IE42328B1 - Reinforced wicket hole directionally tear prone - Google Patents

Abstract

1500365 Perforating plastics sheet UNION CARBIDE CORP 12 Feb 1975 [26 Feb 1974] 5873/75 Heading B5A A plastics sheet 11 has a hole 39 formed therein, the perimeter of which is formed by a continuous bead 43 of melted and rehardened plastics, the thickness of which is diminished at one point 43a to facilitate tearing i.e. the sheet from a wicket-held stack. The sheet is clamped between templates 13, 15 having apertures 17, 21 corresponding to the shape of the desired hole and subjected to a stream of hot gas from means 25, the stream axis being offset from the axis of the apertures. A plate 41 redirects the gas stream, which is heated by an electric element 27 in a tubular housing 25, upwardly. The perforated sheet may provide a wall of a packaging bag.

Description

TATENT APPLICATION BY (71) UNiON CARBIDE CORPORATION, MANUFACTURERS, A CORPORATION ORGANIZED UNDER THE LAWS OF THE STATE OF NEW YORK, UNITED STATES OF AMERICA, OF 270 PARK AVENUE, STATE OF NEW YORK, 10017, UNITED STATES OF AMERICA.

Price 12{p The present invention relates to plastics film hags ,or sheets such as are.furnished in stacked supplies held on wickets and are to he dispensed or removed from the wieket-held stacks either manually or automatically, one at a time, for utilization. g Packing operations in industry are of significant import and interest towards promoting the rapid, efficient and economical packaging of products for the market. Pood packaging generally and the meat packing industry in particular require additionally the strict maintenance of sanitary conditions. Automatic or Ιθ semi-automatic packaging techniques have been developed towards achievement of these desired goals.

Here it should he noted that while the ensuing discussion treats of plastics film packaging hags towards illustrative simplification, this invention applies equally as well to stacked c wicket-held plastics film wrapping sheets and the like. -242328 Whatever the degree of complexity of the apparatus and techniques employed in a packaging operation involving food, meat products in particular, it is of the utmost importance that the supply of packaging hags he maintained in a sanitary condition and that the hag dispensing action he accomplished with facility and without hag waste or the incidental production of tom hag scraps which not only interfere with smooth and efficient operation but also may contaminate the packaged food article. While these desirable characteristics are very important in even the simplest modes of semi-automatic packaging, they are of much greater importance in the more fully automated modes such as, for instance, those involving opening the bags one at a time with an air stream for insertion of a product unit into each bag sequentially. In these more automated techniques the relatively higher packaging speed necessitates a sanitary, continual and consistently reliable bag supply not liable to produce contaminating bag Scraps during the packaging operation. Towards attaining these disiderata, the wicket to bag wicket hole relationship is a significantly important element in the Operation. Bags for such use, irrespective of the complexity of the particular packaging technique, are usually supplied to the user in bulk packages which are opened and the bags loaded by hand into the bag dispensing station or portion of the apparatus or in pre-wicketed packages.

Criteria for the wicket to bag wicket hole relationship design dictate that each bag in turn atop a stack of wioketed bags at a packaging station must be readily removable without the incidental production of bag scraps and with clean direct tears -342328 through the hag material from the wicket holes to the outer open edge of each holed ply of the hag. Known wickets used to hold stacked hag supplies in. the aforedescribed manner are best described as inverted-U-shaped with the U havihg a flat bottom which, with the wicket in place, spans, across the ton bag of the stack along a line between the wicket hole's to define a horizontal bearing member. The heart of the bagging system, however, is the hag itself. A number of bag structures have been shown in the patent literature. Specific reference is made to U.S. Patent Specifications Nos. 3,441,198; 3,317,037; 3,351,411; 3,508,379; 3,156,277 and to Canadian Patent Specification No. 851,553. Bags have been produced from tubular film by sealing the tube at one end and from folded film by sealing at the sides, and others have been made by sealing two superimposed films at perimetral edges. Tn some bags, tho front and rear walls are the same length. These are called flush cut bags. In others, the front wall is shorter than the rear wall.

These are called lipped bags. In some tubular bags, the ends are arcuate and in some the front-'wall has a cut out portion less than the flat width of the bag. The bags may be made of any suitable flexible plastics material. Seals to fabricate the bag . structure may be formed in any way, heat sealing being convenient, economical, and preferred. For packaging meats a preferred material is polyvinylidene chloride. Other suitable materials are; polyolefins, e.g. polyethylene, or polyproplene; nylon; polyethylene terephthaiate; polystyrene; and the copolymers of the foregoing materials.

