Patent Description:
The inline lamination of continuously reinforced thermoplastic composite skins onto a thermoplastic honeycomb core results in cost efficient sandwich panels which provide stiffness and strength at minimal weight for use in a wide range of applications in many industries. Continuously produced thermoplastic honeycomb cores, such as folded honeycombs as described in <CIT> enable significant cost reductions in the large volume production of such sandwich panels.

Typically, woven thermoplastic composite skins or two layers of unidirectional fiber reinforced thermoplastic tapes (UD-tapes) in a <NUM>°/<NUM>° layup are applied on each major surface of the honeycomb core to create a sandwich panel with high bending stiffness and strength in both principal directions of the panel. The patent application <CIT>) describes symmetrical laminates. The patent application <CIT>) presents a method of joining composite honeycomb panels sections. Patent application <CIT>) describes further methods to join honeycomb cores prior to skins being applied onto the joint honeycomb cores. <CIT> discloses a reinforced honeycomb sandwich panel comprising a plurality of honeycomb core sheets having edges and a butt joint between edges of respective laminated reinforced honeycomb core sheets in a side-by-side location of the edges of the laminated reinforced honeycomb core sheets having an increased density at the conjunction of the honeycomb cores, and laminated with multilayered fiber reinforced skins comprising plies with varying fiber orientation including <NUM>° and <NUM>° and a method for its production. <CIT> discloses an equipment for continuous production of a laminated reinforced honeycomb sandwich panel from a plurality of honeycomb cores including means for joining honeycomb cores and a laminator for laminating by thermoplastic welding multilayer skins to the honeycomb cores.

Continuously produced thermoplastic honeycomb cores enable the in-line production of such sandwich panels. Two layers of thermoplastic tapes are typically laminated together in a double belt laminator and rolled up to form a skin laminate. Such laminates are then laminated onto both sides of the honeycomb core, e.g. in-line during the production of the continuously produced thermoplastic honeycomb core to form composite skins. In this in-line process the width of the resulting sandwich panel is limited to the width of the honeycomb production line and by the width of the laminates and laminators, which need to be available. Hence, the honeycomb cores need to be produced prior to the lamination onto the honeycomb core. This can increase the stock that has to be stored to be available at any time to meet specific customer requirements.

An object of embodiments of the present invention is to enable the production of an optionally large width thermoplastic sandwich panel with composite skins in a <NUM>°/<NUM>° unidirectional tape layup. The composite skins can be composed of thermoplastic film or sheet material. Embodiments of the present invention allow rapid production of different widths of completed thermoplastic honeycomb sandwich panels. Thermoplastic film or sheet is used as a reinforcement and is preferably joined/laminated by thermoplastic welding to a honeycomb core.

The honeycomb core is preferably formed from a plurality of polygonal cells arranged in an array, wherein each polygonal cell has lateral cell walls extending between vertices of each polygonal cell. The honeycomb core is preferably a folded honeycomb core. Preferably, each polygonal cell is bounded on two sides by covering-layer planes, the lateral cell walls of each polygonal cell forming a polygonal ring. For half of the cells along one edge of the honeycomb core, the top or bottom of the cell is open and along an opposing edge, for another half of the cells, the top or bottom is closed. This allows on each side edge of the reinforced honeycomb core, a trimming operation to be carried out so that the cells from one reinforced core have open tops and can be cut in half, and joined with cells from an adjacent reinforced core, the cells having closed tops that can be cut in half. These trimmed edges can be pushed together with a certain pressure to provide a reinforcement at the joint between two honeycomb core sheets or honeycomb panels.

Another object of embodiments of the present invention is to enable the production of optionally large width thermoplastic honeycomb panels with thermoplastic composite skins in a <NUM>°/<NUM>° reinforced layup which is based on the use of smaller width honeycomb core sheets joined together without a weak spot or without a serious weakening at the joint of separate honeycomb cores or with a reinforced join.

An advantage of the present invention is that a separate lamination step to create the <NUM>°/<NUM>° laminates uses a further processing of reinforced honeycomb cores with <NUM>° reinforcement layers on both sides of the honeycomb core with a <NUM>° turned production direction to apply second reinforcement layers on both sides of the honeycomb core again in <NUM>° with respect to the new production direction. This results in the first and second laminates having a <NUM>°/<NUM>° lay-up.

The separate lamination steps can be performed at different locations. This has the important advantage that a small-width production of the honeycomb core with first <NUM>° reinforcement layers laminated to the honeycomb core can be fast and cost efficient and the small width panels can be transported easily. The second lamination step to form larger width sandwich panels with finally <NUM>°/<NUM>° composite laminate skins can be done locally, e.g. at the location where these panels are joined to a truck trailer box, or other application.

