Core body made of a plastic composite and method for its manufacture

Description

[0001] The present invention relates to a core body with improved mechanical properties. The present invention further relates to a method for producing a core body from an open-pore support and to a core body produced according to this method.

[0002] Composite cores play a major role in modern lightweight construction. These materials allow for a minimization of the material used, thus reducing weight and material costs. This is achieved because these materials offer high mechanical stiffness at a low weight. These properties make them particularly attractive for use in the aerospace industry. Other areas of application include automotive and shipbuilding. For information on the fundamental properties of cores, see "Honeycomb Technology Materials, design, manufacturing, applications and testing," by Tom Bitzer, published by Chapman & Hall, ISBN 0 412 540509.

[0003] US 5030305 A discloses methods for manufacturing thermoplastic structures, wherein the structure comprises a fiber-reinforced thermoplastic resin.

[0004] JP H07 156318 A discloses a method for producing a core body from aramids.

[0005] George Tochukwu reveals in "Carbon Fiber Composite Cellular Structures", (20140501), core bodies, encompassing carbon fiber materials.

[0006] WO 91 / 02646 A1 describes film-based composite structures.

[0007] EP 0 739 707 A1 discloses honeycomb structures comprising aramid fibers.

[0008] US 2008 / 145599 A1 discloses methods for the production of honeycomb-shaped nuclear bodies.

[0009] Due to the preferred use of such materials in lightweight construction, the material's density is of crucial importance. At the same time, particularly good mechanical properties are desired. Currently available materials suffer from the disadvantage that especially advantageous mechanical properties, particularly with regard to the bulk modulus to density ratio, can only be combined with low densities within certain limits.

[0010] An improvement in mechanical properties can often be achieved by reducing the cell size of the materials. However, a reduction in cell size generally also leads to an increase in density. Thus, currently available materials suffer from the disadvantage that a low density can only be combined with a small cell size within certain limits.

[0011] The present invention was based on the objective of providing core bodies made of a plastic composite that are improved with regard to the aforementioned properties. The term "plastic composite" used here encompasses not only purely synthetically produced plastics (such as resins, adhesives, and the like) but also plastics derived from natural resources, including bio-resins marketed on the market, such as cashew shell oil, from which technical resins similar to phenolic resins can be produced, or furan- or furfural-containing resins that can be obtained from natural products such as sugar carbohydrates. These latter examples are given merely as illustrations and are not intended to limit the scope of the claimed subject matter but rather to extend it beyond purely synthetic resins to include all bio- and nature-based resins, as well as resins synthetically derived from natural products.

[0012] This problem is solved according to the invention by a core body, wherein the following condition a) is fulfilled: a) it has a density of ≤ about 48, in particular ≤ about 40, more preferably ≤ about 32 kg / m³ and most preferably ≤ 26 kg / m³; and where condition b is satisfied: b) it has a bulk modulus to density ratio ≥ approximately 4.5 MPakg / m3 , preferred ≥5.5MPakg / m3 and especially preferred ≥5.8MPakg / m3 on;

[0013] The core bodies according to the invention are distinguished from previously known core bodies by a unique combination of properties. In particular, the core bodies according to the invention exhibit the following properties compared to the core bodies known from the prior art: They exhibit a significantly lower density at the same bulk modulus-to-density ratio. They exhibit a lower density at a higher bulk modulus-to-density ratio. They exhibit the same density at a significantly higher bulk modulus-to-density ratio. They exhibit a significantly lower density at the same cell size. They exhibit a lower density at a smaller cell size. They exhibit the same density at significantly smaller cell sizes.

[0014] In a preferred embodiment, the nucleus body according to the invention is designed such that the nucleus body has a cell size of ≤ about 9.6 mm, in particular ≤ 6.4 mm, preferably ≤ 4.8 mm, particularly preferably ≤ 3.2 mm and most preferably ≤ 1.6 mm.

[0015] In a preferred embodiment, the core body according to the invention is designed such that the core body is a honeycomb body, wherein the honeycomb body has a polygonal, preferably a hexagonal, rectangular or circular cell geometry.

[0016] It has proven advantageous that the core body according to the invention is designed such that the core body is made of glass (E-,S2-), carbon, Kevlar, basalt fiber, preferably a quartz glass fiber, or of hybrid constructions of these fibers.

[0017] In a preferred embodiment, the core body according to the invention is designed to be made of a plastic composite.

[0018] In the context of the present invention, a core body is understood to be a body which, in conjunction with cover layers, is used in the core of a composite component, primarily with the aim of improving the stiffness of this component or other mechanical or physical (e.g. dielectric) properties while reducing weight.

[0019] Among the most commonly used core materials in composite applications are foams (open- or closed-pore), honeycomb cores, corrugated cardboard or corrugated sheets and zigzag geometries derived from them (e.g., folded honeycomb) and also materials directly available from nature such as balsa wood.

[0020] In a preferred embodiment, the core body according to the invention is a honeycomb body. For the purposes of this invention, a honeycomb body is understood to be a body that has a cell-like structure whose cell geometry resembles that of a honeycomb. This designation was therefore derived semantically from this. However, the cell geometry of a honeycomb body within the meaning of the present invention is not limited to hexagonal cell structures.

[0021] In a particularly preferred embodiment, the core body according to the invention, especially in the form of a honeycomb structure, is configured such that it is a plastic composite with an open-pore support. For the purposes of the present invention, the term "open-pore support" is to be understood as meaning that this body is permeable to air or can be permeable to any gaseous or liquid medium.

