WO2021184185A1

WO2021184185A1 - Cold bending forming method for ultrathin high-aluminum cover plate glass

Info

Publication number: WO2021184185A1
Application number: PCT/CN2020/079619
Authority: WO
Inventors: 丁原杰
Original assignee: 福耀玻璃工业集团股份有限公司
Priority date: 2020-03-17
Filing date: 2020-03-17
Publication date: 2021-09-23

Abstract

Disclosed is a cold bending forming method for ultrathin high-aluminum cover plate glass, by means of which high-aluminum cover plate glass can be directly bent at room temperature. The method comprises: firstly, generating compressive stress on two surfaces of a glass plate, strengthening the two surfaces of the glass plate by using the compressive stress, and then thinning one of the surfaces of the glass plate, such that the glass plate is bent and deformed due to the compressive stress at the two surfaces being unbalanced.

Description

Cold bending forming method for ultra-thin high-aluminum cover glass

Technical field

This application is related to the manufacturing method of high-aluminum cover glass, and more specifically refers to a cold-formed manufacturing method that can curve ultra-thin high-aluminum cover glass without going through a high-temperature deformation process.

Background technique

At present, most of the front windshields and sunroofs on the market are made of two physically rigidized soda lime glass panels with a layer of polyvinyl butyral (PVB) glue film in between. These glasses can be flat design or curved design, but according to the fluid mechanics of the appearance, they are often designed into a micro-curved shape. Practice has proved that it is difficult to use physical tempering for glass with a thickness of 2.0mm or less. Therefore, to achieve the strength of the glass after physical rigidization, especially the compressive stress (sigma _s ) of the glass surface, the glass needs to be maintained above 2mm. Thickness, requirements and specific details about physical rigidity are known technologies, so I won’t repeat them here.

Because glass windows have traditionally been made of soda lime glass and PVB film glued, if you want to reduce the thickness of the glass to achieve the effect of weight reduction, while not reducing the mechanical properties of the glued glass window combination, it is limited by sodium. The strength and physical rigidity of lime glass are restricted by the two factors that require the thickness of the glass plate. To overcome this restriction, the soda-lime glass plate can be replaced by a high-alumina glass cover plate. The high-aluminosilicate cover glass has a higher strength than traditional soda-lime glass due to its high content of aluminum and silicon. The thinner thickness reaches the strength of traditional soda-lime glass. At the same time, chemical ion exchange can be used for chemical stiffening. This chemical stiffening method can be applied to any thickness of high-aluminum cover glass, so there is no glass plate thickness. However, the surface strength of the chemically rigidized high-alumina glass plate can be 2 to 3 times that of the physically rigidized soda lime glass plate, which can greatly improve the impact resistance of the glass surface. Therefore, the use of high-aluminum-calcium plate glass as a new material for vehicle windows has gradually become the technological development trend of lightweight vehicle glass. The use of high-aluminum-lime glass of appropriate thickness can partially replace or completely replace the current soda-lime glass for automobiles. However, considering the cost factor that the price of high-aluminum cover glass is higher than that of traditional soda-lime glass, the car window One of the two pieces of glass is replaced by high-aluminum glass, which can not only reduce the weight of the car window glass and maintain the strength of the glass window, but also control the cost within the acceptable range of the end user. This is currently feasible in the industry. Phased lightweight process. The chemical tempering method is not limited by the thickness of the glass. Therefore, for glass plates with a high-aluminum cover glass thickness of less than 2mm, the chemical tempering method can also be used to strengthen the glass surface. Generally speaking, the narrow chemical stiffening of glass refers to the use of ion exchange in the potassium nitrate molten salt for silicate glass containing sodium oxide. Potassium ions exchange with sodium ions on the glass surface. Because the volume of potassium ions is slightly larger than that of sodium ions, when potassium ions replace sodium ions on the glass surface, as shown in Figure 1(a), a surface will be formed on the surface. Compressive stress layer, the depth of this compressive stress layer generally refers to the depth of ion-exchanged layer (DOL), the resulting surface compressive stress (Compressive stress, σ _s ) will be affected by the glass composition and ion exchange Depth and other factors. The area between the compressive stress layers on the two outer surfaces of the glass plate is the central tension zone (Central tension, σ _c ). The surface compressive stress of the glass is in balance with the tensile stress of the central part during the chemical strengthening process. When the surface has a compressive stress to increase its resistance to external impact, the central area will be weakened due to tensile stress. The generalized chemical stiffening of glass refers to any metal ion on the glass surface that can be replaced by ion exchange, and the foreign ions newly placed on the glass surface are usually the same charge valence but slightly larger than the original glass surface. When sufficient kinetic energy is provided, it can diffuse into the glass by ion exchange and achieve the purpose of surface strengthening. Therefore, the exchange of potassium ions and sodium ions in potassium nitrate molten salt for glass containing sodium ions is only the most commonly used glass chemical strengthening method in the industry, but it is not the only way. Other glass chemical strengthening by ion exchange can be Seen in many references, I won't repeat it here.

