US3575763A

US3575763A - Method and apparatus for fabricating high impact strength,contoured-bottom bags

Info

Publication number: US3575763A
Application number: US688717A
Authority: US
Inventors: Harold E Ramsey
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1967-12-07
Filing date: 1967-12-07
Publication date: 1971-04-20
Anticipated expiration: 1988-04-20
Also published as: LU57478A1

Abstract

AN IMPROVED METHOD AND APPARATUS FOR FABRICATING HIGH IMPACT STRENGTH, CONTOURED BOTTOM BAGS WHICH COMPRISES ADVANCING A FOLDED HEAT SEALABLE, THERMOPLASTIC WEB, A FIRST SEALING AND SEVERING OPERATION BY A GENERALLY TRIANGULARLY SHAPED KNIFE TO FORM CONTOURED BOTTOM CORNERS, A SECOND SEALING AND SEVERING OPERATION IN A TRANSVERSE DIRECTION TO COMPLETE THE TRANSVERSE SEAMS WHILE MAINTAINING CONTINUITY OF THE SEAMS RESULTING FROM THE TWO SUCCESSIVE OPERATIONS, AND GATHERING THE FABRICATED BAGS.

Description

prfifl EH H. E. RAMEIEY $7,763

METHOD AND APPARATUS FOR FABRICATING HIGH IMPACT STRENGTH, CONTOURED-BOTTOM BAGS Filed Dec. 7, 1967 I 5 Sheets-Sheet 2,

INVENTOR HAROLD E. RAMSEY :Mw BY g ATTORNEY A ril 2U, WW I H. E. RAMSEY 5 9 METHOD AND APPARATUS FOR FABRICATING HIGH IMPACT STRENGTH, GONTOURED-BOTTOM BAGS Filed Dec. 7, 1967 3 Sheets-Sheet 5 INVENTOR HAROLD E. RAMSEY ATTORNEY United States Patent O METHOD AND APPARATUS FOR FABRICATING HIGH IMPACT STRENGTH, 'CONTOURED-BOT- TOM BAGS Harold E. Ramsey, Wilmington, Del., assignor to E. I. du Pont de N emours and Company, Wilmington, Del.

Filed Dec. 7, 1967, Ser. No. 688,717

- Int. Cl. B32b 31/18 US. Cl. 156-251 9 Claims ABSTRACT OF THE DISCLOSURE An improved method and apparatus for fabricating high impact strength, contoured bottom bags which com.- prises advancing a folded heat scalable, thermoplastic Web, a first sealing and severing operation by a generally triangularly shaped knife to form contoured bottom corners, a second sealing and severing operation in a transverse direction to complete the transverse seams while maintaining continuity of the seams resulting from the two successive operations, and gathering the fabricated bags.

BACKGROUND OF THE INVENTION This invention relates to improvements in the fabrication of bags and more particularly it relates to the fabrication of contoured bottom bags.

A commonly used overwrap for large and/or heavy food items such as turkeys and hams is an envelope of heat shrinkable thermoplastic film. Film types such as polyethylene and polyvinyl chloride are commonly used in such packages. The most prevalent procedure for such packaging is to prefabricate an open top bag by transversely sealing and severing a continuous tubular web of the thermoplastic material opening the thus made bag manually or by machine, inserting the food product into the bag until the product is abutting the bottom transverse bag seal, closing the extended open end of the bag by gathering and banding the excess material, and heat shrinking the overwrap. Several disadvantages are attendant with the use of this procedure. The main ones include the difiiculty in opening a prefabricated thermoplastic bag having colinear front and back panel severance lines for forming the bag opening, the weakened bag bottom along the line of the bottom seal, and the protruding corners at the lower end of the filled bags which result in unsightly distortions upon being heat shrunken.

The first cited disadvantages slows the production rate on the food processing line if the bag opeing is performed manually or necessitates the use of packaging equipment to perform the task automatically. The second cited disadvantage oftentimes results in a finished package having a partially split bottom seam thus exposing the food product to the deleterious effects of the ambient air while the third disadvantage decreases the sales appeal of the packaged product.

