NECK SUPPRESSION FOR LOW-DENSITY POLYETHYLENE (LDPE) BASED TUBULAR POLYMERS FOR EXTRUSION COATING AT MEDIUM AND HIGH LINE SPEED

Abstract

The forms described herein include polymer blends comprising at least 90% by weight of low-density polyethylene (LDPE) polymer; and from 1% to 10% by weight of ethylene acrylate copolymer. The ethylene acrylate copolymer is the polymerized reaction product of: at least 50% by weight of ethylene, based on the total weight of monomers present in the ethylene acrylate copolymer; from 2% to 40% by weight of alkyl acrylate, based on the total weight of monomers present in the ethylene acrylate copolymer; and from 0% to 20% by weight of monocarboxylic acid monomer, based on the total weight of monomers present in the ethylene acrylate copolymer.

Description

NECK SUPPRESSION FOR TUBULAR POLYMERS BASED ON LOW-DENSITY POLYETHYLENE (LDPE) FOR EXTRUSION COATING AT MEDIUM AND HIGH LINE SPEED FIELD OF INVENTION The modalities of the present description generally refer to applications for extrusion coating, where the extrusion coatings include polymer blends that have a low taper value at low to high line speeds. BACKGROUND OF THE INVENTION Extrusion coating is a continuous manufacturing process in which the polymer is melt-processed and extruded through a die to form a thin film that can be coated onto a substrate or used as a co-extrusion adhesive between two substrates. Processability is important for extrusion coating, and there are two critical parameters: taper and stretch. Taper is the contraction of the polymer film between the die exit and the coating substrate (i.e., during the air gap) and is considered a source of material waste. Stretch refers to how quickly the coating line can be run and how thinly the polymer film can be stretched. A good polymer for the Ref. 331C29 Extrusion coating must have low taper (to minimize polymer waste) and high / sufficient stretch (to obtain a thin coating and high yield). Low-density polyethylene (LDPE) polymers are branched polyethylenes with high melt strength. The polymer's high melt strength provides good processability for extrusion coating. Shrinkage and stretch depend on the polymer's properties. For example, LDPE polymers with a higher melt index generally have more shrinkage but greater stretch; LDPE with a lower melt index tends to have less shrinkage and less stretch. For a given piece of equipment, less shrinkage and sufficient / higher stretch are generally preferred. The melt index and melt strength of LDPE polymers can be affected by the reactor used to produce the polymer. Polymerization conditions such as temperature, pressure, and polymer concentrations vary widely in tubular reactor systems, but tend to be more uniform than in autoclave reactor systems. Polymerization conditions in a tubular reactor lead to polymer compositions with a lower molecular weight and / or a higher level of short-chain branching in the low-molecular-weight fraction, making the polymer more processable. Tubular LDPE polymers tend to have greater drawability for faster line speeds and thinner coating thicknesses. In contrast, autoclave processes typically produce polymers with high-molecular-weight fractions.In general, autoclave LDPE has a lower shrinkage value because the polymer is more branched and has a broader molecular weight distribution (MWD). Therefore, autoclave LDPE polymers have more polymer cross-linking to resist shrinkage. Autoclave LDPE tends to have lower shrinkage than tubular LDPE. Generally, tubular LDPE has a lower melt index (MI) (4-5 MI), while autoclave LDPE has a higher melt index (MI) (7-8 MI). Tubular LDPE with a lower melt index generally has a higher shrinkage value and stretches faster than the higher melt index of autoclave LDPE polymers. Polyethylene resins for extrusion coating of paper, cardboard, aluminum, and other materials are typically processed under high-temperature conditions, for example, 270°C to 350°C, and medium- to high-speed extrusion lines (for example, 300 m / min to 800 m / min). These resins can be low-density polyethylene (LDPE) polymers. However, in general, autoclave-cured LDPE polymers tend to have lower taper, while tubular LDPE tends to have more shear thinning and can be processed at faster line speeds and with a thinner coating thickness. BRIEF DESCRIPTION OF THE INVENTION There is a continuing need to create a polymer blend that has low taper and is processable at high extrusion line speeds. The embodiments of this description include polymer blends