Low surface roughness PET release film base film and its preparation method

Abstract

This invention discloses a low-surface-roughness PET release film base and its preparation method. The release film base comprises three layers stacked together: a core layer and two surface layers located on both sides of the core layer. The release film base is obtained by co-extrusion of the three layers using an auxiliary extrusion resin as the raw material for the two surface layers and a main extrusion resin as the raw material for the core layer. The auxiliary extrusion resin is obtained by mixing a PET masterbatch and a PET base material at a mass ratio of 1:5 to 1:15, and the main extrusion resin is pure PET base material. The release film base of this invention has low surface roughness, low haze, and excellent overall performance. In this invention, because the large-particle benzoic acid-modified nano-alumina has a refractive index very similar to that of the PET base film, it can effectively avoid the adverse visual effects caused by the difference in refractive index between the larger-diameter nanoparticles and the resin matrix, and can effectively reduce haze.

Description

Technical Field

[0001] This invention relates to the field of release materials, and in particular to a low surface roughness PET release film base film and its preparation method. Background Technology

[0002] MLCCs (Multilayer Ceramic Chip Capacitors) are among the most widely used basic electronic components, finding extensive applications in consumer electronics. The Chinese MLCC market is growing faster than the global market, with a compound annual growth rate of 21% from 2016 to 2020, indicating continuous expansion in the domestic market. MLCC production consumes a large amount of MLCC release film; the area of ​​release film used to produce a single-layer MLCC is roughly equal to the area of ​​the MLCC itself. The global market size for MLCC release film is approximately 20 billion RMB. Release film is mainly used in the casting process of MLCC production, requiring an organic release agent to be coated onto a PET polyester film to achieve the release effect. MLCCs typically require stacking 300-1000 layers of ceramic dielectric, and each layer requires the same release film. Therefore, the film needs excellent peelability and smoothness to ensure that the dielectric layers are not damaged during peeling. MLCC release film also typically has certain thickness requirements, needing to be of moderate and uniform thickness for easy peeling after the release agent is applied. Currently, MLCC release film is still largely dependent on imports. Japanese companies hold a significant overall market share of 56%, while Chinese MLCC manufacturers account for approximately 6% globally. With the rapid growth of 5G smart terminals / base stations and the increasing popularity of new energy vehicles, the localization of MLCC release film production is imperative.

[0003] Polyethylene terephthalate (PET) is one of the most important synthetic plastics today, widely used in fiber, packaging, and engineering plastics fields, and possesses excellent physicochemical properties. By controlling the crystallinity of the polymer, the basic properties and applications of PET film can be altered to a certain extent. Currently, MLCC release film base films mainly utilize inorganic fillers with small particle sizes as opening agents to prepare a polyester surface structure with low surface roughness and high flatness. However, the selection and addition method of the opening agent significantly affect the surface roughness of the MLCC release film base film. Similarly, the processing technology of PET base film provides guidance for improving the overall application performance of MLCC release film products.

[0004] A patent (CN 215903925 U) discloses a method for preparing a PET release film, which mainly involves the following steps: online coating is applied to both sides of the release film base to form a coating layer, thereby giving the polyester base film excellent roughness on both sides, facilitating subsequent production of MLCC release films. However, this process requires the configuration of online pre-coating equipment on the PET production line, and the coating liquid itself incurs certain costs. Furthermore, the coated surface is easily scratched, making it more expensive than polyester base films.

[0005] Patent CN 116120617 A discloses a release film for MLCCs and its preparation method, which mentions a method for preparing a PET film, mainly consisting of the following steps: coating both sides of a polyester base film with an organosilicon elastomer coating and a silica sol coating, respectively, to reduce the surface roughness of the MLCC release film. This process also requires online or offline coating, and therefore has a higher cost compared to polyester base films.

[0006] Patent CN 113635643 A discloses a polyester film and its preparation method, which mentions a method for preparing an MLCC release film, mainly consisting of the following steps: A PET film is prepared using an ABC three-layer structure, wherein organic and inorganic functional masterbatches are added to the outer A and C layers to improve the film surface roughness. The soft particles added in this process include organic particles such as polyvinylidene acrylate, polymethyl acrylate, polymethyl methacrylate, or nylon. When organic polymers are added as fillers to the PET melt, the soft particles generally have poor heat resistance, and may carbonize during the melting process, potentially increasing defects. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a low surface roughness PET release film base film and its preparation method, in order to address the shortcomings of the prior art.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a low surface roughness PET release film base film, which includes three layers stacked together: a core layer and two surface layers located on both sides of the core layer. The release film base film is obtained by co-extrusion of the three layers using an auxiliary extrusion resin as the raw material for the two surface layers and a main extrusion resin as the raw material for the core layer.

[0009] The auxiliary extrusion resin is obtained by mixing PET masterbatch and PET base material in a mass ratio of 1:5 to 1:15, and the main extrusion resin is pure PET base material.