The object or objects is/are achieved in accordance with embodiments of the present invention by the production of intermediate panels with single ply UD-reinforced skins on both sides of a honeycomb core in <NUM>° direction, in-line with the production direction of the continuously produced honeycomb core. Additional UD-reinforced layers laminated in <NUM>° direction after a <NUM>° rotation of the machine direction of the process, are applied to intermediate panels. Preferably, this includes reinforcement at joints between the intermediate panels. This reinforcement can comprise one or more of :.

All of which these methods can form a strong joint. The core density in a small area at the conjunction of two intermediate panels is then higher than the core density in the rest of the intermediate panel. This ensures a good support of the outer layers (sometimes called "skins") and a perfect core-skin bond at the area of the joint.

Embodiments of the present invention provide a reinforced honeycomb sandwich panel comprising: a plurality of honeycomb core sheets having edges, and having a first core density,.

Embodiments of the present invention provide a method for continuous production of a laminated reinforced honeycomb sandwich panel from a plurality of honeycomb cores as input material, each of the honeycomb cores having two opposed major surfaces, one on each side of each of the honeycomb cores, a further aspect of the method comprising:.

Embodiments of the present invention provide equipment for continuous production of a laminated reinforced honeycomb sandwich panel from a plurality of honeycomb cores as input material, each of the honeycomb cores having two opposed major surfaces, one on each side of each of the honeycomb cores, the equipment comprising:.

For half of the cells along one edge of an intermediate panel or a honeycomb core sheet, the top or bottom of the cell is preferably open and along an opposing edge, for another half of the cells, the top or bottom is closed. This allows on each side edge of the reinforced honeycomb core, or an intermediate panel, a trimming operation can be carried out so that the cells from one reinforced honeycomb core sheet or an intermediate panel have open tops and can be cut in half, and joined with cells from an adjacent reinforced honeycomb core sheet or intermediate panel, the cells of that honeycomb core sheet or intermediate panel having closed tops that can be cut in half. These trimmed edges can be pushed together with a certain pressure. Applying a joint of the first <NUM>° fibre reinforced layers at the location where the honeycomb core sheets penetrate each other, leads to a higher core density local to the join and a substantial improvement of the support for the outer <NUM>° UD layers at this critical location.

Embodiments of the present invention provide a reinforced honeycomb sandwich panel comprising.

Embodiments of the present invention are defined in the appended claims and further developed by further features of the dependent claims.

"Honeycomb core" relates to an array of honeycomb cells forming a sheet whereby the longitudinal axes of the cells are <NUM>° to the sheet. Such a honeycomb core can be manufactured as shown in <FIG>.

"Honeycomb core sheet" is a honeycomb core with layers (sometimes called skins) laminated to the core on both sides thereof.

"Intermediate panel" is a honeycomb core sheet with its major surfaces laminated to a fiber reinforcing layer such as provided by UD tapes with optionally the cells on at least edge thereof, trimmed to provide connections.

"UD tape" is a fiber reinforced thermoplastic material in film or sheet form which can be laminated (e.g. thermoplastically welded) to a honeycomb core or to another fiber reinforced thermoplastic material in film or sheet form. Such tapes are commercially available, e.g.: https://thermoplasticcomposites. de/en/products/ud-tapes/ https://www. de/ud-tape-proud/.

The company Tencate of California provides a UD tape named Cetex TC960 (formerly PMC/Baycomp CFRT® PP) which is a polypropylene-based thermoplastic unidirectional tape. This thermoplastic composite is designed for applications which require high impact resistance. The impact toughness of glass fiber/polypropylene composites make them ideal for use in truck bodies, vehicles and vehicle enclosures.

Tapes are also provided commercially by the company Sabic, Saudi Arabia, for example. "<NUM>° fibre reinforced unidirectional tapes" refers to a tape material reinforced by fibres which extend along the tape. "<NUM>° fibre reinforced unidirectional tapes" refers to an additional tape material reinforced by fibres which fibres extend along the tape but the tape is applied with the fibres perpendicular to the fibres of the <NUM>° fibre reinforced unidirectional tapes. A "cross-ply" refers to a layer of <NUM>° fibre reinforced unidirectional tapes whereby fibres extend along the tape with <NUM>° fibre reinforced unidirectional tapes applied in such a way that the fibres of the <NUM>° fibre reinforced unidirectional tapes are <NUM>° to the fibres of the <NUM>° fibre reinforced unidirectional tapes.

