Layer-by-layer assembly preparation method of multi-layer material

Abstract

The invention belongs to the field of multi-layer material preparation, and particularly discloses a layer-by-layer assembly preparation method of a multi-layer material, and the multi-layer material comprises a CMCS / FA film, a PUL / NTW film and a PVA film which are arranged in sequence; corresponding raw materials are selected, and a CMCS / FA solution, a PUL / NTW solution and a PVA solution are prepared and stored; a continuous stainless steel mesh belt type conveying belt is adopted to drive a mold, a CMCS / FA solution is poured to the surface of the mold through a liquid pouring machine, and a CMCS / FA layer is formed and dried; a PUL / NTW solution is poured to the surface of the dried CMCS / FA layer through a liquid pouring machine, a PUL / NTW layer is formed, and drying is conducted; a PVA solution is poured to the surface of the dried PUL / NTW layer through a liquid pouring machine, a PVA layer is formed, and the PVA layer is dried to obtain a multi-layer structure; a continuous hot press is adopted for carrying out continuous hot pressing and cutting packaging on the multi-layer structure to obtain the multi-layer material, optimized parameters in the whole technological process are designed according to the specific requirements of different food packaging, and precise control over the mechanical performance, the antibacterial performance and other characteristics of the layer is achieved.

Description

Technical Field

[0001] The invention belongs to the field of multilayer material preparation, and in particular relates to a layer-by-layer assembly preparation method of a multilayer material. Background Art

[0002] Foodborne pathogens are a major threat to food safety. They are widely present in the natural environment, such as soil, water and animals, and can contaminate food through various channels, causing a series of serious health problems.

[0003] Eating food contaminated by foodborne pathogens may cause acute illness. For example, Salmonella can cause fever, abdominal pain, diarrhea, nausea and vomiting, and in severe cases may cause sepsis, posing a threat to the life safety of people with weaker resistance (such as the elderly, children and those with weakened immune function).

[0004] In addition, foodborne pathogenic bacteria contamination can also bring long-term health risks. The outbreak of foodborne diseases not only affects personal health, but also has a huge impact on public health and safety, causing social panic, placing a heavy burden on medical resources, and also has a negative impact on the reputation and economic interests of the food industry.

[0005] Among the many strategies to ensure food safety, packaging film is a critical link. As an isolation barrier between food and the external environment, packaging film is one of the effective ways to prevent food from being infected by foodborne pathogens. Suitable packaging film can effectively prevent pathogens in the external environment from contacting food. It can maintain the relative independence of food during storage and transportation, and avoid contamination by pathogens carried in the air, by human touch or other sources of contamination. For example, in the packaging of meat products, good packaging film can prevent salmonella, staphylococcus, bacillus, etc. that may exist in the sales environment from contaminating meat, thereby extending the shelf life of food and ensuring food safety.

[0006] With the enhancement of environmental awareness and the improvement of food safety requirements, degradable multilayer packaging materials containing antibacterial agents have received widespread attention. The applicant's prior application 202410831874.5 discloses a self-cleaning food packaging film based on nano-photocatalysts, with carboxymethyl chitosan (CMCS), pullulan (PUL) and polyvinyl alcohol (PVA) as the matrix, nano-photocatalyst NTW as the antibacterial additive, ferulic acid (FA) as the cross-linking agent, and a layer-by-layer casting method is used to prepare a multilayer antibacterial food packaging film, in order to achieve long-term storage of food and promote the development of degradable food packaging films.

[0007] However, the process used in the laboratory still has many problems in large-scale industrial production, including uniform dispersion of antibacterial agents, interlayer bonding of multilayer materials, stable performance of degradable materials, and cost control. These problems may affect the physical properties or antibacterial properties of packaging materials, limit the widespread application of this advanced packaging material, and thus affect its greater role in ensuring food safety. Summary of the invention

[0008] The purpose of the present invention is to provide a layer-by-layer assembly preparation method of a multi-layer material in view of the problems existing in the prior art.

