TFT alkali-free glass substrate hydroxyl removing method based on gamma-Al2O3 phase change TiO2 synergistic induction

Abstract

The invention discloses a TFT alkali-free glass substrate hydroxyl removing method based on gamma-Al2O3 phase change TiO2 synergistic induction, which comprises the following steps: S1, preparing gamma-Al2O3 powder and TiO2 powder into a suspension, and coating the surface of an alkali-free glass substrate with the suspension; s2, putting the alkali-free glass substrate into a high-temperature furnace, continuously introducing a mixed gas of H2 and N2 into the furnace, heating to 400-500 DEG C at a heating rate of 5-15 DEG C / min, and keeping the temperature for 20-40 minutes; raising the temperature to 700 to 900 DEG C at the temperature raising rate of 10 to 20 DEG C / min; then carrying out periodic temperature fluctuation; and S3, finally, cooling the alkali-free glass substrate to room temperature, and cleaning to complete hydroxyl removal of the alkali-free glass substrate. According to the invention, the phase change characteristic of the gamma-Al2O3 and TiO2 composite coating in the heating process is utilized to induce the hydroxyl in the glass to generate chemical reaction, so that the hydroxyl is efficiently removed.

Description

Technical Field

[0001] The present invention relates to the technical field of glass, and particularly to a method for removing hydroxyl groups from a TFT alkali-free glass substrate synergistically induced by γ-Al2O3 phase change and TiO2. Background Art

[0002] The TFT alkali-free glass substrate, as a core component in high-end electronic display devices such as liquid crystal displays and organic light-emitting diodes (OLEDs), the quality of its performance directly affects the imaging quality, clarity, and long-term use reliability of the display device. β-OH (hydroxyl group), as a key impurity in the alkali-free glass substrate, the level of its content has a crucial impact on the performance of the glass substrate. When the content of β-OH is too high, it will cause the strain point of the glass substrate to decrease, thereby affecting its thermal stability and mechanical properties, and making problems such as image distortion and shortened lifespan likely to occur during the use of the display device.

[0003] Regarding the control of the β-OH content in the alkali-free glass substrate, although the existing technology has taken a series of measures, such as strictly controlling the moisture of raw materials, improving the utilization rate of cullet, adjusting the oxygen-fuel ratio, etc., in order to reduce the hydroxyl content in the glass. However, in the actual production process, these methods generally have the following deficiencies: the operation process is complex, and the requirements for production equipment and technology are relatively high; the production cost increases, affecting the economic benefits of enterprises; the removal effect is limited, and it is difficult to meet the requirements of high-performance display devices.

[0004] Facing this technical problem, the current industry urgently needs to develop a more efficient and economical method for removing hydroxyl groups to improve the hydroxyl removal effect and effectively improve the thermal stability and mechanical properties of the alkali-free glass substrate. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to overcome the deficiencies of the existing technology and provide a method for removing hydroxyl groups from a TFT alkali-free glass substrate synergistically induced by γ-Al2O3 phase change and TiO2, using the phase change characteristics of the composite coating of γ-Al2O3 and TiO2 during heating to induce chemical reactions of the hydroxyl groups in the glass, thereby efficiently removing the hydroxyl groups.

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

[0007] A method for removing hydroxyl groups from a TFT alkali-free glass substrate synergistically induced by γ-Al2O3 phase change and TiO2 includes the following steps:

[0008] S1 Prepare a suspension by mixing γ-Al2O3 powder and TiO2 powder, and coat the suspension on the surface of the alkali-free glass substrate;

