Post-baking process for improving heat resistance and stability of quantum dot color photoresist

Abstract

The invention provides a post-baking process for improving heat resistance and stability of quantum dot color photoresist, and belongs to the technical field of photoresist. The post-baking process comprises the following steps: (1) modifying a composite surface ligand; (2) gradient heat treatment; (3) speed-controlled cooling; all the process steps have a tight synergistic effect, and a complete performance improvement system is formed. The modification of the composite ligand provides a stable quantum dot surface state for subsequent heat treatment, and the introduced multifunctional group provides sufficient reaction sites for a cross-linking reaction in gradient heat treatment; a gradient heating mode ensures that solvent release, resin crosslinking and ligand bonding reactions are sequentially carried out, so that the problem of mutual interference of reactions in a traditional constant-temperature process is avoided; the titanate coupling agent is added in a high-temperature stage, a network structure after resin crosslinking is just utilized, the quantum dots are anchored in a matrix more firmly, and the progressive stabilizing effects of surface protection, structure curing and interface strengthening are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photoresist manufacturing, in particular to a post-baking process for improving the heat resistance and stability of quantum dot color photoresist. BACKGROUND

[0002] In the rapid development process of new generation micro display technologies such as Micro-LED, AR / VR, ultra-high resolution (>1000ppi) display has become the core requirement of the industry, which puts forward higher requirements for the key material quantum dot color photoresist. Quantum dots have become the ideal color conversion material for realizing full-color display due to their advantages such as narrow-band emission and high color purity, and direct photolithography technology gradually replaces traditional inkjet printing technology as the mainstream process because it can realize high-precision pixel patterning below 2μm. However, the existing quantum dot color photoresist still faces many technical problems in actual application.

[0003] The stability of quantum dots is the primary challenge. Traditional quantum dots are usually modified with single ligands such as oleic acid and oleylamine, which have weak binding force with quantum dots. During the preparation and post-baking of photoresist, the ligands are easily detached due to high temperature (>120℃) or solvent erosion. The detachment of ligands will cause the exposure of quantum dots to oxygen and humidity environment, leading to agglomeration and oxidative degradation, significantly reducing the light-emitting efficiency of quantum dots, and even causing device failure. Process compatibility is also a major problem. The existing post-baking process mostly uses a single constant temperature mode, which cannot meet the multiple requirements of solvent release, resin crosslinking and ligand stability. If the baking temperature is too low, the resin crosslinking is insufficient, resulting in poor mechanical properties; if the temperature is too high, the quantum dot ligands will decompose, forming a vicious cycle. At the same time, the compatibility between quantum dots and photoresist resin matrix is insufficient, which easily causes phase separation during high-temperature treatment, resulting in a decrease in coating uniformity and seriously affecting the optical consistency of display devices. These problems make it difficult for existing technologies to meet the actual application requirements of long-term heat resistance and environmental stability for high-resolution display devices. SUMMARY

[0004] The purpose of the present application is to provide a post-baking process for improving the heat resistance and stability of quantum dot color photoresist.

[0005] The present application provides the following technical solutions:

[0006] A post-baking process for improving the heat resistance and stability of quantum dot color photoresist, the quantum dot color photoresist comprising: 40-60% methyl methacrylate-hydroxyethyl acrylate copolymer resin, 12-15% core-shell structure cadmium selenide / cadmium sulfide quantum dots, 2-5% photoinitiator, and the balance solvent.

[0007] The post-baking process comprises the following steps:

[0008] (1) Composite surface ligand modification: the cadmium selenide / cadmium sulfide quantum dots, thiol group-containing silane compound, carboxyl group-containing polymer and amino silane coupling agent are reacted in an aprotic solvent to form a thiol-carboxyl-amino ternary synergistic ligand layer; wherein the amino silane coupling agent is 3-aminopropyl triethoxysilane, and the molar ratio of the amino silane coupling agent to the thiol group-containing silane compound is 1:2-5;

[0009] (2) Gradient heat treatment: the quantum dot color photoresist is post-baked under inert gas protection according to the following parameters:

[0010] First stage: 50-80℃ for 30-40 minutes to release solvent residues;

[0011] Second stage: increase the temperature to 100-130℃ at a rate of 8-10℃ / min, add a crosslinking agent and keep for 60-120 minutes to trigger the crosslinking of the copolymer resin;

[0012] Third stage: increase the temperature to 140-160℃ at a rate of 4-5℃ / min, add a titanate coupling agent and keep for 20-30 minutes to activate ligand passivation and ligand-resin bonding;

[0013] (3) Controlled cooling: after the gradient heat treatment, cool at a rate of ≤5℃ / min, keep for 10-15 minutes when the temperature drops to 80-100℃, and then continue to cool to room temperature.

