US3534901A

US3534901A - Bag construction

Info

Publication number: US3534901A
Application number: US782156A
Authority: US
Inventors: John P Repko; Gerard T Burroughs
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co; Rexam Beverage Can Co
Priority date: 1968-12-09
Filing date: 1968-12-09
Publication date: 1970-10-20
Anticipated expiration: 1987-10-20

Description

Q J. P. REPKO ETAL Oct. 20, 1970 I BAG CONSTRUCTION 2 Sheets-Sheet 1 Filed Dec. 9, 1968 INVENTORS, John 1? Rep/(O Gerard T. Burroughs BYE Ill I ATTORNEY Oct. 20, 1970 J. P. REPKO ETAL BAG CONSTRUCTION 2 Sheets-Sheet 2 Filed Dec. 9, 1968 INVENTORS. epko Gerard 7. fiurroug/ns' BY John P. R

United States Patent 3,534,901 BAG CONSTRUCTION John P. Repko and Gerard T. Burroughs, Midland, Mich.,

assignors to The Dow Chemical Company, Midland,

Mich., a corporation of Delaware Filed Dec. 9, 1968, Ser. No. 782,156 Int. Cl. B65d 33/00 US. Cl. 229-66 Claims ABSTRACT OF THE DISCLOSURE An improved bag construction wherein a heat resistant strip composed of material having superior strength at elevated temperatures is fixed to select outer surface portions of the bag, and more specifically, in regions where heat sealing jaws or elements engage the bag to effect closing operations. The use of these strips or tapes if heat resistant material enables the bag to be efiiciently sealed closed employing higher than normal sealing temperatures, thereby adapting the bag to high speed sealing apparatus. The strip is dual functional in that it further serves as a convenient tear opening device for the bag.

DESCRIPTION OF THE INVENTION Conventional materials for forming thermoplastic bags are frequently characterized as being relatively limp, soft materials that distort and weaken rapidly at elevated temperatures. Typical examples if these are the medium and low density polyethylenes. Materials of this character can be troublesome when used in high speed packaging operations. Oftentimes, the material is not able to satisfactorily withstand the higher than normal sealing temperature desired to obtain maximum sealing speeds. For example, the material can become heat plastified to a degree that it assumes a highly weakened, liquid-like condition in the seal region. A burn through or an excessive thinning in the seal region can result.

Futhermore, unless rapidly cooled, the seal remains in its weakened state for a period of time following the removal of the heated sealing elements. Relative movement between the layers in the seal region during this critical period can result in permanent deformation 01' distortion of the seal.

Accordingly, it is an object of the present invention to provide an improved bag construction wherein the bag can be composed primarily if limp, easily heat distortable materials, as for example, a low or medium density polyethylene, but is so constructed as to be satisfactory for use in high speed filling and sealing apparatus wherein higher than normal temperature ranges are employed to effect a rapid and efficient closure of the bag following fill operations.

Another object of the present invention is to provide such a bag construction wherein the means utilized to adapt the bag for usage in high temperature sealing operations is dual functional in that is also effectively serves as a convenient tear opening device for the bag.

Yet another object of the present invention is to provide an advantageous method whereby such bags can be fabricated efiiciently and with a minimum effort and cost.

A still further object of the present invention is to provide an improved web material so constructed as to be readily formed into the advantageous bag constructions of the present invention.

Briefly then, the invention contemplates inproved bag constructions wherein by the use of heat resistant strips or tapes disposed on the outer surface of the bag, the bag is made suitable for use in high speed filling and Patented Oct. 20, 1970 sealing operations. As a typical and specific embodiment of the present invention, there is provided a bag having a fill opening located between opposed lips or free edge portions, and with a strip of heat resistant material covering the outer surface of each lip and being generally coextensive therewith. When heated sealing jaws or elements are pressed together across the bag lips to close the fill opening of the bag, they engage the heat resistant strips. These strips maintain sufficient strength or structural integrity in the heat plastified or seal region to perirnt the use of higher than normal sealing temperatures in forming the closure seal. At least one of the strips extends a distance below the closure seal and is made separably from that portion in and adjacent to the closure seal by employing a line of weakening between the two portions, as for example, a line of perforation. Below the line of weakening is a sealed region joining the separable portion of the strip to the bag wall. Removal of the separable portion operates to rupture the bag at the aforementioned sealed region whereby the strip additionally functions as a convenient tear opening device for the bag.

