High-haze calcite bopet composite diffusion film and preparation method and application thereof

Abstract

The present application relates to the technical field of optical functional film, disclose a kind of high haze calcite BOPET composite diffusion film and its preparation method and application, by adopting gradient micropore-dense layer composite structure design, and optimizing each layer function composition, on the one hand in surface dense layer, utilize low filling nano calcite to build high dense structure, effectively reduce surface light reflection, improve mechanical strength, while avoiding light transmittance loss;On the other hand in bottom microporous layer, introduce double-particle-size calcite particle nanoparticles and microparticles, build multiscale scattering network, realize the efficient light diffusion of wide spectral range 380-780 nm, significantly reduce interface scattering loss, substantially improve the light transmittance and haze balance of optical film;Meanwhile, through the integration of co-extrusion-biaxial stretching process, optimize inorganic / organic interface combination, effectively solve the problem of filler agglomeration, while reducing the preparation cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical functional film, and particularly relates to a high-haze calcite BOPET composite diffusion film and a preparation method and application thereof. BACKGROUND

[0002] With the continuous development of liquid crystal display technology, the requirements for the optical performance of display devices are also becoming higher and higher. As a key optical element in the backlight module of a liquid crystal display, the main function of a diffusion film is to uniformly diffuse the light emitted by the backlight source, eliminate the point or line marks of the light source, and improve the brightness uniformity of the display screen. At present, the common diffusion film on the market is mainly composed of a polyethylene terephthalate (PET) substrate and a light diffusion agent. By adding light diffusion particles with different refractive indexes in the substrate, the scattering and diffusion effect of light can be achieved.

[0003] In the prior art, the preparation methods of the diffusion film mainly include coating method and co-extrusion method. The coating method is to coat a resin layer containing light diffusion particles on the surface of the PET substrate. The patent with publication number CN106908873A discloses a preparation method of a high-haze high-transmittance diffusion film. A light diffusion layer containing diatomite particles, organic particles, thermosetting acrylic resin and other components is coated on the surface of the base film, and then heat curing is performed to form the light diffusion layer. The co-extrusion method is to directly add light diffusion particles into the substrate, and then the diffusion film is prepared by extrusion molding. The patent with publication number CN111239868A discloses a diffusion film and a manufacturing method thereof. The diffusion film includes an embedded high-haze substrate, a light diffusion layer and an anti-blocking layer. The light diffusion layer includes a resin film-forming substance, spherical light diffusion particles and an additive.

[0004] The existing diffusion film technology still faces a series of challenges. There is an inherent contradiction between high haze and high transmittance. Increasing the concentration of light diffusion agents can improve the haze, but it will cause a significant decrease in transmittance. At the same time, the absorption effect of traditional inorganic particles on the blue light band will cause the color coordinate to deviate, and the dispersion uniformity of inorganic fillers in the polymer matrix is difficult to control, which is easy to form micron-level agglomerates, causing uneven light scattering distribution and regional degradation of film transmittance. In addition, the high-filled diffusion film is brittle due to the stress concentration at the inorganic / organic interface, and the elongation at break decreases, which is difficult to meet the flexible requirements. With the progress of Mini-LED backlight technology, the simultaneous realization of ultra-thin and high light transmittance performance has become a new requirement, and the existing technology is not suitable for this. In the application of flexible foldable screens, the demand for high haze and flexibility further highlights the bottleneck of material design. At the same time, the complex process and high cost also restrict the large-scale application of high-performance diffusion films. SUMMARY

[0005] The present application aims to solve the technical bottleneck of the prior art, i.e., the inversion of haze and light transmittance, poor weather resistance, and high cost of conventional diffusion films. By adopting a gradient micropore-dense layer composite structure design and optimizing the functional composition of each layer, on the one hand, in the surface dense layer, a high-density structure is constructed by using low-filled nanometer calcite to effectively reduce surface light reflection and improve mechanical strength, while avoiding the loss of light transmittance; on the other hand, in the bottom microporous layer, double-particle-size calcite nanoparticles and microparticles are introduced to construct a multi-scale scattering network, achieving efficient light diffusion in a wide spectral range of 380-780 nm, significantly reducing interface scattering loss, and greatly improving the light transmittance and haze balance of the optical film; at the same time, through the integrated molding of co-extrusion-biaxial stretching process, the inorganic / organic interface bonding is optimized, effectively solving the problem of filler agglomeration, and reducing the preparation cost.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0007] Firstly, the present application provides a high-haze calcite BOPET composite diffusion film, which is composed of a gradient structure of a surface dense layer and a bottom microporous layer;

[0008] The porosity of the surface dense layer is <5%, and the thickness is 5-10 μm, and an oriented structure with a crystallinity of ≥85% is formed by longitudinal stretching;

[0009] The porosity of the bottom microporous layer is 20-30%, and the closed micropores with a gradient distribution of pore diameters of 1-8 μm are formed by a synchronous foaming process of transverse stretching, and the closed porosity is ≥90%.

