DE102007050356A1 - Core layer for a sandwich structure, comprises a structure folded out of semi-finished product, which has a layer out of tearproof flat material and a layer out of stiff flat material - Google Patents

Abstract

The core layer (2) for a sandwich structure, comprises a structure folded out of semi-finished product, which has a plastic layer out of polymer fleece, polymer fabric and/or polymer foil, which is double-sidedly coated with a stiff surface material such as fiber, non-woven, paper, paperboard or cardboard. The stiff surface material is reinforced by a strengthening material. The layer out of stiff surface material is partially impregnated with an artificial resin. One of the layers is formed in partially electrical conductive manner. An independent claim is included for a method for the production of core layer.

Description

The The invention relates to a core layer for a sandwich structure according to the preamble of claim 1 and a method for their production.

multilayer Lightweight structures, comprising a core layer between at least two Cover layers is commonly used as Sandwich structures called. Use find such structures in various embodiments, for example in the aircraft, truck, railway, container, furniture and house construction.

For the core layer becomes, for example, materials such as plastic foams, Metal foams or wood, in particular balsa wood, as well so-called honeycombs made of aluminum, aramid paper (known brands for aramid fibers, for example, Nomex or Kevlar, therefore often referred to as Nomex paper) or thermoplastics used. In addition to the specific mechanical properties differ the usual materials, for example, due to different Densities, moisture absorption, fire properties, heat resistance, Thermal conductivities, electrical properties, like electrical conductivity, electrical resistance etc., aging and chemical resistance or the like.

The Most of these core layers are not or only very difficult by means of continuous manufacturing processes in a band operation or the like. So is for example a multi-level Process in batch mode, d. H. with a variety of sequential to be processed process steps, known to be a conventional Honeycomb core layer made of aramid paper. Here are thin, parallel traces of glue on individual aramid papers same line spacing applied. Then be the individual layers produced in this way are stacked on top of one another in such a way that from one layer to another a regular offset given the applied line pattern. The one of a variety single-layer stacks will follow below pressed perpendicular to the stack of applied pressure and the adhesive is cured. As an example, an adhesive thermally activated adhesive used. After curing the individual layers are only connected to the adhesive traces. By Pull apart in a direction perpendicular to the layer receives one, due to the layered alternating adhesive traces forming, hexagonal honeycomb structure. By repeated impregnation the honeycomb structure produced, for example with phenolic resin-based Matrix resins, and respective curing of the infiltrate is the honeycomb structure gradually solidified and stabilized. In the Rule for appropriate honeycomb structures of aramid five to six infiltration and cure cycles needed. Core layers of desired height can be mechanically separated from the honeycomb blank produced, for example by sawing, cutting or the like.

From the DE 102 52 941 A1 a method for producing a structure for a core layer is known, wherein the core structure of a thin foldable starting material with an undefined length, in particular from semi-finished fiber webs, preimpregnated semi-finished fiber products, paper webs, board webs, film webs, sheet metal or the like is produced. For production, wrinkle-allowing folding edges are produced on a material web on the starting material in a pretreatment. In a continuously subsequent step, an initiation of the folding process in the region of the fold lines is carried out on the upper side and the lower side of the material web. The material web is delayed after initiation, ie slows down the forward movement of the now folded material web, and post-treated after the folding process for stabilizing the folding structure.

In accordance with DE 102 52 941 A1 used material web is one-layer material webs. Chemical, thermal, electrical and / or mechanical properties are so largely determined by the choice of material and not independently fixed.

It It is an object of the invention to provide a core layer for a To create a sandwich structure which is simple and inexpensive with a variety of properties using even more cost-effective Raw materials can be produced. It is another object of the invention to provide a method for their production.

These Task is solved by a core layer for a sandwich structure, which is one of at least one semi-finished product having folded folding structure, wherein the semifinished product at least two layers having.

According to the invention the semi-finished product for producing the folding structure is at least two-layered Laminate, wherein the laminate by a variety of methods such as For example, calendering, pressing, laminating or the like can be produced is. For the multilayer material web can Films, nonwovens, metal foils, papers, cardboard, cardboard, tissue and other flat semi-finished products to multilayer laminates get connected.

The use of multi-layered laminates creates the opportunity to make a difference Licher material properties in terms of the planned application requirements. The semi-finished products can be reinforced by carbon fibers, glass fibers and / or carbon nanotubes or the like. The individual layers can be treated before and / or after lamination on the surface.

