US2357415A - Container and method of making same - Google Patents

Description

Sept- 1944f c. a M MANus, JR, an. 2,357,415

couumnn m union or mule sun:

Filed July 18, 1940 maria; .Z'. Mqfanwjz Giles B- Coal-'6'- Patented Sept. 5, 1944 and shapes of the conventional tin can.

GONTAINER AND METHOD or MAKING I sam:

Charles E. McManus, In, Spring Lake, N. 1.. and

Giles B. Cooke, Baltimore, Md;

assignors to Crown Cork'& Seal Company, Inc., Baltimore,

' Md., a corporation of New York 7 .Application July 1s,194o,seriai1vo.z4c,23s 1 Claim. "(01. 220-64) 1 The present invention relates to containers having a novel protective liner of silver and'includes a new articles and method of making the same.

The invention particularly is concerned with metal containers of black iron or steel of the sizes It is equally useful as regards larger metal cans, drums or barrels as wellas small cans and boxes. The metal containers may be of the seamless drawn type, as described in the application of Cal'leson' et al., Serial No. 334,876, and the application of McManus et al., Serial No. 217,274, and of the welded side seam or conventional lock-seam side seam types or of any other construction. Such containers when provided with our silver lining are useful for a wide variety of products among which may be mentioned foods, beverages including carbonated beverages, chemicals, oils,

pharmaceuticals, milk and syrups, and the containers having readily removable closures such as screw, lug or crown caps may be opened, portions of the contents removed and the containersv resealedas often as necessary without injury to the contents or the liner. I

The invention includes a metal container having its entire interior surface lined with a continuous highly reflective and permanently adherent film of pure silver of commercially satisfactory thinness. That is to say, the thickness of the film (a) is sufiicient for it to act as a protective liner in association with an extremely wide variety of contents and (b) requires an amount of silver so markedly small that containers, for example those of the usual tin can shapes and sizes may bemanufactured and sold at popular prices. We produce in accordance with this invention containers having a silver liner coating of a thickness in the neighborhood of five millionths of an inch. Films as thin as from substantially two millionths of an inch to ten millionths of an inch may be applied and usefully employed.

Lacquers, varnishes and enamels are at present generally employed for lining metal containers, but it is recognized that such coatings possess a limited llfe,'a restricted field of application and in general have a resistance and durability substantially less than silver. Silver has a wide field of application and substantially unlimited durability and resistance, but cannot be applied directly to the metal wall of a container of the popular type in a thinness to be economically between the iron and such necessarily thin silver resistant properties-of silver are made available for liner purposes by depositing the thin silver film upon a non-conductive surface of lacquer, enamel or varnish which has been previously applied to the container wall surface. With this construction (1), galvanic action is precluded, (2) there is obtained a smooth continuous permanently adherent and satisfactory protective liner film having a thinness of the order above described, (3) a wide selection of materials for forming the intermediate film is afforded and (4) the life of the intermediate film. is materially extended by theprotective influence of the silver surface film. I

In other words, we produce a container having a composite liner consisting of a non-conducting under coat and a silver surface film which is smooth and attractive and has a durability and resistance of a much higher order than tin coated containers or containers provided with lacquer,

varnish or enamel liners. This composite liner possesses none of the disadvantages mentioned coatings directly applied to container walls of steel. At the same time, we provide a silver liner of a thinness not heretofore obtained for containers and which makes commercially available th highly desirable protective properties of silver at a modest price.

It will be appreciated that the production of such a widely used container of. the general character of the usual tin can having a reliable over-all silver liner, at a popular price, is a particularly important improvement of the present invention. I

The presence of the intermediate film of varnish, lacquer or enamel has the advantages that it protects the metal base and seals any irregularities in the surface thereof, thereby forming a smooth continuous coat for receiving the thin silver film. This intermediate film appears to promote better adherency and in addition reinforces and supports .the thin silver film and assures a bright and lustrous mirrordike appearance for the'liner. J

In preparing the cans for the intermediate coating operating we find it important thatthe can wall surface first b freed as far;- as possible from surface irregularities andp thoronghly cleaned. Thereafter the coating. solution is ,ap-

feasible because galvanic action will take place on the steel basei. e., the container body-b tto We have discoveredthat the durability and or ends, and is baked at such a temperature as to remove all volatile matter and produce a continuous, adherent, glossy and preferably flexible surface film on the metal base.