<FIG> shows a sandwich panel <NUM> with upper (<NUM>, <NUM>, <NUM>) and lower (<NUM>, <NUM>, <NUM>) inner <NUM>° fibre reinforced unidirectional tapes (i.e. UD-tapes) laminated or more preferably thermoplastically welded in the production direction W of the continuously produced honeycomb cores <NUM>, <NUM>, <NUM> (e.g. the W-direction of a folded honeycomb core). The edges of the honeycomb cores <NUM>, <NUM>, <NUM> are parallel with the edges of the upper and lower inner <NUM>° UD-tapes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. These inner <NUM>° UD-tapes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> have been cut in the length direction by cutting in the cross direction together with cutting the honeycomb cores <NUM>, <NUM>, <NUM>. As shown in <FIG> the inner <NUM>° UD-tapes <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are co-terminous with the honeycomb cores <NUM>, <NUM>, <NUM>. The outer UD-tape layers <NUM>, <NUM> are continuous in the L-direction and connect the honeycomb cores <NUM>, <NUM>, <NUM> and the inner <NUM>° UD-tape layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to a larger size sandwich panel. There are mechanical weak points <NUM>, <NUM> between the finite pieces of honeycomb core <NUM>, <NUM>, <NUM> in the L direction.

The honeycomb cores can be made from a single sheet. The honeycomb cores and can be composed of a thermoplastic polymer and/or a thermoplastic elastomeric polymer, or a thermoplastic polymer selected from a group consisting of polyolefins, in particular polyethylene or polypropylene, polyesters, in particular polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate or polyetylene- <NUM>,<NUM>-furandicaboxylate, polyamides, in particular polyamide <NUM> or polyamide <NUM>,<NUM>, polycarbonates, polyetherketones, polyetheretherketones, polyetherketoneketones polyethers, polyetheresters, polyphenylene sulfides, polyetherimides, copolymers and mixtures thereof.

<FIG> shows the layup and the edges of the different layers of honeycomb sheets in a view from/along the W-direction.

To avoid or to reduce the possibility that the interruptions or gaps (caused by cutting and joining) between honeycomb cores <NUM>, <NUM>, <NUM> in the L-direction are leading to a reduction of shear performance, a reinforcement <NUM> can be applied to all the weak spots <NUM>, <NUM> between the pieces of honeycomb cores <NUM>, <NUM>, <NUM>.

In <FIG>, the reinforcement <NUM> is shown as provided by a thermoplastic film <NUM> such as a thermoplastic adhesive film <NUM> which can be applied with an excess loop <NUM> between the adjacent edges of the UD-laminated cores <NUM>, <NUM>, <NUM> to ensure the transfer of shear forces in the cores <NUM>, <NUM>, <NUM>. The thermoplastic film <NUM> or adhesive film <NUM> can be applied over the complete length of the UD tapes, i.e. the upper and/or the lower UD-tapes or the complete length between the UD tapes and the honeycomb cores, on the upper side and/or on the lower side.

The reinforcement <NUM> can be a thermoplastic or thermoset adhesive film (less preferred), or can be a thermoplastic coated metal such as aluminum layer which enables a bonding of the outer UD-tape layers, e.g. by induction heating of the aluminium layer.

<FIG> shows how such a reinforcement, e.g. an adhesive film <NUM>, can sag naturally or be pushed between the spaced UD-laminated cores <NUM>, <NUM>, <NUM> before completing the adhesive process, e.g. by pressure and heat.

<FIG> shows the adhesive film loop <NUM> squeezed between the intermediate panels of honeycomb cores, <NUM>, <NUM>, <NUM> allowing a lower temperature bonding of the cores <NUM>, <NUM>, <NUM> to each other and optionally a bonding of the outer UD-tape layers <NUM>, <NUM> to the intermediate panels.

<FIG> illustrates a sandwich panel production process <NUM> and equipment therefor, according to an embodiment of the present invention.

The input <NUM> material can be a product of an in-line honeycomb core production (shown for example in <FIG>), preferably a continuous in-line honeycomb core production such as described and shown in <CIT> which is incorporated herein by reference. The input material <NUM> can be honeycomb cores <NUM> produced by such a process have an array of honeycomb cells <NUM>, e.g. rectangular, square or hexagonal cells. The array can have columns <NUM>, <NUM> and rows. Each polygonal cell <NUM> has lateral cell walls extending between vertices of each polygonal cell <NUM>, each polygonal cell <NUM> being bounded on two sides by covering-layer planes, the lateral cell walls of each polygonal cell <NUM> being in the form of a polygonal ring. First columns <NUM> in <FIG> can be of cells closed at the top and second columns <NUM> can be cells open at the top. First columns <NUM> alternate with second columns <NUM> as shown in <FIG>. In <FIG> one edge <NUM> of a polygon core can be trimmed to have cells which are open at the top, while the polygonal core can be trimmed on the right edge <NUM> so that the cells are closed on the top. The honeycomb cores can be trimmed lengthwise during production of the continuously produced honeycomb core to produce suitable, edge structures <NUM>, <NUM> and edge connections <NUM>, <NUM> to join two or more panels together using edge connections <NUM>, <NUM>. Alternatively, the trimming can be a method step of processing the honeycomb core <NUM> in the process <NUM>.

