US3666138A

US3666138A - Container closure

Info

Publication number: US3666138A
Application number: US46312A
Authority: US
Inventors: Robert J Morris Jr; Thomas Jayes Hartz
Original assignee: National Can Corp
Current assignee: Rexam Beverage Can Co
Priority date: 1970-06-15
Filing date: 1970-06-15
Publication date: 1972-05-30
Anticipated expiration: 1989-05-30

Abstract

A metal container having a preformed aperture sealed on a side with an easy open tape laminate made of a flexible strip and a pressure sensitive adhesive. The exposed edge of the preformed aperture in the closure is coated with a cured coating composition comprising a low molecular weight epoxy resin and a urea-formaldehyde curing agent.

Description

United States atent Morris, Jr. et al.

[54] CONTAINER CLGSURE [72] Inventors: Robert J. Morris, Jr., Lisle; Thomas Jayes Hartz, Downers Grove, both of 111.

[73] Assignee: National Can Corporation, Chicago, Ill. [22] Filed: June 15, 1970 [21] Appl. No.: 46,312

[52] US. Cl ..220/53, 156/256, 156/280,

156/300, 156/305, 161/186, 161/215, 222/485 [51] Int. Cl. ..B65d l7/20, 865d 17/14 [58] Field ofSearch ..220/53,54; 222/485,487;

[56] References Cited UNITED STATES PATENTS 3,389,827 6/1968 Abere et al. ..220/53 2,713,569 7/1955 Greenlee 161/186X 2,870,935 l/l959 l-loughtelling ..220/53 [451 May 30,1972

2,970,077 l/l96l Groves ..l6l/l86 X 3,386,955 6/1968 Nawakowski et al. .,16l/ l 86 OTHER PUBLICATIONS Handbook of Epoxy Resins," by Lee & Neville, copyright 1967, McGraw- Hill publishers, Chap. 2, pg. 3, chap. 10, pg. 13, Chap. 24, pg. 6

Primary Examiner-Haro1d Ansher Armrney-Robert .l Doherty [5 7 ABSTRACT A metal container having a preformed aperture sealed on a side with an easy open tape laminate made of a flexible strip and a pressure sensitive adhesive. The exposed edge of the preformed aperture in the closure is coated with a cured coating composition comprising a low molecular weight epoxy resin and a urea-formaldehyde curing agent.

1 1 Claims, 3 Drawing Figures PATENTED MM 3 0 1972 BACKGROUND OF THE INVENTION This invention relates to container closures having preformed apertures in which the bare metal edge of an aperture is coated to protect the contents of the containers.

In the packaging industry, containers popularly known as tab or tape open containers have assumed importance because the contents are safely hermetically sealed and yet the tab closure can easily be removed by the consumer. The closure is conventionally formed by sealing an aperture preformed in the lid of a metal container with a tape laminate comprising a flexible strip and a pressure sensitive adhesive. The flexible strip may be a metallic foil, or may be a tough plastic material, such as biaxially oriented polyethylene terephthalate, vapor coated with a thin layer of metal to provide opacity. Various embodiments of the general concept are taught in U.S. Pat. Nos. 3,389,827, 3,251,515 and 3,292,828.

Tape opening cans are manufactured by cutting an aperture in a metal closure formed from tin coated steel. The pressure sensitive tape is applied over the aperture to form a hermetic seal. The lid is fastened to the can after the container has been filled with its contents.

In tape sealed metallic closures the edge of the preformed aperture exposes bare cut steel and tin to the contents of the can. This has created a serious problem when the contents of the can has an acidic character which causes the steel to be anodic to the tin. Beverages such as grape drink, cherry drink or other fruit drinks cause the steel to be anodic to the tin and consequently the beverage dissolves the steel, adversely affecting flavor and causing adulteration of the beverage. Eventually the decomposition of the steel weakens the hermetic seal or otherwise causes perforation of the can thereby exposing the can contents to contamination and spoilage.

Therefore, the use of tape open cans has been restricted to beverages which either cause the tin to be anodic to the steel, or cause the steel to be anodic to the tin to a non-aggressive, or minimal degree. For example, beverages such as peach nectar, or apricot nectar decompose the tin inner coating of the can before attacking the steel and beverages such as tomato juice provide a system in which the steel is not aggressively anodic to the tin. Tin pickup is less of a flavor problem than iron pickup by the beverage from the dissolving steel.

