GB2263434A

GB2263434A - Adhesive laminate for sealable bags

Info

Publication number: GB2263434A
Application number: GB9126745A
Authority: GB
Inventors: Mark Malitskie; Alan Joseph Heeley
Original assignee: FIXIT
Current assignee: FIXIT
Priority date: 1991-12-17
Filing date: 1991-12-17
Publication date: 1993-07-28
Anticipated expiration: 2011-12-17
Also published as: GB9126745D0; GB2263434B

Abstract

An adhesive laminate (29) for use in manufacturing sealable bags is made by contacting a plastics backing layer (22) with a porous polymeric material (23) and forcing an adhesive, e.g. a thermoplastic adhesive at 150 DEG C under pressure, via an adhesive reservoir (25) through the porous polymeric material (23) so that it is coated with adhesive on both sides, one side being bonded to the backing layer (22). The porous polymeric material may have randomly directed fibres and a non-woven structure, and is preferably made of nylon. <IMAGE>

Description

ADHESIVE LAMINATE The present invention relates to an adhesive laminate that can be used to seal bags of plastics material. The laminate has a porous polymeric material that is partially coated on both sides with an adhesive and has a backing layer to protect the adhesive which can be peeled off to expose adhesive for sealing the bags.

Bags of plastics material, such as polyethylene are often made in the art by folding a sheet of plastics material once it has left a supplying roll of material so that there is an overlap. Often an adhesive is applied to the overlap of plastics material which can serve to seal the bag after it has been formed by heat sealing the folded material at appropriate regularly spaced points along the length of material.

It is known to apply the adhesive using a gravity field where the adhesive is dissolved in a solvent. The solvent is then allowed to evaporate to leave the final form of adhesive desired. A release layer, backing layer or liner can then be used to cover the exposed adhesive.

However, due to the presence of evaporating solvent expensive extraction systems must be employed if the solvent is not to constitute a health hazard.

Furthermore, solvent extraction is relatively slow and the cost of installing appropriate ovens to evaporate the solvent is high. In addition, the use of solvent based adhesives can present considerable environmental problems.

One proposed solution to this problem is to employ a tape that can be applied to the sheet of plastics material, the tape having at least one side coated with an adhesive to serve as means for sealing the bag. An example of such a tape is that made by Steratape Limited, Carnaby Industrial Estate, Bridlington, Yorkshire. The tape is coated on both sides with an adhesive and to protect the exposed adhesive two liners, one on either side of the tape, are provided. Due to the fact that there are two liners the tape cannot be properly wound onto itself, or onto a bobbin, and remain stable. Thus, because both adhesive sides of the tape are covered with a liner, one portion of the tape will not adhere to another to form a stable roll or bobbin.In fact, if a roll or bobbin is formed then it tends to unroll and fall apart, and can cause considerable problems if a core of the roll or bobbin becomes detached from the remainder of the roll or bobbin. These are considerable disadvantages for a bag manufacturer since the tape cannot be neatly and stably wound onto a suitable roller allowing for easier application on to the sheet of material from which the bag is made. It is usually preferred that suitable adhesive tapes can be wound onto a bobbin since bobbins can accommodate a greater length of tape. This means that a bag manufacturer needs to halt his bag manufacturing process, or change the supply of adhesive tape, less often. This however, is not a practical proposition for this type of tape.

The two liners are made of polyethylene and paper, respectively. The paper liner needs to be peeled away from the tape before it can be applied to the sheet of material for forming the bag and this presents a handling problem for the bag manufacturer.

A second tape that is coated on both sides with an adhesive is available from Brattle Adhesive Products in Leyton Buzzard under the trade name POLYPEEL. This tape has a single polyethylene liner and can be applied in rolls.

However, with this tape and that supplied by Steratape Limited, to provide adhesive on both sides involves applying or coating on the adhesive from the two sides of the tape (or plastics material). The present invention seeks to overcome (or at least mitigate) these problems by being able to form double sided adhesive tape by applying adhesive from one side only and that can suitably be wound onto itself, such as onto a bobbin.

