US2335865A - Packaging method - Google Patents

Description

Dec. 7, 1.943. F. LANIGAN ETAL PACKAGING METHOD Filed Nov. 17. 1941 Top `senz/fig Bof/0m Patented Dec. 7, 1943 UNITED STATES PATENT,"I OFFICE PACKAGING METHOD Francis W. Lanigan, Evanston, and Thomas F. Cass, Jr., Chicago, Ill., assignors of one-halt to Container Corporation of America, Chicago, l Ill., a corporation of Delaware, and one-half to. y 'Dewey and Almy Chemical Company, Cambridge, Mass., a corporation of Massachusetts Application November 17, 1941, Serial No. 419,468

16 Claims.

This invention relates to an improved packaging method and more particularly to a packaging method involving paperboard containers having a coating material thereon, such as a coating material adapted to impart moisture vapor-proof properties to paperboard.

Many attempts have been made to devise vapor-tight packages including paperboard containers, but heretofore such packages have either been rather expensive or have not attained the necessary degree of resistance to the passage of gases and vapors, especially moisture vapor. The problem of packaging inexpensively products and commodities which are susceptible to deterioration by change in moisture content, and particularly food products such as prepared cereals, confections, soap akes, dried fruits, hygroscopic powered foods, frozen foods andthe like, is a very important one which has not heretofore been satisfactorily solved. Such products are now generally packed in combinations of paperboard containers with special wrappers or linings composed of waxed paper, regenerated cellulose or partially depolymerized rubber sheets or similar materials, but, each of these packages has one or more disadvantages, such a's dimculty of obtaining perfect seals in commercial production, physical instability to temperature changes, and increased labor costs resulting from the necessity of handling such combinations of materials. While attempts have been made to use containers of paperboard coated with a material such 'as paran wax, packages of this type do not have the requisite imperviousness, both because paraffin wax is inherently incapable of producing a package having a high degree of resistance f the passage of moisture vapor and because of the diiiiculty of producing a vapor-tight; seal at the package joints. It has'also been suggested that paperboard containers already filled be dilpped into a bath of parain wax or the like, but this has the obvious disadvantage of allowing free transfer of moisture, flavor and odors from `the product to the paperboard and vice versa, and as to some products, of necessitating the heating of the contents to an undesirable degree.

We have devised a novel packaging method which is inexpensive and which produces a sealed package affording an unusual degree of protection to the contents thereof. Oui` invention is particularly adapted to produce substantially moisture vapor-proof packages, but itis n ot limited thereto, and is applicable to the production of substantially gas-tight or grease-prooi packages. It

is an object of our invention to provide` a packaging method whereby such packages can be inexpensively produced.A Another object is to provide a packaging method which can be carried out conveniently and economically on automatic packaging machinery by the manufacturer of the product to be packed therein using a suitable thermoplastic coatingmaterial and paperboard containers which can be shipped to such manufacturer in a flat or knocked-down condition. Other objects, uses and advantages of our invention will be apparent from the following detailed ,description thereof read in conjunction with the drawing, in which:

Figure 1 is a diagrammatic flow sheet illustrating the steps comprising the method of our invention in one of its embodiments;

Figure 2 is a diagrammatic flow sheet illustrating a modified method according to our invention; f

Figure .3 shows in perspective a paperboard carton suitable for use, in connection with our invention in collapsed or knocked-down form;

Figure 4 shows the carton of Figure 3 in expanded ortubular form; Figure 5 shows the carton of Figure 4 as it would appear after the bottom-sealing step and before the filling step;

Figure 6 is similar to Figure 5, but brings out thelocation of the coating applied in accordance with the modication shown in Figure 2;

Figure 7 illustrates Athe lling step;

Figure 8 shows a filled carton with the top flaps partially closed; and

Figure 9 is an enlarged perspective view of one portion of a carton particularly adapted for use in carrying out our method.

In one of its broad aspects our invention comprises selecting an empty paperboard container having one open end and one closed end, and overlapping flaps adapted to close the open end, coating a1; least the interior surfaces of the container and all surfaces of the open ilaps with a film of a thermoplastic coating material having good 'heat-sealing properties, yfilling the coated containers with a desired product, and closing and heat sealing the coated flaps.' While it is not essential, it is extremely desirable that the paperboard containers used be similar to ordinary folding cartons, so' that they can be v shipped and stored 'in knocked-down condition.

Such cartons are adapted for setting up and bottom sealing with adhesive on conventional automatic equipment and in this form are ready for the coating operation. The flaps at the open or top end of the carton should be arranged so that` they overlap to a very considerable extent and preferably at least the two flaps attached to opposite side Walls should be substantially' fullsized so as to provide the best possible seal.

