A glass-ceramic having high surface compressive stress and a method for making the same

Abstract

The present application improves the problem of low surface compressive stress caused by "less sodium" in components due to the corresponding crystalline phase precipitated in the microcrystalline glass by adding mixed salt bath in the process of sodium infiltration before the crystallization heat treatment of the base glass plate, so that the surface compressive stress value of the microcrystalline glass is obviously improved in the process of chemical strengthening of the microcrystalline glass, thereby having higher hardness and scratch resistance. The prepared glass material has wide use value in the field of electronic consumer products.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of glass-ceramic materials, in particular, to a glass-ceramic with high surface compressive stress. BACKGROUND

[0002] At present, many electronic devices use glass materials as screen and / or back cover protective materials. However, with the large-screen display of mobile terminals, the problem of glass screen being easily broken and scratched is increasingly prominent, and the mechanical properties of the glass protective layer of electronic devices need to be further improved.

[0003] Since the 1950s, when Corning Corporation in the United States realized the controllable preparation of glass-ceramics, glass-ceramics have attracted the attention of relevant researchers. Glass-ceramics have crystalline phases inside, which can have physical property values that cannot be obtained in glass. Because of the existence of crystalline phases, surface or internal microcracks are less likely to further expand or be deflected and thus less likely to diffuse. Compared with original glass, the mechanical strength, thermal shock resistance, and chemical stability of glass-ceramics are significantly improved, and glass-ceramics also have the advantages of adjustable thermal expansion coefficient.

[0004] In order to improve the surface strength of cover plate glass materials, high-temperature ion exchange is often used for surface chemical strengthening, but the surface compressive stress value of the chemically strengthened glass-ceramics is lower than that of the commonly used high-alumina glass materials because the glass-ceramics have high crystallinity and the content of glass phase is low. SUMMARY

[0005] The present application aims to provide a method for improving the surface compressive stress of glass-ceramics, so that the high-surface-compressive-stress glass-ceramics obtained by the method have a high crystal proportion and structural strength, and also have high light transmittance.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A method for preparing high-surface-compressive-stress glass-ceramics, characterized in that it comprises the following steps:

[0008] Step a: immersing a base glass plate in a mixed molten salt of lithium nitrate and sodium nitrate for sodium infiltration treatment, taking it out after a certain period of time, and cleaning;

[0009] Step b: performing crystallization treatment on the base glass plate treated in step a to obtain ion-exchangeable glass-ceramics;

[0010] Step c: performing strengthening treatment on the ion-exchangeable glass-ceramics obtained in step b to obtain high-strength transparent glass-ceramics.

[0011] Preferably, in step a, the base glass plate is prepared by weighing the components according to the design ratio, stirring and mixing, melting at a temperature of 1300-1450℃ for 10-30h, cooling and annealing, and then cutting into a glass plate with a thickness of 0.2-1mm by a calendering method or ingot cutting method.

[0012] Preferably, in step a, the temperature of the molten salt is 250-350℃, the composition is lithium nitrate:sodium nitrate=90:10-99.5:0.5, and the immersion time is 10-200min. The depth of the sodium ion layer into which the base glass penetrates is 10-30μm.

[0013] Preferably, in step b, the crystallization treatment is a two-step heat treatment, the first step being held at a first temperature of 600-640℃ for 2-5h, and the second step being held at a second temperature of 700-760℃ for 2-6h.

[0014] Preferably, in step c, the strengthening treatment step is: first, placing the ion-exchangeable microcrystalline glass in a NaNO3 molten salt at a constant temperature of 400-500℃ for 4-10h to perform a first ion exchange; second, taking out the microcrystalline glass after the first ion exchange and placing it in a KNO3 molten salt at a constant temperature of 350-420℃ for 1-3h to perform a second ion exchange.

[0015] Preferably, the microcrystalline glass with high surface compressive stress has the following component mass fractions: SiO268-74%; Al2O35-9%; TiO20-1%; CaO 0-1%; Li2O 10-14%; Na2O 0.1-1.5%; K2O 0.1-1%; P2O53-6%; ZrO23-6%; BaO 0-1%; Sb2O30-2%; MgO 0-3%; and ZnO 0-2%.

