WO2008047188A1

WO2008047188A1 - A plunger

Info

Publication number: WO2008047188A1
Application number: PCT/IB2007/001927
Authority: WO
Inventors: Albertus Johannes Human
Original assignee: Albertus Johannes Human
Priority date: 2006-10-20
Filing date: 2007-07-10
Publication date: 2008-04-24

Abstract

A plunger for a collapsible tube is provided and is characterised in that the plunger is resiliently deformable to conform to the cross-sectional shape of the tube in travelling along the length thereof. In one embodiment the plunger has a leading end and a trailing end extending from opposite sides of a cylindrical body. The leading end provides a complementary fit in the nozzle of a tube and has a conical neck terminating in a spigot. The trailing end includes an inwardly tapered skirt which may have a biasing member located therein to provide an outward bias on it.

Description

A PLUNGER

FIELD OF THE INVENTION

This invention relates to a plunger for a tube, more specifically to a plunger for a collapsible tube.

BACKGROUND TO THE INVENTION

Collapsible tubes moulded from plastics materials are widely used for dispensing products ranging from tooth paste to grease to medicinal creams and cosmetics. A problem with such tubes is the difficulty experienced in squeezing the contents out without a substantial residue remaining in the tube. Many solutions to this problem have been proposed, including the use of a rigid plunger, also referred to as a follower, shaped to provide a sliding fit in the tube and positioned behind the contents. Squeezing the tube behind the plunger urges it, and the contents in turn, towards the nozzle. Shaping the plunger appropriately ensures that the contents cannot flow between the plunger and tube and wastage is thus eliminated.

Collapsible tubes are generally formed from a tube made of a plastics material having a circular cross-section with a nozzle at one end and the opposite end, the filling end, being sealed closed by simply pinching the tube across its diameter. This results in collapsible tubes having a changing cross-sectional shape along their length from the nozzle end to the filling end. Thus, whilst plungers are fairly effective in rigid tubes, none have found to be very effective in collapsible tubes due to the change in cross-sectional shape.

Numerous plungers are shown in the prior art. US 738,009 discloses a spherical body or ball for use as a follower, as does US 2,361 ,647 which also discloses a plug or piston or differing forms but shaped to provide a tapering rear surface which encourages forward movement of the device in the tube. US 3,201 ,003 describes a piston with a conical leading end, and US 3,297,207 discloses various shaped followers of a rigid construction.

None of these devices enjoyed any degree of success in the market as far as the applicant is aware. It is surmised that this is a reason for an alternative approach which is shown in, for example US 3,946,908, US 4,347,953, US 4,809,887, US 4,913,322, US 4,936,493, US 4,946,076, US 4,949,876, US 4,962,870, US 5,052,592 and US 6,499,989. All these documents disclose the use of a rigid tube and follower with some form of pumping mechanism for moving the follower up the tube. The use of a rigid tube obviates difficulties with changing tube cross-section but requires a fairly complex and relatively expensive pumping mechanism and such rigid tubes have not found widespread acceptance in the market.

A further approach has thus been to provide a device external to the tube which assists in squeezing the tube to the extent that none of the contents of the tube remain behind. Such devices are described in, for example, GB 522,936, US 3,211 ,342, WO 85/03491 , DE 3627701 , US 5,442,839, US 5,732,854, US 5,782,385, US 5,884,812, US 5,920,967, US 6,332,560, US 6,415,479, US 2001/0040172, NL 1024357 and US 7,007,823. This approach has not found widespread acceptance either, probably due to the cumbersome nature of the devices or the inconvenience of having to attach such devices to tubes. OBJECT OF THE INVENTION

It is an object of this invention to provide a plunger which at least partially alleviates some of the abovementioned problems.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a plunger shaped to provide a sliding fit within a collapsible tube which has a nozzle at one end and is sealed closed at the opposite end and wherein the cross-sectional shape of the tube changes along its length, characterised in that the plunger is resiliently deformable to conform to the cross-sectional shape of the tube in travelling along the length thereof.

