US2376256A - Packaging method - Google Patents

Description

May 15, 1945. K. R. KARLsoN PACKAGING METHODS Filed May 26, 1941 2 Sheets-Sheet 1 ser/76 grama/WISO@ KarlR'.KrZson/,

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May 15, 1945. l K. R. KARLSON PACKAGING METHODS Filed May 26, 1941 2 Sheets-Sheet 2 Karlllarlson,

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Patented May 15, 194s PACKAGING METHOD kan' n. Karimi, Montclair, NJ., miglior to Union Bag Paper` Corporation, New York, N. Y., a corporation of New Jersey Application May 26, 1941, Serial No. 395,306

Claims.

It is the primary object of my invention to provide a flexible-wall bag formed of a single ply of material and so designed thatvit may be made on ordinary bag making machinery and without any mechanical alteration of its design.

This primary object andother collateral objects will appear and be clarified not only from the detailed specification which appears hereinafter, but from the following consideration of the general problems which mustbe met.

Many efforts have been made to adapt flexible containers' to the packaging of liquids and to.

the packaging of solids such as ground coffee, either in an inert gas or under vacuum. If a flexible container is either to hold a liquid or to maintain a vacuum over a commercially practical period of time, it must be impervious to a degree which goes infinitely beyond any of the ordinary requirements of sift-proofness. For some time there has been available flexible material which, in itself, possesses the requisite degree of imperviousness. The major difficulty has arisen in connection with the use of such material in the actual formation of containers. Such containers have'bee'n formed and have been successful, but these have all required considerable modification of conventional bag design with consequent modification and specialization of the machinery and processes for making the bags.

If the bag material be a homogeneous film of a non-fibrous material such as the rubber hydrochloride sold under the trade-name P1iofilm, many problems are avoided, but rubber hydrochloride having a very low elastic limit is difficult to handle in bag machines and, in addition, is costly in itself. If the web be formed on a paper base so as to raise the resistance of the web to deformation and reduce the amount of the expensive ingredient to that minimum which is necessary for imperviousness only, the fibrous nature of the paper introduces complications. 1f the thin cross-sectional edge of a web of paper be exposed to a liquid or grease, even though the faces of the sheet are confined between two impervious coatings, the material, by capillary action, will penetrate the paper between the coatings and will discolor the package, rendering it unsalable. If such an edge be exposed to the interior of the package and the package be evacuated, the fibrous paper will provide a porous channel which, however slowly, will nevertheless permit the ingress of air, thus destroying the vacuum far sooner than would otherwise be the case.

In my copending application Serial No. 395,- 305, filed of even date herewith, I have disclosed a combined coating and slittingprocess which produces a web suitable for use in the process and articles claimed herein, which. process and articles are not, however, -herein restricted to the use of webs produced in accordance with said application.

Previous eorts to avoid exposure of a raw edge of paper to the interior of a package having the degree of imperviousness here contemplated, have been directed to avoiding the physical positioning of such an edge inside of the package, but these efforts all have resulted in a very considerable modification of standard bag construction and the resulting packages cannot be made on standard bag equipment. It is particularly to be noted that in all previous efforts it has been impossible to produce bags having preformed bottoms, that is of the types known in the trade as automatic bags or Satchel bottom" bags. Only a part of the difliculty of producing impervious bags with preformed bottoms is due to exposure of a cross-sectional edge of fibrous paper. The major difliculty of this phase of the problem arises from the nature of the preformed bottom construction. Such constructions involve an overlapping and a juxtaposition of the flaps formingthe bottom, and these iiaps must be movable relative to the adjacent portions of the bag body. The relationship is such that, when the liaps are in position to be sealed, heat-sealing may not be resorted to without a resultant sealing together of portions of the bags interior. This would render the bag unusable. On'the other hand, to secure the desired degree of imperviousness requires heat-sealing in which the combination of heat and pressure causes a flowing or movement of the thermoplastic material into such perfect conformity with the parts to be secured that a complete seal results. It is, accordingly, a further object of thisinvention to provide a bag construction and method of packaging which will permit the adaptation of substantially standard preformed-bottom type bags to impervious packaging. v

In another copending application, Serial No. 395,308, filed of even date herewith, I disclose a bag and a method of making the same. The bag disclosed therein may be used according to the process disclosed herein, and the method may be used to make the bags disclosed herein.

In still another copending application, Serial No. 395,307, filed of even date herewith, I disclose an apparatus capable of carrying out the method disclosed herein, and which may be used either, to lseal the bags disclosed herein or the tailed description taken in connection with the annexed drawings in which- Fig. 1 is a section of a coated sheet of paper working limits.

prepared in accordance with my aforesaid copending application.`

Fig. 2 is a similar section showing the additional coating material on a margin of the otherwise uncoated reverse side of the web;

Fig. 3 is a sectional view illustrating the web shown in Fig. 2as formed into a gusseted bag;

Fig. 4 is a section showing the web of Fig. 2 as applied to a non-gusseted bag;

Fig. 5 is a perspective view showing the ap pearance of a ilnished Satchel bottom;

Fig. 6 is a view showing the bottom opened preparatory to iinal folding and sealing;

Fig. 7 is a perspective view ofthe closed bottom of an automatic bag;

Fig. 8 is a view of the ybag bottom of Fig. 7 opened up preparatory to the nal folding step;

Figs. 9 and 9a illustrate two types o1' closures which are formed on so-called flat bags;

Fig. 10 shows a top closure on a gusseted .bag of either the square or automatic type; and

Fig. 11 is a schematic representation of apparatus for carrying out my packaging process.