[0022] In a particularly preferred embodiment, the carrier can have an air permeability measured according to the method in DIN EN ISO 9237 (1995), which measures the airflow in L / min flowing through an area of ​​20 cm² at a differential pressure of 200 Pa. The air permeability according to the present invention is at or above 10 L / dm² / min and particularly preferably well above 716 L / dm² / sec, which currently represents the measurement limit of the measurement method described herein.

[0023] In a particularly preferred embodiment, the core body according to the invention is designed such that the core body is a quartz glass fiber-plastic composite.

[0024] With regard to the plastic component of the plastic composite, the core bodies according to the invention are not subject to any fundamental restrictions. However, it has proven particularly advantageous if the core bodies according to the invention are designed such that the core body is made of a plastic consisting only of a thermoset or thermoplastic matrix, preferably from the family of cyanate esters or polyimides, optionally also phenols, epoxides, benzoxazines, BMI, polyetherimides (PEI), polyetherketones (PEK, PEEK, PAEK, PEKK), polythioethers (PPS), polyethers (PP, PPO), or also from common thermoplastics such as PE, PP, PET, PA, PC, PMMA or the like.

[0025] Particularly good results are achieved when the core body according to the invention is designed such that the core body is a composite consisting of fibers and / or other carrier or filler materials and a plastic comprising a thermoset or thermoplastic matrix, preferably from the family of cyanate esters or polyimides, optionally also phenols, epoxides, benzoxazines, BMI, polyetherimides (PEI), polyetherketones (PEK, PEEK, PAEK, PEKK), polythioethers (PPS), polyethers (PP, PPO), or also from common thermoplastics such as PE, PP, PET, PA, PC, PMMA or the like. In a particularly preferred embodiment, the core body is a composite consisting of fibers and / or other carrier or filler materials and a plastic that is a cyanate ester.

[0026] Particularly good results are achieved when the core body according to the invention is designed such that the core body is a quartz glass fiber-cyanate ester composite.

[0027] In a particularly preferred embodiment, the core body according to the invention is made of a woven fabric and / or a nonwoven-like structure. During the production of the core bodies according to the invention, the fabric is coated or impregnated with the plastic. Particularly good results are achieved when the core body according to the invention is designed such that the fabric is not completely impregnated and / or coated, thus ensuring air permeability through the open-pored cell walls between the cells. This is particularly advantageous when the material is used in the aerospace industry. The reason for this is that air permeability of the open-pored cell walls allows for pressure equalization with the environment. This pressure equalization enables the material to be used without problems in environments with significantly reduced pressure, which is essential in the aerospace industry. frequentlyThis is the case. With previously used nuclei in this area, it was usually necessary to perforate the cell walls to allow such pressure equalization.

[0028] Figure 1 shows a preferred embodiment of the air-permeable porous honeycomb body according to the invention presented here.

[0029] For many design applications, the temperature resistance of the core bodies plays an important role. In a preferred embodiment, the core bodies according to the invention are designed such that the core body exhibits a high temperature resistance of over 350°C.

[0030] For many applications, the dielectric properties of the material are also of great importance. Preferably, the core bodies according to the invention are characterized by the fact that the core body exhibits excellent dielectric properties with a dielectric constant ≤ 1.1, in particular ≤ 1.0, and a loss tangent of < 0.003, in particular < 0.002. Such dielectric properties are particularly advantageous in areas where the properties of the material with respect to electromagnetic radiation, especially in the radar range, are important.

[0031] Another important parameter for many applications is the ratio of compressive strength to density. Preferably, the core bodies according to the invention are designed such that the core body has a ratio of compressive strength to density ≥ approximately 0 , 04 MPa kg / m 3 exhibits.

[0032] The present invention also relates to a method for producing a core body from an open-pore support.

[0033] Until now, such core bodies have been manufactured using the so-called corrugated process. In this state-of-the-art corrugated process, the fabric is pre-impregnated with resin. This pre-impregnated material (also called prepreg) is then embossed into a mold that corresponds to half of the desired cell geometry; in the case of a hexagonal honeycomb, this would be a half-hexagonal shape. The next step involves curing the embossed prepreg. The embossed sections are then bonded together layer by layer to create a core body.

[0034] This corrugated process, known from the prior art, is used in Figure 2 schematically represented.

[0035] The core bodies produced according to this prior art corrugated process have the disadvantage that a low density can only be combined with an advantageous ratio of bulk modulus to density or with a small cell size within certain limits.

[0036] The problem underlying the invention is solved by a method for producing a core body from an open-pored carrier material, wherein the carrier material is a woven fabric and / or a nonwoven structure. i) a web of material made of a carrier material is provided with adhesive strips in regular patterns by means of an application device; ii) stacks of sections of the web of material are formed, which are offset from one another with respect to the stripe patterns, iia) that the strips of a lower section are arranged between the strips of the section above; or iib) that the strips of a lower section are arranged offset but not centered between the strips of the section above; iii) the sections lying on top of each other are glued together in the areas of the strips to form a stack or press block;iv) the stack is expanded, forming a honeycomb shape of any polygonal structure, in particular a honeycomb shape with hexagonal, rectangular, or circular cell geometry for the production of hexagonal, overexpanded, rectangular, and 3D honeycomb cores; v) the honeycomb shape is impregnated and / or coated with a synthetic resin, wherein the support in the form of the honeycomb body is not completely impregnated and / or coated and air permeability is ensured through the open-pored cell walls between the cells; vi) the honeycomb shape coated with the synthetic resin is subjected to a curing step to harden the synthetic resin; vii) the honeycomb shape thus formed is cut to form honeycomb bodies.

