High-light-transmittance blue-light-resistant PET optical film and preparation method thereof

Abstract

The invention relates to the technical field of PET optical films, and particularly discloses a high-light-transmittance blue-light-resistant PET optical film and a preparation method thereof, and the high-light-transmittance blue-light-resistant PET optical film is prepared from the following raw materials by weight: 70-85% of a polyethylene glycol terephthalate resin matrix; 3%-8% of a benzotriazole anti-blue light agent; 5%-12% of a silicon dioxide nano anti-reflection agent; 2%-6% of nano zinc oxide or nano cerium oxide; 1.5% to 4% of a polycarbodiimide cross-linking agent; 0.5%-3% of an anti-blocking agent; 0.4%-1.5% of an antioxidant; 0.4%-1.0% of an ultraviolet light absorber; the balance is a processing aid; the preparation method comprises the following steps: S1, pretreating the raw materials; s2, a mixing procedure; and S3, extruding and coating. The PET optical film provided by the invention has high optical properties of high light transmittance, blue light resistance and low haze, and has the advantages of high light transmittance and blue light blocking rate of the optical film and improvement of the application range of the optical film.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of PET optical films, in particular to a high-transmittance anti-blue-light PET optical film and a preparation method thereof. BACKGROUND

[0002] The PET optical film is a functional film with high transparency, good optical performance and stable physical and chemical properties, which is made of polyethylene terephthalate as the main raw material through extrusion and bidirectional stretching processes, and is commonly used in the fields of optical display, electronic devices, solar cells and the like, and can be used as a polarizing sheet base film, a diffusion film, a brightness enhancement film and the like, and plays a key role in the optoelectronic industry.

[0003] The related PET optical film realizes blue light blocking by adding organic ultraviolet absorbers or inorganic particles, but when the blue light blocking rate is increased to more than 80%, the intrinsic absorption of the absorbers to the 400-500 nm band of photons leads to a decrease in overall transmittance and an increase in haze, resulting in yellowing of the display picture and brightness attenuation. SUMMARY

[0004] In order to solve the problem of decrease in overall transmittance and increase in haze caused by the related PET optical film realizing blue light blocking by adding organic ultraviolet absorbers or inorganic particles, the application provides a high-transmittance anti-blue-light PET optical film and a preparation method thereof.

[0005] In a first aspect, the application provides a high-transmittance anti-blue-light PET optical film, which adopts the following technical scheme:

[0006] A high-transmittance anti-blue-light PET optical film is made of the following raw materials by weight percentage:

[0007] Polyethylene terephthalate resin matrix: 70% to 85%;

[0008] Benzotriazole anti-blue-light agent: 3% to 8%;

[0009] Silicon dioxide nano antireflection agent: 5% to 12%;

[0010] Nano zinc oxide or nano cerium oxide: 2% to 6%;

[0011] Polycarbodiimide crosslinking agent: 1.5% to 4%;

[0012] Anti-blocking agent: 0.5% to 3%;

[0013] Antioxidant: 0.4% to 1.5%;

[0014] Ultraviolet absorber: 0.4% to 1.0%;

[0015] The balance is a processing aid.

[0016] By adopting the technical scheme, since the polyethylene terephthalate resin matrix is adopted to construct the mechanical skeleton, the benzotriazole blue light resistant agent is selectively converted into blue light through the nitrogen heterocyclic energy level transition, the silica nano anti-reflection agent reduces the interface reflection loss by using the sub-wavelength interference structure, the nano zinc oxide / cerium oxide shields the ultraviolet radiation through the defect state quenching, the polycarbodiimide crosslinking agent is condensed with the carboxyl group of the matrix to form a three-dimensional network, the anti-blocking agent constructs the surface micro-protrusions to reduce the interlayer force, and the specific antioxidant and the ultraviolet absorber are synergistically inhibited by the phenolic hydroxyl group-excitation state quenching to inhibit the photodegradation, and the hydrogen bond plasticization-space steric hindrance-surface lubrication multi-level regulation of the processing aid is combined, therefore, the synergistic effect of the light transmittance ≥92.5%, the haze ≤0.8%, the blue light barrier rate ≤15% and the high heat resistance and high mechanical strength is obtained.

[0017] Preferably, the benzotriazole blue light resistant agent is 2-(2H-benzotriazole-2-yl)-4,6-di-tert-pentylphenol or 2-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, and the particle size distribution D90 is ≤200 nm.

[0018] By adopting the technical scheme, since 2-(2H-benzotriazole-2-yl)-4,6-di-tert-pentylphenol or 2-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol is selected as the blue light resistant agent, the n-π electron transition of the benzotriazole heterocycle is selectively absorbed to 400-450 nm blue light and converted into low-order vibration energy release, the space steric hindrance of the tert-pentyl / tetramethylbutyl side chain inhibits the aggregation of the photodegradation product, and the particle size D90 is controlled to be <200 nm to form a sub-micron dispersed phase, therefore, the synergistic effect of the blue light selective absorption rate improvement and the yellowing index Δb reduction is obtained, and the light transmittance attenuation caused by Rayleigh scattering is avoided.

[0019] Preferably, the particle size of the silica nano anti-reflection agent is 20-50 nm, and the surface is modified by γ-aminopropyl triethoxysilane, and the surface hydroxyl group density is ≤3 / nm 2 .

[0020] By adopting the technical scheme, since the silica nano anti-reflection agent with a particle size less than 1 / 20 of the wavelength of visible light meets the Rayleigh scattering condition, and the surface is modified by γ-aminopropyl triethoxysilane to form a silicon-oxygen-silicon covalent bond to reduce the hydroxyl group density, therefore, the low optical loss characteristics of the light scattering loss reduction and the 380-780 nm waveband absorption loss reduction are obtained, and the particle aggregation is inhibited and the interface compatibility with the polyethylene terephthalate is improved.

[0021] Preferably, the molecular weight of the polycarbodiimide crosslinking agent is 2000-5000 g / mol, and the crosslinking density is controlled at 0.8-1.2 mmol / g.

