Antifogging polypropylene sheet and its preparation method and application

Abstract

The application relates to the technical field of high polymer material modification, and discloses an anti-fog polypropylene sheet as well as a preparation method and application thereof. The anti-fog polypropylene sheet comprises a base resin, an anti-fog agent and an additive, the base resin comprises polypropylene A, polypropylene B and linear low-density polyethylene, the anti-fog agent is a non-ionic composite anti-fog agent comprising glycerol monooleate, sorbitan monooleate, lauryl alcohol polyoxyethylene ether, cetyl alcohol polyoxyethylene ether and triglycerol monolaurate, and the additive comprises a compatible dispersant, an antioxidant and a slip agent. Through the synergy between the ternary base compound, the multiple anti-fog components and the functional additives, the anti-fog polypropylene sheet has excellent anti-fog performance, high transparency and good low-temperature toughness. The preparation method improves the transparency of the anti-fog polypropylene sheet through specific processes of mixing, melt blending, flat die extrusion, cooling and shaping and corona treatment.

Description

Technical Field

[0001] This application relates to the field of polymer material modification technology, and in particular to an anti-fog polypropylene sheet, its preparation method and application. Background Technology

[0002] Polypropylene (PP) is widely used in the production of food packaging sheets due to its advantages such as light weight, flexibility, heat resistance, low-temperature resistance, and good food safety, especially in transparent packaging products such as fresh food trays, fruit and vegetable boxes, cooked food containers, and cold drink cup lids. However, PP itself is hydrophobic, with low surface energy and a water contact angle typically above 90°. When the packaging contains moisture or experiences temperature changes, water vapor condenses into numerous fine and discrete water droplets on the inner surface of the PP sheet. These water droplets cause strong diffuse scattering of incident light, resulting in a hazy, whitish appearance on the sheet surface, severely affecting consumers' observation of the product inside and their shopping experience.

[0003] In existing technologies, to impart anti-fogging properties to polypropylene sheets, an anti-fogging coating is typically applied after sheet molding. This method is relatively simple, requiring only the uniform application of an anti-fogging agent solution to the sheet surface. Another common method is to directly blend the anti-fogging agent with polypropylene resin and then produce anti-fogging polypropylene sheets through processes such as extrusion molding. Additionally, anti-fogging performance can be indirectly influenced by altering the molecular structure of the polypropylene resin or adding other additives. However, these technologies still have significant drawbacks. Traditional anti-fogging measures struggle to precisely control the migration rate of the anti-fogging agent within the polypropylene sheet, resulting in a trade-off between anti-fogging effectiveness and sheet properties such as transparency and toughness. For example, increasing the amount of anti-fogging agent to improve the anti-fogging effect often reduces the sheet's transparency and toughness, impacting its performance and application range. Summary of the Invention

[0004] To at least overcome one of the problems existing in the prior art, one objective of this invention is to provide an anti-fogging polypropylene sheet, comprising a matrix resin, an anti-fogging agent, and additives. The matrix resin includes polypropylene A, polypropylene B, and linear low-density polyethylene. The anti-fogging agent is a nonionic composite anti-fogging agent comprising glyceryl monooleate, sorbitan monooleic acid, lauryl polyoxyethylene ether, hexadecyl polyoxyethylene ether, and triglyceride monolaurate. The additives include a compatibilizer, an antioxidant, and a slip agent. Through the synergistic effect of the above-mentioned ternary matrix compounding, multi-component anti-fogging components, and functional additives, the polypropylene composite matrix ensures the rigidity, heat resistance, and transparency of the sheet. The nonionic composite anti-fogging agent achieves rapid hydrophilic spreading and anti-migration properties, and the additives improve the dispersion stability of the system. Therefore, the anti-fogging polypropylene sheet of this application simultaneously possesses excellent anti-fogging performance, high transparency, and good low-temperature toughness. A second objective of this invention is to provide a method for preparing the aforementioned anti-fogging polypropylene sheet. A third objective of this invention is to provide the application of the anti-fog polypropylene sheet in the preparation of food packaging containers or refrigerated display containers.

[0005] Therefore, the present invention adopts the following technical solution: A first aspect of the present invention provides an anti-fogging polypropylene sheet, comprising a matrix resin, an anti-fogging agent, and additives, wherein the weight ratio of the matrix resin, the anti-fogging agent, and the additives is (30~45):(4~9):(0.5~2); the matrix resin comprises polypropylene A, polypropylene B, and linear low-density polyethylene; the anti-fogging agent is a nonionic composite anti-fogging agent, comprising glyceryl monooleate, sorbitan monooleate, lauryl polyoxyethylene ether, cetyl alcohol polyoxyethylene ether, and triglyceride monolaurate; the additives comprise a compatibilizer, an antioxidant, and a slip agent.

