GB2276862A

GB2276862A - A tear strip including a synthetic material deposited in liquid form

Info

Publication number: GB2276862A
Application number: GB9406703A
Authority: GB
Inventors: Barry Turner; John Robert Burchell
Original assignee: Paper Sacks Ltd
Current assignee: Paper Sacks Ltd
Priority date: 1993-04-01
Filing date: 1994-04-05
Publication date: 1994-10-12
Also published as: GB9306880D0; GB9406703D0

Abstract

A tear strip 16b in a paper sack 10 comprises a strip of synthetic material applied initially as a fluid and then allowed to set or dry. A tape or cord may also be included, which may be coated or impregnated by the synthetic material. The synthetic material may form a substantial part of the tear strip or simply glue two plies of a multi-ply sack together to give extra strength along these defined lines. Incisions 17 allow the end of the tear strip to be gripped. A further strip (27, Figure 4) may be provided along the same line as the strip of synthetic material but on the opposite side of a ply or on another ply. <IMAGE>

Description

PAPER SACKS This invention relates to paper sacks and more particularly to the provision of tear lines in paper sacks, tear lines being predetermined lines along which the sacks can readily be torn open if and when required, the tear lines being adapted to keep, or to tend to keep, the tears to where the tear lines are formed in the sacks.

Paper sacks with tear lines formed by tear strips glued to the sack surfaces are known. The glued tear strips are adapted to be taken hold of, that is, manually grasped, at one or both ends thereof and pulled away from the remainder of the sack, leaving a tear the width of the torn-away strip. The tear strips have to be strong enough to resist being torn themselves, that is, they have to be substantially stronger (i.e. tear-resistant) than the remainder of the sack wall in the vicinity of the tear line. The glue contributes very little, if anything, to the strength of the tear strip in the known sack.

It is an object of the invention to provide a single-wall or multi-wall sack with a novel form of tear strip defining a tear line in the sack wall. A single-wall sack has single-ply walls. A multi-wall sack has walls each with two or more plies.

According to one aspect of the invention there is provided a paper sack having a tear line therein, the tear line being at least partly defined by a tear strip in a wall of the sack, the tear strip being formed in at least substantial part by a strip of synthetic material, the material having been applied initially as a fluid in a strip to the wall of the sack, said fluid thereafter having been allowed, or caused, to set, or dry, according to the type of fluid.

It may be preferred, because of relative simplicity of manufacture, for the tear strip to be formed solely by said strip of synthetic material, with no reinforcement of tape or cord.

However, there may be applications, for example extra heavy duty sacks, or sacks for wet or damp goods, where reinforcement of the tear strip is necessary, by means of tape or cord incorporated therein or adhered (directly or indirectly) thereto and/or united therewith. The set or dried fluid may, or may not, be applied so as to cover and thereby waterproof the tape or cord. The set or dried fluid may, or may not, impregnate the tape or cord, or interpenetrate fibres of the tape or cord.

In any event, the fluid may, or may not, impregnate the wall of the sack or interpenetrate fibres of the wall of the sack.

If the wall of the sack is of paper which is china clay-coated, and the fluid is a hot melt, there will likely be minimal interpenetration of the paper fibres by the fluid, though it should still be possible for adhesion of the set fluid strip to the paper wall to be sufficient for the set fluid strip to form a tear strip.

According to another aspect of the invention there is provided a paper sack having each of its walls formed of at least two mutually adjacent plies and a tear line formed by a tear strip in at least one of said walls, the tear strip comprising a film or layer of synthetic material extending in a strip or stripe along the tear line in between the two plies, the synthetic material having been applied as a fluid to one or other ply or to both plies of said one wall and then having been allowed, or caused, to set, or dry, according to the type of fluid.

In one preferred embodiment the synthetic material is a glue, gluing the two plies together along the tear line, so that the glued-together plies themselves form the tear strip.

In a modification of this embodiment, a reinforcing cord or ribbon extends along the tear line in between the two plies. The cord or ribbon may possibly be impregnated or covered by the synthetic material. If so, the cord or ribbon may be water-proofed or damp-proofed by the synthetic material.