[0037] The inventive method is described in Figure 3 schematically described.

[0038] A key difference between the inventive method and the corrugated process known to the prior art is that the impregnation of the substrate material with the synthetic resin only takes place after the honeycomb structure has been formed. Until now, a prejudice existed in the field that would have deterred those skilled in the art from considering such expansion without prior compaction and sealing by means of impregnation, since the production of the honeycomb structure via an expansion process with highly permeable substrates was previously considered unfeasible on an industrial scale.

[0039] Another reason is that a pre-impregnated substrate material (prepreg) is hardly suitable for honeycomb production today if it is to be manufactured using the more economical expansion process. A prepreg would either be too reactive in its composition, causing the laid-down prepreg sheets to stick together completely during the production of the press block, and / or so hard and brittle that the individual layers would be difficult to separate during the expansion process because the material would have become too stiff, sticking and interlocking locally even where there are no gluing lines, and the expansion stresses would therefore become too high, causing the block to crack during expansion.

[0040] Another very significant difference between the inventive method and the corrugated method known in the prior art is that an extremely open-pored substrate can also be used, which can then be easily pre-impregnated. wherein the amount of resin is adjusted so that the porosity of the substrate is brought into the range that can be processed for the printing and expansion process; wherein the chemical formulation of the resin is adapted by, for example, the addition of additives (including elastomers) to make the resin flexible even after complete curing and not to make it hard or embrittle and breakable; wherein in the pre-impregnation process (prepreg process) of the fabric the resin is pre-reacted to such an extent that it neither snags nor sticks together during the pressing process of the individual layers for the production of the press block immediately before the expansion step.

[0041] In a preferred embodiment, the method according to the invention is a method for producing a honeycomb body.

[0042] With regard to the choice of open-pore substrate, the inventive method is not subject to any fundamental restrictions. However, the degree of porosity plays a significant role – such as the mesh size in a woven fabric – in order to find the best possible process settings. Thus, a resin-free substrate or a lightly impregnated but still porous substrate can be used as a precursor material for producing the honeycomb via the expansion process.

[0043] However, particularly advantageous results are achieved when the inventive method is designed such that the open-pore support is a fabric, preferably but not exclusively consisting of glass (E-, S2-, quartz-), carbon-, Kevlar-, basalt-fiber-, or hybrid fabrics of these fibers.

[0044] The inventive method is not subject to any fundamental limitations with regard to the adhesive used for bonding the material webs. Particularly good results are achieved, however, when a thermoset, thermoplastic, or elastomer is used as the adhesive, preferably but not exclusively phenolic, epoxy, polyimide, or cyanate ester adhesives. Surprisingly, it has been shown that, according to the inventive method, it is possible to coat the honeycomb shape formed in process step iv) with a synthetic resin without prior stabilization in step v). The results obtained can be further improved, however, if the honeycomb shape is stabilized by thermal treatment after expansion step iv). Such stabilization of the honeycomb shape by thermal treatment preferably takes place at the softening point of thermoplastic materials or at (if necessary)(even slightly below) the glass transition temperature (TG) of thermosets. With thermoset-free thermosets, even thermal treatment at or above the curing temperature can briefly soften the resin and therefore lead to thermal deformation.

[0045] The duration of thermal treatment can range from a few seconds to minutes when the material is in direct contact with the substrate, as in stamping or embossing processes. For large-volume bodies that are heated with hot air during tempering, or bodies with a high mass and / or heat capacity, the heat treatment can take from a few minutes to several hours.

[0046] Ultimately, the temperature and time of heat treatment depend on the chemical composition, the geometry, and also the hot forming stabilization process.

[0047] With regard to the synthetic resin used, the process according to the invention is not subject to any fundamental limitations. However, it has been shown that particularly good results are achieved when a thermosetting or thermoplastic matrix system is used as the synthetic resin, preferably from the cyanate ester or polyimide family, optionally also phenols, epoxides, benzoxazines, BMI, polyetherimides (PEI), polyetherketones (PEK, PEEK, PAEK, PEKK), polythioethers (PPS), polyethers (PP, PPO), or also from common thermoplastics such as PE, PP, PET, PA, PC, PMMA, or the like. In a particularly preferred embodiment, a cyanate ester is used as the synthetic resin.

[0048] The method according to the invention is preferably carried out such that steps v) and vi) are repeated once or several times to apply one or more further layers of the synthetic resin. Such a repetition of steps v) and vi) enables, on the one hand, an increase in the stability of the honeycomb structure, but on the other hand also leads to an increase in its density. The person skilled in the art will therefore choose, depending on the desired properties of the honeycomb structure produced according to the method of the invention, whether steps v) and vi) are to be repeated once or several times.

[0049] The present invention also relates to a core body produced according to the method described above, in particular in the form of a honeycomb structure. The core body produced according to the inventive method is characterized in that the open-pored support is not completely impregnated and / or coated and ensures air permeability between the cells via the open-pored cell walls.

[0050] Preferably, the core body produced according to the inventive method is designed such that the core body has a ratio of bulk modulus to density ≥ approximately 5 , 5 MPa kg / m 3 and especially preferred ≥ approximately 5 , 8 MPa kg / m 3 exhibits.

