Slow water-soluble food packaging film and preparation method thereof

Abstract

The invention belongs to the technical field of food packaging films, and particularly relates to a slow water-soluble food packaging film and a preparation method thereof. The slow water-soluble food packaging film provided by the invention comprises the following components in percentage by mass: 30-60% of film-forming resin; 15-30% of an alcohol-soluble polyamide solution; 10-30% of an inorganic filler; 2-5% of acetyl triethyl citrate; 1 to 4% of vinyl triethoxy silane; 0.5-2% of emulsified silicone oil; 0.2 to 0.8 percent of superfine silicon dioxide; 1-3% of polyethylene wax; 3-10% of alkylphenol polyvinyl ether; 0.5-2% of polyethylene glycol; and the balance water. When the packaging film provided by the invention is in contact with water for a short time in a use process, the film is not broken and is insoluble in water, but used wastes can be prepared into water-soluble substances by adopting a water soaking method and then prepared into particulate matters for recycling, so that white pollution of the wastes is eliminated.

Description

Technical Field

[0001] This invention belongs to the field of food packaging film technology, specifically relating to a slow-water-soluble food packaging film and its preparation method. Background Technology

[0002] With the improvement of people's living standards and the rapid development of fast food delivery, food processing, agricultural and sideline product processing, tourism food retail, and fruit and vegetable retail, the use of plastic film is increasing daily. Food packaging film has become an indispensable daily necessity and a fast-moving disposable consumer good. Especially various food shopping bags, such as fish and meat packaging, are used almost every day. These discarded food packaging materials and shopping bags accumulate daily, and very few can be recycled and reused. Furthermore, they are non-biodegradable and insoluble in water, causing serious plastic waste pollution and "white pollution."

[0003] Food packaging materials in waste are insoluble in water and non-biodegradable, severely polluting the environment and endangering the food safety of rivers, lakes, seas, and aquatic life. The environmental pollution caused by this waste urgently needs to be addressed. Furthermore, food packaging films are disposable consumer films. Besides requirements for load-bearing capacity, oil resistance, and gas barrier properties, they do not need excessively strong or high mechanical properties. However, existing food packaging films are primarily made of materials such as polyamide, polyethylene, polystyrene, polypropylene, ABS resin, EMA, and EVOH. These materials are all non-biodegradable, have a lifespan of several years or decades, and cannot absorb water or hydrolyze in waste. Food packaging films made from these materials are also difficult to recycle, and recycling requires a second high-temperature melting process. Therefore, secondary recycling is costly and has low utilization value. Consequently, most of these materials are buried underground or incinerated, causing secondary pollution. Summary of the Invention

[0004] The purpose of this invention is to provide a slow-water-soluble food packaging film and its preparation method. The slow-water-soluble food packaging film provided by this invention is water-soluble and biodegradable, and is environmentally friendly.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a slow-water-soluble food packaging film, comprising the following components by weight percentage:

[0007]

[0008]

[0009] The film-forming resin includes an aqueous solution of polyvinyl alcohol, an aqueous solution of glycerol, and water;

[0010] The solid content of the film-forming resin is 30%-50%;

[0011] The degree of alcoholysis of polyvinyl alcohol in the aqueous solution is 87%-89%, 75%-80%, or 99%-99.9%.

[0012] Preferably, the film-forming resin is obtained by mixing an aqueous solution of polyvinyl alcohol, an aqueous solution of glycerol, and water;

[0013] When the degree of alcoholysis of polyvinyl alcohol is 87%-89%, the mass ratio of the polyvinyl alcohol aqueous solution to the glycerol aqueous solution is 65-80:20-35;

[0014] When the degree of alcoholysis of polyvinyl alcohol is 75%-80%, the mass ratio of the polyvinyl alcohol aqueous solution to the glycerol aqueous solution is 80-90:10-20.

[0015] When the degree of alcoholysis of polyvinyl alcohol is 99%-99.9%, the ratio of the aqueous polyvinyl alcohol solution to the aqueous glycerol solution is 75-85:15-25.

[0016] The solid content of the polyvinyl alcohol aqueous solution and the glycerol aqueous solution is independently 30%-50%.

[0017] Preferably, the inorganic filler includes one of calcium carbonate, magnesium sulfate, kaolin, fossil powder, and aluminum hydroxide.

[0018] Preferably, the low-density polyethylene wax has a weight-average molecular weight of 500, and the polyethylene glycol has a weight-average molecular weight of 1000; the water is purified water or deionized water.

[0019] Preferably, the alcohol-soluble polyamide solution has an acid value ≤6 (mgKOH / g), an amine value ≤6mgKOH / g, a viscosity of 110±5mpa·s / 25℃ (mpa), a softening point of 80-100℃, a color of <7, and a freezing point of -5℃.

[0020] Preferably, when the degree of alcoholysis is 87-89%, the weight-average molecular weight of polyvinyl alcohol is 170,000-220,000.

[0021] When the degree of alcoholysis is 75%–80%, the weight-average molecular weight is 50,000–100,000.

[0022] When the degree of alcoholysis is 99%-99.8%, the weight-average molecular weight is 50,000-100,000.

[0023] This invention also provides a method for preparing the slow-water-soluble food packaging film described in the above technical solution, comprising the following steps:

[0024] (1) After spraying an ethanol solution of vinyltrioxyethylsilane onto the inorganic filler and drying it, a modified inorganic filler is obtained.

[0025] (2) Mix film-forming resin, alcohol-soluble polyamide solution, modified inorganic filler, triethyl acetylcitrate, vinyltriethoxysilane, emulsified silicone oil, ultrafine silica, polyethylene wax, alkylphenol polyethylene ether, polyethylene glycol and water to obtain coating liquid;

[0026] (3) The coating solution is coated to form a film;

[0027] (4) A surface of the film is subjected to surface treatment in sequence; the surface treatment includes atomization, first drying, spray washing and second drying in sequence;

[0028] (5) Repeat the surface treatment steps on the other side of the film.

[0029] Preferably, the atomized aqueous solution is a trimethylammonium trihydrogenase aqueous solution or a dimethylurea aqueous solution; the solid content of the trimethylammonium trihydrogenase aqueous solution or the dimethylurea aqueous solution is independently 1-5%.

[0030] Preferably, the solid content of the coating liquid is 30-45%.

