CN112159118B

CN112159118B - Re-strengthening method for chemical cold-bending thinning surface of aluminosilicate cover plate glass

Info

Publication number: CN112159118B
Application number: CN202011101149.0A
Authority: CN
Inventors: 丁原杰; 陈琦
Original assignee: Fuyao Glass Industry Group Co Ltd
Current assignee: Fuyao High Performance Glass Technology Fujian Co ltd
Priority date: 2020-10-15
Filing date: 2020-10-15
Publication date: 2022-09-13
Anticipated expiration: 2040-10-15
Also published as: CN112159118A

Abstract

The invention belongs to the technical field of glass processing, and particularly relates to a method for re-strengthening a chemical cold-bending thinning surface of aluminosilicate cover plate glass. The invention relates to a chemical cold-bending ultrathin high-aluminum cover plate glass, which is characterized in that two surfaces of a glass plate are chemically strengthened firstly, one surface of the glass plate is thinned to form cold-bent glass, and the surface pressure stress and the depth of a stress layer of the thinned surface are partially or completely eliminated, so that the strengthening effect of the thinned surface is reduced or disappears. The method of the invention enables the aluminosilicate cover plate glass to be applied to automobile instrument display, car windows, skylights, display protection cover plates, white home appliances, building glass and other consumer electronic products in a curved surface mode.

Description

Re-strengthening method for chemical cold-bending thinning surface of aluminosilicate cover plate glass

Technical Field

The invention belongs to the technical field of glass processing, and particularly relates to a method for re-strengthening a chemical cold-bending thinning surface of aluminosilicate cover plate glass.

Background

The weight reduction of automobile materials is an important subject in the fields of the development of automobile material technology and energy saving and carbon reduction at present, and the weight reduction of automobile glass is one of important points. Most of the commercially available front windshields and skylights are made of two physically-stiffened soda-lime glass plates bonded together with a Polyvinyl butyral (PVB) film sandwiched therebetween. If the weight reduction effect is achieved by reducing the thickness of the glass and the mechanical performance of the glued glass window combination cannot be reduced, the two factors of the strength and the physical rigidity of the soda-lime glass are limited to the thickness requirement of the glass plate. In order to overcome the restriction factor, the soda-lime glass plate can be replaced by a high-alumina glass-calcium plate, the high-aluminosilicate cover plate glass has higher strength than the traditional soda-lime glass due to high content of aluminum and silicon, and the strength of the traditional soda-lime glass can be achieved by using a thinner thickness.

At present, the thickness of a common soda-lime glass plate is more than 2mm, the softening point temperature of the glass is lower, about 580-620 ℃ (different from the brand type), the precision processing can be realized, the production yield is high, but the high-aluminum cover plate glass is thinner, the thickness is mostly less than 1.8mm, the softening point temperature is as high as about 900 ℃, the high temperature enables the high-aluminum glass and the soda-lime glass to be incapable of being subjected to a hot bending process synchronously in the same furnace, even if the high-aluminum cover plate glass is subjected to the hot bending independently, the bending of the glass is not in place due to uneven temperature distribution of the thin plate glass under high-temperature heating, surface ripples or wrinkles caused by uneven heat conduction, thermal stress of corners caused by incomplete slow cooling, and defects caused by two factors of high temperature and the thin plate. The above problem is a major difficulty that the use of high-aluminum sheet glass for the lightweight automotive glass is currently hindered. Moreover, when two pieces of semi-finished glass after a plurality of kinds of processing at the previous stage are to be glued, a great deal of resources are already put into the whole process and considerable manufacturing cost is generated, at this time, if the shape or the bending surface cannot be tightly bonded during gluing, considerable cost loss can be caused, the difficulty of reworking is extremely high, the problem that the strengthened high-alumina glass and the soda-lime glass cannot be tightly bonded during gluing really occurs in the current industry, the reason is mostly caused by high-alumina cover glass, and the main reason of the non-tight bonding is that the bending degree of the two pieces of glass is not consistent. The chemical cold bending method is a solution to the problem, is simple and easy to use, can be operated at room temperature, does not need a high-temperature die, greatly reduces the cost and is suitable for batch production and application.

The chemical cold bending method of the ultrathin medium and high aluminum glass can finish glass bending on the premise of not heating the glass, and the principle is that the glass has surface compressive stress after being physically tempered or chemically strengthened, when the stress on two surfaces of the glass is in a balanced state, the glass can maintain the original shape during physical tempering or chemical strengthening, namely, if the glass is planar during physical tempering or chemical strengthening, the glass is still planar after the physical tempering or chemical strengthening; if the curved surface is formed during physical toughening or chemical strengthening, the curved surface is still formed after the physical toughening or chemical strengthening. At this time, if one side of the glass plate after stress strengthening is thinned, that is, the surface of the glass plate is removed by a thickness, generally speaking, the thickness is only several micrometers to several tens of micrometers, the surface compressive stress of the slightly thinned glass surface is also reduced, so that the stress on both sides of the glass plate is unbalanced, the glass plate bulges towards the surface with large stress, that is, a bow shape is formed, and the bow is towards the side with larger surface compressive stress, the stress is changed by the thinned thickness, so that the overall bending shape of the glass plate can be controlled by adjusting factors such as the thinned position, the area and the thickness. Conversely, if the strengthened glass sheet is itself in a regular curved shape, such as a bow-shaped curve, the glass sheet can be returned to a planar shape by thinning the glass surface of the convex surface. The prior art, such as US10273184B2, mentioned that a glass plate with a thickness of not more than 0.3mm is strengthened in a bending mode in a strengthening furnace, and then glued to another hard plate after strengthening, and thus the strengthened bent glass is flattened to achieve the effect of strengthening a single glass surface, wherein after the curved strengthened glass is pressed to be flat, the original protruded surface is pressed to form a new compressive stress, which has the effect of strengthening the surface again, but the other surface (original concave surface) is opened, and the surface compressive stress is reduced, so that the surface is selected to be glued to the hard plate, so that a glued glass with a stronger outer surface can be formed, wherein although the two sides of the glass plate have different compressive stresses, the purpose of the glued glass is not to bend the glass, and the technology is not applied to thin the glass surface, and the technology is limited to the glass thickness of not more than 0.3mm, there is a certain technical bottleneck. Furthermore, the prior art, as disclosed in US9302937B2, is to strengthen the inner and outer glass surfaces of the plate glass and the tubular glass under different conditions to generate different surface compressive stresses, to reduce the tensile stress of the central area of the glass by reducing the compressive stress of one of the glass surfaces, and to form a sandwich structure by gluing to achieve the purpose of strengthening the laminated glass plate, and to suppress the micro-bending of the glass due to uneven stress, i.e., the bending of the glass due to uneven stress is regarded as a defect, and there is no mention in the patent that the bending of the glass can be controlled by thinning the glass surface. Furthermore, the prior art, such as that described in US2018370852a1, describes a method of bending glass using a method of applying different stresses on two sides of a glass sheet by ion implantation (ion-implantation) of high energy physical metal ions into one surface of the glass sheet and then ion-exchanging the glass sheet in a chemical tempering furnace, the ion-exchange rate of the glass on the side where the metal ions are implanted being reduced, thereby causing different compressive stresses on the two sides of the glass, thereby deforming the glass during tempering, which method has the disadvantage that (1) ion implantation is a relatively expensive process and is not a suitable quotient for the processing of large window glass, such as vehicle windows; (2) the temperature of the strengthening furnace is as high as more than 400 ℃, the bending shape formed at high temperature is more difficult to operate than the normal temperature, and the shape at high temperature and the like are changed due to the temperature difference when the temperature is reduced to the normal temperature. Also, this patent application does not mention a simple method of glass surface thinning that operates at ambient temperatures. Therefore, one of the technical problems to be solved at present is how to generate stress layers with predetermined thickness on two surfaces of the ultra-thin medium and high aluminum glass plate, and how to control the bending deformation of the glass plate by reducing the predetermined thickness of the glass plate.

