Coextruded, cross-linked polyolefin foam with KEE cover layer

Abstract

The present invention relates to a physically cross-linked, closed-cell continuous multilayer foam structure comprising at least one foamed polypropylene / polyethylene layer and a KEE cover layer. The multilayer foam structure can be obtained by coextruding a multilayer structure comprising at least one foam layer composition layer and at least one cover layer composition layer, irradiating the coextruded structure with ionizing radiation, and continuously foaming the irradiated structure.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of priority to U.S. Non-Provisional Patent Application No. 16 / 370,043, filed on March 29, 2019, and U.S. Non-Provisional Patent Application No. 16 / 370,154, filed on March 29, 2019, the disclosures of which are incorporated herein by reference in their entireties. Technical Field

[0003] The present invention relates to a multilayer foam structure having a KEE (ketone-ethylene-ester) terpolymer cover layer. More particularly, the present invention relates to a physically crosslinked, closed-cell continuous multilayer foam structure comprising a KEE cover layer. Background Art

[0004] Polyolefin foams can be used in various applications, including but not limited to trim parts for vehicle interiors, roof diaphragms and floor liners. When used in these various applications, the polyolefin foam can be bonded to a polyvinyl chloride (PVC) skin or polyvinyl chloride foam. Traditionally, in order to obtain satisfactory adhesion between the polyolefin foam and the polyvinyl chloride, a surface modification treatment such as corona, plasma or chemicals is applied to the polyolefin foam. Thereafter, an adhesion primer and / or a bonding agent is applied to the surface-modified polyolefin foam to obtain satisfactory adhesion.

[0005] However, modifying the surface of a polyolefin foam and subsequently coating the foam with a primer and / or adhesive is an additional processing step between foam manufacture and final application. This can increase costs, which can make the process uneconomical for commercial purposes. In addition, polyolefin surface modification, especially with corona, can also be temporary and can be unsuitable for situations where the treated foam is stored for long periods of time in a warehouse or retail store. Summary of the invention

[0006] It has been discovered that coextrusion of a polyolefin foam layer composition having a KEE (ketone-ethylene-ester) terpolymer cover layer can overcome the problems associated with: (a) treating the surface of a polyolefin foam with corona, plasma or chemicals to modify the foam surface; and (b) applying an adhesion primer and / or adhesive to the surface modified polyolefin foam. Because KEE is highly miscible in (and therefore highly compatible with) PVC, it can be expected that a coextruded polyolefin foam having a KEE cover layer will be readily thermally bonded to PVC without the need for surface treatment, primers and / or adhesives. Additionally, unlike corona, a KEE cover layer does not have a "shelf life" where prolonged storage in a warehouse or retail store would render the product less likely to adhere to a primer or adhesive.

[0007] In some embodiments, a multilayer foam structure is provided, comprising: a coextruded foam layer comprising polypropylene, polyethylene, or a combination of polypropylene and polyethylene; and a coextruded cover layer on one side of the foam layer, the cover layer comprising at least 15 wt% of a ketone-ethylene-ester terpolymer and polypropylene, polyethylene, or a combination of polypropylene and polyethylene. In some embodiments, the coextruded foam layer comprises 2-15 wt% of KEE. In some embodiments, the coextruded foam layer comprises at least 70 wt% of polypropylene, polyethylene, or a combination of polypropylene and polyethylene. In some embodiments, the foam layer comprises additives in an amount of 1-20 wt%. In some embodiments, the cover layer comprises additives in an amount of 1-8 wt%. In some embodiments, the melt flow index of polypropylene at 230°C is 0.1-25 g / 10 min. In some embodiments, the melt flow index of polyethylene at 190°C is 0.1-25 g / 10 min. In some embodiments, the density of the multilayer foam structure is 20-250 kg / m 3 In some embodiments, the multilayer foam structure has a degree of crosslinking of 20-75%. In some embodiments, the multilayer foam structure has an average closed cell size of 0.05-1.0 mm. In some embodiments, the multilayer foam structure has a thickness of 0.2-50 mm.

[0008] In some embodiments, a laminate is provided, comprising a multilayer foam structure comprising a coextruded foam layer comprising polypropylene, polyethylene, or a combination of polypropylene and polyethylene, and a coextruded cover layer on one side of the foam layer, the cover layer comprising at least 15 wt % KEE and polypropylene, polyethylene, or a combination of polypropylene and polyethylene; and a laminate layer on the side of the cover layer opposite the foam layer. In some embodiments, the laminate layer is a flexible film, foil, or foam. In some embodiments, the laminate layer is a semi-flexible or rigid board, thick board, tile, or substrate. In some embodiments, the laminate layer comprises PVC, KEE, or a mixture of PVC and KEE.

[0009] In some embodiments, a method of forming a multilayer structure is provided, the method comprising: coextruding a first layer and a second layer located on one side of the first layer, the first layer comprising polypropylene, polyethylene, or a combination of polypropylene and polyethylene, and a chemical foaming agent, the second layer comprising at least 15 wt% of a ketone-ethylene-ester terpolymer and polypropylene, polyethylene, or a combination of polypropylene and polyethylene; irradiating the coextruded layer with ionizing radiation, and foaming the irradiated coextruded layer. In some embodiments, the first layer comprises 2-15 wt% of KEE. In some embodiments, the first layer comprises at least 70 wt% of polypropylene, polyethylene, or a combination of polypropylene and polyethylene. In some embodiments, the first layer comprises an additive in an amount of 1-20 wt%. In some embodiments, the second layer comprises an additive in an amount of 1-8 wt%. In some embodiments, the melt flow index of polypropylene at 230°C is 0.1-25 g / 10 min. In some embodiments, the melt flow index of polyethylene at 190°C is 0.1-25 g / 10 min. In some embodiments, the amount of the chemical foaming agent in the first layer is 4-10 wt%. In some embodiments, the chemical foaming agent comprises azodicarbonamide. In some embodiments, the first layer comprises a crosslinking agent. In some embodiments, the amount of the crosslinking agent in the first layer is 1-3wt%. In some embodiments, the ionizing radiation is selected from α, β (electron beam), x-rays, γ and neutrons. In some embodiments, the coextruded structure is irradiated up to four independent times. In some embodiments, the ionizing radiation is an electron beam with an accelerating voltage of 200-1500kV. In some embodiments, the absorbed electron beam dose is 10-500kGy. In some embodiments, the ionizing radiation crosslinks the extruded structure to a crosslinking degree of 20-75%. In some embodiments, foaming includes heating the irradiated structure with molten salt and a radiation heater or a hot air oven. In some embodiments, the density of the multilayer foam structure is 20-250kg / m 3 In some embodiments, the average closed cell size of the multilayer foam structure is 0.05-1.0 mm. In some embodiments, the thickness of the multilayer foam structure is 0.2-50 mm.

[0010] Reference herein to "about" a value or parameter includes (and describes) variations involving the value or parameter itself. For example, a description referring to "about X" includes a description of "X." In addition, reference to the words "less than," "greater than," "at most," "at least," "less than or equal to," "greater than or equal to," or other similar words followed by a string of values ​​or parameters means that the words apply to each value or parameter in the string of values ​​or parameters. For example, a statement that a layer has less than about 20 wt%, about 15 wt%, or about 10 wt% chemical blowing agent means that the weight percentage of the chemical blowing agent in the layer may be less than about 20 wt%, less than about 15 wt%, or less than about 10 wt%.

[0011] As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It is also to be understood that, as used herein, the term "and / or" refers to and includes any and all possible combinations of one or more of the relevant listed items. It is further to be understood that the terms "comprises", "includes", "includes", and / or "comprising" when used herein specify the presence of the stated features, integers, steps, operations, elements, parts, and / or units, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, parts, units, and / or groups thereof.

[0012] It is to be understood that the aspects and embodiments described herein include aspects and embodiments that "consist of" and / or "consist essentially of." For all methods, systems, compositions, and devices described herein, the methods, systems, compositions, and devices may include the listed components / components or steps, or may "consist of" or "consist essentially of" the listed components or steps. When a system, composition, or device is described as "consisting essentially of" the listed components / components, the system, composition, or device includes the listed components / components, and may include other components / components that do not substantially affect the performance of the system, composition, or device, but does not include any other components / components other than those components / components explicitly listed that substantially affect the performance of the system, composition, or device; or does not include additional components in concentrations or amounts sufficient to substantially affect the performance of the system, composition, or device. When a method is described as "consisting essentially 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 the method does not include any other steps other than those steps explicitly listed that substantially affect the results of the method.

[0013] In the present invention, "substantially free" of a specific component, a specific composition, a specific compound or a specific ingredient means in various embodiments that 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% by weight of the specific component, the specific composition, the specific compound or the specific ingredient is present. Preferably, "substantially free" of a specific component, a specific composition, a specific compound or a specific ingredient means that less than about 1% by weight of the specific component, the specific composition, the specific compound or the specific ingredient is present.

