KR20260028696A - Polymer films with an excellent combination of processability and abuse resistance - Google Patents

Abstract

Embodiments of the present disclosure relate to a film comprising at least 95 wt% of an ethylene-based polymer, wherein the ethylene-based polymer is a polymerized reaction product of ethylene, a _C3 - _C14 α-olefin monomer, and optionally a polyene, wherein the film comprises a normalized dart strength (DS) in g/mol of at least 400 + 1400 / (MS - 2.7), wherein normalized DS is measured as grams divided by the film thickness in mils (g/mil) as measured according to ASTM 1079 Method A, and MS is the melt strength of the ethylene-based polymer in centinewtons (cN) (Rheotens apparatus, 190°C, 2.4 mm/s2, capillary die having 120 mm from die exit to center of wheel, extrusion speed 38.2 s-1, length 30 mm, diameter 2 mm, and angle of incidence 180°), and wherein the MS is at least 4 cN.

Description

Polymer films with an excellent combination of processability and abuse resistance

Cross-reference to related applications

This application claims the benefit of U.S. Provisional Application No. 63/510,763, filed June 28, 2023, which is hereby incorporated by reference in its entirety.

Technology field

The present invention relates generally to ethylene polymer films, and more particularly to ethylene polymer films having processability and dart strength.

Linear low-density polyethylene (LLDPE), manufactured through solution or vapor-phase processes, typically exhibits excellent mechanical properties but poor melt strength and processability when used in film production. Therefore, to improve processability, a certain amount of LDPE is typically blended with LLDPE, improving the processability and melt strength of the LLDPE resin. Unfortunately, even with the addition of LDPE, the mechanical properties of the resulting blend are reduced compared to pure LLDPE resin.

Therefore, there is a need for ethylene polymer films having processability and excellent mechanical properties (e.g., dartability) without blending with LDPE.

The present embodiment achieves these requirements for processability and mechanical strength by including an ethylene-based polymer having at least one polymer fraction with increased long-chain branching. Without being limited by theory, it is believed that this long-chain branching provides increased melt strength necessary for film processing, while the ethylene-based polymer still maintains excellent abuse resistance properties in the film.

According to one or more embodiments, a film is provided comprising at least 95 wt% of an ethylene-based polymer. The ethylene-based polymer is a polymerized reaction product of ethylene, a C ₃ -C ₁₄ α-olefin monomer, and optionally a polyene. The film comprises a normalized dart strength (DS) of at least 400 + 1400 / (MS - 2.7), wherein normalized DS is measured as grams divided by film thickness in mils (g/mil) as measured according to ASTM 1079 Method A, and MS is the melt strength of the ethylene-based polymer in centinewtons (cN) (Rheotens apparatus, 190°C, 2.4 mm/s ² , 120 mm from die exit to center of wheel, extrusion speed 38.2 s ^-1 , capillary die having a length of 30 mm, a diameter of 2 mm, and an angle of incidence of 180°), and wherein the MS is at least 4 cN.

These embodiments are described in more detail in the detailed description below together with the accompanying drawings.

The following detailed description of specific embodiments of the present disclosure may be best understood when read in conjunction with the accompanying drawings, wherein like structures are represented by like reference numerals.
The following detailed description of specific embodiments of the present disclosure may be best understood when read in conjunction with the accompanying drawings, wherein like structures are represented by like reference numerals.
FIG. 1 is a graphical representation of the molecular weight distribution of a multimodal ethylene polymer of the present invention according to one or more embodiments described herein.
FIG. 2 graphically illustrates the relationship between melt strength and normalized dart strength for multimodal ethylene polymers of the present invention according to one or more embodiments described herein.

Hereinafter, specific embodiments of a method for synthesizing a polymer of the present disclosure and a polymer synthesized by such a method will be described. It should be understood that the method for synthesizing a polymer of the present disclosure may be embodied in various forms and should not be construed as limited to the specific embodiments described in this disclosure. Rather, the embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art.

definition

The term "polymer" refers to a polymer compound prepared by polymerizing monomers of the same or different types. Therefore, the general term "polymer" encompasses both the term "homopolymer," which is commonly used to refer to a polymer prepared from only one type of monomer, and "copolymer," which refers to a polymer prepared from two or more different monomers.

"Polyethylene" or "ethylene polymer" shall mean a polymer comprising more than 50 wt% units derived from ethylene monomers. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of polyethylene known in the art include low density polyethylene (LDPE); linear low density polyethylene (LLDPE); ultra low density polyethylene (ULDPE); very low density polyethylene (VLDPE); single site catalyzed linear low density polyethylene, which includes both linear and substantially linear low density resins (m-LLDPE); medium density polyethylene (MDPE); and high density polyethylene (HDPE).

The term “LDPE” may also be referred to as “high-pressure ethylene polymer” or “highly branched polyethylene,” which is defined to mean that such polymer is partially or fully homopolymerized or copolymerized in an autoclave or tubular reactor at pressures greater than 14,500 psi (100 MPa) using a free-radical initiator such as a peroxide (see, e.g., U.S. Pat. No. 4,599,392, which is incorporated herein by reference in its entirety). LDPE resins typically have a density in the range of 0.916 g/cm ³ to 0.930 g/cm ³ .

