High-transparency bopp heat-seal film

Abstract

The application provides a high-transparency BOPP heat-seal film, which comprises a base film and high-transparency films compounded on both sides of the base film, the base film is prepared from raw materials comprising homopolymerized polypropylene, an antistatic agent, a slip agent, sorbitol and a first rare earth additive, and the high-transparency film is prepared from raw materials comprising copolymerized polypropylene, metallocene polyethylene, SEBS, modified nanometer spherical silica, an anti-fogging agent and a second rare earth additive; wherein the first rare earth additive is nanometer lanthanum oxide and yttrium-based organic salt with a mass ratio of (2-3):1, and the second rare earth additive is cerium salt, lanthanum stearate and dysprosium salt with a mass ratio of 2:(1-1.5):1. The high-transparency BOPP heat-seal film realizes an optimized balance between transparency, heat-seal performance and mechanical strength through synergistic modification of multiple components in the formula.

Description

Technical Field

[0001] The invention relates to the field of BOPP heat-sealing film production, in particular to a high-transparency BOPP heat-sealing film. Background Art

[0002] BOPP heat-sealing film refers to biaxially oriented polypropylene film, a plastic film material produced through a specific process. It is made by co-extruding polypropylene pellets into a sheet, which is then stretched in both the longitudinal and transverse directions. Due to the molecular orientation of the stretched film, this film exhibits excellent physical stability, mechanical strength, and airtightness, as well as high transparency and gloss, and is tough and wear-resistant, making it a widely used printing film.

[0003] Heat-sealing films can be directly heat-sealed to form and package food, textiles, audio-visual products, poker, and more, all of which require excellent heat-sealing properties. Currently, some BOPP heat-sealing films have a high haze, making them difficult to meet the packaging requirements of highly transparent packaging products. Therefore, a highly transparent BOPP heat-sealing film is necessary. Summary of the Invention

[0004] In view of this, the present invention aims to propose a high-transparency BOPP heat-sealing film, which achieves an optimized balance among transparency, heat-sealing performance and mechanical strength through the synergistic modification of multiple components in the formula.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A high-transmittance BOPP heat-sealing film comprises a base film and a high-transmittance film composited on both sides of the base film, wherein the base film is prepared from raw materials including homopolypropylene, an antistatic agent, a lubricant, sorbitol and a first rare earth additive, and the high-transmittance film is prepared from raw materials including copolymerized polypropylene, metallocene polyethylene, SEBS, modified nano-spherical silica, an antifogging agent and a second rare earth additive; wherein the first rare earth additive is nano-lanthanum oxide and yttrium-based organic salt in a mass ratio of (2-3):1, and the second rare earth additive is cerium salt, lanthanum stearate and dysprosium salt in a mass ratio of 2:(1-1.5):1.

[0007] Furthermore, the base film comprises, by weight, 70-80 parts of homopolypropylene, 1-3 parts of antistatic agent, 1-5 parts of lubricant, 1-5 parts of sorbitol and 0.5-0.8 parts of a first rare earth additive; the high-transmittance film comprises, by weight, 50-60 parts of copolymerized polypropylene, 5-10 parts of metallocene polyethylene, 5-8 parts of SEBS, 1-3 parts of modified nano-spherical silica, 1-3 parts of antifogging agent and 0.3-0.5 parts of a second rare earth additive; the thickness of the base film is 20-25 μm, and the thickness of the high-transmittance film is 12-15 μm.

[0008] Furthermore, the particle size of the nano-lanthanum oxide is 50-80nm, and the nano-lanthanum oxide needs to be treated with a silane coupling agent; the yttrium-based organic salt is one of yttrium laurate and yttrium acetate, and the yttrium-based organic salt and sorbitol are prepared into a yttrium-sorbitol complex through a solution coordination method.

[0009] Furthermore, the yttrium-sorbitol complex is prepared by dissolving a yttrium-based organic salt in a solvent to form a yttrium-based organic salt solution, then adding the yttrium-based organic salt solution dropwise into a sorbitol aqueous solution, and stirring at a constant temperature of 70-80° C. for 2-3 hours to obtain the complex.

[0010] Furthermore, the cerium salt is loaded on the modified nano-spherical silica by in-situ deposition. The modified nano-spherical silica is modified by hyperbranched polysiloxane. The particle size of the modified nano-spherical silica is 50-100nm. The cerium salt is one of cerium acetate and cerium nitrate.

[0011] Furthermore, the method of cerium salt loading is:

[0012] Ⅰ. Hyperbranched polysiloxane is used to modify the SiO2 surface to form an active silanol (Si-OH)-rich layer to enhance the density of cerium loading sites;

[0013] Ⅱ. Disperse the modified SiO2 in the cerium salt solution and adjust the pH to 8-9 with ammonia water;

[0014] Ⅲ. Add polyol and hydrothermally react at 70-80℃ for 12-24 hours to make Ce 3+ Oxidized to CeO2 and anchored at the silanol site;

[0015] IV. The product was washed by centrifugation and dried in vacuum at 50-60°C.

