Cross-linked polyethylene foam and method for manufacturing the same

Abstract

This specification describes physically crosslinked closed-cell continuous foam structures comprising low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and olefin block copolymer (OBC). The foam structures can be obtained by extruding a foam composition comprising LDPE, LLDPE, or a combination of LDPE and LLDPE, and OBC, and irradiating the composition with ionizing radiation to foam the composition.

Description

[Technical Field]

[0001] This application claims priority to U.S. Patent Application Publication No. 18 / 194,316, filed on March 31, 2023, and U.S. Patent Application Publication No. 18 / 194,320, filed on March 31, 2023, the entire contents of each application being incorporated herein by reference. The present invention generally relates to crosslinked polyethylene foam structures, and more particularly to crosslinked polyethylene foam structures produced from a blend of polyethylene and polyethylene-based olefin block copolymers. [Background technology]

[0002] Cross-linked polyethylene foam sheets are used in a wide variety of applications, including as tape bases, gaskets, layers or components of automotive interior finishing materials, protective materials in packaging and transport, components of buoyancy devices and buoyancy aids, components of clothing and shoes, components of mattresses and bedding, insulation for walls and pipes, furniture stuffing, underlayment, vibration absorbers, and shock absorbers. These cross-linked polyethylene foams are typically manufactured from low-density polyethylene (LDPE) and / or conventional linear low-density polyethylene (LLDPE) using multi-site Ziegler-Natta catalysts. One type of cross-linked polyethylene foam is manufactured from a blend of polyethylene (LDPE and / or conventional LLDPE) and ethylene vinyl acetate copolymer (EVA). EVA is commonly used to increase the flexibility and pliability of cross-linked polyethylene foam sheets in applications requiring increased flexibility and pliability that is not typically obtained from LDPE and / or conventional LLDPE. One of the raw materials necessary for the manufacture of EVA copolymers is vinyl acetate monomer (VAM). VAM is a raw material used not only in the manufacture of EVA copolymers but also in dispersion adhesives in the automotive, construction, furniture, and paper / packaging industries. VAM is also a raw material for paints and coatings, construction, and textile manufacturing. However, a global shortage of VAM has caused demand to exceed supply, with no prospect of improvement in the future. As a result, the global shortage of VAM is causing price increases and price fluctuations for VAM, and more broadly, for all products that require VAM, i.e., products containing EVA. [Overview of the project]

[0003] It has been discovered that a physically cross-linked closed-cell polyethylene foam structure can be produced from a blend of polyethylene (LDPE and / or conventional LLDPE) and polyethylene-based olefin block copolymer (OBC). While one type of commercially produced polyethylene foam is a cross-linked foam made from a blend of polyethylene (LDPE and / or conventional LLDPE) and EVA copolymer, it has been found that blending OBC in place of EVA into the foam formulation can suitably improve the flexibility and pliability of cross-linked polyethylene foam sheets, even for applications where improved flexibility and pliability not typically obtained from LDPE and / or conventional LLDPE alone are required. Since OBC is not currently and will not be in short supply in the future, the discovered foam can be produced from readily available polymers. Furthermore, due to the sufficient production and supply of OBC, the raw material cost of the discovered foam is expected to be significantly more stable than that of polyethylene foam (LDPE and / or conventional LLDPE) blended with EVA. Sufficient and rapid supply and stable pricing are highly desirable for manufacturers, distributors, and users of cross-linked foams.

[0004] A polyethylene foam sheet can be obtained by (a) extruding a foam composition containing a blend of polyethylene (LDPE and / or LLDPE) and polyethylene-based OBC, (b) irradiating the extruded foam composition with ionizing radiation, and (c) foaming the irradiated extruded foam composition. In some embodiments, the polyethylene foam structure comprises 40-65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and 15-45% by mass of olefin block copolymer (OBC). In some embodiments, the foam structure comprises 50-65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE. In some embodiments, the foam structure comprises 20-35% by mass of olefin block copolymer (OBC). In some embodiments, the foam structure comprises 5-15% by mass of a chemical blowing agent. In some embodiments, the foam structure comprises 1-10% by mass of an antioxidant masterbatch. In some embodiments, the foam structure comprises 0.5-5% by mass of a processing aid masterbatch. In some embodiments, the foam structure comprises 1-10% by mass of a chemical blowing agent decomposition inhibitor masterbatch. In some embodiments, the foamed structure comprises an antiblocking agent masterbatch in an amount of 1 to 10% by mass. In some embodiments, the foamed structure comprises a coloring agent masterbatch in an amount of 1 to 12% by mass. In some embodiments, the foamed structure comprises a foamed structure of 15 to 200 kg / m³. 3 It has a density of . In some embodiments, the foamed structure has a degree of crosslinking of 20 to 75%. In some embodiments, the foamed structure has an average closed cell size of 0.05 to 1.0 mm. In some embodiments, the foamed structure has a thickness of 0.2 to 50 mm. In some embodiments, the foamed structure is a single layer.

[0005] In some embodiments, the laminate comprises a polyethylene foam layer containing 40-65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and 15-45% by mass of olefin block copolymer (OBC), and a laminate layer on one side of the polyethylene foam layer. In some embodiments, the laminate layer is a flexible film, fabric, or foil. In some embodiments, the laminate layer is either unfoamed or foamed. In some embodiments, the adhesive foam tape comprises a polyethylene foam layer containing 40-65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and 15-45% by mass of olefin block copolymer (OBC), and a pressure-sensitive adhesive layer on one side of the polyethylene foam layer. In some embodiments, the tape comprises a second pressure-sensitive adhesive layer on the side of the polyethylene foam layer opposite to the first pressure-sensitive adhesive layer. In some embodiments, either pressure-sensitive adhesive layer contains one or more of acrylic polymers, polyurethanes, thermoplastic elastomers, block copolymers, polyolefins, silicones, rubber-based adhesives, copolymers of ethylhexyl acrylate and acrylic acid, copolymers of isooctyl acrylate and acrylic acid, or combinations thereof.

[0006] In some embodiments, a method for forming a polyethylene foam includes the steps of: extruding a foam layer containing 40-65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and 15-45% by mass of olefin block copolymer (OBC); irradiating the extruded foam layer with ionizing radiation; and foaming the irradiated and extruded foam layer. In some embodiments, the foam layer contains 50-65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE. In some embodiments, the foam layer contains 20-35% by mass of olefin block copolymer (OBC). In some embodiments, the foam layer contains 5-15% by mass of a chemical blowing agent before foaming. In some embodiments, the foam layer contains 1-10% by mass of an antioxidant masterbatch. In some embodiments, the foam layer contains 0.5-5% by mass of a processing aid masterbatch. In some embodiments, the foamed layer contains a masterbatch of a chemical blowing agent decomposition inhibitor in an amount of 1 to 10% by mass. In some embodiments, the foamed layer contains a masterbatch of an antiblocking agent in an amount of 1 to 10% by mass. In some embodiments, the foamed layer contains a masterbatch of a coloring agent in an amount of 1 to 12% by mass. In some embodiments, the foamed layer has a melt flow index of 0.1 to 25 grams per 10 minutes at 190°C. In some embodiments, the foamed, irradiated, and extruded foamed layer has a melt flow index of 15 to 200 kg / m². 3It has a density of . In some embodiments, the foamed, irradiated, and extruded foam layer has an average closed cell size of 0.05 to 1.0 mm. In some embodiments, the foamed, irradiated, and extruded foam layer has a thickness of 0.2 to 50 mm. In some embodiments, the ionizing radiation is selected from the group consisting of alpha rays, beta rays (electron beams), X-rays, gamma rays, and neutrons. In some embodiments, the extruded foam layer is irradiated up to four times. In some embodiments, the ionizing radiation crosslinks the extruded foam layer to a degree of crosslinking of 20 to 75%. In some embodiments, foaming includes the step of heating the irradiated and extruded foam layer with a molten salt and a radiation heater or hot air oven. In some embodiments, the method includes the step of applying a laminate layer to one side of the foamed, irradiated, and extruded foam layer. In some embodiments, the method includes the step of applying a pressure-sensitive adhesive layer to one side of the foamed, irradiated, and extruded foam layer. In some embodiments, the method further includes the step of applying a second pressure-sensitive adhesive layer to the side of the foamed, irradiated, and extruded foam layer opposite to the first pressure-sensitive adhesive layer.

[0007] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural unless explicitly indicated by the context. Furthermore, as used herein, the terms “and / or” should be understood to refer to and include any combination of one or more of the related enumerated items. Additionally, as used herein, the terms “includes,” “comprises,” and / or “comprising” identify the presence of the described features, integers, processes, operations, elements, components, and / or units, but do not exclude the presence or addition of one or more other features, integers, processes, operations, elements, components, units, and / or groups thereof.

[0008] The aspects and embodiments described herein are understood to include "consisting of" and / or "consisting essentially of" the aspects and embodiments. For all methods, systems, compositions, and apparatus described herein, such methods, systems, compositions, and apparatus may include the enumerated components or steps, or may "consist of" or "consisting essentially of" the enumerated components or steps. Where a system, composition, or apparatus is described as "consisting essentially of" the enumerated components, the system, composition, or apparatus may contain the enumerated components and may contain other components that do not substantially affect the performance of the system, but will not contain any other components other than those explicitly enumerated that substantially affect the performance of the system, composition, or apparatus, or will not contain sufficient concentrations or amounts of additional components that substantially affect the performance of the system, composition, or apparatus. Where a method is described as "essentially consisting of" the listed steps, the method includes the listed steps and may include other steps that do not substantially affect the results of the method, but does not include any other steps that substantially affect the results of the method other than those explicitly listed.