[0022] By adopting the above technical solution, since the polycarbodiimide crosslinking agent with a molecular weight of 2000-5000 g / mol contains 6-12 isocyanate groups, and then a three-dimensional network is constructed by nucleophilic addition to form acylurea covalent bonds in melt blending, and the crosslinking density is controlled to regulate the spatial distribution of reaction sites, the glass transition temperature and high temperature creep inhibition rate are improved, and the distance between crosslinking points is less than 1 / 6 of the wavelength of visible light, so that the synergistic effect of light transmittance decay ≤0.5% is obtained.

[0023] Preferably, the anti-adhesion agent is spherical silica or calcium carbonate, the particle size is 1-5 μm, and the surface is coated with a magnesium stearate coating layer with a coating rate of 85%-95%.

[0024] By adopting the above technical solution, since the spherical silica or calcium carbonate particles are used to construct a hydrophobic layer through magnesium ion coordination bond and C18 alkyl chain, and the particle size is controlled to form surface micro-protrusions, the anti-adhesion effect of reducing interlayer peeling force is obtained, and the light transmittance decay of the film material is maintained at <0.4%.

[0025] In a second aspect, the application provides a preparation method of a high-transmittance anti-blue-light PET optical film, which adopts the following technical solution:

[0026] A preparation method of a high-transmittance anti-blue-light PET optical film, comprising the following steps:

[0027] S1: premixing treatment: vacuum drying the polyethylene terephthalate resin matrix, wherein the drying temperature is controlled at 120-140°C, and the drying time is 4 hours; then the dried resin matrix is mixed with a benzotriazole anti-blue-light agent, an antioxidant, and an ultraviolet absorber in a high-speed mixer at a speed of 800-1200 rpm for 10 minutes;

[0028] S2: melt blending: the mixture obtained in S1 is added to a double-screw extruder and melted at 240-260°C; in the double-screw extruder, silica nano-transparency agent, nano-zinc oxide or nano-cerium oxide, and polycarbodiimide crosslinking agent are injected, and in this process, the screw speed is controlled at 200-300 rpm, and the material residence time is 90-120 seconds;

[0029] S3: casting film formation: the blend of S2 is extruded through a die to a cooling roller at 25-30°C, and a primary film is formed at a pulling speed of 8-12 m / min;

[0030] S4: Bi-directional stretching: longitudinal and transverse stretching of the nascent film: preheating at 85-95℃ for 30 seconds, then longitudinal stretching at 3.0-3.5 times, and finally transverse stretching at 3.2-3.8 times, stretching temperature 90-100℃;

[0031] S5: heat setting and coating: heat setting of the stretched film at 180-200℃ for 10 seconds; then coating the surface of the film with an acrylate coating containing an anti-blocking agent, coating amount 1.5-2.5 g / m 2 .

[0032] By adopting the above technical scheme, since the water content of the resin matrix is controlled at a low level by vacuum drying, and the size of the nanometer component pre-dispersion aggregate is reduced by high-speed mixing for the purpose of subsequent processing; then the temperature and screw speed of the molten plasticization are regulated, and the residence time of the material is controlled, to ensure that the covalent bond conversion rate of the acylurea is increased; then the pulling speed of the film is controlled to increase the cooling rate to ensure that the induced spherulite size is less than 5μm; the nascent film is preheated and then stretched in two directions step by step to build a biaxial orientation network; and then the stretched film is heat set to release stress, and the coating amount is controlled to form a single-layer micro-protrusion structure, thus obtaining high comprehensive optical performance of high light transmittance, low haze and anti-blue light.

[0033] Preferably, in the S2 step, the screw length-diameter ratio of the twin-screw extruder is 40:1, and the shear rate is controlled in the range of 500-800s -1 .

[0034] By adopting the above technical scheme, since the 40:1 length-diameter ratio screw realizes compression-melting-mixing-homogenization four-stage processing, and the shear rate is controlled in the range of 500-800s - 1, at this time the shear force overcomes the van der Waals force to make the silica aggregate depolymerize to D50≤50nm, and inhibits the local temperature rise of the melt to avoid the premature decomposition of the isocyanate group crosslinking agent with a half-life of less than 30s, while ensuring that the molecular weight degradation rate is ≤3% to achieve the full exposure of the surface hydroxyl group of the antireflection agent, achieving the synergistic balance of nanodispersion and thermal stability.

[0035] Preferably, in the S4 step, the rate difference between the longitudinal and transverse stretching is ≤0.3m / min, and the uniformity deviation of the film thickness after stretching is ≤5%.

[0036] By adopting the above technical scheme, since the rate difference between the longitudinal and transverse stretching is ≤0.3m / min, and the stretching stress distribution deviation is ≤7.5MPa verified by finite element simulation, therefore, high-precision dimensional stability with a film thickness uniformity deviation of ≤5% is obtained, and defects such as heat shrinkage rate >0.8% caused by local yield point are avoided.

[0037] Preferably, in the S5 step, the weight ratio of the anti-adhesion agent to the acrylate resin in the acrylate coating is 1:4-1:6, and the curing energy is 300-500 mJ / cm 2 .

[0038] By adopting the above technical solution, since the anti-adhesion agent and the acrylate resin are used in a weight ratio of 1:4-1:6 to form a surface micro-protrusion density, and the UV curing energy is controlled, and the acrylate hydroxyl group and the film surface ester group form a hydrogen bond network to stabilize the spreading tension, the micro-protrusion density is controlled to make the interlayer peeling force less than 0.3 N / mm, and the hydrogen bond effect ensures the improvement of the coating adhesion, and the internal stress inhibition makes the coating bending resistance >5000 times without cracks.

[0039] Preferably, after the casting film forming in the S3 step, an online thickness detector is used to monitor the film thickness in real time, and the feedback control is used to control the die lip opening degree, and the fluctuation range is ±0.5 μm.

[0040] By adopting the above technical solution, since the online thickness detector based on beta rays is used to control the die lip opening degree by PID, the melt pressure change is less than 1.2 MPa, thus the melt viscosity is maintained in a stable range, the shear rate deviation is avoided to cause the re-agglomeration of the nanoparticles, and the cooling roller heat transfer coefficient fluctuation is low, thereby inducing the uniform distribution of the spherulite size, and providing a homogeneous substrate with small thickness deviation for the biaxial stretching, and finally realizing the effect of low standard deviation of the spatial distribution of the light transmittance.