Thus according to a first aspect of the present invention there is provided a method of manufacturing an adhesive laminate, the method comprising contacting a backing layer which comprises a plastics material with a layer of porous polymeric material and allowing adhesive to pass through at least part of the layer of porous polymeric material so that the porous polymeric material is at least partially coated on both sides with the adhesive so that one side (such as a first side) adheres to the backing layer.

An advantage of using a plastics material for the backing layer is that the adhesive laminate can be cut by using a heated element which one is unable to do if a part of the adhesive laminate (e.g. the backing layer) is made of paper.

The adhesive will be suitably forced or urged through at least part of the porous -polymeric material although in some circumstances the adhesive may pass through the porous polymeric material without requiring force, such as by capillary action. Thus the adhesive will suitably be applied under pressure.

The adhesive laminate thus suitably comprises two layers, namely the backing layer and the layer of porous polymeric material. The backing layer will suitably cover the adhesive on one side of the porous polymeric material thus acting as a liner. Thus preferably the backing layer will be as wide, or wider, than the layer of porous polymeric material.

The backing layer is suitably removable from the porous polymeric material to expose a side of the porous polymeric material which has been at least partially coated with adhesive. The other side may be used to adhere the laminate to, for example, a bag or a layer of material to be made into a bag. Thus, the adhesive laminate can be used in the manufacture of bags comprising a plastics material.

The backing layer may be contacted with the porous polymeric material before the adhesive is allowed to pass through the porous polymeric material, although it will be preferred that this will happen almost simultaneously.

In this specification the term "layer" covers tapes, strips, sheets and films. Thus, each layer may be in the form of a sheet of film and may at a later stage be cut into one or more tapes or strips.

The polymeric material is suitably sufficiently porous to allow both sides of the material to be at least partially coated with the adhesive. Thus the polymeric material will usually have a sufficiently porous structure to allow passage of the adhesive therethrough. This means that in the manufacture of the adhesive laminate only one application of adhesive is required to at least partially coat both sides of the porous polymeric material. This is considerably more efficient than having to separately coat the two sides of a suitable polymeric material or tissue.

The porous polymeric material will suitably be fibrous, that is to say it will generally comprise individual fibres. These fibres will preferably be randomly directed. In the art, such materials can be referred to as open-weave materials or non-woven materials. The porous polymeric material may therefore be thought of as similar to a tissue in appearance and texture. The polymeric material suitably comprises a plastics material. Preferably the polymeric material will be manufactured by a spin-bonding technique.

The porous polymeric material will suitably be made of nylon, such as nylon 6,6. Preferably the material will have a melting point of at least 2600C. However, suitably the material will be able to withstand temperatures up to 2000C, such as up to 1200C, without deformation taking place.

The preferred thicknesses of the porous polymeric material range from 50 microns (pm) to 250 pm, such as from 100 to 200 ym, optimally from 130 to 160 ym.

The porous polymeric material will suitably have an air permeability of at least 600, such as at least 900, optimally at least 1,100 m3/m2.min. Here air permeability is the measure of ease with which air will pass through a fabric, and is measured in cubic metres of air passing through a square metre of fabric in a minute at a specified pressure differential (196 Pa) across the material. Suitably the air permeability will be no more than 1500 m3/m2.min.

The porous polymeric material will suitably be easily dyed and printed using appropriate ink dyes and pigments.

The material will suitably have a fabric weight of from 5 to 30, such as from 8 to 15, g/m2.

Suitably the polymeric material will be substantially transparent. Thus, there will often be sufficient distance between the fibres to allow the passage of light through the material.

The adhesive may thus soak through the porous polymeric material or may be extruded through it. Often the material will become more clear or transparent once the adhesive has been applied.

Thus an exposed adhesive side of the porous polymeric material (such as the second side) may be applied to a layer of plastics material from which a bag is to be made. Once the bag has been formed the backing layer may be removed to expose the adhesive side of the porous polymeric material (the first side) which may be used to seal the bag.

The backing layer may thus serve to cover the adhesive on one side, such as the first side, of the porous polymeric material and may therefore act as a liner. The backing material will suitably comprise a plastics material such as polyester, polyvinyl chloride, polyethylene and/or polypropylene. Polyester is less preferred since it has a relatively high melting point and therefore higher temperatures may be required to heat-cut it, or a longer time is required toheat-cut at lower temperature. Under some circumstances polyvinyl chloride may be more difficult to apply a silicone release layer to than the other polymers mentioned.

