Abstract:
There is provided a postage stamp construction formed of a plurality of postage stamps adhered to a currency sized release liner by an ooze resistant pressure sensitive adhesive which construction coated with a polymeric coating of the face of the stamp and the undersurface of the release liner and dispensable from an automatic teller machine.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 07/912,317 filed Jul. 13, 1992 now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention is directed to an array of self-adhesive postage stamps presented on a currency sized release liner to form an assembly that is dispensable from an automatic teller machine or ATM. 
     BACKGROUND OF THE INVENTION 
     Various postage services have determined that it would be convenient to serve the public with means to purchase postage stamps through an automatic teller machine or ATM. 
     The postage stamp itself is a rather complex device. To meet current user demands it must be constructed of a face material or backing capable of accepting high quality printing of complex design stable under a variety of environmental conditions and provide an ink cancelable surface, on which cancellation ink dries rapidly, and which is removable from its adhesive to meet the needs of stamp collectors. In addition to being cancelable it should have at its surface means to detect the stamp so that a properly stamped envelope can be cancelled in an automated cancellation machine. 
     Traditionally, a postage stamp has been manufactured with a water soluble adhesive. It has been the desire of the postal service to, no only convert the adhesive to a self-adhesive or pressure sensitive adhesive, but to also present the postage stamps, as part of a laminate construction, which is dispensable from an automatic teller machine. 
     An automatic teller machine is designed to dispense currency. Any postage stamp construction to be dispensable must be dispensable as a laminate of an array of stamps serving as the facestock or backing, an interlayer of a self- or pressure-sensitive adhesive and a continuous release liner which protects the adhesive until the stamps are peeled therefrom and still provide performance characteristics which simulate the currency from which the ATM was configured to dispense. 
     No characteristic of the classic postage stamp can be sacrificed, yet the laminate must behave like currency in an automatic teller machine, otherwise the ATM will not dispense the product. 
     The first attempt at an automatic teller machine dispensable stamp construction consisted of an array of postage stamps formed of a taggant coated polyester laminated to an acrylic based adhesive which was in turn laminated to a polyester based release liner. This arrangement did not meet with public acceptance in the United States. The reason was attributed to the environmentally unfriendly nature of its polyester facestock. 
     A second version featured a 45 pound clear overcoated paper facestock and paper release liner. Because of several problems, including thickness of the construction and tendency of the adhesive to edge ooze, the second version could not be reliably dispensed from an automatic teller machine, and was predominantly sold over the counter. 
     The third version was identical to the second version but uncoated. Although sold through ATM&#39;s on a limited basis it did dispense reliably. 
     We have sought to overcome the problems of our prior constructions by providing a postage stamp construction which would reliably dispense from an ATM and offer high quality postage stamps that would meet the needs of stamp collectors. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided an automatic teller machine dispensable postage stamp construction which comprises a sheetlet consisting of an array of postage stamps adhered by an ooze resistant pressure sensitive adhesive to a continuous release liner of currency size. The stamps comprising paper facestock are of a paper weight of about 56 gm/m 2  having an upper and lower surface. The upper surface is printed with stamp graphics and coated having a surface coefficient of friction greater than 0.45. The coating preferably contains Taggant with an imprintable polymeric coating. The lower surface is coated with a water soluble primer. 
     The water soluble primer is in contact with ooze resistant pressure sensitive adhesive, which is in turn, in contact with the release liner which has an undercoating. Release liner paper weight is about 50 gms/m 2 . 
     In the preferred construction Taggant, a zinc orthosilicate, is contained in the top coat and provided in an amount sufficient to enable automatic location of a postage stamp on an envelope for cancellation purposed. Any other means of stamp detection can be used. 
     The overcoating and the undercoating of the paper serves to cooperate to stiffen the construction, to provide a quasi seal and reduce or eliminate changes in paper dimension with changes in humidity which results in a reduced tendency for edge ooze to occur. The relative frictional characteristics between slip of the surfaces undercoating further prevent the dispensing of multiple stamp sheetlets. Edge ooze is also controlled by choice of an adhesive which has a storage modulus greater than 10,000 dynes/cm 2  at a deformation rate of 10 -7  radian per second. 
     The overall thickness of the construction, and presently preferred construction for the United States market, is a sheetlet which is rectangular in shape, having a width of 2.61&#34;, a length of 6.125&#34; with each stamp having a width of 0.87&#34; and a length of 0.982&#34;. It will be understood that dimensions are controlled by the number of stamps contained on the sheetlet and local overall currency dimensions. 
     It is required that the assembly of multiple stamps on a release liner of currency size have a curl radius in any direction of less than 40 mm and an overall construction thickness between about 4.3 and about 5 mils, preferably about 4.6 mils for purposes of simulating United States currency. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the preferred stamp construction sheetlet of the instant invention. 
     FIG. 2 is a cross sectional exaggerated view of the stamp sheetlet construction of the instant invention. 
