Oxidized Porous Film

Abstract

Porous polymer films and fibers are disclosed that are subjected to oxygen plasma treatment without causing deterioration of mechanical properties. In one aspect, the plasma process can be a low pressure plasma process involving microwave discharge. Exposure time can be minimized to preserve physical properties. Porous polymer films made according to the present disclosure can show dramatically improved wicking properties when tested against electrolyte solutions, indicating a significant enhancement of ionic conductivity.

Description

[Background technology]

[0001] Polyethylene polymers have many and varied uses and applications. For example, high density polyethylenes are useful engineering plastics with a unique combination of abrasion resistance, surface smoothness, chemical resistance and impact strength. They find use in the manufacture of high strength fibers for use in ropes and ballistic molded articles, as well as in the manufacture of other drawn articles, such as membranes for electronic devices. However, the flowability of these materials in the molten state decreases as molecular weight increases, so processing by conventional techniques, such as by melt extrusion, is not always possible.

[0002]

[0002] One alternative method for producing fibers and other drawn components 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 oriented 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. For example, the films can be formed with micropores. Microporous polyethylene films formed through gel processing are particularly suitable for use as separators in batteries, such as lithium ion batteries, for example. The microporous film can separate the anode from the cathode to prevent short circuits between active battery components, for example. At the same time, the microporous film allows ions to pass through due to the porous nature of the material. The ion-permeable nature of the microporous polyethylene film makes the material particularly suitable for controlling the electrochemical reactions in batteries. Summary of the Invention [Problem to be solved by the invention]

[0004]

[0004] In view of the above, one of the important properties of lithium ion battery films is the compatibility between the membrane and the electrolyte. In this regard, the present disclosure is directed to improved methods of enhancing the wicking or soaking compatibility properties of films that may be incorporated into lithium ion batteries. The present disclosure is also directed to porous polymer films that exhibit improved ionic conductivity when positioned between the anode and cathode of an electronic device, such as a lithium ion battery. [Means for solving the problem]

[0005]

[0005] In general, the present disclosure is directed to a porous polymer film well suited for use in electronic devices. The porous polymer film may be used as an ion-permeable membrane located between an anode and a cathode. The porous polymer film is generally formed from one or more high density polyethylene polymers, which also have a high molecular weight. In accordance with the present disclosure, at least one surface of the porous polymer film is subjected to an oxygen plasma treatment that dramatically improves the ionic conductivity of the film, which may be demonstrated through an immersion test. The oxygen plasma treatment of the present disclosure is specifically configured to significantly improve ionic conductivity without causing a significant decrease in mechanical properties.

[0006] In one embodiment, the present disclosure is directed to an ion separator for separating an anode from a cathode. The ion separator includes a porous polymer film made from a high density polyethylene polymer. The polyethylene polymer can have a number average molecular weight greater than about 300,000 g / mol, such as greater than about 400,000 g / mol, such as greater than about 500,000 g / mol, and generally less than about 12,000,000 g / mol, such as less than about 6,000,000 g / mol, such as less than about 2,000,000 g / mol, such as less than about 1,200,000 g / mol, such as less than about 800,000 g / mol. The porous polymer film has a first surface and a second opposing surface. According to the present disclosure, at least the first surface of the porous polymer film is plasma oxidized to form polar groups attached to the high density polyethylene polymer. The polar groups enhance the porosity of the surface of the porous polymer film. The plasma oxidized polar groups are present on the first surface of the film in an amount sufficient to increase the wicking distance of the porous polymer film by more than about 50%, such as more than about 60%, such as more than about 70%, such as more than about 80%, such as more than about 90%, or even more than about 100%, when subjected to an immersion test and tested against propylene carbonate, compared to an identical porous polymer film that has not been plasma oxidized.

[0007] In one embodiment, both the first surface and the second surface of the porous polymer film may be plasma oxidized to form polar groups attached to the high density polyethylene polymer.

[0008] In one embodiment, a low pressure plasma process involving microwave discharge is used. The pressure in the plasma chamber can be, for example, less than about 10,000 pa, for example, less than about 5,000 pa, for example, less than about 500 pa, for example, less than about 200 pa, for example, less than about 150 pa, for example, less than about 100 pa, for example, less than about 30 pa during plasma treatment. The temperature can also be relatively low during plasma treatment. For example, the oxygen plasma process can be carried out at a temperature of less than about 60° C., for example, less than about 40° C., for example, less than about 35° C. It has been discovered that by simply exposing the porous polymer film to oxygen plasma for a relatively short amount of time using low pressure, the microwave plasma process can result in a significant and uniform improvement in ionic conductivity without deteriorating the mechanical properties of the film. In this regard, the first surface of the porous film can be subjected to oxygen plasma for an amount of time of less than about 60 seconds, for example, less than about 30 seconds, for example, less than about 20 seconds, for example, less than about 15 seconds, for example, less than about 10 seconds.

[0008]

[0009] During the plasma process, the porous polymer film may shrink in one direction by about 5% or less, for example about 3% or less, for example about 1% or less. In addition, the porous polymer film may be plasma oxidized without reducing the tensile strength of the film in one direction by more than about 10%, for example more than about 8%, for example more than about 5%. The plasma oxidized porous polymer film may have a tensile strength of, for example, more than about 70 MPa, for example more than about 100 MPa, for example more than about 120 MPa, for example more than about 155 MPa, for example more than about 160 MPa, for example more than about 162 MPa, for example more than about 164 MPa, for example more than about 166 MPa, for example more than about 168 MPa, for example more than about 170 MPa, and generally less than about 250 MPa. At a porosity of about 35% to about 38%, the porous polymer film has a pin puncture strength of greater than about 1000 mN / micron, e.g., greater than about 1200 mN / micron, e.g., greater than about 1450 mN / micron, and a compressibility of greater than about 175 gf / g / cm 2 For example, about 200 gf / g / cm 2 For example, about 225 gf / g / cm 2 For example, about 250 gf / g / cm 2At a porosity of about 38% to about 50%, the porous polymer film can have a pin puncture strength of greater than about 340 mN / micron and a pin puncture strength of greater than about 70 gf / g / cm 2 It has super high pin strength.

[0009]

[0010] The porous polymer film can also have a relatively small contact angle when tested against water.For example, the oxidizing plasma treatment can reduce the contact angle of the porous polymer film by more than about 15%, for example, more than about 25%, for example, more than about 35%, for example, more than about 45%, when measured against water, compared to the same porous polymer film that is not plasma oxidized.The porous polymer film can, for example, exhibit a contact angle of less than about 90°, for example, less than about 80°, for example, less than about 70°, when measured against water.

[0010]

[0011] The porous polymer film may be made primarily of one or more high density polyethylene polymers. The one or more high density polyethylene polymers may be included in the film in an amount of, for example, about 60% to about 99.5% by weight, such as about 80% to about 98% by weight. In one embodiment, the porous polymer film is made of a single high density polyethylene polymer and does not include any polypropylene polymer. The polyethylene polymer may be a Ziegler-Natta catalyzed high molecular weight polyethylene polymer. The porous polymer film may also be a monolayer porous polymer film that may optionally include a coating. Coatings that may be applied to the film include inorganic and / or polymeric coatings. The porous polymer film may be biaxially stretched.

[0011]

[0012] The present disclosure may be better understood with reference to the following drawings. [Brief description of the drawings]

[0012] [Figure 1]1 is an embodiment of an oxygen plasma process that may be used to treat porous polymeric films according to the present disclosure. [Diagram 2] FIG. 1 is a cross-sectional view of an electronic device, such as a battery, incorporating a porous membrane or film made according to the present disclosure.