[0014] For those skilled in the art, additional advantages will become readily apparent from the following detailed description.The embodiments and descriptions described herein are to be considered illustrative rather than limiting. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Various embodiments are described with reference to the accompanying drawings, in which:

[0016] Figure 1A is an image of Example 1A at 30× magnification and 45° to the major surface;

[0017] Figure 1B is an image of Example 1B at 30× magnification and 45° to the major surface;

[0018] Figure 2A is an image of Example 2A at 30× magnification and 45° to the major surface;

[0019] Figure 2B is an image of Example 2B at 30× magnification and 45° to the major surface;

[0020] Figure 3 is an image of Example 3 at 30× magnification and 45° to the main surface;

[0021] Figure 4A is an image of Example 4A at 30× magnification and 45° to the major surface;

[0022] Figure 4B is an image of Example 4B at 30× magnification and 45° to the major surface;

[0023] Figure 5 is an image of Example 5 at 30× magnification and 45° to the main surface;

[0024] Figure 6 is an image of Example 6 at 30× magnification and 45° to the main surface;

[0025] Figure 7 is an image of Example 7 at 30× magnification and 45° to the main surface;

[0026] Figure 8 is an image of Example 8 at 30× magnification and 45° to the main surface;

[0027] Fig. 9 is an image of Example 9 at 30× magnification and 45° to the main surface;

[0028] Fig.10 is an image of Example 10 at 30× magnification and 45° to the major surface; and

[0029] Fig.11 This is an image of Example 11 at 30× magnification and 45° to the major surface. DETAILED DESCRIPTION

[0030] Described herein are cross-linked, closed-cell coextruded polyolefin foams having a KEE covering layer, and methods of producing cross-linked, closed-cell coextruded polyolefin foams having a KEE covering layer. In particular, it has been found that coextruding a polyolefin foam layer composition and a KEE covering layer can overcome the problems associated with treating the polyolefin foam surface with corona, plasma or chemicals and / or applying bonding primers or adhesives to surface-modified polyolefin films. Specifically, the structures disclosed herein can be easily bonded to polyvinyl chloride films and polyvinyl chloride foams, and can avoid the product being less able to adhere to primers and adhesives as shelf life increases.

[0031] A method of producing a cross-linked, closed-cell coextruded polyolefin foam having a KEE cover layer may include the steps of: (a) coextrusion; (b) irradiation; and (c) foaming.

[0032] Coextrusion is the simultaneous extrusion of multilayer materials. This type of extrusion can use two or more extruders to deliver a stable volume production amount of material to an extrusion head (die), which can extrude the material in a desired form. In the coextrusion step, the composition can be fed into multiple extruders to form an unfoamed multilayer structure. For example, an "A" foam layer composition can be fed into one extruder, and a "B" cover layer composition can be fed into a second extruder. The method of feeding the ingredients into the extruder can be based on the design of the available extruders and material handling devices. If necessary, the blending of the ingredients of the foam and cover layer compositions can be carried out before feeding into the extruder to promote their dispersion. A Henshel mixer can be used for such blending. All ingredients can be blended and fed through a single port in the extruder. The ingredients can also be fed separately through ports specifically designed for each ingredient. For example, if a crosslinking promoter or any other additive is a liquid, the promoter and / or additive can be added through one or more feed gates on the extruder or through a vent opening on the extruder (if equipped with vents) instead of blending with solid ingredients. A combination of blended ingredients and single ingredient port feeding may also be used.

[0033] Each extruder can feed a stable amount of each composition into one or more manifolds. One or more manifolds can then be fed through a sheet die to produce an unfoamed, coextruded multilayer sheet. There are two common methods for coextruding materials: (1) a feed block manifold; and (2) multiple manifolds within a die. Elements of a feed block manifold may include: (a) inlets for the upper, middle, and lower layers; (b) a streamlined melt lamination region in which channels divide the flow stream into a laminated melt stream in the feed block; (c) an adapter plate between the feed block and the sheet die; and / or (d) a sheet die (similar to a single-layer die) in which the laminated melt streams enter the center of the die and spread out along the manifold as different multilayer extrudates flowing out of the die outlet. The elements of a multi-manifold die can be: (a) similar to a single-layer die, except that there is more than one feed channel; (b) each melt channel has its own regulating rod to control flow; and / or (c) the melt streams converge near the outlet within the die and exit as distinct multi-layer extrudates.

[0034] The layer thickness of the multilayer structure provided herein can depend on the design of the manifold and / or die head. For example, when the speed and size of each extruder are matched accordingly, an 80 / 20 feed block manifold can convey a composition of about 4:1 ratio. When the speed and size of each extruder are matched accordingly, a 50 / 50 feed block manifold can convey a composition of about 1:1 ratio. These ratios can be adjusted by changing the following, for example: (a) the amount of material fed into each extruder; (b) the relative extrusion speed between each extruder; (c) the relative size of each extruder; and / or (d) the composition (i.e., viscosity) of a single layer.

[0035] The thickness of the entire multilayer sheet can be controlled by the overall die gap. However, the thickness of the entire multilayer sheet can also be adjusted by stretching (ie, "pulling") the molten multilayer extrudate and / or flattening the molten multilayer extrudate through a nip.

[0036] The multilayer structures disclosed herein may comprise at least two layers made of different compositions, at least one of which may comprise a KEE (ketone-ethylene-ester) terpolymer. In addition, the multilayer structures may comprise at least one layer made of a foamable or foamed composition. In some embodiments, the multilayer structures may comprise at least one "A" polyolefin foam layer and at least one "B" KEE cover layer. In some embodiments, the "B" KEE cover layer may also comprise a polyolefin. In some embodiments, the "A" polyolefin foam layer may also comprise KEE. In some embodiments, the "B" KEE cover layer may also be foamable or foamed.

[0037] The foamable composition fed into the extruder may include at least one polypropylene, at least one polyethylene and / or a combination thereof. In some embodiments, the foam layer composition may form a polyolefin foam layer (A) of a multilayer structure. In some embodiments, the foam layer composition may form a KEE cover layer (B) of a multilayer structure.

[0038] The polypropylene of foamable composition can comprise elasticity or softening component.Elasticity or softening component are ethylene or rubber component normally, therefore include but not limited to polypropylene, impact-modified polypropylene, polypropylene-ethylene copolymer, impact-modified polypropylene-ethylene copolymer, metallocene polypropylene, metallocene polypropylene-ethylene copolymer, metallocene polypropylene olefin block copolymer (with controlled block sequence), polyolefin plastomer based on polypropylene, polyolefin elastomer-plastomer based on polypropylene, polyolefin elastomer based on polypropylene, thermoplastic polyolefin blend based on polypropylene and thermoplastic elastomer blend based on polypropylene.In addition, polypropylene can be modified with polyetheramine.

[0039] The polyethylene of the foamable composition includes, but is not limited to, LDPE, LLDPE (homopolymer, copolymer with butene or hexene or octene, terpolymer with butene and / or hexene and / or octene), VLDPE (homopolymer, copolymer with butene or hexene or octene, terpolymer with butene and / or hexene and / or octene), VLLDPE (homopolymer, copolymer with butene or hexene or octene, terpolymer with butene and / or hexene and / or octene), HDPE, polyethylene-propylene copolymers, metallocene polyethylene, metallocene ethylene-propylene copolymers, and metallocene polyethylene olefin block copolymers (with controlled block order), any of which may contain a grafted compatibilizer or copolymer containing acetate and / or ester groups.

[0040] The foam layer composition fed into the extruder may also include at least one KEE. KEEs include ketone-ethylene-ester terpolymers. An example is an ethylene / n-butyl acrylate / carbon monoxide (E / nBA / CO) terpolymer. Other examples include ethylene / vinyl acetate / carbon monoxide (E / VA / CO) terpolymers and ethylene / 2-ethylhexyl acrylate / carbon monoxide (E / EHA / CO) terpolymers. These polymers may exhibit different short chain branching and monomer sequences.

[0041] In some embodiments, the amount of at least one polypropylene and / or at least one polyethylene in the foam layer composition may be greater than or equal to about 70 PPR%, about 75 PPR%, about 80 PPR%, about 85 PPR%, about 90 PPR%, or about 95 PPR% of the composition. In some embodiments, the amount of at least one polypropylene and / or at least one polyethylene in the foam layer composition may be less than or equal to about 100 PPR%, about 95 PPR%, about 90 PPR%, about 85 PPR%, about 80 PPR%, or about 75 PPR% of the composition. In some embodiments, the amount of at least one polypropylene and / or at least one polyethylene in the foam layer composition may be at least about 50 wt%, about 60 wt%, about 65 wt%, about 70 wt%, about 75 wt%, about 80 wt%, about 85 wt%, or about 90 wt% of the foam composition. In some embodiments, the amount of at least one polypropylene and / or at least one polyethylene in the foam layer composition can be less than or equal to about 95wt%, about 90wt%, about 85wt%, about 80wt%, about 75wt%, about 70wt%, about 65wt%, or about 60wt% of the foam layer composition. In some embodiments, the amount of at least one polypropylene and / or at least one polyethylene in the foam layer composition can be about 50-95wt%, about 65-90wt%, about 70-90wt%, or about 70-85wt% of the foam layer composition.

[0042] In some embodiments, the amount of KEE may be less than or equal to about 20 PPR%, about 15 PPR%, about 10 PPR%, or about 5 PPR% of the foam layer composition. In some embodiments, the amount of KEE may be greater than or equal to about 0.1 PPR%, about 1 PPR%, about 5 PPR%, about 10 PPR%, or about 15 PPR% of the foam layer composition. In some embodiments, the amount of KEE in the foam layer composition may be less than or equal to about 20 wt %, about 15 wt %, about 10 wt %, about 5 wt %, or about 1 wt % of the foam layer composition. In some embodiments, the amount of KEE may be greater than or equal to about 0.1 wt %, about 1 wt %, about 5 wt %, about 10 wt %, or about 15 wt % of the foam layer composition. In some embodiments, the amount of KEE may be about 0.1-20 wt %, about 1-15 wt %, about 2-10 wt %, or about 3-5 wt % of the foam layer composition.