SUMMARY OF THE INVENTION According to the present invention heat shrinkable, thermoplastic bags are fabricated by the method and apparatus of this invention from J-folded heat shrinkable, thermoplastic web material by advancing the folded web ice in a flattened condition from an unwind position along a predetermined path, a first sealing and severing operation by a generally triangular shaped knife to form contoured bottom corners, a second sealing and severing 5 operation in a transverse direction to complete the transverse seams and gathering the fabricated bags. Since the bottoms of the bag are formed by the film fold in the continuous web, the corners thereof are contoured to eliminate the excess material, and a convenient bag opening means is provided by the extended lip on one wall, bags so fabricated have exceptionally high impact strength on the bottom fold, will shrink into a tightly fitting overwrap on contoured articles and may be readily grouped into wicket bag packs for use with high speed bag opening and filling machines.

The invention will be described in detail by reference to the drawings.

FIG. 1 schematically shows the sequence of operations of the method of this invention.

FIG. 2 is a perspective view of a typical contour sealing apparatus of this invention.

FIG. 3 is a perspective view of a suitable registration control system.

FIG. 4 is a sectional view of a preferred sealing and '25 severing mechanism for forming contoured bottom corners and side welds shown in a non-operating position. FIG. 5 is a sectional view of the sealing and severing mechanism of FIG. 3 in an operating position.

DESCRIPTION OF THE PREFERRED EMBODIMENT The method for fabricating thermoplastic bags in accordance with this invention is illustrated schematically in FIG. 1. The web of heat-scalable thermoplastic 5 film 1 is folded along the edge 2. Such a fold can be either a centerfold or a 1-fold. In the J-fold, edge 3 protrudes beyond edge 4 to permit the fabricated bags to be wicket packed. The folded rfilm 1 is advanced along a predetermined path and notches such as shown at 5 40 and 6 are cut and edge sealed intermittently along the folded edge 2 of the continuous web 1 by a notch severing and sealing means 7. These notches may be of a triangular shape or a generally triangular shaped contour, as shown. The film 1 is continued in its advancement along its predetermined path to a controlled position where the side seals, such as 8 and 9 are completed by the combined sealing and severing means 10. The transverse seal is registered so as to intersect the apexes of each previously formed notch, thereby maintaining continuity of the seams. Thus the transition from the straight transverse seal 8 to the notched section is symmetrical for adjacent bags.

An apparatus suitable for fabricating bags according to the described method is shown in FIG. 2. This apparatus is adaptable to side weld bag making machines of the type having a frame 20, an unwind device 21 for a roll of folded film 212., a conventional ten'sioning means (not shown) for maintaining a degree of tension in the folded film web 23 as it advances through the machine, a transverse sealing and severing means '51 and a bag grouping means 59. In such machines the web is usually pulled through the machine by a pair of

nip rolls

60 and 61. These nip rolls feed the web to the transverse sealing and severing element where individual side-welded bags are severed from the continuous web while the web is intermittently advanced and stopped. Many side weld bag making machines employ a single layer web of film at the unwind position and form this web into a folded web prior to its passage through the tensioning device. The apparatus of this invention operates equally well with such machines as with the described machine.

The improvement of the present invention in the above apparatus is generally shown in FIG. 2 as the mechanism mounted on frame 24 in combination with the transverse sealing and severing device 51. It comprises frame 24, longitudinal adjusting means 25, manual actuation wheel 26, pneumatic cylinder devices 27 and 53, a sealing and severing mechanism partially comprising a heated knife 28 and

web clamping devices

29 and 30, waste notch receptacle 31, air blow system 32, and transverse adjusting means 33, 34 and 35 The pneumatically operated air cylinders 27 and 53 actuate the sealing and