The coating operation can be carried out by hand or by any suitable machine, the essential requirements being that the entire container be coated internally and that the open flaps be coated on` both sides thereof with a continuous lm of a suitable thermoplastic coating material which impregnates the paperboard only enough to adhere rmly thereto. In one embodiment of the invention, the container body is coated uexternally as well, and this is preferably done by dipping in a molten bath of the coating material, draining and cooling, although flooding or other means can be used. When the outside of the container body is left uncoated, however, iiooding is the most suitable procedure forcoating the interior surfaces thereof. The thermoplastic coating material should have a softening point I such that it will remain in a solid but somewhat pliable condition and not adherent or tacky at any temperature likely to be encountered in storage, shipment or use of the resulting package, and it should have excellent heat-sealing properties which should be superior to those of paraffin wax, for example, so that the container flaps coated with the material and heat-sealed will have substantiallyv no tendency to become detached `during handling. Furthermore, the coating material should be of low viscosity and adapted to dipping or flooding operations When in the liquid state, and it preferably has an intermediate gel state in which it will ilow under heat and pressure. It is obvious, of course, that ,the coating material should have no characteristic such as odor or taste which would make it unsuitable for direct contact with the product being packaged.

The nature of the thermoplastic coating material will depend, of course, upon the properties which it is desired to impart to the package. It can be of such a nature as to be extremely resistant to the passage of moisture vapor or of inert gas or .the like, or to the action of oily or greasy materials, such as peanut butter, for example, or it can have a combination of these properties. In case the product being packed is one which is susceptible to deterioration by change in moisture content, we have found that a particularly suitable thermoplastic coating material is one whicl': is a homogeneous composition including at least 90% of a wax, such as parafln wax, carnauba wax or beeswax, and in the neighborhood of 7 to 8% of depolymerized rubber. Such compositions having a iiow point in the range from about 125 to as high as about 180 F. and especially those having a ilow point in the range of 135 to 145 F., have been found to be particularly satisfactory.

Following the coating operation, the cooled coated containers are filled with the product being packed in the usual way. Finally, the open flaps are closed so as to overlap one another and are heat-sealed to provide a completely sealed package, ready for storage or sale.

A diagrammatic flow sheet illustrating a complete packaging operation embodying our invention is shown in Figure 1, and for convenience this rectangular cross-section having four integral flaps at each end, all of the side wall iiaps being adapted to cover the ends of the carton substantially completely. Such cartons are ordinarily supplied to packers of food products and the like in a fiat condition and with one side wall and one end wall secured together by a manufacturers joint so that it is only necessary to apply pressure to two opposite edges to cause it to assume rectangular shape. Such a carton is illustrated in Figure 3 in substantially flat condition and in Figure 4 in completely expanded condition.

The next step is-to seal by means of adhesive or the like one end of the carton which will become the bottom end. This operation can be carried out conveniently on conventional automatic machinery capable of folding down the two end wall will be described in connection with a preferred faces.

flaps, applying adhesive to both sides of one of the side wall flaps, folding this over upon the end wall flaps and finally folding down the second side Wall ap and holding it in that position until the adhesive has set. The carton then appears as shown in Figure 5.

` The next operation is that of coating the bottom-sealed carton with the desired thermoplastic coating material. In this example, the coating material is a homogeneous composition containing about 92.5% of paraffin wax and about 7.5% of rubber which has been depolymerized or modied by prolonged heating, e. g., for 18 hours, at about 300 F. under oxidizing conditions, the vaporized products being continuously withdrawn. This composition has a flow point in the neighborhood of F. and a so-called gel state at about to 160 F., and is in a thin liquid state at about to 190 F., the viscosity in the liquid state being of the`same order of magnitude as that of the wax used. This material retains its pliable characteristics at temperatures as low as 40 F. so that it will not flake or become dislodged during a freezing operation.

In the modication of Figure 1, the carton isI dipped in a bath maintained at the proper temperature, in this instance about 175 to 185 F. It is extremely desirable that the coating material should not penetrate into the paperboard of the carton more than a very small distance sufficient to cause it to adhere thereto at all points, and for this reason the paperboard should not be too porous or have many minute fibres projecting from its surface to act as wicks.- The dipping operation itself can be accomplished by any suitable means, the essential feature being that the entire carton, including the flaps thereof, is completely coated on its exterior and interior sur- When the carton is withdrawn from the coating bath, it is desirable that the excess coating material should be allowed to drain ltherefrom in vorder that the proper lm thickness can be obtained. Obviously, it is undesirable that the lm should be too thin or inadequate moisture vapor proong will be obtained and it is also undesirable that this lm should be too thick or the coating operation may become uneconomical or the coating may be unevenly deposited so as to produce an undesirable appearance, or it may be more subject to accidental injury or to diiliculty in the heat-sealing operation which will be described belw. For these reasons, the carton is allowed to remain with its open end down in a draining chamber at a temperature of about 170 to F. for a predetermined period of time. By

