NL9200781A - SANDWICH MATERIAL. - Google Patents

Description

Title: Sandwich material

The invention relates to a method for modifying a plate-shaped sandwich material comprising a core material placed between two top layers.

Plate materials, such as sandwich structures, are widely used for those applications where high strength or stiffness is required, combined with low weight. This is the case, for example, in aviation, aerospace and transport applications.

Sandwich constructions generally consist of a core material that is lightweight, with a generally reinforced top layer on both surfaces. Due to the good adhesion between the top layers and the core material, the good stiffness is obtained. The other properties of the material are partly determined by the nature of the various materials.

Well-known sandwich constructions are based on a core material with a honeycomb structure. Another type of sandwich material is described in European Patent Applications 264,495 and 269,148, the contents of which are incorporated by reference herein. This material is fully thermoplastic and consists of a core material that includes a thermoplastic foam and two top layers consisting of a fiber-reinforced plastic such as polycarbonate or polyetherimide.

U.S. Patent 4,889,763 discloses a flame retardant sheet material which is also thermoplastic.

European Patent Application No. 345,855 relates to a non-foamed foil that can be used for the manufacture of a thermoplastic sandwich material.

When using a sandwich construction it may sometimes be desirable for local reinforcements to be applied in the material, sandwich constructions usually have the form of a plate, for instance a wall panel, to which various objects have to be attached. Because this locally can involve quite large forces, it is necessary to apply local reinforcement to enable the attachment of objects, such as aids.

European patent application 383.409 describes a method for applying reinforcements in a, preferably thermoplastic, core of a sandwich material by injecting an amount of plastic material through one of the top layers under pressure into the core material, which hardens after injection. . The 2nd method gives good possibilities for applying aids, such as fasteners, brackets, lamp holders and the like.

Although this method provides a significant improvement over the known methods, it has been found that it is still possible to improve the properties of the final material by performing the application of the article in a specific manner.

The invention therefore relates to a method for modifying a plate-shaped sandwich material comprising a core material arranged between two top layers, wherein an amount of thermoplastic material is injected through one of the top layers under pressure into the core material, an object is placed in the still plastic material, after which the plastic material hardens.

Surprisingly, it has been found that with the method according to the invention a sandwich material is obtained which has a very good adhesion between the sandwich material and the applied modification.

The modification of the sandwich material can take place in various ways. A first possibility is the provision of a reinforcement in which an object is fixedly fixed in the manner according to the invention. Due to the specific method, a very good adhesion is obtained, even when an object with an unusual shape is applied. With the known method, in which the reinforcement is first applied and then an aid is placed after curing, it is not possible or practically impossible to apply such articles.

A second variant of the method according to the invention is the application of an object, which is subsequently removed during or after curing. The removal must then take place after the thermoplastic material has become sufficiently dimensionally stable. This method produces a modification consisting of a reinforcement which is very well adhered in the sandwich material and which is provided with an opening, for example through the material or only through part of the material.

It is also possible to screw in the modification with this method. According to the invention, an object is provided which is provided with a screw thread on the outside. After the plastic hardens, the object is turned out of the modification.

In the embodiment in which the article is removed from the modification, it is possible to provide the article with a release agent, for example a silicone compound, before insertion.

A great advantage of the invention is also that it is possible to repair an attachment once fitted by removing the applied object and installing an oversized new part.

In carrying out the method, it is preferable that the article at the time of application in the plastic material has a temperature lower than the temperature of the plastic material of the reinforcement. It has been found that in such a case an optimal adhesion of the object in the core is obtained. If this temperature is equal to or higher than the temperature of the plastic material, less, but not bad adhesion is obtained. More particularly, the article has a temperature not higher than 75 ° C and most preferably not higher than 35 ° C.

Of course, the material of the reinforcement should not yet be hardened when the object is placed in the core. The temperature of the plastic material should be above its softening point, it should be noted that it is preferable, for considerations of applicability under more or less extreme temperature conditions, to use a thermoplastic plastic with a softening temperature of at least 50 ° C while preferably above 75 ° C (HDT, according to ASTM D 648-56).

At least two steps are used in the implementation of the method according to the invention. In the first step, the plastic material is pressed into the core under pressure. Injection can take place directly through the top layer, provided that the top layer is suitable for this. Otherwise, an opening must first be made in the top layer. This may in particular be necessary if one or both top layers are made of metal or another material which is difficult to penetrate.

