CA2076460A1

CA2076460A1 - Container closures

Info

Publication number: CA2076460A1
Application number: CA002076460A
Authority: CA
Inventors: John Sidney Hewitt; Arthur John Gunstead
Original assignee: Individual
Current assignee: WR Grace and Co Conn
Priority date: 1991-09-04
Filing date: 1992-08-20
Publication date: 1993-03-05
Also published as: EP0531039A1; AU2207392A; ZA926287B; JPH05213350A; GB9118890D0; AU646970B2

Abstract

ABSTRACT
Container Closures A container closure, especially for a drinks can, includes a line of weakness around at least one aperture closed by a displaceable tab. The line of weakness is sealed by a polymeric material which has been applied as a plastisol and then gelled, the polymeric material being free of polyvinylchloride and the fluid plastisol having a low viscosity in the range 200 to 1800 mPa at 100s-1 and 43°C and below 2000 mPa at 441s-1 and 40°C. The opening below 2000 mPa at 441s and 40°C. The opening force for the tab at the or each aperture is in the range 10 to 60N to allow opening by finger or thumb pressure.
The plastisol is for instance based on acrylate ester polymers or styrene/ethylenically unsaturated carboxylic acid copolymers and comprises plasticiser such as dialkyl esters of phthalic or other dibasic carboxylic acid, including polyester type materials and optionally a viscosity depressant such as a volatile diluent, a protective colloid and/or an emulsifier, and filler.

Description

CONT~ rNER CLOSURES 2~7~

~ his invention relates to container closures having a panel that includes an aperture that during use is maintained closed, but that can be opened to allow the removal of the contents of the container.

BAC~GROUND OF THE INVENTION

Containers such as cans and bottles are provided with a closure that often comprises a metal panel. In some instances it is intended that substantially the entire closure should be removed in order to open the container, but in other instances it is intended that opening should be achieved by displacing part or all of the panel, the remainder of the closure being left on the container.
For this purpose, a line of weakness is provided in the panel around the edges of a desired aperture in the panel and this aperture is covered by a displaceable tab. When the container is to be opened, the tab is displaced, either by pulling or pushing, so as to open the aperture. The displacement of the tab may involve total removal of the tab, or it may be displaced into an open hinged position.
In some constructions the line of weakness is formed by scoring or stamping the metal or other panel and a ring pull or other holding means is provided for pulling the area defined by the line of weakness as a tab from the panel when it is desired to open the aperture.
It is intended that the scoring, stamping or other operation that is used to form the line of weakness should not disrupt the continuity of the material of the closure, with the result that leakage of the contents of the container should be incapable of occurring through the line of weakness. However the stamping, scoring or other operation that is used to form the line of weakness is liable to disrupt the continuity of any lacquer or other protective coating on the inner face of the closure and this can lead to corrosion.

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In some containers, the line of weakness can potentially allow for leakage to occur from the container.
This can be due to accidental disruption of the material of the panel, but in some instances it is deliberate. In particular, it is known to provide the panel with an aperture and to provide a displaceable tab hinged to the panel, wherein the edges of the tab overlie and are separated from the edges of the aperture. It is then necessary to provide a seal between the edges of the tab and the aperture. Also, it may be desirable to apply material that will prevent corrosion initiating at the edges.
It is therefore known to provide a layer of polymeric material to cover the line of weakness to seal against corrosion and/or leakage through the line of weakness. Conventionally the layer of polymeric material is a layer of gelled PVC plastisol that has been formed by applying a fluid PVC plastisol and then gelling it. The layer may be in the form of a disc but often is in the form of a ring covering the line of weakness.
GB 2,197,634 describes a container closure in which the removable tab is hinged to the panel and the edges of the tab overlie and are separated from the edges of the aperture and defines the requirements of the PVC plastisol that should be used. In particular, it states that it is necessary to use a PVC plastisol that has a viscosity of 2,000 to 2,800 mPa.s at 40C when measured at a shear of 441 seconds -l. Other necessary properties are also defined.
There are allegations that it is undesirable to allow beverages and foodstuffs to come into contact with PVC products, and this constitutes a potential disadvantage to the system of GB 2,197,634 and other systems where a gelled PVC plastisol covers the line of weakness. It would be desirable to be able to overcome this disadvantage.
SUMMARY 0~ THE INVENTION
A container closure according to the invention comprises a closure panel, a line of weakness in the panel 2 ~fr~