Although high-aluminum cover glass can be chemically stiffened to obtain high surface strength, the surface strength generated by this surface compressive stress is mainly determined by the external ion concentration, temperature and time during ion exchange. Take sodium ion exchange as an example. When the temperature is about 420℃ and the reaction time is about 4 to 5 hours, a surface compressive stress of about 750-900 MPa can be obtained. There is a difference). This surface compressive stress is caused by the distribution of potassium ions in the glass. At this time, if the chemically strengthened glass is reheated and the temperature is higher than the ion exchange temperature, it will give enough kinetic energy to the potassium ions in the glass. And cause potassium ions to continue to diffuse into the glass, which will destroy the original potassium ion concentration distribution and reduce the potassium ion concentration on the glass surface, resulting in a reduction in surface compressive stress, that is, the glass surface is weakened. In addition, not only is the strengthened glass plate not suitable for reheating, but also because the tensile stress in the central area will weaken the strength of the central area, the strengthened glass plate will be more likely to collapse when it is cut and other mechanical processing is performed again than before strengthening. Edges or breakage. The same situation also occurs in physically rigidized glass panels. Therefore, when making glass car windows, whether chemically strengthened high-alumina glass panels or physically rigidized soda-lime glass panels need to be processed with geometric structure first, That is to say, processes related to size and glass curvature, such as cutting, drilling, grinding and polishing, and shape bending, should be completed first, and then the strengthening process should be carried out separately, and the glass plate should be glued after strengthening, and finally all the processes should be completed. The surface decoration process.

It can be seen from the above description that when two pieces of semi-finished glass that have undergone many kinds of processing in the early stage are to be glued, considerable resources have been invested in the entire process and considerable manufacturing costs have been generated. At this time, if the shape or curved surface is found during glueing. Failure to close together will cause considerable cost loss, and the strengthened glass, as mentioned above, is extremely difficult to rework. At present, the problem of inadherence between strengthened high-aluminum glass and soda-lime glass does occur in the industry. The reason is mostly caused by the high-aluminum cover glass, because the main reason for the inability to adhere is the curvature of the two pieces of glass. Inconsistent. Generally speaking, the thickness of soda lime glass is more than 2mm, and the glass softening point temperature is low, about 580～620℃ (depending on the brand model), it can be accurately processed and the production yield is high, but high The aluminum cover glass is relatively thin, the thickness is mostly below 1.8mm, and the softening point temperature is as high as 900 ℃. Such a high temperature makes it impossible for high-alumina glass to simultaneously perform the hot bending process with the soda lime glass in the same furnace, even if the hot bending is performed separately. It is also often because the thin glass under high temperature heating is easy to cause the unevenness of the temperature distribution to make the glass curvature inadequate, or the surface ripples or wrinkles caused by uneven heat transfer, and the corners caused by incomplete cooling. Thermal stress and other defects caused by high temperature and thin plates. The above-mentioned problems are the main difficulties that hinder the use of high-aluminum thin-plate glass to lighten automotive glass.

After a patent search, as mentioned in US Patent No. 10,237,184B2, the glass plate with a thickness of not more than 0.3mm is strengthened in a bending method in a strengthening furnace, and then glued to another hard plate after strengthening, and thereby strengthened The curved glass is flattened to achieve the effect of strengthening a single glass surface. After this curved surface strengthened glass is forcibly flattened, the original convex surface will be squeezed to form a new compressive stress, which has the effect of strengthening the surface again, but The other side (the original concave surface) will be opened, and its surface compressive stress will decrease, so this side is chosen to be attached to the hard plate, so that a stronger outer surface of the glued glass can be formed, although the two sides of the glass plate are also mentioned. It has different compressive stresses, but its purpose is not to bend the glass, nor is it applied to thin the glass surface, and the technology is limited to the thickness of the glass not exceeding 0.3mm. Furthermore, as mentioned in US Patent No. 9,302,937B2, the inner and outer glass surfaces of flat glass and tubular glass are strengthened under different conditions to produce different surface compressive stresses, by reducing one of the surfaces. The compressive stress can reduce the tensile stress in the central area of the glass, and then the sandwich structure is formed by gluing to achieve the purpose of strengthening the flat glued glass, while suppressing the micro-bending of the glass due to uneven stress. That is to say, this patent The bending of the glass caused by the uneven stress is regarded as a defect, and the patent does not mention that the glass surface can be thinned to control the bending of the glass. Furthermore, as described in U.S. Patent Publication No. 2018/0370852A1, a method for bending glass using different stresses on both sides of a glass plate is described. The method is to use ion-implantation technology to The surface is implanted with metal ions by a high-energy physical method, and then this piece of glass is placed in a chemical stiffening furnace for ion exchange. The ion exchange rate of the glass on the side with metal ions implanted will be reduced, resulting in different compressive stresses on both sides of the glass. Therefore, it deforms and bends in the process of strengthening. The disadvantages of this method are (1) ion implantation is a relatively expensive process, and whether it is suitable for processing large window glass, such as car windows, is still debatable; (2) The temperature of the strong furnace is as high as 400℃ or higher, and the curved shape formed at high temperature is more difficult to handle than at room temperature, and the shape at high temperature will change due to temperature difference when it is cooled to room temperature. At the same time, this patent application does not mention the thinning of the glass surface, a simple method that can be operated at room temperature.

