Patent Publication Number: US-2021164163-A1

Title: Coated paperboard and a tray made therefrom

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. provisional application Ser. No. 62/684430 filed on Jun. 13, 2018 and U.S. provisional application Ser. No. 62/749202 filed on Oct. 23, 2018, which are both hereby incorporated by reference in their entirety. 
    
    
     FIELD 
     The present application relates to the field of trays suitable for food packaging, particularly trays suitable for overwrapping of moist food products into a case-ready package for shelf storage. 
     BACKGROUND 
     Various trays are known in the art for carrying moist food products, such as meat, poultry, seafood, and produce. It is desirable that such trays are water- and grease-resistant to effectively carry and store the food products. 
     Such trays may be overwrapped with a transparent wrapping material in order to display the food products carried by the tray and placed on display in retail markets. Thus, it is desirable that such trays handle the overwrapping process without failing. 
     Suitable trays include conventional trays formed from expanded polystyrene. However, there is a growing trend to limit the use of expanded polystyrene trays. 
     Accordingly, those skilled in the art continue with research and development in the field of trays suitable for food packaging. 
     SUMMARY 
     In one embodiment, a coated paperboard includes: a single-ply paperboard substrate having a first major side and a second major side, and having an internal sizing agent incorporated therein; and a barrier coating on the first major side of the single-ply paperboard substrate, the barrier coating having an elastic modulus of at least 1.5 GPa. 
     In another embodiment, a paperboard tray includes: a coated paperboard in the form of a bottom wall, a side wall extending upwardly around the bottom wall, and a flange extending outwardly around the side wall. The coated paperboard includes: a single-ply paperboard substrate having a first major side and a second major side, the first major side corresponding to an upper side of the bottom wall; and a barrier coating on the first major side of the single-ply paperboard substrate, the barrier coating having an elastic modulus of at least 1.5 GPa. 
     In yet another embodiment, a method for manufacturing a paperboard tray includes: forming a paperboard blank from a coated paperboard, wherein the coated paperboard includes a single-ply paperboard substrate having a first major side and a second major side, and a barrier coating on the first major side of the single-ply paperboard substrate, the barrier coating having an elastic modulus of at least 1.5 GPa; and thermoforming the paperboard blank between a male die and a female die into a paperboard tray having a bottom wall, a side wall extending upwardly around the bottom wall, and a flange extending outwardly around the side wall, the first major side corresponding to an upper side of the bottom wall. 
     In yet another embodiment, a method for using a paperboard tray includes: positioning a food product within a paperboard tray, the paperboard tray comprising a coated paperboard in the form of a bottom wall, a side wall extending upwardly around the bottom wall, and a flange extending outwardly around the side wall, the coated paperboard including a single-ply paperboard substrate having a first major side and a second major side, the first major side corresponding to an upper side of the paperboard tray, and a barrier coating on the first major side of the single-ply paperboard substrate, the barrier coating having an elastic modulus of at least 1.5 GPa; and wrapping a film over the product and the paperboard tray. 
     Other embodiments of the disclosed coated paperboard, paperboard tray, method for manufacturing a paperboard tray, and method for using a paperboard tray will become apparent from the following detailed description, the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section of an exemplary coated paperboard according to an embodiment of the present description. 
         FIG. 2  is a roll of the coated paperboard of  FIG. 1 . 
         FIG. 3  is a paperboard blank of the coated paperboard of  FIG. 1 . 
         FIG. 4  is a perspective view of an exemplary paperboard tray according to an embodiment of the present description. 
         FIG. 5  is a top view of the paperboard tray of  FIG. 4 . 
         FIG. 6A  is a side sectional view of the paperboard tray of  FIG. 4  along section A-A. 
         FIG. 6B  is a side sectional view of the paperboard tray of  FIG. 4  according to an alternative variation along section A-A. 
         FIG. 7  is schematic representation of a male die and female die for thermoforming a coated paperboard into a paperboard tray. 
         FIG. 8A  is a side sectional view of the paperboard tray of  FIG. 6A  in the wrapped configuration. 