Polypropylene and in particular polyethylene, are preferred. Particularly preferred materials are high density polyethylene (HDPE) and low density polyethylene (LDPE). Thus, if for example HDPE or LDPE are employed, the backing layer will have a melting point in the range of from 85 to 1100C.

Suitably the backing layer will have at least one side at least partially coated with a friction-reducing material, sometimes termed a release layer in the art. This may reduce adherence between the backing layer and the adhesive and may thus serve to assist removal of the backing layer from the porous polymeric material when this is desired. The friction reducing material is suitably a silicon-containing compound, for example it may comprise silicone. In such circumstances the backing layer may be referred to as being "siliconised".

Preferably both sides of the backing layer are at least partially coated with the friction reducing material.

The backing layer will suitably be from 20 to 80, such as from 40 to 60, ttm thick.

The adhesive may comprise a solvent (for example it may be a solvent based adhesive) in which case it will preferably be an acrylic-type or acrylic-based adhesive.

Preferred adhesives will cross-link on solvent loss.

Suitable solvents include alcohols, although it may be water (e.g. if the adhesive is applied as an aqueous emulsion). Other- adhesives include resins, such as rubber resins.

However, solvent based adhesives are less preferred since evaporating solvent can present health hazards as well as environmental problems. It is preferred that a thermoplastic adhesive is employed. Such an adhesive is suitably a pressure sensitive adhesive, which means that the adhesive may be permanently sticky or tacky (as opposed to some non-pressure sensitive adhesives whose adhesive properties increase with temperature).

The adhesive is suitably allowed to pass through the porous polymeric material at a temperature of from 100 to 2000C, especially from 130 to 180at, and in particular from 140 to 1600C. Although the adhesive may be applied and allowed to pass through the porous polymeric material, it is preferred that the adhesive is applied under pressure This may result in more adhesive passing through the porous polymeric material. The adhesive may be applied at a pressure of from 4 to 7 bar (atmospheres, Atm) such as from 5 to 6 bar.

The adhesive is suitably applied using an adhesive delivery device. Such a device may comprise a reservoir (such as a chamber) for containing adhesive. Such a reservoir will usually be closed or sealed, i.e. not open to the atmosphere. The delivery device will suitably be adapted to apply the adhesive directly to one side of the porous polymeric material, and suitably be adapted to force the adhesive through the porous polymeric material under pressure. This is preferably achieved by applying the adhesive through one or more apertures. This may be a series of holes but is preferably a slot (often called a die in the art).- Suitably the slot will be no wider than the width of the porous polymeric material.

Preferably the slot will be provided in the base of the reservoir (or chamber).

The adhesive delivery device will therefore preferably have a first contact surface which is in contact with the porous polymeric material. The aperture (such as a slot) will thus preferably be provided in the first contact surface. Although the adhesive can be applied to the porous polymeric material, which may be under tension to prevent distortion, preferably a second contact surface may be provided which is in contact with the backing layer. Thus, the backing layer and layer of porous polymeric material may pass between, so as to be sandwiched between, the first and second contact surfaces. This may occur almost simultaneously with the application of the adhesive to the porous polymeric material, although this is not essential and the second contact surface may be provided upstream of (or before) the adhesive delivery device. The second contact surface may thus serve to prevent, or at least inhibit, any deformation of the backing layer or layer of porous polymeric material by providing a rigid surface for supporting the component layers of the adhesive laminate while the adhesive is applied under pressure.

The second contact surface need not be fixed and immobile, indeed it is preferably moving, such as at a same or similar velocity to the backing layer and layer of porous polymeric material. These two layers will also suitably be moving at the same, or similar velocity.

Thus preferably the second contact surface comprises a roller.

The adhesive, if a thermoplastic one, preferably comprises a block copolymer. For example, a preferred adhesive is a block copolymer of styrene/isoprene/styrene (SIS). Thus, a block copolymer of SIS is preferably employed as the polymer matrix. Such adhesives can be obtained from many sources, for example from the following three companies: (a) H.B. Fuller UK Ltd, of Amber Business Centre, Greenhill Lane, Leabrooks, Derbyshire DE55 4BR, England; (b) National Starch and Chemical Co, Adhesives Division, Galvin Road, Slough, Berkshire SL1 4DF, England; and (c) Borden UK Ltd, Industrial Adhesives Department, North Baddersley, Southampton S052 9ZB, England.

