Low-light-transmittance white polyester film and preparation system thereof

Abstract

The utility model discloses a low-transmittance white polyester film and a preparation system thereof, and the film is of a three-layer gradient composite structure and comprises a functional surface layer A, a functional surface layer B and a functional surface layer C, c, an interface transition layer; b layer main light blocking layer; wherein the layer A, the layer C and the layer B are sequentially stacked, the total thickness of the film is 19-75 microns, and the light transmittance is 12%-20%. The utility model further provides a preparation system for the low-light-transmittance white polyester film. The low-transmittance white polyester film disclosed by the utility model adopts a three-layer gradient composite structure, and the layer A directly faces the external environment; and the B layer serves as a light-blocking main body. And the C layer is used as a transition layer to match thermal expansion coefficients of the A / B layers and enhance the stability of the whole structure. Besides, the preparation system provided by the utility model can be used for continuously producing the thin film in batches, and overcomes the defect that a corresponding preparation system is lacked in the prior art.

Description

Technical Field

[0001] This utility model relates to an optical film, especially a low-transmittance optical film that can be used in the fields of solar photovoltaic backsheets, light source shielding materials, electronic tapes, etc., and particularly to a low-transmittance white polyester film and its preparation system. Background Technology

[0002] Low-transmittance optical films have wide applications in solar photovoltaic backsheets, light source shielding materials, and electronic tapes. For example, in solar photovoltaic backsheets, low-transmittance optical films provide excellent light-blocking effects, preventing interference between solar cells and improving the power generation efficiency of the module. In optical light sources, low-transmittance optical films can be used to create decorative wallpapers with special effects, such as blackout wallpaper and glow-in-the-dark wallpaper. They can also be used as the inner layer material of lightbox fabrics, providing uniform backlighting and good light-blocking properties. In electronic tapes, low-transmittance optical films can serve as insulating or shielding layers; their low light transmittance allows them to block light, preventing interference with sensitive electronic components, making them particularly suitable for applications requiring light shading.

[0003] CN 101605841 B discloses a white polyester film and a reflective sheet. This prior art white polyester film is suitable for optical applications, particularly for liquid crystal display devices, backlight devices, and reflectors. The basic design of this prior art white polyester film is a structure containing internal voids, and the resin constituting the film is composed of polyester resin and cyclic olefin copolymer resin. The void ratio of the film needs to be greater than 25% and less than 75% to ensure high brightness and high concealment.

[0004] CN 110837142 B discloses a white polyester reflective film and its application in liquid crystal display backlights. This prior art utilizes an ABA three-layer structure design (outer layer A contains polyester, inorganic particles, and a toughening agent; the middle layer B contains an incompatible resin to form pores), achieving a reflectivity exceeding 96% and a light uniformity exceeding 84.3%, making it suitable for side-lit and direct-lit backlights in ultra-thin electronic devices. The outer layer A of this prior art contains inorganic particles (such as silica) and a toughening agent, improving surface hardness and scratch resistance while initially scattering light. The middle layer B, by adding an incompatible resin (such as polymethylpentene), forms a micron-scale pore structure after stretching, enhancing light scattering and improving reflectivity. This prior art, through a layered isolation design, avoids direct mixing of incompatible resins and surface materials, preventing interface defects and ensuring that each component maximizes its performance.

[0005] However, the existing foam structure readily absorbs moisture, which may lead to expansion and deformation under prolonged humidity, resulting in decreased uniformity. Furthermore, the significant differences in the thermal expansion coefficients of different layers can easily generate internal stress under temperature cycling, causing warping or delamination. Additionally, there is currently no readily available system for the mass production of low-transmittance optical films. Summary of the Invention

[0006] The technical problem to be solved by this utility model is to provide a low-transmittance white polyester film and its preparation system, so as to reduce or avoid the problems mentioned above.

[0007] To solve the above-mentioned technical problems, this utility model proposes a low-transmittance white polyester film. The film has a three-layer gradient composite structure, including a functional surface layer A, an interface transition layer C, and a main light-blocking layer B. The layers A, C, and B are stacked sequentially, with a total film thickness of 19 to 75 μm and a light transmittance of 12% to 20%. Layer A is the outer layer, layer B is the inner layer, and layer C is located between layers A and B.

