SECURITY BAG SEALED BY SILICONE RUBBER ADHESIVE

Abstract: A bag is formed of sheet material and has an opening (8) to enable access to be gained to the interior of the bag. The bag includes a closure member (7) for superposition over the opening to close the opening. The bag includes an adhesive (9) formed of a cured silicone rubber-based composition for securing the closure member over the opening.

Description: SECURITY BAG SEALED BY SILICONE RUBBER ADHESIVE This invention relates to bags and is concerned with security bags which exhibit a visible indication if an attempt has been made to gain access to the contents of the bag. It is known for banking establishments and the like to use bags for transmitting specified sums of money from one department to another. The system operated by the establishment is ordinarily such that it can readily ascertain if such a bag is stolen in transit. Ordinarily, however, it is not readily possible to ascertain whether the bag has been opened in transit and then re-sealed after some of the money has been removed. With a view to overcoming this problem, tamper- evident bags have been devised wherein any attempt to gain access to the interior of the bag is visibly apparent. Typically, such bags are formed of sheet material including an opening giving access to the interior of the bag and the arrangement is such that the opening can be sealed by a closure member adhered to the opening-defining portions of the sheet material by means of a high tack adhesive. Conventionally, such adhesives are hot melt or acrylic systems and although these are generally satisfactory, they have a limited working temperature because of their thermoplastic character. Thus, it is possible, in some cases, for the bag to be opened and re-sealed without evidence of tampering by the use of elevated temperature. Also, such adhesives tend to lose their tackiness at low temperatures. Thus, it is sometimes possible to gain entry to the bag without entry being evident by subjecting the bag to low temperature. Also, in some cases, high ambient temperatures in some countries may exceed the useful working temperature of the adhesive. It is an object of the present invention to provide a bag which is tamper-evident and which retains its tamper-evident properties at extremes of heat or cold. According to the present invention there is provided a bag formed of sheet material and having an opening to enable access to be gained to the interior of the bag, the bag including a closure member for superposition over the opening to close the opening and an adhesive formed of a cured silicone rubber-based composition for securing the closure member over the opening. Examples of silicone rubbers suitable for use in the adhesive compositions used in accordance with the invention areExamples of silicone rubbers suitable for use in the adhesive compositions used in accordance with the invention are dimethyl silicone rubbers. Typically, these include a plurality of structural units of the formula CH 3 — Si 0— I CH 3 Particularly suitable silicone rubbers are those known under the designation 280A, 282, and Q2-7406 of Dow Corning Corporation. These are silicone pressure sensitive adhesives which are ordinarily supplied in solution in xylene. The adhesive solution may be directly applied to the closure member or to the opening-defining portions of the bag so that the adhesive is located on the closure member or the opening-defining portions, respectively. Alternatively the adhesive solution may be coated on to substrate to form a tape for securing to the closure member or to the opening-defining portions of the bag. After application of the adhesive solution, the coating is dried to remove the solvent and leave a tacky layer of the adhesive which will slowly cure in air. The rate of cure can be increased by incorporating a catalyst such as a peroxide or by subjecting the adhesive to elevated temperature. The degree of curing can be varied as desired but, even when fully cured, the adhesive retains its tackiness and, more importantly, it retains its tackiness at temperatures of from -65 C to +90 C. Ordinarily, it is not necessary to apply a primer prior to the application of the adhesive solution in the case where it is being applied to a polyester material. However, a primer may be desirable in the case where the adhesive solution is being applied to a polyethylene or polypropylene. For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:- Fig. 1 is a diagrammatic front view of an open security bag in accordance with a first embodiment of the present invention, Fig. 2 is a diagrammatic section through the bag of Figure 1 on an increased scale, Fig. 3 is a diagrammatic section showing the bag of Figure 2 when the bag is closed, Fig. 4 is a diagrammatic section through an open security bag in accordance with a second embodiment of the present invention, Fig. 5 is a diagrammatic section showing the bag of Figure 4 when it is closed. Fig. 6 is a diagrammatic section through an open security bag in accordance with a third embodiment of the present invention, Fig. 7 is a diagrammatic section through the security bag of Figure 6 in its closed condition. Fig. 8 is a diagrammatic section through an open security bag in accordance with a fourth embodiment of the present invention, and Figure 9 is a diagrammatic section through the bag of Figure 8 in its closed condition. Referring now to Figures 1 and 2, the bag is formed from a single strip 1 of flexible thermoplastic sheet material such as polyethylene or polypropylene which is folded laterally along a fold line 2 to form a first portion 3 and a second portion 4. The thermoplastic sheet material is preferably transparent, partially transparent, or a combination of opaque and transparent so as to make it easier to see the evidence of tampering. The folded portions 3 and 4 are heat welded to each other in zone 5 which extends parallel with and close to each of the longitudinal and each of the lateral edges of the portions to produce an envelope-like bag 6 wherein the second portion 4 is longer than the first portion 3 and has a part in the form of an integral flap 7 forming a closure member. At an end region of the bag 6 closer to the closure member 7 an opening line in the form of slit 8 extends across the first portion 3 terminating at each end at the weld zone 5. The slit 8 provides access to the interior of the bag 6. A 55% xylene solution of silicone rubber adhesive (Dow Corning Q2-7406) is applied across the full width of a part of the flap 7 and dried to remove the xylene to leave a band 9 of fully or partially cured high-tack silicone rubber pressure sensitive adhesive on the flap 7. Applied over the top of the adhesive band 9 is a releasable cover strip 10, (for example formed of corrugated PVC tape) which is somewhat wider than the band 9 so as to provide finger-release edges. A band 11 of security printing, which may for example be micro security printing, is applied across the outer face of portion 3. The band 11 extends across the full width of the portion 3 at such a position longitudinally thereof as to be immediately adjacent the adhesive band 9 when the flap 7 has been brought into its sealing position over the slit 8. The security printing is suitably applied in two inks, one comprising a hydrocarbon base and one comprising a hydrocarbon-free base. Thus, should an attempt be made to release the adhesive bond at the band 9 using a chemical solvent, this fact will be evidenced by the disturbance of at least one of the inks by the solvent. A further security feature is provided by virtue of the weld zone 5 being embossed over its full extent so that it is made impossible to gain access to the interior of the bag 6 across the zone 5 and then to re- seal the bag without the fact being made visually discernible by the consequent distortion of the form of the embossment. A line of perforations (not shown) is preferably provided across the flap 7 centrally of the adhesive band 9 so that any attempt to lift the flap 7 from the bag 6 is likely to be evidenced by tearing of the flap 7 at the line of perforations. Also, a line of perforations 13 is provided across the flap 7 to provide a tear off receipt strip 12 which can be detached by tearing along the line of perforations 13. In use of the security bag, the items to be held in the bag are introduced into it through the slit 8, the cover strip 10 is removed from the adhesive band 9 and the flap 7 is folded over onto the portion 3 with the fold line being close to the laterally extending part of the weld zone 5. The disposition of the adhesive band 9 relative to the fold line for the flap 7 is such that when the flap 7 is brought down onto the portion 3, the part of the flap 7 carrying the adhesive band 9 straddles the slit 8 so that the slit 8 is completely overlain by said part of the flap 7 and the band 9 as shown in Figure 3. Thus, as well as the flap 7 being bonded to the portion 3 in a tamper-evident manner, the slit 8 is completely sealed and there is no access opening whatsoever to the interior of the bag 6. Because of the nature of the silicone rubber adhesive used, it is not possible to lift the flap 7 from the opening, remove the contents of the bag 6, and reseal the flap 7 over the opening without this being evident even if the bag is subjected to extremes of hot and cold temperatures. Referring now to Figures 4 and 5, parts corresponding to parts of Figures 1 to 3 are denoted by like reference numerals. In this case, instead of the adhesive band 9 being directly applied to the flap 7, it is applied to a substrate 15 so as to form a tape 16 which is secured to the flap 7 by a bead of hot melt adhesive 14. The substrate 15 may be, for example, a cellulose film, a polypropylene film or polyester film. In this case, the tape 16 constitutes the closure member and, in use, the cover strip 10 is removed and the tape 16 is folded over the slit 8 to seal the opening as shown in Figure 5. Referring now to Figures 6 and 7, parts corresponding to parts of Figures 1 to 3 are denoted by like reference numerals. In this case, the adhesive 9 is applied to both sides of the substrate 15 to form a double sided tape 17 having adhesive bands 9 at opposite sides. One of the adhesive bands is used to adhere the tape 17 to the flap 7 and then, after removal of the cover strip 10, the other adhesive band is applied over the slit 8 to seal the bag as shown in Figure 7. Referring now to Figures 8 and 9 parts corresponding to parts of Figures 1 to 3 are denoted by like reference numerals. In this case, the silicone rubber based adhesive is present on the portion 3 in bands 9 at each side of the slit 8 and covered by means of cover strip 10. In this case, in use of the bag 6, the cover strips 10 are removed and the flap 7 is superposed over the adhesive bands 9 to close the bag.