[0043] The cover layer composition fed into the extruder may comprise at least one KEE and at least one polypropylene and / or at least one polyethylene (KEE, polypropylene and polyethylene are as described above). In some embodiments, the cover layer composition may form a KEE cover layer (B) of a multi-layer structure.

[0044] In some embodiments, the amount of KEE in the cover composition can be greater than or equal to about 15 PPR%, about 30 PPR%, about 40 PPR%, about 50 PPR%, about 60 PPR%, about 70 PPR%, about 80 PPR%, or about 90 PPR% of the cover composition. In some embodiments, the amount of KEE in the cover composition can be less than or equal to about 100 PPR%, about 90 PPR%, about 80 PPR%, about 70 PPR%, about 60 PPR%, about 50 PPR%, about 40 PPR%, or about 30 PPR% of the cover composition. In some embodiments, the amount of KEE in the cover composition can be at least about 15 wt%, about 30 wt%, about 40 wt%, about 50 wt%, about 60 wt%, about 70 wt%, about 80 wt%, about 90 wt%, or about 95 wt% of the cover composition. In some embodiments, the amount of KEE in the cover composition can be less than or equal to about 100 wt %, about 95 wt %, about 90 wt %, about 80 wt %, about 70 wt %, about 60 wt %, about 50 wt %, about 40 wt %, or about 30 wt % of the cover composition. In some embodiments, the amount of KEE in the cover composition can be about 15-85 wt %, about 30-70 wt %, or about 40-60 wt % of the cover composition.

[0045] In some embodiments, the amount of at least one polypropylene and / or at least one polyethylene in the cover composition may be less than or equal to about 85 PPR%, about 70 PPR%, about 60 PPR%, about 50 PPR%, about 40 PPR%, about 30 PPR%, about 20 PPR%, about 15 PPR%, or about 10 PPR% of the cover composition. In some embodiments, the amount of at least one polypropylene and / or at least one polyethylene in the cover composition may be greater than or equal to about 5 PPR%, about 10 PPR%, about 15 PPR%, about 20 PPR%, about 30 PPR%, about 40 PPR%, about 50 PPR%, about 60 PPR%, or about 70 PPR% of the cover composition. In some embodiments, the amount of at least one polypropylene and / or at least one polyethylene in the cover composition may be less than or equal to about 85 wt%, about 70 wt%, about 60 wt%, about 50 wt%, about 40 wt%, about 30 wt%, about 20 wt%, about 15 wt%, or about 10 wt% of the cover composition. In some embodiments, the amount of at least one polypropylene and / or at least one polyethylene in the cover composition can be greater than or equal to about 5wt%, about 10wt%, about 15wt%, about 20wt%, about 30wt%, about 40wt%, about 50wt%, about 60wt%, or about 70wt% of the cover composition. In some embodiments, the amount of at least one polypropylene and / or at least one polyethylene in the cover composition can be about 15-85wt%, about 30-70wt%, or about 40-60wt% of the cover composition.

[0046] Because a wide range of multilayer structures and foam articles can be formed using the disclosed compositions, a wide range of polypropylenes, polyethylenes, and KEEs can be used in the compositions to meet manufacturing requirements in a variety of processes and commercial end-use requirements.

[0047] Non-limiting examples of commercially available ketone-ethylene-ester (KEE) terpolymers include, but are not limited to, KEE® from Dow Chemical Company. HP series (E / nBa / Co terpolymer) (e.g. HP 441, HP 641, etc.) and also from Dow Chemical Company 741, 742 and 4924 (E / VA / CO terpolymer).

[0048] A non-limiting example of "polypropylene" is isotactic homopolypropylene. Commercially available examples include, but are not limited to, FF018F from Braskem, 3271 from Total Petrochemicals, and COPYLENE from Conoco. TM CH020.

[0049] A non-limiting example of an "impact-modified polypropylene" is a homopolypropylene with an ethylene-propylene (EP) copolymer rubber. The rubber may be amorphous or semi-crystalline, but the amount is insufficient to impart any plastic or elastic properties to the material. Several non-limiting examples of commercially available "impact-modified polypropylenes" are TI4003F and TI4015F from Braskem, and TI4015F from LyondellBasell. 8623 and SB786.

[0050] "Polypropylene-ethylene copolymer" is a polypropylene with random ethylene units. Several non-limiting examples of commercially available "polypropylene-ethylene copolymers" are 6232, 7250FL and Z9421 from Total Petrochemicals, 6D20 and DS6D81 from Braskem, and 1,100 from LyondellBasell. RP311H and ADSYL TM 7415XCP.

[0051] An "impact-modified polypropylene-ethylene copolymer" is a polypropylene having random ethylene units and having an ethylene-propylene (EP) copolymer rubber. The rubber may be amorphous or semi-crystalline, but the amount is insufficient to impart any plastic or elastic properties to the material. A non-limiting example of a commercially available impact-modified polypropylene-ethylene copolymer is EPROM from Braskem. 6910.

[0052] "Metallocene polypropylene" is metallocene syndiotactic homopolypropylene, metallocene atactic homopolypropylene and metallocene isotactic homopolypropylene. A non-limiting example of "metallocene polypropylene" is available under the trade name METOCENE TM Commercially available from LyondellBasell and under the trade name ACHIEVE TM Those commercially available from ExxonMobil. Metallocene polypropylenes are also commercially available from Total Petrochemicals, including but not limited to grades M3551, M3282MZ, M7672, 1251, 1471, 1571 and 1751.

[0053] "Metallocene polypropylene-ethylene copolymers" are metallocene syndiotactic, metallocene atactic and metallocene isotactic polypropylenes with random ethylene units. Commercially available examples include, but are not limited to, MR10MX0 and MR60MC2, and from LyondellBasell SM170G.

[0054] "Metallocene polypropylene olefin block copolymers" are polypropylenes having alternating crystallizable hard "blocks" and amorphous soft "blocks", the blocks being not randomly distributed, i.e. having a controlled block order. Examples of "metallocene polypropylene olefin block copolymers" include, but are not limited to, INTUNE from Dow Chemical Company. TM Product line.

[0055] "Polypropylene-based polyolefin plastomers" (POP) and "polypropylene-based polyolefin elastomeric plastomers" are copolymers based on both metallocene and non-metallocene propylene, having both plastic and elasto-plastic properties. A non-limiting example is the polyolefin plastomer sold under the trade name VERSIFY TM (metallocene) is commercially available from Dow Chemical Company under the trade name VISTAMAXX TM (metallocene) is commercially available from ExxonMobil and under the trade name KOATTRO TM (non-metallocene,) those commercially available from LyondellBasell (butene-1 based plastomer polymers, some grades based on butene-1 homopolymer, and others based on polypropylene-butene-1 copolymer materials).

[0056] "Polyolefin elastomers based on polypropylene" (POE) are copolymers based on both metallocene and non-metallocene propylene, having elastomeric properties. A non-limiting example of a propylene-based polyolefin elastomer is available under the trade name VERSIFY TM (metallocene) is commercially available from Dow Chemical Company and under the trade name VISTAMAXX TM (Metallocene) Those polymers commercially available from ExxonMobil.

[0057] "Polypropylene-based thermoplastic polyolefin blends" (TPO) are polypropylene, polypropylene-ethylene copolymers, metallocene homopolypropylene, and metallocene polypropylene-ethylene copolymers, wherein the amount of ethylene-propylene copolymer rubber is large enough to impart plastic, elasto-plastic or elastic properties to the thermoplastic polyolefin blend (TPO). Non-limiting examples of polypropylene-based polyolefin blend polymers are those sold under the trade name EXCELINK TMCommercially available from JSR Corporation under the trade name THERMORUN TM and ZELAS TM Commercially available from Mitsubishi Chemical Corporation under the trade name ADFLEX TM and SOFTELL TM Commercially available from LyondellBasell and under the trade name TELCAR TM Those polymer blends are commercially available from Teknor Apex Company.

[0058] "Polypropylene-based thermoplastic elastomer blends" (TPE) are polypropylene, polypropylene-ethylene copolymers, metallocene homopolypropylene, and metallocene polypropylene-ethylene copolymers having a diblock or multiblock thermoplastic rubber modifier (SEBS, SEPS, SEEPS, SEP, SERC, CEBC, HSB, etc.) in an amount large enough to impart plastic, elasto-plastic or elastic properties to the thermoplastic elastomer blend (TPE). A non-limiting example of a polypropylene-based thermoplastic elastomer blend polymer is the one sold under the trade name GLS TM DYNAFLEX TM and GLS TM VERSAFLEX TM Commercially available from Polyone Corporation under the trade name Commercially available from Teknor Apex Company and under the trade name Those polymer blends are commercially available from A. Schulman.

[0059] "VLDPE" and "VLLDPE" are very low density polyethylene and linear very low density polyethylene containing an elastomeric or softening component, typically an alpha-olefin of butene and / or hexene and / or octene. Non-limiting examples of VLDPE and VLLDPE are those sold under the trade name FLEXOMER TM Commercially available from Dow Chemical Company, and STAMYLEX from Borealis TM a specific level.