[0051] Another important parameter for many applications is the ratio of compressive strength to density. Preferably, the core bodies according to the invention are designed such that the core body has a ratio of compressive strength to density ≥ approximately 0 , 04 MPa kg / m 3 exhibits.

[0052] In a particularly preferred embodiment, the core body produced according to the inventive method is characterized in that, in addition to the mechanical properties described, the core body has excellent dielectric properties with a dielectric constant ≤ 1.1, in particular ≤ 1.0 and a loss tangent of < 0.003, in particular < 0.002.

[0053] The present invention is explained in more detail below: According to the preferred embodiment of the invention, a honeycomb structure could be produced consisting of a quartz glass fabric and a cyanate ester resin, whereby a pressure modulus of around 275 MPa and a compressive strength of around 1.2 MPa were achieved with a cell size of 6.4 mm and a density of 32 kg / m³.

[0054] The Figures 4 to 12clearly show that the state of the art can hardly achieve a comparable pressure modulus or can only achieve a comparable compressive strength at high density.

[0055] In the Figures 4 to 12 The honeycomb designation ECG-CEQ P-6.4-32 stands for a fiberglass honeycomb manufactured with Q uartzglas and C ynat e steric resin with a cell size of 6,4 mm and a bulk density (RG, density) of 32 kg / m³ < . The P indicates that the cell walls of the honeycomb are porous / air-permeable. It is common practice to introduce this porosity mechanically into the cell walls by perforation. In this preferred embodiment of the invention, however, this porosity is generated naturally by means of a suitable selection of the substrate and the resin, whereby the resin does not completely densify the substrate during coating.

[0056] The in Figure 4 The table shown illustrates the properties of such a honeycomb.

[0057] The Figures 5 and 6 show a graphical plot of the measurement results for pressure modulus and compressive strength.

[0058] With reference to these mechanical values, the ratio of pressure modulus to density (or bulk density) is significantly higher compared to the state of the art: > 5 , 5 MPa kg / m 3 , preferred > 5 , 8 MPa kg / m 3 , which ultimately leads to a high stiffness in the core, which is unique to this day at a low density of 26-48 kg / m 3<.

[0059] In the preferred embodiment of the present invention, the ratio of pressure modulus to density lies between 6 and 10 MPa kg / m 3 at a density of 32 kg / m³< and can even at a density of 48 kg / m³< by a value of 12 MPa kg / m 3 Compared to the state of the art, this value is only at a maximum of 48 kg / m³. 4 MPa kg / m 3 This is in Figure 7 shown.

[0060] Similarly, with reference to these mechanical values, the ratio of compressive strength to density (or bulk density) is also between 0.03 and 0.03, compared to the state of the art. 0 , 047 MPa kg / m 3 even slightly higher than the state of the art, and this with a lower density of 32 kg / m³ compared to 48 kg / m³. Furthermore, it can be seen that with an equivalent density (specific weight) of 48 kg / m³, this ratio of compressive strength to density has a significantly higher value of around... 0 , 07 MPa kg / m 3 compared to,

[0061] State of the art, the maximum around the 0 , 035 MPa kg / m 3 lies. This is in Figure 8 shown.

[0062] Furthermore, according to the preferred embodiment of the present invention, the honeycomb exhibits excellent dielectric properties in addition to its mechanical properties, which can be attributed to the raw materials used here, such as cyanate ester and quartz glass. This is evident in the Figure 9 and 10 shown. The cyanate ester resin is a multifunctional resin system whose functional groups are adjusted accordingly to achieve the mechanical modulus / strength values ​​and dielectric values ​​described here.

[0063] As far as the type of fiber optic cable is concerned, quartz fiber optic cable offers the best conditions for achieving the lowest possible dielectric constant values.

[0064] The cyanate ester resin can be used alongside other resin systems, such as polyimide and even thermoplastics PE, PP, PEEK (and derivatives), fluorine-containing materials (such as ETFA, PTFE and similar) which also exhibit extremely low dielectric values ​​in the form of films or laminates.

[0065] Regarding the preferred embodiment of the present invention, the base component of the cyanate ester resin consists of a difunctional cyanic acid ester which, under the influence of temperature, cyclotrimerizes into a ring-shaped structure and forms a triazine ring. This reaction is initiated at a temperature of at least 165°C. Depending on the addition of catalysts, this temperature can be reduced considerably.

[0066] Crucial for good resin cross-linking is finding curing cycles that take place after each immersion of the honeycomb body.

[0067] Ultimately, it must be guaranteed that the resin is fully cured, no residual reactivity is present, and a temperature resistance of around 400°C is achieved.

[0068] Regarding reactivity, there is little experience in processing uncatalyzed or poorly catalyzed cyanate ester systems. The challenge lies in estimating the reaction rate and the temperatures required for the resin to fully cure.

[0069] Particularly good results were achieved by selecting suitable curing cycles as follows: Between each coating step, a lower curing temperature is used to partially cure the applied layer. This allows each new layer of resin to bond optimally to the partially cured layer below. This curing temperature is the lowest possible curing temperature for the resin. The temperature cycle to reach this reaction temperature can (but does not have to) be multi-stage, so that under optimal conditions the temperature is not reached in a single heating cycle. After the last coating step, a complete curing cycle is carried out in stages up to and above the desired temperature, at which the temperature resistance is ultimately required, in this case 400°C.

[0070] While the final temperature stage plays a crucial role in achieving this temperature resistance, it is the entire manufacturing process with its various curing cycles and intermediate stages that guarantees optimal cross-linking of the coating layers.

