DE202009007494U1 - Multilayer thermoplastic sheet materials and thermoformed articles made therefrom - Google Patents

Abstract

A multilayer sheet having two surface layers and optionally one or more inner layers, said multilayer sheet comprising a non-foamed thermoplastic polymer surface layer (A), a foamed thermoplastic polymer layer (B) and an optional non-foamed thermoplastic polymer surface layer (C) having a total layer thickness of about zero , 5 to about 20 mm and a foam to solid ratio greater than 1, and wherein:
(a) the non-foamed thermoplastic polymer surface layer (A) has a thickness in the range of about 0.25 to about 6 mm, and
(b) the foamed thermoplastic polymer layer (B) results in a total density reduction of at least about 5% by weight and in the absence of the optional surface layer (C) is a surface layer.

Description

The The present invention relates to multilayer thermoplastic films. or sheet materials suitable for thermoforming applications, including the thermoforming of refrigerator linings suitable are. The present invention also relates to articles made of multilayer sheet materials, including thermoformed refrigerator linings, are made. The following is the term "sheet" as generic Term used to refer to the terms "foil" and "leaf" includes.

extruded thermoplastic sheet materials depending on the selection of the thermoplastic base resin are widely used Applications, including parts thermoforming used for durable consumer products, such. B. Refrigerator linings, inserts for Bathtubs and shower units, various bench and seat units, Body panels for different types of vehicles, Signpost plates, etc .. Thinner extruded thermoplastic Sheets can also be used for shaping to packaging materials for a wide range of materials, such as Food, beverages, detergents and cleaning products, Cosmetics, pharmaceuticals, can be used or they can also used when extruded into continuous profiles become.

at the current economic and environmental policy Interest, the cost effectiveness and the efficiency of Products and processes to improve their production, There is a continuing interest in thermoplastic sheet materials to provide and maintain the reduction of raw material quantities and the energy needed for their production and their further use to thermoformed objects to make, to facilitate. Thermoplastic sheet materials with a foamed thermoplastic layer and at least a non-foamed solid thermoplastic layer are also known and are called AB structures (a single solid cover and foam layers) and ABA structures (foam layer between two solid cover layers).

U.S. Patent 6,544,450 teaches a method of making a thermoplastic foam layer comprising contacting a molten polymer with a blowing agent, foaming the mixture in a lower pressure region within a sheet extrusion line, and drawing and compressing the extrudate to form a thermoplastic foam sheet having a uniform thickness form. Sheet materials with a foamed layer between two non-foamed surface layers (ABA structure) are shown.

U.S. Patent 6,589,646 teaches multilayer composite sheet or sheet materials having AB structures comprising at least one thicker solid substrate layer A having a thickness of 0.1 to 50 mm and at least one thinner foamed functional layer B having a thickness of 0.04 to 2 mm. These are directed in particular to the use for producing thermally insulating moldings, such as. As refrigerator liners in which a polyurethane foam insulation is applied to the foamed surface.

GB 1,595,128 describes a tube that is lighter in weight and made of a thermoplastic material having a central foam layer between two outer solid layers (ABA structure). The tube is made by coextrusion and the material for the central layer contains a propellant.

GB 1,411,132 describes moldings made from a closed-cell foam core with a smooth and shiny surface. The molded articles are produced by extruding a thermoplastic material containing a filler and a blowing agent. The surface of the extrusion die is maintained at a temperature below the decomposition temperature of the blowing agent.

U.S. Patent 5,364,696 teaches the use of foamed polystyrene sheets for thermoforming into deep drawn articles optionally having an integral high density surface layer.

EP-A 0 084 360 describes a shrink wrap sheath made from a foamed and a non-foamed polystyrene layer. In order to obtain a sufficient impact absorption, the thickness of the foamed layer is 0.1 to 1 mm. The thickness of the non-foamed layer is 2 to 160 mm. It is used for printability and can also be used as a protective layer for glass bottles.

U.S. Patent 4,069,934 describes another shrink film consisting of an inner foam layer closed cells made of polystyrene and ethylene-vinyl acetate copolymer and from a non-foamed outer layer of polyethylene.

It but it has now been established that, though some of these teachings Benefits, including weight reduction, for provide moldable sheet materials, yet a lasting Interested in obtaining thermoplastic sheet materials, reducing the amounts of both raw material and energy, needed for the production of thermoformed articles will, facilitate. It is also particularly in production of large parts thermoformed by thermoforming, such as As refrigerator linings, found that these teachings do not provide a sufficient balance of properties those for lining products and manufacturing processes of Linings involving polyurethane foams on the surface be applied by thermoformed sheet materials needed become. The main problem in this situation is the necessary one Provide property profile, primarily stiffness and modulus, while reducing the need for starting materials. Alternatively, it would be desirable to have an improved one To get property profile on a product that otherwise comparable amounts of starting materials are used. Other Problems also include improvement and maintenance the resistance to stress cracking in sheet materials where a reduced amount of thermoplastic Starting resin material is used.

Therefore become according to the present invention solutions for one or more of this problem and many other problems provided by a multi-layered sheet with two surface layers and optionally one or more inner layers, this one multilayered sheet a non-foamed surface layer (A) of thermoplastic polymer, a foamed thermoplastic Polymer layer (B) and an optional, non-foamed thermoplastic polymer surface layer (C) and a total sheet thickness of 0.5 to 20 mm and a foam to solid ratio of greater than 1 and wherein: (a) the non-foamed thermoplastic polymer surface layer (A) has a thickness in the range of 0.25 to 6 mm and (b) the foamed thermoplastic polymer layer (B) for a total density reduction of at least about five (5) weight percent and in the absence of the optional surface layer (C) a Surface layer forms. In another embodiment According to the present invention, the thickness of the non-foamed Surface layer (A) at least 0.5 mm, preferably at least 0.75 mm. In one embodiment the foam to solid ratio at least about 1.86, preferably at least about 2.33.

In In another embodiment, the multilayer Sheet according to the invention for a density reduction of at least about 10% by weight, preferably at least about 20% by weight.

In contains further alternative embodiments Layer B in the multilayer sheet is foamed aromatic monovinylidene polymer resin selected from Group consisting of HIPS, GPPS, ABS, mixtures of two or more this and mix one or more of these with one or more several additional polymers. The present invention includes embodiments in which layer A and layer B are coextruded, layer A is film-laminated on layer B. or layer A is extrusion-coated on layer B. In a Another alternative embodiment is B using a physical blowing agent or a chemical blowing agent or a combination of physical blowing agent and chemical Foaming and nucleating agents foamed. In further embodiments the present invention a thermoformed article, the from a multilayer sheet as described above or as described below Process is prepared.