In connection with the intermediate coating, we employ coating compositions which are baked at a high temperature to produce a flexible film free of volatiles and particularly advantageous for foods and beverages. Also we use various types of compositions which may be baked at lower temperatures according to the specific use of the container and produce films of desired flexibility with complete or substantially complete freedom from volatiles. In addition to organic intermediate films, we produce satisfactory enamel films of vitreous nature which generally are not flexible. -The intermediate coating in any case is one upon which the silver will deposit and adhere satisfactorily and which is inert to the silver, the metal container wall and to the contents wher this property is important as with foods, beverages and medicines.

The containers provided with the intermediate coating adjacent to the container wall are delivered to an automatic machine for carrying out the silver coating operation. We preferably deposit the film of pure silver upon the wall of the container from an atmosphere of vaporized silver created by distillation under reduced pressure. That is, we have discovered that eilicient results are obtained by using the container or container body as the vacuum or reduced pressure chamber during deposition. In this manner the container may be coated with or without the bottoms or ends assembled. In the-automatic machine, the cans are continuouslyevacuis not limited in its application to the details of construction and arrangements of parts' illustrated in the accompanying drawing, since the invention .is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation, and it is not intended to limit the invention claimed herein beyond the requirements of the prior art.

In the drawing, Figure 1 is a top plan view of one type of apparatus for carrying out the invention;

Figure 2 is a side elevation partly in section; Figure 3 is an end view partly in section; and Figure 4 is a fragmentary section of a container having a composite coating in accordance with this invention.

Referring to the drawing we will, for purposes of illustration, describe the invention in connection with containers having drawn seamless bodies as disclosed in the aforementioned applications. The container A at the left of Figures 1 and 2 has a cylindrical seamless body and end flanges a and is shown without its bottom or ends assembled. The container B shown at the right of Figures 1 and 2 likewise has a seamless drawn body with integral conical top b, neck c and sealing lip d to receive a removable closure such as a crown, screw, or has the bottom e united.

Each of the containers is provided on its entire inner wall, including the bottom where the same is attached, with a continuous thin fiexible coating or film ill of a suitable non-conducting lacquer, varnish or enamel. This intermediate film I0 may be composed of a single layer produced as by spraying the container wall or may be built up to have the desired thickness and resistance by means of several spray coats. The coating should have a thickness in the neighborhood of from 0.0001 to 0.002 inch.

Examples of suitable coatings are solutions of chlorinated rubber, polyvinyl acetal resin, varnishes of the drying oil type and phenol form-- aldehyde varnishes and enamels which may be termed inorganic because of their predominant vitreous nature. In fact, in view of the protective action of the silver film, practically any of the usual liner materials which may be suitably baked or dried to form an adherent smooth surlug cap, and

face film to which silver will adhere may be utilized. Preferably, those coatings which upon drying or baking will form a glossy, flexible surface film and under the silver coating conditions will not evolve objectionable vapors or disintegrate are employed. There are a large. variety of coating compositions commercially available for this purpose, and as will be appreciated, the protective film of silver permits a considerable range of selection in the varnish, lacquer, or enamel which is. to be used, namely, according to cost, availability and suitability. Such coatings, moreover, may in some cases initially have resistant qualities substantially equal to the properties of the silver, but as stated above, even the beshquality coating compositions disclose a lack of durability far short of that pos-- sessed'by a silver lining. The important functions of the varnish or other intermediate nonconducting film are to preclude galvanic action between the silver film and the metal wall and to assure the deposition of a smooth continuous adherent silver film. The properties of compatibility or receptivity to a deposited silver film and the preventing of galvanic action are equally important because the silver film will provide a protective layer for the varnish or intermediate coating against the action of air, moisture, organic acids and other deteriorating influences.

