Microcrystalline glass and lamination crystallization method thereof

Abstract

This invention discloses a method for crystallizing stacked microcrystalline glass. The method involves melting and rolling microcrystalline glass raw materials to obtain sheet-like glass; then, the sheet-like glass and spacer layers are alternately stacked and crystallized; finally, the crystallized glass is cooled to room temperature and polished to obtain microcrystalline glass. The distance between the sheet-like glass and the upper spacer layer is calculated by combining the thickness of the sheet-like glass, the thermal expansion coefficient of the microcrystalline glass, the thickness of the silicon carbide substrate, and the thermal expansion coefficient of silicon carbide, with a value ranging from 0.01 to 0.03 mm. The reserved gap at both ends of the spacer layer is 0.01 to 0.02 mm. The spacer layer is made of silicon carbide and its thickness is 0.2 to 3.3 times the thickness of the sheet-like glass. This invention reduces the warpage of microcrystalline glass by precisely matching the thermal expansion compensation gap, completely avoids boron nitride powder contamination of the substrate surface, and significantly improves the product appearance, optical precision, and overall quality of microcrystalline glass.

Description

Technical Field

[0001] This invention belongs to the field of microcrystalline glass preparation technology, specifically relating to a microcrystalline glass and its stacking crystallization method. Background Technology

[0002] Microcrystalline glass, also known as "glass-ceramic" or "zero-expansion glass," is a multiphase composite material formed by controlling the crystallization process of a base glass with a specific composition, resulting in the precipitation of numerous tiny crystals within the glass. It cleverly combines the homogeneity, formability, and light transmittance of glass with the high strength, high hardness, and heat resistance of ceramics. Microcrystalline glass possesses advantages such as high mechanical strength, high hardness, good wear resistance, good chemical and thermal stability, high softening temperature, and excellent electrical insulation properties. Furthermore, the composition of microcrystalline glass can be designed to acquire special optical, electrical, magnetic, thermal, and biological functions, thus making it suitable as a material for various technologies. Microcrystalline glass is widely used in structural materials and other special materials; among them, consumer electronics is currently the application area with the highest technological content and added value, especially with the popularization of foldable screen phones and high-end smart wearable devices. However, the density of microcrystalline glass changes during crystallization. If this change is inconsistent in the thickness direction, planar direction, or time axis of the glass plate, it will generate bending moment, leading to warping. This not only affects the appearance of the product, but also directly destroys the "precision" and "uniformity" on which microcrystalline glass depends, seriously affecting dimensional stability and optical accuracy. At the same time, warping means that the internal stress distribution of the glass is uneven, which poses a risk of spontaneous breakage. In addition, warping will also affect subsequent processes such as thinning, polishing, coating, and cutting, seriously affecting the yield of microcrystalline glass products.

[0003] Chinese patent CN113754289A discloses a low-warpage reinforced microcrystalline glass, its preparation method, and its applications. It achieves a uniform compressive stress gradient by controlling the segmented linear distribution of the compressive stress layer: a slope k1 of 2.45-5.05 from the surface to 30 μm, and a slope k2 of 1-1.5 from 30 μm to Dol_zero. Combined with low CS (<550 MPa) and a specific composition (such as a Li₂O / Na₂O ratio), and a two-stage ion exchange process, it suppresses warpage at its source, solving the deformation problem caused by high stress differences. However, it has certain limitations regarding the composition of the raw materials and can only address the warpage problem that occurs during the strengthening process.

[0004] Chinese patent CN115872622A discloses a 3D microcrystalline glass and its preparation method, as well as a pre-crystallized microcrystalline glass, which controls the crystal phase structure (LiAlSi4O) through a pre-crystallization process. 10By using materials with a content greater than Li₂Si₂O₅, pre-crystallized glass-ceramics with a crystallinity ≥35% are obtained. These are then subjected to 3D hot bending, during which crystallization is simultaneously completed, achieving an average crystal particle size ≤50nm and a crystallinity ≥50%. This solves the problems of uncontrollable crystal phase, large warpage, and deterioration of optical performance during hot bending in traditional methods. The resulting 3D glass-ceramics exhibit high dimensional accuracy (warpage ≤0.1mm), high light transmittance (≥90.8%), stable color (b-value ≤0.45), and excellent drop resistance (drop height ≥1.5m). However, this method has limitations in raw material requirements and is complex, requiring steps such as melting, shaping, nucleation, pre-crystallization, 3D hot bending, and chemical strengthening. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a microcrystalline glass and its stacking crystallization method, which reduces the warpage of the microcrystalline glass and improves the product appearance and quality.

