Low-temperature heat-sealing water-based coated paper as well as preparation method and application thereof

Abstract

The invention relates to the field of packaging materials, and discloses low-temperature heat-sealing water-based coated paper and a preparation method and application thereof.The water-based coated paper comprises a base paper layer and a water-based coating, and the water-based coating comprises water-based ethylene-acrylic acid copolymer emulsion, modified nano-silica, a coalescing agent and water; a cardanol derivative is introduced into the water-based ethylene-acrylic acid copolymer emulsion as a functional component; the cardanol derivative is prepared by reacting epoxidized cardanol with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and then grafting with acryloyl chloride. The preparation method comprises the following steps: reacting epoxidized cardanol with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; the modified nano silicon dioxide is prepared by mixing aminated nano silicon dioxide and chitosan and adding a cross-linking agent prepared by grafting phytic acid and ethylene glycol diglycidyl ether. The water-based coating paper prepared by the invention overcomes the defects that the existing BOPP film is not environment-friendly, and the conventional coating paper is high in heat sealing temperature and easy to stick; meanwhile, good mechanical properties, water resistance and flame retardance are achieved.

Description

Technical Field

[0001] This invention belongs to the field of packaging materials technology, specifically relating to a low-temperature heat-sealing water-based coated paper, its preparation method, and its application. Background Technology

[0002] Currently, BOPP (biaxially oriented polypropylene) film is the mainstream material for heat sealing of cosmetic and tobacco packaging. It is mainly divided into two categories: BOPP hot air film and BOPP heat shrink film. Although existing BOPP film can meet the heat sealing requirements, it has significant drawbacks: First, it is a petroleum-based plastic that is difficult to degrade, which does not conform to the "plastic ban" and the development trend of environmentally friendly packaging; second, its heat sealing relies on high-pressure heat sealing head (conventional heat sealing pressure ≥0.5MPa) and high heat sealing temperature (≥150℃), which not only consumes a lot of energy, but also causes great wear and tear on the heat sealing head of the packaging machine.

[0003] To achieve environmentally friendly alternatives, the industry is experimenting with using paper as a base material and applying resin to give it heat-sealing properties. However, existing coated paper has three major problems: First, the heat-sealing temperature is too high (≥140℃), which is incompatible with the conventional heat-sealing parameters of BOPP packaging machines, requiring equipment modification. Second, after the water-based coating dries, the paper is prone to sticking when rolled up due to the coating's tackiness, causing subsequent roll printing and packaging machine feeding delays, affecting production efficiency. Third, the water-based coating has a low solids content (usually <25%), making it prone to uneven coating with conventional coating processes (such as blade coating), and requiring long drying tunnels to ensure thorough drying. However, existing processes are not optimized for this characteristic, resulting in unstable coating quality. In addition, due to the inherent flammability of paper-based materials, coated paper poses a potential fire hazard. Furthermore, the loose and porous structure of the paper-based material surface results in poor mechanical properties, and small water molecules can easily penetrate and wet the fibers through the pores, greatly limiting its application. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a low-temperature heat-sealable water-based coated paper, its preparation method, and its application, overcoming the defects of existing technologies such as the lack of environmental friendliness of BOPP film, the high heat-sealing temperature of conventional coated paper, and its tendency to reverse adhesion, while simultaneously endowing the coated paper with good mechanical properties, water resistance, and flame retardant properties.

[0005] The objective of this invention can be achieved through the following technical solutions: A low-temperature heat-sealable water-based coated paper includes a base paper layer and a water-based coating applied to the surface of the base paper layer. The water-based coating comprises the following components in parts by weight: 40-60 parts of water-based ethylene-acrylic acid copolymer emulsion, 2-5 parts of modified nano-silica, 3-8 parts of film-forming aid, and 30-50 parts of deionized water. The aqueous ethylene-acrylic acid copolymer emulsion comprises the following raw materials in parts by weight: 40-60 parts of ethylene-acrylic acid copolymer, 3-5 parts of mono- and diglyceride fatty acid esters, 2-4 parts of oxidized polyethylene, 10-20 parts of cashew phenol derivative, 10-20 parts of carboxylated styrene-butadiene latex, 1-3 parts of leveling agent, 0.5-1.5 parts of defoamer, and 50-70 parts of deionized water; The cashew phenol derivative is prepared by converting the unsaturated double bond on the side chain of cashew phenol into an epoxy group using m-chloroperoxybenzoic acid to obtain epoxidized cashew phenol. Then, phosphorus-containing cashew phenol is prepared by ring-opening addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide with epoxidized cashew phenol. Subsequently, phosphorus-containing cashew phenol is prepared by nucleophilic substitution reaction of acryloyl chloride with phosphorus-containing cashew phenol. The modified nano-silica is prepared by using 3-aminopropyltriethoxysilane-grafted aminated nano-silica as a nanofiller reinforcing phase, which is mixed with chitosan by solution intercalation and a crosslinking agent is added; the crosslinking agent is prepared by grafting phytic acid onto ethylene glycol diglycidyl ether under the catalysis of tetrabutylammonium bromide.

