AU611543B2

AU611543B2 - Improvements in or relating to extruded plastics film closures

Info

Publication number: AU611543B2
Application number: AU31694/89A
Authority: AU
Inventors: Dennis Mathew Barnes; Neill Peter Gillespie; Peter James Longhurst
Original assignee: Minigrip Flexible Packaging Ltd
Current assignee: CHEQUER Corp Ltd
Priority date: 1988-03-28
Filing date: 1989-03-28
Publication date: 1991-06-13
Anticipated expiration: 2009-03-28
Also published as: NZ224055A; AU3169489A

Description

ii- If 11 5 4 3 COMMONWEALTH OF AUSTRALIA The Patents Act 1952 Name of Applicant(s): MINIGRIP-(-N--)- LIMITED Address of Applicant(s): 6 RON DRIVER PLACE, EAST TAMAKI, AUCKLAND, NEW ZEALAND Actual Inventor(s): Address for Service:

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I-ID.:

IaJ NEILL PETER GILLESPIE, PETER JAMES LONGHURST DENNIS MATHEW BARNES G.R. CULLEN COMPANY, Patent Trade Mark Attorneys, Dalgety House, 79 Eagle Street, Brisbane, Qld. 4000, Australia.

COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: M.0 sWI IMPROVEMENTS IN OR RELATING TO EXTRUDED PLASTICS FILM CLOSURES ii The following statement is a full description of the invention including the best method of performing it known to us: ~a 1 5k This invention relates to extruded plastics film closures.Such closures comprise interlockable elements which can be extruded as an integral part of a parent film and used as a closure for a bag or similar article made from the film. Alternatively the interlocking elements can be extruded as integral elements of a base strip which can subsequently be attached to a film to achieve a similar end.

Closures of the subject type are well known and in a conventional fundamental form comprise a rib profile of arrowhead shape interlockable between a pair of limbs of an opposing and co-operative rib profile.Numerous refinements of the fundamental closure and extrusion method thereof are known,these including,inter alia, the provision of a pair of tracking ribs disposed adjacently parallel and to either side of one or other of the closure rib profiles in particular the arrowheaded profile.The conventional way of engas±ng the profiles is to impinge them together between. a forefinger and thumb and in so doing sliding the forefinger and thumb therealong to continue the engagement of the closure members throughout their length. The object of the tracing ribs is to facilitate the "feel" of such operation, the ribs assisting in alignment of the closure profiles with one another and the positioning of the fingers in sliding therealong.

The lateral spacing of the tracing ribs relative to one another and a closure profile therebetween is

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.7 reasonably critical.In achieving a required spacing problems can arise owing to characteristics of extrusion techniques, for example, draw-down.Merely providing cut-outs in a die at a given spacing will not necessarily result in an extrusion having ribs correspondingly spaced.Further physical restraints in the die may prevent the formation of a die with cutouts sufficiently close together to provide an extrusion with the ribs spaced apart at a required close spacing. One known method of achieving the desired result is by enlarging the cut-out of the die in the region where a closure rib cut-out conjoins with associated tracking rib cut-outs to either side thereof. Apparently this allows more plastics material to flow in this zone and in the resultant extrusion laterally acting stresses result which tend to draw the ribs toward one another. This method requires predetermination of the spacing and size of the cut-outs in the die.It is believed this can reduce the versatility of the method, particularly where blow moulded extrusion film is utilised in .the forming of bags and the ribs are integrally moulded with the films.

An object of this invention is to provide a method of extruding plastics films closures with tracking ribs at a close spacing to one another which will alleviate some of the limitations involved with known methods.In particular the invention is concerned with providing a method of extruding blown plastics film integrally incorporating adjacently spaced apart ribs to form a closure profile with associated tracing ribs to either side thereof.It is envisaged that with this method one die will be suitable for moulding a worthwhile range of container sizes thereby rendering the die more versatile.

According to a first aspect of this invention there is provided a method for extruding a closure rib with a pair of tracking ribs one to either side thereof and at a required spacing therebetween as integral elements of a substantially thinner blown base film comprising the steps of constructing a die with a closure rib cut-out and tracking rib cut-outs in a periphery thereof with 004#D0 Sthe tracking rib cut-outs being spaced from the closure r 15 cut-out,assembling the die in a die ring incorporating at least one co-extrusion port disposed in a zone radially of the closure rib and tracking rib cut-out and extruding the film with,in so doing controlling the i material flow to the co-extrusion port to provide j 20 additional material in the zone at the base of the closure rib cut-out and tracing rib cut-outs to thereby control the draw-down characteristics of the extrusion and obtain a required spacing between the extruded ribs.