         FIG. 8B  is a side sectional view of the paperboard tray of  FIG. 6B  in the wrapped configuration. 
         FIG. 9  is a graph showing result of a finite element model for optimization of the flange of  FIG. 6B  during a simulation of an overwrapping process. 
     
    
    
     DETAILED DESCRIPTION 
     By positioning a high stiffness barrier coating on a side of a single-ply paperboard substrate that corresponds to an inner side of a paperboard tray formed from the single-ply coated paperboard, the paperboard tray can be provided with water- and grease-resistance desirable for carrying moist food items, and the paperboard tray can be provided with sufficient rigidity to withstand using the paperboard tray in an overwrapping process. In an aspect, the present description enables providing a coated paperboard and paperboard tray that are compostable. In another aspect, the present description enables providing a coated paperboard and paperboard tray that are recyclable. In yet another aspect, the present description enables providing a coated paperboard and paperboard tray that are printable or capable of being dyed. 
       FIG. 1  is a cross-section of an exemplary coated paperboard  2 . As shown, the coated paperboard  2  includes a single-ply paperboard substrate  4  having a first major side  6  and a second major side  8 , and a barrier coating  10  on the first major side  6  of the single-ply paperboard substrate  4 . As shown in  FIG. 2 , the coated paperboard  2  may take the form of a roll  12  of coated paperboard. As shown in  FIG. 3 , the coated paperboard  2  may take the form of a paperboard blank  14  of coated paperboard, which has been cut (e.g., die-cut) to the desired silhouette (e.g., a rounded rectangle is shown, but those skilled in the art will appreciate that various silhouettes may be used). 
     Referring to the coated paperboard  2  as illustrated in  FIG. 1 , the barrier coating  10  may be, for example, a single coating layer positioned directly on the first major side  6  of the single-ply paperboard substrate  4 . 
     Referring to the coated paperboard  2  as illustrated in  FIG. 1 , the barrier coating  10  may define a first outermost surface of the coated paperboard  2  and the second major side  8  may define a second outermost surface of the coated paperboard  2 . In an expression, the coated paperboard  2  may include a topcoat on the second major side  8 . In another expression, the coated paperboard  2  may include a topcoat on the barrier coating  10 . 
     In an aspect, the second major side  8  of the coated paperboard may be printable, or capable of being dyed, such as to permit display of graphics and/or text on the paperboard. 
     In an aspect, the coated paperboard  2  has an average caliper thickness of 0.010 inch (254 μm) or greater. In another aspect, the coated paperboard  2  has an average caliper thickness in the range of 0.010 inch to 0.035 inch (254 μm to 890 μm). In yet another aspect, the coated paperboard  2  has an average caliper thickness in the range of 0.016 inch to 0.026 inch (406 μm to 660 μm). 
     The single-ply paperboard substrate  4  may include any cellulosic material that is capable of being coated with the barrier coating layer. The single-ply paperboard substrate  4  may be bleached or unbleached. Appropriate single-ply paperboard substrates  4  include corrugating medium, linerboard, solid bleached sulfate (SBS), folding boxboard (FBB), and coated unbleached kraft (CUK). In a specific expression, the single-ply paperboard substrate  4  is solid bleached sulfate. 
     In an aspect, the single-ply paperboard substrate  4  has an average caliper thickness of 0.010 inch (254 μm) or greater. In another aspect, the single-ply paperboard substrate  4  has an average caliper thickness in the range of 0.010 inch to 0.035 inch (254 μm to 890 μm). In yet another aspect, the single-ply paperboard substrate  4  has an average caliper thickness in the range of 0.016 inch to 0.024 inch (16 point to 24 point; 406 μm to 610 μm). In yet another aspect, the single-ply paperboard substrate  4  has an average caliper thickness in the range of 0.016 inch to 0.022 inch (16 point to 22 point; 406 μm to 559 μm). In yet another aspect, the single-ply paperboard substrate  4  has an average caliper thickness in the range of 0.016 inch to 0.020 inch (16 point to 20 point; 406 μm to 508 μm). In a specific expression, the single-ply paperboard substrate  4  has an average caliper thickness of 0.018 inch (18 point; 457 μm). The high caliper of the single-ply paperboard substrate  4  functions to increase rigidity of the coated paperboard  2  when formed into a paperboard tray to withstand a process of overwrapping the paperboard tray. 