[0006] Preferably, the base paper layer is kraft paper or coated white paperboard with a basis weight of 60~120 g / m³. 2 The thickness is 80~150μm.

[0007] Preferably, the solid content of the water-based coating is 15-25%, and the dry film thickness is 5-15 μm.

[0008] Preferably, the preparation method of the aqueous ethylene-acrylic acid copolymer emulsion includes the following steps: weighing each raw material according to the weight parts, heating the ethylene-acrylic acid copolymer to 200°C to melt it, then slowly adding deionized water while stirring, and gradually cooling to 80°C, then adding mono- and diglyceride fatty acid esters, oxidized polyethylene, leveling agent and defoamer, maintaining the temperature and continuing to stir for 1 hour, finally adding cashew phenol derivative, carboxylated styrene-butadiene latex and sulfuric acid solution to adjust the pH value to 6-7, cooling and discharging to prepare the aqueous ethylene-acrylic acid copolymer emulsion.

[0009] Preferably, the method for preparing the cashew phenol derivative includes the following steps: (1) In a nitrogen atmosphere, a saturated aqueous solution of sodium bicarbonate was added dropwise to a dichloromethane solution containing cashew phenol, and the solution was cooled to 0°C in an ice-water bath. Within 30 min, m-chloroperoxybenzoic acid was added in batches. After reacting for 25-40 min, dichloromethane, a saturated aqueous solution of sodium bicarbonate, and a saturated aqueous solution of sodium thiosulfate were added for extraction. The organic phase was taken, dried with anhydrous sodium sulfate, and the solvent was removed by vacuum distillation. Then, it was purified by silica gel chromatography to prepare epoxidized cashew phenol. (2) Take 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in a reactor, heat it to 145~150℃ until it is completely melted under nitrogen protection, then add epoxidized cashew phenol, and react at 145~150℃ for 3~3.5h to prepare phosphorus-containing cashew phenol; (3) Take phosphorus-containing cashew phenol, triethylamine and dichloromethane into a reactor, stir magnetically at room temperature, slowly add a mixed solution of acryloyl chloride and dichloromethane with a constant pressure dropping funnel, stir the reaction for 1-3 hours, filter and distill under reduced pressure after the reaction is completed to prepare cashew phenol derivative.

[0010] Preferably, the method for preparing the modified nano-silica includes the following steps: ① Take phytic acid and disperse it evenly in propylene glycol methyl ether, then add ethylene glycol diglycidyl ether, stir and mix evenly, then add tetrabutylammonium bromide catalyst and continue stirring for 20-40 min, then place it at 60-70℃ for 0.5-1 h to prepare the crosslinking agent; ② Add 3-aminopropyltriethoxysilane to a mixed solution of ethanol and deionized water, hydrolyze it for 0.5-1 h under stirring at room temperature, then add nano-silica and disperse it evenly by ultrasonication. Then reflux it at 75-85℃ for 8-12 h. After the reaction is completed, filter, wash and dry to prepare aminated nano-silica. ③ Dissolve chitosan powder in a 2% (w / w) aqueous solution of acetic acid to prepare a chitosan solution. Then, adjust the pH of the system to 7.5-8.5 using sodium hydroxide solution. Take aminated nano-silica and ultrasonically disperse it in deionized water to form a suspension. Mix the chitosan solution with the suspension and stir continuously until uniform. Then, add a crosslinking agent and stir at 40-50℃ for 2-4 hours to prepare modified nano-silica.

[0011] Preferably, the mass ratio of chitosan, aminated nano-silica, and crosslinking agent is 10:0.5~2:1~4.

[0012] Preferably, the film-forming aid is any one of propylene glycol methyl ether acetate or dipropylene glycol dimethyl ether; the initiator is any one of azobisisobutylamidine hydrochloride or azobiscyanopentanoic acid; and the emulsifier is any one of sodium dodecyl sulfate or sodium dodecylbenzenesulfonate.

[0013] The preparation method of the low-temperature heat-sealable water-based coated paper as described above includes the following steps: S1. Preparation of water-based coating: Weigh each component according to the weight parts, add water-based ethylene-acrylic acid copolymer emulsion, modified nano-silica, film-forming aid and deionized water into a mixing tank, stir at 300~500r / min at 25~35℃ for 20~40min, mix evenly to prepare water-based coating. S2. Reverse coating with an anilox roller: A water-based coating is applied to the surface of the base paper layer by using an anilox roller with a mesh size of 150~250 mesh in a reverse coating method with the rotation direction of the anilox roller opposite to the conveying direction of the base paper layer. The coating speed is 30~50m / min. S3. Long drying tunnel: The coated base paper layer is fed into a long drying tunnel with a length of 15~25m. The temperature of the drying tunnel is set in sections of 60~70℃, 80~90℃, and 100~110℃. The air velocity in the drying tunnel is 1~2m / s. The total drying time is 3~5min. After drying, the paper is wound up with a tension of 50~80N and the winding temperature is controlled at 30~40℃ to prepare low-temperature heat-sealing water-based coated paper.

[0014] An application of a low-temperature heat-sealing water-based coated paper, wherein the low-temperature heat-sealing water-based coated paper is used for heat-sealing processing of cosmetic outer packaging and tobacco box outer packaging, with a heat-sealing temperature of 110~130℃ and a heat-sealing pressure of 0.1~0.3MPa.

[0015] The beneficial effects of this invention are: This invention utilizes m-chloroperoxybenzoic acid as an oxidant to convert the unsaturated double bonds on the side chains of cashew nutmeg from biomass raw materials into epoxy groups, thus preparing epoxidized cashew nutmeg. Then, a ring-opening addition reaction is performed between the pH bond in 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and the epoxidized cashew nutmeg to prepare phosphorus-containing cashew nutmeg. Subsequently, a nucleophilic substitution reaction is performed between acryloyl chloride and the phenolic hydroxyl group in the phosphorus-containing cashew nutmeg to prepare a cashew nutmeg derivative with an introduced double bond structure. This cashew nutmeg derivative is then used as a functional component in aqueous ethylene-acrylic acid copolymer emulsions. The preparation process introduces flexible long alkyl side chains with good flexibility and hydrophobicity, as well as rigid heterocyclic structures of phosphaphenanthrene with good thermal stability and flame retardancy into the waterborne ethylene-acrylic acid copolymer emulsion. This endows the waterborne coating with good mechanical properties, water resistance and flame retardancy. At the same time, the cashew phenol derivative can form a dense hydrogen bond network with the base paper layer, and the flexible long alkyl side chains improve the fluidity and permeability of the waterborne ethylene-acrylic acid copolymer emulsion during the film formation process, which can effectively improve the adhesion between the waterborne coating and the base paper layer, thereby improving the paper strength of the base paper layer.

[0016] This invention utilizes phytic acid grafted onto ethylene glycol diglycidyl ether under the catalysis of tetrabutylammonium bromide to prepare a crosslinking agent containing multiple epoxy groups. Simultaneously, it utilizes the silanol groups formed by the hydrolysis of 3-aminopropyltriethoxysilane to undergo a dehydration condensation reaction with the hydroxyl groups on the surface of nano-silica to prepare aminated nano-silica, improving the dispersion uniformity and hydrophobicity of nano-silica. Then, the aminated nano-silica is used as a nanofiller reinforcing phase, mixed with chitosan via solution intercalation, and a crosslinking agent is added. The crosslinking agent reacts chemically with the aminated nano-silica and chitosan to form a crosslinked network structure, giving the waterborne coating stronger thermal stability and higher mechanical properties. Furthermore, the phosphorus element introduced by phytic acid is fixed in the polymer backbone, making it less prone to migration and precipitation, achieving long-lasting, environmentally friendly flame retardancy. In addition, the dense crosslinked network structure greatly restricts the movement of polymer chain segments and the penetration path of water molecules, exhibiting excellent water-repellent properties.

[0017] The low-temperature heat-sealable water-based coated paper prepared by this invention consists of a base paper layer and a water-based coating applied to the surface of the base paper layer. The water-based coating uses a water-based ethylene-acrylic acid copolymer emulsion as the core film-forming resin. The carboxyl and hydroxyl groups in its molecular chain can form stable adhesion at lower temperatures, reducing the heat-sealing temperature to 110-130℃ to match the temperature range of BOPP packaging machines. Modified nano-silica particles can form "physical isolation points" on the coating surface, disrupting the adhesion between coating layers and solving the problem of roll-to-roll adhesion without affecting heat-sealing performance. Compound film-forming aids lower the resin film-forming temperature. Using deionized water as a solvent, the coating solid content is controlled at 15-25%, balancing coating smoothness and drying efficiency. The water-based coating is applied to the base paper layer using a reverse coating process with an anilox roller, which enhances the adhesion between the coating and the base paper layer and reduces coating peeling during heat sealing. The finished product is obtained through segmented low-temperature drying in a long drying tunnel. Specifically, it adopts three temperature control stages: 60~70℃, 80~90℃, and 100~110℃. The first stage is low temperature to evaporate a large amount of moisture and prevent the base paper from warping due to rapid dehydration. The second stage is medium temperature to promote the initial film formation of the resin. The third stage is high temperature to ensure thorough film formation. The total drying time is 3~5 minutes, which controls the coating moisture content to ≤0.5% and avoids high temperature damage to the base paper. Moreover, the heat sealing temperature of this coated paper is as low as 110~130℃, which is suitable for the flat ironing head of BOPP packaging machine and the heat sealing requirements of 0.1~0.3MPa light pressure. There is no back-sticking phenomenon in the roll state, which can be directly used for roll printing. It can replace BOPP hot air film and BOPP heat shrink film for cosmetic outer packaging and tobacco box outer packaging, solving the problems of traditional BOPP film being not environmentally friendly and conventional coated paper having high heat sealing temperature and easy back-sticking. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: An aqueous ethylene-acrylic acid copolymer emulsion comprises the following raw materials in parts by weight: 42 parts of ethylene-acrylic acid copolymer, 3.3 parts of mono- and diglyceride fatty acid esters, 2.1 parts of oxidized polyethylene, 12 parts of cashew phenol derivative, 11 parts of carboxylated styrene-butadiene latex, 1.2 parts of leveling agent RM2020, 0.5 parts of polyether modified silicone defoamer, and 52 parts of deionized water; The preparation method of cashew phenol derivatives includes the following steps: (1) In a nitrogen atmosphere, 40 mL of sodium bicarbonate saturated aqueous solution was added dropwise to 40 mL of dichloromethane solution containing 3 g cashew phenol. The solution was cooled to 0 °C in an ice-water bath. 2.6 g of m-chloroperoxybenzoic acid was added in batches over 30 min. After reacting for 30 min, dichloromethane, sodium bicarbonate saturated aqueous solution and sodium thiosulfate saturated aqueous solution were added for extraction. The organic phase was taken, dried with anhydrous sodium sulfate, and the solvent was removed by vacuum distillation. The solution was then purified by silica gel chromatography (V petroleum ether: V ethyl acetate = 8:1) to prepare epoxidized cashew phenol. (2) Take 2.2g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in a reactor, heat it to 150°C until it is completely melted under nitrogen protection, then add 3.7g of epoxidized cashew phenol, and react it at 150°C for 3h to prepare phosphorus-containing cashew phenol; (3) Take 2.9g of phosphorus-containing cashew phenol, 0.6g of triethylamine and 10mL of dichloromethane into a reactor, stir magnetically at room temperature, slowly add 0.5g of acryloyl chloride and 10mL of dichloromethane mixed solution with constant pressure dropping funnel, stir the reaction for 2.5h, filter and distill under reduced pressure after the reaction is completed to prepare cashew phenol derivative.

[0020] The preparation method of the above-mentioned aqueous ethylene-acrylic acid copolymer emulsion includes the following steps: Weigh each raw material according to the weight proportions, heat the ethylene-acrylic acid copolymer to 200℃ to melt it, then slowly add deionized water while stirring, and gradually cool down to 80℃. Subsequently, add mono- and diglyceride fatty acid esters, oxidized polyethylene, leveling agent and defoamer, and continue stirring at this temperature for 1 hour. Finally, add cashew phenol derivative, carboxylated styrene-butadiene latex and sulfuric acid solution to adjust the pH value to 7, cool down and discharge the material to prepare an aqueous ethylene-acrylic acid copolymer emulsion.

[0021] Example 2: A method for preparing modified nano-silica includes the following steps: ① Take 0.5g of phytic acid and disperse it evenly in 5.5g of propylene glycol methyl ether, then add 0.8g of ethylene glycol diglycidyl ether, stir and mix evenly, then add 0.02g of tetrabutylammonium bromide catalyst and continue stirring for 30min, then place it at 65℃ for 0.5h to prepare the crosslinking agent; ② Take 4g of 3-aminopropyltriethoxysilane and add it to a mixed solution of 100mL ethanol and 20mL deionized water. After hydrolyzing for 1h under stirring at room temperature, add 2g of nano-silica and ultrasonically disperse it evenly. Then, reflux it at 80℃ for 10h. After the reaction is completed, filter, wash and dry to prepare aminated nano-silica. ③ Dissolve 10g of chitosan powder in 500mL of 2% acetic acid aqueous solution to prepare chitosan solution. Then adjust the pH of the system to 8 using sodium hydroxide solution. Take 1.5g of aminated nano silica and ultrasonically disperse it in 20mL of deionized water to form a suspension. Mix the chitosan solution with the suspension and stir continuously until uniform. Then add 3g of crosslinking agent and stir at 45℃ for 3h to prepare modified nano silica.

[0022] Example 3: An aqueous coating comprises the following components in parts by weight: 42 parts of the aqueous ethylene-acrylic acid copolymer emulsion prepared in Example 1, 2.2 parts of the modified nano silica prepared in Example 2, 3.3 parts of the film-forming aid propylene glycol methyl ether acetate, and 35 parts of deionized water.

[0023] A method for preparing a low-temperature heat-sealable water-based coated paper includes the following steps: S1. Preparation of water-based coating: Weigh each component according to the weight parts, add water-based ethylene-acrylic acid copolymer emulsion, modified nano-silica, film-forming aid and deionized water into a mixing tank, stir at 30°C and 400 r / min for 30 min, and mix evenly to prepare water-based coating. S2. Anilox Roller Reverse Coating: Using a 200-mesh anilox roller, the water-based coating is applied to the 80g / m² paper using a reverse coating method where the rotation direction of the anilox roller is opposite to the direction of kraft paper feeding. 2 Coating speed on kraft paper surface: 40 m / min; coating amount (wet film): 10 g / m² 2 ; S3. Long drying tunnel: The coated kraft paper is fed into a 20m long drying tunnel. The temperature of the tunnel is set in sections of 65℃, 85℃ and 105℃. The air velocity in the tunnel is 1.5m / s. The total drying time is 4min. After drying, the paper is wound up with a tension of 60N and the winding temperature is controlled at 35℃ to prepare low-temperature heat-sealing water-based coated paper.

[0024] Example 4 An aqueous coating comprises the following components in parts by weight: 45 parts of aqueous ethylene-acrylic acid copolymer emulsion prepared in Example 1, 3 parts of modified nano silica prepared in Example 2, 5 parts of film-forming aid propylene glycol methyl ether acetate, and 47 parts of deionized water.

[0025] The preparation method of a low-temperature heat-sealing water-based coated paper is the same as in Example 3.

[0026] Example 5: An aqueous coating comprises the following components in parts by weight: 57 parts of the aqueous ethylene-acrylic acid copolymer emulsion prepared in Example 1, 4.6 parts of the modified nano silica prepared in Example 2, 7.7 parts of the film-forming aid dipropylene glycol dimethyl ether, and 48 parts of deionized water.

[0027] The preparation method of a low-temperature heat-sealing water-based coated paper is the same as in Example 3.

[0028] Comparative Example 1: An aqueous ethylene-acrylic acid copolymer emulsion comprises the following raw materials in parts by weight: 42 parts of ethylene-acrylic acid copolymer, 3.3 parts of mono- and diglyceride fatty acid esters, 2.1 parts of oxidized polyethylene, 11 parts of carboxylated styrene-butadiene latex, 1.2 parts of leveling agent RM2020, 0.5 parts of polyether modified silicone defoamer, and 52 parts of deionized water; The preparation method of the above-mentioned aqueous ethylene-acrylic acid copolymer emulsion includes the following steps: Weigh each raw material according to the weight parts, heat the ethylene-acrylic acid copolymer to 200℃ to melt it, then slowly add deionized water while stirring, and gradually cool down to 80℃. Then add mono- and diglyceride fatty acid esters, oxidized polyethylene, leveling agent and defoamer, and continue stirring at this temperature for 1 hour. Finally, add carboxylated styrene-butadiene latex and sulfuric acid solution to adjust the pH value to 7, cool down and discharge the material to prepare an aqueous ethylene-acrylic acid copolymer emulsion.

[0029] Comparative Example 2: A method for preparing modified nano-silica includes the following steps: ① Take 4g of 3-aminopropyltriethoxysilane and add it to a mixed solution of 100mL ethanol and 20mL deionized water. After hydrolysis for 1h under stirring at room temperature, add 2g of nano-silica and disperse it evenly by ultrasonication. Then, reflux it at 80℃ for 10h. After the reaction is completed, filter, wash and dry to prepare aminated nano-silica. ② Dissolve 10g of chitosan powder in 500mL of 2% acetic acid aqueous solution to prepare chitosan solution. Then adjust the pH of the system to 8 using sodium hydroxide solution. Take 1.5g of aminated nano silica and ultrasonically disperse it in 20mL of deionized water to form a suspension. Mix the chitosan solution with the suspension and stir continuously until uniform. Then add 3g of ethylene glycol diglycidyl ether and stir at 45℃ for 3h to prepare modified nano silica.