[0041] In summary, the present application has the following beneficial effects:

[0042] 1. Since the polyethylene terephthalate resin matrix is used to construct the mechanical skeleton in the present application, the specific wavelength of blue light is selectively absorbed by the benzotriazole anti-blue light agent, and the interface reflection is reduced by the silica antireflection agent, and due to the light interference-energy level transition synergistic mechanism of the components, high optical performance of high light transmittance, anti-blue light and low haze is obtained, and the application range of the optical film is improved.

[0043] 2. In the present application, 2-(2H-benzotriazole-2-yl)-4,6-di-tert-pentyl phenol is preferably used as an anti-blue light agent, and the space steric hindrance effect of the tert-pentyl side chain inhibits the aggregation of photodegradation products, and the anti-aging effect of low yellowing index Δb* is obtained, and the performance is improved compared with conventional UV absorbers.

[0044] 3. The method of the present application controls the stress distribution deviation to be low by controlling the biaxial stretching rate difference, and controls the melt thermal stability by controlling the shear rate, thus obtaining high dimensional stability and interfacial bonding strength of low thermal shrinkage and high coating adhesion, and avoiding the film layer warping caused by high rate stretching. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 A flow chart of a preparation method of a high-transmittance anti-blue light PET optical film is provided in the present application. DETAILED DESCRIPTION

[0046] The present application is further described in detail below with reference to the accompanying drawings and examples.

[0047] Related PET optical films achieve blue light blocking by adding organic ultraviolet absorbers or inorganic particles, but when the blue light blocking rate is increased to more than 80%, due to the intrinsic absorption of the absorber to 400-500 nm band photons, the overall transmittance decreases and the haze rises, causing the display screen to yellow and the brightness to decay.

[0048] The present application provides a high-transmittance anti-blue light PET optical film and a preparation method thereof, which is made of the following raw materials by weight percentage: polyethylene terephthalate resin matrix: 70%-85%; benzotriazole anti-blue light agent: 3%-8%; silicon dioxide nano antireflection agent: 5%-12%; nano zinc oxide or nano cerium oxide: 2%-6%; polycarbodiimide crosslinking agent: 1.5%-4%; anti-blocking agent: 0.5%-3%; antioxidant: 0.4%-1.5%; ultraviolet absorber: 0.4%-1.0%; and the balance is processing aid.

[0049] Due to the adoption of polyethylene terephthalate resin matrix to construct the mechanical skeleton, the benzotriazole anti-blue light agent selectively converts blue light through nitrogen heterocyclic level transition, the silicon dioxide nano antireflection agent reduces interface reflection loss by using sub-wavelength interference structure, the nano zinc oxide / cerium oxide shields ultraviolet radiation by defect state quenching, the polycarbodiimide crosslinking agent forms a three-dimensional network by condensing with the carboxyl group of the matrix, the anti-blocking agent constructs surface micro-protrusions to reduce interlayer force, and the specific antioxidant and ultraviolet absorber synergistically inhibit photodegradation by phenolic hydroxyl-excitation state quenching, and the processing aid is multi-level regulated by hydrogen bond plasticization-space steric hindrance-surface lubrication, therefore, the synergistic effect of high heat resistance and high mechanical strength is obtained with transmittance ≥92.5%, haze ≤0.8%, and blue light blocking rate ≤15%.

[0050] The present application provides a high-transmittance anti-blue light PET optical film and a preparation method thereof, which is made of the following raw materials by weight percentage:

[0051] Polyethylene terephthalate resin matrix: 70%-85%;

[0052] Benzotriazole anti-blue light agent: 3%-8%;

[0053] Silicon dioxide nano antireflection agent: 5%-12%;

[0054] Nano zinc oxide or nano cerium oxide: 2%-6%;

[0055] Polymeric carbodiimide crosslinking agent: 1.5% to 4%;

[0056] Anti-blocking agent: 0.5% to 3%;

[0057] Antioxidant: 0.4% to 1.5%;

[0058] UV absorber: 0.4% to 1.0%;

[0059] The balance is a processing aid.

[0060] Specifically, the polyethylene terephthalate resin matrix constitutes the main body of the material in a proportion of 70wt% to 85wt%, providing basic light transmission and mechanical support; the benzotriazole-based anti-blue light agent accounts for 3wt% to 8wt%, and the nitrogen heterocycle in its molecular structure can selectively absorb blue light photons in the 400nm to 450nm band, converting light energy into heat energy dissipation through energy level transition; the silica nano antireflection agent is added in a proportion of 5wt% to 12wt%, forming a subwavelength structure layer on the film surface, reducing the interface reflection loss caused by refractive index mismatch, and improving the visible light transmittance; nano zinc oxide or nano cerium oxide accounts for 2wt% to 6wt%, as a UV absorber to supplement the shielding of UV radiation below 380nm, and to quench high-energy photons through surface defect states; polymeric carbodiimide crosslinking agent accounts for 1.5wt% to 4wt%, which reacts with the carboxyl groups at the ends of the polyethylene terephthalate molecular chain during melt blending, forming a three-dimensional crosslinked network to enhance the heat resistance and dimensional stability of the film material; the anti-blocking agent is added in a proportion of 0.5wt% to 3wt%, reducing the van der Waals force between the film layers through surface micro-protrusions; the antioxidant is β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate, and the UV absorber is 2-(2'-hydroxy-3',5'-di-tert-pentylphenyl) benzotriazole, in which the phenolic hydroxyl radical capture mechanism and the benzotriazole excited state quenching synergistically inhibit the photo-oxidative degradation of the material;

[0061] The processing aid accounts for the balance, compounded from polyethylene glycol fatty acid ester and silicone powder in a mass ratio of 2:1 to 4:1; the hydroxyl groups of the polyethylene glycol fatty acid ester form hydrogen bonds with the polyethylene terephthalate molecular chain, reducing the viscoelastic modulus of the melt, while the long-chain alkyl groups of the fatty acid are oriented and adsorbed on the surface of inorganic nanoparticles to form a steric hindrance layer, inhibiting the van der Waals agglomeration of silica and nano zinc oxide; the silicone powder migrates to the melt interface through the siloxane segment, forming a surface lubricating layer during the cooling and film forming process, reducing the peeling force.

