A secondary chemically strengthened ufg glass and a method of making the same

Abstract

This invention discloses a secondary chemically strengthened UFG glass and its preparation method, relating to the field of ultrathin flexible glass technology. The secondary chemically strengthened UFG glass, by molar percentage, comprises the following raw materials: SiO2: 59.85%~69.43%, Al2O3: 11.81%~18.45%, Na2O: 7.5%~10.48%, Li2O: 6.7%~9.0%, B2O3: 0~3.7%, MgO: 0~3.65%, P2O5: 0~4.59%, and SnO2: 0.9%. After the UFG glass undergoes two chemical strengthening processes, the volume expansion rates of the first and second regions of the UFG glass, which have varying thicknesses, are equal. This avoids problems such as distortion, deformation, and wrinkles that easily occur in the strengthened cover glass, improving the yield and facilitating large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of ultrathin flexible glass technology, specifically relating to a secondary chemically strengthened UFG glass and its preparation method. Background Technology

[0002] With the rapid development of the 5G era, single-screen phones can no longer meet the high-end needs of users, while foldable, portable dual-screen and multi-screen phones are gaining increasing popularity among consumers. To protect the flexible screen of foldable phones and extend its lifespan, a cover glass is usually added to the screen surface. Currently, in addition to ultra-thin glass of equal thickness (UTG), flexible cover glass also includes unequal thickness cover glass (UFG). UFG adopts a structure that is thin in the middle and thick on both sides, which can effectively reduce the local stress concentration generated when the flexible screen is folded, making the crease smoother, improving screen durability, and reducing the risk of functional failure due to external factors such as damage, scratches, or minor drops, thereby expanding application scenarios.

[0003] However, during chemical strengthening of UFG glass, its uneven thickness and significant differences in expansion across different regions lead to problems such as distortion, deformation, and wrinkling in the strengthened cover glass. This is primarily because traditional chemical strengthening processes struggle to precisely control the ion exchange process across different thickness regions, resulting in uneven stress distribution within the glass. Furthermore, current technologies lack specific strengthening process designs tailored to the unique structure of UFG glass, failing to guarantee a consistent volume expansion rate across different thickness regions during strengthening, severely impacting product flatness and yield. These technological deficiencies not only restrict the application of UFG glass in high-end foldable screen devices but also hinder the large-scale development of related industries. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a secondary chemically strengthened UFG glass and its preparation method, so as to solve the technical problem that in the prior art, the uneven thickness of this type of glass during the chemical strengthening process leads to significant differences in the amount of expansion in different regions, which in turn causes the strengthened cover plate to warp and wrinkle.

[0005] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a secondary chemically strengthened UFG glass, the raw materials of which, by molar percentage, include: SiO2: 59.85%~69.43%, Al2O3: 11.81%~18.45%, Na2O: 7.5%~10.48%, Li2O: 6.7%~9.0%, B2O3: 0~3.7%, MgO: 0~3.65%, P2O5: 0~4.59%, and SnO2: 0.9%; wherein, the molar percentage ratio of (Li2O+Na2O+MgO+P2O5) / Al2O3 is 1.12~1.60, and the molar percentage ratio of (Na2O+Li2O) / (SiO2+Al2O3+B2O3) is 0.18~0.24.

[0006] A further improvement of the present invention is that the UFG glass includes two symmetrically arranged first regions and a second region, the first regions being located at both ends of the UFG glass and the second region being located at the middle of the UFG glass.

[0007] A further improvement of the present invention is that the thickness of the first region is 60~100μm and the thickness of the second region is 25~40μm.

[0008] Secondly, the present invention also provides a method for preparing secondary chemically strengthened UFG glass, comprising the following steps: S1: Weigh the raw materials according to the ratio, mix, melt and shape the raw materials in sequence to obtain UFG glass substrate; S2: The UFG glass substrate is pretreated and preheated, and then chemically strengthened in the first molten salt to obtain a chemically strengthened UFG glass. S3: Spray an acid-resistant ink protective layer onto the second region of the first chemically strengthened UFG glass, then preheat it, then perform a second chemical strengthening in the second molten salt, and finally perform annealing treatment to obtain the second chemically strengthened UFG glass.

