Abstract:
A method of producing paperboard and cartons made therefrom is described incorporating a waterproof or water resistant coating applied to the interior of the carton except for areas intended for gluing. A coating material is applied to the surface of an applicator roll, and a portion of the coating material is then removed from the roll. Contact between a paperboard web and the roll transfers coating material to the web, creating a coated surface except for an uncoated stripe. A carton may be formed from the coated web with the uncoated portion of the carton cut from the uncoated strip.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of priority under 35 U.S.C. §119(e) of provisional application Ser. No. 60/737,210, filed Nov. 16, 2005. 
     
    
     BACKGROUND  
       [0002]     Paperboard cartons are often used for packaging beverage containers cans and bottles. During packaging, cold or chilled beverage containers may be placed into the cartons and condensation from the air may form on the containers and drip onto the inside surfaces of the paperboard carton. This may weaken the carton, or cause reduced adhesion of external coatings resulting in deterioration or rub-off of graphics printed on the external coatings.  
         [0003]     To protect against moisture absorption, the inside of the paperboard carton may be coated with a waterproofing or water resisting material. However, such materials reduce the adhesion of sealants used upon the flaps of the paperboard carton, so that the integrity of the carton may be compromised. To retain sealant adhesion, it is desirable that the waterproofing material be selectively applied to the interior surface of the paperboard, with the material not applied to areas intended for gluing. For other purposes, selective application may typically be done by a printing method, such as flexographic, rotogravure, or offset printing, but such methods typically cannot apply sufficient coat weights of the waterproofing material. Coat weights in range of 2.5 lb/1000 ft 2  are required, which can be applied by technologies such as rod coating used in papermaking, but these typically coat the entire surface. A method is desired that will allow the waterproofing material to be selectively applied at the higher coat weights that are typically achieved by paper machine coaters.  
       SUMMARY  
       [0004]     The present invention provides a method whereby sufficiently high coat weights of waterproofing materials are applied to the “inside ” surface of a paperboard intended for use as a packaging material. Selected areas of the inside surface, preferably those areas to be glued, are left without the waterproofing material, in order to provide superior glue adhesion.  
         [0005]     A method for producing a paperboard product having separate coated and uncoated areas is provided, in which a substrate web is moved over a rotating applicator roll so as to define a region of contact between the web and the roll. A coating material is applied to the surface of the applicator roll at an application location remote from the region of contact. A coating removal device is positioned adjacent the roll between the application location and the region of contact to remove a portion of the coating material from at least one area on the roll. Contact between the web and the roll transfers the coating material to the web, creating a coated surface except for a stripe corresponding to the portion of the coating material removed the said roll.  
         [0006]     The method may include removing the coating material by a wiping action. The coating removal device may include a doctor blade disposed in contact with the surface of the roll.  
         [0007]     The coating material may be applied to the roll by positioning a coating reservoir containing the coating material adjacent to the roll at the application location so that the surface of the roll contacts the coating material.  
         [0008]     The applicator roll may also include at least one recessed area defined in the surface of the roll, whereby no contact is made between the roll and the web along said recessed area, thereby defining an uncoated area on the web corresponding to the recessed area.  
         [0009]     In accordance with another embodiment of the invention, a method for producing a paperboard product having separate coated and uncoated areas includes the steps of extruding a coating material from an extruder having an elongated slot for the coating material to create a film of coating material. A portion of the slot is blocked to create a gap in the film of coating material. The film of coating material is then applied to a substrate web to produce a coated substrate web with at least one uncoated area thereon.  
         [0010]     In accordance with still another embodiment of the invention, a method for producing a paperboard carton blank includes moving a substrate web over a rotating applicator roll so as to define a region of contact between the web and the roll. A coating material is applied to the surface of the applicator roll at an application location remote from the region of contact. A coating removal device is positioned adjacent the roll between the application location and the region of contact to remove a portion of the coating material from at least one area on the roll. Contact between the web and the roll transfers the coating material to the web, creating a coated surface except for a stripe corresponding to the portion of the coating material removed from the roll. A carton blank is then cut from the web so that an uncoated area of the blank is formed from substrate located along the stripe.  
         [0011]     The uncoated area of the blank may be used to form the flaps of the carton. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  illustrates a typical prior art coating process;  
         [0013]      FIG. 2  illustrates an embodiment of the invention directed to providing uncoated stripes on a paperboard product;  
         [0014]      FIG. 3  illustrates a paperboard carton blank with uncoated areas intended for gluing;  
         [0015]      FIG. 4  illustrates an alternative embodiment of the invention directed to providing patterned uncoated areas on a paperboard product.  
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  illustrates a typical coating process. An applicator roll  110  rotates in a pan  120  containing a coating material  122 . The rotation of the applicator roll  110  through the coating material  122  results in a film of coating material upon the surface of the applicator roll  110  in the region indicated at  124 . A web  150 , for example of paper or paperboard, moves in contact with applicator roll  110 , causing part of the coating film to be transferred onto the web  150 , for example in a contact area or meniscus  126 .  