[0010] The composition of the gradient structure of the surface dense layer and the bottom microporous layer includes, by mass percentage:

[0011] Base material: 75%-85% of polyethylene terephthalate;

[0012] Light diffusion agent: 12%-20% of double-particle-size calcite particles modified by silane coupling agent vapor;

[0013] Foaming agent: 0.5%-1.5% of chemical foaming agent;

[0014] Coupling agent: 0.1%-0.3% of silane coupling agent;

[0015] Antistatic agent: 0.3%-0.8% of non-ionic antistatic agent;

[0016] Thermal stabilizer: 0.2%-0.5% of a compound of phosphite and hindered phenol, wherein the mass ratio of phosphite to hindered phenol is 1:2.

[0017] The double-size calcite particles are nano-calcite with a particle size of 100-300 nm and micron-size calcite with a particle size of 3-8 μm, and the mass ratio of the nano-calcite to the micron-size calcite is 1:2-1:5, wherein the nano-calcite accounts for 1%-3% and the micron-size calcite accounts for 5%-9%.

[0018] The present application realizes efficient light diffusion in a wide spectral range of 380-780 nm by optimizing the ratio and dispersity of the double-size particles, constructing a multi-stage scattering system, reducing the interface scattering loss, and significantly improving the light transmittance and haze balance of the optical film.

[0019] The nano-particles (100-300 nm) have a particle size close to the short wavelength (380-500 nm) of visible light, preferentially scatter blue-violet light through Rayleigh scattering, significantly reduce the forward scattering loss of the short wavelength, and improve the light transmittance;

[0020] The micron-particles (3-8 μm) have a particle size matching the long wavelength (500-780 nm) of visible light, dominate the diffusion of red light and yellow light through Mie scattering, and enhance the haze uniformity. By adjusting the mass ratio (1:2-1:5) of the nano-particles to the micron-particles, a complementary scattering network is formed to avoid the scattering blind area caused by a single particle size.

[0021] Secondly, the double-size calcite particles are prepared by a silane coupling agent vapor injection process, and the preparation method comprises the following steps:

[0022] (1) Calcite pretreatment: dry the calcite powder to reduce the water content to less than 0.3 wt%;

[0023] (2) Silane coupling agent vapor injection: add the pretreated calcite powder into a double-screw extruder for extrusion, and at the same time, inject the silane coupling agent into the vapor injection device of the melt section of the double-screw extruder through a precision metering pump under the protection of nitrogen. Nitrogen is used as the carrier gas to inject into the melt section of the double-screw extruder. The silane coupling agent is instantaneously vaporized under the action of 250-255℃ and a nitrogen carrier gas flow rate of 5-8 L / min to form a uniformly dispersed vapor phase;

[0024] (3) Dynamic grafting: the silanol group reacts with the hydroxyl group on the surface of the calcite to form a stable Si-O-Ca covalent bond, and water molecules are released at the same time;

[0025] (4) Vacuum devolatilization: use a high-vacuum devolatilization system to forcibly discharge small molecular byproducts under a pressure of-0.06-0.08 MPa to finally obtain in-situ grafted calcite.

[0026] Through the above steps, calcite is modified by a silane coupling agent steam injection process. Using nitrogen as a carrier gas, the steam partial pressure is precisely controlled, and at a high temperature environment of 255℃, the silane coupling agent is instantaneously hydrolyzed to generate active silanol groups, which undergo dynamic condensation reactions with the hydroxyl groups on the surface of calcite, achieving in-situ efficient grafting of Si-O-Ca covalent bonds. Compared with traditional solvent pre-modification methods, this steam injection process does not require the use of organic solvents, eliminating the risk of volatile residues, and the reaction time is only 10 seconds, significantly improving the dispersion uniformity and interfacial bonding strength of calcite in the PET matrix.