[0009] In this disclosure, "substantially absent" in various embodiments means that the specific component, specific composition, specific compound, or specific ingredient is present in a mass ratio of less than about 5%, less than about 2%, less than about 1%, less than about 0.5%, less than about 0.1%, less than about 0.05%, less than about 0.025%, or less than about 0.01%. Preferably, "substantially absent" means that the specific component, specific composition, specific compound, or specific ingredient is present in a mass ratio of less than about 1%. Additional advantages will be readily apparent to those skilled in the art from the detailed description below. The examples and descriptions herein are intended to be illustrative and not restrictive. [Modes for carrying out the invention]

[0010] The invention describes a foam structure and a method for producing a crosslinked closed-cell continuous polyethylene foam structure (e.g., a film, layer, sheet, etc.) comprising low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and an olefin block copolymer (OBC). In some embodiments, the OBC may be a multi-block LLDPE copolymer containing rigid, crystallizable LLDPE copolymer "blocks" that are not randomly distributed, i.e., alternately arranged in a controlled (non-random) block arrangement. In some embodiments, the polyethylene foam structure may be obtained by (a) extruding a foam composition, (b) irradiating the extruded foam composition with ionizing radiation, and (c) foaming the extruded and irradiated composition. In the extrusion process, the raw materials for the foam composition can be supplied to the extruder. The method of supplying the components to the extruder may be selected based on the design of the extruder and the available material handling equipment. To facilitate the dispersion of the components, pre-blending of the components of the foam composition may be performed if necessary or desired. If pre-blending is performed, a Henschel mixer may be used. In some embodiments, all components can be pre-blended and supplied through a single port of the extruder. In some embodiments, the components can also be supplied individually through separate designated ports for each component, or to a single port of the extruder. For example, if the components are liquid, the liquid may be added through the feed gate (or multiple gates) of the extruder, or through the exhaust port (if an exhaust port is provided), instead of being pre-blended with the solid components. A combination of pre-blending and supplying individual component ports may also be used. Exemplary extrusion techniques are also disclosed in Chapter 8 of the Handbook of Polymeric Foam and Foam Technology (2nd edition, edited by Daniel Klempner and Vahid Sendijarevic), the contents of which are incorporated herein by reference in their entirety.

[0011] In some embodiments, the extruder can supply a certain amount of foamed composition to the sheet forming die to create a non-foamed sheet composition. The thickness of the non-foamed sheet can be controlled across the entire width of the die gap. However, the sheet thickness can be further adjusted, for example, by stretching (i.e., "drawing") the molten extruder and / or by passing the molten extruder through a nip to flatten it. The term "foamed structure" as used herein should be understood to encompass a variety of foamed structures, including, but not limited to, foamed sheets, films, layers, and the like. The foamed composition supplied to the extruder may include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and olefin block copolymers (OBCs). In some embodiments, the OBC may be a multi-block LLDPE copolymer containing harder, crystallizable LLDPE copolymer "blocks" that are not randomly distributed, i.e., alternately arranged in a controlled (non-random) block arrangement, where amorphous, softer LLDPE copolymer "blocks" are not randomly distributed.

[0012] In some embodiments, the foamed composition supplied to the extruder may be at least about 70% by mass, at least about 75% by mass, at least about 80% by mass, or at least about 85% by mass of LDPE, LLPDE, OBC, or a combination thereof. In some embodiments, the foamed composition supplied to the extruder may be up to about 90% by mass, up to about 87% by mass, up to about 84% by mass, or up to about 81% by mass of LDPE, LLPDE, OBC, or a combination thereof. In some embodiments, the foamed composition supplied to the extruder may be about 70-90% by mass, about 75-87% by mass, or about 80-84% by mass of LDPE, LLPDE, OBC, or a combination thereof.

[0013] In some embodiments, the amount of LDPE, LLDPE, or a combination of LDPE and LLDPE in the polyethylene foam composition supplied to the extruder may be at least about 30% by mass, at least about 35% by mass, at least about 40% by mass, at least about 45% by mass, at least about 48% by mass, at least about 50% by mass, at least about 52% by mass, at least about 55% by mass, at least about 58% by mass, or at least about 60% by mass of LDPE, LLDPE, or a combination of LDPE and LLDPE in the polyethylene foam composition supplied to the extruder. In some embodiments, the amount of LDPE, LLDPE, or a combination thereof in the polyethylene foam composition supplied to the extruder may be up to about 42% by mass, up to about 45% by mass, up to about 50% by mass, up to about 52% by mass, up to about 55% by mass, up to about 58% by mass, up to about 60% by mass, up to about 62% by mass, up to about 65% by mass, up to about 68% by mass, up to about 70% by mass, or a combination of LDPE and LLDPE in the polyethylene foam composition supplied to the extruder. In some embodiments, the amount of LDPE, LLDPE, or a combination thereof in the polyethylene foam composition supplied to the extruder may be about 30-80% by mass, about 35-75% by mass, about 35-70% by mass, about 40-65% by mass, about 40-60% by mass, about 40-55% by mass, about 40-50% by mass, about 45-65% by mass, about 45-60% by mass, about 45-55% by mass, about 48-62% by mass, about 48-60% by mass, about 48-58% by mass, about 50-65% by mass, or about 50-60% by mass of LDPE, LLDPE, or a combination of LDPE and LLDPE.

[0014] In some embodiments, the amount of LDPE, LLDPE, or a combination of LDPE and LLDPE in the polyethylene foam composition supplied to the extruder may be about 15, 20, 25, 30, 35, 40, 45, or 50 PHR or more of LDPE, LLDPE, or a combination of LDPE and LLDPE. In some embodiments, the amount of LDPE, LLDPE, or a combination of LDPE and LLDPE in the polyethylene foam composition supplied to the extruder may be about 50, 55, 60, 65, 70, 75, 80, or 85 PHR or less of LDPE, LLDPE, or a combination of LDPE and LLDPE. In some embodiments, the amount of LDPE, LLDPE, or a combination of LDPE and LLDPE in the polyethylene foam composition supplied to the extruder may be about 15-85, 15-80, 15-75, 20-85, 20-80, 20-75, 50-85, 50-80, 50-75, 50-70, 50-65, 50-60, 60-85, 60-80, 60-75, 70-85, or 70-80 PHR of LDPE, LLDPE, or a combination of LDPE and LLDPE.

[0015] In some embodiments, the amount of LDPE in the polyethylene foam composition supplied to the extruder may be at least about 10% by mass, at least about 15% by mass, at least about 18% by mass, at least about 20% by mass, at least about 22% by mass, at least about 24% by mass, at least about 26% by mass, at least about 30% by mass, at least about 35% by mass, at least about 38% by mass, at least about 40% by mass, at least about 42% by mass, at least about 45% by mass, at least about 48% by mass, at least about 50% by mass, or at least about 55% by mass. In some embodiments, the amount of LDPE in the polyethylene foam composition supplied to the extruder may be up to about 40% by mass, up to about 45% by mass, up to about 48% by mass, up to about 50% by mass, up to about 52% by mass, up to about 55% by mass, up to about 60% by mass, up to about 62% by mass, up to about 65% by mass, up to about 70% by mass, up to about 73% by mass, up to about 75% by mass, or up to about 80% by mass. In some embodiments, the amount of LDPE in the polyethylene foam composition supplied to the extruder may be about 10-80% by mass, about 15-75% by mass, about 20-70% by mass, about 24-65% by mass, about 20-30% by mass, about 35-45% by mass, about 35-55% by mass, about 35-50% by mass, about 45-55% by mass, about 45-60% by mass, about 50-60% by mass, or about 50-65% by mass of LDPE. In some embodiments, the amount of LDPE in the polyethylene foam composition supplied to the extruder may be about 20, 25, 30, 35, 40, 45, or 50 PHR or more of LDPE. In some embodiments, the amount of LDPE in the polyethylene foam composition supplied to the extruder may be about 50, 55, 60, 65, 70, 75, or 80 PHR or less of LDPE. In some embodiments, the amount of LDPE in the polyethylene foam composition supplied to the extruder may be about 20-80, 20-75, 25-80, 25-75, 30-80, 30-75, 30-70, 30-65, 30-60, 30-55, 30-50, 50-80, 50-75, 50-70, 50-60, 60-80, 60-75, or 70-80 PHR of LDPE.

[0016] In some embodiments, the amount of LLDPE in the polyethylene foam composition supplied to the extruder may be at least about 5% by mass, at least about 8% by mass, at least about 10% by mass, at least about 12% by mass, at least about 15% by mass, at least about 17% by mass, at least about 20% by mass, at least about 22% by mass, at least about 24% by mass, at least about 25% by mass, at least about 26% by mass, at least about 30% by mass, or at least about 35% by mass. In some embodiments, the amount of LLDPE in the polyethylene foam composition supplied to the extruder may be up to about 30% by mass, up to about 35% by mass, up to about 40% by mass, up to about 42% by mass, up to about 44% by mass, up to about 45% by mass, up to about 46% by mass, up to about 48% by mass, up to about 50% by mass, up to about 52% by mass, up to about 55% by mass, up to about 60% by mass, or up to about 65% by mass. In some embodiments, the amount of LLDPE in the polyethylene foam composition supplied to the extruder may be about 5-65% by mass, about 5-60% by mass, about 10-55% by mass, about 15-50% by mass, about 10-20% by mass, about 10-30% by mass, about 20-30% by mass, about 20-40% by mass, about 20-50% by mass, about 20-55% by mass, about 40-50% by mass, about 40-55% by mass, about 45-55% by mass, or about 45-50% by mass of LLDPE.

[0017] In some embodiments, the amount of LLDPE in the polyethylene foam composition supplied to the extruder may be about 15, 20, 25, 30, 35, 40, 45, or 50 PHR or more of LLDPE. In some embodiments, the amount of LLDPE in the polyethylene foam composition supplied to the extruder may be about 50, 55, 57.5, 60, 65, or 70 PHR or less of LLDPE. In some embodiments, the amount of LLDPE in the polyethylene foam composition supplied to the extruder may be about 15-70, 15-65, 15-60, 20-70, 20-65, 20-60, 20-40, 20-30, 30-70, 30-65, 30-60, 50-70, 50-65, or 50-60 PHR of LLDPE. In some embodiments, the amount of OBC in the polyethylene foam composition supplied to the extruder may be at least about 10% by mass, at least about 15% by mass, at least about 20% by mass, at least about 22% by mass, at least about 25% by mass, at least about 27% by mass, at least about 30% by mass, at least about 32% by mass, at least about 35% by mass, at least about 38% by mass, or at least about 40% by mass. In some embodiments, the amount of OBC in the polyethylene foam composition supplied to the extruder may be up to about 20% by mass, up to about 25% by mass, up to about 30% by mass, up to about 32% by mass, up to about 35% by mass, up to about 37% by mass, up to about 40% by mass, up to about 45% by mass, up to about 48% by mass, or up to about 50% by mass. In some embodiments, the amount of OBC in the polyethylene foam composition supplied to the extruder may be about 10-50% by mass, about 15-45% by mass, about 20-40% by mass, about 20-35% by mass, about 20-30% by mass, about 22-35% by mass, about 22-32% by mass, about 25-35% by mass, about 30-45% by mass, or about 30-40% by mass of OBC.