Further, the high-aluminum cover glass used for the automobile front bumper or the skylight needs to be subjected to glass toughening treatment before chemical cold bending, and the current practice proves that the glass with the thickness of less than 2.0mm is difficult to be toughened by a physical toughening method, so that the strength of the glass after physical toughening, particularly the Compressive stress (sigma) of the surface of the glass is achieved _s ) The thickness of the glass is required to be maintained at a value of 2mm or more (please refer to the book of Wang Yun et al for details and requirements on physical rigidity, which is not described herein). But chemical strengthening can be carried out by using a chemical ion exchange method, the chemical strengthening method can be applied to high-alumina-calcium glass plates with any thickness, so that the thickness of the glass plates is not limited, the surface strength of the high-alumina glass plates after chemical strengthening can be 2 to 3 times that of the soda-lime glass plates after physical strengthening, and the anti-collision capacity of the glass surfaces can be greatly improved. Chemical strengthening is not limited by glass thickness and, therefore, is effective for highGlass sheets with a thickness of less than 2mm can also be used for glass surface strengthening using chemical strengthening. However, in the case of the high-alumina cover glass which is either chemically strengthened or physically strengthened, after the processing by the "chemical cold bending" method, there is a problem that the reduced area of the glass plate will have a reduced surface compressive stress due to the removal of part or all of the surface compressive stress layer, which will result in the effect of the stress strengthening after the glass strengthening being greatly reduced or even eliminated in the reduced area. Therefore, another new technical problem is created in how to increase the surface stress of the thinned area again.

In general, the narrow sense of chemical strengthening of glass refers to the use of ion exchange method in potassium nitrate fused salt for silicate glass containing sodium oxide component, in the range of about 380-, DOL), the resulting surface Compressive stress (CS, symbol: sigma _s ) The size of (b) is influenced by factors such as glass composition and ion exchange depth. The region between the compressive stress layers on the two outer surfaces of the glass plate is the Central tension region (CT, for the symbol:. sigma.) _c ) When the surface of the glass is enhanced in resistance to external impact due to the compressive stress, the central area is weakened due to the generation of the tensile stress. When the general chemical strengthening method is used for the traditional soda-lime glass plate, the DOL is mostly between 12 and 20 mu m, and the corresponding sigma is _s Approximately 450-600MPa, because σ _s Is also affected by the glass composition, so even if the same DOL is used, the obtained sigma is different for different glass brands and models _s Will also be different. Similarly, chemical strengthening is used in commercial production of high aluminosilicate cover glasses, for example, 0.7mm thick glass, the DOL is mostly between 25-40 μm, σ _s About 650-900 MPa. The glass plate after chemical strengthening can greatly improve the capacity of resisting external impact by about 10-15 times, which is far better than that after physical strengthening by 2-3 times. Glass chemical strengthening in a broad sense means that any ion exchange method can be used to displace some metal ions on the glass surface, and the foreign ions newly introduced into the glass surface are usually ions with the same charge valence but with a volume slightly larger than that of the original glass surface, and can diffuse into the glass in an ion exchange manner when sufficient kinetic energy is provided, so as to achieve the purpose of surface strengthening. Therefore, the exchange of potassium ions and sodium ions of glass containing sodium ions in potassium nitrate molten salt is only the most commonly used glass chemical toughening mode in the industry, but not the only mode, and other glass chemical strengthening performed in an ion exchange mode can be seen in many references, which are not repeated herein, and the application of the invention only takes the ion exchange of potassium ions and sodium ions in high-aluminum cover glass commonly used in the industry as an example to illustrate the formed chemical toughened glass, but is not limited to the chemical toughened glass formed in such an ion exchange mode.

Although the high-alumina cover glass can obtain high surface strength by chemical strengthening, the surface strength generated by the surface compressive stress is mainly determined by controlling the external ion concentration, temperature and time during ion exchange, taking potassium and sodium ion exchange as an example, when the temperature is about 420 ℃ and the reaction time is about 4-5 hours, surface compressive stress of about 750-900MPa (the high-alumina glass of different brands has slight difference due to different glass components) can be obtained, the surface compressive stress is caused by the distribution of potassium ions in the glass, at this time, if the chemically strengthened glass is heated for the second time and the temperature is higher than the ion exchange temperature, the potassium ions in the glass can be given enough kinetic energy and cause the potassium ions to continuously diffuse into the glass, so the original potassium ion concentration distribution can be destroyed and the potassium ion concentration on the glass surface can be reduced, resulting in a reduction of the surface compressive stress, i.e. the glass surface is weakened. Further, not only is the chemically strengthened glass sheet not suitable for reheating, but the tensile stress in the central region weakens the strength of the central region, so that the strengthened glass sheet is more likely to be chipped or damaged during cutting or other machining than before strengthening. The same applies to the physically stiffened glass pane, so that, in the production of a glass window, both the chemically stiffened high-alumina glass pane and the physically stiffened soda-lime glass pane require a geometric processing, i.e. processes relating to size and glass curvature, such as cutting, drilling, grinding and polishing, and hot bending, to be carried out first, then the respective strengthening process is carried out, and after strengthening, the glass pane is subjected to a gluing process, and finally all surface finishing processes are carried out.

Disclosure of Invention

The technical problem that aluminosilicate cover plate glass is not easy to bend and form is solved, and the method for bending and forming the aluminosilicate cover plate glass without raising the temperature is provided, specifically, the aluminosilicate cover plate glass is firstly subjected to glass toughening and then locally chemically thinned, and for a high-alumina glass sheet (the thickness is less than 2.0 mm), the high-alumina glass sheet is subjected to ion exchange to achieve an expected chemical strengthening effect, and then locally chemically thinned, so that two outer surfaces of a glass substrate have different compressive stresses, and the natural bending result of the glass along with stress distribution is achieved by utilizing the principle of stress difference. This process operation at normal temperature can be considered as a bending zone method caused by non-uniform compressive stress on both surfaces due to thinning of the glass surface. The difference of the compressive stress generated by the two outer surfaces of the glass plate can be an evenly distributed stress difference, and can also be an uneven stress difference, the former can cause the symmetrical deformation and Bending of the glass plate, the latter can cause the asymmetrical deformation and Bending, and by controlling the factors such as the position and the area of the thinned area of the glass surface, the thinned thickness and the like, the Bending moment (Bending moment) of each position of the glass plate can be controlled, and further the Bending degree (curvature) of the glass plate at each position can be controlled.

In order to achieve the purpose, the following specific technical scheme is adopted:

the chemical cold-bending forming process of the aluminosilicate cover plate glass comprises the following steps: the method comprises the steps of generating surface stress on the surface of a glass plate by a glass stiffening method on two surfaces of the glass plate, thinning one surface of the glass plate, so that the glass is bent and deformed due to unbalanced stress on the two surfaces, and using the characteristic and controlling to achieve the purpose of glass bending, thereby obtaining the aluminosilicate cover plate glass thinned by chemical cold bending.