[0071] Furthermore, the solids content and the solvent (usually ketone-containing solvents such as acetone, MEK, ketone-butanone, cyclohexanone, diisopropyl ketone, and similar), as well as the application rate for each coating and the actual resin formulation, also play a crucial role in achieving this high temperature resistance. The solids content of the solution used here is between 20% and 70%, but preferably between 40% and 60%.

[0072] The addition of other chemicals, such as but not exclusively epoxy-containing components, for further functionalization and modification of the resin's property profile is also possible.

[0073] Further measurements, such as thermogravimetric analysis, have shown that, taking into account the previously described adapted resin formulation and the coating and curing process, a significant increase in temperature resistance was achieved.

[0074] According to the preferred version of the present invention, a significant change in the resin only takes place at a temperature of 400°C, compared to the prior art, where this change already takes place at 300°C.

[0075] Figure 11 shows a TGA (thermogravimetric) measurement for measuring temperature resistance.

[0076] Another aspect is that the test specimen does not produce outgassing products under the influence of extreme temperatures and vacuum conditions specified in the ECSS-Q-ST-70-02C test standard. The latter is particularly important in critical aerospace applications, as these outgassings can interfere with data transmission and the like.

[0077] The in Figure 12 The table shown summarizes the results achieved here.

[0078] Another important component of the present invention is to design an open-pored honeycomb body by optimally designing the ratio of resin to carrier.

[0079] The latter, however, also depends on the porosity structure (e.g., the weave style in the case of fabric) and on the flow and viscosity behavior of the matrix system during application and curing, so that a resin content of 5-60 wt.%, preferably 5-80 wt.%, is maintained. In the embodiment of the invention preferred here, the resin content is 10-20 wt.%, preferably 9-21 wt.%.

[0080] Using low-viscosity, low-viscosity matrix systems with a viscosity of 100 to 1000 mPas (Cps), air permeability and porosity can be achieved even with high matrix application rates. The latter is almost independent of the mesh size of the fabric, but depends solely on the viscosity and flow behavior of the resin and the application rate for each coating process. In the preferred embodiment of the present system...

[0081] The invention utilizes fabric structures with a porosity of 2-40% and a mesh size of 100-800 micrometers. Without further specifying the latter, a preferred variant relates to a porosity of 20-30% and a mesh size of 200-500 micrometers.

[0082] Figure 13 shows microscopic images of tissues with different porosity and mesh size.

[0083] With higher-viscosity matrix systems, this porosity and air permeability can be maintained even after coating, with matrix systems up to a viscosity of 3000 cps. The latter is then also dependent on the open porosity of the substrate material—in the case of fabrics, the mesh size—which can be defined, among other things, by its air permeability.

[0084] A fabric with a high porosity of 40% and / or a large mesh size of 300-800 micrometers (with large pores) can be coated with matrix systems that are in the higher viscosity range, i.e., around 3000 cps, without the pores completely closing after coating and curing.

[0085] Particularly in the case of high porosities, another preferred embodiment of the invention consists in partially impregnating the open-pored carrier, possibly the fabric, before honeycomb production in order to reduce the open porosity and to simplify further processing according to the expansion manufacturing process described here.

[0086] During pre-impregnation, the substrate or fabric, preferably with high porosity, is generally partially densified with a resin mixture in a weight ratio of 10-75 wt% to the pure substrate weight. A weight ratio of 40-60 wt% is preferred. This resin mixture can consist of resins based on a thermoset and / or thermoplastic matrix system, preferably from the cyanate ester or polyimide family, optionally also phenols, epoxides, benzoxazines, BMI, polyetherimides (PEI), polyetherketones (PEK, PEEK, PAEK, PEKK), polythioethers (PPS), polyethers (PP, PPO)), or from common thermoplastics such as PE, PP, PET, PA, PC, PMMA, or the like. In a particularly preferred embodiment, a cyanate ester is used as the resin.

[0087] These resin mixtures can consist of several of the matrix systems mentioned above, with the aim of obtaining an elastic resin bond that makes the fabric elastic and flexible even after pre-coating / impregnation and, if necessary, subsequent curing.

[0088] Furthermore, these resin mixtures can also contain solvents and additives. These additives can be elastomers to make the resin more flexible, or crosslinkers, hardeners, and / or catalysts to fully crosslink the resin and make it temperature-resistant. The latter is important in the production of the bonded stack—also called a press block—to prevent the actual bonding process from resulting in a partial bond only at the line-shaped knot adhesive, rather than full-surface bonding or interlocking between the individual layers. Such interlocking can render the expansion process impossible.

[0089] The flexibility of the carrier or, if applicable, the fabric, guarantees expansion of the block without the carrier tearing or requiring excessive expansion forces to separate the individual layers. Excessive expansion forces cause the individual layers to detach completely, as the knot adhesive is unable to withstand these forces and therefore detaches from the carrier material, either adhesively or cohesively, leading directly to the complete breakage of the honeycomb block.

[0090] Figure 14 shows another pictorial illustration of a porous honeycomb body that is not completely densely coated.

[0091] The present invention is not limited to honeycombs and core bodies in general that incorporate air permeability and / or porosity, but also relates to fully coated core bodies. The porous variant merely represents a separate form of the present invention, whereby a partially coated and porous variant ultimately represents the weaker variant from a mechanical point of view, but nevertheless achieves mechanical properties (here, in particular, compressive strength and pressure moduli) that exceed the prior art.