[0030] Comparative Example 3: A method for preparing modified nano-silica includes the following steps: ① Take 4g of 3-aminopropyltriethoxysilane and add it to a mixed solution of 100mL ethanol and 20mL deionized water. After hydrolysis for 1h under stirring at room temperature, add 2g of nano-silica and disperse it evenly by ultrasonication. Then, reflux it at 80℃ for 10h. After the reaction is completed, filter, wash and dry to prepare aminated nano-silica. ② Dissolve 10g of chitosan powder in 500mL of 2% acetic acid aqueous solution to prepare chitosan solution. Then adjust the pH of the system to 8 using sodium hydroxide solution. Take 1.5g of aminated nano-silica and ultrasonically disperse it in 20mL of deionized water to form a suspension. Mix the chitosan solution with the suspension and stir continuously until uniform to prepare modified nano-silica.

[0031] Comparative Example 4: An aqueous coating comprises the following components in parts by weight: 45 parts of the aqueous ethylene-acrylic acid copolymer emulsion prepared in Comparative Example 1, 3 parts of the modified nano-silica prepared in Example 2, 5 parts of the film-forming aid propylene glycol methyl ether acetate, and 47 parts of deionized water.

[0032] The preparation method of a low-temperature heat-sealing water-based coated paper is the same as in Example 3.

[0033] Comparative Example 5: An aqueous coating comprises the following components in parts by weight: 45 parts of the aqueous ethylene-acrylic acid copolymer emulsion prepared in Example 1, 3 parts of the modified nano silica prepared in Comparative Example 2, 5 parts of the film-forming aid propylene glycol methyl ether acetate, and 47 parts of deionized water.

[0034] The preparation method of a low-temperature heat-sealing water-based coated paper is the same as in Example 3.

[0035] Comparative Example 6: An aqueous coating comprises the following components in parts by weight: 45 parts of the aqueous ethylene-acrylic acid copolymer emulsion prepared in Example 1, 3 parts of the modified nano-silica prepared in Comparative Example 3, 5 parts of the film-forming aid propylene glycol methyl ether acetate, and 47 parts of deionized water.

[0036] The preparation method of a low-temperature heat-sealing water-based coated paper is the same as in Example 3.

[0037] Performance testing A. Performance testing was conducted on the low-temperature heat-sealable water-based coated paper prepared in Examples 3-5: (1) The low-temperature heat-sealable water-based coated paper prepared in Example 3 was heat-sealed at 112~120℃ for 1s and 0.3MPa. The sealing strength was measured to be 31N / 15mm according to GB / T 10457-2009. After being rolled up and placed at 25℃ and 60% relative humidity for 72h, the coating was unstuck and undamaged. The pattern was clear and the coating was not peeled off when printed on a roll printing machine at a speed of 150m / min. The paper was continuously heat-sealed on a tobacco box BOPP packaging machine for 8h without jamming and the heat-sealing qualification rate was 99.4%.

[0038] (2) The low-temperature heat-sealable water-based coated paper prepared in Example 4 was heat-sealed at 118~122℃ for 1s and 0.2MPa. The sealing strength was measured to be 32N / 15mm according to GB / T 10457-2009. After being rolled up and placed at 25℃ and 60% relative humidity for 72h, the coating was unstuck and undamaged. The pattern was clear and the coating was not peeled off when printed on a roll printing machine at a speed of 150m / min. The paper was continuously heat-sealed on a tobacco box BOPP packaging machine for 8h without jamming and the heat-sealing qualification rate was 99.5%.

[0039] (3) The low-temperature heat-sealable water-based coated paper prepared in Example 5 was heat-sealed at 115~119℃ for 1s and 0.15MPa. The sealing strength was measured to be 34N / 15mm according to GB / T 10457-2009. After being rolled up and placed at 25℃ and 60% relative humidity for 72h, the coating was unrolled without sticking or damage. The pattern was clearly printed on a roll printing machine at a speed of 150m / min, and there was no coating peeling. It was used for heat sealing of cosmetic gift box outer packaging. After heat sealing, the edges and corners of the gift box were flat and without wrinkles.

[0040] B. The performance of the low-temperature heat-sealable water-based coated papers prepared in Examples 3-5 and Comparative Examples 4-6 was tested: the tensile index of the coated paper was determined using an electronic universal tensile tester according to GB / T 12914-2018; the flame retardant performance was tested according to GB / T 14656-2009; and the Cobb value of the coated paper was determined using a Cobb absorbency tester according to GB / T 1540-2002. The test time was 60s, and each sample was tested 3 times. The average value was calculated. The Cobb value reflects the water absorption performance of the coated paper. The higher the Cobb value, the worse the water resistance. The data results are shown in Table 1.

