US2392695A - Method and apparatus for heat sealing - Google Patents

Description

Jan. 8, 1946. H. A. ROHDIN 2,392,595

METHOD AND APPARATUS FOR HEAT SEALING Filed May 29, 1945 3 Sheets-Sheet 1 PX 776 kl?! 20 HO warzlflfiakdiw;

Jan. 8, 1946.

H A. ROHDIN METHOD AND APPARATUS FOR HEAT SEALING Filed May 29, 1945 5 Sheets-Sheet 2 M WW H nw m mw WM HMW 6 .v -i' Howanlflllohd Jan. 8, 1946. H. A. ROHDIN METHOD AND APPARATUS FOR HEAT SEALING Filed May 29, 1943 5 Sheets-Sheet 3 nill Ill! Illillillarlllllllfl lYowanL/lliohdin,

Patented 8, 1946 UNITED METHOD AND APPARATUS FOR HEAT SEALING Howard A. Rohdln, Glen Ridge, is. J. Application May 29, 1943', Serial No. 489,095

8 Claims.

The primary object of my invention is to provide an improved method of heat sealing, together with basic apparatus for carrying out the method, both method and apparatus being basically applicable to the manufacture of any type bag or container or to the closing of any type bag or container after the same is filled.

A further object of my invention is to provide an improved method and apparatus for heat sealing, particularly applicable to the sealing of homogeneous films such, for example, as poly-.

vinyl alcohol, rubber hydrochloride, or polyvinyl chloride.

A further object of my invention applicable, however, only to certain types of films, is to provide a process which, while producing perfect heat seals, will also provide protection for the finished seal.

These and other objects of myinvention will be made clear from the following detailed description taken in connection with the annexed drawings in which:

Figure 1 is a schematic illustration of one form of apparatus for carrying out my process in connection with step by step feeding;

Fig. 2 is a section on the line 2-2 of Fig. 1;

Fig. 3 is a partial schematic view illustrating the adaptation of the method performed by the apparatus of Figs. 1 and 2 to a continuous instead of a step by step feed.

Fig. 4 is a schematic view illustrating a specialized application of my process in which protection of the seal is provided;

Fig. 5 is a section on the line 55 of Fig. 4;;

Fig. 6 is an elevation view showing a modification of the process illustrated in Figs. 4 and Fig. '7 is a section on the line 'l--'l of Fig. 6;

Fig. 8 is a schematic illustration of the application of my process to the step by step formatiOn of tubes on a modification of the conventional tuber;

Fig. 8a illustrates a modification of the apparatus shown in Fig. 8, this being adapted to continuous operation;

Fig. 9 is a section on the line 99 of Fig. 8;

Fig. 10 is a specialized form of apparatus applying my method to the production of bags sealed on three sides;

Fig. 11 is a partial plan view of the portions of Fig. 10 lying between the lines I ll l; and

Fig. 12 is an illustration of a further possible application of my process.

Heat sealing is usually accomplished by subjecting the sheets to be sealed to the simultaneous action of heat and pressure, that is, by pressing the sheets to be sealed between heated members. In such operations the pressure not only contributes to the sealing efiect but also accelerates the transmission of heat from the heated pressure members to the sealable material. Heat sealing considered without regard to the perfection of the seal has a considerable utility in that there is no necessity for waiting after the sealing step for the solvent of a wet adhesive to dry and take a permanent set. However, the materials involved in most heat sealing packages are usually so expensive that in practice heat sealing is resorted to only where an extreme perfection of seal is essential, as in vacuum packaging or in the packaging of greasy solids or liquids.

In recent years there has been an increasing use of synthetic homogeneous films in packaging operations. These films such, for example, as rubber hydrochloride, sold under the trade name of Pliofilm, or polyvinyl chloride, sold under the trade name of Koroseal, are produced in great variety and with numerous specialized properties of imperviousness. All such films are used in forming a heat seal by being brought above a critical temperature (critical for each particular material) at which point, under the effect of pressure, adjacent surfaces merge or coalesce into an integral, homogeneous structure. Only a few such films, under heat and pressure alone, will permanently adhere themselves to materials radically difierent from the films themselves, such as metal, cloth, leather, felt or paper. These films will, however, at or above their particular temperatures of plasticity temporarily adhere to such foreign substances.