Yet additional objects and advantages of the present invention, and its numerous and cognate benefits, are even more apparent and manifest in and by the ensuing description and specification taken in conjunction with the accompanying drawing, in which wheresoever possible, like characters of reference designate corresponding material and parts throughout the several views thereof in which:

FIGJ is a schematic and isometric view illustrating an embodiment of the method employed to construct bags according to the principles of the present invention;

FIG. 2 is a front elevational view of a bag constructed according to the method of FIG. 1;

FIG. 3 is a cross-sectional view of the bag taken along reference line 33 of FIG. 2;

FIG. 4 is a view like FIG. 2 only showing the bag construction of the present invention as incorporated into a package; and

FIG. 5 is an isometric view of the package of FIG. 4 and showing the tear opening device provided therefore partially activated.

Referring now more particularly to the drawings and specifically to FIG. 1, there is shown a continuous length of web stock 10 longitudinally folded over upon itself to form upper and

lower panels

12 and 14 respectively, and with the web stock 10 in its prefolded posture, being received between drive rollers 16 and 18. Normally, the prefolding will be along the longitudinally centerline of web 10 whereby the

opposite edge portions

20 and 22 of the web are substantially aligned with each other. Web 10 is characterized as having a heat sealable first or inner surface 24, this surface being so designated in reference to its location following the folding step.

Drive rollers 16 and 18 receive simultaneously with the prefolded web 10, tapes 26 and 28 composed of heat resistant material, and each of which includes

perforations

27 and 29, respectively, extending continously along the mid-region thereof. The tapes are fed to drive rollers 16 and 18 from rotatably mounted

supply reels

30 and 32 located, respectively, above and below the web 10. Specifically, tape 26 is fed downwardly from reel 30 and laid atop the upper panel 12, while tape 28 is fed upwardly from reel 32 and laid on the other side of the prefolded web 10 opposite tape 26, and more specifically, in superposed relationship with the lower panel 14. For reasons that will become more clear hereinafter, tapes 26 and 28 are normaly laterally positioned so as to be in substantially parallel, contiguous relationship with the aligned

edge portions

20 and 22, as is best shown in FIG. 1.

Located downwardly of drive rollers 16 and 18 is a buffer plate 33 which is fitted between

edge portions

20 and 22 of the folded web 10 such that the upper and

lower panels

12 and 14 continuously pass over and under the buffer plate 33. In working relationship with the topside or upper surface of buffer plate 33 is a heated sealing wheel or rotary sealing mechanism 37. The rotary sealing mechanism 37 cooperates with the topside surface 35 of the buffer plate 33 to apply sufficient heat and pressure to weld or bond the tape 36 to the upper panel 12 along a longitudinally extending strip or line 39. The joined region represented by line 39 is strategically positioned between the line of perforations 27 and the innermost edge 43 of tape 26 to form a tear opening device as will be explained in more detail hereinafter. Tape 28 can in a like manner be joined or united together with the lower panel 14 by a similar sealing arrangement (not shown).

At a location downwardly of buffer plate 33 and rotary sealing mechanism 37, there is positioned a pair of oppositely disposed sealing

jaws

34 and 36, at least one of which is heated. Jaws 34 and 36 cooperate together to laterally seal the folded web stock 10 at regularly spaced intervals thereon. Accordingly, as the folded stock 10 is directed past

jaws

34 and 36, it is compartmented into bags 50 of uniform width. The bags 50 can then be separated from each other along the mid-region of each lateral seal by appropriate cutting or other well known techniques (not shown).

An individual bag 50 separated from the folded and laterally sealed web stock 10 is depicted in FIGS. 2 and 3. Structurally bag 50 includes first and

second walls

38 and 40 disposed in generally superposed relationship with each other and corresponding to the upper and

lower panels

12 and 14 of folded web 10.

Walls

38 and 40 are edgewise joined together along the

opposite sides

42 and 44 of bag 10 by

heat seals

46 and 48. The bottom end 52 of bag is closed by a fold 54, as is best shown if FIG. 3. The top end of top edge portion 56 of bag 10 includes a first free edge 58 associated with the first wall 38, and a second free edge 60 associated with the second wall 40. Free edges 58 and 60 define between them a fill opening 62.

A strip of material 64, comprising part of tape 26, is disposed on the outer surface 63 of the first Wall 38 adjacent the first free edge 58, with the strip 64 extending along the first free edge 58 so as to be substantially coextensive with the meters and bonds thereof. A second strip 66, comprising part of tape 28, is similarly arranged on the outer surface 65 of the second wall 40 of bag 10 opposite strip 64.

Strips

64 and 66 comprise a material that is relatively heat resistant in comparison to the

material comprising walls

38 and 40, and particularly that material forming the

outer surfaces

63 and 65 thereof. In other words, the

material comprising strips

64 and 66 maintains sufficient strength or structural integrity in the region the closure seal is formed (to close-fill opening 62) to permit the use of higher than normal sealing temperatures to form the closure seal.