[0006] To achieve the above objectives, the present invention provides a method for stacking and crystallizing microcrystalline glass, comprising the following steps: (1) The microcrystalline glass raw material is melted, rolled, and cut to obtain sheet glass; (2) The sheet glass and spacer layer are stacked alternately and crystallized; (3) Cool the crystallized glass to room temperature and polish it to obtain microcrystalline glass.

[0007] Preferably, the melting temperature in step (1) is 1500-1620℃ and the rolling speed is 1-3m / min.

[0008] Preferably, the distance between the sheet glass and the upper spacer layer in step (2) is the thickness of the sheet glass × the expansion coefficient of the microcrystalline glass - the thickness of the spacer layer × the expansion coefficient of the spacer layer material.

[0009] More preferably, the spacer layer is silicon carbide, and its thickness is 0.2-3.3 times the thickness of the sheet glass.

[0010] More preferably, the silicon carbide is any one of pressureless sintered silicon carbide, recrystallized silicon carbide, and reaction sintered silicon carbide.

[0011] More preferably, the coefficient of thermal expansion of the microcrystalline glass is 5×10⁻⁶. -6 / ℃-8×10 -6 At / ℃, the coefficient of thermal expansion of silicon carbide is 3×10⁻⁶. -6 / ℃-7×10 -6 / ℃.

[0012] Preferably, the reserved gap at both ends of the spacer layer in step (2) is 1% of the thickness of the spacer layer.

[0013] More preferably, the thickness of the sheet glass is 0.3-5 mm.

[0014] In a further preferred embodiment, the crystallization is carried out in a crystallization tank, wherein the maximum number of sheet glass layers stacked in a single crystallization tank is 40, the total stacking height of the sheet glass and the spacer layer is ≤320mm, and the optimal number of stacked layers for mass production is 10-25.

[0015] Preferably, the crystallization conditions in step (2) are crystallization at 550-850℃ for 1-3 hours.

[0016] Preferably, the polishing speed in step (3) is 2000-4000 rpm, the pressure is 4-7 MPa, and the time is 55-70 s; cerium oxide suspension is used as the polishing liquid during polishing.

[0017] Preferably, the microcrystalline glass raw material described in step (1) is composed of the following components by weight percentage: 60-80% SiO2, 2-14% Al2O3, 3-5% P2O5, 8-14% Li2O, and 0.1-2% Na2O.

[0018] The present invention also provides a microcrystalline glass, which is prepared by the above-mentioned stacking crystallization method, and has a thickness of 0.3-5 mm, a warpage of ≤0.1 mm, and a crystallinity difference of ≤3% within the same batch.

[0019] The beneficial effects of this invention are as follows: 1. This invention places a spacer layer between glass panes and utilizes the difference in high-temperature thermal expansion coefficients between the microcrystalline glass and the silicon carbide substrate. By quantitatively calculating and setting the interlayer compensation spacing, the bidirectional expansion deformation during the heating process is precisely offset, resulting in microcrystalline glass with extremely high flatness. This avoids the need to coat the microcrystalline glass with a boron nitride film for isolation, solves the problem of boron nitride adhesion on the finished microcrystalline glass, improves the appearance quality of the product, significantly reduces warpage, and thus improves the performance of the microcrystalline glass.

[0020] 2. After stacking, the glass undergoes crystallization treatment and is then cooled to room temperature in the furnace. Because the volume of the microcrystalline glass decreases after crystallization, the demolding process becomes smoother. Furthermore, this invention can be used for crystallization treatment of microcrystalline glass with a thickness of 0.3-5mm and a size within 500×500mm by changing the thickness and specifications of the spacer layer, thus having a wide range of applications.

[0021] 3. This invention uses a rolling process to produce sheet-like microcrystalline glass, significantly reducing raw material processing costs; it also effectively improves the production efficiency of microcrystalline glass while ensuring product quality stability. Polishing further improves the surface quality of the microcrystalline glass, enhancing the product's appearance.