[0018] In some embodiments, the amount of OBC in the polyethylene foam composition supplied to the extruder may be about 15, 20, 25, 26, 30, 35, or 40 PHR or more of OBC. In some embodiments, the amount of OBC in the polyethylene foam composition supplied to the extruder may be about 42, 42.5, 43, 45, 50, or 55 PHR or less of OBC. In some embodiments, the amount of OBC in the polyethylene foam composition supplied to the extruder may be about 15-55, 15-50, 15-45, 15-40, 20-55, 20-50, 20-45, 20-40, 25-55, 25-50, 25-45, 25-40, 25-35, 30-55, 30-50, 30-45, 30-40, 35-55, 35-50, 35-45, 40-55, or 40-50 PHR of OBC. Since a wide range of foamed articles can be created using the disclosed foamed compositions, a wide range of LD, LLD, and OBC polyethylenes can be used in the compositions to meet various manufacturing process requirements and commercial end-use requirements.

[0019] "LDPE" is a low-density polyethylene homopolymer commonly produced in high-pressure tubular reactors and autoclave reactors. In the reaction, gaseous ethylene monomers are polymerized under very high pressure and high temperature in the presence of an oxide initiator, generating a polymer structure with long and short chain branches. LDPE is one of the most widely commercially produced general-purpose thermoplastic resins in the world and is manufactured by large multinational companies (Dow, ExxonMobil, LyondellBasell, Sinopec, PetroChina, SABIC, Borealis, etc.) and small and medium-sized enterprises (Westlake, Nova, Japan Polyethylene, Repsol, PKN Orlen, Carmel, etc.). Non-limiting examples of commercial LDPE grades are marketed under various trade names. For example, the LDPE manufacturers listed above sell commercial grades under the trade names Dow™ LDPE (Dow), ExxonMobil™ LDPE (ExxonMobil), SINOPEC LDPE (Sinopec), SABIC® LDPE, Borealis LDPE, Westlake Polyethylene™ (Westlake), NOVAPOL® (Nova), NOVATEC®-LD (Japan Polyethylene), Repsol Alcudia and Repsol PE Ultraclean® (Repsol), Malen (PKN Orlen), and Ipethene® (Carmel).

[0020] "LLDPE" is a linear low-density polyethylene generally produced at a significantly lower temperature than LDPE in a low-pressure fluidized bed reactor. In the reaction, gaseous ethylene monomers (and very common additional α-olefin comonomers) are polymerized by a multi-site transition metal Ziegler-Natta type catalyst, generating a substantially linear polymer structure with much more but shorter branches compared to LDPE. Long chain branches do not exist in LLDPE. LLDPE can be a polyethylene homopolymer, but commercially it is more commonly produced as a random copolymer or a random terpolymer. Most commercial LLDPE is copolymerized with at least one C3-C20 α-olefin, of which 1-butene, 1-hexene, and 1-octene are the most typical.

[0021] Many manufacturers of LDPE polymers also produce LLDPE polymers. Non-limiting examples of commercial LLDPE grades from the LDPE manufacturers listed above are the trade names Dow™ LLDPE and Dowlex™ (Dow), ExxonMobil™ LLDPE and ExxonMobil™ NTX LLDPE (ExxonMobil), SINOPEC LLDPE (Sinopec), SABIC® LLDPE (Sabic), Borealis LLDPE and Borstar® (Borealis), HIFOR® and HIFOR Xtreme® (Westlake), NOVAPOL® and SCLAIR® and SURPASS® (Nova), and NOVATEC®-LL (Japan Polyethylene), which are commercially available and sold. Polyethylene-based OBCs (hereinafter referred to as OBCs) are multi-block LLDPE copolymers containing more rigid, crystallizable LLDPE copolymer "blocks" that are not randomly distributed, but alternately arranged in a controlled (non-random) block arrangement, i.e., amorphous, more flexible LLDPE copolymer "blocks". The more flexible blocks contain a larger amount of comonomers (most commonly C3-C20α-olefins) than the more rigid blocks. OBCs are produced in a reactor by a tandem catalytic process using two "post-metallocene" (non-metallocene single-site and / or non-metallocene single-site) catalysts, with one catalyst used for polymerization of each block. Polymer synthesis is carried out by transferring polymer chains from one catalyst to the other (and vice versa), and is called "chain shuttle copolymerization". Examples of OBCs, but not limited to, include Dow's INFUSE® OBC product line. In the commercially manufactured INFUSE® OBC product line, the comonomer is 1-octene in both the harder and softer blocks.

[0022] The polyethylene in the foamed sheets provided herein may have a melt flow index of about 0.1 to about 25 grams per 10 minutes at 190°C. In some embodiments, the melt flow index of polyethylene is about 0.3 to about 20 grams per 10 minutes at 190°C, or about 0.5 to about 15 grams per 10 minutes at 190°C. The “Melt Flow Index” (MFI) values ​​of polyethylene provided herein are defined and measured according to ASTM D1238 using a 2.16 kg plunger at 190°C for 10 minutes. For resins with relatively high melt flowability, the test time may be shortened.

[0023] MFI can provide a measure of the flow properties of a polymer and is an indicator of the molecular weight and processability of the polymer material. High MFI values ​​correspond to low viscosity. If the MFI value is excessively high, extrusion according to this disclosure may not be satisfactory. Problems associated with excessively high MFI values ​​may include low pressure during extrusion, problems with setting the thickness profile, uneven cooling profile due to low melt viscosity, low melt strength, and / or mechanical problems. Conversely, low MFI values ​​can correspond to high viscosity. Excessively low MFI values ​​may result in high pressure during melt processing, problems with sheet quality and profile, and high extrusion temperatures that lead to the risk of decomposition and activation of chemical blowing agents. The above MFI range represents the viscosity of the material, and since viscosity affects foaming, it can be important for the foaming process. While not bound by theory, there are several possible reasons why a particular MFI value may be more effective. Lower MFI materials may have improved physical properties because the longer molecular chain length increases the energy required for the chains to flow when stress is applied. Also, the longer the molecular chain (higher MW), the more crystalline units that the chain can crystallize into, thus resulting in higher strength through intermolecular bonding. However, excessively low MFI can lead to excessively high viscosity. On the other hand, polymers with higher MFI may have shorter chains. Therefore, a given volume of material with a higher MFI value may contain more chain ends at a microscopic level compared to polymers with a lower MFI, and these can rotate, creating free volume due to the space required for such rotation (e.g., rotation occurs at temperatures higher than the polymer's Tg, i.e., glass transition temperature). This increases the free volume, making it more fluid under stress, which can lead to cell degradation and "collapse" of the foamed polymer blend.

[0024] In addition to the polymer, the composition supplied to the extruder may contain additives suitable for producing the disclosed polyethylene foam. Common additives include, but are not limited to, chemical blowing agents (CFAs), crosslinking accelerators, organic peroxides, antioxidants, lubricants, processing aids, heat stabilizers, colorants, flame retardants, antistatic agents, electrostatic dissipators, nucleating agents, plasticizers, antimicrobial agents, antifungal agents, light stabilizers, UV absorbers, typically anti-tacks, fillers, deodorants, odor adsorbents, anti-fogging agents, volatile organic compound (VOC) adsorbents, semi-volatile organic compound (SVOC) adsorbents, thickeners, bubble size stabilizers, metal deactivators, chemical blowing agent (CFA) decomposition accelerators, chemical blowing agent (CFA) inhibitors, optical clearing agents, and combinations thereof. In some embodiments, the foam composition may contain a chemical blowing agent (CFA). In some embodiments, the extrusion temperature of the foam composition may be at least 10°C lower than the thermal decomposition onset temperature of the chemical blowing agent. If the extrusion temperature exceeds the thermal decomposition temperature of the blowing agent, the blowing agent may decompose, potentially resulting in undesirable "pre-foaming."

[0025] In some embodiments, the foaming composition may include a variety of different chemical blowing agents, including both heat-releasing and heat-absorbing types. Examples of chemical blowing agents include, but are not limited to, azo compounds, hydrazine compounds, carbazides, tetrazoles, nitroso compounds, and carbonates. Furthermore, chemical blowing agents may be used alone or in any combination. One type of chemical blowing agent that may be used in some embodiments is azodicarbonamide (ADCA). Two examples of commercially produced ADCA chemical blowing agents are UNIFOAM® TC-18I (100% ADCA) manufactured by PT Lauten Otsuka Chemical and VINYFOR® AC-961 (≧90% ADCA) manufactured by Eiwa Chemical. The thermal decomposition of ADCA typically occurs at temperatures between approximately 190 and 230°C. In some embodiments, the extrusion temperature may be maintained below 190°C to prevent the ADCA from thermally decomposing in the extruder. The amount of chemical blowing agent in the foamed composition may be about 30 PHR, about 20 PHR, about 15 PHR, or about 11 PHR or less of the composition. In some embodiments, the amount of chemical blowing agent in the foamed composition may be about 2 PHR, about 4 PHR, about 6 PHR, or about 8 PHR or more of the composition. In some embodiments, the amount of chemical blowing agent in the foamed composition may be about 2 to 30 PHR, about 4 to 20 PHR, about 6 to 15 PHR, or about 8 to 11 PHR of the composition. In some embodiments, the amount of chemical blowing agent in the foamed composition may be about 1 to 30% by mass, about 3 to 20% by mass, about 5 to 14% by mass, about 5 to 10% by mass, or about 6 to 9% by mass of the composition. In some embodiments, the amount of chemical blowing agent may depend, among other things, on the thickness of the non-foamed sheet, the desired foam thickness, the desired foam density, the material being extruded, the crosslinking ratio, and the type of chemical blowing agent (different blowing agents may produce significantly different amounts of gas).

[0026] In some embodiments, the amounts of the chemical blowing agents listed above may be specific to ADCA. In some embodiments, other blowing agents may generate different amounts of volume gas per unit mass of CFA and may be taken into consideration accordingly. For example, comparing ADCA with the chemical blowing agent p-toluenesulfonyl semicarbazide (TSS), if a foamed sheet contains 40 PHR of ADCA, approximately 63 PHR of TSS may be required to generate roughly the same amount of gas during the foaming process. In some embodiments, the amount of additives other than the chemical blowing agent in the foaming composition may be about 40 PHR, about 30 PHR, about 25 PHR, or about 20 PHR or less of the composition. In some embodiments, the amount of additives other than the chemical blowing agent in the foaming composition may be about 1 PHR, about 3 PHR, about 4 PHR, or about 5 PHR or more of the composition. In some embodiments, the amount of additives other than the chemical blowing agent in the foaming composition may be about 1 to 40 PHR, about 3 to 30 PHR, about 4 to 25 PHR, or about 5 to 20 PHR of the composition. In some embodiments, the amount of additives other than the chemical blowing agent in the foaming composition may be about 1 to 35% by mass, about 2 to 25% by mass, about 3 to 20% by mass, or about 4 to 16% by mass of the foaming composition.