[0014] As a further technical solution, the viscosity of the quantum dot color photoresist at 25℃ is 100-500 mPa·s, the coating thickness is 2-5 microns, and before baking, 500-800 rpm is used for 10-20 seconds of spin coating;

[0015] The molar ratio of methyl methacrylate to hydroxyethyl acrylate in the methyl methacrylate-hydroxyethyl acrylate copolymer resin is 1:0.3-0.6.

[0016] As a further technical solution, the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone;

[0017] The solvent is propylene glycol methyl ether acetate.

[0018] As a further technical solution, the core-shell molar ratio of the cadmium selenide / cadmium sulfide quantum dots is 1:3-5, the particle size is 6-10 nanometers, and the original ligand on the surface of the quantum dots is oleic acid.

[0019] As a further technical solution, the thiol group-containing silane compound in step (1) is 3-mercaptopropyl trimethoxysilane, and the molar ratio of 3-mercaptopropyl trimethoxysilane to cadmium selenide / cadmium sulfide quantum dots is 1:50-80;

[0020] The carboxyl-containing polymer is polyacrylic acid, which is prepared by free radical polymerization of acrylic acid, has a number average molecular weight of 5,000-20,000, and the mass ratio of polyacrylic acid to cadmium selenide / cadmium sulfide quantum dots is 1:14-20.

[0021] As a further technical solution, the aprotic solvent in step (1) is N,N-dimethylformamide or dimethyl sulfoxide, and the amount of solvent used is 30-50 times the mass of cadmium selenide / cadmium sulfide quantum dots.

[0022] As a further technical solution, the reaction conditions for the composite surface ligand modification in step (1) are: reaction temperature 25-40℃, reaction time 4-8 hours, stirring rate 200-300 rpm, and nitrogen bubbling to remove impurities for 10-15 minutes after the reaction is completed.

[0023] As a further technical solution, in step (2), the inert gas is nitrogen or argon, the gas flow rate is 16-20 ml / min, and the inert gas is continuously introduced into the reaction chamber during the baking process.

[0024] As a further technical solution, the crosslinking agent in the second stage of step (2) is hexamethylene diisocyanate, the amount of hexamethylene diisocyanate is 12-15% of the mass of methyl methacrylate-hydroxyethyl acrylate copolymer resin, and the molar ratio of hexamethylene diisocyanate to carboxyl groups in the carboxyl-containing polymer is 1:1-1.2.

[0025] As a further technical solution, the titanate coupling agent in the third stage of step (2) is isopropyltris(isostearoyl) titanate, the amount of which is 1.2-2% of the mass of cadmium selenide / cadmium sulfide quantum dots, and the stirring rate is increased to 350-400 rpm after the coupling agent is added.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention significantly improves the heat resistance and stability of quantum dot color photoresist through a synergistic process of composite surface ligand modification, gradient heat treatment, and controlled-rate cooling. The functions of each step are as follows: During the composite surface ligand modification process, 3-mercaptopropyltrimethoxysilane forms strong coordination bonds with the quantum dot surface through its thiol groups, providing the first protective barrier for the quantum dots; the carboxyl groups of polyacrylic acid can form hydrogen bonds with the hydroxyl groups in the resin, improving the compatibility between the quantum dots and the matrix; 3-aminopropyltriethoxysilane, through the synergistic effect of its amino groups and other ligands, constructs a three-dimensional stable ligand layer, effectively preventing quantum dot aggregation. The three-stage gradient heat treatment design has different focuses: the first stage, low-temperature holding, fully releases the solvent and avoids solvent boiling and bubble generation at high temperatures; the second stage, medium-temperature crosslinking, enables the resin to form a dense network structure, improving the mechanical properties of the coating; the third stage, high-temperature treatment, strengthens the chemical bonding between the ligands and the resin through titanate coupling agents, further consolidating structural stability. Controlled-rate cooling, through slow cooling and intermediate holding steps, effectively releases internal stress in the coating, preventing cracking and peeling.

[0028] There is a close synergistic effect among the various process steps, forming a complete performance improvement system. The composite ligand modification provides a stable quantum dot surface state for subsequent heat treatment, and the introduced multifunctional groups provide sufficient reaction sites for the crosslinking reaction in the gradient heat treatment; the gradient heating mode ensures that solvent release, resin crosslinking and ligand bonding reactions proceed in an orderly manner, avoiding the problem of mutual interference of reactions in traditional isothermal processes; the addition of titanate coupling agent at the high temperature stage makes good use of the network structure after resin crosslinking, anchoring the quantum dots more firmly in the matrix, and achieving a progressive stabilization effect of surface protection, structural solidification and interface strengthening.