During the injection, the plastic material displaces and / or fuses the core material at the location of the injection. In case the core. of the sandwicb material consists of a thermoplastic material, for example a thermoplastic plastic foam or a thermoplastic honeycomb material, fusion mainly occurs, as is described in European patent application 383.409. If the core material is not thermoplastic, it is displaced by the injected material. From the viewpoint of adhesion and material properties, it is preferable to use a thermoplastic core material.

Preferably, the amount of the material to be injected and its temperature is adjusted so that a portion of the core material, more particularly the foam, melts away at the injection site.

Then, while the material is still plastic, i.e. when it is still hot enough to flow under pressure, the object is introduced into the plastic material. The plastic material flows around the object and hardens almost immediately due to the lower temperature and heat absorption of the object. According to the invention it surprisingly appears that the pressure build-up in the plastic material causes considerably less shrinkage, especially when the object is applied when the thermoplastic material is already hardening on the outside of the modification.

As a plastic material, a thermoplastic plastic or mixture of thermoplastic plastics is preferably used with a softening temperature of at least 50 ° C. Such plastics may be selected from, among others, the group consisting of polystyrene, styrene polymers, acrylate and / or methacrylate polymers, polyolefins, polyesters, such as PET and PBT, polycarbonate, polyetherimide, polyamide, polysulfone, polyether sulfone, polyether ketone, polyether ether ketone, polyether ketone ketone, polyphenylene oxide, polyphenylene sulfide and mixtures of two or more of these plastics. Not only do such materials have the advantage that they can be injected into the core with ease, but they also contribute to improving the compressive strength of the sheet material.

These plastics can optionally contain an amount of fiber, which is also injected. The fibers are preferably selected from the group consisting of glass fibers, polyamide fibers, such as aramid fibers, polyethylene fibers, polyester fibers and carbon fibers.

It is also possible to include an amount of blowing agent in the plastic to be injected, which blowing agent forms a foam of the injected plastic during and after the injection. Of course, it is then desirable that the amount of foaming agent be such that the density of the modification is greater than the density of the surrounding core material, or that the compressive strength of the foam formed is greater than the compressive strength of the core of the sheet-like sandwich material.

It is noted that it is also possible to inject two plastic materials at the same time or in succession, such as in particular injection of two different materials, such that one material forms the core of the injection and the other material forms a kind of skin around it. there. This can be achieved both by simultaneous injection of two or more materials and by consecutive injection of the two or more materials. When applying the object, the desired construction of the reinforcement must be taken into account.

The sandwich material to be modified can be constructed in various ways. generally the material consists of a core and two top layers. The core can also be built up again from a number of layers, for example reinforcement layers and filling layers.

The core may consist of any suitable core material, such as a thermoplastic or non-thermoplastic foam, a thermoplastic or non-thermoplastic honeycomb material, or other suitable material.

Different materials can be used as top layers. Examples are metal plates, for example aluminum, fiber-reinforced plastics and natural materials, such as wood.

The sandwich construction preferably consists of a thermoplastic, foam-like core material and two top layers, which consist of a thermoplastic plastic reinforced with a fabric, a knit, a non-woven fiber or unidirectionally applied fibers. Such a material is described, inter alia, in European patent applications nos. 264 495 and 269 148 mentioned in the introduction.

The materials from which the preferred sandwich material can be made are also described in the aforementioned European patent applications. More specifically, the thermoplastic foam core material is a polyetherimide foam, a polycarbonate foam, a polymethacrylamide foam, a polyester foam such as a PET or PBT foam, a polyether sulfone foam, a polyether ketone foam, a polyether ether ketone foam, a polyether ketone ketone foam , a polyphenylene oxide foam, a polyphenylene sulfide foam, or foam materials made from mixtures of thermoplastic plastics in which at least one of the said thermoplastic plastics is present. It is also possible to use a combination of two or more foams as the core material.

Optionally, fibers can also be added to the foam material. Such fibers may be selected from the group consisting of glass fibers, polyamide fibers, such as aramid fibers, polyethylene fibers, polyester fibers, carbon fibers, and combination of two or more of these fibers.

Also, to improve the mechanical properties of the material, it may be preferable to include liquid crystalline materials in the foam. Especially when the foam is generated in situ during the manufacture of the sandwich material, the use of such materials appears to yield good results.

