Impurity removal agent for glass strengthening salt bath and application method of impurity removal agent

Abstract

The invention discloses an impurity removal agent for a glass strengthening salt bath and an application method of the impurity removal agent, and the impurity removal agent is prepared from the following components in percentage by mass: 20-75% of silicon oxide, 10-30% of aluminum oxide, 10-40% of sodium oxide and 0.5-50% of calcium oxide. The impurity removal agent can effectively reduce the concentration of P ions in molten salt, the effect is improved along with the increase of the impurity removal agent, the linear law is met, and every 300 g of the impurity removal agent can absorb about 50 ppm of P ions. Experiments prove that after a glass product is strengthened in a salt bath treated by the impurity removal agent disclosed by the invention, the surface of the glass has no undesirable phenomena such as concave and convex points.

Description

Technical Field

[0001] The present invention belongs to the field of glass manufacturing, and particularly relates to a impurity removing agent for glass strengthening salt bath and an application method thereof. Background Art

[0002] Glass-ceramics is a new type of high-strength electronic cover glass. Through the heat treatment process, hundreds of millions of crystals can grow on the back of the glass-ceramics, and the crystal size is at the nanometer level. These nanoscale crystal particles can deflect when the crack propagates, thereby increasing the crack propagation energy and reducing the probability of glass breakage. Therefore, it is increasingly favored by mobile phone manufacturers. Currently, glass-ceramics mainly uses a lithium-aluminum-silicon glass-ceramics system, and the main crystals are lithium metasilicate, lithium disilicate, spodumene, etc. Therefore, the lithium content in the glass is much higher than that of conventional high-aluminum-silicon glass. The strengthening process of lithium-aluminum-silicon glass-ceramics generally uses molten salts of sodium nitrate and potassium nitrate with different mass fractions for strengthening. As the number of strengthening times gradually increases, sodium in the molten salt exchanges with lithium in the glass, resulting in an increase in the lithium content in the salt bath. The increase in the lithium content will cause the stress parameters of the subsequent strengthened glass to decrease, thereby affecting the strength index of the glass. Regarding the control of the lithium content, a phosphate-containing solution such as TSP and TKP can be used. The lithium is precipitated by the reaction of phosphate with lithium, and then the precipitate is removed, thereby reducing the lithium content in the salt bath. However, the introduction of phosphate will pollute the salt bath, and when the phosphate in the salt bath exceeds a certain concentration, it will cause adverse phenomena such as uneven points on the glass surface. Therefore, how to remove excess phosphate impurities has become an urgent problem to be solved.

[0003] In the prior art, a method of adding silica and alumina powder is adopted, but it is not environmentally friendly in production operation, the powder is easy to fly, and the powder is easy to agglomerate and adhere to the glass, and it is also easy to form uneven points. In addition, after adding silica and alumina powder, lithium phosphate is adsorbed and precipitated at the bottom of the equipment, making it difficult to operate and remove; as the addition amount continues to increase, the precipitate accumulates at the bottom of the strengthening furnace, resulting in a shortened service life of the strengthening molten salt. Summary of the Invention

[0004] The present invention aims to provide an impurity removing agent for glass strengthening salt bath and an application method thereof to remove excessive P ions in the salt bath, thereby improving the purity of the salt bath and overcoming the problem that uneven points are easily formed on the surface of glass products. The specific technical solution of the present invention is: an impurity removing agent for glass strengthening salt bath, calculated by mass fraction, the impurity removing agent is composed of 20-75% of silicon oxide, 10-30% of aluminum oxide, 10-40% of sodium oxide and 0.5-50% of calcium oxide.

[0005] Further, the finished product form of the impurity removing agent is powder or sheet or strip.

[0006] Further, the preparation method of the powdery impurity remover is as follows: First, mix 20-75 wt% of silicon oxide, 10-30 wt% of aluminum oxide, 10-40 wt% of sodium oxide, and 0.5-50 wt% of calcium oxide evenly. After drying, place them in a platinum or corundum crucible, heat to 1300-1600 °C to melt the raw materials. Quench the melted raw materials, grind the quenched products, and finally dry the obtained powder.

