A flexible ultra-thin glass processing method

Abstract

The application discloses a flexible ultrathin glass processing method and relates to the technical field of flexible ultrathin glass processing. The method comprises the following steps: coating acid-resistant protective oil on both sides of a flexible ultrathin glass mother sheet and solidifying; etching and chamfering after cutting; removing the protective oil and performing fine polishing to remove processing microcracks; placing the fine-polished flexible ultrathin glass sheet in a hardening frame, putting the frame into a hardening furnace to perform chemical strengthening, and executing a specific fast cooling process; and finally performing re-polishing to remove strengthening microcracks. The application effectively solves the problems of microcrack residues, coating defects and poor strengthening effect by optimizing the coating mode, introducing a double microcrack removal mechanism of fine polishing and re-polishing, and adopting a fast cooling process to maintain compressive stress, and significantly improves the limit bending radius and bending times of the flexible ultrathin glass.

Description

Technical Field

[0001] This invention relates to the field of flexible ultrathin glass processing technology, and in particular to a method for processing flexible ultrathin glass. Background Technology

[0002] With the rapid development of flexible display technology, foldable screen electronic devices (such as foldable phones and foldable tablets) are gradually becoming the mainstream in the market. Flexible ultra-thin glass (UTG) is widely used as a cover material for foldable screen electronic devices due to its excellent light transmittance, surface hardness, scratch resistance, and good tactile feel.

[0003] Currently, there are two main production methods for UTG: one-step forming and two-step thinning. While the one-step forming method can directly produce UTG, it has a low yield and high cost. The two-step thinning method involves chemically etching a thicker glass substrate to reduce its thickness; this process is relatively mature and is currently the mainstream choice in the industry. However, during UTG processing, especially in machining steps such as cutting and chamfering, microcracks inevitably form on the glass edges and surface. These microcracks easily become stress concentration points during subsequent bending, leading to glass breakage and severely affecting the strength, bending radius, and number of bends of the UTG. Microcrack source detection on UTG samples revealed that after machining steps such as cutting and chamfering, the depth of the fracture source was approximately 0.8μm-1.4μm. Figures 1-3 Top views of UTG fracture sources at multiple magnifications, obtained by OM phase microscopy and SEM scanning electron microscopy. Among them, Figure 1 Corresponding to sample number 7, the fracture origin depth is 0.88 μm. Figure 2 Corresponding to sample number 6, the fracture origin depth is 1.38 μm. Figure 3 Corresponding to sample No. 3, the fracture origin depth is 1.05 μm.

[0004] To improve the strength of UTG, existing technologies typically employ chemical strengthening (ion exchange) processes. However, in actual production, existing processing techniques still have the following shortcomings: 1. Incomplete removal of microcracks: Existing methods for removing microcracks mainly include physical polishing and etching. Because UTG thickness is extremely small, physical polishing results in a high breakage rate and low yield. Existing etching processes often fail to completely eliminate microcracks generated during processing, or they may reduce the glass thickness excessively while removing microcracks, affecting the product's dimensional accuracy and overall strength.

[0005] 2. Mismatch between strengthening and cooling processes: Traditional chemical strengthening usually involves natural cooling or slow cooling in the furnace, which leads to a decrease in surface compressive stress (CS) generated by ion exchange due to stress relaxation, thus failing to achieve the desired strengthening effect.

[0006] Therefore, there is an urgent need for a flexible ultrathin glass processing method that can effectively eliminate microcracks, improve coating quality, and optimize strengthening and cooling processes to meet the stringent requirements of foldable screen electronic devices for high UTG strength, small bending radius, and multiple bending cycles. Summary of the Invention

[0007] The purpose of this invention is to provide a flexible ultrathin glass processing method, which aims to solve the problems of incomplete removal of microcracks and poor strengthening cooling effect in the existing technology of UTG processing, thereby significantly improving the strength and bending performance of flexible ultrathin glass.

[0008] To achieve the above objectives, the present invention provides a method for processing flexible ultrathin glass, comprising the following steps: S1. Apply acid-resistant protective oil to the two opposite surfaces of the flexible ultra-thin glass mother sheet; S2. Cut away the ineffective areas on the flexible ultra-thin glass mother sheet that are not coated with acid-resistant protective oil, and obtain flexible ultra-thin glass pieces to be processed through cutting and splitting. S3. Remove the acid-resistant protective oil from the surface of the flexible ultra-thin glass sheet; perform fine polishing on the degreased flexible ultra-thin glass sheet to remove the processing micro-cracks on the surface of the flexible ultra-thin glass sheet. S4. Place the finely polished flexible ultrathin glass sheet in a hardening rack and put it into a hardening furnace for chemical strengthening treatment. After the chemical strengthening is completed, perform rapid cooling treatment. S5. After rapid cooling, the flexible ultra-thin glass pieces are polished to remove microcracks generated during the chemical strengthening process.

[0009] In the flexible ultrathin glass processing method of the present invention, the step between S2 and S3 further includes: The edges of the flexible ultrathin glass sheet are etched and chamfered using an etching solution.