[0009] S2 Place the alkali-free glass substrate in a high-temperature furnace, continuously introduce a mixed gas of H2 and N2 into the furnace, heat it at a heating rate of 5 - 15 °C / min to 400 - 500 °C, and keep it warm for 20 - 40 min. At this stage, partial oxidation occurs on the surface of γ-Al2O3 to form an interface layer with high activity. This interface layer can promote the subsequent reaction between γ-Al2O3 and the hydroxyl groups in the alkali-free glass substrate, and also helps the photocatalytic activity of TiO2 in the composite coating to better play its role in the subsequent stage; then heat it at a heating rate of 10 - 20 °C / min to 700 - 900 °C. The specific temperature can be adjusted according to the coating thickness. When the coating is thicker, a higher temperature is selected to ensure that heat can be fully transferred to the inside of the coating to enable γ-Al2O3 to fully undergo phase transformation; when the coating is thinner, a lower temperature is selected to avoid adverse effects on the performance of the alkali-free glass substrate caused by overheating; rapid heating can shorten the time to reach the phase transformation temperature and reduce the occurrence of other side reactions; subsequently, perform periodic temperature fluctuations, that is, on the basis of 700 - 900 °C, perform temperature fluctuations within ±20 °C every 5 min, and the entire periodic temperature fluctuation lasts for 30 - 60 min. This temperature fluctuation can break the balance of the reaction system, promote the phase transformation kinetics of γ-Al2O3, make the phase transformation process more complete, increase the generation quantity of oxygen vacancies, and further improve the hydroxyl scavenging efficiency;

[0010] S3 Finally, cool the alkali-free glass substrate to room temperature and then clean it, that is, complete the scavenging of hydroxyl groups on the alkali-free glass substrate.

[0011] Among them, in step S2, a reducing atmosphere (H2 and N2) is used during the heat treatment process, which can promote the generation of oxygen vacancies in TiO2, prevent the over-oxidation of γ-Al2O3, and maintain the stability of active sites. TiO2 generates oxygen vacancies (V0 2 + ) in the reducing atmosphere, and synergistically acts with the active sites generated by the phase transformation of γ-Al2O3 to accelerate the desorption of hydroxyl groups (β-OH):

[0012] β-OH + V0 2+ (Al or Ti) → H2O↑ + lattice oxygen.

[0013] In step S2, a temperature cycle is formed through periodic temperature fluctuations to induce dynamic reconstruction of the γ-Al2O3 / TiO2 interface and continuously expose fresh active sites.

[0014] Preferably, in step S1, [BMIM][BF4] ionic liquid is used as a dispersant to prepare a suspension of γ-Al2O3 powder and TiO2 powder. The [BMIM][BF4] ionic liquid can effectively improve the stability of nanoparticles during the coating dispersion process and prevent agglomeration.

[0015] Preferably, in step S1, the average particle size of the γ-Al2O3 powder is 30-80 nm, and the average particle size of the TiO2 powder is 20-50 nm.

[0016] Preferably, in step S1, the mass ratio of the γ-Al2O3 powder to the TiO2 powder is (2-4):1.

[0017] Preferably, in step S1, the suspension is coated on the surface of the non-alkali glass substrate by the slit spraying method, the spraying distance is 10-15 cm, and the coating thickness is 3-8 μm.

[0018] Preferably, in step S2, in the mixed gas, the volume ratio of H2 to N2 is 1:(4-6); the flow rate of the mixed gas is 50-100 mL / min, the pressure is 0.5-1 MPa, which enhances the bonding force between the coating and the non-alkali glass substrate, compresses the porosity of the coating at the same time, and increases the oxygen vacancy density.

[0019] Preferably, in step S3, the cooling rate is 3-8 °C / min. After cooling to room temperature, it is first soaked and cleaned with a dilute hydrochloric acid solution for 5-10 min, then subjected to ultraviolet photocatalytic cleaning, and finally dried with supercritical CO2.

[0020] Preferably, the concentration of the dilute hydrochloric acid solution is 5-10 wt.%.

[0021] Preferably, during ultraviolet photocatalytic cleaning, the non-alkali glass substrate is irradiated with ultraviolet light with a wavelength of 254 nm for 15-30 min. Under the action of ultraviolet light, the organic substances remaining on the surface of the non-alkali glass substrate can be photocatalytically decomposed into small molecule substances such as carbon dioxide and water. The TiO2 in the composite coating generates electron-hole pairs under ultraviolet light excitation, and the holes react with the water molecules adsorbed on the surface of TiO2 to generate hydroxyl radicals. Hydroxyl radicals have strong oxidizing properties and can effectively decompose organic substances, thereby more thoroughly removing the impurities on the surface of the non-alkali glass substrate.