[0027] As a preferred, the foaming agent decomposes at 105-115℃ in the transverse stretching stage, and generates CO2 / N2 gas to form a light scattering microporous structure in cooperation with the calcite particles, and the refractive index difference between the gas-solid interface is used to enhance scattering.

[0028] As a preferred, the foaming agent is one or more combinations of azodicarbonamide, 4,4'-oxybisbenzenesulfonylhydrazide, p-toluenesulfonylhydrazide, sodium bicarbonate, and 5-phenyltetrazole.

[0029] As a preferred, the silane coupling agent is one or more combinations of γ-aminopropyl triethoxysilane KH-550, γ-(2,3-epoxypropoxy) propyl trimethoxysilane KH-560, and γ-methacryloyloxypropyl trimethoxysilane KH-570.

[0030] As a preferred, the non-ionic antistatic agent is one or more combinations of ethylene bis-stearamide, glycerol monostearate, stearamide, and erucamide, replacing the traditional quaternary ammonium salt antistatic agent.

[0031] As a preferred, the heat stabilizer is a complex of phosphite and hindered phenol, used to inhibit the thermal oxidation of calcite-catalyzed PET.

[0032] The present application uses a non-ionic antistatic agent (ethylene bis-stearamide (EBS-75)) to replace the traditional quaternary ammonium salt antistatic agent, effectively avoiding decomposition failure during high-temperature extrusion. At the same time, the complex of phosphite (Irgafos 168) and hindered phenol (Irganox 1010) significantly inhibits the thermal oxidation reaction of calcite-catalyzed PET.

[0033] As a preferred, the surface hardness of the surface dense layer is ≥3H, and the haze contribution rate is ≤5%; the haze of the bottom microporous layer is ≥85%, and the light transmittance is ≥88%.

[0034] Thirdly, the present application also provides a preparation method of a high-haze calcite BOPET composite diffusion film, comprising the following steps:

[0035] (1) Double particle size calcite particles and polyethylene terephthalate resin are premixed and added to a twin-screw extruder, and then melt-extruded through the twin-screw extruder under nitrogen protection by means of segmented temperature control (230-240℃ / 250-255℃ / 250-255℃ / 240-250℃ / 240-250℃), with a screw rotation speed of 300-350 rpm;

[0036] (2) After the melt is extruded through a T-shaped die, longitudinal stretching is first performed to form a surface dense layer, and then transverse stretching is performed to form a bottom microporous layer simultaneously.

[0037] Preferably, in step (2), the longitudinal stretching temperature of the gradient structure is 90-100℃, and the stretching ratio is 3.5-4.0; the transverse stretching temperature is 105-115℃, and the stretching ratio is 3.0-3.5, and the foaming agent decomposes to generate gas to form micropores during the transverse stretching process.

[0038] Fourthly, the application also provides a backlight module using the high-haze calcite BOPET composite diffusion film.

[0039] Compared with the prior art, the application has the following beneficial effects:

[0040] The double particle size calcite particles cooperate with the scattering system and the gradient pore structure design, the surface dense layer has a porosity of <5% + the bottom microporous layer has a porosity of 20-30%, which breaks through the bottleneck of mutual restriction between traditional haze and light transmittance, and realizes the high-performance synergistic optimization of haze ≥85% and light transmittance ≥88%.

[0041] The steam injection dynamic grafting technology innovatively uses a steam injection process (nitrogen carrier gas 5-8 L / min, 250-255℃) to realize in-situ grafting of the silane coupling agent, which significantly improves the dispersion uniformity of the calcite. Combined with the two-way stretching and simultaneous foaming technology, a gradient pore structure is constructed, which not only guarantees the optical performance but also effectively reduces the production cost, and is both economical and environmentally friendly.

[0042] The innovative design of the functional additive system successfully solves the failure problem in the high-temperature processing process by using alkyl sulfonate instead of traditional quaternary ammonium salt antistatic agents; at the same time, the introduction of the phosphite and hindered phenol compound stabilizing system effectively inhibits the catalytic effect of calcite on the thermal oxidation of PET, thereby ensuring the long-term stability of the material. This design realizes the synergistic optimization of haze, light transmittance and mechanical properties, not only has the economy of mass production, but also meets the strict requirements of high-order display devices. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is an SEM image of the surface dense layer of the high-haze calcite BOPET composite diffusion film prepared in Example 1 of the application.

[0044] Figure 2 Figure 1 is a SEM image of the bottom microporous layer of the high-haze calcite BOPET composite diffusion film prepared in Example 1 of the present application.

[0045] Figure 3 Figure 1 is a SEM image of the bottom microporous layer of the high-haze calcite BOPET composite diffusion film prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0046] The present application will be further described in conjunction with the specific embodiments.

[0047] In the present application, all the equipment and raw materials can be purchased from the market or commonly used in the industry, and the methods in the following examples are conventional methods in the field unless otherwise specified.

[0048] A high-haze calcite BOPET composite diffusion film composed of a gradient structure of a surface dense layer and a bottom microporous layer;

[0049] In some specific embodiments, the surface dense layer has a porosity of <5% and a thickness of 5-10 μm, and an oriented structure with a crystallinity of ≥85% is formed by longitudinal stretching;

[0050] In some specific embodiments, the bottom microporous layer has a porosity of 20-30%, and closed micropores with a gradient distribution of pore diameters of 1-8 μm and a closed porosity of ≥90% are formed by a transverse stretching and simultaneous foaming process.

[0051] In some specific embodiments, the gradient structure of the surface dense layer and the bottom microporous layer is composed of, by mass percentage:

[0052] Matrix material: 75-85% polyethylene terephthalate;

[0053] Light diffusing agent: 12-20% bimodal calcite particles modified by silane coupling agent vapor;

[0054] Foaming agent: 0.5-1.5% chemical foaming agent;

[0055] Coupling agent: 0.1-0.3% silane coupling agent;

[0056] Antistatic agent: 0.3-0.8% non-ionic antistatic agent;

[0057] Thermal stabilizer: 0.2-0.5% phosphite and hindered phenol complex, wherein the mass ratio of phosphite to hindered phenol is 1:2.

[0058] In some specific embodiments, the bimodal calcite particles are nano-calcite of 100-300 nm and micron-sized calcite of 3-8 μm, and the mass ratio is 1:2-1:5.

[0059] In some embodiments, the dual-size calcite particles are prepared by a silane coupling agent vapor injection process, the preparation method comprising the following steps:

[0060] (1) Calcite pretreatment: dry the calcite powder to reduce the moisture content to less than 0.3wt%;

[0061] (2) Silane coupling agent vapor injection: add the pretreated calcite powder into a twin-screw extruder and extrude, while under nitrogen protection, deliver the silane coupling agent to the vapor injection device of the melt section of the twin-screw extruder through a precision metering pump, inject nitrogen gas into the melt section of the twin-screw extruder, and under the action of nitrogen gas flow of 5-8 L / min at 250-255°C, the silane coupling agent is instantly vaporized to form a uniformly dispersed vapor phase;

[0062] (3) Dynamic grafting: condensation reaction occurs between the silanol group and the hydroxyl group on the surface of the calcite, forming a stable Si-O-Ca covalent bond and releasing water molecules;

[0063] (4) Vacuum devolatilization: through a high-vacuum devolatilization system, forcibly discharge small-molecule byproducts under a pressure of -0.06-0.08 MPa, and finally obtain in-situ grafted calcite.

[0064] In some embodiments, the foaming agent decomposes at 105-115°C during the transverse stretching stage, and generates CO2 / N2 gas to form a light-scattering microporous structure in cooperation with the calcite particles.

[0065] In some embodiments, a high-haze calcite BOPET composite diffusion film, the foaming agent is one or more combinations of azodicarbonamide, 4,4'-oxybisbenzenesulfonylhydrazide, p-toluenesulfonylhydrazide, sodium bicarbonate, and 5-phenyltetrazole;

[0066] And / or, the silane coupling agent is one or more combinations of γ-aminopropyl triethoxysilane KH-550, γ-(2,3-epoxypropoxy) propyl trimethoxysilane KH-560, and γ-methacryloyloxypropyl trimethoxysilane KH-570;

[0067] And / or, the non-ionic antistatic agent is one or more combinations of ethylene bis-stearamide, glycerol monostearate, stearamide, and erucamide, replacing the traditional quaternary ammonium salt antistatic agent;

[0068] And / or, the heat stabilizer is a complex of phosphite and hindered phenol, used to inhibit the thermal oxidation of calcite-catalyzed PET.

[0069] In some embodiments, a high-haze calcite BOPET composite diffusion film, the surface hardness of the surface dense layer is greater than or equal to 3H, and the haze contribution rate is less than or equal to 5%; the haze of the bottom microporous layer is greater than or equal to 85%, and the light transmittance is greater than or equal to 88%.

[0070] In some embodiments, a preparation method of a high-haze calcite BOPET composite diffusion film, comprising the following steps:

[0071] (1) After the double-size calcite particles and polyethylene terephthalate resin are premixed, they are added to a double-screw extruder, and are melt-extruded through the double-screw extruder under the protection of nitrogen, with segmented temperature control (230-240℃ / 250-255℃ / 250-255℃ / 240-250℃ / 240-250℃), and the screw rotation speed is 300-350 rpm;

[0072] (2) After the melt is extruded through a T-shaped die, longitudinal stretching is first performed to form a surface dense layer, and then transverse stretching is performed to form a bottom microporous layer.

[0073] In some embodiments, a preparation method of a high-haze calcite BOPET composite diffusion film, in step (2), the longitudinal stretching temperature of the gradient structure is 90-100℃, and the stretching ratio is 3.5-4.0; the transverse stretching temperature is 105-115℃, and the stretching ratio is 3.0-3.5, and the foaming agent decomposes to generate gas to form micropores during the transverse stretching process.

[0074] A backlight module adopts a high-haze calcite BOPET composite diffusion film.

[0075] The application will be described in detail below through specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not to limit the scope of the application, and any changes and advantages that can be thought of by those skilled in the art without departing from the spirit and scope of the application are included in the application, and the appended claims and any equivalents thereof are the protection scope of the application.

[0076] Example 1

[0077] A high-haze calcite BOPET composite diffusion film, the porosity of the bottom microporous layer is 20%;

[0078] The surface dense layer and the bottom microporous layer of the gradient structure comprise: 83% polyethylene terephthalate (PET, intrinsic viscosity 0.65 dl / g) as a base material;

[0079] Light diffusing agent: 15% double-size calcite (200nm nanoparticles:5μm microparticles, mass ratio 1:3) modified by KH-560 steam;

[0080] Blowing agent: 1.0% azodicarbonamide;

[0081] Coupling agent: 0.2% γ-(2,3-epoxypropoxy) propyl trimethoxysilane (KH-560)

[0082] Antistatic agent: 0.5% ethylene bis-stearamide

[0083] Thermal stabilizer: 0.3% complex system (phosphite: hindered phenol = 1:2)

[0084] The bimodal calcite particles are prepared by a silane coupling agent steam injection process, and the preparation method comprises the following steps:

[0085] (1) Calcite pretreatment: dry the calcite powder at 105°C for 4h to reduce the water content to less than 0.3 wt%;

[0086] (2) Silane coupling agent steam injection: add the pretreated calcite powder into a twin-screw extruder for extrusion, and at the same time, under the protection of nitrogen, a precise metering pump is used to deliver the silane coupling agent to the steam injection device of the melt section of the twin-screw extruder, and nitrogen is used as the carrier gas to inject the melt section of the twin-screw extruder, and the silane coupling agent is instantly vaporized under the action of 252°C and a nitrogen carrier gas flow of 6 L / min, forming a uniformly dispersed vapor phase;

[0087] (3) Dynamic grafting: the silanol group reacts with the hydroxyl group on the surface of the calcite to form a stable Si-O-Ca covalent bond, and water molecules are released at the same time;

[0088] (4) Vacuum devolatilization: through a high-vacuum devolatilization system, small-molecule byproducts are forcibly discharged under a pressure of 0.08 MPa, and finally in-situ grafted calcite is obtained.

[0089] The blowing agent decomposes at 110°C during the transverse stretching stage, and through the generation of CO2 / N2 gas, a light scattering microporous structure is formed in cooperation with the calcite particles.

[0090] A preparation method of a high-haze calcite BOPET composite diffusion film, comprising the following steps:

[0091] (1) After the bimodal calcite particles and polyethylene terephthalate resin are premixed and added to a twin-screw extruder, the melt is extruded through the twin-screw extruder under the protection of nitrogen, and the temperature is controlled in sections (230-240°C / 250-255°C / 250-255°C / 240-250°C / 240-250°C), and the screw rotation speed is 320 rpm;

[0092] (2) After the melt is extruded through a T-shaped die, it is first stretched longitudinally to form a surface dense layer, and the corresponding SEM image is as shown in Figure 2b; Figure 1The SEM images of the bottom microporous layer formed by transverse stretching and synchronous foaming are shown in the accompanying drawings. Figure 2 The SEM images of the bottom microporous layer formed by transverse stretching and synchronous foaming are shown in the accompanying drawings.

[0093] The longitudinal stretching temperature of the gradient structure in step (2) was 95°C, and the stretching ratio was 3.8. The transverse stretching temperature was 110°C, and the stretching ratio was 3.2. The gas generated by the decomposition of the foaming agent during the transverse stretching process formed micropores. The SEM images of the bottom microporous layer formed by transverse stretching and synchronous foaming are shown in the accompanying drawings. Figure 3 The SEM images of the bottom microporous layer formed by transverse stretching and synchronous foaming are shown in the accompanying drawings.

[0094] The thickness of the surface dense layer in this embodiment was 8 μm, and the pore diameter of the bottom microporous layer formed by transverse stretching and synchronous foaming was 3 μm.

[0095] Example 2

[0096] The difference between this embodiment and Example 1 is only that the ratio of calcite is 1:2.

[0097] Example 3

[0098] The difference between this embodiment and Example 1 is only that the ratio of calcite is 1:5.

[0099] Example 4

[0100] The difference between this embodiment and Example 1 is only that the porosity is 25%.

[0101] Example 5

[0102] The difference between this embodiment and Example 1 is only that the porosity is 30%.

[0103] Example 6

[0104] The difference between this embodiment and Example 1 is only that the antistatic agent is replaced by 0.5% ethylene bis stearamide.

[0105] Example 7

[0106] The difference between this embodiment and Example 1 is only that the heat stabilizer (phosphite: hindered phenol = 1:3).

[0107] Example 8

[0108] The difference between this embodiment and Example 1 is only that the longitudinal stretching ratio is 4.0 + the transverse stretching ratio is 3.5.

[0109] Comparative Example 1

[0110] The difference between this comparative example and Example 1 is only that there is no gradient structure, and the porosity is 15%.

[0111] Comparative Example 2

[0112] The difference between this comparative example and Example 1 is only that the single calcite particle size contains only microparticles.

[0113] Comparative Example 3

[0114] The difference between this comparative example and Example 1 is only that the calcite is not modified (mixed directly).

[0115] Comparative Example 4

[0116] The difference between this comparative example and Example 1 is only that a traditional quaternary ammonium salt antistatic agent is used.

[0117] Comparative Example 5

[0118] The difference between this comparative example and Example 1 is only that no thermal stabilizer is added.

[0119] Comparative Example 6

[0120] The difference between this comparative example and Example 1 is only that the longitudinal stretching ratio is 3.0 (low crystallinity).

[0121] The composite diffusion films prepared in the above examples and comparative examples are cut into A4 size, and various performance tests are performed, and the results are shown in Table 1. The test items and methods are as follows:

[0122] Haze contribution rate or light transmittance test: Take an A4 size composite diffusion film to be tested, and place it in a haze tester to measure its light transmittance and haze value.

[0123] Surface hardness test: According to the national standard method GB / T 6739-2006 "Pencil method for testing paint film hardness of color paint and varnish", the surface hardness of the prepared composite diffusion film is tested by a pencil hardness tester.

[0124] Closed cell rate: According to the national standard method GB / T 10799-2008 "Determination of open and closed cell volume percentage of rigid foam plastic", the closed cell rate of the prepared composite diffusion film is tested by a mercury porosimeter.

[0125] Light transmittance decay: According to the national standard method GB / T 15596-2009 "Determination of changes in color and properties of plastics after exposure to glass under sunlight or natural climate or artificial light", a UVB-313 lamp tube is used with an irradiation intensity of 0.76 W / m², and the cycle is 500 h. The light transmittance decay of the prepared composite diffusion film is tested.

[0126] Haze retention rate after folding: According to the national standard method GB / T 30776-2014 "Test method for anti-wrinkling performance of plastic film", a MIT folding resistance tester is used with a folding angle of 135°, a frequency of 100 times / min, and a cycle number of 1000 times. The haze retention rate of the prepared composite diffusion film after folding is tested.