[0092] Another preferred feature of the present invention is to define a honeycomb body in more detail comprising a resin-impregnated or coated carrier, wherein the term resin is to be interpreted in a broader sense and essentially refers to thermosetting and thermoplastic polymer systems.

[0093] Within the scope of the present invention, the term "comprising" can also mean "consisting of".

[0094] The resin-impregnated carrier preferably forms the cell webs of the core or honeycomb body, wherein a key objective of the present invention is to construct a honeycomb body with thin-walled and lightweight cell webs, the latter being precisely determined by the basis weight of the coated carrier that forms the cell web of the core body or, in this case, the honeycomb.

[0095] In the case of a hexagonal cell geometry, which is one of the preferred embodiments of the present invention, the RG (density) of the honeycomb can be calculated from the FG (area density) of the resin support and the cell size as follows: RG Wabe = 4 / 3 * 2 / Zellgrösse * FG Träger + Harz

[0096] Other cell structures, cylindrical, overexpanded, and also the 3D structure of the honeycomb, are calculated in a similar way. Without going into further detail about the calculations, this formula for calculating the density of the honeycomb using the basis weight of the impregnated or coated substrate is applicable even with modified cell geometries with an accuracy of around 20-25%.

[0097] A fundamental objective of the present invention is to produce core bodies, e.g., in the form of honeycomb structures, with a density (RG = specific gravity) of 26-48 kg / m³ and a cell size of 1.6 to 9.6 mm. A key objective of the present invention is that these core bodies exhibit high mechanical properties relative to their specific gravity.

[0098] A pressure modulus to density of is essential. ≥ 4 , 5 MPa kg / m 3 , preferred ≥ 5 , 5 MPa kg / m 3 , especially preferred ≥ 5 , 8 MPa kg / m 3 , which is even particularly preferred 12 MPa kg / m 3 can be achieved. Furthermore, the ratio of compressive strength to density is also important. 0 , 03 MPa kg / m 3 until 0 , 047 MPa kg / m 3 preferred 0 , 06 MPa kg / m 3 that even particularly preferably 0 , 07 MPa kg / m 3 can be achieved. The fact that these high mechanical properties can also be achieved at a low density of < 26 kg / m³ is demonstrated by the Fig 15 .

[0099] This shows that within a measurement tolerance of 5%, which is experimentally permissible, a pressure modulus of 150 N can be achieved even with a low density of the honeycomb structure of < 26 kg / m³. Fig. 15 This area is marked by the circularly marked area of ​​the extrapolated values. Accordingly, the ratio of pressure modulus to density is then... 5 , 5 MPa kg / m 3 preferably 5 , 8 MPa kg / m 3 Even at this low density of 26kg / m³, it is still achievable.

[0100] Another preferred feature of the present invention is that these honeycomb bodies are preferably, but not necessarily, produced via an expansion process.

[0101] Preferred honeycomb body designs and cell sizes are listed below, with tolerances for cell size and density of the honeycomb typically being ±10%. The calculated basis weights for the impregnated honeycomb support are therefore within a tolerance range of approximately ±10 to 25%, preferably ±20%.

[0102] The upper area weight range of the impregnated carrier forming the honeycomb web is calculated from a honeycomb with the largest cell size and the highest density for this cell size of 40 kg / m 3< . For a honeycomb body with a cell size of 9.6mm and a density of 40 kg / m³, the impregnated carrier forming the webs of the honeycomb body has a basis weight of 144g / m².

[0103] The lower area weight range of the impregnated carrier, which forms the honeycomb web, is calculated from a honeycomb with the smallest cell size and the lowest density of 26 kg / m 3< . For a honeycomb body with a cell size of 1.6mm and a density of 26 kg / m³, the impregnated carrier forming the webs of the honeycomb body has a basis weight of 15.6g / m².

[0104] The following examples are further embodiments of the present invention, depending on cell size and honeycomb density, which are preferably considered. For a honeycomb structure with a cell size of 9.6 mm and a density of 26 to 40 kg / m³, the impregnated carrier preferably has an areal weight of 144 to 94 g / m².

[0105] For a honeycomb structure with a cell size of 9.6 mm and a density of 40 kg / m³, the impregnated carrier preferably has a basis weight of 144 g / m².

[0106] For a honeycomb body with a cell size of 9.6 mm and a density of 32 kg / m³ <

[0107] The impregnated carrier preferably has a basis weight of 115 g / m².

[0108] For a honeycomb structure with a cell size of 9.6 mm and a density of 26 kg / m³, the impregnated substrate preferably has a basis weight of 94 g / m².

[0109] For a honeycomb structure with a cell size of 6.4 mm and a density of 26 to 48 kg / m³, the impregnated substrate preferably has a basis weight of 115 to 62 g / m².

[0110] For a honeycomb structure with a cell size of 6.4 mm and a density of 48 kg / m³, the impregnated carrier preferably has a basis weight of 115 g / m².

[0111] For a honeycomb structure with a cell size of 6.4 mm and a density of 40 kg / m³, the impregnated substrate preferably has a basis weight of 96 g / m².

[0112] For a honeycomb structure with a cell size of 6.4 mm and a density of 32 kg / m³, the impregnated substrate preferably has a basis weight of 77 g / m².

[0113] For a honeycomb structure with a cell size of 6.4 mm and a density of 26 kg / m³, the impregnated substrate preferably has a basis weight of 62 g / m².