[0009] A further improvement of the present invention is that the pretreatment in S2 includes: ultrasonically cleaning the UFG glass substrate sequentially in a sodium hydroxide solution with a concentration of 5~10wt%, an oxalic acid solution, and a deionized solution; the ultrasonic cleaning temperature is 25~60℃ and the frequency is 40~120kHz.

[0010] A further improvement of the present invention is that the preheating temperature in S2 is 300~400℃.

[0011] A further improvement of the present invention is that the first molten salt used in the first chemical strengthening treatment in S2 includes NaNO3 and KNO3, wherein the mass percentage of NaNO3 is 90%~100% and the mass percentage of KNO3 is 0%~10%; the temperature of the first chemical strengthening is 380~460℃ and the time is 5~60min.

[0012] A further improvement of the present invention is that the second molten salt used in the second chemical strengthening treatment in S3 includes NaNO3 and KNO3, wherein the mass percentage of NaNO3 is 0%~50% and the mass percentage of KNO3 is 50%~100%; the temperature of the second chemical strengthening is 380~460℃ and the time is 5~60min.

[0013] A further improvement of the present invention is that the acid-resistant protective layer sprayed in S3 is an ink layer.

[0014] A further improvement of the present invention is that the annealing process in S3 is carried out at a cooling rate of 2~10℃ / min to 70~150℃.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a secondary chemically strengthened UFG glass, in which SiO2 and Al2O3, as glass network forgers, jointly construct a stable framework structure, which is key to improving the mechanical strength of the glass. The alkali metal oxides Na2O and Li2O in the composition not only help to lower the melting temperature and viscosity of the glass, but more importantly, Na2O provides the foundation for the ion exchange process in subsequent chemical strengthening. Specific ratios of (Li2O+Na2O+MgO+P2O5) / Al2O3 (1.12~1.60) and (Na2O+Li2O) / (SiO2+Al2O3+B2O3) (0.18~0.24) ensure smooth ion exchange channels, facilitating the formation of a deeper ion exchange layer, thereby significantly improving the strengthening effect and impact resistance of the glass. Furthermore, the introduction of B2O3 and P2O5 helps prevent glass crystallization, lowers the liquidus temperature, and makes the glass structure moderately porous; SnO2, as a clarifying agent, improves the light transmittance of the glass. The UFG glass prepared after adjusting the composition and proportion, combined with a specific secondary chemical strengthening process, can coordinate the volume expansion behavior of different thickness areas of the glass during the strengthening process. The purpose is to make the volume expansion rate of the first and second areas with different thicknesses in the final product equal. This helps to avoid the problem of uneven stress distribution caused by thickness differences, thereby improving the flatness and yield of the product.

[0016] This invention also provides a method for preparing UFG glass with secondary chemical strengthening. The method involves first chemically strengthening the entire glass to achieve basic strength, then applying an acid-resistant ink coating to the second region for protection, followed by a second chemical strengthening. By coordinating the ion exchange process in regions of different thicknesses, the method balances the differences in volume expansion rates that may occur due to variations in thickness. This method effectively avoids the distortion, deformation, and wrinkling that easily occur in the thickness transition zone of unequal-thickness glass in traditional processes, thus improving product flatness and yield. Attached Figure Description

[0017] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components of the invention.

[0018] Figure 1 This is a schematic flowchart of the preparation method of chemically strengthened UFG glass in this invention; Figure 2 This is a schematic cross-sectional view of the chemically strengthened UFG glass in this invention.

[0019] Among them: 1. First region; 2. Second region. Detailed Implementation

[0020] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0021] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0022] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0023] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0024] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0025] In existing technologies, when foldable screen cover glass uses a non-uniform thickness structure, the uneven volume expansion in different areas during the chemical strengthening process due to thickness differences leads to glass warping and surface wrinkling. Traditional chemical strengthening processes cannot effectively regulate the ion exchange rate in different thickness areas, resulting in low product yield and hindering the large-scale application of non-uniform thickness cover glass.