<FIG> shows such a first trimmed honeycomb core <NUM> schematically. On the edge having reference number <NUM>, the cells have been trimmed so that the cells are open at the top and connections <NUM> are produced. <FIG> also shows such a second trimmed honeycomb core, wherein on the edge with reference number <NUM>, the cells have been trimmed so that the cells are open at the top and connections <NUM> are produced.

Such honeycomb cores <NUM> will have much larger in-plane dimensions compared to the cell sizes e.g., the cell size can be <NUM> to <NUM> while the width of the honeycomb core <NUM> can be <NUM> to <NUM> at a length, of, for example, <NUM> to <NUM>.

<FIG>show a honeycomb core, e.g. a <NUM> thick honeycomb core with smaller cell size such as <NUM> cell size. Honeycomb cores from different panels are placed together side-by-side. This can lead to a small gap between the honeycomb core sheets, e.g. because the cutting of the edges is sometimes not perfectly straight. In <FIG>, the honeycomb core sheets are shown as penetrating each other.

Returning to <FIG>, the width <NUM> of the honeycomb core <NUM> produced by the in-line honeycomb core production <NUM> will generally be less than the required width <NUM> of the final product. The final width <NUM> of the thermoplastic sandwich panel is obtained by cutting the honeycomb core <NUM> to length and rotation of the machine direction through <NUM>°. To achieve this, the honeycomb core <NUM> is conveyed towards a laminator <NUM>, especially a calibrator and laminator <NUM>, by a conveyor such as a belt conveyor or caterpillar (not shown). Heating, such as by an infrared lamp or cooling can be provided to bring the honeycomb core <NUM> to the correct processing temperature before entering the laminator <NUM> or <NUM>. The processing is continuous. Before reaching the laminator <NUM> or <NUM>, a <NUM>° UD tape <NUM> is unwound from a roll and applied to the upper surface of the honeycomb core <NUM>, optionally using temperature and/or pressure. At the same time, a <NUM>° UD tape <NUM> is unwound from a roll and applied to the under surface of the honeycomb core <NUM>, optionally using temperature and/or pressure. The reinforcing fibers of the OD tapes <NUM>, <NUM> run in the machine direction, i.e. the machine direction is <NUM>°. In the laminator <NUM>, the lamination of the UD tapes <NUM>, <NUM> can be completed as well as trimming the edges <NUM> and <NUM>, e.g. to make the edge connections <NUM> and <NUM>. The honeycomb cores <NUM> can be trimmed lengthwise. Alternatively, the trimming can be a method step of processing the honeycomb core <NUM> in the process <NUM>. The honeycomb cores <NUM> can be trimmed lengthwise during production of the continuously produced honeycomb core <NUM> to produce suitable edge structures <NUM>, <NUM> and edge connections <NUM>, <NUM>. This allows to join two or more panels together using the edge connections <NUM>, <NUM>. Alternatively, the trimming can be a method step of processing the honeycomb core <NUM> in the process <NUM>. During processing in the laminator and trimmer <NUM> or before or after processing therein, the intermediate panel <NUM> with UD tapes on both sides thereof, which is the output of the laminator and trimmer <NUM>, <NUM>, is cut to length. This length is that length which results in a width <NUM> in the final product.

The intermediate panel <NUM> is then moved to a separate production line <NUM> which runs at <NUM>° to the conveyor. By doing so the machine direction has been moved through <NUM>° but the intermediate panel is not rotated.