Exemplary of materials that maintain structural integrity at higher temperatures (in excess of 350 F.) are cellulose acetate, polyethylene terephalate, and cellophane (regenerated cellulose). The heat sealing characteristics of still other suitable materials are well cataloged in vari ous scientific journals, periodicals, magazines, handbooks and the like, and the appropriate selection of such materials according to their heat resistant qualities for employment in the practice of the present invention should be well within the powers of those skilled in the art. For

7 example, in the 1968 issue of the Modern Packaging Encyclopedia, heat sealing and other characteristics of quite a large number of plastic films are discussed in some depth in an article entitled, Plastic Films-Types and Uses, pages 149, 152, 154, 156, 158, 162-167, 181-186. Most beneficially the orientation or shrink energy of such materials as are selected from

strips

64 and 66 is below that at which significant puckering in the seal region is caused by shrinkage or retraction of the strip material when it is heated.

In contrast to the above specifically noted heat resistant material, medium density polyethylene, a conventional bag stock material, is usually limited to sealing at temperatures in the range of from only about 260 F. to 310 F.

Walls

38 and 40 of bag 10 can comprise single layered film or sheet, as for example, medium or low density polyethylene or multilayered films, as for example, two polyethylene layers sandwiching an inner or core layer of Saran, polyvinyl chloride, nylon, or a like suitable barrier material, as is frequently employed to lessen the rate of gas transmission through the bag walls. Saran in particular does not conduct heat well, that is, it has a retarding effect on the transfer of heat from the sealing elements to the inner surface of the bag, which surfaces must be heat plastified such that they weld together to form the closure seal. In these circumstances, sealing temperatures in the range of 350 F. to 400 F. would oftentimes be appropriate to obtain a satisfactory sealing rate.

Referring now to FIG. 4, there is shown a package 70 comprising a bag 50 filled and bulged out somewhat by a product (not visible) located therewithin. A closure seal 72 joins together the first and

second walls

38 and 40 across the top end 56 of bag 50 whereby a substantially gas and liquid tight enclosure is formed about the product.

FIGS. 4 and 5 particularly illustrate the aforementioned dual functionality of strip '64 in its capacity as a convenient tear opening device for package 70, it being understood that strip 66 can be made to function in a like manner, if desired, such that package 70 is openable from either face.

Toward the end of obtaining a tear opening device, the strip 64 is made of a sufficient width such that its lower edge 43 extends a distance below the lower edge 74 of the closure seal 72. Between

edges

43 and 74 there is located the line of perforations 27 which divides the strip 64 into an upper or first portion 76 and a lower or second portion 78. The upper portion 76 is disposed primarily in the region of closure seal 72, while the lower portion 78 is positioned adjacent the inward side 82 of the upper portion 76. Intermediate of the line of perforations 27 and the lower edge 43 of strip 64, is the sealed region represented by line 39, joining the lower portion 78 of strip 64 to the first wall 38 of bag 50. Along line 39, the first wall 38 is normally thinned, and weakened somewhat, as best illustrated in FIG. 3, by the heat and pressure applied to form the sealed region thereat such that wall 38 exhibits a preference for rupturing or tearing along line 39.

A tab or grasping means for activating the opening device comprises the lowermost part 80 of the lower portion 78 as defined between the lower edge 43 of strip 64 and the sealed region at line 39. In other words, at part 80, the lower portion 78 of strip 64 is free of the first wall 38. Accordingly, opening of package 70 can be obtained by grasping the lower portion 78 at part 80 and separating the lower portion 78 from the upper portion 76 along the line of perforations 27. This separation of portions 76 and 78 is accompanied by a tearing opening of the package 70 along the sealed region at line 39, as is best shown in FIG. 5.

In order for the tear opening device to function properly, the adherence of the lower portion 78 of strip 64 to the first Wall 38 must be of a suflicient degree such that a rupturing of the first wall 38 results when the lower portion 78 is torn or separated from the package. Oftentimes heat resistant material of the type contemplated for

strips

64 and 66 does not heat seal well to conventional bag materials such as the low or medium density polyethylenes. For example, the seal strength obtainable, if any is obtained at all, would frequently be insuflicient to cause a rupturing of wall 38 when the tear opening device is activated. Accordingly, the present invention contemplates the usage of suitable adhesives or glue layers, solvents, primers and the like in instances where necessary to obtain the indicated seal strength between the strip 64 and first wall 38 along line 39.