     FIG. 3 illustrates short axis curl. 
     FIG. 4 illustrates long axis curl. 
     FIG. 5 illustrates the gauge used to determine curl. 
    
    
     DETAILED DESCRIPTION 
     With reference to the Drawing FIG. 1 illustrates the presently preferred stamp sheetlet construction of the instant invention, while FIG. 2 depicts an exaggerated view of the cross section of the construction of FIG. 1. 
     With reference to FIGS. 1 and 2, the preferred stamp sheetlet construction 10 consists of a first array 12 of stamps 14, preferably 9 in number and a second array 16 of stamps 18 also, as shown 9 in number, with 3 stamps 14 of the first array and 3 stamps 18 of the second array 16 being contiguous to a removable bar 20. The removable bar 20 serves to assist until removed, in the sheetlet behaving like currency, as the region for a postal service to add identification information and is removable to allow the sheetlet to be folded in half to depict a booklet of stamps for insertion in a pocket or other holder. Prior to removal, the sheetlet provides in cooperation with the stamps but independent therein uniform opacity. This provides sheetlet of uniform opacity to enable dispensing from ATM machines which detect possible multiple dispenses. 
     In the construction, and with reference to FIGS. 3 and 4, as contemplated for a United States market, the stamp has a width or short axis of about 2.6&#34; and a length or long axis of 6.125&#34;. The width of each stamp in the direction of short axis is of 0.87&#34; and the length of the stamp in the direction of the long axis, which is also the machine direction is 0.982&#34;. 
     As will be understood stamp and sheetlet dimensions will differ depending on the currency size of the country in which the sheetlets are sold as may be the number and the manner in which the array of stamps are configured as the facestock or backing of the sheetlet laminate. 
     We have found, however, that for ATM machines which dispense according to caliper or thickness, as long as the caliper of the construction is more than one half of the caliper of local currency the ATM machine will dispense single sheetlets. For those ATM machines which dispense by opacity the machine will dispense a single sheetlet if it is less opaque than a double layer of local currency. Stamp construction for the U.S. Market having a caliper of 4.5mils have been properly dispensed from ATM machines designed to dispense the currency of Singapore having a caliper of 6 mils. 
     The detail elements of the construction are depicted in FIG. 2. With reference thereto, an individual stamp assembly consists of a top coat of a polymer or varnish coating 22, preferably an acrylic coat which can be applied in a water borne system and when dry is receptive to cancellation inks and which preferably contains means to enable identification of the location of a stamp on an envelope in an automatic cancellation machine to determine if the envelope can be automatically cancelled or rejected for hand cancellation. 
     The preferred overcoat or topcoat 22 is applied as an aqueous acrylic blend containing zinc orthosilicate (Taggant). The presently preferred coating is manufactured and sold by Environmental Ink and Coating Corporation of Morganton, N.C. The coating 22 is applied to a paper layer 24 of about 56 g/m 2  weight. The coatings are preferably the same but may differ provided the coefficient of friction requirements of this invention are satisfied. The undersurface of the paper 24 is a coating of a water soluble primer 26 which allows thorough soaking for a period of no more than 30 minutes separation of the stamp face from the adhesive for stamp collector purposes. The next layer in the construction is an ooze resistant pressure sensitive adhesive 28, preferably applied as an acrylic emulsion, but which may also be hot melt coated or applied from a solvent. 
     The ooze resistant pressure sensitive adhesive has a storage modulus of greater than about 10,000 dynes/cm 2  at a deformation rate of 10 -7  radians per second and is preferably an emulsion acrylic polymer as measured on a Rheometrics RDS-7700. The adhesive is in turn in contact with a release liner 30 having an undercoat 32 or surface of the same or different nature as the overcoat 22. Inclusion of the agent to enable stamp detection for cancellation purposes is not required. This is because the release liner is only a support for the stamps. It may, however, be printed with suitable graphics such as order forms, use instructions coupons and the like. 
     Requirement for the overcoat 22 and the undersurface 32 whether coated or not is that the surface have a static coefficient of friction, namely, the ratio of the force required to start moving a 193.3 gram sled divided by the weight of the sled across about 0.45, preferably between about 0.45 to about 0.7. This corresponds to 135 grams to a static face to imitate sled movement of about 87 grams to about 135 grams. It has been found that provided the friction requirements are met there should be at least a 25% difference between the coefficient of friction of the upper surface and the undersurface. This may be achieved by selection of paper or coatings as well as providing an irregular surface as by embossing or including in a coating fillers or the like. The difference of the coefficient of friction will greatly aid in ensuring single sheetlet dispersing. 
     Coating 22 and coating 32 or under also serve to stiffen the overall construction and aid in sealing the paper to prevent different expansion as between the stamps and release liner which encourages edge ooze of the adhesive. The rheological properties of the adhesive also serve to inhibit edge ooze. 
