Microporous membrane with enhanced wettability of electrolyte

Abstract

A polymer composition for producing gel extrusion articles is described. The polymer composition contains polyethylene particles combined with a plasticizer and one or more surface tension-reducing technologies. In one aspect, the surface tension-reducing technology includes adding fillers or chemical components to the polyethylene polymer to increase wetting. Alternatively, the surface tension-reducing technology may be a surface treatment, such as a plasma treatment. Polymer articles made according to the present disclosure can have dramatically improved wetting properties. In one embodiment, the polymer composition is used to form porous membranes for use as separators in electronic devices.

Description

Background Art

[0001]

[0001] Polyethylene polymers have numerous and diverse uses and applications. For example, high-density polyethylene is a useful engineering plastic having a unique combination of abrasion resistance, surface lubricity, chemical resistance, and impact strength. They find use in the manufacture of high-strength fibers for use in ropes and bulletproof molded articles, as well as in the manufacture of other elongated articles such as films for electronic devices. However, since the fluidity of these materials in the molten state decreases as the molecular weight increases, processing by conventional techniques, such as melt extrusion, is not always possible.

[0002]

[0002] One alternative method of manufacturing fibers and other elongated fabricated articles from polyethylene polymers is by gel processing in which the polymer is combined with a solvent. The resulting gel can be extruded into fibers or films and stretched in one or two directions. After the article is formed, all of the solvent can be removed from the product.

[0003]

[0003] Films made from polyethylene polymers through gel processing can be formed to have many beneficial properties. As an example, the film can be formed with micropores. Microporous polyethylene films formed through gel processing are particularly suitable, for example, for use as separators in batteries, such as lithium-ion batteries. The microporous film can, for example, separate the cathode from the anode to prevent a short circuit between the active battery components. At the same time, the microporous film allows ions to pass through due to the porous nature of the material. The ion-permeable property of the microporous polyethylene film makes the material particularly suitable for controlling the electrochemical reactions within the battery.

Summary of the Invention

Problems to be Solved by the Invention

[0004] In view of the above, one of the important properties of a lithium-ion battery membrane is the compatibility between the membrane and the electrolyte. In this regard, the present disclosure is directed to an improved method for increasing the wetting properties of membranes that can be incorporated into lithium-ion batteries. The present disclosure is also directed to polymeric articles, particularly membranes, having improved wetting properties.

Means for Solving the Problems

[0005]

[0005] Generally, the present disclosure is directed to polyolefin compositions suitable for gel treatment applications. More particularly, the present disclosure is directed to polymeric compositions containing high-density polyethylene polymers suitable for manufacturing microporous ion-permeable membranes that can be used as separators in batteries. According to the present disclosure, the polymeric composition is formulated to have improved wetting properties, particularly with respect to the electrolytes found in lithium-ion batteries. The improved wetting properties increase the mobility of the ions contained within the lithium-ion battery, which increases the efficiency and lifespan of the battery.

[0006]

[0006] In one embodiment, the present disclosure is directed to a polymeric composition for manufacturing gel extruded articles. The polymeric composition includes a plasticizer, high-density polyethylene particles, and a surface tension reducing additive that increases the wettability of the polymeric composition and the articles made from the composition. The surface tension reducing additive can include a hydrophilic inorganic filler or hydrophilic organic polymer particles. The surface tension reducing additive can be incorporated into the polymeric composition (including the high-density polyethylene particles and the plasticizer) in an amount of about 0.1 wt% to about 40 wt%, such as in an amount of about 5 wt% to about 35 wt%, such as in an amount of about 10 wt% to about 30 wt%.

[0007]

[0007] In one aspect, the surface tension reducing additive may be a fatty alcohol glycol ether, an ethylene vinyl alcohol copolymer, an ethylene glycidyl methacrylate copolymer, an ethylene acrylic acid copolymer, a graft copolymer of polyethylene and maleic anhydride, or a mixture thereof. Instead of or in addition to the above additives, the surface tension reducing additive may also include aluminum oxide particles or aluminum hydroxide particles.

[0008]

[0008] Generally, one or more surface tension reducing additives are incorporated in the polymer composition in an amount sufficient to reduce the contact angle measured with respect to water in the polymer composition by more than about 5%, such as more than about 8%, such as more than about 10%, such as more than about 12%, such as more than about 15%. For example, the polymer composition of the present disclosure may exhibit a contact angle of less than about 102°, such as less than about 98°, such as less than about 95° when measured with respect to water.

[0009]

[0009] In a particular aspect, the surface tension reducing additive includes a graft copolymer of polyethylene and maleic anhydride. The polyethylene grafted with maleic anhydride may be linear low density polyethylene or high density polyethylene. For example, the polyethylene can have a molecular weight of more than about 300,000 g / mol, such as more than about 500,000 g / mol, such as more than about 700,000 g / mol. Maleic anhydride can be incorporated into the copolymer in an amount of more than about 1.5 wt% and generally less than about 5 wt%. In one embodiment, the polymer composition contains a graft copolymer of polyethylene and maleic anhydride in an amount of about 15 wt% to about 30 wt%.

[0010]

[0010] In one embodiment, the surface tension reducing additive may be a hydrophilic agent that couples to the polyethylene resin during the production of the resin or during the melt processing of the film. Examples of hydrophilic chemical agents include functional chemical groups that either increase the polarity of the polyethylene polymer or undergo a chemical reaction with other polar molecules that increase the wettability of the resulting film. Examples of hydrophilic chemical agents include maleic anhydride, glycidyl methacrylate, or acrylic acid.

[0011]

[0011] In yet another embodiment, the wettability of the film can be increased through post-treatment of the surface of the film. For example, the film may be plasma treated, subjected to a corona discharge, electron beam treated, gamma ray treated, ultraviolet treated, and / or steam treated. In one embodiment, one or more surface tension reducing agents can be used in combination with the surface treatment.

[0012]

[0012] The high density polyethylene particles used to manufacture the film can, in one embodiment, have a volume average particle size of less than about 150 microns, such as less than about 125 microns, and generally greater than about 50 microns.

[0013]

[0013] Generally, the polymer composition contains high-density polyethylene resin in an amount up to about 50% by weight. The plasticizer can be present in the composition, for example, in an amount greater than about 50% by weight, such as greater than about 60% by weight, such as greater than about 70% by weight, such as greater than about 80% by weight, such as less than about 90% by weight. A variety of different materials can be used as the plasticizer. By way of example, the plasticizer can include mineral oil, paraffinic oil, hydrocarbon oil, alcohol, etc. By way of example, the plasticizer can include decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, or mixtures thereof. In one embodiment, the plasticizer can include C5 - C12 hydrocarbons, such as C5 - C12 saturated hydrocarbons. For example, the plasticizer can include heptane, hexane, paraffin, etc.

[0014]

[0014] In one embodiment, the high-density polyethylene used to produce the particles can have a relatively high molecular weight. The use of high molecular weight polyethylene particles can be beneficial, especially in applications where greater strength properties are required or desired. For example, the polyethylene used to produce the particles can have a molecular weight greater than about 500,000 g / mol, such as greater than about 650,000 g / mol, such as greater than about 1,000,000 g / mol, such as greater than about 1,500,000 g / mol, and can have a molecular weight less than about 4,000,000 g / mol, such as less than about 3,500,000 g / mol. In one embodiment, the polyethylene used to produce the particles includes Ziegler-Natta catalyst high molecular weight polyethylene. In one embodiment, the composition contains only a single polyethylene polymer.

[0015]

[0015] The present disclosure also encompasses polymer articles formed from the above polymer composition. The polymer articles can be manufactured through a gel extrusion method or a gel spinning method. Examples of polymer articles produced in accordance with the present disclosure include fibers, films, such as membranes, etc.

[0016]

[0016] During the formation of the polymeric article, a substantial portion of the plasticizer is removed. For example, in one embodiment, more than 95 wt%, such as more than about 98 wt%, of the plasticizer is removed during the formation of the polymeric article. As a result, polymeric articles made in accordance with the present disclosure generally contain high density polyethylene combined with one or more surface tension reducing additives. For example, the resulting polymeric article can contain high density polyethylene polymer in an amount of from about 60 wt% to about 99.5 wt%, such as in an amount of from about 65 wt% to about 97 wt%. One or more surface tension reducing additives can comprise the balance of the polymeric article. When the surface tension reducing additive comprises a hydrophilic chemical agent that couples to the polyethylene polymer during melt processing, the surface tension reducing agent can generally be present in the final film in an amount of from about 0.01 wt% to about 20 wt%, such as in an amount of from about 0.1 wt% to about 10 wt%.