When using said foam materials, in combination with the thermoplastic plastics for the top layer and the reinforcement mentioned below, an optimum construction of the reinforcement and a maximum strength of the total construction and of the reinforcement points are obtained.

The top layers preferably consist of fiber-reinforced plastic, more in particular of a thermoplastic plastic which is reinforced with a fabric, a knit, a non-woven fiber or unidirectionally applied fibers.

The thermoplastic plastic, the matrix material of the top layers, is generally a plastic or a mixture of plastics with a high softening point, for example polyester, such as PET and PBT, polycarbonate, polyetherimide, polyamide, polysulfone, polyether sulfone, polyether ketone, polyether ether ketone , polyether ketone ketone, polyphenylene oxide, polyphenylene sulfide or a mixture of two or more of these plastics. It is also possible to use two or more different top layers or materials for the top layers.

in the top layer, these plastics are preferably reinforced with glass fibers, polyamide fibers, such as aramid fibers, polyethylene fibers, polyester fibers and carbon fibers. The nature of the fiber reinforcement in the top layer has virtually no influence on the conditions for injecting the thermoplastic plastic into the core, but the degree of reinforcement can influence this. The closer the fiber reinforcement is in the skin, the more pressure will have to be applied to inject through the top layer. However, these pressure variations are always within the usual injection molding pressures. At very high densities of the fibers in the skin, it may in some cases be desirable or advantageous to pre-drill a small hole in the skin,:, ····;

The sandwich construction can be manufactured by bringing the components, core material and top layers to be used together, optionally with adhesive layers between them, whether or not using softening agents, and then adhering the layers together using heat and pressure.

When using a foam-like core material, it is also possible to generate the material in situ, by using a latent foamable material, which foams under heating and / or pressure relief and adheres to the top layers. An example of such a latent foamable material is described in European patent application 345,855, the contents of which are incorporated herein by reference. It is possible to use this material for the core material as well as for an additional adhesive layer. It is also possible to use the known theme-hardening foam materials.

The first step of the method according to the invention is very simple to perform using existing equipment. Namely, when an injection molding machine is used, it is only necessary to place its nozzle in the place to be reinforced and to inject a measured dose of molten thermoplastic plastic.

The object, for example a fastening aid, a part or a product is then applied by hand or by machine. By the choice of materials, one can ensure that good adhesion is obtained between the article and the rest of the core material. In particular, the adhesion to the top layers can leave much to be desired in the known methods for reinforcing sandwich structures.

The usual injection molding machines can be used for the process. If necessary, an adjustment can be made to bring the nozzle to the correct location for the injection. However, it is also possible to use modified equipment, for example injection molding machines, which allow injection of the plastic material directly into the core material. For this purpose, use can for instance be made of a device which is provided with a kind of 'needle-shaped' injection nozzle, which is introduced into the core through the top layer. It is also possible to use nozzles provided with more than one outflow opening, so that more than one plastic material can be used.

When using relatively high injection pressures, it may be desirable to support the plate material at the back, i.e., the side where no injection takes place, to prevent the plastic material from being sprayed through the plate.

It is also possible to inject the thermoplastic plastic from two sides of the sandwich material, for example simultaneously or in rapid succession.

The thermoplastic plastic is dosed depending on the nature of the material, the desired reinforcement in the core and the thickness of the sandwich construction. However, it has been found that the amount is not very critical. For a sandwich construction with a thickness of 8 mm, a dose of 0.5-20 ml of plastic material can be used. Good local reinforcement is then obtained.

According to the invention, modified sandwich materials suitable for various applications are obtained. This includes in particular all kinds of objects that can be used in the aerospace industry. examples are wall panels of aircraft, parts of aircraft seats, parts of trolleys and the like.

The objects to be applied can differ greatly from each other. In the first place, inserts can be applied, such as threaded bushes or other anchoring points. Removable or non-removable moldings can also be applied. These moldings can be applied on the same side from which the injection took place. It is also possible to mount the object from the side.

The object can also be an aid on which a product can be injection molded. This can be done on the top, but also on the side or at the bottom.

The method according to the invention is applicable to flat plate-shaped materials, but also to plate-shaped objects already formed. It is also important here that the reinforcement and the object generally have no influence on the further processability and deformability of the plate-shaped material. This is of great importance for the thermoplastic sandwich constructions of the aforementioned European patent applications, the great advantage of which is that they remain thermoplastic continuously. The manufacturing and processing methods described in the European patent applications mentioned in the introduction can be applied without problems to the materials according to the invention, both before and after the application of the object.

