Preparation method of high-reflectivity optical thin film and high-reflectivity optical thin film

Abstract

The invention relates to the technical field of optical thin films, and particularly discloses a preparation method of a high-reflectivity optical thin film. According to the method, two kinds of resin with the refractive index difference larger than or equal to 0.08 are selected, the resin is extruded in different screw extruders, the surface of resin melt is activated through plasma, the activated resin is stacked, extrusion film forming is conducted through a gradient temperature control die head, and the high-reflectivity optical thin film is obtained. The transmittance of the 300-400nm wave band of the optical thin film reaches 88% or more, the reflectivity reaches 92% or more, the processing yield is high, the interlayer stability of the optical thin film is excellent, and the optical thin film can bear the high temperature of 120 DEG C or more.

Description

Technical Field

[0001] The present invention relates to the technical field of optical thin films, and more specifically, it relates to a method for preparing a high-reflectivity optical thin film and a high-reflectivity optical thin film. Background Art

[0002] Multi-layer optical thin films are laminated with resins having different refractive indices, and have the characteristics of high reflectivity, high transmittance, and light weight, and are widely used in fields such as displays, solar cells, and lasers. At present, high-refractive-index materials in multi-layer optical thin films include polyethylene naphthalate (PEN, refractive index of 1.75), polyethylene terephthalate (PET, refractive index of 1.65), polyurethane (TPU, refractive index of 1.55), etc., and low-refractive-index materials include polymethyl methacrylate (PMMA, refractive index of 1.49), polyethylene (PE, refractive index of 1.50), etc. By increasing the refractive index difference between layers, the infrared reflectivity of the multi-layer optical film can be improved.

[0003] The method for increasing the refractive index difference between layers in the industry is generally to dope inorganic nanoparticles (such as nano-TiO 2 ), although doping inorganic nanoparticles helps to increase the refractive index of the resin, the inorganic nanoparticles are likely to cause resin atomization. At the same time, the inorganic nanoparticles reduce the contact area between the resin layers, which easily leads to a decrease in the stability of the resin layers in a high-temperature environment, and separation is likely to occur between the resin layers.

[0004] Based on the above situation, how to obtain an optical thin film with excellent thermal stability without affecting the optical performance. Summary of the Invention

[0005] In order to solve the problem that the optical thin film cannot have both high optical performance and stability, the present application provides a method for preparing a high-reflectivity optical thin film and a high-reflectivity optical thin film, the optical thin film has high reflectivity and high transmittance, and can maintain excellent stability at high temperature.

[0006] In a first aspect, the present application provides a method for preparing a high-reflectivity optical thin film, adopting the following technical solution: A method for preparing a high-reflectivity optical thin film, comprising the following steps: Resin selection: Select two resins with a refractive index difference ≥ 0.08; Extrusion: The two resins are extruded in different screw extruders respectively; Plasma activation: The two resins converge in a high-temperature molten state and are activated by radicals on the molecular chain through a plasma treatment device. The activation depth of the plasma treatment device for the resin melt is 5-10 nm; Allocation: The two resin melts after plasma activation are stacked in an adaptive distributor and flow through a gradient temperature control die head to be extruded into a film, obtaining a high-reflectivity optical film.

[0007] Further, among the two resins, the refractive index range of one resin is 1.58 - 1.64, and the refractive index range of the other resin is 1.35 - 1.49.

[0008] Further, the combination of the two resins is any one of the following: polycarbonate and polymethyl methacrylate combination, polystyrene and polymethyl methacrylate combination, polyetherimide and polymethyl methacrylate combination, polystyrene and polytetrafluoroethylene combination, or polyphenylene sulfone resin and polytetrafluoroethylene combination.

[0009] Further, the combination of the two resins is polycarbonate and polymethyl methacrylate.

[0010] Further, in the extrusion step, the temperature of the screw extruder is set in zones, and the zone temperatures increase in an equal gradient.

[0011] Further, in the plasma activation step, the power density of the plasma device treatment is 50 - 100 W / cm 2 , and the treatment time is 0.3 - 1 s.

[0012] Further, in the allocation step, the two resin melts in the temperature control die head flow in different channels, and the channels are controlled by independent temperature control units. Before the two resin melts converge, they flow through a gradual slope to adjust the temperature gradient.

