Patent Application
20190048155
The present Application claims priority to commonly owned European patent application having application number EP 16382033.5, filed on Jan. 29, 2016, which Application is incorporated herein by reference in its entirety.
Embodiments of the present disclosure relate to monolayer and multilayer stretch wrap films that include polyethylene, and more particularly, to monolayer and multilayer stretch wrap films that include polyethylene that include a nonpolar, polyethylene wax, and related compositions and methods of making.
Stretch wrap films such as silage wrap films can be used to wrap silage so as to limit the exposure of the silage to air so that the silage can undergo anaerobic fermentation for a desirable amount of time. Because silage can be a rough material to handle, the baled silage can be stored outside in a wide variety of weather conditions, and the baled silage can be handled by heavy equipment, it can be desirable for silage wrap to have highly durable mechanical properties to withstand such conditions while at the same time providing desirable oxygen barrier properties. Unfortunately, material properties that can enhance oxygen barrier properties may degrade mechanical properties.
Accordingly, alternative stretch wrap films having improved oxygen barrier properties while at the same time having durable mechanical properties to contain silage in a wide variety of environmental conditions is desirable.
Disclosed in embodiments herein are monolayer or multilayer films. The films include at least one layer, wherein the at least one layer includes: a) a polyethylene polymer component including linear low density polyethylene; and b) a wax component including nonpolar, polyethylene wax. The nonpolar, polyethylene wax has a density of 0.955 grams/cm3 or greater, and is present in an amount of at least 3 percent by weight of the film.
Also disclosed in embodiments herein are compositions including: a) a polyethylene polymer component comprising linear low density polyethylene; and b) a wax component comprising nonpolar, polyethylene wax. The nonpolar, polyethylene wax has a density of 0.955 grams/cm3 or greater, and is present in an amount of at least 3 percent by weight of the composition.
Also disclosed in embodiments herein are methods of making a film (a monolayer film or a multilayer film). The methods include a) providing a melted blend, wherein the melted blend includes a wax component including melted nonpolar, polyethylene wax and a first polyethylene polymer component including melted linear low density polyethylene. The nonpolar, polyethylene wax has a density of 0.955 grams/cm3 or greater, and is present in an amount of at least 3 percent by weight of the film. The methods further include forming tire melted blend into a film via cast film techniques or blown film techniques.
Reference will now be made in detail to films, compositions, and methods thereof according to the present disclosure. The films may be used as stretch wrap in wrapping silage to allow anaerobic fermentation to occur for a desirable amount of time. It is noted, however, that this is merely an illustrative implementation of the embodiments disclosed herein. The embodiments are applicable to other technologies that are susceptible to similar problems as those discussed herein. For example, the films described herein may be used in other flexible packaging applications, such as, heavy duty shipping sacks, liners, sacks, stand-up pouches, detergent pouches, sachets, etc., all of which are within the purview of the present embodiments.
General film structure and composition film can be monolayer film or multi-layer film.
The polyethylene polymer component can be selected to help provide, e.g., desirable properties in the film so that the film can be used as a stretch wrap such as silage wrap (discussed in section “F” below).
The polyethylene polymer component may include one or more polyethylene polymers in an amount such that the film includes from greater than 50 wt. % to 95 wt. % of one or more polyethylene polymers based on the total weight of the film. All individual values and subranges are included and disclosed herein. For example, in some embodiments, a film can have from 55 wt. % to 95 wt. % of one or more polyethylene polymers based on the total weight of the film, from 60 wt. % to 95 wt. % of one or more polyethylene polymers based on the total weight of the film, or from 60 wt. % to 95 wt. % of one or more polyethylene polymers based on the total weight of the film. In other embodiments, a film can have from 55 wt. % to 90 wt. % of one or more polyethylene polymers based on the total weight of the film, from 60 wt. % to 85 wt. % of one or more polyethylene polymers based on the total weight of the film, or from 60 wt. % to 70 wt. % of one or more polyethylene polymers based on the total weight of the film.
In some embodiments, a film includes only the polyethylene polymer component and the nonpolar, polyethylene wax component (discussed below), where the polyethylene polymer component is present in an amount of 97 wt. % or less based on the total weight of the film and the nonpolar, polyethylene wax component is present in an amount of 3 wt. % or more based on the total weight of the film.
The polyethylene polymer component may include at least linear low density polyethylene. The linear low density polyethylene may include, in polymerized form, a majority weight percent of ethylene based on the total weight of the linear low density polyethylene. In an embodiment, the linear low density polyethylene is an interpolymer of ethylene and at least one ethylenically unsaturated comonomer. In one embodiment, the comonomer can be a C3-C20 α-olefin. In another embodiment, the comonomer is a C3-C8 α-olefin. In another embodiment, the C3-C8 α-olefin can be selected from propylene, 1-butene, 1-hexene, or 1-octene. In an embodiment, the linear low density polyethylene can be selected from the following copolymers: ethylene/propylene copolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/octene copolymer. In a further embodiment, the linear low density polyethylene is an ethylene/octene copolymer.