[0027] In some embodiments, the foam composition may contain one or more antioxidants. In some embodiments, the antioxidant may be in the form of a masterbatch. In some embodiments, the antioxidant masterbatch may include, but is not limited to, PM13633 (Techmer PM), PT213 (Toray Plastics), PM14809 (Techmer PM), each of which may contain a custom blend of commonly used polyolefin antioxidants tailored to the manufacturing process and the end-use performance requirements of the foam. In some embodiments, the amount of antioxidant masterbatch in the foam composition may be about 10 PHR, 8 PHR, or 6 PHR or less of the composition. In some embodiments, the amount of antioxidant masterbatch in the foam composition may be 1 PHR, 2 PHR, 3 PHR, or 4 PHR or more of the composition. In some embodiments, the amount of antioxidant masterbatch in the foam composition may be about 1 to 10 PHR, 1 to 8 PHR, 1 to 6 PHR, 2 to 6 PHR, or 2 to 4 PHR of the composition. In some embodiments, the amount of antioxidant masterbatch in the foamed composition may be about 0.1 to 10% by mass, about 0.25 to 8% by mass, about 0.5 to 6% by mass, about 1 to 4% by mass, about 1.5 to 4% by mass, or about 1.5 to 3.5% by mass of the foamed composition.

[0028] It is important for manufacturers and distributors of antioxidants to note that when disclosing the manufacturing process and performance requirements for the end use, they should recommend one or more specific antioxidants, recommend usage ratios between the recommended antioxidants, and suggest let-down ratios for specific foam compositions. Generally, manufacturers of polyethylene foams use masterbatches of prepared antioxidant blends. Representative manufacturers of antioxidants for polyethylene include, but are not limited to, Adeka, BASF, Clariant, SI Group, and Songwong. In some embodiments, the foaming composition may contain one or more processing aid additives. In some embodiments, the processing aid additives may be in the form of masterbatches. In some embodiments, the processing aid additive masterbatches may include, but are not limited to, TPM11166 (distributed by Techmer PM) and PM125000 (formulated by Techmer PM). In some embodiments, the amount of processing aid masterbatch in the foaming composition may be about 5 PHR, 4 PHR, or 3 PHR or less of the composition. In some embodiments, the amount of processing aid masterbatch in the foaming composition may be 1 PHR, 2 PHR, or 3 PHR or more of the composition. In some embodiments, the amount of processing aid masterbatch in the foaming composition may be about 1 to 5 PHR, 1 to 4 PHR, 1 to 3 PHR, 2 to 4 PHR, or 2 to 3 PHR of the composition. In some embodiments, the amount of processing aid masterbatch in the foamed composition may be about 0.1 to 6% by mass, about 0.1 to 5% by mass, about 0.25 to 5% by mass, about 0.5 to 5% by mass, about 0.5 to 4% by mass, about 0.5 to 3% by mass, about 0.5 to 2% by mass, about 1 to 2% by mass, or about 1.5 to 2% by mass of the foamed composition.

[0029] In some embodiments, the foaming composition may contain one or more chemical blowing agent (CFA) degradation inhibitor additives. In some embodiments, the CFA degradation inhibitor additives may be included in the form of a masterbatch. In some embodiments, examples of CFA degradation inhibitor additive masterbatches include, but are not limited to, Toray Plastics (America) masterbatch part number PT120 (formulated by Techmer PM). In some embodiments, the amount of the CFA degradation inhibitor masterbatch in the foaming composition may be about 10 PHR, 8 PHR, or 6 PHR or less of the composition. In some embodiments, the amount of the CFA degradation inhibitor masterbatch in the foaming composition may be 1 PHR, 2 PHR, 3 PHR, or 4 PHR or more of the composition. In some embodiments, the amount of the CFA degradation inhibitor masterbatch in the foaming composition may be about 1 to 10 PHR, 1 to 8 PHR, 1 to 6 PHR, 2 to 6 PHR, or 2 to 4 PHR of the composition. In some embodiments, the amount of the CFA degradation inhibitor masterbatch in the foamed composition may be about 1-10% by mass, about 1-8% by mass, about 1-6% by mass, about 1-4% by mass, about 1.5-4% by mass, or about 2-4% by mass of the foamed composition.

[0030] In some embodiments, the foaming composition may contain one or more anti-tack additives. In some embodiments, the anti-tack additives may be in the form of masterbatches. In some embodiments, the anti-tack additive masterbatches may include, but are not limited to, TPM1823 talc anti-tack, TPM1922 diatomaceous earth anti-tack, and TPM14287 calcium carbonate anti-tack (all distributed by Techmer PM). In some embodiments, the amount of anti-blocking agent masterbatch in the foaming composition may be about 10 PHR, 8 PHR, or 6 PHR or less of the composition. In some embodiments, the amount of anti-tack masterbatch in the foaming composition may be 2 PHR, 3 PHR, 4 PHR, or 5 PHR or more of the composition. In some embodiments, the amount of anti-blocking agent masterbatch in the foaming composition may be about 1 to 10 PHR, 2 to 8 PHR, 2 to 6 PHR, 3 to 6 PHR, or 4 to 6 PHR of the composition. In some embodiments, the amount of antiblocking agent masterbatch in the foaming composition may be about 1-10% by mass, about 1-8% by mass, about 1-6% by mass, about 1-4% by mass, about 2-6% by mass, about 2-4% by mass, about 2.5-3.5% by mass, or about 3% by mass of the foaming composition.

[0031] In some embodiments, the foaming composition may contain one or more colorant additives. In some embodiments, the colorant additives may be in the form of masterbatches. In some embodiments, examples of colorant additive masterbatches, but not limited to these, may include 62B17226 (black, Penn Color), PM55274 (white, Techmer PM), etc. In some embodiments, the amount of colorant masterbatch in the foaming composition may be about 15 PHR, 13 PHR, or 11 PHR or less of the composition. In some embodiments, the amount of colorant masterbatch in the foaming composition may be 2 PHR, 3 PHR, or 4 PHR or more of the composition. In some embodiments, the amount of colorant masterbatch in the foaming composition may be about 2 to 15 PHR, 2 to 13 PHR, 2 to 11 PHR, 3 to 13 PHR, or 4 to 11 PHR of the composition. In some embodiments, the amount of colorant masterbatch in the foamed composition may be about 1-12% by mass, about 1-10% by mass, about 1-9% by mass, about 2-9% by mass, or about 3-9% by mass of the foamed composition.

[0032] It is important to note that there are many color masterbatch manufacturers worldwide that produce both "off-the-shelf" color masterbatches for distribution and custom color masterbatches based on the coloring requirements of foam manufacturing processes and end-use applications. Representative manufacturers of color masterbatches for polyethylene include, but are not limited to, Techmer PM, Penn Color, Tosaf, Modern Dispersions (MDI), Colors For Plastics, Peacock Colors, Coloron Plastics, and Clariant. In some embodiments, the foaming composition may contain a black coloring agent masterbatch. For example, the amount of black coloring agent in the foaming composition may be 15 PHR, 13 PHR, or 11 PHR or less of the composition. In some embodiments, the amount of black coloring agent masterbatch in the foaming composition may be 4 PHR, 5 PHR, or 6 PHR or more of the composition. In some embodiments, the amount of black coloring agent masterbatch in the foaming composition may be about 4 to 15 PHR, 5 to 13 PHR, or 6 to 11 PHR of the composition. In some embodiments, the amount of black coloring agent masterbatch in the foaming composition may be about 4 to 12% by mass, about 4 to 11% by mass, about 5 to 10% by mass, or about 6 to 9% by mass of the foaming composition.

[0033] In some embodiments, the foaming composition may contain a white coloring agent masterbatch. For example, the amount of white coloring agent masterbatch in the foaming composition may be 10 PHR, 8 PHR, or 7 PHR or less of the composition. In some embodiments, the amount of white coloring agent masterbatch in the foaming composition may be 2 PHR, 3 PHR, or 4 PHR or more of the composition. In some embodiments, the amount of white coloring agent masterbatch in the foaming composition may be about 2 to 10 PHR, about 3 to 8 PHR, or about 4 to 7 PHR of the composition. In some embodiments, the amount of white coloring agent masterbatch in the foaming composition may be about 1 to 8% by mass, about 1 to 7% by mass, about 1 to 6% by mass, or about 2 to 6% by mass of the foaming composition. Regardless of how the components of the foam composition are supplied to the extruder, the shear force and mixing within the extruder may be sufficient to produce a uniform layer (otherwise referred to herein as a sheet, film, structure, etc.). Twin-screw extruders with co-rotating and counter-rotating shafts can provide sufficient shear force and mixing through the extruder barrel to extrude a sheet having uniform properties.

[0034] Specific energy can be an indicator of how much work is applied during the extrusion of a component and how intensive the extrusion process is. Specific energy is defined by normalizing the energy applied to the material processed by the extruder to a per-kilogram basis. Specific energy can be quantified in kilowatts as the energy applied to the total amount of material supplied per kilogram per hour. Specific energy can be calculated according to the following formula:

number

[0035] If there is a large difference between the decomposition temperature of the pyrolytic blowing agent and the melting point of the polymer with the highest melting point, a catalyst may be used to decompose the blowing agent. Exemplary catalysts, but not limited to these, include zinc oxide, magnesium oxide, calcium stearate, glycerin, and urea. The lower limit temperature of extrusion may be the lower limit temperature of the polymer with the highest melting point. If the extrusion temperature is below the melting point of the polymer with the highest melting point, undesirable "unmelted material" may be produced. During foaming, sheets extruded below this lower limit temperature may exhibit uneven thickness, uneven cellular structure, void pockets, and / or other undesirable properties. Regardless of whether the foaming agent is physical, chemical, or a combination, typical extruded foaming can produce polymer sheets (e.g., layers, films, structures) in which both major surfaces may be significantly rougher than equivalent structures produced by the disclosed method. The surface morphology of the foamed sheet can be important in many applications, and therefore extruded foamed sheets may not be suitable for these applications. These applications may include smooth foamed surfaces to obtain desired properties, such as improved contact area ratio when applying pressure-sensitive adhesives (PSAs) to the foamed surface, ease of lamination to films, fabrics, fiber layers, and leathers, contact area ratio in lamination, and / or visual aesthetics. PCT International Publication 2016109544, which is incorporated in its entirety by reference herein, includes examples demonstrating the difference in surface roughness between extruded foamed polymer sheets and equivalent foamed polymer sheets produced by the disclosed method.

