Abstract:
A treatment for silicone liner coatings after undergoing UV curing. The silicone coats a liner to facilitate its removal from the adhesive attached to a label. The silicone, while a liquid, forms a layer on the liner. UV radiation cures the liquid silicone and causes it to become a coherent, virtually solid layer. Heating the cured silicone layer and allowing it to rest for a short period of time then permits the immediate contact with it of the label&#39;s adhesive side without incurring inseparability of the silicone-coated liner from the adhesive-coated label.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The benefit of the filing date of U.S. provisional patent application serial No. 60/299,057, filed Jun. 18, 2001, is claimed for the present application. 
    
    
     BACKGROUND 
     Pressure-sensitive labels have become almost ubiquitous in modern society. As only one example, they appear on the vast majority of all shipped packages. They are also used to identify parts in manufactured goods and manufacturing equipment. Another example of a very large pressure-sensitive “label” is shelf or drawer liner sold as “Contac®” paper. 
     As another instance of the use of pressure-sensitive labels, baggage tags (or more commonly “bag tags”), have become unavoidable, certainly in the vicinity of commercial airports. The airlines affix the tags to passengers&#39; luggage to indicate both the destination of the articles as well as the items&#39; owners. To include this information, airlines actually print tags when a passenger appears for a flight. The attendant then takes the printed tag, removes a liner sheet, slips it through the handle of the luggage, and adheres it to itself. If the parcel has no handle, such as a carton, then the tag simply sticks directly to the item. 
     The construction of a typical pressure-sensitive label currently in use appears in FIG.  1 . There the label, indicated generally at  11 , includes the face sheet  12  upon which appears the desired printing  13 . In the case of a shipped package, the information identifies and locates the shipper and the recipient. For the example of bag tags, the printing may not only identify the bag&#39;s destination and owner, but will usually indicate the airline on which the passenger commences his or her journey. The airline identifier (and logo) typically arrives preprinted on the tag when delivered to the carrier by the tag&#39;s producer. 
     The face sheet generally has a composition of paper or plastic. The information  13  for a general label can be placed on it by a computer&#39;s printer or any suitable device. 
     For a bag tag, the identification of the bag&#39;s destination and owner can only be placed on the tag  11  at the airport. To accomplish this printing, many if not most, baggage tags&#39; face sheet  12  have a thermally printable composition. Suitable thermally-printable papers are provided by Appleton Papers Inc. of Appleton, Wis., and by Ricoh Electronics Inc. of Santa Ana, Calif. Each of the baggage stands then possesses a thermal printer which, through the application of heat, places the necessary information on the tag&#39;s face sheet  12 . 
     Accordingly, the process described below will produce label stock for a very wide range of pressure sensitive labels. Most labels may utilize ordinary paper or plastic as the face sheet  12 . Bag tags can employ the direct thermal printing process described above. 
     In addition, the indirect thermal printing process, as opposed to the direct thermal, process described below, uses ordinary, but smooth, paper as the face sheet  12 . The thermal printing head actually applies the heat to a ribbon which contains ink. The heat releases the ink from the ribbon which deposits it on the face sheet to produce the printing. 
     With the information  13  on the face sheet  12 , the operator removes the liner sheet  15  from the adhesive  16  on the backside of the face sheet  12 . With the adhesive  16  exposed, the user places the face sheet  12  with the adhesive directly on the package or the equipment. Dyna-Tech Adhesives Incorporated of Grafton, W. Va. provides a suitable general-purpose adhesive under the designation DyTac 2057. This adhesive has a composition of a styrene-butadiene polymer and constitutes an organic phase dispersed as an emulsion in an aqueous phase. 
     For a bag tag, the airline personnel places part of the tag through the bag&#39;s handle and sticks the adhesive to a portion of the tag which still the liner sheet attached. Sticking the adhesive to the remaining liner forms a loop of the tag around the handle. Alternately, if the bag or parcel has no handle, the attendant removes all of the liner  15  from the tag  11  and sticks it directly to the item. 
     In either event, the liner must remove virtually completely from the adhesive so that the latter can facilely attach to another surface. If portions of the liner  15 , typically composed of paper, remains on the adhesive  16 , then the covered adhesive would not achieve a secure affixation of the label to its item. In the case of bag tags, the resulting dislodged tag would create a lost bag to the distress of both the passenger and the airline. 
     To achieve a clean separation of the liner  15  from the adhesive  16 , the former carries the silicone coating  19  attached to it. The coating  19 , firmly affixed to the liner  15 , presents a smooth, relatively nonadherent surface to the adhesive  16 . Pulling off the liner  15  with its silicone coating  19  results in a clean, sticky layer of adhesive  16  attached to the face sheet  12 . Stated in other words, the silicone coating  10 , affixed to the liner  15 , permits the release of the adhesive  16  from itself and thus the liner  15 . This leaves the face sheet  12  with an exposed layer of adhesive  16 . 
