GB2046660A

GB2046660A - Apparatus and Method for Producing a Plastics Closure Strip

Info

Publication number: GB2046660A
Application number: GB8010436A
Authority: GB
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1979-03-30
Filing date: 1980-03-28
Publication date: 1980-11-19
Also published as: DK157905C; GB2046660B; IT1127017B; NL188839C; IE800631L; FI72918B; NL188839B; NL8001859A; FR2452371B1; SE435153B; IT8048276A0; FI72918C; CH636047A5; FR2452371A1; FI800957A; BE882517A; AU540476B2; NZ193297A; SE8002384L; DE3011371C2

Abstract

A pair of plastics closure strips for use in a bag, each comprises one of interengageable male and female closure profile portions (20, 22) on one of base portions (21, 23), which are simultaneously extruded from a die body having profile channels (42a, 42c) (communicating with die profile outlet openings (52, 63) for extruding the profile portions, and base channels (43, 42b) communicating with die face outlet openings (45, 66) for extruding the base portions. The channels are adjacent to each other near the die openings and separated by a portion of the die body which terminates short of the outlet face of the die, so that the extruded profile and base portions join together before exiting the die body. The portions may be of different plastics materials. Each channel has a control orifice (56, 57, 43, 48) and an adjustable valve control (58, 59, 44, 49). The profile portions may be extruded from the die in facing relationship. <IMAGE>

Description

SPECIFICATION Apparatus and Method for Producing a Plastics Closure Strip The present invention relates to a method in and an extrusion die apparatus for producing a plastics closure device including two closure strips, wherein each closure strip includes profile and base portions, and particularly to a method and an extrusion die apparatus for producing a plastics closure strip in which the extruded profile and base portions join together before exiting the die body. The invention also relates to a plastics closure whenever produced by the apparatus and method.

Plastics bags including plastics closure devices are well-known and in popular use. Typically, a plastic closure device includes two closure strips which interlock together. Each closure strip includes a profile portion and a base portion.

It is the two complementary profile portions of two closure strips which become occluded when the closure device is closed. The integrity of the shapes of the profile portions must be maintained during the production of the closure strips so that good occlusion is obtained. In addition, the joining together of the profile and base portions must be done in a manner to avoid distortions which can interfere with the preferred shape of the closure strip.

The closure device described in the copending patent application serial No. 892,432, filed March 31, 1978 having the same applicant and assignee as the instant application is a typical closure device suited for being produced by the instant invention.

The prior art method and apparatus for producing a closure strip includes the separate extrusion and forming of profile and base portions and subsequently joining these portions together.

This method has drawbacks and is not suitable for commercial high-rate production of many closure strips. One drawback is that relatively slow cooling, such as air cooling, is required and this results in low production rates.

The instant invention attempts to overcome the problems arising fron the prior art method and apparatus. The invention allows good control of the extrusion of the profile and base portions as well as a good maintenance of the integrity of the shape of the closure strip. An additional feature is that different plastics material can be used for the profile and base portions.

One embodiment of the invention is an extrusion die apparatus for producing at least one plastics closure strip having profile and base portions, comprising a die body having a die face, at least a first profile channel defined in the die body and communicating with a corresponding first profile die opening in the die face for extruding a first profile portion, and at least a first base channel defined in the die body and communicating with a corresponding first base die opening in the die face for extruding a first base portion, the first profile and first base channels being adjacent to each other near the first profile and first base die openings and separated by a first portion of the die body which terminates short of the die face so that the extruded first profile portion and first base portion join together before exiting the die body.

Another embodiment of the invention further includes a second profile channel defined in the die body and communicating with a corresponding second profile die opening in the die face for extruding a second profile portion, and a second base channel defined in the die body and communicating with a corresponding second base die opening in the die face for extruding a second base portion, the second profile and second base channels being adjacent to each other near the second profile and second base die openings and separated by a second portion of the die body which terminates short of the die face so that the extruded second profile portion and second base portion join together before exiting the die body.

A further embodiment of the invention teaches a plurality of separate profile channels defined in the die body and communicating with corresponding profile die openings in the die face for extruding separate profile portions, the plurality of profile channels being adjacent to the first base channel near the die openings and separated by the first portion of the die body so that the extruded plurality of profile portions join the first base portion before all of the portions exit the die body.