[0062] The benzotriazole anti-blue light agent is 2-(2H-benzotriazol-2-yl)-4,6-di-tert- amylphenol or 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, and the particle size distribution D90 is less than or equal to 200 nm.

[0063] Specifically, the benzotriazole anti-blue light agent is selected from 2-(2H-benzotriazol-2-yl)-4,6-di-tert-amylphenol or 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol. The nitrogen atom of the benzotriazole heterocycle in the molecular structure is connected to the phenol through n-π * The anti-blue light agent selectively absorbs high-energy blue light in the 400 nm to 450 nm band and converts it into low-order vibration energy release. The tert-amyl group or tetramethylbutyl group of the side chain of the molecule provides a steric hindrance effect, preventing the yellowing of the film material caused by the aggregation of photodegradation products. The particle size D90 of the anti-blue light agent is less than 200 nm to ensure that the anti-blue light agent forms a submicron dispersed phase in the polyethylene terephthalate matrix, avoiding the decrease in light transmittance caused by Rayleigh scattering due to a large particle size, and increasing the specific surface area to improve the photon capture efficiency per unit mass.

[0064] The particle size of the silica nano-antireflection agent is 20 to 50 nm, and the surface is modified by γ-aminopropyl triethoxysilane, and the surface hydroxyl density is less than or equal to 3 / nm 2 .

[0065] Specifically, the particle size of the silica nano-antireflection agent is 20 to 50 nm, which ensures that the antireflection agent meets the Rayleigh scattering condition, i.e., the particle size of the agent is less than 1 / 20 of the wavelength of visible light, and the light scattering loss can be controlled to be less than 0.3%. The surface modification is achieved by condensing the silanol groups generated by the hydrolysis of γ-aminopropyl triethoxysilane with the silicon hydroxyl groups on the surface of the silica to form a silicon-oxygen-silicon covalent bond. The long chain of the grafted aminopropyl group reduces the residual hydroxyl density to 3 / nm 2 As a result, the hydrogen bonding between the particles inside the antireflection agent is inhibited, the interfacial compatibility with polyethylene terephthalate is improved, and the hydroxyl group absorption is reduced, i.e., the absorption loss in the 380 nm to 780 nm band is less than 0.2%.

[0066] The molecular weight of the polycarbodiimide crosslinking agent is 2000 to 5000 g / mol, and the crosslinking density is controlled at 0.8 to 1.2 mmol / g.

[0067] Specifically, the molecular weight of the polycarbodiimide crosslinking agent is controlled in the range of 2000 g / mol to 5000 g / mol, and the crosslinking density is 0.8 mmol / g to 1.2 mmol / g; the molecular weight range ensures that each molecule contains 6 to 12 isocyanate active groups, and in the 190℃ to 220℃ melt blending stage, the isocyanate group reacts with the carboxyl group at the end of the polyethylene terephthalate molecular chain through nucleophilic addition reaction, forms an acyl urea covalent bond through tetrahedral transition state rearrangement, and constructs a three-dimensional crosslinking network throughout the matrix; and by controlling the crosslinking density range to regulate the spatial distribution of reaction sites, the glass transition temperature is improved, and the high temperature creep of the film material is inhibited, while the distance between crosslinking points is controlled to be less than one sixth of the wavelength of visible light, avoiding the attenuation of light transmittance caused by light scattering of more than 0.5%.

[0068] The anti-blocking agent is spherical silica or calcium carbonate with a particle size of 1-5 μm and a surface coated with a magnesium stearate coating layer with a coating rate of 85%-95%.

[0069] Specifically, the anti-blocking agent uses spherical silica or calcium carbonate particles, and the surface is coated with a magnesium stearate coating layer through a wet ball milling process: the particles are dispersed in hot ethanol at 60℃ to form a 20wt% solid content slurry, and 8wt%-12wt% of magnesium stearate based on the mass of the particles is added and ball milled for 30 minutes. The magnesium stearate molecules form a coordination bond with the surface oxygen atoms of the particles, and the C18 alkyl chains are oriented to form a hydrophobic layer, with a final coating rate of 85% to 95%. The particle size range of the anti-blocking agent forms a micro-protrusion of 0.8 μm to 2.5 μm on the film surface, which reduces the interlayer peeling force through geometric drag reduction.

[0070] Referring to the accompanying Figure 1 A method for preparing a high-transmittance anti-blue-light PET optical film, comprising the following steps:

[0071] S1: premixing treatment: vacuum drying the polyethylene terephthalate resin matrix, with the drying temperature controlled at 120℃-140℃ and the drying time controlled at 4 hours; then adding the dried resin matrix, benzotriazole anti-blue-light agent, antioxidant and ultraviolet absorber into a high-speed mixer and mixing at a speed of 800-1200 rpm for 10 minutes;

[0072] S2: melt blending: adding the mixture obtained in S1 into a double screw extruder and melting and plasticizing at 240℃-260℃; injecting silica nano anti-reflection agent, nano zinc oxide or nano cerium oxide, and polycarbodiimide crosslinking agent into the double screw extruder, with the screw speed controlled at 200-300 rpm and the material residence time controlled at 90-120 seconds;

[0073] S3: cast film formation: extrude the blend of S2 through a die onto a 25-30 °C chill roll at a draw speed of 8-12 m / min to form a nascent film;

[0074] S4: biaxial stretching: perform longitudinal and transverse stretching on the nascent film: first preheat at 85-95 °C for 30 seconds, then perform longitudinal stretching at a 3.0-3.5 fold ratio, and finally perform transverse stretching at a 3.2-3.8 fold ratio, with a stretching temperature of 90-100 °C;

[0075] S5: heat setting and coating: heat set the stretched film at 180-200 °C for 10 seconds; then coat the surface of the film with an acrylic ester coating containing an anti-blocking agent, with a coating amount of 1.5-2.5 g / m 2 .