[0017]

[0017] When the surface tension reducing additive comprises particles combined with the polyethylene polymer, one or more surface tension reducing additives can be present in the polymeric article in an amount of more than about 1 wt%, such as more than about 3 wt%, such as more than about 6 wt%, such as more than about 7 wt%, and generally in an amount of less than about 30 wt%, such as in an amount of less than about 20 wt%. The polymeric article can also contain a variety of other additives in addition to the high density polyethylene and the surface tension reducing additive.

[0018]

[0018] The present disclosure also relates to a method of manufacturing a polymeric article. The method includes the step of forming a gel-like composition from the polymeric composition described above. The gel-like composition is then extruded through a die to form the polymeric article. The polymeric article can include, by way of example, fibers, continuous films, or discontinuous films, such as porous membranes.

[0019]

[0019] In one embodiment, an extraction solvent, such as dichloromethane, is combined with the polymer composition before or during the formation of the polymer article. The extraction solvent can be used to facilitate the removal of the plasticizer.

[0020]

[0020] The porous membrane produced according to the present disclosure can have a blend with excellent physical properties. The porous membrane can, for example, have excellent tensile strength and be puncture resistant.

[0021]

[0021] The present disclosure can be better understood by referring to the following drawings.

Brief Description of the Drawings

[0022] [Figure 1]

[0022] A cross-sectional view of an electronic device, such as a battery, incorporating the porous membrane produced according to the present disclosure.

[0023]

[0023] The repeated use of reference characters in this specification and in the drawings is intended to represent the same or similar features or elements of the present invention.

[0024] Definition

[0024] The melt flow rate of the polymer or polymer composition is measured at 190 °C under a load of 21.6 kg in accordance with ISO Test 1133.

[0025]

[0025] The density of the polymer is measured in units of g / cm 3 in accordance with ISO Test 1183.

[0026] The average particle size (d50) is measured using laser diffraction / light scattering, for example, a suitable HORIBA light scattering device.

[0026]

[0027] The average molecular weight of the polymer is determined using the Margolies’ equation.

[0028] The tensile modulus, yield point tensile stress, yield point tensile strain, 50% breaking point tensile stress, breaking point tensile stress, and breaking point tensile nominal strain are all measured in accordance with ISO Test527-2 / 1B.

[0027]

[0029] The half-width of the melting endothermic peak of the sample is measured by a differential scanning calorimeter (DSC). An electronic balance is used to measure 8.4 g of the sample. The sample is placed in an aluminum sample pan. An aluminum cover is attached to the pan, and this is placed in the differential scanning calorimeter. The sample and the reference sample are held at 40 °C for 1 minute while nitrogen purging is carried out at a flow rate of 20 mL / min, then heated from 40 °C to 180 °C at a heating rate of 10 °C / min, held at 180 °C for 5 minutes, and then cooled to 40 °C at a cooling rate of 10 °C / min. A baseline is drawn from 60 °C to 150 °C in the melting curve obtained during the process, and the half-width of the melting endothermic peak is derived using analysis software such as "Pyris Software (version 7)". The test can be carried out using a DSC Q2000 calorimeter available from TA Instruments.

[0028]

[0030] The half-crystallization time during isothermal crystallization at 123 °C can be determined from the time required for the amount of heat measured during the isothermal crystallization measurement at 123 °C, which corresponds to half of the peak area in the differential scanning calorimetry (DSC) measurement. The test can be carried out using a DSC Q2000 calorimeter available from TA Instruments.

[0029]

[0031] The measurement of the contact angle is carried out on a Kruss DSA 100 instrument. The membrane sample (10×40 mm) is attached to a microscope slide using double-sided adhesive tape. The electrostatic charge is dissipated by moving the prepared sample several times through a U-electrode electrostatic discharger. The sample is placed inside the measuring device, and a 3.5 μl droplet of the test fluid (water or ethylene glycol) is placed on the membrane. The contact angle is determined by passing it through the software for 7 seconds (one measurement per second) after the droplet is placed. These seven data points are averaged to yield the contact angle at the measurement point. Each sample is measured at six different spots or at positions on each side above, and all results are averaged to the reported value.

[0030]

[0032] In addition to the contact angle, the wettability of the membranes fabricated according to the present disclosure can also be tested according to the wettability test as follows.

[0033] The membrane sample (50×15 mm) is sandwiched between two stainless steel sheets (76×30 mm) each having a 20 mm diameter hole in the center. This arrangement is placed under an optical microscope (Olympus BX 41) equipped with a 2.5X objective lens and a CCD camera (Olympus UC30). A 1 μl droplet of propylene carbonate is placed using an Eppendorf pipette on the exposed area of the membrane sample. Immediately, the light-passing image of the droplet and the surrounding membrane area are recorded using image software (Stream Motion). Over the following 10 minutes, images of the same spot are recorded every 30 seconds.

[0031]

[0034] The resulting series of images shows that the film region around the droplet becomes transparent (indicated by the higher brightness in this region). Over time, the transparent region, which resembles a ring around the droplet, increases in size. The diameter of this ring (in both the MD and TD directions of the film) is measured using image software for each image in the time series. The result is two plots of the diameter of the transparent region (for both MD and TD) against time. A faster increase in the diameter of the transparent region is an indicator of better wettability of the film for the electrolyte solvent and is desirable.

Best Mode for Carrying Out the Invention

[0032]

[0035] It will be understood by those skilled in the art that this discussion is a description of only exemplary embodiments and is not intended to limit the broader aspects of the present disclosure.

[0036] Generally, the present disclosure is directed to polymer compositions suitable for manufacturing gel-extruded articles, such as fibers and films comprising porous membranes. The polymer composition contains a polyethylene resin, such as high-density polyethylene particles, in combination with a plasticizer and one or more surface tension reducing additives. The surface tension reducing additives can dramatically reduce the surface tension and increase the wetting properties between the polymer article formed from the polymer composition and a liquid such as water. When manufacturing a porous membrane for an electronic device, one or more surface tension reducing additives can significantly improve the wettability of the membrane when contacted with an electrolyte solution.

[0033]

[0037] In addition to, or instead of, incorporating one or more surface tension reducing additives into the gel-extruded article, in another aspect, the gel-extruded article can be surface treated. Surface treatments, such as plasma treatment, can also dramatically improve the wetting properties of articles made in accordance with the present disclosure, such as membranes.

[0034]

[0038] The use of one or more surface tension reduction techniques in accordance with the present disclosure can impart a variety of advantages and benefits, particularly when forming membranes for lithium-ion batteries. For example, improved wettability helps shorten the immersion time of the battery membrane, which leads to higher productivity. Additionally, increased wettability with respect to the electrolyte can increase the mobility of ions such as lithium ions, which can significantly increase the life of the battery.

[0035]

[0039] A variety of different surface tension reduction techniques may be used in accordance with the present disclosure. As an example, the surface tension reducing additive may be a hydrophilic inorganic filler. Alternatively, the surface tension reducing additive may be a hydrophilic organic polymer that can take the form of particles combined with the matrix polymer used to form the polymeric article. In one aspect, one or more hydrophilic inorganic fillers can be combined with one or more hydrophilic organic polymers and with the matrix polymer. In an alternative aspect, the surface tension reducing additive may be a hydrophilic chemical agent combined with the polyethylene resin during melt processing. The hydrophilic chemical agent can couple (e.g., bond, graft, etc.) to the polyethylene polymer so as to form functional hydrophilic chemical groups on the surface to increase the wettability of the final product. In yet another aspect, the polymeric articles of the present disclosure, such as membranes, can be surface treated after being formed, for example, using plasma treatment, corona discharge, electron beam treatment, gamma ray treatment, UV treatment, vapor treatment, or combinations thereof.

[0036]

[0040] The polymer composition of the present disclosure contains a polyethylene polymer that is particularly well-suited to be combined with one or more surface tension reduction techniques. The polyethylene polymer can be a high-density polyethylene polymer used to form the primary polymer component and the matrix polymer of the polymer composition. The high-density polyethylene has a density of about 0.93 g / cm 3 or more, for example about 0.94 g / cm 3 or more, for example about 0.95 g / cm 3 or more, and generally about 1 g / cm3 less than, for example, about 0.96 g / cm 3 and has a density of less than.

[0037]

[0041] High density polyethylene polymers can be made from units derived from ethylene in excess of 90%, such as units derived from ethylene in excess of 95%, or 100% units derived from ethylene. The polyethylene can be a homopolymer or a copolymer including a terpolymer having other monomer units.

[0038]

[0042] High density polyethylene can be high molecular weight polyethylene, very high molecular weight polyethylene and / or ultra-high molecular weight polyethylene. "High molecular weight polyethylene" refers to a polyethylene composition having an average molecular weight of at least about 3×10 5 g / mol, and when used herein, is intended to include very high molecular weight polyethylene and ultra-high molecular weight polyethylene. For the purposes of this specification, the molecular weights referred to herein are determined according to the Margolies formula ("Margolies molecular weight").

