PVDC-based composite material, preparation method and quantum dot diffusion plate containing PVDC-based composite material

Abstract

The invention belongs to the technical field of quantum dot display and polymer composite materials, and particularly discloses a PVDC-based composite material, a preparation method and a quantum dot diffusion plate comprising the PVDC-based composite material. Polyvinylidene chloride (PVDC) resin, general purpose polystyrene (PS), polycarbonate (PC), CdSe quantum dots, styrene-maleic anhydride copolymer SMA, methyl methacrylate-glycidyl methacrylate copolymer PMMA-co-GMA, an antioxidant and a nano diffusant are used as raw materials, and the composite material is prepared through a multi-layer co-extrusion technology. According to the invention, a symmetric barrier layer is formed by PVDC resin, water and oxygen erosion is effectively isolated, strong interface bonding is formed by utilizing the interaction of anhydride groups of SMA and chlorine atoms of PVDC and the reaction of epoxy groups of PMMA-co-GMA and PC end groups, and efficient light conversion and uniform diffusion are realized through the synergistic optical effect of quantum dots and a diffusant.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot display and polymer composite material technology, specifically relating to a PVDC-based composite material, its preparation method, and a quantum dot diffusion plate containing the same. Background Technology

[0002] In recent years, quantum dot TVs, as an important upgrade direction for LCD display technology, have gradually entered the mass consumer market due to their ability to provide ultra-high color gamut coverage, excellent color reproduction capabilities, and relatively energy-saving characteristics. The quantum dot optical module is the core component that enables its superior picture quality.

[0003] Currently, most mainstream quantum dot TV optical solutions on the market adopt an architecture combining a "quantum dot film" and a "barrier film." The quantum dot film is responsible for light conversion, while the barrier film is used to isolate water and oxygen, protecting the quantum dot materials (especially core-shell quantum dots such as CdSe and CdS) which are extremely sensitive to water and oxygen from quenching failure. However, this "film + film" stacked scheme not only increases material costs but also improves assembly complexity and thickness, resulting in high overall costs and indirectly limiting the widespread adoption of quantum dot technology.

[0004] To save on the cost of quantum dot display backlight films, many manufacturers are now replacing quantum dot films with quantum dot diffusers, which combine the excellent fluorescence properties and long fluorescence lifetime of quantum dots. Quantum dot TVs made with these diffusers offer advantages such as a wide and high color gamut, while also being cost-effective. Most diffusers on the market use more stable quantum dots, resulting in lower efficiency and a general decrease in brightness. The outer layer of the diffuser often uses general-purpose optical resins such as polystyrene (PS) and polymethyl methacrylate (PMMA). These materials have poor water and oxygen barrier properties, making the product's reliability far inferior to quantum dot film solutions that use dedicated barrier films. Summary of the Invention

[0005] The purpose of this invention is to provide a PVDC-based composite material, a preparation method thereof, and a quantum dot diffusion plate comprising the same, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A PVDC-based composite material adopts a symmetrical five-layer laminated structure, consisting of an upper outer layer, an upper middle layer, a core layer, a lower middle layer, and a lower outer layer from the outside to the inside. The composition and parameters of each layer are as follows:

[0008] Both the upper and lower outer layers are PVDC barrier layers, comprising, by weight: 100 parts polyvinylidene chloride (PVDC) resin, 3-5 parts antioxidant 1010, 2-3 parts antioxidant 168, and 2-5 parts anti-yellowing agent; the thickness of the PVDC barrier layer is 30-100 μm.

[0009] Both the upper and lower intermediate layers are PS blend interface layers, comprising, by weight: 50-70 parts general-purpose polystyrene (PS), 10-20 parts styrene-maleic anhydride copolymer (SMA), and 10-20 parts methyl methacrylate-glycidyl methacrylate copolymer (PMMA-co-GMA); the thickness of the PS blend interface layer is 50-150 μm.

[0010] The core layer is a PS-PC-quantum dot blended light-emitting layer, comprising, by weight: 30-40 parts general-purpose polystyrene (PS), 50-60 parts polycarbonate (PC), 3-5 parts PS-maleic anhydride graft (PS-g-MAH), 3-5 parts styrene-ethylene-butene block copolymer (SEBS), and 1-4 parts CdSe-based red and green quantum dots; the thickness of the core layer is 200-300 μm.

[0011] The PVDC-based composite material of the present invention constructs a water and oxygen protection barrier through a PVDC barrier layer, enhances interlayer adhesion and alleviates thermal stress through a PS blend interface layer, and achieves light diffusion and efficient light conversion through a PS-PC-quantum dot core layer. The three work together to solve the technical defects of existing materials.

[0012] Another object of the present invention is to provide a method for preparing the above-mentioned PVDC-based composite material, comprising the following steps:

[0013] S1. Prepare PVDC barrier layer material, PS blended interface layer material, and PS+PC+quantum dot core layer material respectively;

[0014] S2. Each layer of material is fed into the corresponding screw extruder through an independent vacuum feeding system for melting and plasticizing to obtain each layer of melt;

[0015] S3. Each layer of melt is introduced into a co-extrusion die through a distributor. The co-extrusion die is provided with mutually isolated flow channels. Each layer of melt is layered and compounded in the die to form a five-layer composite melt curtain.

[0016] S4. The five-layer composite melt curtain is drawn out and cooled and shaped by a cooling roller group to obtain a composite board.

[0017] Preferably, in step S2, the screw extruder features zoned temperature control:

[0018] The extruder used for the PVDC barrier layer has a melting zone temperature of 160-180℃ and a homogenization zone temperature of 170-175℃.

[0019] The extruder used for the PS blend interface layer has a melting zone temperature of 170-180℃ and a homogenization zone temperature of 180-190℃.

[0020] The extruder used for the core layer has a melting zone temperature of 220-250℃ and a homogenization zone temperature of 240-250℃.

[0021] Preferably, in step S3, each flow channel of the co-extrusion die is temperature-controlled independently.

[0022] The flow channel temperature for the PVDC melt is controlled at 165-170℃;

[0023] The flow channel temperature for the PS blend melt is controlled at 180-185℃;

[0024] The flow channel temperature for the PS+PC+quantum dot melt is controlled at 230-250℃.

[0025] Preferably, in step S4, the cooling process employs multi-stage temperature difference cooling: first, a cooling roller at 60-80℃ is used for preliminary shaping, and then a cooling roller at 25-35℃ is used for forced cooling.

[0026] The third objective of this invention is to provide a quantum dot diffusion plate comprising the above-mentioned PVDC-based composite material, which is made by cutting and cleaning the PVDC-based composite material sheet as the core substrate; after testing at 85°C / 85%RH for 500 hours, the quantum dot diffusion plate retains a brightness of not less than 95%.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] (1) Polyvinylidene chloride (PVDC) is used as the barrier material for the upper and lower outer layers, forming a symmetrical double protective barrier. This structure can delay the penetration of water vapor and oxygen, fundamentally preventing the quantum dots from being quenched and deactivated by photo-oxidation and hydrolysis. This allows the quantum dot diffuser plate to maintain stable optical performance for a long time under harsh environments such as high temperature and high humidity, thereby improving product life and reliability.