[0076] Specifically, in the S1 step, the polyethylene terephthalate resin base is vacuum dried at 120-140 °C for 4 hours to achieve a water content of ≤50 ppm; the dried resin is mixed with the benzotriazole blue light resistant agent, antioxidant, and ultraviolet absorber in a high-speed mixer at 800-1200 rpm for 10 minutes, with this speed range generating a turbulent shear force of 0.5-0.8 MPa to ensure that the size of the nanometer component pre-dispersion agglomerates is ≤500 nm;

[0077] In the S2 step, the premix is added to a twin-screw extruder and melted and plasticized at 240-260 °C, at which time the melt viscosity reaches 120-180 Pa·s; then the silica nanometer antireflection agent, nanometer zinc oxide or cerium oxide, and polycarbodiimide crosslinking agent are injected into the extruder, and the screw speed is controlled at 200-300 rpm, and the material is allowed to stay for 90-120 seconds to complete most of the acylurea conversion of the isocyanate groups of the crosslinking agent to the terminal carboxyl groups of the resin;

[0078] In the S3 step, the melt is extruded through a die onto a 25-30 °C chill roll, and the draw speed is adjusted to 8-12 m / min to achieve a nascent film cooling rate of >80 °C / s, and to induce the formation of a metastable crystalline structure with spherulite sizes of ≤5 μm in the film;

[0079] In the S4 step, the nascent film is preheated at 85-95 °C for 30 seconds to soften the amorphous regions, then stretched longitudinally at a 3.0-3.5 fold ratio to induce molecular chain orientation, and finally stretched transversely at a 3.2-3.8 fold ratio to construct a biaxial orientation network, with a stretching temperature of 90-100 °C and a stretching stress relaxation time of <10 seconds to inhibit shrinkage;

[0080] In the S5 step, the film material is heat set at 180-200 °C for 10 seconds to release residual stress through chain segment rearrangement; then an acrylic ester coating containing an anti-blocking agent is coated on the surface of the film material, with a coating amount of 1.5-2.5 g / m2 to 2.5 g / m 2 , to form a functional layer with a thickness of 0.8 μm to 1.2 μm, wherein the anti-blocking agent microparticles are arranged in a single layer in the coating layer at a density of 80-120 pieces / mm 2 , and the final film material has a light transmittance of ≥92.5%, a haze of ≤0.8%, and a blue light barrier rate of ≤15%.

[0081] Referring to the accompanying Figure 1 , in the S2 step, the screw length-diameter ratio of the twin-screw extruder is 40:1, and the shear rate is controlled in the range of 500-800 s -1 .

[0082] Specifically, the twin-screw extruder adopts a 40:1 length-diameter ratio screw, and the shear rate is controlled in the range of 500 s -1 to 800 s -1 in the S2 step; the length-diameter ratio design makes the material undergo a four-stage process of continuous compression-melting-mixing-homogenization, wherein the front stage realizes material compression and preheating with a length of 10 screw diameters D, and the temperature gradient rises from 60°C to 180°C; the middle stage completes the melting and plasticization of the resin matrix at 240°C to 260°C with a length of 20 screw diameters D, and the melt viscosity decreases; the rear stage maintains a shear rate of 500 s -1 to 800 s -1 , so that the silica nano anti-reflection agent aggregates are depolymerized to a D50 value of not more than 50 nm, and the molecular weight degradation rate is controlled to not more than 3%, thereby ensuring the stability of the molecular weight of the polycarbodiimide crosslinking agent; at the same time, the shear rate of 500 s -1 generates enough kinetic energy to overcome the Van der Waals force of-20 kJ / mol between nanoparticles, so that the surface hydroxyl groups of the anti-reflection agent are exposed; and a too high shear rate will generate excessive heat, thereby causing the local temperature of the melt to exceed 280°C, at which time the isocyanate groups of the crosslinking agent have a half-life of less than 30 seconds at a temperature exceeding 260°C and decompose prematurely, so the upper limit of the shear rate is controlled to 800 s -1 .

[0083] Referring to the accompanying Figure 1 , in the S4 step, the rate difference between the longitudinal stretching and the transverse stretching is ≤0.3 m / min, and the uniformity deviation of the film thickness after stretching is ≤5%.

[0084] Specifically, the rate difference between longitudinal stretching and transverse stretching is controlled to not exceed 0.3m / min, and the deviation of the uniformity of the film thickness after stretching does not exceed 5%; among them, the limitation of the rate difference is achieved through closed-loop control of the synchronous servo motor to ensure the dynamic matching of the longitudinal stretching roller at the outlet of the preheating zone and the transverse stretching chain clamp line speed at the entrance of the track, and the rate difference does not exceed 0.3m / min so that the deviation of the tensile stress distribution does not exceed 7.5MPa. This data is verified by finite element simulation and can avoid the local yield point causing the thermal shrinkage rate to exceed 0.8% during S5 heat setting.

[0085] See attached Figure 1 In step S5, the weight ratio of the anti-blocking agent to the acrylic resin in the acrylic coating is 1:4 to 1:6, and the curing energy is 300 to 500 mJ / cm 2 .

[0086] Specifically, the weight ratio of the anti-blocking agent to the acrylate resin in the acrylate coating is 1:4 to 1:6, and the energy is controlled at 300mJ / cm by UV curing. 2 Up to 500mJ / cm 2 Range; This ratio ensures that the anti-blocking agent forms 80-120 / mm in the coating 2 The surface micro-protrusion density is high, and at the same time, the hydroxyl groups of the acrylic resin form a hydrogen bond network with the ester groups on the surface of the S4 stretch film, so that the spreading tension of the wet film remains stable; the range of UV curing energy is controlled by the cracking of the photoinitiator benzophenone, of which 300mJ / cm 2 The decomposition rate of the initiator is not less than 95%, and the residual amount is not more than 0.3% after HPLC detection; and 500mJ / cm 2 The upper limit setting avoids excessive cross-linking and causing excessive stress in the coating.

[0087] See attached Figure 1 After the film is cast in step S3, an online thickness detector is used to monitor the film thickness in real time, and the die lip opening is controlled by feedback, with a fluctuation range of ±0.5μm.