The linear low density polyethylene may have a density of from 0.890 g/cc to 0.940 g/cc. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the linear low density polyethylene may have a density of from 0.890 g/cc to 0.935 g/cc, 0.890 g/cc to 0.930 g/cc, or 0.900 g/cc to 0.930 g/cc. In other embodiments, the linear low density polyethylene may have a density of from 0.905 g/cc to 0.940 g/cc, 0.910 g/cc to 0.940 g/cc, or 0.915 g/cc to 0.940 g/cc.
The linear low density polyethylene may have a melt index, or I2, of from 0.1 g/10 min to 10 g/10 min. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the linear low density polyethylene may have a melt index (I2) from 0.1 to 6 g/10 min, 0.1 to 5 g/10 min, 0.1 to 4 g/10 min, 0.3 g/10 min to 3.5 g/10 min, 0.1 g/10 min to 2 g/10 min, 0.1 g/10 min to 1.5 g/10 min. In other embodiments, the linear low density polyethylene may have a melt index (I2) from 0.1 g/10 min to 1.1 g/10 min. In further embodiments, the linear low density polyethylene may have a melt index (I2) of 0.2-0.9 g/10 min.
The linear low density polyethylene can be made by a variety of techniques. For example, the linear low density polyethylene may be produced via a gas phase or a solution phase and using single-site catalysts techniques and/or Ziegler-Natta catalyst techniques. Methods for producing olefin polymers using single site catalysts can be U.S. Pat. No. 5,272,236 (Lai et al.), U.S. Pat. No. 5,324,800 (Welborn, Jr. et al.), and U.S. Pat. No. 6,486,284 (Karande et al.), the entirety of which patents are incorporated herein by reference. Single-site catalyst systems may include metallocene catalysts and post-metallocene catalysts. Ziegler-Natta catalysts are described in U.S. Publication Numbers 2008/0038571 (Klitzmiller et al.) and 2008/0176981 (Biscoglio et al.), the entirety of which patent documents are incorporated herein by reference.
In one embodiment, the linear low density polyethylene can be a Ziegler-Natta catalyzed ethylene and octene copolymer. The linear low density polyethylene can have crystallinity from about 40% to about 50%, or about 47%.
In another embodiment, the linear low density polyethylene can be a single-site catalyzed linear low density polyethylene (“sLLDPE”).
As used herein, “sLLDPE” is a LLDPE polymerized using a single site catalyst such as a metallocene catalyst or a constrained geometry catalyst A “metallocene catalyst” is a catalyst composition containing one or more substituted or unsubstituted cyclopentadienyl moiety in combination with a Group 4, 5, or 6 transition metal. A “constrained geometry catalyst” comprises a metal coordination complex comprising a metal of groups 3-10 or the Lanthanide series of the Periodic Table and a delocalized pi-bonded moiety substituted with a constrain-inducing moiety, said complex having a constrained geometry about the metal atom such that the angle at the metal between the centroid of the delocalized, substituted pi-bonded moiety and the center of at least one remaining substituent is less than such angle in a similar complex containing a similar pi-bonded moiety lacking in such constrain-inducing substituent, and provided further that for such complexes comprising more than one delocalized, substituted pi-bonded moiety, only one thereof for each metal atom of the complex is a cyclic, delocalized, substituted pi-bonded moiety. The constrained geometry catalyst further comprises an activating co-catalyst. Nonlimiting examples of suitable constrained geometry catalysts are disclosed U.S. Pat. No. 5,132,380 (Mullins et al.), the entire content of which is incorporated by reference herein.
The sLLDPE, may be unimodal or multimodal (i.e., bimodal). A “unimodal sLLDPE” is a LLDPE polymer prepared from one single-site catalyst under one set of polymerization conditions. A “multimodal sLLDPE is an LLDPE polymer prepared from two or more different catalysts and/or under two or more different polymerization conditions. A “multimodal sLLDPE” comprises al least a lower molecular weight component (LMW) and a higher molecular weight (HMW) component Each component is prepared with a different catalyst and/or under different polymerization conditions. The prefix “multi” relates to the number of different polymer components present in the polymer. A nonlimiting example of multimodal sLLDPE is set forth in U.S. Pat. No. 5,047,468 (Lee et al.), the entire content of which is incorporated by reference herein.
The LLDPE can be present in an amount of from greater than 50 wt. % to 95 wt. % based on the total weight of the film. All individual values and subranges are included and disclosed herein. For example, in some embodiments, a film can have from 55 wt. % to 95 wt. % of LLDPE based on the total weight of the film, from 60 wt. % to 95 wt. % of LLDPE based on the total weight of the film, or from 65 wt. % to 95 wt. % of LLDPE based on the total weight of the film. In other embodiments, a film can have from 55 wt. % to 90 wt. % of LLDPE based on the total weight of the film, from 60 wt. % to 85 wt. % of LLDPE based on the total weight of the film, or from 60 wt. % to 65 wt. % of LLDPE based on the total weight of the film.
