Method for manufacturing a flexible cover window and a flexible cover window manufactured using the method

Abstract

A method for manufacturing a flexible cover window is proposed, which can simultaneously strengthen a plane portion and a bending portion by using alkali metal ions having an ionic radius smaller than that of alkali metal ions contained in glass. A flexible cover window manufactured using the method is also proposed. Using alkali metal ions having a smaller ionic radius than that of alkali metal ions contained in glass, the plane portion and the bending portion are simultaneously strengthened to simplify the process, and the flexible cover window ensures strength characteristics and bending characteristics by controlling the tensile stress of the entire portion of the flexible cover window.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Korean Patent Application No. 10-2020-0178950, filed on December 18, 2020, which is hereby incorporated by reference in its entirety for all purposes. Technical Field

[0003] The present disclosure relates to a manufacturing method for a glass-based cover window and a flexible cover window manufactured using the method. The present disclosure relates to a manufacturing method for a flexible cover window capable of simultaneously reinforcing a planar portion and a bent portion by using alkali metal ions having a smaller ion radius than alkali metal ions included in glass, and to a flexible cover window manufactured by the method. Background Art

[0004] In recent years, electrical and electronic technologies have developed rapidly, and various types of display products have emerged to meet the needs of the new era and the demands of various consumers.

[0005] As far as flexible displays are concerned, research on displays is basically conducted in the form of bending, rolling, and stretching from bending. A cover window for protecting a display panel as well as the display panel should be formed to be flexible.

[0006] Such a flexible cover window should have good flexibility and should not generate marks on the bent portion even when bent repeatedly, and thus should not distort image quality.

[0007] For the cover window of existing flexible displays, a polymer film such as PI or PET is used on the surface of the display panel.

[0008] However, in the case of the polymer film, due to its weak mechanical strength, the polymer film is only used to prevent scratches on the display panel, is easily affected by impact resistance, has low light transmittance, and is known to be relatively expensive.

[0009] In addition, in the case of such a polymer film, as the number of times the display is bent increases, marks are left on the bent portion, resulting in damage to the bent portion. For example, during evaluation of the bending limit (usually 200,000 times), the polymer film may be crushed or torn.

[0010] Recently, various studies on glass-based cover windows have been conducted in order to overcome the limitations of cover windows made of polymer films.

[0011] For a glass-based cover window, the following basic necessary physical properties are required: bending properties are met, the screen has no distortion, it has sufficient strength even when repeatedly touched by, for example, a stylus, and it has a certain pressure.

[0012] In order to meet the strength characteristics of the cover window, the glass should have a certain thickness or greater, and in order to meet the bending characteristics, the glass should be less than a certain thickness. In addition, research is needed on the optimal cover window thickness and structure without distorting the screen.

[0013] According to the related art, there are many technologies for forming glass to satisfy bending characteristics and strength characteristics and forming a bending region (bending portion) of a cover window to be relatively slimmer than other regions (planar portion).

[0014] In order to enhance the strength of this cover window, chemical strengthening method is mainly used. In chemical strengthening, when the alkali-based glass is immersed in high temperature KNO 3 When in molten salt, the potassium ions in the molten salt are replaced by the sodium ions in the glass, generating compressive stress on the surface of the glass. At this time, the volume of the glass increases due to the influence of the potassium ions with large atomic size.

[0015] In particular, when the bent portion is formed to be slim, natural explosion, breakage, or corrugation of the cover window may occur due to a high compression ratio in the bent portion caused by imbalance of tensile stress according to thickness, which will seriously affect the quality of the product.

[0016] Figure 1A and Figure 1B The diagram shows the imbalance of tensile stress caused by the thickness difference between the bent portion and the plane portion in the conventional flexible cover window. As shown in the figure, there is a phenomenon that the thin plane portion increases more, thereby causing the overall quality of the cover window to deteriorate.

[0017] To solve this problem, methods have been tried to adjust the degree of enhancement between the bent portion and the flat portion, but it is difficult to ensure uniform enhancement across the entire cover window. For each cover window position, there is still the problem of non-uniformity of compressive stress (CS) and enhancement depth (DOL). Summary of the invention

[0018] The present disclosure arises from the above-mentioned needs, and an object of the present disclosure is to provide a method for manufacturing a flexible cover window, which uses alkali metal ions having an ionic radius smaller than the ionic radius of alkali metal ions included in glass to simultaneously strengthen a planar portion and a bent portion, and to provide a flexible cover window manufactured using the method.