The art of heat sealing adhesives is too newly operation are time, temperature and pressure.

These are so related that in proper multiple they tend to assume a constant relation. This relationship, as a multiple has not been determined, that is, we know only that f (time, temperature, pressure) K. If any one of the three variables, time, temperature and pressure, be maintained constant, an approximate parametric relationship of the other two may be established. Thus, if T=time, F=temperature, and P=pressure, the approximate relationship under constant temperature is PT==K. At constant time, PF=K, and at constant pressure TF=K, in which K, K and K" are constants. Naturally, for any given heat-sealing compound, the constants vary and each of the quantities-time, temperature and pressureis subject to abrupt The general relationships are, however, as above indicated.

To carry out my method of sealinga bag of the preformed bottom type, it is desirable that the temperature should be high enough to liquefy the particular thermoplastic material used, but not so high as to sear or impair the paper. The pressure applied should be sufiicient at least to cause a flow of the molten or highly plastic ma.. terial into exact conformity with the parts to be secured. In an absolute sense, this pressure is limited by the bursting strength of the bag, since it is applied to a bag with pulverant material which, under a vertical compressive load, will act approximately in the manner of a fluid to develop a bursting stress similar to the eilect of hydrostatic pressure. Good practice would require that the pressure actually applied should be sumciently far below the bursting strength of the average bag to assure that no bag will be ruptured. In practice, a supporting member should be supplied which will afford lateral support for all of the vertical walls ofthe bag. This will minimize the bursting tendency and will permit the application of higher pressures.

I provide a web I0 to one side of which is applied a coating I2 of thermoplastic material. It is essential that the thermoplastic material permitted to overi'low the edges I4 of the web l0 as indicated at I8 in Fig. 1.

Either during the coating of the web I0 or as a printing step in the course of manufacture of the bags, Lone margin I8 of the reverse or uncoated side of the web I0 must receive a strip 20 of thermoplastic material which should merge and become an integral part of portion I6 of thermoplastic material overlying the edge i4 of the paper. Regardless of the type of tube, that is whether gusseted or non-gusseted, the coating I2 should Ibe on the interior, and the margin I8 of. the uncoated side of the web I0 should .be overlapped by the opposite edge 22 of the web I0 so as to bring the margingal coating 20 into contact with the coating I2 to permit the formation of a longitudinal heat seal, the result being that the interior of the bag presents an integral, unbroken surface of imperviousy material to the contents of the bag.

When a bag length is cut from a tube of the type shown in either Fig. 3 or 4, there are several optional closures which may be applied to convert the tube into a bag. The simplest of these bottoms is accomplished by merely squeezing or pinching the walls of the tube together under heat and pressure so as to fuse the thermoplastic surfaces of the interior of the bag into an integral mass, and after filling the mouth of the bag may be closed in a precisely similar manner.

The eect of such closures and the appearance o! the iilled bag is illustrated, as to a non-gusseted or at bag, in Fig. 9 and, as to a gusseted or square bag, in Fig. 10. The treatment of the longitudinal seam heretofore discussed is advantageous no matter what combination of top and bottom closures may be resorted to.

Where, however, a preformed bottom is to be applied, the problem is complicated. The preformed type of bottom is essentially the same whether the bag is gusseted or not. To form the bottom, the front and rear walls of the tube are slit and one of the walls is pulled back against the body of the bag. The result is as shown in Figs. 6and 8 in which the front wall 25 has been slit to form a tab 30 and the rear wall 21 has :been slit to form a tab `4l). The tab 40 remains in the plane of the rear wall 2l while the tab t@ has been pulled back against the front wall 25. Flaps 38 are, by this pulling operation, folded inwardly from each side of the bag and ultimately come substantially into the plane of the nap 36. Depending on the proportions selected, the edges of these flaps 38 may be substantially separated or may, if desired, be brought into overlapping condition. For the purpose of this invention, the flaps 38 should be at least in abutting relationship and preferably should overlap each other.

From the condition shown in Figs. 6 and 8, the Ibottom is completed by iirst folding the tab Bil along the. line :c-x and then by folding the tab 40 along the line y-y to Ibring the tab 4D in a position to overlie the tab 30.