Application content

The main purpose of this application is to provide a cold-bent forming method for ultra-thin high-aluminum cover glass, which can bend the high-aluminum cover glass without heating the glass, is simple and easy to use, and has low cost. Suitable for mass production applications.

In order to achieve the foregoing objective, this application provides a cold-bent forming method for ultra-thin high-aluminum cover glass, which includes the following steps: to generate compressive stress on the surface of the glass plate: firstly, pressure is generated on the two surfaces of a glass plate. The stress is used to strengthen the two surfaces of the glass plate with compressive stress; to bend the glass plate: use the method of thinning one surface of the glass plate to cause the glass plate to bend and deform due to the imbalance of the compressive stress on the two surfaces.

Optionally, in the step of generating compressive stress on the surface of the glass plate, the method for generating compressive stress on the surface of the glass plate is one of chemical stiffening or physical stiffening, and chemical stiffening refers to the surface produced by ion exchange of the glass plate. Compressive stress and physical rigidity refer to the surface thermal stress formed by the rapid temperature drop of the glass sheet after it has been heated up.

Optionally, the step of bending the glass plate is performed at a temperature that does not cause the compressive stress on the surface of the glass plate to quickly disappear.

Optionally, the step of thinning is performed at room temperature.

Optionally, the step of generating compressive stress on the surface of the glass plate is to generate a stress layer with a predetermined thickness on the two surfaces of the glass plate, and the step of bending the glass plate is to control the glass by reducing the predetermined thickness of the glass plate. Bending deformation of the board.

Optionally, the thickness of the thinning is controlled to not exceed the depth of the compressive stress layer on the surface of the glass plate to be thinned.

Optionally, the method of controlling the bending deformation of the glass plate is to control the position, area and thickness of the surface of the glass plate by a thinning pattern calculated according to the required shape and curvature of the glass plate.

Optionally, the thinning thickness is calculated based on the measured chemically rigidized ion exchange layer depth DOL and surface compressive stress σ _s .

Optionally, after the thinning pattern is calculated, the surface of the glass plate is coated according to the pattern, and then the coated glass plate is chemically thinned.

Optionally, the thinning position and area are implemented in the same or different patterns, the patterns including symmetrical or asymmetrical dots, lines, grids, lattices, etc., the formed glass plate The curved shape includes symmetrical and asymmetrical shapes.

Description of the drawings

_{Figure 1a is a schematic diagram of σ s} , σ _c , DOL and the thickness h of the glass plate and the mathematical relationship when Δh=0.

Fig. 1b is _{a schematic diagram of σ s} , σ _c , DOL and the thickness h of the glass plate when Δh<DOL.

Fig. 2 is a schematic diagram illustrating the bending moment and the bending shape formed when the entire glass plate is subjected to uniform stress.

_{Fig. 3 is a schematic diagram illustrating σ s} , σ _c , DOL and the thickness h of the glass plate when DOL<Δh<(h-DOL).

Fig. 4 is a schematic diagram illustrating the bending moment and the bending shape formed when the glass plate is subjected to a non-uniform stress distribution.

Fig. 5 is a graph illustrating graphs generated by various patterns.

Detailed ways

The application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand and implement the application, but the examples cited are not intended to limit the application.

The cold bending forming method of the ultra-thin high-aluminum cover glass of a preferred embodiment of the present application can complete the stable bending of the glass without heating the glass. The principle is that the glass has a surface compressive stress after being strengthened. When the stresses on both sides are in a balanced state, the glass will maintain its original shape during rigidization, that is, if it is flat during strengthening, it will remain flat after strengthening; if it is curved during strengthening, it will remain curved after strengthening. . At this time, if one side of the strengthened glass plate is thinned, that is, a layer of thickness is removed from the glass surface. Generally speaking, the thickness of this layer is only a few micrometers to tens of micrometers, and the glass surface is slightly thinned. The surface compressive stress of the glass plate is also reduced, so the stress on both sides of the glass plate loses balance, and the glass plate will bulge toward the surface with high stress, that is, form an arch, and the bow is facing the direction of greater surface compressive stress, and the thickness will be reduced. The stress is changed, so the overall bending shape of the glass sheet can be controlled by adjusting the thinning position, area, thickness and other factors. Conversely, if the strengthened glass plate itself has a regularly curved shape, such as an arcuate curve, the glass plate can also be restored to a flat shape by thinning the convex surface of the glass.

Specifically, the first step of the present application is to generate compressive stress on the surface of the glass plate: firstly, compressive stress is generated on the two surfaces of a glass plate to strengthen the two surfaces of the glass plate by compressive stress. The method is to first select a suitable high-aluminum cover glass, cut and crack according to the predetermined thickness and size, and trim the edges of the cracked glass to avoid chipping, chipping and micro-cracking as much as possible. Then the cut glass plate is cleaned, dried and then rigidized to generate compressive stress on the surface of the glass plate. The rigidizing method can be chemical rigidizing or physical rigidizing. In this embodiment, chemical rigidizing is used to make The two surfaces of the glass plate undergo ion exchange to generate surface compressive stress, and for the stress layer with a predetermined thickness, the chemical stiffening temperature can be set between 380-470℃, depending on actual needs, the stiffening time is generally 4 hours The above is also determined according to the actual DOL required. After chemical rigidization, the potassium nitrate adhering to the surface of the glass plate is removed.