In another preferred embodiment, the synthetic material forms a moisture barrier and the tear strip comprises an elongate strip of material, possibly paper material, secured along the length of said elongate strip of material to one of the two plies on the surface of said one ply further from the strip of synthetic material. Preferably said surface is the innermost surface of the four respective surfaces of said two plies. If the sack is a two-ply sack, said surface will then (inevitably) be the inner surface of the wall of the sack.

The invention will be further described by way of example with reference to the drawings, wherein: FIG. 1 shows a first form of sack embodying the invention; FIG. 2 is an enlargement of a small part of Fig. 1; FIG. 3 shows a second form of sack embodying the invention; FIG. 4 is an enlargement of a small part of Fig. 3; FIG. 5 is a pictorial view of part of a first form of apparatus for making sacks in accordance with the invention, with a nozzle applicator for the fluid; and FIG. 6 is a pictorial view of part of a second form of apparatus for making sacks in accordance with the invention, with a roll-and-wheel applicator mechanism for the fluid.

Referring to Figs. 1 and 2, there is shown a two-ply paper sack 10, that is, a sack of which the front and back walls 12a, 12b are each two-ply, each wall 12a, 12b having an inner ply 13a, 13b and an outer ply 14a, 14b respectively. The paper sack 10 is not gussetted, but instead the front and back walls 12a, 12b are joined directly together along edges 15a, 15b as shown. That is, inner ply 13a is directly joined to inner ply 13b, and outer ply 14a is directly joined to outer ply 14b, along the said edges 15a, 15b. The fact that paper sack 10 is not gussetted is not essential to the invention, however. It might instead be gussetted (not shown) in well-known manner, to have gussetts between the front and back walls. As thus far described, the two-ply paper sack 10 is well-known and needs no further description or explanation in those respects.

The front wall 12a of the sack 10 has two tear lines defined by respective tear strips 16a, 16b therein. Each tear strip 16a, 16b comprises a strip or stripe of synthetic material, more particularly, glue, in between the two plies 13a and 14a of the sack wall 12a, gluing the two plies 13a, 14a together along each tear strip 16a, 16b. The tear strips 16a, 16b are formed during manufacture of the sack, as will be described, by the application of the synthetic material initially as a fluid in two strips to the sack wall 12a, said fluid thereafter being allowed, or caused, to set, or dry, according to the type of fluid.

At the opposite ends of the two tear strips 16a, 16b are four incisions 17a1, 17a2, 17b1, 17b2 respectively, for the purpose of enabling a user of the paper sack 10 to push his/her finger through a selected one of the four incisions 17awl, 17a2, 17b1, 17b2, grasp hold of the strip of glued wall paper forming the tear strip 16a, 16b and tear it away from the remainder of the sack wall 12a so as to tear the sack 10 open along the tear line. The incisions 17a1, 17a2, 17b1, 17b2 are shown curved, but may instead be straight (transverse).

In the example of the sack 10 of Figs. 1 and 2, in order to obtain the advantage of relative simplicity of manufacture, each tear strip 16a, 16b is without any reinforcement of tape or cord.

In a modification, not shown, a reinforcing cord or ribbon extends along the tear line in between the two plies 13a, 14a. The cord or ribbon may possibly be impregnated or covered by the glue. If so, the cord or ribbon may be water-proofed or damp-proofed by the glue.

Referring to Figs. 3 and 4, there is shown a two-ply paper sack 20 that is similar in some respects to the sack 10 of Figs. 1 and 2. The front and back walls 22a, 22b are each two-ply, each wall 22a, 22b having an inner ply 23a, 23b and an outer ply 24a, 24b respectively. The paper sack 20 is not gussetted, but instead the front and back walls 22a, 22b are joined directly together along edges 25a, 25b as shown. That is, inner ply 23a is directly joined to inner ply 23b, and outer ply 24a is directly joined to outer ply 24b, along the said edges 25a, 25b. The fact that paper sack 20 is not gussetted is not essential to the invention, however. It might instead be gussetted (not shown) in well-known manner, to have gussetts between the front and back walls. As thus far described, the two-ply paper sack 20 is well-known and needs no further description or explanation in those respects.