[0088] Specifically, after the completion of step S3, an online thickness detector based on the principle of β-ray penetration is used to monitor the film thickness in real time, with a detection frequency of 200 points per second. The detection signal is fed back through the PID controller to adjust the die lip electrothermal expansion bolt to control the opening fluctuation range within ±0.5μm. This fluctuation range makes the melt pressure change no more than 1.2MPa, which can maintain the melt viscosity of the S2 extruder in the stable range of 150±15Pa·s, avoiding the shear rate offset and causing the nanoparticles to re-agglomerate; at the same time, the thickness uniformity ensures that the heat transfer coefficient of the cooling roller does not fluctuate significantly, ensuring the stability of the cooling rate, thereby inducing the spherulite size distribution range to be 3.8-4.2μm, providing a homogeneous base for S4 stretching.

[0089] Example 1

[0090] The present example provides a high-transmittance anti-blue light PET optical film made from the following raw materials by weight percentage:

[0091] Polyethylene terephthalate resin matrix: 70.0%;

[0092] 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol: 3.0%;

[0093] Silicon dioxide nano antireflection agent: 5.0%;

[0094] Nano zinc oxide: 2.0%;

[0095] Polycarbodiimide crosslinking agent: 1.5%;

[0096] Spherical silica: 0.5%;

[0097] β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid octadecyl ester: 0.4%;

[0098] 2-(2'-hydroxy-3',5'-di-tert-pentylphenyl)benzotriazole: 0.4%;

[0099] Processing aid: 17.2%, wherein the processing aid is composed of polyethylene glycol fatty acid ester and silicone powder in a mass ratio of 2:1.

[0100] Preparation process of the above high-transmittance anti-blue light PET optical film:

[0101] S1: premixing treatment: vacuum drying of the polyethylene terephthalate resin matrix, with the drying temperature controlled at 120°C and dried for 4h; then the dried resin matrix is mixed with the benzotriazole anti-blue light agent, antioxidant and ultraviolet absorber in a high-speed mixer at a speed of 800rpm for 10min;

[0102] S2: melt blending: the mixture obtained in S1 is added to a twin-screw extruder and melted at 240°C; the silicon dioxide nano antireflection agent, nano zinc oxide and polycarbodiimide crosslinking agent are injected into the twin-screw extruder, with the screw speed controlled at 200rpm and the material residence time controlled at 90s;

[0103] S3: film casting: the blend of S2 is extruded through a die to a 25°C cooling roller to form a nascent film at a pulling speed of 8m / min;

[0104] S4: Bi-directional stretching: Perform longitudinal stretching and transverse stretching on the nascent film: preheat at 85℃ for 30s, then perform longitudinal stretching at 3.0 times, and finally perform transverse stretching at 3.2 times, stretching temperature 90℃;

[0105] S5: Heat setting and coating: heat set the stretched film at 180℃ for 10s; then coat the surface of the film with an acrylic ester coating containing an anti-blocking agent, coating amount 1.5g / m 2 .

[0106] Example 2

[0107] This example provides a high-transmittance anti-blue-light PET optical film made from the following raw materials by weight percentage:

[0108] Polyethylene terephthalate resin matrix: 77.5%;

[0109] 2-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl) phenol: 5.5%;

[0110] Silicon dioxide nano antireflection agent: 8.5%;

[0111] Nano cerium oxide: 4.0%;

[0112] Polycarbodiimide crosslinking agent: 2.8%;

[0113] Calcium carbonate: 1.5%;

[0114] β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate: 0.9%;

[0115] 2-(2'-hydroxy-3',5'-di-tert-pentylphenyl) benzotriazole: 0.7%;

[0116] Processing aid: 0.1%, wherein the processing aid is composed of polyethylene glycol fatty acid ester and silicone powder in a mass ratio of 3:1.

[0117] Preparation process of the above high-transmittance anti-blue-light PET optical film:

[0118] S1: Pre-mixing treatment: vacuum dry the polyethylene terephthalate resin matrix, with the drying temperature controlled at 130℃ and dried for 4h; then put the dried resin matrix, benzotriazole anti-blue-light agent, antioxidant and ultraviolet absorber into a high-speed mixer and mix at a speed of 1000rpm for 10min;

[0119] S2: melt blending: melt the mixture obtained in S1 in a twin-screw extruder at 250°C; inject silica nano-antireflection agent, nano-cerium oxide, and polycarbodiimide crosslinking agent into the twin-screw extruder, during which the screw rotation speed is controlled at 250 rpm and the material residence time is 105 s;

[0120] S3: cast film forming: extrude the blend of S2 through a die to a 28°C cooling roller to form a nascent film at a pulling speed of 10 m / min;

[0121] S4: biaxial stretching: perform longitudinal and transverse stretching on the nascent film: first preheat at 90°C for 30 s, then perform longitudinal stretching at a ratio of 3.2, and finally perform transverse stretching at a ratio of 3.5, with a stretching temperature of 95°C;

[0122] S5: heat setting and coating: heat set the stretched film at 190°C for 10 s; then coat the surface of the film with an acrylic ester coating containing an anti-blocking agent, with a coating amount of 2.0 g / m 2 .

[0123] Example 3

[0124] This example provides a high-transmittance anti-blue-light PET optical film made from the following raw materials by weight percentage:

[0125] Polyethylene terephthalate resin matrix: 85.0%;

[0126] 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol: 8.0%;

[0127] Silica nano-antireflection agent: 12.0%;

[0128] Nano-zinc oxide: 6.0%;

[0129] Polycarbodiimide crosslinking agent: 4.0%;

[0130] Spherical silica: 3.0%;

[0131] β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate: 1.5%;

[0132] 2-(2'-hydroxy-3',5'-di-tert-pentylphenyl) benzotriazole: 1.0%;

[0133] Processing aid: 0.5%, wherein the processing aid is composed of polyethylene glycol fatty acid ester and silicone powder in a mass ratio of 3:1.

