FI ELD O F TH E I NVENTION

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The present invention relates to a container comprising a plastic material whose opacity increases with age, a method for estimating ageing of a plastic material , and use of such a method for esti mating ageing of a tank in a vehicle.

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STATE O F TH E ART

The use of plastic materials, e .g . in containers of various kinds, is now very widespread. Plastic materials have many 15 advantageous characteristics such as impact tolerance, good formability, low weig ht, corrosion resistance and cost-effective manufacture. They are therefore used to a large extent inter alia in the veh icle industry, e.g . for making expansion vessels for cooling systems and tanks for fuel , washer liqu id etc.

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When plastic materials age their mechanical characteristics are adversely affected and the risk of damage to the material increases. Expansion tanks for cooling systems in motor vehicles, as also for example tanks for washer liqu id , are often

25 made of translucent or partly translucent plastic materials such as polypropylene (PP) , polyamide (PA) or glass fibre reinforced polypropylene or polyamide. When plastic materials of this type age , not only their mechan ical characteristics but also their optical characteristics are affected such that they become less

30 translucent, i .e. their opacity increases. How qu ickly the ageing of a plastic material takes place depends inter alia on the stresses to which it is subject. High pressures and temperatures and UV radiation are factors which usually accelerate the ageing of plastic materials. A plastic material used in an expansion tank in a cooling system of a motor vehicle is subject to high pressures and temperatures and therefore ages relatively quickly. When the mechanical characteristics of the material are impaired there is risk of the tank disintegrating, causing for example leakage. One problem is that in the case for example of tanks in motor vehicles it is difficult to decide when the degree of ageing of the material is such that the tank needs to be replaced.

EP0068086 refers to a method for determining ageing of coloured plastic articles by illuminating them and measuring their reflectance. Articles with a reflectance which is outside a certain range are rejected. However, a problem with this method is that it requires access to special measuring equipment.

US 2012/0085155 refers to a method for determining ageing of plastic materials whereby a deformation measurement is performed by means of a test device. However, this method likewise requires the user to have access to special equipment.

SUMMARY OF THE INVENTION

The object of the present invention is to propose an at least in some respects simplified and improved way of deciding whether plastic material of a container has aged such that its mechanical characteristics are thereby impaired. This object is achieved in a first aspect of the invention by a container according to claim 1. The container has an outside wall comprising an at least partly translucent plastic material whose opacity increases with age, and is provided with a marker to indicate ageing of said material. The marker is so placed as to only be visible from outside the container through said outside wall so long as the opacity of the outside wall is less than that corresponding to a certain degree of ageing of the plastic material.

A container according to the invention provided with a marker makes it possible to decide merely by looking at the container whether its plastic material has aged so much that the container needs replacing. If the degree of ageing of the material is unacceptable and the container needs replacing, the marker will no longer be visible by inspection from the outside, making it easy to see by a quick inspection whether the container according to the invention needs replacing. In one embodiment of the invention said plastic material takes the form of polypropylene (PP) or polyamide (PA). PP has good chemical resistance, good fatigue resistance and tolerates high temperatures and can therefore be used with advantage for containers for liquids at temperatures up to 100°C. PP is also a relatively inexpensive material. PA tolerates high temperatures and has good mechanical strength and wear resistance.

In one embodiment of the invention the outside wall comprises only said plastic material, in which case the container will have a lightweight outside wall. In another embodiment of the invention the outside wall comprises not only said plastic material but also glass fibre. The incorporation of glass fibre strengthens the container's outside wall, which may for example comprise 10% glass fibre.

In one embodiment of the invention the marker is situated within the container at a distance from the outside wall. The presence of a marker will thus minimally affect the strength of the container. This embodiment is advantageous in cases where the container is intended for a translucent liquid and is subject to high strength requirements.

In another embodiment of the invention the marker is situated in or on said outside wall and therefore does not affect the space in the container. In this embodiment the marker may also be used for estimating ageing of containers which are filled with non- translucent contents. In one embodiment of the invention the marker takes the form of a fixed element whose colour differs from that of the container. In this case the marker remains clearly visible through the outside wall so long as the opacity of the outside wall allows. In one embodiment of the invention the container is an expansion tank. The container according to the invention is well suited to being an expansion tank, for which it is desirable to have an easy way of deciding whether the tank material has aged such that the tank needs replacing. The tank may for example be an expansion tank in a cooling system of a vehicle. In another embodiment of the invention the aforesaid object is achieved by a method for estimating ageing of an at least partly translucent plastic material whose opacity increases with age. The method comprises the steps of

- placing a marker in a container which is provided with an outside wall comprising said plastic material,

- visual inspection of said marker through said outside wall, and

- estimating on the basis of said inspection the degree of ageing of the plastic material,

the marker being so situated as to only be visible through the outside wall so long as the opacity of the outside wall is less than that corresponding to a certain degree of ageing of the plastic material.

The method according to the invention thus makes it possible to estimate the degree of ageing of a plastic material without access to any special equipment. This is particularly applicable in cases where estimating the degree of ageing is part of a more extensive verification of various characteristics of a plurality of components, as in a full inspection or examination of a vehicle. The method according to the invention makes it possible to estimate quickly and easily the degree of ageing of, for example, an expansion tank in a cooling system of the vehicle.

In one embodiment of this second aspect of the invention the degree of ageing at which the marker is no longer visible through the outside wall is at least partly determined by choosing a distance for the marker to be situated from the outside wall. Increasing the distance from the outside wall will reduce the degree of ageing at which the marker is no longer visible through it. In one embodiment the degree of ageing at which the marker is no longer visible through the outside wall is at least partly determined by choice of colour for the marker. A colour which contrasts to a greater or lesser extent with the container will make it possible to adapt the method so that the degree of ageing at which the marker is no longer visible is respectively increased or reduced.