[0029] The technical effects of this invention are mainly reflected in three aspects: First, it significantly improves heat resistance, with a weight loss rate of less than 1.6% after aging in hot air at 200°C, thanks to the dual protection of the stable ligand layer and the dense resin network; second, it improves optical stability, with a transmittance retention rate of over 89.9% after UV aging, effectively inhibiting the photo-oxidative degradation of quantum dots; and third, it enhances mechanical stability, maintaining grade 0 adhesion even at a high temperature of 150°C, meeting the long-term use requirements of display devices. Attached Figure Description

[0030] Figure 1 This is a flowchart of a post-baking process to improve the heat resistance and stability of quantum dot color photoresist. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention provides a post-baking process to improve the heat resistance and stability of quantum dot color photoresist. The composition and process steps of the quantum dot color photoresist are as follows:

[0033] Composition of quantum dot color photoresist raw materials:

[0034] Methyl methacrylate-hydroxyethyl acrylate copolymer resin: 40-60% by mass, wherein the molar ratio of methyl methacrylate to hydroxyethyl acrylate is 1:0.3-0.6. It is prepared by free radical polymerization. During the polymerization process, the reaction temperature is controlled at 80-90℃ and the reaction time is 6-8 hours to ensure uniform molecular weight distribution of the resin.

[0035] Core-shell structured cadmium selenide / cadmium sulfide quantum dots: mass percentage 12-15%, core-shell molar ratio 1:3-5, particle size 6-10 nanometers, surface original ligand is oleic acid, can be prepared by hot injection method, using selenium powder, cadmium salt, and sodium sulfide as raw materials, reacted in octadecene solvent at 200-220℃ for 30-40 minutes.

[0036] Photoinitiator: 2-5% by mass, specifically 2-hydroxy-2-methyl-1-phenyl-1-propanone (commercially available model 1173), with a purity ≥99%, must be stored in the dark to prevent premature polymerization.

[0037] Solvent: The balance portion is propylene glycol methyl ether acetate (commercially available with a purity ≥99.5%), which needs to be dehydrated by molecular sieve (water content ≤0.1%) to avoid affecting the stability of quantum dots.

[0038] The quantum dot color photoresist has a viscosity of 100-500 mPa·s at 25°C and a coating thickness of 2-5 micrometers. Before baking, it is spin-coated at a rate of 500-800 rpm for 10-20 seconds to ensure a uniform coating without bubbles.

[0039] Post-baking process steps:

[0040] (1) Composite surface ligand modification:

[0041] Cadmium selenide / cadmium sulfide quantum dots, thiol-containing silane compounds, carboxyl-containing polymers, and aminosilane coupling agents are reacted in an aprotic solvent to form a thiol-carboxyl-amino ternary synergistic ligand layer.

[0042] The thiol-containing silane compound is specifically 3-mercaptopropyltrimethoxysilane (commercially available with a purity ≥98%), and its molar ratio with cadmium selenide / cadmium sulfide quantum dots is 1:50-80.

[0043] The carboxyl-containing polymer is specifically polyacrylic acid, which is prepared by free radical polymerization of acrylic acid (using ammonium persulfate as an initiator, reacting at 60-70℃ for 4-5 hours). The number average molecular weight is 5000-20000, and the mass ratio of polyacrylic acid to cadmium selenide / cadmium sulfide quantum dots is 1:14-20.

[0044] The aminosilane coupling agent is specifically 3-aminopropyltriethoxysilane (commercially available with a purity ≥97%), and its molar ratio with the mercaptan-containing silane compound is 1:2-5.

[0045] The aprotic solvent is N,N-dimethylformamide or dimethyl sulfoxide (commercially available with a purity ≥99%), and the amount used is 30-50 times the mass of cadmium selenide / cadmium sulfide quantum dots;

[0046] The reaction conditions are as follows: reaction temperature 25-40℃, reaction time 4-8 hours, stirring speed 200-300 rpm, and nitrogen bubbling for 10-15 minutes after the reaction to remove impurities, with nitrogen purity ≥99.99%.

[0047] (2) Gradient heat treatment:

[0048] Under inert gas protection, the quantum dot color photoresist was post-baked according to three-stage parameters.

[0049] The inert gas is nitrogen or argon (purity ≥99.99%), and the gas flow rate is 16-20 ml / min. It is continuously introduced into the reaction chamber during the baking process to eliminate air interference.

[0050] First stage: Keep warm at 50-80℃ for 30-40 minutes to release residual solvent and prevent subsequent high temperature from causing the solvent to boil and generate bubbles;

[0051] Second stage: Increase the temperature to 100-130℃ at a rate of 8-10℃ / min, add the crosslinking agent and keep warm for 60-120 minutes to trigger crosslinking of the copolymer resin; the crosslinking agent is hexamethylene diisocyanate (commercially available with a purity ≥99%), the amount of which is 12-15% of the mass of methyl methacrylate-hydroxyethyl acrylate copolymer resin, and the molar ratio of hexamethylene diisocyanate to carboxyl groups in the carboxyl-containing polymer is 1:1-1.2;

[0052] The third stage: The temperature is increased to 140-160℃ at a rate of 4-5℃ / min, the titanate coupling agent is added and the temperature is maintained for 20-30 minutes to activate ligand passivation and ligand-resin bonding; the titanate coupling agent is specifically isopropyl tris(isostearoyl) titanate (commercially available model TTS), and the amount used is 1.2-2% of the mass of cadmium selenide / cadmium sulfide quantum dots. After the coupling agent is added, the stirring rate is increased to 350-400 rpm to ensure uniform dispersion of the coupling agent.