comprising at least 90 wt% low-density polyethylene (LDPE) polymer and 1 to 10 wt% ethylene acrylate copolymer. The ethylene acrylate copolymer is the polymerized reaction product of: at least 50 wt% ethylene, based on the total weight of monomers present in the ethylene acrylate copolymer; 2 to 40 wt% alkyl acrylate, based on the total weight of monomers present in the ethylene acrylate copolymer; and 0 to 20 wt% monocarboxylic acid monomer, based on the total weight of monomers present in the ethylene acrylate copolymer. The embodiments of this description include coated polymer substrates comprising a polymer substrate; a coating comprising the polymer mixture of this description; and a coextrusion adhesive disposed between the polymer substrate and the coating. DETAILED DESCRIPTION OF THE INVENTION In one or more embodiments of this description, a polymer blend includes at least 90% by weight of low-density polyethylene (LDPE) polymer and from 1% to 10% by weight of ethylene acrylate copolymer. The polymer blend includes at least 90% by weight of low-density polyethylene (LDPE) polymer and ethylene acrylate copolymer in an amount of 1% to 8% by weight, 1% to 5% by weight, or 1% to 3% by weight. In some embodiments of the polymer blend, the LDPE polymer is produced from a tubular reactor. The LDPE polymer can have a density of 0.910 g / cc to 0.930 g / cc. In some embodiments, the LDPE polymer can have a density of 0.910 g / cc to 0.920 g / cc, 0.916 g / cc to 0.930 g / cc, 0.918 g / cc to 0.926 g / cc, or 0.915 g / cc to 0.920 g / cc. In some embodiments of the polymer blend, the LDPE polymer has a melt index (I2) of 2 g / 10 min to 8 g / 10 min as determined according to ASTM D1238 (190 °C, 2.16 kg). In various embodiments, the LDPE polymer has a melt index (I2) of 2 g / 10 min to 7.7 g / 10 min, 2 g / 10 min to 6 g / 10 min, 2 g / 10 min to 5 g / 10 min, or 2 g / 10 min to 4.5 g / 10 min. In one or more polymer blend forms, the LDPE polymer has a molecular weight distribution (MWD). RQRnnn / zznz / B / YiAi = Mw / Mn) from 5 to 11, from 8 to 10.5, or from 8.5 to 11, as determined by a conventional gel permeation chromatography (GPC) method. In one or more embodiments of the polymer blend, the ethylene acrylate copolymer is the polymerized reaction product of: at least 50 wt% ethylene, based on the total weight of the monomers present in the ethylene acrylate copolymer; from 2 wt% to 40 wt% alkyl acrylate, based on the total weight of the monomers present in the ethylene acrylate copolymer; and from 0 wt% to 20 wt% monocarboxylic acid monomer, based on the total weight of the monomers present in the ethylene acrylate copolymer. In various embodiments of the polymer blend, the ethylene acrylate copolymer includes at least 50% by weight of ethylene, based on the total weight of the monomers present in the ethylene acrylate copolymer, and from 10% to 30% by weight of alkyl acrylate, based on the total weight of the monomers present in the ethylene acrylate copolymer. In one or more embodiments, the ethylene acrylate copolymer comprises from 15% to 30% by weight of alkyl acrylate, based on the total monomers present in the ethylene acrylate copolymer. In some embodiments, the ethylene acrylate copolymer includes at least 75% by weight of ethylene and from 12% to 25% by weight of alkyl acrylate, based on the total monomers present in the ethylene acrylate copolymer. In some embodiments of the polymer blend, the alkyl acrylate of the acrylate copolymer may be, by way of example and not limitation, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, or combinations thereof. In various embodiments, the alkyl acrylate is a C2-Cg-alkyl acrylate, that is, an alkyl acrylate having an alkyl group with 1 to 8 carbons. In various forms of the polymer blend, the monocarboxylic acid monomer comprises acrylic acid, methacrylic acid, or combinations thereof. In one or more embodiments of the polymer blend, the ethylene acrylate copolymer has a melt index (I2) of 2 g / 10 min to 12 g / 10 min as determined in accordance with ASTM D1238 (190 °C, 2.16 kg). In some embodiments, the ethylene acrylate copolymer has a melt index (I2) of 4 g / 10 min to 10 g / 10 min. One or more embodiments of this description include a film comprising a mixture of polymers according to any embodiment previously described in this description. In various forms, the film that includes the polymer mixture has a taper value less than or equal to 140 mm, or less than or equal to 120 mm, or less than or equal to 100 