Non-migrating PVC transparent film for toys and method for preparing the same

Abstract

The application relates to the technical field of high polymer materials, in particular to a non-migration type PVC transparent film for toys and a preparation method thereof. The application discloses a non-migration type PVC transparent film for toys and a preparation method thereof. The preparation method is to construct a liquid phase-solid phase double blocking system, that is, a liquid phase chelation blocking layer is formed in a premixing stage, and a nano-coated filler is introduced to construct a solid phase blocking network, so as to cooperatively block the migration of heavy metals and small molecules; meanwhile, a calendering-quenching optical sizing process is adopted, crystallization is inhibited through high-temperature calendering and mirror roller rapid cooling, and the high transparency of the film is ensured. The PVC transparent film prepared by the application has excellent characteristics of zero heavy metal migration, high transparency and high toughness.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a non-migratory PVC transparent film for toys and its preparation method. Background Technology

[0002] Polyvinyl chloride (PVC) is widely used in the manufacture of various transparent films due to its excellent processing properties and transparency. However, traditional PVC transparent films have long faced a dual migration dilemma: on the one hand, traditional barium-zinc powder stabilizers and mineral sources contain heavy metals, which cannot meet the increasingly stringent requirements of zero-risk leaching in electronic, food, and medical packaging; on the other hand, low-molecular-weight plasticizers diffuse to the surface under heat, solvents, or pressure, causing whitening and increased haze, while multi-layer heterogeneous material barrier schemes block the recycling path.

[0003] Recently, some studies have explored the dual migration problem of PVC transparent films. For example, CN120663612A discloses a mirror-finish PVC composite film and its preparation method. This method uses a PET film to isolate the glossy and matte surfaces of the PVC film, effectively suppressing molecular migration-induced extinction caused by contact between the glossy and matte surfaces. At the same time, an optical-grade PET film is placed on the forming surface of the PVC film through online lamination, eliminating the secondary calendering and brightening coating processes of the mirror roller, and realizing integrated production of calendering-lamination-winding. CN120329613A discloses a novel PVC functionalizing agent that inhibits the release of toxic plasticizers, its preparation method, and its application. Through steps such as co-precipitation, crystallization, and drying of precursor solution and modifier solution, a PVC functionalizing agent based on a layered double hydroxide structure is obtained. Through surface adsorption and the spatial resistance of nanoparticles, it effectively inhibits the migration of harmful substances in PVC, significantly improves the volatility resistance and migration resistance of PVC film, and reduces the potential threat of PVC products to the environment and human health. However, existing technologies either focus on plasticizer migration reduction or simply replace non-toxic fillers, but fail to simultaneously solve heavy metal containment and optical-mechanical-recycling on the same production line.

[0004] In summary, how to innovate a preparation method that can ensure that the migration of heavy metal elements is close to zero, effectively inhibit the migration of plasticizers, prevent the film from whitening, and at the same time ensure that the film has high transparency and good mechanical strength has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a non-migration PVC transparent film for toys and its preparation method, so as to solve the technical problems in the prior art such as excessive leaching of heavy metals, plasticizer migration and whitening, and optical-mechanical conflicts.

[0006] The specific technical solution is as follows:

[0007] A non-migratory PVC transparent film for toys and its preparation method are disclosed. The preparation method involves modifying the interface of the PVC matrix by constructing a liquid-solid dual-blocking network, and on this basis, innovating a calendering-rapid cooling optical shaping process for vacuum homogenization and plasticization. Finally, silica-coated calcium carbonate nanoparticles are filled and mixed for composite reinforcement. This method successfully prepares a non-migratory PVC transparent film for toys that combines extreme safety, high transparency and excellent mechanical properties.

[0008] Furthermore, the liquid-solid dual-blocking refers to the liquid-phase blocking layer and the solid-phase blocking network forming a multi-protection system from the molecular level to the nanoscale through interfacial chemical bonding and physical interweaving. The liquid phase layer achieves molecular anchoring and initial stability, while the solid phase network provides physical blocking and long-term durability. The two are temporally coupled and spatially complementary, jointly achieving the blocking of small molecule plasticizers and heavy metal ions.