[0022] 4. This invention is the first to employ a quantitative thermal expansion formula to precisely design the vertical gap between layers, coupled with the rigid constraint of an integrally sintered silicon carbide substrate. Simultaneously, a lateral expansion release gap is incorporated, eliminating the bending moment induced by thermal expansion from both thickness and planar dimensions. This eliminates the need for complex pre-crystallization and multiple ion exchange processes, resulting in a simpler process, higher yield, and complete elimination of contamination defects in the insulating medium. It overcomes the limitations of existing low-warpage microcrystalline glass, which only improves deformation through chemical composition control, ion exchange stress matching, and pre-crystallization hot bending composite processes, without considering the compressive stress and void deformation caused by the thermal expansion difference between the glass and the insulating medium during crystallization heating.

[0023] 5. This invention is based on the quantitative matching of interlayer compensation gaps according to the thermal expansion difference between two media: During the crystallization heating stage, the sheet-like microcrystalline glass and the silicon carbide substrate undergo simultaneous thermal expansion. Since there is a difference in their expansion coefficients, the vertical interlayer reserved space is precisely calculated using a formula to offset the bidirectional expansion difference in the thickness direction. This avoids the substrate squeezing the glass and generating compressive stress, or excessive gaps causing unrestrained free deformation of the glass. Simultaneously, a 1% lateral reserved gap is set at both ends of the spacer layer to release thermal expansion stress in the planar direction, achieving stress-free crystallization in both thickness and planar directions. The integrally sintered silicon carbide exhibits uniform thermal conductivity and high-temperature non-powdering, replacing the traditional boron nitride isolation layer and completely solving defects such as surface pitting and reduced light transmittance. After crystallization, crystals precipitate inside the glass, and the volume shrinks, causing the glass and silicon carbide to automatically separate. Demolding is scratch-free, significantly reducing the warping and spontaneous breakage rate of the microcrystalline glass. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the crystallization assembly of the sheet glass in Example 1.

[0025] Figure 2 This is a schematic diagram of the crystallization apparatus assembly in Example 1.

[0026] In the diagram, 1 represents the crystallization tank, 2 represents the sheet glass, 3 represents the spacer layer, and 4 represents the crystallization device. a is the distance between the spacer layer and the sidewall of the crystallization tank, and b is the distance between the sheet glass and the upper spacer layer. Detailed Implementation The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0027] In the following embodiments, the microcrystalline glass is composed of the following raw materials by weight percentage: 79% SiO2, 14% Al2O3, 4% P2O5, 10% Li2O, and 1% Na2O.

[0028] All the following embodiments uniformly adopt the following: the coefficient of thermal expansion of the microcrystalline glass is 6×10⁻⁶. -6 At ℃, the coefficient of thermal expansion of silicon carbide is 4×10⁻⁶. -6 / ℃; The distance between the sheet glass and the upper spacer layer = the thickness of the sheet glass × the expansion coefficient of the microcrystalline glass - the thickness of the spacer layer × the expansion coefficient of the silicon carbide substrate. For ease of reference, the distance for ultra-thin glass (0.3-1.1mm) is uniformly set to 0.01mm, the distance for medium-thick glass (1.3-2.0mm) is uniformly set to 0.02mm, and the distance for thick glass (2.5-5mm) is uniformly set to 0.03mm.

[0029] Example 1 (1) The microcrystalline glass raw material is melted at 1500℃ and then rolled by a rolling mill at a rolling speed of 2m / min to obtain glass with thicknesses of 0.3, 0.55, 0.7, 0.9 and 1.1mm respectively. Then it is cut into the required size to obtain sheet glass. (2) Place the sheet glass into the crystallization device and stack them according to the following order: one layer of sheet glass and one layer of silicon carbide plate (spacer layer). Figure 1 A total of 20 layers of sheet glass are stacked, with the silicon carbide substrate being 1mm thick. The distance between the sheet glass and the upper silicon carbide substrate is 0.01mm, and a 0.01mm gap is reserved at both ends of the silicon carbide substrate. Figure 1-2 ); (3) Heat the crystallization apparatus containing sheet glass to 550°C, crystallize for 2 hours, and then cool it to room temperature with the furnace. Remove the crystallized sheet glass. (4) Polish the crystallized microcrystalline glass for 60 seconds using a polishing machine to remove surface dust and improve the appearance quality of the product. Specifically, use a polishing machine with a speed of 3000 rpm, a polishing pressure of 5 MPa, and a cerium oxide polishing liquid (solid content of 20%).

