COATED CELLULOSIC STRUCTURES AND METHOD FOR MANUFACTURING THEREOF
20250333907 ยท 2025-10-30
Inventors
- Rahul BHARDWAJ (Glen Allen, VA, US)
- Justin L. BENNETT (Williamsburg, VA, US)
- Zack SIMONCELLI (Richmond, VA, US)
- Jiebin Pang (Glen Allen, VA)
- Mohammadtaghi SAVOJI (Atlanta, GA, US)
Cpc classification
D21H19/44
TEXTILES; PAPER
D21H19/12
TEXTILES; PAPER
International classification
Abstract
A coated cellulosic structure including a cellulosic substrate having a first major surface and a second major surface and a printability coating on the first major surface of the cellulosic substrate. A moisture vapor barrier coating is disposed on the second major surface of the cellulosic substrate. A primer coating is disposed on the printability coating at a sealing area of the coated cellulosic structure. An overprint water barrier coating is disposed on the printability coating at a non-sealing area of the cellulosic structure.
Claims
1. A coated cellulosic structure, comprising: a cellulosic substrate having a first major surface and a second major surface; a printability coating on the first major surface of the cellulosic substrate; a moisture vapor barrier coating on the second major surface of the cellulosic substrate; a primer coating on the printability coating at a sealing area; and an overprint water barrier coating on the printability coating at a non-sealing area.
2. The coated cellulosic structure of claim 1 in a form of a roll of cellulosic material, a cellulosic blank, a container component, or a container.
3. The coated cellulosic structure of claim 1 wherein the printability coating is on an entirety of the first major surface.
4. The coated cellulosic structure of claim 1 wherein the moisture vapor barrier coating is on an entirety of the second major surface.
5. The coated cellulosic structure of claim 1 wherein the moisture vapor barrier coating comprises polyethylene.
6. The coated cellulosic structure of claim 1 wherein the moisture vapor barrier coating comprises high density polyethylene having a density in a range of between 0.93 and 0.97 g/cm.sup.3.
7. The coated cellulosic structure of claim 1, wherein the primer coating comprises an aqueous primer coating.
8. The coated cellulosic structure of claim 1, wherein the primer coating comprises one or more chemical groups of imine, amides, urethanes, polyester, acrylics, and olefins.
9. The coated cellulosic structure of claim 1, wherein the primer coating comprises polyethyleneimine (PEI).
10. The coated cellulosic structure of claim 1 wherein the sealing area is at least one of a sidewall seam sealing area and a rim sealing area.
11. The coated cellulosic structure of claim 1 wherein the primer coating is on an entirety of the printability coating.
12. The coated cellulosic structure of claim 1 wherein the primer coating is disposed selectively on the printability coating at the sealing area.
13. The coated cellulosic structure of claim 1 wherein the overprint water barrier comprises an aqueous overprint water barrier coating.
14. The coated cellulosic structure of claim 1, wherein the overprint water barrier coating comprises an acrylic material.
15. The coated cellulosic structure of claim 1 wherein the overprint water barrier coating is disposed selectively on the printability coating at the non-sealing area.
16. The coated cellulosic structure of claim 1 wherein the primer coating is on an entirety of the printability coating and the primer coating underlies the overprint water barrier coating at the non-sealing area.
17. The coated cellulosic structure of claim 1 further comprising a printed ink layer between the printability coating and the overprint water barrier coating.
18. The coated cellulosic structure of claim 1 further comprising a printed ink layer between the primer coating and the overprint water barrier coating.
19. The coated cellulosic structure of claim 1 further comprising a printed ink layer between the printability coating and the primer coating.
20. A method for manufacturing a coated cellulosic structure, the method comprising: providing a cellulosic substrate having a first major surface and a second major surface and having a printability coating on the first major surface of the cellulosic substrate; coating a moisture vapor barrier layer on the second major surface of the cellulosic substrate; coating a primer layer on the printability coating at a sealing area; and coating an overprint water barrier layer on the printability coating at a non-sealing area.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
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DETAILED DESCRIPTION
[0020] The present description pertains to a coated cellulosic structure. This structure can manifest in various forms, including, but not limited to, a roll of coated cellulosic material, a coated cellulosic blank (e.g., a sidewall blank), a coated container component (e.g., a sidewall container component), or a container incorporating the coated cellulosic material. The structure features a first major side, which serves as the exterior of a container, and a second major side, designated as the container's interior. The first major side is delineated into a sealing area and a non-sealing area. The sealing area is defined as the portion of the first major side undergoing a sealing process, encompassing potentially a sidewall seam sealing area and/or a rim sealing area. Conversely, the non-sealing area is the portion of the first major side not subjected to sealing, which may bear printed ink.
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[0024] According to the present description, the coated cellulosic structure comprises a cellulosic substrate having a first major surface corresponding to the first major side of the coated cellulosic structure and a second major surface corresponding to the second major side of the coated cellulosic structure. A printability coating may be disposed on the first major surface of the cellulosic substrate corresponding to the exterior side of a resulting container, and a moisture vapor barrier coating may be disposed on the second major surface of the cellulosic substrate corresponding to the interior side of a resulting container. The printability coating and the moisture vapor barrier coating are typically disposed on the entireties of the first and second major surfaces of the cellulosic substrate, respectively. A primer coating is disposed on the printability coating at one or more sealing areas (e.g., a sidewall seam sealing area and a rim sealing area) of the coated cellulosic structure, and an overprint water barrier coating is disposed on the printability coating at a non-sealing area of the coated cellulosic structure. The primer coating may be disposed on the entirety of the printability coating. Alternatively, the primer coating may be disposed selectively at one or more sealing areas, thus being omitted at the non-sealing area or being omitted at a portion of the non-sealing area. The overprint water barrier coating is typically omitted at the sealing areas to ensure effective seal formation. In scenarios where the primer is applied outside the sealing area, it typically underlies the overprint water barrier coating. The coated cellulosic structure may further include a layer of printed ink between the printability and overprint water barrier coatings. The sequence of applying the printed ink and primer coatings can vary, allowing for flexibility in manufacturing. The printed ink layer may be applied on the printability coating before applications of the primer coating, or the primer coating may be applied on the printability coating before applications of the printed ink layer. The present description accommodates potential modifications, such as multiple sub-layers for any of the described coatings or the introduction of other unspecified layers. The present description includes such modifications and is limited only by the scope of the claims.