[0009] The complete technical solution of the present invention includes: A method for preparing a layer-by-layer assembly of a multilayer material, wherein the multilayer material comprises a CMCS / FA film, a PUL / NTW film and a PVA film arranged in sequence; comprising the following steps: (1) Preparation of membrane-forming solution: Select corresponding raw materials, prepare CMCS / FA solution, PUL / NTW solution and PVA solution respectively and store them; (2) Preparation of CMCS / FA layer A continuous stainless steel mesh belt conveyor is used to drive the mold, and a liquid pouring machine is used to pour the CMCS / FA solution onto the mold surface to form a CMCS / FA layer, which is then dried. (3) PUL / NTW layer pouring A liquid casting machine is used to cast the PUL / NTW solution onto the surface of the dried CMCS / FA layer to form a PUL / NTW layer, which is then dried; (4) PVA layer pouring A liquid casting machine is used to cast the PVA solution onto the surface of the dried PUL / NTW layer to form a PVA layer, which is then dried to obtain a multilayer structure; (5) The multilayer structure is continuously hot-pressed by a continuous hot press, and then cut and packaged to obtain a multilayer material.

[0010] Furthermore, in step (1), during the preparation of the CMCS / FA solution, a mixing tank is used to mix CMCS, glycerol and deionized water, and the mixture is stirred while the temperature of the CMCS solution is controlled. Subsequently, FA is added and mixed to obtain a CMCS / FA solution.

[0011] Furthermore, in step (1), during the preparation of the PUL / NTW solution, a dissolution tank is used to mix PUL, glycerol and deionized water, stir and control the solution temperature, and then NTW is added and dispersed to obtain a PUL / NTW solution.

[0012] Furthermore, in step (1), during the preparation of the PVA solution, PVA and deionized water are mixed, stirred and the solution temperature is controlled, so that the PVA is dissolved in the deionized water and degassed to obtain a PVA solution.

[0013] Furthermore, in step (2), the speed of the conveyor belt is determined according to the solution viscosity, the casting speed, the mold width, the target thickness of the CMCS / FA layer and the mold surface roughness.

[0014] Furthermore, the following relationship is adopted in the production process:

[0015] Where V 带 is the conveyor belt speed, in mm / min; h is the target thickness of the CMCS / FA layer, ranging from 0.1 to 0.2 mm; V 浇 is the pouring speed, ranging from 2 to 20 L / min; η is the solution viscosity, in Pa·s; w is the mold width, ranging from 10 to 40 mm; Ra is the mold surface roughness, η0 is the reference viscosity, R a0 is the reference roughness of the mold surface, and k is the fitting coefficient.

[0016] Furthermore, in steps (2) to (4), drying is performed using a multi-stage temperature control method.

[0017] Furthermore, the NTW is N-Nb2CT x / TpPa-1 / m-WO 3-x Composite nano-photocatalytic materials.

[0018] Furthermore, in the multilayer material, the loading content of NTW is ≤0.2%.

[0019] Furthermore, a multilayer material is obtained using the method.

[0020] Furthermore, the multilayer material is used in food packaging.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The present invention prepares a multilayer food packaging film by pouring CMCS / FA solution, PUL / NTW solution and PVA solution layer by layer. According to the specific requirements of different food packaging, the optimized parameters in the entire process are designed, which is particularly suitable for industrial production. The parameters of each layer can also be flexibly adjusted, and the thickness, composition and structure of each layer can be accurately controlled. Thus, the mechanical and antibacterial properties of the layer can be accurately controlled.

[0022] (2) Through the design of multi-layer structures and parameter optimization, each layer can complement and enhance each other's mechanical properties, effectively disperse external forces, and prevent damage to the packaging film caused by local stress concentration, thereby better protecting the integrity of food during transportation and storage, forming a comprehensive barrier system, and effectively extending the shelf life of food.

