Thermoplastic honeycomb structure with multilayer cell walls, process and apparatus for producing same

Abstract

Embodiments of the present invention provide a honeycomb core formed of a plurality of polygonal cells arranged in an array, where each polygonal cell has a side cell wall, the side cell walls of each polygonal cell forming a polygonal loop, the side cell walls comprising a sheet, the sheet is a symmetric three or five layer thermoplastic co-extruded sheet having an inner central layer or core layer and an outer layer. The symmetric three or five layer thermoplastic co-extruded sheet provides better mechanical properties compared to a simple sheet.

Description

[0001] The present invention relates to honeycomb structures (such as folded honeycomb structures), methods and apparatus for producing the same, and in particular, to an improved thermoplastic folded honeycomb structure, methods and apparatus for producing the same. Background Art

[0002] The folded honeycomb known from WO 97 / 03816 is produced continuously from a single layer (e.g. a flat body). The hexagonal cells are constructed by folding after the introduction of the cuts. The cells are bridged by the covering layer connection surfaces. By means of rotary vacuum thermoforming technology, a folded honeycomb without cuts can be produced economically from a continuous layer of thermoplastic film. The folded honeycomb described in WO2006 / 053407 has a connection surface covering every other hexagonal cell. Further honeycomb structures are described in WO2019 / 158743 and WO2006 / 053407, the entire contents of which are incorporated herein.

[0003] A honeycomb cell wall having a three-layer structure is known from US 2022 / 0001643, wherein the three layers are a support layer and two adhesive layers, one adhesive layer on each side of the support layer.

[0004] CN110154490A (China Energy Investment Group Co., Ltd.; Beijing Institute of Low-Carbon and Clean Energy) dated August 23, 2019, relates to material forming, particularly thermoplastic core materials having a multilayer composite structure and equipment including the core materials.

[0005] CN110154490A (China Energy Investment Group Co., Ltd.; Beijing Institute of Low-Carbon and Clean Energy) dated September 13, 2019, relates to material forming, in particular, methods and equipment for producing thermoplastic composite core materials.

[0006] EP3297817A1 of 28 March 2018 (Aconcol GmbH [BE]) relates to a graded sandwich core (20) in the form of a honeycomb, i.e. a lattice material having a repetitive and periodic structure. The sandwich core (20) is composed of a macroscopic honeycomb structure having sandwich cell walls with a mesoscopic porous core. The cell longitudinal axis of the mesoscopic honeycomb cells can be perpendicular to the cell longitudinal axis of the macroscopic honeycomb structure. Summary of the invention

[0007] The present invention relates to sheet materials that can be used to make improved thermoplastic honeycomb cores, and methods and apparatus for producing the same.

[0008] The object of the present invention is to be able to provide a honeycomb body, for example a folded honeycomb body, with improved cell walls, as well as aspects of a method and an apparatus for producing such a honeycomb body or a folded honeycomb body.

[0009] The object of the present invention is to be able to provide a honeycomb body, for example a folded honeycomb body, which has a more robust cell wall geometry, as well as a method and an apparatus for producing such a honeycomb body or a folded honeycomb body.

[0010] An embodiment of the present invention provides a honeycomb core formed by a plurality of polygonal cells arranged in an array, wherein: each polygonal cell has a side cell wall, each polygonal cell is bounded on both sides by a cover layer plane, the side cell walls of each polygonal cell form a polygonal ring, and the side cell walls include a sheet material, the sheet material is a symmetrical three-layer or five-layer thermoplastic co-extruded sheet material having a center (or core) layer or inner layer and an outer layer. Compared with a simple sheet material, the symmetrical three-layer or five-layer thermoplastic co-extruded sheet material provides better mechanical properties. One aspect of the present invention is that when the center (or core) layer or inner layer is made of a material with a lower density than the outer layer material, a three-layer or five-layer sandwich cell wall is used. Therefore, it is preferred that the density of the center (or core) layer or inner layer is significantly lower than that of the outer layer. The density of the center (or core) layer or inner layer is preferably lower than that of the outer layer, for example, the density of the center (or core) layer or inner layer can be 30% to 90% of the density of the outer layer, preferably 50%-70%. This provides a good strength / weight ratio.

[0011] The yield strength of the outer layers is preferably greater than the yield strength of the central (or core) layer or inner layer. This provides improved mechanical properties.

[0012] The center (or core) layer or inner layer may be made by physical or chemical foaming or by including a low density component. The low density component may include hollow glass particles.

[0013] The polymer density of the outer layer is preferably in the range of 0.9 to 1.5 or 0.9 to 2 kg / dm 3 Increasing the polymer density provides improved mechanical properties. For example, when the density of the outer layer is 1.6 kg / dm 3 When the density of the center (or core) layer or inner layer is 1.1kg / dm 3 In addition, the density of the outer layer can be 1kg / dm 3 , then the density of the center (or core) layer or inner layer is equal to or less than 0.9kg / dm 3 .