     In an aspect, the single-ply paperboard substrate  4  may have an uncoated basis weight of at least about 60 pounds per 3000 ft 2  (98 g/m 2 ). In one expression the single-ply paperboard substrate  4  may have an uncoated basis weight ranging from about 60 pounds per 3000 ft 2  (98 g/m 2 ) to about 400 pounds per 3000 ft 2  (650 g/m 2 ). In another expression the single-ply paperboard substrate  4  may have an uncoated basis weight ranging from about 120 pounds per 3000 ft 2  (196 g/m 2 ) to about 250 pounds per 3000 ft 2  (407 g/m 2 ). In another expression the single-ply paperboard substrate  4  may have an uncoated basis weight ranging from about 150 pounds per 3000 ft 2  (245 g/m 2 ) to about 210 pounds per 3000 ft 2  (342 g/m 2 ). In a specific expression the single-ply paperboard substrate  4  has an uncoated basis weight of about 185 pounds per 3000 ft 2  (301 g/m 2 ). 
     In an aspect, the single-ply paperboard substrate  4  has an internal sizing agent incorporated therein. The internal sizing agent may be any chemical or chemicals added, before thermoforming, which exhibit hydrophobicity. The internal sizing agent may be added before the papermaking process, during the papermaking process, after the papermaking process, or combinations thereof. In an example, the internal sizing agent may be added after the papermaking process via a liquid additive system, such as a continuous metering system from CMS Industrial Technologies, LLC, Gainesville, Ga., United States. 
     The internal sizing agent may include, for example, alkyl ketene dimer (AKD), dispersed rosin size (DRS), alkyl succinic anhydride (ASA), and combinations thereon. In a specific expression, the internal sizing agent includes 8 to 12 pounds of DRS per ton of paperboard (4 to 6 kilograms of DRS per metric tonne of paperboard) and 1 pound of AKD per ton of paperboard (0.5 kilogram of AKD per metric tonne of paperboard). 
     When the coated paperboard  2  is formed into a paperboard tray, the barrier coating  10  functions to separate a moist food product carried on the paperboard tray from the single-ply paperboard substrate  4 . Thus, the barrier coating  10  is a coating having water- and grease-resistance. 
     Additionally, the barrier coating  10  is a high stiffness barrier coating having an elastic modulus of at least 1.5 GPa. In an aspect, the barrier coating  10  has an elastic modulus of from 1.5 GPa to 6.0 GPa. In another aspect, the barrier coating  10  has an elastic modulus of from 2.0 GPa to 5.0 GPa. The high stiffness of the barrier coating  10  functions to increase a rigidity of the coated paperboard  2 . Thus, when the coated paperboard  2  is formed into a paperboard tray having the barrier coating  10  on the inner side of the paperboard tray, the paperboard tray can be provided with sufficient rigidity to withstand using the paperboard tray in an overwrapping process. 
     In an aspect, the barrier coating  10  includes polylactic acid (PLA). For example, the barrier coating  10  can be (or can include) one or more of the biopolymer coatings disclosed in Intl. Pat. App. No. PCT/US2016/062136 filed on Nov. 16, 2016, published as WO 2017/091392 A1, the entire contents of which are incorporated herein by reference. In another aspect, the barrier coating  10  includes polyethylene terephthalate (PET). 
     In an aspect, the barrier coating  10  has an average thickness of 0.00025 inch (6.3 μm) or more. In another aspect, the barrier coating  10  has an average thickness of 0.00025 to 0.005 inches (6.3 to 127 μm). In yet another aspect, the barrier coating  10  has an average thickness of 0.0005 to 0.003 inches (12.7 to 76 μm). In yet another aspect, the barrier coating  10  has an average thickness of 0.00075 to 0.002 inches (19 to 51 μm). In yet another aspect, the barrier coating  10  has an average thickness of 0.001 to 0.00175 inches (25.4 to 44.5 μm). In yet another aspect, the barrier coating  10  has an average thickness of 0.001 to 0.0015 inches (25.4 to 38.1 μm). In yet another aspect, the barrier coating  10  has an average thickness of 0.001 to 0.00125 inches (25.4 to 31.8 μm). 
     The barrier coating  10  may be applied, for example, by extrusion coating onto the single-ply paperboard substrate. 
     The coated paperboard  2  as described above may be formed into a paperboard tray. 
       FIG. 4  is a perspective view of an exemplary rectangular paperboard tray  20 .  FIG. 5  is a top view of the paperboard tray  20  of  FIG. 4 .  FIG. 6A  is a side sectional view of the paperboard tray  20  of  FIG. 4  along section A-A.  FIG. 6B  is a side sectional view of the paperboard tray  20  of  FIG. 4  according to an alternative variation along section A-A. 
     Although the paperboard tray  20  is illustrated as having a rectangular shape, the shape is not limited to rectangular and may include any shape, such as circular, square, polygon, or irregular. 
     In a specific expression, the paperboard tray  20  is rectangular. In an aspect, the length is between 8 and 10 inches (20.3 and 25.4 cm), the width is between 6 and 7 inches (15.2 and 17.8 cm), and the height is between 0.75 and 2 inches (1.9 and 5.1 cm). In a specific expression, the length, width, and height are approximately 8.75 inches, 6.5 inches, and 1.25 inches (22.2 cm, 16.5 cm, and 3.2 cm), respectively. However, it will be understood that the present description is not limited to these specific dimensions and other dimensions and shapes are possible and would be desirable. 
     As shown, the paperboard tray  20  includes a coated paperboard  2  in the form of a bottom wall  21 , a side wall  22  extending upwardly around the bottom wall, and a flange  23  extending outwardly around the side wall  22 . As expressed above, the coated paperboard  2  includes the single-ply paperboard substrate  4  having the first major side  6  and the second major side  8  and the barrier coating  10  on the first major side  6  of the single-ply paperboard substrate  4 . The first major side  6  of the paperboard substrate  4  corresponds to an upper side of the bottom wall  21 . By positioning the high stiffness barrier coating  10  on the upper side of the bottom wall  21 , the paperboard tray  20  is provided with water- and grease-resistance desirable for carrying moist food items, and the paperboard tray  20  is provided with sufficient rigidity to withstand using the paperboard tray  20  in an overwrapping process. 
     Two exemplary embodiments of the flange  23  are shown in  FIGS. 6A and 6B . In one example, the flange  23  may include any design, including, for example, a horizontal flange  24  as shown in  FIG. 6A . In another example, the flange  23  includes, as shown in  FIG. 6B , a first flange portion  24  in the form of a horizontal flange and a second flange portion  25  in the form a moveable, downwardly extending flange, in which the first flange portion  24  and second flange portion  25  are coupled by a creased portion  26 . 
     In an aspect, the first flange portion  24  has a length y and the second flange portion  25  has a length x. In an aspect of the present description, a ratio of x/(x+y) is greater than 0 and less than ½. 
     The paperboard tray  20  may be formed by any manufacturing method, such as by a thermoforming method. 
     According to an aspect of the present description, a method for manufacturing the paperboard tray  20  includes forming a paperboard blank  14  from a coated paperboard  2 , in which the coated paperboard  2  includes the single-ply paperboard substrate  4  having the first major side  6  and the second major side  8  and the barrier coating  10  on the first major side of the single-ply paperboard substrate  4 . The method further includes thermoforming the paperboard blank  14  into the paperboard tray  20  having the bottom wall  21 , the side wall  22  extending upwardly around the bottom wall  21 , and the flange  23  extending outwardly around the side wall  22 . 
     The paperboard blank  14  may be formed from a roll  12  of coated paperboard  2 . For example, a roll  12  of coated paperboard  2  may be fed to a forming press. The roll  12  may be unwound at the forming press and directed to a cutting section of the forming press where the coated paperboard  2  is cut to the shaped of the paperboard blank  14 . 
     The paperboard blank  14  may then be transported to a thermoforming section of the same (or different) forming press.  FIG. 7  is schematic representation of a cross-section of a conventional male die  77  and female die  74  used for thermoforming the paperboard blank  14  into a paperboard tray  20 . It will be understood that the male die  77  and the female die  74  as illustrated in  FIG. 7  are merely exemplary, and that thermoforming systems may include a variety of modifications and alternatives. 
     At the thermoforming section  70 , the paperboard blank  14  is thermoformed with the male die  72  and the female die  74  using heat and pressure to form a paperboard tray  20 . Thus, the paperboard blank  14  is heated, drawn into the temperature-controlled female die  74  by the temperature-controlled male die  72 , and then held against the surfaces of the male die  72  and female die  74  until cooled. 
     The temperature of the female die  74  is controlled to be at a higher temperature than the male die  72 . The first major side  6  of the paperboard substrate  4  is arranged to face the male die  72  and the second major side  8  of the paperboard substrate  4  is arranged to face the female die  74 . In an aspect, by applying a higher heat with the female die  74  and a lower heat with the male die  72 , the barrier coating  10  on the first major side  6  of the paperboard substrate  4  is heated to a lesser amount. 
     If the temperature of the male die  72  is too low, then the barrier coating  10  as well as the paperboard substrate  4  may be insufficiently heated and the paperboard tray  20  may not be strongly formed to the desired shape. If the temperature of the male die  72  is too high, then the barrier coating  10  may stick to the male die  72 . Accordingly, in an aspect, the male die  72  preferably has a temperature of approximately 110-220° F. (43-105° C.). In yet another aspect, the male die may have a temperature of approximately 120-200° F. (49-93° C.). In another aspect, the male die may have a temperature of approximately 120-140° F. (49-60° C.). 
     In an aspect, the female die may have a temperature of approximately 200-450° F. (93-232° C.). In another aspect, the female die may have a temperature of approximately 250-350° F. (121-177° C.). In yet another aspect, the female die may have a temperature of approximately 300-325° F. (149-163° C.). 
     The temperature of the male die may depend on the composition of the barrier coating. In a specific example, when the barrier coating includes polylactic acid (PLA), the male die preferably has a temperature of approximately 110-160° F. (43-71° C.), more preferably 120-140° F. (49-60° C.). In another specific example, when the barrier coating includes polyethylene terephthalate (PET), the male die preferably has a temperature of approximately 110-200° F. (43-93° C.), more preferably 120-190° F. (49-88° C.). 
     In an aspect, a moisture content of the coated paperboard  2  is controlled during the thermoforming process. The moisture content may be controlled by, for example, using a humidifier to control an atmospheric humidity or addition of moisture directly to the coated paperboard. 
     If the moisture content of the coated paperboard  2  is too high, then blistering of the barrier coating  10  may occur. If the moisture content of the coated paperboard  2  is too low, then corner cracking of the paperboard substrate  4  and barrier coating  10  may occur. In an aspect, the moisture of the coated paperboard  2  is controlled between 9 and 14% by weight. In another aspect, the moisture of the coated paperboard  2  is controlled between 10 and 13% by weight. 
     Prior to thermoforming, a backside coating may optionally be applied to the substrate. The coating purpose is to prevent purge and other liquids trapped under the tray during overwrapping and throughout shelf-life from being absorbed into the paperboard. Resistance of moisture absorption is critical for maintaining rigidity of the tray during transport and shelf-life. Once moisture penetrates the paperboard surface, the tray may weaken and potentially fail. 
     The coating can be applied as either an overprint coating or extrusion. Examples of suitable coatings include aqueous coatings such as acrylic styrenes, PLA, PET, and other polymers. Such a coating has the primary advantage of resisting moisture absorption, but may also provide advantages such as increased rigidity, compostability and recyclability. Such a coating can further act as a release agent during the thermoforming process thereby improving manufacturing speeds and quality of the tray. 
     According to an aspect of the present description, a method for using the paperboard tray  20  includes positioning a food product within the paperboard tray  20  and wrapping a film  30  over the product and the paperboard tray  20 . 
     In an aspect, the food product may be a moist food product, such as meat, poultry, seafood, and produce, and the food product may be positioned with the paperboard tray  20  manually or by way of an automated process. 
     The step of wrapping the film  30  over the product and the paperboard tray  20  may including a manual overwrapping process or an automatic overwrapping process using an overwrapping machine. 
     By way of example, an exemplary overwrapping machine may take a length of heat sealable film from a roll and fold it around a paperboard tray containing a product. The folded film may then be closed to itself by means of a heated sealing device. However, the overwrapping is not so limited. In a variation, overwrapping may include folding a film around the paperboard tray and lightly sealing the film to itself, such as by way of light heating or adhesive. In another variation, overwrapping may include folding a film around the paperboard tray and sealing the film to the paperboard tray, such as by way of heating or adhesive. 
     In one example, the film may be CRYOVAC® SES-340 oxygen permeable stretch-shrink poultry film. In another example, the film may be formed from a transparent wrapping material, such as CRYOVAC® D-940 Polyolefin Shrink Film Roll—60 gauge. In a variation, the film may be formed from a non-transparent wrapping material. In another variation, the transparent wrapping material or non-transparent wrapping material may be printable such as to permit printing of graphics and/or text on the film. 
       FIG. 8A  shows a side sectional view of the paperboard tray  20  of  FIG. 6A  in a fully wrapped configuration.  FIG. 8B  shows a side sectional view of the paperboard tray  20  of  FIG. 6B  in the fully wrapped configuration. 
     As shown in  FIG. 8A , when the paperboard tray  20  is subjected to an overwrapping process, the flange  23  provides strength to the paperboard tray  20  against an inward buckling of the paperboard tray  20 . However, the flange  23  may still downwardly deflect due to a force applied by the overwrapped film  30 . By positioning the high stiffness barrier coating  10  on a side of a single-ply paperboard substrate  4  that corresponds to an inner side of a paperboard tray  20  formed from the coated paperboard  2 , the paperboard tray can be provided with sufficient rigidity to better withstand using the paperboard tray  20  in the overwrapping process. 
     As shown in  FIG. 8B , when the paperboard tray  20  is subjected to an overwrapping process, the second flange portion  25  folds at the creased portion  26  to defect with the force applied by the overwrapped film. By predetermining the origin of the deflection of the second flange portion  25  (i.e. by folding at the creased portion  26 ), a uniformity of the effect of the overwrapping process on the paperboard tray  20  can be increased. Moreover, during the thermoforming process, the second flange portion  25  can be bent during the thermoforming to the same extent as the bend that will be applied during the overwrapping process. In other words, the second flange portion  25  may be bent during the thermoforming process to up or more than a 90 degrees angle relative to the first flange portion  24  and then unbent to shape illustrated in  FIG. 6B . For example, the second flange portion  25  may be bent during the thermoforming process to an angle of between 90-135 degrees relative to the first flange portion  24 . Accordingly, by this overbending of the second flange portion  25 , then the second flange portion  25  can better withstand using the paperboard tray in the overwrapping process. 
     As previously indicated, the first flange portion  24  has a length y and the second flange portion  25  has a length x. In an aspect of the present description, a ratio of x/(x+y) is greater than 0 and less than ½.  FIG. 9  shows results from a finite element model for optimization of the flange  23  of  FIG. 6B , in which the effect of various ratios of x/(x+y) on Force (N) over Displacement (mm) during a simulation of an overwrapping process. As indicated in  FIG. 9 , improved performance results when a ratio of x/(x+y) is greater than 0 and less than ½. 
     Although various embodiments of the disclosed coated paperboard, paperboard tray, method for manufacturing a paperboard tray, and method for using a paperboard tray have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.