[0114] For a honeycomb structure with a cell size of 4.8 mm and a density of 26 to 48 kg / m³, the impregnated substrate preferably has a basis weight of 86 to 47 g / m².

[0115] For a honeycomb structure with a cell size of 4.8 mm and a density of 48 kg / m³, the impregnated substrate preferably has a basis weight of 86 g / m².

[0116] For a honeycomb structure with a cell size of 4.8 mm and a density of 40 kg / m³, the impregnated substrate preferably has a basis weight of 72 g / m².

[0117] For a honeycomb structure with a cell size of 4.8 mm and a density of 32 kg / m³, the impregnated substrate preferably has a basis weight of 57 g / m².

[0118] For a honeycomb structure with a cell size of 4.8 mm and a density of 26 kg / m³, the impregnated substrate preferably has a basis weight of 47 g / m².

[0119] For a honeycomb structure with a cell size of 3.2 mm and a density of 26-48 kg / m³, the impregnated substrate preferably has a basis weight of 57 to 31 g / m².

[0120] For a honeycomb structure with a cell size of 3.2 mm and a density of 48 kg / m³, the impregnated substrate preferably has a basis weight of 57 g / m².

[0121] For a honeycomb structure with a cell size of 3.2 mm and a density of 40 kg / m³, the impregnated substrate preferably has a basis weight of 48 g / m².

[0122] For a honeycomb structure with a cell size of 3.2 mm and a density of 32 kg / m³, the impregnated substrate preferably has a basis weight of 38 g / m².

[0123] For a honeycomb structure with a cell size of 3.2 mm and a density of 26 kg / m³, the impregnated substrate preferably has a basis weight of 31 g / m².

[0124] For a honeycomb structure with a cell size of 1.6 mm and a density of 26 to 48 kg / m³, the impregnated substrate preferably has a basis weight of 29 to 15 g / m².

[0125] For a honeycomb structure with a cell size of 1.6 mm and a density of 48 kg / m³, the impregnated substrate preferably has a basis weight of 29 g / m².

[0126] For a honeycomb structure with a cell size of 1.6 mm and a density of 40 kg / m³, the impregnated substrate preferably has a basis weight of 24 g / m².

[0127] For a honeycomb structure with a cell size of 1.6 mm and a density of 32 kg / m³, the impregnated substrate preferably has a basis weight of 19 g / m².

[0128] For a honeycomb structure with a cell size of 1.6 mm and a density of 26 kg / m³, the impregnated substrate preferably has a basis weight of 15.6 g / m².

[0129] Fig 16 shows a graphic representation of these previously mentioned forms of execution, in which the basis weight of the coated substrate in the honeycomb is listed, in relation to the honeycomb type with indication of the cell size and the density

[0130] The basis weight of the unimpregnated substrate (raw weight of the substrate) that forms the honeycomb webs and is used as the starting material according to the present invention depends on the weight fraction of the coating on the substrate.

[0131] This weight fraction of the coating, often also referred to as the resin content, is preferably between 5-60 wt.%, particularly preferably between 5-80 wt.%.

[0132] Without limiting the scope of the present invention, in a preferred embodiment of the present invention, the carrier has a raw weight of 60 to 70g / m² for a honeycomb with a cell size of 6.4mm and a density of 32 kg / m³.

[0133] The resin content – ​​the weight percentage of resin on the substrate – can be calculated as follows: Raw bulk density of the block on uncoated / raw substrate according to the formula above: 4 / 3*2 / 6.4*60 to 4 / 3*2 / 6.4*70 = 25 to 29 kg / m³.

[0134] The density of the block after impregnation with the coated substrate is 32 kg / m³.

[0135] From this data, the resin weight in the block (without substrate) is calculated as follows: 32-25 to 32-29 = 3 to 7 kg / m 3< , and the resin content in the block relative to the weight of the coated substrate is then between 3 / 32 to 7 / 32 = 9 to 21 wt%.

[0136] According to the specified basis weight of the impregnated substrate of 16 to 144 g / m² and a resin content of 5 wt.% to 80 wt.%, the raw uncoated substrate as starting material can have a weight range between 3 g / m² and 137 g / m², and the density of the block is also within a tolerance range of ±20%.

[0137] Explanation of abbreviations and technical terms: Cell mass, cell width, and cell size have the same meaning. Compressive strength and compressive strength have the same meaning. Compression modulus and bulk modulus have the same meaning. A stack or stacked honeycomb block produced after the layering process is also called a press block after the gluing process. FG stands for basis weight. RG stands for density.

Claims

1. Core body, wherein the following condition a) is fulfilled: a) it has a density of ≤ approximately 48, in particular ≤ approximately 40, more preferably ≤ approximately 32 kg / m3 and most preferably ≤ 26 kg / m3; and wherein condition b) is fulfilled: b) it has a ratio of compression modulus to density of ≥ approximately 4.5 MPa kg / m 3 , preferably ≥ 5.5 MPa kg / m 3 , particularly preferably ≥ 5.8 MPa kg / m 3 ;2. Core body according to claim 1, characterised in that the core body has a cell size of ≤ approximately 9.6 mm, in particular ≤ 6.4 mm and preferably ≤ 4.8 mm and particularly preferably ≤ 3.2 mm and most particularly preferably ≤ 1.6 mm.

3. Core body according to at least one of the preceding claims, characterised in that the core body is a honeycomb body, wherein the honeycomb body has a polygonal, preferably hexagonal, rectangular, or circular cell geometry.