[0006] In the anti-fogging polypropylene sheet of this application, the matrix resin, anti-fogging agent, and additives are compounded in a weight ratio of (30~45):(4~9):(0.5~2). The matrix resin is a ternary compound of polypropylene A, polypropylene B, and linear low-density polyethylene. The introduction of linear low-density polyethylene not only improves the low-temperature toughness of polypropylene but also provides a good migration channel for the anti-fogging agent. The five specific nonionic composite anti-fogging agents work together to help the anti-fogging agent spread quickly and uniformly in the system. The compatibilizer, antioxidant, and slip agent help improve the overall uniformity of dispersion, processing thermal stability, and surface slip properties of the system. The synergistic effect of the matrix resin, anti-fogging agent, and additives makes it difficult for the anti-fogging agent to precipitate out, maintaining high transparency while possessing excellent anti-fogging performance and low-temperature resistance.

[0007] Preferably, the weight ratio of polypropylene A, polypropylene B, and linear low-density polyethylene is (13~25):(10~18):(5~15). More preferably, the weight ratio of polypropylene A, polypropylene B, and linear low-density polyethylene is (15~25):(12~18):(5~15). Even more preferably, the weight ratio of polypropylene A, polypropylene B, and linear low-density polyethylene is (15~25):(12~18):(7~15).

[0008] Preferably, the polypropylene A is homopolymer polypropylene with a melt flow rate of 1.5~4 g / 10 min at 230℃ / 2.16 kg. More preferably, the polypropylene A is homopolymer polypropylene with a melt flow rate of 2.1~4 g / 10 min at 230℃ / 2.16 kg.

[0009] Preferably, the polypropylene B is a copolymer polypropylene with a melt flow rate of 5~12 g / 10 min at 230℃ / 2.16 kg. More preferably, the polypropylene B is a copolymer polypropylene with a melt flow rate of 9~12 g / 10 min at 230℃ / 2.16 kg.

[0010] Preferably, the linear low-density polyethylene has a density of 0.915~0.935 g / cm³. 3 The melt index is 2~8 g / 10min at 190℃ / 2.16kg. More preferably, the density of the linear low-density polyethylene is 0.915~0.935 g / cm³. 3 The melt index is 4~8 g / 10 min at 190℃ / 2.16 kg.

[0011] Preferably, in the nonionic composite antifogging agent, the weight ratio of glyceryl monooleate, sorbitan monooleate, lauryl polyoxyethylene ether, hexadecyl polyoxyethylene ether, and triglyceride monolaurate is (2~5):(1~4):(1~2):(0.5~1.5):(1~3). More preferably, in the nonionic composite antifogging agent, the weight ratio of glyceryl monooleate, sorbitan monooleate, lauryl polyoxyethylene ether, hexadecyl polyoxyethylene ether, and triglyceride monolaurate is (3~5):(1.5~4):(1~2):(0.5~1.5):(1~3). More preferably, in the nonionic composite antifogging agent, the weight ratio of glyceryl monooleate, sorbitan monooleate, lauryl polyoxyethylene ether, hexadecyl polyoxyethylene ether, and triglyceride monolaurate is (3~5):(1.5~4):(1~2):(0.8~1.5):(1.5~3).

[0012] In the above technical solution, glyceryl monooleate and sorbitan monooleate have a fast migration rate, enabling them to migrate to the surface in a short time, providing a rapid initial hydrophilicity improvement effect for the anti-fog polypropylene sheet, ensuring that the product has good anti-fog performance from the beginning of use; lauryl alcohol polyoxyethylene ether and hexadecyl alcohol polyoxyethylene ether have excellent surface activity, which helps to reduce the surface tension of the sheet, thereby accelerating the spreading rate of condensed water, allowing water droplets to spread into a continuous transparent water film the moment they form; while triglyceride monolaurate has a large molecular weight, high thermal stability, and a slow migration rate, which helps to provide a long-lasting anti-fog effect. When the five components are in a specific ratio, the anti-fog agent will not excessively aggregate on the sheet surface, effectively avoiding the appearance of oil spots on the surface, and ensuring the transparency of the sheet.

[0013] Preferably, in the additive, the weight ratio of the compatibilizer, antioxidant, and slip agent is (3~5):(2~3):(4~8). More preferably, in the additive, the weight ratio of the compatibilizer, antioxidant, and slip agent is (3.5~5):(2~3):(4~8). Even more preferably, in the additive, the weight ratio of the compatibilizer, antioxidant, and slip agent is (4~5):(2~3):(5~8).

[0014] Preferably, the compatibility dispersant is selected from at least one of stearate, polyethylene wax, and modified polysiloxane. More preferably, the compatibility dispersant is selected from at least one of stearate and polyethylene wax. Even more preferably, the compatibility dispersant is composed of stearate and polyethylene wax in a weight ratio of (2~4):(1~2).