The glass tempering method for generating the compressive stress on the surface of the glass plate is one of chemical strengthening and physical stiffening, wherein the chemical strengthening refers to the surface compressive stress generated by ion exchange of the glass plate, and the physical stiffening refers to the surface thermal stress formed by rapidly cooling the glass plate after heating.

Wherein, the thinning process is carried out at normal temperature or any temperature which can not cause the stress on the surface of the glass to disappear; the thinning process is any one of chemical thinning and mechanical thinning methods.

Wherein the thinning process is any one of a chemical etching method, a frosting method, a grinding and polishing method, a laser ablation method, an ion impact thinning method and a hot acid steam bath method.

When the aluminosilicate cover glass is selected as high-alumina cover glass, the thickness of the aluminosilicate cover glass is generally below 2.0 mm.

The chemical cold-bending forming process for the high-aluminum cover plate glass comprises the following steps: generating a compressive stress on the surface of the glass plate: firstly, generating compressive stress on two surfaces of a glass plate to strengthen the two surfaces of the glass plate by utilizing the compressive stress; bending the glass sheet: the glass plate is bent and deformed due to unbalanced compressive stress on two surfaces by thinning one surface of the glass plate.

Furthermore, when the thickness of the high-alumina cover glass is less than 2.0mm, the compressive stress on the surface of the glass can be generated only by using a chemical strengthening method, namely an ion exchange method. Chemical strengthening is a well-known technique, and includes any method that can perform ion exchange on the surface of glass and form compressive stress on the surface of glass.

Further, the surface compressive stress on both sides of the glass sheet may be unbalanced or non-uniform before thinning, including but not limited to that the tin side of float glass reduces the ion exchange rate during chemical strengthening, resulting in a glass sheet with a surface compressive stress on the tin side that is less than the air side; at this time, the glass with a curved shape can be manufactured by using a chemical cold bending and thin surface re-strengthening method, and the glass can be properly thinned to eliminate the glass bending after chemical strengthening.

Further, the step of bending the glass sheet is performed at a temperature that does not cause the compressive stress on the surface of the glass sheet to rapidly disappear.

Further, the thinning step is performed at normal temperature.

Further, the step of generating compressive stress on the surface of the glass plate is to generate stress layers having a predetermined thickness on both surfaces of the glass plate, and the step of bending the glass plate is to control the bending deformation of the glass plate by reducing the predetermined thickness of the glass plate.

Further, the reduced thickness is controlled to be no more than the depth of the compressive stress layer of the surface of the glass sheet being reduced.

Furthermore, the method for controlling the bending deformation of the glass plate is to control the position, area and thickness of the thinning of the surface of the glass plate according to the thinning pattern calculated by the shape and bending degree of the glass plate.

Further, the thickness reduction is based on the measured depth DOL of the chemically stiffened ion exchange layer and the surface compressive stress σ _s To calculate.

And further, after the thinning pattern is calculated, laminating the film on the surface of the glass plate according to the pattern, and then chemically thinning the coated glass plate.

Further, the thinning positions and areas are implemented in the same or different patterns, including symmetrical or asymmetrical dots, lines, grids, lattices, etc., and the curved shape of the glass plate is formed to include symmetrical and asymmetrical shapes.

More specifically, the cold roll forming method for the high-aluminum cover plate glass comprises the following steps:

step S1 is to select a suitable high-alumina cover glass, crack the glass according to a predetermined thickness and size, and trim the edge of the cracked glass, so as to avoid edge chipping, corner chipping, and microcracks as much as possible.

And step S2, cleaning the cut glass plate, drying, transferring to a salt bath furnace filled with molten potassium nitrate for chemical strengthening, cleaning the glass plate after chemical strengthening, and removing potassium nitrate adhered to the surface of the glass plate.

Step S3 measuring chemically stiffened ion exchange layer depth DOL and surface compressive stress σ _s As a basis for calculating the thinning depth, the thinning depth is calculated from the curvature of the glass plate which is designed in advance.

Step S4 is to coat a film according to the calculated thinning pattern according to the designed shape and curvature of the glass plate, wherein the film is an acid-resistant film, and then immerse the coated glass plate in a chemical thinning bath, wherein the thinning process can be performed at normal temperature, and the chemical thinning solution used can be any one of the known acidic solutions in the industry.

Further, the chemical strengthening temperature of step S2 is set between 380 ℃ and 470 ℃, depending on the actual requirement; the strengthening time is generally 4 hours or more, and is determined according to the DOL actually required.

Further, the chemical thinning in step S4 is a technique known in the art, so long as the surface of the glass not covered by the acid-resistant film is etched to uniformly remove the surface structure of the glass, and a uniform thinning effect is obtained, and a chemical thinning process for maintaining the surface of the glass flat and smooth can be used to perform the glass thinning. In addition, the glass can be thinned by any method capable of thinning the surface of the glass, such as a frosting method, a lapping and polishing method, a laser ablation method, or a hot acid steam bath method, and the method can be applied to what is called glass thinning.

For the ultra-thin high-aluminum cover plate glass after the cold roll forming, because the ultra-thin high-aluminum cover plate glass is subjected to local or total chemical thinning or mechanical grinding thinning, the two outer surfaces of the glass plate can have different compressive stresses by the thinning process, and the glass plate can form a shape of a curved surface along with the stress distribution of the two surfaces by utilizing the principle of the stress difference, but the surface compressive stress is reduced in the thinned area of the glass plate because part or all of the surface compressive stress layer is removed, so that the original toughening effect is greatly reduced or even disappears in the thinned area.

In order to improve the phenomenon, the invention adopts the following technical scheme:

the method for chemically strengthening the chemically cold-bent thinning surface of the high-aluminum cover plate glass enables the toughening effect of the thinning area to be improved again, and even the stress layer depth of the whole high-aluminum cover plate glass can be increased more than the original depth.

Further, before the chemical cold-bending thinning surface of the high-aluminum cover plate glass is subjected to chemical strengthening again, the ultra-thin high-aluminum cover plate glass subjected to cold-bending forming by adopting heating treatment can be selected.

Furthermore, the surface compressive stress of the thinned surface after being re-strengthened is not lower than 450MPa, and the depth of the stress layer is not lower than 20 mu m.

Because the surface Compressive Stress (CS) and the depth of stress layer (DOL) of the thinning surface of the glass plate are reduced because a part or all of the surface compressive stress layer is removed, the bent glass plate can be heated and then subjected to chemical ion exchange, so that the surface compressive stress of the glass with the thinning surface can be increased again, the depth of the stress layer is greatly increased, and the bent shape of the glass plate is maintained.

Further, the glass sheet after the heating treatment and the cold bending is a process of causing Stress relaxation (Stress-relaxation) to occur on both the normal surface and the thinned surface of the glass sheet due to temperature rise, and when potassium ions on the surface of the glass are subjected to enough heat energy to overcome activation energy for diffusion (diffusion) in the glass structure, the potassium ions will advance from a high-concentration region on the surface to a low-concentration region in the center of the glass, and the difficulty of the potassium ions entering the glass gradually increases along with the diffusion depth, so that the process is a mathematically complex process and cannot be described by a simple linear relationship. The increasing of the depth DOL of the stress layer is shown as potassium ions are gradually deepened into the glass, but the potassium ion concentration on the surface of the glass is gradually diffused into the glass to be reduced, so that the compressive stress on the surface of the glass is gradually reduced, the process is called a stress relaxation phenomenon, and heating is one of the methods capable of causing the stress relaxation. By controlling the temperature and time of the heat treatment, the stress conditions on both surfaces of the glass sheet can be adjusted, which can provide a good basis for the subsequent ion exchange, and is advantageous for controlling the CS, DOL, and curved surface shape after the ion exchange. It is well known that for products of the type of ultra-thin high-alumina glass sheet, a high CS indicates better impact resistance and a high DOL indicates better scratch resistance, and that high CS and high DOL are always desirable for commercial applications.