[0029] (2) Utilizing the top-level protection provided by PVDC, high-efficiency, narrow half-peak width CdSe-based red and green quantum dots are used for the core layer. At the same time, PC resin provides a rigid dispersion environment for the quantum dots, and the optimized co-extrusion process ensures that they are highly uniformly dispersed. This makes the quantum dot diffusion plate made by this invention have a high color gamut coverage while also improving the peak brightness, achieving a perfect balance between high color gamut and high brightness.

[0030] (3) By designing the PS copolymer interface layer, multi-layer material co-extrusion is achieved. The functional compatibilizer in the interface layer can greatly enhance the interfacial adhesion between polar and non-polar materials. This not only avoids delamination but also effectively alleviates the internal stress caused by the different coefficients of thermal expansion during processing and cooling, thereby reducing the warpage of the sheet and ensuring the flatness and dimensional stability of the product. Attached Figure Description

[0031] Figure 1 This is a line graph showing the changes in brightness retention rate and photoluminescence quantum yield retention rate of the present invention.

[0032] Figure 2 This is a bar chart showing the water vapor transmission rate and the water vapor transmission rate after aging, according to the present invention. Detailed Implementation

[0033] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention; the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0034] Initial optical performance testing

[0035] Performance testing: center point brightness and color gamut coverage

[0036] Reason for testing: The purpose is to verify that the PVDC-based quantum dot diffuser of this invention, while solving the problem of quantum dots being easily quenched by water and oxygen erosion and color shifting under high temperature and high humidity environments through the PVDC barrier layer, does not cause excessive brightness decay or excessive color coordinate drift, thus proving that the product achieves both "high stability" and "long-lasting and efficient optical performance" in high temperature and high humidity scenarios.

[0037] 1) Center point brightness (cd / m 2 )

[0038] Data analysis: Brightness is a core visual indicator of display devices. Higher initial brightness means clearer images and higher contrast in bright light environments (such as indoors during the day).

[0039] Reference standards: GB / T35850-2017 "Diffuser plates for liquid crystal displays", GB / T30262.1-2013 "Information technology flat panel display devices - Part 1: Terminology".

[0040] Test Method: The test environment was a darkroom (ambient light intensity ≤10 lux), with the temperature controlled at 25℃±2℃ and relative humidity at 50%RH±5% (to avoid the influence of ambient light interference and temperature and humidity on the performance of the backlight module); a high-precision luminance meter (such as Konica Minolta CS-2000) with metrological certification was used, and zero-point calibration and range calibration were performed according to the equipment manual; three samples were randomly selected from the same batch of PVDC-based composite materials, each sample measuring 100mm×100mm; the sample surface was cleaned with a lint-free cloth soaked in isopropyl alcohol. Remove oil and dust; fix the sample on the light-emitting surface of a standard LED backlight module (the backlight module needs to be preheated for 30 minutes to ensure stable luminous power, and the backlight color temperature is calibrated to 6500K±200K); adjust the vertical distance between the luminance meter lens and the center point of the sample to 50cm, with the lens facing the center point of the sample; measure each sample three times consecutively, with a 10-second interval between each measurement; calculate the arithmetic mean of the three measurements as the center point luminance of the sample; finally, take the average of the three samples as the initial center point luminance result for this batch of products.

[0041] 2) Color gamut coverage

[0042] Data analysis: Color gamut coverage is an indicator of a display device's ability to reproduce colors. Higher color gamut coverage means that it can present a richer variety of colors and color transitions that are closer to real scenes.

[0043] Reference standards: GB / T34014-2017 "General Specifications for Quantum Dot Color Display Devices", GB / T28125.1-2011 "Measurement Methods for Digital Television Flat Panel Displays - Part 1: General Requirements".

[0044] Test Method: The test environment was a darkroom (ambient light intensity ≤10 lux), with temperature controlled at 25℃±2℃ and relative humidity at 50%RH±5%. A high-precision spectrometer with metrological certification and sensitivity calibration was used. Three samples were randomly selected from the same batch of PVDC-based composite materials, each measuring 100mm×100mm. The sample surface was cleaned with a lint-free cloth soaked in isopropyl alcohol to remove oil and dust. The sample was fixed on the light-emitting surface of a standard LED backlight module (the backlight module needs to be preheated for 30 minutes to ensure stable luminous power, and the backlight color temperature is calibrated to 6500K±200K). The integrating sphere inlet was placed tightly against the sample. At the center point of the sample, the spectrometer is connected to the integrating sphere outlet to collect the spectral power distribution under four emission states: red (630nm), green (530nm), blue (450nm), and white. Based on the spectral data, the CIE1931 color coordinates (x_R, y_R; x_G, y_G; x_B, y_B) are calculated, and the area ratio to the DCI-P3 standard color gamut is calculated using the polygon area method. Each sample is measured three times consecutively, with a 10-second interval between each measurement. The arithmetic mean of the three measurements is calculated as the color gamut coverage of that sample. Finally, the average of the three samples is taken as the initial color gamut coverage result for this batch of products.

[0045] Optical performance stability test after high temperature and high humidity aging

[0046] Performance testing: luminance retention and color coordinate drift

[0047] Reason for testing: To comprehensively evaluate the water and oxygen barrier protection effect of the PVDC barrier layer in the PVDC-based composite material, as well as the anti-aging stability of the quantum dots in the core layer, and to verify the optical performance reliability of the PVDC-based quantum dot diffuser plate in harsh environments with high temperature and high humidity. This test verifies that the product obtained by this invention can achieve both stability and long-lasting and efficient optical performance in high temperature and high humidity scenarios.

[0048] 1) Brightness retention rate

[0049] Data analysis: Brightness retention rate is an indicator for evaluating the optical stability of quantum dot diffusers under high temperature and high humidity conditions. It directly reflects the protective effect of the PVDC barrier layer on quantum dots. The more effective the barrier layer, the less water vapor and oxygen permeate, the lower the degree of quantum dot quenching and inactivation, and the higher the brightness retention rate. This indicates that the product has stronger anti-aging ability and a longer service life.

[0050] Reference standards: GB / T34014-2017 "General Specification for Quantum Dot Color Display Devices" and GB / T2423.3-2016 "Environmental Testing Part 2: Test Methods, Test Cab: Constant Damp Heat Test".

