Patent Application
20110168771
Paper-based containers with barrier properties are typically formed from paper-based blank comprising paperboard substrate and functionalized layers such as oxygen and moisture barrier layers. The blank is die cut to the desired silhouette and then formed into a shape by wrapping it once around a mandrel. The overlapping ends of the blank form a straight seam having an underlying portion and an overlying portion.
One approach is to cover the exposed raw edge of the blank with a strip of barrier tape. Examples of the known materials as a barrier tape to protect the raw edges of the paperboard containers include metal foils such as aluminum foil and tin foil, low density polyethylene (LDPE), ethylene-vinyl alcohol copolymer (EVOH), polyethylene terephthalate (PET), glycol modified PET, nylon, and combinations thereof. U.S. Pat. No. 5,620,135 discloses a technique for covering the raw edge of the body with a protective covering tape. The container body is formed from a blank having one longitudinal edge enclosed by a U-shaped protective covering. Prior to formation of the container body, the protective covered region of the blank is compressed to a reduced thickness such that the entire sheet segment, including the protective region, has an approximately same thickness. PCT Application No. WO 2003/106277 discloses a single wrap container having the exposed underlying edge of the paper-based container body enclosed by a tape that comprises a layer of metalized PET interposed between layers of LDPE. The container body is made of blank comprising layers of, from the inside out, polyolefin, paper stock, polyolefin, metal foil, polyolefin, printed paper and overprint varnish. Using protective tapes to cover the raw edges, however, has several drawbacks. The adhered protective tape is an additional cost, and may be easily removed. Furthermore, an additional process is required to apply the protective tapes, resulting in further increase in cost and complexity of the manufacturing process.
Another approach commonly used in multi-ply tubular container process is to fold the underlying edge portion of the barrier liner ply into an “anaconda” fold, wherein the underlying edge is folded back on itself and adhere to the overlying edge. An example of such a fold is illustrated in U.S. Pat. No. 5,084,284. The main drawback of anaconda fold is the undesired increase in thickness of the seam, as it is three times the thickness of the blank. Cracks tend to form with such high thickness, resulting in a leakage of the contents, an influx of the outside air, and a reduction in barrier performance of the containers. Furthermore, such undesirably high thickness of the seam poses difficulties when attempting to hermetically seal the ends of the container body itself, as well as seal the top lid and bottom to the container body. To address the difficulty in folding the paper-based blank during the formation of the container body, several techniques have been used to reduce the thickness of the blank.
U.S. Pat. No. 6,190,485 teaches a technique of manufacturing a hermetically sealed spiral-wound multi-ply container without using “anaconda” fold. The hollow body component of the hermetically-sealed container comprises a paperboard body ply and a liner ply on the inner surface of the body ply, wherein the inner ply includes a barrier layer and a layer of adhesive that is activatable at a predetermined activated temperature. A continuous body ply formed of paperboard having first and second side edges is advancing towards a shaping mandrel, while a continuous polymeric liner ply having first and second side edges is advancing adjacent to one surface of the paperboard body ply. The liner ply and the body ply are passing in face-to-face contact through a pair of nip rollers with the adhesive layer of the liner ply adjacent to the body ply, such that the first marginal edge of the liner ply extend beyond the first marginal edge of the body ply. The adhesive layer is then heated above its activated temperature so that the liner ply becomes adhered directly to the inner surface body ply. The resulting adhered multi-ply is wrapped around the shaping mandrel such that the second marginal edge of the body ply engages the first marginal edge of the body ply, and the second marginal edge of the liner ply engages the first marginal edge of the liner ply. Finally, the first marginal edge of liner ply is heated to a temperature above the activated temperature of the adhesive so the second marginal edge adheres to the first marginal edge, resulting in a tubular shape that is subsequently cut into discrete lengths to provide the hollow body component of the hermetically sealed paperboard container. This process of producing hermetically seal container uses continuous webs of paperboard ply and liner ply which require rather intensive handlings, relatively high shipping and storage costs.
Another approach of protecting the raw edge of the blank is “skiving and hemming”, as described in U.S. Pat. No. 5,236,408. Skiving is removing half the thickness of the paperboard from the side seam flap. Hemming is folding the skived area back onto itself and sealing the other edge over the hemmed area by heat or flame. This approach has been used for producing gable top cartons for the liquid packaging industry, as described in U.S. Pat. No. 5,810,243. While the raw edge of the vertical side seam of the carton is protected, special sealing techniques using sealing jaws are required, such as those described in the International Patent Application No. WO 2008/025996 and WO 1990/009926, to seal the folded top and bottom flaps to achieve hermetically sealed carton.