[0016] A microcrystalline glass with high surface compressive stress, characterized by being made by the above method.

[0017] Preferably, the crystal phase contains lithium disilicate, petalite and aluminum phosphate crystal phases, and the crystallinity is 60%-90%.

[0018] Preferably, after heat treatment, the maximum size of the overall crystal generated in the glass body is ≤65nm; after strengthening, the Vickers hardness of the microcrystalline glass is ≥950kgf / mm 2 , the surface compressive stress is ≥750MPa, the potassium ion exchange layer depth is ≥6μm, the sodium ion exchange layer depth is ≥85μm, and the transmittance of a 1mm-thick microcrystalline glass in the visible light range is ≥85%.

[0019] The beneficial effects of the present application are: the microcrystalline glass of the present application increases the content of sodium ions on the surface of the glass under the premise of not destroying the composition of the main crystal phase of the glass, so that the degree of potassium-sodium ion exchange in the chemical strengthening process is improved compared with the original "high lithium and low sodium" microcrystalline glass composition, so that the compressive stress value formed on the surface is higher than that of the microcrystalline glass without sodium infiltration treatment, and the surface hardness, scratch resistance and drop resistance of the microcrystalline glass are improved. The microcrystalline glass product produced by the preparation method of the present application can better meet the demand of intelligent mobile terminal electronic display protective cover plate and various glass protective material fields. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a sodium infiltration treatment schematic diagram

[0021] Figure 2 is the differential scanning calorimetry (DSC) curve of measuring example 1 (step 2-base glass preparation)

[0022] Figure 3 is a binary phase diagram of lithium nitrate and sodium nitrate (step 3-surface sodium infiltration treatment)

[0023] Figure 4 is a crystallization heat treatment schematic diagram (step 4-crystallization treatment)

[0024] Figure 5 is the transmittance curve of measuring example 1 (product transmittance)

[0025] Figure 6 is the XRD spectrum of measuring example 1 (product crystal phase)

[0026] Figure 7 is the display picture of FSM-6000 of measuring example 1

[0027] Figure 8 is the potassium-sodium element energy spectrum line scanning of the microcrystalline glass section of example 1 (product sodium infiltration layer)

[0028] Figure 9 is the SEM picture of the glass surface of example 1 after being corroded by HF (product grain size)

[0029] Figure 10 is the indentation formed on the surface of the glass when the hardness of example 1 is tested DETAILED DESCRIPTION

[0030] In order to make the technical features, objectives and effects of the present application more clearly understood, the specific embodiments of the present application will now be described in detail. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the scope of protection of the present application.

[0031] The microcrystalline glass provided by the present application has the following mass fractions of components: SiO2 68-74%; Al2O3 5-9%; TiO2 0-1%; CaO 0-1%; Li2O 10-14%; Na2O 0.1-1.5%; K2O 0.1-1%; P2O5 3-6%; ZrO2 1-6%; BaO 0-1%; Sb2O3 0-2; MgO 0-3%; and ZnO 0-2%. In the present specification, if not otherwise specified, the content of each component is expressed by weight percentage with respect to the total amount of glass substance converted into the composition of oxides. Here, the "composition converted into oxides" refers to the case where, when the oxides, composite salts, etc. used as raw materials of the microcrystalline glass composition of the present application are all decomposed and converted into oxides upon melting, the total amount of the oxides is taken as 100%.

[0032] The specific components, mass fractions, processing procedures and performance parameters of Examples 1-5 are shown in Table 1. The control group in Table 1 is not subjected to sodium infiltration treatment.

[0033] Examples 1-5 are prepared by the following method:

[0034] 1. Component weighing and mixing: selecting respective oxides, hydroxides, carbonates, nitrates, hydroxides and metaphosphoric compounds, etc. as raw materials according to the component proportion range, mixing the raw materials uniformly, and placing the uniform mixture into a platinum or alumina crucible.