Iregulating the temperature of the draining chamber and the time that the carton is within this chamber, it is possible to secure any desired film weight. Finally, the carton is cooled tol solidify the coating material and this is conventionally ydone by subjecting it to a blast of cool air.

l `In the modification of Figure 2, the carton is subjectedto one ormore streams or heavy sprays of the liquid thermoplastic material, which may be directed so as to form-a' complete filmv over lallof the carton and nap surfaces. As pointed out above, however, it is not essential to the production of la substantially moisture vapor-proof package that the outside of the bodyv portion ofthe carton be coated, so that onlytheinterior thereof need be vsubjected to the flooding operation. ',Ihe

top flaps, howevenmst' be completely coated, and

this 'is preferably carried 'out either a's a part of thel flooding operation.' or as' a supplementary partialdippingoperation. The outside coating may extend from the top flaps merely' to their respective score lines, or it may extend a short distance, e. g., als" tog", below these score lines as shown in Figure 6. In all ofthese' modifica- 'tions'the cartons aresubsequentlydrained and cooled as hereinabove described. y v Many advantages" are .obtained byr coating'the carton after they bottom-sealing step, a 'principal one being that theybottom is vthus. completely l sealed,l which' would be extremely di'cult if it ,wereattempted to seal the bottom lend ofthe cartonv after it has'been coated'. .I Furthermore, in the same operation thefmanufacturers joint ,be no .opportunity for.

Cfrom t Ie :interior .ofgthe paperboard eases from the .product ,te be bserbed by4 the -paperboard-th,r,0ugh this .essa f ,Since the cartons @aus prier ,Qneratiomfanother .advantage flies: in .the 1i-act ,i than-with vthe.exceptionof;the closing. of the top -.-.fiaps,,no.further foidingds required; which might y zconceiyabiyfrupture the-continuity of.;th e film-of coating ymateriakAnyrupture ofthe film con- `tinuity.'Wl1. .`'i'.-rxrlislitoccur alongy the upper. hori- -rzontalf.scoielines ducato they folding of thetop iiapsisv repaired during the I vproper operation described below..

heat-sealing .The coatedcarton y.is then' readyV tofbe Afilled with the Adesiredproduct and this operation can be carried-out ina conventional manner, such as illustrated diagrammatically in Figure. 7. r

The final stepis that of top-.sealing the filled l carton. y Since the carton flaps` .are completely coated with. a thermoplastic )materialrv having goodheat-sealing properties and the property of not impregnating the paperboard exceptat the .surface thereof, it is only necessary to fold the naps-attached to the `end walls and then those y attached to the side walls, and to apply heat and pressure to` the top ofthe carton suficient to cause the thermoplastic material to enterits ge1" rstate and to flow into all of the cracks and .crevices between the top flapsand around the edges thereof'so that it forms a continuous nlm sealing the entire top ofthe carton. In order to `in sure complete continuity of the coating material iilmA along the upper Ahorizontal scores, where slight ruptures may conceivably occur due to the folding of the top flaps, the heat should be applied over the` entire top surfaceofthe carton includingl the outside edges along the score lines so as tocause the coating material to ow `in the vicinity of these scores. As mentioned above, it is undesirable to have too great a film thickness; since the excess"thermoplastic-material will only be squeezed from between the naps and may cause an unsightly result, although a "small amount of excess material can be handled if suitable provision is made therefor. Since all of the other points of possible moisture vapor 'transfer have been completely eliminated by the lcoating operation, it is apparent that the proper heat-'sealing operation completes the cone itinuity of the coating material film andproduces a substantiallymoisture vapor-proof package.

In carryngvoutvour invention as hereinabove described, we prefer to use cartons constructed Aas shown in Figure 9 having an extension I0 on the glue strip which is adapted to underlie the end wall iiap4 I2. Thus the cartonl corner which is normally the weakest when the usual cut-back glue strip isused is strengthened, and the continuity ofthe film ofv coating material obtained by heat 'sealing is thus assured.

