Closure with foamed region and methods of forming said closure

Abstract

A closure (750) is provided and comprises a top plate (755) and a sidewall (760) depending from the periphery of the top plate. The closure includes a sealing member (765) which depends from the top plate within the sidewall. The top plate includes a foamed region which is restricted to being within a boundary defined by the sealing member; the sealing member being substantially unfoamed.

Claims

1. A closure comprising a top plate, a sidewall depending from the periphery of the top plate, and a sealing member formed integrally with said top plate and which depends from the top plate within the sidewall, in which the top plate comprises a foamed region and an unfoamed region, the unfoamed region radially outside the foamed region and the foamed region radially restricted to being within a boundary defined by the radial extent of the sealing member, and in which the sealing member is substantially unfoamed and forms an integral part of said unfoamed region of said top plate.

2. A closure as claimed in claim 1, in which the sealing member is a crab claw type seal or a plug seal.

3. A closure as claimed in claim 1, in which the sealing member is formed separately from, and is attachable to, the top plate.

4. A closure as claimed in claim 3, in which the sealing member is a liner, the liner being secured or securable to the top plate and defining a non-sealing region of the top plate within the liner, in which at least part of the non-sealing region includes the foamed region.

5. A closure as claimed in claim 1, in which the sealing member is generally annular.

6. A closure as claimed in claim 1, in which the extremity of the foamed region is spaced from the boundary defined by the sealing member by between 0.5 and 5 mm.

7. A closure as claimed in claim 1, in which the sidewall comprises a screw thread formation and in which the screw thread formation extends radially inwards and in which the foamed region does not extend beyond a boundary defined by the radial extent of the formation.

8. A closure as claimed in claim 1, wherein the unfoamed region has an apparent density of R, and the foamed region has an apparent density in the range of 0.2-0.9*R, the sidewall including a screw thread formation, the material forming the sidewall at least in the region of the formation having an apparent density in the range 0.8-0.99*R whereby shrinkage has been compensated by natural foaming.

9. A closure as claimed in claim 1, in which the sidewall is thinner than the top plate before foaming, after foaming, or before and after foaming.

10. A closure as claimed in claim 1, in which the thickness of the sidewall is down-gauged by 50% or by 20% to 80%.

11. A closure as claimed in claim 1, in which the sidewall comprises a screw thread formation, and in which the depth of the formation is more than 80% of the depth of the sidewall and is up to 120% of the depth of the sidewall.

12. A closure as claimed in claim 1, in which at least part of the sidewall has a foamed region.

13. A closure as claimed in claim 4, in which the liner is generally disc-shaped.

14. A closure as claimed in claim 6, in which the sealing member is generally annular.

15. A closure as claimed in claim 2, in which the sealing member is generally annular.

16. A closure as claimed in claim 3, in which the sealing member is generally annular.

17. A closure as claimed in claim 4, in which the sealing member is generally annular.

18. A closure as claimed in claim 1, in which the extremity of the foamed region is spaced from the boundary defined by the sealing member by between 1 mm and 2 mm.

Description

(1) In the following description, all orientational terms, such as upper, lower, radially and axially, are used in relation to the drawings and should not be interpreted as limiting on the invention.

(2) FIG. 1 shows a core back moulding process used to form closures in accordance with embodiments of the present invention.

(3) FIG. 2 shows an alternative core back moulding process using an inside injection point and an external movable mould part.

(4) FIG. 3 shows an alternative moulding process with an inside injection point and a movable side core.

(5) FIG. 4 shows a further moulding process with an inside injection point and an external movable mould part.

(6) FIG. 5 illustrates an example of the difference between a standard cap and a cap formed using a core back moulding and foaming process.

(7) FIG. 6 illustrates an example of a section of a closure formed in accordance with the present invention.

(8) FIGS. 7 to 10 show closures formed in accordance with different embodiments of the present invention.

(9) FIGS. 11 to 15 show a wide mouth closure formed in accordance with the present invention.

(10) FIG. 16 shows a closure formed according to a further embodiment.

(11) FIG. 17 illustrates a method according to an aspect of the present invention.

KEY

(12) Unfoamed Material (i.e. Intentionally Unfoamed)

(13) Expanded Material (i.e. Naturally Foamed)

(14) Foamed Material (i.e. Intentionally Foamed)

(15) In FIG. 1a core back moulding process suitable for use as part of the present invention is shown.

(16) In a first step molten (foamable) plastics material 5 is injected through a nozzle 10 into a cavity 15 formed by a fixed mould part 20 and a moving mould part 25.

(17) In a second step the cavity fill is complete and a short holding phase is provided, during which time the outer skins of the plastics material cool and begin to solidify.

(18) In a third step the moving mould part 25 is moved and the pressure drop causes foaming of the material in the enlarged cavity. As a result the material between the outer skins of the top plate 30 of the moulded closure foams.

(19) In FIG. 2 a similar core back foaming process is shown, except that in this embodiment the injection nozzle 110 is inside the mould cavity. This means that the mobile mould part 125 can be positioned on the other side of the closure top plate 130.