Also, oils, such as cooking oils can dissolve the pressure sensitive adhesive and weaken or loosen the bond between the flexible strip and the lid, producing an unreliable closure.

Moreover, even with beverages and other liquids that may safely be used in tape open cans certain problems do occur. The tape may form a hermetically sealed container but there can be small spaces adjacent the edge of the preformed aperture. If there is any seepage of the beverage into these areas an unsightly and unappetizing dried residue may be left when the tape is removed.

It has been suggested that a coating be applied to the exposed edge of the preformed aperture after the pressure sensitive adhesive tape has been adhered to the metallic closure. However, resin coatings previously employed in the art were unsuitable for use with tape seals in cans containing grape drink and similar fruit drinks. A coating composition useful for easy open tape seal container closures requires a combination of the following unique properties, (a) the coating composition must be curable at temperatures below about 250 F. because higher temperatures tend to adversely affect the pressure sensitive adhesive of the tape, (b) the coating composition solvents must not adversely affect the structure of the tape laminate, (c) the coating composition solvents must not attack the pressure sensitive adhesive of the tape thereby weakening or destroying the seal, ((1) beverages packaged in the container must remain free of foreign taste even after prolonged exposure to the coating material, (e) the coating composition must form a continuous film covering the exposed metal surface at the area of the preformed aperture, and (f) the coating composition must mechanically fill any spaces between the surface of the can and the tape, thereby preventing seepage which could leave an unattractive and unappetizing residue.

BRIEF SUMMARY OF THE INVENTION Surprisingly, a coating composition which has the desired properties and will cure at low temperatures has been found. The coating composition comprises a solution of epoxy resin having an average molecular weight from about 200 to about 4,000 together with a urea-formaldehyde curing agent. Commercially available epoxy resins which are useful in forming coating compositions are discussed at page 18, in Epoxy Resins by Lee and Neville (McGraw-I-Iill, I957). The ureaformaldehyde cross-linking agent is preferably a urea-formaldehyde resin condensed in the presence of n-butyl alcohol. Suitable epoxy solvents such as ketones, esters and ether alcohols may be used as the solvent vehicles for the coating composition of the instant invention. It has surprisingly been found that coating solutions comprising the foregoing ingredients have the unique combination of properties required for use in coating tape sealed container closures. The solutions of this invention can be air cured at ambient temperatures or may be cured at temperatures up to about 250 F. Curing temperatures above 250 F. are not recommended because higher temperatures tend to weaken the pressure sensitive adhesive seal.

Having briefly described the invention, it will be described in greater detail and may be better understood by reference to the accompanying drawing which is presented for illustrative purposes.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING FIG. 1 is a perspective view of the top of a metallic container closure illustrating a tape sealed metallic closure in which a pressure sensitive tape has been applied on the preformed aperture in the metallic lid.

FIG. 2 is a plan view of the bottom of the metallic container closure of FIG. 1 illustrating the coating layer which covers the aperture and the exposed edge thereof,

FIG. 3 is an enlarged sectional view taken along lines 3-3 of FIG. 2 depicting the tape sealed container lid with the cured coating composition of the instant invention, particularly illustrating the manner in which the contents of the can is protected against undesirable reaction with the aperture edge.

DETAILED DESCRIPTION In the drawing the same number refers to the same element.

Referring with particularity to the drawing, FIG. I illustrates tape sealed container closures in which tape 10 has been applied to form an airtight seal in a metal container closure 12. Metal container closures are commercially manufactured from tin l3 coated on steel 14. The tape 10 comprises a laminate of a metal-coated polyethylene terephthalate film 15 or other suitable plastic material and a pressure sensitive adhesive 16. The tape is applied over an aperture 11 preformed in the container closure. The tape may have additional layers such as priming coats to promote the adhesion of the contact adhesive to the film or may have a metallic foil in place of, or in addition to the plastic film.

An end of the tape is not sealed to the container closure and forms a tab 17 which is used to remove the tape. As illustrated in FIG. 1, the edge 18 of the aperture 11 remains exposed. 1f the closure were to be placed on a can without the cured resin coating of the present invention the contents of the can would be exposed to the raw cut metal edge of the aperture. Beverages which cause steel to be anodic to tin would undergo unwanted reaction with the lid causing adulteration of the can contents and/or perforation of the lid as previously discussed.