In order to apply heat and pressure, heated surfaces must approach each other sufficiently to exert a substantial pressure upon sealable material placed therebetween and inevitably such surfaces must thereafter recede from each other to release the sealable material. This is true whether the heated surfaces be reciprocating members, such as sealing jaws, or cylindrical members, such as heated pressure rolls or the intermediate structure comprising opposed tractor type treads. Since the pressure members are heated, their separation must, as a practical matter, take place while the sealable material is still at an elevated tempert-ure, in fact, at the maximum temperature attained in the particular sealing step. Under such conditions most homogeneous films will have a tacky or sticky quality .or even certain synthetic materials.

or strips of material which under no circumstances will cling to the heated pressure surfaces, I am able to avoid entirely the above described effect. Usually the interposed protective members will have surface characteristics such that not only will such members fail to adhere to the heated pressure surfaces, but they will also fail permanently to adhere to the sheets to be sealed. For some p ses. which will be described hereinafter, permanent adhesion between the protective members and the sheets to be sealed is desirable, but under no circumstances should the protective members have any afllnit for the heated surfaces.

Referring now to Figs. 1 and 2, I show a pair of heated pressure laws Ill. The heating may be accomplished by means of electric coils l2 or by any other suitable means. The jaws H) are moved toward and from each other by a toggle mechanism ll, although any other mechanism for producing the same or an equivalent motion will be equally satisfactory. Between the jaws l run belts l4 and I6. These belts may be formed of any material suitable relative to the particular sheets to be sealed; that is: the belts may be formed of cloth, felt, leather, paper, woven wire, The belts travel in the direction of the arrow A in a step by step movement synchronized with the movement of the jaws III. by any conventional means; that is: the belts I4 and I6 advance in the direction of the arrow A, while the jaws III are separated and the jaws I ll come together to exert pressure during a dwell or pause in the movement of the belts II and I6. Bags l8 have their walls 20 at their open mouths collapsed into a single plane and the collapsed walls 26 are fed between belts II and It. In handling filled packages it will usually be convenient to have the bags travel in a vertical position, in which case the weight of the contents may be supported by a belt 22. If the bags are empty and it is merely desired to form a side or bottom scam, the bags may travel in the horizontal plane, in which case conveyor belt 22 may be eliminated.

The belts I4 and I6 carry the bags Hi to bring the mouths 20 through between the jaws Ill. During a pause in the advance of the belts the jaws l0, actuated by the toggle or other suitable means I I, come together with substantial pressure. The heat of the jaws HI is transmitted through the belts II and I6 to raise the temperature of the walls 20 of the bags l8 and when a suflicient temperature is attained the walls '20 coalesce to form a perfect seal. With any belts other than flat metallic ribbons, that is, belts formed of cloth, leather, felt or woven wire, etc., there is suflicient pliability in the cross section of the belts themselves to eliminate any localization of pressure due to ordinary differences of caliper in the walls 26, and this is an important factor in decreasing the opportunities for the formation of imperfect seals.

Because there is a possibility that the material of the walls 20, under the effect of heat and pressure, may adhere temporarily to the belts or members II and IS, the path of the belts l4 and I6 is maintained in a straight line beyond the jaws w for a suflicient distance to permit the walls 20 to coolbelow the temperature of plasticity. By the term temperature of plasticity" I mean to include any temperature at which the material to be sealed is sufllciently plastic, tacky or adherent to form any appreciable bond between the mateor members I and I6. After the walls Ill have cooled below the temperature of plasticity, the bags Iii may readily be removed from the belts l4 and I6, either by separation of the belts per- 6 mitting the bags [8 to drop or by the use of pickers or strippers, should there be sufficientresidual adhesion oi the walls 20 to the belts l4 and I6 to warrant the use of such means. A slight strain at such a temperature has no efiect upon the er- 19 fection of the seal which is designed and dimensioned to withstand, when cool, a far greater strain than is occasioned by detachment from the belts l4 and I6. The coalescence of the meetin faces of the walls 20 will be complete because of the cooling action. The belts themselves are in substantially non-pressure contact with the bass throughout their travel. Sealing pressure is applied wholly by the laws. 1