     Stamps are formed by die-cutting through coating 22, paper 24, primer 26, and adhesive 28 to release liner 30. The die-cuts are depicted as 34 in FIGS. 1 and 2. As indicated, varnish, however, must provide a coefficient of friction sufficiently high to enable single stamp sheetlet 10 to be dispensed by an automatic teller machine as opposed to dispensing multiple sheetlets 10. 
     To properly function in an automatic teller machine, with reference not to FIGS. 3, 4 and 5, the stamp sheetlet 10 must have, as manufactured, a curl no greater than 40 mm around either the short or the long axis. Curl is determined by holding a sheetlet 10 in the center of an edge and while the sheetlet hangs freely. The sheetlet is placed on the curl gauge depicted in FIG. 5 and if it has a curl greater than 40 mm it is rejected for purposed of dispensing in an automatic teller machine. Curl can be controlled by selection of materials of construction including coating as well as by using stagged slits in the release liner to reduce any tendency for curl, i.e. cause the release liner to conform to the stamps. 
     The overall caliper or thickness of the stamp sheetlet construction 10 is preferably between about 4.3 and 5 mils, preferably about 4.6 mils but in any event should be the design caliper thickness of the ATM which dispenses by caliper or design opacity for ATM machines which dispense by opacity. 
     Friction is determined by securing a sheetlet to a flat surface placing a 193.3 gram sled measuring 6&#34;×20.25&#34; on the sheetlet and pulling the sled with a force gauge to initiate movement of the sled over the sheetlet. The force measured is the force required to initiate movement of the sled over the sheetlet at a rate of 0.5 inch per minute. 
     For proper dispensing as measured by the static coefficient of friction of 0.45 to about 0.7 and coefficient of friction difference ensures preventing multiple dispensing of sheetlets from an automatic teller machine 120 with coefficient of friction differential between the preferred the upper and lower surfaces by about 25% or more. 
     The pressure sensitive adhesive employed in the instant invention is of a nature that it must be of sufficient tack at expected use temperatures and Table 1  below lists adhesive characteristics of the presently preferred adhesive. Such adhesive will enable initial repositionable bonding to a variety of paper substrates over the range expected use temperatures with bond growing to achieve a permanent bond of a level where the stamp cannot be removed from the paper substrate in the absence of paper tear. 
     
                       TABLE 1______________________________________Glass Transition (Tg), °C.Willaim&#39; Plasticity (WPI),       3.42mmMinimum ApplicationTemp,°F.                       10°C.                       -12Adhesive Coat Weight             24(g/m.sup.2)10 minute 90° Peel (pli)                  Initial   1.3 cl/Tear                  6 wk RT   1.5 cl, leg                  6 wk 70° C.                            1.7 TearLooptack (pli)         Initial   1.8 clean                  6 wk RT   2.4 clean                  6 wk 70° C.                            2.3 cleanRepositionability                Initial/6 wk RT          Tyvek   30 seconds                            A/A                  60 seconds                            A/A                  90 seconds                            A/A                  1 hour    A/F          Woven   30 seconds                            D/D                  60 seconds                            NA                  90 seconds                            NA                  1 hour    NA          Bond    30 seconds                            D/D                  60 seconds                            NA                  90 seconds                            NA                  1 hour    NA1 Hour Performance          Tyvek   Initial   F                  6 wk RT   F          Woven   Initial   D                  6 wk RT   D/F          Bond    Initial   F                  6 wk RT   D/F______________________________________ Key for Repositioning and Permanence: A = Clean B = Slight substrate (envelope C = Substrate pick NA = Not Applicable D = Substrate tear E = Face pick F = Face tear G = Spot adhesive transfer 
    
     The primer coat is of a nature which will allow the facestock of the stamp to be separated from the adhesive while still wet after soaking in water for 30 minutes and with slow peeling of the facestock of the stamp from the adhesive layer which stays with the envelope paper. At worst, if some adhesive stay with the stamp then a small amount of rubbing should enable removal of residual adhesive from the stamp. 
     While the stamp is still wet it should not feel tacky and if it retains adhesive, which cannot be easily removed from the stamp by rubbing off, the adhesive or by reimbursing the stamp in water, then the adhesive is unsuitable for overall stamp performance. 
     The stamp sheetlets of the instant invention are presently manufactured by forming a laminate of the release liner pressure sensitive adhesive and facestock. The face is imprinted with stamp graphics and, if desired, the undersurface may also be printed. Water borne inks are preferably used. This is followed by undercoating and overcoating with the water based acrylic coating with the overcoating preferably containing Taggant. The assembly is then die-cut to form the stamps and bar. Finally, the die cut and the assembly cut to the desired sheetlet size. It has been found, as indicated above, that the application of the overcoat and undercoat imparts sufficient stiffness to the assembly for the assembly to behave as currency, and in cooperation with adhesives having characteristics as specified herein, enables trouble free dispensing from an automatic teller machine. If desired the coating can be applied after die-cutting. 
     In use removal of the bar exposed the edges of the stamps for removal from the protective release liner.