EP1182140A1

EP1182140A1 - Food can end

Info

Publication number: EP1182140A1
Application number: EP00301829A
Authority: EP
Inventors: designation of the inventor has not yet been filed The
Original assignee: Crown Cork and Seal Technologies Corp
Current assignee: Crown Packaging Technology Inc
Priority date: 2000-03-06
Filing date: 2000-03-06
Publication date: 2002-02-27

Abstract

An easy open can end (1), for example of the full aperture type with a peripheral score (13) defining a removable portion, has deposits of protective material (17) provided on both sides of the end. The deposits are displaced relative to the score in different directions depending on their location. As a result, debonding of the deposit on opening can be controlled whilst ensuring that a user is protected from injury by the protective material preventing contact with cut edges when the can is opened.

Description

This invention relates to an easy open food can end having a protective material for providing safe edges when the end is opened. In particular, but not exclusively, it relates to a can end having a large aperture such as those commonly known in the trade as "full aperture" can ends.
Full aperture can ends and so-called "easy-open" can ends have been described extensively in the past. Such can ends typically comprise can ends stamped from sheet metal and formed into a shape comprising a centre panel, chuck wall upstanding from the periphery of the centre panel and a flange extending laterally from the top of the chuck wall. A line of weakness, usually formed by scoring, extends around the centre panel near the chuck wall to define a removable panel.
In easy open ends, a pull tab is fixed to an integral rivet raised from the metal of the centre panel. The tab is raised to break or "pop" the score line and then pulled progressively to remove the removable panel by tearing the rest of the score line. The can end may have a full aperture panel which corresponds to the end shape, usually circular or rectangular, or a partial aperture such as may be used as a pouring aperture for soups or other liquid/semi-liquid food products.
It is known to provide annuli of polymeric material bonded to either the removable panel or the remainder of the can end in order to mask the torn edges of the removable panel or the part of the can end which remains fixed to the can body itself. The use of an inwardly directed guard bead formed in the side wall of the can body to mask the remaining part of the can end after opening has also been proposed.
Few of the safety edges proposed have been successfully commercialised for a variety of reasons. Folds and ledges which cover the exposed edge introduce high metal on-cost. Extra manufacturing steps and lacquer repair may also be needed where such folds are severe. Polymeric materials proposed may not be suitable for use with food products or for adhesion to lacquer such as is used to coat can ends. Known systems using polymeric materials have not been found to cover the cut edge in a manner which reliably provides protection from the exposed edge for the user.
According to the present invention, there is provided a food can end comprising: a centre panel; a peripheral score defining a removable panel portion of the centre panel; a remaining portion surrounding centre panel; and a tab positioned on the removable panel adjacent the score; and further comprising deposits of protective material on both sides of the end, in which the deposits are fixed to both the removable panel and the remaining portion but are displaced relative to the score in different directions on either surface of the end such that in use, when the end is opened, the deposit debonds from either the removable panel or from the remaining portion of the end, and a user is protected from injury by protective material preventing contact with both raw edges.
In a preferred embodiment, the protective material is selected from the group comprising polyamides, polyesters, rubber latex, SBR latex, silicone rubber and styrene acrylic.
Not only does the can end of this invention provide a safe edge to both the removable portion and the remainder of the end fixed to the can itself, but the materials selected to cover the raw edges are approved for use with food products and adhere to lacquers.
Preferably, the protective material is selected from the group comprising polyester, SBR latex and styrene acrylic. Polyester may be deposited readily by hot melt, in addition, or alternatively, it may be deposited in powder form. SBR latex and styrene acrylic may be deposited by means of a nozzle or by a printing method with, optionally, a thickener, if necessary. SBR latex and styrene acrylic are applied as aqueous dispersions (35 to 55% water) which react to form solid deposits during curing.
Water-based dispersions of protective material are curable at temperatures of about 100°C and within a few minutes. A powdered polyester, for example, requires a temperature in excess of 160°C in order to be flowed out in the same amount of time.
Ideally, the protective material is deposited such that it remains adhered to the removable part of the centre panel around the majority of the top surface of the end and on the remaining portion, i.e. the annulus or rim, around the majority of the underside of the end.
In use, the tab is raised away from the central panel to break the score over a distance up to a predetermined maximum length so that the protective material may remain adhered to the underside of the central panel and around the top of the annulus over that maximum length.
The protective material is preferably deposited as either a continuous line or as drops. Where the protective material is deposited as drops, the drops should be spaced apart by less than a characteristic radius through a section of a finger contacting the edge. Clearly from a safety point of view it is preferred that the deposits are contiguous since the characteristic radius varies according to the load applied by the finger and stretching of the skin as the load increases.
For contiguous droplets on the removable panel of the end, the smaller the droplet contact radius the safer is the edge whereas with a non-contiguous deposit the larger the droplets the safer is the edge. This situation is reversed for the rim where the curvature of the end is concave, i.e. the reverse of the panel. For discontinuous deposits, a preferred maximum spacing is 2 mm.
Although a continuous deposit or contiguous droplets may be preferred from a safety aspect, there is a maximum limit on droplet/contact radius due to tear force constraint. This may also vary according to the material used for the deposits and whether such material penetrates or wets inside the score itself.
Advantageously, the protective material extends over and outboard of the score by less than the length of a horizontal portion outboard of the score, typically 0.5 mm. Although the overhang could be the same inboard of the score, in practice it is preferred that the overhang is offset twards the panel or rim in order to ensure that the deposit debonds from the appropriate during opening.