Such adhesives are often called reversible melt adhesives in the art. National Starch and Chemical Co. will also supply suitable solvent based adhesives.

If a thermoplastic adhesive is employed, that needs to be heated, then preferably the porous polymeric material and/or backing layer is cooled after the adhesive has been applied to the porous polymeric material. Cooling will preferably be effected after the adhesive has been allowed to pass through at least part of the porous polymeric material.

The cooling may be effected by a cooling device. This may comprise means for blowing cold air (or any other suitable fluid) onto the adhesive laminate. However, it is preferred that the adhesive laminate is cooled by direct contact. Thus the cooling device may have a cooling surface which will suitably be in contact with the backing layer. The cooling surface will suitably comprise a metal surface. Preferably the cooling surface will be curved away from the backing layer, and the backing layer may follow the contours or shape of at least part of the cooling surface. Thus preferably the cooling device comprises a roller, that can be cooled e.g. by fluid, the outer surface forming the cooling surface. If fluid cooled, a specially adapted bearing to allow the passage of fluid to and from the roller can be employed.

The cooling surface can be cooled by a coolant (such as dry ice) although a fluid, e.g. a flowing coolant, is preferred. This will suitably be water. The cooling surface will suitably be at a temperature of from 0 to 8, such as from 4 to 60C.

It will be appreciated that if a heated adhesive is being applied to the porous polymeric material then cooling of the adhesive laminate will be preferable if the hot adhesive is not to deform or even melt either of the backing layer or porous polymeric material. Thus, it is preferred that the time span from application of the adhesive (to the porous polymeric material) to cooling (such as by the cooling device) is from 0.1 to 0.3 seconds, such as from 0.15 to 0.25 seconds. Under most conditions a time span of no more than 0.4 second will be preferred if one is to avoid distortion of the backing layer.Here the time spans refer to the time elapsed for a particular reference point on either the backing layer or layer of porous-polymeric material to travel between appropriate parts of the apparatus conducting the various processes involved in the manufacture of the adhesive laminate, such as application of the adhesive and cooling.

Usually the speed of the backing layer and/or porous polymeric material (which will generally be the same, or similar) will be from 80 to 120 metres per minute (m/min), such as from 90 to 110 m/min. These figures are provided as an approximate guide and for most manufacturers a speed of less than 50 m/min will be a minimum for economic reasons.

Suitably the distance between the point at which the adhesive is applied (such as by the adhesive delivery device) and cooling (such as by the cooling device) will be from 0.15 to 0.45 metres, such as from 0.25 to 0.35 metres. Preferably the distances and time spans referred to will be with reference to the adhesive delivery device (such as the aperture, e.g. slot) and the cooling device (such as the cooling surface or roller).

The method of the present invention may additionally comprise cutting the adhesive laminate such as into one or more tapes or strips. The width of the adhesive laminate that can be accommodated will depend upon the dimensions and type of apparatus used, although for economic reasons it will be as wide as can be viably permitted. Thus suitably the adhesive laminate can initially be up to five, two or one metres in width, such as from 40 to 60 centimetres. Both the backing layer and layer of porous polymeric material will suitably have the same width, which will be the width of the adhesive laminate. Thus the adhesive laminate may be cut into one or more tapes or strips, each of which may be from 6 to 40 mm, such as from 10 to 18 mm, wide.

The method of the invention may additionally comprise providing a line of weakness in the adhesive laminate, such as a line of perforations. This may allow the laminate to be torn along this line. The line of weakness will preferably be parallel to one edge of the laminate. Suitably this line will be off-centre so that on folding of the laminate onto itself along the line of weakness an overlapping portion of the laminate, such as a strip, may be formed. Thus, this overlapping portion may be used to seal a bag. The line of weakness can be formed either by scoring, e.g. with a blade, either the backing material (but preferably) the porous polymeric material or by forming a line of perforations, for example by using a toothed circular blade.

