.sup.rd Tie Layer 203: Same as 2.sup.nd Tie Layer 202. 4.sup.th Barrier Layer 304: Same as 1st Barrier Layer 301. 5.sup.th Barrier Layer 305: Same as 2.sup.nd Barrier Layer 302. 6.sup.th Barrier Layer 306: Same as 1st Barrier Layer 301. 4.sup.th Tie Layer 204: Same as 1st Tie Layer 201. 2.sup.nd Sealant Layer 102: Same as 1st Sealant Layer 101.

Example 2

(20) Example 2 (Ex-2) had the same structure and layer compositions as described above for Example 1 except for 1.sup.st and 2.sup.nd Sealant Layers 101, 102 had the following composition: 1.sup.st/2.sup.nd Sealant Layers 101/102: 56 wt.-% of PP-PE.sub.2, 28 wt.-% of PP-PE.sub.1, and 15 wt.-% of PE.sub.2, and 1.0 wt.-% of processing additives.

Example 3

(21) Example 3 (EX-3) had the same structure and layer compositions as described above for Example 1 except for 1.sup.st and 2.sup.nd Sealant Layers 101, 102 had the following composition: 1.sup.st/2.sup.nd Sealant Layers 101/102: 51 wt.-% of PP-PE.sub.2, 28 wt.-% of PP-PE.sub.1, 10 wt.-% of PE.sub.1, and 10 wt.-% of PE.sub.2, and 1.0 wt.-% of processing additives.

Example 4

(22) Example 4 (Ex-4) had the same structure and layer compositions as described above for Example 1 except for 1.sup.st and 2.sup.nd Sealant Layers 101, 102 had the following composition: 1.sup.st/2.sup.nd Sealant Layers 101/102: 61 wt.-% of PP-PE.sub.2, 28 wt.-% of PP-PE.sub.1, 10 wt.-% of PE.sub.1, and 1.0 wt.-% of processing additives.

Comparative Example-1

(23) Comparative Example-1 (Com.Ex.-1) had the same structure and layer compositions as described above for Example 1 except for 1st and 2.sup.nd Sealant Layers 101, 102 had the following composition: 1.sup.st/2.sup.nd Sealant Layers 101/102: 82.4 wt.-% of a linear low density polyethylene having a melting temperature of 120° C. and a density of 0.921 g/cm.sup.3-DOWLEX™′ 2645G (The Dow Chemical Company, Midland, Mich.), 10 wt.-% of an ultra-low density polyethylene having a melting temperature of 101° C. and a density of 0.914 g/cm.sup.3-ATTANE™ NG 4701G (The Dow Chemical Company, Midland, Mich.), and 7.6 wt.-% of processing additives.

Comparative Example-2

(24) Comparative Example-2 (Com.Ex.-2) had a three-layer structure and layer compositions as described below: 1st Sealant Layer: 40 wt.-% of PP-PE.sub.2, 40 wt.-% of PE-PP and 20 wt.-% of PE.sub.2. 1.sup.st Tie Layer: 100 wt.-% of a maleic anhydride grafted polypropylene having a density of 0.920 g/cm.sup.3 and a melt index of 3.5 dg/min (2.16 kg @ 230° C.)-AMPLIFY® TY XUS 69109.00 (The Dow Chemical Company, Midland, Mich.). 1.sup.st Barrier Layer: 100 wt.-% of a nylon 6 having a melting temperature of 220° C. and a density of 1.13 g/cm.sup.3-Ultramid® B36 01 (BASF Corporation, Wyandotte, Mich.)

(25) PP-PE.sub.1=1.sup.st Polypropylene/Ethylene copolymer having a flexural modulus at 0.05 in/min (0.127 cm/min), 1% secant within the range from 2,000 psi to 100,000 psi as measured in accordance with ASTM D-790 test method. Non-limiting commercially available examples include such polypropylene/ethylene copolymers such as those sold under the trademark VERSIFY™ 2000 and 3000 by The Dow Chemical Company, Inc., Midland, Mich. The VERSIFY™ 2000 copolymer has a density of 0.89 g/cm.sup.3, a total crystallinity of 35% and a flexural modulus (1% secant) of 52,000 psi as measured according to ASTM test method D-790. The VERSIFY™ 3000 copolymer has a density of 0.89 g/cm.sup.3, a total crystallinity of 44% and a flexural modulus (1% secant) of 56,500 psi as measured according to ASTM test method D-790.