[0031] Preferably, during atomization, when the degree of hydrolysis of polyvinyl alcohol is 87%-89%, the temperature of the atomizing aqueous solution is 15℃-50℃; when the degree of hydrolysis of polyvinyl alcohol is 75%-80%, the temperature of the atomizing aqueous solution is 15-20℃; when the degree of hydrolysis of polyvinyl alcohol is 99%-99.8%, the temperature of the atomizing aqueous solution is 95℃; the atomization time is 60-240s; and the atomizing water pressure is 0.5-0.8mps.

[0032] This invention provides a slow-water-soluble food packaging film, comprising the following components by weight percentage: 30-60% film-forming resin; 15-30% alcohol-soluble polyamide solution; 10-30% inorganic filler; 2-5% triethyl acetylacetate; 1-4% vinyltriethoxysilane; 0.5-2% emulsified silicone oil; 0.2-0.8% ultrafine silica; 1-3% polyethylene wax; 3-10% alkylphenol polyvinyl ether; 0.5-2% polyethylene glycol; and water as the balance. The film-forming resin comprises an aqueous solution of polyvinyl alcohol, an aqueous solution of glycerol, and water. The solid content of the film-forming resin is 30%-50%. The degree of alcoholysis of the polyvinyl alcohol in the aqueous solution is 87%-89%, 75%-80%, or 99%-99.9%.

[0033] The slow-water-soluble food packaging film provided by this invention has the following advantages:

[0034] (1) Although the surface layer of the membrane is insoluble in water, it is permeable to water, while the base membrane (the part other than the upper and lower surfaces is called the base membrane) has slow water solubility and slow hygroscopicity. The water solubility rate can be controlled by the thickness of the surface water-insoluble layer and the amount of polyvinyl alcohol in the base membrane.

[0035] (2) Waste membranes can be hydrolyzed, avoiding the pollution of waste plastics and the land area occupied by landfill.

[0036] (3) Waste membranes can be treated simply by water dissolution (the waste membranes can be "soaked in water for hydrolysis first, and then degraded in the form of water-soluble substances"). This method is simple and widely applicable. In addition, compared with existing technologies, it saves energy consumption and carbon emissions from high-temperature melting during the recycling process and avoids the air pollution problems caused by waste membrane incineration. Furthermore, waste membranes can be recycled and reused by dissolving them in water. Waste that cannot be recycled can be dissolved into water-soluble substances for direct discharge, thus improving resource utilization. Detailed Implementation

[0037] This invention provides a slow-water-soluble food packaging film, comprising the following components by weight percentage:

[0038]

[0039] As one embodiment of the present invention, the slow-water-soluble food packaging film comprises 30-60% film-forming resin by weight percentage, specifically 30%, 35%, 40%, 45%, 50%, 55%, or 60%.

[0040] In one embodiment of the present invention, the film-forming resin includes an aqueous solution of polyvinyl alcohol, an aqueous solution of glycerol, and water.

[0041] In this invention, polyvinyl alcohol (PVA) is a water-soluble polymer that becomes sticky after absorbing moisture. Glycerin has extremely strong hygroscopic properties and can reduce the surface viscosity of PVA after it absorbs moisture. For disposable temporary food shopping bags and food packaging films, such as films used for only 1-2 hours or even tens of minutes, a higher amount of glycerin can be selected in the composition. Furthermore, glycerin is also a plasticizer for PVA. For PVA, because it is a hygroscopic, water-soluble polymer, its tensile strength and tear resistance increase with increasing moisture content.

[0042] In one embodiment of the present invention, the degree of alcoholysis of polyvinyl alcohol in the aqueous solution is 87%-89% (for polyvinyl alcohol soluble in both cold and hot water), 75%-80% (for polyvinyl alcohol soluble in cold water), or 99%-99.9% (for polyvinyl alcohol soluble in hot water).

[0043] In one embodiment of the present invention, when the degree of hydrolysis of polyvinyl alcohol is 87-89%, specifically it can be 87%, 87.5%, 88%, 88.5%, or 89%; the weight-average molecular weight can be 170,000 to 220,000, specifically 170,000, 180,000, 190,000, 200,000, 210,000, or 220,000. In another embodiment of the present invention, when the degree of hydrolysis of polyvinyl alcohol is 75%-80%, specifically it can be 75%, 75.5%, 76%, 76.5%, 77%, 77.5%, 78%, 78.5%, 79%, 79.5%, or 80%; the weight-average molecular weight can be 50,000 to 100,000, specifically 50,000, 60,000, 70,000, 80,000, 90,000, or 100,000. As one embodiment of the present invention, when the degree of hydrolysis of polyvinyl alcohol is 99%-99.8%, its degree of hydrolysis can specifically be 99%, 99.2%, 99.4%, 99.6% or 99.8%; the weight-average molecular weight can be 50,000-100,000, specifically 50,000, 60,000, 70,000, 80,000, 90,000 or 100,000.

[0044] In one embodiment of the present invention, the film-forming resin is preferably prepared by mixing a polyvinyl alcohol aqueous solution, a glycerol aqueous solution, and water. In another embodiment, the mixing is preferably carried out under stirring conditions; the stirring speed is preferably 60-180 r / min. In yet another embodiment, the polyvinyl alcohol aqueous solution is prepared using methods well-known to those skilled in the art, with polyvinyl alcohols of different degrees of hydrolysis prepared at appropriate water-soluble temperatures.

[0045] In one embodiment of the present invention, when the degree of hydrolysis of polyvinyl alcohol is 87-89%, the mass ratio of polyvinyl alcohol aqueous solution to glycerol aqueous solution is preferably 65-80:20-35, specifically 65:35, 70:30, 75:25 or 80:20. In one embodiment of the present invention, the solid content of the polyvinyl alcohol aqueous solution and the glycerol aqueous solution is preferably 30-50%, specifically 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%. In another embodiment of the present invention, the solid content of the film-forming resin is preferably 30-50% (at 25°C), specifically 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%.

[0046] When the degree of hydrolysis of polyvinyl alcohol is 75-80%, the mass ratio of the polyvinyl alcohol aqueous solution to the glycerol aqueous solution is preferably 80-90:10-20, and more preferably 80:20, 85:15 or 90:10. In one embodiment of the present invention, the polyvinyl alcohol aqueous solution and the glycerol aqueous solution are independently 30-50%, specifically preferably 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%. In another embodiment of the present invention, the solid content of the film-forming resin is preferably 30-50% (at 25°C), specifically 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%.