[0010] In the flexible ultrathin glass processing method of the present invention, in step S1, acid-resistant protective oil is applied to the A and B surfaces of the flexible ultrathin glass master sheet using an alternating ABAB slit coating method with unequal thicknesses. Specifically, this includes: A first slit coating is applied to surface A of the flexible ultrathin glass substrate, with a coating thickness of the first thickness, followed by a first curing treatment. A first slit coating is applied to the B-side of the flexible ultrathin glass substrate, with a coating thickness equal to the first thickness, followed by a second curing process. A second slit coating is applied to surface A of the flexible ultrathin glass substrate, with a coating thickness equal to the second thickness, followed by a third curing process. A second slit coating is applied to the B-side of the flexible ultrathin glass substrate, with a coating thickness equal to the second thickness, followed by a fourth curing process. Wherein, the first thickness is greater than the second thickness.

[0011] In the flexible ultrathin glass processing method of the present invention, the first thickness is 20±2μm and the second thickness is 15±2μm; the curing treatment is a curing method combining UV light curing and IR infrared baking.

[0012] In the flexible ultrathin glass processing method of the present invention, the fine polishing process in step S3 includes: sequentially cleaning the flexible ultrathin glass sheet with a cleaning agent, cleaning with pure water, and etching with mixed acid, wherein the mixed acid etching uses a hydrofluoric acid solution with a mass fraction of less than 3%, the etching temperature is room temperature, the etching time is 5±1 minutes, and the single-sided removal amount is 1-2μm. The re-polishing process in step S5 includes: sequentially cleaning the flexible ultrathin glass sheet with a cleaning agent, cleaning with pure water, and etching with mixed acid. The mixed acid etching uses a hydrofluoric acid solution with a mass fraction of less than 3%, the etching temperature is room temperature, the etching time is 3±1 minutes, and the removal amount on one side is 0.5-1.5μm.

[0013] In the flexible ultrathin glass processing method of the present invention, the rapid cooling process in step S4 includes the following time sequence steps: The chemically strengthened flexible ultrathin glass sheet was lifted from the hardening furnace to its highest point in 120 seconds. The device hovers and drips onto the reinforced salt solution adhering to the surface, taking 3 seconds. The flexible ultrathin glass piece was transferred to the highest point of the cooling water tank, which took 90 seconds. The flexible ultrathin glass piece was lowered to the bottom of the cooling water tank in 90 seconds; Immerse in the cooling water tank for 10 ± 1 minutes; The cooling water in the cooling water tank is at a temperature of 50±5℃ and is in a state of no circulation and no stirring.

[0014] In the flexible ultrathin glass processing method of the present invention, the parameters of the chemical strengthening treatment in step S4 include: a preheating temperature of 360°C and a preheating time of 29-31 minutes; the strengthening liquid is composed of potassium nitrate with a mass fraction of 99.5% and silica with a mass fraction of 0.4-0.6%, with a volume ratio of 1:1; the strengthening temperature is 380-410°C and the strengthening time is 20 minutes.

[0015] The beneficial effects of this invention are as follows: 1. Dual microcrack removal through fine polishing and repolishing: Fine polishing is performed before chemical strengthening to remove microcracks generated during processing; repolishing is performed after chemical strengthening to remove new microcracks generated during strengthening. By strictly controlling the removal amount on one side (1-2μm for fine polishing, 0.5-1.5μm for repolishing), the complete elimination of microcracks is ensured while avoiding excessive loss of stress layer depth (DOL), significantly improving the ultimate bending radius and number of bends of the UTG.

[0016] 2. Rapid cooling process maintains compressive stress: After chemical strengthening, rapid cooling by immersion in water is carried out using a specific time sequence, which avoids stress relaxation in the traditional slow cooling process and effectively maintains a high surface compressive stress (CS), further enhancing the strength of the glass. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figures 1-3 This is a top view of the fracture origin of the UTG sample.

[0018] Figure 4 This is a flowchart of a flexible ultrathin glass processing method provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of ABAB slit coating provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of two-dimensional parameters for slit coating provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the coating effect of Method 2.

[0019] Figure 8 This is a schematic diagram of the coating effect of method three.

[0020] Figure 9 This is a schematic diagram of the coating effect of method four.

[0021] Figure 10 This is a schematic diagram of the flexible ultrathin glass master sheet used in the implementation of the present invention.

[0022] Figure 11 This is a flowchart of the rapid cooling process provided in an embodiment of the present invention.

[0023] Figures 12-14 This is a top view of the fracture origin of the sample before it was returned to the blasting site.

[0024] Figures 15-16 This is a top view of the fracture origin of the sample after it has been returned to its original state. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] The flexible ultrathin glass processing method provided by this invention is particularly suitable for the large-scale industrial production of flexible ultrathin glass with a thickness of 0.1 mm or less (e.g., 0.05 mm). The UTG finished product produced by this method has extremely high surface hardness, excellent light transmittance, and outstanding resistance to repeated bending, making it an ideal material for flexible display cover plates of high-end electronic products such as foldable screen phones, foldable tablets, and flexible wearable devices.

