GB2152428A - Method of moulding a canister - Google Patents

Abstract

The method resides in shaping a pot-shaped blank 11 from nylon by injection moulding and onto the blank 11 is moulded a likewise pot-shaped outer layer 14 of polyethylene and in that the coated blank is finish-shaped to canister form by a blow moulding process. The nylon acts as a barrier layer which substantially prevents permeation for example of aromatic substances while the outer polyethylene layer 14 can be easily mixed for instance with carbon black in order to prevent electrostatic charge. The method is particularly suitable for manufacturing canisters to hold lead-free petrol, to which instead of lead other additives such as, for example, aromatic substances are added. <IMAGE>

Description

SPECIFICATION Method of manufacturing a canister The invention relates to a method of manufacturing a canister for petrol or the like, according to the preamble to Claim 1.

Canisters differ from motor vehicle tanks above all in that in normal use they are tightly sealed, in other words they have no ventilation. A consequence of this is that often considerable internal pressure is created in the closed canister which constitutes a substantial loading on the canister and its closure means. In addition, canisters must be able to withstand certain test loadings. For example, they must remain stationary on a flat surface which is inclined at 20 They must be able to withstand without damage being dropped from a height of 10 metres and only a quite specific and extremely small quantity of the contents may be lost within a given time. Materials used hitherto have been sufficiently tight where they have to hold petrol which contains lead.There is, however, an increasing endeavour to achieve lead-free petrol which then instead of the lead contains other additives, for example aromatic substances, acyclic and alicyclic compounds. The materials long since used for plastics canisters suffer however from considerable permeation, particularly in respect of these additives, so that they cannot comply with legal requirements.

Methods have therefore been developed whereby canisters consisting of standard polethylene are subsequently provided with a barrier layer by a sulphonation process or fluorination process.

The coating is however very thin and correspondingly the barrier action is not very great. In the most favourable case, a permation reduction of 25% is achieved. This value furthermore relates to motor vehicle tanks in which, of course, there is no internal pressure since the internal pressure in canisters accelerates permeation, these methods are not adequate for the particular field of application which involves canisters.

The object of the invention is to indicate a method of manufacturing a canister of the type mentioned and which provides canisters which can be used successfully with lead-free petrol. At the same time, of course, manufacture should be at a favourable cost so that such canisters are capable of being marketed in competition with sheet metal canisters.

This problem is resolved by the characterising features of Claim 1.

Particularly preferred materials are defined in Claims 2 to 4.

The advantage of the method according to the invention lies above all in that the barrier layer is constituted by what is initially and independent blank, so that this can be given correspondingly adequate wall thicknesses. By virtue of the fact that the outer layer is then injected onto this blank, there is on the one hand a satisfactory connection between both materials while on the other the manufacturing process is simplified. "The bonded blank" manufactured in this way is then finishshaped to canister form by the per se known blowing process. According to the further features of Claim 5, the material of the blank extends over all areas of the canister which will subsequently and in normal use enclose the petrol.Thus, particularly in the region of the canister opening, the edge formed by the outer layer is covered so that when the closure means is fitted, the petrol only comes in contact with the first material. This is particularly importance if the outer layer consists of polyethylene which is steeped in aromatic hydrocarbons.

The protective annular collar prevents such an effect.

The further developing features of Claim 6 provide on the one hand and by way is a very convenient way from the point of view of manufacture, at least one canister carrying handle, but the stand strips provided have a two-fold function. Firstly, they increase the rigidity of the canister when it is standing and then they allow an acceleration of and improvement in the preliminary blowing operation according to the measure set forth in Claim 7. Another consequence is that the coated blank is without problem drawn symmetrically into the blowing mould so that there are no irregular wall thicknesses.

The moulding process is ideally accelerated according to Claim 8 and at the same time an even stretching of the individual wall parts is promoted thereby.

Further expedient developments of the method are indicated in the subsequent sub-claims.

A preferred embodiment of the invention is explained in greater detail hereinafter with reference to the accompanying drawings, in which: Figure 1 shows a longitudinal section through a coated blank according to the method of the invention, and Figure 2 is a front view in the direction of the arrow 2 in Fig. 1.

The drawing relates to a 5-litre canister and is also shown on a smaller scale.

As the first step in the method, a pot-shaped blank 11 consisting for example of a non-hygroscopic nylon, is produced by injection moulding. At its open end it has integrally moulded into it a radially outwardly extending annular collar 12 which expediently has a shoulder 13 which is turned back in an axial direction. The wall thickness of the blank 11 may be 1 to 2 mm.

As the second step in the process, a likewise potshaped outer layer 14, for example of polyethylene, is injected onto the blank 11, a corresponding injection mould already resulting in the screwthread 16 being moulded in the region of what will later be the canister opening, radially projecting integrally moulded shapes 17, 18 and 19 also being formed thereby. The integrally moulded shape 17 is designed to be a centrally located canister carrying handle.

Ideally, this handle is also and at the same time constucted as a clip-in holder 21 for a delivery tube, now shown. Since the outer layer 14 is essentially responsible for the mechanical strength of the canister, its wall thickness is also correspondingly greater.