The term "LLDPE" includes resins prepared using Ziegler-Natta catalyst systems, as well as single-site catalysts including, but not limited to, bis-metallocene catalysts (sometimes referred to as "m-LLDPE"), phosphinimine, and constrained geometry catalysts, and molecular catalysts including, but not limited to, post-metallocene, bis(biphenylphenoxy) catalysts (also referred to as polyvalent aryloxyether catalysts). LLDPE includes linear, substantially linear, or heterogeneous ethylene-based copolymers. LLDPE includes substantially linear ethylene polymers that contain less long chain branching than LDPE and are further defined in U.S. Pat. Nos. 5,272,236, 5,278,272, 5,582,923, and 5,733,155, each of which is incorporated herein by reference in its entirety; homogeneously branched linear ethylene polymer compositions such as those of U.S. Pat. No. 3,645,992, the entirety of which is incorporated herein by reference; heterogeneously branched ethylene polymers such as those made according to the process disclosed in U.S. Pat. No. 4,076,698, the entirety of which is incorporated herein by reference; and blends thereof such as those disclosed in U.S. Pat. No. 3,914,342 and U.S. Pat. No. 5,854,045, the entireties of which are incorporated herein by reference. LLDPE resins can be prepared via gas phase, solution phase, or slurry polymerization, or any combination thereof, using any type of reactor or reactor configuration known in the art.

"Blend,""polymerblend," and similar terms mean a composition of two or more polymers. Such blends may or may not be miscible. Such blends may or may not be phase separated. Such blends may or may not contain one or more domain configurations as determined by transmission electron spectroscopy, light scattering, x-ray scattering, and any other method known in the art. The blend is not a laminate, but one or more layers of a laminate may contain the blend. Such blends may be prepared as dry blends formed in situ (e.g., in a reactor), as melt blends, or using other techniques known to those skilled in the art.

"Multilayer structure" or "multilayer film" means any structure having more than one layer. For example, a multilayer structure (e.g., a film) may have 2, 3, 4, 5, 6, 7, or more layers. A multilayer structure may be described as having layers designated by letters. For example, a three-layer structure designated A/B/C may have a core layer (B), and two outer layers (A) and (C).

As used herein, "multimodal" refers to a polymer prepared from multiple polymer fractions, each produced by a separate catalyst in a separate reaction environment. Multimodal may include a bimodal polymer having two polymer fractions, a trimodal ethylene polymer having three polymer fractions, or a polymer having more than three polymer fractions.

The term "polyene" as used herein refers to a comonomer having at least two double bonds. Polyenes include "dienes" which are comonomers having two double bonds.

The term "gel" or "gelling" refers to a solid composed of at least two components, the first component being a three-dimensional cross-linked polymer and the second component being a medium in which the polymer is not completely dissolved. If the polymer is gelled and not completely dissolved, the reactor may become contaminated with the polymer gel.

The term "long chain branch" refers to a branch having more than 100 carbon atoms. A "branch" refers to a portion of a polymer that extends from a tertiary or quaternary carbon atom. When a branch extends from a tertiary carbon atom, there are two different branches, which collectively can be the polymer strand from which the branch extends. A polymer strand is a linear segment of a polymer, or more specifically, a copolymer, that is optionally connected at its termini by branch junctions. For example, a tetrafunctional branch junction connects the termini of four polymer strands, as opposed to a trifunctional branch junction that connects the termini of three polymer strands.

The terms "comprising," "including," "having," and their derivatives are not intended to exclude the presence of any additional component, step, or procedure, whether or not specifically disclosed. For the avoidance of doubt, all compositions claimed through use of the term "comprising" may include any additional additive, adjuvant, or compound, whether polymeric or otherwise, unless stated otherwise. In contrast, the term "consisting essentially of excludes from the scope of any subsequent recitation any other component, step, or procedure except those not essential to operability. The term "consisting of excludes any component, step, or procedure not specifically described or listed.

ethylene polymer

Embodiments of the present disclosure relate to ethylene-based polymers, and in certain embodiments, trimodal ethylene-based polymers comprising first, second, and third polymer fractions. The first, second, and third polymer fractions each comprise a polymerized reaction product of an ethylene monomer and optionally a C ₃ -C ₁₄ alpha-olefin comonomer, provided that at least one of the first, second, and third polymer fractions comprises a polymerized reaction product of an ethylene monomer, a polyene comonomer, and optionally a C ₃ -C ₁₄ alpha-olefin comonomer.

In one or more embodiments, the polyene can comprise an acyclic non-conjugated diene. The acyclic non-conjugated diene can comprise one or more of 1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, 1,8-nonadiene, 1,9-decadiene, 1,10-undecadiene, 1,11-dodecadiene, dimethyldivinylsilane, dimethyldiallylsilane, and dimethylallylvinylsilane. The polyene may not comprise cyclic or bicyclic polyenes, for example, norbornene compounds, because these cyclic or bicyclic polyenes do not effectively incorporate into polymer chains to form long chain branches.

The C ₃ -C ₁₄ alpha-olefin comonomer may include one or more of 1-propylene, 1-butene, 1-hexene, 1-octene, or a combination thereof.

As mentioned above, the trimodal ethylene polymer of the present invention has excellent processability, which can be quantified in part by its melt strength. As further mentioned above, this processability and melt strength are due to the long chain branching present in the trimodal-ethylene polymer. In one or more embodiments, the trimodal ethylene polymer can have a melt strength (MS) of from 4.0 to 25.0 cN, where MS is the melt strength in cN (Rheotens apparatus, 190°C, 2.4 mm/s ² , 120 mm from die exit to center of wheel, extrusion speed 38.2 s ^-1 , capillary die having a length of 30 mm, a diameter of 2 mm, and an angle of incidence of 180°). In further embodiments, the melt strength (MS) is 4.0 to 20.0 cN, 4.0 to 15.0 cN, 8.0 to 15.0 cN, or 9.0 to 14.0 cN.

Additionally, the trimodal ethylene polymer can have a rheology ratio V _0.1 /V ₁₀₀ of from 4.0 to 12.0, wherein V _0.1 is the viscosity of the trimodal ethylene polymer at an angular frequency of 0.1 radians/second at 190°C, and V ₁₀₀ is the viscosity of the trimodal ethylene polymer at an angular frequency of 100 radians/second at 190°C. In further embodiments, the rheology ratio V _0.1 /V ₁₀₀ is from 4.0 to 8.0, or from 4.0 to 6.5. Without being limited by theory, the rheology ratio indicates shear thinning, and increased long chain branching correlates with increased shear thinning. However, in the present case, shear thinning can be controlled in the trimodal ethylene polymer by, for example, creating one or more fractions in the trimodal ethylene polymer in addition to a small amount of long chain branching.

