Alkali etching process for glass and its applications

Abstract

This is an alkaline etching process for glass, and the technical process involves immersing a glass substrate in an alkaline etching solution. The alkaline etching solution is a 40% to 56% concentration sodium hydroxide solution, the temperature of the alkaline etching solution is 100 to 130°C, and the immersion time is 100 to 300 minutes. The alkaline etching process for glass can be used for thinning glass and anti-glare treatment of glass surfaces, and can also be used to remove the convex points of the uneven micro-nanopoints of anti-glare glass to achieve a non-sparkle effect or a low-sparkle effect. By selecting sodium hydroxide (caustic soda) from the two major industrial alkalis and changing from acid etching to alkaline etching, the etching accuracy of ultrathin electronic glass is improved and manufacturing costs are reduced. In addition, since the manufacturing process does not generate fluorine-containing wastewater or hazardous waste, i.e., fluorine-containing lime sludge, environmental pollution is reduced. This process has a significant effect on environmental protection, innovation, pollution reduction, and emission reduction.

Description

Technical Field

[0001] The present invention relates to a glass etching process, and more particularly to a glass alkali etching process and its applications.

Background Art

[0002] In the field of electronic display screens, common glass processing (treatment) technologies include glass thinning (lamination) and anti-reflection (reflection reduction) treatment processes for glass. Among these, glass thinning mainly thins panel modules and display glass using chemical etching and physical polishing to meet the requirements for lighter and thinner display screens. By thinning the TFT-LCD (Thin Film Transistor Liquid Crystal Display) panel, the following advantages can be obtained in the application of the TFT-LCD panel. 1) By reducing the thickness of the glass panel using chemical or physical methods, a thinner panel can be obtained. 2) The total weight of the display screen is reduced, and a clearer and brighter image quality can be achieved. 3) Space is saved by reducing the total thickness of the TFT-LCD module. For example, more space is secured to increase the battery capacity. 4) By thinning the glass substrate, a certain degree of flexibility is obtained, making it possible to manufacture foldable or curved display screens to improve the visual effect. The thinning process of TFT-LCD glass includes a sealing process, a thinning process by etching, and a polishing process. The anti-reflection (reflection reduction) treatment process for the glass surface may include three types of AG (Anti-Glare) processes, namely, those by etching, spray coating, and film coating. Among these, the AG process by etching is a chemical etching process. Even after such an AG treatment by etching, the treated surface remains the glass surface, so the product is not only less likely to be scratched but also has good transmittance and high image sharpness. Therefore, glass products subjected to the AG process by etching are widely recognized as mainstream AG glass products in the market.

[0003] Currently, the mainstream etching techniques used in the aforementioned glass thinning and etching AG processes involve the use of hydrofluoric acid (HF) chemical solutions. These solutions etch the glass substrate by dissolving the silica (silicon dioxide) through a chemical reaction between HF and silica on the substrate surface. Hydrofluoric acid is known to be extremely corrosive, highly irritating, and poses fluorine-related hazards. Improper use of HF can cause burns to the human body. Inhaling high concentrations of HF vapor can cause bronchitis and hemorrhagic pulmonary edema. HF vapor can also be absorbed through the skin, potentially causing severe poisoning. Therefore, acid etching processes that primarily use HF require higher standards regarding the safety and ventilation of the etching environment. Furthermore, improper handling of HF wastewater can lead to leachate into the soil, causing serious contamination. Excessive discharge of fluorine-containing wastewater can result in serious water environmental accidents. Hydrofluoric acid wastewater is typically neutralized with lime to meet discharge standards. While the process of stirring, coagulation, precipitation, and subsequent neutralization is simple, it generates large amounts of harmful fluorine-containing lime sludge, increasing the cost of hazardous waste disposal and the environmental burden. Furthermore, due to the strong permeability of hydrofluoric acid and mixed acid solutions, the etching rate of glass is very fast, resulting in very short etching times. Therefore, precisely thinning ultrathin glass in such a short time is difficult. It is also difficult to precisely control parameters such as surface roughness, haze, gloss, transparency, clarity, and DOI (image clarity), making it challenging to produce low-sparkle glass essential for high-resolution display images used in fields such as automobiles, mobile phones, computers, and industrial automation. Additionally, acid-etched glass surfaces tend to be relatively dark and not sufficiently clean. Given these circumstances, there is a need to develop safer and more environmentally friendly chemical etching processes to replace acid etching. [Overview of the project]

[0004] According to a first aspect of the present invention, the present invention provides a glass alkali etching process.