[0008] This application also proposes a preparation system for the aforementioned low-transmittance white polyester film. The preparation system includes a first masterbatch mixer for the A-layer functional surface layer masterbatch, a second masterbatch mixer for the B-layer main light-blocking layer masterbatch, and a third masterbatch mixer for the C-layer interface transition layer masterbatch. The outlet of the first masterbatch mixer is connected to the inlet of a first granulator via a pipe, and the outlet of the first granulator is connected to a first dryer via a pipe. The outlet of the second masterbatch mixer is connected to the inlet of the second granulator via a pipe, and the outlet of the second granulator is connected to the second dryer via a pipe. The outlet of the third masterbatch mixer is connected to the inlet of the third granulator via a pipe, and the outlet of the third granulator is connected to the third dryer via a pipe.

[0009] Preferably, the preparation system further includes three independent extruders: a first extruder corresponding to the functional surface layer masterbatch of layer A, a second extruder corresponding to the main light-blocking layer masterbatch of layer B, and a third extruder corresponding to the interface transition layer masterbatch of layer C.

[0010] Preferably, the inlet of the first extruder is connected to the outlet of the first dryer via a pipe, the inlet of the second extruder is connected to the outlet of the second dryer via a pipe, and the inlet of the third extruder is connected to the outlet of the third dryer via a pipe.

[0011] Preferably, all three extruders are equipped with a high-speed shear.

[0012] Preferably, the outlets of the three extruders are further connected to a co-extrusion die, wherein the surface channel of the molten material extruded by the first extruder is input into the co-extrusion die as the functional surface layer A, the inner channel of the molten material extruded by the second extruder is input into the co-extrusion die as the main light-blocking layer B, and the interlayer channel of the molten material extruded by the third extruder is input into the co-extrusion die as the interface transition layer C.

[0013] Preferably, the outlet of the co-extrusion die is further connected to the inlet of the biaxial stretching machine.

[0014] Preferably, the outlet of the biaxial stretching machine is further connected to the inlet of the plasma surface modification treatment machine.

[0015] Preferably, the outlet of the plasma surface modification treatment machine is connected to a winding machine.

[0016] This invention presents a low-transmittance white polyester film employing a three-layer gradient composite structure. Layer A directly faces the external environment, providing weather resistance and scratch resistance. Layer B acts as a light-blocking component, achieving light scattering and concealment effects. Anatase TiO2 hollow microspheres replace the stretched-formed pores, eliminating the sensitivity of porosity to process fluctuations. Layer C serves as a transition layer, matching the thermal expansion coefficients of layers A and B while enhancing the overall structural stability. Layer C acts as a "buffer" and "bond" between layers A and B, minimizing the impact of differences in the properties of the two materials, thereby reducing internal stress and lowering the risk of warping or delamination. Furthermore, the preparation system proposed in this invention can be used for continuous batch production of this film, overcoming the deficiency of existing technologies that lack corresponding preparation systems. Attached Figure Description

[0017] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this utility model.

[0018] Figure 1 The diagram shown is a cross-sectional schematic of a low-transmittance white polyester film according to a specific embodiment of the present invention.

[0019] Figure 2 The diagram shown is a structural schematic of a system for preparing a low-transmittance white polyester film according to another specific embodiment of the present invention. Detailed Implementation

[0020] To provide a clearer understanding of the technical features, objectives, and effects of this utility model, specific embodiments are now described with reference to the accompanying drawings. Identical components are denoted by the same reference numerals.

[0021] In view of the various problems existing in the prior art, this utility model proposes a low-transmittance white polyester film with a three-layer gradient composite structure, such as... Figure 1As shown in the figure. The low-transmittance white polyester film of this invention differs from the traditional three-layer sandwich structure. This invention adopts a gradient composite structure in the form of ACB, as shown in the figure. Layer A is a functional surface layer with a thickness of 10-15%; layer B is the main light-blocking layer with a thickness of 70-80%; and layer C is an interface transition layer with a thickness of 10-15%. The total thickness of the low-transmittance white polyester film of the three-layer gradient composite structure is 19-75 μm.

[0022] In one specific embodiment, the functional surface layer of layer A is based on copolymerized modified polyester chips containing 3-5 wt% isophthalate, and contains 1-3 wt% (by weight of layer A) of nano-barium sulfate to improve surface smoothness and mechanical properties, 0.5-1.0 wt% (by weight of layer A) of boron nitride nanosheets to enhance thermal conductivity, and 3-5 wt% (by weight of layer A) of polyester elastomer TPEE as a toughening agent. Preferably, the nano-barium sulfate has a particle size of 200-500 nm; the boron nitride nanosheets have a transverse dimension of 500 nm to 2 μm and a thickness of 10-50 nm. The boron nitride nanosheets can be domestically produced Tianyuan New Materials' TX-BN10 (1.2 μm ± 0.3 μm transverse, 20 ± 5 nm thickness, hydroxylated surface) or imported Saint-Gobain's BNX-20 (2.0 μm ± 0.5 μm transverse, 30 ± 10 nm thickness, silane coating).