[0010] Preferably, the raw materials for preparing the opening agent PET masterbatch include the following components by weight: 30-120 parts of ethylene glycol, 19-79 parts of terephthalic acid monomer, 0.1-0.4 parts of antimony trioxide, 0.1-0.4 parts of nano-silica, and 0.05-0.2 parts of modified nano-alumina.

[0011] Preferably, the raw materials for preparing the opening agent PET masterbatch include the following components by weight: 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina.

[0012] Preferably, the particle size of the nano-silica is 40nm to 200nm, and the particle size of the modified nano-alumina is 500nm to 2μm.

[0013] Preferably, the modified nano-alumina is prepared by the following method: alumina nanoparticles and benzoic acid are refluxed in toluene solvent at 90°C for 12 hours at a mass ratio of 3:1, followed by washing with ethanol and drying at 80°C to obtain modified nano-alumina.

[0014] Preferably, the opening agent PET masterbatch is prepared by the following method:

[0015] By weight, 30-120 parts of ethylene glycol, 19-79 parts of terephthalic acid monomer, 0.1-0.4 parts of antimony trioxide, 0.1-0.4 parts of nano-silica, and 0.05-0.2 parts of modified nano-alumina are added to a reactor and subjected to esterification at 230-260℃ and 150-180kPa for 1.5-5 hours. Then, polycondensation is carried out at 260-280℃ and 0.4-0.6kPa for 1.5-6 hours. The resulting polyester resin is cooled in water and cut. After removing water droplets in a vibrating screen, it is placed in a dryer and dried at 120-160℃ in a nitrogen atmosphere for 6-24 hours to obtain the opening agent PET masterbatch.

[0016] Preferably, the opening agent PET masterbatch is prepared by the following method:

[0017] By weight, 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina were added to a reactor and subjected to esterification at 255°C and 170 kPa for 2.5 hours. Then, polycondensation was carried out at 270°C and 0.567 kPa for 3 hours. The resulting polyester resin was cooled in water and cut. After removing water droplets in a vibrating screen, it was placed in a dryer and dried at 140°C in a nitrogen atmosphere for 12 hours to obtain the opening agent PET masterbatch.

[0018] Preferably, the extrusion resin is obtained by mixing PET masterbatch and PET base material at a mass ratio of 1:10.

[0019] The present invention also provides a method for preparing the low surface roughness PET release film base film as described above, comprising the following steps:

[0020] S1. Using auxiliary extrusion resin as the raw material for the two outer layers and main extrusion resin as the raw material for the core layer, the resin is melted and then co-extruded in three layers. After the molten polyester resin is extruded and cooled, it is cast into a sheet to obtain a polyester sheet before stretching.

[0021] S2. Longitudinally stretch the polyester casting;

[0022] S3. The longitudinally stretched polyester sheet is then stretched laterally.

[0023] S4. After completing the transverse stretching, heat set, then cool set, and then roll up to obtain the low surface roughness PET release film base film.

[0024] Preferably, the method for preparing the low surface roughness PET release film base film includes the following steps:

[0025] S1. Using auxiliary extrusion resin as the raw material for the two surface layers and main extrusion resin as the raw material for the core layer, the resin is melted at 280℃ and then co-extruded in three layers. The mass ratio of extrusion amount of surface layer: core layer: surface layer is controlled to be 1:8:1. After the molten polyester resin is extruded and cooled, it is cast on a cooling roller at 50℃ to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 120-480μm.

[0026] S2. Preheat the polyester casting at 70°C, and then stretch it longitudinally at 400°C at a speed of 90 m / min, controlling the longitudinal stretching ratio to be 1-4 times.

[0027] S3. The longitudinally stretched polyester sheet is preheated at 120°C and then transversely stretched at 160°C, with the transverse stretching ratio controlled at 2-6 times.

[0028] S4. After completing the transverse stretching, heat set at 240°C, then cool set at 70°C, and then roll up to obtain the low surface roughness PET release film base film.

[0029] The beneficial effects of this invention are:

[0030] This invention provides a low surface roughness PET release film base film and its preparation method. The release film base film of this invention has low surface roughness, low haze, and excellent overall performance.

[0031] In this invention, since the large-particle benzoic acid modified nano-alumina has a refractive index very similar to that of PET base film, it can effectively avoid the adverse visual effects caused by the difference in refractive index between the larger-diameter nanoparticles and the resin matrix, and can effectively reduce haze.

[0032] In this invention, benzoic acid is used to modify nano-alumina, which can improve the dispersibility of the particles. When combined with nano-silica particles of different particle sizes, PET opening agent masterbatch with low surface roughness and excellent friction and winding properties can be obtained. At the same time, by adjusting different stretch ratios to control the crystallinity of the film (a larger stretch ratio corresponds to a higher polymer crystallinity), the tensile strength of the film and the adhesion effect between the film surface and the roller can be improved, and the generation of scratches can be reduced. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the low surface roughness PET release film base film of the present invention.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1—Core layer; 2—Surface layer. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0037] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available. For examples where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments whose manufacturers are not specified, they are all commercially available products.

