FORM ELEMENT COMPRISING A POLAR CLADDING LAYER

The present invention relates to a method for manufacturing a form element, to a form element obtainable using this method, to a form element, to the use of the form element in the manufacture of vehicles, and to a vehicle provided with such a form element.

In the manufacture of vehicles it is a general aim to achieve a lower weight of the vehicle, such as for instance a car or an aircraft. A lower weight has a favourable effect on the fuel consumption of the vehicle. Much use is now being made of plastics in order to achieve this lower weight of vehicles .

Plastics which are much used in the automobile industry to form moulded parts are, among others, polypropylene and polyethylene. Many different products can be made from these plastics, such as for instance bottom plates, doors, seats and so on. Use is particularly also made in the automobile industry of composite materials. These are plastics which are reinforced with another component, for instance glass fibres (such as GMT or LFT) .

Many of these plastic components are nowadays glued to each other, or are glued to natural materials such as leather, glass, or glued to metal parts (such as parts from aluminium, iron, steel and so on) of a vehicle, such as for instance the bodywork of a car. In order to bring about a good adhesion the plastic components must have a relatively polar surface, i.e. a surface with a surface tension greater than 32 dynes/cm, preferably greater than 35 dynes/cm. If this is not the case, a good distribution of the adhesive - over the surface of the plastic part does not take place. This is because the adhesives, such as for instance epoxy resins, polyurethane resins, are relatively polar (both have

a surface tension of about 45 dynes/cm) . The plastic surfaces are generally pretreated in order to make them relatively polar. Such a pretreatment can then for instance consist of a so-called corona treatment and/or flaming of the surface of the plastic part and/or applying different primer layers (such as for instance diphenylmethane diisocyanate) to the surface of the plastic part. Such treatments are relatively expensive because they introduce an additional processing step into the production process and because they are relatively labour-intensive. Use is also made of relatively expensive raw materials in such treatments.

The present invention has for its object to provide a solution to the above stated problems .

A first aspect of the present invention relates to a method for manufacturing a form element, comprising of:

I) arranging a cladding layer of polar plastic material in a mould; ii) bringing at least a part of the cladding layer into contact at increased pressure with thermoplastic plastic material of increased temperature; iii) allowing the thermoplastic plastic material and the polar cladding layer to cool, wherein the thermoplastic plastic material forms a solid plastic element which is adhered to at least a part of the polar cladding layer. An advantage of such a method is that a plastic form element is obtained in efficient and cost-effective manner which has a relatively polar surface and which can be glued properly and efficiently to components of (partially) glass, metal (for instance iron, aluminium, steel) , natural products (for instance leather) or to other relatively polar plastic parts. The form element does not therefore have to be first subjected to for instance a corona treatment and/or flaming after being formed. Nor is it necessary for the form element

and/or the surface of the component to which it is glued to be pretreated with primers.

Owing to the relatively high pressure and high temperature (about 200 ⁰ C at 200-250 bar) the polar cladding layer is attached (by melting and/or mechanical connection) to the thermoplastic plastic material. After cooling a fixed connection forms between the cladding layer and the cooled thermoplastic plastic material, i.e. the formed plastic element. The connection is herein such that the cladding layer can no longer be easily separated from the plastic element. A form element is thus obtained which has a polar surface and which can be connected directly to for instance a metal part of for instance a part of the bodywork of a car. This because the adhesive used, such as for instance 3M Fastbond® (a polyurethane adhesive) , will flow well over both the relatively polar surfaces, and therefore ensure a good connection.

It is recommended that the thermoplastic plastic material for forming the plastic element comprises a fibre- reinforced plastic material. An advantage of the use of fibre-reinforced plastic material is that a form element is obtained with very good mechanical properties. It can hereby be used for instance as an element forming an essential component of the bodywork of a car, i.e. a so-called structural element. The use of fibres further facilitates handling of the plastic material, particularly in the case where the form element is formed in a so-called compression mould.

It is further recommended that the plastic element of the form element is a cladding element. The plastic element which has been formed from the thermoplastic plastic material does not here have a structural function in the vehicle. The plastic element can then be relatively thin or not be

provided with a fibre structure.