The following are examples ofcoating compositions suitable for receiving the deposited silver film:

1. Black varnish This coating is applied by spraying and baked at 600 F. in clean, dry circulating air for fifteen minutes.

2. Chlorinated rubber Chlorinated rubber pounds 80.00 Hydrogenated rosin ester do 10.00 Diamyl phthalate do.. 1.25 Wax ounces 2.00

Salvesso #2 gallons 45.00

Timers a spray coating and is baked erase F.

for thirty minutes in clean, dry circulating air.

In connection with Example 1 we have found that coatings which are baked at a high temperature and produce flexible adherent films which are inert, odorless, tasteless andffree of volatiles, are highly satisfactory for a wide variety of food products and beverages. The solution of Example 1 is representative of a number of coating compositions of this character which I maintain their propertieswhen subjected to high temperatures and therefore have a broad field is preferably sprayed upon the interior wall of the container body before the end or bottom is united'thereto. In some cases this coating may take place after the end or bottom has been united. Preferably the coating compositions are applied-by spraying,'as a continuous operation in which the container walls are smoothed, ifnecessary, cleaned, then coated while traveling on a suitable conveyor, and then transported by fixed in communication with the opening I; in the head and against a suitable gasket M with the body supported upon the saddle II. The container A at the left of Figures 1 and 2 has one of its end flanges a likewise held fixed in communication with the opening 13 being supported in a similar saddle l2, with its opposite end closed bya clamping plate [5 of suitable resilient sealing material.

The openings I3 intercommunicate within the head and are in communication with the opening l6 through the head which in turn is connected with a suitable vacuum pump or other evacuating apparatus not shown through the port H in the base I8 upon which the heads are carried. When this apparatus is operating. the interior of the container or container body will be exhausted and we prefer to operate at a pressure of between substantially 0.1 and 20 microns. Extending up through the opening I6 and supported therein in fixed position are lead-in wires l9. These lead-in wires are connected to heating units or filaments 20 which project from without the openings l3 so as to be received within the-interior of the container or'container body. It will be noted t at protective connector sleeves 2| are provided to insure against overheating at the constricted part of the cone top can B. such sleeves not being necessary where container bodies A are emplayed.

the conveyor through a suitable drying or baking oven. The ends or bottoms are similarly coated and dried or baked. 7

After the baking or drying operation, it will be found that each of the aforesaid coatings forms a smooth continuous glossy and preferably flexible surface film free from volatiles. The coatings are odorless and tasteless and sufiiciently inert so that should there possibly be some pinholes in the silver film, no deleterious action in respect to the contents, the intermediate lining ill or to the wall of the container will result.

The coated containers may have the bottoms or ends united thereto and then be continuously delivered to the automatic silver coating apparatus, or the bodies and ends .or bottoms may be separately provided with the thin silver film. It is preferred to conduct the silver coating operation with the bottom applied to the container B and with one end applied to the container A but this is notnecessary.

In some cases, the containers are transported directly and continuously from the baking oven to the silver coating, apparatus and in such cases the containers may or may not have the ends or bottoms attached thereto. Where it is not desired to have such a continuous and direct delivery from the oven to the silver coating apparatus, the containers and ends may be stored under conditions where they will be maintained clean.

Referring to Figures 1, 2 and 3, the coatin apparatus comprises a fixed head ll, of which a plurality may be mounted upon a rotary turret set up either vertically or horizontally, or arranged in a straight line, Each container having the intermediate film l0 adjacent its inner wall surface, is continuously and automatically fed to each head and positioned on a saddle H. In each case the container or container body will act as the vacuum or reduced pressure chamber during the deposition of the vaporized silver, and

in the case of the container B at the right of Figures 1' and 2, the lip d of the container is held The filaments 20 are preferably formed of tungsten or molybdenum and are platinized or aluminlzed, if desired, to promote adhesion of the small globule orpellicle of molten silver toeach 5 filament. The filaments are composed of wire of 0.015 to 0.040 inch in diameter, wire of 0.025 inch in diameter being preferable.