[0039]

[0043] "Very high molecular weight polyethylene" refers to a polyethylene composition having a weight average molecular weight of less than about 3×10 6 g / mol and greater than about 1×10 6 g / mol. In some embodiments, the molecular weight of the very high molecular weight polyethylene composition is between about 2×10 6 g / mol and less than about 3×10 6 g / mol.

[0040]

[0044] "Ultra-high molecular weight polyethylene" refers to a polyethylene composition having an average molecular weight of at least about 3×10 6 g / mol. In some embodiments, the molecular weight of the ultra-high molecular weight polyethylene composition is between about 3×10 6 g / mol and about 30×10 6 g / mol, or between about 3×10 6 g / mol and about 20×10 6 g / mol, or between about 3×106 between about 10×10 6 g / mol and about 3×10 6 g / mol, or between about 3×10 6 g / mol and about 6×10

[0041]

[0045] In one aspect, the high density polyethylene is a homopolymer of ethylene. In another embodiment, the high density polyethylene may be a copolymer. By way of example, the high density polyethylene may be a copolymer of ethylene and another olefin containing 3 to 16 carbon atoms, such as 3 to 10 carbon atoms, such as 3 to 8 carbon atoms. These other olefins include, but are not limited to, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methylpenta-1-ene, 1-decene, 1-dodecene, 1-hexadecene, and the like. Also available herein are polyene comonomers such as 1,3-hexadiene, 1,4-hexadiene, cyclopentadiene, dicyclopentadiene, 4-vinylcyclohex-1-ene, 1,5-cyclooctadiene, 5-vinylidene-2-norbornene and 5-vinyl-2-norbornene. However, when present, the amount of non-ethylene monomer in the copolymer may be less than about 10 mol%, such as less than about 5 mol%, such as less than about 2.5 mol%, such as less than about 1 mol%, and the mol% is relative to the total moles of monomers in the polymer.

[0042]

[0046] In one embodiment, the high-density polyethylene may have a unimodal molecular weight distribution. Alternatively, the high-density polyethylene may exhibit a bimodal molecular weight distribution. By way of example, a bimodal distribution generally refers to a polymer having a distinct higher molecular weight and a distinct lower molecular weight (e.g., two distinct peaks) on a size exclusion chromatography or gel permeation chromatography curve. In another embodiment, the high-density polyethylene may exhibit more than two molecular weight distribution peaks such that the polyethylene exhibits a multimodal (e.g., trimodal, tetramodal, etc.) distribution. Alternatively, the high-density polyethylene may consist of a blend of a higher molecular weight component and a lower molecular weight component such that the size exclusion chromatography or gel permeation chromatography curve exhibits a broad molecular weight distribution that does not exhibit at least two distinct peaks, but instead exhibits one distinct peak that is broader than the peaks of the individual components.

[0043]

[0047] Polyethylene can be synthesized using any method known in the art. The polyethylene powder is typically produced by catalytic polymerization of ethylene monomer, or optionally one or more other 1-olefin comonomers, using a heterogeneous catalyst and an organoaluminum or magnesium compound as a cocatalyst such that the 1-olefin content in the final polymer is 10% or less of the ethylene content. Ethylene is usually polymerized at relatively low temperatures and pressures in the gas phase or slurry phase. The polymerization reaction can be carried out at a temperature between 50 °C and 100 °C and a pressure within the range of 0.02 to 2 MPa.

[0044]

[0048] The molecular weight of the polyethylene can be adjusted by adding hydrogen. Changes in temperature and / or the type and concentration of the cocatalyst may also be used to finely tune the molecular weight. Additionally, the reaction may be carried out in the presence of an antistatic agent to avoid fouling and product contamination.

[0045]

[0049] Suitable catalyst systems include, but are not limited to, Ziegler-Natta type catalysts. Typically, Ziegler-Natta type catalysts are derived from a combination of transition metal compounds from Groups 4 to 8 of the periodic table and alkyl or hydride derivatives of metals from Groups 1 to 3 of the periodic table. The transition metal derivatives used usually include metal halides or esters, or combinations thereof. Exemplary Ziegler-Natta catalysts include catalysts based on the reaction products of organoaluminum or magnesium compounds, such as, but not limited to, alkylaluminum or magnesium, and halides or esters of titanium, vanadium or chromium. The heterogeneous catalyst may or may not be supported and may be supported on a porous particulate material such as silica or magnesium chloride. Such a support can be added during the synthesis of the catalyst or obtained as a chemical reaction product of the catalyst synthesis itself.

[0046]

[0050] In one embodiment, a suitable catalyst system can be obtained by the reaction of a titanium(IV) compound and a trialkylaluminum compound in an inert organic solvent at a temperature in the range of -40°C to 100°C, preferably -20°C to 50°C. The concentration of the starting materials is in the range of 0.1 to 9 mol / L, preferably 0.2 to 5 mol / L for the titanium(IV) compound, and 0.01 to 1 mol / L, preferably 0.02 to 0.2 mol / L for the trialkylaluminum compound. The titanium component is added to the aluminum compound over a period of 0.1 minute to 60 minutes, preferably 1 minute to 30 minutes, and the molar ratio of titanium to aluminum in the final mixture is in the range of 1:0.01 to 1:4.

[0047]

[0051] In another embodiment, a suitable catalyst system is obtained by a one-step or two-step reaction of a titanium(IV) compound with a trialkylaluminum compound in an inert organic solvent at a temperature in the range of -40°C to 200°C, preferably -20°C to 150°C. In the first step, the titanium(IV) compound is reacted with the trialkylaluminum compound at a temperature in the range of -40°C to 100°C, preferably -20°C to 50°C, using a molar ratio of titanium to alumina in the range of 1:0.1 to 1:0.8. The concentration of the starting materials is in the range of 0.1 to 9.1 mol / L, preferably 5 to 9.1 mol / L for the titanium(IV) compound, and 0.05 to 1 mol / L, preferably 0.1 to 0.9 mol / L for the trialkylaluminum compound. The titanium component is added to the aluminum compound over a period of 0.1 minute to 800 minutes, preferably 30 minutes to 600 minutes. In the second step, when applied, the reaction product obtained in the first step is treated with a trialkylaluminum compound at a temperature in the range of -10°C to 150°C, preferably 10°C to 130°C, using a molar ratio of titanium to alumina in the range of 1:0.01 to 1:5.

[0048]

[0052] In yet another embodiment, a suitable catalyst system is obtained by a procedure in which, in a first reaction stage, a magnesium alcoholate is reacted with titanium chloride in an inert hydrocarbon at a temperature of 50°C to 100°C. In a second reaction stage, the reaction mixture formed is subjected to a heat treatment at a temperature of 110°C to 200°C for about 10 to 100 hours, with evolution of alkyl chloride until no further alkyl chloride is evolved, and then the solid is freed from the soluble reaction products by washing several times with a hydrocarbon.

[0049]

[0053] In a further embodiment, a silica-supported catalyst, such as the commercially available catalyst system Sylopol 5917, can also be used.

[0054] Using such a catalyst system, the polymerization is typically carried out in suspension, in one or more steps, either continuously or batchwise, at low pressure and temperature. The polymerization temperature is typically in the range of 30 °C to 130 °C, preferably in the range of 50 °C to 90 °C, and the partial pressure of ethylene is typically less than 10 MPa, preferably 0.05 MPa and 5 MPa. Trialkylaluminums such as, but not limited to, isoprenylaluminum and triisobutylaluminum are used as co-catalysts such that the ratio of Al:Ti (co-catalyst to catalyst) is in the range of 0.01 to 100:1, more preferably in the range of 0.03 to 50:1. The solvent is an inert organic solvent typically used for Ziegler-type polymerization. Examples are butane, pentane, hexane, cyclohexene, octane, nonane, decane, their isomers and their mixtures. The molecular weight of the polymer is controlled by supplying hydrogen. The ratio of the hydrogen partial pressure to the ethylene partial pressure is in the range of 0 to 50, preferably in the range of 0 to 10. The polymer is separated and dried under nitrogen in a fluidized bed dryer. The solvent can be removed through steam distillation when using a high-boiling solvent. Salts of long-chain fatty acids may be added as stabilizers. Typical examples are calcium stearate, magnesium stearate and zinc stearate.

[0050]

[0055] Optionally, other catalysts such as Phillips catalysts, metallocenes and post-metallocenes can be utilized. Generally, co-catalysts such as each compound of alumoxane or alkylaluminum or alkylmagnesium are also utilized. Other suitable catalyst systems include group 4 metal complexes with phenolate ether ligands.