[0022] Preferably, during drying with supercritical CO2, the cleaned non-alkali glass substrate is placed in a supercritical CO2 drying equipment, the set temperature is 35-40 °C, the pressure is 8-10 MPa, the CO2 flow rate is 5-8 L / min, and the drying time is 30-60 min. Supercritical CO2 has the characteristics of low surface tension and high diffusion coefficient, can quickly penetrate into the tiny pores of the non-alkali glass substrate, displace the moisture therein, and then the CO2 escapes in gaseous form by reducing the pressure. Compared with traditional drying, supercritical CO2 drying can avoid the generation of microcracks on the surface of the non-alkali glass substrate due to the surface tension generated by water evaporation, and effectively protect the surface quality of the non-alkali glass substrate.

[0023] The synergistic mechanism of the method of the present invention is as follows:

[0024] (1) Oxygen Vacancy Synergistic Effect

[0025] 1) Generation of oxygen vacancies under high-temperature reducing atmosphere:

[0026] In a mixed reducing atmosphere of H2 and N2, TiO2 can be partially reduced at high temperature (such as forming Ti 3+ defects), and at the same time, oxygen vacancies (V0 2+ ) are generated. These oxygen vacancies combine with the active sites generated by the phase transformation of γ-Al2O3 to form a double active site network, significantly improving the adsorption and reaction efficiency of hydroxyl groups (β-OH).

[0027] Reaction formula: β-OH + V0 2+ (Al or Ti) → H2O↑ + lattice oxygen

[0028] 2) Synergistic scavenging path:

[0029] The oxygen vacancies of γ-Al2O3 mainly adsorb H in the hydroxyl group + , while the oxygen vacancies of TiO2 promote the detachment of O - through electron transfer. The two work together to achieve the complete path decomposition of hydroxyl groups (H-O bond breakage), avoiding the residue of intermediate products.

[0030] (2) Photocatalytic-assisted scavenging (combined with UV post-treatment)

[0031] 1) UV photocatalytic activity:

[0032] In the post-treatment step, UV photocatalytic cleaning (wavelength 254 nm) is used. TiO2 is excited as a photocatalyst to generate electron-hole pairs (e - -h + ), further decomposing residual hydroxyl groups or organic substances:

[0033] TiO2 + hν → e - + h +

[0034] h + + H2O → ·OH (hydroxyl radical)

[0035] ·OH + β-OH → H2O + O2↑

[0036] 2) Advantages:

[0037] UV photocatalytic cleaning not only removes surface pollutants, but also can secondarily scavenge the hydroxyl groups that are not completely desorbed during heat treatment through photocatalytic reactions, improving the overall cleanliness.

[0038] (3) Heterojunction-enhanced electron transfer

[0039] Formation of γ-Al2O3 / TiO2 heterojunction: A Type-II heterojunction (band bending) is formed at the interface of the two phases, which promotes the transfer of photo-generated electrons from the conduction band of γ-Al2O3 to the conduction band of TiO2, and the holes migrate in the opposite direction. This electron-hole separation effect significantly prolongs the carrier lifetime and enhances the redox ability. The functions are as follows: accelerating the oxidative decomposition of hydroxyl groups (holes directly oxidize β-OH); inhibiting electron-hole recombination and improving energy utilization efficiency.

[0040] (4) Thermal stability and surface structure optimization

[0041] 1) Inhibiting the sintering of γ-Al2O3: As a high-melting-point oxide (melting point 1843 °C), TiO2 can inhibit the agglomeration of γ-Al2O3 particles at high temperatures (700 - 900 °C), maintaining a high specific surface area of the coating (>150 m 2 / g) and ensuring the density of active sites.

[0042] 2) Increasing the surface hydroxyl adsorption sites: The anatase phase of TiO2 (after heat treatment) is rich in Lewis acid sites on the surface, forming an acid-base synergistic effect with the basic sites of γ-Al2O3 and enhancing the directional adsorption ability of hydroxyl groups.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. Through the synergistic effect of the composite coating of γ-Al2O3 and TiO2, the promoting effect of the reducing atmosphere, the optimized heating program, and the innovative post-treatment process, the present invention can more efficiently remove hydroxyl groups in the alkali-free glass substrate, significantly reduce the content of β-OH, further reduce the adverse effects of hydroxyl groups on the electrical properties of the TFT alkali-free glass substrate, and greatly improve the display quality and stability of the TFT liquid crystal display.

