Plastics sandwich panel and method for producing it

Abstract

The present invention relates to a plastics sandwich panel (1) which comprises a core layer (2) and two outer layers (3, 3') of an outer-layer polymer material arranged on both sides of the core layer (2), wherein the core layer (2) is formed from a foamed core-layer polymer material and the core-layer polymer material and the outer-layer polymer material are each formed from a polyester material and comprise at least 80% by weight of the same base polymer type. The present invention also relates to a method for producing such a plastics sandwich panel (1), wherein the two outer layers (3, 3') are each thermally connected to one side of the core layer (2), preferably by using a double-belt press.

Description

[0001] Plastic sandwich panel and method for its production

[0002] The present invention relates to a plastic sandwich panel comprising a core layer and two cover layers made of a cover layer polymer material arranged on both sides of the core layer. Furthermore, the present invention relates to a method for producing a plastic sandwich panel according to the invention.

[0003] Plastic sandwich panels are known in the art and are characterized by their low weight, water resistance, and thermal insulation properties. For example, DE 38 17 224 A1 describes sandwich panels with a core made of a wood-based material arranged between two plastic layers, at least one of which is formed from a polymer casting compound containing an inorganic filler. A color-imparting layer is arranged adjacent to the core on the side of the filled plastic layer. Such sandwich panels are used for furniture construction and can have edging made of a polymer material. Plastic sandwich panels for transportation applications are also known, which have a polyurethane core between metallic cover layers. A disadvantage of such plastic sandwich panels is that they are not fully recyclable.

[0004] Accordingly, the present invention is based on the object of providing a plastic sandwich panel that overcomes the disadvantages of the prior art. In particular, the plastic sandwich panel according to the invention should be as completely recyclable as possible and, in addition, possess the favorable properties of known plastic sandwich panels, such as low weight, water resistance, and good thermal insulation properties.

[0005] According to the invention, this object is achieved by a plastic sandwich panel having the features of claim 1. Preferred embodiments of the plastic sandwich panel according to the invention are described in the dependent claims.

[0006] It has been found that a plastic sandwich panel is fully recyclable if both the core layer and the two cover layers arranged on the sides of the core layer are made of a polyester material that comprises at least 80% by weight of the same base polymer type. Such a plastic sandwich panel is easily and fully recyclable using established mechanical or chemical recycling processes. Any other polymer materials present are compatible with the polyester material, so they do not impede recyclability. Furthermore, such panels are characterized by low weight, water resistance, good strength, and thermal insulation properties. Furthermore, they are thermally deformable (embossing, bending), can be assembled using welding processes, or can be interconnected.

[0007] The present invention thus relates to a plastic sandwich panel comprising a core layer and two cover layers made of a cover layer polymer material arranged on both sides of the core layer. The plastic sandwich panel is further characterized according to the invention in that the core layer is formed from a foamed core layer polymer material, the core layer polymer material and the cover layer polymer material are each formed from a polyester material and comprise at least 80 wt. % of the same base polymer type. Furthermore, the present invention relates to a method for producing a plastic sandwich panel according to the invention, wherein the two cover layers are each thermally bonded to one side of the core layer, preferably using a continuous press or double-belt press.

[0008] As used herein, the term “same basic polymer type” of two polymer materials means that the building block of the two polymer materials, which is repeated many times as the predominant basic unit in the macromolecule and can be described by structural formula, is identical.

[0009] With regard to the plastic sandwich panel according to the invention, it can be advantageous if the core layer polymer material and the cover layer polymer material are each selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethyl terephthalate (PTT), polyethylene furanoate (PEF) as well as copolymers and blends of the aforementioned materials. Ethylene glycol, diethylene glycol, terephthalic acid, isophthalic acid, isosorbitol and / or cyclohexanedimethanol can preferably be used as comonomers in the copolymers. Among these comonomers, diethylene glycol, isophthalic acid, cyclohexanedimethanol or isosorbide are particularly preferred. It can also be advantageous if the cover layer material contains further additives such as viscosity modifiers, preferably reactive glycidyl-containing polymers, tackifiers or lubricants, preferably fatty acids and fatty acid esters.

[0010] The core layer of the plastic sandwich panel according to the invention is preferably obtained from a foamed panel that is cut perpendicular to the extrusion direction, and the cut elements are reassembled at the extrusion surfaces to form a panel. Alternatively, the core layer of the plastic sandwich panel according to the invention can be constructed from a particle foam.

