Foam containing a blend of silicone-functionalized polyethylene and low-density polyethylene

Abstract

According to various embodiments, a microcellular foam is provided, the microcellular foam comprising a polymer blend, the polymer blend comprising 70-95 wt% low-density polyethylene (LDPE) and 5-30 wt% polydimethylsiloxane-grafted LDPE (PDMS-g-LDPE), wherein the microcellular foam has an average cell size of less than 60 μm.

Description

[Technical Field]

[0001] Embodiments of this disclosure generally relate to ethylene polymer foams, and more particularly to foams produced using silicone-functionalized polyethylene and low-density polyethylene. [Background technology]

[0002] Conventional thermoplastic foams utilize low-density polyethylene (LDPE) due to their good processability and mechanical properties. However, there is now a need to produce lighter thermoplastic foams without sacrificing mechanical or electrical properties, and without increasing the volume of the foaming process. [Overview of the Initiative]

[0003] This disclosure satisfies this need by producing foams having polydimethylsiloxane-grafted LDPE (PDMS-g-LDPE) and polymer blends of LDPE, wherein the incorporation of PDMS provides an improved foam expansion ratio and smaller cell size within the foam. The improved expansion ratio can result in weight reduction (i.e., less material is required to obtain the same thickness), while the smaller cell size at similar foam density can improve mechanical properties such as compressive and tensile strength.

[0004] According to one embodiment of the present disclosure, a microporous foam is provided. The microporous foam comprises a polymer blend comprising 70-95% by weight of low-density polyethylene (LDPE) and 5-30% by weight of polydimethylsiloxane-grafted LDPE (PDMS-g-LDPE), and the microporous foam has a bubble size of less than 60 μm.

[0005] Another embodiment of the present disclosure provides a method for producing a microporous foam. The method includes producing a polymer blend by mixing 70-95% by weight of low-density polyethylene (LDPE) and 5-30% by weight of polydimethylsiloxane-grafted LDPE (PDMS-g-LDPE); introducing the polymer blend into a batch foaming unit at a temperature of at least 75°C and a pressure of at least 1000 psig in the presence of a physical foaming agent; and reducing the pressure of the immersed polymer blend to produce a microporous foam having an average bubble size of less than 60 μm.

[0006] These embodiments and other embodiments will be described in more detail in the following embodiments for carrying out the invention. [Brief explanation of the drawing]

[0007] [Figure 1] The melt strength of the samples according to the embodiments disclosed and described herein is shown graphically. [Figure 2A] These are micrographs showing the bubble sizes of samples and comparative samples according to the embodiments disclosed and described herein. [Figure 2B] These are micrographs showing the bubble sizes of samples and comparative samples according to the embodiments disclosed and described herein. [Figure 2C] These are micrographs showing the bubble sizes of samples and comparative samples according to the embodiments disclosed and described herein. [Figure 2D] These are micrographs showing the bubble sizes of samples and comparative samples according to the embodiments disclosed and described herein. [Modes for carrying out the invention]

[0008] Herein, specific embodiments of this application are described. However, this disclosure may be embodied in different forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure may be thorough and complete and so as to convey the scope of the subject matter to those skilled in the art.

[0009] Definition Any reference to the Periodic Table of the Elements shall be a reference to the Periodic Table of the International Union of Pure and Applied Chemistry (IUPAC).

[0010] The numerical ranges disclosed herein include all values from the lower limit to the upper limit, including the upper and lower limits. In the case of a range that includes explicit values (e.g., 1 or 2, or 3 - 5, or 6, or 7), any sub-range between any two explicit values is included (e.g., the range of 1 - 7 above includes sub-ranges such as 1 - 2, 2 - 6, 5 - 7, 3 - 7, 5 - 6, etc.).

[0011] Unless otherwise stated, not implied from the context, or not customary in the art, all parts and percentages are by weight, and all test methods are the latest as of the filing date of this disclosure.

[0012] The term "composition" refers to a mixture of materials that includes the composition, as well as reaction products and decomposition products formed from the materials of the composition.

[0013] The terms "comprising", "including", "having", and their derivatives are not intended to exclude the presence of any additional components, steps, or procedures, whether or not specifically disclosed. In contrast, the term "consisting essentially of" excludes any other components, steps, or procedures, except those that are not essential for operability, from the scope of any subsequent detailed description. The term "consisting of" excludes any component, step, or procedure not specifically described or listed. The term "or" refers to the listed items individually and in any combination, unless otherwise specified. The use of the singular form includes the use of the plural form, and vice versa.

[0014] The term "polymer" refers to a polymer compound prepared by polymerizing the same type or different types of monomers that provide the plurality of and / or repeating "units" constituting the polymer in a polymerized form. Thus, the general term "polymer" includes the term "homopolymer", which is usually used to refer to a polymer prepared from only one type of monomer, as well as "copolymer", which refers to a polymer prepared from two or more different monomers. Polymers are often said to be "made of" one or more specific monomers, "based on" a specific monomer or monomer type, and "containing" a specific monomer content, etc. It should be noted that in this context, the term "monomer" is understood to refer to the polymerized residue of a specific monomer.