The article of the present invention can be made in a thermal environment process comprising: heating a multilayer sheet described herein to a heat softened, thermally plasticized thermoformable state, applying gas, vacuum or physical pressure to the heat softened, thermoplastic plasticized sheet and stretching the sheet to approximately the final part size, adjusting the sheet by vacuum or pressure to the shape of a mold, and separating the thermoplastic part from the mold. According to a further embodiment, the present invention relates to thermally insulating molded parts produced by a method comprising: disposing a thermally insulating foam layer on the side of the foam surface layer of a thermoformed part prepared as described herein, preferably wherein the thermally insulating foam layer is a polyurethane foam more preferably located in a recess or space provided between the foam surface layer of the thermoformed part and an outer housing or termination structure, which is most preferably a refrigerator body or door. Another embodiment relates to a cooling unit comprising a thermally insulating molding which is obtainable according to one or more of the methods described above.

Brief description of the figures

1 Figure 3 is a three-dimensional view of a thermoformed liner for the body portion of a refrigerator.

2 is a schematic representation of a thermoformed lining for the body portion of a refrigerator.

3 is a cross-section of a thermoformed and foamed liner disposed in the body of a refrigerator.

Numerical values In this disclosure, all values include and inclusive the lower and upper values in increments of a unit below the Prerequisite that a separation of at least two units exists between a lower and an upper value. For example, if a composition has physical or other properties, such as B. thickness and density reduction, etc. larger than is 10, it is intended that all individual values, such as z. B. 10, 11, 12, etc. and subregions, such as. 100 to 144, 155 to 170, 197 to 200, etc. are explicitly disclosed. For Areas containing values less than 1 or fractional numbers greater than 1, (e.g., 1.1, 1.5, etc.), a unit is considered as 0.0001, 0.001, 0.01 or 0.1 as appropriate considered. For areas, the single numbers smaller than 10 (eg, 1 to 5), a unit is typically referred to as 0.1 considered. These are only examples of what is intended is and all possible combinations of numerical values between the lowest value and highest value as expressly stated in this disclosure. Numbers are used in this disclosure, inter alia, for Thickness and density reduction indicated.

The multilayered sheets according to the present invention The invention is generally good for thermoforming applications suitable and have specific for use in these applications Thicknesses and surfaces, as they are for the particular Thermoforming application are suitable. Generally, the thermoformable Sheet material has a total thickness of at least about 0.5 mm, preferably at least about 0.75 mm, more preferably at least about 1, more preferably about 1.25, more preferably at least about 1.5, even more preferably at least about 1.75, and most preferably at least about 2 mm, depending on the depth to which the leaf in the forming process and the thickness, the in a final thermoformed part or article is needed. Depending also on the possibilities the forming process and the need for the drawing depth and final part thickness have these sheet materials a thickness of up to about 20 mm, preferably up to about 14 mm, preferably up to about 12, more preferably up to about 10, more preferably up to about 8, and most preferably up to about 5 mm.

As known in the practice of thermoforming, the initial thickness of the sheet during the thermoforming step in general reduced in proportion to the draft depth of the thermoforming step. The thermoformable sheets according to the present invention can provide typical thermoforming draw ratios with many ranging from about 1 to about 5 and generally around 2.5. The initial thickness of the sheet is typically due to the need to have a minimum thickness in the thinnest area and / or critical points of the thermoformed Partially provided (eg 0.5 or 1 mm) determined. In the for thermoformed parts is typical deep drawn areas the minimum thickness (thickness in the thinnest area) at least about 0.25 mm, preferably at least about 0.5 mm and the middle Thickness of the final thermoformed part is in the range from about 0.5 to about 2 mm, preferably about 1 mm. For the leaf structures according to the present invention it has been found that they are particularly deep-drawn can, with typically better thicknesses in critical or thin areas of the thermoformed part can be. This allows either a reduced thickness the starting sheet, or, starting from a given layer thickness Improvements in the final product compared to thermoformable leaf structures according to the prior art, each related to a better thickness maintenance in the critical and / or thin areas.

The foamed and non-foamed layers needed for the sheet material according to the present invention can be selected from a wide range of thermoplastic polymers depending on the requirements of their applications. The range of thermoplastic polymers includes aromatic monovinylidene polymers (also referred to as styrenic polymers including GPPS, HIPS, ABS and SAN), a broad range of polyolefins (including PE, PP, LDPE, LLDPE, HDPE), acrylate and methacrylate polymers such. As polymethyl methacrylate (PMMA), polycarbonate (PC), polyvinyl chloride (PVC), polyethylene terephthalate (PET) and mixtures of two or more thermoplastic polymers of this type.

auf, worin R' Wasserstoff oder Methyl ist, Ar eine aromatische Ringstruktur mit 1 bis 3 aromatischen Ringen mit oder ohne Alkyl-, Halo- oder Haloalkyl-Substitution, worin jegliche Alkylgruppe 1 bis 6 Kohlenstoffatome enthält und Haloalkyl sich auf eine halogensubstituierte Alkylgruppe bezieht. Vorzugsweise ist Ar Phenyl oder Alkylphenyl, wobei Alkylphenyl sich auf eine alkylsubstituierte Phenylgruppe bezieht, wobei Phenyl am meisten bevorzugt ist. Typische aromatische Monovinylidenmonomere, die verwendet werden können, beinhalten Styrol, α-Methylstyrol, alle Isomere von Vinyltoluol, besonders para-Vinyltoluol, alle Isomere von Ethylstyrol, Propylstyrol, Vinylbiphenyl, Vinylnaphthalin, Vinylanthracen und dergleichen und Mischungen davon. Mischungen von zwei oder mehr aromatischen Monovinylidenmonomeren können eingesetzt werden, wie auch Mischungen von ein oder mehreren monoaromatischen Monovinylidenmonomeren mit einem oder mehreren anderen copolymerisierbaren Monomeren. Beispiele solcher copolymerisierbarer Monomere beinhalten, sind aber nicht beschränkt auf Acrylmonomere, wie z. B. Acrylnitril, Methacrylnitril, Methacrylsäure, Methylmethacrylat, Acrylsäure und Methylacrylat; Maleinimid, Phenylmaleinimid und Maleinanhydrid.Aromatic monovinylidene polymers are preferred thermoplastic polymers for use in sheet materials according to the present invention and include homopolymers and copolymers having at least 50% by weight, preferably at least 70% by weight and more preferably at least about 75% by weight, and most preferably at least about 90% by weight, of at least one aromatic monovinylidene monomer, which is incorporated into the final resin as a monomeric repeating unit. Preferably, the aromatic monovinylidene monomer has the formula:

wherein R 'is hydrogen or methyl, Ar is an aromatic ring structure having from 1 to 3 aromatic rings with or without alkyl, halo or haloalkyl substitution, wherein each alkyl group contains from 1 to 6 carbon atoms and haloalkyl refers to a halo-substituted alkyl group. Preferably, Ar is phenyl or alkylphenyl, wherein alkylphenyl refers to an alkyl-substituted phenyl group, with phenyl being most preferred. Typical aromatic monovinylidene monomers which may be used include styrene, α-methylstyrene, all isomers of vinyltoluene, especially para-vinyltoluene, all isomers of ethylstyrene, propylstyrene, vinylbiphenyl, vinylnaphthalene, vinylanthracene and the like, and mixtures thereof. Mixtures of two or more monovinylidene aromatic monomers may be employed, as well as mixtures of one or more monovinylidene monoaromatic monomers with one or more other copolymerizable monomers. Examples of such copolymerizable monomers include, but are not limited to, acrylic monomers, such as acrylic monomers. Acrylonitrile, methacrylonitrile, methacrylic acid, methyl methacrylate, acrylic acid and methyl acrylate; Maleimide, phenylmaleimide and maleic anhydride.

additionally For example, the aromatic monovinylidene polymer may be a dispersed, rubbery Polymer or elastomer included, for improved toughness or to provide impact resistance, these types of aromatic Monovinylidene polymers are considered to be rubber-modified or impact-resistant Called polymers. The rubbery polymer can be obtained by physical Mixing or by polymerizing the aromatic monovinylidene monomer in the presence of an already dissolved rubbery Polymers are made to impact modified or grafted produce rubber-containing products. In particular, the polymer be an impact polystyrene resin. additionally For example, the method described herein may be mixtures or combinations use any of the above-mentioned polymers. Examples suitable aromatic monovinylidene polymers are standard polystyrene (GPPS), impact polystyrene (HIPS), styrene copolymers such as B. poly (styrene-acrylonitrile) (SAN) and butadiene rubber-modified Versions called ABS.

polyolefins are also preferred thermoplastic polymers and include the homopolymers and copolymers of various α-olefins, such as Ethylene, propylene, 1-butene, isobutylene, pentene-1,3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-hedge, octene and 3-methyl-1-hexene, etc., including their copolymers with one or more additional copolymerizable monomers, including other α-olefins and various known copolymerisable Monomers including vinyl acetate, methyl acrylate, ethyl acrylate, Methyl methacrylate, acrylic acid, itaconic acid, maleic acid and maleic anhydride. Polyolefins include polyethylene, Polypropylene, linear low density polyethylene, polyethylene low density, high density polyethylene, olefin copolymers, such as z. B. Ethyloctencopolymere and the like. In a preferred Polyolefin is the preferred olefin monomer ethylene or propylene and the most preferred polyolefin is polypropylene.

The multilayer sheet material according to the present invention Invention has a non-foamed thermoplastic polymer surface layer A, which is generally selected to the appearance or the aesthetic side of the sheet or part / object, which is made to provide. This layer will generally made to be relatively thin and from a material needed to produce specific property and appearance aspects of the final application. For example, such a material may range from a range of thermoplastic Polymers as described above and combined with any incorporated Additives / components are selected to the desired combination gloss, color, printability, paintability, weathering resistance, UV resistance, stiffness, etc. to provide.

The non-foamed thermoplastic polymer surface layer generally becomes on the multilayer sheet material in one provided relatively thin layer, but different and thicker than either a surface layer that typically inherently shaped, if just a Foamed sheet material is produced or film layers (ranging from about 50 to about 100 microns), sometimes be provided on foam sheet materials. In a preferred Embodiment has the non-foamed thermoplastic Polymer surface layer A for the laminated Sheet material has a thickness of at least about 0.25 mm, preferably at least about 0.5 mm, and more preferably at least about 0.75 mm. The thickness of the unfoamed thermoplastic polymer surface layer A in these sheet materials is typically as far as possible reduced to maximum savings in the starting material and energy in the thermoforming process, with layer thicknesses, which is preferably generally less than about 6 mm, preferably less than about 5 mm, more preferably less than about 3 mm and most preferably less than about 2 mm. It should too stated that the claimed multilayer sheet materials according to the present invention, an internal, non-foamed thermoplastic polymer surface layer may contain and / or that the surface layer composed of one or more additional sublayers could be and / or a thin film surface layer depending on coextrusion or film lamination techniques, which can be used optionally to the sheet material structures to produce according to the present invention. In a preferred embodiment, the entire thickness the non-foamed thermoplastic polymer layers in the multilayer sheet including the non-foamed sheet Surface layer and any other non-foamed Layers, wherever they are arranged, are smaller than the total thickness the foamed thermoplastic polymer layer (s). It but is for reasons of product cost savings and optimal Process efficiency and simplicity prefers that the non-foamed thermoplastic polymer surface layer a single plastic polymer layer with optional surface coating layer and / or adhesive backsheet is, most preferably, that it is a single thermoplastic polymer surface layer is.

In terms of the production of the foamed thermoplastic polymer layer is a wide range of techniques known and can be used. The foamed layer of the multilayered Sheet of the present invention may be obtained by vacuum foaming, by physical agitation of the molten thermoplastic Resin composition mixture or by incorporation of a blowing agent be prepared in the polymer composition. In a preferred Embodiment becomes a blowing agent in the thermoplastic Polymer composition introduced to a foamable To provide intermediate polymer composition.

physical Propellants are generally pressurized gases or liquids with low boiling point. Chemical blowing agents are generally solid chemical compounds that decompose and a gas, such as z. As nitrogen, ammonia or carbon dioxide. The foamable Intermediate is then activated by heat activation of the gas-generating chemical propellant or by expansion of the low-boiling gaseous physical propellant during the extrusion of the foamable intermediate into one Allow area of lower pressure to expand (i.e., leave "foaming"). The blowing agent (s) that can be used includes the well-known physical blowing agents, chemical Propellant or a combination thereof.