mm, at a temperature of 290 °C to 320 °C, with a coating weight of 8 g / m2 to 30 g / m2 or 12 g / m2 to 25 g / m2, and a line speed of 300 m / min to 800 m / min, or 300 m / min to 500 m / min. In one embodiment, the film produced from the polymer blend has a taper value of less than 100 mm when coated onto a substrate with a coating weight of 12 g / m² at a line speed of 500 m / min and a temperature of 320 °C. In another embodiment, the film has a taper value of less than 100 mm when coated onto paper with a coating weight of 24 g / m² at a line speed of 500 m / min and a temperature of 320 °C. In other embodiments, the film has a taper value of less than 100 mm when coated onto paper with a coating weight of 24 g / m² at a line speed of 300 m / min and a temperature of 320 °C. The narrowing value refers to the difference between the die width and the final width of the extruded polymer blend in the manufactured article. The narrowing value is influenced by extrudate swelling and, to a lesser extent, by surface tension effects. It is known that for conventional ethylene polymers, narrowing values ​​tend to increase as the melt index increases, and the melt index increases as the molecular weight decreases. The embodiments of this description include a coated polymer substrate. The coated polymer substrate includes a polymer substrate and a coating on the polymer substrate that includes any mixture of polymers of this description and a coextrusion adhesive disposed between the polymer substrate and the coating. In one or more embodiments of the coated polymer substrate, the polymer substrate includes polyethylene, polypropylene, polyethylene terephthalate, or polyamide. In some embodiments, the polymer substrate is uniaxially or biaxially oriented. The polymer blends described herein can be extruded onto a variety of polymer substrates at medium to high extrusion line speeds (e.g., 300 m / min to 800 m / min). The films produced from these polymer blends exhibit low taper at these speeds, enabling high throughput on the coating line. Polymerizations In some embodiments, the LDPE polymer from the polymer blend is produced in a high-pressure, free-radical-initiated polymerization process. For a high-pressure, free-radical-initiated polymerization process, two basic types of reactors are known. The first type is a stirred autoclave vessel having one or more reaction zones (the autoclave reactor). The second type is a lined tube having one or more reaction zones (the tubular reactor). The pressure in each tubular reactor and autoclave zone of the process is typically from 100 MPa to 400 MPa, more typically from 120 MPa to 360 MPa, and even more typically from 150 MPa to 320 MPa. The polymerization temperature in each tubular reactor zone of the process is typically from 100 °C to 400 °C, more typically from 130 °C to 360 °C, and even more typically from 140 °C to 330 °C. The polymerization temperature in each autoclave reactor zone of the process is typically 150°C to 300°C, more typically 165°C to 290°C, and even more typically 180°C to 280°C. In some embodiments, a tubular reactor having at least three reaction zones can be used to produce the LDPE polymer from the polymer blends of this description. Initiators The process for producing LDPE polymers from the polymer blends described here is a free-radical polymerization process. The type of free-radical initiator to be used in this process is not RQRnnn / zznz / B / YiAi critical, but preferably one of the applied initiators should allow operation at high temperatures in the range of 300 °C to 350 °C. Examples of suitable free radical initiators include organic peroxides, such as peresters, percetals, peroxyketones, percarbonates, and multifunctional cyclic peroxides. These organic peroxy initiators are added to the reactor at 0.005 wt% to 0.2 wt%, depending on the total weight of polymerizable monomers in the reactor. The peroxides are typically injected as dilute solutions in a suitable solvent, for example, a hydrocarbon solvent. Other suitable initiators include azodicarboxylic esters, azodicarboxylic dinitriles and 1,1,2,2-tetramethylethane derivatives, and other components capable of forming free radicals in the desired operating temperature range. In one embodiment, an initiator is added to at least one reaction zone of the polymerization reactor. In a further embodiment, the initiators are added to the reactor or the polymerization process at a peak polymerization temperature of 320 °C to 350 °C. In a further embodiment, the