The trimodal ethylene polymer can have a melt index (I ₂ ) of from 0.5 to 2.0 dg/min, or from 0.5 to 1.0 dg/min, where I ₂ is measured according to ASTM D1238 (2.16 kg/190°C). The trimodal ethylene polymer can have an I ₁₀ /I ₂ ratio of from 5.0 to 15.0, or from 5.0 to 10.0.

In one or more embodiments, the trimodal ethylene polymer has a density of from 0.910 to 0.935 g/cc, from 0.910 to 0.920 g/cc, or from 0.912 to 0.920 g/cc.

In one or more embodiments, the trimodal ethylene polymer has a molecular weight distribution (MWD) from 3 to 5, where MWD is defined as Mw/Mn, where Mw is the weight average molecular weight and Mn is the number average molecular weight, as measured by conventional gel permeation chromatography. Furthermore, the trimodal ethylene polymer has a Mn from 20.0 to 35.0 kg/mol, or from 25.0 to 35.0 kg/mol. Furthermore, the trimodal ethylene polymer has a Mw from 100.0 to 130.0 kg/mol, or from 105.0 to 125.0 kg/mol.

method

Various methods and processing parameters are contemplated as suitable for preparing the multimodal and trimodal ethylene polymers of the present disclosure. In one or more embodiments, a method for preparing a multimodal ethylene polymer (e.g., a trimodal ethylene polymer) in a reactor system comprises a first reactor and a second reactor. The method comprises polymerizing ethylene, one or more (C ₃ -C ₁₄ ) α-olefin monomers, and at least one polyene in the first reactor in the presence of one multi-chain catalyst and at least one single-chain catalyst to produce a first reactor polyethylene product comprising long chain branching. The multi-chain catalyst comprises a plurality of polymerization sites, and the long chain branching occurs by cooperatively linking two polymer chains of the multi-chain catalyst with the polyene during polymerization. In a second reactor, ethylene and one or more (C ₃ -C ₁₄ ) α-olefin monomers are polymerized in the absence of an initial polyene feed and in the presence of at least one single-chain catalyst to produce a second reactor polyethylene product. The trimodal ethylene polymer comprises the first reactor and second reactor polyethylene products.

It is contemplated that the polymerization reaction may comprise solution polymerization, slurry polymerization, or gas phase polymerization. In certain embodiments, the solution polymerization is carried out in a first reactor, a second reactor, or both. The first and second reactors may be in parallel or in series. Such solution polymerization processes include utilizing one or more conventional reactors, such as, for example, a loop reactor, an isothermal reactor, an adiabatic reactor, a fluidized bed gas phase reactor, a stirred tank reactor, or a batch reactor in parallel, series, or any combination thereof.

Exemplary solvents used in solution polymerization processes include, but are not limited to, isoparaffins. For example, such solvents are commercially available from ExxonMobil Chemical Company under the trade name ISOPAR™ E.

As mentioned above, one or more single-chain catalysts may be present in the first reactor and the second reactor. In one embodiment, both the first reactor and the single-chain catalyst may comprise a single single-chain catalyst.

As used herein, a "single-chain catalyst," also referred to as a single-site catalyst, is a polymerization catalyst having a single active polymerization site and/or reactive metal center. A variety of single-chain catalysts are considered suitable. Such catalysts may include single-site molecular catalysts, including but not limited to bis-metallocene catalysts, phosphinimines, constrained geometry catalysts, post-metallocene catalysts, and bis(biphenylphenoxy) catalysts (also referred to as polyvalent aryloxyether catalysts).

In one embodiment, the single-chain catalyst in the first reactor, the second reactor, or both comprises a bis(biphenylphenoxy) catalyst. In some embodiments, the bis(biphenylphenoxy) catalyst has a structure according to the following formula (I):

In formula (I), M is a metal selected from titanium, zirconium or hafnium, and the metal is in a formal oxidation state of +2, +3 or +4. The subscript n of (X) _n is 0, 1 or 2. When the subscript n is 1, X is a monodentate ligand or a bidentate ligand, and when the subscript n is 2, each X is selected from a monodentate ligand. Each Z is independently selected from -O-, -S-, -N(R ^N )-, or -P(R ^P )-, and R ¹ and R ¹⁶ are -H, (C ₁ -C ₄₀ )hydrocarbyl, (C ₁ -C ₄₀ )heterohydrocarbyl, -Si(R ^C ) ₃ , -Ge(R ^C ) ₃ , -P(R ^P ) ₂ , -N(R ^N ) ₂ , -OR ^C , -SR ^C , -NO ₂ , -CN, -CF ₃ , R ^C S(O)-, R ^C S(O) ₂ -, -N=C(R ^C ) ₂ , R ^C C(O)O-, R ^C OC(O)-, R ^C C(O)N(R)-, (R ^C ) ₂ NC(O)-, halogen, a radical having the formula (II), the formula (III) and a radical having the formula (IV) are independently selected from the group consisting of:

In formulae (II), (III), and (IV), R ^31-35 , R ^41-48 , and R ^51-59 are each independently selected from -H, (C ₁ -C ₄₀ )hydrocarbyl, (C ₁ -C ₄₀ )heterohydrocarbyl, -Si(R ^C ) ₃ , -Ge(R ^C ) ₃ , -P(R ^P ) ₂ , -N(R ^N ) ₂ , -OR ^C , -SR ^C , -NO ₂ , -CN, -CF ₃ , R ^C S(O)-, R ^C S(O) ₂ -, (R ^C ) ₂ C=N-, R ^C C(O)O-, R ^C OC(O)-, R ^C C(O)N(R ^N )-, (R ^C ) ₂ NC(O)-, or halogen, provided that R ¹ or R ¹⁶ At least one of them is a radical having the chemical formula (II), a radical having the chemical formula (III), or a radical having the chemical formula (IV).