[0025]
[0026] Cellulosic Substrate: The cellulosic substrate may include any web of fibrous material that is capable of applying the coatings of the present description thereon. The web of fibrous material may refer to a sheet-like structure composed of natural fibers, such as cellulose, wood, cotton, linen, hemp, jute, sisal, flax, or bamboo. The cellulosic substrate may be a single layer or may be multiple layers of fibrous material. The web of fibrous material may be formed by various methods, such as papermaking. The cellulosic substrate may be a paperboard substrate. The cellulosic substrate may be bleached or unbleached. For example, the cellulosic substrate may include a coated natural kraft board, a coated or uncoated solid bleached sulfate board, a coated recycled board, a coated white lined chipboard, or a folding boxboard.
[0027] The thickness of the cellulosic substrate may depend on various factors, such as the density of the cellulosic substrate. For example, the cellulosic substrate may have a caliper thickness in a range of 6 points to 36 points (1 point equals 0.001 inch). As one specific example, the cellulosic substrate may have a caliper thickness of 7 points to 30 points. As another specific example, the cellulosic substrate may have a caliper thickness in a range of 9 points to 25 points. As another specific example, the cellulosic substrate may have a caliper thickness in a range of 10 points to 20 points. As yet another specific example, the cellulosic substrate may have a caliper thickness in a range of 12 points to 16 points. As used herein, 1 point equals 0.001 inches, which equals 25.4 micrometers (m).
[0028] The weight of the cellulosic substrate may depend on various factors. For example, the cellulosic substrate may have a basis weight ranging from 60 to 350 pounds per 3,000 square feet. As one specific example, the cellulosic substrate may have a basis weight of 100 to 300 pounds per 3000 ft.sup.2. As another specific example, the cellulosic substrate may have a basis weight of 140 to 220 pounds per 3000 ft.sup.2.
[0029] Printability Coating: The printability coating may be disposed to the first major surface paperboard substrate to enhance the printing quality of the cellulosic substrate. This coating also provides a better hold out of over print moisture barrier coating. The printability coating may comprise a mixture of pigment and binder, where the pigment serves to improve the visual and physical properties of the printed surface. The pigment component can include a variety of inorganic pigments or organic pigments. Inorganic pigments may include, for example, clay, such as kaolin, which improves ink adhesion and surface smoothness, calcium carbonate (CaCO3), for ability to enhance brightness and opacity; titanium dioxide (TiO2), which provides exceptional brightness and opacity. Other pigments may include silica (SiO2), aluminum hydroxide (Al (OH) 3), barium sulfate (BaSO4), zinc oxide (ZnO), and carbon black.
[0030] The binder component in the printability coating serves to adhere the pigment to the cellulosic substrate and may include natural or synthetic polymers. Examples of binders that can be used include starch, casein, soy protein, latexes (such as styrene-butadiene, acrylic, or polyvinyl acetate), and other water-soluble or water-dispersible polymers. A typical binder is an emulsion polymer binder which has excellent adhesion and flexibility properties. These binders can provide a durable bond between the pigment particles and the cellulosic substrate, ensuring that the printability coating remains intact even under conditions of direct contact with moisture. Emulsion polymer binders can be made from a variety of monomers, including, but not limited to, acrylics, vinyl acetates, styrene, and butadiene.
[0031] The printability coating's binder content can differ based on the pigment type, application and desired coating properties. Too little binder in the printability coating could reduce the pigment's attachment to the cellulosic substrate, affecting print quality or coating durability. Too much binder in the printability coating could lower the coating's porosity, resulting in less ink uptake and poorer print quality. A common range for binder to pigment ratio in a printability coating is 5 to 30 weight parts of binder for every 100 weight parts of pigment. In one example, the printability coating may have 5 to 25 weight parts of binder for every 100weight parts of pigment. In another example, the printability coating may have 10 to 20 weight parts of binder for every 100 weight parts of pigment.
[0032] The printability coating may be applied in any manner that is capable of applying the printability coating onto the cellulosic substrate. Examples of coaters which may be employed include air knife coaters, blade coaters, rod coaters, bar coaters, multi-head coaters, roll coaters, roll/blade coaters, cast coaters, laboratory coaters, gravure coaters, kiss coaters, liquid application systems, reverse roll coaters, curtain coaters, spray coaters and extrusion coaters.
[0033] Moisture Vapor Barrier Coating: The moisture vapor barrier coating is applied to the second major surface of the cellulosic substrate, serving to substantially prevent the transmission of moisture vapor through the cellulosic structure. The presence of this coating maintains the structural integrity and usability of the container, especially when it is used to hold liquids or moisture-rich foods. The composition of the moisture vapor barrier coating can vary, depending on the desired barrier properties and the nature of the contents to be contained. The material of the moisture vapor barrier coating may be selected for hydrophobic properties and ability to form a continuous film that effectively blocks or slows down the moisture penetration. Typical moisture vapor barrier coating include different polyethylenes, polylactic acid and polyethylene terephthalate.