[0026] To address the aforementioned issues, researchers discovered that the composition ratio of the glass matrix directly affects the migration rate of alkali metal ions during ion exchange. By adjusting the ratio of specific oxides, the volume expansion behavior of regions with different thicknesses can be controlled. Based on this, a method was proposed to achieve a coordinated expansion balance in regions of different thicknesses during the strengthening process by limiting the content range of key components and specific molar ratio parameters.

[0027] This invention provides a secondary chemically strengthened UFG glass, the raw materials of which, by molar percentage, include: SiO2: 59.85%~69.43%, Al2O3: 11.81%~18.45%, Na2O: 7.5%~10.48%, Li2O: 6.7%~9.0%, B2O3: 0~3.7%, MgO: 0~3.65%, P2O5: 0~4.59%, and SnO2: 0.9%; wherein, the molar percentage ratio of (Li2O+Na2O+MgO+P2O5) / Al2O3 is 1.12~1.60, and the molar percentage ratio of (Na2O+Li2O) / (SiO2+Al2O3+B2O3) is 0.18~0.24.

[0028] In this process, SiO2, as a network formant, ensures the stability of the glass structure within its content range; fused silica can be used as the main raw material. Al2O3, as a network intermediate, adjusts the glass viscosity and ion diffusion rate within its content range; alumina powder can be used as the raw material. Na2O and Li2O, as alkali metal oxides, control the alkali metal ion concentration gradient during ion exchange within their content range; sodium carbonate and lithium carbonate can be used as the raw materials. B2O3, MgO, and P2O5, as auxiliary components, fine-tune the glass's thermal expansion coefficient within their content range; boric acid, magnesium oxide, and phosphate can be used as the raw materials. SnO2, as a clarifying agent, eliminates bubble defects during glass melting within its fixed content; tin oxide powder can be used as the raw material. The controlled ratio of Li2O+Na2O+MgO+P2O5 to Al2O3 ensures sufficient network modifier content and maintains appropriate glass network openness. The ratio of Na2O+Li2O to SiO2+Al2O3+B2O3 can be controlled to balance the relationship between the total amount of alkali metal ions and the density of the network structure.

[0029] In some embodiments, such as Figure 2 As shown, the chemically strengthened UFG glass includes a first region 1 and a second region 2. The first region 1 is located at both ends of the chemically strengthened UFG glass, and the second region 2 is located in the middle of the chemically strengthened UFG glass. The thickness of the first region 1 is 60-100 μm, and the thickness of the second region 2 is 25-40 μm. The first region 1 refers to the epitaxially distributed support region in the glass structure, which can be achieved by adjusting the chemical strengthening process parameters. The thicker structure in this region helps to enhance the mechanical strength of the edge areas. The second region 2 refers to the core region in the glass structure that bears bending deformation, which can be achieved by controlling the temperature gradient during melting and forming. The thinner structure in this region helps to reduce stress concentration during folding.

[0030] In some embodiments, the UFG glass undergoes chemical strengthening treatment, and the volume expansion rates of the first and second regions are equal. Equal volume expansion rates mean that regions of different thicknesses experience consistent volume changes due to ion exchange during the strengthening process. This can be achieved by matching the salt bath ratios and process parameters of the two chemical strengthening treatments, thereby offsetting the expansion deviations caused by thickness differences.

[0031] Furthermore, the UFG glass has a transmittance of not less than 90%, a bending radius of not more than 0.7 mm, a static bending life of not less than 500,000 cycles, a pen impact height of not less than 45 cm, and a surface hardness of not less than 5H.