[0009] Furthermore, the liquid phase blocking layer refers to the chelating protective layer formed by preferentially spreading high-purity liquid calcium-zinc stabilizer on the surface of PVC resin particles during the low-temperature premixing stage. This protective layer achieves initial thermal stabilization by coordinating calcium-zinc (Ca-Zn) metal ions with active chlorine atoms on the PVC molecular chain, while changing the surface polarity of the resin, thus building an interface bridge for the efficient wetting of subsequent plasticizers.

[0010] Furthermore, the solid-phase blocking network refers to the introduction of nano-CaCO3 filler with a SiO2 layer on its surface after liquid-phase blocking is completed. The filler interacts strongly with the stabilizer and PVC chains in the liquid-phase blocking layer through the silanol groups on its surface, and is uniformly dispersed in the matrix to form a three-dimensional labyrinth-like physical barrier network. This network restricts the movement of small molecules and cuts off migration channels through steric hindrance effect.

[0011] Furthermore, the calendering-quenching process refers to obtaining a dense and uniform melt through full plasticization in the calendering stage, and then fixing this ideal form through rapid freezing in the quenching stage. The two processes work together to control the crystallization kinetics and condensed state structure of PVC, thereby simultaneously achieving optical performance with high light transmittance and ultra-low haze.

[0012] A non-migratory PVC transparent film for toys and its preparation method, comprising the following steps:

[0013] S1: First, put PVC resin powder into a high-speed mixing unit with a cold water jacket, then add high-purity liquid Ca-Zn stabilizer, phosphite and oxidized polyethylene wax, and premix under cold water protection to form a liquid phase chelate sealing layer.

[0014] S2: After completing the liquid phase sealing, pump in the plasticizer, heat up and evacuate, maintain the vacuum until no bubbles are visible breaking the film, thus completing the vacuum oil absorption and full wetting of the plasticizer.

[0015] S3: After vacuum oil removal is completed, the vacuum is broken and functional additives and high-purity SiO2-coated CaCO3 are sprinkled in sequentially. Mixing continues to make the nano-coated particles evenly embedded and form a solid-phase blocking network.

[0016] S4: After the solid particles are dispersed, the dry mixture is fed into a three-roll calendering line. The first and second rolls are at 165°C and the third roll is at 170°C to press it into a film. Then, it is cooled to below 50°C by a mirror cooling roller and wound up to complete the shaping. It is then sent to the laboratory to determine the content of heavy metals and phthalates, thus realizing the preparation of a zero-metal migration film.

[0017] Furthermore, the high-purity liquid Ca-Zn stabilizer described in S1 has a mass composition of 1.5 to 3.0 parts; it is premixed under cold water protection, and the conditions are premixing at 45 to 60°C for 2 to 5 minutes.

[0018] Further, in step S2, the plasticizer is pumped in sequentially, consisting of dioctyl phthalate (DOP), diisononyl phthalate (DINP), and dioctyl terephthalate (DOTP), with mass components of 15-30 parts, 5-15 parts, and 3-20 parts, respectively; the heating and vacuuming process is carried out at 75-85°C for 3-8 minutes; and the vacuum is maintained at a vacuum level of -0.095 to -0.08 MPa.

[0019] Furthermore, the functional additives mentioned in S3 are flame retardants, mildew inhibitors, antistatic agents, and UV stabilizers, with mass components of 3-8 parts, 0.3-1.0 parts, 0.2-0.8 parts, and 0.3-1.0 parts, respectively; the high-purity SiO2-coated CaCO3 has a mass component of 5-15 parts.

[0020] Furthermore, in step S4, the film pressing is performed at a linear speed of 15-30 m / min; the rapid cooling via the mirror cooling roller is performed under the condition of passing through a mirror cooling roller at 10-20°C for 8-15 seconds.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) Zero migration of heavy metals and high safety: Through the formation of complexes between high-purity calcium and zinc stabilizers and phosphites, and the dual effect of nano-coated fillers, all heavy metal elements in the film are locked inside the matrix.