[0015] As used herein, the term "blend" or "polymer blend" refers to a mixture of two or more polymers. The blend may or may not be miscible (not phase-separated at the molecular level). The blend may or may not be phase-separated. The blend can be achieved by physically mixing two or more polymers at the macro level (e.g., melt blend resin or compounding) or at the micro level (e.g., simultaneous molding in the same reactor).

[0016] "Polyethylene," "ethylene polymer," or "ethylene-based polymer" means a polymer containing units derived from more than 50 mol% of ethylene monomer. This includes polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of polyethylene known in the art include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ultra-low-density polyethylene (ULDPE), very low-density polyethylene (VLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE).

[0017] The term “LDPE” may also be referred to as “high-pressure ethylene polymer” or “highly branched polyethylene,” and is defined to mean that the polymer is partially or completely homopolymerized or copolymerized in an autoclave or tubular reactor at a pressure greater than 14,500 psig (100 MPa) using a free radical initiator such as a peroxide (see, for example, U.S. Patent No. 4,599,392 incorporated herein by reference). LDPE resins typically have a density in the range of 0.916 to 0.935 g / cc.

[0018] As used herein, the term “siloxane” includes polysiloxanes and siloxanes with lower molecular weights. In embodiments, the siloxane is polydimethylsiloxane (PDMS) having various terminal groups as described below.

[0019] As used herein, the terms “foam” and “foam composition” refer to a structure composed of polymers, including a plurality of channels extending from the surface of the structure into and through the structure. The channels are non-directional with respect to the longitudinal extension of the structure. The channels include a plurality of foam bubbles that are in fluid communication with the external atmosphere. As used herein, the terms “foam bubble” or “bubble” refer to a separate space within the foam composition. The foam bubbles are separated by a membrane wall containing the polymer of the foam composition, or are otherwise defined.

[0020] As used herein, the term “physical blowing agent” means a compound or composition that is sufficiently soluble in the polymer composition under those conditions, is dissolved in the polymer composition under extrusion conditions, and (ii) is released from the solution under the conditions (temperature, pressure) that the foaming composition encounters during the formation of the foam composition when it exits the die. A physical blowing agent is added to a polymer blend under extrusion conditions to form a foaming composition. As used herein, the term “foaming composition” means a mixture of a polymer blend and a physical blowing agent under extrusion conditions.

[0021] As used herein, the term "microporous foam" means a foam having an average cell size of less than 70 μm. Microporous foam may include closed-cell foam or open-cell foam.

[0022] The term "foaming temperature" refers to the final set temperature in the foam extruder or other suitable heat exchanger, cooling section, or cooling section of another suitable heat exchanger located immediately upstream of the outlet die. For example, the foaming temperature may be the set temperature in the last zone of an extruder used to cool the foaming composition. The set temperature may or may not be different from the melting temperature of the extruder (foaming composition) measured at the outlet die.

[0023] Embodiments of the present disclosure relate to a microporous foam comprising a polymer blend containing 70-95% by weight of low-density polyethylene (LDPE) and 5-30% by weight of polydimethylsiloxane-grafted LDPE (PDMS-g-LDPE), wherein the microporous foam has an average cell size of less than 60 μm. In further embodiments, the microporous foam is intended to have an average cell size of less than 50 μm. In other words, the microporous foam has an average cell size of 40 μm to 60 μm. In further embodiments, the microporous foam comprises 80-90% by weight of LDPE and 10-20% by weight of PDMS-g-LDPE.

[0024] In one or more embodiments, polydimethylsiloxane-grafted LDPE (PDMS-g-LDPE) has a structure in which a portion of an ethylene-based polymer (e.g., LDPE) is bonded to one or more silicon atoms. In certain embodiments, at least one LDPE is bonded to a siloxane at a silicon atom. PDMS-g-LDPE can be formed by high-pressure free-radical polymerization by reacting an ethylene monomer with PDMS, or by reacting an ethylene monomer with one or more polydimethylsiloxanes. In one embodiment, polydimethylsiloxane-grafted LDPE is formed by free-radical grafting of LDPE onto a radicalized PDMS molecule.

[0025] In various embodiments described herein, the polysiloxane is a polydimethylsiloxane (PDMS) containing one or more functional groups, and is therefore referred to as functionalized PDMS or f-PDMS. In various embodiments, the f-PDMS is a (meth)acrylate ester functionalized PDMS, where the (meth)acrylate ester group is bonded to the PDMS via a crosslinking group. The PDMS may be monofunctional, difunctional, or polyfunctional, and the functional group(s) may be linked at terminal or pendant positions on the siloxane.

[0026] As is well known to those skilled in the art, polydimethylsiloxanes contain two methyl groups bonded to each silicon atom. Suitable PDMS compounds and PDMS-g-LDPE compounds are those taught in U.S. Patent No. 8,691,923, which is incorporated herein by reference.