In one or more embodiments, each X, independently of any other ligand X, can be a monodentate ligand that is halogen, unsubstituted (C ₁ -C ₂₀ )hydrocarbyl, unsubstituted (C ₁ -C ₂₀ )hydrocarbylC(O)O—, or R ^K R ^L N— (wherein R ^K and R ^L are each independently unsubstituted (C ₁ -C ₂₀ )hydrocarbyl).

Additional details and examples of bis(biphenylphenoxy) catalysts are provided in International Publication Nos. WO 2011/146291, WO 2018/183056, WO 2019/190925, and U.S. Pat. No. 7,060,848 B2, which are incorporated herein by reference in their entireties.

In one embodiment, the single-chain catalyst in the first reactor, the second reactor, or both may comprise a phosphinimine catalyst. The phosphinimine precatalyst may have a structure represented by the following formula (V):

In the formula (V), each Q is (C ₁ -C ₅₀ )hydrocarbyl, (C ₁ -C ₅₀ )heterohydrocarbyl, -CH ₂ Si(R ^C ) _3-Q (OR ^C ) _Q , -Si(R ^C ) _3-J (OR ^C ) _J , -OSi(R ^C ) _3-J (OR ^C ) _J , -CH ₂ Ge(R ^C ) _3-J (OR ^C ) _J , -Ge(R ^C ) _3-J (OR ^C ) _J , -P(R ^C ) _2-W (OR ^C ) _W , -P(O)(R ^C ) _2-W (OR ^C ) _W , -N(R ^C ) ₂ , -NH(R ^C ), -N(Si(R ^C ) ₃ ) ₂ , -NR ^C Si(R ^C ) ₃ , -NHSi(R ^C ) ₃ , -OR ^C , -SR ^C , -NO ₂ , -CN, -CF ₃ , -OCF ₃ , -S(O)R ^C , -S(O) ₂ R ^C , -OS(O) ₂ R ^C , -N=C(R ^C ) ₂ , -N=CH(R ^C ), -N=CH ₂ , -N=P(R ^C ) _{3 ,} -OC(O)R ^C , -C(O)OR ^C , -N(R ^C )C(O)R ^C , -N(R ^C )C(O)H, -NHC(O)R ^C , -C(O)N(R ^C ) ₂ , -C(O)NHR ^C , -C(O)NH ₂ , halogen, B(R ^Y ) ₄ , Al(R ^Y ) ₄ , or Ga(R ^Y ) ₄ , or hydrogen A monodentate ligand, wherein each R ^C is independently (C ₁ -C ₃₀ )hydrocarbyl, or (C ₁ -C ₃₀ )heterohydrocarbyl, each J is 0, 1, 2, or 3, and each W is 0, 1, or 2; each R ^Y is —H, (C ₁ -C ₃₀ )hydrocarbyl, or a halogen atom, and two X ligands can be linked to form a metal acyclic ring;

In formula (V), each Y is independently a Lewis base; optionally, Q and Y may be linked to form a ring. Each subscript m is 1 and 2; and each subscript n is 0, 1, and 2. The metal-ligand complex is overall charge-neutral.

In formula (V), M ₂ is titanium, zirconium, or hafnium; R ⁶⁰ , R ⁶¹ , R ⁶² , R ⁶³ , and R ⁶⁴ are independently (C ₁ -C ₅₀ )hydrocarbyl, (C ₁ -C ₅₀ )heterohydrocarbyl, and any one of R ⁶¹ , R ⁶² , R ⁶³ , and R ⁶⁴ is optionally linked to form a ring structure; R ⁶⁵ , R ⁶⁶ , and R ⁶⁷ are independently (C ₁ -C ₂₀ )hydrocarbyl, (C ₁ -C ₂₀ )heterohydrocarbyl, (C ₆ -C ₃₀ )aryl, (C ₅ -C ₃₀ )heteroaryl, and two of R ⁶⁵ , R ⁶⁶ , and R ⁶⁷ are optionally linked to form a ring.

In various embodiments, in formula (V), (A) R ⁶⁰ and R ⁶¹ are joined to form a ring, optionally substituted with one or more R ^S ; (B) R ⁵² and R ⁶³ are joined to form a ring, optionally substituted with one or more R ^S ; or (C) both (A) and (B). Thus, when (A), (B), or (C) occurs, the cyclopentadienyl of formula (V) has a structure selected from the group consisting of:

As described above, the multi-chain catalyst produces a polymer fraction having long-chain branches. The multi-chain catalyst is a metal-ligand catalyst having at least two polymerization sites that promote the propagation of at least two individual polymer chains. Suitable multi-chain catalysts and their mechanisms of action are described in International Publication Nos. WO 2020/069364, WO 2020/205585, and WO 2021195502 A1, which are incorporated herein by reference in their entireties and are briefly summarized herein. At a high level, the long-chain branched fraction is produced through the addition of a polyene, particularly an acyclic, non-conjugated diene, in the presence of a multi-chain catalyst. The polyene is added to the polymer chain in a manner similar to an α-olefin, but leaves a pendant vinyl group, which can be inserted a second time into the polymer chain to produce long-chain branches. As stated above, the multi-chain catalyst has at least two polymer chain sites that grow two individual polymer chains. One alkene of the polyene is incorporated into one polymer chain, and due to the proximity of the propagation sites, the second alkene of the polyene is believed to then rapidly incorporate into the second polymer chain, forming a bridge or rung. This sequential addition of dienes is referred to as "cooperative" addition of polyenes, which is distinguished from catalysts without two proximal chains, in which polyene addition leads to a concentration of vinyl-containing polymer in the later reacting reactor. This cooperative addition of polyenes has been referred to as a "ladder" mechanism. The term "rung" refers to a diene that is incorporated into two individual polymer strands, linking them together. The first and second polymer strands can continue to grow until the polymer is released from the catalyst, the catalyst fails, or another diene is added.

