Plastic-free container meeting SUPD plastic-free requirement and preparation method of plastic-free container

Abstract

The invention relates to the technical field of environment-friendly containers, and particularly discloses a plastic-free container meeting SUPD plastic-free requirements, the plastic-free container comprises a main body structure and an auxiliary structure, the main body structure and the auxiliary structure are both made of composite paperboards, and each composite paperboard comprises a base paper layer and a regenerated cellulose barrier layer arranged on the surface of the base paper layer; the regenerated cellulose barrier layer is a compact film formed by regenerating dissolving pulp cellulose fibers after being dissolved in a phenolic imidazole [C2mim] [Oh] ionic liquid (IL) and N, N-dimethylformamide (DMF) mixed solvent system, and the plastic-free container is free of any plastic component and conforms to the European SUPD plastic-free definition; the plastic-free container meeting the SUPD plastic-free requirement has the advantages that the environmental protection property comprehensively reaches the standard, the barrier property is excellent, the heat sealing forming is efficient and stable, the cost and process advantages are remarkable, and the like.

Description

Technical Field

[0001] This invention relates to the field of environmentally friendly container technology, specifically to a plastic-free container that meets the SUPD plastic-free requirements, and also to a method for preparing a plastic-free container that meets the SUPD plastic-free requirements. Background Technology

[0002] Currently, plastic pollution has become a global environmental problem, with single-use packaging containers being one of the main sources of pollution. To achieve waterproof and oil-proof functions, traditional paper-based containers often have plastic films such as polyethylene (PE) and polyethylene terephthalate (PET) laminated onto the surface of the paper substrate. This makes it difficult to separate the paper fibers from the plastic during recycling, resulting in low recycling value. Most of these containers can only be incinerated or landfilled, exacerbating the environmental burden.

[0003] From a life cycle (LCA) perspective, ideal packaging materials should be both recyclable and environmentally degradable. However, existing solutions have many shortcomings: biodegradable polymers such as polybutylene adipate / terephthalate (PBAT) and polylactic acid (PLA) are still essentially plastics, requiring specific industrial composting environments to degrade, and may produce microplastics, which can also interfere with the recycling of paper-based materials; natural polymer coatings such as starch, protein, and seaweed polysaccharides have problems such as poor barrier properties, insufficient folding resistance, inability to be heat-sealed, high cost, and scarce resources; although nanocellulose (CNF) has good biodegradability, its preparation is energy-intensive, has poor water vapor barrier properties, and poor heat-sealing performance, requiring composite hydrophobic materials, which increases cost and process complexity.

[0004] For example, the existing patent with publication number CN102717574A- "A thermally insulated composite paper container that can carry liquid" relates to a composite paper container, which has a water-proof and anti-reflective layer composed of a plastic film and aluminum foil bonded together on one side of the paper substrate through a polypropylene / polyethylene composite adhesive layer, and a thermal insulation layer on the other side.

[0005] Existing defects:

[0006] Material compliance issues: The use of synthetic polymers such as polypropylene and polyethylene, as well as aluminum foil, completely fails to comply with SUPD requirements for plastic-free packaging.

[0007] Poor environmental friendliness: The composite structure of plastic and aluminum foil is difficult to recycle and cannot be biodegraded in the natural environment. The aluminum-plastic separation technology is complex and costly.

[0008] Microplastic risks: Plastic components may generate microplastic pollution during use and disposal, causing long-term harm to the environment.

[0009] For example, the public announcement number CN1119168A "composite container" has an internal container formed by blow molding or stretch blow molding of a resin composite material containing at least two resins (one of which is a barrier resin), which aims to reduce the amount of paper and plastic used and have good resistance to drop impact and good barrier properties against oxygen and water vapor.

[0010] Existing defects:

[0011] Material compliance and recycling challenges: The container explicitly contains a plastic inner container, which is a material restricted by SUPD. Although the patent specification mentions that the container can be completely separated into paper and plastic upon disposal, the actual separation and recycling process may be complex and costly, making it difficult to implement effectively on a large scale and affecting its circular economy value.

[0012] Limited biodegradability: Plastic inner containers are difficult to biodegrade in the natural environment. If they are not effectively separated and recycled and enter the environment, they will cause persistent pollution.