[0013] Repeat use of reference characters in the present specification and in the drawings is intended to represent same or analogous features or elements of the invention.

[0014] definition The melt flow rate of a polymer or polymer composition is measured at 190° C. under a load of 21.6 kg in accordance with ISO Test 1133.

[0015] The density of the polymer is measured in g / cm according to ISO Test 1183. 3 It is measured in units of.

[0016] The average particle size (d50) is measured using laser diffraction / light scattering, for example a suitable HORIBA light scattering instrument.

[0016]

[0017] The average molecular weight of a polymer is determined using Margolies' formula.

[0018] Tensile modulus, tensile stress at yield, tensile strain at yield, tensile stress at 50% break, tensile stress at break and nominal tensile strain at break are all measured in accordance with ISO Test 527-2 / 1B.

[0017]

[0019] The half-width of the melting endothermic peak of the sample is measured by differential scanning calorimetry (DSC). An electronic balance is used to measure 8.4 g of sample. The sample is placed in an aluminum sample pan. An aluminum cover is attached to the pan, which is placed in the differential scanning calorimeter. The sample and the reference sample are held at 40°C for 1 minute, 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, while a nitrogen purge is performed at a flow rate of 20 mL / min. A baseline is drawn from 60°C to 150°C on 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.

[0018]

[0020] The crystallization half-time during isothermal crystallization at 123° C. can be determined from the time required for the amount of heat measured during isothermal crystallization measurement at 123° C. that corresponds to half the peak area in a differential scanning calorimetry (DSC) measurement. The test can be performed using a DSC Q2000 calorimeter available from TA Instruments.

[0019]

[0021] Contact angle measurements are performed on a Kruss DSA 100 instrument. Membrane samples (10 x 40 mm) are attached to a microscope slide using double-sided adhesive tape. Electrostatic charges are dissipated by moving the prepared sample through a U-electrode static discharger several times. The sample is placed in the measurement device and a 3.5 μl droplet of test fluid (water or ethylene glycol) is placed on the membrane. The contact angle is determined 7 seconds after droplet placement through the software (one measurement per second). These seven data points are averaged to yield the contact angle at the point of measurement. Each sample is measured at six different spots or positions on each side and all results are averaged into the reported value.

[0020]

[0022] An immersion test can be used to determine the wicking properties of membranes made according to the present disclosure, according to the following procedure.

[0023] For the immersion test, a glass vessel with the following dimensions is used: 20x10 cm upper area (covered with metal plate) / 19x8 cm lower area (bottom) / height: 10 cm). Two pieces of filter paper are taped inside the glass vessel. 300 ml of propylene carbonate are then filled into the vessel (fluid height: 2 cm). The vessel is covered with a metal plate and the propylene carbonate is allowed to fill the gas space for 20 minutes.

[0021]

[0024] The membrane is cut into pieces with scissors (length: 70 mm, width: 7 mm). This is done with nitrile gloves to avoid touching the membrane with bare hands. The pieces are mounted on an anodized metal plate (140 mm x 70 mm, frame width: 10 mm, inclination: 80°) with the help of a magnet. The MD direction of the membrane should point upwards (=direction of immersion).

[0022]

[0025] The metal frame with the fixed membrane is then moved through a deionizer 40 times to remove the static charge. The frame is then placed in a container filled with propylene carbonate at room temperature, and the membrane is immersed in the propylene carbonate for the desired time. The container is closed with a metal plate while the immersion is taking place. The different immersion distances of the membrane are measured every 30 minutes by taking a photograph and measuring the distance with a suitable computer program.

[0023]

[0026] The immersion distances of the tested membranes are compared to draw conclusions on their battery electrolyte compatibility.

[0027] Gurley permeability can be measured using a Gurley permeability tester, such as a Gurley Densometer, Model KRK 2060c, available from Kumagai Riki Kogyo Co., Ltd., in accordance with the Gurley Test. The test is conducted in accordance with ISO Test 5636. The Gurley Test measures air permeability as a function of time required for a specific amount of air to pass through a specific area under a specific pressure. Units are reported in seconds / 100 ml.

[0024]

[0028] The porosity (%) is measured according to the following procedure. During this procedure, the following ASTM Standards are used as references: D622 Standard Test Method for Apparent Density of Rigid Cellular Plastics1; and D729 Standard Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement1. The following instruments are used: Calibrated Analytical Balance (0.0001 grams); Lorentzen & Wettre Micrometer, code 251 (0.1 um); and Deli 2056 art knife.

[0025] procedure: 1.1. Samples and sample preparation Using a specimen art knife, cut each sample material into a minimum of three 60 mm±0.5×60 mm±0.5 specimens.

[0026] 1.2. Instruments and Measurements 3.2.1 Using an L&W micrometer, take five thickness readings on each 60 mm x 60 mm sample (average of the five readings). Record this value as the thickness of that sample.

[0027] 3.2.2 Weigh the sample directly on the balance. Record this value as the weight of this sample. 3.2.3 Mount three specimens of the same sample together and repeat step 3.2.1 and step 3.2.2 to obtain the [bulk] thickness and [bulk] weight. Calculate the density for the three important numbers as follows: aDfilm = density(film) = Sample weight THK * square D = density of the sample (mg / mm 3 ) Wt = weight of sample (mg) THK = sample thickness (mm) Square = sample area (mm 2 ) bD polymer = density (polymer) 0.95 (g / cm 3 ) D Polymer: Non-porous, raw material density c. Porosity = (1-D film / D polymer) * 100%

[0029] As used herein, the pin puncture strength is measured according to ASTM Test D3763 and measures the ability of a film to withstand foreign particles causing holes or defects. The test is performed in a testing apparatus, such as an Instron CEAST 9340 apparatus. The drop height is 0.03-1.10 m. The impact velocity is 0.77-4.65 m / sec. The maximum drop mass is 37.5 kg and the maximum potential energy is 405 J. The pin puncture strength is measured in slow velocity puncture mode at 1.67 mm / sec. The pin puncture strength can be normalized by dividing by the film thickness resulting in units of mN / micron.

[0028]

[0030] The heat shrinkage of the membrane is determined by placing a piece of membrane [3 in. x 3 in.] in an oven for 1 hour at 105° C. The shrinkage is calculated by measuring the size in MD and TD before and after heat treatment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029]

[0031] It will be understood by those skilled in the art that this discussion is a description of exemplary embodiments only and is not intended to limit the broader aspects of the disclosure.

[0032] In general, the present disclosure is directed to a porous polymer film made of a high density polyethylene polymer that has been subjected to oxygen plasma treatment on at least one surface of the film. The porous polymer film is particularly well suited for use as an ion separator in electronic devices, such as lithium ion batteries. These battery cells are filled with an electrolyte solution. The electrolyte solution typically contains an alkylene carbonate, such as propylene carbonate, in combination with a lithium compound, such as lithium hexafluorophosphate. The lithium compound is dissolved in the electrolyte solution. Although the porous polymer film made of a high density polyethylene polymer has excellent mechanical and porous properties, the film does not have a high affinity for polar electrolytes. This incompatibility leads to a time-consuming battery manufacturing process in which the porous polymer film made of a polyethylene polymer needs to be soaked with polar electrolytes. Incomplete electrolyte filling and poor compatibility between the porous polymer film and the electrolyte can lead to reduced performance, shortened life, high internal resistance, and reduced energy density of the battery. In this regard, the porous polymeric films of the present disclosure are subjected to an oxygen plasma treatment on at least one side which greatly enhances the affinity of the film's surface for polar electrolytes.