[0047] When the degree of hydrolysis of polyvinyl alcohol is 99-99.8%, the mass ratio of the polyvinyl alcohol aqueous solution to the glycerol aqueous solution is preferably 75-85:15-25, and more preferably 75:25, 80:20 or 85:15. In one embodiment of the present invention, the polyvinyl alcohol aqueous solution and the glycerol aqueous solution are independently 30-50%, specifically preferably 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%. In another embodiment of the present invention, the solid content of the film-forming resin is preferably 30-50% (at 25°C), specifically 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%.

[0048] In one embodiment of the present invention, the slow-water-soluble food packaging film comprises, by weight percentage, 15-30% of an alcohol-soluble polyamide solution, specifically 15%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%. In another embodiment, the alcohol-soluble polyamide preferably has an acid value ≤6 (mgKOH / g), an amine value ≤6 (mgKOH / g), a viscosity of 110±5 mpa·S / 25℃, a color <7, a softening point of 80-100℃, and a freezing point of -5℃. In this invention, the alcohol-soluble polyamide acts as both a film-forming agent and a filler that slows down the water solubility of the film. By adjusting the proportion of polyamide in the film components, different water solubility rates of the films can be obtained.

[0049] In this invention, alcohol-soluble polyamide has a low melting point, minimal pollution, and poses no harm to humans or the environment. It is non-toxic and environmentally friendly. Furthermore, its low softening point allows it to be blended with polyvinyl alcohol at 95°C, enabling film formation via coating, which significantly reduces energy consumption and carbon emissions. Additionally, polyamide exhibits high strength, wear resistance, oil resistance, resistance to organic chemicals, and ozone resistance. It also has good compatibility with water-soluble polyvinyl alcohol, making it an excellent material for energy conservation, environmental protection, and carbon reduction.

[0050] In one embodiment of the present invention, the slow-water-soluble food packaging film comprises 10-30% inorganic filler by weight percentage, specifically 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%; the particle size of the inorganic filler may be 800-1000 mesh. In another embodiment of the present invention, the inorganic filler preferably comprises one of calcium carbonate, magnesium sulfate, kaolin, fossil powder, and aluminum hydroxide.

[0051] In one embodiment of the present invention, the slow-water-soluble food packaging film comprises 2% to 5% triethyl acetylglucosyl citrate by weight percentage, specifically 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, or 5.0%. In the present invention, triethyl acetylglucosyl citrate is a plasticizer for polyamide, improving film-forming properties.

[0052] In one embodiment of the present invention, the slow-water-soluble food packaging film comprises 1%-4% vinyltriethoxysilane by weight percentage, specifically 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, or 4.0%, which mainly acts as a coupling agent in the composition.

[0053] In one embodiment of the present invention, the slow-water-soluble food packaging film comprises 0.5-2% emulsified silicone oil by weight percentage, specifically 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%, which acts as an antifoaming agent in the composition.

[0054] In one embodiment of the present invention, the slow-water-soluble food packaging film comprises 0.2-0.8% ultrafine silica by weight percentage, specifically 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, or 0.8%; the particle size of the ultrafine silica is preferably 1000 mesh; the ultrafine silica acts as an anti-settling agent in the composition.

[0055] In one embodiment of the present invention, the slow-water-soluble food packaging film comprises 1%-3% polyethylene wax by weight percentage, specifically 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3.0%. In another embodiment of the present invention, the polyethylene wax has a weight-average molecular weight of 500 and mainly functions as an anti-friction agent in the composition. It also acts as an internal lubricant during processing, thereby improving the coating flow rate.

[0056] As one embodiment of the present invention, the slow-water-soluble food packaging film comprises 3-10% alkylphenol polyvinyl ether by weight percentage, specifically 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5% or 10%, which acts as a wetting and dispersing agent in the composition.

[0057] In one embodiment of the present invention, the slow-water-soluble food packaging film comprises 0.5-2% polyethylene glycol by weight percentage, specifically 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%. In another embodiment of the present invention, the polyethylene glycol has a weight-average molecular weight of 1000. The polyethylene glycol acts as a solution stabilizer in the composition. Furthermore, polyethylene glycol has hygroscopic and water-retaining properties, which can also promote rapid hydrolysis of waste after it absorbs water in garbage, thus reducing garbage pollution.

[0058] The slow-water-soluble food packaging film of this invention utilizes polyvinyl alcohol, which has high gas barrier properties. Therefore, the film exhibits excellent gas barrier properties, effectively blocking not only oxygen but also the special odors emitted by air and the packaged product.

[0059] In one embodiment of the present invention, the slow-water-soluble food packaging film includes a surplus of water by weight percentage; the water can be purified water or deionized water, mainly serving as a solvent to adjust the solid content.

[0060] In one embodiment of the present invention, the thickness of the film is 30-80 mm.

[0061] This invention also provides a method for preparing the slow-water-soluble food packaging film described in the above technical solution, comprising the following steps:

[0062] (1) After spraying an ethanol solution of vinyltrioxyethylsilane onto the inorganic filler and drying it, a modified inorganic filler is obtained.

[0063] (2) Mix film-forming resin, alcohol-soluble polyamide solution, modified inorganic filler, triethyl acetylcitrate, vinyltriethoxysilane, emulsified silicone oil, ultrafine silica, polyethylene wax, alkylphenol polyethylene ether, polyethylene glycol and water to obtain coating liquid;

[0064] (3) The coating solution is coated to form a film;

[0065] (4) A surface of the film is subjected to surface treatment in sequence; the surface treatment includes atomization, first drying, spray washing and second drying in sequence;

[0066] (5) Repeat the surface treatment steps on the other side of the film.

[0067] The present invention involves spraying an ethanol solution of vinyltrioxyethylsilane onto an inorganic filler and then drying it to obtain a modified inorganic filler.

[0068] In one embodiment of the present invention, the drying temperature is preferably 80°C and the drying time is preferably 1 hour; in another embodiment of the present invention, the drying is preferably carried out in a drying chamber, which is preferably equipped with an exhaust fan to discharge the evaporated ethanol gas and recover and neutralize it; the recovery and neutralization can be carried out using methods and operations well known in the art.

[0069] After obtaining the modified inorganic filler, the present invention mixes the film-forming resin, alcohol-soluble polyamide solution, modified inorganic filler, triethyl acetylcitrate, vinyltriethoxysilane, emulsified silicone oil, ultrafine silica, polyethylene wax, alkylphenol polyethylene ether, polyethylene glycol and water to obtain a coating liquid.