4. Core body according to at least one of the preceding claims, characterised in that the core body is made of glass (E, S2) fibre, carbon fibre, Kevlar fibre, basalt fibre, preferably quartz glass fibre, or hybrid constructions of these fibres.

5. Core body according to at least one of the preceding claims, characterised in that the core body is a quartz glass fibre-plastic composite.

6. Core body according to at least one of the preceding claims, characterised in that the core body is made of a plastic comprising a thermosetting or thermoplastic matrix, preferably from the family of cyanate esters or polyimides, possibly also phenols, epoxides, benzoxazines, BMI, polyetherimides (PEI), polyetherketones (PEK, PEEK, PAEK, PEKK), polythioethers (PPS), and polyethers (PP, PPO).

7. Core body according to at least one of the preceding claims, characterised in that the core body is a composite consisting of fibres and / or other carrier or filler materials and a plastic comprising a thermosetting or thermoplastic matrix, preferably from the family of cyanate esters or polyimides, or possibly also phenols, epoxides, benzoxazines, BMI, polyetherimides (PEI), polyetherketones (PEK, PEEK, PAEK, PEKK), polythioethers (PPS), and polyethers (PP, PPO).

8. Core body according to at least one of the preceding claims, characterised in that the core body is made of a fabric and / or a fleece-like structure.

9. Core body according to claim 8, characterised in that the fabric is not completely impregnated and / or coated and ensures air permeability via the open-pored cell walls between the cells.

10. Core body according to at least one of the preceding claims, characterised in that the core body has a high temperature resistance of over 350°C.

11. Core body according to at least one of the preceding claims, characterised in that the core body has excellent dielectric properties with a dielectric constant ≤ 1.1, in particular ≤ 1.0, and a loss factor (Loss Tangent) of < 0.003, in particular < 0.002.

12. Core body according to at least one of the preceding claims, characterised in that the core body has a ratio of compressive strength to density of ≥ approximately 0.04 MPa kg / m 3 preferably ≥ 0.06 MPa kg / m 3 .

13. Method for producing a core body from an open-pored carrier material, wherein the carrier material is a fabric and / or a fleece-like structure i) A material web made of a carrier material is provided with adhesive strips in regular patterns by means of an application device; ii) stacks of sections of the material web are formed, which lie on top of each other in such a way that they are offset relative to each other with respect to the strip patterns, iia) that the strips of a lower section are each arranged between the strips of the respective upper section; or iib) that the strips of a lower section are offset but not centred between the strips of the respective upper section; iii) overlapping sections in the areas of the strips are glued together; iv) the stack is expanded, wherein a honeycomb shape of any polygonal structure is formed, in particular a honeycomb shape with hexagonal, rectangular or circular cell geometry for the production of hexagonal, overexpanded, rectangular and 3D honeycomb cores; v) the honeycomb shape is impregnated and / or coated with a synthetic resin, wherein the carrier in the form of the honeycomb body is not completely impregnated and / or coated with resin and air permeability is ensured via the open-pored cell walls between the cells; vi) the honeycomb shape coated with the synthetic resin is subjected to a curing step to cure the synthetic resin; vii) the honeycomb shape thus formed is cut to form honeycomb bodies.

14. Method according to claim 13, characterised in that the open-pored carrier preferably, but not exclusively, consists of glass (E, S2, quartz) fibre, carbon fibre, Kevlar fibre, basalt fibre or hybrid fabrics of these fibres.

15. Method according to claim 14, characterised in that the carrier is partially pre-impregnated or coated with a resin to reduce the porosity prior to the expansion process, wherein after coating the porosity is less than 40% and the coating is in a weight ratio of 10-75% to the weight of the carrier, and the coated carrier is temperature-stable at 160-250°C after coating and, if necessary, curing, and is designed to be flexible in order to implement the reshaping of these pre-impregnated layers during the expansion process with low expansion forces.

16. Method according to one of claims 13 to 15, characterised in that the used adhesive is a thermosetting plastic, thermoplastic or elastomer, preferably but not exclusively a phenolic, epoxy, polyimide or cyanate ester adhesive.

17. Method according to at least one of claims 13 to 16, characterised in that, after the expansion step iv), the honeycomb shape is stabilised by thermal treatment.

18. Method according to at least one of claims 13 to 17, characterised in that a thermosetting or thermoplastic matrix system is used as a resin, preferably from the family of cyanate esters or polyimides, or possibly also phenols, epoxides, benzoxazines, BMI, polyetherimides (PEI), polyetherketones (PEK, PEEK, PAEK, PEKK), polythioethers (PPS) and polyethers (PP, PPO).

19. Method according to at least one of claims 13 to 18, characterised in that steps v) and vi) are repeated once or several times in order to apply one or more further layers of the synthetic resin.

20. Core body according to claim 1, manufactured according to the method according to at least one of claims 13 to 19.

21. Core body according to claim 20, characterised in that the open-pored carrier is not completely impregnated and / or coated and ensures air permeability via the open-pored cell walls between the cells.

22. Core body according to claims 20 and 21, characterised in that the core body has excellent dielectric properties with a dielectric constant ≤ 1.1, in particular ≤ 1.0, and a loss tangent of < 0.003, in particular < 0.002.

23. Core body according to claims 20 to 22, characterised in that the core body has a ratio of compression modulus to density of ≥ approximately 5.5 MPa kg / m 3 , preferably ≥ approximately 5.8 MPa kg / m 3 .