[0014] The thickness of the three-layer or five-layer coextruded cell wall is preferably less than or equal to 1 mm and at least 0.1 mm. The thickness of the center (or core) layer or inner layer of the coextruded cell wall is preferably equal to or greater than 1 / 3 of the total thickness of the cell wall, or preferably equal to or greater than 1 / 2, most preferably 67% to 90%. The center (or core) layer may preferably account for 50% to 67% of the total thickness of the symmetrical three-layer (ABA) coextruded sheet. Each outer layer 6 may preferably account for 25% to 16.5% of the total thickness of the symmetrical three-layer (ABA) coextruded sheet.

[0015] The outer layer is preferably flat and smooth with no out-of-plane irregularities compared to the ideal plane of the cell wall, wherein the irregularities of the outer layer are less than the thickness of the outer layer. The out-of-plane irregularities compared to the ideal plane of the cell wall can be measured using micro-CT or laser profile sensors.

[0016] The symmetrical three-layer or five-layer thermoplastic coextruded sheet can be selected from thermoplastic polymers and / or thermoplastic elastomeric polymers, or is a thermoplastic polymer selected from the following group: polyolefins, especially polyethylene or polypropylene, polyesters, especially polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate or polyethylene 1,2-furandicarboxylate, polyamides, especially polyamide 6 or polyamide 6,6, polycarbonates, polyetherketones, polyetheretherketones, polyetherketoneketones, polyethers, polyetheresters, polyphenylene sulfides, polyetherimides, copolymers and mixtures thereof, with or without fillers, reinforcements and / or air or gas inclusions.

[0017] The inner core of the symmetrical three-layer or five-layer thermoplastic coextruded sheet may be a foam, such as a mechanical foam or a chemical foam.

[0018] The central (or core) layer or inner layer and the outer layers preferably comprise the same thermoplastic polymer.

[0019] An embodiment of the present invention provides a method for producing a folded honeycomb core from a sheet material by the following process:

[0020] a) direct coextrusion of symmetrical multilayer sheets and transfer for rotational vacuum thermoforming followed by folding, or

[0021] b) The coextruded or laminated multilayer sheet is reheated and transferred for rotational vacuum thermoforming or sequential compression molding followed by folding.

[0022] The sheet can be wound onto a roll directly after coextrusion or after reheating and then unwound from the roll in order to be transferred for folding.

[0023] The method may include forming a plurality of polygonal units arranged in an array, wherein: each polygonal unit has side unit walls, each polygonal unit is bounded on two sides by a covering layer plane, the side unit walls of each polygonal unit form a polygonal ring, the side unit walls include a sheet, and the sheet is a symmetrical three-layer or five-layer thermoplastic co-extruded sheet.

[0024] Symmetrical three-layer or five-layer thermoplastic coextruded sheets offer improved mechanical properties compared to simple sheets.

[0025] The method also includes: when the center (or core) layer or inner layer is made of a material with a lower density than the outer layer material, a three-layer or five-layer sandwich cell wall is used. Therefore, it is preferred that the density of the center (or core) layer or inner layer is significantly lower than the outer layer. The density of the center (or core) layer or inner layer is preferably lower than the outer layer, for example, the density of the center (or core) layer or inner layer can be 30% to 90% of the density of the outer layer, preferably 50%-70%. This provides a good strength / weight ratio.

[0026] In this method, preferably the yield strength of the outer layer is preferably greater than the yield strength of the central (or core) layer or inner layer. This provides improved mechanical properties.

[0027] In this method, the central (or core) layer may be made by physical or chemical foaming or by including a low density component. The low density component may include hollow glass particles.

[0028] In this method, the polymer density of the outer layer is preferably in the range of 0.9 to 1.5 or 0.9 to 2 kg / dm 3 Increasing the polymer density provides improved mechanical properties. For example, when the density of the outer layer is 1.6 kg / dm 3 When the density of the center (or core) layer or inner layer is 1.1kg / dm 3 In addition, the density of the outer layer can be 1kg / dm 3 , then the density of the inner core is equal to or less than 0.9kg / dm 3 .

[0029] In this method, the thickness of the three-layer or five-layer coextruded cell wall is preferably less than or equal to 1 mm and at least 0.1 mm. The thickness of the center (or core) layer or inner layer of the coextruded cell wall is preferably equal to or greater than 1 / 3 of the total thickness of the cell wall, or preferably equal to or greater than 1 / 2, most preferably 67% to 90%. The center (or core) layer 8 may preferably account for 50% to 67% of the total thickness of the symmetrical three-layer (ABA) coextruded sheet. Each outer layer 6 may preferably account for 25% to 16.5% of the total thickness of the symmetrical three-layer (ABA) coextruded sheet.

[0030] In this method, the outer layer is preferably flat and smooth with no out-of-plane unevenness compared to the ideal plane of the cell wall, wherein the unevenness of the outer layer is less than the thickness of the outer layer. The out-of-plane unevenness compared to the ideal plane of the cell wall can be measured using micro-CT or laser profile sensors.