Further features of the invention provide for the plunger to have a leading end and a trailing end; for the leading end and trailing end to extend from opposite ends of a cylindrical body; for the leading end to provide a complementary fit in the nozzle of a tube; for the leading end to include a conical neck terminating in a spigot; and for the trailing end to include an inwardly tapered skirt.

Still further features of the invention provide for the plunger to include a plurality of ribs on the inner surface thereof; and for a beveled shoulder to extend between the neck and the body and between the skirt and the body.

Yet further features of invention provide for the skirt to be outwardly biased; for a resilient member to bias the skirt outwardly; for the resilient member to include a plurality of resiliently flexible arms extending from a hub; and for there to be a pair of arms extending from a coiled hub, both the arms and hub being formed from a length of spring steel. Further features of the invention provide for the plunger to include ribs internally thereof; and for the plunger to be moulded

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described, by way of example only, with reference to the drawings in which:

Figure 1 is top perspective view of the plunger;

Figure 2 is a bottom perspective view of the plunger in Figure 1 ;

Figure 3 is a side elevation of a tube;

Figures 4A-4C are part-sectional side elevations of the plunger in Figure 1 in use with the tube in Figure 3;

Figures 5A & 5B are part-sectional perspective views of the plunger and tube in Figures 4A and 4B;

Figure 6 is top perspective view of a second embodiment of a plunger;

Figure 7 is a bottom perspective view of the plunger in Figure 6; Figure 8 is a bottom perspective view of the plunger in Figure 1 having biasing means; and

Figure 9 is a part-sectional side elevation of a tube with the plunger in

Figure 8 progressing down its length.

DETAILED DESCRIPTION OF THE DRAWINGS

A plunger (1) is shown in Figures 1 and 2 and is moulded from a resiliency deformable plastics material, in this embodiment polyethylene terephthalate (PET). The plunger (1) includes a squat, cylindrical body (2) with a leading end

(3) and a trailing end (4). The leading end (3) has a conical neck (7) ending in a spigot (9). The trailing end (4) is provided by a skirt (11) which tapers arcuately inwardly.

As shown in the inset, a beveled, radially outwardly stepped shoulder (15) extends between the body (2) and the neck (7). A similar shoulder (17) extends between the skirt (11) and the body (2) except that the bevel is shallower.

The plunger (1) is shaped to fit within a collapsible tube (20) as shown in Figure 3. The tube (20) is of conventional shape and has a nozzle (21) at one end (22) with the opposite end (23) being the filling end. The nozzle (21 ) includes a conical neck (25) ending in a male threaded, hollow extrusion nipple (26) to receive a female threaded screw cap (not shown). The leading end (3) of the plunger is shaped to provide a complementary fit within a nozzle (21) of the tube (20).

Referring also to Figures 4A and 5A, once the tube (20) has been filled through the filling end (23) the plunger (1) is inserted into the filling end (23), leading end (3) first, and the filling end (23) then sealed closed.

Whilst the tube (20) has a circular cross-section adjacent the nozzle end (22), sealing the tube (20) flattens the filling end (23) so that that end takes on a more elliptical shape. The cross-sectional shape of the tube (20) thus changes along its length between its ends (22, 23).

The neck (7) and skirt (11 ) of the plunger (1 ) at the respective shoulders (15, 17) are of the same diameter as tube (20) adjacent the nozzle (21) and the plunger (1) is thus shaped provide a sliding fit in the tube (20). However, after the filling end (23) is sealed closed it assumes the more flattened shape at that end (23) as described above. The shape of the plunger (1) and the plastics material used result in it being resiliently flexible and the plunger (1) thus deforms to conform to the cross-sectional shape of the tube (20) at that end (23). As the plunger (1) travels along the length of the tube (20), from the flattened filling end towards the circular nozzle end, its resilient flexibility enables it to conform to the shape of the cross-sectional shape of the tube (20). The shoulders (15, 17) thus maintain contact with the sides of the tube (20) in travelling along its length and in so doing prevent the contents escaping between plunger and sides. The content of the tube is thus propelled towards the nozzle as the plunger travels along its length.