[0034] In an example, the moisture vapor barrier coating of the present description includes a polyethylene coating. The choice of polyethylene for the moisture vapor barrier coating is attributed to its compatibility with cellulosic substrates, moisture vapor barrier properties, and heat sealability. Polyethylene, being a hydrophobic material, offers a robust barrier against moisture, which is important for maintaining the structural integrity and functionality of cellulosic containers that are intended to hold liquids or moisture-sensitive contents. Polyethylene also provides heat sealability, thereby enabling for directly sealing to the seal areas of the first major side of the coated cellulosic structure with necessitating application of an additional heat sealing material. Polyethylene coatings can be applied in various forms, including low-density polyethylene (LDPE) and high-density polyethylene (HDPE), each offering distinct advantages. LDPE coatings may be chosen for their flexibility and superior heat sealability.
[0035] In another example, the moisture vapor barrier coating of the present description includes a high-density polyethylene (HDPE) coating. High-density polyethylene (HDPE) may be selected for excellent moisture vapor barrier properties and stiffness. Compared with LDPE, HDPE's high density translates into a tightly packed molecular structure and higher crystallinity that significantly reduces the permeability of moisture through the coating. In a specific example, the moisture vapor barrier coating includes one or more high density polyethylene layers having a density in a range of between 0.90 and 0.97 g/cm.sup.3. In another specific example, the moisture vapor barrier coating includes high density polyethylene having a density in a range of between 0.93 and 0.97 g/cm.sup.3. In another specific example, the moisture vapor barrier coating includes high density polyethylene having a density in a range of between 0.94 and 0.97 g/cm.sup.3. High density polyethylene has a lower moisture vapor transmission rate compared with low density polyethylene, polylactic acid and polyethylene terephthalate.
[0036] The stiffness attribute of high-density polyethylene (HDPE) as a moisture vapor barrier coating plays a role in enhancing the structural integrity and functional performance of cellulosic containers, especially in their sidewalls and rims. This characteristic is particularly significant for containers designed to hold liquids or moisture-rich foods, where the maintenance of shape and prevention of deformation under load are desired. For the sidewalls of containers, such as cups, bowls, or boxes, the stiffness imparted by HDPE coatings contributes to the container's ability to retain its shape under various conditions, including when filled with contents, stacked, or subjected to external forces. This ensures that the container remains functional and aesthetically pleasing throughout its lifecycle, from packaging and transportation to end-user handling. Similarly, the stiffness of HDPE is beneficial for the rim areas of containers. Rims are important for ensuring a secure closure when lids are applied to containers, such as in the case of beverage cups or food containers. The enhanced stiffness provided by HDPE coatings in these areas ensures that the rims maintain their integrity, facilitating effective lid attachment and seal formation. This is particularly important for preventing spillage and preserving the contents' freshness.
[0037] The moisture vapor barrier coating has a thickness sufficient to achieve the desired moisture vapor barrier properties. The thickness of the moisture vapor barrier coating may depend on the composition of the moisture vapor barrier coating. When high density polyethylene is used as the moisture vapor barrier coating, the high density polyethylene may enable reducing the polymer layer thickness and hence enable for plastic reduction for the resulting coated cellulosic container. In an example, the moisture vapor barrier coating has a thickness ranging from 0.2 to 8 mils, wherein 1 mil equals 0.001 inch. In another example, the moisture vapor barrier coating has a thickness ranging from 0.5 to 4 mils. In a specific example, the moisture vapor barrier coating has a thickness ranging from 1.0 to 1.4 mils, centering on 1.2 mils. In another specific example, the moisture vapor barrier coating has a thickness ranging from 1.3 to 1.7 mils, centering on 1.5 mils.
[0038] The moisture vapor barrier coating may be applied to the second major surface of the cellulosic substrate using any available technique. The method of application of the moisture vapor barrier coating may depend on the composition of the moisture vapor barrier coating. Examples of suitable techniques for applying a polyethylene layer (e.g., HDPE layer) include extrusion coating and lamination coating. One method for applying polyethylene (PE), including high-density polyethylene (HDPE), involves extruding the molten polymer onto the cellulosic substrate. Extrusion coating produces a uniform and continuous layer of the coating material for effective moisture barrier properties. Extrusion coating allows for precise control over the thickness of the applied layer. Co-extrusion is a variation of the extrusion process that allows for the simultaneous application of multiple layers of the same different materials. This technique can be used to apply a multi-layered moisture vapor barrier that includes HDPE as one of the layers, potentially combined with other polymers to achieve specific barrier properties or to enhance the mechanical strength of the coating. Lamination involves bonding a pre-formed polyethylene film to the cellulosic substrate using adhesives or heat and pressure. This method is particularly useful when applying multi-layer coatings or when incorporating additional functional layers into the moisture barrier coating. In a specific example, multiple high-density polyethylene layers may be coextruded onto the paperboard substrate. In another example, a first high-density polyethylene layer may be laminated onto the paperboard, and then a second high-density polyethylene layer may be extruded onto the paperboard. In yet another example, a first high-density polyethylene layer may be extruded onto the paperboard, and then a second high-density polyethylene layer may be laminated onto the paperboard.
[0039] The moisture vapor barrier coating may be applied such that, on the second major side, the cellulosic substrate has low 30 minute Water Cobb test value, preferably a 30 minute Water Cobb test value of 3 grams per square meter or less on the second major side of the cellulosic substrate, more preferably 2 grams per square meter or less, more preferably 1.5 grams per square meter or less, more preferably 1.4 grams per square meter or less, more preferably 1.3 grams per square meter or less, more preferably 1.2 grams per square meter or less.
[0040] The moisture vapor barrier coating may be applied such that, on the second major side, the cellulosic substrate has low moisture vapor transmission rate, preferably a moisture vapor transmission rate of 100 grams per square meter per day or less at 38 C. and 90% relative humidity on the second major side of the cellulosic substrate, more preferably 50 grams per square meter per day or less, more preferably 25 grams per square meter per day or less, more preferably 10 grams per square meter per day or less, more preferably 9 grams per square meter per day or less, more preferably 8 grams per square meter per day or less, more preferably 7 grams per square meter per day or less, more preferably 6 grams per square meter per day or less, more preferably 5 grams per square meter per day or less.