[0031] For this method, the symmetrical three-layer or five-layer thermoplastic coextruded sheet can be selected from thermoplastic polymers and / or thermoplastic elastomeric polymers, or is a thermoplastic polymer selected from the following group: polyolefins, in particular polyethylene or polypropylene, polyesters, in particular polyethylene terephthalate, polypropylene terephthalate, butylene terephthalate or polyethylene 1,2-furandicarboxylate, polyamides, in particular polyamide 6 or polyamide 6,6, polycarbonates, polyetherketones, polyetheretherketones, polyetherketoneketones, polyethers, polyetheresters, polyphenylene sulfides, polyetherimides, copolymers and mixtures thereof, with or without fillers, reinforcements and / or air or gas inclusions.

[0032] In this method, the inner core of the symmetrical three-layer or five-layer thermoplastic coextruded sheet can be a foam, such as a mechanical foam or a chemical foam.

[0033] In this method, the central (or core) layer or inner layer and the outer layers preferably comprise the same thermoplastic polymer.

[0034] An embodiment of the present invention provides a method for producing a folded honeycomb core from a sheet material by the following process:

[0035] a) direct coextrusion of symmetrical multilayer sheets and transfer for rotational vacuum thermoforming followed by folding, or

[0036] b) reheating the coextruded or laminated multilayer sheet and transferring it for rotational vacuum thermoforming or sequential compression molding, followed by folding;

[0037] The method also includes forming a plurality of polygonal units arranged in an array, wherein: each polygonal unit has side unit walls, each polygonal unit is bounded on both sides by a covering layer plane, the side unit walls of each polygonal unit form a polygonal ring, the side unit walls include a sheet, the sheet is a symmetrical three-layer or five-layer thermoplastic co-extruded sheet, having a center (or core) layer or inner layer and an outer layer, the density of the center (or core) layer or inner layer is 30% to 90% of the density of the outer layer, preferably 50% to 70%.

[0038] An embodiment of the present invention provides an apparatus for producing a folded honeycomb core from a sheet material, comprising:

[0039] a) an apparatus for direct coextrusion of symmetrical multilayer sheets and transfer for rotational vacuum thermoforming followed by folding, or

[0040] b) Apparatus for reheating coextruded or laminated multilayer sheets and transferring for rotational vacuum thermoforming or sequential compression molding followed by folding.

[0041] The apparatus may include a device for forming a plurality of polygonal units arranged in an array, wherein: each polygonal unit has side unit walls, each polygonal unit is bounded on both sides by a covering layer plane, the side unit walls of each polygonal unit form a polygonal ring, the side unit walls include a sheet, and the sheet is a symmetrical three-layer or five-layer thermoplastic co-extruded sheet.

[0042] Further embodiments are disclosed in the detailed description of the invention and in the dependent claims.

[0043] definition

[0044] Wherever it appears in this application, the following test shall be used to assess the density of cellular plastics and rubber: Cellular plastics and rubber - Determination of apparent density (ISO 845:2006);

[0045] DIN EN ISO 845:2009-10

[0046] Wherever it appears in this application, the following test shall be used to evaluate the density of non-cellular plastics and rubbers:

[0047] DIN EN ISO 1183-1:2019-09

[0048] Plastics -- Determination of density of non-cellular plastics -- Part 1: Immersion method, liquid pycnometer method and titration method (ISO 1183-1:2019, revised 2019-05);

[0049] The following test shall be used wherever it appears in this application to evaluate the yield strength of foams and rubbers:

[0050] DIN EN ISO 527-1:2019-12

[0051] Plastics -- Determination of tensile properties such as yield strength -- Part 1: General principles (ISO 527-1:2019).

[0052] BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figures 1 to 9 An embodiment of the present invention is shown, wherein Figure 1 An overview of a method and apparatus according to an embodiment of the invention is shown.

[0054] Figure 2shows a single unit of a honeycomb core comprising a sheet according to an embodiment of the present invention, Figure 3 Shows Figure 2 details.

[0055] Figure 4 and Figure 5 A cross section of a symmetrical three layer (ABA) coextruded sheet 6, 8, 6 according to an embodiment of the present invention is shown.

[0056] Figure 6 An apparatus for folding a honeycomb core according to an embodiment of the invention is shown.

[0057] Figure 7 A symmetrical three-layer material according to an embodiment of the present invention is shown, with one side showing unevenness.

[0058] Figure 8 and Fig. 9 A cross section of a symmetrical five layer (CABAC) coextruded sheet 16, 6, 8, 6, 16 is shown in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0059] Figure 1 An overview of a method and apparatus according to an embodiment of the invention is shown. Figure 2 Shows the Figure 1 A single cell of a honeycomb core is shown.

[0060] According to an embodiment of the present invention, the honeycomb core may include a sheet, such as a symmetrical multilayer, such as a symmetrical three-layer (ABA layer) sheet or a symmetrical five-layer sheet (CABAC layer). Any of these materials can be made by coextruding a first thermoplastic material with a second thermoplastic material. The first thermoplastic material forms the core B, and the second thermoplastic material forms the outer layers A and C.

[0061] All of these honeycomb cores are made of sheets, and symmetrical three-layer or five-layer sheets according to embodiments of the present invention can be used to manufacture these honeycomb cores.