Suitable physical blowing agents include carbon dioxide (CO ₂ ), nitrogen (N ₂ ), water (H ₂ O), aliphatic hydrocarbons, such as. As propane, butane, isobutane, pentane, neopentane, isopentane and hexane, alicyclic hydrocarbons such. As cyclobutane, cyclopentane and cyclohexane and halogenated hydrocarbons, such as. Methyl chloride, methylene chloride, dichlorofluoromethane, trichlorofluoromethane and dichlorodifluoromethane, but are not limited thereto. A preferred physical blowing agent contains carbon dioxide. Carbon dioxide is preferably used as a liquid in the practice of the present invention, although the use of carbon dioxide gas would also be acceptable. Nitrogen is preferably used as a gas, while water is typically used as a liquid, although any form is acceptable.

Dry Propellants include sodium bicarbonate, ammonium carbonate and ammonium bicarbonate, Citric acid and citrates, such as. Sodium citrate, sodium glutaminate, Phthalic anhydride, benzoic acid, benzoates, such as z. Example, aluminum benzoate, azodicarbonamide, azoisobutyronitrile and Dinitropentamethylen. Contains a preferred chemical blowing agent Including mixtures of sodium bicarbonate and citric acid Foamazole 72 CBA, which is a concentrate containing a mixture of Contains citric acid and sodium bicarbonate in pellet form, which is commercially available from Bergen International.

The blowing agent is generally employed in amounts necessary to provide the desired level of density reduction in the foam layer. The term "density reduction" and the percentage of density reduction means the percentage of density that is reduced in the foam layer and / or sheet material by using chemical and / or physical blowing agents. For example, starting from a starting polymer density (solid sheet) of 1 g / cm ³ , a reduction of the density to 0.9 g / cm ^{3 is} a 10% density reduction, to 0.85 g / cm ³ a 15% density reduction.

Around a combination of cost-effectiveness and performance has reached the foamed thermoplastic polymer layer desirably a density reduction of at least about 5% by weight, based on the density of the thermoplastic starting polymer, preferably at least about 10% by weight, most preferably at least about 15% by weight. To the performance characteristics and thermoformability of the sheet has the foamed thermoplastic Polymer layer desirably a density reduction of not more than about 40% by weight, based on the density of the thermoplastic Starting polymer, preferably up to about 35 wt .-%, especially preferably up to about 30% by weight and most preferably up to about 25% by weight. Preferably, these density reduction areas become and grades in the final multilayer leaf structure provided.

In terms of the use of gas-generating liquids or others physical blowing agents in a foam extrusion process depends the added amount of physical blowing agent that enters the foamable Composition is introduced, of the desired degree the density reduction and the efficiency and effectiveness of the respective propellant, but it has been found that it is suitable, amounts of at least about 0.0001, preferably at least about 0.001, preferably at least about 0.01, more preferably at least about 0.063% by weight, based on the total weight to be added to physical blowing agent and up to amounts of about 0.07 wt .-%, preferably up to about 0.3, more preferably to at about 0.2 and most preferably up to about 0.128 wt% physical blowing agent, based on the total weight to add.

The foamable thermoplastic polymer composition can optionally contain a nucleating agent to size to control the foam cells. Contain preferred nucleating agents finely divided inorganic substances, such as. Barium sulfate, barium carbonate, Calcium sulfate, calcium carbonate, lead sulfate, silicic acid, Silicum dioxide, silicates, such as. Calcium silicate, talc, clay alumina, Aluminum silicates, sulphides, titanium dioxide, magnesium oxide, magnesium carbonate, Clay, carbon, metal powder, zinc oxide, asbestos, glass fibers, barium stearate and diatomaceous earth. The particle sizes of the finely divided inorganic nucleating agents generally range from about 0.005 to about 10 microns, preferably from about 0.01 to about 1 μm. An optional finely divided inorganic nucleating agent component may be in amounts of at least about 0.001 parts by weight per 100 Parts by weight of polymer resin are used, preferably at least about 0.02 parts by weight per 100 parts by weight of a polymer resin. In general, the optional nucleating agent should be available in quantities less than about 10 parts by weight per 100 parts by weight of polymer resin, preferably less than about 2 parts by weight per hundred parts by weight Polymer resin can be used.

It It has also been found that a small amount of one chemical blowing agent, which is insufficient to a significant To produce density reduction, but nucleation in a physical can provide foamed thermoplastic polymer. These optional nucleating agents, based on their active ingredient and their effectiveness may be in amounts of at least about 0.0004 parts by weight per 100 parts by weight of polymer resin, preferably at least about 0.008, more preferably at least about 0.04, and even more preferably at least about 0.08 parts by weight per 100 parts by weight a polymer resin can be used. In general, these should be optional nucleating agent in amounts of less than about 0.02 Parts by weight per 100 parts by weight of polymer resin, preferably less as about 0.15, more preferably less than about 0.14, and still more preferably less than about 0.12 parts by weight per 100 parts by weight Polymer resin can be used.

As mentioned above, the non-foamed thermoplastic Polymer layer of the same or different polymers selected from those listed above. Preferably become the layers of the leaf structures according to the present invention of the same polymer or the same polymer type manufactured for optimal layer compatibility and adhesion to provide and the possibility of the blending and to maximize the recycling of end products. Preferably are for Refrigerator lining applications both layers thermoplastic aromatic monovinylidene polymers, preferably for the foamed layer to be selected which are known to have the best stress crack resistance provide.

It can also be situations where the multilayer sheet contains two or more foamed thermoplastic layers. Foaming may be for the purpose of maximum and / or cost-effective Density reduction can be optimized using an inner foam layer and one of them different foamed thermoplastic Layer can be used as a surface layer and can be tailored to optimum surface properties in terms of adhesion to polyurethane or other insulating To obtain foam components. As with the non-foamed Layers can be the multilayer sheet according to the present invention, one or more optional layer in addition to or as part of the foamed thermoplastic surface layer contain. As used herein, the total thickness of the "foamed" thermoplastic includes Polymer layer in the multilayer sheet all foamed Layers wherever they are arranged. For a product cost saving and optimal process efficiency and simplicity, but before it that the multilayer sheet only the non-foamed surface layer (s) and a single foamed thermoplastic polymer surface layer as a foamed thermoplastic polymer layer with a optional non-foamed adhesive underlayer and most preferably only the single foamed thermoplastic Polymer surface layer contains.