[0041] Primer Coating: The primer coating is positioned to enhance the adhesion between the cellulosic substrate's printability coating and the subsequent layers that are applied to the sealing areas, such as the moisture vapor barrier coating. The primer coating is disposed on the printability coating at one or more sealing areas (e.g., a sidewall seam sealing area and a rim sealing area) of the coated cellulosic structure. The primer coating may be disposed on the entirety of the printability coating. Alternatively, the primer coating may be disposed selectively at one or more sealing areas, thus being omitted at the non-sealing area or being omitted at a portion of the non-sealing area. The presence of primer at the sealing areas enables for better heat sealing leading to good rim and sidewall seam formation compared to a container which does not have a primer. A stronger upper rim is significant for providing increased rigidity to the container.
[0042] In an aspect, the primer coating can be an aqueous primer coating. A reason for utilizing an aqueous primer coating is its compatibility with the environmentally friendly production processes. The composition of an aqueous primer coating typically includes polymers that are designed to interact chemically with both the underlying printability coating and the overlying sealing layers. This interaction promotes a strong bond, ensuring that the seals remain intact under various conditions, including those involving moisture, stress, and temperature changes. The improved adhesion facilitated by the primer is especially important at the sidewall seam and rim sealing areas, where the integrity of the seal is paramount for preventing leaks and maintaining the container's shape and strength. Additionally, the use of an aqueous primer can improve the heat sealing process's efficiency by lowering the activation temperature required to achieve a dependable seal.
[0043] The primer coatings can include water-based solutions, emulsions, or dispersions. Water-based solutions, emulsions, and dispersions are formulations that use water as the primary solvent or medium to disperse or dissolve other substances. Each of these formulations has distinct characteristics based on the nature of the mixture and the interactions between its components. A water-based solution is a homogeneous mixture where all the components are dissolved in water. Water-based solutions can be used when the solute can be completely dissolved in water. The advantages of water-based solutions include ease of application, low toxicity, and minimal environmental impact. A water-based emulsion is a type of mixture where one liquid is dispersed in another liquid, with which it is not miscible (water), stabilized by an emulsifying agent. Emulsions combine the beneficial properties of both the water with the desired film-forming or adhesive characteristics of the dispersed phase. Dispersion in the context of water-based systems refers to a system in which fine particles (solid particles or liquid droplets) are dispersed in a continuous water phase. The dispersed particles do not dissolve but remain suspended throughout the water with the help of dispersing agents or stabilizers.
[0044] Exemplary primer coatings can include one or more chemical groups of imine, amides, urethanes, polyester, acrylics, and olefins. In the context of the aqueous primer, these chemical groups plays a role in determining the adhesion, durability, and overall performance of the primer coating. Each of these chemical groups can contributes properties to the primer, enhancing its effectiveness in bonding the printability coating with subsequent layers, particularly in sealing areas. Understanding the role of each chemical group can provide insight into how primer formulations can be optimized for specific applications. Imines, characterized by the presence of a carbon-nitrogen double bond, can improve primer adhesion through their reactivity and ability to form covalent bonds with other compounds. In primer coatings, imines can be used to promote cross-linking reactions that enhance the mechanical strength and chemical resistance of the adhesive layer, contributing to the durability of the seal. Amides contain a carbonyl group linked to a nitrogen atom, which can offer strong hydrogen bonding capabilities, improving the cohesion and flexibility of the primer. This chemical group is valuable in primer formulations for its ability to enhance primer-substrate interaction, providing a balance between flexibility and strength in the sealed areas. Urethanes, or polyurethanes, are formed by the reaction of an isocyanate with a polyol. They are known for their excellent abrasion resistance, toughness, and flexibility. In primers, urethanes contribute to the elasticity and impact resistance of the coating, ensuring that the seal remains intact under mechanical stress. Polyesters are synthetic resins formed by the condensation of polyols and acids. They offer good adhesion, chemical resistance, and durability. Polyester-based primers can provide a strong bond to various substrates and coatings, making them suitable for use in areas requiring high strength and stability. Acrylic polymers have excellent clarity, color retention, UV resistance, and flexibility. They can adhere well to a wide range of substrates. Acrylics in primer coatings enhance the aesthetic properties of the cellulosic structure while providing a durable bond that resists environmental degradation. Olefins, or polyolefins, are polymers derived from alkenes. They are characterized by their chemical resistance, strength, and lightweight. Olefin-based primers are particularly useful for improving the water and vapor barrier properties of coatings, contributing to the preservation of the container's contents. By incorporating these chemical groups into primer formulations, manufacturers can achieve a tailored balance of properties, such as enhanced adhesion, flexibility, chemical resistance, and durability, which are critical for the performance of coated cellulosic structures. The specific composition of the primer coating can be determined based on the requirements of the sealing area, the nature of the cellulosic substrate, and the intended use of the final product, ensuring optimal performance throughout its lifecycle.
[0045] A specific example of a primer coating is a water-based dispersion comprising polyethyleneimine (PEI). Polyethyleneimine (PEI) is a highly branched polymer that exhibits a high density of amine groups along its backbone. This molecular structure lends PEI exceptional characteristics suitable for use as a primer coating in applications involving coated cellulosic structures. PEI offers several distinct advantages, including adhesion enhancement and heat sealability improvement. The abundance of amine groups in PEI facilitates strong adhesion to both hydrophilic and hydrophobic surfaces. This property is beneficial for creating a robust interface between the printability coating on the cellulosic substrate and subsequent layers, such as moisture vapor barrier coatings. The enhanced adhesion is important in sealing areas, where the integrity of the bond directly impacts the container's overall performance and durability. Additionally, the application of a PEI primer can lower the activation temperature required for effective heat sealing. This is particularly advantageous in high-speed manufacturing environments, where reducing heat sealing temperatures can lead to energy savings and increased throughput. Additionally, the strong bond formed by PEI can improve the reliability of the heat seal, ensuring that the container remains closed and intact throughout its lifecycle. Furthermore, the use of PEI as a primer does not limit the choice of overprint coatings or inks. Its ability to bond with a variety of materials allows for flexibility in the selection of subsequent coatings. A working example of a primer coating is a water-based, modified polyethyleneimine (PEI), single-component resin dispersion having solids in range of 19-21%, which can be further diluted in the application range below 10%. Presence of PEI primer showed strong heat seal initiation at lower temperature in lab bar sealer test and helped in stronger rim and sidewall in subsequent cup forming experiment.
[0046] The primer coating has a thickness sufficient to achieve the desired effect. The thickness of the primer coating may depend on the composition of the primer coating. An exemplary application of a primer coating is preferably in the range of 0.01 to 0.3 lbs/3msf, more preferably in the range of 0.03 to 0.1 lbs/3 msf. In one working example, a PEI primer was applied in range of 0.03 lbs./3 msf (0.05 gsm) to 0.12 lbs./3 msf (0.2 gsm).
[0047] The application of the primer coating can be executed through various techniques that provide even distribution and adhesion to the cellulosic substrate. The techniques for applying primer coatings include, but are not limited to, spray coating, roll coating, curtain coating, gravure coating, flexographic coating, dip coating, and rod coating. In a specific example, the primer can be applied by flood coating using a roll applicator, offset, flexo or gravure press. The primer could also be pattern printed in the critical sealing area of the container blanks e.g., rim and sidewall. The primer could be applied during extrusion coating process or during offline printing and coating step. In one specific example, a primer application at extrusion process could be followed with application of graphic printing and an overprint coating in offline step. In other example, the clay coated side is printed first, followed with flood coating of primer and pattern application of overprint coating leaving the sealable area having the primer. In other examples, primer can pattern printed at sealable area of the blank during printing step followed by pattern application of over print coating leaving sealing area only having primer. In one working example, PEI primer was applied using flexo press, metered with anilox roller of 2 BCM volume in single bump and 2 BCM in double bump. Solids were at 3 and 6% targeting dry coat weight in range of 0.03 lbs./3 msf (0.05 gsm) to 0.12 lbs./3 msf (0.2 gsm) One example of primer being used is from Mica corporation's MICA H-788.
[0048] Printed Ink Layer: The coated cellulosic structure may include a printed ink layer between the printability coating and the overprint water barrier coating to display information relating to the contents of a container. The coated cellulosic structure may be printed with indicia, such as advertising text and graphics, by a printing operation. The printing operation may include any apparatus or system capable of marking the coated cellulosic structure with indicia. For example, the printing operation may include a printing press capable of printing text and/or graphics onto the coated cellulosic structure. Specific examples of printing techniques include offset printing, gravure printing, flexographic printing and digital printing.
[0049] Overprint Water Barrier Coating: The overprint water barrier coating serves as an overprint layer and provides water barrier properties to protect the cellulosic substrate from exterior moisture, such as due to condensation. Suitable overprint coatings include acrylic and polyurethane materials, which can provide for clarity, flexibility, and moisture resistance. These materials are particularly suited for applications where a clear, protective finish is desired. Acrylic coatings, for instance, offer a balance of hardness and flexibility, making them ideal for resisting abrasion and providing a durable barrier against water ingress. Polyurethane coatings, on the other hand, provide enhanced toughness and chemical resistance, which can be beneficial in environments where the coated cellulosic structure may be exposed to various substances.
[0050] In an aspect, the overprint water barrier coating of the present description is an aqueous overprint water barrier coating. The aqueous formulation is particularly advantageous for its environmental friendliness and ease of application. Moreover, the use of water as the solvent aligns with sustainability goals. In a more specific aspect, the overprint water barrier coating of the present description is an aqueous overprint water barrier coating composed of an acrylic emulsion polymer. These polymers offer a combination of clarity, flexibility, and moisture resistance. The clarity of acrylic emulsion polymers ensures that the printed graphics beneath the coating remain vibrant and visible, enhancing the aesthetic appeal and functionality of the packaging by preserving its brand identity and informational content. Flexibility is another attribute of acrylic emulsion polymers, allowing the overprint water barrier coating to adhere well to the cellulosic substrate and withstand physical stresses such as bending, folding, or crushing without cracking or peeling. This flexibility contributes to the durability of the packaging, ensuring it remains intact and functional throughout its lifecycle. Moisture resistance provided by acrylic emulsion polymers is significant for protecting the cellulosic substrate and printed ink from water ingress, condensation, and other sources of moisture. This protection prevents smearing, bleeding, or fading of the printed materials, thereby maintaining the integrity and legibility of the packaging content. The moisture barrier also contributes to the structural stability of the cellulosic structure, preventing softening, warping, or degradation that could compromise the package's performance. In an example, the aqueous overprint water barrier coating may include a combination of acrylic resin, styrene-acrylic copolymer, and diammonium zinc bicarbonate. In particular, a specific coating useful as an aqueous overprint water barrier coating of the present description is ACTGREEN BARRIER CTG AQ2149000-2. In another example, the aqueous overprint water barrier coating may include an amine salt of modified acrylic copolymer. Another exemplary specific coating useful as an aqueous overprint water barrier coating is coating 1918M from Coatings & Adhesives Corporation.
