WO2011042856A1

WO2011042856A1 - Blocking resistant bags

Info

Publication number: WO2011042856A1
Application number: PCT/IB2010/054483
Authority: WO
Inventors: Vinay Kaul
Original assignee: Carter Holt Harvey Limited
Priority date: 2009-10-07
Filing date: 2010-10-05
Publication date: 2011-04-14

Abstract

A lie-flat bag having its band(s) of heat activatable adhesive used to effect bag close protected from a tendency to block by an outstand of the band(s) provided by a cohesive spidery, swirly or lattice- like skeletal form wax outstand.

Description

"BLOCKING RESISTANT BAGS"

The present invention relates to blocking resistant bags and/or to hot melt wax overlay systems.

A difficulty encountered with areas of heat reactivatable hot melt adhesive when applied to lie flat materials that are accumulated in a stack type bundle is the tack of the hot melt adhesive at ambient temperatures achieving some measure of adhesion to an overlying or underlying item, ie, so called blocking.

An example of the difficulty of blocking is with he flat bags (of one or more plies of material (usually a kraft paper) and optionally including an inner plastics sleeve). Such lie flat bags, often with pinch or block bottom, or "factory" end typically have a fold over flap at its "customer" end. This fold over flap normally has applied to it a band of heat activatable adhesive. That banded layer of heat activatable adhesive may or may not be intended to match and adhere to a coextensive or less extensive, or more extensive, banded area of adhesive on a receiving outer surface of a ply of the bag.

In most preferred forms of the present invention there are two or more plies of kraft paper material and a stagger of the plies of one or both lie flat panels at the customer closure end such that there can be a near flush effect upon flap fold over and its adhesion.

The present invention recognises irrespective of whether or not each banded area is defined by one or several bands of heat activatable adhesive, of providing a system whereby the lie flat bags can be used as they are conventionally used but without encountering blocking of the bags in a stack situation.

It is therefore an object of the present invention to provide a blocking resistant bag or a wax overlay system for a heat activatable adhesive system that reduces blocking.

In a first aspect the invention consists in a bag, envelope, sheet or the like ("bag") having at least one heat activatable hot melt adhesive band of its, or one of its, ply or plies of substrate material;

wherein the at least one heat activatable adhesive band has a wax outstand from the band.

Preferably the bag is a lie flat bag form having a closure flap at a "customer" end.

Preferably the flap carries said band of heat activatable hot melt adhesive across its lateral extent or substantially across its lateral extent.

The wax outstand is preferably not a drizzle or other intermittent single— locis or multi- loci outstand. Wliilst this can work, there is too much prospect of dislodgement and consequential product contamination. Preferably said wax outstand from the band is of a spidery, swirly or lattice-like skeletal form (or any other skeletal form) able to be achieved in order to provide an outstand from part only of the area of heat activatable hot melt adhesive.

Preferably the effect of the skeletal outstand is to at least substantially reduce the availability for contact in a stack situation of any substantial part, or a sufficient part of the unwaxed outstand covered region, of the band to cause a blocking difficulty.

Preferably the arrangement is substantially as hereinafter described and/ or is formed substantially as hereinafter described.

Preferably the band of the flap is to mate with and/ or is to separately adhere in concert with one or more bands of a heat activatable hot melt adhesive or a complementary adhesive on the outside of the he flat bag.

Preferably the band of the flap is to mate with and/ or is to separately adhere in concert with regions of heat activable hot melt adhesive or a complementary adhesive on the outside of the lie flat bag.

Preferably said regions are adjacent the edges of the panel of the He flat bag.

Preferably the regions are of an interrupted band.

Preferably said adhesive on the outstand of the lie flat bag has wax outstands.

Preferably the he flat bag has no wax outstands on its said adhesive on the outside.

Preferably said bag has a staggered end to multiple plies at the customer end.

Optionally the bag has a block bottom at the factory end.

Optionally the bag has gussets or no gussets along the edges of its main panels in the he flat form.

Optionally the bag includes a plastic sleeve contained within the inner of the plies of preferably a kraft paper.