[0016] Furthermore, dysprosium salt and SEBS were mixed by solution to prepare Dy 3+ -SEBS chelate, the dysprosium salt is one of dysprosium sulfate and dysprosium nitrate.

[0017] Further, Dy 3+ -SEBS chelate preparation method is:

[0018] ⅰ, SEBS styrene block is grafted with maleic anhydride and carboxyl modified to form active carboxyl groups as Dy 3+ Coordination site;

[0019] ii. The modified SEBS was washed with acetone to remove free acid and then dried in vacuum;

[0020] iii. dissolving the modified SEBS in a toluene / tetrahydrofuran mixed solvent to prepare a solution;

[0021] iv. Add dysprosium sulfate solution to the solution prepared in step iii, controlling the pH to 6-8;

[0022] v. Stir at a constant temperature of 70-80°C for 4-6 hours, precipitate in methanol, and dry in vacuo at 50-60°C to obtain chelate particles.

[0023] Furthermore, the antistatic agent is one of PEG fatty acid ester and sorbitan fatty acid ester;

[0024] The lubricant is one of erucamide, oleamide, and stearamide;

[0025] The anti-fog agent is one of glycerol fatty acid ester and polyoxyethylene sorbitan fatty acid ester.

[0026] The present invention also provides a method for preparing the high-transparency BOPP heat-sealing film as described above, the method comprising the following steps:

[0027] 1. Weigh the following raw materials in proportion: homopolymer polypropylene, antistatic agent, lubricant, sorbitol, nano-lanthanum oxide, yttrium-based organic salt, copolymer polypropylene, metallocene polyethylene, SEBS, modified nano-spherical silica, antifogging agent, cerium salt, lanthanum stearate and dysprosium salt;

[0028] 2. Treating nano-lanthanum oxide with silane coupling agent;

[0029] 3. preparing a yttrium-sorbitol complex by a solution coordination method with an yttrium-based organic salt and sorbitol;

[0030] Fourth, cerium salt is loaded on modified nano-spherical silica by in-situ deposition to obtain nano-silica loaded cerium;

[0031] 5. Dysprosium salt and SEBS are mixed by solution to prepare Dy 3+ -SEBS chelate;

[0032] 6. Mixing homopolypropylene, antistatic agent, lubricant, yttrium-sorbitol complex and nano-lanthanum oxide and stirring evenly, and then putting them into a twin-screw extruder for melt extrusion and granulation to obtain basement membrane masterbatch;

[0033] 7. Copolymerized polypropylene, metallocene polyethylene, nano-silica loaded with cerium, anti-fog agent, lanthanum stearate and Dy 3+ -SEBS chelate is mixed and stirred evenly, and then put into a twin-screw extruder for melt extrusion and granulation to obtain high-transmittance film masterbatch;

[0034] 8. The base film masterbatch and the high-transmittance film masterbatch are co-extruded through a three-layer co-extrusion die head. After the melt sheet is cooled and formed, it is sequentially stretched longitudinally and transversely to obtain a high-transmittance BOPP heat-sealing film.

[0035] Compared with the prior art, the high-transparency BOPP heat-sealing film of the present invention has the following advantages:

[0036] (1) The high-transparency BOPP heat-sealing film of the present invention is modified with rare earth elements, wherein the first rare earth additive is nano-lanthanum oxide and yttrium-based organic salt, and the second rare earth additive is cerium salt, lanthanum stearate and dysprosium salt; sorbitol forms a complex with yttrium-based organic salt as a synergistic nucleating agent, and together with nano-lanthanum oxide, refines the size of PP spherulites, reduces haze, improves transparency, and can also synergistically improve antistatic durability and thermal stability; nano-lanthanum oxide can refine crystals, reduce light scattering, and improve transparency; the modified nano-lanthanum oxide is entangled with polypropylene chain segments and can also enhance interface bonding; the modified nano-silica has a dispersed particle size of <200nm in polyolefin, which can reduce light scattering. In addition, the cerium salt is loaded on the modified nano-silica, which can inhibit the thermal oxidation breakage of polypropylene chain segments during the heat sealing process, thereby improving thermal stability and reducing light loss; the Dy 3+ -SEBS chelates form a rare earth-elastomer synergistic network, which can improve the toughness of the heat seal layer.