Yet another embodiment of the invention is in the method for producing at least one plastics closure strip having profile and base portions comprising extruding at least a first profile portion, extruding at least a first base portion, and joining the first profile and first base portions together, the improvement wherein the first profile and first base portions are joined together before exiting the die body.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description, taken in connection with the accompanying drawings, in which: Fig. 1 shows a cross-sectional view of two closure strips which form a closure device and which are suitable for being produced by the invention; Fig. 2 shows a plastics bag incorporating a closure device as shown in Fig. 1; Fig. 3 shows diagrammatic side elevational view of an extrusion system including an apparatus according to the invention; Fig. 4 is a diagrammatic sectional view of an apparatus according to the invention; Fig. 5 is a diagrammatic partial sectional view showing another embodiment of an apparatus according to the invention; Fig. 6 is a perspective view of a control bar used in Fig. 4;; Fig. 7 is a perspective sectional view of another control bar used in Fig 4 Fig. 8A, 8B, and 8C are sectional views of different control bars; Fig. 9 is a diagrammatic partial sectional view showing another embodiment of a flow diverter for the apparatus shown in Fig. 4; and Figs. 1 OA and 1 OB each shows a crosssectional view of a combined closure strip produced by an apparatus according to the invention.

In carrying the invention into effect, certain embodiments have been selected for illustration in the accompanying drawings and for description in the specification, reference being had to the Figs. 1 to 10.

Fig. 1 shows a closure device in accordance with the aforementioned co-pending patent application serial number 892,432. The profile portion 20 is joined to a base portion 21 and profile portion 22 is joined to base portion 23. The profile portions 20 and 22 are complementary and profile portion 20 can be engaged in the profile portion 22. The two closure strips 25A and 25B constitute a closure device.

Fig. 2 shows a typical plastic bag 24 which includes a closure device 26. It has been found economical to produce the two closure strips of the closure device 26 separately and connect them to a film web during the manufacturing of the bag 24.

Thus, it is desirable to have an economical and reliable extrusion die apparatus for producing the closure strips which constitute closure device 26.

The closure strips of closure device 26 can be made by an extrusion system which includes an extrusion die apparatus in accordance with the invention as shown in Fig. 3. Extruder 27 is connected by a conduit 28 to an extrusion die apparatus 29. Extruded closure strips 31 and 32 are produced by the extrusion die apparatus and enter a cooling bath 33, such as a container of water and are then redirected by rollers 34 and 36 to nip rollers 37 where the closure strips 31 and 32 are occluded together to form a continuous closure device 38. The rate at which the continuous closure device 38 is produced depends upon the size and screw speed of the extruder 27, melt flow of the material, the speed of the nip rollers 37, the cooling rate, and the adjustment of the die components producing the closure strips 31 and 32 as well as other factors.

Generally, equipment for extruding plastics material is well-known in the art and considerable prior art exists relevant to the extrusion of closure devices. Fig. 4 shows a partial sectional view of an extrusion die apparatus in accordance with the invention and details such as assembly screws, die heaters, sensing control elements, etc. have been omitted for clarity. The flow diverter 40 establishes the distribution pattern for the plastics material being supplied. Plastics material under pressure is directed into the channels 41 and 42 and then through the flow diverter 40. Channel 41 is connected to a control orifice 43 and an adjustable valve control 44 before reaching control bar 46 and die opening 45. The die opening 45 is an outlet and shape controller for, a base portion.

The channel 42 is connected to channels 42a, 42b and 42c. The channel 42a goes through a control orifice 48 and an adjustable valve control 49 before reaching control bar 51 and die opening 52. The die opening 52 is an outlet and shape controller for a closure profile. The die body portion 47 between the channels 41 and 42a terminates short of the face of the die body so that the profile and base portions contact each other and join together before exiting from the die body to form a closure strip 54.

The apparatus shown in Fig. 4 includes a part for producing another closure strip 68 which is complementary to the closure strip 54.

The channels 42b and 42c pass through control orifices 56 and 57 and adjustable valve controls 58 and 59 and eventually reach control bars 61 and 62. Die opening 63 is an outlet and shape controller for a profile portion 64 and die opening 66 is an outlet and shape controller for a base portion 67.

The profile portion 64 and base portion 67 contact each other and join together before exiting the die body to form closure strip 68. The closure strips 54 and 68 enter a water bath 69 for cooling the plastic material.

Fig. 5 shows, in part, another embodiment for the extrusion of closure strips. For the embodiment in Fig. 5, the closure strips are reversed as compared to the embodiment shown in Fig. 4. That is, profiles 70 and 71 face each other while the base portions 72 and 73 are on the outside of the closure strips 74 and 76. The difference in the arrangement shown between Fig. 4 and 5 can be achieved by the choice of arrangement of the control bars 46, 51, 61 and 62.

Fig. 6 shows a typical control bar 81 for producing a base portion of a closure strip. A lead-in taper 82, control "land" 83, and recess 84 are factors determining the size and shape of the extruded material. The control land 83 and recess 84 are shown as being linear, but this is not necessarily the preferred embodiment. Generally, the control land 83 can be either a gentle contour or have steps of different depths. The control land 83 can be straight in the direction determining width and have a variable height so that thickness variations can be controlled.

The width of the control land 83 depends upon the width of the base portion desired. Mounting holes 86 allow the control bar 81 to be mounted or removed conveniently.