[0070] In one embodiment of the present invention, the mixing is preferably carried out by first mixing alcohol-soluble polyamide with film-forming resin under stirring, and then adding modified inorganic filler, triethyl acetylglucosamine, vinyltriethoxysilane, emulsified silicone oil, ultrafine silica, polyethylene wax, alkylphenol polyethylene ether, polyethylene glycol and water to the first mixture for a second mixing to obtain a coating liquid.

[0071] In one embodiment of the present invention, the mixing speed of the film-forming resin under stirring is preferably 60 r / min; the mixing speed of the first mixing is preferably 60-180 r / min, and the mixing time is preferably 15-25 min. In another embodiment of the present invention, the first mixing is preferably carried out in a mixer provided with an ethanol gas exhaust port, and the ethanol gas is discharged and then neutralized through a recovery treatment system (according to the operation known to those skilled in the art).

[0072] In one embodiment of the present invention, the rotational speed of the second mixing is preferably 60-180 r / min; the mixing time is preferably 30-40 min.

[0073] In one embodiment of the present invention, the solid content of the coating liquid is preferably 30%-45%, and the viscosity of the coating liquid is preferably 150-300 mPa·s / (25℃).

[0074] After obtaining the coating liquid, the present invention applies the coating liquid to form a film.

[0075] In one embodiment of the present invention, the coating film formation is preferably carried out using a drip coating process (including coating film formation and coating drying).

[0076] In one embodiment of the present invention, the temperature of the coating liquid during film formation is preferably 15-60°C, specifically 50°C; the linear velocity during film formation depends on the coating thickness and drying degree, specifically 6-20 m / min; the coating drying temperature is preferably 80-100°C; after coating drying, it is preferably dried by rewinding once or twice; the rewinding drying temperature is preferably 40-50°C. The coating drying is preferably carried out in a down-blowing enclosed drying channel, with both the coating section and drying section equipped with induced draft and external replenishment air systems, discharging the discharged ethanol gas through the exhaust treatment system and the rear airflow.

[0077] After obtaining the film, the present invention performs surface treatment on one surface of the film; the surface treatment includes sequentially performing atomization, first drying, spraying and second drying.

[0078] In one embodiment of the present invention, the surface treatment preferably involves fixing the film parallel to itself on an automatic conveyor rack in the film feeding chamber, attaching PP film to both ends of the film, and then passing it parallel to itself at a certain linear speed through a water atomization chamber for atomization with an atomized aqueous solution, through a drying chamber for drying, through a water washing chamber for spraying, and through a water drying chamber for final drying. In another embodiment of the present invention, after drying, the film is further wound up in a winding chamber.

[0079] In one embodiment of the present invention, the length of the PP film is the total length of the surface treatment channel; the preferred length of the surface treatment channel is the sum of the lengths of the film feeding chamber, atomizing chamber, drying chamber, washing chamber, water drying chamber, and winding chamber. Specifically, in this embodiment of the present invention, the film feeding chamber and the winding chamber are each 4m; the atomizing chamber, drying chamber, washing chamber, and water drying chamber are calculated based on the fastest linear speed of 300mm / s and the longest processing time of 240s; that is, the total length of the atomizing channel is film feeding chamber (4m) + atomizing chamber (300mm / s × 240s) + drying chamber (300mm / s × 300s) + washing chamber (300mm / s × 300s) + water drying chamber (300mm / s × 300s) + winding chamber 4m. In addition, the atomizing channel can also be designed with three speed settings: 150mm / s, 250mm / s, and 300mm / s, which will save even more time.

[0080] In one embodiment of the present invention, the atomized aqueous solution is a trimethylammonium trihydrogenase aqueous solution or a dimethylurea aqueous solution; the solid content of the trimethylammonium trihydrogenase aqueous solution or the dimethylurea aqueous solution is independently 1-5%. In one embodiment of the present invention, during atomization, when the degree of hydrolysis of polyvinyl alcohol is 87%-89%, the water atomization temperature is 15-50℃. (2) When the degree of hydrolysis of polyvinyl alcohol is 75-80%, the water atomization temperature is 15-20℃; (3) When the degree of hydrolysis of polyvinyl alcohol is 99-99.8%, the water atomization temperature is 95℃; the atomization time is preferably 60-240s; the atomization water pressure is preferably 0.5-0.8mps, and the nozzle diameter of the atomized aqueous solution is preferably 0.5-1.5mm; the nozzle is a down-spray nozzle; in one embodiment of the present invention, the temperature of the first drying is preferably 40-50℃, and the drying time is preferably 180s-300s.

[0081] In this invention, polyvinyl alcohol (PVA) is a water-soluble polymer that dissolves rapidly in water. However, the addition of certain insoluble agents can cause PVA to lose its water solubility. Therefore, in this invention, the surface layer is treated with an atomization process using an aqueous solution containing 1-5% trimethylammonium trihydride or dimethylurea to render the PVA in the surface layer water-insoluble. By adjusting the concentration of the atomizing aqueous solution and the atomization time, a film with the desired water solubility time can be obtained. Therefore, in this invention, trimethylammonium trihydride (or dimethylurea) is an insoluble agent for PVA.

[0082] In this invention, the thickness of the water-insoluble layer on the membrane surface can be prepared in various ways, depending on the relative humidity of different regions and different applications. For example, for everyday disposable food and vegetable shopping bags, whose lifespan may only be tens of minutes or a few hours, the atomization time of the membrane surface preparation can be shortened, the water penetration rate of the membrane surface can be accelerated, and the water dissolution rate can also be faster. As another example, for packaging bags for dried black fungus with a shelf life of 12 months, the atomization time of the membrane surface needs to be extended, the concentration of the atomized aqueous solution needs to be increased, and the membrane will significantly reduce its hygroscopicity and water dissolution rate. Therefore, the thickness of the polyvinyl alcohol water-insoluble layer on the surface is not fixed in this invention; it depends on the actual needs. Moreover, for temporary disposable membranes or temporary fruit and vegetable and food shopping bags, the surface layer can be used directly without further treatment.