[0051] Test Method: Before testing, measure the initial center point brightness (denoted as L0) of three 100mm×100mm PVDC-based composite material samples from the same batch using the "Center Point Brightness" method in the "Initial Optical Performance Test". Measure each sample three times and take the average value. Fix the cleaned samples on a dedicated sample holder and place them in a constant humidity and heat test chamber. Set the aging conditions to 85℃±2℃, 85%RH±3%, and 500 hours. During aging, avoid contact between samples or with the chamber walls. After aging, remove the samples and cool them for 2 hours in an environment of 25℃±2℃ and 50%RH±5%. Once the sample temperature matches the ambient temperature, measure the center point brightness (denoted as L1) of each sample again using the initial brightness test method. Calculate the brightness retention rate of each sample using the formula "Brightness Retention Rate = (L1 / L0)×100%". Repeat the calculation three times for each sample and take the average value. Finally, take the average brightness retention rate of the three samples as the brightness retention rate result after high temperature and high humidity aging of this batch of products.

[0052] 2) Color coordinate drift

[0053] Data analysis: Color coordinate drift is a key indicator for measuring the color stability of quantum dot diffusers after high-temperature and high-humidity aging. If quantum dots undergo chemical structural changes due to water and oxygen erosion (such as core-shell damage), it will lead to a shift in the emission wavelength, manifested as color coordinate drift. The human eye's perception threshold for color coordinate changes is approximately Δu'v' = 0.005. Exceeding this value will result in a noticeable color cast (such as red appearing yellowish and green appearing dark). The lower the color coordinate drift Δu'v', the more stable the quantum dot's luminescent properties, and the stronger the consistency of product color reproduction.

[0054] Reference standards: GB / T34014-2017 "General Specification for Quantum Dot Color Display Devices" and GB / T39474-2020 "Test Methods for Optical Performance of Quantum Dot Display Devices".

[0055] Test Method: Before testing, the initial CIE1976 u'v' color coordinates (denoted as u'0, v'0) of three 100mm×100mm PVDC-based composite material samples from the same batch were measured according to the "Color Gamut Coverage" method in "Initial Optical Performance Test". Each sample was measured three times and the average value was taken. After cleaning, the samples were subjected to constant damp heat aging under the aging conditions of the "Brightness Retention Rate" test (85℃±2℃, 85%RH±3%, 500 hours). After aging, the samples were cooled to ambient temperature. At a temperature of 25℃±2℃ and 50%RH±5%, the CIE1976 u'v' color coordinates (denoted as u'1 and v'1) of each sample were measured again using the initial color coordinate test method. The color coordinate shift of each sample was calculated using the formula "Δu'v'=√[(u'1-u'0)2+(v'1-v'0)2]". The calculation was repeated 3 times for each sample, and the average value was taken. Finally, the average value of the color coordinate shift of the 3 samples was taken as the color coordinate shift result of this batch of products after high temperature and high humidity aging.

[0056] Quantum Dot Microscopic Performance Testing

[0057] Performance Testing: Photoluminescence Quantum Yield (PLQY)

[0058] Reason for testing: The decrease in brightness is essentially due to a decrease in the luminous efficacy (PLQY) of the quantum dots. This test helps demonstrate that, protected by this invention, the quantum dot itself suffers minimal damage.

[0059] Data analysis: Photoluminescence quantum yield (PLQY) is a core microscopic indicator that measures the efficiency of quantum dots in "absorbing light and converting it into light emission". It directly determines the brightness performance of the diffuser plate. The higher the PLQY and PLQY retention rate, the stronger the light emission ability of the quantum dots, the brighter the diffuser plate, and the better the resistance to aging damage. It also confirms that the PVDC barrier layer has a more prominent protective effect.

[0060] Reference standards: GB / T39474-2020 "Test Methods for Optical Performance of Quantum Dot Display Devices", GB / T34014-2017 "General Specifications for Quantum Dot Color Display Devices".

[0061] Test Method: The test environment was a dark room (ambient light intensity ≤10 lux), with the temperature controlled at 25℃±2℃ and relative humidity at 50%RH±5%. A high-precision integrating sphere-spectrometer system with metrological certification was used, and wavelength and sensitivity calibration were completed according to the equipment manual. Three powder samples, each weighing 50 mg, were carefully scraped from the core layer of the same batch of PVDC-based composite materials using a blade. After cleaning with anhydrous ethanol, the samples were dried in a 60℃ oven for 30 minutes. The samples were evenly spread on the sample holder inside the integrating sphere, and the excitation wavelength was set to 450 nm. The excitation and emission signals were collected and calculated according to the formula: "PLQY = [total number of emitted photons / (excitation wavelength / emission wavelength)]". The initial PLQY (denoted as PLQY0) is calculated as follows: [Total number of emitted photons - Total number of unabsorbed excitation photons] × 100%. Each sample is measured three times consecutively, with a 10-second interval between each measurement, and the arithmetic mean is taken. Another three samples of the same specification are aged for 500 hours at 85℃±2℃ / 85%RH±3%. After cooling, the above test is repeated to obtain the aged PLQY (denoted as PLQY1), and the PLQY retention rate is calculated as "PLQY retention rate = (PLQY1 / PLQY0) × 100%". Finally, the average value of the initial PLQY and the average value of the PLQY retention rate of the three samples are taken as the test results of the quantum dot microscopic performance of this batch of products.

[0062] Through three tests—initial optical performance, optical performance after high temperature and humidity aging, and quantum dot microscopic performance—it can be verified that the quantum dot diffuser plate made by this invention can achieve a balance between high color gamut and high brightness, and can also rely on the PVDC barrier layer to ensure high stability under high temperature and humidity conditions. This solves the problem in the prior art that in order to maintain the high stability of the quantum dot diffuser plate, quantum dots with lower luminous efficiency are forced to be selected, which ultimately leads to a decrease in the overall brightness of the diffuser plate.

[0063] Initial water and oxygen barrier performance test

[0064] Performance tests: Water vapor transmission rate (WVTR) and oxygen transmission rate (OTR)

[0065] Reason for testing: To verify the actual water and oxygen barrier effect of the PVDC barrier layer, to confirm whether it can build an effective protective barrier for the core quantum dots, to solve the problem of quantum dot failure caused by insufficient barrier from the source, and to provide a basic guarantee for the stability of the subsequent optical performance of quantum dots.

[0066] 1) Water vapor transmission rate

[0067] Data analysis: Water vapor transmission rate (WVTR) is an indicator of a material's ability to prevent water vapor penetration; the lower the value, the better the barrier effect.

[0068] Reference standard: GB / T26253-2010 "Determination of water vapor transmission rate of plastic films and sheets - Infrared sensor method".

[0069] Test Method: The test environment temperature was controlled at 23℃±2℃ and the relative humidity at 50%RH±5%. An infrared sensor-type water vapor transmission rate tester with metrological certification was used and calibrated according to the equipment manual. Three samples were randomly selected from the same batch of PVDC-based composite materials, each sample measuring 100mm×100mm. Both sides of the samples were cleaned with a lint-free cloth soaked in isopropyl alcohol to remove oil and dust. After drying, the samples were fixed between the test chambers of the tester (one side was a high-humidity environment of 38℃ / 90%RH, and the other side was a dry environment). The test time was set to 24 hours. After the test system stabilized, the water vapor transmission rate was recorded hourly. The average water vapor transmission rate over 24 hours was calculated. Each sample was tested twice and the average value was taken. Finally, the average value of the three samples was taken as the initial water vapor transmission rate result for this batch of products.