[0035] 2. Preparation of base glass plate: according to the melting difficulty of the glass composition, heating in an electric furnace at a temperature of 1300-1450°C for 10-30h to make it uniformly melt, cooling and annealing, and then forming a base glass plate with a thickness of 0.2-1mm by ingot cutting or calendering method.

[0036] 3. Surface sodium infiltration treatment: immersing the base glass plate into a mixed molten salt of lithium nitrate and sodium nitrate, taking it out after keeping for a certain time, and cleaning. The temperature of the mixed molten salt is 250-350°C, for example 280°C, 300°C, 320°C or 340°C; the composition is lithium nitrate:sodium nitrate=90:10-99.5:0.5, for example 91:9, 95:5, 97:3 or 99:1; and the immersion time is 10-200min, for example 1h, 2h or 3h.

[0037] 4. Crystallization: The base glass sheet obtained in the above step is subjected to two-stage heat treatment: the first stage is to keep at a first temperature of 600-640℃ for 2-5h, and the second stage is to keep at a second temperature of 700-760℃ for 2-6h, to obtain ion-exchangeable glass-ceramics. In the embodiments of the present application, the heat treatment conditions of the first stage are recorded in the column of "Nucleation Process" in Table 1, and the heat treatment conditions of the second stage are recorded in the column of "Crystallization Process" in Table 1. The temperature and the holding time at the temperature of the heat treatment are as described in the table.

[0038] 5. Preparation of strengthened glass-ceramics: The ion-exchangeable glass-ceramics obtained in step 4 is cut, ground and polished to form a sheet, and is strengthened by two-step high-temperature ion exchange. The chemical strengthening process is as follows: first, the ion-exchangeable glass-ceramics is placed in a molten NaNO3 salt bath at a constant temperature of 400-500℃ for 4-10h to perform the first ion exchange; second, the glass-ceramics after the first ion exchange is taken out and placed in a molten KNO3 salt bath at a constant temperature of 350-420℃ for 1-3h to perform the second ion exchange.

[0039] 6. Finally, the strengthened glass-ceramics sheet is finely polished, and the overall thickness is reduced by 1-3μm.

[0040] Regarding the strengthening conditions of the ion-exchangeable glass-ceramics described above, the following is explained: the glass-ceramics can be immersed in a molten NaNO3 salt bath at a temperature of 420-460℃ for 5-16h to perform ion exchange, in which embodiment, Na ions replace part of the Li ions in the glass-ceramics, thereby forming a surface compressive stress layer to make the glass-ceramics exhibit high mechanical properties; or the glass-ceramics can be immersed in a molten KNO3 salt bath at a temperature of 380-450℃ for 1-6h to perform ion exchange, preferably for 2-4h.

[0041] In the embodiments of the present application, the two-step high-temperature ion exchange method is adopted for strengthening (i.e. step 5), and the specific parameters are described in the column of "Strengthening Process" in Table 1. However, the strengthening conditions of the glass-ceramics of the present application are not limited to those in Table 1.

[0042] The crystal phase of the glass-ceramics obtained by the above steps contains two or more of lithium disilicate, petalite, aluminum metaphosphate and the like.

[0043] In the embodiments, the crystal phase of the glass-ceramics before high-temperature ion exchange strengthening is analyzed by X-ray diffractometer to obtain the corresponding crystal phase in the glass-ceramics and the corresponding crystallinity calculated therefrom.

[0044] Average grain size: measured by scanning electron microscope, the surface of the glass-ceramics was treated by HF acid, then the surface of the glass-ceramics was treated by gold spraying, the diameter of the grain was observed under the scanning electron microscope, and the average diameter size of all grains was obtained by adding up the diameter of all grains and dividing by the number of grains in the image. Figure 9 ].

[0045] Vickers hardness: measured by Vickers hardness tester, the loading force was 200g, and the loading time was 15s (Table 1).

[0046] CS: surface compressive stress layer formed by potassium ions, measured by glass surface stress tester FSM-6000 (Table 1).

[0047] DOC: sodium ion exchange layer depth, measured by glass surface stress tester SLP-1000 of Japan Zaoquan Industrial Co., Ltd. (Table 1).