The intermediate panel <NUM> includes the honeycomb core <NUM> with UD tapes <NUM>, <NUM> now applied in the cross-direction to the new machine direction. A first panel <NUM> is now joined to a second identical panel <NUM> by placing the first and second panels side by side and the connections <NUM>, <NUM> side by side, each in one panel <NUM>, respectively. Connections <NUM>, <NUM> are brought together to join the first and second panels together in a region of overlap. The intermediate panel <NUM> is conveyed towards a second laminator <NUM> by a conveyor such as a belt conveyor or caterpillar (not shown). A <NUM>° UD tape <NUM> is unwound from a roll and applied to the upper surface of the intermediate panel <NUM>, optionally using temperature and/or pressure. At the same time a <NUM>° UD tape <NUM> is unwound from a roll and applied to the under surface of the intermediate panel <NUM>,<NUM> optionally using temperature and/or pressure. The reinforcing fibers of the OD tapes <NUM>, <NUM> run in the machine direction, i.e. the machine direction is <NUM>°. The joined panels are then conveyed to the laminator <NUM> where the lamination of the UD tapes <NUM>, <NUM> can be completed. The completed honeycomb sheet with a plurality of intermediate panels <NUM> with edge connections completed and crossed UD tape reinforcement applied exits the laminator <NUM> with a width <NUM> which is larger than the width <NUM> of the honeycomb core <NUM>, e.g. <NUM>%, or larger.

<FIG> illustrates another embodiment of a sandwich panel production method and equipment therefor. The method steps and equipment are identical to those described with reference to <FIG> except for additional steps mentioned below. Referring to <FIG>, the input material can be the same product <NUM> of an in-line honeycomb core production <NUM> as described with respect to <FIG>. The width <NUM> of the honeycomb core <NUM> produced by the in-line honeycomb core production <NUM> will generally be less than the required width <NUM> of the final product. The device, method and equipment of this embodiment processes the optional additional reinforcement such as bonding layers, e.g. a lower melting thermoplastic adhesive film <NUM>. These bonding layers can also be thermoset adhesive films or thermoplastic adhesive films or thermoplastic coated aluminum layers which could enable a bonding of the outer UD-tape layers by induction heating. In <FIG> as in <FIG>, the reinforcement <NUM> is shown as provided by a thermoplastic film <NUM>, such as a thermoplastic adhesive film, which can be applied with an excess loop <NUM> between the adjacent edges of the UD-laminated cores <NUM>, <NUM>, <NUM> to ensure the transfer of shear forces in the cores <NUM>, <NUM>, <NUM>. The thermoplastic film or adhesive film <NUM> can be applied over the complete length of the UD tapes, i.e. the upper and/or the lower UD-tapes or the complete length between the UD tapes and the honeycomb cores, on the upper side and/or on the lower side.

The reinforcement <NUM> can be a thermoplastic or thermoset adhesive film (less preferred, or can be a thermoplastic coated aluminum layer which enables a bonding of the outer UD-tape layers, e.g. by induction heating of the aluminium layer.

<FIG> shows how such a reinforcement, e.g. an adhesive film <NUM>, can sag naturally or be pushed between the still somewhat spaced UD-laminated cores <NUM>, <NUM>, <NUM> before completing the adhesive process, e.g. by pressure and heat.

<FIG> shows the adhesive film loop <NUM> squeezed between the intermediate panels of honeycomb cores, <NUM>, <NUM>, <NUM> allowing a lower temperature bonding of the cores <NUM>, <NUM>, <NUM> to each other and, optionally, a bonding of the outer UD-tape layers <NUM>, <NUM> to the intermediate panels <NUM>.

An advantage compared to sandwich panels laminated with woven thermoplastic composites skins or composite skins which have been laminated from <NUM>°/<NUM>° UD-tape layers is that with embodiments of the present invention the thermoplastic welding or lamination of the inner UD-tapes can be done in a fast and simple continuous process, in-line with the continuous production of the honeycomb core. This results in intermediate panels with single ply UD-tape reinforced skins.

The width of the final sandwich panel can be achieved by a <NUM>° rotation of the machine direction for the processing intermediate panels. The final width can be obtained by cutting to length the honeycomb core with UD reinforcing tapes. These tapes are applied to obtain an intermediate panel with the single ply UD-reinforced skins. This reduces waste and leads to a cost advantage.

The final panel width is only limited by the width of a second laminator or thermoplastic welder. This allows to produce <NUM> to <NUM> wide panels with a honeycomb core production as an input, of only <NUM> to <NUM> wide for example.

A faster inline production speed of the honeycomb core is possible because the calibration and lamination of first skin layer requires less heat flux. Less heat has to pass through thinner skin material (single ply) in order to reach to core for the core-skin bonding process by thermoplastic welding.

The flexible usage of variable tape width and an easy width modification is possible by placing several rolls of smaller width UD-tape next to each other in one or both first and second lamination steps. This leads to cost advantages and makes the sourcing of UD tapes easier. Furthermore, the dependency on the availability of a large width cross-ply production line is reduced.

The intermediate unwinding and upwinding steps of UD tape during cross-ply production are not necessary. Compared to the separate handling of pre-cut <NUM>° UD tape sheets in the production of a cross-ply skin laminate, the handling of the single ply UD-reinforced intermediate panels is much easier. Furthermore, the proposed process enables an improved surface quality of the final panel due to lower lamination temperature of a second skin layer.