severing mechanism

28 and 29. Many types of such mechanisms which are well known in the art can be employed in the practice of this invention. For example, a cylinder similar to 27 may be used to actuate the heated knife 28 and an additional cylinder 53 used to operate the web clamping device 29, both cylinders being pneumatically connected for sequential operation. The particular mechanism shown, in FIG. 2 has a hot knife sealing and severing element 28 which is actuated in the vertical direction by the piston rod 52 of the air cylinder 27. The clamping device 29 is actuated by pneumatically operated cylinder 53. A comparable clamping device is mounted in symmetry on the opposite side of the web. Thus when air cylinder 53 is actuated, the clamping device 29 first engages the web 23 and holds it in position until the hot knife 28 seals and severs a notch such as 38, in the web 23 along its folded-web edge. The web 23 is then advanced by the side weld bag making machine to the transverse seal station 51 where the transverse seal is continued across the web from the apex of the previously formed notch.

Cylinder 53 can be eliminated by attaching clamping device 29 to knife 28 by use of compression spring assemblies, not shown. Thus, when cylinder 27 is actuated both the clamping device 29 and hot knife 28 are lowered simultaneously. Clamping device 29 engages the web 23 first and flattens it out. The compression spring assemblies then compress and permit the hot knife to pass through the web 23 to effect the desired sealing and severing.

Transverse seal station 51 comprises heated knife 55 and spring loaded

clamps

56 and 57. As the knife 55 is driven downward by a cam and slide linkage mechanism the

clamps

56 and 57 engage the web 23 and hold it in position until knife 55 severs and seals the web in a transverse line. As knife 55 is caused to ascend the

clamps

56 and 57 release the web 23.

The side seals of the bag are thus formed in a two step operation comprising the contoured portion, which is formed on the double walled web while the web layers are under tensile forces, and a transverse seal. This improved procedure minimizes unsightly puckering of the web material adjacent to the seams and provides for stronger seals in the contoured portions of the bags.

The operation of the notching unit can be conveniently controlled by first positioning frame 24 by operating the actuation wheel 26 so as to position the apex of the notch a distance from the transverse sealing and severing means which is a multiple of the bag width and then synchronizing the downward movement of the piston rod 52 of air cylinder 27 and the downward movement of the transverse sealing and severing device 51, by a suitable registration control system. One such system known in the art is shown in FIG. 3. In this system combined mechanical and electrical means are employed to achieve synchronism of movements between the notching unit, the draw rolls and the transverse sealing and severing device.

As shown in FIG. 3 the machines main drive shaft 63 is driven by sprocket 64 and chain 65 from a motorreducer, not shown. Mounted on the main drive shaft 63 are microswitch control earns 66 through 70, transverse knife raising and lowering cam 71 and adjustable crank 72. The adjustable crank 72 drives the gear rack 73 via pin connection 74 and guide 75. Gear rack 73, in turn, drives pinion 76 which drives one-way clutch 77 in both directions as shown by arrows 78. The magnitude of the sinusoidal displacement of gear rack 73 is varied -by adjusting the location of the pin connection 74 within the adjustable crank 72.

The one-way clutch 77 has an output shaft 79 that is driven in but one direction, shown by arrow 80, by the clutch. Power is transmitted by output shaft 79 to electrically operated eddy current clutch and brake 81. The output from the clutch and brake 81 is transmitted via shaft 82 to lower draw roll 61 and thence to upper draw roll 60. One bag is fabricated for each revolution of drive shaft 63 and thus each revolution of cams 66 through 71. The web material is advanced in the machine by draw rolls 60 and 61 during half a revolution of the drive shaft 63 and is stopped during the remaining half revolution by the one-way clutch 77. The advance of the web material during the one half of the revolution of the main drive shaft can be selectively controlled by use of the electric clutch and brake 81.

Cams 66 through 70 are used to actuate microswitches 83 through 87. The cams actuate the microswitches during preselected portions of the rotary cycle of the cams. The cams 66 through 70 and their corresponding microswitches 83 through 87 control the operation of pneumatic cylinders 27 and 53 via electrically operated solenoid control valves, not shown; the air blow system 32 via electrically operated solenoid control valves, not shown; and the electric clutch and brake 81. The operation of the transverse sealing and severing unit 51 is controlled from cam 71 via the motion of linkage 88 and cam follower 89.