[0045] 2. Although the present invention adds some innovative steps, the overall process is reasonably designed, and the operation difficulty does not increase significantly, and it is easier to realize industrial production. Moreover, the present invention has little impact on other properties of the glass substrate: Under the condition of strictly controlling each process parameter, the method of the present invention will not have an obvious negative impact on other properties of the alkali-free glass substrate (such as thermal expansion coefficient, Young's modulus, etc.), fully ensuring the original excellent characteristics of the glass substrate, and at the same time improving key performance indicators such as the strain point and light transmittance. Detailed implementation manners

[0046] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention.

[0047] Example 1

[0048] Take an alkali-free glass substrate with a size of 10 cm × 10 cm, and measure the initial content of β-OH to be 53 ppm by a Fourier transform infrared spectrometer; the coefficient of thermal expansion is 3.5×10 -6 / ℃, and the Young's modulus is 70 GPa.

[0049] The method for scavenging hydroxyl groups on the alkali-free glass substrate of the TFT induced by the phase transformation of γ-Al2O3 and TiO2 in this embodiment includes the following steps:

[0050] S1 Prepare a suspension and spray it

[0051] S11 Prepare a suspension

[0052] Prepare γ-Al2O3 powder with an average particle size of 50 nm and TiO2 powder with an average particle size of 30 nm, and accurately weigh the powders according to the mass ratio of γ-Al2O3 powder to TiO2 powder of 2:1. Using the ionic liquid [BMIM][BF4] as a dispersant, mix the two powders and ultrasonically disperse them for 45 min to make a uniform suspension.

[0053] S12 Coat the coating

[0054] Use the slit spraying method to coat the suspension on the surface of the alkali-free glass substrate: Use a slit coater, place the alkali-free glass substrate on the coating table. When spraying, pour the suspension into the material tank of the equipment, adjust the pressure to 0.5 MPa through the pressure control system of the equipment, so that the suspension is evenly ejected from the slit, the spraying distance is 12 cm, and the coating thickness is 5 μm.

[0055] S2 Heat treatment

[0056] S21 Pre-oxidation stage

[0057] Put the alkali-free glass substrate into a high-temperature furnace, continuously introduce a mixed gas of H2 and N2 with a volume ratio of 1:5 into the furnace, control the gas flow rate at 75 mL / min, and maintain a pressure of 0.8 MPa. Raise the temperature to 450 °C at a heating rate of 10 °C / min and keep it warm for 30 min.

[0058] S22 Rapid heating stage

[0059] Raise the temperature to 800 °C at a heating rate of 15 °C / min.

[0060] S23 Cyclic heat preservation stage

[0061] Perform periodic temperature fluctuations at 800 °C, that is, through the temperature control system of the high-temperature furnace, switch the temperature between 785 °C and 815 °C every 5 min, and the whole fluctuation process lasts for 40 min.

[0062] S3 Cooling and cleaning

[0063] After cooling the alkali-free glass substrate to room temperature at a rate of 5 °C / min, it was first soaked and cleaned in an 8 wt.% dilute hydrochloric acid solution for 8 min, then irradiated with ultraviolet light with a wavelength of 254 nm for 20 min, and finally the cleaned alkali-free glass substrate was placed in a supercritical CO2 drying equipment, with the set temperature of 38 °C, pressure of 9 MPa, CO2 flow rate of 6 L / min, and drying time of 45 min.

[0064] Performance tests were carried out on the alkali-free glass substrate before and after the treatment of this example: the β-OH content dropped to 10 ppm, the strain point increased from 625 °C to 650 °C, the light transmittance increased from 90.3% to 91.5%, and the thermal expansion coefficient was 3.4×10 -6 / °C, and the Young's modulus was 71 GPa.

[0065] Example 2

[0066] An alkali-free glass substrate with the same size as that in Example 1 was taken, and its initial β-OH content was measured to be 52 ppm, the thermal expansion coefficient was 3.6×10 -6 / °C, and the Young's modulus was 69 GPa.

[0067] The method for scavenging hydroxyl groups of the TFT alkali-free glass substrate based on the synergistic induction of γ-Al2O3 phase change and TiO2 in this example includes the following steps:

[0068] S1 Prepare a suspension and spray it

[0069] S11 Prepare a suspension

[0070] Prepare γ-Al2O3 powder with an average particle size of 40 nm and TiO2 powder with an average particle size of 25 nm, and accurately weigh the powders according to the mass ratio of γ-Al2O3 powder to TiO2 powder of 4:1. Using the ionic liquid [BMIM][BF4] as a dispersant, the two powders were mixed and ultrasonically dispersed for 50 min to make a uniform suspension.