[0036] The rough surface of extruded foamed articles can generally be caused by larger-sized bubbles (compared to foams manufactured according to this disclosure). While bubble size and bubble size distribution may not be a concern for most commercial applications, surface roughness is a function of bubble size, and therefore, in applications requiring a smooth foamed surface, foams with larger bubbles may be less desirable than foams with smaller bubbles. The thickness of the non-foamed extruded sheet may be approximately 0.1 to 30 mm, approximately 0.2 to 25 mm, approximately 0.3 to 20 mm, or approximately 0.4 to 15 mm. In some embodiments, the non-foamed extruded sheet may have a thickness of approximately 0.1 to 5 mm, approximately 0.5 to 3 mm, approximately 1 to 2 mm, or approximately 1 to 1.5 mm. In some embodiments, the non-foamed extruded sheet may have a thickness of approximately 5 mm, approximately 3 mm, approximately 2 mm, approximately 1.5 mm, approximately 1 mm, or approximately 0.5 mm or less. In some embodiments, the non-foamed extruded sheet may have a thickness of approximately 0.1 mm, approximately 0.5 mm, approximately 1 mm, approximately 1.5 mm, approximately 2 mm, or approximately 3 mm or more. In this disclosure, the thickness of a non-foamed extruded sheet is measured using a thickness gauge, the sheet is placed on a flat horizontal surface and brought into contact with a spring-loaded plunger incorporated into the gauge. A hemispherical tip with a diameter of 3 mm is attached to the plunger and contacts the sheet with a force of 26.5 ± 3.5 grams.

[0037] There is a difference between "physical" crosslinking and "chemical" crosslinking. In chemical crosslinking, crosslinking is generated using a crosslinking accelerator, but ionizing radiation is not used. Chemical crosslinking typically involves the use of peroxides, silanes, or vinylsilanes. In peroxide crosslinking processes, crosslinking typically occurs within the extrusion die. In silane and vinylsilane crosslinking processes, crosslinking typically occurs in a post-extrusion secondary operation, where heat and moisture promote crosslinking of the extruded material. Regardless of the chemical crosslinking method, chemically crosslinked foam sheets may typically exhibit a significantly rougher primary surface than equivalent structures produced by the disclosed methods. The surface morphology of foam sheets can be important in many applications, and therefore chemically crosslinked foam sheets may not be suitable for certain applications. These applications may include obtaining desired properties, such as a smooth foam surface to improve the contact area ratio when applying pressure-sensitive adhesives (PSAs) to the foam surface, ease of lamination to films, fabrics, fiber layers, and leathers, contact area ratio in lamination, and / or visual aesthetics. PCT International Publication 2016109544 includes an example demonstrating the difference in surface roughness between a chemically crosslinked foamed polymer sheet and an equivalent foamed polymer sheet manufactured by the disclosed method.

[0038] The rough surface of chemically crosslinked foams can generally be caused by larger-sized bubbles (compared to foams manufactured according to this disclosure). While size and bubble size distribution may not be a concern for most commercial applications, surface roughness is a function of bubble size, and therefore, foams with larger bubbles may be less desirable than foams with smaller bubbles in applications requiring a smooth foam surface.

[0039] Examples of ionizing radiation include, but are not limited to, alpha rays, beta rays (electron beams), X-rays, gamma rays, and neutrons. Among these, electron beams with uniform energy can be used to crosslink foamed sheets. The exposure time, irradiation frequency (i.e., number of passes or exposures to radiation), and / or acceleration voltage during electron beam irradiation can vary considerably depending on the intended degree of crosslinking and the thickness of the non-foamed sheet. However, ionizing radiation can generally be in the range of about 10 to about 500 kGy, about 20 to about 300 kGy, or about 20 to about 200 kGy. If the exposure is too low, the crosslinking may be insufficient, and the stability of the bubbles may not be maintained during foaming. If the exposure is too high, the irradiated sheet may curl or ripple excessively during foaming, making it difficult to produce a flat and uniform foamed sheet. Also, highly irradiated sheets may become highly crosslinked, and this crosslinking significantly reduces the ability of the polymer system to substantially stretch. When the extensibility of the polymer system decreases, the foam may tear or burst during foaming if the expansion of the foam exceeds the final elongation characteristics of the irradiated composition. Furthermore, exposure to electron beam radiation can cause exothermic heat release, softening of non-foamed sheets, and excessive exposure may lead to structural deformation. In addition, polymer components may degrade due to the severance of excess polymer chains.

[0040] Non-foamed sheets may be irradiated up to four times, two times or less, or only once. If the number of irradiations exceeds approximately four, the polymer components may degrade, and during foaming, for example, uniform bubbles may not be formed in the resulting foam. If the thickness of the extruded sheet exceeds approximately 4 mm, irradiating each major surface of the sheet with ionizing radiation can make the degree of crosslinking more uniform throughout the depth direction of the sheet. Electron beam irradiation offers the advantage of effectively crosslinking extruded sheets of various thicknesses by controlling the electron acceleration voltage. The acceleration voltage can generally range from approximately 200 to 1500 kV, 300 to 1200 kV, or 400 to 1000 kV. If the acceleration voltage is below approximately 200 kV, the radiation may not reach the inner portion of the extruded sheet. As a result, the bubbles in the inner portion may be coarse and non-uniform during foaming. Furthermore, an acceleration voltage excessively low for a given thickness profile may cause arc discharge, potentially resulting in "pinholes" or "tunnels" in the foamed structure. On the other hand, if the acceleration voltage exceeds approximately 1500 kV, the polymer may degrade due to excessive radiation exposure.

[0041] Regardless of the type of ionizing radiation selected, crosslinking results in the extruded structure being crosslinked to approximately 15% to 75%, 20% to 60%, 25% to 50%, or 30% to 40% when measured by the Toray Gel Fraction Percentage Method. According to the Toray Gel Fraction Percentage Method, tetralin solvent is used to dissolve the non-crosslinked components in the composition. In principle, the non-crosslinked material dissolves in tetralin, and the degree of crosslinking is expressed as the mass percentage of the crosslinked material in the entire composition. Apparatus used to determine the percentage of polymer crosslinking includes a 100-mesh (0.0045-inch wire diameter) Type 304 stainless steel bag, numbered wires and clips, a Miyamoto constant temperature oil bath apparatus, an analytical balance, a fume hood, a gas burner, a high-temperature oven, an anti-static gun, and three 3.5-liter wide-mouth stainless steel containers with lids. Reagents and materials used include tetralin high molecular weight solvent, acetone, and silicone oil. In detail, an empty wire mesh bag is weighed and its mass recorded. For each sample, 100 milligrams ± 5 milligrams of sample are weighed and transferred to a wire mesh bag. The mass of the wire mesh bag and the sample in the form of typically thinly sliced ​​foam sections is recorded. Each bag is attached to a wire and clip with the corresponding number. When the solvent temperature reaches 130°C, the bundle (bags and sample) is immersed in the solvent. The sample is shaken up and down about 5-6 times to remove air bubbles and thoroughly wet the sample. The sample is placed in a stirrer and stirred for 3 hours to allow the solvent to dissolve the foam. The sample is then cooled in a fume hood. The sample is washed by shaking it up and down about 7-8 times in a container with the first acetone. The sample is washed a second time with a second acetone wash. The washed sample is washed again in a third container with fresh acetone in the same manner as above. The sample is then suspended in a fume hood for about 1-5 minutes to allow the acetone to evaporate. Next, dry the sample in a 120°C drying oven for approximately 1 hour. Cool the sample for at least 15 minutes. Weigh the wire mesh bag using an analytical balance and record the mass.Next, the degree of crosslinking is calculated using the formula 100 × (CA) / (BA) (wherein A = mass of the empty wire mesh bag, B = mass of the wire bag + foam sample before tetralin immersion, and C = mass of the wire bag + dissolved sample after tetralin immersion).

[0042] No crosslinking accelerators were added to the exemplary formulations of this disclosure. However, crosslinking accelerators may be optionally used to reduce the exposure of the foamed sheet to ionizing radiation and to obtain the desired gel. Suitable crosslinking accelerators include, but are not limited to, commercially available bifunctional, trifunctional, tetrafunctional, pentafunctional, and more functional monomers. Such crosslinking monomers are available in liquid, solid, pellet, and powder forms. Examples, though not limited to these, include acrylates or methacrylates, such as 1,6-hexanediol diacrylate, 1,6-hexanediol dimethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethyl acrylate, trimethylolpropane trimethyl acrylate, tetramethylolmethane triacrylate, 1,9-nonanediol dimethacrylate, and 1,10-decanediol dimethacrylate; allyl esters of carboxylic acids (e.g., triallyl trimellitate, triallyl pyromellitate, and diallyl oxalate); allyl esters of cyanuric acid or isocyanuric acid, such as triallyl cyanurate and triallyl isocyanurate; maleimide compounds, such as N-phenylmaleimide and N,N'-m-phenylenebismaleimide; compounds having at least two tribonds, such as dipropagyl phthalate and dipropagyl maleate; and divinylbenzene. Furthermore, such crosslinking accelerators may be used alone or in any combination.