Examples of objects to be applied are, for example, screw bushings, hinges, hinge points, and the like.

The invention is now elucidated by means of an example, but is not limited thereto.

example

A sandwich sheet consisting of a polyetherimide foam core with a specific gravity of 90 kg / m3 and two top layers of glass fiber (107 g / m2), impregnated with polyetherimide (50%), and a thickness of 5 mm, was provided with a reinforcement. This was done by injecting molten polyetherimide through an injection mold through the top layer. On one side of the sandwich plate it was supported with a metal plate, while on the other side the spray head was placed against the surface of the top layer. The spray head was provided with a surface enlargement. Due to the force of the injection, the material was injected into the core with an injection time of 2 seconds.

a screw sleeve which was at room temperature was then placed in the still plastic material of the reinforcement.

The resulting reinforced surface had a diameter of 30 mm. The compression strength at the reinforcement was 170 N / mm2. The compression strength of the plate itself was 3 N / mm2. The pull-out value of the screw bush was 240 kg. The same threaded sleeve, applied in an already hardened reinforcement, yielded a pull-out value of 160 kg.

Claims (18)

Method for modifying a plate-shaped sandwich material comprising a core material arranged between two top layers, wherein an amount of thermoplastic material is injected through one of the top layers under pressure into the core material, an object is placed in the still plastic material, after which the plastic material hardens. The method of claim 1, wherein the article is an insert, a fastening aid, a part or a product. The method of claim 1, wherein the article is removed during or after curing. A method according to claim 1 or 2, wherein the article at the time of application in the plastic material has a temperature lower than the temperature of the plastic material. The method of claim 4, wherein the article has a temperature not higher than 75 ° C, more particularly not higher than 35 ° C. A method according to claims 1-5, wherein the object consists wholly or partly of metal. A method according to claims 1-6, wherein as thermoplastic material a thermoplastic plastic is used with a softening temperature of at least 50 ° C. A method according to claims 1-7, wherein the thermoplastic plastic to be injected is selected from polystyrene, styrene polymers, acrylate and / or methacrylate polymers, polyolefins, polycarbonate, polyetherimide, polyamide, polysulfone, polyether sulfone, polyether ketone, polyether ether ketone, polyether ketone ketone , polyphenylene oxide, polyphenylene sulfide and mixtures of two or more of these materials. A method according to claims 1-8, wherein the thermoplastic plastic to be injected also contains fibers. The method of claim 9, wherein the fibers are selected from the group consisting of glass fibers, polyamide fibers, such as aramid fibers, polyethylene fibers, polyester fibers and carbon fibers. A method according to claims 1-10, wherein the core material is a thermoplastic or non-thermoplastic plastic foam or a thermoplastic or non-thermoplastic honeycomb material. A method according to claim 11, wherein a thermoplastic foamed core material is used, which is selected from polyetherimide foam, polycarbonate foam, polymethacrylamide foam, polyester foam such as a pet or pbt foam, polyether sulfone foam, polyether ketone foam, polyether ether ketone foam, polyether ketone ketone foam, polyphenylene oxide foam, polyphenylene sulfide foam, or a foam material made from mixtures of thermoplastic materials in which at least one of the said thermoplastic materials is contained. A method according to claim 11 or 12, wherein the thermoplastic foam-like core material also contains fibers. The method of claim 13, wherein the fibers are selected from the group consisting of glass fibers, polyamide fibers, such as aramid fibers, polyethylene fibers, polyester fibers and carbon fibers. Method as claimed in claims 1-14, wherein as top layer a thermoplastic plastic is used, which plastic is reinforced with fibers, preferably in the form of a fabric, a knit, a fiber fleece or unidirectionally applied fibers. The method of claim 15, wherein the top layer thermoplastic plastic is selected from polyester such as PET and PBT, polycarbonate, polyetherimide, polyamide, polysulfone, polyether sulfone, polyether ketone, polyether ether ketone, polyether ketone ketone, polyphenylene oxide, polyphenylene sulfide, and mixtures of two or more of these plastics. The method of claim 15 or 16, wherein the reinforcement material in the top layer is selected from glass fibers, polyamide fibers, such as aramid fibers, polyethylene fibers, polyester fibers and carbon fibers. Sandwich material provided with an object or an opening obtained by using the method according to one or more of claims 1-17.