[0039] Reference Figure 1 The present invention provides a low surface roughness PET release film base film, which includes three layers stacked together: a core 1 and two surface layers 2 located on both sides of the core layer 1. The release film base film is obtained by co-extrusion of the three layers using an auxiliary extrusion resin as the raw material for the two surface layers 2 and a main extrusion resin as the raw material for the core layer 1.

[0040] The auxiliary extrusion resin is obtained by mixing the opening agent PET masterbatch and PET base material at a mass ratio of 1:5 to 1:15. The main extrusion resin is pure PET base material. If the PET masterbatch content is low, it has no anti-blocking properties. If the PET masterbatch content is too high, the appearance is poor.

[0041] The PET base material can be selected from one or more of the following: FG600 base material type film-grade polyester chips provided by Sinopec Yizheng Chemical Fiber Co., Ltd.; CZ-5011 ultra-bright polyester chips provided by Jiangsu Sanfangxiang Group Co., Ltd.; and TN8065S film-grade polyester chips provided by Teijin Co., Ltd. of Japan.

[0042] In a preferred embodiment, the raw materials for preparing the opening agent PET masterbatch include the following components by weight: 30-120 parts of ethylene glycol, 19-79 parts of terephthalic acid monomer, 0.1-0.4 parts of antimony trioxide, 0.1-0.4 parts of nano-silica, and 0.05-0.2 parts of modified nano-alumina.

[0043] More preferably, the raw materials for preparing the opening agent PET masterbatch include the following components by weight: 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina.

[0044] In a preferred embodiment, the particle size of the nano-silica is 40nm to 200nm, and the particle size of the modified nano-alumina is 500nm to 2μm.

[0045] In a preferred embodiment, the modified nano-alumina is prepared by the following method: alumina nanoparticles and benzoic acid are refluxed in toluene solvent at 90°C for 12 hours at a mass ratio of 3:1, followed by washing with ethanol and drying at 80°C to obtain the modified nano-alumina.

[0046] In a preferred embodiment, the opening agent PET masterbatch is prepared by the following method:

[0047] By weight, 30-120 parts of ethylene glycol, 19-79 parts of terephthalic acid monomer, 0.1-0.4 parts of antimony trioxide, 0.1-0.4 parts of nano-silica, and 0.05-0.2 parts of modified nano-alumina are added to a reactor and subjected to esterification at 230-260℃ and 150-180kPa for 1.5-5 hours. Then, polycondensation is carried out at 260-280℃ and 0.4-0.6kPa for 1.5-6 hours. The resulting polyester resin is cooled in water and then cut. After removing water droplets in a vibrating screen, it is placed in a dryer and dried at 120-160℃ in a nitrogen atmosphere for 6-24 hours to obtain the opening agent PET masterbatch.

[0048] In a preferred embodiment, the method for preparing the low surface roughness PET release film base film includes the following steps:

[0049] S1. Using auxiliary extrusion resin as the raw material for the two surface layers and main extrusion resin as the raw material for the core layer, the resin is melted at 280℃ and then co-extruded in three layers. The mass ratio of extrusion amount of surface layer: core layer: surface layer is controlled to be 1:8:1. After the molten polyester resin is extruded and cooled, it is cast on a cooling roller at 50℃ to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 120-480μm.

[0050] S2. Preheat the polyester casting at 70°C, and then stretch it longitudinally at 400°C at a speed of 90m / min. Control the longitudinal stretching ratio to be 1-4 times. If the ratio is too high, the film is easy to break.

[0051] S3. The longitudinally stretched polyester sheet is preheated at 120°C and then transversely stretched at 160°C. The transverse stretching ratio is controlled to be 2-6 times to improve the mechanical strength in this direction.

[0052] S4. After completing the transverse stretching, heat set at 240℃, then cool and set at 70℃, and then roll up to obtain a low surface roughness PET release film base film.

[0053] In this invention, benzoic acid-modified nano-alumina and nano-silica, with a refractive index similar to that of the PET substrate, are used as opening agents and fillers. The refractive index of the modified nano-alumina (1.76) is similar to that of the polyester film, and it exhibits good compatibility and high heat resistance. The large-particle size of the nano-alumina used as the opening agent has a low probability of being visually identifiable during light irradiation. Simultaneously, the nano-silica has a relatively regular surface and a particle size only one-fifteenth to one-fifth the size of the modified nano-alumina particles. Using small-particle-size nano-silica improves dispersibility. Even after processing, despite low surface roughness, it maintains excellent frictional properties, resulting in excellent film winding characteristics. Furthermore, the temperature resistance of the MLCC release film base film can be effectively improved by precisely controlling the stretching process conditions.

