NL8701188A - Plastic foam core sandwich panel - has thermoplastic foam core and thermoplastic skin to allow shaping at elevated temps - Google Patents

Abstract

A sandwich material comprises a core of lightweight plastic foam covered on both faces with a plastics skin, both the plastic foam and the skin material being softenable at elevated temps. to allow shaping.

Description

sf * NO 34473 1 «*

Short designation: Sandwich material and method of manufacture thereof.

In the first instance, the invention relates to sandwich material formed by a core of light plastic foam covered on both sides with a plastic skin.

It is known that sandwich material with a foam-core and a plastic skin at a low weight has a high bending stiffness. Sandwich materials described in the literature (see, for example, British Patent Application 2,134,845) have a skin of thermosetting material which is optionally reinforced with fibers. This finished sandwich material is unsuitable for undergoing thermoplastic deformation.

The object of the invention is to overcome these drawbacks and to provide a slightly rigid sandwich material that can be thermoplastic deformed.

According to the invention, the plastic foam and the two plastic skins can be softened at a higher temperature, so that deformation is allowed.

Essential for the effect to be obtained with the invention is that the skin material softens by heating so that it can be stretched; the foam material can become tough by heating so that it can be deformed and compressed to obtain a locally higher density. The sandwich structure is retained when the material is thermally deformed. The thermoplastic skin can be reinforced with fibers.

In addition to the aforementioned advantages of thermal deformability, low weight and high rigidity, the sandwich material according to the invention also exhibits the following favorable properties: high impact strength, good insulation value, good chemical resistance, good temperature resistance, a wide range of applications.

Examples of thermally deformable foam materials are poly-30 with acryllimide, polyvinyl chloride and polyurethane. As the thermoplastic material for the sandwich skins, polyvinyl chlorides, acrylonitrile butadiene styrene, polystyrene, polyvinyl fluoride, polyvinylidene fluoride, polyprolylene, polycarbonate, polyetherimide and polyethylene can be used.

The sandwich material can be manufactured by various methods. A first option is to skin 8701188 »

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2 and core material to be joined together by means of a separate adhesive layer. In principle, many types of glue are eligible for this.

A suitable adhesive for these materials must meet the condition that it is deformable at the temperature at which the sandwich is deformed. If the skin and core are difficult to connect by means of a separate adhesive layer, it is preferred that incisions or indentations are made in the two surfaces of a foam plate made of thermoplastic plastic material, powder of a thermoplastic plastic is applied to each surface of the foam plate. arranged that the indentations or cuts are filled and that a layer forms on the respective foam surface and this layer is formed into a skin with a heated plate under application of a low pressure. If the viscosity of the skin material is sufficiently low by heating, a connection between foam and skin material can be established even without any auxiliary material (glue, powder).

It is noted that the manufacture of the sandwich and the shaping can take place at the same time. Generally, a sandwich body will be formed from a flat sandwich intermediate and this intermediate will be softened by heating so that it can be finalized in a mold (usually a relatively inexpensive single mold) .

The temperature at which the deformability occurs is chosen such that the foam-shaped core is ductile and does not decompose, while the skin continues to form a closed whole during the change of shape.

The invention relates not only to the flat sandwich material, but also to the sandwich material which is thermally deformed at least partly, with at least one of the skins 30 being locally stretched. The foam can be compressed at the area of the stretched skin part. The two skins can be brought together, optionally after removal of foam, so that they are joined.

If the portion of compressed foam and stretched skin is at the edge of the sandwich, the opportunity is created to obtain an effective force initiation into the skin with little load on the foam. This edge can be further processed as is usual with sheet material.

Also, the compressed foam portion and stretched skin portion could be spaced from the edge, creating a solid point of attachment for a bolted connection at the smallest thickness of sandwich. This bolt connection serves, for example, to attach a profile or the like.

A blind opening can be provided in the material, wherein a plastic plug is placed in that opening, which is connected to the skin material using frictional heat.

Welding sandwich plates together is also possible. Two sandwich materials at an angle to each other will be welded together by the skin material flowing together and optionally using a welding wire of the same material as the skin or equivalent material.