In another aspect the invention consists in a lie flat bag having a "customer" end closer- flap;

wherein there is a heat activatable hot melt adhesive band on at least its flap;

and wherein that heat activatable adhesive band has a wax outstand from the band.

Preferably the wax outstand is not co-extensive with the area of the band ie, it is skeletal and outstands from only part of the band but is sufficiendy distributed over the band preferably by virtue of some spread of its swirl, spidery, lattice or other type form there across to achieve the desired outcome.

Preferably the wax of the outstand by weight is no more than about 20% of the weight of the hot melt adhesive forming said band.

Preferably the percentages is substantially as hereinafter described. Preferably the nature of the wax and the nature of the heat activatable hot melt adhesive is substantially as hereinafter described.

Preferably there is at least a second band to co-act with, or separately in concert with, that of the flap upon closure ("the or a co-acting band"), that co-acting band can be of lesser band width.

Preferably neither the band of the flap or the band, if any, to complement it or act in concert with it is of multiple bands.

Preferably the or a co-acting band is interrupted to provide regions adjacent the edges of the main panel only.

In another aspect the invention consists in a lie flat bag of multiple paper plies having a "customer" end able to be closed by a flap from one panel mating on closure over the outside of the other panel,

wherein each of the inside of the flap and the other panel has a heat activatable hot melt adhesive band to co act, one with the other or in concert upon closure after, with and/or prior to heat activation;

and wherein at least one of the heat activatable adhesive bands has a wax outstand from the band to confer some enhanced blocking resistance.

Preferably the arrangement is substantially as herein described.

In another aspect the invention is a lie flat bag of one or more paper plies, (optionally with a plastics sleeve),

wherein, at its customer end, there is a fold over flap of one panel having a heat activatable hot melt adhesive region or regions

(and optionally on a receiving outer surface of the other panel there is a heat activatable adhesive region);

wherein at least one of the adhesive regions a hot melt adhesive have at least partly thereover an outstand of a compatible wax.

Preferably the arrangement is substantially as herein described.

In a further aspect the present invention consists in an anti-blocking adhesive system of a lie flat bag where a band of heat activatable hot melt adhesive is partly covered by a wax outstand.

Preferably that partly covered band of heat activatable hot melt adhesive is to co-act with a complementary area or band of heat activatable hot melt adhesive.

That other band may or may not be at least in part covered by a wax outstand. If it is not covered at least in part by a wax outstand, preferably it is of lesser total area (most preferably reduced width of the band) when compared to that of the other. That other band may without a wax outstand be no more than strip areas or the like adjacent an edge of the lie flat bag to add to closure strength at or near the edges.

Preferably the wider band is to be that of a fold over flap to affix to a lesser band on the outside of a panel, eg, a stagger customer ended panel of a multi ply paper bag.

In a further aspect the invention consists in an anti blocking system substantially as herein described with reference to any one or more of the accompanying drawings.

In yet a further aspect the invention consists in a heat activatable hot melt adhesive band substantially as herein described having a wax outstand arranged substantially as herein described with or without reference to Figure 3 of the accompanying drawings.

In yet a further aspect the invention consists in a lie fiat bag substantially as herein described and/ or any related uses or methods.

The present invention also consists in a method of forming a blocking resistant adhesive area as a band across a ply or plies of a multi ply lie flat bag when performed in a manner substantially as hereinafter described.

In yet a further aspect the invention consists in an anti blocking lie flat bag produced by a method substantially as hereinafter described.

The present invention consists in a bag substantially as hereinafter described with reference to the accompanying drawings or any one or more of the accompanying drawings.

As used herein "heat activatable adhesive" includes hot melt adhesive(s).

As used herein "hot melt adhesive" is typified by those referred to hereafter.

Hot melt adhesives (PIMA) with the development of high speed manufacturing and processing equipment can be found in many diverse areas. These include packaging applications.

A hot melt adhesive is a thermoplastic material, solid at room temperature, which is applied both heated and in its molten form and will adhere to a surface when cooled to a temperature below its melting point. They differ from other liquid adhesives in that they set simply by cooling rather than by chemical curing-or the evaporation of a solvent.