[0051] The aqueous overprint water barrier coating is applied in an amount sufficient to provide water barrier properties to resist penetration of external condensation. The coat weight applied may depend on the composition of the aqueous overprint water barrier coating. In an example, the coat weight of the aqueous overprint water barrier coating applied ranges from 5 to 50 BCM (billion cubic microns per square inch). In another example, the coat weight of aqueous overprint water barrier coating applied ranges from 5 to 10 BCM (billion cubic microns per square inch). In another example, the coat weight of aqueous overprint water barrier coating applied ranges from 10 to 20 BCM (billion cubic microns per square inch). In another example, the coat weight of aqueous overprint water barrier coating applied ranges from 20 to 50 BCM (billion cubic microns per square inch).
[0052] The aqueous overprint water barrier coating may be applied such that, on the first major side, the cellulosic substrate has low 30 minute Water Cobb test value, preferably a 30 minute Water Cobb test value of 80 grams per square meter or less, preferably 70 grams per square meter or less, more preferably 60 grams per square meter or less, more preferably 50 grams per square meter or less, more preferably 40 grams per square meter or less, more preferably 30 grams per square meter or less, more preferably 20 grams per square meter or less, more preferably 10 grams per square meter or less.
[0053] Roll of Coated Cellulosic Material: The coated cellulosic material, as described, can be manufactured and stored in the form of a roll. This roll serves as a precursor to the various structures detailed earlier, such as sidewall components for containers. Within this roll format, the coated cellulosic material retains its fundamental layered construction, facilitating subsequent processing steps. Specifically, the primer coatingan element for enhancing adhesion in sealing areas-can be uniformly applied across the entire first major side of the roll or selectively pattern printed. This selective application ensures that the primer is present only in regions that will correspond to the sealed areas of the final product, optimizing material usage and functional performance. Furthermore, the roll may incorporate a printed ink layer, which can be applied either before or after the primer coating. The presence of the printed ink layer enables the roll to carry branding, informational content, or decorative graphics, enhancing the aesthetic and communicative value of the final product. Additionally, the aqueous overprint coating, known for its water barrier properties, can be pattern applied to specific regions of the roll. These regions are chosen to align with the non-sealed areas of the final structure, providing targeted protection against external moisture while preserving the integrity of printed designs.
[0054] Sidewall Blank: The blanking process transforms the roll of coated cellulosic material into sidewall blanks, which are precursors to the sidewall components of containers. This process involves cutting and, if necessary, scoring the roll material into flat pieces of predetermined shapes and sizes, tailored to the specific design requirements of the final container. The resulting sidewall blank embodies the layered construction inherent to the roll material, featuring the cellulosic substrate as its core, surrounded by the various coatings that confer printability, moisture barrier, and sealing properties.
[0055] Each sidewall blank includes a first major side and a second major side, reflecting the exterior and interior of the eventual container, respectively. The first major side is prepared with a primer coating, either covering its entirety or applied selectively to areas designated for sealing. This ensures that the sidewall blank is ready for the sealing process, which will occur once it is formed into a container component. The primer's strategic placement is critical for achieving strong adhesion at the seam and rim areas during the sealing process.
[0056] Additionally, the sidewall blank may feature a printed ink layer that carries branding, informative details, or decorative elements. This layer can be applied before or after the primer, depending on the manufacturing sequence chosen to optimize the adhesion of printed designs and their protection against wear and moisture. Overprint water barrier coating is applied to the non-sealing areas of the first major side, safeguarding the printed designs from external moisture and enhancing the durability of the sidewall blank.
[0057] The blanking process, combined with the layered configuration of the roll material, results in sidewall blanks that are structurally ready for subsequent forming and sealing into container components and also visually prepared to meet the aesthetic and functional standards of the final product.
[0058] Sidewall Component: The transformation of a sidewall blank into a sidewall component involves shaping and forming the flat sidewall blank into a cylindrical or conical structure that serves as the main body of the container. During this step, the inherent flexibility and strength of the coated cellulosic material are important for allowing precise and durable formation. The first major side of the blank, designed to be the exterior of the container, features the previously applied coatings-primarily the printability and overprint water barrier coatings outside of the sealing areas, and the primer coating within the sealing areas. These coatings ensure that the sidewall component retains its aesthetic appeal, moisture resistance, and structural integrity throughout the manufacturing process and in the final application.
[0059] To form a sidewall component, the blank is typically wrapped around a mandrel or through a series of forming plates that gradually curve the flat material into the desired shape. The ends of the sidewall blank (longitudinal edges) are brought together to form the sidewall seam. This seam is an important structural element, as it must be securely sealed to ensure the container's integrity. The position of the primer coating on the designated sealing areas of the sidewall blank is significant at this stage, as it enhances the adhesion for a strong and reliable seam.
[0060] Sidewall Seam: The creation of the sidewall seam involves the joining of the two longitudinal ends of the sidewall component, utilizing heat, pressure, or a combination of heat and pressure, to activate the sealing process. The primer coating plays an important role here, facilitating the bonding of the coated cellulosic layers. For containers requiring liquid resistance, the seam must be impermeable to ensure no leakage occurs. This is achieved by controlling the sealing parameters to soften the heat seal layer (which may be the moisture barrier layer in the case of a polyethylene moisture barrier layer), and in some scenarios, the primer coating provides chemical and physical interaction thereby creating a cohesive bond that solidifies upon cooling. The sealing process can vary depending on the type of container being produced and the specific materials used in the coated cellulosic structure. Once formed, the sidewall seam becomes a line that maintains the structural continuity of the sidewall component. The integrity of this sidewall seam is important, as it directly impacts the container's strength and functionality. The success of this sidewall seam sealing process underscores the importance of the primer coating application. Stronger sidewall sealing can be achieved with the presence of primer.