[0027] Example 1 This embodiment provides a flexible ultrathin glass processing method, mainly used for UTG cover plate processing of foldable screen electronic devices (such as foldable phones, foldable tablets, etc.). This process, through meticulous design of key steps such as coating, etching, strengthening, and cooling, aims to minimize microcracks on the glass surface and improve its mechanical strength and bending life.

[0028] The physical basis for the ability of UTG to be repeatedly bent lies in its core structure: the main structure of UTG is a silicate framework. When the glass is bent, the maximum bending normal stress on the cross-section occurs at the point farthest from the neutral axis. When the glass thickness is reduced to 0.1 mm or less, the upper and lower surfaces are sufficiently close to the neutral axis, and the normal stress at the farthest point is insufficient to break the silicate framework, macroscopically manifesting as the ability to be repeatedly bent. However, microcracks generated during processing become stress concentration points, significantly reducing the actual bending strength of the glass. Therefore, the core objective of this invention is to systematically eliminate microcracks introduced at each processing stage, thereby fully realizing the bending potential of UTG.

[0029] Figure 4 This is a flowchart illustrating a flexible ultrathin glass processing method provided in an embodiment of the present invention. Figure 4 As shown, the flexible ultrathin glass processing method includes the following steps: S1. Apply acid-resistant protective oil to the two opposite surfaces of the flexible ultra-thin glass mother sheet.

[0030] In this embodiment, a flexible ultrathin glass substrate with dimensions of 600×500mm and a thickness of 0.45mm, manufactured by Schott AG of Germany, was selected as the processing material. A UV-sensitive acid-resistant protective oil was applied to both sides of the substrate using an alternating ABAB slit coating method with varying thicknesses. Each coating was followed by an alternating curing process.

[0031] Slot coating is a precision thin-film coating technology that involves dynamic wetting. Its working principle is as follows: acid-resistant protective oil is delivered to the slot coating die via a metering pump. The ink flows out evenly from the slot outlet of the die, forming a stable liquid film bridge between the die and the UTG substrate. As the UTG substrate moves at a uniform speed, the liquid film bridge spreads across the substrate surface, forming a uniform wet film layer.

[0032] Figure 6 This is a schematic diagram of two-dimensional parameters for slit coating provided in an embodiment of the present invention. Figure 6 As shown, the key parameters for slot coating include: V is the exit speed of the coating die, W is the width between the upstream and downstream coating dies (i.e., slot width), H is the height of the coating die from the UTG substrate (i.e., coating gap), L is the wet film thickness of the applied acid-resistant protective oil, and U is the moving speed of the UTG substrate. The wet film thickness L can be accurately calculated using the following formula: L = Q / (a ​​× U) In the formula, Q is the coating amount (the volume of ink flowing out of the die per unit time), a is the coating width, and U is the substrate moving speed. By precisely controlling these three parameters—coating amount Q, coating width a, and substrate moving speed U—precise control of the wet film thickness L can be achieved.

[0033] The protective oil used in this embodiment is a photosensitive and thermosetting acid-resistant protective ink, model 128B-12. The ink is prepared as follows: weigh the crude oil and curing agent at a mass ratio of 100:7, with a solid content of 80%. Before use, manually stir the crude oil for 3-5 minutes until homogeneous, then add the curing agent and stir for another 3-5 minutes until no obvious stratification occurs. After stirring, filter the ink through a 300-400 mesh screen to remove any possible particulate impurities, ensuring that the viscosity of the diluted ink is controlled within the range of 70-90 cps.

[0034] This ink possesses the following key performance indicators: After curing, it is transparent with a transmittance greater than 80% at wavelengths greater than 500nm, meeting the requirements for subsequent laser cutting; it exhibits strong adhesion, with a cross-cut adhesion test result of ≥4B, ensuring the ink layer will not peel off during subsequent processing; it demonstrates excellent acid resistance, withstanding immersion in a 3% HF solution for 30 minutes without acid staining or ink peeling, meeting the requirements for HF etching and chamfering. Furthermore, this ink can undergo a photochemical reaction under 365nm ultraviolet light irradiation, achieving UV curing.

[0035] Figure 5 This is a schematic diagram of ABAB slit coating provided in an embodiment of the present invention, wherein the white area is flexible ultrathin glass, the dark area is ink, the left side is side A, and the right side is side B. Figure 5 As shown, this invention employs an alternating ABAB coating method with varying thicknesses. The specific coating process is as follows: Step 1: Apply the first slit coating to side A of the flexible ultrathin glass substrate. The coating thickness is 20±2μm. Immediately after coating, perform UV+IR curing treatment. Step 2: Apply the first slit coating to the B side of the flexible ultrathin glass master sheet. The coating thickness is 20±2μm. Immediately after coating, perform UV+IR curing treatment. Step 3: Apply a second slit coating to side A of the flexible ultrathin glass substrate. The coating thickness is 15±2μm. Immediately after coating, perform UV+IR curing treatment. Step 4: Apply a second slit coating to the B side of the flexible ultrathin glass master sheet. The coating thickness is 15±2μm. Immediately after coating, perform UV+IR curing treatment.