[0062] Figure 2 and Figure 3 A honeycomb core is shown according to an embodiment of the present invention formed of a sheet material forming a polygonal cell having four or six cell walls, the sheet material being a symmetrical three-layer or five-layer ( Figure 8 and Fig. 9 ) sheet. The honeycomb core of the present invention may have a cell wall 2 or a cell wall made of 6 and 8, or a cell wall made of 16, 6 and 8, each of which has a single thickness. Alternatively, one cell wall 4 of the honeycomb core may have two layers of sheet.

[0063] Embodiments of the present invention may provide a honeycomb structure, such as a folded honeycomb structure, or a method and apparatus for producing the same. In particular, the present invention relates to an improved thermoplastic honeycomb structure, a method and apparatus for producing the same.

[0064] An advantage of the present invention is that it utilizes molding techniques such as vacuum forming or rotary vacuum forming. Thermoforming techniques may also be used. These techniques may be used as a honeycomb core manufacturing step, thereby achieving continuous and cost-effective production.

[0065] The honeycomb product produced according to the embodiment of the present invention has better compression resistance and can further reduce the amount of materials used.

[0066] Embodiments of the present invention provide a honeycomb body that is not fanned out or expanded from a stack of sheets, such as a stack of sheets that are bonded together.

[0067] An embodiment of the present invention provides a honeycomb formed by a plurality of polygonal cells arranged in an array, wherein: each polygonal cell has side cell walls extending between vertices of each polygonal cell, each polygonal cell is bounded on two sides by a covering layer plane, and the side cell walls (sometimes referred to as cell side walls) of each polygonal cell include a sheet.

[0068] Embodiments of the present invention provide a honeycomb core having rectangular, square or hexagonal cells, wherein the cell walls of the honeycomb core include at least two materials. In some embodiments, the sheet material used to make the honeycomb core is a symmetrical three-layer ABA (or five-layer CABAC, such as with an adhesive layer) structure. Preferably, the density of the B layer is lower than that of the A layer or the C layer. The outer layer A is preferably smooth. The smoothness of the surface can be measured by micro CT (micro-computed tomography) and a laser profile sensor.

[0069] The symmetrical three-layer or five-layer structure is preferably made by film extrusion, for example, more preferably by co-extrusion of layers. Parameters that may affect the performance of the symmetrical three-layer ABA or five-layer CABAC structure may include providing higher strength and stiffness in the outer layer A and / or C. The lower density of the inner layer B than the outer layer A or C significantly improves the mechanical properties of the honeycomb core made of the symmetrical three-layer ABA or five-layer CABAC structure. The inner layer B is preferably extruded or co-extruded, and its density is preferably lower than the density of the outer layers A and C, for example, 30%-90% (most preferably 50-70%) of the density of the outer layers A and C. The low density can be provided by a low-density component, for example, layer B is made by physical foaming (such as foaming) or chemical foaming, or by adding a low-density component (such as hollow glass balls or other low-density fillers). The polymer density of the outer layer can be from 0.9 to 1.5 or even 2 kg / dm 3Varies, depending on the type of polymer and fillers used in the polymer. If the polymer density of the outer layer A or C is 1.6 kg / dm 3 , then the lower density of the inner layer B can be 1.1kg / dm 3 If the polymer density of the outer layer A or C is 1kg / dm 3 , then the density of the inner layer B should be at least 0.9kg / dm 3 , thereby gaining advantages in terms of weight specific bending and buckling performance of the cell wall.

[0070] Preferably, the symmetrical three-layer ABA or five-layer CABAC sheet is fed directly into a forming process, an example of which is rotary vacuum forming.

[0071] An alternative is to produce a three-dimensional structure in the extruded / cast sheet by cast film extrusion into a symmetrical three- or five-layer structure which can then be fed directly to a vacuum forming roll.

[0072] To obtain good panel surface quality, the cell size should be kept small, so the coextruded wall thickness is preferably less than 1 mm and at least 0.1 mm to result in a significant increase in cell wall thickness.

[0073] To achieve reasonably low density, the thickness of the center (or core) layer or inner layer of the coextruded cell wall is at least 1 / 3 of the total thickness of the cell wall, or preferably at least 1 / 2, and most preferably 67% to 90%. The optimal specific gravity cell wall flexural strength is also a function of the density ratio between the different layers. For optimal performance, the weight of the center (or core) layer or inner layer should be one-third (1 / 3) to one-half (1 / 2) of the total weight of the cell wall. A large ratio between the density of the outer layer material and the density of the center (or core) layer material will result in very thin outer layers and a large percentage of the thickness of the inner layer. Larger density ratios are preferred, but are difficult to achieve in the coextrusion process.

[0074] Preferably, all three A, B, C layers are based on the same thermoplastic polymer or compatible polymers to facilitate recovery and re-stocking of edge trim.