More specifically, the process for re-strengthening the thinned surface of the high-aluminum cover plate glass after the cold roll forming specifically comprises the following steps:

step S100, cleaning the glass subjected to the cold bending forming and thinning, removing potassium nitrate and other salts remained on the surface of the glass, and fully drying the glass to form a curved surface, wherein the curved surface glass is subjected to heating treatment without heating treatment or is placed into a muffle furnace for heating treatment, so that the glass is subjected to moderate stress relaxation;

and step S200, transferring the glass subjected to the step S100 into a chemical strengthening furnace to perform ion exchange in a salt bath manner, cleaning and drying the glass after the salt bath is completed, and then performing quality inspection and completing the whole construction procedure.

Further, the heating treatment in step S100 is specifically heating in an environment at a temperature of not lower than 380 ℃ for at least 60 minutes, so that the compressive stress of the side with higher compressive stress, i.e. the non-thinned side, of the two surfaces of the glass is moderately reduced to a state of not lower than 200 MPa.

Further, the heating treatment in step S100 is specifically heating to 380-460 ℃, and the temperature is not more than 4 hours.

Further, the salt bath in step S200 is specifically: salt bath selectively adding a material selected from KNO having a property of cutting off a network of glass represented by Si-O-Si bond ₃ 、K ₂ CO ₃ 、KHCO ₃ 、K ₃ PO ₄ 、K ₂ SO ₄ And KOH (hereinafter, sometimes referred to as "flux").

Further, the flux of the salt bath is KNO ₃ Mainly, the molar content is not lower than 90 percent; the salt bath temperature is 380-460 ℃; the time is not more than 4 hours.

The invention has the following remarkable advantages:

(1) the invention provides a method for bending and molding high-aluminum cover plate glass without raising temperature, namely, the high-aluminum cover plate glass is firstly subjected to ion exchange to achieve the expected chemical strengthening effect, and then a local chemical thinning method is used at normal temperature, so that two outer surfaces of a glass substrate have different compressive stresses, and the natural bending result of the glass along with stress distribution is achieved by utilizing the principle of stress difference. The invention particularly provides a stress cold bending method, and the curved surface forming method of the high-aluminum cover plate glass by using stress cold bending can be suitable for automobile instrument display, car windows, panoramic skylights, display protection cover plates and appearance protection of other consumer electronic products, particularly for occasions where the high-aluminum cover plate glass is not suitable for high-temperature softening forming, can directly finish a glass bending process at room temperature without a mould, and can avoid various defects caused in a glass hot bending forming process. Moreover, compared with the hot bending forming process, the equipment and operation of the stress cold bending process are relatively simple, the cost is low, the product reproducibility is high, and the competitive advantage is achieved. Furthermore, the stress cold bending process can be applied not only to chemically strengthened high-alumina cover glass, but also to other chemically strengthened and physically strengthened glass, including soda-lime glass plates, based on the same principle and method.

(2) The invention provides a solution, which can improve the chemical tempering effect of the thinned area again, even the stress layer depth of the whole high-aluminum cover plate glass can be increased more than the original depth, and the high-aluminum cover plate glass treated by the method not only can keep the curved surface shape after cold bending, but also has high surface compressive stress and higher stress layer depth after tempering. The method can be applied to cold-bending glass plates made of high-aluminum cover plate glass, and can be suitable for automobile instrument display, car windows, panoramic skylights, display protection cover plates, building glass, refrigerator doors and related daily household appliances and consumer electronics.

Drawings

σ when graph Δ h in fig. 1 (a) is 0 _s 、σ _c A schematic diagram of DOL and glass plate thickness h and a mathematical relationship thereof;

(b) graph Δ h<σ at DOL _s 、σ _c DOL and glass sheet thickness h.

FIG. 2 is a schematic diagram illustrating the bending moment and shape of a glass sheet when the entire sheet is uniformly stressed.

FIG. 3 illustrates DOL as<Δh<At (h-DOL), σ _s 、σ _s DOL and glass sheet thickness h.

FIG. 4 is a schematic diagram illustrating the bending moment and bending shape that are formed when a glass sheet is subjected to a non-uniform stress distribution.

Detailed Description

For further disclosure, but not limitation, the present invention is described in further detail below with reference to examples.

The cold roll forming principle of the high-aluminum cover plate glass of the invention is explained in detail as follows:

description of the symbols:

t is the temperature;

t is time;

k is the thermal conductivity;

rho is density;

C _p specific heat;

x is the coordinate value of the thickness direction of the glass plate;

y is the coordinate value of the length direction of the glass plate;

r is curvature radius;

k is glass thermal diffusivity (K is K/rho. C) _p )；

h is the thickness of the glass plate;

d is ion diffusion coefficient;

c, ion concentration;

b: lattice expansion constant (Lattice expansion constant);

σ _s : the compressive stress (Surface compressive stress) of the glass Surface;

σ _c : tensile stress (Central tension stress) in the Central region of the glass;

v: poisson's ratio.

As shown in fig. 1, if the thickness of the glass is t, after the potassium ions in the potassium nitrate molten salt exchange sodium ions on the surface and inside of the glass through a chemical rigidization process, the volume of the potassium ions is slightly larger than that of the sodium ions, so that the potassium ions generate a squeezing effect on the surface of the glass, and simultaneously, a compressive stress σ is generated on the surface of the glass _s (Surface compressive stress) and a corresponding tensile stress σ is generated in the central portion of the glass _c (Central tension stress). At this time, if the ion exchange depth is DOL, the following formula can be obtained according to the stress balance principle:

since the glass breaking behavior is under a compressive stress σ _s And tensile stress sigma _c The results produced by the combined action, according to the results of our laboratory tests, it was found that when the glass surface is free of compressive stress (and the central zone is also free of corresponding tensile stress), the glass breaking texture takes on a radially elongated and sharp shape; when the glass surface has compressive stress, the central region also has tensile stress, and at this time, the sigma _s Can cause strengthening of the glass surface, but σ _c The impact resistance of the central region of the glass is weakened.

Chemical strengthening of high-alumina cover glass mainly uses ion exchange to exchange metal ions on the glass surface with larger metal ions in the external molten salt, and the exchanged ions usually have the same electrovalence, for example, potassium ions in molten potassium nitrate are used to replace sodium ions on the glass surface in the most common combination currently in the industry, and the temperature is between 390 ℃ and 470 ℃. The volume of potassium ions is slightly larger than that of sodium ions, so that the surface of the glass generates compressive stress due to the volume effect, and simultaneously generates tensile stress at the central part of the glass correspondingly. Compressive stress on the glass surface may improve the ability of the glass surface to resist external impacts, but tensile stress in the central region of the glass may weaken the impact resistance in the center of the glass.