As a specific but not limiting example, the invention comprises in combination: a bag 50 formed of a multilayered film comprising low density polyethylene, thickness 0.65 mils/a copolymer of 72 weight percent ethylene, 28 weight percent vinyl acetate, thickness :10 mils/ a vinylidene copolymer (Saran), thickness 0.50 mils/ a copolymer of 72 weight percent ethylene, 28 weight percent vinyl acetate, thickness 0.10 mils/a low density polyethylene thickness 0.65 mils; strips 64 and 66 including a 1.5 mil layer of low density polyethylene as the glue

layer joining strips

64 and 66 of a polyethylene terephthalate to the walls of bag 50. The polyethylene terephalate part of

strips

64 and 66 is at a thickness in the range of from about 0.5 mils to about 2.0 mils. To obtain a tight bond between the polyethylene terephalate and polyethylene layers of

strips

64 and 66, respectively, it is customary to first treat the polyethylene terephalate with a suitable primer coat, as for example, a polyethyleneimine, and then extrusion coat the polyethylene over the primer layer.

For a more detailed description of the multi-layered bag 50 material as set out in the above example wherein a basic layer arrangement of polyethylene/ethylene-vinyl acetate copolymer/Saran/ethylene-vinyl. acetate copolymer/polyethylene is employed, reference can he had to Belgian Pat. No. 683,208 or French Pat. No. 1,484,153.

While certain representaitve embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention.

Accordingly, what is claimed as new is:

1. A bag of the type having first and second walls located opposite each other, a fill opening defined along an edge portion of the bag, the edge portion including a first free edge associated with the first wall and a second free edge associated with the second wall, the first and second free edges defining therebetween said fill opening, wherein the improvement comprises a strip of material overlying the outer surface of said first wall at a position generally adjacent said first free edge, said strip comprising a first portion which covers at least that area of said first wall where the closure seal will be formed to close said fill opening, said strip further comprising a second portion integral with said first portion, a line of weakness located between said first and second portions whereby said second portion can be separated from said first portion along said line of weakness, a seal joining said second portion to said first wall, said seal being of sufficient strength such that separation of said second portion from said first portion and said bag is accompanied by a rupturing of said first Wall at said seal thereby opening said bag.

2. The bag of claim 1 wherein said first and second walls comprise synthetic resinous thermoplastic material, said strip comprising at least heat resistant material which permits the closure seal for said bag to be formed at a temperature higher than would otherwise be appropriate for the heat sealing of the thermoplastic mterial forming said first and second walls.

3. The bag of claim 2 wherein said heat resistant material of said strip is characterized as being able to main tain sufiicient structural integrity in the closure seal region to permit the use of sealing temperatures of at least 350 F. to form the closure seal.

4. The bag of claim 2 wherein said heat resistant material is characterized as having greater structural integrity than the material comprising the outer surface of said walls at a temperature of 350 F.

5. The bag of claim 2 wherein said second wall ineludes a strip of material located atop the outer surface thereof generally opposite said strip overlying said first wall, said strip overlying said second wall comprising heat resistant material of similar character to the heat resistant material of said strip overlying said first wall.

6. A package including a bag of the type having first and second Walls located opposite each other, a product located within the bag, and a closure seal joining together said first at second walls thereby securing said product within said bag, wherein the improvement comprises a strip overlying the outer surface of said first wall, said strip comprising a first portion located at least in part in said closure seal region, and a second portion integral with said first portion, a line of weakness located between said first and second portions whereby said second portion can be separated from said first portion along said line of weakness, a seal joining said second portion to said first wall, said seal being of sufficient strength such that separation of said second portion from said first portion and said bag is accompanied by a rupturing of said first wall at said seal thereby opening said bag.

7. The package of claim 6 wherein said first and second walls comprise thermoplastic material, said strip com prising heat resistant material which permits said closure seal to be formed at a temperature higher than would have otherwise been appropriate for the heat sealing of the thermoplastic material forming said first and second walls.

8. The package of claim 7 wherein said heat resistant material is characterized as being able to maintain suffieient structural integrity in the closure seal region to permit the use of temperatures in excess of 350 F. to form said closure seal.

9. The package of claim 7 wherein said heat resistant material is characterized as having greater structural integrity than the material comprising the outer surface of said Walls at a temperature of 350 F.

10. The package of claim 7 wherein said second wall includes a strip overlying the outer surface thereof and located at least in the region of said closure seal, said strip overlying said second Wall comprising heat resistant material of similar character to the heat resistant material of the strip overlying said first wall.

References Cited UNITED STATES PATENTS 2,819,010 1/1958 Amiguet 229-62 3,341 108 9/1967 Kirk 22966 DAVID M. BOCKENER, Primary Examiner US. Cl. X.R. 22953; 20646