[0019] In order to achieve the above-mentioned objectives, the present disclosure provides a method for manufacturing a flexible cover window, which uses alkali metal ions having an ionic radius smaller than the ionic radius of alkali metal ions included in glass to simultaneously strengthen a planar portion and a bent portion, and provides a flexible cover window manufactured using the method.

[0020] Furthermore, the alkali metal ion having an ion radius smaller than that of the alkali metal ion contained in the glass is preferably lithium.

[0021] Furthermore, the manufacturing method of the flexible cover window is preferably performed using a molten salt including potassium ions and lithium ions.

[0022] Furthermore, the molten salt preferably comprises KNO 3 、NaNO 3 and LiNO 3 .

[0023] In addition, according to the method of manufacturing the flexible cover window, a first reinforcement process may be performed by using a molten salt including potassium ions and lithium ions, and then a second reinforcement process may be performed by using a molten salt including potassium ions.

[0024] Furthermore, the molten salt used in the first enhancement process preferably contains KNO 3 、NaNO 3 and LiNO 3 .

[0025] In addition, based on the total molten salt, KNO 3 The content of LiNO should be 20 to 70 parts by weight, and LiNO 3 The content should be 0.1 parts by weight to 5 parts by weight.

[0026] Furthermore, the molten salt used in the second enhancement process preferably includes LiNO 3 and NaNO 3 Any one or both of, including KNO 3 .

[0027] In addition, LiNO 3 The amount of LiNO is preferably equal to or less than that of LiNO in the first enhancement process. 3 The amount.

[0028] In addition, based on the total molten salt, LiNO 3 The amount of is preferably contained in an amount of 0.1 parts by weight to 2 parts by weight.

[0029] The present disclosure relates to a glass-based cover window. In particular, the present disclosure provides a flexible cover window that maintains an enhanced glass-specific texture while simultaneously reinforcing a planar portion and a bending portion using alkali metal ions having a smaller ion radius than alkali metal ions contained in the glass to simplify the process. By adjusting the tensile stress of the entire region, a flexible cover window that ensures strength characteristics and bending characteristics is provided.

[0030] In particular, the present disclosure provides a method for preventing deformation, bending and damage of a glass substrate after strengthening due to a difference in tensile stress caused by a thickness difference between a flat portion and a bent portion. By performing a chemical strengthening process using metal ions, an additional process such as a mask process is not required in the existing partial chemical strengthening process, thereby improving mass productivity.

[0031] Therefore, by chemically reinforcing the flat portion and the bent portion simultaneously, the reinforcing unevenness problem such as the dispersion and precision coating of the coating solution as a conventional partial chemical reinforcing process and the deviation problem of the upper end and the lower end due to the stagnation phenomenon of the coating solution are completely solved. Since the mask process is not performed, the process can be simply performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1A and Figure 1B is a view showing a photograph of a flexible cover window according to the related art;

[0033] Figure 2 and Figure 3 is a schematic diagram for explaining the principle of the present disclosure; and

[0034] Figure 4 is a view showing a photograph of a flexible cover window according to the present disclosure. DETAILED DESCRIPTION

[0035] The present disclosure relates to a glass-based cover window. In particular, the present disclosure provides a flexible cover window that maintains an enhanced glass-specific texture while reinforcing a plane portion and a bending portion using alkali metal ions having a smaller ion radius than alkali metal ions included in the glass to simplify the process. By adjusting the tensile stress of the entire area, a flexible cover window that ensures strength characteristics and bending characteristics is provided.

[0036] In particular, the present disclosure provides a flexible cover window for preventing deformation, bending and damage due to a tensile stress difference of a strengthened glass substrate caused by a thickness difference between a flat portion and a bent portion. By performing a chemical strengthening process using metal ions, an additional process such as a mask process is not required in the existing partial chemical strengthening process, thereby improving mass productivity.

[0037] Therefore, by chemically reinforcing the flat portion and the bent portion at the same time, the reinforcing unevenness problem such as the dispersion and precision coating of the coating solution as a conventional partial chemical reinforcing process and the deviation problem of the upper end and the lower end due to the stagnation phenomenon of the coating solution are completely solved. Since the mask process is not performed, the process can be simply performed.

[0038] The present disclosure relates to a method of manufacturing a flexible cover window by simultaneously reinforcing a planar portion and a bent portion using alkali metal ions having a smaller ion radius than alkali metal ions included in glass, and to a flexible cover window manufactured using the method.