[0030]

[0033] In the past, those skilled in the art have proposed modifying the surface of polymer membranes to increase hydrophilicity through plasma methods. As described in Korean Patent No. 100349606, which is incorporated herein by reference, challenges have been experienced in using plasma to surface treat membranes. For example, KR'606 describes that due to the unique properties of the plasma itself, it is difficult to control the uniformity. Also, plasma is associated with various undesirable side reactions. In addition, plasma treatment has been found to physically damage the membrane. As described in KR'606, the result is a decrease in mechanical properties, making it difficult to manufacture separators with high levels of physical properties.

[0031]

[0034] However, the present disclosure is directed to an oxygen plasma treatment that not only greatly improves the compatibility of porous polymer films with electrolyte solutions and enhances ionic conductivity, but does so without adversely affecting the mechanical properties of the films.

[0032]

[0035] For example, in one embodiment, the plasma method of the present disclosure is carried out using microwave discharge. In addition, the method can be carried out at very low pressures and extremely short contact times to preserve the physical properties of the porous polymer film.

[0033]

[0036] One embodiment of a plasma process that may be used in accordance with the present disclosure is shown in Figure 1. With reference to Figure 1, the plasma process includes a microwave supply 50 in communication with a vacuum chamber 52 via a resonant cavity 53. The resonant cavity 53 may include or be associated with an impedance matching system. A substrate holder 54 is housed within the vacuum chamber 52. The vacuum chamber 52 is also associated with a pressure monitoring system 58.

[0034]

[0037] To apply a vacuum to the chamber 52, the chamber 52 may be placed in communication with a pump 56. The vacuum chamber 52 is also in communication with an exhaust system 60.

[0038] As shown in Figure 1, the vacuum chamber 52 may also be placed in fluid communication with one or more gas supplies. In the embodiment illustrated in Figure 1, three different gas supplies are shown at 62, 64 and 66. Each gas supply 62, 64 and 66 is placed in association with a corresponding mass flow rate controller 68, 70 and 72. The gas supplies 62, 64 and 66 are for supplying oxygen, either alone or in combination with other gases, to the vacuum chamber 52.

[0035]

[0039] As mentioned above, in one embodiment, a microwave plasma reactor is used to deliver oxygen plasma to the porous polymer film. Although other plasma reactors may be used according to the present disclosure, in one embodiment, a low pressure plasma system with microwave discharge is preferred. In the past, for example, an inductively coupled plasma system, which contains an RF generator, was typically used. However, the two reactors differ in many different aspects, including the conditions under which they are produced and the method applied. When using a microwave reactor, for example, the porous polymer film sample is placed outside the active plasma zone, while in an inductively coupled plasma reactor, the sample may be subjected to a significant amount of ion bombardment. Therefore, the flux of charged particles that reaches the sample may be very different between the two methods. In addition, it is believed that an inductively coupled plasma reactor can heat the substrate much faster than when used in a plasma reactor.

[0036]

[0040] During oxygen plasma treatment, the porous polymer film sample is placed into a vacuum chamber 52, which is evacuated using a pump 56. The plasma is then generated by a microwave supply 50 in association with one or more gases containing oxygen, which are supplied to the vacuum chamber 52. The source of oxygen may vary depending on the particular application. In one embodiment, pure oxygen gas is supplied to the vacuum chamber 52. However, in alternative embodiments, oxygen may be combined with other gases, such as inert gases. As an example, oxygen may be combined with nitrogen. In one embodiment, air is supplied to the plasma chamber 52. Other sources of oxygen include hydrogen peroxide, water (steam), nitrous oxide, ozone, and the like. In one embodiment, the gas supplied to the plasma chamber 52 contains more than about 20% oxygen by volume, such as more than about 30% oxygen by volume, such as more than about 50% oxygen by volume.

[0037]

[0041] During oxygen plasma treatment, ionized gas is formed, which contains a wide variety of different positive and negative ions and optionally free radicals, photons and neutral species. The ionized gas initiates a reaction on the surface of the porous polymer film, which ultimately modifies the surface chemistry. As an example, polyethylene polymer can be oxidized in the presence of oxygen. The plasma oxidized surface can contain a variety of different polar groups, which, as an example, enhances the porosity of the surface of the porous polymer film.

[0038]

[0042] During the plasma process, the conditions in the plasma chamber 52 may vary. In one embodiment, the oxygen plasma process is carried out at low pressure. For example, the pressure in the chamber may be maintained at less than 1 atmosphere. For example, the pressure in the chamber may be less than about 10,000 Pa, such as less than about 5,000 Pa, such as less than about 1,000 Pa, such as less than about 500 Pa, such as less than about 300 Pa, such as less than about 200 Pa. In one embodiment, the process is carried out at very low pressure, such as less than about 150 Pa, such as less than about 130 Pa, such as less than about 100 Pa, such as less than about 80 Pa, such as less than about 50 Pa, such as less than about 30 Pa. The temperature during the process may generally be less than about 60° C., such as less than about 50° C., such as less than about 40° C., such as less than about 30° C., such as less than about 28° C., such as less than about 25° C., and generally greater than about 15° C., such as greater than about 20° C.

[0039]

[0043] According to the present disclosure, the contact time between the porous polymer film and the oxygen plasma may be relatively short in one embodiment. For example, in one embodiment, each side of the porous polymer film may be exposed to the plasma for a time period of less than about 30 seconds, such as less than about 25 seconds, such as less than about 20 seconds, such as less than about 15 seconds, such as less than about 12 seconds, such as less than about 10 seconds, such as less than about 8 seconds, such as less than about 6 seconds. The contact time is generally greater than about 1 second, such as greater than about 2 seconds, such as greater than about 3 seconds. It has been discovered that extremely short contact times provide the necessary ionic conductivity without adversely affecting the physical properties of the film, especially when using microwave-generated plasma at low pressure.

[0040]

[0044] The porous polymer film made according to the present disclosure possesses excellent ionic conductivity properties in combination with excellent physical properties. The ionic conductivity properties can be demonstrated by testing the affinity of the film to an electrolyte solution, for example, in a soaking test that determines the film's ability to wick electrolyte fluid. For example, when subjected to a soaking test in propylene carbonate, the oxygen plasma treatment of the present disclosure can increase the wicking distance by more than about 50%, for example more than about 60%, for example more than about 70%, for example more than about 80%, for example more than about 90%, for example more than about 100%, compared to the same porous polymer film that is not plasma oxidized. The soaking distance of the film can vary depending on many factors, such as the porosity and pore size of the film.

[0041]

[0045] The porous polymer film can also have increased wettability.For example, the plasma oxidized film of the present disclosure can reduce the contact angle of the film by more than about 15%, for example, more than about 25%, for example, more than about 35%, for example, more than about 45% when measured against water compared to the same porous polymer film that is not plasma oxidized.The porous polymer film that has been subjected to the oxygen plasma process can, for example, exhibit a contact angle of less than about 90°, for example, less than about 80°, for example, less than about 70°, and generally more than about 20° when measured against water.

[0042]

[0046] In one embodiment, the above properties are obtained without substantially impairing the mechanical properties of the plasma oxidized porous polymer film.For example, the oxygen plasma process can reduce the tensile strength of the film in one direction by about 10% or less, for example about 8% or less, for example about 5% or less.In addition, the process can be controlled to prevent the film from shrinking.For example, the porous polymer film can be plasma oxidized without causing the film to shrink in one direction by more than about 5%, for example more than about 3%, for example more than about 1%.

[0043]

[0047] The porous membrane or film produced according to the present disclosure can generally have a thickness of more than about 5 microns, such as more than about 6 microns, such as more than about 7 microns, such as more than about 8 microns, such as more than about 9 microns, such as more than about 10 microns, such as more than about 11 microns. The thickness of the membrane or film is generally less than about 20 microns, such as less than about 16 microns, such as less than about 14 microns, such as less than about 12 microns, such as less than about 10 microns, such as less than about 8 microns.