When the general chemical tempering method is used in the traditional soda lime glass plate, the DOL is mostly between 12-20μm, and the corresponding σ _{s is} about 450-600MPa range. Because σ _s is also affected by the glass composition at the same time, even if the same DOL, for the difference in chemical composition caused by different glass brands and models, the obtained σ _s will also be different. Similarly, when the chemical tempering method is used for the commercial mass production of high-aluminosilicate cover glass, taking 0.7mm thickness glass as an example, the DOL is mostly between 25-40μm, and σ _{s is} about 650 -1000MPa. The chemically toughened glass plate can greatly increase the resistance to external impact by about 10-15 times, which is far better than the physical toughened 2-3 times.

The second step of the application is to bend the glass plate: at a temperature (including but not limited to room temperature) that does not cause the compressive stress on the surface of the glass plate to disappear, the surface of the glass plate is thinned to make the glass plate The glass plate is bent and deformed due to the imbalance of the compressive stress on the two surfaces. It is mainly based on the required glass plate shape and the pre-designed glass plate curvature to calculate the thinning pattern and thinning depth to control the surface reduction of the glass plate. The position, area and thickness of the thinning are calculated based on the measured chemically rigidized ion exchange layer depth DOL and the surface compressive stress σ _s , and are controlled to not exceed the depth of the compressive stress layer on the surface of the glass plate to be thinned. After the thinning pattern is calculated, the surface of the glass plate is coated (applied with an acid-resistant film) according to the pattern, and then the coated glass plate is chemically thinned. The so-called chemical thinning here is a technology known in the industry. The glass surface without the acid-resistant film is etched to remove the glass surface structure uniformly, and the uniform thinning effect is obtained, and the chemical thinning process that maintains the smooth and clean glass surface can be used to perform the so-called here. For glass thinning, the chemical thinning liquid used can be any known acidic liquid in the industry. In addition, glass thinning can also use frosting method, grinding and polishing method, laser ablation method, hot acid steam bath method, etc., any method that can thin the glass surface, all of which can be applied to the so-called glass reduction method. Thin.

In addition, the difference in compressive stress generated by the two outer surfaces of the glass plate can be a uniformly distributed stress difference or an uneven stress difference. The former will cause symmetrical deformation and bending of the glass plate, and the latter will cause asymmetry. The deformation and bending of the glass surface can control the bending moment of each position of the glass plate by controlling the position and area size of the thinning area of the glass surface, the thickness of the thinning and other factors, thereby controlling the bending degree of the glass plate at each position (Curvature). After thinning, the glass plate is cleaned, thickness, shape, and bending rate are measured and quality management is performed, and the subsequent gluing process is connected.

It can be seen from the above that this application aims at the technical problem that high-aluminum sheet glass is not easy to be bent and formed, and provides a method for bending high-aluminum cover glass without increasing the temperature, that is, the high-aluminum cover glass is first passed through After ion exchange and the expected chemical strengthening effect are achieved, local chemical thinning is used at room temperature to make the two outer surfaces of the glass substrate have different compressive stresses. Using the principle of this stress difference, the glass is naturally natural with the stress distribution. The result of bending.

In other words, the manufacturing method of this application can be regarded as a stress cold bending method. This high aluminum cover glass uses a stress cold bending curved surface forming method that can be applied to automobile instrument displays, car windows, panoramic sunroofs, and display protection covers. , And the appearance protection of other consumer electronic products, especially for the occasions where high-aluminum cover glass is not suitable for high-temperature softening molding. The glass bending process can be completed directly at room temperature without the need for molds, which can avoid glass bending Many shortcomings caused by the molding process. Moreover, compared with the hot bending process, the equipment and operation of the stress cold bending process are relatively simple, not only the cost is low, but the product reproducibility is high, and it has a great competitive advantage. What's more, this stress cold bending process can not only be applied to chemically strengthened high-aluminum cover glass, but the same principle and method can also be applied to other chemically strengthened and physically rigidized glass, including soda-lime glass plates.

Hereinafter, the principle of the stress cold bending process of the manufacturing method of this application will be described in detail:

Symbol description in the formula:

T: temperature;

t: time;

K: Thermal conductivity;

ρ: density;

C _p : specific heat;

x: the coordinate value in the thickness direction of the glass plate;

y: the coordinate value in the length direction of the glass plate;

R: radius of curvature;

k: Thermal diffusivity of glass (k=K/ρ·C _p );

h: thickness of glass plate;

D: Ion diffusion coefficient;

C: ion concentration;

B: Lattice dilation constant;

σ _s : Surface compressive stress on the glass surface;

σ _c : the central tension stress of the glass (Central tension stress);

ν: Poisson’s ratio.