The blank 11 coated with the outer layer 14 is then fitted onto a core which is divided in two in the longitudinal direction, but which is not shown in the drawing, which is in addition heated and its outside surrounded by a heated mould. At the same time, air is blown under pressure into the interior of the blank 11 to encourage the stretching.

This procedural step of preliminary blowing is further assisted in that gripper strips, likewise not shown, are positioned in the blowing mould to grip the integrally moulded shapes 18 and 19 and to pull them in the direction of the arrows 22 and 23 towards their final position. This also ensures that the blank evenly fills the blowing mould, i.e.

ensuring for example that the left-hand wall is not thinner than the right-hand wall. Since here in addition the integrally moulded shapes 18 and 19 are intended to form standing strips of the finished canister, it is also important that they should actually be located in the corner zones. This, too, is guaranteed by the gripper strips.

Normally the blowing process is sub-divided into two stages with the already discussed stage of preliminary blowing which is then followed by a second stage, at the end of which the final canister shape is achieved. For this, at the end of the preliminary blowing, the aforementioned two-part core is removed and the still warm and therefore malleable neck part (with the screwthread 16) is bent upwards into its final oblique position indicated by reference numeral 24. Finish-shaping in the heated blowing mould now takes place with the supply of compressed air into the interior of the blank 11, the shaping process being possibly encouraged by vacuum assistance, because then any air pockets which might disturb the final shape can be avoided. Figs. 1 and 2 show the final form of the canister by dash-dotted lines.Here, too, the size relationships are not entirely accurate having regard to the drawing area available. It should, however, present no difficulty to match up the sizes in order to understand the invention.

The advantage of the "bonded structure" which can be achieved by this method resides in that the necessary barrier layer can without problem be made in the necessary wall thickness but that on the other hand only as much as this expensive material is used as is actually required. The real carrying function is fulfilled by the less expensive polyethylene, and since this latter does not have to perform a sealing action, it can be dyed without problem and can also be mixed, for example, with carbon black in order to increase its electrical conductivity. This avoids electrostatic charges which might result in spark formation. Therefore, the two materials satisfy different functions and at the same time make it possible to manufacture a canister which can meet with the numerous legal and practical requirements which occur. It is not particularly shown in the drawings but the wall thicknesses of the blank and of the outer layer can, in those areas which are more intensely weakened by the subsequent blowing process, be made thicker so that in the finished state, the wall thickness of the canister is true to the desired gauge. The aforedescribed method is particularly suitable for the manufacture of 5 and 10-litre canisters, preferably for 5-litre canisters. In the case of 10-litre canisters, it is above all the design of handle and the anchoring which will differ from the example illustrated, since with such canisters the usual desire will be to obtain what is known as the jerry can. However, the outer shape of the canister does not in any way affect the principle of "bonded construction".

Claims (14)

1. Method of manufacturing a canister for petrol or the like, characterised in that a pot-shaped blank (11) is injection moulded from a first material which admits of the least possible permeation of acyclic, alicyclic and/or aromatic compounds where these are contained in petrol, and in that injected onto the blank (11) is a similar pot-shaped outer layer (14) consisting of a second material which substantially determines the mechanical strength of the canister, and in that the coated blank is finish-shaped to canister form by a blowing process.

2. Method according to Claim 1, characterised in that a non-hygroscopic nylon is envisaged as the first material.

3. Method according to Claim 1, characterised in that polyethylene is envisaged as the second material.

4. Method according to Claim 3, characterised in that high molecular polyethylene of medium to high density if envisaged.

5. Method according to one of the foregoing Claims, characterised in that at its open end the blank (11) is formed with a radially outwardly widening annular collar (12, 13) which in the finishformed condition of the canister overlaps at least the end of the stage of the canister opening.

6. Method according to one of the preceding Claims, characterised in that the outer layer (14) is injected with integrally moulded shapes (17, 18, 19) which project radially from the pot shape in order to form at least one canister carrying handle, and also with two projecting stand strips disposed opposite each other on what will subsequently be the underside of the canister.

7. Method according to Claim 6, characterised in that the integrally moulded shapes (18, 19) provided in order to form the stand strips are, at least during the preliminary blowing, picked up in the blowing mould by movable gripper strips and are pulled in the direction (22, 23) of their final position.

8. Method according to one of the preceding Claims, characterised in that during preliminary blowing, a core which is divided longitudinally in two is inserted into the blank (11) and spread open.

9. Method according to one of Claims 7 or 8, characterised in that after the preliminary blowing, the core is removed and the neck part of the canister opening is shaped into the envisaged oblique position (24) before finish shaping takes place by the application of blowing pressure and possibly with vacuum assistance.

10. Method according to one of the preceding Claims, characterised in that the wall thicknesses of blank (11) and outer layer (14) are made thicker in those areas which are more intensely weakened by the subsequent blowing process.

11. Method according to one of the preceding Claims, characterised in that it is used for the manufacture of 5 and 10-litre canisters.

12. Method of manufacturing 5-litre canisters according to Claim 11, characterised in that the canister handle is simultaneously moulded to serve as a clip support for the delivery tube.

13. A method of manufacturing a canister as claimed in Claim 1 substantially as described by way of example disclosed herein.

14. A canister substantially as herein described with reference to the accompanying drawings.