US3341105A - Foamed seal package - Google Patents

Description

Sept. 12, 1967 "r. o. CURRAN I I FoAMEp SEAL PACKAGE Filed June 1, 1965 INVENTOR. THOMAS D. CURFPAN ATTORNEYS United States Patentv O 3,341,105 FOAMED SEAL PACKAGE Thomas D. Curran, Walnut Creek, Calif., assignor to Fibreboard Paper Products Corporation, San Francisco, Calif., a corporation of Delaware Filed June 1, 1965, Ser. No. 460,250 3 Claims. (Cl. 229-37) The present invention relates to methods for sealing packages, and more specifically to a method of sealing packages wherein an expandable material is utilized to fill all gaps and voids in the package closures.

Paper, paperboard and plastic film containers, which are utilized to form packages for particular goods such as food, cleaning materials and other perishable products, must fulfill a number of functions. Among these functions the package must protect the contents, depending upon their nature, from moisture change; deterioration in texture, flavor and general market acceptability due to oxidation and light; sifting, where the product is powdered or granular, through package gaps or openings; and the entry of insects or other foreign material such as dust, dirt, etc.

In order to protect the contents from the above noted types of deterioration, the industry has resorted to heatsealed bags, pouches and overwraps or inner containers of thin papers coated with wax or plastic or other polymeric film materials. Such wax papers or plastic films provide barrier protection and generally produce good, acceptable, tight closures. Such thin barrier materials have several disadvantages, however. For instance they do not alone provide the necessary structural strength required for many fragile products such as cereals. Unles supported by other means, these thin materials do not stack well or provide a sufiiciently flat surface for good display of advertising messages. Further such thin film packages are subject to breakage, especially in larger unit packs. Additionally, packaging line speeds are generally much lower for pouches and overwraps than for rigid or semirigid carton materials. These lower packaging line speeds generally increase the over-all cost of using such thin film materials.

In view of the limitation of such thin film materials as pointed out above, many packages not only use these thin film barriers, but also incorporate a rigid or semirigid paper or paperboard carton therewith. For instance many dried fruits are packed with an inner sealed bag of Waxed paper or plastic film, a folding paperboard carton container, plus a printed wax paper or plastic film overwrap. Many cereals are packed in double or single barrier bags with a printed folding carton, while still others are packed in a plain carton with a printed barrier overwrap. Frozen foods almost from their introduction into home use have used unprinted wax paperboard cartons with a printed heat sealed wax paper overwrap.

While such multiple containers as noted above generally do an excellent job of protecting the products packaged therein, it can also be understood that such packages not only require an excessive amount of materials of difierent varieties to produce the package but further involve repetitive packaging operations which greatly tend to increase the price of the product. In addition the multiple'operations necessary to package the product result in greater total packaging line times with subsequent in- "crease in ultimate cost.

For the above reasons the industry has made a concentrated development effort on packages which combine the structural strength of a semi-rigid or rigid paperboard carton combined with the barrier properties of wax paper or plastic film bags and overwraps all in one structure. Such containers as have been developed are known as wrapperless cartons or single wall structure cartons. Such wrapperless cartons offer the advantages of reducing the variety of materials necessary to package the product, eliminating many operations in the packaging process, thus reducing labor requirements with consequent cost reductions, permitting higher machine speeds on packaging lines through the use of rigid or semi-rigid materials only, the utilization of special convenience features such as easy-opening tear strips and recloseable spouts for pour-and-store items, and increased protection of the package integrity since the necessary barrier films are strongly adhered to the more rigid paperboard. The consequence of which is that such wrapperless packages are not as subject to damage and loss of barrier protection in handling as previous multi-layer packages.

Although presently available wrapperless containers offer many of the advantages indicated above, they are still subject to the problems of any single barrier package, in that the closure areas are particularly susceptible to the formation of gaps and openings (especially at the corners) wherein the primary problems of sifting, insect and foreign matter entry, and oxidation are still present. Further steps to combat these problems have also been taken through the introduction of extra sealing flaps, addition of thin membrane films glued to the closure portion of the container, and sealing of the sealed package by dipping in melts of wax or other plastics. However, all such processes involve the addition of extra materials to the package or extra operations which once again tend to increase the packaging costs and packaging time. Thus the closing of corner holes and flap gaps has been found to be the major problem remaining in the wrapperless package.