In a second aspect of this invention there is provided an extruded plastics film closure comprised of interlocking rib profiles with tracking ribs extending adjacently alongside,but spaced therefrom,at least one p -rr~l3i6-a~~ of the rib profiles characterised in that the tracking ribs have in part been formed by co-extrusion of additional material into the parent material flow forming the associated closure,the material of the closure in the zone extending across the base of the tracking ribs and the associated closure rib therebetween being of increased thickness forming an enlargement on the face of the closure opposite the ribs.

ne V.t In to further describing the invention reference is made the accompanying drawings wherein; Fig.l is a cross-sectional view partly schematic view of one half of a blow forming die with a coextrusion unit assembled therewith,and Fig.2 is a plan view,in the direction of arrow "A"on Fig.l of the closure and tracking rib region of the die,and Fig 3 is an end view of a closure element and associated tracking ribs section of a film formed by the method of this invention.

Interlocking closure profile ribs 3,5 are moulded as integral elements of a base film 6.In a conventional way a blow moulding die 7 and method are utilised to provide one or two sets of closure profiles 3,5 in the one film 6.

Preferably a first closure profile 5 is of an arrowheaded shape and hereinafter is referred to as the male i i ii I ii profile. The co-operating profile 3 is of a generally C-shape with,in a completed closure,the opening thereof being disposed toward the male profile 5 and preferably incorporates inwardly directed lips 8 to facilitate engagement with the arrow-headed configuration of the male profile The die 7 is constructed with cut-outs 3a and conforming to the required profile shapes of the closure members3,5.Referring in particular to Fig 2 in conventional manner these are formed in the periphery 4. .of a the die 7.To either side of the male profile cutout 5a and spaced clear thereof,tracking rib cut-outs 9a are also formed. The tracking rib cut-outs 9a are preferably of a truncated triangular cross-sectional shape with a base and wider section of a rib cut-out 9a being at the periphery of the die and the cut-outs 9a tapering radially inward thereof. The depth of a rib cut-out 9a is preferably limited to a depth substantially less than the depth of the associated 20 male cut-out 5a with in the preferred form a rib cut- R out 9a being of a depth of about two thirds that of an j Q associated male cut-out 5a.At the full extent of the depth of a rib cut-out 9a the side walls thereof are preferably still spaced apart to provide the truncated triangular shape as depicted. In assembly the die 7 is assembled within a die-ring 10 in conventional manner with,as depicted in Fig 2,the space 11 between the periphery of the die 7 and the die-ring 10 dictating r i

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i i i i ;i I i the basic therethrough.

thickness of the film 6 extruded 0 a 9 o 080 o 0 0oo 9o 0 o 08J 00 0 0000 In known manner with such extrusion material also flows into and through the closure profiles cut-outs and the tracking rib cut-outs 9a to thus integrally mould those profiles3,5 and 9a formed thereby together with the parent film 6. As will be understood a similar extrusion process is utilised in moulding closure and tracking rib profiles on a parent closure strip suitable for subsequent affixing to a film to provide closures for containers fabricated from the film.

The die 7 is assembled in the die-ring 10 with the male rib cut-out 5a and the associated tracking rib cut-outs 9a disposed in a zone in radial alignment with at least 15 one co-extrusion port 12 formed in the die ring 10. The co-extrusion port 12 is appropriately coupled to a source of the extrusion material and the flow therethrough can be controlled to dispense a required quantity into the space 11 between the die ring 10 and die 7 to thus blend with the parent extruded plastics material represented by arrow 6a.In utilising the method of the invention the die 7 is used in conventional manner to blow mould the plastics film 6 and simultaneously extrude the closure ribs 3,5 and tracking ribs 9 as integral elements thereof.In so doing the flow of the co-extrusion material,represented by arrow 13 is controlled to provide sufficient additional material to that of the parent extrusion 6a ~nru 0- 0 0 00 o 0 0 o Jo o 00 material in the zone about the male closure rib 5 and the tracking ribs 9 to obtain a required spacing 14 between the male rib 5 and the associated tracking ribs 9.Thus,the spacing 14 of the resultant product is monitored and the flow characteristics of both extrusion flows 6a,13 altered in particular the amount of material fed via the co-extrusion port 12 to obtain a required spacing 14.