A modification Vwhich can be used involves the .application of a special thermoplastic adhesive along the. edges .of one or more yof the top flaps which is not miscible with the thermoplastic coaty which increases the strengthof the bondbetween thel various overlapping flaps. l

It Vwill be seenfrom the above that we. have devised-a novel and extremelyuseful .packaging canreadily be madelby those skilled in the art uct to bepacked inllthe artonfo foranylignids'.. ,-,l--without departing ,fromthespirit ofour invenmethod and that various modifications -`thereof y tion. .*We do not desire to be limited-therefore, by thespecific embodiments employed in describappended claims..

I Weclaim:

ing our invention, but only by the scope of the 1.. lhe` method of.,rpa,otkaging a produ-ct.` which comprises selecting an empty paperboard conv-tainer having one open end'and one closed end,

tainer and all surfaces of said flaps With anim of -a Lthermoplastic coating material' whichi is fsolid ,andvpliable at normalftemperatures"and adheres. to 'but `does notmaterially impregnate said paperboard whenabove itsfiow point, filling thev coated container :with said product, vclosing `said-.'ilaps, and applying suflicient heat tothe closed flaps to=cause saidy material toi-lowland -f to form a continuous iilm completely sealing said flaps, and holding the same in'closed position.

2. The method of packaging a product which comprises .completely coating an empty paperboard containerhaving one open end and Ione yclosed end, anda plurality of flaps on the side Walls thereof and integral therewith adapted to ybe overlapped to close said'open end, with a 4continuous' lm of a thermoplastic coating material which is solid and pliable at normal temperatures and adheres to but does not materially impregnato said paperboard when above its ow point, lling the coated container with said product, closing said flaps, and applying sufficient heat to the closed flaps to cause said material to flow and vto form al continuous nlm completely sealing said flaps, and holding the samei'n closed position.

3. The method of packaginga product susceptible to deterioration by change in moisture content which comprises completely coating an empty paperboard container having one open end and one closed end, and a plurality of iiaps on the side walls thereof and integral therewith adapted to be overlapped to close said open end, with a continuous film of a thermoplastic coating material substantially impervious to moisture vapor which is solid and pliable at normal temperatures and adheres to but does not materially impregnate said paperboard when above its ilow point, lling the coated container with said product and closing and heat-sealing said aps to form a continuous film holding said flaps in closed position.

4. The method of packaging al product according to claim 3 wherein said thermoplastic coating material is a homogeneous composition including at least 90% of a wax and about 7% to 8% of partially depolymerized rubber.

5. The method of packaging a product which comprises setting up a tubular paperboard carton having integral naps on the side walls thereof adapted to overlap so as to form closures lying substantially in planes perpendicular to said side walls.at both ends thereof, closing and sealing with adhesive the ilaps at one end of said carton, coating at least the interior surfaces of said carton and all surfaces of the ilaps at the other end oi said carton with a continuous film of a thermoplastic coating material which is solid and pliable at normal temperatures and adheres to but does not materially impregnate said paperboard when above its ilow point, lling the coated carton with said product, and closing and heat-sealing said last-mentioned flaps to form a continuous film holding said flaps in closed position.

6. The method of packaging a product which comprises settin-g up a tubular paperboard carton having integral flaps on the side walls thereof adapted to overlap so as to form closures lying substantially in planes perpendicular to said side walls at both ends thereof, closing and sealing with adhesive the ilaps at one end of said carton, completely coating said carton with a continuous film of a thermoplastic coating material which is solid and pliable at normal temperatures and adheres to but does not materially impregnatesaid paperboard when above its ilow point, filling the coated carton with said product, and closing and heat sealing the flaps at the other end of said carton'to form a continuous film holding said flaps in closed position.

7. The method of packaging a product which comprises dipping an empty paperboard container having one open end and one closed end, and a plurality of flaps on the side walls thereof and integral therewith adapted to be overlapped to close said open end, in a molten bath of a thermoplastic coating material which is solid and pliable at normal temperatures and adheres to but does not materially impregnate said paperboard when above its ow point, whereby both interior and exterior surfaces of said container and flaps come in contact with saidmaterial and are coated with a continuous lrn thereof, removing said container from said bath, cooling said container to solidify the coating material thereon, filling the coated container with said product, and closing and heat-sealing said flaps to form a continuous film holding said aps in closed position.

48. The method of packaging a product according to claim 7 wherein said thermoplastic coatlill ing material is a homogeneous composition including about 92.5% of parafn wax and from about 7.5% of rubber which has been depolymerized by prolonged heating, said material having a softening point in the range of to 14 5 F.