The front wall 22a of the sack 20 has two tear lines defined by respective tear strips 26a, 26b comprising strips 27a, 27b, of paper or other material(s), which are glued to the inside surface of the inner ply 23a of the front wall 22a. Each tear strip 26a, 26b also comprises a strip or stripe of synthetic material 28a, 28b, more particularly, a moisture barrier material, in between the two plies 23a and 24a of the sack wall 22a, extending along each tear strip 26a, 26b. The strips or stripes 28a, 28b of moisture barrier material are formed during manufacture of the sack, as will be described, by the application of the synthetic material initially as a fluid in two strips to the inside surface of the outer ply 24a of the sack wall 22a, said fluid thereafter being allowed, or caused, to set, or dry, according to the type of fluid.

At the opposite ends of the two tear strips 26a, 26b are four incisions 29at, 29a2, 29b1, 29b2 respectively, for the purpose of enabling a user of the paper sack 20 to push his/her finger through a selected one of the four incisions 29a1, 29a2, 29b1, 29b2, grasp hold of the tear strip 26a, 26b and tear it away from the remainder of the sack wall 22a so as to tear the sack 20 open along the tear line. The incisions 29a1, 29a2, 29b1, 29b2 are shown curved, but may instead be straight (transverse).

In the case of the sack 10 of Figs. 1 and 2 and/or the sack 20 of Figs. 3 and 4, the fluid may, or may not, impregnate the wall 12a, 22a of the sack 10, 20 or interpenetrate fibres of the wall 12a, 22a of the sack 10, 20.

In both paper sack 10 of Figs. 1 and 2 and paper sack 20 of Figs. 3 and 4, the tear strips 16a, 16b, 26a and 26b are shown as terminating just short of the four incisions 17a1, 17a2, 17b1, 17b2 in paper sack 10 and the four incisions 29a1, 29a2, 29b1, 29b2 in paper sack 20 respectively. However, the strips 27a, 27b of paper or other material(s) extend from end to end of the sack 20, for ease of manufacture, since this avoids having to cut them to length except where the sack walls are cut to length.

Each of the sacks 10, 20 has a conventional (or unconventional) end closure l91o, 1920 respectively, according to requirements.

It was described earlier herein, how each tear line in the sack 10 of Figs. 1 and 2 comprises a strip 16a, 16b of synthetic material in between the two plies 13a and 14a of the sack wall 22a. Now, referring firstly to Fig. 5 and then to Fig. 6, there will be described how the tear strips 16a, 16b are formed during manufacture of the sack, by the application of the synthetic material, e.g. the glue, initially as a fluid in two strips to the sack wall 12a, the glue thereafter being allowed, or caused, to set, or dry.

Fig. 5 is a pictorial view of part of a first form of apparatus 30 for making sacks in accordance with the invention, with a nozzle applicator 31 for the glue, as mentioned above. Besides the nozzle applicator 31 for the fluid, the apparatus 30 comprises guide rolls 32 and 33 for guiding the substrate, namely, the outer ply 14a, 24a, just before the outer ply 14a, 24a is brought together with the inner ply (not shown), which travels along a horizontal path (not shown) just above the horizontal reach 14 of the outer ply 14a, 24a, downstream of the second, upper guide roll 33.

As shown, the outer ply 14a, 24a passes upwardly and over the first guide roll 32, after which it passes vertically from guide roll 32 to guide roll 33. The outer ply 14a, 24a then passes around guide roll 33 and thereafter proceeds generally horizontally (in the direction of arrow 34 in Fig. 5) to where it meets the inner ply 15a, 25a (not shown in Fig. 5).

The nozzle applicator 31 is positioned to apply a narrow strip, or "bead", of glue 35 to the outer ply 14a, 24a just where the latter passes around guide roll 33. This bead 35 is squashed into the form of the wider strip when, and where, the outer ply 14a, 24a comes into contact with the inner ply 13a, 23a.

Fig. 6 is a pictorial view of part of a second form of apparatus 40 for making sacks in accordance with the invention, with a roll-and-wheel applicator mechanism 41 for the glue in place of the nozzle applicator 31 of apparatus 30 of Fig. 5. In all other respects, the apparatus 40 of Fig. 6 is identical to apparatus 30 of Fig. 5 and the same references are used accordingly.

