WO2004056912A1

WO2004056912A1 - Core or support element

Info

Publication number: WO2004056912A1
Application number: PCT/AT2003/000384
Authority: WO
Inventors: Hugo Lenhard-Backhaus; Josef Hrovath
Original assignee: Hugo Lenhard-Backhaus; Josef Hrovath
Priority date: 2002-12-23
Filing date: 2003-12-23
Publication date: 2004-07-08
Also published as: AU2003294511A1

Abstract

The invention relates to a core made of at least one mixture that comprises several components, at least one component representing particles, preferably at least essentially in the form of beads, while another component represents a resin system which is common for cores. Said core is characterized by the fact that the particles are made of foamed polystyrol and/or swollen corn and/or swollen wheat. Reinforcement fibers can be added to the resin system.

Description

Core or support element

The invention relates to a so-called core, also called a support element, which consists of at least one mixture comprising several constituents, at least one constituent of the mixture being low-density particles, possibly at least approximately in the form of spheres, and a further constituent one for cores Common resin system, optionally in a foamed state.

Such cores are used in technology in a variety of forms and configurations, if necessary, an object, for example a ski, a snowboard, a support, a plate, a component of an aircraft or ship, a structural element of a building, or the like. to give high strength and / or desired dynamic properties, and this is achieved by arranging special materials on the surface (or at least parts of the surface) of the body and a core inside the body, which usually corresponds to that on the Surface arranged materials is fixed, or flat, connected.

Examples of such cores are as follows:

DE 200 13 721 U discloses a sandwich-like supporting element, the shell of which is made of glass fiber reinforced plastic (GRP) and the core of which consists of a synthetic resin and mixed spheres, which may consist of expanded clay.

DE 28 56 717 A discloses a panel made of phenolic resin, which is arranged around a core. The core has balls or microspheres made of glass or expanded clay.

DE 39 07 521 A discloses a method for producing a lightweight building board, in which the outer sides are used as lost formwork and the core contains balls made of expanded glass, expanded clay, pumice granules, mica etc. in a matrix made of foamed resin.

DE 23 34 184 A discloses a band or plate-shaped Nerbundmaterial made of synthetic resin, the core of which contains mineral fillers, glass and plastic fibers in a matrix of resin. DE 38 41 007 A discloses a particle board in which polystyrene from waste in molten form is used as a binder for the wood chips. In the finished plate, the polystyrene is unfoamed in thin layers as a kind of adhesive.

DE 37 15 487 A and, regardless of this, US Pat. No. 5,846,357 A, each disclose a method for producing components whose core consists of expanded clay particles in an epoxy resin. If necessary, tearing wool can be added, the epoxy resin can be foamed in a heated area between two pressure stamps during the production of the component.

FR 2 828 110 A discloses the core of a sports device such as skis or snowboards, which has cork granules in a matrix of epoxy resin.

The materials on the surface of such a multi-layer structure are usually one or more layers of fiber-reinforced plastics, in particularly stressed cases it is carbon fibers that are wound directly around the core and connected to it by their filler, usually a resin system, whereby Usually several layers of such fiber-reinforced layers are applied. If the fibers in the individual layers are not stoichastic, but are ordered (for example, parallel to each other), the individual layers are usually applied in such a way that the fiber directions change from layer to layer at least differently, by the forces that are expected on the finished body act, be transferred and recorded as best as possible.

Since the transmission of these forces in the outer layers provided for this purpose is only possible if it is ensured that their specified geometry is retained even under load, the core must be resistant to pressure and shear forces in particular, while otherwise only required of it, if possible to be light, ie to have the lowest possible density and, at least in most cases, to dampen vibrations that occur. Of course, due to its chemical composition, it must be able to withstand the anticipated conditions of use (temperature, aggressive media, etc.) and must also be resistant to aging within the foreseeable future. For this reason, previous cores have been made in the prior art in addition to the materials mentioned at the outset from a wide variety of other materials that achieve these goals as far as possible, starting with wooden cores, but above all with cores made of different resins (alone), in corresponding shapes be potted and that can be easily and extremely reliably and strongly connected or connected with the casing materials. Despite the general usability of known cores, it is a constant concern to improve them and, in particular, to further reduce their density. This is also the aim of the invention.