[0054] The above is the general concept of the present invention. Based on this, detailed embodiments and comparative examples are provided below to further illustrate the present invention.

[0055] The sources of the main raw materials involved in the following examples and comparative examples are as follows:

[0056] The PET base material was FG600 type film-grade polyester chips provided by Sinopec Yizheng Chemical Fiber Co., Ltd. Ethylene glycol was purchased from Shanghai Xiangheyi Chemical Technology Co., Ltd., terephthalic acid from Hengli Petrochemical, and antimony trioxide from Wuxi Zhengmao Chemical Co., Ltd. Other products without specified manufacturers were all commercially available conventional products.

[0057] Example 1

[0058] A low surface roughness PET release film base film, the preparation method of which includes the following steps:

[0059] I. Preparation of modified nano-alumina:

[0060] Modified nano-alumina was obtained by refluxing alumina nanoparticles and benzoic acid in toluene solvent at a mass ratio of 3:1 at 90°C for 12 hours, followed by washing with ethanol and drying at 80°C.

[0061] II. Preparation of PET masterbatch for opening agents:

[0062] By weight, 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina were added to a reactor and subjected to esterification at 255°C and 170 kPa for 2.5 hours. Then, polycondensation was carried out at 270°C and 0.567 kPa for 3 hours. The resulting polyester resin was cooled in water and cut. After removing water droplets in a vibrating screen, it was put into a dryer and dried at 140°C in a nitrogen atmosphere for 12 hours to obtain the opening agent PET masterbatch.

[0063] III. Preparation of Release Film Base Film:

[0064] S1. The PET masterbatch and PET base material are mixed at a mass ratio of 1:10 to obtain the auxiliary extrusion resin. The auxiliary extrusion resin is used as the raw material for the two surface layers and the main extrusion resin is used as the raw material for the core layer. After melting at 280°C, three-layer co-extrusion is carried out. The mass ratio of the extrusion amount of the surface layer: core layer: surface layer is controlled to be 1:8:1. After precise metering by a metering pump, the molten polyester resin is extruded from the lip die and cast on a cooling roller at 50°C to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 480μm.

[0065] S2. The polyester casting is preheated at 70°C and then longitudinally stretched in an infrared heating zone at 400°C at a speed of 90 m / min. The longitudinal stretching ratio is controlled to be 4 times, and the film thickness after longitudinal stretching is about 120 μm.

[0066] S3. The longitudinally stretched polyester film is preheated at 120°C and then transversely stretched at 160°C. The transverse stretching ratio is controlled to be 4 times, and the film thickness after transverse stretching is 30μm.

[0067] S4. After completing the transverse stretching, heat set at 240℃, then cool and set at 70℃, and then roll up to obtain a low surface roughness PET release film base film.

[0068] Example 2

[0069] A low surface roughness PET release film base film, the preparation method of which includes the following steps:

[0070] I. Preparation of modified nano-alumina:

[0071] Modified nano-alumina was obtained by refluxing alumina nanoparticles and benzoic acid in toluene solvent at a mass ratio of 3:1 at 90°C for 12 hours, followed by washing with ethanol and drying at 80°C.

[0072] II. Preparation of PET masterbatch for opening agents:

[0073] By weight, 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina were added to a reactor and subjected to esterification at 255°C and 170 kPa for 2.5 hours. Then, polycondensation was carried out at 270°C and 0.567 kPa for 3 hours. The resulting polyester resin was cooled in water and cut. After removing water droplets in a vibrating screen, it was put into a dryer and dried at 140°C in a nitrogen atmosphere for 12 hours to obtain the opening agent PET masterbatch.

[0074] III. Preparation of Release Film Base Film:

[0075] S1. The PET masterbatch and PET base material are mixed at a mass ratio of 1:10 to obtain the auxiliary extrusion resin. The auxiliary extrusion resin is used as the raw material for the two surface layers and the main extrusion resin is used as the raw material for the core layer. After melting at 280°C, three-layer co-extrusion is carried out. The mass ratio of the extrusion amount of the surface layer: core layer: surface layer is controlled to be 1:8:1. After precise metering by a metering pump, the molten polyester resin is extruded from the lip die and cast on a cooling roller at 50°C to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 240μm.

[0076] S2. The polyester casting is preheated at 70°C and then longitudinally stretched in an infrared heating zone at 400°C at a speed of 90 m / min. The longitudinal stretching ratio is controlled to be 2 times, and the film thickness after longitudinal stretching is about 120 μm.

[0077] S3. The longitudinally stretched polyester film is preheated at 120°C and then transversely stretched at 160°C. The transverse stretching ratio is controlled to be 4 times, and the film thickness after transverse stretching is 30μm.

[0078] S4. After completing the transverse stretching, heat set at 240℃, then cool and set at 70℃, and then roll up to obtain a low surface roughness PET release film base film.