FIG. 2 is a plan view of the bottom of the metallic container closure of FIG. 1 illustrating the coating layer 19 of the instant invention. The composition is applied to the tape sealed aperture completely coating the exposed edge 18 thereof and the pressure sensitive adhesive over the aperture.

The use of soluble resin coating materials to coat the exposed edge of tape sealed apertures and the exposed adhesive layer thereover has been suggested in the above-identified U.S. Pat. No. 3,3 89,827. However, prior to this invention no coating composition has been used or suggested which combines the unique combination of properties specified above.

Surprisingly a resin composition has now been found which has the unique combination of properties necessary to form a protective coating when applied to the exposed edge of the aperture along the inner surface of a container closure. It has now been found that the soluble coating composition 19 of the present invention has all the requisite properties previously enumerated and can be quickly cured at temperatures below about 250 F. so that the hermetic seal of the tape closure is not adversely affected.

The coating composition of the present invention comprises a soluble epoxy resin cured with a urea-formaldehyde curing agent, and preferably a urea-formaldehyde curing agent produced by alkylation of urea-formaldehyde condensation products during the production thereof with n-butyl alcohol which is used as a solvent for the system. Epoxy resins generally useful in forming coating compositions are known in the art and are described, for example, in the Lee and Neville text referred to above. Methods of making urea-formaldehyde and urea-formaldehyde condensation products suitable for this invention are discussed at pages l73-176 of The Chemistry of Commercial Plastics, by Wakeman (Reinhold, 1947). The Lee and Neville text refers to coating compositions made of epoxy resins and urea-formaldehyde at page 278.

The epoxy resins useful in the composition of the present invention have an average molecular weight from about 200 to about 4,000. Solvents such as aromatic hydrocarbons, ketones, esters, alcohols and mixtures of these solvents can be used as the solvent vehicle for the present coating composition. Minor amounts of flow control agents and catalysts such as acid catalysts like p-toluenesulfonic acid, or other known catalysts (e.g., metal driers, such as cobalt naphthenate) may be used to enhance the curing times and temperatures, if desired. A coating composition according to the present invention showing amounts of the composition components by weight is set forth in the following example.

EXAMPLE Approx. Amount Acid catalyst, flow agent and other additives 2.9

The resin content of the composition is preferably in the range of about 20-30 percent, and most preferably about 25 percent, as illustrated in the example. The viscosity of the coating solution is -12 sec. at 77 F. by the No. 4 Ford cup test. The composition can be applied by conventional techniques such as brushing or spraying and may be cured at room temperature in about 24 hours or may be cured to form tack free coatings in about 3 minutes at 200 F., or at other schedule equivalents.

The lip of container closure 12 is shown with a cellular resin coating 25 which is commonly applied to the inner side of container lips in order to insure an improved seal when the lid is attached to the can.

FIG. 3 is an enlarged sectional view taken along lines 3-3 of FIG. 2 depicting the tape sealed container lid with the cured epoxy urea-formaldehyde resin composition 21 of the instant invention.

It can be seen that the composition forms a cohesive coating which essentially covers the exposed metal surface at the area of the preformed aperture; thus protecting the contents of the container from unwanted reaction with the metal of the container closure. When the instant cured coating composition 21 is used, comestible container contents may safely be stored for periods longer than have heretofore been available.

FIG. 3 also illustrates another desirable advantage of this invention. In the manufacture of tape sealed container closures, small spaces are sometimes created between the tape seal and the lip area adjacent to the preformed aperture. While these spaces usually do not afi'ect the hermetic seal, seepage of the contents of the container into these spaces may leave a dried residue which is unsightly and unappetizing to the consumer when the tape is removed. This problem is particularly prevalent when the contents of the container is a beverage such as tomato juice. The coating material of the present invention tends to mechanically fill such spaces as shown at

points

23 and 24 improving the tape seal and insuring that food residues do not seep onto the surface of the can.

While specific embodiments of the coating composition and method of manufacturing container closures coated with low temperature cured resin compositions have been disclosed in the foregoing description, it is understood that various modifications within the scope and spirit of the invention may occur to those skilled in the art. Therefore, it is intended that no limitation be placed on the scope of the invention as defined by the claims appended hereto.

We claim:

1. In a metallic closure for a hermetically sealed container, said closure having a preformed aperture, said aperture being sealed on a side with a tape laminate comprising a flexible strip and a pressure sensitive adhesive material, the improve ment comprising a cured resinous coating layer covering the exposed edge of said aperture, said coating layer having been formed by curing, at a temperature below about 250 F., a composition comprising a solvent solution of an epoxy resin having an average molecular weight of from about 200 to about 4,000 and a urea-formaldehyde curing agent.