[0023] Specifically, the copolymer-modified polyester in the functional surface layer A is prepared from monomers in the following weight ratio: dimethyl isophthalate (DMI), dimethyl terephthalate (DMT), and ethylene glycol (EG) in a weight ratio of 1.0:(24.0-24.5):(25.0-25.5).

[0024] Furthermore, the copolymerized modified polyester can be prepared by the following process: DMI with a purity of ≥99%, DMT with a purity of ≥99.8%, and EG with a purity of 99.5% are weighed according to a set weight ratio and added to an esterification tank for esterification. The reaction temperature in the esterification tank is 160-190℃, and the reaction is carried out at atmospheric pressure under nitrogen protection for 2-4 hours. During the reaction, 0.02-0.05 wt% of tetrabutyl titanate or 0.03-0.06 wt% of antimony acetate is added as a catalyst, and 0.05-0.1 wt% of triphenyl phosphate (TPP) is added as a heat stabilizer. During the reaction, DMT / DMI undergoes transesterification with EG under the action of a catalyst, generating corresponding oligomers (such as BHET and BMIT) and releasing methanol (which needs to be condensed and recovered). The esterification reaction is stopped when the methanol distillation reaches more than 90% of the theoretical value. The esterification product is then transferred to a polycondensation tank for polycondensation. The reaction temperature in the polycondensation tank is 270-290℃, and the reaction is carried out for 2-3 hours under a vacuum of less than 100 Pa. The reaction is terminated when the intrinsic viscosity reaches 0.65-0.75 dL / g. The polycondensed melt is then discharged from the polycondensation tank to a granulator, granulated to a size of 2-4 mm, and dried at 180℃ for 4 hours. The performance parameters of the prepared copolymerized modified polyester are as follows: DSC: glass transition temperature (Tg) and melting temperature (Tm). The introduction of isophthalic acid esters leads to a decrease in Tm of about 10-20℃ (typical values: pure PET Tm = 250℃, 4wt% DMI modified PET Tm ≈ 235℃); FTIR: characteristic peak of isophthalic acid (inter-substituted peak of benzene ring, 1150-1170cm-1); NMR: DMI content 3-5wt%. As an A-layer substrate, the introduction of isophthalic acid weakens crystallinity and reduces haze, making it suitable for low-transmittance films (transmittance <20%).

[0025] In another specific embodiment, the B-layer main light-blocking layer is made of film-grade polyester chips with an intrinsic viscosity of 0.62-0.65 dL / g as the substrate, and contains 20-25 wt% anatase TiO2 of the total B-layer mass to obtain optimal light scattering efficiency, 8-10 wt% porous SiO2 hollow microspheres of the total B-layer mass to replace the traditional pore structure, and 0.3-0.5 wt% silane coupling agent KH-570 of the total B-layer mass.

[0026] The preferred anatase TiO2 particles have a diameter of 400-600 nm; the porous SiO2 hollow microspheres have a diameter of 5-8 μm and a wall thickness of 0.2 μm. The anatase TiO2 can be LR-988 from Longbai Group, R-2498 from CNNC Titanium Dioxide, Ti-Pure R-960 from Chemours, or TIPAQUECR-60 from Ishihara Sangyo. The porous SiO2 hollow microspheres can be SiliCellMF-7 from JGC Catalysts and Chemicals; K37 K-series hollow glass microspheres from 3M; or NHS-820 from Nantong Nahong Nanomaterials.

[0027] In another specific embodiment, the C-layer interface transition layer is based on epoxy-modified copolyester chips containing 8-10% epoxidation components, and contains 0.1-0.3 wt% of benzotriazole UV absorber and 0.5 wt% of fatty acid ester lubricant by weight of the total C-layer.