[0060] "LDPE" and "LLDPE" are low density polyethylene and linear low density polyethylene, respectively. Non-limiting examples of LDPE and LLDPE include at least TM(eg LLP8501.67) and those provided by Dow Chemical Company (eg DFDA-7059NT 7). Commercially available LLDPE polymers are typically copolymers of alpha-olefins containing butene and / or hexene and / or octene.

[0061] "Metallocene polyethylene" is a metallocene-based polyethylene having properties ranging from inelastic to elastic. A non-limiting example of a metallocene polyethylene is sold under the trade name ENGAGE TM Commercially available from Dow Chemical Company under the trade name ENABLE TM and EXCEED TM Commercially available from ExxonMobil TM , and under the trade name QUEO TM Commercially available from Borealis.

[0062] "Metallocene polyethylene olefin block copolymers" are polyethylenes having alternating crystallizable hard "blocks" and amorphous soft "blocks", the blocks being not randomly distributed, i.e. having a controlled block order. An example of a "metallocene polyethylene olefin block copolymer" includes, but is not limited to, INFUSE from Dow Chemical Company. TM Product line.

[0063] These polyethylenes may also be copolymers and terpolymers containing acetate and / or ester groups. Comonomer groups include, but are not limited to, vinyl acetate, methyl acrylate, ethyl acrylate, butyl acrylate, glycidyl methacrylate, and acrylic acid. Non-limiting examples include those sold under the trade name and Commercially available from Dow Chemical Company; under the trade name and Commercially available from Arkema; ​​under the trade name ESCORENE TM 、ESCOR TM and OPTEMA TM Commercially available from ExxonMobil.

[0064] The polypropylene and polyethylene listed above can be functionalized. Functionalized polypropylene and polyethylene include grafted monomers. Typically, the monomers have been grafted to polypropylene or polyethylene by free radical reactions. Suitable monomers for preparing functionalized polypropylene and polyethylene are, for example, ethylenically unsaturated monocarboxylic acids such as acrylic acid or methacrylic acid, and corresponding tert-butyl esters such as (meth) tert-butyl acrylate, ethylenically unsaturated dicarboxylic acids such as fumaric acid, maleic acid and itaconic acid, and corresponding mono- and / or di-tert-butyl esters such as mono- or di-tert-butyl fumarate and mono- or di-tert-butyl maleate, ethylenically unsaturated dicarboxylic anhydrides such as maleic anhydride, ethylenically unsaturated monomers containing sulfonic or sulfonyl groups such as p-styrenesulfonic acid, 2-(meth)acrylamido-2-methylpropenesulfonic acid or 2-sulfonyl-(meth)acrylate, ethylenically unsaturated monomers containing oxazoline groups such as vinyloxazoline and vinyloxazoline derivatives, and ethylenically unsaturated monomers containing epoxy groups such as glycidyl (meth)acrylate or allyl glycidyl ether.

[0065] The most commonly commercially available functionalized polypropylene is polypropylene functionalized with maleic anhydride.

[0066] A non-limiting example is from Mitsui Chemicals QF and QB series, from LyondellBasell 6000 Series, from Dow Chemical Company 5000 series, and from Arkema PP series.

[0067] The most commonly commercially available functionalized polyethylenes are those functionalized with maleic anhydride. A non-limiting example is NF and SE series, from LyondellBasell 1000, 2000 and 3000 series from Dow Chemical Company 2100, 3000, 3800, 3900, 4000 series, and from Arkema PE, T and Some of the series.

[0068] Polyethylenes functionalized with other grafted monomers are also commercially available. Non-limiting examples include POLY(R) from Dow Chemical Company. 1100, 2200 and 3100 series, and from Arkema AX series.

[0069] It is noted that polymers other than polypropylene and polyethylene functionalized with maleic anhydride are also commercially available. For example, The KRATON series is a series of EPDM rubbers functionalized with maleic anhydride. In another example, KRATON from Kraton TM The FG series is a series of SEBS polymers functionalized with maleic anhydride.

[0070] The composition of any foamable layer and any covering layer provided herein may contain at least one polypropylene having a melt flow index of about 0.1 to about 25 g / 10 min at 230° C., and / or at least one polyethylene having a melt flow index of about 0.1 to about 25 g / 10 min at 190° C. In some embodiments, the melt flow index of polypropylene and / or polyethylene at 230° C. and 190° C., respectively, is preferably about 0.3 to about 20 g / 10 min, more preferably about 0.5 to about 15 g / 10 min at 230° C. and 190° C., respectively. The "melt flow index" (MFI) value of a polymer is defined and measured according to ASTM D1238, at 230° C. for polypropylene and polypropylene-based materials, at 190° C. for polyethylene and polyethylene-based materials, using a 2.16 kg plunger for 10 minutes. For relatively high melt flow resins, the test time can be reduced.

[0071] MFI can provide a measure of the flow characteristics of a polymer and is an indicator of the molecular weight and processability of a polymer material. A high MFI value corresponds to a low viscosity. If the MFI value is too high, extrusion according to the present invention cannot be performed satisfactorily. Problems associated with too high MFI values ​​include low pressure during extrusion, problems with setting the thickness curve, uneven cooling curves due to low melt viscosity, poor melt strength, and / or machining problems. In contrast, a low MFI value corresponds to a high viscosity. Too low MFI values ​​can cause high pressure during melt processing, sheet quality and profile problems, and higher extrusion temperatures, which trigger the risk of decomposition and activation of the foaming agent.

[0072] The above MFI ranges are also important for foaming processes because they reflect the viscosity of the material, which has an impact on foaming. Without being limited to any theory, it is believed that there are several reasons why specific MFI values ​​are more effective. Lower MFI materials can improve some physical properties as the molecular chain length is larger, so that more energy is required to make the chain flow when stress is applied. Similarly, the longer the molecular chain (MW), the more crystalline entities the chain can crystallize, thereby providing greater strength through intermolecular connections. However, when the MFI is too low, the viscosity becomes too high. On the other hand, polymers with higher MFI values ​​have shorter chains. Therefore, in a material with a higher MFI value for a given volume, there are more chain ends at a microscopic level, which can rotate and due to the space required for such rotation (for example, higher than the T of the polymer), the chain ends are more likely to rotate and form larger chains. g This increases the free volume, allowing easy flow under stress.

[0073] In addition to polymer, the composition fed into the extruder can also include additives compatible with the disclosed multilayer structure of production. Common additives include but are not limited to organic peroxides, antioxidants, lubricants, processing aids, heat stabilizers, colorants, flame retardants, antistatic agents, nucleators, plasticizers, antibacterial agents, fungicides, light stabilizers, UV absorbers, anti-caking agents, fillers, deodorants, odor adsorbents, antifogging agents, volatile organic compounds (VOC) adsorbents, semi-volatile organic compounds (SVOC) adsorbents, thickeners, pore size stabilizers, metal passivators, and combinations thereof. Suitable antioxidant packages include PR023, which is a blend of standard antioxidants developed by Toray Industries, Inc. and compounded by Techmer PM, and / or PR086, which is a blend of antioxidants prepared by Toray Plastics (America), Inc. and blended by Amfine Chemical. Suitable processing aids can include TPM11166 from Techmer PM. Additional examples of suitable additives may include PM91399, which is a black concentrate from Techmer PM.

[0074] In some embodiments, the amount of additives other than chemical blowing agents and cross-linking promoters in the foam layer composition and / or the cover layer composition may be less than or equal to about 20 PPR%, about 15 PPR%, about 10 PPR%, about 8 PPR%, about 6 PPR%, about 4 PPR%, about 2 PPR%, or about 1 PPR% of the composition. In some embodiments, the amount of additives other than chemical blowing agents and cross-linking promoters in the foam layer composition and / or the cover layer composition may be greater than or equal to about 0.5 PPR%, about 1 PPR%, about 2 PPR%, about 4 PPR%, about 6 PPR%, about 8 PPR%, about 10 PPR%, or about 15 PPR% of the composition. In some embodiments, the amount of additives other than chemical blowing agents and cross-linking promoters in the foam layer composition and / or the cover layer composition may be about 0.5-20 PPR%, about 1-10 PPR%, about 1.5-5 PPR%, or about 2-3 PPR% of the composition. In some embodiments, the amount of additives other than chemical blowing agents and cross-linking accelerators in the foam layer composition can be about 1-20 wt %, about 3-15 wt %, about 5-10 wt %, or about 6-8 wt % of the foam layer composition. In some embodiments, the amount of additives other than chemical blowing agents and cross-linking accelerators in the cover layer composition can be about 0.5-10 wt %, about 1-6 wt %, or about 1.5-5 wt % of the cover layer composition.

[0075] Regardless of how the ingredients are fed into the extruder, the shear and mixing within the extruder will be sufficient to produce a uniform layer. Co-rotating and counter-rotating twin screw extruders can provide sufficient shear and mixing to extrude a layer with uniform properties through the extruder barrel.

[0076] Specific energy is an indication of how much work is applied during the extrusion of the composition of the layer and how intense the extrusion process is. Specific energy is defined as the energy applied by the extruder to the material being processed, normalized to a per kilogram basis. Specific energy is quantified in units of energy applied (kW) / total material fed per hour (kg). Specific energy is calculated according to the following formula:

[0077] in

[0078]

[0079] Specific energy can be used to quantify the amount of shear and mixing of the ingredients within the extruder. The extruder used to form the multilayer structure disclosed herein can be used to generate a specific energy of at least about 0.100 kW·h / kg, preferably at least about 0.120 kW·h / kg, and more preferably at least about 0.150 kW·h / kg.