[0013] Another example is the public announcement (CN208715892U) titled "A Edgeless Composite Paper Container Sheet." Its structure includes a printed film layer, a composite adhesive layer, a paper layer, and a coated PE layer. It employs edgeless composite technology to avoid contamination of the contents by adhesives and printing inks, and the sheet does not require slitting to remove adhesive waste edges, thus reducing costs.

[0014] Existing defects:

[0015] Use of non-SUPD compliant materials: The structure explicitly includes a coated PE layer (plastic). Polyethylene (PE) is a synthetic polymer restricted by SUPD, which makes the container non-compliant with SUPD's "plastic-free" requirement.

[0016] Insufficient environmental friendliness: The presence of the PE coating makes the composite sheet difficult to biodegrade, and its recycling is complicated by the presence of plastic. The use of plastic components may cause the packaging to persist in the natural environment for a long time, and if not disposed of properly, it will still impose an environmental burden.

[0017] Potential microplastic risks: Plastic components may generate microplastics during use and degradation, posing potential harm to the environment.

[0018] The European SUPD has clearly defined plastics, excluding natural polymer materials that have not been artificially modified on a large scale. The market urgently needs a container solution that can completely eliminate dependence on plastics, meet the SUPD's plastic-free requirements, and has excellent barrier properties, efficient heat-sealing capabilities, and low cost. Summary of the Invention

[0019] The purpose of this invention is to address the shortcomings of existing technologies by proposing a plastic-free container that meets the SUPD plastic-free requirements and its preparation method.

[0020] To achieve the above objectives, the present invention adopts the following technical solution:

[0021] A plastic-free container that meets the SUPD plastic-free requirements includes a main structure and an auxiliary structure, both of which are made of composite paperboard. The composite paperboard includes a base paper layer and a regenerated cellulose barrier layer disposed on the surface of the base paper layer. The regenerated cellulose barrier layer is a dense film formed by dissolving cellulose fibers in dissolution pulp through a mixed solvent system of phenolic imidazole [C2mim][Oph] ionic liquid (IL) and N,N-dimethylformamide (DMF). The plastic-free container contains no plastic components and meets the European SUPD plastic-free definition.

[0022] In a preferred embodiment of the present invention, the water vapor permeability (38℃, 90%RH) of the regenerated cellulose barrier layer is ≤ Oxygen permeability (23℃, 0%RH) ≤ .

[0023] As a preferred embodiment of the present invention, the main structure is formed by rolling or folding and heat sealing at least one piece of composite cardboard. The seams between the main structure and the auxiliary structure, and between the main structure itself, are formed by hot pressing and bonding with a special food contact grade heat sealant that has been positioned and coated. The special food contact grade heat sealant is only present in the strip area where the seam is located.

[0024] As a preferred embodiment of the present invention, the peel strength of the joint is ≥4.0N / 15mm.

[0025] As a preferred embodiment of the present invention, the plastic-free container is in the shape of a barrel, box, or cup, and has a biodegradability rate of ≥90% within 90 days.

[0026] As a preferred embodiment of the present invention, the auxiliary structure includes a bottom and / or a cover, the material of which is the same as the composite cardboard of the main structure.

[0027] This invention also provides a method for preparing a plastic-free container that meets the SUPD plastic-free requirements, comprising the following steps:

[0028] S1. Preparation and coating of dissolving pulp cellulose barrier coating: Prepare a mixed solvent of IL and DMF, disperse the dissolving pulp cellulose fibers in the mixed solvent, heat and stir to dissolve, forming a cellulose coating solution, coat the coating solution on the surface of the base paper layer and then immerse it in a deionized water coagulation bath to regenerate the cellulose and form a gel film. After washing and drying, a composite paperboard with a regenerated cellulose barrier layer is obtained.

[0029] S2. Positioning and gluing: Use a special food contact grade heat sealant with a solid content of >40% and apply the glue only to the predetermined heat seal edge area of ​​the composite paperboard to form a strip or line of special food contact grade heat sealant.

[0030] S3. Drying and forming: After the composite paperboard with positioning glue is pre-dried, it is rolled or folded according to the container structure so that the heat-sealed edge areas overlap and are heat-pressed to seal, forming a seam;

[0031] S4. Assembly: Assemble the main structure and auxiliary structure of the container to obtain a plastic-free container that meets the SUPD plastic-free requirements.