[0036] Each coating is cured using a combined UV and IR curing process within 3 minutes. The UV light wavelength is 365nm, with an energy of 1600-2000mJ / cm², and an irradiation time of 50 seconds; the IR infrared baking energy is 200-350mw / cm², and the baking time is 80 seconds. This combined UV and IR curing method not only ensures complete curing of the UV-sensitive acid-resistant protective oil but also effectively removes small molecule water generated during the chemical reaction and releases internal stress generated during curing, ensuring the density and adhesion of the ink layer.

[0037] The inventors conducted a systematic comparative test on four different coating methods, using 33 UTG samples for each method. The test results are as follows: Method 1: Both sides of A and B are coated with a single layer of 35±2μm and cured with UV+IR twice. The number of defective acid prints is 13 (defect rate 39.4%). Method 2: AABB continuous coating on the same side, i.e., coating 20±2μm on side A without curing, then coating another 15±2μm on side A, and then curing side A with UV+IR. Then coating side B twice to make the coating thickness on one side 35±2μm, and then curing side B with UV+IR. The number of acid-printed defects is 5 pieces (defect rate 15.2%). Method 3: Alternating ABAB coating with unequal thickness, ink thickness >50±2μm, 4 UV+IR curing cycles, 8 defective acid prints (defect rate 24.2%). Method 4: Alternating ABAB coating with unequal thickness, ink thickness 35±2μm, 4 UV+IR curing cycles, only 1 defective piece was produced (defect rate 3.0%).

[0038] The comparative data above show that the fourth method (alternating ABAB layers with unequal thickness, total thickness 35±2μm) used in this invention significantly reduces the acid printing defect rate compared to the other three methods. Its technical principle is as follows: (1) In Method 1, when coating once, the UTG surface coated with acid-resistant protective oil inevitably has defects such as foreign matter, oil spillage, pinholes, and bubbles. During the subsequent HF etching and chamfering process, HF will penetrate into the UTG surface through the defect location, producing in-plane etched acid marks.

[0039] (2) In Method 2, the B side is always exposed during the process of coating and curing the A side twice. As the number of operations increases, the risk of scratches, abrasions, fragments and foreign matter adhesion on the B side increases significantly. Figure 7 This is a schematic diagram of the coating effect of Method 2, as shown below. Figure 7 As shown, when AABB applies continuous coating on the same side, the defects from the two coatings are usually located in the same position, and the ink layer of the second coating cannot cover the defects produced by the first coating.

[0040] (3) In method three, when the thickness of the single-sided ink coating exceeds 50μm, after the ink is cured, the invalid area on the mother film needs to be removed by laser cutting and the mother film is cut into small pieces. If the thickness of the ink coating is too large, the energy required for laser cutting will increase, and the cutting area is prone to ink delamination, edge chipping and other defects. HF penetrates into the UTG surface through the ink delamination and edge chipping positions, resulting in poor edge acid penetration. Figure 8 This is a schematic diagram of the coating effect of method three, as shown below. Figure 8 As shown, even if the ink thickness exceeds 50μm, abnormalities such as ink splatter, bubbles, and pinholes will still inevitably occur.

[0041] (4) In Method 4, the thickness of the first coating (20±2μm) is greater than that of the second coating (15±2μm). This is because the first layer of ink bears the main acid resistance protection function and requires a thicker film layer to ensure the reliability of the protection. The main function of the second layer of ink is to cover the defects of the first layer. It does not need to be the same thickness as the first layer. A thinner film layer can meet the coverage requirements, while avoiding the total thickness being too large and affecting subsequent laser cutting. Figure 9 This is a schematic diagram of the coating effect of method four, as shown below. Figure 9 As shown, after the first UV+IR baking, the volume of defects such as foreign matter (excluding foreign matter whose volume remains unchanged after baking), oil spillage, and pinholes will generally decrease. As long as the pinholes, oil spillage, and foreign matter defects generated in the first coating are not in the same location as the defects generated in the second coating, it is generally possible to avoid HF penetrating into the UTG surface through the defect location and causing in-plane etching acid marks. The second, thinner ink layer can effectively cover these defect locations. Method four controls the total thickness on one side to 35±2μm (20±2μm for the first coating + 15±2μm for the second coating), which ensures the effect of double-layer protection and avoids the laser cutting problem caused by excessive ink thickness.

[0042] Acid etching on the UTG surface not only affects the appearance but also the strength of the UTG. This invention significantly reduces acid etching on the UTG surface by employing an alternating ABAB coating method with varying thicknesses, thus ensuring the strength of the UTG product.

[0043] S2. Cut away the ineffective areas on the flexible ultrathin glass mother sheet that are not coated with acid-resistant protective oil, and obtain flexible ultrathin glass pieces to be processed through cutting and splitting.

[0044] During slot coating, due to the edge effect of the coating die and the edge area limitation of the UTG master sheet, the surface of the UTG master sheet can be divided into two regions: the effective region and the ineffective region. The effective region refers to the area where the acid-resistant protective oil is evenly coated, the film layer is complete, and meets the requirements of subsequent processing; the ineffective region refers to the area located at the edge of the master sheet that is uncoated or unevenly coated. The acid-resistant protective oil film layer in the ineffective region is incomplete and cannot provide effective protection during the subsequent HF etching and chamfering process, therefore it must be removed before etching. Figure 10 This is a schematic diagram of the flexible ultrathin glass master sheet used in this embodiment. The dark part of the outer frame is the inactive area. The internal area is divided into multiple equal small squares by multiple intersecting lines. By cutting and splitting along the lines, the master sheet can be divided into multiple small pieces.