[0028] Specifically, the epoxy-modified copolyester can be prepared by the following process: Terephthalic acid (PTA) with a purity of ≥99.5% and ethylene glycol (EG) with a purity of ≥99.5% are weighed and added to a reaction vessel at a set molar ratio of 1:2. Then, 4-8% molar fraction of epoxycyclohexane adipate (ACHD) with a purity of ≥99% is added to the reaction vessel for esterification. The esterification reaction in the reaction vessel is carried out at 180℃ under normal pressure for 3-6 hours. When the esterification rate reaches 85%, the reaction system in the reaction vessel changes from turbid to transparent, and the esterification is complete. During the reaction, 0.02-0.05 wt% tetrabutyl titanate is added to the esterification vessel as a catalyst, and 0.05-0.1 wt% triphenyl phosphate (TPP) is added as a heat stabilizer. After esterification, the temperature is raised to 220℃ for pre-polymerization for 2-5 hours, until the EG content in the reaction vessel is removed by 90%. Then, the temperature is raised to 250℃ for final polymerization. Final polymerization takes 2-6 hours under a vacuum of less than 100 Pa. The reaction is terminated when the intrinsic viscosity reaches 0.62-0.65 dL / g. The polymerized melt is then transferred from the reaction vessel to a granulator, granulated to a size of 2-4 mm, and dried at 180℃ for 4 hours. The fatty acid ester lubricant can be a fatty acid ester, such as LOXIOL G12-V40 (fatty acid ester) from Henkel, Germany.

[0029] This invention discloses a low-transmittance white polyester film employing a gradient composite structure in the form of ACB. Layer A directly faces the external environment, possessing surface functions such as weather resistance and scratch resistance. Layer B, as the light-blocking main body, requires a high filler content to achieve light scattering and concealment effects. Anatase TiO2 hollow microspheres are used instead of stretched-formed bubbles, eliminating the sensitive influence of process fluctuations on porosity. Layer C, as a transition layer, harmonizes the interface between the two layers, matches the thermal expansion coefficients of layers A and B, and enhances the overall structural stability. Layer C acts as a "buffer" and "bond" between layers A and B, minimizing the impact of differences in the properties of the two materials (such as thermal expansion coefficients, mechanical properties, and surface properties), thereby reducing internal stress and lowering the risk of warping or delamination.

[0030] Furthermore, the low-transmittance white polyester film of this invention can be prepared by the following method: First, the raw material masterbatch is prepared and pretreated.

[0031] Preparation of the A-layer functional surface layer masterbatch: Polyester chips containing 3–5 wt% isophthalate-modified, 1–3 wt% barium sulfate nanoparticles, 0.5–1.0 wt% boron nitride nanosheets, and 3–5 wt% polyester elastomer (TPEE) are pre-mixed uniformly according to the specified ratio and then granulated. The material moisture content is kept low to prevent hydrolysis or bubble formation during melting. The drying temperature is 120°C to 150°C, and the drying time is 4 to 6 hours.

[0032] To prepare the masterbatch for the B-layer main light-blocking layer, premixed polyester chips with an intrinsic viscosity of 0.62–0.65 dL / g were mixed uniformly with 20–25 wt% anatase TiO2, 8–10 wt% porous SiO2 hollow microspheres, and 0.3–0.5 wt% silane coupling agent KH-570, followed by granulation and drying. The drying temperature was 120℃ to 150℃, and the drying time was 4 to 6 hours.

[0033] To prepare the C-layer interface transition layer masterbatch, epoxy-modified copolyester chips containing 8–10% epoxidized components were premixed with 0.1–0.3 wt% benzotriazole UV absorber and 0.5 wt% fatty acid ester lubricant, then granulated and dried. The drying temperature was 120°C to 150°C, and the drying time was 4 to 6 hours.

[0034] Then, at least three independent extruders are used to melt-extrude each layer of masterbatch. The pre-mixed masterbatch for layers A, B, and C is fed into its respective extruder. Each extruder is set with an appropriate temperature range based on the material characteristics (layer A 310-315℃; layer B 305-310℃; layer C 295-300℃) to ensure complete melting of the raw materials without thermal degradation. Each extruder is equipped with a high-speed shear press to further ensure the uniform dispersion of additives (such as nano-barium sulfate, boron nitride nanosheets, etc.).

[0035] A three-layer composite film is obtained by co-extrusion stretching using a die. A multi-channel co-extrusion die is used to simultaneously feed the molten material of each layer into the die. An A–C–B structure is adopted, that is: layer A serves as the outer surface layer (functional surface layer); layer C serves as the interface transition layer, sandwiched between layers A and B; layer B serves as the inner layer, providing the main light-blocking function.

[0036] After co-extrusion by the die head, the film is biaxially stretched. First, it is stretched longitudinally (MD) with a ratio of 3.0-3.5 and a longitudinal stretching temperature of 100-110℃. Then, it is stretched transversely (TD) with a ratio of 3.2-3.8 and a transverse stretching temperature of 115-120℃.

[0037] Finally, the prepared three-layer composite film can be subjected to plasma surface modification treatment. The surface is treated with an Ar / O2 mixed gas at a temperature of 200℃ to 230℃ for 3-5 seconds to improve printing / coating adhesion.