[0070] 2) Oxygen transmission rate

[0071] Data analysis: Oxygen permeability (OTR) is the core indicator for measuring a material's ability to prevent oxygen penetration; the lower the value, the better the barrier effect.

[0072] Reference standard: GB / T19789-2005 "Determination of oxygen permeability of plastic films and sheets for packaging materials - coulometric method".

[0073] Test Method: The ambient temperature was controlled at 23℃±2℃ and the relative humidity at 50%RH±5%. A coulometric oxygen transmission rate tester with metrological certification was used and calibrated according to the equipment manual. Three samples were randomly selected from the same batch of PVDC-based composite materials, each measuring 100mm×100mm. Both sides of the samples were cleaned with a lint-free cloth soaked in isopropyl alcohol, dried, and then fixed between the upper and lower test chambers of the tester (oxygen with a purity ≥99.99% was introduced into the upper chamber, and nitrogen was introduced into the lower chamber as the carrier gas). The test time was set to 24 hours. After the system stabilized, the amount of oxygen detected by the coulometric meter was recorded. The average oxygen transmission rate over 24 hours was calculated, and each sample was tested twice and the average value was taken. Finally, the average value of the three samples was taken as the initial oxygen transmission rate result for this batch of products.

[0074] Barrier performance stability test after high temperature and high humidity aging

[0075] Performance Test: Water Vapor Transmission Rate (WVTR) after Aging

[0076] Reason for testing: To verify whether the PVDC barrier layer can still maintain good water vapor barrier capability under the harsh environment of 85℃ / 85%RH for 500 hours, avoid the decline in barrier performance due to aging, and thus continuously provide reliable water vapor protection for the core quantum dots, further confirming the long-term protective value of the PVDC barrier layer.

[0077] Data analysis shows that the lower the water vapor transmission rate (WVTR) after aging, the more intact the water vapor barrier layer is after high temperature and high humidity aging, and the more reliable the long-term protection effect on quantum dots.

[0078] Reference standards: GB / T2423.3-2016 Environmental testing - Part 2: Test methods - Cab: Constant damp heat test; GB / T26253-2010 Determination of water vapor transmission rate of plastic films and sheets - Infrared sensor method.

[0079] Test Method: Three samples were randomly selected from the same batch of PVDC-based composite materials. Each sample was 100mm × 100mm in size. Both sides of the samples were cleaned with a lint-free cloth dampened with isopropyl alcohol to remove oil and dust, and then air-dried. The cleaned samples were fixed on a dedicated sample holder and placed in a constant humidity and heat test chamber. The aging conditions were set according to the parameters specified in the document: temperature 85℃ ± 2℃, relative humidity 85%RH ± 3%, and aging time 500 hours. During the aging process, the samples were ensured not to come into contact with each other or to be close to the chamber walls. After aging, the samples were removed and cooled for 2 hours in a standard environment of 25℃ ± 2℃ and 50%RH ± 5% until the sample temperature and humidity were consistent with the environment. Afterwards, the sample surface was cleaned again with a lint-free cloth soaked in isopropyl alcohol to remove any impurities that might have adhered to the chamber. An infrared sensor-type water vapor transmission rate tester with metrological certification was used, and the instrument was calibrated according to the reference standard and the equipment manual. The pretreated sample was fixed between the test chambers of the tester, with high humidity gas of 38℃ / 90%RH introduced on one side and a dry environment on the other side. The test time was set to 24 hours. After the test system stabilized, the water vapor transmission rate was recorded every hour, and the average WVTR of each sample over 24 hours was calculated. Each sample was tested twice and the average value was taken. Finally, the average WVTR of the three samples was taken as the water vapor transmission rate result of this batch of products after high temperature and high humidity aging.

[0080] The invention verifies that the quantum dot diffusion plate can achieve efficient initial water and oxygen barrier performance and stable barrier performance after aging by initial water and oxygen barrier performance test and high temperature and humidity aging test. This continuously builds a water and oxygen protection barrier for the core quantum dots, thereby solving the problem of quantum dot quenching caused by poor initial barrier performance and barrier attenuation after aging in existing diffusion plates.

[0081] Mechanical and interface performance testing

[0082] Performance tests: interlayer adhesion, impact strength, warpage

[0083] Reason for testing: To verify the reliability of the interface bonding of the five-layer structure, its overall resistance to damage and dimensional flatness, and to ensure that the material does not exhibit defects such as delamination, breakage, or warping during processing, transportation, assembly and use.

[0084] 1) Interlayer adhesion

[0085] Data judgment: The core judgment index is the 180° peel strength (5N / 25mm). The higher the value, the tighter the interface bonding between the PVDC barrier layer and the PS blend interface layer, and between the PS blend interface layer and the core layer. This means that the possibility of interlayer separation during processing, subsequent cutting or use is smaller.

[0086] Reference standard: GB / T2790-1995 "Adhesives - 180° Peel Strength Test Method - Flexible Materials vs. Rigid Materials"

[0087] Test Method: Three samples were randomly selected from the same batch of PVDC-based composite materials. Each sample was 150mm × 25mm in size, ensuring that the sample contained a complete five-layer structure. The "PVDC barrier layer-PS blend interface layer" or "PS blend interface layer-core layer" at one end of the sample was carefully peeled off by 10mm with a blade as the peeling start point, avoiding damage to the interface to be tested. The sample was fixed on the upper and lower clamps of the tensile testing machine (the peeling start point was clamped on the upper and lower clamps respectively, ensuring that the peeling direction was 180°), and the tensile speed was set to 300mm / min. The testing machine was started, and the force value change during the peeling process was recorded. The average force value of the peeled section (excluding the initial 10mm and the last 10mm) was taken as the 180° peel strength of the sample. Each sample was tested twice, and the average value was taken. Finally, the average peel strength of the three samples was taken as the interlayer adhesion test result.

[0088] 2) Impact strength

[0089] Data analysis: Based on the unnotched impact strength of a simply supported beam (kJ / m) 2 The core indicator is the PVDC-based composite material. The higher the value, the stronger its ability to resist external impacts, and the less likely it is to crack or break during transportation, assembly collisions, or daily use (such as accidental impacts).

[0090] Reference standard: GB / T1043.1-2008 "Determination of impact properties of simply supported plastic beams - Part 1: Non-instrumental impact test".