[0039] In the present disclosure, the term "front surface" means a surface that can be touched by a user, which means a surface that a stylus or the like touches, and means a surface in an upward direction in the drawings. In the present disclosure, the "rear surface" is a surface opposite to the front surface, and means a surface opposite to the touch, that is, a surface in a direction toward the display panel, and means a surface in a downward direction in the drawings.

[0040] In the present disclosure, the "bending zone" of the display refers to the area where the display is bent or curved in half, and in the present disclosure, the area where the cover window is bent to correspond to this area is referred to as the "bending portion" (F) of the cover window. The flat area other than the bending portion (F) is referred to as the "planar portion" (P) of the cover window.

[0041] In particular, the present invention is formed on a glass-based substrate, and the glass substrate 100 is formed to be completely flat (the thickness of the bent portion (F) is the same as the thickness of the flat portion (P)), or the bent portion (F) is divided into one or more sections. Therefore, the glass substrate 100 can be integrally formed into two pieces, three pieces, etc.

[0042] In addition, the bent portion (F) may be formed to have a thickness thinner than that of the plane portion (P) by slimming. Typically, the thickness of the plane portion (P) of the cover window is 30 μm to 300 μm, and the thickness of the bent portion (F) is about 10 μm to 100 μm, and the bent portion (F) is formed by processing a very thin glass plate.

[0043] Here, the bending portion (F) may have a uniform thickness, or may be formed to have a thickness gradually increasing from the center toward the outside of the bending region. That is, the cross section of the bending portion (F) may be formed in a straight line shape or a curved shape.

[0044] When the bending portion (F) is formed in a straight line shape, the bending characteristics are further improved compared to the technology formed in a curved shape. If the bending portion (F) has a curved shape, the range of the minimum thickness is relatively small, and when bending is repeated, the bending characteristics in the thick portion, such as breakage during bending, are reduced. When the bending portion (F) has a uniform thickness as a whole, that is, when the bending portion is formed in a straight line shape with the same thickness, the area constituting the minimum thickness is widely formed to improve flexibility, restoring force, and elastic force, thereby improving the bending characteristics.

[0045] In addition, it is not easy to align the center portion of the bent portion (F) during mechanical assembly, but according to the present disclosure, the bent portion (F) has a uniform thickness. During assembly, that is, when bonded to the front of the display panel, it is possible to reduce assembly tolerance, thereby minimizing the quality difference between products and reducing the defect rate.

[0046] As described above, the advantages of the straight-line shaped bending portion (F) are greater than those of the curved-shaped bending portion (F), but the bending portion can be manufactured by selecting the straight-line shaped bending portion (F) or the curved-shaped bending portion (F) according to the specifications of the product.

[0047] Here, the width of the bent portion (F) is designed to take into account the curvature radius when the cover window is bent, and is approximately set to the curvature radius xπ. The cover window is formed to have a thickness of 10 μm to 100 μm in the bent portion (F), which is related to the bent portion (F).

[0048] If the depth of the bending portion F is too deep, that is, if the bending area of ​​the cover window is too thin, the bendability is good, but wrinkles or strength during the reinforcement process are disadvantageous. When the bending area of ​​the cover window is too thick, the flexibility, restoring force and elastic force in the bending area are degraded, and therefore, the thickness of the cover window in the bending portion (F) may be appropriately about 10 μm to 100 μm.

[0049] The cover window in the present disclosure is formed based on glass to have a thickness of about 30 μm to 300 μm, and is chemically reinforced and used. In this thickness, the width and depth of the bending portion (F) are appropriately designed as described above. If the cover window is thinner than the above thickness, the thickness of the bending area of ​​the cover window becomes too thin after the bending portion (F) is formed, and thus the above problem occurs. Even if the cover window is thicker than the above thickness, the flexibility, resilience and elasticity based on the above glass will be reduced, and the weight reduction of the display product will be hindered.

[0050] According to an embodiment of the present disclosure, the bent portion (F) is formed into a shape in which the bent portion (F) of the cover window becomes thinner inward, and is generally formed into a rectangular groove shape. An inclined portion having a thickness gradually increasing in the bent portion (F) may be formed at both side ends of the bent portion (F) so as to be connected to the flat portion of the cover window.

[0051] In particular, by forming inclined portions with a low slope at both ends of the bent portion (F) (boundary portions with the flat portion (P)), the size of the reflection angle of the reflecting surface is similarly adjusted in the entire area of ​​the bent portion (F), thereby minimizing light interference and visual visibility on the reflecting surface.