[0030] Table 1 Warpage of Glass-Ceramic

[0031] Example 2 (1) The microcrystalline glass raw material is melted at 1560℃ and then rolled by a rolling mill at a rolling speed of 2m / min to obtain glass with thicknesses of 1.3, 1.5, 1.8 and 2.0mm respectively. Then it is cut into the required size to obtain sheet glass. (2) The sheet glass is placed into the crystallization device and stacked in a manner of one layer of sheet glass and one layer of silicon carbide plate (spacer layer), for a total of 15 layers of sheet glass. The thickness of the silicon carbide plate is 1mm, the distance between the sheet glass and the upper silicon carbide plate is 0.02mm, and a gap of 0.01mm is reserved at both ends of the silicon carbide plate. (3) Heat the crystallization apparatus containing sheet glass to 700°C, crystallize for 2 hours, and then cool it to room temperature with the furnace. Remove the crystallized sheet glass. (4) Polish the crystallized microcrystalline glass for 60 seconds using a polishing machine to remove surface dust and improve the appearance quality of the product. Specifically, use a polishing machine with a speed of 3000 rpm, a polishing pressure of 5 MPa, and a cerium oxide polishing liquid (solid content of 20%).

[0032] Table 2 Warpage of Glass-Ceramic

[0033] Example 3 (1) The microcrystalline glass raw material is melted at 1620℃ and then rolled by a rolling mill at a rolling speed of 2m / min to obtain glass with thicknesses of 2.5, 3, 4 and 5mm respectively. Then it is cut into the required size to obtain sheet glass. (2) The sheet glass is placed into the crystallization device and stacked in a layer of sheet glass and a layer of silicon carbide plate (spacer layer), for a total of 25 layers of sheet glass. The thickness of the silicon carbide plate is 1mm, the distance between the sheet glass and the upper silicon carbide plate is 0.03mm, and the gap at both ends of the silicon carbide plate is 0.02mm. (3) Heat the crystallization apparatus containing sheet glass to 850°C, crystallize for 2 hours, and then cool it to room temperature with the furnace. Remove the crystallized sheet glass. (4) Polish the crystallized microcrystalline glass for 60 seconds using a polishing machine to remove surface dust and improve the appearance quality of the product. Specifically, use a polishing machine with a speed of 3000 rpm, a polishing pressure of 5 MPa, and a cerium oxide polishing liquid (solid content of 20%).

[0034] Table 3 Warpage of Glass-Ceramic

[0035] Comparative Example 1 The method and steps are the same as in Example 1, except that the thickness of the sheet glass is 1.1 mm, and the silicon carbide plate is not set in the crystallization device, and the sheet glass is directly crystallized to prepare microcrystalline glass.

[0036] Comparative Example 2 The method and steps are the same as in Example 1, except that the thickness of the sheet glass is 1.1 mm, and the thickness of the silicon carbide plate is changed to 5 mm to prepare microcrystalline glass.

[0037] Comparative Example 3 The method and steps are the same as in Example 1, except that the thickness of the sheet glass is 1.1 mm, and the distance between the sheet glass and the upper silicon carbide plate is adjusted to 0, that is, the sheet glass is directly brought into contact with the upper silicon carbide plate to prepare microcrystalline glass.

[0038] Comparative Example 4 The method and steps are the same as in Example 1, except that the thickness of the sheet glass is 1.1 mm, and the distance between the sheet glass and the upper silicon carbide plate is adjusted to 1 mm to prepare microcrystalline glass.