Nonlimiting examples of suitable and commercially available linear low density polyethylene are LLDPE sold under the tradenames DOWLEX™ 2045 S, DOWLEX™ SL2103G, and ELITE™ AT 6301, available from The Dow Chemical Company, Midland, Mich.
In some embodiments, the polyethylene component includes only LLDPE.
Optionally, in sonic embodiments, the polyethylene component includes a blend of LLDPE with one or more additional polyethylene polymers chosen from the group of ultra-high-molecular-weight polyethylene (UHMWPE), high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), very low-density polyethylene (VLDPE), and ultra-low-density polyethylene (ULDPE). In some embodiments, the polyethylene component includes a blend of linear low density polyethylene and at least one polyethylene polymer chosen from low density polyethylene, medium density polyethylene, and high density polyethylene.
The one or more additional polyethylene polymers can be present in an amount of from greater than 0.5 wt. % to 50 wt. % based on the total weight of the film. All individual values and subranges are included and disclosed herein. For example, in some embodiments, a film can have from 5 wt. % to 40 wt. % of one or more additional polyethylene polymers based on the total weight of the film, or from 10 wt. % to 20 wt. % of one or more additional poly-ethylene polymers based on the total weight of the film. In other embodiments, a film can have from 0.5 wt. % to 15 wt. % of one or more additional polyethylene polymers based on the total weight of the film, or from 0.5 wt. % to 10 wt. % of one or more additional polyethylene polymers based on the total weight of the film.
A nonlimiting example a of suitable and commercially available ULDPE is ULDPE sold under the tradename ATTANE™, available from The Dow Chemical Company, Midland, Mich.
The polyethylene polymer component can optionally be blended with one more polymers in addition to polyethylene polymers. Exemplary optional polymers include propylene-based polymers, ethylene-vinyl acetate (EVA) copolymers, ethylene vinyl alcohol (EVOH) copolymers, and other polymers useful in forming mechanically tough oxygen barriers such as silage wrap.
The one or more optional polymers can be present in an amount of from greater than 0.5 wt. % to 50 wt. % based on the total weight of the film. All individual values and subranges are included and disclosed herein. For example, in some embodiments, a film can have from 5 wt. % to 40 wt. % of one or more optional polymers based on the total weight of the film, or from 10 wt. % to 20 wt. % of one or more optional polymers based on the total weight of the film.
The wax component according to the present disclosure can include one or more waxes to help decrease oxygen transmission rate of the film while at the same time not negatively impacting the mechanical properties of the film to an undue degree (e.g., so that the film can be used to wrap silage without tearing and the like to an undue degree). It has been discovered that a film including at least one nonpolar, polyethylene wax having a density of 0.955 grams/cm3 or greater, and in on amount of at least 3 percent by weight of the film can unexpectedly provide a significant reduction in stretched oxygen transmission rate (e.g., stretched OTR) while at the same time providing film mechanical properties that are sufficient for the film to be used as a silage wrap. This finding is unexpected because, without being bound by theory, H is believed that as the crystallinity of a polymer used in a film increases, the stretched oxygen transmission rate of the film tends to decrease, but the mechanical properties of the film tend to degrade to an undue degree, especially in the context of a silage wrap.
As used herein, “nonpolar” refers to a polyethylene wax that has an acid value of no more than 5 (mg KOH/g). In some embodiments, the nonpolar, polyethylene wax may have an acid value of from 0 to 5 (mg KOH/g). All individual values and subranges are included and disclosed herein. For example, in some embodiments, the nonpolar, polyethylene wax may have an acid value of from 0 to 4, 0 to 3, 0 to 2, or 0 to 1 (mg KOH/g). In some embodiments, a nonpolar, polyethylene wax does not include any polar functional groups.
The nonpolar, polyethylene wax may have a saponification value of no more than 5 (mg KOH/g). In some embodiments, the nonpolar, polyethylene wax may have a saponification value of from 0 to 5 (mg KOH/g). All individual values and subranges are included and disclosed herein. For example, in some embodiments, the nonpolar, polyethylene wax may have a saponification value of from 0 to 4, 0 to 3, 0 to 2, or 0 to 1 (mg KOH/g).