Fig. 7 shows a sectional perspective view of a control bar 87 for producing a profile portion of a closure strip. A counter bore 88 receives the plastics material being supplied under pressure and it also communicates with channel 89 which defines the shape of the profile portion. The channel 89 can be formed with good precision through the use of an electro-deposition method in accordance with known technology. The ,mounting hole 91 permits the mounting and removal of the control bar 87.

Figs. 8A, 88, and 8C show cross-sectional yiews of three control bars having profile channels in different locations. Profile bar 92A shows profile channel 93A with die opening 94A spaced apart from the location of where the die opening for the base portion would be so that the base and profile portions join together outside the die body in accordance with the prior art. Control bar 92B shows profile channel 93B having a die opening 94B which will produce base and profile portions which will join together just before exiting the die body because the die body portion 96B is just short of the die face.Control bar 92C includes a profile channel 93C and a die opening 94C and features a die body portion 96C which is recessed from about 0.010 inch (0.0254 cm) to about 0.250 inch (0.635 cm) away from the face 97C, preferably from about 0.015 inch (0.038 cm) to about 0.09 inch (0.229 cm). The separation between the profile and base channels at the die openings is less than 0.040 inch (0.102 cm) and preferably about 0.020 inch (0.051 cm) and more preferably yet from about 0.002 inch (0.0051 cm) to about 0.008 inch (0.024 cm). The profile and base portions produced will join together before exiting the die body. The control bar 92C can be used advantageously with a low draw ratio of about 1:4, a high operating speed of about 300 feet per minute, and rapid cooling means such as a water bath. Cooling can also be established by liquid spray or other known ways.

Fig. 9 shows a partial sectional view of another embodiment of a flow diverter. Channel 100 supplies plastics material to one base portion extrusion opening whereas channel 101 communicates with channels 101 a, 101 b, and 101 c for forming two profile portions as well as one base portion. This arrangement permits the selection of one of the portions as being a different color or composition from the other portions.

Figs. 1 OA and 1 OB show two intermediate products which can be extruded from an extrusion die apparatus according to the invention by positioning two profile die openings near a wide base die opening. Cutting base portion 106 between the profile portions 107 and 108 will produce two closure strips. Similar operations on base portion 109 will produce four closure strips.

It is to be understood that there is no desire for the invention to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

Claims

1. An extrusion die apparatus for producing at least one plastics closure strip having profile and base portions, comprising a die body having a die face, at least a first profile channel defined in said die body and communicating with a corresponding first profile die opening in said die face for extruding a first profile portion; and at least a first base channel defined in said die body and communicating with a corresponding first base die opening in said die face for extruding a first base portion; said first profile and first base channels being adjacent to each other near said first profile and first base die openings and separated by a first portion of said die body which terminates short of said die face so that the extruded first profile portion and first base portion join together before exiting said die body.

2. The apparatus of claim 1 , further comprising a second profile channel defined in said die body and communicating with a corresponding second profile die opening in said die face for extruding a second profile portion; and a second base channel defined in said die body and communicating with a corresponding second base die opening in said die face for extruding a second base portion; said second profile and second base channels being adjacent to each other near said second profile and second base die openings and separated by a second portion of said die body which terminates short of said die face so that the extruded second profile portions and second base portion join together before exiting said die body.

3. The apparatus of claim 2, wherein said first profile and first base portions define a first closure strip and said second profile and base portions define a second closure strip, said first and second profiles being adapted to be occluded together whereby said first and second closure strips define a closure device.

4. The apparatus of any of claims 1 to 3, wherein said first die body portion terminates from about 0.0254 cm to about 0.635 cm short of said die face.

5. The apparatus of claim 4, wherein said first die body portion terminates from about 0.038 cm to about 0.229 cm short of said die face.

6. The apparatus of any of claims 1 to 5, wherein the separation between said profile and base channels at said die openings is less than about 0.102 cm.

7. The apparatus of claim 6, wherein the separation between said profile and base channels at said die openings is less than about 0.051 cm.

8. The apparatus of claim 7, wherein the separation between said profile and base channels at said die openings is from about 0.0051 cm to about 0.0204 cm.

9. The apparatus of claim 1, comprising a plurality of separate profile channels defined in said die body and communicating with corresponding profile die openings in said die face for extruding separate profile portions; said plurality ci profile channels being adjacent to said first base channel near said die openings and separated by said first portion of said die body so that the extruded plurality of profile portions join said first base portion before all of the portions exit said die body.

10. The method for producing from a die body at least one plastics closure strip having profile and base portions, comprising extruding at least a first profile portion, extruding at least a first base portion, and joining the first profile and first base portions together; the improvement wherein said first profile and first base portions are joined together before exiting said die body.

11. Apparatus according to claim 1 , for extruding a plastics closure strip, substantially as hereinbefore described with reference to the accompanying drawings.

12. A method according to claim 10, for extruding a plastics closure strip, substantially as hereinbefore described with reference to the accompanying drawings.

13. A plastics bag closure device whenever produced by the method or apparatus of any of the preceding claims.