[0032] like Figure 1As shown, the present invention also provides a method for preparing UFG glass with secondary chemical strengthening, comprising the following steps: weighing raw materials, mixing, melting and molding the raw materials sequentially to obtain UFG glass; subjecting the UFG glass to pretreatment, preheating and first chemical strengthening treatment sequentially to obtain UFG glass with primary chemical strengthening; spraying acid-resistant ink onto the second region of the first chemically strengthened UFG glass, and then subjecting it to preheating, second chemical strengthening treatment and annealing treatment sequentially to obtain UFG glass with secondary chemical strengthening.

[0033] The pretreatment process involves cleaning impurities from the glass surface using chemical solutions, specifically ultrasonic cleaning with sodium hydroxide alkaline solution, oxalic acid solution, and deionized water. This process removes surface contaminants, enhancing the subsequent strengthening effect. The first chemical strengthening treatment involves replacing lithium ions on the glass surface with sodium ions. This is achieved by treating the glass with a salt bath containing 90%-100% NaNO3 and 0%-10% KNO3 at 380-460℃ for 5-60 minutes, controlling the sodium ion penetration depth to form an initial compressive stress layer. Acid-resistant ink spraying applies a protective layer to the intermediate area using an ink coating process. This coating prevents molten salt from contacting the intermediate area, thus regulating the ion exchange range. The second chemical strengthening treatment involves replacing surface sodium ions with potassium ions. This is achieved by treating the glass with a salt bath containing 0%-50% NaNO3 and 50%-100% KNO3 at 380-460℃ for 5-60 minutes, further increasing surface compressive stress. Annealing refers to eliminating residual stress by cooling at a rate of 2-10℃ / min, which can be achieved by gradient cooling to 70-150℃ to ensure the stability of the glass structure.

[0034] By combining phased chemical strengthening with regional selective protection, after establishing the basic stress distribution in the first strengthening stage, an acid-resistant coating is applied to the thinner central area to limit its ion exchange capacity. Subsequently, in the second strengthening stage, the stress level of the thicker areas on both sides is enhanced. This regional differentiated treatment makes the volume expansion of different thickness areas tend to be balanced, thereby avoiding stress imbalance caused by thickness differences. Through the above technical solution, this application solves the problem of deformation after strengthening of UFG glass due to uneven thickness, achieving a balance between the expansion of the thinner central area and the thicker side areas, effectively suppressing wrinkles and warping on the glass surface. This preparation method, by combining staged strengthening with regional protection, improves the process controllability of chemical strengthening, resulting in finished glass with uniform stress distribution and stable structural morphology, providing a reliable technical path for the large-scale production of UFG glass for foldable devices.

[0035] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0036] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0037] Examples of the preparation method of the secondary chemically strengthened UFG glass of the present invention: Examples 1-20 all provide UFG glasses with secondary chemical strengthening. The preparation method of the UFG glass with secondary chemical strengthening includes the following steps: S1: Weigh the raw materials according to the ratio, mix, melt and shape the raw materials in sequence to obtain UFG glass substrate; S2: The UFG glass substrate is pretreated and preheated, and then chemically strengthened in the first molten salt to obtain a chemically strengthened UFG glass. S3: Spray an acid-resistant ink protective layer onto the second region of the first chemically strengthened UFG glass, then preheat it, then perform a second chemical strengthening in the second molten salt, and finally perform annealing treatment to obtain the second chemically strengthened UFG glass.

[0038] The pretreatment involves ultrasonically cleaning the UFG glass sequentially in a sodium hydroxide alkaline solution, oxalic acid, and water. The ultrasonic cleaning temperature is 25–60°C, and the frequency is 40–120 kHz. The preheating temperature is 300–400°C.

[0039] The first chemical strengthening process involves a salt bath of 10%–90% NaNO3 and 0%–10% KNO3 at a temperature of 380–460°C for 5–60 minutes. A protective ink layer is applied only to the surface of the first region. The second chemical strengthening process involves strengthening the first region again (using a salt bath of 0%–50% NaNO3 and 50%–100% KNO3 at a temperature of 380–460°C for 5–60 minutes). The chemically strengthened UFG glass is then cooled to 70–150°C at a cooling rate of 2–10°C / min, and then allowed to cool naturally to room temperature. This completes the two chemical strengthening processes, yielding the target glass, i.e., the second-strengthened UFG glass.