[0023] (2) The plasticizer does not migrate and does not turn white after long-term use: The nano-SiO2 coating CaCO3 and other components introduced in the formulation of this invention significantly inhibit the tendency of plasticizer to migrate to the surface. On the one hand, the addition of nanoparticles increases the diffusion resistance of plasticizer in PVC matrix and reduces its migration rate; on the other hand, the inorganic coating layer such as silica has good compatibility with the interface of PVC and plasticizer system, and it is not easy to form plasticizer enrichment area, so there is no obvious oil separation phenomenon.

[0024] (3) High transparency and high strength, balanced performance: Although a certain amount of functional additives are added to this invention, the film still maintains excellent transparency and mechanical properties through nano-sizing and surface coating technology. At the same time, this invention constructs an invisible chelating network and coating barrier inside, which not only avoids the negative impact of the outer coating, but also gives full play to the advantages of nanofillers in strengthening and toughening, thus achieving a balance between transparency and mechanical properties. Attached Figure Description

[0025] Figure 1 This is a flowchart illustrating a non-migration-resistant PVC transparent film for toys and its preparation method according to the present invention.

[0026] Figure 2 This is a product appearance diagram of the zero-metal migration film prepared in Example 1 of the present invention.

[0027] Figure 3 This is a schematic diagram of the solid-phase blocking network structure of the zero-metal migration film in Embodiment 1 of the present invention.

[0028] Figure 4 This is a comparison chart of the experimental results of haze, light transmittance, elongation at break, and tensile strength in Experiment Example 1 of the present invention. Detailed Implementation

[0029] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0030] The technical solution designed by this invention to solve the existing problems includes the following key points:

[0031] 1. Liquid-solid dual-blocking timing coupling

[0032] Traditional PVC transparent film production typically employs a simple physical blending process, where resin, plasticizer, stabilizer, and other additives are added to a mixer all at once or in a disordered manner. This extensive mixing method cannot ensure uniform dispersion and stable bonding of the components, and the insufficient compatibility between small-molecule plasticizers and PVC resin creates potential problems for subsequent migration. This invention designs a time-coupled mixing process of liquid-phase pre-blocking and solid-phase meshing. PVC resin powder is pre-mixed with high-purity liquid calcium-zinc (Ca-Zn) stabilizer, phosphite, and oxidized polyethylene wax at a low temperature of 50°C. Utilizing the liquid-phase properties of the stabilizer and lubricant, a uniform liquid-phase chelate blocking layer is formed on the surface of the PVC resin particles. This film not only provides pre-heat stability protection but, more importantly, alters the polarity of the resin surface, creating an ideal interface for efficient and uniform wetting of the plasticizer. Subsequently, the plasticizer is added under vacuum. Vacuum conditions completely eliminate air from the material gaps, forcing the liquid plasticizer to penetrate, spread, and firmly adhere to the PVC resin surface modified by the liquid phase layer without hindrance. This achieves vacuum oil absorption and thorough wetting, constructing the first anti-migration barrier. Finally, specially coated nanoparticles are introduced. These particles are high-purity silica-coated calcium carbonate particles, formed by coating a silica shell onto the surface of precipitated calcium carbonate using the sol-gel method. The resulting silica shell is approximately 10 nm thick, with a coating rate >95%, a core impurity lead content ≤0.5 ppm, and a whiteness change ΔL within +2. The coating layers on these particles have good compatibility with the PVC matrix. After being uniformly embedded in the plasticized matrix, they do not simply fill the gaps but form a dense solid-phase blocking network, physically blocking the migration paths of small molecules through a maze effect. The entire mixing process must be strictly carried out in the sequence of liquid phase pre-blocking, vacuum oil removal, and solid phase embedding. The order cannot be reversed to ensure that the liquid phase layer is fully spread, the plasticizer is completely wetted, and the solid phase particles are uniformly embedded. Any skipping of the sequence or simultaneous feeding will lead to the failure of the blocking.