[0041] Table 1 Sample performance test results

[0042] As can be seen from the data in Table 1, the low-temperature heat-sealable waterborne coated paper prepared in Examples 3-5 of this invention has a high tensile index and also possesses good water resistance and flame retardant properties. In Comparative Example 4, the waterborne ethylene-acrylic acid copolymer emulsion added did not contain cashew phenol derivatives, and its measured tensile index, water resistance, and flame retardant properties were lower than those in Examples 3-5. This is because the cashew phenol derivatives promote the bonding between the waterborne coating and the base paper layer, making the bonding between the fibers of the base paper layer tighter and effectively improving the paper strength. Furthermore, the introduction of the rigid heterocyclic structure of phosphaphenanthrene is beneficial to improving the flame retardant properties of the material. Additionally, the introduced flexible long alkyl side chains are beneficial to improving the hydrophobicity of the material. In Comparative Example 5, the modified nano-silica replaced the crosslinking agent with ethylene glycol diglycidyl ether. The modified nano-silica added in Example 6 did not contain a crosslinking agent. The flame retardant performance of Comparative Examples 5-6 was lower than that of Examples 3-5, indicating that the introduction of phytic acid improved the flame retardant performance of the material to a certain extent. The flame retardant performance of Comparative Example 6 was lower than that of Comparative Example 5, and the tensile index and water resistance were lower than those of Examples 3-5. This is because the crosslinking agent can react chemically with aminated nano-silica and chitosan to form a crosslinked network structure, which greatly restricts the movement of polymer chain segments and the penetration path of water molecules, while making the water-based coating exhibit stronger thermal stability and higher mechanical properties.

[0043] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0044] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A low-temperature heat-sealable water-based coated paper, characterized in that, The material includes a base paper layer and an aqueous coating applied to the surface of the base paper layer. The aqueous coating comprises the following components in parts by weight: 40-60 parts of aqueous ethylene-acrylic acid copolymer emulsion, 2-5 parts of modified nano-silica, 3-8 parts of film-forming aid, and 30-50 parts of deionized water. The aqueous ethylene-acrylic acid copolymer emulsion comprises the following raw materials in parts by weight: 40-60 parts of ethylene-acrylic acid copolymer, 3-5 parts of mono- and diglyceride fatty acid esters, 2-4 parts of oxidized polyethylene, 10-20 parts of cashew phenol derivative, 10-20 parts of carboxylated styrene-butadiene latex, 1-3 parts of leveling agent, 0.5-1.5 parts of defoamer, and 50-70 parts of deionized water; The cashew phenol derivative is prepared by converting the unsaturated double bond on the side chain of cashew phenol into an epoxy group using m-chloroperoxybenzoic acid to obtain epoxidized cashew phenol. Then, phosphorus-containing cashew phenol is prepared by ring-opening addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide with epoxidized cashew phenol. Subsequently, phosphorus-containing cashew phenol is prepared by nucleophilic substitution reaction of acryloyl chloride with phosphorus-containing cashew phenol. The modified nano-silica is prepared by using 3-aminopropyltriethoxysilane-grafted aminated nano-silica as a nanofiller reinforcing phase, which is mixed with chitosan by solution intercalation and a crosslinking agent is added; the crosslinking agent is prepared by grafting phytic acid onto ethylene glycol diglycidyl ether under the catalysis of tetrabutylammonium bromide.

2. The low-temperature heat-sealable water-based coated paper according to claim 1, characterized in that, The base paper layer is kraft paper or coated white paperboard with a basis weight of 60~120g / m³. 2 The thickness is 80~150μm.

3. The low-temperature heat-sealable water-based coated paper according to claim 1, characterized in that, The water-based coating has a solid content of 15-25% and a dry film thickness of 5-15 μm.

4. The low-temperature heat-sealable water-based coated paper according to claim 1, characterized in that, The preparation method of the aqueous ethylene-acrylic acid copolymer emulsion includes the following steps: weigh each raw material according to the weight parts, heat the ethylene-acrylic acid copolymer to 200°C to melt it, then slowly add deionized water while stirring, and gradually cool down to 80°C, then add mono- and diglyceride fatty acid esters, oxidized polyethylene, leveling agent and defoamer, maintain the temperature and continue stirring for 1 hour, finally add cashew phenol derivative, carboxylated styrene-butadiene latex and sulfuric acid solution to adjust the pH value to 6~7, cool down and discharge the material to prepare the aqueous ethylene-acrylic acid copolymer emulsion.