[0040] The proportions of raw materials and the secondary chemical strengthening process of UFG glass are shown in Tables 1 and 2.

[0041] Table 1. Raw material composition ratios and chemical strengthening processes for chemically strengthened UFG glasses in Examples 1-10.

[0042] Table 2. Raw material composition ratios and chemical strengthening processes for chemically strengthened UFG glasses in Examples 11-20.

[0043] The cross-sections of the chemically strengthened UFG glasses prepared in Examples 1-20 were examined, such as... Figure 2 As shown, the chemically strengthened UFG glass includes a first region 1 and a second region 2. The first region 1 is located at both ends of the chemically strengthened UFG glass, and the second region 2 is located in the middle of the chemically strengthened UFG glass.

[0044] In the preparation process of chemically strengthened UFG glass in Examples 1-20, the expansion rate of the first region 1 and the second region 2 formed during the chemical strengthening process was detected. The expansion rate was obtained based on the volume change of the first region 1 and the second region 2, with the length and width dimensions of the volume calculated as 140mm×140mm. At the same time, the thickness of the first region 1 and the second region 2 of the prepared chemically strengthened UFG glass was detected, and the results are shown in Tables 3 and 4.

[0045] Table 3 Thickness and expansion rate of the first and second regions in Examples 1-10

[0046] Table 4 Thickness and expansion rate of the first and second regions in Examples 11-20

[0047] As can be seen from Tables 3 and 4, the thickness of the first region 1 is 60~100μm, and the thickness of the second region 2 is 25~40μm. During the chemical strengthening process of UFG glass, the volume expansion rates of the first region 1 and the second region 2 are equal; and during the preparation process, the volume expansion rates of the first region 1 and the second region 2 remain stable.

[0048] The chemically strengthened UFG glasses obtained in Examples 1-20 above were subjected to relevant performance tests.

[0049] Specifically, transmittance test: Using an Analytik Jena SPECORD 50 visible spectrophotometer, the sample is placed vertically in the optical path of the spectrophotometer, and the light transmittance of the sample to air is measured at a wavelength of 550 nm. The standard is that the transmittance is not less than 90%, then the product is considered qualified (OK).

[0050] Surface hardness test: Pencil hardness test.

[0051] Bending strength test: Shangzhun RS-N8000 universal material testing machine. During the bending strength test, a special clamping fixture is used to clamp the chemically strengthened UFG glass. The instrument moves forward step by step from top to bottom until the product is crushed. The bending radius of the product when it is crushed is recorded. This is a destructive test. The judgment standard is: if the product does not break when the bending radius is <0.7mm, the product is considered qualified (OK); otherwise, the product is considered unqualified (NG).

[0052] Static bending test: Fix both ends of the product's long side to the bending fatigue testing machine. Set the machine's reciprocating frequency to 30 times / min. Once the product reaches the bending radius, move the plate back to the starting position to complete one bending fatigue test. Then, repeat the test on the same plate. The judgment criteria are: if the product does not break after more than 500,000 static bending cycles, it is considered qualified (OK); otherwise, it is considered unqualified (NG).

[0053] The specific test results are shown in Tables 5 and 6.

[0054] Table 5 Performance test results of the chemically strengthened UFG glasses prepared in Examples 1-10

[0055] Table 6 Performance test results of the chemically strengthened UFG glasses prepared in Examples 11-20

[0056] As shown in Tables 5 and 6, the transmittance of the chemically strengthened UFG glass in Examples 1-20 of this invention is not less than 90%; the surface hardness is above 5.0H, and can reach a maximum of 5.5H; in the bending strength test, the bending radius of the products is less than 0.7mm, and can be as low as 0.52mm, which is considered qualified (OK); the impact height of the pen is above 45cm, and can reach a maximum of 54cm; the chemically strengthened UFG glass prepared in the embodiments of this invention remains unbroken after more than 500,000 static bending cycles, which is considered qualified (OK).