As shown in Figure 1a and Figure 1b, if the thickness of the glass is t, the potassium ions in the potassium nitrate molten salt are chemically rigidized to exchange sodium ions on the surface and inside of the glass. Since the volume of potassium ions is slightly larger than the volume of sodium ions, This causes potassium ions to produce a squeezing effect on the glass surface, and at the same time causes a compressive stress σ _s (Surface compressive stress) on the glass surface, and a corresponding tensile stress σ _c (Central tension stress) at the center of the glass. At this time, if the ion exchange depth is DOL, according to the principle of stress balance, the following formula can be obtained:

When there is compressive stress on the glass surface, the central area will also correspond to the tensile stress. At this time, σ _s can cause the strengthening of the glass surface, but σ _c will weaken the impact resistance of the central area of the glass.

The chemical strengthening of high-aluminum cover glass mainly uses ion exchange to exchange metal ions on the surface of the glass with larger metal ions in the external molten salt. Usually, the exchanged ions have the same electricity price, for example, At present, the most commonly used combination in the industry is to use potassium ions in molten potassium nitrate to replace sodium ions on the surface of the glass, and the temperature is between 390°C and 470°C. Since the volume of potassium ions is slightly larger than that of sodium ions, compressive stress is generated on the glass surface due to the volume effect, and tensile stress is generated correspondingly in the center of the glass. The compressive stress on the glass surface can improve the ability of the glass surface to resist external impact, but the tensile stress in the central area of the glass will weaken the impact resistance of the glass center.

When external ions can diffuse into the glass through the glass surface at a sufficient temperature, this diffusion behavior can be expressed by Fick’s diffusion law:

Boundary condition is

C=C ₁ , when

(The right surface of the glass plate)

C=C ₂ , when

(Left surface of glass plate)

The initial condition (Initial condition) is

C=C ₀ when t=0 and C ₀ ＜C ₁ , C ₀ ＜C ₂

After the ion exchange process, if the concentration of foreign ions on the left and right sides of the glass plate is the same, it means C ₁ =C _2. According to the law of diffusion, the concentration distribution of foreign ions in the right half of the glass can be expressed as follows:

when

Here the error function is defined as:

And meets erf(0)=0, erf(1)=0.8427

In the same way, the concentration distribution of foreign ions on the left half of the glass plate can be expressed as follows:

when

Because C(x) is a function of x, the average concentration C _av can be obtained by integrating C(x) on the entire plate thickness, which means that for

Points, the results are as follows:

Here,

At this time, the stress distribution from the left to the right of the glass plate thickness can be expressed by the following formula:

Here, B is the lattice expansion constant (Lattice dilation constant).

Therefore, the compressive stress σ _{s of the} glass on the two surfaces and the central tensile stress σ _c between the compressive stress zones can be calculated:

According to the stress distribution curves in formulas (8) and (9), it presents a left-right symmetrical form. When a larger volume of external ions diffuse into the glass, the surface concentration distribution and surface compressive stress show a consistent trend, meaning that the higher the concentration The compressive stress generated by the area is also greater. At this time, if the surface of any one side of the glass plate is thinned, that is, the surface layer is removed. If a layer of glass is removed from the right S1 glass surface and the thickness is Δh, the thickness of the right half in Figure 1b is reduced Δh, but the ion concentration distribution curve of the remaining glass is the same as before, and it will not be redistributed due to the thinning of the surface. However, the stress distribution curve will reduce the compressive stress on the left half, and the thinned glass plate must be readjusted in the x-axis (thickness) direction to rebalance the overall compressive stress and tensile force.

According to formula (3), if the thickness of the right half is reduced by Δh from the surface, the concentration of foreign ions on the right surface will become:

when

After finishing:

when

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

Therefore, the compressive stresses on the left and right sides of the glass plate are not equal, resulting in a difference in compressive stress, which will cause the glass plate to bend. Since the left side is not thinned, the compressive stress will be larger, and the two ends of the glass plate will be pressed to the right. This phenomenon can be used as follows Expression expression:

Substituting formula (10) into formula (12) can obtain the mathematical relationship between Δσ and Δh.

Secondly, for a thin plate whose four sides are not fixed, it will deform when subjected to a uniform compressive stress. At this time, due to the stress relationship, as shown in Figure 2, its 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 also represents the stress difference between the left and right sides of the thin plate. Therefore, w can be regarded as Δσ, that is, w=Δσ.

The arcuate surface formed by the bending of the thin plate caused by the above-mentioned two-sided stress imbalance is also suitable for the high-alumina glass thin plate discussed here. Here the arc height δ can be expressed by the following formula:

Here L is the length of the long side of the glass plate, and R is the radius of curvature of the bow. The R value is closely related to the mechanical properties of the glass sheet and can be expressed by the following formula:

Substituting formula (13) into formula (15), after sorting, formula (16) can be obtained as follows:

Then substituting Δσ in formula (12) into formula (16), we can get

If we substitute formulas (16) and (17) into formula (14), we can get

The negative sign in the above formula means that the bow is convex to the left.

Item representative material factor,

Represents the geometric factor of the glass plate, and C ₁ -C' _x represents the difference in compressive stress caused by the difference in the concentration of foreign ions on both sides.

It can be known from formula (18) that when C′ _x → C ₁ , the bow height δ → 0, on the contrary, when C′ _x → 0, the bow height δ will have the maximum value δ _max . In the same way, an increase in the length of the board or a decrease in h after the board will cause an increase in the bow height δ.

For high aluminum cover glass of the same material, length and width shape, and thickness, formula (18) can be simplified as

The constant in the above formula

As shown in Figure 3, when Δh=DOL, the ion exchange layer on the right side of the glass plate has been completely removed. At this time, C _x′ =0, resulting in σ _x′ =0, and the result is Δσ=σ _s . It is the maximum value of the compressive stress difference between the two glass surfaces. Therefore, if the glass on the right continues to be thinned, Δh>DOL, and the central tensile stress layer of the glass is directly exposed on the right surface. When the tensile stress area continues to be thinned, because σ _s has reached the maximum compressive stress, the bending moment of the glass plate will not continue to increase, but as Δh increases in the tensile stress area, the tensile stress area According to formula (1) and rearranged, _{the relationship between the tensile stress σ c} and the thickness of the thinned glass plate h-Δh and σ _s (compressive stress on the left side of the glass) can be obtained:

This formula applies to (h-DOL)＞Δh＞DOL (21)

For a specific glass sample, DOL, h, and σ _s are all fixed. When Δh increases (the thinning of the glass continues), σ _c will continue to increase until Δh→(h-DOL), at which time σ _c → ∞ means that as the glass continues to be thinned, the central tensile stress will increase all the way and provide new power for the glass sheet to bend until the tensile stress exceeds the glass's material breaking strength, causing the pull to break or break.

Further discuss the bending moment formed in the tensile stress area, if σ _c ⁰ represents the tensile stress when Δh = DOL, then

Δσ _c =σ _c -σ _c ⁰ and

Substituting formulas (13)(14)(15) again, we can get M, R, δ:

In the above formula

Item representative material factor,

Represents the geometric factor of the glass plate,

Represents the increased tensile stress after the central area is thinned. It can be known from formula (24) that when

When the bow height δ _c → 0, it means that the bow height of the glass plate is still maintained at the original δ, which is the bow height caused by the difference in compressive stress. On the contrary

The arch height δ _c will increase with the increase of tensile stress until the glass breaks. In the same way, the increase of the plate length L or the decrease of the plate thickness h will cause the increase of the bow height δ.

For high aluminum cover glass of the same material, length and width shape, and thickness, formula (25) can be simplified as

The constant in the above formula

When reducing the thickness exceeds DOL, bending moment in the glass sheet is composed of two parts, δ and Δh of at Δh≤DOL> when DOL δ _c. If Ф represents the total bow height caused by these two reasons, then

It can be observed from formula (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 in tensile stress in the central region. It should also be noted here that the concentration of foreign ions in the compressive stress layer and the σ _c ⁰ in the tensile stress layer are both determined by the process conditions in the ion exchange, and the resulting surface compressive stress σ _s The DOL and the depth of the compressive stress layer, together with the material properties of the glass itself, especially the Young’s coefficient and the ratio of pine and cypress, become the main factors affecting the stress bending deformation. Of course, the geometric factors of the glass, such as length and thickness, also apply this method. Basic factors when designing the bending process.

Regarding the central tensile stress σ _c , it can be expressed by the following formula after finishing:

1. When Δh=0,

2. When 0＜Δh＜DOL,

In this interval, the central tensile stress will decrease with the increase of Δh.

3. When Δh=DOL,

4. When DOL＜Δh＜(h-DOL),

In this interval, the central tensile stress will increase with the increase of Δh, and the tensile stress will increase the bending effect. In addition to the bending effect produced by the original compressive stress, the combined bending moment makes the glass plate continue to bend until the glass breaks. .

Furthermore, when the stress applied to the surface of the glass plate becomes non-uniformly distributed, the above mathematical relationship still exists, but the difference is that the bending moment will change with different stress distributions, which will result in different bending shapes. For example, the situation shown in Figure 4 is the simplest one of the uneven distribution of stress. The stress in the figure is unevenly distributed between point B and point C, so a bending moment to the right is formed, and the bending shape The bow height also changes accordingly. The situation in Figure 4 is only the non-uniform distribution on the long axis (long side) of the glass plate. If the non-uniform distribution of stress is also performed on the short axis (wide side) at the same time, the curved shape of the glass plate will follow The long and wide sides are unevenly bent at the same time, and the final bending shape of the entire glass plate will be determined by the balanced bending moment.

In the process implementation method, to achieve a non-uniform stress distribution, you can simply take the partial thinning of the glass plate, because the thinned position will have a stress difference and bending moment, and the position without thinning is still in the stress balance (no The state of stress difference), controlling the position and thickness of the thinning of one or both sides of the glass sheet can determine the curved shape of the glass sheet, especially the asymmetrical curved shape.

Hereinafter, several embodiments and related parameters of the manufacturing method of this application are cited:

Example 1:

This example uses the high-aluminum cover glass of Rainbow Special Glass, model Irico CG-01, thickness 0.7mm; uses a standardized strong furnace with built-in potassium nitrate (purity above 99%), the strengthening temperature is 400 ℃, and the use of Japan after chemical rigidization The FSM-6000LE surface stress meter of Orihara Manufacturing Co., Ltd. measures DOL and σ _s . The size of the glass sample is 140mm x 70mm. All glass test pieces are edge-treated to eliminate edge micro-cracks as much as possible. The finished glass pieces are cleaned and dried first, and then placed in a chemical furnace for chemical rigidity. The chemical rigidization time will depend on the required DOL and can range from 4 hours to 48 hours.

_{DOL and σ s were} measured after cleaning and drying the chemically hardened glass sample. In this example, the ion exchange depth of chemically rigidized glass is 40μm, and the measured surface compressive stress is 858MPa. The material parameters of CG-01 high-aluminum cover glass are listed in Table 1, which can be used to calculate and verify mathematical models and experiments. result.

Table 1

After chemically hardened samples, one glass surface is covered with an acid-resistant film, and the other surface is completely exposed and placed in a chemical solution for etching. The main component of the chemical solution is a mixture of sulfuric acid and hydrofluoric acid. The concentration of sulfuric acid is 5%, the concentration of hydrofluoric acid is 2%. In this chemical solution, the chemically hardened glass sample is thinned to the specified thickness. After the sample is chemically etched and thinned, the shape and bow height can be measured. For glass plate samples with uniform stress distribution, the bow height can be used to calculate the radius of curvature, so it also represents the curvature of the glass.

The different thinning thickness Δh and the corresponding bow height δ after bending are measured and arranged in Table 2, and the bow height of the measured side under each thinning thickness and the calculated bending radius are calculated according to the aforementioned mathematical formula. R, the compressive stress difference Δσ, the bow height δ generated by the compressive stress difference, and the tensile stress σ _c after Δh>DOL, and the bow height δ _c caused by the tensile stress. Table 2 shows that when Δh=0, σ _c ＝10.74 can be calculated by formula (1). At this time, the bow height is 0 and the glass plate is in a state of stress equilibrium; when DOL>Δh>0, δ is produced by the pressure difference , As the second item in Table 2; when Δh=DOL, Δσ=σ _s , and the material factor can be calculated using formula (21)

The value calculated here is 4.8x10 ^-12 MPa ^-1 ^{, which is a bit larger than the value 2.58x10 -12} MPa ^-1 calculated using the Young’s coefficient and Poisson’s ratio in Table 1. In line with expectations, because the values in Table 1 are in the state before ion exchange, when potassium ions gradually diffuse from the glass surface into the glass, the internal structure of the glass is strengthened by the lattice expansion effect, so the material factor will increase slightly, just like It is the same reason that the surface hardness of the glass after chemical hardening will increase. _{When Δh>DOL, the three values of σ c} , Δσ _c and δ _c can be calculated by formulas (21), (22) and (25), and at the same time, the residual compressive stress difference Δσ and the corresponding δ can be calculated at the same time .

Table 2

Example 2:

The glass plate sample used in this example is the same as that in Example 1. The only difference is that the ion exchange depth is different. The DOL in Example 2 is 67 μm, and the measured surface compressive stress is 789 MPa. The sample preparation method is the same as that in Example 1. Calculation method to get the material factor

The value of is 6.99x10 ^-12 MPa ^-1 . The measurement and calculation results are summarized in Table 3:

table 3

Example 3:

The glass plate sample used in this example is the same as that in Example 1. The only difference is that the ion exchange depth is different. The DOL in Example 3 is 92 μm, and the measured surface compressive stress is 722 MPa. The sample preparation method is the same as that in Example 1. Calculation method to get the material factor

The value of is 8.83x10 ^-12 MPa ^-1 . The measurement and calculation results are summarized in Table 4:

Table 4

Example 4:

This example uses low-aluminum glass produced by Langfang CSG, model NB3, thickness 0.7mm; uses a standardized strong furnace with built-in potassium nitrate (purity above 99%), and the chemical strength temperature is 400℃. After chemical rigidization, it is made by Japan Orihara The FSM-6000LE surface stress meter measured DOL and σ _s . The size of the glass sample is 140mm x 70mm. The finished glass sheets are cleaned and dried first, and then placed in a chemical strengthening furnace for chemical stiffening. The material parameters are summarized in Table 5.

table 5

The DOL after chemical rigidization is 24.5μm, and the measured surface compressive stress is 666MPa. Using the same sample preparation method and calculation method as in Example 1, the material factor is obtained

The value of is 3.38x10 ^-12 MPa ^-1 ^{, the value of the glass material factor before chemical stiffening is 2.50x10 -12} MPa ^-1 calculated using the parameters in Table 5, which is in line with expectations, and is slightly smaller than the value after chemical strengthening. The measurement and calculation results are summarized in Table 6:

Table 6

Example 5:

In the second step of this application, different thinning patterns can produce various curved shapes on the glass surface, forming a non-uniform distribution of stress on the glass surface, thus affecting the final curved shape of the glass. The graphs generated here are only examples but the stress cold bending technique is not limited to these patterns and curved shapes.