     The manufacture of the label  11  generally commences with the coating of the paper liner  15  with the silicone  19 . A type of silicone finding frequent use in this day of environmental concerns takes the form of a UV curable silicone polymerizable liquid. Use of this category of silicone avoids the problem of evaporating hydrocarbons into the atmosphere. Curing the liquid silicone entail shining it with UV radiation. This causes the silicone monomers to combine, leaving a unified mass of silicone coating  19  firmly attached to the liner  15 . Blissfully, the process places substantially no pollutants into the atmosphere. 
     Suitable components for UV-curable silicone solutions are supplied by Rhodia Inc. of Rock Hill, S.C. A liquid for an easily releasable layer may include 100 parts of UV-curable silicone polymer (Rhodia product PC-600); 2.5 parts of cationic photoinitiator (PC-702); and CRA-minus release modifier (PC-670). The silicone itself has a composition of an epoxy-modified polydimethylsiloxane. This type of compound comes from the class of epoxy-modified polysiloxanes which may well provide other suitable moieties. 
     For a silicone layer with a tighter release, the above solution may include 5 to 55 parts (depending upon the desired characteristics of the silicone layer) of CRA-plus release modifier (PC-680). Free radical photoinitiators may alternately find use in appropriate solutions. 
     Promptly after receiving the UV radiation, the silicone  19  cures into a reasonably hard mass firmly affixed to the paper liner  15 . However, it cannot then receive the adhesive  16 , Placing the adhesive onto the newly cured silicone layer  19  will cause these two layers  16  and  19  to stick together. This represents a clearly unacceptable situation. Instead, to avoid this clearly deleterious situation, the silicone layer  19  must sit on the liner  15  at least several hours if not a whole day before contacting the adhesive  16  to avoid the unacceptable results indicated above. The necessity for delay seems remarkable in light of the fact that the newly cured silicone seems hard, smooth, and ready for further use. In fact, during the delay, the silicone-coated liner can be wrapped into a large roll and, after the delay period, unrolled and used without displaying any negative effects. 
     In fact, rolling the liner with the newly cured silicone into a large cylinder represents the usual manufacturing process. Simply stated, the liner with the new silicone coating cannot remain on the manufacturing equipment and render it useless for the time required for the silicone to remain out of contact with an adhesive. Accordingly, the usual manufacturing process involves a machine placing the uncured silicone on the liner  15 . The silicone undergoes UV curing. Then the machine rolls the liner  15  with the cured silicone layer  19  onto a roll, which is removed from the machinery and left to sit for the substantial period of time necessary to render the silicone substantially less adherent to the adhesive  16 . After the delay period, the roll is then placed onto machinery. This permits the completion of the manufacturing process by placing adhesive  16  onto the silicone  19  and then attaching the face sheet  12 . 
     Removing the roll of silicone-coated liner, allowing it to simply stand for an extended period of time, and placing it back on a machine again represents a substantial manufacturing effort. Eliminating these steps would achieve a significant economy in the production of pressure-sensitive label stock. 
     SUMMARY 
     Heating the silicone coating after its UV curing and waiting briefly before applying an adhesive permits the further processing of the material without the necessity of removing it from the equipment and allowing it to stand idle. Although the silicone appears cured and hard, the subsequent heating and short wait places it in condition to contact the adhesive without excessively sticking to it. 
     Fundamentally, an improved method of treating a UV-cured silicone layer on a substrate comprises first heating the UV-cured silicone at an elevated temperature. After heating the silicone layer at the elevated temperature, the silicone layer is kept free from contact with an adhesive for a predetermined period of time. This time period conditions the heated silicone to receive the adhesive without deleterious effects and depends primarily on the silicone and the adhesive. 
     After the passage of the predetermined period of time after heating the silicone at the elevated temperature, an adhesive layer may be applied to the silicone. This process permits the subsequent separation of the two layers when they constitute part of a label. 
     Completing the pressure-sensitive label stock involves adhering a face sheet to the adhesive. The face sheet, of course, will carry the information identifying the equipment, the package&#39;s sender and recipient, or the bag&#39;s destination and owner. Actually, the face sheet may adhere to the adhesive either before the adhesive is applied to the liner or after. If before, the adhesive forms a layer on the face sheet and the two placed against the liner with the silicone coating, with the adhesive contacting the silicone. 
     Actually, the complete process of making the label stock starts with coating a liner sheet, usually paper, with an uncured, liquid, UV-curable silicone. The film of liquid silicone undergoes curing through exposure to UV radiation. Finishing the bag tags then proceeds through the various steps outlined above. With the heating of the cured silicone followed by the short delay, the materials need never leave the manufacturing equipment from the beginning to the end. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 illustrates the construction of an ordinary pressure-sensitive label as currently used by many airlines amongst others. 