The present invention presents a method of sealing packages wherein gaps and other holes in the closure portion, including the corner holes of a package, are effectively and securely eliminated without the introduction of additional materials, extra closure flaps or other special design, and without the introduction of additional steps into the packaging operation. Briefly the method of the present invention involves the use of a material that expands or foams" to fill all gaps and hole in the package closure.

Is is, therefore, an object of the present invention to provide a method of sealing packages wherein a foamed material fills all gaps and holes in the package closure.

It is another object of the present invention to provide 'a' method of sealing packages wherein extra flaps or special designs of the carton are eliminated from the closure.

It is another object of the present invention to provide a method of sealing packages wherein the container glue or adhesive not only seals the package flaps, but also expands or foams to fill all gaps or voids in the pack age.

It is yet another object of the present invention to provide a method of sealing packages wherein the package is sealed with an expanding adhesive which not only glues the package flaps, but also expands to fill all gaps or voids in the package closure wherein sifting, easy insect or foreign matter entry, and oxidizing gas entry, is eliminated.

The invention will be better understood from the fol lowing description taken in conjunction with the accompanying drawing of which:

FIG. 1 is an isometric view of one end of a typical wrapperless carton showing the end flaps in the opened position but with the sealing material applied thereto just prior to the sealing operation;

FIG. 2 is an isometric view of a closure portion of the typical package of FIG. 1 illustrating the package after the end flaps have been closed and the gaps and holes have been filled by the foamed material; and

FIG. 3 is a cross-sectional view of the package of FIG. 1 across the end closure thereof.

In the practice of the present invention any wrapperless paperboard carton of simple conventional design may be utilized. The end flap closure construction of the carton may be extremely simple, like that construction as illustrated in FIGS. 1 and 2 of the drawing.

While the drawing illustrates a simple noncomplicated carton, it should be understood that other carton designs, even of a more complex nature, may be utilized equally well in the practice of the present method.

Specifically, with reference to FIG. 1, a carton 11 is formed with side walls 12, 12, 12" (and another one which is not shown) to form a generally rectangular inner volume. One of the side walls 12 is extended to form an end flap 13, while each of the other sides is similarly extended to form end flaps 14 and 16 and a fourth end flap not shown in the illustration. A fold line 17 defines the junction between side wall 12 and end flap 13, while fold lines 18 and 19 define the junction between side wall 12' and end flap 14 and side wall 12" and end flap 16, respectively. A similar fold line is formed between the fourth side Wall and fourth end flap not shown in the illustration. End flap 13 is cut to a length whereby the upper edge 21 thereof will extend approximately partially across the end opening of the box when the flap is folded at right angles to side wall 12. End flap 14, on the other hand, is cut to a length slightly shorter than the length of fold line 17 whereby its upper edge 22 will nearly touch, or at least come in close proximity, to the opposite wall of the carton when flap 14 is folded at right angles to side wall 12. Similarly end flap 16 is cut to a length approximately equal to the length of fold line 17 whereby its upper edge 23 will extend all the way across end flap 14 when folded down at right angles to side wall 12". The fourth flap (not shown) is cut to a length equal to that of end fiap 13 whereby when it is folded down it will extend inwardly of its respective side wall.

FIG. 1 illustrates the carton 11 at a time just prior to the folding and sealing operation during the practice of the method of the invention, so the material that serves to glue the end flaps of carton 11 together i shown applied to the flaps. Thus a patch of material 24 is shown applied to the upper surface of flap 13 adjacent its upper edge 21, another patch of material 26 is shown applied to the upper surface of flap 14 adjacent its upper edge 22, and another patch of material 27 is shown applied to the under surface of flap 16 adjacent its upper edge 23. Another patch of material similar to that of patch 24 is applied to the fourth flap (not shown).

It should also be noted that small patches of material 28 and 29 are applied to the upper surface of flap 13 adjacent the end of fold line 17 thereof. Similar patches are applied to the identical position of the fourth flap which is not shown in the illustration.