[0033] 2. Dual-speed coupling of calendering and quenching

[0034] Traditional PVC film calendering and cooling often employs natural air cooling or ordinary water bath cooling, which results in slow and uneven cooling rates. This allows the PVC molecular chains ample time to form large spherulite structures. These spherulites, with their different refractive indices compared to amorphous regions, become light scattering points, leading to increased film haze and decreased transparency. This invention achieves precise control of the film's microstructure and ultimate optimization of its optical properties through a precisely designed synergistic process of high-temperature calendering and mirror-like rapid cooling. Calendering using precisely temperature-controlled rollers ensures full plasticization and excellent flowability of the material, resulting in a film preform with uniform thickness and a smooth, flawless surface. Immediately afterward, the calendered preform undergoes a rapid cooling process for 10 seconds in direct contact with a high-precision mirror-like cooling roller, with the temperature strictly controlled at 15°C. During this process, the mirror surface ensures uniform cooling by providing a smooth contact interface, achieving uniform and efficient heat exchange with the film preform. This avoids watermarks or orange peel texture caused by uneven contact in ordinary cooling methods. At the same time, due to the extremely high cooling rate of rapid cooling, the film temperature drops rapidly from 170℃ to below 50℃ in a short time. This rapid cooling greatly inhibits the movement of PVC molecular chains, preventing them from arranging in an orderly manner to form large-sized crystals, thereby controlling the crystallinity at an extremely low level.

[0035] Example 1

[0036] A non-migratory PVC transparent film for toys and its preparation method, comprising the following steps:

[0037] S1: First, put 100 parts of PVC resin powder into a high-speed mixing unit with a cold water jacket, then add 2.0 parts of high-purity liquid Ca-Zn stabilizer, 0.3 parts of phosphite ester and 0.3 parts of oxidized polyethylene wax, and premix for 3 minutes at 50°C under cold water protection to form a liquid phase chelate sealing layer.

[0038] S2: After completing the liquid phase sealing, pump in 20 parts DOP, 10 parts DINP and 8 parts DOTP in sequence, heat to 80℃ and evacuate for 5 minutes, maintain vacuum at -0.09MPa until no bubbles are visible to break the film, thus completing the vacuum oil absorption and full wetting of the plasticizer.

[0039] S3: After vacuum oil removal, break the vacuum and sequentially sprinkle in 4 parts flame retardant, 0.5 parts mildew inhibitor, 0.4 parts antistatic agent, 0.5 parts UV stabilizer, and 10 parts high-purity SiO2 coated CaCO3. Continue mixing for 2 minutes to allow the nano-coated particles to be evenly embedded and form a solid-phase blocking network.

[0040] S4: After the solid particles are dispersed, the dry mixture is fed into a three-roll calendering line. The first and second rolls are at 165°C, the third roll is at 170°C, and the linear speed is 20m / min to press it into a 0.12mm film. Then, it is rapidly cooled to below 50°C by a 15°C mirror cooling roller for 10 seconds and then wound up to complete the shaping. The film is then sent to the laboratory to determine the content of heavy metals and phthalates, thus realizing the preparation of a zero-metal migration film.

[0041] Example 2

[0042] The preparation method is the same as in Example 1, except that:

[0043] S1: Replace 2.0 parts of high-purity liquid Ca-Zn stabilizer with 1.5 parts of high-purity liquid Ca-Zn stabilizer; replace the premixing time of 3 minutes at 50°C under cold water protection with the premixing time of 2 minutes at 45°C under cold water protection.

[0044] S2: Replace 20 parts DOP, 10 parts DINP and 8 parts DOTP with 15 parts DOP, 5 parts DINP and 3 parts DOTP; replace heating to 80℃ and evacuating for 5 minutes with heating to 75℃ and evacuating for 3 minutes; replace maintaining a vacuum of -0.09MPa with maintaining a vacuum of -0.095MPa.

[0045] S3: 4 parts flame retardant, 0.5 parts mildew inhibitor, 0.4 parts antistatic agent, 0.5 parts UV stabilizer and 10 parts high-purity SiO2 coated CaCO3 are replaced with 3 parts flame retardant, 0.3 parts mildew inhibitor, 0.2 parts antistatic agent, 0.3 parts UV stabilizer and 5 parts high-purity SiO2 coated CaCO3.

[0046] S4: Line speed 20m / min is replaced with line speed 15m / min; 10 seconds of 15℃ mirror cooling roller is replaced with 8 seconds of 10℃ mirror cooling roller;

[0047] All other steps are the same.