[0091] Test Method: Three samples were randomly selected from the same batch of PVDC-based composite materials. Each sample was 80mm × 10mm × actual sample thickness. The test environment was controlled at 23℃ ± 2℃ and relative humidity 50% RH ± 5%. The samples were placed in this environment for 24 hours. The pendulum energy of the simply supported beam impact testing machine was adjusted, and the zero point of the testing machine was calibrated. The sample was placed stably on the simply supported beam support of the testing machine, ensuring that the length direction of the sample was parallel to the support without any offset. The pendulum was released to impact the middle of the sample, and the absorbed energy at the time of impact fracture was recorded. The impact strength of each sample was calculated according to the formula "impact strength = absorbed energy / sample width × sample thickness". Each sample was tested once, and the average impact strength of the three samples was taken as the test result.

[0092] 3) Warpage

[0093] Data analysis: The core indicator is the warpage height per unit length (mm / m). The lower the value, the better the flatness of the PVDC-based composite material. This means that when the quantum dot diffuser plate is assembled with the backlight module and display panel, they will fit together better and are less prone to deformation.

[0094] Reference standard: GB / T3398.2-2008 "Determination of hardness of plastics - Part 2: Rockwell hardness".

[0095] Test Method: Three samples were randomly selected from the same batch of PVDC-based composite materials. Each sample was 1000mm × 1000mm in size. The sample surface was cleaned and impurities were removed. A horizontal test platform was prepared, and height gauges were placed at the four corners and the center of the platform. The samples were laid flat on the horizontal platform, ensuring that there was no external force pulling them, and left to rest naturally for 30 minutes. The height values ​​at the four corners and the center of the sample were measured with height gauges, and the maximum value (Hmax) and the minimum value (Hmin) were recorded. The warpage of each sample was calculated according to the formula "Warpage = (Hmax - Hmin) / Sample Side Length". Each sample was measured twice, and the average value was taken. Finally, the average warpage of the three samples was taken as the test result.

[0096] Example 1:

[0097] A PVDC-based composite material comprises the following five layers stacked sequentially: an upper outer layer, an upper middle layer, a core layer, a lower middle layer, and a lower outer layer. The upper outer layer and the lower outer layer are both polyvinylidene chloride (PVDC) barrier layers. The upper middle layer and the lower middle layer are both blended interface layers of polystyrene (PS) and copolymers, used to improve the interfacial adhesion between the PVDC barrier layer and the core layer and to alleviate thermal stress. The core layer is a blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots.

[0098] The polyvinylidene chloride (PVDC) barrier layer, by weight, includes the following raw materials: 100 parts polyvinylidene chloride (PVDC) resin, 3 parts antioxidant 1010, 2 parts antioxidant 168, 3 parts anti-yellowing agent Y-180, 2 parts zinc stearate, and 2 parts nano-kaolin.

[0099] The blending interface layer of polystyrene (PS) and copolymer comprises, by weight, the following raw materials: 60 parts general-purpose polystyrene (PS), 15 parts styrene-maleic anhydride copolymer (SMA), 15 parts methyl methacrylate-glycidyl methacrylate copolymer (PMMA-co-GMA), 1 part nano titanium dioxide (TiO2), and 1 part nano silica (SiO2).

[0100] The blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots comprises, by weight, the following raw materials: 35 parts general-purpose polystyrene (PS), 55 parts polycarbonate (PC), 4 parts PS grafted with maleic anhydride (PS-g-MAH), 4 parts styrene-ethylene-butene-styrene block copolymer (SEBS), 1.5 parts CdSe / ZnS core-shell structured red quantum dots (630nm emission), 1.5 parts CdSe / ZnS core-shell structured green quantum dots (530nm emission), 3 parts nano-titanium dioxide (TiO2), 4 parts nano-silica (SiO2), 0.5 parts antioxidant 1010, and 0.3 parts auxiliary antioxidant 626.

[0101] A method for preparing a PVDC-based composite material includes the following steps:

[0102] S1. Place the raw material for the PVDC barrier layer in a high-speed mixer and mix at 800 rpm for 5 minutes to obtain a uniform PVDC barrier layer material;

[0103] The raw materials for the PS blend interface layer were placed in a high-speed mixer and mixed at 1000 rpm for 8 minutes to obtain a uniform PS blend interface layer material.

[0104] The raw materials of PS+PC+quantum dot core layer (quantum dots and nanopowders are added last) are placed in a high-speed mixer and mixed at 1200 rpm for 10 minutes to obtain uniform PS+PC+quantum dot core layer material.

[0105] S2. The three mixed materials are fed into the corresponding co-rotating twin-screw extruders (L / D=40) through three independent vacuum feeders for melting and plasticizing, with a vacuum degree of -0.08MPa;

[0106] The extruder temperatures for each section used in the PVDC barrier layer are set as follows: feeding section 135℃, melting section 170℃, homogenization section 172℃, and die 165℃; the extruder temperatures for each section used in the PS blend interface layer are set as follows: feeding section 145℃, melting section 175℃, homogenization section 185℃, and die 182℃; and the extruder temperatures for each section used in the core layer are set as follows: feeding section 175℃, melting section 235℃, homogenization section 245℃, and die 240℃. After melting and plasticizing, three uniform, bubble-free melts are obtained.

[0107] S3. The three melts mentioned above are introduced into a five-layer co-extrusion die head via a distributor; the PVDC melt is distributed to the upper and lower outer layer channels, the PS blend melt is distributed to the middle upper and middle lower layer channels, and the PS+PC+quantum dot melt is distributed to the core layer channel; each channel in the die head is independently temperature controlled: the temperature of the PVDC channel is controlled at 168℃, the temperature of the PS blend channel is controlled at 183℃, and the temperature of the PS+PC+quantum dot channel is controlled at 242℃; the melts are layered and stacked in the die head, and extruded through the die lip to form a five-layer composite melt curtain.

[0108] S4. The extruded five-layer composite melt curtain is drawn out through traction rollers, first undergoing preliminary shaping via a 75°C metal cooling roller, and then forced cooling via a 30°C metal cooling roller to achieve complete glass transition of the melt. Finally, the cooled and shaped composite sheet is cut to the required dimensions to obtain the PVDC-based composite material.

[0109] Following the steps above, the total thickness of the quantum dot diffusion plate is approximately 1.0 mm, with the following layer thicknesses: the upper outer PVDC barrier layer is 50 μm, the middle upper PS blend interface layer is 80 μm, the core layer PS+PC+quantum dot is 300 μm, the middle lower PS blend interface layer is 80 μm, and the lower outer PVDC barrier layer is 50 μm.

[0110] Example 2:

[0111] A PVDC-based composite material with the same five-layer structure as in Example 1.

[0112] The polyvinylidene chloride (PVDC) barrier layer, by weight, includes the following raw materials: 100 parts polyvinylidene chloride (PVDC) resin, 4 parts antioxidant 1010, 2.5 parts antioxidant 168, 4 parts anti-yellowing agent Y-180, 2 parts zinc stearate, and 2 parts nano-kaolin.

[0113] The raw materials and proportions of the blended interface layer of polystyrene (PS) and copolymer are the same as those in Example 1.