According to the invention, this aim is achieved in that the low-density particles are foamed polystyrene particles, popped corn or popped grain. These are particularly light, combine excellently with the resin systems customary for the production of cores and are also inexpensive to obtain. For the purposes of the invention, grain is understood to mean cereal grains including rice.

It has been shown that such particles made of foamed polystyrene, popped (expanded) corn or grain in a matrix, which at least partially consists of a conventional resin system, give the core not only the low density known and expected from foamed polystyrene, but also Surprisingly also a compressive strength, bending strength, toughness and particularly vibration-damping properties (important among other things for skis, snowboards, etc.), which are extremely desirable for a core.

The resin system can be any of the resin systems hitherto used for cores, the only requirement being that it can be cast at temperatures at which the particles used do not melt and that it contains no constituents or forms during solidification, which the polystyrene or attack the particles chemically. Particularly suitable are, for example, solvent-free two-component adhesives based on polyurethane, such as: UK812 (yUK5400 in a weight ratio of 100/60 or UK8103 / UK5400 in a weight ratio of 5/1. In a variant of the invention, it is provided to add other particles with low density, such as cork crumbs or expanded clay, or air-filled or gas-filled glass or plastic beads (microspheres) to the particles made of foamed polystyrene. For this purpose, the particles only have to be closed-pore to such an extent that the resin does not penetrate them or does not penetrate them to a noticeable extent, have a low density and, optionally after a surface treatment, deal with the resin system with which they are cast. connect without being attacked by him. Depending on the material used, different, but always unexpectedly good mechanical properties of the respective cores are achieved.

It is completely surprising for a person skilled in the art in the production of the cores that such structures, such as polystyrene particles, which are not mechanically strong enough on their own, or other above-mentioned or similar particles with a diameter of up to a few millimeters (depending on the size of the finished core, the larger it is, the larger the individual particles can also be), after being embedded in a conventional resin system, have strengths that are at least equal to those of conventional cores, which consist of only one resin system, but with better notch have impact strength values and, above all, are orders of magnitude lighter than cores from the prior art.

In a variant, which is generally favorable when used at high temperatures and when the finished structure is used in areas where there is a risk of fire, such as airplanes, ships, mass transportation or the like, the use of polystyrene particles, the surface of which is glazed by thermal treatment. Such particles are known per se or from lightweight concrete, for example from AT 401 774 B. The content of this document is incorporated into the present application by reference. The treatment consists of brief heating to surface temperatures between 300 ° C and 800 ° C and subsequent cooling by cold air or water. The surface becomes brittle and becomes glassy, making it highly fire-retardant. Cores with particles treated in this way are still extremely light, mechanically extremely strong and surprisingly fire-retardant, despite the surface areas of the particles becoming denser when glazed. ben of the glazed surface of the individual particles contributes to poor heat conduction, which protects the areas inside the core.

In this case, for example, the phenolic resin or epoxy resin with a so-called H-type solvent (90% ethanol and 10% acetone) or an HE-type solvent (pure ethanol) can be used as resin systems. Phenolic resin also has the advantage of being flame retardant.

In another embodiment of the invention, short (a few millimeters to a few centimeters long) fibers are added to the resin system for mechanical reinforcement. These fibers further increase the bending stiffness and the tensile and compressive strength of the core thus constructed. The fibers include, for example, glass fibers, carbon fibers, Kevlar fibers, cellulose fibers and the like. in question.

In one embodiment of the invention it is provided that the cores are first produced as a semi-finished product, as a so-called prepreg (derived from “preimpregnated”), and in this form to be encased, as is described, for example, in AT 400 954 B for fabrics or scrims. The content of this document is incorporated into the present application by reference.