[0023] (3) The present invention uses nano-photocatalysts as new bactericidal active substances, which can effectively utilize sunlight. The synthesis method is simple and easy to operate, and can promote carrier transfer and inhibit the recombination of photogenerated electron-hole pairs. The preparation process synergistically produces a stronger and more tightly bound three-dimensional network structure through chemical cross-linking and physical cross-linking, thereby enhancing the mechanical properties of the packaging material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of the layer-by-layer assembly method of the present invention. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only for illustration and are not intended to limit the present application.

[0026] The present invention is described in detail below in conjunction with the embodiments and drawings, but it should be understood that the embodiments and drawings are only used to exemplify the present invention and do not constitute any limitation on the protection scope of the present invention. All reasonable changes and combinations within the scope of the inventive concept of the present invention fall within the protection scope of the present invention.

[0027] A method for preparing a multilayer material by assembling it layer by layer, such as Figure 1 As shown, the following steps are included: (1) Configuration of film-forming solution Preparation of CMCS / FA solution: Using a stainless steel batching tank, CMCS and glycerol are placed in a batching tank with deionized water in a certain ratio (mass ratio 2:1) through an automatic weighing system. The batching tank is equipped with a stirring paddle with a power of 5~10kW and a stirring speed of 200~300rpm to ensure that CMCS is fully dispersed in deionized water. At the same time, it is equipped with a jacket that can be heated by hot water or steam to control the solution temperature at 30~40℃ to improve the dissolution efficiency of CMCS.

[0028] Subsequently, FA is added to the previously prepared CMCS solution at a predetermined mass ratio (approximately 1 / 4 of the mass of CMCS) through a metering pump. An online mixer is used, which is equipped with mixing blades to further mix the CMCS and FA solutions during the flow process. The liquid flow rate in the mixer is 0.5~1m / s.

[0029] Then, coarse filtration (filter mesh pore size is 1~2mm) and fine filtration (filter element pore size is 5~10μm) are performed to remove impurities and undissolved particles in the solution. The filtered CMCS / FA solution is stored in a stainless steel storage tank equipped with a stirring device for continuous stirring to prevent the solution from stratification while maintaining the solution temperature at 25~30℃.

[0030] PUL / NTW solution preparation: Use a stainless steel dissolution tank with stirring and heating functions, add PUL and glycerol into the dissolution tank in a certain mass ratio, control the amount of deionized water added by the liquid level sensor, turn on the stirring device, the stirring power is 3~5kW, the stirring speed is 300~400rpm, and turn on the heating system to raise the temperature in the tank to 50~60℃ to accelerate the dissolution process of PUL.

[0031] NTW is then premixed with a dispersant and then dispersed in a certain amount of deionized water using a high-speed disperser at a speed of 1000-2000 rpm to form a NTW dispersion. The NTW dispersion is then added to the PUL solution at a preset mass ratio with the PUL using a high-precision metering system, with the metering error controlled within ±0.2%.

[0032] The PUL / NTW mixed solution was homogenized by a high-pressure homogenizer (pressure 30~50MPa) to uniformly disperse NTW in the PUL solution to form a stable solution. The homogenized PUL / NTW solution was stored in a storage tank with an insulation jacket at a temperature of 20~25°C. The tank was equipped with a stirring device to maintain the rotation speed at 50~100rpm.

[0033] In a preferred embodiment, the NTW preparation process used in the present invention is: First, WO3 containing mesopores and oxygen vacancies, namely m-WO 3-x ; Then prepare the amino Nb2CT x , namely N-Nb2CT x ; Then the N-Nb2CT obtained above x and m-WO 3-x Add N,N-dimethylformamide (DMF), and then add trialdehyde pyrogallol, p-phenylenediamine, mesitylene and 1,4-dioxane in sequence, and then add acetic acid aqueous solution as a catalyst. Ultrasonication is used to make it uniformly dispersed, and then nitrogen is bubbled, and then reacted at a certain temperature for a certain time, washed, centrifuged and dried to obtain NTW; In the above preparation process, a decision tree method was used to conduct systematic research and analysis to explore the optimized process suitable for large-scale production. Specifically, it includes: 1) Data collection Collect data from the entire preparation process. The collected data specifically includes: m-WO 3-x The quality of m-WO 3-x The oxygen vacancy concentration of m-WO 3-x Specific surface area of ​​mesoporous structure, N-Nb2CT x The quality of N-Nb2CT x The degree of amination, the volume of N,N-dimethylformamide, the mass of trialdehyde pyrogallol, the mass of p-phenylenediamine, the volume of mesitylene, the volume of 1,4-dioxane, nitrogen bubbling time, reaction temperature, reaction time, and the photocatalytic bactericidal efficiency of NTW.