[0013] Further, in the allocation step, the temperature of the convergence zone of the two resin melts is 250 - 270 °C.

[0014] In a second aspect, the present application provides a high-reflectivity optical film, adopting the following technical solution: A high-reflectivity optical film is prepared by the aforementioned method for preparing a high-reflectivity optical film.

[0015] Further, the reflectivity of the high-reflectivity optical film at 300 - 400 nm is ≥92%, and the heat distortion temperature is ≥120 °C.

[0016] The present application has at least the following advantages: First, two pure resins with a refractive index difference ≥ 0.08 are selected as the lamination raw materials in this application; due to the large refractive index difference between the two resins, their structures are different and their processing properties are different. Therefore, the two resins are melted in different temperature ranges of two extruders, and a runner with a gradient slope is set before the two resin melts converge to adjust the temperature difference between the two resins, solving the problem of mismatched melt flow between layers caused by a large processing temperature difference. The two resins are treated by plasma before entering the distributor for lamination, free radicals appear on the resins, the free radicals of the two resins combine, and new chemical bonds are formed at the resin lamination interface, thereby increasing the interfacial bonding strength between the two resins. The interlayer thermal stress of the optical film is matched, and problems such as cracking, bending, and delamination are not likely to occur in a high-temperature environment. At the same time, after the general continuous-mode plasma treatment, the light transmittance of the material generally decreases by 5% - 10%, and the haze increases to more than 20%. However, in this application, pulsed plasma is used to replace the continuous mode, avoiding over-treatment, reducing thermal damage, and controlling the light transmittance loss < 2%, and the haze increase is within 0 - 0.5%.

[0017] Secondly, control the power and time of the plasma treatment to control the formation of free radicals on the resin surface; when the plasma treatment power increases and the time becomes longer, although more free radicals are generated on the resin surface, it is easy to cause resin aging and yellowing, resulting in a red shift of the ultraviolet-visible light absorption edge and fluctuations in the refractive index, leading to abnormal optical path differences in the optical film. When the plasma treatment power decreases and the time is shortened, it is easy to cause insufficient activation of resin free radicals and a decrease in the interlayer bonding force of the optical film. Description of the Drawings

[0018] Figure 1 It is the reflection spectrum of the high-reflectivity optical film of Example 1 of this application. Detailed Embodiments

[0019] Unless otherwise specified, the raw material sources of each preparation example and embodiment in this application are as follows: PC: Grade Mitsubishi Chemical HL-4002M, refractive index value: 1.58; PMMA: Grade CHIMEI CM-207, refractive index value: 1.49; PS: Grade CHIMEI PG-383, refractive index value: 1.59; PEI: Grade SABIC ULTEM™ CRS5011, refractive index value: 1.63; PPSU: Grade Solvay Radel® R-5500, refractive index value: 1.63; PTEF: Grade Daikin Polyflon™ M-12, refractive index value: 1.35.

[0020] Example 1

[0021] A high-reflectivity optical film is made according to the following steps: Material selection: Select PMMA resin particles with a refractive index of 1.49 and PC resin particles with a refractive index of 1.58 as the main raw materials for the laminated film; the refractive index difference between the PMMA resin particles and the PC resin particles is 0.09; Extrusion: Put the PMMA resin particles and the PC resin particles into two single-screw extruders respectively; control the set temperature of the extrusion machine zones for PMMA to be 180 / 220 / 240 / 250 °C; control the set temperature of the extrusion machine zones for PC to be 260 / 280 / 290 / 300 °C; Plasma activation: The molten PMMA resin and PC resin melts are processed by a plasma processor. The plasma processor is protected by an argon atmosphere. The resin melts flow into the plasma reaction chamber. Control the processing power in the reaction chamber to be 50 W / cm 2 , the frequency is 13.56 MHz, and the processing time is 0.5 s; free radicals are excited at a depth of 5-10 nm on the melt surface; Distribution: The PMMA resin melt and the PC resin melt after plasma treatment enter a thousand-layer distributor. The distributor cuts the multi-layer melts into thousands of independent microchannels, and the melts flow stably through the micro-size effect (the diameter of the microchannels is 0.1-0.5 mm), and a thousand-layer structure with alternating stacking of PMMA and PC is formed at the outlet of the distributor. Control the number of stacked layers to be 500 layers; The stacked fluid enters a temperature-controlled die head. The interior of the temperature-controlled die head is designed with multi-layer independent channels, and the PMMA and PC melts flow through different paths respectively; each channel corresponds to an independent heating / cooling unit, and the temperature control accuracy is ±1 °C; before the two resin melts converge, they pass through a gradually sloping channel to adjust the temperature gradient; the temperature of the resin melts in the convergence zone is 260-265 °C; the resin melts are extruded into a film at the outlet of the temperature-controlled die head; After film formation, the high-temperature melt contacts a mirror roller for rapid cooling and forming, and then is traction-wound. The temperature of the water-cooling roller is set at 30-50 °C, the gap of the calender roller is 0.1 mm ± 0.002 mm, and the traction speed is 5-8 m / min.