Achieving hermetically sealed barrier paperboard cup using the “skiving and hemming” approach is difficult on the paperboard cup forming machine, which is typically designed to produce liquid-tight container with a top rim not designed for gas tight seal. The increased thickness of the skived/hemmed edge area over the original paperboard provided additional challenge in producing hermetically sealed bottom in the area where the thick skived/hemmed seam meets the bottom in the overlapped area. The skived edge also substantially increases the abrupt step at the seam of the top rim formed by the overlapped ends of the blank, and the non-planar hill-like surface of the rim makes hermetic seal of the lidding membrane (film or paper) more difficult.
GB Patent Application No. 2055743 discloses a paper-based container comprising a hollow container body having recessed structure on the upper and lower ends, a top lip positioning on the recessed top of the container body, and a bottom positioning on the recessed bottom. The hollow container body is produced by skiving one longitudinal end of a paper-based blank to substantially half its thickness for a predetermined width and then forming a longitudinal groove substantially at the center of the skived portion. A heat-resistant adhesive, such as vinyl acetate emulsion and the like, is applied to the skived portion, and the adhesive is irradiated with infrared rays to evaporate water contained therein. The skived portion is then folded about the groove so that the end face of the skived paper and the end face of the unskived portion contact each other. Subsequently, the container body is formed by adhering both longitudinal ends of the blank together in overlapping relation with the folded longitudinal end inside the other longitudinal end. The paper-based blank consists of, from the outside: a thermo plastic synthetic resin layer, a paper layer, an adhesive layer, a metal layer, a heat-resistant adhesive layer, and a thermoplastic synthetic resins layer. The top lid and bottom components may be made of the same or similar material as that for the body component. This process of producing barrier container is, however, rather complicated and high cost due to the use of adhesives and the recessed structure of the upper and lower ends.
Up until the present disclosure, to the inventor's knowledge, hermetically sealed barrier paperboard cup has not been achieved commercially using the “skiving/hemming/flame sealing” approach without adhesives on regular cup forming machines.
Accordingly, there is still a need for hermetically sealed paperboard containers with enhanced barrier and seal performances that may be produced by a process that is more effective and economical using commercially available high-speed liquid packaging skiving/hemming/sealing equipment and cup forming machines without the use of adhesives. One advantage of such approach is the potential for the in-plant system, where skived blanks can be shipped flat to the packaging plant where the barrier cups are formed using in-plant cup forming machines.
It is further beneficial to have hermetically sealed paperboard containers with excellent barrier performance that do not require the use of metal foils to impart the barrier properties.
A hermetically sealed paperboard container with enhanced barrier and seal performances is disclosed that may be produced by a more effective and economical process for the in-plant system. The presently disclosed process overcomes the known difficulties of producing hermetically sealed cup from skived/hemmed blanks with increased thickness on the seam using regular cup forming machines. The disclosed process involves a combination of barrier material structure, skived/hemmed side seam, and optimization of cup forming and lid sealing processes to eliminate any pinholes or gas leakage area without sacrificing seal strength. The disclosed container includes a container body component, a bottom, and a top lid hermetically sealed to the body component. The container body is formed from a blank comprising a paperboard having one surface coated with a first sealant layer and the opposite surface coated with a barrier layer, and a second sealant layer applied over the barrier layer. One longitudinal end of the blank is skived to a predetermined thickness for a predetermined width, folded over onto the blank, and sealed to form a folded longitudinal end with slightly increased thickness. Then, the folded longitudinal end of the blank is overlapped inside the other longitudinal end of the blank to form a body seam that is subsequently sealed to provide the hollow container body. A bottom end formed of the same barrier paperboard structure is attached at the bottom end of the container body. The bottom end has a downwardly directed skirt which secures the end to the container body wall by being folded and squeezed within an upturned edge of the body wall. As such, the bottom seal is formed of three plies of paperboard. A rim curl at the top of the container is formed to provide more container strength and better appearance. A lid of barrier material is applied over the rim of the container to form hermetically sealed container for food packaging applications.
The present disclosure now will be described more fully hereinafter, but not all embodiments of the disclosure are necessarily shown. While the disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof.
The hermetically sealed paperboard container with enhanced barrier performance of the present disclosure includes:
The method of producing a hermetically sealed paperboard container of the present disclosure comprises steps of:
The container body component is formed from a blank that is made of a substrate including:
A variety of paperboard may be used in the present disclosure. These include, but are not limited to, coated natural kraft board (CNK board), solid bleached sulfate board (SBS), solid unbleached sulfate board (SUS), coated recycled board (CRB), coated white lined chipboard (WLC), folding boxboard (FBB), and other paperboard grades suitable for cup formation.
Suitable sealer layers for use in the present disclosure include, but are not limited to, polyester; low density polyethylene (LDPE); high density polyethylene (HDPE); ethylene-vinyl acetate copolymer (EVA); ethylene methyl acrylate (EMA) copolymer; ionomer polymers such as poly(ethylene-co-methacrylic acid) (EMAA) copolymer SURLYN® commercially available from DuPont; and combinations thereof.
Barrier layers suitable for use in the present disclosure include, but are not limited to, nylon polymers, ethylene-vinyl alcohol copolymer (EVOH), polyethylene terephthalate (PET), materials derived from water-based barrier coatings, polyamide, polyvinylidene chloride, cyclic olefin copolymer, metalized polymer film, and combinations thereof. A variety of water-based barrier coatings known for imparting the barrier properties to paperboard may be used in the present disclosure to provide a barrier layer. When desired, the water-based barrier coatings may include nanoparticles to provide the tortuous effect that hinders the diffused molecules through the coating.
In one embodiment of the present disclosure, the water-based barrier coating composition comprises a polymeric binder, an amine stabilizer, and optionally filler particles, wherein the water-based composition has a pH of greater than or equal to pKa of the amine stabilizer. Examples of suitable fillers include, but are not limited to, layered fillers capable of being at least partially exfoliated such as bentonite, vermiculite, montmorillonite, smectite, kaoline; nanoparticle filler such as nanotalc particle; conventional low-cost fillers commonly used for the paper coating such as kaolin clay, talc, calcined clay, structured clay, ground calcium carbonate, precipitated calcium carbonate, titanium dioxide, aluminum trihydrate, satin white, silica, zinc oxide, and barium sulfate; and mixtures thereof. A variety of polymeric binders known for paper coating applications may be used. These include, but are not limited to, polyesters, styrene-acrylic polymers, styrene-butadiene polymers, vinyl-acrylic polymers, polyvinyl acetate, polyurethanes, polyacrylic acid, sodium polyacrylate, ammonium polyacrylate, sulfo-polyesters, urethane-acrylic copolymer, and combinations thereof. The water-based barrier coating composition may further include processability or functional additives which include, but are not limit to, colorants, pigments, defoaming agents, dispersing agents, tackifiers, surfactants, emulsifiers, coalescing agents, plasticizers, buffers, neutralizers, wetting agents, leveling agents, thickeners, rheology modifiers, biocides, waxes, water repellants, slip or mar aids, antioxidants, additive fillers, starch, and combinations thereof.
The sealant layer and barrier layers may be applied to the substrate by any known methods. Examples of these applications include, but are not limited to, extrusion coating, extrusion laminate, curtain coating, and adhesive lamination.
The water-based barrier composition may be applied onto the substrate by any coating techniques commonly utilized in the paper coating applications either on-line during paperboard making process or off-line. These include, but are not limited to, size press application, brushing, spraying, roll coating, rod-coatings, dipping, spreading, printing methods, air knife coating, and curtain coating. When desired, the water-based barrier coating composition may be applied onto the paperboard on-line during the papermaking process to reduce both production cost and complexity.
The substrate is die cut to a desired silhouette to provide a blank including a first and a second longitudinal ends. The first longitudinal end of the blank is skived to a predetermined thickness for a predetermined width. The resulting skived end of the blank is treated with heat, then folded and sealed over the blank to provide the folded first longitudinal end. As shown in
The lid component may include a barrier paper-based substrate, a barrier polymeric film, or combinations thereof. In one embodiment of the present disclosure, the lid component comprises a paperboard, a barrier layer applied over the paperboard, and a sealant layer positioned over the barrier layer. When desired, the top lid component may be made of the same or similar material as that for the container body component. Several methods may be used for hermetically sealing the lid component to the container body component. Example of such hermetic seals include, but are not limited to, hermetically seal the top with a plastic rim; a sealant bead dropped at the step-down area; a sealant bead added to the entire top rim before lidding; a lidding material with a heavy sealant such as those lidding film used for sealing barrier trays; a higher sealing pressure to press down lidding material to flatten the rim for maximum seal; and combinations thereof.
In one embodiment of the present disclosure, the bottom comprises a paperboard, a barrier layer applied over the paperboard, and a sealant layer positioned over the barrier layer. When desired, the bottom component may be made of the same or similar material as that for the container body component. The bottom may be assembled to the container body component by various sealing technologies. Examples of such sealing may include, but not limited to, hot air heat seal and ultrasound sealing. The sealing process may be optimized based on various factors. Some of these factors include, but are not limited to, the thickness of the sealant layer on the bottom; and the processing conditions such as lower sealing temperature to prevent the formation of pinhole, and higher sealing pressure to minimize the formation of gap between the bottom and the body component.
After formation of the container body component, the configuration of the upper and lower ends of the body may be constructed to support the sealing with the lid and the bottom components. Any known configurations for the upper and lower ends of the container body may be used in the present disclosure, and the selection of such configuration depends on the desired packaging applications of the container. Example of the configurations for the upper and lower ends of the container body include, but are not limited to, recessed structure, rolled bead, flange, and combinations thereof.