[0079] Example 3

[0080] A low surface roughness PET release film base film, the preparation method of which includes the following steps:

[0081] I. Preparation of modified nano-alumina:

[0082] Modified nano-alumina was obtained by refluxing alumina nanoparticles and benzoic acid in toluene solvent at a mass ratio of 3:1 at 90°C for 12 hours, followed by washing with ethanol and drying at 80°C.

[0083] II. Preparation of PET masterbatch for opening agents:

[0084] By weight, 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina were added to a reactor and subjected to esterification at 255°C and 170 kPa for 2.5 hours. Then, polycondensation was carried out at 270°C and 0.567 kPa for 3 hours. The resulting polyester resin was cooled in water and cut. After removing water droplets in a vibrating screen, it was put into a dryer and dried at 140°C in a nitrogen atmosphere for 12 hours to obtain the opening agent PET masterbatch.

[0085] III. Preparation of Release Film Base Film:

[0086] S1. The PET masterbatch and PET base material are mixed at a mass ratio of 1:10 to obtain the auxiliary extrusion resin. The auxiliary extrusion resin is used as the raw material for the two surface layers and the main extrusion resin is used as the raw material for the core layer. After melting at 280°C, three-layer co-extrusion is carried out. The mass ratio of the extrusion amount of the surface layer: core layer: surface layer is controlled to be 1:8:1. After precise metering by a metering pump, the molten polyester resin is extruded from the lip die and cast on a cooling roller at 50°C to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 360μm.

[0087] S2. The polyester casting is preheated at 70°C and then longitudinally stretched in an infrared heating zone at 400°C at a speed of 90 m / min. The longitudinal stretching ratio is controlled to be 3 times, and the film thickness after longitudinal stretching is about 120 μm.

[0088] S3. The longitudinally stretched polyester film is preheated at 120°C and then transversely stretched at 160°C. The transverse stretching ratio is controlled to be 4 times, and the film thickness after transverse stretching is 30μm.

[0089] S4. After completing the transverse stretching, heat set at 240℃, then cool and set at 70℃, and then roll up to obtain a low surface roughness PET release film base film.

[0090] Example 4

[0091] A low surface roughness PET release film base film, the preparation method of which includes the following steps:

[0092] I. Preparation of modified nano-alumina:

[0093] Modified nano-alumina was obtained by refluxing alumina nanoparticles and benzoic acid in toluene solvent at a mass ratio of 3:1 at 90°C for 12 hours, followed by washing with ethanol and drying at 80°C.

[0094] II. Preparation of PET masterbatch for opening agents:

[0095] By weight, 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina were added to a reactor and subjected to esterification at 255°C and 170 kPa for 2.5 hours. Then, polycondensation was carried out at 270°C and 0.567 kPa for 3 hours. The resulting polyester resin was cooled in water and cut. After removing water droplets in a vibrating screen, it was put into a dryer and dried at 140°C in a nitrogen atmosphere for 12 hours to obtain the opening agent PET masterbatch.

[0096] III. Preparation of Release Film Base Film:

[0097] S1. The PET masterbatch and PET base material are mixed at a mass ratio of 1:10 to obtain the auxiliary extrusion resin. The auxiliary extrusion resin is used as the raw material for the two surface layers and the main extrusion resin is used as the raw material for the core layer. After melting at 280°C, three-layer co-extrusion is carried out. The mass ratio of the extrusion amount of the surface layer: core layer: surface layer is controlled to be 1:8:1. After precise metering by a metering pump, the molten polyester resin is extruded from the lip die and cast on a cooling roller at 50°C to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 225μm.

[0098] S2. The polyester casting is preheated at 70°C and then longitudinally stretched in an infrared heating zone at 400°C at a speed of 90 m / min. The longitudinal stretching ratio is controlled to be 3 times, and the film thickness after longitudinal stretching is about 75 μm.

[0099] S3. The longitudinally stretched polyester film is preheated at 120°C and then transversely stretched at 160°C, with the transverse stretching ratio controlled at 2.5 times, and the film thickness after transverse stretching is 30μm.

[0100] S4. After completing the transverse stretching, heat set at 240℃, then cool and set at 70℃, and then roll up to obtain a low surface roughness PET release film base film.

[0101] Example 5

[0102] A low surface roughness PET release film base film, the preparation method of which includes the following steps:

[0103] I. Preparation of modified nano-alumina:

[0104] Modified nano-alumina was obtained by refluxing alumina nanoparticles and benzoic acid in toluene solvent at a mass ratio of 3:1 at 90°C for 12 hours, followed by washing with ethanol and drying at 80°C.

[0105] II. Preparation of PET masterbatch for opening agents:

[0106] By weight, 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina were added to a reactor and subjected to esterification at 255°C and 170 kPa for 2.5 hours. Then, polycondensation was carried out at 270°C and 0.567 kPa for 3 hours. The resulting polyester resin was cooled in water and cut. After removing water droplets in a vibrating screen, it was put into a dryer and dried at 140°C in a nitrogen atmosphere for 12 hours to obtain the opening agent PET masterbatch.