[0027] Alternatively, the PDMS in PDMS-g-LDPE may be prepared before or separately from the reaction process with LDPE. Chain transfer agents (CTAs) are typically used to control the melt index in free radical polymerization processes. Chain transfer is associated with stopping the growth of polymer chains and therefore limits the final molecular weight of the polymer material. Chain transfer agents are typically hydrogen atom donors that react with the growing polymer chains and stop the polymerization reaction of the chains. In the case of high-pressure free radical polymerization, these agents can be many different types, such as saturated hydrocarbons, unsaturated hydrocarbons, aldehydes, ketones, or alcohols. Typical CTAs that may be used include, but are not limited to, propylene, isobutane, n-butane, 1-butene, methyl ethyl ketone, propionaldehyde, ISOPAR (ExxonMobil Chemical), and isopropanol.

[0028] In one embodiment, a free radical initiator may be used in a process to initiate graft sites on PDMS by extracting extractable hydrogen from PDMS. Examples of free radical initiators include the aforementioned free radical initiators such as peroxides and azo compounds. In one embodiment, ionizing radiation may also be used to liberate extractable hydrogen and generate radicalization sites on PDMS. Inducement initiators that extract extractable hydrogen include, for example, dicumyl peroxide, di-tert-butyl peroxide, t-butyl perbenzoate, benzoyl peroxide, cumene hydroperoxide, t-butyl peroctoate, methyl ethyl ketone peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, lauryl peroxide, and tert-butyl peracetate, t-butyl α-cumyl peroxide, di-t-butyl peroxide, di-t-amyl peroxide. Luoxide, t-amylperoxybenzoate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, α-α'-bis(t-butylperoxy)-1,3-diisopropylbenzene, α-α'-bis(t-butylperoxy)-1,4-diisopropylbenzene, 2,5-bis(t-butylperoxy)-2,5-dimethylhexane, and 2,5-bis(t-butylperoxy)-2,5-dimethyl-3-hexine are suitable means for use. A suitable azo compound is azobisisobutylnitrite.

[0029] In one embodiment, PDMS-g-LDPE may be treated with one or more stabilizers, for example, antioxidants (IRGANOX1010 and IRGAFOS168 (Ciba Specialty Chemicals, Glattburgh, Switzerland)). Generally, the polymer is treated with one or more stabilizers before extrusion or other melting processes. In one embodiment, additives to other polymers include, but are not limited to, UV absorbers, antistatic agents, pigments, dyes, nucleating agents, fillers, slip agents, flame retardants, plasticizers, processing aids, lubricants, stabilizers, smoke suppressants, viscosity modifiers, and anti-tack agents. A PDMS-g-LDPE composition may contain, for example, one or more additives in a total weight of less than 10% based on the weight of PDMS-g-LDPE.

[0030] PDMS-g-LDPE may be further incorporated. In one PDMS-g-LDPE composition, one or more antioxidants may be further incorporated into the polymer, and the incorporated polymer is pelletized. The ethylene-based polymer composition may contain any amount of one or more antioxidants. For example, the ethylene-based polymer composition may contain 200 to 600 parts of one or more phenolic antioxidants per 1 million parts of the ethylene-based polymer composition. In addition, the ethylene-based polymer composition may contain 800 to 1200 parts of phosphite antioxidants per 1 million parts of the ethylene-based polymer composition. The compounded polymer may further contain 300 to 1250 parts of calcium stearate per 1 million parts of the polymer.

[0031] Characteristics of PDMS-g-LDPE and LDPE In one embodiment, PDMS-g-LDPE is, 13 It contains at least 0.15, or at least 0.5, or at least 0.8 units of amyl groups per 1000 carbon atoms, as determined by 13C nuclear magnetic resonance (NMR). In one embodiment, PDMS-g-LDPE is 13 It contains at least 1, or at least 1.2, or at least 1.4 units of C6+ branching, as determined by 13C NMR.

[0032] In one embodiment, PDMS-g-LDPE 13 contains no detectable methyl branches as determined by 13C NMR. In one embodiment, PDMS-g-LDPE 13 contains no detectable propyl branches as determined by 13C NMR. In one embodiment, PDMS-g-LDPE 13 contains units of amyl groups of 5 or less, or 3 or less, or 2 or less per 1000 carbon atoms as determined by 13C NMR.

[0033] In one embodiment, PDMS-g-LDPE has a density of at least 0.925 g / cm 3 , or 0.925 - 0.950 g / cm 3 . LDPE can have a density of 0.916 - 0.935 g / cm 3 or 0.916 - 0.925 g / cm 3 . LDPE can have a melt index (I2) of 0.15 - 10.0 g / 10 min, or 0.5 - 3.0 g / 10 min, or 1.5 - 2.5 g / 10 min.

[0034] Furthermore, PDMS-g-LDPE has a melt index (I2) of less than 10, or less than 5, or less than 3. Conversely, PDMS-g-LDPE has a melt index (I2) of greater than 0.5 or greater than 1.0.