[0037] (2) The high-transmittance BOPP heat-sealing film of the present invention has a light transmittance of >90%, a haze of <1.0%, a heat-sealing strength of >15N / 15mm, a continuous anti-fog time of >80 hours at 4°C, a longitudinal tensile strength of >160Mpa, and a transverse tensile strength of >250Mpa. DETAILED DESCRIPTION

[0038] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0039] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0040] Example 1

[0041] A high-transmittance BOPP heat-sealing film comprises a base film and high-transmittance films composited on both sides of the base film, wherein the base film has a thickness of 20 μm and the high-transmittance film has a thickness of 12 μm.

[0042] The base film includes 70 parts of homopolypropylene, 1 part of antistatic agent, 1 part of lubricant, 1 part of sorbitol and 0.5 parts of the first rare earth additive in parts by weight; the antistatic agent is PEG fatty acid ester, the lubricant is erucamide, and the first rare earth additive is nano-lanthanum oxide and yttrium laurate in a mass ratio of 2:1. The particle size of the nano-lanthanum oxide is 50-80nm with continuous grading, and the nano-lanthanum oxide needs to be treated with silane coupling agent KH560.

[0043] The high-transmittance film includes 50 parts of copolymerized polypropylene, 5 parts of metallocene polyethylene, 5 parts of SEBS, 1 part of modified nano-spherical silica, 1 part of anti-fogging agent and 0.3 parts of a second rare earth additive by weight; the modified nano-spherical silica is modified by hyperbranched polysiloxane, and the particle size of the modified nano-spherical silica is continuously graded from 50 to 100 nm. The second rare earth additive is cerium nitrate, lanthanum stearate and dysprosium sulfate in a mass ratio of 2:1:1, and the anti-fogging agent is glycerol fatty acid ester.

[0044] The preparation method of high-transparency BOPP heat-sealing film is as follows:

[0045] 1) Weigh the following raw materials in proportion: homopolypropylene, antistatic agent, lubricant, sorbitol, nano-lanthanum oxide, yttrium-based organic salt, copolymerized polypropylene, metallocene polyethylene, SEBS, modified nano-spherical silica, antifogging agent, cerium salt, lanthanum stearate, and dysprosium salt;

[0046] 2) treating the nano-lanthanum oxide with a silane coupling agent to obtain modified nano-lanthanum oxide;

[0047] 3) Preparation of yttrium-sorbitol complex:

[0048] Yttrium laurate is dissolved in anhydrous ethanol to form an yttrium laurate solution, sorbitol and water are prepared into a sorbitol aqueous solution, and then the yttrium laurate solution is added dropwise to the sorbitol aqueous solution at a rate of 1-2 drops / second while stirring, and then stirred at a constant temperature of 70°C for 2 hours to obtain;

[0049] 4) Cerium loading:

[0050] i) Hyperbranched polysiloxane was used to modify the SiO2 surface to form an active silanol (Si-OH)-rich layer, thereby enhancing the density of cerium loading sites;

[0051] ii) dispersing the modified SiO2 in a cerium salt aqueous solution and adjusting the pH to 8-9 with ammonia water;

[0052] iii) Then add ethylene glycol and hydrothermal reaction at 70℃ for 12 hours to make Ce 3+ Oxidized to CeO2 and anchored at the silanol site;

[0053] iv) the product was washed by centrifugation and dried under vacuum at 50°C to obtain nano-silica loaded with cerium;

[0054] 5) Preparation of Dy 3+ -SEBS Chelate:

[0055] i) SEBS styrene block is grafted with maleic anhydride and carboxylated to form active carboxyl groups as Dy 3+ coordination sites, the grafting rate is about 10%;

[0056] ii) The modified SEBS was washed with acetone to remove free acid and then dried in vacuum;

[0057] iii) dissolving the modified SEBS in a toluene / tetrahydrofuran mixed solvent to prepare a solution;

[0058] iv) adding dysprosium sulfate solution to the solution prepared in step iii) to control the pH to 6-8;

[0059] v) stirring at 70°C for 4 hours, precipitating in methanol, separating the precipitate, washing at least twice, and drying under vacuum at 50°C to obtain chelate particles;

[0060] 6) Homopolymer polypropylene, antistatic agent, lubricant, yttrium-sorbitol complex, and nano-lanthanum oxide are mixed and stirred evenly, and then fed into a twin-screw extruder for melt extrusion and granulation to obtain a base film masterbatch; the temperatures from the feeding section to the die are 145°C, 170°C, 180°C, and 170°C, respectively;

[0061] 7) Copolymerized polypropylene, metallocene polyethylene, nano-silica loaded with cerium, anti-fog agent, lanthanum stearate and Dy 3+ -SEBS chelate was mixed and stirred evenly, and then fed into a twin-screw extruder for melt extrusion and granulation to obtain high-transmittance film masterbatch; the temperature from the feeding section to the die was 130℃, 160℃, 170℃, and 160℃ in sequence;

[0062] 8) The base film masterbatch and the high-transparency film masterbatch are co-extruded through a three-layer co-extrusion die head. After the melt sheet is cooled and formed, it is sequentially stretched longitudinally and transversely to obtain a high-transparency BOPP heat-sealing film.