5. The low-temperature heat-sealable water-based coated paper according to claim 1, characterized in that, The method for preparing the cashew phenol derivative includes the following steps: (1) In a nitrogen atmosphere, a saturated aqueous solution of sodium bicarbonate was added dropwise to a dichloromethane solution containing cashew phenol, and the solution was cooled to 0°C in an ice-water bath. Within 30 min, m-chloroperoxybenzoic acid was added in batches. After reacting for 25-40 min, dichloromethane, a saturated aqueous solution of sodium bicarbonate, and a saturated aqueous solution of sodium thiosulfate were added for extraction. The organic phase was taken, dried with anhydrous sodium sulfate, and the solvent was removed by vacuum distillation. Then, it was purified by silica gel chromatography to prepare epoxidized cashew phenol. (2) Take 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in a reactor, heat it to 145~150℃ until it is completely melted under nitrogen protection, then add epoxidized cashew phenol, and react at 145~150℃ for 3~3.5h to prepare phosphorus-containing cashew phenol; (3) Take phosphorus-containing cashew phenol, triethylamine and dichloromethane into a reactor, stir magnetically at room temperature, slowly add a mixed solution of acryloyl chloride and dichloromethane with a constant pressure dropping funnel, stir the reaction for 1-3 hours, filter and distill under reduced pressure after the reaction is completed to prepare cashew phenol derivative.

6. The low-temperature heat-sealable water-based coated paper according to claim 1, characterized in that, The method for preparing the modified nano-silica includes the following steps: ① Take phytic acid and disperse it evenly in propylene glycol methyl ether, then add ethylene glycol diglycidyl ether, stir and mix evenly, then add tetrabutylammonium bromide catalyst and continue stirring for 20-40 min, then place it at 60-70℃ for 0.5-1 h to prepare the crosslinking agent; ② Add 3-aminopropyltriethoxysilane to a mixed solution of ethanol and deionized water, hydrolyze it for 0.5-1 h under stirring at room temperature, then add nano-silica and disperse it evenly by ultrasonication. Then reflux it at 75-85℃ for 8-12 h. After the reaction is completed, filter, wash and dry to prepare aminated nano-silica. ③ Dissolve chitosan powder in a 2% (w / w) aqueous solution of acetic acid to prepare a chitosan solution. Then, adjust the pH of the system to 7.5-8.5 using sodium hydroxide solution. Take aminated nano-silica and ultrasonically disperse it in deionized water to form a suspension. Mix the chitosan solution with the suspension and stir continuously until uniform. Then, add a crosslinking agent and stir at 40-50℃ for 2-4 hours to prepare modified nano-silica.

7. The low-temperature heat-sealable water-based coated paper according to claim 6, characterized in that, The mass ratio of chitosan, aminated nano-silica, and crosslinking agent is 10:0.5~2:1~4.

8. The low-temperature heat-sealable water-based coated paper according to claim 1, characterized in that, The film-forming aid is any one of propylene glycol methyl ether acetate or dipropylene glycol dimethyl ether; the initiator is any one of azobisisobutylamidine hydrochloride or azobiscyanopentanoic acid; and the emulsifier is any one of sodium dodecyl sulfate or sodium dodecylbenzenesulfonate.

9. The method for preparing low-temperature heat-sealable water-based coated paper according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Preparation of water-based coating: Weigh each component according to the weight parts, add water-based ethylene-acrylic acid copolymer emulsion, modified nano-silica, film-forming aid and deionized water into a mixing tank, stir at 300~500r / min at 25~35℃ for 20~40min, mix evenly to prepare water-based coating. S2. Reverse coating with an anilox roller: A water-based coating is applied to the surface of the base paper layer by using an anilox roller with a mesh size of 150~250 mesh in a reverse coating method with the rotation direction of the anilox roller opposite to the conveying direction of the base paper layer. The coating speed is 30~50m / min. S3. Long drying tunnel: The coated base paper layer is fed into a long drying tunnel with a length of 15~25m. The temperature of the drying tunnel is set in sections of 60~70℃, 80~90℃, and 100~110℃. The air velocity in the drying tunnel is 1~2m / s. The total drying time is 3~5min. After drying, the paper is wound up with a tension of 50~80N and the winding temperature is controlled at 30~40℃ to prepare low-temperature heat-sealing water-based coated paper.

10. An application of the low-temperature heat-sealable water-based coated paper according to claim 1, characterized in that, The low-temperature heat-sealing water-based coated paper is used for heat-sealing processing of cosmetic outer packaging and tobacco box outer packaging, with a heat-sealing temperature of 110~130℃ and a heat-sealing pressure of 0.1~0.3MPa.

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