As used herein, “polyethylene wax” refers to both ethylene homopolymers and copolymers of ethylene with α-olefins having a chain length of C3-C18. Nonpolar polyethylene waxes according to the present disclosure can be made by polymerizing ethylene to produce a relatively high density polyethylene wax having properties as described herein below. Nonpolar, polyethylene wax can be prepared by thermal degradation of branched or unbranched polyethylene polymers or by direct polymerization of ethylene. Examples of suitable polymerization processes include free-radical processes, in which ethylene is reacted under high pressures and temperatures to form a wax with a greater or lesser degree of branching, and also processes in which ethylene and/or higher 1-olefins are polymerized to branched or unbranched waxes using organometallic catalysts, such as Ziegler-Natta or metallocene catalysts, for example. Corresponding methods of preparing olefin homopolymer and copolymer waxes are described for example in U.S. Pat. No. 8,763,848 (Fell et al.), the entirety of which patent is incorporated herein by reference.
The nonpolar, polyethylene wax may have a density of 0.955 g/cc or greater, or even 0.965 g/cc or greater. In some embodiments, the nonpolar, polyethylene wax may have a density of from 0.955 g/cc to 0.995 g/cc. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the nonpolar, polyethylene wax may have a density may have a density of from 0.955 g/cc to 0.990 g/cc, 0.955 g/cc to 0.980 g/cc, or 0.955 g/cc to 0.975 g/cc. In other embodiments, the linear low density polyethylene may have a density of from 0.960 g/cc to 0.995 g/cc, 0.965 g/cc to 0.990 g/cc, or 0.970 g/cc to 0.985 g/cc.
The nonpolar, polyethylene wax may have a viscosity of from 100 (mPa-s) to 30,000 (mPa-s). All individual values and subranges art included and disclosed herein. For example, in some embodiments, the nonpolar, polyethylene wax may have a viscosity of from 100 (mPa-s) to 600 (mPa-s), 100 (mPa-s) to 400 (mPa-s), or 300 (mPa-s) to 400 (mPa-s). In other embodiments, the nonpolar, polyethylene wax may have a viscosity of from 20,000 (mPa-s) to 30,000 (mPa-s), 20,000 (mPa-s) to 28,000 (mPa-s), or 22,000 (mPa-s) to 27,000 (mPa-s).
The nonpolar, polyethylene wax may have a drop point of from 125° C. to 145° C. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the nonpolar, polyethylene wax may have a drop point of from 125° C. to 140° C., 125° C. to 135° C., or 125° C. to 130° C. In other embodiments, the nonpolar, polyethylene wax may have a drop point of from 130° C. to 145° C., 135° C. to 145° C., or 140° C. to 145° C.
The wax component may include nonpolar, polyethylene wax in an amount such that the film includes from 3 wt. % to 30 wt. % of nonpolar, polyethylene wax based on the total weight of the film. All individual values and subranges are included and disclosed herein. For example, in some embodiments, a film can have from 3 wt. % to 25 wt. % of nonpolar, polyethylene wax based on the total weight of the film, from 3 wt. % to 20 wt. % of nonpolar, polyethylene wax based on the total weight of the film, from 3 wt. % to 15 wt. % of nonpolar, polyethylene wax based on the total weight of the film, or from 3 wt. % to 10 wt. % of nonpolar, polyethylene wax based on the total weight of the film. In other embodiments, a film can have from 5 wt. % to 30 wt. % of nonpolar, polyethylene wax based on the total weight of the film, from 10 wt. % to 30 wt. % of nonpolar, polyethylene wax based on the total weight of the film, or from 15 wt. % to 30 wt. % of nonpolar, polyethylene wax based on the total weight of the film.
Nonlimiting examples of suitable and commercially available nonpolar, polyethylene waxes are nonpolar, polyethylene wax sold under the tradenames LICOWAX® 130 or LICOWAX® 190 from Clariant International Ltd., Muttenz, Switzerland.
One or more layers of a film disclosed herein may further include one or more additives. Additives can be individually present in an amount of up to about 2% based on the total weight of the polyethylene-based film. Such additives include, but are not limited to, antistatic agents, color enhancers, dyes, lubricants, fillers, pigments, primary antioxidants, secondary-antioxidants, processing aids, UV stabilizers, anti-blocks, slip agents, tackifiers, fire retardants, anti-microbial agents, odor reducer agents, anti-fungal agents, and combinations thereof. For example, one or more layers of a film disclosed herein may include additives that facilitate forming a stretch wrap such as silage wrap. Exemplary silage wrap additives include polyisobutylene (PIB). One or more layers of a film disclosed herein may include from about 0.01 to about 10 percent by the combined weight of such additives, based on the total weight of the polyethylene-based film.
A film according to the present disclosure may be a monolayer film or a multilayer film that includes: a polyethylene polymer component comprising linear low density polyethylene; and a wax component comprising nonpolar, polyethylene wax, wherein the nonpolar, polyethylene wax has a density of 0.955 grams/cm3 or greater, and wherein the nonpolar, polyethylene wax is present in an amount of at least 3 percent by weight of the film. For multilayer films, one or more layers of the multilayer film can include: a polyethylene polymer component comprising linear low density polyethylene; and a wax component comprising nonpolar, polyethylene wax, wherein the nonpolar, polyethylene wax has a density of 0.955 grams/cm3 or greater, and wherein the nonpolar, polyethylene wax is present in an amount of at least 3 percent by weight of the film.