[0032] Specifically, in step S1, the mass ratio of IL to DMF is 1:1, the solid content of cellulose in the cellulose coating solution is 5%-15%, and the α-cellulose content of the dissolving pulp cellulose fiber is >95%.

[0033] Specifically, in step S1, the heating temperature is 80-120℃, the coating method is scraper, micro-gravure or spraying, and the drying method is hot air drying or oven drying; in step S3, the hot pressing sealing temperature is 100-150℃, and the pressure is 0.3-0.8MPa.

[0034] Specifically, in step S2, the application method of the special food contact grade heat sealant is spraying, slot coating or gravure printing, and the width of the predetermined heat seal edge area is 10-25mm; in step S1, the residual IL / DMF mixed solvent after washing can be recycled.

[0035] This invention provides a plastic-free container that meets SUPD requirements and its preparation method, which, compared with the prior art:

[0036] Environmental compliance is fully met: No plastic components are added to the container throughout the entire process. The regenerated cellulose barrier layer is derived from natural cellulose and fully complies with the European SUPD definition of plastic-free. The base paper layer is recyclable and reusable, and the regenerated cellulose barrier layer is completely biodegradable in the natural environment, with a biodegradability rate of ≥90% within 90 days. This achieves the dual environmental protection attributes of "recyclable-degradable" and reduces plastic pollution from the source.

[0037] Excellent barrier properties: The regenerated cellulose barrier layer is formed through a dissolution-regeneration process, with high crystallinity and dense structure, which can effectively block the penetration of oxygen and water vapor. It not only meets the long-term liquid carrying requirements, but also enables the primary preservation of puffed food, expanding the applicable scenarios of the container.

[0038] Highly efficient and stable heat-sealing molding: The innovative design of "barrier layer + positioning food contact grade heat sealant" bypasses the technical bottleneck that regenerated cellulose itself cannot be heat-sealed; the positioning adhesive is precisely applied only to the joint area, and the amount of special food contact grade heat sealant used is more than 60% less than that used for full-area coating. After heat-pressing and sealing, the joint strength meets the usage requirements, while improving production efficiency and adapting to large-scale industrial production.

[0039] Significant cost and process advantages: The IL / DMF mixed solvent has high cellulose dissolution efficiency, requires no inert atmosphere protection, and the solvent can be recycled and reused, reducing raw material loss; the overall process steps are simplified, requiring no complex equipment modification, and the mechanical strength of the composite paperboard is significantly improved due to the tight entanglement between the regenerated cellulose barrier layer and the base paper layer, extending the service life of the container. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the manufacturing process of the plastic-free large barrel of the present invention.

[0041] Figure 2 This is a schematic diagram of the composite paperboard structure in this invention.

[0042] In the diagram: 100, composite paperboard; 110, base paper layer; 120, regenerated cellulose barrier layer. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] A plastic-free container that meets the SUPD requirements includes a main structure and an auxiliary structure. Both the main structure and the auxiliary structure are made of composite paperboard 100. The composite paperboard 100 includes a base paper layer 110 and a regenerated cellulose barrier layer 120 disposed on the surface of the base paper layer 110.

[0045] Regenerated cellulose barrier layer 120 is a dense film formed by regenerating dissolved pulp cellulose fibers after dissolution in a mixed solvent system of phenolic imidazole [C2mim][Oph] ionic liquid (IL) and N,N-dimethylformamide (DMF). Its water vapor transmission rate (38℃, 90%RH) is ≤ Oxygen permeability (23℃, 0%RH) ≤ The main structure is formed by rolling or folding and heat sealing at least one piece of composite cardboard 100. The seams between the main structure and the auxiliary structure, and between the main structure itself, are formed by hot pressing with a special food contact grade heat sealant that is positioned and coated. The special food contact grade heat sealant is only present in the strip area where the seam is located, and the seam peel strength is ≥4.0N / 15mm.

[0046] The plastic-free container is in the shape of a barrel, box, or cup, contains no plastic components, and has a biodegradability rate of ≥90% within 90 days, meeting the European SUPD definition of plastic-free; the auxiliary structure includes the bottom and / or lid, the material of which is the same as the composite cardboard 100 of the main structure.