(20) FIG. 3 is similar to FIG. 2, with an inside injection point. In this embodiment the core back movement is at the outside face of one side of the sidewall 235.

(21) FIG. 4 is also similar to FIG. 2, with an exterior core back movement above the top plate 330. In FIGS. 2 and 4 the top plates 130, 330 include a depending annular seal 132, 332. In FIG. 2 the movable mould part is positioned so that the cavity gap is formed radially inwards of the seal 132. However, the present inventors have realised that it is possible to cause foaming of the top plate above the seal without causing foaming in the seal itself because the seal is perpendicular to the mould parting line (so they will maintain their dimensional integrity). Accordingly, in FIG. 4 the movable mould part 325 is an outside part and extends wider than the seal. With an inside injection point and an outside core back function this means that a larger area can be foamed than with an inside injection/inside movement system and consequentially a larger area can be foamed.

(22) FIGS. 5 and 6 illustrate some examples of foaming conducted in accordance with the present invention.

(23) The closure 450 of FIG. 7 includes a disc-shape top plate 455 and a generally cylindrical sidewall 460 depending from the periphery of the plate 455. The sidewall 460 includes an internal screw thread formation 462. The sidewall (excluding the thickness of the formation) is thinner than the top plate. The top plate 455 is unfoamed and the sidewall 460 is expanded.

(24) In FIG. 8 the closure 550 includes an expanded side wall 560. An annular plug seal 565 depends from the underside of the top plate 555. The top plate 555 includes a foamed core region 557 and an unfoamed region 559 (radially) outside of the core region 557. The seal 565 is located in the unfoamed region 559 so there is no foaming of the seal 565, which maintains dimensional repeatability and functional sealing performance.

(25) FIG. 9 shows a closure 650. Expanded material in the sidewall 660 is only in the region of the formation 662. The top plate 655 includes an unfoamed peripheral region 659 and a central region 657 with a foamed core. An annular seal 665 depends from the top plate in the region 659.

(26) In FIG. 10 the closure 750 includes a top plate 755 with a foamed core within the boundary of a sealing member 765, and an unfoamed, unexpanded sidewall 760.

(27) FIGS. 11 and 12 show a jar lid generally indicated 850. The lid 850 comprises a generally disc shape top plate 855 and a cylindrical sidewall 820. The top plate 855 includes a disc-shape central region 857 and an inclined, shoulder-like peripheral region 859 which merges into the sidewall 860.

(28) The region 859 includes a sealing arrangement comprising an annular crab claw seal 858.

(29) FIG. 12 shows the closure prior to foaming.

(30) The closure is manufactured using a foamable plastics composition and by a core back process illustrated in FIG. 13, in which part of the core corresponding to the central region moves to cause foaming. Foaming is thereby restricted so as to be within only the central region and therefore spaced from the seal (which remains unfoamed).

(31) FIG. 14 shows part of a closure similar to the closure of FIGS. 11 to 13. In this embodiment the thickness of the sidewall 860 is reduced. Because the entire closure is formed from a formulation containing a foaming agent, the material which enters the part of the mould cavity corresponding to the sidewall expands, avoiding sink marks.

(32) FIG. 15 shows a jar lid 800 formed according to a further embodiment. The lid 800 comprises a top plate 801 and a depending sidewall 802. An annular seal 803 depends from the top plate. A central region 804 of the top plate 801 is foamed (with a foamed core 804a sandwiched between outer skin layers 804b, 804c). The region 804 is inboard of the seal 803.

(33) The sidewall 802 includes and internal screw thread formation 805. No specific foaming is induced in the sidewall. However, natural expansion of the inherently foamable material will compensate for any shrinkage in the area, in particular at the exterior of the sidewall adjacent the screw thread formation.

(34) FIG. 16 shows a closure 950 formed according to a further embodiment. The closure includes a top plate 955 with a depending sidewall 960. The sidewall 960 includes a screw thread formation 962. A separate sealing liner 970 is provided and fits under the top plate 955. The top plate 955 has a foamed region 957. The foamed region is restricted to be within a boundary defined by the radial extent of the formation 962.

(35) FIG. 17 shows a sequential moulding process in which there is an initial injection moulding phase to form a closure body 1070, followed by a foaming phase to form a body. Following the foaming phase a layer of material 1075 is moulded over the body. This would allow, for example, a cheaper material to be used for the initial body followed by a more expensive finish material.

(36) FIG. 18 shows a known closure sidewall 1160 with an internal screw thread formation 1162. Conventionally the thickness t of the screw thread is no greater than 80% of the thickness f of the sidewall if sink marks in the exterior face of the sidewall behind the thread are to be avoided.

(37) Referring to FIG. 19, the present inventors have found that the relative thickness of a thread 1262 can be significantly increased with respect to a sidewall 1260 (i.e. the thickness of the sidewall can be reduced) by using a foamable plastics material. During the moulding process the foamable material expands to naturally counteract material shrinkage in the mould which would otherwise form sink marks in the exterior face of the sidewall.

(38) Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiments shown and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention.