Abstract:
A method for forming an extrusion coated paperboard including the steps of providing an uncoated paperboard, providing at least one extrusion device and at least one moisture application device on a single extrusion process line, extruding a material onto a first side of the paperboard with the extrusion device and applying a moisture composition onto a second side of the paperboard, opposite of the first side, with the moisture application device such that an equilibrium moisture content of the extrusion coated paperboard is about 6 to about 15 percent based on total extrusion coated paperboard weight.

Description:
[0001]     This application is a divisional application of U.S. Ser. No. 10/899,650 filed on Jul. 27, 2004, pending, which claims priority from U.S. Provisional Ser. No. 60/491,718 filed on Aug. 1, 2003, expired, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     The present application relates to methods for increasing moisture content in an extrusion coated paperboard.  
         [0003]     Conventional methods for extrusion coating paperboard are well known. Conventional extrusion coated paperboards have been used to form a variety of packages. Generally, a paperboard is coated with one or more coatings of a polymer material to enhance barrier or aesthetic properties of the paperboard. The extrusion process typically involves the application of a molten polymer material to a moving web of paperboard using a conventional extrusion coater system. The extruded polymer is immediately cooled after application and the extrusion coated paperboard is rolled for shipment. At a converter, the paperboard is unwound, printed, and cut into container blanks. The container blanks are then formed into packages using known conventional techniques.  
         [0004]     A conventional package forming technique involves thermoforming the container blank into the container shape. This technique involves applying heat and mechanical force concurrently to the container blank in a container forming die. Exemplary container thermoforming equipment is commercially available from Gralex Corporation of Lewis Center, Ohio. For proper container thermoforming with extrusion coated paperboard, the container blank must have a minimum moisture content. This is even more critical for a solid paperboard container blank as compared to a corrugated container blank. Corrugated container blanks have some inherent deformability due to their fluted layers. Proper moisture content in a solid paperboard container blank is critical to prevent catastrophic failure, such as tearing, during thermoforming. Without being limited to any particular theory, the applicants believe that the increased moisture content is necessary to ensure sufficient elasticity in the container blank during thermoforming. The elevated moisture content counter balances the various “moisture drying effects” that the paperboard substrate is subject to. For example, the paperboard is typically treated during the extrusion process to improve polymer adhesion. This “flame treatment,” along with the application of a hot, molten polymer, causes the paperboard to lose moisture. The extruded paperboard also loses moisture during shipping, handling, storage, and printing. During the thermoforming process, the blank&#39;s moisture content is further reduced when heat is transferred to the container blank. If the moisture content of the extrusion coated paperboard container blank is too low prior to the thermoforming process, defective formation may occur.  
         [0005]     Conventional techniques for increasing the moisture content of the container blank involved the additional step of moistening a surface of the paperboard after the extrusion process and prior to printing and die cutting.  
         [0006]     Exemplary moistening equipment includes an ITM-HD moisture application device manufactured by Peerless Machine and Tool Co. of Marion, Ind., and a Dahlgren-type system manufactured by Coating &amp; Moisturizing Systems, Inc. of Gainesville, Ga. Typically, a container manufacturer or converter, such as Pactiv Corporation, purchases an extrusion coated paperboard from a manufacturer, such as International Paper Corporation or Blue Ridge Corporation. The converter then moistens the paperboard at his converting site using the moisture application device. The paperboard is then either printed and die cut with the printed blanks left to reach moisture equilibrium, or the moistened roll is left until moisture equilibrium is reached prior to printing and die cutting. To reach moisture equilibrium, the moisture that was applied to the surface of the paperboard must be absorbed throughout the entire paperboard until constant moisture content is reached. This process generally takes up to 24 hours. Whether printing and die cutting are done before or after the equilibrium period, container thermoforming cannot be performed until paperboard moisture equilibrium is reached. This moistening step increases the converter&#39;s production cost in at least two ways. First, each converter must have suitable moistening equipment at his converting site. Second, the moistening step extends his production or converting time due to the time required for moisture equilibrium. Accordingly, there is a need for a method of increasing the moisture content of extrusion coated paperboard immediately after the extrusion process, thus eliminating the need for converters to increase the paperboard moisture content during their converting process.  
       SUMMARY  
       [0007]     In one aspect, an extrusion coated paperboard is provided and includes a paperboard, an extruded material adhered to a first side of said paperboard and a moisture composition applied in-line during the extrusion process to a second side, opposite of said first side, of said paperboard such that a moisture content of said extrusion coated paperboard has an equilibrium moisture content range of about 6 to about 15 percent by weight based on total extrusion coated paperboard weight.  
         [0008]     In another aspect, a method for forming an extrusion coated paperboard is provided and includes the steps of providing an uncoated paperboard, providing at least one extrusion device, providing at least one moisture application device, extruding a material onto a first side of said paperboard with said extrusion device and applying a moisture composition onto a second side of said paperboard, opposite of said first side, with said moisture application device such that an equilibrium moisture content of said extrusion coated paperboard is about 6 to about 15 percent total extrusion coated paperboard weight.  
