GB1570782A

GB1570782A - Methods of forming self-sealing bags or envelopes

Info

Publication number: GB1570782A
Application number: GB13392/76A
Authority: GB
Original assignee: Metal Closures Venue Packaging Ltd
Current assignee: Metal Closures Venue Packaging Ltd
Priority date: 1977-03-25
Filing date: 1977-03-25
Publication date: 1980-07-09
Also published as: IL51770A; IL51770A0

Description

(54) IMPROVEMENTS IN OR RELATING TO METHODS OF FORMING SELF-SEALING BAGS OR ENVELOPES (71) We, METAL CLOSURES VENUS PACKAGING LIMITED (formerley known as VENUS PACKAGING LIMITED). A British Company of Lower Middleton Street, Ilkeston, Nottingham do hereby declare the invention for which we pray that a Patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention is for improvements in or relating to self-seal bags or envelopes and is particularly but not exclusively concerned with providing an improved bag and method of forming a bag which has self-seal facilities for a flap to close the bag and which flap may be opened and resealed a number of times. Self-seal bags particularly for synthetic plastic material are known but suffer from a number of disadvantages.The invention also includes self-seal bags in which the bag can only be opened by damaging the seal or the material forming the bag i.e. non re-sealable bags.

One such known construction consists of a bag which has a flap and on the interior of the flap is located a film which is adhesive on both sides. One side is adhered to the interior of the flap and the other side is normally masked by a paper strip which has a release coating thereon such as a silicone coating. In the manufacture of bags of this kind the disadvantage exists that the paper masking strip cannot be cut by a hot knife guillotine which is customary for sealing the edges and forming the sides of a synthetic plastic bag.

The result is that the flap for such a bag has to have the corners chamfered and this has to be cut by a blade guillotine; an operation additional to the hot knife guillotine for forming the bag.

In other known constructions a hot melt adhesive is applied to the flap of a bag and a release strip of material which may be convenient material maks the hot melt adhesive, but the disadvantage with this arrangement is that hot melt adhesives of the kind hitherto known tend to form a permanent bond both with the bag and with the flap so that on sealing a bag with this arrangement the flap is not easily re-opened and if it is there has been a transfer of adhesive from the fap to the bag. Furthermore the hot melt adhesive used in this kind of process tends to cure so that after a period of time the bond becomes more and more permanent.

In yet another arrangement a bag made of synthetic plastic material has a flap with holes formed therein on one side. An adhesive tape of known kind is secured to outside of the flap so that through the holes forming the flap the adhesive on that tape appears on the other side of the flap.

There is a release tape usually silicone tape masking the adhesive appearing through the holes.

When it is desired to use the bag and to form the self-sealing effect the release tape is removed and the flap pressed down on to the bag. Again the disadvantage of this is that it is necessary to chamfer the corners to the flap because the nature of the tapes makes it impossible to cut them with a hot knife guillotine.

The present invention provides a method of forming a self-sealing bag or envelope which consists in feeding a folded sheet of synthetic plastics material together with a masking tape, formed of a material which has a higher melting point than the material of the folded sheet and which tape has a coating of silicone and to which coating has been applied permanently tacky resin adhesive, to a roller to force the tape with the resin on to the synthetic plastics material, thereby sandwiching the adhesive between the synthetic plastics material and the tape. Thereafter the synthetic plastics material with the tape applied thereto may be fed to a hot knife guillotine to sever both the synthetic plastics material and the tape.

In order that the present invention may be more readily understood reference is now made to the accompanying drawings in which: Figure 1 - is a diagrammatic illustration of a preferred method of forming a bag according to the present invention; Figure 2 - is a perspective view of a bag when formed according to the present invention; Figure 3 - is a perspective view of a machine for performing the method according to the present invention.

Diagrammatically in Figure 1 a supply of synethic plastic material is shown on a roll 1 and is fed as a web 2 to a roller 3.

In practice the roll 1 will normally be printed and will be taken from a roll and fed to a folding station so that web 2 consists of a single folded sheet of synthetic plastics material which when cut at either side will form a bag with a flap.

A trough of appropriate glue 8 has a tape 10 from a supply spool 7 passing over it. The glue in the trough 8 is acrylic based resin such as that supplied by National Adhesives Limited under the code AD80/1000. An alternative glue is AD/30/1197 also supplied by National Adhesives Limited. These are a permanently tacky adhesive in a spirit solvent so that when the spirit is removed the acrylic resin remains which retains its tackyness almost permanently and does not transfer from one surface to another.

The tape 10 is preferably a high density polythene. A high density polythene is used in order to prevent fusion of the tape when the web and tape pass through the hot knife guillotine to sever the lengths of the web 2 and to form them into bags.

The high density polythene tape does not fuse to the bag at the temperature at which the hot knife guillotine operates. A high density polythene has higher melting and fusing temperature than the synthetic plastics material of which the bag itself will be made. Desirably the bag will either be of polypropylene or polyethylene material and in particularly bags made of polypropylene having a high optical property such as polypropylene made from a resin which produces a particularly soft effect of the plastic material is desirable.

