High-transmittance alkali-free gradient thermal expansion coefficient glass substrate and preparation method thereof

Abstract

The invention discloses a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate and a preparation method thereof, and belongs to the technical field of glass. The thermal expansion coefficient gradient which is sequentially reduced from the center to the edge is formed in the glass substrate, so that the problem of thermal stress concentration in a high-temperature manufacturing process is effectively solved, and meanwhile, high transmittance and good mechanical performance are kept.

Description

Technical Field

[0001] The present invention relates to the technical field of glass, and in particular to a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate and a preparation method thereof. Background Art

[0002] The manufacturing process of flat-panel display devices such as liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs) often requires high-temperature processes on glass substrates. For example, low-temperature polycrystalline silicon (LTPS) technology requires annealing at temperatures of 600-700°C. During this process, due to the mismatch between the coefficient of thermal expansion (CTE) of the glass substrate and the CTE of the various functional thin films deposited on it (such as metal electrodes and semiconductor layers), significant thermal stress is generated, leading to problems such as substrate warping, cracking or delamination of the thin films, and seriously affecting device performance and yield.

[0003] Traditional solutions primarily involve optimizing the glass composition to adjust its CTE or applying a low-expansion coating to the glass substrate. However, these approaches have significant limitations. For example, simply optimizing the glass composition makes it difficult to achieve a gradient CTE distribution within the substrate, and thus cannot effectively address the thermal stress concentration caused by temperature gradients. Coating methods, on the other hand, suffer from insufficient adhesion between the coating and the glass substrate, complex and costly coating processes, and the potential for the coating to affect the substrate's optical properties.

[0004] Therefore, there is an urgent need for a new glass substrate and its preparation method, which can effectively solve the problem of thermal stress concentration in high-temperature processes while ensuring high transmittance and good mechanical properties, and improve the manufacturing yield and performance of display devices. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate and its preparation method. By forming a thermal expansion coefficient gradient that decreases from the center to the edge inside the glass substrate, the problem of thermal stress concentration in high-temperature processes is effectively solved while maintaining high transmittance and good mechanical properties.

[0006] The technical solution of the present invention is:

[0007] In one aspect, the present invention provides a method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate, comprising the following steps:

[0008] S1 prepares glass batch 1 and glass batch 2, both of which contain low-expansion crystallites, and the content of low-expansion crystallites in glass batch 1 is lower than the content of low-expansion crystallites in glass batch 2;

[0009] S2: putting glass batch material 1 and glass batch material 2 into a melting furnace to melt them into glass liquid;

[0010] S3 introduces the two types of glass liquid into the roller forming equipment respectively. The roller forming equipment includes a shell, a forming disk is arranged inside the shell, a central pressure roller is arranged at the center of the forming disk, and an edge pressure roller is arranged at both ends of the central pressure roller. Electric heating wires are arranged in the central pressure roller and the edge pressure roller to electrically heat the central pressure roller and the edge pressure roller, and the temperature of the central pressure roller is higher than that of the edge pressure roller; a glass liquid tank is respectively arranged above the forming disk corresponding to the central pressure roller and the edge pressure roller area, and a valve is provided at the feed port of the glass liquid tank; the glass liquid tank corresponding to the central pressure roller area is filled with glass liquid formed by melting the glass batch material, and the edge pressure roller area is filled with a glass liquid formed by melting the glass batch material. The corresponding glass liquid tank is filled with glass liquid formed by melting the glass batch material; a rotating shaft is passed through the central pressing roller and the edge pressing roller, and the central pressing roller and the edge pressing roller are driven to rotate by a motor. The glass liquid is roll-pressed into shape by the central pressing roller and the edge pressing roller. During the roll-pressing process, the heat diffusion caused by the temperature gradient is driven: the diffusion coefficient of the microcrystals in the high-temperature area (central area) is higher, which promotes the directional migration of the microcrystals to the low-temperature area (edge ​​area). By controlling the temperature difference between the rollers, the gradient distribution is controllable, and finally the central area, transition area and edge area are formed on the formed glass substrate, and the thermal expansion coefficients of the glass substrates in the three areas decrease in sequence.

[0011] S4 annealing is performed to obtain a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate.

[0012] Preferably, in step S1, glass batch material 1 and glass batch material 2 include components in the following mass percentages, wherein the total mass of the remaining components in glass batch material 1 and glass batch material 2 except low-expansion microcrystals is calculated as 100%, and the low-expansion microcrystals are calculated as a percentage of the total mass of the remaining components: SiO2: 55-65%, Al2O3: 13-18%, B2O3: 8-12%, MgO: 6-9%, CaO: 1-5%, SrO: 0.5-3%, BaO: 0.1-1.5%, ZrO2: 0.1-2% and low-expansion microcrystals, the mass percentage of low-expansion microcrystals in glass batch material 1 is 15-18%, and the mass percentage of low-expansion microcrystals in glass batch material 2 is 19-22%.

[0013] Preferably, the method for preparing low expansion crystallites comprises the following steps:

[0014] 1) Sol synthesis

[0015] a) Preparation of metal ion solution

[0016] Add MgO and Al2O3 to dilute nitric acid and stir while heating to 60-80°C. Continue stirring until completely dissolved to form a metal ion solution. After cooling to room temperature, filter to remove insoluble impurities.

[0017] b) Preparation of silicon source solution

[0018] TEOS was dissolved in anhydrous ethanol, PEG-400 was added as a dispersant, and ultrasonic dispersion was performed to form a uniform silicon source solution;

[0019] c) Mixing and pH adjustment

[0020] Under stirring conditions, the silicon source solution was added dropwise to the metal ion solution. The pH value was monitored in real time during the addition process and the pH value of the system was adjusted to 6.5±0.1. After the addition was completed, stirring was continued to form a uniform and transparent sol.

[0021] 2) Aging treatment

[0022] The prepared sol is allowed to stand and age at room temperature;

[0023] 3) Hydrothermal crystallization

[0024] a) transferring the aged sol to a hydrothermal reactor, placing the hydrothermal reactor in a high-temperature furnace, heating to 190-210° C. at a heating rate of 4-6° C. / min, and maintaining the temperature for 16-20 hours for crystallization;

[0025] b) After the crystallization is completed, the high-temperature furnace is turned off and the hydrothermal reactor is allowed to cool naturally to room temperature;

[0026] 4) Cooling separation and multi-stage washing

[0027] a) opening the hydrothermal reactor, taking out the product, transferring it to a centrifuge tube and centrifuging it, and discarding the supernatant;

[0028] b) adding deionized water to the centrifuge tube, performing ultrasonic dispersion, centrifuging again, and discarding the supernatant;

[0029] c) repeating the above step b) several times to wash the product;

[0030] d) After washing, take the supernatant and add silver nitrate solution. If no white precipitate is formed, it indicates that NO3 - The ions have been washed away and microcrystals are obtained;

[0031] 5) Surface coating

[0032] a) redispersing the washed microcrystals in an ethanol solution containing TEOS and performing ultrasonic dispersion;

[0033] b) Under stirring conditions, adjusting the pH value of the system to 8-10, and then stirring to hydrolyze TEOS on the surface of the microcrystal to form a SiO2 coating layer;

[0034] c) After the coating is completed, the product is cooled to room temperature and collected by centrifugation;

[0035] 6) Ultrasonic dispersion and freeze drying

[0036] a) dispersing the coated microcrystals in anhydrous ethanol, and destroying particle agglomerates by ultrasonication to obtain a dispersion;

[0037] b) Transfer the dispersion to a sample tray of a freeze dryer and prefreeze to -70 to -60°C for 2-3 hours;

[0038] c) Turn on the vacuum pump, reduce the vacuum degree to below 5 Pa, and freeze-dry at -70 to -60°C for 36 to 40 hours to obtain low-expansion microcrystals.

[0039] Preferably, in step 1) a), the mass ratio of MgO and Al2O3 is 1:(1.5-2.5), the concentration of dilute nitric acid is 5wt.%, and the mass volume ratio of MgO and dilute nitric acid is 1g:(10-15)mL; in step 1) b), the mass volume ratio of TEOS, PEG-400, and anhydrous ethanol is 1g:(0.005-0.01)g:(2-3)mL; in step 1) c), the mass ratio of the silicon source solution to the metal ion solution is 1:(0.4-1), and the dropping speed is 1-3 drops / s; in step 4) d), the concentration of the silver nitrate solution is 0.1mol / L; in step 5) a), in the TEOS-containing ethanol solution, the TEOS concentration is 5wt.%, and the mass ratio of microcrystals to TEOS is 1:(0.5-1).

[0040] Preferably, the method further includes step 7) high-temperature crystallization heat treatment: placing the freeze-dried low-expansion microcrystals in a high-temperature furnace, heating them to 800-900°C at a heating rate of 5-8°C / min under a nitrogen protective atmosphere, keeping the temperature for 2-3 hours, and then cooling them to room temperature with the furnace.

[0041] Preferably, in step S2, the melting temperature is 1565-1595°C, and the melting time is 2-3 hours.

[0042] Preferably, in step S3, an electric heating wire is provided outside the glass liquid tank to maintain the temperature of the glass liquid in the tank at 1565-1595°C.

[0043] Preferably, in step S3, both ends of the rotating shaft are connected to a vertical rod 1 respectively, the two vertical rods 1 are connected by a horizontal rod, the center of the horizontal rod is connected to a vertical rod 2, and the vertical rod 2 is connected to the output shaft of the motor.

[0044] Preferably, in step S3, the temperature of the center pressing roller is 600-620°C, and the temperature of the edge pressing roller is 520-540°C; in step S4, the roller-formed glass substrate is sent to an annealing furnace and kept at 520-550°C for 2-3 hours to eliminate internal stress; then cooled to room temperature at a cooling rate of 5-8°C / min to obtain a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate.

[0045] On the other hand, the present invention provides a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate, which is prepared by the above-mentioned preparation method of the high-transmittance alkali-free gradient thermal expansion coefficient glass substrate.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. The glass substrate of the present invention has a significant thermal stress relief effect: by forming a gradient thermal expansion coefficient from the center to the edge inside the substrate, it effectively matches the temperature gradient distribution in high-temperature processes, significantly reduces thermal stress concentration, reduces thermal stress, and reduces substrate deformation rate, meeting the requirements of high-precision photolithography processes.

[0048] 2. Improved compatibility with TFT process: The thermal expansion coefficient of the edge area of ​​the glass substrate of the present invention (2.8×10 -6 / ℃) and the thermal expansion coefficient difference between TFT metal electrode materials (such as Mo) is reduced to 2.2×10 -6 / ℃, significantly reducing the interface stress between the film and the substrate, lowering the risk of film cracking and peeling, and improving the yield and reliability of TFT devices.

[0049] 3. Maintaining high optical performance: Through the surface SiO2 coating of low-expansion microcrystals and the optimization of glass phase composition, the transmittance of the glass substrate is ensured to be greater than 90%, meeting the optical requirements of high-end display devices.

[0050] 4. Good mechanical properties: The uniform dispersion and gradient distribution of low-expansion microcrystals, as well as the strengthening effect of ZrO2, make the bending strength of the glass substrate greater than 200MPa, thereby improving the processing performance and reliability of the substrate.

[0051] 5. High process feasibility: Through the gradient roll forming process, the directional migration and gradient distribution of low-expansion microcrystals are achieved. The process parameters are highly controllable and suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a structural schematic diagram of the central pressing roller and the edge pressing rollers in the roller forming equipment of the present invention.

[0053] In the figure, 1. Center pressure roller; 2. Edge pressure roller; 3. Rotating shaft; 4. Vertical rod 1; 5. Horizontal rod; 6. Vertical rod 2; 7. Motor. DETAILED DESCRIPTION

[0054] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0055] The roll forming equipment used in the following embodiments includes a housing, and a forming plate is arranged inside the housing, such as Figure 1 As shown, a central pressure roller 1 is provided at the center of the forming disk, and an edge pressure roller 2 is provided at both ends of the central pressure roller 1. Electric heating wires are provided inside the central pressure roller 1 and the edge pressure roller 2 to electrically heat the central pressure roller 1 and the edge pressure roller 2, and the temperature of the central pressure roller 1 is higher than that of the edge pressure roller 2. A glass liquid tank is provided above the forming disk in the corresponding areas of the central pressure roller 1 and the edge pressure roller 2, respectively, and a valve is provided at the feed port of the glass liquid tank. The glass liquid tank corresponding to the area of ​​the central pressure roller 1 is filled with glass liquid formed by melting glass batch material 1, and the glass liquid tank corresponding to the area of ​​the edge pressure roller 2 is filled with glass liquid formed by melting glass batch material 2. Electric heating wires are provided outside the glass liquid tank to maintain the temperature of the glass liquid in the tank at 1565-1595℃, which is consistent with the melting temperature, to ensure that the glass liquid remains in liquid state. The discharge port of the glass liquid tank is a long strip opening. The valve controls the quantitative drop of the glass liquid onto the center pressure roller 1 and the edge pressure roller 2 of the forming disk. It is located in front of the center pressure roller 1 and the edge pressure roller 2. The center pressure roller 1 and the edge pressure roller 2 rotate to spread the two types of glass liquid.

[0056] A rotating shaft 3 is provided through the center roller 1 and the edge rollers 2. A vertical rod 1 4 is connected to each end of the rotating shaft 3. The two vertical rods 1 4 are connected by a crossbar 5. A vertical rod 2 6 is connected to the center of the crossbar 5. The vertical rod 2 6 is connected to the output shaft of a motor 7. The center roller 1 and the edge rollers 2 are driven by a motor 7 to rotate. The center roller 1 and the edge rollers 2 are used to roll-form the molten glass. During the roll-forming process, low-expansion crystallites in the molten glass at the junction of the center roller 1 and the edge rollers 2 migrate toward the edge regions, forming a central region, a transition region, and an edge region on the formed glass substrate. The thermal expansion coefficients of the glass substrates in these three regions decrease in sequence.

[0057] Example 1

[0058] The method for preparing the high-transmittance alkali-free gradient thermal expansion coefficient glass substrate of this embodiment is characterized by comprising the following steps:

[0059] S1 prepares glass batch 1 and glass batch 2

[0060] Glass batch 1: SiO2: 60%, Al2O3: 16%, B2O3: 11%, MgO: 7%, CaO: 3%, SrO: 1.5%, BaO: 1%, ZrO2: 0.5% and low expansion microcrystals: 15%;

[0061] Glass batch 2: SiO2: 60%, Al2O3: 16%, B2O3: 11%, MgO: 7%, CaO: 3%, SrO: 1.5%, BaO: 1%, ZrO2: 0.5% and low expansion crystallites: 19%.

[0062] The method for preparing low-expansion glass-ceramics comprises the following steps:

[0063] 1) Sol synthesis

[0064] a) Preparation of metal ion solution

[0065] 10 g of MgO and 15 g of Al2O3 were added to 100 mL of 5 wt.% dilute nitric acid and stirred at 800 rpm on a magnetic stirrer while heating to 60°C. Stirring was continued until the metal ions were completely dissolved to form a clear and transparent metal ion solution. After cooling to room temperature, the solution was filtered through a 0.45 μm microporous membrane to remove any insoluble impurities.

[0066] b) Preparation of silicon source solution

[0067] 100 g of TEOS was dissolved in 200 mL of anhydrous ethanol, 0.5 g of PEG-400 was added as a dispersant, and ultrasonic dispersion was performed in an ultrasonic cleaner for 15 min to form a uniform silicon source solution;

[0068] c) Mixing and pH adjustment

[0069] The silicon source solution was added dropwise to the metal ion solution through a constant pressure dropping funnel with stirring at 600 rpm. The dropping rate was controlled at 1 drop / s. The pH value was monitored in real time during the addition. 25 wt.% ammonia water was added dropwise to adjust the pH value of the system to 6.5 ± 0.1. After the addition was completed, stirring was continued for 1 h to form a uniform and transparent sol.

[0070] 2) Aging treatment

[0071] The prepared sol was aged at room temperature for 12 h to promote the uniform formation of the gel network and reduce the uneven particle size caused by sudden nucleation in the subsequent hydrothermal process;

[0072] 3) Hydrothermal crystallization

[0073] a) transferring the aged sol to a 500 mL polytetrafluoroethylene-lined hydrothermal reactor with a filling degree controlled at 60-80%. The hydrothermal reactor was placed in a high-temperature furnace and heated to 190° C. at a heating rate of 4° C. / min. The temperature was maintained for 16 hours for crystallization.

[0074] b) After the crystallization is completed, the high-temperature furnace is turned off and the hydrothermal reactor is allowed to cool naturally to room temperature, with the cooling rate controlled at ≤3°C / min;

[0075] 4) Cooling separation and multi-stage washing

[0076] a) Open the hydrothermal reactor, remove the product, transfer it to a centrifuge tube, centrifuge at 3500 rpm for 15 min, and discard the supernatant;

[0077] b) adding deionized water to the centrifuge tube, ultrasonically dispersing for 5 minutes, and then centrifuging again at 3500 rpm for 15 minutes, and discarding the supernatant;

[0078] c) repeating step b) three times, washing the product a total of four times;

[0079] d) After washing, take the supernatant and add 0.1 mol / L silver nitrate solution. If no white precipitate is formed, it indicates that NO3 - The ions have been washed away and microcrystals are obtained;

[0080] 5) Surface coating

[0081] a) 5 g of washed microcrystals were redispersed in 100 mL of ethanol solution containing 5 wt.% TEOS and ultrasonically dispersed for 30 min;

[0082] b) Under stirring conditions, 25.wt% ammonia water was added dropwise to adjust the pH value of the system to 8, and then stirred at 60°C for 2 hours to hydrolyze TEOS on the surface of the microcrystals to form a SiO2 coating layer;

[0083] c) After coating, the mixture was cooled to room temperature and centrifuged at 4000 rpm for 20 min to collect the product;

[0084] 6) Ultrasonic dispersion and freeze drying

[0085] a) dispersing the coated microcrystals in 50 mL of anhydrous ethanol and ultrasonically treating the microcrystals at a power of 600 W and a frequency of 40 kHz for 45 minutes to fully destroy particle agglomerates to obtain a dispersion;

[0086] b) Transfer the dispersion to a sample tray of a freeze dryer and prefreeze to -60°C for 2 hours;

[0087] c) Turn on the vacuum pump, reduce the vacuum degree to below 5 Pa, and freeze-dry at -60°C for 36 hours;

[0088] 7) High temperature crystallization heat treatment

[0089] In order to further improve the crystallinity of the microcrystals, the freeze-dried low-expansion microcrystals were placed in a high-temperature furnace, heated to 800°C at a heating rate of 5°C / min under a nitrogen protective atmosphere, kept warm for 2 hours, and then cooled to room temperature with the furnace to obtain low-expansion microcrystals.

[0090] S2 Melting

[0091] Glass batch material 1 and glass batch material 2 were respectively put into a melting furnace and melted at 1565° C. for 2 hours to form a uniform glass liquid.

[0092] S3 Roll Forming

[0093] The two glass liquids were introduced into a roller-pressing device respectively, wherein the center roller temperature was 600° C., the edge roller temperature was 520° C., and the roller speed was 1 m / min, to form a glass substrate with a thickness of 0.5 mm.

[0094] S4 annealing

[0095] The roll-formed glass substrate was sent to an annealing furnace and kept at 520°C for 2 hours to eliminate internal stress; then cooled to room temperature at a cooling rate of 5°C / min to obtain a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate.

[0096] The glass substrate prepared in this embodiment was subjected to performance testing, and the test results are as follows:

[0097] Thermal expansion coefficient of the central area: 3×10 -6 / ℃;

[0098] Thermal expansion coefficient of edge area: 2.8×10 -6 / ℃;

[0099] Transmittance: 90.8%;

[0100] Flexural strength: 215MPa;

[0101] Deformation rate after annealing at 650℃: 0.045%;

[0102] Interface stress between metal electrode (Mo) and glass substrate: 85MPa;

[0103] After 1000 thermal cycles (25-300℃), are there any micro cracks on the metal electrode? No.

[0104] Example 2

[0105] The method for preparing the high-transmittance alkali-free gradient thermal expansion coefficient glass substrate of this embodiment is characterized by comprising the following steps:

[0106] S1 prepares glass batch 1 and glass batch 2

[0107] Glass batch 1: SiO2: 55%, Al2O3: 18%, B2O3: 11%, MgO: 9%, CaO: 1.5%, SrO: 3%, BaO: 0.5%, ZrO2: 2% and low expansion microcrystals: 16%;

[0108] Glass batch 2: SiO2: 55%, Al2O3: 18%, B2O3: 11%, MgO: 9%, CaO: 1.5%, SrO: 3%, BaO: 0.5%, ZrO2: 2% and low expansion crystallites: 20%.

[0109] The method for preparing low-expansion glass-ceramics comprises the following steps:

[0110] 1) Sol synthesis

[0111] a) Preparation of metal ion solution

[0112] 12.5 g of MgO and 25 g of Al2O3 were added to 156.25 mL of 5 wt.% dilute nitric acid and stirred at 800 rpm on a magnetic stirrer while heating to 70°C. Stirring was continued until the metal ions were completely dissolved to form a clear and transparent metal ion solution. After cooling to room temperature, the solution was filtered through a 0.45 μm microporous membrane to remove any insoluble impurities.

[0113] b) Preparation of silicon source solution

[0114] 100 g of TEOS was dissolved in 250 mL of anhydrous ethanol, 0.75 g of PEG-400 was added as a dispersant, and ultrasonic dispersion was performed in an ultrasonic cleaner for 15 min to form a uniform silicon source solution;

[0115] c) Mixing and pH adjustment

[0116] The silicon source solution was added dropwise to the metal ion solution through a constant pressure dropping funnel with stirring at 600 rpm. The dropping rate was controlled at 2 drops / s. The pH value was monitored in real time during the addition. 25 wt.% ammonia water was added dropwise to adjust the pH value of the system to 6.5 ± 0.1. After the addition was completed, stirring was continued for 1 hour to form a uniform and transparent sol.

[0117] 2) Aging treatment

[0118] The prepared sol was aged at room temperature for 16 h to promote the uniform formation of the gel network and reduce the uneven particle size caused by sudden nucleation in the subsequent hydrothermal process;

[0119] 3) Hydrothermal crystallization

[0120] a) transferring the aged sol to a 500 mL polytetrafluoroethylene-lined hydrothermal reactor with a filling degree controlled at 60-80%. The hydrothermal reactor was placed in a high-temperature furnace and heated to 200° C. at a heating rate of 5° C. / min. The temperature was maintained for 18 hours for crystallization.

[0121] b) After the crystallization is completed, the high-temperature furnace is turned off and the hydrothermal reactor is allowed to cool naturally to room temperature, with the cooling rate controlled at ≤3°C / min;

[0122] 4) Cooling separation and multi-stage washing

[0123] a) Open the hydrothermal reactor, remove the product, transfer it to a centrifuge tube, centrifuge at 3500 rpm for 15 min, and discard the supernatant;

[0124] b) adding deionized water to the centrifuge tube, ultrasonically dispersing for 5 minutes, and then centrifuging again at 3500 rpm for 15 minutes, and discarding the supernatant;

[0125] c) repeating step b) three times, washing the product a total of four times;

[0126] d) After washing, take the supernatant and add 0.1 mol / L silver nitrate solution. If no white precipitate is formed, it indicates that NO3 - The ions have been washed away and microcrystals are obtained;

[0127] 5) Surface coating

[0128] a) 6 g of washed microcrystals were redispersed in 100 mL of ethanol solution containing 5 wt.% TEOS and ultrasonically dispersed for 30 min;

[0129] b) Under stirring conditions, 25.wt% ammonia water was added dropwise to adjust the pH value of the system to 9, and then stirred at 60°C for 2 hours to hydrolyze TEOS on the surface of the microcrystals to form a SiO2 coating layer;

[0130] c) After coating, the mixture was cooled to room temperature and centrifuged at 4000 rpm for 20 min to collect the product;

[0131] 6) Ultrasonic dispersion and freeze drying

[0132] a) dispersing the coated microcrystals in 50 mL of anhydrous ethanol and ultrasonically treating the microcrystals at a power of 600 W and a frequency of 40 kHz for 45 minutes to fully destroy particle agglomerates to obtain a dispersion;

[0133] b) Transfer the dispersion to a sample tray of a freeze dryer and pre-freeze to -65°C for 2 hours;

[0134] c) Turn on the vacuum pump, reduce the vacuum degree to below 5 Pa, and freeze-dry at -65°C for 38 hours;

[0135] 7) High temperature crystallization heat treatment

[0136] In order to further improve the crystallinity of the microcrystals, the freeze-dried low-expansion microcrystals were placed in a high-temperature furnace, heated to 850°C at a heating rate of 5°C / min under a nitrogen protective atmosphere, kept warm for 2.5 hours, and then cooled to room temperature with the furnace to obtain low-expansion microcrystals.

[0137] S2 Melting

[0138] Glass batch material 1 and glass batch material 2 were respectively put into a melting furnace and melted at 1580° C. for 2.5 hours to form a uniform glass liquid.

[0139] S3 Roll Forming

[0140] The two glass liquids were introduced into a roller-pressing device respectively, wherein the center roller temperature was 610° C., the edge roller temperature was 530° C., and the roller speed was 1 m / min, to form a glass substrate with a thickness of 0.5 mm.

[0141] S4 annealing

[0142] The roll-formed glass substrate was sent to an annealing furnace and kept at 530°C for 2.5 hours to eliminate internal stress; then cooled to room temperature at a cooling rate of 6.5°C / min to obtain a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate.

[0143] The glass substrate prepared in this embodiment was subjected to performance testing, and the test results are as follows:

[0144] Thermal expansion coefficient of the central area: 3×10 -6 / ℃;

[0145] Thermal expansion coefficient of edge area: 2.7×10 -6 / ℃;

[0146] Transmittance: 91.2%;

[0147] Flexural strength: 205MPa;

[0148] Deformation rate after annealing at 650℃: 0.048%;

[0149] Interface stress between metal electrode (Mo) and glass substrate: 90MPa;

[0150] After 1000 thermal cycles (25-300℃), are there any micro cracks on the metal electrode? No.

[0151] Example 3

[0152] The method for preparing the high-transmittance alkali-free gradient thermal expansion coefficient glass substrate of this embodiment is characterized by comprising the following steps:

[0153] S1 prepares glass batch 1 and glass batch 2

[0154] Glass batch 1: SiO2: 65%, Al2O3: 13%, B2O3: 9%, MgO: 6%, CaO: 5%, SrO: 0.5%, BaO: 1%, ZrO2: 0.5% and low expansion microcrystals: 18%;

[0155] Glass batch 2: SiO2: 65%, Al2O3: 13%, B2O3: 9%, MgO: 6%, CaO: 5%, SrO: 0.5%, BaO: 1%, ZrO2: 0.5% and low expansion crystallites: 22%.

[0156] The method for preparing low-expansion glass-ceramics comprises the following steps:

[0157] 1) Sol synthesis

[0158] a) Preparation of metal ion solution

[0159] 15 g of MgO and 37.5 g of Al2O3 were added to 225 mL of 5 wt.% dilute nitric acid and stirred at 800 rpm on a magnetic stirrer while heating to 80°C. Stirring was continued until the metal ions were completely dissolved to form a clear and transparent metal ion solution. After cooling to room temperature, the solution was filtered through a 0.45 μm microporous membrane to remove any insoluble impurities.

[0160] b) Preparation of silicon source solution

[0161] 100 g of TEOS was dissolved in 300 mL of anhydrous ethanol, 1 g of PEG-400 was added as a dispersant, and ultrasonic dispersion was performed in an ultrasonic cleaner for 15 min to form a uniform silicon source solution;

[0162] c) Mixing and pH adjustment

[0163] The silicon source solution was added dropwise to the metal ion solution through a constant pressure dropping funnel with stirring at 600 rpm. The dropping rate was controlled at 3 drops / s. The pH value was monitored in real time during the addition. 25 wt.% ammonia water was added dropwise to adjust the pH value of the system to 6.5 ± 0.1. After the addition was completed, stirring was continued for 1 h to form a uniform and transparent sol.

[0164] 2) Aging treatment

[0165] The prepared sol was aged at room temperature for 12 h to promote the uniform formation of the gel network and reduce the uneven particle size caused by sudden nucleation in the subsequent hydrothermal process;

[0166] 3) Hydrothermal crystallization

[0167] a) transferring the aged sol to a 500 mL polytetrafluoroethylene-lined hydrothermal reactor with a filling degree controlled at 60-80%. The hydrothermal reactor was placed in a high-temperature furnace and heated to 210° C. at a heating rate of 6° C. / min. The temperature was maintained for 20 h for crystallization.

[0168] b) After the crystallization is completed, the high-temperature furnace is turned off and the hydrothermal reactor is allowed to cool naturally to room temperature, with the cooling rate controlled at ≤3°C / min;

[0169] 4) Cooling separation and multi-stage washing

[0170] a) Open the hydrothermal reactor, remove the product, transfer it to a centrifuge tube, centrifuge at 3500 rpm for 15 min, and discard the supernatant;

[0171] b) adding deionized water to the centrifuge tube, ultrasonically dispersing for 5 minutes, and then centrifuging again at 3500 rpm for 15 minutes, and discarding the supernatant;

[0172] c) repeating step b) three times, washing the product a total of four times;

[0173] d) After washing, take the supernatant and add 0.1 mol / L silver nitrate solution. If no white precipitate is formed, it indicates that NO3 - The ions have been washed away and microcrystals are obtained;

[0174] 5) Surface coating

[0175] a) 4 g of washed microcrystals were redispersed in 100 mL of ethanol solution containing 5 wt.% TEOS and ultrasonically dispersed for 30 min;

[0176] b) Under stirring conditions, 25 wt.% ammonia water was added dropwise to adjust the pH value of the system to 10, and then stirred at 60° C. for 2 h to hydrolyze TEOS on the surface of the microcrystals to form a SiO2 coating layer;

[0177] c) After coating, the mixture was cooled to room temperature and centrifuged at 4000 rpm for 20 min to collect the product;

[0178] 6) Ultrasonic dispersion and freeze drying

[0179] a) dispersing the coated microcrystals in 50 mL of anhydrous ethanol and ultrasonically treating the microcrystals at a power of 600 W and a frequency of 40 kHz for 45 minutes to fully destroy particle agglomerates to obtain a dispersion;

[0180] b) Transfer the dispersion to a sample tray of a freeze dryer and prefreeze to -70°C for 2 hours;

[0181] c) Turn on the vacuum pump, reduce the vacuum degree to below 5 Pa, and freeze-dry at -70°C for 40 hours;

[0182] 7) High temperature crystallization heat treatment

[0183] In order to further improve the crystallinity of the microcrystals, the freeze-dried low-expansion microcrystals were placed in a high-temperature furnace, heated to 900°C at a heating rate of 5°C / min under a nitrogen protective atmosphere, kept warm for 3 hours, and then cooled to room temperature with the furnace to obtain low-expansion microcrystals.

[0184] S2 Melting

[0185] Glass batch material 1 and glass batch material 2 were respectively put into a melting furnace and melted at 1595° C. for 3 hours to form a uniform glass liquid.

[0186] S3 Roll Forming

[0187] The two glass liquids were introduced into a roller-forming device respectively, wherein the center roller temperature was 620° C., the edge roller temperature was 540° C., and the roller speed was 1 m / min, to form a glass substrate with a thickness of 0.5 mm.

[0188] S4 annealing

[0189] The roll-formed glass substrate was sent to an annealing furnace and kept at 550°C for 3 hours to eliminate internal stress; then cooled to room temperature at a cooling rate of 8°C / min to obtain a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate.

[0190] The glass substrate prepared in this embodiment was subjected to performance testing, and the test results are as follows:

[0191] Thermal expansion coefficient of the central area: 3×10 -6 / ℃;

[0192] Thermal expansion coefficient of edge area: 2.75×10 -6 / ℃;

[0193] Transmittance: 90.5%;

[0194] Flexural strength: 220MPa;

[0195] Deformation rate after annealing at 650℃: 0.042%;

[0196] Interface stress between metal electrode (Mo) and glass substrate: 80MPa;

[0197] After 1000 thermal cycles (25-300℃), are there any micro cracks on the metal electrode? No.

[0198] Comparative Example 1

[0199] Preparation method:

[0200] The difference from Example 1 is that in step S1, the low-expansion crystallite content in glass batch 1 and glass batch 2 is both 15%; in step S3, the temperature of the central pressing roller and the edge pressing roller is the same, both 570°C.

[0201] The performance test of the glass substrate prepared in Comparative Example 1 was carried out, and the test results are as follows:

[0202] Thermal expansion coefficient of the entire glass substrate: 3×10 -6 / ℃;

[0203] Transmittance: 88%;

[0204] Flexural strength: 190MPa;

[0205] Deformation rate after annealing at 650℃: 0.18%;

[0206] Interface stress between metal electrode (Mo) and glass substrate: 153MPa;

[0207] After 1000 thermal cycles (25-300℃), are there any micro cracks on the metal electrode? There are obvious cracks.

[0208] By comparing Example 1 with Comparative Example 1, it can be seen that since Comparative Example 1 does not form a thermal expansion coefficient gradient on the glass substrate, it cannot match the temperature gradient in the high-temperature process, resulting in thermal stress concentration; the microcrystals are evenly distributed, no stress buffer layer is formed, the interface stress is large, and the film is prone to cracking; single temperature rolling causes microcrystals to agglomerate, affecting optical properties and mechanical strength.

[0209] Comparative Example 2

[0210] The difference from Example 1 is that in step S1, low expansion microcrystals are not added to glass batch material 1 and glass batch material 2; in step S3, after the glass is formed, an Al2O3 low expansion coating (thickness 5 μm, thermal expansion coefficient 2.8×10 -6 / ℃).

[0211] The performance test of the glass substrate prepared in Comparative Example 2 was carried out, and the test results are as follows:

[0212] Thermal expansion coefficient of the entire glass substrate: 3×10 -6 / ℃;

[0213] Transmittance: 85%;

[0214] Flexural strength: 180MPa;

[0215] Deformation rate after annealing at 650℃: 0.15%;

[0216] Interface stress between metal electrode (Mo) and glass substrate: 120MPa;

[0217] After 1000 thermal cycles (25-300℃), are there any micro cracks on the metal electrode? There are obvious cracks.

[0218] Comparing Example 1 with Comparative Example 2, it can be seen that the thermal expansion coefficient of the coating used in Comparative Example 2 is still different from that of the glass (glass CTE = 3.2×10 -6 / ℃, coating CTE=2.8×10 -6 / ℃), the interface stress is significant; the coating process introduces pores and microcracks, the bonding force is insufficient, and the optical properties are affected by the scattering of the coating; there is no low-expansion microcrystal reinforcement effect, and the mechanical strength is lower than that of Example 1.

[0219] Comparative Example 3

[0220] The difference from Example 1 is that in step S1, low-expansion crystallites are not added to the glass batch material 1 and the glass batch material 2.

[0221] The performance test of the glass substrate prepared in Comparative Example 3 was carried out, and the test results are as follows:

[0222] Thermal expansion coefficient of the entire glass substrate: 3.2×10 -6 / ℃;

[0223] Transmittance: 90%;

[0224] Flexural strength: 170MPa;

[0225] Deformation rate after annealing at 650℃: 0.22%;

[0226] Interface stress between metal electrode (Mo) and glass substrate: 150MPa;

[0227] After 1000 thermal cycles (25-300℃), are there micro cracks on the metal electrode? Large-scale cracking.

[0228] Comparing Example 1 with Comparative Example 3, it can be seen that since low expansion microcrystals are not added in Comparative Example 3, the effect of forming a CTE gradient on the glass substrate cannot be achieved, and the overall CTE of the glass substrate is significantly different from that of the metal electrode (3.2×10 -6 / ℃vs 5×10 -6 / ℃), thermal stress concentration is serious; lack of low expansion microcrystal reinforcement, the substrate has insufficient bending strength and cannot withstand high temperature process stress.

[0229] Comparative Example 4

[0230] The difference from Example 1 is that in step S1 , the content of low-expansion crystallites in the first glass batch is 23%, and the content of low-expansion crystallites in the second glass batch is 25%.

[0231] The performance test of the glass substrate prepared in Comparative Example 4 was carried out, and the test results are as follows:

[0232] Thermal expansion coefficient of the central area: 2.9×10 -6 / ℃;

[0233] Thermal expansion coefficient of edge area: 2.5×10 -6 / ℃;

[0234] Transmittance: 82%;

[0235] Flexural strength: 185MPa;

[0236] Deformation rate after annealing at 650℃: 0.085%;

[0237] Interface stress between metal electrode (Mo) and glass substrate: 220MPa;

[0238] After 1000 thermal cycles (25-300℃), are there any micro cracks on the metal electrode? Micro cracks appear (stress concentration at the microcrystal agglomeration point).

[0239] By comparing Example 1 with Comparative Example 4, it can be seen that due to excessive addition of low-expansion microcrystals in the glass batch of Comparative Example 4, the viscosity of the glass liquid increases sharply, migration is hindered and agglomeration is serious during rolling, which not only reduces the optical transmittance, but also weakens the strength of the glass matrix, and the thermal stress release efficiency is significantly reduced.

[0240] In summary, the present invention solves the contradictions in thermal stress, optical performance and mechanical strength of traditional methods through gradient distribution of low-expansion microcrystals and temperature-driven rolling process, significantly improves the manufacturing yield and reliability of display devices, and the process is suitable for industrial production.

Claims

1. A method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate, characterized in that: The following steps are involved: S1 prepares glass batch 1 and glass batch 2, both of which contain low-expansion crystallites, and the content of low-expansion crystallites in glass batch 1 is lower than the content of low-expansion crystallites in glass batch 2; S2: putting glass batch material 1 and glass batch material 2 into a melting furnace to melt them into glass liquid; S3 introduces two kinds of glass liquid into the roller forming equipment respectively. The roller forming equipment includes a shell, a forming disk is arranged inside the shell, a central pressing roller (1) is arranged at the center of the forming disk, and an edge pressing roller (2) is arranged at both ends of the central pressing roller (1). Electric heating wires are arranged in the central pressing roller (1) and the edge pressing roller (2) to electrically heat the central pressing roller (1) and the edge pressing roller (2), and the temperature of the central pressing roller (1) is higher than that of the edge pressing roller (2); a glass liquid tank is respectively arranged in the area corresponding to the central pressing roller (1) and the edge pressing roller (2) above the forming disk, and a valve is arranged at the feed port of the glass liquid tank; the glass liquid tank corresponding to the area of ​​the central pressing roller (1) is equipped with a valve. A glass liquid is formed by melting a first glass batch material, and a glass liquid tank corresponding to an edge pressing roller (2) region is filled with a glass liquid formed by melting a second glass batch material. A rotating shaft (3) is provided in the center pressing roller (1) and the edge pressing roller (2). The center pressing roller (1) and the edge pressing roller (2) are driven to rotate by a motor (7). The glass liquid is roll-formed by the center pressing roller (1) and the edge pressing roller (2). During the roll-forming process, low-expansion microcrystals in the glass liquid at the junction of the center pressing roller (1) and the edge pressing roller (2) move toward the edge region, forming a center region, a transition region, and an edge region on the formed glass substrate, and the thermal expansion coefficients of the glass substrates in the three regions decrease in sequence. S4 annealing is performed to obtain a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate.

2. The method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate according to claim 1, wherein: In step S1, glass batch material 1 and glass batch material 2 include components in the following mass percentages, wherein the total mass of the remaining components in glass batch material 1 and glass batch material 2 except low-expansion microcrystals is calculated as 100%, and the low-expansion microcrystals are calculated as a percentage of the total mass of the remaining components: SiO2: 55-65%, Al2O3: 13-18%, B2O3: 8-12%, MgO: 6-9%, CaO: 1-5%, SrO: 0.5-3%, BaO: 0.1-1.5%, ZrO2: 0.1-2% and low-expansion microcrystals, the mass percentage of low-expansion microcrystals in glass batch material 1 is 15-18%, and the mass percentage of low-expansion microcrystals in glass batch material 2 is 19-22%.

3. The method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate according to claim 1 or 2, wherein: The method for preparing low expansion microcrystals comprises the following steps: 1) Sol synthesis a) Preparation of metal ion solution Add MgO and Al2O3 to dilute nitric acid and stir while heating to 60-80°C. Continue stirring until completely dissolved to form a metal ion solution. After cooling to room temperature, filter to remove insoluble impurities. b) Preparation of silicon source solution TEOS was dissolved in anhydrous ethanol, PEG-400 was added as a dispersant, and ultrasonic dispersion was performed to form a uniform silicon source solution; c) Mixing and pH adjustment Under stirring conditions, the silicon source solution was added dropwise to the metal ion solution. The pH value was monitored in real time during the addition process and the pH value of the system was adjusted to 6.5±0.

1. After the addition was completed, stirring was continued to form a uniform and transparent sol. 2) Aging treatment The prepared sol is allowed to stand and age at room temperature; 3) Hydrothermal crystallization a) transferring the aged sol to a hydrothermal reactor, placing the hydrothermal reactor in a high-temperature furnace, heating to 190-210° C. at a heating rate of 4-6° C. / min, and maintaining the temperature for 16-20 hours for crystallization; b) After the crystallization is completed, the high-temperature furnace is turned off and the hydrothermal reactor is allowed to cool naturally to room temperature; 4) Cooling separation and multi-stage washing a) opening the hydrothermal reactor, taking out the product, transferring it to a centrifuge tube and centrifuging it, and discarding the supernatant; b) adding deionized water to the centrifuge tube, performing ultrasonic dispersion, centrifuging again, and discarding the supernatant; c) repeating the above step b) several times to wash the product; d) After washing, take the supernatant and add silver nitrate solution. If no white precipitate is formed, it indicates that NO3 - The ions have been washed away and microcrystals are obtained; 5) Surface coating a) redispersing the washed microcrystals in an ethanol solution containing TEOS and performing ultrasonic dispersion; b) Under stirring conditions, adjusting the pH value of the system to 8-10, and then stirring to hydrolyze TEOS on the surface of the microcrystal to form a SiO2 coating layer; c) After the coating is completed, the product is cooled to room temperature and collected by centrifugation; 6) Ultrasonic dispersion and freeze drying a) dispersing the coated microcrystals in anhydrous ethanol, and destroying particle agglomerates by ultrasonication to obtain a dispersion; b) Transfer the dispersion to a sample tray of a freeze dryer and prefreeze to -70 to -60°C for 2-3 hours; c) Turn on the vacuum pump, reduce the vacuum degree to below 5 Pa, and freeze-dry at -70 to -60°C for 36 to 40 hours to obtain low-expansion microcrystals.

4. The method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate according to claim 3, wherein: In step 1) a), the mass ratio of MgO and Al2O3 is 1:(1.5-2.5), the concentration of dilute nitric acid is 5wt.%, and the mass volume ratio of MgO and dilute nitric acid is 1g:(10-15)mL; in step 1) b), the mass volume ratio of TEOS, PEG-400, and anhydrous ethanol is 1g:(0.005-0.01)g:(2-3)mL; in step 1) c), the mass ratio of silicon source solution to metal ion solution is 1:(0.4-1), and the dropping speed is 1-3 drops / s; in step 4) d), the concentration of silver nitrate solution is 0.1mol / L; in step 5) a), in the ethanol solution containing TEOS, the concentration of TEOS is 5wt.%, and the mass ratio of microcrystals to TEOS is 1:(0.5-1).

5. The method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate according to claim 3, wherein: The process also includes step 7) high-temperature crystallization heat treatment: placing the freeze-dried low-expansion microcrystals in a high-temperature furnace, heating them to 800-900°C at a heating rate of 5-8°C / min under a nitrogen protective atmosphere, keeping the temperature for 2-3 hours, and then cooling them to room temperature with the furnace.

6. The method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate according to claim 1, wherein: In step S2, the melting temperature is 1565-1595° C., and the melting time is 2-3 hours.

7. The method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate according to claim 1, wherein: In step S3, an electric heating wire is provided outside the glass liquid tank to maintain the temperature of the glass liquid in the tank at 1565-1595°C.

8. The method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate according to claim 1, wherein: In step S3, the two ends of the rotating shaft (3) are respectively connected to the vertical rod 1 (4), the two vertical rods 1 (4) are connected by a cross bar (5), the center of the cross bar (5) is connected to the vertical rod 2 (6), and the vertical rod 2 (6) is connected to the output shaft of the motor (7).

9. The method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate according to claim 1, wherein: In step S3, the temperature of the center pressing roller (1) is 600-620°C, and the temperature of the edge pressing roller (2) is 520-540°C; in step S4, the glass substrate after roller pressing is sent to an annealing furnace, kept at 520-550°C for 2-3 hours, and then cooled to room temperature at a cooling rate of 5-8°C / min to obtain a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate.

10. High transmittance alkali-free gradient thermal expansion coefficient glass substrate, characterized in that: The glass substrate is prepared by the method for preparing a high-transmittance alkali-free gradient thermal expansion coefficient glass substrate according to any one of claims 1 to 9.

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