[0071] S12 Coating

[0072] The suspension was coated on the surface of the alkali-free glass substrate by the slit spraying method: using a slit coater, the alkali-free glass substrate was placed on the coating table. During spraying, the suspension was poured into the feed tank of the equipment, and the pressure was adjusted to 0.6 MPa through the pressure control system of the equipment, so that the suspension was evenly ejected from the slit, the spraying distance was 13 cm, and the coating thickness was 6 μm.

[0073] S2 Heat treatment

[0074] S21 Pre-oxidation stage

[0075] Put the non-alkali glass substrate into a high-temperature furnace, continuously introduce a mixed gas of H2 and N2 with a volume ratio of 1:4 into the furnace, control the gas flow rate at 80 mL / min, and maintain a pressure of 0.7 MPa. Raise the temperature to 480 °C at a heating rate of 10 °C / min and keep it warm for 30 min.

[0076] S22 Rapid heating stage

[0077] Raise the temperature to 750 °C at a heating rate of 15 °C / min.

[0078] S23 Cyclic heat preservation stage

[0079] Perform periodic temperature fluctuations at 750 °C, that is, through the temperature control system of the high-temperature furnace, switch the temperature between 735 °C and 765 °C every 5 min, and the entire fluctuation process lasts for 45 min.

[0080] S3 Cooling and cleaning

[0081] After cooling the non-alkali glass substrate to room temperature at a rate of 6 °C / min, first soak and clean it with a 7 wt.% dilute hydrochloric acid solution for 7 min, then irradiate the non-alkali glass substrate with ultraviolet light with a wavelength of 254 nm for 25 min, and finally put the cleaned non-alkali glass substrate into a supercritical CO2 drying device, set the temperature at 36 °C, the pressure at 8.5 MPa, the CO2 flow rate at 7 L / min, and the drying time at 50 min.

[0082] Perform performance tests on the non-alkali glass substrate before and after the treatment of this example: the β-OH content drops to 12 ppm, the strain point increases from 620 °C to 645 °C, the light transmittance increases from 90.5% to 91.3%, the thermal expansion coefficient is 3.5×10 -6 / °C, and the Young's modulus is 70 GPa.

[0083] Example 3

[0084] Take a non-alkali glass substrate with the same size as that in Example 1, and measure its initial β-OH content to be 55 ppm, the thermal expansion coefficient to be 3.4×10 -6 / °C, and the Young's modulus to be 71 GPa.

[0085] The method for scavenging hydroxyl groups of the TFT non-alkali glass substrate based on the synergistic induction of γ-Al2O3 phase change and TiO2 in this example includes the following steps:

[0086] S1 Prepare a suspension and spray it

[0087] S11 Prepare a suspension

[0088] Prepare γ-Al2O3 powder with an average particle size of 60 nm and TiO2 powder with an average particle size of 40 nm, and accurately weigh the powders according to the mass ratio of γ-Al2O3 powder to TiO2 powder of 7:3. Using the ionic liquid [BMIM][BF4] as a dispersant, mix the two powders and ultrasonically disperse them for 35 min to make a uniform suspension.

[0089] S12 Coating

[0090] Coat the suspension on the surface of the E-glass substrate by the slot-die coating method: Use a slot-die coater, place the E-glass substrate on the coating table. During spraying, pour the suspension into the feed tank of the equipment, adjust the pressure to 0.7 MPa through the pressure control system of the equipment, so that the suspension is evenly ejected from the slot, the spraying distance is 11 cm, and the coating thickness is 4 μm.

[0091] S2 Heat treatment

[0092] S21 Pre-oxidation stage

[0093] Put the E-glass substrate into a high-temperature furnace, continuously introduce a mixed gas of H2 and N2 with a volume ratio of 1:6 into the furnace, control the gas flow rate at 60 mL / min, and maintain a pressure of 0.9 MPa. Raise the temperature to 420 °C at a heating rate of 10 °C / min and hold for 30 min.

[0094] S22 Rapid heating stage

[0095] Raise the temperature to 850 °C at a heating rate of 10 °C / min.