[0015] Preferably, the antioxidant is selected from at least one of hindered phenolic antioxidants and phosphite antioxidants. More preferably, the antioxidant is composed of hindered phenolic antioxidants and phosphite antioxidants in a weight ratio of (1~3):(1~2.5).

[0016] Preferably, the slip agent is selected from at least one of fatty acid amides, polysiloxanes, and fatty acid esters. More preferably, the slip agent is selected from at least one of fatty acid amides and fatty acid esters.

[0017] A 3-5 part by weight of compatibility dispersant helps to uniformly disperse the matrix resin and antifogging agent in the blend system, preventing the agglomeration of highly polar antifogging agents in the non-polar polypropylene matrix. It also improves the interfacial bonding between linear low-density polyethylene and polypropylene in the matrix resin, forming a more stable blend system. In the 2-3 part by weight of antioxidant, hindered phenolic antioxidants capture free radicals and interrupt the oxidation chain reaction, while phosphite antioxidants decompose hydrogen peroxide. Under specific ratios, these two types of antioxidants help to effectively prevent the thermo-oxidative degradation of polypropylene during high-temperature extrusion processing, improving the thermal stability of the system. A 4-8 part by weight of slip agent facilitates migration to the sheet surface, effectively reducing the coefficient of friction and improving anti-blocking and slip properties during molding and winding processes. The synergistic effect of these three agents ensures the processing stability and product uniformity of the multi-component blend system.

[0018] A second aspect of the present invention provides a method for preparing the anti-fog polypropylene sheet according to the first aspect of the present invention, comprising the following steps: S1. Mix the matrix resin, antifogging agent and additives to obtain a mixture; S2. The mixture is added to an extruder for melt blending to form a melt; S3. The melt is extruded through a flat die to form a sheet-like molten ingot; S4. The sheet-shaped ingot is cooled and shaped by a cooling roller assembly to obtain a sheet substrate; S5. Perform corona discharge treatment on one surface of the sheet substrate, and then roll it up with the corona-treated surface facing inward to obtain the anti-fog polypropylene sheet.

[0019] Preferably, in step S2, the screw speed of the extruder is 50-150 rpm, the temperature of the feeding zone is 160-190℃, the temperature of the compression zone is 180-210℃, the temperature of the metering zone is 190-220℃, and the temperature of the die zone is 195-215℃. More preferably, in step S2, the screw speed of the extruder is 70-150 rpm, the temperature of the feeding zone is 165-190℃, the temperature of the compression zone is 180-210℃, the temperature of the metering zone is 190-220℃, and the temperature of the die zone is 195-215℃. Even more preferably, in step S2, the screw speed of the extruder is 90-150 rpm, the temperature of the feeding zone is 165-190℃, the temperature of the compression zone is 185-210℃, the temperature of the metering zone is 200-220℃, and the temperature of the die zone is 205-215℃.

[0020] Preferably, in step S4, the cooling roller assembly includes two cooling rollers, wherein the temperature of the first cooling roller is 40~60℃ and the temperature of the second cooling roller is 30~50℃. More preferably, in step S4, the cooling roller assembly includes two cooling rollers, wherein the temperature of the first cooling roller is 45~60℃ and the temperature of the second cooling roller is 40~50℃.

[0021] Preferably, in step S5, the power of the corona discharge treatment is 2~10kW. More preferably, in step S5, the power of the corona discharge treatment is 4~10kW.

[0022] The preparation method of this application employs a process of mixing, melt blending, flat die extrusion, cooling and shaping, and corona treatment. Mixing and melt blending ensure sufficient dispersion of each component; flat die extrusion promotes uniform sheet thickness and surface smoothness; the cooling and shaping process rapidly releases internal stress, preventing warping; and corona treatment with a power of 2-10 kW increases surface tension, facilitating the migration of the anti-fogging agent to the surface and the formation of a uniform and dense hydrophilic layer, enhancing the adhesion of subsequent printing, heat sealing, or bonding. This preparation method ensures uniform material mixing, stable melt state, and controllable molding, effectively solving problems such as uneven component dispersion and poor anti-fogging durability in existing processes.

[0023] A third aspect of this application provides the application of an anti-fog polypropylene sheet in the preparation of food packaging containers or refrigerated display containers, wherein the anti-fog polypropylene sheet is the anti-fog polypropylene sheet described above, or is prepared by the above-described preparation method.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects: 1) The anti-fog polypropylene sheet of this application, through a specific ratio of matrix resin, anti-fog agent and additives, especially the ternary matrix compound of polypropylene A, polypropylene B and linear low density polyethylene, the anti-fog agent of the multi-component nonionic compound, and the synergistic effect of the additives, effectively solves the technical problems of easy precipitation of anti-fog agent, decreased transparency, and difficulty in balancing anti-fog effect and mechanical properties in existing anti-fog polypropylene materials.