[0051]

[0056] Polyethylene polymers that are particularly well-suited for use in the present disclosure have a half-width of the melting endotherm peak that is greater than about 6 °C, such as greater than about 6.2 °C, such as greater than about 6.4 °C, such as greater than about 6.5 °C, such as greater than about 6.8 °C, when measured with a differential scanning calorimeter, and generally have a half-width of the melting endotherm peak that is less than about 9 °C. The polyethylene polymer can also have a half-crystallization time that is greater than about 2 minutes, such as greater than about 2.5 minutes, such as greater than about 3.0 minutes, such as greater than about 3.5 minutes, such as greater than about 4.0 minutes, such as greater than about 4.5 minutes, during isothermal crystallization at 123 °C, and generally can have a half-crystallization time that is less than about 12 minutes. In the past, polyethylene polymers having a shorter time than those described above were thought to provide optimal results. However, the inventors have discovered that a selected surface tension reducing additive, or a selected combination of surface tension reducing additives, can dramatically improve one or more strength characteristics of a porous membrane made from a polymer composition containing a polyethylene polymer as described above.

[0052]

[0057] According to the present disclosure, high density polyethylene polymers are formed into particles and combined with a plasticizer. In one embodiment, the polyethylene particles are made from a polyethylene polymer having a relatively low bulk density as measured in accordance with DIN53466. By way of example, in one embodiment, the bulk density is generally less than about 0.4 g / cm 3 , such as less than about 0.35 g / cm 3 , such as less than about 0.33 g / cm 3 , such as less than about 0.3 g / cm 3 , such as less than about 0.28 g / cm 3 , such as less than about 0.26 g / cm 3 . The bulk density is generally greater than about 0.1 g / cm 3 , such as greater than about 0.15 g / cm 3 . In one embodiment, the polymer has a bulk density of from about 0.2 g / cm 3 to about 0.27 g / cm 3 .

[0053]

[0058] In one embodiment, the polyethylene particles may be free-flowing powders. The particles can have a volume median particle size (d50) of less than 200 microns. For example, the median particle size (d50) of the polyethylene particles can be less than about 150 microns, such as less than about 125 microns. The median particle size (d50) is generally greater than about 20 microns. The particle size of the powder can be measured using the laser diffraction method according to ISO13320.

[0054]

[0059] In one embodiment, 90% of the polyethylene particles can have a particle size of less than about 250 microns. In other embodiments, 90% of the polyethylene particles can have a particle size of less than about 200 microns, such as less than about 170 microns.

[0055]

[0060] The molecular weight of the polyethylene polymer can vary depending on the specific application. The polyethylene polymer can have, by way of example, an average molecular weight determined by the Margules equation. The molecular weight can be determined by first measuring the viscosity number in accordance with DIN EN ISO Test1628. The dry powder flow is measured using a 25 mm nozzle. The molecular weight is then calculated from the viscosity number using the Margules equation. The average molecular weight is generally greater than about 300,000 g / mol, such as greater than about 500,000 g / mol, such as greater than about 650,000 g / mol, such as greater than about 1,000,000 g / mol, such as greater than about 2,000,000 g / mol, such as greater than about 2,500,000 g / mol, such as greater than about 3,000,000 g / mol, such as greater than about 4,000,000 g / mol. The average molecular weight is generally less than about 12,000,000 g / mol, such as less than about 10,000,000 g / mol. In one aspect, the number average molecular weight of the high-density polyethylene polymer can be less than about 4,000,000 g / mol, such as less than about 3,000,000 g / mol.

[0056]

[0061] In one aspect, the composition or film can comprise only a single polyethylene polymer. The single polyethylene polymer can have an average molecular weight of 500,000 g / mol or more, for example greater than about 600,000 g / mol, and generally can have an average molecular weight of less than 2,500,000 g / mol.

[0057]

[0062] Polyethylene is determined using its concentration in decahydronaphthalene at 0.0002 g / mL in accordance with ISO 1628 part 3, and can have an intrinsic viscosity ranging from at least 100 mL / g, for example at least 500 mL / g, for example at least 550 mL / g, to less than about 6,000 mL / g, for example less than about 5,000 mL / g, for example less than about 4,000 mL / g, for example less than about 3,000 mL / g, for example less than about 1,000 mL / g.

[0058]

[0063] High-density polyethylene can have a crystallinity of at least about 40% to 85%, for example 45% to 80%. In one aspect, the crystallinity can be greater than about 50%, for example greater than about 55%, for example greater than about 60%, for example greater than about 65%, for example greater than about 70%, and generally can be less than about 80%.

[0059]

[0064] Generally, high-density polyethylene particles are present in the polymer composition in an amount of up to about 50 wt%. By way of example, high-density polyethylene particles can be present in the polymer composition in an amount of less than about 45 wt%, for example less than about 40 wt%, for example less than about 35 wt%, for example less than about 30 wt%, for example less than about 25 wt%, for example less than about 20 wt%, for example less than about 15 wt%. The polyethylene particles can be present in the composition in an amount greater than about 5 wt%, for example greater than about 10 wt%, for example greater than about 15 wt%, for example greater than about 20 wt%, for example greater than about 25 wt%.

[0060]

[0065] During the gel treatment, the plasticizer is combined with high-density polyethylene particles, which can be substantially or completely removed during the formation of the polymeric article. For example, in one embodiment, the resulting polymeric article can contain high-density polyethylene polymer in an amount greater than about 50 wt%, such as greater than about 60 wt%, such as greater than about 65 wt%, such as greater than about 70 wt%, such as greater than about 75 wt%.

[0061]

[0066] According to the present disclosure, a polymer composition for manufacturing a gel extruded article can contain one or more surface tension reducing additives in combination with high-density polyethylene particles. The one or more surface tension reducing additives can be combined with the polyethylene polymer before being combined with the plasticizer, or can be combined simultaneously with the polyethylene polymer and the plasticizer. In one aspect, the one or more surface tension reducing additives can be pre-compounded with the polyethylene polymer to form polymer particles that are later combined with the plasticizer. In one embodiment, the surface tension reducing additive can be a hydrophilic chemical agent that is combined with the polyethylene polymer in situ or during the molten state to increase the wetting properties of the resulting article.

[0062]

[0067] Surface tension reducing additives that can be used in accordance with the present disclosure generally include any suitable additive that can be melt processed with high-density polyethylene particles to reduce the surface tension of an article made from the polymer composition and / or increase the wetting properties of an article made from the composition. The surface tension reducing additive can be, by way of example, a hydrophilic inorganic filler, hydrophilic organic polymer particles, a hydrophilic chemical agent that forms functional hydrophilic chemical groups on the polymer, or a combination thereof.

[0063]

[0068] In one aspect, the surface tension reducing agent can include a polyolefin polymer, particularly a polyethylene polymer functionalized with an organic acid, such as an organic acid anhydride. For example, the polyolefin polymer, such as a polyethylene polymer, can be modified to include hydrophilic carboxyl groups. The carboxyl groups can be added to the polymer by oxidation, by polymerization, or by grafting. For example, in one aspect, a carboxyl-containing unsaturated monomer can be grafted onto a polyolefin polymer, such as a polyethylene polymer. The carboxyl-containing unsaturated monomer can be, by way of example, maleic anhydride.

[0064]

[0069] For example, in one aspect, the surface tension reducing additive can be a polyethylene polymer functionalized with maleic anhydride. The polyethylene polymer can be the same as the high-density polyethylene polymer combined with the surface tension reducing additive, or it can be a different polyethylene polymer. For example, the polyethylene polymer functionalized with maleic anhydride can be a low-density polyethylene polymer, such as a linear low-density polyethylene polymer. Alternatively, the polyethylene polymer functionalized with maleic anhydride can be a high-density polyethylene polymer. The high-density polyethylene polymer can have a molecular weight greater than about 300,000 g / mol, such as greater than about 500,000 g / mol, such as greater than about 700,000 g / mol, and can generally have a molecular weight less than about 2,500,000 g / mol.

[0065]

[0070] Polyethylene functionalized with maleic anhydride can contain maleic anhydride in an amount generally greater than about 1.5% by weight, for example greater than about 1.8% by weight, for example greater than about 2% by weight, for example greater than about 2.5% by weight, for example greater than about 3% by weight, for example greater than about 3.5% by weight, for example greater than about 4% by weight, for example greater than about 4.5% by weight. Polyethylene functionalized with maleic anhydride can generally contain maleic anhydride in an amount less than about 20% by weight, for example less than about 10% by weight, for example less than about 8% by weight, for example less than about 5% by weight. Polyethylene functionalized with maleic anhydride can be in the form of a powder or particles that are combined with or compounded with high-density polyethylene particles.