[0007] Further, the preparation method of the flaky impurity remover is as follows: First, mix 20-75 wt% of silicon oxide, 10-30 wt% of aluminum oxide, 10-40 wt% of sodium oxide, and 0.5-50 wt% of calcium oxide evenly. After drying, place them in a platinum or corundum crucible, heat to 1300-1600 °C to melt the raw materials. Cool the high-temperature glass liquid to near the Ts softening point, roll it into a thin sheet using a shaft roller, and then quickly cool the thin sheet to form a flaky material with a porous surface.

[0008] Further, the preparation method of the strip-shaped impurity remover is as follows: First, mix 20-75 wt% of silicon oxide, 10-30 wt% of aluminum oxide, 10-40 wt% of sodium oxide, and 0.5-50 wt% of calcium oxide evenly to obtain raw material A. Then mix raw material A with 10-40 wt% of an organic resin based on raw material A, and then cast and form it into a strip. Then sinter and degrease the strip at a high temperature of 1000-1200 °C to form the required impurity remover.

[0009] Furthermore, the organic resin is polyvinyl alcohol, polyvinyl butyral, acrylic resin, cellulose resin (such as methyl cellulose, ethyl cellulose, etc.), polycarbonate alkylene ester, etc.

[0010] Preferably, the particle size of the prepared powdery impurity remover is 0.85-10 mm, and the porosity of the surface is 20-40%.

[0011] Preferably, the thickness of the prepared flaky impurity remover is 0.3-2 mm, and the width is 10-100 mm; the porosity of the surface is 20-40%.

[0012] Preferably, the thickness of the prepared strip-shaped impurity remover is 0.1-2 mm, and the width is 10-300 mm; the porosity of the surface is 20-50%.

[0013] For the application method of the impurity remover of the above glass strengthening salt bath, add the impurity remover to the high-temperature salt bath and leave it for no less than 0.5 hours. Preferably, the time for the impurity remover to be placed in the salt bath is 0.5-10 hours.

[0014] Further, the relationship n between the added mass m of the impurity remover and the change content of P ions in the salt bath is: n = 0.147×m, where the unit of m is grams; n is the change concentration of P ions in the salt bath, with the unit of ppm, specifically referring to the concentration at which the expected P ion concentration decreases. For example, if the initial concentration of P ions in the salt bath is 200 ppm and it is expected to drop to 20 ppm, then n is 180 ppm at this time.

[0015] Furthermore, when the added impurity remover is in the form of powder, sheet or strip, it is loaded into the high-temperature salt bath using a stainless steel wire cage.

[0016] The present invention provides a new type of impurity remover that can effectively reduce the concentration of P ions in the molten salt, and the effect improves as the amount of the impurity remover increases, following a linear pattern. Every 300 g of the impurity remover can absorb approximately 50 ppm of P ions. Judging from the main components, it is considered that the main component in the impurity remover is CaO. Based on the compounds of P ions and Ca elements, it is speculated that during the process, phosphate radicals chemically react with CaO in the impurity remover to form calcium phosphate. The specific reaction equation is as follows: 2PO4 3- +3Ca 2+ =Ca3(PO4) 2 In addition, since substances such as CaO cannot be directly added to the molten salt because the powdered CaO raw material cannot directly react with P ions in the molten salt to form a precipitate, and its powder is easily suspended in the molten salt, which will cause adverse concave and convex point impurities to adhere to the glass surface quality. The present invention uses a water quenching method to make the impurity remover into a powdered form, or other methods to make it into a sheet or strip form, overcoming the disadvantages of easy suspension and easy flying after the powder is directly added. The prepared impurity remover has more pores on the surface, increasing the contact area and improving the reaction efficiency, which plays a certain role in the absorption of P ions. By adding a sufficient amount of the impurity remover, the P ions in the salt bath can be reduced to the expected value. It has been experimentally confirmed that after the glass products are strengthened in the salt bath treated with the impurity remover of the present invention, there are no adverse phenomena such as concave and convex points on the glass surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 SEM photograph of the glass after strengthening treatment in a salt bath containing high-concentration P ions (surface concave points); Figure 2 SEM photograph of the glass after strengthening treatment in a salt bath containing high-concentration P ions (surface convex points); Figure 3 SEM photograph of the glass after strengthening treatment in the salt bath after impurity removal. EMBODIMENTS Example 1