Embodiments of the present disclosure utilize minimal amounts of a multi-chain catalyst and a single-chain catalyst in the first reactor. Without being bound by theory, the single-chain catalyst will polymerize ethylene and optionally an alpha-olefin comonomer, but will not produce significant amounts of long-chain branching with the polyene, particularly because the single-chain catalyst does not produce two polymer chains in close proximity with the polyene incorporated therebetween. Therefore, the single-chain catalyst will produce a polymer fraction substantially free of long-chain branching, and the multi-chain catalyst will produce a long-chain branched polymer fraction in the same reactor without gel formation or reactor fouling. Accordingly, the polyethylene product from the first reactor comprises a first fraction having long-chain branching and a second fraction substantially free of long-chain branching. As used herein, "substantially free of long-chain branching" means less than 0.01 long-chain branches per 1000 carbon atoms (LCB/1000C) as determined by NMR. In the following examples, the first reactor polyethylene product can have a density greater than 0.930 g/cc and a melt index (I ₂ ) greater than 3 dg/min, and therefore the first reactor is referred to as a high-density reactor. In one or more embodiments, the trimodal ethylene polymer comprises from 35 to 55 wt % of the first reactor polyethylene product, which comprises a first fraction and a second fraction.

In one or more embodiments, the first fraction, i.e., the long-chain branched fraction, can comprise about 2 to 10 wt% of the multimodal ethylene polymer (e.g., the trimodal ethylene polymer).

A second reactor, which does not include an initial polyene feed and does not include a multi-chain catalyst, also produces a second reactor polyethylene product that is substantially free of long-chain branching. In this case, the single-chain catalyst in the second reactor will polymerize ethylene and optionally an alpha-olefin comonomer. In one or more embodiments, the trimodal ethylene-based polymer comprises from 45 to 65 wt % of the second reactor polyethylene product, which comprises at least a third polymer fraction. In the examples below, the second reactor polyethylene product can have a density less than 0.910 g/cc, a melt index (I ₂ ) less than 0.8 dg/min, and a MWD less than 3.0, and thus the second reactor is referred to as a low-density reactor. For trimodal ethylene polymers, the combination of a first reactor (high-density reactor) with a first fraction and a second fraction having long chain branching and a second reactor (low-density reactor) with a third fraction polyethylene product provides a molecular weight distribution as shown in FIG. 1.

film

Additional embodiments of the present disclosure relate to films. In some embodiments, the films may comprise a multimodal ethylene polymer or a trimodal ethylene polymer as described above.

In another embodiment, the film can comprise an ethylene-based polymer that is a polymerized reaction product of ethylene, a C ₃ -C ₁₄ α-olefin monomer, and optionally a polyene. In embodiments, such ethylene-based polymer can be multimodal and/or trimodal. In further embodiments, the ethylene-based polymer of the film can comprise a polymerized reaction product of ethylene, a C ₃ -C ₁₄ α-olefin monomer, and a polyene. In certain embodiments, the film can comprise at least 95 wt % ethylene-based polymer, at least 97 wt % ethylene-based polymer, at least 99 wt % ethylene-based polymer, or at least 99.5 wt % ethylene-based polymer. In further embodiments, the film is substantially free of any other polymer components.

For these film embodiments, the film can comprise a normalized dart strength (DS) in units of grams per mil of at least 400 + 1400/(MS - 2.7), where normalized DS is measured in grams (g) as measured in accordance with ASTM 1709 Method A divided by the film thickness in mils, provided that the melt strength (MS) is at least 4 cN. This relationship between normalized dart strength and melt strength is illustrated in FIG. 2. By simultaneously achieving higher normalized dart strength and melt strength, the films of the present invention do not suffer from the degradation in abuse resistance performance that occurs due to the processability tradeoff in LLDPE/LDPE blends. In additional embodiments also illustrated in FIG. 2, the normalized DS in g/mil is greater than or equal to 430 + 2000/(MS - 2.4), greater than or equal to 400 + 2736/(MS - 2.2), or greater than or equal to 390 + 3900/(MS - 2.5). Additionally, the normalized DS of the film can be from 750 to 1750 g/mil, or from 750 to 1500 g/mil.

The film may comprise a single-layer film or a multi-layer film. The films of the present disclosure may have various thicknesses. The thickness of the film may depend on a number of factors, including, for example, the number of layers of the film, the composition of the layers of a multilayer film, the desired properties of the film, the desired end-use application of the film, the manufacturing process of the film, and the like. In embodiments, the film may have a thickness of 0.5 to 5 mils, 1 to 4 mils, or 1.5 to 2.5 mils.

Various methodologies for manufacturing the films of the present disclosure are contemplated. In one or more embodiments, the process for manufacturing the films may include cast film extrusion or blown film extrusion.

additives

It should be understood that the multimodal ethylene polymer, trimodal ethylene polymer, or films made therefrom described above may further comprise one or more additives known to those skilled in the art, such as, for example, plasticizers, stabilizers such as viscosity stabilizers, hydrolysis stabilizers, primary and secondary antioxidants, ultraviolet absorbers, antistatic agents, dyes, pigments or other colorants, inorganic fillers, flame retardants, lubricants, reinforcing agents such as glass fibers and flakes, synthetic (e.g., aramid) fibers or pulp, foams or blowing agents, processing aids, slip additives, antiblocking agents such as silica or talc, release agents, tackifying resins, or combinations of two or more thereof. Inorganic fillers such as calcium carbonate may also be incorporated into the film.

article

Embodiments of the present disclosure also relate to articles, such as packaging materials, formed from films of the present disclosure. The films of the present disclosure are particularly useful for articles requiring excellent tear strength and dart strength. Examples of such items may include flexible packages, pouches, stand-up pouches, and pre-fabricated packaging or pouches. Various methods for making embodiments of articles from the films disclosed herein will be familiar to those skilled in the art.