[0005] A technical solution provided by a first aspect of the present invention is a glass alkali etching process comprising the step of immersing a glass substrate in an alkali etching solution, wherein the alkali etching solution is a sodium hydroxide solution having a concentration of 40% to 56%, the temperature of the alkali etching solution is 100°C to 130°C, and the glass substrate is immersed in the alkali etching solution for 100 to 300 minutes.

[0006] Furthermore, the alkaline etching solution is stirred while the glass substrate is immersed in it. Stirring the alkaline etching solution increases the fluidity of the high-temperature alkaline etching solution in the furnace, ensuring a uniform temperature during immersion of the glass substrate in the alkaline etching solution, thereby resulting in more uniform etching and a glossy alkaline-etched surface. When applied to anti-glare processing of glass, it can make the height of the surface irregularities more uniform.

[0007] Furthermore, the glass substrate is pre-treated by sandblasting, partial sandblasting, laser engraving, or frosting. The glass alkali etching process of the present invention achieves both glare-preventing surface treatment and improved transparency in a sandblasted or partially sandblasted glass substrate.

[0008] Furthermore, the concentration of the sodium hydroxide solution is 46% to 55%. After sandblasting, the surface of the glass substrate is rough, white, and cloudy, which affects the transmittance of the glass substrate and the clarity of the final display screen. Also, such a surface is prone to dirt that is difficult to wipe off during use. Therefore, the glass etching process is necessary to remove the cloudy appearance on the rough surface. The glass needs to retain the anti-glare and anti-reflective properties of the roughened surface formed by sandblasting or laser engraving, while at the same time, the roughened surface needs to be made transparent and the protrusions created by sandblasting smoothed out in order to make the displayed image clearer. Alkali etching provides a smoother, whiter, and more glossy anti-glare glass product than that obtained by acid etching.

[0009] Furthermore, a partially sandblasted glass substrate has at least one transparent area before sandblasting, which does not require anti-glare treatment, and this at least one transparent area is printed with an alkali-inresistant protective ink before sandblasting. When the glass substrate enters the alkaline etching furnace, the printed protective ink automatically peels off because it is not resistant to alkali, exposing the at least one transparent area. Since the alkaline etching solution etches the glass substrate and removes the protective ink at the same time, no additional removal steps are required, streamlining the alkaline etching process and reducing manufacturing costs.

[0010] According to a second aspect of the present invention, the present invention provides an application for the glass alkali etching process.

[0011] A technical solution provided in a second aspect of the present invention is a method for smoothing microscale and nanoscale protrusions on the uneven surface of glare-preventing glass, a method for thinning a glass substrate with a thickness of less than 1 mm, or a method for thinning a glass substrate with a thickness of less than 0.2 mm, by using the glass alkali etching process described above.

[0012] The glass alkali etching process provided in this invention can be applied to both glass thinning and surface glare prevention (anti-glare) treatment. This invention selects sodium hydroxide (caustic soda), one of the two major industrial alkalis, and replaces conventional acid etching with alkali etching. This improves the etching accuracy of ultrathin electronic glass, reduces manufacturing costs, and minimizes the amount of dissolved glass (sodium silicate) in the alkali etching solution. Compared to alkali wastewater generated in industries such as textiles, papermaking, and metals, the waste alkali solution produced after immersing glass in an alkali etching solution is far cleaner. The alkali wastewater generated from the glass alkali etching process of this invention can be reused as a raw material for the production of sodium silicate (water glass) by a wet process, or as an alkali neutralizer in wastewater treatment plants. This eliminates the generation of fluorine-containing wastewater and harmful fluorine lime sludge, reduces environmental pollution, and provides significant and innovative environmental benefits in reducing waste discharge.