[0066]

[0071] In other embodiments, the surface tension reducing additive may be a fatty alcohol glycol ether, such as an ethylene-vinyl alcohol copolymer. The surface tension reducing additive can also be an ethylene acrylic acid copolymer. The ethylene acrylic acid copolymer can generally have an acrylic acid content greater than 5% by weight, for example greater than about 8% by weight, for example greater than about 10% by weight, and can generally have an acrylic acid content less than about 30% by weight, for example less than about 20% by weight, for example less than about 15% by weight, for example less than about 12% by weight.

[0067]

[0072] The surface tension reducing additive can be any suitable acrylate polymer and / or graft copolymer containing an olefin. An olefin polymer, such as polyethylene, can act as a graft base and can be grafted to at least one vinyl polymer or one ether polymer.

[0068]

[0073] Examples of the surface tension reducing additive as described above include ethylene-acrylic acid copolymer, ethylene-maleic anhydride copolymer, ethylene-alkyl (meth) acrylate-maleic anhydride terpolymer, ethylene-alkyl (meth) acrylate-glycidyl (meth) acrylate terpolymer, ethylene-acrylic ester-methacrylic acid terpolymer, ethylene-acrylic ester-maleic anhydride terpolymer, ethylene-methacrylic acid-alkali metal methacrylate (ionomer) terpolymer, and the like. In one embodiment, by way of example, the surface tension reducing additive can include a random terpolymer of ethylene, methyl acrylate, and glycidyl methacrylate. The terpolymer may have a glycidyl methacrylate content of about 5% to about 20%, such as about 6% to about 10%. The terpolymer may have a methyl acrylate content of about 20% to about 30%, such as about 24%.

[0069]

[0074] The surface tension reducing additive can be a linear or branched homopolymer or copolymer (such as random, graft, block, etc.) containing epoxy functional groups, such as terminal epoxy groups, skeletal oxirane units, and / or pendant epoxy groups. By way of example, the surface tension reducing additive can be a copolymer including at least one monomer component containing an epoxy functional group. The monomer units of the surface tension reducing additive can be diverse. For example, the surface tension reducing additive can include epoxy-functional methacrylic monomer units. As used herein, the term "(meth)acrylic" generally refers to both acrylic monomers and methacrylic monomers, as well as their salts and esters, such as acrylate monomers and methacrylate monomers. Epoxy-functional (meth)acrylic monomers that can be incorporated into the surface tension reducing additive include those containing a 1,2-epoxy group, such as glycidyl acrylate and glycidyl methacrylate, but are not limited thereto. Other suitable epoxy-functional monomers include allyl glycidyl ether, glycidyl ethacrylate, and glycidyl itaconate.

[0070]

[0075] Examples of other monomers include, for example, ester monomers, olefin monomers, amide monomers, and the like. In one embodiment, the surface tension reducing additive can include at least one linear or branched α-olefin monomer, such as those having 2 to 20 carbon atoms, or 2 to 8 carbon atoms. Specific examples include ethylene; propylene; 1-butene; 3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentene having one or more methyl, ethyl, or propyl substituents; 1-hexene having one or more methyl, ethyl, or propyl substituents; 1-heptene having one or more methyl, ethyl, or propyl substituents; 1-octene having one or more methyl, ethyl, or propyl substituents; 1-nonene having one or more methyl, ethyl, or propyl substituents; ethyl, methyl, or dimethyl-substituted 1-decene; 1-dodecene; and styrene.

[0071]

[0076] In one embodiment, the surface tension reducing additive may be a terpolymer containing an epoxy functional group. By way of example, the surface tension reducing additive can include a methacrylic component containing an epoxy functional group, an α-olefin component, and a methacrylic component not containing an epoxy functional group. For example, the surface tension reducing additive may be poly(ethylene-co-methacrylate-co-glycidyl methacrylate), which has the structure:

[0072]

Chemical formula

[0073] (wherein a, b, and c are 1 or more) having.

[0077] In another embodiment, the surface tension reducing additive can be a random copolymer of ethylene, ethyl acrylate, and maleic anhydride, having the structure:

[0074]

Chemical formula

[0075] (wherein x, y, and z are 1 or more) has

[0078] The relative proportions of the various monomer components of the surface tension reducing additive of the copolymer are not particularly limited. As an example, in one embodiment, the epoxy-functional methacrylic monomer component can form from about 1 wt.% to about 25 wt.%, or from about 2 wt.% to about 20 wt.% of the surface tension reducing additive of the copolymer. The α-olefin monomer can form from about 55 wt.% to about 95 wt.%, or from about 60 wt.% to about 90 wt.% of the surface tension reducing additive of the copolymer. When utilized, other monomer components (e.g., non-epoxy-functional methacrylic monomers) can constitute from about 5 wt.% to about 35 wt.%, or from about 8 wt.% to about 30 wt.% of the surface tension reducing additive of the copolymer.

[0076]

[0079] The molecular weight of the above surface tension reducing additive can vary widely. For example, the surface tension reducing additive can have a number average molecular weight of from about 7,500 to about 250,000 grams per mole, in some embodiments from about 15,000 to about 150,000 grams per mole, and in some embodiments from about 20,000 to 100,000 grams per mole, and the polydispersity index is typically in the range of 2.5 to 7.

[0077]

[0080] In yet another embodiment, the surface tension reducing additive may be a surfactant capable of melt processing with the high density polyethylene resin. For example, the surfactant may be a nonionic surfactant in solid form at 23°C. In one aspect, by way of example, the surface tension reducing additive may be an alkyl polyethylene glycol ether. The alkyl polyethylene glycol ether can be made from linear saturated C10 - C28, for example C16 - C18 fatty alcohols. For example, the surfactant may be a reaction product of a fatty alcohol with ethylene oxide. The surfactant can contain an ethoxylation degree of more than about 8 mol, for example more than about 10 mol, for example more than about 20 mol, for example more than about 30 mol, for example more than about 40 mol, and generally can contain an ethoxylation degree of less than about 100 mol, for example less than about 80 mol, for example less than about 60 mol.

[0078]

[0081] In yet another embodiment, the surface tension reducing additive may be a hydrophilic inorganic filler such as aluminum oxide or aluminum hydroxide. Aluminum oxide, for example, can have a BET surface area of more than about 85 m 2 / g, for example more than about 90 m 2 / g, for example more than about 100 m 2 / g, and generally can have a BET surface area of less than about 500 m 2 / g, for example less than about 200 m 2 / g.

[0079]

[0082] The hydrophilic inorganic filler generally can have a D50 particle size of less than about 30 microns, for example less than about 20 microns, for example less than about 15 microns, for example less than about 10 microns, and generally can have a D50 particle size of more than about 0.1 microns, for example more than about 0.5 microns, for example more than about 1 micron, for example more than about 3 microns, for example more than about 5 microns.

[0080]

[0083] In another aspect, the surface tension reducing additive may be a hydrophilic chemical agent that couples to the polyethylene polymer during melt processing or in situ during polymer formation to increase the wetting properties of the resulting article. The hydrophilic chemical agent can, for example, be chemically grafted to a polyethylene polymer having a functional chemical group that enhances the polarity of the polymer. Alternatively, the hydrophilic chemical agent can undergo a chemical reaction with other polar molecules on the polyethylene polymer to reduce the surface tension.

[0081]

[0084] In one aspect, for example, the surface tension reducing additive may be an organic acid anhydride as described above that is combined with the polyethylene polymer during melt processing. For example, the organic acid anhydride can include maleic anhydride. Alternatively, the surface tension reducing agent may be an acrylate or methacrylate, such as glycidyl methacrylate. In yet another alternative embodiment, the surface tension reducing agent can include acrylic acid that contacts and binds to the polyethylene polymer in its molten form.

[0082]

[0085] In still another aspect of the present disclosure, a polymer article made in accordance with the present disclosure can be surface treated to improve the wetting properties of the article. For example, the polymer article can be surface treated using one of many techniques. Suitable surface treatments that can be used include plasma treatment, corona discharge, electron beam treatment, gamma ray treatment, UV treatment, steam treatment, and combinations thereof. The surface treatment of the polymer article can be used in combination with one or more of the surface tension reducing additives as described above to further increase the wetting properties.

[0083]

[0086] The amount of one or more surface tension reducing additives incorporated in the polymer composition and in the polymer articles made from the composition can vary depending on a variety of factors. Generally, one or more surface tension reducing additives are incorporated into the polymer composition such that the porous membrane made from the composition has an increase in wettability. For example, in one embodiment, one or more surface tension reducing additives are incorporated into the polymer composition such that the polymer composition and the articles made from the composition experience a decrease in contact angle of more than about 4%, such as more than about 5%, such as more than about 7%, such as more than about 10%, such as more than about 12%, such as more than about 15%, such as more than about 18%, such as more than about 20%. The contact angle can, by way of example, be further reduced by more than about 25%, such as more than 30%, such as more than about 40%, and up to about 60% at most. The above decrease in contact angle can be observed when the polymer composition is tested against any suitable liquid, including water or ethylene glycol.