[0038] Corresponding to the above preparation method, this application proposes a preparation system for the low-transmittance white polyester film of this utility model, which can be used for uninterrupted mass production of low-transmittance white polyester film.

[0039] like Figure 2As shown, corresponding to the masterbatch preparation and pretreatment stages of the raw materials, the preparation system of this application includes a first masterbatch mixer 10 for the A-layer functional surface layer masterbatch, a second masterbatch mixer 20 for the B-layer main light-blocking layer masterbatch, and a third masterbatch mixer 30 for the C-layer interface transition layer masterbatch. The first masterbatch mixer 10 is used to pre-uniformly mix 3–5 wt% isophthalate-modified polyester chips, 1–3 wt% nano-barium sulfate, 0.5–1.0 wt% boron nitride nanosheets, and 3–5 wt% polyester elastomer (TPEE) according to a specified ratio. The outlet of the first masterbatch mixer 10 is connected to the inlet of a first granulator 11 via a pipe, and the outlet of the first granulator 11 is connected to a first dryer 12 via a pipe. Similarly, the second masterbatch mixer 20 is used to pre-uniformly mix membrane-grade polyester chips with an intrinsic viscosity of 0.62–0.65 dL / g with 20–25 wt% anatase TiO2, 8–10 wt% porous SiO2 hollow microspheres, and 0.3–0.5 wt% silane coupling agent KH-570. The outlet of the second masterbatch mixer 20 is connected to the inlet of the second granulator 21 via a pipe, and the outlet of the second granulator 21 is connected to the second dryer 22 via a pipe. Likewise, the third masterbatch mixer 30 is used to pre-uniformly mix epoxy-modified copolyester chips containing 8–10% epoxidized components with 0.1–0.3 wt% benzotriazole UV absorber and 0.5 wt% fatty acid ester lubricant. The outlet of the third masterbatch mixer 30 is connected to the inlet of the third granulator 31 via a pipe, and the outlet of the third granulator 31 is connected to the third dryer 32 via a pipe.

[0040] The preparation system of this application further includes three independent extruders for melt extruding the masterbatches of each layer: a first extruder 13 corresponding to the functional surface layer masterbatch (layer A), a second extruder 23 corresponding to the main light-blocking layer masterbatch (layer B), and a third extruder 33 corresponding to the interface transition layer masterbatch (layer C). The inlet of the first extruder 13 is connected to the outlet of the first dryer 12 via a pipe; the inlet of the second extruder 23 is connected to the second dryer 22 via a pipe; and the inlet of the third extruder 33 is connected to the third dryer 32 via a pipe. To ensure that the raw materials are fully melted and do not undergo thermal degradation, each of the three extruders is equipped with a high-speed shear.

[0041] The outlets of the three extruders are further connected to the co-extrusion die 40. The molten material extruded by the first extruder 13 is input into the surface channel of the co-extrusion die 40 as the functional surface layer A. The molten material extruded by the second extruder 23 is input into the inner channel of the co-extrusion die 40 as the main light-blocking layer B. The molten material extruded by the third extruder 33 is input into the interlayer channel of the co-extrusion die 40 as the interface transition layer C. The C layer is sandwiched between the A layer and the B layer.

[0042] The outlet of the co-extrusion die 40 is further connected to the inlet of the biaxial stretching machine 50. The biaxial stretching machine 50 stretches the thick sheet output from the co-extrusion die 40 longitudinally and then laterally to form a film.

[0043] The outlet of the biaxial stretching machine 50 is further connected to the inlet of the plasma surface modification treatment machine 60, through which the surface of the film obtained by biaxial stretching is modified.

[0044] Finally, the film output from the plasma surface modification treatment machine 60 is fed into the winding machine 70, where the prepared film product is collected into a roll for easy storage and transportation.

[0045] The low-transmittance white polyester film obtained by the system applied for has an overall transmittance of 12-20% and a pencil hardness of ≥2H for the surface A layer; in terms of humid heat stability, the transmittance fluctuates by ±0.3% after 500h at 80℃ / 85% RH; in terms of bending resistance, the MIT withstands >800 folds (load 500g); and the processing yield is ≥98% (for 75μm thick film).

[0046] Nine specific embodiments are given below (all using an ACB layer structure, i.e., layer A is the functional surface layer, layer C is the interface transition layer, layer B is the main light-blocking layer, and layer C is located between layers A and B). By controlling the proportion of additives in each layer within the raw material formulation range, low-transmittance white polyester films with a total thickness of 19–75 μm and a transmittance controlled at 12–20% are prepared. The specific formulations and key performance parameters of each embodiment are as follows.