A multilayer film can include two more or more layers. For example, three layers, four layers, five layers, six layers, seven layers, etc. In some embodiments, a multilayer film can include at least a first layer, a second layer, and a third layer. The second layer is between the first layer and the third layer. The second layer can include a polyethylene polymer component comprising linear low density polyethylene; and a wax component comprising nonpolar, polyethylene wax, wherein the nonpolar, polyethylene wax has a density of 0.955 grams/cm3 or greater, and wherein the nonpolar, polyethylene wax is present in an amount of at least 3 percent by weight of the film. In some embodiments, the first layer can be referred to as the first outer layer, the second layer can be referred to as the core layer, and the third layer can be referred to as the second outer layer. In embodiments herein, the multilayer films may further include one or more intermediate layers positioned between the core layer and at least one outer layer. In some embodiments, the multilayer films may include one or more intermediate layers positioned between the core layer and the first outer layer. In other embodiments, the multilayer films may include one or more intermediate layers positioned between the core layer and the second outer layer. In further embodiments, the multilayer films may include one or more intermediate layers positioned between the core layer and the first outer layer, and between the core layer and the second outer layer. Any layer of a multilayer film may be compositionally the same as or different from the second (or core) layer. The one or more intermediate layers may include ethylene-based polymers, such as, LDPE, LLDPE, MDPE, HDPE, or blends thereof.
For multilayer films having first and second outer layers, the first and second outer layers may be the same or different in composition and/or thickness. For example, a three-layer film may have an ABA film structure, where the A skin layers may be the same or different in thickness, but are symmetrical in the composition, or an ABC film structure, where the A and C may be the same or different in thickness, but the skin layers are unsymmetrical in composition. This type of characterization can be similarly applied to multilayer films having more than three layers (e.g., 5, 7, or more layers).
The thickness ratio of the at least one outer layer to the core layer can be any desirable ratio. In some embodiments, the thickness ratio of the at least one outer layer to the core layer can be any ratio suitable to maintain the oxygen barrier and mechanical properties of a silage wrap film, in some embodiments, the thickness ratio of the at least one outer layer to the core layer may be 1:5 to 1:1, 1:4 to 1:1, 1:3 to 1:1, 1:2 to 1:1, or 1:1.5 to 1:1. The thickness ratio of the at least one outer layer to the core layer can also be captured by percentages. For example, in some embodiments, the core layer comprises from about 50 wt. % to about 95 wt. % of the overall film thickness. In other embodiments, the core layer comprises from about 60 wt. % to about 90 wt. % of toe overall film thickness. In further embodiments, the core layer comprises from about 65 wt. % to about 85 wt. % of the overall film thickness.
In further embodiments, where the multilayer film includes a core layer positioned between the first and second outer layers, the thickness ratio of the first and second outer layers to the core layer can be any ratio suitable to maintain the oxygen barrier and mechanical properties of the film. In some embodiments, the thickness ratio of the first and second outer layers to the core layer may be 1:10 to 1:1,1:5 to 1:1,1:4 to 1:1, 1:2 to 1:1, or 1:1.5 to 1:1. The thickness ratio of the first and second outer layers to the core layer can also be captured by percentages. For example, in some embodiments, the core layer is from about 50 wt. % to about 95 wt. % of the overall film thickness. In other embodiments, the core layer is from about 60 wt. % to about 90 wt. % of the overall film thickness. In further embodiments, the core layer is from about 65 wt. % to about 85 wt. % of the overall film thickness. These percentages may be similarly applied to multilayer films having more than three layers (e.g., 5, 7, or more layers). The first and second outer layers may have an equal thickness, or alternatively, may have an unequal thickness. The monolayer or multilayer films described herein may have a total film thickness of 100 microns or less. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the monolayer or multilayer films described herein may have a total film thickness of from 10 to 75 microns, from 10 to 50 microns, or from 10 to 30 microns. While there is no minimum thickness contemplated for the monolayer or multilayer films of the present disclosure, practical considerations of current manufacturing equipment suggests that the minimum thickness will be at least 10 microns.
In some embodiments, the monolayer or multilayer films described herein that include a nonpolar, polyethylene wax can have a 100% stretched, oxygen transmission rate (OTR) of at least 10 percent less than the 100% stretched, oxygen transmission rate of the same film without the nonpolar, polyethylene wax.
In some embodiments the monolayer or multilayer films described herein can have a silage puncture resistance of from 45 (J/cm3) to 200 (J/cm3). All individual values and subranges are included and disclosed herein. For example, in some embodiments the monolayer or multilayer films described herein may have a silage puncture resistance of from 45 (J/cm3) to 150 (J/cm3), or from 50 (J/cm3) to 100 (J/cm3).