[0047] Example 1: Preparation of a 75-ounce plastic-free bucket (a type of plastic-free container)

[0048] S1. Preparation and application of dissolved cellulose barrier coating;

[0049] a. Solvent preparation: Mix phenolic imidazole [C2mim][Oph] ionic liquid and N,N-dimethylformamide (DMF) in a mass ratio of 1:1 and stir until homogeneous to form a mixed solvent.

[0050] b. Preparation of coating solution: Select dried dissolving pulp cellulose fibers with α-cellulose content >95%, add them to the above mixed solvent, and stir at 100℃ for 6 hours to completely dissolve the cellulose, thereby obtaining a transparent viscous coating solution with a solid content of 8%.

[0051] c. Coating and Recycling: Using a doctor blade coater, the coating liquid is evenly coated on the surface of 300g / m² unbleached kraft paperboard (base paper layer 110) at a coating amount of 15g / m² (dry weight); immediately after coating, the kraft paperboard is immersed in a 20°C deionized water coagulation bath for 30 seconds to form a uniform regenerated cellulose gel film on the surface.

[0052] d. Washing and drying: The kraft paperboard with gel film is washed thoroughly in three water washing tanks until no DMF is detected in the effluent; then it is dried at 100°C for 3 minutes to obtain composite paperboard 100.

[0053] S2. Positioning and gluing;

[0054] The composite paperboard 100 is cut into fan-shaped pieces required for the main body of the container. Special food contact grade heat sealant (EAA, acrylic) is used to spray the adhesive on the predetermined heat-sealing edge area with a width of 15mm on both sides of the fan-shaped piece using CNC gravure printing equipment. The amount of adhesive applied is 20g / m² (wet weight).

[0055] S3. Drying and shaping;

[0056] After positioning and applying the adhesive, the fan-shaped sheet is placed in a 60℃ preheating zone for 15 seconds to pre-dry. Then, it is rolled into shape by a rolling machine, so that the edge areas coated with special food contact grade heat sealant overlap. A hot press roller is used to press it at 120℃ and 0.5MPa pressure for 4 seconds to form a strong seam, resulting in a cylindrical main structure.

[0057] S4. For the final assembly, a circular bottom is made using the same composite cardboard 100 as the main structure. The bottom is then bonded and fixed to the bottom of the main structure using a special food contact grade heat sealant, resulting in a complete 75-ounce plastic-free bucket.

[0058] Performance tests are as follows:

[0059] The composite paperboard 100 and the plastic-free drum prepared in Example 1 were tested:

[0060] Water vapor transmission rate (WVTR, 38℃, 90%RH): ≤ It is close to the level of low-density polyethylene film.

[0061] Oxygen permeability (OTR, 23℃, 0%RH): ≤ It exhibits excellent oxygen barrier properties.

[0062] Seam peel strength: ≥4.0N / 15mm, meeting the national standard requirements for packaging drums.

[0063] Biodegradability (according to ISO 14855): Under standard composting conditions, the biodegradability exceeds 90% within 90 days.

[0064] Example 2: Preparation of a 16-ounce plastic-free cup (suitable for hot and cold beverage scenarios)

[0065] S1. Preparation and application of dissolved cellulose barrier coating

[0066] Solvent preparation: Mix phenolic imidazole [C2mim][Oph] ionic liquid (IL) and N,N-dimethylformamide (DMF) in a mass ratio of 1:1, and stir magnetically for 30 minutes until the system is homogeneous and transparent to obtain a mixed solvent.

[0067] Preparation of coating solution: Dissolving pulp cellulose fibers with 96% α-cellulose content are selected and added to the mixed solvent. The cellulose solid content is controlled at 12%. The mixture is stirred at 110℃ for 4 hours, and ultrasonically dispersed for 10 minutes every 30 minutes to ensure that the cellulose is completely dissolved and form a uniform and viscous coating solution.

[0068] Coating and Regeneration: Using a micro-gravure coating machine, the coating liquid is evenly coated on both sides of 250g / m² food-grade white cardboard (base paper layer) at a coating amount of 12g / m² (dry weight); immediately after coating, the white cardboard is immersed in a 25℃ deionized water coagulation bath for 40 seconds to allow the surface cellulose to regenerate rapidly and form a gel film.

[0069] Washing and drying: The white cardboard with gel film was sequentially passed through a 4-stage washing tank, with each stage lasting 20 seconds. After washing, the residual DMF in the effluent was measured to be ≤0.01%. Subsequently, it was dried in a drying cylinder with the temperature controlled at 90℃ for 2 minutes to obtain a composite paperboard with a regenerated cellulose barrier layer on both sides.

[0070] S2. Positioning and gluing: Cut the composite cardboard into fan-shaped pieces that unfold into cups (120° unfolding angle). Use a special food contact grade heat sealant with a solid content of 45%. Apply the glue in a linear fashion on the predetermined heat-sealing edge area (12mm wide) on both sides of the fan-shaped piece using a slot coating device. The amount of glue applied is 18g / m² (wet weight), ensuring that the glue line is continuous and without breaks.

[0071] S3. Drying and Shaping: Place the fan-shaped sheet after positioning and gluing into a 70℃ preheating oven for 20 seconds to pre-dry and remove surface moisture; then roll it through a paper cup forming machine to ensure precise overlap of the glued edges, and hot press it at 130℃ and 0.6MPa pressure for 3 seconds to form the cup body seam; then use a hot pressing forming process to heat seal the bottom edge of the cup body to the pre-cut circular composite cardboard (bottom structure) at a heat sealing temperature of 125℃, a pressure of 0.4MPa, and a time of 2.5 seconds.

[0072] S4. Assembly: The cup lid is made of composite cardboard of the same material, with an 8mm overlap edge. It is then bonded to the top edge of the cup body using a special food contact grade heat sealant at a pressure of 0.3MPa and a temperature of 80℃ to obtain a complete 16-ounce plastic-free cup.

[0073] Performance test results

[0074] Water vapor transmission rate (38℃, 90% RH): To meet the leak-proof requirements when serving hot and cold drinks;

[0075] Oxygen permeability (23℃, 0% RH): It can effectively delay the oxidation and spoilage of beverages;

[0076] Joint peel strength: 4.8N / 15mm; no leakage or cracking after repeated pouring of liquid.

[0077] Biodegradability (ISO14855 standard): 93% within 90 days, meeting the requirements for biodegradable environmental protection;

[0078] Heat resistance: Can withstand soaking in 95℃ hot water without deformation or odor.

[0079] Example 3: Preparation of a 32-ounce plastic-free food container (suitable for dry goods and cooked food packaging)

[0080] S1. Preparation and application of dissolved cellulose barrier coating

[0081] Solvent preparation: Mix IL and DMF at a mass ratio of 1:1 and mechanically stir for 60 minutes to ensure that the system is fully mixed and there is no layering.

[0082] Preparation of coating solution: Select dissolving pulp cellulose fibers with 97% α-cellulose content, add them to the mixed solvent, control the cellulose solid content to 6%, stir at 90℃ for 5 hours, and use nitrogen protection during the process (to avoid solvent evaporation) to obtain a transparent and uniform low viscosity coating solution.

[0083] Coating and Recycling: Using a spraying process, the coating liquid is evenly sprayed onto the inner side of a 350g / m² high-strength corrugated core paper (base paper layer) at a coating amount of 10g / m² (dry weight); after spraying, the paperboard is immersed in a 22℃ deionized water coagulation bath for 35 seconds to regenerate cellulose and form a dense gel film.

[0084] Washing and drying: The paperboard is washed through a 3-stage countercurrent water washing tank, with each stage lasting 25 seconds. The residual IL / DMF mixed solvent is recovered to a distillation device and the solvent with a purity of ≥95% is recovered by vacuum distillation (80℃, 0.08MPa) and can be recycled. The paperboard is dried with hot air at a wind speed of 3m / s, a temperature of 105℃ and a drying time of 3 minutes to obtain a composite paperboard with a regenerated cellulose barrier layer on the inner side.

[0085] S2. Positioning and gluing: Cut the composite cardboard into food box body and lid unfolded pieces, and use a special food contact grade heat sealant with a solid content of 43%. Using gravure printing equipment, apply the glue in strips along the edges of the box body seams (20mm wide) and the overlap edges of the lid (15mm wide), with an application amount of 22g / m² (wet weight), to ensure that the glue layer evenly covers the predetermined area.

[0086] S3. Drying and Shaping: After positioning and gluing, the box body and lid unfolded pieces are placed in a 65℃ preheating zone for pre-drying for 25 seconds; the box body is folded and shaped using a folding machine, so that the seam edges overlap, and then hot-pressed at 110℃ and 0.7MPa pressure for 5 seconds to form a rectangular box body; after the lid is folded, the overlap between the box body and the lid is sealed by hot pressing at 105℃, 0.5MPa pressure, and 3 seconds to ensure sealing performance.

[0087] S4. Assembly: Apply a small amount of food-grade heat sealant to the inside of the bottom of the box, attach and fix the bottom structure made of the same composite cardboard, press it down, and dry it at 50°C for 10 minutes to obtain a 32-ounce plastic-free food box with a sealed lid.

[0088] Performance test results

[0089] Water vapor transmission rate (38℃, 90% RH): This can effectively prevent dried goods from absorbing moisture and clumping;

[0090] Oxygen permeability (23℃, 0% RH): It can extend the shelf life of cooked food;

[0091] Seam peel strength: 5.2N / 15mm, compressive strength ≥300N, meeting the requirements for warehouse stacking;

[0092] Biodegradability (ISO 14855 standard): 91% within 90 days; biodegradable after disposal.

[0093] Oil resistance: After holding fried food for 24 hours, there is no oil leakage and the cardboard does not soften.

[0094] Example 4:

[0095] 16oz Plastic-Free Cup with Carnauba Wax (a Natural Hydrophobic Agent) (Reinforced Hydrophobic and Leak-Proof)

[0096] S1. Preparation and application of dissolved cellulose barrier coating

[0097] Solvent preparation: Mix phenolic imidazole [C2mim][Oph] ionic liquid (IL) and N,N-dimethylformamide (DMF) in a mass ratio of 1:1, and stir magnetically for 30 minutes until the system is homogeneous and transparent to obtain a mixed solvent.

[0098] Preparation of hydrophobic cellulose coating solution: Dissolving pulp cellulose fibers with 96% α-cellulose content were selected and added to a mixed solvent, with the cellulose solid content controlled at 12%; the temperature was raised to 90℃ and stirred for 2 hours to partially dissolve the cellulose, and then 5% of carnauba wax (crushed to a particle size ≤3μm to improve dispersibility) by weight of cellulose was added, and the temperature was raised to 110℃ and stirred at a constant temperature for 4 hours. During this period, ultrasonic dispersion was performed for 10 minutes every 30 minutes to ensure that the carnauba wax was uniformly dispersed in the coating solution to form a uniform and viscous hydrophobic composite coating solution.

[0099] Coating and Regeneration: Using a micro-gravure coating machine, the coating liquid is evenly coated on both sides of 250g / m² food-grade white cardboard (base paper layer) at a coating amount of 12g / m² (dry weight); immediately after coating, the white cardboard is immersed in a 25℃ deionized water coagulation bath for 40 seconds to allow the cellulose and carnauba wax to be regenerated simultaneously, forming a "cellulose matrix-wax hydrophobic phase" composite gel film.

[0100] Washing and drying: The white cardboard with the composite gel film was sequentially passed through a 4-stage washing tank, with each stage lasting 20 seconds. After washing, the residual DMF in the effluent was measured to be ≤0.01%. Subsequently, it was dried in a drying cylinder with the temperature controlled at 90℃ and the drying time at 2 minutes to obtain a composite paperboard with a hydrophobic regenerated cellulose barrier layer on both sides.

[0101] S2. Positioning and gluing: Cut the composite cardboard into fan-shaped pieces that unfold into cups (120° unfolding angle). Use a special food contact grade heat sealant (EAA, acrylic) and apply it in a linear fashion to the predetermined heat-sealing edge area (12mm wide) on both sides of the fan-shaped piece using a slot coating device. The amount of glue applied is 18g / m² (wet weight), ensuring that the glue line is continuous and without breaks.