The potential disadvantage when joining core sheets to produce a large size sandwich panel is that the interruption of the core reduces the shear performance and the skin support of the core, which could significantly reduce the mechanical properties of the final large size sandwich panel. The present invention avoids this reduction of the mechanical properties by at least one means and preferably more than one means providing a reinforcement in or across gaps between honeycomb core panels in the joint area. This reinforcement can be achieved by interlocking and/or overlapping the core layers and/or interpenetration of the core edges. This can also be achieved by an in-line edge trimming of both edges of the intermediate single ply UD-reinforced honeycomb core panel, in-line with the production of the optionally continuously produced honeycomb core. This trimming and preparation of the edges results in a reinforcement including improved edges of the panels to enable a better side by side joining of the panels with an overlap of the core sheets at the joint.

For high temperature thermoplastics, the welding of thermoplastic composite skin layers has to be performed at a temperature ><NUM> which does not allow to use lower cost PTFE belt laminators. The sandwich panel production according to embodiments of the present invention allows to laminate or weld the honeycomb core to the inner <NUM>°-UD-tapes (e.g. from high temperature thermoplastics, like PEI/CF or PEEK/CF) in small width in-line with the high temperature thermoplastic honeycomb production via a small width steel belt laminator. Then the second outer layers of <NUM>°-UD-tapes (after the machine direction of the honeycomb core with the first inner UD layers are rotated by <NUM>°) are applied with a lower melting thermoplastic adhesive via a large width PTFE belt laminator.

For cost efficient sandwich panels composed of polypropylene (PP), it is of interest to laminate the UD tape in the outer layers in the second step at lower temperatures because the surface quality is improved at lower lamination temperatures. A decorative surface layer can be laminated together with the second UD-tape layers in the second lamination step at lower temperatures, which enables to maintain a high-quality surface finish, even if the decorative layer is made from the same polymer, which is desirable to enable the recycling of the full sandwich panel.

For large size sandwich panels e.g., for side walls of truck trailers or for truck boxes it is advantageous to produce the final large width panel in a cost-efficient process locally just in time to reduce transportation costs and storage costs of the sandwich panels.

Honeycomb core sheets according to embodiments of the present invention have an array of polygonal cells such as hexagonal, rectangular or square cells, the array having rows and columns. Each polygonal cell has lateral cell walls extending between vertices of each polygonal cell, each polygonal cell being bounded on two sides by covering-layer planes, the lateral cell walls of each polygonal cell being in the form of a polygonal ring. First columns <NUM> in <FIG> can be of cells closed at the top and second columns <NUM> can be cells open at the top. First columns <NUM> alternate with second columns <NUM> as shown in <FIG>. In <FIG> one edge <NUM> of the core sheets can have cells which are open at the top, while the core sheets are trimmed on the right edge <NUM> so that the cells are closed on top. The honeycomb core sheets can be trimmed lengthwise during production of the continuously produced honeycomb core to produce suitable edge structures to join two or more panels together using edge connections made with trimmed honeycomb cores with first and second edge connections <NUM> and <NUM>.

<FIG> shows such a trimmed honeycomb core sheet schematically. On the edge <NUM> the cells have been trimmed so that the cells are open at the top and connections <NUM> are produced.

Typically, such core sheets will have much larger in-plane dimensions compared to the cell sizes e.g., the cell size can be <NUM> to <NUM> while the width of the core sheet can be <NUM> to <NUM> with a length of, for example, <NUM> to <NUM>.

<FIG> show joining of two honeycomb cores in accordance with embodiments of the present invention. <FIG> shows two honeycomb core sheets with trimmed edges, side by side. In <FIG>, two honeycomb core sheets are shown with an overlap, so that the L-cell walls of the left edge of one core sheet are between the W-cell walls and in the honeycomb cells on the right side of the neighboring core sheet. This results in some interpenetration at the joint position which results in an area of higher core density, i.e. in an overlap region of the two neighboring honeycomb sheets.

<FIG> shows on the left side a 3D image of a honeycomb core sheet with the left and right edge trimmed according to the present invention.

<FIG> shows two neighboring core sheets which overlap to create an area of larger core density.

<FIG> shows a side view of two honeycomb cores with the left and right edges of the adjacent panels trimmed according to the present invention to provide edge connections. This creates the possibility for the two honeycomb cores to be pushed together to form an overlap. Each honeycomb core <NUM> is preferably formed from a plurality of polygonal cells arranged in an array, wherein each polygonal cell has lateral cell walls (shown as vertical lines), each polygonal cell being bounded on two sides by covering-layer planes, the lateral cell walls of each polygonal cell forming a polygonal ring. Such a core and its manufacture are shown for example in <FIG>.