         [0009]     In another aspect, a method for forming an extrusion coated paperboard is provided and includes the steps of providing an uncoated paperboard, providing at least one extrusion device, providing at least one moisture application device, wherein the moisture application device and the extrusion device are on a single extrusion process line, extruding a material onto a first side of the paperboard with the extrusion device and applying a moisture composition onto a second side of the paperboard, opposite of the first side, with the moisture application device such that an equilibrium moisture content of the extrusion coated paperboard is about 6 to about 15 percent based on total extrusion coated paperboard weight.  
         [0010]     In another aspect, a method is provided for applying a polymeric extrusion and a moisture composition in a single extrusion process line. Following the extrusion process and moisture application, the paperboard may be wound in a roll and shipped.  
         [0011]     Other aspects will become apparent from the following detailed description, the accompanying drawings and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a schematic view of an exemplary system according to one aspect of the disclosed system and method;  
         [0013]      FIG. 2  is a schematic view of a moisture application device of the system of  FIG. 1 ;  
         [0014]      FIG. 3  is a front elevational view, shown in cross-section, of an extrusion coated paperboard;  
         [0015]      FIG. 4  is a front elevational view, shown in cross-section, of the paperboard of  FIG. 3  after a moisture composition has been applied thereto; and  
         [0016]      FIG. 5  is a front elevational view, shown in cross-section, of the paperboard of  FIG. 4  after moisture equilibrium has been reached. 
     
    
     DETAILED DESCRIPTION  
       [0017]      FIG. 1  illustrates a schematic view of an exemplary extrusion system  300  according to one aspect of the disclosed system and method. It should be understood that the present application is applicable to a wide range of extrusion coating systems  300 .  FIG. 1  is only intended to illustrate an exemplary system and does not limit the scope of the present application.  
         [0018]     The system  300  is illustrated with a paperboard  100  formed as a web and placed on the system  300  as a roll  310 . The present invention is applicable to a wide range of conventional paper or paperboard materials that provided sufficient strength for their intended end use. An exemplary paperboard  100  is a non-claycoated solid bleached sulphate (SBS) paperboard material. The paperboard  100  could be bleached or unbleached as desired. A bleached surface is desirable when the paperboard  100  will be used in a cooking application. Typical basis weights for the paperboard  100  are in the range of about 70 pounds per 3,000 square feet to about 350 pounds per 3,000 square feet. Typically, the paperboard  100  has a thickness or caliper range of about 0.007 inches to about 0.035 inches. The present invention covers the full range of paper or paperboard substrates, as applied to the packaging field and other suitable applications.  
         [0019]     As shown in  FIGS. 1 and 3 , a roll  310  is placed into an extrusion system  300  using conventional techniques and unwound. A first surface  102  of the paperboard  100  is optionally heated with one or more flame apparatus  320  to improve the bond between the paperboard  100  and an extruded material  120  applied to the surface  102  of the paperboard  100 . The extruded material  120  is extruded onto the surface  102  of the paperboard  100  using conventional extrusion equipment  330 . The extruded material  120  is typically selected such that a contact surface  122  may be in contact with an article (not shown) placed inside a container (not shown) formed from the paperboard  100 . One common extruded material  120  is a material suitable for food contact.  
         [0020]      FIG. 3  illustrates a paperboard  100  with the extruded material  120  secured to the paperboard surface  102 . The extruded material  120  may be any suitable extrusion material  120 . Exemplary extruded materials  120  include polyethylene terephthalate (PET), polymethylpentene (PMP), polyethylene (PE), polybutylterephthalate (PBT), polypropylene (PP), Nylon (PA) and other suitable materials. Suitable coat weight ranges for PET include a coat weight range of about 8 pounds per 3,000 square feet to about 30 pounds per 3,000 square feet with an exemplary range of about 15 pounds per 3,000 square feet or greater. Suitable coat weight ranges for PMP include a coat weight range of about 5 pounds per 3,000 square feet to about 15 pounds per 3,000 square feet with an exemplary range of about 8 pounds per 3,000 square feet or greater. Suitable coat weight ranges for PE include a coat weight range of about 5 pounds per 3,000 square feet to about 30 pounds per 3,000 square feet with an exemplary range of about 8 pounds per 3,000 square feet or greater. Suitable coat weight ranges for PA include a coat weight range of about 5 pounds per 3,000 square feet to about 30 pounds per 3,000 square feet. If PA is used as a layer within a composite structure that may include any other suitable extruded materials, an exemplary coat weight range is about 8 to about 12 pounds per 3,000 square feet. Suitable coat weight ranges for PP include a coat weight range of about 5 pounds per 3,000 square feet to about 30 pounds per 3,000 square feet, with an exemplary range of about 8 pounds per 3,000 square feet or greater. Suitable coat weight ranges for PBT include a coat weight range of about 5 pounds per 3,000 square feet to about 30 pounds per 3,000 square feet with an exemplary range of about 15 pounds per 3,000 square feet or greater. It is to be understood that multiple extruded materials  120  could be applied during the extrusion process in one or more layers, using one or more extrusion apparatus  330 . It is to be further understood that one or more pigments, additives or other compositions could be added or blended with the extruded material  120 . For example, a pigment could be added to alter the color, opacity or aesthetic properties of the extruded material  120  or paperboard  100 .  