The notch severing unit and the transverse sealing and severing device 51 are thus actuated during the latter half cycle of the drive shaft 63 when drive shaft 82 is at rest.

Contoured-bottom bags can be fabricated by the method and apparatus of this invention from unprinted web material by use of the system just described. The operation of the transverse sealing and severing device and the notching device is synchronized with the web dwell. Minor variations in registration are not noticeable at the mtersection of the transverse seal and the apex of the notch because of the amount of web material used to form the transverse seal.

When it is desired to fabricate contoured-bottom bags from printed web material the method and apparatus of this invention can be operated with a comparable system so that the web material is advanced during slightly less than the first half revolution of the drive shaft and using a signal obtained from a photo-electric registration control system, which is well known in the art, to precisely control the cut-off point of the electric clutch and brake 81 at which the web advancement is stopped. The registratron marks for photo-cell detection are uniformly spaced indicia on the printed web.

In the preferred method and apparatus of this invention cooling means are provided for the web material in the areas of the transverse seal and the contoured notch as they are formed and cooling means are provided for the portion of the web having the formed notches at a point between the two sealing and severing operations. Cooling plate 39 shown in FIG. 2 is provided in the apparatus at a position longitudinally aligned with and subsequent to the sealing and severing

mechanism

28 and 29. The cooled surface of this plate is in contact with the web edge having the formed notches as the web passes from the notching mechanism to the transverse sealing and severing mechanism. This surface provides sufiicient cooling of the web to ensure solidification of the beaded notch prior to the completion of the transverse seal. Air outlet duct 90 can be applied to further cool the beads and to assure close contact between the web and the cooling plate 39.

The preferred sealing and severing device 28 for use in the practice of this invention is shown schematically in cross-sectional form in FIG. 4. This preferred device has a tapered knife 28 which is heated by an electrical resistance element 40. This knife is operable in the vertical direction by the actuated piston rod 52 of the cylinder 27 shown in FIG. 2. The clamping device 29 moves with the heating element 28 and is arranged to engage the web 23 upon being depressed prior to the engagement of the knife 28 into and through the Web 23. A fixed

fastening device

41 and 42 is affixed to and form a part of the web clamping device 29. Both the clamping and fastening devices are provided with cored

closed path channels

43, 44, 45 and 46 to permit the circulation of a coolant within the structures of said devices. This preferred sealing and severing device permits the film to be clamped between cooled surfaces, to be heat severed, and to be reinforced by a bead formed from the molten material which was severed from the web.

FIG. shows the mechanism of FIG. 4 in an operating position. It is important that the clearance between the upper portion of the clamping device 29 and the knife 28 in this operating position be approximately 0.050" to 0.075" in order to provide sufiicient material from the Web 23 to be melted. This clearance is designated by

numbers

47 and 48 in FIG. 5.

The waste web material, that is the Waste notches formed by the use of this method do not readily fall into a receptacle such as notch receptacle 31 shown in FIG. 2. It has been found that a small air jet 32 directed at the apex of the triangularly shaped knife and-thus at the apex of the waste notch and actuated after the clamping device 29 returns to its at rest position will not only provide adequate motive power to lift and move the severed notch to the waste receptacle 31 but also initiates the cooling of the bead formed at the notch. In addition, jets of air can be supplied from ducts below the notch position in the lower web clamping device 30 to initially lift the waste notch after it is severed. By use of such directed streams of compressed air, the waste notch is raised and blown into the proximate entrance opening of the waste receptacle 31 and thus to the trim container 58 to be conveyed away from the machine.

The primary advantage of the bags of the present invention is the combination of such properties as exceptionally high impact strength on the bottom fold, the ability to shrink into a tightly fitting overwrap on contoured articles and the adaptability for use with high speed bag opening and filling machines. The method of the present invention provides an efficient, economical, direct route for the fabrication of such bags.

Bags prepared according to this process are particularly useful for packaging whole frozen poultry such as turkeys, ducks and chickens, cut-up poultry in trays, paper plates, and other contour shaped containers.

