GB2294896A - Gasketing of container closures - Google Patents

Abstract

A gasket is moulded on the inside of the floor of a twist-off jar lid or a bottle cap 8 by injecting plastics material using an injector head 1. The material is distributed an injection chamber 2 to a radially outer injection channel, either in the form of individual bores 4 or in the form of a continuous annular slot. Hold-down means 5 are provided to hold the plastics composition in contact with the cap or lid blank 8 during extraction of all or part of the remainder of the injector head 1. Following extraction of the injector head the cap 8 is moved to a moulding station (see Figure 3) where a moulding head 9 descends to complete shaping of the gasket. <IMAGE>

Description

IMPROVEMENTS RELATING TO GASKETING OF CONTAINER CLOSURES The present invention relates to the gasketing of container closures, and in particular to the type of cap for a jar rim or a large diameter bottle neck known as a lug cap or twist-off cap.

In the past bottle caps of all sizes and jar lids have been lined using a spin-lining or flowing-in process in which a plastisol is injected around the annular channel at the circumference of the top panel of a larger diameter cap or lid on its inside, or introduced centrally into a smaller diameter cap, and then the cap or lid is spun in order to distribute that plastisol regularly in the corner of the cap, whereupon heating of the cap, by various means which are well-known to the expert in the art, will result in the plastisol solidifying or fusing.

Recently, it has been proposed that the lining of bottle caps should be carried out using a plastic material which is injected under pressure into the cap, or placed in the form of a pellet, in the centre of a cap, and then stamped to define the gasket formation. During the stamping process, the centrally placed pellet or piece of plastics material is squeezed outwardly towards the location where the gasket is to have its greatest thickness, and the central panel of the bottle cap is left with a very thin layer of the composition.This is distinct from the "spin-lining" or "flowing-in" process described above using a plastisol in that in the spinlining or flowing-in process, there is either no compound deposited on the central panel of the cap, or only a thin centre panel of compound left there after spinning the cap, and it is instead all injected peripherally to be concentrated around the seal area near the periphery of the cap.

However, the spin-lining or flowing-in processes have the disadvantage that they require the presence of polyvinyl chloride in the plastisol and environmentalists have expressed the view that this is undesirable. Non-PVC plastieols are an alternative but currently extruding molten material is preferred.

The application of this substantially "non-PVCW technology to larger diameter bottle caps or to jar lids has not been possible because the application of a piece such as a shaped pellet centrally in the jar lid or bottle cap and its subeequent squeezing in a radially outward direction requiree such a drastic deformation of the pellet of plastics material that flowing to the corner of the lid or cap may not be achieved and in any case, given the large diameter of the central panel of a jar lid, the compound wasted through even a very thin residual layer on the ineide of the top panel of the cap or lid constitutes an economic disadvantage of considerable proportions. Ae an example, we can indicate that the conventional gasket stamping process referred to above in connection with bottle caps is common on 28 = screw caps or on crown closures of comparable diameters (28 mm being a standard size for screw caps); however lug caps are known which have a diameter of 100 mm or more, and screw bottle tops are known which have diameters of up to 63 mm.

It is known to apply plastics composition to the rim of a thermoformed tray by means of an injection channel formed in a moulding sleeve engaging the tray rim, as disclosed in EP-A-0 440 550.

It ie furthermore known from JP-A-93/029532, to place individual pieces of molten plastics material in a circular array from which they can be moulded to form a continuous circular gasket. The molten material is extruded as strands from a dispenser and then the end of each etrand is cut off by a rotating blade.

JP-A-62/198414 discloses loading solid particulate resin into the annuls of the closure and then heating it and moulding it to form a gasket.

It is an object of the present invention to provide a process which will allow the use of a gasket stamping operation with localised application of the molten plastic at the periphery of a jar lid or larger diameter bottle cap.

Accordingly, one aspect of the present invention provides apparatus for moulding peripheral gaskets in container closures, comprising an injector head having an injection passage; means for applying said injector head against the closure blank and for withdrawing the injector head from the closure blank; and injector means operative to eject plastics material from said injection passage to be placed in the container closure for moulding, while the injector head defines with the container closure a mould cavity.

A second aspect of the invention provides method of applying a molten plastics composition into a container closure blank for forming a gasket therein, comprising placing an injector head in an inverted said closure blank and applying an injector means against molten plastics composition to eject the plastics composition against the floor of the inverted closure blank through said injector head.