To the Folds become folded edges in one embodiment incorporated as a material web present semifinished product and then the material web is folded. By the combination of semi-finished products such as non-woven, paper or fabric fabrics with thin tear-resistant Plastic films or nonwovens, it is possible such To use semi-finished products alone as single-layer semi-finished products due to their rigidity for the embossing and Folding process would be inappropriate, but just because of this Rigidity give good mechanical properties of the final product. In addition, it is also possible to use inexpensive starting materials deploy.

at suitable folding become drainage channels in the folding structure educated. The drainage channels are preferably transversely formed to a feed direction of the web during manufacture. Through a liquid-tight layer, such as a liquid-tight Plastic film may, in certain embodiments, the semifinished product according to the invention also serve as a barrier. Through the layer of a homogeneous, po renfreien film material, in particular of a plastic (polymer) or metal, a gas-tightness of the semifinished product is further achieved. For single-layered aramid paper semi-finished products can be same uses here multiple Nachimprägnierschritte necessary to achieve adequate gas tightness. By a suitable material combination of the layers of the semifinished product is It is thus possible to have a hermetic separation of the two To achieve Faltstrukturseiten, as for example for Applications are of interest as heat exchangers.

In an advantageous embodiment of the invention, the semifinished product at least one layer of a tear-resistant material, in particular a plastic from a group comprising polyimide, Polycarbonate, polyester, polyamide and the like, and a layer from a substantially rigid surface, in particular a fabric, a fleece, paper, cardboard or cardboard. Possible For example, stiff fabrics are also carbon fiber or carbon fiber glass fiber reinforced materials. Such surface materials usually can only be due to the stiffness difficult wrinkles, for example because the semi-finished tears when folding. The tear-resistant plastic takes over according to the invention during of the embossing and folding process the function of a film hinge. It will be on the rigid surface in one embodiment for folding scratched, perforated and / or severed folding edges educated.

In a development of the invention, the semifinished product at least three layers comprising an inner layer of a polymer, as a polymer film or a polymer fleece, which on both sides with a substantially rigid sheet, such as a fabric, a non-woven, a paper, a cardboard or a cardboard, in particular a reinforced surface, is coated. The inner layer or inner layer acts for both adjacent layers as a film hinge. This will be a cost effective and through continuous manufacturing, from material webs of undefined length producible core layer created which at least the same Strength as conventional batch produced Having honeycomb structures. As semi-finished example, a laminate two layers of uncalendered, long-fiber paper and one interposed polyester film used. The paper layers For example, have thicknesses between 20 to 250 microns, preferably 40 to 120 microns, on and have a basis weight from 10 to 300 g / m2, for example 30 to 220 g / m2. The polyester layer in one embodiment has a thickness of 10 to 150 μm, in particular from 20 to 50 μm. The two Layers adjacent to the inner layer are in one embodiment made of different materials.

When have advantageous in two- or multi-layer laminates for example, film thicknesses greater than 5 microns, in particular greater than 8 microns, especially larger 10 μm for polyester and larger 10 μm, preferably greater than 15 μm, in particular greater than 20 microns in polyimide proved. Especially with larger honeycomb heights can during the curing of the matrix resin the Net weight of the surface material for deformation of the honeycomb geometry to lead. By using thicker, inherently rigid films this can be counteracted. For folding honeycomb heights greater than 40 mm are, for example, film thicknesses can be used up to 200 μm or up to 300 μm.

In a further embodiment of the invention is at least one layer, in particular a layer of a surface material from the Group comprising fabric, non-woven, cardboard, cardboard and paper, impregnated. For the impregnation is preferably a synthetic resin used. As low-cost semi-finished products are in embodiments cellulose or cotton-based papers with films or Nonwovens combined. In particular, uncalendered or only weak Many papers have an open porosity on that a complete impregnation with matrix resins allowed.

In a development, at least one layer is electrically conductive. In one embodiment, there is a purpose for this purpose Layer of a film, which is provided with electrically conductive structures. Depending on the structure of the structure can be integrated into the structure of a suitable function, such as a heating, antenna, sensor, actuator function. The structure may have point, line or sheet-like elements which are applied by adhesive, pressure and / or etching processes or the like to a film layer. In other embodiments, at least two layers are provided, wherein one layer fulfills the geometric and mechanical shape function and the second layer serves to fulfill secondary functions.

The The object is further achieved by a method for the production a core layer for a sandwich structure, wherein according to the invention a multilayer semifinished product is folded into a folded structure.

The Compressive strength of the folding structure is characterized by a rigidity of the Semi-finished, a thickness of the semifinished product and a Vorkrümmung the cell walls, d. H. the folding, determined. Too high Pressure loading of a sandwich structure can lead to a local buckling failure in the folding or cell walls. The area moment of inertia The cell walls is among other things also by the thickness of the Semi-finished influences, with the internal material areas - such as For example, an internal foil - made of geometric Aspects (neutral fiber) contribute little to the moment of inertia. However, this inner layer is for a shear strength, for example, at a bending load of the sandwich structure relevant. thrusts act on the substantially perpendicular to the sandwich structure extending folding edges, which rule between the individual cell or folding walls lie. When using a multi-layer laminate for the Folded structures are increasing depending on the combination of materials up to 10% in the specific buckling strength of the folding walls Folding structures can be realized with single-layer semifinished products.