[0048] Example 3

[0049] The preparation method is the same as in Example 1, except that:

[0050] S1: Replace 2.0 parts of high-purity liquid Ca-Zn stabilizer with 3.0 parts of high-purity liquid Ca-Zn stabilizer; replace the premixing time of 3 minutes at 50°C under cold water protection with the premixing time of 5 minutes at 60°C under cold water protection.

[0051] S2: Replace 20 parts DOP, 10 parts DINP and 8 parts DOTP with 30 parts DOP, 15 parts DINP and 20 parts DOTP; replace heating to 80°C and evacuating for 5 minutes with heating to 85°C and evacuating for 8 minutes; replace maintaining a vacuum of -0.09MPa with maintaining a vacuum of -0.08MPa.

[0052] S3: 4 parts flame retardant, 0.5 parts mildew inhibitor, 0.4 parts antistatic agent, 0.5 parts UV stabilizer and 10 parts high-purity SiO2 coated CaCO3 are replaced with 8 parts flame retardant, 1.0 part mildew inhibitor, 0.8 parts antistatic agent, 1.0 part UV stabilizer and 15 parts high-purity SiO2 coated CaCO3.

[0053] S4: Line speed 20m / min is replaced with line speed 30m / min; 10 seconds of 15℃ mirror cooling roller is replaced with 15 seconds of 20℃ mirror cooling roller;

[0054] All other steps are the same.

[0055] Comparative Example 1

[0056] Skip steps S1 and S2, add all raw materials into the mixer at once, and mix at 80°C until homogeneous;

[0057] All other steps are the same.

[0058] Comparative Example 2

[0059] The preparation method is the same as in Example 1, except that:

[0060] S3: Replace 10 parts of high-purity SiO2-coated CaCO3 with 10 parts of ordinary active calcium carbonate;

[0061] All other steps are the same.

[0062] Comparative Example 3

[0063] The preparation method is the same as in Example 1, except that:

[0064] S4: The step of rapid cooling with mirror cooling rollers is omitted. The calendered film is slowly cooled in a conventional warm water bath at a temperature of 35~40℃.

[0065] All other steps are the same.

[0066] Experimental Example 1

[0067] The zero-metal migration films prepared in Examples 1-3 and Comparative Examples 1-3 were measured:

[0068] (1) Haze: Referring to GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics", PVC transparent film was cut into 50mm×50mm samples, ensuring the surface was clean and free of scratches, fingerprints, stains and bubbles. An integrating sphere haze meter was used for measurement. First, the total incident light flux was measured without the sample, and then the total transmitted light flux and the light flux scattered by the sample were measured after the clean sample was placed in the sample. Finally, the haze was calculated as the percentage of scattered light flux to the total transmitted light flux. This value directly characterizes the clarity of the film. The lower the value, the weaker the light scattering caused by internal defects in the material and the higher the transparency. Three samples were taken for the experiment, and the average value was taken.

[0069] (2) Transmittance: Referring to GB / T 2410-2008 "Determination of transmittance and haze of transparent plastics", PVC transparent film was cut into 50mm×50mm samples, ensuring the surface was clean and free of scratches, fingerprints, stains, and bubbles. An integrating sphere haze meter was used for measurement. First, the total incident light flux was measured without the sample as a baseline. Then, a clean, scratch-free sample of the film was placed in the sample, and the total light flux transmitted through the sample and the light flux scattered by the sample were measured respectively. Finally, the transmittance was calculated as the percentage of the total light flux transmitted through the sample to the total incident light flux. Three samples were measured, and the average value was taken.

[0070] (3) Elongation at break: Referring to GB / T 1040.3-2006 "Determination of tensile properties of plastics—Part 3: Test conditions for films and sheets", a standard dumbbell-shaped film sample was accurately marked with its original gauge length and clamped in a fixture. The sample was then stretched at a constant speed until it broke. During this process, the gauge length at the moment of breakage was accurately recorded using an elongation meter or optical tracking system. Finally, the elongation at break was calculated as a percentage of the elongation at break to the original gauge length. Three samples were tested, and the average value of the results was taken.