The instantaneous bond strength supplied by these adhesives has allowed the

development of high speed production machinery. This includes machinery for making lie flat bags. Their higher viscosity compared to solvent based systems allows them be used on substrates (eg, kraft paper) without sacrificing bond strength. In addition because they do not set by means of solvent evaporation they do not create a pollution problem This latter fact is becoming increasingly important with the rising environmental awareness being experienced world-wide.

The role of wax in hot melt adhesives

^■ The low viscosity of the wax is used to reduce the high viscosity of the polymer and resin to ensure efficient mixing. This reduction in viscosity is particularly important during the application stage. A low viscosity is required to pump the molten adhesive from the storage tank to the application area and to ensure proper surface wetting when applied.

^■ The degree-of ciystallinity and the congealing point of the wax in the adhesive formulation control the open and set times of the HMA as well as the flexibility and elongation properties.

^■ Wax plays a major role in increasing the blocking point of the final adhesive

preventing the adhesive pastilles from sticking together during transport and storage.

^■ The high temperature properties of a hot melt adhesive are - largely controlled by the melt range of the wax being used.

A typical HMA contains 10-30% wax.

The most important waxes for the hot melt adhesive formula tor are those derived from: synthesis

^■ Fischer-Tropsch waxes

crude oil I refining

^■ paraffin waxes

■ micfocrystallirie waxes

^■ Polyolefin waxes (eg, polyethylene wax, ethylene vinyl acetate wax, oxidized

polyethylene wax, polypropylene wax, etc.).

Hot melt adhesives usually acquire some tack often at sometimes encountered ambient temperature conditions and/ or a temperature below their surface melting temperature and thus can present a blocking difficulty.

As used herein "wax" includes those referred to above.

As used herein the term "and/ or" means "and" or "or", or both.

As used herein the term "(s)" following a noun includes, as might be appropriate, the singular or plural forms of that noun.

As used herein "gsm" means grams/ square metre.

Preferred forms of the present invention will now be described with reference to the accompany drawings in which

Figure 1 is a perspective view of one side, customer end to the foremost, of a dual ply kraft paper bag (without optional side gussets) with a block bottom at its factory end and with an optional included plastics laminate sleeve, Figure 2 is the other side of the he flat bag of Figure 1 showing die customer end ply staggering and the adhesive banding for a flush closed customer end, and

Figure 3 shows a preferred skeletal or spidery patterning to achieve with a compatible wax an antiblocking outstand.

A preferred embodiment or range of embodiments of the present invention will now be described but only as exemplifications of the wider application of the invention.

A typical multi-ply bag that is supplied is that of Carter Holt Harvey Packaging, a business unit of Carter Holt Harvey Liixiited, New Zealand- Such bags usually with a block bottom are typically made from two plies of kraft paper. By way of example, if for, for example, a milk powder in a volume of, for example, 25kg, a typical lie flat block bottom bag may have no side gussets, a block or pinch bottom and be of inner kraft paper 125gsm and outer kraft paper 115gsm. For some uses it might be a 125gsm outer kraft paper and the same for the inner kraft paper ply.

In some instances it may even be a range of 115 to 150 gsm kraft paper. In still other embodiments triples might be encountered such as, for example, 125/65/65gsm kraft papers.

Typically, when for milk powder, a sleeve is attached within the substrate material or materials of paper. Such a plastic sleeve is typically polyediylene and may, by way of example, be of 60 to 100 microns (more preferably about 71 or about 83 microns) thick either as a single layer or as a multi layer sleeve.

Irrespective of the bag form, as can be seen from Figure 2 of the drawings, there are preferably at least two plies of the paper substrate and there is provision for a fold over flap from one panel that will fit smoothly in the stagger back of the other panel thus to hold closure.

Typically there is a receiving area of adhesive (eg, preferably as a continuous band laterally of the he flat bag) as well to co-act under heat activation with that (preferably also as a continuous band laterally of the lie flat bag of the fold over flap.

It is typical for the single or multiple bands of the fold over flap adhesive area(s) to be greater in width, or cumulative than that of the single or multiple band(s) to receive the band(s). This however is no way essential.