[0044]

[0048] The membrane or film made according to the present disclosure can have excellent physical properties. For example, a membrane or film having a porosity of about 35% to about 38% can have a pin puncture strength of more than about 1,000 mN / micron, such as more than about 1,200 mN / micron, such as more than about 1,400 mN / micron, such as more than about 1,475 mN / micron, such as more than about 1,500 mN / micron, such as more than about 1,525 mN / micron, such as more than about 1,550 mN / micron, such as more than about 1,575 mN / micron, such as more than about 1,600 mN / micron, such as more than about 1,625 mN / micron, such as more than about 1,650 mN / micron, and generally less than about 3,000 mN / micron. The pin strength is about 200 gf / g / cm 2 For example, about 250 gf / g / cm 2 For example, about 252 gf / g / cm 2 For example, about 254 gf / g / cm 2 For example, about 256 gf / g / cm 2 For example, about 258 gf / g / cm 2 For example, about 260 gf / g / cm 2 For example, about 262 gf / g / cm 2 and generally around 300 gf / g / cm 2 It can be less than.

[0045]

[0049] At a membrane or film porosity of about 45% to about 50%, the membrane or film may have a pin puncture strength of greater than about 300 mN / micron, such as greater than about 340 mN / micron, for example greater than about 350 mN / micron, such as greater than about 360 mN / micron, for example greater than about 370 mN / micron, such as greater than about 380 mN / micron, for example greater than about 390 mN / micron, such as greater than about 400 mN / micron, and typically less than about 600 mN / micron, and generally less than about 60 gf / g / cm 2 For example, about 65 gf / g / cm 2 For example, about 72 gf / g / cm 2 For example, about 74 gf / g / cm 2 For example, about 76 gf / g / cm 2 For example, about 78 gf / g / cm 2 For example, about 80 gf / g / cm 2 For example, about 82 gf / g / cm 2 and generally around 150 gf / g / cm 2 The pin strength may be less than 1 / 2.

[0046]

[0050] The membrane or film made according to the present disclosure can also have excellent tensile strength properties in either the machine direction or the cross machine direction. For example, in either direction, the membrane or film can have a tensile strength of more than about 100 MPa, such as more than about 125 MPa, such as more than about 140 MPa, such as more than about 150 MPa, such as more than about 160 MPa, such as more than about 162 MPa, such as more than about 164 MPa, such as more than about 166 MPa, such as more than about 168 MPa, such as more than about 170 MPa, and generally less than about 250 MPa.

[0047]

[0051] Polymeric membranes or films made according to the present disclosure may have a thermal stability of more than about 105 sec / 100ml, such as more than about 150 sec / 100ml, for example more than about 200 sec / 100ml, such as more than about 225 sec / 100ml, for example more than about 250 sec / 100ml, such as more than about 275 sec / 100ml, for example more than about 300 sec / 100ml, such as more than about 325 sec / 100ml, for example more than about 350 sec / 100ml, such as more than about 375 sec / 100ml, e.g. For example, it may have a Gurley permeability of greater than about 400 sec / 100 ml, such as greater than about 425 sec / 100 ml, for example greater than about 450 sec / 100 ml, such as greater than about 475 sec / 100 ml, for example greater than about 500 sec / 100 ml, such as greater than about 525 sec / 100 ml, for example greater than about 550 sec / 100 ml, such as greater than about 575 sec / 100 ml, for example greater than about 600 sec / 100 ml, and typically less than about 1,000 sec / 100 ml.

[0048]

[0052] As noted above, the porous polymeric films made according to the present disclosure are formed from one or more high density polyethylene polymers. High density polyethylene has a density of about 0.93 g / cm 3 More than 0.94g / cm 3 More than 0.95g / cm 3 and generally has a density of about 1 g / cm 3 Less than about 0.96 g / cm 3 has a density of less than .

[0049]

[0053] High density polyethylene polymers can be made from greater than 90% ethylene derived units, such as greater than 95% ethylene derived units, or 100% ethylene derived units. The polyethylene can be a homopolymer or a copolymer, including terpolymers with other monomeric units.

[0050]

[0054] 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 polyethylene having a molecular weight of at least about 3×10 5"Margolies molecular weight" refers to a polyethylene composition having an average molecular weight in grams per mole, and as used herein is intended to include very high molecular weight polyethylene and ultra-high molecular weight polyethylene. For purposes of this specification, molecular weights referenced herein are determined according to the Margolies formula ("Margolies molecular weight").

[0051]

[0055] "Very high molecular weight polyethylene" is about 3 × 10 6 Less than 1×10 g / mol 6 In some embodiments, the molecular weight of the very high molecular weight polyethylene composition is greater than about 2×10 6 g / mol to about 3 × 10 6 between 0.01 and 0.15 g / mol.

[0052]

[0056] "Ultra-high molecular weight polyethylene" is at least about 3 × 10 6 In some embodiments, the molecular weight of the ultra high molecular weight polyethylene composition is about 3×10 6 g / mol to about 30×10 6 g / mol, or about 3×10 6 g / mol to about 20×10 6 g / mol, or about 3×10 6 g / mol to about 10 × 10 6 g / mol, or about 3×10 6 g / mol to about 6 × 10 6 g / mol.

[0053]

[0057] 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-methylpent-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, if present, the amount of non-ethylene monomer in the copolymer may be less than about 10 mol%, such as less than about 5 mol%, for example less than about 2.5 mol%, for example less than about 1 mol%, where mol% is based on the total moles of monomer in the polymer.

[0054]

[0058] In one embodiment, the high density polyethylene may have a monomodal 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 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 exhibit a broad molecular weight distribution such that the size exclusion or gel permeation chromatography curve does not exhibit at least two distinct peaks, but instead exhibits one distinct peak that is broader than the peaks of the individual components, due to the fact that it is composed of a blend of a higher molecular weight component and a lower molecular weight component.

[0055]

[0059] Polyethylene can be synthesized using any method known in the art. Polyethylene powder is typically produced by catalytic polymerization of ethylene monomer, or optionally with one or more other 1-olefin comonomers, using heterogeneous catalysts and organoaluminum or magnesium compounds as cocatalysts, such that the 1-olefin content in the final polymer is 10% or less of the ethylene content. Ethylene is usually polymerized in gas or slurry phase at relatively low temperatures and pressures. The polymerization reaction can be carried out at temperatures between 50° C. and 100° C., and pressures in the range of 0.02-2 MPa.

[0056]

[0060] The molecular weight of the polyethylene can be adjusted by adding hydrogen. Varying the temperature and / or the type and concentration of cocatalyst may also be used to fine-tune the molecular weight. In addition, the reaction may be carried out in the presence of antistatic agents to avoid fouling and product contamination.

[0057]

[0061] 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, with halides or esters of titanium, vanadium or chromium. Heterogeneous catalysts may be unsupported or supported on porous particulate materials, such as silica or magnesium chloride. Such supports may be added during the synthesis of the catalyst or may be obtained as a chemical reaction product of the catalyst synthesis itself.

[0058]

[0062] In one embodiment, a suitable catalyst system can be obtained by reaction of a titanium(IV) compound with a trialkylaluminum compound in an inert organic solvent at a temperature ranging from -40°C to 100°C, preferably from -20°C to 50°C. The concentrations of the starting materials are in the range of 0.1-9 mol / L, preferably 0.2-5 mol / L for the titanium(IV) compound and 0.01-1 mol / L, preferably 0.02-0.2 mol / L for the trialkylaluminum compound. The titanium component is added to the aluminum compound over a period of 0.1 min to 60 min, preferably 1 min to 30 min, and the molar ratio of titanium to aluminum in the final mixture is in the range of 1:0.01 to 1:4.