[0127] Table 1 Performance test results of a high-haze calcite BOPET composite diffusion film

[0128] Haze contribution rate (%) Transmittance (%) Surface hardness (H) Closed cell ratio (%) Transmittance decay (%) Haze retention rate after folding (%) Example 1 4.2 89.5 3.2 92 2.1 98.5 Example 2 3.8 90.2 3.1 91 2.3 97.8 Example 3 4.8 88.7 3.3 93 1.9 99.1 Example 4 5.1 87.9 3.0 89 2.5 96.3 Example 5 6.3 86.2 2.8 85 3.2 94.7 Example 6 4.3 89.3 3.2 92 2.2 98.2 Example 7 4.1 89.8 3.2 92 1.8 99.3 Example 8 4.0 90.1 3.5 94 1.7 99.6 Comparative Example 1 12.5 82.4 1.5 70 5.8 85.2 Comparative Example 2 7.2 85.3 3.0 88 3.5 92.4 Comparative Example 3 4.5 83.1 2.5 75 7.2 88.7 Comparative Example 4 4.3 86.7 3.1 90 4.1 89.5 Comparative Example 5 4.4 84.2 3.1 90 9.6 82.3 Comparative Example 6 4.6 87.3 2.0 86 3.8 90.1

[0129] As can be seen from the results in Table 1, the high-haze calcite BOPET composite diffusion film prepared by the method of the present application in Examples 1-8 effectively reduces surface light reflection, improves mechanical strength, and avoids loss of light transmittance; at the same time, the film greatly improves the light transmittance and haze balance of the optical film.

[0130] Compared with Example 1, Comparative Example 1 uses a non-gradient structure, with a porosity of 15%, a higher haze, and a significant attenuation of light transmittance. This shows that the non-gradient structure leads to an imbalance in performance, while the use of low-filling nano-calcite to construct a high-density structure effectively reduces surface light reflection, improves mechanical strength, and avoids loss of light transmittance.

[0131] Compared with Example 1, Comparative Example 2 contains only a single particle size of micron-sized calcite particles, with a higher haze than the dual-particle-size calcite and a lower light transmittance, which confirms that single-particle-size particles have a lower scattering efficiency. By introducing dual-particle-size calcite particles, i.e., nano-particles and micron-particles, to construct a multi-scale scattering network, efficient light diffusion is successfully achieved in a wide spectral range of 380-780 nm, significantly reducing interface scattering loss and greatly improving the light transmittance and haze balance of the optical film.

[0132] Compared with Example 1, the calcite in Comparative Example 3 is not modified and is mixed directly, with a significantly reduced closed porosity, which shows that the unmodified group has uneven micro-pore distribution due to agglomeration, which in turn causes a significant decrease in light transmittance. This proves that the presence of Si-O-Ca bonds can effectively reduce interface light loss.

[0133] Compared with Example 5, Comparative Example 4 uses a traditional quaternary ammonium salt antistatic agent, which causes accelerated aging problems due to ion migration. However, by replacing the traditional quaternary ammonium salt antistatic agent with an alkyl sulfonate, the failure problem during high-temperature processing is successfully overcome.

[0134] Compared with Example 6, Comparative Example 5 does not add a thermal stabilizer, with a significant attenuation of light transmittance, which shows that calcite catalyzes PET chain scission, causing accelerated decline in light transmittance. The introduction of a stabilizing system composed of phosphite and hindered phenol effectively inhibits the catalytic effect of calcite on PET thermal oxidation, thereby ensuring long-term stability of the material.

[0135] Compared with Example 7, the longitudinal stretch ratio of Comparative Example 6 is increased to 3.0, and the hardness is reduced to 2H, which indicates that low crystallinity leads to a decrease in mechanical strength. However, by adopting the composite structure of the longitudinally stretched surface dense layer and the transversely stretched bottom microporous layer, the surface hardness of the surface dense layer is successfully realized to be more than 3H, verifying that high orientation crystallization can effectively enhance the rigidity of the dense layer; at the same time, the haze contribution rate of the bottom microporous layer is controlled to be less than 5%, effectively decoupling the conflict between the hardness and the scattering function.

[0136] Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The raw materials and equipment used in the present application are conventional raw materials and equipment in the art, which can be obtained from conventional commercial channels, unless otherwise specified. The methods used in the present application are conventional methods in the art, unless otherwise specified.

[0137] The above description is only the preferred embodiment of the present application, not any limitation on the present application, any simple modification, change and equivalent transformation of the above embodiment according to the technical essence of the present application still belong to the protection scope of the technical solution of the present application.