[0018] First, prepare the ion impurity remover according to the following steps: Step 1, raw material preparation: Weigh by mass fraction: SiO2: 40%, Al2O3: 10%, Na2O: 40%, CaO: 10%. Mix them evenly, dry and place them in a clean platinum or corundum crucible. Step 2, set the target temperature of the electric furnace, the temperature is 1300 - 1600 °C. Place the crucible containing the raw material powder in the electric furnace, heat it up to the target temperature, and maintain the temperature for 1 - 10 hours to completely decompose and melt the raw materials. Then pour the raw materials into a water tank filled with cold water at high temperature for quenching. Step 3, collect and dry the quenched powder, sieve it through a 20 - mesh sieve to obtain an impurity remover with a particle size of about 0.85 - 10 mm and a porosity of 20 - 40%. Store it in a dry environment.

[0019] The application method of the ion impurity remover of the present invention can adopt the following steps: Step 1, salt bath preparation: The salt bath is a mixed salt containing a certain proportion of sodium nitrate and potassium nitrate. The molten salt can be a single pure salt, such as pure sodium nitrate or pure potassium nitrate; it can also be a mixed salt, where the proportion of sodium nitrate is 10 - 50 wt%, and the proportion of potassium nitrate is 50 - 90 wt%. In addition, a certain amount of lithium nitrate needs to be added to the salt bath to ensure the ion exchange rate. The temperature of the salt bath can be set to 350 - 500 °C.

[0020] Step 2, introduction of phosphate: Add a certain mass of trisodium phosphate, tripotassium phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, etc. to simulate the enrichment of phosphorus elements in the molten salt.

[0021] Step 3, weigh the ion impurity remover powder, sheet or strip according to a certain mass, then load it into a stainless - steel wire cage and add it to the high - temperature salt bath. Remove it after placing for a period of time. Step 4, use ICP means to analyze the concentration changes of each ion before and after the salt bath process to obtain the adsorption situation of the ion impurity remover for phosphate ions.

[0022] First, test the removal effect of the impurity remover prepared in this example on high - concentration p ions: Load the prepared impurity remover into a stainless - steel wire cage and add it to the high - temperature salt bath. Remove the excessive p ions in the salt bath after placing for a period of time. Take 300 g of the impurity remover and add it to a high - temperature molten salt containing about 350 ppm phosphorus concentration. Set the temperature of the molten salt to 500 °C; Take a sample of the molten salt for ICP test every 2 hours. The results are shown in Table 1.

[0023] Table 1: Concentration of P ions in the molten salt after impurity removal in Example 1 (high P concentration) Sampling time / h 0 2 4 8 P / ppm 340.951 323.736 298.963 292.8425 As can be seen from Table 1, in the molten salt with a higher P ion concentration, when 300 g of the impurity remover was added, the P ion concentration decreased significantly. After 8 hours, it decreased by about 48 ppm. Combining with the SEM photos, Figure 1 and Figure 2 For the polished glass wafer taken out under this strengthening condition, there are micron-level uneven points on the surface. The formation of these uneven points is due to the reaction of high-concentration phosphate ions in the molten salt with elements such as Na, K, and Li on the surface of the glass substrate, generating particulate substances such as Li3PO4, LiNa2PO4, Li2NaPO4, Na3PO4, and K3PO4. Some of them are removed during the polishing process leaving holes, and some are not removed forming convex points. The source of these uneven points is closely related to the P ion concentration, increasing the appearance defects in actual production.

[0024] Different masses of the impurity remover prepared in this example were added to the salt bath with similar P ion concentrations (8 h), and the impurity removal effect is shown in Table 2.