2. The container closure of claim 1 wherein the solvent of said composition is selected from the group consisting of esters, ketones, alcohols, aromatic hydrocarbons and mixtures thereof.

3. The container closure of claim 1 in which the solvent of said composition is a mixture comprising butyl acetate, methyl ethyl ketone and toluene.

4. The container closure of claim 1 wherein said composition is cured at ambient temperatures.

5. The container closure of claim 1 wherein said curing agent is a urea-formaldehyde condensed in the presence of nbutyl alcohol.

6. A container hermetically sealed with the improved closure of claim 1.

7. In a hermetically sealed container closure having a metallic end with a preformed aperture, said aperture being sealed on a side with a tape laminate comprising a flexible strip and a pressure sensitive adhesive material, the improvement comprising a cured resinous coating layer covering the exposed edge of said aperture, said coating layer having been formed by curing, at a temperature below about 250 F., a composition comprising Approx. Percent 8. A container hermetically sealed with the improved closure of claim 7.

9. The method of manufacturing a closure for a hermetically sealed container from a metallic end having an aperture therein comprising sealing said aperture on a side with a tape laminate comprising a flexible strip and a pressure sensitive adhesive material and thereafter coating the exposed edge of said aperture with a coating composition comprising a solvent solution of an epoxy resin having an average molecular weight of from about 200 to about 4,000 and a urea-formaldehyde curing agent and curing said composition at a temperature below about 250 F.

10. The method of manufacture of claim 9 in which the coating composition comprises Approx. Percent ingredient By Weight a. an epoxy resin having an 13.9

average molecular weight from about 200 to about 4,000 b. butylated urea-formaldehyde 10.8

curing agent 0. butyl acetate 30.8 d. methyl ethyl ketone 29.0 e. toluene 12.7 f. flow agents, acid catalyst and 2.9

other additives 11. The method of packaging a liquid in a container which comprises inserting said liquid into a topless container and sealing the container with the closure of claim 1.

Claims

2. The container closure of claim 1 wherein the solvent of said composition is selected from the group consisting of esters, ketones, alcohols, aromatic hydrocarbons and mixtures thereof.
3. THe container closure of claim 1 in which the solvent of said composition is a mixture comprising butyl acetate, methyl ethyl ketone and toluene.
4. The container closure of claim 1 wherein said composition is cured at ambient temperatures.
5. The container closure of claim 1 wherein said curing agent is a urea-formaldehyde condensed in the presence of n-butyl alcohol.
6. A container hermetically sealed with the improved closure of claim 1.
7. In a hermetically sealed container closure having a metallic end with a preformed aperture, said aperture being sealed on a side with a tape laminate comprising a flexible strip and a pressure sensitive adhesive material, the improvement comprising a cured resinous coating layer covering the exposed edge of said aperture, said coating layer having been formed by curing, at a temperature below about 250* F., a composition comprising Approx. Percent Ingredient By Weight a. an epoxy resin having an 13.9 average molecular weight from about 200 to about 4,000b. butylated urea-formaldehyde10.8 curing agentc. butyl acetate30.8 d. methyl ethyl ketone29.0 e. toluene12.7 f. flow agents, acid catalyst and2.9 other additives
8. A container hermetically sealed with the improved closure of claim 7.
9. The method of manufacturing a closure for a hermetically sealed container from a metallic end having an aperture therein comprising sealing said aperture on a side with a tape laminate comprising a flexible strip and a pressure sensitive adhesive material and thereafter coating the exposed edge of said aperture with a coating composition comprising a solvent solution of an epoxy resin having an average molecular weight of from about 200 to about 4,000 and a urea-formaldehyde curing agent and curing said composition at a temperature below about 250* F.
10. The method of manufacture of claim 9 in which the coating composition comprises Approx. PercentIngredient By Weight a. an epoxy resin having an13.9 average molecular weight from about 200 to about 4,000b. butylated urea-formaldehyde10.8 curing agentc. butyl acetate30.8 d. methyl ethyl ketone29.0 e. toluene12.7 f. flow agents, acid catalyst and2.9 other additives
11. The method of packaging a liquid in a container which comprises inserting said liquid into a topless container and sealing the container with the closure of claim 1.