FIBER CANS Alternates for Metal Containers

R. P. BIGGER, Research Department, American Can Co., Maywood, III.

SOME of the more noticeable changes wrought by the war have been in the field of packaging. Even the most

casual observer must be struck by the great differences in many of the containers now displayed in drug and grocery stores as compared with those which were seen only a year ago. Restrictions on the use of metals have, of course, been respon­sible for most of these changes. Manufac­turers and users of containers have had to look to less critical materials as packag­ing media, and many of them have found paper and paper products the answers to their problems.

Paper and paperboard can be applied to packaging in a variety of ways—as set-up boxes, fiber cans, bags, or wrapping mate­rials. Each of these types of packages has a definite place in meeting the problems of today, and each has peculiar advantages which, make it most useful for holding certain types of products. In this paper it is proposed to discuss fiber cans as alter­nate packages and to point out the fields in which they find their most effective uses. To do this it is desirable first to re­view the more common types of fiber cans and the methods employed to give them special protective qualities such as moisture resistance, grease and oil resist­ance, and waterproofness.

Types of Fiber Can Bodies and Their Manufacturing Methods

A fiber can is composed of a paperboard tube or body to which is applied ends of metal or paper. While wide variation in the design of the end closures is possible, there are only three general types of bodies known in the trade as "spirally wound", "convolutely wound", or "laminated", and "lap-seam", respectively.

Spirally wound bodies are manufactured by a machine known as a spiral winder. This machine consists essentially of a sta-

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tionary round steel mandrel over which is looped a moving endless belt near one end of the mandrel. At the other extremity of the mandrel there is a traveling saw. The paper stocks to be used in making the cans are slit into narrow rolls and placed on suitable stands on each side of the mandrel. From these rolls the paper is carried over adhesive applicators and onto the mandrel under the endless belt at an angle of approximately 45 degrees. The pressure of the moving belt combines the various plies of paper and causes them to move forward in a spiral motion along the mandrel. This results in the fabrica­tion of a continuous tube which is auto­matically cut into convenient lengths

by the traveling saw at the end of the mandrel. The tubes manufactured in this operation are in turn cut into a num­ber of can bodies of the proper height by placing them over a steel mandrel against which ride small steel cutting wheels. From four to ten bodies are usually cut from one spiral tube. The nature of spiral winding is such that normally only round bodies are made.

Convolutely wound bodies are made on a convolute or laminated winder. This machine consists of a mandrel which turns intermittently under the action of a cam. By adjustment of this mechanism the mandrel can be made to go through two or more revolutions before stopping

Spiral Winding

C H E M I C A L A N D E N G I N E E R I N G N E W S

Convolute Winding

for an interval. A roll of paper sufficiently wide to make one or more bodies is placed in position at one side of the mandrel. The web of paper from the roll is carried over a glue applicator and onto the mandrel at an angle of 90 degrees. Each revolution of the mandrel results in one ply in the can body. After the required number of plies have been wound, the web of paper is cut, and the bodies are pushed down the mandrel to a station where labels are automatically applied. Following this, the bodies are discharged from the machine. B y convolute wind­ing, a body of any regular shape cant be produced.

Prior to the present emergency nearly all fiber can bodies were either spirally or convolutely wound. Needless to state, there has been a tremendously increased demand on fiber can production facilities, and in some cases existing equipment, operating at full capacity, could not carry the load. In addition, the curtailment in the use of steel has made it impossible to obtain new machinery for any uses ex­cept very direct war work. To supply the increased demand for fiber cans, there­fore, the only alternative seemed to be to look for new manufacturing methods, and this search has resulted in the fuller development of the lap-seam fiber can.

In this style of container, an adhesive either of the thermoplastic, solvent, or water-dispersed type i s applied along one margin of a body blank. This blank: is then formed around a mandrel into a single ply body, so that the margin hold­ing the adhesive overlaps slightly at "the side seam. The side seam is then formed by pressure applied by some suitable means, such as a hammer blow. The operations involved are very similar to those used in the manufacture of metal can bodies on a body-making machine, and it has been found that it is a relatively simple matter to change over a body-maker formerly used for metal can fabrica­tion to the manufacture of lap-seam finer can bodies. Curtailment in the use of metal in packaging has resulted in -the shutting down of many metal can manu­facturing lines. Therefore a great deal of metal can equipment is available which might be converted to make lap-seam fiber cans. Unfortunately, however, this type of fiber package is more limited in its ap-plication than spirally and convolutely wound containers, and hence i ts use is not so widespread. Like the convolutely wound can, the lap-seam, body can be made in any regular shape.