The adhesive laminate, once made, can be wound onto a roll or cylinder. If the adhesive laminate is sufficiently narrow (such as in the form of a tape or strip) it can be wound to a bobbin. This means that the adhesive laminate can be wound onto a roll or cylinder during (preferably reciprocal) relative transverse movement between the (source of the) laminate and roll or cylinder. Such transverse movement is preferably along the axis of the cylinder. Although either the laminate (or source of it) or the-roll or cylinder can be moved, to effect relative transverse motion, the former is preferred.

The side of the porous polymeric material that is at least partially coated with the adhesive and is exposed (that is to say, the second side or the side other than that adhered to the backing layer, the first side) will thus assist in winding of the adhesive laminate onto a roll or cylinder. This will allow the adhesive laminate to be sold to a bag manufacturer in the form of a roll (or preferably a bobbin) for use in manufacturing sealable bags.

The method of the present invention may additionally comprise removing a portion of the porous polymeric material. This will preferably involve removal of part of the porous polymeric material from the backing layer, so that, for example, the backing layer has a greater width than the porous polymeric material. Usually a portion of the porous polymeric material removed will be along one edge of the adhesive laminate, and so the removed portion may be in the form of a strip. Thus a strip of porous polymeric material, parallel to the edge of the adhesive laminate, may be removed from the backing layer. This may thus form an overlapping portion or strip of the backing layer which may be desirable for the user of the bag, since the overlapping portion of the backing layer may assist in its removal from the porous polymeric material (often termed fingerlift in the art).

Such overlapping portions may be provided along one, or preferably both, edges of the adhesive laminate.

To remove a portion of the porous polymeric material (such as in the form of a strip) the porous polymeric material should first be cut. This may achieved by using a blade. Such a blade may be a fixed blade or may be mounted on a roller, so for example the blade is a circular blade, suitably perpendicular to the axis of rotation of the roller. If a circular blade is employed, it may be made to rotate in a direction opposite to the movement of the adhesive laminate (a contra-rotating blade). Suitably the blade will have a depth, such as protrude or upstand (e.g. from the rolier) by a distance which is greater than the thickness of the porous polymeric material, such as from 2 to 3 mm.

The portion of porous polymeric material to be removed may then be lifted off or pulled away from the backing material by a finger or blade. Such a portion will suitably be a strip that is from 3 to 15 mm, such as from 3 to 12 mm, wide.

A second aspect of the present invention relates to an adhesive laminate comprising a backing layer, which comprises a plastic material, adhered to a layer of porous polymeric material which is at least partially coated on both sides with an adhesive.

The adhesive laminate may be made by the method of the first aspect. Preferred features and characteristics of the second aspect are as for the first aspect mutatis mutandis.

As has been discussed, the adhesive laminate can be used in the manufacture of bags, and therefore a third aspect relates to a method of manufacturing a sealable bag, the method comprising: (a) applying an adhesive laminate to a layer of plastics material, the laminate comprising a backing layer, which comprises a plastics material, that is adhered to a layer of porous polymeric material which is at least partially coated on both sides with an adhesive, so that a side of the porous polymeric material, other than the side adhered to the backing layer, is adhered to the plastics material; and (b) forming a bag from the layer of plastics material; the adhesive laminate positioned so that it can be used to seal the bag once at least a portion of (and preferably all of) the backing layer has been removed from the porous polymeric material.

Stages (a) and (b) are interchangeable. The adhesive laminate can be applied to the layer of plastics material before or after the bag is formed. However, in preferred embodiments the adhesive laminate is applied before the bag is formed.

The bag will suitably be formed by sealing appropriate parts of the layer of plastics material. This may be achieved by using an adhesive although it is preferred to use heat, so that sides of the bag are formed by heat sealing. This may be achieved using a heating element.

The method may additionally comprise either separating one bag from an adjacent bag (such as by cutting, for example using a guillotine) or by providing a line of weakness between adjacent bags (for example by forming a line of perforations). This line of weakness may allow individual bags to be separated from a neighbouring bag, for example by tearing.

Preferably the line of weakness will also be formed at the same time as sealing, such as heat sealing. Thus the stage of forming the bag by heat sealing may simultaneously provide a line of weakness between the bags (such as by providing perforations). This may be achieved by a "hot wire" technique. This may involve use of a heated blade or contact with a heated element, suitably provided on a roller, for example along a line parallel to the axis of rotation of the roller.