It will be apparent that the extent and positioning of the patches may be varied depending upon the end flap shapes and folding procedures. Of course the patches can be placed in other positions at any portion of the carton body, if it is intended to seal any gaps or channels. However it is only necessary to apply the material in such cations as to ensure secure sealing of adjacent flaps when the carton is folded and further in such amounts as to force the expanding material into all gaps and hole areas of the closure. The carton construction of the drawing is merely one of a great number of closure configurations in use and variations in placement of material and amounts used for each type of carton construction and size variation will be apparent to those in the packaging industry.

The material utilized to form patches 24, 26, 27, 28, 29 and other patches on the end flaps of the carton is critical to the operation of the present invention. Specifically, the material must be composed of a material having the following properties: (I) It must be capable of adhering to the two adjacent surfaces of paperboard or other carton material. (2) It must have the property of expanding and flowing after application to the carton surface and prior to setting.

Many self-foaming plastics are suitable materials for use as the material in the present invention. Specifically, the material utilized to seal any gaps or channels in the carton 11 may be any suitable material that foams up or expands under the proper conditions. It is only necessary that such material adheres to the adjacent carton walls and that the resultant foamed structure be stable under any expected environmental conditions to which the package is subjected.

For instance it has been found that polyethylene can be foamed using p,p'-oxybisbenzenesulfonylhydrazide as a blowing agent. In this instance the blowing agent, in powder form, is melted into the polyethylene below its decomposition point. The plastic polyethylene-blowing agent melt is then applied to the carton 11 in thin films in the positions referred to. The opened flaps are heated by a hot air blast at a temperature between 400-1000 F. for a period of 1-10O seconds, depending on the speed of the machine. The flaps are closed and kept under heat and pressure until the polyethylene has expanded into the gaps and channels in carton 11. On cooling the polyethylene solidifies, thus keeping the carton tightly sealed.

The foamable polyethylene can either be applied in a patterned form as shown or additionally in areas where glue would normally be applied, in which case it may function as a sealant at critical edges and corners, but also act as an adhesive for securing the end flaps in place.

Usually foamable polyethylene can best be used on a heat sealable coated surface, where the majority of the adhesion of the end flaps to one another would be accomplished by the heat seal coating, while the patterned foamed polyethylene would protect the critical areas having holes and channels.

While such a foamable material is suitable for use in the invention, other materials are also particularly well suited for use therein and especially preferred. Thus, polyether foam systems such as polyurethane are especially desirable. This is particularly so, since polyurethane not only forms an excellent foamed material for sealing gaps and channels, but in addition, strongly adheres to the usual carton materials. Thus the polyurethane serves the dual purpose of foaming to seal carton gaps and channels and gluing the carton together. Utilizing such a material eliminates the need for separate adhesives or heat sealable surface coating to effect carton sealing. However, it should be understood that under certain circumstances, separate adhesives and foaming materials are the desirable materials for effecting carton closure and gap sealing.

With respect to the single adhesive-foam systems, polyether systems such as are used in the preparation of rigid unicellular polyurethane foam having density from about 2 to 30 or more pounds per cubic foot, have been found to be particularly suitable for use in the present invention.

Such polyether foam systems are well known in the industry and are commercially available from several sources. For instance one such system known as Polyite is available from Reichold Chemicals Inc. This system basically employs two separate products, a resin and a prepolymer. The resin component contains a catalyst and a suitable blowing agent, usually a fluorocarbon. The prepolymer comprises a selected isocyanate, which when contacted with the resin component, reacts to polymerize to a self-foaming, self-curing unicellular material having the desired adhesive and expansion properties.

The product foamed adhesive is produced by properly mixing in the correct ratio the required amounts of the system components. Mixing can be carried out either batchwise or with automatic metering, mixing and dispersing equipment.

In any event, the mixture, if a single adhesive-foam, or the separate adhesive and foam material, if a two component system, is applied in a thin film to the proper areas of the package end flaps as pointed out above. The end flaps are then immediately folded over and held under pressure until the foam cures sufliciently and forms a bond to the adjacent surfaces of contact of the carton. Machinery for automatically folding and holding the cartons until the bond forms is common in the industry and is readily available for this purpose.