[0022] Example 2

[0023] A high-reflectivity optical film is made according to the following steps: Material selection: Select PMMA resin particles with a refractive index of 1.49 and PS resin particles with a refractive index of 1.59 as the main raw materials for the laminated film; the refractive index difference between the PMMA resin particles and the PS resin particles is 0.1; Extrusion: Put PMMA resin particles and PS resin particles into two single-screw extruders respectively; control the partition temperature of the PMMA extruder to be set at 180 / 220 / 240 / 250 °C; control the partition temperature of the PS extruder to be set at 180 / 200 / 220 / 240 °C; Plasma activation: The molten PMMA resin and PS resin melts are processed by a plasma processor. The plasma processor is protected by an argon atmosphere. The resin melts flow into the plasma reaction chamber. Control the processing power in the reaction chamber to be 50 W / cm 2 , the frequency is 13.56 MHz, and the processing time is 0.4 s; free radicals are excited at a depth of 5-10 nm on the melt surface; Distribution: The PMMA resin melt and PS resin melt after plasma treatment enter a multi-layer distributor. The distributor cuts the multi-layer melts into thousands of independent micro-channels, and stably flows through the micro-size effect (micro-channel diameter 0.1-0.5 mm), and forms a multi-layer structure with PMMA and PS stacked alternately at the outlet of the distributor. Control the number of stacked layers to be 500 layers; The stacked fluid enters a temperature-controlled die head. The interior of the temperature-controlled die head is designed with multi-layer independent channels, and the PMMA and PS melts flow through different paths respectively; each channel corresponds to an independent heating / cooling unit, and the temperature control accuracy is ±1 °C; before the two resin melts converge, they pass through a gradually sloping channel to adjust the temperature gradient; the temperature of the resin melt in the convergence zone is 240-250 °C; the resin melt is extruded into a film at the outlet of the temperature-controlled die head; After film formation, the high-temperature melt contacts a mirror roller for rapid cooling and forming, and then is drawn and wound up; the temperature of the water-cooled roller is set at 30-50 °C, the calender roll gap is 0.1 mm ± 0.002 mm, and the drawing speed is 5-8 m / min.

[0024] Example 3

[0025] A high-reflectivity optical film is made according to the following steps: Material selection: Select PMMA resin particles with a refractive index of 1.49 and PEI resin particles with a refractive index of 1.63 as the main raw materials for the laminated film; the refractive index difference between the PMMA resin particles and the PEI resin particles is 0.14; Extrusion: Put PMMA resin particles and PEI resin particles into two single-screw extruders respectively; control the partition temperature of the PMMA extruder to be set at 180 / 220 / 240 / 250 °C; control the partition temperature of the PEI extruder to be set at 300 / 310 / 320 / 340 °C; Plasma activation: The molten PMMA resin and PEI resin melts are processed by a plasma processor. An argon atmosphere is used for protection inside the plasma processor. The resin melts flow into the plasma reaction chamber. The processing power in the reaction chamber is controlled at 50 W / cm 2 , the frequency is 13.56 MHz, and the processing time is 0.5 s; Free radicals are excited at a depth of 5 - 10 nm on the melt surface; Distribution: The PMMA resin melt and PEI resin melt after plasma treatment enter a multi-layer distributor. The distributor cuts the multi-layer melts into thousands of independent microchannels, and they flow stably through the micro-size effect (the diameter of the microchannels is 0.1 - 0.5 mm), and a multi-layer structure with alternating stacking of PMMA and PEI is formed at the outlet of the distributor. The number of stacked layers is controlled at 500 layers; The stacked fluid enters a temperature-controlled die head. The inside of the temperature-controlled die head is designed with multi-layer independent channels, and the PMMA and PEI melts flow through different paths respectively; Each channel corresponds to an independent heating / cooling unit, and the temperature control accuracy is ±1°C; Before the two resin melts converge, they pass through a tapered channel to adjust the temperature gradient; The temperature of the resin melts at the convergence zone is 250 - 270°C; The resin melts are extruded into a film at the outlet of the temperature-controlled die head; After film formation, the high-temperature melt contacts a mirror roller for rapid cooling and forming, and then is drawn and wound up; The temperature of the water-cooled roller is set at 30 - 50°C, the gap of the calender roller is 0.1 mm ± 0.002 mm, and the drawing speed is 5 - 8 m / min.