[0025] 2) This application uses a nonionic composite antifogging agent composed of glyceryl monooleate, sorbitan monooleate, lauryl alcohol polyoxyethylene ether, cetyl alcohol polyoxyethylene ether, and triglyceride monolaurate. Among them, glyceryl monooleate and sorbitan monooleate provide rapid initial hydrophilic modification, lauryl alcohol polyoxyethylene ether and cetyl alcohol polyoxyethylene ether reduce surface tension to accelerate water droplet spreading and film formation, and triglyceride monolaurate provides antifogging effect. The three work together to overcome the defects of insufficient antifogging effect of single antifogging components and significantly improve the antifogging performance of antifogging polypropylene sheets.

[0026] 3) The preparation method of this application, through specific processes of mixing, melt blending, flat die extrusion, cooling and shaping, and corona treatment, combined with the specific composition and ratio of each component, makes the obtained anti-fog polypropylene sheet have good surface flatness and transparency, which is suitable for industrial production. Detailed Implementation

[0027] The present invention will be further described in detail below through specific embodiments, comparative examples and tables, but is not limited to all the discussions and data.

[0028] Homopolymer polypropylene: purchased from Lee Chang Yung Chemical Co., Ltd., model 6524; melt flow rate (230℃ / 2.16kg) is 3.6g / 10min.

[0029] Copolymer polypropylene: purchased from Borealis, model BD212CF, melt flow rate (230℃ / 2.16kg) is 5.0g / 10min.

[0030] Linear low-density polyethylene: purchased from ExxonMobil, USA, model LL 1002BU, melt flow rate (190℃ / 2.16kg) is 2.0g / 10min, density is 0.918g / cm³. 3 .

[0031] Glyceryl monooleate: CAS number 25496-72-4.

[0032] Sorbitol monooleate: CAS number 1338-43-8.

[0033] Lauryl alcohol polyoxyethylene ether: CAS number 9002-92-0, purchased from Nantong Zhonghe Chemical New Materials Co., Ltd., molecular weight: 1199.55.

[0034] Cetyl alcohol polyoxyethylene ether: purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0035] Triglyceride monolaurate: CAS number 51033-31-9.

[0036] The polyethylene wax, model 400PE wax, was purchased from Wuhan Xindongyi Chemical Co., Ltd.

[0037] It is particularly important to emphasize that, unless otherwise specified, the raw materials, reagents, or devices used in this invention can all be obtained through conventional commercial channels. Unless otherwise specified, "parts" in this invention refers to parts by weight.

[0038] Examples of anti-fog polypropylene sheets: An anti-fog polypropylene sheet is prepared by the following steps: S1. Mix 30-45 parts of matrix resin, 4-9 parts of antifogging agent and 0.5-2 parts of additives to obtain a mixture; S2. Add the mixture to the extruder, control the screw speed of the extruder to be 50~150 rpm, the temperature of the feeding zone to be 160~190℃, the temperature of the compression zone to be 180~210℃, the temperature of the metering zone to be 190~220℃, and the temperature of the die zone to be 195~215℃, and carry out melt blending to form a melt. S3. Control the width of the flat die head to 400~1200mm and the die lip clearance to 0.5~1.0mm, and extrude the melt through the flat die head to form a sheet-like molten ingot; S4. The sheet-shaped ingot is cooled and shaped by a cooling roller group with a first cooling roller temperature of 40~60℃ and a second cooling roller temperature of 30~50℃ to obtain a sheet substrate. S5. The sheet substrate is guided to the corona treatment machine by the conveying roller, and corona discharge treatment is performed on one surface of the sheet substrate at a power of 2~10kW. Then, it is wound up with the corona surface facing inward to obtain the anti-fog polypropylene sheet.