[0035] In one embodiment, PDMS-g-LDPE has a melt flow ratio (I 10 / I2) of at least 13, or at least 20, or at least 40, or at least 100, or at least 200. Furthermore, PDMS-g-LDPE can have a melt index (I2) of 0.5 - 15.0 g / 10 min. In another embodiment, PDMS-g-LDPE has a melt flow ratio (I 10 / I2) of at least 100 or at least 200. In one embodiment, PDMS-g-LDPE has an I2 of less than 5 and an I 10In another embodiment, the PDMS-g-LDPE of any of the preceding embodiments has an I2 of less than 5 or less than 3 and an I2 of greater than 30 or greater than 40. 10 In yet another embodiment, the PDMS-g-LDPE of any of the above embodiments has an I2 of less than 20 or less than 15 and an I2 greater than 12. 10 It has / I2. In another embodiment, the PDMS-g-LDPE has a molecular weight distribution (MWD = Mw / Mn) of 5-50, or 7.0-50.0, or 7-25, or 7-10, or 5-10. The MWD is determined using gel permeation chromatography as detailed below. Furthermore, the PDMS-g-LDPE has a melt strength of at least 5 cN as measured by the methodology defined below.

[0036] In one embodiment, PDMS-g-LDPE contains 1 to 40 weight percent of PDMS based on the weight of PDMS-g-LDPE, or 1 to 20 weight percent of PDMS based on the weight of PDMS-g-LDPE, or 1 to 15 weight percent of PDMS based on the weight of PDMS-g-LDPE.

[0037] Method for producing microporous foam According to one or more embodiments, a microporous foam may be produced by first generating a polymer blend by mixing 70-95% by weight of low-density polyethylene (LDPE) and 5-30% by weight of polydimethylsiloxane-grafted LDPE (PDMS-g-LDPE). The blend may be produced by various methods well known to those skilled in the art. For example, the components may be blended in an extruder or mixer (e.g., a melt blend). The polymer blend is then passed through a batch former at a temperature of at least 75°C and a pressure of at least 1000 psig in the presence of a blowing agent, and the polymer blend is then rapidly depressurized to produce a microporous foam having a bubble size of less than 60 μm.

[0038] In one or more embodiments, the polymer blend is immersed in a batch former for at least two hours, or at least four hours. In alternative embodiments, the immersion may be carried out at a temperature of 100°C or above, or 125°C or above. Furthermore, the immersion process may be carried out at a pressure of 1200 psig or above. Many embodiments are considered suitable for batch formers. These batch former units may include extruders, which are detailed below. While not theoretical, the temperature and pressure should include a sufficiently high pressure to (i) prevent the blowing agent from expanding the polymer composition and / or foaming composition in the extruder or other suitable melting equipment, and (ii) allow for homogeneous dispersion of the blowing agent within the polymer composition.

[0039] In one or more embodiments, depressurization may occur in less than 30 seconds, less than 5 seconds, or less than 1 second. In one embodiment, depressurization may reduce the pressure to less than 1 psig.

[0040] As described above, in addition to PDMS-g-LDPE, the composition in which the foam is formed includes a physical blowing agent. In one or more embodiments, the physical blowing agent includes isobutane, nitrogen, carbon dioxide, isomers of n-butane and pentane, hydrocarbons, fluorocarbons, hydrofluorocarbons, or mixtures thereof, or mixtures thereof. The physical blowing agent (e.g., isobutane or CO2) may be present in an amount of 0.5 to 30% by weight, 2 to 25% by weight, 5 to 20% by weight, or 8 to 15% by weight, based on the total weight of the foaming composition, depending on the particular embodiment. In embodiments, PDMS-g-LDPE exhibits improved foaming efficiency, allowing for a reduction in the amount of physical blowing agent compared to similar foaming compositions that do not contain PDMS-g-LDPE (e.g., compositions containing LDPE and a blowing agent).

[0041] In other embodiments, one or more additional components may be added to the polymer composition, such as permeability modifiers, bubble nucleating agents, olefin polymers, antistatic agents, pigments, fillers, or other additives known and used in the art.

[0042] When added to an extruder, a nucleating agent can promote the formation of one or more foam bubbles, resulting in smaller bubble sizes and higher bubble densities. In one or more embodiments, the nucleating agent may be talc, calcium carbonate, or a chemical blowing agent. For example, the nucleating agent may be added to the extruder as a talc coating. If included, the nucleating agent may be present in an amount of 0.01 to 10.0% by weight based on the total weight of the foaming composition. In one or more embodiments, PDMS-g-LDPE can also act as a nucleating agent.

[0043] Furthermore, one or more antistatic agents, pigments, fillers, or other additives may be included in the composition. Other additives include, but are not limited to, antioxidants, acid scavengers, ultraviolet absorbers, flame retardants, processing aids, and extrusion aids. If present, such additives may be present in an amount of more than 0 to 20% by weight based on the total weight of the foaming composition.