In order that the present invention may be more easily understood, the following description is given, merely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a first embodiment of injector head or die for feeding molten plastics material to a stamped metal blank for a lug cap, before the application of the lug formation to the skirt of the cap; Figure 2 is a sectional view taken on the line 22 of Figure 1; Figure 3 is a view corresponding to Figure 1 showing the subsequent stage of moulding the gasket from the molten plastics material injected using the injector head of Figure 1 in the cap blank shown in Figure 1; Figure 4 is a schematic perspective view showing the injection plungers of Figures 1 and 2 but also showing a first modified form of the first embodiment of injector head or die;; Figure 5 is a diametral sectional view, corresponding to Figure 1, but showing the first modification illustrated in Figure 4; Figure 6 is a diametral sectional view of a second modification of the first embodiment (of Figures 1 and 4); Figure 7 is a view of the apparatus of Figure 6 later during the injection process; Figure 8 is a view corresponding to that of Figure 4 but showing a second embodiment of the present invention; Figure 9 is a view corresponding to Figure 5 but showing a modification of the second embodiment (shown in Figure 8).

Referring now to the drawings, Figure 1 shows an injector head or die 1 having a central inlet chamber 2 in the form of an inverted mushroom (i.e. having a diametral cross-section in the shape of an inverted T). From the "head" of the mushroom, a plurality of distribution channels 3 (Figure 2) extends radially outwardly to open into a plurality of vertically extending corresponding injector channels 4 which extend parallel to the axis of the injector head and are each provided with an injector pin 5 driven by means (not shown) to execute vertical motion according to a desired cycle.

At the bottom end of each injector channel 4, is a widened portion 6, in this case in the form of a continuous groove around the bottom end face of the injector head 1 and along which the molten plastics material injected by way of the central channel 2, the radial distribution channels 3 and the vertical injector channels 4, may distribute itself during the latter stages of the injection phase. Other forms of widened portion can be used.

The injector head 1 is furthermore provided with heating elements 7 for maintaining the head at a temperature sufficient to maintain the molten plastics material in an injectable liquid state.

The seetional view of the injector head, shown in Figure 2, includes a section through the skirt of a cap 8 in which the gasket is being formed.

In Figures 1 and 2, the cap blank 8 is shown at a stage just after it has been stamped from flat sheet metal but before the lugs or other twist formations have been formed in the cap to give it its twist-off characteristics.

Such a cap is referred to in the art as a "lug cap".

Figure 3 shows the same cap blank 8 during the subsequent gasket moulding stage where a moulding head 9, mounted on an axially reciprocable vertical support shaft 10, is driven down onto the floor of the cap blank so that a gasket-moulding groove 11 in the bottom end face of the moulding head 9 defines the final shape for the gasket. In practice, the height and width (the dimension measured along the radius of the cap blank 8) of the gasket-defining groove 11 in the moulding head 9 may be slightly less than the corresponding dimensions of the groove 6 in the injector head 1, thereby exerting compression on the molten plastics material and completing the action of distributing the individually placed injected pieces of plastics material around the annular formation required for the finished gasket.

In operation, the device shown in Figures 1 to 3 operates as follows: Initially, a cap blank 8 is placed on the chuck 12 and held in position by means not shown, ready for the injection operation.

Then, the injector head 1 descends into the cap blank 8 and contacts the floor of the cap blank, whereupon the injector pins 5 displace molten plastics composition from the injector channels 4 onto the floor of the cap blank 8 and into the groove 6. All of the pins 5 may move in unison, or if desired there may be a certain slight difference in the movement of the pins, for example in order to promote movement of the molten plastics composition around the groove 6.

A preferred operating cycle is one in which the injector pins 5 will normally (i.e. initially) be in the position 5a shown for the right-hand side of Figure 1 where they close off the ends of the respective radial distribution channels 3. Upon arrival of the injector head 1 in the position shown in Figure 1 in contact with the floor of the cap blank 8, or just prior to such arrival, the pins 5 then rise relative to the body of the die 1 to the position Sb shown for the left-hand side of Figure 1.

They thereby open the respective distribution channels 3 and allow the molten plastics material under pressure in the chamber 2 to be allowed to enter the injection channels 4 below the pins 5b. After a desired time interval to allow the required quantity of molten plastics composition to enter the injection channels 4, the pins 5 then descend so as once again to close off the respective distribution channels 3 and subsequently to drive the metered quantity of molten plastics material downwardly against the floor of the cap blank 8 and into the groove 6.