Fiber Can End Closures

Following the manufacture of the can body by one of these three methods, metal or fiber ends are assembled to make the finished container. Metal ends are usually seamed on in the same type of seaming machines which are used in the manufacture of metal cans. The fiber can

seam is produced by crimping the metal end against the paper body walls, and consequently differs from the familiar "double seam" of metal cans, in which the flanged body is actually hooked and locked into a curled end. • There are several styles of paper end closures, and the method of assembly depends upon the type. One of the most common types is the paper slip-cover usually seen on salt cans. These caps are drawn from special grades of paper-board in double-action punch presses. The can bodies are passed by rolls which apply a bead or fillet of glue around the periphery of the outside of each end, and the caps are pushed into place in a ma­chine known as a capper. Another com­mon style of paper end closure is that in which the body itself is curled down against a heavy paperboard disk. To carry out this operation it is usually neces­sary to support the can body on a steel post. This is most conveniently done in a dial press.

I t has been found possible to make a seamed paper end on modified metal-end seaming equipment. The seam produced is, in effect, the paper counterpart of the crimped metal end closure. Recently, a plug type of end closure, consisting of a reformed paper slip-cover, has been de­veloped experimentally. This plug is inserted into the body and glued in place.

All of these closures can be modified to give reclosure and dispensing features. Pouring spouts, plugs, and slip-covers can be made from both metal and fiber and can be used in several combinations to give a variety of effects. Probably the most widely used and effective types of closures for fiber-bodied cans are the

metal friction ring and plug, and the pour­ing spout.

In the case of every package it i s im­portant to design a closure which will of­fer the greatest convenience to the packer in his filling and closing operations. Some closures that are very practical from other standpoints, may require an involved as­sembly, resulting in slow operation and high cost.

Some Comparisons of Fiber Can Types Each of the three types of fiber cans de­

scribed above possesses certain advan­tages and disadvantages. As will be shown in the next section, the spirally wound container is perhaps the most versatile since it lends itself most easily to the incorporation of various protective quali­ties. Unfortunately, however, this type of container normally can be produced only in round form. This is a great dis­advantage when it is necessary to con­serve space, as for instance, in transoceanic shipments. In contrast, both convolute and lap-seam cans may be produced in a variety of shapes, including square and rectangular.

In general, convolute winding limits the material used to the same type of stock in each ply, and as a result it is not possible to get the same variety of effects as in spirally wound bodies. Where the same grade of paper and number of plies are used in both spiral and convolute cans, the latter has been found to be much stronger in resistance to vertical compression. The nature of the spiral body is such that initial failure occurs at the juncture of the spiral plies where the only support is due to the paper itself. In convolute cans, on the other hand, initial failure usually occurs just above the top or bottom seams.

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Manufacture of lap-seam can bodies on converted metal can bodymaker

Convolutely wound cans have the fur­ther advantage of lending themselves easily to automatic labeling, whereas this is a more difficult operation with spirally wound containers. In the case of the latter, it is possible to apply a continuous label as the outer ply of the tube in wind­ing, but such a label is usually limited to an over-all design, and printed directions and advertising must be eliminated or kept to a bare minimum. More com­mon practices are to apply a multiple label by hand to the spiral tube, or to pass the finished can through a labeling ma­chine before or after filling.

Production rates on spiral winders are usually higher than those obtained on convolute machines. A fully automatic spiral can line may operate at a speed of 165 cans per minute, whereas good produc­tion for a corresponding convolute line is in the neighborhood of 70 cans per minute.

As compared to spiral and convolute cans, lap-seam containers also have both advantages and disadvantages. Since the can body consists of only one ply of paper-board, the strength of this construction is inherently limited. To obtain maximum rigidity with this single ply more expensive grades of board must be used, and any saving which could be realized by the use of less stock is usually more than offset by the higher unit cost. In spite of this higher cost, the container is somewhat less sturdy than either the convolute or spiral can.

Since lap-seam cans, in contrast to the other two types, are produced from sheets rather than from rolls of paper, it is pos­sible to decorate them, prior to fabrica­tion, in lithographic presses. This elimi­

nates the operation of labeling after the can is made. Because lap-seam cans are made on converted high-speed metal can bodymakers, it is possible, in theory at least, to get production rates far higher than on spiral or convolute winders with resultant manufacturing economy.

Increasing Fiber Can Resistance Without the use of special stocks or fur­

ther treatment, a fiber can is just a simple paper container with all the defects and weaknesses of paper—permeability to water vapor and gases, poor water and oil resistance, and easy destructibility. For­tunately, there are many ways of correct­ing these defects so that fiber containers can be made which function very success­fully as packages for such products as paint, motor oil, lye, and vegetable short­ening.