     FIG. 2 shows the steps in the construction of the label of FIG. 1 but which the necessity of a lengthy delay period between the UV curing of the silicone layer and the application of an adhesive. In this figure: 
     FIG. 2A illustrates the application of a layer of liquid UV curable silicone to a liner face sheet. 
     FIG. 2B diagrams the curing of the silicone layer through the application of UV radiation. 
     FIG. 2C gives the post-cure treatment of the silicone layer through heating. 
     FIG. 2D shows the waiting period after the heating of the heated silicone layer achieved by a convoluted path followed by the liner with the cured and heated silicone. 
     FIG. 2E illustrates the application of an adhesive to the cured and heated silicone layer after the latter has undergone the waiting period of FIG.  2 D. 
     FIG. 2F gives the last step in the creation of a label in which the face sheet attaches to the remaining layers through contact with the adhesive layer. 
     FIG. 3 provides a general diagram of apparatus of equipment manufacturing pressure-sensitive labels through the process illustrated in FIG.  2 . 
     FIG. 4 gives an enlarged view of the portion of the portion of the equipment of FIG. 3 which applies liquid silicone to the liner, cures it, and then heats it and provides a subsequent delay period. 
    
    
     DETAILED DESCRIPTION 
     FIG. 2A shows the first step in the manufacturing of the pressure-sensitive label  11  of FIG.  1 . In FIG. 2A, the dispenser  23  places a thin coating  24  of UV-curable, liquid silicone  25  onto the roller  28 . The roller  28 , in turn, transfers the coating  24  of silicone onto the liner sheet  15  in the form of the thin layer  29  of liquid silicone. In FIG. 2B, The lamp  30  shines UV radiation onto the liquid silicone  29  to cure it into the solid film  19  adhered to the liner  15 . 
     In FIG. 2A, the infrared irradiator heats the cured silicone layer  19  at an elevated temperature. The ambient temperature may rise to 125, 150, or even 200 F. 
     After passing through the IR heater, the liner  15  with its cured and heated silicone layer passes over the series of rollers  36 . The extended, convoluted path created by the rollers provides a short delay between the heating of the IR irradiators and the subsequent treatment of the liner  15  with the heated silicone layer  19 . The delay need not be long. Ten seconds will typically permit the immediate “tandem” processing of the silicone layer by placing an adhesive upon it. However, even shorter periods of seven or even three seconds may suffice to treat the cured silicone. 
     After the short delay caused by the convoluted path set up by the rollers  36 , the silicone layer  15  may then immediately and safely come into contact with an adhesive. This occurs in FIG. 2E where the glue dispenser  37  places the adhesive  38  as the thin film  16  onto the silicone layer  19 . The three layers  15 ,  16 , and  19  then pass through the oven  42  to partially dry the adhesive  16 . 
     After departing the oven  42 , the sandwich of the three layers  15 ,  16 , and  19  receives the face sheet  13  from the roll  43  which sticks to the adhesive  19 . The four-layer structure is finally reeled into the roll  45 . The roll  45  may undergo further processing as necessary such as receiving the airline&#39;s name and logo and die cutting for use in the bag-tag printer at the airport. 
     As a slight variation in the process, the face sheet  12  may receive the adhesive  38  from the dispenser  37 . This combination of face sheet  12  and adhesive  16  then passes through the oven  42  to dry the latter. Then the adhesive  16 , lining the face sheet  12 , contacts and sticks to the silicone layer  19  on the liner  15  to form the final four-layer label structure  11  of FIG.  1 . 
     The actual equipment for preparing the four-layer label of FIG. 1 by the “tandem” process appears in FIG. 3 with the details for the post-cure treatment of the silicone shown in FIG.  4 . As stated above, this process permits the complete preparation of the label stock without removing the partially treated material from the equipment, especially between the curing of the silicone and the placement of the adhesive on it. Aside from the components discussed below with regards to FIG. 4, the apparatus in FIG. 3 represents standard equipment obtained from the Faustel company in Germantown, Wis. 
     To begin the process, the liner sheet  15  comes off the roll  47  held on the unwind stand  48 . The unwinder  48  permits the placement of a second roll in location for subsequent use as the first roll  47  becomes completely consumed. From the unwinder  48 , the liner  19  travels to the unwind splicer  51 . As the end of the roll  47  passes to the splicer  51 , the beginning edge of the next roll travels there as well. The splicer  51  then attaches the end of the first roll to the beginning of the second roll to establish a continuous web of material passing through the apparatus indicated generally at  53 . 