[0047] Example 1

[0048] Layer A is a functional surface layer, accounting for 10% of the total layer thickness. Substrate: Copolymer modified polyester chips containing 3 wt% isophthalate, barium sulfate nanoparticles: 3 wt%, boron nitride nanosheets: 0.5 wt%, polyester elastomer (TPEE): 5.5 wt%.

[0049] Layer C is an interface transition layer, accounting for 10% of the total layer thickness. Substrate: epoxy-modified copolyester chips containing 8% epoxidation component, benzotriazole UV absorber: 0.3wt%, lubricant: 0.3wt%.

[0050] Layer B is the main light-blocking layer, accounting for 80% of the total layer thickness. Substrate: polyester chips for film (intrinsic viscosity 0.62 dL / g), anatase TiO2: 25 wt%, porous SiO2 hollow microspheres: 4.5 wt%, silane coupling agent KH-570: 0.5 wt%.

[0051] Overall parameters: Total thickness: 50μm, light transmittance: 15%, reflectance: 85%, tensile strength: 120MPa, thermal stability: approximately 200℃.

[0052] Example 2

[0053] Layer A, accounting for 15% of the total layer thickness. Substrate: Copolymer modified polyester chips containing 4 wt% isophthalate, barium sulfate nanoparticles: 4 wt%, boron nitride nanosheets: 0.7 wt%, TPEE: 5.3 wt%.

[0054] Layer C, comprising 15% of the total layer thickness. Substrate: Modified copolyester chips containing approximately 9 wt% epoxidized components, 0.5 wt% benzotriazole UV absorber, and 0.3 wt% lubricant.

[0055] Layer B, accounting for 70% of the total layer thickness. Substrate: Polyester chips for film (intrinsic viscosity 0.63 dL / g), TiO2: 24 wt%, porous SiO2 hollow microspheres: 7.5 wt%, KH-570: 0.5 wt%.

[0056] Overall parameters: Total thickness: 45μm, light transmittance: 14%, reflectance: 86%, tensile strength: 125MPa, thermal stability: approximately 205℃.

[0057] Example 3

[0058] Layer A, accounting for 10% of the total layer thickness. Substrate: Copolymer modified polyester chips containing 5 wt% isophthalate, barium sulfate nanoparticles: 5 wt%, boron nitride nanosheets: 1.0 wt%, TPEE: 5.0 wt%.

[0059] Layer C, accounting for 15% of the total layer thickness. Substrate: epoxy-modified copolyester chips containing 10wt% epoxidizing components, benzotriazole UV absorber: 0.7wt%, lubricant: 0.3wt%.

[0060] Layer B, accounting for 75% of the total layer thickness. Substrate: Polyester chips for film (intrinsic viscosity 0.64 dL / g), TiO2: 23 wt%, porous SiO2 hollow microspheres: 10 wt%, KH-570: 1.0 wt%.

[0061] Overall parameters: Total thickness: 55μm, light transmittance: 13%, reflectance: 87%, tensile strength: 130MPa, thermal stability: approximately 210℃.

[0062] Example 4

[0063] Layer A, accounting for 15% of the total layer thickness. Substrate: Copolymer modified polyester chips containing 3.5 wt% isophthalate, barium sulfate nanoparticles: 4 wt%, boron nitride nanosheets: 0.7 wt%, TPEE: 5.0 wt%.

[0064] Layer C, accounting for 10% of the total layer thickness. Substrate: epoxy-modified copolyester chips containing 8.5 wt% epoxidizing component, benzotriazole UV absorber: 0.2 wt%, lubricant: 0.5 wt%.

[0065] Layer B, accounting for 75% of the total layer thickness. Substrate: Polyester chips for film (intrinsic viscosity 0.62 dL / g), TiO2: 22 wt%, porous SiO2 hollow microspheres: 8 wt%, KH-570: 0.5 wt%.

[0066] Overall parameters: Total thickness: 60μm, light transmittance: 16%, reflectance: 84%, tensile strength: 122MPa, thermal stability: approximately 208℃.

[0067] Example 5

[0068] Layer A, accounting for 12% of the total layer thickness. Substrate: Copolymer modified polyester chips containing 4 wt% isophthalate, barium sulfate nanoparticles: 3 wt%, boron nitride nanosheets: 0.5 wt%, TPEE: 5.5 wt%.

[0069] Layer C, accounting for 14% of the total layer thickness. Substrate: epoxy-modified copolyester chips containing 9 wt% epoxidized components, benzotriazole UV absorber: 0.3 wt%, lubricant: 0.3 wt%.

[0070] Layer B, accounting for 74% of the total layer thickness. Substrate: Polyester chips for film (intrinsic viscosity 0.63 dL / g), TiO2: 25 wt%, porous SiO2 hollow microspheres: 8.5 wt%, KH-570: 0.3 wt%.

[0071] Overall parameters: Total thickness: 19μm, light transmittance: 18%, reflectance: 82%, tensile strength: 118MPa, thermal stability: approximately 202℃.

[0072] Example 6

[0073] Layer A, accounting for 14% of the total layer thickness. Substrate: Copolymer modified polyester chips containing 4.5 wt% isophthalate, barium sulfate nanoparticles: 2 wt%, boron nitride nanosheets: 1.0 wt%, TPEE: 3.5 wt%.

[0074] Layer C, accounting for 12% of the total layer thickness. Substrate: epoxy-modified copolyester chips containing 10 wt% epoxidizing components, benzotriazole UV absorber: 0.7 wt%, lubricant: 0.3 wt%.

[0075] Layer B, accounting for 74% of the total layer thickness. Substrate: Polyester chips for film (intrinsic viscosity 0.63 dL / g), TiO2: 24 wt%, porous SiO2 hollow microspheres: 7 wt%, KH-570: 0.5 wt%.

[0076] Overall parameters: Total thickness: 30μm, light transmittance: 12%, reflectance: 88%, tensile strength: 135MPa, thermal stability: approximately 215℃.

[0077] Example 7

[0078] Layer A, accounting for 13% of the total layer thickness. Substrate: Copolymer modified polyester chips containing 3 wt% isophthalate, barium sulfate nanoparticles: 1 wt%, boron nitride nanosheets: 0.5 wt%, TPEE: 3 wt%.

[0079] Layer C, accounting for 13% of the total layer thickness. Substrate: epoxy-modified copolyester chips containing 8 wt% epoxidizing component, benzotriazole UV absorber: 0.1 wt%, lubricant: 0.4 wt%.

[0080] Layer B, accounting for 74% of the total layer thickness. Substrate: Polyester chips for membranes (intrinsic viscosity 0.64 dL / g), TiO2: 23 wt%, porous SiO2 hollow microspheres: 9 wt%, KH-570: 0.3 wt%.

[0081] Overall parameters: Total thickness: 35μm, light transmittance: 20%, reflectance: 80%, tensile strength: 110MPa, thermal stability: approximately 195℃.

[0082] Example 8

[0083] Layer A, accounting for 14% of the total layer thickness. Substrate: Copolymer modified polyester chips containing 5 wt% isophthalate, barium sulfate nanoparticles: 3 wt%, boron nitride nanosheets: 0.8 wt%, TPEE: 4 wt%.

[0084] Layer C, accounting for 11% of the total layer thickness. Substrate: epoxy-modified copolyester chips containing 9 wt% epoxidizing component, benzotriazole UV absorber: 0.5 wt%, lubricant: 0.3 wt%.

[0085] Layer B, accounting for 75% of the total layer thickness. Substrate: Polyester chips for film (intrinsic viscosity 0.65 dL / g), TiO2: 26 wt%, porous SiO2 hollow microspheres: 10 wt%, KH-570: 0.5 wt%.

[0086] Overall parameters: Total thickness: 70μm, light transmittance: 12%, reflectance: 88%, tensile strength: 140MPa, thermal stability: approximately 220℃.

[0087] Example 9

[0088] Layer A, accounting for 11% of the total layer thickness. Substrate: Copolymer modified polyester chips containing 4 wt% isophthalate, barium sulfate nanoparticles: 2.5 wt%, boron nitride nanosheets: 0.6 wt%, TPEE: 4.9 wt%.

[0089] Layer C, accounting for 14% of the total layer thickness. Substrate: epoxy-modified copolyester chips containing 9 wt% epoxidizing component, benzotriazole UV absorber: 0.4 wt%, lubricant: 0.3 wt%.

[0090] Layer B, accounting for 75% of the total layer thickness. Substrate: Polyester chips for film (intrinsic viscosity 0.63 dL / g), TiO2: 25 wt%, porous SiO2 hollow microspheres: 8 wt%, KH-570: 0.3 wt%.

[0091] Overall parameters: Total thickness: 75μm, light transmittance: 15%, reflectance: 85%, tensile strength: 128MPa, thermal stability: approximately 210℃.