[0083] As one embodiment of the present invention, the linear velocity through the atomization channel is preferably 150-300 mm / s, specifically 150 mm / s, 250 mm / s, or 300 mm / s. In the present invention, the atomization time and linear velocity can be set according to the usage environment and purpose of the membrane and the required surface water resistance. For example: (1) If it is a disposable food shopping bag, the surface does not need strong water resistance, so the water atomization time should be as short as possible and the linear velocity should be fast. (2) For packaged dry food products with a long shelf life, the atomization time should be long and the linear velocity should be slow. The surface water insolubility should be good and the water solubility should be slow. (3) For various frozen food bags and films used temporarily, such as those used within 1-24 hours, the surface water resistance of the film does not need to be too strong, so the water atomization time can also be shortened. The present invention does not have special limitations or precise parameter requirements for the surface water resistance and water solubility time of the membrane. For example, for fruit and vegetable bags used temporarily in major shopping malls, which are fast-moving consumer goods used within a few hours, the surface water resistance treatment is not required. Therefore, the slow-water-soluble food packaging film of the present invention needs to be surface water-resistant treated or exempted from water-resistant treatment according to actual needs, because the formulation components of the present invention have already added an excessive amount of glycerin, so even if the PVA in the film absorbs moisture, its surface will not become sticky and can be used normally.

[0084] In one embodiment of the present invention, the water temperature for the spray washing is preferably 40-50°C, and the time is preferably 60-120 seconds. In another embodiment of the present invention, the temperature for the second drying is preferably 40-50°C, and the air drying time is preferably 180-300 seconds.

[0085] After the second drying, the other side of the film undergoes the same surface treatment step. After the other side is completed, preferably, the film also includes removing the two ends of the PP film, rewinding it, letting it stand for 24 hours, and then packaging it. The inner layer is made of PP film, and the outer layer is wrapped with waxed kraft paper.

[0086] The slow-water-soluble food packaging film of this invention is widely applicable to disposable shopping bags for food, fruits and vegetables, fast food, meat and eggs, dried fruits, etc., and is also suitable for express delivery packaging. Compared with existing polyolefin materials, it has a lower processing temperature, reducing energy consumption and high carbon emissions during processing. In addition, the used waste film can be hydrolyzed into water-soluble substances in water (referring to water suitable for the water solubility temperature of polyvinyl alcohol), eliminating "white pollution".

[0087] The water-soluble food packaging film of the present invention allows its water-soluble substances to be directly discharged without harming the soil, and the polyvinyl alcohol also has a water-retaining effect on the soil.

[0088] To further illustrate the present invention, the following detailed description of the embodiments is provided in conjunction with the present invention, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0089] Example 1

[0090]

[0091] The degree of alcoholysis of polyvinyl alcohol is 87.5%, and the weight-average molecular weight is 180,000. The alcohol-soluble polyamide solution has an acid value ≤6 mgKOH / g, an amine value ≤6 mgKOH / g, a viscosity (ring and ball method) of 110±5 mPa·s / 25℃, a softening point of 80℃, a color <7, and a freezing point of -5℃.

[0092] Preparation of polyvinyl alcohol aqueous solution:

[0093] Add 80% of the calculated amount of water to the container, turn on the stirrer, and set the water temperature to 25°C. While stirring, directly sprinkle polyvinyl alcohol into the water vortex (to avoid clumping). Stir until a uniform aqueous solution is formed, then heat it to 95°C using steam and a steam jacket. Stir at a constant temperature for 30 minutes, and cool it to room temperature while stirring. Add an appropriate amount of water to adjust the solid content to 30%, thus obtaining a polyvinyl alcohol solution.

[0094] Preparation of glycerol aqueous solution:

[0095] Add 80% of the calculated amount of water to a container at a temperature of 25°C. Turn on the stirrer and add glycerin while stirring. Stir for 20 minutes, raise the water temperature to 40°C, add the remaining 20% ​​of water, adjust to a solid content of 30%, and stir well to obtain a glycerin aqueous solution. Store in a jar for later use.

[0096] Preparation of coating solution

[0097] ① Preparation of film-forming resin

[0098] 65 parts of polyvinyl alcohol aqueous solution and 35 parts of glycerol aqueous solution were placed in a mixer and mixed. Then, an appropriate amount of water was added to adjust the solid content to 30%. The mixing speed was 60 r / min. After uniform mixing, a film-forming resin was obtained.

[0099] ② Preparation of modified inorganic fillers

[0100] Three parts of vinyltrioxyethylsilane were dissolved in ethanol and then sprayed onto 30 parts of calcium carbonate. After stirring evenly, the mixture was dried at 80°C for 1 hour to obtain modified calcium carbonate.

[0101] ③ Mixing of various materials

[0102] (1) Place 35 parts of film-forming resin into a mixer, turn on the mixer, and stir at a speed of 60 r / min. While stirring, slowly add 15 parts of alcohol-soluble polyamide solution and mix at a speed of 60 r / min for 25 min to obtain a mixture. During the mixing process, ethanol gas is discharged through the exhaust port of the mixer and then neutralized through the gas treatment system.

[0103] (4) Place the mixture of film-forming resin and alcohol-soluble polyamide solution into a mixer, turn on the stirrer, and stir at a speed of 60 r / min. While stirring, add 30 parts modified calcium carbonate, 4 parts triethyl acetylacetic acid, 0.8 parts emulsified silicone oil, 0.2 parts ultrafine silica, 1 part polyethylene wax, 10 parts alkylphenol polyethylene ether and 0.5 parts polyethylene glycol in sequence. After the materials are added, mix at a speed of 60 r / min for 30 min, then add an appropriate amount of water to adjust to a solution with a solid content of 40% and a viscosity of 150 mpa·s / 25℃ to obtain the coating solution of slow water-soluble food packaging film.

[0104] Membrane preparation

[0105] (1) The membrane is designed to be 1000m long, 1m wide, and 30μm thick.

[0106] (2) The temperature of the coating liquid is 50℃.

[0107] (3) Coating drying temperature: 95℃.

[0108] (4) Set the linear velocity to 12 m / min.

[0109] (5) The coating and drying process is adopted. The coating and drying are carried out in a closed-loop drying channel with downward airflow. Both the coating section and the drying section are equipped with exhaust air and external air supply systems. The discharged ethanol gas is discharged through the exhaust treatment system and the rear air. The film is dried in 1000m rolls (at a temperature of 50℃) at a linear speed of 50m / min to obtain the saliva film.

[0110] Membrane surface treatment:

[0111] (1) Dissolve 1 part by mass of trimethyltrihydrogen ammonium in 99 parts by mass of water to prepare a 1% aqueous solution.