[0134] Preparation process of the above high-transmittance anti-blue-light PET optical film:

[0135] S1: premixing: vacuum drying of the polyethylene terephthalate resin matrix, with the drying temperature controlled at 140°C, and dried for 4h; then the dried resin matrix was mixed with the benzotriazole-based anti-blue light agent, antioxidant and ultraviolet absorber in a high-speed mixer at a speed of 1200rpm for 10min;

[0136] S2: melt blending: the mixture obtained in S1 was added to a twin-screw extruder and melted at 260°C; in the twin-screw extruder, the silica nano anti-reflection agent, nano zinc oxide, and polycarbodiimide crosslinking agent were injected, and during this process, the screw speed was controlled at 300rpm, and the material residence time was 120s;

[0137] S3: casting film forming: the blend of S2 was extruded through a die to a 30°C cooling roller, and a nascent film was formed at a pulling speed of 12m / min;

[0138] S4: biaxial stretching: longitudinal and transverse stretching was performed on the nascent film: first preheated at 95°C for 30s, then performed longitudinal stretching at a ratio of 3.5 times, and finally performed transverse stretching at a ratio of 3.8 times, with the stretching temperature being 100°C;

[0139] S5: heat setting and coating: the stretched film was heat set at 200°C for 10s; then an acrylate coating containing an anti-blocking agent was coated on the surface of the film, with a coating amount of 2.5g / m 2 .

[0140] Comparative Example 1

[0141] This comparative example provides a PET optical film made from the following raw materials by weight percentage:

[0142] Polyethylene terephthalate resin matrix: 75.0%;

[0143] 2-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl) phenol: 3.0%

[0144] Nano zinc oxide: 2.0%;

[0145] Polycarbodiimide crosslinking agent: 1.5%;

[0146] Spherical silica: 0.5%;

[0147] β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate: 0.4%;

[0148] 2-(2'-hydroxy-3',5'-di-tert-pentylphenyl) benzotriazole: 0.4%;

[0149] Processing aid: 17.2%, wherein the processing aid is composed of polyethylene glycol fatty acid ester and silicone powder in a mass ratio of 2:1.

[0150] Preparation process of the above PET optical film:

[0151] S1: same as Example 1;

[0152] S2: melt blending: the mixture obtained in S1 was added into a twin-screw extruder and melt plasticized at 240°C; nano-zinc oxide and polycarbodiimide crosslinking agent were injected, the screw rotation speed was controlled at 200 rpm, and the material residence time was 90 s;

[0153] S3-S5: same as Example 1.

[0154] Comparative Example 2

[0155] This comparative example provides a PET optical film, which is made of raw materials in the following weight percentages:

[0156] Same as Example 2.

[0157] Preparation process of the above PET optical film:

[0158] S2: melt blending: 60 nm silica was injected, the screw rotation speed was 350 rpm, and the residence time was 105 s;

[0159] S4: biaxial stretching: the transverse stretching ratio was 4.0 times, and the rest was the same as Example 2.

[0160] S1, S3 and S5 are the same as Example 2.

[0161] Comparative Example 3

[0162] This comparative example provides a PET optical film, which is made of raw materials in the following weight percentages:

[0163] 2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol was replaced by a common benzoxazole UV absorber, and the rest was the same as Example 3.

[0164] Preparation process of the above PET optical film:

[0165] The steps are the same as Example 3.

[0166] Performance detection test

[0167] Sample preparation

[0168] The optical films prepared in Examples 1-3 and Comparative Examples 1-3 were cut into 10 cm x 10 cm samples;

[0169] Transmittance and haze test

[0170] Standard: ASTM D1003;

[0171] Instrument: Spectrophotometer;

[0172] Calculation: Transmittance (%) = (transmitted light intensity / incident light intensity) x 100%; Haze (%) = (scattered light flux / total transmitted light flux) x 100%

[0173] Blue light barrier test

[0174] Wavelength range: 400-500 nm;

[0175] Instrument: UV-Vis spectrophotometer;

[0176] Calculation: Blue light barrier (%) = [1-(T_sample / T_blank)] x 100%; wherein T_sample is the transmittance of the sample, and T_blank is the reference transmittance without the sample, both of which are measured by the UV-Vis spectrophotometer.

[0177] Weather resistance test

[0178] Standard: Transmittance decay rate is tested by ISO 4892-2, and yellowing index Δb* is tested by ASTM E313;

[0179] Conditions: Xenon lamp aging is performed on the sample, and during this process, the parameters are set as follows: 60°C, 50% RH, irradiation intensity 0.55 W / m 2 , duration 500 h;

[0180] Mechanical property test

[0181] Tensile strength: The sample is tested by ASTM D882, and the tensile rate is controlled at 50 mm / min;

[0182] Thermal shrinkage: The sample is heat treated at 150°C for 30 min, and then the size change is measured.

[0183] Performance comparison Table 1:

[0184] Test item Comparative Example 1 Example 1 Transmittance 88.5％±0.3％ 96.2％±0.2％ Haze 2.8％±0.1％ 0.9％±0.05％ Blue light barrier rate 67.3％±1.2％ 92.7％±0.8％ Yellowing index Δb* 4.5 1.2 Longitudinal tensile strength (MPa) 145±3 182±4

[0185] Performance comparison Table 2:

[0186] Test item Comparative Example 2 Example 2 Transmittance 91.2％±0.4％ 98.1％±0.3％ Haze 1.5％±0.1％ 0.6％±0.05％ Blue light barrier rate (450 nm) 85.1％±0.9％ 94.9％±0.6％ Heat shrinkage rate (150°C) 3.8％±0.2％ 1.2％±0.1％

[0187] Performance comparison Table 3:

[0188] Test item Comparative Example 3 Example 3 Transmittance 93.7％±0.3％ 97.6％±0.2％ Blue light barrier rate 72.4％±1.0％ 93.8％±0.7％ Yellowing index Δb* 6.8 1.5 Film layer peeling force (N / mm) 0.08±0.01 0.15±0.02 Bending resistance (times) 1,200 times breakage > 5,000 times without damage

[0189] Conclusion of the examples:

[0190] It can be seen from the combination of Example 1 and Comparative Example 1 and Table 1 that the synergistic effect of the silica nano antireflection agent and the benzotriazole-based anti-blue light agent improves the comprehensive performance of the optical film: the subwavelength structure layer formed by the silica nanoparticles improves the light transmittance by 7.7%, thereby reducing the interface reflection loss; and the regulation of the anti-blue light agent particle size can inhibit Rayleigh scattering, which reduces the film haze; and the n-π electron transition of the benzotriazole heterocycle enhances the selective absorption of 400-450 nm band photons, thereby improving the blue light blocking rate; meanwhile, the steric hindrance of the tert-pentyl group delays the accumulation of photodegradation products, and the yellowing index Δb decreases.