FIG. 2 illustrates the carton of FIG. 1 after end flap 13 and its opposite flap (not shown) have been folded in, end flap 14 has been folded over the inner flap and outermost flap 16 has been folded over the entire end of the carton.

The end flaps 13, 14, 16 and flaps 13 opposite flap are folded immediately after application of the adhesive or foam material patches thereto. The flaps are held in the folded position while the material cures during which time it foams and expands into adjacent areas. Thus the end gap 31 created where the edge 22 of flap 14 overlies the underneath flaps, and where the under surface of end flap 16 is folded thereover, is filled by the material expanding thereinto.

Similarly any holes or gaps occurring at corners 32 and 33 of the carton are filled by patches 28, 29 expanding thereinto. Similarly all other gaps and holes occurring in the end closure of the carton are filled by the expanding material.

As the material expands into the gaps and holes in the carton structure it solidifies into an impermeable foam structure. Also, in the event a single adhesive-foam system is used, the material forms an excellent adhesive, it securely adheres to adjacent portions of the carton structure to provide a secure seal of the gap or holes, as well as the end flaps, during subsequent handling operations.

After the material has solidified any flashing material that is extruded from the edge of the flaps or out through the holes and gaps may be removed by a simple abrasive or cutting operation. In fact, once suflicient experience is had with a particular carton design and size, exact amounts of expandable material may be applied thereto whereby any excess amount is eliminated and such subsequent abrasive or cutting operation to remove flashing is eliminated.

Semi-rigid or flexible closed cell foam materials, as well as rigid foam materials, are suitable for use as the expandable material in practicing the method of the invention. The selection of a semi-rigid or flexible closed cell foam for use as the gap filling material of the package will depend upon the use to which the package is to be put and the conditions expected during its transportation and storage. For example, where packages may fall on a corner, a flexible foam which is not so subject to break-age as a rigid foam would be a suitable material for filling the corner holes of such packages.

Experiments were conducted to compare cartons sealed by the method of the present invention with other cartons of identical design sealed by other prior art means. Table I below presents data obtained on a lock-style carton made out of paperboard having a 1 mil polyethylene coating on the outside and a web wax coating on the inside thereof.

One of these cartons, prepared by the method of the present invention, had the flap areas thereof coated with a freshly prepared polyurethane foam mixture of about 2 /2 pounds per cubic foot density. The flap areas were then locked in position and held under a pressure of a few pounds per square inch weight. After a few minutes the bond was sufliciently strong to allow removal of the pressure. This carton, along with other cartons produced by other methods known in the art, was then tested in a diffusion apparatus which measured the percentage of moisture transmission through the carton structure. The results of these tests-are illustrated in Table I.

TABLE I Moisture vapor transmission Specimen rate at 100 F., 88% relative Percentage humidity difference, grams transmission per 100 sq. ins. per day (1) Total carton moisture vapor trans. rate 22. 5 100 (2) Carton w/one locked end sealed with mierowax 8. 14 35. 9 (3) Carton w/both locked ends sealed with mierowax 3. 86 17. 9 (4) Carton w/both locked ends and easy opening perforations sealed with microwax 2. 83 12. 4 .(5) Carton sealed by method of the 6. 4

invention 1.

Table I above illustrates that a carton laboratory sealed by the process of the present invention is more tightly sealed than a similar carton in which all vulnerable leakage points were laboratory sealed with localized applications of hot microwax. The results of the tests in Table I were made utilizing apparatus and testing methods fully disclosed and described in an article entitled, Test Sealed Carton Barriers Quickly and Reliably, by T. David Curran and Gordon C. Wheeler, appearing in volume 10, No. 2, February 1965 edition of the publication Package Engineering.

The results of another series of tests utilizing apparatus comprising two matched fiowmeters is presented in Table II. The outlet of one flowmeter was sealed into the package interior, while the input to the second flowmeter Was also sealed into the package interior. A small air pump and ancillary equipment gave a smooth regulated flow of air. The air flow rate was controlled by a needle valve. If a package had no leakage both input and output flowmeters would read the same. If leakage occurs the output flowmeter reading falls off directly in proportion to the loss through the package walls.