[0080] Any foamable layer may contain a chemical blowing agent (CFA). The extrusion temperature of any foamable layer may be at least 10°C lower than the thermal decomposition start temperature of the chemical blowing agent. If the extrusion temperature exceeds the thermal decomposition temperature of the blowing agent, the blowing agent will decompose, resulting in undesirable "pre-foaming". The extrusion temperature of any covering layer may be at least 10°C lower than the thermal decomposition start temperature of the chemical blowing agent in any foamable layer adjacent to the covering layer. If the extrusion temperature of the covering layer exceeds the thermal decomposition temperature of the blowing agent in the adjacent layer, the blowing agent in the adjacent layer will decompose, which also results in undesirable "pre-foaming".

[0081] The foam layer composition may include a variety of different chemical foaming agents. Examples of chemical foaming agents include, but are not limited to, azo compounds, hydrazine compounds, carbohydrazides, tetrazoles, nitroso compounds, and carbonates. In addition, chemical foaming agents may be used alone or in any combination. One chemical foaming agent that may be used in some embodiments is azodicarbonamide (ADCA). An example of a chemical foaming agent is PTLauten Otsuka Chemical's TC-18I, which was imported by Biddle Sawyer Corporation and sold under the TC-18I is sold in the U.S. Thermal decomposition of ADCA generally occurs at a temperature of about 190-230° C. To prevent thermal decomposition of ADCA in the extruder, the extrusion temperature may be maintained at 190° C. or lower.

[0082] The amount of chemical blowing agent in the foam layer composition and / or the cover layer composition may be less than or equal to about 30 PPR%, about 20 PPR%, about 15 PPR%, about 10 PPR%, about 8 PPR%, or about 5 PPR% of the composition. In some embodiments, the amount of chemical blowing agent in the foam layer composition and / or the cover layer composition may be greater than or equal to about 1 PPR%, about 5 PPR%, about 10 PPR%, about 15 PPR%, or about 20 PPR% of the composition. In some embodiments, the amount of chemical blowing agent in the foam layer composition and / or the cover layer composition may be about 1-30 PPR%, about 2-20 PPR%, about 5-15 PPR%, or about 6-10 PPR% of the composition. In some embodiments, the amount of chemical blowing agent in the foam layer composition may be about 1-20wt%, about 2-15wt%, about 5-10wt%, or about 6-8wt% of the foam layer composition. In some embodiments, the amount of chemical blowing agent in the cover layer composition can be about 0.1-5 wt %, about 0.5-3 wt %, or about 1-2 wt % of the cover layer composition. The amount of chemical blowing agent can depend on the unfoamed sheet thickness, the desired foam thickness, the desired foam density, the material being extruded, the percentage of crosslinking, the type of chemical blowing agent (different blowing agents will produce significantly different amounts of gas), etc.

[0083] It should be noted that the amounts of chemical blowing agents listed above may be specific to ADCA only. Other blowing agents may produce different amounts of gas volume per unit mass of CFA and may be considered accordingly. For example, when comparing ADCA to the chemical blowing agent toluenesulfonyl semicarbazide (TSS), if the foamable layer contains 40 PPHR of ADCA, then about 63 PPHR of TSS will be required to produce about the same amount of gas in the foaming step.

[0084] If the difference between the decomposition temperature of the thermally decomposable blowing agent and the melting point of the polymer with the highest melting point is high, a catalyst for the decomposition of the blowing agent can be used. Exemplary catalysts include, but are not limited to, zinc oxide, magnesium oxide, calcium stearate, glycerol, and urea. The lower temperature limit for extrusion can be the melting point of the polymer with the highest melting point. If the extrusion temperature drops below the melting temperature of the polymer with the highest melting point, undesirable "unmelt" will occur. After foaming, the extruded layer extruded below this lower temperature limit will exhibit uneven thickness, uneven pore structure, cavities of collapsed pores and other undesirable properties.

[0085] Extrusion of unfoamed multilayer sheets and extrusion foamed multilayer sheets (commonly referred to as "extrusion foaming") are distinct. Extrusion foaming can be performed with a physical foaming agent, a chemical foaming agent, or a mixture of physical and chemical foaming agents. Physical foaming agents can be inorganic and organic gases (nitrogen, carbon dioxide, pentane, butane, etc.) that are injected directly into the polymer melt under high pressure. The gas can nucleate and expand as the polymer melt leaves the extrusion die to produce a foamed polymer. Chemical foaming agents, such as the aforementioned examples, can be solids that exothermically or endothermically decompose at a decomposition temperature to produce a gas. Typical gases produced by chemical foaming agents include nitrogen, carbon monoxide, carbon dioxide, ammonia, etc. In order to perform extrusion foaming with a chemical foaming agent, the chemical foaming agent can be dispersed in the polymer melt and, while still in the extruder and die, the melt is heated to a temperature above the decomposition temperature of the chemical foaming agent. The foamed polymer can be manufactured as a polymer melt leaving the extrusion die.

[0086] Regardless of whether the blowing agent is physical, chemical, or a combination thereof, typical extrusion foaming produces a polymer sheet in which the two major surfaces are significantly rougher than the equivalent structure produced in the disclosed method. The surface profile of multilayer (as well as single-layer) foam sheets can be critical for many applications, so extrusion foamed sheets cannot be used for these applications. These applications may require a smooth foam surface to obtain desired properties, such as easy lamination to films, fabrics, fiber layers, and leather; percentage of contact area in lamination; visual aesthetics, etc. PCT publication WO2016109544, the entire contents of which are incorporated herein by reference, includes examples showing the gap in surface roughness between extrusion foamed polymer sheets and equivalent foamed polymer sheets produced by the disclosed method.

[0087] The rougher surface of the extrusion foamed article can generally be caused by the larger size of the cells (when compared to the foam produced according to the present invention). Although the cell size and cell size distribution may not be critical in most commercial applications, because the surface roughness is a function of the cell size, for applications requiring a smooth foam surface, a foam with larger cells may not be as desirable as a foam with smaller cells.

[0088] The thickness of the unfoamed, coextruded multilayer structure can be about 0.1 to about 30 mm, about 0.2 to about 25 mm, about 0.3 to about 20 mm, or about 0.4 to about 15 mm. The thickness of any single A or B layer can be at least about 0.05 mm, at least about 0.1 mm, at least about 0.15 mm, or at least about 0.2 mm. The thickness of any single A or B layer can be less than or equal to about 0.2 mm, about 0.15 mm, or about 0.10 mm. In some embodiments, the thickness of the cover layer of the unfoamed, coextruded multilayer structure can be about 0.1 to 300 microns, about 25 to 200 microns, or about 30 to 175 microns. In some embodiments, the cover layer of the unfoamed, coextruded multilayer structure may have a thickness of less than 300 microns, less than 250 microns, less than 200 microns, less than 175 microns, less than 150 microns, less than 125 microns, less than 100 microns, less than 90 microns, less than 80 microns, less than 70 microns, less than 60 microns, less than 50 microns, less than 40 microns, less than 30 microns, less than 20 microns, less than 10 microns, less than 5 microns, or less than 1 micron. In some embodiments, the cover layer of the unfoamed, coextruded multilayer structure may have a thickness greater than 1 micron, greater than 5 microns, greater than 10 microns, greater than 20 microns, greater than 30 microns, greater than 40 microns, greater than 50 microns, greater than 60 microns, greater than 70 microns, greater than 80 microns, greater than 90 microns, greater than 100 microns, greater than 125 microns, greater than 150 microns, greater than 175 microns, greater than 200 microns, or greater than 250 microns. There is no limit to how thin the unfoamed cover thickness can be relative to the overall unfoamed coextruded multilayer sheet, and can be as thin as about 0.1 μm, or the typical thickness of very thin tie layers used in multilayer flexible packaging and barrier films. In some embodiments, the thickness of the foam layer of the unfoamed, coextruded multilayer structure can be about 0.1-5 mm, about 0.5-3 mm, about 1-2 mm, or about 1-1.5 mm. In some embodiments, the thickness of the foam layer of the unfoamed, coextruded multilayer structure can be less than or equal to about 5 mm, about 3 mm, about 2 mm, about 1.5 mm, about 1 mm, or about 0.5 mm. In some embodiments, the thickness of the foam layer of the unfoamed, coextruded multilayer structure can be greater than or equal to about 0.1 mm, about 0.5 mm, about 1 mm, about 1.5 mm, about 2 mm, or about 3 mm.

[0089] For the case where the cover layer is not intended to be foamed or only slightly foamed, the cover can be thin and easy to bend when melted, so as not to significantly hinder the expansion of the foamable layer in the foaming step. The thickness, flexibility, melt strength and cross-linking percentage of the cover belong to many physical properties that will hinder the foaming expansion of other layers. Similarly, the thickness, flexibility, melt strength and cross-linking percentage of the foamable layer and the final thickness and density of the foamable layer are also factors that determine whether the cover hinders the expansion of the foamable layer. The general principle for the maximum cover thickness is that it should not be greater than about 20%, about 15%, about 10%, or about 5% of the entire coextruded unfoamed sheet. If the cover thickness is greater than about 20% of the entire coextruded unfoamed sheet, when the multilayer sheet is heated and foamed, the problem of curling, bending and self-folding of the multilayer sheet will occur.