In Fig. 3, I show belts 30 and 32 and a collapsed bag mouth 34 between the belts, all passing between heated pressure rollers 36. The surfaces of the rollers 36 separate immediately following the application of pressure at the nip of the rollers 36. The belts 30 and 32 continue in a straight line, after, passing through the nip of rollers 36,

for a suflicient distance to permit cooling the bag mouth 34 below the temperature of plasticity. As any substantial speed is attained it is obvious that there will be very little time in which the rollers 36 may act to raise the temperature of the bag the most advantageous arrangement is where the protective strips, under the action of the same heat and pressure which effects the chief seal, will laminate themselves to the material of the bag mouth, and it is such a condition that I illustrate in Figs. 4 and 5. It is entirely possible, however, to apply either to the bag'mouths or to the reinforcing strips, or both, a fluid adhesive which will insure lamination of the protective strips tothe bag mouth. In most cases, paper will be most satisfactory material for the protective strips.

In Figs. 4 and 5, I indicate pressure jaws Ill, electrically heated by coils l2, and I also indicate a reel 44 supplying a protective strip 46 and a reel 48 supplying a protective strip 50. Bags are fed between strips 46 and 50 and pass between the members 40, which apply heat and pressure as hereinbefore described with respect to laws III of Figs. 1 and 2. The strips 46 and 50 are thus permanently adhered to the bag mouths and form a chain of scaled bags. This chain is drawn forward by draw rolls 52 for a su-flicient distance from the jaws 40 to permit the requisite cooling to take place. Immediately afterthe draw rolls 52 is a cutter 54 which severs the strips 46 and ill between bags. The apparatus illustrated in Figs. 4 and 5, like that shown in Figs. 1 and 2, will operate with the bags in a vertical plane when p closing filled packages and will usually operate with the bags in the horizontal plane when forming seams during the manufacture of the bags.

In Figs. 6 and '7, I illustrate a modification of the form of Figs. 4 and 5. In this case a reel 60 rial to be sealed and the material of the belts supplies a strip 62 which passes through a folder aaeaoos 84 which bends the strip 82 into a U-shaped cross section. Bags 88 are supported on a belt 88 and are placed with their mouths 10 inside the U-shaped cross section of folded strips 62. The strip 62, containing the bag mouth 10, then passes between a pair of heated rollers 12. Obviously pressure jaws or a pressure tractor could be substituted for the heated rollers. The result is a chain of bags joined by the folded strips 62. The chain is fed by draw rollers 14, and cutters 16 operate to sever the strip 62 between bags. The draw rollers 14 are synchronized with the belt 68 and the cutters 16 by any conventional means. There must, however, be sufilcient travel between the heated pressure rolls 12 and the draw rolls 14 to permit the requisite cooling to take place.

In Fig. 8, I illustrate the application of my process to the formation of side or center seams on aconventional tuber. A web of thermoplastic material 80 is drawn from a reel 82 and passed over a roller 84, thence over a tuber 86, where its margins are brought into overlapping relationship to form a tube. Ordinarily in the formation of such a tube it is brought into flattened condition as rapidly as possible. In the application of my process, however, I form the tuber 86 in such manner as to maintain. for an appreciable distance, the maximum cross sectional area of the tube. Within the tuber 88 I place a standard 88 which supports a pressure member 90 heated by coils 92. Above the tuber 86 I provide a reciprocating pressure member 94 heated by coils 96. A belt 98 passes under the pressure member 94 between it and the overlapped margins I of the web 80, while a belt I02 passes above the pressure member 90 and below the overlapped margins I00. The web 80 in this form advances step by step 1 and during each pause in the forward movement the upper pressure member 94 is brought down to compress and heat the margin I00 of the web 80 between the belts 98 and I02. As mentioned before, there must be a suflicient undisturbed travel of the belts 98 and I02 following the action of the pressure members 90 and 94 to permit the requisite cooling to take place, and the forward steps of the Web 80 will usually be calculated with reference to the length of the pressure members 90 and 94 to assure the formation of a continuous seam. Following the formation of the seam and its discharge from the belts 98 and I02, the tube is brought into conventional flattened condition, at which time consecutive bag lengths are severed therefrom and one end of each length may be closed by any of the methods heretofore discussed.