Such tests, that determined air leakage rates from the various packages sealed as indicated in the table, are a measure of the absolute seal achieved by the different methods. It will be noted that test (5) shows packages sealed according to the method of the present invention. A further review of such results will reveal that such methods produced packages far better than any other method with the exception of triple barrier packages comprising successive layers of heat sealed polyethylene, foil and a paper pouch. This improvement may be understood by remembering that conventional water based adhesives used in gluing packages shrink considerably on drying to about 10 to 30% of their volume when applied wet. Hot melt adhesives remain about the same volume or shrink slightly on solidifying, however, the foamed adhesive used in this invention can be made to expand as much as fifty-fold its initial volume at application, and in addition it remains flowable long enough to allow gaps and holes to be completely filled.

TABLE II.AIR LEAKAGE RATES OF COMMERCIALLY SEALED PACK- AGES VS. FOAM SEAL GARTON AT 4.34 LITRES/MIN. INPUT FLOW Package Package leakage, leakage rate, Package description Product packaged litres/min, litres/min,

individual avg.

values (1) Glue end carton, paper/poly- Sugar 4.34; 3.78; 2.77 3. 6

ethylene/paperboard sandwich w/ metal pour spout.

(2) Cellopane wrap, heat sealed Raisins 2.54; 2.73; 2.33 2. 5

over carton.

(3) Reyseal foiloverwrapped carton, Water condi- 1.94; 1.42; 2.85 2. 1

papcr/microwax/i'oil lamination tioner. heat sealed.

(4) tEll/axed paper overwrapped Raisins 4.34; 3.99; 1.94 3.4

car on.

(5) Paperboard carton w/polyethyl- 0.14; 0.44; 0.39 0.3

ene coating, both sides sealed w/ olyurethane foam.

(oi laperboard carton w/V an Buren Powdered deter- 1.93; 2.54; 2.44 2. 3

ears. gen

(7) Paperboard carton overwrapped Corn Starch 1.14; 3.08; 2.35 2. 2

w/glued paper.

(8) Heat sealed polyethylene/foil/ Dehydrated .0; 0.19; 0.09 0.0.9

paper pouch. potato granules.

(9) Heat sealed polyethylene bag Dehydrated 0.82; 0.19; 1.14 0.7

potato flakes.

Considering the purposes and eifects of the method of the invention will also reveal that not only may gaps and channels be sealed in packages but, in addition, other useful results can be achieved. For instance, it is oftentimes desirable to exclude moisture vapor, gas and liquid water transfer through the interior channels of corrugated paperboard panels or boxes. Utilizing the method of the invention a film of expandable material is applied to the open ends of such paperboard. Subsequently, the material is permitted to cure, whereby it foams, expands, and flows into the open channel ends; or if a heat sensitive foaming material is utilized, hot air is blown on the coated ends of the paperboard, whereby the material foams, expands and fills the ends of the channels in the paperboard. Thus the corrugated paperboard has its open ends sealed by the expandable materials, and moisture vapor, gas and liquid water transfer through the interior channels thereof is eliminated.

Other applications and uses of the method of the present invention will be apparent and all such are contemplated by this specification as particularly encompassed by the following claims.

What is claimed is:

1. A wrapperless package including a closure portion having overlapped closure flaps with holes, gaps and channels therebetween, said flaps being adhesively sealed by an adhesive composition comprising a closed cell foam structure which fills said holes, gaps and channels.

2. The wrapperless package of claim 1 wherein the closed cell structure is formed of blown polyethylene.

3. The wrapperless package of claim 1 wherein the closed cell structure is formed of polyurethane.

References Cited 45 JOSEPH R. LECLAIR, Primary Examiner.

DAVIS T. MOORHEAD, Examiner.

Claims (1)

1. A WRAPPERLESS PACKAGE INCLUDING A CLOSURE PORTION HAVING OVERLAPPED CLOSURE FLAPS WITH HOLES, GAPS AND CHANNELS THEREBETWEEN, SAID FLAPS BEING ADHESIVELY SEALED BY AN ADHESIVE COMPOSITION COMPRISING A CLOSED CELL FOAM STRUCTURE WHICH FILLS SAID HOLES, GASP AND CHANNELS.

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