[0061] Edge Protection Tape: Before sealing the sidewall seam, an edge protection tape can be applied to the innermost overlapping ends. This tape may function as a moisture barrier layer for the longitudinal end and may have heat sealing properties for sealing the longitudinal ends. It can be composed of either a single layer or multiple layers of various polymeric materials. While this description focuses on the application of edge protection tape for sealing, it is important to note that other methods for sealing the ends are also viable and included within the scope of this approach. An alternative sealing method involves folding the innermost end and using heat to merge the polyethylene layers from opposite ends of the cellulosic structure, creating a seamless bond. Additionally, the application of a primer is expected to improve the adherence of the tape to the printability coating, further enhancing the seal's effectiveness.
[0062] Upper Rim: The upper rim of the coated cellulosic container may be formed by shaping an upper end of the sidewall component. The upper rim may have a curved or flat profile and may include one or more flanges or lips to facilitate sealing with the lid component. The upper rim includes the primer coating to improve adhesion and bonding of the upper rim. The upper rim may be formed by curling, folding, pressing, heating, or combinations thereof of the upper end of the sidewall component. The primer coating results in better rim formation compared with a structure which does not have a primer. The presence of primer enables better sealing leading to good rim formation. A stronger rim provides more rigidity to the container. Additionally, presence of primer can exhibit strong heat seal initiation at lower temperature. A stronger rim makes a positive impact on cup rigidity. In an example, the upper rim may have the form of a three-fold flat rim. The three-fold flat rim may be formed by rolling the upper end, and then pressing the rolled upper rim into the configuration of a three-fold flat rim. Presence of primer helped in forming a flat and strong rim.
[0063] Bottom Component: The bottom component of the coated cellulosic container may be formed from the same coated cellulosic structure as the sidewall component or from a different structure. Various techniques may be used to seal the bottom component to the sidewall component. As one example, a lower end of the sidewall component may be shaped to form a circumferential recess. The bottom component may be placed into the recess and sealed to the sidewall component. Suitable techniques for sealing the bottom component to the sidewall component include hot air heat seal and ultrasound sealing. Presence of primer on printability side of bottom will also aid in better sealing on the outside flange.
[0064] Lid Component: The coated cellulosic container may further include a lid component enclosing the upper end of the sidewall component. The lid component may be sealed to the upper rim of the sidewall component. The lid component may be made from the disclosed cellulosic structure, a different cellulosic structure or a different material such as a film material (e.g., polymer; metal; metal-polymer combination). Various techniques may be used to seal the lid component to the upper rim of the sidewall component. The lid component may be sealed to the upper rim by, for example, connecting and heating a polyethylene layer (e.g., high density polyethylene layer) of a paperboard lid component to a polyethylene layer (e.g., high density polyethylene layer) of the upper rim. As another example, a film lid component may be sealed to the upper rim, by, for example, a heat-seal or an adhesive. The coated cellulosic container may further include a food product contained in an internal volume of the coated cellulosic container, in particularly a cold food product such as yogurt.
[0065] Packaging: During packaging, a food product (e.g., cold food product such as yogurt.) may be placed into the internal volume of the coated cellulosic container and then the lid may be sealed to the sidewall of the coated cellulosic container. After placing the food product into the internal volume, the lid may be sealed using any available technique and may depend on, among other possible factors, the type of lid being used.
[0066] Although various operations of making coated cellulosic container are described above, it will be understood that one or more operations may be performed in a different order, that one or more operations may be combined in a single operation, that one operation may be separated into multiple operations, or that one or more operations may be performed by a single machine or system.
EXPERIMENTAL RESULTS
[0067] A. Comparative Samples: The project aimed to develop high-barrier, recyclable paper cups to serve as alternatives to double-sided (P2S) paper cups or single-use plastic cups, particularly for yogurt packaging. The envisioned structure comprised a 1.2 or 1.5 mil High-Density Polyethylene (HDPE) coating on a 14 pt. Polarshield board (clay-coated). Initial trials focused on manufacturing rolls for subsequent ink printing and overprint coating applications, which were then fabricated into cups using the Horauf BMP200 machine. These trials successfully produced cups of satisfactory quality; however, enhancements in rim formation and sealing were deemed necessary to augment the cup's robustness.
[0068] B. Innovative Samples: To address the identified need for improved rim formation and sealing, the exploration of a primer coating was initiated. The hypothesis was that a stronger rim would significantly contribute to the cup's rigidity, thereby enhancing its overall functionality.
[0069] Equipment Utilized for Pilot Plant Evaluation: Pilot Flexo Press.
[0070] Primer Details: Mica H788 (19% Solids)a modified polyethyleneimine (PEI) solution, diluted to 3% and 6% solids concentration.
[0071] Application Method: Single and double application using a 2 BCM anilox roller with a drying temperature set at 185 F. and a line speed of 50 feet per minute.
TABLE-US-00001 TABLE 1 Trial Outcomes: Anilox Color Volume Speed Layer Substrate Coating Trial ID Indicator (bcm) (ft/min) Count Observations 14 pt Polarshield Mica H788 RB001 Blue 2 50 1 Successful Frozen/HDPE (3%) execution 14 pt Polarshield Mica H788 RB002 Red 2 + 2 50 2 Successful Frozen/HDPE (3%) execution 14 pt Polarshield Mica H788 RB003 Black 2 50 1 Successful Frozen/HDPE (6%) execution 14 pt Polarshield Mica H788 RB004 Green 2 + 2 50 2 Successful Frozen/HDPE (6%) execution
[0072] Heat Seal Testing Methodology: Utilizing a bar sealer, a comparative analysis was conducted between samples with and without the primer application, focusing on the HDPE side to Clay interface with single-side heating. Temperature parameters ranged from 275 F. to 375 F., under 60 psi pressure and a 3-second dwell time, employing a T-peel sample type.