[0039] Regarding step S1, in some specific embodiments, the amount of the base resin can be 30 parts, 35 parts, 40 parts, or 45 parts; the amount of the antifogging agent can be 4 parts, 6 parts, 8 parts, or 9 parts; and the amount of the additives can be 0.5 parts, 1 part, 1.5 parts, or 2 parts. The base resin includes polypropylene A, polypropylene B, and linear low-density polyethylene; the weight ratio of polypropylene A, polypropylene B, and linear low-density polyethylene can be 13:10:7, 20:15:8, 20:18:7, 20:15:15, or 25:15:6; polypropylene A is homopolymer polypropylene, and its melt flow rate at 230℃ / 2.16kg is 1.5g / 10min, 2.5g / 10min, 3.6g / 10min, or 4g / 10min. Polypropylene B is a copolymer polypropylene with melt flow rates of 5 g / 10 min, 7 g / 10 min, 10 g / 10 min, or 12 g / 10 min at 230℃ / 2.16 kg; the density of linear low-density polyethylene is 0.915 g / cm³. 3 0.920g / cm 3 0.925g / cm 3 Or 0.935g / cm 3The melt flow index is 2 g / 10 min, 5 g / 10 min, 6 g / 10 min, or 8 g / 10 min at 190℃ / 2.16 kg. The antifogging agent is a nonionic composite antifogging agent, which includes glyceryl monooleate, sorbitan monooleate, lauryl polyoxyethylene ether, hexadecyl polyoxyethylene ether, and triglyceride monolaurate. In the nonionic composite antifogging agent, the weight ratio of glyceryl monooleate, sorbitan monooleate, lauryl polyoxyethylene ether, hexadecyl polyoxyethylene ether, and triglyceride monolaurate can be 2:1:2:1.5:1, 2:3:2:0.5:2, 3:4:2:1:2, 5:3:1:1.5:2, or 5:4:1:1:3. The additives include compatibilizers, antioxidants, and slip agents; the weight ratio of the compatibilizer, antioxidant, and slip agent can be 3:2:5, 3:3:4, 5:2:6, 5:3:7, or 5:2:8; the compatibilizer is selected from at least one of stearates, polyethylene wax, and modified polysiloxanes, and can be composed of stearates and polyethylene waxes in a weight ratio of 2:1, 3:1, 4:1, or 3:2; the antioxidant is selected from at least one of hindered phenolic antioxidants and phosphite antioxidants, and can be composed of hindered phenolic antioxidants and phosphite antioxidants in a weight ratio of 1:1, 3:1, 2:2.5, 1:2.5, or 1:2; the slip agent is selected from at least one of fatty acid amides, polysiloxanes, and fatty acid esters.

[0040] Regarding step S2, in some specific embodiments, the screw speed of the extruder can be 50 rpm, 70 rpm, 100 rpm, 120 rpm or 150 rpm, the temperature of the feeding zone can be 160℃, 170℃, 180℃ or 190℃, the temperature of the compression zone can be 180℃, 190℃, 205℃ or 210℃, the temperature of the metering zone can be 190℃, 200℃, 210℃ or 220℃, and the temperature of the die head zone can be 195℃, 205℃ or 215℃.

[0041] Regarding step S3, in some specific implementations, the width of the flat die head can be 400mm, 500mm, 700mm, 900mm or 1200mm, and the die lip gap can be 0.5mm, 0.6mm, 0.8mm or 1.0mm.

[0042] Regarding step S4, in some specific implementations, the temperature of the first cooling roller can be 40°C, 50°C, or 60°C, and the temperature of the second cooling roller can be 30°C, 40°C, or 50°C.

[0043] For step S5, in some specific implementations, the power of the corona treatment can be 2kW, 5kW, 8kW or 10kW. Example 1

[0044] An anti-fog polypropylene sheet is prepared by the following steps: S1. Add 43 parts of matrix resin (20 parts of 6524 type homopolymer polypropylene, 15 parts of BD212CF type copolymer polypropylene and 8 parts of LL 1002BU type linear low-density polyethylene) to a high-speed mixer and stir at 600 rpm for 5 min; then add 7.5 parts of antifogging agent (2 parts of glyceryl monooleate, 1 part of dehydrated sorbitan monooleate, 2 parts of lauryl polyoxyethylene ether, 1.5 parts of cetyl alcohol polyoxyethylene ether, 1 part of triglyceride monolaurate) and 2 parts of additives (a compatibility dispersant composed of 0.4 parts of zinc stearate and 0.2 parts of 400PE wax-type polyethylene wax, an antioxidant composed of 0.2 parts of hindered phenolic antioxidant 1010 and 0.4 parts of phosphite antioxidant 168, and 0.8 parts of slip agent oleamide), and continue stirring at 600 rpm for 10 min until all components are evenly dispersed and there are no lumps, thus obtaining a mixture; S2. Add the mixture to the extruder, control the screw speed of the extruder to 120 rpm, the temperature of the feeding zone to 180℃, the temperature of the compression zone to 190℃, the temperature of the metering zone to 200℃, and the temperature of the die zone to 205℃, and carry out melt blending to form a melt. S3. Control the width of the flat die head to 500mm and the die lip clearance to 0.8mm, and extrude the melt through the flat die head to form a sheet-like molten ingot; S4. The sheet-shaped molten billet is cooled and shaped by a cooling roller group with the first cooling roller at a temperature of 50°C and the second cooling roller at a temperature of 40°C to obtain a sheet substrate. S5. The sheet substrate is guided to the corona treatment machine by the conveyor roller, and corona discharge treatment is performed on one surface of the sheet substrate at a power of 5kW. Then, it is wound up with the corona side facing inward to obtain the anti-fog polypropylene sheet. Example 2