[0096] S23 Cyclic holding stage

[0097] Perform periodic temperature fluctuations at 850 °C, that is, through the temperature control system of the high-temperature furnace, switch the temperature between 830 °C and 870 °C every 5 min, and the whole fluctuation process lasts for 50 min.

[0098] S3 Cooling and cleaning

[0099] After cooling the E-glass substrate to room temperature at a rate of 4 °C / min, first soak and clean it with a 9 wt.% dilute hydrochloric acid solution for 9 min, then irradiate the E-glass substrate with ultraviolet light with a wavelength of 254 nm for 18 min, and finally put the cleaned E-glass substrate into a supercritical CO2 drying equipment, set the temperature at 39 °C, the pressure at 9.5 MPa, the CO2 flow rate at 5 L / min, and the drying time at 35 min.

[0100] Perform performance tests on the non-alkali glass substrate before and after the treatment in this embodiment: the β-OH content is reduced to 9 ppm, the strain point is increased from 630 °C to 652 °C, the light transmittance is increased from 90% to 91.5%, and the thermal expansion coefficient is 3.3×10 -6 / °C, and the Young's modulus is 72 GPa.

[0101] Comparative Example 1

[0102] Take a non-alkali glass substrate with a size of 10 cm × 10 cm. The initial β-OH content is measured to be 50 ppm by a Fourier transform infrared spectrometer, and the thermal expansion coefficient is 3.5×10 -6 / °C, and the Young's modulus is 70 GPa.

[0103] In the method for removing hydroxyl groups from the TFT non-alkali glass substrate of Comparative Example 1, in step S11, TiO2 powder is not added; the remaining steps are the same as those in Example 1.

[0104] Perform performance tests on the non-alkali glass substrate before and after the treatment of Comparative Example 1: the β-OH content is reduced to 30 ppm, the strain point is increased from 622 °C to 630 °C, the light transmittance is increased from 90.1% to 90.8%, and the thermal expansion coefficient is 3.5×10 -6 / °C, and the Young's modulus is 70.2 GPa.

[0105] Since TiO2 powder is not sprayed on the surface of the non-alkali glass substrate, the synergistic mechanism of oxygen vacancy synergy, photocatalytic-assisted scavenging, and heterojunction-enhanced electron transfer cannot be formed. The hydroxyl scavenging mainly depends on γ-Al2O3 itself, and the effect is significantly weakened, and the improvement effect on the strain point and light transmittance is limited.

[0106] Comparative Example 2

[0107] Take a non-alkali glass substrate with a size of 10 cm × 10 cm. The initial β-OH content is measured to be 51 ppm by a Fourier transform infrared spectrometer, and the thermal expansion coefficient is 3.6×10 -6 / °C, and the Young's modulus is 69 GPa.

[0108] In the method for removing hydroxyl groups from the TFT non-alkali glass substrate of Comparative Example 2, in step S11, γ-Al2O3 powder is not added; the remaining steps are the same as those in Example 1.

[0109] Perform performance tests on the non-alkali glass substrate before and after the treatment of Comparative Example 2: the β-OH content is reduced to 25 ppm, the strain point is increased from 620 °C to 632 °C, the light transmittance is increased from 90.2% to 90.6%, and the thermal expansion coefficient is 3.6×10 -6 / °C, and the Young's modulus is 69.3 GPa.

[0110] Since the γ-Al2O3 powder was not added, the γ-Al2O3 / TiO2 composite coating could not be formed, and the active sites generated by the phase transformation of γ-Al2O3 could not be utilized. It was difficult to efficiently adsorb and decompose hydroxyl groups only by the action of TiO2, resulting in poor hydroxyl group scavenging effect and limited improvement in the strain point and light transmittance.

[0111] Comparative Example 3

[0112] A piece of non-alkali glass substrate with a size of 10 cm × 10 cm was taken, and the initial content of β-OH was measured to be 54 ppm by Fourier transform infrared spectrometer, and the thermal expansion coefficient was 3.4×10 -6 / °C, and the Young's modulus was 71 GPa.

[0113] In the method for scavenging hydroxyl groups on the TFT non-alkali glass substrate of Comparative Example 3, in step S22, the temperature was raised to 800 °C at a heating rate of 15 °C / min and held for 20 min, and step S23 was not carried out; the remaining steps were the same as those in Example 1.