When external ions are at a sufficient temperature to diffuse into the glass via the glass surface, the diffusion behavior can be expressed as Fick's diffusion law:

the Boundary condition (Boundary condition) is

C＝C ₁ When it comes to

(Right surface of glass plate)

C＝C ₂ When is coming into contact with

(left surface of glass plate)

Initial conditions (Initial conditions) are

C＝C ₀ When t is 0 and C ₀ ＜C ₁ ，C ₀ ＜C ₂

After the ion exchange process, if the concentrations of the external ions on the left and right sides of the glass plate are the same, that is C ₁ ＝C ₂ According to the law of diffusion, foreign bodyThe concentration distribution of the molecules in the right half of the glass can be expressed as follows:

when in use

The Error function (Error function) is defined here as:

and satisfy erf (0) ═ 0, erf (1) ═ 0.8427

Similarly, the concentration profile of the foreign ions at the left half of the glass sheet can be expressed as follows:

when the temperature is higher than the set temperature

Since C (x) is a function of x, the average concentration C _av Can be obtained by C (x) integration of the whole thickness of the plate, i.e. for

Integration, the results are as follows:

here, the number of the first and second electrodes,

at this time, the stress distribution from the left to the right with respect to the thickness of the glass sheet can be expressed by the following equation:

here, B is a Lattice expansion constant (Lattice dimension constant).

From this, the compressive stress σ of the glass on both surfaces can be estimated _s And a central tensile stress sigma between the compressive stress regions _c ：

The stress distribution curves in the formulas (8) and (9) are in a left-right symmetrical form; when the ions of the external large volume diffuse into the glass, the surface concentration distribution of the ions has a consistent trend with the surface compressive stress, i.e., the higher the concentration, the higher the compressive stress generated by the region. At this time, if one of the surfaces of the glass sheet is thinned, i.e., one layer of the surface is removed, if one layer of glass is removed from the right side S1 glass surface and the thickness is Δ h, the thickness in the right half of fig. 1 (b) is reduced by Δ h, but the ion concentration profile of the remaining glass is the same as before and is not redistributed due to the thinning of the surface. However, the stress distribution curve is reduced due to the compressive stress at the left half, and the stress distribution of the thinned glass plate must be readjusted in the x-axis (thickness) direction, so that the overall compressive stress and the overall tensile force are balanced again.

According to equation (3), if the thickness of the right half is decreased from the surface by Δ h, the foreign ion concentration of the right surface will be:

when in use

After finishing, the following can be obtained:

when in use

At this time, at the position x, the stress value can be calculated by equation (8):

therefore, the compressive stress on the left side and the right side of the glass plate is not equal, so that the compressive stress difference is generated, the glass plate is bent, the compressive stress on the left side is not reduced, the edges of the two ends of the glass plate are pressed to the right side, and the phenomenon can be expressed by the following operation formula:

substituting equation (10) into equation (12) yields the mathematical relationship between Δ σ and Δ h.

For a sheet with four sides not fixed, it will deform when it is subjected to a uniform compressive stress, and because of the stress relationship, as shown in fig. 2, its Bending moment (Bending moment) M is:

in the above formula, w is the uniform compressive stress acting on the thin plate, and L is the plate length; here, w represents the stress difference between the left and right surfaces of the thin plate, and therefore w can be regarded as Δ σ, that is, w is Δ σ.

The bow formed by the sheet bending resulting from such a two-sided stress imbalance described above is also applicable to the high alumina glass sheets discussed herein. The arch height δ can be expressed here by the following formula:

where L is the length of the long side of the glass plate and R is the Radius of curvature (Radius of curvature) of the bow. The R value is closely related to the mechanical properties of the glass sheet material and can be expressed by the following formula:

substituting the formula (13) into the formula (15), and obtaining the formula (16) after arrangement as follows:

when Δ σ in formula (12) is substituted into formula (16), the result is obtained

If the formulas (16) and (17) are respectively substituted into the formula (14), the final product can be obtained

In the above formula the minus sign indicates that the bow is convex to the left,

the items represent the material factor and the material factor,

representing the geometric factor of the glass sheet, C ₁ -C′ _x Is represented by the concentration of foreign ions on both sidesThe difference in degree causes the difference in compressive stress. From the formula (18), when C' _x →C ₁ Shi Gao delta → 0, and vice versa when C' _x The maximum value delta appears at the arch height delta → 0 _max . Similarly, an increase in plate length L or a decrease in plate height h will result in an increase in bow height δ.

For high-aluminum cover plate glass with the same material, length, width, shape and thickness, the formula (18) can be simplified into

Constant in the above formula

As shown in fig. 3, when Δ h ═ DOL, the ion exchange layer on the right side of the glass sheet has been completely removed, at which time C is present _x ' 0, results in _x ' 0, results in Δ σ _s This is the maximum difference in compressive stress between the two glass surfaces. Thus, if the right glass continues to be thinned, Δ h > DOL, while the central tensile stress layer of the glass is directly exposed to the right surface. When the tensile stress area is continuously thinned, the stress area is reduced because of sigma _s The maximum value of the compressive stress is reached, the Bending moment (Bending moment) of the glass plate cannot be continuously improved, but the thickness of the tensile stress area is gradually reduced along with the increase of delta h in the tensile stress area, and the tensile stress sigma can be obtained according to the formula (1) and after rearrangement _c The thickness h-delta h and sigma of the thinned glass plate _s (compressive stress on the left side of the glass):

this formula applies to (h-DOL) > Δ h > DOL (21)

DOL, h, σ for a particular glass sample _s Are all fixed, and when Δ h increases (continuing to thin the glass), σ _c Will continue to increase until Δ h → (h-DOL), at which point σ continues to increase _c → infinity, meaning that the glass continues to be thinnedThe central tensile stress will increase all the way and provide new momentum for the bending of the glass sheet until it exceeds the material failure strength of the glass causing the glass to break or fracture.

Further discussion of the bending moment created in the tensile stressed region, if σ _c ⁰ Tensile stress when Δ h is DOL, then

By substituting equations (13), (14) and (15), M, R, δ can be obtained:

in the above formula

The items represent the material factor and the material factor,

representing the geometric factor of the glass sheet,

representing the increased tensile stress after the central region is thinned. As can be seen from the formula (24), when

Height delta of time bow _c → 0, indicates that the glass sheet bow height remains at the original delta, i.e., the bow height caused by the compressive stress differential. On the contrary, when

Height delta of time bow _c Increases with increasing tensile stress until the glass breaks. Similarly, an increase in the plate length L or a decrease in the plate thickness h will cause an increase in the bow height δ.

For high-aluminum cover plate glass with the same material, length, width, shape and thickness, the formula (25) can be simplified into

Constant in the above formula

When the reduced thickness exceeds DOL, the bending moment acting on the glass sheet is composed of two parts, delta when delta h is less than or equal to DOL and delta when delta h is greater than DOL _c . If Φ represents the sum of the heights of the arches due to these two causes, then

It can be observed from equation (27) that the former is determined by the concentration of foreign ions in the compressive stress layer, and the latter is determined by the increase of the tensile stress in the central region. It should also be noted here that the concentration of the foreign ions in the compressive stress layer and the σ in the tensile stress layer _c ⁰ All determined by the process conditions in ion exchange, the final resulting surface compressive stress σ _s The depth DOL of the compressive stress layer, in addition to the material properties of the glass itself, especially Young's modulus and conifer ratio, is the main factor affecting the bending deformation of the stress, and of course, the geometrical factors of the glass, such as length and thickness, are also the basic factors for the design of the bending process using this method.