[0071] (4) Tensile strength: Referring to GB / T 1040.3-2006 "Determination of tensile properties of plastics—Part 3: Test conditions for films and sheets", the film was made into dumbbell-shaped strips using a standard cutter, and its width and thickness were accurately measured to calculate the initial cross-sectional area. Subsequently, the strips were vertically clamped in the upper and lower clamps of a universal testing machine and stretched at a constant speed until they broke. The testing machine simultaneously recorded the stress-strain curves throughout the process. Finally, the tensile strength of the material could be calculated by dividing the maximum load value on the curve by the initial cross-sectional area of ​​the strip. This index objectively reflects the maximum ability of the film to resist tensile failure. Three samples were tested, and the average value was taken.

[0072] (5) Heavy metals and phthalates: Refer to EN 71-3:2019+A2:2024 "Toy safety - Part 3: Migration of certain elements" and EN14372:004 "Childcare products - Feeding spoons and forks - Safety requirements and test methods", place the membrane sample in 25 mL of 50% ethanol solution, seal it, and shake it in a constant temperature water bath at 50°C for 72 hours at a shaking frequency of 100 rpm. After extraction, the sample was cooled to room temperature, filtered, and 5 mL of the filtrate was diluted to 10 mL with 2% HNO3. The metal content was determined using inductively coupled plasma mass spectrometry (ICP-MS). A concentration of all eight heavy metals <0.02 mg / kg was considered acceptable. Approximately 0.1 g of shredded film sample was accurately weighed, and a suitable organic solvent was added. The sample was completely dissolved by shaking, sonication, or heating to fully extract the target plasticizer into the solvent. The extract was injected into a gas chromatography system. Different phthalate esters were efficiently separated in the column due to their different retention characteristics. The separated components were then detected by a mass spectrometer, and qualitative and quantitative analysis was performed using characteristic ion fragments. By comparing the spectra and peak areas of the sample and standard, the specific content of each phthalate ester was accurately calculated. The results are shown in Table 2.

[0073] Table 1. Comparison of experimental results between Examples 1-3 and Comparative Examples 1-3

[0074]

[0075] Table 2. Detection report of soluble heavy metals and phthalates in Example 1.

[0076]

[0077] Note: All data in Table 2 are from product testing reports. The product testing report numbers are CANEC25009045903 and CANEC25009045905; sample name: PVC transparent film; batch numbers are A20020250411-08 and A192 20250410-01; SGS work number is GZP25-010741.

[0078] The experimental results of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1 and 2. Figure 4As shown, the zero-metal migration film prepared by this invention exhibits excellent optical performance with a haze of 1.8% and a light transmittance of 92.5%. Furthermore, it achieves an optimal balance between strength and toughness, with a tensile strength of 28.5 MPa and an elongation at break of 305%, making it the optimal implementation point. As shown in Table 2, the film prepared in Example 1 showed no detection in 19 tests for soluble heavy metals, including strictly controlled substances such as lead, cadmium, and hexavalent chromium, fully complying with the stringent standards for toys and consumer products. Phthalate esters were also not detected, ensuring the product's non-toxicity and safety from the source.

[0079] Example 2, by reducing the amount of plasticizer, decreasing the amount of filler, and using a gentler processing temperature, improved light transmittance and haze, but this change resulted in significant performance sacrifices. The reduction in total plasticizer directly weakened the material's flexibility, leading to a significant decrease in elongation at break and tensile strength; halving the filler reduced the reinforcing effect of the solid-phase blocking network. Therefore, Example 2 sacrificed mechanical properties and material toughness for a limited improvement in optical performance, and its overall balance was far inferior to Example 1. Example 3, by significantly increasing the amount of plasticizer and filler and improving processing strength, achieved excellent elongation at break and tensile strength, but the surge in total plasticizer led to an increase in phthalate content, greatly increasing environmental and migration risks; the high filler content introduced too many light scattering interfaces, resulting in increased haze and decreased light transmittance, damaging the transparent texture; at the same time, the formulation cost increased significantly, and the high-energy-consuming processing conditions placed more stringent demands on equipment and control. Therefore, the overall technical benefits were inferior to Example 1.