A Outer layer of the semifinished product is preferably before folding at the fold edges, which at a folding outside to lie down, weakened, in particular scratched, perforated or severed. This will cause an elongation of the outer layer when folding possible. Preferably, a so in the outer layer resulting gap when gluing or bonding with a cover layer for forming the sandwich structure with an adhesive, in particular a synthetic resin, filled

Further Advantages of the invention will become apparent from the following description of embodiments of the invention shown in the drawings are shown schematically. For same or similar Components are given the same reference numerals in the drawings. As described or illustrated as part of an embodiment Features may also be in another embodiment used to form a further embodiment of the invention to obtain.

In The drawings show schematically:

1 a perspective view of a sandwich structure with a core layer according to the invention;

2 : a folding of a semifinished product;

3 a section through a semifinished product according to the invention;

4 a section through the folding structure of the core layer in a perspective view;

5 : a detail V according to 4 in a sectional view;

6 : a detail V according to 4 a further embodiment of the invention in a sectional view and

7 : the detail V according to 6 when attached to a cover layer in a sectional view.

1 shows a sandwich structure 1 with a core layer 2 which is between an upper cover layer 3 and a lower cover layer 4 is arranged. The upper cover layer 3 includes several - in the illustrated embodiment, three - layers 3a . 3b . 3c , wherein the third, inner layer 3c by means of an adhesive layer 30 with the core layer 2 connected is. The layers 3a . 3b . 3c For example, they are constructed from a prepreg material impregnated with phenol resin (also referred to as prepreg material), which may each comprise a multidirectional fiber reinforcement material. For the adhesive layer 30 can pasty or liquid adhesive z. B. on epoxy, acrylate or phenolic resin (among others) or adhesive films on z. As epoxy, phenolic, polyamide or polyurethane base can be used. The lower cover layer 4 is also configured in an embodiment of several layers.

The core layer 2 has a 3-dimensional folding structure. The directions are indicated by a three-dimensional coordinate system, wherein the z-direction is perpendicular to the folding structure and the x- and y-direction are referred to as longitudinal or transverse direction. In the illustrated embodiment are by folding or cell walls 20 drainage channels 21 formed, which is the core layer 2 durchdrin in a transverse direction y gene.

Production of the folding structure depends on a semi-finished product used for the folding structure. In principle, however, a desired folding pattern for forming the 3-dimensional folding structure is applied to the semi-finished product. The folding pattern is impressed on a material web of the semifinished product used for the folding structure by suitable devices, such as embossing machines, CNC-controlled embossing plotters, one, for the desired folding pattern individual embossing roller pair or the like, and / or it be by means of a device such as a CNC plotter defined folding edges applied by scoring the flat semi-finished product. After applying the fold pattern, the web is folded to obtain the 3-dimensional structure. The special folding patterns are preferably designed so that a thrust free folding is guaranteed. The erection of the fold in the z-direction leads to a length and width reduction, ie a reduction of the dimensions in the x and y direction according to 1 , opposite the flat semi-finished product.

To The folding structure can be impregnated with an erecting of the fold become. By flat semi-finished products with high inherent rigidity in the unimpregnated state, the risk of re-deformation the folded structure during post-crosslinking in sequence a re-softening of a partially crosslinked resin reduced.

2 schematically shows a possible folding of a substantially flat semi-finished product 2a to a core layer according to the invention 2 , On the substantially flat semi-finished product 2a the folding pattern is applied and then the semifinished product 2a folded to the three-dimensional structure of the core layer 2 to obtain. The folding comprises two steps in the illustrated embodiment, but depending on the folding pattern, more or fewer steps for folding may also be necessary.

3 schematically shows a section through a semifinished product according to the invention 2a , The semi-finished product 2a according to the invention has at least two layers 22 . 23 on. In the illustrated embodiment, an inner layer 23 with two substantially similar layers 22 laminated, which in the embodiment in each case via an adhesive layer 24 with the inner layer 23 are connected. The inner layer 23 is preferably made of a homogeneous, non-porous sheet material, in the illustrated embodiment, the inner layer 23 as a plastic film, formed as a polymer film. As cover layers or outer layers 22 Tissues are used in the illustrated embodiment. In other embodiments are called outer layers 22 Nonwoven, paper, cardboard, cardboard or other semi-finished products used with a high rigidity.