For central tensile stress sigma _c After finishing, the formula can be expressed as follows:

1. when Δ h is equal to 0,

2. when the delta h is more than 0 and less than DOL,

the central tensile stress in this interval decreases as Δ h increases.

3. When Δ h is equal to DOL,

4. when DOL < Δ h < (h-DOL),

the central tensile stress in this interval will increase with the increase of Δ h, the tensile stress will increase the bending effect, and the bending effect generated by the original compressive stress is added, so that the bending moment after the two are added together will make the glass plate continue to bend until the glass is broken.

Furthermore, the above mathematical relationship still exists when the stress applied to the surface of the glass sheet becomes non-uniformly distributed, but differs in that the bending moment varies with different stress distributions, and thus different bending shapes are also created. For example, the situation shown in fig. 4 is the simplest case of non-uniform stress distribution, in which the stress is distributed in a non-uniform manner between points B and C, thereby creating a bending moment biased to the right, and the bending shape and bow height are thus changed. The situation in fig. 4 is that the long axis (long side) of the glass sheet is unevenly distributed, and if the short axis (wide side) is also unevenly distributed, the bending shape of the glass sheet is unevenly bent along the long and wide sides, and finally the bending shape of the entire glass sheet is determined by the balanced bending moment.

In the process implementation method, the local thinning of the glass plate can be simply adopted to realize the non-uniform stress distribution, because the thinned position can generate stress difference and bending moment, the non-thinned position is still in a stress balance (no stress difference), and the thinning position and thickness of one side or two sides of the glass plate are controlled to determine the bending shape of the glass plate, in particular to the asymmetric bending shape.

Specifically, the process for re-strengthening the thinned surface of the thinned cold-bent glass plate comprises the following steps:

1. selecting proper high-alumina cover plate glass, cracking according to the preset thickness and size, and trimming the edge of the cracked glass to avoid edge breakage, corner breakage and microcrack as much as possible.

2. And cleaning the cut glass plate, drying, and then transferring to a salt bath furnace filled with molten potassium nitrate for chemical strengthening. The chemical strengthening temperature can be set between 380 ℃ and 470 ℃ according to actual needs; the stiffening time is generally 4 hours or more, and is determined by the DOL actually required. And cleaning the chemically strengthened glass plate, and removing potassium nitrate adhered to the surface of the glass plate.

3. And measuring the depth DOL and the surface compressive stress of the chemically strengthened ion exchange layer as a basis for calculating the thinning depth, wherein the thinning depth is calculated by the bending degree of the glass plate which is designed in advance.

4. The method comprises the steps of calculating a thinning pattern according to the designed shape and the bending degree of a glass plate, coating a film according to the pattern, wherein the film is an acid-resistant film, then immersing the coated glass plate into a chemical thinning pool, and carrying out the thinning process at normal temperature, wherein the used chemical thinning liquid can be any one of acid liquid medicines known in the industry. The chemical thinning process is well known in the art, and can be performed by etching the glass surface without the acid-resistant film to uniformly remove the surface structure of the glass, and obtaining a uniform thinning effect, and maintaining the glass surface smooth and clean. In addition, the glass may be thinned by any method of thinning the surface of the glass by a frosting method, a lapping and polishing method, a laser ablation method, a hot acid bath method, or the like, and the method may be applied to the so-called glass thinning.

5. Cleaning the thinned glass, removing potassium nitrate and other salts remained on the surface of the glass, fully drying, then forming a curved surface on the glass plate, putting the curved glass into a muffle furnace, heating to 380-460 ℃ as required, keeping the temperature for no more than 4 hours, and enabling the glass plate to be subjected to moderate stress relaxation.

6. And (4) transferring the glass subjected to the step (5) into a chemical strengthening furnace to perform ion exchange in a salt bath mode, wherein the salt bath operation temperature can be 380-460 ℃ according to requirements. After the salt bath is completed, the glass is cleaned and dried, and then quality inspection is performed and the whole construction procedure is completed.

Example 1

The effect of heat treatment on CS and DOL on the surface of the chemically strengthened glass and the effect of secondary chemical strengthening are as follows:

in the embodiment, the rainbow special glass, namely high-aluminum cover plate glass, is Irico CG-01, and the thickness of the cover plate glass is 1.0 mm; potassium nitrate (purity more than 99%) is placed in a standard strengthening furnace, the strengthening temperature is 400 ℃, the holding time is 4 hours, and after chemical strengthening, the DOL and the CS are measured by using a FSM-6000LE surface stress meter manufactured by Japan dogma. The size of the glass sample is 50mm x 50mm, the thickness is 1.0mm, all glass test pieces are subjected to edge treatment and edge microcracks are eliminated as much as possible, and the glass pieces after being finished are cleaned and dried firstly and then are placed into a strengthening furnace for chemical strengthening.

In the chemical strengthening process, the glass is soaked in molten potassium nitrate at 400 ℃, potassium ions enter the glass from the surface of the glass and exchange sodium ions in the glass, and after 4 hours, the potassium ions can form a stress distribution on the surface and in the glass as shown in figure 1, and the stress distribution also approximately represents the concentration distribution of the potassium ions. And cleaning and drying the glass sample subjected to chemical strengthening, and then carrying out DOL and CS measurement. In this example, the ion exchange depth of the chemically strengthened glass was about 26 μm, the measured average data of the surface compressive stress was 917MPa, and the material parameters of the CG-01 high-alumina cover glass are summarized in Table 1.

TABLE 1

Placing the strengthened flat glass sample in a box type furnace at 450 ℃ for 4 hours, taking out the sample, cooling, measuring CS and DOL, finding that after stress relaxation caused by heat treatment on two sides of the glass plate, the CS value is reduced to about 240MPa, and the DOL is increased to about 57 mu m. It is expected that when the heat treatment time is long enough, the potassium ions will tend to be distributed evenly inside the glass plate, i.e. there will be no difference in the concentrations of the internal and external potassium ions, and at this time, CS will tend to be zero, and as the difference in the concentrations of the internal and external potassium ions of the glass gradually disappears, the FSM-6000LE surface stress meter will not be able to measure the DOL value by the principle of optical interference, i.e. when the concentration of the potassium ions inside the glass is too low, the sensitivity of the FSM-6000LE surface stress meter will be lower, and the low concentration potassium ions in this region will be ignored.

The heat-treated glass sample, namely the glass sample with the CS of 240MPa and the DOL of 57 mu m is placed in a strengthening furnace and is kept at the temperature of 400 ℃ for 2 hours, and the sample is taken out, cooled, cleaned, dried and measured with the CS and the DOL.

As shown in table 2, after ion exchange for 2 hours at 400 ℃ for the glass sample that had been stress relaxed after heat treatment, CS reached 822MPa, representing that potassium ions re-entered the glass and reconstructed the stress distribution, it is expected that more potassium ions would be allowed to enter the glass as the ion exchange time extended and the CS value would continue to increase. Further observing the DOL, it can be found that the FSM-6000LE surface stress meter can measure the stress layer depth of about 45 μm, which is much deeper than 26 μm after the first strengthening, but slightly less than 57 μm after the heat treatment (stress relaxation), presumably because the original potassium ions in the glass continue to diffuse to the central region of the glass and have thinner concentration when ion exchange is performed again at 400 ℃, wherein the potassium ion concentration of a part of the diffusion front is lower than the detection lower limit of the surface stress meter, so that the potassium ions cannot be detected, and the value of 45 μm is the part of the signal which can be detected by the stress meter. From experimental data on a flat high-alumina glass sample, the heat treatment can eliminate the surface stress of the partially strengthened glass, and can improve the surface stress and increase the depth of the stress layer through ion exchange again.