It is further recommended that the plastic element is formed into a plate. The form element, i.e. the plastic element with the polar cladding layer attached thereto, hereby also acquires a plate form. The obtained form element can then be substantially flat, such as a base plate of a car, although it can also be a plate with a determined relief, such as a cover plate for an engine or an engine compartment covering. The so-called surface tension is often measured in order to determine the polar properties of a surface. This surface tension is measured with a standard test, the DIN 53 354 test, this being a standard test for measuring the surface tension of a surface. It is the case here that the higher the surface tension of a surface, the more polar it is. It is recommended that the cladding layer of polar plastic material used in the present method has a surface tension higher than 35 dynes/cm, preferably 40-50 dynes/cm, more preferably about 40-43 dynes/cm. When such a cladding layer is used the surface tension of the obtained form element then comes to lie above 32, preferably above 35 dynes/cm, this being desirable for a good adhesion with the adhesive and the surface to which the form element is glued, such as for instance a metal surface.

It is particularly recommended that the polar plastic material of the cladding layer comprises polyester, polyamide and/or polyvinyl chloride. These materials impart very good polar properties to the surface of the form element. They can further be readily connected to the thermoplastic plastic material of the plastic element. The polyesters polyethylene terephthalate and polybutene terephthalate are particularly recommended as polar plastic material of the cladding layer.

The cladding layer is preferably a woven or a non-woven. One of the advantages of the use of such materials is that

they are easily handled and therefore easy to process.

It is further recommended that the cladding layer is a film or a fleece.

In step I) of the above described method two cladding layers are preferably arranged in the mould and in step ii) the thermoplastic plastic material is preferably arranged between the cladding layers. A form element is thus obtained wherein the plastic element is covered over its whole outer surface with a polar cladding layer. This therefore means that the form element can be glued over its whole outer surface.

The thermoplastic plastic material for forming the plastic element preferably has a surface tension lower than 30 dynes/cm. It is particularly recommended that the thermoplastic plastic material is a polyolefin, preferably polypropylene, polyethylene or polyamide. These plastic materials are very versatile, relatively inexpensive and can be made into all kinds of desired forms.

These plastic materials are preferably fibre-reinforced. The fibre percentage then preferably lies in the range of 5 to 80% by weight, preferably 10 to 40% by weight, more preferably about 25% by weight. The fibres preferably further comprise glass fibres and/or basalt fibres and/or natural fibres. The natural fibres can herein comprise hemp fibres, banana fibres, coconut fibres and/or flax fibres. It is particularly recommended that the mould comprises a so-called compression mould. In such a mould the cladding layer is for instance placed in the mould first, and a plastic element with increased temperature is then arranged thereon. The mould then closes and presses the plastic element against the cladding layer and the wall of the mould. Owing to the relatively high temperature of the plastic element the cladding layer fuses to the plastic element. The desired form of the form element is further obtained due to the high

(pressure) force and the form of the wall of the mould.

Instead of a compression mould use can also be made of a so-called injection mould. The thermoplastic plastic material is then introduced into the mould under high pressure, preferably between 200 and 400 bar, and at a temperature in the range of 150 ⁰ C to 300 ⁰ C, preferably 190°C to 25O ⁰ C. The plastic material then flows against the cladding layer, and this cladding layer is then pressed against the wall of the mould together with the plastic material, and they fuse together. A form element is thus obtained with a determined desired form and with a surface having polar properties.

A second aspect of the present invention relates to a form element obtainable according to the above described method. A third aspect of the present invention relates to a form element comprising a plastic element of thermoplastic plastic material, wherein at least a part of the surface of the plastic element is covered with a cladding layer of polar plastic material. A fifth aspect of the present invention relates to the use of the above described form element in the manufacture of vehicles, such as cars, trucks, aircraft and ships.

A final aspect of the present invention relates to a vehicle provided with a form element as described above. Mentioned and other features of the form element and the method for manufacturing this element according to the invention will be further elucidated hereinbelow on the basis of a number of exemplary embodiments, which are given only by way of example without the invention being deemed limited thereto. Reference is made here to the accompanying drawings, in which:

Example 1 describes experimental results of five tests which were performed and which show that a form element

according to the present invention has very good adhesive properties compared to untreated, fibre-reinforced polypropylene (GMT) .

Figure 1 shows a view of an embodiment of a method for manufacturing an embodiment of a form element according to the invention/

Figure 2 shows a view of the compression mould of Figure 1 for manufacturing an embodiment of a form element according to the invention, and an embodiment of a form element according to the invention;

Figure 3 shows a view of an embodiment of a form element according to the invention and a metal surface of a vehicle to which the form element is attached;

Figure 4 shows a view with exploded parts of an embodiment of a form element according to the present invention.