[0059]

[0063] In another embodiment, a suitable catalyst system is obtained by one-step or two-step reaction of titanium(IV) compound with trialkylaluminum compound in an inert organic solvent at a temperature ranging from -40°C to 200°C, preferably from -20°C to 150°C. In the first step, titanium(IV) compound is reacted with trialkylaluminum compound at a temperature ranging from -40°C to 100°C, preferably from -20°C to 50°C, using a molar ratio of titanium to alumina ranging from 1:0.1 to 1:0.8. The concentration of the starting materials is in the range of 0.1-9.1 mol / L, preferably 5-9.1 mol / L for titanium(IV) compound and 0.05-1 mol / L, preferably 0.1-0.9 mol / L for trialkylaluminum compound. The titanium component is added to the aluminum compound over a period of 0.1 min to 800 min, preferably 30 min to 600 min. In the second step, if applicable, the reaction product obtained in the first step is treated with a trialkylaluminum compound with a titanium to aluminum molar ratio in the range of 1:0.01 to 1:5 at a temperature in the range of -10°C to 150°C, preferably 10°C to 130°C.

[0060]

[0064] In yet another embodiment, a suitable catalytic system is obtained by a procedure in which, in a first reaction stage, magnesium alcoholate is reacted with titanium chloride in an inert hydrocarbon at a temperature between 50° C. and 100° C. In a second reaction stage, the reaction mixture formed is subjected to a heat treatment at a temperature between 110° C. and 200° C. for about 10 to 100 hours, accompanied by the release of alkyl chlorides, until no more alkyl chlorides are released, and then the solid is liberated from the soluble reaction products by washing several times with a hydrocarbon.

[0061]

[0065] In a further embodiment, silica supported catalysts may also be used, such as the commercially available catalyst system Sylopol 5917.

[0066] Using such catalytic systems, the polymerization is usually carried out in suspension, in one or several steps, continuous or batch, 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 between 0.05 MPa and 5 MPa. Trialkylaluminum, such as but not limited to isoprenylaluminum and triisobutylaluminum, is used as cocatalyst, such that the ratio of Al:Ti (cocatalyst 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 mixtures thereof. The molecular weight of the polymer is controlled through feeding hydrogen. The ratio of hydrogen partial pressure to ethylene partial pressure is in the range of 0 to 50, preferably in the range of 0 to 10. The polymer is isolated and dried under nitrogen in a fluidized bed dryer. The solvent can be removed through steam distillation if a high boiling point solvent is used. Salts of long chain fatty acids may be added as stabilizers. Typical examples are calcium stearate, magnesium stearate and zinc stearate.

[0062]

[0067] Optionally, other catalysts, such as Phillips catalysts, metallocenes and post-metallocenes, may be utilized. In general, cocatalysts, such as alumoxanes or alkylaluminum or alkylmagnesium compounds, are also utilized. Other suitable catalyst systems include Group 4 metal complexes of phenolate ether ligands.

[0063]

[0068] Polyethylene polymers that are particularly well suited for use in the present disclosure have a half-height width of the melting endothermic peak 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., as measured by differential scanning calorimetry, and typically have a half-height width of the melting endothermic peak less than about 9° C. The polyethylene polymer may also have a half-height crystallization time 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 typically have a half-height crystallization time less than about 12 minutes.

[0064]

[0069] According to the present disclosure, a high density polyethylene polymer is 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 according to DIN 53466. As an example, in one embodiment, the bulk density is generally about 0.4 g / cm. 3 Less than about 0.35 g / cm 3 Less than about 0.33 g / cm 3 Less than about 0.3 g / cm 3 Less than about 0.28 g / cm 3 Less than about 0.26 g / cm 3 The bulk density is generally less than about 0.1 g / cm 3 For example, about 0.15 g / cm 3 In one embodiment, the polymer has a density of about 0.2 g / cm 3 ~Approx. 0.27g / cm 3 It has a bulk density of

[0065]

[0070] In one embodiment, the polyethylene particles may be a free-flowing powder. The particles may have a volume median particle size (d50) of less than 200 microns. For example, the polyethylene particles may have a median particle size (d50) of 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 may be measured using laser diffraction according to ISO 13320.

[0066]

[0071] In one embodiment, 90% of the polyethylene particles can have a particle size less than about 250 microns. In another embodiment, 90% of the polyethylene particles can have a particle size less than about 200 microns, such as less than about 170 microns.

[0067]

[0072] The molecular weight of the polyethylene polymer may vary depending on the particular application. The polyethylene polymer may have, for example, an average molecular weight determined by the Margolies equation. The molecular weight may be determined by first measuring the viscosity number according to DIN EN ISO Test1628. The dry powder stream is measured using a 25 mm nozzle. The molecular weight is then calculated from the viscosity number using the Margolies 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 number 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 embodiment, 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.

[0068]

[0073] In one embodiment, the composition or film may comprise only a single polyethylene polymer. The single polyethylene polymer may have an average molecular weight of 500,000 g / mol or more, for example, greater than about 600,000 g / mol, and generally less than 2,500,000 g / mol, for example less than about 1,200,000 g / mol, for example less than about 900,000 g / mol, for example less than about 800,000 g / mol.

[0069]

[0074] The polyethylene may have a viscosity number of at least 100 mL / g, such as at least 500 mL / g, for example at least 550 mL / g, up to a viscosity number of less than about 6,000 mL / g, such as less than about 5,000 mL / g, for example less than about 4000 mL / g, for example less than about 3,000 mL / g, for example less than about 1,000 mL / g, determined according to ISO 1628 part 3 using a concentration in decahydronaphthalene of 0.0002 g / mL.

[0070]

[0075] The high density polyethylene may have a crystallinity of at least about 40% to 85%, such as 45% to 80%. In one embodiment, the crystallinity may be greater than about 50%, such as greater than about 55%, such as greater than about 60%, such as greater than about 65%, such as greater than about 70%, and generally less than about 80%.

[0071]

[0076] When combined with plasticizer in forming porous film or membrane, high density polyethylene particles are present in the polymer composition in an amount of up to about 50% by weight.For example, high density polyethylene particles can be present in the polymer composition in an amount of less than about 45% by weight, such as less than about 40% by weight, such as less than about 35% by weight, such as less than about 30% by weight, such as less than about 25% by weight, such as less than about 20% by weight, such as less than about 15% by weight.Polyethylene particles can be present in the composition in an amount of more than about 5% by weight, such as more than about 10% by weight, such as more than about 15% by weight, such as more than about 20% by weight, such as more than about 25% by weight.

[0072]

[0077] During gel processing, the plasticizer is combined with the 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% by weight, such as greater than about 60% by weight, such as greater than about 65% by weight, such as greater than about 70% by weight, such as greater than about 75% by weight, such as greater than about 80% by weight, such as greater than about 85% by weight, such as greater than about 90% by weight, such as greater than about 95% by weight, such as greater than about 98% by weight, such as greater than about 99% by weight, such as greater than about 99.5% by weight.

[0073]

[0078] In one aspect, the porous polymer film can be made exclusively of one or more high density polyethylene polymers. In an alternative embodiment, one or more surface tension reducing agents can be combined with the polyethylene polymer to further improve the wetting properties of the article made from the composition. The surface tension reducing additive that can be used according to the present disclosure generally includes any suitable additive that can be melt processed with high density polyethylene particles and reduce the surface tension of the article made from the polymer composition. The surface tension reducing additive can be, for example, a hydrophilic inorganic filler, a hydrophilic organic polymer particle, a hydrophilic chemical agent that forms functional hydrophilic chemical groups on the polymer, or a combination thereof.