[0026] Example 4

[0027] A high-reflectivity optical film is made according to the following steps: Material selection: PTFE resin particles with a refractive index of 1.35 and PS resin particles with a refractive index of 1.59 are selected as the main raw materials for the laminated film; The refractive index difference between the PTFE resin particles and the PS resin particles is 0.24; Extrusion: The PTFE resin particles and PS resin particles are respectively put into two single-screw extruders; The set temperature of the extrusion machine zones for PTFE is controlled at 300 / 310 / 320 / 330°C; The set temperature of the extrusion machine zones for PS is controlled at 180 / 200 / 220 / 240°C; Plasma activation: The molten PTFE resin and PS resin melts are processed by a plasma processor. An argon atmosphere is used for protection inside the plasma processor. The resin melts flow into the plasma reaction chamber. The processing power in the reaction chamber is controlled at 50 W / cm 2 , the frequency is 13.56 MHz, and the processing time is 0.55 s; Free radicals are excited at a depth of 5 - 10 nm on the melt surface; Dispensing: The PTFE resin melt and the PS resin melt after plasma treatment enter a multi-layer dispenser. The dispenser cuts the multi-layer melt into thousands of independent micro-channels, and the melt flows stably through the micro-size effect (the diameter of the micro-channel is 0.1 - 0.5 mm), and a multi-layer structure with alternating PTFE and PS is formed at the outlet of the dispenser. The number of stacked layers is controlled to be 500 layers; The stacked fluid enters a temperature-controlled die head. The interior of the temperature-controlled die head is designed with multiple independent channels, and the PTFE and PS melts flow through different paths respectively; each channel corresponds to an independent heating / cooling unit, and the temperature control accuracy is ±1 °C; before the two resin melts converge, they pass through a gradually sloping channel to adjust the temperature gradient; the temperature of the resin melt in the convergence zone is 250 - 270 °C; the resin melt is extruded into a film at the outlet of the temperature-controlled die head; After film formation, the high-temperature melt contacts the mirror roller for rapid cooling and forming, and then is drawn and wound up; the temperature of the water-cooled roller is set at 30 - 50 °C, the gap of the calender roller is 0.1 mm ± 0.002 mm, and the drawing speed is 5 - 8 m / min.

[0028] Example 5

[0029] A high-reflectivity optical film is made according to the following steps: Material selection: Select PTFE resin particles with a refractive index of 1.35 and PPSU resin particles with a refractive index of 1.63 as the main raw materials of the laminated film; the refractive index difference between the PTFE resin particles and the PPSU resin particles is 0.28; Extrusion: The PTFE resin particles and the PPSU resin particles are respectively put into two single-screw extruders; the temperature of the extrusion zones of the PTFE extruder is controlled to be set at 300 / 310 / 320 / 330 °C; the temperature of the extrusion zones of the PPSU extruder is controlled to be set at 300 / 310 / 320 / 330 °C; Plasma activation: The molten PTFE resin and PPSU resin melts are treated by a plasma processor. The plasma processor is protected by an argon atmosphere. The resin melt flows into the plasma reaction chamber. The treatment power in the reaction chamber is controlled to be 50 W / cm 2 , the frequency is 13.56 MHz, and the treatment time is 0.6 s; free radicals are excited at a depth of 5 - 10 nm on the melt surface; Dispensing: The PTFE resin melt and the PPSU resin melt after plasma treatment enter a multi-layer dispenser. The dispenser cuts the multi-layer melt into thousands of independent micro-channels, and the melt flows stably through the micro-size effect (the diameter of the micro-channel is 0.1 - 0.5 mm), and a multi-layer structure with alternating PTFE and PPSU is formed at the outlet of the dispenser. The number of stacked layers is controlled to be 500 layers; After stacking, the fluid enters the temperature-controlled die head. The interior of the temperature-controlled die head is designed with multiple independent channels, and the PTFE and PPSU melts flow through different paths respectively; each flow channel corresponds to an independent heating / cooling unit, and the temperature control accuracy is ±1°C; before the two resin melts converge, they pass through a flow channel with a gradual slope to adjust the temperature gradient; the temperature of the resin melt in the convergence zone is 320 - 330°C; the resin melt is extruded into a film at the outlet of the temperature-controlled die head; After film formation, the high-temperature melt contacts the mirror roller for rapid cooling and forming, and then is drawn and wound; the temperature of the water-cooled roller is set at 30 - 50°C, the calender roll gap is 0.1mm ± 0.002mm, and the drawing speed is 5 - 8m / min.