[0013] The sodium hydroxide solution used in the alkaline etching process described in this invention reacts more slowly than the acids used in conventional acid etching processes, making it easier to control the thickness of the glass substrate obtained in the glass thinning process. Therefore, it is particularly suitable for thinning glass with a thickness of less than 1 mm, especially ultra-thin glass with a thickness of less than 0.2 mm. Furthermore, when used for glare prevention treatment of glass substrates, the alkaline etching process can improve the transparency and transmittance of the glass substrate by removing the milky white layer created by sandblasting on the frosted glass surface of the glass substrate to be treated, which has microscale or nanoscale indentations and holes (fine indentations and holes), and making the milky white layer transparent. By precisely adjusting the concentration of the alkaline etching solution and the immersion time, millions of transparent fine indentations and holes can be preserved. This allows for suppression and control of the internal brightness of the LCD screen while maintaining the diffuse reflection effect, resulting in the achievement of an optimal DOI value for the display screen. In this art, it is known that a higher DOI value for a display screen is not always better. Rather, it needs to be adjusted according to the internal brightness of high-resolution (HD) displays such as 4K, 5K, and 8K. To find the optimal balance between diffuse reflection and internal reflection, the pixel variation of the HD display, the depth of the fine indentations and holes in the easy-to-write AG glass, and the Hz frequency are taken into consideration. This ultimately determines the DOI value. The alkaline etching process described in this invention provides excellent conditions for controlling and adjusting the above parameters because it has a slow reaction rate and allows for high-precision adjustment. By precisely adjusting the concentration, temperature, and immersion time of the alkaline etching solution, protrusions on the uneven glass surface with fine indentations and holes can be reduced in height or smoothed out, thereby reducing snowflake-like sparkle defects caused by high, raised protrusions. This achieves a low-sparkle or non-sparkle effect on the resulting display screen.In summary, the alkaline etching process produces glare-free glass products with smoother, brighter, cleaner, and more transparent surfaces compared to products manufactured using conventional acid etching. [Modes for carrying out the invention]

[0014] [Example 1] The glass alkali etching process includes the step of immersing a partially sandblasted glass substrate in an alkaline etching solution, the alkaline etching solution being a 40% concentration sodium hydroxide solution, the temperature of the alkaline etching solution being 120°C, and the glass substrate being immersed in the alkaline etching solution for 300 minutes, during which time the alkaline etching solution is stirred.

[0015] Furthermore, the glass substrate has at least one transparent area that does not require anti-glare treatment, and this at least one transparent area is printed with alkali-resistant protective ink.

[0016] [Examples 2-8] Examples 2-8 follow the same process as Example 1, but with differences in process parameters. Specific parameters are shown in Table 1. Table 1 also shows Comparative Examples 1-3, as well as the haze, gloss, DOI (image clarity), and sparkle values ​​for each example and comparative example of the present invention. Sparkle values ​​were tested using the SMS-1000 sparkle evaluation system.

[0017] [Table 1]

[0018] As can be seen from Table 1, Examples 1 to 8 involve alkaline etching of a glass substrate to which the same sandblasting or partial sandblasting process is applied, using process parameters as disclosed in the present invention. The resulting products have high gloss and low sparkle values ​​and are therefore suitable for the manufacture of HD display screens. HD display devices processed in this way achieve brighter and more uniform brightness and achieve a sparkle-preventing effect, as the human eye cannot perceive sparkles at the focal point. In contrast, the products obtained from Comparative Examples 1 to 3 have low gloss and high sparkle values ​​and low transparency, are defective, and do not meet the standards.

[0019] In an example of the present invention, an alkali-resistant protective ink is printed on at least one transparent area of ​​a glass substrate that does not require anti-glare treatment. The alkaline etching solution performs etching and ink removal simultaneously on the glass substrate, eliminating the need for additional removal steps. This simplifies the process of the present invention and reduces manufacturing costs. The glass substrate obtained by the alkaline etching process can be further processed for the creation of dials, positioning markers, speaker grilles, and camera holes, among others.

[0020] The present invention also provides examples of applying a glass alkali etching process to glass thinning. Specifically, these are as follows:

[0021] [Example 9] The glass alkali etching process includes the step of immersing a glass substrate in an alkaline etching solution, the alkaline etching solution being a 40% concentration sodium hydroxide solution, the temperature of the alkaline etching solution being 120°C, and the glass substrate being immersed in the alkaline etching solution for 300 minutes, during which time the alkaline etching solution is stirred.

[0022] [Examples 10-13] Examples 10 to 13 follow the same process as Example 9, but there are differences in the process parameters. The specific parameters are shown in Table 2. Table 2 also shows the change in the thickness of the glass substrate before and after alkali etching.