[0080] Comparative Examples 1-3, lacking key technologies, showed varying degrees of reduced overall performance compared to the examples. Comparative Example 1 lacked an ordered liquid-phase pre-blocking and vacuum plasticizing process, resulting in fundamental defects in the material system. All raw materials were mixed haphazardly in a single step, preventing the liquid stabilizer from forming a uniform chelated protective layer on the PVC resin surface, and the plasticizer from achieving sufficient penetration and wetting in a vacuum environment. This directly manifested as a significant increase in haze and a comprehensive deterioration of mechanical properties. Simultaneously, uneven stabilizer dispersion prevented the formation of an effective blocking network, ultimately leading to severely excessive heavy metal migration and a complete loss of the product's core safety attributes. Comparative Example 2 lacked the crucial blocking material of high-purity SiO2-coated CaCO3, using ordinary activated calcium carbonate as a substitute. These fillers, without purified and isolated surfaces, could themselves become sources of heavy metal impurities. Furthermore, ordinary fillers have poor compatibility with the PVC matrix, easily agglomerating within the matrix and forming micron-sized scattering centers, resulting in a sharp increase in haze. As the concentration of light increased to 9.5%, the film transparency decreased significantly. These aggregates also became stress defects in the matrix, significantly reducing the tensile strength and elongation at break of the material. Ultimately, due to the failure to construct a dense physical barrier layer, the migration pathways of small molecules were unobstructed, resulting in heavy metal migration far exceeding the standard, demonstrating the irreplaceable nature of the core functional material. Comparative Example 3 omitted the crucial optical shaping process of rapid cooling with mirror-finished rollers and used a conventional warm water bath for slow cooling, giving the PVC molecular chains sufficient time to arrange themselves in an orderly manner, forming a large number of spherulites with sizes reaching or exceeding the wavelength of visible light. The significant difference in refractive index between these spherulites and the amorphous regions caused severe light scattering, resulting in the film haze soaring to 20.5% and the transmittance plummeting to 75.8%. The material changed from the designed high-transparency state to an opaque frosted state, completely failing to meet the application requirements of transparent films. This comparative result strongly demonstrates that the coupling of the "calendering-rapid cooling" process is the decisive link in achieving high transparency, and the rapid cooling process is crucial for freezing the amorphous structure of PVC and inhibiting crystallization.

[0081] In summary, this invention successfully prepared a zero-metal migration PVC transparent film for toys by constructing a "liquid-solid dual-blocking" network and an innovative "calendering-rapid cooling" optical shaping process. This film combines ultimate safety, high transparency, and excellent mechanical properties, systematically solving the industry problem of difficulty in balancing migration, transparency, and performance in traditional technologies, and providing a complete material solution for high-end toy manufacturing.

Claims

1. A method for preparing a non-migratory PVC transparent film for toys, comprising mixing and calendering, characterized in that, The mixing process involves sequentially mixing different raw materials according to different stages. These stages consist of interface modification, vacuum homogenization and plasticization, and composite reinforcement, arranged sequentially. Interface modification involves premixing stabilizers and lubricants with PVC resin raw materials to form a liquid-phase sealing layer encapsulating the PVC resin. Vacuum homogenization and plasticization involves adding plasticizers under vacuum to achieve penetration and adhesion. Composite reinforcement involves filling and mixing silica-coated calcium carbonate nanoparticles, uniformly dispersing them, and embedding them into the PVC matrix to form a solid-phase sealing network. The calendering process consists of a three-roll high-temperature calendering section with differentiated temperature settings and an independent mirror cooling section. The temperature setting of the mirror cooling section is less than [temperature value missing]. The rolling temperature of the calendering section is set such that the difference is greater than 100°C. The three-roll high-temperature calendering section with differentiated temperature settings and the independent mirror cooling section work together to achieve temporal control of the microstructure of PVC. The preparation method of the liquid phase blocking layer and the solid phase blocking network is as follows: PVC resin powder is premixed with high-purity liquid calcium-zinc stabilizer, phosphite, and oxidized polyethylene wax under cold water protection to form a liquid phase chelate blocking layer. After the liquid phase blocking is completed, plasticizer is pumped in, the temperature is raised and a vacuum is drawn, and the vacuum is maintained until no bubbles are visible and the film is broken, thus completing the vacuum oil absorption and full wetting of the plasticizer. After the vacuum oil absorption is completed, the vacuum is broken and functional additives and high-purity silica-coated calcium carbonate are added in sequence, and mixing is continued to form a solid phase blocking network.