Example

Twenty test rods of fibre-reinforced polypropylene (GMT) about 10 cm long, 1.6 cm wide and 0.5 cm thick were used in the present tests. Fifteen of these rods were provided with a polar cladding layer of polyethylene terephthalate. The treated surface of these rods had a surface tension of about 34 dynes/cm. The other five rods were untreated and had a surface tension of about 28 dynes/cm.

Five of the fifteen rods provided with a polar cladding layer were provided with a layer of adhesive (3M Fastbond Contact Adhesive 30) about 0.5 cm thick. This layer of adhesive extended over a length of about 5 cm and over the whole width of the rods, i.e. about 1.6 cm. After some drying time (as prescribed by the manufacturer) the five rods provided with adhesive were brought into contact with five

untreated rods. A connection was thus formed between the rods. After hardening of the adhesive the rods were subjected to a tensile test (5 mm/min) wherein the shear stress to break was measured. The results hereof are shown in table 1. Five of the fifteen rods provided with a polar cladding layer (surface tension about 45 dynes/cm) were then provided with adhesive in the same manner as the rods above. These rods were subsequently connected to the five other rods provided with a polar cladding layer. A connection was thus formed between the rods which were provided with a polar cladding layer. After curing of the adhesive these rods were also subjected to a tensile test (5 mm/min) , wherein the shear stress to break was measured. The results hereof are shown in table 2. Tables 1 and 2 clearly show that the shear stress of the connection between rods which are both provided with a polar cladding layer is considerably higher than in the case of the connection between an untreated rod and a rod provided with a polar cladding layer.

Table 1: Shear stress GMT rod provided with polar cladding layer and untreated GMT rod

Table 2 : Shear stress GMT rod provided with polar cladding layer and GMT rod provided with polar cladding layer

Figures

Figure IA shows a first part 2 of a compression mould 1 for manufacturing a form element 3. A cladding layer 4 of polyester (surface tension of about 42-46 dynes/cm) is arranged in this first part 2 as shown in Figure IB. Part 2 of mould 1 has a specific form 5 with which a determined form of the surface of moulding 3 can be obtained. After the cladding layer has been arranged on part 2 of mould 1 a plastic element 6 of fibre-reinforced polypropylene (GMT) is arranged on cladding layer 4. This plastic element 6 is heated to about 22O ⁰ C in an infrared oven before being placed in the mould. Owing to the heating the thermoplastic material becomes soft and flows under pressure, whereby it can be pressed into a desired form relatively easily. It is noted here that it is not necessary for plastic element 6 to extend wholly over cladding layer 4 before pressing. This is because during the pressing of the soft plastic element 6 the thermoplastic material will flow out fully. Figure ID shows mould 1 in closed position, wherein the plastic element and the cladding layer are pressed into the desired form. During this pressing

the thermoplastic plastic material of plastic element β flows over the cladding layer and they fuse together. The whole is then allowed to cool such that the thermoplastic plastic material and the cladding layer become solid and thus form a form element.

Figure 2 shows a cross-section of mould 1 of Figure 1, wherein a form element 3 is formed. Form element 3 comprises plastic element 6 in solid state to which cladding layer 4 is adhered by means of fusing and/or mechanical connection. Depending on the structure of cladding layer 4 (for instance a honeycomb structure) and the pressure applied, a part of plastic element 6 can be situated on the surface of form element 3.

Figure 3 shows a view of a form element 8 of fibre- reinforced polypropylene provided on the underside with a cladding layer 9 of polar plastic material (polyester fleece) . The downward extending container 10 forming part of form element 8 is not provided with cladding layer 9. This container 10 can for instance serve to stow a spare tyre of a car. Figure 3 further shows a part 11 of the metal chassis of a car. This part 11 of the car is provided with a layer of adhesive 12 (for instance Betaseal 1759® or 3M Fastbond Contact Adhesive 30) . By bringing the part of form element 8 provided with cladding layer 9 into contact with the part 11 of the bodywork provided with the adhesive, a good connection is obtained between these two parts.

Figure 4 shows a view with exploded parts of a form element 13. Form element 13 comprises a cladding layer 14 of polyester (surface tension 42-46 dynes/cm) , which is attached to a plastic part 15 by means of a melting and/or mechanical connection. The plastic part comprises fibre-reinforced polypropylene which has a surface tension of about 29 dynes/cm. The surface of the form element with the cladding

layer attached thereto has a surface tension of about 34 dynes/cm.

The present invention is not limited to the above described embodiments, the rights sought rather being defined by the following claims, within the scope of which many possible modifications can be envisaged, such as among others a combination of the above described embodiments.