[0063] Example 2

[0064] A high-transmittance BOPP heat-sealing film comprises a base film and high-transmittance films composited on both sides of the base film, wherein the base film has a thickness of 23 μm and the high-transmittance film has a thickness of 14 μm.

[0065] The base film includes 75 parts of homopolypropylene, 2 parts of antistatic agent, 3 parts of lubricant, 3 parts of sorbitol and 0.7 parts of the first rare earth additive in parts by weight; the antistatic agent is sorbitan fatty acid ester, the lubricant is oleic acid amide, and the first rare earth additive is nano-lanthanum oxide and yttrium laurate in a mass ratio of 2:1. The particle size of the nano-lanthanum oxide is 50-80nm with continuous grading, and the nano-lanthanum oxide needs to be treated with silane coupling agent KH560.

[0066] The high-transmittance film includes 55 parts of copolymerized polypropylene, 8 parts of metallocene polyethylene, 7 parts of SEBS, 1.5 parts of modified nano-spherical silica, 1.5 parts of anti-fog agent and 0.4 parts of second rare earth additive in parts by weight; the modified nano-spherical silica is modified by hyperbranched polysiloxane, and the particle size of the modified nano-spherical silica is continuously graded from 50 to 100 nm. The second rare earth additive is cerium acetate, lanthanum stearate and dysprosium sulfate in a mass ratio of 2:1:1, and the anti-fog agent is glycerol fatty acid ester.

[0067] The preparation method of high-transparency BOPP heat-sealing film is as follows:

[0068] 1) Weigh the following raw materials in proportion: homopolypropylene, antistatic agent, lubricant, sorbitol, nano-lanthanum oxide, yttrium-based organic salt, copolymerized polypropylene, metallocene polyethylene, SEBS, modified nano-spherical silica, antifogging agent, cerium salt, lanthanum stearate, and dysprosium salt;

[0069] 2) treating the nano-lanthanum oxide with a silane coupling agent to obtain modified nano-lanthanum oxide;

[0070] 3) Preparation of yttrium-sorbitol complex:

[0071] Yttrium laurate is dissolved in anhydrous ethanol to form an yttrium laurate solution, sorbitol and water are prepared into a sorbitol aqueous solution, and then the yttrium laurate solution is added dropwise to the sorbitol aqueous solution at a rate of 1-2 drops / second while stirring, and then stirred at a constant temperature of 75°C for 3 hours to obtain;

[0072] 4) Cerium loading:

[0073] i) Hyperbranched polysiloxane was used to modify the SiO2 surface to form an active silanol (Si-OH)-rich layer, thereby enhancing the density of cerium loading sites;

[0074] ii) dispersing the modified SiO2 in a cerium salt aqueous solution and adjusting the pH to 8-9 with ammonia water;

[0075] iii) Then add ethylene glycol and hydrothermal reaction at 75℃ for 14 hours to make Ce 3+ Oxidized to CeO2 and anchored at the silanol site;

[0076] iv) The product is washed by centrifugation, vacuum dried at 50°C to obtain nanosilica loaded cerium;

[0077] 5) Preparation of Dy 3+ - SEBS chelate:

[0078] i) Maleic anhydride grafting is used for the styrene block of SEBS to perform carboxyl modification, forming active carboxyl groups as Dy 3+ coordination sites, and the grafting rate is about 10%;

[0079] ii) The modified SEBS is washed with acetone to remove free acid and vacuum dried;

[0080] iii) The modified SEBS is dissolved in a toluene / tetrahydrofuran mixed solvent to form a solution;

[0081] iv) Dysprosium sulfate solution is added to the solution prepared in step iii) to control pH = 6-8;

[0082] v) Stir at 75°C for 5 hours, precipitate in methanol, separate the precipitate, wash at least twice, and vacuum dry at 55°C to obtain chelate particles;

[0083] 6) After the homopolymer polypropylene, antistatic agent, slip agent, yttrium-sorbitol complex, and nanometer lanthanum oxide are uniformly mixed and stirred, they are fed into a double screw extruder for melt extrusion and granulation to obtain a base film master batch; the temperature from the feeding section to the die head is 145°C, 170°C, 180°C, and 170°C, respectively;

[0084] 7) After the copolymer polypropylene, metallocene polyethylene, nanosilica loaded cerium, anti-fog agent, lanthanum stearate, and Dy 3+ - SEBS chelate are uniformly mixed and stirred, they are fed into a double screw extruder for melt extrusion and granulation to obtain a high-transparency film master batch; the temperature from the feeding section to the die head is 130°C, 160°C, 170°C, and 160°C, respectively;

[0085] 8) The base film master batch and the high-transparency film master batch are co-extruded through a three-layer co-extrusion die head, and after the melt sheet is cooled and formed, longitudinal stretching and transverse stretching are performed in sequence to obtain a high-transparency type BOPP heat-seal film.