Upon completion of this injection operation, all of the distribution channels 3 will have been closed off and all of the injector pins 5 will be in a lowermost position, just in contact with the metered and injected piece of molten plastics material held under pressure against the floor of the inverted cap or lid. The injector head 1, with its injector pins flush with the bottom ends of the injection passages, thus defines a moulding head so that the injected molten plastics material is moulded into a gasket by the end of the injection step.

The injector head 1 is then lifted clear of the floor of the cap blank 8, possibly while the injector pins 5 are held down so as to prevent detachment of the injected molten plastics material from the cap blank floor, and subsequently the pins 5 themselves will then be lifted in order to complete separation of the injector head from the injected plastics material.

In order to enhance this separation action, the lower end face of the injector head 1 and the bottom end faces of the injector pins 5 may be coated with a suitable non-stick material such ae PTFE to promote the eeparation action.

Subsequently, the assembly of the cap blank 8 with its injected molten plastics material is carried round to the moulding station shown in Figure 3, where the moulding head 9 descends to complete the shaping of the gasket.

In order to liberate air or other gases from within the enclosure defined by the moulding head and the cap blank, the moulding head includes a vent channel 13 to allow a flow 14 of the gases to escape.

Figure 4 shows a first modification of the injector head shown in Figures 1 and 2 in that in this case there is a continuous conical distribution passage defined between two (male and female) conical faces of separate parts of the injector head, avoiding the need for drilling separate distribution channels as shown in Figure 1. For example, to drill the passages 3 shown in Figure 1 may require the manufacture of the injector head 1 to include a first step in which the individual distribution channels 3 are drilled by movement of drilling heads radially inwardly of the injector head body, and then subsequently aligned injection channels 4 are drilled by vertical movement of a different set of drilling heads; finally the external portions of the previously drilled distribution channels 3 may need to be blocked in order to define the arrangement shown in Figure 1.

However, manufacture of the modified form of injector head shown in Figure 4 is more straightforward in that first of all the upper part 15 of the injector head is formed with a female conical bottom wall at 16 and then the inner, lower, portion 17 of the injector head is formed with a male conical surface 18, preferably having the same conicity as the female wall 16 of the upper injector head portion 15, so that subsequently the central portion 18 can be inserted into a cylindrical receee 19 of the upper portion 15 and held in place by friction fit of a set of luge 20, of which three are shown in Figure 4.

This alternative form of injector head has various advantages over the shape shown in Figure 1: (a) The direction of flow of the molten plastics material maintains a downward component of movement, even in the conical distribution duct region between the female and male conical walls 16 and 18, and this generates less shear forces in the flow of the molten plastics composition being injected.

(b) Additionally, the incoming flow is itself annular and may therefore undergo a much more gradual deflection from a single inlet path (because the plastics composition at the top of the central portion 17 is dispersed over a much larger radius, thereby having a radial distribution closer to that required of the eventual gasket). If desired, the smoothness of the deflection of plastic flow to arrive at this configuration may be enhanced by the addition of a conical apex to the central, lower, injector head body portion 17, as will be described below with reference to Figure 8.

As with the first form of this first embodiment, shown in Figures 1 and 2, the variation shown in Figure 4 includes a plurality of injection channels 4 and injector pins 5 with the pins driven at an appropriate time in order to drive an injected piece of the molten plastics material down onto the floor of the cap blank 8.

However, whereas in Figure 1 the widened portion at the bottom of the injection channel 4 was exemplified as being a continuous groove 6 around the bottom face of the injector head, to define an annular groove to start circumferential distribution of the injected molten plastics material, in Figure 4 each of the injection channels 4 includes at its bottom, a respective widened portion 21 which will not in any way promote flow of the injected molten plastics composition circumferentially around the floor of the cap blank, but will instead ensure that, provided the injector pin 5 is not driven down too fiercely against the injected piece of plastics material, contact of the injected piece of plastics material with the side wall of the injection channel 4 at the widened portion 21 will be avoided and hence the ease of separation of the injector head 1 from the gasket and cap blank 8 will be enhanced.

As with the embodiment of Figures 1 and 2, timing of the lifting of the injector head 1 in relation to the lifting of the pins 5 will be such that the pins 5 hold the injected plastics material down in contact with the floor of the blank 8 during the initial separation movement of the injector head 1 from the blank 8.