         [0021]     In containers used for cooking applications made from the paperboard, the extruded material  120  should ideally be mass stable or have a melting point of about 450 degrees Fahrenheit or higher and have chloroform-soluble extractives not exceeding 0.5 milligrams per square inch of the food contact surface.  
         [0022]     Returning to  FIG. 1 , a cooling roll  335 , commonly referred to as a chill roll, contacts the extruded material  120  immediately after it is applied to the paperboard  100  by the extrusion apparatus  330 . The chill roll  335  helps to form a strong bond between the extruded material  120  and the paperboard  100 .  
         [0023]     As illustrated in  FIGS. 1, 2  and  4 , a moisture composition  90  is applied to the underside  101  of the paperboard  100  by a moisture application device  340 . A typical moisture composition  90  includes water. It is to be understood that one or more additives or moisture retention aids may be mixed in with the moisture composition  90 . Also, numerous compositions and concentrations of moisture composition  90  are within the scope of the invention.  
         [0024]      FIG. 2  schematically illustrates, in detail, an exemplary moisture application device  340 . The device of  FIG. 2  is commonly referred to as a Dahlgren type moisture application device  340 . One conventional device  340  is manufactured by Coating and Moisturizing Systems of Gainsville, Ga. It is to be understood that the invention covers a wide range of moisture application devices  340  or moisture application means, such as spraying systems and other roll applicator systems. The key feature is that the moisture device  340  be operated in a manner to increase the moisture content of the paperboard  100  to a desired moisture level to improve converting properties of the paperboard. As illustrated in  FIG. 2 , the Dahlgren system has three main rolls: a metering roll  342 , a transfer roll  344 , and a backing roll  346 . The metering roll  342  is in contact with the moisture composition  90 . The moisture composition  90  is retained in a moisture container  341 . In one system according to the present invention, the transfer roll  344  is chemically treated to create an attraction to the moisture  90 . A thin film of moisture  90  is metered to the transfer roll  344  by controlling nip pressures and differential speed between the metering roll  342  and transfer roll  344 . At high transfer roll  344  speeds in the reverse direction of the paperboard&#39;s  100  travel direction, the moisture  90  is impregnated into the paperboard  100 . As shown in  FIG. 1 , an exemplary moisture sensor  350  is positioned downstream from the moisture application device  340  and can be used to monitor the moisture content of the paperboard  100 . Although not shown, a moisture sensor  350  could also be placed upstream of the moisture application device  340 . It is to be understood that system  300  could also include various controls (not shown) and other sensor devices (not shown), such as computers, software, electrical, pneumatic, or mechanical devices to communicate and control the system  300  and or the moisture application device  340 .  
         [0025]     It is to be understood that the moisture composition  90  should ideally be applied after the extruded material  120  has been secured to the paperboard  100 .  FIG. 5  depicts the paperboard  100  after the moisture composition  90  of  FIG. 4  has been absorbed throughout the paperboard  100  and moisture equilibrium has been reached. Moreover, while only one moisture application device  340  has been illustrated in  FIG. 1 , it is to be understood that two or more (not shown) moisture devices  340  could be used with the system  300 . Also, the location of the moisture device  340  could be varied. For example, one device  340  (not shown) could be placed upstream of the extrusion apparatus  330 . Of course, if too much moisture is added upstream it may result in poor adhesion between the extruded material  120  and the paperboard  100 . Likewise, two or more (not shown) moisture devices  340  could be placed downstream of the extrusion apparatus  330 .  
         [0026]     Returning to  FIG. 1 , the finished paperboard is typically wound into a roll  360  for shipment to a converter. It is to be understood that the paperboard could also be sheeted prior to shipment. Although not shown, it is also to be understood that the roll  360  is ideally placed in a moisture barrier package and shipped and handled within certain temperature and humidity ranges to increase the shelf life of the paperboard and to maintain the paperboard&#39;s moisture content. It is to be further understood that extrusion coated paperboard manufactured according to the invention could also be converted into container blanks (not shown). The container blanks could then be thermoformed into a vessel or container. However, the invention covers any use of extrusion coated paperboard produced according to the present invention.  
         [0027]     Given the above detailed description, many other embodiments, features, modifications or improvements will become apparent to those skilled in the art. Such other embodiments, features, modifications and/or improvements are therefore considered to be a part of the present invention, the scope of which is to be determined by the following claims.