[0045] The preparation method of an anti-fog polypropylene sheet is the same as in Example 1, except that in Example 2, the matrix resin in step S1 is 30 parts, which consists of 13 parts of 6524 type homopolymer polypropylene, 10 parts of BD212CF type copolymer polypropylene and 7 parts of LL 1002BU type linear low-density polyethylene. Example 3

[0046] The preparation method of an anti-fog polypropylene sheet is the same as in Example 1, except that in Example 3, the anti-fog agent in step S1 is 7 parts, which consists of 2.5 parts of glyceryl monooleate, 2 parts of dehydrated sorbitan monooleate, 0.5 parts of lauryl polyoxyethylene ether, 0.5 parts of cetyl alcohol polyoxyethylene ether, and 1.5 parts of triglyceride monolaurate. Example 4

[0047] The preparation method of an anti-fog polypropylene sheet is the same as in Example 1, except that in Example 4, the additive in step S1 is 1.5 parts, consisting of a compatibility dispersant composed of 0.4 parts zinc stearate and 0.1 parts 400PE wax-type polyethylene wax, an antioxidant composed of 0.1 parts hindered phenolic antioxidant 1010 and 0.1 parts phosphite antioxidant 168, and a slip agent oleamide.

[0048] Comparative Example 1: A method for preparing an anti-fogging polypropylene sheet is the same as in Example 1, except that in Comparative Example 1, the total weight of the anti-fogging agent is changed to 10 parts, and its composition and ratio are the same as in Example 1.

[0049] Comparative Example 2: The preparation method of an anti-fog polypropylene sheet is the same as in Example 1, except that in Comparative Example 2, 43 parts of matrix resin are composed of 15 parts of 6524 type homopolymer polypropylene, 10 parts of BD212CF type copolymer polypropylene and 18 parts of LL 1002BU type linear low-density polyethylene.

[0050] Comparative Example 3: The preparation method of an anti-fog polypropylene sheet is the same as in Example 1, except that in Comparative Example 3, 43 parts of matrix resin are composed of 23 parts of 6524 type homopolymer polypropylene and 20 parts of BD212CF type copolymer polypropylene.

[0051] Comparative Example 4: The preparation method of an anti-fogging polypropylene sheet is the same as in Example 1, except that in Comparative Example 4, 7.5 parts of anti-fogging agent are composed of 2 parts of glyceryl monooleate, 1 part of dehydrated sorbitan monooleate, 2.5 parts of lauryl polyoxyethylene ether, 1.5 parts of cetyl alcohol polyoxyethylene ether, and 0.5 parts of triglyceride monolaurate.

[0052] Comparative Example 5: The preparation method of an anti-fog polypropylene sheet is the same as in Example 1, except that in Comparative Example 5, 7.5 parts of anti-fog agent are composed of 2 parts of glyceryl monooleate, 1 part of dehydrated sorbitan monooleate, 3.5 parts of cetyl alcohol polyoxyethylene ether, and 1 part of triglyceride monolaurate.

[0053] Comparative Example 6: A method for preparing an anti-fog polypropylene sheet is the same as in Example 1, except that in Comparative Example 6, the power of the corona treatment in step S5 is 12kW.

[0054] Material performance testing: The anti-fog polypropylene sheets of Examples 1-4 and Comparative Examples 1-6 were subjected to various performance tests, and the test methods are as follows: 1. Anti-fog performance: Cut the test sheet into a 10cm×10cm specimen, take a 500mL beaker and inject boiling water at 100°C to two-thirds of the beaker's volume, place the specimen over the beaker mouth with the corona-treated side of the specimen facing the inside of the beaker (i.e., the side in contact with water vapor), let it stand for 5 minutes, and observe the water droplet formation on the lower surface of the specimen, namely the corona surface, under natural light. The anti-fog grade is evaluated according to the following criteria: Grade 1 means no visible water droplets and completely transparent; Grade 2 means extremely small amount of fine water droplets (diameter less than 0.3mm) and substantially transparent; Grade 3 means a relatively large number of medium-sized water droplets (diameter 0.3~1.0mm) and translucent; Grade 4 means a large number of large water droplets (diameter greater than 1.0mm) or partial whitening and opaque; Grade 5 means complete whitening and completely opaque. Grade 1 or Grade 2 is judged as qualified.

[0055] 2. Haze: The test is carried out in accordance with the standard GB / T 2410-2008 "Determination of Transmittance and Haze of Transparent Plastics".