Figure 5 shows in more detail the variant of Figure 4 and illustrates the way in which the widened bottom end 21 to the injection channel 4 helps to avoid contact of the injected piece 22 with the side wall of the bottom of the injection channel 4.

Figure 6 shows a second modification of the embodiment of Figures 1 and 2 in that in this case the injector pin 5 is surrounded by a shut off sleeve 23 having an injection port 24 at the side facing towards the axis of the body of the injector head 1 (i.e. rightwardly as shown in Figure 6).

Again, the separation action involves a hold-down of the injected piece 22 by the pin 5, but in this case, the pin 5 can remain in the position shown in Figure 6 throughout all but the last part of the injection cycle, and the shut off sleeve 23 carries out many of the functions which were expected of the injector pins 5 in Figures 1, 2, 4 and 5.

In the modification shown in Figure 6, the injector pin 5 has its lower end just clear of the distribution duct 25 whose shape is defined by opposing concave and convex conical surfaces as explained above with reference to Figure 4. This allows the injected molten plastics material to pass in through the port 24 and downwardly to form the injected piece 22 of the desired volume.

On completion of the injection flow into the injection channel 4 via port 24, the shut off sleeve 23 rises sufficiently to cause the port 24 to move clear of the conical distribution channel 25 and hence to shut off the outlet end of the channel 25 and to prevent further flow of molten plastics material into the injection channel 4. This will also liberate the lower part of the injected piece and will leave a clear gap between the sides of the injected piece and the adjacent sides of the injection channel 4.

During this action, the injector pin 5 may descend slightly in order to ensure positive contact of the injected piece 22 with the surface of the floor of the cap blank 8, but movement must not be so extensive that the injected piece is compressed outwardly into contact with the sides of the injection channel (i.e. so that the diameter of the injected piece equals the external diameter of the shut off sleeve 23).

Once the shut off sleeve 23 reaches the position shown in Figure 7 and is therefore clear of the top of the injected piece 22 (while still in sliding contact with the cylindrical surface of the injector pin 5), the entire injection head may be lifted clear of the injected piece 22 and, given the preferred non-stick nature of the bottom end of the injection pin 5, there will be a clean separation leaving the various injected pieces around the blank 8 ready for moulding by a subsequent process using a moulding head at a downstream moulding station.

A second embodiment of the injector head in accordance with the present invention is shown in Figure 8 where the individual injector pins 5 are replaced by an injector sleeve 26, again in combination with a conical injection channel 27 defined by opposing concave and convex conical surfaces on the upper injector head body portion 28 and the inner, lower, injector head body portion 29, respectively.

The form of the second embodiment shown in Figure 8 is a slightly simplified version of the variant shown in Figure 9; these two injector heads differ only in that in Figure 8 there is no change in the width (radial extent) of the annular injector duct 30, whereas in Figure 9, that corresponding duct 30 has a widened lower end defined by a groove 31 similar to the groove 6 shown in Figure 1.

In each case, once the injector head has come into contact with the floor of the cap blank 8, the injector sleeve 26 can rise sufficiently to expose the downstream (radially outer) end of the downwardly divergent conical distribution duct 27 whereupon the head of pressure on the injected piece of molten plastics material will allow a quantity to enter the annular dispensing duct and to form an injected piece 22 beneath the lower end face of the injector sleeve 26. Once the desired quantity of molten plastics material has been metered out to form this piece, the injector sleeve 26 descends so as firstly to close off the downstream end of the downwardly divergent distribution duct 27 and secondly to press the injected piece into contact with the floor of the cap blank 8.

In the embodiment of Figure 9, the downward movement of the injector sleeve 26 must be limited so that it does not press the injected piece 22 so firmly against the floor of the cap blank 8 that the sides of the injected piece 22 bulge out into contact with the widened lower end 31 of the injection duct (to take up the clearance 30 shown in Figure 9). In Figure 8, no such clearance exists and the arrangement relies on failure of the plastics material to adhere to the radially inner and radially outer walls of the annular injection duct (possibly enhanced by coating the lower portion of these injection duct walls with PTFE or other non-stick agent).

As with the previous embodiments, the injector sleeve 26 stays down to hold the injected piece 22 in contact with the floor of the cap blank 8 as the injector head starts to rise.

As explained above, the embodiment shown in Figure 8 has an additional feature in the form of a conical apex 32 at the top end of the inner, lower, injection body portion 29, thereby streamlining still further flow of molten plastics composition from a central injection passage 33 towards the downwardly divergent continuous distribution duct 27. Such a feature could be incorporated in all of the variants shown in Figures 4 to 7 and 9.