around the edges of an aperture in the panel that is covered by a displaceable tab, and a layer of gelled plastisol that covers the line of weakness and seals aqainst corrosion and/or leakage through the line of weakness and which has been formed by applying on to the line of weakness a fluid plastisol of polymeric material and then gelling the plastisol. In the invention, the polymeric material of the plastisol is free of polyvinyl chloride and the fluid plastisol has a viscosity that is below 2,000 mPa measured at a shear of 441 seconds -1 and 40C and that is in the range 200 to 1,800 mPa at 100 seconds -1 and 43C.
DETAILED DESCRIPTION OF THE INV~NTION
Thus we have found that if an attempt is made to deposit a layer of plastisol that is free of polyvinyl chloride, it is not possible to obtain satisfactory results when the material complies with the viscosity requirements that are stated in GB 2,197,634 to be essential. Instead, it is essential for the plastisol to have a much lower viscosity than t~le lowest values stated as being acceptable in GB 2,197,634. The reason for this is unclear but, irrespective of the reason, we find that it is a fact that satisfactory results are not achieved unless the viscosity is much lower than suggested as being essential in GB
2,197,634.
In addition to the closure end, the invention also includes containers fitted with the closure end and, in particular, sealed containers containing a beverage or foodstuff, methods in which the plastisol is lined on to the closure and then gelled, and plastisol for use in these methods.
The container can be a bottle, for instance of glass or organic polymeric material, in which event the closure can be a bottle cap. More usually, the container is a can, in which event the closure will be a can end. The can and/or can end could be of polymeric material but generally both are of metal.

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A variety of fillings can be stored within the container ~ut preferably the filling is a foodstuff or beverage. P~eferably the filling is one that is packed under pressure and so the invention is of particular pressure when the filling is a carbonated beverage, especially beer.
The line of weakness may be a score line or press line that defines a tab provided with a ring pull or other means for removal or hinging, as described above. The invention is then primarily of use for preventing corrosion of the inner face of the closure. Preferably however the displaceable tab is hinged to the panel, the edges of the tab overlie and are separated from the edges of the aperture, and the layer of gelled plastisol seals between the edges of the tab and the aperture. The layer of gelled plastisol generally also extends over the edges of the tab and the parts of the panel that surround the edges of the tab. The plastisol will therefore prevent leakage between the tab edges and the aperture edges, and will also seal against corrosion initiating at the edges.
Preferably the tab is positioned on the inner face of the closure and the closure is intended for a pressurised container (such as beer) since the internal pressure then forces the tab against the panel. The aperture can be opened by pressing the tab inwardly.
It can be convenient to provide two apertures, each with its associated tab and layer of gel plastisol, in the closure panel, for instance as described in GB 2,197,634.
The tensile strength and elongation values of the gelled plastisol should be selected having regard to the size of the aperture such that it is possible to open the aperture by the application of convenient finger or thumb pressure.
The aperture is often relatively small (typically in the range 5 to 20mm diameter) and suitable opening forces are typically in the range 10 to 60N. In order to obtain these values it is then convenient for the gelled plastisol to have a tensile strength of about 0.4 to lN/mm2 and a 2~
.
maximum elongation of about 120 to 250%. In particular, when the closure has an aperture of 15 to 20mm, e.g., around 16.5m~, diameter for pouring and an aperture of 5 to 12mm, e.g., around 8mm, diameter for venting, the gelled plastisol is preferably such that the opening force required for the pouring aperture is about 20 to 60N
preferably 20 to 40N or 20 to 30N while the opening force for the venting aperture is about 10 to 40N preferably 15 to 25N. The opening force is determined when there is no counter pressure.
Although GB 2,197,634 states that it is essential for the viscosity to have the value of above 2,000mPa at 441 sec1 and 40C in order to achieve satisfactory penetration between the edges of the tab and the aperture, satisfactory results are not achieved at these values when the plastisol is free of polyvinyl chloride and, instead, the fluid plastisol should have a viscosity of below 1,500mPa at 100s1 and 43C. Generally the viscosity under these conditions is at least 250mPa and preferably at least 400mPa. Generally it is not more than 1,000mPa and preferably it is not above 750mPa. The viscosity measured at 40C and 441 sec typically is also below 1500mPa but above 200mPa.
Plastisols for use in the invention comprise a dispersion of thermoplastic polymeric particles in a liquid organic plasticiser into which the particles will dissolve on heating to form a gelled structure.
The polymeric component preferably comprises a homopolymer or copolymer of an acrylic ester or a copolymer of an olefin with maleic anhydride or blends of these or blends of either or both of these with other polymers that are free of polyvinyl chloride.
Other suitable polymers are copolymers of styrene and/or alkyl styrene (e.g., a-methyl styrene) with unsaturated carboxylic acid such as methacrylic acid.
Suitable maleic anhydride copolymers are those disclosed in U.S. 4,020,966, comprising copolymers of 2~ ~ s~