[0043] The crosslinking efficiency of a crosslinking accelerator may vary depending on the dose of ionizing radiation, the chemical structure of the polymer and monomer being crosslinked, the number of functional groups in the monomer, and / or whether the monomer is a liquid or a powder. Crosslinking may be generated using a variety of different techniques and can be formed both intermolecularly between different polymer molecules and intramolecularly between parts of a single polymer molecule. Such techniques include, but are not limited to, (a) a step of exposing polymer molecules to ionizing radiation, (b) a step of providing a crosslinking promoter separate from the polymer chain and exposing the crosslinking promoter and the polymer to ionizing radiation, and / or (c) a step of providing a polymer chain incorporating the crosslinking promoter as a functional group capable of forming crosslinks or that can be activated to form crosslinks. Foaming may be achieved by irradiating the extruded sheet and then heating the crosslinked sheet to a temperature higher than the decomposition temperature of the pyrolytic foaming agent. In some embodiments, foaming can be carried out in a continuous process at approximately 200-260°C or approximately 220-240°C. A continuous foaming process may be preferred over a batch process in the production of continuously foamed sheets. Foaming can typically be carried out by heating the crosslinked sheet with molten salt, a radiation heater, a vertical or horizontal hot air oven, microwave energy, or a combination of these methods. Alternatively, foaming may be carried out by an impregnation process using nitrogen in an autoclave, for example, followed by free foaming via molten salt, a radiation heater, a vertical or horizontal hot air oven, microwave energy, or a combination of these methods. Optionally, the crosslinked sheet can be softened by preheating before foaming. This can help stabilize the expansion of the structure during foaming, especially in thick and rigid sheets.

[0044] In some embodiments, the polyethylene foam structure may include at least about 70% by mass, at least about 75% by mass, at least about 80% by mass, or at least about 85% by mass of LDPE, LLPDE, or a combination of LDPE and LLDPE, and OBC. In some embodiments, the polyethylene foam structure may be up to about 90% or less, up to about 87%, up to about 84%, or up to about 81% of LDPE, LLPDE, or a combination of LDPE and LLDPE, and OBC. In some embodiments, the polyethylene foam structure may be about 70-90% by mass, about 75-87% by mass, or about 80-84% by mass of LDPE, LLPDE, or a combination of LDPE and LLDPE, and OBC.

[0045] In some embodiments, the amount of LDPE, LLDPE, or a combination of LDPE and LLDPE in the polyethylene foam structure may be at least about 30% by mass, at least about 35% by mass, at least about 40% by mass, at least about 45% by mass, at least about 48% by mass, at least about 50% by mass, at least about 52% by mass, at least about 55% by mass, at least about 58% by mass, or at least about 60% by mass of LDPE, LLDPE, or a combination of LDPE and LLDPE. In some embodiments, the amount of LDPE, LLDPE, or a combination thereof in the polyethylene foam structure may be up to about 42% by mass, up to about 45% by mass, up to about 50% by mass, up to about 52% by mass, up to about 55% by mass, up to about 58% by mass, up to about 60% by mass, up to about 62% by mass, up to about 65% by mass, up to about 68% by mass, up to about 70% by mass, or a combination of LDPE and LLDPE. In some embodiments, the amount of LDPE, LLDPE, or a combination thereof in the polyethylene foam structure may be about 30-80% by mass, about 35-75% by mass, about 35-70% by mass, about 40-65% by mass, about 40-60% by mass, about 40-55% by mass, about 40-50% by mass, about 45-65% by mass, about 45-60% by mass, about 45-55% by mass, about 48-62% by mass, about 48-60% by mass, about 48-58% by mass, about 50-65% by mass, or about 50-60% by mass of LDPE, LLDPE, or a combination of LDPE and LLDPE.

[0046] In some embodiments, the amount of LDPE, LLDPE, or a combination of LDPE and LLDPE in the polyethylene foam structure may be about 15, 20, 25, 30, 35, 40, 45, or 50 PHR or more of LDPE, LLDPE, or a combination of LDPE and LLDPE. In some embodiments, the amount of LDPE, LLDPE, or a combination of LDPE and LLDPE in the polyethylene foam structure may be about 50, 55, 60, 65, 70, 75, 80, or 85 PHR or less of LDPE, LLDPE, or a combination of LDPE and LLDPE. In some embodiments, the amount of LDPE, LLDPE, or a combination of LDPE and LLDPE in the polyethylene foam structure may be approximately 15-85, 15-80, 15-75, 20-85, 20-80, 20-75, 50-85, 50-80, 50-75, 50-70, 50-65, 50-60, 60-85, 60-80, 60-75, 70-85, or 70-80 PHR of LDPE, LLDPE, or a combination of LDPE and LLDPE.

[0047] In some embodiments, the amount of LDPE in the polyethylene foam structure may be at least about 10% by mass, at least about 15% by mass, at least about 18% by mass, at least about 20% by mass, at least about 22% by mass, at least about 24% by mass, at least about 26% by mass, at least about 30% by mass, at least about 35% by mass, at least about 38% by mass, at least about 40% by mass, at least about 42% by mass, at least about 45% by mass, at least about 48% by mass, at least about 50% by mass, or at least about 55% by mass. In some embodiments, the amount of LDPE in the polyethylene foam structure may be up to about 40% by mass, up to about 45% by mass, up to about 48% by mass, up to about 50% by mass, up to about 52% by mass, up to about 55% by mass, up to about 60% by mass, up to about 62% by mass, up to about 65% by mass, up to about 70% by mass, up to about 73% by mass, up to about 75% by mass, or up to about 80% by mass. In some embodiments, the amount of LDPE in the polyethylene foam structure may be about 10-80% by mass, about 15-75% by mass, about 20-70% by mass, about 24-65% by mass, about 20-30% by mass, about 35-45% by mass, about 35-55% by mass, about 35-50% by mass, about 45-55% by mass, about 45-60% by mass, about 50-60% by mass, or about 50-65% by mass of LDPE.

[0048] In some embodiments, the amount of LDPE in the polyethylene foam structure may be about 20, 25, 30, 35, 40, 45, or 50 PHR or more of LDPE. In some embodiments, the amount of LDPE in the polyethylene foam structure may be about 50, 55, 60, 65, 70, 75, or 80 PHR or less of LDPE. In some embodiments, the amount of LDPE in the polyethylene foam structure may be about 20-80, 20-75, 25-80, 25-75, 30-80, 30-75, 30-70, 30-65, 30-60, 30-55, 30-50, 50-80, 50-75, 50-70, 50-60, 60-80, 60-75, or 70-80 PHR of LDPE. In some embodiments, the amount of LLDPE in the polyethylene foam structure may be at least about 5% by mass, at least about 8% by mass, at least about 10% by mass, at least about 12% by mass, at least about 15% by mass, at least about 17% by mass, at least about 20% by mass, at least about 22% by mass, at least about 24% by mass, at least about 25% by mass, at least about 26% by mass, at least about 30% by mass, or at least about 35% by mass. In some embodiments, the amount of LLDPE in the polyethylene foam structure may be up to about 30% by mass, up to about 35% by mass, up to about 40% by mass, up to about 42% by mass, up to about 44% by mass, up to about 45% by mass, up to about 46% by mass, up to about 48% by mass, up to about 50% by mass, up to about 52% by mass, up to about 55% by mass, up to about 60% by mass, or up to about 65% by mass. In some embodiments, the amount of LLDPE in the polyethylene foam structure may be about 5-65% by mass, about 5-60% by mass, about 10-55% by mass, about 15-50% by mass, about 10-20% by mass, about 10-30% by mass, about 20-30% by mass, about 20-40% by mass, about 20-50% by mass, about 20-55% by mass, about 40-50% by mass, about 40-55% by mass, about 45-55% by mass, or about 45-50% by mass of LLDPE.

[0049] In some embodiments, the amount of LLDPE in the polyethylene foam structure may be about 15, 20, 25, 30, 35, 40, 45, or 50 PHR or more of LLDPE. In some embodiments, the amount of LLDPE in the polyethylene foam structure may be about 50, 55, 57.5, 60, 65, or 70 PHR or less of LLDPE. In some embodiments, the amount of LLDPE in the polyethylene foam structure may be about 15-70, 15-65, 15-60, 20-70, 20-65, 20-60, 20-40, 20-30, 30-70, 30-65, 30-60, 50-70, 50-65, or 50-60 PHR of LLDPE.

[0050] In some embodiments, the amount of OBC in the polyethylene foam structure may be at least about 10% by mass, at least about 15% by mass, at least about 20% by mass, at least about 22% by mass, at least about 25% by mass, at least about 27% by mass, at least about 30% by mass, at least about 32% by mass, at least about 35% by mass, at least about 38% by mass, or at least about 40% by mass. In some embodiments, the amount of OBC in the polyethylene foam structure may be up to about 20% by mass, up to about 25% by mass, up to about 30% by mass, up to about 32% by mass, up to about 35% by mass, up to about 37% by mass, up to about 40% by mass, up to about 45% by mass, up to about 48% by mass, or up to about 50% by mass. In some embodiments, the amount of OBC in the polyethylene foam structure may be about 10-50% by mass, about 15-45% by mass, about 20-40% by mass, about 20-35% by mass, about 20-30% by mass, about 22-35% by mass, about 22-32% by mass, about 25-35% by mass, about 30-45% by mass, or about 30-40% by mass of OBC. In some embodiments, the amount of OBC in the polyethylene foam structure may be about 15, 20, 25, 26, 30, 35, 40 PHR or more. In some embodiments, the amount of OBC in the polyethylene foam structure may be about 42, 42.5, 43, 45, 50, or 55 PHR or less. In some embodiments, the amount of OBC in the polyethylene foam structure may be about 15-55, 15-50, 15-45, 15-40, 20-55, 20-50, 20-45, 20-40, 25-55, 25-50, 25-45, 25-40, 25-35, 30-55, 30-50, 30-45, 30-40, 35-55, 35-50, 35-45, 40-55, or 40-50 PHR of OBC.

[0051] During the foaming process, the chemical blowing agent may decompose into one or more gases and one or more solids. Gas generation due to the decomposition of CFA can cause the non-foamed crosslinked sheet to expand into a buoyant structure. In the case of ADCA, the decomposition products include gases, solid organic decomposition products which may further decompose into more gases and other solid organic substances, and / or solid decomposition products. In some embodiments, after complete foaming, the polyethylene foam structure may be essentially or substantially free of CFA (e.g., ADCA). In some embodiments, the mass loss due to gas generation from the decomposition of CFA (e.g., ADCA) (including subsequent secondary decomposition reactions) ranges from about 30% to about 40%, with the remaining mass (about 60% to about 70%) consisting of various solid organic decomposition products. In some embodiments, these solid decomposition products typically do not impart any functional or useful properties to the polyethylene foam structure. In some embodiments, the amount of CFA (e.g., ADCA) solid degradation products in the polyethylene foam structure may be about 21 PHR, about 14 PHR, about 10.5 PHR, or less than or equal to about 7.7 PHR of CFA solid degradation products. In some embodiments, the amount of CFA (e.g., ADCA) solid degradation products in the polyethylene foam structure may be about 1.2 PHR, about 2.44 PHR, about 3.6 PHR, or more than about 4.8 PHR of CFA solid degradation products. In some embodiments, the amount of CFA (e.g., ADCA) solid degradation products in the polyethylene foam structure may be about 1.2 to 21 PHR, about 2.4 to 14 PHR, about 3.6 to 10.5 PHR, or about 4.8 to 7.7 PHR of CFA solid degradation products. In some embodiments, the amount of CFA (e.g., ADCA) solid degradation products in the polyethylene foam structure can be about 0.6–21% by mass, about 1.8–14% by mass, about 3–9.8% by mass, about 3–7% by mass, or about 3.6.3% by mass of CFA solid degradation products.