[0086] Example 3

[0087] A high-transparency type BOPP heat-seal film, comprising a base film and high-transparency films compounded on both sides of the base film, the thickness of the base film is 25μm, and the thickness of the high-transparency film is 15μm.

[0088] The base film includes 80 parts of homopolypropylene, 3 parts of antistatic agent, 5 parts of lubricant, 5 parts of sorbitol and 0.8 parts of the first rare earth additive in parts by weight; the antistatic agent is PEG fatty acid ester, the lubricant is erucamide, and the first rare earth additive is nano-lanthanum oxide and yttrium acetate in a mass ratio of 3:1. The particle size of the nano-lanthanum oxide is 50-80nm continuously graded, and the nano-lanthanum oxide needs to be treated with silane coupling agent KH560.

[0089] The high-transmittance film includes 60 parts of copolymerized polypropylene, 10 parts of metallocene polyethylene, 8 parts of SEBS, 3 parts of modified nano-spherical silica, 3 parts of anti-fog agent and 0.5 parts of second rare earth additive in parts by weight; the modified nano-spherical silica is modified by hyperbranched polysiloxane, and the particle size of the modified nano-spherical silica is continuously graded from 50 to 100 nm. The second rare earth additive is cerium nitrate, lanthanum stearate and dysprosium nitrate in a mass ratio of 2:1.5:1, and the anti-fog agent is polyoxyethylene sorbitan fatty acid ester.

[0090] The preparation method of high-transparency BOPP heat-sealing film is as follows:

[0091] 1) Weigh the following raw materials in proportion: homopolypropylene, antistatic agent, lubricant, sorbitol, nano-lanthanum oxide, yttrium-based organic salt, copolymerized polypropylene, metallocene polyethylene, SEBS, modified nano-spherical silica, antifogging agent, cerium salt, lanthanum stearate, and dysprosium salt;

[0092] 2) treating the nano-lanthanum oxide with a silane coupling agent to obtain modified nano-lanthanum oxide;

[0093] 3) Preparation of yttrium-sorbitol complex:

[0094] Yttrium acetate is dissolved in anhydrous ethanol to form an yttrium acetate solution, sorbitol and water are mixed to form a sorbitol aqueous solution, and the yttrium acetate solution is then added dropwise to the sorbitol aqueous solution at a rate of 1-2 drops per second while stirring, and then stirred at a constant temperature of 80°C for 2.5 hours to obtain;

[0095] 4) Cerium loading:

[0096] i) Hyperbranched polysiloxane was used to modify the SiO2 surface to form an active silanol (Si-OH)-rich layer, thereby enhancing the density of cerium loading sites;

[0097] ii) dispersing the modified SiO2 in a cerium salt aqueous solution and adjusting the pH to 8-9 with ammonia water;

[0098] iii) Then add ethylene glycol and hydrothermal reaction at 80℃ for 18 hours to make Ce 3+ Oxidized to CeO2 and anchored at the silanol site;

[0099] iv) the product was washed by centrifugation and dried under vacuum at 60°C to obtain nano-silica loaded with cerium;

[0100] 5) Preparation of Dy 3+ -SEBS Chelate:

[0101] i) SEBS styrene block is grafted with maleic anhydride and carboxylated to form active carboxyl groups as Dy 3+ coordination sites, the grafting rate is about 10%;

[0102] ii) The modified SEBS was washed with acetone to remove free acid and then dried in vacuum;

[0103] iii) dissolving the modified SEBS in a toluene / tetrahydrofuran mixed solvent to prepare a solution;

[0104] iv) adding dysprosium nitrate solution to the solution prepared in step iii) to control the pH to 6-8;

[0105] v) stirring at 80°C for 6 hours, precipitating in methanol, separating the precipitate, washing at least twice, and drying in vacuo at 60°C to obtain chelate particles;

[0106] 6) Homopolymer polypropylene, antistatic agent, lubricant, yttrium-sorbitol complex, and nano-lanthanum oxide are mixed and stirred evenly, and then fed into a twin-screw extruder for melt extrusion and granulation to obtain a base film masterbatch; the temperatures from the feeding section to the die are 145°C, 170°C, 180°C, and 170°C, respectively;

[0107] 7) Copolymerized polypropylene, metallocene polyethylene, nano-silica loaded with cerium, anti-fog agent, lanthanum stearate and Dy 3+ -SEBS chelate was mixed and stirred evenly, and then fed into a twin-screw extruder for melt extrusion and granulation to obtain high-transmittance film masterbatch; the temperature from the feeding section to the die was 130℃, 160℃, 170℃, and 160℃ in sequence;

[0108] 8) The base film masterbatch and the high-transparency film masterbatch are co-extruded through a three-layer co-extrusion die head. After the melt sheet is cooled and formed, it is sequentially stretched longitudinally and transversely to obtain a high-transparency BOPP heat-sealing film.