For example, in the case of a bathtub, it may be necessary to provide the sandwich with a rounded edge. With the sandwich material according to the invention, this edge can easily be obtained if the material is folded in half.

The edges of the sandwich material can also be covered with thermoplastic skin material. To this end, strips of thermoplastic material are welded to the skin on the side of the sandwich.

The invention will now be explained in more detail with reference to the figures, in which a number of exemplary embodiments of the sandwich material according to the invention are shown.

Figure 1 shows a section of flat sandwich. material according to the invention.

Figure 2 shows a cross-section of a body formed from the material according to Figure 1.

Figure 3 shows a section through sandwich material 30 with an attachment point.

Figure 4 shows a section through sandwich material with finished edge.

Figure 5 shows a section through sandwich material with plug with internal thread.

Figure 6 shows a section through two sandwich materials welded together.

Figure 7 shows a section through a sandwich folded at the edge.

Figure 8 shows a perspective view of 8701168 4 sandwich material with an edge cover.

Figure 9 shows a perspective view illustrating a preferred method of manufacturing the sandwich material of the invention.

The sandwich material shown in figure 1 comprises a foam core 1 of plastic material which becomes tough deformable by heating and two skins 2 of a thermoplastic deformable solid plastic material. Examples of foam materials to be used are polymetacrylimide, polyvinyl chloride and polyurethane. As the thermoplastic skin materials, polyvinylidene fluoride, polypropylene, polycarbonate, polyetherimide and polyethylene can be used.

Figure 2 shows an example of an object formed from the flat sandwich material according to Figure 1. By heating, the foam core has been made ductile, while the viscosity of the skins has been brought to a low level, so that the sandwich can be deformed in a single mold. The skin material is stretched on the outside of the corners (see arrows). Sandwich structure and all good properties have been retained.

Figure 3 shows a body formed from the flat sandwich material 20, whereby the skins have been brought together by thermal deformation, whereby a fixing point for a bolt 3 has been created. This serves to fix a profile 4. The introduction of forces takes place with a minimal load on the foam.

Figure 4 shows a piece of sandwich material with a finished edge obtained by thermoforming. Here, too, the introduction of forces can take place with virtually no load on the foam.

Figure 5 shows a sandwich material in which a blind hole has been made in the material by milling or drilling, the foam being completely removed and a plug 5 with an internal thread of 30 made from a thermoplastic plastic, optionally with a metal insert, whereby friction heat is produced by rotating the plug which has led to fusion of the plug material with the skin material on both sides.

Figure 6 shows a welded connection between two sandwich plates in which a welding wire 6 of the same material as the skin 2 is used. Such a welding wire is not always necessary. The contacting skin materials of both sandwiches are fused.

The sandwich material according to figure »7 is folded in half on the edge after 8701188 v 5 * heating. In part 7, the outer skin is stretched and the foam is pressed together. The inner skins may be linked together. This double folded material is for example suitable for a bathtub with a round edge.

Figure 8 shows perspective sandwich material, part of the edges of which are covered with a strip of material of approximately the same thermoplastic properties as the skins. The strips are joined to the sandwich by a hot seal method, in which both the sandwich and the strips are heated.

Figure 9 illustrates a possible manufacturing method of the sandwich material of Figure I. In each of the surfaces of the foam core, parallel slots are cut in two mutually perpendicular directions. Successively, so much powder 10 of thermoplastic plastic 15 is sprinkled on each surface that the slots are filled and a layer of uniform thickness has formed. Finally, a plate is pressed onto the powder layer and the plate is heated to the appropriate temperature (e.g. 200 ° C). After cooling of the plate, a close connection of the formed skin with the foam core is obtained.

If a material is used for the thermoplastic powder with a relatively high softening point relative to the temperature at which the core material can withstand, then such a fast heating must be applied that the skin material takes on a higher temperature than the core material. This is particularly the case with a combination of polyetherimide as thermoplastic and polymetacrylimide as foam core. The skin is heated to 250 - 310 ° C and the major part of the core must not get warmer than 200 ° C.

The invention is further elucidated by means of further examples.