[0112] (2) Place the trimethylammonium trihydride aqueous solution into the water mist tank of the atomization chamber, adjust the atomizing gas pressure to 0.5 MPa, and evenly distribute multiple nozzles with a nozzle diameter of 0.5 mm from top to bottom to spray water mist. The distance between the nozzle and the membrane surface is 400 mm. The atomization time of the membrane entering the atomization chamber is 120 s, the running linear velocity is 150 mm / s, the atomizing water temperature is 30 ℃, and the drying temperature after atomization is 40 ℃ for air drying.

[0113] (3) First attach a PP film of the same length as the atomization chamber to both ends of the membrane, pass the membrane parallel through the atomization chamber channel, and fix it on the membrane main tube.

[0114] (4) Turn on the atomizing pump and transmission system in the atomizing chamber to start atomization and drying.

[0115] (5) The atomized dried membrane is then washed with atomized water (the water is domestic water) for 60 seconds at a water temperature of 40°C and a linear velocity of 150 mm / s, and then dried to remove moisture at a drying temperature of 40°C.

[0116] (6) After the first side is completed, the second side is processed in the same way. After both sides are processed, the film is rolled up and dried to obtain a slow-water soluble food packaging film.

[0117] Example 2

[0118]

[0119]

[0120] The degree of alcoholysis of polyvinyl alcohol was 89%, and the weight-average molecular weight was 220,000. The parameters of the alcohol-soluble polyamide were the same as those in Example 1, and the weight-average molecular weights of polyethylene wax and polyethylene glycol were the same as those in Example 1.

[0121] Preparation of polyvinyl alcohol aqueous solution: The preparation method is the same as in Example 1, and the solid content of the obtained polyvinyl alcohol aqueous solution is 50%; Preparation of glycerol aqueous solution: The preparation method is the same as in Example 1, and the solid content of the obtained glycerol aqueous solution is 50%.

[0122] Preparation of coating solution

[0123] ① The difference between the preparation of the film-forming resin and Example 1 is that: after mixing polyvinyl alcohol aqueous solution and glycerol aqueous solution at a ratio of 70:30, and then mixing with an appropriate amount of water, a film-forming resin with a solid content of 45% is obtained.

[0124] ② The preparation of modified inorganic fillers and ③ the mixing of each material differ from Example 1 only in that the raw materials and dosages are replaced with the raw materials and dosages corresponding to Example 2. After the materials are added, they are mixed according to the parameters of a mixing speed of 90 r / min and a mixing time of 25 min. The resulting coating liquid has a solid content of 45% and a viscosity of 300 mpa·s / 25℃.

[0125] Membrane preparation

[0126] (1) The membrane width is designed to be 1.2m, the length is 1000m / roll, and the thickness is 30μm.

[0127] (2) The temperature of the coating liquid is 60℃.

[0128] (3) The coating drying temperature is 95℃.

[0129] (4) The coating line speed is 10m / min.

[0130] (5) Other processes and requirements are the same as in Example 1.

[0131] Membrane surface treatment

[0132] (1) Dissolve 3 parts by weight of trimethylammonium trihydrogen in 97 parts by weight of water to prepare an aqueous solution with a solid content of 3%. The atomization water temperature is the same as in Example 1.

[0133] (2) The atomizing pressure is 0.8 MPa, the nozzle diameter is Φ0.7, the atomization time is 120 s, the linear velocity is 180 mm / s, the drying temperature is 40 ℃, and the other processes are the same as in Example 1, so as to obtain the slow water-soluble food packaging film of Example 2.

[0134] Example 3

[0135]

[0136]

[0137] The degree of alcoholysis of polyvinyl alcohol is 75%, and the weight-average molecular weight is 50,000.

[0138] Preparation of polyvinyl alcohol aqueous solution: The preparation method differs from Example 1 in that the water temperature is replaced with 20°C, resulting in a polyvinyl alcohol aqueous solution with a solid content of 40%. Preparation of glycerol aqueous solution: The preparation method is the same as in Example 1, and the resulting glycerol aqueous solution has a solid content of 40%. The technical parameters of the alcohol-soluble polyamide are the same as in Example 1. The weight-average molecular weights of polyethylene wax and polyethylene glycol are the same as in Example 1.

[0139] Preparation of coating solution

[0140] ① The difference between the preparation of the film-forming resin and Example 1 is that: after mixing polyvinyl alcohol aqueous solution and glycerol aqueous solution at a ratio of 90:10, and then mixing with an appropriate amount of water, a film-forming resin with a solid content of 40% is obtained.

[0141] ② The preparation of modified inorganic fillers and ③ the mixing of various materials differ from those in Example 1 only in that the raw materials and dosages are replaced with those in Example 3. The resulting coating liquid has a solid content of 40% and a viscosity of 200 mPa·s / 25℃.

[0142] Membrane preparation

[0143] (1) The membrane width is designed to be 1.2m, the length is 1000m / roll, and the thickness is 40μm.

[0144] (2) The temperature of the coating liquid is 15℃.

[0145] (3) The coating drying temperature is 80℃.

[0146] (4) The coating line speed is 8m / min.

[0147] (5) Other processes and requirements are the same as in Example 1.

[0148] Membrane surface treatment

[0149] (1) Dissolve 4 parts by weight of trimethylammonium trihydrogen in 96 parts by weight of water to prepare an aqueous solution with a solid content of 4%. The atomization water temperature is 15°C, the atomization time is 240s, the linear velocity is 300mm / s, the drying temperature after atomization and the drying temperature after washing are 50°C, the washing time is 90s, and other processes are the same as in Example 1 to obtain a slow water-soluble food packaging film.

[0150] Example 4

[0151]

[0152]

[0153] The degree of alcoholysis of polyvinyl alcohol is 80%, and the weight-average molecular weight is 100,000. The technical parameters of the alcohol-soluble polyamide solution are the same as in Example 1, and the weight-average molecular weights of low-density polyethylene wax and polyethylene glycol are the same as in Example 1.

[0154] The preparation and solid content of the polyvinyl alcohol aqueous solution were the same as in Example 3. The preparation and solid content of the glycerol aqueous solution were the same as in Example 3. The technical parameters of the alcohol-soluble polyamide were the same as in Example 1. The weight-average molecular weights of the polyethylene wax and polyethylene glycol were the same as in Example 1.