[0044] Following the addition of a physical blowing agent, the composition comprising the polymer blend and the physical blowing agent (hereinafter referred to as the “foaming composition”) is cooled to a foaming temperature. For example, the foaming composition may be cooled in a cooling extruder. In one or more embodiments, the foaming temperature is about 50°C to about 180°C. For example, the foaming temperature may be 70°C to 160°C, 90°C to 140°C, 100°C to 130°C, 100°C to 120°C, 100°C to 110°C, 105°C to 110°C, or 105°C to 118°C.

[0045] After cooling to the foaming temperature, in the embodiment, the foaming composition is extruded from the outlet die at the end of the cooling extruder and cured to form a foamed composition. Foaming is achieved when the foaming composition passes through the extruder die to a region of lower pressure compared to the pressure inside the extruder, and as a result the foaming composition experiences a pressure drop as it exits the extruder's outlet die. This pressure drop causes the foaming composition to expand due to the physical foaming agent, thereby resulting in foaming.

[0046] Purpose The embodiments of the foam described herein may include, but are not limited to, any known physical form such as extruded sheets, rods, plates, and films. Such foams may be used, for example, in cushion packaging, sports and recreation products, egg cartons, meat trays, building structures, acoustic insulation liners, pipe insulation, gaskets, vibration pads, luggage liners, desk pads, shoe holes, gymnastics mats, greenhouse insulation blankets, case inserts, absorbent foams (for example, for purifying purposes such as health and hygiene applications), and display foams. Other applications such as insulation for refrigeration, buoyancy applications, and floral and craft applications are conceived and possible.

[0047] Test method The test method includes the following:

[0048] Melt index (I2) and (I 10 ) Melt index (I2) and Melt index (I 10 The 2.16 kg and 10 kg values ​​are measured at 190°C according to ASTM D-1238 using Method B. The value is reported as g / 10 min (or dg / min), which corresponds to the grams eluted per 10 minutes.

[0049] density The density of the polymer was measured at 25°C according to ASTM D792-08 Method B, in grams / cubic centimeter (g / cc or g / cm³). 3 ) will be reported.

[0050] Melt strength Melt strength measurements were performed using Gottfert Rheotens 71.97 (Gottfert Inc.; Rock Hill, SC) coupled to a Gottfert Rheotester 2000 capillary rheometer. A molten sample (approximately 25-30 grams) was fed into a Gottfert Rheotester 2000 capillary rheometer with a length of 30 mm, a diameter of 2.0 mm, and a flat inlet angle (180 degrees) with an aspect ratio (length / diameter) of 15. After equilibrating the sample at 190°C for 10 minutes, the piston was operated at a constant piston speed of 0.265 mm / second. The standard test temperature was 190°C. The sample was then subjected to a set of acceleration nips located 100 mm below the die at a speed of 2.4 mm / second. 2 Uniaxial stretching was performed at the specified acceleration. Tensile force was recorded as a function of the nip roll winding speed. Melt strength was expressed as the peak or maximum plateau force (cN) before the strand fractured. The following conditions were used for melt strength measurements: plunger speed = 0.265 mm / sec, wheel acceleration = 2.4 mm / sec. 2 Capillary diameter = 2.0 mm, capillary length = 30 mm, and barrel diameter = 12 mm.

[0051] Gel Permeation Chromatography (GPC) The GPC system consists of a PolymerChar GPC-IR (Valencia, Spain) high-temperature GPC chromatograph equipped with an internal IR5 infrared detector (IR5), and a 4-capillary solution viscometer (DV) coupled to a Precision Detectors (now Agilent Technologies, Amherst, MA) 2-angle laser light scattering (LS) detector Model 2040. A GPC with the last two independent detectors and at least one of the initial detectors is sometimes referred to as a "3D-GPC," but the term "GPC" alone generally refers to a conventional GPC. For all absolute light scattering measurements, a 15-degree angle was used. The autosampler's oven compartment was operated at 160°C, and the column compartment was operated at 150°C. The columns used were four Agilent "Mixed A" 30 cm, 20 micrometer linear mixed-bed columns. The chromatography solvent used was 1,2,4-trichlorobenzene, containing 200 ppm butylated hydroxytoluene (BHT). The solvent source was sparged with nitrogen. The polyethylene sample was gently stirred at 160°C for 4 hours. The injection volume was 200 μL. The flow rate through the GPC was set to 1 mL / min.

[0052] Prior to performing the examples, the GPC column set was calibrated by running at least 20 polystyrene standards with narrow molecular weight distributions. The molecular weights (MW) of the standards ranged from 580 to 8,400,000 g / mol, and the standards contained six “cocktail” mixtures. Each standard mixture had at least an order of magnitude of spacing between individual molecular weights. The standard mixtures were purchased from Agilent Technologies. Polystyrene standards were prepared at a rate of 0.025 g in 50 mL of solvent for molecular weights of 1,000,000 g / mol or more, and 0.05 g in 50 mL of solvent for molecular weights less than 1,000,000 g / mol. The polystyrene standards were dissolved at 80°C for 30 minutes with gentle stirring. The narrow standard mixtures were performed first, and then in an order of decreasing the highest molecular weight component to minimize degradation. The standard peak molecular weight of polystyrene was converted to the molecular weight of polyethylene using Equation 2 (as described in Williams and Ward, J. Polym. Sci., Polym. Let., 6, 621 (1968)): M polyethylene =A × (M polystyrene ) B (Formula 2) In the formula, M is the molecular weight of polyethylene (as marked), A has a value of 0.43, and B is equal to 1.0.