[0011] Furthermore, it may be beneficial if the core layer polymer material and / or the cover layer polymer material are at least partially bio-based and / or at least partially made from recycled polymer material. The use of bio-based and / or recycled polymer material in the core layer and / or the cover layers of the plastic sandwich panel according to the invention further contributes to its environmental friendliness.

[0012] In preferred embodiments of the plastic sandwich panel according to the invention, the core layer polymer material and the cover layer polymer material each comprise at least 85 wt.% of the same base polymer type, in particular at least 90 wt.% of the same base polymer type, and preferably at least 95 wt.% of the same base polymer type. In this way, the compatibility differences between the polymer materials are further reduced, so that the polymer materials forming the plastic sandwich panel according to the invention can be better used after recycling.

[0013] Additionally or alternatively, the plastic sandwich panel according to the invention can further comprise a decorative layer and / or a boundary profile. Such a decorative layer can be required when using the plastic sandwich panel according to the invention as a furniture panel, while such a boundary profile can be required for use of the plastic sandwich panel according to the invention in motor vehicle bodies. The boundary profile can preferably comprise polymer material of the same base polymer type as the core and cover layers, particularly preferably in a proportion of at least 50 wt.% of the same base polymer type, in particular at least 70 wt.% of the same base polymer type and preferably at least 90 wt.% of the same base polymer type. In preferred embodiments, the boundary profile can also have a heat resistance without deformation or shrinkage at temperatures of at least 70°C and / or improved impact strength.The improved impact strength can be achieved through suitable process control or formulation, for example, using nucleating agents or additives to modify impact strength or flowability. In alternative embodiments, the boundary profile can have high stiffnesses, in particular a tensile modulus of elasticity (ISO 527) of 3 GPa, preferably 4 GPa, and more preferably 6 GPa. Such high stiffnesses can be achieved by incorporating fillers such as glass fibers (short and continuous glass fibers), carbon fibers, natural fibers, or inorganic fillers such as talc or chalk, or by intrinsic fiber reinforcement.

[0014] It may also be advantageous if the core layer polymer material has a density of at most 0.6 g / cm 3 , preferably not more than 0.4 g / cm 3 Such a low density of the core layer polymer material considerably reduces the overall weight of the plastic sandwich panel according to the invention.

[0015] Additionally or alternatively, it can be advantageous if the core layer itself comprises at least two layers of different densities. A low-density DO layer can achieve thermal insulation, which is advantageous for use in transport applications for refrigerated goods. A higher-density D1 layer can be advantageous for mechanically connecting to other elements of an application via hinges, screws, hooks or similar connecting elements. The arrangement of layers DO and D1 can be wholly or partially layered or sequentially across the area between the cover layers. In addition, layers of different densities can influence the pore structure of the foamed core layers and their surface, which can be advantageous for the thermal connection with the cover layers.

[0016] It can also be useful if the cover layer polymer material has a lower glass transition temperature and / or a lower degree of crystallinity than the core layer polymer material. The lower glass transition temperature and / or lower degree of crystallinity allow adhesive-free thermal bonding without destroying the foam structure of the core layer, which significantly improves the recyclability of the panel. This layer can be equipped with absorbers for electromagnetic radiation (microwave, IR, laser) so that selective heating can occur during the bonding process between core and cover layer. Additionally or alternatively, the cover layer polymer material can have a two-layer structure, preferably comprising a bonding layer facing the core layer, which has a lower glass transition temperature and / or a lower degree of crystallinity than the core layer polymer material.The lower glass transition temperature and / or the lower degree of crystallinity in turn allow adhesive-free thermal bonding without affecting the foam structure of the core layer, which significantly improves the recyclability of the board.

[0017] Furthermore, it can be helpful if the cover layer polymer material is reinforced. Such reinforcement of the cover layer polymer material contributes to the mechanical stability of the plastic sandwich panel according to the invention. The reinforcement is preferably a fibrous reinforcement, in particular a reinforcement using glass fibers, carbon fibers, intrinsic fiber reinforcement, natural fibers (such as flax fibers or basalt fibers), or mineral fibers. The cover layer of the plastic sandwich panel according to the invention can preferably be obtained by pressing a nonwoven, in particular a fiber nonwoven, preferably a nonwoven containing glass fibers and / or PET fibers, in situ as such, so that the nonwoven functions as the cover layer polymer material, or by pressing it with the cover layer polymer material.By using a nonwoven fabric containing PET fibers, a direct bond between the cover layer and the core layer can be achieved through thermal bonding. The thickness of the cover layers can be varied by selecting the layer thickness of the nonwoven fabric. It can be advantageous if the PET fibers of the nonwoven fabric are formed as multilayer fibers or as PET fibers with different crystallinity (sr-PET). This facilitates pressing and bonding. Preferably, the reinforcement can also be in the form of an organic sheet incorporated into the polymer material of the respective cover layer. Examples of such organic sheets are PETG 5843.1 and rPET 584X from Avient and 50001 C from Comfil ApS.