[0155] Preparation of coating solution

[0156] ① The difference between the preparation of the film-forming resin and Example 1 is that: a polyvinyl alcohol aqueous solution with a solid content of 45% and a glycerol aqueous solution with a solid content of 45% are mixed at a ratio of 80:20 and then mixed with an appropriate amount of water to obtain a film-forming resin with a solid content of 45%.

[0157] ② The preparation of modified inorganic fillers and ③ the mixing of various materials differ from those in Example 1 only in that the raw materials and dosages are replaced with those in Example 4. The resulting coating liquid has a solid content of 45% and a viscosity of 300 mPa·s / 25℃.

[0158] Membrane preparation

[0159] (1) The designed membrane width is 1.2m, length is 1000m / roll, and thickness is 50μm. The coating line speed is 8m / min.

[0160] (2) Other processes and requirements are the same as in Example 3.

[0161] The membrane surface treatment is the same as in Example 3.

[0162] Example 5

[0163]

[0164]

[0165] The degree of alcoholysis of polyvinyl alcohol is 99.8%, and the weight-average molecular weight is 50,000. The technical parameters of the polyamide solution are the same as in Example 1, and the weight-average molecular weights of the polyethylene wax and polyethylene glycol are the same as in Example 1.

[0166] Preparation of polyvinyl alcohol aqueous solution: (1) Add 80% of the calculated amount of water to a container, turn on the stirrer, and while stirring, sprinkle polyvinyl alcohol into the water vortex. (2) Heat the mixture to 95°C with steam and mix for 30 minutes at a stirring speed of 180 r / min. (3) Add the remaining water to adjust the solution to a 40% solid content polyvinyl alcohol aqueous solution, and cool it to room temperature for later use.

[0167] Preparation of glycerol aqueous solution: The preparation method is the same as in Example 1, and the solid content of the resulting glycerol aqueous solution is 40%. The technical parameters of the alcohol-soluble polyamide are the same as in Example 1.

[0168] Preparation of coating solution

[0169] ① The difference between the preparation of the film-forming resin and Example 1 is that: after mixing the polyvinyl alcohol aqueous solution and the glycerol aqueous solution at a ratio of 75:25, and then mixing with an appropriate amount of water, a film-forming resin with a solid content of 40% is obtained.

[0170] ② The preparation of modified inorganic fillers and ③ the mixing of various materials differ from those in Example 1 only in that the raw materials and dosages are replaced with those in Example 5. The resulting coating liquid has a solid content of 40% and a viscosity of 200 mPa·s / 25℃.

[0171] Membrane preparation

[0172] (1) The membrane is designed to be 1.2m wide, 1000m long / roll, and 70μm thick. The coating line speed is 6m / min.

[0173] (2) Other processes and requirements are the same as in Example 1.

[0174] Membrane surface treatment

[0175] (1) Dissolve 4 parts by weight of trimethylammonium trihydrogen in 96 parts by weight of water to prepare an aqueous solution with a solid content of 4%. The atomization water temperature is 95°C, the atomization time is 300s, the linear velocity is 150mm / s, and other processes are the same as in Example 1 to obtain a slow water-soluble food packaging film.

[0176] The film of Example 5 can be used as a food freezing film and also as a temporary fruit and vegetable packaging film. If it is used as a temporary fruit and vegetable packaging film, no surface treatment is required.

[0177] Example 6

[0178]

[0179] The degree of alcoholysis of polyvinyl alcohol is 99%, and the weight-average molecular weight is 100,000. The technical specifications of the alcohol-soluble polyamide solution are consistent with those of Example 1, as are the weight-average molecular weights of the polyethylene wax and polyethylene glycol.

[0180] Preparation of polyvinyl alcohol aqueous solution: The preparation method is the same as in Example 5, and the solid content of the polyvinyl alcohol aqueous solution is 45%.

[0181] Preparation of glycerol aqueous solution: The preparation method is the same as in Example 1, and the solid content of the resulting glycerol aqueous solution is 45%. The technical parameters of the alcohol-soluble polyamide are the same as in Example 1.

[0182] Preparation of coating solution

[0183] ① The difference between the preparation of the film-forming resin and Example 1 is that: after mixing polyvinyl alcohol aqueous solution and glycerol aqueous solution at a ratio of 80:20, and then mixing with an appropriate amount of water, a film-forming resin with a solid content of 45% is obtained.

[0184] ② The preparation of modified inorganic fillers and ③ the mixing of various materials differ from those in Example 1 only in that the raw materials and dosages are replaced with those in Example 6. The resulting coating liquid has a solid content of 45% and a viscosity of 300 mPa·s / 25℃.

[0185] The membrane preparation and membrane surface treatment are the same as in Example 5.

[0186] test

[0187] (1) Cut the six slow water-soluble food packaging films of Examples 1-6 into sizes of 300×300mm and fix them on a plastic mesh frame.

[0188] (2) Each type of membrane was tested at three different water temperatures.

[0189] (3) Insert the membrane fixed on the plastic mesh frame vertically into the fixed frame of the test chamber, and let the water submerge the membrane. The test is conducted in a transparent tempered glass box.

[0190] (4) A time-lapse video recorder was used to record the water dissolution time of the membrane through a tempered glass box.

[0191] (5) The water temperature was determined based on the degree of alcoholysis of the polyvinyl alcohol selected in Examples 1-6, and the entire process was conducted under constant temperature conditions: Wherein:

[0192] 1) In Examples 1-2, the test water temperatures were 15℃ and 50℃.

[0193] 2) In Examples 3-4, the test water temperatures were 15℃ and 50℃.

[0194] 3) In Examples 5-6, the test water temperatures were 15℃ and 95℃.

[0195] The test results are shown in Table 1.

[0196] Table 1 Results of water solubility test

[0197]

[0198] The results of the water solubility tests in Examples 1-6 show that:

[0199] (1) When the degree of alcoholysis of polyvinyl alcohol in the membrane component is 87%-89%, the prepared membrane is soluble in both cold and hot water.

[0200] (2) When the degree of alcoholysis of polyvinyl alcohol in the membrane component is 75%-80%, the resulting membrane is only soluble in cold water and not in hot water.

[0201] (3) When the degree of alcoholysis of polyvinyl alcohol in the membrane component is 99%-99.8%, the prepared film is only soluble in hot water above 95°C and insoluble in cold water.

[0202] (4) The experimental results also show that:

[0203] 1) The water solubility rate of the membrane is related to the content of polyvinyl alcohol in the components. As the content increases, the water solubility rate of the membrane increases.