The disclosed method of producing hermetically sealed paperboard containers utilizes the flat blanks of paperboard having functionalized coating layers, rather than continuous webs of paperboard ply and inner ply of functionalized layers. The flat blanks used in the present disclosure may be shipped and stored flat; therefore, a substantial saving may be achieved due to a reduced storage and shipping costs. Furthermore, the handling efficiency during manufacturing production may be improved significantly because of the compactness of the flat blanks.
In one embodiment of the present disclosure, the barrier paperboard cups were made from paperboard blanks comprising layers of LDPE/paperboard/LDPE/EVOH/tie-layer/LDPE. The blanks were constructed into cup shape using a cup forming process. The paperboard blank structure and the thickness of each layer were critical for the formation of pin-hole free, hermetically sealed cups. In one example, the outer surface of a SBS paperboard substrate of 310 gsm (gram per square meter) was extrusion-coated with 35 gsm (1.5 mil thick) LDPE. The inner surface was coextrusion-coated with the following layers, starting from the paperboard: a 13-gsm layer of LDPE, a 10-gsm layer of EVOH, a 6.5-gsm tie-layer, and a 35-gsm layer of LDPE. The total coating thickness of the barrier layers on the inner surface of the paperboard was 2.7 mil. Same multilayer structure was used for the bottom component, except that the substrate used was a 220-gsm SBS paperboard.
The longitudinal end of the side wall blank that formed the inner side seam was skived to half of its thickness, folded, and then flame sealed to itself to provide a raw edge protection for hermetic seal when the cups was formed. A high speed cup forming machine (e.g. model 1001 from Paper Machinery Corporation) was used to produce the barrier cups using the above materials and structures. The heat-molten polymer and pressure were used as means to secure the sidewall seam, and the bottom seal during the cup forming process.
The conventional cups formed from typical LDPE-coated cupstock or even barrier board substrates are known to provide unavoidable pin holes in LDPE layer during that heat sealing processing. The presence of pin-holes on the formed cups was acceptable for liquid-tight applications such as cold or hot drinks. However, these pinholes are not acceptable in packaging containers for gas-tight applications such as snack foods. The pin-hole formation in LDPE could be minimized by reducing an excessive heat, but seal strength would be compromised.
The aforementioned known pin-hole formations may be eliminated in the hermetically sealed paperboard cups of the present disclosure. Surprisingly, a pin-hole free hermetically sealed cup could be achieved using the disclosed paperboard material even when the board structure comprises a predetermined barrier and heat-seal layers structure with certain thickness (total of 3 mils or more polymer layers preferred). It is believed that the absence of pinhole and the enhancement of hermetic seal performances of the disclosed paperboard cups may be due to the synergistic effect between several factors: the use of an improved barrier multilayer board structure with certain polymer thickness; the enhancement of skived/hemmed side seam, the optimization of cup forming process conditions such as a selected heat seal temperatures at which the oxygen-barrier layer remains intact and pin-hole free, and the lid sealing using barrier lidding material with certain polymer coating thickness and heat sealing conditions. In one embodiment, the thickness of the polymer coating is at least 3 mils. To form a hermetic lid seal over the rolled rim of the container, particularly over the step-down area (504 in
In one exemplary embodiment, 12-ounce round hermetically sealed cup with a package surface area of 0.03 m2 was formed using the aforementioned materials and procedure. The oxygen transmission rate (OTR) of the hermetically sealed cups of the present disclosure was measured and compared to those of the two controls: the conventional cup with LDPE layer, and the barrier cup with EVOH barrier layer but without skived side seam. The OTR measurement was performed at 23° C. and 0% relative humidity using an oxygen transmission analyzer commercially available from Mocon Inc. The OTR measurement of the disclosed hermetically sealed cup was about 0.1 cc/package/day. In comparison, the OTR measurement of the control conventional cup was about 119 cc/package/day, and that of the barrier cup with EVOH barrier material but without skived side seam was about 20 cc/package/day. These results demonstrated the improved barrier performance of the disclosed hermetically sealed, skived cup.
In the present disclosure, the hermetically sealed cup that is pin-hole free may be produced without sacrificing seal integrity, by using a properly designed barrier material structure and optimized converting cup process conditions.
While the disclosure has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. It is intended that the disclosure not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
This non-provisional application relies on the filing date of provisional U.S. Application Ser. No. 61/180,143 filed on May 21, 2009, the entire contents of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2010/035704 | 5/21/2010 | WO | 00 | 8/20/2010 |
| Number | Date | Country | |
|---|---|---|---|
| 61180143 | May 2009 | US |