[0107] III. Preparation of Release Film Base Film:

[0108] S1. The PET masterbatch and PET base material are mixed at a mass ratio of 1:10 to obtain the auxiliary extrusion resin. The auxiliary extrusion resin is used as the raw material for the two surface layers and the main extrusion resin is used as the raw material for the core layer. After melting at 280°C, three-layer co-extrusion is carried out. The mass ratio of the extrusion amount of the surface layer: core layer: surface layer is controlled to be 1:8:1. After precise metering by a metering pump, the molten polyester resin is extruded from the lip die and cast on a cooling roller at 50°C to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 180μm.

[0109] S2. The polyester casting is preheated at 70°C and then longitudinally stretched in an infrared heating zone at 400°C at a speed of 90 m / min. The longitudinal stretching ratio is controlled at 1.5 times, and the film thickness after longitudinal stretching is about 120 μm.

[0110] S3. The longitudinally stretched polyester film is preheated at 120°C and then transversely stretched at 160°C. The transverse stretching ratio is controlled to be 4 times, and the film thickness after transverse stretching is 30μm.

[0111] S4. After completing the transverse stretching, heat set at 240℃, then cool and set at 70℃, and then roll up to obtain a low surface roughness PET release film base film.

[0112] Example 6

[0113] A low surface roughness PET release film base film, the preparation method of which includes the following steps:

[0114] I. Preparation of modified nano-alumina:

[0115] Modified nano-alumina was obtained by refluxing alumina nanoparticles and benzoic acid in toluene solvent at a mass ratio of 3:1 at 90°C for 12 hours, followed by washing with ethanol and drying at 80°C.

[0116] II. Preparation of PET masterbatch for opening agents:

[0117] By weight, 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina were added to a reactor and subjected to esterification at 255°C and 170 kPa for 2.5 hours. Then, polycondensation was carried out at 270°C and 0.567 kPa for 3 hours. The resulting polyester resin was cooled in water and cut. After removing water droplets in a vibrating screen, it was put into a dryer and dried at 140°C in a nitrogen atmosphere for 12 hours to obtain the opening agent PET masterbatch.

[0118] III. Preparation of Release Film Base Film:

[0119] S1. The PET masterbatch and PET base material are mixed at a mass ratio of 1:10 to obtain the auxiliary extrusion resin. The auxiliary extrusion resin is used as the raw material for the two surface layers and the main extrusion resin is used as the raw material for the core layer. After melting at 280°C, three-layer co-extrusion is carried out. The mass ratio of the extrusion amount of the surface layer: core layer: surface layer is controlled to be 1:8:1. After precise metering by a metering pump, the molten polyester resin is extruded from the lip die and cast on a cooling roller at 50°C to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 120μm.

[0120] S2. The polyester casting is preheated at 70°C and then longitudinally stretched in an infrared heating zone at 400°C at a speed of 90 m / min. The longitudinal stretching ratio is controlled to be 1, and the film thickness after longitudinal stretching is about 120 μm.

[0121] S3. The longitudinally stretched polyester film is preheated at 120°C and then transversely stretched at 160°C. The transverse stretching ratio is controlled to be 4 times, and the film thickness after transverse stretching is 30μm.

[0122] S4. After completing the transverse stretching, heat set at 240℃, then cool and set at 70℃, and then roll up to obtain a low surface roughness PET release film base film.

[0123] Comparative Example 1

[0124] A low surface roughness PET release film base film, the preparation method of which includes the following steps:

[0125] I. Preparation of PET masterbatch for opening agent:

[0126] By weight, 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, and 0.2 parts of nano-silica were added to a reactor and subjected to esterification reaction at 255℃ and 170kPa for 2.5 hours. Then, polycondensation reaction was carried out at 270℃ and 0.567kPa for 3 hours. The resulting polyester resin was cooled in water and cut. After removing water droplets in a vibrating screen, it was put into a dryer and dried at 140℃ in a nitrogen atmosphere for 12 hours to obtain PET masterbatch for opening agent.

[0127] III. Preparation of Release Film Base Film:

[0128] S1. The PET masterbatch and PET base material are mixed at a mass ratio of 1:10 to obtain the auxiliary extrusion resin. The auxiliary extrusion resin is used as the raw material for the two surface layers and the main extrusion resin is used as the raw material for the core layer. After melting at 280°C, three-layer co-extrusion is carried out. The mass ratio of the extrusion amount of the surface layer: core layer: surface layer is controlled to be 1:8:1. After precise metering by a metering pump, the molten polyester resin is extruded from the lip die and cast on a cooling roller at 50°C to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 480μm.