As mentioned in the last section, the spirally wound can is probably the most versatile type. The material used as the inner ply of a spirally wound can may be overlapped and adhered to itself with a suitable adhesive. Thus, if an oilproof inner liner is used, it i s possible to cover all the unprotected paper stock and make a can body which is completely oilproof on the inside. It is for this reason that practically all fiber cans for oily or greasy products have spirally wound bodies. The inner liner is usually a highly grease­proof sheet, such as vegetable parchment, mechanical parchment, glassine paper, or paper impregnated with greaseproof mate­rials. To make a truly greaseproof con­tainer, it is also necessary to treat the top and bottom seams regardless of whether they are made of metal or paper. There are many materials that can be

used for this purpose, but perhaps the commonest are polyvinyl acetate resins, animal glue and gelatin, cellulose deriva­tives, and some types of synthetic rubber. There are also several ways in which these "seam dopes" can be applied, but the one which probably finds most uni­versal application is that in which a bead or fillet of the material is applied to the ends of the body in equipment very similar to that used to apply adhesive to can bodies prior to the assembly of paper slip-covers. Another method, consisting of spraying a fillet of dope into the space between the countersink of the metal end and the paper wall of the body after the end has been assembled, is also used.

In the case of containers for products which are extremely hard to hold, such as paint and motor oil, it is usually best to have a safety factor in the form of some auxiliary oilproofness. This can be obtained by spraying or flushing the can with some highly oil-resistant mate­rial either before or after assembly of the ends. Some commercial proteins, vinyl acetate-chloride copolymers, and some cellulose derivatives, can all be used for this purpose.

Both spiral and convolute containers can be made effectively waterproof on the inside by spraying or flushing with paraf­fin or microcrystalline waxes. Contain­ers of this type have been successful in tests with a number of miscellaneous aqueous products.

Both of the above types of cans can also be rendered very moisture-resistant. I n the case of spiral cans, various plies of moisture-resistant papers are wound into the body and in some cases a moisture-resistant label is applied, as well. The moisture-resistant stocks commonly used include wax and asphalt combined and impregnated papers, moisture-resistant lacquer-coated papers, and cellophane. I t is also possible to use moistureproof adhesives, such as asphalt, between the various plies. Convolutely wound con­tainers can be prepared from moisture-resistant laminated stocks. These stocks are usually made by applying a moisture-resistant adhesive such as a wax-resin composition, or asphalt, to a carrier sheet of glassine, parchment, or cello­phane, and then combining to board. Another useful moisture-resistant stock is called "KB board", which is made by applying an asphalt emulsion between the various layers of pulp as the stock is built up on a cylinder-type paperboard ma­chine. As the web of paper dries, the emulsion is broken and a board is pro­duced with several layers of asphalt sand­wiched between plies of paper.

Lap-seam cans may be made somewhat moistureproof by coating the body stock i n the flat with a moisture-resistant lac­quer. Unfortunately, the most satis­factory coating materials are now re­stricted, and it has been necessary to look for other means of improving the

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moisture resistance of lap-seam cans. Spraying or flushing the can body with paraffin or microcrystalline wax accom­plishes this. Although i t is difficult to make this type of can moistureproof with a coating of lacquer, there are materials available which will make it moderately greaseproof. As a result of this, the lap-seam can makes an admirable alternate package for slightly oily materials.

Spirally wound cans may be made re­sistant to alkali and acids by winding an inner ply, coated or impregnated with a relatively nonreactivo material. Paper coated with vinyl acetate-chloride co­polymers, and paper impregnated with asphaltic bodies, have shown some promise as inner liners for lye containers. Sheets impregnated with asphalt compounds have been satisfactory in tests with some grades of chlorine bleaches. Convolute bodies can also be made somewhat resistant to the action of alkalies by spraying or flush­ing with macrocrystalline; waxes.

There does not appear to be any ef­fective way of making a commercial type of fiber can truly gasproof at the present time. All organic films seem t o have the unfortunate property of permeability to carbon dioxide. Also, when carbon di­oxide i s present in sufficient concentra­tion, the oxygen permeability of a film otherwise fairly resistant, is greatly in­creased. The most promising material available is lead foil laminated with as­phalt t o various types of kraft and bond papers. However, even with a perfectly resistant body wall, which under some circumstances might be obtained with such a film, there is still the problem of making gas-tight end seams, and this difficulty apparently has not a s yet been overcome effectively.