         [0017]     Typically there may be an excess of coating deposited onto the web. To remove excess coating, a device such as rod  130  may be placed in contact with web  150 . The rod  130  may be supported by rod bed  135 . A backing roll  140  may be provided to form a nip between the backing roll  140  and the rod  130 , through which the web  150  passes, thus removing excess coating from the web, as shown by excess coating  137  draining away from the rod  130 , and back into pan  120 . Finally, the coated web  150 ′ continues on, for example to a drying process.  
         [0018]     In accordance with a preferred embodiment of the invention,  FIG. 2  illustrates a method for providing an uncoated stripe on a web. To accomplish this, a holder  210  holds a wiper  220  against the applicator roll  110 , so that the coating material film  124  may be wiped clean from the applicator roll as shown by area  230 . The wiper  220  may be a rigid, semi-rigid, or flexible device, for example a doctor blade, squeegee, wiper, roller, air blast, etc. When the web  150  contacts the applicator roll  110 , the web is left with a dry stripe  235 . Upon contact with the rod  130 , there may be some spreading of the coating upon the web, but typically there will still remain a dry stripe on the web in the machine direction, as evidenced by an area  240  of no excess wipe-off by the rod  130 . It may be necessary to use a short series of trials to determine the best placement and width of wiper  220  in order to provide the correct width of the final dry stripe  237  upon web  150 . The wiper  220  may be supported upon a support beam  215 , from whence its position may be adjusted. More than one wiper may be used to give multiple dry stripes.  
         [0019]     The coated web may be used in the manufacture of paperboard articles such as cartons. The web  150 ′, after leaving the coating apparatus may be wound into a roll and transported to separate equipment for carton manufacture. Alternatively, the coating apparatus may be incorporated into the carton manufacturing equipment. In such case, the web  150 ′ may be fed into one or more printing stations where the web is printed using flexographic, gravure, or other printing methods on the side opposite the applied coating  124 . The printed web is then directed into cutting equipment that cuts printed carton blanks from the moving web.  
         [0020]      FIG. 3  illustrates the formation of two paperboard carton blanks  300 ,  302  from the coated web. Although only two are shown for illustration purposes, typically several blanks would be fitted in the cross direction of a paperboard web, and hundreds or thousands would fit in the machine (long) direction of a paperboard web. The blanks may be offset slightly in the long direction (as shown) in order to minimize waste of the paperboard material. The carton blanks have flaps  310  that are typically folded and glued during assembly. These flaps  310  fit in areas  320 ,  322 ,  324  that are not coated. The non-flap portions of the carton blanks fit in areas  330 ,  332  that are coated, for example with a waterproofing material. The coating may preferably extend partway onto the flaps  310  provided uncoated area sufficient for gluing is left uncoated on the tabs. However, depending on the carton design, the coating areas  330 , etc. may be narrower or wider than shown.  
         [0021]     In addition to imparting water resistance or water proofing, the coating may impart additional strength to the carton blank, and allow the use of lighter weight or lower caliper paperboard. The coating may itself provide strength, or may prevent loss of strength that may occur if the paperboard were to become wetted.  
         [0022]     Carton blanks with portions coated to provide desirable properties (such as water resistance or water proofing) and other portions not coated to provide other desirable properties (such as superior gluability) may also be produced by methods such as extrusion coating. For example, to create uncoated stripes using an extrusion coater, portions of the extruder die slot may be closed, for example with blocks, to prevent flow from those areas of the slot. An extrusion coating upon exit from a die may exhibit “die swell” and upon travel from the die to the substrate may exhibit “neck-down”, either of which may cause the width of the uncoated stripe to differ from the width of a block in the die opening. Simple experimentation will suffice to determine the appropriate block width to achieve the desired uncoated stripe width.  
         [0023]      FIG. 4  illustrates an alternate embodiment for the present invention in which further areas of the web may be left uncoated. This can be particularly useful, e.g., if a transverse region of a carton blank is to be used for gluing. The apparatus is the same as that shown in  FIG. 2 , except that a recess  350  is formed into the surface of applicator roll  110  to correspond to the desired uncoated area. As roll is rotated through the coating material  122 , either no coating material will adhere to the roll on the recess  350 , or if it does, it will be carried at the bottom of recess  350 . In either case, no coating will be transferred to web  150  in this area, with the result that an uncoated area  360  will be formed repeatedly in a corresponding pattern on web  150 ′. By properly selecting and positioning one or more recesses  350  on roll  110 , the desired uncoated pattern may be produced.  
         [0024]     Suitable coating materials are known to those skilled in the art. Such materials may be selected based upon the desired properties to be achieved by coating. For example, such coatings may be used to provide enhanced water resistance, grease or oil resistance, or improved tearing strength.  
         [0025]     Methods of making and using the paperboard and the paperboard carton in accordance with the invention should be readily apparent from the mere description as provided herein. No further discussion or illustration of such products or methods, therefore, is deemed necessary.  
         [0026]     While preferred embodiments of the invention have been described and illustrated, it should be apparent that many modifications to the embodiments and implementations of the invention can be made without departing from the spirit or scope of the invention. Although the preferred embodiments illustrated herein have been described in connection with a paperboard structure with a waterproofing material applied in a pattern through a particular coating process, these embodiments may easily be implemented in accordance with the invention in other structures or to by other application methods.  
         [0027]     It is to be understood therefore that the invention is not limited to the particular embodiments disclosed (or apparent from the disclosure) herein, but only limited by the claims appended hereto.