[0073] Findings: Graphical Analysis (
[0074] Findings: Visual Inspection (
[0075] Cup Forming Process: The cup forming process for creating yogurt containers involves a series of steps aimed at transforming flat, coated cellulosic blanks into functional cups. This process was carried out using specialized yogurt cup tooling and the Horauf BMP200 machine, known for its precision and efficiency in cup manufacturing. The process includes four main stages:
[0076] 1. Application of Edge Protection Tape on Blanks: This initial step involves applying a protective tape along an edge of the cellulosic blanks. The purpose of this tape is to enhance the moisture barrier at the edges and to reinforce the heat sealability at the areas that will form the seams of the cup.
[0077] 2. Sidewall Sealing: Following the application of edge protection tape, the blanks are shaped into cylindrical forms, and the longitudinal edges are sealed together to form the sidewall seam.
[0078] 3. Bottom Sealing: Once the sidewall seam is securely sealed, the bottom of the cup is attached. A separate piece of coated cellulosic material, cut to fit the bottom opening of the formed sidewall, is sealed onto the lower edge of the sidewall.
[0079] 4. Rim Flattening-Transforming the Rolled Rim into a Three-Fold Flat Rim: This step in the cup forming process involves finishing the top rim of the cup to ensure it is smooth and strong, providing a flat edge against suitable for sealing a lid thereon. The initially rolled rim of the cup is flattened and folded into a three-fold structure, significantly reinforcing the rim's rigidity.
[0080] Comparative Analysis: Control vs. Innovative Cups:
[0081] The application of primer resulted in flatter and stronger rims as evidenced by the following rim measurements, comparing a cup with primer vs. a cup with no primer, subject to the same cups forming conditions, on the same machine, on the same day.
TABLE-US-00002 TABLE 2 Rim Integrity: Topside of Rim Underside of Rim (Looking Down into (Looking Up from Cup) Underside of Cup) Notes larger is Smaller is better, Better, 264 is 96 is target target Sample ID Average Topside Average Underside Angle of from Angle of from Inside Target () Sidewall Target () Sidewall to to Top of Underside Rim () of Rim () Control: 248.88 15.12 114.27 18.27 No Primer Cup with 257.14 6.86 102.15 6.15 PEI Primer
[0082] Sidewall Seam Evaluations: Adding a primer layer improved the sealing of the sidewalls, which is important for the effective sealing of edge protection tape and the HDPE to clay-coated interface. Benefits of primer include: (1) Widens sealing window, lowers seal initiation temperature for sidewall sealing; (2) Enhances forming & flatness of rims; (3) In cups formed on the same machine on the same day with the same settings, we observed these differences in cups: (3A) In cups without PEI primer, we see 90-100% fiber tear in the 5 mm tape area--in the area without tape, just clay there is 33-66% fiber tear; (3B) In cups with PEI primer, we see 100% fiber tear in the 5 mm wide tape area and 75-100% fiber tear in the area between the tape and print.
[0083] Conclusion: The experimental investigation underscores the significant impact of utilizing a modified polyethyleneimine (PEI) primer in enhancing the structural integrity and sealing performance of recyclable paper cups, positioning this innovation as a viable alternative to traditional packaging solutions.
[0084] Additional Application Scenarios: The coated cellulosic structures and containers designed for packaging applications, particularly for cold food products such as yogurt, offer a versatile platform for various application scenarios beyond their primary use. These scenarios are aimed at enhancing the functional properties of the packaging, improving its environmental footprint, and expanding its utility in the packaging industry. Three significant additional application scenarios have been identified:
1. Flood Coating with a Roll Coater During the Extrusion Process:
[0085] Objective: To uniformly apply a protective or functional coating across the entire surface of the cellulosic substrate during the extrusion process. This approach aims to enhance barrier properties, improve printability, or impart additional characteristics such as antimicrobial properties.
[0086] Methodology: Utilize roll coaters in conjunction with the extrusion process to apply coatings such as moisture vapor barriers, printability layers, or primer coatings. This method ensures a consistent and uniform application, crucial for maintaining the quality and performance of the packaging.
[0087] Benefits: Improved efficiency in the coating process, enhanced barrier properties, and the potential for introducing multifunctional coatings that contribute to the sustainability and recyclability of the packaging.
2. Pattern Printing on Seal Areas (Rim and Sidewall) Using Offset or Flexographic Techniques:
[0088] Objective: To apply precise and localized coatings or inks to specific areas of the cellulosic structures, particularly around the rim and sidewalls, where sealing integrity is critical. This targeted approach is designed to improve seal strength, facilitate effective adhesion, and enhance the overall appearance of the packaging.
[0089] Methodology: Implement offset or flexographic printing techniques to apply primer coatings or decorative elements in a patterned manner, focusing on areas that require enhanced adhesion or specific aesthetic features. This allows for the selective application of coatings, optimizing material use and functional performance.
[0090] Benefits: Increased sealing efficiency and strength, reduced material wastage by targeting specific areas for coating application, and the ability to incorporate visually appealing designs that improve consumer engagement and product differentiation.
3. Application as an Overprint Coating Utilizing a Flexographic Press:
[0091] Objective: To apply an overprint coating that provides a protective layer over printed graphics, enhancing their durability against moisture, abrasion, and fading. This scenario aims to preserve the aesthetic qualities of the packaging while maintaining its structural integrity.
[0092] Methodology: Use flexographic presses to apply aqueous overprint water barrier coatings over areas that have been previously printed. This method allows for precise control over the application, ensuring that the protective coating is applied only where necessary, without compromising the packaging's recyclability.
[0093] Benefits: Enhanced protection of printed graphics, improved product shelf appeal, and extended lifespan of the packaging. The use of aqueous coatings aligns with environmental sustainability goals by ensuring that the packaging remains recyclable and biodegradable.
[0094] These scenarios may contribute to the development of environmentally friendly, high-performance packaging solutions that meet the demands of modern consumers and regulatory standards.
[0095] Although various examples of the disclosed coated cellulosic structures 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.