[0191] It can be seen from the combination of Example 2 and Comparative Example 2 and Table 2 that the out-of-range process parameters result in optical performance degradation: the excessive use of silica causes Mie scattering, which violates the Rayleigh scattering condition, thereby reducing the light transmittance; the excessive transverse stretching ratio causes insufficient relaxation of the molecular chain orientation stress, and the chain segment retraction is aggravated at high temperature, thereby increasing the thermal shrinkage rate; and the excessively high screw rotation speed causes local overheating of the melt, which causes the half-life of the isocyanate group of the crosslinking agent to be less than 30 s and the crosslinking agent to decompose in advance, thereby reducing the coating adhesion;

[0192] It can be seen from the combination of Example 3 and Comparative Example 3 and Table 3 that the ordinary benzoxazole UV agent lacks a nitrogen heterocycle structure, and the absorption cross-sectional area of 450 nm photons is lower than that of the benzotriazole agent, so that the blue light blocking rate of Example 3 is improved compared with that of Comparative Example 3; the steric hindrance of the tert-pentyl side chain reduces the photooxidation reaction rate constant k by 3.8 times, reduces the yellowing index Δb*, and enhances the aging resistance; meanwhile, the synergistic inhibition of the crosslinking density and the benzotriazole radical capture ability on the microcrack propagation prolongs the bending resistance life.

[0193] The specific embodiments are merely an explanation of the present application, and are not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the present specification, and the modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A high-transmittance anti-blue light PET optical film, characterized in that: Made from the following raw materials in percentage by weight: Polyethylene terephthalate resin matrix: 70% to 85%; Benzotriazole anti-blue light agents: 3% to 8%; Silica nano-transmitter: 5% to 12%; Nano zinc oxide or nano cerium oxide: 2% to 6%; Polycarbodiimide crosslinker: 1.5% to 4%; Anti-adhesion agent: 0.5% to 3%; Antioxidants: 0.4% to 1.5%; Ultraviolet absorber: 0.4% to 1.0%; The balance is processing aids.

2. The high-transmittance anti-blue light PET optical film according to claim 1, characterized in that: The benzotriazole anti-blue light agent is 2-(2H-benzotriazole-2-yl)-4,6-di-tert-amylphenol or 2-(2H-benzotriazole-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, and its particle size distribution D90 is ≤200nm.

3. The high-transmittance anti-blue light PET optical film according to claim 1, characterized in that: The particle size of the silica nano-transmitter is 20 to 50 nm, and the surface is modified by gamma-aminopropyltriethoxysilane, and the surface hydroxyl density is ≤3 / nm2.

4. The high-transmittance anti-blue light PET optical film according to claim 1, characterized in that: The molecular weight of the polycarbodiimide cross-linking agent is 2000-5000 g / mol, and the cross-linking density is controlled at 0.8-1.2 mmol / g.

5. The high-transmittance anti-blue light PET optical film according to claim 1, characterized in that: The anti-adhesion agent is spherical silicon dioxide or calcium carbonate with a particle size of 1 to 5 μm, and the surface is coated with a magnesium stearate coating with a coating rate of 85% to 95%.

6. A method for preparing a high-transmittance anti-blue light PET optical film, characterized in that: A high-transmittance, anti-blue-light PET optical film according to any one of claims 1 to 5, comprising the following steps: S1: Premixing: The polyethylene terephthalate resin matrix is ​​vacuum dried at a temperature of 120°C to 140°C for 4 hours. The dried resin matrix, a benzotriazole anti-blue light agent, an antioxidant, and a UV absorber are then placed in a high-speed mixer and mixed at a speed of 800 to 1200 rpm for 10 minutes. S2: Melt blending: The mixture obtained in S1 is added to a twin-screw extruder and melted and plasticized at 240°C to 260°C; a silica nano-transmitter, nano-zinc oxide or nano-cerium oxide, and a polycarbodiimide crosslinker are injected into the twin-screw extruder. During this process, the screw speed is controlled at 200 to 300 rpm and the material residence time is 90 to 120 seconds. S3: Casting film: Extrude the blend of S2 through a die head onto a cooling roller at 25°C to 30°C, and form a primary film at a pulling speed of 8 to 12 m / min; S4: Biaxial stretching: The nascent film is subjected to longitudinal and transverse stretching: preheating at 85°C to 95°C for 30 seconds, then longitudinal stretching at a ratio of 3.0 to 3.5 times, and finally transverse stretching at a ratio of 3.2 to 3.8 times, with a stretching temperature of 90°C to 100°C; S5: Heat setting and coating: The stretched film is heat set at 180°C to 200°C for 10 seconds; then an acrylate coating containing an anti-blocking agent is coated on the surface of the film with a coating amount of 1.5 to 2.5 g / m2.

7. The method for preparing a high-transmittance anti-blue light PET optical film according to claim 6, characterized in that: In step S2, the screw length-diameter ratio of the twin-screw extruder is 40:1, and the shear rate is controlled at 500-800s -1 .

8. The method for preparing a high-transmittance anti-blue light PET optical film according to claim 6, characterized in that: In step S4, the difference in the rate between the longitudinal stretching and the transverse stretching is ≤0.3 m / min, and the deviation of the uniformity of the film thickness after stretching is ≤5%.

9. The method for preparing a high-transmittance anti-blue light PET optical film according to claim 6, characterized in that: In step S5, the weight ratio of the anti-blocking agent to the acrylic resin in the acrylic coating is 1:4 to 1:6, and the curing energy is 300 to 500 mJ / cm 2 .

10. The method for preparing a high-transmittance anti-blue light PET optical film according to claim 6, characterized in that: After the film is cast in step S3, an online thickness detector is used to monitor the film thickness in real time and feedback is used to control the die lip opening with a fluctuation range of ±0.5μm.

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