Obviously, either or both of the belts 98 and I02 may be eliminated in favor of strips such as 46 and 50 of Fig. 4, where reinforcement is desired and the nature of the material makes the substitution possible. This also applies in the case of Fig. 8a hereinafter described.

In Fig. 8a, I illustrate a modification of Fig. 8 in which a web IIO passes over a tuber I I2 in which is arranged a heated pressure roller H4 and its associated belt I I8, while above the tuber is a heated pressure roller H8 and a belt I20. Such an arrangement offers the opportunity for continuous travel of the web IIO as distinct from the step by step movement of the web 80 of Fig. 8.

In Figs. 10 and 11, I illustrate a further application of my invention to the manufacture of flat bags of the type which are produced by forming seams along three consecutive edges. In this application a web of thermoplastic material I80 is drawn from a reel I82 and superimposed upon a web I84 of similar material drawn from a reel I88.

The superimposed webs I80 and I84 then pass between a pair of belts I88 which completely overlie the superimposed webs. The belts I88 and the nip of the rollers I52 they pass between rotary cutters I64 which sever the webs I80 and I34 midway of the sealed areas I46, I48 and I50 to form individual bags I56. The travel between heated pressure rollers I and draw rollers I52 must be suflicient to permit the requisite cooling. Obviously, this particular method is adaptable to step byv step travel of the webs I30 and I34, in which case flat bed pressure members would be utilized instead of rollers I40. It-is clear that for the belts I88 there could be substituted an equivalent pair of continuous webs in the manner illustrated in Fig. 4, wherever the nature of the material admits. If this be done, not only the .seam but the entire package is protected by the lamination of the protective webs to the heat sealable material.

In Fig. 12, I illustrate the adaptation of my invention to a form of sealing which has been successful heretofore but which has required the use of a paper outer ply laminated to contacting inner plies of thermoplastic material. In Fig. 12, I show member I 60 heated by coils I62 and having a groove I84 in its active face. Opposed to I the member I60 is a member I68 heated by coils I10 and having on its active face a rib I12 in alignment with the groove I 84,of the member I60. Bags I14, formed of thermoplastic material and having collapsed mouths I16, are passed between a belt I18 adjacent to member I60 and a belt I80 adjacent the member I88. The clearance between members I60 and I68 is such that the rib I12 will flex and. bend the belts I18 and I80and the bag mouths I16 into the groove I64 of the member I60. This fiexure assures sealing contact between the inner surfaces of the bag mouths I16, and for materials having a low temperature of plasticity, the pressure occasioned by the flexing is sufiicient to effect aseal. Such materials, however, have a pronounced tendency toward tackiness and would be distorted and the eflicacy of the seal destroyed were it not for the protection afforded by the belts I18 and I80. The belts should remain, naturally, in undisturbed contact with the bag mouth I16 for a sufiicient period following the action of members I80 and I68 to permit the requisite cooling. This is done by prolongations of members I60 and I68, such prolongations being thermally separated from said heated members. For filled bags a supporting or carrying belt I82 should be provided, in which case the bags will travel in the vertical. Naturally, for empty bags the travel may be in the horizontal, in which case the carrier belt may possible to dispense with one of the'proteetivebelts or members.

In the subjoined claims I refer to the sealing of sheets of material." These may be simplysheets which it is desired-to laminate or they may be the ously withdrawing both the heat and pressure from said members while maintaining said members in undisturbed substantially non-pressure contact with said sheets until cooled below the temperature of plasticity, and thereupon separating said members to release said sheet, said members having the property, relative to the source of said heat and pressure and relative to said sheets. of not sticking either to said source or said sheets.

