A device for the use of a thin wall package

The present invention refers to a cartridge assembly according to the introduction of independent claim 1.

The use of a thin wall plastic film or plastic film/metal foil laminate membrane sausage shaped package to contain and to dispense a chemical such as an adhesive or sealant is well known such as disclosed in EP-A-666 823 in that it is placed within a cartridge type container which acts as a mechanical support while the membrane is scraped off the cartridge wall and compacted to expel its content, the cartridge type container being re-usable. This above mentioned principle of compacting the package requires a much greater dispensing force in relation to a conventional cartridge due to the force required for scraping off and progressively compacting the foil package from the supporting inner cartridge wall while the package is under significant hydraulic pressure. This issue of force is very important especially for manually actuated dispensing devices where only a limited hand force is available.

A cartridge assembly according to the introduction of claim 1 is known from EP-A-0 369 723, which patent application discloses a device for extruding substances such as custard, whipped cream, food stuffs or grease like materials, where a membrane is turned "outside in" by a relatively short plunger, rather than being scraped off the wall under pressure and compacted, which considerably increases the relative mechanical efficiency.

However, in view of the substances foreseen to be extruded and in particular in view of the relatively short plunger it is evident that the problem of sealing has not been considered as being of importance.

Thus, the prior art according to the introduction of the independent claim, acknowledges that a leak path of the package content will exist between the two adjacent membrane walls and also that the leak path will be smaller or greater depending upon the clearance between the plunger and the cartridge cylinder internal diameter which determines the gap between the two adjacent membrane walls. Therefore, dependant upon viscosity of the liquid chemical content, the pressure being applied in order to dispense the content and the size of leak path, the effect can be to discharge part of the content of the membrane rearwards past the plunger instead of ahead of the plunger and out of the package, thus disturbing the ratio and increasing waste. This rearwards discharge is the result of leak between the two package membranes adjacent to the plunger and into the trailing membrane package behind the plunger where it will inflate, and may burst, the membrane under pressure.

Pistons, which are generally used for dispensing chemicals can be provided with sealing means like sealing lips or sealing rings, but sealing means for plungers are not known in the prior art.

Based upon this prior art, the object of this invention is to provide for a cartridge assembly which can use conventional sausage type bags and offers a better sealing thus that no material can leak out beyond the rear of the piston or plunger. This object is attained by the cartridge assembly according to independent claim 1.

Further embodiments and improvements are defined in the dependent claims.

The invention will be explained in more detail hereinafter with reference to drawings of embodiments.

Fig. 1

shows a longitudinal section of an embodiment of the invention with a plunger without sealing lips or rings in a first position,

Fig. 2

shows the embodiment of Fig. 1 in a second position of the plunger, and

Fig. 3

shows a further embodiment of the invention in the same position as shown in Fig. 7.

The proposed invention, using a piston with a pressure activated sealing lip, offers a considerable improvement over the prior art method of use of a thin membrane sausage type package in that the membrane is not scraped off, collapsed and compacted by the front edge of a plunger while under considerable and adverse hydraulic pressure but instead, the package is progressively emptied and turned "outside in" within itself by the piston as it is driven towards the outlet side of the cartridge. As it does so, the membrane of the package is free to be progressively peeled off from the inner wall of the cartridge cylinder behind the piston where no adverse hydraulic pressure exists and is turned over "outside in" and trailed behind the piston.

In the present embodiment of the invention the plunger is without any lip sealing means. In order to prevent a leak path between the adjacent membranes therefore, it is necessary to have a minimum gap between the plunger and the cartridge wall. To achieve the latter the plunger must be accurately aligned, in particular at the entry of the plunger, relative to the double walls of the cartridge supported membrane package and the length of the plunger must be at least equal to the length of the double walls of the cartridge supported membrane package after complete displacement action of the plunger. Also, the diameter of the plunger must be substantially equal or less than the inside diameter of the cylinder minus twice the double wall thickness of the membrane.