[0109] The performance tests were conducted on the BOPP heat-sealing films produced in Examples 1-3 and conventional commercially available BOPP heat-sealing films. The results are shown in Table 1.

[0110] Table 1 Performance test of Examples 1-3 and conventional commercial BOPP heat-sealing films

[0111]

[0112] Comparative Example 1

[0113] The difference from Example 1 is that the first rare earth additive is nano-lanthanum oxide and yttrium laurate in a mass ratio of 1:1, and the rest is the same as Example 1.

[0114] Changing the proportion of the first rare earth additive mainly affects the optical properties, with the transmittance dropping to 92%, the haze rising to 1%, and the longitudinal tensile strength decreasing to 142 MPa. It has little effect on the transverse tensile strength, which is 251 MPa. The heat seal strength is mainly determined by the metallocene polyethylene, SEBS and other components of the high-transmittance film, and is unrelated to the first rare earth ratio of the base film. The heat seal strength does not change much, at 17 N / 15 mm. The anti-fog duration is mainly determined by the anti-fog agent and nano-SiO2 adsorption of the high-transmittance film, and does not change significantly, at 82 hours. The friction coefficient depends on the migration of the base film lubricant (erucamide), and is unrelated to the rare earth ratio, and does not change significantly, at 0.18.

[0115] Comparative Example 2

[0116] The difference from Example 1 is that the first rare earth additive is nano-lanthanum oxide, and the rest is the same as Example 1.

[0117] The first rare earth additive, using only nano-lanthanum oxide, undergoes multi-dimensional changes due to the lack of yttrium laurate and the yttrium-sorbitol complex it forms with sorbitol. Transmittance decreases to 90%, haze rises to 1.5%, and mechanical properties also decline, with longitudinal tensile strength reaching 145 MPa and transverse tensile strength reaching 216 MPa. Similarly, heat seal strength, primarily determined by the high-transmittance film's metallocene polyethylene and SEBS components, shows little change, at 17 N / 15 mm. However, the base film is susceptible to slight shrinkage during heat sealing due to insufficient heat resistance. Nano-lanthanum oxide lacks long-chain organic groups and cannot synergize with lubricants, resulting in an increase in the film's coefficient of friction to 0.26. Similarly, the anti-fog duration changes minimally, at 81 hours.

[0118] Comparative Example 3

[0119] The difference from Example 1 is that the first rare earth additive is yttrium laurate, and the rest is the same as Example 1.

[0120] Using only yttrium laurate as the first rare earth additive will alter various membrane properties. Mechanical properties will significantly decline. The lack of nano-lanthanum oxide prevents physical reinforcement, significantly reducing the tensile strength and tear resistance of the base membrane. This weakens the overall mechanical stability of the membrane, making it prone to localized thinning or fracture during stretching. This leads to poor thickness uniformity and increased scrap rates. Transmittance drops to 93%, and haze increases to 1%.

[0121] Comparative Example 4

[0122] The difference from Example 1 is that yttrium laurate is not prepared into yttrium-sorbitol complex by solution coordination method, but is directly mixed with sorbitol to prepare basement membrane masterbatch. Other steps are the same as Example 1.

[0123] Direct mixing alters the dispersibility, compatibility, and interfacial interactions of yttrium laurate and sorbitol, leading to significant changes in several properties. Transparency deteriorates significantly, with transmittance dropping to 89% and haze increasing to 2.2%. Mechanical properties also decline, with longitudinal tensile strength at 140 MPa and transverse tensile strength at 227 MPa. Direct mixing can cause agglomeration of yttrium laurate and sorbitol, which can adsorb some erucamide, increasing the friction coefficient. Furthermore, this agglomeration can lead to uneven heating during heat sealing, resulting in localized overheating or incomplete fusion, reducing heat seal strength.

[0124] Comparative Example 5

[0125] The difference from Example 1 is that the second rare earth additive is cerium nitrate, lanthanum stearate and dysprosium sulfate in a mass ratio of 1:1:1, and the rest is the same as Example 1.

[0126] As the proportion of cerium nitrate decreases, the light transmittance decreases; after the proportion of cerium decreases, the nano-enhancement effect weakens, resulting in a slight decrease in tensile strength.

[0127] Comparative Example 6

[0128] The difference from Example 1 is that the second rare earth additive is cerium nitrate and lanthanum stearate in a mass ratio of 2:1, and the rest is the same as Example 1.