initiator comprises at least one peroxide group incorporated into a ring structure. Examples of suitable initiators for polymerizing polyethylene include, but are not limited to, TRIGONOX 301 (3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane) and TRIGONOX 311 (3,3,5,7,7-pentamethyl-1,2,4-trioxepane), both available from Akzo Nobel, and HMCH-4-AL (3,3,6,6,9,9-hexamethyl-1,2,4,5-tetroxonane), available from United Initiators. Additional initiators are described in International Publications No. WO 02 / 14379 and WO 01 / 68723 and are incorporated by reference in this description. Additives One or more additives can be added to the polymer blend. Suitable additives include stabilizers, fillers such as organic or inorganic particles, including clays, talc, titanium dioxide, zeolites, or powdered metals; organic or inorganic fibers, including carbon fibers, silicon nitride fibers, steel wire or mesh, and nylon or polyester cords; nano-sized particles; clays; tackifiers; and oil extenders, including paraffinic or naphthenic oils. Polymer fabrications The polymer blend described here can be used in a variety of thermoplastic manufacturing processes to produce useful articles, including extrusion coatings and extrusion laminations. DEFINITIONS Unless otherwise stated, implied by the context, or customary in the art, all parts and percentages are by weight, and all testing methods are current as of the date of submission of this description. The terms polymer blend or polymer mixture, as used in this description, mean an intimate physical mixture of two or more polymers without any physical or chemical reaction between the polymers. A blend may be miscible, with no phase separation at the molecular level, or it may be immiscible, exhibiting some degree of phase separation at the molecular level. A blend may include, but does not necessarily include, one or more domain configurations that can be determined from transmission electron spectroscopy, light diffraction, X-ray scattering, and other methods known in the art. Blending may be effected by physically mixing the two or more polymers at a macro or micro level. Examples of physical blending at the macro level include the melt blending of resins or the formation of compounds. An example of physical blending at the micro level includes the simultaneous formation of the two or more polymers within the same reactor. The term polymer refers to a composition prepared by the polymerization of monomers, whether of the same or different types. Polymers include homopolymers prepared with a single type of monomer, with the understanding that minimal amounts of impurities can be incorporated into the polymer structure. The term ethylene-based polymer or ethylene polymer refers to a polymer comprising at least 50% by weight of polymerized ethylene, based on the total weight of the polymer. Ethylene-based polymers and ethylene polymers may be ethylene homopolymers or may include one or more comonomers, provided that ethylene has the largest weight fraction of the polymer among all the monomers in the polymer. TEST METHODS Density: Samples for density measurement are prepared in accordance with ASTM D 1928. Polymer samples are pressed at 190 °C and 30,000 psi for three minutes, and then at 21 °C and 207 MPa for one minute. Measurements are performed within one hour of sample pressing using ASTM D792, Method B. Melting index: The melting index, or I2, (grams / 10 minutes or dg / min) is measured in accordance with ASTM D 1238, condition 190 °C / 2.16 kg. Triple detector gel permeation chromatography (3D-GPC) The chromatographic system includes a PolymerChar GPC-IR high-temperature GPC chromatograph (Valencia, Spain), equipped with an internal IR5 infrared detector (IR5) coupled to a 2-micron laser light scattering (LS) detector RQRnnn / zznz / B / YiAi Precision Detectors (now Agilent Technologies) model 2040. For all light scattering measurements, a 15-degree angle was used. The autosampler oven compartment was set to 160 °C and the column compartment to 150 °C. The columns that can be used include four 30-cm Agilent Mixed A 20-micrometer linear mixed-bed columns. The chromatographic solvent that can be used includes 1,2,4-trichlorobenzene and contains 200 ppm butylated hydroxytoluene (BHT). The solvent source is sprayed with nitrogen. The injection volume that can be used includes 200 microliters (µL), and the flow rate was 1.0 milliliters / minute. The calibration of the GPC column array is performed using at least 20 narrow