2. A method of heat sealing comprising: superimposing a plurality of sheets to be sealed, applying to the external surfaces of said sheets a pair of members; advancing said sheets and said members to a predetermined location and there applying heat and pressure to said members with said sheets therebetween simultaneously withdrawing both the heat and pressure from said members, and advancing said members and said sheets in substantially non-pressure contact beyond said sealing point until said sheets have cooled below the temperature of plasticity, and thereupon separating said members to release said sheet, said members having the property, relative to the source of said heat and pressure and relative to said sheets of not sticking to said source or to said sheets.

3. A method of heat sealing which comprises: superimposing a plurality of sheets to be sealed; applying to the external surfaces of said sheets a pair of members; bringing together a pair of heated surfaces with said members and said sheets therebetween to exert a sealing pressure thereon; thereafter separating said heated surfaces; and maintaining said members in undis- 4 turbed substantially non-pressure contact with said sheets during the separation of said surfaces and until said sheets have cooled below the temperature of plasticity, and thereupon separating said members to release said sheet, said members having the property, relative to said heated surfaces and relative to said sheets of not sticking to said surfaces or said sheets.

4. A, method ofheat sealing comprising: superimposing a. plurality of sheets tobe sealed; applying to the external surfaces of said sheets a pair of members; advancing said sheets and said members between a pair of heated surfaces; bringing said heated surfaces toward each other with said sheets and members therebetween to exert a sealing pressure thereon; thereafter separating said heated surfaces; maintaining said members in undisturbed substantially non-pressure contact with said sheets during the separation of said heated members and until said sheets have cooled below the temperature of plasticity and advancing said members and said sheets beyond the meeting point of said heated surfaces, and separating said members after said sheets have thus cooled to release said sheets, said members having the property relative to said heated surfaces and relative to said sheets of not sticking to said surfaces or said sheets.

5. A method of heat sealing which comprises: superimposing a plurality of sheets to be sealed; covering each external surface of the superimposed sheets with a protective ply; applying heat and pressure to said protective ply andsaid sheets; and simultaneously withdrawing both the heat and pressure from said ply while maintaining said ply in undisturbed substantially non-pressure contact with said sheets until cooled below the temperature of plasticity and thereupon separating said plies from said sheets to release said sheets, said ply having'the property, relative to the source of said heat and pressure and relative to said sheets, of not sticking to said source or said sheets.

6. A method of heat sealing comprising: superimposing a plurality of sheets to be sealed, covering each external surface of the superimposed sheets with a protective ply; advancing said sheets and said ply to a predetermined location and there applying heat and pressure to said ply and said sheets, simultaneously withdrawing both the heat and pressure and advancing said ply and said sheets in substantially non-pressure contact be- ,yond said sealing point until said sheets have cooled below the temperature of plasticity and thereupon separating said plies from said sheets to release said sheets, said ply having the quality relative to the source of said heat .and pressure and relative to said sheets of not sticking to said source or to said sheets.

7. Apparatus for heat sealing comprising: a pair of opposed, flexible members, means for advancing said members with superimposed heat sealable plies therebetween; means for applying heat and pressure to said heat sealable plies through said members, such means being located along the path of advance of said members, means operable after the operation of said heat and pressure applying means for separating said members from said heat sealable plies and the action of said member separating means being deferred until said heat sealable plies have cooled below their temperature of plasticity, said members having the property, relative to said plies and to said heat and pressure applying means of not sticking either to said plies or to said heat and pressure applying means. e

8. A method of heat sealing comprising: superimposing sheetshaving both surfaces of each sheet heat sealable; advancing said superimposed sheets between a pair of protective members; advancing said 4 members concurrently with said sheets; applying heat and pressure to said members and thereby to said sheets to seal said sheets together during said advance; terminating the application of heat while continuing said advance and maintaining said members in undisturbed contact with said sheets during such advance until said sheets have cooled below sealing temperature and thereafter separating said members to release said sheets.

HOWARD A. ROHDIN.

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