Alternatively the heated element can be mounted on a blade, or a reciprocating platten. The means for forming a line of weakness (e.g. perforations) may also be mounted on such a block or reciprocating platten. Such means may comprise a serrated blade or a line of teeth.

Preferably the bag will be formed by heat, and at the same time one may also provide the line of weakness between adjacent bags. This process may also serve to cut the adhesive laminate. This of course can be achieved if the adhesive laminate is first applied to the layer of plastics material before the bag is formed.

Suitably before stage (a) or (b) the layer of plastics material is folded, so that an upper and lower layer of plastics material is obtained. The bag may then be easily formed by heat-sealing the upper and lower layers together. This may simultaneously occur with providing a line of weakness between neighbouring bags. Preferably the layer of plastics material is folded so that either the upper or lower layer overlaps. Thus, it is preferred that an overlapping portion is formed (such as a flap), which will usually be in the form of a strip. Although the adhesive laminate can be applied near a lip or opening of the bag (so that the overlapping portion can be folded down onto the laminate), preferably it is to the overlapping portion that the adhesive laminate is applied. Preferably the lower layer will be provided with the overlapping portion.This will generally be near the edge of the sheet of plastics material, and parallel to the edge of the plastics material. The bags can thus be sealed by removing at least part of the backing layer from the porous polymeric material thus exposing adhesive (on the porous polymeric material, and by folding over the overlapping portion (e.g. flap) to thereby seal the bag.

In one embodiment the laminate has a line of weakness provided in it, preferably off-centre and parallel to an edge, and can be applied to an overlapping portion of the plastics material. The line of weakness is suitably formed in the porous polymeric material, such as a line of perforations, and the laminate is applied to the overlapping portion so that the line of weakness is closer to the lip or opening of the bag than to a distal edge of the overlapping portion. On removal of at least part of the backing layer, the overlapping portion can be folded towards the lip or opening of the bag along the line of weakness provided in the laminate. The adhesive being exposed, the laminate can be folded onto itself to not only adhere to itself but to thereby form an overlapping portion of the laminate which can adhere to the lip or opening of the bag.For example, the laminate can be applied to an overlapping portion of the lower layer of the plastics material and removal of the backing layer and folding of the said overlapping portion causes the adhesive on the porous polymeric material to adhere to the upper layer of the plastics material. This may result in a fluid-tight seal, that is to say, a watertight or air-tight seal. This is exemplified in Figure 2.

A fourth aspect of the present invention relates to a sealable bag comprising a plastics material, the bag being provided with an adhesive laminate of the second aspect located such that the bag can be sealed after removal of at least a portion of (and preferably all of) the backing layer from the porous polymeric material.

Suitably the laminate will be provided near to an opening of the bag, such as on an outside of the bag, e.g. near a lip of the bag, or, preferably on an overlapping portion of the plastics material that may be folded to seal the bag (e.g. a flap).

The laminate may be provided with a line of weakness, e.g. a line of perforations along which it can be folded, suitably onto itself. The line of weakness will suitably be off-centre such that the line is closer to an edge of the laminate near the lip or opening of the bag. Thus, on removal of the backing layer and folding the overlapping portion (e.g. flap) along the line of weakness the exposed adhesive on the porous polymeric material will not only adhere the material (and thereby the overlapping portion) to itself but also to the outside of the bag near the lip or opening. This may create a fluid-tight seal that may be used for containing medical equipment or chemicals in a sterile environment.

Other preferred features and characteristics of the third and fourth aspects are as for the first and second aspect mutatis mutandis.

The invention will now be described by way of example with reference to the accompanying drawings and Examples which are provided to illustrate the invention and which are not to be construed as being limiting.

In the drawings: Figure 1 is a schematic view of an apparatus for manufacturing an adhesive laminate according to the present invention; and Figure 2 is a schematic section of a sealable bag of the present invention.

EXAMPLE 1 - Manufacture of Adhesive Laminate A coating machine 35 as shown in Figure 1 was employed that had means to support a roll of backing layer material 22 (liner) which was HDPE 50 im thick, siliconised on both sides, obtained from NMC Silicones Limited, Broomhill Road, Brislington, Bristol, BS4 5RW, England. Also provided was a roll of porous polymeric material 23 manufactured by James River Corporation.