[0048] DOL: potassium ion exchange layer depth, measured by glass surface stress tester FSM-6000 of Japan Zaoquan Industrial Co., Ltd. (Table 1).

[0049] Ball drop height: the two surfaces of the strengthened glass-ceramics plate with a length, width and height of 160x70x0.8mm were polished and then placed on a rubber stand, a 102g steel ball was dropped from a specified height, and the maximum ball drop height that the glass plate could withstand without breaking (Table 1).

[0050] Transmittance: tested by ultraviolet-visible spectrophotometer on a 1mm thick polished glass sheet. In the examples provided by the present application (Table 1), the glass-ceramics has a transmittance of 89%-93% in the visible spectrum of 400nm-750nm, which makes the glass-ceramics have good light transmittance while having high strength, and can replace ordinary glass as a cover protection material for electronic display devices.

[0051] The present application will be further described in conjunction with specific examples, but the present application is not limited to these examples.

[0052] Table 1

[0053]

[0054]

Claims

1. A method for preparing a high surface compressive stress microcrystalline glass, characterized in that, Includes the following steps: Step a: Immerse the base glass plate in a mixed molten salt of lithium nitrate and sodium nitrate for sodium infiltration treatment, keep it for a certain period of time, then remove and clean it; Step b: The base glass plate obtained in step a is subjected to crystallization treatment to obtain ion-exchangeable microcrystalline glass; Step c: The ion-exchangeable glass-ceramic obtained in step b is subjected to strengthening treatment to obtain high-strength transparent glass-ceramic. The mass fractions of each component of the high surface compressive stress glass-ceramic are as follows: SiO2 68-74%; Al2O3 5-9%; TiO2 0-1%; CaO 0-1%; Li2O 9-13%; Na2O 0.1-1.5%; K2O 0.1-1%; P2O5 3-6%; ZrO2 1-6%; BaO 0-1%; Sb2O3 0-2%; MgO 0-3%; ZnO 0-2%.

2. The preparation method according to claim 1, characterized in that, In step a, the preparation method of the basic glass plate is as follows: weigh each component according to the design ratio, stir and mix them, melt them at a temperature of 1300-1450℃ for 10-30 hours, cool and anneal them, and make a glass plate with a thickness of 0.2-1mm by rolling or casting and cutting.

3. The preparation method according to claim 1, characterized in that, In step a, the molten salt temperature is 250-350℃, the composition is lithium nitrate: sodium nitrate = 90:10-99.5:0.5, the immersion time is 10-200 min, and the depth of the sodium ion layer in the base glass is 10-30 μm.

4. The preparation method according to claim 1, characterized in that, In step b, the crystallization treatment is a two-step heat treatment: the first step is to maintain the temperature at a first temperature of 600-640°C for 2-5 hours, and the second step is to maintain the temperature at a second temperature of 700-760°C for 2-6 hours.

5. The preparation method according to claim 1, characterized in that, In step c, the strengthening treatment step is as follows: First, the ion-exchangeable glass-ceramic is placed in NaNO3 molten salt and kept at a constant temperature of 400-500℃ for 4-10 hours for the first ion exchange; Second, the glass-ceramic that has completed the first ion exchange is taken out and placed in KNO3 molten salt and kept at a constant temperature of 350-420℃ for 1-3 hours for the second ion exchange.

6. A microcrystalline glass with high surface compressive stress, characterized in that, It is prepared by the method described in claim 1.

7. The microcrystalline glass as described in claim 6, characterized in that, Its crystal phases include lithium disilicate, petalite, and aluminum phosphate, with a crystallinity of 60% to 95%.

8. The microcrystalline glass as described in claim 6, characterized in that, After heat treatment, the maximum size of the overall crystals formed within the glass is ≤65nm; after strengthening, the Vickers hardness of the microcrystalline glass is ≥950kgf / mm. 2 The surface compressive stress is ≥750MPa, the potassium ion exchange layer depth is ≥6μm, the sodium ion exchange layer depth is ≥85μm, and the transmittance of a 1mm thick microcrystalline glass in the visible light range is above 85%.

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