Claims

1. A high haze calcite BOPET composite diffusion film, characterized in that, The gradient structure is composed of a surface dense layer and a bottom microporous layer; The surface dense layer has a porosity of <5% and a thickness of 5-10 μm, and forms an oriented structure with a crystallinity of ≥85% by longitudinal stretching; the bottom microporous layer has a porosity of 20-30%, and forms closed micropores with a gradient distribution of pore sizes of 1-8 μm and a closed porosity of ≥90% by a synchronous foaming process of transverse stretching; The surface dense layer and the bottom microporous layer of the gradient structure comprise, by mass percentage: Base material: 75-85% polyethylene terephthalate; Light diffusion agent: 12-20% double-size calcite particles modified by a silane coupling agent vapor; Foaming agent: 0.5-1.5% chemical foaming agent; Coupling agent: 0.1-0.3% silane coupling agent; Antistatic agent: 0.3-0.8% non-ionic antistatic agent; Thermal stabilizer: 0.2-0.5% phosphite and hindered phenol compound, wherein the mass ratio of phosphite to hindered phenol is 1:2; The double-size calcite particles are 100-300 nm nano calcite and 3-8 μm micron calcite, and the mass ratio is 1:2-1:5; The surface dense layer is longitudinally stretched at a temperature of 90-100 ℃ and a stretching ratio of 3.5-4.0; and the bottom microporous layer is transversely stretched at a temperature of 105-115 ℃ and a stretching ratio of 3.0-3.

5.

2. A high haze calcite BOPET composite diffusion film according to claim 1, characterized in that, The double-size calcite particles are prepared by a silane coupling agent vapor injection process, and the preparation method comprises the following steps: (1) Calcite pretreatment: drying the calcite powder to reduce the water content to less than 0.3 wt%; (2) Silane coupling agent vapor injection: adding the pretreated calcite powder into a double-screw extruder for extrusion, and injecting a silane coupling agent into the melting section of the double-screw extruder through a precision metering pump under nitrogen protection, with nitrogen as the carrier gas, the injection temperature of the silane coupling agent being 250-255 ℃, and the carrier gas flow being 5-8 L / min; (3) Dynamic grafting: condensation reaction between silanol groups and calcite surface hydroxyl groups; (4) Vacuum devolatilization: discharging small molecule byproducts under a pressure of -0.06-0.08 MPa through a high-vacuum devolatilization system, and finally obtaining in-situ grafted calcite.

3. A high haze calcite BOPET composite diffusion film according to claim 1, characterized in that, The foaming agent decomposes at a temperature of 105-115 ℃ in the transverse stretching stage.

4. A high haze calcite BOPET composite diffusion film according to claim 1, characterized in that, The foaming agent is one or more combinations of azodicarbonamide, 4,4'-oxybisbenzenesulfonylhydrazide, p-toluenesulfonylhydrazide, sodium bicarbonate, and 5-phenyltetrazole; The silane coupling agent is one or more combinations of γ-aminopropyltriethoxysilane KH-550, γ-(2,3-epoxypropoxy)propyltrimethoxysilane KH-560, and γ-methacryloyloxypropyltrimethoxysilane KH-570; The non-ionic antistatic agent is one or more combinations of ethylene bis-stearamide, glycerol monostearate, stearamide, and erucamide.

5. A high haze calcite BOPET composite diffusion film according to claim 1, characterized in that, The surface hardness of the surface dense layer is greater than or equal to 3H, and the haze contribution rate is less than or equal to 5%; the haze of the bottom microporous layer is greater than or equal to 85%, and the light transmittance is greater than or equal to 88%.

6. The method of claim 1, wherein the method of preparing a high haze calcite BOPET composite diffusion film is characterized by, The method comprises the following steps: (1) the base material, light diffuser, foaming agent, coupling agent, antistatic agent, and thermal stabilizer are premixed and then added into a double-screw extruder, and the melt is extruded by the double-screw extruder under the protection of nitrogen and through segmented temperature control, and the screw rotation speed is 300-350 rpm; (2) after the melt is extruded through a T-shaped die, longitudinal stretching is first performed to form a surface dense layer, and then transverse stretching is performed to form a bottom microporous layer.

7. The method of claim 6, wherein the high-haze calcite BOPET composite diffusion film is prepared by the steps of: (a) preparing a calcite BOPET film; (b) coating the calcite BOPET film with a coating solution; and (c) drying the coated calcite BOPET film. In step (2), the longitudinal stretching temperature is 90-100℃, and the stretching ratio is 3.5-4.0; the transverse stretching temperature is 105-115℃, and the stretching ratio is 3.0-3.5, and the foaming agent is decomposed to generate gas to form micropores during the transverse stretching process.

8. A backlight module, characterized in that, The high-haze calcite BOPET composite diffusion film is adopted.

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