[0090] After the coextruded sheet has been produced (e.g., by a twin extruder), the extruded multilayer sheet can be subjected to irradiation with ionizing radiation at a given exposure to crosslink the composition of the multilayer sheet, thereby obtaining an irradiated crosslinked multilayer structure. Ionizing radiation is often not useful for producing a sufficient degree of crosslinking on polypropylene, polypropylene-based materials, some polyethylenes, and some polyethylene-based materials. Therefore, a crosslinking promoter can be added to the composition fed into the extruder to promote crosslinking. Polymers crosslinked by ionizing radiation are generally referred to as "physical crosslinks."

[0091] It is important to distinguish between "physical" crosslinking and "chemical" crosslinking. In chemical crosslinking, crosslinking is produced by a crosslinking accelerator, but ionizing radiation is not used. Chemical crosslinking generally includes the use of peroxides, silanes or vinyl silanes. In peroxide crosslinking methods, crosslinking generally occurs in the extrusion die. For silane and vinyl silane crosslinking methods, crosslinking generally occurs in a secondary operation after extrusion, where heat and moisture are used to accelerate the crosslinking of the extruded material. Regardless of the chemical crosslinking method, chemically crosslinked foam sheets generally exhibit a significantly rougher main surface than the equivalent structure produced by the disclosed method. The surface profile of multilayer (and single-layer) foam sheets can be critical in many applications, so chemically crosslinked foam sheets cannot be used in these applications. These applications will require a smooth foam surface to obtain the desired properties, such as easy lamination to films, fabrics, fiber layers and leather; contact area percentage in lamination; visual aesthetics, etc. PCT Publication WO2016109544 includes examples showing the gap in surface roughness between chemically crosslinked foamed polymer sheets and equivalent foamed polymer sheets produced by the disclosed method.

[0092] The rougher surface of chemically crosslinked foamed articles can generally result from larger pore sizes (when compared to foams produced according to the present invention). Although pore size and pore size distribution may not be critical in most commercial applications, since surface roughness is a function of pore size, foams with larger pores may not be as desirable as foams with smaller pores for applications requiring a smooth foam surface.

[0093] Examples of ionizing radiation include, but are not limited to, α, β (electron beam), x-rays, γ and neutrons. Among them, electron beams with uniform energy can be used to prepare crosslinked polyolefin foam / KEE covering structures. The exposure time, irradiation frequency and accelerating voltage of electron beam irradiation can vary greatly according to the crosslinking degree of the target and the thickness of the multilayer structure. However, the ionizing radiation can generally be about 10-about 500 kGy, about 20-about 300 kGy, or about 20-about 200 kGy. If the exposure is too low, the cell stability cannot be maintained during foaming. If the exposure is too high, the formability of the multilayer foam structure formed will be poor. When the multilayer foam sheet is used for thermoforming applications, formability is a desired property. Similarly, the unfoamed sheet can be softened by exothermic release exposed to electron beam radiation, whereby the structure will be deformed when the exposure is too high. In addition, the polymer component can also be degraded due to excessive polymer chain scission.

[0094] The coextruded unfoamed multilayer sheet can be irradiated up to four independent times, preferably no more than two times, and more preferably only once. If the irradiation frequency is more than about four times, the polymer components will suffer degradation, so that uniform pores will not be produced in the foamed layer formed, for example, by foaming. When the thickness of the extruded structure is greater than about 4 mm, it may be preferred to irradiate each major surface of the multilayer profile with ionizing radiation to make the degree of crosslinking of the major surfaces and the inner layers more uniform.

[0095] The advantage provided by electron beam irradiation is that coextruded sheets of different thicknesses can be effectively crosslinked by controlling the accelerating voltage of the electrons. The accelerating voltage can generally be about 200-about 1500kV, about 400-about 1200kV, or about 600-about 1000kV. If the accelerating voltage is less than about 200kV, the radiation cannot reach the inside of the coextruded sheet. As a result, the holes in the inside can be rough and uneven when foaming. In addition, for a profile of a given thickness, too low an accelerating voltage can cause arc discharge, forming "pinholes" or "channels" in the foamed structure. On the other hand, if the accelerating voltage is greater than about 1500kV, the polymer can degrade. In some embodiments, the radiation source can face the B layer of the coextruded, unfoamed multilayer sheet during the irradiation process. In some embodiments, the radiation source can face the A layer of the coextruded, unfoamed multilayer sheet during the irradiation process.

[0096] Regardless of the type of ionizing radiation selected, crosslinking is performed so that the composition of the extruded structure is crosslinked by about 20 to about 75%, or about 30 to about 60%, as measured by the "Toray Gel Fraction Percentage Method". According to the "Toray Gel Fraction Percentage Method", a tetralin solvent is used to dissolve the non-crosslinked components in the composition. In principle, the non-crosslinked material is dissolved in tetralin, and the degree of crosslinking is expressed as the weight percentage of the crosslinked material in the entire composition. The equipment used to determine the percentage of crosslinking of the polymer includes: 100 mesh (0.0045 inch wire diameter); 304 type stainless steel bag; numbered wire mesh and clamps; Miyamo constant temperature oil bath equipment; analytical balance; fume hood; gas stove; high temperature oven; antistatic gun; and 3.5L three-wide mouth stainless steel container with lid. The reagents and materials used include tetralin high molecular weight solvent, acetone and silicone oil. Specifically, the empty wire mesh bag is weighed and the weight is recorded. For each sample, 100 mg ± 5 mg of sample is weighed and transferred to the wire mesh bag. Record the weight of the wire mesh bag and the sample (which is usually in the form of a thin foam cutout). Connect each bag to the corresponding numbered wire mesh and clamp. When the solvent temperature reaches 130°C, immerse the bundle (bag and sample) in the solvent. Shake the sample up and down about 5 or 6 times to release any bubbles and completely wet the sample. Connect the sample to a stirrer and stir for three (3) hours so that the solvent can dissolve the foam. Then cool the sample in a fume hood. Shake up and down about 7 or 8 times in a container that is mainly acetone to clean the sample. Wash the sample a second time in the second acetone wash. The washed sample is cleaned again as above in a third container of fresh acetone. The sample is then hung in a fume hood to evaporate the acetone for about 1 to about 5 minutes. The sample is then dried at 120°C in a drying oven for about 1 hour. The sample is cooled for a minimum of about 15 minutes. Weigh the wire mesh bag on an analytical balance and record the weight. The degree of crosslinking was then calculated using the formula 100 x (CA) / (BA), where A = empty mesh bag weight; B = mesh bag weight before immersion in tetralin + foam sample; and C = mesh bag weight after immersion in tetralin + dissolved sample.

[0097] Suitable crosslinking promoters include, but are not limited to, commercially available difunctional, trifunctional, tetrafunctional, pentafunctional and higher functionality monomers. Such crosslinking monomers can be used in liquid, solid, granular and powdered forms. Examples include, but are not limited to, acrylates or methacrylates such as 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, 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-phenylene bismaleimide; compounds having at least two triple bonds such as dipropargyl phthalate and dipropargyl maleate; and divinylbenzene. In addition, such crosslinking accelerators may be used alone or in any combination. Divinylbenzene (DVB, a difunctional liquid crosslinking monomer) can be used as a crosslinking accelerator in the present invention. For example, suitable commercially available DVB can include DVB HP from Dow Chemical Company.

[0098] The amount of crosslinking accelerator in the foam layer composition and / or the cover layer composition may be less than or equal to about 5 PPR%, about 4 PPR%, about 3 PPR%, about 2.5 PPR%, about 2 PPR%, about 1.5 PPR%, or about 1 PPR% of the composition. In some embodiments, the amount of crosslinking accelerator in the foam layer composition and / or the cover layer composition may be greater than or equal to about 0.5 PPR%, about 1 PPR%, about 1.5 PPR%, about 2 PPR%, about 2.5 PPR%, about 3 PPR%, or about 4 PPR% of the composition. In some embodiments, the amount of crosslinking accelerator in the foam layer composition and / or the cover layer composition may be about 0.1-5 PPR%, about 0.5-3 PPR%, about 1-3 PPR%, or about 2-3 PPR% of the composition. In some embodiments, the amount of crosslinking accelerator in the foam layer composition may be about 0.5-5wt% of the foam layer composition, or about 1-3wt%.

[0099] It should be noted that the amounts of crosslinking promoters listed above may be used exclusively for DVB only. The crosslinking efficiency of other crosslinking promoters may be higher or lower than that of DVB. Therefore, the amount required for another crosslinking promoter should be considered accordingly. The crosslinking efficiency of a crosslinking promoter may vary based on the ionizing radiation dose, the polymer to be crosslinked, the chemical structure of the monomer, the number of functional groups on the monomer, and whether the monomer is a liquid or a powder.

[0100] Crosslinks can be produced using a variety of different techniques and can be formed between molecules, between different polymer molecules, and within molecules, between parts of a single polymer molecule. Such techniques include, but are not limited to, providing a crosslinking promoter separated from the polymer chain, and providing a polymer chain into which a crosslinking promoter is introduced, the crosslinking promoter containing functional groups that can form crosslinks or can be activated to form crosslinks.