The multilayered sheet structures according to the present invention Invention may also be an optional, non-foamed Surface layer (C) containing one of the thermoplastic However, polymers as mentioned above are produced preferably the same or one to the non-foamed Surface layer (A) similar material. If used, this layer provides a surface layer ready for the foamed layer (B), too is referred to as ABA structure. If used, the optional non-foamed Surface layer (C) has a thickness that is less than that of the non-foamed surface layer (A) generally in the range of at least 0.03 mm, preferably at least about 0.05 mm, more preferably at least about 0.07 mm and less as about 1 mm, preferably less than about 0.07 mm and most preferably less than about 0.5 mm. It should be noted that for the application of further insulating foam layers on the multilayer leaves according to the present invention for producing thermally insulating articles can be a surface treatment of the optional non-foamed Surface layer (C) may be necessary to a sufficient Adhesion and surface coverage for the insulating To get foam. In one embodiment of the present invention Invention, the foamed layer (B), the second Surface layer of the multilayer sheet ready and the optional non-foamed surface layer (C) is not used.

In a preferred embodiment of the present invention, the desired savings in raw material and energy to achieve in the thermal deformation process, have the foamed layer or layers of the multilayer sheets according to the present invention thicknesses that are greater than that of non-foamed or solid thermoplastic Polymer layer (s). The relationship between the foam and the non-foamed layer thicknesses is also called "foam to solid material thickness ratio "referred to and when the total foam layer thickness is larger as the total solid material layer thickness, this is done with a "foam" to solid material thickness ratio "of greater referred to as 1. Preferably, the relative thickness the foamed polymer layer (s) more than 50%, especially preferably more than 55%, even more preferably more than 60%, even more preferably greater than 65% and most preferred more than 70% of the thickness of the multilayer sheet material. These relative thicknesses correspond to the preferred "foam" Solid material thickness ratio "of preferably greater than about 1, more preferably 1.22, more preferably more at about 1.50, more preferably at more than about 1.86, and most preferably more than about 2.33.

Provided that the above-described layers and relative layer thicknesses are obtained, there are various known methods and processes that can be used to make or apply layers to multilayer sheets, including coextrusion, extrusion coating, and / or film lamination. These processes and their application to provide coated sheet materials are generally well known to those skilled in the art of making and using thermoplastic polymer sheet materials, and the use of the relative layer thickness teachings provided in the present invention can be readily used to produce multilayered sheets To provide sheet materials according to the present invention. See im In general, The Definite Processing Guide and Handbook, by Giles, Harold F. Jr., Wagner, John R. Jr., and Mount, Eldridge, published in 2005 by William Andrew Publishing / Plastics Design Library, their relevant areas by reference in this disclosure Part VI: Coextrusion on page 391; Part VII: Sheet and cast films on page 435 and Part VII: Extrusion coating and lamination on page 465.

For example, a coextrusion process is also in U.S. Patent 6,544,450 described, which can be adapted to a combination of foamed and non-foamed surface layers according to to provide the present invention. In U.S. Patent 6,589,646 For example, a film lamination process is shown to provide a foamed layer on a non-foamed thermoplastic polymer layer.

In preferred embodiments of the present invention, a multilayer sheet according to the present invention is used to provide an improved thermoforming process and improved thermoformed articles. Thermoforming is a generally well-known technology for providing moldings or articles of formable thermoplastic sheet materials. Thermoformed parts or objects are especially for the production of thermally insulating moldings, such. As transport boxes, heat accumulators, refrigerator or freezer equipment or components, in particular refrigerator doors by applying an additional insulating foam layer such. B. produce a polyurethane foam. Thermoforming processes are known in the art and may be used in different ways, e.g. In "Technologist of Thermoforming", Throne, James; Hanser Publishers; 1996; Pages 16-29 taught to be performed. In a "positive" thermoforming process, gas or air pressure is applied to the softened sheet and the sheet is then stretched and pulled out like a bubble, and a male mold is inserted into the bladder from the inside. Then vacuum is applied to pull the part further and make it conform to the male mold surface. In this thermoforming process, biaxial stretching is performed primarily in one step when a gas or air pressure is applied to the softened sheet. The shaping step is then completed with the vacuum and male mold to freeze the sheet orientation for a good balance of physical and aesthetic properties.

In a "negative" thermoforming process Vacuum or a stamp applied to the heat-softened sheet and you stretch and draw the leaf to approximately the final one Portion size. Then it is by positive air pressure from the inside or in addition external vacuum from the outside of the sheet is pulled and in line brought with an outer female form, the Orientation in the polymer is frozen and the sheet becomes molded into the object. In the types of thermoforming processes, usually for refrigerator linings are used, the extruded thermoformable sheets formed on rotating or continuous shaping devices, Leaves first to different heating sections (Preheating by contact heat followed by infrared heat) before being transported to the "positive" forming sections to be brought. As generally known to those skilled in the art during this preheating / heating, the sheet on a thermoformable, heat-softening, heat-plasticizing Temperature heated, which depends on the polymer. in the Generally this is a temperature for amorphous polymers from about 20 ° C to about 60 ° C above its glass transition temperature ( "Tg"). In general, for polypropylene and semi-crystalline polymers this is a temperature just below their melting temperature.

• A. Erwärmen eines Blatts zu einem wärmeerweichten, wärmeplastifiziertem thermoformbaren Zustand;
• B. Anwenden von Gas, Vakuum und/oder physikalischem Druck auf das wärmeerweichte, wärmeplastifizierte, thermoformbare Blatt und Strecken des Blatts auf annähernd die endgültige Teilgröße;
• C. Anpassen des Blatts durch Vakuum oder Druck an die Gestalt der Form; und
• D. Separieren des thermogeformten Teils von der Form.

In the forming section, the heat-plasticized sheet is stretched by generating a vacuum. The produced bladder is sometimes further preformed using a closure aid, e.g. For molding a freezer body. Thereafter, stretch forming and shaping of the sheet follows over the "positive" mold and then the corners and insert guide etc. are drawn into the mold by applying vacuum. After removal of the tool, the part can be trimmed, holes punched in and corners cut out as needed to make the lining. The general steps involved in a method of making a thermoformed part, such as a thermoformed part. B. a refrigerator lining are performed, are:

• A. heating a sheet to a heat softened, thermally plasticized thermoformable state;
• B. applying gas, vacuum and / or physical pressure to the heat softened, heat plastified, thermoformable sheet and stretching the sheet to approximately the final portion size;
• C. adjusting the sheet by vacuum or pressure to the shape of the mold; and
• D. Separating the thermoformed part from the mold.