[0030] Comparative Example 1 An optical film is made according to the following steps: Material selection: Select PMMA resin particles with a refractive index of 1.49 and PC resin particles with a refractive index of 1.58 as the main raw materials for the laminated film; the refractive index difference between the PMMA resin particles and the PC resin particles is 0.09; Extrusion: Put the PMMA resin particles and the PC resin particles into two single-screw extruders respectively; control the set temperature of the extrusion zones of the PMMA extruder to be 180 / 220 / 240 / 250°C; control the set temperature of the extrusion zones of the PC extruder to be 260 / 280 / 290 / 300°C; Distribution: The PMMA resin melt and the PC resin melt enter the thousand-layer distributor. The distributor cuts the multi-layer melt into thousands of independent micro-channels, and the melt flows stably through the micro-size effect (the diameter of the micro-channel is 0.1 - 0.5mm), and a thousand-layer structure with alternating PMMA and PC is formed at the outlet of the distributor. Control the number of laminated layers to be 500 layers; After stacking, the fluid enters the temperature-controlled die head. The interior of the temperature-controlled die head is designed with multiple independent channels, and the PMMA and PC melts flow through different paths respectively; each flow channel corresponds to an independent heating / cooling unit, and the temperature control accuracy is ±1°C; before the two resin melts converge, they pass through a flow channel with a gradual slope to adjust the temperature gradient; the temperature of the resin melt in the convergence zone is 260 - 265°C; the resin melt is extruded into a film at the outlet of the temperature-controlled die head; After film formation, the high-temperature melt contacts the mirror roller for rapid cooling and forming, and then is drawn and wound; the temperature of the water-cooled roller is set at 30 - 50°C, the calender roll gap is 0.1mm ± 0.002mm, and the drawing speed is 5 - 8m / min.

[0031] Comparative Example 2 An optical film is made according to the following steps: Material selection: Select PMMA resin particles with a refractive index of 1.49 and PC resin particles with a refractive index of 1.58 as the main raw materials for the laminated film; the refractive index difference between the PMMA resin particles and the PC resin particles is 0.09; Extrusion: Put PMMA resin particles and PC resin particles into two single-screw extruders respectively; control the partition temperature of the PMMA extruder to be set at 180 / 220 / 240 / 250 °C; control the partition temperature of the PC extruder to be set at 260 / 280 / 290 / 300 °C; Plasma activation: The molten PMMA resin and PC resin melts are processed by a plasma processor. An argon atmosphere is used for protection inside the plasma processor. The resin melts flow into the plasma reaction chamber. Control the processing power in the reaction chamber to be 50 W / cm 2 , the frequency is 13.56 MHz, and the processing time is 0.5 s; free radicals are excited at a depth of 5 - 10 nm on the melt surface; Distribution: The PMMA resin melt and PC resin melt after plasma treatment enter a multi-layer distributor. The distributor cuts the multi-layer melts into thousands of independent micro-channels, and they flow stably through the micro-size effect (the diameter of the micro-channels is 0.1 - 0.5 mm), and a multi-layer structure with PMMA and PC stacked alternately is formed at the outlet of the distributor. Control the number of stacked layers to be 500 layers; the resin melt is directly extruded into a film; After film formation, the high-temperature melt contacts the mirror roller for rapid cooling and forming, and then is traction-reeled; the temperature of the water-cooling roller is set at 30 - 50 °C, the gap of the calender roller is 0.1 mm ± 0.002 mm, and the traction speed is 5 - 8 m / min.