[0075] Another factor is that both outer layers A and C should be flat and smooth. Foaming of inner layer B or low density fillers in the inner layer can cause uneven surfaces of outer layer A or C. Micro-CT or laser profile sensors can be used to measure the out-of-plane unevenness compared to the ideal plane of the cell wall. The unevenness of the skin layer should be less than the thickness of the skin layer. Figure 7The left side shows a three-layer ABA or five-layer CABAC ( Fig. 9 ) sheets, forming a sandwich cell wall; while on the right is a sandwich cell wall with a flat skin 14 and an out-of-plane uneven skin 12, where the unevenness at two points (see arrows) is greater than the skin thickness (this is also possible for a five-layer CABAC). Such a skin will buckle earlier than a flat skin under in-plane compressive loads.

[0076] For the compressive performance of the cell wall, and thus the compressive strength of the honeycomb core, advantageously, at least one or both of the two outer layers A and C are flat and have only smooth thickness variations.

[0077] A flat and smooth first outer layer A or C can be achieved by contacting with the outer smooth surface of a rotating vacuum forming roller. However, the foaming process and / or filler may cause local density variations in the inner layer B, which may cause thickness variations in the inner layer B, resulting in uneven second outer layer A or C.

[0078] For good compression properties of the honeycomb core and good flexural properties of the sandwich cell walls, it has been found that it is also possible and useful for the second outer layer to be flat and smooth.

[0079] This can be achieved by means of chill rolls, which cool the other side of the coextruded film and flatten the other outer layer before the still hot coextruded film is deformed in the vacuum forming rolls.

[0080] There are other options to flatten the outer layers A and C, such as calendaring the coextruded film after the foaming process or during the foaming process and before rotary vacuum forming or other vacuum forming.

[0081] In the three-layer ABA cell wall, the B layer should have a lower density. Glass fiber (2.5 kg / dm 3) Reinforcement materials usually increase density. Other A layers and C layers can also use such reinforcement materials, but for the inner layer B, low density is a more important parameter. This lower density allows the inner layer to be thicker without adding too much weight, and a larger total thickness will bring performance advantages. The density ratio between the inner layer and the other layers is an important parameter of the present invention. It leads to a larger cell wall thickness. The thickness of the cell wall is a power of 3 function of the buckling resistance of the other layers A of the sandwich cell wall. For the center layer B, fillers such as hollow glass balls can be used to reduce the polymer density. Therefore, different types of fibers and fillers can also be used for other layers A, C, but preferably co-extrusion and vacuum or use a mold plug (i.e., mold plug assisted thermoforming) or use a counter roller (counter roller) or thermoplastic molding between two matching ABA cell wall molds.

[0082] Figures 1 to 9 A honeycomb core, ie, a folded honeycomb core, is disclosed in which symmetrical multi-layer (three-layer ABA or five-layer CABAC) sheets of embodiments of the present invention may be used.

[0083] Figure 2 and Figure 3 A cross-sectional view of a flat sheet or web made of a plastically deformable material is shown. The flat sheet may be provided by a symmetrical three-layer ABA or five-layer CABAC sheet according to any embodiment of the present invention. The three-layer ABA or five-layer CABAC sheet according to any embodiment of the present invention is a plastically deformable material and is made of a thermoplastic polymer material or a fiber composite material or the like. The three-layer ABA or five-layer CABAC sheet according to an embodiment of the present invention comprises a thermoplastic polymer and / or a thermoplastic elastomeric polymer, or a thermoplastic polymer selected from the group consisting of polyolefins, in particular polyethylene or polypropylene, polyesters, in particular polyethylene terephthalate, polytrimethylene terephthalate, butylene terephthalate or polyethylene 1,2-furandicarboxylate, polyamides, in particular polyamide 6 or polyamide 6,6, polycarbonates, polyetherketones, polyetheretherketones, polyetherketoneketones, polyethers, polyetheresters, polyphenylene sulfides, polyetherimides, copolymers and mixtures thereof, with or without fillers, reinforcements and / or air or gas inclusions. The inner core of the symmetrical three-layer or five-layer thermoplastic coextruded sheet may be a foam, such as a mechanical foam or a chemical foam.

[0084] According to an embodiment of the present invention, a flat coil or sheet (three-layer ABA or five-layer CABAC according to an embodiment of the present invention) has plastic deformation bodies 101, 102 formed therein, mainly perpendicular to the material coil. In regions 101 and 102, the material is deformed, for example, polygonal with the plane of the coil, such as trapezoidal, sinusoidal, arcuate, etc. The deformation bodies form ridges 108 and valleys 109, each of which is not continuous. For example, the ridge 108 includes a series of linear deformation portions 101, 102, such as polygonal, such as trapezoidal, sinusoidal or arcuate portions, etc. Preferably, the ridge has a top surface 115, which may be initially (e.g., when formed) parallel to the plane of the material coil. When the three-dimensional structure is rotated (also called "folded") to form a honeycomb unit, the two top surfaces 115 will meet each other, thereby forming a cell wall with a double sheet thickness.

[0085] The production direction is preferably Figure 1 However, a perpendicular direction thereto (parallel to axes 105 and 106) may also be used.