[0045] In this embodiment, an IR Pico laser cutting device is used to remove the invalid areas. The laser parameters are set as follows: wavelength 1064nm, maximum power 100W, laser cutting speed 150mm / s, laser cutting frequency 30000Hz, duty cycle 80%, and dot pitch 5μm.

[0046] In this embodiment, the cut-off width of the invalid region is calculated based on the current thickness D (in μm) of the flexible ultrathin glass piece using the following formula: Width of the ineffective area in the non-ink coating direction: w = 30 - 0.5 × D - 1 (unit: mm); Width of the ineffective area in the ink coating direction: w = 63 - 0.5 × D - 1 (unit: mm).

[0047] The width of the ineffective area in the ink coating direction is greater than that in the non-ink coating direction. This is because the ink thickness uniformity at the start and end positions of the die head is poor in the coating direction, requiring the removal of a larger edge area to ensure the quality of the ink layer in the remaining area.

[0048] In some embodiments of the present invention, between steps S2 and S3, the method further includes: using an etching solution to etch and chamfer the edges of the flexible ultrathin glass sheet.

[0049] In this embodiment, the cut flexible ultrathin glass flakes are placed on an HF etching and chamfering conveyor belt for edge chamfering. The purpose of etching and chamfering is to remove microcracks and stress concentration areas generated during laser cutting of the flexible ultrathin glass flakes through chemical etching, forming smooth edge chamfers, thereby improving the edge strength and bending resistance of the UTG.

[0050] The chamfering was etched using a conveyor belt continuous etching machine with a total conveyor belt length of 19.5m. The etching temperature was controlled at 21±1℃, and the spray pressure was 0.5±0.3MPa. The etching rate was 3±0.3μm / min.

[0051] The etching reagent is a 3% (w / w) HF mixed acid solution. The specific preparation method is as follows: Weigh 70 kg of deionized water, add 30 kg of 10% (w / w) HF mixed acid, and stir until homogeneous to obtain an HF etching solution with a (w / w) concentration of approximately 3%.

[0052] The conveyor speed V of the conveyor belt is precisely controlled according to the following formula: V = (100 × L × u) / (D × 60) In the formula, L is the conveyor belt length (m), u is the etching rate (μm / min), and D is the target etching removal amount (μm). This formula allows for precise adjustment of the conveyor speed according to different etching removal requirements, ensuring that the flexible ultrathin glass sheet achieves uniform and precise edge etching and chamfering during its passage through the conveyor belt.

[0053] S3. Remove the acid-resistant protective oil from the surface of the flexible ultra-thin glass sheet; perform fine polishing on the degreased flexible ultra-thin glass sheet to remove the processing micro-cracks on the surface of the flexible ultra-thin glass sheet.

[0054] After etching and chamfering, the acid-resistant protective ink layer on the surface of the flexible ultra-thin glass sheet needs to be removed. The flexible ultra-thin glass sheet is placed in a NaOH solution with a mass fraction of 8-10% and a temperature of 78-82℃, and immersed for 14-16 minutes to completely remove the acid-resistant protective ink layer.

[0055] During the degreasing process, the NaOH solution destroys the molecular structure of the acid-resistant protective ink through alkaline hydrolysis, causing it to detach from the UTG surface. The mass fraction of the NaOH solution is controlled at 8-10% because if the concentration is too low, the degreasing will be incomplete, and residual ink will affect the uniformity of subsequent fine polishing processes; if the concentration is too high, it may cause excessive corrosion to the surface of the flexible ultra-thin glass sheet. The temperature is controlled at 78-82℃ because this temperature range can effectively accelerate the hydrolysis reaction rate of NaOH on the ink without adversely affecting the surface quality of the flexible ultra-thin glass sheet. The immersion time is 14-16 minutes, which has been experimentally verified as the shortest time required for complete ink removal.

[0056] During the machining processes such as cutting and chamfering, microcracks inevitably form on the surface and edges of flexible ultrathin glass sheets. These microcracks are a key factor affecting the bending strength of UTG (Ultra-Thin Glass). This invention introduces a fine polishing process to completely eliminate these microcracks before chemical strengthening, providing a high-quality glass matrix for subsequent chemical strengthening.

[0057] In this embodiment, the fine polishing process uses chemical polishing. Specifically, the degreased flexible ultrathin glass sheet is placed in a 13-slot automated fine polishing machine and undergoes the following treatments sequentially: Tanks 1 to 3 are NaOH cleaning sections, with a temperature of 50℃ and a pH value of 13±1. The treatment time for each tank is 5±1 minutes. The purpose of the NaOH cleaning agent is to remove residual organic and inorganic impurities from the UTG surface, providing a clean surface for subsequent mixed acid etching.

[0058] Tank 4 is a pure water rinsing section with a pH value of 7±2 and a processing time of 5±1 minutes, used to rinse away any residue from the preceding cleaning agent.