[0032] Comparative Example 3 An optical film is made according to the following steps: Material selection: Select PMMA resin particles with a refractive index of 1.49 and PET resin particles doped with 0.1 wt% TiO 2 as the main raw materials of the laminated film; the refractive index difference between the PMMA resin particles and the PET resin particles doped with 0.1 wt% TiO 2 is 0.12; Extrusion: Put PMMA resin particles and PET resin particles doped with 1 wt% TiO 2 into two single-screw extruders respectively; control the partition temperature of the PMMA extruder to be set at 180 / 220 / 240 / 250 °C; control the partition temperature of the PET resin particles doped with 1 wt% TiO 2 to be set at 210 / 230 / 260 / 260 °C; Distribution: The PMMA resin melt and the PET resin particles doped with 1 wt% TiO 2The PET resin melt enters the multi-layer distributor. The distributor cuts the multi-layer melt into thousands of independent micro-channels, and the melt flows stably through the micro-size effect (the diameter of the micro-channel is 0.1 - 0.5 mm), and a multi-layer structure with alternating stacking of PMMA and PET is formed at the outlet of the distributor, and the number of stacked layers is controlled to be 500 layers; The stacked fluid enters the temperature-controlled die head. The interior of the temperature-controlled die head is designed with multi-layer independent channels, and the PMMA and PET melts flow through different paths respectively; each channel corresponds to an independent heating / cooling unit, and the temperature control accuracy is ±1°C; before the two resin melts converge, they pass through a gradually sloping channel to adjust the temperature gradient; the temperature of the resin melt in the convergence area is 260 - 265°C; the resin melt is extruded into a film at the outlet of the temperature-controlled die head; After film formation, the high-temperature melt contacts the mirror roller for rapid cooling and forming, and then is drawn and wound up; the temperature of the water-cooled roller is set at 30 - 50°C, the gap between the calender rollers is 0.1 mm ± 0.002 mm, and the drawing speed is 5 - 8 m / min.

[0033] Test data Samples of Examples 1 - 5 and Comparative Examples 1 - 3 were made with the following specifications: stacked in 500 layers, the total thickness of the product is 30 μm, and the reflectivity and transmittance of the test samples at 300 - 400 nm were measured. The test results are as follows: Table 1. Test data of Examples 1 - 5

[0034] Table 2. Test data of Comparative Examples 1 - 3

[0035] Conclusion: Comparative Examples 1 - 3 are compared with this application. By changing the following parameters, the changes in the related properties such as the reflectivity, heat distortion temperature, transmittance, and interlayer bonding strength of the optical film are explored.

[0036] In Comparative Example 1, the plasma activation technology was not used, and extrusion was directly carried out according to the conventional method. Since the extrusion temperatures of PMMA and PC are quite different, during the stacking process of the two, the melt flow between layers does not match, the co-extrusion difficulty increases, and defects such as micropores, bubbles, and uneven thickness are likely to appear between the layers of the optical film. These defects cause deviations or losses in the propagation and reflection of light in the optical film, and it is difficult for the optical film to achieve a high reflectivity within the set wavelength range. At the same time, defects such as micropores and bubbles affect the interfacial bonding strength between the layers of the optical film. Compared with Example 1, the interfacial bonding strength of Comparative Example 1 decreased significantly. In addition, since the layers of the optical film are bonded by in-situ interfacial chemical bonds, the structural stability of the optical film is enhanced, and the thermal stress between the layers of the optical film is matched, so that problems such as cracking, bending, and delamination are not likely to occur in a high-temperature environment, and the heat distortion temperature of the optical film is significantly increased.

[0037] In Comparative Example 2, extrusion was carried out without using a temperature-controlled die head. PC and PMMA could not be accurately temperature-controlled, and the temperature difference between PC and PMMA was large when the melts converged. The mismatch of thermal stress between the layers of the optical film led to a decrease in the heat distortion temperature. Based on this, it can be seen that by combining the use of a temperature-controlled die head and plasma treatment, the problem of mismatch of thermal stress between the PC and PMMA melts can be effectively solved, thereby significantly increasing the heat distortion temperature of the optical film made of PC / PMMA.