[0114] The raw materials and proportions of the blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots are the same as in Example 1.

[0115] A method for preparing a PVDC-based composite material, wherein steps S1, S2, S3, and S4 are the same as in Example 1.

[0116] Following the steps above, the total thickness of the quantum dot diffusion plate is approximately 1.0 mm, with the following layer thicknesses: the upper outer PVDC barrier layer is 50 μm, the middle upper PS blend interface layer is 80 μm, the core layer PS+PC+quantum dot is 300 μm, the middle lower PS blend interface layer is 80 μm, and the lower outer PVDC barrier layer is 50 μm.

[0117] Example 3:

[0118] A PVDC-based composite material with the same five-layer structure as in Example 1.

[0119] The polyvinylidene chloride (PVDC) barrier layer uses the same raw materials and proportions as in Example 1.

[0120] The raw materials and proportions of the blended interface layer of polystyrene (PS) and copolymer are the same as those in Example 1.

[0121] The blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots comprises, by weight, the following raw materials: 30 parts general-purpose polystyrene (PS), 60 parts polycarbonate (PC), 5 parts PS grafted with maleic anhydride (PS-g-MAH), 3 parts styrene-ethylene-butene-styrene block copolymer (SEBS), 2 parts CdSe / ZnS core-shell structured red quantum dots, 2 parts CdSe / ZnS core-shell structured green quantum dots, 2 parts nano-titanium dioxide (TiO2), 3 parts nano-silica (SiO2), 0.5 parts antioxidant 1010, and 0.3 parts auxiliary antioxidant 626.

[0122] A method for preparing a PVDC-based composite material, wherein steps S1, S2, S3, and S4 are the same as in Example 1.

[0123] Following the steps above, the total thickness of the quantum dot diffusion plate is approximately 1.0 mm, with the following layer thicknesses: the upper outer PVDC barrier layer is 50 μm, the middle upper PS blend interface layer is 80 μm, the core layer PS+PC+quantum dot is 320 μm, the middle lower PS blend interface layer is 80 μm, and the lower outer PVDC barrier layer is 50 μm.

[0124] Example 4:

[0125] A PVDC-based composite material with the same five-layer structure as in Example 1.

[0126] The polyvinylidene chloride (PVDC) barrier layer uses the same raw materials and proportions as in Example 1.

[0127] The blended interface layer of polystyrene (PS) and copolymer comprises, by weight, the following raw materials: 70 parts general-purpose polystyrene (PS), 10 parts styrene-maleic anhydride copolymer (SMA), 10 parts methyl methacrylate-glycidyl methacrylate copolymer (PMMA-co-GMA), 1 part nano titanium dioxide (TiO2) (for the upper intermediate layer), and 1 part nano silica (SiO2) (for the lower intermediate layer).

[0128] The raw materials and proportions of the blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots are the same as in Example 1.

[0129] A method for preparing a PVDC-based composite material, wherein steps S1, S3, and S4 are the same as in Example 1.

[0130] S2. The three mixed materials are fed into the corresponding co-rotating twin-screw extruders (L / D=40) through three independent vacuum feeders for melt plasticization, with a vacuum degree of -0.08MPa. The temperatures of each section of the extruder used for the PVDC barrier layer are set as follows: feeding section 135℃, melting section 170℃, homogenization section 172℃, and die 165℃; the temperatures of each section of the extruder used for the PS blend interface layer are set as follows: feeding section 145℃, melting section 175℃, homogenization section 185℃, and die 182℃; the temperatures of each section of the extruder used for the core layer are set as follows: feeding section 175℃, melting section 230℃, homogenization section 240℃, and die 235℃. After melt plasticization, three uniform, bubble-free melts are obtained.

[0131] Following the steps above, the total thickness of the quantum dot diffusion plate is approximately 1.0 mm, with the following thicknesses for each layer: the upper outer PVDC barrier layer is 50 μm, the middle upper PS blend interface layer is 100 μm, the core layer PS+PC+quantum dot is 300 μm, the middle lower PS blend interface layer is 100 μm, and the lower outer PVDC barrier layer is 50 μm.

[0132] Comparative Example 1:

[0133] A PVDC-based composite material comprises the following three layers stacked sequentially: an upper outer layer, a core layer, and a lower outer layer. The upper and lower outer layers are both polyvinylidene chloride (PVDC) barrier layers, and the core layer is a blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots.

[0134] The upper and lower outer layers, by weight, include the following raw materials: 100 parts polyvinylidene chloride (PVDC) resin, 3 parts antioxidant 1010, 2 parts antioxidant 168, 3 parts anti-yellowing agent Y-180, 2 parts zinc stearate, and 2 parts nano kaolin.

[0135] The core layer, by weight, comprises the following raw materials: 35 parts general-purpose polystyrene (PS), 55 parts polycarbonate (PC), 4 parts PS grafted with maleic anhydride (PS-g-MAH), 4 parts styrene-ethylene-butene-styrene block copolymer (SEBS), 1.5 parts CdSe / ZnS core-shell structured red quantum dots, 1.5 parts CdSe / ZnS core-shell structured green quantum dots, 3 parts nano titanium dioxide (TiO2), 4 parts nano silica (SiO2), 0.5 parts antioxidant 1010, and 0.3 parts auxiliary antioxidant 626.

[0136] A method for preparing a composite material includes the following steps:

[0137] S1. Place the raw material for the outer layer of PVDC in a high-speed mixer and mix at 800 rpm for 5 minutes to obtain a uniform outer layer material of PVDC; place the raw material for the core layer in a high-speed mixer and mix at 1200 rpm for 10 minutes to obtain a uniform core layer material.

[0138] S2. The two mixed materials are fed into the corresponding co-rotating twin-screw extruders (L / D=40) through two independent vacuum feeders for melt plasticization, with a vacuum degree of -0.08MPa. The temperatures of each section of the extruder used for the outer layer of PVDC are set as follows: feeding section 135℃, melting section 170℃, homogenization section 172℃, and die 165℃. The temperatures of each section of the extruder used for the core layer are set as follows: feeding section 175℃, melting section 235℃, homogenization section 245℃, and die 240℃. After melt plasticization, two uniform, bubble-free melts are obtained.

[0139] S3. The two melt streams are introduced into a three-layer co-extrusion die via a distributor; wherein, the PVDC melt is distributed to the upper and lower outer layer channels, and the PS+PC+quantum dot melt is distributed to the core layer channel; each channel in the die is independently temperature controlled: the temperature of the PVDC channel is controlled at 168℃, and the temperature of the PS+PC+quantum dot channel is controlled at 242℃; each layer of melt is layered and stacked in the die, and extruded through the die lip to form a three-layer composite melt curtain.

[0140] S4. Same as Example 1.

[0141] Following the steps above, the total thickness of the resulting board is approximately 1.0 mm, with the following layer thicknesses: the upper outer PVDC layer is 100 μm, the core layer PS+PC+quantum dot is 800 μm, and the lower outer PVDC layer is 100 μm.