[0053] Polynomials between the third and fifth orders were used to fit the respective polyethylene equivalent calibration points. The total plate count of the GPC column set was performed using Eicosane (prepared at 0.04 g in 50 mL of TCB and dissolved for 20 minutes with gentle agitation). Plate count (Equation 3) and symmetry (Equation 4) were measured with 200 μL injections according to the following formulas:

[0054]

number

[0055]

number

[0056] The sample was prepared semi-automatically using PolymerChar "Instrument Control" software, with a target weight of 2 mg / mL. The solvent (containing 200 ppm BHT) was added to a pre-nitrogen-spared vial with a septum cap via a PolymerChar high-temperature autosampler. The sample was dissolved at 160°C for 2 hours with "low-speed" shaking.

[0057] Mn (GPC) , Mw (GPC) , and Mz (GPC) The molecular weight was calculated based on the GPC results using the PolymerChar GPCOne™ software, an IR chromatograph with the baseline subtracted at each equally spaced data acquisition point (i), and the polyethylene equivalent molecular weight obtained from the narrow standard calibration curve at point (i) from Equation 2, using the internal IR5 detector (measurement channel) of the PolymerChar GPC-IR chromatograph according to Equations 5-7.

[0058]

number

[0059] To monitor deviations over time, a flow rate marker (decane) was introduced into each sample via a micropump controlled by a PolymerChar GPC-IR system. This flow rate marker (FM) was used to linearly correct the pump flow rate (nominal flow rate) for each sample by matching the RV of each decane peak in the sample (RV(FM sample)) with the RV of the decane peak in the narrow standard calibration (RV(FM calibrated)). Subsequently, it was assumed that any change in the decane marker peak over time was related to a linear shift in the flow rate (effective flow rate) throughout the experiment. To facilitate the highest accuracy of RV measurement of the flow rate marker peak, a least-squares fitting routine was used to fit the peaks of the flow rate marker concentration chromatogram to a quadratic equation. The true peak position was then solved using the first derivative of the quadratic equation. After calibrating the system based on the flow rate marker peak, the effective flow rate (with respect to the narrow standard calibration) was calculated as shown in Equation 8. Processing of the flow rate marker peaks was performed via PolymerChar's GPCOne® software. An acceptable flow rate correction is one in which the effective flow rate is within + / - 2% of the nominal flow rate.

[0060]

number

[0061] Triple detector GPC (3D-GPC) The chromatography system, analytical conditions, column set, column calibration, and conventional molecular weight moment calculations and distributions were performed according to the methods described for gel permeation chromatography (GPC).

[0062] Regarding the determination of viscometer and light scattering detector offsets from the IR5 detector, a systematic method for determining multiple detector offsets was performed in a manner consistent with that published by Balke, Mourey et al. (Mourey and Balke, Chromatography Polym., Chapter 12, (1992)) (Balke, Thitiratsakul, Lew, Cheung, Mourey, Chromatography Polym., Chapter 13, (1992)), using PolymerChar GPCOne® software to obtain triple detector logs (M) from a wide range of single polymer polyethylene standards (Mw / Mn>3). w The results (and intrinsic viscosity) are optimized for the narrow standard column calibration results from the narrow standard calibration curve.

[0063] Absolute molecular weight data were obtained using PolymerChar GPCOne® software in a format consistent with those published by Zimm (Zimm, BH, J. Chem. Phys., 16, 1099 (1948)) and Kratochvil (Kratochvil, P., Classical Light Scattering from Polymer Solutions, Elsevier, Oxford, NY (1987)). The total injection concentration used in determining the molecular weight was obtained from the mass detector area and mass detector constant derived from one of the following: a suitable linear polyethylene homopolymer or a polyethylene standard material with a known weight-average molecular weight. The molecular weight calculated (using GPCOne®) is obtained using the light scattering constant and the refractive index concentration coefficient, dn / dc, of 0.104, derived from one or more of the polyethylene standards described. In general, the mass detector response (IR5) and light scattering constant (determined using GPCOne®) should be determined from linear standards having a molecular weight greater than approximately 50,000 g / mol. The calibration of the viscometer (determined using GPCOne®) can be achieved using the method described by the manufacturer, or alternatively, by using the published values ​​of a suitable linear reference material such as Standard Reference Material (SRM) 1475a (available from the National Institute of Standards and Technology, NIST). The viscometer constant (obtained using GPCOne®) is calculated, relating the specific viscosity area (DV) and injected mass of the calibration standard to its intrinsic viscosity. The chromatographic concentration is assumed to be low enough to eliminate the consideration of a second viral coefficient effect (concentration effect on molecular weight).