Preferred embodiments of the invention will now be described by way of example only, with reference to the drawings, in which:
Figure 1 is a plan view of an easy open end;
Figure 2 is a plan view of the removable panel of the easy open end of figure 1; and
Figure 3 is an underplan view of the removable panel of figure 2.
In figure 1, a full aperture easy open end 1 comprises a centre panel 3 having a tab 5 with a nose 7 and a ring 9 fixed to the centre panel by a rivet. The end also comprises a chuck wall and flange 11 around the periphery of the centre panel 3. A circumferential score 13 on the centre panel defines a removable panel 15 which is shown in isolation in figures 2 and 3.
Discrete deposits 17 of protective material have been provided around the end, both above and below the score 13. As better seen in figures 2 and 3, these deposits 17 are provided around the major arc between points A-A on the top (tab side) of the removable panel 15 (figure 2) and around the minor arc A-A of the underside of the removable panel (figure 3).
Although the deposits 17 shown in figure 1 adhere to both surfaces of the end, they are offset towards the removable panel around the major arc A-A and towards the periphery (rim) of the centre panel around the minor arc A-A. Conversely, on the underside of the end, deposits are offset towards the rim of the centre panel around the major arc A-A.
The deposits 17 are shown in the drawings as discrete elements approximately 1.5 mm in diameter and spaced approximately 0.5 mm apart. In practice, however, the shape, size and spacing may vary, provided that the spacing is not so great that a user may come into contact with the cut edge 19 of the panel (or that of the remainder of the end) with subsequent risk of injury. In addition, the deposits must extend sufficiently over the cut edges for adequate safety performance, whilst not contacting the reverse wall of a countersink as this would adversely influence debonding. In practice this means that the external deposit should not extend by more than 0.5 mm beyond the score for a 73 mm diameter end.
Alternatively, in another embodiment, instead of discrete elements a continuous line of protective material may be provided between points A-A in the same manner as the discrete deposits, although this requires a greater quantity of material with associated costs and the overlap must be very small in order to overcome the high tear force.
In use, the can end 1 is opened in the usual manner by raising tab 5 so that the nose 7 breaks the score 13. the tab 5 is raised until the handle 9 overlies flange 11 and the score 13 "pops" (i.e. is broken), typically between points A-A in the embodiment shown. The end shown in the drawings includes reinforcing ribs 21 which assist in controlling the opening of the end.
Since the deposits are offset towards the underside of the removable panel and towards the rim on the top between A-A, the forces involved in popping the score are not affected to any large degree. Opening of the end is completed by pulling the tab by ring 9, thereby tearing the rest of the score line. The tear force is increased by the need to debond the deposits from one side of the score.
This increase in tear force requires a limit to be placed on the number and size of droplets, according to the material type. The process of debonding is complex since it is a mixture of peel and shear and the stresses in the two parts of the material are unequal. Furthermore, the score may increase of decrease the bond area, depending upon whether or not the deposit wets inside the score. In practice, the limit on tear force increase due to the deposits of the present invention should not be more than 25%. It is possible to offset some of this increase by modifications in end design but any increase over 25% is not acceptable for openability.
Full aperture easy open ends of the type shown in the figures are commonly used in the packaging of food products. We have found that the selection of materials used for the deposits of protective material are therefore critical.
Possible food grade protective materials must be capable of withstanding the sort of temperature involved in sterilisation processes and must adhere to the lacquer coating which is customarily applied to the can end. Clearly it would be unacceptable for deposits to become detached from the end and fall into the food product within the can, for example. Furthermore, the method of application of the material may be dictated by the phase (liquid or solid), viscosity, and format in which the material is available.
The following materials have been selected for possible use in the ends of the invention: polyamides, polyesters, rubber latex, SBR latex, silicone rubber and styrene acrylic. However, certain of these materials, although fitting the above criteria, may require excessive temperatures and/or time for curing or may be prohibitively expensive. Polyamide, for example, is also not a preferred material due to its poor water resistance.
Another problem which the selected materials address is the ease (and associated cost) of application. Alternative methods may depend on the type of material but include hot melt gun or a powder spray for polyester, or nozzle or printing application (with a thickener if necessary) for an aqueous dispersion of SBR latex or styrene acrylic. These three materials represent the preferred materials for use with the food can ends of the present invention.
Application of the two fluid materials, can be carried out with a rotary indexing machine using either sequential deposition from one nozzle onto a spinning end or simultaneous deposition from multiple nozzles onto a stationary end.
In sequential deposition, the unoriented end is indexed into a permanently spinning chuck which then rises to place the spinning end beneath the application nozzle. An optical sensor detects a printed mark on the seaming panel (to which the printing and tab are oriented) and a timing system for each nozzle is activated. Recognition of the mark occurs during a first revolution and deposition of the droplets starts within the second revolution. The chuck then drops. Two deposition stations are required, one for deposition on each side, with an inversion station between the two.
For simultaneous deposition, the end must be oriented on the machine before it is indexed into the deposition station since it is not spun in the station. Two applicator heads are used, one for each surface, with no inversion required. These are located on the surfaces of the end and all droplets are delivered in one firing. The heads then move apart and the end is indexed to an exit station.
The embodiment described above is just one example of applications for the invention and changes such as shape of the end and removable panel may be made within the scope of the invention as defined in the claims.