[0114] Performance tests were carried out on the non-alkali glass substrate before and after the treatment of Comparative Example 3: the content of β-OH decreased to 28 ppm, the strain point increased from 627 °C to 642 °C, the light transmittance increased from 90.4% to 90.7%, and the thermal expansion coefficient was 3.4×10 -6 / °C, and the Young's modulus was 71.2 GPa.

[0115] Since there was no cyclic heat preservation stage during the heat treatment in Comparative Example 3, the phase transformation of γ-Al2O3 was insufficient, the number of generated oxygen vacancies decreased, which affected the hydroxyl group scavenging efficiency, resulting in a small decrease in the content of β-OH and a slightly worse improvement effect on the strain point and light transmittance.

[0116] Comparative Example 4

[0117] A piece of non-alkali glass substrate with a size of 10 cm × 10 cm was taken, and the initial content of β-OH was measured to be 51 ppm by Fourier transform infrared spectrometer, and the thermal expansion coefficient was 3.5×10 -6 / °C, and the Young's modulus was 70 GPa.

[0118] In the method for scavenging hydroxyl groups on the TFT non-alkali glass substrate of Comparative Example 4, in step S3, ultraviolet photocatalytic cleaning was not carried out; the remaining steps were the same as those in Example 1.

[0119] Performance tests were carried out on the non-alkali glass substrate before and after the treatment of Comparative Example 4: the content of β-OH decreased to 17 ppm, the strain point increased from 625 °C to 645 °C, the light transmittance increased from 90.2% to 90.7%, and the thermal expansion coefficient was 3.5×10 -6 / °C, and the Young's modulus was 70.3 GPa.

[0120] Since the ultraviolet photocatalytic cleaning was not carried out in Comparative Example 4, the photocatalytic activity of TiO2 could not be used to further decompose the residual hydroxyl groups and organic substances, resulting in incomplete removal of hydroxyl groups, which had a certain impact on the reduction of β-OH content and the improvement of light transmittance.

[0121] Comparative Example 5

[0122] A piece of alkali-free glass substrate with a size of 10 cm × 10 cm was taken, and the initial β-OH content was measured to be 52 ppm by Fourier transform infrared spectrometer, and the coefficient of thermal expansion was 3.6×10 -6 / °C, and the Young's modulus was 69 GPa.

[0123] In the method for removing hydroxyl groups from the TFT alkali-free glass substrate of Comparative Example 5, in step S3, oven drying was used during drying, the drying temperature was 80 °C, and the drying time was 2 h; the remaining steps were the same as those in Example 1.

[0124] Performance tests were carried out on the alkali-free glass substrate before and after the treatment of Comparative Example 5: the β-OH content decreased to 15 ppm, the strain point increased from 623 °C to 640 °C, the light transmittance increased from 90.3% to 90.6%, and the coefficient of thermal expansion was 3.6×10 -6 / °C, and the Young's modulus was 69.1 GPa.

[0125] Since Comparative Example 5 adopted the traditional oven drying method, relying on the convection of hot air to carry away moisture, during the evaporation of moisture, microcracks were easily generated on the surface of the alkali-free glass substrate due to the surface tension effect, which affected the surface quality of the glass substrate, and then had a negative impact on the hydroxyl group removal effect and the improvement of the strain point and light transmittance.

[0126] Comparative Example 6

[0127] A piece of alkali-free glass substrate with a size of 10 cm × 10 cm was taken, and the initial β-OH content was measured to be 53 ppm by Fourier transform infrared spectrometer, and the coefficient of thermal expansion was 3.4×10 -6 / °C, and the Young's modulus was 71 GPa.

[0128] In the method for removing hydroxyl groups from the TFT alkali-free glass substrate of Comparative Example 6, in step S2, during the heat treatment process, a mixed gas of H2 and N2 was not introduced into the high-temperature furnace; the remaining steps were the same as those in Example 1.

[0129] Performance tests were carried out on the alkali-free glass substrate before and after the treatment of Comparative Example 6: the β-OH content decreased to 22 ppm, the strain point increased from 624 °C to 638 °C, the light transmittance increased from 90.2% to 90.5%, and the coefficient of thermal expansion was 3.4×10 -6 / °C, and the Young's modulus was 71.1 GPa.