[0142] Comparative Example 2:

[0143] A PVDC-based composite material with the same five-layer structure as in Example 1.

[0144] The polyvinylidene chloride (PVDC) barrier layer uses the same raw materials and proportions as in Example 1.

[0145] The blending interface layer of polystyrene (PS) and copolymer comprises, by weight, the following raw materials: 60 parts general-purpose polystyrene (PS), 30 parts general-purpose polystyrene (PS), 1 part nano-titanium dioxide (TiO2), and 1 part nano-silica (SiO2).

[0146] The raw materials and proportions of the blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots are the same as in Example 1.

[0147] A method for preparing a PVDC-based composite material, wherein steps S1, S2, S3, and S4 are the same as in Example 1.

[0148] Following the steps above, the total thickness of the quantum dot diffusion plate is approximately 1.0 mm, with the following layer thicknesses: the upper outer PVDC barrier layer is 50 μm, the middle upper PS blend interface layer is 80 μm, the core layer PS+PC+quantum dot is 300 μm, the middle lower PS blend interface layer is 80 μm, and the lower outer PVDC barrier layer is 50 μm.

[0149] Comparative Example 3:

[0150] A PVDC-based composite material with the same five-layer structure as in Example 1.

[0151] The polyvinylidene chloride (PVDC) barrier layer uses the same raw materials and proportions as in Example 1.

[0152] The raw materials and proportions of the blended interface layer of polystyrene (PS) and copolymer are the same as those in Example 1.

[0153] The blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots comprises, by weight, the following raw materials: 35 parts general-purpose polystyrene (PS), 55 parts polycarbonate (PC), 4 parts PS grafted with maleic anhydride (PS-g-MAH), 4 parts styrene-ethylene-butene-styrene block copolymer (SEBS), 3 parts InP / ZnS core-shell structured red quantum dots, 3 parts InP / ZnS core-shell structured green quantum dots, 3 parts nano-titanium dioxide (TiO2), 4 parts nano-silica (SiO2), 0.5 parts antioxidant 1010, and 0.3 parts auxiliary antioxidant 626.

[0154] A method for preparing a PVDC-based composite material, wherein steps S1, S2, S3, and S4 are the same as in Example 1.

[0155] Following the steps above, the total thickness of the quantum dot diffusion plate is approximately 1.0 mm, with the following layer thicknesses: the upper outer PVDC barrier layer is 50 μm, the middle upper PS blend interface layer is 80 μm, the core layer PS+PC+quantum dot is 300 μm, the middle lower PS blend interface layer is 80 μm, and the lower outer PVDC barrier layer is 50 μm.

[0156] Comparative Example 4:

[0157] A PVDC-based composite material with the same five-layer structure as in Example 1.

[0158] The polyvinylidene chloride (PVDC) barrier layer comprises, by weight, the following raw materials: 100 parts ethylene-vinyl alcohol copolymer (EVOH) resin, 3 parts antioxidant 1010, 2 parts antioxidant 168, and 2 parts zinc stearate.

[0159] The raw materials and proportions of the blended interface layer of polystyrene (PS) and copolymer are the same as those in Example 1.

[0160] The raw materials and proportions of the blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots are the same as in Example 1.

[0161] A method for preparing a PVDC-based composite material, wherein steps S1, S3, and S4 are the same as in Example 1.

[0162] S2. The three mixed materials are fed into the corresponding co-rotating twin-screw extruders (L / D=40) through three independent vacuum feeders for melt plasticization, with a vacuum degree of -0.08MPa. The temperatures of each section of the extruder used for the EVOH barrier layer are set as follows: feeding section 150℃, melting section 190℃, homogenization section 195℃, and die 190℃. The temperatures of each section of the extruder used for the PS blend interface layer are set as follows: feeding section 145℃, melting section 175℃, homogenization section 185℃, and die 182℃. The temperatures of each section of the extruder used for the core layer are set as follows: feeding section 175℃, melting section 235℃, homogenization section 245℃, and die 240℃. After melt plasticization, three uniform, bubble-free melts are obtained.

[0163] Following the steps above, the total thickness of the quantum dot diffusion plate is approximately 1.0 mm, with the following layer thicknesses: the upper outer PVDC barrier layer is 50 μm, the middle upper PS blend interface layer is 80 μm, the core layer PS+PC+quantum dot is 300 μm, the middle lower PS blend interface layer is 80 μm, and the lower outer PVDC barrier layer is 50 μm.

[0164] Comparative Example 5:

[0165] A PVDC-based composite material with the same five-layer structure as in Example 1.

[0166] The polyvinylidene chloride (PVDC) barrier layer uses the same raw materials and proportions as in Example 1.

[0167] The raw materials and proportions of the blended interface layer of polystyrene (PS) and copolymer are the same as those in Example 1.

[0168] The raw materials and proportions of the blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots are the same as in Example 1.

[0169] A method for preparing a PVDC-based composite material, wherein steps S1 and S2 are the same as in Example 1.

[0170] S3. The above three melts are introduced into a five-layer co-extrusion die head via a distributor; the PVDC melt is distributed to the upper and lower outer layer channels, the PS blend melt is distributed to the middle upper and middle lower layer channels, and the PS+PC+quantum dot melt is distributed to the core layer channel; each channel in the die head adopts a unified temperature control, and the temperature is controlled at 220℃; each layer of melt is stacked in layers in the die head and extruded through the die lip to form a five-layer composite melt curtain.

[0171] S4. The extruded five-layer composite melt curtain is drawn out through the traction roller and directly passed through the 25°C cooling roller for forced cooling.

[0172] Following the steps above, the total thickness of the quantum dot diffusion plate is approximately 1.0 mm, with the following layer thicknesses: the upper outer PVDC barrier layer is 50 μm, the middle upper PS blend interface layer is 80 μm, the core layer PS+PC+quantum dot is 300 μm, the middle lower PS blend interface layer is 80 μm, and the lower outer PVDC barrier layer is 50 μm.

[0173] The quantum dot diffusion plates prepared using the raw materials and steps of Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3, 4, 5 were grouped and labeled as KSB1001, KSB1002, KSB1003, KSB1004, KSB1005, KSB1006, KSB1007, KSB1008, and KSB1009, respectively. Performance tests were then conducted on the products from the Examples and Comparative Examples.

[0174] Table 1

[0175]

[0176] As shown in Table 1, the optical performance of Embodiment 1 of the present invention is superior to that of the comparative example in all aspects. It has the highest initial brightness (4850 nits) and color gamut (118% NTSC), and after 500 hours of aging, it has the highest brightness retention rate (96.5%) and the smallest color coordinate drift (Δu'v'=0.006).

[0177] High initial brightness and color gamut result in good display performance, while high brightness retention and minimal color drift mean that the quantum dot diffuser can maintain vivid and bright image quality with almost no degradation after long-term use, thus achieving a balance between high brightness, high color gamut and high stability.