[0059] Tank 5 to Tank 6 are pure water cleaning sections with a temperature of 50℃ and a pH value of 7±1. Each tank is treated for 5±1 minutes to further remove surface residues.

[0060] Tank 7 is the HF mixed acid etching section, using a hydrofluoric acid solution with a mass fraction of less than 3%, at a temperature of 20℃ (room temperature), a pH value of 1±1, and a processing time of 5±1 minutes. This tank is the core step in the fine polishing process, using HF to uniformly chemically etch the surface of the flexible ultrathin glass, removing the processing microcrack layer on the surface, with the removal amount on a single side strictly controlled within 1-2μm.

[0061] Tank 8 is a pure water cleaning section, at room temperature, pH 7±2, and a processing time of 5±1 minutes, used to terminate the HF etching reaction and rinse off residual acid.

[0062] Tanks 9 to 11 are multi-stage pure water cleaning sections with a temperature of 60℃ and a pH value of 7±1. Each tank has a treatment time of 5±1 minutes. The cleaning efficiency is accelerated by increasing the temperature to ensure that there are no residual chemicals on the UTG surface.

[0063] Tank 12 is the pure water rinsing section before drying, with a temperature of 60℃, a pH value of 7±1, and a treatment time of 5±1 minutes.

[0064] Tank 13 is a high-temperature drying section with a temperature of 100℃ and a processing time of 5±1 minutes to ensure that the UTG surface is completely dry.

[0065] like Figures 1-3 As shown, through fracture source testing of the samples, it was found that the fracture source depth of the flexible ultrathin glass before fine polishing could reach 0.8μm-1.4μm. These deep microcracks mainly originated from the mechanical and chemical stresses during laser cutting and HF etching chamfering processes. In this embodiment, the single-sided removal amount during fine polishing was strictly controlled within 1-2μm. After fine polishing, a depth of 1-2μm on the UTG surface was removed, and the processing microcracks were effectively eliminated. Controlling the removal amount during fine polishing within 1-2μm has important critical significance: if the removal amount is too small, the microcracks will not be completely removed, and the remaining microcracks will still become stress concentration points during subsequent bending; if the removal amount is too large, it will lead to excessive reduction in UTG thickness, affecting the dimensional accuracy and uniformity of the product, and will also increase the ion exchange depth required for subsequent chemical strengthening.

[0066] S4. Place the finely polished flexible ultrathin glass sheet in a hardening rack and put it into a hardening furnace for chemical strengthening treatment. After the chemical strengthening is completed, perform rapid cooling treatment.

[0067] After fine polishing, the flexible ultrathin glass sheets are placed into a hardening frame and then placed in a hardening furnace for chemical strengthening. After the strengthening is completed, a rapid cooling process is immediately performed.

[0068] The specific process parameters for chemical strengthening are as follows: First, the hardening furnace is preheated at 360℃ for 29-31 minutes to ensure uniform temperature distribution within the furnace and prevent thermal stress cracking caused by excessive temperature gradients when the flexible ultrathin glass sheets are introduced into the furnace. The strengthening solution is prepared by mixing 99.5% potassium nitrate (KNO3) and 0.4-0.6% silica (H2SiO3) in a 1:1 volume ratio. KNO3 provides potassium ions (K... + ) is used to react with sodium ions (Na) on the glass surface + Ion exchange is performed to form a compressive stress layer on the glass surface; the addition of H2SiO3 helps to precipitate impurities and reduce defects such as bumps and foreign matter. The strengthening temperature is 380-410℃, the strengthening time is 20 minutes, and the suspension time is 1 minute.

[0069] Figure 11 This is a flowchart illustrating the rapid cooling process provided in an embodiment of the present invention. Figure 11 As shown, immediately after chemical strengthening, a rapid cooling process with the following specific time sequence is executed: The first stage – lifting: The hardening frame carrying the flexible ultrathin glass sheet is lifted from the strengthening liquid in the hardening furnace to the highest point of the furnace, taking 120 seconds. The purpose of this stage is to remove the hardening frame from the high-temperature molten salt, while allowing most of the strengthening salt liquid to drip naturally back into the furnace.

[0070] The second stage – salt dripping: The glass is suspended at the highest point of the furnace body, allowing the residual strengthening salt solution adhering to the surface of the flexible ultra-thin glass sheet to drip off completely, taking 3 seconds. This stage is relatively short because the freezing point of strengthening salt solutions such as KNO3 is 334°C. When suspended at the highest point of the hardening furnace body for 3 seconds, the strengthening salt solution will usually solidify due to air cooling; further increasing the suspension time generally does not help with salt dripping.

[0071] The third stage – transfer: The hardening rack is horizontally transferred from the highest point of the hardening furnace to the highest point of the cooling water tank, which takes 90 seconds.

[0072] The fourth stage – descent: Slowly lower the stiffened frame from the highest point of the cooling water tank to the bottom of the tank, taking 90 seconds. The descent speed needs to be controlled within a reasonable range; too fast a speed will cause the flexible ultra-thin glass pieces to break due to the impact of the water.