9. The method of packaging a. product which comprises selecting an` empty paperboard conl tainer having one closed end and integral flaps on the side walls thereof adapted to be folded into overlapping relation so as to form a closure lying substantially in a plane perpendicular to said side walls at the other end, coating said container and said flaps internally and externally with a continuous film of a. thermoplastic coating material, said material being a solid at normal temperatures and a relatively thin liquid at temperatures well above its flow point, and having a, plastic or gel state at intermediate temperatures, lling the container so coated with said product, closing said flaps, applying sumcient heat to said flaps to cause the coating material thereon to enter its gel state and ow into the adjacent cracks and crevices, and allowing said flaps to cool in closed position, whereby a continuous film of said material is formed completely sealing said flaps, and holding the same in closed position.

10. The method of packaging a product which comprises setting up a tubular paperboard carton having integral overlapping flaps on the side walls thereof adapted to overlap so as to form closures lying substantially in planes perpendicular to said side wallslat both ends thereof, closing and sealing with adhesive the flaps at one end of said carton, coating vat least the interior surfaces of said carton and all surfaces of the ilaps at the other end of said carton with a continuous lm of Aa normally solid thermoplastic coating material, said material having a plastic state at temperatures up to about 30 F. to 40 F. above its ilow point wherein it will ilow under light vpressure and being a relatively thin liquid at higher temperatures which has the property of impregnating paperboardfmaterially less than molten paraiiin wax, closing and applying sutilcient heat and pressure to said last-mentioned naps to cause the coating material thereon to ilow and to flll the cracks and crevices between and adjacent said flaps, and allowing said aps to cool in closed position, whereby a continuous film of said material is obtained which completely seals said carton, prevents all Contact between the paperboard of said carton and the contents thereof and holds said flaps in closed position.

l1. The method of claim 10 wherein said coating material is a homogeneous composition containing about 92.5% of a wax and about 7.5% of rubber which has been partially depolymerized by. heating at a high temperature in the presence of oxygen and with the continuous removal of vaporized decomposition products.

12. The method of packaging a product which comprises setting up a tubular paperboard carton having integral overlapping flaps on the side walls'thereof adapted to overlap so as to form closures lying substantially in planes perpendicular to said sidewalls at both ends thereof, closing and sealing with adhesive the ilaps at one end of said carton, dipping said carton in a molten bath of a normally solid thermoplastic coating material, said material having a plastic state at temperatures up to 30-40 F. above its flow point wherein it will flow under light pressure, and being a relatively thin liquid at higher temperatures which has the property of impregnating paperboard materially less than molten paraflin wax, removingl said ycarton from said bath, draining excess thermoplastic material therefrom and cooling the drained carton whereby said carton is completely coated With a continuous illm of said material, filling -the coated cartonwithsaid product, closing the flaps at the other end of said carton, applying suicient heat and pressure to said last-mentioned ilaps to cause the coating material thereon to flow and to fill the cracks and crevices between and adjacent said flaps, and allowing said flaps to cool in closed position, whereby a continuous lm of said material is obtained which completely seals said carton.

13. The method of claim 12 wherein said coating material is a homogeneous composition containing about 92.5% of a wax and about 7.5% of rubber which has been partially depolymerized by prolonged heating ata high temperature in the neighborhood of 300 F. under oxidizing conditions and with the continuous removal of vaporized decomposition products.

14. The method of claim l2 wherein said coating material is a homogeneous composition containing about 92.5% of paraffin Wax and about 7.5% of rubber which has been partially depolymerized by prolonged heating at a hi-gh temperature in the neighborhood of 300 F. under oxidizing conditions and with the continuous removal of vaporized decomposition products.

15. The method of sealing one end of a paperboard container having integral naps on the side Walls thereof adapted to be folded into overlapping relation so as to form a closure for said end lying substantially in a plane perpendicular to said side walls which comprises coating at least said aps internally and externally with a continuous film of a thermoplastic coating material, said material being a solid'at normal temperatures and a relatively thin liquid at temperatures Well above its flow point, and having a plas-v tic or gel state at intermediate temperatures, closing said flaps, applying suflicient heat and pressure to said aps to cause the coating material thereon tolenter its gel state and to now into the cracks and crevices between and adjacent said flaps, and allowing said aps to cool in closed position, whereby a continuous film of said material is formed Completely sealing said flaps and holding the same in closed position.

16. The method of sealing at least one end of a paperboard container having a plurality of flaps on the side walls thereof adapted to be overlapped to close said end which comprises coating at least the interior surfaces of said container and all surfaces of said aps with a lm of a thermoplastic coating material which is solid and pliable at normal temperatures and adheres to but does not materially impregnate said paperboard when above its flow point, closingV said aps, and applying sufcient heat to the closed flaps to cause said material to oW and to form a continuous lm completely sealing said flaps and holding the same in closed position.

FRANQIS W. LANIGAN. THOMAS F. CASS. JR.

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