[0101] After irradiating the coextruded sheet, foaming can be accomplished by heating the crosslinked multilayer sheet to a temperature above the decomposition temperature of the thermally decomposable blowing agent. Foaming can be performed in a continuous process at about 200-260° C. or about 220-240° C. A continuous foaming process may be preferred over a batch process for producing a continuous foam sheet.

[0102] Foaming can be performed typically by heating the crosslinked multilayer sheet with molten salt, radiant heater, vertical or horizontal hot air oven, microwave energy, or a combination of these methods. Foaming can also be performed in an impregnation process using, for example, nitrogen in an autoclave, followed by free foaming via molten salt, radiant heater, vertical or horizontal hot air oven, microwave energy, or a combination of these methods. Optionally, the crosslinked multilayer sheet can be preheated to soften prior to foaming. This can help stabilize the expansion of the structure during foaming, particularly for thick and hard sheets.

[0103] The density of the multilayer foam sheet can be defined and measured using a cross-sectional or "bulk" density, rather than a "core" density, such as measured by JIS K6767. The multilayer foam sheet produced using the above method can produce a cross-sectional or "bulk" density of about 20-250 kg / m 3 , about 30-200kg / m 3 , or about 50-150kg / m 3 The cross-sectional density can be controlled by the amount of blowing agent and the thickness of the extruded structure. If the density of the multilayer foam sheet is less than about 20 kg / m 3 , the sheet cannot be foamed effectively because a large amount of chemical foaming agent is required to obtain the density. In addition, if the density of the sheet is less than about 20 kg / m 3 , the expansion of the sheet during the foaming step becomes increasingly difficult to control. In addition, if the density of the multilayer foam sheet is less than about 20 kg / m 3 , the foam will become more susceptible to cell collapse. Therefore, at densities less than about 20 kg / m 3 When the thickness of the foam sheet is uniform, it is difficult to produce a multi-layer foam sheet with uniform cross-sectional density and thickness.

[0104] Multilayer foam sheet is not limited to about 250kg / m 3 It is also possible to produce a cross-sectional density of about 350kg / m3 , about 450kg / m 3 , or about 550kg / m 3 However, it is preferred that the density of the foam sheet can be less than about 250 kg / m 3 , as greater density is often a cost limitation compared to other materials that can be used for a given application.

[0105] The foam layer produced using the above method can have closed cells. Preferably, at least 90% of the cells have undamaged cell walls, preferably at least 95%, and more preferably greater than 98%. The average pore size can be from about 0.05 to about 1.0 mm, preferably from about 0.1 to about 0.7 mm. If the average pore size is less than about 0.05 mm, the density of the foam structure will generally be greater than 250 kg / m 3 . If the average pore size is greater than 1 mm, the foam will have an uneven surface. If the pore population in the foam does not have the preferred average pore size, there is also the possibility of undesirable tearing of the foam structure. This can occur when the foam structure is stretched or parts of it are subjected to secondary processing. The pore size of the foam layer can have a bimodal distribution, which represents a pore population in the core of the foam structure, which is relatively round, and a pore population in the skin layer near the surface of the foam structure, which is relatively flat, thin and / or oval.

[0106] The overall thickness of the multilayer polyolefin foam / KEE cover sheet can be about 0.2mm to about 50mm, about 0.4mm to about 40mm, about 0.6mm to about 30mm, or about 0.8mm to about 20mm. If the thickness is less than about 0.2mm, the foaming is not effective due to the large amount of gas loss from the main surface. If the thickness is greater than about 50mm, the expansion in the foaming step will become more and more difficult to control. Therefore, it will become more and more difficult to produce a multilayer polyolefin foam / KEE cover sheet with uniform cross-sectional density and thickness. In some embodiments, the thickness of the cover layer of the foamed, coextruded multilayer structure can be about 0.1-100 microns, about 1-100 microns, or about 5-75 microns. In some embodiments, the thickness of the foam layer of the foamed, coextruded multilayer structure can be about 0.1-5mm, about 0.5-5mm, about 1-5mm, about 2-5mm, or about 2-4mm.

[0107] In some embodiments, the desired thickness can be obtained by secondary processing such as slicing, skiving or bonding. Slicing, skiving or bonding can produce a thickness of about 0.1 mm to about 100 mm.

[0108] For cases where the cover layer is intended to be unfoamed or slightly foamed, the thickness of the cover layer may decrease as the multilayer sheet foams. This may be due to the foamable layer expanding and thus stretching the cover layer. Thus, for example, if the multilayer sheet expands to twice its initial area, the thickness of the cover may be expected to be approximately halved. If the multilayer sheet expands to four times its initial area, the thickness of the cover may be expected to be reduced to about one-quarter of its initial thickness.

[0109] The disclosed multilayer polyolefin foam / KEE cover sheet can be used in applications requiring adhesion to PVC. The PVC can be a flexible film, foil or foam. The PVC can also be a semi-flexible or rigid board, slab, tile or substrate. The board, slab, tile or substrate can be solid or foam. Importantly, the PVC can be the surface layer of a multilayer structure.

[0110] In some embodiments, the multilayer foam structure is a laminate containing a multilayer foam and a flexible laminate layer. Preferably, the laminate layer can be applied to the KEE covered side of the multilayer foam. In these laminates, the multilayer foam structure can be, for example, combined with a film, foil or foam. Examples of suitable materials for such laminate layers include, but are not limited to, flexible PVC films, flexible PVC foils and flexible PVC foams. Such layers can be manufactured using conventional techniques well known to those skilled in the art. Importantly, the multilayer foam of the present invention can be laminated to one or both sides of these materials and can include multiple other layers. If the multilayer foam is laminated to both sides, it is preferred that these laminate layers can be applied to the KEE covering layer of the multilayer foam.

[0111] The multilayer foam structure (or laminate comprising the multilayer foam structure) can also be thermoformed. In order to thermoform the multilayer foam structure or laminate, the foam can be heated to the melting point of the blend of all layers in the multilayer foam / KEE cover structure. If any layer has an immiscible polymer, the multilayer foam structure will exhibit more than one melting point. In this case, when the foam is heated to a temperature midpoint between the lowest melting point and the highest melting point of the multilayer foam layer composition, the multilayer foam structure can generally be thermoformed. In addition, the multilayer foam structure can be thermoformed onto a substrate such as hard polypropylene, ABS or a wood fiber composite. Heat-activated adhesives can be used to improve the bonding of the substrate to the covered or uncovered side of the multilayer foam / KEE cover structure. In the case of a laminate, the laminate can be on the opposite side of the substrate (e.g., in the case where the laminate is used for protective and / or decorative purposes). The substrate itself can also be thermoformed simultaneously with the multilayer foam structure.

[0112] In some embodiments, multilayer foam structures or laminates (which may or may not be thermoformed) can be used for automotive interior parts such as door panels, door rolls, door inserts, door fillers, trunk fillers, armrests, center consoles, seat cushions, seat backs, headrests, seat back panels, dashboards, knee pads or canopies. These multilayer foam structures or laminates (which may or may not be thermoformed) can also be used for furniture (such as commercial, office and residential furniture) such as chair cushions, chair backs, sofa cushions, sofa decorations, recliner cushions, recliner decorations, couch cushions, couch decorations, berth cushions or berth decorations. These multilayer foam laminates or structures (which may or may not be thermoformed) can also be used in walls such as module walls, movable walls, wall panels, module panels, office system panels, room dividers or movable partitions. Multilayer foam laminates or structures can also be used for storage shells (such as commercial, office and residential), which can be mobile or fixed. In addition, the multi-layer foam laminates and structures (which may or may not be thermoformed) can also be used for coverings such as chair cushion coverings, chair back coverings, armrest coverings, sofa coverings, sofa cushion coverings, recliner cushion coverings, recliner coverings, couch cushion coverings, couch coverings, sleeper cushion coverings, couch coverings, sleeper cushion coverings, sleeper coverings, wall coverings and building coverings.

[0113] In some embodiments, the multi-layer foam structure or laminate can be used as a roof membrane and as a roof flashing component. For laminates: PVC, KEE and PVC / KEE blends are very suitable as laminate layers of multi-layer foam structures. The KEE cover layer of the multi-layer foam structure can face the laminate layer.

[0114] In some embodiments, the multilayer foam structure is a laminate containing a multilayer foam and a non-flexible laminate layer. Preferably, the multilayer foam can have the KEE cover side applied to the laminate layer. In these laminates, the multilayer foam structure can be combined with a board, a thick board, a brick or a substrate, for example. The board, the thick board, the brick or the substrate can be a foam. Such layers can be manufactured using conventional techniques known to those skilled in the art. Importantly, the multilayer foam of the present invention can be laminated to one or both sides of these materials and can include multiple other layers. If the multilayer foam is laminated to both sides, it is preferred that these laminate layers can be applied to the cover layer of the multilayer foam.

[0115] Some embodiments include a first layer of the disclosed multi-layer foam structure and a second layer consisting of vinyl floor tiles or wood-PVC composites for floors or walls. In these laminates, the first layer can be connected to adjacent tiles or composites by fusion bonding. Preferably, the KEE cover layer of the multi-layer foam structure can be on the side of the first layer facing the second layer.

[0116] Multiple layers of foam attached to vinyl floor tiles or wood-PVC composites can serve several purposes. The foam can reduce the reflected sound pressure level when the panels are impacted, such as when a boot or high heel walks on the panels. The foam can also act as a moisture vapor barrier between the panels and the subfloor (plywood, oriented strand board (OSB), concrete, etc.), and can help provide a more even laydown between multiple panels, as the foam will cushion any unevenness, ridges, or spikes (such as protruding nail heads) in the subfloor. These tiles and composites are commonly installed in homes, office buildings, and other commercial buildings.