Typically closure is affected by a blast of hot air or other heat provision such that adhesion results.

The present invention envisages a skeletal swirl or other spidery outstand of a suitable wax on the underlying hot melt adhesive such that blocking is the outcome when stacks of the Ue flat bag are in register in bundles in a stack form.

Figures 1 and 2 show from the customer end 1 both sides of a Ue flat bag of two kraft paper pHes. The edges 2 are of a simple fold form between one panel 3 and the other panel 4. A block bottom as is known in the art is provided at 5 although other factory end bottoms can be provided.

By a staggering of the panel 3 which is of two plies at 5 and 6 respectively there can be presented on one of the plies 7 a narrow band 8 of a heat activatable adhesive that is to

complement the wax outstand provided wider band of heat activatable adhesive 9.

The band of adhesive 9 is on at least one of the plies from which the panel 3 is formed (whether the flap 10 is stagger ended or not).

Closure is affected by the manner herein described by mating the complementary heat activated bands 8 and 9.

A preferred form of a band 9 is as shown in Figure 3. There the white on the black background shows the outstand of wax (as white) and that has been applied in a manner as herein described by a single nozzle, the black indicating the underlying preferably solid layer of hot melt heat activatable adhesive. The swirling can be caused by any suitable means (robotic, eccentric mounted nozzle, etc). Examples include an application carriage to act transversely of bag forming advance direction to apply across the width as the web advances intermittently.

The wax can instead be applied from multi nozzles to provide more than one swirling loci yet still provide a substantially cohesive wax application.

It has been the experience that with the appropriate choice of heat activatable hot melt adhesive and the appropriate choice of wax and proportion of wax used in an outstand pattern that it is not necessary for a thinner band, such as 8, to have a wax overlay ot any kind. This is because there is insufficient contact area from that lesser band alone when there is substantially no tact blocking from the wider band with its skeletal wax outstand.

The present invention envisages the use of any hot melt adhesive, preferably with a wax inclusion, able to be heat activated.

A variety_' of different adhesive types of this kind are available including those of, for example,

^■ 3M New Zealand Limited has 3M jet-melt Adhesive 3755-LM-TC, 3762-LM-TC,

3762-TC, 3792-LM-TC, and 3792-TC Hot Melt Adhesives.

^■ Advanced Adhesives (NZ) Ltd has HM 2230, XM 2100 and XM 2106 hot melt adhesives.

^■ G & A Sales Limited has GA3030 HDT Melt Adhesive.

^■ H.B. Fuller Company Australia Pty. Ltd has Advantra PFIC 9450A and Cleanmelt

PHC 7450 hot melt adhesives. ^■ Henkel New Zealand Limited has Technomelt 4126, 4135 and 4174 hot melt adhesives.

Preferably the hot melt adhesive is one that can be applied at temperatures of, for example, from 60°C to 300°C more preferably 80°C to 200°C (preferably about 160°C).

Such a preferred adhesive is one able to be heat activated by, for example, an air blast of, for example, about 230°C which may give rise to a temperature of about 190°C at the surface of the hot melt adhesive band(s) over the period during which it is being heat activated.

Preferably that is at or about its melting point.

With such a hot air blast going preferably to both mating surfaces, those surfaces are able to be mated.

By way of example, in a two ply bag, typicaEy the strip width of the single band of fold over flap might be, for example, from 10mm to 20mm wide.

Most preferably it is about 14mm wide as a continuous layer providing a solid band able to attach on a receiving surface of an outei" surface of a ply of the bag that might be from 1mm to 20 mm wide. Preferably it is from 33m to 8mm. Most preferably about 5mm wide. It may even coact with a band of adhesive as a receiving surface.

The outstand spidery, swirling, lattice-like, or other skeletal forms are of a compatible wax for the adhesive system.

Such a wax preferably melts at a temperature difference of 100°C to 30°C (most preferably about 60°C) lower to that of the underlying hot melt adhesive.

It is envisaged that a suitable wax is for example a SASOL™ wax which is also preferably in the hot melt adhesive itself although not necessarily so. Other waxes can be used include but are not limited to those referred to previously.