The plunger has been found to be highly effective in expelling the contents of collapsible tubes and this is ascribed to its ability to conform to the changing cross-sectional shape thereof. This ability in turn results from the resiliently flexible nature of the plunger.

It will be appreciated, however, that many other embodiments of a plunger exist which fall within the scope of the invention, particularly as regards the configuration thereof. For example, the plunger can have any suitable shape and this will to a large extent be dictated by the shape of the tube in which it fits. The tube could thus have an oval shape in cross-section and plunger be similarly oval in shape. Also, any suitable moulding process, including stretch blow moulding, can be used. Whilst PET has a good memory which makes it useful in this application, any suitable material can be used.

If desired, detents, such as barb-shaped protrusions, can be provided on the plunger, preferably on the skirt, to prevent the plunger moving backwards in the tube. Alternatively, a vent hole could be provided in the side of the tube adjacent the sealed end to prevent formation of a vacuum behind the plunger. Any suitable biasing member could be used, although it is not essential that one be used.

As shown in Figures 6 and 7, ribs (60) can also be provided in the neck (7) of the plunger (1) to enhance the resilience thereof. In this embodiment, six ribs (60) are centrally arranged in the collar (7) evenly circumferentially spaced and extending downwardly towards the skirt (11). The ribs (60) are elongate with a box-like shape with radiused corners (62) and are shorter than the radius of the collar (7). An opening (64) extends into each rib (60) from the upper side (66) of the skirt (7).

The shape of the ribs (60) still permits flexing of the plunger (1) whilst augmenting its tendency to resume its normal shape. Clearly any suitable ribs or reinforcing can be used.

As shown in Figures 8 and 9, a biasing member (80), in this embodiment a steel spring having a pair of arms (81) extending from a coiled hub (82), can be inserted in to the skirt (11 ) before sealing the filling end (8). This ensures that the skirt (11) is outwardly biased and assists in it progression along the tube (20).

A moulded plastics biasing member of any suitable shape could also be used and the skirt could be provided with pockets to receive the ends of the arms of the biasing member.

Also, the plunger could be configured to have two halves separated by a blade or other cutting device. This would be useful in tubes having a central membrane separating the tube into two compartments, as proposed in US 5,244,120, as it permits the plunger to cut the membrane as it moves up the tube and thus allows a single plunger to be used in such tubes.

Furthermore, the plunger of the invention can be used with any suitable tube, including a transparent tube with graduations and multi-layered tubes. The tube could also be supplied with a unidirectional valve, preferably at its nozzle, to permit the contents to be expelled whilst preventing air from being drawn into the tube.

Claims

1. A plunger shaped to provide a sliding fit within a collapsible tube which has a nozzle at one end and is sealed closed at the opposite end and wherein the cross-sectional shape of the tube changes along its length, characterised in that the plunger is resiliently deformable to conform to the cross-sectional shape of the tube in travelling along the length thereof.

2. A plunger as claimed in claim 1 wherein the plunger has a leading end and a trailing end extending from opposite ends of a cylindrical body, with the leading end shaped to provide a complementary fit in the nozzle of a tube.

3. A plunger as claimed in claim 2 wherein the leading end includes a conical neck terminating in a spigot.

4. A plunger as claimed in claim 3 wherein the trailing end includes an inwardly tapered skirt.

5. A plunger as claimed in claim 4 wherein the neck and the skirt are outwardly stepped from the body.

6. A plunger as claimed in claim 5 wherein a beveled shoulder extends between each of the neck and the body and between the skirt and the body.

7. A plunger as claimed in any one of claims 4 to 6 wherein the skirt is outwardly biased.

8. A plunger as claimed in claim 7 wherein a resilient member biases the skirt outwardly.

9. A plunger as claimed in claim 8 wherein the resilient member includes a plurality of resiliently flexible arms extending from a hub.

10. A plunger as claimed in claim 9 wherein a pair of arms extend from a coiled hub, both the arms and hub being formed from a length of spring steel.

11. A plunger as claimed in any one of the preceding claims which includes a plurality of ribs internally thereof.

12. A plunger as claimed in any one of the preceding claims which is moulded from a resiliently flexible plastics material.