[0129] Removal of dysprosium sulfate, Dy 3+ The SEBS chelate complex cannot form, and the dispersion of SEBS in the matrix becomes poor, which easily leads to local aggregation, resulting in enhanced light scattering and ultimately reduced transmittance. At the same time, the uneven dispersion also leads to a decrease in mechanical properties.

[0130] Comparative Example 7

[0131] The difference from Example 1 is that the second rare earth additive is cerium nitrate and dysprosium sulfate in a mass ratio of 2:1, and the rest is the same as Example 1.

[0132] The lack of lanthanum stearate will affect the optical properties, resulting in a decrease in transmittance and an increase in haze; the lubricating effect of lanthanum stearate can promote the uniform migration of the anti-fog agent. In the absence of lanthanum stearate, the migration of the anti-fog agent is hindered, resulting in a decrease in the anti-fog effect.

[0133] Comparative Example 8

[0134] The difference from Example 1 is that the second rare earth additive is lanthanum stearate and dysprosium sulfate in a mass ratio of 1:1, and the rest is the same as Example 1.

[0135] After removing cerium nitrate, the nano-SiO2 surface loses CeO2 anchoring, and its dispersibility depends on hyperbranched polysiloxane modification, which increases the risk of agglomeration, resulting in enhanced light scattering and a significant decrease in the transparency of the film; at the same time, the tensile strength also decreases.

[0136] Comparative Example 9

[0137] The difference from Example 1 is that cerium nitrate is not loaded on nano-spherical silica, but is directly mixed to prepare a high-transmittance film masterbatch. Other steps are the same as in Example 1.

[0138] When cerium nitrate is directly mixed, many core properties will change significantly due to changes in the dispersibility, compatibility with the matrix and functional effects of cerium nitrate.

[0139] Comparative Example 10

[0140] The difference from Example 1 is that dysprosium sulfate is not used to prepare Dy 3+ -SEBS chelate, but directly mixed to prepare high-transmittance film masterbatch, and other aspects were the same as in Example 1.

[0141] Dysprosium sulfate is directly mixed into the high-transmittance film masterbatch. 3+ The dispersibility, compatibility with the matrix, and functional synergy of the adhesive are destroyed, resulting in significant changes in several core properties. These include a significant decrease in transparency and tensile strength, unstable heat sealing performance, and brittleness at the heat-sealed edge.

[0142] Comparative Example 11

[0143] The difference from Example 1 is that no metallocene polyethylene is added to the high-transmittance membrane, and the rest is the same as Example 1.

[0144] The lack of metallocene polyethylene will lead to a significant decrease in transparency, deterioration of heat sealing performance, and a decrease in the composite compatibility of the high-transmittance film and the base film; and due to the lack of metallocene polyethylene, the material is unevenly dispersed during the extrusion process, resulting in local agglomeration, which affects the mechanical properties.

[0145] Table 2 Comparison of the performance of various heat-sealing films in the comparative examples

[0146]

[0147] Tables 1 and 2 show that the heat-sealing films prepared according to Examples 1-3 of this application exhibit excellent optical and mechanical properties, with light transmittance >90%, haze <1.0%, heat seal strength >15N / 15mm, continuous anti-fog duration >80 hours at 4°C, longitudinal tensile strength >160 MPa, and transverse tensile strength >250 MPa. In contrast, the performance of the heat-sealing films in the comparative examples may be affected to varying degrees by inadequate proportions, lack of certain components, or inadequate compounding.

[0148] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-transparency BOPP heat-sealing film, characterized by: The invention comprises a base film and a high-transmittance film composited on both sides of the base film, wherein the base film is prepared from raw materials including homopolypropylene, an antistatic agent, a lubricant, sorbitol and a first rare earth additive, and the high-transmittance film is prepared from raw materials including copolymerized polypropylene, metallocene polyethylene, SEBS, modified nano-spherical silica, an anti-fogging agent and a second rare earth additive; wherein the first rare earth additive is nano-lanthanum oxide and yttrium-based organic salt in a mass ratio of (2-3):1, and the second rare earth additive is cerium salt, lanthanum stearate and dysprosium salt in a mass ratio of 2:(1-1.5):1; the yttrium-sorbitol complex is prepared by a solution coordination method with sorbitol, the cerium salt is loaded on the modified nano-spherical silica by an in-situ deposition method, and the dysprosium salt is prepared by a solution blending method with SEBS. 3+ -SEBS chelate.

2. The high-transparency BOPP heat-sealing film according to claim 1, characterized in that: The base film comprises 70-80 parts of homopolypropylene, 1-3 parts of antistatic agent, 1-5 parts of lubricant, 1-5 parts of sorbitol and 0.5-0.8 parts of the first rare earth additive in parts by weight; the high-transmittance film comprises 50-60 parts of copolymerized polypropylene, 5-10 parts of metallocene polyethylene, 5-8 parts of SEBS, 1-3 parts of modified nano-spherical silica, 1-3 parts of antifogging agent and 0.3-0.5 parts of the second rare earth additive in parts by weight; the thickness of the base film is 20-25 μm, and the thickness of the high-transmittance film is 12-15 μm.