[0073] Fifth stage – Immersion cooling: The hardened rack is completely submerged in cooling water for 10 ± 1 minutes. The cooling water temperature is 50 ± 5℃, and the water tank is in a state of no circulation and no stirring.

[0074] The setting of this rapid cooling time sequence has strict critical significance. If the total time from lifting to water immersion is too long, the UTG will cool slowly in the air during the transfer process, causing the surface compressive stress (CS) generated by ion exchange to decrease significantly due to the stress relaxation effect at high temperatures, failing to achieve the purpose of maintaining compressive stress through rapid cooling. If the total time is too short, the equipment needs to move too fast, resulting in excessive impact force when the hardened frame enters the water, which can easily lead to UTG fragmentation. The cooling water temperature is set at 50±5℃ with no circulation and no agitation to avoid the UTG cracking due to thermal shock caused by excessively low water temperature or water flow impact, while ensuring a sufficient cooling rate to maintain a high CS value.

[0075] To verify the difference between rapid cooling and conventional slow cooling, 36 pieces of chemically strengthened flexible ultrathin glass were selected. The first group underwent rapid cooling, while the second group underwent slow cooling. The surface compressive stress (CS) and stress layer depth (DOL) of each glass sample were then measured. In the first group, the average surface compressive stress (CS) was 999.05 MPa, and the average stress layer depth (DOL) was 9.30 μm. In the second group, the average surface compressive stress (CS) was 944.46 MPa, and the average stress layer depth (DOL) was 10.00 μm. This demonstrates that rapid cooling achieves higher surface compressive stress and a shallower stress layer depth compared to slow cooling. Rapid cooling improves the strength of the flexible ultrathin glass, reduces the bending radius, and increases the number of bends.

[0076] S5. After rapid cooling, the flexible ultra-thin glass pieces are polished to remove microcracks generated during the chemical strengthening process.

[0077] During chemical fortification, due to potassium ions (K... + Replace sodium ions (Na) + The volume expansion effect caused by processing and the effects of high-temperature thermal stress may generate new nanoscale microcracks (i.e., strengthening microcracks) on the glass surface. Although these strengthening microcracks are much smaller than processing microcracks, they can still become stress concentration points during bending, affecting the ultimate bending performance of UTG. This invention introduces a re-polishing process to eliminate these strengthening microcracks, achieving a dual microcrack removal mechanism of "fine polishing to remove processing microcracks + re-polishing to remove strengthening microcracks".

[0078] In this embodiment, the repolishing process uses chemical polishing. Specifically, the rapidly cooled flexible ultrathin glass sheet is placed in a 12-slot automated repolishing machine and undergoes the following processing steps: Tanks 1 to 3 are for NaOH cleaning agent cleaning, with a temperature of 50℃, a pH value of 13±1, and a treatment time of 3±1 minutes per tank.

[0079] Tank 4 is a pure water rinsing section with a pH value of 7±2 and a treatment time of 3±1 minutes.

[0080] Tank 5 to Tank 6 are pure water cleaning sections, with a temperature of 50℃, a pH value of 7±1, and a treatment time of 3±1 minutes per tank.

[0081] Tank 7 is the HF mixed acid etching section, using a hydrofluoric acid solution with a mass fraction of less than 3%, at a temperature of 20℃ (room temperature), a pH value of 1±1, and a processing time of 3±1 minutes. This tank performs precision etching on the chemically strengthened UTG surface using HF to remove the strengthening microcrack layer, with the removal amount on one side strictly controlled within 0.5-1.5μm.

[0082] Tank 8 is the pure water rinsing section, at room temperature, pH 7±2, and a treatment time of 3±1 minutes.

[0083] Tanks 9 to 11 are multi-stage pure water cleaning sections with a temperature of 60℃, a pH value of 7±1, and a treatment time of 3±1 minutes per tank.

[0084] Tank 12 is a high-temperature drying section with a temperature of 100℃ and a processing time of 3±1 minutes.

[0085] The main difference between repolishing and fine polishing is that the processing time per tank for repolishing is 3±1 minutes (5±1 minutes for fine polishing), and the removal amount per side is 0.5-1.5μm (1-2μm for fine polishing). The removal amount for repolishing is less than that for fine polishing because the depth of the strengthening microcracks is much smaller than that of the processing microcracks, and a smaller removal amount can effectively eliminate them. At the same time, excessive removal will lead to the over-removal of the compressive stress layer (DOL) formed by chemical strengthening, which will reduce the strength of UTG.

[0086] The microcracks before polishing are mainly caused by the chemical strengthening process. Figures 12-14 The image shows a top view of the fracture source of the samples before polishing. The fracture source depths of the samples are 127.88 nm, 267.24 nm, and 97.51 nm, respectively. In this embodiment of the invention, the single-sided removal amount during polishing is 0.5-1.5 μm. After polishing, the depth where the fracture source is located is effectively removed. Figures 15-16 This is a top view of the fracture source of the sample after polishing. The fracture sources are all located on the glass surface, which also indicates that the strengthening microcracks have been effectively eliminated.