It is envisaged that from 2 to 15% by weight of wax is added as the swirling, spidery, lattice-like or other skeletal outstand form over the band (or bands) of underlying hot melt adhesive with respect to the weight of that underlying hot melt adhesive layer.

Preferably the amount is up to 10% and preferably not less than say 4%. Most preferably it is about 7-10%.

A typical system has the adhesive applied at, for example, 160°C or 165°C to be resealed at a higher temperature of, for example, about 190°C or thereabouts or even greater at the adhesive surface.

The wax is preferably applied at about 130°C and can, once set at a congealing point that is lower, remelt at about 130°C which is about 60°C less than the temperature at wliich heat activation of its underlying hot melt adhesive is preferably to occur. The preferred hot melt adhesive has preferably between 15 and 30% w/w of its hot melt adhesive composition. Such a wax (preferably a Fischer-Tropsch wax or a polyolefin wax) has some or all characteristics similar to, if not identical to, that of the overlying wax to be used.

Anti Blocking Trials

To address ongoing issues with hotmelt blocking on the top of the dairy type bags, it was decided to apply a thin layer of wax over the hotmelt strip during the production run which will form a skeletal swirl or spidery outstand as a spacing barrier between the heat activable hotmelt strip and the next bag in a bundle.

The wax will be applied during production by means of a shaped slot nozzle; this will enable a skeletal or spidery pattern (eg, of lapping spirals), or a lattice-like form, of wax to be applied to the top of the hotmelt strip.

The non application of a solid layer of wax will allow a lower coating weight of wax to be applied to the hot melt strip surface and will also allow mainly uncovered regions of the hot melt strip so that the properties of die hotmelt will not be affected.

The wax in the trialling was the same wax which is used in the hotmelt adhesive and was no more than 10% by weight to the weight of the hotmelt application weight.

Protocol and Results

All bags were sealed with hot air at 230°C with no alterations required to sealing temperatures or sealing equipment.

Plain bags were run on a production environment where the bottomer was run at normal production speed of 140-160 bags per minute and showed that wax could indeed be applied at production speed. A skeletal or spidery pattern coating weight of 5% and 8% with respect to the weight of the hot melt strip was applied to bags for testing.

(A) Samples were placed under weights (150 Kg) for 24 hours at ambient temperatures to look for signs of blocking and compared with standard samples.

No blocking was found on the wax overlay samples. However, some blocking occurred on the standard samples.

(B) Bags with no wax (standard samples), 5% wax and 8% wax were bundled together and pressed to 2500Kg and strapped to simulate palletising.

The pallet was then placed in an oven at 45°C for 6 hours and then separated to look for signs of blocking.

No blocking was observed on the standard or test samples.

(C) Another lot of bags as in (B) was placed under the same conditions. However, the temperature was raised to 55°C to simulate maximum temperatures observed in containers during shipping. No blocliing was observed on test samples but was observed on standard samples.

Claims

WHAT WE CLAIM IS:

1. A bag, envelope, sheet ot the like ("bag") having at least one heat activatable hot melt adhesive band of its, or one of its, ply or plies of substrate material;

2. A bag of claim 1 which is a lie flat bag form having a closure flap at a "customer" end.

3. A bag of claim 2 wherein the flap carries said band of heat activatable hot melt adhesive across its lateral extent or substantially across its lateral extent.

4. A bag of any one of the preceding claims wherein the

outstand is not of a single locus or multi-loci drizzle.

5. A bag of any one of claims 2 or 3 wherein said wax outstand from the band is of a spidery, swkly or lattice-like skeletal form or any other skeletal form able to be achieved in order to provide an outstand from part only of the area of heat activatable hot melt adhesive.

6. A bag of claim 5 wherein the effect of the skeletal outstand is to at least substantially reduce the availability for contact in a stack situation of any substantial part, or a sufficient part of the unwaxed outstand covered region, of the band to cause a blocking difficulty.

7. Preferably the arrangement is substantially as hereinafter described and/ or is formed substantially as hereinafter described.