[0064] Absolute weight average molecular weight (Mw (Abs)) is obtained by dividing the light scattering (LS) area integrated chromatogram (factored by the light scattering constant) (using GPCOne®) by the mass recovered from the mass constant and the mass detector (IR5) area. The molecular weight and intrinsic viscosity response are linearly extrapolated at the edge of the chromatography where the signal-to-noise ratio is low (using GPCOne®). Other respective moments Mn (Abs) and Mz (Abs) This is calculated according to equations 9-10 as follows.

[0065]

number

[0066] The following embodiments illustrate the features of the present disclosure, but are not intended to limit the scope of the present disclosure.

[0067] In the following examples, the foam was produced from PDMS-g-LDPE, AGILITY® 1021 LDPE, and a blend of both.

[0068] AGILITY® 1021, manufactured by Dow Inc, Midland, MI, is an LDPE with a density of 0.919 g / cc and 1.9 g / 10 min of I2.

[0069] PDMS-g-LDPE was prepared in a continuous stirred tank reactor (CSTR) with a volume of 54 mL at 1925 bar (27,920 psig). The reaction temperature was 240°C. The CSTR was equipped with an external heating jacket. The stirrer speed was 1600 revolutions per minute (rpm). The ethylene flow rate was 5450 g / hour. Polydimethylsiloxane (PDMS) (Dow Corning PMX-200 Fluid 12,500 CST) was dissolved in ethyl acetate at a rate of 40% by weight. The PDMS solution was injected into the CSTR at a flow rate of 93.1 mL / hour (34.4 g / hour of pure PDMS) so that ethylene polymerization would occur in the presence of PDMS. Propylene was used as a chain transfer agent (CTA). The initiator consisted of 96.4 g of tert-butylperoxyacetate dissolved in 2172 mL of Isopar E, which was injected into the CSTR at a flow rate of 36.2 mL / hour. PDMS-g-LPDE containing 5 wt% PDMS was collected in a permeable polyethylene bottle, and excess gas was evacuated. The subsequent process was used to pelletize the PDMS-g-LDPE before blending. The results for PDMS-g-LPDE are shown in Table 1. Figure 1 shows the melt strength of various samples graphically.

[0070] [Table 1]

[0071] A blend was prepared in a Haake mixer at a temperature of 180°C, a rotor speed of 60 rpm, and a mixing time of 10 minutes. After mixing, the blend was compression molded to obtain plaques measuring 1 / 4 inch (0.64 cm) in length, 1 / 4 inch (0.64 cm) in width, and 1 / 16 inch (0.16 cm) in thickness. The plaque samples were fed into a 1000 mL batch former using CO2 as a foaming agent. The samples were held in the batch former at a temperature of 100°C and a pressure of 1200 psig for a 4-hour immersion time. The samples were then depressurized to approximately 0 psig in less than 1 second. This rapid depressurization played a role in producing the foam bubble sizes listed in Table 2. After depressurization, the foam cross-section was sliced, and the bubble size was evaluated by scanning electron microscopy (SEM).

[0072] [Table 2]

[0073] As shown, Examples 1 and 2 of the present invention, which are blends of LDPE and PDMS-g-LDPE, achieved an average foam bubble size of less than 60 μm. In contrast, the all-LDPE in Comparative Example B achieved a much larger average foam bubble size of 92 μm, which is much larger than the foam bubble sizes of Examples 1 and 3 of the present invention. Furthermore, the all-PDMS-g-LDPE in Comparative Example A also achieved an average bubble size of less than 60 μm. However, large gas pockets were formed in the foam, which is problematic for the mechanical strength properties of the foam. Only the examples of the present invention achieved a balance between a smaller average bubble size and adequate strength. The bubble sizes are shown in the micrographs in Figures 2A to 2D.

[0074] It will be apparent that modifications and changes are possible without departing from the scope of this disclosure as defined in the attached claims. More specifically, certain aspects of this disclosure are identified herein as preferred or particularly advantageous, but this disclosure is intended not to be limited to these aspects. This application provides, for example, the following inventions: [1] A microporous foam containing a polymer blend, 70-95% by weight of low-density polyethylene (LDPE) and It contains 5-30% by weight of polydimethylsiloxane grafted LDPE (PDMS-g-LDPE), A microporous foam with a bubble size of less than 60 μm. [2] The microporous foam according to [1] above, wherein the microporous foam comprises 80-90% by weight of LDPE and 10-20% by weight of PDMS-g-LDPE. [3] The LDPE has a density of 0.916 to 0.935 g / cc and a melt index of 0.5 to 10.0 g / 10 min (I 2 A microporous foam according to [1] or [2] above, having ) [4] The PDMS-g-LDPE has a density of 0.915 to 0.955 g / cc and a melt index of 0.5 to 15.0 g / 10 min (I 2 A microporous foam according to any one of the above [1] to [3], having ) [5] The microporous foam according to any one of the above [1] to [4], wherein the PDMS-g-LDPE contains 1 to 40% by weight of PDMS based on the weight of the PDMS-g-LDPE. [6] A method for producing a microporous foam, A polymer blend is produced by mixing 70-95% by weight of low-density polyethylene (LDPE) and 5-30% by weight of polydimethylsiloxane-grafted LDPE (PDMS-g-LDPE), The polymer blend is introduced into a batch former at a temperature of at least 75°C and a pressure of at least 1000 psig in the presence of a physical blowing agent. A method comprising reducing the pressure of the immersed polymer blend to produce a microporous foam having a bubble size of less than 60 μm in less than 5 seconds. [7] The method according to [6] above, wherein the depressurization is performed in less than 1 second. [8] The method according to [6] or [7] above, wherein the reduction in pressure is less than 5 psig. [9] The method according to any one of the above [6] to [8], wherein the physical blowing agent comprises isobutane, nitrogen, carbon dioxide, isomers of n-butane, pentane, hydrocarbons, fluorocarbons, hydrofluorocarbons, or mixtures thereof.