[0084]

[0087] For example, when tested against water, the polymer compositions of the present disclosure containing one or more surface tension reducing additives can exhibit a contact angle of less than about 102°, such as less than about 98°, such as less than about 95°, such as less than about 93°, such as less than about 90°, such as less than about 88°, such as less than about 85°, such as less than about 83°, such as less than about 80°. The contact angle, when tested against water, is generally greater than about 50°. When tested against ethylene glycol, the polymer composition and the articles made from the composition can exhibit a contact angle of less than about 79°, such as less than about 77°, such as less than about 75°, such as less than about 73°, such as less than about 70°, such as less than about 68°, such as less than about 66°, such as less than about 63°, such as less than about 60°. The contact angle when tested against ethylene glycol is generally greater than about 30°.

[0085]

[0088] The actual amount of one or more surface tension reducing agents contained in the polymer composition can depend on a variety of factors. Polymer articles made in accordance with the present disclosure can contain, for example, one or more surface tension reducing agents in an amount generally from about 0.1 wt% to about 40 wt%, including all increments of 1 wt% therebetween. For example, when one or more surface tension reducing agents are in the form of a filler or particles, they can be present in the polymer article in an amount greater than about 2 wt%, such as greater than about 5 wt%, such as greater than about 8 wt%, such as greater than about 10 wt%, such as greater than about 12 wt%, such as greater than about 15 wt%, such as greater than about 17 wt%, such as greater than about 20 wt%, such as greater than about 22 wt%, such as greater than about 25 wt%. One or more surface tension reducing agents are generally contained in the polymer article in an amount less than about 35 wt%, such as less than about 30 wt%.

[0086]

[0089] When one or more surface tension reducing agents are in the form of a hydrophilic chemical agent added in situ to a polyethylene polymer, the resulting polymer article can contain one or more surface tension reducing agents in an amount generally greater than about 0.01 wt%, such as greater than about 0.1 wt%, such as greater than about 0.5 wt%, such as greater than about 1 wt%, such as greater than about 2 wt%, such as greater than about 4 wt%, such as greater than about 5 wt%, such as greater than about 7 wt%, and can generally contain less than about 20 wt%, such as less than about 10 wt%, such as less than about 7 wt%, such as less than about 6 wt%.

[0087]

[0090] As described above, the polymer composition made in accordance with the present disclosure for use in manufacturing polymer articles contains a high density polyethylene resin, a plasticizer, one or more surface tension reducing agents, and one or more other additives. The plasticizer is contained in the composition to facilitate the formation of the polymer article and is then substantially removed from the formed polymer article. When the polymer composition contains from about 50 wt% to about 85 wt% of the plasticizer, the polymer composition contains one or more surface tension reducing additives in an amount greater than about 0.01 wt%, such as greater than about 1 wt%, such as greater than about 2 wt%, such as about 2.5 wt%, such as greater than about 3 wt%, such as greater than about 5 wt%, such as greater than about 7 wt%, such as greater than about 9 wt%, such as greater than about 10 wt%, such as greater than about 12 wt%. One or more surface tension reducing additives can be present in the formed article in an amount less than about 20 wt%, such as less than about 15 wt%.

[0088]

[0091] Generally, any suitable plasticizer can be combined with the other components as long as the plasticizer is capable of forming a gel-like material suitable for gel spinning or extrusion. The plasticizer may include, by way of example, hydrocarbon oils, alcohols, ethers, esters, such as diesters, or mixtures thereof. By way of example, suitable plasticizers include mineral oil, paraffinic oil, decalin, and the like. Other plasticizers include xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, octane, nonane, kerosene, toluene, naphthalene, tetralin, and the like. In one embodiment, the plasticizer may include a halogenated hydrocarbon, such as monochlorobenzene. Cycloalkanes and cycloalkenes may also be used, such as camphene, methane, dipentene, methylcyclopentadiene, tricyclodecane, 1,2,4,5-tetramethyl-1,4-cyclohexadiene, and the like. The plasticizer may also include any mixtures and combinations of the foregoing.

[0089]

[0092] Plasticizers are generally present in the composition used to form the polymer article in an amount greater than about 50% by weight, for example greater than about 55% by weight, for example greater than about 60% by weight, for example greater than about 65% by weight, for example greater than about 70% by weight, for example greater than about 75% by weight, for example greater than about 80% by weight, for example greater than about 85% by weight, for example greater than about 90% by weight, for example greater than about 95% by weight, for example greater than about 98% by weight. In fact, plasticizers can be present in amounts up to about 99.5% by weight.

[0090]

[0093] High density polyethylene particles and surface tension reducing additives are blended with the plasticizer to form a homogeneous gel-like material.

[0094] To form a polymer article according to the present disclosure, the high density polyethylene particles are combined with one or more surface tension reducing additives and a plasticizer and extruded through a die of a desired shape. In one embodiment, the composition can be heated in an extruder. For example, the plasticizer can be combined with the particle mixture and fed into the extruder. According to the present disclosure, the plasticizer and the particle mixture form a homogeneous gel-like material, and then the extruder is caused to form a polymer article with little to no impurities from a polymer article with some impurities.

[0091]

[0095] In one embodiment, an elongated article is formed during the gel spinning or extrusion process. The polymer article can be, by way of example, in the form of a fiber or a film, such as a membrane.

[0092]

[0096] During the method, at least a portion of the plasticizer is removed from the final product. The method of plasticizer removal can occur due to evaporation when a relatively volatile plasticizer is used. Otherwise, an extraction liquid can be used to remove the plasticizer. The extraction liquid can include, by way of example, a hydrocarbon solvent. One example of an extraction liquid is, by way of example, dichloromethane. Other extraction liquids include acetone, chloroform, alkanes, hexene, heptene, alcohols, or mixtures thereof.

[0093]

[0097] If desired, the resulting polymer article can be stretched at a temperature increase below the melting point of the polymer mixture to enhance strength and elasticity. Suitable temperatures for stretching are in the range of from approximately ambient temperature to about 155 °C. The draw ratio can generally be greater than about 4, such as greater than about 6, such as greater than about 8, such as greater than about 10, such as greater than about 15, such as greater than about 20, such as greater than about 25, such as greater than about 30. In certain embodiments, the draw ratio can be greater than about 50, such as greater than about 100, such as greater than about 110, such as greater than about 120, such as greater than about 130, such as greater than about 140, such as greater than about 150. The draw ratio is generally less than about 1,000, such as less than about 800, such as less than about 600, such as less than about 400. In one embodiment, a lower draw ratio is used, such as from about 4 to about 10. The polymer article can be stretched uniaxially or biaxially.

[0094]

[0098] Polymer articles made in accordance with the present disclosure have numerous uses and applications. For example, in one embodiment, a method for manufacturing a membrane is used. The membrane can be used, by way of example, as a battery separator. Alternatively, the membrane can be used as a microfilter. When manufacturing fibers, the fibers can be used to manufacture non-woven fabrics, ropes, nets, and the like. In one embodiment, the fibers can be used as a filling material in bulletproof clothing.

[0095]

[0099] Referring to FIG. 1, an embodiment of a lithium-ion battery 10 fabricated in accordance with the present disclosure is shown. The battery 10 includes an anode 12 and a cathode 14. The anode 12 can be made of, for example, lithium metal. On the other hand, the cathode 14 can be made from sulfur or from a lithium metal oxide into which lithium has been inserted. According to the present disclosure, the battery 10 further includes a porous membrane 16 or a separator disposed between the anode 12 and the cathode 14. The porous membrane 16 allows the passage of ions, such as lithium ions, while minimizing an electrical short circuit between the two electrodes. As shown in FIG. 1, in one embodiment, the porous membrane 16 is a single-layer polymer membrane and does not include a multilayer structure. In one aspect, the single-layer polymer membrane may also include a coating. The coating can be, for example, an inorganic coating made from aluminum oxide or titanium oxide. Alternatively, the single-layer polymer membrane may also include a polymer coating. The coating can impart enhanced heat resistance.

[0096]

[0100] Polymer compositions and polymer articles fabricated in accordance with the present disclosure may contain a variety of other additives such as heat stabilizers, light stabilizers, UV absorbers, acid scavengers, flame retardants, lubricants, colorants, and the like.

[0097]

[0101] In one embodiment, a heat stabilizer may be present in the composition. Heat stabilizers include, but are not limited to, phosphites, amine antioxidants, phenolic antioxidants, or any combination thereof.

[0098]

[0102] In one embodiment, an antioxidant may be present in the composition. Antioxidants include, but are not limited to, secondary aromatic amines, benzofuranones, sterically hindered phenols, or any combination thereof.