(26) PP-PE.sub.2=2.sup.nd Polypropylene/Ethylene copolymer having a flexural modulus at 0.05 in/min (0.127 cm/min), 1% secant within the range from 101,000 psi to 300,000 psi as measured in accordance with ASTM D-790 test method. Non-limiting commercially available examples include polypropylene/ethylene copolymers such as LyondellBasell Pro-fax SA861 random polypropylene supplied by LyondellBasell, Houston, Tex. and Braskem PP RP 650 random polypropylene supplied by Braskem America Inc., Philadelphia, Pa. The LyondellBasell Pro-fax SA861 copolymer has a density of 0.90 g/cm.sup.3, a melt flow of 6.5 g/10 min, and a flexural modulus (1% secant at 0.05 in/min) of 133,000 psi as measured according to ASTM test method D-790. The Braskem PP RP 650 copolymer has a melt flow rate of 2.0 g/10 min (230° C./2.16 kg) and a flexural modulus (1% secant at 0.05 in/min) of 170,000 psi as measured according to ASTM test method D-790.

(27) PE-PP=Polyethylene/propylene copolymer having a mole ratio of 60% to 80% ethylene and 20% to 60% propylene. A commercially available example of such as material is TAFMER™ P supplied by Mitsui Petrochemical Industries, Ltd.

(28) PE.sub.1=High density polyethylene (HDPE). A non-limiting commercially available example of such a material includes LyondellBasell Alathon® M6020 supplied by LyondellBasell, Houston, Tex. which has a density of 0.96 g/cm.sup.3 and a melting temperature of between 199-210° C.

(29) PE.sub.2=Linear low density polyethylene (LLDPE). A specific non-limiting commercially available examples of a suitable LLDPE includes DOWLEX™ 2045G having a specific gravity of 0.922, a melt flow rate of 1.0 g/10 min, and a melting temperature of 118.9° C. which can be obtained from The Dow Chemical Company, Inc., Midland, Mich.

(30) The hot tack properties of Examples 1, 2, 3 and 4 and Comparative Examples 1 and 2 were measured by heat sealing the films to themselves (sealant layer to sealant layer) at different temperatures under 40 psi, a one second dwell time, and allowed to cool for 0.1 second. The hot tack values at different temperatures of these examples are reported in Chart 1 in FIG. 2.

(31) To demonstrate the increase of the seal initiation temperature, broadening of the seal initiation temperature range and/or increase in seal strength at elevated temperatures, the films were heat sealed to itself (sealant layer to sealant layer) at different temperatures under 40 psi and a one second dwell time, and allowed to cool to ambient temperature. The seal strengths or force required to delaminate the sealed films at a 90 degree angle was measured using an Instron Tensile Tester. The results are reported in CHART 2 in FIG. 3.

(32) The seal strength and hot tack test results indicate that the hot-fill/retort packaging films having a sealant composition of a first polypropylene-ethylene copolymer, a second polypropylene-ethylene copolymer and polyethylene exhibit an increase of seal initiation temperature of about 50 degrees from 127° C. to 204° C. (260° F. to 400° F.) and/or an increase in seal strength compared to conventional hot-fill/retort films without the sealant layer composition. The tests also demonstrate that hot-fill/retort packaging films self-tack to themselves at temperatures above 110° C. (230° F.), which is required for hot-fill processing.

(33) The above description and examples illustrate certain embodiments of the present invention and are not to be interpreted as limiting. Selection of particular embodiments, combinations thereof, modifications, and adaptations of the various embodiments, conditions and parameters normally encountered in the art will be apparent to those skilled in the art and are deemed to be within the spirit and scope of the present invention.