[0204] 2) The water solubility rate of the membrane is inversely proportional to the amount of alcohol-soluble polyamide used; as the content increases, the water solubility rate of the membrane decreases.

[0205] 3) The water dissolution rate of the membrane is inversely proportional to the membrane thickness; the thicker the membrane, the slower the water dissolution rate.

[0206] 4) The water solubility rate of the membrane is related to the surface treatment time and the concentration of the aqueous solution. The higher the concentration of the aqueous solution and the longer the water atomization treatment time, the better the water resistance of the membrane and the longer the water solubility time. However, the main purpose of the surface treatment is to ensure that the surface of the membrane does not stick to the hand or become sticky after absorbing moisture during use.

[0207] Experimental results show that:

[0208] The water solubility rate of the slow-water-soluble food packaging film of the present invention can be fully adjusted by adjusting the amount of polyvinyl alcohol and alcohol-soluble polyamide in the formulation components to achieve the applicable slow-water solubility performance and usage requirements.

[0209] In summary: The slow-water-soluble food packaging film of the present invention comprises three degrees of alcoholysis of polyvinyl alcohol, wherein:

[0210] (1) A membrane made of polyvinyl alcohol with a degree of alcoholysis of 75%-80% is only soluble in cold water and not in hot water. This membrane is suitable for packaging hot food and hot drinks, and is also suitable for microwave heating of food. Waste of this membrane can be directly dissolved in cold water for discharge or recycling.

[0211] (2) Membranes with a degree of alcoholysis of 87%-89% are soluble in both cold and hot water. These membranes are suitable for packaging dry foods such as rice, flour, paddy, dried fruit, dried food, and fungi such as wood ear and mushrooms. Waste membranes can be directly dissolved in cold and hot water to become water-soluble substances, or they can be dissolved in garbage and natural water to become water-soluble substances. The water-soluble substances are non-toxic and non-polluting.

[0212] (3) A membrane with a degree of alcoholysis of 99%-99.8% is only soluble in hot water above 95°C and insoluble in cold water. This type of membrane is suitable for packaging frozen food and for long-term storage of fish and meat products stored at around 0°C. The waste from this type of membrane can be dissolved in hot water or steam at 95°C to form water-soluble substances for discharge or recycling.

[0213] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A slow-water-soluble food packaging film, comprising the following components by weight percentage: The film-forming resin includes an aqueous solution of polyvinyl alcohol, an aqueous solution of glycerol, and water; The solid content of the film-forming resin is 30%-50%; The degree of alcoholysis of polyvinyl alcohol in the aqueous solution is 87%-89%, 75%-80%, or 99%-99.9%.

2. The slow-water-soluble food packaging film as described in claim 1, characterized in that, The film-forming resin is obtained by mixing polyvinyl alcohol aqueous solution, glycerol aqueous solution and water; When the degree of alcoholysis of polyvinyl alcohol is 87%-89%, the mass ratio of the polyvinyl alcohol aqueous solution to the glycerol aqueous solution is 65-80:20-35; When the degree of alcoholysis of polyvinyl alcohol is 75%-80%, the mass ratio of the polyvinyl alcohol aqueous solution to the glycerol aqueous solution is 80-90:10-20. When the degree of alcoholysis of polyvinyl alcohol is 99%-99.9%, the ratio of the aqueous polyvinyl alcohol solution to the aqueous glycerol solution is 75-85:15-25. The solid content of the polyvinyl alcohol aqueous solution and the glycerol aqueous solution is independently 30%-50%.

3. The slow-water-soluble food packaging film as described in claim 1, characterized in that, The inorganic filler includes one of calcium carbonate, magnesium sulfate, kaolin, fossil powder, and aluminum hydroxide.

4. The slow-water-soluble food packaging film as described in claim 1, characterized in that, The low-density polyethylene wax has a weight-average molecular weight of 500, and the polyethylene glycol has a weight-average molecular weight of 1000; the water is purified water or deionized water.

5. The slow-water-soluble food packaging film as described in claim 1, characterized in that, The alcohol-soluble polyamide solution has an acid value ≤6 (mgKOH / g), an amine value ≤6mgKOH / g, a viscosity of 110±5mpa·s / 25℃ (mpa), a softening point of 80-100℃, a color of <7, and a freezing point of -5℃.

6. The slow-water-soluble food packaging film as described in claim 1, characterized in that, When the degree of alcoholysis is 87-89%, the weight-average molecular weight of polyvinyl alcohol is 170,000-220,000. When the degree of alcoholysis is 75%–80%, the weight-average molecular weight is 50,000–100,000. When the degree of alcoholysis is 99%-99.8%, the weight-average molecular weight is 50,000-100,000.

7. A method for preparing the slow-water-soluble food packaging film according to any one of claims 1 to 6, comprising the following steps: (1) After spraying an ethanol solution of vinyltrioxyethylsilane onto the inorganic filler and drying it, a modified inorganic filler is obtained. (2) Mix film-forming resin, alcohol-soluble polyamide solution, modified inorganic filler, triethyl acetylcitrate, vinyltriethoxysilane, emulsified silicone oil, ultrafine silica, polyethylene wax, alkylphenol polyethylene ether, polyethylene glycol and water to obtain coating liquid; (3) The coating solution is coated to form a film; (4) A surface of the film is subjected to surface treatment in sequence; the surface treatment includes atomization, first drying, spray washing and second drying in sequence; (5) Repeat the surface treatment steps on the other side of the film.

8. The preparation method according to claim 7, characterized in that, The atomized aqueous solution is a trimethylammonium trihydrogenase aqueous solution or a dimethylurea aqueous solution; the solid content of the trimethylammonium trihydrogenase aqueous solution or the dimethylurea aqueous solution is independently 1-5%.

9. The preparation method according to claim 7, characterized in that, The solid content of the coating liquid is 30-45%.

10. The preparation method according to claim 7 or 8, characterized in that, During atomization, when the degree of hydrolysis of polyvinyl alcohol is 87%-89%, the temperature of the atomizing aqueous solution is 15℃-50℃; when the degree of hydrolysis of polyvinyl alcohol is 75%-80%, the temperature of the atomizing aqueous solution is 15-20℃; when the degree of hydrolysis of polyvinyl alcohol is 99%-99.8%, the temperature of the atomizing aqueous solution is 95℃; the atomization time is 60-240s; and the atomizing water pressure is 0.5-0.8mps.

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