The high density polythene strip 10 will have been coated with a silicone release surface. The tape 10 after being coated with the solvent base tacky adhesive then passes along an extended path in order to evaporate the solvent base. It may for example pass beneath a cold air duct 9 and beneath a hot element 11 or in front of a heated stream of air issuing from a nozzle 15 (Fig 3), or around any such other combinations in order to evaporate the solvent from the adhesive. It is essential to the illustrated method that when the tape with the adhesive is presented to the web 2 at the roll 3 that the solvent shall have been evaporated from the adhesive.

The tape 10 is then pressed on to the web 2 and the web and tape then pass around rollers 4 and are presented to a hot knife guillotine station 5 which forms the web into discrete bags forming a stack 6.

In figure 2 the formed bag is illustrated which consists of a bag portion proper 12 with a turnover flap 13 and with the self adhesive component consisting of the tage 10 which is masking the permanently tacky adhesive 14 applied to the body of the bags. In order to use the bag in the mask consisting of the tape 10 is peeled off thus exposing the adhesive 14 so that when the flap 13 is turned over it is securely held by the permanently tacky adhesive 14 and the mouth of the bag is sealed.

It is a relatively simple matter to open the bag by peeling back the flap 13 and opening the bag and repeated sealing and opening of the bag is possible. In figure 3 the stream of hot air issuing from nozzle 15 is heated by a heater 17. The tape roll 7 is driven by a variable speed motor 16.

A machine frame 19 supports the rolls 3 and a support structure 20 for the tape roll and adhesive dispenser.

The operation of the machine is controlled by an on/off switch 18.

In a modified construction the adhesive in dispenser 18 is one which forms a permanent bond between the flap 13 and bag 12 so that the bag can only be opened by destroying part of the bag or flap. Such a bag is useful for security purposes to prevent shop lifting. The bag will be made in substantially the same manner and once the desired article has been inserted the flap is sealed on to the bag. This prevents a customer from opening a releasable type bag and inserting additional and non paid for articles therem. Any attempt to open a non resealable bag is readily apparent. The adhesive used to form a permanent bond is also a permanently tack adhesive but is one which has a degree of tackiness in excess of the sheer strength of the materials between which the adhesive is located so that as the materials (i.e. the bag glap and the bag) are pulled apart those materials are damaged i.e. torn or distorted so that it is not possible to re-seal the flap to the bag.

A suitable adhesive to form such a permanently sealed bag such as 089-1017, is suppled by the National Adhesives Limited.

It will be appreciated that with the present invention it is not necessary to chamfer the corners of the flap or to use any of the other more complicated processes of known self sealing bags which are formed of synthetic plastics material.

It is thought that the present invention provides both a simple and useful contribution to the art of self sealing bags formed of synthetic plastics material.

WHAT WE CLAIM IS: 1. A method of forming a self-sealing bag or envelope which consists in feeding a folded sheet of synthetic plastics material together with a masking tape, formed of a material which has a higher melting point than the material of the folded sheet and which tape has a coating of silicone and to which coating has been applied permanently tacky resin adhesive, to a roller to force the tape with the resin on to the synthetic plastics material, thereby sandwiching the adhesive between the synthetic plastics material and the tape.

2. A method according to claim 1 which further consists in feeding the synthetic plastics material with the tape applied thereto to a hot knife guillotine to sever both the tape and the synthetic plastics material.

3. A method according to claims 1 or 2 in which the tape is of high density polythene material.

4. A method according to any of the preceeding claims in which the adhesive is a permanently tacky acrylic based resin.

5. A method according to any of the claims 1 to 3 in which the adhesive has a degree of tackiness in excess of the sheer strength of the material of the folded sheet.

6. A method according to any of the preceeding claims in which the tape is fed to an adhesive dispenser thereafter the tape is passed beneath a stream of cold and hot air to evaporate solvent from said adhesive.

7. A method according to any of the preceeding claims in which the synthetic plastics material is polypropleyne having a high optical property.

8. A method of forming a self sealing bag substantially as described herein with reference to the accompanying drawings.

9. A self sealing bag made of synthetic plastics materials by a method according to any of the preceding claims.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. suppled by the National Adhesives Limited. It will be appreciated that with the present invention it is not necessary to chamfer the corners of the flap or to use any of the other more complicated processes of known self sealing bags which are formed of synthetic plastics material. It is thought that the present invention provides both a simple and useful contribution to the art of self sealing bags formed of synthetic plastics material. WHAT WE CLAIM IS:

1. A method of forming a self-sealing bag or envelope which consists in feeding a folded sheet of synthetic plastics material together with a masking tape, formed of a material which has a higher melting point than the material of the folded sheet and which tape has a coating of silicone and to which coating has been applied permanently tacky resin adhesive, to a roller to force the tape with the resin on to the synthetic plastics material, thereby sandwiching the adhesive between the synthetic plastics material and the tape.