Because of the porous structure of the particles used according to the invention, it is possible and preferred to keep the core under increased pressure during the curing of the resin system. This results in the deformation of the polystyrene particles or the particles of popped corn or grain from approximately spherical to approximately octahedral, and thereby further mechanical solidification of the finished core, which is much higher than the density increased somewhat by pressing. The reaction of the particles, which are already in the foamed (expanded) state when the pressure on them is increased, is completely different from the foaming under increased pressure, in the latter case there is no formation of such deformed particles. The pressure to be used in this case can easily be found by the person skilled in the art with knowledge of the invention in a few experiments, pressures between 1, 2 and 5 bar are suitable in most cases. Particularly when using polystyrene particles, it is possible to use lattices instead of discrete particles, in which spherical structures are connected to their neighboring spheres by narrow bridges. In this way, an orderly and directional structure is obtained which can be adapted in a suitable manner to the load directions to be expected. In particular, the orderly insertion of the particles is facilitated if the "bridges" break easily and contribute less to the properties of the finished core than this order.

These grids can be produced by foaming the polystyrene in appropriate forms. It is also possible, by inserting threads into the molds in which the polystyrene is foamed, to obtain "crosslinked" polystyrene particles which, however, are freely movable with respect to one another within predetermined limits through the use of threads.

In this way it is possible, in particular to equip surface areas of cores with “ordered” particles and thus to achieve excellent properties, in particular when forces are introduced into the core. This possibility exists for all particles which are produced or are assembled and thus allow the creation of thin connections or the integration of threads.

It is also possible to introduce particles of different sizes, whether made of polystyrene or not, whether coherent or not, in layers into the corresponding shape and thus, for example, to essentially fill the gaps between the large balls with small balls. Combinations of these configurations and combinations of different materials are of course also possible and can be easily selected by a person skilled in the art in the field of the production of composite materials with knowledge of the invention.

Instead of the previously known, homogeneous cores made of one material or with hard, practically “rigid” particles, it is thus possible by means of the invention to produce cores by using particles of low density and predetermined elasticity in connection with a conventional resin system much lighter and yet as firm but not as brittle as cores of the prior art. The mechanical properties obtained, in particular the damping properties against vibrations and the fire resistance, can be predetermined within wide limits by the choice of the particles or their surface treatment, but also by the combination of different or different sized particles.

The possibility of using “crosslinked” particles or the combination of particles of different sizes, which are not completely random, makes it possible to achieve special mechanical properties with a further reduced density.

By introducing fibers into the resin system, the tensile, compressive and flexural and flexural fatigue strengths can be significantly improved without any noticeable influence on the density.

By casting at elevated pressure, excess resin is pressed out on the one hand, and on the other hand, the mechanical properties of the finished core are further improved by the deformation of the particles or the particle surfaces, which leads to a kind of honeycomb structure on average.

As explained in the description, it is possible to combine these individual configurations in a wide range or to further develop them, which no problem for the person skilled in the field of composite materials knowing the invention.

Claims

claims:

1. Core which consists of at least one mixture comprising several constituents, at least one constituent being particles, preferably at least essentially in the form of spheres, and another constituent being a resin system which is customary for cores, characterized in that the particles consist of foamed polystyrene and / or expanded corn and / or expanded grain.

2. Core according to claim 1, characterized in that the particles are polystyrene particles which have a glassy surface by heat treatment.

3. Core according to one of claims 1 or 2, characterized in that the resin system contains fibers.

4. Core according to claim 3, characterized in that the fibers are glass fibers and / or carbon fibers and / or Kevlar fibers and / or cellulose fibers.

5. Core according to one of claims 1 to 3, characterized in that at least some of the particles are connected to one another by means of a grid or by means of threads.

6. A method for producing a core according to one of the preceding claims, wherein the particles are introduced into a mold and then cast with the resin, which may contain fibers, characterized in that the casting and / or curing of the resin under increased pressure, preferably between 1.2 and 5 bar.

7. The method according to claim 7 or 8, characterized in that particles of different sizes are used.

8. The method according to any one of the preceding claims, characterized in that the particles are placed in an orderly manner in the mold, edge regions of the core having a disproportionate number of smaller particles and the interior of the core having a disproportionate number of larger particles.