In the operation of the apparatus, a small quantity of silver such as a predetermined length 4g of wire, is automatically positioned within the convolutions of each filament, whereupon. the container bodies are positioned automatically as above described and connection automatically made to the exhausting apparatus. When a sufficient vacuum has been created within the con-1 tainer bodies, the current is automatically supplied to the wires l9 and causes the filaments 20 to heat and vaporize the silver. Under the reduced pressure thesilver deposits from the metal atmosphere upon the intermediate non-conducting film III on the inner wall of a. container body to form the thin film 22 of pure or elemental silver. .We employ a current of from about ten to thirty amperes and five to ten volts for periods ranging from four seconds to two minutes. The deposition of a thin continuous film of pure silver is caused by the fact that the wall of the container body is of lower temperature than that of the metal vapor and this promotes condensation.

The thickness of the coating is controlled by feed- 'ing a predetermined amount of silver to each filament; this charge of silver being completely volatilized at each energization of the filament. The entire operation consumes less than one minute, actual operating times having been frequently about 26 seconds. In connection with theopcrating time, one consideration is the necessity for permitting the filaments 20 to cool before breaking the vacuum and allowing the air to enter, so that the silver coated containers may be removed from the head.

We have not found it necessary to preheatthe I can to secure adherency,. but there are certain types of lacquers, enamels, or varnishes in which the adherency is enhanced by heating to a tem- ,timed relation with the operation of the apparatus. Such crucibles replace the filaments ZII and the wires J9 serve to carry the high frequency current to a suitable coil disposed around each crucible, the crucible and coil being located approximately at the center of the container.

The silver coating may also be applied by cathode sputtering, by chemical reduction as well as by heat vaporization using the exploding wire method. This latter involves the discharge of a relatively large amount of electrical energy in an exceedingly small period of time, the energy being liberated between silver electrodes and volatilizing portions thereof. Alternatively a predetermined current of very, high amperage is passed through a fine silver wire, thus instantaneously vaporizing the silver wire.

In some cases, multiple silver coatings are provided as for example in the case of relatively large drums and barrels where increased thickness is advantageous or in other instances where the relatively uneven surface of the container wall makes the provision of two or more films particularly desirable.

Also, while we have described the provision of the production of the external coating, 9. suitable bell jar type of vacuum chamber may be utilized in which the containers are placed, filaments being positioned so as to coat both the inside and outside simultaneously or simply the outside, as desired. In the case of containers having walls of a thickness or design which does not permit the use of the container body as its vacuum chamber, the bell jar apparatus may be utilized as the chamber for forming the vacuum.

While we have described the preferred embodiment of the invention, namely the coating or containers made of black iron or steel, we have found thatjcontainers of tin plate coated or not with an intermediate non-conducting coating III as required, containers of Bakelite or other molded resin, galvanized iron containers to which an intermediate coating is first applied, paper and glass containers and, in fact, receptacles formed of a wide variety of materials may be lined with a thin silver film in accordance with this invention. Glass bottles may be provided with a thin silver film by direct deposition upon the cleaned glass.

additional continuous protective coating of silver a lining, it is to be understood that the exterior of the container may also be given a silver coating, the same being formed upon an intermediate non-conducting film as herein described. For

We claim:

A metal food and. beverage container having a lining comprising a base coating of a substance which is galvanically inactive to silver, and an thereon and of a thickness between substantially 2 millionths of an inch and 10 millionths of an inch deposited on said first coating by condensation thereon from an atmosphere of silver vapor, said first coating rendering the metal can wall and the silver lining chemically inactive relative to one another.

CHARLES E. MCMANUS, JR. GILES B. COOKE.

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