[0056] 3. Low-temperature notched impact strength: The notched impact strength of the anti-fog polypropylene sheet is tested at -10°C in accordance with the standard GB / T 1843-2008 "Plastics - Determination of Izod Impact Strength".

[0057] The various test properties of the anti-fog polypropylene sheets of Examples 1 to 4 and Comparative Examples 1 to 6 are shown in Table 1 below:

[0058] The anti-fog polypropylene sheets of Examples 1 to 4 use a ternary blend of polypropylene A, polypropylene B and linear low-density polyethylene as the base resin, combined with a nonionic composite anti-fog agent composed of five components: glycerol monooleate, sorbitan monooleate, lauryl alcohol polyoxyethylene ether, cetyl alcohol polyoxyethylene ether, and triglycerol monolaurate, as well as the synergistic effect of the compatibilizing dispersant, antioxidant and slipping agent, so that the anti-fog polypropylene sheet of the present application simultaneously has excellent anti-fog performance, high transparency and good low-temperature toughness. The results show that the anti-fog grade of the anti-fog polypropylene sheets of Examples 1 to 4 is Grade 1 or Grade 2, which is qualified, the haze is 10.7%~12.9%, and the notched impact strength at -10°C is 7.2~8.6 kJ / m 2 . It can be seen that the present application solves the technical defects in the existing anti-fog polypropylene materials that the anti-fog agent is prone to precipitation, the transparency decreases, and the anti-fog effect and mechanical properties are difficult to be achieved at the same time, and meets the use requirements of food packaging containers or refrigerated display containers for anti-fog clarity, high transparency and low-temperature impact resistance.

[0059] Compared with Example 1, Comparative Example 1 was prepared using the same method, except that the total weight of the antifogging agent in Comparative Example 1 was changed to 10 parts. The results showed that the haze of Comparative Example 1 was 16.3%. This may be because when the antifogging agent is excessive, the excess antifogging agent, exceeding the carrying capacity of the matrix resin, accumulates excessively on the sheet surface, forming oily exudates, which in turn leads to increased light scattering and decreased transparency.

[0060] Comparative Example 2 was prepared using the same method as Example 1, except that the 43 parts of matrix resin in Comparative Example 2 consisted of 15 parts homopolymer polypropylene, 10 parts copolymer polypropylene, and 18 parts linear low-density polyethylene. The results showed that Comparative Example 2 had a haze of 15.8% and a notched impact strength reduced to 6.1 kJ / m² at -10°C. 2 This may be because excessive linear low-density polyethylene (LLDPE) increases the phase interface between it and polypropylene, thereby exacerbating light scattering and leading to increased haze. At the same time, excessive LLDPE may disrupt the continuous phase structure of the matrix resin, weakening the rigid support of polypropylene and resulting in a decrease in the low-temperature impact strength of the anti-fog polypropylene sheet.

[0061] Comparative Example 3 was prepared using the same method as Example 1, except that the 43 parts of matrix resin in Comparative Example 3 consisted of 23 parts homopolymer polypropylene and 20 parts copolymer polypropylene, and did not contain linear low-density polyethylene. The results showed that Comparative Example 3 had an anti-fogging rating of level 4 and a notched impact strength of only 4.7 kJ / m at -10℃. 2 This may be because when linear low-density polyethylene is not added to the matrix resin, the anti-fogging agent migrates too quickly in the matrix resin, causing the anti-fogging agent to precipitate prematurely and form oil spots, resulting in a significant decrease in the anti-fogging effect of the sheet; in addition, the absence of linear low-density polyethylene causes the sheet to lose the low-temperature toughening component, and the low-temperature brittleness of polypropylene itself directly leads to insufficient impact strength of the sheet.

[0062] Compared with Example 1, Comparative Example 4 was prepared using the same method, except that the 7.5 parts of antifogging agent in Comparative Example 4 consisted of 2 parts glyceryl monooleate, 1 part sorbitan monooleate, 2.5 parts lauryl polyoxyethylene ether, 1.5 parts cetyl alcohol polyoxyethylene ether, and 0.5 parts triglyceride monolaurate. The results showed that the antifogging level of Comparative Example 4 decreased to level 2, while the haze increased to 13.6%, and the notched impact strength at -10℃ fluctuated slightly. This may be because the proportions of the components in the antifogging agent were imbalanced, weakening the hydrophilic spreading effect on the sheet surface; simultaneously, the uniformity of the antifogging components decreased, and localized micro-agglomerations increased light scattering, resulting in increased haze and a slight decrease in the antifogging effect.