[0099]

[0103] In one embodiment, a light stabilizer may be present in the composition. Examples of light stabilizers include, but are not limited to, 2-(2'-hydroxyphenyl)-benzotriazole, 2-hydroxy-4-alkoxybenzophenone, nickel-containing light stabilizers, 3,5-di-tert-butyl-4-hydroxybenzoate, hindered amines (HALS), or any combination thereof.

[0100]

[0104] In one embodiment, a UV absorber may be present in the composition instead of or in addition to the light stabilizer. Examples of UV absorbers include, but are not limited to, benzotriazole, benzoate, or any combination or any arbitrary combination thereof.

[0101]

[0105] In one embodiment, a halogenated flame retardant may be present in the composition. Examples of halogenated flame retardants include, but are not limited to, tetrabromobisphenol A (TBBA), tetrabromophthalic anhydride, dodecachloropentacyclooctadecadiene (dechlorane), hexabromocyclododecane, chlorinated paraffin, or any combination thereof.

[0102]

[0106] In one embodiment, a non-halogenated flame retardant may be present in the composition. Examples of non-halogenated flame retardants include, but are not limited to, resorcinol tetraphenyl diphosphate (RDP), ammonium polyphosphate (APP), phosphinic acid derivatives, triaryl phosphate, trichloropropyl phosphate (TCPP), magnesium hydroxide, aluminum trihydroxide, antimony trioxide.

[0103]

[0107] In one embodiment, a lubricant may be present in the composition. Examples of lubricants include, but are not limited to, silicone oil, wax, molybdenum disulfide, or any combination thereof.

[0104]

[0108] In one embodiment, a colorant may be present in the composition. Examples of colorants include, but are not limited to, inorganic and organic-based color pigments.

[0109] In one aspect, an acid scavenger may be present in the polymer composition. The acid scavenger may include, by way of example, an alkali metal salt or an alkaline earth metal salt. The salt may include a salt of a fatty acid, such as a stearate. Other acid scavengers include carbonates, oxides or hydroxides. Specific acid scavengers that may be incorporated into the polymer composition include metal stearates, such as calcium stearate. Still other acid scavengers include zinc oxide, calcium carbonate, magnesium oxide, and mixtures thereof.

[0105]

[0110] These additives may be used alone or in any combination thereof. Generally, each additive may be present in an amount of at least about 0.05 wt.%, such as at least about 0.1 wt.%, such as at least about 0.25 wt.%, such as at least about 0.5 wt.%, such as at least about 1 wt.%, and generally in an amount of less than about 20 wt.%, such as less than about 10 wt.%, such as less than about 5 wt.%, such as less than about 4 wt.%, such as less than about 2 wt.%. The sum of the wt.% of all components containing any additives, if present, utilized in the polymer composition is 100 wt.%.

[0106]

[0111] The present disclosure may be better understood with reference to the following examples. The following examples are given by way of illustration and not by way of limitation. The following experiments were conducted to demonstrate some of the benefits and advantages of the present invention.

Examples

[0107] Example 1

[0112] A variety of resin compositions were formulated by incorporating a base resin of high density polyethylene having a variety of surface tension reducing additives. The surface tension reducing additives were blended with the high density polyethylene using a tumble blender. The resin compositions were prepared into films in the conventional manner via gel extrusion, biaxial stretching and solvent extraction.

[0108]

[0113] The polyethylene polymer used in the examples had an average molecular weight of about 700,000 g / mol and an average particle size of about 115 microns. The polymer had a melt flow rate of 0.5 g / 10 min and a density of 0.94 g / cm 3 . The polymer had a viscosity number of 600 cm 3 / g when measured in accordance with ISO Test 1628-3.

[0109]

[0114] The following surface tension reduction techniques were examined. The following filling amounts are those of the final film after removing the plasticizer.

[0110]

Table 1

[0111]

[0115] The blend was gel extruded using a resin with a solids content of 30 wt.% and paraffin oil at a temperature of about 190 °C to about 240 °C and a screw speed of 200 rpm. After extrusion, the resulting film was solidified on a chill roller set at 40 °C. Stretching was carried out at a temperature of 120 °C at a 7×7 ratio (MD / TD). Extraction of the stretched film was carried out in acetone. The film was annealed at 130 °C for 10 minutes.

[0112]

[0116] Next, the film was tested for the contact angle with respect to ethylene glycol, and the following results were obtained.

[0113]

Table 2

[0114] Example 2

[0117] In this example, two different films were subjected to a plasma post-treatment method and tested for the contact angle. The first film had a thickness of 9 microns, while the second film had a thickness of 20 microns. The films were tested for the contact angle with respect to water and ethylene glycol. The following results were obtained.

[0115]

Table 3

[0116]

[0118] As shown above, the plasma treatment resulted in a significant decrease in the contact angle between the membrane and the test fluid. The use of surface treatment techniques, such as plasma treatment, is particularly well-suited for combination with one or more of the above-mentioned tension-reducing additives.

[0117]

[0119] These and other changes and modifications to the present invention can be practiced by those skilled in the art without departing from the spirit and scope of the invention as more particularly shown in the appended claims. In addition, it should be understood that aspects of the various embodiments may be compatible, both in whole or in part. Further, those skilled in the art will recognize that the foregoing description is by way of example only and is not intended to limit the invention as further described in such appended claims. The following is a transcription of the claims of the present application at the time of filing. [Aspect 1] A polymer composition for manufacturing a gel extrusion article, comprising a plasticizer, high-density polyethylene particles, and a surface tension reducing additive that increases the wettability of the polymer composition wherein the surface tension reducing additive includes a hydrophilic inorganic filler, hydrophilic organic polymer particles, or a hydrophilic chemical agent containing a hydrophilic chemical group coupled to the high-density polyethylene, a polymer composition. [Aspect 2] The polymer composition according to Aspect 1, wherein the surface tension reducing additive includes a graft copolymer of polyethylene and maleic anhydride. [Aspect 3] The polymer composition according to Aspect 1, wherein the surface tension reducing additive includes a graft copolymer of polyethylene and maleic anhydride, a fatty alcohol glycol ether, an ethylene vinyl alcohol copolymer, an ethylene glycidyl methacrylate copolymer, an ethylene acrylic acid copolymer, or a mixture thereof. [Aspect 4] The polymer composition according to Aspect 1, wherein the surface tension reducing additive includes aluminum oxide or aluminum hydroxide. [Aspect 5] The polymer composition according to Aspect 1, wherein the surface tension reducing additive includes a hydrophilic chemical agent. [Aspect 6] The polymer composition according to Aspect 1, wherein the surface tension reducing additive includes aluminum oxide or aluminum hydroxide in combination with a graft copolymer of polyethylene and maleic anhydride, a fatty alcohol glycol ether, an ethylene vinyl alcohol copolymer, an ethylene glycidyl methacrylate copolymer, or an ethylene acrylic acid copolymer. [Aspect 7] The polymer composition according to any one of Aspects 1 to 6, wherein the surface tension reducing additive is present in the composition in an amount of about 5 wt% to about 15 wt%, for example, in an amount of about 3 wt% to about 12 wt%, for example, in an amount of about 4 wt% to about 10 wt%. [Aspect 8] The polymer composition according to any one of Aspects 1 to 7, wherein the surface tension reducing additive is present in the composition in an amount sufficient to reduce the contact angle measured against water of a polymer article formed from the polymer composition by more than about 5%, for example, by more than about 8%, for example, by more than about 10%. [Aspect 9] The polymer composition according to any one of Aspects 1 to 8, wherein the polymer article formed from the polymer composition exhibits a contact angle of less than about 102°, such as less than about 98°, such as less than about 95°, as measured against water. [Aspect 10] The polymer composition according to Aspect 2, wherein the polyethylene in the graft copolymer of polyethylene and maleic anhydride is linear low density polyethylene, low density polyethylene or high density polyethylene. [Aspect 11] The polymer composition according to Aspect 2, wherein the polyethylene in the graft copolymer of polyethylene and maleic anhydride is polyethylene having a molecular weight of more than about 300,000 g / mol, such as more than about 500,000 g / mol, such as more than about 700,000 g / mol. [Aspect 12] The polymer composition according to Aspect 2, wherein the graft copolymer of polyethylene and maleic anhydride contains maleic anhydride in an amount of more than about 1% by weight and less than about 4% by weight. [Aspect 13] The polymer composition according to Aspect 2, 10, 11 or 12, wherein the graft copolymer of polyethylene and maleic anhydride is present in the polymer composition in an amount of about 5% to about 15% by weight. [Aspect 14] The polymer composition according to any one of Aspects 1 to 13, wherein the high density polyethylene particles have a volume median particle size of about 70 microns to about 210 microns. [Aspect 15] The polymer composition according to any one of Aspects 1 to 14, wherein the high density polyethylene particles are present in the composition in an amount of up to about 50% by weight. [Aspect 16] The polymer composition according to any one of Aspects 1 to 15, wherein the plasticizer includes mineral oil, paraffinic oil, hydrocarbon, alcohol, ether, ester, or a mixture thereof. [Aspect 17] The polymer composition according to any one of Aspects 1 to 16, wherein the high density polyethylene has a molecular weight of more than about 600,000 g / mol, such as more than about 650,000 g / mol, such as more than about 1,500,000 g / mol, and less than about 4,000,000 g / mol, such as less than about 3,500,000 g / mol. [Aspect 18] The polymer composition according to Aspect 15, containing only a single high density polyethylene polymer. [Aspect 19] The polymer composition according to any one of Aspects 1 to 18, wherein the high density polyethylene is Ziegler-Natta catalyst high molecular weight polyethylene. [Aspect 20] The polymer composition according to any one of Aspects 1 to 19, wherein the plasticizer contains decalin, paraffin oil, white oil, mineral oil, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, octane, nonane, kerosene, toluene, naphthalene, tetralin, monochlorobenzene, camphene, methane, dipentene, methylcyclopentadiene, tricyclodecane, 1,2,4,5-tetramethyl-1,4-cyclohexadiene, or a mixture thereof. [Aspect 21] The polymer composition according to any one of Aspects 1 to 20, which is free of polypropylene. [Aspect 22] A method for manufacturing a polymer article, comprising the step of forming the polymer composition according to any one of Aspects 1 to 21 into a gel-like composition, and the step of extruding the gel-like composition through a die to form a polymer article and wherein the polymer article includes a film. Method. [Aspect 23] The method according to Aspect 20, further comprising the step of removing at least a part of the plasticizer from the polymer article. The method according to Aspect 20. [Aspect 24] The method according to Aspect 20 or 21, wherein an extraction solvent is added to the polymer composition during the method to facilitate the removal of the plasticizer from the polymer article. [Aspect 25] The method according to Aspect 22, wherein the extraction solvent contains dichloromethane, acetone, chloroform, alkane, hexene, heptene, alcohol, or a mixture thereof. [Aspect 26] A porous membrane comprising high-density polyethylene combined with a surface tension reducing additive, wherein the surface tension reducing additive contains a hydrophilic inorganic filler, hydrophilic organic polymer particles, or a hydrophilic chemical agent coupled to high-density polyethylene, and the porous membrane presents a contact angle of less than about 102° when measured against water. The porous membrane. [Aspect 27] The porous membrane according to Aspect 26, wherein the surface tension reducing agent contains a graft copolymer of polyethylene and maleic anhydride. [Aspect 28] The porous membrane according to Aspect 26 or 27, wherein the surface tension reducing additive is present in the membrane in an amount of about 0.1 wt% to about 40 wt%, for example, in an amount of about 2 wt% to about 30 wt%. [Aspect 29] The porous membrane according to any one of Aspects 26 to 28, whose surface has been subjected to surface treatment. [Aspect 30] The porous membrane according to Aspect 29, wherein the surface treatment includes plasma treatment. [Aspect 31] The porous membrane according to Aspect 29, wherein the surface treatment includes corona discharge, electron beam treatment, gamma ray treatment, ultraviolet treatment, or steam treatment.