[0178] Comparative Example 3, a commercially available product, had the lowest initial brightness because it used inefficient InP quantum dots in exchange for stability. Comparative Example 1, a three-layer structure, had poor performance in multiple aspects, proving that its structure could not protect the quantum dots. In contrast, the embodiments of this invention utilize a five-layer structure built with a PVDC barrier layer, making it possible to use high-efficiency CdSe quantum dots. At the same time, a specific interface layer and an optimized core layer ensured the high efficiency and stability of the quantum dots during processing and use.

[0179] Table 2

[0180]

[0181] As shown in Table 2, the water and oxygen barrier performance of Example 1 of the present invention far exceeds that of Comparative Examples 1 and 3. Its water vapor transmission rate (WVTR = 0.85 g / m³) is significantly higher. 2 •day) and oxygen permeability (OTR = 1.1cm) 3 / m 2 The day-atm (WVTR) is very low, and after aging, WVTR (0.87) hardly changes.

[0182] Such low WVTR and OTR mean that external moisture and oxygen have difficulty penetrating into the material, which can effectively prevent the photo-oxidation and hydrolytic quenching of quantum dots (especially CdSe quantum dots), thereby greatly improving the lifespan and reliability of quantum dot diffusers.

[0183] Comparative Example 1, due to the lack of a good interface layer, exhibited microscopic defects or weak bonding between the PVDC layer and the core layer, resulting in poor barrier effect and a sharp decline in performance. This, in turn, demonstrates the necessity of a complete and continuous PVDC outer layer and interface layer in the five-layer structure design of this invention. Comparative Example 4 showed significant performance degradation after aging, proving the stability advantage of PVDC in humid and hot environments.

[0184] The difference between Example 1 and Comparative Example 5 shows that the present invention not only has good barrier properties, but also achieves a long-lasting barrier performance through precise process control.

[0185] Table 3

[0186]

[0187] As shown in Table 3, Embodiment 1 of the present invention exhibits the most balanced and excellent mechanical and interfacial properties. It has the highest interlayer peel strength (5.8 N / 25 mm) and impact resistance (15.5 kJ / m²). 2 It has the strongest properties and extremely low warpage (1.2mm / m).

[0188] High peel strength ensures that the five-layer structure will not delaminate during processing and use, high impact strength guarantees the product's durability against drops and shocks, and low warpage ensures the flatness of the sheet material, making it easy to assemble in the backlight module and preventing optical hot spots, directly improving the product's yield and reliability.

[0189] Comparative Example 1 exhibited almost no peel strength and severe warping, demonstrating that the three-layer asymmetric structure generates enormous internal stress and interfacial bonding difficulties. Comparative Example 2 showed a significant decrease in peel strength, proving that specific copolymers in the interfacial layer play a decisive role in generating strong interfacial bonds, which cannot be replaced by ordinary PS.

[0190] The comparison between the embodiments of the present invention and the comparative examples shows that the design of its five-layer symmetrical structure and functionalized interface layer not only solves the optical and barrier problems, but also unexpectedly brings good mechanical properties and dimensional stability.

[0191] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A PVDC-based composite material, characterized in that, The structure comprises the following five layers stacked sequentially: an upper outer layer, an upper middle layer, a core layer, a lower middle layer, and a lower outer layer. The upper and lower outer layers are both polyvinylidene chloride (PVDC) barrier layers. The upper middle and lower middle layers are both blended interface layers of polystyrene (PS) and copolymers, used to improve the interfacial adhesion between the PVDC barrier layer and the core layer and to alleviate thermal stress. The core layer is a blended light-emitting layer of polystyrene (PS), polycarbonate (PC), and quantum dots.

2. The PVDC-based composite material according to claim 1, characterized in that, The PVDC barrier layer has a thickness of 30-100 μm and contains 100 parts by weight of PVDC resin, 3-5 parts of antioxidant 1010, 2-3 parts of antioxidant 168, and 2-5 parts of anti-yellowing agent; the thickness of the blend interface layer of PS and copolymer has a thickness of 50-150 μm; and the thickness of the core layer has a thickness of 200-300 μm.

3. The PVDC-based composite material according to claim 2, characterized in that, The blended interface layer of polystyrene (PS) and copolymer comprises, by weight: 50-70 parts general-purpose polystyrene (PS), 10-20 parts styrene-maleic anhydride copolymer (SMA), and 10-20 parts methyl methacrylate-glycidyl methacrylate copolymer (PMMA-co-GMA).

4. The PVDC-based composite material according to claim 3, characterized in that, The core layer comprises, by weight: 30-40 parts general-purpose polystyrene (PS), 50-60 parts polycarbonate (PC), 3-5 parts PS-g-MAH (a graft of PS and maleic anhydride), 3-5 parts styrene-ethylene-butene block copolymer (SEBS), and 1-4 parts CdSe-based red and green quantum dots.

5. A method for preparing the PVDC-based composite material as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Prepare PVDC barrier layer material, PS blended interface layer material, and PS+PC+quantum dot core layer material respectively; S2. Each layer of material is fed into the corresponding screw extruder through an independent vacuum feeding system for melting and plasticizing to obtain each layer of melt; S3. Each layer of melt is introduced into a co-extrusion die through a distributor. The co-extrusion die is provided with mutually isolated flow channels. Each layer of melt is layered and compounded in the die to form a five-layer composite melt curtain. S4. The five-layer composite melt curtain is drawn out and cooled and shaped by a cooling roller group to obtain a composite board.

6. The method according to claim 5, characterized in that, In step S2, the screw extruder is temperature-controlled in zones: The extruder used for the PVDC barrier layer has a melting zone temperature of 160-180℃ and a homogenization zone temperature of 170-175℃. The extruder used for the PS blend interface layer has a melting zone temperature of 170-180℃ and a homogenization zone temperature of 180-190℃. The extruder used for the core layer has a melting zone temperature of 220-250℃ and a homogenization zone temperature of 240-250℃.

7. The method according to claim 5, characterized in that, In step S3, each flow channel of the co-extrusion die is temperature-controlled independently: The flow channel temperature for the PVDC melt is controlled at 165-170℃; The flow channel temperature for the PS blend melt is controlled at 180-185℃; The flow channel temperature for the PS+PC+quantum dot melt is controlled at 230-250℃.

8. The method according to claim 5, characterized in that, In step S4, the cooling process adopts multi-stage temperature difference cooling: first, a cooling roller at 60-80℃ is used for preliminary shaping, and then a cooling roller at 25-35℃ is used for forced cooling.

9. A quantum dot diffusion plate, characterized in that, It includes the PVDC-based composite material as described in any one of claims 1-4.

10. The quantum dot diffusion plate according to claim 9, characterized in that, After being tested at 85℃ / 85%RH for 500 hours, the quantum dot diffusion plate retains a brightness of no less than 95%.

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