In the present embodiment, it is advantageous at the withdrawal of the plunger from the partially used package that, at the time of withdrawal, a vacuum relief passage allows air to pass through to between the plunger and the package so as to prevent a vacuum from forming and so as to allow the piston to withdraw and the package to remain.

The invention pertains to a cartridge assembly with one cylinder and one package assembly as well as to a cartridge assembly with two or more cylinders having package assemblies with one common cartridge outlet receiving, sealingly, the package outlet adaptors.

The invention is now explained in detail. Fig. 1 shows a longitudinal section of a sausage type thin wall membrane package assembly 50 containing a liquid chemical 2 and comprising a thin, strong and chemical resistant flexible plastic film or plastic film/ metal foil laminate membrane 51.

As shown in Figure 1 the membrane 51 is integrally formed and seamless and having an open neck end 5N. Whereas this kind of seamless, integrally formed membrane is best suited for the plunger with a flat end as shown, the invention, however, is not limited to this type of seamless membrane. A membrane having to open ends, from which one is closed f. ex. by a crimped ring, can also be used and the outlet end of the plunger can be adapted thereto.

The outlet end 5N of the membrane 51 is attached to an outlet adaptor 58, the latter having an outlet 5 with two sealing lips 6 and 7 on its outer diameter. The inner face of the outlet adaptor 58 is flat.

The cartridge assembly 54 is provided with a cartridge outlet 23 receiving the outlet 5 of outlet adaptor 58 and having a tapered bore 39.

The plunger 52 with vacuum relief passage 77 is shown having entered an inlet adaptor 53 in the cartridge assembly 54. The inlet adaptor 53 can be a ring inserted into the cartridge wall 55 or it can consist of at least three centring ribs moulded integrally with the cartridge wall. The inlet adaptor 53 has at its inlet end a chamfer 56 and has an inner diameter which is slightly larger than the plunger. The inlet adaptor 53 forms a plunger entry alignment chamfer, with the plunger aligning coaxial within the cartridge assembly 54 and the flexible membrane 51. The bottom face of the plunger is flat.

Fig. 2 shows the same components as Fig. 1 but after displacement of the liquid chemical through the outlet 5.

For proper functioning, the length L of the plunger must be equal or greater than the length DW of the double walls 51A, 51B of the cartridge supported membrane package 51 after complete displacement of the content by the plunger, as shown in Fig. 2. The diameter of the plunger must be, as near as technically possible, substantially the same or smaller than the inner diameter of the cartridge cylinder minus twice the double thickness of the membrane.

Fig. 3 shows another embodiment of the invention similar to Fig. 2 with the same parts having the same function and numerals. The cartridge assembly 60 contains a membrane package assembly 57 comprising the "outside in" turned membrane 69 with the double walls 69A and 69B. Plunger 52 is shown to have a tapered front section 79A as well as a tapered rear section 79B to ensure plunger 52 entry and exit alignment via inlet adaptor 53.

In deference to the previously shown embodiments, cylinder wall 61 is provided with an inside collar 62 at the end of the cylindrical section for retaining a shoulder 64 at the outlet adaptor 63, the collar enabling a radius or taper for a smoother transition of the membrane 69 at its end 70N from the cylindrical section to the front face, whereby the taper and/or radius of the collar matches the taper and/or radius of the plunger 52 front section.

The collar 62 at the end of the cylindrical section of the cartridge wall and the shoulder 64 at the outlet adaptor is not only advantageous in connection with a plunger type assembly as shown in Figs. 1 to 3 but also with any other outlet adaptor means.

The same applies to the outlet variant shown in Fig. 3 whereby the outside of outlet 70 of outlet adaptor 63 is cylindrical and provided with sealing lips 65 and 66 similar to sealing lips 6 and 7, and fitting within a cylindrical outlet 67 of the cartridge outlet 68.

While the cartridge assembly according to the invention is foreseen for all kind of chemicals and dimensions of the cartridge, the man of the art recognises that assemblies using plungers instead of conventional pistons are best suited for small to very small cartridges since the sealing is effectuated by the length of the plunger only.