Claims

A food can end comprising:

a centre panel;

a peripheral score defining a removable panel portion of the centre panel;

a remaining portion surrounding centre panel; and

a tab positioned on the removable panel adjacent the score;

and further comprising deposits of protective material on both sides of the end,

in which the deposits are fixed to both the removable panel and the remaining portion but are displaced relative to the score in different directions on either surface of the end;

such that in use, when the end is opened, the deposit debonds from either the removable panel or from the remaining portion of the end, and a user is protected from injury by protective material preventing contact with both raw edges.
An end according to claim 1, in which the protective material is selected from the group comprising polyamides, polyesters, rubber latex, SBR latex, silicone rubber and styrene acrylic.
An end according to claim 1 or claim 2, in which the protective material is selected from the group comprising polyester, SBR latex and styrene acrylic.
An end according to any one of claims 1 to 3, in which the protective material is deposited on the centre panel around the majority of the top of the end and on the annulus around the majority of the underside of the end.
An end according to any one of claims 1 to 4, in which, in use, the tab is raised away from the central panel to break the score over a distance up to a predetermined maximum length and the protective material is deposited on the underside of the central panel and around the top of the annulus over that maximum length.
An end according to any one of claims 1 to 5, in which the protective material is deposited as a continuous line or as drops.
An end according to claim 6, in which the protective material is deposited as drops which are contiguous.
An end according to any one of claims 1 to 7, in which the protective material extends over the score by up to 0.5 mm.