[0074]

[0079] In one embodiment, 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, a 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 embodiment, a carboxyl-containing unsaturated monomer can be grafted to the polyolefin polymer, such as a polyethylene polymer. The carboxyl-containing unsaturated monomer can be, for example, maleic anhydride.

[0075]

[0080] For example, in one embodiment, the surface tension reducing additive may be a polyethylene polymer functionalized with maleic anhydride. The polyethylene polymer may be the same as or different from the high density polyethylene polymer combined with the surface tension reducing additive. For example, the polyethylene polymer functionalized with maleic anhydride may be a low density polyethylene polymer, such as a linear low density polyethylene polymer. Alternatively, the polyethylene polymer functionalized with maleic anhydride may be a high density polyethylene polymer. The high density polyethylene polymer may 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 generally less than about 2,500,000 g / mol.

[0076]

[0081] The maleic anhydride-functionalized polyethylene can generally contain maleic anhydride in an amount greater than about 1.5% by weight, such as greater than about 1.8% by weight, such as greater than about 2% by weight, such as greater than about 2.5% by weight, such as greater than about 3% by weight, such as greater than about 3.5% by weight, such as greater than about 4% by weight, such as greater than about 4.5% by weight. The maleic anhydride-functionalized polyethylene can generally contain maleic anhydride in an amount less than about 20% by weight, such as less than about 10% by weight, such as less than about 8% by weight, such as less than about 5% by weight. The maleic anhydride-functionalized polyethylene can be in the form of a powder or particles that are combined or compounded with high density polyethylene particles.

[0077]

[0082] 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 may also be an ethylene acrylic acid copolymer. The ethylene acrylic acid copolymer may generally have an acrylic acid content of more than 5% by weight, such as more than about 8% by weight, such as more than about 10% by weight, and may generally have an acrylic acid content of less than about 30% by weight, such as less than about 20% by weight, such as less than about 15% by weight, such as less than about 12% by weight.

[0078]

[0083] The surface tension reducing additive may be any suitable acrylate polymer and / or graft copolymer containing an olefin. An olefin polymer, such as polyethylene, may serve as the graft base and may be grafted to at least one vinyl polymer or one ether polymer.

[0079]

[0084] Examples of such surface tension reducing additives include ethylene-acrylic acid copolymers, ethylene-maleic anhydride copolymers, ethylene-alkyl (meth)acrylate-maleic anhydride terpolymers, ethylene-alkyl (meth)acrylate-glycidyl (meth)acrylate terpolymers, ethylene-acrylic ester-methacrylic acid terpolymers, ethylene-acrylic ester-maleic anhydride terpolymers, ethylene-methacrylic acid-alkali metal salt of methacrylic acid (ionomer) terpolymers, and the like. In one embodiment, examples of the surface tension reducing additives include random terpolymers of ethylene, methyl acrylate, and glycidyl methacrylate. The terpolymers may have a glycidyl methacrylate content of about 5% to about 20%, for example about 6% to about 10%. The terpolymers may have a methyl acrylate content of about 20% to about 30%, for example about 24%.

[0080]

[0085] The surface tension reducing additive may be a linear or branched homopolymer or copolymer (e.g., random, graft, block, etc.) containing epoxy functional groups, such as terminal epoxy groups, backbone oxirane units, and / or pendant epoxy groups. As an example, the surface tension reducing additive may be a copolymer including at least one monomeric component that includes epoxy functional groups. The monomeric units of the surface tension reducing additive may vary. For example, the surface tension reducing additive may include an epoxy functional methacrylic monomeric unit. As used herein, the term "(meth)acrylic" generally refers to both acrylic and methacrylic monomers, as well as salts and esters thereof, such as acrylate and methacrylate monomers. Epoxy functional (meth)acrylic monomers that may be incorporated into the surface tension reducing additive include, but are not limited to, those containing 1,2-epoxy groups, such as glycidyl acrylate and glycidyl methacrylate. Other suitable epoxy functional monomers include allyl glycidyl ether, glycidyl ethacrylate, and glycidyl itaconate.

[0081]

[0086] 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 with one or more methyl, ethyl, or propyl substituents; 1-hexene with one or more methyl, ethyl, or propyl substituents; 1-heptene with one or more methyl, ethyl, or propyl substituents; 1-octene with one or more methyl, ethyl, or propyl substituents; 1-nonene with one or more methyl, ethyl, or propyl substituents; ethyl, methyl, or dimethyl-substituted 1-decene; 1-dodecene; and styrene.

[0082]

[0087] In one embodiment, the surface tension reducing additive may be a terpolymer containing epoxy functionality. By way of example, the surface tension reducing additive may include a methacrylic component containing epoxy functionality, an α-olefin component, and a methacrylic component without epoxy functionality. For example, the surface tension reducing additive may be poly(ethylene-co-methacrylate-co-glycidyl methacrylate), which has the structure:

[0083] [ka]

[0084] (wherein a, b and c are 1 or more). has.

[0088] In another embodiment, the surface tension reducing additive can be a random copolymer of ethylene, ethyl acrylate, and maleic anhydride, having the structure:

[0085] [ka]

[0086] (wherein x, y and z are 1 or greater). has.

[0089] The relative proportions of the various monomer components of the copolymer surface tension-reducing additive are not particularly limited. For example, in one embodiment, the epoxy-functional methacrylic monomer component can form about 1 wt.% to about 25 wt.%, or about 2 wt.% to about 20 wt.% of the copolymer surface tension-reducing additive. The α-olefin monomer can form about 55 wt.% to about 95 wt.%, or about 60 wt.% to about 90 wt.% of the copolymer surface tension-reducing additive. When utilized, the other monomer components (e.g., non-epoxy functional methacrylic monomers) can comprise about 5 wt.% to about 35 wt.%, or about 8 wt.% to about 30 wt.% of the copolymer surface tension-reducing additive.

[0087]

[0090] The molecular weight of the surface tension-reducing additives can vary widely. For example, the surface tension-reducing additives can have a number average molecular weight of about 7,500 to about 250,000 grams per mole, in some embodiments about 15,000 to about 150,000 grams per mole, and in some embodiments about 20,000 to 100,000 grams per mole, with a polydispersity index typically ranging from 2.5 to 7.

[0088]

[0091] In yet another embodiment, the surface tension reducing additive may be a surfactant that is melt processable with the high density polyethylene resin. For example, the surfactant may be a non-ionic surfactant in the form of a solid 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 may be made from linear, saturated, C10-C28, e.g., C16-C18 fatty alcohols. For example, the surfactant may be a reaction product of a fatty alcohol with ethylene oxide. The surfactant may contain a degree of ethoxylation of more than about 8 mol, e.g., more than about 10 mol, e.g., more than about 20 mol, e.g., more than about 30 mol, e.g., more than about 40 mol, and generally less than about 100 mol, e.g., less than about 80 mol, e.g., less than about 60 mol.

[0089]

[0092] 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, has a viscosity of about 85 μm. 2 / g, e.g., about 90m 2 / g, e.g., about 100m 2 / g and typically has a BET surface area of ​​about 500 m 2 / g, e.g., about 200m 2 / g.

[0090]

[0093] The hydrophilic inorganic fillers may generally have a D50 particle size of less than about 30 microns, such as less than about 20 microns, for example less than about 15 microns, for example less than about 10 microns, and may generally have a D50 particle size of more than about 0.1 microns, such as 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.

[0091]

[0094] 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 formation of the polymer to increase the wetting properties of the resulting article. The hydrophilic chemical agent can, for example, be chemically grafted to the polyethylene polymer with functional chemical groups that increase the polarity of the polymer. Alternatively, the hydrophilic chemical agent can undergo chemical reactions with other polar molecules on the polyethylene polymer to reduce the surface tension.

[0092]

[0095] In one aspect, by way of 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. By way of example, the organic acid anhydride may 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 may include acrylic acid that contacts and bonds with the polyethylene polymer in molten form.

[0093]

[0096] For example, in one embodiment, the surface tension reducing additive can include a polyethylene polymer grafted with acrylic acid. The amount of acrylic acid grafted to the polyethylene polymer can generally be more than about 0.5% by weight, for example more than about 1% by weight, for example more than about 2% by weight, and generally less than about 25% by weight, for example less than about 15% by weight, for example less than about 10% by weight, for example less than about 8% by weight. The acrylic acid grafted polyethylene polymer can then be combined with an unmodified or ungrafted high density polyethylene polymer to form a porous polymer film. The resulting film can contain acrylic acid groups in an amount of more than about 0.01% by weight, for example more than about 0.1% by weight, for example more than about 0.5% by weight, for example more than about 2% by weight, and generally less than about 15% by weight, for example less than about 10% by weight.

[0094]

[0097] In one embodiment, once the acrylic acid is grafted to the polyethylene polymer, the acrylic acid can be saponified. Saponification can occur on the polymer resin or polymer particles, or can occur after the article is formed. In one aspect, the acrylic acid groups can be saponified by contacting the acrylic acid groups with a base, for example, sodium hydroxide.

[0095]

[0098] The grafted polyethylene polymer can be in the form of particles, optionally blended with non-modified high density polyethylene polymer particles.The particles can have an average particle size by volume (d50), for example, less than about 400 microns, for example less than about 300 microns, for example less than about 200 microns, for example less than about 170 microns, for example less than about 150 microns, for example less than about 125 microns.The average particle size can be greater than about 20 microns, for example greater than about 30 microns, for example greater than about 40 microns, for example greater than about 50 microns.

[0096]

[0099] In forming a porous polymeric film in accordance with the present disclosure, high density polyethylene particles are combined with a plasticizer and then gel extruded.

[0100] The plasticizer may include, for example, a hydrocarbon oil, an alcohol, an ether, an ester, such as a diester, or a mixture thereof. For 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 an 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 mixtures and combinations of any of the above.

[0097]

[0101] The plasticizer is generally present in the composition used to form the polymeric article in an amount greater than about 50% by weight, such as greater than about 55% by weight, such as greater than about 60% by weight, such as greater than about 65% by weight, such as greater than about 70% by weight, such as greater than about 75% by weight, such as greater than about 80% by weight, such as greater than about 85% by weight, such as greater than about 90% by weight, such as greater than about 95% by weight, such as greater than about 98% by weight. In fact, the plasticizer can be present in an amount up to about 99.5% by weight.

[0098]

[0102] The high density polyethylene particles are blended with a plasticizer to form a homogenous gel-like material.

[0103] To form a polymer article according to the present disclosure, high density polyethylene particles are combined with a plasticizer and extruded through a die of a desired shape. In one embodiment, the composition can be heated in the 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 particle mixture form a homogenous gel-like material, which is then allowed to form a polymer article with little to no impurities.

[0099]

[0104] In one embodiment, the stretched article is formed during a gel spinning or extrusion process. The polymer article may be in the form of, for example, a fiber or a film, such as a membrane.

[0100]

[0105] During the process, at least a portion of the plasticizer is removed from the final product. The process 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, for example, a hydrocarbon solvent. One example of an extraction liquid is, for example, dichloromethane. Other extraction liquids include acetone, chloroform, alkanes, hexenes, heptenes, alcohols, or mixtures thereof.

[0101]

[0106] If desired, the resulting polymeric article may be stretched at an elevated temperature below the melting point of the polyethylene polymer to enhance strength and elasticity. Suitable temperatures for stretching are within the range of about ambient temperature to about 155°C. The stretch 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 stretch 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 stretch 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 stretch ratio is used, such as from about 4 to about 10. The polymeric article may be stretched uniaxially or biaxially.

[0102]

[0107] The polymeric articles made according to the present disclosure have numerous uses and applications. For example, in one embodiment, a method is used to make a membrane. The membrane or film can be used, for example, as a battery separator. Alternatively, the membrane can be used as a microfilter. When making fibers, the fibers can be used to make non-woven fabrics, ropes, nets, etc. In one embodiment, the fibers can be used as a filler material in bulletproof clothing.

[0103]

[0108] Referring to FIG. 2, an embodiment of a lithium-ion battery 10 made according to the present disclosure is shown. The battery 10 comprises an anode 12 and a cathode 14. The anode 12 can be made of lithium metal, for example. The cathode 14, on the other hand, can be made of sulfur or intercalated lithium metal oxide. According to the present disclosure, the battery 10 further comprises a porous membrane 16, or separator, disposed between the anode 12 and the cathode 14. The porous membrane 16 minimizes electrical shorts between the two electrodes while allowing the passage of ions, for example lithium ions. As shown in FIG. 2, 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 may be an inorganic coating, for example, made of aluminum oxide or titanium oxide. Alternatively, the single layer polymer membrane may also include a polymer coating. The coating may provide enhanced heat resistance.

[0104]

[0109] The polymeric compositions and articles made according to 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.

[0105]

[0110] In one embodiment, a heat stabilizer may be present in the composition, including but not limited to a phosphite, an amine antioxidant, a phenolic antioxidant, or any combination thereof.

[0106]

[0111] In one embodiment, an antioxidant may be present in the composition, including, but not limited to, secondary aromatic amines, benzofuranones, sterically hindered phenols, or any combination thereof.

[0107]

[0112] In one embodiment, a light stabilizer may be present in the composition.The light stabilizer may include, but is not limited to, 2-(2'-hydroxyphenyl)-benzotriazole, 2-hydroxy-4-alkoxybenzophenone, nickel-containing light stabilizer, 3,5-di-tert-butyl-4-hydroxybenzoate, sterically hindered amines (HALS), or any combination thereof.

[0108]

[0113] In one embodiment, a UV absorber may be present in the composition instead of or in addition to the light stabilizer, including but not limited to benzotriazoles, benzoates, or combinations thereof or any combination thereof.

[0109]

[0114] In one embodiment, a halogenated flame retardant may be present in the composition, including, but not limited to, tetrabromobisphenol A (TBBA), tetrabromophthalic anhydride, decachloropentacyclooctadecadiene (dechlorane), hexabromocyclodedecane, chlorinated paraffins, or any combination thereof.

[0110]

[0115] In one embodiment, non-halogenated flame retardants may be present in the composition, including, but not limited to, resorcinol diphosphate tetraphenyl ester (RDP), ammonium polyphosphate (APP), phosphinic acid derivatives, triaryl phosphates, trichloropropyl phosphate (TCPP), magnesium hydroxide, aluminum trihydroxide, and antimony trioxide.

[0111]

[0116] In one embodiment, a lubricant may be present in the composition, including but not limited to silicone oil, wax, molybdenum disulfide, or any combination thereof.

[0112]

[0117] In one embodiment, colorants may be present in the composition. Colorants include, but are not limited to, inorganic and organic based color pigments.

[0118] In one embodiment, an acid scavenger can be present in the polymer composition. The acid scavenger can include, for example, an alkali metal salt or an alkaline earth metal salt. The salt can include a salt of a fatty acid, such as a stearate salt. Other acid scavengers include carbonates, oxides, or hydroxides. Specific acid scavengers that can 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.

[0113]

[0119] 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 may be present 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 all wt.% of the components utilized in the polymer composition, including any additives, if present, equals 100 wt.%.