2. The method for preparing a non-migratory PVC transparent film for toys as described in claim 1, characterized in that, The plasticizer comprises a compound system of phthalate plasticizers and environmentally friendly plasticizers, wherein the phthalate plasticizers are dioctyl phthalate and diisononyl phthalate, and the environmentally friendly plasticizer is dioctyl terephthalate; the mirror cooling section refers to the immediate introduction of the calendered film preform into an independently set mirror cooling roller, the surface temperature of which is 10~20℃, and the film preform undergoes contact cooling on its surface for 5~15 seconds, reducing the temperature to below 50℃, thereby achieving shaping.

3. The method for preparing a non-migratory PVC transparent film for toys as described in claim 1, characterized in that, The high-purity liquid calcium-zinc stabilizer is a liquid stabilizer of calcium-zinc organic salts that does not contain any toxic heavy metal impurities; the premixing under cold water protection is set to premix at 45~60℃ for 2~5 minutes.

4. The method for preparing a non-migratory PVC transparent film for toys as described in claim 1, characterized in that, The pumping of plasticizers involves sequentially pumping in dioctyl phthalate, diisononyl phthalate, and dioctyl terephthalate; the heating and vacuuming process involves heating to 75-85°C and evacuating for 3-8 minutes; and the vacuum level is maintained at -0.095 to -0.08 MPa.

5. The method for preparing a non-migratory PVC transparent film for toys as described in claim 1, characterized in that, The functional additives are flame retardants, mildew inhibitors, antistatic agents, and UV stabilizers. The functional additives must be added first, followed by the high-purity silica-coated calcium carbonate. The order of addition cannot be reversed. The high-purity silica-coated calcium carbonate has a shell thickness of 10 nm, a coating rate of >95%, lead content of ≤0.5 ppm, and a whiteness of ΔL+2.

6. The method for preparing a non-migratory PVC transparent film for toys as described in claim 1, characterized in that, The steps after the liquid phase blocking layer and the solid phase blocking network are prepared are as follows: after the solid phase particles are dispersed, the dry mixture is fed into the calendering line and pressed into a film. Then, it is cooled to below 50°C by a mirror cooling roller and wound up to complete the shaping. It is then sent to the laboratory to determine the content of heavy metals and phthalates, so as to realize the preparation of zero metal migration film.

7. The method for preparing a non-migratory PVC transparent film for toys as described in claim 6, characterized in that, The film pressing process is carried out at a linear speed of 15-30 m / min; the rapid cooling process via the mirror cooling roller is set to be carried out for 8-15 seconds via a mirror cooling roller at 10-20°C.

8. A non-migration-resistant PVC transparent film for toys prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The PVC transparent film has the following components in its formula, by weight: 100 parts PVC resin, 23-65 parts plasticizer, 0.2-0.5 parts oxidized polyethylene wax, 1.5-3.0 parts high-purity liquid calcium-zinc stabilizer, 0.2-0.5 parts phosphite, 5-15 parts silica-coated calcium carbonate, and 3.8-10.8 parts functional additives.

9. The non-migratory PVC transparent film for toys as described in claim 8, characterized in that, The 23-65 parts of plasticizer specifically comprises 15-30 parts of dioctyl phthalate, 5-15 parts of diisononyl phthalate, and 3-20 parts of dioctyl terephthalate; the 3.8-10.8 parts of functional additives specifically comprises 3-8 parts of flame retardant, 0.3-1.0 parts of mildew inhibitor, 0.2-0.8 parts of antistatic agent, and 0.3-1.0 parts of UV stabilizer.

10. The non-migratory PVC transparent film for toys as described in claim 8, characterized in that, The non-migration PVC transparent film for toys has a haze ≤1.3%, light transmittance ≥91.0%, tensile strength ≥25.8MPa, and elongation at break ≥285%.

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