[0018] Additionally or alternatively, it may prove advantageous if an intermediate layer, preferably in the form of a film, preferably with a thickness of less than 500 μm, preferably less than 200 μm, particularly preferably less than 50 μm, is introduced between the core layer and the cover layers. This intermediate layer comprises a polyester, a co-polyester or a polyester blend and has a lower softening and / or melting temperature than the core layer and / or the cover layers. As an alternative to such a film, a nonwoven fabric can also be introduced as an intermediate layer between the core layer and the cover layers. The thickness of the nonwoven fabric is preferably less than 500 μm, more preferably less than 200 μm and particularly preferably less than 50 μm. The nonwoven fabric comprises a polyester, a co-polyester or a polyester blend. It has a lower softening and / or melting temperature than the core layer and / or the cover layers.Such films and / or fleeces serve to strengthen the connection between the respective layers.

[0019] In preferred embodiments of the present invention, the thickness of the plastic sandwich panel according to the invention is in the range from 0.5 cm to 10 cm, preferably in the range from 1.5 cm to 8 cm. The thickness of the core layer, the thickness of the plastic sandwich panel according to the invention is preferably in the range from 0.4 cm to 9 cm, particularly preferably in the range from 1 cm to 8 cm, while the thickness of the cover layers of the plastic sandwich panel according to the invention is preferably in the range from 0.05 cm to 0.5 cm, particularly preferably in the range from 0.07 cm to 0.3 cm.

[0020] It may be helpful if the plastic sandwich panel according to the invention has a bending strength according to DIN EN 310:1993 in the range of 10 N / mm 2 up to 20 N / mm 2 , preferably in the range of 10 N / mm 2 up to 50 N / mm 2 has.

[0021] In addition, it may be helpful if the plastic sandwich panel according to the invention has a modulus of elasticity according to DIN EN 320:2011 in the range from 1.0 GPa to 3 GPa, preferably in the range from 1.6 GPa to 2 GPa.

[0022] The plastic sandwich panel according to the invention can be used, for example, as a panel in furniture construction or as a panel for forming the walls of vehicle bodies.

[0023] The production of the layers constituting the plastic sandwich panel according to the invention is preferably carried out by means of known forming processes (e.g., extrusion) and their subsequent connection by welding or gluing. In particularly preferred embodiments, plastic sandwich panels according to the invention are produced by thermally bonding all components / layers of the plastic sandwich panel according to the invention in-line in a double-belt press, in particular by means of microwaves, lasers, or hot air, i.e., preferably without adhesives. The bonding of the cover layers to the core layer can also be carried out indirectly by introducing the intermediate layer on one side of the core layer or on both sides of the core layer. The present invention will be explained in detail below with reference to the embodiments illustrated in the figures.

[0024] Fig. 1 is a schematic cross-sectional view of a plastic sandwich panel according to an embodiment of the present invention; and

[0025] Fig. 2 is a schematic cross-sectional view of a plastic sandwich panel according to another embodiment of the present invention.

[0026] Fig. 1 shows a plastic sandwich panel 1 according to an embodiment of the present invention in a schematic cross-sectional view. In the embodiment shown in Fig. 1, the plastic sandwich panel 1 according to the invention comprises a core layer 2 and two cover layers 3, 3'. The two cover layers 3, 3' are each arranged on one side of the core layer 2. The cover layer 3 is the actual cover layer, while the cover layer on the side opposite the cover layer 3 is often also referred to as the counter-layer 3'.