[0053] (3) Speed-controlled cooling:

[0054] After the gradient heat treatment is completed, the coating is cooled at a rate of ≤5℃ / min to avoid excessive temperature difference that could cause the coating to crack. When the temperature drops to 80-100℃, it is held for 10-15 minutes to release internal stress. Then, it is cooled to room temperature to obtain the final quantum dot color photoresist coating.

[0055] This invention solves the problems of poor heat resistance and low stability of traditional quantum dot color photoresists by using a synergistic process of composite surface ligand modification, gradient heat treatment, and controlled-rate cooling. The composite ligand layer enhances the compatibility between quantum dots and resin, the gradient heat treatment enables solvent release, resin crosslinking, and ligand bonding in stages, and the controlled-rate cooling reduces internal stress. Ultimately, this significantly improves the heat resistance, optical stability, and mechanical properties of the photoresist coating. Furthermore, the process is easy to operate, highly repeatable, and suitable for industrial production.

[0056] The following are specific examples:

[0057] Example 1: Preparation of quantum dot color photoresist: The raw materials were weighed according to the following mass ratios: 50% methyl methacrylate-hydroxyethyl acrylate copolymer resin (molar ratio 1:0.45), 13.5% core-shell structured cadmium selenide / cadmium sulfide quantum dots (core-shell molar ratio 1:4, particle size 8 nm), 3.5% 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 33% propylene glycol methyl ether acetate. The mixture was stirred at 250 rpm for 30 minutes at 25°C to obtain a uniform photoresist solution. The viscosity of the photoresist solution at 25°C was 300 mPa·s. The coating thickness was 3.5 μm by spin coating at 650 rpm for 15 seconds.

[0058] Composite surface ligand modification: Take 10g of the above quantum dots, add 3-mercaptopropyltrimethoxysilane (molar ratio to quantum dots 1:65), polyacrylic acid (number average molecular weight 12000, mass ratio to quantum dots 1:17), and 3-aminopropyltriethoxysilane (molar ratio to 3-mercaptopropyltrimethoxysilane 1:3.5), using N,N-dimethylformamide as solvent (the amount used is 40 times the mass of quantum dots); stir at 250 rpm for 6 hours at 32℃, and after the reaction is completed, purge with nitrogen gas for 12 minutes to remove impurities, and obtain modified quantum dots.

[0059] Gradient heat treatment: The photoresist coating containing modified quantum dots was placed in the reaction chamber and nitrogen gas was introduced (flow rate 18 mL / min); in the first stage, the temperature was raised to 65 °C and held for 35 minutes; in the second stage, the temperature was raised to 115 °C at a rate of 9 °C / min, hexamethylene diisocyanate (13.5% of the mass of the copolymer resin, with a molar ratio of 1:1.1 to the carboxyl group) was added, and the temperature was held for 90 minutes; in the third stage, the temperature was raised to 150 °C at a rate of 4.5 °C / min, isopropyltris(isostearoyl)titanate (1.6% of the mass of the quantum dots) was added, the stirring rate was increased to 375 rpm, and the temperature was held for 25 minutes.

[0060] Controlled cooling: Cool at a rate of 4℃ / minute, hold at 90℃ for 12 minutes, and continue cooling to room temperature to obtain the photoresist coating product.

[0061] Example 2: Preparation of quantum dot color photoresist: The raw materials were weighed according to the following mass ratios: 45% methyl methacrylate-hydroxyethyl acrylate copolymer resin (molar ratio 1:0.35), 12.5% ​​core-shell structured cadmium selenide / cadmium sulfide quantum dots (core-shell molar ratio 1:3.5, particle size 7 nm), 2.5% 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 39% propylene glycol methyl ether acetate. The mixture was stirred at 220 rpm for 35 minutes at 25°C to obtain a uniform photoresist solution. The viscosity of the photoresist solution at 25°C was 200 mPa·s. The coating thickness was 2.8 μm by spin coating at 550 rpm for 18 seconds.