In some embodiments the monolayer or multilayer films described herein can have an Elmendorf Tear Strength CD greater than 500 grams. In some embodiments the monolayer or multilayer films described herein may have an Elmendorf Tear Strength CD of from greater than 500 grams to 2000 grams. All individual values and subranges are included and disclosed herein. For example, in some embodiments, the monolayer or multilayer films described herein may have an Elmendorf Tear Strength CD of from greater than 500 grams to 1500 grams or from greater than 500 grams to 1000 grams.
Films described herein can be made using a variety of techniques including cast film techniques and/or blown film techniques. A method of making blown films is described in U.S. Pat. No. 6,521,338 (Maka), the entirety of which patent is incorporated herein by reference. A method of making a cast film is described in U.S. Pat. No. 7,847,029 (Butler et al.), the entirety of which patent is incorporated herein by reference. In some embodiments, the monolayer film and/or the multilayer film is a blown film. As used herein, a “blown film” is a film produced by extruding (or coextruding) a polymer melt(s) from an annular die into a tube which is simultaneously pulled away from the die, and over a bubble of air trapped between the die and a collapsing device, such as one or more nip rolls, while the air is blown around the outer film tube surface to stabilize and quench the tube. In a blown film process, contact of the outer film tube surface and optionally also the inner film tube surface with room temperature or cooler air can cool the radially expanding tubular polymer melt as it leaves the die and travels over the trapped bubble thereby causing it to solidify. The point of transition from polymer melt to solid can be referred to as the frost line. Above the frost line, the blown or inflated tube is collapsed and fed through nip rolls which can trap air within the tube to maintain an expanded bubble of fluid (typically air). Optionally, this air bubble may be used to internally cool the expanded film tube by continuously delivering cool air (e.g., at about 45-55° F. (7-13° C.)) while simultaneously removing warm air from inside the bubble via the die. This exchange of air can be performed at a constant rate to produce a final blown film of uniform size. The internal bubble cooling can assist in quenching the film and may also produce a film having improved optical properties (i.e., lower haze and higher gloss). The blow up ratio is the ratio of the film circumference after radial expansion and cooling to the die opening circumference and may be determined from the known annular die opening dimensions and by measuring the transverse width of the flattened, expanded and cooled tubular film. Blow up ratios can range from 2:1 to 5:1, Dimensions and properties of the blown film may be adjusted by altering the blow up ratio and/or the haul off (or draw) speed of the film as it is pulled out of the die in the machine direction, for example, by driven nip rolls.
One or more layers of a film according to the present disclosure can be a melt blend. As used herein, a “melt blend” (which includes a “melted blend” ) means two or more layer components (e.g., linear low density polyethylene a nonpolar, polyethylene wax) are melted and blended together via an apparatus such as a compounding apparatus. The melt blend can be directly extruded or cooled to form a solid composition (e.g., pellets) for subsequent use.
In some embodiments, a method of making a film includes providing a melted blend, extruding the melted blend in an extruder to form a tube; and cooling the tube to form a blown stretch film. The melted blend can include a wax component including a melted nonpolar, polyethylene wax as described above and a first polyethylene polymer component including a melted linear tow density polyethylene as also described above.
A melted blend as described herein can be provided in a variety of ways. For example, a composition including a dry mixture of a first and second plurality of particles can be melted and blended to form a melted blend, followed by directly extruding the melted blend. The first plurality of particles can include a polyethylene polymer component including linear low density polyethylene; and the second plurality of particles can include a wax component including nonpolar, polyethylene wax, wherein the nonpolar, polyethylene wax has a density of 0.955 grams/cm3 or greater and is present in an amount of at least 3 percent by weight of the melted blend.
Alternatively, the first and second plurality of particles a dry mixture of a first and second plurality of particles can be melted and blended to form a melted blend, followed by forming the melted blend into a composition including a third plurality of particles. The third plurality of particles are a melt blend of the first and second plurality of particles and can be stored, transported, sold, and the like for subsequent extrusion. As used herein, “particles” refer to any kind of plurality of discrete units that are solid at 25° C. such as pellets, powder, and the like. In some embodiments, a melt blend of the first and second plurality of particles can form a second layer (e.g., a “core” layer as described above) in a multilayer film where extruding the melted blend in an extruder to form a tube includes co-extruding the melted blend with a second polyethylene polymer component to form a tube including a first layer, a third layer, and the second layer between toe first layer and the third layer. The first and third layers include the second polyethylene polymer component, which includes linear tow density polyethylene. After extruding, the tube can be cooled to form a multilayer blown, stretch wrap film.
A monolayer film and/or the multilayer film can be subjected to one or more post processing techniques. Nonlimiting examples of post processing techniques include radiation treatment and/or corona treatment. Sealing techniques to which the mono-/multi-layer film can be exposed include heat sealing, adhesive sealing, heat bar settling, impulse heating, side welding, and/or ultrasonic welding.