[0027] According to this embodiment of the plastic sandwich panel 1 according to the invention, the core layer 2 is formed from a foamed core layer polymer material, namely foamed polyethylene terephthalate (PET) with a density of 50 kg / m 3 , formed. Several versions of the plastic sandwich panel 1 according to the invention were produced, in which the thickness of the core layer 2 is in the range from 60 mm to 80 cm. The cover layers 3, 3' are layers of preferably recycled polyethylene terephthalate with a thickness in the range from 0.7 mm to 1.2 mm, wherein in selected cases these are fiber-reinforced, preferably using glass fibers (PETG 5843.1 and rPET 584X from Avient, sample material from Porcher, 50001 C from Comfil ApS), alternatively unreinforced PET mono-sheets (Axpet® polyester sheets, Exolon Group GmbH or Sustadur® PET, Röchling SE & Co. KG) were used.

[0028] The plastic sandwich panel 1 according to the invention was produced by thermally bonding the cover layers 3, 3' to one side of the core layer 2 using a Teflon tape in a double-belt press (supplied by Schott und Meissner Maschinen- und Anlagenbau GmbH, 74572 Blaufelden, Germany, with three heating zones and two cooling zones, approximately 8 m long and 2500 mm wide). The resulting product was cut into panels with a base area of ​​800 mm x 600 mm. After use, the plastic sandwich panels 1 according to the invention can be fully recycled using conventional methods.

[0029] Selected examples according to the invention with properties:

[0030] Panel construction with glass fiber reinforced cover layers (0.7 mm on both sides, flexural modulus of the cover layer: 29 GPa) with core layer made of recycled PET (rPET) with a foam density of 50 kg / m3.

[0031] Thermal conductivity according to DIN EN 12667: 2001-05 of 0.032 W / m*K,

[0032] 4-point bend test (ASTM C393 - 2020):

[0033] Flexural modulus of elasticity: 720 MPa

[0034] Bending strength: 3700 N

[0035] Board construction with PET mono-layers (thickness 2 mm, unreinforced) with core layer made of recycled PET (rPET) with a foam density of 0.15 g / cm3:

[0036] 4-point bend test (ASTM C393 - 2020):

[0037] Flexural modulus of elasticity: 1,260 MPa

[0038] Bending strength: 28 N / mm 2

[0039] Screw extraction force (surface): 950 N

[0040] Board construction with self-fiber reinforced cover layers (thickness 2.2 mm, PET fiber reinforced) with core layer made of recycled PET (rPET) with a foam density of 0.2 g / cm3:

[0041] 4-point bend test (ASTM C393 - 2020):

[0042] Flexural modulus of elasticity: 1,910 MPa

[0043] Flexural strength: 35.8 N / mm 2

[0044] Maximum breaking force: 1748 N Panel construction with fleece cover layers (0.25 g / cm 3 , PET fiber fleece) with a core layer made of recycled PET (rPET) with a foam density of 0.2 g / cm3:

[0045] 4-point bend test (ASTM C393 - 2020):

[0046] Flexural modulus of elasticity: 1,540 MPa

[0047] Bending strength: 34.2 N / mm 2

[0048] Maximum breaking force: 1279 N

[0049] A further embodiment of the plastic sandwich panel 1 according to the invention is shown in Fig. 2 in a schematic cross-sectional view. Also according to this embodiment of the present invention, the plastic sandwich panel 1 according to the invention comprises a core layer 2 and two cover layers 3, 3' as well as two additional decorative layers 4, 4'. The two cover layers 3, 3' are each arranged on one side of the core layer 2, while the cover layer 3 is the actual cover layer, while the two decorative layers 4, 4' are arranged on the side of a cover layer 3, 3' opposite the core layer 2.

[0050] The core layer 2 of the plastic sandwich panel 1 according to the invention is, according to this embodiment, made of foamed polyethylene terephthalate (PET) with a density of 60 kg / m 3and has a thickness of 60 mm. The cover layers 3, 3' are preferably made of recycled polyethylene terephthalate with a thickness in the range of 1.0 mm. According to this embodiment of the present invention, the decorative layers 4, 4' are also made of preferably recycled polyethylene terephthalate with a thickness in the range of 0.7 mm, with the side of the decorative layers 4, 4' facing away from the core layer 2 being printed.

[0051] The plastic sandwich panel 1 according to the invention was produced by thermally bonding the cover layers 3, 3' to one side of the core layer 2 using a Teflon tape, and by thermally bonding the decorative layers 4, 4' to one side of the cover layers 3, 3', likewise using a Teflon tape, using a double-belt press (supplied by Schott und Meissner Maschinen- und Anlagenbau GmbH, 74572 Blaufelden, 3 heating zones, 2 cooling zones, approximately 8 m long, 2500 mm production width). The resulting product was cut into panels with a base area of ​​800 mm x 600 mm. After use, the plastic sandwich panels 1 according to the invention can be fully recycled using conventional methods.