[0102] S3. Drying and Shaping: Place the fan-shaped sheet after positioning and gluing into a 70℃ preheating oven for 20 seconds to pre-dry and remove surface moisture; then roll it through a paper cup forming machine to ensure precise overlap of the glued edges, and hot press it at 130℃ and 0.6MPa pressure for 3 seconds to form the cup body seam; then use a hot pressing forming process to heat seal the bottom edge of the cup body to the pre-cut circular composite cardboard (bottom structure) at a heat sealing temperature of 125℃, a pressure of 0.4MPa, and a time of 2.5 seconds.

[0103] S4. Assembly: The cup lid is made of composite cardboard of the same material, with an 8mm overlap edge. It is then bonded to the top edge of the cup body using a special food contact grade heat sealant at a pressure of 0.3MPa and a temperature of 80℃ to obtain a complete 16-ounce hydrophobic plastic-free cup.

[0104] Performance test results

[0105] Water contact angle: 108° (72° for conventional hydrophobic systems), water droplets roll off the cup wall in a spherical shape without sticking to the wall;

[0106] Water vapor transmission rate (38℃, 90% RH): (The conventional system is) The hydrophobicity is improved by 31%;

[0107] Water resistance: After holding 95℃ hot water for 24 hours, the cup body showed no deformation or leakage, and the base paper layer did not absorb water or soften; Oil resistance: After holding milk tea (including milk foam and oil) for 12 hours, there was no oil penetration, and the barrier layer remained intact;

[0108] Seam peel strength: 4.9N / 15mm; Biodegradability (ISO14855 standard): 94% within 90 days, fully compliant with SUPD plastic-free requirements;

[0109] Food contact safety: heat sealant migration ≤5mg / dm², heavy metal residues not detected, meets FDA food contact material safety standards.

[0110] It should be noted that this embodiment only uses carnauba wax as one solution. For those skilled in the art, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. For example, carnauba wax can be replaced with other hydrophobic agents such as octyl succinate starch ester. All such modifications and substitutions should be included within the scope of protection of this invention.

[0111] In summary, the present invention has the following advantages:

[0112] The positioning adhesive application process for plastic-free bulk containers is not only for environmental protection, but more importantly, it complements existing precision printing positioning adhesive processes. Using specialized food-contact grade heat-sealing adhesives (EAA, acrylic-based), it effectively heat-seals the bonding areas of paper cups, significantly improving production efficiency. Previously, the process required coating-printing-forming; now, with positioning adhesive application, some existing waterproof and oil-proof papers (which lack heat-sealing properties) can be used, skipping the coating step and applying adhesive during the printing process, greatly improving production efficiency. Positioning adhesive application is not limited to IL / DMF mixed solvent coatings; it has many other applications, including paper bags, paper cups, and paper bowls.

[0113] The specialized food-contact grade heat sealant for positioning and application features high solids content, low viscosity, and a relatively low initial sealing temperature. It is suitable for direct food contact and has good water resistance and weather resistance.

[0114] The dissolved pulp cellulose barrier coating also has good stiffness retention, which can further reduce the basis weight of the base paper coating, thereby achieving the goal of saving resources.

[0115] Environmental compliance is fully met: No plastic components are added to the container throughout the entire process. The regenerated cellulose barrier layer is derived from natural cellulose and fully complies with the European SUPD definition of plastic-free. The base paper layer is recyclable and reusable, and the regenerated cellulose barrier layer is completely biodegradable in the natural environment, with a biodegradability rate of ≥90% within 90 days. This achieves the dual environmental protection attributes of "recyclable-degradable" and reduces plastic pollution from the source.

[0116] Excellent barrier properties: The regenerated cellulose barrier layer is formed through a dissolution-regeneration process, with high crystallinity and dense structure, which can effectively block the penetration of oxygen and water vapor. It not only meets the long-term liquid carrying requirements, but also enables the primary preservation of puffed food, expanding the applicable scenarios of the container.

[0117] Highly efficient and stable heat-sealing molding: The innovative design of "barrier layer + positioning food contact grade heat sealant" bypasses the technical bottleneck that regenerated cellulose itself cannot be heat-sealed; the positioning adhesive is precisely applied only to the joint area, and the amount of special food contact grade heat sealant used is more than 60% less than that used for full-area coating. After heat-pressing and sealing, the joint strength meets the usage requirements, while improving production efficiency and adapting to large-scale industrial production.