A characteristic of a closure film 6 formed by the method of this invention is that the thickness of the material of the closure film 6 at the base of the tracking ribs 9 is increased relative to what would be the case without the additional co-extrusion material 13 and in particular this thickness forms an enlargement 15 on the face of the closure film 6 in a zone opposite the male rib 5 and the tracking ribs 9.

Further, while the tracking rib cut-outs 9a are of a depth less than that of an associated male profile rib cut-out 5a the resultant tracking ribs 9 can be and preferable are extruded to a height greater than that of the male rib 5.This is achieved by increasing the quantity of co-extrusion material 13 being fed into the flow of parent material 6a.This together with the unrestricted shaping of the tracking cut-outs 9a enables the cut-outs 9a to be force fed or over filled.Controlling the extrusions rate allows for the flow of the film material 6,upon leaving the restraints of the die 7 to extend the overall height of the formed 9 ribs 9 prior to solidifying.The greater height of the tracking ribs 9 assists alignment of the male closure rib 9 within the female ribs 3.

4 4 000' ~i 00 40 0 00 00 0 40 0 0~J 0 0004 (4

Claims

1. A method for extruding a closure rib with a pair of tracking ribs one to either side thereof and at a required spacing therebetween as integral elements of a substantially thinner blown base film comprising the steps of constructing a die with a closure rib cut-out and tracking rib cut-outs in a periphery thereof with the tracking rib cut-outs being spaced from the closure cut- 0 out, assembling the die in a die ring incorporating at least one co-extrusion port disposed in a zone radially of the closure rib and tracking rib cut-out and extruding the film with, in so doing controlling the material flow to the co-extrusion port to provide additional material in the zone at the base of the closure rib cut-out and tracing rib cut-outs to thereby control the draw-down characteristics of the extrusion and obtain a required spacing between the extruded ribs. 00..0 moo 010 o a o n o 0 oo 0 0 0 claim the there incre the f

4. flow of f extru track the a 20 0o 4 o r 2. A method as claimed in claim one wherein the closure rib cut-outs are configured to form a pair of interengagable male and female members and the tracking rib cut-outs are formed to either side of the male rib cut-out. 3. A method as claimed in claim 2 wherein the tracking rib cut-outs are of a depth less than that of the male closure rib cut-out.

6. .0000 0 claim B V eo000oo ,o0 o trunc o0 o00 there 0 20 7. S0 0 oo o adjac of th ribs addit the a the z and t f; ii r 'z *1 11 4. A method as claimed in claim 3 wherein the material flow to the co-extrusion port is controlled to the extent of force feeding the tracking rib cut-outs and the extrusion rate is controlled such that the resultant tracking ribs are of a height greater than the height of the associated closure rib. A method as claimed in any one of the preceding .a claims wherein the thickness of the film in the zone of Sao. 10 the closure rib and the tracking ribs associated 0OOo therewith is greater than the remainder of the film, the 0oo0 o increased thickness taking the form of an enlargement on om, uc So o0 the face of the closure opposite the ribs. 6. A method as claimed in any one of the preceding 60000 claims wherein the tracking rib cut-outs are of a 0000 0 0 0 .o truncated triangular shape with a base and wider section 0. thereof being disposed at a periphery of the die. 0oO020 7. An extruded plastics film closure comprised of S 00 0 interlocking rib profiles with tracking ribs extending adjacently alongside, but spaced therefrom, at least one of the rib profiles characterised in that the tracking ribs have in part been formed by co-extrusion of additional material into the parent material flow forming the associated closure, the material of the closure in the zone extending across the base of the tracking ribs and the associated closure rib therebetween being of 12 increased thickness forming an enlargement on the face of the closure opposite the ribs.

8. An extruded plastics film closure as claimed in claim 7 wherein the height of the tracking ribs is greater than the height of the associated closure rib.

9. An extruded plastics film closure as claimed in claim 7 or claim 8 wherein the tracking ribs are of a truncated triangular shape. o 0

10. A method of extruding a closure rib with a pair of 0 00 0 tracking ribs one to either side thereof and at a required spacing therebetween as integral elements of a substantially thinner blown base film substantially as S herein described with reference to the accompanying oo.' drawings. O 4T

11. An extruded plastics film closure substantially as S t20 herein described with reference to the accompanying drawings. DATED this 18th day of March 1991 MINIGRIP FLEXIBLE PACKAGING LIMITED By their Patent Attorneys CULLEN CO. T Rj 0 f i