normal ~-olefin and maleic anhydride in a one to one ~olar ratio in suspension in a polyepoxide plasticiser, for example epoxidised soy bean oil.
Suitable acrylic ester copolymers include those described in U.S. 4,199,486 and comprise homo- or co-polymers of methyl methacrylate as the resin, in suspension in organic plasticisers such as phthalate plasticiers, for example dioctylphthalate or dibutylphthalate.
Further suitable acrylate polymers are disclosed in DE
2,454,235 and DE 2,529,732, and include homo- or co-polymers of alkyl methacrylates and alkylacrylates with methacrylic acid esters with C2 to 10 aliphatic alcohol, acrylic acid esters with Cl to 10 aliphatic alcohol, styrene and/or ~-methyl styrene. Suitable alkyl acrylates or alkyl methacrylates include methyl methacrylate, tertiary butyl acrylate, ethyl methacrylate, N-propyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate or cyclohexyl methacrylate.
Any plasticiser suitable for the particular polymer or polymer ble~d may be used, and it should be capable of solvating or dissolving the polymer or polymer blend when heated and of remaining essentially compatible on cooling.
Suitable materials from which the plasticisers may be selected include, for example, dialkyl phthalates such as dibutyl, diisodecyl or dioctyl, diethylhexyl or octyldecyl phthalate, alkylphthalylal~yl glycolate, such as ethylphthalyl glycolate and butylphthalylbutyl glycolate;
dialkyl esters of alkane dicarboxylic acids such as diisobutyladipate and dibutylsebacate, acetyltrialkyl citrates, such as acetyltributyl citrate; tralkyl and triaryl phosphates such as trioctyl phosphate and tricresyl phosphate; alkyl esters of fatty acids such as octylstearate; epoxidised trigycerides such as epoxidised soy bean oil; polymeric polyester plasticisers such as polymeric glycol adipate; polyesters derived from dibasic acids and glycols for example dipropyleneglycolbenzoate, diethyleneglycoldibenzoate, triethyleneglycoldibenzoate, polyethyleneglycol 200 dibenzoate, polyethylene glycol 600 dibenzoate. Mixtures of the above plasticisers may also be used.
The amount of plasticiser used in the plastisol composition may for example be between 60 and 300 preferably 80 to 200, phr (parts by weight per 100 parts by weight of the resin).
The non~PVC plastisols used in the invention may also comprise filler materials such as aluminium trihydrate, barytes, china clay, chalk, kaolin, mica flour`, wood flour and diato~aceous earth. The amount typically is in the range 60 to 600, often 100 to 400, phr.
The plastisol may, if desired, comprise a finely divided suspension of particles comprising a core material which reacts well with the plasticiser to form a suitable seal after fluxing, and a shell material which is less readily able to react with the plasticisèr and which prevents contact between the plasticiser and the core material until the plastisol is heated to flux it.
By appropriate selection of the resin component or components, the plasticiser or plasticisers and any other components in the plastisol it is possible to formulate a plastisol that after gelling will give a gelled layer having elongation and tensile strength values that are suitable for the intended use of the composition.
Such fluid plastisols are liable to have too high a viscosity for use in the invention and so it is generally necessary to include a viscosity depressant. This is normally selected from one or more volatile diluents, emulsifiers and protective colloids. Suitable volatile diluents include low boiling olefinic hydrocarbons such as C10-C16 hydrocarbons. Suitable emulsifiers include salts or esters of fatty acids, ethylene oxide condensates with alkyl phenyls and fatty alcohols, zinc resinate and zinc/magnesium octoate. Suitable protective colloids include lecithin.