[0086] The deformed portions 101 and 102 are preferably formed so as to be inclined towards each other around axes 105 and / or 106, i.e. rotated, to additionally form U-shaped or V-shaped connecting areas 103 and 104. The connecting areas or connecting portions 103 and 104 separate the deformed portions (ridge portions) 101, 102, for example, polygonal portions, such as trapezoidal portions, or sinusoidal portions, or arcuate portions or the like in a row of deformed portions 101, 102. One connecting portion 103, 104 is located between two portions 101, 102, and the connecting portions 103 and the connecting portions 104 are arranged alternately along the rows of portions 101, 102. The connecting areas 103, 104 form cross valleys, i.e. perpendicular to the valleys 109. Adjacent cross valleys are located on both sides of the coil. The rotation of the portions 101, 102 brings them into contact with each other. Figure 1 The initial position of the web is preferably carried out simultaneously with the placement of the deformed body into the web. The web is stretched at the transition between the sections 101 and 102, forming regions 103 and 104 which are substantially perpendicular to the outer surface 115 of the sections 101 and 102. The angle between the surfaces 103 and 104 of the different ridge sections 101 and 102 allows the entry of parts of the tool to form these sections. The width direction of the web is preferably elongated in the direction of the axes 105 and 106, while the endless length direction of the web is continuous in the production direction at the line 107.

[0087] The purpose of deformation of the coils or sheets (three-layer ABA or five-layer CABAC according to an embodiment of the present invention) in regions 101 and 102 is to form three-dimensional shapes that form half walls of the cells in the folded product. The cells thus formed are structural elements and load-bearing elements of the folded honeycomb core, and the cell walls extend transversely to the longitudinal direction of the folded product. The use of three-layer ABA sheets or five-layer CABAC sheets according to an embodiment of the present invention improves the mechanical properties. The cross-section of the cell formed by folding is preferably cylindrical, and the axis of the cylinder extends transversely to the longitudinal direction of the folded product and the thickness direction of the finally produced planar honeycomb core. The basic cross-sectional shape of the honeycomb can be selected as required, such as circular or polygonal, in particular even-numbered polygons, such as hexagons. The final cell shape depends on the shape of the deformed regions 101 and 102 in the original coil and how they are folded together. As Figure 1 As shown, when the coil is fully folded, each unit is formed by two half-units. The units are arranged in rows. Each final unit is formed by the bottom and side of two longitudinally adjacent (in the sheet or coil) valleys 109. The half-units are preferably connected together by contacting the top surfaces 115 of two longitudinally adjacent (in the coil) ridges 108. Therefore, a folded honeycomb is provided, which is formed by a plurality of units arranged in rows, having the following characteristics: all are made of three-layer ABA sheets or five-layer CABAC sheets according to embodiments of the present invention, and the units have transverse cell walls, which are adjacent to each other in the form of rings and are bounded by the cover layer planes toward the two openings of the unit, whereby each unit is bridged or completely closed on one or the other cover layer plane. According to embodiments of the present invention, the folded honeycomb can be formed by a substantially uncut flat coil, i.e., a continuous sheet without pores, such as a three-layer ABA or five-layer CABAC sheet. The sheet is extruded, preferably co-extruded. The plastic deformation of the sheet forms a three-dimensional (3D) structure. Thus, the folded honeycomb comprises a plurality of three-dimensional structures, such as polygonal, sinusoidal or arcuate portions (101 and 102) formed by plastic deformation, and connecting portions (103 and 104) on the plane of the covering layer produced by plastic deformation. At least a portion of the cell walls are preferably fully or partially permanently connected to each other, such as by glue, adhesive or welding.

[0088] The final honeycomb structure is a planar product in which the cells are arranged perpendicular to the plane of the product and across the thickness. The cells on alternating sides of the planar structure are closed by connecting parts 103 and 104. All cells can be closed by one or more covering layers, for example, by laminating the planar product of the invention with a covering sheet. The present invention includes within its scope the possibility that after the deformed roll is folded, the cross-sections (three-dimensional structures) 101, 102 in the roll forming the cell walls, such as trapezoidal, sinusoidal or circular structures, are not completely perpendicular and / or do not touch each other, thereby forming a structure that is open in the plane in at least one direction.

[0089] Back to Figure 1 The production method is continued by further rotating the portions 101 and 102 so that the surfaces 115 of adjacent ridge portions 108 are adjacent to each other or preferably in contact with each other. Figure 1 Another intermediate state of folded honeycomb production is shown. The web is plastically deformed and narrowed by the folding operation about folding lines or axes 105 and 106. U-shaped or V-shaped connecting portions 103 and 104 are unfolded and lie flat in a plane perpendicular to the cell walls. The connecting portions 103 and 104 are introduced to avoid substantial deformation of the three-dimensional structure of the web, such as the deformed portions 101 or 102, which are polygonal (e.g., trapezoidal, sinusoidal or arcuate).