[0129] S2. The polyester casting is preheated at 70°C and then longitudinally stretched in an infrared heating zone at 400°C at a speed of 90 m / min. The longitudinal stretching ratio is controlled to be 4 times, and the film thickness after longitudinal stretching is about 120 μm.

[0130] S3. The longitudinally stretched polyester film is preheated at 120°C and then transversely stretched at 160°C. The transverse stretching ratio is controlled to be 4 times, and the film thickness after transverse stretching is 30μm.

[0131] S4. After completing the transverse stretching, heat set at 240℃, then cool and set at 70℃, and then roll up to obtain a low surface roughness PET release film base film.

[0132] Comparative Example 2

[0133] A low surface roughness PET release film base film, the preparation method of which includes the following steps:

[0134] I. Preparation of PET masterbatch for opening agent:

[0135] By weight, 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of nano-alumina were added to a reactor and subjected to esterification at 255°C and 170 kPa for 2.5 hours. Then, polycondensation was carried out at 270°C and 0.567 kPa for 3 hours. The resulting polyester resin was cooled in water and cut. After removing water droplets in a vibrating screen, it was put into a dryer and dried at 140°C in a nitrogen atmosphere for 12 hours to obtain the opening agent PET masterbatch.

[0136] III. Preparation of Release Film Base Film:

[0137] S1. The PET masterbatch and PET base material are mixed at a mass ratio of 1:10 to obtain the auxiliary extrusion resin. The auxiliary extrusion resin is used as the raw material for the two surface layers and the main extrusion resin is used as the raw material for the core layer. After melting at 280°C, three-layer co-extrusion is carried out. The mass ratio of the extrusion amount of the surface layer: core layer: surface layer is controlled to be 1:8:1. After precise metering by a metering pump, the molten polyester resin is extruded from the lip die and cast on a cooling roller at 50°C to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 480μm.

[0138] S2. The polyester casting is preheated at 70°C and then longitudinally stretched in an infrared heating zone at 400°C at a speed of 90 m / min. The longitudinal stretching ratio is controlled to be 4 times, and the film thickness after longitudinal stretching is about 120 μm.

[0139] S3. The longitudinally stretched polyester film is preheated at 120°C and then transversely stretched at 160°C. The transverse stretching ratio is controlled to be 4 times, and the film thickness after transverse stretching is 30μm.

[0140] S4. After completing the transverse stretching, heat set at 240℃, then cool and set at 70℃, and then roll up to obtain a low surface roughness PET release film base film.

[0141] The release membrane base films prepared in Examples 1-6 and Comparative Examples 1-2 were subjected to relevant performance tests, and the test results are shown in Table 1 below:

[0142] Table 1

[0143]

[0144] In the table:

[0145] 1. Surface roughness is tested according to the international standard ISO468-1982 using an Enkey VR-6000 3D profile measuring instrument.

[0146] 2. Crystallinity was tested using Mettler Toledo's STAR thermal analysis system.

[0147] 3. Transmittance and haze were tested using a Sanenshi haze and transmittance meter, model: YS6002-M benchtop transmittance and color haze meter, according to the method specified in ASTM D1003.

[0148] 4. The elongation at break was tested using a SYSTESTER tensile strength / elongation at break tester.

[0149] 5. Processing stability assessment: The film surfaces prepared in the examples and comparative examples were tested (hard coating and winding), collected in A4 size, and the number of cavitation cells in the A4 was counted using a fluorescent reflective light source. The evaluation criteria in this case are as follows.

[0150] ◎: Very good (0 or fewer) / A4

[0151] △: Normally 1 to 5 per A4

[0152] ×: 6 or more missing / A4

[0153] 6. Appearance: Cut a piece of finished polyester film, 1 meter wide and 1 meter long, and observe its appearance using a strong flashlight. If there are no scratches / abrasions, mark “◎”; if a very slight scratch / abrasion is faintly visible but uncertain, mark “○”; if obvious scratches / abrasions are visible, n (number) ≤ 5, mark “△”; if obvious scratches / abrasions are visible across the entire surface, mark “×”.

[0154] According to the test results in Table 1, the release film base films prepared in Examples 1-6 have low surface roughness, low haze, and excellent overall performance.

[0155] Unlike Example 1, the PET masterbatch for opening agent in Comparative Example 1 did not contain modified nano-alumina, while the PET masterbatch for opening agent in Comparative Example 2 used unmodified nano-alumina. Based on the test results of Comparative Examples 1, 2, and 1, the release film base film prepared in Example 1 shows significant advantages in transmittance and haze performance compared to the comparative examples. In Example 1, because the modified nano-alumina particles with relatively large particle sizes are closer to the refractive index of the PET substrate, the visual effect of different refractive index interfaces is less likely to appear. Because benzoic acid was used to modify the nano-alumina in the examples, the dispersibility of the particles was improved, and when combined with nano-silica particles of different particle sizes, a PET masterbatch with low surface roughness and excellent friction and winding properties could be obtained. Simultaneously, by adjusting different stretch ratios to control the film crystallinity (a larger stretch ratio corresponds to higher polymer crystallinity), the tensile strength of the film and the adhesion effect between the film surface and the roller can be improved, reducing scratches.