[0034] 2) Feature Engineering The above data are characterized and divided into three groups according to their characteristics. One group is the dosage ratio, the second group is the raw material properties, and the third group is the process parameters. The first group includes m-WO 3-x The quality of N-Nb2CT x The mass of , the volume of N,N-dimethylformamide, the mass of trialdehyde pyrogallol, the mass of p-phenylenediamine, the volume of mesitylene, and the volume of 1,4-dioxane were standardized, expressed in a proportional manner, and vectorized. The second group includes m-WO 3-x The oxygen vacancy concentration of m-WO 3-x Specific surface area of ​​mesoporous structure and N-Nb2CT x The third group includes nitrogen bubbling time, reaction temperature and reaction time.

[0035] The above three sets of data are used as input features. The photocatalytic bactericidal efficiency of NTW is used as the output feature to construct the data set.

[0036] 3) Model training Select the decision tree regression model, divide the data set into training set, validation set and test set, and perform model training.

[0037] During the training process, the model selects the best partitioning points according to each input feature, so that the subsets after partitioning have the smallest variance in photocatalytic sterilization efficiency. The above partitioning process is repeated continuously to generate a binary tree structure. Each internal node represents a partitioning condition on a feature, and each leaf node represents a predicted photocatalytic sterilization efficiency. The photocatalytic sterilization efficiency value corresponding to each leaf node is the predicted value when all partitioning conditions on this path are met.

[0038] 4) Process optimization In the actual production process, the required photocatalytic sterilization efficiency value is set according to the usage scenario, and the corresponding preparation parameters are selected according to the actual needs (such as the cost fluctuations of each raw material), and the parameters are combined into a new input feature vector, and the photocatalytic sterilization efficiency value is predicted using the trained model. If the conditions are met, the above parameters can be used. If not, the corresponding parameters are adjusted until the required photocatalytic sterilization efficiency value is met, thereby optimizing the preparation process.

[0039] Preparation of PVA solution: Use a stainless steel dissolution tank, add PVA according to the preset mass ratio, turn on the steam heating coil of the dissolution tank, and raise the water temperature to 90~95℃. Use a stirring device with a power of 8~12kW and a stirring speed of 400~600rpm to fully dissolve PVA in deionized water to form a solution.

[0040] The PVA solution is then transferred to a degassing tank and vacuum degassing technology is used with a vacuum degree of 80-90 kPa to remove bubbles in the solution. The degassed PVA solution is stored in a storage tank at a temperature of 25-30°C and equipped with a stirring device to maintain a rotation speed of 30-50 rpm.

[0041] (2) CMCS / FA layer pouring The mold is driven by a continuous stainless steel mesh belt conveyor, and the mold is fixed on the conveyor belt. The mold is a stainless steel plate, the size is determined according to the product specifications, and the surface is finely polished.

[0042] A high-precision liquid pouring machine is used to transfer the CMCS / FA solution from the storage tank to the pouring head through a pipeline. The pouring machine has a flow accuracy control of ±0.5%, and the pouring head can move evenly across the width of the mold for pouring.

[0043] In the above pouring process, it is very important to accurately control the thickness of the layer, especially for some food packaging with high requirements for barrier properties and mechanical properties, such as high-fat food packaging, the thickness of the CMCS / FA layer needs to be accurately controlled to ensure a good barrier effect, so as to effectively block the penetration of substances such as oxygen and moisture, prevent food from spoiling and extend the shelf life of food. In addition, in industrial large-scale production, the entire pouring and drying process can be carried out in a relatively stable state, reducing production fluctuations caused by human factors or unreasonable process parameters, which is conducive to the realization of large-scale, efficient and high-quality packaging film production.