At first sight, it would seem that the wicket- holes of what-442328 ever shape desired could be formed multiply in stacks of such packaging bags by relatively simple techniques such as straight mechanical punching or by hot punching, that is with a punch element heated sufficiently to melt the plastics as the punch pierces the bag stack. Mechanical punching through stacked bags, however, produces wicket holes with all sorts of random irregularities in the preselected shape and in hole edge integrity, with consequent high incidences of bag rejection in the production process and, even more detrimentally, bag failures through improper wicket tear-offs in use in packaging operations. The hot mechanical punch techniques are impractical for hole formation in stacked bags because the molten plastics flows from bag to bag in the stack, and the bags become, in effect, welded or heat sealed together at their wicket holes. Wicket hole formation in the bags individually, that is one at a time, similarly may utilize straight mechanical punching or the hot punch techniques.

Bag production, however, is necessarily a high speed operation and must be so due to the production economics involved. High speed single bag wicket hole punching with a straight mechanical punch inherently produces film material scraps, requires punch replacement from time to time as the punch die or cutting edge dulls, and is thus not as completely a satisfactory solution as could be hoped for. The wicket holes thus formed, even if made to a pre-selected shape, have only simple shear cut edges and therefore contribute less than satisfactorily towards the goal of a wicket to bag hole relationship which effects the desired clean direct tears through -542328 the. bag material from the wicket holes to the outer open edge of each holed ply of the hag without coincidental random tearing and production of contaminating bag scraps.

Hot punching the wicket holes in each hag one at a time, has been generally used in the industry. It is particularly in one at a time hag wicket hole forming with' hot punches that experimental and developmental efforts have been directed towards making the wicket holes with directionally prone tear characteristics, that is to say the hole edge is so formed and/or shaped that the bag tends.to resist tearing from the wicket in all hut a preselected tearing direction. Hot punching produces a hole of whatever shape selected having a bead of melted and rehardened plastics around the hole edge. If the hole is tear drop shaped or outwardly notched in the desired tear direction, that is towards, the bag mouth outer edge, a linear pulling force will tend to impose· stress concentrations at the hole notch or tear drop point, and the hag, hopefully, will tend to tear linearly from the wicket holes to and through the hag mouth edge. It has been found however that the beads of melted and rehardened plastics around the edges of wicket holes thus formed do pat have the consistently reproducible, physical characteristics to meet commercial use standards. The beads around holes so formed have been found frequently to include charred particles of resin from the plastics making for at worst ' contamination necessitating quality control rejection, and at best unsightly appearance.

The problems attending wicket hole forming described herein-642328 above, particularly when the holes formed have no edge reinforcing whatsoever, are even more serious with oriented plastics film sheet materials, since any nick, weakness, or irregularity in a hole edge can cause hag tearing failure along the weakest orientat5 ion line which may he in a completely unwanted direction.

The present invention seeks to provide a plastics film packaging hag or sheet for wicket mounting having a wicket hole which is directionally tear prone in a preselected desired direction.

According to the present invention a plastics film sheet has -a ' wicket hole therein with a hole edge formed by a continuous bead of melted and rehardened plastics, the thickness of said head of melted and rehardened plastics being diminished at a point of the hole edge.

The invention further provides a method for the production of plastics film packaging bags or sheets having head reinforced edge wicket holes which -are directionally tear oriented in a preselected direction unrelated to any orientation of the plastics film material itself. ?0 According to the present invention a method of making a hole, having a varying thickness perimeter of melted and rehardened plastics, in a plastics film sheet material comprises the steps of: masking the plastics film sheet material with a heat resistant masking template having an opening therein of a size and shape substantially congruent with a preselected size and -742328 shape of the hole to he formed; disposing the plastics film sheet material and the masking template on a hacking template having an opening therein of a size and. shape substantially similar to the size and shape of the opening in the masking template, the opening in the masking template and the opening in the backing template being juxtaposed in substantially coaxial alignment; directing a stream of gas heated to a temperature sufficient to effect rapid melting of the plastics film material into impingement on the masking template and the plastics film sheet material between the openings in the masking template and the backing template for a time sufficient to melt through the plastics film sheet material between said openings, the axis of said stream being offset eccentrially from the axis of the juxtaposed openings in the masking and backing templates; removing the stream of gas from impingement on the masking template; and removing the plastics film sheet material from the templates 2Q after the melted plastics film material has at least partially rehardened.

Apparatus to practise the aforesaid method to produce the aforesaid bags or sheets is also comprehended in this invention.