[0156] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A low surface roughness PET release film base film, characterized in that, The release film base film comprises three layers stacked together: a core layer and two surface layers located on both sides of the core layer. The release film base film is obtained by co-extrusion of the three layers using an auxiliary extrusion resin as the raw material for the two surface layers and a primary extrusion resin as the raw material for the core layer. The auxiliary extrusion resin is obtained by mixing PET masterbatch and PET base material in a mass ratio of 1:5 to 1:15, and the main extrusion resin is pure PET base material. The raw materials for preparing the opening agent PET masterbatch include the following components by weight: 30-120 parts of ethylene glycol, 19-79 parts of terephthalic acid monomer, 0.1-0.4 parts of antimony trioxide, 0.1-0.4 parts of nano-silica, and 0.05-0.2 parts of modified nano-alumina. The particle size of the nano-silica is 40nm~200nm, and the particle size of the modified nano-alumina is 500nm~2μm; The modified nano-alumina was prepared by the following method: alumina nanoparticles and benzoic acid were refluxed in toluene solvent at 90°C for 12 hours at a mass ratio of 3:1, and then washed with ethanol and dried at 80°C to obtain modified nano-alumina.

2. The low surface roughness PET release film base film according to claim 1, characterized in that, The raw materials for preparing the opening agent PET masterbatch include the following components by weight: 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina.

3. The low surface roughness PET release film base film according to claim 1, characterized in that, The opening agent PET masterbatch is prepared by the following method: By weight, 30-120 parts of ethylene glycol, 19-79 parts of terephthalic acid monomer, 0.1-0.4 parts of antimony trioxide, 0.1-0.4 parts of nano-silica, and 0.05-0.2 parts of modified nano-alumina are added to a reactor and subjected to esterification at 230-260℃ and 150-180kPa for 1.5-5 hours. Then, polycondensation is carried out at 260-280℃ and 0.4-0.6kPa for 1.5-6 hours. The resulting polyester resin is cooled in water and cut. After removing water droplets in a vibrating screen, it is placed in a dryer and dried at 120-160℃ in a nitrogen atmosphere for 6-24 hours to obtain the opening agent PET masterbatch.

4. The low surface roughness PET release film base film according to claim 3, characterized in that, The opening agent PET masterbatch is prepared by the following method: By weight, 60 parts of ethylene glycol, 39.5 parts of terephthalic acid monomer, 0.2 parts of antimony trioxide catalyst, 0.2 parts of nano-silica, and 0.1 parts of modified nano-alumina were added to a reactor and subjected to esterification at 255°C and 170 kPa for 2.5 hours. Then, polycondensation was carried out at 270°C and 0.567 kPa for 3 hours. The resulting polyester resin was cooled in water and cut. After removing water droplets in a vibrating screen, it was placed in a dryer and dried at 140°C in a nitrogen atmosphere for 12 hours to obtain the opening agent PET masterbatch.

5. The low surface roughness PET release film base film according to claim 1, characterized in that, The extrusion resin is obtained by mixing PET masterbatch and PET base material at a mass ratio of 1:

10.

6. A method for preparing a low surface roughness PET release film base film as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Using auxiliary extrusion resin as the raw material for the two outer layers and main extrusion resin as the raw material for the core layer, the resin is melted and then co-extruded in three layers. After the molten polyester resin is extruded and cooled, it is cast into a sheet to obtain a polyester sheet before stretching. S2. Longitudinally stretch the polyester casting; S3. The longitudinally stretched polyester sheet is then stretched laterally. S4. After completing the transverse stretching, heat set, then cool set, and then roll up to obtain the low surface roughness PET release film base film.

7. The method for preparing a low surface roughness PET release film base film according to claim 6, characterized in that, Includes the following steps: S1. Using auxiliary extrusion resin as the raw material for the two surface layers and main extrusion resin as the raw material for the core layer, the resin is melted at 280℃ and then co-extruded in three layers. The mass ratio of extrusion amount of surface layer: core layer: surface layer is controlled to be 1:8:

1. After the molten polyester resin is extruded and cooled, it is cast on a cooling roller at 50℃ to obtain a polyester casting sheet before stretching. The thickness of the casting sheet is controlled to be 120-480μm. S2. Preheat the polyester casting at 70°C, and then stretch it longitudinally at 400°C at a speed of 90 m / min, controlling the longitudinal stretching ratio to be 1-4 times. S3. The longitudinally stretched polyester sheet is preheated at 120°C and then transversely stretched at 160°C, with the transverse stretching ratio controlled at 2-6 times. S4. After completing the transverse stretching, heat set at 240°C, then cool set at 70°C, and then roll up to obtain the low surface roughness PET release film base film.

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