The roll-and-wheel applicator mechanism 41 comprises:- a tray 42 for the glue (or other fluid); a pick-up-and-transfer roll 43, for picking-up and transferring glue.from tray 42; a metering roll 44, for regulating the amount of glue picked-up by roll 43; and an applicator wheel 45, which engages the roll 43 for glue to be transferred from roll 43 to wheel 45, and which engages the outer ply 14a, 24a as the latter passes vertically from guide roll 32 to guide roll 33.

Suitable drive means, not shown, are provided for one or other or both of guide rolls 32, 33 in each of Figs. 5 and 6. One or other of the guide rolls 32, 33 may be an idler roll in accordance with normal practice.

Likewise, suitable drive means, not shown, are provided for one or more rotatable members of the roll-and-wheel applicator mechanism 41 (Fig. 6). One or more rotatable members of the roll-and-wheel applicator mechanism 41 may be an idler or idlers.

In a modification, (referring to Fig. 5 and/or Fig.

6), an initially fluid, cross-linkable material may be used in place of ordinary glue, in either apparatus 30 (Fig. 5) or apparatus 40 (Fig. 6), in combination with a simple spreader roll positioned downstream of where either the nozzle applicator 31 or the wheel 45 applies the bead of glue 35 to the outer ply 14a, 24a, and in combination with suitable means, dependent upon the nature of the cross-linkable fluid, downstream of the spreader roll, to cause the cross-linking. Such means may, as is well known, be perhaps a heater, an ultra-violet lamp or other radiation source, or even a reagent applicator of some kind. The cross-linked material can be selected and made strong enough to act by itself as a tear strip, stuck to the outer ply 14a, 24a.

In this event the paper sack could even be single ply.

Claims

Claims:

1. A paper sack having a tear line therein, the tear line being at least partly defined by a tear strip in a wall of the sack, the tear strip being formed in at least substantial part by a strip of synthetic material, the material having been applied initially as a fluid in a strip to the wall of the sack, said fluid thereafter having been allowed, or caused, to set, or dry, according to the type of fluid.

2. A paper sack as claimed in claim 1, wherein the tear strip is formed solely by said strip of synthetic material, with no reinforcement of tape or cord.

3. A paper sack as claimed in claim 1, wherein the tear strip is reinforced by means of tape or cord incorporated therein or adhered (directly or indirectly) thereto and/or united therewith.

4. A paper sack as claimed in claim 3, wherein the set or dried fluid is applied so as to cover and thereby waterproof the tape or cord.

5. A paper sack as claimed in claim 3 or 4, wherein the set or dried fluid impregnates the tape or cord, and/or interpenetrates fibres of the tape or cord.

6. A paper sack as claimed in any preceding claim, wherein the set or dried fluid impregnates the wall of the sack and/or interpenetrates fibres of the wall of the sack.

7. A paper sack as claimed in any preceding claim, wherein the wall of the sack is of paper which is china clay-coated, and the fluid is a hot melt, such that there is minimal interpenetration of the paper fibres by the fluid.

8. A paper sack having each of its walls formed of at least two plies and a tear line formed by a tear strip in at least one of said walls, the tear strip comprising a film or layer of synthetic material extending in a strip or stripe along the tear line in between the plies, the synthetic material having been applied as a fluid to one or other ply or to both plies of said one wall and then having been allowed, or caused, to set, or dry, according to the type of fluid.

9. A paper sack as claimed in claim 8, wherein the synthetic material is a glue, gluing the plies together along the tear line, so that the glued-together plies themselves form the tear strip.

10. A paper sack as claimed in claim 8 or 9, wherein a reinforcing cord or ribbon extends along the tear line in between the plies.

11. A paper sack as claimed in claim 10, wherein the cord or ribbon is impregnated or covered by the synthetic material.

12. A paper sack as claimed in claim 11, wherein the cord or ribbon is water-proofed or damp-proofed by the synthetic material.

13. A paper sack as claimed in claim 8, wherein the synthetic material forms a moisture barrier and the tear strip comprises an elongate strip of material secured along the length of said elongate strip of material to one of the plies on the surface of said one ply further from the strip of synthetic material.

14. A paper sack as claimed in claim 13, wherein said surface is the innermost surface of the respective surfaces of the plies.

15. A paper sack as claimed in claim 13, wherein said sack is a two-ply sack, and said surface is the inner surface of the wall of the sack.