TABLE 2

Example 2

The effect of heat treatment and re-ion exchange on the surface Compressive Stress (CS) and depth of stress layer (DOL) of curved glass after cold bending:

in the embodiment, the rainbow special glass, namely high-alumina cover plate glass, is Irico CG-01, and the thickness is 0.7 mm; potassium nitrate (purity more than 99%) is placed in a standard strengthening furnace, the strengthening temperature is 400 ℃, the holding time is 4 hours, and after chemical strengthening, the DOL and the CS are measured by using a FSM-6000LE surface stress meter manufactured by Japan dogma. The size of the glass test piece is 130mm x 70mm, the thickness is 0.7mm, all glass test pieces are subjected to edge treatment and edge microcracks are eliminated as much as possible, the glass pieces after being finished are cleaned and dried, and then the glass pieces are placed into a strengthening furnace for chemical strengthening.

During the chemical strengthening process, the glass is soaked in molten potassium nitrate at 400 ℃, potassium ions enter the glass from the surface of the glass and exchange sodium ions in the glass, and after 4 hours, the potassium ions can form a stress distribution on the surface and in the glass as shown in figure 1, and the stress distribution also approximately represents the concentration distribution of the potassium ions. And cleaning and drying the glass sample subjected to chemical strengthening, and then carrying out DOL and CS measurement. In this example, the ion exchange depth of the chemically strengthened glass is about 25 μm, the average measured surface compressive stress data is 933MPa, one of the glass surfaces of all the chemically strengthened samples is covered with an acid-resistant film, the other glass surface is completely exposed and is etched in a chemical liquid, the main component of the chemical liquid is a mixed solution of sulfuric acid and hydrofluoric acid, the concentration of the sulfuric acid is 5 wt%, and the concentration of the hydrofluoric acid is 2 wt%, the chemically stiffened glass sample is thinned by 12 μm in the chemical liquid, the sample is chemically etched and thinned, the DOL is reduced to 9 μm, the CS is reduced to 194MPa, and the two data are used as new reference points for reestablishing high DOL and CS. All samples were again divided into two groups at this time: a group and B group, wherein A group samples are subjected to heat treatment at 460 ℃ for 2 hours and then subjected to ion exchange at 390 ℃ for 75 minutes; the B group was directly subjected to ion exchange at 390 ℃ for 75 minutes without heat treatment. The results obtained are collated in Table 3.

TABLE 3

It can be verified again from sample a in table 3 that even after the curved glass after cold bending is thinned again, the ion exchange can be performed again after the heat treatment to obtain higher CS and DOL. Sample B was further analyzed for its effectiveness in heat treatment as a control sample A, which had been ion exchanged again to a higher CS as expected, and which had been re-strengthened directly from the thinned CS (192MPa) to an initial value of 89MPa higher than the CS (103MPa) of sample A, so that after the same re-ion exchange procedure, the resulting CS (1003MPa) was also about 74MPa higher than the CS (929MPa) of sample A, and in the DOL portion, after ion exchange for 75 minutes at 390 ℃ for sample A, potassium ions diffused further into the glass interior than in the previous heat treatment and thus had a larger DOL value, but was limited by the sensitivity and measurement error of the surface stress meter, and showed no stable measurement data above 22 μm, and thus could only be represented by >22 μm, and the DOL of sample B increased to 13 μm after ion exchange for 75 minutes at 390 ℃, although there was an increase, the amplitude was less than sample a.

Example 3

The influence of heat treatment and secondary chemical ion exchange on the arch height of the curved high-alumina glass after chemical cold bending is as follows:

in this embodiment, a rainbow special glass, such as high-alumina cover glass, model Irico CG-01, with a thickness of 0.7mm is used; potassium nitrate (purity more than 99%) is placed in a standard strengthening furnace, the strengthening temperature is 400 ℃, the holding time is 4 hours, and after chemical strengthening, the DOL and the CS are measured by using a FSM-6000LE surface stress meter manufactured by Japan dogma. The size of the glass test piece is 130mm x 70mm, the thickness is 0.7mm, all glass test pieces are subjected to edge treatment and edge microcracks are eliminated as much as possible, the glass pieces after being finished are cleaned and dried, and then the glass pieces are placed into a strengthening furnace for chemical strengthening.

During the chemical strengthening process, the glass is soaked in molten potassium nitrate at 400 ℃, potassium ions enter the glass from the surface of the glass and exchange sodium ions in the glass, and after 4 hours, the potassium ions can form a stress distribution on the surface and in the glass as shown in figure 1, and the stress distribution also approximately represents the concentration distribution of the potassium ions. And cleaning and drying the glass sample subjected to chemical strengthening, and then carrying out DOL and CS measurement. In this embodiment, the ion exchange depth of the chemically strengthened glass is about 25 μm, the average measured surface compressive stress data is 933MPa, one of the glass surfaces of all chemically strengthened samples is covered with an acid-resistant film, the other glass surface is completely exposed and is placed in a chemical liquid for etching, the main component of the chemical liquid is a mixed solution of sulfuric acid and hydrofluoric acid, the concentration of sulfuric acid is 5 wt%, and the concentration of hydrofluoric acid is 2 wt%, the chemically strengthened glass sample is thinned by 12 μm in the chemical liquid, the bow height of the sample after chemical etching and thinning can be measured for the curved surface shape, for the glass plate sample with uniform stress distribution in the whole plate, the bow height can be used for calculating the curvature radius, so the bow ratio represents the glass, and the mathematical relationship between the two is as follows:

in the above formula, δ represents the bow height, L represents the length of the long side of the glass sheet, and R represents the radius of curvature. All samples were again divided into two groups at this time: a group and B group, wherein A group samples are subjected to heat treatment at 460 ℃ for 2 hours and then ion exchange at 390 ℃ for 75 minutes; group B was subjected to ion exchange at 390 ℃ for 75 minutes with heat treatment omitted, and the bow height was measured and converted to an R value for comparison in each process. The results obtained are collated in Table 4.

TABLE 4

The height of the bow of each sample represents the curvature of the sample, which is caused by the stress difference of the two surfaces of the glass plate, for example, sample A is thinned by 12 μm to generate a height of 2.5mm, which is equivalent to a curved surface with a curvature radius of 845mm, when the sample A is subjected to heat treatment at 460 ℃ for 2 hours, the two surfaces of the glass are subjected to stress relaxation, but the height of the bow is not changed, which indicates that the effect of the stress relaxation on the two glass surfaces is the same, that is, the surface stresses of the two glass surfaces are reduced at the same time in the same size, so the stress difference of the two surfaces is still the same, that is, the shape of the curved surface is not changed. After sample a was then subjected to ion exchange at 390 c for 75 minutes, the bow height decreased to 2mm, corresponding to an R value of 1056mm, and still maintained a fairly good curved shape, at which point the ion exchange rate for the thinned surface was faster than the normal surface, thus reducing the stress difference between the two glass surfaces, resulting in a decrease in bow height. From this, it can be inferred that if the ion exchange time is long enough, the final two surface stresses tend to be consistent, so for the engineering application of chemical cold bending, proper control of the time and temperature of the second time (ion exchange) can raise CS and DOL of the thinning surface and maintain the curved surface shape of the glass. Sample B can be regarded as a special case of sample a, i.e. when the heat treatment time is 0, the glass sample enters into the ion exchange again without stress relaxation, as discussed in examples 1 and 2, this way can also increase CS but the increase of DOL is smaller than that of the heat treated sample, and the whole process is still controllable, quantifiable and suitable for mass production.