[0062] Composite surface ligand modification: Take 10g of the above quantum dots, add 3-mercaptopropyltrimethoxysilane (molar ratio to quantum dots 1:55), polyacrylic acid (number average molecular weight 8000, mass ratio to quantum dots 1:15), and 3-aminopropyltriethoxysilane (molar ratio to 3-mercaptopropyltrimethoxysilane 1:2.5), using dimethyl sulfoxide as solvent (the amount used is 35 times the mass of quantum dots); stir at 220 rpm for 5 hours at 28℃, and after the reaction is completed, purge with nitrogen gas for 10 minutes to remove impurities, and obtain modified quantum dots.

[0063] Gradient heat treatment: The photoresist coating containing modified quantum dots was placed in the reaction chamber and argon gas was introduced (flow rate 16 mL / min); in the first stage, the temperature was raised to 55 °C and held for 38 minutes; in the second stage, the temperature was raised to 105 °C at a rate of 10 °C / min, hexamethylene diisocyanate (12.5% ​​of the mass of the copolymer resin, with a molar ratio of 1:1.05 to the carboxyl group) was added, and the temperature was held for 110 minutes; in the third stage, the temperature was raised to 145 °C at a rate of 5 °C / min, isopropyltris(isostearoyl)titanate (1.3% of the mass of the quantum dots) was added, the stirring rate was increased to 350 rpm, and the temperature was held for 28 minutes.

[0064] Controlled cooling rate: Cool at a rate of 3℃ / minute, hold at 85℃ for 14 minutes, and continue cooling to room temperature to obtain the photoresist coating product.

[0065] Example 3: Preparation of quantum dot color photoresist: The raw materials were weighed according to the following mass ratios: 55% methyl methacrylate-hydroxyethyl acrylate copolymer resin (molar ratio 1:0.55), 14.5% core-shell structured cadmium selenide / cadmium sulfide quantum dots (core-shell molar ratio 1:4.5, particle size 9 nm), 4.5% 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 26% propylene glycol methyl ether acetate. The mixture was stirred at 280 rpm for 25 minutes at 25°C to obtain a uniform photoresist solution. The viscosity of the photoresist solution at 25°C was 400 mPa·s. Spin coating was performed at 750 rpm for 12 seconds to achieve a coating thickness of 4.2 μm.

[0066] Composite surface ligand modification: Take 10g of the above quantum dots, add 3-mercaptopropyltrimethoxysilane (molar ratio to quantum dots 1:75), polyacrylic acid (number average molecular weight 18000, mass ratio to quantum dots 1:19), and 3-aminopropyltriethoxysilane (molar ratio to 3-mercaptopropyltrimethoxysilane 1:4.5), using N,N-dimethylformamide as solvent (the amount used is 45 times the mass of quantum dots); stir at 280 rpm for 7 hours at 38℃, and after the reaction is completed, purge with nitrogen gas for 15 minutes to remove impurities, and obtain modified quantum dots.

[0067] Gradient heat treatment: The photoresist coating containing modified quantum dots was placed in the reaction chamber and nitrogen gas was introduced (flow rate 20 mL / min); in the first stage, the temperature was raised to 75°C and held for 32 minutes; in the second stage, the temperature was raised to 125°C at a rate of 8°C / min, hexamethylene diisocyanate (14.5% of the mass of the copolymer resin, with a molar ratio of 1:1.15 to the carboxyl group) was added, and the temperature was held for 70 minutes; in the third stage, the temperature was raised to 155°C at a rate of 4°C / min, isopropyltris(isostearoyl)titanate (1.9% of the mass of the quantum dots) was added, the stirring rate was increased to 400 rpm, and the temperature was held for 22 minutes.

[0068] Controlled cooling rate: Cool at a rate of 5℃ / minute, hold at 95℃ for 11 minutes, and continue cooling to room temperature to obtain the photoresist coating product.

[0069] Example 4: Preparation of quantum dot color photoresist: The raw materials were weighed according to the following mass ratios: 48% methyl methacrylate-hydroxyethyl acrylate copolymer resin (molar ratio 1:0.4), 13% core-shell structured cadmium selenide / cadmium sulfide quantum dots (core-shell molar ratio 1:3.8, particle size 7.5 nm), 3% 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 36% propylene glycol methyl ether acetate. The mixture was stirred at 240 rpm for 28 minutes at 25°C to obtain a uniform photoresist solution. The viscosity of the photoresist solution at 25°C was 280 mPa·s. Spin coating was performed at 600 rpm for 16 seconds to achieve a coating thickness of 3.2 μm.

[0070] Composite surface ligand modification: Take 10g of the above quantum dots, add 3-mercaptopropyltrimethoxysilane (molar ratio to quantum dots 1:60), polyacrylic acid (number average molecular weight 10000, mass ratio to quantum dots 1:16), and 3-aminopropyltriethoxysilane (molar ratio to 3-mercaptopropyltrimethoxysilane 1:3), using dimethyl sulfoxide as solvent (the amount used is 38 times the mass of quantum dots); stir at 240 rpm for 5.5 hours at 30℃, and after the reaction is completed, purge with nitrogen gas for 13 minutes to remove impurities, and obtain modified quantum dots.