[0044] In order to achieve the above objectives, the present invention collects and studies the key parameter data in the casting process, selects the relevant parameters that have a greater impact on the uniformity of layer thickness through weight analysis, conducts experiments and performs data analysis and fitting. Based on this, the following relationship used in the production process is obtained:

[0045] Where V 带 is the conveyor belt speed, in mm / min; h is the target thickness of the CMCS / FA layer, which is in the range of 0.1~0.2mm; V 浇 is the pouring speed, the selection range is 2~20L / min; η is the solution viscosity, the unit is Pa·s, measured by a rotational viscometer and a capillary viscometer before pouring; w is the mold width, the range is 10~40mm; Ra is the reference roughness of the mold surface, η0 and R a0 are the base viscosity and the base roughness of the mold surface, which are determined by experiments in production, and k is the fitting coefficient, which is determined by experiments in production. It can be seen that in industrial production, in order to achieve stable film formation and obtain a film layer with uniform thickness, the conveyor belt speed needs to be appropriately reduced when the viscosity is high, and the conveyor belt speed can be appropriately increased when the mold surface is ideal (lower roughness).

[0046] After pouring, the conveyor belt will take the poured mold into the drying process. The hot air circulation system is used. The temperature is divided into multiple stages. The temperature of the front stage is 40~50℃, the temperature of the middle stage is 50~60℃, and the temperature of the back stage is 40~50℃. The air flow rate is 2~3m / s, and the drying time is about 10~20min, so that the solvent can be fully volatilized to form a CMCS / FA layer. Multi-stage control is used in this process. In the early stage of drying, the solvent content is high, and the temperature of the front stage can quickly volatilize the solvent. If the temperature is too high and the solvent evaporates quickly, the solvent volatilization speed on the surface and inside of the film layer may be inconsistent, resulting in greater internal stress, thereby causing the film layer to rupture. Therefore, the lower temperature of the front stage can make the solvent evaporate slowly and evenly to avoid film rupture. As the drying process proceeds, the solvent in the film layer decreases, and the temperature needs to be adjusted so that the film layer is further solidified and stabilized in a relatively mild temperature environment when it is close to drying, so as to avoid excessive deformation caused by continuous high temperature.

[0047] (3) PUL / NTW layer pouring On the surface of the dried CMCS / FA layer, a crosslinker solution with a mass fraction of 0.5% is evenly sprayed through a spray system. The spray pressure of the spray system is 0.3~0.5MPa, and the distance between the nozzle and the membrane surface is kept at 10~15cm to ensure uniform coverage of the crosslinker solution.

[0048] Subsequently, a casting machine was used to cast the PUL / NTW solution onto the first film layer at a casting speed of 8-16 L / min and a solution thickness of 0.1-0.2 mm. During the casting process, the delivery speed was determined using an optimization method similar to step (2).

[0049] After pouring, the mold enters the drying process again. The drying temperature and air flow rate are the same as those of the CMCS / FA layer. The drying time is 12~24min to ensure that the PUL / NTW layer is completely dried.

[0050] (4) PVA layer pouring On the surface of the dried PUL / NTW layer, a crosslinker solution with a mass fraction of 0.3% was sprayed through a spray system, and the spray parameters were the same as those of the first layer of crosslinker spraying.

[0051] The PVA solution was poured at a speed of 12-20 L / min using a pouring machine, with a thickness of about 0.1-0.2 mm. During the pouring process, the conveying speed was determined using an optimization method similar to step (2). The poured multilayer film was sent to the drying process, with a drying temperature of 60-70°C in the front section, 70-80°C in the middle section, and 60-70°C in the rear section. The air flow rate was 2-3 m / s, and the drying time was 15-25 min.