Test method

The test method includes:

Melting index

Melt indices I ₂ and I ₁₀ of polymer samples were measured according to ASTM D-1238 (Method B) at 190°C with loads of 2.16 kg and 10 kg, respectively.

density

Samples for density measurements were prepared according to ASTM D4703. Measurements were performed within 1 hour of sample pressurization according to ASTM D792, Method B.

ASTM D1709 Dart Drop

The film dart drop test measures the energy required to cause failure of a plastic film under specific impact conditions caused by a freely falling dart. The test result is expressed as the energy relative to the weight of the missile dropped from a specified height that causes 50% failure of the tested specimen.

After the film was produced, it was conditioned for at least 40 hours at 23°C (+/- 2°C) and 50% R.H. (+/- 5) according to ASTM standards. Standard test conditions are 23°C (+/- 2°C) and 50% R.H. (+/- 5) according to ASTM standards.

Test results are recorded by Method A, using a 1.5" diameter dart head and a 26" drop height. The sample thickness is measured at the center of the sample, and the sample is then clamped in an annular specimen holder with an inside diameter of 5 inches. The dart is loaded over the center of the sample and released by a pneumatic or electromagnetic mechanism.

The test is conducted using the "staircase" method. If a sample fails, a new sample is tested with a dart weight reduced by a known fixed amount. If the sample does not fail, a new sample is tested with a dart weight increased by a known amount. After testing 20 specimens, the number of failures is determined. If this number is 10, the test is complete. If the number is less than 10, the test continues until 10 failures are recorded. If the number is greater than 10, the test continues until the total number of non-failures reaches 10. The dart drop strength is determined from these data according to ASTM D1709 and is expressed in grams as a Type A dart drop impact. All samples analyzed were 2 mil thick.

Instrumented dart impact

The instrumented dart impact test is performed on plastic film specimens using an Instron CEAST 9350 impact tester, according to ASTM D7192. Testing is performed using a 12.7 mm diameter tup with a hemispherical head and a 75 mm diameter clamping assembly with rubber-surface grips. The machine is equipped with an environmental chamber for testing at low or high temperatures. The typical specimen size is 125 mm x 125 mm. The standard test speed is 200 m/min.

Gel Permeation Chromatography Size Exclusion Chromatography (SEC) (conventional GPC)

GPC-SEC (conventional GPC) measurements were performed according to the test procedure defined in International Publication No. WO 2021195502 A1.

Triple Detector GPC (TD) (Absolute GPC)

GPC-TD (absolute GPC) measurements were performed according to the test procedure defined in International Publication No. WO 2021195502 A1.

MD tear

MD tearing was measured according to ASTM D-1922. The force in grams required to propagate a tear across a film specimen was measured using an Elmendorf tear tester. Under the influence of gravity, a pendulum swings in an arc, tearing the specimen through a pre-cut slit. The tear propagates transversely. The sample is conditioned at a specified temperature for at least 40 hours prior to testing.

Dynamic rheology analysis

To characterize the rheological behavior of substantially linear ethylene polymers, S. Lai and G. W. Knight introduced the Dow Rheology Index (DRI), a new rheological measure representing the "normalized relaxation time as a result of long chain branching" of the polymer (ANTEC '93 Proceedings, Insite (TM) Technology Polyolefins (ITP)-New Rules in the Structure/Rheology Relationship of Ethylene α-Olefin Copolymers, New Orleans, La., May 1993). S. Lai et al. (ANTEC '94, Dow Rheology Index (DRI) for Insite(TM) Technology Polyolefins (ITP): Unique structure-Processing Relationship, pp. 1814-1815) defined DRI as the extent to which the rheology of ethylene-octene copolymers known as ITPs (Dow's Insite Technology Polyolefins) incorporating long chain branches into the polymer backbone deviates from the rheology of conventional linear homogeneous polyolefins reported to have no long chain branches (LCB):

DRI ₌ [ _3650000

τ ₀ is the characteristic relaxation time of the material and is the zero shear rate complex viscosity of the material. The DRI is calculated by a least squares fit of the rheology curve (dynamic complex viscosity η*(ω) versus the applied frequency (ω), e.g., 0.01 to 100 radians/sec) as described in U.S. Patent No. 6,114,486 according to the following generalized intersection equation:

η* (ω) = η ₀ /[1+(ω·τ ₀ ) ⁿ ] (Equation 2)

n is the power law exponent of the material, and η*(ω) and ω are the measured complex viscosity and applied frequency data, respectively.

Dynamic rheology measurements are performed according to ASTM D4440 on a dynamic rheometer (e.g., an ARES rheometer from TA Instruments) with 25 mm diameter parallel plates in dynamic mode under an inert atmosphere. For all experiments, the rheometer was thermally stabilized at 190°C for at least 30 minutes before inserting a compression-molded sample, adequately stabilized (with antioxidant additives), into the parallel plates. The plates were then closed with a positive normal force registered by the meter to ensure good contact. After approximately 5 minutes at 190°C, the plates were gently compressed, and excess polymer around the plate circumference was trimmed. An additional 10 minutes were allowed for thermal stability and for the normal force to decrease back to zero. In other words, all measurements were performed after the sample had equilibrated at 190°C for approximately 15 minutes and under a full nitrogen blanket.