[0052] In addition, an etching pattern may be formed on the bending portion (F) and the planar portion (P) or on the bending portion (F) to improve strength characteristics and bending characteristics on the glass substrate 100 .

[0053] In the present disclosure, a cover window is formed on a front surface of a display panel to protect the display panel by maintaining bending and strength characteristics, and may be disposed on a transparent polyimide (CPI) cover to protect the CPI cover.

[0054] As described above, the present disclosure will provide a flexible cover window formed on a glass base and having a bending portion (F) as a thin plate with enhanced strength characteristics and bending characteristics so as to be applied to a flexible display, and the glass substrate 100 constituting the flexible cover window can be integrally formed to have the same thickness in the entire area, or a slim portion having a thickness thinner than that of the planar portion (P) can be formed.

[0055] First, according to the present disclosure, in a method for manufacturing a flexible cover window, a bending portion (F) is formed on one or both surfaces of a glass substrate.

[0056] A photoresist layer is formed on the glass substrate to form a bending portion (F), and a resist layer is patterned to form a resist pattern layer having an open area for forming the bending portion (F) on the glass substrate.

[0057] The photoresist layer is formed by laminating a photoresist coating or a dry film resist (DFR) on a glass substrate and patterning the resist layer to form a resist pattern layer for forming a bending portion (F) on the glass substrate. Then, the bending portion (F) is formed using the resist pattern layer as a mask.

[0058] The bent portion (F) can be formed using a pattern layer as a mask, by using at least one of a mask process such as wet etching, polishing, laser forming, mask ink, or dry film resist (DFR), or a combination of two or more thereof, or by using a mask process such as wet etching, laser forming as post-processing.

[0059] In an embodiment of the present disclosure, after the DFR is laminated on the glass substrate, wet etching is performed using the DFR as a wet mask to form the bent portion (F). Here, the inclined portion of the bent portion (F) is formed when the etching solution penetrates between the DFR and the glass substrate due to the lifting of the end portion of the DFR on the bent portion (F) side.

[0060] According to the designed shape of the bending portion, the slope of the inclined portion or the length of the effective area of ​​the inclined portion, and the process conditions are adjusted, such as the thickness of the DFR, the degree of lift of the DFR at the end of the bending portion (F), the concentration of the etchant, the temperature, and the etching time.

[0061] The effective area (L) of the inclined portion is determined according to the inclination of the inclined portion, and about 50 μm to 5000 μm is suitable. In this case, the inclination (A) of the inclined portion preferably has a slope (A) of 1° to 20° with respect to the plane portion (P).

[0062] The inclination of the inclined portion will minimize the visibility of the boundary portion due to light reflection. That is, when the inclined portion (boundary) has no inclination (90°), the reflective surface at the boundary is visually recognized by the side reflection of the plane portion (P), thereby reducing the distortion or separation of the screen. In the present disclosure, the bent portion (F) and the plane portion (P) are connected with a gentle slope to minimize the visibility of the boundary portion.

[0063] As described above, the present disclosure provides for simultaneously reinforcing a planar portion and a bent portion by using alkali metal ions having an ion radius smaller than that of alkali metal ions included in a glass substrate in which a bent portion is formed.

[0064] According to the present disclosure, the base metals used in the chemical enhancement process are shown in Table 1 below.

[0065] (Table 1)

[0066]

[0067]

[0068] When alkaline glass is immersed in high temperature KNO 3When in molten salt, compressive stress is generated on the surface of the glass due to the replacement of potassium ions in the molten salt with sodium ions in the glass.

[0069] At this time, the volume of the glass increases due to the influence of potassium ions having a large atomic size, while the volume of the glass decreases in the case of lithium ions because the atomic radius is smaller than that of sodium ions of the glass.

[0070] This feature is particularly evident in the case of thin glass, which can be summarized as shown in Table 2 below. Figure 2 Shown in.

[0071] (Table 2)

[0072] Division Thick glass Thin Glass Potassium Small stretch Big stretch lithium Small reduction Big reduction

[0073] Tables 3 and 4 below measure the amount of change in length for each glass thickness according to the amount of added lithium in the case where lithium is not added to the molten salt and in the case where lithium is added.

[0074] (Table 3)

[0075]

[0076] (Table 4)

[0077]

[0078]

[0079] Reference embodiments of the present disclosure are as follows.