[0039] Comparative Example 5 (1) The microcrystalline glass raw material is melted at 1500℃ and then rolled by a rolling mill at a rolling speed of 2m / min to obtain glass with a thickness of 1.1mm. Then it is cut into the required size to obtain sheet glass. (2) The glass sheet is placed in the crystallization device and stacked in a layer of glass sheet and a layer of silicon carbide powder (particle size of 50μm), wherein the thickness of the silicon carbide powder is 0.5mm. (3) Heat the crystallization apparatus containing sheet glass to 550°C, crystallize for 2 hours, and then cool it to room temperature with the furnace. Remove the crystallized sheet glass. (4) Polish the crystallized microcrystalline glass for 60 seconds using a polishing machine to remove surface dust and improve the appearance quality of the product. Specifically, use a polishing machine with a speed of 3000 rpm, a polishing pressure of 5 MPa, and a cerium oxide polishing liquid (solid content of 20%).

[0040] Table 4 Warpage of Glass-Ceramic

[0041] The results showed that in the comparative example, when direct crystallization without a spacer layer, silicon carbide powder as the isolation medium, and the thickness / interlayer gap of the silicon carbide plate were used, the warpage of the glass-ceramic increased significantly, all exceeding 0.2 mm, which could not meet the optical dimensional accuracy requirements of consumer electronics cover plates. In the embodiment, when silicon carbide plates were stacked in an alternating manner, and the interlayer expansion compensation gap, plate thickness, and expansion gaps were reserved at both ends were matched and limited, the warpage of the glass-ceramic in the entire thickness range of 0.3-5 mm could be controlled within 0.02-0.1 mm, and the dimensional accuracy was significantly improved. The silicon carbide plate can uniformly constrain the expansion of the glass plane in all directions and avoid local stress concentration. The powder isolation layer has no rigid support, is prone to collapse at high temperatures, and is subject to uneven stress, which cannot effectively suppress warpage.

[0042] The optical transmittance of the microcrystalline glass (1.1 mm thick) prepared in the above examples and comparative examples was tested in the visible light band of 400-700 nm. The visible light transmittance of the microcrystalline glass prepared in the examples can reach 89.0-92%, and the crystallinity difference within the same batch is ≤3%. The transmittance of the control group without silicon carbide spacer layer is only 82-88%, and the crystallinity difference is >5%. This shows that the process parameters in the examples have significant technical advantages in terms of flatness, optical performance and batch consistency of the prepared microcrystalline glass.

Claims

1. A method for stacking and crystallizing microcrystalline glass, characterized in that: Includes the following steps: (1) Microcrystalline glass raw materials are melted, rolled, and cut to obtain sheet glass; (2) The sheet glass and spacer layer are stacked alternately and crystallized; (3) Cool the crystallized glass to room temperature and polish it to obtain microcrystalline glass.

2. The method for stacking and crystallizing microcrystalline glass according to claim 1, characterized in that: The melting temperature in step (1) is 1500-1620℃ and the rolling speed is 1-3m / min.

3. The method for stacking and crystallizing microcrystalline glass according to claim 1, characterized in that: The distance between the sheet glass and the upper spacer layer in step (2) is the thickness of the sheet glass × the expansion coefficient of the microcrystalline glass - the thickness of the spacer layer × the expansion coefficient of the silicon carbide substrate spacer layer.

4. The method for stacking and crystallizing microcrystalline glass according to claim 1 or 3, characterized in that: The spacer layer is made of silicon carbide and has a thickness of 0.2-3.3 times that of the sheet glass.

5. The method for stacking and crystallizing microcrystalline glass according to claim 4, characterized in that: The silicon carbide is any one of pressureless sintered silicon carbide, recrystallized silicon carbide, or reaction sintered silicon carbide.

6. The method for stacking and crystallizing microcrystalline glass according to claim 1, characterized in that: The reserved gap at both ends of the spacer layer in step (2) is 1% of the thickness of the spacer layer.

7. The method for stacking and crystallizing microcrystalline glass according to claim 1, characterized in that: The thickness of the sheet glass is 0.3-5mm.

8. The method for stacking and crystallizing microcrystalline glass according to claim 1, characterized in that: The crystallization conditions described in step (2) are crystallization at 550-850℃ for 1-3 hours.

9. A method for stacking and crystallizing microcrystalline glass according to claim 1, characterized in that: The microcrystalline glass raw material mentioned in step (1) is composed of the following components by weight percentage: 60-80% SiO2, 2-14% Al2O3, 3-5% P2O5, 8-14% Li2O, and 0.1-2% Na2O.

10. A microcrystalline glass prepared by the stacking crystallization method of the microcrystalline glass as described in any one of claims 1-9.

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