[0023]

Table 2

[0024] As shown in Table 2, Examples 9 to 13 demonstrate that within the disclosed ranges of sodium hydroxide solution concentration, immersion temperature, and immersion time, the alkali etching process described in the present invention can replace the conventional acid etching process for thinning the glass substrate. This meets the requirements for lighter and thinner display products. By adjusting the concentration of the alkali etching solution, the immersion time of the glass substrate in the alkali etching solution, and the heating temperature of the alkali etching solution, the thickness of the thinned glass substrate and the thinning efficiency of the glass substrate can be controlled.

[0025] In the alkali etching process of the present invention, since the amount of glass material (sodium silicate) dissolved in the alkali etching solution after thinning is very small, the alkali waste liquid generated after immersion of the glass substrate is much cleaner compared to the alkali waste liquid generated in industries such as fiber, papermaking, and metal. The alkali waste liquid generated from the glass alkali etching process of the present invention can be reused as a raw material for the production of sodium silicate (water glass) by a wet method or as an alkali neutralizer in a wastewater treatment plant. This eliminates the generation of fluorine-containing wastewater and harmful fluorine lime sludge, reduces environmental pollution, and realizes important and innovative environmental advantages in reducing waste emissions. In the future, if the acid etching process is gradually replaced by the alkali etching process and the alkali waste liquid is reused for the production of sodium silicate, the factory can achieve waste-free production and bring significant positive environmental impacts on environmental and waterway protection.

[0026] The alkaline etching solution described in this invention is a sodium hydroxide solution having a concentration of 40% to 56%. If the concentration of the sodium hydroxide solution is lower than 40%, the immersion time will be excessively long. If the concentration exceeds the saturation concentration of 56%, a safety risk arises during operation. The temperature of the alkaline etching solution is set between 100°C and 130°C. If the temperature of the alkaline etching solution is too low, thinning cannot be effectively achieved, and if the process includes removing the milky frosted surface of the glass substrate during the anti-glare treatment, a temperature that is too low will result in a longer processing time, and prolonged immersion of the glass substrate in the alkaline etching solution will degrade the appearance of the glass. If the temperature of the alkaline etching solution is too high, the alkaline etching solution will boil and evaporate into the air, posing a significant safety risk during manufacturing. Within the concentration and temperature ranges of the alkaline etching solution described in this invention, the immersion time for chemical etching should not exceed 100 to 300 minutes. If the immersion time is too short, etching will be insufficient, and the appearance and specifications of the final product will not meet the standards. If the etching time is too long, the alkaline etching solution will excessively corrode the product surface, resulting in a poor appearance.

[0027] The above description is merely an example of the present invention and does not limit its scope. Any process modification that achieves equivalent technical effects, or any direct or indirect application of the present invention in other related technical fields, are also included within the scope of protection of the present invention.

Claims

1. A glass alkali etching process comprising immersing a glass substrate in an alkaline etching solution, wherein the alkaline etching solution is a sodium hydroxide solution having a concentration of 40% to 56%, the temperature of the alkaline etching solution is 100°C to 130°C, and the glass substrate is immersed in the alkaline etching solution for 100 to 300 minutes.

2. The glass alkali etching process according to claim 1, wherein the alkaline etching solution is stirred while the glass substrate is immersed in the alkaline etching solution.

3. The glass alkali etching process according to claim 1, wherein the glass substrate is pre-treated by sandblasting, partial sandblasting, laser engraving, or frosting.

4. The glass alkali etching process according to claim 3, wherein the concentration of the sodium hydroxide solution is 46% to 55%.

5. The glass alkali etching process according to claim 3, wherein the glass substrate that has been partially sandblasted has at least one transparent region before sandblasting, the at least one transparent region is a region that does not require anti-glare treatment, and the at least one transparent region is printed with an alkali-inresistant protective ink before sandblasting.

6. A method for thinning a glass substrate with a thickness of 1 mm or less, comprising the glass alkali etching process described in claim 1.

7. A method for thinning a glass substrate with a thickness of 0.2 mm or less, comprising the glass alkali etching process described in claim 1.

8. A method for smoothing microscale or nanoscale protrusions on the uneven surface of glare-preventing glass, comprising the glass alkali etching process described in claim 1.

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