molecular weight distribution polystyrene standards with molecular weights ranging from 580 to 8,400,000, arranged in six cocktail mixes at least a decade apart, meaning there is an order of magnitude of approximately a factor of 10 between the individual molecular weights. The standards are purchased from Agilent Technologies. The polystyrene standards are prepared at 0.025 grams in 50 milliliters of solvent for molecular weights equal to or greater than 1,000,000, and at 0.05 grams in 50 milliliters of solvent for molecular weights less than 1,000,000. The polystyrene standards are dissolved at 80 RQRnnn / zznz / B / YiAi degrees Celsius, with gentle stirring, for 30 minutes. The peak molecular weights of the polyethylene standard are converted to polyethylene molecular weights by using Equation 1 (as described in Williams and Ward, J. Polym. Sci., Polym. Let., 6, 621 (1968)): ^polyethylene 71 X (Mpolystyrene^ (EC 1) where M is the molecular weight, A has a value of 0.4315 and B is equal to 1.0. A fifth-order polynomial is used to adjust the respective polyethylene-equivalent calibration points. A small adjustment to A (from approximately 0.415 to 0.44) is made to correct for column resolution and band-widening effects to obtain the NIST NBS 1475 standard at 52,000 Mw. The total plate count of the GPC column array is performed using eicosane (prepared at 0.04 g in 50 mL of TCB and dissolved for 20 minutes with gentle stirring). The plate count (Equation 2) and symmetry (Equation 3) are measured in a 200-microliter injection according to the following equations: / \2 Plate count = 5.54 * | (rvpeak maximum----j \ Peak width to -height / (EC 2) where RV is the retention volume in milliliters, peak width is in milliliters, peak maximum is the maximum peak height and height is ½ peak maximum height. Symmetric (Back peak RVeleventh of height-P^Maximum peak) (EC 3) (Maximum peak-Front peak RVeleventh of height) where RV is the retention volume in milliliters, peak width is in milliliters, maximum peak is the maximum peak position, one-tenth of height is 1 / 10 of the maximum peak height, and where back peak refers to the peak tail in subsequent retention volumes compared to the maximum peak, and where front peak refers to the peak front in previous retention volumes compared to the maximum peak. The plate count for the chromatographic system must be greater than 24000 and the symmetry must be between 0.98 and 1.22. The samples were prepared semi-automatically using PolymerChar's Instrument Control software, where the samples were directed by weight to 2 mg / ml, and the solvent (containing 200 ppm of BHT) was added to a septum-capped vial previously sprayed with nitrogen, using PolymerChar's high-temperature autosampler. The samples were dissolved for 2 hours at 160°C with low-speed stirring. The calculations of Mn(GPC), Mw(gpc> and Mz <gpc) se basan en los resultados de GPC mediante el uso del detector interno IR5 (canal de medición) del cromatógrafo PolymerChar GPC-IR de acuerdo con las ecuaciones 4-6, mediante el uso del software PolymerChar GPCOne™, el cromatograma del valor inicial IR sustraído en cada uno de los puntos de recolección de datos (i) espaciados por igual, y el peso molecular equivalente de polietileno obtenido de la curva de calibración estándar estrecha para el punto (i) de la Ecuación 1. Μηορο TUR,i Δ / 1Ι SPO = ---------:------------(EC4) (EC5) AL · GR ? = —:-----------------* \í , , I -*·1pohenleno:(EC6) To monitor deviations over time, a flow rate marker (decane) is introduced into each sample via a micropump controlled by the PolymerChar GPC-IR system. This flow rate marker (FM) is used to linearly correct the pump flow rate (nominal flow rate) for each sample by aligning the RV of the respective decane peak within the sample (RV(FM Sample)) with that of the decane peak within the narrow calibration of the standards (RV(FM Calibrated)). It is then assumed that any change over time in the decane marker peak corresponds to a linear change in flow rate (effective flow rate) throughout the run.To facilitate maximum accuracy in a flow marker peak RV measurement, a least-squares fitting routine is used to fit the flow marker concentration chromatogram peak to a quadratic equation. The first derivative of the quadratic equation is used to determine the true peak position. After calibrating the system against a flow marker peak, the effective flow rate (relative to the tight calibration of the standards) is calculated as Equation 7. Flow marker peak processing was