Many fiber containers in which food products are packed are being shipped to subtropical and tropical climates. For use in such climates, it i s usually neces­sary not only to make a fiber body which is highly moistureproof but to provide a construction which cannot be penetrated by insects. Lead foil, and some asphalt treated stocks have proved to be among the more insect-resistant stocks for use in such cans.

Recently the treatment of paper and paperboard to inhibit the formation of molds i n some products packed in fiber containers has received attention. Small amounts of such compounds as the chloro-phenols are added to the paper stock during manufacture.

I t has also been found possible to inhibit rancidity in some products b y treating the paper stock used in the manufacture of the cans with phosphates and silicate coat­ings. Low pH i n paper stock appears to accelerate rancidity, while a neutral condition or a high pH in "the stock seems to delay the development of rancidity. Thus the presence of alum, or sizing mate­rial, generally seems to accelerate ran­cidity.

N e w Applications of Fiber Cans

In the foregoing sections, an attempt has been made to cover the main points in the construction and treatment of fiber cans to obtain specific qualities. Every product, other than those which are prac­tically inert to the atmosphere, requires a container possessing one or more of these qualities to a greater or lesser degree. In designing a fiber container for any par­ticular use, it is necessary first to consider the properties of the product to be packed and to determine the conditions under which it will be filled and held. Once this qualitative analysis has been made, it is necessary in most instances to determine the degree of protection re­quired by the product. This can be done by a series of standard empirical tests. After these data are all assembled, it is then possible to design a container construction. In the case of a new type of product, it is usually necessary to make an actual pack of the material in the cans. This pack is subjected to suitable testing conditions, and after a period of time which may vary from a few days to several months, depending upon the product in question, adequate verification of the suitability of the construction designed may be obtained.

In the case of some of the new fiber containers for products formerly packed in other containers such as paint and motor oil, it is necessary to make shipping and handling tests in addition to static hold­ing tests. Analyses of the products packed in the new containers after the holding tests are also advisable if there is any doubt about the insolubility of the proofing materials.

The above general procedures have been used to design fiber containers as alter­nate packages for a whole host of products formerly packed in metal cans. It is not within the scope of this paper to list them all, but some of the more important can

Close-up of mandrel of spiral winding

be mentioned. Motor oil probably repre­sents the greatest potentialities as far as volume use of fiber cans is concerned. Under WPB regulations, no metal what­soever is allowed for containers for this product and it has been necessary to develop cans made wholly of paperboard. There are at least four general methods of making such containers oilproof on the inside. These are by dipping the whole container in a proofing material, spraying it on the inside, flushing out the inside, and by winding an oil-resistant inner liner. In the last case, it is also necessary to apply a seam dope t o both ends of the can. The top closure also offers some difficulties, but there seem to be several ways of overcom­ing these.

During the past few months fiber-bodied paint cans with metal ends in one-gallon and one-quart sizes have been manu­factured and used successfully on a com­mercial scale. The problems involved in designing these containers were somewhat simpler than in the case of the all-fiber oil can, chiefly because metal ends were used. There are several very satisfactory grease­proof inner liners for the body, and it is a relatively easy matter to apply a protec­tive compound to the seams before or after assembly of the ends.

Prior to the war a great many dry prod­ucts and a few oily and wet products were packed in fiber cans. These included salt, many dry chemicals and drugs, baking powder, gelatin and starch dessert pow­ders, scouring powder, spices, cocoa, tea, malted milk powders, biscuit dough, some chemical specialties, soil inoculators, lard, cereals, and some tobacco products. For all of these commodities the fiber can has served and is now serving as a prac­tical and economical package. Again, in the present emergency, fiber containers which have been developed as alternate packages are in most cases performing satisfactorily. In the case of such prod­ucts as paint, motor oil, vegetable short­ening, and coffee, there can be little doubt as to the superiority of the metal con­tainer. At the end of the war these products will, in all likelihood, again be packed in metal. Coffee must be closed under a high vacuum if maximum protec­tion is to be obtained, and this is not pos­sible in a fiber can. Metal cans for motor oil can be produced at a lower cost than fiber containers, chiefly because of higher production speeds. In the case of paint, it is very difficult to manufacture a fiber-bodied can in the same cost range as an all-metal package which will show the strength of the latter. There are, how­ever, a number of other products such as spices, baking powder, and some dehy­drated foods for which the fiber can makes an ideal package, and it can be expected that many of these products will remain in fiber containers permanently.

PRESENTED before Division of Agricultural and Food Chemistry a t the Detroit Meeting of the AMERICAN CHEMICAL SOCIETY, April 12, 1943.

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