[0080] 1) Method 1: Two-step enhancement method

[0081] A. First Enhancement (KNO 3 +NaNO 3 +LiNO 3 )

[0082] a. By passing KNO 3 Set from 20% to 70% to control CS / DOL

[0083] b. LiNO 3 Added at 0.1% to 5% to reduce glass.

[0084] c. The enhancement temperature is 350°C to 460°C, and the time is 5 minutes to 10 hours.

[0085] B. Secondary enhancement (Table 5)

[0086] (Table 5)

[0087]

[0088] 2) Method 2: One-step enhancement method

[0089] A.KNO 3 100%+LiNO 3 (0.1% to 5%)

[0090] B.KNO 3 50% to 99%+NaNO 3 1% to 50% + LiNO 3 0.1% to 5%

[0091] ※The function of offsetting the length increase that occurs during potassium ion replacement by lithium ion replacement (the amount of potassium ion replacement can be increased as the lithium content increases)

[0092] According to the principle of the embodiment of the present disclosure, Figure 3 Medium picture.

[0093] As a whole, the stretching portion and the contraction portion are offset to reinforce both the bending portion and the plane portion, and the tensile stress of the entire area of ​​the flexible cover window is adjusted to provide a flexible cover window ensuring strength characteristics and bending characteristics.

[0094] Figure 4 A photograph of a flexible cover window manufactured according to an embodiment of the present disclosure is shown. It is confirmed that deformation or bending as in the related art is minimized in the entire area of ​​the bent portion and the plane portion.

[0095] As described above, the present invention is to prevent deformation, bending and damage caused by the difference in tensile stress of the glass substrate after strengthening due to the thickness difference between the flat part and the bent part. By performing the chemical strengthening process using metal ions, an additional process such as a mask process is not required in the existing partial chemical strengthening process, thereby improving mass production.

[0096] Therefore, by chemically reinforcing the flat portion and the bent portion simultaneously, the reinforcing unevenness problem such as the dispersion and precision coating of the coating solution as a conventional partial chemical reinforcing process and the deviation problem of the upper end and the lower end due to the stagnation phenomenon of the coating solution are completely solved. Since the mask process is not performed, the process can be simply performed.

Claims

1. A method for manufacturing a flexible glass cover window, the glass cover window comprising a flat portion and a bent portion, the method comprising: a first strengthening step of simultaneously immersing the planar portion and the bent portion of the glass cover window in a molten salt including sodium ions, potassium ions and lithium ions, thereby reducing the lengths of the planar portion and the bent portion, and a second strengthening step after the first strengthening step: simultaneously immersing the planar portion and the bent portion of the glass cover window in a molten salt including potassium ions, thereby increasing the lengths of the planar portion and the bent portion and thus offsetting the reduction in the lengths of the planar portion and the bent portion occurring in the first strengthening step, and Wherein, the thickness of the bent portion of the glass cover window is thinner than the thickness of the flat portion of the glass cover window.

2. The method according to claim 1, wherein: The molten salt used in the first enhancement step includes KNO3, NaNO3 and LiNO3.

3. The method according to claim 2, wherein: In the first reinforcing step, the content of KNO 3 is 20 to 70 parts by weight based on the total weight of the molten salt in the first reinforcing step, and the content of LiNO 3 is 0.1 to 5 parts by weight based on the total weight of the molten salt in the first reinforcing step.

4. The method according to claim 2, wherein: The molten salt used in the second enhancement step includes any one or both of LiNO 3 and NaNO 3 and KNO 3 .

5. The method according to claim 4, wherein: The amount of LiNO 3 used in the second strengthening step is equal to or smaller than the amount of LiNO 3 used in the first strengthening step.

6. The method according to claim 5, wherein: In the second strengthening step, the content of LiNO 3 in the molten salt is 0.1 parts by weight to 2 parts by weight based on the total weight of the molten salt.

7. The method according to claim 1, wherein: The thickness of the planar portion is 30 μm to 300 μm, and the thickness of the bent portion is 10 μm to 100 μm.

8. The method according to claim 1, wherein: The molten salt of the second enhancement step consists of KNO3.

9. The method according to claim 1, wherein: In the first reinforcing step, the length reduction amount of the bent portion is greater than the length reduction amount of the flat portion, and in the second reinforcing step, the length increase amount of the bent portion is greater than the length increase amount of the flat portion.

10. A flexible glass cover window manufactured according to the method of claim 1.

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