[0025] Table 2: Concentration of P ions in the molten salt after impurity removal by the impurity remover in Example 1 with different masses Mass of impurity removing agent Initial P concentration / ppm Final P concentration ppm Changed P concentration / ppm 100g 350.423 338.791 11.632 300g 354.760 305.340 49.42 600g 360.186 265.753 84.656 1200g 347.217 120.459 226.756 1800g 349.581 89.427 260.154 2400g 342.89 12.256 330.634 As can be seen from Table 2, there is a certain relationship between the addition amount of the impurity remover and the change amount of the final P concentration. The larger the addition amount of the impurity remover, the greater the change amount of the phosphorus concentration. The relationship n between the mass m of the impurity remover added and the change amount of P ions in the salt bath is: n = 0.147×m, where the unit of m is grams; n is the change concentration of P ions in the salt bath, and the unit is ppm.

[0026] Then, the impurity remover prepared in this example was applied to remove low-concentration P ions: the prepared impurity remover was loaded into a stainless steel wire cage and added to the high-temperature salt bath. After standing for a period of time, excessive p ions in the salt bath were removed. 300 g of the impurity remover was added to the high-temperature molten salt containing about 50 ppm of phosphorus concentration, and the molten salt temperature was set at 500 °C. The molten salt was sampled every 2 hours for ICP testing, and the results are shown in Table 3.

[0027] Table 3: Concentration of P ions in the molten salt after impurity removal by the impurity remover prepared in Example 1 (low P concentration) Sampling time / h 0 2 4 8 P / ppm 50.643 44.349 33.723 21.521 The P removal effect of the impurity remover and the state of the glass surface at low P concentration; under the same strengthening conditions, when the P concentration was controlled near 50 ppm, the initial state of the glass surface after strengthening was similar to Figure 1 , Figure 2 and there were also many micron-level uneven points. After adding the impurity remover, the P concentration was reduced to 20 ppm. At this time, the strengthened glass was verified, such as Figure 3As shown, it is found that the surface uneven points basically disappear. Therefore, there is a certain relationship between the surface uneven points and the P concentration, and this impurity remover can effectively reduce the P concentration in the molten salt, thereby ensuring the surface quality of the glass after strengthening and polishing, and significantly improving the processing yield. Example 2

[0028] Prepare the ionic impurity remover according to the following steps: Step 1, raw material preparation. Weigh by mass fraction: SiO2: 40%, Al2O3: 10%, Na2O: 10%, CaO: 40%. Mix them evenly, dry them, and then place them in a clean platinum or corundum crucible. Step 2, set the target temperature of the electric furnace, and the temperature range is 1300 - 1600 °C. Place the crucible containing the raw material powder in the electric furnace, heat it up to the target temperature, and maintain the temperature for 1 - 10 hours to completely decompose and melt the raw materials. Then pour the raw materials into a water tank filled with cold water at high temperature for water quenching.

[0029] Step 3, collect and dry the water-quenched powder, pass it through a 20-mesh sieve to prepare an impurity remover with a particle size of about 0.85 - 10 mm and a porosity of 20 - 40%, and store it in a dry environment.

[0030] Examples 3 - 12 Different from Example 1, the composition of the raw materials is different or the form of the product made is different. See Table 3 for details. Conduct application tests on the impurity removers prepared in Examples 1 - 12 for removing P ions, and the results are listed in Table 4 together.

[0031] Table 4 Changes in the raw material composition, form, porosity of the impurity removers prepared in Examples 1 - 12 and the concentration of P ions in the molten salt after impurity removal Oxide (wt%) Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Example 11 Example 12 <![CDATA[SiO2]]> 40 40 40 40 40 40 40 40 40 50 60 70 <![CDATA[Al2O3]]> 10 10 10 10 10 10 10 10 10 10 10 10 <![CDATA[Na2O]]> 40 10 12 14 16 18 20 25 10 20 15 10 CaO 10 40 38 36 34 32 30 25 40 20 15 10 Final form of product Powder Powder Powder Powder Powder Sheet Sheet Sheet Sheet Strip Strip Strip Porosity of product surface 30% 27% 29% 33% 28% 30% 32% 30% 45% 38% 35% 25% Change of p ion concentration (impurity removing agent 300g, impurity removing time 8h) 48 70 50 53 48 45 56 60 47 44 49 53 Example 13