To determine the linear viscoelastic strain that produces a torque signal greater than 10% of the subscale of the transducer over the entire frequency range (e.g., 0.01 to 100 radians/s), two strain sweep (SS) experiments are initially performed at 190°C. The first SS experiment is performed at a low applied frequency of 0.1 radians/s. This test is used to determine the torque sensitivity at low frequencies. The second SS experiment is performed at a high applied frequency of 100 radians/s. This is to ensure that the selected applied strain is well within the linear viscoelastic region of the polymer, so that the oscillatory rheology measurements do not induce structural changes in the polymer during the test. Additionally, time sweep (TS) experiments are performed at a low applied frequency of 0.1 radians/s at the selected strain (as determined by the SS experiment) to verify the stability of the sample during the test.

The values of the storage (or elastic) modulus, loss (or viscous) modulus (G"), complex modulus (G*), complex viscosity (η*) and tan δ (the ratio of the loss modulus and the storage modulus, G'VG') were obtained as a function of frequency (ω) at a given temperature (e.g., 190°C).

ASTM D1922 MD (Machine Direction) and CD (Cross Direction) Elmendorf Tear Type B

The Elmendorf tear test uses an Elmendorf type tear tester to determine the average force required to propagate a tear through a specified length of plastic film or non-rigid sheet after tearing has been initiated.

After producing films from the samples to be tested, the films were conditioned at 23°C (+/- 2°C) and 50% R.H. (+/- 5) for at least 40 hours according to ASTM standards. Standard test conditions were 23°C (+/- 2°C) and 50% R.H. (+/- 5) according to ASTM standards.

Using a precisely calibrated pendulum device, the force (in grams) required to propagate a tear across a film or sheet specimen was measured. In the test, a gravity-driven pendulum rotated through an arc, tearing the specimen through a pre-cut slit. The specimen was held by the pendulum on one side and by a clamping member on the other. The energy loss from the pendulum was displayed by a pointer or electronic scale. The scale reading was a function of the force required to tear the specimen.

The sample specimen geometry used in the Elmendorf tear test was a "constant radius geometry" as specified in ASTM D1922. The test is typically performed on specimens cut in both the MD and CD directions of the film. Prior to testing, the film specimen thickness was measured at the center of the sample. A total of 15 specimens were tested per film direction, and the average tear strength and average thickness were reported. The average tear strength was normalized to the average thickness.

Example

The following examples illustrate the features of the present disclosure and are not intended to limit the scope of the present disclosure. The following experiments analyzed the performance of embodiments of the multilayer films described herein.

polymer synthesis

Trimodal ethylene polymers 1 to 11 of the present invention prepared by a dual reactor having a multi-chain catalyst and two single-chain catalysts inside were prepared by the methods described below. Comparative Example C1 was a bimodal ethylene polymer prepared in a dual reactor system having a single-chain catalyst in each reactor but no multi-chain catalyst. Comparative Example C2 was a bimodal ethylene polymer prepared in a single reactor system having a single-chain catalyst and a multi-chain catalyst. Comparative Example C3 was a unimodal ethylene polymer prepared in a single reactor system having a single-chain catalyst.

All raw materials (monomers and comonomers) and process solvents (narrow boiling range, high purity isoparaffin solvent ISOPAR-E) were purified with molecular sieves before introduction into the reaction environment. Hydrogen was supplied under pressure as a high purity grade and was not further purified. The reactor monomer feed stream was pressurized above the reaction pressure via a mechanical compressor. The solvent and comonomer feeds were pressurized above the reaction pressure via pumps. The individual catalyst components were manually diluted batchwise with purified solvent and pressurized above the reaction pressure. All reaction feed streams were measured by mass flow meters and independently controlled using a computer-automated valve control system.

Two reactor systems were used in a parallel configuration. Each continuous solution polymerization reactor consisted of a liquid-filled, non-adiabatic, isothermal, heat-removed continuous stirred tank reactor (CSTR). Independent control of all fresh solvent, monomer, comonomer, diene, hydrogen, and catalyst components was possible. All fresh feed streams (solvent, monomer, comonomer, diene, and hydrogen) to each reactor were temperature-controlled to maintain a single solution phase by passing the feed stream through a heat exchanger. The catalyst components were directly injected into the polymerization reactors. The primary catalyst component feed was computer-controlled to maintain each reactor monomer conversion at a specified target. The cocatalyst component was fed based on a calculated specific molar ratio to the primary catalyst component. The reactor feeds are listed in Tables 1A and 1B. Immediately following the reactor feed injection location, the feed stream was mixed with the circulating polymerization reactor contents using a static mixing element. The reactor had an oil jacket which served to maintain an isothermal reaction environment at a specified temperature.

In a dual parallel reactor configuration, the effluent from each polymerization reactor (containing solvent, monomer, comonomer, hydrogen, catalyst components, and polymer) was discharged to the appropriate reactor and blended. The contents were inertized by addition of isopropanol. At this same reactor outlet location, another additive was added for polymer stabilization (a conventional antioxidant suitable for stabilization during extrusion and film production).

After catalyst deactivation and additive addition, the reactor effluent was introduced into a devolatilization system, where the polymer was removed from the non-polymer stream. The isolated polymer melt was pelletized and collected. While recirculation is not performed in this process, it can generally be achieved.

[Table 1A]

[Table 1B]

Cocatalyst A (CoCat A) is bis(hydrogenated tallow alkyl)methylammonium tetrakis(pentafluorophenyl)borate.

Cocatalyst B (CoCat B) is MMAO-3A or modified methyl aluminoxane

The structures for CAT A, CAT B, and CAT C described in Tables 1A and 1B are provided in Table 2 as follows.

[Table 2]

Film processing

Films were processed using Examples 1 to 11 of the present invention, Comparative Example C1 , and commercial resins and blends C4 to C7 .