The amount will be selected according to the other c:omponents in the composition and the desired viscosity at t:he conditions of application, but is generally in the range 5 to 100, usually 10 to 50, phr.
The compositions can contain other conventional additives, for instance pigments such as carbon blacX and titanium dioxide.
The formulation of the plastisol is preferably such that, having regard to the lacquer or other surface characteristics of the closure, the plasti~ol wets the surface adequately, for instance forming an edge angle of around 30 to 40.
The plastisol can be applied through a ring nozzle as described in DE 2,421,315 or by other suitable lining apparatus to a thickness as described in GB 2,197,634.
For further details of suitable fillers and methods of application, reference can be made to GB 2,197,634.
After applying the fluid plastisol the closure carrying it is then subjected to heating in order to cause gelling and fluxing of the plastisol. This generally requires exposure to a temperature of 150 to 250C for from 5 seconds to 10 minutes. Often the temperature is in the range 180 to 230C and the time is often in the range ~ to 2 minutes.
The following examples illustrate the invention.
Example 1 A fluid plastisol is formulated from (in parts ~y weight) MMA/BMA carboxylated copolymer (paste Grade) 70 MMA/BMA copolymer (Filler Grade) 30 30 Aluminium trihydrate 200 Barytes 60 Titanium dioxide 3 Diethyl hexyl phthalate 100 Volatile diluent (tetradecene) 28 35 Protective colloid (lecithin) S
Emulsifiers (blend of Zn/Mg octoate and ethoylated nonyl phenol) 4.5 9 2~ `J~
MMA/BMA stands for copolymer of methyl methacrylate and butyl methacrylate. This composition has a viscosity of 690mPa at 441 seconds1 and 400C and 600mPa at 100 sec and 430C.
A can end is provided with a pouring aperture about 16mm in diameter and a venting aperture about 8mm in diameter, and each aperture has a hinged tab covering it, of slightly larger diameter so that the edges of the tab overlie the edges of the associated aperture, with the tab on the side of the can end that has been coated with lacquer and that is intended to be inside the can. The general arrangement is described in GB 2,197,634.
The plastisol is applied as a ring around each aperture, as described in GB 2,197,634 to give coatings having a thickness of 0.5mm at the pouring aperture and 0.4mm at the vent ring aperture and which extend between the adjacent edges of the associated apertures and tabs.
The lined can end is then heated to a temperature of 210C for 1 minute in order to flux and gel the plastisol.
The force required to open the pouring and venting apertures is 30N and 17N respectively.
Example 2 Two fiuid plastisols are formulated from (parts by weight):-A B
Carboxylated MMA/BMA core/shell 70 70 cap alymer (Paste grade) Carboxylated MMA/BMA conventional 30 30 cap alymer (Filler grade) 30 Diethyl hexyl phthalate loO 130 Di-iso decyl phthalate 2.5 2.5 Aluminium trihydrate 50 50 Barytes 60 60 Titanium Dioxide 3 3 35 Carbon Black 0.1 0.1 Lecithin 5 5 Zn/Mg octoate 2.5 2.5 10 2 g~ ! 6 ~
Ethoxylated monyl phenol 2 2 The compositions have the following viscosities (in mPa):-~ B
441 secl at 40C 909 325 100 secl at 43C 1042 407 When applied using the same conditions as described in Example 1 (except that the fluxing was carried out at 180C
for 3 minutes) to can ends the opening forces for the two lo apertures are as follows (in N):-A B
Venting aperture 28 21 Pouring aperture 56 43 While the present invention has been described in relation to its preferred embodiments, other equivalents, modifications, or variations can achieve the same result. Equivalents, modifications and variatlons of the present invention will be obvious to those skilled ln the art and it ls lntended in the appended claims to cover all such modifications variations and equlvalents as fall within the true spirit and scope of this invention.