[0052] In some embodiments, the amount of additives other than the decomposed chemical blowing agent in the polyethylene foam structure may be about 40 PHR, about 30 PHR, about 25 PHR, or about 20 PHR or less. In some embodiments, the amount of additives other than the decomposed chemical blowing agent in the polyethylene foam structure may be about 1 PHR, about 3 PHR, about 4 PHR, or about 5 PHR or more. In some embodiments, the amount of additives other than the decomposed chemical blowing agent in the polyethylene foam structure may be about 1 to 40 PHR, about 3 to 30 PHR, about 4 to 25 PHR, or about 5 to 20 PHR. In some embodiments, the amount of additives other than the decomposed chemical blowing agent in the polyethylene foam structure may be about 1 to 35% by mass, about 2 to 25% by mass, about 3 to 20% by mass, or about 4 to 16% by mass. In some embodiments, the amount of antioxidant masterbatch in the polyethylene foam structure may be about 10 PHR, 8 PHR, or 6 PHR or less. In some embodiments, the amount of antioxidant masterbatch in the polyethylene foam structure may be 1 PHR, 2 PHR, 3 PHR, or 4 PHR or more. In some embodiments, the amount of antioxidant masterbatch in the polyethylene foam structure may be about 1 to 10 PHR, 1 to 8 PHR, 1 to 6 PHR, 2 to 6 PHR, or 2 to 4 PHR. In some embodiments, the amount of antioxidant masterbatch in the polyethylene foam structure may be about 0.1 to 10% by mass, about 0.25 to 8% by mass, about 0.5 to 6% by mass, about 1 to 4% by mass, about 1.5 to 4% by mass, or about 1.5 to 3.5% by mass.

[0053] In some embodiments, the amount of processing aid masterbatch in the polyethylene foam structure may be about 5 PHR, 4 PHR, or 3 PHR or less. In some embodiments, the amount of processing aid masterbatch in the polyethylene foam structure may be 1 PHR, 2 PHR, or 3 PHR or more. In some embodiments, the amount of processing aid masterbatch in the polyethylene foam structure may be about 1 to 5 PHR, 1 to 4 PHR, 1 to 3 PHR, 2 to 4 PHR, or 2 to 3 PHR. In some embodiments, the amount of processing aid masterbatch in the polyethylene foam structure may be about 0.1 to 6% by mass, about 0.1 to 5% by mass, about 0.25 to 5% by mass, about 0.5 to 5% by mass, about 0.5 to 4% by mass, about 0.5 to 3% by mass, about 0.5 to 2% by mass, about 1 to 2% by mass, or about 1.5 to 2% by mass.

[0054] In some embodiments, the amount of CFA degradation inhibitor masterbatch in the polyethylene foam structure may be about 10 PHR, 8 PHR, or 6 PHR or less. In some embodiments, the amount of CFA degradation inhibitor masterbatch in the polyethylene foam structure may be 1 PHR, 2 PHR, 3 PHR, or 4 PHR or more. In some embodiments, the amount of CFA degradation inhibitor masterbatch in the polyethylene foam structure may be about 1 to 10 PHR, 1 to 8 PHR, 1 to 6 PHR, 2 to 6 PHR, or 2 to 4 PHR. In some embodiments, the amount of CFA degradation inhibitor masterbatch in the polyethylene foam structure may be about 1 to 10% by mass, about 1 to 8% by mass, about 1 to 6% by mass, about 1 to 4% by mass, about 1.5 to 4% by mass, or about 2 to 4% by mass. In some embodiments, the amount of antiblocking agent masterbatch in the polyethylene foam structure may be about 10 PHR, 8 PHR, or 6 PHR or less. In some embodiments, the amount of antiblocking agent masterbatch in the polyethylene foam structure may be 2 PHR, 3 PHR, 4 PHR, or 5 PHR or more. In some embodiments, the amount of antiblocking agent masterbatch in the polyethylene foam structure may be about 1 to 10 PHR, 2 to 8 PHR, 2 to 6 PHR, 3 to 6 PHR, or 4 to 6 PHR. In some embodiments, the amount of antiblocking agent masterbatch in the polyethylene foam structure may be about 1 to 10% by mass, about 1 to 8% by mass, about 1 to 6% by mass, about 1 to 4% by mass, about 2 to 6% by mass, about 2 to 4% by mass, about 2.5 to 3.5% by mass, or about 3% by mass.

[0055] In some embodiments, the amount of colorant masterbatch in the polyethylene foam structure may be about 15 PHR, 13 PHR, or 11 PHR or less. In some embodiments, the amount of colorant masterbatch in the polyethylene foam structure may be 2 PHR, 3 PHR, or 4 PHR or more. In some embodiments, the amount of colorant masterbatch in the polyethylene foam structure may be about 2 to 15 PHR, 2 to 13 PHR, 2 to 11 PHR, 3 to 13 PHR, or 4 to 11 PHR of colorant. In some embodiments, the amount of colorant masterbatch in the polyethylene foam structure may be about 1 to 12% by mass, about 1 to 10% by mass, about 1 to 9% by mass, about 2 to 9% by mass, or about 3 to 9% by mass. In some embodiments, the polyethylene foam structure may contain a black coloring agent masterbatch. For example, the amount of black coloring agent masterbatch in the polyethylene foam structure may be 15 PHR, 13 PHR, or 11 PHR or less. In some embodiments, the amount of black coloring agent masterbatch in the polyethylene foam structure may be 4 PHR, 5 PHR, or 6 PHR or more. In some embodiments, the amount of black coloring agent masterbatch in the polyethylene foam structure may be about 4 to 15 PHR, 5 to 13 PHR, or 6 to 11 PHR. In some embodiments, the amount of black coloring agent masterbatch in the polyethylene foam structure may be about 4 to 12% by mass, about 4 to 11% by mass, about 5 to 10% by mass, or about 6 to 9% by mass.

[0056] In some embodiments, the polyethylene foam structure may contain a white coloring agent masterbatch. For example, the amount of white coloring agent masterbatch in the polyethylene foam structure may be 10 PHR, 8 PHR, or 7 PHR or less. In some embodiments, the amount of white coloring agent masterbatch in the polyethylene foam structure may be 2 PHR, 3 PHR, or 4 PHR or more. In some embodiments, the amount of white coloring agent masterbatch in the polyethylene foam structure may be about 2 to 10 PHR, 3 to 8 PHR, or 4 to 7 PHR. In some embodiments, the amount of white coloring agent masterbatch in the polyethylene foam structure may be about 1 to 8% by mass, about 1 to 7% by mass, about 1 to 6% by mass, or about 2 to 6% by mass.

[0057] The density of foamed sheets can be defined and measured using cross-sectional density or "overall" density, rather than the "core" density measured according to JIS K6767. Foamed sheets manufactured using the above method have a density of approximately 15-200 kg / m². 3 , about 30~150kg / m 3 , or approximately 50-125 kg / m 3 A foam having a cross-sectional density or "overall" density can be obtained. In some embodiments, the cross-sectional density can be controlled by the amount of foaming agent and the thickness of the extruded sheet. The density of the foamed sheet is approximately 15 kg / m³. 3If it is less than, the sheet may not foam efficiently due to a large amount of chemical foaming agent to achieve that density. Further, if the density of the sheet is about 15 kg / m 3 If it is less than, it may become increasingly difficult to control the expansion of the sheet during the foaming process. Further, if the density of the foamed sheet is about 15 kg / m 3 If it is less than, the foam may be increasingly prone to cell collapse. Therefore, at a density of less than about 15 kg / m 3 It may be difficult to produce a foamed sheet with a uniform cross-sectional density and thickness.

[0058] The foamed sheet is not limited to a cross-sectional density of about 200 kg / m 3 Foams having a cross-sectional density of about 300 kg / m 3 about 400 kg / m 3 or about 500 kg / m 3 can also be produced. However, the foamed sheet may have a density of less than about 200 kg / m because a higher density is generally cost-disadvantageous compared to other materials that can be used in a given application. 3 In some embodiments, the foam produced using the above method may have closed cells. In some embodiments, at least 90%, at least 95% or more than 98% of the cells have undamaged cell walls when measured using a pycnometer in accordance with ASTM D6226 or ISO 4590. In some embodiments, the average cell size can be from about 0.05 mm to about 1.0 mm, or from about 0.1 mm to about 0.7 mm when measured in accordance with ASTM D3576. If the average cell size is less than about 0.05 mm, the density of the foamed structure is typically 200 kg / m 3 ​This can be exceeded. If the average bubble size exceeds 1 mm, the foam may have a non-uniform surface. Also, if the cluster of bubbles within the foam does not have a desirable average bubble size, the foam may undergo undesirable rupture. This can occur when the foam is stretched, when shear force is applied to the foam, and / or when a portion of it is subjected to a secondary process. In some embodiments, the bubble size in the foam may have a bimodal distribution, representing a cluster of relatively round bubbles in the foam core and a cluster of relatively flat, thin, and / or oval bubbles in the skin near the surface of the foam structure.

[0059] The overall thickness of the polyethylene foam sheet is measured according to JIS K6767 and can be approximately 0.2 mm to 50 mm, approximately 0.4 mm to 40 mm, approximately 0.6 mm to 30 mm, or approximately 0.8 mm to 20 mm. If the thickness is less than approximately 0.2 mm, foaming may not be efficient due to significant gas loss from the main surface. If the thickness exceeds approximately 50 mm, controlling expansion during the foaming process can become increasingly difficult. Therefore, it can become increasingly difficult to produce polyethylene foam sheets with uniform cross-sectional density and thickness. In some embodiments, the polyethylene foam sheet may have a thickness of approximately 0.5 to 5 mm, approximately 1 to 4 mm, or approximately 2 to 3 mm. In some embodiments, the desired foam thickness can be obtained by a secondary process, such as cutting, skiving, or joining. Thicknesses ranging from approximately 0.1 mm to approximately 100 mm can be obtained by cutting, skiving, or joining.