This is sold under the trade marks CEREX 30TM and PBN-IITM by its marketing Department, Fiberweld, Greenville, SC, 29607 U.S.A This is spun-bonded nylon 6,6 woven material with randomly directed fibres. A material 145 pm thick, sold under reference number CO1OL2N was used.

The HDPE liner 22 and nylon material 23 were brought together between a slot die in an adhesive reservoir 25 and a roller 27 rotating at a similar velocity to the sheets of material at 100 m/min. A paper leader was first used to pull the sheets of material between the slot die and roller 27. The slot was the same width as both the liner 21 and nylon porous polymeric material 23 (50 cm wide) and adhesive was applied to the nylon material 23 at a temperature of 1500C through the slot.

Adhesive was forced through the slot at a pressure of 5 to 6 bar and heated prior to application through a heated hose connecting the reservoir and slot die. The adhesive employed was obtained from H.B. Fuller UK Ltd. and was a thermoplastic pressure sensitive adhesive, employing a styrene/isoprene/ styrene block copolymer. The adhesive, under pressure, was forced through the nylon material 23 to coat both sides of the nylon material 23 and thereby bond the nylon material 23 to the liner 22. Once the nylon material 23 and the liner 22 had been bonded together to form an adhesive laminate 29 this was by passing the liner over a cooled rotating metal roller 31 cooled by flowing water at 50C. The distance from the slot to the cooling surface was 30 cm.

The resultant adhesive laminate 29 was then cut into tapes or strips at from 10 to 18 mm wide and wound onto a bobbin 33.

EXAMPLE 2 - Manufacture of Sealable Bags The adhesive laminate 29 made in Example 1 was used in the manufacture of polythene bags. Apparatus was set up to include the coating machine 35 used in Example 1 together with means to support a roll of polythene material which was folded over onto itself once the material has been taken off the roll. This formed an upper and lower layer of the material, with a small overlapping portion on the bottom layer. The adhesive laminate was applied to the overlapping portion using the side of the nylon material coated with adhesive other than that bonded to the liner. The folded polythene sheet was then heat cut by a hot wire technique to form the individual bags. The adhesive laminate was simultaneously cut by the heat. The finished bags were then collected into a suitable container.

EXAMPLE 3 - Manufacture of Air-Tisht Sealable Baas An adhesive laminate made in Example 1 was used except that during the manufacturing process a line of perforations had been provided in the layer of nylon porous polymeric material parallel to one edge of the material but off-centre. The line of perforations allowed easier folding of the nylon material and were produced by using a circular rotating toothed blade.

The method of making polythene bags and applying the adhesive laminate of Example 2 was followed.

Figure 2 is a section of the sealable bag formed. The bag 1 formed of polythene material has an upper layer 3 and a lower layer 5 which overlaps to form an overlapping portion 7 in the form of a flap. The adhesive laminate 9 is applied to the overlapping portion 7, comprising a backing layer 11 which is the liner and a layer of porous polymeric material 13 coated on both sides with an adhesive. The porous polymeric material has a line of perforations 15. The backing layer 11 is of greater width than the porous polymeric material 13 thereby providing an overlapping portion which can ease removal of the backing layer 11 from the porous polymeric material 13 (often called a fingerlift portion). Once adhesive has been exposed on the porous polymeric material 13 the overlapping portion 7 is folded over in the direction of the arrow towards the upper layer 3 along the line of perforations 15. The layer of porous polymeric material 13 is therefore divided into a first section 17 which is close to a lip 19 of the bag 1 near an opening of the bag and a second section 21. Thus the second section 21 will adhere to the first section 17 and also to the upper layer 3 so forming an air-tight seal.

Claims

1. A method of manufacturing an adhesive laminate the method comprising contacting a backing layer which comprises a plastics material with a layer of porous polymeric material and allowing adhesive to pass through at least part of the layer of- porous polymeric material so that the porous polymeric material is at least partially coated on both sides with the adhesive so that one side adheres to the backing layer.

2. A method as claimed in claim 1 wherein the adhesive is forced under pressure through at least part of the porous polymeric material.