Embodiments of the present disclosure include monolayer and/or multilayer films that have not undergone any orientation processes (drawing or stretching) and, thus, are not oriented films (not monoaxially or biaxially oriented films).
Monolayer and multilayer films according to the present disclosure can be used as stretch films, especially to contain items so as to limit or prevent their exposure to air (e.g., silage wrap or “silage bale wrap” ). A film as described herein may also be useful in silo bags and silo bunker barriers.
Silage bale wrap can be described as a film designed to wrap silage so as to improve the nutritional value of silage (e.g., grass and other vegetable fodder) for cattle. Silage wrap helps baled silage to undergo anaerobic fermentation of the vegetable organic material inside the bale. The fermentation process can increase the amount of protein and make the silage more easily digestible. Silage wrap can facilitate anaerobic fermentation by keeping the oxygen content inside the bale as low as possible. For example, as the fodder is being wrapped with silage wrap, the silage wrap can facilitate pressing air out of the fodder. Further, the oxygen barrier properties of the silage wrap can facilitate keeping air out of the mapped silage. To help facilitate this, silage wrap can have good mechanical properties, adhesion properties, and oxygen barrier properties. The mechanical properties of silage wrap are desirably good enough to prevent damage to the film from puncturing, stretching, tearing or other mechanical abuse, that could potentially break the film and allow air inside. The adhesion properties between successive layers of film in a bale are desirably good enough to provide a tight and hermetic closing of a bale. The oxygen barrier properties of the film (especially as the film is stretched to wrap silage) are desirably good enough to prevent oxygen in air from going through the layers of film into the bale.
An example of baling silage is described herein below. Silage can be baled by wrapping and stretching a silage wrap film around a bale of a forage crop and forming a barrier around the bale, it is noted that a silage wrap film may stretch up to 80-100% when it is being tightly wrapped around silage by a silage bale wrapping machine. As used herein, a “silage wrap film” is a monolayer film or any multilayer film disclosed herein. The silage wrap film can be wrapped and stretched around the bale to produce a barrier that is composed of one, two, three, four, or more layers of the silage wrap film. Thus, the barrier can be a single layer of the silage wrap film or multiple layers of the silage wrap film. As used herein, a “barrier” is an airtight covering or an airtight encasement that can reduce the permeation of oxygen in air so that the OTR is as described herein.
As used herein, “bale silage” is one or more forage crops formed into a bale and covered with a silage wrap film to help exclude oxygen. A “forage crop” is any plant that is grown and fed to livestock. Nonlimiting examples of forage crops suitable for bale silage include beans, clover, corns, cornstalk, grasses, grains (barley, oats, rice, wheat, rye, millet), hay, legumes (alfalfa, red clover, white clover, alsike clover, birdsfoot trefoil, vetches, sweetclover), sorghums, soybeans, vegetables, and any combination of the foregoing.
A bale of silage can be wrapped using, e.g., a bale wrapping device that wraps and stretches the silage wrap film around the bale to form the barrier. A bale wrapping device can include a loading arm that lifts the bale and places it on a wrapping table. The wrapping table can include rollers and belts which rotate the bale while the table itself revolves. A dispensing device can provide one or more rolls of the silage wrap film. As the bale turns, the silage wrap film can be stretched as it is pulled through the dispensing device and wrapped tightly around the bale to help remove oxygen from the bale. When the table has revolved a predetermined number of times, a lift device can tilt the wrapping table to tip the wrapped bale off of the wrapping table. The dispensing device can cut the silage wrap film prior to the wrapped bale falling from the wrapping table. Operation of the bale wrapping device can be controlled automatically (by way of a computer or similar logic) or manually. In scene embodiments, bale wrapping procedures can involve wrapping a bale with about four to about six layers of the silage wrap film to produce bale silage.
Once wrapped, the forage crop can undergo an ensiling process whereby anaerobic microorganisms ferment carbohydrates present in the forage crop to lactic acid forming silage.
An example of silage wrap is also disclosed in US 2011/0185683 (Domenech et al.).
The density of toe polymers in the polyethylene polymer component is measured according to ASTM D792, Method B.
The density of the nonpolar, polyethylene wax in the wax component is measured according to ISO 1183 at 23° C.
The Melt Index (I2) is measured according to ASTM D-1238 (condition 190® C./2.16 kg).