[0090] Figure 1 Also shown is the almost complete folding of the material into two rows of hexagonal honeycomb cells. Figure 1 As shown, due to the folding together, adjacent parts 103 (corresponding to 104) are butted against each other. Then, at least one side (bottom side or top side) of each honeycomb unit is closed by the connecting part 103 or 104. That is, the honeycomb unit has a closed surface formed by the connecting parts 103, 104 at one end. The surfaces 115 can be connected to each other by glue, adhesive or welding (such as ultrasonic welding). However, such connection is not an essential requirement of the present invention.

[0091] The above process relies on the folding of a deformed web (ie a three-layer ABA or five-layer CABAC sheet according to an embodiment of the present invention) wherein the portions (three-dimensional structures) 101, 102 and connecting portions 103, 104 are formed in such a way as to simplify the folding and rotating process. Figure 1 Also shown is a side view of the formed web before the folding operation. To facilitate the folding operation, the plastically deformed web has axes 105 and 106 (about which the material regions 101 and 102 rotate during the folding process) which are preferably located out of the plane with a positive dimension "x" (for more details please refer to WO 2006 / 053407, in particular its Figure 7). The dimension x is chosen so that the lowest vertex connection point of the cross valley (formed by the connecting portion) 103 or the portion of the cross valley (formed by the connecting portion) 104 on the upper surface of the material on the valley axis 106 is higher than the vertex connection point of the cross valley on the axis 105 on the lower surface of the coil. The longitudinal forces in the production direction will act through the axes 105 and 106 and by doing so will exert a bending moment about the axes 105, 106. This allows the formed coil to be folded by simple compression in the production direction.

[0092] Production can be run continuously. Preferably, paired rollers are used to push the coil or sheet together along the production direction. However, a rotating tool, an oscillating translating tool or a guiding profile can be used to help or ensure the folding of the coil or sheet. Therefore, an independent aspect of the present invention is to form a folded honeycomb by non-cutting, continuous, static plasticity (optionally non-rotating) or plastic rotation of the coil. Plastic deformation can be carried out, for example, by rotary vacuum thermoforming or vacuum-free rotary thermoforming or by a static forming process. The sheet or coil can be provided as a stack of films, can also be provided by rollers, or can be provided by a film from an extruder die. The mold has a profile that engages with each other, for example, on each of the two mold surfaces or on rollers relative to each other.

[0093] The surface of the mold or roller, such as a vacuum roller for sheet or coil thermoforming, has a relatively complex geometry so that in the formed coil, not only are the portions 101 and 102 formed, but the portions 101 and 102 are preferably slightly rotated toward each other (e.g. 10 to 30°). This allows the formation of the V-shaped regions 103 and 104 and ensures that the shape of the coil is configured to be vacuum thermoformable and airtight, and the coil can be folded by further rotation of the regions 101 and 102 about the axes 105 and 106 (e.g. about 80° to 60°).

[0094] Figure 6 A side view of a sheet or coil during a folding operation and a cross section of a folding apparatus according to an embodiment of the present invention are shown. For a semi-closed thermoplastic honeycomb core having a thickness of 8 mm and a unit dimension cross section of 6.4 mm, the velocity of the unfolded sheet or coil relative to the folded honeycomb core (i.e., the material take-up factor) can be expressed as 2.696 (in arbitrary velocity units); it is reduced to 2.5 in the first set of rollers 120 and then further reduced to 1 in the second set of rollers 122. The final velocity is the throughput of the folded honeycomb planar structure.

[0095] The folding device comprises a pair of feed rollers 120, for example coated with rubber on their outer surface 110 and having grooves 110a in the outer surface of the feed rollers 120, which are placed upstream of the guide grid 111 to keep the web in the plane during the folding process; it also comprises a second set or second pair of push or counter-thrust rollers 122, for example coated with rubber on their outer surface 112, which have similar grooves 112a to apply counter-pressure, which ensures sufficient in-plane compression force to achieve folding. The compression force between the lower and upper feed rollers 120 can reduce the tilting and rotation of the areas 101 and 102 towards each other by elastic deformation, but in the portion between the feed rollers 20 and the counter-thrust rollers 122, as the folding continues, preferably but not necessarily without the help of tools or guides 111a, the web will move back to its thermoformed shape. The gate control and / or brake mechanism initially slows down or stops the web. It opens only under the force generated in the complete folding stage of the web. When the folded web is formed, it continues to apply friction in the open state.

[0096] Preferably, the folded honeycomb is directly further processed into a lightweight sandwich panel by lamination or direct extrusion of cover sheets or films 114 onto both sides of the honeycomb core, for example with lamination rollers or belts 123. The apparatus provided by the invention may comprise a deformation and folding device as well as a core bonding or welding device and a lamination device.

[0097] The coiled sheet (three-layer ABA or five-layer CABAC according to an embodiment of the present invention) can be provided directly from a suitable forming device (such as an extruder or a co-extruder) from a rolled coil or a pile of sheets (three-layer ABA or five-layer CABAC according to an embodiment of the present invention). Optionally, the coil or sheet is kept at a certain temperature or heated to a molding or forming temperature. The regions (three-dimensional structures) 101, 102 are formed in the coil or sheet by any suitable process (such as vacuum forming or hot rollers). In addition to using vacuum drawing, relative forming pressure plates can be used to apply pressure and heat to an extensible (such as a heat-extensible) thermoplastic sheet (three-layer ABA or five-layer CABAC according to an embodiment of the present invention) to form a half unit. This allows the use of perforated materials, which would not be possible if a vacuum was applied. The perforations of the perforated material can be produced while applying pressure, or can be made into the sheet (three-layer ABA or five-layer CABAC according to an embodiment of the present invention) before the pressure forming step. Making a honeycomb core (three-layer ABA or five-layer CABAC according to embodiments of the invention) from perforated sheets is beneficial for noise attenuation. Pressure molding can also be used.