3. A method as claimed in claim S or 2 wherein the layer is in the form of a sheet, film, strip or tape.

4. A method as claimed in any preceding claim wherein the porous polymeric material is a plastics material.

5. A method as claimed in any preceding claim wherein the porous polymeric material is an open weave and/or non-woven material.

6. A method as claimed in any preceding claim wherein the porous polymeric material comprises randomly directed fibres.

7. A method as claimed in any preceding claim wherein the porous polymeric material comprises nylon.

8. A method as claimed in any preceding claim wherein the adhesive is a thermoplastic and/or pressure sensitive adhesive.

9. A method as claimed in any preceding claim wherein the adhesive is a styrene/isoprene/styrene block copolymer.

10. A method as claimed in any preceding claim wherein the adhesive is applied to the porous polymeric material at a temperature of from 130 to 1800C.

11. A method as claimed in any preceding claim wherein the adhesive is applied at a pressure of from 5 to 6 bar.

12. A method as claimed in any preceding claim wherein the adhesive is applied by an adhesive delivery device.

13. A method as claimed in any preceding claim wherein the adhesive is applied through a slot.

14. A method as claimed in claim 12 or 13 wherein the adhesive delivery device comprises a reservoir which leads to a slot.

15. A method as claimed in any preceding claim wherein the backing material comprises polyethylene and/or polypropylene.

16. A method as claimed in any preceding claim wherein the backing material comprises HDPE and/or LDPE.

17. A method as claimed in any preceding claim wherein the backing layer is coated with a friction reducing material.

18. A method as claimed in claim 17 wherein the friction reducing material comprises silicone.

19. A method as claimed in any preceding claim wherein the adhesive laminate is cooled after the adhesive has been applied to the porous polymeric material.

20. A method as claimed in claim 19 wherein cooling is achieved by contacting the backing layer with a cooling surface.

21. A method as claimed in claim 19 or 20 wherein the time from application of the adhesive to cooling is from 0.1 to 0.3 seconds.

22. A method as claimed in any preceding claim additionally comprising cutting the adhesive laminate into one or more tapes or strips.

23. A method as claimed in claim 22 additionally comprising winding the adhesive laminate onto a bobbin.

24. An adhesive laminate comprising a backing layer, which comprises a plastics material, adhered to a layer of porous polymeric material which is at least partially coated on both sides with an adhesive.

25. A laminate as claimed in claim 24 prepared by a method according to any of claims 1 to 23.

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26. A method of manufacturing a sealable bag, the method comprising: (a) applying an adhesive laminate to a layer of plastics material, the laminate comprising a backing layer, which comprises a plastics material, adhered to a layer of porous polymeric material which is at least partially coated on both sides with an adhesive, so that a side of the porous polymeric material other than the side adhered to the backing layer, is adhered to the-plastics material; and (b) forming a bag from the layer of plastics material; the adhesive laminate being positioned so that it can be used to seal the bag once at least a portion of the backing layer has been removed from the porous polymeric material.

27. A method as claimed in claim 26 wherein the adhesive laminate is prepared according to a method of any of claims 1 to 23 or is according to any of claims 24 or 25.

28. A method as claimed in claim 26 or 27 wherein the bag is formed by folding the layer of plastics material and heat-sealing.

29. A method as claimed in any of claims 26 to 28 wherein a line of weakness separating neighbouring bags is formed.

30. A method as claimed in claim 29 wherein the folded layer of plastics mateiial has an upper and lower layer, one layer having an overlapping portion to which the adhesive laminate is applied.

31. A sealable bag comprising a plastics material, the bag having an adhesive laminate comprising a backing layer, which comprises a plastics material, adhered to a layer of porous polymeric material which is at least partially coated on both sides with an adhesive, the laminate being located such that the bag can be sealed after removal of at least a portion of the backing layer from the porous polymeric material.

32. A bag as claimed in claim 31 which has been manufactured according to the method as claimed in any of claims 26 to 30.

33. An adhesive laminate, or a method of manufacturing an adhesive laminate, specifically as herein described with reference to the accompanying Examples.

34. A method of manufacturing a sealable bag substantially as herein described with reference to the accompanying Examples.