Percent crystallinity for ethylene-based polymers (e.g., LLDPE) is determined by differential scanning calorimetry (DSC), using a TA Instruments Model QlOOO Differential Scanning Calorimeter. A sample of about 5-8 mg size is cut from the material to be tested, and placed directly in the DSC pan for analysis. For higher molecular weight materials, a thin film is normally pressed from the sample, but for some lower molecular weight samples, they may be either too sticky or flow too readily during pressing. Samples for testing may, however, be cut from plaques that are prepared, and used, for density testing. The sample is first heated at a rate of about 10° C./min to 180° C. for ethylene-based polymers, and held isothermally for three minutes at that temperature to ensure complete melting (the first heat). Then the sample is cooled at a rate of 10° C. per minute to −60° C. for ethylene-based polymers, and held there isothermally for three minutes, after which, it is again heated (the second heat) at a rate of 10° C. per minute until complete melting. The thermogram from this second heat is referred to as toe “second heat curve.” Thermograms are plotted as watts/gram versus temperature. The percent crystallinity in the ethylene-based polymers may be calculated using heat of fusion data, generated in the second heat curve (toe heat of fusion is normally computed automatically by typical commercial DSC equipment, by integration of toe relevant area under the heat curve). The equation for ethylene-based polymers is percent Cryst.=(Hf÷292 J/g)×100; and the equation for propylene-based polymers is: percent Cryst.=(Hf÷165 J/g)×100. The “percent Cryst.” represents the percent crystallinity and “Hf” represents the heat of fusion of the polymer in Joules per gram (J/g).
The acid value (mg KOH/g) of the nonpolar, polyethylene wax in the wax component is measured according to ISO 2114.
The saponification value (mg KOH/g) of the nonpolar, polyethylene wax in the wax component is measured according to ISO 3681.
The viscosity (mPa-s) of the nonpolar, polyethylene wax in the wax component is measured according to DIN53019 at 140° C.
The drop point (° C.) of the nonpolar, polyethylene wax in the wax component is measured according to ASTM D 3954.
Oxygen transmission rate is reported as (cubic centimeters (cc) of oxygen/(m2*day)) and is measured at 23° C., 75% Relative Humidity, 1 atm using a MOCON Ox-Tran Model 2/21 analyzer in accordance with ASTM D 3985-05. The test specimen is held such that it separates two sides of a test chamber. One side is exposed to a nitrogen atmosphere while the other side is exposed to an oxygen atmosphere. A coulometric sensor monitoring the exit port of the nitrogen side measures the amount of oxygen present. Testing is complete when the concentration of oxygen in the nitrogen side atmosphere is constant For a 100% stretched sample, the film is first stretched using an Instron tensile machine by stretching the film at 2 inches/minute until the film length is two times its original length. The stretched film is then held on a metallic frame to avoid film relaxation, the film-on-frame subsequently placed in the chamber to measure the oxygen transmission.
Puncture Resistance is measured in accordance with ASTM 05748-95 using an Instron® testing machine.
Silage Puncture Resistance as measured in accordance with UNE-EN 14932 using an Instron® testing machine as modified according to UNE-EN 14932.
Elmendorf Tear Strength, CD is measured according to ASTM D 1922-09 using an FX3750 Elmendorf Tester from TEXTEST Instruments. Elmendorf Tear Strength, CD measures the tear strength of a plastic film in the cross (or transversal) direction. Elmendorf Tear Strength, CD can be reported in grams (g).
Elmendorf Tear Strength, MD measures the tear strength of a plastic film in the machine direction. Elmendorf Tear Strength, MD can be reported in grams (g) and can be measured according to ASTM D1922.
Both monolayer films and three-layer films were made in Example 1 using small scale blown film lines.
In the three-layer films (table 4), we sec that the film with 10% Licowax 130 in the core layer, which means 6% wax in the total structure, also meets the OTR decrease and the mechanical properties are maintained or improved. In the comparative examples, other PE waxes and paraffin waxes are included but they do not show the desired balance of properties.
Example 2 was carried out using a semi-industrial scale blown extrusion, three-layer line. In this experiment we have used Resin XZ, which is a blend of 90% ELITE AT 6301 and 10% LICOWAX 130. This blend has been melt compounded (total of 2000 kg).
The films are three layer with A/B/C structure, relative thickness of each layer 15%/70%/15% and total thickness of 23 microns. They were fabricated with an ALPINE blown film line, with toe following characteristics in Table 5:
Specific details of processing conditions are given in Table 6:
The composition of each ABC layer and film properties are shown in Table 7 below.
Table 7. Layer composition and properties of films produced in the ALPINE blown film line.
These structures reflect the ones actually used in the industry, including a tackifier additive (poly-isobutylene, PIB), a cling layer that includes ATTANE® SL4100G ultra-low density polyethylene, ethylene/1-octene copolymer, made in the solution process with Ziegler-Natta catalyst, with I2=1.0 dg/min, density=0.912. LDPE 150 is made with the high pressure process in a tubular reactor and has I2=0.25 dg/min and density*0.9210 g/cm3.
E1 example shows a lower oxygen transmission rate, for both the un-stretched and stretched film, while mechanical properties are maintained at good levels.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16382033.5 | Jan 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/013708 | 1/17/2017 | WO | 00 |