performed using PolymerChar GPCONe™ software. The acceptable flow rate correction is such that the effective flow rate must be within ±2% of the nominal flow rate. Effective flow rate = Nominal flow rate * (RV(FM calibrated) / RV(FM sample)) (EC 7) The systematic approach to determining the displacements of multiple detectors is carried out in a manner consistent with that published by Balke, Mourey et al. (Mourey and Balke, Chromatography Polym. Chapter 12, (1992)) (Balke, Thitiratsakul, Lew, Cheung, Mourey, Chromatography Polym. RQRnnn / zznz / B / YiAi Chapter 13, (1992)), optimizing the triple detector logarithm (MW and IV) results of a wide homopolymer polyethylene standard (Mw / Mn >3) to narrow standard column calibration results from the narrow standards calibration curve using PolymerChar GPCONe™ software. Absolute molecular weight data were obtained in accordance with the publications of Zimm (Zimm, BH, J. Chem. Phys., 16, 1099 (1948)) and Kratochvil (Kratochvil, P., Classical Light Scattering of Polymer Solutions, Elsevier, Oxford, NY (1987)) using PolymerChar GPCOne™ software. The overall injected concentration used in the molecular weight determination was obtained from the mass detector area and the mass detector constant, derived from a suitable linear polyethylene homopolymer or one of the known weight-average molecular weight polyethylene standards. The calculated molecular weights (using GPCOne™) were obtained using a light scattering constant, derived from one or more of the polyethylene standards listed below, and a refractive index concentration coefficient, dn / dc, of 0.104.Generally, the mass detector (IR5) response and light scattering constant (determined using GPCOne™) must be determined from a linear standard with a molecular weight greater than approximately 50,000 g / mol. Viscometer calibration (determined using GPCOne™) can be performed using the methods described by the manufacturer or, alternatively, using published values ​​for suitable linear standards, such as Standard Reference Material (SRM) 1475a (available from the National Institute of Standards and Technology (NIST)). A viscometer constant (obtained using GPCOne™) is calculated that relates the specific viscosity area (DV) and the injected mass of the calibration standard to its intrinsic viscosity. Chromatographic concentrations are assumed to be low enough to eliminate the effects of the second viral coefficient (concentration effects on molecular weight). Other respective moments, Mn <abs) y mz(abs) se calculan de acuerdo con las ecuaciones 8-9 la siguiente manera:^IR;. i I (EC 8) - I -m- = -----------------------(EC9) Extrusion coating: To produce a coated substrate by extrusion, Davis Standard ER-WE-PA, Maschinenfabrik Erkrath, is used. No. 7237, manufactured in 1990, with an EBR (Edge Microsphere Reduction) plane. The Davis Standard ER-WE-PA, Maschinenfabrik Erkrath Nr., has a 1050 mm wide slotted die (maximum substrate width of 800 mm) and is equipped with a feed block co-extrusion system. The extruders have a production capacity of up to 350 kg / h of polymer. The molten polymer exits the die at a temperature of 260-340 °C; the air gap is set to 250 mm and the kerf to -15 mm. These evaluations were conducted using a single-slot feed block and the larger extruder A with a 3.5-inch L / D 32 ET Barr double-span compression screw. This Davis Standard ER-WE-PA line is part of the Pack Studio in Horgen. The molten polymer is coated onto the paper substrate and cooled with the cooling roller at a cooling roller temperature of 15°C. Air space: 250 mm. Cutting offset: -15 mm Extrusion temperature set: 320 °C Substrate: 60 g / m2 kraft paper EXAMPLES Six example compositions were prepared and the polymer characteristics of each were measured. Example 1 was a polymer blend prepared from 97 wt% AGILITY™ EC 7000 manufactured by Dow Inc. as the LDPE component and 3% ELVALOY™ AC 2618 manufactured by Dow Inc. as the acrylate copolymer. Example 2 was a polymer blend prepared from 97 wt% AGILITY™ EC 7000 manufactured by Dow Inc. as the LDPE component and 3% ELVALOY™ AC 3427 manufactured by Dow Inc. as the acrylate copolymer. Example 3 was a polymer blend prepared from 97 wt% AGILITY™ EC 7000 manufactured by Dow Inc. as the LDPE component and 3% ELVALOY™ AC 3717 manufactured by Dow Inc. as the acrylate copolymer. Example 4 was a polymer blend prepared from 97 wt% AGILITY™ EC 7000 manufactured by Dow Inc. as the LDPE component and 3% ELVALOY™ AC 1820 manufactured by Dow Inc. as the acrylate