[0038] One of the raw materials in Comparative Example 3 was PET resin doped with TiO 2 to obtain a high-refractive-index raw material by doping the PET resin with nano-inorganic powder; however, the reflectivity of the optical film made was not much different from that of Example 1 (pure resin), but the transmittance decreased significantly. From this, it can be seen that doping nano-inorganic powder in the resin has limited improvement in reflectivity, and it is also likely to cause a decrease in the transmittance of the optical film and an increase in haze. At the same time, the nano-inorganic powder reduces the contact area between the resin layers, resulting in a decrease in the interfacial bonding strength between the layers of the optical film.

[0039] Examples 1-5 used pure resins with different refractive indices as raw materials. See Figure 1 , Figure 1Figure showing the relationship between the wavelength and reflectivity of the optical film prepared in Example 1 is clearly given to prove that the optical film prepared in Example 1 exhibits a high reflectivity in the wavelength range of 300 - 400 nm, with an average reflectivity reaching 92%. In Example 2, the melt extrusion temperatures of PS and PMMA are close, and the thermal stresses are relatively well-matched. Although the heat distortion temperature of PS itself is lower than that of PC, through the formation of new chemical bonds at the interface, the overall heat distortion temperature of the PS / PMMA optical film is increased, and the interfacial bonding strength is enhanced. In Examples 4 - 5, the difference in refractive indices of the raw materials is large, and the reflectivity in the wavelength range of 300 - 400 nm is high. However, the surface energy of PTFE is low. After plasma interface activation treatment, the interfacial bonding strength of the optical film can be maintained above 7.5 MPa. Also, it can be seen from Examples 4 - 5 that when the melt extrusion temperatures are relatively close, it is helpful for the thermal stress matching between layers and enhances the interfacial bonding strength of the optical film.

[0040] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0041] Moreover, the above-described embodiments only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed. However, it should not be construed as a limitation to the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing a high reflectivity optical film, characterized in that: The steps include: Resin selection: Select two resins with a refractive index difference of ≥ 0.08; Extrusion: The two resins are extruded in different screw extruders; Plasma activation: The two resins are combined in a high-temperature molten state, and the free radicals on the molecular chain are activated by a plasma treatment device. The activation depth of the resin melt by the plasma treatment device is 5 to 10 nm. Distribution: The two resin melts activated by plasma are stacked in an adaptive distributor, flow through a gradient temperature-controlled die and are extruded into a film to obtain a high-reflectivity optical film.

2. The method for preparing a high reflectivity optical film according to claim 1, characterized in that: Of the two resins, one resin has a refractive index ranging from 1.58 to 1.64, and the other resin has a refractive index ranging from 1.35 to 1.

49.

3. A method for preparing a high reflectivity optical film according to claim 2, characterized in that: The combination of the two resins is any one of the following: a combination of polycarbonate and polymethyl methacrylate, a combination of polystyrene and polymethyl methacrylate, a combination of polyetherimide and polymethyl methacrylate, a combination of polystyrene and polytetrafluoroethylene, or a combination of polyphenylene sulfone resin and polytetrafluoroethylene.

4. The method for preparing a high reflectivity optical film according to claim 1, characterized in that: In the extrusion step, the temperature of the screw extruder is set in different zones, and the temperature of each zone rises in an isogradient manner.

5. The method for preparing a high reflectivity optical film according to claim 3, characterized in that: In the plasma activation step, the power density of the plasma device is 50 to 100 W / cm 2 , the processing time is 0.3~1s.

6. The method for preparing a high reflectivity optical film according to claim 1, characterized in that: In the distribution step, the two resin melts in the temperature-controlled die head flow in different flow channels, the flow channels are temperature-controlled by independent temperature control units, and the two resin melts flow at a gradual slope before merging to adjust the temperature gradient.

7. A method for preparing a high reflectivity optical film according to claim 6, characterized in that: In the distribution step, the temperature of the converging zone of the two resin melts is 250-270°C.

8. A high reflectivity optical film, characterized in that: The high reflectivity optical film is prepared by the method for preparing the high reflectivity optical film according to claim 1.

9. The high reflectivity optical film according to claim 8, characterized in that: The high-reflectivity optical film has a reflectivity of ≥92% at 300-400nm and a thermal deformation temperature of ≥120°C.

Images