Claims

1. A container closure end comprising a closure panel, a line of weakness in the panel around the edges of an aperture in the panel that is covered by a displaceable tab, and a layer of gelled plastisol that covers the line of weakness and seals against corrosion and/or leakage through the line of weakness the polymeric material is free of polyvinyl chloride and the fluid plastisol has a viscosity that is below 2,000 mPa at 400 seconds -1 and 40°C and that is in the range 200 to 1,800 mPa at 100 seconds -1 and 43°C.

2. A closure according to claim 1 wherein the displaceable tab is hinged to the panel, the edges of the tab overlie and are separated from the edges of the aperture, and the layer of gelled plastisol seals between the edges of the tab and the aperture.

3. A closure according to claim 1 wherein the aperture has a diameter of from 5 to 25mm and the tensile strength and coating thickness of the plastisol are close so that the opening force required to open the aperture (measured without counter pressure) is from about 10 to about 60N.

4. A closure according to claim 3 wherein the closure has two of the said apertures, one aperture having a diameter in the range 15 to 20mm and requiring an opening force (with no counter pressure) of about 20 to about 60N and the other aperture having a diameter of 5 to 12mm and requiring an opening force of about 10 to about 30N.

5. A closure according to claim 4 wherein the opening force for the larger aperture is in the range of about 20 to about 40N and the opening force for the smaller aperture is in the range of about 15 to about 25N.

6. A closure according to claim 1 wherein the closure is a can end.

7. A closure according to claim 1 wherein the polymeric material comprises a polymer or copolymer of an acrylic ester, a copolymer of styrene or alkyl styrene with an unsaturated carboxylic acid, or a copolymer of an olefin with an unsaturated carboxylic acid.

8. A closure according to claim 1 wherein the plastisol is formed of 100 parts by weight of the polymer, 60 to 600 phr filler and 60 to 600 phr plasticiser and S to 100 phr viscosity depressant.

9. A closure according to claim 1 wherein the viscosity of the fluid plastisol is in the range 250-1,500,preferably 250-750, mPa at 100 seconds -1 and 43°C.

10. A can end comprising a closure panel, a line of weakness in the panel around the edges of an aperture in the panel that is covered by a displaceable tab, and a layer of gelled plastisol that covers the line of weakness and seals against corrosion and/or leakage through the line of weakness and has been formed by applying on to the line of weakness a fluid plastisol of polymeric material and then gelling the plastisol, wherein the polymeric material is free of polyvinyl chloride and the fluid plastisol has a viscosity that is below 2,000 mPa at 400 seconds -1 and 40°C and that is in the range 200 to 1,800 mPa at 100 seconds -1 and 43°C.

11. A closure according to claim 10 wherein the displaceable tab is hinged to the panel, the edges of the tab overlie and are separated from the edges of the aperture, and the layer of gelled plastisol seals between the edges of the tab and the aperture.

12. A closure according to claim 10 wherein the aperture has a diameter of from 5 to 25mm and the tensile strength and coating thickness of the plastisol are close so that the opening force required to open the aperture (measured without counter pressure) is from about 10 to about 60N.

13. A closure according to claim 10 wherein the closure has two of the said apertures, one aperture having a diameter in the range 15 to 20mm and requiring an opening force (with no counter pressure) of about 20 to about 60N
and the other aperture having a diameter of 5 to 12mm and requiring an opening force of about 10 to about 30N.

14. A closure according to claim 10 wherein the polymeric material comprises a polymer or copolymer of an acrylic ester, a copolymer of styrene or alkyl styrene with an unsaturated carboxylic acid, or a copolymer of an olefin with an unsaturated carboxylic acid.

15. A container closure end having a closure panel, a line of weakness in the panel around the edges of an aperture in the panel that is covered by a displaceable tab, and a layer of gelled plastisol that covers the line of weakness and seals against corrosion and/or leakage through the line of weakness the polymeric material is free of polyvinyl chloride and the fluid plastisol has a viscosity that is below 2,000 mPa at 400 seconds -l and 40°C and that is in the range 200 to 1,800 mPa at 100 seconds -1 and 43°C
wherein the gelled plastisol has been formed by applying on to the line of weakness a fluid plastisol of polymeric material and then heating the plastisol.