copolymer. Comparative Example C1 was 100% by weight of AGILITY™ EC 7000 manufactured by Dow Inc. as an example of an LDPE produced in a tubular reactor. Comparative Example C2 was 100% by weight LDPE PT 7007 manufactured by Dow Inc. and an example of an LDPE produced in an autoclave reactor. The characteristics of each of the polymer blends and comparator polymers are summarized in Table 1. κοβηηη / ζζηζ / Ε / γίΛΐ Table 1: Polymer characteristics Example Composition MI dg / min Density g / cm3 Monomer* % Example 1 AGILITY EC 7000 3.9 0.919 EE 97 ELVALOYTM AC2618 6 EA 3 Example 2 AGILITY EC 7000 3.9 0.919 EE 97 ELVALOYTM AC 3427 4 BA 3 Example 3 AGILITY EC 7000 3.9 0.919 EE 97 ELVALOYTM AC 3717 7 BA 3 Example 4 AGILITY EC 7000 3.9 0.919 EE 97 ELVALOYTM AC 1820 8 MA 3 Comparative C1 AGILITY EC 7000 3.9 0.919 EE 100 Comparative C2 LDPE PT 7007 7.4 EE * Abbreviations - EE: ethylene; EA: ethyl acrylate; BA: butyl acrylate; MA: methyl acrylate. Each inventive and comparative example was extruded on a 3.5-inch diameter screw, with a length-to-diameter (L / D) ratio of 32, onto 70 g / m² Kraft paper at a coating weight of 25 g / m². Melt pressure and melt temperature were recorded using thermocouples mounted on the adapter. The melt was transferred through a Davis Standard / ErWe-Pa 510A series flexible lip-edge bead reduction die, nominally set to a die gap of 0.7 mm. Melt drawing and vertical melt application onto the moving substrate were performed with a 250 mm air gap and a 15 mm shear offset toward the pressure roll. The melt was applied onto the moving substrate at the laminator groove (the point where the pressure roll and substrate make contact), with a surface rubber layer in contact with the RQRnnn / zznz / B / YiAi The water-cooled cooling roll with a matte surface finish was maintained at a temperature of 15°C to 20°C. The air gap is defined as the vertical distance between the die lip and the rolling mill groove. The cutting offset is defined as the horizontal displacement of the die lip relative to the rolling mill groove. Table 2 summarizes the results of the narrowing determination for Comp. Cl, Comp. C2, and Examples 1 to 4. To determine the narrowing value of the polymer blends, specifically Examples 1 to 4, each polymer blend and the comparative examples were coated onto a substrate, specifically paper, as previously described. The conditions, listed in Table 1, included a line speed of 300 m / min or 500 m / min. The polymer substrates were coated to a coating weight of 12 g / m² or 24 g / m² at a temperature of 320 °C. Table 2 Contraction values ​​in extrusion coating at speeds of 300 m / min and 500 m / min Example Narrowing (mm) 24 g / m2 and 300 m / min 24 g / m2 and 500 m / min 12 g / m2 and 500 m / min Comparison C1 124 118 112 Comparison C2 103 N / A / N / A Example 1 96 99 93 Example 2 96 96 91 Example 3 96 98 90 Example 4 100 98 92 When evaluating the performance of each polymer blend in Examples 1–4 and the polymers in the comparative examples, the desired narrowing value is as small as possible. A suitable narrowing value for extrusion coating is less than or approximately equal to 100 mm. Lower narrowing values ​​indicate greater dimensional stability of the sheet—the polymer after being extruded through the die. When the sheet is more dimensionally stable, the substrate coating can be more precisely controlled, allowing for smooth application of the polymer to the substrate. Comparative C1 was an ethylene polymer produced in a tubular reactor. Comparative C2 was an ethylene polymer produced in an autoclave reactor. Comparative C1 had a narrowing value greater than 100 mm at line speeds of 300 m / min and 500 m / min. C2 had a taper value of 103 mm at an average speed of 300 m / min, but it could not be extruded onto the substrate at 500 m / min. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A polymer mixture characterized in that it comprises: at least 90% by weight of low-density polyethylene (LDPE) polymer; and from 1% to 10% by weight of ethylene acrylate copolymer, wherein the ethylene acrylate copolymer is the polymerized reaction product of: at least 50% by weight of ethylene, depending on the total weight % of the monomers present in the ethylene acrylate copolymer; from 2% to 40% by weight of alkyl acrylate, depending on the weight % of the monomers present in the ethylene acrylate copolymer; and from 0 to 20% by weight of monocarboxylic acid monomer, depending on the total weight % of the monomers present in the ethylene acrylate copolymer.