[0032] The raw material composition is the same as that of Example 1. Mix the raw materials evenly, dry them, and then place them in a platinum or corundum crucible. Heat them to 1300 - 1600 °C to melt the raw materials. Cool the high-temperature glass liquid to near the Ts softening point, and roll it into a thin sheet using a shaft roller. Then quickly cool the thin sheet to form a sheet-like material with porous surfaces. The thickness of the sheet-like impurity remover of the prepared sheet-like material is 0.3 - 2 mm, and the width is 10 - 100 mm; the porosity of the surface is 20 - 40%. Example 14

[0033] The raw material composition is the same as that in Example 1. The raw materials are mixed evenly, and then the raw materials are mixed with an organic resin accounting for 10-40 wt% of the raw materials, and then cast into a strip, and then the strip is sintered and degreased at a high temperature of 1000-1200 °C to form the required impurity removing agent. The thickness of the prepared strip impurity removing agent is 0.1-2 mm, and the width is 10-300 mm; the porosity of the surface is 20-50%.

Claims

1. An impurity remover for glass strengthening salt bath, characterized in that, By mass fraction, the impurity remover is composed of 20 - 75% silicon oxide, 10 - 30% aluminum oxide, 10 - 40% sodium oxide, and 0.5 - 50% calcium oxide.

2. The impurity removing agent for the glass strengthening salt bath according to claim 1, characterized in that, The impurity remover is in the form of powder, flakes, or strips.

3. The impurity removing agent for the glass strengthening salt bath according to claim 2, characterized in that, The preparation method of the powdered impurity remover is as follows: First, 20 - 75wt% silicon oxide, 10 - 30wt% aluminum oxide, 10 - 40wt% sodium oxide, and 0.5 - 50wt% calcium oxide are mixed evenly, dried, and then placed in a platinum or corundum crucible. Heat to 1300 - 1600°C to melt the raw materials. Quench the melted raw materials, grind the quenched products, and finally dry the obtained powder.

4. The impurity removing agent for the glass strengthening salt bath according to claim 2, wherein, The preparation method of the flake impurity remover is as follows: First, 20 - 75wt% silicon oxide, 10 - 30wt% aluminum oxide, 10 - 40wt% sodium oxide, and 0.5 - 50wt% calcium oxide are mixed evenly, dried, and then placed in a platinum or corundum crucible. Heat to 1300 - 1600°C to melt the raw materials. Cool the high-temperature glass liquid to near the Ts softening point and roll it into flakes using a shaft roller. Then, quickly cool the flakes to form a flaky material with porous surfaces.

5. The impurity removing agent for the glass strengthening salt bath according to claim 2, wherein, The preparation method of the strip impurity remover is as follows: First, 20 - 75wt% silicon oxide, 10 - 30wt% aluminum oxide, 10 - 40wt% sodium oxide, and 0.5 - 50wt% calcium oxide are mixed evenly to obtain raw material A. Then, 10 - 40wt% of an organic resin based on raw material A is mixed. Cast and form it into strips, and then sinter and degrease the strips at a high temperature of 1000 - 1200°C to obtain the strip impurity remover.

6. The impurity remover for the glass strengthening salt bath according to claim 3, wherein, The particle size of the prepared powdered impurity remover is 0.85 - 10mm, and the surface porosity is 20 - 40%.

7. The impurity removing agent for glass strengthening salt bath according to claim 4, characterized in that, The thickness of the prepared flake impurity remover flakes is 0.3 - 2mm, and the width is 10 - 100mm; the surface porosity is 20 - 40%.

8. The impurity removing agent for the glass strengthening salt bath according to claim 5, characterized in that, The thickness of the prepared strip impurity remover is 0.1 - 2mm, and the width is 10 - 300mm; the surface porosity is 20 - 50%.

9. The application method of the impurity removing agent for the glass strengthening salt bath according to claim 1 or 2, characterized in that, Add the impurity remover to the high-temperature salt bath and let it stand for at least 0.5 hours.

10. The application method of the impurity removing agent for the glass strengthening salt bath according to claim 9, characterized in that, The relationship (n) between the added mass (m) of the impurity remover and the changed P ion content in the salt bath is: n = 0.147×m, where the unit of m is grams; n is the changed P ion content in the salt bath, and the unit is ppm.

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