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Example I

A sheet of polyvinyl chloride foam material having a thickness of 10 mm and a specific weight of 55 kg / m 2 is covered on both sides with a glue foil of polyurethane of 0.1 mm thickness and a sheet of solid hard polyvinyl chloride of 1 mm thickness. This assembly was then placed between two metal plates between which a reduced pressure was created, which kept said assembly under pressure. Then the metal plates were heated to a temperature of 130 ° C and this temperature was maintained for 1 minute, after which 8701 188 6

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The assembly was cooled while maintaining said pressure.

. Thus, a flat sandwich structure was formed which forms a rigid whole and whose skins formed a tight connection to the core.

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Example II

Instead of the solid hard polyvinyl chloride material, a plate of 1 ram thick acrylic butadiene styrene was used.

Example III

In a sheet of foam material of polymethacrylimide (Rohacel 51) with a thickness of 20 mm, parallel slots were cut to a thickness of 1.2 mm and a distance of 1.5 mm in two mutually perpendicular directions. A powder consisting of polyvinylidene fluoride (PVDF) was then sprinkled on this plate on one side and rubbed into the grooves until they were completely filled with PVDF. An additional amount of powder was then distributed on the surface. The plate thus composed was covered with a heatable plate which was drawn on the surface 20 by applying reduced pressure. The plate was then heated to a temperature of 200 ° C and this temperature was maintained for 3 minutes after which the plate was cooled to ambient temperature.

After this, the same operation was repeated on the other side of the core. The result was a sandwich structure, the skin of which formed a tight bond with the foam core.

Example IV

A sheet of PMMA with a thickness of 1.2 mm was placed on one of the surfaces of the sandwich structure of Example I. This composition was subjected to the same heat treatment as in Example 1, thereby creating a connection between PVDF and PMMA. This operation was then repeated with the second surface.

The result is a sandwich structure whose PMMA bonds closely to the foam core, using PVDF as the bonding layer.

Example V

The procedure of Example I was repeated, using polycarbonate instead of polyvinylidene fluoride.

8701188 7 *

Example VI

The plate material of Example I was placed between two sheets of silicone rubber between which a reduced pressure was created so that the rubber closed tightly over the plate material. This assembly was then heated to 120 ° C and drawn into a mold by vacuum. After cooling, the object thus formed could be removed between the rubber sheets.

Example VII

The plate-shaped material of Example II was formed in the same manner as in Example VI, but the temperature chosen was 190 ° C.

Several variants are possible within the scope of the invention.

8701188

Claims (11)

Sandwich material formed by a core of light plastic foam covered on both sides with a plastic skin, characterized in that the plastic of both the foam and the two skins softens at a higher temperature and thereby permits deformation. 2. Method for manufacturing a sandwich material according to claim 1, characterized in that incisions or indentations are made in the two surfaces of a foam plate of thermoplastic plastic material, powder of a thermoplastic plastic is applied to each surface of the foam plate that the indentations or cuts are filled and a layer forms on the respective foam surface and this layer is formed into a skin with a heated plate under application of a low pressure. Sandwich material according to claim 1, characterized in that at least a part of the material is thermoplastic deformed with at least one of the skins being locally stretched. 4. Sandwich material according to claim 3, characterized in that the foam is pressed together at the area of the stretched skin part. Sandwich material according to claim 4, characterized in that the portion of compressed foam and stretched skin is located at the edge of the sandwich. Sandwich material according to claim 4, characterized in that the portion of compressed foam and stretched skin is spaced from the edge. 7. Sandwich material according to claim 6, characterized in that a bolt protrudes through the sandwich at the location of the smallest thickness of the sandwich to fasten a profile or the like. 8. Sandwich material according to claim 1, characterized in that a blind opening is arranged in the material and a plastic plug is placed in said opening, which is connected to the skin material using frictional heat. 9 J η standing sandwich materials are welded together by skin material and possibly using a welding wire of the same material as the skin. 9. Sandwich material according to claim 1, characterized in that two are at an angle to each other 870 1 188 10. Sandwich material according to claim 1, characterized in that the material is folded in half to form a round edge. Sandwich material according to claim 1, characterized in that the edges of the sandwich are provided with strips of thermoplastic material which are welded to the sandwich material by a hot seal method. 8701188