     The equipment  53  next utilizes the infeed drawer  54  to actually pull the liner  15  off the roll  47  and through the splicer  51 . The liner  15  next passes to the #1 coater  55  where it receives a film of liquid silicone. 
     The components of the equipment  53  that place and treat the silicone appear in greater detail in FIG.  4 . They permit the continuous, “tandem” treatment of the liner  15  from placing the silicone through the application of the adhesive without the necessity of removing the partially completed material and later replacing it on the equipment. 
     After departing the coater  55 , the liner now has a thin film of essentially liquid silicone, with the two layers collectively identified as  58 . From there, it travels to the curing unit  59  which shines UV radiation from the lamps  60  onto the silicone coating on the liner  58 . The UV radiation “cures” the silicone to a substantially rigid layer  19 . 
     The liner  15  with the rigid film  19 , now identified as  63 , then passes from the curing unit  59  directly to the heater  64 . There, infrared heaters provide an atmosphere at an elevated temperature to help prepare the silicone for the adhesive. As indicated above and depending upon the actual silicone used and the delay period, the temperature may rise to 125, 150, 200 degrees or even higher. Suitable IR lamps include the Radplane series 80 infrared heaters from Glenro Inc. in Patterson, N.J. 
     As indicated above, after the warming at the heater  64 , the coated liner  63  must wait a short period of time, usually 10 seconds, before receiving the application of the adhesive. Without the brief waiting period, the adhesive will firmly bond to the silicone, destroying the very reason for having the silicone on the liner. The apparatus shown in FIG.  3  and more particularly in FIG. 4 accomplishes the delay while still allowing the coated liner to move through the equipment  53  at its normal pace of so many linear feet per minute, which may typically run at approximately 300 TO 450 ft./min. 
     After departing the heater  64 , the coated liner  63  then follows the convoluted path created by the rollers  36 . After leaving the rollers  36 , the coated liner  63  travels along the overhead path  65  until it reaches the next treating station  66 . The combined length of coated liner on the rollers  36  plus that on the overhead path  65  amounts to 51 feet Travelling at the above speed of 300 ft/min., the path length of 51 feet induces a delay of about 10 seconds from the time that the cured silicone passes through heater  64  until it reaches the next treating station  66 . At a line speed of approximately 450 ft./min., a delay of about seven seconds. In either event, the delay permits the heated silicone to pass into a state where it has only a slight affinity for the adhesive that will subsequently be applied to it. 
     The next, or second coating, station  66 , applies a thin layer of generally liquid adhesive to the silicone-coated liner  65 . In particular, the coater #2  66  places the adhesive in contact with the silicone. 
     From the second coater  66 , the three layer structure  69  now incorporating the liner, cured silicone, and wet adhesive travels to the dryer indicated generally at  70  in the two drawing sheets  2 / 4  and  3 / 4 . The dryer  70  really has the two oven zones  71  and  72 , the latter appearing more fully on sheet  3 / 4 . The dryer  70  utilizes heat to largely dry the adhesive placed on the silicone at the second coater  66 . The drying process also benefits from the action of the fan  76  which draws heat produced by the UV lamps  60  away from the equipment  59 . In doing so, the fan  76  brings this hot air into contact with the adhesive-coated material  69  to help dry it. 
     After leaving the second zone  72  of the dryer  70 , the material  69  with the dried adhesive travels to the laminator  75 . There it meets the face sheet  12  which has arrived from the roll  77  held on the unwinder  78  and passed through the unwind splicer  79 . The unwinder  78  and the splicer  79  serve exactly the same functions for the face sheet  12  as the unwinder  48  and splicer  51  serve for the liner  15 . The laminator  75 , however, in part fulfills the function of the drawer  54  to pull the face sheet  12  off of the roll  77 . 
     More importantly, the laminator  75  brings the face sheet  12  into contact with the adhesive on the three-layer structure  69 . This step creates the laminated, four-layer structure  11  which will serve as the pressure-sensitive label. The final four-layer laminate  11  then goes to the outfeeder  81  which moves the label structure  11  to the rewind splicer  82  and then to the rewinder  83 . The rewinder  83  forms the arriving label stock  11  into the roll  84 . The rewind splicer  82  will cut the arriving label sandwich  11  upon the completion of the roll  84 . It will then place the label material  11  onto a new cardboard core to start a new roll. All of this proceeds automatically and needs no operator intervention (aside from taking off a completed roll  84  and placing a new core on the rewinder  83 ). 
     The material on the core may then undergo additional treatment to prepare it for subsequent printing and use. This can include cutting the material on the roll  84  to the width and length for the printer. In the case of many labels including bag tags, it may also involve printing the user&#39;s or airline&#39;s name and logo on the label material. The material may then be placed into smaller rolls or in a fan-fold configuration and shipped to the user.