8. A bag of any one of claims 2, 3, 5 or 6 wherein the band or bands of the flap is to mate with and/ or is to separately adhere in concert with regions of heat activable hot melt adhesive or a complementary adhesive on the outside of the lie flat bag.

9. A bag of claim 8 wherein said regions are adjacent the edges of the panel of the he flat bag.

10. A bag of claim 9 wherein the regions are of an interrupted band.

11. A bag of any one of claims 7 to 10 wherein said adhesive on the outside of the he flat bag has wax outstands.

12. A bag of any one of claims 7 to 10 wherein the he flat bag has no wax outstands on its said adhesive on the outside.

13. A bag of claim 2 wherein it has a staggered end to multiple plies at the customer end.

14. A bag of claim 2 or 13 wherein it has a block bottom at the factory end.

15. A bag of claim 2, 13 or 14 wherein it has gussets along the edges of its main panels in the lie flat form.

16. A bag of claim 2, 13 or 14 wherein there are not gussets along the edges of the main panels in the he flat form.

17. A bag of claim 1 or claim 2 which has a plastic sleeve contained within one ply or the inner of plies of a kraft paper.

18. A lie flat bag having a "customer" end closer flap;

19. A bag of claim 18 wherein the wax outstand is not co-extensive with the area of the band, i.e., it is skeletal and outstands from only part of the band but is sufficiently distributed over the band preferably by virtue of some spread of its swirl, spider_}", lattice or other type form there across to achieve the desired outcome.

20. A bag of claims 18 or 19 wherein the wax of the outstand by weight is no more than about 20% by weight of the weight of the hot melt adhesive forming said band.

21. A bag of any one of claims 18 to 20 wherein the nature of the wax and the nature of the heat activatable hot melt adhesive is substantially as herein described.

22. A bag of any one of claims 18 to 21 wherein there is at least a second band to co-act with, or separately in concert with, that of the flap upon closure.

23. A bag of claim 22 wherein the or a co-acting band is of lesser band width.

24. A bag of claim 22 or 23 wherein neither the band of the flap or the band, if any, to complement it or act in concert with it is of multiple bands.

25. A bag of claim 22 or 23 wherein the or a co-acting band is interrupted to provide regions adjacent the edges of the main panel only.

26. A lie flat bag of multiple paper plies having a "customer" end able to be closed by a flap from one panel mating on closure over the outside of the other panel,

wherein each of the inside of the flap and the other panel has a heat activatable hot melt adhesive band to co act, one with the other or in concert upon closure after, with and/ or prior to heat activation;

27. A bag of claim 26 wherein the arrangement is substantially as herein described with or without reference to any of the drawings.

28. A he flat bag of one or more paper plies, (optionally with a plastics sleeve),

(and optionally on a receiving outer surface of the other panel there is a heat activatable adhesive region); wherein at least one of the adhesive regions a hot melt adhesive have at least partly thereover an outstand of a compatible wax.

29. A bag of claim 28 wherein the arrangement is substantially as herein described with or without reference to any of the drawings.

30. An anti-blocking adhesive system of a lie flat bag where a band of heat activatable hot melt adhesive is partly covered by a wax outstand.

31. A system of claim 30 wherein that pardy covered band of heat activatable hot melt adhesive is to co-act with a complementary area or band of heat activatable hot melt adhesive.

32. A system of claim 31 wherein that other band may or may not be at least in part covered by a wax outstand.

33. A system of claim 31 where that other band is of lesser total area when compared to that of die other.

34. An anti blocking system substantially as herein described with reference to any one or more of the accompanying drawings.

35. A heat activatable hot melt adhesive band substantially as herein described having a wax outstand arranged substantially as herein described with or without reference to Figure 3 of the accompanying drawings.

36. A lie flat bag substantially as herein described and/or any related uses or methods.

37. A method of forming a blocking resistant adhesive area as a band across a ply or plies of a multi ply lie flat bag when performed in a manner substantially as hereinafter described.

38. An anti blocking lie flat bag produced by a method substantially as hereinafter described.

39. A bag substantially as herein described with reference to the accompanying drawings or any one or more of the accompanying drawings.