[0071] Gradient heat treatment: The photoresist coating containing modified quantum dots was placed in the reaction chamber and argon gas was introduced (flow rate 17 mL / min); in the first stage, the temperature was raised to 60 °C and held for 36 minutes; in the second stage, the temperature was raised to 110 °C at a rate of 9.5 °C / min, hexamethylene diisocyanate (13% of the mass of the copolymer resin, with a molar ratio of 1:1.08 to the carboxyl group) was added, and the temperature was held for 85 minutes; in the third stage, the temperature was raised to 148 °C at a rate of 4.2 °C / min, isopropyltris(isostearoyl)titanate (1.8% of the mass of the quantum dots) was added, the stirring rate was increased to 380 rpm, and the temperature was held for 24 minutes.

[0072] Controlled cooling rate: Cool at a rate of 3.5℃ / min, hold at 88℃ for 13 minutes, and continue cooling to room temperature to obtain the photoresist coating product.

[0073] Example 5: Preparation of quantum dot color photoresist: The raw materials were weighed according to the following mass ratios: 52% methyl methacrylate-hydroxyethyl acrylate copolymer resin (molar ratio 1:0.5), 14% core-shell structured cadmium selenide / cadmium sulfide quantum dots (core-shell molar ratio 1:4.2, particle size 8.5 nm), 4% 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 30% propylene glycol methyl ether acetate. The mixture was stirred at 260 rpm for 26 minutes at 25°C to obtain a uniform photoresist solution. The viscosity of the photoresist solution at 25°C was 350 mPa·s. Spin coating was performed at 700 rpm for 14 seconds to achieve a coating thickness of 3.8 μm.

[0074] Composite surface ligand modification: Take 10g of the above quantum dots, add 3-mercaptopropyltrimethoxysilane (molar ratio to quantum dots 1:70), polyacrylic acid (number average molecular weight 15000, mass ratio to quantum dots 1:18), and 3-aminopropyltriethoxysilane (molar ratio to 3-mercaptopropyltrimethoxysilane 1:4), using N,N-dimethylformamide as solvent (the amount used is 48 times the mass of quantum dots); stir at 260 rpm for 6.5 hours at 35℃, and after the reaction is completed, purge with nitrogen gas for 14 minutes to remove impurities, and obtain modified quantum dots.

[0075] Gradient heat treatment: The photoresist coating containing modified quantum dots was placed in the reaction chamber and nitrogen gas was introduced (flow rate 19 mL / min); in the first stage, the temperature was raised to 70 °C and held for 34 minutes; in the second stage, the temperature was raised to 120 °C at a rate of 8.5 °C / min, hexamethylene diisocyanate (14% of the mass of the copolymer resin, with a molar ratio of 1:1.12 to the carboxyl group) was added, and the temperature was held for 80 minutes; in the third stage, the temperature was raised to 152 °C at a rate of 4.8 °C / min, isopropyltris(isostearoyl)titanate (1.5% of the mass of the quantum dots) was added, the stirring rate was increased to 360 rpm, and the temperature was held for 26 minutes.

[0076] Controlled cooling rate: Cool at a rate of 4.5℃ / min, hold at 92℃ for 12.5 minutes, and continue cooling to room temperature to obtain the photoresist coating product.

[0077] Comparative Example 1: Preparation of Quantum Dot Color Photoresist: Completely consistent with Example 1, namely 50% methyl methacrylate-hydroxyethyl acrylate copolymer resin (molar ratio 1:0.45), 13.5% core-shell structured cadmium selenide / cadmium sulfide quantum dots (core-shell molar ratio 1:4, particle size 8 nm, original ligand oleic acid), 3.5% 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 33% propylene glycol methyl ether acetate. Stirred at 250 rpm for 30 minutes at 25°C, the viscosity of the photoresist was 300 mPa·s. Spin-coated at 650 rpm for 15 seconds, the coating thickness was 3.5 μm.

[0078] Omitted composite surface ligand modification: directly use quantum dots with original oleic acid ligands on the surface, without adding 3-mercaptopropyltrimethoxysilane, polyacrylic acid and 3-aminopropyltriethoxysilane, and without carrying out ligand modification reaction.

[0079] Gradient heat treatment: exactly the same as in Example 1, i.e., nitrogen flow rate of 18 mL / min, first stage 65°C held for 35 minutes, second stage 9°C / min increase to 115°C, hexamethylene diisocyanate dosage of 13.5%, held for 90 minutes, third stage 4.5°C / min increase to 150°C, isopropyl tris(isostearoyl) titanate dosage of 1.6%, stirring at 375 rpm, held for 25 minutes.