[0117] To meet the requirements of any of the above applications, the structures disclosed in the present invention may undergo various secondary processes including, but not limited to, embossing, corona or plasma treatment, surface roughening, surface flattening, perforation or microperforation, splicing, slicing, scraping, delamination, bonding and punching.

[0118] Example

[0119] Raw materials of the examples

[0120] Table 1 below provides a listing of the various components used in the following examples and a description of those components.

[0121] Table 1

[0122]

[0123]

[0124]

[0125]

[0126]

[0127]

[0128]

[0129]

[0130]

[0131] The multilayer structures of Examples 1A, 1B, 2A, 2B, 3, 4A, 4B, 5, 6, 7, 8, 9, 10 and 11 can be seen at 30× magnification and 45° to the major surface, respectively. Figure 1A , 1B, 2A, 2B, 3, 4A, 4B, 5, 6, 7, 8, 9, 10, and 11.

[0132] This application discloses some numerical ranges in the text and drawings. The disclosed numerical ranges inherently support any range or value within the disclosed numerical range, including the endpoints, even if the specification does not verbatim state the exact range limitation, because the present invention can be practiced within the entire disclosed numerical range.

[0133] The above description is presented to enable those skilled in the art to make and use the invention, and is provided in the context of a specific application and its requirements. Different changes to the preferred embodiments will be readily understood by those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Therefore, the present invention is not intended to be limited to the embodiments shown, but rather to the widest range consistent with the principles and features disclosed herein. Finally, the entire contents of the patents and publications mentioned in this application are incorporated herein by reference.

Claims

1. A multilayer foam structure comprising: a coextruded foam layer comprising polypropylene, polyethylene, or a combination of polypropylene and polyethylene; A coextruded cover layer on one side of the foam layer, the cover layer consisting of: 15-85 wt% of a ketone-ethylene-ester terpolymer, wherein the ester in the ketone-ethylene-ester terpolymer comprises n-butyl acrylate or 2-ethylhexyl acrylate; Optionally 1-8 wt% of additives; and Polypropylene, polyethylene, or a combination of polypropylene and polyethylene; and a polyvinyl chloride layer on a side of the coextruded cover layer opposite the coextruded foam layer, Wherein the multilayer foam structure does not include corona, plasma or chemical surface treatments, and does not include a bonding primer or adhesive between the coextruded cover layer and the polyvinyl chloride layer.

2. The multilayer foam structure according to claim 1, wherein the coextruded foam layer comprises 2-15 wt% of the ketone-ethylene-ester terpolymer.

3. The multilayer foam structure of claim 1, wherein the coextruded foam layer comprises at least 70 wt% polypropylene, polyethylene, or a combination of polypropylene and polyethylene.

4. The multilayer foam structure according to claim 1, wherein the foam layer comprises the additive in an amount of 1-20 wt%.

5. The multilayer foam structure according to claim 1, wherein the polypropylene has a melt flow index of 0.1-25 g / 10 min at 230°C.

6. The multilayer foam structure according to claim 1, wherein the polyethylene has a melt flow index of 0.1-25 g / 10 min at 190°C.

7. The multilayer foam structure according to claim 1, wherein the density of the multilayer foam structure is 20-250 kg / m 3 .

8. The multilayer foam structure according to claim 1, wherein the crosslinking degree of the multilayer foam structure is 20-75%.

9. The multilayer foam structure according to claim 1, wherein the average closed cell size of the multilayer foam structure is 0.05-1.0 mm.

10. The multilayer foam structure according to claim 1, wherein the thickness of the multilayer foam structure is 0.2-50 mm.

11. A laminate comprising: A multilayer foam structure comprising: a coextruded foam layer comprising polypropylene, polyethylene, or a combination of polypropylene and polyethylene; and A coextruded cover layer on one side of the foam layer, the cover layer consisting of: 15-85 wt% of a ketone-ethylene-ester terpolymer, wherein the ester in the ketone-ethylene-ester terpolymer comprises n-butyl acrylate or 2-ethylhexyl acrylate; Optionally 1-8 wt% of additives; and Polypropylene, polyethylene, or a combination of polypropylene and polyethylene; and a laminated polyvinyl chloride layer on a side of the cover layer opposite to the foam layer, Wherein the laminate does not include corona, plasma or chemical surface treatments, nor does it include a bonding primer or adhesive between the coextruded cover layer and the laminated polyvinyl chloride layer.

12. The laminate according to claim 11, wherein the laminated polyvinyl chloride layer is a flexible film or foil.

13. The laminate according to claim 11, wherein the laminated polyvinyl chloride layer is a semi-flexible or rigid board, a thick board, a tile or a substrate.

14. The laminate according to claim 11, wherein the laminated polyvinyl chloride layer is unfoamed or foamed.

15. The laminate according to claim 11, wherein the coextruded foam layer comprises 2-15 wt% of the ketone-ethylene-ester terpolymer.

16. The laminate of claim 11, wherein the coextruded foam layer comprises at least 70 wt% polypropylene, polyethylene, or a combination of polypropylene and polyethylene.

17. The laminate according to claim 11, wherein the foam layer comprises the additive in an amount of 1-20 wt%.

18. The laminate according to claim 11, wherein the polypropylene has a melt flow index of 0.1-25 g / 10 min at 230°C.

19. The laminate according to claim 11, wherein the polyethylene has a melt flow index of 0.1-25 g / 10 min at 190°C.

20. A floor system comprising: PVC top flooring layer; Subfloor layer; and at least one cushioning layer positioned between the subflooring layer and the polyvinyl chloride top flooring layer, wherein the at least one cushioning layer comprises a multi-layer foam structure comprising: a coextruded foam layer comprising polypropylene, polyethylene, or a combination of polypropylene and polyethylene; and A coextruded cover layer on one side of the foam layer, the cover layer consisting of: 15-85 wt% of a ketone-ethylene-ester terpolymer, wherein the ester in the ketone-ethylene-ester terpolymer comprises n-butyl acrylate or 2-ethylhexyl acrylate; Optionally 1-8 wt% of additives; and Polypropylene, polyethylene or a combination of polypropylene and polyethylene, wherein the polyvinyl chloride top flooring layer is located on a side of the coextruded cover layer opposite the coextruded foam layer, Wherein the flooring system does not include corona, plasma or chemical surface treatments, nor does it include a bonding primer or adhesive between the coextruded cover layer and the polyvinyl chloride top flooring layer.

21. A method of forming a multilayer structure, comprising: Coextrusion: The first layer, which contains: Polypropylene, polyethylene or a combination of polypropylene and polyethylene; Chemical blowing agents; and A second layer on one side of the first layer, the second layer consisting of: 15-85 wt% of a ketone-ethylene-ester terpolymer, wherein the ester in the ketone-ethylene-ester terpolymer comprises n-butyl acrylate or 2-ethylhexyl acrylate; Optionally 1-8 wt% of additives; and Polypropylene, polyethylene or a combination of polypropylene and polyethylene; irradiating the coextruded layer with ionizing radiation; foaming the irradiated coextruded layer; and Adhere the polyvinyl chloride layer to the side of the second layer opposite to the first layer, The multilayer structure does not include corona, plasma or chemical surface treatment, nor does it include a bonding primer or adhesive between the second layer and the polyvinyl chloride layer.

22. The method of claim 21, wherein the first layer comprises 2-15 wt% of a ketone-ethylene-ester terpolymer.

23. The method of claim 21, wherein the first layer comprises at least 70 wt% polypropylene, polyethylene, or a combination of polypropylene and polyethylene.

24. The method of claim 21, wherein the first layer comprises the additive in an amount of 1-20 wt%.

25. The method according to claim 21, wherein the polypropylene has a melt flow index of 0.1-25 g / 10 min at 230°C.

26. The method of claim 21, wherein the polyethylene has a melt flow index of 0.1-25 g / 10 min at 190°C.

27. The method of claim 21, wherein the amount of chemical blowing agent in the first layer is 4-10 wt%.

28. The method of claim 21, wherein the chemical blowing agent comprises azodicarbonamide.

29. The method of claim 21, wherein the first layer comprises a cross-linking agent.

30. The method of claim 29, wherein the amount of crosslinking agent in the first layer is 1-3 wt%.

31. The method of claim 21, wherein the ionizing radiation is selected from the group consisting of alpha, beta electron beams, x-rays, gamma, and neutrons.

32. The method of claim 21, wherein the coextruded structure is irradiated up to four separate times.

33. The method of claim 31, wherein the ionizing radiation is an electron beam with an acceleration voltage of 200-1500 kV.

34. The method of claim 33, wherein the absorbed electron beam dose is 10-500 kGy.

35. The method of claim 21, wherein the ionizing radiation crosslinks the extruded structure to a degree of crosslinking of 20-75%.

36. The method of claim 21, wherein foaming comprises heating the irradiated structure with molten salt and a radiant heater or a hot air oven.

37. The method according to claim 21, wherein the density of the multilayer foam structure is 20-250 kg / m 3 .

38. The method of claim 21, wherein the multilayer foam structure has an average closed cell size of 0.05-1.0 mm.

39. The method according to claim 21, wherein the thickness of the multilayer foam structure is 0.2-50 mm.

Images