[0052] (5) Hot pressing A large-scale continuous hot press is used, with a hot pressing temperature of 80~100℃, a pressure of 5~10MPa, and a hot pressing time of 30~60s, which is controlled by the conveyor belt speed and the length of the hot pressing area, to further enhance the interlayer bonding force. The heating plate of the hot press adopts a high-precision temperature control system with a temperature control accuracy of ±1℃ and a pressure control system accuracy of ±0.1MPa.

[0053] (6) Cutting and packaging Use an automated cutting machine to cut the packaging film according to the preset size. The cutting accuracy of the cutting machine is ±1mm and the cutting speed is 5~10m / min. Use an automatic packaging machine to pack the cut packaging film, and then store the packaged multi-layer food packaging film in a warehouse with a temperature of 20~25℃ and a relative humidity of 40%~60%.

[0054] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a multilayer material by assembling it layer by layer, wherein the multilayer material comprises a CMCS / FA film, a PUL / NTW film and a PVA film arranged in sequence, wherein the NTW is N-Nb2CT x / TpPa-1 / m-WO 3-x Composite nano-photocatalytic material; characterized in that, The steps include: (1) Preparation of membrane-forming solution: Select corresponding raw materials, prepare CMCS / FA solution, PUL / NTW solution and PVA solution respectively and store them; (2) Preparation of CMCS / FA layer A continuous stainless steel mesh belt conveyor is used to drive the mold. A liquid pouring machine is used to pour the CMCS / FA solution onto the mold surface to form a CMCS / FA layer, which is then dried. The speed of the conveyor belt is determined based on the solution viscosity, pouring speed, mold width, target thickness of the CMCS / FA layer, and mold surface roughness. The drying process uses a multi-stage temperature control method. (3) PUL / NTW layer pouring A liquid casting machine is used to cast the PUL / NTW solution onto the surface of the dried CMCS / FA layer to form a PUL / NTW layer, which is then dried. The drying process is controlled by a multi-stage temperature control method. (4) PVA layer pouring A liquid casting machine is used to cast the PVA solution onto the surface of the dried PUL / NTW layer to form a PVA layer, which is then dried to obtain a multi-layer structure. The drying process is controlled by a multi-stage temperature control method. (5) The multilayer structure is continuously hot-pressed by a continuous hot press, and then cut and packaged to obtain a multilayer material.

2. A layer-by-layer assembly preparation method of a multi-layer material according to claim 1, characterized in that: In step (1), during the preparation of the CMCS / FA solution, a mixing tank is used to mix CMCS, glycerol and deionized water, and the mixture is stirred while the temperature of the CMCS solution is controlled. Subsequently, FA is added and mixed to obtain a CMCS / FA solution.

3. The method for preparing a multilayer material by assembling it layer by layer according to claim 2, characterized in that: In step (1), during the preparation of the PUL / NTW solution, a dissolution tank is used to mix PUL, glycerol and deionized water, stir and control the solution temperature, and then NTW is added and dispersed to obtain a PUL / NTW solution.

4. The method for preparing a multilayer material by assembling it layer by layer according to claim 3, characterized in that: In step (1), during the preparation of the PVA solution, PVA and deionized water are mixed, stirred and the solution temperature is controlled, so that the PVA is dissolved in the deionized water and degassed to obtain a PVA solution.

5. The method for preparing a multi-layer material by assembling it layer by layer according to claim 4, characterized in that: The mold is made of stainless steel.

6. The method for preparing a multi-layer material by assembling it layer by layer according to claim 5, characterized in that: The NTW is made of WO3 containing mesopores and oxygen vacancies and amino Nb2CT x , adding N,N-dimethylformamide, trialdehyde pyrogallol, p-phenylenediamine, mesitylene and 1,4-dioxane, and adding acetic acid aqueous solution as a catalyst to react and prepare the product.

7. The method for preparing a multi-layer material by assembling it layer by layer according to claim 6, characterized in that: In the multilayer material, the loading content of NTW is ≤0.2%.

8. A multilayer material obtained by the method of claim 7.

9. Use of the multilayer material according to claim 8 in food packaging.

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