<FIG> shows a side view of two neighboring cores <NUM> as shown in <FIG> (as, <NUM>, <NUM>, <NUM>) which have been joined together by means of an overlap created by the trimming step to create a limited area of larger core density at the join and, therefore, provides some reinforcement.

<FIG> shows a side view of two intermediate panels with the <NUM>° UD-tapes <NUM>, <NUM> on the honeycomb cores <NUM>. The UD tape layers <NUM>, <NUM> are laminated onto the honeycomb core <NUM> whereby the top layer <NUM> on the left-hand side and the bottom layer <NUM> on the right hand side of <FIG> are formed with a small offset e.g., equal to one cell wall width a = c/√<NUM> or half the cell size c. This provides a further reinforcement at the joint between two panels.

<FIG> shows how those neighboring intermediate panels are placed together. The outer UD-tape layers <NUM>, <NUM> are continuous over the connection of the intermediate panels. Underneath these layers are the layers <NUM>, <NUM>. This provides a further reinforcement at the joint between two panels.

Referring to <FIG>, an example of honeycomb core manufacture is described such as folded honeycomb cores which can be used with any of the embodiments of the present invention. An advantage of this honeycomb is that it can be manufactured continuously. Some ends of the cells are open. <FIG> shows the use of a flat sheet or web which is made of a plastically deformable material. The plastically deformable material may be a thermoplastic polymeric material, or a fiber composite material, or similar, wherein the sheet is composed of a thermoplastic polymer and/or a thermoplastic elastomeric polymer, or a thermoplastic polymer selected from a group consisting of polyolefins, in particular polyethylene or polypropylene, polyesters, in particular polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate or polyetylene- <NUM>,<NUM>-furandicaboxylate, polyamides, in particular polyamide <NUM> or polyamide <NUM>,<NUM>, polycarbonates, polyetherketones, polyetheretherketones, polyetherketoneketones polyethers, polyetheresters, polyphenylene sulfides, polyetherimides, copolymers and mixtures thereof.

In accordance with this embodiment the flat web or sheet has plastic deformations <NUM>, <NUM> formed therein mainly perpendicular to the material web. In the regions <NUM> and <NUM>, the material is deformed, e.g. polygonally, for example trapezoidally, or sinusoidally, or arcuately or the like, from the plane of the web. The deformations form ridges <NUM> and valleys <NUM> whereby each of these is not continuous. For example, the ridges are composed of a linear series of deformed sections <NUM>, <NUM>, e.g. polygonal, for example trapezoidal, or sinusoidal, or arcuate sections or the like. Preferably, the ridges have a top surface that may be initially (e.g. as formed) parallel to the plane of the web of material. Two such surfaces will abut each other when the 3D structures are rotated (also called "folded") to form the honeycomb cells. The production direction is preferably as shown in <FIG> however a direction perpendicular thereto (parallel to the axes <NUM> and <NUM>) could be used as well.

The regions <NUM> and <NUM> are preferably formed inclined, i.e. rotated towards each other around the axis <NUM> and/or <NUM>, to form additionally u- or v-shaped connection areas <NUM> and <NUM>. The connecting areas <NUM> and <NUM> separate the ridge sections <NUM>,<NUM>, e.g. the polygonal, for example trapezoidal, or sinusoidal, or arcuate sections or the like in one row of regions <NUM>, <NUM>. One connecting area103, <NUM> is placed between two ridge sections <NUM>, <NUM> and connecting areas <NUM> alternate along the row of regions <NUM>, <NUM> with connecting areas <NUM>. The connecting areas <NUM>, <NUM> form cross-valleys, i.e. perpendicular to the valleys <NUM>. Adjacent cross-valleys are on opposite sides of the web material. The rotation of the ridge sections <NUM>, <NUM> to bring them into the initial position of <FIG> is preferably performed at the same time as the deformations are placed into the web of material. The web material is stretched at the transitions between the ridge sections <NUM> and <NUM> to form the connecting areas <NUM> and <NUM>, which are substantially perpendicular to the outer surfaces of the ridge sections <NUM> and <NUM>. The angle between connecting areas <NUM>, <NUM> on different ridge sections, allows a part of a tool to enter and, thus, to form these sections. In the direction of its width, the material web can change its dimensions in the direction of the axis <NUM> and the axis <NUM>, while in the production direction, the length of the material web does not change in dimension.