Thermoformed parts or articles made from the multilayer sheet according to the present invention are particularly useful for making thermally insulating moldings, such as molded articles. As transport baskets, heat accumulators, refrigerator or freezer equipment or components, in particular refrigerator linings (including both door linings and inner body liners) by additionally applying an additional thermally insulating foam layer, such as. As polyurethane foam, preferably suitable for a foamed thermoplastic polymer surface layer. For example, as in 3 shown in the case of a foamed refrigerator interior lining 1 is the thermoformed lining part 4 in the outer housing or the end structure of the refrigerator 2 arranged and has a layer of a thermally insulating foam. Preferably, the foam by filling a cavity or cavity between the liner and the outer housing with a foamable mixture. For example, a foamable polyurethane mixture is introduced or injected into the void area between the thermoformed liner (preferably in contact with a foamed surface layer side) and the housing and outer termination including a refrigerator housing, refrigerator door housing or other finishers. The thermal insulating layer may also be provided by other known foaming or foaming techniques.

• E. Bereitstellen einer thermisch isolierenden Schicht, wie z. B. ein Polyurethanschaum zu der Oberfläche des thermogeformten Teils, vorzugsweise einer geschäumten Oberflächenschicht und vorzugsweise durch Bereitstellen einer schäumbaren Mischung in einer Kavität oder einem Raum, die zwischen der Oberfläche des thermogeformten Teils und einem externen Gehäuse oder Verschlussstruktur, vorzugsweise einem Kühlschrank, erzeugt wurde.

In this case of producing a thermally insulating molding, the above-mentioned thermoforming steps are followed by the additional general foaming step.

• E. Providing a thermally insulating layer such. A polyurethane foam to the surface of the thermoformed part, preferably a foamed surface layer, and preferably by providing a foamable mixture in a cavity or space created between the surface of the thermoformed part and an external housing or closure structure, preferably a refrigerator.

As Commonly known is for refrigerator linings one of the most important features the stress crack resistance ("ESCR"), what the needed chemical Resistance of the resin to blowing agents, which are used in PU insulation, compared to cleaning agents and oily foods that come into contact with the interior of the lining is. In which Phenomenon known as stress cracking, can use the propellants when applying and producing polyurethane foam, as well as oily ones Ingredients of chilled foods the surface attack or impair the molded plastic part and cause them at relatively low powers or stress is torn or destroyed. In this situation, plastics tend to be liquid at the same time or gaseous chemical stress cracks generating Means and a strain are exposed to, at lower Failures or shorter durations than they would do it in a drier air atmosphere. For polymers such. B. HIPS, which fail by Haarrissbildung, It is believed that the stress cracking agents are the polymer in plasticize the environment of surface defects. surface defects cause stress concentration and act as hairline initiation sites. When both an applied stress and a stress cracking agent are present, hairline cracks will form and from the defect grow out at lower voltages compared to when no liquid or vapor chemical stress cracking agent would be present. It has been found that thermoformed Parts made from the sheet materials according to the present invention, using less Polymer and / or blowing agent as in leaf structures according to the Prior art, provide a very good level of ESCR.

Although it is known that a sheet material with a thin layer of foamed thermoplastic can be used to make some articles or to provide a foamed surface layer (e.g. U.S. Patent 6,589,646 ), it would not be expected that a sheet material having a thicker layer (ie, increasing the "foam to solid ratio") could provide an improved thermoforming process.

It but is surprisingly according to the present invention, that a sheet material, that a thicker foam layer and a thinner solid Layer contains a good balance or combination of Properties, including combinations of thermoformed Particle thickness distribution (especially in critical thin Areas of the thermoformed part), ESCR performance, Sheet stiffness and energy savings in the thermoforming process when thermoformed into parts. Therefore allow the leaf structures according to the present invention an improved extrusion of thermoformable sheets, an improved thermoforming molding throughput (reduction of the Cycle time) and energy cost reduction in the molding process compared to a solid plastic sheet and / or a multilayered one Leaf, based on a thin foam layer. In a Embodiment relates to the present invention Thermoforming process, taking for the manufacturing configuration the leaf structures according to the present invention and currently available standard sheet extrusion and thermoforming equipment be used. Benefits are also improved by thermoformed provided insulating parts or objects that contain an additional insulating foam layer, such as z. B. thermoformed refrigerator lining with an additional insulating foam material layer on the thermoformed part is applied with improved uniform application and adhesion the additional insulating foam material, in particular Polyurethane foam.

It has been found that with the sheet materials according to the present invention, when a Foam or foamable mixture, such as. For example, as a foaming polyurethane is applied to provide a thermally insulating layer, the foam surface also facilitates complete and uniform coverage of the urethane foam on the foam surface of the thermoformed part with good foam adhesion while maintaining sufficient sheet stiffness and stress crack resistance.

The The following examples are provided to various embodiments to illustrate the invention. You are not meant to the invention as otherwise described and claimed to restrict. All numerical values are approximated and all parts and percentages are by weight, if not otherwise stated. The following nomenclature and / or abbreviations are used in the examples.

Experiments 1 to 4 represent examples according to the present invention. As summarized in Table 1 below, 4.0 mm multilayer thermoplastic sheets are extruded on a Reifenhauser coextrusion line with a non-foamed thermoplastic polymer surface layer and a foamed thermoplastic polymer surface layer using the chemical blowing agent ("CBA"), or CO ₂ as the physical blowing agent ("PBA ") With a CBA nucleating agent. STYRON A-TECH 1175 impact polystyrene ("HIPS") thermoplastic polymer was used for both the foamed and non-foamed layers. In a two extruder starting material coextrusion process, blowing agent-containing HIPS and HIPS without blowing agent are coextruded through a flat extrusion die and cooled by drawing through a vertically oriented 3-roll assembly. This produces a coextruded sheet according to the present invention which is 4 mm thick with a 3 mm foamed layer and with a 1 mm non-foamed or solid layer.

The propellant-containing HIPS resin layer, as indicated in Table 1 below, was provided with the indicated amounts of CO ₂ physical blowing agent and / or contained the indicated amounts of dispersed CBA. Here is CBA Foamazole 72, a mixture of citric acid and sodium bicarbonate in a Masterbatch with Polystyrene from Bergen International, which provides 40% by weight of the active ingredient and again produces 0.2 g of CO ₂ per g of CBA. The term "CBA% by weight" in Table 1, below, means the weight percentage of CBA incorporated into the thermoplastic polymer of the foamable / foamed layer (as a master batch with 40% active ingredients). For example, in Experiment 4, 100 grams of foamable polystyrene contained 0.5 grams of CBA masterbatch, providing 0.2 grams of active CBA and producing 0.04 grams of CO ₂ in the foamable polystyrene layer. The CBA was incorporated into the thermoplastic polymer by melt blending in the extruder.