Claims

1. A polymer composition for manufacturing a gel extrusion article, comprising: a plasticizer, high-density polyethylene particles, and a surface tension reducing additive that increases the wettability of the polymer composition wherein the surface tension reducing additive comprises a graft copolymer of polyethylene, wherein the surface tension reducing additive comprises a hydrophilic chemical group that couples or is coupled to the high-density polyethylene, wherein the polymer article formed from the polymer composition exhibits a contact angle of less than 102° when measured against water.

2. The polymer composition according to claim 1, wherein the graft copolymer of polyethylene is a graft copolymer of polyethylene and maleic anhydride.

3. The polymer composition according to claim 1 or 2, wherein the surface tension reducing additive further comprises a fatty alcohol glycol ether, an ethylene vinyl alcohol copolymer, an ethylene glycidyl methacrylate copolymer, an ethylene acrylic acid copolymer, or a mixture thereof.

4. The polymer composition according to any one of claims 1 to 3, wherein the surface tension reducing additive further comprises aluminum oxide or aluminum hydroxide.

5. The polymer composition according to claim 1, wherein the surface tension reducing additive further comprises a hydrophilic chemical agent.

6. The polymer composition according to any one of claims 1 to 5, wherein the surface tension reducing additive is present in the composition in an amount of 5% to 15% by weight.

7. The polymer composition according to any one of claims 1 to 6, wherein the surface tension reducing additive is present in the composition in an amount sufficient to reduce the contact angle measured against water of the polymer article formed from the polymer composition by more than 5%.

8. The polymer composition according to claim 2, wherein the polyethylene in the graft copolymer of polyethylene and maleic anhydride is linear low-density polyethylene, low-density polyethylene, or high-density polyethylene.

9. The polymer composition according to claim 2, wherein the polyethylene in the graft copolymer of polyethylene and maleic anhydride has a molecular weight of more than 300,000 g / mol when calculated using the Margolies equation from the viscosity number measured in accordance with DIN EN ISO Test 1628.

10. ​ The polymer composition according to claim 2, wherein the graft copolymer of polyethylene and maleic anhydride contains maleic anhydride in an amount of more than 1% by weight and less than 4% by weight.

11. The polymer composition according to claim 2, 8, 9 or 10, wherein the graft copolymer of polyethylene and maleic anhydride is present in the polymer composition in an amount of 5% to 15% by weight.

12. The polymer composition according to any one of claims 1 to 11, wherein the high-density polyethylene particles have a volume median particle diameter of 70 microns to 210 microns.

13. The polymer composition according to any one of claims 1 to 12, wherein the high-density polyethylene particles are present in the composition in an amount of up to 50% by weight.

14. The polymer composition according to any one of claims 1 to 13, wherein the plasticizer comprises mineral oil, paraffinic oil, hydrocarbon, alcohol, ether, ester, or a mixture thereof.

15. The polymer composition according to any one of claims 1 to 14, wherein the high-density polyethylene has a molecular weight of more than 600,000 g / mol when calculated using the Margolies equation from the viscosity number measured in accordance with DIN EN ISO Test 1628.

16. The polymer composition according to claim 13, containing only a single high-density polyethylene polymer.

17. The polymer composition according to any one of claims 1 to 16, wherein the high-density polyethylene is a Ziegler-Natta catalyst high molecular weight polyethylene.

18. The polymer composition according to any one of claims 1 to 17, wherein the plasticizer comprises decalin, paraffin oil, white oil, mineral oil, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, octane, nonane, kerosene, toluene, naphthalene, tetralin, monochlorobenzene, camphene, methane, dipentene, methylcyclopentadiene, tricyclodecane, 1,2,4,5-tetramethyl-1,4-cyclohexadiene, or a mixture thereof.

19. The polymer composition according to any one of claims 1 to 18, which does not contain polypropylene.

20. A method for manufacturing a polymer article, Forming the polymer composition according to any one of claims 1 to 19 into a gel-like composition; Extruding the gel-like composition through a die to form a polymer article comprising: wherein the polymer article includes a film. Method.

21. Further comprising removing at least a portion of the plasticizer from the polymer article. The method according to claim 20.

22. An extraction solvent is added to the polymer composition during the method to facilitate removal of the plasticizer from the polymer article. The method according to claim 20 or 21.

23. The method according to claim 22, wherein the extraction solvent includes dichloromethane, acetone, chloroform, alkane, hexene, heptene, alcohol, or a mixture thereof.

24. A porous membrane comprising high-density polyethylene combined with a surface tension reducing additive, wherein the surface tension reducing additive includes a graft copolymer of polyethylene, the surface tension reducing additive includes a hydrophilic chemical group coupled to the high-density polyethylene, and the porous membrane presents a contact angle of less than 102° when measured against water. The porous membrane.

25. The porous membrane according to claim 24, wherein the graft copolymer of polyethylene is a graft copolymer of polyethylene and maleic anhydride.

26. The porous membrane according to claim 24 or 25, wherein the surface tension reducing additive is present in the membrane in an amount of 0.1% to 40% by weight.

27. The porous membrane according to any one of claims 24 to 26, the surface of which has been subjected to surface treatment.

28. The porous membrane according to claim 27, wherein the surface treatment includes plasma treatment.

29. The porous membrane according to claim 27, wherein the surface treatment includes corona discharge, electron beam treatment, gamma ray treatment, ultraviolet treatment, or steam treatment.

Images