In accordance with the present invention apparatus for making -842328 a hole having a varying thickness perimeter of melted and rehardened plastics film sheet material comprises in combination; a masking template having an opening of size and shape substantially congruent with a preselected size and shape of the hole to be formed; a backing template having an opening of size and shape substantially similar to the size and shape of the opening in the masking template; clamping means to hold the masking template and the backing template juxtaposed with their respective said openings substantially in alignment; and hot gas stream sunply means arranged to direct a hot gas stream at the opening in the masking template such that the axis of the stream is offset eccentrically from the axis of the openings in the templates.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:Figure 1 is a uerspective view showing apparatus according to the invention holding a plastics film material sheet to be wicket holed according to the invention; Figures 2, 3 and 4 show various forms of apexed wicket holes in plastics film sheet materials according to the invention; Figure 5 is a sectional view through apparatus according to the invention showing a plastics film sheet in the process of being -943328 wicket holed; and Figure 6 is a sectional view through Figure 5 along the section line 6-6.

With reference to the drawings, Figure 1 shows a plastics 5 . film sheet 11 clamped between a masking template 13 and a backing template 15. The masking template 13 is provided with an opening 17, generally circular in form but with, an outwardly extending notch or apex 19.· The backing template 15 is provided with a substantially similar, at most very slightly larger, opening 21 with an outwardly extending notch or apex (not shown).

' : The assembled arrangement of the plastics film sheet, the masking template 13 and the backing template 15, clamped securely by any suitable means not shown in the drawings for purposes of simplification and clearer illustration, is shown positioned beneath a hole making head comprising a generally tubular outer housing of any suitable insulative material, having an electrical heating element 27 disposed interiorly thereof and connected to electric circuit wires 29, 31 which pass through a connection bushing 33 mounted atop the housing 25. The circuit wires in turn 2Q connect to a suitable electric power circuit not shown in the drawings.

A gas supply conduit 35 is connected by way of a bushing 37 and a flow control orifice (not shown) to the centre of the -1042328 top of the housing 25 and provides a stream of pressurized gas, compressed air for example, from a pressurized gas supplysource not shown in the drawings.

A typical hole making head assembly, available as a unit, t, might be a flameless electric torch.

Figure 5 is an elevational sectional view showing the plastics film sheet 11 clamped between the masking template 13 and the backing template 15 and disposed beneath the hole making head assembly comprising the outer housing 25 and the interiorly mounted electric heating element 27. A wicket hole 39 is in the process of being formed by a hot gas stream impinging downwardly as shown on the masking template and film material, exposed in the masking template opening 17. In Figure 5, a bottom plate 41 is shown contacting the underside of the backing template. This arrangement, it has been found, redirects the hot gas stream upwards to the film underside as soon as hole formation starts and accelerates the melting process.

As the hole 39 forms, molten plastics film material retracts towards the hole edge, forming a bead 43 which, upon rehardening, acts to reinforce the hole edge against tearing.

Figure 6, a section through Figure 5, shows that the axis of the hole making head assembly is offset eccentrially from the axis of the juxtaposed openings in the masking and backing templates towards the apices in the templates. With this arrange-11423 28 ment, the hole edge head 43 is significantly thinned as at 43a, thus producing a’hole with a reinforced edge having one relatively weak point which is located so as to permit tearing in the desired direction. Figures 2, 3 and 4 of the drawings show, respectively, plastics film sheets having wicket holes of a tear drop shape, a circular shape with a sharp pointed inverted V notch, and a keyhole shape, all of which are apexed in one form or another and yield desired results according to the invention. Other apexed shapes will work equally well. θ Here it should he noted that while the forms of wicket hole shown in these drawing figures for illustrative purposes are generally tear drop shaped, that is to say generally circular with a point or apex, other hole shapes are equally advantageous, it being necessary only that the hole has a relatively weak point on its perimeter arranged to permit tearing in the desired direction, and that the perimetral head of melted and rehardened plastics film material he. somewhat thinner and weaker at this point than elsewhere around the hole edge.

In practice, the method and apparatus of the invention is automated.

In a typical operation with a production capability of 260 bags per minute, a commercially available flame'less electric torch, Sylvania model No. DGH116501, is selected as the hole making head and mounted on a single revolution clutch drive powered by an electric motor. The hole making head is connected to a 50 psig -1242328 compressed air linn and a 53 volt A.O. ρ I citric supply source.

The masking and hacking templates are of j thick aluminium sheet material, each apertured for hole forming openings to a diameter circular hole with a keyhole form notch /(, wide 3 and / deep oriented in the desired hag tearing direction.

A bottom plate of -g thick aluminium is disposed and clamped below the backing template.

In operation, the hole making head moves reciprocally between a Lower position with its outlet end above the masking 10 template wherein a 15 millisecond burst of approximately 1200 1500°F hot air forms the wicket hole, and an upper position with its outlet end if above the masking template. The motion of the head is arcuate, swinging between its upper and lower positions on an arc of 8^ radius from a pivot point 3i above the top surface of the masking template, and the relationship between the' head and the masking template is arranged so that in the lower or hole forming position, the axis of the flameless torch, and thus the axis of the Hot air stream, is aligned directly with the tip of' tne apex of the hole forming opening in the masking template. In 2q the lower or hole making position, the air supply to the hole making head is switched on, and is switched off by valve means during each up stroke. The .electrical heating energy is maintained on continuously during operation.