Claims: Claims : 1. A bag formed of sheet material and having an opening (8) to enable access to be gained to the interior of the bag, the bag including a closure member (7) for superposition over the opening to close the opening and an adhesive (9) formed of a cured silicone rubber-based composition for securing the closure member over the opening. 2. A bag as claimed in claim 1 wherein the silicone rubber is a dimethyl silicone rubber. 3. A bag as claimed in claim 2 wherein the silicone rubber includes a plurality of structural units of the formula CH 3 Si 0— I CH 3 4. A bag as claimed in any one of claims 1 to 3 wherein the adhesive is located on the closure member (7). 5. A bag as claimed in any one of claims 1 to 4 wherein the adhesive is located on the opening-defining portions (3) of the bag. 6. A bag as claimed in any one of the preceding claims wherein the adhesive is present as a coating on a substrate (15) to form a tape (16) (17). 7. A bag as claimed in any one of the preceding claims wherein the opening is in the form of a slit in the sheet material.

Inventors: LIVESLEY DAVID JOHN, TODMAN VICTOR, LIVESLEY, DAVID, JOHN, TODMAN, VICTOR
Applicants: LAWSON MARDON GROUP UK LTD, LAWSON MARDON GROUP UK LIMITED
Application year: 1991
Main classification: B65D33
IPC codes: B65D33