[0063] Compared with Example 1, Comparative Example 5 was prepared using the same method, except that the 7.5 parts of antifogging agent in Comparative Example 5 consisted of 2 parts glyceryl monooleate, 1 part sorbitan monooleate, 3.5 parts cetyl alcohol polyoxyethylene ether, and 1 part triglyceride monolaurate. The results showed that Comparative Example 5 achieved an antifogging level of 3. This may be because the antifogging agent did not contain lauryl alcohol polyoxyethylene ether, which has excellent surface activity and can effectively reduce the surface tension of the sheet, allowing condensed water droplets to quickly spread into a continuous, transparent water film upon formation. When this component is lacking, the surface tension of the sheet is not sufficiently reduced, which slows down the spreading rate of the water droplets to some extent, causing them to accumulate on the surface before spreading and forming visible droplets, thus affecting the antifogging effect.

[0064] Compared with Example 1, Comparative Example 6 was prepared using the same method, except that the corona treatment power in step S5 of Comparative Example 6 was 12kW. The results showed that the haze of Comparative Example 6 was 16.4%. This may be because when the corona power is too high, the strong corona discharge can cause excessive oxidation or even etching damage to the sheet surface, disrupting the surface smoothness and forming a fine uneven structure, increasing light scattering and thus leading to a significant increase in haze.

[0065] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. An anti-fog polypropylene sheet, characterized in that, It includes a base resin, an anti-fogging agent, and additives, wherein the weight ratio of the base resin, the anti-fogging agent, and the additives is (30~45):(4~9):(0.5~2). The matrix resin includes polypropylene A, polypropylene B, and linear low-density polyethylene; The antifogging agent is a nonionic composite antifogging agent, which includes glyceryl monooleate, sorbitan monooleate, lauryl polyoxyethylene ether, cetyl alcohol polyoxyethylene ether, and triglyceride monolaurate. The additives include compatibility dispersants, antioxidants, and slip agents.

2. The anti-fog polypropylene sheet according to claim 1, characterized in that, In the matrix resin, the weight ratio of polypropylene A, polypropylene B and linear low-density polyethylene is (13~25):(10~18):(5~15).

3. The anti-fog polypropylene sheet according to claim 1, characterized in that, The polypropylene A is homopolymer polypropylene, and its melt flow rate is 1.5~4g / 10min at 230℃ / 2.16kg. And / or, the polypropylene B is a copolymer polypropylene with a melt flow rate of 5~12g / 10min at 230℃ / 2.16kg. And / or, the density of the linear low-density polyethylene is 0.915~0.935 g / cm³. 3 The melt index is 2~8g / 10min at 190℃ / 2.16kg.

4. The anti-fog polypropylene sheet according to claim 1, characterized in that, In the nonionic composite antifogging agent, the weight ratio of glyceryl monooleate, sorbitan monooleate, lauryl polyoxyethylene ether, hexadecyl polyoxyethylene ether, and triglyceride monolaurate is (2~5):(1~4):(1~2):(0.5~1.5):(1~3).

5. The anti-fog polypropylene sheet according to claim 1, characterized in that, In the aforementioned additives, the weight ratio of the compatibility dispersant, antioxidant, and slip agent is (3~5):(2~3):(4~8).

6. The anti-fog polypropylene sheet according to claim 1, characterized in that, The compatibility dispersant is selected from at least one of stearate, polyethylene wax, and modified polysiloxane; And / or, the antioxidant is selected from at least one of hindered phenolic antioxidants and phosphite antioxidants; And / or, the slip agent is selected from at least one of fatty acid amides, polysiloxanes, and fatty acid esters.

7. A method for preparing an anti-fog polypropylene sheet as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Mix the matrix resin, antifogging agent and additives to obtain a mixture; S2. The mixture is added to an extruder for melt blending to form a melt; S3. The melt is extruded through a flat die to form a sheet-like molten ingot; S4. The sheet-shaped ingot is cooled and shaped by a cooling roller assembly to obtain a sheet substrate; S5. Perform corona discharge treatment on one surface of the sheet substrate, and then roll it up with the corona-treated surface facing inward to obtain the anti-fog polypropylene sheet.

8. The method for preparing the anti-fog polypropylene sheet according to claim 7, characterized in that, In step S2, the screw speed of the extruder is 50~150 rpm, the temperature of the feeding zone is 160~190℃, the temperature of the compression zone is 180~210℃, the temperature of the metering zone is 190~220℃, and the temperature of the die head zone is 195~215℃.

9. The method for preparing the anti-fog polypropylene sheet according to claim 7, characterized in that, In step S4, the cooling roller assembly includes two cooling rollers, wherein the temperature of the first cooling roller is 40~60℃ and the temperature of the second cooling roller is 30~50℃. In step S5, the power of the corona discharge treatment is 2~10kW.

10. The use of the anti-fog polypropylene sheet according to any one of claims 1 to 6 or the anti-fog polypropylene sheet prepared by the preparation method according to any one of claims 7 to 9 in the preparation of food packaging containers or refrigerated display containers.

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