[0080] Controlled cooling rate: exactly the same as in Example 1, i.e., cooling at 4°C / minute, holding at 90°C for 12 minutes, and cooling to room temperature.

[0081] Comparative Example 2: Preparation of quantum dot color photoresist: completely consistent with Example 1, with the same composition, viscosity, and spin coating parameters.

[0082] Composite surface ligand modification: completely consistent with Example 1, with the same preparation conditions and raw material ratios for the modified quantum dots.

[0083] Isothermal heat treatment replaces gradient heat treatment: The photoresist coating containing modified quantum dots is placed in the reaction chamber and nitrogen gas is introduced (flow rate 18 mL / min); the temperature is directly raised to 150°C (without staged heating), and hexamethylene diisocyanate (13.5%) and isopropyl tris(isostearoyl) titanate (1.6%) are added at the same time. The stirring rate is 375 rpm, and the temperature is kept constant for 150 minutes (the total time is the same as the total time of gradient heat treatment in Example 1).

[0084] Controlled cooling rate: exactly the same as in Example 1, i.e., cooling at 4°C / minute, holding at 90°C for 12 minutes, and cooling to room temperature.

[0085] Experimental verification:

[0086] To verify the effect of the process of the present invention on improving the heat resistance and stability of quantum dot color photoresist, the test subjects were the photoresist coating products of Examples 1-5 and Comparative Examples 1-2. The test data and analysis are as follows:

[0087] Test 1: Heat resistance test (hot air aging test);

[0088] Referring to GB / T11026.1-2021, the photoresist coating samples were placed in a hot air aging chamber at 200℃ for 24 hours. Before and after the test, the sample mass was weighed using a precision electronic balance (accuracy 0.1 mg), and the weight loss rate was calculated (weight loss rate = (mass before test - mass after test) / mass before test × 100%). A lower weight loss rate indicates better heat resistance (no obvious agglomeration or detachment of quantum dots, no obvious decomposition of resin). The results are as follows:

[0089] Table 1

[0090] Sample No. Mass before test (mg) Mass after test (mg) Mass loss rate (%) Example 1 205.6 202.9 1.31 Example 2 210.3 207.7 1.24 Example 3 208.5 205.2 1.58 Example 4 206.8 203.9 1.40 Example 5 209.2 206.0 1.53 Comparative Example 1 204.9 195.7 4.49 Comparative Example 2 207.1 200.5 3.19

[0091] As shown in Table 1, Examples 1-5 all exhibited a weight loss rate of less than 1.6%, indicating excellent heat resistance. This is because the composite surface ligand layer forms strong coordination bonds with the quantum dots, while simultaneously bonding with the copolymer resin via a titanate coupling agent, preventing quantum dot desorption at high temperatures. The gradient heat treatment process involves three stages: the first stage fully releases the solvent, the second stage achieves resin cross-linking to form a dense network, and the third stage strengthens the ligand-resin bond. These three stages synergistically suppress mass loss at high temperatures. Comparative Example 1, on the other hand, showed a weight loss rate as high as 4.49%. The core reason for this was the lack of composite ligand modification. The original oleic acid ligands on the quantum dot surface had poor compatibility with the resin, leading to easy desorption at high temperatures. Furthermore, the poor thermal stability of the oleic acid ligands caused them to decompose easily at 200°C, resulting in quantum dot aggregation and significant mass loss.

[0092] Experiment 2: Optical stability test (transmittance retention rate after UV aging);

[0093] According to GB / T2410-2021, the initial transmittance of the sample was determined using a transmittance meter (test wavelength 550nm, which is near the main peak of quantum dot emission).

[0094] Referring to GB / T16422.3-2014, the sample was placed in an ultraviolet aging chamber with an ultraviolet wavelength of 340 nm and an irradiation intensity of 0.71 W / m². 2 Temperature 60℃, heat preservation for 100 hours;

[0095] After aging, the transmittance was measured again, and the transmittance retention rate was calculated (retention rate = transmittance after aging / initial transmittance × 100%). The higher the retention rate, the better the optical stability (no obvious photo-oxidation of quantum dots and no obvious yellowing of resin). The results are as follows:

[0096] Table 2

[0097] Sample No. Initial light transmittance (%) Light transmittance after aging (%) Light transmittance retention rate (%) Example 1 92.5 85.3 92.2 Example 2 91.8 83.6 91.1 Example 3 93.2 84.8 91.0 Example 4 92.1 82.9 89.9 Example 5 92.8 83.9 90.4 Comparative Example 1 90.5 58.8 64.9 Comparative Example 2 91.2 65.7 72.0

[0098] As shown in Table 2, Examples 1-5 all exhibited a transmittance retention rate higher than 89.9%, demonstrating excellent optical stability. This is because the thiol and amino groups in the composite ligand layer can capture free radicals generated by ultraviolet light, inhibiting the photo-oxidation of quantum dots; the dense resin cross-linked network formed by gradient heat treatment reduces oxygen entry into the coating, preventing the quantum dots from being oxidized; and the titanate coupling agent strengthens the bonding between the quantum dots and the resin, preventing the decrease in transmittance caused by quantum dot aggregation.