3. The high-transparency BOPP heat-sealing film according to claim 1, characterized in that: The particle size of the nano-lanthanum oxide is 50-80nm, and the nano-lanthanum oxide needs to be treated with a silane coupling agent; the yttrium-based organic salt is one of yttrium laurate and yttrium acetate.

4. The high-transparency BOPP heat-sealing film according to claim 3, characterized in that: The preparation method of the yttrium-sorbitol complex comprises the following steps: dissolving a yttrium-based organic salt in a solvent to form a yttrium-based organic salt solution, then adding the yttrium-based organic salt solution dropwise into a sorbitol aqueous solution, and stirring at a constant temperature of 70-80° C. for 2-3 hours to obtain the complex.

5. The high-transparency BOPP heat-sealing film according to claim 1, characterized in that: The modified nano-spherical silica is modified by using hyperbranched polysiloxane. The particle size of the modified nano-spherical silica is 50-100 nm. The cerium salt is one of cerium acetate and cerium nitrate.

6. The high-transparency BOPP heat-sealing film according to claim 5, characterized in that: The method of cerium salt loading is: Ⅰ. Using hyperbranched polysiloxane to modify the SiO2 surface to form an active silanol-rich layer and enhance the density of cerium loading sites; Ⅱ. Disperse the modified SiO2 in the cerium salt solution and adjust the pH to 8-9 with ammonia water; Ⅲ. Add polyol and hydrothermally react at 70-80℃ for 12-24 hours to make Ce 3+ Oxidized to CeO2 and anchored at the silanol site; IV. The product was washed by centrifugation and dried in vacuum at 50-60°C.

7. The high-transparency BOPP heat-sealing film according to claim 1, characterized in that: Dysprosium salt is one of dysprosium sulfate and dysprosium nitrate.

8. The high-transparency BOPP heat-sealing film according to claim 7, characterized in that: Dy 3+ -SEBS chelate preparation method is: ⅰ, SEBS styrene block is grafted with maleic anhydride and carboxyl modified to form active carboxyl groups as Dy 3+ Coordination site; ii. The modified SEBS was washed with acetone to remove free acid and then dried in vacuum; iii. dissolving the modified SEBS in a toluene / tetrahydrofuran mixed solvent to prepare a solution; iv. Add dysprosium sulfate solution to the solution prepared in step iii, controlling the pH to 6-8; v. Stir at a constant temperature of 70-80°C for 4-6 hours, precipitate in methanol, and dry in vacuo at 50-60°C to obtain chelate particles.

9. The high-transparency BOPP heat-sealing film according to claim 1, characterized in that: The antistatic agent is one of PEG fatty acid ester and sorbitan fatty acid ester; The lubricant is one of erucamide, oleamide, and stearamide; The anti-fog agent is one of glycerol fatty acid ester and polyoxyethylene sorbitan fatty acid ester.

10. A method for preparing the high-transparency BOPP heat-sealing film according to any one of claims 1 to 9, characterized in that: The method comprises the following steps:

1. Weigh the following raw materials in proportion: homopolymer polypropylene, antistatic agent, lubricant, sorbitol, nano-lanthanum oxide, yttrium-based organic salt, copolymer polypropylene, metallocene polyethylene, SEBS, modified nano-spherical silica, antifogging agent, cerium salt, lanthanum stearate and dysprosium salt; 2. Treating nano-lanthanum oxide with silane coupling agent; 3. preparing a yttrium-sorbitol complex by a solution coordination method with an yttrium-based organic salt and sorbitol; Fourth, cerium salt is loaded on modified nano-spherical silica by in-situ deposition to obtain nano-silica loaded cerium; 5. Dysprosium salt and SEBS are mixed by solution to prepare Dy 3+ -SEBS chelate; 6. Mixing homopolypropylene, antistatic agent, lubricant, yttrium-sorbitol complex and nano-lanthanum oxide and stirring evenly, and then putting them into a twin-screw extruder for melt extrusion and granulation to obtain basement membrane masterbatch; 7. Copolymerized polypropylene, metallocene polyethylene, nano-silica loaded with cerium, anti-fog agent, lanthanum stearate and Dy 3+ -SEBS chelate is mixed and stirred evenly, and then put into a twin-screw extruder for melt extrusion and granulation to obtain high-transmittance film masterbatch; 8. The base film masterbatch and the high-transmittance film masterbatch are co-extruded through a three-layer co-extrusion die head. After the melt sheet is cooled and formed, it is sequentially stretched longitudinally and transversely to obtain a high-transmittance BOPP heat-sealing film.

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