What is claimed is:

1. In an apparatus for forming bags from folded, heat sealable thermoplastic web material comprising a combination of means for advancing the folded web in a flattened condition from an unwind position along a predetermined path, for combined sealing and severing of the web in spaced, generally transverse direction and for gathering the fabricated bags, the improvement comprising a combination of means for forming transverse seals having a contoured portion comprising:

(a) a first sealing and severing element capable of being heated and arranged in a generally open triangular shape having an apex pointing in a generally transverse direction to the path of the web, said first sealing and severing element being positioned along the path of travel of the folded edge of the web;

(b) a second sealing and severing element capable of being heated and arranged in generally transverse direction to the path of the web travel located in a position after said first sealing and severing element along the predetermined path of travel of said folded web;

(0) means to actuate the first and second sealing and severing elements; and

(d) a registration control system to synchronize the vertical movement of the second sealing and severing element with the position of the apex of the notch formed in the Web by the first sealing and severing element.

2. The apparatus of claim 1 having cooling means located in a position after the first sealing and severing element along the predetermined path of web travel and arranged to contact at least the portion of the folded web that was sealed and severed by said first sealing and severing element.

3. In an apparatus for forming contoured-bottom bags from folded, heat-scalable thermoplastic web comprising a combination of means for advancing the folded web in a flattened condition from an unwind position along a predetermined path, for combined sealing and severing of the web in spaced, generally transverse directions and for gathering the fabricated bags, the improvement comprising means for forming the contoured portion of the transverse seals comprising:

(a) a frame;

(b) a pneumatic cylinder mounted on the frame and having a movable piston rod;

(c) a knife of generally triangular shape mounted to be actuated by the piston rod;

(d) means to heat said knife;

(e) a clamping device of generally triangular shape formed to loosely fit around the contour of the knife and having a lower fiat surface;

(f) clamping device actuating means to maintain the web in a flattened state in the vicinity of the path of the knife;

(g) a registration control system to actuate the pneumatic cylinder and clamping device actuating means in synchronism with the operation of the web advancing means.

4. The apparatus of claim 3 wherein said clamping device has closed path cooling channels located near its fiat surfaces facing the Web.

5. The apparatus of claim 3 wherein the clamping device actuating means comprises a second pneumatic cylinder mounted on the frame and having a movable piston rod and wherein the clamping device is mounted to be actuated by the piston rod of said second pneumatic cylinder.

6. The apparatus of claim 5 wherein said clamping device has closed path cooling channels located near its fiat surfaces facing the web.

7. In a method of continuously fabricating thermoplastic bags from a folded, heat sealable thermoplastic web material comprising advancing the folded web in a flattened condition from an unwind position along a predetermined path, sealing and severing the web in spaced, generally transverse directions and gathering the fabricated bags, the improvement comprising forming transverse seals having a contoured portion comprising:

(a) a first sealing and severing of the web at spaced intervals along the folded edge of the web in a manner to cut notches having apexes pointing in a generally transverse direction to the path of the web, and

(b) a second sealing and severing of the Web in a transverse direction so as to intersect each of the previously formed apexes.

8. The method of claim 7 wherein the portions of said 7 8 web that are to be sealed and severed are cooled prior t 3,395,622 8/1968 Kugler 93-35 said first and said second sealing and severing. (Heat Seal Digest) 9. The method of claim 8 wherein the portions of said 3,397,633 8/1968 Harris 156498X Web that Were sealed and severed by the first sealing and 3,399,291 8/ 1968 Limbach 156-498X severing are cooled after said first sealing and severing. 5 F0 G PA REI N TENTS References Cited 880,041 10/1961 Great Britain. UNITED STATES PATENTS 1,180,927 11/1964 Germany 156--251 2,195,583 4/1940 Schultz et 211. 2,800,163 7/1957 Rusch. 2,916,053 12/1959 Klasingetal. 3,054,441 9/1962 GCX Ct a1 156 515 3,330,716 7/1967 Zelnick 156515X 156515 3,384,528 5/1968 Lehmacheretal 156 515 10 VERLIN R. PENDEGRASS, Primary Examiner