[0130] Since no mixed gas of H2 and N2 is introduced during the heat treatment in Comparative Example 6, a reducing atmosphere cannot be created, it is difficult for TiO2 to generate oxygen vacancies, and γ-Al2O3 may also lose some active sites due to overoxidation, weakening the oxygen vacancy synergy effect, resulting in a decrease in the hydroxyl scavenging efficiency and poor improvement effects on the strain point and light transmittance.

Claims

1. A method for removing hydroxyl groups from TFT alkali-free glass substrate based on synergistic induction of γ-Al2O3 phase transition and TiO2, characterized in that: The following steps are involved: S1 prepares γ-Al2O3 powder and TiO2 powder into a suspension, and coats the suspension on the surface of an alkali-free glass substrate; S2: Place the alkali-free glass substrate into a high-temperature furnace, continuously introduce a mixed gas of H2 and N2 into the furnace, heat it to 400-500°C at a heating rate of 5-15°C / min, and keep it warm for 20-40min; then heat it to 700-900°C at a heating rate of 10-20°C / min; then perform periodic temperature fluctuations, that is, perform temperature fluctuations within ±20°C every 5min at 700-900°C, and the entire periodic temperature fluctuation lasts for 30-60min; Finally, in S3, the alkali-free glass substrate is cooled to room temperature and then cleaned, thereby completing the removal of hydroxyl groups from the alkali-free glass substrate.

2. The method for removing hydroxyl from TFT alkali-free glass substrate based on synergistic induction of γ-Al2O3 phase transition and TiO2 according to claim 1, characterized in that: In step S1, γ-Al2O3 powder and TiO2 powder are prepared into a suspension using ionic liquid [BMIM][BF4] as a dispersant.

3. The method for removing hydroxyl from TFT alkali-free glass substrate based on synergistic induction of γ-Al2O3 phase transition and TiO2 according to claim 1, characterized in that: In step S1, the average particle size of γ-Al2O3 powder is 30-80nm, and the average particle size of TiO2 powder is 20-50nm.

4. The method for removing hydroxyl from TFT alkali-free glass substrate based on synergistic induction of γ-Al2O3 phase transition and TiO2 according to claim 1, characterized in that: In step S1, the mass ratio of γ-Al2O3 powder to TiO2 powder is (2-4):

1.

5. The method for removing hydroxyl from TFT alkali-free glass substrate based on synergistic induction of γ-Al2O3 phase transition and TiO2 according to claim 1, characterized in that: In step S1, the suspension is coated on the surface of the alkali-free glass substrate by a slit spraying method, the spraying distance is 10-15 cm, and the coating thickness is 3-8 μm.

6. The method for removing hydroxyl from TFT alkali-free glass substrate based on γ-Al2O3 phase transition TiO2 synergistic induction according to claim 1, characterized in that: In step S2, the volume ratio of H2 to N2 in the mixed gas is 1:(4-6); the flow rate of the mixed gas is 50-100 mL / min, and the pressure is 0.5-1 MPa.

7. The method for removing hydroxyl from TFT alkali-free glass substrate based on synergistic induction of γ-Al2O3 phase transition and TiO2 according to claim 1, characterized in that: In step S3, the cooling rate is 3-8°C / min. After cooling to room temperature, the sample is first soaked and cleaned with a dilute hydrochloric acid solution for 5-10 minutes, then cleaned with ultraviolet light catalysis, and finally dried with supercritical CO2.

8. The method for removing hydroxyl from TFT alkali-free glass substrate based on synergistic induction of γ-Al2O3 phase transition and TiO2 according to claim 7, characterized in that: The concentration of the dilute hydrochloric acid solution is 5-10wt.%.

9. The method for removing hydroxyl from TFT alkali-free glass substrate based on synergistic induction of γ-Al2O3 phase transition and TiO2 according to claim 7, characterized in that: During ultraviolet photocatalytic cleaning, ultraviolet light with a wavelength of 254 nm is used to irradiate the alkali-free glass substrate for 15-30 minutes.

10. The method for removing hydroxyl from TFT alkali-free glass substrate based on synergistic induction of γ-Al2O3 phase transition and TiO2 according to claim 7, characterized in that: When using supercritical CO2 drying, the cleaned alkali-free glass substrate is placed in a supercritical CO2 drying device, the temperature is set to 35-40°C, the pressure is 8-10MPa, the CO2 flow rate is 5-8L / min, and the drying time is 30-60min.