[10] The method according to any one of the above [6] to [9], wherein the polymer blend is maintained in the batch former for at least 0.5 hours.

[11] The method according to any one of the above [6] to

[10] , wherein the microporous foam comprises 80 to 90% by weight of LDPE and 5 to 20% by weight of PDMS-g-LDPE.

[12] The LDPE has a density of 0.916 to 0.935 g / cc and a melt index of 0.5 to 10.0 g / 10 min (I 2 The method described in any one of the above [6] to

[11] , wherein the method is provided for the member having

[13] The PDMS-g-LDPE has a density of 0.915 to 0.955 g / cc and a melt index of 0.5 to 15.0 g / 10 min (I 2 The method according to any one of the above [6] to

[12] , wherein the method is having )

[14] The method according to any one of the above [6] to

[12] , wherein the PDMS-g-LDPE contains 1 to 40% by weight of PDMS based on the weight of the PDMS-g-LDPE.

Claims

1. A microporous foam containing a polymer blend, 70-95% by weight of low-density polyethylene (LDPE) and It contains 5 to 30% by weight of polydimethylsiloxane grafted LDPE (PDMS-g-LDPE), A microporous foam having an average bubble size of 40 μm or more and less than 60 μm.

2. The microporous foam according to claim 1, wherein the microporous foam comprises 80 to 90% by weight of LDPE and 10 to 20% by weight of PDMS-g-LDPE.

3. The LDPE has a density of 0.916 to 0.935 g / cc and a melt index (I) of 0.5 to 10.0 g / 10 min. ２ A microporous foam according to claim 1 or 2, having the following characteristics:

4. The PDMS-g-LDPE has a density of 0.915 to 0.955 g / cc and a melt index (I) of 0.5 to 15.0 g / 10 min. ２ A microporous foam according to any one of claims 1 to 3, having the following characteristics:

5. The microporous foam according to any one of claims 1 to 4, wherein the PDMS-g-LDPE contains 1 to 40% by weight of PDMS based on the weight of the PDMS-g-LDPE.

6. A method for producing a microporous foam, A polymer blend is produced by mixing 70-95% by weight of low-density polyethylene (LDPE) and 5-30% by weight of polydimethylsiloxane-grafted LDPE (PDMS-g-LDPE), The polymer blend is introduced into a batch former at a temperature of at least 75°C and a pressure of at least 1000 psig (6.90 MPa) in the presence of a physical blowing agent. A method comprising reducing the pressure of the immersed polymer blend to produce a microporous foam having an average bubble size of 40 μm or more and less than 60 μm in less than 5 seconds.

7. The method according to claim 6, wherein the depressurization is performed in less than one second.

8. The method according to claim 6 or 7, wherein the reduction in pressure reduces the pressure to less than 5 psig (0.0345 MPa).

9. The method according to any one of claims 6 to 8, wherein the physical blowing agent comprises isobutane, nitrogen, carbon dioxide, isomers of n-butane and pentane, hydrocarbons, fluorocarbons, hydrofluorocarbons, or mixtures thereof.

10. The method according to any one of claims 6 to 9, wherein the polymer blend is maintained in the batch former for at least 0.5 hours.

11. The method according to any one of claims 6 to 10, wherein the microporous foam comprises 80 to 90% by weight of LDPE and 5 to 20% by weight of PDMS-g-LDPE.

12. The LDPE has a density of 0.916 to 0.935 g / cc and a melt index (I) of 0.5 to 10.0 g / 10 min. ２ The method according to any one of claims 6 to 11, having )

13. The PDMS-g-LDPE has a density of 0.915 to 0.955 g / cc and a melt index (I) of 0.5 to 15.0 g / 10 min. ２ The method according to any one of claims 6 to 12, having )

14. The method according to any one of claims 6 to 12, wherein the PDMS-g-LDPE contains 1 to 40% by weight of PDMS based on the weight of the PDMS-g-LDPE.

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