4 shows a section through the folding structure of the core layer 2 , wherein an upper fold line or edge 200. , a bottom fold line or edge 201 and the cutting plane 202 reinforced by wide lines are shown.

An excessive pressure load on a folding structure 2 can cause a local buckling failure in the fold or cell walls 20 to lead. The moment of inertia of the cell walls 20 is partly due to the thickness of the semi-finished product 2a influenced, wherein the internal material areas - such as an internal film 23 according to 3 - form the neutral fiber and so contribute little to the stiffness. This inner layer 23 However, for a shear strength, for example, at a bending load of the folding structure 2 relevant. Shearing forces act on the folded edges, which in the cutting plane 202 lie and which are substantially perpendicular to the folding structure 2 (in z-direction according to 1 ).

5 shows a detail V of the core layer 2 according to 4 in an enlarged view, the three layers 22 . 23 of the semifinished product are visible. As in 5 Recognizable, may be a folding of the laminate with the three layers 22 . 23 cause a shift 22 at one point 5 buckle and tear and get rid of the inner layer 23 solves. Depending on the configuration of the layers, preferably at least one residual capacity of the folded structure remains 2 despite the detachment received. By an advantageous embodiment according to 6 a detachment can be avoided.

6 shows a detail V of the core layer 2 according to 4 , which was produced by a method according to the invention. The core layer 2 corresponds substantially to the embodiment according to 5 and for the same components, the same reference numerals are used. In this case, an inner layer formed by a polymer film or the like 23 with two outer layers 22a . 22b , which are for example made of paper, laminated. In contrast to 5 becomes an outer layer 22a scratched, perforated or severed at least at a folding outer layer A prior to folding, so that when folding a lengthening of the outer layer 22a at the folding edge of the pleated outer layer A is possible. The inner layer 23 acts as a kind of film hinge. Due to the targeted weakening of the outer layer 22a becomes an unwanted detachment of the outer layer 22b prevented at a folding inner layer. A resulting from the weakening of the fold recess 6 is preferably used in curing the impregnated phenolic resin by temporary viscosity reduction of the phenolic resin filled during the Hochheizphase kapilarkraftinitiiert. The complete filling takes place at the latest when gluing with the cover layers by the adhesive used.

7 shows the detail V according to 6 when attaching the core layer 2 on a cover layer 4 according to 1 , When attaching the core layer 2 by bonding with the top layer 4 This is the result of scribing or perforation recess 6 filled. In the illustrated embodiment, the core layer 2 with the top layer 4 with a phenol resin-free polyamide 40 glued, wherein the polyamide the recess 6 fills.

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• - DE 10252941 A1 [0005, 0006]

Claims (10)

Core layer for a sandwich structure, wherein the core layer ( 2 ) one of at least one semi-finished product ( 2a ) has folded folding structure, characterized in that the semifinished product ( 2a ) at least two layers ( 22 . 23 ) having. Core layer according to claim 1, characterized in that the semifinished product ( 2a ) at least one layer ( 23 ) of a tear-resistant sheet, in particular a plastic from a group comprising polyimide, polycarbonate, polyester, polyamide and the like, and a layer ( 22 . 22a . 22b ) of a substantially rigid sheet, in particular a fabric, non-woven, paper, cardboard or cardboard. Core layer according to claim 1 or 2, characterized in that the semifinished product ( 2a ) at least three layers ( 22 . 22a . 22b . 23 comprising an inner layer formed of a polymer ( 23 ), in particular a polymer nonwoven, a polymer fabric and / or a polymer film, which on both sides with a substantially rigid surface ( 22 . 22a . 22b ), such as a woven fabric, a non-woven, a cardboard, a cardboard or a paper, in particular a surface material coated. Core layer according to claim 2 or 3, characterized in that the rigid surface material ( 22 . 22a . 22b ) is reinforced by a reinforcing material. Core layer according to one of claims 1 to 4, characterized in that at least one layer ( 22 . 22a . 22b ), In particular a layer of a fabric from the group comprising send fabric, nonwoven, cardboard, cardboard and paper, at least partially impregnated. Core layer according to claim 5, characterized in that the layer ( 22 . 22a . 22b ) is impregnated with a synthetic resin. Core layer according to one of claims 1 to 6, characterized in that at least one layer at least partially is electrically conductive. Method for producing a core layer ( 2 ) for a sandwich structure ( 1 ) according to one of claims 1 to 7, wherein a semifinished product ( 2a ) is folded into a folding structure. Method according to claim 8, characterized in that at least one outer layer ( 22a ) of the semifinished product ( 2a ) is weakened prior to folding on a folding outer fold edge. A method according to claim 9, characterized in that a recess formed by the weakening ( 6 ) is filled in a hardening.