[0087] In this embodiment, a rubbing test was conducted on the repolished flexible ultrathin glass to verify its strength. The test conditions were: plate spacing 1.692±0.15mm, rubbing speed 5mm / s, bending time 3s, rubbing stroke 5mm, and suction pressure 45KPa. The test results showed that the flexible ultrathin glass, after undergoing both fine polishing and repolishing to remove microcracks, exhibited excellent extreme bending performance, verifying the effectiveness of the dual microcrack removal mechanism of this invention. Furthermore, a 2PB test was conducted on the repolished flexible ultrathin glass, further verifying its strength performance. Finally, a dynamic bending test was conducted, verifying that its bending life was greater than 250,000 cycles, while the industry standard for bending life is greater than 200,000 cycles. The dynamic bending test conditions are: plate spacing 1.692±0.15mm, cycle time: 6S (3S unfolding time + 3S folding time), air intake 45KPa, temperature conditions include: (1) room temperature: 25℃; (2) -20℃; (3) 65℃ / 90%RH; (4) HFCU thermal shock, -40℃ to 80℃ programmed temperature rise and fall, temperature change rate: 5℃ / min.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for processing flexible ultrathin glass, characterized in that, Includes the following steps: S1. Apply acid-resistant protective oil to the two opposite surfaces of the flexible ultra-thin glass mother sheet; S2. Cut away the ineffective areas on the flexible ultra-thin glass mother sheet that are not coated with acid-resistant protective oil, and obtain flexible ultra-thin glass pieces to be processed through cutting and splitting. S3. Remove the acid-resistant protective oil from the surface of the flexible ultra-thin glass sheet; perform fine polishing on the degreased flexible ultra-thin glass sheet to remove the processing micro-cracks on the surface of the flexible ultra-thin glass sheet. S4. Place the finely polished flexible ultrathin glass sheet in a hardening rack and put it into a hardening furnace for chemical strengthening treatment. After the chemical strengthening is completed, perform rapid cooling treatment. S5. After rapid cooling, the flexible ultra-thin glass pieces are polished to remove microcracks generated during the chemical strengthening process.

2. The flexible ultrathin glass processing method according to claim 1, characterized in that, The step between S2 and S3 also includes: The edges of the flexible ultrathin glass sheet are etched and chamfered using an etching solution.

3. The flexible ultrathin glass processing method according to claim 1, characterized in that, In step S1, an acid-resistant protective oil is applied to surfaces A and B of the flexible ultrathin glass substrate using an alternating ABAB slit coating method with varying thicknesses. Specifically, this includes: A first slit coating is applied to surface A of the flexible ultrathin glass substrate, with a coating thickness of the first thickness, followed by a first curing treatment. A first slit coating is applied to the B-side of the flexible ultrathin glass substrate, with a coating thickness equal to the first thickness, followed by a second curing process. A second slit coating is applied to surface A of the flexible ultrathin glass substrate, with a coating thickness equal to the second thickness, followed by a third curing process. A second slit coating is applied to the B-side of the flexible ultrathin glass substrate, with a coating thickness equal to the second thickness, followed by a fourth curing process. Wherein, the first thickness is greater than the second thickness.

4. The flexible ultrathin glass processing method according to claim 3, characterized in that, The first thickness is 20±2μm, and the second thickness is 15±2μm; the curing process is a curing method that combines UV light curing and IR infrared baking.

5. The flexible ultrathin glass processing method according to claim 1, characterized in that, The fine polishing process in step S3 includes: sequentially cleaning the flexible ultrathin glass sheet with a cleaning agent, cleaning with pure water, and etching with mixed acid. The mixed acid etching uses a hydrofluoric acid solution with a mass fraction of less than 3%, the etching temperature is room temperature, the etching time is 5±1 minutes, and the removal amount on one side is 1-2μm. The re-polishing process in step S5 includes: sequentially cleaning the flexible ultrathin glass sheet with a cleaning agent, cleaning with pure water, and etching with mixed acid. The mixed acid etching uses a hydrofluoric acid solution with a mass fraction of less than 3%, the etching temperature is room temperature, the etching time is 3±1 minutes, and the removal amount on one side is 0.5-1.5μm.

6. The flexible ultrathin glass processing method according to claim 1, characterized in that, The rapid cooling process in step S4 includes the following time-series steps: The chemically strengthened flexible ultrathin glass sheet was lifted from the hardening furnace to its highest point in 120 seconds. The device hovers and drips onto the reinforced salt solution adhering to the surface, taking 3 seconds. The flexible ultrathin glass sheet was transferred to the highest point of the cooling water tank, which took 90 seconds. The flexible ultrathin glass sheet was lowered to the bottom of the cooling water tank in 90 seconds; Immerse in the cooling water tank for 10 ± 1 minutes; The cooling water in the cooling water tank is at a temperature of 50±5℃ and is in a state of no circulation and no stirring.

7. The flexible ultrathin glass processing method according to claim 1, characterized in that, In step S4 The parameters of the chemical strengthening treatment include: a preheating temperature of 360℃ and a preheating time of 29-31 minutes; the strengthening solution is composed of potassium nitrate with a mass fraction of 99.5% and silica with a mass fraction of 0.4-0.6%, with a volume ratio of 1:1; the strengthening temperature is 380-410℃ and the strengthening time is 20 minutes.

Images