It will be clear from a consideration of Figs. 5-8 inclusive that, if the interior surface of the paper is coated with thermoplastic, it will be impossible to apply heat and pressure to the bag bottoms while they are in the flattened condition shown in Figs. 5 and 7. To do so would result in sealing what must ultimately be a portion of the vertical wall to the necessarily horizontal bottom of the bag. I have solved this problem by applying to the spread out bag bottom, in the condition shown in Figs. 6 and 8, an area of adhesive E which is so located and pro-v portioned that upon folding of the flap 80 along the line :c-:c the flap `8|), and particularly the relatively open corners 3|, will be deposited in the still fluid body of adhesive 88 and upon folding of the flap 40 along the line y-y the portion of the adhesive area 60 which is lying on the flap tic material in a suitable solution. The solution' will have evaporated shortly after the manufacture of the bags and the adhesive at the time the bags are filled will be in perfectly solid condition.

The bags are opened and filled and are then pressed down on a heated surface. The combination of heat and pressure serves to liquefy, or at any rate to render highly plastic, the adhesive previously applied over the area 60 and enables it to flow into perfect conformity withthe parts to be secured, thus forming a far better seal than would otherwise possibly be the case.

In Fig. 11 Ishow a bag 80 resting on a plate 82. The bag is supported laterally by a frame 4 84 which completely surrounds the bag and sup ports it against bursting' stresses occasioned by the semi-hydrostatic effect of the pulverant material usually contained in the bag. A coil 86 serves to heat the plate 82 and a pressure member 88 serves to thrust the bag 80 against the plate 82.

Referring once again to Figs. 6 and 8, I wish to direct attention to the perforations 10 which are formed in the flaps 38 adjacent the intersection of these flaps with the flap 40. These intersection points are the most difl'lcult to seal of any portions of the bag bottom. These perforations permit the a'dhesive in the area 60 to flow, when it is applied in liquid condition, in between the flaps 38 and the flap 40. Under ordinary circumstances, capillary attraction will tend to draw any adhesive coating through the perforations toward the intersection points previously mentioned. It is clear that the area 60 cannot extend to the extreme margins of the flap 40 since, if this were done, then upon folding and pressing of the flap 40 the adhesive would be extruded to the exterior of the bag and when the bags were stacked. as in the drier, this could result in sealing one bag to another with consequent waste.

While I am aware that perforations have heretofore been used in generally similar locations in the bag bottom, I am not aware that they have ever been so placed as to lead adhesive toward the above-mentioned intersection points. It is "desirable that the perforatlons be placed on'a line bisecting the angle between the fold line 12 of the flaps 88. Such a location takes advantage of the converging passageway formed by the fold line 'I2 and the edge'14 to drawthe adhesive by capillarity toward the intersection point. .y

I have also provided perforations lll in lthe flap 38. These perforations. when the flap," is folded into contact with the wet adhesive on the area Il, permit a flow of the adhesiveto the back face of the flap 8l. When the nap 40, bearing wet adhesive is folded over into contact with the flap III. the adhesive seals through the perforations 10' and forms, when it solidifies, actual keys between the flap 40 and the flaps 38.

Referring now to Fig. 9, a fllledbag |08 of the flat, ungusseted type has one end ||0 closed by mere straight line collapse of the walls which are then heat sealed. This method of sealing produces ears I I0' at each side of the package. The bottom ||2 of the bag has been closed in the same manner, but the n formed by the heat sealing has been turned down against the bag bottom, and the ears ||2' have then been folded upwardly against the sides of the package.

In Fig. 10 I show a filled square or gusseted bag |28 which has been closed by simple collapse of its mouth and by heat sealing to form the nn |22. The fin |22, it will be noted, is of the same width as the `bag |20 so that no ears are formed. v

My invention is perfectly applicable to bags formed of thermoplastic material or from paper coated on both sides with such material. In any case, heat sealing of the bottom may not be accomplished until the bag is opened.

While specific examples and embodiments of my invention have been here disclosed, I do not intend to be limited to these precise structures, but only as set forth in the subjoined claims, which are to be broadly construed.

What is claimed is:

1. A process of packaging which comprises forming a gusseted tube from a sheet of paper coated with impervious theremoplastic material, the coating lying on the inside of the tube, slitting the tube at four spaced points to provide bottom tab portions and bottom flap portions, folding the bottom aps so that they overlap, applying thermoplastic adhesive in solution over a predetermined area of the folded flaps and a bottom tab, folding the bottom tabs in overlapped relation over upon the folded flaps to form a bag bottom, drying the said solution to form a bond, filling the so-formed bag, heating the bag bot-l tom after filling to activate said thermoplastic material and so form a bottom seal for the bag.

2. A process of packaging which comprisesforming'a tube from a sheet of paper coated with a thermoplastic material, the coating lying on the inside of the tube, slitting the tube to provide bottom flaps and bottom tabs, folding the flaps4v inwardly, applying an adhesive in solution over a portion of the folded flaps and a tab, folding the tabs in overlapped relation over upon the folded flapsto form a bag bottom, drying the said solution, filling the so-formed bag, and then heating the bag bottom to activate the thermoplastic material.

3. Process according to claim 2 in which pressure is applied to the filled bag during heating to activate thethermoplastic material.

4. Process according to claim 2 in which pressure is applied'to the filled bag while resting on a ing-the bag bottom to activate the thermoplastic v material.

v KARL R. KARLSON.

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