[0060] The disclosed polyethylene foam can be used in a variety of applications. In one embodiment, the polyethylene foam may be a base material for a single-sided or double-sided adhesive foam tape. In this embodiment, a pressure-sensitive adhesive layer is placed on a portion of at least one or both of the main foam surfaces. Any pressure-sensitive adhesive known in the art may be used. Examples of such pressure-sensitive adhesives include acrylic polymers, polyurethanes, thermoplastic elastomers, block copolymers, polyolefins, silicones, rubber-based adhesives, copolymers of ethylhexyl acrylate and acrylic acid, copolymers of isooctyl acrylate and acrylic acid, blends of acrylic adhesives and rubber-based adhesives, and combinations thereof. The foam tape can be commercially manufactured and sold in roll or sheet form and can be used in a variety of applications, such as mounting, bonding, gaskets, filler materials, and cushioning materials. In some embodiments, the polyethylene foam may be a laminate containing the foam layer and the laminate layer disclosed herein. The laminate layer may be applied to one side (i.e., the surface) of the foam. In these laminates, the polyethylene foam may be combined with, for example, a film and / or foil. Examples of suitable materials for such layers, but not limited to, polyvinyl chloride (PVC), thermoplastic polyolefin (TPO), thermoplastic polyurethane (TPU), fabrics such as polyester, polypropylene, clothing and other fabrics, and fibrous layers such as leather and / or nonwoven fabrics. Such layers may be manufactured using standard techniques well known to those skilled in the art. Importantly, the polyethylene foam may be laminated with these materials on one or both sides, and may contain multiple other layers.

[0061] In these laminates, layers may be joined to adjacent layers by chemical bonds, mechanical means, or a combination thereof. Adjacent laminate layers may also be fixed to each other by any other means, including the use of attractive forces between materials having opposite electromagnetic charges, or attractive forces between materials that are primarily hydrophobic, or between materials that are primarily hydrophilic.

[0062] In other embodiments, polyethylene foam or laminates may be used in automotive interior components, such as door panels, door rolls, door inserts, door stuffers, trunk stuffers, armrests, center consoles, seat cushions, seat backs, headrests, seat back panels, knee pads, or headliners. These polyethylene foams or laminates may also be used in furniture (e.g., commercial, office, and residential furniture), such as chair cushions, chair backs, sofa cushions, sofa trims, recliner cushions, recliner trims, bench cushions, bench trims, sleeper cushions, or sleeper trims. These polyethylene foams or laminates may also be used as wall components, such as modular walls, movable walls, wall panels, modular panels, office system panels, room dividers, or portable partitions. Polyethylene foams or laminates may also be used as components of storage cases (e.g., commercial, office, and residential), which may be movable or fixed. Furthermore, polyethylene foam or laminate can also be used for covers, such as chair cushion covers, chair back covers, armrest covers, sofa covers, sofa cushion covers, recliner cushion covers, recliner covers, bench cushion covers, bench covers, sleeper cushion covers, sleeper covers, wall covers, and building covers. To meet the requirements of any of the above applications, the structures disclosed in this disclosure may be subjected to various secondary processes, for example, but not limited to, embossing, corona or plasma treatment, surface roughening, surface smoothing, drilling or micro-drilling, joining, cutting, skiving, lamination, joining, and drilling. [Examples]

[0063] Raw materials of the example Table 1 below lists the various components used in the following examples and provides a description of those components. [Table 1-1] [Table 1-2]

[0064] Transformation process of the example Table 2 below shows the formulations of Examples 1, 2a, 2b, 2c, 3a, 3b, 3c, 3d, and 3e. [Table 2]

[0065] [Table 3]

[0066] Table 3 below shows the extrusion, irradiation, and foaming characteristics of polyethylene foams for Examples 1, 2a, 2b, 2c, 3a, 3b, 3c, 3d, and 3e. [Table 4]

[0067] [Table 5]

[0068] This application discloses multiple numerical ranges in the text. Since the disclosed numerical ranges are enforceable across the entire disclosed numerical range, they essentially support any range or value within the disclosed numerical range, including its endpoints, even if the exact range limitations are not verbatim stated in the specification. The above description is provided to enable those skilled in the art to implement and use this disclosure, and is provided in the context of a particular use and its requirements. Various modifications to preferred embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments and uses without departing from the spirit and scope of this disclosure. Accordingly, this disclosure is not intended to be limited to the embodiments shown, but should be given the broadest scope that corresponds to the principles and features disclosed herein. Finally, the entire disclosures of the patents and publications referenced in this application are incorporated herein by reference.

Claims

1. A method for forming polyethylene foam, 40-65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and 15-45% by mass of olefin block copolymer (OBC) A process of extruding a foamed layer containing, A process of irradiating an extruded foam layer with ionizing radiation, and A process of irradiating and foaming the extruded foam layer. Methods that include...

2. The method according to claim 1, wherein the foamed layer comprises 50 to 65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE.

3. The method according to claim 1, wherein the foamed layer comprises 20 to 35% by mass of olefin block copolymer (OBC).

4. The method according to claim 1, wherein the foamed layer contains 5 to 15% by mass of a chemical blowing agent before foaming.

5. The method according to claim 1, wherein the foamed layer comprises an antioxidant masterbatch in an amount of 1 to 10% by mass.

6. The method according to claim 1, wherein the foamed layer contains a processing aid masterbatch in an amount of 0.5 to 5% by mass.

7. The method according to claim 1, wherein the foam layer comprises a chemical foaming agent decomposition inhibitor masterbatch in an amount of 1 to 10% by mass.

8. The method according to claim 1, wherein the foamed layer comprises an antiblocking agent masterbatch in an amount of 1 to 10% by mass.

9. The method according to claim 1, wherein the foamed layer comprises a coloring agent masterbatch in an amount of 1 to 12% by mass.

10. The method according to claim 1, wherein the foamed layer has a melt flow index of 0.1 to 25 grams per 10 minutes at 190°C.

11. The foamed, irradiated, and extruded foam layer has a density of 15-200 kg / m 3 The method of claim 1, having the density of

12. The method according to claim 1, wherein the foamed, irradiated, and extruded foam layer has an average closed cell size of 0.05 to 1.0 mm.

13. The method according to claim 1, wherein the foamed, irradiated, and extruded foamed layer has a thickness of 0.2 to 50 mm.

14. The ionizing radiation is selected from the group consisting of alpha rays, beta rays (electron beams), X-rays, gamma rays, and neutron rays. The method according to claim 1.

15. The method according to claim 1, wherein the extruded foam layer is irradiated up to four times.

16. The method according to claim 1, wherein the ionizing radiation crosslinks the extruded foam layer to a degree of crosslinking of 20 to 75%.

17. The method according to claim 1, wherein the foaming step includes heating the irradiated and extruded foam layer with molten salt and a radiation heater or hot air oven.

18. The method according to claim 1, further comprising the step of applying a laminate layer to one side of a foamed, irradiated, and extruded foam layer.

19. The method according to claim 1, further comprising the step of applying a pressure-sensitive adhesive layer to one side of a foamed, irradiated, and extruded foam layer.

20. The method according to claim 19, further comprising the step of applying a second pressure-sensitive adhesive layer to the side of a foamed, irradiated, and extruded foamed layer opposite to the first pressure-sensitive adhesive layer.

21. 40-65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and 15-45% by mass of olefin block copolymer (OBC) A polyethylene foam structure, including [a specific component].

22. The polyethylene foam structure according to claim 21, comprising 50 to 65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE.

23. The polyethylene foam structure according to claim 21, comprising 20 to 35% by mass of olefin block copolymer (OBC).

24. The polyethylene foam structure according to claim 21, further comprising 5 to 15% by mass of a chemical blowing agent before foaming.

25. The polyethylene foam structure according to claim 21, further comprising an antioxidant masterbatch in an amount of 1 to 10% by mass.

26. The polyethylene foam structure according to claim 21, further comprising a processing aid masterbatch in an amount of 0.5 to 5% by mass.

27. The polyethylene foam structure according to claim 21, further comprising a chemical foaming agent decomposition inhibitor masterbatch in an amount of 1 to 10% by mass.

28. The polyethylene foam structure according to claim 21, further comprising an antiblocking agent masterbatch in an amount of 1 to 10% by mass.

29. The polyethylene foam structure according to claim 21, further comprising a colorant masterbatch in an amount of 1 to 12% by mass.

30. 15-200kg / m 3 A polyethylene foam structure according to claim 21, comprising the density of the polyethylene foam.

31. A polyethylene foam structure according to claim 21, comprising a degree of crosslinking of 20 to 75%.

32. The polyethylene foam structure according to claim 21, comprising an average closed cell size of 0.05 to 1.0 mm.

33. A polyethylene foam structure according to claim 21, including a thickness of 0.2 to 50 mm.

34. 40-65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and 15-45% by mass of olefin block copolymer (OBC) A polyethylene foam layer containing, A laminate layer on one side of the polyethylene foam layer and A laminated body containing [something].

35. The laminated body according to claim 34, wherein the laminate layer is a flexible film, a fabric, or a foil.

36. The laminate body according to claim 34, wherein the laminate layer is either not foamed or is foamed.

37. 40-65% by mass of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or a combination of LDPE and LLDPE, and 15-45% by mass of olefin block copolymer (OBC) A polyethylene foam layer containing, A pressure-sensitive adhesive layer on one side of the polyethylene foam layer and Adhesive foam tape, including

38. The adhesive foam tape according to claim 37, further comprising a second pressure-sensitive adhesive layer on the side of the polyethylene foam layer opposite to the first pressure-sensitive adhesive layer.

39. The adhesive foam tape according to claim 37, wherein the adhesive foam tape is in the form of a roll or a flat plate.

40. The adhesive foam tape according to claim 37, wherein the pressure-sensitive adhesive layer comprises one or more of the following: acrylic polymer, polyurethane, thermoplastic elastomer, block copolymer, polyolefin, silicone, rubber-based adhesive, copolymer of ethylhexyl acrylate and acrylic acid, copolymer of isooctyl acrylate and acrylic acid, or a combination thereof.

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