2. The polymer blend according to claim 1, characterized in that the LDPE has a density of 0.910 g / cc to 0.930 g / cc and a melt index (I2) of 2 g / 10 min to 5 g / 10 min as determined according to RQRnnn / zznz / B / YiAi ASTM D1238 (190 °C, 2.16 kg).

3. The polymer blend according to claim 1, characterized in that the ethylene acrylate copolymer has a melt index (I2) of 4 g / 10 min to 10 g / 10 min as determined according to ASTM D1238 (190 °C, 2.16 kg).

4. The polymer mixture according to claim 1, characterized in that it comprises from 1% to 5% by weight of ethylene acrylate copolymer.

5. The polymer mixture according to claim 1, characterized in that the ethylene acrylate copolymer comprises at least 75% by weight of ethylene, and from 12% to 25% by weight of alkyl acrylate.

6. The polymer mixture according to claim 1, characterized in that the alkyl acrylate comprises methyl acrylate, ethyl acrylate, n-butyl acrylate or isobutyl acrylate, or combinations thereof, and the monocarboxylic acid monomer comprises one or more of acrylic acid, methacrylic acid or combinations thereof.

7. The polymer mixture according to claim 1, characterized in that the LDPE polymer is a tubular polymer.

8. A film characterized in that it comprises the polymer mixture in accordance with any preceding claim RQRnnn / zznz / B / YiAi.

9. The film according to claim 8, characterized in that it has a narrowing of less than 100 mm, when coated onto paper with a coating weight of 12 g / m2 at a line speed of 500 m / min and a temperature of 320 °C.

10. A coated polymer substrate characterized in that it comprises: a polymer substrate; a coating comprising the polymer mixture according to claims 1-6; and a coextrusion adhesive disposed between the polymer substrate and the coating.

11. The coated polymer substrate according to claim 10, characterized in that it comprises polyethylene, polypropylene, polyethylene terephthalate or polyamide.

12. The coated polymer substrate according to claim 10, characterized in that it is uniaxially or biaxially oriented RQRnnn / zznz / B / YiAi.