The deformation of the web or sheet material in the regions <NUM> and <NUM> serves the purpose of the formation of three-dimensional shapes, which form the walls of cell halves in the folded end product. The cells thus formed are structural and load bearing elements of the folded honeycomb core, the walls of which extend transversely to the longitudinal direction of the folded end product. The cells formed by folding are preferably cylindrical in cross section, the axis of the cylinder extending transversely with respect to the longitudinal direction of the folded end product and in thickness direction of the planar honeycomb core finally produced. The basic cross-sectional shape of a cell can be selected as desired, for example circular or polygonal, in particular even-numbered polygonal, for example hexagonal. The final cell shape is determined by the shape of the deformed ridge sections <NUM>, <NUM> in the original web and how they fold together. As shown schematically on the right-hand side in <FIG> when the web is fully folded, each cell is formed from two half-cells. The cells are arranged in rows. Each final cell is formed by the bottom and sides of two longitudinally adjacent (in the sheet or web material) valley sections <NUM>. The half cells are joined preferably together across touching surfaces from two longitudinally adjacent (in the web material) ridge sections <NUM>. Accordingly, a folded honeycomb is provided, formed from a plurality of cells arranged in rows, with the following features: the cells have lateral cell walls which adjoin one another in the form of a ring and are bounded towards two opening sides of the cell by covering-layer planes whereby the cells are each bridged or closed completely in one or other of the covering-layer planes. The folded honeycomb can be formed from a substantially uncut flat web, i.e. a continuous sheet that is not porous. The sheet can be extruded. Plastic deformation of the sheet forms 3D structures. Hence, the folded honeycomb contains a plurality of 3D-structures, e.g. polygonally, sinusoidally or arcuately shaped regions (<NUM> and <NUM>) formed by plastic deformation and connecting areas (<NUM> and <NUM>) in the covering-layer planes produced by the plastic deformation. At least part of adjacent cell walls are preferably wholly or partly permanently connected to one another, e.g. by glue or adhesive or welding. After the manufacturing processing described above, the honeycomb core <NUM> is conveyed towards a laminator <NUM> especially a calibrator and laminator <NUM> by a conveyor such as a belt conveyor or caterpillar (not shown). - see <FIG> and <FIG>. A <NUM>° UD tape <NUM> is unwound from a roll and applied to the upper surface of the honeycomb core <NUM>, optionally using temperature and/or pressure.

The present invention includes the final folded product being a mixture of cells of different sizes or shapes.

An important improvement of the honeycomb core for the performance of the sandwich panel is the support of the skins by the honeycomb core. A small area with higher core density at the joint of the intermediate panels comprising honeycomb cores can ensure that the final large size sandwich panel has no weak spot at the connection between panels.

The panel's edges can be cut with a slope, but with trim knifes for standard edges it is easier to have the panels cut straight with the core and the skins cut at the same position in width.

The small offset where no <NUM>° UD-tape layers are on the honeycomb core is preferably created by an offset in the lamination process. Alternatively, a small strip of the UD-tape is removed after the UD-tapes have been laminated and the complete panel edges have been trimmed.

An aim is to ensure that there is a bit more skin material and especially a bit more core material to make the support for the outer <NUM>° UD-tape layers better and results thus in better mechanical properties at the panel connection.

Contrary to overlapping honeycomb core material at junctions between intermediate panels creating an overlap of the UD tapes when pushing the panels together, because the UD-tapes do not have much in-plane tension strength in the direction transverse to the UD fiber orientation, in <NUM>° direction to the panel connection. However, to avoid positioning of the UD-tapes and the additional trimming of the UD-tapes to create the offset, it is also an option to push the UD-tape layers together and create an overlap.

One edge of the honeycomb core sheets is cut at the end of the L-cell walls, while the other edge of the honeycomb core sheets is cut at the beginning of the L-cell walls.

Claim 1:
A reinforced honeycomb sandwich panel comprising: a plurality of honeycomb core sheets having edges, and having a first core density,
first skin layers with <NUM>° fiber reinforcement laminated on both sides of each of the plurality of honeycomb core sheets, to form laminated reinforced honeycomb core sheets,
a butt joint between edges of respective laminated reinforced honeycomb core sheets in a side-by-side location of the edges of the laminated reinforced honeycomb core sheets so that the edges overlap each other or interpenetrate each other or are deformed to create an area of a second core density higher than the first core density at the conjunction of the laminated reinforced honeycomb cores and of the first skin layers with <NUM>° fiber reinforcement layer above and below a position where the edges of the honeycomb cores join,
second skin layers with <NUM>° fiber reinforcement layer on both sides of the laminated reinforced honeycomb cores on the <NUM>° fiber reinforced layers, to form a laminated reinforced honeycomb sandwich panel.