To introduce the physical blowing agent into the foamed layer, the HIPS in the extruders is fed to a sheet extrusion line having a high pressure piston pump to deliver CO ₂ into the extrusion vessel at the exit port location where it is mixed with the plasticized molten polymer. The CO ₂ physical blowing agent is mixed with the molten polymer stream by means of a screw designed to mix the liquefied propellant and the polymer while moving "downstream" without allowing the added liquid to be pushed "upstream" , The term "CO ₂ PBA wt%" in Table 1, below, refers to the weight percentages of carbon dioxide gas (liquid) mixed with the molten polymer stream of the foamable / foamed layer, based on the weight of thermoplastic polymer. The term "CO ₂ release in wt%" means the total weight percent of carbon dioxide gas released by CBA and / or PBA, based on the thermoplastic polymer in the sheet structures, and is calculated from the known amounts of propellant added using of the ideal gas law.

The "sheet density" in g / cm ³ is calculated by measuring the sheet weight and dividing by the calculated sheet volume and is given in Table 1, below. The "foam layer density" (P _foam ) is calculated by the formula: ρ foam = (ρ total · t total - ρ firmly · t firmly ) / T foam where ρ _{foam is} the density of the foam layer, ρ _{total is} the total density of the sheet, t _{total is} the total thickness of the sheet, ρ _{solid is} the density of the solid layer, t _{solid is} the thickness of the solid layer, and t _{foam is} the thickness of the foam layer ,

The term "density reduction in%" means the percentage of the density by which the foamed thermoplastic and the sheet structure are reduced by using chemical and / or physical blowing agents was and is shown in Table 1.

The Sheet is pulled through a 3-roller polishing assembly and compressed, around the final 4 mm sheet and layer thicknesses as in table 1, shown below.

• A. Erwärmen des Blattmaterials zu einem wärmeerweichten, wärmeplastifizierten thermoformbaren Zustand, der abzusacken beginnt;
• B. Anwenden von Gasdruck auf das wärmeerweichte, wärmeplastifizierte thermoformbare Blatt und Strecken des Blatts auf annähernd die endgültige Teilegröße;
• C. Anpassen des Blatts durch Vakuum an die Gestalt der Form; und
• D. Separieren des thermogeformten Teils von der Form.

These leaf samples were then thermoformed into liners for a small size refrigerator ("mini refrigerator"). The mini-refrigerator liners were thermoformed on an ILLIG UA-100 Laboratory Thermoforming Unit from the specified inventive and comparative solid sheet samples. In these thermoforming experiments, the two sheet samples are thermoformed for mini-refrigerators as follows, with all process settings of the thermoforming process being the same for both sheets: IR heater temperature, mold temperature, pre-foaming pressure, Vosch foaming time and cooling time:

• A. heating the sheet material to a heat softened, thermally plasticized, thermoformable state which begins to sag;
• B. applying gas pressure to the heat softened, thermally plasticized thermoformable sheet and stretching the sheet to approximately the final part size;
• C. adapting the sheet to the shape of the mold by vacuum; and
• D. Separating the thermoformed part from the mold.

It However, it is noted that, as summarized in Table 2 below, the leaves according to the present invention require a shorter heating time (40 compared to 55 seconds) and therefore a 27% reduction in process cycle time in comparison to provide a solid sheet.

The rated mini refrigerator lining structures, as in 1 to 3 , provide an inner lining of the refrigerator body with two chambers and dimensions approximately one-half the physical size of current refrigerators of normal size. The mini-refrigerator liner designs have several features to sharpen test conditions (including thermoforming and ESCR). Important aspects of this embodiment are (i) sharp corners (8 mm radius, than 50 in 2 shown) (ii) designed mounting guides (3 mm radius, such as 60 in 2 and (iii) very large depth of draft (shown as "d" in FIG 2 ) of the separating element (5 in 32 and 3 ) between the two chambers, which corresponds to a very high draw ratio for the relatively small area of the thermoformable sheet. Obtaining a critical minimum thickness of 0.6 mm on the wall (30 of the 2 ) of the deep-drawn chamber separation (5 in 2 and 3 ) is critical to successful sheet thermoformability and partial thermoformability and has been achieved using the various 4 mm thermoformable sheets used in the experiments below.

• * Vergleichsexperiment, kein Beispiel der vorliegenden Erfindung

To investigate the structural stiffness of the wall in the mini refrigerator structure, an MTS 810 hydraulic frame is used to place the liner 10 mm to a specific location (marked by the "x" and 100 in 2 shown). The resulting resistance force is recorded as a function of the deflection. The force at final deformation, listed as "maximum force" in Newton, is a measure of the overall stiffness of the lining. In order to eliminate the effects of the density of the sheet and to compare properties per gram of polymer, the deformation force was divided by the sample weight to arrive at the recorded structural stiffness per gram of polymer as shown in Table 1. This is not a destructive test and was performed twice for each sample unit, demonstrating a relatively high degree of consistency and manufacturability. Table 1 - Experiment on extruded 4 mm sheet and thermoformed refrigerator lining Example # Primary propellant "Foam to solid material thickness ratio" CBA (wt%) active ingredient CO ₂ PBA (% by weight) CO ₂ release (% by weight) Foam layer density (g / cm ³ ) Foam Layer Density Reduction (%) Sheet density (g / cm ³ ) Leaf density reduction (%) Maximum force (N) / double Firmly* No n / A n / A n / A n / A n / A n / A 1.04 n / A 27.3 / 26 1 PBA 3 0.1 0.39 0,044 0.82 21.3% 0.87 16 14.8 / 14 2 PBA 3 0.1 0.48 0,051 0.76 26.6% 0.83 20 14.1 / 13.8 3 CBA 3 0.24 0 0,036 0.82 21.3% 0.87 16 14.7 / 14.7 4 CBA 3 0.2 0 0.03 0.86 17.3% 0.90 13 18.7 / 17.5

• * Comparative experiment, not an example of the present invention

The Analysis of the results listed in Table 1, that the claimed multi-layered foamed Leaf structures and foaming processes efficient and effective and provide significant density and weight reduction.

As was expected to show the analysis results of the tests on the structural Stiffness of mini refrigerator lining good performance characteristics through the sheet material with a foam layer, although the maximum force, which is needed to deform the structures by 10 mm, lower than for the solid lining reference material.