[0114]

[0120] After the porous polymer film is formed according to the present disclosure and optionally subjected to a stretching process, the film is exposed to the oxygen plasma process described above. In one embodiment, only one side of the film is subjected to the oxygen plasma treatment. In an alternative embodiment, each side of the film may be subjected to the oxygen plasma treatment.

[0115]

[0121] The present disclosure may be better understood with reference to the following examples, which are offered below by way of illustration and not by way of limitation. The following experiments were performed to demonstrate some of the benefits and advantages of the present invention. EXAMPLES

[0116] Example 1

[0122] Porous polymer films were prepared and subjected to oxygen plasma treatment according to the present disclosure. The films were tested for wicking distance and wettability and compared to films that were not subjected to oxygen plasma treatment.

[0117]

[0123] A single high density polyethylene polymer was used to produce the film. The polyethylene polymer had a molecular weight of 600,000 g / mol and an average particle size (d50) of 115 microns. The polyethylene polymer had a viscosity of 950 kg / m 3 and had a melt flow rate of 1.1 g / 10 min.

[0118]

[0124] Polyethylene polymer was combined with a plasticizer and conventionally formed into a porous polymer film via gel extraction, biaxial stretching and solvent extraction. The extracted gel composition had a solid content of 30 wt.% resin in paraffin oil. Gel extraction was carried out at a temperature of 190°C to 240°C and a screw speed of 200 rpm. After extraction, the resulting porous polymer film was solidified on a chill roller set at 40°C. Stretching was carried out at a temperature of 120°C in a 7x7 ratio (MD / TD). Extraction of the stretched film was carried out in acetone. The porous polymer film was annealed at 130°C for 10 minutes.

[0119]

[0125] Samples of the porous polymer film described above were then subjected to an oxygen plasma process in accordance with the present disclosure. One film was produced in which it was subjected to oxygen plasma treatment on one side. Another sample was produced in which both sides of the film were subjected to oxygen plasma treatment.

[0120]

[0126] The film was then subjected to the above-mentioned immersion test with propylene carbonate. A film that was not subjected to plasma treatment was also tested. The following results were obtained:

[0121] [Table 1]

[0122]

[0127] As shown above, subjecting the porous polymer film to oxygen plasma treatment increased the wicking distance by more than 100%, exhibiting a wicking distance of more than 10 mm (and generally less than 30 mm). When both sides of the film were treated, the wicking distance increased by more than 225%. In addition, there was no noticeable deterioration in mechanical properties. The film was found to have mechanical properties within the above ranges.

[0123]

[0128] The above samples No. 1 and No. 2 were also tested for contact angle with water. The plasma treated samples were subjected to plasma treatment for different time periods to determine the effect. Specifically, samples were prepared in which the plasma treatment lasted for 5 seconds, 10 seconds, 30 seconds or 60 seconds. The following results were obtained:

[0124] [Table 2]

[0125]

[0129] As shown above, the contact angle of the plasma-treated sample was more than 50% smaller than that of the untreated sample. Also as shown above, the exposure time did not have any significant effect on the contact angle. However, the exposure time may affect the physical properties of the film and may cause the film to shrink. Thus, in one aspect, the present disclosure is directed to producing plasma oxidized films that had an exposure time of less than about 30 seconds, such as less than about 20 seconds, such as less than about 10 seconds, or even less than about 5 seconds.

[0126]

[0130] These and other modifications and variations to the present invention may be practiced by those skilled in the art without departing from the spirit and scope of the present invention, as more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchangeable, both in whole or in part. Furthermore, those skilled in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention as further set forth in such appended claims.

Claims

1. An ion separator that separates the anode from the cathode, Equipped with a porous polymer film, The porous polymer film has a number-average molecular weight of more than 300,000 g / mol The porous polymer film comprises a high-density polyethylene polymer, and the porous polymer film has a first surface and Having a second opposite surface, at least the first surface of the porous polymer film The porous polymer film is plasma-oxidized at a pressure of less than 10,000 Pa to form polar groups that enhance the polarity of the surface of the porous polymer film, which are bonded to the high-density polyethylene polymer. Here, the plasma-oxidized polar group is subjected to an immersion test and propylene carbonate When tested against the same porous polymer film that has not been plasma-oxidized, They are present in amounts exceeding 50% in total, sufficient to increase the wicking distance of the porous polymer film. The aforementioned ion separator.

2. The ion separator according to claim 1, wherein the porous polymer film exhibits a contact angle of less than 90° when measured against water.

3. The plasma-oxidized polar group was subjected to an immersion test against propylene carbonate. The ion separator according to claim 1, which, when tested, is present on the porous polymer film in an amount sufficient to increase the wicking distance by more than 70% compared to the same porous polymer film that has not been plasma-oxidized.

4. When the plasma-oxidized polar group is measured against water, the plasma-oxidized The ion separator according to claim 1, wherein the ion separator is present on the porous polymer film in an amount sufficient to reduce the contact angle of the porous polymer film by more than 15% compared to an identical porous polymer film without the ion separator.

5. The ion separator according to claim 1, wherein the porous polymer film is plasma-oxidized without causing a shrinkage of more than 5% of the film.

6. The ion separator according to claim 1, wherein the porous polymer film is plasma-oxidized without causing a decrease of more than 10% in the unidirectional tensile strength of the film.

7. The ion separator according to claim 1, wherein the high-density polyethylene is Ziegler-Natta catalyst high molecular weight polyethylene.

8. The ion separator according to claim 1, wherein the porous polymer film has a thickness of 4 microns to 25 microns and a porosity of 20% to 50%.

9. The ion separator according to claim 1, wherein the high-density polyethylene polymer is present in the porous film in an amount of 60% to 99% by weight.

10. The ion separator according to claim 1, wherein the high-density polyethylene has a molecular weight greater than 400,000 g / mol and less than 12,000,000 g / mol.

11. The ion separator according to claim 1, wherein the high-density polyethylene has a molecular weight greater than 400,000 g / mol and less than 1,200,000 g / mol.

12. The ion separator according to claim 1, which is a single-layer polymer porous film that may optionally include a coating.

13. The single-layer polymer porous film includes a coating, and the coating is inorganic Ion separator according to claim 12, comprising a coating or polymer coating 。

14. The ion separator according to claim 1, wherein the porous polymer film does not contain polypropylene.

15. The porous polymer film has a porosity of 35% to 38%, a puncture strength of over 1000 mN / micron, and a puncture strength of 200 gf / g / cm². ２ An ion separator according to claim 1, having ultra-high pin strength.

16. The ion separator according to claim 1, wherein the porous polymer film has a porosity of 38% to 50%, a puncture strength of more than 300 mN / micron, and a pin strength of more than 70 gf / g / cm².

17. The ion separator according to claim 1, wherein the porous polymer film is biaxially stretched.

18. The ion separator according to claim 1, wherein the porous polymer film has a tensile strength of more than 100 MPa and less than 250 MPa.

19. The second surface of the porous polymer film is also plasma-oxidized, and the high-density polymer The ion separator according to claim 1, wherein polar groups are formed by bonding to a polyethylene polymer.

20. A method for producing an ion separator according to any one of claims 1 to 19, The method wherein the first surface of the porous film is subjected to an oxidizing plasma for less than 30 seconds.

21. The first surface of the porous film is subjected to an oxygen plasma accompanied by microwave discharge. A method for producing an ion separator according to any one of claims 1 to 19.

22. A method for producing an ion separator according to any one of claims 1 to 19, wherein the first surface of the porous film is subjected to an oxygen plasma at a temperature of less than 60°C and a pressure of less than 10,000 Pa.

23. The ion separator according to claim 10, wherein the high-density polyethylene has a molecular weight greater than 500,000 g / mol and less than 12,000,000 g / mol.

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