In one embodiment the step of placing the marker in the container takes place during the manufacture of the container, making it possible for the marker to be integrated with the container, e.g. by being moulded jointly with it.

The invention relates also to use of a method as above for estimating ageing of a tank in a vehicle, e.g. an expansion tank in a cooling system of the vehicle.

Other advantageous features of the invention and advantages of the invention are indicated by the description set out below. BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described below in more detail on the basis of embodiment examples with reference to the attached drawings, in which Fig. 1 depicts a schematic perspective view of a container according to the invention in the form of an expansion tank,

Fig.2 depicts a view as seen obliquely from above of part of the container in Fig. 1 ,

Fig.3 depicts a side view of part of the container in Fig. 1 , Fig.4 depicts a flowchart illustrating a method according to the invention. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

A container according to a first embodiment of the invention depicted schematically in Figs. 1-3 takes the form of an expansion tank 1 for coolant in a cooling system of a motor vehicle. The tank is made of translucent polypropylene reinforced with 10% glass fibre and is manufactured by the moulding of two elements, here depicted as a lower element 2 and an upper element 3. The two elements 2, 3 have thereafter been welded together to form a container by a weld seam 4 running round the container. The tank thus has a single continuous outside wall 5 whose opacity depends on the degree of ageing of the polypropylene. With increasing age the opacity of the outside wall also increases. The container is provided with a marker 6 for estimating ageing of the plastic material. The marker takes here the form of a strongly coloured knob of plastic material which is situated within the expansion tank at a distance L from the outside wall. In the embodiment depicted the marker 6 is fastened on an element 7 which protrudes upwards from the tank's lower element 2. This protruding element is here formed integrally with the lower element 2 and its length is such that it protrudes into the u pper element 3 of the tank. After the weld ing together of the lower element 2 and the upper element 3 , the marker 6 wi ll thus be situated in the tank's u pper element at a distance L from the outside wal l 5. The tank also has internal wal ls 8 which inter alia equal ise stresses in the plastic material and increase the strength of the tank. For the sake of clarity, the internal walls 8 in the tank's upper element 3 are on ly depicted in Figs. 2-3. The tank is of course also provided with passages for liqu id flows to and from it and between the cells 9 which are del ineated by the internal walls 8, but for sake of clarity these passages have been omitted from the d iagrams .

When the expansion tank 1 is fresh from manufacture, the marker 6 wi ll be clearly visible throug h the outside wall 5. During use , the tank will be subject to large changes of pressu re and temperatu re and its material wi ll therefore age relatively qu ickly. When the tank ages , the opacity of the outside wal l 5 increases and the visibility of the marker 6 is affected . When the opacity of the outside wall exceeds that correspond ing to a certain degree of ageing of the plastic material of the outside wall the marker will no longer be visible through the outside wall , which is an ind ication that the tank needs replacing . The degree of ageing at which the marker is no longer visible can be controlled by adapting the colour of the marker and/or its distance L from the outside wall . Th is d istance may for example be adapted by making the upward ly protrud ing element 7 longer or shorter or by varying the th ickness of the knob which in th is embodiment serves as the marker. The marker may of course also be arranged otherwise than as described above in the contai ner. It may for example be painted in a contrasting colou r on an upwardly protrud ing element in the container.

I n another embodiment (not depicted) a container according to the i nvention is provided with a marker in the form of a marking on the inside of the outside wall . The colou r of the marking wil l be chosen so as to be no longer visible through the outside wal l when the latter has aged so much that the container needs replacing . Here the marki ng is pressed or pai nted directly on the outside wall but it might also be a colou red area or a smal l amou nt of material of contrasting colour mou lded into the inside of the outside wall .

The contai ner according to the invention may also take the form of a tank for washer liqu id or fuel , in a vehicle or some other fuel- powered mach ine. The contai ner may of course also be intended for other applications where it is desired to have an easy way of mon itoring its degree of ageing .

Fig 4 depicts a method accord ing to the invention for esti mating ageing of an at least partly translucent plastic material whose opacity increases with age. As a first step S1 a marker is placed in a container, e.g . in an expansion tank or some other container as described above . Th is step S1 takes place with advantage during the manufacture of the contai ner. The container is provided with one or more outside wal ls comprising said plastic material . The marker is so situated as to be visible through at least one of these outside walls when the container is fresh from manufacture. As a second step S2, which takes place with advantage at regular intervals, the marker is inspected visually through said outside wall. On the basis of this inspection the degree of ageing of the plastic material is then estimated, as a step S3. If the opacity of the outside wall is less than that corresponding to a certain degree of ageing of the plastic material in the outside wall, the marker will be visible and the container may continue to be used. When a certain time has passed, inspection step S2 will be repeated. If the opacity of the outside wall is then greater than that corresponding to a certain degree of ageing of the plastic material in the outside wall, the marker will no longer be visible and the container will need to be replaced, as a step S4. The method according to the invention is feasible for any suitable container but is particularly suitable for tanks in a motor vehicle, e.g. a truck, bus or car. The fact that these tanks are often subject to large changes of temperature and pressure makes it difficult to predict their ageing process.

The invention is of course in no way restricted to the embodiments described above, since numerous possibilities for modifications thereof are likely to be obvious to one skilled in the art without deviating from the invention's basic concept such as defined in the attached claims.