[0099] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification.

Claims

1. A post-baking process for improving the heat resistance and stability of quantum dot color photoresist, characterized in that, The quantum dot color photoresist comprises: 40-60% methyl methacrylate-hydroxyethyl acrylate copolymer resin, 12-15% core-shell structured cadmium selenide / cadmium sulfide quantum dots, 2-5% photoinitiator and the balance solvent. The post-baking process includes the following steps: (1) Composite surface ligand modification: The cadmium selenide / cadmium sulfide quantum dots, thiol-containing silane compounds, carboxyl-containing polymers and aminosilane coupling agents are reacted in an aprotic solvent to form a thiol-carboxyl-amino ternary synergistic ligand layer; wherein, the aminosilane coupling agent is 3-aminopropyltriethoxysilane, and the molar ratio of the aminosilane coupling agent to the thiol-containing silane compound is 1:2-5; (2) Gradient heat treatment: Under inert gas protection, the quantum dot color photoresist is post-baked according to the following parameters: First stage: Keep warm at 50-80℃ for 30-40 minutes to release residual solvent; Second stage: Heat to 100-130℃ at a rate of 8-10℃ / min, add crosslinking agent and keep warm for 60-120 minutes to trigger crosslinking of copolymer resin; Third stage: Heat to 140-160℃ at a rate of 4-5℃ / min, add titanate coupling agent and keep warm for 20-30 minutes to activate ligand passivation and ligand-resin bonding. (3) Controlled cooling: After the gradient heat treatment is completed, cool at a rate of ≤5℃ / min. When the temperature drops to 80-100℃, keep it at that temperature for 10-15 minutes, and then continue to cool to room temperature.

2. The process according to claim 1, characterized in that, The quantum dot color photoresist has a viscosity of 100-500 mPa·s at 25°C, a coating thickness of 2-5 micrometers, and is spin-coated at 500-800 rpm for 10-20 seconds before baking. In methyl methacrylate-hydroxyethyl acrylate copolymer resin, the molar ratio of methyl methacrylate to hydroxyethyl acrylate is 1:0.3-0.

6.

3. The process according to claim 1, characterized in that, The photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone; The solvent is propylene glycol methyl ether acetate.

4. The process according to claim 1, characterized in that, The core-shell molar ratio of the cadmium selenide / cadmium sulfide quantum dots is 1:3-5, the particle size is 6-10 nanometers, and the original ligand on the surface of the quantum dots is oleic acid.

5. The process according to claim 1, characterized in that, In step (1), the thiol-containing silane compound is 3-mercaptopropyltrimethoxysilane, and the molar ratio of 3-mercaptopropyltrimethoxysilane to cadmium selenide / cadmium sulfide quantum dots is 1:50-80. The carboxyl-containing polymer is polyacrylic acid, which is prepared by free radical polymerization of acrylic acid, has a number average molecular weight of 5,000-20,000, and the mass ratio of polyacrylic acid to cadmium selenide / cadmium sulfide quantum dots is 1:14-20.

6. The process according to claim 1, characterized in that, The aprotic solvent in step (1) is N,N-dimethylformamide or dimethyl sulfoxide, and the amount of solvent used is 30-50 times the mass of cadmium selenide / cadmium sulfide quantum dots.

7. The process according to claim 1, characterized in that, The reaction conditions for the composite surface ligand modification in step (1) are: reaction temperature 25-40℃, reaction time 4-8 hours, stirring rate 200-300 rpm, and nitrogen bubbling for 10-15 minutes after the reaction is completed to remove impurities.

8. The process according to claim 1, characterized in that, In step (2), the inert gas is nitrogen or argon, the gas flow rate is 16-20 ml / min, and the inert gas is continuously introduced into the reaction chamber during the baking process.

9. The process according to claim 1, characterized in that, In step (2), the crosslinking agent in the second stage is hexamethylene diisocyanate. The amount of hexamethylene diisocyanate is 12-15% of the mass of methyl methacrylate-hydroxyethyl acrylate copolymer resin, and the molar ratio of hexamethylene diisocyanate to carboxyl groups in the carboxyl-containing polymer is 1:1-1.

2.

10. The process according to claim 1, characterized in that, In step (2), the titanate coupling agent in the third stage is isopropyl tris(isostearoyl) titanate, and its amount is 1.2-2% of the mass of cadmium selenide / cadmium sulfide quantum dots. After the coupling agent is added, the stirring rate is increased to 350-400 rpm.

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