[0092] Summary and Explanation. The above nine embodiments fine-tuned the raw material ratios of layers A, C, and B within the ACB structure. Results show that, within the predetermined raw material ratio range, all embodiments achieved a total thickness control of 19–75 μm and a light transmittance maintained within the target range of 12%–20%. Adjusting the toughening agent and nanofiller in layer A improved surface smoothness and scratch resistance. The ratio of epoxy-modified polyester to UV absorber and lubricant in layer C effectively enhanced interlayer adhesion and UV resistance, ensuring uniform interface transition. The combination of TiO2 and porous SiO2 hollow microspheres in layer B, while ensuring optimal light scattering efficiency, replaced the traditional pore structure, thus avoiding moisture absorption and expansion issues. Key performance parameters (such as tensile strength, thermal stability, and optical properties) were relatively consistent across all embodiments, indicating that the product possesses excellent practicality and stability within the designed formulation range.

[0093] The above nine embodiments demonstrate that, within the range of raw material ratios, by rationally controlling the composition of each layer, not only can the requirements of optical thin films for low light transmittance, weather resistance, mechanical strength, and thermal management be met, but also reliable technical support can be provided for further process optimization and industrialization promotion.

[0094] In conjunction with the above embodiments, this utility model further provides comparative examples, and the relevant performance parameters are shown in the table below. The parameters not shown in each comparative example are the same as those in the corresponding embodiments; the table only shows the comparison schemes with adjusted parameters.

[0095]

[0096]

[0097] The analysis of the comparative examples above demonstrates that the content and selection of each component in the original embodiments are crucial for ensuring the overall performance of the film, including low light transmittance, mechanical strength, and weather resistance. Appropriate raw material ratios and component selection can produce low-light-transmittance white polyester films with uniform and stable performance and excellent practicality.

[0098] The above description is merely an illustrative embodiment of this utility model and is not intended to limit the scope of this utility model. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of this utility model should fall within the protection scope of this utility model.

Claims

1. A low-transmittance white polyester film, characterized in that, The film has a three-layer gradient composite structure, including a functional surface layer (A layer), an interface transition layer (C layer), and a main light-blocking layer (B layer). The A, C, and B layers are stacked sequentially, with a total film thickness of 19 to 75 μm and a transmittance of 12% to 20%. The A layer is the outer layer, the B layer is the inner layer, and the C layer is located between the A and B layers.

2. A system for preparing the low-transmittance white polyester film according to claim 1, characterized in that, The preparation system includes a first masterbatch mixer for the A-layer functional surface layer masterbatch, a second masterbatch mixer for the B-layer main light-blocking layer masterbatch, and a third masterbatch mixer for the C-layer interface transition layer masterbatch. The outlet of the first masterbatch mixer is connected to the inlet of the first granulator via a pipe, and the outlet of the first granulator is connected to the first dryer via a pipe. The outlet of the second masterbatch mixer is connected to the inlet of the second granulator via a pipe, and the outlet of the second granulator is connected to the second dryer via a pipe. The outlet of the third masterbatch mixer is connected to the inlet of the third granulator via a pipe, and the outlet of the third granulator is connected to the third dryer via a pipe.

3. The preparation system according to claim 2, characterized in that, The preparation system further includes three independent extruders: a first extruder corresponding to the A-layer functional surface layer masterbatch, a second extruder corresponding to the B-layer main light-blocking layer masterbatch, and a third extruder corresponding to the C-layer interface transition layer masterbatch.

4. The preparation system according to claim 3, characterized in that, The inlet of the first extruder is connected to the outlet of the first dryer via a pipe, the inlet of the second extruder is connected to the outlet of the second dryer via a pipe, and the inlet of the third extruder is connected to the outlet of the third dryer via a pipe.

5. The preparation system according to claim 3 or 4, characterized in that, All three extruders are equipped with high-speed shearing machines.

6. The preparation system according to claim 3 or 4, characterized in that, The outlets of the three extruders are further connected to the co-extrusion die. The molten material extruded by the first extruder is fed into the surface channel of the co-extrusion die as the functional surface layer A. The molten material extruded by the second extruder is fed into the inner channel of the co-extrusion die as the main light-blocking layer B. The molten material extruded by the third extruder is fed into the interlayer channel of the co-extrusion die as the interface transition layer C.

7. The preparation system according to claim 6, characterized in that, The outlet of the co-extrusion die is further connected to the inlet of the biaxial stretching machine.

8. The preparation system according to claim 7, characterized in that, The outlet of the biaxial stretching machine is further connected to the inlet of the plasma surface modification treatment machine.

9. The preparation system according to claim 8, characterized in that, The outlet of the plasma surface modification treatment machine is connected to a winding machine.

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