As mentioned above and as summarized in the thermoforming experiments for the mini refrigerator lining, as shown in Table 2, using the foamed sheets of the experiment 2 according to the present invention for the thermoforming, the heating time and the thermoforming cycle become 27% as compared to FIG fixed sheet reduced. In these thermoforming trials, the two sheet samples are thermoformed into mini-refrigerator liners, with all settings of the thermoforming process being the same for both sheets. Table 2 - Thermoforming Experiments Firmly page 2 Total sheet thickness (mm) 4 4 heating time 55 40 Cycle duration reduction% 0 27

wobei d die Dicke der Probe ist und r der Radius des Formgebers.When exposed to liquid stress cracking agents, such. For example, foods, oils, or liquid propellants, one of the most common laboratory simulations to test ESCR is a test based on ISO 4599 ( ASTM D543 ). Thermoformed samples of multilayer sheets were similar in their resistance to stress cracking upon exposure to liquid stress cracking agents in a test ISO 4599 examined. In this test, dog bone iso-like cut tensile specimens are maintained at a constant tension using a bending clamp, also referred to as a "former", which holds the specimen in a bent or cocked position. The nominal stress ε at the surface of the sample is determined by the radius of the bend provided in the former and is calculated as follows:

where d is the thickness of the sample and r is the radius of the former.

• * Vergleichsexperiment, kein Beispiel der vorliegenden Erfindung

These specimens, which are held under tension in the former (0.35%), are then exposed (dipped) to corn oil at room temperature to test ESCR foods. Tensile properties (% elongation at break) according to ISO 527 or ASTM D638 M ) are measured after increased immersion time (in days) and compared with the initial tensile properties. The less the property has been reduced compared to the original measurement property, the better the material is deemed to be resistant to exposure to substances. Table 3 - Stress cracking resistance Solid leaf * Experimental Sheet 1 Experimental Sheet 4 Immersion time in days Crack elongation (%) Reduction in tensile strength (%) Crack elongation (%) Reduction in tensile strength (%) Crack elongation (%) Reduction in tensile strength (%) 0 58 34 31 1 21 64% 30 12% 32 -3% 2 22 62% 26 24% 33 -6% 4 20 66% 28 18% 26 16% 7 24 59% 26 24% 25 19% 11 18 69% 16 53% 21 32%

• * Comparative experiment, not an example of the present invention

As summarized in Table 3 above, are the final ones Tensile strength values after 11 days immersion for structures according to the present invention (21 and 16) satisfactorily. These applications generally require values of about 10%. The observed values are roughly the same as for the prior art solid sheet of FIG. 11 Days immersion (18) and - especially important - show a relatively low reduction in yield compared to the Original characteristics (53% and 32% tensile elongation according to the present invention compared to 69% for the solid Leaf).

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 6544450 [0004, 0042]
• - US 6589646 [0005, 0042, 0049]
• - GB 1595128 [0006]
• - GB 1411132 [0007]
• - US 5364696 [0008]
• - EP 0084360 A [0009]
• - US 4069934 [0010]

Cited non-patent literature

• - General The Definite Processing Guide and Handbook, by Giles, Harold F. Jr., Wagner, John R. Jr. and Mount, Eldridge, published in 2005 by William Andrew Publishing / Plastics Design Library, whose relevant areas are incorporated by reference in this disclosure to be incorporated: Part VI: Coextrusion on page 391; Part VII: Sheet and cast films on page 435 and Part VII: Extrusion coating and lamination on page 465. [0041]
• - "Technologist of Thermoforming", Throne, James; Hanser Publishers; 1996; Pages 16-29 [0043]
• - ISO 4599 [0066]
• ASTM D543 [0066]
• - ISO 4599 [0066]
• - ISO 527 [0067]
• ASTM D638M [0067]

Claims (21)

A multilayer sheet with two surface layers and optionally one or more inner layers, this one multilayer sheet a non-foamed thermoplastic Polymer surface layer (A), a foamed thermoplastic polymer layer (B) and an optional, non-foamed thermoplastic polymer surface layer (C) with a total layer thickness of about 0.5 to about 20 mm and a Foam to solid matter ratio of greater as 1 and wherein: (a) the non-foamed thermoplastic Polymer surface layer (A) has a thickness in the range of about 0.25 to about 6 mm and (b) the foamed thermoplastic polymer layer (B) to a total density reduction of at least about 5% by weight, and in the absence of optional surface layer (C) a surface layer is. Multilayer sheet according to claim 1, wherein the thickness of the non-foamed surface layer (A) at least 0.5 mm. Multilayer sheet according to claim 1, wherein the thickness of the non-foamed surface layer (A) is at least 0.75 mm. Multilayer sheet according to claim 1, wherein the foam to solid ratio is at least 1.86 is. Multilayer sheet according to claim 1, wherein the foam to solid ratio is at least 2.33 is. Multilayer sheet according to claim 1, with a density reduction of at least about 10%. Multilayer sheet according to claim 1, with a density reduction of at least about 20%. Multilayer sheet according to claim 1, wherein the total layer thickness is about 1 to about 10 mm. Multilayer sheet according to claim 1, wherein the total layer thickness is about 2 to about 5 mm. Multilayer sheet according to claim 1, wherein layer B is a foamed aromatic monovinylidene polymer resin, selected from the group consisting of HIPS, GPPS, ABS, Mixtures two or more of these and mixtures of one or more this with one or more additional polymers, is. Multilayer sheet according to claim 1, wherein layers A and B are co-extruded. Multilayer sheet according to claim 1, wherein layer A is foil laminated on layer B. Multilayer sheet according to claim 1, wherein layer A is extrusion coated on layer B. Multilayer sheet according to claim 1, wherein B using a physical blowing agent or a combination of a physical blowing agent and a chemical Propellant that acts as a nucleating agent or only below Foamed using a chemical blowing agent. Thermoformed article made from one Multilayer sheet according to one of the claims 1 to 14. Thermoformed article according to claim 15, available by a thermoforming process comprising: A. heating a multilayer sheet according to any one of the claims 1 to 14 to a heat-softened, heat plastified, thermoformable state; B. applying gas pressure, Vacuum or physical pressure on the heat-softened, heat plastified, thermoformable sheet and stretch of the sheet to approximately the final part size; C. Adjusting the sheet by vacuum or pressure to the shape of a Shape; and D. separating the thermoformed part from the mold. Thermally insulating molding containing a thermoformed article according to the claims 15 or 16 and a thermally insulating foam layer in contact with the thermoformed article. Thermally insulating molding according to claim 17, wherein the thermally insulating foam layer is a polyurethane foam having. Thermally insulating molding according to Claims 17 or 18, wherein the thermally insulating layer is provided in a cavity or space between the Foam surface layer of the thermoformed article and an outer housing or a Closure structure is formed. Cooling unit containing a thermally insulating Molded part according to one of claims 17 until 19. Cooling unit according to claim 20, characterized that it is a fridge or a freezer.