[0057] This demonstrates that the chemically strengthened UFG glass provided by this invention exhibits excellent performance in terms of transmittance, bending strength, pen impact resistance, surface hardness, and 500,000 static bending cycles. During the folding process, the chemically strengthened UFG glass makes it less prone to twisting, deformation, and wrinkling of glass cover plates with uneven thicknesses, thus improving the yield rate and facilitating mass production.

[0058] This invention can effectively improve the strength of flexible glass, thereby helping to overcome the destructive effect of stress concentration on the glass surface. The strengthened flexible glass has good flexibility properties such as bending or folding, and is suitable for making flexible screens and related equipment.

[0059] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A UFG glass with secondary chemical strengthening, characterized in that, The raw materials, by molar percentage, include: SiO2: 59.85%~69.43%, Al2O3: 11.81%~18.45%, Na2O: 7.5%~10.48%, Li2O: 6.7%~9.0%, B2O3: 0~3.7%, MgO: 0~3.65%, P2O5: 0~4.59%, and SnO2: 0.9%; among which, the molar percentage ratio of (Li2O+Na2O+MgO+P2O5) / Al2O3 is 1.12~1.60, and the molar percentage ratio of (Na2O+Li2O) / (SiO2+Al2O3+B2O3) is 0.18~0.

24.

2. The UFG glass with secondary chemical strengthening according to claim 1, characterized in that, The UFG glass includes two symmetrically arranged first regions and a second region. The first regions are located at both ends of the UFG glass, and the second region is located in the middle of the UFG glass.

3. The UFG glass with secondary chemical strengthening according to claim 2, characterized in that, The thickness of the first region is 60~100μm, and the thickness of the second region is 25~40μm.

4. A method for preparing secondary chemically strengthened UFG glass as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Weigh the raw materials according to the ratio, mix, melt and shape the raw materials in sequence to obtain UFG glass substrate; S2: The UFG glass substrate is pretreated and preheated, and then chemically strengthened in the first molten salt to obtain a chemically strengthened UFG glass. S3: Spray an acid-resistant ink protective layer onto the second region of the first chemically strengthened UFG glass, then preheat it, then perform a second chemical strengthening in the second molten salt, and finally perform annealing treatment to obtain the second chemically strengthened UFG glass.

5. The method for preparing a secondary chemically strengthened UFG glass according to claim 4, characterized in that, The pretreatment in S2 includes: ultrasonically cleaning the UFG glass substrate sequentially in sodium hydroxide alkaline solution, oxalic acid solution and deionized water; the ultrasonic cleaning temperature is 25~60℃ and the frequency is 40~120kHz.

6. The method for preparing a secondary chemically strengthened UFG glass according to claim 4, characterized in that, The preheating temperature in S2 is 300~400℃.

7. The method for preparing UFG glass with secondary chemical strengthening according to claim 4, characterized in that, The first molten salt used in the first chemical strengthening treatment in S2 includes NaNO3 and KNO3, wherein the mass percentage of NaNO3 is 90%~100% and the mass percentage of KNO3 is 0%~10%; the temperature of the first chemical strengthening is 380~460℃ and the time is 5~60min.

8. The method for preparing UFG glass with secondary chemical strengthening according to claim 4, characterized in that, The second molten salt used in the second chemical strengthening treatment in S3 includes NaNO3 and KNO3, wherein the mass percentage of NaNO3 is 0%~50% and the mass percentage of KNO3 is 50%~100%; the temperature of the second chemical strengthening is 380~460℃ and the time is 5~60min.

9. The method for preparing UFG glass with secondary chemical strengthening according to claim 4, characterized in that, The acid-resistant protective layer sprayed in S3 is an ink layer.

10. The method for preparing a secondary chemically strengthened UFG glass according to claim 4, characterized in that, In S3, the annealing process involves cooling the temperature to 70-150°C at a rate of 2-10°C / min.

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