[0052] Fig. 3 shows a schematic cross-sectional view of a plastic sandwich panel 1 according to a further embodiment of the present invention. According to this embodiment of the plastic sandwich panel 1 according to the invention, it also consists of a core layer 2 and two cover layers 3, 3', wherein, according to the embodiment of the plastic sandwich panel 1 according to the invention shown in Fig. 3, an intermediate layer 5, 5' is arranged between the core layer 2 and the two cover layers 3, 3'. According to this embodiment of the present invention, the intermediate layer 5, 5' is in the form of a PET film with a thickness of 40 pm. The intermediate layer serves to more firmly bond the respective cover layers 3, 3' to the core layer 2. In alternative embodiments, the intermediate layers 5, 5' can also be in the form of a nonwoven.In addition, a decorative layer 4, 4' can be applied to the cover layers 3, 3'.

[0053] The core layer 2 of the plastic sandwich panel 1 according to the invention is, according to this embodiment, made of foamed polyethylene terephthalate (PET) with a density of 60 kg / m 3 and has a thickness of 60 mm. The cover layers 3, 3' are preferably made of recycled polyethylene terephthalate with a thickness in the range of 1.0 mm. According to these embodiments of the present invention, the decorative layers 4, 4' are also made of preferably recycled polyethylene terephthalate with a thickness in the range of 0.5 mm.

[0054] The plastic sandwich panel 1 according to the invention was produced by thermally bonding the cover layers 3, 3', using the respective intermediate layer 5, 5', to one side of the core layer 2 using a double-belt press (supplied by Schott und Meissner Maschinen- und Anlagenbau GmbH, 74572 Blaufelden, Germany, with three heating zones and two cooling zones, approximately 8 m long and 2500 mm wide). The resulting product was cut into panels with a base area of ​​800 mm x 600 mm. After use, the plastic sandwich panels 1 according to the invention can be fully recycled using conventional methods.

[0055] The present invention has been explained in detail above with reference to the embodiments of the plastic sandwich panel 1 according to the invention shown in the figures. It is understood that the present invention is not limited to these embodiments. Rather, the scope of the present invention is defined by the appended claims.

[0056] - Patent claims -

Claims

Patent claims 1. Plastic sandwich panel (1), comprising a core layer (2) and two cover layers (3, 3') arranged on both sides of the core layer (2) and made of a cover layer polymer material, characterized in that the core layer (2) is formed from a foamed core layer polymer material, the core layer polymer material and the cover layer polymer material are each formed from a polyester material and comprise at least 80 wt.% of the same base polymer type.

2. Plastic sandwich panel (1) according to claim 1, characterized in that the core layer polymer material and the cover layer polymer material are each selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethyl terephthalate (PTT), polyethylene furanoate (PEF) as well as copolymers and blends of the aforementioned materials.

3. Plastic sandwich panel (1) according to claim 1 or claim 2, characterized in that the core layer polymer material and / or the cover layer polymer material are at least partially bio-based and / or at least partially recycled.

4. Plastic sandwich panel (1) according to one of claims 1 to 3, characterized in that the core layer polymer material and the cover layer polymer material contain at least 85 wt.% of the same base polymer type, in particular at least 90 wt.% of the same base polymer type.

5. Plastic sandwich panel (1) according to one of claims 1 to 4, characterized in that the plastic sandwich panel (1) further comprises at least one decorative layer (4, 4') and / or a boundary profile.

6. Plastic sandwich panel (1) according to one of claims 1 to 5, characterized in that the core layer polymer material has a density of at most 0.6 g / cm 3 owns.

7. Plastic sandwich panel (1) according to one of claims 1 to 6, characterized in that the core layer (2) itself comprises at least two layers (2.1, 2.2) of different densities.

8. Plastic sandwich panel (1) according to one of claims 1 to 7, characterized in that the cover layer polymer material has a lower glass transition temperature and / or a lower degree of crystallinity than the core layer polymer material.

9. Plastic sandwich panel (1) according to one of claims 1 to 7, characterized in that the cover layer polymer material is reinforced.

10. A method for producing a plastic sandwich panel (1) according to one of claims 1 to 9, characterized in that the two cover layers (3, 3') are each thermally bonded to one side of the core layer (2), preferably using a double-belt press.

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