[0118] Significant cost and process advantages: The IL / DMF mixed solvent has high cellulose dissolution efficiency, requires no inert atmosphere protection, and the solvent can be recycled and reused, reducing raw material loss; the overall process steps are simplified, requiring no complex equipment modification, and the mechanical strength of the composite paperboard is significantly improved due to the tight entanglement between the regenerated cellulose barrier layer and the base paper layer, extending the service life of the container.

[0119] The above embodiments fully demonstrate the effectiveness and superiority of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0120] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A plastic-free container that meets the SUPD plastic-free requirements, characterized in that, The container includes a main structure and an auxiliary structure, both of which are made of composite paperboard. The composite paperboard includes a base paper layer and a regenerated cellulose barrier layer disposed on the surface of the base paper layer. The regenerated cellulose barrier layer is a dense film formed by dissolving cellulose fibers in dissolution pulp through a mixed solvent system of phenolic imidazole [C2mim][Oph] ionic liquid (IL) and N,N-dimethylformamide (DMF). The plastic-free container contains no plastic components and complies with the European SUPD definition of plastic-free.

2. The plastic-free container according to claim 1, characterized in that, The water vapor transmission rate (38℃, 90%RH) of the regenerated cellulose barrier layer is ≤ Oxygen permeability (23℃, 0%RH) ≤ .

3. The plastic-free container according to claim 1, characterized in that, The main structure is formed by rolling or folding and heat sealing at least one piece of composite cardboard. The seams between the main structure and the auxiliary structure, as well as the seams within the main structure itself, are formed by hot pressing together with a special food-contact grade heat sealant that has been applied in a positioning manner. The special food-contact grade heat sealant is only present in the strip area where the seam is located.

4. The plastic-free container according to claim 3, characterized in that, The peel strength of the joint is ≥4.0N / 15mm.

5. The plastic-free container according to claim 1, characterized in that, The plastic-free container is in the shape of a barrel, box, or cup, and has a biodegradability rate of ≥90% within 90 days.

6. The plastic-free container according to claim 1, characterized in that, The auxiliary structure includes a bottom and / or a cover, the material of which is the same as the composite cardboard of the main structure.

7. A method for preparing a plastic-free container conforming to the SUPD plastic-free requirements as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Preparation and coating of dissolving pulp cellulose barrier coating: Prepare a mixed solvent of IL and DMF, disperse the dissolving pulp cellulose fibers in the mixed solvent, heat and stir to dissolve, forming a cellulose coating solution, coat the coating solution on the surface of the base paper layer and then immerse it in a deionized water coagulation bath to regenerate the cellulose and form a gel film. After washing and drying, a composite paperboard with a regenerated cellulose barrier layer is obtained. S2. Positioning and gluing: Use a special food contact grade heat sealant with a solid content of >40% and apply the glue only to the predetermined heat seal edge area of ​​the composite paperboard to form a strip or line of special food contact grade heat sealant. S3. Drying and forming: After the composite paperboard with positioning glue is pre-dried, it is rolled or folded according to the container structure so that the heat-sealed edge areas overlap and are heat-pressed to seal, forming a seam; S4. Assembly: Assemble the main structure and auxiliary structure of the container to obtain a plastic-free container that meets the SUPD plastic-free requirements.

8. The method according to claim 7, characterized in that, In step S1, the mass ratio of IL to DMF is 1:1, the solid content of cellulose in the cellulose coating solution is 5%-15%, and the α-cellulose content of the dissolving pulp cellulose fiber is >95%.

9. The method according to claim 7, characterized in that, In step S1, the heating temperature is 80-120℃, the coating method is scraper, micro-gravure or spraying, and the drying method is hot air drying or oven drying; in step S3, the hot pressing sealing temperature is 100-150℃ and the pressure is 0.3-0.8MPa.

10. The method according to claim 7, characterized in that, In step S2, the special food contact grade heat sealant is applied by spraying, slot coating or gravure printing, and the width of the predetermined heat seal edge area is 10-25mm; in step S1, the residual IL / DMF mixed solvent after washing can be recycled.

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