[0098] The coils formed with the three-dimensional structure are folded together to form the honeycomb core. Optionally, lamination of one or more cover layers or other layers is performed in-line or off-line. Post-forming operations may be performed, such as cutting the honeycomb material to a certain length or forming a certain shape, such as pressing or fixing the honeycomb material to another material, such as a metal part.

[0099] The present invention comprises a folded honeycomb wherein the connecting regions or portions 103 and 104 are removed later (eg during lamination of the nonwoven cover layer), for example by cutting or melting, leaving all cells open on both sides to form a three-dimensionally formable sandwich preform.

Claims

1. A honeycomb core formed by a plurality of polygonal units arranged in an array, wherein: Each polygonal unit has a side unit wall, each polygonal unit is bounded on both sides by a covering layer plane, the side unit walls of each polygonal unit form a polygonal ring, the side unit walls include a sheet, the sheet is a symmetrical three-layer or five-layer thermoplastic coextruded sheet having a center (or core) layer or inner layer and an outer layer, the density of the center (or core) layer or inner layer is 30% to 90% of the density of the outer layer, preferably 50% to 70%.

2. The honeycomb core according to claim 1, wherein: The yield strength of the outer layers is greater than the yield strength of the center (or core) or inner layers.

3. The honeycomb core according to claim 1 or 2, wherein: The central (or core) layer or inner layer is made by physical or chemical foaming or by including a low density component.

4. The honeycomb core according to claim 3, wherein: The low-density component includes hollow glass particles.

5. A honeycomb core according to any one of the preceding claims, wherein: The polymer density of the outer layer ranges from 0.9 to 1.5 or 0.9 to 2 kg / dm 3 .

6. A honeycomb core as claimed in any one of the preceding claims, wherein: When the density of the outer layer is 1.6kg / dm 3 When the density of the center (or core) layer or inner layer is 1.1kg / dm 3 .

7. The honeycomb core according to claim 6, wherein: If the density of the outer layer is 1kg / dm 3 , the density of the inner core is equal to or less than 0.9kg / dm 3 .

8. The honeycomb core according to any one of claims 3 to 7, wherein: The thickness of the three-layer or five-layer coextruded wall is less than or equal to 1 mm and at least 0.1 mm.

9. The honeycomb core according to claim 8, wherein: The thickness of the central (or core) or inner layer of the coextruded wall is preferably at least 1 / 3, more preferably 67% to 90%, or preferably at least 1 / 2 of the total thickness of the cell wall.

10. A honeycomb core according to any one of the preceding claims, wherein: Compared to the ideal plane of the cell wall, the outer layer is flat and smooth without out-of-plane unevenness, wherein the unevenness of the outer layer is smaller than the thickness of the outer layer.

11. A honeycomb core as claimed in any one of the preceding claims, wherein: The symmetrical three-layer or five-layer thermoplastic coextruded sheet is selected from thermoplastic polymers and / or thermoplastic elastomeric polymers, or is a thermoplastic polymer selected from the following group: polyolefins, especially polyethylene or polypropylene, polyesters, especially polyethylene terephthalate, polytrimethylene terephthalate, butylene terephthalate or polyethylene 1,2-furandicarboxylate, polyamides, especially polyamide 6 or polyamide 6,6, polycarbonates, polyetherketones, polyetheretherketones, polyetherketoneketone polyethers, polyetheresters, polyphenylene sulfides, polyetherimides, copolymers and mixtures thereof, with or without fillers, reinforcements and / or air or gas inclusions.

12. The honeycomb core according to claim 11, wherein: The central (or core) layer or inner layer and the outer layers comprise the same thermoplastic polymer.

13. A honeycomb core according to any one of the preceding claims, wherein: The outer layer comprises a structural thermoplastic material, or the outer layer comprises a solid thermoplastic material.

14. A method for producing a folded honeycomb core from a sheet material by the following steps: a) direct coextrusion of symmetrical multilayer sheets and transfer for rotary vacuum thermoforming followed by folding, or b) The coextruded or laminated multilayer sheet is reheated and transferred for rotary vacuum thermoforming or sequential compression molding followed by folding.

15. The method of claim 14, further comprising forming a plurality of polygonal units arranged in an array, wherein: Each polygonal unit has a side unit wall, each polygonal unit is bounded on two sides by a cover layer plane, the side unit wall of each polygonal unit forms a polygonal ring, and the side unit wall comprises a sheet material, which is a symmetrical three-layer or five-layer thermoplastic co-extruded sheet material.

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