This process and apparatus can be used with container closures having any kind of pilfer proof or tamper-evident feature. One example of such a feature is a ring formed as an extension of the closure skirt to engage under a bead on the exterior of the bottle neck or jar rim.

Claims (17)

1. Apparatus for moulding peripheral gaskets in container closures, comprising:- an injector head having an injection passage; means for applying said injector head against the closure blank and for withdrawing the injector head from the closure blank; and injector means operative to eject plastics material from said injection passage to be placed in the container closure for moulding, while the injector head defines with the container closure a mould cavity.

2. Apparatus according to claim 1, and including means for holding down said injector means in contact with the injected plastics material in the interior of a said closure blank during extraction of all or part of said injector head from the closure blank.

3. Apparatus according to claim 1 or 2, and including shut off means alongside and in surrounding contact with said injector means, and movable relative to the remainder of the injector head so as to retract from the floor of the closure blank in advance of retraction of the injector means, to clear the injected plastics material before retraction of the rest of the injector means.

4. Apparatus according to claim 3, wherein said injector means comprise a plurality of injector pins extending in a circular array around the injector head, and said shut off means comprise a plurality of shut off sleeves, each surrounding a respective one of said injector pins and mounted for movement axially relatively to said injector pin, wherein in an advanced position of said shut off sleeve it contacts the floor of a cap blank into which plastics material is being injected by the injector head, and in a retracted position said shut off means extends to a location where it permits the inlet of plastics composition to a cylindrical said injection passage within which said injector pin moves.

5. Apparatus according to any one of the preceding claims, wherein said injector head comprises separate first and second injector head body members, said first injector head body member fitting inside the second injector head body member and defining therebetween an annular flow channel for inlet of plastics composition to be injected, wherein said first injector head body member includes a male first conical surface and said second injector head body member includes a female second conical surface whereby said first and second conical surfaces define therebetween a conical distribution channel which diverges axially between said annular flow channel and said injection passage.

6. Apparatus according to claim 5, when appendant to claim 1 alone, wherein said injector means includes an injector sleeve mounted for axial movement within said injection passage of annular form, and said divergent conical distribution channel extends from an upper radially inner end communicating with an inlet channel and a lower radially outer end communicating with said annular injection passage.

7. Apparatus according to claim 5 or 6, wherein said first injection head body member is a force fit inside said second injection head body member by means of fins on one of said injection head body members disposed within said annular flow channel and engaging a wall of the other injection head body member which also defines said flow channel.

8. Apparatus according to any one of the preceding claims, wherein said injector means includes a non-stick coating on a surface which will contact said injected plastics material to facilitate retraction of the injector means from contact with the injected plastics material upon retraction of the injector means.

9. Apparatus for moulding gaskets in closure blanks, substantially as hereinbefore described with reference to and as illustrated in Figures 1 and 2, or Figures 4 and 5, or Figures 6 and 7, or Figure 8, or Figure 9 of the accompanying drawings.

10. Apparatus according to any one of claims 1 to 9 and including a moulding station downstream of said injection head to carry out a moulding operation subsequent to injection of the molten plastics composition into the closure.

11. A method of applying a molten plastics composition into a container closure blank for forming a gasket therein, comprising placing an injector head in an inverted said closure blank and applying an injector means against molten plastics composition to eject the plastics composition against the floor of the inverted closure blank through said injector head.

12. A method according to claim 11, and including the step of holding down said injector means on said injected plastics material while withdrawing all or a part of said injector head from the cap blank floor to maintain the injected plastics material in contact with the floor of said closure blank by means of said injector means.

13. A method according to claim 11 or 12, wherein said injected plastics material is in the form of a plurality of separate pieces distributed around the closure blank near its periphery.

14. A method according to claim 11 or 12, wherein said injected plastics material is in the form of a continuous annular array extruded from the end of said injection head and held down in contact with the cap blank floor during extrusion of the injector head.

15. A method according to any one of claims 11 to 14, wherein said container closure is a bottle cap blank or a jar lug cap blank.

16. A method according to any one of claims 11 to 15 and including the step of subsequently moulding the already injected molten plastics composition in the closure.

17. A method of holding a gasket in a container closure, substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 7, or Figures 8 and 9 of the accompanying drawings.