Lipped bags fabricated from tubular stock of biaxially -1342328 oriented polyvinylidene chloride and provided with wicket holes on this arrangement were tested in a commercial packaging operation :in comparison with similar hags wicket holed‘by cold punching and. by hot' punching and found to be significantly superior in tear proneness from mounting wickets in the desired direction, to consistently tear more linearly and cleanly than the other bags, and to tear without producing any incidental shards or scraps of bag plastics film material.

Numerous alternative modes of practising this invention 10 will, in the light of the foregoing description, -undoubtedly occur to persons familiar with the art. The backing template, .. for instance, may be in any form, from a plate as shown and : described to a simple ring grommet or a tubular brace, it being necessary only that the film being holed be held up snugly against the masking template opening.

Claims (14)

1. A method of making a hole, having a varying thickness perimeter of melted and rehardened plastics,in a plastics film sheet material comprising the steps of; j masking the plastics film sheet material with a heat 1 resistant masking template having an opening therein of a size and shape substantially congruent with a preselected size and shape of the hole to be formed; disposing the plastics film sheet material and the masking 10 template on a backing template having an opening therein of a size and shape substantially similar to the size and shape of the opening in the masking template, the opening in the masking template and the opening in the backing template being juxtaposed in substantially coaxial alignment; V, directing a stream of gas heated to a temperature sufficient to effect rapid melting of the plastics film sheet material into impingement on the masking template and the plastics film sheet material between the openings in the masking template and the backing template for a time sufficient to melt 20 through the plastics film sheet material between said openings, the axis of said stream being offset v eccentrically from the , -1542338 axis of the juxtaposed openings in the masking and hacking template's; removing the stream of gas from impingement on the masking template; and5 removing the plastics film sheet material from the templates after the melted plastics- film material has at least partially rehardened.

2. A method as claimed in claim 1 with the added step of redirecting the gas stream, in a direction counter to its initial 10 flow, from the opening in the backing template towards the opening in the masking template.

3. Apparatus for making a hole having a varying thickness perimeter of melted and rehardened plastics film sheet material comprising, in combination; a masking template having an opening of size and shape substantially congruent with a preselected size and shape of the hole to be formed; a backing template having an opening of size and shape substantially similar to the size and shape of the opening 20 in the masking template; clamping means to hold the masking template and the backing template juxtaposed with their respective said openings -1642328 substantially in alignment; and hot gas stream supply means arranged to direct a hot gas stream at the opening in the masking template such that the axis of the stream is offset eccentrically from the axis 5 of the openings in the templates.

4. Apparatus as claimed in claim 3 in combination with a closure means contiguous to the opening in the backing template said closure means being arranged to redirect the gas stream counter to its initial flow, from the opening in the backing 10 template towards the opening in the masking template.

5. Apparatus as claimed in claim 3 or 4 in which the hot gas stream supply means comprises a tubular housing whioh is connected to a gas supply conduit and which contains an electrical heating element. j 1C)

6. Apparatus as claimed in claim 4 or claim 5 when dependent thereon, in which the closure means is a backing plate held against the outer side of the backing template.

7. A plastics film sheet having a wicket hole therein with a hole edge formed by a continuous bead of melted arid rehardened 20 plastics, the thickness of said bead of melted and rehardened plastics being diminished at a point of the hole edge. -1742328

8. A plastics film sheet as claimed in claim 7 comprising a wall of a packaging hag.

9. A plastics film sheet as claimed in claim 7 or 8 wherein the film material is oriented plastics. 5

10. A plastics film sheet as claimed in claim 7, 8 or 9 whereini the film material.is biaxially- oriented plastics.

11. A plastics film sheet as claimed in claim 10 wherein the film material is-:polyvinylidene chloride.

12. A method of making a hole having a varying thickness perils meter of melted and rehardened plastics material in a plastics film sheet substantially as particularly described herein with reference to the accompanying drawings.

13. · Apparatus for making a hole having a varying thickness perimeter of melted and rehardened plastics film sheet material sub15 stantially as herein particularly described with reference to and as illustrated in Figs. 1, 5 and 6 of the accompanying drawings.

14. -A plastics film sheet containing a wicket hole substantially as herein particularly described with reference to and as illustrated in the accompanying drawings in Figs. 2,5 and 6; or Figs. 3,5 and 6; 2Q or Figs. 4, 5 and 6.