It must be mentioned that the thinning process in the manufacturing method of this application can use any one or more of the following methods, but not limited to the following methods, such as: chemical etching, frosting, grinding and polishing, laser Ablation method, ion impact thinning method, hot acid steam bath method, etc., and the molten salt used includes but not limited to potassium nitrate, sodium nitrate, or other metal salts that can be eutectic with potassium nitrate. Secondly, the surface compressive stress on both sides of the glass plate can be unbalanced or uneven before thinning, including but not limited to the tin surface of float glass, which will reduce the ion exchange rate when chemically stiffened, resulting in the surface of the tin surface of the glass plate. The compressive stress is less than the air surface. At this time, the stress cold bending method can still be used to make curved glass by thinning the glass surface, or the air surface can be appropriately thinned to eliminate the glass bending after chemical rigidization.

To sum up, the cold bending forming method of ultra-thin high-aluminum cover glass provided in this application mainly refers to the method of cold-bending the high-aluminum cover glass, which is to first pass the ultra-thin high-aluminum cover glass plate through After the chemical strengthening treatment, the method of local chemical thinning is used to make the two outer surfaces of the glass plate have different compressive stresses. Using the principle of this stress difference, the glass plate is naturally bent with the stress distribution, and high temperature heating can be avoided. , The bending of the glass plate is directly completed at room temperature without the need for hot bending molds. These curved surface forming methods for high-aluminum cover glass using stress cold bending can be applied to automobile instrument displays, car windows, panoramic sunroofs, and display protection covers. , Compared with the appearance protection of other consumer electronic products, especially for the occasions where high-aluminum cover glass is not suitable for high-temperature softening molding, the process and equipment of this method are simple, easy to control, and the production cost is much lower than the high-temperature softening molding process of glass plates. Very practical value.

The above-mentioned embodiments are only preferred embodiments for fully explaining the present application, and the protection scope of the present application is not limited thereto. The equivalent substitutions or transformations made by those skilled in the art on the basis of this application are all within the protection scope of this application. The scope of protection of this application is subject to the claims.

Industrial applicability

This application provides a cold-bent forming method for ultra-thin high-aluminum cover glass, which can bend the high-aluminum cover glass without heating the glass, is simple and easy to use, has low cost, and is suitable for mass production applications. Possess industrial applicability.

Claims

A cold bending forming method for ultra-thin high-aluminum cover glass includes the following steps:

Generate compressive stress on the surface of the glass plate: first generate stress on two surfaces of a glass plate to strengthen the two surfaces of the glass plate by compressive stress; and

Bending the glass plate: By thinning one surface of the glass plate, the glass plate is bent and deformed due to the imbalance of the compressive stress on the two surfaces.
The cold-bent forming method of ultra-thin and high-aluminum cover glass according to claim 1, wherein in the step of generating compressive stress on the surface of the glass plate, the method for generating compressive stress on the surface of the glass plate is chemical stiffening or physical One of stiffening, chemical stiffening refers to the surface compressive stress generated by ion exchange of the glass plate, and physical stiffening refers to the surface thermal stress formed by the rapid cooling of the glass plate after the temperature rises.
3. The cold-bent forming method for ultra-thin high-aluminum cover glass according to claim 1, wherein the step of bending the glass plate is performed at a temperature that does not cause the surface compressive stress of the glass plate to quickly disappear.
8. The cold-bent forming method of ultra-thin high-aluminum cover glass according to claim 3, wherein the step of thinning is carried out at room temperature.
The cold-formed manufacturing method of ultra-thin and high-aluminum cover glass according to claim 3, wherein the step of generating compressive stress on the surface of the glass plate is to generate a stress layer with a predetermined thickness on two surfaces of the glass plate, so that 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.
5. The cold-formed manufacturing method of ultra-thin high-aluminum cover glass according to claim 5, wherein the thickness of the thinning is controlled to not exceed the depth of the compressive stress layer on the surface of the thinned glass plate.
8. The cold-bent forming method of ultra-thin high-aluminum cover glass according to claim 6, wherein the method of controlling the bending deformation of the glass plate is a thinning pattern calculated based on the required shape and curvature of the glass plate. To control the thinning position, area and thickness of the glass plate surface.
8. The cold-bent forming method for ultra-thin high-aluminum cover glass according to claim 7, wherein the thickness reduction is calculated based on the measured chemically stiffened ion exchange layer depth and surface compressive stress σ s .
8. The cold bending forming method of ultra-thin high-aluminum cover glass according to claim 8, wherein after calculating the thinning pattern, the surface of the glass plate is coated according to the pattern, and then the coated glass plate is chemically thinned.
The cold bending forming method of ultra-thin high-aluminum cover glass according to claim 7, wherein the position and area of the thinning are implemented in the same or different patterns, and the patterns include symmetrical or asymmetrical dots. , Line, grid, dot matrix, etc. The curved shape of the glass plate formed includes symmetrical and asymmetrical shapes.