C4 comprised 80 wt% C1 and 20 wt% AGILITY™ 1021. AGILITY™ 1021, commercially available from Dow Inc., Midland, Michigan, is an LDPE resin having a density of 0.919 g/cc and a melt index (I ₂ ) of 1.9 dg/min.

C5 comprised 100 wt% of a comparative bimodal polyethylene resin having a density of 0.918 g/cc and a melt index (I ₂ ) of 0.85 dg/min. The comparative bimodal polyethylene resin was prepared according to the methodology of Example 1 of International Publication No. WO 2015200742, which is incorporated herein by reference.

C6 contained 90 wt% C5 and 10 wt% AGILITY™ 1021.

C7 contained 80 wt% C5 and 20 wt% AGILITY™ 1021.

Specifically, 2 mil blown films were produced using a single-layer Dr. Collin blown film line. The line included a 30:1 L/D single-screw extruder with a grooved feed zone and a 30 mm screw diameter. The annular die had a 60 mm diameter and used a dual-lip air ring cooling system. The die lip gap was 2 mm and the blow-up ratio (BUR) was 2.0. The lay flat width was approximately 48 cm. The frost line height was 5 to 6 inches. The total output rate was 5 to 8 kg/hr. The melt temperature was 200 to 220°C, and the die temperature was set at 225°C.

Film and polymer data

[Table 3A]

[Table 3B]

[Table 3C]

As shown in Tables 3A-3C, Samples 1-11 of the present invention had melt strengths ranging from 4.7 to 13.3 cN and normalized dart A values ranging from 760 to 1373 g/mil. These normalized dart A values are significantly higher than those of C5 single resin films as well as blends of C4 , C6 , and C7 with LDPE to enhance melt strength. This demonstrates that while LDPE increases melt strength and processability, there is a trade-off in that it significantly reduces abuse resistance, i.e., normalized dart A.

Also, as shown in Comparative Example C1 , which does not contain a multi-chain catalyst or diene, the melt strength was lower (3.2 cN) due to the lack of long chain branching. Furthermore, the first reactor bimodal polymer (Comparative Example C2 ) cannot achieve the melt strength of the polymer of the present invention (2.2 cN) due to its high melt index (I ₂ of 29.5 dg/min), although long chain branching is present. Finally, the unimodal Comparative Example C3 is essentially free of long chain branching and has a melt strength of 4.5 cN, but this is achieved by having a very low melt index (I ₂ ) of 0.26 dg/min.

While the subject matter of this disclosure has been described in detail and with reference to specific embodiments, it should be noted that the various details disclosed in this disclosure should not be construed as implying that such details relate to elements that are essential components of the various embodiments described in this disclosure. Furthermore, it will be apparent that modifications and variations are possible without departing from the scope of this disclosure, which includes, but is not limited to, the embodiments defined in the appended claims.

Claims (16)

A film comprising at least 95 wt% of an ethylene polymer,
Ethylene polymers are polymerized reaction products of ethylene, C ₃ -C ₁₄ α-olefin monomers, and optionally polyenes,
The film comprises a normalized dart strength (DS) in g/mil of at least 400 + 1400 / (MS - 2.7), wherein normalized DS is the dart strength measured in grams (g) divided by the film thickness in mils as measured according to ASTM 1079 Method A, and MS is the melt strength of the ethylene polymer in centinewtons (cN) (Rheotens apparatus, 190°C, 2.4 mm/s ² , 120 mm from die exit to center of wheel, extrusion speed 38.2 s ^-1 , capillary die having a length of 30 mm, a diameter of 2 mm and an angle of incidence of 180°), and wherein the MS is at least 4 cN. A film according to claim 1, which substantially does not contain any other polymer component. A film according to claim 1 or 2, wherein the film is a single-layer or multi-layer film. A film according to any one of claims 1 to 3, wherein the ethylene polymer is a polymerized reaction product of ethylene, a C ₃ -C ₁₂ α-olefin monomer, and optionally a polyene. A film according to any one of claims 1 to 4, wherein the ethylene polymer has a rheology ratio V _0.1 /V ₁₀₀ of 4.0 to 12, wherein V _0.1 is a viscosity of the ethylene polymer at an angular frequency of 0.1 radian/second at 190°C, and V ₁₀₀ is a viscosity of the ethylene polymer at an angular frequency of 100 radian/second at 190°C. A film in claim 5, wherein the rheology ratio V _0.1 /V ₁₀₀ is 4.0 to 8.0. A film according to any one of claims 1 to 6, wherein the ethylene polymer has an I ₂ of 0.5 to 2.0 dg/min as measured according to ASTM D1238 (2.16 Kg/190°C). A film according to any one of claims 1 to 7, wherein the ethylene polymer has a density of 0.910 to 0.935 g/cc. A film according to any one of claims 1 to 8, wherein the ethylene polymer is a multimodal polymer. A film according to any one of claims 1 to 9, wherein the ethylene polymer has an MWD of 3.0 to 5.0, wherein MWD is defined as M _w /M _n , where M _w is the weight average molecular weight and M _n is the number average molecular weight, as measured by conventional gel permeation chromatography. A film according to any one of claims 1 to 10, wherein the melt strength (MS) is 4.0 to 25 cN, or 8.0 to 15 cN. A film according to any one of claims 1 to 11, wherein the normalized DS of the film is 750 to 1750 g/mil. A film according to any one of claims 1 to 12, wherein the normalized DS in g/mil is 430 + 2000 / (MS - 2.4) or more. A film according to any one of claims 1 to 13, wherein the normalized DS in g/mil is 400 + 2736 / (MS - 2.2) or more. A film according to any one of claims 1 to 14, wherein the normalized DS in g/mil is 390 + 3900 / (MS - 2.5) or more. A film according to any one of claims 1 to 15, wherein the film has an average thickness of 1.0 to 3.0 mil.