Example 4

Example of cold-formed high alumina glass that retains its original shape and bow height after heat treatment and chemical ion exchange again:

in this embodiment, a rainbow special glass, such as high-alumina cover glass, model Irico CG-01, with a thickness of 0.7mm is used; potassium nitrate (purity more than 99%) is placed in a standard strengthening furnace, the strengthening temperature is 400 ℃, the holding time is 4 hours, and after chemical strengthening, DOL and CS are measured by using FSM-6000LE surface stress meter manufactured by Japan dogma. The size of the glass test piece is 130mm x 70mm, the thickness is 0.7mm, all glass test pieces are subjected to edge treatment and edge microcracks are eliminated as much as possible, the glass pieces after being finished are cleaned and dried, and then the glass pieces are placed into a strengthening furnace for chemical strengthening. One glass surface of the chemically strengthened sample is covered by an acid-resistant film, the other glass surface of the chemically strengthened sample is completely exposed and is placed in a chemical liquid for etching, the main component of the chemical liquid is a mixed solution of sulfuric acid and hydrofluoric acid, the concentration of the sulfuric acid is 5 wt%, the concentration of the hydrofluoric acid is 2 wt%, the chemically strengthened glass sample is thinned by 10 micrometers in the chemical liquid, and the bow height measurement of the curved surface shape can be carried out after the sample is chemically etched and thinned. The heat treatment temperature in this example was 450 ℃ for 4 hours, and the ion exchange temperature was 400 ℃ for 2 hours, which is different from the test conditions in the previous 2 examples.

In this example, the ion exchange depth, surface compressive stress, bow height, and data after heat treatment and re-ion exchange of the chemically strengthened glass are summarized in table 5:

TABLE 5

It is evident from the experimental data in table 5 that when the thickness reduction and heat treatment conditions are matched with the ion exchange conditions again, for example, sample a, the CS can be raised again to 926MPa, and the DOL is greater than 41 μm, the actual depth cannot be measured by the sensitivity of the current surface stress meter, and the bow height of the cold-bent glass is always maintained at 1.6mm, that is, the curvature can be kept constant at 1320mm, which fully proves the teachings claimed in the present patent. Sample B was also expected to increase the CS value to 951MPa and the DOL to a level of 25 μm, but lower than the DOL of sample A, and the original cold-bent shape was inferior to the mode and process conditions of sample A in terms of maintaining the shape of the cold-bent glass, because the bow height decreased while the glass was bent, i.e., the curvature increased.

Claims

1. The method for re-strengthening the chemical cold-bending thinning surface of the aluminosilicate cover plate glass is characterized by comprising the following steps: the thickness of the aluminosilicate cover plate glass is less than 2mm, surface stress is generated on the surface of the glass plate on the two surfaces of the glass plate through a chemical toughening method, one surface is thinned at the moment, so that the glass is bent and deformed due to unbalanced stress on the two surfaces, the characteristic is used and controlled, the purpose of bending the glass is achieved, and the chemically cold-bent thinned aluminosilicate cover plate glass is obtained; directly carrying out heat treatment on the cover plate glass, and then carrying out chemical ion exchange, so that the thinning surface is strengthened again, and the bent shape of the glass plate is maintained;

performing chemical ion exchange again, namely performing salt bath treatment on the chemically cold-bent and thinned aluminosilicate cover plate glass; the flux of the salt bath is KNO ₃ Mainly, the molar content is not lower than 90 percent; the salt bath temperature is 380-460 ℃; the time is not more than 4 hours; the heat treatment condition is specifically that the temperature is raised to 380-460 ℃, and the temperature is kept for no more than 4 hours;

the curvature of the glass sheet is determined by the reduced thickness, wherein the reduced thickness is controlled to be not more than the depth of the compressive stress layer on the surface of the glass sheet to be reduced; the thinning thickness is calculated according to the measured depth DOL of the chemically stiffened ion exchange layer and the surface compressive stress sigma s;

when delta h is less than or equal to DOL and the height of the arch formed by the curved glass after being thinned by delta h on one side is delta

Wherein

When h-DOL > delta h is more than or equal to DOL, the bow height phi of the curved glass is

Φ＝δ+δc，

Wherein

Δσ _c ＝σ _c -σ _c ⁰ And is

The delta value of the glass plate after the single-side thinning glass plate is subjected to heat treatment and secondary ion exchange treatment is consistent with that before the heat treatment;

the symbols in the above mathematical formula are illustrated as follows:

t is time

x is the coordinate value of the thickness direction of the glass plate

L is the length of the glass plate

Delta height of curved surface in compressive stress area of glass surface

δ _c When the curved surface is delta h greater than DOL, the height of the bow in the central tensile stress area of the glass

Delta sigma is the stress difference between two outer side surfaces of glass

h is the thickness of the glass plate

Δ h: depth of thinning of glass surface

D:K ⁺ Diffusion coefficient of ions

C ₀ :K ⁺ Original concentration of ions in glass composition

C ₁ :K ⁺ Concentration of ions on glass surface after 1 st chemical tempering method

C _x :K ⁺ The surface concentration of ions after the glass surface of the 1 st chemical toughening method is thinned by delta h

σ _s : compressive stress on glass surface after 1 st chemical tempering

σ _x : the stress of the glass in the surface compressive stress region after being thinned for delta h by the 1 st chemical toughening method is less than or equal to DOL

σ _c After the 1 st chemical toughening method is used for reducing the glass by delta h, the stress in the central tensile stress area of the glass is delta h>DOL

B:K ⁺ Na ion-entering into glass surface layer ⁺ Lattice expansion constant generated in situ

V. glass material's cedar ratio

E, elastic modulus.

2. The method for re-strengthening the chemical cold-bending thinned surface of the aluminosilicate cover glass according to claim 1, wherein: the surface compressive stress of the thinning surface after being re-strengthened is not lower than 450MPa, and the depth of the stress layer is not lower than 20 mu m.

3. The method for re-strengthening the chemical cold-bending thinned surface of the aluminosilicate cover glass according to claim 1, wherein: the thinning process is carried out at normal temperature or at any temperature which does not cause the stress on the surface of the glass to disappear; the thinning process is any one of chemical thinning and mechanical thinning methods.

4. The method for re-strengthening the chemical cold-bending thinned surface of the aluminosilicate cover glass according to claim 3, wherein: the thinning process is any one of a chemical etching method, a frosting method, a grinding and polishing method, a laser ablation method, an ion impact thinning method and a hot acid steam bath method.

5. The method for re-strengthening the chemical cold-bending thinned surface of the aluminosilicate cover glass according to claim 1, wherein: the chemically cold-bent thinned aluminosilicate cover plate glass is subjected to heat treatment, wherein the heat treatment condition is specifically that the aluminosilicate cover plate glass is heated for at least 60 minutes in an environment with the temperature not lower than 380 ℃, so that the compressive stress of the side with higher compressive stress, namely the non-thinned side, of the two surfaces of the glass is properly reduced to a state not lower than 200 MPa.

6. The method for re-strengthening the chemically cold-bent thinned surface of the aluminosilicate cover glass according to claim 5, wherein: the surface compressive stress of the thinned surface after heat treatment and ion exchange is not lower than 700MPa, and the depth of a stress layer is not lower than 25 mu m.